Advanced Nanocarriers for Delivering Traditional Chinese Medicine Monomers in Rheumatoid Arthritis: Prospects and Challenges.

Introduction

Rheumatoid arthritis (RA) is a chronic autoimmune disease primarily affecting synovial joints, leading to persistent inflammation, cartilage degradation, and progressive joint destruction. RA is more common in the developed parts of the world, due to a number of reasons including genetic predisposition, exposure to environment, and lifestyle choices. Despite many developments that have been made in treatment methods during the past few decades, RA still poses a difficult clinical problem due to its complicated immunopathology and unpredictable course.1,2 Traditional Disease-Modifying Antirheumatic Drugs (DMARDs), including methotrexate and glucocorticoids, continue to be at the heart of rheumatoid arthritis treatment, with biological DMARDs, which act on certain components of the immune system, being used more often for personalizing treatments.3,4 The high cost and possible side effects that accompany biological agents illustrate the pressing need for new and safe treatment alternatives-particularly for early identification of non-responders to existing treatment options.5,6

The immunopathogenesis of rheumatoid arthritis (RA) involves an organized but deregulated immune system reaction (Figure 1). T helper lymphocytes of the CD4+ group are essential for the onset of inflammation through the production of pro-inflammatory cytokines interleukin-17 (IL-17) and interferon-gamma (IFN-γ). The latter are responsible for attracting and stimulating the activity of cells of the innate immune system such as macrophages and neutrophils.

Synovial fibroblasts release MMPs to break down cartilage elements and extracellular matrix when activated. Deregulated proliferation of fibroblasts and immune cells leads to pannus formation.7 Concurrently, the production of autoantibodies such as RF and anti-citrullinated protein antibodies (ACPAs) exacerbates tissue damage through immune complex formation and complement system activation.8 This cycle initiates a cycle of inflammation that leads to the destruction of joints seen in patients with RA. One mechanism responsible for the development of RA is oxidative stress that links inflammation with cell injury.

The immune cells present in the inflamed synovium release excess reactive oxygen species (ROS) that include superoxide anions, hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). While ROS are critical in physiological responses and immune response, the excess production of ROS in patients with RA activates pathways like nuclear factor-kappa B (NF-κB) and MAPK, leading to increased levels of pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). This creates a cycle where inflammation leads to the production of ROS, and ROS causes more inflammation and joint destruction.

Together, these factors lead to disease progression and clinical symptoms of stiffness and pain of the joints.9Figure 1The pathophysiology of RA is the consequence of the interplay between genetic, environmental, and immunological factors that initiate citrullination mediated by PADI4, resulting in T-cells, B-cells, and plasma cells activation. T helper 1 and T helper 17 cell subsets induce pro-inflammatory cytokines production, while chondrocytes and fibroblast-like synoviocytes (FLS) stimulate matrix destruction. Autoantibodies participate in immune complex formation, pannus development, cartilage destruction, and bone erosion.

Modified after the following reference.10The diagram explains rheumatoid arthritis (RA) pathophysiology, focusing on genetic, environmental and immunological interactions. It starts with peptide citrullination by PADI4, influenced by genetics, environment, smoking, bacteria, viruses and autophagy. Dendritic cells present antigens to naive T-cells, activating T helper 1 and 17 cells, which release pro-inflammatory cytokines like TNF alpha, IL-1 and IL-17.

These cytokines activate macrophages and chondrocytes, causing matrix degradation. B-cells and plasma cells create autoantibodies, forming immune complexes that lead to pannus formation, cartilage destruction and bone erosion. Osteoclasts, neutrophils, mast cells and macrophages contribute to joint damage, with cytokines IL-6, IL-8 and TNF alpha enhancing inflammation.

The diagram includes a knee joint affected by RA, showing cartilage damage.RA pathophysiology: genes, environment, immunity cause citrullination, immune response, joint damage.Abbreviations: ACPA, anti-citrullinated protein antibodies; PAD4, peptidyl arginine deiminase 4; RF, rheumatoid factor; MHC II, major histocompatibility complex class II; TCR, T-cell receptor; Th1/Th17, T helper cell subsets; TNF-α, tumor necrosis factor alpha; IL, interleukin; MMP, matrix metalloproteinase; RANK/RANKL, receptor activator of nuclear factor kappa-B (ligand); ROS, reactive oxygen species; NO, nitric oxide; GM-CSF.

There exist certain bioactive monomers found in Traditional Chinese Medicine (TCM) that have shown promise as being immunomodulatory and anti-inflammatory agents for RA treatment.11 In the current review, TCM monomers are defined as pure compounds extracted from Traditional Chinese Medicine herbs which are not considered extracts, blends, or drug combinations. Curcumin, berberine, baicalin, and resveratrol have been identified as being involved in modulation of immune cells and pro-inflammatory cytokine secretion.12 These molecules may block the activation of signaling pathways such as NF-κB. For instance, curcumin blocks the activation of the NF-κB pathway, leading to the inhibition of immune cell proliferation and cytokine-induced inflammation.

However, berberine controls the activity of macrophages and T-cells in order to reduce inflammation and tissue damage.13 Further increase in therapeutic efficiency can be achieved through their conjugation with polymers or nanocarriers that enhance their solubility, stability, bioavailability, and delivery to the target inflammation sites. Nanotechnology-mediated drug delivery systems for TCM monomers include various approaches, including physical encapsulation, chemical conjugation, and multi-stimuli responsive delivery systems. While physical encapsulation offers flexibility in loading the drug onto the carrier, it may involve premature release into the bloodstream.

Conversely, multi-stimuli-responsive drug delivery systems, triggered by factors such as pH, redox reaction, or enzymatic action, provide for controlled and targeted release of the drugs to the disease site, thus increasing the effectiveness of treatment and decreasing systemic toxicity. Considering RA treatment, the inflammatory joint environment features acidosis, increased reactive oxygen species (ROS) level, and activity of MMPs, which, in turn, can act as stimuli for controlled and targeted drug release. Moreover, novel nanocarrier systems allow delivering several TCM monomers simultaneously to exert a synergistic effect on inflammation and immunity.14–18

This literature review provides an advanced insight into the use of nanotechnology carriers for the delivery of TCM monomers in RA, distinguishing itself from the previous studies that have been conducted on nanotechnological methods of treatment or nanodelivery techniques of complex TCM formulations. The present review places emphasis on the recent advancements made in multisite-responsive nanosystems and co-delivery techniques, together with the specific issues faced in translating such nanodelivery systems of TCM monomers.

Pathophysiology of RA

Immune Mechanisms

The RA is an autoimmune disorder characterized by aberrant immune cell crosstalk between innate and adaptive immunity. CD4⁺ T-cell populations, including Th1, Th17, Tfh, and Tph cell populations, play key roles in the development and progression of disease. Th1 cells generate IFN-γ, thereby enhancing macrophages activity, while Th17 cells generate IL-17A/F, IL-21, IL-22, and GM-CSF that induce the expression of chemokines (CXCL1, CXCL8, CCL2, CCL20), immune cells recruitment.19,20 T-regulatory cells (Tregs) have impaired functions in the inflammatory milieu because of the presence of IL-1β and IL-6, causing decreased Foxp3 expression and loss of immune tolerance.

The role of B cells in RA is to produce autoantibodies (RF and ACPAs), antigen presentation, and cytokine generation. These autoantibodies generate immune complex that activates complement and Fcγ receptors to generate TNF-α, IL-1β, and IL-6. In addition, B-cells stimulate osteoclastogenesis by producing RANKL, while Bregs are diminished in RA.21–23

Macrophage functional polarization involves M1 macrophages mediating inflammation by cytokines and MMPs, but M2 macrophages resolving inflammation through IL-10 and TGF-β. Dendritic cells control antigen presentation and polarization of T cells, while innate lymphoid cells (ILCs) help in mediating early stages of inflammation (ILC1/ILC3) or resolution (ILC2). All these immune responses lead to continuous synovial inflammation.24–26 Moreover, schematic presentation of the IL-23/IL-17/NF-κB signaling pathway in the etiology of RA is illustrated in Figure 2.

Figure 2Schematic diagram of the signaling cascade of IL-23/IL-17/NF-κB associated with the development of RA. IL-23 initiates the activation of Th17 cells via IL-23R, resulting in the release of IL-17 in the inflammatory synovium. IL-17 acts on the IL-17 receptor expressed by synovial fibroblasts and macrophages, which leads to activation of the IKK complex and NF-κB pathway through the involvement of TRAF6.

Translocation of NF-κB (p65/p50) to the nucleus results in the transcription of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6, which play a role in immune cell infiltration, synovitis, and destruction of the joint tissue in RA. Modified from.27The diagram illustrates the IL-23/IL-17/NF-kappa B axis associated with rheumatoid arthritis development. IL-23 activates Th17 cells via IL-23R, leading to IL-17 release in the inflamed synovium.

IL-17 interacts with IL-17 receptors on synovial fibroblasts and macrophages, activating the IKK complex and NF-kappa B pathway through TRAF6. The NF-kappa B complex, composed of p65 and p50, translocates to the nucleus, promoting transcription of pro-inflammatory cytokines TNF-alpha, IL-1 beta and IL-6. These cytokines contribute to immune cell infiltration, synovitis and joint tissue destruction.IL-23/IL-17/NF-kB axis: RA signaling with Th17 cells, synovial fibroblasts, macrophages.Abbreviations: IL-23, interleukin-23; IL-23R, interleukin-23 receptor; IL-17, interleukin-17; IL-17R, interleukin-17 receptor; Th17, T helper 17 cells; NF-κB, nuclear factor kappa B; IκBα, inhibitor of NF-κB alpha; IKKα.

Inflammatory Signaling Pathways

Inflammation of rheumatoid arthritis is regulated through important intracellular signaling cascades like NF-κB, MAPK, and JAK-STAT pathways. NF-κB signaling pathway plays an important role in regulation of inflammation and is triggered through TLRs, cytokines, and immune complexes and results in transcription of TNF-α, IL-1β, IL-6, chemokines, and MMPs. MAPK signaling pathway (ERK, JNK, p38) regulates the cytokine secretion, fibroblast proliferation in synovium, and apoptosis of chondrocytes.

The JAK-STAT signaling pathway gets activated due to the action of cytokines like IL-6, GM-CSF, and IFN-γ. The STAT3/STAT5 signaling regulates the activation of immune cells and inflammatory gene expression.28–30

Autoantibodies and Bone/Cartilage Damage

Autoantibodies such as RF and ACPAs play an important role not only for diagnosing but also for pathogenic processes in RA. ACPAs stimulate osteoclast differentiation by interacting with citrullinated antigens of osteoclast progenitor cells, and immune complexes act through complement and Fcγ receptors, stimulating TNF-α secretion and neutrophils activation. These mechanisms trigger an amplification cycle resulting in inflammation of synovial tissue and damage to joints.

Activation of osteoclasts via RANKL and MMPs-dependent degradation of cartilage due to synoviocyte stimulation lead to erosion of bones and pannus formation. ROS, produced because of mitochondrial disorders and NOX activation, further stimulate NF-κB and MAPK cascades, which stimulate production of cytokines, apoptosis of chondrocytes, and activity of osteoclasts.8,31–33

Chondrocyte Apoptosis

The process of chondrocyte apoptosis is central to cartilage degeneration in RA. Pro-inflammatory cytokines (TNF-α, IL-1β) and reactive oxygen species lead to mitochondrial dysfunction, endoplasmic reticulum stress, and activation of apoptosis. Besides apoptosis, ferroptosis, due to lipid peroxidation and glutathione deficiency, is also a process that leads to chondrocyte death.

These processes inhibit the synthesis of extracellular matrix and increase its degradation.9,34,35

Matrix Metalloproteinases (MMPs)

Matrix metalloproteinases (MMPs) are zinc-requiring proteinases that participate in the degradation of extracellular matrix in RA patients. The highest expression levels are detected for MMP-1, MMP-3, MMP-9, and MMP-13, which play the role in the destruction of type II collagen and other matrix proteins. The induction of MMPs is mediated by proinflammatory cytokines TNF-α, IL-1β, and IL-17 through NF-κB and MAPK pathways.

Besides degrading the extracellular matrix, MMPs have the ability to modulate the activity of cytokines, facilitate cell migration, participate in angiogenesis and immunity.36–38

Therapeutic Potential of TCM-Derived Monomers

Curcumin

Curcumin is a polyphenolic molecule isolated from Curcuma longa possessing effective anti-inflammatory and antioxidant activities pertinent to RA. The action of this compound occurs primarily due to its inhibition of NF-κB signaling pathway by inhibiting IKK activity and IκBα phosphorylation, which results in the down-regulation of TNF-α, IL-1β, and IL-6 levels. Moreover, curcumin activates PPAR-γ and inhibits TLR4-MD2 signaling pathway, which reduces the activity of the inflammatory pathway.

Furthermore, curcumin acts by inhibiting M1 phenotype and inducing M2 phenotype in macrophages, ensuring the balance of immunity in RA. Nevertheless, the clinical use of this compound is hindered by its poor water solubility, fast metabolism, low bioavailability, and rapid clearance.39–42

Resveratrol

Resveratrol is a stilbenoid polyphenol that exhibits anti-inflammatory, antioxidant, and immunomodulatory properties. In RA-related studies, resveratrol has been found to have an inhibitory effect on inflammation through the inhibition of NF-κB and JNK pathways and stimulation of the SIRT1/NF-κB pathway, with resultant decreased expression of IL-1β, IL-6, and COX-2. Although resveratrol is easily absorbed, its clinical applications have been limited due to its rapid metabolism, instability, and rapid first-pass effect.43–46

Quercetin

Quercetin is a polyphenolic flavonoid which has potent antioxidant and anti-inflammatory properties. It acts on RA pathogenesis through suppression of inflammation via inhibition of NF-κB and MAPK (JNK/ERK) signaling pathways and inhibition of TNF-α synthesis. Besides, quercetin regulates macrophages polarization and induces AMPK/SIRT1 signaling pathway, thus exerting chondroprotective and anti-apoptotic actions.

Nevertheless, its effect on immune system depends on circumstances because it affects macrophage phenotypes. Clinical use is hampered by poor water solubility, significant first-pass effect, quick elimination and poor oral availability.47–49

Berberine

Berberine is an isoquinoline alkaloid possessing wide-ranging anti-inflammatory properties. The mechanism of berberine action in RA-specific pathways includes inhibition of NF-kappa B and MAPK pathway activation, whereas activation of AMPK and Nrf2 pathways leads to the reduced production of IL-1beta, IL-6, and iNOS. Moreover, berberine influences immune response via regulating gut microbiota and blocking IgE-induced inflammation.

Despite its good pharmacological properties, the medicinal use of this compound is limited by poor oral bioavailability and first-pass effect.50–52

Advanced Nanocarriers for TCM Monomer Delivery

Polymeric Nanoparticles

The advent of polymeric nanocarriers represents an advanced strategy for delivery of active molecules that can be extracted from the TCM due to their tailor-made physical and chemical properties. These systems are typically fabricated using biocompatible and biodegradable polymers, enabling diverse drug incorporation strategies such as covalent conjugation, encapsulation within nanostructures, and dispersion in polymer matrices. Such a high degree of flexibility ensures that the polymeric nanoparticles can encapsulate diverse types of drug cargos, such as lipophilic small molecule drugs, peptides, proteins, and nucleic acids.

Furthermore, polymers can improve the pharmacokinetics of bioactive compounds due to their improved solubility, prolonged retention, and targeted delivery to diseased sites. In the case of rheumatoid arthritis, such nanoparticles are capable of accumulating in inflamed synovium due to increased permeability of blood vessels and additional modification for the delivery to macrophages or fibroblasts. The list of such active targeting strategies includes the recognition of overexpressed folate receptor, CD44, scavenger receptor, and integrin on inflammatory cells of rheumatoid arthritis synovium.

Such a property of reduction of systemic toxicity without loss of therapeutic effect was used during development of several drug formulations such as Risperdal Consta (risperidone), Trelstar (triptorelin pamoate), Sandostatin LAR (octreotide acetate), and Eligard (leuprolide acetate), Genexol (paclitaxel), Nanoxel (paclitaxel), and Somatuline Autogel (lanreotide acetate). Therefore, polymeric nanoparticles are especially promising carriers for increasing bioavailability and efficacy of poorly soluble TCM monomers.16,53,54 A comparative analysis of the advantages and limitations of major nanocarriers for RA therapy are given in Table 1.55–64Table 1Comparison of Advantages and Disadvantages of Different Nanocarriers for RA TherapyNanocarrierCharacteristicsLimitationsAdvantagesReferencesLiposomesPhospholipid bilayer vesicles encapsulating hydrophilic/lipophilic drugsRapid clearance by mononuclear phagocyte system, Limited stability and premature leakage, Low target specificity (conventional liposomes)High biocompatibility and low immunogenicity, Ability to carry both hydrophilic and lipophilic TCM monomers, Improved drug stability and half-life, Passive (EPR) and ligand-based targeting possible[55,56]Polymeric Nanoparticles (eg, PLGA, chitosan)Solid colloidal systems with controlled drug releasePotential polymer toxicity, Complex synthesis and scale-up challenges, Possible burst release issuesControlled and sustained release, High structural stability, Tunable surface for active targeting, Suitable for hydrophobic TCM compounds[57]Lipid-Based Nanocarriers (SLNs, NLCs, micelles)Lipid matrix-based carriers enhancing solubilityLimited drug loading (SLNs), Physical instability (polymorphic transitions), Possible drug expulsion during storageEnhanced bioavailability of poorly soluble drugs, Improved pharmacokinetics and tissue penetration, Reduced systemic toxicity[58]Polymer–Drug Conjugates/Prodrug NanoparticlesDrug covalently linked to polymer backboneComplex synthesis and characterization, Potential variability in drug release kinetics, Regulatory challengesHigh drug loading capacity, Improved stability and circulation time, Reduced systemic toxicity, Controlled activation at target site[59]Cell Membrane-Coated Nanoparticles (Biomimetic NPs)Synthetic cores cloaked with natural cell membranesDifficult large-scale production, Membrane source variability, Stability concernsImmune evasion and prolonged circulation, Enhanced targeting via homologous adhesion, High biocompatibility[60,61]Nanoemulsions/Niosomes/PhytosomesSurfactant-based or vesicular carriers for herbal compoundsPhysical instability (coalescence, leakage), Limited long-term stability, Lower drug loading vs solid systemsImproved solubility of TCM monomers, Enhanced permeability and absorption, Relatively easy formulation[62]Inorganic Nanoparticles (eg, gold, silica, magnetic NPs)Metal/oxide-based nanostructures with functional surfacesPotential long-term toxicity, Poor biodegradability, Accumulation in organsUnique optical/magnetic properties (theranostics), High surface area for drug loading, Potential for imaging + therapy[63]Hydrogel-based Nanocarriers/Nanocomposites3D polymeric networks for local deliveryLimited systemic targeting, Mechanical instability, Difficult sterilizationSustained and localized drug release, Injectable systems for intra-articular delivery, Reduced systemic exposure[64]

Polymeric Micelles

Polymeric micelles are self-assembled nanoparticles composed of amphiphilic block copolymers that form core-shell structures in water. The hydrophobic core acts as a reservoir for poorly soluble drugs, whereas the hydrophilic shell provides stability of nanostructure and prevents proteins’ adsorption, reducing recognition and elimination by the reticuloendothelial system. Due to sizes of about 10–100 nanometers, polymeric micelles increase the solubility of drugs, prolong the circulation in the blood, and promote penetration through tissues.

In RA, owing to their small size, micelles penetrate very deeply into the inflamed synovial membrane and hence become suitable carriers for hydrophobic TCM monomers. Genexol-PM is one of such formulations that is already being clinically approved and consists of methoxy polyethylene glycol–poly (D, L-lactic acid) (mPEG-b-PDLLA) block copolymer and contains paclitaxel. Such micelle formulation not only increases the solubility of paclitaxel but also is used in ovarian and non-small cell lung cancers.53 Many more experimental studies have confirmed the drug delivery benefits of polymeric micelles.

For example, a new method for the preparation of PEGylated poly (lactide-co-glycolide) (PLGA) nanoparticles was used to deliver digoxin.65 The resultant system was found to have high encapsulation efficiency, prolonged release of the drug over 48 hours, and an increased cellular permeability up to 2.5 times that of free digoxin. Of importance, the PEGylated PLGA micelles were found to be non-cytotoxic and were capable of preventing the efflux of digoxin through the P-glycoprotein mechanism. In yet another experiment, a novel redox responsive nanoparticle system has been synthesized for docetaxel delivery using cystamine linked amphiphilic polymers containing disulfide bonds.

The resulting micelles showed increased drug release in reduced intracellular conditions, which resulted in better anti-tumor efficacy and reduced side effects. Redox responsive micelles were also synthesized using cross-linked xanthan gum and were found to have particle sizes of 110–180 nm.66–68

Polymeric Vesicles

Polymersomes, which refer to polymeric vesicles, represent nanovesicular structures generated due to the self-assembly of amphiphilic block copolymers. In terms of structure, they resemble liposomes in that polymersomes possess an aqueous interior surrounded by a bilayer of hydrophobic membranes, hence making it possible for polymersomes to carry both hydrophilic and hydrophobic therapeutics. Polymersomes tend to be more mechanically stable and structurally tuneable than liposomes, hence facilitating the customization of their physicochemical properties to suit biomedical needs.

Polymersomes have been shown to have great prospects in the delivery of bioactive molecules obtained from TCM.69,70 The application of vesicles in RA can prove useful for the co-delivery of hydrophilic anti-inflammatory medicines and hydrophobic TCM monomers so as to enhance the modulation of immune functions in the synovial milieu. For instance, polymer vesicles of PEG--poly(propylene thioether) have been developed, which contain hydroxychloroquine within the aqueous core and tunicamycin in the hydrophobic shell. The vesicles proved to induce ER stress and autophagy flux inhibition in the tumor cells and therefore enhanced their antitumor effect.53 In another experiment, paclitaxel and doxorubicin were encapsulated in the PEG-PLA/PEG-PBD hybrid vesicle formulation, which showed better tolerance and higher efficacy than drug monotherapy in tumor bearing mice after intravenous injection.53 Hybrid vesicles have also been employed in an attempt to enhance the delivery of natural products.71 One example of this is the use of chitosan-coated liposome-polymer hybrid vesicles for quercetin delivery, whose properties include particle sizes below 180 nm, an entrapment efficiency above 90%, and pH-sensitive drug release, thereby increasing its intestinal availability.

On the other hand, Liu et al designed a mucus binding vesicle of chitosan-thioglycolic acid and Pluronic F127 for the oral administration of paclitaxel. This formulation has shown increased stability, better mucosal binding, and increased intestinal absorption.72

Polymeric Hydrogels

Hydrogels refer to three dimensional polymeric networks with the capacity of retaining substantial amounts of water/biological fluids without losing their structure. Hydrogels have attracted considerable attention for use in drug delivery because of the following attributes, which include biocompatibility, adjustable mechanical strength, and delivery of localized and sustained drug release. With respect to RA, it is highly important to appreciate the function that hydrogels play when delivered through injections, which will help in the localized delivery of the TCM monomers to the joints cavities hence preventing synovitis.

It is possible to encapsulate either hydrophilic or hydrophobic drugs in hydrogels, making them highly suitable for the delivery of bioactive compounds from TCM.51,73 For example, catechol-conjugated chitosan hydrogels have been created to administer extracts from Panax notoginseng as wound healing applications.74 They showed adhesive property with bond strength of about 9.72 kPa, which could sustain the release of the encapsulated drugs for up to 72 hours. Animal trials revealed better wound healing, angiogenesis, and fewer cases of infections. Likewise, a hydrogel that was modified using catechol and chitosan was used to release flavones from Resina Draconis, which gave complete wound healing in seven days.75 Intranasal delivery of berberine has been carried out by utilizing thermosensitive hydrogels based on hydroxypropyl-β-cyclodextrin and poloxamers.76 It greatly enhanced bioavailability and produced more than 100-fold enhancement over oral delivery while providing controlled drug release and increased effectiveness of the antidepressants.

Advanced composite systems have also been used for tissue engineering. The lipo-hydrogel system where liposomes were incorporated into the double network hydrogel system is one of those advanced systems which allowed sequential release of drugs wherein angiogenic factors were delivered first and followed by protein and hydrophobic drugs.77

Polymer–Drug Conjugates

Another promising strategy for enhancing the delivery of TCM-derived compounds involves the use of polymer-drug conjugates.51 In these systems, therapeutic molecules are covalently attached to polymer backbones, forming macromolecular prodrugs with well-defined pharmacodynamic and pharmacokinetic profiles. Covalent conjugation minimizes drug aggregation, improves solubility and stability, and allows precise control over the drug-to-polymer ratio. These conjugates have some benefits in RA because of their ability to provide sustained circulation of the TCM monomers and allow stimulus-responsive delivery under the acidic and ROS conditions of the synovial environment.

The process of releasing the active component usually occurs due to physiological triggers such as acidic pH and redox conditions in the affected area. For instance, the application of an amphiphilic copolymer of N-(2-hydroxypropyl) methacrylamide with paclitaxel, gadolinium, and Cyanine5.5 significantly inhibited tumor cell growth in mice with breast cancer.78 Similarly, monomethoxy polyethylene glycol-poly(lactide) conjugated with docetaxel via an ester linker yielded a formulation that sustained drug release for approximately 160 hours and exhibited enhanced antitumor activity.79 In vivo studies showed a threefold reduction in tumor volume compared with free curcumin. Polyethylene glycol-betulinic acid conjugates have also been reported to possess enhanced anti-inflammatory and antioxidant properties, as well as the ability to induce apoptosis in pancreatic cancer cells.80,81 Intracellular drug delivery to Starving Superior has also been made possible by the application of redox-sensitive linkages.

Further improvement in intracellular drug delivery can be made by the application of redox-sensitive linkages. This was achieved in a hydroxyethyl starch-folic acid conjugate, which is capable of forming theranostic nanoparticles carrying a doxorubicin dimer conjugated to a disulfide molecule and the photothermal agent IR780 iodide. The theranostic nanoparticles accumulate selectively in tumors and release the drug upon increased glutathione levels inside cancer cells.81,82

Lipid-Based Nanocarriers

Lipid nanoparticles make up a new type of drug delivery system that possesses a number of important features distinguishing it from other nanoparticle systems such as colloidal and polymeric nanoparticles. These features include high biocompatibility and biodegradability of the system, its large-scale production capacity, and precise adjustment of drug release characteristics. Out of two types of lipid nanoparticles – solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs), the second generation of carriers has proved to possess better characteristics in targeted delivery of drugs and, therefore, is preferable for a variety of delivery routes.

Lipid nanoparticles can carry both hydrophilic and lipophilic drugs and can be delivered through a variety of administration routes including topical, oral, parenteral, ocular, pulmonary, and brain delivery. In the case of RA, lipid nanoparticles can use enhanced accumulation in the inflamed joint due to increased vascular permeability and be modified to achieve active targeting of synovial macrophages.19 The surface modifications could include the coupling of antibodies, peptides, folic acid, or hyaluronic acid, enabling specific attachment to the inflammatory cells found within the arthritic joint. Each form of administration has its own advantages and disadvantages.83,84 The time of these nanosystems in systemic circulation can be increased by coating with biocompatible polymer coatings eg PEG as shown in Figure 3.

Figure 3Illustration of the structure of nanocarriers, which comprises a solid core, surfactant shell, and polyethylene glycol (PEG). Nanocarriers can be designed for drug delivery, gene delivery, active targeting using surface ligands, and imaging due to the presence of contrast agents. Multifunctional nanocarriers facilitate combination therapy, providing better targeted accumulation, release, and efficiency in the treatment of inflammation disorders like RA.

From the reference.85A diagram illustrates functionalized nanoparticles for biomedical delivery and imaging. On the left, a large spherical nanoparticle features a solid core and surfactant layer, with chain-like structures extending outward. A legend lists components: Solid Core, Surfactant and Polyethylene Glycol (PEG), each with an icon.

The middle section shows four nanoparticle applications: 1) DRUG DELIVERY: Includes drug payloads inside the core, represented by dot symbols. 2) GENE DELIVERY: Features cationic agents and genetic material, with surface symbols and no core payloads. 3) ACTIVE TARGETING: Displays Y-shaped ligands for targeting moieties.

4) IMAGING: Incorporates a contrast agent with an outer ring layer. The right section, labeled MULTITHERAPY, presents three nanoparticle designs: Top shows payload symbols in the core and chain structures on the surface; Middle includes payload symbols and Y-shaped ligands; Bottom features payload symbols and an outer ring layer.Diagram of nanoparticle designs for drug/gene delivery, targeting, imaging and multitherapy.

Regarding the RA condition, accumulation of nanocarriers into inflamed joints may be accomplished via passive or active targeting. The first approach is based on enhanced vascular permeability in inflamed joints, allowing preferential leakage and accumulation of nanosized carriers into arthritic tissues. This mechanism is similar to enhanced permeability and retention (EPR) phenomenon for tumors and is responsible for the high accumulation of drugs in sites of inflammation.

However, active targeting involves functionalization of nanocarriers with specific ligands, antibodies, peptides, etc, interacting with receptors that are overexpressed on macrophages, fibroblast-like synoviocytes, endothelial cells, and other cells involved in inflammation process. While passive targeting increases joint accumulation, active targeting provides higher cellular uptake and efficacy. Moreover, the comparative analysis of advanced nanocarriers for delivery of monomers of TCM in rheumatoid arthritis is provided in Table 2.59,86–91Table 2Advanced Nanocarriers for TCM Monomers in Rheumatoid Arthritis – Comparative SummaryNanocarrier TypeTCM MonomersMajor AdvantagesLimitationsReferencesPolymeric NanoparticlesCurcumin, Triptolide, Celastrol, BaicaleinHigh drug-loading capacity, controlled release, protection of unstable compounds, facile surface functionalization for active targetingComplex manufacturing, potential polymer-related toxicity, scale-up challenges[86,87]Polymeric MicellesCurcumin, Celastrol, Tanshinone IIA, TriptolideExcellent solubilization of hydrophobic compounds, prolonged circulation, enhanced penetration into inflamed synovium, stimulus-responsive design possiblePotential instability upon dilution, premature drug leakage[87,88]Polymeric Vesicles (Polymersomes)Quercetin, Curcumin, BerberineSimultaneous encapsulation of hydrophilic and hydrophobic agents, high structural stability, tunable membrane propertiesMore complex fabrication and characterization, limited clinical translation[89,90]Polymeric HydrogelsBerberine, Curcumin, Panax notoginseng constituentsSustained and localized drug release, prolonged intra-articular retention, injectable formulations, reduced systemic toxicityPossible burst release, limited loading of highly hydrophobic compounds, mechanical instability in some formulations[86,89]Polymer–Drug ConjugatesCurcumin conjugates, Triptolide conjugates, Betulinic acid derivativesImproved solubility and pharmacokinetics, prolonged circulation, stimulus-responsive release, enhanced targetabilityRequires chemical modification of active compounds, synthetic complexity, regulatory challenges[59]Lipid-Based Nanocarriers (SLNs/NLCs)Triptolide, Curcumin, Berberine, ResveratrolExcellent biocompatibility, scalable production, enhanced bioavailability, suitability for multiple administration routesPhysical instability during storage, limited loading of some hydrophilic compounds[87,91]

Targeting Strategies for Nanocarrier-Mediated Drug Delivery in RA

As RA progresses, phenotypic changes occur in immune and stromal cells, including the altered expression of specific surface receptors on macrophages, synovial fibroblasts, endothelial cells, and lymphocytes. These molecular alterations create opportunities for the design of nanocarriers capable of selectively targeting inflammation-associated cells within arthritic joints. Active-targeting nanocarriers are commonly functionalized with ligands that bind to receptors overexpressed in inflamed tissues, thereby enhancing drug accumulation, cellular uptake, and therapeutic efficacy.

This efficiency is greatly aided by the unique inflammatory microenvironment of RA joints, which is marked by increased vascular permeability, immune cell infiltration, ROS production, increased MMP levels, and mildly acidic extracellular environment. All these pathological conditions facilitate accumulation of nanocarriers in inflamed tissue as well as drug delivery from them due to stimuli responsiveness. Over the past few years, different ligand-mediated targeting methods involving small molecules, polymers, peptides, proteins, and biomimetics have been used for the targeted drug delivery in RA.92,93

Small-Molecule-Mediated Targeting

Small molecule ligands are widely used to enhance the recognition of nanoparticles by inflammatory cells. Folic acid (FA) is one of the most extensively studied targeting ligands, owing to the high expression of folate receptors on activated macrophages within the synovium in RA. For instance, a folate-conjugated dextran-methotrexate conjugate that self-assembles into micelles has been developed, resulting in increased macrophage uptake and improved biodistribution in inflamed tissues.

These FA-modified micelles demonstrated a pronounced therapeutic effect in collagen-induced arthritis (CIA) mice compared with free methotrexate and unmodified micelles.94 In another study, Sun et al prepared FA-conjugated PEG-PLGA nanoparticles for the delivery of Mcl-1 siRNA to inflamed joints. Incorporation of a pH-sensitive linker enabled efficient intracellular siRNA delivery, leading to improved clinical outcomes and reduced levels of pro-inflammatory cytokines. Other small molecules besides folate have also been studied as ligands for active drug targeting.

Sialic Acid (SA), which is naturally occurring monosaccharide found in cell membrane, is capable of binding to E-selectin receptors.95 In an experiment conducted by Xu et al, the efficacy of methotrexate-SA-dextran-octadecanoic acid micelles (SA-Dex-OA/MTX) was observed to suppress inflammatory responses and bone repair in patients with RA. In vivo experiments revealed increased accumulation of these micelles in inflamed paws, attributed to SA-mediated targeting.96,97 Based on fluorescence imaging and biodistribution studies, it was shown that there was considerably higher uptake of targeted micelles at arthritic joints in comparison to non-targeted micelles, thus highlighting the importance of ligand-mediated targeting to achieve selective drug accumulation. Galactosylated nanoparticles have also been used as macrophage targeted drug delivery systems.

In a recent study, amphiphilic galactosylated dextran-retinal (GDR) nanoparticles have been synthesized through conjugation of all-trans retinal to dextran through hydrazone bond which is cleavable by all-trans retinal and further addition of galactosyl group for directing macrophage targeting. These nanoparticles showed tendency to accumulate at sites of inflammation, and upon loading with anti-inflammatory drug triptolide, it inhibited inflammatory infiltration. In addition to the ligands mentioned above, mannose and sialyl Lewis X have also been explored, given the high expression of their corresponding receptors on monocytes and macrophage-derived cells in arthritic synovial tissues.96

Polymer-Based Targeting

Active targeting systems have been studied widely for rheumatoid arthritis using biocompatible polymers. Hyaluronic acid (HA) has been chosen because of its strong affinity towards CD44 receptors, which are highly overexpressed by activated macrophages and lymphocytes at inflamed sites. Therefore, nanocarriers based on hyaluronic acid can accumulate selectively at sites of inflammation.98 For instance, the development of nanocarriers based on PEGylated hyaluronic acid and mineralized calcium phosphate has been reported for delivering methotrexate through a pH-triggered release process, where HA-CD44 interaction is used for targeting efficiency.

This system showed good therapeutic efficacy and favorable safety properties despite the high doses of drug.99 Yet another polymer-based ligand frequently employed is dextran sulfate (DS), which recognizes the class A scavenger receptors located on the surface of the activated macrophages. In particular, the polymer DS has been conjugated with polycaprolactone to develop an amphiphilic copolymer known as DS-b-PCL, forming micelles with high targeting ability towards the inflamed joints. Studies have shown that the accumulation of DS-b-PCL micelles in the arthritic joints is about ten times higher compared to control cases.100 Such results emphasize the necessity of performing biodistribution studies on living organisms to evaluate the efficiency of the delivery system, which proves that polymer-coated nanoparticles could be selectively targeted to the inflamed synovial membrane.

Peptide-Based Targeting

Peptide ligands also form a successful targeting approach because of their great specificity and small molecular weight. The tetrapeptide consisting of arginine, glycine, and aspartic acid (RGD) and its derivatives have been extensively applied in targeting αvβ3 integrin receptors that play a role in angiogenesis and inflammation. RGD-decorated nanoparticles can help improve the efficiency of treatment by providing higher specificity for inflamed endothelial tissue.

Many other peptides have been tried out in RA,101,102 including Vasoactive Intestinal Peptide (VIP), the Synovial Fibroblast-Homing Peptide HAP-1, and the Macrophage-Targeting Peptide Tuftsin, all of which have shown favorable efficiency in drug delivery applications. A nine-amino acid peptide ligand, ADK, discovered using phage display technology, selectively targets inflamed joints. ADK modified liposomes have improved binding to endothelial cells and accumulation in arthritic tissue.101 The administration of this drug using these liposomes resulted in better control of the symptoms of RA than either free IL-27 or other non-functional liposomes.103 Cook et al studied cystine-rich peptides (CRPs), which have been extracted from venoms of snakes, spiders, and scorpions.

One particular cystine-rich peptide CDP-11R showed a perfect half-life along with accumulation in the cartilage tissue when administered intravenously.104 The combination of CDP-11R with a steroid provided a peptide-steroid conjugate that relieved joint inflammation but decreased toxicity caused by the steroid. Another way of using peptides for targeted delivery is the utilization of collagen-binding peptide (CBP), which is a decorin-derived peptide that can bind to cartilage collagen. The combination of CBP with transforming growth factor-beta increased drug accumulation in inflamed tissues.105

Protein-Based Targeting

Protein-mediated targeting is based on the use of antibodies that identify particular antigens present on inflammatory cells. Inflammatory immune cells that play a role in the disease mechanism can be specifically targeted through antibody-conjugated nanocarriers with drugs.106 For instance, liposome conjugation of CD134 antibody was utilized for targeting activated T cells in arthritic joints. In addition, carriers with CD163 antibodies have been engineered for delivering glucocorticoids to macrophages with expression of hemoglobin scavenger receptor CD163.

Albumin is another example of a natural targeting ligand. Active rheumatoid arthritis is characterized by higher metabolic activity, resulting in greater albumin metabolism in the inflamed joint. Albumin possesses a high affinity for secreted protein acidic and rich in cysteine (SPARC), a protein upregulated in the synovial tissues of both RA patients and experimental models.

This suggests that albumin-based drug delivery systems may also enable targeted accumulation of therapeutics at sites of inflammation.46,107,108

Biomimetic Targeting

Recently, biomimetic nanocarriers based on cell membrane-camouflaged nanoparticles have emerged as a promising strategy for achieving natural targeting of inflamed joints. These systems inherit the membrane proteins of the source cells, thereby recapitulating key biological interactions involved in inflammation and immune cell trafficking (Figure 4). For instance, Li et al fabricated macrophage membrane-coated PLGA nanoparticles by extracting membranes following treatment with cytochalasin B, which loosens cytoskeleton-membrane interactions.

These biomimetic nanoparticles exhibited enhanced targeting of inflamed tissues, and when loaded with tacrolimus, they significantly attenuated arthritis progression in animal models.109 In vivo fluorescence imaging studies also indicated enhanced circulation and accumulation of membrane-coated nanoparticles at the arthritic site as compared to that of uncoated nanoparticles. Similar results were obtained in a study where Zhang et al constructed neutrophil membrane-coated nanoparticles based on the ability of neutrophil-derived microvesicles to capture inflammatory cytokines in order to protect the synovium. These nanoparticles could penetrate deep into the cartilage to prevent inflammatory injury to it.

The inflammation could be resolved effectively along with tissue repair without carrying any drug payload. Using a similar approach, platelet-mimicking nanoparticles were designed by using P-selectin interaction between platelets and inflamed tissues. These nanoparticles circulated for a long time and preferentially accumulated at inflamed joints.

Additionally, TRAIL-engineered cell membranes have been conjugated to hydroxychloroquine-loaded PLGA nanoparticles to facilitate active delivery of therapeutic agents and inhibit inflammatory cytokine receptors in RA.110,111Figure 4Schematic diagram of the inflammation microenvironment of RA joints, which consists of immune cells, including T cells, macrophages, neutrophils, platelets, and high amounts of cytokines. The bio-inspired nanocarriers can be fabricated by the surface modification of nanoparticles with cell membranes and ligand targeting molecules to achieve the active targeting at the inflammation synovial tissue site. The technique is beneficial in delivering bioactive molecules, such as TCM monomers, to the RA sites more efficiently.

Reference adapted from.112The diagram illustrates the inflammation microenvironment of rheumatoid arthritis joints, highlighting the presence of immune cells such as T cells, macrophages, neutrophils, platelets and cytokines. On the left, a section of inflamed joint tissue is shown with various immune cells labeled. The central part depicts the joint with inflamed synovial tissue.

On the right, the process of biomimetic nanomedicine delivery is detailed. It includes preparation of biomimetic nanomedicines, coating of the cell membrane, functionalization and attachment of ligands. Nanoparticles are shown targeting the inflamed synovial tissue site, aiming for active targeting to the target site.

The diagram emphasizes the delivery of bioactive molecules to rheumatoid arthritis sites efficiently.Diagram of RA joint inflammation with immune cells and nanomedicine delivery.

Stimulus-Responsive Nanocarriers for Controlled Drug Release in RA

Pathological microenvironment of RA consists of a number of abnormal physiologic parameters, which include the following: low pH, increased oxidative stress, and the overexpression of pro-inflammatory enzymes. In particular, the extracellular pH of inflamed joint is reduced to approximately 6.0 and may drop to less than 5.5 in case of highly inflamed tissues. At the same time, overproduction of ROS due to activated macrophages and neutrophils causes oxidative stress, whereas the overexpression of enzymes like MMPs and PLA2 can be observed in the synovium.

These distinctive features provide opportunities for the development of stimulus-responsive nanocarriers capable of selectively releasing therapeutic agents within inflamed joints. Such smart delivery systems enhance therapeutic efficacy while minimizing systemic toxicity. A variety of endogenous and exogenous stimuli—such as pH, ROS, enzymes, temperature, ultrasound, and magnetic fields—have been explored for triggering drug release from targeted nanomedicines in RA.55,113,114

pH-Responsive Nanocarriers

The joints affected with RA demonstrate an acidic microenvironment with a pH value of around 6.0, which may reduce up to 5.0 during the development of the disease process. The acidic nature of these joints has been used significantly for designing the pH-sensitive delivery systems using acid-labile linkages such as hydrazone or acetal linkages. For instance, pH-sensitive micelles have been formed through the linkage of hydrophobic dexamethasone and hydrophilic PEGs with the help of hydrazone linkages.

Such a strategy helps reduce drug leakage in the circulation while allowing selective drug release at the arthritic joints due to the acidic environment. Acetal linkages show greater sensitivity to acids than hydrazone linkages.115 A prodrug of dexamethasone, decorated by DSPE-PEG using an acetal linker, was synthesized for development of pH responsive nanoparticles which can accumulate selectively within inflamed joints for effective release of drug without any trace.59 Using another strategy, Alam et al synthesized biomineralized nanoparticles made up of PEGylated hyaluronic acid and calcium phosphate that had better distribution to the arthritic paws and helped release methotrexate in an acidic environment. Moreover, acidic environments have also been exploited for causing changes in the morphology of nanocarriers like the transformation of vesicles into fibers.116

Redox-Responsive Nanocarriers

RA patients exhibit high levels of ROS in their inflamed synovial tissues, and these are highly linked to inflammation and tissue damage. To exploit this feature, oxidation-sensitive linkers—such as thioether, selenium-containing compounds, thioketal, and phenylboronic ester—have been utilized in the development of ROS-responsive nanocarriers. Xu et al designed folic acid-functionalized ROS-responsive nanoparticles incorporating a 4-phenylboronic acid pinacol ester linker.

These nanoparticles exhibited ROS-triggered drug release and efficient H2O2 scavenging in activated macrophages. When loaded with dexamethasone, they significantly reduced histological damage and inflammation in CIA models. Similarly, Fan et al developed berberine-loaded micelles based on a selenocystamine-containing polymer that is cleavable under ROS conditions.

These ROS-responsive micelles enabled controlled drug delivery to inflamed tissues and achieved nearly tenfold higher therapeutic efficacy compared with free berberine.117 In another study, folate-modified liposomes were used to co-encapsulate methotrexate and catalase. Catalase-mediated oxygen generation under high ROS conditions disrupted the liposomal structure, leading to controlled release of methotrexate.118

Enzyme-Responsive Nanocarriers

RA is characterized by inflamed joints with elevated levels of disease-associated enzymes, particularly MMPs and phospholipase A2 (PLA2). The above enzymes have been extensively used as an initiator in the development of enzyme sensitive drug delivery systems. MMP-sensitive nanocarriers usually employ MMP sensitive peptide substrates for either controlling drug delivery or for removal of the PEG shell so as to facilitate better tissue penetration.

For example, He et al prepared MMP responsive nanoparticles using the co-assembly of triglycerol monostearate (TGMS) with DSPE-PEG. Dexamethasone was quickly released after MMP triggered degradation of ester linkage present in TGMS in response to inflammation. In vivo study revealed that intravenous delivery of these nanoparticles resulted in remarkable alleviation of joint swelling and inflammatory reactions in animal models of arthritis.

Another enzyme, phospholipase A2, which is secreted by activated macrophages and neutrophils, can be used as the enzyme trigger for RA treatment. Wang et al reported the preparation of lipid tubules made up of DC8,9PC molecules and facilitated release of drugs on hydrolysis of PLA2 in inflamed joints.119,120

External Stimulus-Responsive Systems

In addition to endogenous signals, many other external signals including temperature, ultrasonic signals, and magnetic signals have been considered for the purpose of controlled drug delivery for treating RA. For instance, PLGA nanospheres encapsulating methotrexate and gold nanoparticles allow targeted heating when exposed to near-infrared light, resulting in faster drug delivery at the site of inflammation. Temperature-responsive polymers have also been utilized for developing such responsive systems.121 In order to enhance the stability of biologic drugs in physiological condition, a temperature-sensitive nanocarrier loaded with an amphiphilic polyelectrolyte and etanercept was synthesized, which resulted in improved stability of the biologic drug at body temperature.122 Nanocarriers activated by ultrasound have also shown promise.

According to Zhu et al, there have been the development of stimuli-responsive nanoparticles known as “nanobombs”, which consist of a perfluorocarbon core coated in a PEG phospholipid layer that is modified with folic acid. Upon exposure to ultrasound in arthritic animals, the nanobombs delivered the therapeutic payload and greatly reduced joint inflammation and cartilage degradation. Altogether, stimulus-responsive nanocarriers constitute a viable approach to deliver drugs to specific sites on demand in the treatment of rheumatoid arthritis.123

Preclinical and Experimental Studies

Many pieces of preliminary data have been accumulated in support of the application of TCM monomers delivered via nanoparticles for the treatment of RA. Nanotechnology-based delivery systems have been studied in vitro cell cultures and animal models, showing increased bioavailability and improved anti-inflammatory activity along with enhanced targeted accumulation of phytochemicals in the joints. Notably, biodistribution experiments on RA animal models revealed the selective delivery of TCM monomer-loaded nanocarriers to the inflammatory synovium tissues, leading to increased efficiency and decreased systemic availability of the loaded drugs in comparison with the free drug.

It has been confirmed by many researchers that curcumin-loaded nanocarriers are efficacious in animal models of RA. For example, curcumin bound with polymeric nanoparticles decreased the levels of proinflammatory cytokines, such as TNF-α, IL-1β, and IL-6 in CIA models.124 This nanoformulation enhanced curcumin stability and sustained its release, leading to reduced synovial inflammation and protection against cartilage degradation.125 In addition, treatment with nanoparticle-entrapped curcumin led to more suppression of TNF-α, IL-1β, and IL-6 compared with free curcumin. It was emphasized that there is a synergistic effect in the combination of TCM monomers and nanocarrier technology.

Furthermore, resveratrol-entrapped nanoparticles are able to manage oxidative stress and inflammatory signaling through blocking NF-κB activation and ROS generation in synovial tissue. Moreover, quercetin-entrapped nanoparticles showed promising results for RA treatment models.126 Studies using quercetin-loaded liposomes and polymeric micelles revealed enhanced anti-inflammatory effects, attributed to the downregulation of inflammatory mediators and reduced macrophage infiltration into the synovial membrane. Compared with free quercetin, these nanoformulations resulted in decreased joint swelling and prevented structural joint damage in CIA rat models, primarily due to improved solubility and targeted delivery.127,128 Imaging studies and histological analysis further provided support for increased synovial accumulation of nano-formulated quercetin, which was associated with better suppression of inflammatory cells infiltration and cartilage degradation.

Besides the widely studied phytochemicals, several other compounds derived from Chinese traditional medicine have also been loaded in nanoparticles. For instance, Tripterygium wilfordii active components have been encapsulated in polymeric nanoparticles and liposomes in order to decrease their toxicity without compromising the strong immunosuppressive effect.129 Preclinical studies have shown that triptolide-loaded nanoparticles exert substantial anti-proliferative and anti-inflammatory effects on synovial tissues and suppress the production of inflammatory cytokines in RA animal models.130 Nanocarriers were found to offer better safety and enhanced efficacy against arthritogenic activity in terms of lower synovial hyperplasia and down-regulation of inflammatory cytokines compared to the free forms of triptolide. In addition, nanocarriers with berberine were found to possess the capability of modulating macrophage polarization and inflammatory signaling pathways.

This was attributed to lowering levels of pro-inflammatory factors such as TNF-α, IL-1β, and IL-6. Lipid-based nanocarriers, including liposomes and solid lipid nanoparticles, have also been explored as delivery systems for plant-derived anti-arthritic agents. These formulations enhance drug stability and prolong circulation time, facilitating more efficient accumulation of therapeutic agents in inflamed joints via the enhanced permeability and retention (EPR) effect.

In various animal studies, liposomal formulations of phytochemicals exhibited superior anti-arthritic efficacy compared with conventional preparations.131 In order to enhance the disease-related specificity of the study, a specific table including all the preclinical investigations related to rheumatoid arthritis (RA) is provided below (Table 3).132–137 In the current table, types of nanocarriers, types of TCM monomers, type of animal models, and therapeutic effects of TCM monomers on RA are included. Overall, from the above results, it can be concluded that the use of nanocarriers improves the therapeutic efficacy of TCM monomers by increasing their bioavailability. Table 3Nanocarrier-Mediated Preclinical Studies on TCM Monomers for RA TreatmentNanocarrierTCM MonomerRA ModelKey FindingsReferencePolymeric nanoparticles (Responsive systems)CurcuminCollagen-induced arthritis (CIA) rat modelReduce TNF-α, IL-1β, IL-6; reduced synovial inflammation; improved bioavailability[132]Folate-modified liposomesTriptolide (Tripterygium wilfordii)CIA mouse modelTargeted activated macrophages; reduced cartilage destruction; lower systemic toxicity[133]Inflammation-targeted nanoparticles (dextran-based)TriptolideCIA mouse modelSuppressed inflammatory cytokines (TNF-α, IL-1β, IL-6); reduced joint swelling[134]Free drug (comparative nano studies in CIA)TriptolideCIA mouse modelReduced MMP-3, MMP-13; inhibited NF-κB; cartilage protection[135]Liposome-based immunomodulatory system (curcumin/quercetin co-delivery)Curcumin/QuercetinAntigen-induced arthritis mouse modelNF-κB inhibition; induction of Treg cells; suppression of arthritis progression[136]Methotrexate hybrid nanocarrier (RA benchmark system)Methotrexate + siRNACIA mouse modelNF-κB suppression; reduced joint inflammation; targeted delivery[137]

Safety, Toxicity and Biocompatibility

Although nanocarrier systems hold great promise for delivering TCM monomers in RA, safety and biocompatibility remain critical considerations in both preclinical and translational studies. Examples of representative clinical trials on TCM-derived monomers and plant extracts that may be useful for the management of rheumatoid arthritis are listed in Table 4.138–143 While there is still a lack of clinical evidence compared with traditional DMARD drugs, curcumin, resveratrol, and Tripterygium wilfordii extracts have shown promising results in randomized controlled trials and meta-analyses. Several nanocarriers, such as polymer, lipid, micellar, hydrogels, and biomimetic systems, have different biological interactions that can affect the cellular toxicity, immunogenicity, and tissue effects.

Polymer nanocarriers made up of PLGA, PEGylated polymer, and chitosan polymers are well-known for their degradability and good safety profiles. However, the metabolites generated from their degradation and the nature of their surfaces can cause stress to cells. For example, the degradation process inside macrophages or synovial fibroblasts may lead to an increase in the levels of ROS that affect mitochondria and activate the apoptosis pathway.

Moreover, the very cationic nature of the polymers may damage the cell membranes and cause hemolysis and cytotoxicity. While PEGylation is used to prevent the opsonization process, oxidation of the PEGs causes immune reactions.144–148 Therefore, despite the mostly good safety records of polymeric carriers, precise control over surface chemistry and dose administration is critical for reducing the risks of subclinical inflammation and/or sensitization. Lipid-based carriers, including liposomes, solid lipid nanoparticles (SLNs), and nanostructured lipid carriers (NLCs) are often perceived as biocompatible due to their resemblance to biological membranes.

However, they have their own set of safety issues. Complement activation-related pseudoallergy (CARPA) has been demonstrated to be a condition where lipid vesicles can induce complement activation (C3a/C5a) and cause hypersensitive responses, temporary inflammation, and even cardiovascular complications in sensitive individuals. Moreover, SLNs and NLCs containing unsaturated lipids may undergo oxidation in vivo and produce toxic substances that will increase oxidative stress in hepatocytes and macrophages.148–150Table 4Representative Clinical Trials on TCM-Based Compounds for RAStudy DesignPopulationInterventionMajor FindingsReferencesRandomized controlled clinical trial100 RA patientsResveratrol (1 g/day) + conventional DMARD therapy vs conventional therapy aloneResveratrol significantly reduced DAS28 scores, CRP, ESR, TNF-α, IL-6, MMP-3, and joint tenderness/swelling, suggesting benefit as an adjunctive therapy.[138]Double-blind, placebo-controlled trialPatients with longstanding RATripterygium wilfordii Hook F (TWHF) extract (180–360 mg/day)Significant clinical improvement was observed compared with placebo, demonstrating efficacy in patients with refractory RA.[139]Phase III double-blind randomized placebo-controlled trialRA patients in remission undergoing DMARD withdrawalCurcumin supplementation vs placeboCurcumin improved maintenance of remission and demonstrated a favorable safety profile over 52 weeks.[140]Multicenter randomized double-blind triple-dummy controlled trialActive RA patientsTripterygium wilfordii Hook F + TNF inhibitor vs methotrexate-based regimensCombination therapy achieved higher ACR50 response rates than methotrexate-based treatment with comparable safety.[141]Systematic review and meta-analysis14 RCTs; RA patientsTWHF extracts alone or combined with DMARDsTWHF significantly improved grip strength, morning stiffness, CRP, tender joint count, and inflammatory markers; combination therapy outperformed DMARD monotherapy.[142]Systematic review and meta-analysis733 RA patientsTWHF extracts vs placebo or DMARDsDemonstrated therapeutic efficacy with acceptable safety; common adverse effects included gastrointestinal symptoms and menstrual disturbances.[143]

Larger or poorly stabilized lipid vehicles have been observed to get accumulated within the mononuclear phagocyte system especially the liver and the spleen with consequent temporary increase in liver enzymes and changes in the phenotype of macrophages. This implies that proper optimization of the composition of the lipids and surface modifications like PEGylation or zwitterionic surfaces becomes necessary in order to prevent complement activation and lipid peroxidation. The amphiphilic block copolymers such as PEG-PLA and PEG-PDLLA are effective in improving the solubility of hydrophobic TCM monomers; however, their stability in biological media becomes a safety issue because dilution in the blood will result in premature dissolution and release of surfactant monomers that may destabilize the cellular membrane, and more complex micelles capable of escaping from the endosomes may damage lysosomal membranes of non-target cells.151 These mechanisms of toxicity highlight the need for optimization of micelle stability and release profile to avoid any off target cytotoxicity.

Hydrogels and nanohydrogels are some of the safest nano carriers because of their high water content, gentle mechanical strength, and sustained release mechanism.152 However, thermally or pH-sensitive hydrogels injected into tissues might lead to a temporary irritation and swelling at the injection site due to a high degree of crosslinking density or toxic degradation products. Some crosslinkers, like hydrazone and Schiff bases, may be subject to degradation and produce smaller molecules capable of disrupting proper functioning of immune cells, or inducing inflammation locally, especially in case of repeated intra-articular delivery, which is a typical therapy for RA.153 Nanocarriers based on exosomes and nanoparticles cloaked by cell membranes are endogenous in nature and thus considered highly biocompatible. But this does not imply their safety.

The presence of foreign surface antigens in allogenic exosomes can induce immune reaction. Due to rapid adsorption of proteins when exposed to proteins present in blood, the formation of protein corona can reveal cryptic antigens and lead to activation of complement and Toll-like receptor pathways. Therefore, standardized sourcing of exosomes and evaluation of donor compatibility still play an important role.

Immunogenicity is a key issue in all nanocarriers.154

This question is especially important in the context of diseases of the immune system that occur because of the malfunctioning immune response, for example, rheumatoid arthritis, where the immune system suffers from constant activation of both innate and adaptive immune responses. Here, there could be another type of interaction between nanocarriers and immune cells circulating within the blood vessels, along with other components involved in the inflammation process, such as autoantibodies, complement proteins, and factors of inflammation. The specific disease-related protein corona around the surface of the nanoparticles will influence the mechanism of distribution and uptake of nanocarriers by immune cells.

Even without any presence of pathogenic ligands, nanocarriers have the ability to interact with pattern recognition receptors (for instance, TLR2/4), activate NF-κB signaling, and stimulate the production of pro-inflammatory cytokines. The strategies employed for immune protection and maintenance of targeting include surface shielding (such as PEGylation or zwitterionic surface modification) and the size tuning from 50 to 150 nm. Because of the chronic character of the RA therapy, long-term safety studies are needed.

Although cancer treatment typically implies the use of the therapeutic agent for relatively short periods of time, the treatment of RA implies administration of the drug multiple times and during prolonged periods of time. Thus, it is necessary to perform the studies taking into account such aspects as accumulation due to repeated dosing, biodistribution upon repeated dosing, etc. Repeated dosing can lead to accumulation of nanosystems in reticuloendothelial tissues, changes in macrophage activity, chronic inflammation, sensitization, etc.

Chronic exposure can cause appearance of anti-carrier antibodies, faster blood clearance, and change in drug efficacy.

Repeated administration may result in distinct organ biodistribution patterns; non-degradable cores (eg, inorganic silica or metal oxides) can progressively accumulate in the liver, spleen, or lung macrophages, posing risks of low-grade chronic inflammation, fibrosis, or functional impairment. Long-term studies also suggest that certain nanomaterials at high cumulative doses may compromise genomic integrity or reproductive tissue function, underscoring the need to evaluate genotoxicity, immunotoxicity, and reproductive toxicity in extended preclinical models. There is a need to assess the effects that prolonged use of nanocarriers may have on maintaining the immune status in RA patients.

In view of the fact that many nanotherapies are intended to target the control of macrophages, dendritic cells, T-cells, or cytokines, their use would inevitably impact the mechanism of defense against infections or surveillance by the immune system in the host. This will be highly significant in the case of nanocarriers that will be combined with DMARDs or biologics with immunosuppressive action.

Modern strategies for developing nanocarriers include the use of biodegradable carriers, controllable functionalization of their surfaces, and responsive linkers that would result in release of cargo only under the pathological conditions such as the inflammation in joints. The safety is additionally ensured through predictable degradation products that could easily be eliminated via renal and/or hepatic mechanisms.155

In addition, future research needs to target the development of long-term evaluation methods of safety that will be applicable to nanomedicine delivery systems of TCM monomers in chronic inflammatory diseases. Such an evaluation process should include multiple dose toxicities, immunotoxicity in autoimmune disease models, biodistribution studies, degradation studies, and recovery after the formulation of administration. The incorporation of the above three processes is important in the advancement of nanocarriers for delivery of TCM monomers for treatment of RA.

Challenges in Clinical Translation

Despite promising results in the pre-clinical phase, there is still considerable gap in moving from nanomedicine-based treatment strategies to actual clinical application in RA. The majority of existing investigations are limited to in vivo/in vitro experiments, where superior targetability, controlled delivery, and minimized side effects are successfully achieved; yet, in the majority of cases, such results cannot be translated into the clinic owing to species-specific differences and heterogeneous nature of the disease, and lack of extensive clinical validation of the technology.57,156

In terms of the immune response, recent evidence has revealed that apart from serving as drug carriers, nanocarriers are also capable of modulating immune response. Indeed, it has been shown that nanocarriers possess the potential to regulate various immune cells such as macrophages, dendritic cells, and Tregs in order to bring back immune tolerance in patients suffering from RA.157,158 For example, using nanoparticle-based delivery of immunomodulators (such as rapamycin-based systems) helps in expanding Treg and controlling autoreactive immunity; thus, achieving immune homeostasis.158 However, there are still many unknowns regarding the long-term impacts of such immune modulation, including the risks of immune suppression and unintended immunotoxicity. As such, it is necessary for future research to incorporate the aspects of immunological safety assessment, standardized regulatory policies, and clinical trials in order to close the translational gap in RA.

Although nanocarrier-based systems have demonstrated considerable potential for treating RA in preclinical models, significant barriers remain to their successful translation from bench to bedside. One of the foremost challenges is scaling up manufacturing processes from laboratory prototypes to industrial-scale production. Laboratory-scale protocols typically require precise control over parameters such as particle size, drug loading, surface chemistry, and morphology characteristics that are difficult to reproduce consistently at a commercial scale.

Even minor variations in size distribution or surface properties during scale-up can alter pharmacokinetics and biodistribution, potentially compromising both efficacy and safety. This reproducibility challenge is compounded by the complexity of manufacturing steps (such as homogenization, solvent evaporation, and sterilization), which demand highly controlled conditions and specialized equipment in compliance with Good Manufacturing Practice (GMP) standards. Consequently, the development of robust, scalable, and reproducible manufacturing strategies remains a critical hurdle in nanomedicine translation.

Apart from scale-up factors, successful clinical translation necessitates the development of manufacturing processes that are compliant with GMP for use in the manufacturing of nanomedicines. Key quality attributes (CQA) such as particle size distribution, polydispersity index, zeta potential, encapsulation efficiency, surface modification, and drug release should be consistently ensured in each batch produced. New manufacturing technologies such as microfluidics, continuous flow processes, and process analytical technology (PAT) have the potential to address these issues.

Closely linked to manufacturing challenges are regulatory issues arising from the unique physicochemical properties of nanocarriers. Regulatory frameworks in major markets such as the United States and the European Union have yet to be fully adapted to the distinctive characteristics of nanomedicines, which often exhibit heterogeneous structures and multifunctional components that do not fit neatly within conventional drug evaluation paradigms.159,160 Regulators typically require detailed documentation of critical quality attributes-including particle size distribution, surface charge, and composition-as part of clinical trial applications and marketing authorization dossiers.150 However, standardized definitions and measurement methodologies tailored to nanocarriers are still evolving, making regulatory submissions more complex and unpredictable The lack of harmonized international requirements further complicates efforts to obtain approval across multiple regions. The aspect of quality control (QC) is another big problem facing the development of nanomedicine.

Apart from traditional analysis of drugs, the physicochemical properties of nanocarriers need thorough investigation using orthogonal analytical methods for the assessment of particle shape and size, colloidal stability, drug encapsulation and release kinetics, sterility, endotoxins, and residual solvent analysis. Moreover, biological characterization, which includes formation of protein corona, immunological reactions, complement activation, cellular uptake, and distribution, is becoming increasingly important. The absence of unified standards for these analyses makes comparison of results difficult.

Stability and storage represent additional translational challenges.161 Nanocarriers are prone to physical instability during storage and handling, including aggregation, fusion, sedimentation, and drug leakage. Over time, changes in particle size or surface properties can adversely affect the therapeutic performance, bioavailability, and safety of the encapsulated TCM monomers. These instability issues may be exacerbated by environmental factors such as temperature, humidity, and mechanical stress during transportation, underscoring the need for carefully optimized formulation and storage conditions.

Although strategies such as lyophilization and the use of stabilizing excipients have been explored to mitigate these problems, further process development and validation are required.162

Cost considerations also pose major obstacles to the translation and clinical implementation of nanocarrier systems. The synthesis, purification, and quality control of nanoparticles involve complex procedures that significantly increase costs compared with conventional drug formulations. Investments in specialized infrastructure, analytical technologies, and extensive nonclinical and clinical testing further escalate development expenses.

These financial burdens are particularly pronounced in the context of chronic diseases such as RA, where long-term treatment regimens are anticipated and cost-effectiveness is a critical consideration for payers and healthcare systems. High production costs may limit the accessibility of advanced nanotherapeutics, especially in resource-constrained settings.163

Finally, clinical translation is complicated by regulatory uncertainty and evolving guidelines. Although regulatory agencies such as the FDA and EMA have begun issuing frameworks to guide nanomedicine developers, universal standards for evaluating complex nanocarrier platforms have not yet been established. This regulatory ambiguity creates uncertainty regarding the required data packages, characterization protocols, and clinical endpoints, potentially delaying approvals and discouraging investment in translational efforts.

Despite the release of many guidance documents related to nanotech therapeutics by regulatory bodies like the FDA and EMA, nanomedicines continue to be evaluated on a case-by-case basis due to the complexity of their structure and function. It is anticipated that future regulations will make extensive use of QbD (Quality by Design) concepts, which focus on risk assessment, characterization of CQAs (Critical Quality Attributes), process validation, and life cycle management. Collaborative efforts among researchers, industry stakeholders, and regulatory authorities will be essential to address these gaps by establishing comprehensive, nanotechnology-specific standards that balance safety with innovation.164

Future Perspectives

The rapid advancement of nanotechnology has opened promising avenues for addressing long-standing challenges in the treatment of RA, particularly regarding the delivery of TCM monomers. While conventional nanocarriers, such as polymeric nanoparticles, liposomes, and micelles, have demonstrated improved bioavailability and targeting in preclinical models, future developments are likely to focus on adaptive, multifunctional, and precision-oriented systems capable of responding to the complexity of RA pathophysiology and individual patient biology.

Smart nanocarriers represent the next generation of drug delivery technology, integrating molecular recognition, decision-making elements, and programmable behavior into nanostructures.165 These systems can detect and respond to disease-specific signals, such as inflammatory mediators, enzyme levels, or microenvironmental changes, thereby maximizing targeting precision while minimizing off-target effects. For instance, nanocarriers activated by specific biomarkers of synovial inflammation (eg, elevated cytokine levels or surface receptors on activated macrophages) can release their therapeutic payload in a spatiotemporally controlled manner. By combining diagnostic sensing and therapeutic functions within a single platform-a theranostic approach-real-time monitoring of drug delivery and treatment response may be achieved, facilitating the development of more effective and safer RA therapies.166 The evolution of theranostic nanoplatforms can help in improving the management of RA patients through the provision of both therapeutic and diagnostic functions in one platform.

This can be done through the use of imaging modalities like magnetic resonance imaging (MRI), fluorescence imaging, photoacoustic imaging, or positron emission tomography (PET) in order to allow for the visualization of nanoparticle delivery, drug release, and effects of therapy on the joints that are affected by inflammation.

Although stimuli-responsive delivery systems (eg, pH-, ROS-, and enzyme-responsive carriers) have shown considerable promise in preclinical RA models, emerging research is expanding the capabilities of this technology. Future designs are expected to incorporate multi-stimuli-responsive features capable of integrating multiple pathological signals, such as joint acidity, oxidative stress, and aberrant enzyme expression, within a single delivery vehicle. This approach can enhance site-specific release and reduce systemic leakage.167 Next-generation nanoparticles may employ hierarchical triggering mechanisms, such as active targeting via surface ligands followed by intracellular release triggered by ROS or MMPs specifically expressed in inflamed synovium.

Such multifunctional responsiveness would enable on-demand drug release with high precision, adapting to dynamic disease conditions.168 The future multi-responsive nanocarriers will be able to combine multiple pathological stimuli, which include acidic pH, increased levels of ROS, MMPs, hypoxia, and inflammatory cytokines. There is a possibility that hierarchical response mechanism will make it possible for the nanocarriers to respond sequentially by first accumulating themselves in the inflamed synovium via active targeting followed by the release of drugs after being exposed to the intracellular inflammatory stimuli.

Personalized medicine has already transformed fields such as oncology and genomics, and its integration with nanotechnology is beginning to influence the management of inflammatory diseases like RA. Future therapeutic strategies are likely to leverage patient-specific biomarkers, genomic data, and immune profiling to design tailored nanocarrier systems suited to individual disease subtypes, severity, and drug response patterns. Artificial intelligence and machine learning are increasingly being applied to analyze complex patient datasets and predict optimal nanocarrier formulations, targeting ligands, and release kinetics.

Moreover, the convergence of nanomedicine with wearable devices and advanced imaging techniques may enable real-time tracking of drug distribution and therapeutic response, allowing for dynamic treatment adjustments.4 Improvements in genomics, transcriptomics, proteomics, and immunology are anticipated to expedite the advent of tailored nanomedicine therapies in RA. In the future, nanocarriers can possibly be designed based on individual molecular biomarker signatures and disease phenotypes and responses to therapy. In addition to artificial intelligence and machine learning technologies, these factors can aid in the improvement of the therapeutic benefit of the treatment while lowering the risks associated with unnecessary use of drugs.

TCM offers a rich source of bioactive monomers with distinctive anti-inflammatory and immunomodulatory properties. However, their clinical application has historically been limited by unfavorable pharmacokinetics and instability. The integration of nanotechnology with traditional medicine provides a means to harness the full therapeutic potential of these natural compounds while overcoming these limitations.

Future efforts will likely focus on the synergistic combination of multiple TCM monomers within a single nanocarrier, creating multi-agent systems that reflect the holistic approach of traditional medicine while enabling precise delivery and controlled pharmacodynamic effects. Additionally, nanocarrier platforms offer the opportunity for co-delivery of TCM monomers with DMARDs or biologics, potentially enhancing efficacy and reducing adverse effects. The application of combination therapy through nanocarrier-based co-delivery of TCM monomers and standard disease-modifying antirheumatic drugs (DMARDs) can be considered an especially promising avenue.

Antioxidant and anti-inflammatory properties of curcumin, triptolide, resveratrol, and quercetin can contribute to the efficacy of methotrexate, leflunomide, or biological drugs through their complementary modes of action. Combined delivery in one and the same nanocarrier can improve pharmacodynamics, promote joint inflammation targeting, and provide controlled release of both medicines. These approaches can allow reducing the dose of DMARDs, lowering the risk of side effects, and acting on multiple mechanisms responsible for the development of RA.

Despite some promising results observed in preclinical research, additional studies are required to improve their efficacy and clinical applications.

Biomimetic and bioinspired carriers represent another promising direction. Approaches such as using plant-derived exosomes or vesicles as natural vehicles for TCM monomers exemplify the integration of native delivery systems with modern nanotechnology. Such strategies may better preserve the complex compositional integrity of multi-component TCM preparations while achieving improved stability and targeted delivery.169,170 The use of nanoparticles with cell membrane coating, vesicles inspired by exosomes, and plant-based extracellular vesicles can add more value to the clinical application of nanomedicine through their ability to achieve prolonged circulation time, escape immune system recognition, and target inflammatory sites.

Such biomimetic systems can be employed as flexible platforms for the combined delivery of TCM monomers, DMARD drugs, biologicals, or nucleic acids to develop multifunctional and customized therapies for RA patients.

Despite a variety of promising experimental data on the therapeutic potential of the delivery of TCM monomers via nanocarriers in rheumatoid arthritis, several important drawbacks need to be addressed. First, almost all experiments have been performed on animals and mainly on collagen-induced arthritis (CIA) model that is far from mimicking human RA. Second, even with the improved efficacy of delivery, there are significant differences between the size, characteristics of the surface of nanoparticles, and loading capacity of nanocarriers used in different studies.

In addition to this, despite the substantial decrease in pro-inflammatory cytokines like TNF-α, IL-1β, and IL-6, the long-term safety and toxicity of such nanocarriers is not studied properly. For instance, accumulation of polymeric nanoparticles and lipid-based nanosystems in the wrong targets can lead to chronic toxicity and immunogenicity problems. Moreover, the problem of scalability, reproducibility, and regulation poses major challenges to the translation of these nanosystems into the clinic.

As compared to each other, lipid-based systems possess greater biocompatibility and clinical applicability, while polymeric carriers give better opportunities for drug delivery and modification. Nevertheless, none of these two systems can be considered the ideal choice. Therefore, the development of hybrid nanocarriers seems to be the way forward.

Future research needs to be concentrated on establishing standard evaluation protocols, conducting long-term toxicity studies, and carrying out clinical trials.

Conclusion

The rheumatoid arthritis (RA) is characterized as a chronic, heterogeneous autoimmune and inflammatory disease with a heterogeneous clinical course from patient to patient. The combination of TCM-based monomers with nanocarriers appears to be a new promising approach for the treatment of RA. These naturally existing biologically active molecules are known to possess strong anti-inflammatory and immunomodulating abilities, but their use is hampered by poor pharmacokinetic characteristics and low bioavailability.

With the help of advanced nanocarrier-based delivery platforms, such as stimuli-responsive, biomimicking and engineered nanosystems, it becomes possible to increase the selective delivery of the TCM monomers into inflamed joints, thus achieving the controlled and sustained release of the drugs while decreasing their side effects. Nevertheless, it should be mentioned that the majority of the existing data are obtained from preclinical in vitro and in vivo studies, without the clinical verification of the findings in humans.

Some of the major limitations are the problems related to manufacturing on an industrial scale, inadequate safety information in the long term, regulatory aspects, and individual variations in the treatment response. Besides, there are problems like reproducibility in the manufacturing process, stability in storage, and immunogenicity that are important obstacles for the use of nanocarriers in clinical practice. Thus, future studies need to bridge the existing gap between laboratory research and clinical applications of nanocarrier technology through proper production process and toxicity testing.

In more detail, future research needs to concentrate on development of clinically applicable nanocarriers, validation on animal/human subjects, and determination of predictive biomarkers for personalizing the treatment process. Moreover, the implementation of real-time monitoring systems and combinatorial approach, including the use of conventional drugs and/or various TCM monomers, can increase the effectiveness of the therapy. Although nanocarrier systems for TCM monomers have great potential in the next generation of RA therapy, their clinical success will depend on overcoming these challenges.