Self-actuating inflammation responsive hydrogel microsphere formulation for controlled drug release in rheumatoid arthritis (RA): Animal trials and study in human fibroblast like synoviocytes (hFLS) of RA patients.

Patients with rheumatoid arthritis (RA) often have one or more painfuljoints despite adequate medicine. Local drug delivery to the synovial cavity bids for high drug concentration with minimal systemic adverse effects. However, anti-RA drugs show short half-lives in inflamed joints after intra-articular delivery. To improve the therapeutic efficacy, it is essential to ensure that a drug is only released from the formulation when it is needed. In this work, we developed an intelligent "Self-actuating" drug delivery system where Disease-modifying anti-rheumatic Drug (DMARD) methotrexate is incorporated within a matrix intended to be injected directly into joints. This formulation has the property to sense the need and release medication only when joints are inflamed in response to inflammatory enzyme Matrix metalloproteinases (MMP). These enzymes are important proteases in RA pathology, and several MMP are present in augmented levels in synovial fluid and tissues. A high level of MMP present in synovial tissues of RA patients would facilitate the release of drugs in response and ascertain controlled drug release. The formulation is designed to be stable within the joint environment, but to dis-assemble in response to inflammation. The synthesized enzyme-responsive methotrexate (Mtx) encapsulated micron-sized polymer-lipid hybrid hydrogel microspheres (Mtx-PLHM) was physiochemically characterized and tested in synovial fluid, Human Fibroblast like synoviocytes (h-FLS) (derived from RA patients) and a rat arthritic animal model. Mtx-PLHM can self-actuate and augment the release of Mtx drug upon contact with either exogenously added MMP or endogenous MMP present in the synovial fluid of patients with RA. The drug release from the prepared formulation is significantly amplified to several folds in the presence of MMP-2 and MMP-9 enzymes. In the rat arthritic model, Mtx-PLHM showed promising therapeutic results with the significant alleviation of RA symptoms through decrease in joint inflammation, swelling, bone erosion, and joint damage examined by X-ray analysis, histopathology and immune-histology. This drug delivery system would be nontoxic as it releases more drug only during the period of exacerbation of inflammation. This will simultaneously protect patients from unwanted side effects when the disease is inactive and lower the need for repeated joint injections.

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.