Development, characterization and in vitro evaluation of biodegradable rhein-loaded microparticles for treatment of osteoarthritis.

Rhein is an active metabolite of the drug diacerein, whose anti-inflammatory properties have been demonstrated in both in vitro and in vivo models. However, the low oral bioavailability of rhein has limited its utility as a potential treatment of osteoarthritis (OA), a chronic inflammatory disease. In order to overcome this limitation, the aim of this work was the development of a drug delivery system intended for intra-articular administration of rhein, based on polymeric biodegradable PLGA microparticles (MPs) loaded with the drug. The MPs, prepared by the emulsion-solvent evaporation technique were characterized in terms of several parameters including morphology, encapsulation efficiency, molecular interactions between components of the formulation and in vitro release profiling. Furthermore, cell-based in vitro studies were performed to evaluate the cytotoxicity of the formulations and their effect on the release of inflammatory markers including pro-inflammatory cytokines and reactive oxygen species (ROS). Scanning electron microscopy demonstrated that the prepared MPs exhibited an almost spherical shape with smooth surface. The size distribution of the prepared MPs ranged between 1.9 and 7.9µm, with mean diameter of 4.23±0.87µm. The optimal encapsulation efficiency of rhein was 63.8±3.0%. The results of powder X-ray diffraction and differential scanning calorimetry studies demonstrated that the active ingredient is partially the crystalline state, dispersed in the polymer matrix. This outcome is somewhat reflected in the release kinetics of rhein from the MPs. The cytotoxicity evaluation, carried out in macrophages derived from THP-1 cells, showed that both rhein-loaded MPs and unloaded MPs did not significantly affect the cell viability at MP concentrations up to 13.8µM. In lipopolysaccharide-activated macrophages, the rhein-loaded MPs significantly decreased the production of interleukin-1ß (IL-1ß) and (ROS), when compared to the unloaded MPs. In conclusion, the results of this preliminary study suggest that an MP-based formulation of rhein could be tested in animal models of inflammation, aiming for an injectable commercial product capable of providing a therapeutic solution to patients suffering from chronic joint diseases.