Preparation and testing of cyclosporine microsphere and solution formulations in the treatment of polyarthritis in rats

We prepared a microencapsulated sustained-release formulation of cyclosporine A (CsA) and compared its efficacy to the solution formulation of cyclosporine A (Sandimmune, Sandoz) in an attempt to improve the treatment of rheumatoid arthritis. Microspheres containing cyclosporine were prepared with poly(lactic co-glycolic acid) (PLGA), a polymer in the submicron particle range of 0.22-0.8 micron. Studies were carried out to determine uptake rates and mechanisms of lymphocyte inhibition mediated by macrophages containing CsA microspheres in vitro. The results of these studies were used to establish whether lower doses of the microencapsulated cyclosporine could be used in in vivo studies in the polyarthritic rat model for rheumatoid arthritis. In vitro dissolution testing revealed that CsA was released extremely slowly from microspheres for up to 48 hr (0.002%). Radiolabeled 3H CsA was incorporated into some PLGA microspheres or the microspheres were labeled using a 99mTc radioligand when needed, and radiolabeling efficiency was consistently above 50%. Uptake studies at various microsphere-to-macrophage ratios (1:1, 1:5, 1:10) were carried out using 99mTc radiolabeled microspheres and macrophages obtained from normal and polyarthritic rats. Normal macrophages behaved significantly differently from arthritic macrophages throughout the study. Arthritic macrophages cause increased amounts of CsA to be released (68% of the dose) into the culture medium past 24 hr compared to normal macrophages (48% of the dose). This factor may account for the significantly increased inhibition (68.2%) of mixed lymphocyte culture proliferation in the presence of arthritic macrophages containing CsA-loaded PLGA microspheres over normal macrophages (48.2%) that were pre-exposed to the same microsphere dose. The equivalent quantity of CsA as that contained in the microspheres when placed in solution or the same quantity of blank PLGA microspheres caused decreased levels of lymphocyte inhibition when compared to the effects of CsA microspheres in macrophages of normal cells, but significantly decreased levels of inhibition in arthritic cells. From the in vivo studies, it is evident that CsA microspheres, even at low dose levels, were highly effective in inhibiting polyarthritis in rats.