In vitro and in vivo study of thymosin alpha1 biodegradable in situ forming poly(lactide-co-glycolide) implants

The purpose of this study was to develop poly(lactide-co-glycolide) (PLGA) based in situ forming implants (ISFI) for controlled release of thymosin alpha 1 (T alpha 1). The ISFI was prepared by dissolving PLGA in N-methyl-2-pyrrolidone (NMP) or mixtures of NMP and triacetin. T alpha 1 microparticles, prepared by spray-freeze drying method with chitosan or bovine serum albumin as a protectant, were suspended in PLGA solutions. The effects of T alpha 1 pre-encapsulation, PLGA molecular weight, PLGA concentration and organic solvents composition on the in vivo T alpha 1 release were evaluated by subcutaneously injecting T alpha 1 loaded ISFI into Sprague-Dawley Rats. The pharmacological efficacy of T alpha 1-loaded ISFI was examined using immunosuppressive BALB/c mice induced by cyclophosphamide. The ISFI composed of T alpha 1 pre-encapsulated with chitosan, higher molecule-weight PLGA at higher concentration and more triacetin showed a lower initial release and a longer sustained release period. The optimal prescription of our study showed a low initial release of 29.3% (24 h), followed by a slow and continuous drug release up to 28 d in vivo. An in vitro release device was designed to mimic the in vivo release of T alpha 1, and good correlation was observed between the in vitro and in vivo releases, with the linear correlation coefficient of 0.9899. T alpha 1-loaded ISFI showed low cytotoxicity as tested by CCK-8 assay. T alpha 1-loaded ISFI significantly increased the thymic index and spleen index of immunosuppressive mice. These results suggest that the ISFI is a suitable system for controlled release of T alpha 1. (C) 2010 Elsevier B.V. All rights reserved.