Preparation and characterization of PLGA microspheres containing a staphylokinase variant (K35R).

Aim: To produce poly (lactic-co-glycolic acid) (PLGA) microspheres, containing a staphylokinase variant (K35R, DGR) with reduced immunogenecity and antiplatelet aggregation activities, which allowed the preservation of protein stability during both particle processing and drug release.

Methods: DGR-loaded microspheres were fabricated using a double emulsion-solvent evaporation technique. The effects of preparative parameters, such as stirring rate, polymer concentration, and the excipients of both internal and external aqueous phase (W2), on DGR encapsulation efficiency and microsphere characteristics were investigated. In vitro and in vivo release of DGR were conducted and the cause for instability of DGR during release was also investigated.

Results: Moderate ultrasonic treatment of aqueous DGR/dichloromethane mixtures caused approximately. Eighty four per cent DGR denaturation. However, the activity recovery of DGR almost amounted to 100% when 2% polyvinyl alcohol (PVA) was addled into the aqueous phase. It was found that NaCl in the external water phase significantly increased DGR encapsulation efficiency. Furthermore, NaCl in the external water phase played a role in determining size and surface morphology of microsphere. In vitro release test showed a burst release of DGR from microspheres, followed by sustained release of 50% total activity over 15 days. In vivo experiments showed that DGR released from microspheres sustained 5 days. Denaturation of DGR within microspheres might be resulted from acidic microclimate.

Conclusion: The stability of DGR was effectively protected during microencapsulation and a relatively high encapsulation efficiency of DGR was obtained. PLGA microspheres could be an effective carrier for DGR.