Improved α-chymotrypsin stability upon encapsulation in PLGA microspheres by solvent replacement

Purpose. To investigate the potential of different solvents with better biocompatibility to replace CH2Cl2 in the encapsulation of alpha-chymotrypsin in poly (lactic-co-glycolic) acid ( PLGA) microspheres without causing protein instability. Methods. The oil-to-water (O: W) ratio in the emulsification step of the solid-in-oil-in-water (s/o/w) encapsulation process was optimized with respect to maximizing protein stability and encapsulation efficiency for various solvents. Formation of insoluble aggregates and residual enzyme activity were primarily used as stability parameters. Several solvents possessing low toxicity with different water solubility were used to prepare alpha-chymotrypsin loaded PLGA microspheres. Results. The O: W ratio in the emulsification step is critical with respect to maintaining protein stability. This was related to the solvents' water solubility. In general, hydrophilic solvents were detrimental to protein stability and encapsulation efficiency. However, after optimization of the O: W ratio for solvents with different water solubility, protein stability was preserved during encapsulation using butyl acetate when poly ( ethylene glycol) ( PEG) was used as the emulsifying agent (ca. 1% of non-covalent aggregates and 93 +/- 10% of residual specific activity). Conclusions. The s/o/w technique was successfully improved by replacing the ICH class 2 solvent CH2Cl2 with the class 3 solvent butyl acetate without compromising alpha-chymotrypsin stability.