Highly porous large poly(lactic-co-glycolic acid) microspheres adsorbed with palmityl-acylated exendin-4 as a long-acting inhalation system for treating diabetes

A porous large poly(lactic-co-glycolic acid) (PLGA) microspheres (MS) adsorbed with palmityl-acylated exendin-4 (Ex4-C₁₆) was devised as an inhalation delivery system. The porous MS was prepared by a single o/w emulsification/solvent evaporation method using extractable Pluronic F68/F127, and its fabrication and formulation conditions were carefully optimized. Results show that the prepared MS was in the appropriate size range for inhalation and contained many surfaces and internal pores meaning low aerodynamic density. Ex4-C₁₆ was more efficiently adsorbed onto porous PLGA MSs than native exendin-4, and an approximately 5% loading of Ex4-C₁₆ onto this porous MS (RG504H) was achieved. This optimized porous MS was found to be efficiently deposited throughout the entire lungs of mice including alveoli region. Furthermore, this porous MS adsorbed with Ex4-C₁₆ (approx. 100 μg/mouse) displayed much protracted hypoglycemic efficacy in non-fasted type 2 diabetic db/db mice. Porous PLGA MS with adsorbed Ex4-C₁₆ showed the dual-advantages of (i) sustained release and acceptable drug-loading due to strong hydrophobic interaction and (ii) longer in vivo pulmonary hypoglycemic duration due to albumin-binding by the palmityl group. We consider that this new prototype of porous PLGA MS has considerable pharmaceutical potential as a type 2 anti-diabetic inhalation treatment.