Microcosmic Mechanism of Dication for Inhibiting Acylation of Acidic Peptide

For long-effective peptide formulation based on poly(d,l-lactic-co-glycolic acid) (PLGA) microspheres, acylation often leads to peptide instability during its release and reduced drug efficacy. Among the reported solving strategies, adding dication such as Ca2+ and Mn2+ in the formulation was the most convenient method for inhibiting basic peptide acylation. However, the strategies for the acidic peptide still remain unexplored, possibly due to the peptide's changeable charge state in acid environment within degraded PLGA microspheres. Moreover, the previous studies mainly focusing on the macroscopical adsorption of peptide to PLGA cannot demonstrate the inhibition mechanism. Acylation inhibition for acidic peptide (exenatide) by dications (Ca2+, Mn2+ and Zn2+) was studied for the first time, and Quartz Crystal Microbalance with Dissipation (QCM-D) was innovatively employed to analyze microcosmic mechanism of the inhibition. These dications played different roles in acylation inhibition of acidic peptide. The effects of dications on acylation outside or inside PLGA microspheres indicated that Ca2+ did not work, Mn2+ played a weak role, and Zn2+ possessed the greatest inhibition. Zn2+ was the most effective dication for the acylation inhibition because of the complex formation and its steric-hindrance effect, which was a new function for this dication.