The mechanism of binding with the α-glucosidase in vitro and the evaluation on hypoglycemic effect in vivo: Cocrystals involving synergism of gallic acid and conformer

Abstract

Cocrystallization of Active Pharmaceutical Ingredients (API) with formers can induce positive or negative synergistic effects on activity; however, the underlying mechanism is unclear. In this study, we screened two cocrystals of gallic acid (GA): GA-p-aminobenzoic acid (cocrystal A) and GA-amino acetic acid (cocrystal B). Solubility, dissolution rate, and oral bioavailability and hypoglycemic effect of the two cocrystals were evaluated. Additionally, we examined the effect induced by cocrystallization of GA with each former on inhibition activity on α-glucosidase, a protein target involved in hypoglycemic effects. Cocrystals A and B were constructed in a 1:1 API/former molar ratio by CO⋯HN and OH⋯OC hydrogen bonds, respectively. As predicted, cocrystallization improved oral bioavailability; AUC0-∞s of cocrystal A and B were 2.24-fold and 1.70-fold higher than that of GA. Interestingly, the α-glucosidase inhibition rate increased with cocrystal A (i.e., positive synergism) and decreased with cocrystal B (i.e., negative synergism) compared to GA alone. For each cocrystal system, an obvious difference in the α-glucosidase inhibition rate between cocrystal and its physical mixture (PM) of API and former was observed. The 1H NMR analysis of two cocrystals and their respective PM indicated that hydrogen bond interactions between API and former molecules were just present in the solutions of cocrystal; but not in that of PMs. Molecular docking indicated that the hydrogen bonds between GA and CCF achieved binding with α-glucosidase in the form of supramolecular. Due to improvements in both oral bioavailability and α-glucosidase inhibition rate, the maximum hypoglycemic rate in diabetic mice treated with cocrystal A was 3.4-fold higher than that of GA alone. Conversely, although cocrystal B displayed improved bioavailability compared with GA alone, the maximum hypoglycemic rate remained almost unchanged due to the negative synergism on α-glucosidase inhibition activity of GA and amino acetic acid. Cocrystallization with each former induced variation not only on physiochemical properties and bioavailability but also on biological profiles involving inhibition rate on target proteins, which likely contributed to the observed positive and negative synergistic effects on API activity.