Chemical profiling of secondary metabolites from Himatanthus drasticus (Mart.) Plumel latex with inhibitory action against the enzymes α-amylase and α-glucosidase: In vitro and in silico assays

Ethnopharmacological relevance: Himatanthus drasticus is an important medicinal plant whose latex is traditionally used in Northeast Brazil to treat various diseases, including diabetes. The use of a-amylase and alpha-glucosidase inhibitors can be an effective strategy to modulate levels of postprandial hyperglycemia via control of starch metabolism. Aims of the study: This study aimed to verify if H. drasticus latex has inhibitory activity against enzymes linked to type 2 diabetes, besides chemically characterizing the metabolites responsible for such activities. In addition, in silico analysis was performed to support the traditional claim of possible antidiabetic activity of this latex. Materials and methods: Latex from H. drasticus stems was sequentially partitioned with n-hexane (FHDH), CHCl3 (FHDC) and EtOH (FHDHA). Wash extraction of the FHDHA fraction was performed to obtain the other extract fractions. The FHDHA was submitted to chromatography in a SPE C-18 cartridge using gradient elution with MeOH/H2O to produce five fractions: FHDHA1, FHDHA2, FHDHA3, FHDHA4 and FHDHA5. The FHDHAl was subjected to semi-preparative reverse phase HPLC. Lineweaver-Burk plots were used to investigate the kinetic parameters of alpha-amylase and alpha-glucosidase inhibitory activity. The interactions between plumieride and porcine pancreatic alpha-amylase and alpha-glucosidase were analyzed through an in silico molecular docking study. Results: Phytochemical identification of compounds present in the FHDHA fraction of H. drasticus latex was possible by 1H, 13C NMR analysis and mass spectrometry, and the results were compared with the literature. The identified compounds were alpha-ethyl glucoside, protocatechuic acid, 3-O-caffeoylquinic acid, 15-demethyl-plumieride acid, 5-O-caffeoylquinic acid, caffeic acid, vanillic acid, plumieride, and catechin. The inhibition results of the fractions tested against a-amylase and alpha-glucosidase showed inhibitory activities dependent on the increase of fractions and compound concentrations. The IC50 results obtained from FHDHA, FHDHA1 and plumieride fractions against alpha-amylase were 36.46, 72.61, 33.87 mu g/mL respectively. The IC50 of plumieride was the closest to that of acarbose (22.52 mu g/mL), a result similar to that obtained for alpha-glucosidase. The type of inhibition was competitive for both enzymes. Conclusions: There was strong inhibition of alpha-amylase and alpha-glucosidase by FHDHA, FHDHA1 and plumieride, suggesting that these enzymes slow glucose absorption.