Inhibition mechanism of alpha-amylase, a diabetes target, by a steroidal pregnane and pregnane glycosides derived from Gongronema latifolium Benth.

Alpha-amylase is widely exploited as a drug target for preventing postprandial hyperglycemia in diabetes and other metabolic diseases. Inhibition of this enzyme by plant-derived pregnanes is not fully understood. Herein, we used in vitro, in silico, and in vivo studies to provide further insights into the alpha-amylase inhibitory potential of selected pregnane-rich chromatographic fractions and four steroidal pregnane phytochemicals (SPPs), viz: marsectohexol (P1), 3-O-[6-deoxy-3-O-methyl-ß-D-allopyranosyl-(1→14)-ß-D-oleandropyranosyl]-11,12-di-O-tigloyl-17ß-marsdenin (P2), 3-O-[6-deoxy-3-O-methyl-ß-D-allopyranosyl-(1→4)-ß-D-oleandropyranosyl]-17ß-marsdenin (P3), and 3-O-[6-deoxy-3-O-methyl-ß-D-allopyranosyl-(1→4)-ß-D-canaropyranosyl]-17ß-marsdenin (P4) derived from Gongronema latifolium Benth. The results revealed that the SPPs source pregnane-rich chromatographic fractions and the SPPs (P1-P4) exhibited inhibitory potential against porcine pancreatic alpha-amylase in vitro. Compounds P1 and P2 with IC50 values 10.01 and 12.10 µM, respectively, showed greater inhibitory potential than the reference acarbose (IC50 = 13.47 µM). Molecular docking analysis suggests that the SPPs had a strong binding affinity to porcine pancreatic alpha-amylase (PPA), human pancreatic alpha-amylase (HPA), and human salivary alpha-amylase (HSA), interacting with the key active site residues through an array of hydrophobic interactions and hydrogen bonds. The strong interactions of the SPPs with Glu233 and Asp300 residues may disrupt their roles in the acid-base catalytic mechanism and proper orientation of the polymeric substrates, respectively. The interactions with human pancreatic amylase were maintained in a dynamic environment as indicated by the root mean square deviation, radius of gyration, surface accessible surface area, and number of hydrogen bonds computed from the trajectories obtained from a 100-ns molecular dynamics simulation. Key loop regions of HPA that contribute to substrate binding exhibited flexibility and interaction potential toward the compounds as indicated by the root mean square fluctuation. Furthermore, P1 significantly reduced blood glucose levels and area under the curve in albino rats which were orally challenged with starch. Therefore, Gongronema latifolium and its constituent SPPs may be exploited as inhibitors of pancreatic alpha-amylase as an oral policy for impeding postprandial blood glucose rise.

Iloneoside: a cytotoxic ditigloylated pregnane glycoside from the leaves of Gongronema latifolium Benth.

Gongronema latifolium Benth (Asclepiadaceae) is an edible-green-leafy vegetable with known medicinal value. A chemical investigation of the 80% methanolic extract of the leaves led to the isolation of a new pregnane glycoside: iloneoside (3-O-[6-deoxy-3-O-methyl-ß-D-allopyranosyl-(1→14)-ß-D-oleandropyranosyl]-11,12-di-O-tigloyl-17ß-marsdenin), together with four known constituents. Their chemical structures were determined by spectroscopic analysis. The isolates were tested for their in vitro growth inhibitory activity against human leukemia HL-60 cells. Iloneoside was the most active and gave apoptotic response. Molecular docking analysis demonstrated that iloneoside could be accommodated within hot spots of anti-apoptotic protein Bcl-2. These results suggest G. latifolium as a reliable source of potent anticancer compounds.