Magnoflorine from Tinospora cordifolia stem inhibits α-glucosidase and is antiglycemic in rats

Antidiabetic potential of Tinospora cordifolia stem is well proven. In the course of screening of useful α-glucosidase inhibitors, we prepared alkaloid fraction (AFTC) and isolated three isoquinoline alkaloids, namely, jatrorrhizine, palmatine and magnoflorine as active candidates for α-glucosidase inhibition. The enzyme kinetics was studied using sucrose and maltose as substrates. Michaelis–Menten constant (Km) and maximal velocity (Vmax) values were estimated. A significant decrease in Vmax and unaltered Km was observed in case of jatrorrhizine and palmatine (non-competitive inhibition). Magnoflorine was found to increase apparent Km and shown to be reversible, competitive inhibition. The IC50 value as sucrase inhibitor was 36.25, 23.46 and 9.8 μg/mL for jatrorrhizine, palmatine and magnoflorine, respectively, and as maltase inhibitor was 22.05, 38.42 and 7.6 μg/mL for jatrorrhizine, palmatine and magnoflorine, respectively. In vivo studies were conducted on rats to determine oral glucose tolerance test (OGTT), using different substrates: glucose, sucrose and maltose. The increase in plasma glucose level was significantly suppressed (P < 0.01) by all the three alkaloids at 20 mg/kg b.w. Magnoflorine possessed the most potential activity as α-glucosidase inhibitor in vitro and in vivo.

► α-Glucosidase inhibitory activity of Tinospora cordifolia stem is described.
► Three isoquinoline alkaloids were isolated from Tinospora cordifolia stem.
► In vitro α-glucosidase inhibitory activity of isolated alkaloids was performed.
► Hypoglycemic activity of isolated alkaloids was evaluated in vivo using rats.
► Magnoflorine found to possess reversible, competitive inhibition of α-glucosidase.