Blood glucose-lowering effect of Tectona grandis flowers in type 2 diabetic rats: a study on identification of active constituents and mechanisms for antidiabetic action.

BACKGROUND: Ayurveda documents antidiabetic activity of Tectona grandis flowers. However, until now, the effects of T. grandis flowers in preclinical models of type 2 diabetes (T2D) have been unknown. Hence, the aim of the present study was to evaluate the blood glucose-lowering effect of methanol extract of T. grandis flowers (METGF) in T2D rats and to identify possible active constituents as well as the mechanisms for the antidiabetic action.

METHODS: Rats were rendered diabetic by administration of streptozotocin-nicotinamide (65 mg/kg-110 mg/kg, i.p.). After the induction of diabetes, Groups 3 and 4 received METGF (100 and 200 mg/kg respectively) while Group 5 received glibenclamide (5 mg/kg) orally for 4 weeks. Blood glucose and body weight were determined at the end of Weeks 2 and 4. Hemoglobin, HbA1c, total protein, urea, creatinine, insulin, and lipid levels were determined in Week 4. Active constituents in METGF were identified using HPLC analysis. Antidiabetic mechanisms of METGF were evaluated by investigating the insulin sensitizing action and inhibition of α-amylase and α-glucosidase activity.

RESULTS: Both METGF and glibenclamide significantly improved body weight, reduced blood glucose, and normalized altered biochemical parameters (P < 0.001) in T2D rats. The presence of polyphenolic active constituents, such as gallic acid, quercetin, rutin, ellagic acid, ferulic acid, and kaempferol, in METGF was confirmed by HPLC. In vitro, METGF, gallic acid, quercetin, and rutin exhibited significant (P < 0.001) insulin sensitizing action and inhibition of α-amylase and α-glucosidase activity.

CONCLUSIONS: Polyphenolic active constituents present in METGF are possibly responsible for the blood glucose-lowering effect in T2D rats via an insulin-sensitizing action, as well as inhibition of α-amylase and α-glucosidase activity.