Phytochemical and antidiabetic evaluation of Bauhinia tomentosa L. aerial parts

BACKGROUND: Members of the genus Bauhinia L., commonly known as cow's hoof, are important species in the family Fabaceae and are traditionally used to treat diabetes and other diseases. This study aimed to identify antidiabetic bioactive compounds from Bauhinia tomentosa aerial parts via bioassay-directed fractionation. METHODS: Determination of serum glucose and insulin levels was conducted on nicotinamide + STZ-induced diabetic rats treated with different fractions via a glucose oxidase assay kit and a rat insulin ELISA kit. In addition, GLUT4 protein levels in muscle homogenates were quantified via an ELISA kit. The ethyl acetate (EtOAc) fraction (the most active fraction) was fractionated via column chromatography (CC), and the isolated compounds were identified on the basis of their spectroscopic data. Additionally, the EtOAc fraction was characterized via LC‒QTOF‒MS/MS analysis. All the isolated compounds were evaluated for their antioxidant, α-glucosidase, and α-amylase inhibitory activities. RESULTS: The EtOAc fraction markedly reduced the serum glucose level in the nicotinamide + STZ-induced type 2 diabetic rats (136.6 ± 12.17 mg/dL). Moreover, it showed a significant increase in serum insulin level (0.344 ± 0.04 µIU/mL). Four compounds (1-4) were isolated, of which luteolin showed potent inhibition of α-amylase activity, with an IC50 value of 19.32 ± 1.046 µM, as well as significant DPPH scavenging capacity. The LC-QTOF-MS/MS profiling validated the phytoconstituent composition and confirmed its chemotaxonomic relationship with closely related species. CONCLUSIONS: The antidiabetic effects of EtOAc fraction and its isolates may be attributed to its insulinotropic, antioxidant, and carbohydrate-hydrolysing enzyme inhibitory activities. Luteolin has been shown to be at least partially responsible for the antidiabetic activity of B. tomentosa.