Fenugreek (Trigonellafoenum-Graecum L) Seed Phytochemicals Protect DNA from Free Radical Induced Oxidative Damage and Inhibit Dipeptidyl Peptidase-IV an Enzyme Associated with Hyperglycemia

Fenugreek (Trigonellafoenum-graecum L.; methi) seeds and leaves are used in Asia, Africa, and Mediterranean countries for their nutritional and therapeutic value. It is an ingredient in many traditional Unani and Ayurvedic medicinal systems in India and proven to be very effective in managing blood glucose homeostasis. However, there is a dearth of information on the biochemical rationale for its use in the management of diabetes. In this study, protective effects of fenugreek seed phytochemicals on oxidative stress and inhibition of dipeptidyl peptidase-IV (DPP-IV), a key enzyme associated with diabetes were evaluated. Compositional analysis of phenolics by HPLC revealed that gallic and ferulic acids were the major phenolic acids, and myricetin and rutin were predominant flavonoids in phenolic extracts of fenugreek seeds. Trigonelline content in alkaloid extract was quantitatively determined by reverse phase HPLC and found to be 8.6 mg/g. Alkaloid extract showed superior radical scavenging and metal chelating activities. Besides, these phytochemical extracts also prevented OH• radical-induced DNA damage. Michaelis-Menton and Line weaver-Burk derivations were applied to establish modes of inhibition of DPP-IV activity. Phenolic and alkaloid extracts inhibited DPP-IV activity by mixed non-competitive and non-competitive inhibition mechanisms, respectively. Inhibitory constants of enzyme inhibitor complexes indicate strong affinity of phenolic (Ki, 34.93 ± 0.14 μg) and alkaloid extracts (Ki, 32.3 ± 4.8 μg) for DPP-IV. These results suggest that isolated phytochemicals have the potential as lead compounds for the development of DPP-IV inhibitors to control hyperglycemia and manage diabetes.