Dipeptidyl Peptidase-IV (DPP-IV) Inhibitory Activity, Antioxidant Property and Phytochemical Composition Studies of Herbal Constituents of Thai Folk Anti-Diabetes Remedy

Type 2 diabetes mellitus (T2DM) patient numbers have dramatically increased by almost 10 times within the past 10 years. Several groups of drugs have been developed to treat T2DM, including dipeptidyl peptidase-IV inhibitor. The Krom Luang Chomphon folk recipe was used as alternative anti-diabetes recipe; however, no scientific data on the DPP-IV inhibitory activities of this recipe has been evaluated. In the present study, 14 selected medicinal herb extracts from this recipe were prepared and investigated for their DPP-IV inhibitory activity, antioxidant property, and phytochemical compositions. The results demonstrated that all extracts exhibited DPP-IV inhibitory activity, but at different levels. The highest inhibitory activities, at 50 µ g/mL, were detected in Lagerstroemia speciose (L.) Pers. (71.07±0.07 %) and Terminalia catappa L. (69.89±0.43 %), while diprotin A (standard) gave 90.07±0.39 % inhibition. All extracts displayed antioxidant activity at varying levels. The lowest IC 50 in the DPPH assay was found in the ethanolic extract from leaves of T.catappa (4.39±0.12 µ g/mL), comparable to that of ascorbic acid (IC 50 = 4.28±0.01 µ g/mL) and BHT (IC 50 = 4.82±0.01 µ g/mL). Phenolic, flavonoid, and anthocyanin compounds were detected in the extracts, alkaloids were detected in 10 extracts, and terpenoids were detected in 11 extracts. Their phytochemical compositions were evaluated for their relationship with DPP-IV inhibitory and antioxidant activities. The results revealed that DPP-IV inhibitory activity was significantly related with phenolic content ( p < 0.05, r 2 = 0.560) while antioxidant activity (DPPH) was related with phenolic content ( p < 0.05, r 2 = 0.500). Therefore, the DPP-IV inhibitory activity and antioxidant activity of each herb extract may vary, depending on the content of terpenoid and phenolic compounds. All selected herbs, especially the leaves of T. catappa and L. speciose , showed the ability to be used as DPP-IV inhibitors and antioxidants for T2DM treatment. Furthermore, our results are the first reported of DPP-IV inhibitory activity in the 14 herb extracts which are the main ingredients in the Krom Luang Chomphon folk recipe. These findings also support the potential use of this recipe as an alternative treatment for diabetes through a new mechanism.