Inhibitory Activity of PTP1B and α-Glucosidase by Compounds from Whole Plants of Houttuynia cordata Thunb

In this study, twenty known compounds were isolated from Houttuynia cordata Thunb., including four megastigmanes (1‒4), four phenolics (5, 6, 9, and 10), one tetrahydro-2-one derivative (12), four coumarins (7, 13, 14, and 16), six caffeic acid derivatives (8, 11, 15, 17, 18, and 19), and one triterpenoid (20). Their chemical structures were established using NMR spectra and comparison with literature. The anti-diabetic activity of the isolated compounds was assessed by investigating their inhibitory effects on protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase. The results revealed that ginnalin A (10) and 3-(4′-hydroxyphenyl)2-propenoic acid (4′′-carboxyl)-phenyl ester (13) exhibited significant inhibitory effects on both PTP1B and αglucosidase with IC₅₀ values of 7.9 ‒ 37.6 and 13.9 ‒ 31.9 μM, respectively. In the kinetic study, these two compounds showed noncompetitive-type PTP1B and α-glucosidase inhibition, with K_i values of 35.6 and 7.3 μM for PTP1B and 13.9 and 31.0 μM for α-glucosidase, respectively. These findings highlight the potential of the isolated compounds as candidates for the development of novel therapeutic agents for diabetes.