Composition of four polyphenol fractions extracted from partridge tea and their mechanisms on ameliorate insulin resistance in HepG2 cells

Partridge tea is a plant used as a speciality tea drink in Hainan Province, China. The aim of this study was to isolate polyphenols from partridge tea, investigate their main constituent compositions and ameliorative effects on insulin resistance in insulin resistant HepG2 (IR-HepG2) cells. PTP was obtained from partridge tea, then PTP1, PTP-2 and PTP-3 were obtained after further purification. The polyphenol contents of PTP, PTP-1, PTP-2, PTP3 were determined to be 15.9%, 51.4%, 42.51% and 22.74%, respectively. PTP and PTP-1 had similar compositions, and the contents of the main components of PTP-1 was higher than that of PTP. Structural compositions and contents of PTP-2 and PTP-3 differ significantly. Further analysis indicated that PTP failed to have significant hypoglycaemic activity, while other three polyphenols regulated the fat metabolism disorders caused by insulin resistance, thus improving the body's utilization of blood glucose. In addition, the three polyphenols reversed the damage caused by insulin resistance in IR-HepG2 cells by up-regulating the activities of HK (200 mu g/mL PTP-1: 2.8414 mol/min/mL) and PK (200 mu g/mL PTP-1: 10.7204 U/L), increasing the activity of SOD and CAT and decreasing the level of MDA. The mRNA results showed that PTP-1, PTP-2 and PTP-3 could achieve hypoglycaemic efficacy in the body by regulating the IRS-1/PI3K/AKT signal pathway. In summary, our results suggested that the polyphenols of partridge tea could be a promising natural source for preventing and treating hyperglycemia.