| In the present study, mature Chinese bayberry (Myrica rubra Sieb. et Zucc.) fruit of 17 cultivars from Zhejiang and Jiangsu provinces were used for the investigation of fruit nutritional quality attibutes, including total phenolics, flavonoids, and antioxidant capacity. Main phenolic compounds were identified and quantified. By using the HepG2 cell model, glucose consumption activity of bayberry fruit extracts were evaluated in vitro and cultivars and phenolic compounds with high glucose consumption activity was selected.’Biqi’ fruit extract was further tested for the antidiabetic effect in vivo and the possible mechanism was also investigated. The main results were as follows:1. Total phenolics, flavonoids, and antioxidant activity showed significantly difference among tested cultivars. Dark-red pulp bayberry cultivars such as ’Biqi’, ’Tanmei’, ’Ciji’, and ’Wandao’ had higher total phenolics and flavonoids content than pink or white pulp bayberry cultivars such as ’Fenhong’ and’Shuijing’. A total of 12 phenolic compounds were identified combining HPLC and MS technologies, including five anthocyanidins, i.e. delphinidin-hexoside (Dp-Hex), Vupplemen-3-O-galactoside (C-3-Gal), Vupplemen-3-O-glucoside (C-3-Glu), pelargonidin-3-O-glucoside (Pg-3-Glu), peonidin-3-O-glucoside (Pn-3-Glu), and seven flavonols compounds, i.e., myricetin-3-O-rhamnoside (M-3-Rha), myricetin deoxyhexoside-gallate (M-DH-G), quercetin-3-O-galactoside (Q-3-Gal), quercetin-3-O-glucoside (Q-3-Glu), quercetin-3-O-rhamnoside (Q-3-Rha), kaempferol-3-O-galactoside (K-3-Gal), and kaempferol-3-O-glucoside (K-3-Glu). The significant differences in phenolic compositions among cultivars were observed. Furthermore, there were significantly positive correlation between antioxidant capacities and total phenolics and flavonoids contents among cultivars.2. Glucose consumption activities of bayberry fruit extracts from nine cultivars and five phenolic compounds were studied using HepG2 cells. They varied significantly among cultivars.’Tanmei’,’Biqi’, and’Ciji’ etc. cultivars showed relative high glucose consumption enhancement activity, which were well correlated with their high total phenolics, total flavonoids contents, and DPPH· scavenging activities. Furthermore, C-3-Glu and three quercetin-3-O-glycosides (Q-3-Glys, i.e. Q-3-Gal, Q-3-Glu, and Q-3-Rha), but not M-3-Rha, showed significant enhancement of glucose consumption in HepG2 cells. There were significant correlations between the glucose consumption activity with the contents of C-3-Glu and the sum of three Q-3-Glys, respectively. Therefore, C-3-Glu and Q-3-Glys may be key composition for glucose consumption activity of bayberry fruit extracts.3. Male diabetic KK-Ay mice were used to investigate the antidiabetic effect of ’Biqi’ fruit extract in a dose of 200 mg/kg BW by gavage for 5 weeks. The results showed that ’Biqi’ fruit extract significantly lowered fasting blood glucose levels, improved oral glucose tolerance and insulin sensitivity of diabetic KK-Ay mice. Meanwhile,’Biqi’fruit extract markedly reduced serum concentrations of glucose metabolism markers such as insulin, glucagon, and leptin etc. in diabetic KK-Ay mice. In addition, serum total cholesterol (TC), triglycerides (TG), low density lipoprotein cholesterol (LDL-c), alanine aminotransferase (ALT), interl-eukin-1β (IL-1β) levels as well as liver weight and liver lipids accumulation were sighnificantly reduced in ’Biqi’ fruit extract supplemented mice as compared to water Vlupplemented diabetic mice.4. Antidiabetic mechanisms of ’Biqi’ fruit extract was also discussed. In HepG2 cells, ’Biqi’ fruit extract significantly reduced hepatic gluconeogenesis and increased glycolysis, which may be related with the AMPK activation and the down-regulated gluconeogenesis gene expressions of PGC-1α, PEPCK, and G6Pase. Similarly, AMPK activation and down-regulated hepatic gene expressions of PGC-1α and PEPCK were also observed in the liver of KK-Ay mice with ’Biqi’ fruit extract supplemented. In addition, ’Biqi’ fruit extract markedly reduced hepatic lipids metabolism genes such as PAP, ACAT, and CIDEA, and hepatic inflammatory markers genes such as TNFa, IL-6, and MCP-1 expressions. Collectively, these results indicated that the antidiabetic effects of ’Biqi’ fruit extract may be related to the activation of hepatic AMPK proteins, inhibition of hepatic gluconeogenesis and hepatic lipid accumulation, and the reduction of hepatic inflammatory status.Our findings may provide important foundation for further evaluation of Chinese bayberry resource for their antidiabetic activity. It may also provide scientific evidence for bayberry breeding program and the guide for cosumers especially the diabetic patients, which may eventually promote the development of bayberry industry. |
PDF Full Text Request