Effects Of Flavonoids From Seed Residues Of Hippophae Rhamnoides L. On Glucose And Lipid Metabolism And Its Mechanism

Hippophae rhamnoides L., of the Elaeagnaceae family, not only has good soil improvement and soil conservation function, but also has a high medicinal value. After oil extraction, a large amount of seed residue remains with bioactive substances. In our previous study, the flavonoids from seed residues of Hippophae rhamnoides L (FSH) exhibited hypoglycemic and hypolipidemic properties, however, its efficacy in modulating blood lipid and glucose levels has not been investigated in depth. Therefore, the effects of FSH on glucose metabolism and differentiation of adipocytes were investigated in the present study. Furthermore, high-fat diet fed mice were used to evaluate the hypoglycemic and hypolipidemic effects of FSH and its mechanisms.First, isolated rat adipocytes were used to screening several plants'active ingredients by glucose consumption test, and FSH showed the strongest ability to increase glucose consumption.200～1000μg/mL FSH significantly increased the glucose consumptions in rat adipocytes, moreover, FSH could enhance the effect of insulin.Further observations were carried out in 3T3-L1 adipocytes by glucose consumption test. The results showed that 10-1000μg/mL FSH had no obvious effects on glucose consumptions of 3T3-L1 preadipocytes. however,200～800μg/mL FSH could increase glucose consumptions in differentiated 3T3-L1 adipocytes. Meanwhile, treatment of differentiated adipocytes with 200μg/mL FSH could upregulate GLUT4 mRNA expression. These results suggested that FSH could enhance glucose consumption in 3T3-L1 adipocytes. which may related to upregulation of GLUT4 mRNA expression.3T3-L1 preadipocytes were induced under standard differentiation process in the presence of various concentrations of FSH. Oil red O staining and measurement of triglyceride contents were performed to investigate the effect of FSH on adipocytes differentiation. The results showed that FSH could inhibit adipogenesis of 3T3-L1 adipocytes as well as inhibit the proliferation of 3T3-L1 preadipocytes detected by MTT assay.In vitro experiments showed that FSH could increase glucose consumption and inhibit adipogenesis of adipocytes, suggesting that adipocytes may be a target of FSH, and its ability to regulating lipid and glucose metabolism may due to its effect on adipocytes. Thus, a high-fat diet fed mice model was used to investigate the effects of FSH on glucose and lipid metabolism and its mechanisms. Oral administration with FSH (50,100 and 150 mg/kg) for 12 w reduced the body, liver and epididymal fat pad weights of mice when compared with high-fat diet control group, without obvious effects on average food intake, water intake, heart, spleen and kidney weights. As compared with high-fat diet control group, treatment with FSH decreased serum TC, LDL-C, LDL-C/TC and glucose levels and increased levels of HDL-C/TC, without obvious changes in serum insulin level and insulin sensitivity index while improving oral glucose tolerance. FSH also lowered TC and TG concentrations in liver, results corroborated by transmission electron microscope findings, however, there was no significant changes in muscle TC and TG levels. Although FSH had no obvious effects on liver LPL, HL activities and muscle LPL activity, it could decrease the LPL activity in adipose tissue. Additionally, FSH could increase GSH-PX and SOD activities in liver but had no obvious effects on GSH, MDA and T-AOC. These results suggested that liver and adipose tissue may be the major target tissues of FSH, therefore, we detected the expressions of several genes that related to lipid and glucose metabolism in liver and adipose tissue. Compared with high-fat diet control group, the LDLR and PPARa mRNA expressions in liver were upregulated by FSH treatment, but the G-6-Pase mRNA expression was downregulated by FSH, and GK mRNA expression was increased by 50 mg/kg FSH. In adipose tissue,150 mg/kg FSH increased GLUT4 and PPARγmRNA expressions. Moreover, FSH decreased IRS-2 mRNA expression while increased IR mRNA and PI3K, Akt protein expressions.These results suggested that FSH possess hypolipidemic and hypoglycemic properties in mice fed high-fat diet. Its lipid lowering action may be partly related to upregulated LDLR and PPARαmRNA expressions in liver. The inhibition effects of FSH on adipocytes differentiation and preadipocytes proliferation may be a mechanism to control body weight gain. Downregulated G-6-Pase mRNA expression and upregulated GK mRNA expression in liver, increased GLUT4, PPARγ, IR mRNA and PI3K, Akt protein expressions in adipose tissue may collectively contribute to the hypoglycemic effect of FSH. Moreover, decreasing LPL activity in adipose tissue and preventing excess lipids accumulation in tissues may contribute to the ability of FSH to maintain lipid and glucose homeostasis.