Effect of Longan (Dimocarpus longan Lour.) Flower Water Extract on Metabolic Syndrome in Fructose-Fed Rats
| Autor: | Hui-Yun Tsai, 蔡蕙芸 |
|---|---|
| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 Metabolic syndrome is a cluster of disorders, including hyperinsulinemia, insulin resistance, hypertriglyceridemia and hypertension that increase one''s risk for type 2 diabetes and cardiovascular disease. Natural antioxidants were reported to ameliorate metabolic syndrome. Previous study in our laboratory has shown that Longan (Dimocarpus longan Lour.) flower had strong antioxidant activity in vitro. Therefore, the objective of this study was to evaluate the effect of the supplemention of Longan flower extract on metabolic syndrome. The first stage of this study was to analyze the antioxidative activity of Longan flower in vitro, the crude extracts were prepared by extracting Longan flower with boiling water and two solvents (95% ethanol, methanol) at room temperature. Then, the three different solvent extracts of Longan flower were tested for two different antioxidant assays, including DPPH free radical scavenging effect and the inhibition of Cu2+-induced oxidation of human LDL. The results of antioxidant assays revealed that the best effect was exhibited by the water extract, followed by ethanol and methanol. The EC50 value of water extract in scavenging DPPH radicals was 3.75±0.61 µg/mL, and its effect on delaying LDL oxidation is 1.57 times better than trolox at the same concentration level (1 µg/mL). The second stage of the study was to observe the glucose tolerance of rats after the acute treatment with Longan flower crude extract (125 mg/kg or 250 mg/kg) and glucose. Results of oral glucose tolerance test (OGTT) in rats showed that the plasma glucose levels of the Sprague-Dawley rats administered 250 mg/kg BW of Longan flower water extract (LFWE) were lower than the control group after 30 minutes of ingestion but insulin concentrations showed no difference with the control group at each time intervals. However, both the plasma glucose and insulin levels of the rats ingested Longan flower ethanol extract showed no significant difference with control group. These findings suggest that Longan flower water extract may delay or interference with the sugar absorption in the gastrointestinal tract without changing insulin secretion and its action. The third stage is to investigate the effect of long-term treatment of LFWE on rats with metabolic syndrome induced by high fructose diet. Male Sprague-Dawley rats of body weight around 250 g were randomly divided into four groups: group C, fed with standard Purina chow; group F, fed with high fructose diet alone; group L, fed with high fructose diet plus LFWE 125 mg/kg BW per day by gavage (a low dose group) and group H, fed high fructose diet plus LFWE 250 mg/kg BW per day by gavage (a high dose group). The dietary manipulation lasted for 14 weeks. Results of our study showed that, high fructose feeding for 2 weeks cause significant increase in sytosolic blood pressure, fasting plasma triglyceride and insulin levels without elevating fasting plasma glucose. And insulin resistance was demonstrated after the 4th week by OGTT. These results indicated that fructose-rich diet could cause a cluster of disorders in metabolic syndrome. In antioxidative capacity analyses, at the end of the 12-week experiment high fructose diet increased plasma TBARS and significantly decreased liver antioxidant enzyme activity. The supplementation of LFWE ameliorated insulin resistance by enhancing the expression of insulin signaling pathway related proteins, including GLUT 4 and insulin receptor substrate-1. LFWE supplementation was also found to decrease SBP and ameliorated oxidative stress. These findings indicate that Longan flower water extract may improve the symptoms of the metabolic syndrome in fructose-fed rats. |
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