Effects of Sesame Meal Lignan Glycosides Crude Extract on Insulin Resistance in Fructose-Fed Rats

• Main Authors: shuo-Fen Kang, 康碩芬
• Other Authors: Lucy Sun Hwang
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/81219475304577600167

碩士 === 國立臺灣大學 === 食品科技研究所 === 89 === Sesame contains abundant lignans which are well known to have antioxidative activity. In defatted sesame meal, however, the contents of lipid-soluble lignans are only in trace amount and the water-soluble lignan glycosides are found to be the major antioxidants. Sesame meal is generally used as feed or fertilizer. In vivo studies show that dietary sesame meal decreases oxidative stress in animals, perhaps due to the antioxidative activity of lignans, which are hydrolyzed from lignan glycosides by β-glucosidase in the gastrointestinal tract. There is evidence that increased oxidative stress may impair insulin action, thus contributing to the generation of hyperglycemia. Therefore, the objective of this study is to investigate the effect of sesame meal lignan glycosides on blood glucose and insulin action in order to upgrade the utilization of sesame meal. The first stage of the study was to observe the glucose tolerance of rats after the acute treatment with sesame meal lignan glycisides crude extract and glucose. The second stage of the study was designed to evaluate the effect of sesame meal lignan glycosides crude extract supplementation on hyperinsulinemia, insulin resistance, hypertriglyceridemia and hypertension in the fructose-fed rat model. Unroasted black sesame was ground, defatted with n-hexane, extracted with 80﹪ethanol, and then freeze-dried to obtain the sesame meal lignan glycosides crude extract (SLGE). Results of oral glucose tolerance test (OGTT) in rats showed that the plasma glucose levels of the Sprague-Dawley rats administered 0.5g/kg BW or 1.0g/kg BW of SLGE were lower than the control group after 30 minutes of ingestion. There was no significant difference, however, on insulin concentration and the area under glycemic curve. It was also observerd that the plasma glucose levels of the rats ingested 1.0g/kg BW of SLGE were higher than the control group after 90 and 120 minutes of ingestion. These findings suggest that sesame meal lignan glycosides crude extract may delay the sugar absorption in the gastrointestinal tract without changing insulin secretion and its action. Long-term treatment of SLGE was performed in the fructose-fed rat model. Sprague-Dawley rats weighing 240 to 280g were divided into four groups, eight rats per group, and fed different diets：group C, standard Purina Chow；group LG, standard Purina Chow with SLGE supplementation (1.0g/kg BW per day)；group F, high-fructose diet alone；group FLG, high-fructose diet with SLGE supplementation (1.0g/kg BW per day). The dietary manipulation lasted for 8 weeks. No significant differences were observed on the metabolic status and insulin action between group C and group LG. Fructose feeding (group F) for 2 weeks caused significant increase in non-fasting plasma triglyceride and insulin levels without elevating plasma glucose level. Thereafter, blood pressure increased after the 4th week and insulin resistance was demonstrated on the 7th week by OGTT. At the end of the 8-week experiment, both insulin-stimulated glucose uptake and insulin binding of adipocytes were significantly redued in group F. In addition, fasting plasma insulin, triglyceride, free fatty acid levels, hepatic triglyceride and TBARS concentrations were all higher than group C. These results indicated fructose-rich diet could cause a cluster of metabolic abnormalities, including hyperlipidemia, hyperinsulinemia, insulin resistance and hypertension. Rats fed the same high-fructose diet but supplemented with SLGE (group FLG) had amelioration of hypertension and resistance to insulin-stimulated glucose uptake in rat adipocytes. Fasting plasma insulin and triglyceride levels in group FLG were significantly lower than group F. Hepatic triglyceride and TBARS concentrations were not different between group FLG and group C, however, insulin resistance was still observed by OGTT. Based on these results, we suggest that sesame meal lignan glycosides crude extract supplementation in the fructose-fed rat model stimulates the metabolism of triglyceride, alleviates hypertension, fasting hyperinsulinemia and glucose disposal, but still exihibits insulin resistance.