Effects of glycine on insulin resistance and cognitive impairment induced by high-fructose diet

AIM: To investigate the role of intestinal endotoxemia (IETM) in insulin resistance (IR) and cognitive impairment, and to explore the protective mechanisms of glycine in rats with high-fructose diet. METHODS: The rats in model group were fed with 8% fructose water, and the rats in intervention group were fed with water containing 8% fructose and 1% glycine. The body weight and systolic pressure were measured monthly. After 8 months, plasma glucose, plasma lipids, glucose tolerance and plasma endotoxin (LPS) were detected. Plasma insulin, pro-inflammatory cytokines in plasma and cerebral cortex were determined by ELISA, and HOMA-IR was also calculated. The molecules of insulin signaling pathway in cerebral cortex were determined by Western blotting. The cognitive functions of the rats were tested by Morris water maze. RESULTS: The weight gain in model group was increased from the 3rd month to the 6th month, and systolic pressure was increased after the 3rd month as compared with control group. Glycine significantly reduced the weight gain in the 4th month and the 6th month, and significantly reduced the systolic pressure from the 4th month to the 6th month. Meanwhile, glycine partly attenuated dyslipidemia and glucose intolerance, and lowered the levels of plasma LPS, plasma insulin, HOMA-IR and pro-inflammatory cytokines in plasma and cortex. Furthermore, glycine attenuated the abnormal expression of insulin signaling proteins and cognitive impairment. CONCLUSION: Long-term fructose diet induces the rats to peripheral and neuronal IR, which accompanies IETM and low-grade inflammation. Glycine attenuates IR and cognitive impairment by lowering IETM.