[Long-term high-fat diet inhibits hippocampal expression of insulin receptor substrates and accelerates cognitive deterioration in obese rats].

OBJECTIVE: To assess the effect of long-term high-fat diet on the expressions of insulin receptor substrates in the hippocampus and spatial learning and memory ability of obese rats. METHODS: A total of 100 4-week-old male SD rats were randomly divided into two groups and fed with common diet (CD group, n=40) or high-fat diet (HFD group, n=60) for 16 weeks. At 4, 8, 12, 16 and 20 weeks, 8 rats were randomly selected from each group for testing their spatial learning and memory function using Morris water maze. After the tests, the rats were sacrificed for measurement of the metabolic parameters and detection of the expressions of insulin receptor substrate-1 (IRS-1) and IRS-2 mRNAs in the CA1 region of the hippocampus. RESULTS: Compared with those in CD group, the rats in HFD group showed a prolonged escape latency, longer swimming distance, faster average swimming speed, and shorter stay in the platformat 12 weeks. In HFD group, the serum levels of total cholesterol, triglyceride, low-density lipoprotein cholesterol, and fasting insulin were all significantly increased (P<0.05) and the level of high-density lipoprotein cholesterol decreased (P<0.01) in comparison with those in CD group at each of the time points. No significant difference was found in fast glucose levels between the two groups (P>0.05), but the expressions of IRS-1 and IRS-2 mRNAs were significantly decreased in HFD group at 12 weeks (P<0.05). CONCLUSION: In obese rats, long-term feeding with high-fat diet leads to insulin resistance, which interferes with hippocampal expression of insulin receptor substrates and insulin metabolism to cause impairment of the cognitive function and accelerate cognitive deterioration.

Effects of Chaihu-Shugan-San and Shen-Ling-Bai-Zhu-San on p38 MAPK Pathway in Kupffer Cells of Nonalcoholic Steatohepatitis.

This study aimed to investigate the effects of Chaihu-Shugan-San (CSS), Shen-Ling-Bai-Zhu-San (SLBZS), and integrated recipe of the above two recipes on inflammatory markers and proteins involved in p38 MAPK pathway in Kupffer cells of NASH rats induced by high fat diet (HFD). Rats were administered at low or high dose of CSS, SLBZS, and integrated recipe except normal group and model group for 16 weeks. The levels of hepatic lipid, TNF- α , IL-1, and IL-6 in liver tissues were measured. Kupffer cells were isolated from livers to evaluate expressions of TLR4, p-p38 MAPK, and p38 MAPK by Western blotting. The results showed that the NASH model rats successfully reproduced typical pathogenetic and histopathological features. Levels of hepatic lipid and liver tissues inflammatory factors in high-dose SLBZS group and integrated recipe group were all lower than that of model group decreased observably. Expressions of TLR4, p-p38 MAPK, and p38 MAPK in Kupffer cells were decreased in all treatment groups, but there was no significant difference between treatment groups. The high-dose SLBZS group had the lowest expression levels of TLR4, and the most visible downtrend in the expression levels of p-p38 MAPK and p38 MAPK was found in the high-dose integrated recipe group. The ratio of p-p38 MAPK to total p38 MAPK protein was obviously increased in all treatment groups. Therefore, our study showed that the activation of p38 MAPK pathway in Kupffer cells might be related to the release of inflammatory factors such as TNF- α , IL-1, and IL-6 in NASH rats. High dose of SLBZS and integrated recipe might work as a significant anti-inflammatory effect in Kupffer cells of NASH rats induced by HFD through suppression of p38 MAPK pathway. It indicated that p38 MAPK pathway may be the possible effective target for the recipes.