Effect Of High Fat Induced-Oxidative Stress On Somatostatin Secretion And Gene Expression Of Intestine And Liver

Digestive system is the main digestive, absorptive and metabolic organ in animal. High fat diet (HFD) increased ROS level and may have an effect on the function and gene expression of digestive system, which in turn modulate nutrient metabolism. Somatostatin (SS) may protect organism from overnutrition-induced oxidative stress by inhibiting pancreatic endocrine and exocrine secretion, gastrointestinal digestion and absorption. The aim of our experiment was to study the effect and regulation mechanism of HFD and antioxidant LA on gastrointestinal redox status, function, somatostatin secretion, lipid metabolism, glycometabolism and gene expression of liver and intestine.1. Effect of HFD and LA on the redox status and ROS level of miceMale C57BL/6 mice were fed an ordinary diet, HFD (21.45% fat, w/w) and HFD plus 0.1% LA respectively for 1, 3 or 6 weeks. The redox status was examined. The results showed that there was not significant difference in ROS level and MDA content for 1 week (P>0.05). A significant increase in the level of ROS in panscreas, liver and intestine was observed in the group fed the HFD for 3 weeks and there was a further increase after 3 weeks. A progressively increase (P<0.05) in the level of plasma MDA was observed in the group fed the HFD for 6 weeks with a similar pattern of increase in the panscreas, liver, and intestine. Treatment with LA brought about a significant improvement in redox homeostasis of HFD-fed mice.2. Effect of OA and LA on redox status and secretion of SS in rat GMCsThe effect of the different dose oleic acid (OA) on redox status and SS secretion of rat gastric mucosal cells (GMCs) in vitro was studied. The results showed that low OA (0.1 mmol) increased SS secretion by 2.85-fold and cellular ROS by 2.71-fold at 5 h. LA at 0.5 mmol significantly inhibited OA-induced SS secretion and cellular ROS in GMCs. Both of ROS and MDA increased gradually with the increase of OA concentration (P<0.05). 1 mmol OA significantly increased cellular ROS by 8.08-fold, MDA content by 3.69-fold and significantly decreased the GSH/GSSG ratio and the activity of SOD and GSH-Px (P<0.05). These results strongly suggested that GMCs exposed to high OA could induce its oxidative stress and injury. High OA concentration decreased SS levels. LA (0.5 mmol) partially restored SS secretion levels through inhibition of high OA-induced oxidative stress. A nonlinear regression relationship between SS level and ROS was observed except high OA group (y=25.645Ln(X)-159.93, R2=0.8467).The results suggested that properly increased ROS may as messenger induced SS secretion, while high ROS brought about oxidative damage.3. Effect of HFD and LA on the secretion and expression of SS, lipid metabolism and glycometabolismThe objective of this study was to investigate the effect of HFD and antioxidant LA on the secretion and expression of SS, lipid metabolism and glycometabolism. The results showed that there was not significant difference in lipid and glucose level for 1 week (P>0.05). A marked increase in the levels of lipid, glucose, insulin and homeostasis model assessment (HOMA) index was detected in the group fed the HFD for 6 weeks. Hyperlipidemia and glycometabolism disorders, accompanied by a depressed antioxidant defense system, were observed in HFD-fed mice for 6 weeks. These changes were partially restored in the LA-treated group. A significant increase (P<0.05) in the levels of SS in plasma, panscreas and intestine, was observed in the group fed with HFD for 1 week compared with the control group. However, after 3 and 6 weeks, significant decrease in the SS level was observed in the group fed with HFD. No change of the steady state level of SS mRNA expression in intestine was observed in mice fed the HFD for 1 week. However, significant decrease in the SS expression level was observed for 6 weeks (P<0.05). Treatment with LA partially restored the SS mRNA and its protein levels to that of control levels for 6 weeks. These results suggested that SS can modulate ROS level by controlling digestive system function for 1 week. Then, oxidative stress brought about damage to SS secretion, which in turn aggravated redox imblanace and metabolic dysfunction.4. Reduced serum somatostatin levels in hyperlipidemic subjectsWe measured serum SS level and antioxidant status in 28 hyperlipidemic (total cholesterol>4.5 mmolol/L, triglycerides >1.7 mmolol/L) and the age- and sex-matched control subjects. We found that subjects with hyperlipidemia have insulin resistance and high levels of oxidative stress. Median somatostatin (18.28±7.42 vs. 23.25±8.69 pg/mL; P<0.05) levels were lower in hyperlipidemic than in normolipidemic subjects. A significant inverse relationship between SS level and AI (r =-0.33, P=0.007) was observed. These results suggest a possible protective role of endogenous SS at least on hyperlipidemia and atherosclerosis that are attributed to excess energy intake and oxidative stress. Of course these preliminary results should be supported by prospective studies.5. Effects of high fat diet and LA supplement on redox, digestive and transport related gene expression of intestine in C57BL/6 miceEffects of high fat diet and LA supplement on gene expression of intestine in C57BL/6 mice were analyzed using the Affymetrix MOE430A GenChip. Significant changed GO terms were studied by Genmapp, which revealed that the differentially expressed genes were mainly related to reactive oxygen species metabolism, DNA repair, induction of apoptosis, transport, digestive enzyme, signal transduction and immolune response. HFD and HFD+LA significantly influenced biological process was analyzed using Mappfinder based on KEGG and GenMAPP database, which revealed that LA up-regulated the expression of genes related to free-radical scavenger enzymes and SS. Then, the transport, digestive enzyme, DNA repair, JAK-STAT cascade and immolune response related gene were up-regulated, while those involved in apoptosis were down-regulated. These results suggested LA can improve intestinal function of HFD fed mice.6. Effects of high fat diet and LA supplement on redox and lipid metabolism related gene expression of liver in C57BL/6 miceEffects of high fat diet and LA supplement on gene expression of liver in C57BL/6 mice were analyzed using the Affymetrix MOE430A GenChip. Significant changed GO terms were studied by Genmapp, which revealed that the differentially expressed genes were mainly related to lipid metabolism, glucose metabolism, metabolic enzyme, stress response, immolune response and signal transduction. HFD and HFD+LA significantly influenced biological process was analyzed using Mappfinder based on KEGG and GenMAPP database, which revealed that LA ingestion up-regulated the expression of genes related to free-radical scavenger enzymes, ?-oxidation and AMPK cascade, while those involved in NF-kB cascade and cholesterol synthesis were down-regulated. LA activated AMPK cascade by improving oxidative stress. AMPK plays an important role in lipid metabolism acting as a sensor of cellular energy status. LA decreased TNF-αexpression level by inactivating NF-kB cascade, and improved insulin resistance.