Study Of The Cholesterol-lowering Ability In Vitro And In Vivo Of Two Lactobacilli Strains And The Related Mechanisms

Chapter1Screening and Identification of Bacteria strains with Cholesterol-reducing ability in vitroObjective:To screen bacteria strains with the ability to reduce cholesterol in vitro from bacteria isolated from fecal samples of healthy adults and to give the targeted strains an identification for further study.Methods:We use modified cholesterol-MRS medium as the model to screen the potential targeted bacteria strains.After screeing,we selected two strains with better ability to reduce cholesterol and identified the two strains.Results:We screened out two strains with the cholesterol-reducing rate above30%,the detail rate is9-41-A36.8%and M1-1631.5%respectively. By preliminary identification we identified9-41-A as Lactobacillus plantarum strain and M1-16as Lactobacillus fermentum stain.Conclusion:9-41-A and M1-16had strong cholesterol-reducing,acid and bile acid tolerance abilities in vitro. Results of identification showed that 9-41-A and M2-1were Lactobacillus plantarum and Lactobacillus fermentum respectively.We plan to apply them in animal models to tset their cholesterol-lowering ability in vivo. Chapter2Effects of two Lactobacillus strains on lipid metabolism and intestinal microflora of rats fed on a high-cholesterol dietObjective:To evaluate the effects of Lactobacillus plantarum9-41-A and Lactobacillus fermentum M1-16on body weight gain,lipid metabolism intestinal microflora and fecal water content of rats fed on high-cholesterol diet.Methods:Fourty Sprague Dawley rats were randomly divided into four groups.Control group received normal diet,model group received high-cholesterol diet,and intervention groups received high-cholesterol diet added with Lactobacillus plantarum9-41-A and Lactobacillus fermentum M1-16respectively. After a six-weeks feeding period,all rats were executed.Body weight (BW), Lee’s index,liver index and fat index,cholesterol and lipid levels of serum and liver,fecal cholesterol and bile acid concentrations,intestinal microflora and fecal water content were measured.Liver lipid deposition was also classified pathologically.Results:In lactic acid bacteria (LAB) treated groups:(1)serum total cholesterol,low-density lipoprotein and triglycerides greatly reduced than rats in model group, while high-density lipoprotein appeared almost the same. Atherogenic indexes were improved.(2) hepatic cholesterol and triglycerides were also reduced obviously and liver lipid deposition was ameliorated after a high-cholesterol diet.(3) the level of fecal cholesterol and bile acid were significantly higher than control groups.(4) both strains of lactobacilli were able to increase Lactobacillus colony and Bifidobacterium colony and decrease Escherichia coli populations in intestine compared to rats fed with high-cholesterol diet only.Moreover, LAB treated groups excreted feces with more water. Besides,compared with the model group, L.9-41-A induced a decrease in BW gain.Conclusion:Hypocholesterolemic effect of LAB may differ among strains.The two local strains may have the ability to exert hypocholesterol effect, increase lactobacillus colony and Bifidobacterium colony count and fecal water content,thus beneficially affect the host.Moreover, L.9-41-A might act in controlling body weight. Chapter3Effects of Administration of two Lactobacillus strains on mRNA levels of cholesterol metabolism related genes in SD RatsObjective:In order to furtherly understand the possible mechanisms in vivo,we investigate the Effects of Administration of two Lactobacillus strains on mRNA levels of cholesterol metabolism genes involved in cholesterol homeostasis in SD Rats.Methods:mRNA expression of3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR),LDL-receptor (LDL-R),cytochrome P4507α-1(CYP7A1) and farnesoid receptor (FXR) of SD rats were measured by real-time PCR.Results:The hepatic HMGCR levels in LAB treated rats were significantly lower than in rats of control and model groups and the LDLR,CYP7A1and FXR mRNA levels were significantly elevated.Conclusion:The mechanisms of the hypocholesterolemic effect of our two strains in vivo may related to some key regulate factors in the metabolism of cholesterol and bile acids of SD rats. The hepatic HMGCR levels in LAB treated rats were significantly reduced and the LDLR,CYP7A1and FXR mRNA levels were significantly elevated.