Study Of The Effects And Molecular Mechanism Of Lactobacillus Reuteri HI120 On Lipid Metabolism In C57BL/6 Obese Mice

BackgroundWith the gradual improvement in living standards around the world,the number of obese people continues to increase.In turn,obesity is closely related to chronic diseases such as cardiovascular diseases and endocrine diseases,and seriously threatens human health.Therefore,it is of great importance to take active and effective measures to curb the occurrence and development of obesity,and to explore potential therapeutic drugs or foods to regulate lipid metabolism and reduce weight.Intestinal probiotics is a hot topic related to obesity in medical research at present.Intestinal probiotics include microorganisms which originate from the host’s gut and improve health by regulating the host’s gastrointestinal tract balance.Probiotics such as bifidobacteria and lactobacilli can improve obesity and metabolic diseases,affect lipid metabolism directly or indirectly,and hence,individual energy balance and body weight.However,the mechanisms are unclear.Conjugated linoleic acid(CLA),an isomer of linoleic acid(LA),also plays a role in a variety of important physiological functions including weight loss and lipid reduction.Like probiotics,the molecular mechanism of CLA activity is not completely clear.ObjectivesThe aim of this study was to verify the effects of Lactobacillus reuteri HI120 on lipid metabolism in C57BL/6 obese mice and to explore the molecular mechanisms involved.Methods(1)The 16S rRNA gene of isolated L.reuteri HI120 was sequenced and the rate of conversion of LA to CLA by HI120 determined.(2)To examine the effect of HI120 on lipid metabolism,thirty male adult C57BL/6 obese mice were divided into five groups and fed a high-fat diet to establish the model.Diet intake,body weight,serum triglycerides,and serum total cholesterol were recorded.mRNA and protein expression levels of NPC1L1,SREBP-2,HMG-CR,CYP7A1,LXR,and FXR were determined by fluorescence quantitative PCR and western blotting,respectively.(3)The molecular mechanisms involved in lipid metabolism were explored in HepG2/Caco-2 cells.After treatment,mRNA and protein expression levels of NPCIL1,SREBP-2,HMG-CR,CYP7A1,LXR,and FXR were determined by fluorescence quantitative PCR and western blotting,respectively.Results(1)The homology between the 16S rRNA sequence of HI120 and other 16S rRNA gene sequences of L.reuteri was 99%,and the homology between the LAI amino acid sequence of HI120 and that of the L.reuteri standard strain was 87%.Mixing HI120 and LA together generated a large amount of CLA.(2)Food and water intake,body weight,and serum triglyceride levels of mice fed a mixture of HI120 and LA did not change significantly,but the serum total cholesterol level decreased.Gene expression levels of NPC1L1,SREBP-2,and HMG-CR in the small intestine and liver of the mice decreased,but the gene expression levels of CYP7A1,LXR,and FXR did not change significantly.(3)In HepG2/Caco-2 cells treated with a mixture of HI120 and LA,gene expression levels of NPC1L1,SREBP-2,and HMG-CR similarly decreased,while that of CYP7A1,LXR,and FXR did not change significantly.SREBP-2 siRNA interference experiments resulted in a decrease in NPC1L1 and HMG-CR gene expression and cholesterol absorption.ConclusionsL.reuteri HI120 can efficiently convert LA to CL A.A mixture of HI120 and LA fed to C57BL/6 obese mice can reduce their serum total cholesterol levels.The molecular mechanism may be due to the regulation of absorption and synthesis of cholesterol by CLA.CLA decreased the absorption of cholesterol presumably through SREBP-2,which resulted in decreased levels of NPC1L1 and HMG-CR.