The Effects Of Lactobacillus Plantarum On Attenuating Body Weight Gain Induced By Low-Dose Glycerol Monolaurate Intake In Mice And Mechanism Exploration

The worldwide prevalence of chronic disease-obesity and its metabolic complications such as type 2 diabetes,dyslipidemia and nonalcoholic fatty liver disease have attacted increased attentions.Glycerol Monolaurate(GML),generally recognized as safe(GRAS),is a commonly used food emulsifier,which also possesses excellent bacteriostatic properties.Recent studies have found that low-dose GML(150 mg/kg)intake could induce metabolic syndrome characterized by excess weight gain,systemic low-grade inflammation and gut microbiota dysbiosis in mice fed normal diet.In this work,we used probiotics as an intervention method,and explored the effects of probiotics on attentuating body weight gain induced by glycerol monolaurate-containing diet in mice and the possible mechanism of action from the perspective of gut microbiota.The main results are as follows:1.In this study,five LAB strains were screened from Chinese traditional sourdoughs collected from three different regions of China,based on in vitro probiotic properties including the resistance to simulated human gastrointestinal juice,resistance to bile salts and cholesterol lowering ability.All the five strains were identified as Lactobacillus plantarum by 16S rRNA gene sequencing.Among them,Lactobacillus plantarum ZJUFT34(T34)could tolerate simulated gastric juice of pH 2.5 and simulated intestinal juice,grow in 1.6%bile salts solution,and lower cholesterol levels in vitro.Lactobacillus plantarum ZJUFT17(T17)possessed good aggregation ability(related to adhesion ability)and could inhibit 4 species of gut pathogens.Moreover,T34 and T17 were found to be able to survive with a GML concentation of 300 mg/L and no vitality loss was found.In order to facilitate subsequent research and possible applications,the preparation process of the LAB powder and its preservation period were explored.The suitable protective agent was 5%skim milk and 5%lactose.The resuspeded LAB solution was pre-freezed at-80 ℃ for 15 h,and then lyophilized for 48 h.The T34 and T17 powders were stored at 4 ℃ for 1 year and could maintain more than 75%survival rates.2.The C57BL/6J mice fed normal chow diet with or without GML supplementation were intragastrically administered with T34 and T17 for 6 weeks.It was found that T34 and T17 could reverse the increased body weight gain caused by GML,especially T17.T17 also significantly(p<0.05)reduced the serum levels of total cholesterol(T-CHO)and low-density lipoprotein cholesterol(LDL-C),and decreased the pro-inflammatory cytokine IL-6 levels induced by GML.Meanwhile,T17 changed the structure and β-diversity of the gut microbiota.The simultaneous intake of T17 and GML significantly(p<0.05)decreased body weight gain,epididymal adipocyte hypertrophy,serum pro-inflammatory cytokine TNF-a levels and increased the relative abundance of Saccharibacteria_genera_incertae_sedis compared to control group.3.The C57BL/6J mice fed high fat diet(with or without 150 mg/kg GML supplementation)were intragastrically administered with T17 for 10 weeks.It was found that T17 could significantly(p<0.05)reduce the body weight gain,as well as ameliorate the increased levels of serum total triglyceride(TG),T-CHO,LDL-C,LPS and TNF-a and reduced the level of serum T-SOD induced by high-fat diet after 10-week intervention.Moreover,T17 significantly(p<0.05)suppressed the increase of body weight and epididymal fat weight,serum MDA and IL-1β levels in mice induced by high-fat diet containing GML,and the effect was better than GML-free group.T17 also alleviated insulin resistance,leptin resistance and systemic low-grade inflammation induced by obesity,and could restore the level of adiponectin to a certain extent.Meanwihle,H&E sections of epididymal fat and liver showed that T17 reduced not only adipocyte size but also lipid accumulation in the liver.4.The feces of mice fed high-fat diet for 10 weeks were collected and their possible mechanism of action was studied based on the analysis of changes of gut microbiota.The survival ability of T17 to pass through the gastrointestinal tract was identified and verified by pure culturing of stools.High-fat diet could significantly change the diversity of gut microbiota and the impact on the diversity of gut microbiota was much greater than the intake of exogenous probiotics.Mice administered with T17 and GML were rich in the genera Flavonifractor,Osclillibacter,Enterorhabdus and Saccharibacteria_genera_incertae_sedis.The significant negative correlation between the genera Flavonifractor,Osclillibacter,Enterorhabdus and total weight gain were analyzed.Considering two significantly related metabolic pathways,MAPK and PPAR signaling pathway,and the results of body weight and adipocyte,it was speculated that the T17 ameliorates high-fat diet-induced obesity and alleviated the inflammatory response by changing the composition of gut microbiota and inhibiting the MAPK and PPAR-y signaling pathways.