Effect Of Metformin On Gut Microbiota,Short-chain Fatty Acids And Glucagon-like Peptide-1 In High-fat Diet-induced Obese Mice

Objective: As one of the environmental factors,gut microbiota is involved in the development of obesity,diabetes and related metabolic diseases.Short-chain fatty acids(SCFAs)can stimulate the secretion of glucagon-like peptide-1(GLP-1)from enteroendocrine L cells.Recently studies have shown that metformin has effect on intestinal function but it is not clear.This study was to investigate the effect of metformin on gut microbiota,SCFAs and GLP-1 in high-fat diet-induced obese mice,for providing some new clues for pharmacological effects of metformin.Methods: C57BL/6J mice were fed low-fat diet or high-fat diet for 11 weeks to establish obese models,then to be divided into three groups: low-fat diet control group(LFD-CT,n = 8),high-fat diet control group(HFD-CT,n = 8)and a high-fat diet + metformin intervention group(HFD-Met,n = 8).After metformin intervention for 7 weeks,serum and fecal samples were collected.Serum insulin and GLP-1 were measured by enzyme linked immunosorbent assay(ELISA).The DNA of fecel samples were extracted and amplification were performed targeting the variable regions 1-3 of the 16 S rRNA gene.The fecal microbiota were characterized using pyrosequencing of 16 S rRNA genes on the Illumina Miseq PE 250 / PE300 platform.SCFAs were detected by gas chromatography(GC).All data were analyzed using SPSS version 19.0.Results:(1)Compared with LFD-CT group,mice in HFD-CT group had a higher level of body weight,blood glucose and serum insulin(P<0.05),and a lower level of GLP-1 concentration(P = 0.635)although no statistical significance.Compared with HFD-CT group,mice in HFD-Met group had a lower level of body weight,blood glucose and serum insulin(P<0.05),and a significantly higher concentration of GLP-1(P<0.05).(2)Compared with LFD-CT group,mice in HFD-CT group had reduced gut microbiota diversity and disorder of community structure.Compared with HFD-CT group,mice in HFD-Met group showed a lower abundance of Firmicutes(P<0.05),a trend of increase in Bacteroidetes(P=0.185)and Verrucomicrobia(P=0.136),a significantly higher abundance of Helicobacter(P=0.033),Granulicatella(P=0.017)and Staphylococcus(P=0.015),a significantly lower abundance of Lachnospiraceae_incertae_sedis(P=0.006)and a trend of increase in Akkermansia(P=0.136).(3)Mice in HFD-CT group had a higher concentration of acetic acid,propionic acid and butyric acid compared with LFD-CT group(P<0.05).The SCFAs were lower after metformin intervention(P<0.05).Conclusions: 1.Metformin affects the structure of gut microbiota in high-fat diet-induced obese mice,changing gut composition at phylum and genus level.2.The type of diet and metformin have a significant impact on fecal SCFAs.3.Gut microbiota-SCFAs axis may not be involved in the mechanism of metformin increasing GLP-1 level.