Toxic Effects Of Microcystin-LR On Intestinal Microbiota Structure And Short Chain Fatty Acids

Microcystins(MCs),a hepatotoxin produced by cyanobacteria,can induce intestinal damage when ingested by humans or animals,but the cause of MCs-induced intestinal damage in humans or animals is not clear.Therefore,this experiment was conducted to investigate the mechanism of MCs-induced intestinal injury in mice by subchronic exposure to intestinal microbiota and its metabolites(Short-chain fatty acids(SCFAs)).In this study,mice were exposed to MC-LR(L for leucine and R for arginine)by gavage for 8 weeks with a dose of 400 ?g/kg of MC-LR and an equal volume of saline.The mice did not die during the experiment,but the results of histopathological sections of the mouse cecum showed that the experimental group was infiltrated with inflammatory cells(basophils)and the intestinal wall was thinned compared to the control group.The above results demonstrated that this experiment has successfully established an MC-LR-induced intestinal injury model in mouse cecum.To analyze the kinetic changes of SCFAs in feces,this experiment was performed to detect the concentration changes of SCFAs in mouse feces by gas chromatography-tandem mass spectrometry.The results showed that at the initial stage of subchronic exposure(week 2)of MC-LR,the concentrations of six SCFAs,namely acetic acid,propionic acid,butyric acid,isobutyric acid,valeric acid,and isovaleric acid,decreased significantly in the experimental group compared with the control group.With the continuous exposure of MC-LR,the concentrations of the six SCFAs tended to increase,and the concentrations of the remaining five SCFAs in the experimental group,except acetic acid,did not exceed those in the control group until the end of the experiment.The above results indicated that the subchronic exposure of MC-LR changed the dynamic balance of SCFAs.To investigate the effect of MC-LR on the structure and function of microorganisms in the mouse cecum,16 S rDNA sequencing was performed on the contents of the mouse cecum in this experiment.The results showed that the alpha diversity(Richness,ACE,Chao1,and Shannon index)of the experimental group was significantly smaller than that of the control group,and the above results indicated that MC-LR reduced the alpha diversity of microorganisms in the mouse cecum.The results of species analysis showed that at the phylum level,a total of 32 known phyla were detected,and six phyla,including Candidatus Saccharibacteria,showed significant changes in abundance.At the genus level,40 known genera were detected,and 11 genera with significant changes in abundance were Clostridium IV,Bacteroides,Alloprevotella,etc.Analysis of the difference in KEGG functional abundance showed that a total of 17 functions were significantly changed in the experimental group compared with the control group,mainly including metabolism and disease.The above results collectively suggest that MC-LR can alter the microbial structure and function in the mouse cecum by inducing a decrease in microbial ?-diversity,an increase in the abundance of pathogenic bacteria such as Bacteroides and Alloprevotella,and a decrease in the abundance of short-chain fatty acid-producing bacteria,which in turn induces cecum injury in mice.In conclusion,MC-LR exposure not only altered the structure and function of microorganisms in the mouse cecum but also disrupted the dynamic balance of microbial metabolites SCFAs,which in turn induced imbalance of microbiota,abnormal enrichment of pathogenic microorganisms,and disruption of the intestinal barrier in the mouse cecum,leading to cecum injury in mice.