Effects of nNOS inhibition on the Escherichia coli and butyrate-producing bacteria in IBS rats with visceral hypersensitivity

Abstract

Abstract Background: Irritable bowel syndrome (IBS) is described as a disorder of the microbiota-gut-brain axis, with a distinguishing feature of visceral hypersensitivity. An imbalanced gut microbiota is closely related to the occurrence of IBS. Neuronal nitric oxide synthase (nNOS) may be an essential regulatory factor in stress-induced IBS. However, the relationship between gut microbiota and nNOS expression is still poorly understood. The aim of the present study is to investigate the effects of nNOS inhibition on the changes of Escherichia coli and butyrate-producing bacteria in IBS rats with visceral hypersensitivity. Method: Colorectal distention (CRD) combined with restraint stress (RS) was used to generate an IBS rat model with visceral hypersensitivity. L-NAME was administered as an nNOS inhibitor. Abdominal withdrawal reflex (AWR) test was used to evaluate visceral sensitivity in rats. Western blotting and real-time PCR were used to determine expression levels of nNOS in the distal colon of rats. The content of nitric oxide (NO) andnitritein the distal colon of rats was determined using colorimetric methods. Gut microbiota was assessed by fluorescence qPCR. Liquid chromatography-mass spectrometry (LC-MS/MS) was used to quantify butyrate content in the feces and distal colon of rats. Results: nNOS inhibiton could attenuate visceral hypersensitivity in stress-induced IBS rats. Gut microbiota was changed after treatment with nNOS inhibiton, which was characterized by a decrease in the abundance of Escherichia coli and an increase in the abundance of butyrate-producing bacteria. Moreover, nNOS inhibiton decreased the contents of NO and nitrite and increased butyrate content in the distal colon of rats. From further Spearman’s correlation analysis, nNOS expression was positively correlated with Escherichia coliand negatively correlated with butyrate-producing bacteria. Conclusion: nNOS inhibiton reduced the production of NO and nitrite by down-regulation of expression levels of nNOS, thus regulating the imbalance of gut microbiota,as demonstrated by a decrease in the abundance of Escherichia coli, as well as an increase in the abundance of butyrate-producing bacteria, which contributed to attenuating the visceral hypersensitivity in IBS rats.