Review article: nitric oxide from dysbiotic bacterial respiration of nitrate in the pathogenesis and as a target for therapy of ulcerative colitis

Background Factors initiating human ulcerative colitis (UC) are unknown. Dysbiosis of bacteria has been hypothesized to initiate UC but, to date, neither the nature of the dysbiosis nor mucosal breakdown has been explained. Aim To assess whether a dysbiosis of anaerobic nitrate respiration could explain the microscopic, biochemical and functional changes observed in colonocytes of UC. Methods Published results in the gastroenterological, biochemical and microbiological literature were reviewed concerning colonocytes, nitrate respiration and nitric oxide in the colon in health and UC. A best-fit explanation of results was made regarding the pathogenesis and new treatments of UC. Results Anaerobic nitrate respiration yields nitrite, nitric oxide (NO) and nitrous oxide. Colonic bacteria produce NO and UC in remission has a higher lumenal NO level than control cases. NO with sulphide, but not NO alone, impairs beta-oxidation, lipid and protein synthesis explaining the membrane, tight junctional and ion channel changes observed in colonocytes of UC. The observations complement therapeutic mechanisms of those probiotics, prebiotics and antibiotics useful in treating UC. Conclusions The prolonged production of bacterial NO with sulphide can explain the initiation and barrier breakdown, which is central to the pathogenesis of UC. Therapies to alter bacterial nitrate respiration and NO production need to evolve. The production of NO by colonic bacteria and that of the mucosa need to be separated to pinpoint the sequential nature of NO damage in UC.