The Biological Basis Of Irritable Bowel Syndrome Caused By Maternal Separation And Injury Role Of Homocysteine On Intestinal Epithelial Barrier Function

Irritable bowel syndrome (IBS) is considered to be a functional gastrointestinaldisorder characterized by chronic abdominal symptoms including pain or discomfortand altered bowel habit (constipation and/or diarrhea), in the absence of structural orbiochemical abnormalities that can be identified after a standard diagnostic work-up.IBS continues to be a major problem for clinical gastroenterologists worldwide andimposes considerable personal and social burdens. As a syndrome detailedunderstanding of its etiology and pathophysiology is lacking，and its therapeuticstrategy mainly approached to symptomatic treatment. Numerous reports provideevidence for a prominent role of stress in the pathophysiology and clinicalpresentation of IBS symptoms.1. The symptomatic characteristic of IBS caused by maternal separationMaternal separation (MS) in rodents is a well-studied model of early life stress,and as a model of brain–gut axis dysfunction, the separated phenotype ischaracterized by alterations of the intestinal barrier function, altered balance in entericmicroflora, exaggerated stress response and visceral hypersensitivity, which are allevident in IBS.Rat pups were separated daily from their dam as a litter for3h during postnataldays2-21in MS procedure. The behavioral response to colorectal distension (CRD)according to the abdominal withdrawal refex (AWR) score criteria that record thesensation threshold value. Our results showed that MS rats develop visceralhyperalgesia in response to CRD, stress-induced increase in colonic motility andincreased depression-and anxiety-like behavior. Additionally, there is no differencesin body weight, and absence of any obvious histopathologic appearances using routineprocessing of colonic samples for H&E staining between IBS rats and control.Thereby mimicking all the main features of IBS, animal model was established.There was sex-dependent differences in MS-induced IBS rats, wheresignificantly more visceral hypersensitivity and behaviors symptoms are associated with the female gender. But, the main manifestations of IBS were not related to thestress intensity including duration and manner of separation.2. The biological basis of IBS caused by neonatal maternal separationAfter the last stress session, rats were killed at PND60-70by anesthesia withsodium pentobarbital. Intracardiac blood samples were drawn for the measurement ofplasma or serum concentrations of GC, Ach,5-HT, Hcy, and so on.In adulthood, dysfunctions of the HPA axis and the autonomic nervous systemwere evident, MS is enough to increase both basal and stress-induced levels of GCand Ach in plasma of IBS rat. Other neurotransmitters permanently altered by MSinclude5-HT、CGRP、SP and GAS which was found to be increased in plasma. Theresults suggested that MS produced long-lasting changes in neuroendocrine, andresulted in stress susceptibility, which may be the pathophysiologic basis ofstress-induced IBS.The results showed that the pro-inflammatory cytokine TNF-α was significantlyincreased in IBS caused by MS, and further increased after acute stress, but NO levelswas significantly decreased. Meanwhile, colonic mucosal mast cell hyperplasia anddegranulation was observed in MS rat. These results indicated that inflammationactivation may be the pathogenesis of IBS caused by MS.Serum metabolite levels were detected using gas chromatography/time-of-flightmass spectrometry,45metabolites were identified from the191distinct compoundsfound in the study, and7metabolic molecules including serine, glycine and valinewere significantly elevated in MS rats. Hcy levels in plasma were significantlyincreased in MS rats, and further increased after acute stress. Combined metabolomicsresults, serine as a critical substrate in transsulfuration metabolism of Hcy, indicatingthat Hcy transsulfuration metabolic pathways may be inhibited.3. The injury role of Hcy on intestinal epithelial barrier function of IBSThe results showed in the animal model that Hcy-lowering treatment with folicacid plus vitamin B6and B12does have a powerful effect on IBS symptoms,amelioration in their stress responsiveness including visceral hyperalgesia and colonicmotor dysfunction were positively correlated with Hcy Level. The intestinal permeability was increased induced by MS using colonic(sucralose) and small intestinal (lactulose/mannitol) permeability markers, theultra-structural damage of tight junction was found in colon of MS using transmissionelectron microscope, and the expression and distribution of tight junctiontransmembrane protein occludin was altered. There is a benefit of Hcy-loweringtreatment in preserving tight junction integrity and intestinal barrier function. In vitroexprements showed that Hcy could directly injury intestinal epithelial tight junctionbarrier, and was not TNF-α-dependent pathway.In conclusion, our findings have shown that the existence of increased Hcy atcirculating levels in MS-induced IBS rat, may contribute to the intestinal epithelialbarrier defects associated with IBS symptoms such as sensorimotor abnormality. Thedata demonstrated that a persistent increase in Hcy triggered tight junction breakdownand increased intestinal paracellular permeability in IBS, in which the damagingeffect that could be alleviated by Hcy scavenging. Hcy may be involved in thepathophysiology of IBS caused by MS and regarded as a potential pharmacologicaltarget.The interaction of neuro-endocrine-immune and metabolic regulatory networksmay be the molecular basis of IBS caused by maternal separation, these observationsmight open new insights into our understanding of IBS pathogenesis.