Elevated colonic lumenal serine protease activity of IBS-D patients evokes a PAR-2-mediated colonic epithelial barrier dysfunction and subsequent allodynia in mice, suggesting a novel organic background in the pathogenesis of IBS.

Neonatal maternal deprivation (NMD) increases gut paracellular permeability (GPP) through mast cells and nerve growth factor (NGF), and modifies corticotrophin-releasing factor (CRF) and corticosterone levels. CRF, corticosterone and mast cells are involved in stress-induced mucosal barrier impairment. Consequently, this study aimed to specify whether corticosteronaemia and colonic expression of both preproCRF and CRF are modified by NMD, and to determine if altered expression may participate in the elevated GPP in connection with NGF and mast cells. Male Wistar rat pups were either separated from postnatal days 2-14, or left undisturbed with their dam. At 12 weeks of age, adult rats were treated with mifepristone (an antagonist of corticoid receptors), α-helical CRF (9-41) (a non-specific CRF receptor antagonist), or SSR-125543 (CRF-R 1 receptor antagonist). We also determined corticosteronaemia and both colonic preproCRF and CRF expression. Then, control rats were treated by CRF, doxantrazole (mast cell stabilizer), BRX-537A (a mast cell activator) and anti-NGF antibody. NMD did not modify colonic CRF level but increased colonic preproCRF expression and corticosteronaemia. Peripheral CRF, via CRF-R 1 receptor, but not corticosterone, was involved in the elevated GPP observed in these rats, through a mast-cell-mediated mechanism, since the increase of GPP induced by exogenous CRF was abolished by doxantrazole. Anti-NGF antibody treatment also reduced the elevated GPP induced by CRF or BRX-537A. CRF acts through CRF-R 1 receptors to stimulate NGF release from mast cells, which participates in the elevated GPP observed in NMD adult rats. This suggests that early traumatic experience induced neuro-endocrine dysfunction, involved in alterations of gut mucosal barrier.

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The streptozotocin-induced diabetic rat model was used to investigate the relation between the deranged gut motility and the segment-specific quantitative changes in the nitrergic myenteric neurons. Additionally, we studied the effectiveness of early insulin replacement to prevent the diabetes-induced changes. Rats were divided into three groups: controls, diabetics and insulin-treated diabetics. Ten weeks after the onset of diabetes, animals were chosen from each group for intestinal transit measurements. The remainder were killed and gut segments were processed for NADPH-diaphorase histochemistry and HuC/HuD immunohistochemistry. The diabetic rats displayed faster transit than that for the controls. In the insulin-treated group, the transit time was the same as that in the controls. In the duodenum of the diabetic rats, the number of nitrergic neurons was decreased, while the total neuronal number was not altered. In the jejunum, ileum and colon, both the total and the nitrergic neuronal cell number decreased significantly. Insulin treatment did not prevent the nitrergic cell loss significantly in the duodenum and jejunum, but it did prevent it significantly in the ileum and colon. These findings comprise the first evidence that the nitrergic neurons located in different intestinal segments exhibit different susceptibilities to a diabetic state and to insulin treatment.

Elevated colonic luminal serine-protease (Ser-P) activity of diarrhea-predominant IBS (IBS-D) patients evokes a proteinase-activated receptor (PAR)-2-mediated colonic hypersensitivity in mice. Despite similarly elevated Ser-P levels in feces, patients with IBD exhibit visceral hypo- or normosensitivity to rectal distension, as opposed to IBS-D. To explain these discrepancies we studied the effect of colonic infusion of fecal supernatants from ulcerative colitis (UC) patients to colorectal mechanical sensitivity of mice and explored the involvement of PAR-4 and its activator Cathepsin-G (Cat-G). Fecal protease activities were assayed in healthy subjects, IBS-D and UC patients in presence or not of antiproteases or Cat-G inhibitor. Following intracolonic infusion of fecal supernatants from healthy subjects, IBS-D and UC patients or PAR-4 activating peptide (PAR-4-AP) or Cat-G, EMG response to colorectal balloon distension was recorded in mice. This nociceptive response was also determined after treatment with pepducin (PAR-4 antagonist) on UC supernatant or after a preincubation with antiproteases or Cat-G inhibitor. In contrast to IBS-D supernatant, UC supernatant promoted colonic hyposensitivity to distension, an effect mimicked by PAR-4-AP or Cat-G. UC supernatant-induced hypoalgesia was inhibited by a cocktail of antiproteases. However, blockade of PAR-4 or Cat-G inhibition resulted in colonic hypersensitivity similar to that observed after IBS-D supernatant infusion. Despite similarly elevated Ser-P activities, IBS-D and UC fecal supernatant display visceral pro- and antinociceptive effects in mice, respectively. Visceral hyposensitivity induced by fecal supernatant from UC patients results from PAR-4 activation by cathepsin-G, counterbalancing the pronociceptive effect of simultaneous PAR-2 activation.