L 9. Transient receptor potential vanilloid 1, substance P and reactive oxygen species mediate ethanol - induced gastric injury in mice

Background and aims. Ingestion of elevated amounts of ethanol (EtOH) can cause hemorrhagic ulceration of the stomach in humans and experimental animals by mechanisms that are incompletely understood. Although previous report showed that coadministration of neurokinin 1 receptor (NK1) agonist aggravated and NK1 receptor antagonists prevent ethanol-induced gastric lesions, the mechanisms by which ethanol releases substance P (SP) and SP damages the mucosa are unknown. We recently reported that ethanol by lowering the threshold temperature for channel activation, stimulate TRPV1 and cause the release of sensory neuropeptides. Thus, we hypothesized that ethanol activates transient receptor potential vanilloid 1 (TRPV1) on sensory nerves to release SP, which stimulates epithelial NK1 receptors to generate damaging reactive oxygen species. Methods and results. SP release was measured from segments of mouse stomach, and lesions were assessed by macroscopic and microscopic examination of whole stomach. Reactive oxygen species were detected using dichlorofluorescein-diacetate, and NK1 receptors were localized by immunofluorescence. Ethanol stimulated SP release, and antagonism of transient receptor potential vanilloid 1 prevented this effect. High dose ethanol caused lesions, and TRPV1 antagonism and NK1 receptor antagonism or genetic deletion of NK1 receptor inhibited lesion formation. Co-administration of low, innocuous doses of ethanol and SP caused lesions by a TRPV1-independent but NK1 receptor-dependent process. Ethanol, capsaicin and SP stimulated generation of reactive oxygen species by superficial gastric epithelial cells, expressing NK1 receptors, by a NK1 receptor-dependent mechanism. Diverse reactive oxygen species scavengers (acorbic acid, lipolic acid and n-acetyl cysteine) ameliorated lesions induced by a high ethanol dose or a low ethanol dose plus SP. Conclusions. Present results indicate that gastric lesions are caused by an initial detrimental effect of ethanol, which is damaging only if associated with TRPV1 activation and SP release from sensory nerves. SP, by stimulation of NK1 receptors on gastric epithelial cells cause the release of and tissue damaging reactive oxygen species.