Abstract
Cholera is caused by infection with Vibrio cholerae. This study aimed to investigate the pathophysiology of diarrhea caused by the V. cholerae O1 El Tor variant (EL), a major epidemic strain causing severe diarrhea in several regions. In the ligated ileal loop model of EL-induced diarrhea in the ICR mice, a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor and a calcium-activated chloride channel (CaCC) inhibitor similarly inhibited intestinal fluid secretion. In addition, barrier disruption and NF-κB-mediated inflammatory responses, e.g., iNOS and COX-2 expression, were observed in the infected ileal loops. Interestingly, intestinal fluid secretion and barrier disruption were suppressed by NF-κB and COX-2 inhibitors, whereas an iNOS inhibitor suppressed barrier disruption without affecting fluid secretion. Furthermore, EP2 and EP4 PGE2 receptor antagonists ameliorated the fluid secretion in the infected ileal loops. The amount of cholera toxin (CT) produced in the ileal loops by the EL was ∼2.4-fold of the classical biotype. The CT transcription inhibitor virstatin, a toll-like receptor-4 (TLR-4) antibody and a CT antibody suppressed the EL-induced intestinal fluid secretion, barrier disruption and COX-2 expression. The CT at levels detected during EL infection induced mild intestinal barrier disruption without inducing inflammatory responses in mouse intestine. Collectively, this study indicates that CT-induced intestinal barrier disruption and subsequent TLR-4-NF-κB-mediated COX-2 expression are involved in the pathogenesis of EL-induced diarrhea and represent promising novel therapeutic targets of cholera.