Fluid secretion caused by aerolysin-like hemolysin of Aeromonas sobria in the intestines is due to stimulation of production of prostaglandin E ₂ via cyclooxygenase 2 by intestinal cells

To clarify the mechanisms of diarrheal disease induced by Aeromonas sobria, we examined whether prostaglandin E₂ (PGE₂) was involved in the intestinal secretory action of A. sobria hemolysin by use of a mouse intestinal loop model. The amount of PGE₂ in jejunal fluid and the fluid accumulation ratio were directly related to the dose of hemolysin. The increase over time in the level of PGE₂ was similar to that of the accumulated fluid. In addition, hemolysin-induced fluid secretion and PGE ₂ synthesis were inhibited by the selective cyclooxygenase 2 (COX-2) inhibitor NS-398 but not the COX-1 inhibitor SC-560. Western blot analysis revealed that hemolysin increased the COX-2 protein levels but reduced the COX-1 protein levels in mouse intestinal mucosa in vivo. These results suggest that PGE₂ functions as an important mediator of diarrhea caused by hemolysin and that PGE₂ is produced primarily through a COX-2-dependent mechanism. Subsequently, we examined the relationship between PG_E2, cyclic AMP (cAMP), and cystic fibrosis transmembrane conductance regulator (CFTR) Cl^- channels in mouse intestinal mucosa exposed to hemolysin. Hemolysin increased the levels of cAMP in the intestinal mucosa. NS-398 inhibited the increase in cAMP production, but SC-560 did not. In addition, H-89, a cAMP-dependent protein kinase A (PKA) inhibitor, and glibenclamide, a CFTR inhibitor, inhibited fluid accumulation. Taken together, these results indicate that hemolysin activates PGE₂ production via COX-2 and that PGE₂ stimulates cAMP production. cAMP then activates PKA, which in turn stimulates CFTR Cl^- channels and finally leads to fluid accumulation in the intestines.