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

Abstract

ABSTRACT To clarify the mechanisms of diarrheal disease induced by Aeromonas sobria , we examined whether prostaglandin E 2 (PGE 2 ) was involved in the intestinal secretory action of A. sobria hemolysin by use of a mouse intestinal loop model. The amount of PGE 2 in jejunal fluid and the fluid accumulation ratio were directly related to the dose of hemolysin. The increase over time in the level of PGE 2 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 PGE 2 functions as an important mediator of diarrhea caused by hemolysin and that PGE 2 is produced primarily through a COX-2-dependent mechanism. Subsequently, we examined the relationship between PGE 2 , 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 PGE 2 production via COX-2 and that PGE 2 stimulates cAMP production. cAMP then activates PKA, which in turn stimulates CFTR Cl − channels and finally leads to fluid accumulation in the intestines.