Tumor necrosis factor-alpha potentiates phospholipase A2-stimulated release and metabolism of arachidonic acid in cultured intestinal epithelial cells (INT 407).

Tumor necrosis factor-alpha (TNF-alpha), a known pro-inflammatory cytokine, has been suggested to play a role in the pathogenesis of inflammatory bowel disease (IBD) by mediating damage to the intestinal epithelial cells. The present study demonstrates that TNF-alpha potentiates release and metabolism of 14C-labeled arachidonic acid (14C-AA) in cultured intestinal epithelial cells (INT 407). Although TNF-alpha on its own was but a weak stimulator of cellular 14C-AA turnover, it significantly potentiated the release of 14C-AA and 14C-labeled prostaglandin E2(14C-PGE2) after stimulation with three known phospholipase A2 activators: phospholipase. C from Clostridium perfringens, the calcium ionophore A23187, and the phorbol ester 4-beta-phorbol-12-myristate-13-acetate (PMA). The phospholipase A2 inhibitor quinacrine significantly reduced both AA and PGE2 release after combined stimulation with phospholipase C and TNF-alpha. In contrast to its effect on the AA turnover, TNF-alpha did not affect the phospholipase C-stimulated production of platelet-activating factor (PAF-acether). Taken together, these findings indicate that a) TNF-alpha potentiates phospholipase A2-stimulated AA release from cultured intestinal epithelial cells; b) TNF-alpha may stimulate phospholipase A2-dependent AA release without affecting the formation of PAF-acether and c) pretreatment with TNF-alpha potentiates the formation of PGE2 after stimulation with phospholipase A2 activators. In summary, the present investigation points to the possibility that TNF-alpha may stimulate intestinal epithelial cells to produce biologically active AA metabolites and that this stimulation may be modulated by components of the intestinal luminal content, like bacterial toxins.