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 cyto kine, has been suggested to play a role in the pathogenesis of inflamm atory bowel disease (IBD) by mediating damage to the intestinal epithe lial cells. The present study demonstrates that TNF-alpha potentiates release and metabolism of C-14-labeled arachidonic acid (C-14-AA) in c ultured intestinal epithelial cells (INT 407). Although TNF-alpha on i ts own was but a weak stimulator of cellular C-14-AA turnover, it sign ificantly potentiated the release of C-14-AA and C-14-labeled prostagl andin E2 (C-14-PGE2) after stimulation with three known phospholipase A2 activators: phospholipase C from Clostridium perfringens, the calci um ionophore A23187, and the phorbol ester 4-beta-phorbol-12-myristate -13-acetate (PMA). The phospholipase A2 inhibitor quinacrine significa ntly reduced both AA and PGE2 release after combined stimulation with phospholipase C and TNF-alpha. In contrast to its effect on the AA tur nover, TNF-alpha did not affect the phospholipase C-stimulated product ion of platelet-activating factor (PAF-acether). Taken together, these findings indicate that a) TNF-alpha potentiates phospholipase A2-stim ulated AA release from cultured intestinal epithelial cells; b) TNF-al pha may stimulate phospholipase A2-dependent AA release without affect ing the formation of PAF-acether, and c) pretreatment with TNF-alpha p otentiates the formation of PGE2 after stimulation with phospholipase A2 activators. In summary, the present investigation points to the pos sibility that TNF-alpha may stimulate intestinal epithelial.cells to p roduce biologically active AA metabolites and that this stimulation ma y be modulated by components of the intestinal luminal content, like b acterial toxins.