THE PHENYTOIN METABOLITE P-HPPH UP-REGULATES PROSTAGLANDIN BIOSYNTHESIS IN HUMAN GINGIVAL FIBROBLASTS CHALLENGED TO INTERLEUKIN-1

The effects of and interactions between the major phenytoin (PHT) metabolite 5-parahydroxyphenyl-5-phenylhydantoin (p-HPPH) and interleukin-1 (IL-1alpha, IL-1beta) or tumor necrosis factor alpha (TNFalpha) on prostaglandin biosynthesis in human gingival fibroblasts were studied. IL-1alpha, IL-1beta and TNFalpha, dose-dependently, stimulated PGE2 formation in gingival fibroblasts. The metabolite, p-HPPH (1.2-2.4 mug/ml), did not induce PGE2 formation itself but potentiated IL-1alpha and IL1beta induced PGE2 formation in the gingival fibroblasts in a manner dependent on the concentration of both IL-1 and p-HPPH. The metabolite also stimulated IL-1 induced formation of 6-Keto PGF1alpha, the stable breakdown product of PGI2, in a dose dependent manner. IL-1beta induces release of [H-3]-arachidonic acid ([H-1]-AA) from prelabelled fibroblasts, which was potentiated by p-HPPH (greater-than-or-equal-to 1.2 mug/ml). TNFalpha (greater-than-or-equal-to 1 ng/ml) significantly stimulated the biosynthesis of PGE2 by a process that was also potentiated by p-HPPH. Addition of exogenous, unlabelled AA (10 muM) caused an increase of PGE2 formation in the fibroblasts that was not potentiated by p-HPPH (1.6 mug/ml). The results indicate that treatment with p-HPPH results in upregulation of prostaglandin synthesis in gingival fibroblasts challenged to IL-1 or TNFalpha at the level of phospholipase A2.