The phenytoin metabolite p-HPPH upregulates prostaglandin biosynthesis in human gingival fibroblasts challenged to interleukin-1

Abstract

The effects of and interactions between the major phenytoin (PHT) metabolite 5-parahydroxyphenyl-5-phenylhydantoin (p-HPPH) and interleukin-1 (IL-1α, IL-1β) or tumor necrosis factor α (TNFα) on prostaglandin biosynthesis in human gingival fibroblasts were studied. IL-1α, IL-1β and TNFα, dose dependently, stimulated PGE 2 formation in gingival fibroblasts. The metabolite, p-HPPH (1.2–2.4 μg/ml), did not induce PGE 2 formation itself but potentiated IL-1α and IL1β induced PGE 2 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 PGF 1α, the stable breakdown product of PGI 2, in a dose dependent manner. IL-1β induces release of [ 3H]-arachidonic acid ([ 3H]-AA) from prelabelled fibroblasts, which was potentiated by p-HPPH (≥1.2 μg/ml). TNFα (≥1 ng/ml) significantly stimulated the biosynthesis of PGE 2 by a process that was also potentiated by p-HPPH. Addition of exogenous, unlabelled AA (10μM) caused an increase of PGE 2 formation in the fibroblasts that was not potentiated by p-HPPH (1.6 μg/ml). The results indicate that treatment with p-HPPH results in upregulation of prostaglandin synthesis in gingival fibroblasts challenged to IL-1 or TNFα at the level of phospholipase A 2.