INHIBITION OF INDUCIBLE NITRIC-OXIDE SYNTHASE BY PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR AGONISTS - CORRELATION WITH INDUCTION OF HEME OXYGENASE-1

Genetic knock-out in mice of peroxisome proliferator-activated recepto r-alpha (PPAR alpha) can prolong inflammation in response to leukotrie ne beta(4). Although cyclooxygenase 2 has been shown to be induced by PPAR activation, the effect of PPAR agonists ore the key inflammatory enzyme systems of nitric oxide synthase (NOS) and stress proteins has not been investigated, The effect on these of naturally occurring eico sanoid PPAR agonists (leukotriene beta(4) and 8(S)-hydroxyeicosatetrae noic acid, which are PPAR alpha selective; PGA(2), PGD(2), PGJ(2), and Delta(12)PGJ(2), which are PPAR gamma selective) and the synthetic PP AR alpha agonist Wy14,643 was examined in activated RAW264.7 murine ma crophages. Leukotriene beta(4) and 8(S)-hydroxyeicosatetraenoic acid s timulated nitrite accumulation, indicative of enhanced NOS activity, P GA(2), PGD(2), PGJ(2), Delta(12)PGJ(2), and WS14,643 reduced nitrite a ccumulation, with Delta(12)PGJ(2) being the most effective, The mechan ism behind this reduction was examined using Western blotting. Inhibit ion of nitrite accumulation was associated with a fall in inducible NO S protein and an induction of heme oxygenase 1, correlating both dose dependently and temporally, Other proteins examined (cyclooxygenase 2, heme oxygenase 2, heat shock protein 70, and glucose-regulated protei n 78) were unaffected. The data suggest that naturally occurring PPAR agonists can inhibit the inducible NOS enzyme pathway. This inhibition may be mediated by modulation of the stress protein, heme oxygenase 1 . Thus, the generation of eicosanoid breakdown products during inflamm ation may contribute to its eventual resolution by activation of the P PAR system. This system may thus represent a novel target for therapeu tic intervention in inflammatory disease.