Modulation of haem oxygenase-1 expression by nitric oxide and leukotrienes in zymosan-activated macrophages

1. Phagocytosis of unopsonized zymosan by RAW 264.7 macrophages upregulated protein expression of haem oxygenase-1 (HO-1), inducible nitric oxide synthase (iNOS) and cyclo-oxygenase-2 (COX-2) in a time- and concentration-dependent manner. 2 In the presence of zymosan, exogenous prostaglandin E-2 (PGE(2)) did not exert significant effects on the expression of these three enzymes. In contrast, exogenous leukotriene B-4 (LTB4) and LTC4 in the nanomolar range inhibited HO-I and iNOS expression, as well as nitrite accumulation. 3 The COX inhibitors indomethacin and NS398 weakly inhibited HO-I expression but had no effect on iNOS and COX-2 expression or nitrite. In contrast, the 5-lipoxygenase (5-LO) inhibitor ZM 230,487 significantly decreased HO-T, iNOS and nitrite, which were not affected by zileuton. Dexamethasone showed an inhibitory effect on HO-I expression induced by zymosan. 4 ZM 230,457 but not zileuton, inhibited the shift due to nuclear factor-kappaB (NF-kappaB), whereas they did not modify activator protein-1 (AP-1) binding. Our results suggest that inhibition of NF-kappaB binding could mediate the effects of ZM 230,487 on the modulation of HO-I and iNOS protein expression. 5 NOS inhibition by L-N-G-nitroarginine methyl ester (L-NAME) or 1400 W abolished nitrite production and strongly reduced HO-I expression. These results show an induction of HO-1 protein expression by zymosan phagocytosis in macrophages, with a positive modulatory role for endogenous NO and a negative regulation by exogenous LTs, likely dependent on the reduction of iNOS expression and NO production.