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

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Abstract
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. In the presence of zymosan, exogenous prostaglandin E2 (PGE2) did not exert significant effects on the expression of these three enzymes. In contrast, exogenous leukotriene B4 (LTB4) and LTC4 in the nanomolar range inhibited HO‐1 and iNOS expression, as well as nitrite accumulation. The COX inhibitors indomethacin and NS398 weakly inhibited HO‐1 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‐1, iNOS and nitrite, which were not affected by zileuton. Dexamethasone showed an inhibitory effect on HO‐1 expression induced by zymosan. ZM 230,487 but not zileuton, inhibited the shift due to nuclear factor‐κB (NF‐κB), whereas they did not modify activator protein‐1 (AP‐1) binding. Our results suggest that inhibition of NF‐κB binding could mediate the effects of ZM 230,487 on the modulation of HO‐1 and iNOS protein expression. NOS inhibition by L‐NG‐nitroarginine methyl ester (L‐NAME) or 1400 W abolished nitrite production and strongly reduced HO‐1 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. British Journal of Pharmacology (2001) 133, 920–926; doi:10.1038/sj.bjp.0704145