N-[3,4-dimethoxycinnamoyl]-anthranilic acid (tranilast) suppresses microglial inducible nitric oxide synthase (iNOS) expression and activity induced by interferon-γ (IFN-γ)

1 Microglial cells up-regulate inducible nitric oxide synthase (iNOS) expression in response to various pro-inflammatory stimuli including interferon-gamma (IFN-gamma), allowing for the release of nitric oxide (NO). Tranilast (N-[3,4-dimethoxycinnamoyl]-anthranilic acid) is an antiallergic compound with suppressive effects on the activation of monocytes. 2 Here, we show that N9 murine microglial cells express iNOS mRNA and protein and release nitri oxide into the culture medium in response to IFN-gamma (200 u ml(-1)) as measured by Northern and Western blot analyses and Griess assay. 3 Exposure to non-toxic doses of tranilast (30-300 mum) leads to a concentration-dependent inhibition of IFN-gamma -induced (200 u ml(-1)) iNOS mRNA and protein expression. This is paralleled by a suppression of NO-release into the cell culture medium. 4 Inhibition of IFN-gamma -induced iNOS mRNA expression by tranilast is paralleled by an inhibition of nuclear factor-kappaB (NF-kappaB) activation and phosphorylation of inhibitory kappaB (I kappaB) as determined by Western blot analyses and NF-kappaB reporter gene assay. 5 These results suggest that tranilast-mediated suppression of microglial iNOS activity induced by IFN-gamma involves the inhibition of NF-kappaB-dependent iNOS mRNA expression.