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

1 Microglial cells up-regulate inducible nitric oxide synthase (iNOS) expre ssion 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 prote in 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 Gries s assay. 3 Exposure to non-toxic doses of tranilast (30-300 mum) leads to a concentr ation-dependent inhibition of IFN-gamma -induced (200 u ml(-1)) iNOS mRNA a nd protein expression. This is paralleled by a suppression of NO-release in to the cell culture medium. 4 Inhibition of IFN-gamma -induced iNOS mRNA expression by tranilast is par alleled by an inhibition of nuclear factor-kappaB (NF-kappaB) activation an d 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 i NOS activity induced by IFN-gamma involves the inhibition of NF-kappaB-depe ndent iNOS mRNA expression.