INHIBITION OF INDUCIBLE NITRIC-OXIDE SYNTHASE GENE-EXPRESSION AND ENZYME-ACTIVITY BY EPIGALLOCATECHIN GALLATE, A NATURAL PRODUCT FROM GREENTEA

Chronic inflammation has been implicated as the underlying factor in t he pathogenesis of many disorders. In the past decade, inflammation-re lated endogenous production of reactive nitrogen species, similar to o xygen free radicals, has also been suggested as a risk factor for canc er, in addition to the well-studied exogenous nitroso compounds. Epide miological, in vitro, and animal model studies have implicated green t ea to be protective against nitroso compound-induced and inflammation- related cancer. Therefore, we investigated the effect of epigallocatec hin-3-gallate (EGCG), one of the known biologically active catechins c ontained in tea, on the production of nitric oxide (NO.). We have show n previously that EGCG reduces NO. production as measured by nitrite a ccumulation in the culture medium. Expanding on this finding, in this report we show that EGCG may do so by two mechanisms: reduction of ind ucible nitric oxide synthase (iNOS) gene expression and inhibition of enzyme activity. Addition of 1-10 mu M EGCG to lipopolysaccharide-and interferon-gamma-activated mouse peritoneal cells reduced iNOS mRNA ex pression concentration dependently, to 82-14%, as measured by relative reverse transcription-polymerase chain reaction. Addition of 50-750 m u M EGCG, in a concentration dependent manner, inhibited the enzyme ac tivity of iNOS, to 85-14%, and neuronal nitric oxide synthase (nNOS), to 93-56%, as measured by citrulline formation. EGCG competitively inh ibited binding of arginine and tetrahydrobiopterin, and the gallate st ructure is important for this action. (C) 1997 Elsevier Science Inc.