Is the cancer protective effect correlated with growth inhibitions by green tea (-)-epigallocatechin gallate mediated through an antioxidant mechanism?

The preferential inhibition by (-)-epigallocatechin gallate (EGCg) of growt h of cancer cells (e.g. HeLa) in culture correlates with the ability of EGC g to inhibit a growth-related, cell surface hydroquinone oxidase with prote in disulfide-thiol interchange activity (tNOX) measured as an NADH oxidase and specifically associated with tumorigenically-transformed cells and tiss ues. tNOX is reduced or absent from the surface of non-cancer cells. Variou s oxidizing conditions known to render other antioxidants such as thiols, a scorbate and vitamin E ineffective did not reduce the effectiveness of EGCg in inhibiting either the tNOX activity or the growth of HeLa cells. Only a fter Fenton reaction with iron catalysis in the presence of hydrogen peroxi de was the effectiveness of the EGCg reduced. We conclude that it is unlike ly that the anticancer action of green tea EGCg on the tNOX protein is medi ated through antioxidant properties of EGCg. (C) 2001 Elsevier Science Irel and Ltd. All rights reserved.