INFLUENCE OF DT DIAPHORASE ON QUINONE-MEDIATED GENOTOXICITY IN HUMAN AND FISH CELL-LINES

The influence of the quinone-reducing enzyme, DT diaphorase [NAD(P)H: (quinone acceptor) oxidoreductase], on the genotoxicity of quinones wa s examined in two cell lines, namely a human hepatoma cell line, HepG2 and a brown bullhead fibroblast cell line, BE. The quinone-reductive characteristics of these two cell lines were examined using an acetyla ted cytochrome c reduction assay for enzymatic reductase activity. Sub sequently, the influence of DT diaphorase on the genotoxicity of two m odel quinones, menadione (MND) and 9,10-phenanthrenequinone (PQ) was e xamined in an alkaline unwinding assay for DNA single-strand breaks. R esults revealed that DT diaphorase was the predominant quinone reducta se in cytosols of both cell lines, and that levels of specific DT diap horase activity were generally equivalent in the two species. Despite these similarities, results revealed marked qualitative differences be tween the two species in terms of the influence of DT diaphorase on qu inone-mediated genotoxicity. When pretreated with the DT diaphorase in hibitor, dicoumarol, HepG2 cells exhibited a marked exacerbation of ge notoxicity in the presence of either MND or PQ, indicating a protectiv e influence of the enzyme. In contrast, quinone genotoxicity in BE cel ls was not affected by DT diaphorase inhibition, indicating the lack o f a protective effect of DT diaphorase. This study illustrates the man ner in which functionally analogous enzymes may have markedly distinct influences on xenobiotic toxicity in different cellular systems.