ROLES OF DT DIAPHORASE IN THE GENOTOXICITY OF NITROAROMATIC COMPOUNDSIN HUMAN AND FISH CELL-LINES

The genotoxicity of nitroaromatic compounds was examined in two cultur ed cell lines, namely, a human hepatoma cell line, HepG2, and a brown bullhead fibroblast cell line, BE. Furthermore, the role of the quinon e-reducing enzyme DT diaphorase [NAD(P)H:(quinone acceptor) oxidoreduc tase] was examined with respect to its influence on the genotoxic effe cts of model nitroaromatic pollutants. The nitroreductive characterist ics of these two cell lines were examined using an acetylated cytochro me c reduction assay for enzymatic nitroreductase activity. Subsequent ly, the influence of DT diaphorase on the genotoxicity of two model ni troaromatics, 4-nitroquinoline 1-oxide (4NQ) and nitrofurantoin (NF), revealed that DT diaphorase was the predominant 4NQ reductase in cytos ols of both cell lines, but played a lesser role in NF reduction in bo th species. Despite these interspecific similarities, results revealed marked qualitative differences between the two species in terms of th e influence of DT diaphorase on quinone-mediated genotoxicity. When pr etreated with the DT diaphorase inhibitor dicoumarol, HepG2 cells exhi bited an exacerbation of genotoxicity in the presence of 4NQ, indicati ng a protective influence of the enzyme. In contrast, 4NQ genotoxicity in BE cells was reduced in the presence of dicoumarol, indicating a d eleterious effect of DT diaphorase activity. Conversely, dicoumarol pr etreatment was moderately protective against NE-mediated genotoxicity in HepG2 cells but exacerbated NF toxicity in Ba cells. This study ill ustrates the manner in which functionally analogous enzymes may have m arkedly distinct influences on xenobiotic toxicity in different cellul ar systems.