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A major source of oxidative stress in animals is plant stress metabolites, also termed phytoalexins. The aromatic hydrocarbon-responsive [Ah] gene battery is considered here as a model system in which we can study metabolically coordinated enzymes that respond to phytoalexin-induced oxidative stress. In the mouse, the [Ah] battery comprises at least six genes: two Phase I genes, CYP1A1 and CYP1A2; and four Phase II genes, Nmo-1, Aldh-1, Ugt-1, and Gt-1. All six genes appear to be regulated positively by inducers such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other ligands of the Ah receptor. In the absence of foreign inducer, the control of Nmo-1 gene expression is independent of the control of CYP1A1 and CYP1A2 gene expression. The radiation deletion homozygote c14CoS/c14CoS mouse is lacking about 1.1 centiMorgans of chromosome 7. Although having no detectable CYP1A1 or CYP1A2 activation, the untreated c14CoS/c14CoS mouse exhibits markedly elevated transcripts of the Nmo-1 gene and three growth arrest- and DNA damage-inducible (gadd) genes. These data suggest that the missing region on chromosome 7 in the c14CoS/c14CoS mouse contains a gene(s), which we propose to call Nmo-1n, encoding a trans-acting factor(s) that is a negative effector of the Nmo-1 and gadd genes. The three other [Ah] battery Phase II genes behave similarly to Nmo-1 in the c14CoS/c14CoS mouse. This coordinated response to oxidative stress and DNA damage, by way of the release of a mammalian battery of genes from negative control, bears an interesting resemblance to the SOS response in bacteria.

1,4-Benzoquinone is cytotoxic in V79 Chinese hamster cells and induces gene mutations and micronuclei. The cell-damaging effects of quinones are usually attributed to thiol depletion, oxidation of NAD(P)H, and redox-cycling involving the formation of semiquinone radicals and reactive oxygen species. To elucidate the role of these mechanisms in the genotoxicity of 1,4-benzoquinone, we measured various genotoxic effects, cytotoxicity, and the levels of glutathione, NADPH, NADH, and their oxidized forms all in the same experiment. 1,4-Naphthoquinone, which does not induce gene mutations in V79 cells, was investigated for comparative reasons. The quinones had a similar effect on the levels of cofactors. Total glutathione was depleted, but levels of oxidized glutathione were slightly increased. The levels of NADPH and NADH were reduced at high concentrations of the quinones with a simultaneous increase in the levels of NADP+ and NAD+. Both compounds induced micronuclei, but neither increased the frequency of sister chromatid exchange. Only 1,4-benzoquinone induced gene mutations. This effect was observed at low concentrations, where none of the other parameters studied was affected. When the cells were depleted of glutathione prior to treatment with the quinones, the induction of gene mutations and micronuclei remained virtually unchanged. We conclude that a) induction of micronuclei and glutathione depletion by the two quinones are not linked causally, b) 1,4-benzoquinone induces gene mutations by a mechanism different from oxidative stress and glutathione depletion, and c) glutathione does not fully protect the cells against the genotoxicity of quinones.

A survey of the literature indicates that several chemicals whose reduced metabolites are capable of undergoing redox cycling in biological systems also possess significant teratogenic properties when tested in vivo. We have initiated investigations to determine whether the embryotoxic effects of such chemicals could result from their redox cycling properties and whether redox cycling could be an important mechanism in chemical teratogenesis. In order to obviate the potentially confounding influences of maternal factors, our initial studies have been performed with a whole embryo culture system with redox cycling agents added directly to the culture medium. Several representative redox cycling agents including doxorubicin, paraquat, a series of nitroheterocycles, nitrosofluorene, and diethylstilbestrol (converted metabolically to redox cycling quinone/semiquinone radicals) have been investigated thus far. The nitroheterocycles which bear nitro groups with comparatively high redox potentials produced a striking, asymmetric defect involving primarily the right half of the prosencephalic and mesencephalic regions. The effect was exacerbated under conditions of low O2 tension. Accumulated data to date strongly suggest that reduction of the nitro group is an essential feature in the embryotoxic mechanism. Quinones (doxorubicin, paraquat) and compounds metabolically converted to quinones (diethylstilbestrol) appeared to produce embryotoxic effects via mechanisms not associated with redox cycling. Nitrosofluorene embryotoxicity was markedly exacerbated by changes in both intra- and extracellular glutathione levels, but definitive dependence on a radical-mediated effect or redox cycling was not demonstrated.

The characterization and identification of semiquinone radicals from catechol(amine)s and catechol estrogens by electron spin resonance spectroscopy is addressed. The use of diamagnetic metal ions, especially Mg2+ and Zn2+ ions, to detect transient semiquinone radicals in biological systems and to monitor their reactions, is discussed. A brief account of the identification and reactions of quinones is also presented.

Using the 59Fe uptake method of Lee et al. it was shown that erythropoiesis in female mice was inhibited following IP administration of benzene, hydroquinone, p-benzoquinone, and muconaldehyde. Toluene protected against the effects of benzene. Coadministration of phenol plus either hydroquinone or catechol resulted in greatly increased toxicity. The combination of metabolites most effective in reducing iron uptake was hydroquinone plus muconaldehyde. We have also shown that treating animals with benzene leads to the formation of adducts of bone marrow DNA as measured by the 32P-postlabeling technique.