© 1994 Oxford University Press
research-article |
Role of oxidative DNA damage in the mechanism of fecapentaene 12 genotoxicity
Department of Health Risk Analysis and Toxicology
1Present address: Department of Natural Sciences, Open University PO Box 2960, 6401 DL Heerlen, The Netherlands
2Department of Oncology, Free University van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
3Department of Human Biology, University of Limburg PO Box 616, 6200 MD Maastricht
Fecapentaene-12 (FP-12), a fecal unsaturated, ether-linked lipid excreted by most human individuals in Western populations, has been found to be a potent genotoxin in mammalian cells. Its mechanism of genotoxicity may be mediated by oxygen radical-induced DNA damage or by direct DNA alkylation, of which the relative importance remains to be determined. In the present study, induction of oxidative genetic damage by FP-12 has been investigated, in combination with the biological inactivation of single-stranded bacteriophage 
X-174 DNA. It was shown that formation of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG), a marker for oxidative DNA damage, is induced dose dependently by FP-12 in 2'-deoxyguanosine (dG). It was demonstrated by application of radical scavengers that production of both the superoxide anion and singlet oxygen may be involved in the induction of 8-oxodG. The effect of OH radical scavenging appeared to be less pronounced. Eniyinatic peroxidation of FP-12, which has been demon strated to stimulate oxygen radical formation, was found to increase the hydroxylation ratio in dG, an effect which was less pronounced in single-stranded DNA and even absent in double-stranded DNA. No induction of 8-oxodG was observed after exposure of human skin fibroblasts to 60 µM FP-12 for 3 h in vitro. It was concluded that the induction of 8-oxodG by FP-12 is determined by the accessibility of the guanlne molecule rather than the rate of oxygen radical formation. Although free radical forma tion is known to be stimulated by en.zymatic peroxidation of FP-12, the inactivation of X-174 DNA spontaneously induced by FP-12 was found to be reduced by application of peroxidases. This furthermore demonstrates that the increased formation of reactive oxygen species by enzymatic peroxidation of FP-12 does not directly relate to increased induction of genotoxic effects. The fact that addition of radical scavengers shows limited effects on the inactivation of X-174 DNA suggests that the contribution of oxidative DNA damage to the genotoxic potential of FP-12 is only of minor importance.