1-(1-glycero)dodeca-1-3-5-7-9-pentaene and 5-5-dimethyl-1-pyrroline-1-oxide

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 phi 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. Enzymatic peroxidation of FP-12, which has been demonstrated 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 microM 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 guanine molecule rather than the rate of oxygen radical formation. Although free radical formation is known to be stimulated by enzymatic peroxidation of FP-12, the inactivation of phi 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 phi X-174 DNA suggests that the contribution of oxidative DNA damage to the genotoxic potential of FP-12 is only of minor importance.

Topics: Animals; Bacteriophage phi X 174; Cyclic N-Oxides; DNA; DNA Damage; DNA, Single-Stranded; DNA, Viral; Hydroxyl Radical; Mutagens; Oxidation-Reduction; Polyenes; Rats; Superoxide Dismutase

Fecapentaenes form a class of potent fecal mutagens and have been suggested to play an initiating role in colon carcinogenesis. Although several indications have been found that fecapentaenes may induce oxidative DNA damage as well as DNA alkylation, the mechanism of genotoxicity remains unknown. In this study, electron spin resonance spectroscopy with several spin traps has been used in order to determine whether reactive oxygen species can be formed by fecapentaene-12 (FP-12). No specific conditions could be defined that resulted in the direct formation of oxygen radicals from FP-12. However, peroxidation of FP-12 by various peroxidative enzymes has been shown to result in the formation of superoxide adducts of the spin traps alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Addition of superoxide dismutase resulted in a decreased spectrum intensity, whereas the hydroxyl radical scavenger t-butyl alcohol (tBA) appeared of no influence on the signal, both confirming the formation of superoxide. The formation of hydroxyl radical spin adducts has been demonstrated after peroxidation of FP-12 in incubations with the spin-trapping agent 2,2,6,6-tetramethyl-piperidine (TMP). Further, the effects of scavenging hydroxyl radicals with respect to the genotoxic potential of FP-12 in the Salmonella mutagenicity assay has been investigated. It was clearly shown that radical scavenging reduced the number of revertants in Salmonella strains TA100, TA102 and TA104. This mutagenicity-reducing effect was more convincing using both spin traps DMPO and TMP as compared to the effect of hydroxyl radical scavengers tBA and DMSO. Based on these findings, a reaction scheme is proposed that suggests the formation of superoxide after peroxidation of FP-12, which is subsequently converted to hydroxyl radicals by the iron-catalysed Haber-Weiss reaction.

Topics: Benzene Derivatives; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Free Radical Scavengers; Free Radicals; Hydrogen Peroxide; Hydroxides; Hydroxyl Radical; Mutagenicity Tests; Mutagens; Peroxides; Polyenes; Salmonella typhimurium; Spin Labels; tert-Butylhydroperoxide

Fecapentaene-12 (fec-12), excreted in human faeces, is genotoxic to human cells and a known animal carcinogen. The mechanism of its genotoxicity is unknown but may involve direct alkylation and/or free-radical generation. The formation of reactive species during fec-12 aerobic degradation was thus investigated by electron paramagnetic resonance (EPR) and NMR spectroscopic techniques. Oxy- and alkyl-radicals were detected as the 5,5'-dimethyl-1-pyrroline-N-oxide spin-trap adducts at fec-12 concentrations of between 0.1 and 2.0 mM. Under anaerobic conditions no free-radical generation was observed. NMR spectroscopy indicated that fec-12 degraded at least initially into three unsaturated aldehydes. The co-formation of free-radicals and unsaturated aldehydes suggests that fec-12 decomposed aerobically via a process analogous to lipid peroxidation. As both types of species, thus formed, may subsequently interact with DNA to form adducts, fec-12-induced DNA damage was investigated by 32P-postlabelling techniques. Using procedures that detect alkyl-type adducts, a number of putative adducts were detected in fec-12-treated DNA; two of similar mobility were observed in fec-12-treated 2'-deoxyguanosine-3'-monophosphate. Adducts with similar mobility have been detected in acrolein-treated DNA. One adduct with similar mobility was also observed in DNA obtained from normal human fibroblasts treated with fec-12. Using a C-18 ODS column, these putative adducts were eluted in 60-85% methanol, whereas 8-hydroxydeoxyguanosine-3'-monophosphate (8OHdGp) was eluted with 1% acetonitrile. Also unlike these putative adducts, the detection of 8OHdGp required HPLC fractionation prior to 32P-postlabelling. The formation of adducts, possibly aldehyde-related, and free-radical damage suggests that fec-12 genotoxicity may be the result of several different mechanisms, the relative importance of each is as yet unknown. Hydroxyl radicals were also detected during the aerobic decomposition of deca-2,4,6,8-tetraenal, a possible degradation product of fec-12 and a less potent mutagen, suggesting that free-radical generation may have only a minor role in fec-12-induced genotoxicity.

Topics: Autoradiography; Cyclic N-Oxides; Deoxyguanine Nucleotides; DNA; Humans; Mutagens; Phosphorus Radioisotopes; Polyenes; Spin Labels