| Abstract: | DNA damage due to NADPH-dependent lipid peroxidation of liposomes was examined using liposomes prepared from lipids, NADPH-cytochrome P-450 reductase and cytochrome P-450 isolated from rat liver microsomes. Plasmid pBR322 DNA was incubated in the reaction mixture for liposomal lipid peroxidation and introduced to Escherichia coli CSR603 (uvrArecA). More of the transforming activity of the DNA was lost as the lipid peroxidation progressed, and this inactivation was dependent on the extent of lipid peroxidation. Single strand breaks occurred in the plasmid DNA. Hydroxyl radical scavengers could not prevent most of the strand breaks or the lipid peroxidation reaction. Chloroform extracts from the reaction mixture of peroxidized microsomes also inactivated the transforming activity of pBR322 DNA but did not cause strand breaks. The 105 000 X g supernatant of the reaction mixture, which contained more than 85% of the thiobarbituric acid-reactive substances, did not inactivate the plasmid DNA. The degradative products of U-14C]arachidonic acid in the liposomes did not bind to DNA. These results led to the conclusion that at least two types of DNA damaging agent are produced during NADPH-dependent microsomal lipid peroxidation. One induces single strand breaks of DNA and another inactivates the plasmid-transforming activity without inducing strand breaks. |
