Lipid peroxides as endogenous oxidants forming 8-oxo-guanosine and lipid-soluble antioxidants as suppressing agents

抄録

The oxidation of guanosine to 8-oxo-2'-deoxyguanosine (8-oxo-dG) in DNA is closely associated with induction of various diseases, but the endogenous oxidant species involved remains unclear. Hydrogen peroxides (H₂O₂) have been considered to be the oxidant, while lipid peroxides are another possible oxidant because generated easily in bio-membranes surrounding DNA. The oxidant potency was compared between lipid peroxides and H₂O₂. Linoleic acid hydroperoxides (LOOH) formed 8-oxo-dG at a higher level than H₂O₂ in guanosine or double-stranded DNA. In the presence of a physiological concentration of Fe²⁺ to produce hydroxyl radicals, LOOH was also a stronger oxidant. In a lipid micelle, LOOH markedly produced 8-oxo-dG at a concentration one-tenth of that of H₂O₂. Upon adding to rat hepatic mitochondria, phosphatidylcholine hydroperoxides produced 8-oxo-dG abundantly. Employing HepG2 cells after pretreated with glutathione peroxidase inhibitor, LOOH formed 8-oxo-dG more abundantly than H₂O₂. Then, antioxidants to suppress the 8-oxo-dG formation were examined, when the nuclei of pre-incubated HepG2 with antioxidants were exposed to LOOH. Water-soluble ascorbic acid, trolox, and N-acetyl cysteine showed no or weak antioxidant potency, while lipid-soluble 2,6-dipalmitoyl ascorbic acid, α-tocopherol, and lipid-soluble phytochemicals exhibited stronger potency. The present study shows preferential formation of 8-oxo-dG upon LOOH and the inhibition by lipid-soluble antioxidants.