δ-Aminolevulinic acid (ALA) is a heme precursor accumulated in lead poisoning and acute intermittent porphyria. ALA-induced DNA damage in the presence of metal ions was investigated with a DNA sequencing technique and a high-performance liquid chromatograph equipped with an electrochemical detector. ALA caused damage to DNA fragments obtained from c-Ha-ras proto-oncogene in the presence of Cu(II), but only slightly in the presence of Fe(II). ALA + Cu(II) induced piperidine-labile sites at thymine residues, especially in the 5′-GTC-3′ and 5′-CTG-3′ sequences of double-stranded DNA. Catalase and bathocuproine inhibited DNA damage induced by ALA + Cu(II). Typical ⋅OH scavengers did not inhibit DNA damage, suggesting that active species other than ⋅OH play a more important role in DNA damage. 8-Hydroxy-2′-deoxyguanosine formation by ALA increased with ALA concentration in the presence of Cu(II). Electron spin resonance studies using α-(1-oxy-4-pyridyl)-N-tert-butylnitrone as spin trap showed that carbon-centered radicals were generated during Cu(II)-catalyzed autoxidation of ALA. The major pathway of ALA autoxidation consists of the formation of 4,5-dioxovaleric acid and NH4+. Formation of a pyrazine derivative through ALA autocondensation was also observed. Concomitantly, O2- and H2O2 were generated during the Cu(II)-catalyzed ALA autoxidation. These results indicate that H2O2 reacts with Cu(I) to form a crypto-OH radical, such as the Cu(I)-peroxide complex, causing DNA damage. The possible mechanism for metal-dependent DNA damage by ALA is discussed in relation to the carcinogenicity of lead compounds and the increased frequency of liver cancer in acute intermittent porphyria.

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This work was supported by a research grant from the Fujiwara Foundation of Kyoto University and Grants-in-Aid for Scientific Research Nos. 06557028 and 06454227 from the Ministry of Education, Science, and Culture of Japan.

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