5-AMINOLEVULINIC ACID MEDIATES THE IN-VIVO AND IN-VITRO FORMATION OF 8-HYDROXY-2'-DEOXYGUANOSINE IN DNA

5-Aminolevulinic acid (ALA), a heme precursor accumulated in chemical and inborn porphyrias, may behave as an endogenous pro-oxidant. In chronically treated rats (40 mg ALA/kg body wt every 2 days for 15 days) the steady-state level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in liver DNA (94.5 +/- 23.3 residues/10(6) dG) was 4.5 times higher than in non-treated rats (21 +/- 7.5 residues/10(6) dG). In vitro exposure of calf thymus DNA to ALA (0.055 mM) in the presence of 10 mu M Fe2+ caused the formation of 8-OHdG. The amount of 8-OHdG rose from 135 +/- 15 residues/10(6) dG in the control system to 1140 +/- 150 residues/10(6) dG after incubation with 5 mM ALA and 10 mu M Fe2+. Diethylenetriaminepentaacetic acid (5 mM) or mannitol (100 mM) inhibited the formation of 8-OHdG by 63 and 69% respectively, evidencing the involvement of both H2O2 and HO. in this process. Hydrogen peroxide (100 mu M) or Fe2+ alone did not cause DNA oxidation. The present data support the hypothesis that ALA-generated reactive oxygen species can oxidize DNA and may be involved in the development of primary liver cell carcinoma in individuals with symptomatic acute intermittent porphyria.