5-AMINOLEVULINIC ACID INDUCES SINGLE-STRAND BREAKS IN PLASMID PBR322 DNA IN THE PRESENCE OF FE2+ IONS

5-Aminolevulinic acid (ALA), a heme precursor accumulated in chemical and inborn porphyrias, has been demonstrated to produce reactive oxygen species upon metal-catalyzed aerobic oxidation and to cause oxidative damage to proteins, liposomes and subcellular structures. Exposure of plasmid pBR322 DNA to ALA (0.01-3 mM) in the presence of 10 mu M Fe2+ ions causes DNA single-strand breaks (ssb), revealed by agarose gel electrophoresis as an increase in the proportion of the open circular form (75 +/- 7.5% at 3 mM ALA) at the expense of the supercoiled form. Addition of either anti-oxidant enzymes such as superoxide dismutase (10 mu g/ml) and catalase (20 mu g/ml), or a metal chelator (DTPA, 2.5 mM), or a HO. scavenger(mannitol, 100 mM) inhibited the damage (by 30, 45, 55, and 81%, respectively), evidencing the involvement of O-2(-)., H2O2 and HO. (by the Haber-Weiss reaction) in this process. Hydrogen peroxide (100 mu M) or Fe2+ (10 mu M) alone were of little effect on the extent of DNA ssb. The present data may shed light on the correlation reported between primary liver-cell carcinoma and intermittent acute porphyria.