N-acetylcysteine, a cancer chemopreventive agent, causes oxidative damage to cellular and isolated DNA

Although N-acetylcysteine is an antioxidant which has been expected to be a cancer chemopreventive agent, its safety and risk assessment have not been evaluated. N-acetylcysteine increased the amount of 8-oxo-7,8-dihydro-2 'd eoxyguanosine (8-oxodG), a characteristic oxidative DNA lesion, in human le ukemia cell line HL-60, whereas the amount of 8-oxodG in HP100, which is a hydrogen peroxide (H2O2)-resistant cell line derived from HL-60, was not in creased. To clarify the mechanism of cellular DNA damage, we investigated D NA damage and its site specificity induced by N-acetylcysteine, using P-32- labeled DNA fragments obtained from the human p53 tumor suppressor gene and the c-Ha-ras-l protooncogene. N-acetylcysteine induced extensive DNA damag e in the presence of Cu(II), The DNA cleavage was enhanced by piperidine tr eatment, suggesting that N-acetylcysteine plus Cu(II) caused not only deoxy ribose phosphate backbone breakage but also base modification. N-acetylcyst eine plus Cu(II) frequently modified thymine and guanine residues. Bathocup roine, a specific Cu(I) chelator, and catalase inhibited the DNA damage, in dicating the participation of Cu(I) and H2O2 in the DNA damage, Typical hyd roxyl radical scavengers did not inhibit N-acetylcysteine plus Cu(II)-induc ed DNA damage, whereas methional completely inhibited it. These results sug gest that reactive species derived from the reaction of H2O2 with Cu(I) par ticipates in N-acetylcysteine plus Cu(II)-induced DNA damage. The content o f 8-oxodG in calf thymus DNA was increased by N-acetylcysteine in the prese nce of Cu(II), The present study has demonstrated that N-acetylcysteine cou ld induce metal-dependent H2O2 generation and, subsequently, damage to cell ular and isolated DNA, Therefore, it is reasonable to consider that N-acety lcysteine may have the dual function of carcinogenic and anti-carcinogenic potentials. This work requires further studies on safety and risk assessmen t of N-acetylcysteine.