Differences between cysteine and homocysteine in the induction of deoxyribose degradation and DNA damage

The effect of two naturally occurring thiols, such as cysteine and homocyst eine, has been examined for their ability to induce deoxyribose degradation and DNA. damage. Copper(II) ions have been added to incubation mixtures an d oxygen consumption measurements have been performed in order to correlate the observed damaging effects with the rate of metal catalyzed thiol oxida tion. Ascorbic acid plus copper has been used as a positive control of deox yribose and DNA oxidation due to reactive oxygen species. Cysteine or homoc ysteine in the presence of copper ions induce the degradation of deoxyribos e and the yield of 8-hydroxy-2'-deoxyguanosine (8-OHdG), although important differences are observed between the two thiols tested, homocysteine being less reactive than cysteine. DNA cleavage is induced by cysteine in the pr esence of copper(II) ions but not by homocysteine. Catalase and thiourea, b ut not superoxide dismutase (SOD), were shown to inhibit the damaging effec ts of cysteine on deoxyribose or DNA suggesting that H2O2 and (OH)-O-. radi cals are responsible for the observed induced damage. The results indicate that there are differences between the damaging effects of the two thiols t ested towards deoxyribose and DNA damage. The pathophysiological importance will be discussed. (C) 2001 Elsevier Science Inc.