DNA CLEAVAGE INDUCED BY GLYCATION OF CU,ZN-SUPEROXIDE DISMUTASE

Human Cu,Zn-superoxide dismutase (Cu,Zn-SOD) undergoes site-specific a nd random fragmentation by non-enzymic glycosylation (glycation). Rele ased Cu2+ from the glycated Cu,Zn-SOD probably facilitates a Fenton re action to convert H2O2 into hydroxy radical, which then participates i n the non-specific fragmentation [Ookawara et al. (1992) J. Biol. Chem . 267, 18505-18510]. In the present study, we investigated the effects of glycated Cu,Zn-SOD on cloned DNA fragments and nuclear DNA and ana lysed the formation of 8-hydroxydeoxyguanosine (8-OH-dG). Incubation o f cloned DNA fragments with Cu,Zn-SOD and reducing sugars resulted in cleavage of the DNA. The extent of the cleavage corresponded to the re ducing capacity of the sugar. Metal-chelating reagents, EDTA and batho cuproine, and an H2O2 scavenger, catalase, inhibited the DNA cleavage. Hydroxy radical scavengers and aminoguanidine, an inhibitor of glycat ion, also inhibited the reaction. Moreover, the glycation of Cu,Zn-SOD caused the substantial formation of 8-OH-dG in DNA. When isolated nuc lei were incubated with CuCl2, plus H2O2, nuclear DNA cleavage was obs erved. Incubation of isolated nuclei with Cu,Zn-SOD that had been pre- incubated with glucose also resulted in nuclear DNA cleavage. These re sults suggest that hydroxy radical is produced through a Fenton reacti on by Cu2+ and H2O2 released from the glycated Cu,Zn-SOD, and particip ates in nuclear DNA cleavage. This mechanism may partly explain the de terioration of organs under diabetic conditions.