MENADIONE-INDUCED DNA FRAGMENTATION WITHOUT 8-OXO-2'-DEOXYGUANOSINE FORMATION IN ISOLATED RAT HEPATOCYTES

Menadione (2-methyl-1,4-naphthoquinone) induces oxidative stress in ce lls causing perturbations in the cytoplasm as well as nicking of DNA. The mechanisms by which DNA damage occurs are still unclear, but a wid ely discussed issue is whether menadione-generated reactive oxygen spe cies (ROS) directly damage DNA. In the present study, we measured the effect of menadione on formation of 7,8-dihydro-8-oxo-2'-deoxyguanosin e (8-oxodG), an index of oxidative DNA base modifications, and on DNA fragmentation. Isolated hepatocytes from phenobarbital-pretreated rats were exposed to menadione, 25-400 mu M, for 15, 90 or 180 min with or without prior depletion of reduced glutathione (GSH) by diethyl malea te. Menadione caused profound GSH depletion and internucleosomal DNA f ragmentation, which was demonstrated by a prominent fragmentation ladd er on agarose gel electrophoresis. We found no oxidative modification of DNA in terms of increased 8-oxodG formation. In contrast, the posit ive control of sunlamp light increased 8-oxodG 5-fold in rat hepatocyt es. We conclude that oxidative modification of DNA bases is unlikely t o be important in menadione-induced DNA damage.