Molecular mechanism of the short-term cardiotoxicity caused by 2 ',3 '-dideoxycytidine (ddC): Modulation of reactive oxygen species levels and ADP-ribosylation reactions

The short-term cardiac side effects of 2',3'-dideoxycytidine (ddC, zalcitab ine) were studied in rats in order to understand the biochemical events con tributing to the development of ddC-induced cardiomyopathy. In developing a nimals, ddC treatment provoked a surprisingly rapid appearance of cardiac m alfunctions characterized by prolonged RR, PR, and QT intervals and J point depression. The energy metabolism in the heart was compromised, characteri zed by a decreased creatine phosphate/creatine ratio (from 2.05 normal valu e to 0.75) and a decreased free ATP/ADP ratio (from 332 normal value to 121 ). The activity of respiratory complexes (NADH: cytochrome c oxidoreductase and cytochrome oxidase) also decreased significantly. Southern blot and po lymerase chain reaction analysis did not show deletions or a decrease in th e quantity of mitochondrial DNA (mtDNA) deriving from ddC-treated rat heart s, indicating that under our experimental conditions, ddC-induced heart abn ormalities were not the direct consequence of mtDNA-related damage. The ddC treatment of rats significantly increased the formation of reactive oxygen species (ROS) in heart and skeletal muscle as determined by the oxidation of non-fluorescent dihydrorhodamine123 to fluorescent rhodamine123 and the oxidation of cellular proteins determined from protein carbonyl content. An activation of the nuclear poly-(ADP-ribose) polymerase (EC 2.4.2.30) and a n increase in the mono-ADP-ribosylation of glucose-regulated protein and de smin were observed in the cardiac tissue from ddC-treated animals. A decrea se in the quantity of heat shock protein (HSP)70s was also detected, while the level of HSP25 and HSP60 remained unchanged. Surprisingly, ddC treatmen t induced a skeletal muscle-specific decrease in the quantity of three prot eins, one of which was identified by N-terminal sequencing as myoglobin, an d another by tandem mass spectrometer sequencing as triosephosphate isomera se (EC 5.3.1.1). These data show that the short term cardiotoxicity of ddC is partially based on ROS-mediated signalling through poly- and mono-ADP-ri bosylation reactions and depression of HSP70 levels, whose processes repres ent a new mtDNA independent mechanism for ddC-induced cell damage. (C) 1999 Elsevier Science Inc.