Toxic Effects of Free and DNA‐linked Daunorubicin on Isolated Rat Cardiac Myocytes

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Abstract
Isolated cardiac myocytes from adult rats were used as a model to study the cardiotoxicity of free and DNA‐linked daunorubicin. The toxic effects on the myocytes were evaluated by studying morphological changes, trypan blue exclusion and cell membrane permeability to NADH, as determined by LDH‐activity. At a concentration of 100 μM daunorubicin caused an increased plasma membrane permeability within 30 min. Using light microscopy, the myocytic injury induced by daunorubicin could be distinguished from that induced by anoxia or elevated pH. In contrast to the effect of the free drug, no toxic effects could be demonstrated after incubation with DNA‐linked daunorubicin (100 μM) for 5 hours. The higher toxicity of the free drug was related to a much higher intracellular accumulation of daunorubicin. No fluorescent metabolites of daunorubicin could be detected in the myocardial cells. Daunorubicin did not induce lipid peroxidation, as judged by the absence of malondialdehyde production and evolution of ethane. It is concluded that daunorubicin exerts toxic effects on rat cardiac myocytes by mechanisms that do not involve lipid peroxidation. Isolated cardiac cells from adult rats seem to be a useful model for the further study of such mehanisms.