A major impediment in the cancer chemotherapeutic application of Adriamycin is its cardiotoxicity. Studies have shown that production of reactive oxygen species during its intracellular metabolism is responsible for the cytotoxic effect of Adriamycin. Catalase is a major enzyme involved in detoxification of hydrogen peroxide (H2O2) in mammalian cells. Previous studies have shown that catalase activity per g heart tissue is very low in comparison to other organs, being only about 2% that of liver in the mouse. The other important H202 detoxification enzyme glutathione peroxidase also exhibits lower activity in the heart than in the liver in most strains of mice. This relative deficit in the heart in its ability to dispose of reactive oxygen species may be responsible for the unusual sensitivity of the heart to Adriamycin toxicity. We have recently developed 15 healthy transgenic mouse lines in which catalase activity is constitutively overexpressed specifically in the heart tissue. Each line exhibits a stably elevated catalase activity, ranging from 2- to 500-fold higher than normal. The model is ideal to study the role of catalase in protection against Adriamycin-induced heart damage. Therefore, we propose to use these transgenic mice to test the hypothesis that elevated catalase activity provides protection against Adriamycin cardiotoxicity. Our long term goal is to provide a molecular and biochemical basis for understanding the unusual susceptibility of the heart to Adriamycin.
The specific aims and experimental procedures to be carried out in this study are as follows: (1) To determine whether elevated catalase activity confers cardiac resistance to Adriamycin toxicity, we will select 5 transgenic lines spanning the range of elevated catalase activity from 2 to 200-fold and compare the acute and chronic toxicities of Adriamycin between the catalase-enriched transgenic hearth and controls. We will determine the effects of varying catalase activities on Adriamycin induced morphological and functional alterations and on the lethality of the drug. (2) To investigate possible mechanisms by which elevated catalase activity provides protection against Adriamycin cardiotoxicity, we will determine the effects of varying catalase activities on Adriamycin induced lipid peroxidation in the heart. Furthermore, to determine whether the catalase provides cardioprotection against Adriamycin by detoxifying H2O2 we will use primary cultures of myocytes isolated from catalase enriched transgenic hearts and controls to compare she effects of varying catalase activities on cell injuries induced by Adriamycin and by H202. (3) To estimate the importance of the catalase contribution to cellular defense against Adriamycin cardiotoxicity, we will determine whether catalase can replace the protective role of the glutathione peroxidase/glutathione system in transgenic hearts depleted of glutathione(by buthionine sulfoximine). We will also determine the importance of cell type to which the catalase is expressed and the enzyme~s subcellular localizations in the cardioprotection. These studies should provide a substantial base of information for future clinical investigations, potentially leading to improved use of Adriamycin in cancer chemotherapy.
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