Gene expression in distinct regions of the heart

Background Cytochrome P450 mono-oxygenases bring about metabolism of marry drugs, including verapamil, but no information is available on the metabolism of such drugs in the human heart. Methods We investigated the gene expression of major human cytochrome P450 monooxygenases in the various regions of explanted hearts from six patients with dilated cardiomyopathy and one with transposition of the arterial trunk. For comparison we also studied samples of liver and lung from three patients and two samples of normal heart. The biological significance of tissue-specific cytochrome monooxygenase gene expression was further investigated by study of the microsomal metabolism of verapamil in ventricular tissue. Findings mRNA for the cytochromes 1A1, 2B6/7, 2C8-19, 2D6, and 4B1 was predominantly expressed in the right ventricle, the unilateral expression of the 2D6 gene in right-venticular tissue is important because of its key role in the metabolism of beta-blockers. A strong correlation between tissue-specific gene expression and enzyme activity was found; microsomal metabolism of verapamil was confined to the right ventricle. By contrast, cytochrome P450 3A genes (which are the major drug-metabolising enzymes in the liver and the lung) were not expressed in any of the human heart tissues, and mRNA transcripts for epoxide hydrolase, cytochrome P450 2E1, and flavin-containing monooxygenases 2 and 5 were detected in all regions of the human heart and the great vessels. Interpretation These findings show that expression of genes for cytochrome P450 monooxygenases and verapamil metabolism are found predominantly in the right side of the heart. This finding may explain lack of efficacy of certain cardioselective drugs.