["Stress proteins" as a cellular endpoint to detect cardiotoxicity in vitro]

Toxic chemical or physical influences induce the de novo formation of protective "stress proteins" in cells. The detection of de novo synthetized "stress proteins" in cultured cardiac myocytes is used as an in vitro assay for the toxicity of pharmaceutics and chemical compounds. First, typical agents inducing "stress protein" formation ("heat shock", H2O2, CdCl2) were examined producing the expected responses in cultured heart cells. Allylamine, a toxin causing myocardial fibrosis in vivo, induces the synthesis of the same "stress protein". We tested pharmaceutics relevant in transplant medicine: Methyl-prednisolone, azathioprine, and cyclosporine A evoke the de novo synthesis of a 30 kDa "stress protein" in a concentration dependent manner. Cardiotoxicity is the main obstacle for the therapeutic use of high dosage anthracycline chemotherapeutics. Doxorubicin and daunomycin inhibit protein synthesis almost completely. The reduction of global protein formation induced by the anthracyclines also inhibits "stress protein" synthesis. Exposition of the cultured cardiac myocytes first to the anthracyclines and afterwards to another toxin (CdCl2) causes a significant inhibition of "stress" protein formation indicating that the cells are less resistant to the second damaging influence. Cardioprotective effects can also be documented by measurement of "stress protein" synthesis. The calcium channel blocking drugs diltiazem, verapemil and nifedipine stimulate the de novo formation of the 30 kDa "stress protein". After a pre-incubation of the cardiac myocytes with the calcium antagonists, the synthesis of "stress proteins" evoked by a toxin (CdCl2) is significantly reduced while total protein synthesis remains unaffected. In conclusion: 1. cardiac myocytes respond to typical inductors of "stress protein" formation and to toxin exposition with the de novo synthesis of these proteins. 2. The "stress protein" formation is concentration dependent. 3. The anthracycline cardiotoxicity is partly due to an inhibition of global protein synthesis diminishing "stress protein" formation. 4. A pre-treatment with calcium antagonists reduces the "stress protein" response while total protein synthesis is unaltered indicating that in the presence of calcium channel blockers less "stress" is working on the heart cells which might be an equivalent of the cardioprotection exerted by the drugs. These results on "stress protein" formation may contribute to the development of an in vitro assay for the determination of cardiotoxicity and cardioprotection in a sensitive and organ specific manner in order to reduce the number of animal experiments required.