Cardiomyocyte Resistance to Doxorubicin Mediated by A3 Adenosine Receptor

Recently, we reported that the activation of A3 adenosine receptor (A3R) in newborn cultured cardiomyocytes by highly selective agonist Cl-IB-MECA (2-chloro-N6-(3-iodobenzyl)adenosine-5′-N-methyluronamide) induces protection against the anthracycline antibiotic doxorubicin (DOX) cardiotoxicity. The present study was undertaken to further characterize the cardioprotective action of A3R activation by revealing the structural changes in cardiomyocytes elicited upon exposure to DOX. Morphological observations (ultrastructural and immunocytochemical) indicate that after DOX treatment, the cardiomyocytes undergo destructive alterations, and protective action of A3R is not connected with its anti-apoptotic activity. A3R activation appeared to prevent destructive alterations of cardiomyocyte mitochondria and dissipation of mitochondrial membrane potential. In DOX-treated cardiomyocytes, appearance of disorganized desmin and contractile filaments was related to detrimental alterations in the mitochondrial structure, in particular their position and transmembrane potential. In intact cardiomyocytes, diazoxide, a selective mitochondrial KATP channel opener, induced an increase in ATP synthesis within 15 min of application. Similar effect was obtained by activation of adenosine A1R. However, A3R agonist Cl-IB-MECA did not affect ATP synthesis. Neither A1R agonist CCPA (2-chloro-N6-cyclopentyladenosine) nor diazoxide protected cardiomyocytes from the detrimental effects of DOX. Thus, the opening of mitochondrial KATP channels does not seem to be effective during the slow development of anthracycline cytotoxicity. Our results indicate that DOX increases the activity of lysosomes, which may contribute to cell injury in an “oncotic” manner and also demonstrate the proinflammatory potency of the drug. Furthermore, the decreased acidification of cytoplasm upon activation of A3R may attenuate the ongoing inflammatory response. The present study identifies a novel role for A3R selective agonist Cl-IB-MECA and suggests its importance in regulating cardiac cellular function.