Influence Of BFGF On IL-1β-induced Cardiac Myocyte Apoptosis And The Express Of The Apoptotic Relevant Genes-An Experimental Study

Nitric oxide, a short-lived free radical-generating gas, is an important signal-transduction molecule in cardiovascular system cell bypes, regulalating such diverse functions as vasomotor tone, neurotransmission, mediation of immune response. In the cardiac myocyte, the major physiological rose of NO appears to involve depression of contractility and electrophysiological stabilization through elevation of intracellular cGMP. A rise in myocardial NO levels may account for the contractile depression observed during sepsis, and in isolated cardiac myocytes following exposure to macrophage-conditrioned medium. No is generated by 2 different enzymes in myocardium, which are macrophage-type, or inducible No synthase(iNOS), and endothelial-type NO synthase(eNOS). Macrophage-derived cytokines have been shown to exert negative inotropic and toxic effects on cardiac myocytes through the transcriptional activation of iNOS and subsequent production of NO iNOS is strongly induced in cardiac myocytes exposed to macrophage-derived cytokines, induding interleukin(IL)-l P tumor necrosis factor(TNF)- a and interferon(INF)- y .However, the mechanisms of cytokine-induced cardiac cardiac myocyte cell death are nuclear. To analyce these mechanisms in detail, we treated cultured neonatal cardiac myocytes in serum-free culture with a combination of the macrophage-derived cytokines interleukin-l P, tumor necrosis factor- a, and interferon- y . IL-i P caused a time-dependent and concentration-dependent -4- induction of cardiac myocyte apoptosis, beginning 72 hours after treatment, as determined by nuclean morphology, DNA internucleosomal cleavage, reflecting caspase activation. Apoptosis was preceded by a 750-fold induction of inducible NO synthase mRNA and the release of large amounts (5-8nmoll i~ g protein)of NO metabolites(NOX) into the medium. Interferon- Y and tumor necrosis factor- a had no independent effects on apoptosis or on NOX production. However, IFN- y accelerates the onset of apoptosis induced by IL-i P ,IL-l P -induced 4- myocyte apoptosis was completely blocked by an NO synthase inhibitor(L-NMMA). IL-I induced myocyte apoptosis through NO production. NO is the effector of cytokine-mediated apoptosis and exerts its effects through several mechanisms. The NO donor S-nitrosoglutathione(GSNO) caused a time-dependent and concentration-dependent induction of cardiac myoeyte apoptosis. Oxidative stress is a potent inducer of apoptosis, and redox state influences both cardiac myocyte signal transduction and gene transcription. The present studies argue in favor of an oxidative, rather than a cOMP-dependent, mechanism for cytokirie/NO-mediated apoptosis in neonatal rat cells. Most importantly, KT5823, a cGMP-dependent protein-i inhibitor, failed to prevent cytokine /NO,mediated apoptosis, while having to independent toxic effects. The inhibition of cytokine-mediated apoptosis by methylene blue can be directly attributed to quenching of NO. Since the degree to which NO forms peroxynitrite is dependent on the availability ox oxygen free radicals, the redox state of individual myocytes may be an important variable in determing the apoptotic response to NO. This possibility is supported by the fact that the antioxidants NAC and DTT were each able...