The antioxidant effects of a novel iron chelator salicylaldehyde isonicotinoyl hydrazone in the prevention of H2O2 injury in adult cardiomyocytes

Objective: This study was designed to investigate the cardioprotective effe ct of the novel lipophilic iron chelator salicylaldehyde isonicotinoyl hydr azone (SIH) against the oxidative stress exerted by H2O2 through the produc tion of (OH)-O-. radical via the Fenton reaction and to compare them with t hose of the hydrophilic iron chelator deferoxamine (DFO) and the Na+/H+ exc hange inhibitor methylisobutyl amiloride (MIA). Methods: We used long-term cultures of spontaneously beating adult guinea-pig Ventricular cardiomyocyt es developed and characterized previously in our laboratory. We assessed th eir contractile activity by video-recording as well as the underlying Ca tr ansients by Fura 2 fluorescence. In some experiments we also recorded these functional parameters, plus the electrical activity (action potentials) in response to electrical stimulation via suction pipettes, in individual fre shly isolated myocytes. Results: Exposure of the regularly and synchronousl y beating cultured cardiomyocytes to 100 mu M H2O2 initially caused a subst antial prolongation of Ca-i(2+) transients accompanied by an irregular cont ractile activity, then in contractile arrest and a severalfold increase in cytosolic [Ca2+] that occurred, within 30 min of H2O2 application. Similar effects were also observed using freshly isolated cardiomyocytes. The latte r effects were first accompanied by significant prolongation of the action potential duration (APD) with superimposed early afterdepolarizations follo wed by a second phase with a very fast decrease in APD, contractions, as we ll as Ca-i(2+) transients and a third phase of inexcitability, contractile arrest, increased cytoplasmic [Ca2+] and a final contracture. AU these effe cts were irreversible in both types of preparations but they could be fully prevented by a 15-min preincubation with 200 mu M SIH. Similar protective effects were observed with DFO, but in this case a much higher concentratio n had to be used (1 mM) and much longer (2 h) preincubation was needed. By contrast, 5 mu M MIA failed to fully protect the cardiomyocytes, although a significant delay (10 min) of the effects of H2O2 was observed. Conclusion s: The data indicate that SIH provides a very powerful and very fast protec tion against the oxidative stress exerted by H2O2 presumably via the iron-m ediated Fenton reaction producing hydroxyl radical ((OH)-O-.), whereas the protective effect of DFO is hindred by its very slow and rather limited int racellular entry, and the protection that MIA exerts via the inhibition of Na+/H+ exchange against H2O2 much less effective. (C) 2000 Elsevier Science B.V. All rights reserved.