The peroxynitrite evoked contractile depression can be partially reversed by antioxidants in human cardiomyocytes

In this study, we aimed to determine the contribution of peroxynitrite‐dependent sulfhydryl group (SH) oxidation to the contractile dysfunction in permeabilized left ventricular human cardiomyocytes using a comparative approach with the SH‐oxidant 2,2′‐dithiodipyridine (DTDP). Additionally, different antioxidants: dithiothreitol (DTT), reduced glutathione (GSH) or N‐acetyl‐L‐cysteine (NAC) were employed to test reversibility. Maximal isometric active force production ( F o ) and the maximal turnover rate of the cross‐bridge cycle ( k tr,max ) illustrated cardiomyocyte mechanics. SH oxidation was monitored by a semi‐quantitative Ellman’s assay and by SH‐specific protein biotinylation. Both peroxynitrite and DTDP diminished F o in a concentration‐dependent manner (EC 50,peroxynitrite = 49 μM; EC 50,DTDP = 2.75 mM). However, k tr,max was decreased only by 2.5‐mM DTDP, but not by 50 μM peroxynitrite. The diminution of F o to zero by DTDP was paralleled by the complete elimination of the free SH groups, while the peroxynitrite‐induced maximal reduction in free SH groups was only to 58 ± 6% of the control (100%). The diminutions in F o and free SH groups evoked by 2.5‐mM DTDP were completely reverted by DTT. In contrast, DTT induced only a partial restoration in F o (Δ F o, :∼13%; P < 0.05) despite full reversion in protein SH content after 50 μM peroxynitrite. Although, NAC or DTT were equally effective on F o after peroxynitrite exposures, NAC or GSH did not restore F o or k tr,max after DTDP treatments. Our results revealed that the peroxynitrite‐evoked cardiomyocyte dysfunction has a small, but significant component resulting from reversible SH oxidation, and thereby illustrated the potential benefit of antioxidants during cardiac pathologies with excess peroxynitrite production.