176 - Mitochondria-targeted Hydrogen Sulfide (H2S), but not Untargeted H2S, Reverses Ventricular Arrhythmia at Reperfusion

Abstract

The ‘gasomediator’ hydrogen sulfide has rapidly grown in importance as a potential therapeutic approach for cardiovascular and ischemia-reperfusion conditions including myocardial infarction. Indeed, infarct limitation by postconditioning the heart against myocardial infarction has been demonstrated with either slow-releasing or mitochondrial-targeted H2S donor in vivo such as GYY4137 and AP39 respectively. In this current study we characterised the effects of H2S donors, and their respective control compounds, on reperfusion-induced arrhythmia, an additional form of myocardial reperfusion injury. Inactin®-anaesthetised Sprague Dawley rats underwent 30 minutes regional myocardial ischaemia and 120 minutes reperfusion with all interventions were given 10 minutes before reperfusion. We utilised different H2S donors; two which target mitochondria (AP39 and AP123; 1 µmol/kg) and one non-targeted H2S donor (GYY4137; 266 µmol/kg). We also evaluated the effects of donor controls at the same doses to ensure our observations were to due H2S and not the parent compound or decomposition products formed during/after H2S release. For example, for mitochondrial targeting without H2S-releasing moieties we used AP219 (TPP+-decanoate), for mitochondrial H2S donors alone, anethole dithiolethione (for AP39) and thiohydroxybenzamide (for AP123) and for GYY4137 we used its decomposition product, (4-methoxyphenylphosphon-amidothioate). We also used ischemic preconditioning (IPC) as a positive control. Hemodynamics and electrocardiographic records, obtained using lead II electrodes, were examined to identify ventricular premature beats (VPBs), ventricular tachycardia (VT), sustained VT (>30 seconds) and ventricular fibrillation (VF) during the first 10 minutes of reperfusion in the presence and absence of H2S donors or their control compounds. AP39 significantly (p<0.01; ANOVA with post hoc Dunnett’s test) attenuated the occurrence of VPBs in the early reperfusion by 56% compared to the vehicle group. Moreover, postconditioning with GYY4137 and AP123 reduced the incidence of VPBs by 41% and 31%, respectively, however, this did not achieve statistical significance. AP39 also significantly limited the incidence of reperfusion-triggered sustained VT and VF by 69% and 67%, respectively, compared to the control (each p<0.01; ANOVA). There were no detectable effects for any of the controls on any form of ventricular arrhythmia. In sharp contrast to previously published findings with ‘non-targeted H2S’ by sulfide or GYY4137, the reversal of ventricular arrthymia by AP39 was independent of the salvage kinase pathways since L-NAME (to inhibit nitric oxide synthase), LY294002 (to inhibit phosphoinositide-3 kinases) or ODQ (to inhibit guanylyl cyclase) failed to reverse the effects of AP39 on VT, VF or VPBs. Additionally AP39 did not induce the phosphorylation of eNOS, Akt, GSK-3β or ERK1/2. Presumably this was because H2S delivery was mitochondrial rather than ‘global’. Indeed, AP39 (but not GYY4137) also reversed ‘oxidant’ production and increased calcium retention, potentiating the effect of cyclosporine A, in subsarcolemmal and interfibrillar mitochondria isolated from the left ventricle. Our results show for the first time the potential inhibitory effect of selective mitochondrial delivery of H2S on reperfusion-induced ventricular arrhythmia in vivo and add to the increasing body of evidence for the therapeutic potential of H2S, and mitochondria-targeted H2S, for the treatment of cardiovascular disorders.