Introduction Sudden cardiac arrest (CA) is a leading cause of death worldwide. Breathing nitric oxide (NO) reduces ischemia-reperfusion (IR) injury in animal models and in patients. The objective of this study was to learn whether inhaled NO improves outcomes after CA and cardiopulmonary resuscitation (CPR). Methods and Results Adult male mice were subjected to potassium-induced CA for 7.5 min whereupon CPR was performed with chest compression and mechanical ventilation. One hour after CPR, mice were extubated and breathed air alone or air supplemented with 40 parts per million (ppm) NO for 23h. Mice that were subjected to CA/CPR and breathed air exhibited a poor 10-day survival rate (4/13), depressed neurological and left ventricular (LV) function, and increased caspase-3 activation and inflammatory cytokine induction in the brain. Magnetic resonance imaging revealed brain regions with marked water diffusion abnormality 24h after CA/CPR in mice that breathed air. Breathing air supplemented with NO for 23h starting 1h after CPR attenuated neurological and LV dysfunction 4 days after CA/CPR and markedly improved 10-day survival rate (11/13, P=0.003 vs Air). The protective effects of inhaled NO on the outcome after CA/CPR were associated with reduced water diffusion abnormality, caspase-3 activation, and cytokine induction in the brain and increased serum NOx levels. Deficiency of the α1 subunit of soluble guanylate cyclase (sGC), a primary target of NO, abrogated the ability of inhaled NO to improve outcomes after CA/CPR. Conclusions These results suggest that NO inhalation after CA and successful CPR improves outcome via sGC-dependent mechanisms.

BackgroundHydrogen sulfide (H2S) exhibits protective effects in various disease models including cerebral ischemia–reperfusion (I/R) injury. Nonetheless, mechanisms and identity of molecules responsible for neuroprotective effects of H2S remain incompletely defined. In the current study, we observed that thiosulfate, an oxidation product of H2S, mediates protective effects of an H2S donor compound sodium sulfide (Na2S) against neuronal I/R injury.Methods and ResultsWe observed that thiosulfate in cell culture medium is not only required but also sufficient to mediate cytoprotective effects of Na2S against oxygen glucose deprivation and reoxygenation of human neuroblastoma cell line (SH‐SY5Y) and murine primary cortical neurons. Systemic administration of sodium thiosulfate (STS) improved survival and neurological function of mice subjected to global cerebral I/R injury. Beneficial effects of STS, as well as Na2S, were associated with marked increase of thiosulfate, but not H2S, in plasma and brain tissues. These results suggest that thiosulfate is a circulating “carrier” molecule of beneficial effects of H2S. Protective effects of thiosulfate were associated with inhibition of caspase‐3 activity by persulfidation at Cys163 in caspase‐3. We discovered that an SLC13 family protein, sodium sulfate cotransporter 2 (SLC13A4, NaS‐2), facilitates transport of thiosulfate, but not sulfide, across the cell membrane, regulating intracellular concentrations and thus mediating cytoprotective effects of Na2S and STS.ConclusionsThe protective effects of H2S are mediated by thiosulfate that is transported across cell membrane by NaS‐2 and exerts antiapoptotic effects via persulfidation of caspase‐3. Given the established safety track record, thiosulfate may be therapeutic against ischemic brain injury.

Background:Hydrogen sulfide (H 2 S) exerts neuroprotective effects, whereas H 2 S may cause neurotoxicity via N-methyl-D-aspartate receptor (NMDAR) activation. Results: A newly-synthesized H 2 S-releasing NMDAR antagonist S-memantine exerted lower neurotoxicity and prevented ischemic neuronal death more markedly than conventional H 2 S-releasing compounds or memantine alone. Conclusion: S-memantine prevents ischemic brain injury without neurotoxicity. Significance: H 2 S-releasing NMDAR antagonists may prevent neurodegeneration of various causes.