The recent discovery that hydrogen sulfide (H2S) is an endogenously produced gaseous second messenger capable of modulating many physiological processes, much like nitric oxide, prompted us to investigate the potential of H2S as a cardioprotective agent. In the current study, we demonstrate that the delivery of H2S at the time of reperfusion limits infarct size and preserves left ventricular (LV) function in an in vivo model of myocardial ischemiareperfusion (MI-R). This observed cytoprotection is associated with an inhibition of myocardial inflammation and a preservation of both mitochondrial structure and function after I-R injury. Additionally, we show that modulation of endogenously produced H2S by cardiac-specific overexpression of cystathionine ␥-lyase (␣-MHC-CGL-Tg mouse) significantly limits the extent of injury. These findings demonstrate that H2S may be of value in cytoprotection during the evolution of myocardial infarction and that either administration of H2S or the modulation of endogenous production may be of clinical benefit in ischemic disorders.

Rationale: The recent emergence of hydrogen sulfide (H 2 S) as a potent cardioprotective signaling molecule necessitates the elucidation of its cytoprotective mechanisms. Objective: The present study evaluated potential mechanisms of H 2 S-mediated cardioprotection using an in vivo model of pharmacological preconditioning. Methods and Results: H 2 S (100 g/kg) or vehicle was administered to mice via an intravenous injection 24 hours before myocardial ischemia. Treated and untreated mice were then subjected to 45 minutes of myocardial ischemia followed by reperfusion for up to 24 hours, during which time the extent of myocardial infarction was evaluated, circulating troponin I levels were measured, and the degree of oxidative stress was evaluated. In separate studies, myocardial tissue was collected from treated and untreated mice during the early (30 minutes and 2 hours) and late (24 hours) preconditioning periods to evaluate potential cellular targets of H 2 S. Initial studies revealed that H 2 S provided profound protection against ischemic injury as evidenced by significant decreases in infarct size, circulating troponin I levels, and oxidative stress. During the early preconditioning period, H 2 S increased the nuclear localization of Nrf2, a transcription factor that regulates the gene expression of a number of antioxidants and increased the phosphorylation of protein kinase C and STAT-3. During the late preconditioning period, H 2 S increased the expression of antioxidants (heme oxygenase-1 and thioredoxin 1), increased the expression of heat shock protein 90, heat shock protein 70, Bcl-2, Bcl-xL, and cyclooxygenase-2 and also inactivated the proapoptogen Bad. Key Words: hydrogen sulfide Ⅲ cardioprotection Ⅲ antioxidant signaling Ⅲ myocardial infarction Ⅲ Nrf2 H ydrogen sulfide (H 2 S) is an endogenously produced gaseous signaling molecule with a diverse physiological profile. Its production in mammalian systems has been attributed to 2 key enzymes in the cysteine biosynthesis pathway, cystathionine ␤-synthase (CBS) and cystathionine ␥-lyase (CGL). The rate of H 2 S production in tissue homogenates is in the range of 1 to 10 pmol per second per milligram of protein, resulting in low micromolar extracellular concentrations. 1,2 It is at these physiological concentrations that H 2 S is cytoprotective in various models of cellular injury. 3,4 The reported cytoprotective effects of H 2 S are partially related to its ability to neutralize reactive oxygen species (ROS), to inhibit leukocyte-endothelial cell interactions, to promote vascular smooth muscle relaxation, to reduce apoptotic signaling, and to reversibly modulate mitochondrial respiration. 5 Pretreatment with NaHS has been reported to reduce the number and duration of arrhythmias in isolated hearts subjected to global ischemia/reperfusion (I/R) 6 and to enhanced the viability of isolated rat ventricular myocytes exposed to glucose deprivation and 2-deoxyglucose. 4 Recently, Elrod et al 7 reported that the administration of H 2 S at the time of reperfu...

Nitrite (NO2 −) is an intrinsic signaling molecule that is reduced to NO during ischemia and limits apoptosis and cytotoxicity at reperfusion in the mammalian heart, liver, and brain. Although the mechanism of nitrite-mediated cytoprotection is unknown, NO is a mediator of the ischemic preconditioning cell-survival program. Analogous to the temporally distinct acute and delayed ischemic preconditioning cytoprotective phenotypes, we report that both acute and delayed (24 h before ischemia) exposure to physiological concentrations of nitrite, given both systemically or orally, potently limits cardiac and hepatic reperfusion injury. This cytoprotection is associated with increases in mitochondrial oxidative phosphorylation. Remarkably, isolated mitochondria subjected to 30 min of anoxia followed by reoxygenation were directly protected by nitrite administered both in vitro during anoxia or in vivo 24 h before mitochondrial isolation. Mechanistically, nitrite dose-dependently modifies and inhibits complex I by posttranslational S-nitrosation; this dampens electron transfer and effectively reduces reperfusion reactive oxygen species generation and ameliorates oxidative inactivation of complexes II–IV and aconitase, thus preventing mitochondrial permeability transition pore opening and cytochrome c release. These data suggest that nitrite dynamically modulates mitochondrial resilience to reperfusion injury and may represent an effector of the cell-survival program of ischemic preconditioning and the Mediterranean diet.