Introduction Cystathionine gamma-lyase (CSE) produces H2S via enzymatic conversion of L-cysteine and plays a critical role in cardiovascular homeostasis. We investigated the effects of genetic modulation of CSE and exogenous H2S therapy in the setting of pressure overload-induced heart failure. Methods and Results Transverse aortic constriction (TAC) was performed in wild-type (WT), CSE knockout (KO), and cardiac specific CSE transgenic (CS-CSE Tg) mice. In addition, C57BL/6J or CSE KO mice received a novel–H2S donor (SG-1002). Mice were followed for 12 weeks using echocardiography. We observed a >60% reduction in myocardial and circulating H2S levels following TAC. CSE KO mice exhibited cardiac dilatation and dysfunction significantly greater than WT mice following TAC and CS-CSE Tg mice maintained cardiac structure and function following TAC. H2S therapy with SG-1002 resulted in cardioprotection during TAC via upregulation of the VEGF-Akt-eNOS-nitric oxide-cGMP pathway with preserved mitochondrial function, attenuated oxidative stress, and increased myocardial vascular density. Conclusions Our results demonstrate that H2S levels are decreased in mice in the setting of heart failure. Moreover, CSE plays a critical role in the preservation of cardiac function in heart failure and oral H2S therapy prevents the transition from compensated to decompensated heart failure in part via upregulation of endothelial nitric oxide synthase (eNOS) and increased NO bioavailability.

Significance: An abundance of experimental evidence suggests that hydrogen sulfide (H 2 S) plays a prominent role in physiology and pathophysiology. Many targets exist for H 2 S therapy. The molecular targets of H 2 S include proteins, enzymes, transcription factors, and membrane ion channels. Recent Advances: Novel H 2 S precursors are being synthesized and discovered that are capable of releasing H 2 S in a slow and sustained manner. This presents a novel and advantageous approach to H 2

SummaryRecent studies demonstrate robust molecular cross talk and signaling between hydrogen sulfide (H2S) and nitric oxide (NO). Heart failure (HF) patients are deficient in both H2S and NO, two molecules that are critical for cardiovascular homeostasis. A phase I clinical trial of a novel H2S prodrug (SG1002) was designed to assess safety and changes in H2S and NO bioavailability in healthy and HF subjects. Healthy subjects (n = 7) and heart failure patients (n = 8) received oral SG1002 treatment in escalating dosages of 200, 400, and 800 mg twice daily for 7 days for each dose. Safety and tolerability were assessed by physical examination, vital signs, and ECG analysis. Plasma samples were collected during a 24‐h period each week for H2S and NO analysis. BNP and glutathione levels were analyzed as markers of cardiac health and redox status. Administration of SG1002 resulted in increased H2S levels in healthy subjects. We also observed increased H2S levels in HF subjects following 400 mg SG1002. Nitrite, a metabolite of NO, was increased in both healthy and HF patients receiving 400 mg and 800 mg SG1002. HF subjects treated with SG1002 displayed stable drug levels over the course of the trial. SG1002 was safe and well tolerated at all doses in both healthy and HF subjects. These data suggest that SG1002 increases blood H2S levels and circulating NO bioavailability. The finding that SG1002 attenuates increases in BNP in HF patients suggests that this novel agent warrants further study in a larger clinical study.

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Significance: Sulfur has a critical role in protein structure/function and redox status/signaling in all living organisms. Although hydrogen sulfide (H 2 S) and sulfane sulfur (SS) are now recognized as central players in physiology and pathophysiology, the full scope and depth of sulfur metabolome's impact on human health and healthy longevity has been vastly underestimated and is only starting to be grasped. Since many pathological conditions have been related to abnormally low levels of H 2 S/SS in blood and/or tissues, and are amenable to treatment by H 2 S supplementation, development of safe and efficacious H 2 S donors deserves to be undertaken with a sense of urgency; these prodrugs also hold the promise of becoming widely used for disease prevention and as antiaging agents. Recent Advances: Supramolecular tuning of the properties of well-known molecules comprising chains of sulfur atoms (diallyl trisulfide [DATS], S 8) was shown to lead to improved donors such as DATS-loaded polymeric nanoparticles and SG1002. Encouraging results in animal models have been obtained with SG1002 in heart failure, atherosclerosis, ischemic damage, and Duchenne muscular dystrophy; with TC-2153 in Alzheimer's disease, schizophrenia, age-related memory decline, fragile X syndrome, and cocaine addiction; and with DATS in brain, colon, gastric, and breast cancer. Critical Issues: Mode-of-action studies on allyl polysulfides, benzyl polysulfides, ajoene, and 12 ringsubstituted organic disulfides and thiosulfonates led several groups of researchers to conclude that the anticancer effect of these compounds is not mediated by H 2 S and is only modulated by reactive oxygen species, and that their central model of action is selective protein S-thiolation. Future Directions: SG1002 is likely to emerge as the H 2 S donor of choice for acquiring knowledge on this gasotransmitter's effects in animal models, on account of its unique ability to efficiently generate H 2 S without byproducts and in a slow and sustained mode that is dose independent and enzyme independent. Efficient tuning of H 2 S donation characteristics of DATS, dibenzyl trisulfide, and other hydrophobic H 2 S prodrugs for both oral and parenteral administration will be achieved not only by conventional structural modification of a lead molecule but also through the new ''supramolecular tuning'' paradigm. Antioxid. Redox Signal. 33, 1010-1045.

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