H 2 S: Synthesis and functions

H 2 S: Synthesis and functions 1

Signaling gas molecules: O 2, NO and CO Then, H 2 S - Fourth singling gas molecule after O 2, NO and CO 2

Nothing Rotten About Hydrogen Sulfide s Medical Promise Science 320, 1155 (2008) Science fiction? Hydrogen sulfide might someday help people survive trauma and illness in a hibernation-like state. Heart healthy. After a simulated heart attack, the scarred heart of a control mouse (left) contrasts with the ruddy tissue of a mouse treated with hydrogen sulfide (right). Gassing up. As this mouse breathes hydrogen sulfide, its heart rate, metabolic rate, and body temperature will plummet. 3

Hot Spa (Hot Spring) Volcano (Mt. Fuji et al.) Smell H 2 S. Suicide gas Danger for ski and spa. 4

A new gaseous signaling molecule emerges: Cardioprotective role of hydrogen sulfide Copyright 2007 by the National Academy of Sciences Fig. 1. Summary of the physiological actions of hydrogen sulfide (H2S) Lefer, David J. (2007) Proc. Natl. Acad. Sci. USA 104, 17907-17908 6

Hydrogen sulfide mediates the vasoactivity of garlic Proc. Nat. Acad. Sci. USA 104, 17977 (2007) The consumption of garlic is inversely correlated with the progression of cardiovascular disease, although the responsible mechanisms remain unclear. Here we show that human RBCs convert garlic-derived organic polysulfides into hydrogen sulfide (H2S), an endogenous cardioprotective vascular cell signaling molecule. This H2S production, measured in real time by a novel polarographic H2S sensor, is supported by glucosemaintained cytosolic glutathione levels and is to a large extent reliant on reduced thiols in or on the RBC membrane. H2S production from organic polysulfides is facilitated by allyl substituents and by increasing numbers of tethering sulfur atoms. Allyl-substituted polysulfides undergo nucleophilic substitution at the α carbon of the allyl substituent, thereby forming a hydropolysulfide (RSnH), a key intermediate during the formation of H2S. Organic polysulfides (R-Sn-R ; n > 2) also undergo nucleophilic substitution at a sulfur atom, yielding RSnH and H2S. Intact aorta rings, under physiologically relevant oxygen levels, also metabolize garlic-derived organic polysulfides to liberate H2S. The vasoactivity of garlic compounds is synchronous with H2S production, and their potency to mediate relaxation increases with H2S yield, strongly supporting our hypothesis that H2S mediates the vasoactivity of garlic. Our results also suggest that the capacity to 7 produce H2S can be used to standardize garlic dietary supplements.

Proposed model of garlic-induced H2S production and H2S function in the vascular system. Garlicderived organic polysulfides with allyl moieties and more than two sulfur atoms (see Fig. 5) react with exofacial membrane thiols and cross the cell membrane to react with GSH to produce H2S. Glucose is the main energy source of RBCs, supporting glycolysis and pentose phosphate pathway (PPP) reduction of NADP+ to NADPH, a cofactor of GSH reductase (GR), which maintains the intracellular GSH pool. GSH may also participate in transmembrane electron transfer to reduce 8 exofacial thiols (16). H2S production then leads to vasorelaxation via vascular smooth muscle cell KATP-linked hyperpolarization (8).

Hydrogen sulphide and its therapeutic potential Nature Review Drug Discovery 6, 917 (2007). Hydrogen sulphide (H 2 S) is increasingly being recognized as an important signalling molecule in the cardiovascular and nervous systems. The production of H 2 S from L-cysteine is catalysed primarily by two enzymes, cystathionine -lyase and cystathionine -synthase. Evidence is accumulating to demonstrate that inhibitors of H 2 S production or therapeutic H 2 S donor compounds exert significant effects in various animal models of inflammation, reperfusion injury and circulatory shock. H 2 S can also induce a reversible state of hypothermia and suspendedanimation-like state in rodents. This article overviews the physiology and biochemistry of H 2 S, summarizes the effects of H 2 S inhibitors or H 2 S donors in animal models of disease and outlines the potential options for the therapeutic exploitation of H 2 S. 9

Box1. H 2 S biosynthesis 10

Nature Review Mol. Cell Biol. 13, 499 (2012) H 2 S signalling through protein sulfhydration and beyond Hydrogen sulfide (H 2 S) has recently emerged as a mammalian gaseous messenger molecule, akin to nitric oxide and carbon monoxide. H 2 S is predominantly formed from Cys or its derivatives by the enzymes cystathionine β-synthase and cystathionine γ-lyase. One of the mechanisms by which H 2 S signals is by sulfhydration of reactive Cys residues in target proteins. Although analogous to protein nitrosylation, sulfhydration is substantially more prevalent and usually increases the catalytic activity of targeted proteins. Physiological actions of sulfhydration include the regulation of inflammation and endoplasmic reticulum stress signalling as well as of vascular tension. 14

Figure 2. Mechanisms of Hydrogen sulfide-induced Vasodilation. 15

Figure 1 16

Figure 5 Defective H2S CO pathways leading to preeclampsia. Decreased production of hydrogen sulfide (H2S) and carbon monoxide (CO) as a result of downregulation of cystathionine γ-lyase (CSE) and heme oxygenase 1 (HO-1), respectively, lowers the levels of soluble Flt-1 (sflt-1) and soluble endoglin (seng) and increases placental growth factor (PGF) production. These 18 alterations constitute pathogenic factors for endothelial dysfunction (EDF) in preeclampsia.

H2S (SH-) does not interact with Cys SH (S-). 20

Proposed pathways of H2S and NO interaction. Coletta C et al. PNAS 2012;109:9161-9166 26 2012 by National Academy of Sciences

Rounding up the usual suspects in O 2 sensing: CO, NO, and H 2 S! Sci. Signal. Vol. 8 Issue 373 fs10 (2015) Oxygen sensing by the carotid body is essential in vertebrates to adapt to reduced arterial oxygen tension. In this issue of Science Signaling, Yuan et al. report an intricate signaling system to transduce a physical parameter oxygen tension into a biological cellular signal (neural discharge) through changes in the production of carbon monoxide (CO), the second messenger cyclic guanosine monophosphate, and hydrogen sulfide (H 2 S). 27

Protein kinase G regulated production of H2S governs oxygen sensing Sci. Signal Vol. 8 Issue 373 ra37 (2015) Signaling when to breathe When oxygen concentrations in the blood are low, the carotid body triggers breathing reflexes, a response that requires the gasotransmitter hydrogen sulfide, which is generated by the enzyme CSE. When blood is adequately oxygenated, the enzyme HO-2 generates carbon monoxide, which inhibits CSE and decreases neural activity in the carotid body. Yuan et al. identified two cysteine residues that enabled HO-2 to generate carbon monoxide in an oxygen-sensitive manner. They found that carbon monoxide triggered an increase of the second messenger cgmp, which stimulated protein kinase G to phosphorylate CSE, thereby inhibiting this enzyme and suppressing carotid body activity. Reflexes initiated by the carotid body, the principal O2-sensing organ, are critical for maintaining cardiorespiratory homeostasis during hypoxia. O2 sensing by the carotid body requires carbon monoxide (CO) generation by heme oxygenase-2 (HO-2) and hydrogen sulfide (H2S) synthesis by cystathionine-γ-lyase (CSE). We report that O2 stimulated the generation of CO, but not that of H2S, and required two cysteine residues in the heme regulatory motif (Cys265 and Cys282) of HO-2. CO stimulated protein kinase G (PKG) dependent phosphorylation of Ser377 of CSE, inhibiting the production of H2S. Hypoxia decreased the inhibition of CSE by reducing CO generation resulting in increased H2S, which stimulated carotid body neural activity. In carotid bodies from mice lacking HO- 2, compensatory increased abundance of nnos (neuronal nitric oxide synthase) mediated O2 sensing through PKG-dependent regulation of H2S by nitric oxide. These results provide a mechanism for how three gases work in concert in the carotid body to regulate breathing. 29