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Until recently, hydrogen sulfide (H2S) was exclusively viewed a toxic gas and an environmental hazard, with its toxicity primarily attributed to the inhibition of mitochondrial Complex IV, resulting in a shutdown of mitochondrial electron transport and cellular ATP generation. Work over the last decade established multiple biological regulatory roles of H2S, as an endogenous gaseous transmitter. H2S is produced by cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). In striking contrast to its inhibitory effect on Complex IV, recent studies showed that at lower concentrations, H2S serves as a stimulator of electron transport in mammalian cells, by acting as a mitochondrial electron donor. Endogenous H2S, produced by mitochondrially localized 3-MST, supports basal, physiological cellular bioenergetic functions; the activity of this metabolic support declines with physiological aging. In specialized conditions (calcium overload in vascular smooth muscle, colon cancer cells), CSE and CBS can also associate with the mitochondria; H2S produced by these enzymes, serves as an endogenous stimulator of cellular bioenergetics. The current article overviews the biochemical mechanisms underlying the stimulatory and inhibitory effects of H2S on mitochondrial function and cellular bioenergetics and discusses the implication of these processes for normal cellular physiology. The relevance of H2S biology is also discussed in the context of colonic epithelial cell physiology: colonocytes are exposed to high levels of sulfide produced by enteric bacteria, and serve as a metabolic barrier to limit their entry into the mammalian host, while, at the same time, utilizing it as a metabolic ‘fuel’. Linked Articles This article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue-8

Emerging work demonstrates the dual regulation of mitochondrial function by hydrogen sulfide (H2S), including, at lower concentrations, a stimulatory effect as an electron donor, and, at higher concentrations, an inhibitory effect on cytochrome C oxidase. In the current article, we overview the pathophysiological and therapeutic aspects of these processes. During cellular hypoxia/acidosis, the inhibitory effect of H2S on complex IV is enhanced, which may shift the balance of H2S from protective to deleterious. Several pathophysiological conditions are associated with an overproduction of H2S (e.g. sepsis), while in other disease states H2S levels and H2S bioavailability are reduced and its therapeutic replacement is warranted (e.g. diabetic vascular complications). Moreover, recent studies demonstrate that colorectal cancer cells up-regulate the H2S-producing enzyme cystathionine β-synthase (CBS), and utilize its product, H2S, as a metabolic fuel and tumour-cell survival factor; pharmacological CBS inhibition or genetic CBS silencing suppresses cancer cell bioenergetics and suppresses cell proliferation and cell chemotaxis. In the last chapter of the current article, we overview the field of H2S-induced therapeutic ‘suspended animation’, a concept in which a temporary pharmacological reduction in cell metabolism is achieved, producing a decreased oxygen demand for the experimental therapy of critical illness and/or organ transplantation. Linked Articles This article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue-8

It is well established that exposure of mammalian cells to hydrogen sulfide (H(2)S) suppresses mitochondrial function by inhibiting cytochrome-c oxidase (CcOX; complex IV). However, recent experimental data show that administration of H(2)S to mammalian cells can serve as an electron donor and inorganic source of energy. The aim of our study was to investigate the role of endogenously produced H(2)S in the regulation of mitochondrial electron transport and oxidative phosphorylation in isolated liver mitochondria and in the cultured murine hepatoma cell line Hepa1c1c7. Low concentrations of H(2)S (0.1-1 μM) elicited a significant increase in mitochondrial function, while higher concentrations of H(2)S (3-30 μM) were inhibitory. The positive bioenergetic effect of H(2)S required a basal activity of the Krebs cycle and was most pronounced at intermediate concentrations of succinate. 3-mercaptopyruvate (3-MP), the substrate of the mitochondrial enzyme 3-mercaptopyruvate sulfurtransferase (3-MST) stimulated mitochondrial H(2)S production and enhanced mitochondrial electron transport and cellular bioenergetics at low concentrations (10-100 nM), while at higher concentrations, it inhibited cellular bioenergetics. SiRNA silencing of 3-MST reduced basal bioenergetic parameters and prevented the stimulating effect of 3-MP on mitochondrial bioenergetics. Silencing of sulfide quinone oxidoreductase (SQR) also reduced basal and 3-MP-stimulated bioenergetic parameters. We conclude that an endogenous intramitochondrial H(2)S-producing pathway, governed by 3-MST, complements and balances the bioenergetic role of Krebs cycle-derived electron donors. This pathway may serve a physiological role in the maintenance of mitochondrial electron transport and cellular bioenergetics.

BACKGROUND AND PURPOSE Hydrogen sulphide (H2S), considered as a novel gas transmitter, is produced endogenously in mammalian tissue from L-cysteine by two enzymes, cystathionine β-synthase and cystathionine γ-lyase. Recently, it has been reported that H2S contributes to the local and systemic inflammation in several experimental animal models. We conducted this study to investigate on the signalling involved in H2S-induced inflammation. EXPERIMENTAL APPROACH L-cysteine or sodium hydrogen sulphide (NaHS) was injected into the mouse hind paw and oedema formation was evaluated for 60 min. In order to investigate H2S-induced oedema formation, we used 5-HT and histamine receptor antagonists, and inhibitors of KATP channels or arachidonic acid cascade. Prostaglandin levels were determined in hind paw exudates by radioimmunoassay. Paws injected with L-cysteine or NaHS were examined by histological methods. KEY RESULTS Both NaHS and L-cysteine caused oedema characterized by a fast onset which peaked at 30 min. This oedematogenic action was not associated with histamine or 5-HT release or KATP channel activation. However, oedema formation was significantly inhibited by the inhibition of cyclooxygenases and selective inhibition of phospholipase A2. Prostaglandin levels were significantly increased in exudates of hind paw injected with NaHS or L-cysteine. The histological examination clearly showed an inflammatory state with a loss of tissue organization following NaHS or L-cysteine injection. CONCLUSIONS AND IMPLICATIONS Phospholipase A2 and prostaglandin production are involved in pro-inflammatory effects of H2S in mouse hind paws. The present study contributes to the understanding of the role of L-cysteine/H2S pathway in inflammatory disease.

Introduction: Bidirectional paracrine signaling between cancer cells and fibroblasts in the stroma facilitates tumor progression. We have shown that CRC cells upregulate cystathionine β synthase (CBS), resulting in H2S production, when compared to normal colonic epithelium, and that CRC-derived H2S increases CRC growth, migration, and tumor angiogenesis. The aims of this study are to determine whether H2S can promote CAF proliferation and migration, and stimulate NCF to develop into a CAF-like phenotype. Methods: Human CAF from CRC and NCF were collected under an IRB approved protocol and established in culture. CAF were grown for up to 120h in the presence of vehicle or a slow-release H2S donor, GYY4137. CAFs were allowed to migrate through transwell chambers toward conditioned media (CM) from HCT116 or normal colon mucosal cells (NCM356). Western blots for NCF and CAF were performed to determine CBS expression levels. Results: H2S donor GYY4137 (30-300μM) significantly increased proliferation of CAF, bu...