Hydrogen sulphide is a mediator of carrageenan-induced hindpaw oedema in the rat

Hydrogen sulfide and inflammation: the good, the bad, the ugly and the promising

Hydrogen sulfide is rapidly gaining ground as a physiological mediator of inflammation, but there is no clear consensus as to its precise role in inflammatory signaling. This article discusses the disparate anti-inflammatory ('the good') and proinflammatory ('the bad') effects of endogenous and pharmacological H(2)S in disparate animal model and cell culture systems. We also discuss 'the ugly', such as problems of using wholly specific inhibitors of enzymatic H(2)S synthesis, and the use of pharmacological donor compounds, which release H(2)S too quickly to be physiologically representative of endogenous H(2)S synthesis. Furthermore, recently developed slow-release H(2)S donors, which offer a more physiological approach to understanding the complex role of H(2)S in acute and chronic inflammation ('the promising') are discussed.

Physiological implications of hydrogen sulfide: a whiff exploration that blossomed

The important life-supporting role of hydrogen sulfide (H(2)S) has evolved from bacteria to plants, invertebrates, vertebrates, and finally to mammals. Over the centuries, however, H(2)S had only been known for its toxicity and environmental hazard. Physiological importance of H(2)S has been appreciated for about a decade. It started by the discovery of endogenous H(2)S production in mammalian cells and gained momentum by typifying this gasotransmitter with a variety of physiological functions. The H(2)S-catalyzing enzymes are differentially expressed in cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems and affect the functions of these systems through the production of H(2)S. The physiological functions of H(2)S are mediated by different molecular targets, such as different ion channels and signaling proteins. Alternations of H(2)S metabolism lead to an array of pathological disturbances in the form of hypertension, atherosclerosis, heart failure, diabetes, cirrhosis, inflammation, sepsis, neurodegenerative disease, erectile dysfunction, and asthma, to name a few. Many new technologies have been developed to detect endogenous H(2)S production, and novel H(2)S-delivery compounds have been invented to aid therapeutic intervention of diseases related to abnormal H(2)S metabolism. While acknowledging the challenges ahead, research on H(2)S physiology and medicine is entering an exponential exploration era.

H(2)S functions as a nociceptive messenger through transient receptor potential ankyrin 1 (TRPA1) activation

Hydrogen sulfide (H(2)S), an endogenous gasotransmitter, modulates various biological functions, including nociception. It is known that H(2)S causes neurogenic inflammation and elicits hyperalgesia. Here we show that H(2)S activates mouse transient receptor potential ankyrin 1 (TRPA1) channels and elicits acute pain, using TRPA1-gene deficient mice (TRPA1(-/-)) and heterologous expression system. In wild-type mouse sensory neurons, H(2)S increased the intracellular Ca(2+) concentration ([Ca(2+)](i)), which was inhibited by ruthenium red (a nonselective TRP channel blocker) and HC-030031 (a TRPA1 blocker). H(2)S-responsive neurons highly corresponded to TRPA1 agonist-sensitive ones. [Ca(2+)](i) responses to H(2)S were observed in neurons from transient receptor potential vanilloid 1 (TRPV1(-/-)) mice but not from TRPA1(-/-) mice. Heterologously expressed mouse TRPA1, but not mouse TRPV1, was activated by H(2)S. H(2)S-induced [Ca(2+)](i) responses were inhibited by dithiothreitol, a reducing agent. Analyses of the TRPA1 mutant channel revealed that two cysteine residues located in the N-terminal internal domain were responsible for the activation by H(2)S. Intraplantar injection of H(2)S into the mouse hind paw caused acute pain which was significantly less in TRPA1(-/-) mice. The [Ca(2+)](i) responses to H(2)S in sensory neurons and in heterologously expressed channels, and pain-related behavior induced by H(2)S were enhanced under acidic conditions. These results suggest that H(2)S functions as a nociceptive messenger through the activation of TRPA1 channels. TRPA1 may be a therapeutic target for H(2)S-related algesic action, especially under inflammatory conditions.

Transplant tolerance is associated with reduced expression of cystathionine-γ-lyase that controls IL-12 production by dendritic cells and TH-1 immune responses

Antigen-activated T lymphocytes undergo an immune or tolerogeneic response in part according to the activation status of their antigen-presenting cells. However, factors controlling the activation of antigen-presenting cells are not fully understood. In this study, we demonstrate that immune tolerance after organ allotransplantation in the rat is associated with a repressed intragraft expression of several enzymes of the trans-sulfuration pathway, including cystathionine γ-lyase (CSE). The pharmacologic blockade of CSE with propargylglycine delayed heart allograft rejection and abrogated type IV hypersensitivity but did not modify antibody responses, and was associated with a selective inhibition of the TH-1 type factors T-bet, IL-12, and IFN-γ. IL-12 repression could also be induced by propargylglycine in vitro in monocytes and dendritic cells (DCs), a phenomenon not mediated by changes to nuclear factor-κ B or hydrogen sulfide but that occurred together with a modulation of intracellular cysteine content. Intracellular cysteine levels were predominantly controlled in DCs by CSE activity, together with extracellular import via the Xc− transporter. Our results indicate that CSE plays a critical role in regulating IL-12 in monocytes and DCs and is down-modulated in transplant tolerance, presumably participating in the maintenance of the tolerant state.

Effects of S-propargyl-cysteine (SPRC) in caerulein-induced acute pancreatitis in mice

Hydrogen sulfide (H₂S), a novel gaseous messenger, is synthesized endogenously from L-cysteine by two pyridoxal-5′-phosphate-dependent enzymes, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). S-propargyl-cysteine (SPRC) is a slow H₂S releasing drug that provides cysteine, a substrate of CSE. The present study was aimed to investigate the effects of SPRC in an in vivo model of acute pancreatitis (AP) in mice. AP was induced in mice by hourly caerulein injections (50 µg/kg) for 10 hours. Mice were treated with SPRC (10 mg/kg) or vehicle (distilled water). SPRC was administered either 12 h before or 3 h before the induction of pancreatitis. Mice were sacrificed 1 h after the last caerulein injection. Blood, pancreas and lung tissues were collected and processed to measure the plasma amylase, plasma H₂S, myeloperoxidase (MPO) activities and cytokine levels in pancreas and lung. The results revealed that significant reduction of inflammation, both in pancreas and lung was associated with SPRC given 3 h prior to the induction of AP. Furthermore, the beneficial effects of SPRC were associated with reduction of pancreatic and pulmonary pro-inflammatory cytokines and increase of anti-inflammatory cytokine. SPRC administered 12 h before AP induction did not cause significant improvement in pancreatic and lung inflammation. Plasma H₂S concentration showed significant difference in H₂S levels between control, vehicle and SPRC (administered 3 h before AP) treatment groups. In conclusion, these data provide evidence for protective effects of SPRC in AP possibly by virtue of its slow release of endogenous H₂S.

Hydrogen sulfide: a gasotransmitter of clinical relevance

Though the existence of hydrogen sulfide (H2S) in biological tissues has been known for over 300 years, it is the most recently appreciated of the gasotransmitters as a physiologic messenger molecule. The enzymes cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS) had long been speculated to generate H2S, and inhibitors of these enzymes had been employed to characterize influences of H2S in various organs. Definitive evidence that H2S is a physiologic regulator came with the development of mice with targeted deletion of CSE and CBS. Best characterized is the role of H2S, formed by CSE, as an endothelial derived relaxing factor that normally regulates blood pressure by acting through ATP-sensitive potassium channels. H2S participates in various phases of the inflammatory process, predominantly exerting anti-inflammatory actions. Currently, the most advanced efforts to develop therapeutic agents involve the combination of H2S donors with non-steroidal anti-inflammatory drugs (NSAIDs). The H2S releasing moiety provides cytoprotection to gastric mucosa normally adversely affected by NSAIDs while the combination of H2S and inhibition of prostaglandin synthesis may afford synergistic anti-inflammatory influences.

Effect of endogenous hydrogen sulfide inhibition on structural and functional renal disturbances induced by gentamicin

Animal models of gentamicin nephrotoxicity present acute tubular necrosis associated with inflammation, which can contribute to intensify the renal damage. Hydrogen sulfide (H₂S) is a signaling molecule involved in inflammation. We evaluated the effect of DL-propargylglycine (PAG), an inhibitor of endogenous H₂S formation, on the renal damage induced by gentamicin. Male Wistar rats (N = 8) were injected with 40 mg/kg gentamicin (im) twice a day for 9 days, some of them also received PAG (N = 8, 10 mg·kg⁻¹·day⁻¹, ip). Control rats (N = 6) were treated with saline or PAG only (N = 4). Twenty-four-hour urine samples were collected one day after the end of these treatments, blood samples were collected, the animals were sacrificed, and the kidneys were removed for quantification of H₂S formation and histological and immunohistochemical studies. Gentamicin-treated rats presented higher sodium and potassium fractional excretion, increased plasma creatinine [4.06 (3.00; 5.87) mg%] and urea levels, a greater number of macrophages/monocytes, and a higher score for tubular interstitial lesions [3.50 (3.00; 4.00)] in the renal cortex. These changes were associated with increased H₂S formation in the kidneys from gentamicin-treated rats (230.60 ± 38.62 µg·mg protein⁻¹·h⁻¹) compared to control (21.12 ± 1.63) and PAG (11.44 ± 3.08). Treatment with PAG reduced this increase (171.60 ± 18.34), the disturbances in plasma creatinine levels [2.20 (1.92; 4.60) mg%], macrophage infiltration, and score for tubular interstitial lesions [2.00 (2.00; 3.00)]. However, PAG did not interfere with the increase in fractional sodium excretion provoked by gentamicin. The protective effect of PAG on gentamicin nephrotoxicity was related, at least in part, to decreased H₂S formation.

Hydrogen sulfide is an endogenous potentiator of T cell activation

H(2)S is an endogenous signaling molecule that may act via protein sulfhydrylation to regulate various physiological functions. H(2)S is also a byproduct of dietary sulfate metabolism by gut bacteria. Inflammatory bowel diseases such as ulcerative colitis are associated with an increase in the colonization of the intestine by sulfate reducing bacteria along with an increase in H(2)S production. Consistent with its increased production, H(2)S is implicated as a mediator of ulcerative colitis both in its genesis or maintenance. As T cells are well established mediators of inflammatory bowel disease, we investigated the effect of H(2)S exposure on T cell activation. Using primary mouse T lymphocytes (CD3+), OT-II CD4+ T cells, and the human Jurkat T cell line, we show that physiological levels of H(2)S potentiate TCR-induced activation. Nanomolar levels of H(2)S (50-500 nM) enhance T cell activation assessed by CD69 expression, interleukin-2 expression, and CD25 levels. Exposure of T cells to H(2)S dose-dependently enhances TCR-stimulated proliferation with a maximum at 300 nM (30% increase, p < 0.01). Furthermore, activation increases the capacity of T cells to make H(2)S via increased expression of cystathionine γ-lyase and cystathionine β-synthase. Disrupting this response by silencing these H(2)S producing enzymes impairs T cell activation, and proliferation and can be rescued by the addition of 300 nM H(2)S. Thus, H(2)S represents a novel autocrine immunomodulatory molecule in T cells.

Hydrogen sulfide and neurogenic inflammation in polymicrobial sepsis: involvement of substance P and ERK-NF-κB signaling

Hydrogen sulfide (H₂S) has been shown to induce transient receptor potential vanilloid 1 (TRPV1)-mediated neurogenic inflammation in polymicrobial sepsis. However, endogenous neural factors that modulate this event and the molecular mechanism by which this occurs remain unclear. Therefore, this study tested the hypothesis that whether substance P (SP) is one important neural element that implicates in H₂S-induced neurogenic inflammation in sepsis in a TRPV1-dependent manner, and if so, whether H₂S regulates this response through activation of the extracellular signal-regulated kinase-nuclear factor-κB (ERK-NF-κB) pathway. Male Swiss mice were subjected to cecal ligation and puncture (CLP)-induced sepsis and treated with TRPV1 antagonist capsazepine 30 minutes before CLP. DL-propargylglycine (PAG), an inhibitor of H₂S formation, was administrated 1 hour before or 1 hour after sepsis, whereas sodium hydrosulfide (NaHS), an H₂S donor, was given at the same time as CLP. Capsazepine significantly attenuated H₂S-induced SP production, inflammatory cytokines, chemokines, and adhesion molecules levels, and protected against lung and liver dysfunction in sepsis. In the absence of H₂S, capsazepine caused no significant changes to the PAG-mediated attenuation of lung and plasma SP levels, sepsis-associated systemic inflammatory response and multiple organ dysfunction. In addition, capsazepine greatly inhibited phosphorylation of ERK_1/2 and inhibitory κBα, concurrent with suppression of NF-κB activation even in the presence of NaHS. Furthermore, capsazepine had no effect on PAG-mediated abrogation of these levels in sepsis. Taken together, the present findings show that H₂S regulates TRPV1-mediated neurogenic inflammation in polymicrobial sepsis through enhancement of SP production and activation of the ERK-NF-κB pathway.

Role of endogenous hydrogen sulfide on renal damage induced by adriamycin injection

A single injection of adriamycin (ADR) induces marked and persistent proteinuria in rats that progress to glomerular and tubulointerstitial lesions. It has been shown that ADR-induced nephrotoxicity is mediated, at least in part, by oxidative stress that lead to inflammation. Endogenous hydrogen sulfide (H₂S) is synthesized from L-cysteine and is an important signaling molecule in inflammation. This study evaluates the effect of DL-propargylglycine (PAG), an inhibitor of endogenous H₂S formation, on the evolution of renal damage induced by ADR. The rats were injected i.p. with 0.15 M NaCl or PAG (50 mg/kg) 2 h after ADR injection (3.5 mg/kg). Control rats were injected with 0.15 M NaCl or PAG only. Twenty hours urine samples were collected for albuminuria and creatinine measurements on days 1 and 14 after saline or ADR injections and on days 2 and 15 blood samples were collected to measure plasma creatinine, then the rats were killed. The kidneys were removed for H₂S formation evaluation, renal lipid peroxidation and glutathione levels, and histological and immunohistochemical analysis. On day 2 after ADR injection the rats presented increase in oxidative stress associated with neutrophils and macrophages influx in renal tissue. On day 15 the rats also presented increased desmin expression at glomerular edge and vimentin in cortical tubulointerstitium, as well as albuminuria. All these alterations were reduced by PAG injection. The protective effect of PAG on ADR nephrotoxicity was associated to decreased H₂S formation and to restriction of oxidative stress and inflammation in the renal cortex.

Endogenous hydrogen sulfide is an anti-inflammatory molecule in dextran sodium sulfate-induced colitis in mice

BACKGROUND

Endogenous hydrogen sulfide (H(2)S) is increasingly being recognized as an important gaseous physiological mediator. Accumulating evidence shows the functions of H(2)S in various models of disease, but rarely in colitis. In this study, we investigated the role of endogenous H(2)S in a dextran sodium sulfate (DSS)-induced colitis model.

METHODS

Acute colitis was induced using 8% DSS in male BALB/c mice. The mRNA expression of cystathionine γ-lyase (CSE), the primary synthetase of H(2)S in the gastrointestinal tract, and cystathionine-β-synthetase (CBS) was measured by real-time RT-PCR. The amount of H(2)S in the colonic mucosa was measured by gas chromatography. Colitis severity was evaluated clinically, histologically, and biochemically under the condition of co-treatment with DL-propargylglycine (PAG), an irreversible CSE inhibitor, and sodium sulfide (Na(2)S), an H(2)S donor.

RESULTS

The mRNA expression levels of CSE and CBS, and the H(2)S content in the colonic mucosa were increased with time after DSS administration. The disease activity index, which was determined by weight loss, stool consistency, and intestinal bleeding, increased after DSS administration. PAG significantly enhanced the increase in the disease activity index scores. PAG also significantly increased tissue-associated myeloperoxidase activity and thiobarbituric acid-reactive substances in the inflamed mucosa. Moreover, Na(2)S counteracted these effects of PAG.

CONCLUSIONS

Taken together, the results indicated that the inhibition of endogenous H(2)S generation caused the deterioration of DSS-induced colitis. We conclude that physiological H(2)S might act as an anti-inflammatory molecule in colitis.

Preprotachykinin-A gene deletion regulates hydrogen sulfide-induced toll-like receptor 4 signaling pathway in cerulein-treated pancreatic acinar cells

OBJECTIVE

This study aimed to determine the effect of hydrogen sulfide (H2S) on Toll-like receptor 4 (TLR4)-mediated innate immune signaling in acute pancreatitis (AP) via substance P.

METHODS

Male Swiss mice were treated with hourly intraperitoneal injections of cerulein (50 μg/kg) for 10 hours. dl-propargylglycine ([PAG] 100 mg/kg, intraperitoneally), an inhibitor of H2S formation, was administered 1 hour after the induction of AP. Pancreatic acinar cells from male preprotachykinin-A gene-knockout mice (PPTA) and their wild-type counterparts were incubated with or without cerulein (10 M for 60 minutes). To better understand the effect of H2S in inflammation, acinar cells were stimulated with cerulein after addition of H2S donor, sodium hydrosulfide. In addition, cerulein-treated pancreatic acinar cells were pretreated with PAG (30 μM) for 1 hour.

RESULTS

The H2S inhibitor PAG eliminated TLR4, interleukin 1 receptor-associated kinase 4, tumor necrosis factor receptor-associated factor 6, and nuclear factor-κB (NF-κB) levels in in vitro and in vivo models of cerulein-induced AP. PPTA gene deletion reduced TLR4, myeloid differentiation factor 88, interleukin 1 receptor-associated kinase 4, tumor necrosis factor receptor-associated factor 6, and NF-κB in cerulein-treated pancreatic acinar cells, whereas administration of sodium hydrosulfide resulted in a further rise in TLR4 and NF-κB levels in cerulein-treated pancreatic acinar cells.

CONCLUSION

The present findings show for the first time that in AP, H2S may up-regulate the TLR4 pathway and NF-κB via substance P.

Hydrogen sulphide induces mouse paw oedema through activation of phospholipase A2

BACKGROUND AND PURPOSE

Hydrogen sulphide (H(2)S), 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 H(2)S contributes to the local and systemic inflammation in several experimental animal models. We conducted this study to investigate on the signalling involved in H(2)S-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 H(2)S-induced oedema formation, we used 5-HT and histamine receptor antagonists, and inhibitors of K(ATP) 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 K(ATP) channel activation. However, oedema formation was significantly inhibited by the inhibition of cyclooxygenases and selective inhibition of phospholipase A(2). 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 A(2) and prostaglandin production are involved in pro-inflammatory effects of H(2)S in mouse hind paws. The present study contributes to the understanding of the role of L-cysteine/H(2)S pathway in inflammatory disease.

Acidic pH facilitates peripheral αβmeATP-mediated nociception in rats: differential roles of P2X, P2Y, ASIC and TRPV1 receptors in ATP-induced mechanical allodynia and thermal hyperalgesia

Peripheral ischemia is commonly associated with an increase in tissue ATP concentration and a decrease in tissue pH. Although in vitro data suggest that low tissue pH can affect ATP-binding affinities to P2 receptors, the mechanistic relationship between ATP and low pH on peripheral nociception has not been fully examined. This study was designed to investigate the potential role of an acidified environment on intraplantar αβmeATP-induced peripheral pain responses in rats. The mechanical allodynia (MA) produced by injection of αβmeATP was significantly increased in animals that received the drug diluted in pH 4.0 saline compared to those that received the drug diluted in pH 7.0 saline. Moreover, animals injected with αβmeATP (100 nmol) in pH 4.0 saline developed thermal hyperalgesia (TH), which did not occur in animals treated with αβmeATP diluted in pH 7.0 saline. To elucidate which receptors were involved in this pH-related facilitation of αβmeATP-induced MA and TH, rats were pretreated with PPADS (P2 antagonist), TNP-ATP (P2X antagonist), MRS2179 (P2Y1 antagonist), AMG9810 (TRPV1 antagonist) or amiloride (ASIC blocker). Both PPADS and TNP-ATP dose-dependently blocked pH-facilitated MA, while TH was significantly reduced by pre-treatment with MRS2179 or AMG9810. Moreover, amiloride injection significantly reduced low pH-induced facilitation of αβmeATP-mediated MA, but not TH. These results demonstrate that low tissue pH facilitates ATP-mediated MA via the activation of P2X receptors and ASICs, whereas TH induced by ATP under low pH conditions is mediated by the P2Y1 receptor and TRPV1, but not ASIC. Thus distinct mechanisms are responsible for the development of MA and TH under conditions of tissue acidosis and increased ATP.

Interaction of hydrogen sulfide with ion channels

1. Hydrogen sulfide (H(2)S) is a signalling gasotransmitter. It targets different ion channels and receptors, and fulfils its various roles in modulating the functions of different systems. However, the interaction of H(2)S with different types of ion channels and underlying molecular mechanisms has not been reviewed systematically. 2. H(2)S is the first identified endogenous gaseous opener of ATP-sensitive K(+) channels in vascular smooth muscle cells. Through the activation of ATP-sensitive K(+) channels, H(2)S lowers blood pressure, protects the heart from ischemia and reperfusion injury, inhibits insulin secretion in pancreatic beta cells, and exerts anti-inflammatory, anti-nociceptive and anti-apoptotic effects. 3. H(2)S inhibited L-type Ca(2+) channels in cardiomyocytes but stimulated the same channels in neurons, thus regulating intracellular Ca(2+) levels. H(2)S activated small and medium conductance K(Ca) channels but its effect on BK(Ca) channels has not been consistent. 4. H(2)S-induced hyperalgesia and pro-nociception seems to be related to the sensitization of both T-type Ca(2+) channels and TRPV(1) channels. The activation of TRPV(1) and TRPA(1) by H(2)S is believed to result in contraction of nonvascular smooth muscles and increased colonic mucosal Cl(-) secretion. 5. The activation of Cl(-) channel by H(2)S has been shown as a protective mechanism for neurons from oxytosis. H(2)S also potentiates N-methyl-d-aspartic acid receptor-mediated currents that are involved in regulating synaptic plasticity for learning and memory. 6. Given the important modulatory effects of H(2)S on different ion channels, many cellular functions and disease conditions related to homeostatic control of ion fluxes across cell membrane should be re-evaluated.

Cot/tpl2 (MAP3K8) mediates myeloperoxidase activity and hypernociception following peripheral inflammation

Cot/tpl2 (also known as MAP3K8) has emerged as a new and potentially interesting therapeutic anti-inflammatory target. Here, we report the first study of Cot/tpl2 involvement in acute peripheral inflammation in vivo. Six hours after an intraplantar injection of zymosan, Cot/tpl2(-/-) mice showed a 47% reduction in myeloperoxidase activity, concomitant with a 46% lower neutrophil recruitment and a 40% decreased luminol-mediated bioluminescence imaging in vivo. Accordingly, Cot/tpl2 deficiency provoked a 25-30% reduction in luminol-mediated bioluminescence and neutrophil recruitment together with a 65% lower macrophage recruitment 4 h following zymosan-induced peritonitis. Significantly impaired levels of G-CSF and GM-CSF and of other cytokines such as TNFα, IL-1β, and IL-6, as well as some chemokines such as MCP-1, MIP-1β, and keratinocyte-derived chemokine, were detected during the acute zymosan-induced intraplantar inflammatory response in Cot/tpl2(-/-) mice. Moreover, Cot/tpl2 deficiency dramatically decreased the production of the hypernociceptive ligand NGF at the inflammatory site during the course of inflammation. Most importantly, Cot/tpl2 deficiency significantly reduced zymosan-induced inflammatory hypernociception in mice, with a most pronounced effect of a 50% decrease compared with wild type (WT) at 24 h following intraplantar injection of zymosan. At this time, Cot/tpl2(-/-) mice showed significantly reduced NGF, TNFα, and prostaglandin E(2) levels compared with WT littermates. In conclusion, our study demonstrates an important role of Cot/tpl2 in the NGF, G-CSF, and GM-CSF production and myeloperoxidase activity in the acute inflammatory response process and its implication in inflammatory hypernociception.

Inhibition of hydrogen sulphide formation reduces cisplatin-induced renal damage

BACKGROUND

Cisplatin (CP)-induced renal damage is associated with inflammation. Hydrogen sulphide (H2S) is involved in models of inflammation. This study evaluates the effect of DL-propargylglycine (PAG), an inhibitor of endogenous H2S formation, on the renal damage induced by CP.

METHODS

The rats were injected with CP (5 mg/kg, i.p.) or PAG (5 mg/kg twice a day, i.p.) for 4 days, starting 1 h before CP injection. Control rats were injected with 0.15 M NaCl or PAG only. Blood and urine samples were collected 5 days after saline or CP injections for renal function evaluation. The kidneys were removed for tumour necrosis factor (TNF)-α quantification, histological, immunohistochemical and Western blot analysis. The cystathionine γ-lyase (CSE) activity and expression were assessed. The direct toxicity of H(2)S in renal tubular cells was evaluated by the incubation of these cells with NaHS, a donor of H2S.

RESULTS

CP-treated rats presented increases in plasma creatinine levels and in sodium and potassium fractional excretions associated with tubulointerstitial lesions in the outer medulla. Increased expression of TNF-α, macrophages, neutrophils and T lymphocytes, associated with increased H2S formation rate and CSE expression, were also observed in the outer medulla from CP-injected rats. All these alterations were reduced by treatment with PAG. A direct toxicity of NaHS for renal tubular epithelial cells was not observed.

CONCLUSIONS

Treatment with PAG reduces the renal damage induced by CP. This effect seems to be related to the H2S formation and the restriction of the inflammation in the kidneys from PAG + CP-treated rats.

Hydrogen sulfide and substance P in inflammation

Hydrogen sulfide (H(2)S) plays an important role in cardiovascular, central nervous, and gastrointestinal systems. Being the third gaseous mediator, H(2)S has been shown to act as a vasodilator. In recent times, more and more attention has been paid to the biological functions of H(2)S in inflammation. Substance P is an 11 amino acid neuropeptide that is released from nerve endings in many tissues. Subsequent to its release, substance P binds to neurokinin-1 (NK-1) receptors on the surface of effector cells and, in addition to being a mediator of pain, it plays an important role in many inflammatory states including asthma, immune-complex-mediated lung injury, experimental arthritis, and inflammatory bowel disease. Substance P has been shown to increase microvascular permeability and promote plasma extravasation. Using animal models of inflammation of different etiologies such as acute pancreatitis, sepsis, and burns, studies in our laboratory have recently shown an important role of the pro-inflammatory action of H(2)S and substance P.

Physiological and pathophysiological roles of hydrogen sulfide in the gastrointestinal tract

Like nitric oxide and carbon monoxide, hydrogen sulfide has historically been recognized as an industrial pollutant, but in recent years, it has been shown to be an important mediator of many physiological processes. Hydrogen sulfide contributes to the maintenance of gastrointestinal mucosal defense and repair. It also exerts many antiinflammatory effects, including inhibition of leukocyte adherence to the vascular endothelium and leukocyte migration to sites of inflammation. Conversely, inhibition of endogenous hydrogen sulfide synthesis leads to a loss of mucosal integrity and to an increase in mucosal inflammation. Hydrogen sulfide therefore appears to have overlapping actions with nitric oxide and prostaglandins in terms of modulating mucosal defense and resolution of inflammation. Recent evidence suggests that these properties of hydrogen sulfide can be exploited in the design of novel therapies for ulcerative and inflammatory diseases of the gastrointestinal tract.

Role of hydrogen sulfide in severe burn injury-induced inflammation in mice

Endogenous hydrogen sulfide (H(2)S) is naturally synthesized in many types of mammalian cells from L-cysteine in the reactions catalyzed by cystathionine-β-synthase and cystathionine-γ-lyase (CSE). H(2)S has been demonstrated to play a proinflammatory role in various animal models of hindpaw edema, acute pancreatitis, lipopolysaccharide-induced endotoxemia and cecal ligation, and puncture-induced sepsis. Full-thickness burns that exceed 25% of the total body surface area (TBSA) produce a profound systemic inflammatory reaction characterized by leukocyte activation and plasma leakage in the microvasculature of tissues and organs remote from the wound. The aim of this study was to investigate the effect of local burn injury on induced distant organ endogenous H(2)S release and expression of CSE. Male BALB/c mice were subjected to 30% TBSA full-thickness burn and treated with saline (administered intraperitoneally [i.p.]); DL-propargylglycine (PAG, 50 mg/kg i.p.), which is a CSE inhibitor; or sodium hydrosulfide (NaHS, 10 mg/kg i.p.), which is an H(2)S donor. PAG was administered either 1 h before or 1 h after the burn injury, whereas NaHS was given at the same time as the burn injury. Measurements of liver myeloperoxidase (MPO) activities, liver H(2)S-synthesizing activity, plasma H(2)S level and liver and lung CSE mRNA expression and histological examination of tissues were performed after burn injury. Burn injury significantly increased the plasma H(2)S level and liver H(2)S synthesis 8 h after burn compared with the sham group. Burn injury also resulted in a significant upregulation of CSE mRNA in liver and lung. Prophylactic as well as therapeutic administration of PAG significantly reduced burn-associated systemic inflammation, as evidenced by MPO activity and histological changes in liver and lung. Injection of NaHS significantly aggravated burn-associated systemic inflammation. Therefore, our findings show for the first time the role of H(2)S in contributing to inflammatory damage after burn injury.

Differing effects of exogenous and endogenous hydrogen sulphide in carrageenan-induced knee joint synovitis in the rat

BACKGROUND AND PURPOSE

Recent findings suggest that the noxious gas H(2)S is produced endogenously, and that physiological concentrations of H(2)S are able to modulate pain and inflammation in rodents. This study was undertaken to evaluate the ability of endogenous and exogenous H(2)S to modulate carrageenan-induced synovitis in the rat knee.

EXPERIMENTAL APPROACH

Synovitis was induced in Wistar rats by intra-articular injection of carrageenan into the knee joint. Sixty minutes prior to carrageenan injection, the rats were pretreated with indomethacin, an inhibitor of H(2)S formation (DL-propargylglycine) or an H(2)S donor [Lawesson's reagent (LR)].

KEY RESULTS

Injection of carrageenan evoked knee inflammation, pain as characterized by impaired gait, secondary tactile allodynia of the ipsilateral hindpaw, joint swelling, histological changes, inflammatory cell infiltration, increased synovial myeloperoxidase, protein nitrotyrosine residues, inducible NOS (iNOS) activity and NO production. Pretreatment with LR or indomethacin significantly attenuated the pain responses, and all the inflammatory and biochemical changes, except for the increased iNOS activity, NO production and 3-NT. Propargylglycine pretreatment potentiated synovial iNOS activity (and NO production), and enhanced macrophage infiltration, but had no effect on other inflammatory parameters.

CONCLUSIONS AND IMPLICATIONS

Whereas exogenous H(2)S delivered to the knee joint can produce a significant anti-inflammatory and anti-nociceptive effect, locally produced H(2)S exerts little immunomodulatory effect. These data further support the development and use of H(2)S donors as potential alternatives (or complementary therapies) to the available anti-inflammatory compounds used for treatment of joint inflammation or relief of its symptoms.

Glucocorticoids suppress cystathionine gamma-lyase expression and H2S production in lipopolysaccharide-treated macrophages

Hydrogen sulfide (H(2)S) plays an important role in inflammation. We showed that macrophages expressed the H(2)S-forming enzyme cystathionine gamma-lyase (CSE) and produced H(2)S. Lipopolysaccharide (LPS) stimulated the CSE expression and H(2)S production rate. l-cysteine reduced LPS-induced nitric oxide (NO) production. CSE inhibitor blocked the inhibitory effect of l-cysteine. CSE knockdown increased, whereas CSE overexpression decreased LPS-induced NO production. Dexamethasone suppressed LPS-induced CSE expression and the H(2)S production rate as well as NO production. l-arginine increased, whereas N(G)-nitro-l-arginine methyl ester (l-NAME) decreased LPS-induced CSE expression and H(2)S production. Dexamethasone plus l-NAME significantly decreased LPS-induced CSE expression and H(2)S production compared to l-NAME. Our results suggest that macrophages are one of the H(2)S producing sources. H(2)S might exert anti-inflammatory effects by inhibiting NO production. Dexamethasone may directly inhibit CSE expression and H(2)S production, besides the NO-dependent way. Inhibition of H(2)S and NO production may be a mechanism by which glucocorticoids coordinate the balance between pro- and anti-inflammatory mediators during inflammation.

Hydrogen sulfide improves neutrophil migration and survival in sepsis via K+ATP channel activation

RATIONALE

Recovering the neutrophil migration to the infectious focus improves survival in severe sepsis. Recently, we demonstrated that the cystathionine gamma-lyase (CSE)/hydrogen sulfide (H(2)S) pathway increased neutrophil recruitment to inflammatory focus during sterile inflammation.

OBJECTIVES

To evaluate if H(2)S administration increases neutrophil migration to infectious focus and survival of mice.

METHODS

Sepsis was induced by cecal ligation and puncture (CLP).

MEASUREMENTS AND MAIN RESULTS

The pretreatments of mice with H(2)S donors (NaHS or Lawesson's reagent) improved leukocyte rolling/adhesion in the mesenteric microcirculation as well as neutrophil migration. Consequently, bacteremia levels were reduced, hypotension and lung lesions were prevented, and the survival rate increased from approximately 13% to approximately 80%. Even when treatment was delayed (6 h after CLP), a highly significant reduction in mortality compared with untreated mice was observed. Moreover, H(2)S pretreatment prevented the down-regulation of CXCR2 and l-selectin and the up-regulation of CD11b and G protein-coupled receptor kinase 2 in neutrophils during sepsis. H(2)S also prevented the reduction of intercellular adhesion molecule-1 expression in the endothelium of the mesenteric microcirculation in severe sepsis. Confirming the critical role of H(2)S on sepsis outcome, pretreatment with dl-propargylglycine (a CSE inhibitor) inhibited neutrophil migration to the infectious focus, enhanced lung lesions, and induced high mortality in mice subjected to nonsevere sepsis (from 0 to approximately 80%). The beneficial effects of H(2)S were blocked by glibenclamide (a ATP-dependent K(+) channel blocker).

CONCLUSIONS

These results showed that H(2)S restores neutrophil migration to the infectious focus and improves survival outcome in severe sepsis by an ATP-dependent K(+) channel-dependent mechanism.

Hydrogen sulfide promotes transient receptor potential vanilloid 1-mediated neurogenic inflammation in polymicrobial sepsis

OBJECTIVE

To investigate the interaction and involvement of hydrogen sulfide and transient receptor potential vanilloid type 1 in the pathogenesis of sepsis. Hydrogen sulfide has been demonstrated to be involved in many inflammatory states including sepsis. Its contribution in neurogenic inflammation has been suggested in normal airways and urinary bladder. However, whether endogenous hydrogen sulfide would induce transient receptor potential vanilloid type 1-mediated neurogenic inflammation in sepsis remains unknown.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory.

SUBJECT

Male Swiss mice.

INTERVENTIONS

Mice were subjected to cecal ligation and puncture-induced sepsis and treated with transient receptor potential vanilloid type 1 antagonist capsazepine (15 mg/kg subcutaneous) 30 mins before cecal ligation and puncture. To investigate hydrogen sulfide-mediated neurogenic inflammation in sepsis, DL-propargylglycine (50 mg/kg intraperitoneal), an inhibitor of hydrogen sulfide formation was administrated 1 hr before or 1 hr after the induction of sepsis, whereas sodium hydrosulfide (10 mg/kg intraperitoneal), a hydrogen sulfide donor, was given at the same time as cecal ligation and puncture. Lung and liver myeloperoxidase activities, liver cystathionine-gamma-lyase activity, plasma hydrogen sulfide level, histopathological examination, and survival studies were determined after induction of sepsis.

MEASUREMENTS AND MAIN RESULTS

Capsazepine treatment attenuates significantly systemic inflammation and multiple organ damage caused by sepsis, and protects against sepsis-induced mortality. Similarly, administration of sodium hydrosulfide exacerbates but capsazepine reverses these deleterious effects. In the presence of DL-propargylglycine, capsazepine causes no significant changes to the attenuation of sepsis-associated systemic inflammation, multiple organ damage, and mortality. In addition, capsazepine has no effect on endogenous generation of hydrogen sulfide, suggesting that hydrogen sulfide is located upstream of transient receptor potential vanilloid type 1 activation, and may play a critical role in regulating the production and release of sensory neuropeptides in sepsis.

CONCLUSIONS

The present study shows that hydrogen sulfide induces systemic inflammation and multiple organ damage characteristic of sepsis via transient receptor potential vanilloid type 1-mediated neurogenic inflammation.

Hydrogen sulfide as a gasotransmitter

Nitric oxide (NO) and carbon monoxide (CO) are well established as messenger molecules throughout the body, gasotransmitters, based on striking alterations in mice lacking the appropriate biosynthetic enzymes. Hydrogen sulfide (H(2)S) is even more chemically reactive, but until recently there was little definitive evidence for its physiologic formation. Cystathionine beta-synthase (EC 4.2.1.22), and cystathionine gamma-lyase (CSE; EC 4.4.1.1), also known as cystathionine, can generate H(2)S from cyst(e)ine. Very recent studies with mice lacking these enzymes have established that CSE is responsible for H(2)S formation in the periphery, while in the brain cystathionine beta-synthase is the biosynthetic enzyme. Endothelial-derived relaxing factor activity is reduced 80% in the mesenteric artery of mice with deletion of CSE, establishing H(2)S as a major physiologic endothelial-derived relaxing factor. H(2)S appears to signal predominantly by S-sulfhydrating cysteines in its target proteins, analogous to S-nitrosylation by NO. Whereas S-nitrosylation typically inhibits enzymes, S-sulfhydration activates them. S-nitrosylation basally affects 1-2% of its target proteins, while 10-25% of H(2)S target proteins are S-sulfhydrated. In summary, H(2)S appears to be a physiologic gasotransmitter of comparable importance to NO and carbon monoxide.

Effects of hydrogen sulfide on inflammation in caerulein-induced acute pancreatitis

BACKGROUND

Hydrogen sulfide (H(2)S), a gaseous mediator plays an important role in a wide range of physiological and pathological processes. H(2)S has been extensively studied for its various roles in cardiovascular and neurological disorders. However, the role of H(2)S in inflammation is still controversial. The current study was aimed to investigate the therapeutic potential of sodium hydrosulfide (NaHS), an H(2)S donor in in vivo model of acute pancreatitis in mice.

METHODS

Acute pancreatitis was induced in mice by hourly caerulein injections (50 mug/kg) for 10 hours. Mice were treated with different dosages of NaHS (5 mg/kg, 10 mg/kg or 15 mg/kg) or with vehicle, distilled water (DW). NaHS or DW was administered 1 h before induction of pancreatitis. Mice were sacrificed 1 h after the last caerulein injection. Blood, pancreas and lung tissues were collected and were processed to measure the plasma amylase, myeloperoxidase (MPO) activities in pancreas and lung and chemokines and adhesion molecules in pancreas and lung.

RESULTS

It was revealed that significant reduction of inflammation, both in pancreas and lung was associated with NaHS 10 mg/kg. Further the anti-inflammatory effects of NaHS 10 mg/kg were associated with reduction of pancreatic and pulmonary inflammatory chemokines and adhesion molecules. NaHS 5 mg/kg did not cause significant improvement on inflammation in pancreas and associated lung injury and NaHS 15 mg/kg did not further enhance the beneficial effects seen with NaHS 10 mg/kg.

CONCLUSION

In conclusion, these data provide evidence for anti-inflammatory effects of H(2)S based on its dosage used.

Inhibition of endogenous hydrogen sulfide synthesis by PAG protects against ethanol-induced gastric damage in the rat

Hydrogen sulfide (H(2)S) is a gaseous mediator involved in a multitude of physiological functions; however the role of H(2)S in the gut is far from being understood completely. The aim of this study was to determine the effect of d-l-propargylglycine (PAG), an inhibitor of H(2)S synthesis, on ethanol-induced gastric injury in rat and to examine the role of l-cysteine, exogenous H(2)S, prostaglandins, non-protein sulphydryls groups, nitric oxide and K(ATP) channels in the gastroprotective effect of PAG. Administration of PAG (3.12 to 75mg/kg i.p.) or l-cysteine (0.3 to 300mg/kg, p.o.) exhibited a dose-dependent protective effect after intragastric administration of 1ml of ethanol to induce gastric injury. The gastroprotective effect of PAG (25mg/kg i.p.) was maintained after post-treatment with l-cysteine (10mg/kg p.o.), while NaHS (8.4mg/kg p.o.) inhibited this effect. The levels of gastric hydrogen sulfide were increased after ethanol-induced gastric damage and they were reverted by PAG while prostaglandin E(2) levels in gastric tissue were decreased by ethanol and PAG did not revert to this effect. Pretreatment with indomethacin (10mg/kg i.p.) and N-ethylmaleimide (NEM, 10mg/kg s.c.) resulted in a reversion of the gastroprotective effect of PAG while N(G)-nitro-l-arginine methyl ester (L-NAME, 70mg/kg s.c.), glibenclamide (1mg/kg i.p.) or diazoxide (3mg/kg i.p.) did not induce any changes. These results suggest that ethanol-induced gastric injury is related with an increment of endogenous H(2)S levels, and therefore a decrement of H(2)S levels by PAG is a benefit to protect gastric injury caused by ethanol.

Site-directed mutagenesis on human cystathionine-gamma-lyase reveals insights into the modulation of H2S production

In recent years, increased interest has been directed towards hydrogen sulfide (H2S) as the third gasotransmitter and its role in various diseases. Cystathionine-gamma-lyase (CSE) is one of the enzymes responsible for the endogenous production of H2S in mammals. With the aid of the crystal structures of human CSE and site-directed mutagenesis studies, we have identified several amino acid residues in CSE that are actively involved in the catalysis of H2S production. Contrary to reports suggesting that Tyr114 is required for substrate binding, our results reveal a significant increase in the production of H2S upon mutation of Tyr114 to phenylalanine. This is attributed to an increased rate of pyridoxal 5'-phosphate (PLP) regeneration due to weakened pi-stacking interactions between Phe114 and PLP. Thr189 is also identified as a crucial residue where hydrogen bonding to Asp187 keeps the latter in an optimal position for hydrogen bonding to the pyridoxal nitrogen of PLP. Furthermore, mutation of Glu339 to lysine, alanine or tyrosine reveals the importance of the hydrophobicity of the 339th amino acid in determining the specificity of the enzyme for the catalysis of alpha,gamma-elimination or alpha,beta-elimination reaction. Our study also shows that the rate of H2S production is increased with increasing exogenous PLP concentration, hence supporting our hypothesis that apo-CSE is formed during the catalysis of H2S production. Taken together, these findings suggest novel routes towards the design of activators or inhibitors that modulate the production of H2S; these modulators may also serve as lead compounds in the development of drugs or mechanistic probes in the study of various H2S-related diseases.

Anti-inflammatory agents as cancer therapeutics

Cancer prevention sometimes referred to as tertiary prevention or chemoprevention makes use of specific xenobiotics or drugs to prevent, delay, or retard the development of cancer. Over the last two decades or so cancer prevention has made significant strides. For example, prevention of lung cancer through smoking cessation; cervical cancer prevention through regular Pap smear tests; colon cancer prevention through screening colonoscopy; and prostate cancer reductions by prostate-specific antigen measurements in conjunction with regular prostate examinations. The seminal epidemiological observation that nonsteroidal anti-inflammatory drugs (NSAIDs) prevent colon and other cancers has provided the impetus to develop novel chemoprevention approaches against cancer. To that end, a number of "designer drugs" have been synthesized that are in different stages of development, evaluation, and deployment. Some include the cyclooxygenase-2-specific inhibitors (coxibs), nitric oxide-releasing NSAIDs (NO-NSAIDs and NONO-NSAIDs), hydrogen sulfide-releasing NSAIDs, modulators of the lipoxygenase pathway, prostanoid receptor blockers, and chemokine receptor antagonists. In addition to these novel agents, there are also a host of naturally occurring compounds/micronutrients that have chemopreventive properties. This chapter reviews these classes of compounds, their utility and mechanism(s) of action against the background of mediators that link inflammation and cancer.

The endogenous hydrogen sulfide producing enzyme cystathionine-beta synthase contributes to visceral hypersensitivity in a rat model of irritable bowel syndrome

Background

The pathogenesis of visceral hypersensitivity, a characteristic pathophysiological feature of irritable bowel syndrome (IBS), remains elusive. Recent studies suggest a role for hydrogen sulfide (H₂S) in pain signaling but this has not been well studied in visceral models of hyperalgesia. We therefore determined the role for the endogenous H₂S producing enzyme cystathionine-β-synthetase (CBS) in a validated rat model of IBS-like chronic visceral hyperalgesia (CVH). CVH was induced by colonic injection of 0.5% acetic acid (AA) in 10-day-old rats and experiments were performed at 8–10 weeks of age. Dorsal root ganglion (DRG) neurons innervating the colon were labeled by injection of DiI (1,1'-dioleyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate) into the colon wall.

Results

In rat DRG, CBS-immunoreactivity was observed in approximately 85% of predominantly small- and medium-sized neurons. Colon specific DRG neurons revealed by retrograde labeling DiI were all CBS-positive. CBS-positive colon neurons co-expressed TRPV1 or P2X3 receptors. Western blotting analysis showed that CBS expression was significantly increased in colon DRGs 8 weeks after neonatal AA-treatment. Furthermore, the CBS inhibitor hydroxylamine markedly attenuated the abdominal withdrawal reflex scores in response to colorectal distention in rats with CVH. By contrast, the H₂S donor NaHS significantly enhanced the frequency of action potentials of colon specific DRG neurons evoked by 2 times rheobase electrical stimulation.

Conclusion

Our results suggest that upregulation of CBS expression in colonic DRG neurons and H₂S signaling may play an important role in developing CVH, thus identifying a specific neurobiological target for the treatment of CVH in functional bowel syndromes.

Hydrogen sulphide: A novel physiological inhibitor of LDL atherogenic modification by HOCl

Hypochlorite (HOCl), the product of the activated myeloperoxidase/H(2)O(2)/chloride (MPO/H(2)O(2)/Cl(- )) system is favored as a trigger of LDL modifications, which may play a pivotal role in early atherogenesis. As HOCl has been shown to react with thiol-containing compounds like glutathione and N-acetylcysteine protecting LDL from HOCl modification, we have tested the ability of hydrogen sulfide (H(2)S) - which has recently been identified as an endogenous vasorelaxant - to counteract the action of HOCl on LDL. The results show that H(2)S could inhibit the atherogenic modification of LDL induced by HOCl, as measured by apolipoprotein alterations. Beside its HOCl scavenging potential, H(2)S was found to inhibit MPO (one may speculate that this occurs via H(2)S/heme interaction) and destroy H(2)O(2). Thus, H(2)S may interfere with the reactants and reaction products of the activated MPO/H(2)O(2)/Cl(- ) system. Our data add to the evidence of an anti-atherosclerotic action of this gasotransmitter taking the role of HOCl in the atherogenic modification of LDL into account.

Physiological and pharmacological features of the novel gasotransmitter: hydrogen sulfide

Hydrogen sulfide (H(2)S) has been known for hundreds of years because of its poisoning effect. Once the basal bio-production became evident its pathophysiological role started to be investigated in depth. H(2)S is a gas that can be formed by the action of two enzymes, cystathionine gamma-lyase and cystathionine beta-synthase, both involved in the metabolism of cysteine. It has several features in common with the other two well known "gasotransmitters" (nitric oxide and carbon monoxide) in the biological systems. These three gasses share some biological targets; however, they also have dissimilarities. For instance, the three gases target heme-proteins and open K(ATP) channels; H(2)S as NO is an antioxidant, but in contrast to the latter molecule, H(2)S does not directly form radicals. In the last years H(2)S has been implicated in several physiological and pathophysiological processes such as long term synaptic potentiation, vasorelaxation, pro- and anti-inflammatory conditions, cardiac inotropism regulation, cardioprotection, and several other physiological mechanisms. We will focus on the biological role of H(2)S as a molecule able to trigger cell signaling. Our attention will be particularly devoted on the effects in cardiovascular system and in cardioprotection. We will also provide available information on H(2)S-donating drugs which have so far been tested in order to conjugate the beneficial effect of H(2)S with other pharmaceutical properties.

Pro-inflammatory effects of hydrogen sulphide on substance P in caerulein-induced acute pancreatitis

Hydrogen sulphide (H₂S), a novel gasotransmitter, has been recognized to play an important role in inflammation. Cystathionine-γ-lyase (CSE) is a major H₂S synthesizing enzyme in the cardiovascular system and DL-propargylglycine (PAG) is an irreversible inhibitor of CSE. Substance P (SP), a product of preprotachykinin-A (PPT-A) gene, is a well-known pro-inflammatory mediator which acts principally through the neurokinin-1 receptor (NK-1R). We have shown an association between H₂S and SP in pulmonary inflammation as well as a pro-inflammatory role of H₂S and SP in acute pancreatitis. The present study was aimed to investigate the interplay between pro-inflammatory effects of H₂S and SP in a murine model of caerulein-induced acute pancreatitis. Acute pancreatitis was induced in mice by 10 hourly intraperitoneal injections of caerulein (50 (g/kg). PAG (100 mg/kg, i.p.) was administered either 1 hr before (prophylactic) or 1 hr after (therapeutic) the first caerulein injection. PAG, given prophylactically as well as therapeutically, significantly reduced plasma H₂S levels and pancreatic H₂S synthesizing activities as well as SP concentrations in plasma, pancreas and lung compared with caerulein-induced acute pancreatitis. Furthermore, prophylactic as well as therapeutic administration of PAG significantly reduced PPT-A mRNA expression and NK-1R mRNA expression in both pancreas and lung when compared with caerulein-induced acute pancreatitis. These results suggest that the pro-inflammatory effects of H₂S may be mediated by SP-NK-1R pathway in acute pancreatitis.

Hydrogen sulfide decreases adenosine triphosphate levels in aortic rings and leads to vasorelaxation via metabolic inhibition

AIMS

Hydrogen sulfide (H(2)S) at low concentrations serves as a physiological endogenous vasodilator molecule, while at higher concentrations it can trigger cytotoxic effects. The aim of our study was to elucidate the potential mechanisms responsible for the effects of H(2)S on vascular tone.

MAIN METHODS

We measured the vascular tone in vitro in precontracted rat thoracic aortic rings and we have tested the effect of different oxygen levels and a variety of inhibitors affecting known vasodilatory pathways. We have also compared the vascular effect of high concentrations of H(2)S to those of pharmacological inhibitors of oxidative phosphorylation. Furthermore, we measured adenosine triphosphate (ATP)-levels in the same vascular tissues.

KEY FINDINGS

We have found that in rat aortic rings: (1) H(2)S decreases ATP levels; (2) relaxations to H(2)S depend on the ambient oxygen concentration; (3) prostaglandins do not take part in the H(2)S induced relaxations; (4) the 3':5'-cyclic guanosine monophosphate (cGMP)-nitric oxide (NO) pathway does not have a role in the relaxations (5) the role of K(ATP) channels is limited, while Cl(-)/HCO(3)(-) channels have a role in the relaxations. (6): We have observed that high concentrations of H(2)S relax the aortic rings in a fashion similar to sodium cyanide, and both agents reduce cellular ATP levels to a comparable degree.

SIGNIFICANCE

H(2)S, a new gasotransmitter of emerging importance, leads to relaxation via Cl(-)/HCO(3)(-) channels and metabolic inhibition and the interactions of these two factors depend on the oxygen levels of the tissue.

Cell-mediated immune response to unrelated proteins and unspecific inflammation blocked by orally tolerated proteins

Oral tolerance promotes a generalized decrease in specific immune responsiveness to proteins previously encountered via the oral route. In addition, parenteral immunization with a tolerated protein also triggers a significant reduction in the primary responsiveness to a second unrelated antigen. This is generally explained by 'innocent bystander suppression', suggesting that the transient and episodic effects of inhibitory cytokines released by contact with the tolerated antigen would block responses to the second antigen. In disagreement with this view, we have previously shown that: (i) these inhibitory effects do not require concomitance or contiguity of the injections of the two proteins; (ii) that intravenous or intragastric exposures to the tolerated antigen are not inhibitory; and (iii) that the inhibitory effect, once triggered, persists in the absence of further contact with the tolerated protein, possibly by inhibition of secondary responsiveness (immunological memory). The present work confirms that immunological memory of the second unrelated antigen is hindered by exposure to the tolerated antigen and, in addition, shows that this exposure: (i) inhibits the inflammation triggered by an unrelated antigen through the double effect of inhibiting production of leucocytes in the bone marrow and blocking their migration to inflammed sites; and (ii) significantly blocks footpaw swelling triggered by carrageenan. Taken together, these results conclusively demonstrate that inhibitory effects of parenteral injection of tolerated antigens are much more general than suggested by the 'innocent bystander suppression' hypothesis.

A nociceptive-intensity-dependent role for hydrogen sulphide in the formalin model of persistent inflammatory pain

The present study investigated the hypothesis that hydrogen sulfide (H2S) is pro-nociceptive in the formalin model of persistent inflammatory pain in the adult rat. Hind paw injection of formalin evoked a concentration-dependent increase in the hind paw concentration of H2S. Increased concentration of H2S was found in homogenates prepared from hind paws injected with 5% (but not 1.25%) formalin. Correspondingly, animal nociceptive flinching and hind paw edema were maximal with 5% formalin. Both nociceptive flinching and hind paw edema induced by injection of 5% formalin were attenuated by pretreatment with DL-propargylglycine (PPG; 50 mg/kg, i.p.) which is an inhibitor of the H2S synthesizing enzyme cystathionine-gamma-lyase (CSE). The effect of pretreatment with PPG was selective and the drug did not influence animal behavior or hind-paw edema with injection of 1.25% formalin. Furthermore, PPG pretreatment attenuated the induction of c-Fos in spinal laminae I-II following injection of 5% formalin. In contrast, co-injection of 1.25% formalin with sodium hydrogen sulfide (NaHS; 1 nmol/0.1 ml), a H2S donor, into the hind paw increased animal nociceptive behavior. Collectively, these findings show that the effect of peripheral H2S in the pathogenesis of inflammatory pain depends, at least in part, on the nociceptive intensity level.

Leukocyte trafficking and pain behavioral responses to a hydrogen sulfide donor in acute monoarthritis

Hydrogen sulfide (H(2)S) is an endogenous gaseous mediator with the ability to modulate tissue inflammation and pain. The aim of this study was to determine the effect of an H(2)S donor (Na(2)S) on leukocyte-endothelium interactions, blood flow, and pain sensation in acutely inflamed knee joints. Acute arthritis was induced in urethane anesthetized C57bl/6 mice by intra-articular injection of kaolin/carrageenan (24-h recovery), and the effect of local administration of Na(2)S on leukocyte trafficking was measured by intravital microscopy. Synovial blood flow was measured in inflamed knees by laser Doppler perfusion imaging. Finally, the effect of an intra-articular injection of Na(2)S on joint pain in control and inflamed rats was determined by hindlimb incapacitance and von Frey hair algesiometry. Local administration of an H(2)S donor to inflamed knees caused a dose-dependent reduction in leukocyte adherence and an increase in leukocyte velocity. These effects could be inhibited by coadministration of the ATP-sensitive K(+) channel blocker glibenclamide. Local administration of Na(2)S to inflamed joints caused a pronounced vasoconstrictor response; however, there was no observable effect of Na(2)S on joint pain. These findings establish H(2)S as a novel signaling molecule in rodent knee joints. H(2)S exhibits potent anti-inflammatory properties, but with no detectable effect on joint pain.