Acetylcholine- and Sodium Hydrosulfide^|^ndash;Induced Endothelium-Dependent Relaxation and Hyperpolarization in Cerebral Vessels of Global Cerebral Ischemia^|^ndash;Reperfusion Rat

Hyperoside ameliorates cerebral ischaemic-reperfusion injury by opening the TRPV4 channel in vivo through the IP3-PKC signalling pathway

CONTEXT

Hyperoside (Hyp), one of the active flavones from Rhododendron (Ericaceae), has beneficial effects against cerebrovascular disease. However, the effect of Hyp on vasodilatation has not been elucidated.

OBJECTIVE

To explore the effect of Hyp on vasodilatation in the cerebral basilar artery (CBA) of Sprague-Dawley (SD) rats suffering with ischaemic-reperfusion (IR) injury.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly divided into sham, model, Hyp, Hyp + channel blocker and channel blocker groups. Hyp (50 mg/kg, IC₅₀ = 18.3 μg/mL) and channel blocker were administered via tail vein injection 30 min before ischaemic, followed by 20 min of ischaemic and 2 h of reperfusion. The vasodilation, hyperpolarization, ELISA assay, haematoxylin-eosin (HE), Nissl staining and channel-associated proteins and qPCR were analysed. Rat CBA smooth muscle cells were isolated to detect the Ca²⁺ concentration and endothelial cells were isolated to detect apoptosis rate.

RESULTS

Hyp treatment significantly ameliorated the brain damage induced by IR and evoked endothelium-dependent vasodilation rate (47.93 ± 3.09% vs. 2.99 ± 1.53%) and hyperpolarization (-8.15 ± 1.87 mV vs. -0.55 ± 0.42 mV) by increasing the expression of IP3R, PKC, transient receptor potential vanilloid channel 4 (TRPV4), IK_Ca and SK_Ca in the CBA. Moreover, Hyp administration significantly reduced the concentration of Ca²⁺ (49.08 ± 7.74% vs. 83.52 ± 6.93%) and apoptosis rate (11.27 ± 1.89% vs. 23.44 ± 2.19%) in CBA. Furthermore, these beneficial effects of Hyp were blocked by channel blocker.

DISCUSSION AND CONCLUSIONS

Although Hyp showed protective effect in ischaemic stroke, more clinical trial certification is needed due to the difference between animals and humans.

Hydrogen sulfide and its donors for the treatment of cerebral ischaemia-reperfusion injury: A comprehensive review

As an endogenous gas signalling molecule, hydrogen sulfide (H₂S) is frequently present in a variety of mammals and plays a significant role in the cardiovascular and nervous systems. Reactive oxygen species (ROS) are produced in large quantities as a result of cerebral ischaemia-reperfusion, which is a very serious class of cerebrovascular diseases. ROS cause oxidative stress and induce specific gene expression that results in apoptosis. H₂S reduces cerebral ischaemia-reperfusion-induced secondary injury via anti-oxidative stress injury, suppression of the inflammatory response, inhibition of apoptosis, attenuation of cerebrovascular endothelial cell injury, modulation of autophagy, and antagonism of P2X7 receptors, and it plays an important biological role in other cerebral ischaemic injury events. Despite the many limitations of the hydrogen sulfide therapy delivery strategy and the difficulty in controlling the ideal concentration, relevant experimental evidence demonstrating that H₂S plays an excellent neuroprotective role in cerebral ischaemia-reperfusion injury (CIRI). This paper examines the synthesis and metabolism of the gas molecule H₂S in the brain as well as the molecular mechanisms of H₂S donors in cerebral ischaemia-reperfusion injury and possibly other unknown biological functions. With the active development in this field, it is expected that this review will assist researchers in their search for the potential value of hydrogen sulfide and provide new ideas for preclinical trials of exogenous H₂S.

Protection against Hypoxia-Reoxygenation Injury of Hippocampal Neurons by H2S via Promoting Phosphorylation of ROCK2 at Tyr722 in Rat Model

The RhoA-ROCK signaling pathway is associated with the protective effects of hydrogen sulfide (H₂S) against cerebral ischemia. H₂S protects rat hippocampal neurons (RHNs) against hypoxia-reoxygenation (H/R) injury by promoting phosphorylation of RhoA at Ser188. However, effect of H₂S on the phosphorylation of ROCK₂-related sites is unclear. The present study was designed to investigate whether H₂S can play a role in the phosphorylation of ROCK₂ at Tyr722, and explore whether this role mediates the protective effect of H/R injury in RHNs. Prokaryotic recombinant plasmids ROCK₂^wild-pGEX-6P-1 and ROCK₂^Y722F-pGEX-6P-1 were constructed and transfected into E. coli in vitro, and the expressed protein, GST-ROCK₂^wild and GST-ROCK₂^Y722F were used for phosphorylation assay in vitro. Eukaryotic recombinant plasmids ROCK₂^Y722-pEGFP-N1 and ROCK₂^Y722F-pEGFP-N1 as well as empty plasmid were transfected into the RHNs. Western blot assay and whole-cell patch-clamp technique were used to detect phosphorylation of ROCK₂ at Tyr722 and BK_Ca channel current in the RHNs, respectively. Cell viability, leakages of intracellular enzymes lactate dehydrogenase (LDH), and nerve-specific enolase (NSE) were measured. The H/R injury was indicated by decrease of cell viability and leakages of intracellular LDH and NSE. The results of Western blot have shown that NaHS, a H₂S donor, significantly promoted phosphorylation of GST-ROCK₂^wild at Tyr722, while no phosphorylation of GST-ROCK₂^Y722F was detected. The phosphorylation of ROCK₂^wild promoted by NaHS was also observed in RHNs. NaHS induced more potent effects on protection against H/R injury, phosphorylation of ROCK₂ at Tyr722, inhibition of ROCK₂ activity, as well as increase of the BK_Ca current in the ROCK₂^Y722-pEGFP-N1-transfected RHNs. Our results revealed that H₂S protects the RHNs from H/R injury through promoting phosphorylation of ROCK₂ at Tyr722 to inhibit ROCK₂ activity and potentially by opening channel currents.

Roles of the RhoA-ROCK Signaling Pathway in the Endothelial H2S Production and Vasodilation in Rat Cerebral Arteries

Cerebral endothelial H₂S protects against cerebral ischemia-reperfusion injury through vasodilation, but its cerebral vasodilation mechanism and regulation of production are poorly understood. The RhoA-ROCK pathway plays important roles in vascular function. In this study, the roles of this pathway in the endothelial H₂S production and vasodilation in rat cerebral arteries were investigated. Acetylcholine significantly increased H₂S-generating enzyme cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) protein expressions and H₂S production in rat cerebrovascular endothelial cells (ECs), but the increases were markedly decreased by the M receptor blocker atropine or the CSE inhibitor dl-propargylglycine. Pretreatment with dl-propargylglycine or the 3-MST inhibitor l-aspartic acid markedly reduced the acetylcholine-increased H₂S; CSE protein expression and H₂S levels in the ECs were obviously attenuated by the RhoA agonist U₄₆₆₁₉ but increased by the RhoA inhibitor C3 transferase. U₄₆₆₁₉ also reduced 3-MST protein expression; Acetylcholine markedly inhibited RhoA protein expression and activity, but the inhibition was obviously reversed by atropine, dl-propargylglycine, and l-aspartic acid, respectively; Acetylcholine-induced endothelium-dependent vasodilation in rat cerebral basilar artery was significantly attenuated by pretreatment with dl-propargylglycine or l-aspartic acid or RhoA inhibitor CCG-1423 or ROCK inhibitor KD025, and was further decreased by co-pretreatment with dl-propargylglycine (or l-aspartic acid) and CCG-1423 (or KD025); NaHS significantly relaxed rat cerebral basilar artery vascular smooth muscle cells and inhibited ROCK_1/2 activities, phosphorylated myosin light chain (MLC) protein expression, and KCl-increased [Ca²⁺]_i, but these relaxation and inhibitions were markedly attenuated by pretreatment with C3 transferase or ROCK inhibitor Y27632. Our results demonstrated that endothelial H₂S production is promoted by activation of the M receptor but inhibited by the RhoA-ROCK pathway in rat cerebral arteries; the endothelial H₂S induces cerebral vasodilation by inhibiting this pathway to reduce phosphorylation of MLC and [Ca²⁺]_i in vascular smooth muscle cells.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

VEGFR2 in vascular smooth muscle cells mediates H2S-induced dilation of the rat cerebral basilar artery

INTRODUCTION

The aim of present study was to study whether the vascular endothelial growth factor receptor 2 (VEGFR₂) mediates hydrogen sulfide (H₂S)-induced relaxation of the rat cerebral vasculature.

METHODS

Relaxation of cerebral basilar artery (CBA) and vascular smooth muscle cells (VSMCs) was measured by using a pressure myograph system and image analysis system, respectively. The intracellular calcium concentration ([Ca²⁺]_i) in VSMCs was detected using fluorescence imaging analysis.

RESULTS

We found that H₂S donor NaHS induced significant relaxation of VSMCs from the CBA of wild type rat, but in VEGFR₂ knockdown VSMCs, NaHS-induced relaxation reduced markedly. In addition, NaHS-induced vasodilation of rat CBA also attenuated obviously when the expression of VEGFR₂ was knocked down in vivo. In addition, pretreatment with the VEGFR₂ blocker SU5416 likewise lowered the NaHS-induced relaxation of rat CBA. Nevertheless, the VEGFR₂ agonist, vascular endothelial growth factor 164 (VEGF164), induced a concentration-dependent relaxation of CBA, which is similar to the effect of NaHS. Furthermore, we found that both NaHS and VEGF164 significantly inhibited the U₄₆₆₁₉-induced increase of [Ca²⁺]_i fluorescence intensity in the VSMCs. However, the inhibitory effect of NaHS on the [Ca²⁺]_i fluorescence intensity in VSMCs was markedly inhibited by pretreatment with SU5416 or VEGFR₂ knockdown.

CONCLUSION

These findings indicated that H₂S-induced CBA dilation and reduction of [Ca²⁺]_i in VSMCs occur by acting on VEGFR₂.

Endothelium-derived hydrogen sulfide acts as a hyperpolarizing factor and exerts neuroprotective effects via activation of large-conductance Ca2+ -activated K+ channels

BACKGROUND AND PURPOSE

Endothelium-derived hyperpolarizing factor (EDHF) has been suggested as a therapeutic target for vascular protection against ischaemic brain injury. However, the molecular entity of EDHF and its action on neurons remains unclear. This study was undertaken to demonstrate whether the hydrogen sulfide (H₂ S) acts as EDHF and exerts neuroprotective effect via large-conductance Ca²⁺ -activated K⁺ (BK_Ca /K_Ca 1.1) channels.

EXPERIMENTAL APPROACH

The whole-cell patch-clamp technology was used to record the changes of BK_Ca currents in rat neurons induced by EDHF. The cerebral ischaemia/reperfusion model of mice and oxygen-glucose deprivation/reoxygenation (OGD/R) model of neurons were used to explore the neuroprotection of EDHF by activating BK_Ca channels in these neurons.

KEY RESULTS

Increases of BK_Ca currents and membrane hyperpolarization in hippocampal neurons induced by EDHF could be markedly inhibited by BK_Ca channel inhibitor iberiotoxin or endothelial H₂ S synthase inhibitor propargylglycine. The H₂ S donor, NaHS-induced BK_Ca current and membrane hyperpolarization in neurons were also inhibited by iberiotoxin, suggesting that H₂ S acts as EDHF and activates the neuronal BK_Ca channels. Besides, we found that the protective effect of endothelium-derived H₂ S against mice cerebral ischaemia/reperfusion injury was disrupted by iberiotoxin. Importantly, the inhibitory effect of NaHS or BK_Ca channel opener on OGD/R-induced neuron injury and the increment of intracellular Ca²⁺ level could be inhibited by iberiotoxin but enhanced by co-application with L-type but not T-type calcium channel inhibitor.

CONCLUSION AND IMPLICATIONS

Endothelium-derived H₂ S acts as EDHF and exerts neuroprotective effects via activating the BK_Ca channels and then inhibiting the T-type calcium channels in hippocampal neurons.

Potential role of hydrogen sulfide in diabetes-impaired angiogenesis and ischemic tissue repair

Diabetes is one of the most prevalent metabolic disorders and is estimated to affect 400 million of 4.4% of population worldwide in the next 20 year. In diabetes, risk to develop vascular diseases is two-to four-fold increased. Ischemic tissue injury, such as refractory wounds and critical ischemic limb (CLI) are major ischemic vascular complications in diabetic patients where oxygen supplement is insufficient due to impaired angiogenesis/neovascularization. In spite of intensive studies, the underlying mechanisms of diabetes-impaired ischemic tissue injury remain incompletely understood. Hydrogen sulfide (H₂S) has been considered as a third gasotransmitter regulating angiogenesis under physiological and ischemic conditions. Here, the underlying mechanisms of insufficient H₂S-impaired angiogenesis and ischemic tissue repair in diabetes are discussed. We will primarily focuses on the signaling pathways of H₂S in controlling endothelial function/biology, angiogenesis and ischemic tissue repair in diabetic animal models. We summarized that H₂S plays an important role in maintaining endothelial function/biology and angiogenic property in diabetes. We demonstrated that exogenous H₂S may be a theraputic agent for endothelial dysfunction and impaired ischemic tissue repair in diabetes.

Contribution of Hydrogen Sulfide to Dilation of Rat Cerebral Arteries after Ischemia/Reperfusion Injury

The study examined the effect of H₂S on the tone of cerebral arteries in rats after global cerebral ischemia/reperfusion injury and cooperation between NO and H₂S in the control over cerebral circulation during the postischemic period. In control sham-operated and in experimental rats with ischemia/reperfusion injury, the diameter of pial arteries was repeatedly measured in vivo under a light microscope after removal of parietal bone and dura mater in 1 h and in 7 days after the surgery. The study established that H₂S is an important signaling molecule in pial arteries, where it is responsible for vasodilation. Interaction of H₂S and NO augmented dilation of pial arteries; in these arteries, H₂S up-regulated the effect of NO/cGMP/sGC/PKG signaling pathways. Partially, the dilating effect of H₂S is realized via activation of ATP-sensitive K⁺ channels in plasmalemma of smooth muscle cells. In the brain, ischemia/reperfusion injury degrades the ability of pial arteries to dilate via inhibition of NO-mediated signaling pathway.

Hydrogen sulfide-mediated endothelial function and the interaction with eNOS and PDE5A activity in human internal mammary arteries

Objective

To investigate the role of hydrogen sulfide (H2S) in human internal mammary arteries (IMA) and its interaction with endothelial nitric oxide synthase (eNOS) and phosphodiesterase (PDE)5A activity.

Methods

Human IMA segments from patients undergoing coronary artery bypass grafting (CABG) were studied by myography for acetylcholine and sodium hydrosulfide (NaHS)-induced relaxation. Locations of 3-mercaptopyruvate sulfurtransferase (3-MPST) and cysteine aminotransferase (CAT) were examined immunohistochemically. Levels of H2S, eNOS, phosphorylated-eNOSser1177, and PDE5A were measured.

Results

In IMA segments from 47 patients, acetylcholine-induced relaxation (resistant to NG-nitro-L-arginine and indomethacin) was significantly attenuated by aminooxyacetic acid or L-aspartate (CAT inhibitors), iberiotoxin (large-conductance calcium-activated K+ channel blocker), TRAM-34 plus apamin (intermediate- and small-conductance Ca2+-activated K+ channel blockers) or glibenclamide (ATP-sensitive K+ channel blocker). 3-MPST and mitochondrial CAT were found in endothelial and smooth muscle cells while cytosolic CAT was located only in endothelial cells. Acetylcholine significantly increased the H2S levels. The H2S donor, NaHS, increased eNOS phosphorylation and down-regulated PDE5A.

Conclusions

Human conduit artery endothelium releases H2S under basal and stimulated conditions, involving the 3-MPST/CAT pathway, eNOS phosphorylation, PDE5A activity, and potassium channels. These findings may provide new therapeutic targets for treating vasospasm in CABG grafts and facilitate the development of new vasodilator drugs.

Total Flavone of Rhododendron Improves Cerebral Ischemia Injury by Activating Vascular TRPV4 to Induce Endothelium-Derived Hyperpolarizing Factor-Mediated Responses

Background

Total flavonoids of Rhododendron (TFR) is extracted from Rhododendron, a herbal medicine widely used in China. The main components are flavone compounds such as warfarin, rutin, quercetin, and hyperoside. We investigated the role of TRPV4 channel in the TFR induced endothelium-dependent hyperpolarizing factor- (EDHF-) mediated responses against ischemia/reperfusion injury (IR) in cerebral IR (CIR) rats.

Methods

The morphological changes of cerebral cortex, the relaxation of cerebral basal artery (CBA), and cell membrane potential recording were studied in CIR rats. The outward potassium current in smooth muscle cell was recorded by whole-cell patch clamp recording. The protein expression of TRPV4, SKca, and IKca was determined. Confocal laser was used to measure the Ca²⁺ fluorescence intensity.

Results

After treatment with TFR, the number of pyramidal cells in brain tissue increased and the number of empty or lightly stained cells decreased and these effects were eliminated by using HC-067047, Apamin, or TRAM-34. TFR induced and EDHF-mediated dilatation and hyperpolarization in CBA were also attenuated by using these inhibitors. The increased outward current density elicited by TFR in acutely isolated CBA smooth muscle cells was abolished by using TRAM-34 and Apamin. TFR upregulated the protein expression of TRPV4, SKca, and IKca that was also eliminated by these inhibitors. Laser scanning showed that the increased mean fluorescence intensity of Ca²⁺ by CIR was decreased by using TFR and that this effect was again eliminated by the above inhibitors.

Conclusions

We conclude that in the CBA of the CIR rats the protective effect of TFR on ischemic cerebrovascular injury may be related to the activation of the TRPV4 in both endothelium and smooth muscle by increasing its expression and activity. The activation of TRPV4 channel in the endothelium may be linked to the opening of endothelial IKca/SKca channels that induces EDHF-mediated relaxation and hyperpolarization in the smooth muscle cell. In addition, the activation of TRPV4 in the smooth muscle cell in CBA may be linked with the activation of BK_Ca channel through a TRPV4-dependent pathway, reduce Ca²⁺ concentration in the cell, and relaxes the vessel. These findings may form a new therapeutic target for protection of ischemic brain injury and facilitate the use of Chinese medicine in brain protection.

Hyperhomocysteinemia potentiates diabetes-impaired EDHF-induced vascular relaxation: Role of insufficient hydrogen sulfide

Insufficient hydrogen sulfide (H₂S) has been implicated in Type 2 diabetic mellitus (T2DM) and hyperhomocysteinemia (HHcy)-related cardiovascular complications. We investigated the role of H₂S in T2DM and HHcy-induced endothelial dysfunction in small mesenteric artery (SMA) of db/db mice fed a high methionine (HM) diet. HM diet (8 weeks) induced HHcy in both T2DM db/db mice and non-diabetic db/+ mice (total plasma Hcy: 48.4 and 31.3 µM, respectively), and aggravated the impaired endothelium-derived hyperpolarization factor (EDHF)-induced endothelium-dependent relaxation to acetylcholine (ACh), determined by the presence of eNOS inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME) and prostacyclin (PGI₂) inhibitor indomethacin (INDO), in SMA from db/db mice but not that from db/+ mice. A non-selective Ca²⁺-active potassium channel (K_Ca) opener NS309 rescued T2DM/HHcy-impaired EDHF-mediated vascular relaxation to ACh. EDHF-induced relaxation to ACh was inhibited by a non-selective K_Ca blocker TEA and intermediate-conductance K_Ca blocker (IK_Ca) Tram-34, but not by small-conductance K_Ca (SK_Ca) blocker Apamin. HHcy potentiated the reduction of free sulfide, H₂S and cystathionine γ-lyase protein, which converts L-cysteine to H₂S, in SMA of db/db mice. Importantly, a stable H₂S donor DATS diminished the enhanced O₂^- production in SMAs and lung endothelial cells of T2DM/HHcy mice. Antioxidant PEG-SOD and DATS improved T2DM/HHcy impaired relaxation to ACh. Moreover, HHcy increased hyperglycemia-induced IK_Ca tyrosine nitration in human micro-vascular endothelial cells. EDHF-induced vascular relaxation to L-cysteine was not altered, whereas such relaxation to NaHS was potentiated by HHcy in SMA of db/db mice which was abolished by ATP-sensitive potassium channel blocker Glycolamide but not by K_Ca blockers.

Conclusions

Intermediate HHcy potentiated H₂S reduction via CSE-downregulation in microvasculature of T2DM mice. H₂S is justified as an EDHF. Insufficient H₂S impaired EDHF-induced vascular relaxation via oxidative stress and IK_Ca inactivation in T2DM/HHcy mice. H₂S therapy may be beneficial for prevention and treatment of micro-vascular complications in patients with T2DM and HHcy.

The mechanism of action and role of hydrogen sulfide in the control of vascular tone

Our knowledge about hydrogen sulfide (H₂S) significantly changed over the last two decades. Today it is considered as not only a toxic gas but also as a gasotransmitter with diverse roles in different physiological and pathophysiological processes. H₂S has pleiotropic effects and its possible mechanisms of action involve (1) a reversible protein sulfhydration which can alter the function of the modified proteins similar to nitrosylation or phosphorylation; (2) direct antioxidant effects and (3) interaction with metalloproteins. Its effects on the human cardiovascular system are especially important due to the high prevalence of hypertension and myocardial infarction. The exact molecular targets that affect the vascular tone include the K_ATP channel, the endothelial nitric oxide synthase, the phosphodiesterase of the vascular smooth muscle cell and the cytochrome c oxidase among others and the combination of all these effects lead to the final result on the vascular tone. The relative role of each effect depends immensely on the used concentration and also on the used donor molecules but several other factors and experimental conditions could alter the final effect. The aim of the current review is to give a comprehensive summary of the current understanding on the mechanism of action and role of H₂S in the regulation of vascular tone and to outline the obstacles that hinder the better understanding of its effects.

The structural and functional effects of fine particulate matter from cooking oil fumes on rat umbilical cord blood vessels

A growing body of epidemiological evidence has supported the association between maternal exposure to airborne fine particulate matter (PM2.5) during pregnancy and adverse pregnancy outcomes. However, the specific biological mechanisms implicated in the causes of adverse pregnancy outcomes are not well defined. In this study, a pregnant rat model of exposure to different doses of cooking oil fumes (COFs)-derived PM2.5 by tail intravenous injection in different pregnant stages was established. The results indicated that exposure to COFs-derived PM2.5 was associated with adverse pregnancy outcomes, changed the structure of umbilical cord blood vessels, decreased the diameter and lumen area, and increased wall thickness. What's more, a significant increase of maximum contraction tension was observed in the early pregnancy high-dose exposure group and pregnant low-dose exposure group compared to the control group. Based on the maximum contraction tension, acetylcholine (ACh) did not induce vasodilation but caused a dose-dependent constriction, and there were significant differences in the two groups compared to the control group. Exposure to COFs-derived PM2.5 impaired the vasomotor function of umbilical veins by affecting the expression of NO and ET-1. This is the first study that evaluated the association of risk of adverse pregnancy outcomes and pregnant rats exposed to COFs-derived PM2.5 and primarily explored the potential mechanisms of umbilical cord blood vessels injury on a rat model. More detailed vitro and vivo studies are needed to further explore the mechanism in the future.

Sodium Sulfide, a Hydrogen Sulfide-Releasing Molecule, Attenuates Acute Cerebral Ischemia in Rats

AIMS

Acute cerebral ischemia may lead to ischemic stroke, which is a major cause of death and disability worldwide. Hydrogen sulfide (H2 S) functions importantly in mammalian systems. The present work was designed to study the effect of sodium sulfide, a donor of H2 S, on acute cerebral ischemia.

METHODS

Acute cerebral focal ischemia was produced by middle cerebral artery occlusion (MCAO) in Sprague-Dawley (SD) rats. Bilateral vertebral arteries and common carotid arteries were blocked to establish cerebral global ischemia in SD rats. Acute cerebral anoxia was produced by hypobaric anoxia in C57BL/6 mice and hypoxic anoxia in SD rats. Nimodipine and aspirin were set as positive control separately.

RESULTS

Infarct size after MCAO was decreased by sodium sulfide. Sodium sulfide improved cerebral energy metabolism after cerebral global ischemia and prolonged survival time of animals with acute cerebral anoxia. In addition, increased cerebral blood flow and decreased cerebrovascular resistance, blood viscosity, and thrombogenesis were observed in animals treated with sodium sulfide. In cultured neurons, sodium sulfide increased cell viability and decreased cell apoptosis induced by oxygen-glucose deprivation.

CONCLUSION

Sodium sulfide, a H2 S donor, presents protective effect on acute cerebral ischemia, and might be a promising therapeutic drug.

Effects of hydrogen sulphide in smooth muscle

In recent years, it has become apparent that the gaseous pollutant, hydrogen sulphide (H2S) can be synthesised in the body and has a multitude of biological actions. This review summarizes some of the actions of this 'gasotransmitter' in influencing the smooth muscle that is responsible for controlling muscular activity of hollow organs. In the vasculature, while H2S can cause vasoconstriction by complex interactions with other biologically important gases, such as nitric oxide, the prevailing response is vasorelaxation. While most vasorelaxation responses occur by a direct action of H2S on smooth muscle cells, it has recently been proposed to be an endothelium-derived hyperpolarizing factor. H2S also promotes relaxation in other smooth muscle preparations including bronchioles, the bladder, gastrointestinal tract and myometrium, opening up the opportunity of exploiting the pharmacology of H2S in the treatment of conditions where smooth muscle tone is excessive. The original concept, that H2S caused smooth muscle relaxation by activating ATP-sensitive K(+) channels, has been supplemented with observations that H2S can also modify the activity of other potassium channels, intracellular pH, phosphodiesterase activity and transient receptor potential channels on sensory nerves. While the enzymes responsible for generating endogenous H2S are widely expressed in smooth muscle preparations, it is much less clear what the physiological role of H2S is in determining smooth muscle contractility. Clarification of this requires the development of potent and selective inhibitors of H2S-generating enzymes.

Activation of endothelial IKCa channels underlies NO-dependent myoendothelial feedback

Agonist-induced vasoconstriction triggers a negative feedback response whereby movement of charged ions through gap junctions and/or release of endothelium-derived (NO) limit further reductions in diameter, a mechanism termed myoendothelial feedback. Recent studies indicate that electrical myoendothelial feedback can be accounted for by flux of inositol trisphosphate (IP3) through myoendothelial gap junctions resulting in localized increases in endothelial Ca(2+) to activate intermediate conductance calcium-activated potassium (IKCa) channels, the resultant hyperpolarization then conducting back to the smooth muscle to attenuate agonist-induced depolarization and tone. In the present study we tested the hypothesis that activation of IKCa channels underlies NO-mediated myoendothelial feedback. Functional experiments showed that block of IP3 receptors, IKCa channels, gap junctions and transient receptor potential canonical type-3 (TRPC3) channels caused endothelium-dependent potentiation of agonist-induced increase in tone which was not additive with that caused by inhibition of NO synthase supporting a role for these proteins in NO-mediated myoendothelial feedback. Localized densities of IKCa and TRPC3 channels occurred at the internal elastic lamina/endothelial-smooth muscle interface in rat basilar arteries, potential communication sites between the two cell layers. Smooth muscle depolarization to contractile agonists was accompanied by IKCa channel-mediated endothelial hyperpolarization providing the first demonstration of IKCa channel-mediated hyperpolarization of the endothelium in response to contractile agonists. Inhibition of IKCa channels, gap junctions, TRPC3 channels or NO synthase potentiated smooth muscle depolarization to agonists in a non-additive manner. Together these data indicate that rather being distinct pathways for the modulation of smooth muscle tone, NO and endothelial IKCa channels are involved in an integrated mechanism for the regulation of agonist-induced vasoconstriction.

Aurantio-obtusin relaxes systemic arteries through endothelial PI3K/AKT/eNOS-dependent signaling pathway in rats

Aurantio-obtusin is a natural effective compound isolated from Semen Cassiae, which possesses hypotensive and hypolipidemic effects. Although its hypotensive effect have been clarified, mechanisms Aurantio-obtusin relaxes systemic arteries remain unclear. This study was to investigate effects and mechanisms of Aurantio-obtusin on isolated mesenteric arteries (MAs). We examined MAs relaxation induced by Aurantio-obtusin on rat isolated MAs, expression and activity of endothelial nitric oxide synthase (eNOS) and protein kinase B (AKT), and nitric oxide (NO) production in bovine artery endothelial cells (BAECs). Findings showed Aurantio-obtusin elicited dose-dependent vasorelaxation with phenylephrine (PE) precontracted rat MA rings (diameter: 200-300 μm), which can be diminished by denudation of endothelium and inhibition of eNOS activity, while having no effect on rat isolated pulmonary artery (PA) rings. Aurantio-obtusin increased NO production by promoting phosphorylations of eNOS at Ser-1177 and Thr-495 in endothelial cells. Aurantio-obtusin also promoted phosphorylations of Akt at Ser-473. PI3K inhibitor LY290042 could diminish vasorelaxation induced by Aurantio-obtusin. Moreover Aurantio-obtusin also elicited dose-dependent vasorelaxation effect with PE precontracted MA rings (diameter: 100-150 μm). Therefore, vasorelaxation induced by Aurantio-obtusin was dependent on endothelium integrity and NO production, which mediated by endothelial PI3K/Akt/eNOS pathway. Results suggest Aurantio-obtusin may offer therapeutic effects in hypertension, as a new potential vasodilator.

H2S and Blood Vessels: An Overview

The physiological and biomedical importance of hydrogen sulfide (H2S) has been fully recognized in the cardiovascular system as well as in the rest of the body. In blood vessels, cystathionine γ-lyase (CSE) is a major H2S-producing enzyme expressed in both smooth muscle and endothelium as well as periadventitial adipose tissues. Regulation of H2S production from CSE is controlled by a complex integration of transcriptional, posttranscriptional, and posttranslational mechanisms in blood vessels. In smooth muscle cells, H2S regulates cell apoptosis, phenotypic switch, relaxation and contraction, and calcification. In endothelial cells, H2S controls cell proliferation, cellular senescence, oxidative stress, inflammation, etc. H2S interacts with nitric oxide and acts as an endothelium-derived relaxing factor and an endothelium-derived hyperpolarizing factor. H2S generated from periadventitial adipose tissues acts as an adipocyte-derived relaxing factor and modulates the vascular tone. Extensive evidence has demonstrated the beneficial roles of the CSE/H2S system in various blood vessel diseases, such as hypertension, atherosclerosis, and aortic aneurysm. The important roles signaling in the cardiovascular system merit further intensive and extensive investigation. H2S-releasing agents and CSE activators will find their great applications in the prevention and treatment of blood vessel-related disorders.

Sirtuin 6 is essential for sodium sulfide-mediated cytoprotective effect in ischemia/reperfusion-stimulated brain endothelial cells

BACKGROUND

Our recent data demonstrated that hydrogen sulfide (H2S), the third gaseous transmitter, had a protective effect on stroke. The purpose of this study was to investigate the protective effect of H2S in oxygen glucose deprivation and reperfusion (OGD/R)-stimulated brain endothelial cells and its association with sirtuin 6 (SIRT6).

METHODS

Cultured bEnd.3 brain endothelial cells were exposed to OGD/R. The effects of sodium sulfide (Na2S, an exogenous H2S donor) on cell death, lactate dehydrogenase release, intracellular reactive oxygen species (ROS) production, superoxide dismutase (SOD) and catalase (CAT) activities, H2S level, cystathionine γ-lyase (CSE) expression, and sirtuin 6 (SIRT6) expression/activity were tested to elucidate the protective mechanisms of H2S.

RESULTS

Application of Na2S concentration dependently reduced OGD/R-induced cell death, accompanying with decreasing intracellular ROS production and increasing activities of SOD and CAT. In addition, Na2S also enhanced H2S level and CSE expression associated with upregulation of SIRT6 expression and activity in OGD/R-stimulated brain endothelial cells, whereas CSE inhibitor DL-propargylglycine further deteriorated the decrease of SIRT6 expression and activity as well as the reduction of H2S level and CSE expression caused by OGD/R. Furthermore, SIRT6 knockdown abolished Na2S-mediated CSE expression and cytoprotection action in OGD/R-stimulated cells.

CONCLUSIONS

Na2S protected brain endothelial cells against simulated ischemic injury through SIRT6-dependent mechanisms.

Hydrogen sulfide and endothelium-dependent vasorelaxation

In addition to nitric oxide and carbon monoxide, hydrogen sulfide (H2S), synthesized enzymatically from l-cysteine or l-homocysteine, is the third gasotransmitter in mammals. Endogenous H2S is involved in the regulation of many physiological processes, including vascular tone. Although initially it was suggested that in the vascular wall H2S is synthesized only by smooth muscle cells and relaxes them by activating ATP-sensitive potassium channels, more recent studies indicate that H2S is synthesized in endothelial cells as well. Endothelial H2S production is stimulated by many factors, including acetylcholine, shear stress, adipose tissue hormone leptin, estrogens and plant flavonoids. In some vascular preparations H2S plays a role of endothelium-derived hyperpolarizing factor by activating small and intermediate-conductance calcium-activated potassium channels. Endothelial H2S signaling is up-regulated in some pathologies, such as obesity and cerebral ischemia-reperfusion. In addition, H2S activates endothelial NO synthase and inhibits cGMP degradation by phosphodiesterase 5 thus potentiating the effect of NO-cGMP pathway. Moreover, H2S-derived polysulfides directly activate protein kinase G. Finally, H2S interacts with NO to form nitroxyl (HNO)-a potent vasorelaxant. H2S appears to play an important and multidimensional role in endothelium-dependent vasorelaxation.

Protective Effect and Mechanism of Total Flavones from Rhododendron simsii Planch on Endothelium-Dependent Dilatation and Hyperpolarization in Cerebral Ischemia-Reperfusion and Correlation to Hydrogen Sulphide Release in Rats

We for the first time investigated the effect and mechanism of the total flavones of Rhododendron simsii Planch (TFR), a widely-used Chinese herb for a thousand years, on vasodilatation and hyperpolarization in middle cerebral artery (MCA) of rats subject to global cerebral ischemia-reperfusion (CIR). TFR (11~2700 mg/L) evoked dose-dependent vasodilation and hyperpolarization in MCA of both sham and CIR that were partially inhibited by 30 μM N-nitro-L-arginine-methyl-ester and 10 μM indomethacin and further attenuated by endogenous H₂S synthese-CSE inhibitor PPG (100 μM) or Ca²⁺-activated potassium channel (K_ca) inhibitor TEA (1 mM). In whole-cell patch clamp recording, TFR remarkably enhanced the outward current that was inhibited by TEA. CIR increased CSE mRNA expression and the contents of H₂S that were further increased by TFR. We conclude that, in MCA of CIR rats, TFR induces non-NO and non-PGI₂-mediated effects of vasodilatation and hyperpolarization involving K_ca and increases CSE mRNA expression level in endothelial cells and H₂S content in the cerebrum. These findings suggest that the response induced by TFR is potentially related to endothelium-derived hyperpolarizing factor mediated by the endogenous H₂S and promote the use of TFR in protection of brain from ischemia-reperfusion injury.

Endothelial dysfunction in experimental models of arterial hypertension: cause or consequence?

Hypertension is a risk factor for other cardiovascular diseases and endothelial dysfunction was found in humans as well as in various commonly employed animal experimental models of arterial hypertension. Data from the literature indicate that, in general, endothelial dysfunction would not be the cause of experimental hypertension and may rather be secondary, that is, resulting from high blood pressure (BP). The initial mechanism of endothelial dysfunction itself may be associated with a lack of endothelium-derived relaxing factors (mainly nitric oxide) and/or accentuation of various endothelium-derived constricting factors. The involvement and role of endothelium-derived factors in the development of endothelial dysfunction in individual experimental models of hypertension may vary, depending on the triggering stimulus, strain, age, and vascular bed investigated. This brief review was focused on the participation of endothelial dysfunction, individual endothelium-derived factors, and their mechanisms of action in the development of high BP in the most frequently used rodent experimental models of arterial hypertension, including nitric oxide deficient models, spontaneous (pre)hypertension, stress-induced hypertension, and selected pharmacological and diet-induced models.

Endothelial dysfunction in experimental models of arterial hypertension: cause or consequence?

Hypertension is a risk factor for other cardiovascular diseases and endothelial dysfunction was found in humans as well as in various commonly employed animal experimental models of arterial hypertension. Data from the literature indicate that, in general, endothelial dysfunction would not be the cause of experimental hypertension and may rather be secondary, that is, resulting from high blood pressure (BP). The initial mechanism of endothelial dysfunction itself may be associated with a lack of endothelium-derived relaxing factors (mainly nitric oxide) and/or accentuation of various endothelium-derived constricting factors. The involvement and role of endothelium-derived factors in the development of endothelial dysfunction in individual experimental models of hypertension may vary, depending on the triggering stimulus, strain, age, and vascular bed investigated. This brief review was focused on the participation of endothelial dysfunction, individual endothelium-derived factors, and their mechanisms of action in the development of high BP in the most frequently used rodent experimental models of arterial hypertension, including nitric oxide deficient models, spontaneous (pre)hypertension, stress-induced hypertension, and selected pharmacological and diet-induced models.

A hypothesis: hydrogen sulfide might be neuroprotective against subarachnoid hemorrhage induced brain injury

Gases such as nitric oxide (NO) and carbon monoxide (CO) play important roles both in normal physiology and in disease. Recent studies have shown that hydrogen sulfide (H₂S) protects neurons against oxidative stress and ischemia-reperfusion injury and attenuates lipopolysaccharides (LPS) induced neuroinflammation in microglia, exhibiting anti-inflammatory and antiapoptotic activities. The gas H₂S is emerging as a novel regulator of important physiologic functions such as arterial diameter, blood flow, and leukocyte adhesion. It has been known that multiple factors, including oxidative stress, free radicals, and neuronal nitric oxide synthesis as well as abnormal inflammatory responses, are involved in the mechanism underlying the brain injury after subarachnoid hemorrhage (SAH). Based on the multiple physiologic functions of H₂S, we speculate that it might be a promising, effective, and specific therapy for brain injury after SAH.

Leptin-induced endothelium-dependent vasorelaxation of peripheral arteries in lean and obese rats: role of nitric oxide and hydrogen sulfide

Adipose tissue hormone leptin induces endothelium-dependent vasorelaxation mediated by nitric oxide (NO) and endothelium-derived hyperpolarizing factors (EDHF). Previously it has been demonstrated that in short-term obesity the NO-dependent and the EDHF-dependent components of vascular effect of leptin are impaired and up-regulated, respectively. Herein we examined the mechanism of the EDHF-dependent vasodilatory effect of leptin and tested the hypothesis that alterations of acute vascular effects of leptin in obesity are accounted for by chronic hyperleptinemia. The study was performed in 5 groups of rats: (1) control, (2) treated with exogenous leptin for 1 week to induce hyperleptinemia, (3) obese, fed highly-palatable diet for 4 weeks, (4) obese treated with pegylated superactive rat leptin receptor antagonist (PEG-SRLA) for 1 week, (5) fed standard chow and treated with PEG-SRLA. Acute effect of leptin on isometric tension of mesenteric artery segments was measured ex vivo. Leptin relaxed phenylephrine-preconstricted vascular segments in NO- and EDHF-dependent manner. The NO-dependent component was impaired and the EDHF-dependent component was increased in the leptin-treated and obese groups and in the latter group both these effects were abolished by PEG-SRLA. The EDHF-dependent vasodilatory effect of leptin was blocked by either the inhibitor of cystathionine γ-lyase, propargylglycine, or a hydrogen sulfide (H2S) scavenger, bismuth (III) subsalicylate. The results indicate that NO deficiency is compensated by the up-regulation of EDHF in obese rats and both effects are accounted for by chronic hyperleptinemia. The EDHF-dependent component of leptin-induced vasorelaxation is mediated, at least partially, by H2S.