Hydrogen sulfide depolarizes neurons in the nucleus of the solitary tract of the rat

Hydrogen sulfide production in the medullary respiratory center modulates the neural circuit for respiratory pattern and rhythm generations

Hydrogen sulfide (H2S), which is synthesized in the brain, modulates the neural network. Recently, the importance of H2S in respiratory central pattern generation has been recognized, yet the function of H2S in the medullary respiratory network remains poorly understood. Here, to evaluate the functional roles of H2S in the medullary respiratory network, the Bötzinger complex (BötC), the pre-Bötzinger complex (preBötC), and the rostral ventral respiratory group (rVRG), we observed the effects of inhibition of H2S synthesis at each region on the respiratory pattern by using an in situ arterially perfused preparation of decerebrated male rats. After microinjection of an H2S synthase inhibitor, cystathionine β-synthase, into the BötC or preBötC, the amplitude of the inspiratory burst decreased and the respiratory frequency increased according to shorter expiration and inspiration, respectively. These alterations were abolished or attenuated in the presence of a blocker of excitatory synaptic transmission. On the other hand, after microinjection of the H2S synthase inhibitor into the rVRG, the amplitude of the inspiratory burst was attenuated, and the respiratory frequency decreased, which was the opposite effect to those obtained by blockade of inhibitory synaptic transmission at the rVRG. These results suggest that H2S synthesized in the BötC and preBötC functions to limit respiratory frequency by sustaining the respiratory phase and to maintain the power of inspiration. In contrast, H2S synthesized in the rVRG functions to promote respiratory frequency by modulating the interval of inspiration and to maintain the power of inspiration. The underlying mechanism might facilitate excitatory synaptic transmission and/or attenuate inhibitory synaptic transmission.

Effect of exogenous hydrogen sulfide in the nucleus tractus solitarius on gastric motility in rats

BACKGROUND

Hydrogen sulfide (H2S) is a recently discovered gaseous neurotransmitter in the nervous and gastrointestinal systems. It exerts its effects through multiple signaling pathways, impacting various physiological activities. The nucleus tractus solitarius (NTS), a vital nucleus involved in visceral sensation, was investigated in this study to understand the role of H2S in regulating gastric function in rats.

AIM

To examine whether H2S affects the nuclear factor kappa-B (NF-κB) and transient receptor potential vanilloid 1 pathways and the neurokinin 1 (NK1) receptor in the NTS.

METHODS

Immunohistochemical and fluorescent double-labeling techniques were employed to identify cystathionine beta-synthase (CBS) and c-Fos co-expressed positive neurons in the NTS during rat stress. Gastric motility curves were recorded by inserting a pressure-sensing balloon into the pylorus through the stomach fundus. Changes in gastric motility were observed before and after injecting different doses of NaHS (4 nmol and 8 nmol), physiological saline, Capsazepine (4 nmol) + NaHS (4 nmol), pyrrolidine dithiocarbamate (PDTC, 4 nmol) + NaHS (4 nmol), and L703606 (4 nmol) + NaHS (4 nmol).

RESULTS

We identified a significant increase in the co-expression of c-Fos and CBS positive neurons in the NTS after 1 h and 3 h of restraint water-immersion stress compared to the expressions observed in the control group. Intra-NTS injection of NaHS at different doses significantly inhibited gastric motility in rats (P < 0.01). However, injection of saline, first injection NF-κB inhibitor PDTC or transient receptor potential vanilloid 1 (TRPV1) antagonist Capsazepine or NK1 receptor blockers L703606 and then injection NaHS did not produce significant changes (P > 0.05).

CONCLUSION

NTS contains neurons co-expressing CBS and c-Fos, and the injection of NaHS into the NTS can suppress gastric motility in rats. This effect may be mediated by activating TRPV1 and NK1 receptors via the NF-κB channel.

Hydrogen sulfide as a neuromodulator of the vascular tone

Hydrogen sulfide (H₂S) is a unique signaling molecule that, along with carbon monoxide and nitric oxide, belongs to the gasotransmitters family. H₂S is endogenously synthesized by enzymatic and non-enzymatic pathways. Three enzymatic pathways involving cystathionine-γ-lyase, cystathionine-β-synthetase, and 3-mercaptopyruvate sulfurtransferase are known as endogenous sources of H₂S. This gaseous molecule has recently emerged as a regulator of many systems and physiological functions, including the cardiovascular system where it controls the vascular tone of small arteries. In this context, H₂S leads to vasorelaxation by regulating the activity of vascular smooth muscle cells, endothelial cells, and perivascular nerves. Specifically, H₂S modulates the functionality of different ion channels to inhibit the autonomic sympathetic outflow-by either central or peripheral mechanisms-or to stimulate perivascular sensory nerves. These mechanisms are particularly relevant for those pathological conditions associated with impaired neuromodulation of vascular tone. In this regard, exogenous H₂S administration efficiently attenuates the increased activity of the sympathetic nervous system often seen in patients with certain pathologies. These effects of H₂S on the autonomic sympathetic outflow will be the primary focus of this review. Thereafter, we will discuss the central and peripheral regulatory effects of H₂S on vascular tone. Finally, we will provide the audience with a detailed summary of the current pathological implications of H₂S modulation on the neural regulation of vascular tone.

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.

Hydrogen Sulfide Subchronic Treatment Improves Hypertension Induced by Traumatic Brain Injury in Rats through Vasopressor Sympathetic Outflow Inhibition

Traumatic brain injury (TBI) represents a critical public health problem around the world. To date, there are no accurate therapeutic approaches for the management of cardiovascular impairments induce by TBI. In this regard, hydrogen sulfide (H₂S), a novel gasotransmitter, has been proposed as a neuro- and cardioprotective molecule. This study was designed to determine the effect of subchronic management with sodium hydrosulfide (NaHS) on hemodynamic, vasopressor sympathetic outflow and sensorimotor alterations produced by TBI. Animals underwent a lateral fluid percussion injury, and changes in hemodynamic variables were measured by pletismographic methods. In addition, vasopressor sympathetic outflow was assessed by a pithed rat model. Last, sensorimotor impairments were evaluated by neuroscore test and beam-walking test. At seven, 14, 21, and 28 days after moderate-severe TBI, the animals showed: (1) a decrease on sensorimotor function in the neuroscore test and beam-walking test; (2) an increase in heart rate, systolic, diastolic, and mean blood pressure; (3) progressive sympathetic hyperactivity; and (4) a decrease in vasopressor responses induced by noradrenaline (α_1/2-adrenoceptors agonist) and UK 14,304 (selective α₂-adrenoceptor agonist). Interestingly, intraperitoneal daily injections of NaHS, an H₂S donor (3.1 and 5.6 mg/kg), during seven days after TBI prevented the development of the impairments in hemodynamic variables, which were similar to those obtained in sham animals. Moreover, NaHS treatment prevented the sympathetic hyperactivity and decreased noradrenaline-induced vasopressor responses. No effects on sensorimotor dysfunction were observed, however. Taken together, our results suggest that H₂S ameliorates the hemodynamic and sympathetic system impairments observed after TBI.

The role of gasotransmitters in neonatal physiology

The gasotransmitters, nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO), are endogenously-produced volatile molecules that perform signaling functions throughout the body. In biological tissues, these small, lipid-permeable molecules exist in free gaseous form for only seconds or less, and thus they are ideal for paracrine signaling that can be controlled rapidly by changes in their rates of production or consumption. In addition, tissue concentrations of the gasotransmitters are influenced by fluctuations in the level of O₂ and reactive oxygen species (ROS). The normal transition from fetus to newborn involves a several-fold increase in tissue O₂ tensions and ROS, and requires rapid morphological and functional adaptations to the extrauterine environment. This review summarizes the role of gasotransmitters as it pertains to newborn physiology. Particular focus is given to the vasculature, ventilatory, and gastrointestinal systems, each of which uniquely illustrate the function of gasotransmitters in the birth transition and newborn periods. Moreover, given the relative lack of studies on the role that gasotransmitters play in the newborn, particularly that of H₂S and CO, important gaps in knowledge are highlighted throughout the review.

The effects of dietary methionine restriction on the function and metabolic reprogramming in the liver and brain - implications for longevity

Methionine is an essential sulphur-containing amino acid involved in protein synthesis, regulation of protein function and methylation reactions. Dietary methionine restriction (0.12-0.17% methionine in food) extends the life span of various animal species and delays the onset of aging-associated diseases and cancers. In the liver, methionine restriction attenuates steatosis and delays the development of non-alcoholic steatohepatitis due to antioxidative action and metabolic reprogramming. The limited intake of methionine stimulates the fatty acid oxidation in the liver and the export of lipoproteins as well as inhibits de novo lipogenesis. These effects are mediated by various signaling pathways and effector molecules, including sirtuins, growth hormone/insulin-like growth factor-1 axis, sterol regulatory element binding proteins, adenosine monophosphate-dependent kinase and general control nonderepressible 2 pathway. Additionally, methionine restriction stimulates the synthesis of fibroblast growth factor-21 in the liver, which increases the insulin sensitivity of peripheral tissues. In the brain, methionine restriction delays the onset of neurodegenerative diseases and increases the resistance to various forms of stress through antioxidative effects and alterations in lipid composition. This review aimed to summarize the morphological, functional and molecular changes in the liver and brain caused by the methionine restriction, with possible implications in the prolongation of maximal life span.

Age-Dependent, Subunit Specific Action of Hydrogen Sulfide on GluN1/2A and GluN1/2B NMDA Receptors

Hydrogen sulfide (H₂S) is an endogenously produced neuroactive gas implicated in many key processes in the peripheral and central nervous system. Whereas the neuroprotective role of H₂S has been shown in adult brain, the action of this messenger in newborns remains unclear. One of the known targets of H₂S in the nervous system is the N-methyl-D-aspartate (NMDA) glutamate receptor which can be composed of different subunits with distinct functional properties. In the present study, using patch clamp technique, we compared the effects of the H₂S donor sodium hydrosulfide (NaHS, 100 μM) on hippocampal NMDA receptor mediated currents in rats of the first and third postnatal weeks. This was supplemented by testing effects of NaHS on recombinant GluN1/2A and GluN1/2B NMDA receptors expressed in HEK293T cells. The main finding is that NaHS action on NMDA currents is age-dependent. Currents were reduced in newborns but increased in older juvenile rats. Consistent with an age-dependent switch in NMDA receptor composition, in HEK239T cells expressing GluN1/2A receptors, NaHS increased NMDA activated currents associated with acceleration of desensitization and decrease of the deactivation rate. In contrast, in GluN1/2B NMDA receptors, which are prevalent in newborns, NaHS decreased currents and reduced receptor deactivation without effect on the desensitization rate. Adenylate cyclase inhibitor MDL-12330A (10 μM) did not prevent the age-dependent effects of NaHS on NMDA evoked currents in pyramidal neurons of hippocampus. The reducing agent dithiothreitol (DTT, 2 mM) applied on HEK293T cells prevented facilitation induced by NaHS on GluN1/2A NMDA receptors, however in GluN1/2B NMDA receptors the inhibitory effect of NaHS was still observed. Our data indicate age-dependent effect of H₂S on NMDA receptor mediated currents determined by glutamate receptor subunit composition. While the inhibitory action of H₂ on GluN1/2B receptors could limit the excessive activation in early age, the enhanced functionality of GluN1/2A receptor in the presence of this gasotransmitter can enlarge synaptic efficacy and promote synaptic plasticity in adults.

Hydrogen-Rich Saline Alleviates Kidney Fibrosis Following AKI and Retains Klotho Expression

Purpose: Acute kidney injury (AKI) is a prominent risk factor for the development of chronic kidney disease (CKD). To date, the related mechanism and effective therapy have not been rigorously explored. The present study aims to investigate the reno-protection of hydrogen-rich saline (HRS) against ischemia/reperfusion (IR)-induced AKI.

Methods: Adult male C57 mice were randomly allocated into three groups: Sham, IR, IR+HRS. Renal IR injury model was generated via 35 min occlusion of bilateral kidney pedicles, and then, mice were administered with different treatments intraperitoneally in various groups. After 14- or 28-day treatment, mice were perfused and the kidneys were collected following reperfusion. Many proteins were detected by western blots, including renal fibrotic proteins [a-smooth muscle actin (a-SMA), collagen I (Col I)], Klotho, the methylation of Klotho, damage-regulated autophagy modulator (Beclin-1), and microtubule-associated protein light 3-II (LC3-II). Finally, the levels of serum blood urea nitrogen (BUN) and creatinine (Cr) were measured to investigate the renal function.

Results: Histological data showed that the HRS treatment significantly decreased the fibrosis in renal tissues when compared with the IR group, and both of BUN and Cr were lower in the HRS group than IR group (8.9 ± 0.6 vs. 9.9 ± 0.1 mmol/l, 51 ± 6.5 vs. 60 ± 5.8 μmol/l) (P < 0.05). The expression of fibrotic markers, a-SMA and Col I, showed a robust increase in IR injury models than the Sham group, which was consistent with the result of Trichrome staining. However, the levels of a-SMA and Col I expression were sharply decreased in the IR+HRS group (P < 0.05). IR injury also enhanced LC3-II and Beclin-1 expression, but decreased Klotho level. The Klotho level was alleviated by HRS, but LC3-II and Beclin-1 were starkly enhanced in HRS group (P < 0.05).

Conclusion: HRS showed a protective effect in the prevention of renal injury and could inhibit renal fibrosis after IR injury in mice. This role of HRS might be exerted via retaining Klotho expression and activating autophagy in the kidney.

High glucose increases action potential firing of catecholamine neurons in the nucleus of the solitary tract by increasing spontaneous glutamate inputs

Glucose is a crucial substrate essential for cell survival and function. Changes in glucose levels impact neuronal activity and glucose deprivation increases feeding. Several brain regions have been shown to respond to glucoprivation, including the nucleus of the solitary tract (NTS) in the brain stem. The NTS is the primary site in the brain that receives visceral afferent information from the gastrointestinal tract. The catecholaminergic (CA) subpopulation within the NTS modulates many homeostatic functions including cardiovascular reflexes, respiration, food intake, arousal, and stress. However, it is not known if they respond to changes in glucose. Here we determined whether NTS-CA neurons respond to changes in glucose concentration and the mechanism involved. We found that decreasing glucose concentrations from 5 mM to 2 mM to 1 mM, significantly decreased action potential firing in a cell-attached preparation, whereas increasing it back to 5 mM increased the firing rate. This effect was dependent on glutamate release from afferent terminals and required presynaptic 5-HT₃Rs. Decreasing the glucose concentration also decreased both basal and 5-HT₃R agonist-induced increase in the frequency of spontaneous glutamate inputs onto NTS-CA neurons. Low glucose also blunted 5-HT-induced inward currents in nodose ganglia neurons, which are the cell bodies of vagal afferents. The effect of low glucose in both nodose ganglia cells and in NTS slices was mimicked by the glucokinase inhibitor glucosamine. This study suggests that NTS-CA neurons are glucosensing through a presynaptic mechanism that is dependent on vagal glutamate release, 5-HT₃R activity, and glucokinase.

Involvement of endogenous central hydrogen sulfide (H2S) in hypoxia-induced hypothermia in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) display autonomic imbalance and abnormal body temperature (Tb) adjustments. Hydrogen sulfide (H2S) modulates hypoxia-induced hypothermia, but its role in SHR thermoregulation is unknown. We tested the hypothesis that SHR display peculiar thermoregulatory response to hypoxia and that endogenous H2S overproduced in the caudal nucleus of the solitary tract (NTS) of SHR modulates this response. SHR and Wistar rats were microinjected into the fourth ventricle with aminooxyacetate (AOA, H2S-synthezing enzyme inhibitor) or sodium sulfide (Na2S, H2S donor) and exposed to normoxia (21% inspired O2) or hypoxia (10% inspired O2, 30 min). Tb was continuously measured, and H2S production rate was assessed in caudal NTS homogenates. In both groups, AOA, Na2S, or saline (i.e., control; 1 μL) did not affect euthermia. Hypoxia caused similar decreases in Tb in both groups. AOA presented a longer latency to potentiate hypoxic hypothermia in SHR. Caudal NTS H2S production rate was higher in SHR. We suggest that increased bioavailability of H2S in the caudal NTS of SHR enables the adequate modulation of excitability of peripheral chemoreceptor-activated NTS neurons that ultimately induce suppression of brown adipose tissue thermogenesis, thus accounting for the normal hypoxic hypothermia.

Cryogenic role of central endogenous hydrogen sulfide in the rat model of endotoxic shock

Thermoregulatory responses to lipopolysaccharide (LPS) are affected by modulators that increase (propyretic) or decrease (cryogenic) body temperature (Tb). We tested the hypothesis that central hydrogen sulfide (H₂S) acts as a thermoregulatory modulator and that H₂S production in the anteroventral preoptic region of the hypothalamus (AVPO) is increased during hypothermia and decreased during fever induced by bacterial lipopolysaccharide (LPS, 2.5mg/kg i.p.) in rats kept at an ambient temperature of 25°C. Deep Tb was recorded before and after pharmacological inhibition of the enzyme cystathionine β-synthase (CBS - responsible for H₂S endogenous production in the brain) combined or not with LPS administration. To further investigate the mechanisms responsible for these thermoregulatory adjustments, we also measured prostaglandin D₂ (PGD₂) production in the AVPO. LPS caused typical hypothermia followed by fever. Levels of AVPO H₂S were significantly increased during hypothermia when compared to both euthermic and febrile rats. Intracerebroventricular (icv) microinjection of aminooxyacetate (AOA, a CBS inhibitor; 100 pmol) neither affected Tb nor basal PGD₂ production during euthermia. In LPS-treated rats, AOA caused increased Tb values during hypothermia, along with enhanced PGD₂ production. We conclude that the gaseous messenger H₂S modulates hypothermia during endotoxic shock, acting as a cryogenic molecule.

Physiological Importance of Hydrogen Sulfide: Emerging Potent Neuroprotector and Neuromodulator

Hydrogen sulfide (H2S) is an emerging neuromodulator that is considered to be a gasotransmitter similar to nitrogen oxide (NO) and carbon monoxide (CO). H2S exerts universal cytoprotective effects and acts as a defense mechanism in organisms ranging from bacteria to mammals. It is produced by the enzymes cystathionine β-synthase (CBS), cystathionine ϒ-lyase (CSE), 3-mercaptopyruvate sulfurtransferase (MST), and D-amino acid oxidase (DAO), which are also involved in tissue-specific biochemical pathways for H2S production in the human body. H2S exerts a wide range of pathological and physiological functions in the human body, from endocrine system and cellular longevity to hepatic protection and kidney function. Previous studies have shown that H2S plays important roles in peripheral nerve regeneration and degeneration and has significant value during Schwann cell dedifferentiation and proliferation but it is also associated with axonal degradation and the remyelination of Schwann cells. To date, physiological and toxic levels of H2S in the human body remain unclear and most of the mechanisms of action underlying the effects of H2S have yet to be fully elucidated. The primary purpose of this review was to provide an overview of the role of H2S in the human body and to describe its beneficial effects.

Hydrogen-Rich Saline Promotes the Recovery of Renal Function after Ischemia/Reperfusion Injury in Rats via Anti-apoptosis and Anti-inflammation

Purpose: Hydrogen is a proven novel antioxidant that selectively reduces hydroxyl radicals. In this study, we investigated the effects of hydrogen-rich saline solution on the prevention of renal injury induced by ischemia/reperfusion (I/R) and on renal function recovery.

Methods: A rat model of renal I/R injury was induced by 45 min occlusion of the left renal pedicle, followed by 108 h reperfusion. The right kidney was surgically removed. Then, 0.9% NaCl solution (1 ml/kg) or hydrogen-rich saline solution (HRSS; 1 ml/kg) was injected into the abdominal cavity at 4 h intervals. We assessed the influence of HRSS or control saline solution on the recovery of renal function after I/R injury. Kidney tissues were taken at different time points (24, 36, 48, 72, and 108 h after reperfusion) and frozen (-80°C). Kidney cell apoptosis was evaluated using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive staining. Additionally, the apoptotic factors (Bcl-2, Bax, caspase-3, caspase-9, and caspase-8) and the pro-inflammatory cytokines (IL-6 and TNF-α) were measured in the kidney tissues. Finally, serum blood urea nitrogen (BUN) and creatinine (Cr) levels were measured.

Results: Histological analyses revealed a marked reduction of interstitial congestion, edema and hemorrhage in renal tissue after HRSS treatment compared to saline treatment. After I/R injury, BUN, Cr, Bcl-2, caspase-3, caspase-9, caspase-8, IL-6, and TNF-α were all significantly increased, while Bax expression was decreased. HRSS remarkably reversed these changes. Moreover, BUN and Cr decreased more rapidly in the rats treated with HRSS compared to the rats treated with control saline solution.

Conclusions: HRSS showed a protective effect in the prevention of renal injury and could promote renal function recovery after I/R injury in rats. HRSS might partially exert its role through an anti-apoptotic and anti-inflammatory action in kidney cells.

Recent advances in central cardiovascular control: sex, ROS, gas and inflammation

The central nervous system (CNS) in concert with the heart and vasculature is essential to maintaining cardiovascular (CV) homeostasis. In recent years, our understanding of CNS control of blood pressure regulation (and dysregulation leading to hypertension) has evolved substantially to include (i) the actions of signaling molecules that are not classically viewed as CV signaling molecules, some of which exert effects at CNS targets in a non-traditional manner, and (ii) CNS locations not traditionally viewed as central autonomic cardiovascular centers. This review summarizes recent work implicating immune signals and reproductive hormones, as well as gasotransmitters and reactive oxygen species in the pathogenesis of hypertension at traditional CV control centers. Additionally, recent work implicating non-conventional CNS structures in CV regulation is discussed.