H2S protects hippocampal neurons from anoxia-reoxygenation through cAMP-mediated PI3K/Akt/p70S6K cell-survival signaling pathways

Pyridoxal-5-phosphate mitigates age-related metabolic imbalances in the rat heart through the H2S/AKT/GSK3β signaling axis

Pyridoxal-5-phosphate (PLP) enhances the synthesis of endogenous hydrogen sulfide, a potent regulator of cell metabolism. We used 24-month-old rats to investigate the PLP mitoprotective function in the aging heart. We demonstrated improvement of mitochondrial bioenergetic functions, inhibition of mPTP opening after PLP administration. Moreover, PLP treatment increased glucose consumption and utilization, decreased lipid transport into the cells, but increased fatty acid β-oxidation, providing sufficient energy. An ECG study showed a significant improvement in cardiac function in PLP-treated old rats. Our data suggest that PLP may exert its effect through the H2S/AKT/GSK3β axis with further targeting of the Sirt1/PGC-1α signaling pathway.

Protective Effect of Hydrogen Sulfide on Cerebral Ischemia-Reperfusion Injury

The brain is the most sensitive organ to hypoxia in the human body. Hypoxia in the brain will lead to damage to local brain tissue. When the blood supply of ischemic brain tissue is restored, the damage will worsen, that is, cerebral ischemia-reperfusion injury. Hydrogen sulfide (H2S) is a gaseous signal molecule and a novel endogenous neuroregulator. Indeed, different concentrations of H2S have different effects on neurons. Low concentration of H2S can play an important protective role in cerebral ischemia-reperfusion injury by inducing anti-oxidative stress injury, inhibition of inflammatory response, inhibition of cell apoptosis, reduction of cerebrovascular endothelial cell injury, regulation of autophagy, and other ways, which provides a new idea for clinical diagnosis and treatment of related diseases. This review aims to report the recent research progress on the dual effect of H2S on brain tissue during cerebral ischemia/reperfusion injury.

Senkyunolide H protects PC12 cells from OGD/R-induced injury via cAMP-PI3K/AKT signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Senkyunolide H (SNH) is a bioactive phthalide isolated from Ligusticum chuanxiong Hort rhizome and was reported to have multiple pharmacological effects.

AIM OF THE STUDY

The study was performed to verify the potency of SNH protecting PC12 cells from oxygen glucose deprivation/reperfusion (OGD/R)-induced injury and to elucidate the underlying mechanisms.

MATERIALS AND METHODS

OGD/R model was established in PC12 cells and the cell viability was measured by MTT assay. The cell morphology was observed using scanning electron microscope (SEM). The potential targets of SNH and related targets of OGD/R were screened, and a merged protein-protein interaction (PPI) network of SNH and OGD/R was constructed based on the network pharmacology analysis. Kyoto Encyclopedia of Genes and Genomes (KEGG) database was used for pathway analysis. Intracellular cAMP level and the protein expression levels were measured to elucidate the underlying mechanisms.

RESULTS

SNH pretreatment protected PC12 cells against OGD/R-induced cell death. SNH also significantly protected the cell protrusion. A merged PPI network was constructed and the shared candidate targets significantly enriched in cAMP signaling pathway. The level of intracellular cAMP and the protein level of p-CREB, p-AKT, p-PDK1 and PKA protein were up-regulated after the treatment of SNH compared with OGD/R modeling.

CONCLUSIONS

The present study indicated that SNH protected PC12 cells from OGD/R-induced injury via cAMP-PI3K/AKT signaling pathway.

Astrocytic Hydrogen Sulfide Regulates Supraoptic Cellular Activity in the Adaptive Response of Lactating Rats to Chronic Social Stress

Maternal social stress among breastfeeding women can be adapted in chronic process. However, neuroendocrine mechanisms underlying such adaptation remain to be identified. Here, we report the effects of 2 hr/day unfamiliar male rat invasion (UMI) stress on maternal behaviors in lactating rats during postpartum day 8 (UMI8) to postpartum day 12 (UMI12). Rat dams at UMI8 presented signs of maternal anxiety, depression, and attacks toward male intruder. These changes partially reversed at UMI12 except the sign of anxiety. In the supraoptic nucleus (SON), UMI12 but not UMI8 significantly increased the expression of c-Fos and phosphorylated extracellular signal-regulated protein kinase 1/2. At UMI8 but not UMI12, length of glial fibrillary acidic protein (GFAP, astrocytic cytoskeletal element) filaments around oxytocin (OT) neurons was significantly longer than that of their controls; the amount of GFAP fragments at UMI12 was significantly less than that at UMI8. Expression of cystathionine β-synthase (CBS, enzyme for H₂S synthesis) at UMI12 was significantly higher than that at UMI8. CBS expression did not change significantly in the somatic zone of the SON but decreased significantly at the ventral glia lamina at UMI8. In brain slices of the SON, aminooxyacetate (a CBS blocker) significantly increased the expression of GFAP proteins that were molecularly associated with CBS. Aminooxyacetate also reduced the firing rate of OT neurons whereas Na₂S, a donor of H₂S, increased it. The adaptation during chronic social stress is possibly attributable to the increased production of H₂S by astrocytes and the subsequent retraction of astrocytic processes around OT neurons.

Neuroprotective mechanisms of mangiferin in neurodegenerative diseases

The central nervous system (CNS) regulates and coordinates an extensive array of complex processes requiring harmonious regulation of specific genes. CNS disorders represent a large burden on society and cause enormous disability and economic losses. Traditional Chinese medicine (TCM) has been used for many years in the treatment of neurological illnesses, such as Alzheimer's disease, Parkinson's disease, stroke, and depression, as the combination of TCM and Western medicine has superior therapeutic efficacy and minimal toxic side effects. Mangiferin (MGF) is an active compound of the traditional Chinese herb rhizome anemarrhenae, which has antioxidant, anti-inflammation, anti-lipid peroxidation, immunomodulatory, and anti-apoptotic functions in the CNS. MGF has been demonstrated to have therapeutic effects in CNS diseases through a multitude of mechanisms. This review outlines the latest research on the neuroprotective ability of MGF and the diverse molecular mechanisms involved.

Role of adenosine in functional recovery following anoxic coma in Locusta migratoria

When exposed to prolonged anoxia insects enter a reversible coma during which neural and muscular systems temporarily shut down. Nervous system shut down is a result of spreading depolarization throughout neurons and glial cells. Upon return to normoxia, recovery occurs following the restoration of ion gradients. However, there is a delay in the functional recovery of synaptic transmission following membrane repolarization. In mammals, the build-up of extracellular adenosine following spreading depolarization contributes to this delay. Adenosine accumulation is a marker of metabolic stress and it has many downstream effects through the activation of adenosine receptors, including the inhibition of cAMP production. Here we demonstrate that adenosine lengthens the time to functional recovery following anoxic coma in locusts. Caffeine, used as an adenosine receptor antagonist, decreased the time to recovery in intact animals and lengthened the time to recovery in semi-intact animals. A cAMP inhibitor, NKH 477, delayed recovery time in male animals. Our results show that the rate of recovery in insect systems is affected by the presence of adenosine.

Hydrogen Sulfide as Potential Regulatory Gasotransmitter in Arthritic Diseases

The social and economic impact of chronic inflammatory diseases, such as arthritis, explains the growing interest of the research in this field. The antioxidant and anti-inflammatory properties of the endogenous gasotransmitter hydrogen sulfide (H₂S) were recently demonstrated in the context of different inflammatory diseases. In particular, H₂S is able to suppress the production of pro-inflammatory mediations by lymphocytes and innate immunity cells. Considering these biological effects of H₂S, a potential role in the treatment of inflammatory arthritis, such as rheumatoid arthritis (RA), can be postulated. However, despite the growing interest in H₂S, more evidence is needed to understand the pathophysiology and the potential of H₂S as a therapeutic agent. Within this review, we provide an overview on H₂S biological effects, on its role in immune-mediated inflammatory diseases, on H₂S releasing drugs, and on systems of tissue repair and regeneration that are currently under investigation for potential therapeutic applications in arthritic diseases.

The H₂S Donor GYY4137 Stimulates Reactive Oxygen Species Generation in BV2 Cells While Suppressing the Secretion of TNF and Nitric Oxide

GYY4137 is a hydrogen sulfide (H₂S) donor that has been shown to act in an anti-inflammatory manner in vitro and in vivo. Microglial cells are among the major players in immunoinflammatory, degenerative, and neoplastic disorders of the central nervous system, including multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, and glioblastoma multiforme. So far, the effects of GYY4137 on microglial cells have not been thoroughly investigated. In this study, BV2 microglial cells were stimulated with interferon-gamma and lipopolysaccharide and treated with GYY4137. The agent did not influence the viability of BV2 cells in concentrations up to 200 μM. It inhibited tumor necrosis factor but not interleukin-6 production. Expression of CD40 and CD86 were reduced under the influence of the donor. The phagocytic ability of BV2 cells and nitric oxide production were also affected by the agent. Surprisingly, GYY4137 upregulated generation of reactive oxygen species (ROS) by BV2 cells. The effect was mimicked by another H₂S donor, Na₂S, and it was not reproduced in macrophages. Our results demonstrate that GYY4137 downregulates inflammatory properties of BV2 cells but increases their ability to generate ROS. Further investigation of this unexpected phenomenon is warranted.

Overexpression of microRNA-183 promotes apoptosis of substantia nigra neurons via the inhibition of OSMR in a mouse model of Parkinson's disease

The present study aimed to investigate the effect of microRNA-183 (miR-183) on substantia nigra neurons by targeting oncostatin M receptor (OSMR) in a mouse model of Parkinson’s disease (PD). The positive expression rates of OSMR and the apoptosis of substantia nigra neurons were detected by immunohistochemistry and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling, respectively. Substantia nigra neurons in normal and PD mice were cultured in vitro. The association between miR-183 and OSMR was verified using a dual luciferase reporter gene assay. The expression of miR-183 and the phosphoinositide 3-kinase-Akt signaling pathway-associated genes were detected by reverse transcription-quantitative polymerase chain reaction and western blot analysis, respectively. Cell apoptosis was detected by flow cytometry. OSMR is the target gene of miR-183. The number of OSMR-positive cells and the apoptotic rate of substantia nigra neurons were increased in the PD group. Neurons transfected with miR-183 mimic exhibited elevated expression levels of miR-183, B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax) and caspase-9 and increased apoptotic rate, and reduced expression levels of OSMR, Akt, phosphorylated (p-)Akt, glycogen synthase kinase-3 (GSK-3β), p-GSK-3β, Bcl-2, insulin-like growth factor 1 (IGF-1), mammalian target of rapamycin (mTOR) and p-mTOR. The miR-183 inhibitor decreased the expression levels of miR-183, Bax and caspase-9 and the apoptotic rate; however, increased the expression of OSMR, Akt, p-Akt, GSK-3β, p-GSK-3β, Bcl-2, IGF-1, mTOR and p-mTOR. The results of the present study provide evidence that the overexpression of miR-183 promotes the apoptosis of substantia nigra neurons by inhibiting the expression of OSMR.

Influence of mTOR signaling pathway on ketamine-induced injuries in the hippocampal neurons of rats

OBJECTIVE

To explore the influences of mammalian target of rapamycin (mTOR) signaling pathway on ketamine-induced apoptosis, oxidative stress and Ca²⁺ concentration in the hippocampal neurons of rats.

METHODS

The primary hippocampal neurons isolated from fetal Sprague Dawley rats were treated with ketamine (0, 50, 100 and 500 μM) for 4 days to observe its effect on mTOR signaling pathway and apoptosis of rat hippocampal neurons. Then, the hippocampal neurons were divided into C (Control), R (Rapamycin, an inhibitor of mTOR signaling pathway), K (Ketamine) and R + K (Rapamycin + Ketamine) groups to detect the apoptosis, reactive oxygen species (ROS) production, and Ca²⁺ concentration via the terminal transferase uridyl nick end labelling (TUNEL) assay, dichloro-dihydro-fluorescein diacetate (DCFH-DA) method and Fluo-3 acetoxymethyl ester (Fluo-3AM) staining, respectively. The expressions of mTOR signaling pathway and apoptosis-related proteins in hippocampal neurons were examined by qRT-PCR and Western blot.

RESULTS

Ketamine could dose-dependently promote the apoptosis of rat hippocampal neurons with upregulation of p-mTOR and its downstream regulators (p-4E-BP-1 and p-p70S6K). However, ketamine-induced apoptosis in hippocampal neurons was reversed significantly by the administration of rapamycin, as evident by the decrease in expressions of pro-apoptotic proteins (Bax and cleaved Caspase-3) and the increase in anti-apoptotic protein (Bcl-2). Meanwhile, the ROS generation and Ca²⁺ concentration was inhibited accompanied with reduced malonildialdehyde levels but elevated superoxide and glutathione peroxidase activities.

CONCLUSION

Inhibition of mTOR signaling pathway protected rat hippocampal neurons from ketamine-induced injuries via reducing apoptosis, oxidative stress, as well as Ca²⁺ concentration.

ABBREVIATIONS

mTOR: mammalian target of rapamycin; SD: Sprague-Dawley; SPF: Specific-pathogen free; ROS: reactive oxygen species; TUNEL: terminal transferase uridyl nick end labelling; DCFH-DA: Dichloro-dihydro-fluorescein diacetate; Fluo-3A: Fluo-3 acetoxymethyl ester; NMDAR: non-competitive N-methyl-D-aspartame glutamate receptor; 4E-BP1: 4E binding protein 1; p70S6K: p70 S6 Kinase; PCR: Polymerase chain reaction; MDA: malonildialdehyde; GSH-PX: glutathione peroxidase; ANOVA: One-way Analysis of Variance.

Brain-derived neurotrophic factor inhibits hyperglycemia-induced apoptosis and downregulation of synaptic plasticity-related proteins in hippocampal neurons via the PI3K/Akt pathway

It is not known whether brain-derived neurotrophic factor (BDNF) protects hippocampal neurons from high glucose-induced apoptosis and/or synaptic plasticity dysfunction. The present study aimed to assess whether BDNF exerted a neuroprotective effect in rat hippocampal neurons exposed to high glucose and examine the underlying mechanisms. The apoptosis of primary hippocampal neurons was assessed by Annexin V-fluorescein isothiocyanate/propidium iodide staining. The mRNA and protein expression levels were measured by reverse transcription- quantitative polymerase chain reaction and western blot experiments, respectively. Synaptic plasticity was evaluated by the immunolocalization of synaptophysin (Syn). Exposure of the hippocampal neurons to high glucose (75 mM for 72 h) resulted in cell apoptosis, decreased mRNA and protein expression levels of three synaptic plasticity-related proteins (Syn, Arc and cyclic AMP response element-binding protein), and changes in the cellular distribution of Syn, indicating loss of synaptic density. These effects of high glucose were partially or completely reversed by prior administration of BDNF (50 ng/ml for 24 h). Pre-treatment with wortmannin, a phosphatidylinositol-3-kinase (PI3K) inhibitor, suppressed the ability of BDNF to inhibit the effects of high glucose. In addition, BDNF significantly upregulated the tropomyosin-related kinase B, its cognate receptor, Akt and phosphorylated Akt at the protein levels under high glucose conditions. In conclusion, high glucose induced apoptosis and downregulated synaptic plasticity-related proteins in hippocampal neurons. These effects were reversed by BDNF via the PI3K/Akt signaling pathway.

The role of hydrogen sulfide in cyclic nucleotide signaling

Hydrogen sulfide (H₂S) is recognized as an endogenous gaseous transmitter alongside nitric oxide (NO) and carbon monoxide (CO). By integrating into multiple signaling pathways, H₂S elicits biological functions in various mammalian systems. Among these pathways, cyclic nucleotide signaling has gradually gained attention in the past decade. Based on current evidence, it seems that H₂S may differentially affect the activity of resting adenylyl cyclases (ACs) and activated ACs, therefore playing a dual role in the regulation of cyclic adenosine monophosphate (cAMP) mediated signaling. However, how H₂S achieves the differential regulation on ACs remains unknown at molecular level. In the context of cyclic guanosine monophosphate (cGMP) regulation, H₂S augments its downstream signaling at least through three different mechanisms: (1) H₂S potentiates the response of soluble guanylyl cyclases (sGCs) to NO; (2) H₂S inhibits activity of phosphodiesterases (PDEs); and (3) H₂S enhances the production of NO. By regulating cyclic nucleotide signaling, H₂S possesses therapeutic potentials particularly for hypertension and cardiac injury which have also been discussed in the current review. Nevertheless, a detailed portrayal of H₂S mediated interaction with target proteins is still required for a better understanding of the role of this important gaseous mediator in regulating cyclic nucleotide signaling.

Effects of scalp electroacupuncture on the PI3K/Akt signalling pathway and apoptosis of hippocampal neurons in a rat model of cerebral palsy

Background Substantial evidence from clinical reports has established that most cerebral palsy (CP) patients benefit from a comprehensive rehabilitation exercise training programme. Such advances are enhanced when scalp electroacupuncture (EA), applied at a location corresponding to the projection of the motor area, is combined with rehabilitation exercise training. However, little information exists regarding the mechanistic basis for these effects. Objective To examine whether EA stimulation within the scalp projection location of the motor area can inhibit apoptosis of hippocampal neurons by regulating the PI3k/Akt signalling pathway in a rat model of CP. Methods Fifty male Sprague-Dawley rats underwent surgical modelling of CP. Five were used to confirm successful establishment of the model and the remaining 45 rats were randomly divided into one of three groups that remained untreated (CP group, n=15) or received EA treatment alone (CP+EA group, n=15) or EA in combination with a PI3K/Akt inhibitor (CP+EA+LY294002 group, n=15)). An otherwise healthy negative control group of rats undergoing sham surgery was also included (Control group, n=15). In the CP+EA and CP+EA+LY294002 groups, EA was applied to the scalp surface at alocation corresponding to the projection of the motor area. Basso, Beattie and Bresnahan (BBB) locomotor scores, hippocampal protein expression of Akt and p-Akt (by Western blot analysis) and neuronal apoptosis in hippocampal tissue (by histopathology) were assessed at 7, 14 and 21 days post-CP induction. Results CP rats receiving scalp EA treatment demonstrated improved behavioural scores, less hippocampal neuronal apoptosis and higher expression levels of Akt and p-Akt (p<0.05) at all time points studied compared with untreated CP rats. There were no significant differences observed between CP+EA+LY294002 and untreated CP model groups. Conclusions The effects of scalp EA on the PI3K/ Akt signalling pathway may represent one of the mechanisms involved in the inhibition of hippocampal neuronal apoptosis and improvement of deficits associated with CP in a rat model.

Hydrogen sulfide attenuates isoflurane-induced neuroapoptosis and cognitive impairment in the developing rat brain

Background

Isoflurane-induced neuroapoptosis and cognitive impairment has been previously reported. Hydrogen sulfide (H₂S) has been shown to be a neuromodulator that is thought to have anti-apoptotic, anti-inflammatory, and anti-oxidative benefits. However, it is not known if H₂S is protective against anesthesia-induced apoptosis and cognitive defects.

Methods

In this study, postnatal day 7 (P7) Sprague-Dawley rats were randomly divided into four groups: control group (normal saline), H₂S group (NaHS 28 μM/kg), isoflurane group (normal saline +0.75% isoflurane) and H₂S preconditioning group (NaHS 28 μM/kg + 0.75% isoflurane). After exposure to isoflurane for 6 h, half the numbers of rats in each group were euthanized, and the hippocampus and cerebral cortex were dissected and examined for apoptosis by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) technique and western blot. After 6 weeks, the remaining rats were subjected to a Morris water maze (MWM) test for behavioral assessment.

Results

The TUNEL assay and western blot showed that when rats were preconditioned with NaHS, neuroapoptosis decreased significantly both in hippocampus and cerebral cortex compering with the isofulrane group. The MWM showed that P7 rats administration of NaHS improved cognitive impairments induced by isoflurane.

Conclusions

The current study demonstrates that H₂S attenuates isoflurane-induced neuroapoptosis and improves cognitive impairments in the developing rat brain.

Upregulation of cystathionine β-synthase and p70S6K/S6 in neonatal hypoxic ischemic brain injury

Encephalopathy of prematurity (EOP) is a complex form of cerebral injury that occurs in the setting of hypoxia-ischemia (HI) in premature infants. Using a rat model of EOP, we investigated whether neonatal HI of the brain may alter the expression of cystathionine β-synthase (CBS) and the components of the mammalian target of rapamycin (mTOR) signaling. We performed unilateral carotid ligation and induced HI (UCL/HI) in Long-Evans rats at P6 and found increased CBS expression in white matter (i.e. corpus callosum, cingulum bundle and external capsule) as early as 24 h (P7) postprocedure. CBS remained elevated through P21, and, to a lesser extent, at P40. The mTOR downstream target 70 kDa ribosomal protein S6 kinase (p70S6K and phospho-p70S6K) and 40S ribosomal protein S6 (S6 and phospho-S6) were also overexpressed at the same time points in the UCL/HI rats compared to healthy controls. Overexpression of mTOR components was not observed in rats treated with the mTOR inhibitor everolimus. Behavioral assays performed on young rats (postnatal day 35-37) following UCL/HI at P6 indicated impaired preference for social novelty, a behavior relevant to autism spectrum disorder, and hyperactivity. Everolimus restored behavioral patterns to those observed in healthy controls. A gait analysis has shown that motor deficits in the hind paws of UCL/HI rats were also significantly reduced by everolimus. Our results suggest that neonatal HI brain injury may inflict long-term damage by upregulation of CBS and mTOR signaling. We propose this cascade as a possible new molecular target for EOP-a still untreatable cause of autism, hyperactivity and cerebral palsy.

The roles of parafibromin expression in ovarian epithelial carcinomas: a marker for differentiation and prognosis and a target for gene therapy

Parafibromin is a protein encoded by hyperparathyroidism 2 (HRPT2) and its downregulated expression is involved in the pathogenesis of parathyroid, breast, gastric, colorectal, lung, head and neck cancers. We aimed to investigate the roles of parafibromin expression in tumorigenesis, progression, or prognostic evaluation of ovarian cancers. HRPT2-expressing plasmid was transfected into ovarian cancer cells with the phenotypes and related molecules examined. The messenger RNA (mRNA) and protein expression of parafibromin were also examined in ovarian normal tissue, benign and borderline tumors and cancers by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, or immunohistochemistry respectively. It was found that parafibromin overexpression caused a lower growth, migration and invasion, higher sensitivity to cisplatin and apoptosis than the mock and control (P < 0.05). The transfectants showed the hypoexpression of phosphoinositide 3-kinase (PI3K), Akt, p70 ribosomal protein S6 kinase (p70s6k), Wnt5a, B cell lymphoma-extra large (Bcl-xL), survivin, vascular endothelial growth factor (VEGF) and matrix metallopeptidase 9 (MMP-9) than the mock and control at both mRNA and protein levels (P < 0.05). According to real-time PCR, parafibromin mRNA level was lower in ovarian benign tumors and cancers than normal ovary (P < 0.05), while parafibromin was strongly expressed in metastatic cancers in omentum than primary cancers by Western blot. Immunohistochemically, parafibromin expression was stronger in primary cancers than that in ovarian normal tissue (P < 0.05) but weaker than the metastatic cancers (P < 0.05) with a positive correlation with dedifferentiation, ki-67 expression and the lower cumulative survival rate (P < 0.05). These findings indicate that parafibromin downregulation might promote the pathogenesis, dedifferentiation and metastasis of ovarian cancers possibly by suppressing aggressive phenotypes, such as proliferation, cell cycle, apoptosis, migration and invasion.

Neuroprotective effects of hydrogen sulfide and the underlying signaling pathways

Hydrogen sulfide (H

Exogenous hydrogen sulfide promotes proliferation and inhibits apoptosis of hepatocytes via PI3K/Akt pathway

AIM: To explore the effect of exogenous hydrogen sulfide on rat hepatocyte proliferation and apoptosis and the role of phosphoinositide-3-kinase (PI3K)/Akt pathway.

METHODS: Female SD rats were subcutaneously injected with carbon tetrachloride to induce hepatic fibrosis, and hepatocytes were isolated from the rats. Primary hepatocytes were divided into three groups: a normal control group, a hydrogen sulfide group, and an LY294002 plus hydrogen sulfide group. MTT method was used to determine cell proliferation. Apoptosis of liver cells was detected by Hoechst 33342 staining. The expression of PI3K and phosphorylated Bad protein was detected by Western blot.

RESULTS: Sodium hydrosulfide at 50 μmol/L promoted cell proliferation (P < 0.05, compared with the control group), while 50 μmol/L LY294002 inhibited cell proliferation (P < 0.05, compared with the control group). Compared with the control group and sodium hydrosulfide group, the LY294002 plus hydrogen sulfide group had a significantly higher rate of cell apoptosis (P < 0.05). The expression of PI3K and phosphorylated Bad protein in the sodium hydrosulfide group was significantly higher than that in the control group and LY294002 plus hydrogen sulfide group (P < 0.05). However, PI3K and phospho-Bad protein expression in the LY294002 plus hydrogen sulfide group was significantly less than in the control group (P < 0.05).

CONCLUSION: Hydrogen sulfide promotes primary hepatocyte proliferation and inhibits its apoptosis possibly through the PI3K/Akt pathway.

Self administration of oxycodone alters synaptic plasticity gene expression in the hippocampus differentially in male adolescent and adult mice

Abuse and addiction to prescription opioids such as oxycodone (a short-acting Mu opioid receptor (MOP-r) agonist) in adolescence is a pressing public health issue. We have previously shown differences in oxycodone self-administration behaviors between adolescent and adult C57BL/6J mice and expression of striatal neurotransmitter receptor genes, in areas involved in reward. In this study, we aimed to determine whether oxycodone self-administration differentially affects genes regulating synaptic plasticity in the hippocampus of adolescent compared to adult mice, since the hippocampus may be involved in learning aspects associated with chronic drug self administration. Hippocampus was isolated for mRNA analysis from mice that had self administered oxycodone (0.25 mg/kg/infusion) 2h/day for 14 consecutive days or from yoked saline controls. Gene expression was analyzed with real-time polymerase chain reaction (PCR) using a commercially available "synaptic plasticity" PCR array containing 84 genes. We found that adolescent and adult control mice significantly differed in the expression of several genes in the absence of oxycodone exposure, including those coding for mitogen-activated protein kinase, calcium/calmodulin-dependent protein kinase II gamma subunit, glutamate receptor, ionotropic AMPA2 and metabotropic 5. Chronic oxycodone self administration increased proviral integration site 1 (Pim1) and thymoma viral proto-oncogene 1 mRNA levels compared to controls in both age groups. Both Pim1 and cadherin 2 mRNAs showed a significant combined effect of Drug Condition and Age × Drug Condition. Furthermore, the mRNA levels of both cadherin 2 and cAMP response element modulators showed an experiment-wise significant difference between oxycodone and saline control in adult but not in adolescent mice. Overall, this study demonstrates for the first time that chronic oxycodone self-administration differentially alters synaptic plasticity gene expression in the hippocampus of adolescent and adult mice.

Hydrogen sulfide augments survival signals in warm ischemia and reperfusion of the mouse liver

BACKGROUND AND PURPOSE

Hydrogen sulfide (H2S) ameliorates hepatic ischemia and reperfusion injury (IRI), but the precise mechanism remains elusive. We investigated whether sodium hydrogen sulfide (NaHS), a soluble derivative of H2S, would ameliorate hepatic IRI, and if so, via what mechanism.

METHODS

Mice were subjected to partial warm ischemia for 75 min followed by reperfusion. Either NaHS or saline was administered intravenously 10 min before reperfusion. The liver and serum were collected 3, 6, and 24 h after reperfusion.

RESULTS

In the NaHS(-) group, severe IRI was apparent by the ALT leakage, tissue injury score, apoptosis, lipid peroxidation, and inflammation (higher plasma TNF-α, IL-6, IL-1β, IFN-γ, IL-23, IL-17, and CD40L), whereas IRI was significantly ameliorated in the NaHS(+) group. These effects could be explained by the augmented nuclear translocation of Nrf2, and the resulting up-regulation of HO-1 and thioredoxin-1. Phosphorylation of the PDK-1/Akt/mTOR/p70S6k axis, which is known to mediate pro-survival and anti-apoptotic signals, was significantly augmented in the NaHS(+) group, with a higher rate of PCNA-positive cells thereafter.

CONCLUSION

NaHS ameliorated hepatic IRI by direct and indirect anti-oxidant activities by augmenting pro-survival, anti-apoptotic, and anti-inflammatory signals via mechanisms involving Nrf-2, and by accelerating hepatic regeneration via mechanisms involving Akt-p70S6k.

(R)-(+)-α-lipoic acid protected NG108-15 cells against H₂O₂-induced cell death through PI3K-Akt/GSK-3β pathway and suppression of NF-κβ-cytokines

Alpha-lipoic acid, a potent antioxidant with multifarious pharmacological benefits has been reported to be neuroprotective in several neuronal models and used to treat neurological disorders such as Alzheimer's disease. Nonetheless, conclusive mechanisms of alpha-lipoic acid for its protective effects particularly in NG108-15 cells have never been investigated. In this study, the intricate neuroprotective molecular mechanisms by (R)-(+)-alpha-lipoic acid (R-LA) against H2O2-induced cell death in an in vitro model of neurodegeneration were elucidated. Pretreatment with R-LA (2 hours) significantly increased NG108-15 cell viability as compared to H2O2-treated cells and mitigated the induction of apoptosis as evidenced by Hoechst 33342/propidium iodide staining. R-LA (12.5-50 μM) aggrandized the reduced glutathione over glutathione disulfide ratio followed by a reduction in the intracellular reactive oxygen species level and an increase in mitochondrial membrane potential following H2O2 exposure. Moreover, pretreatment with R-LA stimulated the activation of PI3K-Akt through mTORC1 and mTORC2 components (mTOR, rictor and raptor) and production of antiinflammatory cytokine, IL-10 which led to the inactivation of glycogen synthase kinase-3β (GSK-3β) and reduction of both Bax/Bcl2 and Bax/Bcl-xL ratios, accompanied by inhibition of the cleaved caspase-3. Additionally, this observation was preceded by the suppression of NF-κβ p65 translocation and production of proinflammatory cytokines (IL-6 and TNF-α). The current findings accentuate new mechanistic insight of R-LA against apoptogenic and brain inflammatory factors in a neuronal model. These results further advocate the therapeutic potential of R-LA for the treatment of neurodegenerative diseases.

Cadmium-induced hydrogen sulfide synthesis is involved in cadmium tolerance in Medicago sativa by reestablishment of reduced (homo)glutathione and reactive oxygen species homeostases

Until now, physiological mechanisms and downstream targets responsible for the cadmium (Cd) tolerance mediated by endogenous hydrogen sulfide (H₂S) have been elusive. To address this gap, a combination of pharmacological, histochemical, biochemical and molecular approaches was applied. The perturbation of reduced (homo)glutathione homeostasis and increased H₂S production as well as the activation of two H₂S-synthetic enzymes activities, including _L-cysteine desulfhydrase (LCD) and _D-cysteine desulfhydrase (DCD), in alfalfa seedling roots were early responses to the exposure of Cd. The application of H₂S donor sodium hydrosulfide (NaHS), not only mimicked intracellular H₂S production triggered by Cd, but also alleviated Cd toxicity in a H₂S-dependent fashion. By contrast, the inhibition of H₂S production caused by the application of its synthetic inhibitor blocked NaHS-induced Cd tolerance, and destroyed reduced (homo)glutathione and reactive oxygen species (ROS) homeostases. Above mentioned inhibitory responses were further rescued by exogenously applied glutathione (GSH). Meanwhile, NaHS responses were sensitive to a (homo)glutathione synthetic inhibitor, but reversed by the cotreatment with GSH. The possible involvement of cyclic AMP (cAMP) signaling in NaHS responses was also suggested. In summary, LCD/DCD-mediated H₂S might be an important signaling molecule in the enhancement of Cd toxicity in alfalfa seedlings mainly by governing reduced (homo)glutathione and ROS homeostases.

Transcriptional and epigenetic regulation of Hebbian and non-Hebbian plasticity

The epigenome is uniquely positioned as a point of convergence, integrating multiple intracellular signaling cascades into a cohesive gene expression profile necessary for long-term behavioral change. The last decade of neuroepigenetic research has primarily focused on learning-induced changes in DNA methylation and chromatin modifications. Numerous studies have independently demonstrated the importance of epigenetic modifications in memory formation and retention as well as Hebbian plasticity. However, how these mechanisms operate in the context of other forms of plasticity is largely unknown. In this review, we examine evidence for epigenetic regulation of Hebbian plasticity. We then discuss how non-Hebbian forms of plasticity, such as intrinsic plasticity and synaptic scaling, may also be involved in producing the cellular adaptations necessary for learning-related behavioral change. Furthermore, we consider the likely roles for transcriptional and epigenetic mechanisms in the regulation of these plasticities. In doing so, we aim to expand upon the idea that epigenetic mechanisms are critical regulators of both Hebbian and non-Hebbian forms of plasticity that ultimately drive learning and memory.

Sodium/calcium exchanger is upregulated by sulfide signaling, forms complex with the β1 and β3 but not β2 adrenergic receptors, and induces apoptosis

Hydrogen sulfide (H2S) as a novel gasotransmitter regulates variety of processes, including calcium transport systems. Sodium calcium exchanger (NCX) is one of the key players in a regulation calcium homeostasis. Thus, the aims of our work were to determine effect of sulfide signaling on the NCX type 1 (NCX1) expression and function in HeLa cells, to investigate the relationship of β-adrenergic receptors with the NCX1 in the presence and/or absence of H2S, and to determine physiological importance of this potential communication. As a H2S donor, we used morpholin-4-ium-4-methoxyphenyl(morpholino) phosphinodithioate-GYY4137. We observed increased levels of the NCX1 mRNA, protein, and activity after 24 h of GYY4137 treatment. This increase was accompanied by elevated cAMP due to the GYY4137 treatment, which was completely abolished, when NCX1 was silenced. Increased cAMP levels would point to upregulation of β-adrenergic receptors. Indeed, GYY4137 increased expression of β1 and β3 (but not β2) adrenergic receptors. These receptors co-precipitated, co-localized with the NCX1, and induced apoptosis in the presence of H2S. Our results suggest that sulfide signaling plays a role in regulation of the NCX1, β1 and β3 adrenergic receptors, their co-localization, and stimulation of apoptosis, which might be of a potential importance in cancer treatment.

Hindbrain GLP-1 receptor-mediated suppression of food intake requires a PI3K-dependent decrease in phosphorylation of membrane-bound Akt

Glucagon-like peptide-1 (GLP-1) receptors (GLP-1R) expressed in the nucleus tractus solitarius (NTS) are physiologically required for the control of feeding. Recently, NTS GLP-1R-mediated suppression of feeding was shown to occur via a rapid PKA-induced suppression of AMPK and activation of MAPK signaling. Unknown are the additional intracellular signaling pathways that account for the long-term hypophagic effects of GLP-1R activation. Because cAMP/PKA activity can promote PI3K/PIP3-dependent translocation of Akt to the plasma membrane, we hypothesize that hindbrain GLP-1R-mediated control of feeding involves a PI3K-Akt-dependent pathway. Importantly, the novel evidence presented here challenges the dogmatic view that PI3K phosphorylation results in an obligatory activation of Akt and instead supports a growing body of literature showing that activation of cAMP/PKA can inhibit Akt phosphorylation at the plasma membrane. Behavioral data show that inhibition of hindbrain PI3K activity by a fourth icv administration of LY-294002 (3.07 μg) attenuated the food intake- and body weight-suppressive effects of a fourth icv administration of the GLP-1R agonist exendin-4 (0.3 μg) in rats. Hindbrain administration of triciribine (10 μg), an inhibitor of PIP3-dependent translocation of Akt to the cell membrane, also attenuated the intake-suppressive effects of a fourth icv injection of exendin-4. Immunoblot analyses of ex vivo NTS tissue lysates and in vitro GLP-1R-expressing neurons (GT1-7) support the behavioral findings and show that GLP-1R activation decreases phosphorylation of Akt in a time-dependent fashion. Current data reveal the requirement of PI3K activation, PIP3-dependent translocation of Akt to the plasma membrane, and suppression in phosphorylation of membrane-bound Akt to mediate the food intake-suppressive effects of hindbrain GLP-1R activation.

Hydrogen sulfide-mediated stimulation of mitochondrial electron transport involves inhibition of the mitochondrial phosphodiesterase 2A, elevation of cAMP and activation of protein kinase A

Although hydrogen sulfide (H₂S) is generally known as a mitochondrial poison, recent studies show that lower concentrations of H₂S play a physiological role in the stimulation of mitochondrial electron transport and cellular bioenergetics. This effect involves electron donation at Complex II. Other lines of recent studies demonstrated that one of the biological actions of H₂S involves inhibition of cAMP and cGMP phosphodiesterases (PDEs). Given the emerging functional role of the mitochondrial isoform of cAMP PDE (PDE2A) in the regulation of mitochondrial function the current study investigated whether cAMP-dependent mechanisms participate in the stimulatory effect of NaHS on mitochondrial function. In isolated rat liver mitochondria, partial digestion studies localized PDE2A into the mitochondrial matrix. NaHS exerted a concentration-dependent inhibitory effect on recombinant PDE2A enzyme in vitro. Moreover, NaHS induced an elevation of cAMP levels when added to isolated mitochondria and stimulated the mitochondrial electron transport. The latter effect was inhibited by Rp-cAMP, an inhibitor of the cAMP-dependent protein kinase (PKA). The current findings suggest that the direct electron donating effect of NaHS is amplified by an intramitochondrial cAMP system, which may involve the inhibition of PDE2A and subsequent, cAMP-mediated stimulation of PKA.

Promoter demethylation of cystathionine-β-synthetase gene contributes to inflammatory pain in rats

Hydrogen sulfide (H(2)S), an endogenous gas molecule synthesized by cystathionine-β-synthetase (CBS), is involved in inflammation and nociceptive signaling. However, the molecular and epigenetic mechanisms of CBS-H(2)S signaling in peripheral nociceptive processing remain unknown. We demonstrated that peripheral inflammation induced by intraplantar injection of complete Freund adjuvant significantly up-regulated expression of CBS at both protein and mRNA levels in rat dorsal root ganglia (DRG). The CBS inhibitors hydroxylamine and aminooxyacetic acid attenuated mechanical hyperalgesia in a dose-dependent manner and reversed hyperexcitability of DRG neurons in inflamed rats. Intraplantar administration of NaHS (its addition mimics CBS production of H(2)S) or l-cysteine in healthy rats elicited mechanical hyperalgesia. Application of NaHS in vitro enhanced excitability and tetrodotoxin (TTX)-resistant sodium current of DRG neurons from healthy rats, which was attenuated by pretreatment of protein kinase A inhibitor H89. Methylation-specific PCR and bisulfite sequencing demonstrated that promoter region of cbs gene was less methylated in DRG samples from inflamed rats than that from controls. Peripheral inflammation did not alter expression of DNA methyltransferase 3a and 3b, the 2 major enzymes for DNA methylation, but led to a significant up-regulation of methyl-binding domain protein 4 and growth arrest and DNA damage inducible protein 45α, the enzymes involved in active DNA demethylation. Our findings suggest that epigenetic regulation of CBS expression may contribute to inflammatory hyperalgesia. H(2)S seems to increase TTX-resistant sodium channel current, which may be mediated by protein kinase A pathway, thus identifying a potential therapeutic target for the treatment of chronic pain.

The early activation of PI3K strongly enhances the resistance of cortical neurons to hypoxic injury via the activation of downstream targets of the PI3K pathway and the normalization of the levels of PARP activity, ATP, and NAD⁺

Phosphatidylinositol 3-kinase (PI3K) plays several important roles in neuronal survival. Activation of the pathway is essential for the neuroprotective mechanisms of materials that shield neuronal cells from many stressful conditions. However, there have been no reports to date about the effect of the direct activation of the pathway in hypoxic injury of neuronal cells. We investigated whether the direct activation of the PI3K pathway inhibits neuronal cell death induced by hypoxia. Primary cultured cortical neurons (PCCNs) were exposed to hypoxic conditions (less than 1 mol% O2) and/or treated with PI3K activator. Hypoxia reduced the viability of PCCNs in a time-dependent manner, but treatment with PI3K significantly restored viability in a concentration-dependent manner. Among the signaling proteins involved in the PI3K pathway, those associated with survival, including Akt and glycogen synthase kinase-3β, were decreased shortly after exposure to hypoxia and those associated with cell death, including BAX, apoptosis-induced factor, cytochrome c, caspase-9, caspase-3, and poly(ADP-ribose) polymerase (PARP), were increased. However, treatment with PI3K activator normalized the expression levels of those signaling proteins. PARP activity and levels of ATP and NAD(+) altered by hypoxia were also normalized with direct PI3K activation. All these findings suggest that direct and early activation is important for protecting neuronal cells from hypoxic injury.

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.

Hydrogen sulfide and resolution of acute inflammation: A comparative study utilizing a novel fluorescent probe

Hydrogen sulfide is an essential gasotransmitter associated with numerous pathologies. We assert that hydrogen sulfide plays an important role in regulating macrophage function in response to subsequent inflammatory stimuli, promoting clearance of leukocyte infiltrate and reducing TNF-α levels in vivo following zymosan-challenge. We describe two distinct methods of measuring leukocyte hydrogen sulfide synthesis; methylene blue formation following zinc acetate capture and a novel fluorescent sulfidefluor probe. Comparison of these methods, using pharmacological tools, revealed they were complimentary in vitro and in vivo. We demonstrate the application of sulfidefluor probe to spectrofluorimetry, flow cytometry and whole animal imaging, to monitor the regulation of hydrogen sulfide synthesis in vivo during dynamic inflammatory processes. Both methodologies revealed that granulocyte infiltration negatively affects hydrogen sulfide synthesis. Our report offers an insight into the profile of hydrogen sulfide synthesis during inflammation and highlight opportunities raised by the development of novel fluorescent hydrogen sulfide probes.

Transplantation of mesenchymal stem cells preconditioned with hydrogen sulfide enhances repair of myocardial infarction in rats

Stem cell transplantation has become a promising therapeutic approach for the treatment of myocardial infarction (MI). However, the poor survival of the donor cells after transplantation has restricted its therapeutic efficacy. Hydrogen sulfide (H(2)S), one gaseous signaling molecule, has been applied to inhibit cell apoptosis and promote cell survival. In the present study, we therefore examined the effects of H(2)S on the survival of mesenchymal stem cells (MSCs). MSCs were isolated from the femur of male Sprague-Dawley rats (about 4 weeks old, 100 g). Preconditioning MSCs with 200 µmol/L NaHS (as the donor of H(2)S) for 30 min decreased the hypoxia-induced cell apoptosis in vitro. The mechanisms contributing to the beneficial effects of H(2)S on MSCs were associated with increased levels of phosphorylated Akt (pAkt), phosphorylated Erk1/2 (pErk1/2) and phosphorylated glycogen synthase kinase-3β (pGSK-3β) in MSCs. Subsequently, MSCs (1 × 10(6)), MSCs preconditioned with H(2)S (1 × 10(6)), or phosphate buffered saline (PBS) were injected into rat hearts immediately after MI (the ligation of the left anterior descending of coronary artery). Real-time PCR for the Sry gene, located on the Y chromosome, indicated that preconditioning with H(2)S improved the survival rate of the transplanted MSCs in infarcted myocardium 4 days after MI, compared with the untreated MSCs. Furthermore, transplantation of the H(2)S-pretreated MSCs reduced the infarct size and increased left ventricular (LV) function, as judged by transthoracic echocardiography. In conclusion, H(2)S preconditioning effectively promotes MSCs survival under ischemic injury and helps cardiac repair after MI, which has great clinical significance.

Regulation of the glutamate transporter EAAT3 by mammalian target of rapamycin mTOR

The serine/threonine kinase mammalian target of rapamycin (mTOR) is stimulated by insulin, growth factors and nutrients and confers survival of several cell types. The kinase has previously been shown to stimulate amino acid uptake. In neurons, the cellular uptake of glutamate by the excitatory amino-acid transporters (EAATs) decreases excitation and thus confers protection against excitotoxicity. In epithelia, EAAT3 accomplishes transepithelial glutamate and aspartate transport. The present study explored, whether mTOR regulates EAAT3 (SLC1A1). To this end, cRNA encoding EAAT3 was injected into Xenopus oocytes with or without cRNA encoding mTOR and the glutamate induced current (I(glu)), a measure of glutamate transport, determined by dual electrode voltage clamp. Moreover, EAAT3 protein abundance was determined utilizing chemiluminescence. As a result, I(glu) was observed in Xenopus oocytes expressing EAAT3 but not in water injected oocytes. Coexpression of mTOR significantly increased I(glu), an effect reversed by rapamycin (100 nM). mTOR coexpression increased EAAT3 protein abundance in the cell membrane. The decay of I(glu) following inhibition of carrier insertion with brefeldin A in oocytes coexpressing EAAT3 with mTOR was similar in the presence and absence of rapamycin (100 nM). In conclusion, mTOR is a novel powerful regulator of EAAT3 and may thus contribute to protection against neuroexcitotoxicity.

Cyclic AMP is both a pro-apoptotic and anti-apoptotic second messenger

The second messenger cyclic AMP (cAMP) can either stimulate or inhibit programmed cell death (apoptosis). Here, we review examples of cell types that show pro-apoptotic or anti-apoptotic responses to increases in cAMP. We also show that cells can have both such responses, although predominantly having one or the other. Protein kinase A (PKA)-promoted changes in phosphorylation and gene expression can mediate pro-apoptotic responses, such as in murine S49 lymphoma cells, based on evidence that mutants lacking PKA fail to undergo cAMP-promoted, mitochondria-dependent apoptosis. Mechanisms for the anti-apoptotic response to cAMP likely involve Epac (Exchange protein activated by cAMP), a cAMP-regulated effector that is a guanine nucleotide exchange factor (GEF) for the low molecular weight G-protein, Rap1. Therapeutic approaches that activate PKA-mediated pro-apoptosis or block Epac-mediated anti-apoptotisis may provide a means to enhance cell killing, such as in certain cancers. In contrast, efforts to block PKA or stimulate Epac have the potential to be useful in diseases settings (such as heart failure) associated with cAMP-promoted apoptosis.

Hydrogen sulfide as a cryogenic mediator of hypoxia-induced anapyrexia

Hypoxia causes a regulated decrease in body temperature (Tb), a response that has been aptly called anapyrexia, but the mechanisms involved are not completely understood. The roles played by nitric oxide (NO) and other neurotransmitters have been documented during hypoxia-induced anapyrexia, but no information exists with respect to hydrogen sulfide (H(2)S), a gaseous molecule endogenously produced by cystathionine β-synthase (CBS). We tested the hypothesis that H(2)S production is enhanced during hypoxia and that the gas acts in the anteroventral preoptic region (AVPO; the most important thermosensitive and thermointegrative region of the CNS) modulating hypoxia-induced anapyrexia. Thus, we assessed CBS and nitric oxide synthase (NOS) activities [by means of H(2)S and nitrite/nitrate (NO(x)) production, respectively] as well as cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) levels in the anteroventral third ventricle region (AV3V; where the AVPO is located) during normoxia and hypoxia. Furthermore, we evaluated the effects of pharmacological modifiers of the H(2)S pathway given i.c.v. or intra-AVPO. I.c.v. or intra-AVPO microinjection of CBS inhibitor caused no change in Tb under normoxia but significantly attenuated hypoxia-induced anapyrexia. During hypoxia there were concurrent increases in H(2)S production, which could be prevented by CBS inhibitor, indicating the endogenous source of the gas. cAMP concentration, but not cGMP and NO(x), correlated with CBS activity. CBS inhibition increased NOS activity, whereas H(2)S donor decreased NO(x) production. In conclusion, hypoxia activates H(2)S endogenous production through the CBS-H(2)S pathway in the AVPO, having a cryogenic effect. Moreover, the present data are consistent with the notion that the two gaseous molecules, H(2)S and NO, play a key role in mediating the drop in Tb caused by hypoxia and that a fine-balanced interplay between NOS-NO and CBS-H(2)S pathways takes place in the AVPO of rats exposed to hypoxia.