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.

H2S signaling and extracellular matrix remodeling in cardiovascular diseases: A tale of tense relationship

Extracellular matrix (ECM) is a non-cellular three-dimensional macromolecular network that not only provides mechanical support but also transduces essential molecular signals in organ functions. ECM is constantly remodeled to control tissue homeostasis, responsible for cell adhesion, cell migration, cell-to-cell communication, and cell differentiation, etc. The dysregulation of ECM components contributes to various diseases, including cardiovascular diseases, fibrosis, cancer, and neurodegenerative diseases, etc. Aberrant ECM remodeling is initiated by various stress, such as oxidative stress, inflammation, ischemia, and mechanical stress, etc. Hydrogen sulfide (H₂S) is a gasotransmitter that exhibits a wide variety of cytoprotective and physiological functions through its anti-oxidative and anti-inflammatory actions. Amounting research shows that H₂S can attenuate aberrant ECM remodeling. In this review, we discussed the implications and mechanisms of H₂S in the regulation of ECM remodeling in cardiovascular diseases, and highlighted the potential of H₂S in the prevention and treatment of cardiovascular diseases through attenuating adverse ECM remodeling.

Relationship Between Endogenous Hydrogen Sulfide and Pulmonary Vascular Indexes on High-Resolution Computed Tomography in Patients with Chronic Obstructive Pulmonary Disease

Objective

To explore the relationship between endogenous hydrogen sulfide (H₂S) and high-resolution computed tomography (HRCT) indexes in pulmonary vascular remodeling.

Methods

A total of 94 stable chronic obstructive pulmonary disease (COPD) patients were recruited for the study．Plasma H₂S levels were measured using fluorescence probe. Fluorescence quantitative polymerase chain reaction was used to measure H₂S synthase cystathionine-γ-lyase (CSE) mRNA and cystathionine-β-synthesis enzyme (CBS) mRNA. The main pulmonary artery diameter (mPAD), axial diagonal mPAD, coronal mPAD, sagittal mPAD, right pulmonary artery diameter (RPAD), left pulmonary artery diameter (LPAD), and ascending aortic diameter (AAD) and the percentage of total cross-sectional area of vessels less than 5 mm² of total lung area (%CSA <5) on HRCT were measured. Pulmonary arterial systolic pressure (PASP) of echocardiography, blood gas analysis, and routine blood tests were performed. Correlation analysis and multivariate linear regression were performed using SPSS 22.0.

Results

H₂S was negatively correlated with mPAD, axial diagonal mPAD, and sagittal mPAD (r = -0.25~-0.32) and positively correlated with PaO₂ (r = 0.35). Relative expression of CSE mRNA was positively correlated with PASP, coronal mPAD, sagittal mPAD, white blood cell count (WBC), and neutrophil count (N) (r = 0.30~0.44). The relative expression of CBS mRNA was positively correlated with PASP, WBC, and N (r = 0.34~0.41). In separate models predicting pulmonary vascular indexes, a 1μmol/L increase in H₂S predicted lower pulmonary artery diameter (for axial diagonal mPAD, 0.76mm lower; for mPAD/AAD, 0.68mm lower). All P values were less than 0.05.

Conclusion

Endogenous H₂S may be involved in pulmonary vascular remodeling, providing a new method for the diagnosis and treatment of COPD. The generation of H₂S may be inhibited by hypoxia, inflammation, etc.

Hydrogen sulfide and vascular regulation - An update

BACKGROUND

Hydrogen sulfide (H₂S) is considered to be the third gasotransmitter after carbon monoxide (CO) and nitric oxide (NO). It plays an important role in the regulation of vascular homeostasis. Vascular remodeling have has proved to be related to the impaired H₂S generation.

AIM OF REVIEW

This study aimed to summarize and discuss current data about the function of H₂S in vascular physiology and pathophysiology as well as the underlying mechanisms.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Endogenous hydrogen sulfide (H₂S) as a third gasotransmitter is primarily generated by the enzymatic pathways and regulated by several metabolic pathways. H₂S as a physiologic vascular regulator, inhibits proliferation, regulates its apoptosis and autophagy of vascular cells and controls the vascular tone. Accumulating evidence shows that the downregulation of H₂S pathway is involved in the pathogenesis of a variety of vascular diseases, such as hypertension, atherosclerosis and pulmonary hypertension. Alternatively, H₂S supplementation may greatly help to prevent the progression of the vascular diseases by regulating vascular tone, inhibiting vascular inflammation, protecting against oxidative stress and proliferation, and modulating vascular cell apoptosis, which has been verified in animal and cell experiments and even in the clinical investigation. Besides, H₂S system and angiotensin-converting enzyme (ACE) inhibitors play a vital role in alleviating ischemic heart disease and left ventricular dysfunction. Notably, sulfhydryl-containing ACEI inhibitor zofenopril is superior to other ACE inhibitors due to its capability of H₂S releasing, in addition to ACE inhibition. The design and application of novel H₂S donors have significant clinical implications in the treatment of vascular-related diseases. However, further research regarding the role of H₂S in vascular physiology and pathophysiology is required.

The effects of gasotransmitters on bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), which remains a major clinical problem for preterm infants, is caused mainly by hyperoxia, mechanical ventilation and inflammation. Many approaches have been developed with the aim of decreasing the incidence of or alleviating BPD, but effective methods are still lacking. Gasotransmitters, a type of small gas molecule that can be generated endogenously, exert a protective effect against BPD-associated lung injury; nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) are three such gasotransmitters. The protective effects of NO have been extensively studied in animal models of BPD, but the results of these studies are inconsistent with those of clinical trials. NO inhalation seems to have no effect on BPD, although side effects have been reported. NO inhalation is not recommended for BPD treatment in preterm infants, except those with severe pulmonary hypertension. Both CO and H₂S decreased lung injury in BPD rodent models in preclinical studies. Another small gas molecule, hydrogen, exerts a protective effect against BPD. The nuclear factor erythroid-derived 2 (Nrf2)/heme oxygenase-1 (HO-1) axis seems to play a central role in the protective effect of these gasotransmitters on BPD. Gasotransmitters play important roles in mammals, but further clinical trials are needed to explore their effects on BPD.

Association of cystathionine beta-synthase polymorphisms and aneurysmal subarachnoid hemorrhage

OBJECTIVE

Cystathionine β-synthase (CBS) is involved in homocysteine and hydrogen sulfide (H2S) metabolism. Both products have been implicated in the pathophysiology of cerebrovascular diseases. The impact of CBS polymorphisms on aneurysmal subarachnoid hemorrhage (aSAH) and its clinical sequelae is poorly understood.

METHODS

Blood samples from all patients enrolled in the CARAS (Cerebral Aneurysm Renin Angiotensin System) study were used for genetic evaluation. The CARAS study prospectively enrolled aSAH patients at 2 academic institutions in the United States from 2012 to 2015. Common CBS polymorphisms were detected using 5′exonuclease genotyping assays. Analysis of associations between CBS polymorphisms and aSAH was performed.

RESULTS

Samples from 149 aSAH patients and 50 controls were available for analysis. In multivariate logistic regression analysis, the insertion allele of the 844ins68 CBS insertion polymorphism showed a dominant effect on aSAH. The GG genotype of the CBS G/A single nucleotide polymorphism (rs234706) was independently associated with unfavorable functional outcome (modified Rankin Scale Score 3–6) at discharge and last follow-up, but not clinical vasospasm or delayed cerebral ischemia (DCI).

CONCLUSIONS

The insertion allele of the 844ins68 CBS insertion polymorphism was independently associated with aSAH while the GG genotype of rs234706 was associated with an unfavorable outcome both at discharge and last follow-up. Increased CBS activity may exert its neuroprotective effects through alteration of H2S levels, and independent of clinical vasospasm and DCI.

A novel mouse model of high flow-induced pulmonary hypertension-surgically induced by right pulmonary artery ligation

BACKGROUND

This study sought to establish a new model of high-flow pulmonary hypertension (PH) in mice. This model may be useful for studies seeking to reduce the pulmonary vascular resistance and delay the development of PH caused by congenital heart disease.

MATERIALS AND METHODS

The right pulmonary artery was ligated via a right posterolateral thoracotomy. Pulmonary hemodynamics was evaluated by right heart catheterization immediately after ligation and at 2, 4, 8, and 12 wk postoperatively. The right ventricle (RV) and the left ventricle (LV) with septum (S) were weighed to calculate the RV/(LV + S) ratio as an index of right ventricular hypertrophy. Morphologic changes in the left lungs were analyzed, and percentages of muscularized pulmonary vessels were assessed by hematoxylin and eosin, elastica van Gieson and alpha-smooth muscle actin staining. All the study data were compared with data from a model of PH generated by hypoxic stimulation.

RESULTS

A pulmonary hypertensive state was successfully induced by 2 wk after surgery. However, the morphologic analysis demonstrated that pulmonary vascular muscularization, as evaluated using right ventricular systolic pressure and RV/(LV + S), was not significantly increased until 4 wk postoperatively. When mice from the new model and the hypoxic model were compared, no significant differences were observed in any of the evaluated indices.

CONCLUSIONS

High-flow PH can be induced within 4 wk after ligation of the right pulmonary artery, which is easily performed in mice. Such mice can be used as a model of high-flow PH.

Reverse Regulatory Pathway (H2S / PGE2 / MMP) in Human Aortic Aneurysm and Saphenous Vein Varicosity

Hydrogen sulfide (H₂S) is a mediator with demonstrated protective effects for the cardiovascular system. On the other hand, prostaglandin (PG)E₂ is involved in vascular wall remodeling by regulating matrix metalloproteinase (MMP) activities. We tested the hypothesis that endogenous H₂S may modulate PGE₂, MMP-1 activity and endogenous tissue inhibitors of MMPs (TIMP-1/-2). This regulatory pathway could be involved in thinning of abdominal aortic aneurysm (AAA) and thickening of saphenous vein (SV) varicosities. The expression of the enzyme responsible for H₂S synthesis, cystathionine-γ-lyase (CSE) and its activity, were significantly higher in varicose vein as compared to SV. On the contrary, the endogenous H₂S level and CSE expression were lower in AAA as compared to healthy aorta (HA). Endogenous H₂S was responsible for inhibition of PGE₂ synthesis mostly in varicose veins and HA. A similar effect was observed with exogenous H₂S and consequently decreasing active MMP-1/TIMP ratios in SV and varicose veins. In contrast, in AAA, higher levels of PGE₂ and active MMP-1/TIMP ratios were found versus HA. These findings suggest that differences in H₂S content in AAA and varicose veins modulate endogenous PGE₂ production and consequently the MMP/TIMP ratio. This mechanism may be crucial in vascular wall remodeling observed in different vascular pathologies (aneurysm, varicosities, atherosclerosis and pulmonary hypertension).

Hydrogen sulfide attenuates neurodegeneration and neurovascular dysfunction induced by intracerebral-administered homocysteine in mice

High levels of homocysteine (Hcy), known as hyperhomocysteinemia are associated with neurovascular diseases. H2S, a metabolite of Hcy, has potent anti-oxidant and anti-inflammatory activities; however, the effect of H2S has not been explored in Hcy (IC)-induced neurodegeneration and neurovascular dysfunction in mice. Therefore, the present study was designed to explore the neuroprotective role of H2S on Hcy-induced neurodegeneration and neurovascular dysfunction. To test this hypothesis we employed wild-type (WT) males ages 8-10 weeks, WT+artificial cerebrospinal fluid (aCSF), WT+Hcy (0.5 μmol/μl) intracerebral injection (IC, one time only prior to NaHS treatment), WT+Hcy+NaHS (sodium hydrogen sulfide, precursor of H2S, 30 μmol/kg, body weight). NaHS was injected i.p. once daily for the period of 7 days after the Hcy (IC) injection. Hcy treatment significantly increased malondialdehyde, nitrite level, acetylcholinestrase activity, tumor necrosis factor-alpha, interleukin-1 beta, glial fibrillary acidic protein, inducible nitric oxide synthase, endothelial nitric oxide synthase and decreased glutathione level indicating oxidative-nitrosative stress and neuroinflammation as compared to control and aCSF-treated groups. Further, increased expression of neuron-specific enolase, S100B and decreased expression of (post-synaptic density-95, synaptosome-associated protein-97) synaptic protein indicated neurodegeneration. Brain sections of Hcy-treated mice showed damage in the cortical area and periventricular cells. Terminal deoxynucleotidyl transferase-mediated, dUTP nick-end labeling-positive cells and Fluro Jade-C staining indicated apoptosis and neurodegeneration. The increased expression of matrix metalloproteinase (MMP) MMP9, MMP2 and decreased expression of tissue inhibitor of metalloproteinase (TIMP) TIMP-1, TIMP-2, tight junction proteins (zonula occulden 1) in Hcy-treated group indicate neurovascular remodeling. Interestingly, NaHS treatment significantly attenuated Hcy-induced oxidative stress, memory deficit, neurodegeneration, neuroinflammation and cerebrovascular remodeling. The results indicate that H2S is effective in providing protection against neurodegeneration and neurovascular dysfunction.

Further evidence of endogenous hydrogen sulphide as a mediator of relaxation in human and rat bladder

We investigated the expression of hydrogen sulphide (H2S) in human and rat lower urinary tract (including bladder, prostate and urethra) tissues, and we sought to determine whether H2S induces relaxation of human and Sprague-Dawley (SD) rat bladder strips. Human normal lower urinary tract tissue was obtained for the evaluation of endogenous H2S productivity using a sulphide-sensitive electrode and for the analysis of the expression levels of all three synthases of endogenous H2S, cystathionine β-synthase (CBS), cystathionine γ lyase (CSE) and 3-mercaptopyruvate sulphur transferase (MPST, as known as 3-MST) by Western blot assay. CBS, CSE and MPST were located in human sample slides by immunohistochemistry. Human and male adult SD rat bladder strips were tested for H2S function with a transducer and recorded. All experiments were repeated six times. The endogenous H2S productivity and the H2S synthases had various distributions in the human and rat lower urinary tract tissues and were located in both epithelial and stromal sections. L-cysteine (L-Cys, a substrate of CBS, CSE and MPST) elicited relaxation in a dose-dependent manner on human bladder strips pre-contracted by acetylcholine chloride. This effect could be diminished by the ATP-sensitive potassium ion (KATP) channel blocker glibenclamide (GLB), the CSE inhibitor DL-propargylglycine (PPG) and the CBS inhibitor hydroxylamine (HA). H2S and its three synthases were present in the human and rat lower urinary tract tissues and relaxed human and rat bladder strips, which implied that endogenous H2S might play a role in physiological function and pathological disorders of the lower urinary tract symptoms (LUTS) or overactive bladder (OAB).

Nutritional essentiality of sulfur in health and disease

Sulfur is the seventh most abundant element measurable in the human body and is supplied mainly by the intake of methionine (Met), an indispensable amino acid found in plant and animal proteins. Met controls the initiation of protein synthesis, governs major metabolic and catalytic activities, and may undergo reversible redox processes safeguarding protein integrity. Withdrawal of Met from customary diets causes the greatest downsizing of lean body mass following either unachieved replenishment (malnutrition) or excessive losses (inflammation). These physiopathologically unrelated morbidities nevertheless stimulate comparable remethylation reactions from homocysteine, indicating that Met homeostasis benefits from high metabolic priority. Inhibition of cystathionine-β-synthase activity causes the upstream sequestration of homocysteine and the downstream drop in cysteine and glutathione. Consequently, the enzymatic production of hydrogen sulfide and the nonenzymatic reduction of elemental sulfur to hydrogen sulfide are impaired. Sulfur operates as cofactor of several enzymes critically involved in the regulation of oxidative processes. A combination of malnutrition and nutritional deprivation of sulfur maximizes the risk of cardiovascular disorders and stroke, constituting a novel clinical entity that threatens plant-eating population groups.

The role of endogenous H2S formation in reversible remodeling of lung tissue during hibernation in the Syrian hamster

During hibernation, small mammals alternate between periods of metabolic suppression and low body temperature ('torpor') and periods of full metabolic recovery with euthermic temperatures ('arousal'). Previously, we demonstrated marked structural remodeling of the lung during torpor, which is rapidly reversed during arousal. We also found that cooling of hamster cells increased endogenous production of H(2)S through the enzyme cystathionine-β-synthase (CBS). H(2)S suppresses the immune response and increases deposition of collagen. Therefore, we examined inflammatory markers and matrix metalloproteinase (MMP) activity in relation to CBS expression and H(2)S levels in lungs of euthermic and hibernating Syrian hamsters. Lung remodeling during torpor was confirmed by a strong increase in both collagenous and non-collagenous hydroxyproline content. The number of leukocytes in lung was unchanged in any phase of hibernation, while adhesion molecules VCAM-1 and ICAM-1, and the inflammatory marker NF-κB (P65) were modestly upregulated in torpor. Gelatinase activity was decreased in lungs from torpid animals, indicating inhibition of the Zn(2+)-dependent MMP-2 and MMP-9. Moreover, expression of CBS and tissue levels of H(2)S were increased in torpor. All changes normalized during arousal. Inhibition of gelatinase activity in torpor is likely caused by quenching of Zn(2+) by the sulphide ion of H(2)S. In accord, inhibition of CBS normalized gelatinase activity in torpid animals. Conversely, NaHS decreased the gelatinase activity of euthermic animals, which was attenuated by excess Zn(2+). Similar results were obtained on the activity of the Zn(2+)-dependent angiotensin converting enzyme. Our data indicate that increased production of H(2)S through CBS in hamster lungs during torpor contributes to remodeling by inhibition of gelatinase activity and possibly by suppression of the inflammatory response. Although administration of H(2)S is known to induce metabolic suppression in non-hibernating mammals ('suspended animation'), this is the first report implying endogenous H(2)S production in natural hibernation.

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 attenuates cardiac hypertrophy and fibrosis induced by abdominal aortic coarctation in rats

Hydrogen sulfide (H2S) has been recently found to be an endogenous signaling gasotransmitter. Cardiac hypertrophy often develops in the course of heart failure. It is unknown whether or not endogenous H2S protects cardiac hypertrophy. This study was conducted to examine the effects of H2S on cardiac hypertrophy and fibrosis induced by abdominal aortic coarctation and to explore its mechanisms. Male Sprague-Dawley rats were randomly divided into five groups: normal, sham, abdominal aortic coarctation (AAC), AAC treated with enalapril and AAC treated with H2S. One week after surgery, enalapril and sodium hydrosulfide (NaHS)-treated rats were fed for 28 consecutive days and sacrificed. After that, the left ventricle mass index (LVMI), cardiomyocyte size and areas, collagen volume fraction (CVF) of the rats were measured. In the AAC rats, the LVMI, the cardiomyocyte size and areas, and the CVF were all markedly increased while in the H2S groups they were significantly reduced. H2S decreased the levels of Ang-II in the heart, but not in plasma. In addition, H2S also improved the expression of connexin 43 (Cx43). Our results suggest that H2S can significantly suppress cardiac hypertrophy and fibrosis induced by overloaded pressure, possibly by inhibiting the activity of intracardiac Ang-II and by modifying expression of Cx43.

Emerging role of hydrogen sulfide in health and disease: critical appraisal of biomarkers and pharmacological tools

H2S (hydrogen sulfide) is a well known and pungent gas recently discovered to be synthesized enzymatically in mammalian and human tissues. In a relatively short period of time, H2S has attracted substantial interest as an endogenous gaseous mediator and potential target for pharmacological manipulation. Studies in animals and humans have shown H2S to be involved in diverse physiological and pathophysiological processes, such as learning and memory, neurodegeneration, regulation of inflammation and blood pressure, and metabolism. However, research is limited by the lack of specific analytical and pharmacological tools which has led to considerable controversy in the literature. Commonly used inhibitors of endogenous H2S synthesis have been well known for decades to interact with other metabolic pathways or even generate NO (nitric oxide). Similarly, commonly used H2S donors release H2S far too quickly to be physiologically relevant, but may have therapeutic applications. In the present review, we discuss the enzymatic synthesis of H2S and its emerging importance as a mediator in physiology and pathology. We also critically discuss the suitability of proposed 'biomarkers' of H2S synthesis and metabolism, and highlight the complexities of the currently used pharmacological H2S 'donor' molecules and 'specific' H2S synthesis inhibitors in their application to studying the role of H2S in human disease.

Hydrogen sulphide: novel opportunity for drug discovery

Hydrogen sulphide (H(2)S) is emerging as an important endogenous modulator, which exhibits the beneficial effects of nitric oxide (NO) on the cardiovascular (CV) system, without producing toxic metabolites. H(2)S is biosynthesized in mammalian tissues by cystathionine-β-synthase and cystathionine-γ-lyase. H(2)S exhibits the antioxidant properties of inorganic and organic sulphites, behaving as a scavenger of reactive oxygen species. There is also clear evidence that H(2)S triggers other important effects, mainly mediated by the activation of ATP-sensitive potassium channels (K(ATP)). This mechanism accounts for the vasorelaxing and cardioprotective effects of H(2)S. Furthermore, H(2)S inhibits smooth muscle proliferation and platelet aggregation. In non-CV systems, H(2)S regulates the functions of the central nervous system, as well as respiratory, gastroenteric, and endocrine systems. Conversely, H(2)S deficiency contributes to the pathogenesis of hypertension. Likewise, impairment of H(2)S biosynthesis is involved in CV complications associated with diabetes mellitus. There is also evidence of a cross-talk between the H(2)S and the endothelial NO pathways. In particular, recent observations indicate a possible pathogenic link between deficiencies of H(2 S activity and the progress of endothelial dysfunction. These biological aspects of endogenous H(2)S have led several authors to look at this mediator as "the new NO" that has given attractive opportunities to develop innovative classes of drugs. In this review, the main biological actions of H(2)S are discussed. Moreover, some examples of H(2)S-donors are shown, as well as some hybrids, in which H(2)S-releasing moieties are added to well-known drugs, for improving their pharmacodynamic profile or reducing the potential for adverse effects, are reported.

Hydrogen sulfide mitigates matrix metalloproteinase-9 activity and neurovascular permeability in hyperhomocysteinemic mice

An elevated level of homocysteine (Hcy), known as hyperhomocysteinemia (HHcy), was associated with neurovascular diseases. At physiological levels, hydrogen sulfide (H(2)S) protected the neurovascular system. Because Hcy was also a precursor of hydrogen sulfide (H(2)S), we sought to test whether the H(2)S protected the brain during HHcy. Cystathionine-beta-synthase heterozygous (CBS+/-) and wild type (WT) mice were supplemented with or without NaHS (30 microM/L, H(2)S donor) in drinking water. Blood flow and cerebral microvascular permeability in pial vessels were measured by intravital microscopy in WT, WT+NaHS, CBS-/+ and (CBS-/+)+NaHS-treated mice. The brain tissues were analyzed for matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP) by Western blot and RT-PCR. The mRNA levels of CBS and cystathionine gamma lyase (CSE, enzyme responsible for conversion of Hcy to H(2)S) genes were measured by RT-PCR. The results showed a significant increase in MMP-2, MMP-9, TIMP-3 protein and mRNA in CBS (-/+) mice, while H(2)S treatment mitigated this increase. Interstitial localization of MMPs was also apparent through immunohistochemistry. A decrease in protein and mRNA expression of TIMP-4 was observed in CBS (-/+) mice. Microscopy data revealed increase in permeability in CBS (-/+) mice. These effects were ameliorated by H(2)S and suggested that physiological levels of H(2)S supplementation may have therapeutic potential against HHcy-induced microvascular permeability, in part, by normalizing the MMP/TIMP ratio in the brain.