Sulfur dioxide relaxes rat aorta by endothelium-dependent and -independent mechanisms

Effect of sulfur dioxide on vascular biology

Gasotransmitters, such as nitric oxide, carbon monoxide and hydrogen sulfide, can be generated endogenously. These gasotransmitters play important roles in vascular biology, including vasorelaxation and inhibition of vascular smooth muscle cell (VSMC) proliferation. In recent years, sulfur dioxide (SO₂) has been considered as a fourth gasotransmitter. SO₂ is present in air pollution. Moreover, SO₂ toxicity, including oxidative stress and DNA damage, has been extensively reported in previous studies. Recent studies have shown that SO₂ can be endogenously generated in various organs and vascular tissues, where it regulates vascular tone, vascular smooth cell proliferation and collagen synthesis. SO₂ can decrease blood pressure in rats, inhibit smooth muscle cell proliferation and collagen accumulation and promote collagen degradation, and improve vascular remodelling. SO₂ can decrease cardiovascular atherosclerotic plaques by enhancing the antioxidant effect and upregulating nitric oxide/nitric oxide synthase and hydrogen sulfide/cystathionine-γ-lyase pathways. SO₂ can also ameliorate vascular calcification via the transforming growth factor - β1/Smad pathway. The effect of SO₂ on vascular regulation has attracted great interest. SO₂ may be a novel mediator in vascular biology.

H2S, Polysulfides, and Enzymes: Physiological and Pathological Aspects

We have been studying the general aspects of the functions of H₂S and polysulfides, and the enzymes involved in their biosynthesis, for more than 20 years. Our aim has been to elucidate novel physiological and pathological functions of H₂S and polysulfides, and unravel the regulation of the enzymes involved in their biosynthesis, including cystathionine β-synthase (EC 4.2.1.22), cystathionine γ-lyase (EC 4.4.1.1), thiosulfate sulfurtransferase (rhodanese, EC 2.8.1.1), and 3-mercaptopyruvate sulfurtransferase (EC 2.8.1.2). Physiological and pathological functions, alternative biosynthetic processes, and additional functions of H₂S and polysulfides have been reported. Further, the structure and reaction mechanisms of related enzymes have also been reported. We expect this issue to advance scientific knowledge regarding the detailed functions of H₂S and polysulfides as well as the general properties and regulation of the enzymes involved in their metabolism. We would like to cover four topics: the physiological and pathological functions of H₂S and polysulfides, the mechanisms of the biosynthesis of H₂S and polysulfides, the properties of the biosynthetic enzymes, and the regulation of enzymatic activity. The knockout mouse technique is a useful tool to determine new physiological functions, especially those of H₂S and polysulfides. In the future, we shall take a closer look at symptoms in the human congenital deficiency of each enzyme. Further studies on the regulation of enzymatic activity by in vivo substances may be the key to finding new functions of H₂S and polysulfides.

Sulfur dioxide reduces lipopolysaccharide-induced acute lung injury in rats

INTRODUCTION

Recent studies suggested that sulfur dioxide (SO2) can be produced endogenously by pulmonary vessels and attenuate acute lung injury (ALI) with vasorelaxant effects. This study was conducted to determine whether SO2 can inhibit lung inflammation and relax pulmonary arteries via inhibition of the mitogen-activated protein kinase (MAPK) pathway.

MATERIAL AND METHODS

Forty-eight adult male Sprague Dawley rats (250~300 g) were randomly divided into six treatment groups: control (n = 8), control + SO2 (n = 8), control + L-aspartic acid-β-hydroxamate (HDX) (n = 8), LPS (n = 8), LPS + SO2 (n = 8) and LPS + HDX (n = 8).

RESULTS

Six hours after LPS treatment, rats exhibited elevated pulmonary artery hypertension (PAH), marked pulmonary structure injury with elevated pulmonary myeloperoxidase (MPO) activity and increased expression of intercellular adhesion molecule 1 (ICAM-1) and CD11b, along with decreased pulmonary SO2 production and reduced pulmonary aspartate aminotransferase (AAT) activity. Pretreatment with SO2 saline solution significantly reduced, while HDX (AAT inhibitor) aggravated, the pathogenesis of LPS-induced ALI. Moreover, SO2 saline solution significantly down-regulated expression of Raf-1, MEK-1 and phosphorylated ERK (p-ERK). It also prevented pulmonary hypertension in association with an up-regulated SO2/AAT pathway. However, HDX advanced pulmonary hypertension and inflammatory responses in the lung were associated with a down-regulated SO2/AAT pathway.

CONCLUSIONS

Our results suggest that SO2 markedly relieved inflammatory responses, in association with Raf-1, MEK-1 and p-ERK during ALI induced by LPS. The down-regulation of the SO2/AAT pathway may be involved in the mechanism(s) of LPS-induced lung injury.

Comparative effects of quercetin and hydroalcoholic extract of Otostegia persica boiss with atorvastatin on atherosclerosis complication in male wistar rats

The use of herbal remedies is significantly considered in the atherosclerosis treatment, reduction of fatty elements, and prevention of activity of oxidative stress factors. The present study was conducted on 48 rats in 6 groups. The experimental and sham groups were fed with 2% cholesterol for 40 days; and experimental groups were separately treated by atorvastatin, quercetin, and hydroalcoholic extract for 4 weeks. After treatment procedure, some serum factors such as low-density lipoprotein (LDL), total cholesterol (TC), malondialdehyde (MDA), and reactive oxygen species (ROS) were evaluated. Serum levels of LDL, TC, MDA, and ROS were significantly lower in experimental groups than sham group (p < .01). There was a significant decrease in serum MDA levels of these two groups in comparison with the atorvastatin-treated group (p < .05). Blood pressure parameters were decreased in treated with quercetin and hydroalcoholic extract in comparison with the sham group (p < .05). Quercetin and hydroalcoholic extract similar to atorvastatin could decrease serum lipids [except high-density lipoprotein (HDL)], oxidative stress factors, aorta contraction, weight gain, and blood pressure. These reagents improved the vascular structure and prevented the plaque formation.

Sulfur dioxide improves endothelial dysfunction by downregulating the angiotensin II/AT1R pathway in D-galactose-induced aging rats

The aim of this study was to investigate the protective effects of sulfur dioxide (SO₂) on the endothelial function of the aorta in D-galactose (D-gal)-induced aging rats. Sprague Dawley rats were randomized into a D-gal group, a D-gal + SO₂ group and a control group, then injected with D-gal, D-gal + SO₂ donor or equivalent volumes of saline, respectively, for 8 consecutive weeks. After 8 weeks, the mean arterial pressure was significantly increased in the D-gal group, but was lowered by SO₂. SO₂ significantly ameliorated the endothelial dysfunction induced by D-gal treatment. The vasorelaxant effect of SO₂ was associated with the elevated nitric oxide levels and upregulated phosphorylation of endothelial nitric oxide synthase. In the D-gal group, the concentration of angiotensin II in the plasma was significantly increased, but was decreased by SO₂. Moreover, levels of vascular tissue hydrogen peroxide (H₂O₂) and malondialdehyde were significantly lower in SO₂-treated groups than those in the D-gal group. Western blot analysis showed that the expressions of oxidative stress-related proteins (the angiotensin II type 1 receptor (AT₁R), and nicotinamide adenine dinucleotide phosphate oxidase subunits) were increased in the D-gal group, while they were decreased after treatment with SO₂. In conclusion, SO₂ attenuated endothelial dysfunction in association with the inhibition of oxidative stress injury and the downregulation of the angiotensin II/AT₁R pathway in D-gal-induced aging rats.

Sulfur dioxide prodrugs: triggered release of SO2via a click reaction

Sulfur dioxide (SO₂) is being recognized as a possible endogenous gasotransmitter with importance on par with that of NO, CO, and H₂S. Herein we describe a series of SO₂ prodrugs that are activated for SO₂ release via a bioorthogonal click reaction. The release rate can be tuned by adjusting the substituents on the prodrug.

Multiple role of 3-mercaptopyruvate sulfurtransferase: antioxidative function, H2 S and polysulfide production and possible SOx production

Rat 3-mercaptopyruvate sulfurtransferase (MPST) is a 32 808 Da simple protein. Cys247 is a catalytic site, and Cys154 and Cys263 are on the enzyme surface. MPST is found in all tissues, particularly in the kidneys, although the localization of its activity differs in each tissue. In this review, four functions of MPST are reviewed: (i) antioxidative function: Cys247 is redox-sensitive and serves as a redox-sensing switch. It is oxidized to cysteine sulfenate, which has a low redox potential, upon which the enzyme is inactivated. Then, reduced thioredoxin (Trx) with a reducing system (Trx reductase and NADPH) reduces the sulfenate to restore activity; meanwhile, Cys154 and Cys263 form an intermolecular disulfide bond, which serves as another redox-sensing switch. Consequently, Trx specifically cleaves the intermolecular disulfide bond by converting it from the inactive form (dimer) to the active form (monomer). (ii) Hydrogen sulfide and polysulfide production: hydrogen sulfide is produced via reduction of the persulfurated sulfur-acceptor substrate by reduced Trx or Trx with a reducing system; as an alternative process, stable polysulfurated or persulfurated Cys247 as a reaction intermediate is reduced by Trx with a reducing system to release hydrogen sulfide and polysulfides. (iii) Possible sulfur oxide production: sulfur oxides (SO, SO2 and SO3 ) can be produced in the redox cycle of sulfane sulfur formed at the catalytic site Cys247 (Cys-SO- , Cys-SO2- and Cys-SO3- ) as reaction intermediates and released by reduced Trx or Trx with a reducing system. (iv) Possible anxiolytic-like effects: MPST-knockout mice exhibited anxiolytic-like effects.

Sulfur Dioxide Inhibits Extracellular Signal-regulated Kinase Signaling to Attenuate Vascular Smooth Muscle Cell Proliferation in Angiotensin II-induced Hypertensive Mice

Background:

Clarifying the mechanisms underlying vascular smooth muscle cell (VSMC) proliferation is important for the prevention and treatment of vascular remodeling and the reverse of hyperplastic lesions. Previous research has shown that the gaseous signaling molecule sulfur dioxide (SO₂) inhibits VSMC proliferation, but the mechanism for the inhibition of the angiotensin II (AngII)-induced VSMC proliferation by SO₂ has not been fully elucidated. This study was designed to investigate if SO₂ inhibited VSMC proliferation in mice with hypertension induced by AngII.

Methods:

Thirty-six male C57 mice were randomly divided into control, AngII, and AngII + SO₂ groups. Mice in AngII group and AngII + SO₂ group received a capsule-type AngII pump implanted under the skin of the back at a slow-release dose of 1000 ng·kg⁻¹·min⁻¹. In addition, mice in AngII + SO₂ received intraperitoneal injections of SO₂ donor. Arterial blood pressure of tail artery was determined. The thickness of the aorta was measured by elastic fiber staining, and proliferating cell nuclear antigen (PCNA) and phosphorylated-extracellular signal-regulated kinase (P-ERK) were detected in aortic tissues. The concentration of SO₂ in serum and aortic tissue homogenate supernatant was measured using high-performance liquid chromatography with fluorescence determination. In the in vitro study, VSMC of A7R5 cell lines was divided into six groups: control, AngII, AngII + SO₂, PD98059 (an inhibitor of ERK phosphorylation), AngII + PD98059, and AngII + SO₂ + PD98059. Expression of PCNA, ERK, and P-ERK was determined by Western blotting.

Results:

In animal experiment, compared with the control group, AngII markedly increased blood pressure (P < 0.01) and thickened the aortic wall in mice (P < 0.05) with an increase in the expression of PCNA (P < 0.05). SO₂, however, reduced the systemic hypertension and the wall thickness induced by AngII (P < 0.05). It inhibited the increased expression of PCNA and P-ERK induced by AngII (P < 0.05). In cell experiment, PD98059, an ERK phosphorylation inhibitor, blocked the inhibitory effect of SO₂ on VSMC proliferation (P < 0.05).

Conclusions:

ERK signaling is involved in the mechanisms by which SO₂ inhibits VSMC proliferation in AngII-induced hypertensive mice via ERK signaling.

Sulfur-containing gaseous signal molecules, ion channels and cardiovascular diseases

Sulfur-containing gaseous signal molecules including hydrogen sulphide and sulfur dioxide were previously recognized as toxic gases. However, extensive studies have revealed that they can be generated in the cardiovascular system via a sulfur-containing amino acid metabolic pathway, and have an important role in cardiovascular physiology and pathophysiology. Ion channels are pore-forming membrane proteins present in the membrane of all biological cells; their functions include the establishment of a resting membrane potential and the control of action potentials and other electrical signals by conducting ions across the cell membrane. Evidence has now accumulated suggesting that the sulfur-containing gaseous signal molecules are important regulators of ion channels and transporters. The aims of this review are (1) to discuss the recent experimental evidences in the cardiovascular system regarding the regulatory effects of sulfur-containing gaseous signal molecules on a variety of ion channels, including ATP-sensitive potassium, calcium-activated potassium, voltage-gated potassium, L- and T-type calcium, transient receptor potential and chloride and sodium channels, and (2) to understand how the gaseous signal molecules affect ion channels and cardiovascular diseases.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Role of Endogenous Sulfur Dioxide in Regulating Vascular Structural Remodeling in Hypertension

Sulfur dioxide (SO₂), an emerging gasotransmitter, was discovered to be endogenously generated in the cardiovascular system. Recently, the physiological effects of endogenous SO₂ were confirmed. Vascular structural remodeling (VSR), an important pathological change in many cardiovascular diseases, plays a crucial role in the pathogenesis of the diseases. Here, the authors reviewed the research progress of endogenous SO₂ in regulating VSR by searching the relevant data from PubMed and Medline. In spontaneously hypertensive rats (SHRs) and pulmonary hypertensive rats, SO₂/aspartate aminotransferase (AAT) pathway was significantly altered. SO₂ inhibited vascular smooth muscle cell (VSMC) proliferation, promoted apoptosis, inhibited the synthesis of extracellular collagen but promoted its degradation, and enhanced antioxidative capacity, thereby playing a significant role in attenuating VSR. However, the detailed mechanisms needed to be further explored. Further studies in this field would be important for the better understanding of the pathogenesis of systemic hypertension and pulmonary hypertension. Also, clinical trials are needed to demonstrate if SO₂ would be a potential therapeutic target in cardiovascular diseases.

The vasodilatory effect of sulfur dioxide via SGC/cGMP/PKG pathway in association with sulfhydryl-dependent dimerization

The present study was designed to explore the role of soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP)/PKG pathway in sulfur dioxide (SO2)-induced vasodilation. We showed that SO2 induced a concentration-dependent relaxation of phenylephrine (PE)-precontracted rat aortic rings in association with an increase in cGMP concentration, whereas l-aspartic acid β-hydroxamate (HDX), an inhibitor of SO2 synthase, contracted rings in a dose-dependent manner. Pretreatment of aortic rings with the sGC inhibitor ODQ (30 μM) attenuated the vasodilatory effects of SO2, suggesting the involvement of cGMP pathway in SO2-induced vasodilation. Mechanistically, SO2 upregulated the protein levels of sGC and PKG dimers, while HDX inhibited it, indicating SO2 could promote cGMP synthesis through sGC activation. Furthermore, the dimerization of sGC and PKG and vasodilation induced by SO2 in precontracted rings were significantly prevented by thiol reductants dithiothreitol (DTT). In addition, SO2 reduced the activity of phosphodiesterase type 5 (PDE5), a cGMP-specific hydrolytic enzyme, implying that SO2 elevated cGMP concentration by inhibiting its hydrolysis. Hence, SO2 exerted its vasodilatory effects at least partly by promoting disulfide-dependent dimerization of sGC and PKG, resulting in an activated sGC/cGMP/PKG pathway in blood vessels. These findings revealed a new mode of action and mechanisms by which SO2 regulated the vascular tone.

Endogenous Sulfur Dioxide: A New Member of Gasotransmitter Family in the Cardiovascular System

Sulfur dioxide (SO2) was previously regarded as a toxic gas in atmospheric pollutants. But it has been found to be endogenously generated from metabolism of sulfur-containing amino acids in mammals through transamination by aspartate aminotransferase (AAT). SO2 could be produced in cardiovascular tissues catalyzed by its synthase AAT. In recent years, studies revealed that SO2 had physiological effects on the cardiovascular system, including vasorelaxation and cardiac function regulation. In addition, the pathophysiological effects of SO2 were also determined. For example, SO2 ameliorated systemic hypertension and pulmonary hypertension, prevented the development of atherosclerosis, and protected against myocardial ischemia-reperfusion (I/R) injury and isoproterenol-induced myocardial injury. These findings suggested that endogenous SO2 was a novel gasotransmitter in the cardiovascular system and provided a new therapy target for cardiovascular diseases.

Health effects of carbon-containing particulate matter: focus on sources and recent research program results

Air pollution is a complex mixture of gas-, vapor-, and particulate-phase materials comprised of inorganic and organic species. Many of these components have been associated with adverse health effects in epidemiological and toxicological studies, including a broad spectrum of carbonaceous atmospheric components. This paper reviews recent literature on the health impacts of organic aerosols, with a focus on specific sources of organic material; it is not intended to be a comprehensive review of all the available literature. Specific emission sources reviewed include engine emissions, wood/biomass combustion emissions, biogenic emissions and secondary organic aerosol (SOA), resuspended road dust, tire and brake wear, and cooking emissions. In addition, recent findings from large toxicological and epidemiological research programs are reviewed in the context of organic PM, including SPHERES, NPACT, NERC, ACES, and TERESA. A review of the extant literature suggests that there are clear health impacts from emissions containing carbon-containing PM, but difficulty remains in apportioning responses to certain groupings of carbonaceous materials, such as organic and elemental carbon, condensed and gas phases, and primary and secondary material. More focused epidemiological and toxicological studies, including increased characterization of organic materials, would increase understanding of this issue.

Signal pathways involved in the biological effects of sulfur dioxide

Gasotransmitters, such as nitric oxide, carbon monoxide and hydrogen sulfide, play important roles in life and have attracted great interest in scientists. In recent years, sulfur dioxide (SO2) has also been found to play important roles in mammals. The redox pathway is involved in the biological effects of SO2, such as the protective effect on myocardial ischemia reperfusion, myocardial injury, pulmonary hypertension and atherosclerosis. Ion channels, such as L-type calcium and adenosine triphosphate-sensitive potassium channels, as well as 3'-5'-cyclic guanosine monophosphate and 3'-5'-cyclic adenosine monophosphate pathways are also involved in the vasorelaxant effect of SO2. The mitogen-activated protein kinase pathway plays roles in vascular remodeling during pulmonary hypertension and vascular smooth muscle cell proliferation. Understanding these signaling mechanisms would help to clarify the pathophysiological effect and therapeutic potential of SO2.

The ERK1/2 signaling pathway is involved in sulfur dioxide preconditioning-induced protection against cardiac dysfunction in isolated perfused rat heart subjected to myocardial ischemia/reperfusion

Ischemia/reperfusion injury (IRI) occurs frequently during reperfusion of ischemic myocardium, and preconditioning has been regarded as one of the best strategies to prevent myocardial injury during the ischemia/reperfusion process. Our previous studies indicated that a small dose of sulfur dioxide (SO₂) used as preconditioning exerts cardioprotection. However, the mechanisms underlying the cardioprotection remain unclear. The present study was designed to examine if the extracellular regulated protein kinases 1/2 (ERK1/2) signaling pathway mediated protection against cardiac dysfunction after SO₂ preconditioning in isolated rat hearts subjected to ischemia/reperfusion (I/R). Langendorff heart perfusion was performed in vitro, where 56 male Wistar rats were randomly divided into seven groups: control group, 5 μmol/L SO₂ group (S5), 2-(2-Amino-3-methoxyphenyl)-4H-1-benzopyran-4-one (PD98059) + 5 μmol/L SO₂ (PD98059 + S5) group, PD98059 group, I/R group, 5 μmol/L SO₂ + I/R (S5 + I/R) group and PD98059 + 5 μmol/L SO₂ + I/R (PD98059 + S5 + I/R) group. Cardiac function and myocardial phosphorylated ERK1/2 protein were measured. We found that I/R in isolated rat heart resulted in cardiac dysfunction with a significant increase in phosphorylated ERK1/2 protein. SO₂ preconditioning markedly suppressed phosphorylated ERK1/2 protein and improved cardiac function in isolated rat heart with I/R (p < 0.05). However, pre-treatment with PD98059 could prevent the above effects of SO₂ preconditioning. In conclusion, SO₂ preconditioning protected against cardiac dysfunction in isolated rat heart subjected to I/R via suppression of the over-activation of the ERK1/2 signaling pathway.

Sulfur dioxide preconditioning increases antioxidative capacity in rat with myocardial ischemia reperfusion (I/R) injury

BACKGROUND

The study was designed to explore if sulfur dioxide (SO2) preconditioning increased antioxidative capacity in rat with myocardial ischemia reperfusion (I/R) injury.

METHODS

The myocardial I/R model was made by left coronary artery ligation for 30min and reperfusion for 120min in rats. Myocardial infarct size and plasma lactate dehydrogenase (LDH) and creatine kinase (CK) activities, plasma superoxide dismutase (SOD), malondialdehyde (MDA), glutathione peroxidase (GSH-Px) and glutathione (GSH) changes were detected for the rats. The contents of myocardial hydrogen sulfide (H2S) and nitric oxide (NO) were measured. Myocardial protein expressions of SOD1, SOD2, cystathionine γ-lyase (CSE) and iNOS were tested using Western blot.

RESULTS

Myocardial infarction developed and plasma CK and LDH activities were significantly increased in I/R group compared with those in control group, but SO2 preconditioning significantly reduced myocardial infarct size, and plasma CK and LDH activities. SO2 preconditioning successfully increased plasma SOD, GSH and GSH-Px levels and myocardial SOD1 protein expression, but decreased MDA level in rats of I/R group. Compared with controls, the myocardial H2S level and CSE expression were decreased after I/R, but myocardial NO level and iNOS expression were increased. With the treatment of SO2, myocardial H2S level and CSE expression were increased, but myocardial NO level and iNOS expression were decreased compared with those in I/R group.

CONCLUSIONS

SO2 preconditioning could significantly reduce I/R-induced myocardial injury in vivo in association with increased myocardial antioxidative capacity, upregulated myocardial H2S/CSE pathway but downregulated NO/iNOS pathway.