Therapeutic importance of hydrogen sulfide in age-associated neurodegenerative diseases

Hydrogen sulfide(H2S)is a gasotransmitter that acts as an antioxidant and exhibits a wide variety of cytoprotective and physiological functions in age-associated diseases.One of the major causes of age-related diseases is oxidative stress.In recent years,the importance of H2S has become clear,although its antioxidant function has not yet been fully explored.The enzymes cystathionineβ-synthase,cystathionineγ-lya-se,and 3-mercaptopyruvate sulfurtransferase are involved in the enzymatic production of H2S.Previously,H2S was considered a neuromodulator,given its role in long-term hippocampal potentiation,but it is now also recognized as an antioxidant in age-related neurodegeneration.Due to aerobic metabolism,the central nervous system is vulnerable to oxidative stress in brain aging,resulting in age-associated degenerative diseases.H2S exerts its antioxidant effect by limiting free radical reactions through the activation of antioxidant enzymes,including superoxide dismutase,catalase,and glutathione peroxidase,which protect against the effects of aging by regulating apoptosis-related genes,including p53,Bax,and Bcl-2.This review explores the implications and mechanisms of H2S as an antioxidant in age-associated neurodegenerative diseases,including Alzheimer’s disease,Parkinson’s disease,Huntington’s disease,and Down syndrome.

Neuroprotective mechanism of L-cysteine after subarachnoid hemorrhage

Hydrogen sulfide,which can be generated in the central nervous system from the sulfhydryl-containing amino acid,L-cysteine,by cystathionine-β-synthase,may exert protective effects in experimental subarachnoid hemorrhage;however,the mechanism underlying this effect is unknown.This study explored the mechanism using a subarachnoid hemorrhage rat model induced by an endovascular perforation technique.Rats were treated with an intraperitoneal injection of 100 mM L-cysteine(30μL)30 minutes after subarachnoid hemorrhage.At 48 hours after subarachnoid hemorrhage,hematoxylin-eosin staining was used to detect changes in prefrontal cortex cells.L-cysteine significantly reduced cell edema.Neurological function was assessed using a modified Garcia score.Brain water content was measured by the wet-dry method.L-cysteine significantly reduced neurological deficits and cerebral edema after subarachnoid hemorrhage.Immunofluorescence was used to detect the number of activated microglia.Reverse transcription-polymerase chain reaction(RT-PCR)was used to detect the levels of interleukin 1β and CD86 mRNA in the prefrontal cortex.L-cysteine inhibited microglial activation in the prefrontal cortex and reduced the mRNA levels of interleukin 1βand CD86.RT-PCR and western blot analysis of the complement system showed that L-cysteine reduced expression of the complement factors,C1q,C3αand its receptor C3aR1,and the deposition of C1q in the prefrontal cortex.Dihydroethidium staining was applied to detect changes in reactive oxygen species,and immunohistochemistry was used to detect the number of NRF2-and HO-1-positive cells.L-cysteine reduced the level of reactive oxygen species in the prefrontal cortex and the number of NRF2-and HO-1-positive cells.Western blot assays and immunohistochemistry were used to detect the protein levels of CHOP and GRP78 in the prefrontal cortex and the number of CHOP-and GRP78-positive cells.L-cysteine reduced CHOP and GRP78 levels and the number of CHOP-and GRP78-positive cells.The cystathionine-β-synthase inhibitor,aminooxyacetic acid,significantly reversed the above neuroprotective effects of L-cysteine.Taken together,L-cysteine can play a neuroprotective role by regulating neuroinflammation,complement deposition,oxidative stress and endoplasmic reticulum stress.The study was approved by the Animals Ethics Committee of Shandong University,China on February 22,2016(approval No.LL-201602022).

Localization of the hydrogen sulfide and oxytocin systems at the depth of the sulci in a porcine model of acute subdural hematoma

In the porcine model discussed in this review,the acute subdural hematoma was induced by subdural injection of autologous blood over the left parietal cortex,which led to a transient elevation of the intracerebral pressure,measured by bilateral neuromonitoring.The hematoma-induced brain injury was associated with albumin extravasation,oxidative stress,reactive astrogliosis and microglial activation in the ipsilateral hemisphere.Further proteins and injury markers were validated to be used for immunohistochemistry of porcine brain tissue.The cerebral expression patterns of oxytocin,oxytocin receptor,cystathionine-γ-lyase and cystathionine-β-synthase were particularly interesting:these four proteins all co-localized at the base of the sulci,where pressure-induced brain injury elicits maximum stress.In this context,the pig is a very relevant translational model in contrast to the rodent brain.The structure of the porcine brain is very similar to the human:the presence of gyri and sulci(gyrencephalic brain),white matter to grey matter proportion and tentorium cerebelli.Thus,pressure-induced injury in the porcine brain,unlike in the rodent brain,is reflective of the human pathophysiology.

Changes in Hydrogen Sulfide in Rats with Hepatic Cirrhosis in Different Stages

This study aimed to observe changes in the hydrogen sulfide（H_2S） system in the blood and liver tissue of rats with hepatic cirrhosis at different stages by studying the effect of H_2S on the course of hyperdynamic circulation in rats with hepatic cirrhosis. H_2S concentration in the blood from the portal vein and inferior vena cava of hepatic cirrhosis rat model induced with carbon tetrachloride was detected on the 15 th, 30 th, and 52 nd day. The expression of cystathionine β-synthase（CBS） and cystathionine γ-lyase（CSE） protein, and CBS and CSE mRNA in the liver was detected by immunohistochemistry and reverse transcriptase polymerase chain reaction（RT-PCR）, respectively. The results indicated that H_2S concentration in the blood from the portal vein and inferior vena cava of rats with hepatic cirrhosis was significantly lower than that in the control group. H_2S was gradually decreased with the development of the disease and significantly lower in the blood from portal vein than in the blood of inferior vena cava at the mid-stage and the late stage groups. The expression levels of CBS and CSE protein, and CBS and CSE mR NA in the livers with hepatic cirrhosis at different stages were all higher than those in the control group, and the expression gradually increased with the development of the disease. The expression of CBS was lower than CSE in the same stages. The results indicated that the CSE mRNA was expressed predominantly in the cirrhosis groups as compared with CBS mRNA. Among experimental rats, the H_2S system has an important effect on the occurrence and development of hyperdynamic circulation in rats with hepatic cirrhosis. This finding adds to the literature by demonstrating that H_2S protects vascular remodelling in the liver, and that CSE is indispensable in this process.

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 y 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 ere-contracted by acetylcholine chloride. This effect could be diminished by the ATe-sensitive potassium ion （KATe） channel blocker glibenclamide （GLB）, the CSE inhibitor DL-propargylglycine （PEG） 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）.

Hyperhomocysteinemia dysregulates plasma levels of polyunsaturated fatty acids-derived eicosanoids

Hyperhomocysteinemia(HHcy)contributes to the incidence of many cardiovascular diseases(CVD).Our group have previously established crucial roles of eicosanoids and homocysteine in the incidence of vascular injury in diabetic retinopathy and renal injury.Using cystathionine-β-synthase heterozygous mice(cβs^(+/-))as a model of HHcy,the current study was designed to determine the impact of homocysteine on circulating levels of lipid mediators derived from polyunsaturated fatty acids(PUFA).Plasma samples were isolated from wild-type(WT)and cβs^(+/-)mice for the assessment of eicosanoids levels using LC/MS.Plasma 12/15-lipoxygenase(12/15-LOX)activity significantly decreased in cβs^(+/-)vs.WT control mice.LOX-derived metabolites from both omega-3 and omega-6 PUFA were also reduced in cβs^(+/-)mice compared to WT control(P<0.05).Contrary to LOX metabolites,cytochrome P450(CYP)metabolites from omega-3 and omega-6 PUFA were significantly elevated in cβs^(+/-)mice compared to WT control.Epoxyeicosatrienoic acids(EETs)are epoxides derived from arachidonic acid(AA)metabolism by CYP with anti-inflammatory properties and are known to limit vascular injury,however their physiological role is limited by their rapid degradation by soluble epoxide hydrolase(sEH)to their corresponding diols(DiHETrEs).In cβs^(+/-)mice,a significant decrease in the plasma EETs bioavailability was obvious as evident by the decrease in EETs/DiHETrEs ratio relative to WT control mice.Cyclooxygenase(COX)metabolites were also significantly decreased in cβs^(+/-)vs.WT control mice.These data suggest that HHcy impacts eicosanoids metabolism through decreasing LOX and COX metabolic activities while increasing CYP metabolic activity.The increase in AA metabolism by CYP was also associated with increase in sEH activity and decrease in EETs bioavailability.Dysregulation of eicosanoids metabolism could be a contributing factor to the incidence and progression of HHcy-induced CVD.