Hydrogen Sulfide Differentially Affects The Hepatic Vasculature In Response To Phenylephrine And Endothelin 1 During Endotoxemia

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Hydrogen Sulfide Actions in the Vasculature

Hydrogen sulfide (H2 S) is a small, gaseous molecule with poor solubility in water that is generated by multiple pathways in many species including humans. It acts as a signaling molecule in many tissues with both beneficial and pathological effects. This article discusses its many actions in the vascular system and the growing evidence of its role to regulate vascular tone, angiogenesis, endothelial barrier function, redox, and inflammation. Alterations in some disease states are also discussed including potential roles in promoting tumor growth and contributions to the development of metabolic disease. © 2021 American Physiological Society. Compr Physiol 11:1-22, 2021.

Sodium Thiosulfate Improves Intestinal and Hepatic Microcirculation Without Affecting Mitochondrial Function in Experimental Sepsis

Introduction

In the immunology of sepsis microcirculatory and mitochondrial dysfunction in the gastrointestinal system are important contributors to mortality. Hydrogen sulfide (H₂S) optimizes gastrointestinal oxygen supply and mitochondrial respiration predominantly via K(ATP)-channels. Therefore, we tested the hypothesis that sodium thiosulfate (STS), an inducer of endogenous H₂S, improves intestinal and hepatic microcirculation and mitochondrial function via K(ATP)-channels in sepsis.

Methods

In 40 male Wistar rats colon ascendens stent peritonitis (CASP) surgery was performed to establish sepsis. Animals were randomized into 4 groups (1: STS 1 g • kg^-1 i.p., 2: glibenclamide (GL) 5 mg • kg^-1 i.p., 3: STS + GL, 4: vehicle (VE) i.p.). Treatment was given directly after CASP-surgery and 24 hours later. Microcirculatory oxygenation (µHBO₂) and flow (µflow) of the colon and the liver were continuously recorded over 90 min using tissue reflectance spectrophotometry. Mitochondrial oxygen consumption in tissue homogenates was determined with respirometry. Statistic: two-way ANOVA + Dunnett´s and Tukey post - hoc test (microcirculation) and Kruskal-Wallis test + Dunn’s multiple comparison test (mitochondria). p < 0.05 was considered significant.

Results

STS increased µHbO₂ (colon: 90 min: + 10.4 ± 18.3%; liver: 90 min: + 5.8 ± 9.1%; p < 0.05 vs. baseline). Furthermore, STS ameliorated µflow (colon: 60 min: + 51.9 ± 71.1 aU; liver: 90 min: + 22.5 ± 20.0 aU; p < 0.05 vs. baseline). In both organs, µHbO₂ and µflow were significantly higher after STS compared to VE. The combination of STS and GL increased colonic µHbO₂ and µflow (µHbO₂ 90 min: + 8.7 ± 11.5%; µflow: 90 min: + 41.8 ± 63.3 aU; p < 0.05 vs. baseline), with significantly higher values compared to VE. Liver µHbO₂ and µflow did not change after STS and GL. GL alone did not change colonic or hepatic µHbO₂ or µflow. Mitochondrial oxygen consumption and macrohemodynamic remained unaltered.

Conclusion

The beneficial effect of STS on intestinal and hepatic microcirculatory oxygenation in sepsis seems to be mediated by an increased microcirculatory perfusion and not by mitochondrial respiratory or macrohemodynamic changes. Furthermore, the effect of STS on hepatic but not on intestinal microcirculation seems to be K(ATP)-channel-dependent.

Interplay of cardiovascular mediators, oxidative stress and inflammation in liver disease and its complications

The liver is a crucial metabolic organ that has a key role in maintaining immune and endocrine homeostasis. Accumulating evidence suggests that chronic liver disease might promote the development of various cardiac disorders (such as arrhythmias and cardiomyopathy) and circulatory complications (including systemic, splanchnic and pulmonary complications), which can eventually culminate in clinical conditions ranging from portal and pulmonary hypertension to pulmonary, cardiac and renal failure, ascites and encephalopathy. Liver diseases can affect cardiovascular function during the early stages of disease progression. The development of cardiovascular diseases in patients with chronic liver failure is associated with increased morbidity and mortality, and cardiovascular complications can in turn affect liver function and liver disease progression. Furthermore, numerous infectious, inflammatory, metabolic and genetic diseases, as well as alcohol abuse can also influence both hepatic and cardiovascular outcomes. In this Review, we highlight how chronic liver diseases and associated cardiovascular effects can influence different organ pathologies. Furthermore, we explore the potential roles of inflammation, oxidative stress, vasoactive mediator imbalance, dysregulated endocannabinoid and autonomic nervous systems and endothelial dysfunction in mediating the complex interplay between the liver and the systemic vasculature that results in the development of the extrahepatic complications of chronic liver disease. The roles of ageing, sex, the gut microbiome and organ transplantation in this complex interplay are also discussed.

Serum ammonia levels on admission for predicting sepsis patient mortality at D28 in the emergency department: A 2-center retrospective study

We assessed the predictive value of serum ammonia level on admission for the 28-day mortality of patients with sepsis.We retrospectively included septic patients admitted to the emergency department of West China Hospital, Sichuan University and The Fourth People's Hospital of Zigong city from June 2017 to May 2018. Patients were divided into 2 groups according to 28-day survival. Comparisons of serum ammonia level and sequential organ failure assessment (SOFA) score were made between 2 groups. Multivariate logistic regression models were employed to determine independent risk factors affecting 28-day mortality rate, and receiver operating characteristic (ROC) curve was also used to evaluate the efficacy of risk factors.Total of 316 patients were included into the study, 221 survived to 28 days and 95 were died before 28 days. The 28-day mortality rate was 30.06%. Multivariate logistic regression analyses revealed that the ammonia level, C reactive protein, SOFA score, and the leukocyte were independent risk factors for the 28-day mortality rate. In predicting the 28-day mortality rate, the SOFA score presented an area under the ROC curve (AUC) of 0.815, and the ammonia levels presented the AUC of 0.813.The ammonia level, C reactive protein, SOFA score, and the leukocyte are independent risk factors for 28-day mortality rate in septic patients. Moreover, the serum ammonia and SOFA score have similar predictive values. The serum ammonia level is also a suitable early indicator for prognostic evaluation of patients with sepsis as well.

Increased circulating peroxiredoxin-4 in sepsis model rats involves secretion from hepatocytes and is mitigated by GYY4137

Circulating peroxiredoxin-4 (Prx4) is suggested as a prognosis marker as well as a regulator of many diseases. We aimed to examine 1) whether Prx4 is secreted from the liver in an animal model of sepsis and 2) effects of GYY4137, a hydrogen sulfide donor molecule, on septic liver injury as well as the hepatic secretion of Prx4. Rats (Wistar, male, 6 weeks old) were administered lipopolysaccharide (LPS, 15 mg/kg body weight, i.p.) with or without pre-administration of GYY4137 (50 mg/kg body weight, i.p.) and sacrificed 24 h after LPS administration. Hematoxylin-eosin and Elastica Masson-Goldner stains were used to evaluate hepatic injuries. Cytokine expression levels were determined by qPCR, and the levels of Prx4 in the serum and liver were determined by immunoblotting. Hepatocytes were isolated from rat liver, and the levels of Prx4 in the medium as well as the cells were determined 24 h after the administrations of LPS (1 µg/ml), tumor necrosis factor-α (TNFα, 50 ng/ml), or interleukin-1β (IL-1β, 10 ng/ml), with or without GYY4137 (300 µM). Hepatic inflammation and damage in LPS-administered rats were suppressed by GYY4137. An increase in plasma Prx4 level caused by LPS was observed, but the increase was attenuated by pre-administration of GYY4137. Prx4 was secreted from isolated hepatocytes after stimulation with LPS, TNFα, or IL-1β. GYY4137 attenuated the IL-1β-induced Prx4 secretion from hepatocytes. Secretion from hepatocytes is likely involved in the increase in circulating Prx4 during sepsis. GYY4137 attenuates not only hepatic injury but also Prx4 secretion.

Hydrogen Sulfide as a Novel Regulatory Factor in Liver Health and Disease

Hydrogen sulfide (H₂S), a colorless gas smelling of rotten egg, has long been recognized as a toxic gas and environment pollutant. However, increasing evidence suggests that H₂S acts as a novel gasotransmitter and plays important roles in a variety of physiological and pathological processes in mammals. H₂S is involved in many hepatic functions, including the regulation of oxidative stress, glucose and lipid metabolism, vasculature, mitochondrial function, differentiation, and circadian rhythm. In addition, H₂S contributes to the pathogenesis and treatment of a number of liver diseases, such as hepatic fibrosis, liver cirrhosis, liver cancer, hepatic ischemia/reperfusion injury, nonalcoholic fatty liver disease/nonalcoholic steatohepatitis, hepatotoxicity, and acute liver failure. In this review, the biosynthesis and metabolism of H₂S in the liver are summarized and the role and mechanism of H₂S in liver health and disease are further discussed.

Colonic hydrogen sulfide produces portal hypertension and systemic hypotension in rats

Hydrogen sulfide, a toxic gas, at low concentrations is also a biological mediator in animals. In the colon, hydrogen sulfide is produced by intestinal tissues and gut sulfur bacteria. Gut-derived molecules undergo liver metabolism. Portal hypertension is one of the most common complications contributing to the high mortality in liver cirrhosis. We hypothesized that the colon-derived hydrogen sulfide may affect portal blood pressure. Sprague-Dawley rats were maintained either on tap water (controls) or on water solution of thioacetamide to produce liver cirrhosis (CRH-R). Hemodynamics were measured after administration of either saline or Na₂S, a hydrogen sulfide donor, into (1) the colon, (2) the portal vein, or (3) the femoral vein. Expression of enzymes involved in hydrogen sulfide metabolism was measured by RT-PCR. CRH-R showed a significantly higher portal blood pressure but a lower arterial blood pressure than controls. Saline did not affect hemodynamic parameters. In controls, intracolonic hydrogen sulfide decreased arterial blood pressure and portal blood flow but increased portal blood pressure. Similarly, hydrogen sulfide administered into the portal vein decreased arterial blood pressure but increased portal blood pressure. In contrast, hydrogen sulfide administered into the systemic vein decreased both arterial and portal blood pressures. CRH-R showed significantly greater responses to hydrogen sulfide than controls. CRH-R had a significantly higher liver concentration of hydrogen sulfide but lower expression of rhodanese, an enzyme converting hydrogen sulfide to sulfate. In conclusion, colon-administered hydrogen sulfide increases portal blood pressure while decreasing the systemic arterial blood pressure. The response to hydrogen sulfide is more pronounced in cirrhotic rats which show reduced hydrogen sulfide liver metabolism. Therefore, colon-derived hydrogen sulfide may be involved in the regulation of portal blood pressure, and may contribute to portal hypertension. Impact statement Accumulating evidence suggests that gut-derived molecules affect the control of the circulatory system. Mechanisms controlling liver circulation have been profoundly studied; however, the effects of gut bacteria-derived molecules on portal blood pressure have not been established. In the colon, hydrogen sulfide is produced by intestinal tissues and gut sulfur bacteria. We found that colon-administered hydrogen sulfide increases portal blood pressure while decreasing the systemic arterial blood pressure. The hemodynamic response to hydrogen sulfide was more pronounced in cirrhotic rats which showed reduced hydrogen sulfide liver metabolism, i.e. lower expression of rhodanese, an enzyme converting hydrogen sulfide to sulfate. We propose that colon-derived hydrogen sulfide may affect the regulation of portal and arterial blood pressures and may be involved in portal hypertension.

Correlation between plasma endothelin-1 levels and severity of septic liver failure quantified by maximal liver function capacity (LiMAx test). A prospective study

Aim

To investigate the relationship between the degree of liver dysfunction, quantified by maximal liver function capacity (LiMAx test) and endothelin-1, TNF-α and IL-6 in septic surgical patients.

Methods

28 septic patients (8 female, 20 male, age range 35–80y) were prospectively investigated on a surgical intensive care unit. Liver function, defined by LiMAx test, and measurements of plasma levels of endothelin-1, TNF-α and IL-6 were carried out within the first 24 hours after onset of septic symptoms, followed by day 2, 5 and 10. Patients were divided into 2 groups (group A: LiMAx ≥100 μg/kg/h, moderate liver dysfunction; group B: LiMAx <100 μg/kg/h, severe liver dysfunction) for analysis and investigated regarding the correlation between endothelin-1 and the severity of liver failure, quantified by LiMAx test.

Results

Group B showed significant higher results for endothelin-1 than patients in group A (P = 0.01, d5; 0.02, d10). For TNF-α, group B revealed higher results than group A, with a significant difference on day 10 (P = 0.005). IL-6 showed a non-significant trend to higher results in group B. The Spearman's rank correlation coefficient revealed a significant correlation between LiMAx and endothelin-1 (-0.434; P <0.001), TNF-α (-0.515; P <0.001) and IL-6 (-0.590; P <0.001).

Conclusions

Sepsis-related hepatic dysfunction is associated with elevated plasma levels of endothelin-1, TNF-α and IL-6. Low LiMAx results combined with increased endothelin-1 and TNF-α and a favourable correlation between LiMAx and cytokine values support the findings of a crucial role of Endothelin-1 and TNF-α in development of septic liver failure.

The CBS/CSE system: a potential therapeutic target in NAFLD?

Non-alcoholic fatty liver disease (NAFLD) is a broad spectrum liver disorder diagnosed in patients without a history of alcohol abuse. NAFLD is growing at alarming rates worldwide. Its pathogenesis is complex and incompletely understood. The cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) system regulates homocysteine and cysteine metabolism and contributes to endogenous hydrogen sulfide (H2S) biosynthesis. This review summarizes our current understanding of the hepatic CBS/CSE system, and for the first time, positions this system as a potential therapeutic target in NAFLD. As will be discussed, the CBS/CSE system is highly expressed and active in the liver. Its dysregulation, presenting as alterations in circulating homocysteine and (or) H2S levels, has been reported in NAFLD patients and in NAFLD-associated co-morbidities such as obesity and type 2 diabetes. Intricate links between the CBS/CSE system and a number of metabolic and stress related molecular mediators have also emerged. Various dysfunctions in the hepatic CBS/CSE system have been reported in animal models representative of each NAFLD spectrum. It is anticipated that a newfound appreciation for the hepatic CBS/CSE system will emerge that will improve our understanding of NAFLD pathogenesis, and give rise to new prospective targets for management of this disorder.

Polymorphisms of cystathionine beta-synthase gene are associated with susceptibility to sepsis

Sepsis is the systemic inflammatory host response to infection. Cystathionine beta-synthase (CBS)-dependent homocysteine (Hcy) pathway was demonstrated to affect disease severity and mortality in patients with severe sepsis/septic shock. Independent studies identified a single-nucleotide polymorphism (SNP, rs6586282, hg19 chr21:g.44478497C>T) in intron 14 of the CBS-coding gene (CBS) associated with Hcy plasma levels. We aimed to describe the association of this SNP and variants of a splice donor-affecting variable-number tandem repeat (VNTR, NG_008938.1:g.22763_22793[16_22]) 243 bp downstream of rs6586282 with severe human sepsis. We analyzed the VNTR structure and genotyped variants of rs6586282 and a neighboring SNP (rs34758144, hg19 chr21:g.44478582G>A) in two case-control studies including patients with severe sepsis/septic shock from Germany (n=168) and Greece (n=237). In both studies, we consistently observed an association of CBS VNTR alleles with sepsis susceptibility. Risk linearly increased with number of tandem repeats (per allele odds ratio in the adjusted analysis 1.34; 95% confidence interval (CI)=1.17-1.55; P<0.001). Association had also been shown for rs34758144 whose risk allele is in linkage disequilibrium with one long VNTR allele (19 repeat). In contrast, we observed no evidence for an effect on 28-day survival in patients with severe sepsis/septic shock (per allele hazard ratio in the adjusted analysis for VNTR 1.10; 95% CI=0.95-1.28; P=0.20). In a minigene approach, we demonstrated alternative splicing in distinct VNTR alleles, which, however, was independent of the number of tandem units. In conclusion, there is no ordinary conjunction between human CBS and severe sepsis/septic shock, but CBS genotypes are involved in disease susceptibility.

Advances in sepsis-associated liver dysfunction

Recent studies have revealed liver dysfunction as an early event in sepsis. Sepsis-associated liver dysfunction is mainly resulted from systemic or microcirculatory disturbances, spillovers of bacteria and endotoxin (lipopolysaccharide, LPS), and subsequent activation of inflammatory cytokines as well as mediators. Three main cell types of the liver which contribute to the hepatic response in sepsis are Kupffer cells (KCs), hepatocytes and liver sinusoidal endothelial cells (LSECs). In addition, activated neutrophils, which are also recruited to the liver and produce potentially destructive enzymes and oxygen-free radicals, may further enhance acute liver injury. The clinical manifestations of sepsis-associated liver dysfunction can roughly be divided into two categories: Hypoxic hepatitis and jaundice. The latter is much more frequent in the context of sepsis. Hepatic failure is traditionally considered as a late manifestation of sepsis-induced multiple organ dysfunction syndrome. To date, no specific therapeutics for sepsis-associated liver dysfunction are available. Treatment measure is mainly focused on eradication of the underlying infection and management for severe sepsis. A better understanding of the pathophysiology of liver response in sepsis may lead to further increase in survival rates.

The liver in sepsis: patterns of response and injury

PURPOSE OF REVIEW

Sepsis elicits profound changes in the concentrations of plasma proteins synthesized by liver parenchymal cells referred to as acute-phase proteins. Mechanisms controlling this orchestrated response include release of cytokines that induce acute-phase proteins, while other 'house-keeping' genes are downregulated.

RECENT FINDINGS

Although some acute-phase proteins help to control damage, functions of many other acute-phase reactants remain obscure. Changes in acute-phase gene expression are primarily subject to transcriptional regulation and can be comprehensively monitored by array techniques. Emerging evidence from such strategies implies that in addition to a 'common host response' also highly specific pathways are induced in specific disease contexts. Applying a systems biology approach to the integrated response of the hepatocyte to infection would suggest that the reprogramming of metabolic functions occurs in parallel with a severity-dependent disruption of phase I and II biotransformation and canalicular transport, that is, excretory failure. Although traditionally bilirubin serves to monitor excretion, emerging evidence suggests that bile acids indicate liver dysfunction with higher sensitivity and specificity.

SUMMARY

Sepsis induces reprogramming of the hepatic transcriptome. This includes induction of adaptive acute-phase proteins but also repression of phase I, II metabolism and transport with important implications for monitoring and pharmacotherapy.

Hydrogen sulfide modulates sinusoidal constriction and contributes to hepatic microcirculatory dysfunction during endotoxemia

Hydrogen sulfide (H₂S) affects vascular resistance; however, its effect on the hepatic microcirculation has not been investigated. Hepatic sinusoidal perfusion is dysregulated during sepsis, contributing to liver injury. Therefore, the present study determined the effect of H₂S on the hepatic microcirculation and the contribution of endogenous H₂S to hepatic microcirculatory dysfunction in an endotoxin model of sepsis. Portal infusion of H₂S increased portal pressure in vivo (6.8 ± 0.2 mmHg before H₂S vs. 8.6 ± 0.8 mmHg peak during H₂S infusion, P < 0.05). Using intravital microscopy, we observed decreased sinusoidal diameter (6.2 ± 0.27 μm before H₂S vs. 5.7 ± 0.3 μm after H₂S, P < 0.05) and increased sinusoidal heterogeneity during H₂S infusion (P < 0.05) and net constriction. Since hepatic H₂S levels are elevated during sepsis, we used the cystathionine γ lyase inhibitor DL-propargylglycine (PAG) to determine the contribution of H₂S to the hypersensitization of the sinusoid to the vasoconstrictor effect of endothelin-1 (ET-1). PAG treatment significantly attenuated the sinusoidal sensitization to ET-1 in endotoxin-treated animals. ET-1 infusion increased portal pressure to 175% of baseline in endotoxemic animals, which was reduced to 143% following PAG treatment (P < 0.05). PAG abrogated the increase in sinusoidal constriction after ET-1 infusion in LPS-treated rats (30.9% reduction in LPS rats vs. 11.6% in PAG/LPS rats, P < 0.05). Moreover, PAG treatment significantly attenuated the increase in NADH fluorescence following ET-1 exposure during endotoxemia (61 grayscale units LPS vs. 21 units in PAG/LPS, P < 0.05), suggesting an improvement in hepatic oxygen availability. This study is the first to demonstrate a vasoconstrictor action of H₂S on the hepatic sinusoid and provides a possible mechanism for the protective effect of PAG treatment during sepsis.