Of mice and men (and sheep, swine etc.): the intriguing hemodynamic and metabolic effects of hydrogen sulfide (H2S)

Progress and perspective on hydrogen sulfide donors and their biomedical applications

Following the discovery of nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H₂ S) has been identified as the third gasotransmitter in humans. Increasing evidence have shown that H₂ S is of preventive or therapeutic effects on diverse pathological complications. As a consequence, it is of great significance to develop suitable approaches of H₂ S-based therapeutics for biomedical applications. H₂ S-releasing agents (H₂ S donors) play important roles in exploring and understanding the physiological functions of H₂ S. More importantly, accumulating studies have validated the theranostic potential of H₂ S donors in extensive repertoires of in vitro and in vivo disease models. Thus, it is imperative to summarize and update the literatures in this field. In this review, first, the background of H₂ S on its chemical and biological aspects is concisely introduced. Second, the studies regarding the H₂ S-releasing compounds are categorized and described, and accordingly, their H₂ S-donating mechanisms, biological applications, and therapeutic values are also comprehensively delineated and discussed. Necessary comparisons between related H₂ S donors are presented, and the drawbacks of many typical H₂ S donors are analyzed and revealed. Finally, several critical challenges encountered in the development of multifunctional H₂ S donors are discussed, and the direction of their future development as well as their biomedical applications is proposed. We expect that this review will reach extensive audiences across multiple disciplines and promote the innovation of H₂ S biomedicine.

Recent Development of Hydrogen Sulfide Releasing/Stimulating Reagents and Their Potential Applications in Cancer and Glycometabolic Disorders

As an important endogenous gaseous signaling molecule, hydrogen sulfide (H₂S) exerts various effects in the body. A variety of pathological changes, such as cancer, glycometabolic disorders, and diabetes, are associated with altered endogenous levels of H₂S, especially decreased. Therefore, the supplement of H₂S is of great significance for the treatment of diseases containing the above pathological changes. At present, many efforts have been made to increase the in vivo levels of H₂S by administration of gaseous H₂S, simple inorganic sulfide salts, sophisticated synthetic slow-releasing controllable H₂S donors or materials, and using H₂S stimulating agents. In this article, we reviewed the recent development of H₂S releasing/stimulating reagents and their potential applications in two common pathological processes including cancer and glycometabolic disorders.

Hydrogen sulfide (H2S) releasing agents: chemistry and biological applications

Hydrogen sulfide (H2S) is a newly recognized signaling molecule with very potent cytoprotective actions. The fields of H2S physiology and pharmacology have been rapidly growing in recent years, but a number of fundamental issues must be addressed to advance our understanding of the biology and clinical potential of H2S in the future. Hydrogen sulfide releasing agents (also known as H2S donors) have been widely used in these fields. These compounds are not only useful research tools, but also potential therapeutic agents. It is therefore important to study the chemistry and pharmacology of exogenous H2S and to be aware of the limitations associated with the choice of donors used to generate H2S in vitro and in vivo. In this review we summarized the developments and limitations of currently available donors including H2S gas, sulfide salts, garlic-derived sulfur compounds, Lawesson's reagent/analogs, 1,2-dithiole-3-thiones, thiol-activated donors, photo-caged donors, and thioamino acids. Some biological applications of these donors were also discussed.

Inhalation exposure model of hydrogen sulfide (H₂S)-induced hypometabolism in the male Sprague-Dawley rat

Hydrogen sulfide (H2S) has been accepted as a physiologically relevant cell-signaling molecule with both toxic and beneficial effects depending on its concentration in mammalian tissues. Notably, exposure to H2S in breathable air has been shown to decrease aerobic metabolism and induce a reversible hypometabolic-like state in laboratory rodent models. Herein, we describe an experimental exposure setup that can be used to define the reversible cardiovascular and metabolic physiology of rodents (rats) during H2S-induced hypometabolism and following recovery.

Regulation of cellular gas exchange, oxygen sensing, and metabolic control

Cells must continuously monitor and couple their metabolic requirements for ATP utilization with their ability to take up O2 for mitochondrial respiration. When O2 uptake and delivery move out of homeostasis, cells have elaborate and diverse sensing and response systems to compensate. In this review, we explore the biophysics of O2 and gas diffusion in the cell, how intracellular O2 is regulated, how intracellular O2 levels are sensed and how sensing systems impact mitochondrial respiration and shifts in metabolic pathways. Particular attention is paid to how O2 affects the redox state of the cell, as well as the NO, H2S, and CO concentrations. We also explore how these agents can affect various aspects of gas exchange and activate acute signaling pathways that promote survival. Two kinds of challenges to gas exchange are also discussed in detail: when insufficient O2 is available for respiration (hypoxia) and when metabolic requirements test the limits of gas exchange (exercising skeletal muscle). This review also focuses on responses to acute hypoxia in the context of the original "unifying theory of hypoxia tolerance" as expressed by Hochachka and colleagues. It includes discourse on the regulation of mitochondrial electron transport, metabolic suppression, shifts in metabolic pathways, and recruitment of cell survival pathways preventing collapse of membrane potential and nuclear apoptosis. Regarding exercise, the issues discussed relate to the O2 sensitivity of metabolic rate, O2 kinetics in exercise, and influences of available O2 on glycolysis and lactate production.

Compared effects of inhibition and exogenous administration of hydrogen sulphide in ischaemia-reperfusion injury

Introduction

Haemorrhagic shock is associated with an inflammatory response consecutive to ischaemia-reperfusion (I/R) that leads to cardiovascular failure and organ injury. The role of and the timing of administration of hydrogen sulphide (H₂S) remain uncertain. Vascular effects of H₂S are mainly mediated through K⁺_ATP-channel activation. Herein, we compared the effects of D,L-propargylglycine (PAG), an inhibitor of H₂S production, as well as sodium hydrosulphide (NaHS), an H₂S donor, on haemodynamics, vascular reactivity and cellular pathways in a rat model of I/R. We also compared the haemodynamic effects of NaHS administered before and 10 minutes after reperfusion.

Methods

Mechanically ventilated and instrumented rats were bled during 60 minutes in order to maintain mean arterial pressure at 40 ± 2 mmHg. Ten minutes prior to retransfusion, rats randomly received either an intravenous bolus of NaHS (0.2 mg/kg) or vehicle (0.9% NaCl) or PAG (50 mg/kg). PNU, a pore-forming receptor inhibitor of K⁺_ATP channels, was used to assess the role of K⁺_ATP channels.

Results

Shock and I/R induced a decrease in mean arterial pressure, lactic acidosis and ex vivo vascular hyporeactivity, which were attenuated by NaHS administered before reperfusion and PNU but not by PAG and NaHS administered 10 minutes after reperfusion. NaHS also prevented aortic inducible nitric oxide synthase expression and nitric oxide production while increasing Akt and endothelial nitric oxide synthase phosphorylation. NaHS reduced JNK activity and p-P38/P38 activation, suggesting a decrease in endothelial cell activation without variation in ERK phosphorylation. PNU + NaHS increased mean arterial pressure when compared with NaHS or PNU alone, suggesting a dual effect of NaHS on vascular reactivity.

Conclusion

NaHS when given before reperfusion protects against the effects of haemorrhage-induced I/R by acting primarily through a decrease in both proinflammatory cytokines and inducible nitric oxide synthase expression and an upregulation of the Akt/endothelial nitric oxide synthase pathway.

Keywords: hydrogen sulphide, inflammation mediators, therapeutic use, shock, hemorrhagic/drug therapy, haemodynamics/drug effects