The Impact of H2S on Obesity-Associated Metabolic Disturbances

Natural H2S-donors: A new pharmacological opportunity for the management of overweight and obesity

The prevalence of overweight and obesity has progressively increased in the last few years, becoming a real threat to healthcare systems. To date, the clinical management of body weight gain is an unmet medical need, as there are few approved anti-obesity drugs and most require an extensive monitoring and vigilance due to risk of adverse effects and poor patient adherence/persistence. Growing evidence has shown that the gasotransmitter hydrogen sulfide (H2S) and, therefore, H2S-donors could have a central role in the prevention and treatment of overweight/obesity. The main natural sources of H2S-donors are plants from the Alliaceae (garlic and onion), Brassicaceae (e.g., broccoli, cabbage, and wasabi), and Moringaceae botanical families. In particular, polysulfides and isothiocyanates, which slowly release H2S, derive from the hydrolysis of alliin from Alliaceae and glucosinolates from Brassicaceae/Moringaceae, respectively. In this review, we describe the emerging role of endogenous H2S in regulating adipose tissue function and the potential efficacy of natural H2S-donors in animal models of overweight/obesity, with a final focus on the preliminary results from clinical trials. We conclude that organosulfur-containing plants and their extracts could be used before or in combination with conventional anti-obesity agents to improve treatment efficacy and reduce inflammation in obesogenic conditions. However, further high-quality studies are needed to firmly establish their clinical efficacy.

[Diet as a source of hydrogen sulfide and its effects on health and disease]

Introduction

Initially known for its deleterious health effects, hydrogen sulfide (H2S) has recently been recognized as a biologically important gas carrier, like nitric oxide and carbon monoxide. H2S is produced endogenously in mammalian cells by enzymatic and non-enzymatic pathways. When it is produced by the enzymatic pathway, its synthesis is carried out from the amino acid L-cysteine through the transsulfuration pathway. It can also be produced endogenously from exogenous compounds that function as H2S donors as, for example, the naturally occurring organic donors found in some plants. Currently, the role of S2H is well known as brain and cardiac protector, and its research as a therapeutic adjuvant in metabolic diseases such as obesity and type-2 diabetes is becoming increasingly important. The objective of this review is to examine how the contribution of donors and precursors of hydrogen sulfide by the diet impacts health and disease.

Mediterranean diet and olive oil, microbiota, and obesity-related cancers. From mechanisms to prevention

Olive oil (OO) is the main source of added fat in the Mediterranean diet (MD). It is a mix of bioactive compounds, including monounsaturated fatty acids, phytosterols, simple phenols, secoiridoids, flavonoids, and terpenoids. There is a growing body of evidence that MD and OO improve obesity-related factors. In addition, obesity has been associated with an increased risk for several cancers: endometrial, oesophageal adenocarcinoma, renal, pancreatic, hepatocellular, gastric cardia, meningioma, multiple myeloma, colorectal, postmenopausal breast, ovarian, gallbladder, and thyroid cancer. However, the epidemiological evidence linking MD and OO with these obesity-related cancers, and their potential mechanisms of action, especially those involving the gut microbiota, are not clearly described or understood. The goals of this review are 1) to update the current epidemiological knowledge on the associations between MD and OO consumption and obesity-related cancers, 2) to identify the gut microbiota mechanisms involved in obesity-related cancers, and 3) to report the effects of MD and OO on these mechanisms.

The Impact of Drugs on Hydrogen Sulfide Homeostasis in Mammals

Mammalian cells and tissues have the capacity to generate hydrogen sulfide gas (H₂S) via catabolic routes involving cysteine metabolism. H₂S acts on cell signaling cascades that are necessary in many biochemical and physiological roles important in the heart, brain, liver, kidney, urogenital tract, and cardiovascular and immune systems of mammals. Diminished levels of this molecule are observed in several pathophysiological conditions including heart disease, diabetes, obesity, and immune function. Interestingly, in the last two decades, it has become apparent that some commonly prescribed pharmacological drugs can impact the expression and activities of enzymes responsible for hydrogen sulfide production in cells and tissues. Therefore, the current review provides an overview of the studies that catalogue key drugs and their impact on hydrogen sulfide production in mammals.

Yohimbine Alleviates Oxidative Stress and Suppresses Aerobic Cysteine Metabolism Elevated in the Rat Liver of High-Fat Diet-Fed Rats

Yohimbine is a small indole alkaloid derived from the bark of the yohimbe tree with documented biological activity, including anti-inflammatory, erectile dysfunction relieving, and fat-burning properties. Hydrogen sulfide (H₂S) and sulfane sulfur-containing compounds are regarded as important molecules in redox regulation and are involved in many physiological processes. Recently, their role in the pathophysiology of obesity and obesity-induced liver injury was also reported. The aim of the present study was to verify whether the mechanism of biological activity of yohimbine is related to reactive sulfur species formed during cysteine catabolism. We tested the effect of yohimbine at doses of 2 and 5 mg/kg/day administered for 30 days on aerobic and anaerobic catabolism of cysteine and oxidative processes in the liver of high-fat diet (HFD)-induced obese rats. Our study revealed that HFD resulted in a decrease in cysteine and sulfane sulfur levels in the liver, while sulfates were elevated. In the liver of obese rats, rhodanese expression was diminished while lipid peroxidation increased. Yohimbine did not influence sulfane sulfur and thiol levels in the liver of obese rats, however, this alkaloid at a dose of 5 mg decreased sulfates to the control level and induced expression of rhodanese. Moreover, it diminished hepatic lipid peroxidation. It can be concluded that HFD attenuates anaerobic and enhances aerobic cysteine catabolism and induces lipid peroxidation in the rat liver. Yohimbine at a dose of 5 mg/kg can alleviate oxidative stress and reduce elevated concentrations of sulfate probably by the induction of TST expression.

Bempedoic Acid Restores Liver H2S Production in a Female Sprague-Dawley Rat Dietary Model of Non-Alcoholic Fatty Liver

We previously demonstrated that treatment with BemA (bempedoic acid), an inhibitor of ATP citrate lyase, significantly reduces fatty liver in a model of liver steatosis (HFHFr-female Sprague-Dawley rat fed a high-fat high-fructose diet). Since the hepatic production of the gasotransmitter H₂S is impaired in liver disorders, we were interested in determining if the production of H₂S was altered in our HFHFr model and whether the administration of BemA reversed these changes. We used stored liver samples from a previous study to determine the total and enzymatic H₂S production, as well as the expression of CBS (cystathionine β-synthase), CSE (cystathionine γ-lyase), and 3MST (3-mercaptopiruvate sulfurtransferase), and the expression/activity of FXR (farnesoid X receptor), a transcription factor involved in regulating CSE expression. Our data show that the HFHFr diet reduces the total and enzymatic production of liver H₂S, mainly by decreasing the expression of CBS and CSE. Furthermore, BemA treatment restored H₂S production, increasing the expression of CBS and CSE, providing evidence for the involvement of FXR transcriptional activity and the mTORC1 (mammalian target of rapamycin1)/S6K1 (ribosomal protein S6 kinase beta-1)/PGC1α (peroxisome proliferator receptor gamma coactivator1α) pathway.

Function of gaseous hydrogen sulfide in liver fibrosis

Over the past few years, hydrogen sulfide (H₂S) has been shown to exert several biological functions in mammalian. The endogenous production of H₂S is mainly mediated by cystathione β-synthase, cystathione γ-lyase and 3-mercaptopyruvate sulfur transferase. These enzymes are broadly expressed in liver tissue and regulates liver function by working on a variety of molecular targets. As an important regulator of liver function, H₂S is critically involved in the pathogenesis of various liver diseases, such as non-alcoholic steatohepatitis and liver cancer. Targeting H₂S-generating enzymes may be a therapeutic strategy for controlling liver diseases. This review described the function of H₂S in liver disease and summarized recent characterized role of H₂S in several cellular process of the liver.

Reactive sulfur species and their significance in health and disease

Reactive sulfur species (RSS) have been recognized in the last two decades as very important molecules in redox regulation. They are involved in metabolic processes and, in this way, they are responsible for maintenance of health. This review summarizes current information about the essential biological RSS, including H₂S, low molecular weight persulfides, protein persulfides as well as organic and inorganic polysulfides, their synthesis, catabolism and chemical reactivity. Moreover, the role of RSS disturbances in various pathologies including vascular diseases, chronic kidney diseases, diabetes mellitus Type 2, neurological diseases, obesity, chronic obstructive pulmonary disease and in the most current problem of COVID-19 is presented. The significance of RSS in aging is also mentioned. Finally, the possibilities of using the precursors of various forms of RSS for therapeutic purposes are discussed.

Recent Advances in Molecular Research on Hydrogen Sulfide (H2S) Role in Diabetes Mellitus (DM)-A Systematic Review

Abundant experimental data suggest that hydrogen sulfide (H₂S) is related to the pathophysiology of Diabetes Mellitus (DM). Multiple molecular mechanisms, including receptors, membrane ion channels, signalingmolecules, enzymes, and transcription factors, are known to be responsible for the H₂S biological actions; however, H₂S is not fully documented as a gaseous signaling molecule interfering with DM and vascular-linked pathology. In recent decades, multiple approaches regarding therapeutic exploitation of H₂S have been identified, either based on H₂S exogenous apport or on its modulated endogenous biosynthesis. This paper aims to synthesize and systematize, as comprehensively as possible, the recent literature-related data regarding the therapeutic/rehabilitative role of H₂S in DM. This review was conducted following the “Preferred reporting items for systematic reviews and meta-analyses” (PRISMA) methodology, interrogating five international medically renowned databases by specific keyword combinations/“syntaxes” used contextually, over the last five years (2017–2021). The respective search/filtered and selection methodology we applied has identified, in the first step, 212 articles. After deploying the next specific quest steps, 51 unique published papers qualified for minute analysis resulted. To these bibliographic resources obtained through the PRISMA methodology, in order to have the best available information coverage, we added 86 papers that were freely found by a direct internet search. Finally, we selected for a connected meta-analysis eight relevant reports that included 1237 human subjects elicited from clinical trial registration platforms. Numerous H₂S releasing/stimulating compounds have been produced, some being used in experimental models. However, very few of them were further advanced in clinical studies, indicating that the development of H₂S as a therapeutic agent is still at the beginning.

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.

Reduced Levels of H2S in Diabetes-Associated Osteoarthritis Are Linked to Hyperglycaemia, Nrf-2/HO-1 Signalling Downregulation and Chondrocyte Dysfunction

Different findings indicate that type 2 diabetes is an independent risk factor for osteoarthritis (OA). However, the mechanisms underlying the connection between both diseases remain unclear. Changes in the balance of hydrogen sulphide (H2S) are thought to play an important role in the pathogenesis of diabetes and its complications, although its role is still controversial. In this study, we examined the modulation of H2S levels in serum and chondrocytes from OA diabetic (DB) and non-diabetic (non-DB) patients and in cells under glucose stress, in order to elucidate whether impairment in H2S-mediated signalling could participate in the onset of DB-related OA. Here, we identified a reduction in H2S synthesis in the cartilage from OA-DB patients and in cells under glucose stress, which is associated with hyperglycaemia-mediated dysregulation of chondrocyte metabolism. In addition, our results indicate that H2S is an inductor of the Nrf-2/HO-1 signalling pathway in cartilage, but is also a downstream target of Nrf-2 transcriptional activity. Thereby, impairment of the H2S/Nrf-2 axis under glucose stress or DB triggers chondrocyte catabolic responses, favouring the disruption of cartilage homeostasis that characterizes OA pathology. Finally, our findings highlight the benefits of the use of exogeneous sources of H2S in the treatment of DB-OA patients, and warrant future clinical studies.

Cell-Trappable BODIPY-NBD Dyad for Imaging of Basal and Stress-Induced H2S in Live Biosystems

H₂S is a gaseous signaling molecule that is involved in many physiological and pathological processes. In general, the level of intracellular H₂S (<1 μM) is much lower than that of GSH (∼1-10 mM), leading to the remaining challenge of selective detection and differentiation of endogenous H₂S in live biosystems. To this end, we quantitatively demonstrate that the thiolysis of NBD amine has much higher selectivity for H₂S over GSH than that of the reduction of aryl azide. Subsequently, we developed the first NBD-based cell-trappable probe 1 (AM-BODIPY-NBD) for highly selective and ultrasensitive imaging of intracellular H₂S. Probe 1 demonstrates a 207-fold fluorescence enhancement at 520 nm after reaction with H₂S/esterase to produce a bright BODIPY (quantum yield 0.42) and a detection limit of 15.7 nM. Probe 1 is water-soluble, cell-trappable, and not cytotoxic. Based on this excellent chemical tool, relative levels of basal H₂S in different cell lines were measured to reveal a positive correlation between endogenous H₂S and the metastatic potential of colon and breast cancer cells. In addition, H₂S biogenesis in vivo was also validated by probe 1 both in tobacco leaves under viral infection and in zebrafish after tail amputation. It is anticipated that probe 1 will have widespread applications in imaging and for investigating different H₂S-related biological processes and diseases.