Hydrogen Sulfide in Exhaled Gases From Ventilated Septic Neonates and Children: A Preliminary Report

Hydrogen Sulfide: A Versatile Molecule and Therapeutic Target in Health and Diseases

In recent years, research has unveiled the significant role of hydrogen sulfide (H2S) in many physiological and pathological processes. The role of endogenous H2S, H2S donors, and inhibitors has been the subject of studies that have aimed to investigate this intriguing molecule. The mechanisms by which H2S contributes to different diseases, including inflammatory conditions, cardiovascular disease, viral infections, and neurological disorders, are complex. Despite noteworthy progress, several questions remain unanswered. H2S donors and inhibitors have shown significant therapeutic potential for various diseases. This review summarizes our current understanding of H2S-based therapeutics in inflammatory conditions, cardiovascular diseases, viral infections, and neurological disorders.

Exhaled Biomarkers for Point-of-Care Diagnosis: Recent Advances and New Challenges in Breathomics

Cancers, chronic diseases and respiratory infections are major causes of mortality and present diagnostic and therapeutic challenges for health care. There is an unmet medical need for non-invasive, easy-to-use biomarkers for the early diagnosis, phenotyping, predicting and monitoring of the therapeutic responses of these disorders. Exhaled breath sampling is an attractive choice that has gained attention in recent years. Exhaled nitric oxide measurement used as a predictive biomarker of the response to anti-eosinophil therapy in severe asthma has paved the way for other exhaled breath biomarkers. Advances in laser and nanosensor technologies and spectrometry together with widespread use of algorithms and artificial intelligence have facilitated research on volatile organic compounds and artificial olfaction systems to develop new exhaled biomarkers. We aim to provide an overview of the recent advances in and challenges of exhaled biomarker measurements with an emphasis on the applicability of their measurement as a non-invasive, point-of-care diagnostic and monitoring tool.

Hydrogen Sulfide and Substance P Levels in Patients with Escherichia coli and Klebsiella pneumoniae Bacteraemia

Hydrogen sulfide (H2S) and substance P (SP) are known from animal models and in vitro studies as proinflammatory mediators. In this study, peripheral blood concentrations of H2S and SP were measured in patients with Escherichia coli or Klebsiella pneumoniae bacteraemia. Fifty patients were recruited from general wards at Christchurch Hospital, during 2020-2021. Samples from age- and sex-matched healthy subjects previously recruited as controls for studies of cardiovascular disease were used as controls. The concentrations of H2S were higher than controls on day 0, day 1, and day 2, and SP was higher than controls on all 4 days. The concentrations of H2S were highest on day 0, whereas SP concentrations were higher on day 2 than other days. Interleukin-6 and C-reactive protein were significantly higher on day 0 and day 1, respectively. The concentrations of H2S and SP did not differ between 15 non-septic (SIRS 0-1) and the 35 septic subjects (SIRS ≥ 2). Substance P concentrations were higher in subjects with abdominal infection than urinary tract infections on day 0 (p = 0.0002) and day 1 (p = 0.0091). In conclusion, the peak H2S concentrations precede the SP peak in patients with Gram-negative bacteraemia, but this response varies with the site of infection.

Au@Ag Nanorods-PDMS Wearable Mouthguard as a Visualized Detection Platform for Screening Dental Caries and Periodontal Diseases

The development of easy-to-use, low-cost, and visualized detection platforms for screening human dental caries and periodontal diseases is in urgent demand. In this work, a Au@Ag nanorods-poly(dimethylsiloxane) (Au@Ag NRs-PDMS) wearable mouthguard, which can visualize the tooth lesion sites through the color change of it at the corresponding locations, is presented. The Au@Ag NRs-PDMS composite exhibits a distinct color response to hydrogen sulfide (H₂ S) gas generated by bacterial decay at the lesion sites. Moreover, the Au@Ag NRs-PDMS mouthguard is demonstrated to own desired mechanical properties, excellent chemical stability, as well as good biocompatibility, and can accurately locate the lesion sites in human oral cavity. These findings suggest that the mouthguard has the potential to be utilized on a large scale to help people self-monitor their oral health in daily life, and treat oral diseases locally.

Emerging roles of cystathionine β-synthase in various forms of cancer

The expression of the reverse transsulfuration enzyme cystathionine-β-synthase (CBS) is markedly increased in many forms of cancer, including colorectal, ovarian, lung, breast and kidney, while in other cancers (liver cancer and glioma) it becomes downregulated. According to the clinical database data in high-CBS-expressor cancers (e.g. colon or ovarian cancer), high CBS expression typically predicts lower survival, while in the low-CBS-expressor cancers (e.g. liver cancer), low CBS expression is associated with lower survival. In the high-CBS expressing tumor cells, CBS, and its product hydrogen sulfide (H₂S) serves as a bioenergetic, proliferative, cytoprotective and stemness factor; it also supports angiogenesis and epithelial-to-mesenchymal transition in the cancer microenvironment. The current article reviews the various tumor-cell-supporting roles of the CBS/H₂S axis in high-CBS expressor cancers and overviews the anticancer effects of CBS silencing and pharmacological CBS inhibition in various cancer models in vitro and in vivo; it also outlines potential approaches for biomarker identification, to support future targeted cancer therapies based on pharmacological CBS inhibition.

Gases in Sepsis: Novel Mediators and Therapeutic Targets

Sepsis, a potentially lethal condition resulting from failure to control the initial infection, is associated with a dysregulated host defense response to pathogens and their toxins. Sepsis remains a leading cause of morbidity, mortality and disability worldwide. The pathophysiology of sepsis is very complicated and is not yet fully understood. Worse still, the development of effective therapeutic agents is still an unmet need and a great challenge. Gases, including nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S), are small-molecule biological mediators that are endogenously produced, mainly by enzyme-catalyzed reactions. Accumulating evidence suggests that these gaseous mediators are widely involved in the pathophysiology of sepsis. Many sepsis-associated alterations, such as the elimination of invasive pathogens, the resolution of disorganized inflammation and the preservation of the function of multiple organs and systems, are shaped by them. Increasing attention has been paid to developing therapeutic approaches targeting these molecules for sepsis/septic shock, taking advantage of the multiple actions played by NO, CO and H2S. Several preliminary studies have identified promising therapeutic strategies for gaseous-mediator-based treatments for sepsis. In this review article, we summarize the state-of-the-art knowledge on the pathophysiology of sepsis; the metabolism and physiological function of NO, CO and H2S; the crosstalk among these gaseous mediators; and their crucial effects on the development and progression of sepsis. In addition, we also briefly discuss the prospect of developing therapeutic interventions targeting these gaseous mediators for sepsis.

Hydrogen Sulfide and the Immune System

Hydrogen sulfide (H₂S) is the "third gasotransmitter" recognized alongside nitric oxide (NO) and carbon monoxide (CO). H₂S exhibits an array of biological effects in mammalian cells as revealed by studies showing important roles in the cardiovascular system, in cell signalling processes, post-translational modifications and in the immune system. Regarding the latter, using pharmacological and genetic approaches scientists have shown this molecule to have both pro- and anti-inflammatory effects in mammalian systems. The anti-inflammatory effects of H₂S appeared to be due to its inhibitory action on the nuclear factor kappa beta signalling pathway; NF-kB representing a transcription factor involved in the regulation pro-inflammatory mediators like nitric oxide, prostaglandins, and cytokines. In contrast, results from several animal model describe a more complicated picture and report on pro-inflammatory effects linked to exposure to this molecule; linked to dosage used and point of administration of this molecule. Overall, roles for H₂S in several inflammatory diseases spanning arthritis, atherosclerosis, sepsis, and asthma have been described by researchers. In light this work fascinating research, this chapter will cover H₂S biology and its many roles in the immune system.

Use of Nasal Pathology in the Derivation of Inhalation Toxicity Values for Hydrogen Sulfide

Nasal pathology can play an important role in the risk assessment process. For example, olfactory neuron loss (ONL) is one of the most sensitive end points seen in subchronic rodent hydrogen sulfide (H₂S) studies and has been used by several agencies to derive health-protective toxicity values. Alternative methods that rely on computational fluid dynamics (CFD) models to account for the influence of airflow on H₂S-induced ONL have been proposed. The use of CFD models result in toxicity values that are less conservative than those obtained using more traditional methods. These alternative approaches rely on anatomy-based CFD models. Model predictions of H₂S delivery (flux) to the olfactory mucosal wall are highly correlated with ONL in rodents. Three major areas of focus for this review include a brief description of nasal anatomy, H₂S-induced ONL in rodents, derivation of a chronic inhalation reference concentration for H₂S, and the use of CFD models to derive alternative toxicity values for this gas.

High-Dose Vitamin B12 in Vasodilatory Shock: A Narrative Review

Vasodilatory shock, as observed in postoperative states and sepsis, is hallmarked by low systemic vascular resistance and low blood pressure compensated by increased cardiac output. Gasotransmitters, such as nitric oxide and hydrogen sulfide, are implicated in the development and perpetuation of vasodilatory shock. Established therapies do not target these physiologic drivers of vasodilation. Due to their nontoxic and pleotropic effects, micronutrients are being used as rescue therapy in postoperative vasoplegia and septic shock. Here, we outline the pathophysiology of vasodilatory shock, describe the rationale for vitamin B12 (hydroxocobalamin) in vasodilatory shock, and identify literature evaluating its use in vasoplegic states.

H2S attenuates sepsis-induced cardiac dysfunction via a PI3K/Akt-dependent mechanism

The heart is the most vulnerable target organ in sepsis, and it has been previously reported that hydrogen sulfide (H₂S) has a protective role in heart dysfunction caused by sepsis. Additionally, studies have demonstrated that the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signaling pathway has a protective function during sepsis. However, the potential association between H₂S and PI3K/Akt in sepsis-induced cardiac dysfunction is unclear. Therefore, the PI3K inhibitor LY294002 was used to investigate the role of PI3K/Akt signaling in the protective effects of H₂S during sepsis-induced myocardial injury. A rat sepsis model was established using cecal ligation and puncture (CLP) surgery. Sodium hydrosulfide, a H₂S donor, was administered intraperitoneally (8.9 µmol/kg), and serum myocardial enzyme levels, inflammatory cytokine levels, cardiac histology and cardiomyocyte apoptosis were assessed to determine the extent of myocardial damage. The results demonstrated that exogenous H₂S reduced serum myocardial enzyme levels, decreased the levels of the inflammatory factors tumor necrosis factor (TNF)-α and interleukin (IL)-6, and increased the level of anti-inflammatory IL-10 following CLP. Staining of histological sections demonstrated that myocardial damage and cardiomyocyte apoptosis were alleviated by the administration of exogenous H₂S. Western blot analysis was used to detect phosphorylated and total PI3K and Akt levels, as well as NF-κB, B-cell lymphoma-2, Bcl-2-associated X protein (Bax) and caspase levels, and the results demonstrated that H₂S significantly increased PI3K and Akt phosphorylation. This indicated that the PI3K/Akt signaling pathway was activated by H₂S. Additionally, H₂S reduced Bax and caspase expression, indicating that apoptosis was inhibited, and decreased NF-κB levels, indicating that inflammation was reduced. Furthermore, the PI3K inhibitor LY294002 eliminated the protective effects of H₂S. In conclusion, the results of the current study suggest that exogenous H₂S activates PI3K/Akt signaling to attenuate myocardial damage in sepsis.

Inflammasomes: Pandora's box for sepsis

Sepsis was known to ancient Greeks since the time of great physician Hippocrates (460-377 BC) without exact information regarding its pathogenesis. With time and medical advances, it is now considered as a condition associated with organ dysfunction occurring in the presence of systemic infection as a result of dysregulation of the immune response. Still with this advancement, we are struggling for the development of target-based therapeutic approach for the management of sepsis. The advancement in understanding the immune system and its working has led to novel discoveries in the last 50 years, including different pattern recognition receptors. Inflammasomes are also part of these novel discoveries in the field of immunology which are <20 years old in terms of their first identification. They serve as important cytosolic pattern recognition receptors required for recognizing cytosolic pathogens, and their pathogen-associated molecular patterns play an important role in the pathogenesis of sepsis. The activation of both canonical and non-canonical inflammasome signaling pathways is involved in mounting a proinflammatory immune response via regulating the generation of IL-1β, IL-18, IL-33 cytokines and pyroptosis. In addition to pathogens and their pathogen-associated molecular patterns, death/damage-associated molecular patterns and other proinflammatory molecules involved in the pathogenesis of sepsis affect inflammasomes and vice versa. Thus, the present review is mainly focused on the inflammasomes, their role in the regulation of immune response associated with sepsis, and their targeting as a novel therapeutic approach.

International Union of Basic and Clinical Pharmacology. CII: Pharmacological Modulation of H2S Levels: H2S Donors and H2S Biosynthesis Inhibitors

Over the last decade, hydrogen sulfide (H2S) has emerged as an important endogenous gasotransmitter in mammalian cells and tissues. Similar to the previously characterized gasotransmitters nitric oxide and carbon monoxide, H2S is produced by various enzymatic reactions and regulates a host of physiologic and pathophysiological processes in various cells and tissues. H2S levels are decreased in a number of conditions (e.g., diabetes mellitus, ischemia, and aging) and are increased in other states (e.g., inflammation, critical illness, and cancer). Over the last decades, multiple approaches have been identified for the therapeutic exploitation of H2S, either based on H2S donation or inhibition of H2S biosynthesis. H2S donation can be achieved through the inhalation of H2S gas and/or the parenteral or enteral administration of so-called fast-releasing H2S donors (salts of H2S such as NaHS and Na2S) or slow-releasing H2S donors (GYY4137 being the prototypical compound used in hundreds of studies in vitro and in vivo). Recent work also identifies various donors with regulated H2S release profiles, including oxidant-triggered donors, pH-dependent donors, esterase-activated donors, and organelle-targeted (e.g., mitochondrial) compounds. There are also approaches where existing, clinically approved drugs of various classes (e.g., nonsteroidal anti-inflammatories) are coupled with H2S-donating groups (the most advanced compound in clinical trials is ATB-346, an H2S-donating derivative of the non-steroidal anti-inflammatory compound naproxen). For pharmacological inhibition of H2S synthesis, there are now several small molecule compounds targeting each of the three H2S-producing enzymes cystathionine-β-synthase (CBS), cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase. Although many of these compounds have their limitations (potency, selectivity), these molecules, especially in combination with genetic approaches, can be instrumental for the delineation of the biologic processes involving endogenous H2S production. Moreover, some of these compounds (e.g., cell-permeable prodrugs of the CBS inhibitor aminooxyacetate, or benserazide, a potentially repurposable CBS inhibitor) may serve as starting points for future clinical translation. The present article overviews the currently known H2S donors and H2S biosynthesis inhibitors, delineates their mode of action, and offers examples for their biologic effects and potential therapeutic utility.

Circulating levels of hydrogen sulfide and substance P in patients with sepsis

OBJECTIVE

To determine alterations of circulating levels of hydrogen sulfide and substance P in patients with sepsis compared to non-sepsis patients with similar disease severity and organ dysfunction.

METHODS

This study included 23 septic and 14 non-septic patients during 2015-16 study period at the Christchurch Hospital Intensive Care Unit, Christchurch, New Zealand. Blood samples were collected from the time of admission to 96 h, with collection at different time points (0 h, 12 h, 24 h, 48 h, 72 h and 96 h) and subjected to measurement of hydrogen sulfide, substance P, procalcitonin, C-reactive protein, interleukin-6 and lactate levels.

RESULTS

Patients with sepsis showed higher circulating hydrogen sulfide and substance P levels compared to patients without sepsis. Hydrogen sulfide levels were significantly higher at 12 h (1.45 vs 0.75 μM; p < 0.05) and 24 h (1.11 vs 0.72 μM; p < 0.01), whereas substance P levels were higher at 48 h (0.55 vs 0.31 ng/mL; p < 0.05). Increased hydrogen sulfide and substance P levels in septic patients were associated with increased levels of inflammatory mediators - procalcitonin, C-reactive protein and interleukin-6.

CONCLUSIONS

These results provide evidence that higher circulating levels of hydrogen sulfide and substance P are associated with increased inflammatory response in patients with sepsis.