Hydrogen sulfide intoxication

Intratracheal cobinamide (vitamin B12 analog) administration increases survivability in rabbits exposed to a lethal dose of inhaled hydrogen sulfide

BACKGROUND

Hydrogen sulfide is a highly toxic, flammable, and colorless gas. Hydrogen sulfide has been identified as a potential terrorist chemical threat agent in mass-casualty events. Our previous studies showed that cobinamide, a vitamin B12 analog, effectively reverses the toxicity from hydrogen sulfide poisoning. In this study, we investigate the effectiveness of intratracheally administered cobinamide in treating a lethal dose hydrogen sulfide gas inhalation and compare its performance to saline control administration.

METHODS

A total of 53 pathogen-free New Zealand White rabbits were used for this study. Four groups were compared: (i) received no saline solution or drug intratracheally (n = 15), (ii) slow drip saline intratracheally (n = 15), (iii) fast drip saline intratracheally (n = 15), and (iv) slow drip cobinamide intratracheally (n = 8). Blood pressure was continuously monitored, and deoxy- and oxyhemoglobin concentration changes were monitored in real-time in vivo using continuous wave near-infrared spectroscopy.

RESULTS

The mean (± standard deviation) weight for all animals (n = 53) was 3.87 ± 0.10 kg. The survival rates of the slow cobinamide and the fast saline groups were 75 percent and 60 percent, respectively, while the survival rates in the slow saline and control groups were 26.7 percent and 20 percent, respectively. A log-rank (Mantel-Cox) test showed that survival in fast saline and slow cobinamide groups were significantly greater than those of no saline control and slow saline groups (P < 0.05). The slow and no saline control groups were not significantly different (P = 0.59). The slow cobinamide group did significantly better than the slow saline group (P = 0.021).

DISCUSSION

The ability to use intratracheal cobinamide as an antidote to hydrogen sulfide poisoning is a novel approach to mass-casualty care. The major limitations of this study are that it was conducted in a single species at a single inhaled hydrogen sulfide concentration. Repeated investigations in other species and at varying levels of hydrogen sulfide exposure will be needed before any definitive recommendations can be made.

CONCLUSIONS

We demonstrated that intratracheal cobinamide and fast saline drip improved survival for hydrogen sulfide gas inhalation in rabbit models. Although further study is required, our results suggest that intratracheal administration of cobinamide and fast saline may be useful in hydrogen sulfide mass-casualty events.

Observation and comparison of gas formation during holmium:YAG laser lithotripsy of cystine, uric acid, and calcium oxalate stones: a chromatographic and electron microscopic analysis

The primary aim of the present in vitro study is to analyze the chemical content of the bubbles occurring during the fragmentation of cystine stones with both the high-power and low-power holmium:YAG (Ho:YAG) lasers. The secondary aim is to discuss their clinical importance. Three types of human renal calculi calcium oxalate monohydrate (COM), cystine, and uric acid were fragmented with both low-power and high-power Ho:YAG lasers in separate experimental setups at room temperature, during which time it was observed whether gas was produced. After laser lithotripsy, a cloudy white gas was obtained, after the fragmentation of cystine stones only. A qualitative gas content analysis was performed with a gas chromatography-mass spectrometry (GC-MS) device. The fragments in the aqueous cystine calculi setup were dried and taken to the laboratory to be examined by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray diffraction analysis. No gas production was observed after fragmentation in the COM and uric acid stones. Free cystine, sulfur, thiophene, and hydrogen sulfide gas were produced by both low-power and high-power Ho:YAG laser lithotripsy of the cystine stones. In the SEM-EDX mapping analysis, a free cystine molecule containing 42.8% sulfur (S), 21% oxygen (O), 14.9% carbon (C), and 21% nitrogen (N) atoms was detected in the cystine stone experimental setup. The evidence obtained, which shows that hydrogen sulfide emerges in the gaseous environment during Ho:YAG laser fragmentation of cystine stones, indicates that caution is required to prevent the risk of in vivo production and toxicity.

Case report: Analysis of a case of hydrogen sulfide poisoning in a waste treatment plant

This paper summarizes and analyzes the clinical data of a patient with Occupational hydrogen sulfide poisoning admitted to our hospital on March 4, 2023. On the morning of March 2, 2023, the patient worked at an environmental energy company (waste treatment plant) in Shandong Province for the first time, The job was to flush the sludge from the walls of the sludge treatment tank (anaerobic tank) with a water gun, which can release hydrogen sulfide gas. When the patient was about to start work after entering the tank for about 1 min, he suddenly smelled a harsh and pungent odor, felt dizzy and weak, and then the patient suddenly fainted. After hearing the sound of the patient fainting, the workman waiting at the entrance of the tank immediately called someone to go into the tank and quickly pull the patient out, and sent to the local hospital. In the local hospital, the patient was confused, accompanied by irritability, convulsion and other manifestations, and was treated with sedation and nutritional support. Two days later, the patient's condition did not improve. For further diagnosis and treatment, the patient was transferred to the Department of Poisoning and Occupational Diseases in our hospital. After comprehensive treatment in our hospital, the patient got better and was discharged. Subsequent reexamination and follow-up showed that the patient recovered well. The work unit of the patient did not provide any personal protective equipment. According to the field investigation after the accident, the pipeline around the sludge treatment tank was blocked by sludge, resulting in a large amount of high concentration of H2S accumulated in the tank, causing the patient to faint soon after entering the tank, and his worker should be in the tank for a short time, and no health abnormalities were found. Hydrogen sulfide has a strong irritation to the human body, which can lead to asphyxia or even death in severe cases. The safety prevention and prevention knowledge of hydrogen sulfide poisoning should be popularized among enterprises and workers to reduce the occurrence of such incidents.

A case of syncope in a villager with hypertrophic cardiomyopathy after hydrogen sulfide exposure by an unauthorized discharge of wastewater

Background

Hydrogen sulfide is a toxic substance that humans can be exposed to occupationally, and cases of hydrogen sulfide poisoning of workers in industrial sites are commonly reported. However, there have been no cases of poisoning of the public due to an unauthorized discharge of wastewater, so it is important to describe this incident.

Case presentation

In a small village in Jeollanam-do, Republic of Korea, accounts of a terrible stench had been reported. A 26-year-old man who lived and worked in a foul-smelling area was taken to the emergency room with a headache, dizziness, nausea, and repeated syncope. A subsequent police and Ministry of Environment investigation determined that the cause of the stench was the unauthorized discharge of 9 tons of wastewater containing hydrogen sulfide through a stormwater pipe while the villagers were sleeping. The patient had no previous medical history or experience of symptoms. Leukocytes and cardiac markers were elevated, an electrocardiogram indicated biatrial enlargement, left ventricular hypertrophy, and corrected QT interval prolongation. Myocardial hypertrophy was detected on a chest computed tomography scan, and hypertrophic cardiomyopathy was confirmed on echocardiography. After hospitalization, cardiac marker concentrations declined, symptoms improved, and the patient was discharged after 7 days of hospitalization. There was no recurrence of symptoms after discharge.

Conclusions

We suspect that previously unrecognized heart disease manifested or was aggravated in this patient due to exposure to hydrogen sulfide. Attention should be paid to the possibility of unauthorized discharge of hydrogen sulfide, etc., in occasional local incidents and damage to public health. In the event of such an accident, it is necessary to have government guidelines in place to investigate health impact and follow-up clinical management of exposed residents.

Acute hydrogen sulfide-induced neurochemical and morphological changes in the brainstem

Hydrogen sulfide (H₂S) is a toxin affecting the cardiovascular, respiratory, and central nervous systems. Acute H₂S exposure is associated with a high rate of mortality and morbidity. The precise pathophysiology of H₂S-induced death is a controversial topic; however, inhibition of the respiratory center in the brainstem is commonly cited as a cause of death. There is a knowledge gap on toxicity and toxic mechanisms of acute H₂S poisoning on the brainstem, a brain region responsible for regulating many reflective and vital functions. Serotonin (5-HT), dopamine (DA), and γ-aminobutyric acid (GABA) play a role in maintaining a normal stable respiratory rhythmicity. We hypothesized that the inhibitory respiratory effects of H₂S poisoning are mediated by 5-HT in the respiratory center of the brainstem. Male C57BL/6 mice were exposed once to an LCt₅₀ concentration of H₂S (1000 ppm). Batches of surviving mice were euthanized at 5 min, 2 h, 12 h, 24 h, 72 h, and on day 7 post-exposure. Pulmonary function, vigilance state, and mortality were monitored during exposure. The brainstem was analyzed for DA, 3,4-dehydroxyphenyl acetic acid (DOPAC), 5-HT, 5-hydroxyindoleatic acid (5-HIAA), norepinephrine (NE), GABA, glutamate, and glycine using HPLC. Enzymatic activities of monoamine oxidases (MAO) were also measured in the brainstem using commercial kits. Neurodegeneration was assessed using immunohistochemistry and magnetic resonance imaging. Results showed that DA and DOPAC were significantly increased at 5 min post H₂S exposure. However, by 2 h DA returned to normal. Activities of MAO were significantly increased at 5 min and 2 h post-exposure. In contrast, NE was significantly decreased at 5 min and 2 h post-exposure. Glutamate was overly sensitive to H₂S-induced toxicity manifesting a time-dependent concentration reduction throughout the 7 day duration of the study. Remarkably, there were no changes in 5-HT, 5-HIAA, glycine, or GABA concentrations. Cytochrome c oxidase activity was inhibited but recovered by 24 h. Neurodegeneration was observed starting at 72 h post H₂S exposure in select brainstem regions. We conclude that acute H₂S exposure causes differential effects on brainstem neurotransmitters. H₂S also induces neurodegeneration and biochemical changes in the brainstem. Additional work is needed to fully understand the implications of both the short- and long-term effects of acute H₂S poisoning on vital functions regulated by the brainstem.

Analysis of CT and MR imaging features of the brain in patients with hydrogen sulfide poisoning based on clinical symptom grading

Objective

To retrospectively analyze CT and MR imaging features of the brain in patients with hydrogen sulfide poisoning based on clinical symptom grading and to investigate their correlations with clinical symptoms and patients’ prognosis.

Methods

A retrospective analysis was performed of CT and MR imaging data of the brain in 40 patients with hydrogen sulfide poisoning in our hospital. There were four main imaging manifestations. Patients were clinically graded according to the central nervous system symptom scores of the Poisoning Severity Score (PSS) and staged according to the gas inhalation time segment. Based on clinical symptom grading, the frequencies and proportions of four imaging signs that occurred in each group were counted, their development trends were analyzed, and the correlations of imaging features with clinical grading and prognosis were calculated.

Results

Forty patients were divided into minor, moderate and severe clinical grades and classified into four stages. In patients with minor and moderate clinical grading, only one patient suffered from generalized brain edema at stage 1, with a good prognosis. Patients with severe clinical grade showed the highest probability of presenting with the four imaging signs. The imaging signs were correlated with the severe clinical grade and a poor prognosis (P = 0.000, R = 0.828; P = 0.000, R = 0.858).

Conclusion

In patients with the severe clinical grade, generalized brain edema and symmetrical hypodensity/abnormal signals in the bilateral basal ganglia and around the lateral ventricles were the main findings and were shown to persist. The presence of imaging signs can assist in the clinically effective evaluation of clinical symptom grade.

Meta-Analysis of the Composition of Human Intestinal Gases

BACKGROUND

Understanding intestinal gases volume and composition may contribute to diagnosing digestive diseases and the microbiome's status. This meta-analysis aimed to define the composition of human intestinal gases and changes associated with diet.

METHODS

Studies were identified by systematic research of the MEDLINE(Ovid), Scopus, and Cochrane databases. Studies that measured the concentration of intestinal gases in healthy adult humans were retrieved. The JBI critical appraisal tool was used to evaluate the risk of bias. The primary outcomes analysed were the concentration of the most prevalent colonic gases. Participants were divided into groups according to dietary fibre content.

RESULTS

Eleven studies were included. The following gases were identified in similar concentrations across all studies (mean ± standard deviation): nitrogen (65.1 ± 20.89%), oxygen (2.3 ± 0.98%), carbon dioxide (9.9 ± 1.6%), hydrogen (2.9 ± 0.7%), and methane (14.4 ± 3.7%). Differences according to the dietary fibre were observed, with a positive correlation between fibre and volume of gas produced, particularly in fermented gases (carbon dioxide, hydrogen, and methane).

DISCUSSION

The meta-analysis has found defined concentrations of the five most common gases present in human colonic gas. Limitations included heterogenic methodologies, a low number of participants, and few recent studies. These findings may be helpful in diagnostic applications where colonic gas volume and composition are crucial factors, including functional disorders, microbiome analyses, and bowel perforation diagnostics.

Unmet needs in glaucoma therapy: The potential role of hydrogen sulfide and its delivery strategies

Glaucoma is an optic neuropathy disorder marked by progressive degeneration of the retinal ganglion cells (RGC). It is a leading cause of blindness worldwide, prevailing in around 2.2% of the global population. The hallmark of glaucoma, intraocular pressure (IOP), is governed by the aqueous humor dynamics which plays a crucial role in the pathophysiology of the diesease. Glaucomatous eye has an IOP of more than 22 mmHg as compared to normotensive pressure of 10-21 mmHg. Currently used treatments focus on reducing the elevated IOP through use of classes of drugs that either increase aqueous humor outflow and/or decrease its production. However, effective treatments should not only reduce IOP, but also offer neuroprotection and regeneration of RGCs. Hydrogen Sulfide (H₂S), a gasotransmitter with several endogenous functions in mammalian tissues, is being investigated for its potential application in glaucoma. In addition to decreasing IOP by increasing aqueous humor outflow, it scavenges reactive oxygen species, upregulates the cellular antioxidant glutathione and protects RGCs from excitotoxicity. Despite the potential of H₂S in glaucoma, its delivery to anterior and posterior regions of the eye is a challenge due to its unique physicochemical properties. Firstly, development of any delivery system should not require an aqueous environment since many H₂S donors are susceptible to burst release of the gas in contact with water, causing potential toxicity and adverse effects owing to its inherent toxicity at higher concentrations. Secondly, the release of the gas from the donor needs to be sustained for a prolonged period of time to reduce dosing frequency as per the requirements of regulatory bodies. Lastly, the delivery system should provide adequate bioavailability throughout its period of application. Hence, an ideal delivery system should aim to tackle all the above challenges related to barriers of ocular delivery and physicochemical properties of H₂S itself. This review discusses the therapeutic potential of H₂S, its delivery challenges and strategies to overcome the associated chalenges.

Highly Selective Electrochemiluminescence Chemosensor for Sulfide Enabled by Hierarchical Reactivity

Hydrogen sulfide (H₂S) is a well-known toxic gas with the odor of rotten eggs. Several reaction-based electrochemiluminescence (ECL) chemosensors for H₂S have been developed; however, no homogeneous ECL probe with high selectivity toward H₂S in aqueous media has been reported. Herein, we report an iridium(III) complex-based ECL chemodosimetric probe employing two 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) groups known as a photo-induced electron transfer quencher and a reaction site for the selective detection of H₂S; the detection mechanism involves H₂S being clearly distinguished from biothiols based on the different cleavage rates of the two NBD groups and extremely weak ECL interferences caused by reaction by-products. The probe was rationally designed to improve selectivity toward H₂S within the ECL analysis platform by enabling the removal of nonspecific background signals observed via fluorescence analysis. This analytical system exhibited remarkable selectivity toward H₂S, a rapid reaction rate, and high sensitivity (LOD = 57 nM) compared to conventional fluorescence methods. Furthermore, the probe could successfully quantify H₂S in tap water samples and commercial ammonium sulfide solutions, which demonstrates the effectiveness of this probe in field monitoring.

Quantitative proteomics reveals tissue-specific toxic mechanisms for acute hydrogen sulfide-induced injury of diverse organs in pig

Hydrogen sulfide (H₂S) is a highly toxic gas in many environmental and occupational places. It can induce multiple organ injuries particularly in lung, trachea and liver, but the relevant mechanisms remain poorly understood. In this study, we used a TMT-based discovery proteomics to identify key proteins and correlated molecular pathways involved in the pathogenesis of acute H₂S-induced toxicity in porcine lung, trachea and liver tissues. Pigs were subjected to acute inhalation exposure of up to 250 ppm of H₂S for 5 h for the first time. Changes in hematology and biochemical indexes, serum inflammatory cytokines and histopathology demonstrated that acute H₂S exposure induced organs inflammatory injury and dysfunction in the porcine lung, trachea and liver. The proteomic data showed 51, 99 and 84 proteins that were significantly altered in lung, trachea and liver, respectively. Gene ontology (GO) annotation, KEGG pathway and protein-protein interaction (PPI) network analysis revealed that acute H₂S exposure affected the three organs via different mechanisms that were relatively similar between lung and trachea. Further analysis showed that acute H₂S exposure caused inflammatory damages in the porcine lung and trachea through activating complement and coagulation cascades, and regulating the hyaluronan metabolic process. Whereas antigen presentation was found in the lung but oxidative stress and cell apoptosis was observed exclusively in the trachea. In the liver, an induced dysfunction was associated with protein processing in the endoplasmic reticulum and lipid metabolism. Further validation of some H₂S responsive proteins using western blotting indicated that our proteomics data were highly reliable. Collectively, these findings provide insight into toxic molecular mechanisms that could potentially be targeted for therapeutic intervention for acute H₂S intoxication.

Carbon monoxide and a change of heart

The relationship between carbon monoxide and the heart has been extensively studied in both clinical and preclinical settings. The Food and Drug Administration (FDA) is keenly focused on the ill effects of carbon monoxide on the heart when presented with proposals for clinical trials to evaluate efficacy of this gasotransmitter in a various disease settings. This review provides an overview of the rationale that examines the actions of the FDA when considering clinical testing of CO, and contrast that with the continued accumulation of data that clearly show not only that CO can be used safely, but is potently cardioprotective in clinically relevant small and large animal models. Data emerging from Phase I and Phase II clinical trials argues against CO being dangerous to the heart and thus it needs to be redefined and evaluated as any other substance being proposed for use in humans. More than twenty years ago, the belief that CO could be used as a salutary molecule was ridiculed by experts in physiology and medicine. Like all agents designed for use in humans, careful pharmacology and safety are paramount, but continuing to hinder progress based on long-standing dogma in the absence of data is improper. Now, CO is being tested in multiple clinical trials using innovative delivery methods and has proven to be safe. The hope, based on compelling preclinical data, is that it will continue to be evaluated and ultimately approved as an effective therapeutic.

Influence of Gypsum Waste Utilization on Properties and Leachability of Fired Clay Brick

Wastewater treatment activities in the chemical industry have generated abundant gypsum waste, classified as scheduled waste (SW205) under the Environmental Quality Regulations 2005. The waste needs to be disposed into a secure landfill due to the high heavy metals content which is becoming a threat to the environment. Hence, an alternative disposal method was evaluated by recycling the waste into fired clay brick. The brick samples were incorporated with different percentages of gypsum waste (0% as control, 10, 20, 30, 40 and 50%) and were fired at 1050 °C using 1 °C per minute heating rate. Shrinkage, dry density, initial rate of suction (IRS) and compressive strength tests were conducted to determine the physical and mechanical properties of the brick, while the synthetic precipitation leaching procedure (SPLP) was performed to scrutinize the leachability of heavy metals from the crushed brick samples. The results showed that the properties would decrease through the incorporation of gypsum waste and indicated the best result at 10% of waste utilization with 47.5% of shrinkage, 1.37% of dry density, 22.87% of IRS and 28.3% of compressive strength. In addition, the leachability test highlighted that the concentrations of Fe and Al was significantly reduced up to 100% from 4884 to 3.13 ppm (Fe) and from 16,134 to 0.81 ppm (Al), respectively. The heavy metals content in the bricks were oxidized during the firing process, which signified the successful remediation of heavy metals in the samples. Based on the permissible incorporation of gypsum waste into fired clay brick, this study promised a more green disposing method for gypsum waste, and insight as a potential towards achieving a sustainable end product.

Application of adverse outcome pathway networks to integrate mechanistic data informing the choice of a point of departure for hydrogen sulfide exposure limits

Acute exposure to hydrogen sulfide initiates a series of hallmark biological effects that occur progressively at increasing exposure levels: odor perception, conjunctivitis, olfactory paralysis, "knockdown," pulmonary edema, and apnea. Although effects of exposure to high concentrations of hydrogen sulfide are clear, effects associated with chronic, low-level exposure in humans is under debate, leading to uncertainty in the critical effect used in regulatory risk assessments addressing low dose exposures. This study integrates experimental animal, observational epidemiology, and occupational exposure evidence by applying a pathway-based approach. A hypothesized adverse outcome pathway (AOP) network was developed from 34 studies, composed of 4 AOPs sharing 1 molecular initiating events (MIE) and culminating in 4 adverse outcomes. A comparative assessment of effect levels and weight of evidence identified an AOP leading to a biologically-plausible, low-dose outcome relative to the other outcomes (nasal lesions, 30 ppm versus olfactory paralysis, >100 ppm; neurological effects, >80 ppm; pulmonary edema, >80 ppm). This AOP (i.e. AOP1) consists of the following key events: cytochrome oxidase inhibition (>10 ppm), neuronal cell loss (>30 ppm), and olfactory nasal lesions (defined as both neuronal cell loss and basal cell hyperplasia; >30 ppm) in rodents. The key event relationships in this pathway were supported by moderate empirical evidence and have high biological plausibility due to known mechanistic understanding and consistency in observations for diverse chemicals.

Markers for the Comparison of the Performances of Anoxic Biotrickling Filters in Biogas Desulphurisation: A Critical Review

The agriculture and livestock industry generate waste used in anaerobic digestion to produce biogas containing methane (CH4), useful in the generation of electricity and heat. However, although biogas is mainly composed of CH4 (~65%) and CO2 (~34%), among the 1% of other compounds present is hydrogen sulphide (H2S) which deteriorates engines and power generation fuel cells that use biogas, generating a foul smell and contaminating the environment. As a solution to this, anoxic biofiltration, specifically with biotrickling filters (BTFs), stands out in terms of the elimination of H2S as it is cost-effective, efficient, and more environmentally friendly than chemical solutions. Research on the topic is uneven in terms of presenting performance markers, underestimating many microbiological indicators. Research from the last decade was analyzed (2010–2020), demonstrating that only 56% of the reviewed publications did not report microbiological analysis related to sulphur oxidising bacteria (SOB), the most important microbial group in desulphurisation BTFs. This exposes fundamental deficiencies within this type of research and difficulties in comparing performance between research works. In this review, traditional and microbiological performance markers of anoxic biofiltration to remove H2S are described. Additionally, an analysis to assess the efficiency of anoxic BTFs for biogas desulphurisation is proposed in order to have a complete and uniform assessment for research in this field.

Hydrogen Sulfide, an Endogenous Stimulator of Mitochondrial Function in Cancer Cells

Hydrogen sulfide (H₂S) has a long history as toxic gas and environmental hazard; inhibition of cytochrome c oxidase (mitochondrial Complex IV) is viewed as a primary mode of its cytotoxic action. However, studies conducted over the last two decades unveiled multiple biological regulatory roles of H₂S as an endogenously produced mammalian gaseous transmitter. Cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST) are currently viewed as the principal mammalian H₂S-generating enzymes. In contrast to its inhibitory (toxicological) mitochondrial effects, at lower (physiological) concentrations, H₂S serves as a stimulator of electron transport in mammalian mitochondria, by acting as an electron donor—with sulfide:quinone oxidoreductase (SQR) being the immediate electron acceptor. The mitochondrial roles of H₂S are significant in various cancer cells, many of which exhibit high expression and partial mitochondrial localization of various H₂S producing enzymes. In addition to the stimulation of mitochondrial ATP production, the roles of endogenous H₂S in cancer cells include the maintenance of mitochondrial organization (protection against mitochondrial fission) and the maintenance of mitochondrial DNA repair (via the stimulation of the assembly of mitochondrial DNA repair complexes). The current article overviews the state-of-the-art knowledge regarding the mitochondrial functions of endogenously produced H₂S in cancer cells.

A Portable Environmental Data-Monitoring System for Air Hazard Evaluation in Deep Underground Mines

Air-quality measurements in a deep underground mine are a critical issue. The cost of ventilation, as well as the geometry of the considered mine, make this process very difficult, and local air quality may be a danger to miners. Thus, portable, personal devices are required to inform miners about gas hazards. There are available tools for that purpose; however, they do not allow the storage of data collected during a shift. Moreover, they do not allow the basic analysis of the acquired data cost-effectively. This paper aims to present a system using low-cost gas sensors and microcontrollers, and takes advantage of commonly used smartphones as a computing and visualization resource. Finally, we demonstrate monitoring system results from a test in an underground mine located in Poland.

Characterization of hydrogen sulfide toxicity to human corneal stromal fibroblasts

Hydrogen sulfide gas (H2 S) is a chemical weapon and a common environmental pollutant. H2 S intoxication is lethal to humans and animals. H2 S contact to the eye can cause vision loss. However, the molecular mechanisms associated with H2 S toxicity to the cornea remain unclear, and no specific therapy exists to mitigate ocular damage from H2 S. Here, we report H2 S-induced cytotoxicity and the parameters contributing to the molecular mechanisms associated with corneal toxicity using primary human corneal stromal fibroblasts (hCSFs) in vitro. Sodium hydrosulfide (NaSH) was used as a source of H2 S, and the cytotoxicity of H2 S was determined by treating hCSF cells with varying concentrations of NaSH (0-10 mM) for 0-72 hours. Changes in cell proliferation, oxidative stress factors, and the expression of inflammatory and fibrotic genes were studied using standard commercial kits and qRT-PCR. NaSH exposure to hCSFs showed dose- and time-dependent cytotoxicity. The IC50 of NaSH was determined to be 5.35 mM. NaSH 5.35 mM exposure led to significantly decreased cytochrome c oxidase activity, increased ROS production, and increased expression of inflammatory and fibrotic genes in hCSF cells. H2 S/NaSH exposure alters normal mitochondrial function, oxidative stress, and inflammatory and fibrotic gene responses in corneal stromal fibroblasts in vitro.

Fatal poisoning of four workers in a farm: Distribution of hydrogen sulfide and thiosulfate in 10 different biological matrices

We evaluate the distribution of sulfide and thiosulfate (TS) in biological samples of four dairy farmers died inside a pit connected to a manure lagoon. Autopsies were performed 4 days later. Toxicological analyses of sulfide and TS were made using an extractive alkylation technique combined with gas chromatography/mass spectrometry (GC/MS). Autopsies revealed: multiorgan congestion; pulmonary edema; manure inside distal airways of three of the four victims. Sulfide concentrations were cardiac blood: 0.5-3.0 μg/mL, femoral blood: 0.5-1.2 μg/mL, bile: <0.1-2.2 μg/mL; liver 2.8-8.3 μg/g, lung: 5.0-9.4 μg/g, brain: 2.7-13.9 μg/g, spleen: 3.3-6.3 μg/g, fat: <0.1-1.5 μg/g, muscle: 2.6-3.5 μg/g. TS concentrations were cardiac blood: 2.1-4.9 μg/mL, femoral blood: 2.1-2.3 μg/mL, bile: 2.5-4.4 μg/mL, urine: <0.5-1.8 μg/mL; liver <0.5-2.6, lung: 2.8-5.4 μg/g, brain: <0.5-1.9 μg/g, spleen: 1.2-2.9 μg/g, muscle: <0.5-5.6 μg/g. The cause of death was assessed to be acute poisoning by hydrogen sulfide (H₂S) for all the victims. Manure inhalation contributed to the death of three subjects. The measurement of sulfide and TS concentrations in biological samples contributed to better understand the sequence of the events. Subjects 3 provided the highest concentration of sulfide in brain, thus, supporting the hypothesis of a rapid loss of consciousness and respiratory depression. One by one, the other farmers entered the pit in attempts to rescue the coworkers but collapsed. Despite the rapid death, subject 3 was the only one with TS detectable in urine. This could be due to differences in metabolism of H₂S.

The role of medical gas in stroke: an updated review

Medical gas is a large class of bioactive gases used in clinical medicine and basic scientific research. At present, the role of medical gas in neuroprotection has received growing attention. Stroke is a leading cause of death and disability in adults worldwide, but current treatment is still very limited. The common pathological changes of these two types of stroke may include excitotoxicity, free radical release, inflammation, cell death, mitochondrial disorder, and blood-brain barrier disruption. In this review, we will discuss the pathological mechanisms of stroke and the role of two medical gases (hydrogen and hydrogen sulfide) in stroke, which may potentially provide a new insight into the treatment of stroke.

Emerging pharmacological tools to control hydrogen sulfide signaling in critical illness

Hydrogen sulfide (H2S) has long been known as a toxic environmental hazard. Discovery of physiological roles of H2S as a neurotransmitter by Kimura and colleagues triggered an intensive research in the biological roles of H2S in the past decades. Manipulation of H2S levels by inhibiting H2S synthesis or administration of H2S-releasing molecules revealed beneficial as well as harmful effects of H2S. As a result, it is now established that H2S levels are tightly controlled and too much or too little H2S levels cause harm. Nonetheless, translation of sulfide-based therapy to clinical practice has been stymied due to the very low therapeutic index of sulfide and the incomplete understanding of endogenous sulfide metabolism. One potential strategy to circumvent this problem is to use a safe and stable sulfide metabolite that may mediate effects of H2S. Alternatively, endogenous sulfide levels may be controlled using specific sulfide scavengers. In this review article, the role of endogenous H2S production and catabolism will be briefly reviewed followed by an introduction of thiosulfate and H2S scavengers as novel pharmacological tools to control H2S-dependent signaling.

Transcriptomic profile analysis of brain inferior colliculus following acute hydrogen sulfide exposure

Hydrogen sulfide (H2S) is a gaseous molecule found naturally in the environment, and as an industrial byproduct, and is known to cause acute death and induces long-term neurological disorders following acute high dose exposures. Currently, there is no drug approved for treatment of acute H2S-induced neurotoxicity and/or neurological sequelae. Lack of a deep understanding of pathogenesis of H2S-induced neurotoxicity has delayed the development of appropriate therapeutic drugs that target H2S-induced neuropathology. RNA sequencing analysis was performed to elucidate the cellular and molecular mechanisms of H2S-induced neurodegeneration, and to identify key molecular elements and pathways that contribute to H2S-induced neurotoxicity. C57BL/6J mice were exposed by whole body inhalation to 700 ppm of H2S for either one day, two consecutive days or 4 consecutive days. Magnetic resonance imaging (MRI) scan analyses showed H2S exposure induced lesions in the inferior colliculus (IC) and thalamus (TH). This mechanistic study focused on the IC. RNA Sequencing analysis revealed that mice exposed once, twice, or 4 times had 283, 193 and 296 differentially expressed genes (DEG), respectively (q-value < 0.05, fold-change> 1.5). Hydrogen sulfide exposure modulated multiple biological pathways including unfolded protein response, neurotransmitters, oxidative stress, hypoxia, calcium signaling, and inflammatory response in the IC. Hydrogen sulfide exposure activated PI3K/Akt and MAPK signaling pathways. Pro-inflammatory cytokines were shown to be potential initiators of the modulated signaling pathways following H2S exposure. Furthermore, microglia were shown to release IL-18 and astrocytes released both IL-1β and IL-18 in response to H2S. This transcriptomic analysis data revealed complex signaling pathways involved in H2S-induced neurotoxicity and may provide important associated mechanistic insights.

Hydrogen Sulfide as a Potential Alternative for the Treatment of Myocardial Fibrosis

Harmful, stressful conditions or events in the cardiovascular system result in cellular damage, inflammation, and fibrosis. Currently, there is no targeted therapy for myocardial fibrosis, which is highly associated with a large number of cardiovascular diseases and can lead to fatal heart failure. Hydrogen sulfide (H₂S) is an endogenous gasotransmitter similar to nitric oxide and carbon monoxide. H₂S is involved in the suppression of oxidative stress, inflammation, and cellular death in the cardiovascular system. The level of H₂S in the body can be boosted by stimulating its synthesis or supplying it exogenously with a simple H₂S donor with a rapid- or slow-releasing mode, an organosulfur compound, or a hybrid with known drugs (e.g., aspirin). Hypertension, myocardial infarction, and inflammation are exaggerated when H₂S is reduced. In addition, the exogenous delivery of H₂S mitigates myocardial fibrosis caused by various pathological conditions, such as a myocardial infarct, hypertension, diabetes, or excessive β-adrenergic stimulation, via its involvement in a variety of signaling pathways. Numerous experimental findings suggest that H₂S may work as a potential alternative for the management of myocardial fibrosis. In this review, the antifibrosis role of H₂S is briefly addressed in order to gain insight into the development of novel strategies for the treatment of myocardial fibrosis.

A Novel Application of Electroactive Polyimide Doped with Gold Nanoparticles: As a Chemiresistor Sensor for Hydrogen Sulfide Gas

This research paper presents a new application of electroactive polyimide doped with gold nanoparticles (PI/AuNPs) as a chemiresistor sensor for detecting hydrogen sulfide gas. The synthesis of PI/AuNPs was done in a simple 3-step process of polymerization using the as prepared amine-capped aniline trimer (ACAT), followed by imidization, and doping. Spectral analyses via FTIR, LC-MS and ¹H-NMR confirmed the formation of amine-capped aniline trimer with a MW of 288 g mol⁻¹. Comparison of ACAT, BSAA, and PI FTIR spectra showed successful polymerization of the last, while XRD validated the incorporation of metal nanoparticles onto the polymer matrix, showing characteristic diffraction peaks corresponding to gold. Furthermore, TEM, and FE-SEM revealed the presence of well-dispersed Au nanoparticles with an average diameter of about 60 nm. The electroactive PI/AuNPs-based sensor showed a sensitivity of 0.29% ppm⁻¹ H₂S at a linear concentration range of 50 to 300 ppm H₂S (r = 0.9777). The theoretical limit of detection was found at 0.142 ppm or 142 ppb H₂S gas. The sensor provided a stable response reading at an average response time of 43 ± 5 s, which was easily recovered after an average time of 99 ± 5 s. The sensor response was highly repeatable and reversible, with RSD values of 8.88%, and 8.60%, respectively. Compared with the performance of the conventional conducting polyaniline also doped with gold nanoparticles (PANI/AuNPs), the fabricated electroactive PI/AuNPs exhibited improved sensing performance making it a potential candidate in monitoring H₂S in the environment and for work-related safety.

An excellent heterojunction nanocomposite solar-energy material for photocatalytic transformation of hydrogen sulfide pollutant to hydrogen fuel and elemental sulfur: A mechanistic insight

Hydrogen sulfide (H₂S) is a noxious gas for living organisms and devastating/corrosive agent for metallic structures, which is generated in large scale through natural [geothermal/bacterial] activities or industrial processes, particularly by petroleum and gas industries. Photocatalytic elimination of this plentiful-perilous pollutant and its transformation into hydrogen green fuel and elemental sulfur is a novel/sustainable strategy, which is intriguing from energy and environmental science as well as technological viewpoints. To this end, the design and synthesis of low-price, environmentally friendly, effective photocatalyst/solar-energy materials are highly in demand. Herein, through a facile hydrothermal route, a set of new pn junction xBi₂S₃·yMnS nanocomposite photocatalysts were synthesized and employed in an alkaline H₂S medium (pH = 11) to generate hydrogen fuel and elemental sulfur under atmospheric pressure at room temperature conditions. The maximum conversion yield was attained at the molar ratio xy=2, where the photocatalyst exhibited the lowest charge recombination, strong photon absorption, and the greatest surface area among the synthesized nanocomposite materials. Furthermore, it was witnessed that disulfide (S₂^2-) was the only oxidation product in the reaction medium, which could be effortlessly precipitated as elemental sulfur by acidification of the medium and lowering the pH to about 5.

A Novel Mechanism To Prevent H2S Toxicity in Caenorhabditis elegans

Hydrogen sulfide (H2S) is an endogenously produced signaling molecule that can be cytoprotective, especially in conditions of ischemia/reperfusion injury. However, H2S is also toxic, and unregulated accumulation or exposure to environmental H2S can be lethal. In Caenorhabditis elegans, the hypoxia inducible factor (hif-1) coordinates the initial transcriptional response to H2S, and is essential to survive exposure to low concentrations of H2S. We performed a forward genetic screen to identify mutations that suppress the lethality of hif-1 mutant animals in H2S. The mutations we recovered are specific for H2S, as they do not suppress embryonic lethality or reproductive arrest of hif-1 mutant animals in hypoxia, nor can they prevent the death of hif-1 mutant animals exposed to hydrogen cyanide. The majority of hif-1 suppressor mutations we recovered activate the skn-1/Nrf2 transcription factor. Activation of SKN-1 by hif-1 suppressor mutations increased the expression of a subset of H2S-responsive genes, consistent with previous findings that skn-1 plays a role in the transcriptional response to H2S. Using transgenic rescue, we show that overexpression of a single gene, rhy-1, is sufficient to protect hif-1 mutant animals in H2S. The rhy-1 gene encodes a predicated O-acyltransferase enzyme that has previously been shown to negatively regulate HIF-1 activity. Our data indicate that RHY-1 has novel, hif-1 independent, function that promotes survival in H2S.

Hydrogen Sulfide Toxicity: Mechanism of Action, Clinical Presentation, and Countermeasure Development

INTRODUCTION

Hydrogen sulfide (H₂S) is found in various settings. Reports of chemical suicide, where individuals have combined readily available household chemicals to produce lethal concentrations of H₂S, have demonstrated that H₂S is easily produced. Governmental agencies have warned of potential threats of use of H₂S for a chemical attack, but currently there are no FDA-approved antidotes for H₂S. An ideal antidote would be one that is effective in small volume, readily available, safe, and chemically stable. In this paper we performed a review of the available literature on the mechanism of toxicity, clinical presentation, and development of countermeasures for H₂S toxicity.

DISCUSSION

In vivo, H₂S undergoes an incomplete oxidation after an exposure. The remaining non-oxidized H₂S is found in dissolved and combined forms. Dissolved forms such as H₂S gas and sulfhydryl anion can diffuse between blood and tissue. The combined non-soluble forms are found as acid-labile sulfides and sulfhydrated proteins, which play a role in toxicity. Recent countermeasure development takes into account the toxicokinetics of H₂S. Some countermeasures focus on binding free hydrogen sulfide (hydroxocobalamin, cobinamide); some have direct effects on the mitochondria (methylene blue), while others work by mitigating end organ damage by generating other substances such as nitric oxide (NaNO2).

CONCLUSION

H₂S exists in two main pools in vivo after exposure. While several countermeasures are being studied for H₂S intoxication, a need exists for a small-volume, safe, highly effective antidote with a long shelf life to treat acute toxicity as well as prevent long-term effects of exposure.

Toxic exposures and the senses of taste and smell

This review addresses the adverse influences of neurotoxic exposures on the ability to smell and taste. These chemical senses largely determine the flavor of foods and beverages, impact food intake, and ultimately nutrition, and provide a warning for spoiled or poisonous food, leaking natural gas, smoke, airborne pollutants, and other hazards. Hence, toxicants that damage these senses have a significant impact on everyday function. As noted in detail, a large number of toxicants encountered in urban and industrial air pollution, including smoke, solvents, metals, and particulate matter can alter the ability to smell. Their influence on taste, i.e., sweet, sour, bitter, salty, and savory (umami) sensations, is not well documented. Given the rather direct exposure of olfactory receptors to the outside environment, olfaction is particularly vulnerable to damage from toxicants. Some toxicants, such as nanoparticles, have the potential to damage not only the olfactory receptor cells, but also the central nervous system structures by their entrance into the brain through the olfactory mucosa.

Metabolic acidosis after sodium thiosulfate infusion and the role of hydrogen sulfide

Sodium thiosulfate (STS), first-line treatment for calcific uremic arteriolopathy, causes a mild asymptomatic acidosis in many patients. However, severe, life-threatening acidosis out of proportion with the expected acid load of STS may occur, potentially due to metabolism of STS to hydrogen sulfide.

Broad spectrum proteomics analysis of the inferior colliculus following acute hydrogen sulfide exposure

Acute exposure to high concentrations of H₂S causes severe brain injury and long-term neurological disorders, but the mechanisms involved are not known. To better understand the cellular and molecular mechanisms involved in acute H₂S-induced neurodegeneration we used a broad-spectrum proteomic analysis approach to identify key molecules and molecular pathways involved in the pathogenesis of acute H₂S-induced neurotoxicity and neurodegeneration. Mice were subjected to acute inhalation exposure of up to750 ppm of H₂S. H₂S induced behavioral deficits and severe lesions including hemorrhage in the inferior colliculus (IC). The IC was microdissected for proteomic analysis. Tandem mass tags (TMT) liquid chromatography mass spectrometry (LC-MS/MS)-based quantitative proteomics was applied for protein identification and quantitation. LC-MS/MS identified 598, 562, and 546 altered proteomic changes at 2 h, and on days 2 and 4 post-H₂S exposure, respectively. Of these, 77 proteomic changes were statistically significant at any of the 3 time points. Mass spectrometry data were subjected to Perseus 1.5.5.3 statistical analysis, and gene ontology heat map clustering. Expressions of several key molecules were verified to confirm H₂S-dependent proteomics changes. Webgestalt pathway overrepresentation enrichment analysis with Panther engine revealed H₂S exposure disrupted several biological processes including metabotropic glutamate receptor group 1 and inflammation mediated by chemokine and cytokine signaling pathways among others. Further analysis showed that energy metabolism, integrity of blood-brain barrier, hypoxic, and oxidative stress signaling pathways were also implicated. Collectively, this broad-spectrum proteomics data has provided important clues to follow up in future studies to further elucidate mechanisms of H₂S-induced neurotoxicity.

A timeline of hydrogen sulfide (H2S) research: From environmental toxin to biological mediator

The history of H2S - as an environmental toxin - dates back to 1700, to the observations of the Italian physician Bernardino Ramazzini, whose book "De Morbis Artificum Diatriba" described the painful eye irritation and inflammation of "sewer gas" in sewer workers. The gas has subsequently been identified as hydrogen sulfide (H2S), and opened three centuries of research into the biological roles of H2S. The current article highlights the key discoveries in the field of H2S research, including (a) the toxicological studies, which characterized H2S as an environmental toxin, and identified some of its modes of action, including the inhibition of mitochondrial respiration; (b) work in the field of bacteriology, which, starting in the early 1900s, identified H2S as a bacterial product - with subsequently defined roles in the regulation of periodontal disease (oral bacterial flora), intestinal epithelial cell function (enteral bacterial flora) as well as in the regulation of bacterial resistance to antibiotics; and (c), work in diverse fields of mammalian biology, which, starting in the 1940s, identified H2S as an endogenous mammalian enzymatic product, the functions of which - among others, in the cardiovascular and nervous system - have become subjects of intensive investigation for the last decade. The current review not only enumerates the key discoveries related to H2S made over the last three centuries, but also compiles the most frequently cited papers in the field which have been published over the last decade and highlights some of the current 'hot topics' in the field of H2S biology.

Midazolam Efficacy Against Acute Hydrogen Sulfide-Induced Mortality and Neurotoxicity

Hydrogen sulfide (H₂S) is a colorless, highly neurotoxic gas. It is not only an occupational and environmental hazard but also of concern to the Department of Homeland Security for potential nefarious use. Acute high-dose H₂S exposure causes death, while survivors may develop neurological sequelae. Currently, there is no suitable antidote for treatment of acute H₂S-induced neurotoxicity. Midazolam (MDZ), an anti-convulsant drug recommended for treatment of nerve agent intoxications, could also be of value in treating acute H₂S intoxication. In this study, we tested the hypothesis that MDZ is effective in preventing/treating acute H₂S-induced neurotoxicity. This proof-of-concept study had two objectives: to determine whether MDZ prevents/reduces H₂S-induced mortality and to test whether MDZ prevents H₂S-induced neurological sequelae. MDZ (4 mg/kg) was administered IM in mice, 5 min pre-exposure to a high concentration of H₂S at 1000 ppm or 12 min post-exposure to 1000 ppm H₂S followed by 30 min of continuous exposure. A separate experiment tested whether MDZ pre-treatment prevented neurological sequelae. Endpoints monitored included assessment of clinical signs, mortality, behavioral changes, and brain histopathological changes. MDZ significantly reduced H₂S-induced lethality, seizures, knockdown, and behavioral deficits (p < 0.01). MDZ also significantly prevented H₂S-induced neurological sequelae, including weight loss, behavior deficits, neuroinflammation, and histopathologic lesions (p < 0.01). Overall, our findings show that MDZ is a promising drug for reducing H₂S-induced acute mortality, neurotoxicity, and neurological sequelae.

Gypsum in animal slurry systems enhances generation of hydrogen sulphide and increases occupational exposure hazard

Hydrogen sulphide gas (H₂S) produced by sulphate reducing bacteria (SRB) in stored animal slurry is highly toxic and, if emitted into poorly ventilated confined spaces, can build up to concentrations capable of causing asphyxiation. Therefore it is important to understand factors influencing H₂S emission from slurry. Powdered gypsum (hydrated calcium sulphate) may be used as animal bedding and, if it enters slurry systems, could be metabolised by SRB and further increase H₂S generation. Cattle slurry and cattle bedding collected from farms was used in laboratory-scale experiments sealed in 20litre vessels fitted with mechanical stirrers. H₂S was monitored in head space above the slurry using real-time gas detectors before and after stirring, and before and after adding 1% of two sources of gypsum powder. In one set of experiments, gypsum was already present in the slurry having been used in bedding on the farm. H₂S monitoring continued daily for up to 25days. Before stirring, H₂S levels in head spaces were minimal. After stirring, even without gypsum, maximum head space H₂S levels with slurry or bedding ranged from 330 to 1190ppm. By comparison, the UK short-term (15min) Workplace Exposure Limit is 10ppm. Statistically significant increases in H₂S levels were associated with gypsum addition, as high as 1772ppm with slurry and 3940ppm with bedding. Emissions peaked at around day 15 with slurry and bedding to which gypsum was freshly added, but within 5days when added to slurry already containing farm-added gypsum. Levels of H₂S produced from stirred slurry would constitute a hazard to anyone exposed to it, and adding gypsum further increased emission levels. Therefore, if gypsum residues enter slurry it could increase the risk of H₂S accumulation in confined spaces associated with slurry systems. It is important therefore to take this into account in managing risk.

Cobinamide is effective for treatment of hydrogen sulfide-induced neurological sequelae in a mouse model

Hydrogen sulfide (H2 S) is a highly neurotoxic gas. Acute exposure can lead to neurological sequelae among survivors. A drug for treating neurological sequelae in survivors of acute H2 S intoxication is needed. Using a novel mouse model we evaluated the efficacy of cobinamide (Cob) for increasing survival of, and reducing neurological sequalae in, mice exposed to sublethal doses of H2 S. There were two objectives: (1) to determine the dose-response efficacy of Cob and (2) to determine the effective therapeutic time window of Cob. To explore objective 1, mice were injected intramuscularly with Cob at 0, 50, or 100 mg/kg at 2 min after H2 S exposure. For objective 2, mice were injected intramuscularly with 100 mg/kg Cob at 2, 15, and 30 min after H2 S exposure. For both objectives, mice were exposed to 765 ppm of H2 S gas. Cob significantly reduced H2 S-induced lethality in a dose-dependent manner (P < 0.05). Cob-treated mice exhibited significantly fewer seizures and knockdowns compared with the H2 S-exposed group. Cob also reversed H2 S-induced weight loss, behavioral deficits, neurochemical changes, cytochrome c oxidase enzyme inhibition, and neurodegeneration in a dose- and time-dependent manner (P < 0.01). Overall, these findings show that Cob increases survival and is neuroprotective in a mouse model of H2 S-induced neurological sequelae.

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.

Efficacy of Intravenous Cobinamide Versus Hydroxocobalamin or Saline for Treatment of Severe Hydrogen Sulfide Toxicity in a Swine (Sus scrofa) Model

BACKGROUND

Hydrogen sulfide (H₂ S) is a potentially deadly gas that naturally occurs in petroleum and natural gas. The Occupational Health and Safety Administration cites H₂ S as a leading cause of workplace gas inhalation deaths. Mass casualties of H₂ S toxicity may be caused by exposure from industrial accidents or release from oil field sites. H₂ S is also an attractive terrorism tool because of its high toxicity and ease with which it can be produced. Several potential antidotes have been proposed for hydrogen sulfide poisoning but none have been completely successful.

OBJECTIVE

The objective was to compare treatment response assessed by the time to spontaneous ventilation among groups of swine with acute H₂ S-induced apnea treated with intravenous (IV) cobinamide (4 mg/kg in 0.8 mL of 225 mmol/L solution), IV hydroxocobalamin (4 mg/kg in 5 mL of saline), or saline alone.

METHODS

Twenty-four swine (45-55 kg) were anesthetized, intubated, and instrumented with continuous femoral and pulmonary artery pressure monitoring. After stabilization, anesthesia was adjusted such that animals would spontaneously ventilate with an FiO₂ of 0.21. Sodium hydrosulfide (NaHS; concentration of 8 mg/mL) was begun at 1 mg/kg/min until apnea was confirmed for 20 seconds by capnography. This infusion rate was sustained for 1.5 minutes postapnea and then decreased to a maintenance rate for the remainder of the study to replicate sustained clinical exposure. Animals were randomly assigned to receive cobinamide (4 mg/kg), hydroxocobalamin (4 mg/kg), or saline and monitored for 60 minutes beginning 1 minute postapnea. G* power analysis using the Z-test determined that equal group sizes of eight animals were needed to achieve a power of 80% in detecting a 50% difference in return to spontaneous ventilations at α = 0.05.

RESULTS

There were no significant differences in baseline variables. Moreover, there were no significant differences in the mg/kg dose of NaHS (5.6 mg/kg; p = 0.45) required to produce apnea. Whereas all of the cobinamide-treated animals survived (8/8), none of the control (0/8) or hydroxocobalamin (0/8)-treated animals survived. Mean (±SD) time to spontaneous ventilation in the cobinamide-treated animals was 3.2 (±1.1) minutes.

CONCLUSIONS

Cobinamide successfully rescued the severely NaHS-poisoned swine from apnea in the absence of assisted ventilation.

A rapid evaluation of acute hydrogen sulfide poisoning in blood based on DNA-Cu/Ag nanocluster fluorescence probe

Hydrogen sulfide (H₂S) is a highly toxic gas as a cause of inhalational death. Accurate detection of H₂S poisoning concentration is valuable and vital for forensic workers to estimate the cause of death. But so far, it is no uniform and reliable standard method to measure sulfide concentrations in H₂S poisoning blood for forensic identification. This study introduces a fluorescence sensing technique into forensic research, in which a DNA-templated copper/silver nanocluster (DNA-Cu/AgNCs) fluorescence probe has been proposed to selective detection of S^2-. Under an optimized condition, the proposed method can allow for determination of S^2- in the concentration range of 10 pM to 1 mM with a linear equation: y = -0.432 lg[S^2-] + 0.675 (R² = 0.9844), with the limit of detection of 3.75 pM. Moreover, acute H₂S poisoning mouse models were established by intraperitoneally injected different doses of Na₂S, and the practical feasibility of the proposed fluorescence sensor has been demonstrated by 35 poisoning blood samples. This proposed method is proved to be quite simple and straightforward for the detection of H₂S poisoning blood. Also it may provide a basis for sulfide metabolizing study in body, and it would be meaningful to further push forensic toxicology identification and clinical laboratory research.

Characterizing a mouse model for evaluation of countermeasures against hydrogen sulfide-induced neurotoxicity and neurological sequelae

Hydrogen sulfide (H₂ S) is a highly neurotoxic gas. It is the second most common cause of gas-induced deaths. Beyond mortality, surviving victims of acute exposure may suffer long-term neurological sequelae. There is a need to develop countermeasures against H₂ S poisoning. However, no translational animal model of H₂ S-induced neurological sequelae exists. Here, we describe a novel mouse model of H₂ S-induced neurotoxicity for translational research. In paradigm I, C57/BL6 mice were exposed to 765 ppm H₂ S for 40 min on day 1, followed by 15-min daily exposures for periods ranging from 1 to 6 days. In paradigm II, mice were exposed once to 1000 ppm H₂ S for 60 minutes. Mice were assessed for behavioral, neurochemical, biochemical, and histopathological changes. H₂ S intoxication caused seizures, dyspnea, respiratory depression, knockdowns, and death. H₂ S-exposed mice showed significant impairment in locomotor and coordinated motor movement activity compared with controls. Histopathology revealed neurodegenerative lesions in the collicular, thalamic, and cortical brain regions. H₂ S significantly increased dopamine and serotonin concentration in several brain regions and caused time-dependent decreases in GABA and glutamate concentrations. Furthermore, H₂ S significantly suppressed cytochrome c oxidase activity and caused significant loss in body weight. Overall, male mice were more sensitive than females. This novel translational mouse model of H₂ S-induced neurotoxicity is reliable, reproducible, and recapitulates acute H₂ S poisoning in humans.

Lens Opacity and Hydrogen Sulfide in a New Zealand Geothermal Area

PURPOSE

Hydrogen sulfide (H2S) is a highly toxic gas with well-established, acute irritation effects on the eye. The population of Rotorua, New Zealand, sited on an active geothermal field, has some of the highest ambient H2S exposures in the world. Evidence from ecological studies in Rotorua has suggested that H2S is associated with cataract. The purpose of the present study was, using more detailed exposure characterization, clinical examinations, and anterior eye photography, to more directly investigate this previously reported association.

METHODS

Enrolled were 1637 adults, ages 18 to 65, from a comprehensive Rotorua primary care medical register. Patients underwent a comprehensive ophthalmic examination, including pupillary dilation and lens photography to capture evidence of any nuclear opacity, nuclear color, and cortical and posterior subcapsular opacity. Photographs were scored for all four outcomes on the LOCS III scale with decimalized interpolation between the exemplars. H2S exposure for up to the last 30 years was estimated based on networks of passive samplers set out across Rotorua and knowledge of residential, workplace, and school locations over the 30 years. Data analysis using linear and logistic regression examined associations between the degree of opacification and nuclear color or cataract (defined as a LOCS III score ≥2.0) in relation to H2S exposure.

RESULTS

No associations were found between estimated H2S exposures and any of the four ophthalmic outcome measures.

CONCLUSIONS

Overall, results were generally reassuring. They provided no evidence that H2S exposure at the levels found in Rotorua is associated with cataract. The previously found association between cataract and H2S exposure in the Rotorua population seems likely to be attributable to the limitations of the ecological study design. These results cannot rule out the possibility of an association with cataract at higher levels of H2S exposure.

Ambient geothermal hydrogen sulfide exposure and peripheral neuropathy

The mechanism of toxicity of hydrogen sulfide (H₂S) gas is thought mainly to operate through effects on the nervous system. The gas has high acute toxicity, but whether chronic exposure causes effects, including peripheral neuropathy, is yet unclear. The city of Rotorua, New Zealand, sits on an active geothermal field and the population has some of the highest measured ambient H₂S exposures. A previous study in Rotorua provided evidence that H₂S is associated with peripheral neuropathy. Using clinical methods, the present study sought to investigate and possibly confirm this association in the Rotorua population. The study population comprised 1635 adult residents of Rotorua, aged 18-65. Collected data relevant to the peripheral neuropathy investigation included symptoms, ankle stretch reflex, vibration sensitivity, as measured by the timed-tuning fork test and a Bio-Thesiometer (Bio-Medical Instrument Co., Ohio), and light touch sensitivity measured by monofilaments. An exposure metric, estimating time-weighted H₂S exposure across the last 30 years was used. Principal components analysis was used to combine data across the various indicators of possible peripheral neuropathy. The main data analysis used linear regression to examine associations between the peripheral nerve function indicators and H₂S exposure. None of the peripheral nerve function indicators were associated with H₂S exposure, providing no evidence that H₂S exposure at levels found in Rotorua is a cause of peripheral neuropathy. The earlier association between H₂S exposure and peripheral neuropathy diagnoses may be attributable to the ecological study design used. The possibility that H₂S exposure misclassification could account for the lack of association found cannot be entirely excluded.