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

Metabolomic Signatures of Brainstem in Mice following Acute and Subchronic Hydrogen Sulfide Exposure

Hydrogen sulfide (H2S) is an environmental toxicant of significant health concern. The brain is a major target in acute H2S poisoning. This study was conducted to test the hypothesis that acute and subchronic ambient H2S exposures alter the brain metabolome. Male 7-8-week-old C57BL/6J mice were exposed by whole-body inhalation to 1000 ppm H2S for 45 min and euthanized at 5 min or 72 h for acute exposure. For subchronic study, mice were exposed to 5 ppm H2S 2 h/day, 5 days/week for 5 weeks. Control mice were exposed to room air. The brainstem was removed for metabolomic analysis. Enrichment analysis showed that the metabolomic profiles in acute and subchronic H2S exposures matched with those of cerebral spinal fluid from patients with seizures or Alzheimer's disease. Acute H2S exposure decreased excitatory neurotransmitters, aspartate, and glutamate, while the inhibitory neurotransmitter, serotonin, was increased. Branched-chain amino acids and glucose were increased by acute H2S exposure. Subchronic H2S exposure within OSHA guidelines surprisingly decreased serotonin concentration. In subchronic H2S exposure, glucose was decreased, while polyunsaturated fatty acids, inosine, and hypoxanthine were increased. Collectively, these results provide important mechanistic clues for acute and subchronic ambient H2S poisoning and show that H2S alters brainstem metabolome.

Disrupted brain mitochondrial morphology after in vivo hydrogen sulfide exposure

Changes in mitochondrial dynamics are often associated with dietary patterns, medical treatments, xenobiotics, and diseases. Toxic exposures to hydrogen sulfide (H2S) harm mitochondria by inhibiting Complex IV and via other mechanisms. However, changes in mitochondrial dynamics, including morphology following acute exposure to H2S, are not yet fully understood. This study followed mitochondrial morphology changes over time after a single acute LCt50 dose of H2S by examining electron microscopy thalami images of surviving mice. Our findings revealed that within the initial 48 h after H2S exposure, mitochondrial morphology was impaired by H2S, supported by the disruption and scarcity of the cristae, which are required to enhance the surface area for ATP production. At the 72-h mark point, a spectrum of morphological cellular changes was observed, and the disordered mitochondrial network, accompanied by the probable disruption of mitophagy, was tied to changes in mitochondrial shape. In summary, this study sheds light on how acute exposure to high levels of H2S triggers alterations in mitochondrial shape and structure as early as 24 h that become more evident at 72 h post-exposure. These findings underscore the impact of H2S on mitochondrial function and overall cellular health.

Investigations into hydrogen sulfide-induced suppression of neuronal activity in vivo and calcium dysregulation in vitro

Acute exposure to high concentrations of hydrogen sulfide (H2S) leads to sudden death and, if survived, lingering neurological disorders. Clinical signs include seizures, loss of consciousness, and dyspnea. The proximate mechanisms underlying H2S-induced acute toxicity and death have not been clearly elucidated. We investigated electrocerebral, cardiac and respiratory activity during H2S exposure using electroencephalogram (EEG), electrocardiogram (EKG) and plethysmography. H2S suppressed electrocerebral activity and disrupted breathing. Cardiac activity was comparatively less affected. To test whether Ca2+ dysregulation contributes to H2S-induced EEG suppression, we developed an in vitro real-time rapid throughput assay measuring patterns of spontaneous synchronized Ca2+ oscillations in cultured primary cortical neuronal networks loaded with the indicator Fluo-4 using the fluorescent imaging plate reader (FLIPR-Tetra®). Sulfide >5 ppm dysregulated synchronous calcium oscillation (SCO) patterns in a dose-dependent manner. Inhibitors of NMDA and AMPA receptors magnified H2S-induced SCO suppression. Inhibitors of L-type voltage gated Ca2+ channels and transient receptor potential channels prevented H2S-induced SCO suppression. Inhibitors of T-type voltage gated Ca2+ channels, ryanodine receptors, and sodium channels had no measurable influence on H2S-induced SCO suppression. Exposures to > 5 ppm sulfide also suppressed neuronal electrical activity in primary cortical neurons measured by multi-electrode array (MEA), an effect alleviated by pretreatment with the nonselective transient receptor potential channel inhibitor, 2-APB. 2-APB also reduced primary cortical neuronal cell death from sulfide exposure. These results improve our understanding of the role of different Ca2+ channels in acute H2S-induced neurotoxicity and identify transient receptor potential channel modulators as novel structures with potential therapeutic benefits.

A comprehensive review of treatments for hydrogen sulfide poisoning: past, present, and future

Hydrogen sulfide (H₂S) poisoning remains a significant source of occupational fatalities and is the second most common cause of toxic gas-induced deaths. It is a rapidly metabolized systemic toxicant targeting the mitochondria, among other organelles. Intoxication is mostly acute, but chronic or in-between exposure scenarios also occur. Some genetic defects in H₂S metabolism lead to lethal chronic H₂S poisoning. In acute exposures, the neural, respiratory, and cardiovascular systems are the primary target organs resulting in respiratory distress, convulsions, hypotension, and cardiac irregularities. Some survivors of acute poisoning develop long-term sequelae, particularly in the central nervous system. Currently, treatment for H₂S poisoning is primarily supportive care as there are no FDA-approved drugs. Besides hyperbaric oxygen treatment, drugs in current use for the management of H₂S poisoning are controversial. Novel potential drugs are under pre-clinical research development, most of which target binding the H₂S. However, there is an acute need to discover new drugs to prevent and treat H₂S poisoning, including reducing mortality and morbidity, preventing sequalae from acute exposures, and for treating cumulative pathology from chronic exposures. In this paper, we perform a comprehensive review of H₂S poisoning including perspectives on past, present, and future.

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.

Treatment of life-threatening H2S intoxication: Lessons from the trapping agent tetranitrocobinamide

We sought to evaluate the efficacy of trapping free hydrogen sulfide (H2S) following severe H2S intoxication. Sodium hydrosulfide solution (NaHS, 20 mg/kg) was administered intraperitoneally in 69 freely moving rats. In a first group (protocol 1), 40 rats were randomly assigned to receive saline (n = 20) or the cobalt compound tetranitrocobinamide (TNCbi) (n = 20, 75 mg/kg iv), one minute into coma, when free H2S was still present in the blood. A second group of 27 rats received TNCbi or saline, following epinephrine, 5 min into coma, when the concentration of free H2S has drastically decreased in the blood. In protocol 1, TNCbi significantly increased immediate survival (65 vs 20 %, p < 0.01) while in protocol 2, administration of TNCbi led to the same outcome as untreated animals. We hypothesize that the decreased efficacy of TNCbi with time likely reflects the rapid spontaneous disappearance of the pool of free H2S in the blood following H2S exposure.

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.

A Sulfonyl Azide-Based Sulfide Scavenger Rescues Mice from Lethal Hydrogen Sulfide Intoxication

Exposure to hydrogen sulfide (H2S) can cause neurotoxicity and cardiopulmonary arrest. Resuscitating victims of sulfide intoxication is extremely difficult, and survivors often exhibit persistent neurological deficits. However, no specific antidote is available for sulfide intoxication. The objective of this study was to examine whether administration of a sulfonyl azide-based sulfide-specific scavenger, SS20, would rescue mice in models of H2S intoxication: ongoing exposure and post-cardiopulmonary arrest. In the ongoing exposure model, SS20 (1,250 µmol/kg) or vehicle was administered to awake CD-1 mice intraperitoneally at 10 minutes after breathing 790 ppm of H2S followed by another 30 minutes of H2S inhalation. Effects of SS20 on survival was assessed. In the post-cardiopulmonary arrest model, cardiopulmonary arrest was induced by an intraperitoneal administration of sodium sulfide nonahydrate (125 mg/kg) in anesthetized mice. After 1 minute of cardiopulmonary arrest, mice were resuscitated with intravenous administration of SS20 (250 µmol/kg) or vehicle. Effects of SS20 on survival, neurological outcomes, and plasma H2S levels were evaluated. Administration of SS20 during ongoing H2S inhalation improved 24-hour survival (6/6 [100%] in SS20 versus 1/6 [17%] in vehicle; P = 0.0043). Post-arrest administration of SS20 improved 7-day survival (4/10 [40%] in SS20 versus 0/10 [0%] in vehicle; P = 0.0038) and neurological outcomes after resuscitation. SS20 decreased plasma H2S levels to pre-arrest baseline immediately after reperfusion and shortened the time to return of spontaneous circulation and respiration. The current results suggest that SS20 is an effective antidote against lethal H2S intoxication, even when administered after cardiopulmonary arrest.

Behavioral and Neuronal Effects of Inhaled Bromine Gas: Oxidative Brain Stem Damage

The risk of accidental bromine (Br2) exposure to the public has increased due to its enhanced industrial use. Inhaled Br2 damages the lungs and the heart; however, adverse effects on the brain are unknown. In this study, we examined the neurological effects of inhaled Br2 in Sprague Dawley rats. Rats were exposed to Br2 (600 ppm for 45 min) and transferred to room air and cage behavior, and levels of glial fibrillary acidic protein (GFAP) in plasma were examined at various time intervals. Bromine exposure resulted in abnormal cage behavior such as head hitting, biting and aggression, hypervigilance, and hyperactivity. An increase in plasma GFAP and brain 4-hydroxynonenal (4-HNE) content also was observed in the exposed animals. Acute and delayed sympathetic nervous system activation was also evaluated by assessing the expression of catecholamine biosynthesizing enzymes, tryptophan hydroxylase (TrpH1 and TrpH2), and tyrosine hydroxylase (TyrH), along with an assessment of catecholamines and their metabolites. TyrH was found to be increased in a time-dependent manner. TrpH1 and TrpH2 were significantly decreased upon Br2 exposure in the brainstem. The neurotransmitter content evaluation indicated an increase in 5-HT and dopamine at early timepoints after exposure; however, other metabolites were not significantly altered. Taken together, our results predict brain damage and autonomic dysfunction upon Br2 exposure.

Synthesis, Optimization, and Biological Evaluation of Corrinated Conjugates of the GLP-1R Agonist Exendin-4

Corrination is the conjugation of a corrin ring containing molecule, such as vitamin B₁₂ (B12) or B12 biosynthetic precursor dicyanocobinamide (Cbi), to small molecules, peptides, or proteins with the goal of modifying pharmacology. Recently, a corrinated GLP-1R agonist (GLP-1RA) exendin-4 (Ex4) has been shown in vivo to have reduced penetration into the central nervous system relative to Ex4 alone, producing a glucoregulatory GLP-1RA devoid of anorexia and emesis. The study herein was designed to optimize the lead conjugate for GLP-1R agonism and binding. Two specific conjugation sites were introduced in Ex4, while also utilizing various linkers, so that it was possible to identify Cbi conjugates of Ex4 that exhibit improved binding and agonist activity at the GLP-1R. An optimized conjugate (22), comparable with Ex4, was successfully screened and subsequently assayed for insulin secretion in rat islets and in vivo in shrews for glucoregulatory and emetic behavior, relative to Ex4.

Pre-exposure to hydrogen sulfide modulates the innate inflammatory response to organic dust

Animal production units produce and store many contaminants on-site, including organic dust (OD) and hydrogen sulfide (H₂S). Workers in these settings report various respiratory disease symptoms. Both OD and H₂S have shown to induce lung inflammation. However, impact of co-exposure to both H₂S and OD has not been investigated. Therefore, we tested a hypothesis that pre-exposure to H₂S modulates the innate inflammatory response of the lungs to organic dust. In a mouse model of H₂S and organic dust extract (ODE) exposure, we assessed lung inflammation quantitatively. We exposed human airway epithelial and monocytic cells to medium or H₂S alone or H₂S followed by ODE and measured cell viability, oxidative stress, and other markers of inflammation. Exposure to 10 ppm H₂S followed by ODE increased the lavage fluid leukocytes. However, exposure to 10 ppm H₂S alone resulted in changes in tight junction proteins, an increase in mRNA levels of tlr2 and tlr4 as well as ncf1, ncf4, hif1α, and nrf2. H₂S alone or H₂S and ODE exposure decreased cell viability and increased reactive nitrogen species production. ODE exposure increased the transcripts of tlr2 and tlr4 in both in vitro and in vivo models, whereas increased nfkbp65 transcripts following exposure to ODE and H₂S was seen only in in vitro model. H₂S alone and H₂S followed by ODE exposure increased the levels of IL-1β. We conclude that pre-exposure to H₂S modulates lung innate inflammatory response to ODE.

Comparison of MS2, synchronous precursor selection MS3, and real-time search MS3 methodologies for lung proteomes of hydrogen sulfide treated swine

Tandem mass tags (TMTs) have increasingly become an attractive technique for global proteomics. However, its effectiveness for multiplexed quantitation by traditional tandem mass spectrometry (MS²) suffers from ratio distortion. Synchronous precursor selection (SPS) MS³ has been widely accepted for improved quantitation accuracy, but concurrently decreased proteome coverage. Recently, a Real-Time Search algorithm has been integrated with the SPS MS³ pipeline (RTS MS³) to provide accurate quantitation and improved depth of coverage. In this mechanistic study of the impact of exposure to hydrogen sulfide (H₂S) on the respiration of swine, we used TMT-based comparative proteomics of lung tissues from control and H₂S-treated subjects as a test case to evaluate traditional MS², SPS MS³, and RTS MS³ acquisition methods on both the Orbitrap Fusion and Orbitrap Eclipse platforms. Comparison of the results obtained by the MS² with those of SPS MS³ and RTS MS³ methods suggests that the MS³-driven quantitative strategies provided a more accurate global-scale quantitation; however, only RTS MS³ provided proteomic coverage that rivaled that of traditional MS² analysis. RTS MS³ not only yields more productive MS³ spectra than SPS MS³ but also appears to focus the analysis more effectively on unique peptides. Furthermore, pathway enrichment analyses of the H₂S-altered proteins demonstrated that an additional apoptosis pathway was discovered exclusively by RTS MS³. This finding was verified by RT-qPCR, western blotting, and TUNEL staining experiments. We conclude that RTS MS³ workflow enables simultaneous improvement of quantitative accuracy and proteome coverage over alternative approaches (MS² and SPS MS³). Graphical abstract.

Acute myocardial injury following hydrogen sulfide poisoning

BACKGROUND

Hydrogen sulfide poisoning can cause severe myocardial injury, but the damage is subtle and can be easily misdiagnosed. This report presents the dynamic observation of myocardial injury associated with hydrogen sulfide poisoning.

CASE REPORT

Two young men presented with symptoms of "lightning-like" death immediately after entering a tank. They were found and rescued in 20 min at a time when they were already in a coma. Case 1 had no spontaneous breathing and pulse, while case 2 had spontaneous breathing and a pulse. Upon transfer to a local hospital, case 1 received continuous cardiopulmonary resuscitation which led to the recovery of his heart rate 3 min after arriving at the hospital. However, the patient remained in a Glasgow coma scale of 3. He was transferred to our hospital where he, unfortunately, died on the seventh day due to multiple organ failure. Case 2 was also transferred to the intensive care unit in our hospital and on the fourth day of hospitalization, the patient presented ST-segment elevation and dynamic changes in markers of myocardial injury. Changes in electrocardiogram and markers of myocardial injury were monitored and examination improved through conventional echocardiography, coronary artery CT, radionuclide myocardial perfusion imaging, and two-dimensional speckle tracking imaging strain. The treatment gradually improved the patient's myocardial injury and was discharged from the hospital.

CONCLUSION

Hydrogen sulfide poisoning can cause damage to myocardial function and the damage can be more insidious in nature and with a delayed onset. Recovery from myocardial damage can be very slow.

Intramuscular aminotetrazole cobinamide as a treatment for inhaled hydrogen sulfide poisoning in a large swine model

Hydrogen sulfide (H₂ S), a high-threat chemical agent, occurs naturally in a variety of settings. Despite multiple incidents of exposures and deaths, no FDA-approved antidote exists. A rapid-acting, easy to administer antidote is needed. We conducted a randomized control trial in swine comparing intramuscular administration of aminotetrazole cobinamide (2.9 mL, 18 mg/kg) to no treatment following inhalation of H₂ S gas. We found that aminotetrazole cobinamide administered 2 min after the onset of respiratory depression-defined as a tidal volume of less than 3 mL/kg for 2 consecutive minutes-yielded 100% survival, while all control animals died. Respiratory depression resolved in the treatment group within 3.6 ± 1.5 min (mean ± SD) of cobinamide administration, whereas control animals had intermittent gasping until death. Blood pressure and arterial oxygen saturation (SO₂ ) returned to baseline values within 5 and 10 min, respectively, of cobinamide treatment, and plasma lactate concentration decreased to less than 50% of the highest value by the end of the experiment. In control animals, plasma lactate rose continuously until death. We conclude that intramuscular aminotetrazole cobinamide is effective in a large animal, inhalational model of acute, severe H₂ S poisoning.

Intramuscular cobinamide versus saline for treatment of severe hydrogen sulfide toxicity in swine

INTRODUCTION

Hydrogen sulfide (H₂S) is found in petroleum, natural gas, and decaying organic matter. Terrorist groups have attempted to use it in enclosed spaces as a chemical weapon. Mass casualty scenarios have occurred from industrial accidents and release from oil field sites. There is no FDA approved antidote for sulfide poisoning. We have previously reported that intravenous cobinamide is effective for sulfide poisoning. A rapid-acting antidote that is easy to administer intramuscularly (IM) would be ideal for use in a prehospital setting. In this study, we assessed survival in sulfide-poisoned swine treated with IM cobinamide.

METHODS

Eleven 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 ventilated spontaneously with a FiO₂ of 0.21. Sodium hydrosulfide (NaHS, 8 mg/mL) was infused intravenously at 0.9 mg/kg.min until apnea or severe hypotension. Animals were randomly assigned to receive cobinamide (4 mg/kg), or no treatment at the apnea/hypotension trigger. The NaHS infusion rate was sustained for 1.5 min post trigger, decreased to 0.2 mg/kg.min for 10 min, and then discontinued.

RESULTS

The amount of NaHS required to produce apnea or hypotension was not statistically different in both groups (cobinamide: 9.0 mg/kg ±6.1; saline: 5.9 mg/kg ±5.5; mean difference: -3.1, 95% CI: -11.3, 5.0). All of the cobinamide treated animals survived (5/5), none of the control (0/6) animals survived (p < .01). Mean time to return to spontaneous ventilation in the cobinamide treated animals was 3.2 (±1.1) min. Time to return to baseline systolic blood pressure (±5%) in cobinamide-treated animals was 5 min.

CONCLUSION

Intramuscular cobinamide was effective in improving survival in this large swine model of severe hydrogen sulfide toxicity.

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.