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

Which Environmental Pollutants Are Toxic to Our Ears?-Evidence of the Ototoxicity of Common Substances

Ototoxicity refers to the adverse effects of substances on auditory or vestibular functions. This study examines the evidence of ototoxicity's association with exposure to common environmental pollutants, as documented in toxicological profiles by the Agency for Toxic Substances and Disease Registry. Our aim was to evaluate whether the evidence supports modifying the charting of ototoxic effects in the summary tables of these toxicological profiles and providing a guide for scientists to access these data. Health outcomes of interest included hearing loss, vestibular effects, cochlear lesions, tonal alterations, cellular damage, and ototoxicity-related outcomes (neurological, nephrotoxic, hepatic, and developmental effects). We obtained ototoxicity information for 62 substances. Hearing-related effects were reported, along with neurological effects. Overall, 26 profiles reported strong evidence of ototoxicity, including 13 substances previously designated as ototoxic by other health and safety agencies. Commonly studied outcomes included hearing loss, damage to ear anatomy, and auditory dysfunction. Vestibular dysfunction and tinnitus are rarely studied. Our findings highlight the lack of conclusive evidence of ototoxic properties for many substances, especially for pesticides and herbicides. This review supports charting the evidence of ototoxicity separately in toxicological profiles' summary tables. Improving the communication of ototoxicity-related health effects might impact their recognition and prompt further research. A stronger evidence base could support improved prevention efforts in terms of serious health outcomes.

Role of hydrogen sulfide in health and disease

In the past, hydrogen sulfide (H2S) was recognized as a toxic and dangerous gas; in recent years, with increased research, we have discovered that H2S can act as an endogenous regulatory transmitter. In mammals, H2S-catalyzing enzymes, such as cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase, are differentially expressed in a variety of tissues and affect a variety of biological functions, such as transcriptional and posttranslational modification of genes, activation of signaling pathways in the cell, and metabolic processes in tissues, by producing H2S. Various preclinical studies have shown that H2S affects physiological and pathological processes in the body. However, a detailed systematic summary of these roles in health and disease is lacking. Therefore, this review provides a thorough overview of the physiological roles of H2S in different systems and the diseases associated with disorders of H2S metabolism, such as ischemia-reperfusion injury, hypertension, neurodegenerative diseases, inflammatory bowel disease, and cancer. Meanwhile, this paper also introduces H2S donors and novel release modes, as well as the latest preclinical experimental results, aiming to provide researchers with new ideas to discover new diagnostic targets and therapeutic options.

Central sleep apnea and exposure to ambient hydrogen sulfide emissions from massive strandings of decomposing sargassum in the Caribbean

BACKGROUND

Sargassum invasion of Caribbean and American shorelines is a recurring environmental hazard. Potential health effects of long-term chronic exposure to sargassum gaseous emissions, notably hydrogen sulfide (H2S), are overlooked. H2S plays an important role in neurotransmission and is involved in generating and transmitting respiratory rhythm. Central sleep apnea (CSA) has been attributed to the depression of respiratory centers.

OBJECTIVE

Evaluate the effects of exposure to sargassum-H2S on CSA.

METHODS

This study, set in the Caribbean, describes the clinical and polysomnographic characteristics of individuals living and/or working in areas impacted by sargassum strandings, in comparison with non-exposed subjects. Environmental exposure was estimated by the closest ground H2S sensor. Multivariate linear regression was applied to analyze CSA changes according to cumulative H2S exposure over time. Effects of air pollution and other sargassum toxic compounds (NH3) on CSA were also controlled.

RESULTS

Among the 685 study patients, 27 % were living and/or working in sargassum impacted areas. Compared with non-exposed patients, exposed ones had similar sleep apnea syndrome risk factors, but had increased levels of CSA events (expressed as absolute number or % of total sleep apnea). Multivariate regression retained only male gender and mean H2S concentration over a 6-month exposure period as independent predictors of an increase in CSA events. A minimal exposure length of 1 month generated a significant rise in CSA events, with the latter increasing proportionally with a cumulative increase in H2S concentration over time.

CONCLUSION

This pioneer work highlights a potential effect of sargassum-H2S on the central nervous system, notably on the modulation of the activity of the brain's respiratory control center. These observations, jointly with previous studies from our group, constitute a body of evidence strongly supporting a deleterious effect of sargassum-H2S on the health of individuals chronically exposed to low to moderate concentration levels over time.

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.

Highly Selective and Fast Response/Recovery Cataluminescence Sensor Based on SnO2 for H2S Detection

In the present work, three kinds of nanosized SnO2 samples were successfully synthesized via a hydrothermal method with subsequent calcination at temperatures of 500 °C, 600 °C, and 700 °C. The morphology and structure of the as-prepared samples were characterized using X-ray diffraction, transmission electron microscopy, selected area electron diffraction, Brunauer-Emmett-Teller analysis, and X-ray photoelectron spectroscopy. The results clearly indicated that the SnO2 sample calcined at 600 °C had a higher amount of chemisorbed oxygen than the SnO2 samples calcined at 500 °C and 700 °C. Gas sensing investigations revealed that the cataluminescence (CTL) sensors based on the three SnO2 samples all exhibited high selectivity toward H2S, but the sensor based on SnO2-600 °C exhibited the highest response under the same conditions. At an operating temperature of 210 °C, the SnO2-600 °C sensor showed a good linear response to H2S in the concentration range of 20-420 ppm, with a detection limit of 8 ppm. The response and recovery times were 3.5 s/1.5 s for H2S gas within the linear range. The study on the sensing mechanism indicated that H2S was oxidized into excited states of SO2 by chemisorbed oxygen on the SnO2 surface, which was mainly responsible for CTL emission. The chemisorbed oxygen played an important role in the oxidation of H2S, and, as such, the reason for the SnO2-600 °C sensor showing the highest response could be ascribed to the highest amount of chemisorbed oxygen on its surface. The proposed SnO2-based gas sensor has great potential for the rapid monitoring of H2S.

Hydrogen sulfide and its donors for the treatment of cerebral ischaemia-reperfusion injury: A comprehensive review

As an endogenous gas signalling molecule, hydrogen sulfide (H₂S) is frequently present in a variety of mammals and plays a significant role in the cardiovascular and nervous systems. Reactive oxygen species (ROS) are produced in large quantities as a result of cerebral ischaemia-reperfusion, which is a very serious class of cerebrovascular diseases. ROS cause oxidative stress and induce specific gene expression that results in apoptosis. H₂S reduces cerebral ischaemia-reperfusion-induced secondary injury via anti-oxidative stress injury, suppression of the inflammatory response, inhibition of apoptosis, attenuation of cerebrovascular endothelial cell injury, modulation of autophagy, and antagonism of P2X7 receptors, and it plays an important biological role in other cerebral ischaemic injury events. Despite the many limitations of the hydrogen sulfide therapy delivery strategy and the difficulty in controlling the ideal concentration, relevant experimental evidence demonstrating that H₂S plays an excellent neuroprotective role in cerebral ischaemia-reperfusion injury (CIRI). This paper examines the synthesis and metabolism of the gas molecule H₂S in the brain as well as the molecular mechanisms of H₂S donors in cerebral ischaemia-reperfusion injury and possibly other unknown biological functions. With the active development in this field, it is expected that this review will assist researchers in their search for the potential value of hydrogen sulfide and provide new ideas for preclinical trials of exogenous H₂S.