Physiological and biochemical effects of acute exposure of fish to hydrogen sulfide

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.

Fast and slow releasing sulphide donors engender distinct transcriptomic alterations in Atlantic salmon hepatocytes

Hydrogen sulphide (H₂S) is a naturally occurring compound generated either endogenously or exogenously and serves both as a gaseous signalling molecule and an environmental toxicant. Though it has been extensively investigated in mammalian systems, the biological function of H₂S in teleost fish is poorly identified. Here we demonstrate how exogenous H₂S regulates cellular and molecular processes in Atlantic salmon (Salmo salar) using a primary hepatocyte culture as a model. We employed two forms of sulphide donors: the fast-releasing salt form, sodium hydrosulphide (NaHS) and the slow-releasing organic analogue, morpholin-4-ium 4-methoxyphenyl(morpholino) phosphinodithioate (GYY4137). Hepatocytes were exposed to either a low (LD, 20 µg/L) or high (HD, 100 µg/L) dose of the sulphide donors for 24 hrs, and the expression of key sulphide detoxification and antioxidant defence genes were quantified by qPCR. The key sulphide detoxification genes sulfite oxidase 1 (soux) and the sulfide: quinone oxidoreductase 1 and 2 (sqor) paralogs in salmon showed pronounced expression in the liver and likewise responsive to the sulphide donors in the hepatocyte culture. These genes were ubiquitously expressed in different organs of salmon as well. HD-GYY4137 upregulated the expression of antioxidant defence genes, particularly glutathione peroxidase, glutathione reductase and catalase, in the hepatocyte culture. To explore the influence of exposure duration, hepatocytes were exposed to the sulphide donors (i.e., LD versus HD) either transient (1h) or prolonged (24h). Prolonged but not transient exposure significantly reduced hepatocyte viability, and the effects were not dependent on concentration or form. The proliferative potential of the hepatocytes was only affected by prolonged NaHS exposure, and the impact was not concentration dependent. Microarray analysis revealed that GYY4137 caused more substantial transcriptomic changes than NaHS. Moreover, transcriptomic alterations were more marked following prolonged exposure. Genes involved in mitochondrial metabolism were downregulated by the sulphide donors, primarily in NaHS-exposed cells. Both sulphide donors influenced the immune functions of hepatocytes: genes involved in lymphocyte-mediated response were affected by NaHS, whereas inflammatory response was targeted by GYY4137. In summary, the two sulphide donors impacted the cellular and molecular processes of teleost hepatocytes, offering new insights into the mechanisms underlying H₂S interactions in fish.

Wind Impact Assessment of a Sour Gas Release in an Offshore Platform

Complex installations that involve dangerous substances, such as oil and gas or nuclear plants, must mandatorily undergo a quantitative risk assessment (QRA) according to current regulations. This requires, among others, the simulation of hundreds of accidental scenarios, which are typically carried out using empirical tools due to their fast response. Nonetheless, since they are not able to guarantee sufficient accuracy, especially when complex geometries are involved, computational fluid dynamics (CFD) tools are increasingly used. In this work, a high-pressure accidental release of a sour gas (CH4-H2S) in an offshore platform under several wind conditions is considered. A methodology used to perform a wind sensitivity analysis via CFD, while avoiding high computational costs, is presented. The wind intensity impact on some risk-related figures of merit, such as the high lethality or irreversible injuries areas, is discussed in relation to the flammability and toxicity limits of the released mixture. The results show that even a very low amount of H2S in the released mixture can strongly affect the threat zones. A progressive decrease in the toxic and flammable volumes in the platform is observed as the wind velocity increases; nonetheless, a saturation effect appears in high wind speed scenarios.

Faunal mortality associated with massive beaching and decomposition of pelagic Sargassum

In 2018, the Mexican Caribbean coast received a massive influx of pelagic Sargassum spp. that accumulated and decayed on beaches producing organic decomposition products that made the water turbid and brown. Between May and September of the same year there were several reports of mass mortality of marine biota in this area. From these reports we estimate that organisms belonging to 78 faunal species died as result of this event, with demersal neritic fish and Crustacea being the most affected groups. The cause of mortality appears to be the combined effect of high ammonium and hydrogen sulfide concentrations, together with hypoxic conditions. If massive arrival of pelagic Sargassum spp. continues and algae is left to decay on the beach in large volumes then deterioration in water quality could affect coral reefs close to shore. Furthermore, barriers placed in lagoons to intercept the Sargassum spp. before it reaches the beach could impact reef fauna if the algae is left to die and sink on site.

Hydrogen Sulfide Affects Radical Formation in the Hippocampus of LPS Treated Rats and the Effect of Antipsychotics on Hydrogen Sulfide Forming Enzymes in Human Cell Lines

Objectives: Psychiatric disorders, such as schizophrenia and other neuroinflammatory diseases are accompanied by an increase in the oxidative stress and changes in the immune system and in the metabolic, hormonal and neurological components of the central nervous system (CNS). Hydrogen sulfide (H2S) is a gaseous molecule that is endogenously produced in the peripheral and central nervous system through cysteine by the following major H2S producing enzymes in the brain: cystathionine-γlyase (CSE), cystathionine ß-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (MPST). The physiological effects of H2S are broad, with antioxidative properties being a major role in the body. The aims of our investigation were to analyze the central nervous antioxidant, metabolic and neuronal effects in the hippocampus of the rat after inflammatory peripheral lipopolysaccharide (LPS) treatment; and to examine the effects of antipsychotics on the expression of these enzymes in human cell lines. Material and Methods: Male Lewis rats (250 g) received an i.p. LPS injection (1 mg/kg) 24 h before microdialysis experiments. Conscious rats were infused via these probes (1.5 μl/min) with a radical scavenger 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH) in Krebs-Ringer solution. Sodiumhydrogensulfide (NaHS, 10 μg/min) was infused after a 2- h baseline for 1 h. Corticosterone, glutamate, glucose and lactate were measured by Elisa. Reactive oxygen species (ROS) were detected by electron spin resonance spectroscopy (ESR). The impact of the antipsychotics haloperidol, clozapine, olanzapine and risperidone on the expression of genes encoding the key enzymes of H2S synthesis was studied at the human neuroblastoma SH-SY5Y and monocytic U-937 cell lines. The cells were incubated for 24 h with 30 μM antipsychotic following which mRNA levels were measured by polymerase chain reaction. Results: Microdialysate glucose and lactate levels dramatically increased in the hippocampus of LPS untreated rats by local application of NaHS. By contrast, in the LPS pretreated rats, there was no effect of NaHS infusion on glucose but a further significant increase in microdialysate lactate was found. It was LPS pretreatment alone that particularly enhanced lactate levels. There was a marked increase in hippocampal microdialysate glutamate levels after local NaHS infusion in LPS untreated animals. In LPS treated rats, no change was observed by NaHS, but LPS itself had the strongest effect on microdialysate glutamate levels. Microdialysate corticosterone levels were reduced by NaHS in both LPS pretreated and untreated rats. The formation of free radicals in the hippocampus significantly reduced in LPS pretreated rats, while in LPS untreated rats a significant increase was observed after NaHS infusion. In human SH-SY5Y and U-937 cells, all three major enzymes of H2S-Synthesis, namely cystathionine-γ-lyase, cystathione ß-synthase and 3-mercaptopyruvate sulfurtransferase, could be detected by PCR. The antipsychotics haloperidol, clozapine, olanzapine and risperidone affected all three enzymes in different ways; with haloperidol and risperidone showing major effects that led to reductions in CBS or CSE expression. Discussion: The local application of NaHS in the hippocampus of the rat strongly affected glucose, lactate and glutamate release. Contrastingly, in LPS pretreated rats, a decreased radical formation was the only effect found. H2S synthetizing enzymes may be involved in antipsychotic mechanisms, although no clear common mechanism could be found.

In situ organism-sediment interactions: Bioturbation and biogeochemistry in a highly depositional estuary

Organic matter (OM) production and degradation is important in coastal estuaries, and OM fate is strongly influenced by the coupled interactions of bioturbation and biogeochemistry. From April to September 2013 sediment cores and a benthic observing system, Wormcam, were used to investigate the in situ relationship of biogeochemistry and macrofauna bioturbation in Cape Lookout Bight North Carolina. Wormcam imagery provided a vivid depiction of macrofauna functioning in an environment not previously observed, and affirmed the importance of fine-scale temporal observations of the benthic environment in situ. Observation of macrofauna presence and bioturbation during the summer contradicted previous studies that found this area to be azoic during methane activity and sulfide build-up. Sulfate concentrations decreased while sulfide and dissolved inorganic carbon concentrations increased during the summer. This coincided with changes in the depth and rates of bioturbation. Summer burrow depths (~0.8 cm) and rates (~0.4 cm h-1) were significantly less than spring burrow depths (~3.0 cm) and rates (~1.0 cm h-1). While sulfate reduction and OM degradation increased with temperature at a microscopic level, macroscopic OM degradation was reduced. As a result, reduced conditions dominated and a thin aerobic sediment layer, a few millimeters in thickness, was visible at the sediment surface. Decreases in macrofauna burrow depth and rates diminishes the area of influence of bioturbators, limiting bioturbation and subsequently the important ecosystem functions these organisms provide.

Effects of long-term exposure to hydrogen sulfide on human red blood cells

Background:

Hydrogen sulfide (H2S) exhibits both physiological and toxicological roles in the biological systems. Acute exposure to high levels of H2S is life threatening while longterm exposure to ambient levels of H2S elicits human health effects.

Objective:

To study the harmful effects of long-term exposure to low levels of H2S on human blood cells.

Methods:

110 adult workers from Iran who were occupationally exposed to 0–90 ppb H2S for 1–30 years were studied. The participants aged between 18 and 60 years and were exposed directly or indirectly to sulfur compounds (exposed group). The origin of H2S was natural gas processing plants. A control group consisting of 110 males who were not in contact with H2S was also studied. For all participants, hematological profile including total hemoglobin and red blood cell count and sulfhemoglobin, methemoglobin levels were measured.

Results:

Among all parameters evaluated in this study the mean methemoglobin and sulfhemoglobin levels were significantly higher among workers who were exposed to sulfur compounds than the control group. Major differences throughout the study period for sulfhemoglobinemia among exposed groups were observed.

Conclusion:

Long-term exposure to even low levels of H2S in workplaces may have potential harmful effects on human health.

Assessment of genotoxic potency of sulfate-rich surface waters on medicinal leech and human leukocytes using different versions of the Comet assay

The aim of the present study was to investigate how exposure to sulfate-rich surface waters affects the level of primary DNA damage in hemocytes of leech Hirudo medicinalis. Samples of surface water were collected at two sites near a gypsum factory (Knin, Croatia) and two reference sites. In the laboratory, samples were subjected to detailed chemical analysis and used in toxicity testing. For that purpose, previously acclimatized individuals of H. medicinalis were sub-chronically exposed (for 28 days) to tested water samples. Levels of primary DNA damage were evaluated using the alkaline Comet assay in hemocytes collected on days 7, 14, 21 and 28 of exposure and compared with their baseline values. Genotoxic potency of the water sample with the highest sulfate concentration was further evaluated using the alkaline, neutral and hOGG1-modified Comet assay on human peripheral blood leukocytes exposed ex vivo for 30 min. The purpose was to explore which mechanisms are responsible for DNA damage. Chemical analysis revealed that sulfate concentrations in two water samples collected in Mali Kukar Lake (1630 mg/L SO₄) and Kosovčica River (823.3 mg/L SO₄) exceeded the WHO and US EPA defined limits for sulfate in drinking water. Increased levels of metals were found only in the water sample collected in Mali Kukar Lake. However, of the 65 elements analyzed, only nickel and titanium exceed the value legally accepted in Croatia for drinking water. The levels of DNA damage, estimated by the alkaline Comet assay in hemocytes of medicinal leech, increased with the duration of exposure to two sulfate-rich water samples. Since hemocytes responded sensitively to treatment, they could be used for biomonitoring purposes. As observed on treated human peripheral blood leukocytes, all versions of the Comet assay were effective in detecting DNA damage, which was measured in samples with sulfate concentrations equal to or higher than the legally accepted levels for drinking water. Based on the obtained results, it can be assumed that genotoxicity was a consequence both of direct (single- and double-strand DNA breaks) and indirect effects (oxidative damage) caused by the combined effects of all contaminants present in the tested water samples. Our results indicate the need for in situ monitoring and purification of gypsum mine water prior to its release in the natural environment.

Hydrogen sulfide oxidation and the arterial chemoreflex: effect of methemoglobin

Endogenous H(2)S has been proposed to transduce the effects of hypoxia in the carotid bodies (CB). To test this hypothesis, we created a sink for endogenously produced H(2)S by inducing ∼10% methemoglobinemia via the injection of 250 mg of sodium nitrite in spontaneously breathing anaesthetized sheep. Methemoglobinemia has been shown to catalyze the oxidation of large quantities of sulfide in the blood and tissues. We found that the presence of metHb completely abolished the ventilatory stimulation induced by 10 mg NaHS (i.v.), which in control conditions mimicked the effects of breathing 6-7 tidal volumes of nitrogen, confirming the dramatic increase in the oxidative power of the blood for sulfide. The ventilatory responses to hypoxia (10% O(2)), nitrogen and hyperoxia were in no way depressed by the metHb. Our results demonstrate that the ventilatory chemoreflex is not depressed in the presence of a high oxidative capacity for sulfide and challenge the view that H(2)S transduces the effects of hypoxia in the CB.

Oxygen consumption, ventilation frequency and cytochrome c oxidase activity in blue cod (Parapercis colias) exposed to hydrogen sulphide or isoeugenol

The effects of hydrogen sulphide (H(2)S) and isoeugenol exposure on activity, oxygen consumption (VO(2)), ventilation frequency (Vf) and cytochrome c oxidase activity in a teleost fish are reported. In H(2)S (200 microM Na(2)S) exposed animals VO(2) and Vf decreased significantly (both to 40% of resting) after 30 min, concurrent with a loss of equilibrium and narcosis. Post-flushing, VO(2) increased to resting values, but Vf remained depressed (P<0.05) until 30 min of recovery. Subsequently, equilibrium and mobility were regained accompanied by increases in VO(2) (66%) and Vf (15%) between 60-70 min of recovery. Isoeugenol (0.011 g L(-1)) exposed fish reached stage 4-5 of anaesthesia accompanied by decreases (P<0.05) in VO(2) (64%) and Vf (38%) by 35 min. Post-flushing, VO(2) and Vf recovered to resting values, followed by a rise (P<0.05) in VO(2) (45%) and Vf (25%). Overall, VO(2) in relation to the resting rate was reduced in isoeugenol treated animals. Conversely, VO(2) was increased (P<0.05) relative to the resting rate in H(2)S exposed fish. 20 and 200 microM Na(2)S reduced cytochrome c oxidase activity (P<0.05) in skeletal muscle and gill lamellae by between 69 and 97%, while isoeugenol had no effect in any tissue.

Survival in an extreme habitat: the roles of behaviour and energy limitation

Extreme habitats challenge animals with highly adverse conditions, like extreme temperatures or toxic substances. In this paper, we report of a fish (Poecilia mexicana) inhabiting a limestone cave in Mexico. Several springs inside the cave are rich in toxic H(2)S. We demonstrate that a behavioural adaptation, aquatic surface respiration (ASR), allows for the survival of P. mexicana in this extreme, sulphidic habitat. Without the possibility to perform ASR, the survival rate of P. mexicana was low even at comparatively low H(2)S concentrations. Furthermore, we show that food limitation affects the survival of P. mexicana pointing to energetically costly physiological adaptations to detoxify H(2)S.

Strategies adopted by the mudskipper Boleophthalmus boddaerti to survive sulfide exposure in normoxia or hypoxia

The effects of sulfide on the energy metabolism of Boleophthalmus boddaerti in normoxia and hypoxia were examined. The 24-, 48-, and 96-h LC50 values of sulfide for B. boddaerti with body weight ranging from 11.6 to 14.2 g were 0.786, 0.567, and 0.467 mM, respectively. The tolerance of B. boddaerti to sulfide was not due to the presence of a sulfide-insensitive cytochrome c oxidase. There was no accumulation of lactate in the muscle and liver of specimens exposed to sulfide in normoxia. In addition, the levels of ATP, AMP, and energy charge in both the muscle and the liver were unaffected. These results indicate that B. boddaerti was able to sustain the energy supply required for its metabolic needs via mainly aerobic respiration when exposed to sulfide (up to 0.4 mM) in normoxia. Exposure of B. boddaerti simultaneously to hypoxia and 0.2 mM sulfide for 48 h resulted in decreases in the ATP levels in the muscle and liver. However, the energy charge in both tissues remained unchanged, and the level of lactate accumulated in the muscle was too low to have any major contribution to the energy budget of the fish. Our results reveal that B. boddaerti possesses inducible mechanisms to detoxify sulfide in an ample supply or a lack of O2. In normoxia, it detoxified sulfide to sulfate, sulfite, and thiosulfate. There were significant increases in the activities of sulfide oxidase in the muscle and liver of specimens exposed to sulfide, with that in the liver being >13-fold higher than that in the muscle. However, in hypoxia, sulfide oxidase activity in the liver was suppressed in response to environmental sulfide. In such conditions, there were significant increases in the activities of sulfane sulfur-forming enzyme(s) in the muscle and liver that were not observed in specimens exposed to sulfide in normoxia. Correspondingly, there were no changes in the levels of sulfate or sulfite in the muscle or liver. Instead, B. boddaerti detoxified sulfide mainly to sulfane sulfur in hypoxia. In conclusion, B. boddaerti was able to activate different mechanisms to detoxify sulfide, producing different types of detoxification products in normoxia and hypoxia.

Physiological responses to sulfide toxicity by the air-breathing catfish, Hoplosternum littorale (Siluriformes, Callichthyidae)

Hemolytic anemia accompanied by changes in the immunology system is one of the sulfide intoxication harmful effects on Hoplosternum littorale. Hematological parameters are considered as effective indicators of stress caused by this hydrogen sulfide. During sulfide exposure, H. littorale neither alters the methemoglobin concentration nor forms sulfhemoglobin in the presence of high levels of dissolved sulfide in the water. Cytochrome c oxidase shows little activity in the gills and blood of H. littorale when exposed to sulfide. Alternative metabolic routes are suggested through which the accumulation of pyruvate leads to the formation of an end product other than lactate.

Vertebrate phylogeny of hydrogen sulfide vasoactivity

Hydrogen sulfide (H(2)S) is a recently identified endogenous vasodilator in mammals. In steelhead/rainbow trout (Oncorhynchus mykiss, Osteichthyes), H(2)S produces both dose-dependent dilation and a unique dose-dependent constriction. In this study, we examined H(2)S vasoactivity in all vertebrate classes to determine whether H(2)S is universally vasoactive and to identify phylogenetic and/or environmental trends. H(2)S was generated from NaHS and examined in unstimulated and precontracted systemic and, when applicable, pulmonary arteries (PA) from Pacific hagfish (Eptatretus stouti, Agnatha), sea lamprey (Petromyzon marinus, Agnatha), sandbar shark (Carcharhinus milberti, Chondrichthyes), marine toad (Bufo marinus, Amphibia), American alligator (Alligator mississippiensis, Reptilia), Pekin duck (Anas platyrhynchos domesticus, Aves), and white rat (Rattus rattus, Mammalia). In otherwise unstimulated vessels, NaHS produced 1) a dose-dependent relaxation in Pacific hagfish dorsal aorta; 2) a dose-dependent contraction in sea lamprey dorsal aorta, marine toad aorta, alligator aorta and PA, duck aorta, and rat thoracic aorta; 3) a threshold relaxation in shark ventral aorta, dorsal aorta, and afferent branchial artery; and 4) a multiphasic contraction-relaxation-contraction in the marine toad PA, duck PA, and rat PA. Precontraction of these vessels with another agonist did not affect the general pattern of NaHS vasoactivity with the exception of the rat aorta, where relaxation was now dominant. These results show that H(2)S is a phylogenetically ancient and versatile vasoregulatory molecule that appears to have been opportunistically engaged to suit both organ-specific and species-specific homeostatic requirements.