Hydrogen Sulfide and Methyl Mercaptan Toxicity J Periodontal Res 1992 Sep;27(5):476-483
Modulation of human gingival fibroblast cell metabolism by methyl mercaptan. Johnson PW, Ng W, Tonzetich J Department of Oral Biology, Faculty of Dentistry, University of British Columbia, Vancouver, Canada.
Methyl mercaptan (CH3SH) is a malodorous compound whose levels are elevated in mouth and crevicular air of individuals with active periodontal disease. Since it may play a role in the disease process, its effects were evaluated using human gingival fibroblast cultures and viable porcine unkeratinized oral mucosal tissue sections. Results showed that the protein content of CH3SH-exposed cell cultures pulsed with [14C]-labelled glycine and proline was decreased by approximately 25%. Furthermore, this deleterious effect was irreversible in test cultures subsequently incubated for 24 h in a control 95% air/5% CO2 mercaptan-free environment. The supporting slab-gel electrophoresis profiles yielded evidence that exposure to CH3SH caused an alteration in collagen metabolism and a pooling of Type I procollagens. In addition, DNA synthesis was suppressed in CH3SH-exposed cultures by 44.1% at the 24 to 26 h peak of DNA synthesis. This is a true inhibition and not a shift in peak of maximum DNA synthesis as the shape and location of time-course curves of control and test systems is very similar. Proline transport study using [14C]-proline indicated a reduction in proline transport in the range of 40 to 50% in cultures exposed for 24 to 30 h to CH3SH. Significantly even 15 min exposure to 6.7 ng CH3SH/ml of incubating atmosphere suppressed proline transport by approximately 24%. This indicates that even brief exposure to low concentrations of CH3SH has a significant adverse effect on proline transport. Fluorescent staining of tissue sections exposed to mercaptan indicated that the agent elevated the number of cells stained with vital dye.
J Nutr 1986 Feb;116(2):204-215 The effect of methanethiol and methionine toxicity on the activities of cytochrome c oxidase and enzymes involved in protection from peroxidative damage. Finkelstein A, Benevenga NJ
The tissue changes characteristic of methionine toxicity may be caused by methanethiol (CH3SH) inhibition of enzymes involved in protection from peroxidative damage. Methanethiol is an intermediate of the transaminative pathway of methionine metabolism. Glutathione peroxidase, glutathione reductase, catalase and superoxide dismutase activities were therefore tested for susceptibility of CH3SH. Cytochrome c oxidase activity was also measured because of its known inhibition by mercaptans. A 10-min exposure to CH3SH depressed hepatic cytochrome c oxidase activity to 28% of the incubated control value, while hepatic, splenic and erythrocyte catalase activities were depressed, respectively, to 53, 52 and 71% of the incubated control. Similar reductions in catalase and cytochrome c oxidase activities were observed in rats fed a diet containing 3% L-methionine as compared to rats pair-fed a control diet containing 0.3% methionine. There was no difference in the amount of lipid peroxidation as monitored by the presence of malondialdehyde in the livers of these rats. In rats injected i.p. with 50 or 75 mumol of 3-methylthiopropionate, an intermediate of methionine catabolism, the maximum levels of exhaled methanethiol coincided with depressions in liver catalase and cytochrome c oxidase activity to 40-50% of control values. The activities of these enzymes returned to control values within 2 to 4 h. The inhibition of catalase activity does not appear to be the cause of the membrane damage observed in methionine toxicity.
J Pharmacol Exp Ther 1984 Jan;228(1):103-108 Effects of methanethiol on erythrocyte membrane stabilization and on Na+,K+-adenosine triphosphatase: relevance to hepatic coma. Ahmed K, Zieve L, Quarfoth G
Methanethiol (CH3SH) has been implicated in the pathogenesis of hepatic coma. Studies are presented to identify the possible biochemical basis of anesthesia-like effects of methanethiol and those features which distinguish such effects from common anesthetics and may represent the basis of its toxicity. CH3SH was found to stabilize erythrocyte membranes against hypotonic hemolysis at relatively low concentrations. At 37 degrees C the AH25 value for human erythrocyte antihemolysis was observed at a concentration of 0.34 mumol of CH3SH bound per mg of erythrocyte protein. Similar results were obtained with rat erythrocytes. This property of CH3SH is in common with other anesthetic agents. Anesthetic agents also inhibit the membrane-associated Na+,K+-adenosine triphosphatase (ATPase); however, for effective and nontoxic agents of this type the inhibition of ATPase activity is elicited at concentrations which are at least an order of magnitude higher than those which influence the membrane stability characterized by the antihemolysis effect (P. Seeman, Pharmacol. Rev. 24: 583-655, 1972). CH3SH was also found to inhibit the membrane Na+,K+-ATPase activity. The I25 value for the inhibition of human erythrocyte ATPase activity was obtained at CH3SH concentration of 0.12 mM which corresponded to 0.3 mumol of CH3SH bound per mg of erythrocyte membrane protein. Rat erythrocyte membrane ATPase was somewhat more sensitive to CH3SH. In all cases the binding of CH3SH to erythrocytes occurred primarily on the membrane. These results indicate that no differential exists with respect to the dose-response of these two activities associated with human erythrocyte membrane.
J Toxicol Environ Health 1981 Jul;8(1-2):71-88 Acute and subchronic toxicity studies of rats exposed to vapors of methyl mercaptan and other reduced-sulfur compounds. Tansy MF, Kendall FM, Fantasia J, Landin WE, Oberly R, Sherman W
Acute inhalation experiments were conducted to determine 24-h LC50 values for adult Sprague-Dawley rats of both sexes exposed to vapors of methyl mercaptan and other reduced-S compounds for 4 h periods. Using calculated gas concentrations, the following LC50 value for each gas and combination was determined: metyhl mercaptan, 675 ppm; dimethyl sulfide, 40,250 ppm; dimethyl disulfide, 805 ppm; hydrogen sulfide, 444 ppm; and an equimolar mixture of methyl mercaptan, dimethyl sulfide, and dimethyl disulfide, 550 ppm. The effects of body and tissue weights, gross metabolic performance, O2 consumption, systolic blood pressure, various blood parameters, and intestinal transit time associated with 3-mo exposures of young adult male rats to chemically verified concentrations of 2, 17, and 57 ppm methyl mercaptan vapor are summarized in this report. No mortality was experienced by any group. Histopathological findings were essentially nil except for microscopic suggestions of liver damage. The most readily apparent phenomenon was the decrease in body weight. Average values of terminal body weights for all exposed groups were lower than that for the sham control group. This difference was significant in the 57 ppm group and followed a statistically significant dose-related trend.
J Toxicol Environ Health 1991 May;33(1):57-64 Cytotoxic effects of hydrogen sulfide on pulmonary alveolar macrophages in rats. Khan AA, Yong S, Prior MG, Lillie LE Animal Sciences Division, Alberta Environmental Centre, Vegreville, Canada.
Respiratory rates (basal and zymosan-stimulated) and cell viability were monitored in pulmonary alveolar macrophages (PAM) from rats exposed to 0, 70, 280, and 560 mg/m3 (0, 50, 200, and 400 ppm) hydrogen sulfide (H2S) gas for 4 h. Zymosan-stimulated respiratory rates were markedly reduced in PAM collected from rats exposed to 280 and 560 mg/m3 H2S; however, their basal respiratory rates were not affected. Significant decrease in cell viability was also observed in samples from 560 mg/m3 H2S-treated rats, but it remained high and unchanged in other treatments. In vitro incubation of PAM from control rats with sulfide (a precursor of H2S) and its two oxidation products, sulfite and sulfate, showed that sulfide was markedly more inhibitory to both respiratory rates than sulfite or sulfate. These treatments did not affect cell viability.
Alteration of the morphology and neurochemistry of the developing mammalian nervous system by hydrogen sulphide. Roth SH, et al Clin Exp Pharmacol Physiol 1995 May;22(5):379-380
1. Hydrogen sulphide (H2S) is a broad spectrum toxicant that occurs widely in nature and is also released by a variety of industrial activities and processes.
2. The central nervous system (CNS) appears to be the major target organ.
3. There is great potential for insult or injury to the developing or immature CNS.
4. The risk of chronic or repeated exposures to low concentrations have not been well defined.
5. Exposure to low concentrations of H2S to time-pregnant rats from day 5 postcoitus until day 21 postnatal results in architectural modification of cerebellar Purkinje cells, alteration of putative amino acid neurotransmitters and changes in monoamine levels in the developing rat brain up to day 21 postnatal.
6. H2S-induced alterations in monoamine tissue levels observed in the developing rat brain return to control values if exposure is discontinued during development, that is, at day 21 postnatal.
Toxicol Ind Health 1990 May;6(3-4):389-401 Growth and development in the rat during sub-chronic exposure to low levels of hydrogen sulfide. Hayden LJ, Goeden H, Roth SH Department of Pharmacology and Therapeutics, University of Calgary, Calgary, Alberta, Canada.
The effects of low levels of hydrogen sulfide (H2S) on mammalian growth and development are unknown although it has long been postulated that H2S can inhibit critical developmental functions through the cleavage of disulfide bonds and chelation of essential metal ions. Gravid rat dams exposed to H2S (less than or equal to 75 PPM) from day 6 of gestation until day 21 postpartum (PP) demonstrated normal reproductive parameters until parturition. At parturition, however, delivery time was extended in a dose dependent manner with a maximum increase of 42% at 75 PPM. Maternal liver cholesterol content was elevated significantly on day 21 postpartum following exposure to 75 PPM H2S each day for 6 weeks. Pups which were exposed in utero and neonatally to day 21 postpartum developed with a subtle decrease in time of ear detachment and hair development and with no other observed change in growth and development through day 21 postpartum.
J Toxicol Environ Health 1990 Sep;31(1):45-52 Exposure to low levels of hydrogen sulfide elevates circulating glucose in maternal rats. Hayden LJ, Goeden H, Roth SH Department of Pharmacology and Therapeutics, University of Calgary, Alberta, Canada.
Although the lethal effect of hydrogen sulfide (H2S) has long been known, the results of exposure to low levels of H2S have not been well documented. Rat dams and pups were exposed to low levels of H2S (less than or equal to 75 ppm) from d 1 of gestation until d 21 postpartum and analyzed for changes in circulating enzymatic activity and metabolites. Blood glucose was significantly elevated in maternal blood on d 21 postpartum at all exposure levels. This increase in glucose was accompanied by a possible decrease in serum triglyceride in the pups and in the dams on d 21 postpartum. There was no evidence of alterations in serum alkaline phosphatase, lactate dehydrogenase, or serum glutamate oxaloacetate transaminase.
Hydrogen sulfide exposure alters the amino acid content in developing rat CNS. Hannah RS, Hayden LJ, Roth SH Neurosci Lett 1989 May 8;99(3):323-327
Hydrogen sulfide is a widespread environmental pollutant that may produce severe effects on the developing nervous system. Putative amino acid neurotransmitter levels in the rat cerebrum and cerebellum were determined to evaluate the effects of exposure to hydrogen sulfide during perinatal development. The levels of aspartate, GABA, glutamate, glycine and taurine were quantitated using high-performance liquid chromatography. With the exception of glycine, all of the amino acids examined were affected by the treatment. On day 21 postnatal, which was the last day of the exposure, aspartate, glutamate and GABA in the cerebrum and aspartate and GABA in the cerebellum were significantly depressed. The observed alterations in the amino acid levels during this critical phase of development may have chronically affected the activity of the neurotransmitters, their receptor sensitivity or their individual target areas. The consequence of one or a combination of such alterations may lead to behavioral and structural abnormalities.
Chronic exposure to low concentrations of hydrogen sulfide produces abnormal growth in developing cerebellar Purkinje cells. Hannah RS, Roth SH Neurosci Lett 1991 Jan 28;122(2):225-228
Hydrogen sulfide (H2S) may produce deleterious effects on the developing central nervous system. The dendritic fields of developing cerebellar Purkinje cells were analyzed to determine the effects of chronic exposure to low concentrations of H2S during perinatal development. Treatment with two concentrations (20 and 50 ppm) of H2S produced severe alterations in the architecture and growth characteristics of the Purkinjec cell dendritic fields. The architectural modifications included longer branches, an increase in the vertex path length and variations in the number of branches in particular areas of the dendritic field. The treated cells also exhibited a nonsymmetrical growth pattern at a time when random terminal branching is normally occurring. These findings suggest that developing neurons exposed to low concentrations of H2S are at risk of severe deficits.
Effects of repeated exposures of hydrogen sulphide on rat hippocampal EEG. Skrajny B, et al. Toxicol Lett 1996 Jan;84(1):43-53
Exposure to high levels of hydrogen sulphide (H2S) in humans has been associated with a number of respiratory and neurological symptoms. Acute toxicity following exposure to high concentrations is well-documented, however, there is little scientific information concerning the effects of exposure to low concentrations. The effects of low levels of H2S on electroencephalographic (EEG) activity in the hippocampus and neocortex were investigated on the freely moving rat (Sprague-Dawley). Hippocampal electrodes were implanted in the dentate gyrus (DG) and CA1 region. Activity was recorded for 10 min just prior to H2S exposure in the presence of air (pre-exposure). Rats were exposed to H2S (25, 50, 75, or 100 ppm) for 3 h/day; data was collected during the final 10 min of each exposure. The total power of hippocampal theta activity increased in a concentration-dependent manner in both DG and CA1; repeated exposures for 5 consecutive days resulted in a cumulative effect that required 2 weeks for complete recovery. The effects were found to be highly significant at all concentrations within subjects. Neocortical EEG and LIA (Large Amplitude Irregular Activity) were unaffected. The results demonstrate that repeated exposure to low levels of H2S can produce cumulative changes in hippocampal function and suggest selectivity of action of this toxicant.
Sulfide-induced perturbations of the neuronal mechanisms controlling breathing in rats. Greer JJ, Reiffenstein RJ, Almeida AF, Carter JE J Appl Physiol 1995 Feb;78(2):433-440
The effects of sulfide on neonatal rat respiration were studied. Two in vitro experimental models were utilized: the isolated brain stem-spinal cord preparation and the medullary slice preparation containing respiratory rhythm-generating regions from neonatal rats. Plethysmographic measurements of the effects of sulfide on the breathing patterns of unanesthetized neonatal rats were also made to compare the sensitivities of neonatal and adult rats to sulfide toxicity. In vitro, sulfide acted at sites within the ventrolateral medulla to depress the frequency of respiratory rhythmic discharge by approximately 50-60%. However, the neuronal network underlying respiratory rhythmogenesis continued to function in the presence of concentrations of sulfide far beyond those deemed to be lethal in vivo. Intraperitoneal administration of sulfide caused a dose-dependent decrease in the frequency and amplitude of breathing of neonatal rats of all ages (0-19 days postnatal), although the sensitivity to sulfide increased with age. We hypothesize that the rapid suppression of breathing caused by sulfide is due to changes in neuronal excitability within respiratory rhythm-generating centers rather than, as previously hypothesized, to perturbations of cellular oxidative metabolism.
Low concentrations of hydrogen sulphide alter monoamine levels in the developing rat central nervous system. Skrajny B, Hannah RS, Roth SH. Can J Physiol Pharmacol 1992 Nov;70(11):1515-1518
The central nervous system is one of the primary target organs for hydrogen sulphide (H2S) toxicity; however, there are limited data on the neurotoxic effects of low-dose chronic exposure on the developing nervous system. Levels of serotonin and norepinephrine in the developing rat cerebellum and frontal cortex were determined following chronic exposure to 20 and 75 ppm H2S during perinatal development. Both monoamines were altered in rats exposed to 75 ppm H2S compared with controls; serotonin levels were significantly increased at days 14 and 21 postnatal in both brain regions, and norepinephrine levels were significantly increased at days 7, 14, and 21 postnatal in cerebellum and at day 21 in the frontal cortex. Exposure to 20 ppm H2S significantly increased the levels of serotonin in the frontal cortex at day 21, whereas levels of norepinephrine were significantly reduced in the frontal cortex at days 14 and 21, and at day 14 in the cerebellum.
Toxicology of hydrogen sulfide. Reiffenstein RJ, Hulbert WC, Roth SH Annu Rev Pharmacol Toxicol 1992;32:109-134
Significant progress has been made in determining the action of sulfide on the primary target organs. It is reasonably clear that sulfide causes both K(+)-channel-mediated hyperpolarization of neurons and potentiation of other inhibitory mechanisms. It is not clear whether these processes are similar to those that occur in anoxia. Changes in perinatal and adult brain neurotransmitter content and release may be related to clinical impairment of cognition. H2S exposures at concentrations below the current occupational limits cause physiological changes in pulmonary function, thus suggesting that asthmatics are at risk. Studies of fetal and neonatal brain tissue have shown an abnormal development, and the long-term consequences of these neuronal changes have not yet been assessed. Finally, new approaches to therapy are required, such as the use of agents that actively remove sulfide from its sites of action. This may prove more useful in preventing some of the long-term adverse sequelae than the use of nitrites and hyperbaric O2, although the latter should be used in cases of pulmonary edema.
Hydrogen sulphide. Guidotti TL Occupational Health Program, Occup Med (Oxf) 1996 Oct;46(5):367-371
Hydrogen sulphide (H2S) is the primary chemical hazard in natural gas production in ‘sour’ gas fields. It is also a hazard in sewage treatment and manure-containment operations, construction in wetlands, pelt processing, certain types of pulp and paper production, and any situation in which organic material decays or inorganic sulphides exist under reducing conditions. H2S dissociates into free sulphide in the circulation. Sulphide binds to many macromolecules, among them cytochrome oxidase. Although this is undoubtedly an important mechanism of toxicity due to H2S, there may be others H2S provides little opportunity for escape at high concentrations because of the olfactory paralysis it causes, the steep exposure-response relationships, and the characteristically sudden loss of consciousness it can cause which is colloquially termed ‘knockdown.’ Other effects may include mucosal irritation, which is associated at lower concentrations with a keratoconjunctivitis called ‘gas eye’ and at higher concentrations with risk of pulmonary oedema. Chronic central nervous system sequelae may possibly follow repeated knockdowns: this is controversial and the primary effects of H2S may be confounded by anoxia or head trauma. Treatment is currently empirical, with a combination of nitrite and hyperbaric oxygen preferred. The treatment regimen is not ideal and carries some risk.
The actions of hydrogen sulfide on dorsal raphe serotonergic neurons in vitro. Kombian SB, Reiffenstein RJ, Colmers WF J Neurophysiol 1993 Jul;70(1):81-96
1. The actions of hydrogen sulfide (HS-) on membrane and synaptic properties of dorsal raphe (DR) serotonergic cells were studied in the in vitro brain stem slice preparation, using intracellular sharp microelectrode and whole-cell recording techniques. 2. Sulfide produced two reversible, concentration-dependent effects on resting membrane properties of DR cells: (1) 14% responded to HS- with a slow onset hyperpolarization or an outward current accompanied by an conductance increase in voltage clamp (holding potential = -60 mV; monophasic outward cell) or (2) 39% responded with a rapid-onset depolarization corresponding to a weakly voltage-dependent inward current showing little or no change in conductance between -115 and -40 mV (monophasic inward cell). In addition, 29.5% showed both the above effects, responding first with a rapid-onset depolarization and then a sustained hyperpolarization. Such cells had membrane currents very similar to those seen in the monophasic inward and outward cells (biphasic cells). Finally, 17.5% of DR cells had no measurable postsynaptic membrane response to HS-. 3. The outward current induced in the presence of HS- had a reversal potential of about -90 mV when recorded either with 2 M KCl or 145 mM potassium gluconate in the pipette and was accompanied by an increase in conductance, suggesting that it is caused by an elevated conductance to K+. 4. This current was sensitive to the removal of external Ca2+ and blockade by Cd2+, suggesting that it is activated by an elevation in internal [Ca2+]. It was also blocked by apamin or Ba2+ and Cs+, both of which revealed an underlying inward current. The outward current was insensitive to the application of a large variety of antagonists to other known voltage- and calcium-dependent K+ channels. Elevation of intracellular ATP using a patch pipette did not prevent the activation of the outward current. 5. HS- reversibly suppressed a voltage-dependent outward current activated in the voltage range of -50 to -40 mV. This current was also blocked by 10 mM tetraethylammonium, suggesting that HS- suppresses the delayed rectifier in DR cells. 6. The inward current could be observed in the presence of HS- not only in monophasic inward cells but also in monophasic outward or biphasic cells whose outward current was selectively blocked. This inward current was sensitive to the removal of extracellular Ca2+, or the the application of relatively low concentrations of Cd2+, suggesting that it is carried by Ca2+. Both these manipulations also blocked the outward current in monophasic outward or biphasic cells.
Hydrogen sulfide and reduced-sulfur gases adversely affect neurophysiological functions.Kilburn KH, Warshaw Toxicol Ind Health 1995 Mar;11(2):185-197
Hydrogen sulfide (H2S) above 50 parts per million (ppm) causes unconsciousness and death. Lower doses of H2S and related gases have been regarded as innocuous, but the effects of prolonged exposure have not been studied. This study was designed to determine whether people exposed to sulfide gases as a result of working at or living downwind from the processing of “sour” crude oil demonstrate persistent neurobehavioral dysfunction. Thirteen former workers and 22 neighbors of a refinery complained of headaches, nausea, vomiting, depression, personality changes, nosebleeds, and breathing difficulties. Their neurobehavioral functions and a profile of mood states (POMS) were compared to 32 controls, matched for age and educational level. The exposed subjects’ mean values were statistically significantly abnormal compared to controls for two-choice reaction time, balance (as speed of sway), color discrimination, digit symbol, trail-making A and B, and immediate recall of a story. Their POMS scores were much higher than those of controls. Visual recall was significantly impaired in neighbors, but not in exworkers. It was concluded that neurophysiological abnormalities were associated with exposure to reduced sulfur gases, including H2S from crude oil desulfurization.