Cobalt salts: effects in cyanide and sulfide poisoning and on methemoglobinemia

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.

Hydrogen sulfide intoxication induced brain injury and methylene blue

Hydrogen sulfide (H₂S) remains a chemical hazard in the gas and farming industry. It is easy to manufacture from common chemicals and thus represents a potential threat for the civilian population. It is also employed as a method of suicide, for which incidence has recently increased in the US. H₂S is a mitochondrial poison and exerts its toxicity through mechanisms that are thought to result from its high affinity to various metallo-proteins (such as - but not exclusively- the mitochondrial cytochrome c oxidase) and interactions with cysteine residues of proteins. Ion channels with critical implications for the cardiac and the brain functions appear to be affected very early during and following H₂S exposure, an effect which is rapidly reversible during a light intoxication. However, during severe H₂S intoxication, a coma, associated with a reduction in cardiac contractility, develops within minutes or even seconds leading to death by complete electro-mechanical dissociation of the heart. If the level of intoxication is milder, a rapid and spontaneous recovery of the coma occurs as soon as the exposure stops. The risk, although probably very small, of developing long-term debilitating motor or cognitive deficits is present. One of the major challenges impeding our effort to offer an effective treatment against H₂S intoxication after exposure is that the pool of free/soluble H₂S almost immediately disappears from the body preventing agents trapping free H₂S (cobalt or ferric compounds) to play their protective role. This paper (1) presents and discusses the neurological symptoms and lesions observed in various animals models and in humans following an acute exposure to sub-lethal or lethal levels of H₂S, (2) reviews the potential interest of methylene blue (MB), a potent cyclic redox dye - currently used for the treatment of methemoglobinemia - which has potential rescuing effects on the mitochondrial activity, as an antidote against sulfide intoxication.

Methylene Blue Counteracts H2S-Induced Cardiac Ion Channel Dysfunction and ATP Reduction

We have previously demonstrated that methylene blue (MB) counteracts the effects of hydrogen sulfide (H₂S) cardiotoxicity by improving cardiomyocyte contractility and intracellular Ca²⁺ homeostasis disrupted by H₂S poisoning. In vivo, MB restores cardiac contractility severely depressed by sulfide and protects against arrhythmias, ranging from bundle branch block to ventricular tachycardia or fibrillation. To dissect the cellular mechanisms by which MB reduces arrhythmogenesis and improves bioenergetics in myocytes intoxicated with H₂S, we evaluated the effects of H₂S on resting membrane potential (E_m), action potential (AP), Na⁺/Ca²⁺ exchange current (I_NaCa), depolarization-activated K⁺ currents and ATP levels in adult mouse cardiac myocytes and determined whether MB could counteract the toxic effects of H₂S on myocyte electrophysiology and ATP. Exposure to toxic concentrations of H₂S (100 µM) significantly depolarized E_m, reduced AP amplitude, prolonged AP duration at 90% repolarization (APD₉₀), suppressed I_NaCa and depolarization-activated K⁺ currents, and reduced ATP levels in adult mouse cardiac myocytes. Treating cardiomyocytes with MB (20 µg/ml) 3 min after H₂S exposure restored E_m, APD₉₀, I_NaCa, depolarization-activated K⁺ currents, and ATP levels toward normal. MB improved mitochondrial membrane potential (∆ψ_m) and oxygen consumption rate in myocytes in which Complex I was blocked by rotenone. We conclude that MB ameliorated H₂S-induced cardiomyocyte toxicity at multiple levels: (1) reversing excitation-contraction coupling defects (Ca²⁺ homeostasis and L-type Ca²⁺ channels); (2) reducing risks of arrhythmias (E_m, APD, I_NaCa and depolarization-activated K⁺ currents); and (3) improving cellular bioenergetics (ATP, ∆ψ_m).

Methylene blue counteracts H2S toxicity-induced cardiac depression by restoring L-type Ca channel activity

We have previously reported that methylene blue (MB) can counteract hydrogen sulfide (H2S) intoxication-induced circulatory failure. Because of the multifarious effects of high concentrations of H2S on cardiac function, as well as the numerous properties of MB, the nature of this interaction, if any, remains uncertain. The aim of this study was to clarify 1) the effects of MB on H2S-induced cardiac toxicity and 2) whether L-type Ca(2+) channels, one of the targets of H2S, could transduce some of the counteracting effects of MB. In sedated rats, H2S infused at a rate that would be lethal within 5 min (24 μM·kg(-1)·min(-1)), produced a rapid fall in left ventricle ejection fraction, determined by echocardiography, leading to a pulseless electrical activity. Blood concentrations of gaseous H2S reached 7.09 ± 3.53 μM when cardiac contractility started to decrease. Two to three injections of MB (4 mg/kg) transiently restored cardiac contractility, blood pressure, and V̇o2, allowing the animals to stay alive until the end of H2S infusion. MB also delayed PEA by several minutes following H2S-induced coma and shock in unsedated rats. Applying a solution containing lethal levels of H2S (100 μM) on isolated mouse cardiomyocytes significantly reduced cell contractility, intracellular calcium concentration ([Ca(2+)]i) transient amplitudes, and L-type Ca(2+) currents (ICa) within 3 min of exposure. MB (20 mg/l) restored the cardiomyocyte function, ([Ca(2+)]i) transient, and ICa The present results offer a new approach for counteracting H2S toxicity and potentially other conditions associated with acute inhibition of L-type Ca(2+) channels.

Immediate and Long-Term Outcome of Acute H2S Intoxication Induced Coma in Unanesthetized Rats: Effects of Methylene Blue

BACKGROUND

Acute hydrogen sulfide (H2S) poisoning produces a coma, the outcome of which ranges from full recovery to severe neurological deficits. The aim of our study was to 1--describe the immediate and long-term neurological effects following H2S-induced coma in un-anesthetized rats, and 2--determine the potential benefit of methylene blue (MB), a compound we previously found to counteract acute sulfide cardiac toxicity.

METHODS

NaHS was administered IP in un-sedated rats to produce a coma (n = 34). One minute into coma, the rats received MB (4 mg/kg i.v.) or saline. The surviving rats were followed clinically and assigned to Morris water maze (MWM) and open field testing then sacrificed at day 7.

RESULTS

Sixty percent of the non-treated comatose rats died by pulseless electrical activity. Nine percent recovered with neurological deficits requiring euthanasia, their brain examination revealed major neuronal necrosis of the superficial and middle layers of the cerebral cortex and the posterior thalamus, with variable necrosis of the caudate putamen, but no lesions of the hippocampus or the cerebellum, in contrast to the typical distribution of post-ischemic lesions. The remaining animals displayed, on average, a significantly less effective search strategy than the control rats (n = 21) during MWM testing. Meanwhile, 75% of rats that received MB survived and could perform the MWM test (P<0.05 vs non-treated animals). The treated animals displayed a significantly higher occurrence of spatial search than the non-treated animals. However, a similar proportion of cortical necrosis was observed in both groups, with a milder clinical presentation following MB.

CONCLUSION

In conclusion, in rats surviving H2S induced coma, spatial search patterns were used less frequently than in control animals. A small percentage of rats presented necrotic neuronal lesions, which distribution differed from post-ischemic lesions. MB dramatically improved the immediate survival and spatial search strategy in the surviving rats.

Effects of infusion of human methemoglobin solution following hydrogen sulfide poisoning

RATIONALE

We have recently reported that infusion of a solution containing methemoglobin (MetHb) during exposure to hydrogen sulfide results in a rapid and large decrease in the concentration of the pool of soluble/diffusible H2S in the blood. However, since the pool of dissolved H2S disappears very quickly after H2S exposure, it is unclear if the ability of MetHb to "trap" sulfide in the blood has any clinical interest and relevance in the treatment of sulfide poisoning.

METHODS

In anesthetized rats, repetition of short bouts of high level of H2S infusions was applied to allow the rapid development of an oxygen deficit. A solution containing MetHb (600 mg/kg) or its vehicle was administered 1 min and a half after the end of H2S intoxication.

RESULTS

The injection of MetHb solution increased methemoglobinemia to about 6%, almost instantly, but was unable to affect the blood concentration of soluble H2S, which had already vanished at the time of infusion, or to increase combined H2S. In addition, H2S-induced O2 deficit and lactate production as well as the recovery of carotid blood flow and blood pressure were similar in treated and control animals.

CONCLUSION

Our results do not support the view that administration of MetHb or drugs-induced methemoglobinemia during the recovery phase following severe H2S intoxication in sedated rats can restore cellular oxidative metabolism, as the pool of diffusible sulfide, accessible to MetHb, disappears rapidly from the blood after H2S exposure.

Kinetics and mechanism of the reaction of hydrogen sulfide with diaquacobinamide in aqueous solution

We conducted a detailed kinetic study of the reaction of the vitamin B12 analog diaquacobinamide ((H2O)2Cbi(III)) with hydrogen sulfide in water from pH 3 to 11. The reaction proceeds in three steps: (i) formation of three different complexes between cobinamide and hydrogen sulfide, viz. (HO-)(HS-)Cbi(III), (H2O)(HS-)Cbi(III), and (HS-)2Cbi(III); (ii) inner-sphere electron transfer (ISET) in the two complexes with one coordinated HS- to form the reduced cobinamide complex [(H)S]Cbi(II); and (iii) addition of a second molecule of hydrogen sulfide to the reduced cobinamide. ISET does not proceed in the (HS-)2Cbi(III) complex. The final products of the reaction between cobinamide and hydrogen sulfide were found to be independent of pH, with the main product being a complex of cobinamide(II) with the anion-radical SSH2-.

In vivo interactions between cobalt or ferric compounds and the pools of sulphide in the blood during and after H2S poisoning

Hydrogen sulphide (H2S), a chemical hazard in oil and gas production, has recently become a dreadful method of suicide, posing specific risks and challenges for the first responders. Currently, there is no proven effective treatment against H2S poisoning and its severe neurological, respiratory or cardiac after-effects. We have recently described that H2S is present in various compartments, or pools, in the body during sulphide exposure, which have different levels of toxicity. The general goals of our study were to (1) determine the concentrations and kinetics of the various pools of hydrogen sulphide in the blood, i.e., gaseous (CgH2S) versus total sulphide, i.e., reacting with monobromobimane (CMBBH2S), during and following H2S exposure in a small and large mammal and (2) establish the interaction between the pools of H2S and a methemoglobin (MetHb) solution or a high dose of hydroxocobalamin (HyCo). We found that CgH2S during and following H2S infusion was similar in sedated sheep and rats at any given rate of infusion/kg and provoked symptoms, i.e., hyperpnea and apnea, at the same CgH2S. After H2S administration was stopped, CgH2S disappeared within 1 min. CMBBH2S also dropped to 2-3μM, but remained above baseline levels for at least 30 min. Infusion of a MetHb solution during H2S infusion produced an immediate reduction in the free/soluble pool of H2S only, whereas CMBBH2S increased by severalfold. HyCo (70 mg/kg) also decreased the concentrations of free/soluble H2S to almost zero; CgH2S returned to pre-HyCo levels within a maximum of 20 min, if H2S infusion is maintained. These results are discussed in the context of a relevant scenario, wherein antidotes can only be administered after H2S exposure.

Hypoxia-induced arterial chemoreceptor stimulation and hydrogen sulfide: too much or too little?

This brief review presents and discusses some of the important issues surrounding the theory which asserts that endogenous hydrogen sulfide (H(2)S) is the mediator of, or at least an important contributor to, hypoxia-induced arterial chemorereceptor stimulation. The view presented here is that before H(2)S can seriously be considered as a candidate for transducing the O(2)-signal in the carotid bodies (CB), fundamental contradictions need to be resolved. One of these major contradictions is certainly the discrepancy between the levels of H(2)S endogenously present in the CB during hypoxia compared to the levels required to stimulate the arterial chemoreceptors in vitro. Very small amounts of H(2)S are thought to be produced endogenously during a given level of hypoxia, yet the partial pressure of tissue H(2)S which is needed to produce an effect commensurate with that of hypoxia is thousands to millions of times higher. This review discusses this and other contradictions in light of what is known about H(2)S concentration and production in various tissues, the lessons we have learnt from the response to exogenous sulfide and the ability of the blood and the mitochondria to oxidize very large amounts of sulfide. These considerations suggest that the increased production of H(2)S in hypoxia and exogenous sulfide cannot produce the same effect on the carotid bodies and breathing. While the effects of the endogenous H(2)S on breathing remains to be established, the effects exogenous sulfide can be accounted for by its long established toxicity on cytochrome C oxidase.

3-(1-Adamant-yl)-1-{[4-(2-meth-oxy-phen-yl)piperazin-1-yl]meth-yl}-4-methyl-1H-1,2,4-triazole-5(4H)-thione

The title compound, C(25)H(35)N(5)OS, is a functionalized triazoline-3-thione with substituted piperazine and adamantyl substituents attached at the 2- and 5-positions, respectively, of a triazole spacer with an approximately C-shaped conformation of the mol-ecule. The piperazine ring adopts a chair conformation.

Acute exposure to cobalt induces transient methemoglobinuria in rats

We observed transient excretion of dark-brown urine after acute exposure to cobalt in rats and investigated the mechanism of it. We injected cobalt into rats s.c. at a dose of 15 mg/kg and collected urine, peripheral blood, and organ samples at the indicated times after injection. Biochemical and histopathological examinations of these samples were conducted. Obvious macroscopic and biochemical methemoglobinuria was observed just after injection of cobalt, but the level of urinary methemoglobin decreased gradually, almost disappearing by 24 h. The levels of cobalt in peripheral blood and urine showed a very similar pattern to that of methemoglobinuria. Neither anemia nor bilirubinemia was observed, indicating no extrarenal intravascular hemolysis. Pathological examination of the kidneys revealed that the glomerular capillaries were filled with red blood cells at 1 h after injection. Electron microscopy showed deformed red blood cells in the glomerular capillaries and condensed hemoglobin in Bowman's capsule that passed through the basement membrane. There were no trends toward increases in plasma levels of creatinine or blood urea nitrogen. These results indicate that exposure to cobalt induces transient methemoglobinuria through the lysis of red blood cells and oxidation of iron in hemoglobin at the glomerular capillaries without causing renal dysfunction.

Application of a hepatocyte-erythrocyte coincubation system to studies of cyanide antidotal mechanisms

A coincubation system composed of hepatocytes in primary monolayer culture and erythrocytes suspended in the culture medium was developed and used as a model for investigations of mechanisms of cyanide antidote action at the cellular level. Hepatocyte ATP was used as the cytotoxicity indicator. Treatment of rat hepatocytes in the coincubation system with KCN (1.0 mM) for 10 min at 37 degrees C selectively reduced hepatocyte ATP levels to 33 +/- 15% of control (no KCN added) levels. 4-dimethylaminophenol (DMAP), cobalt(II) chloride, sodium nitrite, sodium thiosulfate, or a combination of the last two antidotes added to the KCN-containing medium significantly reversed ATP depression and the response was concentration dependent. The relative effectiveness, on a molar basis, was estimated to be DMAP greater than CoCl2 much greater than NaNO2 congruent to Na2S2O3. NaNO2 and DMAP induced methemoglobin formation in the absence of cyanide and cyanmethemoglobin formation in its presence; erythrocytes were required in the medium for effectiveness. CoCl2 produced neither cyanmethemoglobin nor thiocyanate in appreciable quantities nor required erythrocytes for antagonism. Na2S2O3 converted cyanide to thiocyanate and reversed ATP depression without erythrocytes in the medium. The addition of erythrocytes increased these rates significantly and to a greater extent than albumin. The overall results are consistent with previously proposed modes of action for these antidotes. However, the enhancement in cyanide metabolism and ATP recovery with Na2S2O3 and erythrocytes in the system was unexpected and raises the possibility that erythrocytes may contribute to cyanide disposition and antagonism in vivo when this antidote is administered.

A critical review of the literature on hydrogen sulfide toxicity

The information available on the biological activity of hydrogen sulfide has been examined for present status of critical results pertaining to the toxicity of hydrogen sulfide. This review of the literature is intended as an evaluative report rather than an annotated bibliography of all the source material examined on hydrogen sulfide. The information was selected as it might relate to potential toxic effects of hydrogen sulfide to man and summarized, noting information gaps that may require further investigation. Several recommendations are listed for possible consideration for either toxicological research or additional short- and long-term tests. Two bibliographies have been provided to assist in locating references considered in this report: (1) literature examined but not cited and (2) reference citations. The majority of the references in the first bibliography were considered peripheral information and less appropriate for inclusion in this report.

Inhibition of methemoglobin and metmyoglobin reduction by cobalt

Because cobalt compounds tend to form stable complexes, there has been continued interest in the use of the salts and chelates of cobalt in cyanide poisoning, and continued uncertainty about the precise nature of their protective effects. We have found that cobalt ions inhibit the enzymatic reduction of both methemoglobin and metmyoglobin. Virtually total inhibition of methemoglobin and metmyoglobin reductase activity occurred with the addition of 2.5 mM cobalt acetate to the assay system. Both enzymes were inhibited by lower levels of cobalt in a dose-dependent manner. The similarity in susceptibility of cobalt inhibition is further evidence that the enzymes which reduce methemoglobin and metmyoglobin are functionally comparable. The inhibition of methemoglobin reductase activity may be, in part, responsible for the therapeutic effectiveness of cobalt salts and chelates in cyanide poisoning.

Management of acute sulfide poisoning. Effects of oxygen, thiosulfate, and nitrite

Oxygen (100% at 1 atmosphere) did not protect mice against death from acute sulfide poisoning as compared with animals maintained under air at 1 atmosphere. Sodium thiosulfate had a small, but statistically significant (P less than .05) protective effect against death due to sodium sulfide, whether the mice were maintained under air or oxygen. Pretreatment with sodium nitrite, however, increased the acute intraperitoneal lethal dose for 50% survival of the group (LD50) of sodium sulfide 2.5 times. Neither oxygen, thiosulfate, nor the combination potentiated the protective effects of nitrite against sulfide poisoning. Antidotal effects of nitrite in acute sulfide poisoning were demonstrated in rats. The therapeutic efficacy of nitrite in acute poisoning is clearly superior to that of oxygen, which is the more widely recommended antidote.

Acute cyanide poisoning

Cyanide poisoning results in cytotoxic hypoxia due to the inactivation of mitochondrial cytochrome oxidase. The pathophysiology of this intoxication is discussed and antidotal therapies are examined and contrasted.

Two case reports of patients with acute poisoning are presented. The importance of general supportive measures, the administration of 100 per cent oxygen and reversal of metabolic acidosis are stressed.