Novel, orally effective cyanide antidotes

Dimethyl Sulfoxide (DMSO) as a Potential Source of Interference in Research Related to Sulfur Metabolism-A Preliminary Study

Dimethyl sulfoxide (DMSO), an organosulfur compound, is widely used as the gold standard solvent in biological research. It is used in cell culture experiments and as a component of formulations in in vivo studies. Unfortunately, parameters related to sulfur metabolism are often not taken into account when using DMSO. Therefore, in this work we aim to show that the addition of DMSO to the culture medium (even in amounts commonly considered acceptable) alters some parameters of sulfur metabolism. For this study, we used three cell lines: a commercially available Caco-2 line (HTB-37, ATCC) and two lines created as part of our early studies (likewise previously described in the literature) to investigate the anomalies of sulfur metabolism in mucopolysaccharidosis. As the negative effects of DMSO on the cell membrane are well known, additional experiments with the partial loading of DMSO into polymerosomes (poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide), PEG-PLGA) were performed to eliminate these potentially disruptive effects. The results show that DMSO is a source of interference in studies related to sulfur metabolism and that there are not just simple effects that can be corrected in the final result by subtracting control values, since complex synergisms are also observed.

The two faces of cyanide: an environmental toxin and a potential novel mammalian gasotransmitter

Cyanide is traditionally viewed as a cytotoxic agent, with its primary mode of action being the inhibition of mitochondrial Complex IV (cytochrome c oxidase). However, recent studies demonstrate that the effect of cyanide on Complex IV in various mammalian cells is biphasic: in lower concentrations (nanomolar to low micromolar) cyanide stimulates Complex IV activity, increases ATP production and accelerates cell proliferation, while at higher concentrations (high micromolar to low millimolar) it produces the previously known ('classic') toxic effects. The first part of the article describes the cytotoxic actions of cyanide in the context of environmental toxicology, and highlights pathophysiological conditions (e.g., cystic fibrosis with Pseudomonas colonization) where bacterially produced cyanide exerts deleterious effects to the host. The second part of the article summarizes the mammalian sources of cyanide production and overviews the emerging concept that mammalian cells may produce cyanide, in low concentrations, to serve biological regulatory roles. Cyanide fulfills many of the general criteria as a 'classical' mammalian gasotransmitter and shares some common features with the current members of this class: nitric oxide, carbon monoxide, and hydrogen sulfide.

Leveraging an enzyme/artificial substrate system to enhance cellular persulfides and mitigate neuroinflammation

Persulfides and polysulfides, collectively known as the sulfane sulfur pool along with hydrogen sulfide (H2S), play a central role in cellular physiology and disease. Exogenously enhancing these species in cells is an emerging therapeutic paradigm for mitigating oxidative stress and inflammation that are associated with several diseases. In this study, we present a unique approach of using the cell's own enzyme machinery coupled with an array of artificial substrates to enhance the cellular sulfane sulfur pool. We report the synthesis and validation of artificial/unnatural substrates specific for 3-mercaptopyruvate sulfurtransferase (3-MST), an important enzyme that contributes to sulfur trafficking in cells. We demonstrate that these artificial substrates generate persulfides in vitro as well as mediate sulfur transfer to low molecular weight thiols and to cysteine-containing proteins. A nearly 100-fold difference in the rates of H2S production for the various substrates is observed supporting the tunability of persulfide generation by the 3-MST enzyme/artificial substrate system. Next, we show that the substrate 1a permeates cells and is selectively turned over by 3-MST to generate 3-MST-persulfide, which protects against reactive oxygen species-induced lethality. Lastly, in a mouse model, 1a is found to significantly mitigate neuroinflammation in the brain tissue. Together, the approach that we have developed allows for the on-demand generation of persulfides in vitro and in vivo using a range of shelf-stable, artificial substrates of 3-MST, while opening up possibilities of harnessing these molecules for therapeutic applications.

Hyaluronic Acid-Based Nanocapsules as Efficient Delivery Systems of Garlic Oil Active Components with Anticancer Activity

Diallyl disulfide (DADS) and diallyl trisulfide (DATS) are garlic oil compounds exhibiting beneficial healthy properties including anticancer action. However, these compounds are sparingly water-soluble with a limited stability that may imply damage to blood vessels or cells after administration. Thus, their encapsulation in the oil-core nanocapsules based on a derivative of hyaluronic acid was investigated here as a way of protecting against oxidation and undesired interactions with blood and digestive track components. The nuclear magnetic resonance (¹H NMR) technique was used to follow the oxidation processes. It was proved that the shell of the capsule acts as a barrier limiting the sulfur oxidation, enhancing the stability of C=C bonds in DADS and DATS. Moreover, it was shown that the encapsulation inhibited the lysis of the red blood cell membrane (mainly for DADS) and interactions with serum or digestive track components. Importantly, the biological functions and anticancer activity of DADS and DATS were preserved after encapsulation. Additionally, the nanocapsule formulations affected the migration of neoplastic cells—a desirable preliminary observation concerning the inhibition of migration. The proposed route of administration of these garlic extract components would enable reaching their higher concentrations in blood, longer circulation in a bloodstream, and thus, imply a better therapeutic effect.

2-Mercaptomethyl-thiazolidines use conserved aromatic-S interactions to achieve broad-range inhibition of metallo-β-lactamases

Infections caused by multidrug resistant (MDR) bacteria are a major public health threat. Carbapenems are among the most potent antimicrobial agents that are commercially available to treat MDR bacteria. Bacterial production of carbapenem-hydrolysing metallo-β-lactamases (MBLs) challenges their safety and efficacy, with subclass B1 MBLs hydrolysing almost all β-lactam antibiotics. MBL inhibitors would fulfil an urgent clinical need by prolonging the lifetime of these life-saving drugs. Here we report the synthesis and activity of a series of 2-mercaptomethyl-thiazolidines (MMTZs), designed to replicate MBL interactions with reaction intermediates or hydrolysis products. MMTZs are potent competitive inhibitors of B1 MBLs in vitro (e.g., K i = 0.44 μM vs. NDM-1). Crystal structures of MMTZ complexes reveal similar binding patterns to the most clinically important B1 MBLs (NDM-1, VIM-2 and IMP-1), contrasting with previously studied thiol-based MBL inhibitors, such as bisthiazolidines (BTZs) or captopril stereoisomers, which exhibit lower, more variable potencies and multiple binding modes. MMTZ binding involves thiol coordination to the Zn(ii) site and extensive hydrophobic interactions, burying the inhibitor more deeply within the active site than d/l-captopril. Unexpectedly, MMTZ binding features a thioether-π interaction with a conserved active-site aromatic residue, consistent with their equipotent inhibition and similar binding to multiple MBLs. MMTZs penetrate multiple Enterobacterales, inhibit NDM-1 in situ, and restore carbapenem potency against clinical isolates expressing B1 MBLs. Based on their inhibitory profile and lack of eukaryotic cell toxicity, MMTZs represent a promising scaffold for MBL inhibitor development. These results also suggest sulphur-π interactions can be exploited for general ligand design in medicinal chemistry.

Murine cellular model of mucopolysaccharidosis, type IIIB (MPS IIIB) - A preliminary study with particular emphasis on the non-oxidative l-cysteine metabolism

The lack of the N-alpha-glucosaminidase (Naglu) is responsible for the incidence of a rare disease - mucopolysaccharidosis, type IIIB (MPS IIIB). To date, studies have been conducted based on cells derived from patients suffering from MPS or using in vivo MPS mouse models. These limitations have allowed for defining our research goal - to create and characterize the first in vitro murine cellular MPS IIIB model. In the current work we present a new, stable cell line with confirmed accumulation of glycosaminoglycans. The line stability was achieved by immortalization using a lentivirus carrying the T-antigens of SV40. The Naglu^-/- cells were confirmed to produce no Naglu enzyme. To confirm the proper functioning of the in vitro MPS IIIB model, we determined the activity and expression of cystathionine γ-lyase, rhodanese and 3-mercaptopyruvate sulfurtransferase, as well as the level of low molecular-weight thiols (reduced and oxidized glutathione, cysteine and cystine). The results were referred to our earlier findings originating from the studies on the tissues of the Naglu^-/- mice that were used to create the lines. The results obtained in the Naglu^-/- cells were in accordance with the results found in the mouse model of MPS IIIB. It suggests that the presented murine Naglu^-/- cell lines might be a convenient in vitro model of MPS IIIB.

Sulfur metabolism and its contribution to malignancy

Metabolic dysregulation is an appreciated hallmark of cancer and a target for therapeutic intervention. Cellular metabolism involves a series of oxidation/reduction (redox) reactions that yield the energy and biomass required for tumor growth. Cells require diverse molecular species with constituent sulfur atoms to facilitate these processes. For humans, this sulfur is derived from the dietary consumption of the proteinogenic amino acids cysteine and methionine, as only lower organisms (e.g., bacteria, fungi, and plants) can synthesize them de novo. In addition to providing the sulfur required to sustain redox chemistry, the metabolism of these sulfur-containing amino acids yield intermediate metabolites that constitute the cellular antioxidant system, mediate inter- and intracellular signaling, and facilitate the epigenetic regulation of gene expression, all of which contribute to tumorigenesis.

Synthesis, Characterisation and Reactivity of 3-Mercaptopyruvic Acid

The synthesis, isolation and spectroscopic characterisation of the sulfur metabolic compound 3-mercaptopyruvic acid (3-MPH) is reported, for the first time. The compound is isolated without tedious workup, with a purity of 97 %, as indicated by chemical and biochemical analyses. Detailed kinetic and thermodynamic studies of its complex behaviour in solution are discussed. 3-MPH is stable in the enol form in non-polar solvent. In polar solvent, a fast equilibrium between the α-ketoacid and a cyclic dimer dithiane is observed. The formation of the dimer confers increased stability to 3-MPH towards hydrogen peroxide, in comparison with cysteine.

The Role of Nitroglycerin and Other Nitrogen Oxides in Cardiovascular Therapeutics

The use of nitroglycerin in the treatment of angina pectoris began not long after its original synthesis in 1847. Since then, the discovery of nitric oxide as a biological effector and better understanding of its roles in vasodilation, cell permeability, platelet function, inflammation, and other vascular processes have advanced our knowledge of the hemodynamic (mostly mediated through vasodilation of capacitance and conductance arteries) and nonhemodynamic effects of organic nitrate therapy, via both nitric oxide-dependent and -independent mechanisms. Nitrates are rapidly absorbed from mucous membranes, the gastrointestinal tract, and the skin; thus, nitroglycerin is available in a number of preparations for delivery via several routes: oral tablets, sublingual tablets, buccal tablets, sublingual spray, transdermal ointment, and transdermal patch, as well as intravenous formulations. Organic nitrates are commonly used in the treatment of cardiovascular disease, but clinical data limit their use mostly to the treatment of angina. They are also used in the treatment of subsets of patients with heart failure and pulmonary hypertension. One major limitation of the use of nitrates is the development of tolerance. Although several agents have been studied for use in the prevention of nitrate tolerance, none are currently recommended owing to a paucity of supportive clinical data. Only 1 method of preventing nitrate tolerance remains widely accepted: the use of a dosing strategy that provides an interval of no or low nitrate exposure during each 24-h period. Nitric oxide's important role in several cardiovascular disease mechanisms continues to drive research toward finding novel ways to affect both endogenous and exogenous sources of this key molecular mediator.

An Official American Thoracic Society Workshop Report: Chemical Inhalational Disasters. Biology of Lung Injury, Development of Novel Therapeutics, and Medical Preparedness

This report is based on the proceedings from the Inhalational Lung Injury Workshop jointly sponsored by the American Thoracic Society (ATS) and the National Institutes of Health (NIH) Countermeasures Against Chemical Threats (CounterACT) program on May 21, 2013, in Philadelphia, Pennsylvania. The CounterACT program facilitates research leading to the development of new and improved medical countermeasures for chemical threat agents. The workshop was initiated by the Terrorism and Inhalational Disasters Section of the Environmental, Occupational, and Population Health Assembly of the ATS. Participants included both domestic and international experts in the field, as well as representatives from U.S. governmental funding agencies. The meeting objectives were to (1) provide a forum to review the evidence supporting current standard medical therapies, (2) present updates on our understanding of the epidemiology and underlying pathophysiology of inhalational lung injuries, (3) discuss innovative investigative approaches to further delineating mechanisms of lung injury and identifying new specific therapeutic targets, (4) present promising novel medical countermeasures, (5) facilitate collaborative research efforts, and (6) identify challenges and future directions in the ongoing development, manufacture, and distribution of effective and specific medical countermeasures. Specific inhalational toxins discussed included irritants/pulmonary toxicants (chlorine gas, bromine, and phosgene), vesicants (sulfur mustard), chemical asphyxiants (cyanide), particulates (World Trade Center dust), and respirable nerve agents.

In-vitro mercaptopyruvate sulfurtransferase species comparison in humans and common laboratory animals

Cyanide is a metabolic poison that inhibits cytochrome c oxidase. Its broad applications in manufacturing and history as an agent of warfare/terror highlight the limitations in approved cyanide antidotes for mass casualties. Sulfanegen, a pre-clinical antidote for cyanide poisoning, exploits an endogenous detoxification pathway and should be amenable to mass-casualty scenarios. Because human studies are unethical, determination of appropriate animal species as models in translational studies for FDA approval under the "Animal Rule" are critical. Here, we compared the specific activities of mercaptopyruvate sulfurtransferase (MST, required for sulfanegen's activity), across common laboratory models of cyanide intoxication, and humans. Human MST activities in erythrocytes (measured as micromole pyruvate/min/10⁶ rbc) were closest to those of Swiss-Webster mice and NZW rabbits. Similar species were selected for a more detailed tissue-specific comparison of MST activities. NZW Rabbits were closest to humans in the liver and kidney mitochondrial fractions, the Swiss-Webster mouse was closest to humans in the liver cytosolic fraction, while C57BL/6 mouse was closest in the kidney cytosolic fraction. These data comparing MST activities in animal models will help justify the use of those specific animals per the animal rule. Interestingly, statistically significant differences were found in MST activities of liver mitochondria between human smokers and non-smokers (p=0.0030).

Development of sulfanegen for mass cyanide casualties

Cyanide is a metabolic poison that inhibits the utilization of oxygen to form ATP. The consequences of acute cyanide exposure are severe; exposure results in loss of consciousness, cardiac and respiratory failure, hypoxic brain injury, and dose-dependent death within minutes to hours. In a mass-casualty scenario, such as an industrial accident or terrorist attack, currently available cyanide antidotes would leave many victims untreated in the short time available for successful administration of a medical countermeasure. This restricted therapeutic window reflects the rate-limiting step of intravenous administration, which requires both time and trained medical personnel. Therefore, there is a need for rapidly acting antidotes that can be quickly administered to large numbers of people. To meet this need, our laboratory is developing sulfanegen, a potential antidote for cyanide poisoning with a novel mechanism based on 3-mercaptopyruvate sulfurtransferase (3-MST) for the detoxification of cyanide. Additionally, sulfanegen can be rapidly administered by intramuscular injection and has shown efficacy in many species of animal models. This article summarizes the journey from concept to clinical leads for this promising cyanide antidote.

Dimethyl trisulfide: A novel cyanide countermeasure

In the present studies, the in vitro and in vivo efficacies of a novel cyanide countermeasure, dimethyl trisulfide (DMTS), were evaluated. DMTS is a sulfur-based molecule found in garlic, onion, broccoli, and similar plants. DMTS was studied for effectiveness as a sulfur donor-type cyanide countermeasure. The sulfur donor reactivity of DMTS was determined by measuring the rate of the formation of the cyanide metabolite thiocyanate. In experiments carried out in vitro in the presence of the sulfurtransferase rhodanese (Rh) and at the experimental pH of 7.4, DMTS was observed to convert cyanide to thiocyanate with greater than 40 times higher efficacy than does thiosulfate, the sulfur donor component of the US Food and Drug Administration-approved cyanide countermeasure Nithiodote^® In the absence of Rh, DMTS was observed to be almost 80 times more efficient than sodium thiosulfate in vitro The fact that DMTS converts cyanide to thiocyanate more efficiently than does thiosulfate both with and without Rh makes it a promising sulfur donor-type cyanide antidote (scavenger) with reduced enzyme dependence in vitro The therapeutic cyanide antidotal efficacies for DMTS versus sodium thiosulfate were measured following intramuscular administration in a mouse model and expressed as antidotal potency ratios (APR = LD₅₀ of cyanide with antidote/LD₅₀ of cyanide without antidote). A dose of 100 mg/kg sodium thiosulfate given intramuscularly showed only slight therapeutic protection (APR = 1.1), whereas the antidotal protection from DMTS given intramuscularly at the same dose was substantial (APR = 3.3). Based on these data, DMTS will be studied further as a promising next-generation countermeasure for cyanide intoxication.

Past, present and future of cyanide antagonism research: From the early remedies to the current therapies

This paper reviews milestones in antidotal therapies for cyanide (CN) spanning early remedies, current antidotal systems and research towards next generation therapies. CN has been a part of plant defense mechanisms for millions of years. It became industrially important in the nineteenth century with the advent of CN assisted gold mining and the use of CN as a pest control agent. The biochemical basis of CN poisoning was actively studied and key mechanisms were understood as early as 1929. These fundamental studies led to a variety of antidotes, including indirect CN binders that generate methemoglobin, direct CN binders such as hydroxocobalamin, and sulfur donors that convert CN to the less toxic thiocyanate. Research on blood gases at the end of the twentieth century shed new light on the role of nitric oxide (NO) in the body. The discovery of NO’s ability to compete with CN for enzymatic binding sites provided a previously missed explanation for the rapid efficacy of NO generating antidotes such as the nitrites. Presently used CN therapies include: methemoglobin/NO generators (e.g., sodium nitrite, amyl nitrite, and dimethyl aminophenol), sulfur donors (e.g., sodium thiosulfate and glutathione), and direct binding agents [(e.g., hydroxocobalamin and dicobalt salt of ethylenediaminetetraacetic acid (dicobalt edetate)]. A strong effort is being made to explore novel antidotal systems and to formulate them for rapid administration at the point of intoxication in mass casualty scenarios. New antidotes, formulations, and delivery systems are enhancing bioavailability and efficacy and hold promise for a new generation of improved CN countermeasures.

Sodium nitroprusside in 2014: A clinical concepts review

Sodium nitroprusside has been used in clinical practice as an arterial and venous vasodilator for 40 years. This prodrug reacts with physiologic sulfhydryl groups to release nitric oxide, causing rapid vasodilation, and acutely lowering blood pressure. It is used clinically in cardiac surgery, hypertensive crises, heart failure, vascular surgery, pediatric surgery, and other acute hemodynamic applications. In some practices, newer agents have replaced nitroprusside, either because they are more effective or because they have a more favorable side-effect profile. However, valid and adequately-powered efficacy studies are sparse and do not identify a superior agent for all indications. The cyanide anion release concurrent with nitroprusside administration is associated with potential cyanide accumulation and severe toxicity. Agents to ameliorate the untoward effects of cyanide are limited by various problems in their practicality and effectiveness. A new orally bioavailable antidote is sodium sulfanegen, which shows promise in reversing this toxicity. The unique effectiveness of nitroprusside as a titratable agent capable of rapid blood pressure control will likely maintain its utilization in clinical practice for the foreseeable future. Additional research will refine and perhaps expand indications for nitroprusside, while parallel investigation continues to develop effective antidotes for cyanide poisoning.

Determination of 3-mercaptopyruvate in rabbit plasma by high performance liquid chromatography tandem mass spectrometry

Accidental or intentional cyanide poisoning is a serious health risk. The current suite of FDA approved antidotes, including hydroxocobalamin, sodium nitrite, and sodium thiosulfate is effective, but each antidote has specific major limitations, such as large effective dosage or delayed onset of action. Therefore, next generation cyanide antidotes are being investigated to mitigate these limitations. One such antidote, 3-mercaptopyruvate (3-MP), detoxifies cyanide by acting as a sulfur donor to convert cyanide into thiocyanate, a relatively nontoxic cyanide metabolite. An analytical method capable of detecting 3-MP in biological fluids is essential for the development of 3-MP as a potential antidote. Therefore, a high performance liquid chromatography tandem mass spectrometry (HPLC-MS-MS) method was established to analyze 3-MP from rabbit plasma. Sample preparation consisted of spiking the plasma with an internal standard ((13)C3-3-MP), precipitation of plasma proteins, and reaction with monobromobimane to inhibit the characteristic dimerization of 3-MP. The method produced a limit of detection of 0.1μM, a linear dynamic range of 0.5-100μM, along with excellent linearity (R(2)≥0.999), accuracy (±9% of the nominal concentration) and precision (<7% relative standard deviation). The optimized HPLC-MS-MS method was capable of detecting 3-MP in rabbits that were administered sulfanegen, a prodrug of 3-MP, following cyanide exposure. Considering the excellent performance of this method, it will be utilized for further investigations of this promising cyanide antidote.

Accelerated stability and bioassay of a new oral α-ketoglutarate formulation for treating cyanide poisoning

CONTEXT

Due to several limitations of existing cyanide antidotes, α-ketoglutarate (α-KG) has been proposed as a promising treatment for cyanide.

OBJECTIVE

This study reports the accelerated stability and bioassay of a new oral α-KG formulation.

MATERIALS AND METHODS

Amber-colored PVDF bottles containing 100 ml of 10% α-KG in 70% sorbitol, preservative (sodium methyl paraben and sodium propyl paraben), sweetener (sodium saccharine), flavor (American ice-cream soda and peppermint) and color (tartrazine), at pH 7.0-8.0 were stored in stability chamber (40 ± 2 °C and 75 ± 5% humidity) for 6 months in a GMP compliant facility. Various physical (pH, color, evaporation, extractable volume and clarity), chemical (identification and quantification of active ingredient) and microbiological (total aerobic count) analyses, together with protection studies were carried periodically in mice. Acute toxicity of the formulation and bioavailability of α-KG were assessed in rats at the beginning of the experiment.

RESULTS

No physical changes and microbiological growth were observed in the formulation. After 6 months, α-KG content in the formulation diminished by ∼24% but its protective efficacy against cyanide remained at 5.9-fold. Protection was further characterized spectrophotometrically by disappearance of α-KG spectrum in the presence of cyanide, confirming cyanohydrin formation. Oral LD50 of α-KG formulation in rats was >7.0 g/kg body weight, and did not produce any acute toxicity of clinical significance. Also, an appreciable amount of α-KG was measured in blood.

CONCLUSION

As per the guidelines of International Conference on Harmonization, the new α-KG formulation exhibited satisfactory stability, bioefficacy and safety as cyanide antidote.

Exposure to lead in water and cysteine non-oxidative metabolism in Pelophylax ridibundus tissues

Chronic, low-level exposure to metals is an increasing global problem. Lead is an environmentally persistent toxin that causes many lead-related pathologies, directly affects tissues and cellular components or exerts an effect of the generation of reactive oxygen species causing a diminished level of available sulfhydryl antioxidant reserves. Cysteine is one of substrates in the synthesis of glutathione - the most important cellular antioxidant, and it may also undergo non-oxidative desulfuration that produces compounds containing sulfane sulfur atoms. The aim of the experiment was to examine changes of the non-oxidative metabolism of cysteine and the levels of cysteine and glutathione in the kidneys, heart, brain, liver and muscle of Marsh frogs (Pelophylax ridibundus) exposed to 28mg/L Pb(NO(3))(2) for 10 days. The activities of sulfurtransferases, enzymes related to the sulfane sulfur metabolism - 3-mercaptopyruvate sulfurtransfearse, γ-cystathionase and rhodanese - were detected in tissue homogenates. The activity of sulfurtransferases was much higher in the kidneys of frogs exposed to lead in comparison to control frogs, not exposed to lead. The level of sulfane sulfur remained unchanged. Similarly, the total level of cysteine did not change significantly. The total levels of glutathione and the cysteine/cystine and GSH/GSSG ratios were elevated. Thus, it seems that the exposure to lead intensified the metabolism of sulfane sulfur and glutathione synthesis in the kidneys. The results presented in this work not only confirm the participation of GSH in the detoxification of lead ions and/or products appearing in response to their presence, such as reactive oxygen species, but also indicate the involvement of sulfane sulfur and rhodanese in this process (e.g. brain). As long as the expression of enzymatic proteins (rhodanese, MPST and CST) is not examined, no answer will be provided to the question whether changes in their activity are due to differences in the concentrations of substrates and/or compounds affecting their activity or to changes in their level in response to some parameters, e.g. associated with oxidative stress.

Cyanide antidotes for mass casualties: water-soluble salts of the dithiane (sulfanegen) from 3-mercaptopyruvate for intramuscular administration

Current cyanide antidotes are administered by IV infusion, which is suboptimal for mass casualties. Therefore, in a cyanide disaster, intramuscular (IM) injectable antidotes would be more appropriate. We report the discovery of the highly water-soluble sulfanegen triethanolamine as a promising lead for development as an IM injectable cyanide antidote.

Noninvasive monitoring of treatment response in a rabbit cyanide toxicity model reveals differences in brain and muscle metabolism

Noninvasive near infrared spectroscopy measurements were performed to monitor cyanide (CN) poisoning and recovery in the brain region and in foreleg muscle simultaneously, and the effects of a novel CN antidote, sulfanegen sodium, on tissue hemoglobin oxygenation changes were compared using a sub-lethal rabbit model. The results demonstrated that the brain region is more susceptible to CN poisoning and slower in endogenous CN detoxification following exposure than peripheral muscles. However, sulfanegen sodium rapidly reversed CN toxicity, with brain region effects reversing more quickly than muscle. In vivo monitoring of multiple organs may provide important clinical information regarding the extent of CN toxicity and subsequent recovery, and facilitate antidote drug development.

Cyanide toxicity in juvenile pigs and its reversal by a new prodrug, sulfanegen sodium

BACKGROUND

Cyanide (CN) toxicity is a serious clinical problem and can occur with sodium nitroprusside (SNP) administration, accidental smoke inhalation, industrial mishaps, and bio-terrorism. In this study, we induced severe CN toxicity independently with SNP or sodium cyanide (NaCN) in a juvenile pig model to demonstrate reversal of severe CN toxicity with a new antidote, sulfanegen sodium, a prodrug of 3-mercaptopyruvate.

METHODS

SNP study: A pilot study in 11 anesthetized, mechanically ventilated juvenile pigs allowed us to determine the dose of SNP to induce CN toxicity. Blood CN, serum lactates, and blood gases were monitored. CN toxicity was defined as the occurrence of severe lactic acidosis accompanied by significant elevation in blood CN levels. Based on this pilot study, 8 anesthetized pigs received a high-dose i.v. infusion of SNP (100 mg/h) for 2 hours to induce CN toxicity. They were then randomized to receive either sulfanegen sodium or placebo. Four pigs received 3 doses of sulfanegen sodium (2.5 g i.v.) every hour after induction of severe CN toxicity, and 4 pigs received placebo. NaCN study: A pilot study was conducted in 4 spontaneously ventilating pigs sedated with propofol plus ketamine to demonstrate hemodynamic and metabolic stability for several hours. After this, 6 pigs were similarly sedated and given NaCN in bolus aliquots to produce CN toxicity ultimately resulting in death. Hemodynamics and metabolic variables were followed to define peak CN toxicity. In another group of 6 pigs, severe CN toxicity was induced by this method, and at peak toxicity, the animals were given sulfanegen sodium (2.5 g i.v.) followed by a repeat dose 60 minutes later in surviving animals.

RESULTS

SNP study: The pilot study demonstrated the occurrence of a significant increase in blood CN levels (P < 0.05) accompanied by severe lactic acidemia (P < 0.05) in all pigs receiving a high dose of SNP. Administration of the sulfanegen antidote resulted in progressive significant reduction in blood lactate and CN levels with 100% survival (P < 0.05), whereas the placebo-treated pigs deteriorated and did not survive (P < 0.05). NaCN study: NaCN injection resulted in CN toxicity accompanied by severe lactic acidosis and mortality in all the pigs. Sulfanegen sodium reversed this toxicity and prevented mortality in all the pigs treated with this antidote.

CONCLUSIONS

CN toxicity can be successfully induced in a juvenile pig model with SNP or NaCN. The prodrug, sulfanegen sodium, is effective in reversing CN toxicity induced by SNP or NaCN.

The combination of cobinamide and sulfanegen is highly effective in mouse models of cyanide poisoning

CONTEXT

Cyanide is a component of smoke in residential and industrial fires, and accidental exposure to cyanide occurs in a variety of industries. Moreover, cyanide has the potential to be used by terrorists, particularly in a closed space such as an airport or train station. Current therapies for cyanide poisoning must be given by intravenous administration, limiting their use in treating mass casualties.

OBJECTIVE

We are developing two new cyanide antidotes--cobinamide, a vitamin B(12) analog, and sulfanegen, a 3-mercaptopyruvate prodrug. Both drugs can be given by intramuscular administration, and therefore could be used to treat a large number of people quickly. We now asked if the two drugs would have an augmented effect when combined.

MATERIALS AND METHODS

We used a non-lethal and two different lethal models of cyanide poisoning in mice. The non-lethal model assesses neurologic recovery by quantitatively evaluating the innate righting reflex time of a mouse. The two lethal models are a cyanide injection and a cyanide inhalation model.

RESULTS

We found that the two drugs are at least additive when used together in both the non-lethal and lethal models: at doses where all animals died with either drug alone, the combination yielded 80 and 40% survival in the injection and inhalation models, respectively. Similarly, drug doses that yielded 40% survival with either drug alone, yielded 80 and 100% survival in the injection and inhalation models, respectively. As part of the inhalation model, we developed a new paradigm in which animals are exposed to cyanide gas, injected intramuscularly with an antidote, and then re-exposed to cyanide gas. This simulates cyanide exposure of a large number of people in a closed space, because people would remain exposed to cyanide, even after receiving an antidote.

CONCLUSION

The combination of cobinamide and sulfanegen shows great promise as a new approach to treating cyanide poisoning.

Sulfanegen sodium treatment in a rabbit model of sub-lethal cyanide toxicity

The aim of this study is to investigate the ability of intramuscular and intravenous sulfanegen sodium treatment to reverse cyanide effects in a rabbit model as a potential treatment for mass casualty resulting from cyanide exposure. Cyanide poisoning is a serious chemical threat from accidental or intentional exposures. Current cyanide exposure treatments, including direct binding agents, methemoglobin donors, and sulfur donors, have several limitations. Non-rhodanese mediated sulfur transferase pathways, including 3-mercaptopyruvate sulfurtransferase (3-MPST) catalyze the transfer of sulfur from 3-MP to cyanide, forming pyruvate and less toxic thiocyanate. We developed a water-soluble 3-MP prodrug, 3-mercaptopyruvatedithiane (sulfanegen sodium), with the potential to provide a continuous supply of substrate for CN detoxification. In addition to developing a mass casualty cyanide reversal agent, methods are needed to rapidly and reliably diagnose and monitor cyanide poisoning and reversal. We use non-invasive technology, diffuse optical spectroscopy (DOS) and continuous wave near infrared spectroscopy (CWNIRS) to monitor physiologic changes associated with cyanide exposure and reversal. A total of 35 animals were studied. Sulfanegen sodium was shown to reverse the effects of cyanide exposure on oxyhemoglobin and deoxyhemoglobin rapidly, significantly faster than control animals when administered by intravenous or intramuscular routes. RBC cyanide levels also returned to normal faster following both intramuscular and intravenous sulfanegen sodium treatment than controls. These studies demonstrate the clinical potential for the novel approach of supplying substrate for non-rhodanese mediated sulfur transferase pathways for cyanide detoxification. DOS and CWNIRS demonstrated their usefulness in optimizing the dose of sulfanegen sodium treatment.

A novel paradigm for assessing efficacies of potential antidotes against neurotoxins in mice

Historically, antidotal potencies of cyanide antagonists were measured as increases in the experimental LD(50) for cyanide elicited by the antidotes. This required the use of high doses of cyanide following pre-treatment with the putative antidote. Since IACUC guidelines at our institutions strongly discourage LD(50) determinations: we developed a new test paradigm that allowed for maximal survival of cyanide-treated animals with greatly reduced numbers of animals. Symptoms of cyanide toxicity include disruption of neuromuscular coordination, i.e., the righting reflex. Therefore, to establish a dose-response curve, the times required for recovery of this righting reflex with increasing doses of cyanide were measured. A cyanide dose that disrupted this righting reflex for approximately 1h with minimal deaths was then selected. Using this paradigm, the current cyanide antidotes, viz., nitrite plus thiosulfate and hydroxocobalamin, as well as some potential cyanide antidotes that we developed, were evaluated pre- and post-cyanide. This allowed, for the first time, the assessment of the post-cyanide effectiveness of the current antidotes against cyanide poisoning in a live animal. In addition, some prototype compounds were found to exhibit antidotal efficacy not only when injected i.p. following cyanide, but also when administered orally 30 min before cyanide. Pre-cyanide oral efficacy suggests that such compounds have the potential of being administered prophylactically before exposure to cyanide. This new test paradigm was found to be a powerful tool for assessing the efficacies of some novel antidotes against cyanide and should be equally applicable for evaluating putative antidotes for other neurotoxins.