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

Cyanide and Cyanogenic Compounds-Toxicity, Molecular Targets, and Therapeutic Agents

Cyanide (CN) is a well-known mitochondrial poison. CN poisoning may result from acute or long-term exposure to a number of CN compounds. Recent insight into the chemical affinities of the CN anion has increased our understanding of its toxicity and the mechanisms of antidotal actions, which, together with information on various exposure sources, are reviewed in the present article. A literature search in Scopus, Embase, Web of Science, PubMed, and Google Scholar for the period 2001-2024 revealed that the CN anion after exposure or degradation of CN compounds is distributed to vulnerable copper and iron-containing targets, especially in mitochondria, thus blocking the electron transport chain. Intake of cyanogenic compounds may exert subacute or chronic toxic effects, also because of the interaction with cobalt in vitamin B12. Antidotal agents exert their effects through the affinity of CN for cobalt- or iron-containing compounds. Research on CN interactions with metalloproteins may increase our insight into CN toxicity and efficient antidotal regimens.

Designing hollow-core PCF sensors for high-performance terahertz detection of NaCN and KCN

Cyanide is very poisonous and raises environmental problems because of its industrial application and potential as a terrorist weapon. Given CN's toxicity and possible hazard to people, an effective and adaptive detection approach is needed. This specification suggests using a PCF to build a terahertz Hexagonal Core and Curved rectangular air holes sensor to detect NaCN and KCN. The recently created PCF analysis, which was promptly delivered, reveals an RS concentration of 99.62 % for NaCN and a maximum concentration of KCN is 99.08 %. In addition, we analyzed the Confinement Loss (CL) at a value of 5.88 × 10-09 dB/m and 2.07 × 10-05 dB/m, as well as EML at values of 0.0020 cm-1 and 0.0026 cm-1, accordingly, about these hazardous substances. The designed detector can identify NaCN and KCN at low concentrations even with small RI shifts due to its high sensitivity. Real-time NaCN and KCN detection and monitoring through nerve reflexes is essential for life-threatening conditions. It can selectively work in NaCN and KCN, ensuring accurate detection even in complex chemical compositions. Additionally, its tiny size allows for emergency use.

A reaction based carbazole-indolium conjugate probe for the selective detection of environmentally toxic ions

A nucleophilic addition based chemodosimeter was designed and synthesized with a carbazole donor and an indole acceptor. The addition of a cyanide ion to an electron-deficient indole moiety disrupts the acceptor-donor relationship, resulting in noticeable color shifts and spectrum differences in both the absorption and emission profiles. The design has a D-π-A molecular arrangement. Selectivity was investigated in 90% aqueous DMSO solution of probe CI with various anions such as SCN-, PF6-, NO3-, N3-, I-, HSO4-, CN-, H2PO4-, F-, HS-, ClO4-, Cl-, Br-, and AcO-. An intermolecular charge transfer (ICT) band at 506 nm in the UV-visible spectra vanished and the intensity of emission was quenched at 624 nm upon the addition of CN- ions. These outcomes demonstrate the effective nucleophilic addition of cyanide ions to the electron-deficient indole moiety of the probe, resulting in the formation of a new adduct in which the ICT transition is interrupted when π conjugation is blocked. The Job plot, 1H NMR spectroscopy, and HRMS analysis confirmed the formation of a new product. An outstanding response was shown by paper test strips made using probe molecules for the easy detection of cyanide ions in aqueous solutions. Besides, the probe selectively senses cyanide ions in different water samples.

Elucidating the binding properties of methemoglobin in red blood cell to cyanide, hydrosulfide, and azide ions using artificial red blood cell

Methemoglobin (metHb), the oxidized form of hemoglobin, lacks the ability of reversible oxygen binding; however, it has a high binding affinity to toxic substances such as cyanide, hydrosulfide, and azide. This innate property of metHb offers the clinical option to treat patients poisoned with these toxins, by oxidizing the endogenous hemoglobin in the red blood cells (RBCs). The binding properties of naked metHb (isolated from RBC) with these toxins has been studied; however, the binding behaviors of metHb under the intracellular conditions of RBC are unclear because of the difficulty in detecting metHb status changes in RBC. This study aimed to elucidate the binding properties of metHb in RBC under physiological and poisoned conditions using artificial RBC, which was hemoglobin encapsulated in a liposome. The mimic-circumstances of metHb in RBC (metHb-V) was prepared by oxidizing the hemoglobin in artificial RBC. Spectroscopic analysis indicated that the metHb in metHb-V exhibited a binding behavior different from that of naked metHb, depending on the toxic substance: When the pH decreased, (i) the cyanide binding affinity of metHb-V remained unchanged, but that of naked metHb decreased (ii) the hydrosulfide binding affinity was increased in metHb-V but was decreased in naked metHb. (iii) Azide binding was increased in metHb-V, which was similar to that in naked metHb, irrespective of the pH change. Thus, the binding behavior of intracellular metHb in the RBC with cyanide, hydrosulfide, and azide under physiological and pathological conditions were partly elucidated using the oxidized artificial RBC.

Study on the performance of Anerinibacillus sp. in degrading cyanide wastewater and its metabolic mechanism

Cyanide extraction dominates the gold smelting industry, which leads to the generation of large amounts of cyanide-containing wastewater. In this study, Aneurinibacillus tyrosinisolvens strain named JK-1 was used for cyanide wastewater biodegradation. First, we tested the performance of JK-1 in degrading cyanide under different conditions. Then, we screened metabolic compounds and pathways associated with cyanide degradation by JK-1. Finally, we explored the potential JK-1-mediated cyanide degradation pathway. Our results showed that the optimal pH and temperature for cyanide biodegradation were 7.0 and 30 °C, respectively; under these conditions, a degradation rate of >98% was achieved within 48 h. Untargeted metabolomics results showed that increased cyanide concentration decreased the abundance of metabolic compounds by 71.1% but upregulated 32 metabolic pathways. The Kyoto Encyclopedia of Genes and Genomes enrichment results revealed significant changes in amino acid metabolism pathways during cyanide degradation by JK-1, including cyanoamino acid metabolism, β-alanine metabolism, and glutamate metabolism. Differential metabolic compounds included acetyl-CoA, l-asparagine, l-glutamic acid, l-phenylalanine, and l-glutamine. These results confirmed that cyanide degradation by JK-1 occurs through amino acid assimilation. This study provides new insights into the mechanism of cyanide biodegradation, which can be applied in the treatment of cyanide wastewater or tailings.

2023 American Heart Association Focused Update on the Management of Patients With Cardiac Arrest or Life-Threatening Toxicity Due to Poisoning: An Update to the American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care

In this focused update, the American Heart Association provides updated guidance for resuscitation of patients with cardiac arrest, respiratory arrest, and refractory shock due to poisoning. Based on structured evidence reviews, guidelines are provided for the treatment of critical poisoning from benzodiazepines, β-adrenergic receptor antagonists (also known as β-blockers), L-type calcium channel antagonists (commonly called calcium channel blockers), cocaine, cyanide, digoxin and related cardiac glycosides, local anesthetics, methemoglobinemia, opioids, organophosphates and carbamates, sodium channel antagonists (also called sodium channel blockers), and sympathomimetics. Recommendations are also provided for the use of venoarterial extracorporeal membrane oxygenation. These guidelines discuss the role of atropine, benzodiazepines, calcium, digoxin-specific immune antibody fragments, electrical pacing, flumazenil, glucagon, hemodialysis, hydroxocobalamin, hyperbaric oxygen, insulin, intravenous lipid emulsion, lidocaine, methylene blue, naloxone, pralidoxime, sodium bicarbonate, sodium nitrite, sodium thiosulfate, vasodilators, and vasopressors for the management of specific critical poisonings.

The Rhodanese PspE Converts Thiosulfate to Cellular Sulfane Sulfur in Escherichia coli

Hydrogen sulfide (H₂S) and its oxidation product zero-valent sulfur (S⁰) play important roles in animals, plants, and bacteria. Inside cells, S⁰ exists in various forms, including polysulfide and persulfide, which are collectively referred to as sulfane sulfur. Due to the known health benefits, the donors of H₂S and sulfane sulfur have been developed and tested. Among them, thiosulfate is a known H₂S and sulfane sulfur donor. We have previously reported that thiosulfate is an effective sulfane sulfur donor in Escherichia coli; however, it is unclear how it converts thiosulfate to cellular sulfane sulfur. In this study, we showed that one of the various rhodaneses, PspE, in E. coli was responsible for the conversion. After the thiosulfate addition, the ΔpspE mutant did not increase cellular sulfane sulfur, but the wild type and the complemented strain ΔpspE::pspE increased cellular sulfane sulfur from about 92 μM to 220 μM and 355 μM, respectively. LC-MS analysis revealed a significant increase in glutathione persulfide (GSSH) in the wild type and the ΔpspE::pspE strain. The kinetic analysis supported that PspE was the most effective rhodanese in E. coli in converting thiosulfate to glutathione persulfide. The increased cellular sulfane sulfur alleviated the toxicity of hydrogen peroxide during E. coli growth. Although cellular thiols might reduce the increased cellular sulfane sulfur to H₂S, increased H₂S was not detected in the wild type. The finding that rhodanese is required to convert thiosulfate to cellular sulfane sulfur in E. coli may guide the use of thiosulfate as the donor of H₂S and sulfane sulfur in human and animal tests.

Identification of Platinum(II) Sulfide Complexes Suitable as Intramuscular Cyanide Countermeasures

The development of rapidly acting cyanide countermeasures using intramuscular injection (IM) represents an unmet medical need to mitigate toxicant exposures in mass casualty settings. Previous work established that cisplatin and other platinum(II) or platinum(IV)-based agents effectively mitigate cyanide toxicity in zebrafish. Cyanide's in vivo reaction with platinum-containing materials was proposed to reduce the risk of acute toxicities. However, cyanide antidote activity depended on a formulation of platinum-chloride salts with dimethyl sulfoxide (DMSO) followed by dilution in phosphate-buffered saline (PBS). A working hypothesis to explain the DMSO requirement is that the formation of platinum-sulfoxide complexes activates the cyanide scavenging properties of platinum. Preparations of isolated NaPtCl₅-DMSO and Na (NH₃)₂PtCl-DMSO complexes in the absence of excess DMSO provided agents with enhanced reactivity toward cyanide in vitro and fully recapitulated in vivo cyanide rescue in zebrafish and mouse models. The enhancement of the cyanide scavenging effects of the DMSO ligand could be attributed to the activation of platinum(IV) and (II) with a sulfur ligand. Unfortunately, the efficacy of DMSO complexes was not robust when administered IM. Alternative Pt(II) materials containing sulfide and amine ligands in bidentate complexes show enhanced reactivity toward cyanide addition. The cyanide addition products yielded tetracyanoplatinate(II), translating to a stoichiometry of 1:4 Pt to each cyanide scavenger. These new agents demonstrate a robust and enhanced potency over the DMSO-containing complexes using IM administration in mouse and rabbit models of cyanide toxicity. Using the zebrafish model with these Pt(II) complexes, no acute cardiotoxicity was detected, and dose levels required to reach lethality exceeded 100 times the effective dose. Data are presented to support a general chemical design approach that can expand a new lead candidate series for developing next-generation cyanide countermeasures.

Root-Associated Bacteria Are Biocontrol Agents for Multiple Plant Pests

Biological control is an important process for sustainable plant production, and this trait is found in many plant-associated microbes. This study reviews microbes that could be formulated into pesticides active against various microbial plant pathogens as well as damaging insects or nematodes. The focus is on the beneficial microbes that colonize the rhizosphere where, through various mechanisms, they promote healthy plant growth. Although these microbes have adapted to cohabit root tissues without causing disease, they are pathogenic to plant pathogens, including microbes, insects, and nematodes. The cocktail of metabolites released from the beneficial strains inhibits the growth of certain bacterial and fungal plant pathogens and participates in insect and nematode toxicity. There is a reinforcement of plant health through the systemic induction of defenses against pathogen attack and abiotic stress in the plant; metabolites in the beneficial microbial cocktail function in triggering the plant defenses. The review discusses a wide range of metabolites involved in plant protection through biocontrol in the rhizosphere. The focus is on the beneficial firmicutes and pseudomonads, because of the extensive studies with these isolates. The review evaluates how culture conditions can be optimized to provide formulations containing the preformed active metabolites for rapid control, with or without viable microbial cells as plant inocula, to boost plant productivity in field situations.

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.

Glyoxylate protects against cyanide toxicity through metabolic modulation

Although cyanide's biological effects are pleiotropic, its most obvious effects are as a metabolic poison. Cyanide potently inhibits cytochrome c oxidase and potentially other metabolic enzymes, thereby unleashing a cascade of metabolic perturbations that are believed to cause lethality. From systematic screens of human metabolites using a zebrafish model of cyanide toxicity, we have identified the TCA-derived small molecule glyoxylate as a potential cyanide countermeasure. Following cyanide exposure, treatment with glyoxylate in both mammalian and non-mammalian animal models confers resistance to cyanide toxicity with greater efficacy and faster kinetics than known cyanide scavengers. Glyoxylate-mediated cyanide resistance is accompanied by rapid pyruvate consumption without an accompanying increase in lactate concentration. Lactate dehydrogenase is required for this effect which distinguishes the mechanism of glyoxylate rescue as distinct from countermeasures based solely on chemical cyanide scavenging. Our metabolic data together support the hypothesis that glyoxylate confers survival at least in part by reversing the cyanide-induced redox imbalances in the cytosol and mitochondria. The data presented herein represent the identification of a potential cyanide countermeasure operating through a novel mechanism of metabolic modulation.

Sodium Thiosulfate Improves Intestinal and Hepatic Microcirculation Without Affecting Mitochondrial Function in Experimental Sepsis

Introduction

In the immunology of sepsis microcirculatory and mitochondrial dysfunction in the gastrointestinal system are important contributors to mortality. Hydrogen sulfide (H₂S) optimizes gastrointestinal oxygen supply and mitochondrial respiration predominantly via K(ATP)-channels. Therefore, we tested the hypothesis that sodium thiosulfate (STS), an inducer of endogenous H₂S, improves intestinal and hepatic microcirculation and mitochondrial function via K(ATP)-channels in sepsis.

Methods

In 40 male Wistar rats colon ascendens stent peritonitis (CASP) surgery was performed to establish sepsis. Animals were randomized into 4 groups (1: STS 1 g • kg^-1 i.p., 2: glibenclamide (GL) 5 mg • kg^-1 i.p., 3: STS + GL, 4: vehicle (VE) i.p.). Treatment was given directly after CASP-surgery and 24 hours later. Microcirculatory oxygenation (µHBO₂) and flow (µflow) of the colon and the liver were continuously recorded over 90 min using tissue reflectance spectrophotometry. Mitochondrial oxygen consumption in tissue homogenates was determined with respirometry. Statistic: two-way ANOVA + Dunnett´s and Tukey post - hoc test (microcirculation) and Kruskal-Wallis test + Dunn’s multiple comparison test (mitochondria). p < 0.05 was considered significant.

Results

STS increased µHbO₂ (colon: 90 min: + 10.4 ± 18.3%; liver: 90 min: + 5.8 ± 9.1%; p < 0.05 vs. baseline). Furthermore, STS ameliorated µflow (colon: 60 min: + 51.9 ± 71.1 aU; liver: 90 min: + 22.5 ± 20.0 aU; p < 0.05 vs. baseline). In both organs, µHbO₂ and µflow were significantly higher after STS compared to VE. The combination of STS and GL increased colonic µHbO₂ and µflow (µHbO₂ 90 min: + 8.7 ± 11.5%; µflow: 90 min: + 41.8 ± 63.3 aU; p < 0.05 vs. baseline), with significantly higher values compared to VE. Liver µHbO₂ and µflow did not change after STS and GL. GL alone did not change colonic or hepatic µHbO₂ or µflow. Mitochondrial oxygen consumption and macrohemodynamic remained unaltered.

Conclusion

The beneficial effect of STS on intestinal and hepatic microcirculatory oxygenation in sepsis seems to be mediated by an increased microcirculatory perfusion and not by mitochondrial respiratory or macrohemodynamic changes. Furthermore, the effect of STS on hepatic but not on intestinal microcirculation seems to be K(ATP)-channel-dependent.

RETRACTED: Proof of concept efficacy study of intranasal stabilized isoamyl nitrite (SIAN) in rhesus monkeys against acute cyanide poisoning

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editors-in-Chief as the authors were unable to provide documentation of approval for the interinstitutional assurance /vertebrate animal section of the paper by the relevant authority, Public Health Service (PHS) Office of Laboratory Animal Welfare (OLAW) in the time that was provided.

Inhalation Injury: Unmet Clinical Needs and Future Research

Pulmonary and systemic insults from inhalation injury can complicate the care of burn patients and contribute to significant morbidity and mortality. However, recent progress in diagnosis and treatment of inhalation injury has not kept pace with the care of cutaneous thermal injury. There are many challenges unique to inhalation injury that have slowed advancement, including deficiencies in our understanding of its pathophysiology, the relative difficulty and subjectivity of bronchoscopic diagnosis, the lack of diagnostic biomarkers, the necessarily urgent manner in which decisions are made about intubation, and the lack of universal recommendations for the application of mucolytics, anticoagulants, bronchodilators, modified ventilator strategies, and other measures. This review represents a summary of critical shortcomings in our understanding and management of inhalation injury identified by the American Burn Association's working group on Cutaneous Thermal Injury and Inhalation Injury in 2018. It addresses our current understanding of the diagnosis, pathophysiology, and treatment of inhalation injury and highlights topics in need of additional research, including 1) airway repair mechanisms; 2) the airway microbiome in health and after injury; and 3) candidate biomarkers of inhalation injury.

Characterisation of the Cyanate Inhibited State of Cytochrome c Oxidase

Heme-copper oxygen reductases are terminal respiratory enzymes, catalyzing the reduction of dioxygen to water and the translocation of protons across the membrane. Oxygen consumption is inhibited by various substances. Here we tested the relatively unknown inhibition of cytochrome c oxidase (CcO) with isocyanate. In contrast to other more common inhibitors like cyanide, inhibition with cyanate was accompanied with the rise of a metal to ligand charge transfer (MLCT) band around 638 nm. Increasing the cyanate concentration furthermore caused selective reduction of heme a. The presence of the CT band allowed for the first time to directly monitor the nature of the ligand via surface-enhanced resonance Raman (SERR) spectroscopy. Analysis of isotope sensitive SERR spectra in comparison with Density Functional Theory (DFT) calculations identified not only the cyanate monomer as an inhibiting ligand but suggested also presence of an uretdion ligand formed upon dimerization of two cyanate ions. It is therefore proposed that under high cyanate concentrations the catalytic site of CcO promotes cyanate dimerization. The two excess electrons that are supplied from the uretdion ligand lead to the observed physiologically inverse electron transfer from heme a₃ to heme a.

Association between hydroxocobalamin administration and acute kidney injury after smoke inhalation: a multicenter retrospective study

Background

The use of hydroxocobalamin has long been advocated for treating suspected cyanide poisoning after smoke inhalation. Intravenous hydroxocobalamin has however been shown to cause oxalate nephropathy in a single-center study. The impact of hydroxocobalamin on the risk of acute kidney injury (AKI) and survival after smoke inhalation in a multicenter setting remains unexplored.

Methods

We conducted a multicenter retrospective study in 21 intensive care units (ICUs) in France. We included patients admitted to an ICU for smoke inhalation between January 2011 and December 2017. We excluded patients discharged at home alive within 24 h of admission. We assessed the risk of AKI (primary endpoint), severe AKI, major adverse kidney (MAKE) events, and survival (secondary endpoints) after administration of hydroxocobalamin using logistic regression models.

Results

Among 854 patients screened, 739 patients were included. Three hundred six and 386 (55.2%) patients received hydroxocobalamin. Mortality in ICU was 32.9% (n = 243). Two hundred eighty-eight (39%) patients developed AKI, including 186 (25.2%) who developed severe AKI during the first week. Patients who received hydroxocobalamin were more severe and had higher mortality (38.1% vs 27.2%, p = 0.0022). The adjusted odds ratio (95% confidence interval) of AKI after intravenous hydroxocobalamin was 1.597 (1.055, 2.419) and 1.772 (1.137, 2.762) for severe AKI; intravenous hydroxocobalamin was not associated with survival or MAKE with an adjusted odds ratio (95% confidence interval) of 1.114 (0.691, 1.797) and 0.784 (0.456, 1.349) respectively.

Conclusion

Hydroxocobalamin was associated with an increased risk of AKI and severe AKI but was not associated with survival after smoke inhalation.

Trial registration

ClinicalTrials.gov, NCT03558646

Determination of free cyano-cobinamide in swine and rabbit plasma by liquid chromatography tandem mass spectrometry

In recent years, Cobinamide (Cbi) has shown promise as a therapeutic for cyanide poisoning. There are several forms of Cbi based on the identity of the ligands bound to the cobalt in Cbi and these different forms of Cbi have divergent behavior (e.g., the aquo and hydroxo forms of Cbi readily bind to proteins, limiting their distribution significantly, whereas [Cbi(CN)₂] does not). While current analysis techniques only measure total Cbi, methods to elucidate the behavior of 'available' Cbi versus cyanide-complexed Cbi would be valuable for biomedical and pharmacokinetic studies. Therefore, a method was developed for the analysis of cyanide-complexed Cbi in plasma via liquid chromatography tandem mass spectrometry (LC-MS-MS). Plasma samples were prepared by denaturing proteins with 10% ammonium hydroxide in acetonitrile. The resulting mixture was centrifuged, and the supernatant was removed, dried, and reconstituted. Cyanide-complexed Cbi was then analyzed via LC-MS-MS. The limit of detection was 0.2 μM, and the linear dynamic range was between 1 and 200 μM. The accuracy was 100 ± 17% and the precision, measured by relative standard deviation (%RSD), was ≤18.5%. Carryover, a severe problem when analyzing Cbi via liquid chromatography was eliminated using a polymeric-based stationary phase (PLRP-S) and a controlled washing protocol. The method allowed evaluation of the cyanide-bound and 'available' Cbi from treated animals and, when paired with a method for total Cbi analysis, allows for estimation of Cbi utilization when treating cyanide poisoning.

Sealing Effects on the Storage Stability of the Cyanide Antidotal Candidate, Dimethyl Trisulfide

Background

Dimethyl trisulfide (DMTS) is a highly lipid-soluble cyanide (CN) antidote candidate molecule. In prior studies with various US FDA-approved co-solvents, surfactants, and their combinations, aqueous solutions containing 15% polysorbate 80 (Poly80) were found to effectively solubilize DMTS in formulations for intramuscular administration. However, DMTS formulated in 15% aqueous Poly80 solutions showed gradual losses over time when stored in vials with septum-based seals.

Objective

The present study tested whether storing DMTS formulations in hermetically sealed glass ampules could mitigate storage losses.

Methods

Samples consisted of 1-mL aliquots of a 50 mg/ml stock solution of DMTS in 15% aqueous Poly80. The control samples were stored using a vial-within-a-vial system—the inner and outer vials were sealed respectively, with a snap cap, and with a crimped septum. The hermetically sealed test samples were stored in fire-sealed glass ampules. The DMTS content was measured by HPLC–UV analysis at specific time points over a 100-day period.

Results

While the control samples exhibited systematic DMTS losses, no DMTS losses were observed from the test samples stored in hermetically sealed glass ampules over the 100-day testing period.

Conclusion

DMTS formulated in 15% aqueous Poly80 solution has excellent stability when stored in fire-sealed glass ampules and thus has the potential to be effectively stored as an intramuscular CN countermeasure for mass casualty scenarios.

From the Cover: In Vitro and In Vivo Blood-Brain Barrier Penetration Studies with the Novel Cyanide Antidote Candidate Dimethyl Trisulfide in Mice

Recent in vitro and in vivo studies highlight the strong potential of dimethyl trisulfide (DMTS) as an antidote for cyanide (CN) intoxication. Due to its high oxygen demand, the brain is one of the main target organs of CN. The blood-brain barrier (BBB) regulates the uptake of molecules into the brain. In the literature, there is no data about the ability of DMTS to penetrate the BBB. Therefore, our aim was to test the in vitro BBB penetration of DMTS and its in vivo pharmacokinetics in blood and brain. The in vitro BBB penetration of DMTS was measured by using a parallel artificial membrane permeability assay (BBB-PAMPA), and a triple BBB co-culture model. The pharmacokinetics was investigated in a mouse model by following the DMTS concentration in blood and brain at regular time intervals following intramuscular administration. DMTS showed high penetrability in both in vitro systems (apparent permeability coefficients: BBB-PAMPA 11.8 × 10-6 cm/s; cell culture 158 × 10-6 cm/s) without causing cell toxicity and leaving the cellular barrier intact. DMTS immediately absorbed into the blood after the intramuscular injection (5 min), and rapidly penetrated the brain of mice (10 min). In addition to the observed passive diffusion in the in vitro studies, the contribution of facilitated and/or active transport to the measured high permeability of DMTS in the pharmacokinetic studies can be hypothesized. Earlier investigations demonstrating the antidotal efficacy of DMTS against CN together with the present results highlight the promise of DMTS as a brain-protective CN antidote.

Identification of specific metabolic pathways as druggable targets regulating the sensitivity to cyanide poisoning

Cyanide is a potent toxic agent, and the few available antidotes are not amenable to rapid deployment in mass exposures. As a result, there are ongoing efforts to exploit different animal models to identify novel countermeasures. We have created a pipeline that combines high-throughput screening in zebrafish with subsequent validation in two mammalian small animal models as well as a porcine large animal model. We found that zebrafish embryos in the first 3 days post fertilization (dpf) are highly resistant to cyanide, becoming progressively more sensitive thereafter. Unbiased analysis of gene expression in response to several hours of ultimately lethal doses of cyanide in both 1 and 7 dpf zebrafish revealed modest changes in iron-related proteins associated with the age-dependent cyanide resistance. Metabolomics measurements demonstrated significant age-dependent differences in energy metabolism during cyanide exposure which prompted us to test modulators of the tricarboxylic acid cycle and related metabolic processes as potential antidotes. In cyanide-sensitive 7 dpf larvae, we identified several such compounds that offer significant protection against cyanide toxicity. Modulators of the pyruvate dehydrogenase complex, as well as the small molecule sodium glyoxylate, consistently protected against cyanide toxicity in 7 dpf zebrafish larvae. Together, our results indicate that the resistance of zebrafish embryos to cyanide toxicity during early development is related to an altered regulation of cellular metabolism, which we propose may be exploited as a potential target for the development of novel antidotes against cyanide poisoning.

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.

Method development for detecting the novel cyanide antidote dimethyl trisulfide from blood and brain, and its interaction with blood

The antidotal potency of dimethyl trisulfide (DMTS) against cyanide poisoning was discovered and investigated in our previous studies. Based on our results it has better efficacy than the Cyanokit and the Nithiodote therapies that are presently used against cyanide intoxication in the US. Because of their absence in the literature, the goal of this work was to develop analytical methods for determining DMTS from blood and brain that could be employed in future pharmacokinetic studies. An HPLC-UV method for detection of DMTS from blood, a GC-MS method for detection of DMTS from brain, and associated validation experiments are described here. These analytical methods were developed using in vitro spiking of brain and blood, and are suitable for determining the in vivo DMTS concentrations in blood and brain in future pharmacokinetic and distribution studies. An important phenomenon was observed in the process of developing these methods. Specifically, recoveries from fresh blood spiked with DMTS were found to be significantly lower than recoveries from aged blood spiked in the same manner with DMTS. This decreased DMTS recovery from fresh blood is important, both because of the role it may play in the antidotal action of DMTS in the presence of cyanide, and because it adds the requirement of sample stabilization to the method development process. Mitigation procedures for stabilizing DMTS samples in blood are reported.

Stability Characterization of a Polysorbate 80-Dimethyl Trisulfide Formulation, a Cyanide Antidote Candidate

Novel cyanide countermeasures are needed for cases of a mass-exposure cyanide emergency. A lead candidate compound is dimethyl trisulfide (DMTS), which acts as a sulfur donor for rhodanese, thereby assisting the conversion of cyanide into thiocyanate. DMTS is a safe compound for consumption and, in a 15% polysorbate 80 (DMTS-PS80) formulation, has demonstrated good efficacy against cyanide poisoning in several animal models. We performed a stability study that investigated the effect of temperature, location of formulation preparation, and pH under buffered conditions. We found that while the stability of the DMTS component was fairly independent of which laboratory prepared the formulation, the concentration of DMTS in the formulation was reduced 36-58% over the course of 29 weeks when stored at room temperature. This loss typically increased with increasing temperatures, although we did not find statistical differences between the stability at different storage temperatures in all formulations. Further, we found that addition of a light buffer negatively impacted the stability, whereas the pH of that buffer did not impact stability. We investigated the factors behind the reduction of DMTS over time using various techniques, and we suggest that the instability of the formulation is governed at least partially by precipitation and evaporation, although a combination of factors is likely involved.

Intravascular Residence Time Determination for the Cyanide Antidote Dimethyl Trisulfide in Rat by Using Liquid-Liquid Extraction Coupled with High Performance Liquid Chromatography

These studies represent the first report on the intravascular residence time determinations for the cyanide antidote dimethyl trisulfide (DMTS) in a rat model by using high performance liquid chromatography coupled with ultraviolet absorption spectroscopy (HPLC-UV). The newly developed sample preparation included liquid-liquid extraction by cyclohexanone. The calibration curves showed a linear response for DMTS concentrations between 0.010 and 0.30 mg/mL with R2 = 0.9994. The limit of detection for DMTS via this extraction method was 0.010 mg/mL, and the limit of quantitation was 0.034 mg/mL. Thus this calibration curve provided a tool for determining DMTS in the range between 0.04 and 0.30 mg/mL. Rats were given 20 mg/kg DMTS dose (in 15% Polysorbate 80) intravenously, and blood samples were taken 15, 60, 90, 120, and 240 min after DMTS injections. The data points were plotted as DMTS concentration in RBCs versus time, and the intravascular residence time was determined graphically. The results indicated a half-life of 36 min in a rat model, suggesting that the circulation time is long enough to provide a reasonable time interval for cyanide antagonism.

Plant-derived cardiac glycosides: Role in heart ailments and cancer management

Cardiac glycosides, the cardiotonic steroids such as digitalis have been in use as heart ailment remedy since ages. They manipulate the renin-angiotensin axis to improve cardiac output. However; their safety and efficacy have come under scrutiny in recent times, as poisoning and accidental mortalities have been observed. In order to better understand and exploit them as cardiac ionotropes, studies are being pursued using different cardiac glycosides such as digitoxin, digoxin, ouabain, oleandrin etc. Several cardiac glycosides as peruvoside have shown promise in cancer control, especially ovary cancer and leukemia. Functional variability of these glycosides has revealed that not all cardiac glycosides are alike. Apart from their specific affinity to sodium-potassium ATPase, their therapeutic dosage and behavior in poly-morbidity conditions needs to be considered. This review presents a concise account of the key findings in recent years with adequate elaboration of the mechanisms. This compilation is expected to contribute towards management of cardiac, cancer, even viral ailments.

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.

Biodegradation of cyanide wastes from mining and jewellery industries

Cyanide, one of the known most toxic chemicals, is widely used in mining and jewellery industries for gold extraction and recovery from crushed ores or electroplating residues. Cyanide toxicity occurs because this compound strongly binds to metals, inactivating metalloenzymes such as cytochrome c oxidase. Despite the toxicity of cyanide, cyanotrophic microorganisms such as the alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 may use cyanide and its derivatives as a nitrogen source for growth, making biodegradation of cyanurated industrial waste possible. Genomic, transcriptomic and proteomic techniques applied to cyanide biodegradation ('cyan-omics') provide a holistic view that increases the global insights into the genetic background of cyanotrophic microorganisms that could be used for biodegradation of industrial cyanurated wastes and other biotechnological applications.