COBALT COMPOUNDS AS ANTIDOTES FOR HYDROCYANIC ACID

Investigating the Replacement of Carboxylates with Carboxamides to Modulate the Safety and Efficacy of Platinum(II) Thioether Cyanide Scavengers

Cyanide represents a persistent threat for accidental or malicious misuse due to easy conversion into a toxic gas and access to large quantities through several industries. The high safety index of hydroxocobalamin is a cornerstone quality as a cyanide scavenger. Unfortunately, intravenous infusion of hydroxocobalamin limits the utility in a mass casualty setting. We previously reported platinum(II) [Pt(II)] complexes with trans-directing sulfur ligands as an efficacious alternative to hydroxocobalamin when delivered by a bolus intramuscular injection in mice and rabbits. Thus, to enable Pt(II) as an alternative to hydroxocobalamin, a high safety factor is needed. The objective is to maintain efficacy and mitigate the risk for nephrotoxicity. Platinum amino acid complexes with the ability to form five- or six-membered rings and possessing either carboxylates or carboxamides are evaluated in vitro for cyanide scavenging. In vivo efficacy was evaulated in the zebrafish and mice cyanide exposure models. In addition, Pt(II) complex toxicity and pharmacokinetics were evaluated in a cyanide naive Sprague-Dawley model. Doses for toxicity are escalated to 5x from the efficacious dose in mice using a body surface area adjustment. The results show the carboxamide ligands display a time and pH dependence on cyanide scavenging in vitro and efficacy in vivo. Additionally, exchanging the carboxylate for carboxamide showed reduced indications of renal injury. A pharmacokinetic analysis of the larger bidentate complexes displayed rapid absorption by intramuscular administration and having similar plasma exposure. These findings point to the importance of pH and ligand structures for methionine carboxamide complexes with Pt(II).

Highly Stable Upconverting Nanocrystal-Polydiacetylenes Nanoplates for Orthogonal Dual Signaling-Based Detection of Cyanide

Although the unique optical signaling properties of polydiacetylene (PDA) have been exploited in diverse bio-chemosensors, the practical application of most PDA sensor systems is limited by their instability in harsh environments and fluorescence signal weakness. Herein, a universal design principle for a highly stable PDA sensor system with a practical dual signaling capability is developed to detect cyanide (CN) ions, which are commonly found in drinking water. Effective metal intercalation and enhanced hydrophobic intermolecular interactions between PDA-metal supramolecules are used to construct highly stacked PDA-metal nanoplates that feature unusual optical stability upon exposure to strong acids, bases, organic solvents, and thermal/mechanical stresses, and can selectively detect CN anions, concomitantly undergoing a specific supramolecular structure change. To realize the practical dual signaling capability of the PDA sensor system, upconverting nanocrystals (UCNs) are incorporated into highly stacked PDA-metal nanoplates, and practical dual signaling (orthogonal changes in luminescence and visible color) is demonstrated using a portable detection system. The presented universal design principle is expected to be suitable for the development of other highly stable and selective PDA sensor systems with practical dual signaling capability.

Modest and variable efficacy of pre-exposure hydroxocobalamin and dicobalt edetate in a porcine model of acute cyanide salt poisoning

Background: Dicobalt edetate and hydroxocobalamin are widely used to treat hydrogen cyanide poisoning. However, comparative and quantitative efficacy data are lacking. Although post-exposure treatment is typical, it may be possible to administer these antidotes before exposure to first attenders entering a known site of cyanide release, as supplementary protection to their personal protective equipment.Methods: We established an anaesthetised Gottingen minipig model of lethal bolus potassium cyanide (KCN) injection to simulate high dose hydrogen cyanide inhalation. Doses were similar to human lethal doses of KCN. Dicobalt edetate and hydroxocobalamin were administered shortly before KCN and their effect on metabolic and cardiovascular variables and survival time were measured.Results: Increases in arterial lactate were similar after 0.08 and 0.12 mmol/kg KCN. KCN 0.08 mmol/kg was survived by 4/4 animals with moderate cardiovascular effects, while the 0.12 mmol/kg dose was lethal in 4/4 animals, with a mean time to euthanasia of 28.3 (SEM: 13.9) min. Administration of dicobalt edetate (0.021 mmol/kg, 8.6 mg/kg) or hydroxocobalamin (0.054 mmol/kg, 75 mg/kg) at clinically licenced doses had modest effect on lactate concentrations but increased survival after administration of KCN 0.12 mmol/kg (survival: dicobalt edetate 4/4, hydroxocobalamin 2/4) but not 0.15 mmol/kg (0/4 and 0/4, respectively). In a subsequent larger study, doubling the dose of hydroxocobalamin (0.108 mmol/kg, 150 mg/kg) was associated with a modest but inconsistent increased survival after 0.15 mmol/kg KCN (survival: control 0/8, 75 mg/kg 1/10, 150 mg/kg 3/10) likely due to variable pharmacokinetics.Conclusions: In this porcine study of cyanide exposure, with pre-exposure antidote administration, licenced doses of dicobalt edetate and hydroxocobalamin were effective at just lethal doses but ineffective at less than twice the estimated LD₅₀. The efficacy of a rapidly-administered double-dose of hydroxocobalamin was limited by variable pharmacokinetics. In clinical poisoning scenarios, with delayed administration, the antidotes are likely to be even less effective. New antidotes are required for treatment of cyanide exposures appreciably above the minimum lethal dose.

Rationally Designed Circularly Arranged Sextuple Molecule with Dimethoxyphenolic Tentacles for Ample Hunting of Cyanide

Herein, we report the design, synthesis, and cyanide-scavenging behavior of circularly arranged sextuple molecule 4. The six syringaldehyde units carrying equal number of dimethoxyphenolic moieties projecting at the periphery make the molecule highly efficient for cleaning up cyanide from the aqueous solution. The stoichiometric data 1:6 showed that six units of cyanide interact with one unit of compound 4. The association constant of the compound for cyanide was 2.5 × 10⁴ M^-1, and its detection limit for cyanide was 10 nM. The compound was also found to remove cyanide bound to cytochrome c oxidase.

Physician Beware: Severe Cyanide Toxicity from Amygdalin Tablets Ingestion

Despite the risk of cyanide toxicity and lack of efficacy, amygdalin is still used as alternative cancer treatment. Due to the highly lethal nature of cyanide toxicity, many patients die before getting medical care. Herein, we describe the case of a 73-year-old female with metastatic pancreatic cancer who developed cyanide toxicity from taking amygdalin. Detailed history and physical examination prompted rapid clinical recognition and treatment with hydroxocobalamin, leading to resolution of her cyanide toxicity. Rapid clinical diagnosis and treatment of cyanide toxicity can rapidly improve patients' clinical outcome and survival. Inquiries for any forms of ingestion should be attempted in patients with clinical signs and symptoms suggestive of poisoning.

Sodium Nitrite and Sodium Thiosulfate Are Effective Against Acute Cyanide Poisoning When Administered by Intramuscular Injection

STUDY OBJECTIVE

The 2 antidotes for acute cyanide poisoning in the United States must be administered by intravenous injection. In the out-of-hospital setting, intravenous injection is not practical, particularly for mass casualties, and intramuscular injection would be preferred. The purpose of this study is to determine whether sodium nitrite and sodium thiosulfate are effective cyanide antidotes when administered by intramuscular injection.

METHODS

We used a randomized, nonblinded, parallel-group study design in 3 mammalian models: cyanide gas inhalation in mice, with treatment postexposure; intravenous sodium cyanide infusion in rabbits, with severe hypotension as the trigger for treatment; and intravenous potassium cyanide infusion in pigs, with apnea as the trigger for treatment. The drugs were administered by intramuscular injection, and all 3 models were lethal in the absence of therapy.

RESULTS

We found that sodium nitrite and sodium thiosulfate individually rescued 100% of the mice, and that the combination of the 2 drugs rescued 73% of the rabbits and 80% of the pigs. In all 3 species, survival in treated animals was significantly better than in control animals (log rank test, P<.05). In the pigs, the drugs attenuated an increase in the plasma lactate concentration within 5 minutes postantidote injection (difference: plasma lactate, saline solution-treated versus nitrite- or thiosulfate-treated 1.76 [95% confidence interval 1.25 to 2.27]).

CONCLUSION

We conclude that sodium nitrite and sodium thiosulfate administered by intramuscular injection are effective against severe cyanide poisoning in 3 clinically relevant animal models of out-of-hospital emergency care.

pH-Responsive Relaxometric Behaviour of Coordination Polymer Nanoparticles Made of a Stable Macrocyclic Gadolinium Chelate

Lanthanide-containing nanoscale particles have been widely explored for various biomedical purposes, however, they are often prone to metal leaching. Here we have created a new coordination polymer (CP) by applying, for the first time, a stable Gd(III) chelate as building block in order to prevent any fortuitous release of free lanthanide(III) ion. The use of the Gd-DOTA-4AmP complex as a design element in the CP allows not only for enhanced relaxometric properties (maximum r1 =16.4 mm(-1)  s(-1) at 10 MHz), but also for a pH responsiveness (Δr1 =108 % between pH 4 and 6.5), beyond the values obtained for the low molecular weight Gd-DOTA-4AmP itself. The CP can be miniaturised to the nanoscale to form colloids that are stable in physiological saline solution and in cell culture media and does not show cytotoxicity.

The efficacy and adverse effects of dicobalt edetate in cyanide poisoning

INTRODUCTION

Dicobalt edetate is one of a number of cobalt compounds that have been studied in the treatment of cyanide poisoning, their efficacy being based upon the fact that cyanide combines with cobalt to form relatively non-toxic complexes. Inorganic cobalt salts are quite toxic (cyanide and cobalt antagonise one another's toxicity) and complexes such as dicobalt edetate were studied with the aim of identifying compounds that were less acutely toxic, but which retained the antidotal properties of cobalt salts. The proprietary preparation, Kelocyanor™, contains free cobalt and glucose as well as dicobalt edetate.

OBJECTIVE

The aim of this study was to evaluate the published evidence for the efficacy and adverse effects of dicobalt edetate.

METHODS

A Pubmed search was undertaken for the period 1961-September 2015. The search terms were "dicobalt edetate", "cobalt edetate" and "Kelocyanor", which produced 24 relevant citations. A review of the references in four relevant books (L'intoxication cyanhydrique et son traitement, Clinical and Experimental Toxicology of Cyanides, Antidotes for Poisoning by Cyanide and Antidotes) produced three further relevant papers, making a total of 27 papers. Efficacy of dicobalt edetate: There is evidence from animal pharmacodynamic studies that dicobalt edetate is an effective cyanide antidote in experimental animals. Some 39 cases of human poisoning treated with dicobalt edetate have been reported, but in only nine cases were blood cyanide concentrations measured, although administration of dicobalt edetate procured survival in four of the seven patients with concentrations in the lethal range (>3.0 mg/L). It is unlikely that death in any of the adequately documented fatal cases was attributable to treatment failure with dicobalt edetate, as it is probable that they all had suffered anoxic brain damage before treatment could be initiated. Furthermore, in one case, acute gold toxicity contributed substantially to death. Adverse effects of dicobalt edetate: Adverse effects reported have included hypertension, tachycardia, nausea, retrosternal pain, sweating, palpebral, facial and laryngeal oedema, vomiting, urticaria and/or a feeling of impending doom. Such effects appear to be more prevalent where the antidote has been administered without evidence of substantial systemic poisoning or where other antidotes have been used which might have been expected also to combine with cyanide. Although the adverse effects observed were doubtless unpleasant, and some were severe, no fatal reactions were found.

CONCLUSIONS

Dicobalt edetate is an effective cyanide antidote when given to patients with systemic cyanide poisoning, but it has the potential to give rise to adverse reactions, particularly when administered in the absence of intoxication.

Successful Use of Hydroxocobalamin and Sodium Thiosulfate in Acute Cyanide Poisoning: A Case Report with Follow-up

Hydroxocobalamin is an effective first-line antidote used mainly in monotherapy of cyanide poisonings, while the opinions are different on the effects of its combination with sodium thiosulfate. A 58-year-old male committed a suicide attempt by ingesting of 1200-1500 mg of potassium cyanide; he was unconscious for 1-1.5 min. after ingestion with the episode of generalized seizures. On admission to the ICU, the patient was acidotic (pH 7.28; HCO3 14.0 mmol/L, base excess -12.7 mmol/L, saturation O2 0.999) with high serum lactate (12.5 mmol/L). Hydroxocobalamin was administered 1.5 hr after ingestion in two subsequent intravenous infusions at a total dose of 7.5 g. The infusion was followed by continuous intravenous administration of 1 mL/hr/kg of 10% sodium thiosulfate at a total dose of 12 g. No complications and adverse reactions were registered. Serum lactate decreased to 0.6 mmol/L the same day, and arterial blood gases became normal (pH 7.49; HCO3 27.2 mmol/L, base excess 2.2 mmol/L, saturation O2 0.994). The follow-up examination 5 months later revealed no damage of basal ganglia and cerebellum on magnetic resonance imaging. The neurological examination revealed no pathological findings. On the ocular coherence tomography, the retinal nerve fibres layer was normal. In visual evoked potentials, there was a normal evoked complex on the left eye and minor decrease in amplitude on the right eye. Combination of hydroxocobalamin and sodium thiosulfate can have a positive effect on the survival without long-term neurological and visual sequelae in the cases of massive cyanide poisonings due to the possibility of a potentiation or synergism of hydroxocobalamin effects by sodium thiosulfate. This synergism can be explained by the different time-points of action of two antidotes: the initial and immediate effect of hydroxocobalamin, followed by the delayed, but more persistent effect of sodium thiosulfate.

Anti-Cyanide Drugs: Kinetics of the Removal of Copper(II) and Nickel(II) from N-Methyl-tetra(4-sulfonatophenyl)porphyrins by Cyanide. LD50s of Common Metalloporphyrins and Metallophthalocyanines

The purpose of this project was to develop prophylactic water-soluble anti-cyanide drugs. The 24 h mean LD 50s in mice of 13 common metalloporphyrins and metallophthalocyanines are reported. At doses of 1/4, 1/16 and 1/64 of the LD 50 administered 15 or 60 min prior to a 2LD50 challenge of sodium cyanide, none of these compounds protected mice against cyanide. While Co ( H 2 O )6 Cl 2 and Ni ( H 2 O )6Cl2 were found to be effective, they are too toxic to be useful. A stable metalloporphyrin that could scavenge cyanide by donating metal ions to produce non-toxic polycyano species in the presence of cyanide would be desirable. We found that nickel(II) and copper(II) are removed from their N-methyl-tetra(4-sulfonato)porphyrins by cyanide and hydrogen cyanide. These reactions are not observed with the parent tetra(4-sulfonatophenyl)porphyrins. Equilibrium constants for cyanide addition to both types of metalloporphyrins and the rate laws for metal removal by cyanide and HCN are reported. The medical implications of these findings are discussed.

Cyanide: an unreported cause of neurological complications following smoke inhalation

Although the combustion of natural and synthetic products can yield cyanide, its toxic role in residential fires is unclear. This case concerns a woman aged over 50 years who presented comatose, pulseless and apnoeic after a domestic fire. Cardiopulmonary resuscitation and on-site administration of 2.5 g hydroxocobalamin as an antidote to cyanide resulted in a return of spontaneous circulation. On admission to the intensive care unit, the patient was treated with hyperbaric oxygen for suspected carbon monoxide poisoning. In a blood specimen collected at the scene before hydroxocobalamin administration, blood cyanide and carbon monoxide levels were 68 µmol/l and 10.9%. On admission to hospital, plasma lactate was at 4.6 mmol/l. Brain scans revealed lesions which were confirmed 2 months later, consistent with the haemorrhagic necrosis often seen after poisoning by cyanide. These data suggest that smoke inhalation in a residential fire may cause cyanide poisoning. This case provides clinical, biological, analytical and brain imaging data supporting the hypothesis of the toxic role of smoke-induced cyanide poisoning which may result in neurological sequelae.

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.

Cobinamide is superior to other treatments in a mouse model of cyanide poisoning

CONTEXT

Cyanide is a rapidly acting cellular poison, primarily targeting cytochrome c oxidase, and is a common occupational and residential toxin, mostly via smoke inhalation. Cyanide is also a potential weapon of mass destruction, with recent credible threats of attacks focusing the need for better treatments, as current cyanide antidotes are limited and impractical for rapid deployment in mass casualty settings.

OBJECTIVE

We have used mouse models of cyanide poisoning to compare the efficacy of cobinamide (Cbi), the precursor to cobalamin (vitamin B(12)), to currently approved cyanide antidotes. Cbi has extremely high affinity for cyanide and substantial solubility in water.

MATERIALS AND METHODS

We studied Cbi in both an inhaled and intraperitoneal model of cyanide poisoning in mice.

RESULTS

We found Cbi more effective than hydroxocobalamin, sodium thiosulfate, sodium nitrite, and the combination of sodium thiosulfate-sodium nitrite in treating cyanide poisoning. Compared to hydroxocobalamin, Cbi was 3 and 11 times more potent in the intraperitoneal and inhalation models, respectively. Cobinamide sulfite (Cbi-SO(3)) was rapidly absorbed after intramuscular injection, and mice recovered from a lethal dose of cyanide even when given at a time when they had been apneic for over 2 min. In range-finding studies, Cbi-SO(3) at doses up to 2000 mg/kg exhibited no clinical toxicity.

DISCUSSION AND CONCLUSION

These studies demonstrate that Cbi is a highly effective cyanide antidote in mouse models, and suggest it could be used in a mass casualty setting, because it can be given rapidly as an intramuscular injection when administered as Cbi-SO(3). Based on these animal data Cbi-SO(3) appears to be an antidote worthy of further testing as a therapy for mass casualties.

Sodium Thiosulfate or Hydroxocobalamin for the Empiric Treatment of Cyanide Poisoning?

Cyanide poisoning must be seriously considered in victims of smoke inhalation from enclosed space fires; it is also a credible terrorism threat agent. The treatment of cyanide poisoning is empiric because laboratory confirmation can take hours or days. Empiric treatment requires a safe and effective antidote that can be rapidly administered by either out-of-hospital or emergency department personnel. Among several cyanide antidotes available, sodium thiosulfate and hydroxocobalamin have been proposed for use in these circumstances. The evidence available to assess either sodium thiosulfate or hydroxocobalamin is incomplete. According to recent safety and efficacy studies in animals and human safety and uncontrolled efficacy studies, hydroxocobalamin seems to be an appropriate antidote for empiric treatment of smoke inhalation and other suspected cyanide poisoning victims in the out-of-hospital setting. Sodium thiosulfate can also be administered in the out-of-hospital setting. The efficacy of sodium thiosulfate is based on individual case studies, and there are contradictory conclusions about efficacy in animal models. The onset of antidotal action of sodium thiosulfate may be too slow for it to be the only cyanide antidote for emergency use. Hydroxocobalamin is being developed for potential introduction in the United States and may represent a new option for emergency personnel in cases of suspected or confirmed cyanide poisoning in the out-of-hospital setting.

Pediatric cyanide poisoning: causes, manifestations, management, and unmet needs

Confirmed cases of childhood exposure to cyanide are rare despite multiple potential sources including inhalation of fire smoke, ingestion of toxic household and workplace substances, and ingestion of cyanogenic foods. Because of its infrequent occurrence, medical professionals may have difficulty recognizing cyanide poisoning, confirming its presence, and treating it in pediatric patients. The sources and manifestations of acute cyanide poisoning seem to be qualitatively similar between children and adults, but children may be more vulnerable than adults to poisoning from some sources. The only currently available antidote in the United States (the cyanide antidote kit) has been used successfully in children but has particular risks associated with its use in pediatric patients. Because hemoglobin kinetics vary with age, methemoglobinemia associated with nitrite-based antidotes may be excessive at standard adult dosing in children. A cyanide antidote with a better risk/benefit ratio than the current agent available in the United States is desirable. The vitamin B12 precursor hydroxocobalamin, which has been used in Europe, may prove to be an attractive alternative to the cyanide antidote kit for pediatric patients. In this article we review the available data on the sources, manifestations, and treatment of acute cyanide poisoning in children and discuss unmet needs in the management of pediatric cyanide poisoning.

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.

Effect of cyanide antidotes on the metabolic conversion of cyanide to thiocyanate

The excretion of thiocyanate following the administration of equitoxic doses of cyanide to unprotected mice and to animals pretreated with various cyanide antidotes has been studied. The results demonstrate that cyanide given alone or to animals pretreated with thiosulfate is extensively converted to thiocyanate. Animals pretreated with sodium nitrite or a combination of nitrite and sodium thiosulfate excreted even higher amounts of thiocyanate. This demonstrates that cyanide originally detoxified by combination with methemoglobin is ultimately converted to thiocyanate in the animal body. Pretreatment of animals with cobalt compounds (cobaltous chloride or dicobalt-EDTA) or a combination of cobalt compounds and thiosulfate resulted, on the other hand, in a less efficient conversion of cyanide to thiocyanate. The cyanide detoxified by trapping as highly undissociated cobalt-cyanide complexes is instead excreted in the urine, as demonstrated by detection of high amounts of cobalt ions and strongly complex-bound cyanide in the urine from animals treated with cobalt compounds and cyanide. A method for the determination of cyanide present as cobalt-cyanide complexes is described and its forensic application is proposed.