Sarcoendoplasmic Reticulum Ca2+ ATPase. A Critical Target in Chlorine Inhalation–Induced Cardiotoxicity

Autopsy specimens from human victims or experimental animals that die due to acute chlorine gas exposure present features of cardiovascular pathology. We demonstrate acute chlorine inhalation–induced reduction in heart rate and oxygen saturation in rats. Chlorine inhalation elevated chlorine reactants, such as chlorotyrosine and chloramine, in blood plasma. Using heart tissue and primary cardiomyocytes, we demonstrated that acute high-concentration chlorine exposure in vivo (500 ppm for 30 min) caused decreased total ATP content and loss of sarcoendoplasmic reticulum calcium ATPase (SERCA) activity. Loss of SERCA activity was attributed to chlorination of tyrosine residues and oxidation of an important cysteine residue, cysteine-674, in SERCA, as demonstrated by immunoblots and mass spectrometry. Using cardiomyocytes, we found that chlorine-induced cell death and damage to SERCA could be decreased by thiocyanate, an important biological antioxidant, and by genetic SERCA2 overexpression. We also investigated a U.S. Food and Drug Administration–approved drug, ranolazine, used in treatment of cardiac diseases, and previously shown to stabilize SERCA in animal models of ischemia–reperfusion. Pretreatment with ranolazine or istaroxime, another SERCA activator, prevented chlorine-induced cardiomyocyte death. Further investigation of responsible mechanisms showed that ranolazine- and istaroxime-treated cells preserved mitochondrial membrane potential and ATP after chlorine exposure. Thus, these studies demonstrate a novel critical target for chlorine in the heart and identify potentially useful therapies to mitigate toxicity of acute chlorine exposure.This work was supported by the CounterACT Program, National Institutes of Health, Office of the Director, and the National Institute of Environmental Health Sciences grant U54 ES015678 (C.W.W.), and by Children’s Hospital of Colorado/Colorado School of Mines Pilot Award G0100394 and a Children’s Hospital of Colorado Research Institute’s Pilot Award (S.A.)

A Review on Ingested Cyanide: Risks, Clinical Presentation, Diagnostics, and Treatment Challenges

Cyanide, a metabolic poison, is a rising chemial threat and ingestion is the most common route of exposure. Terrorist organizations have threatened to attack the USA and international food and water supplies. The toxicokinetics and toxicodynamics of oral cyanide are unique, resulting in high-dose exposures, severe symptoms, and slower onset of symptoms. There are no FDA-approved therapies tested for oral cyanide ingestions and no approved intramuscular or oral therapies, which would be valuable in mass casualty settings. The aim of this review is to evaluate the risks of oral cyanide and its unique toxicokinetics, as well as address the lack of available rapid diagnostics and treatments for mass casualty events. We will also review current strategies for developing new therapies. A review of the literature using the PRISMA checklist detected 7284 articles, screened 1091, and included 59 articles or other reports. Articles referenced in this review were specific to risk, clinical presentation, diagnostics, current treatments, and developing therapies. Current diagnostics of cyanide exposure can take hours or days, which can delay treatment. Moreover, current therapies for cyanide poisoning are administered intravenously and are not specifically tested for oral exposures, which can result in higher cyanide doses and unique toxicodynamics. New therapies developed for oral cyanide exposures that are easily delivered, safe, and can be administered quickly by first responders in a mass casualty event are needed. Current research is aimed at identifying an antidote that is safe, effective, easy to administer, and has a rapid onset of action

Intramuscular sodium tetrathionate as an antidote in a clinically relevant swine model of acute cyanide toxicity

Background: Cyanide is a metabolic poison used in multiple industries and is a high threat chemical agent. Current antidotes require intravenous administration, limiting their usefulness in a mass casualty scenario. Sodium tetrathionate reacts directly with cyanide yielding thiosulfate and the non-toxic compound thiocyanate. Thiosulfate, in turn, neutralizes a second molecule of cyanide, thus, per mole, sodium tetrathionate neutralizes two moles of cyanide. Historical studies examined its efficacy as a cyanide antidote, but it has not been evaluated in a clinically relevant, large animal model, nor has it previously been administered by intramuscular injection.Objective: The objective of this study is to evaluate the efficacy of intramuscular sodium tetrathionate on survival and clinical outcomes in a large, swine model of severe cyanide toxicity.Methods: Anesthetized swine were instrumented for continuous monitoring of hemodynamics, then acclimated and breathing spontaneously prior to potassium cyanide infusion (0.17 mg/kg/min). At 6-min post-apnea (no breaths for 20 s), the cyanide infusion was terminated, and animals were treated with sodium tetrathionate (∼18 mg/kg) or normal saline control. Clinical parameters and laboratory values were evaluated at various time points until death or termination of the experiment (90 min post-treatment).Results: Laboratory values, vital signs, and time to apnea were similar in both groups at baseline and treatment. Survival in the sodium tetrathionate treated group was 100% and 17% in controls (p = 0.0043). All animals treated with sodium tetrathionate returned to breathing at a mean time of 10.85 min after antidote, and all but one control remained apneic through end of the experiment. Animals treated with tetrathionate showed improvement in blood lactate (p ≤ 0.002) starting at 30 min post-treatment. The average time to death in the control group is 63.3 ± 23.2 min. No systemic or localized adverse effects of intramuscular administration of sodium tetrathionate were observed.Conclusion: Sodium tetrathionate significantly improves survival and clinical outcomes in a large, swine model of acute cyanide poisoning

Efficacy of oral administration of sodium thiosulfate in a large, swine model of oral cyanide toxicity

IntroductionCyanide is a deadly poison, particularly with oral exposure where larger doses can occur before symptoms develop. Prior studies and multiple governmentagencies highlight oral cyanide as an agent with the potential for use in a terrorist attack. Currently, there are no FDA approved antidotes specific to oralcyanide. An oral countermeasure that can neutralize and prevent absorption of cyanide from the GI tract after oral exposure is needed. Our objective was toevaluate the efficacy of oral sodium thiosulfate on survival and clinical outcomes in a large, swine model of severe cyanide toxicity.MethodsSwine (45-55kg) were instrumented, sedated, and stabilized. Potassium cyanide (8 mg/kg KCN) in saline was delivered as a one-time bolus via an orogastric tube. Three minutes after cyanide, animals randomized to the treatment group received sodium thiosulfate (510 mg/kg, 3.25 M solution) via orogastric tube. Our primary outcome was survival at 60 minutes after exposure. We compared survival between groups by log-rank, Mantel-Cox analysis and trended labs and vital signs.ResultsAt baseline and time of treatment all animals had similar weights, vital signs, and laboratory values. Survival at 60 min was 100% in treated animals compared to 0% in the control group (p=0.0027). Animals in the control group became apneic and subsequently died by 35.0 min (20.2,48.5) after cyanide exposure. Mean arterial pressure was significantly higher in the treatment group compared to controls (p=0.008). Blood lactate (p=0.02) and oxygen saturation (p=0.02) were also significantly different between treatment and control groups at study end.ConclusionOral administration of sodium thiosulfate improved survival, blood pressure, respirations, and blood lactate concentrations in a large animal model of acute oral cyanide toxicity

Characterization of a Swine (Sus scrofa) Model of Oral Potassium Cyanide Intoxication.

Cyanide is a readily available and potentially lethal substance. Oral exposure can result in larger doses, compared with other routes. Currently, there are no antidotes specific for use in the treatment of oral cyanide poisoning, and studies cannot be done in humans. We report on a new large animal model of oral cyanide toxicity to evaluate potential antidotes. Six female swine (Sus scrofa; weight, 45 to 55 kg) were anesthetized, intubated, and instrumented. Animals received a KCN bolus of either 5 or 8 mg/kg delivered via orogastric tube. Time to apnea was recorded; parameters monitored included heart rate, respiratory rate, blood pressure, pulse oximetry, end-tidal CO2, arterial blood gasses, and lactate concentrations. The Welch t test was used to calculate confidence intervals, mean, and standard deviation, and a Kaplan-Meier survival curve was used to compare survival between the 2 groups. At baseline, all animals in both groups were similar. Animals in the 5-mg/kg group had a more rapid time to apnea (5.1 ± 2.1 min), longer time to death (48.5 ± 38.1 min), and a greater rate of survival than the 8-mg/kg group (apnea, 10.6 ± 10.7 min; death, 26.1 ± 5.8 min). All animals displayed signs of toxicity (acidemia, hyperlactatemia, hypotension, apnea). We here report a large animal (swine) model of oral cyanide poisoning with dose-dependent effects in regard to time to death and survival rate. This model likely will be valuable for the development of medical countermeasures for oral cyanide poisoning