Intramuscular administration of glyoxylate rescues swine from lethal cyanide poisoning and ameliorates the biochemical sequalae of cyanide intoxication

Abstract

Cyanide—a fast-acting poison—is easy to obtain given its widespread use in manufacturing industries. It is a high-threat chemical agent that poses a risk of occupational exposure in addition to being a terrorist agent. FDA-approved cyanide antidotes must be given intravenously, which is not practical in a mass casualty setting due to the time and skill required to obtain intravenous access. Glyoxylate is an endogenous metabolite that binds cyanide and reverses cyanide-induced redox imbalances independent of chelation. Efficacy and biochemical mechanistic studies in an FDA-approved preclinical animal model have not been reported. Therefore, in a swine model of cyanide poisoning, we evaluated the efficacy of intramuscular glyoxylate on clinical, metabolic, and biochemical endpoints. Animals were instrumented for continuous hemodynamic monitoring and infused with potassium cyanide. Following cyanide-induced apnea, saline control or glyoxylate was administered intramuscularly. Throughout the study, serial blood samples were collected for pharmacokinetic, metabolite, and biochemical studies, in addition, vital signs, hemodynamic parameters, and laboratory values were measured. Survival in glyoxylate-treated animals was 83% compared to 12% in saline-treated control animals (p < 0.01). Glyoxylate treatment improved physiological parameters including pulse oximetry, arterial oxygenation, respiration, and pH. In addition, levels of citric acid cycle metabolites returned to baseline levels by the end of the study. Moreover, glyoxylate exerted distinct effects on redox balance as compared to a cyanide-chelating countermeasure. In our preclinical swine model of lethal cyanide poisoning, intramuscular administration of the endogenous metabolite glyoxylate improved survival and clinical outcomes, and ameliorated the biochemical effects of cyanide.

Redirecting Intermediary Metabolism to Counteract Cyanide Poisoning

“…In regards to metabolite markers of therapeutic efficacy, previously, we demonstrated that cyanide poisoning induces substantially increased second-span citric acid cycle metabolites (26,46,59). Moreover, efficacious cyanide countermeasures restore normal levels of these metabolites.…”

“…Pharmacokinetic studies demonstrated rapid glyoxylate absorption I both models. Finally, glyoxylate was well tolerated in rats at 1-and 5-days postadministration (26).…”

“…Therefore, the cellular metabolism of glyoxylate may lead to the regeneration of essential co-factors that were depleted during cyanide intoxication. Concordantly, following glyoxylate administration to cyanide-poisoned animals, pyruvate was consumed, and the TCA cycle was reactivated in rabbit and swine models of lethal cyanide poisoning (26,46). In both animal models survival significantly improved.…”

“…Complex I becomes stuck in a reduced state and therefore cannot oxidize nicotinamide adenine dinucleotide (NADH) to regenerate the NAD+ that is required for the tricarboxylic acid (TCA) cycle. As NADH/NAD+ ratio increases, negative feedback inhibition on the TCA cycle ensues (25,26). This forces the cell to shift from aerobic to anaerobic metabolism.…”

“…To elucidate new mechanisms of cyanide poisoning, novel therapeutic targets, and unique chemical matter for drug development, we conducted several chemical screens in zebrafish models of cyanide poisoning (1,46,47,60). Through these screening campaigns, we identified novel metabolic modulators that ameliorate cyanide toxicity in mammalian model of cyanide poisoning, with all these compounds having their genesis in zebrafish screens (26,46,59,60,64).…”