Preclinical evaluation of injectable reduced hydroxocobalamin as an antidote to acute carbon monoxide poisoning

BACKGROUND: Current management of acute inhalational carbon monoxide (CO) toxicity includes hyperbaric or normobaric O(2) therapy. However, efficacy has not been established. The purpose of this study was to establish therapeutic proof of concept for a novel injectable antidote consisting of the combination of hydroxocobalamin and ascorbic acid into a reduced form (B(12r)) as demonstrated by clinically-significant increase (> 500 ppm) in CO(2) production, reduced carboxyhemoglobin (COHgb) half-life (COHgb t(1/2)), and increased cerebral O(2) delivery and attenuation of CO-induced microglial damage in a preclinical rodent model of CO toxicity. METHODS: B(12R)-mediated conversion of CO to CO(2) and COHgb t(1/2) in human blood were measured by gas analysis and Raman resonance spectroscopy. Rats were exposed to either air or CO, then injected with saline or B(12r). Cognitive assessment was tested in a Morris water maze. Brain oxygenation was measured with Licox. Brain histology was assessed by fluorescent antibody markers and cell counts. RESULTS: B(12r) resulted in significant CO(2) production (1170 ppm), compared to controls. COHgb t(1/2) was reduced from 33 min (NS) to 17.5 (p < 0.001). In rat models, severe CO-induced brain hypoxia (Pb(t)O(2) 18 mmHg) was followed by significant reduction in τ(25) to 12 min for B(12r) rats vs 40 min for NS-treated rats (p < 0.0001). There was major attenuation of CO-induced microglial damage, although cognitive performance differences were minimal. CONCLUSION: Our preclinical data suggest that the novel synergism of hydroxocobalamin with ascorbic acid has the potential to extract CO through conversion to CO(2,) independently of high-flow or high-pressure O(2). This resulted in a clinically-significant off-gassing of CO(2) at levels 5 to 8 times greater than controls, a clinically-significant reduction in COHgb half-life, and evidence of increased brain oxygenation and amelioration of myoglial damage in rat models. Reduced hydroxocobalamin has major potential as an injectable antidote for CO toxicit