Historically, antidotal potencies of cyanide antagonists were measured as increases in the experimental LD50 for cyanide elicited by the antidotes. This required the use of high doses of cyanide following pre-treatment with the putative antidote. Since IACUC guidelines at our institutions strongly discourage LD50 determinations: we developed a new test paradigm that allowed for maximal survival of cyanide-treated animals with greatly reduced numbers of animals. Symptoms of cyanide toxicity include disruption of neuromuscular coordination, i.e., the righting reflex. Therefore, to establish a dose-response curve, the times required for recovery of this righting reflex with increasing doses of cyanide were measured. A cyanide dose that disrupted this righting reflex for approximately 1 h with minimal deaths was then selected. Using this paradigm, the current cyanide antidotes, viz., nitrite plus thiosulfate and hydroxocobalamin, as well as some potential cyanide antidotes that we developed, were evaluated pre- and post-cyanide. This allowed, for the first time, the assessment of the post-cyanide effectiveness of the current antidotes against cyanide poisoning in a live animal. In addition, some prototype compounds were found to exhibit antidotal efficacy not only when injected i.p. following cyanide, but also when administered orally 30 min before cyanide. Pre-cyanide oral efficacy suggests that such compounds have the potential of being administered prophylactically before exposure to cyanide. This new test paradigm was found to be a powerful tool for assessing the efficacies of some novel antidotes against cyanide and should be equally applicable for evaluating putative antidotes for other neurotoxins.
Bibliographical noteFunding Information:
We thank Mary Mullett for technical assistance. We thank Ashley Burkhart of Starr Life Sciences Corporation, Oakmont, PA for the excellent mouse oximeter demonstration that provided us with percent oxygen saturation data. This study was supported by a Seed Grant from the Center for Drug Design, Academic Health Center, University of Minnesota, Minneapolis, MN, and by the National Institutes of Health CounterACT Program through the National Institute of Neurological Disorders and Stroke (award # 1U01NS058087-01).
- Animal model
- Oral efficacy
- Righting reflex