A Potential Antidote for Both Azide and Cyanide Poisonings

There do not appear to be any established therapeutics for treating azide poisoning at this time, and presently available antidotes to cyanide poisoning are far from ideal, being particularly impractical for use if multiple victims present. The cobalt (II/III) complex of the Schiff-base ligand trans-[14]-diene (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene (CoN₄[14]) is shown to act as an effective antidote to both azide and cyanide toxicity in mice. Groups of animals challenged with an LD₄₀ dose of NaCN (100 µmol/kg i.p.) exhibited significantly faster recovery from knockdown and fewer (zero) deaths if given CoN₄[14] (50 μmol/kg i.p.) 2 minutes after the toxicant. Groups of animals challenged with an essentially lethal dose of NaCN (1.5 x LD₅₀ = 150 µmol/kg i.p.) all survived if given the CoN₄[14] (75 μmol/kg i.p.) 5 minutes before the toxicant dose. These data represent improved antidotal capability over the Food and Drug Administration-approved cobalt-based cyanide antidote hydroxocobalamin. Recovery of animals challenged sublethally with NaN₃ (415 μmol/kg i.p.) was assessed employing a modified pole-climbing test. Mice given the CoN₄[14] antidote (70 μg/kg i.p.) 5 minutes after the toxicant dose recovered twice as fast as the controls given no antidote. The interactions of cyanide and azide with CoN₄[14] in vitro (buffered aqueous solutions) have been further investigated by a combination of spectroscopic approaches. The Co(II) form of the complex is able to bind two CN^- anions while only binding a single N₃ ^-, providing a reasonable explanation for the difference between their therapeutic abilities. SIGNIFICANCE STATEMENT: The Schiff-base complex CoN₄[14] is shown to be an effective antidote to cyanide in mice, with improved therapeutic capabilities compared to the Food and Drug Administration-approved cobalt-containing hydroxocobalamin. CoN₄[14] is also antidotal in mice toward azide poisoning, for which there is seemingly no approved therapy currently available. The activity toward cyanide involves a "redox-switching" mechanism that could be a common, but largely unrecognized, feature of all cobalt-based cyanide antidotes in use and under development.