Cyanide (both HCN and CN^- are represented by CN) has multiple industrial applications, is commonly found in some foods, and is a component of fire smoke. Upon exposure, CN blocks production of adenosine triphosphate, causing cellular hypoxia and cytotoxic anoxia, which can eventually result in death. Considering CN's quick onset of action and the long analysis times associated with current techniques, the objective of this study was to develop and validate a rapid and field-portable sensor to detect blood CN concentrations focusing on both concentration and diagnostic accuracy. The sensor takes advantage of the chemical properties of CN by converting it exclusively to HCN via acidification of whole blood. High-speed headspace transfer is used to deliver HCN to a capture solution where it is reacted with naphthalene dialdehyde and taurine to produce a fluorescent β-isoindole product. Simple spectrofluorometric analysis of the product provides quantitative analysis of CN from whole blood in 60 s and requires only 25 μL of blood (obtainable via fingerstick). A limit of detection of 5 μM, a linear range of 10-200 μM (with ≥15 μM considered CN exposed), and excellent accuracy (100 ± 15%) and precision (≤15.2% relative standard deviation) were obtained. To evaluate the diagnostic accuracy of the sensor, rabbit blood samples (N = 190, including 24 blinded samples) were analyzed by both the sensor and a lab-based spectrophotometric method. An excellent positive correlation was obtained between the sensor and the lab-based method (R² ˃ 0.995) confirming the concentration accuracy of the CN sensor. Moreover, the sensor produced no false positives or negatives when diagnosing CN poisoning.

Context

Hydrogen cyanide and methanethiol are two toxic gases that inhibit mitochondrial cytochrome c oxidase. Cyanide is generated in structural fires and methanethiol is released by decaying organic matter. Current treatments for cyanide exposure do not lend themselves to treatment in the field and no treatment exists for methanethiol poisoning. Sodium tetrathionate (tetrathionate), a product of thiosulfate oxidation, could potentially serve as a cyanide antidote, and, based on its chemical structure, we hypothesized it could react with methanethiol.

Results

We show that tetrathionate, unlike thiosulfate, reacts directly with cyanide in vitro under physiological conditions, and based on rabbit studies where we monitor cyanide poisoning in real-time, tetrathionate likely reacts directly with cyanide in vivo. We found that tetrathionate administered by intramuscular injection rescues >80% of juvenile, young adult, and old adult mice from exposure to inhaled hydrogen cyanide gas that is >80% lethal. Tetrathionate also rescued young adult rabbits from intravenously administered sodium cyanide. Tetrathionate was reasonably well-tolerated by mice and rats, yielding a therapeutic index of ∼5 in juvenile and young adult mice, and ∼3.3 in old adult mice; it was non-mutagenic in Chinese Hamster ovary cells and by the Ames bacterial test. We found by gas chromatography-mass spectrometry that both tetrathionate and thiosulfate react with methanethiol to generate dimethyldisulfide, but that tetrathionate was much more effective than thiosulfate at recovering intracellular ATP in COS-7 cells and rescuing mice from a lethal exposure to methanethiol gas.

Conclusion

We conclude that tetrathionate has the potential to be an effective antidote against cyanide and methanethiol poisoning.