A stable in vitro method for assessing the toxicity of potassium cyanide and its antidote.

Background: Hydrogen cyanide possesses a high acid-dissociation constant of 9.14, favoring its vaporization and depletion from the culture media at physiological pH, which may cause the cyanide toxicity unstable in vitro.
Objective: We investigated whether adjustment of culture medium pH stabilizes cyanide concentration and decreases the effective concentration of potassium cyanide (KCN).
Methods: Murine fibroblast cells were exposed to different concentrations of KCN in media maintained at pH 7.4 or 9.2, in the presence or absence of hydroxocobalamin. After incubation for 1 h, we evaluated medium pH, cyanide concentration, cytochrome activity, and cell viability.
Results: Cyanide concentration decreased to 18.8% in pH 7.4 medium compared to 83.2% in pH 9.2 medium. A significant decrease in cytochrome activity was observed at 40 mM and 1.25 mM KCN in pH 7.4 and pH 9.2 media, respectively. In pH 9.2 medium, dose-dependent cytotoxicity of KCN and antidotal effects of hydroxocobalamin were observed.
Conclusion: Adjustment of culture medium pH to 9.2 could stabilize cyanide concentration and decrease the effective concentration of KCN, allowing stable evaluation of KCN toxicity and antidotal efficacy.