Quantitative assessment of cyanide in cystic fibrosis sputum and its oxidative catabolism by hypochlorous acid

Abstract Rationale Cystic fibrosis (CF) patients are known to produce cyanide (CN - ) although challenges exist in determinations of total levels, the precise bioactive levels, and specificity of its production by CF microflora, especially P. aeruginosa . Our objective was to measure total CN - levels in CF sputa by a simple and novel technique in P. aeruginosa positive and negative adult patients, to review respiratory tract (RT) mechanisms for the production and degradation of CN - , and to interrogate sputa for post-translational protein modification by CN - metabolites. Methods Sputa CN - concentrations were determined by using a commercially available CN - electrode, measuring levels before and after addition of cobinamide, a compound with extremely high affinity for CN - . Detection of protein carbamoylation was measured by Western blot. Measurements and main results The commercial CN - electrode was found to overestimate CN - levels in CF sputum in a highly variable manner; cobinamide addition rectified this analytical issue. Although P. aeruginosa positive patients tended to have higher total CN - values, no significant differences in CN - levels were found between positive and negative sputa. The inflammatory oxidant hypochlorous acid (HOCl) was shown to rapidly decompose CN - , forming cyanogen chloride (CNCl) and the carbamoylating species cyanate (NCO - ). Carbamoylated proteins were found in CF sputa, analogous to reported findings in asthma. Conclusions Our studies indicate that CN - is a transient species in the inflamed CF airway due to multiple biosynthetic and metabolic processes. Stable metabolites of CN - , such as cyanate, or carbamoylated proteins, may be suitable biomarkers of overall CN - production in CF airways.