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

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.