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

• Published in: Free radical biology & medicine 2018-12, Vol.129, p.146-154
• Main Authors: Eiserich, Jason P., Ott, Sean P., Kadir, Tamara, Morrissey, Brian M., Hayakawa, Keri A., La Merrill, Michele A., Cross, Carroll E.
• Format: Article
• Language: English
• Subjects: Carbamylated protein; Cyanate; Cyanide; Cyanogen chloride; Cystic fibrosis; Hypochlorous acid; Ion-specific electrode; Myeloperoxidase; Neutrophils; P. aeruginosa
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2018.09.007

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. 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. 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. 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. [Display omitted] •Ion-specific electrode and cobinamide used to quantify CN- in CF sputum.•Sputum CN- levels do not correlate with infection or lung function.•Hypochlorous acid rapidly degrades CN- into cyanogen chloride and cyanate.•CF respiratory tract biosynthetic and catabolic pathways of CN- reviewed.•Carbomoylated proteins are present in CF sputum.