Comparison of cadmium and enzyme-catalyzed nitrate reduction for determination of NO 2−/NO 3− in breath condensate

Abstract

Background: Analysis of NO 2 −/NO 3 − in expired breath condensate (EBC) has been proposed as a marker of inflammation in various lung diseases. Methods: NO 2 − and total NO 3 −/NO 2 − concentrations were determined in EBC collected from healthy and asthmatic subjects. The NO 3 − was first reduced to NO 2 −, and total NO 2 − was detected by colorimetric Griess reaction. Two methods of NO 3 − reduction were compared. To reduce NO 3 −, cadmium (600 μl EBC-macromethod) and enzyme–NADPH–nitrate reductase (60 μl EBC-micromethod) were used. Results: Macromethod: Mean NO 2 − concentrations in EBC were 1.64±0.24 μmol/l in healthy subjects and 0.42±0.17 μmol/l in asthmatic patients. Mean total NO 2 −/NO 3 − levels were 3.64±0.43 μmol/l in healthy subjects and 3.27±0.34 μmol/l in asthmatic. Micromethod: NO 2 − level: 1.69±0.23 μmol/l in healthy subjects and 0.53±0.21 μmol/l in asthmatics. Total NO 2 −/NO 3 − levels: 3.56±0.37 μmol/l in healthy subjects and 3.57±1.17 μmol/l in asthmatics. Variability index was 27% and 6% for macro- and micromethod, respectively. Recovery of NO 3 − added to EBC was 100% for enzymatic and almost 88% for cadmium reduction. There was no correlation between total NO 2 −/NO 3 − levels determined by macro- and micromethod. Conclusions: We recommend enzymatic reduction as a better method for NO 3 − determination in EBC.