Submitted on October 2, 2008
Revised on March 13, 2009
Accepted on March 19, 2009
Mass Spectrometric Analysis of Biomarkers and Dilution Markers in Exhaled Breath Condensate Reveals Elevated Purines in Asthma and Cystic Fibrosis
Charles R Esther Jr.1*, Gunnar Boysen1, Bonnie M. Olsen1, Leonard B. Collins1, Andrew J Ghio2, James W. Swenberg1, and Richard C. Boucher3
1 UNC Chapel Hill
2 EPA
3 University of North Carolina
* To whom correspondence should be addressed. E-mail: Charles_Esther{at}med.unc.edu.
Exhaled breath condensate (EBC) analyses promise simple and non-invasive methods to measure airway biomarkers but pose considerable methodological challenges. We utilized mass spectrometry to measure EBC purine biomarkers adenosine and AMP plus urea to control for dilutional variability in two studies: (1) a cross-sectional analysis of 28 healthy, 40 cystic fibrosis (CF), and 11 asthmatic children and (2) a longitudinal analysis of 26 CF children before and after treatment of a pulmonary exacerbation. EBC adenosine, AMP, and urea were readily detected and quantified by mass spectrometry, and analysis suggested significant dilutional variability. Using biomarker/urea ratios to control for dilution, the EBC AMP/urea ratio was elevated in CF (median 1.3, IQR 0.7-2.3) versus control (median 0.75, IQR 0.3-1.4, p<0.05) and the adenosine/urea ratio was elevated in asthma (median 1.5, IQR 0.9-2.9) versus control (median 0.4, IQR 0.2-1.6, p<0.05). Changes in EBC purine/urea ratios correlated with changes in percent predicted FEV1 (r = -0.53 AMP/urea, r = 0.55 adenosine/urea, p<0.01 for both) after CF exacerbation treatment. Similar results were observed using dilution factors calculated from serum to EBC urea ratios or EBC electrolytes, and the comparable ratios of EBC electrolytes to urea in CF and control (median 3.2, IQR 1.6-6.0 CF; median 5.5, IQR 1.4-7.7 control) validated use of airway urea as an EBC dilution marker. These results show that mass spectrometric analyses can be applied to measurement of purines in EBC, and demonstrate that EBC adenosine/urea and AMP/urea ratios are potential non-invasive biomarkers of airways disease.
