Noninvasive Markers of Airway Inflammation in Asthma

Noninvasive Markers of Airway Inflammation in Asthma Samuel H. Wedes, B.S.1, Sumita B. Khatri, M.D.2, Renliang Zhang M.D., Ph.D.1,3, Weijia Wu, Ph.D.4, Suzy A. A. Comhair, Ph.D.1,5, Sally Wenzel, M.D.6, William G. Teague, M.D.7, Elliot Israel, M.D.8, Serpil C. Erzurum, M.D.1,5,9, and Stanley L. Hazen, M.D., Ph.D.1,3,10 Abstract Background: Although airway inflammation plays a major role in the pathophysiology of asthma, quantitative markers of airway inflammation are limited in clinical practice. Objective: To determine if the levels of noninvasive markers of eosinophil-catalyzed oxidation, lipid peroxidation, and nitric oxide (NO) production are associated with asthma. Methods: Participants were enrolled from academic medical centers participating in the Severe Asthma Research Program. Clinical characteristics, laboratory data, pulmonary function tests, and the levels of the following noninvasive markers were obtained: urinary bromotyrosine (BrTyr), a marker of eosinophil-catalyzed oxidation, urinary F2-isoprostanes (F2-IsoPs), markers of lipid peroxidation, and exhaled NO, a marker of airway inflammation. Results: Fifty-seven asthmatic participants and 38 healthy participants were enrolled. BrTyr, F2-IsoPs, and exhaled NO were each significantly increased in asthmatic participants versus controls ( p < 0.01). An elevated level (greater than the median) of any marker was associated with a significant 3- to 6-fold greater odds of having asthma. Participants with two or more elevated marker levels showed an 18-fold greater odds of having asthma. Relationships were also noted with airflow obstruction and bronchodilator response. Conclusion: The findings from this pilot study indicate that urinary levels of BrTyr and F2-IsoPs, in addition to exhaled NO levels, are associated with asthma. Keywords: asthma, biomarkers, inflammation Introduction Asthma is a chronic inflammatory disorder of the airways characterized by recurrent episodes of wheezing, dyspnea, chest tightness, and cough.1 As airway inflammation and oxidative stress play integral roles in asthma pathophysiology, a directed assessment of the inflammatory pathways could be helpful in the evaluation and management of patients with asthma.2–4 The inflammatory milieu of the airways in asthma can generate multiple distinct oxidant species that can cause tissue injury and produce bronchial hyperresponsiveness.5,6 Although the labile nature of oxidant species makes them difficult to quantify in vivo, stable end products of distinct oxidation pathways may be used as reliable indices of airway oxidative stress. For example, we have shown in allergen-induced asthma that when eosinophils are recruited to the airways and undergo respiratory bursts, they generate brominating oxidants such as hypobromous acid (HOBr) that promote posttranslational modification of protein tyrosine residues to form 3-bromotyrosine (BrTyr).7,8 Similarly, numerous oxidation pathways can initiate lipid peroxidation, forming F2-isoprostanes (F2-IsoPs), free-radical oxidation products of arachidonic acid, which also serve as global indices of oxidative stress. Elevated levels of F2-IsoPs have been detected in both urine and exhaled breath condensates of asthmatic patients.9,10 Last, numerous studies have demonstrated increased nitric oxide (NO) production in the airways of asthmatic patients due, at least in part, to upregulation of inducible nitric oxide synthase (iNOS) in cells like bronchial epithelial cells and alveolar macrophages.11–16 Protein bromination, lipid peroxidation, and NO production represent distinct biochemical pathways that have all been associated with the pathophysiology of asthma.8–10,17–20 Furthermore, BrTyr, F2-IsoPs, and NO serve as stable and quantifiable end products of these respective pathways.7,8,16 In this study, we determined the levels of urinary BrTyr, urinary F2-IsoPs (both 8-epi-PGF2α and its metabolite 2,3-dinor-8-epi-PGF2α), and exhaled NO in a cohort of asthmatic patients and healthy controls. We hypothesized that the levels of these markers of airway inflammation and oxidative stress would be higher in asthmatic patients than in controls, correlate with the presence and reversibility of airway obstruction, and predict asthma status, particularly when pooled together as a panel. The present results reveal that a panel of noninvasive inflammatory markers may have diagnostic and prognostic utility by evaluating the presence and activity of asthma. Preliminary results from this study were previously reported in the form of an abstract.21 Methods Subject enrollment and characterization Individuals enrolled in the Severe Asthma Research Program (SARP) were included in this cross-sectional study. Participants were recruited by individual centers participating in the SARP and gave written informed consent by signing a consent document approved by the institutional review board at the enrolling center and the SARP Data Safety and Monitoring Board. Utilizing the definition of asthma described by the Proceedings of the American Thoracic Society Workshop on Refractory Asthma,22 the participants were classified as healthy controls, nonsevere asthmatic patients, or severe asthmatic patients. Additional healthy controls were enrolled locally. The healthy controls lacked any cardiopulmonary symptoms and had normal baseline spirometry 1 Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, Ohio, USA; 2Department of Medicine, Case Western Reserve University School of Medicine, MetroHealth Medical Center, Cleveland, Ohio, USA; 3Department of Cell Biology, Lerner Research Institute, Cleveland, Ohio, USA; 4PrognostiX, Inc., Cleveland, Ohio, USA; 5 Department of Pathobiology, Lerner Research Institute, Cleveland, Ohio, USA; 6University of Pittsburgh, Pittsburgh, Pennsylvania, USA; 7Emory University, Atlanta, Georgia, USA; 8 Brigham and Women’s Hospital, Boston, Massachusetts, USA; 9Respiratory Institute, Cleveland Clinic, Cleveland, Ohio, USA;10Center for Cardiovascular Diagnostics and Prevention and Department of Cardiovascular Medicine, Cleveland Clinic, Cleveland, Ohio, USA. Correspondence: SL Hazen ([email protected]) DOI: 10.1111/j.1752-8062.2009.00095.x 112 VOLUME 2 • ISSUE 2 WWW.CTSJOURNAL.COM Wedes et al. Inflammatory Markers and Asthma ■ and methacholine challenge results.3,23 The exclusion criteria for all participants included smoking within the past year, former smokers with ≥5 pack-year total history, and/or pregnancy. Measurement of lung function, NO, and atopy Spirometry was performed with an automated spirometer, as described elsewhere,23 consistent with the American Thoracic Society standards.24 Exhaled NO was measured by an online method at a constant flow rate of 50 mL/s, consistent with the American Thoracic Society standards.25,26 Atopy was determined by skin prick testing. Laboratory analysis Complete blood counts with differentials and IgE levels were performed under standard laboratory conditions at enrolling centers within the SARP. For urine analyses, spot urine collections were obtained. The samples were spun to remove potential cellular debris and casts and then frozen at –80°C until the time of analysis. Urinary creatinine (Cr) levels were quantified on an Abbott Architect machine (Abbott Diagnostics, Abbott Park, IL, USA), according to the manufacturer’s instructions. Urinary free 3-BrTyr levels were determined by stable isotope dilution HPLC with online electrospray ionization tandem mass spectrometry using turbidometric solid-phase extraction coupled to a reverse-phase analytic separation on a Cohesive Technologies Aria LX HPLC instrument (Franklin, MA, USA) interfaced to an API 4000 triple quadrupole mass spectrometer (Applied Biosystems, Foster City, CA, USA). Synthetic [13C6]-BrTyr was used as an internal standard, and [13C9,15N1]-tyrosine was included to simultaneously monitor potential artificial generation of analyte. Under the conditions employed for the assay, no artificial bromination was detected, the average spike and recovery was 101% and ranged from 98 to 105%, and assay precision of <7% was noted across all concentrations ranges examined. Urinary levels of 8-epi-PGF2α and 2,3-dinor-8-epi-PGF2α were analyzed by stable isotope dilution HPLC with online electrospray ionization tandem mass spectrometry using a HPLC interfaced to a Micromass Ultima triple quadrupole mass spectrometer (Waters, Milford, MA, USA). Immediately after thawing, an internal standard (9α,11α,15S-trihydroxy5Z,13E-dien-1-oic-3,3,4,4-d4 acid; PGF2α-d4; Cayman Chemical Company, Ann Arbor, MI, USA) was added to the sample. The average spike and recovery was 103% and ranged from 94 to 108% across low-, mid-, and high-level control samples, and assay precision of <10% was noted across all concentrations ranges examined. To adjust for variations in urinary dilution, the results of BrTyr and F2-IsoPs are reported as ratios with urine Cr concentrations. Statistical analysis Baseline characteristics and marker levels among the groups were compared with t-test and analysis of variance for continuous normally distributed variables, the Wilcoxon rank-sum test and Kruskal–Wallis test for continuous nonnormally distributed variables, and the likelihood ratio χ 2 test for categorical variables. Appropriate Bonferroni adjustments were made for pairwise comparisons. Correlations among marker levels and other variables were assessed using Spearman’s rank-sum correlation coefficients or Pearson’s correlation coefficients, if the data was normally distributed. A p-value ≤0.05 was WWW.CTSJOURNAL.COM defi ned as statistically signifi cant. One asthmatic and one control subject were excluded from statistical analyses based upon the predetermined criteria of marker levels greater than 5 standard deviations above the mean. All statistical analyses were performed in JMP version 5.1 and SAS version 9.0 (SAS Institute, Cary, NC, USA). Results Fifty-seven asthmatic and 38 control participants were included in this study. As noted in Table 1, asthmatic patients were similar to controls with respect to age, gender, and BMI. Asthmatic patients had higher leukocyte counts (p = 0.006) and frequency of atopy (p = 0.03) than controls. As expected, asthmatic patients had greater airway obstruction and increased bronchodilator responsiveness than controls. Asthmatic patients had significantly higher levels of each marker measured compared with healthy controls (Table 1): BrTyr (p = 0.003), 8-epi-PGF2α (p = 0.007), 2,3-dinor-8-epiPGF2α (p = 0.005), and exhaled NO (p = 0.04). Interestingly, higher levels of urinary BrTyr and exhaled NO each correlated with severer airway obstruction as monitored by % predicted forced expiratory volume in 1 second (FEV1) (R[p] of –0.30[0.02] and –0.30[0.03] for BrTyr and NO, respectively) and the ratio of the forced expiratory volume in 1 second to the forced vital capacity (FEV1/FVC) (R[p] of –0.35[0.006] and –0.29[0.04] for BrTyr and NO, respectively). Higher NO levels also correlated significantly with greater bronchodilator response (Table 2). Leukocyte counts did not correlate with urinary biomarkers, including no correlation between urinary BrTyr and absolute eosinophil count. However, exhaled NO levels were strongly correlated with both increased eosinophils and serum IgE levels (Table 2), consistent with previous reports.27,28 Although F2-IsoP levels did not demonstrate any correlation with leukocyte counts or indices of airway obstruction and bronchodilator responsiveness, they did correlate significantly with BMI, especially the urinary metabolite 2,3-dinor-8-epi-PGF2α. As expected, the levels of isoprostanes significantly correlated with one another (Table 2). The values for each noninvasive marker were dichotomized into above median levels and below median levels and evaluated for their ability to predict the presence of asthma and indices of airway obstruction and bronchodilator responsiveness (Table 3). The median values were 0.16 ng/mg Cr for BrTyr, 2.86 ng/mg Cr for 8-epi-PGF2α, 37.2 ng/mg Cr for 2,3-dinor-8-epi-PGF2α, and 26.7 parts per billion (ppb) for NO. High (above median) levels of BrTyr, 8-epi-PGF2α, 2,3-dinor-8-epi-PGF2α, and NO were all individually associated with greater odds of asthma (Table 3 and Figure 1). High NO levels were further associated with increased airway obstruction and bronchodilator responsiveness. In order to assess whether a panel of markers in aggregate predicted asthma and indices of airway obstruction and bronchodilator responsiveness, individuals with two or more markers above median (“high”) values were compared with those with one or no high values. Exhaled NO and BrTyr were each considered one marker. Elevated isoprostanes, 8-epi-PGF2α and/or 2,3-dinor-8-epi-PGF2α, were considered together as a third marker, given their strong correlation with one another. Subjects with two or more high levels of noninvasive markers were approximately 18 times as likely to have asthma, 4 times more likely to have airway obstruction, and 7 times as likely to have bronchial responsiveness to bronchodilator (Table 3 and Figure 1). VOLUME 2 • ISSUE 2 113 Wedes et al. Inflammatory Markers and Asthma ■ Previous findings support the possibility that end products of protein Number (%) 38 (40) 57 (60) bromination, for example, BrTyr, may Age (years) 30.0 (25.0–43.0) 28.5 (21.3–46.8) 0.69 be used as molecular fingerprints of eosinophil activation,7,8,19,34 including Gender, M:F 18:19 31:25 0.53 in subjects with status asthmaticus.19 BMI (kg/m2) 25.2 (22.3–27.6) 25.9 (22.3–35.3) 0.29 Elevated levels of F 2-IsoPs, global Total WBC × 106 (serum)† 5.5 (4.4–6.7) 6.4 (5.3–8.9) 0.006 markers of oxidative stress, have been reported in asthmatic subjects in some % Eosinophils 2.5 (1.6–3.4) 2.7 (1.3–5.5) 0.45 studies,9,10 though the relationship of % Neutrophils 57.0 (51.5–66.0) 55.7 (45.6–66.2) 0.70 these markers to indices of asthma IgE (IU/mL) 60.5 (33.3–130.0) 93.0 (16.3–195.8) 0.82 severity and alternative noninvasive markers of inflammation and oxidative Atopy‡ 0.0 (0.0–1.5) 2.0 (0.0–4.0) 0.03 stress such as NO and BrTyr have not 106.0 (97.0–113.0) 79.0 (62.0–91.0) <0.001 % Predicted FEV1 been reported. FEV1/FVC 0.82 (0.75–0.88) 0.69 (0.59–0.77) <0.001 Despite serving as a marker 2.0 (0.0–4.2) 10.3 (4.3–17.3) <0.001 % Change FEV1 post-BD for eosinophil-mediated oxidative pathways, BrTyr did not correlate BrTyr§ 0.13 (0.05–0.20) 0.19 (0.12–0.32) 0.003 with percent eosinophils. This result 1.9 (1.3–3.9) 3.4 (2.2–5.3) 0.007 8-epi-PGF2α emphasizes the notion that eosinophil2,3-dinor-8-epi-PGF2α 23.9 (17.2–48.9) 46.9 (28.6–71.5) 0.005 mediated oxidation is not specifically a function of eosinophil concentration, Exhaled NO (ppb) 15.9 (11.9–21.6) 41.6 (16.4–83.1) 0.004 but rather of eosinophil activation All variables expressed as median (interquartile range), unless otherwise specified. by a variety of inflammatory stimuli, *p-values calculated by unpooled t-test for normally distributed data and Wilcoxon’s rank-sum test for nonnormally distributed data. which facilitates the respiratory burst †Complete blood count with differentials and spirometry were performed on a random sampling of controls, N = 20 and release of eosinophil peroxidase.8 and 21, respectively. F2-IsoPs also did not correlate with ‡Atopy is defined as the number of skin tests positive of 12 allergens tested. §Urinary markers (BrTyr, 8-epi-PGF , and 2,3-dinor-8-epi-PGF ) are measured in ng/mg creatinine. percent eosinophils; however, F2-IsoPs BrTyr = bromotyrosine; NO = nitric oxide. are not specific markers of eosinophilmediated oxidative pathways, but Table 1. Features of study participants. rather are general markers of oxidative stress, which can be induced by myriad inflammatory cells and Discussion mediators.16 Current guidelines from the National Institutes of Health The results of the present pilot study demonstrate that urinary emphasize the need for not only symptom control but also levels of BrTyr and F2-IsoPs (both 8-epi-PGF2α and 2,3-dinor-8reduction of airway inflammation in the treatment of asthma.1 epi-PGF2α), in addition to exhaled NO, demonstrate significant However, current standards of practice depend on clinical history, associations with the presence of asthma. Of particular clinical physical examination, and pulmonary function tests to determine relevance, higher levels of more than one of the three general the presence and severity of asthma, none of which quantifiably classes of noninvasive markers (BrTyr, F2-IsoPs, or NO) was measure airway inflammation. Utilizing a panel of markers to associated with markedly increased odds of having asthma. diagnose asthma and monitor asthma severity directly in terms Despite uniformly predicting asthma status, the markers of airway inflammation could allow clinicians to gauge disease measured in this study demonstrated variability in predicting activity at the molecular level and optimize the effectiveness of airway obstruction and bronchodilator response. Higher levels of anti-inflammatory treatment regimens. all markers except F2-IsoPs were associated with increased odds Exhaled NO is an FDA-cleared diagnostic that has been used of airway obstruction and/or reversibility of airway obstruction. previously to measure airway inflammation.29 Many studies have Pooling the markers amplified this effect. demonstrated decreases in exhaled NO with treatment of asthma, It is important to note that all participants had samples corresponding with improved symptoms and lung function.30,31 and clinical data collected only at baseline and not during However, the measurement of exhaled NO requires special an exacerbation. As all of the asthmatic patients were at a equipment, which is not readily available at most primary care relatively stable baseline at the time of data collection, how physician offices. Moreover, although titrating treatment to reach these findings may vary during an acute exacerbation is not normal NO levels may provide a metric for anti-inflammatory yet known. However, it should be noted that modest increases therapy, recent studies demonstrate that this treatment strategy in urinary F2-IsoPs have been reported in a small cohort of does not necessarily reduce the rate of asthma exacerbations.31–33 subjects following allergen challenge,9 and dramatic increases One potential mechanism for this shortcoming is the diversity of in bronchoalveolar lavage levels of BrTyr have been observed inflammatory processes at play in asthmatic airways in addition to following whole-lung allergen challenge, segmental allergen those monitored by exhaled NO. In addition, exhaled NO is affected challenge, and asthma exacerbation.8,19 The majority of the by various factors, including diet, time relative to exacerbations asthmatic patients in this study were being treated with inhaled and spirometric testing, technique (rate of exhalation and airway corticosteroids, which may have attenuated the strength of resistance), and contamination of the sample with upper airway the relationships observed. In particular, the percentage of (nasal) secretions.14,22 Thus, identification of other markers is of eosinophils was not significantly higher in asthmatic patients considerable interest. compared with controls, which may have been a result of Characteristic Controls 2α 114 VOLUME 2 • ISSUE 2 Asthmatic patients p-value* 2α WWW.CTSJOURNAL.COM Wedes et al. Inflammatory Markers and Asthma ■ Characteristic BrTyr* 8-epi-PGF2α 2,3-dinor-8-epi-PGF2α NO 0.13 0.27 0.42 0.05 0.30 0.03 <0.001 0.73 –0.30 0.0002 –0.15 –0.30 1.00 0.23 0.03 –0.35 0.17 –0.03 –0.29 0.006 0.18 0.83 0.04 BMI (kg/m2) R† p % Predicted FEV1 R p 0.02 FEV1/FVC R p R 0.23 –0.14 0.05 0.51 p 0.08 0.25 0.68 <0.001 R 0.02 –0.01 –0.20 0.44 p 0.87 0.91 0.09 <0.001 Atopy‡ R 0.05 0.19 0.04 0.25 p 0.68 0.13 0.76 0.08 % Eosinophils R –0.06 –0.02 –0.13 0.43 p 0.66 0.85 0.28 0.001 % Neutrophils R 0.07 –0.02 0.08 –0.08 p 0.59 0.87 0.49 0.58 % Change FEV1 IgE (IU/mL) BrTyr 8-epi-PGF2α R – 0.10 0.19 0.08 p – 0.35 0.07 0.57 R – – p R 2,3-dinor-8-epi-PGF2α – 0.71 0.04 <0.001 0.75 – –0.10 – p 0.48 *Urinary markers (BrTyr, 8-epi-PGF 2α , and 2,3-dinor-8-epi-PGF 2α) are measured in ng/mg creatinine; NO is measured in ppb. †All R values represent Spearman’s correlation coefficients; p-value was calculated accordingly. ‡Atopy is defined as the number of skin tests positive of 12 allergens tested. BrTyr = bromotyrosine; NO = nitric oxide. Table 2. Correlations of markers and indices of asthma severity. Condition BrTyr* 8-epi-PGF2α 2,3-dinor-8-epiPGF2α NO High levels ≥2 markers† Asthma 3.1 4.2 4.2 5.9 18.2 (1.3–7.4) (1.7–10.2) (1.7–10.2) (1.4–24.0) (3.5–95.2) 0.01 <0.001 <0.001 0.007 <0.001 1.8 0.6 0.8 3.1 4.2 (0.6–5.3) (0.2–1.5) (0.3–2.3) (0.9–10.2) (1.1–15.8) % Predicted FEV1 <80 FEV1/FVC <0.70 % Change FEV1 >12 0.28 0.26 0.71 0.06 0.03 2.8 0.5 0.6 5.3 4.2 (0.9–8.3) (0.2–1.5) (0.2–1.7) (1.5–18.7) (1.1–15.8) 0.06 0.23 0.37 0.006 0.03 1.8 0.8 2.3 9.0 7.1 (0.6–5.9) (0.3–2.5) (0.7–7.1) (1.7–46.9) (1.4–37.7) 0.31 0.77 0.15 0.003 0.009 *Urinary markers (BrTyr, 8-epi-PGF 2α , and 2,3-dinor-8-epi-PGF 2α) are measured in ng/mg creatinine; NO is measured in ppb. †High levels are defined as levels above the median: 0.16 ng/mg creatinine for BrTyr, 2.86 ng/mg creatinine for 8-epi-PGF 2α , 37.19 ng/mg creatinine for 2,3-dinor-8-epi-PGF 2α , and 26.7 ppb for NO. For this analysis, F 2-isoprostanes were considered as one marker with high levels, defined as 8-epi-PGF 2α and/or 2,3-dinor-8-epi-PGF 2α greater than median levels. BrTyr = bromotyrosine; NO = nitric oxide. Table 3. Odds ratios of asthma diagnosis and indices of asthma severity relative to marker levels. WWW.CTSJOURNAL.COM VOLUME 2 • ISSUE 2 115 Wedes et al. Inflammatory Markers and Asthma ■ Acknowledgments Supported by National Institutes of Health grants P01 HL081064-020003, P01 HL087018020001, and R01 HL69170 and the Case Western Reserve University/Cleveland Clinic CTSA (1KL2RR024990 and 1UL1RR024989). Urinary bromotyrosine levels were determined by PrognostiX, Inc., Cleveland, OH. Conflict of Interest Mr. Wedes, Dr. Khatri, and Dr. Zhang report no conflicts of interest. Dr. Wu reports that he has been named as co-inventor on patents held by the Cleveland Clinic relating to diagnostic tests in asthma and other inflammatory disorders. Dr. Wu also reports that he is employed by PrognostiX, Inc., a diagnostics Figure 1. Odds ratios and 95% confidence intervals for the association between the presence of company that developed the urinary elevated marker levels, individually and in combination, versus the diagnosis of asthma. Results shown bromotyrosine assay. Dr. Comhair reports represent the odds ratio (filled circle) and 95% confidence interval (line) of having the diagnosis of asthma for a participant possessing a high level (above median) of the indicated marker or combination of markers compared that she has been named as co-inventor on with subjects possessing below median levels of the indicated marker(s). When calculating the odds ratio for having patents held by the Cleveland Clinic relating two or more markers above median levels, three marker classes were used (i.e., NO, BrTyr, and a composite F2-isoP to diagnostic tests in asthma. Dr. Wenzel score) to avoid overweighting the highly correlated 8-epi-PGF2α and 2,3-dinor-8-epi-PGF2α. The F2-IsoP score was considered “high” if levels of 8-epi-PGF2α and/or 2,3-dinor-8-epi-PGF2α were greater than their respective median reports that she has no conflicts of interest. levels. Median levels of markers within the cohort were 0.16 ng/mg Cr for BrTyr, 2.86 ng/mg Cr for 8-epi-PGF2α, Dr. Teague reports that he has received 37.19 ng/mg Cr for 2,3-dinor-8-epi-PGF2α, and 26.7 ppb for NO. speaking honoraria from Merck. Dr. Israel reports that he has no conflicts of interest. Dr. Erzurum reports that she participated inhaled corticosteroid use.1 The study’s sample size was not in the Asthmatx Study of Bronchial Thermoplasty but received large enough to provide a range of normal values or shapes no compensation. Dr. Hazen reports that he has been named as of the distributions of marker levels in control and asthmatic co-inventor on patents held by the Cleveland Clinic relating to populations. diagnostic tests in asthma and other inflammatory disorders. Dr. Hazen reports that he is the scientific founder of PrognostiX, Inc., Conclusion has received speaking honoraria from Pfizer, AstraZeneca, Merck, Findings from this pilot study indicate that urinary levels of BrTyr Merck Schering Plough, BioSite, Lilly, Wyeth, and Abbott, has and F2-IsoPs, in addition to exhaled NO levels, are associated with received research grant support from Abbott Diagnostics, Pfizer, asthma. These results provide evidence supporting the potential Merck, PrognostiX, Inc., Hawaii Biotech, ArgiNOx, Sanofi, and utility of a panel of noninvasive markers of inflammation and Takeda, and has received consulting fees from Abbott Diagnostics, oxidative stress in asthma. Additional studies are required to Pfizer, PrognostiX Inc, Wyeth, BioPhysical, and AstraZeneca. No investigate more thoroughly the clinical utility of BrTyr and F2other disclosures were reported. IsoPs in asthmatic patients. As discoveries of newer metabolic and inflammatory pathways in asthma emerge, additional markers References may be identified to expand noninvasive panels and strengthen 1. NHLBI. Expert Panel Report 3: Guidelines for the diagnosis and management of asthma—full their predictive values. In addition, a better understanding of report. NHLBI, Bethesda, MD, USA, 2007. Available at: http://www.nhlbi.nih.gov/guidelines/ asthma. Accessed February 10, 2009. asthma’s pathogenesis may allow researchers to pinpoint specific 2. Comhair SA, Bhathena PR, Farver C, Thunnissen FB, Erzurum SC. 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