Methylation of cysteinyl leukotriene receptor 1 genes associates with lung function in asthmatics exposed to traffic-related air pollution.

Air pollution is associated with early declines in lung function and increased levels of asthma-related cysteinyl leukotrienes (CysLT) but a biological pathway linking this rapid response has not been delineated. In this randomized controlled diesel exhaust (DE) challenge study of 16 adult asthmatics, increased exposure-attributable urinary leukotriene E4 (uLTE4, a biomarker of cysteinyl leukotriene production) was correlated (p = 0.04) with declines in forced expiratory volume in 1-second (FEV1) within 6 hours of exposure. Exposure-attributable uLTE4 increases were correlated (p = 0.02) with increased CysLT receptor 1 (CysLTR1) methylation in peripheral blood mononuclear cells which, in turn, was marginally correlated (p = 0.06) with decreased CysLTR1 expression. Decreased CysLTR1 expression was, in turn, correlated (p = 0.0007) with FEV1 declines. During the same time period, increased methylation of GPR17 (a negative regulator of CysLTR1) was observed after DE exposure (p = 0.02); this methylation increase was correlated (p = 0.001) with decreased CysLTR1 methylation which, in turn, was marginally correlated (p = 0.06) with increased CysLTR1 expression; increased CysLTR1 expression was correlated (p = 0.0007) with FEV1 increases. Collectively, these data delineate a potential mechanistic pathway linking increased DE exposure-attributable CysLT levels to lung function declines through changes in CysLTR1-related methylation and gene expression.

Health effects of concurrent ambient and tobacco smoke-derived particle exposures at low concentrations in children with asthma.

Exposure to particulate matter less than 2.5 microns from either ambient pollution (AMB-PM2.5) or secondhand smoke (SHS-PM2.5) have been associated with asthma worsening, but there is little information on effects and relative potency with concurrent exposures. We studied health effects of concurrent exposures to AMB-PM2.5 and SHS-PM2.5 over a 6-year period in schoolchildren with asthma. Regression calibration with instrumental variables (RCIV) was utilized to estimate effects of personal exposure to low-level SHS and AMB-PM2.5 on daily albuterol usage and urinary leukotriene E4 (uLTE4; a biomarker of asthma-related inflammation) using urine cotinine and concentrations from fixed and personal pollution monitors. Each IQR increase in SHS-PM2.5 exposure was associated with a 6.7% increase (95% CI: 1.0-12.8%) in uLTE4 on the same day and 9.4% increase (95% CI: -2.6 to 22.7%) in albuterol use the next day, when children were co-exposed to mean levels of AMB-PM2.5. The dose-response relationship between health outcomes and one pollutant was higher at lower levels of the other pollutant. For example, at lower levels of predicted SHS-PM2.5 exposure, increases in health outcomes per IQR increase in AMB-PM2.5 ranged between 2 and 5%, but were negligible at higher SHS-PM2.5 levels. Comparing at equivalent co-exposure levels, SHS-PM2.5 was 1.6 times more potent than AMB-PM2.5 for uLTE4 (95% CI: 1.1-2.3); estimates for albuterol usage were similar but less significant. Effects at mean co-exposure levels were closer [SHS to AMB-PM2.5 potency ratio = 1.2 (95% CI: 0.9-1.5) for uLTE4 and 1.2 (95% CI: 0.7-1.9) for albuterol usage]. In summary, concurrent exposure to relatively low levels of SHS and AMB-PM2.5 were associated with health outcomes in asthmatic schoolchildren. Dose responses varied with changes in the relative amounts of each pollutant; SHS-PM2.5 was observed to be more potent than AMB-PM2.5 when co-exposure levels were equivalent.

Urinary Leukotriene E4 as a Biomarker of Exposure, Susceptibility, and Risk in Asthma: An Update.

Measurement of urinary leukotriene E4 (uLTE4) is a sensitive and noninvasive method of assaying total body cysteinyl leukotriene (CysLT) production and changes in CysLT production. Recent studies have reported on novel LTE4 receptor interactions and genetic polymorphisms causing CysLT variability. The applications of uLTE4 as a biomarker continue to expand, including evaluation of environmental exposures, asthma severity risk, aspirin sensitivity, predicting atopy in preschool age children, obstructive sleep apnea, and predicting susceptibility to leukotriene receptor antagonists.

Predictors of asthma control and lung function responsiveness to step 3 therapy in children with uncontrolled asthma.

BACKGROUND: Predictors of improvement in asthma control and lung function to step 3 therapy in children with persistent asthma have not been identified despite reported heterogeneity in responsiveness. OBJECTIVE: We sought to evaluate potential predictors of asthma control and lung function responsiveness to step 3 therapy. METHODS: A post hoc analysis from the Best Add-On Giving Effective Response (BADGER) study tested the association between baseline biological, asthma control, pulmonary function, and demographic markers and responsiveness to step-up to a higher dose of inhaled corticosteroid (ICS step-up therapy) or addition of leukotriene receptor antagonist (LTRA step-up therapy) or long-acting ß2-agonist (LABA step-up therapy). RESULTS: In multivariate analyses higher impulse oscillometry reactance area was associated (P = .048) with a differential FEV1 response favoring LABA over ICS step-up therapy, whereas higher urinary leukotriene E4 levels were marginally (P = .053) related to a differential FEV1 response favoring LTRA over LABA step-up therapy. Predictors of differential responses comparing ICS with LTRA step-up therapy were not apparent, probably because of suppression of allergic markers with low-dose ICS treatment. Minimal overlap was seen across FEV1 and asthma control day predictors, suggesting distinct mechanisms related to lung function and asthma control day responses. CONCLUSION: Levels of impulse oscillometry reactance area indicating peripheral airway obstruction and urinary leukotriene E4 levels indicating cysteinyl leukotriene inflammation can differentiate LABA step-up responses from responses to LTRA or ICS step-up therapy. Further studies with physiologic, genetic, and biological markers related to these phenotypes will be needed to predict individual responses to LABA step-up therapy.

Regression calibration for models with two predictor variables measured with error and their interaction, using instrumental variables and longitudinal data.

Regression calibration provides a way to obtain unbiased estimators of fixed effects in regression models when one or more predictors are measured with error. Recent development of measurement error methods has focused on models that include interaction terms between measured-with-error predictors, and separately, methods for estimation in models that account for correlated data. In this work, we derive explicit and novel forms of regression calibration estimators and associated asymptotic variances for longitudinal models that include interaction terms, when data from instrumental and unbiased surrogate variables are available but not the actual predictors of interest. The longitudinal data are fit using linear mixed models that contain random intercepts and account for serial correlation and unequally spaced observations. The motivating application involves a longitudinal study of exposure to two pollutants (predictors) - outdoor fine particulate matter and cigarette smoke - and their association in interactive form with levels of a biomarker of inflammation, leukotriene E4 (LTE 4 , outcome) in asthmatic children. Because the exposure concentrations could not be directly observed, we used measurements from a fixed outdoor monitor and urinary cotinine concentrations as instrumental variables, and we used concentrations of fine ambient particulate matter and cigarette smoke measured with error by personal monitors as unbiased surrogate variables. We applied the derived regression calibration methods to estimate coefficients of the unobserved predictors and their interaction, allowing for direct comparison of toxicity of the different pollutants. We used simulations to verify accuracy of inferential methods based on asymptotic theory.

Indoor pollutant exposures modify the effect of airborne endotoxin on asthma in urban children.

RATIONALE: The effect of endotoxin on asthma morbidity in urban populations is unclear. OBJECTIVES: To determine if indoor pollutant exposure modifies the relationships between indoor airborne endotoxin and asthma health and morbidity. METHODS: One hundred forty-six children and adolescents with persistent asthma underwent repeated clinical assessments at 0, 3, 6, 9, and 12 months. Home visits were conducted at the same time points for assessment of airborne nicotine, endotoxin, and nitrogen dioxide (NO2) concentrations. The effect of concomitant pollutant exposure on relationships between endotoxin and asthma outcomes were examined in stratified analyses and statistical models with interaction terms. MEASUREMENTS AND MAIN RESULTS: Both air nicotine and NO2 concentrations modified the relationships between airborne endotoxin and asthma outcomes. Among children living in homes with no detectable air nicotine, higher endotoxin was inversely associated with acute visits and oral corticosteroid bursts, whereas among those in homes with detectable air nicotine, endotoxin was positively associated with these outcomes (interaction P value = 0.004 and 0.07, respectively). Among children living in homes with lower NO2 concentrations (<20 ppb), higher endotoxin was positively associated with acute visits, whereas among those living in homes with higher NO2 concentrations, endotoxin was negatively associated with acute visit (interaction P value = 0.05). NO2 also modified the effect of endotoxin on asthma symptom outcomes in a similar manner. CONCLUSIONS: The effects of household airborne endotoxin exposure on asthma are modified by coexposure to air nicotine and NO2, and these pollutants have opposite effects on the relationships between endotoxin and asthma-related outcomes.

Urinary leukotriene E4 as a biomarker of exposure, susceptibility and risk in asthma.

Measurement of urinary leukotriene E(4) (uLTE(4)) is a sensitive and noninvasive method of assaying total body cysteinyl leukotriene production and changes in cysteinyl leukotriene production. Recent studies have reported on novel uLTE(4) receptor interactions, and new applications for uLTE(4), as a biomarker of environmental exposure to tobacco smoke and ambient air pollution, a predictor of risk for asthma exacerbations related to tobacco smoke, and a marker of susceptibility to leukotriene receptor antagonists.

The response of children with asthma to ambient particulate is modified by tobacco smoke exposure.

RATIONALE: Ambient particulate matter concentrations have been positively associated with urinary leukotriene E(4) (LTE(4)) levels and albuterol usage in children with asthma but interactions with environmental tobacco smoke (ETS) exposure have not been demonstrated despite obvious exposure to both pollutants in an urban setting. OBJECTIVES: To assess the health effects of concurrent ETS and ambient particulate matter exposure in children with asthma. METHODS: Albuterol usage and LTE(4) levels were monitored in 82 urban schoolchildren with asthma over three consecutive fall to spring school periods. Concentrations of morning maximum ambient particulate matter <2.5 µm in aerodynamic diameter (mmPM(2.5)) and urine cotinine levels were also measured daily. MEASUREMENTS AND MAIN RESULTS: Albuterol usage and LTE(4) were related to mmPM(2.5) concentrations on days when urine cotinine levels were low (<10 ng/ml/mg creatinine); on these days, mean albuterol usage and LTE(4) increased up to 5 or 6% per 10 µg/m(3) increase in mmPM(2.5). In contrast, no significant relationship was observed when cotinine was high, although mean albuterol usage and LTE(4) levels were greater in this case. Model fits for LTE(4) levels as a function of mmPM(2.5) concentrations were improved when mmPM(2.5) concentrations were logged, suggesting a nonlinear dose-response relationship between particulate matter exposure concentrations and airway mediators of asthma, for which the relationship tends to flatten at higher concentrations. CONCLUSIONS: This study suggests that ETS modifies the acute effects of low-level ambient PM(2.5) exposure on childhood asthma. This negative interaction, the smaller effect of particulate matter exposure in children exposed to higher ETS, may be related to a nonlinear dose-response relationship between asthma mediators and particulate exposures.

Urinary leukotriene E4 levels identify children with tobacco smoke exposure at risk for asthma exacerbation.

BACKGROUND: Children with asthma exposed to secondhand smoke (SHS) might be at higher risk for severe exacerbations, but biomarkers of susceptibility to SHS exposure have not been previously reported. OBJECTIVES: We sought to assess the usefulness of urinary leukotriene E(4) (uLTE4) levels in the prediction of increased risk of severe asthma exacerbations requiring emergency department (ED) or urgent care (UC) visits. METHODS: Forty-four schoolchildren with moderate-to-severe asthma receiving inhaled corticosteroids were followed for 5 months with repeated measurements of uLTE4 and monitoring of ED and UC visits. SHS exposure status was determined by using prestudy questionnaires and repeated measurements of urinary cotinine during the study. RESULTS: Nine (45%) of 20 children with SHS exposure experienced a severe exacerbation requiring an ED or UC visit compared with 3 (12.5%) of 24 children without significant SHS exposure (relative risk, 3.6; 95% CI, 1.1-11.5; P = .02). The uLTE4 level was a significant predictor of exacerbation risk in children exposed to SHS (area under the curve, 0.85; P = .003). Other predictors, such as nighttime symptom frequency, prebronchodilator and postbronchodilator lung function, and exhaled nitric oxide levels, were not related to exacerbations in this group. uLTE4 levels at or greater than 106 pg/mg achieved 67% (6/9) sensitivity and 100% (11/11) specificity for predicting children with SHS exposure who required an ED or UC visit. CONCLUSIONS: Children exposed to SHS are at increased risk for severe asthma exacerbations, despite use of inhaled corticosteroids. uLTE4 levels identify children exposed to SHS at high risk for asthma exacerbations.

Leukotriene-E4 in human urine: Comparison of on-line purification and liquid chromatography-tandem mass spectrometry to affinity purification followed by enzyme immunoassay.

A new analytical method suitable for high throughput measurements of LTE(4) in human urine is described. The methodology utilizes on-line enrichment and liquid chromatography/tandem mass spectrometry (LC/MS/MS). The novel LC/MS/MS method is rapid, linear from 5 to 500pg/ml in spiked urine samples of both healthy and asthmatic subjects and more accurate and precise than enzyme immunoassay (EIA) and previous LC/MS/MS methods. Results from sample integrity experiments and preliminary values of urinary LTE(4) from healthy adults and children are reported.

Exposure to tobacco smoke increases leukotriene E4-related albuterol usage and response to montelukast.

BACKGROUND: Cysteinyl leukotrienes (CysLTs) are important mediators of asthma in children. Predictors of susceptibility to CysLT effects have not been developed. OBJECTIVES: To identify susceptibility markers to CysLT effects and montelukast response. METHODS: Twenty-seven schoolchildren were followed for 5 months with measurements of urinary leukotriene E4 (LTE(4)), cotinine, fractional exhaled nitric oxide (FENO), and monitoring of albuterol use. After a baseline run-in, children were randomized to receive daily montelukast or placebo without change in their current controller medications. RESULTS: At baseline, a significant (P = .003) positive association was observed between LTE(4) levels and albuterol use 2 days later. LTE(4)-related albuterol usage (ie, change per interquartile increase in LTE(4)) declined significantly after montelukast treatment (12% decline; P = .0005 for relative difference between intervals) but not placebo (2% increase; P = .80). Declines in LTE(4)-related albuterol usage between intervals tended to be greater in girls (P = .01 for girls; P = .21 for boys; P = .07 for interaction) and were greater among children with higher cotinine levels (P = .01 for high cotinine group; P = .17 for low cotinine group; P = .04 for interaction). Children with high LTE(4) levels relative to FENO demonstrated significant (P = .05) declines in LTE(4)-related albuterol usage between intervals (P = .89 for low ratio group; P = .25 for interaction). CONCLUSION: Increased individual CysLT levels are associated with subsequent albuterol usage. CysLT-related albuterol usage and montelukast responsiveness are increased in children exposed to tobacco smoke and tend to be greater in girls than boys. Measurement of LTE(4) to FENO ratios may help predict susceptibility to montelukast.

Urinary leukotriene E4.

Measurement of urinary leukotriene E4 (LTE4) is a sensitive and noninvasive method of assaying total body cysteinyl leukotriene production and changes in cysteinyl leukotriene levels in specific microenvironments, such as the airway. Urinary LTE4 measurements can be used as sensitive biomarkers of exposure to asthma triggers, such as air pollution and viral infections. Recent studies suggest the potential of using urinary LTE4 concentrations as predictors of asthma control and markers of susceptibility to treatment with leukotriene receptor antagonists.

Urine leukotriene E4 levels are associated with decreased pulmonary function in children with persistent airway obstruction.

BACKGROUND: Use of leukotriene receptor antagonists improves disease control in children and adults with asthma. However, the relationship between cysteinyl leukotriene levels and indices of daily asthma control has not been studied directly. OBJECTIVES: We sought to assess the relationship between daily variability in urinary leukotriene E(4) (LTE(4)) levels and daily lung function in children primarily taking inhaled corticosteroids (ICSs) and long-acting beta-agonists (LABAs). METHODS: Fifty children primarily with moderate-to-severe asthma were followed with measurements of urinary LTE(4), monitoring of FEV(1), and albuterol use. RESULTS: Increasing urinary LTE(4) levels were associated with significant (P = .006) decreases in percent predicted FEV(1) (ppFEV(1)) averaging 4.7% per interquartile range increase in LTE(4) and accompanied by increased albuterol use (P = .03). Children with lower FEV(1)/forced vital capacity ratios demonstrated larger LTE(4)-related FEV(1) decreases (6.4%) compared to those with higher ratios (4.2%, P = .009). This association was blunted in children taking montelukast (1.4% ppFEV(1) decrease) compared with that in children not taking this medication (5.4% ppFEV(1) decrease, P = .05). Children with lower lung function ratios demonstrated greater blunting of the LTE(4) effect with montelukast (0.9% ppFEV(1) decrease) compared to those with higher ratios (3.6% ppFEV(1), P = .0002). CONCLUSIONS: Daily variability in LTE(4) levels is associated with clinically significant decreases in pulmonary function. In children who demonstrate a response associated with an increase in urinary LTE(4) levels, leukotriene receptor antagonists protect against daily FEV(1) decreases. This protection might be greatest in those with persistent airway obstruction despite use of ICS and LABA therapy. CLINICAL IMPLICATIONS: Therapies designed to block cysteinyl leukotriene production or function might benefit children receiving ICS and LABA therapy who continue to experience persistent disease.