The Response of Children with Asthma to Ambient Particulate Is Modified by Tobacco Smoke Exposure

Abstract

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 mm 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 mg/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.Keywords: air pollution; leukotriene E 4 ; asthma; interaction; environmental tobacco smoke A number of panel studies have demonstrated a relationship between levels of airborne particulate matter less than 10 or 2.5 mm in aerodynamic diameter (PM 10 or PM 2.5 ) and acute asthma severity indices including hospital admissions (1-3), declines in pulmonary function, and increases in medication use and symptoms (4)(5)(6)(7)(8)(9)(10)(11)(12). Almost all such studies estimate ambient health effects without taking into account concurrent exposures that may impact asthma, such as environmental tobacco smoke (ETS). However, in the setting of urban asthma, where high ambient exposures are assumed, concurrent exposures to ETS are also prevalent (13-20). There are limited data on the response to ambient or indoor exposures in the typical urban environment where these concurrent exposures often occur. As such, it is unclear whether acute exposures to both ETS and ambient air pollution produce additive or synergistic effects or whether adaptive responses occur, limiting cumulative health effects from concurrent exposures.In previous analyses involving a panel of Denver urban schoolchildren with as...

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