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* From the Division of Pulmonary, Allergy, Critical Care Medicine (Dr. Miller and Ms. Horton), Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY; Columbia Center for Childrens Environmental Health (Drs. Garfinkel, Perera, Whyatt, and Kinney), Department of Environmental Health Sciences, Mailman School of Public Health, Columbia University, New York, NY; and Department of Analytical and Environmental Chemistry (Mr. Camann), Southwest Research Institute, San Antonio, TX.
Correspondence to: Rachel L. Miller, MD, PH8C, 630 168th St, New York, NY 10032; e-mail:rlm14{at}columbia.edu
| Abstract |
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Design/participants: To test our hypotheses, we recruited 303 pregnant women from northern Manhattan believed to be at high risk for exposure to both PAH and ETS, collected 48-h personal PAH exposure measurements, and monitored their children prospectively.
Results: By 12 months of age, more cough and wheeze were reported in children exposed to prenatal PAH in concert with ETS postnatally (PAH x ETS interaction odds ratios [ORs], 1.41 [p < 0.01] and 1.29 [p < 0.05], respectively). By 24 months, difficulty breathing and probable asthma were reported more frequently among children exposed to prenatal PAH and ETS postnatally (PAH x ETS ORs, 1.54 and 1.64, respectively [p < 0.05]).
Conclusions: Our results suggest that early exposure to airborne PAH and ETS can lead to increased respiratory symptoms and probable asthma by age 12 to 24 months. Interventions to lower the risk of respiratory disease in young children living in the inner city may need to address the importance of multiple environmental exposures.
Key Words: asthma environmental tobacco smoke polycyclic aromatic hydrocarbons
| Introduction |
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The particulate fraction of DEP is formed mainly of elemental carbon particles to which organic compounds, including polycyclic aromatic hydrocarbons (PAH), are adsorbed. The relatively small size (ie, mass median diameter of 0.05 to 0.3 µm) of DEP facilitates their deep penetration in the respiratory system,8 and multiple mechanisms have been proposed for their effects on airway inflammation. These include increased cytokine production, altered oxidative processes, up-regulated chemokine production (ie, regulated upon activation, normal T-cell expressed and secreted, and monocyte chemotactic protein-1), increased free-radical formation, increased nitric oxide, and direct binding of DEP to allergens.9 PAH that usually comprise DEP specifically have been associated with augmented IgE production.10
We hypothesized that exposure to the PAH, derived from local emissions from diesel and non-diesel motor vehicles, as well as residential heating, power generation, tobacco smoking, and other combustion sources, is associated with adverse respiratory outcomes such as asthma symptoms in young children. We chose to focus on prenatal exposure to PAH because growing evidence suggests that the prenatal period may represent a window when the impact of inhaled environmental agents on respiratory outcomes is heightened. For example, the offspring of mice exposed either to allergens or residual oil fly ash (consisting of heavy metals, PAH) during pregnancy have been found to develop airway hyperreactivity and increased airway eosinophilia.1112 In light of studies131415 demonstrating that environmental tobacco smoke (ETS) exposure is associated with abnormal lung function in infancy that persists through adolescence, we also hypothesized that additional exposure to ETS may worsen respiratory outcomes beyond that observed following PAH alone. To test our hypotheses, we recruited a cohort of pregnant women from northern Manhattan, collected 48-h personal PAH exposure measurements in the third trimester of pregnancy, and monitored their children prospectively for the onset of respiratory symptoms. Our results suggest that the interaction of prenatal exposure to PAH and postnatal exposure to ETS leads to increased respiratory symptoms and probable diagnosis of asthma by age 12 to 24 months.
| Materials and Methods |
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Questionnaires
During the last trimester of pregnancy, information was elicited on demographic information, residential history, history of active and passive smoking, medical history, occupational history, home characteristics including heating and cooking sources and ventilation, and consumption of PAH-containing foods (ie, fried, broiled, and barbecued meat). The questionnaire also addressed the psychosocial environment and typical daily activities, including usual routes and methods of community travel. Following delivery, biomedical information was abstracted from the mothers and infants medical records, including measures of fetal growth and any medical complications or events that were not recorded during the pregnancy. Additional questionnaires were administered to the mothers by telephone every 3 months after delivery, and in person at 6 months, 12 months, and 24 months. These included questions addressing the childs medical history, respiratory symptoms, and health-care utilization (including doctor and emergency department visits and hospitalizations). These questionnaires were used to determine postnatal respiratory outcomes.
PAH Exposure
During the third trimester of pregnancy, each woman wore a personal air monitor for 48 h to determine exposure levels to PAH, as described.17 The personal air-sampling pumps operated continuously over this period, collecting vapors and particles up to 2.5 µm in aerodynamic diameter on a quartz microfiber filter and a polyurethane foam cartridge backup. The samples were analyzed at Southwest Research Institute for eight PAH compounds: benz(a)anthracence, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene, benzo(a)pyrene, chrysene/iso-chrysene, dibenz(a,h)anthracene, and indeno(1,2,3)pyrene.
During this 48-h period, information also was gathered on day-to-day activities and environmental exposures. To validate whether subjects complied with carrying the personal air-monitoring devices, motion detectors were installed in the devices of 113 randomly selected women. These data were analyzed to determine the total number of motions detected during typical waking (6 AM to 10 PM) and nonwaking hours (10 PM to 6 AM), and whether they reached a specific threshold. On average, nearly 95% of the total number of motion detections occurred during waking hours, suggesting that subjects complied with wearing the personal air monitors. For quality control, each personal monitoring result was coded as to accuracy in flow rate, time, and completeness of documentation. Data of unacceptable quality (n = 8) were excluded.
ETS Exposure
ETS was determined by questionnaires administered prenatally and at 6 months, 12 months, and 24 months after birth and addressed exposure to ETS from either the mother or any other household member. Plasma cotinine was collected from maternal and cord blood at birth and analyzed by the Centers for Disease Control and Prevention using high-performance liquid chromatography atmospheric-pressure ionization tandem mass spectrometry.18
Statistical Analysis
PAH exposure was determined from an average concentration over 48 h. Because the eight PAH air concentration measures were significantly intercorrelated (r values ranging from 0.45 to 0.94; all p values < 0.001 by Spearman rank),17 total PAH was computed as the sum of the eight PAH air concentrations. Prenatal ETS was defined as the presence of ETS exposure at home or at work during the entire course of the pregnancy, as revealed on questionnaire data. Postnatal ETS was defined as any reported ETS at home from either the mother or another household member at 6 months, 12 months, or 24 months of age.
Respiratory outcomes were examined as individual symptoms (cough, difficulty breathing, wheeze, or probable asthma) at three time points (6 months, 12 months, and 24 months) [Fig 1
]. Probable asthma was defined as the mothers report of physician diagnosis of asthma or probable asthma. The associations between exposure to PAH or recent postnatal ETS and individual respiratory symptoms were analyzed by logistic regression, controlling for exposure to prenatal ETS, and repeated controlling for maternal history of asthma, heating season, and birth weight. The interaction effect of PAH and ETS on individual symptoms also was tested using logistic regression. Because almost all of the subjects exposed to postnatal ETS were also exposed to prenatal ETS, the interaction effect was examined only between prenatal PAH and postnatal ETS. Total respiratory score represented the sum of individual respiratory symptoms, and was scored as 0 for no respiratory symptoms, 1 for one respiratory symptom, 2 for two respiratory symptoms, 3 for three respiratory symptoms, and 4 for the presence of cough, difficulty breathing, wheeze, and probable asthma. Responses needed to be provided for all four questions to be considered valid. Scores of 3 and 4 were collapsed into one group and analyzed using general linear model procedures. A Cronbach
reliability coefficient was computed for the total respiratory score, yielding
= 0.68 at 12 months and
= 0.65 at 24 months. Most data were analyzed with SPSS software (SPSS; Chicago, IL); means ± 1 SD are shown. The exceptions were the exposure response curves (Fig 2, 3
) that were analyzed using STATA software (STAT v. 7; StataCorp; College Station, TX); p < 0.05 was considered statistically significant. Missing data occurred when the mother was unavailable or unable to complete a questionnaire after repeated attempts at contact or did not answer a specific question at age 12 to 24 months. Data were missing in 17 cases at 12 months, and in 66 cases at 24 months.
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| Results |
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The averaged total PAH levels for those participants who reported ETS exposure during pregnancy (mean PAH level, 3.53 ± 2.81 ng/m3) did not differ significantly from those who did not report ETS exposure during pregnancy (mean PAH level, 3.64 ± 4.14 ng/m3). We also did not find a significant correlation between total PAH levels and cotinine levels at birth, regardless of the history of ETS exposure during pregnancy (data not shown). These observations suggest that PAH contained in sidestream cigarette smoke do not contribute greatly to the prenatal total PAH levels we recorded.
PAH, ETS Exposure, and Respiratory Symptoms at Age 6 Months, 12 Months, and 24 Months
Overall, respiratory symptoms (cough, difficulty breathing, wheeze, and probable asthma) were relatively frequent in our cohort (Fig 1). Children born to mothers exposed to higher levels of PAH during pregnancy did not experience significantly more respiratory symptoms (Tables 2, 3
). Recent postnatal ETS exposure (ie, during 6 months preceding questionnaire administration) was independently associated with cough (odds ratio [OR], 2.06; 95% confidence interval [CI], 1.16 to 3.65; p < 0.05) and probable asthma (OR, 3.3; 95% CI, 1.00 to 10.8; p = 0.05) at age 6 months and probable asthma at 12 months (p < 0.05; Table 2) when adjusted for prenatal ETS and PAH exposure.
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| Discussion |
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It has been hypothesized that intrauterine environmental exposures may increase the risk for subsequent diseases, such as ischemic heart disease (ie, Barker hypothesis20). In the case of PAH, we and others1721 have linked fetal exposure to the nonrespiratory outcomes of reduced head circumference and birth weight. The results reported here are the first evidence implicating prenatal PAH exposure, in the setting of other environmental exposures, to asthma symptoms. We recognize that because personal air monitoring for PAH was not repeated postnatally, it is uncertain whether our findings represent delayed effects of prenatal PAH exposure on children, or more immediate effects of postnatal PAH exposure during the first 2 years of life that are similar to those recorded prenatally. Nonetheless, the risk for increased respiratory problems following exposure to PAH appears to begin very early.
Potentially hazardous environmental exposures usually do not occur in isolation, particularly in high-risk communities that are disproportionately exposed to diesel traffic, ETS, poor housing, and increased social stress.5162223 Hence, it is of particular interest that two environmental exposures may act in synergy to worsen respiratory outcomes at age 12 to 24 months. PAH readily reach the fetus and frequently damage DNA, forming PAH-DNA adducts,17 and these or other mediators could increase risk for later disease by modulating developmental programming through altered gene expression or chromatin remodeling. Our results suggest that prenatal PAH exposure interacted with ETS exposure that occurred postnatally instead of prenatally. One possibility is that the apparent inhibitory effects of PAH on birth weight in turn affected airway caliber in the young child, making the airways more susceptible to future insults. Other mechanisms by which PAH could increase airway inflammation include their ability to up-regulate allergic or proinflammatory cytokines such as granulocyte macrophage-colony stimulating factor, interleukin (IL)-4, IL-2, IL-8,24252627 augment antigen-specific IgE isotype switching,102829 or induce oxidative stress.30 PAH or DEP could also act as adjuvants or allergen carriers.31 DEP exposure has been shown to reduce host defense to viruses.32 In addition, ETS has been shown to increase airway inflammation in multiple studies.32333435
Based on the high correlation between our questionnaire data and cotinine levels at birth, we believe the ETS histories are relatively reliable. Others36 as well have validated questionnaire data when estimating the presence of ETS exposure. Certainly some discrepancies can be attributed to the short half-life of cotinine that could underestimate true ETS exposure over time.37 We also doubt that significant levels of side-stream emissions from nearby cigarettes contributed to our total PAH levels. This conclusion is based in part on our finding that personal total PAH levels were not higher among pregnant women reporting ETS. Nonetheless, we recognize that a noteworthy contribution to our analyses of PAH derived from ETS (eg, chrysene) instead of from diesel emission cannot be completely ruled out.
Our data also may suggest that by age 24 months, boys become more susceptible to the respiratory effects of combined PAH and ETS exposure. While gender differences in the early response to PAH exposure have not been reported previously, boys have been found to be more susceptible to prenatal ETS-induced wheeze by age 18 to 30 months.13 The largest percentage deficits in response to in utero exposure to ETS occurred in measures related to small airway flow, such as maximal midexpiratory flow and forced expiratory flow at 75% of vital capacity.14 Hence, we propose that the relatively smaller airways reported in young boys38 may increase the risk for inflammation-induced respiratory symptoms or airway hyperreactivity. It is important to recognize, however, that given the large number of statistical tests we performed, we should be cautious not to overinterpret the pattern of gender-specific results.
In conclusion, prenatal exposure to PAH and early exposure to ETS in an urban cohort was associated with increased respiratory symptoms and probable asthma by age 12 to 24 months. Our data suggest that interventions to lower the risk of respiratory disease in young children living in the inner city may need to address the importance of multiple environmental exposures.
| Acknowledgements |
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| Footnotes |
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Grant support was provided by the National Institute of Environmental Health Sciences (grants P501 ES09600 and 5 RO1 ES08977, RO1ES111158, RO1 ES012468), National Institute of Environmental Health Sciences Center for Environmental Health in Northern Manhattan (P30 ES09089), Environmental Protection Agency (grants R827027, 8260901), Irving General Clinical Research Center (grant RR00645), Bauman Family Foundation, Gladys & Roland Harriman Foundation, W. Alton Jones Foundation, New York Community Trust, Educational Foundation of America, Rockefeller Financial Services, Horace W. Smith Foundation, Beldon Fund, John Merck Fund, and V. Kann Rasmussen Foundation.
Received for publication November 19, 2003. Accepted for publication April 21, 2004.
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This article has been cited by other articles:
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L L Magnusson, H Wennborg, J P Bonde, and J Olsen Wheezing, asthma, hay fever, and atopic eczema in relation to maternal occupations in pregnancy Occup. Environ. Med., September 1, 2006; 63(9): 640 - 646. [Abstract] [Full Text] [PDF] |
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