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Understanding Environmental Tobacco Smoke Exposure and Effects in Asthmatic Children through Determination of Urinary Cotinine and Targeted Metabolomics of Plasma
Citation:
MacMillan, D., Dan Zehr, J. Crooks, BJ George, AND J. Gallagher. Understanding Environmental Tobacco Smoke Exposure and Effects in Asthmatic Children through Determination of Urinary Cotinine and Targeted Metabolomics of Plasma. Presented at American Society for Mass Spectrometry, Minneapolis, MN, June 09 - 13, 2013.
Impact/Purpose:
The purpose of this portion of the study is to better understand associations between ETS exposure, endogenous metabolites, and clinical indicators of asthma severity.
Description:
Understanding Environmental Tobacco Smoke Exposure and Effects in Asthmatic Children through Determination of Urinary Cotinine and Targeted Metabolomics of Plasma Introduction Asthma is a complex disease with multiple triggers and causal factors, Exposure to environmental tobacco smoke (ETS), a major source of indoor air pollution, is linked to increased asthma in children, and can exacerbate symptom severity. Understanding the health impacts of ETS exposure in asthmatic children living in households with smokers may be enhanced by an integrative approach that combines measures of ETS exposure and endogenous metabolites, in relation to asthma status. ETS exposure can be measured by assessing urinary cotinine, a stable metabolite of the major ETS component nicotine. Targeted metabolomics provides a rapid screen of multiple biochemical classes of metabolites representing key biological pathways. Methods Urine and plasma were collected from 197 children for the USEPA Mechanistic Indicators of Childhood Asthma (MICA) Study. Urinary cotinine was extracted with Waters Oasis MCX solid phase extraction cartridges and analyzed by LC/MS/MS with electrospray ionization in positive ion mode on a Thermo TSQ Quantum Ultra AM triple quadrupole mass spectrometer. Quantitation was by isotope dilution and multiple reaction monitoring. A Biocrates p180 Kit was used to prepare 92 plasma samples for targeted analysis of 187 selected metabolites from five biochemical classes (biogenic amines, amino acids, acylcarnitines, glycerophospholipids, sphingolipids) plus hexose on an AB Sciex 4000 QTrap linear ion trap mass spectrometer. Biocrates MetIDQ software was used for validation of the kit and preliminary statistical processing of the data. Preliminary Data Targeted metabolomics was performed on plasma from 92 children in MICA. Of these, 46.7% (n=43) had cotinine levels above the detection limit and 43.2 % (n=42) had an asthma attack within the previous 12 months. The 92 children were further differentiated by body mass index, gender, and age. Statistical analysis (Mann-Whitney test) of the metabolite data based on measured urinary cotinine showed significantly higher median concentrations of several acylcarnitines, as well as a higher median ratio of short chain acylcamitines to free carnitine (p = 0.023), suggesting differences in p-oxidation activity in the ETS-exposed children. A Mann-Whitney test of metabolites in non-asthmatic children of normal body weight (n=3 1) indicated a significant difference in fatty acid uptake between those with and without detectable cotinine (p=0.039). Ratios of concentrations of polyunsaturated fatty acids to monounsaturated fatty acids (p=O.Ol6), and concentrations of lysoPC a C20:3 (p = 0.030), lysoPC a C20:4 (p=O.O3O), phenylalanine (p=O.035), and several acylcarnitines were found to be significantly different between asthmatic children of normal body weight with no detectable urinary cotinine compared to asthmatic children of normal body weight with measurable urinary cotimne. Comparing metabolite concentrations between asthmatic and non-asthmatic children of normal body weight (with no detectable urinary cotinine) resulted in statistically significant lower concentrations of hydroxyhexadecadienylcamitine (p = 0.019), but higher lysoPC a C24:0 (p =0.019) and PC aa C30:2 (p = 0.031) in the asthmatic children. The preliminary analysis of metabolomic data suggests that cellular energy pathways are one of the processes impacted in asthmatic children exposed to ETS. Additional statistical analyses will be conducted to better understand associations between ETS exposure, endogenous metabolites, and clinical indicators of asthma severity. Disclaimer: This abstract does not necessarily reflect EPA policy.