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. Author manuscript; available in PMC: 2020 Sep 1.
Published in final edited form as: Environ Int. 2019 Jun 22;130:104935. doi: 10.1016/j.envint.2019.104935

Table 3.

Associations between long-term1 near-roadway air pollution (NRAP) exposure and metabolomic principal component (PC) scores estimated from 173 adolescents and young adults in the Children’s Health Study.

Entire sample
(N=173)		 Normal weight
(N=46)3 		Overweight
(N=77)3 		Obese
(N=50)3 		Interaction
p4
β2 p3 β2 p3 β2 p3 β2 p3
Outcome=PC15
 Freeway NRAP −0.34 0.0 44 −0. 77 0.23 −0. 36 0.18 −0.48 0.09 0.71
 Non-freeway NRAP −0.07 0.63 −0.67 0.12 −0.37 0.16 0.45 0.08 0.10
 Total NRAP −0.33 0.049 −0.88 0.15 −0.39 0.14 −0.37 0.21 0.51
Outcome=PC26
 Freeway NRAP 0.09 0.58 0.08 0.85 0.01 0.97 0.10 0.73 0.53
 Non-freeway NRAP 0.30 0.038 −0.21 0.51 0.51 0.039 0.68 0.007* 0.047
 Total NRAP 0.14 0.42 0.003 0.99 0.07 0.78 0.23 0.44 0.48
Outcome=PC37
 Freeway NRAP −0.21 0.18 0.25 0.64 −0.03 0.91 −0.80 0.006* 0.66
 Non-freeway NRAP 0.03 0.81 −0.01 0.99 0.17 0.47 0.01 0.96 0.87
 Total NRAP −0.19 0.22 0.22 0.67 0.002 0.99 −0.86 0.005* 0.60
Outcome=PC48
 Freeway NRAP −0.01 0.92 −0.07 0.82 −0.10 0.66 0.16 0.57 0.49
 Non-freeway NRAP −0.03 0.80 −0.24 0.24 0.001 1.00 −0.36 0.18 0.96
 Total NRAP −0.02 0.87 −0.11 0.68 −0.09 0.69 0.09 0.76 0.50
Outcome=PC59
 Freeway NRAP 0.21 0.24 −0.20 0.71 0.30 0.33 0.22 0.44 0.75
 Non-freeway NRAP 0.21 0.19 0.25 0.49 0.38 0.22 −0.27 0.30 0.17
 Total NRAP 0.24 0.18 −0.10 0.85 0.34 0.27 0.17 0.56 0.66
1.

Long-term air pollution exposure was estimated by cumulative averages of monthly exposure concentrations over one year prior to the study visit and were weighted by time spent at each different address.

2.

Mixed effects model was used to estimate regression associations between freeway, nonfreeway and total NRAP exposure with the outcome variables of metabolomic factor scores after adjusting for confounders including age, sex, race/ethnicity, parental education levels as a proxy for social economic status, whether or not smoked cigarettes during the last week, ever/never smoked electronic cigarettes, season of the study visit and random intercepts for CHS communities and metabolomics analytical batches. NRAP exposure was scaled by 2 standard deviations. Association estimates (β) and p-values for significance of statistical tests are presented in the table.

3.

Stratified analysis was conducted in each subgroups of body mass index (BMI) categories: normal weight (BMI<25 kg/m2), overweight (BMI≥25 and <30 kg/m2) and obese (BMI≥30 kg/m2) groups.

4.

Interaction p-values<0.05 represent statistically significant differences in effect sizes for the associations between NRAP exposure and metabolomic PC scores across three BMI categories.

5.

Metabolomic principal component (PC) 1 represents a variety of short- and median-chain acylcarnitines and explains 26.3% variance of concentrations of all metabolites analyzed in the study samples. More details of the loadings of specific metabolites for each PC are described in Supplemental Table 4.

6.

PC2 represents non-esterified fatty acids (NEFA) and NEFA oxidation by-products including long-chain acylcarnitines, acetylcarnitine (C2) and 3-Hydroxybutyrylcarnitine (C4-OH), which explains 10.2% variance of concentrations of all metabolites analyzed in the study samples.

7.

PC3 represents metabolites involved in branched-chain amino-acid (BCAA) catabolism, which explains 7.2% variance of concentrations of all metabolites analyzed in the study samples.

8.

PC4 represents amino acids involved in general amino acid catabolism and the urea cycle, which explains 4.9% variance of concentrations of all metabolites analyzed in the study samples.

9.

PC5 represents amino acids involved in glycine metabolism, which explains 4.1% variance of concentrations of all metabolites analyzed in the study samples.

*

Association tests are significant after FDR adjustment for multiple testing of five PC scores (FDR<0.1).