Phthalates may increase the
asthma risk in children. Mechanisms underlying this association remain to be addressed. This study assesses the effect of
phthalate exposures on epigenetic changes and the role of epigenetic changes for
asthma. In the first step, urine and blood samples from 256 children of the Childhood Environment and Allergic diseases Study (CEAS) were analyzed. Urine 5OH-MEHP levels were quantified as an
indicator of exposure, and
asthma information was collected. DNA methylation (
DNA-M) was measured by quantitative PCR. In the screening part of step 1,
DNA-M of 21 potential human candidate genes suggested by a toxicogenomic data were investigated in 22 blood samples. Then, in the testing part of step 1, positively screened genes were tested in a larger sample of 256 children and then validated by
protein measurements. In step 2, we replicated the association between
phthalate exposure and gene-specific
DNA-M in 54 children in the
phthalate contaminated food event. In step 3, the risk of
DNA-M for
asthma was tested in 256 children from CEAS and corroborated in 270 children from the Isle of Wight (IOW) birth cohort.
RESULTS: Differential methylation in three genes (AR, TNFα, and IL-4) was identified through screening. Testing in 256 children showed that methylation of the TNFα gene promoter was lower when children had higher urine 5OH-MEHP values (β = -0.138, P = 0.040). Functional validation revealed that TNFα methylation was inversely correlated with TNFα
protein levels (β = -0.18, P = 0.041). In an additional sample of 54 children, we corroborated that methylation of the TNFα gene promoter was lower when urine 5OH-MEHP concentrations were higher. Finally, we found that a lower methylation of 5'CGI region of TNFα was associated with
asthma in 256 CEAS children (OR = 2.15, 95% CI = 1.01 to 4.62). We replicated this in 270 children from the IOW birth cohort study. Methylation of the CpG site cg10717214 was negatively associated with
asthma, when children had 'AA' or 'AG' genotype of the TNFα single
nucleotide rs1800610.
CONCLUSIONS: