Secondhand Tobacco Smoke Exposure Associations With DNA Methylation of the Aryl Hydrocarbon Receptor Repressor.
BACKGROUND
Cigarette smoking is inversely associated with DNA methylation of the aryl hydrocarbon receptor repressor (AHRR; cg05575921). However, the association between secondhand tobacco smoke (SHS) exposure and AHRR methylation is unknown.


METHODS
DNA methylation of AHRR cg05575921 in CD14+ monocyte samples, from 495 never-smokers and 411 former smokers (having quit smoking ≥15 years) from the Multi-Ethnic Study of Atherosclerosis (MESA), was cross-sectionally compared with concomitantly ascertained self-reported SHS exposure, urine cotinine concentrations, and estimates of air pollutants at participants' homes. Linear regression was used to test for associations, and covariates included age, sex, race, education, study site, and previous smoking exposure (smoking status, time since quitting, and pack-years).


RESULTS
Recent indoor SHS exposure (hours per week) was inversely associated with cg05575921 methylation (β ± SE = -0.009 ± 0.003, p = .007). The inverse effect direction was consistent (but did not reach significance) in the majority of stratified analyses (by smoking status, sex, and race). Categorical analysis revealed high levels of recent SHS exposure (≥10 hours per week) inversely associated with cg05575921 methylation (β ± SE = -0.28 ± 0.09, p = .003), which remained significant (p < .05) in the majority of stratified analyses. cg05575921 methylation did not significantly (p < .05) associate with low to moderate levels of recent SHS exposure (1-9 hours per week), urine cotinine concentrations, years spent living with people smoking, years spent indoors (not at home) with people smoking, or estimated levels of air pollutants.


CONCLUSIONS
High levels of recent indoor SHS exposure may be inversely associated with DNA methylation of AHRR in human monocytes.


CONCLUSIONS
DNA methylation is a biochemical alteration that can occur in response to cigarette smoking; however, little is known about the effect of SHS on human DNA methylation. In the present study, we evaluated the association between SHS exposure and DNA methylation in human monocytes, at a site (AHRR cg05575921) known to have methylation inversely associated with current and former cigarette smoking compared to never smoking. Results from this study suggest high levels of recent SHS exposure inversely associate with DNA methylation of AHRR cg05575921 in monocytes from nonsmokers, albeit with weaker effects than active cigarette smoking.
Department of Epidemiology and Prevention, Division of Public Health Sciences, Wake Forest School of Medicine, Winston-Salem, NC.
Lindsay M
LM
Reynolds
Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD.
Hoda S
HS
Magid
Department of Epidemiology, School of Public Health, University of Washington, Seattle, WA.
Gloria C
GC
Chi
Department of Biostatistics, Division of Public Health Sciences, Wake Forest School of Medicine, Winston-Salem, NC.
Kurt
K
Lohman
Departments of Medicine and Epidemiology, Columbia University Medical Center, New York, NY.
R Graham
RG
Barr
Department of Epidemiology, School of Public Health, University of Washington, Seattle, WA.|Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, Seattle, WA.
Joel D
JD
Kaufman
Virginia Bioinformatics Institute and Department of Statistics, Virginia Tech, Blacksburg, VA.
Ina
I
Hoeschele
Ciccarone Center for the Prevention of Heart Disease, Johns Hopkins Medical Institutions, Baltimore, MD.
Michael J
MJ
Blaha
Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD.|Department of Environmental Health Sciences, Columbia University Mailman School of Public Health, New York, NY.
Ana
A
Navas-Acien
Department of Epidemiology and Prevention, Division of Public Health Sciences, Wake Forest School of Medicine, Winston-Salem, NC.
Yongmei
Y
Liu
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019175:DNA Methylation / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics*; D014028:Tobacco Smoke Pollution / Q000032:analysis / Q000706:statistics & numerical data
D018336:Receptors, Aryl Hydrocarbon; D014028:Tobacco Smoke Pollution