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1.  Propensity score-based diagnostics for categorical response regression models 
Statistics in medicine  2013;33(3):455-469.
For binary or categorical response models, most goodness-of-fit statistics are based on the notion of partitioning the subjects into groups or regions and comparing the observed and predicted responses in these regions by a suitable chi-squared distribution. Existing strategies create this partition based on the predicted response probabilities, or propensity scores, from the fitted model. In this paper, we follow a retrospective approach, borrowing the notion of balancing scores used in causal inference to inspect the conditional distribution of the predictors, given the propensity scores, in each category of the response to assess model adequacy. This diagnostic can be used under both prospective and retrospective sampling designs and may ascertain general forms of misspecification. We first present simple graphical and numerical summaries that can be used in a binary logistic model. We then generalize the tools to propose model diagnostics for the proportional odds model. We illustrate the methods with simulation studies and two data examples (i) a case-control study of the association between cumulative lead exposure and Parkinson’s Disease in the Boston, Massachusetts area and (ii) and a cohort study of biomarkers possibly associated with diabetes, from the VA Normative Aging Study.
PMCID: PMC3911784  PMID: 23934948
Balancing Score; Multinomial Logistic; Proportional Odds; Residual Diagnostic; Score Test
2.  Associations Between Short-term Changes in Air Pollution and Correlates of Arterial Stiffness: The Veterans Affairs Normative Aging Study, 2007–2011 
American Journal of Epidemiology  2013;179(2):192-199.
We investigated associations between short-term exposure to air pollution and central augmentation index and augmentation pressure, correlates of arterial stiffness, in a cohort of elderly men in the Boston, Massachusetts, metropolitan area. This longitudinal analysis included 370 participants from the Veterans Affairs Normative Aging Study with up to 2 visits between 2007 and 2011 (n = 445). Augmentation index (as %) and augmentation pressure (in mmHg) were measured at each visit by using radial artery applanation tonometry for pulse wave analysis and modeled in a mixed effects regression model as continuous functions of moving averages of air pollution exposures (over 4 hours and 1, 3, 7, and 14 days). The results suggest that short-term changes in air pollution were associated with augmentation index and augmentation pressure at several moving averages. Interquartile range (IQR) increases in 3-day average exposure to particles with aerodynamic diameter less than 2.5 μm (3.6-μg/m3 IQR increase) and sulfate (1.4-μg/m3 IQR increase) and 1-day average exposure to particle number counts (8,741-counts/cm3 IQR increase) were associated with augmentation index values that were 0.8% (95% confidence interval (CI): 0.2, 1.4), 0.6% (95% CI: 0.1, 1.2), and 1.7% (95% CI: 0.4, 2.9) higher, respectively. Overall, the findings were similar for augmentation pressure. The findings support the hypothesis that exposure to air pollution may affect vascular function.
PMCID: PMC3873113  PMID: 24227017
air pollution; particulate matter; pulse wave analysis
3.  Effects of Temperature and Relative Humidity on DNA Methylation 
Epidemiology (Cambridge, Mass.)  2014;25(4):561-569.
Previous studies have found relationships between DNA methylation and various environmental contaminant exposures. Associations with weather have not been examined. Because temperature and humidity are related to mortality even on non-extreme days, we hypothesized that temperature and relative humidity may affect methylation.
We repeatedly measured methylation on long interspersed nuclear elements (LINE-1), Alu, and 9 candidate genes in blood samples from 777 elderly men participating in the normative aging Study (1999–2009). We assessed whether ambient temperature and relative humidity are related to methylation on LINE-1 and Alu, as well as on genes controlling coagulation, inflammation, cortisol, DNA repair, and metabolic pathway. We examined intermediate-term associations of temperature, relative humidity, and their interaction with methylation, using distributed lag models.
Temperature or relative humidity levels were associated with methylation on tissue factor (F3), intercellular adhesion molecule 1 (ICAM-1), toll-like receptor 2 (TRL-2), carnitine O-acetyltransferase (CRAT), interferon gamma (IFN-γ), inducible nitric oxide synthase (iNOS), and glucocorticoid receptor, LINE-1, and Alu. For instance, a 5°c increase in 3-week average temperature in ICAM-1 methylation was associated with a 9% increase (95% confidence interval: 3% to 15%), whereas a 10% increase in 3-week average relative humidity was associated with a 5% decrease (−8% to −1%). The relative humidity association with ICAM-1 methylation was stronger on hot days than mild days.
DNA methylation in blood cells may reflect biological effects of temperature and relative humidity. Temperature and relative humidity may also interact to produce stronger effects.
PMCID: PMC4224120  PMID: 24809956
4.  Testing Departure from Additivity in Tukey’s Model using Shrinkage: Application to a Longitudinal Setting 
Statistics in medicine  2014;33(29):5177-5191.
While there has been extensive research developing gene-environment interaction (GEI) methods in case-control studies, little attention has been given to sparse and efficient modeling of GEI in longitudinal studies. In a two-way table for GEI with rows and columns as categorical variables, a conventional saturated interaction model involves estimation of a specific parameter for each cell, with constraints ensuring identifiability. The estimates are unbiased but are potentially inefficient because the number of parameters to be estimated can grow quickly with increasing categories of row/column factors. On the other hand, Tukey’s one degree of freedom (df) model for non-additivity treats the interaction term as a scaled product of row and column main effects. Due to the parsimonious form of interaction, the interaction estimate leads to enhanced efficiency and the corresponding test could lead to increased power. Unfortunately, Tukey’s model gives biased estimates and low power if the model is misspecified. When screening multiple GEIs where each genetic and environmental marker may exhibit a distinct interaction pattern, a robust estimator for interaction is important for GEI detection. We propose a shrinkage estimator for interaction effects that combines estimates from both Tukey’s and saturated interaction models and use the corresponding Wald test for testing interaction in a longitudinal setting. The proposed estimator is robust to misspecification of interaction structure. We illustrate the proposed methods using two longitudinal studies — the Normative Aging Study and the Multi-Ethnic Study of Atherosclerosis.
PMCID: PMC4227925  PMID: 25112650
adaptive shrinkage estimation; gene-environment interaction; longitudinal data; Tukey’s one df test for non-additivity
5.  Short-term airborne particulate matter exposure alters the epigenetic landscape of human genes associated with the mitogen-activated protein kinase network: a cross-sectional study 
Environmental Health  2014;13(1):94.
Exposure to air particulate matter is known to elevate blood biomarkers of inflammation and to increase cardiopulmonary morbidity and mortality. Major components of airborne particulate matter typically include black carbon from traffic and sulfates from coal-burning power plants. DNA methylation is thought to be sensitive to these environmental toxins and possibly mediate environmental effects on clinical outcomes via regulation of gene networks. The underlying mechanisms may include epigenetic modulation of major inflammatory pathways, yet the details remain unclear.
We sought to elucidate how short-term exposure to air pollution components, singly and/or in combination, alter blood DNA methylation in certain inflammation-associated gene networks, MAPK and NF-κB, which may transmit the environmental signal(s) and influence the inflammatory pathway in vivo. To this end, we utilized a custom-integrated workflow—molecular processing, pollution surveillance, biostatical analysis, and bioinformatic visualization—to map novel human (epi)gene pathway-environment interactions.
Specifically, out of 84 MAPK pathway genes considered, we identified 11 whose DNA methylation status was highly associated with black carbon exposure, after adjusting for potential confounders—age, sulfate exposure, smoking, blood cell composition, and blood pressure. Moreover, after adjusting for these confounders, multi-pollutant analysis of synergistic DNA methylations significantly associated with sulfate and BC exposures yielded 14 MAPK genes. No associations were found with the NF-κB pathway.
Exposure to short-term air pollution components thus resulted in quantifiable epigenetic changes in the promoter areas of MAPK pathway genes. Bioinformatic mapping of single- vs. multi-exposure-associated epigenetic changes suggests that these alterations might affect biological pathways in nuanced ways that are not simply additive or fully predictable via individual-level exposure assessments.
Electronic supplementary material
The online version of this article (doi:10.1186/1476-069X-13-94) contains supplementary material, which is available to authorized users.
PMCID: PMC4273424  PMID: 25395096
6.  Lead Exposure, B Vitamins, and Plasma Homocysteine in Men 55 Years of Age and Older: The VA Normative Aging Study 
Environmental Health Perspectives  2014;122(10):1066-1074.
Background: Lead (Pb) exposure may influence the plasma concentration of homocysteine, a one-carbon metabolite associated with cardiovascular and neurodegenerative diseases. Little is known about the associations between Pb and homocysteine over time, or the potential influence of dietary factors.
Objectives: We examined the longitudinal association of recent and cumulative Pb exposure with homocysteine concentrations and the potential modifying effect of dietary nutrients involved in one-carbon metabolism.
Methods: In a subcohort of the Veterans Affairs (VA) Normative Aging Study (1,056 men with 2,301 total observations between 1993 and 2011), we used mixed-effects models to estimate differences in repeated measures of total plasma homocysteine across concentrations of Pb in blood and tibia bone, assessing recent and cumulative Pb exposure, respectively. We also assessed effect modification by dietary intake and plasma concentrations of folate, vitamin B6, and vitamin B12.
Results: An interquartile range (IQR) increment in blood Pb (3 μg/dL) was associated with a 6.3% higher homocysteine concentration (95% CI: 4.8, 7.8%). An IQR increment in tibia bone Pb (14 μg/g) was associated with a 3.7% higher homocysteine (95% CI: 1.6, 5.6%), which was attenuated to 1.5% (95% CI: –0.5, 3.6%) after adjusting for blood Pb. For comparison, a 5-year increase in time from baseline was associated with a 5.7% increase in homocysteine (95% CI: 4.3, 7.1%). The association between blood Pb and homocysteine was significantly stronger among participants with estimated dietary intakes of vitamin B6 and folate below (vs. above) the study population medians, which were similar to the U.S. recommended dietary allowance intakes.
Conclusions: Pb exposure was positively associated with plasma homocysteine concentration. This association was stronger among men with below-median dietary intakes of vitamins B6 and folate. These findings suggest that increasing intake of folate and B6 might reduce Pb-associated increases in homocysteine, a risk factor for cardiovascular disease and neurodegeneration.
Citation: Bakulski KM, Park SK, Weisskopf MG, Tucker KL, Sparrow D, Spiro A III, Vokonas PS, Nie LH, Hu H, Weuve J. 2014. Lead exposure, B vitamins, and plasma homocysteine in men 55 years of age and older: the VA Normative Aging Study. Environ Health Perspect 122:1066–1074;
PMCID: PMC4181916  PMID: 24905780
7.  Associations between Changes in City and Address Specific Temperature and QT Interval - The VA Normative Aging Study 
PLoS ONE  2014;9(9):e106258.
The underlying mechanisms of the association between ambient temperature and cardiovascular morbidity and mortality are not well understood, particularly for daily temperature variability. We evaluated if daily mean temperature and standard deviation of temperature was associated with heart rate-corrected QT interval (QTc) duration, a marker of ventricular repolarization in a prospective cohort of older men.
This longitudinal analysis included 487 older men participating in the VA Normative Aging Study with up to three visits between 2000–2008 (n = 743). We analyzed associations between QTc and moving averages (1–7, 14, 21, and 28 days) of the 24-hour mean and standard deviation of temperature as measured from a local weather monitor, and the 24-hour mean temperature estimated from a spatiotemporal prediction model, in time-varying linear mixed-effect regression. Effect modification by season, diabetes, coronary heart disease, obesity, and age was also evaluated.
Higher mean temperature as measured from the local monitor, and estimated from the prediction model, was associated with longer QTc at moving averages of 21 and 28 days. Increased 24-hr standard deviation of temperature was associated with longer QTc at moving averages from 4 and up to 28 days; a 1.9°C interquartile range increase in 4-day moving average standard deviation of temperature was associated with a 2.8 msec (95%CI: 0.4, 5.2) longer QTc. Associations between 24-hr standard deviation of temperature and QTc were stronger in colder months, and in participants with diabetes and coronary heart disease.
In this sample of older men, elevated mean temperature was associated with longer QTc, and increased variability of temperature was associated with longer QTc, particularly during colder months and among individuals with diabetes and coronary heart disease. These findings may offer insight of an important underlying mechanism of temperature-related cardiovascular morbidity and mortality in an older population.
PMCID: PMC4169528  PMID: 25238150
8.  Influence of multiple APOE genetic variants on cognitive function in a cohort of older men – results from the Normative Aging Study 
BMC Psychiatry  2014;14(1):223.
APOE is the biomarker with the greatest known influence on cognitive function; however, the effect of complex haplotypes involving polymorphisms rs449647, rs405509, rs440446, rs429358 and rs7412 has never been studied in older populations.
We evaluated APOE polymorphisms using multiplex PCR for genotyping and Mini-Mental State Examination (MMSE) to evaluate cognitive function in 819 individuals from VA Normative Aging Study.
Combinatorial analysis of all polymorphisms and individual analysis of polymorphisms rs449647, rs405509, rs440446 and rs7412 did not show any association with cognitive performance. Polymorphism rs429358 was associated with better cognitive performance (odds of MMSE ≤ 25 = 0.63, 95% CI 0.42-0.95; p = 0.03) in the oldest subsample (5th quintile of age) (odds of MMSE ≤ 25 = 0.34; 95% CI 0.13-0.86; p = 0.02). APOE allele ε4 was also associated with better cognitive performance (odds of MMSE ≤ 25 = 0.61, 95% CI 0.40-0.94; p = 0.02), also in the oldest subsample (odds of MMSE ≤ 25 = 0.35, 95% CI 0.14-0.90; p = 0.03).
These results suggest a beneficial effect of polymorphism rs429358 in the oldest men.
Electronic supplementary material
The online version of this article (doi:10.1186/s12888-014-0223-x) contains supplementary material, which is available to authorized users.
PMCID: PMC4149270  PMID: 25085564
APOE; Epsilon; Alleles; Haplotypes; Cognitive decline; Aging; Genetic variants
9.  Epigenetic Influences on Associations between Air Pollutants and Lung Function in Elderly Men: The Normative Aging Study 
Environmental Health Perspectives  2014;122(6):566-572.
Background: Few studies have been performed on pulmonary effects of air pollution in the elderly—a vulnerable population with low reserve capacity—and mechanisms and susceptibility factors for potential effects are unclear.
Objectives: We evaluated the lag structure of air pollutant associations with lung function and potential effect modification by DNA methylation (< or ≥ median) at 26 individual CpG sites in nine candidate genes in a well-characterized cohort of elderly men.
Methods: We measured forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1), and blood DNA methylation one to four times between 1999 and 2009 in 776 men from the Normative Aging Study. Air pollution was measured at fixed monitors 4 hr to 28 days before lung function tests. We used linear mixed-effects models to estimate the main effects of air pollutants and effect modification by DNA methylation.
Results: An interquartile range (IQR) increase in subchronic exposure (3 to 28 days cumulated), but not in acute exposure (during the previous 4 hr, or the current or previous day), to black carbon, total and nontraffic particles with aerodynamic diameter ≤ 2.5 μm (PM2.5), carbon monoxide, and nitrogen dioxide was associated with a 1–5% decrease in FVC and FEV1 (p < 0.05). Slope estimates were greater for FVC than FEV1, and increased with cumulative exposure. The estimates slopes for air pollutants (28 days cumulated) were higher in participants with low (< median) methylation in TLR2 at position 2 and position 5 and high (≥ median) methylation in GCR.
Conclusions: Subchronic exposure to traffic-related pollutants was associated with significantly reduced lung function in the elderly; nontraffic pollutants (particles, ozone) had weaker associations. Epigenetic mechanisms related to inflammation and immunity may influence these associations.
Citation: Lepeule J, Bind MAC, Baccarelli AA, Koutrakis P, Tarantini L, Litonjua A, Sparrow D, Vokonas P, Schwartz JD. 2014. Epigenetic influences on associations between air pollutants and lung function in elderly men: the Normative Aging Study. Environ Health Perspect 122:566–572;
PMCID: PMC4050500  PMID: 24602767
10.  Mitochondrial haplogroups modify the effect of black carbon on age-related cognitive impairment 
Environmental Health  2014;13:42.
Traffic-related air pollution has been linked with impaired cognition in older adults, possibly due to effects of oxidative stress on the brain. Mitochondria are the main source of cellular oxidation. Haplogroups in mitochondrial DNA (mtDNA) mark individual differences in oxidative potential and are possible determinants of neurodegeneration. The aim of this study was to investigate whether mtDNA haplogroups determined differential susceptibility to cognitive effects of long-term exposure to black carbon (BC), a marker of traffic-related air pollution.
We investigated 582 older men (72 ± 7 years) in the VA Normative Aging Study cohort with ≤4 visits per participant (1.8 in average) between 1995–2007. Low (≤25) Mini Mental State Examination (MMSE) was used to assess impaired cognition in multiple domains. We fitted repeated-measure logistic regression using validated-LUR BC estimated in the year before their first visit at the participant’s address.
Mitochondrial haplotyping identified nine haplogroups phylogenetically categorized in four clusters. BC showed larger effect on MMSE in Cluster 4 carriers, including I, W and X haplogroups, [OR = 2.7; 95% CI (1.3-5.6)], moderate effect in Cluster 1, including J and T haplogroups [OR = 1.6; 95% CI: (0.9-2.9)], and no effect in Cluster 2 (H and V haplogroups) [OR = 1.1; 95% CI: (0.8-1.5)] or Cluster 3 (K and U haplogroups) [OR = 1.0; 95% CI: (0.6-1.6)]. BC effect varied only moderately across the I, X, and W haplogroups or across the J and T haplogroups.
The association of BC with impaired cognition was worsened in carriers of phylogenetically-related mtDNA haplogroups in Cluster 4. No BC effects were detected in Cluster 2 and 3 carriers. MtDNA haplotypes may modify individual susceptibility to the particle cognitive effects.
PMCID: PMC4049407  PMID: 24884505
mtDNA haplogroups; Air pollution; Black carbon; Cognitive decline; Mini-mental state examination
11.  Novel Likelihood Ratio Tests for Screening Gene-Gene and Gene-Environment Interactions with Unbalanced Repeated-Measures Data 
Genetic epidemiology  2013;37(6):581-591.
There has been extensive literature on modeling gene-gene interaction (GGI) and gene-environment interaction (GEI) in case-control studies with limited literature on statistical methods for GGI and GEI in longitudinal cohort studies. We borrow ideas from the classical two-way analysis of variance (ANOVA) literature to address the issue of robust modeling of interactions in repeated-measures studies. While classical interaction models proposed by Tukey and Mandel have interaction structures as a function of main effects, a newer class of models, additive main effects and multiplicative interaction (AMMI) models, do not have similar restrictive assumptions on the interaction structure. AMMI entails a singular value decomposition of the cell residual matrix after fitting the additive main effects and has been shown to perform well across various interaction structures. We consider these models for testing GGI and GEI from two perspectives: likelihood ratio test based on cell means and a regression based approach using individual observations. Simulation results indicate that both approaches for AMMI models lead to valid tests in terms of maintaining the type I error rate, with the regression approach having better power properties. The performance of these models was evaluated across different interaction structures and 12 common epistasis patterns. In summary, AMMI model is robust with respect to misspecified interaction structure and is a useful screening tool for interaction even in the absence of main effects. We use the proposed methods to examine the interplay between the hemochromatosis gene and cumulative lead exposure on pulse pressure in the Normative Aging Study.
PMCID: PMC4009698  PMID: 23798480
likelihood ratio test; longitudinal data; mixed model; non-additivity; parametric bootstrap; singular value decomposition; two-step regression
12.  A Novel Genetic Score Approach Using Instruments to Investigate Interactions between Pathways and Environment: Application to Air Pollution 
PLoS ONE  2014;9(4):e96000.
Air pollution has been associated with increased systemic inflammation markers. We developed a new pathway analysis approach to investigate whether gene variants within relevant pathways (oxidative stress, endothelial function, and metal processing) modified the association between particulate air pollution and fibrinogen, C-reactive protein (CRP), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1). Our study population consisted of 822 elderly participants of the Normative Aging Study (1999–2011). To investigate the role of biological mechanisms and to reduce the number of comparisons in the analysis, we created pathway-specific scores using gene variants related to each pathway. To select the most appropriate gene variants, we used the least absolute shrinkage and selection operator (Lasso) to relate independent outcomes representative of each pathway (8-hydroxydeoxyguanosine for oxidative stress, augmentation index for endothelial function, and patella lead for metal processing) to gene variants. A high genetic score corresponds to a higher allelic risk profile. We fit mixed-effects models to examine modification by the genetic score of the weekly air pollution association with the outcome. Among participants with higher genetic scores within the oxidative stress pathway, we observed significant associations between particle number and fibrinogen, while we did not find any association among participants with lower scores (pinteraction = 0.04). Compared to individuals with low genetic scores of metal processing gene variants, participants with higher scores had greater effects of particle number on fibrinogen (pinteraction = 0.12), CRP (pinteraction = 0.02), and ICAM-1 (pinteraction = 0.08). This two-stage penalization method is easy to implement and can be used for large-scale genetic applications.
PMCID: PMC3995963  PMID: 24755831
13.  Ambient particulate air pollution and microRNAs in elderly men 
Ambient particulate matter (PM) has been associated with mortality and morbidity for cardiovascular disease (CVD). MicroRNAs control gene expression at a post-transcriptional level. Altered microRNA expression has been reported in processes related to CVD and PM exposure, e.g. systemic inflammation, endothelial dysfunction and atherosclerosis. Polymorphisms in microRNA-related genes could influence response to PM.
We investigated the association of exposure to ambient particles in several time windows (4-hours to 28-days moving averages) and blood-leukocyte expression changes in fourteen candidate microRNAs, in 153 elderly males from the Normative Aging Study (examined 2005–2009). Potential effect modification by six single nucleotide polymorphisms (SNPs) in three microRNA-related genes was investigated. Fine PM (PM2.5), black carbon, organic carbon and sulfates were measured at a stationary ambient monitoring site. Linear regression models, adjusted for potential confounders, were used to assess effects of particles and SNP-by-pollutant interaction. An in silico pathways analysis was performed on target genes of miRNAs associated with the pollutants.
We found a negative association for pollutants in all moving averages and miR-1, -126, -135a, -146a, -155, -21, -222 and -9. The strongest associations were observed with the 7-day moving averages for PM2.5 and black carbon and with the 48-hour moving averages for organic carbon. The association with sulfates was stable across the moving averages. The in silico pathway analysis identified 18 pathways related to immune response shared by at least two miRNAs; in particular, the “HMGB1/RAGE signaling pathway” was shared by miR-126, -146a, -155, -21 and -222.
No important associations were observed for miR-125a-5p, -125b, -128, -147, -218 and -96. We found significant SNP-by-pollutant interactions for rs7813, rs910925 and rs1062923 in GEMIN4 and black carbon and PM2.5 for miR-1, -126, -146a, -222 and -9, and for rs1640299 in DGCR8 and SO42− for miR-1 and -135a.
Exposure to ambient particles could cause a downregulation of microRNAs involved in processes related to PM exposure. Polymorphisms in GEMIN4 and DGCR8 could modify these associations.
PMCID: PMC3977338  PMID: 24257509
14.  Air Pollution and Homocysteine: More Evidence that Oxidative Stress-related Genes Modify Effects of Particulate Air Pollution 
Epidemiology (Cambridge, Mass.)  2010;21(2):198-206.
Ambient particles are associated with cardiovascular events, and recently with total plasma homocysteine. High total plasma homocysteine is a risk for human health. However, the biological mechanisms are not fully understood. One of putative pathways is through oxidative stress. We aimed to examine whether associations of PM2.5 and black carbon with homocysteine were modified by genotypes including HFE H63D, C282Y, CAT (rs480575, rs1001179, rs2284367 and rs2300181), NQO1 (rs1800566), GSTP1 I105V, GSTM1, GSTT1(deletion vs non-deletion) and HMOX-1 (any short vs both long). We attempted to replicate identified genes in an analysis of heart rate variability, and in other outcomes reported in the literature.
Study subjects were 1000 white non-Hispanic men in the Boston area, participating in a cohort study of aging. PM2.5, black carbon, total plasma homocysteine and other covariates were measured at several points in time between 1995 and 2006. We fit mixed models to examine effect modification of genes on associations of pollution with total plasma homocysteine.
Interquartile range (IQR) increases in PM2.5 and black carbon (7-day moving averages) were associated with 1.5% (95% confidence interval = 0.2% to 2.8%) and 2.2% (0.6% to 3.9%) increases in total plasma homocysteine, respectively. GSTT1 and HFE C282Y modified effects of black carbon on total plasma homocysteine, and HFE C282Y and CAT (rs2300181) modified effects of PM2.5 on homocysteine. Several genotypes marginally modified effects of PM2.5 and black carbon on various endpoints. All genes with significant interactions with particulate air pollution had modest main effects on total plasma homocysteine.
Effects of PM2.5 and black carbon on various endpoints appeared to be mediated by genes related to oxidative stress pathways.
PMCID: PMC3939788  PMID: 20110814
15.  Lipid and endothelial related genes, ambient particulate matter, and heart rate variability --the VA Normative Aging Study 
Many studies have shown that exposures to air pollution are associated with cardiovascular events although the mechanism remains to be clarified. To identify whether exposures to ambient particles act on autonomic function via the lipid/endothelial metabolism pathway, we evaluated whether the effects of particulate matter < 2.5 µm in aerodynamic diameter (PM2.5) on heart rate variability (HRV) were modified by gene polymorphisms related to those pathways.
We used HRV and gene data from the Normative Aging Study and PM2.5 from a monitor located a kilometer from the examination site. We fitted a mixed effect model to investigate the associations between PM2.5 and repeated measurements of HRV by gene polymorphisms of apolipoprotein E (APOE), lipoprotein lipase (LPL) and vascular endothelial growth factor (VEGF) adjusting for potential confounders chosen a priori.
A 10-µg/m3 increase of PM2.5 in the two days before the examination was associated with 3.8% [95% confidence interval (CI): 0.2%, 7.4%], 7.8% [95 CI: 0.4%, 15.3%] and 10.6% [95% CI: 1.8 %, 19.4%] decreases of the standard deviation of normal-to-normal intervals, low frequency and high frequency, respectively. In general, carriers of wild type APOE, LPL and VEGF genes had stronger effects of particles on HRV compared to those with hetero- or homozygous types. Variations of LPL-N291S, LPL-D9N and APOE-G113C significantly modified effects of PM2.5 on HRV.
Associations between PM2.5 and HRV were modified by gene polymorphisms of APOE, LPL and VEGF and biological metabolism remains to be identified.
PMCID: PMC3935361  PMID: 19602472
air pollution; heart rate variability; effect modification; apolipoprotein E; lipoprotein lipase; vascular endothelial growth factor
16.  Association between blood pressure and DNA methylation of retrotransposons and pro-inflammatory genes 
Background Methylation of deoxyribonucleic acid (DNA) is an epigenetic regulator of gene expression that changes with age, but its contribution to aging-related disorders, including high blood pressure (BP), is still largely unknown. We examined the relation of BP to the methylation of retrotransposon sequences of DNA and of selected candidate genes.
Methods This investigation included 789 elderly participants in the Normative Aging Study, ranging in age from 55 to 100 years, who had longitudinal measurements of DNA methylation. In these subjects’ DNA we measured the proportion of methylated sites in retrotransposable sequences and in pro-inflammatory genes, expressed as the percent of 5-methylated cytosines (%5mC) among all cytosines. From one to four methylation measurements were made for each subject between 1999 and 2009. We fit mixed-effects models, using repeated measures of BP as the outcome and DNA methylation as the explanatory variable, adjusting for confounding variables. We also fit a Bayesian mixed-effects structural equation model to account for heterogeneity in the effects of methylation sites within each gene.
Results An increase in inter-quartile range (IQR) in the methylation of Alu elements was associated with an increase of 0.97 mm Hg in diastolic blood pressure (DBP) (95% CI 0.32–1.57), but no such association was observed for long interspersed nuclear element-1 (LINE-1). We also found positive associations between DBP and methylation of the genes for toll-like receptor 2 (TLR2) and inducible nitric oxide synthase (iNOS), and a negative association between DBP and methylation of the gene for interferon-γ (IFN-γ). Associations between methylation and systolic blood pressure (SBP) were weaker than those between methylation and DBP. Bayesian mixed-effects structural equation model results were similar for both DBP and SBP models.
Conclusions The results of our study suggest that changes in DNA methylation of some pro-inflammatory genes and retrotransposable elements are related to small changes in BP.
PMCID: PMC3600626  PMID: 23508416
Epigenetics; DNA methylation; blood pressure; inflammation; Bayesian model
17.  Allergen sensitization is associated with increased DNA methylation in older men 
Variation in epigenetic modifications, arising from either environmental exposures or internal physiological changes, can influence gene expression, and may ultimately contribute to complex diseases such as asthma and allergies. We examined the association of asthma and allergic phenotypes with DNA methylation levels of retrotransposon-derived elements.
We used data from 704 men (mean age 73) in the longitudinal Normative Aging Study to assess the relationship between asthma, allergic phenotypes and DNA methylation levels of the retrotransposon derived elements Alu and LINE-1. Retrotransposons represent a large fraction of the genome (> 30%), and are heavily methylated to prevent expression. Percent methylation of Alu and LINE-1 elements in peripheral white blood cells was quantified using PCR pyrosequencing. Data on sensitization to common allergens by skin prick testing, asthma, and methacholine responsiveness was gathered approximately 8 years prior to DNA methylation analysis.
Prior allergen sensitization was associated with increased methylation of Alu (β=0.32 [sensitized vs. non-sensitized], p value 0.003), in models adjusted for pack-years, BMI, smoking, air pollutants, percent eosinophils, white blood cell count and age. Of the men interviewed, 5 % of subjects reported diagnosis of asthma. Neither Alu, nor LINE-1 methylation was associated with asthma.
These data suggest that increased DNA methylation of repetitive elements may be associated with allergen sensitization, but does not appear to be associated with asthma. Future work is needed to identify potential underlying mechanisms for these relationships.
PMCID: PMC3730837  PMID: 23257623
allergen sensitization; DNA methylation; Alu; and LINE-1
18.  Vitamin D Deficiency, Smoking, and Lung Function in the Normative Aging Study 
Rationale: Vitamin D has immunomodulatory and antiinflammatory effects that may be modified by cigarette smoke and may affect lung function.
Objectives: To examine the effect of vitamin D deficiency and smoking on lung function and lung function decline.
Methods: A total of 626 men from the Normative Aging Study had 25-hydroxyvitamin D levels measured at three different times between 1984 and 2003 with concurrent spirometry. Vitamin D deficiency was defined as serum level ≤ 20 ng/ml. Statistical analysis was performed using multivariable linear regression and mixed effects models.
Measurements and Main Results: In the overall cohort, there was no significant effect of vitamin D deficiency on lung function or on lung function decline. In both cross-sectional and longitudinal multivariable models, there was effect modification by vitamin D status on the association between smoking and lung function. Cross-sectional analysis revealed lower lung function in current smokers with vitamin D deficiency (FEV1, FVC, and FEV1/FVC; P ≤ 0.0002), and longitudinal analysis showed more rapid rates of decline in FEV1 (P = 0.023) per pack-year of smoking in subjects with vitamin D deficiency as compared with subjects who were vitamin D sufficient.
Conclusions: Vitamin D deficiency was associated with lower lung function and more rapid lung function decline in smokers over 20 years in this longitudinal cohort of elderly men. This suggests that vitamin D sufficiency may have a protective effect against the damaging effects of smoking on lung function. Future studies should seek to confirm this finding in the context of smoking and other exposures that affect lung function.
PMCID: PMC3480523  PMID: 22822023
vitamin D; vitamin D deficiency; lung function decline; smoking; effect modification
19.  Structural equation modeling of parasympathetic and sympathetic response to traffic air pollution in a repeated measures study 
Environmental Health  2013;12:81.
Traffic-related air pollution has been associated to a range of adverse health impacts, including decreased heart rate variability (HRV). The association between traffic-related pollution and HRV, however, has varied by traffic-related or HRV marker as well as by study, suggesting the need for a more comprehensive and integrative approach to examining air pollution-mediated biological impacts on these outcomes. In a Bayesian framework, we examined the effect of traffic pollution on HRV using structural equation models (SEMs) and looked at effect modification by participant characteristics.
We studied measurements of 5 HRV markers [high frequency (HF), low frequency (LF), 5-min standard deviation of normal-to-normal intervals (SDNN), square root of the mean squared differences of successive normal-to-normal intervals (rMSSD), and LF/HF ratio (LF/HF)] for 700 elderly men from the Normative Aging Study. Using SEMs, we fit a latent variable for traffic pollution that is reflected by levels of carbon monoxide, nitrogen monoxide, nitrogen dioxide, and black carbon (BC) to estimate its effect on latent variable for parasympathetic tone that included HF, SDNN and rMSSD, and the sympathetic tone marker, LF/HF. Exposure periods were assessed using 4-, 24-, 48-, 72-hour moving average pre-visit. We compared our main effect findings using SEMs with those obtained using linear mixed models.
Traffic pollution was not associated with mean parasympathetic tone and LF/HF for all examined moving averages. In Bayesian linear mixed models, however, BC was related to increased LF/HF, an inter quartile range (IQR) increase in BC was associated with a 6.5% (95% posterior interval (PI): -0.7%, 14.2%) increase in mean LF/HF 24-hours later. The strongest association observed was for the 4-hour moving average (10.1%; 95% PI: 3.0%, 17.6%). The effect of traffic on parasympathetic tone was stronger among diabetic as compared to non-diabetic participants. Specifically, an IQR increase in traffic pollution in the 48-hr prior to the clinic visit was associated with a 44.3% (95% PI: -67.7%, -4.2%) lower mean parasympathetic tone among diabetics, and a 7.7% (95% PI: -18.0%, 41.4%) higher mean parasympathetic tone among non-diabetics.
BC was associated with adverse changes LF/HF in the elderly. Traffic pollution may decrease parasympathetic tone among diabetic elderly.
PMCID: PMC3907044  PMID: 24059437
Bayesian; Diabetes; HRV; Obesity; Parasympathetic response; Structural equation models; Sympathetic response and Traffic air pollution
20.  Arsenic exposure and DNA methylation among elderly men 
Epidemiology (Cambridge, Mass.)  2012;23(5):668-676.
Arsenic exposure has been linked to epigenetic modifications such as DNA methylation in in vitro and animal studies. This association has also been explored in highly exposed human populations, but studies among populations environmentally exposed to low arsenic levels are lacking.
We evaluated the association between exposure to arsenic, measured in toenails, and blood DNA methylation in Alu and Long Interspersed Nucleotide Element-1 (LINE-1) repetitive elements in elderly men environmentally exposed to low levels of arsenic. We also explored potential effect modification by plasma folate, cobalamin (vitamin B12), and pyridoxine (vitamin B6). The study population was 581 participants from the Normative Aging Study in Boston, of whom 434, 140, and 7 had 1, 2, and 3 visits, respectively, between 1999-2002 and 2006-2007. We used mixed-effects models and included interaction terms to assess potential effect modification by nutritional factors.
There was a trend of increasing Alu and decreasing LINE-1 DNA methylation as arsenic exposure increased. In subjects with plasma folate below the median (< 14.1 ng/ml), arsenic was positively associated with Alu DNA methylation (β=0.08 [95% confidence interval = 0.03 to 0.13] for one interquartile range [0.06μg/g] increase in arsenic) while a negative association was observed in subjects with plasma folate above the median (β=-0.08 [-0.17 to 0.01]).
We found an association between arsenic exposure and DNA methylation in Alu repetitive elements that varied by folate level. This suggests a potential role for nutritional factors in arsenic toxicity.
PMCID: PMC3448132  PMID: 22833016
21.  Forced Expiratory Volume in 1 Second and Cognitive Aging in Men 
To evaluate forced expiratory volume in 1 second (FEV1, a measure of overall lung function), long-term average FEV1, and rate of decline in FEV1 in relation to cognition and cognitive decline in older men.
Prospective observational study.
Community-based population.
Eight hundred sixty-four older men from the Normative Aging Study.
Starting in 1984, participants underwent triennial clinical evaluations. Lung function assessments provided estimates of FEV1. Cognitive assessments entailing tests of several cognitive abilities began in 1993. FEV1 measured approximately 12 years before baseline cognitive testing, average FEV1 over the 12-year period, and rate of change in FEV1 were all evaluated in relation to baseline and change in performance on the cognitive tests.
In multivariable-adjusted analyses, associations between FEV1 and baseline cognitive scores were mixed, although average FEV1 predicted significantly better performance on tests of visuospatial ability (P =.04) and general cognition (P =.03). Higher FEV1 was more consistently associated with slower cognitive decline, but only the association between historical FEV1 and attention was significant (difference per standard deviation in FEV1 = 0.056, P =.05). Rate of FEV1 decline was not consistently associated with cognitive function or decline. Findings were generally similar or stronger in men who had never smoked. To account for potential bias due to selective attrition, inverse probability of censoring weights were applied to the cognitive decline analyses, yielding slightly larger estimates; the inadequate prognostic power of the censoring models limited this approach.
Overall, the data provide limited evidence of an inverse association between FEV1 and cognitive aging.
PMCID: PMC3758858  PMID: 21718272
lung function; cognition; cognitive decline; epidemiology; aging
22.  Repetitive element hypomethylation in blood leukocyte DNA and cancer incidence, prevalence and mortality in elderly individuals: the Normative Aging Study 
Cancer causes & control : CCC  2010;22(3):437-447.
Global genomic hypomethylation is a common epigenetic event in cancer that mostly results from hypomethylation of repetitive DNA elements. Case-control studies have associated blood leukocyte DNA hypomethylation with several cancers. Because samples in case-control studies are collected after disease development, whether DNA hypomethylation is causal or just associated with cancer development is still unclear.
In 722 elderly subjects from the Normative Aging Study cohort, we examined whether DNA methylation in repetitive elements (Alu, LINE-1) was associated with cancer incidence (30 new cases, median follow-up: 89 months), prevalence (205 baseline cases), and mortality (28 deaths, median follow-up: 85 months). DNA methylation was measured by bisulfite pyrosequencing.
Individuals with low LINE-1 methylation (
These findings suggest that individuals with lower repetitive element methylation are at high risk of developing and dying from cancer.
PMCID: PMC3752839  PMID: 21188491
Repetitive elements; DNA methylation; Epigenetics; Blood; Cancer risk
American Journal of Epidemiology  2012;176(3):224-232.
DNA methylation is a potential pathway linking air pollution to disease. Studies indicate that psychological functioning modifies the association between pollution and morbidity. The authors estimated the association of DNA methylation with ambient particulate matter less than 2.5 µm in diameter (PM2.5) and black carbon, using mixed models. DNA methylation of the inducible nitric oxide synthase gene, iNOS, and the glucocorticoid receptor gene, GCR, was measured by quantitative polymerase chain reaction pyrosequencing of 1,377 blood samples from 699 elderly male participants in the VA Normative Aging Study (1999–2009). The authors also investigated whether this association was modified by psychological factors including optimism or pessimism, anxiety, and depression. iNOS methylation was decreased after acute exposure to both black carbon and PM2.5. A 1-μg/m3 increase in exposure to black carbon in the 4 hours preceding the clinical examination was associated with a 0.9% decrease in 5-methylcytosine (95% CI: 0.4, 1.4) in iNOS, and a 10-μg/m3 increase in exposure to PM2.5 was associated with a 0.6% decrease in 5-methylcytosine (95% CI: 0.03, 1.1) in iNOS. Participants with low optimism and high anxiety had associations that were 3–4 times larger than those with high optimism or low anxiety. GCR methylation was not associated with particulate air pollution exposure.
PMCID: PMC3491965  PMID: 22798479
air pollution; DNA methylation; psychology
Epidemiology (Cambridge, Mass.)  2010;21(6):819-828.
Epigenetic features such as DNA hypomethylation have been associated with conditions related to cardiovascular risk. We evaluated whether lower blood DNA methylation in heavily methylated repetitive sequences predicts the risk of ischemic heart disease and stroke.
We quantified blood DNA methylation of LINE-1 repetitive elements through PCR-pyrosequencing in 712 elderly individuals from the Boston-area Normative Aging Study. We estimated risk-factor adjusted relative risks (RRs) for ischemic heart disease and stroke at baseline (242 prevalent cases); as well as in incidence (44 new cases; median follow-up, 63 months); and subsequent mortality from ischemic heart disease (86 deaths; median follow-up, 75 months).
Blood LINE-1 hypomethylation was associated with baseline ischemic heart disease (RR=2.1 [95% confidence interval = 1.2 to 4.0] for lowest vs. highest methylation quartile) and for stroke (2.5 [0.9 to 7.5]). Among participants free of baseline disease, individuals with methylation below the median also had higher risk of developing ischemic heart disease (4.0 [1.8 to 8.9]) or stroke (5.7 [0.8 to 39.5]). In the entire cohort, persons with methylation below the median had higher mortality from ischemic heart disease (3.3 [1.3 to 8.4]) and stroke (2.8 [0.6 to 14.3]). Total mortality was also increased (2.0 [1.2 to 3.3]). These results were confirmed in additional regression models using LINE-1 methylation as a continuous variable.
Subjects with prevalent IHD and stroke exhibited lower LINE-1 methylation. In longitudinal analyses, persons with lower LINE-1 methylation were at higher risk for incident ischemic heart disease and stroke, and for total mortality.
PMCID: PMC3690659  PMID: 20805753
Particulate air pollution is associated with cardiovascular events, but the mechanisms are not fully understood. The main objective was to assess the relationship between long-term exposure to traffic-related air pollution and blood pressure (BP).
The authors used longitudinal data from 853 elderly men participating in the Veterans Administration Normative Aging Study, followed during 1996–2008. Long-term average exposures to traffic particles were created from daily predictions of black carbon (BC) exposure at the geocoded address of each subject, using a validated spatiotemporal model based on ambient monitoring at 82 Boston-area locations. The authors examined the association of these exposures with BP using a mixed model. The authors included the following covariates: age, body mass index, smoking, alcohol, fasting glucose, creatinine clearance, use of cardiovascular medication, education, census-level poverty, day of week and season of clinical visit.
The authors found significant positive associations between 1-year average BC exposure and both systolic and diastolic blood pressure. An IQR increase in 1-year average BC exposure (0.32 µg/m3) was associated with a 2.64 mm Hg increase in systolic blood pressure (95% CI 1.47 to 3.80) and a 2.41 mm Hg increase in diastolic blood pressure (95% CI 1.77 to 3.05).
Long-term exposure to traffic particles is associated with increased BP, which may explain part of the association with myocardial infarctions and cardiovascular deaths reported in cohort studies.
PMCID: PMC3597742  PMID: 22383587

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