Air pollution and markers of coagulation, inflammation, and endothelial function: associations and epigene-environment interactions in an elderly cohort. Epidemiology. 2012;23:332-340. [PMID: 22237295 DOI: 10.1097/ede.0b013e31824523f0]

Environmental NO2 and CO Exposure: Ignored Factors Associated with Uremic Pruritus in Patients Undergoing Hemodialysis

Uremic pruritus (UP), also known as chronic kidney disease-associated pruritus, is a common and disabling symptom in patients undergoing maintenance hemodialysis (MHD). The pathogenesis of UP is multifactorial and poorly understood. Outdoor air pollution has well-known effects on the health of patients with allergic diseases through an inflammatory process. Air pollution-induced inflammation could occur in the skin and aggravate skin symptoms such as pruritus or impair epidermal barrier function. To assess the role of air pollutants, and other clinical variables on uremic pruritus (UP) in HD patients, we recruited 866 patients on maintenance HD. We analyzed the following variables for association with UP: average previous 12-month and 24-month background concentrations for nitrogen dioxide (NO2) and carbon monoxide (CO), and suspended particulate matter of <2.5 μm (PM2.5). In a multivariate logistic regression, hemodialysis duration, serum ferritin levels, low-density lipoprotein levels, and environmental NO2/CO levels were positively associated with UP, and serum albumin levels were negatively associated with UP. This cross-sectional study showed that air pollutants such as NO2 and CO might be associated with UP in patients with MHD.

Leveraging Methylome-Environment Interaction to Detect Genetic Determinants of Disease

OBJECTIVE

The association between DNA methylation and a trait of interest may depend on an environmental exposure, and incorrectly accounting for this dependence can lead to a reduction in power of the standard tests used in epigenome-wide association studies. We present the M-ME test to jointly test for the main effect of DNA methylation and methylation-environment interaction.

METHODS

Through simulation, we compare the power and type 1 error of the M-ME test to a standard marginal test (M test) and a standard interaction test (ME test) under 1,800 different underlying models. These models allow for methylation-environment correlation and measurement error in the exposure.

RESULTS

In many true underlying models, either the M test or the ME test has very low power, but the M-ME test has optimal or nearly optimal power to detect a DNA methylation effect in all models considered, including those with methylation- environment dependence and measurement error in the exposure. Type 1 error inflation occurs in the tests when the exposure is measured with error and correlated with DNA methylation.

CONCLUSION

The M-ME test is an attractive choice for studies aiming to detect any DNA methylation association when little is known about the epigenetic associations a priori.

Associations of Residential Long-Term Air Pollution Exposures and Satellite-Derived Greenness with Insulin Resistance in German Adolescents

BACKGROUND

Epidemiological studies have identified associations between air pollution and green space access with type 2 diabetes in adults. However, it remains unclear to what extent associations with greenness are attributable to air pollution exposure.

OBJECTIVES

We aimed to investigate associations between long-term exposure to air pollution and satellite-derived greenness with insulin resistance in adolescents.

METHODS

A total of 837 participants of two German birth cohorts (LISAplus and GINIplus) were included in the analysis. Generalized additive models were used to determine the association of individual satellite-derived greenness defined by the Normalized Difference Vegetation Index (NDVI), long-term air pollution exposure estimated by land-use regression (LUR) models with insulin resistance (HOMA-IR) in 15-year-old adolescents. Models were adjusted for study area, cohort, socioeconomic, and individual characteristics such as body mass index, physical activity, and smoking.

RESULTS

Increases of 2 SDs in nitrogen dioxide (NO2; 8.9 μg/m3) and particulate matter ≤ 10 μm in diameter (PM10; 6.7 μg/m3) were significantly associated with 11.4% (95% CI: 4.4, 18.9) and 11.4% (95% CI: 0.4, 23.7) higher HOMA-IR. A 2-SD increase in NDVI in a 1,000-m buffer (0.2 units) was significantly associated with a lower HOMA-IR (-7.4%; 95% CI: -13.3, -1.1). Associations tended to be stronger in adolescents who spent more time outside and in those with lower socioeconomic status. In combined models including both air pollution and greenness, only NO2 remained significantly associated with HOMA-IR, whereas effect estimates for all other exposures attenuated after adjustment for NO2.

CONCLUSIONS

NO2, often considered as a marker of traffic, was independently associated with insulin resistance. The observed association between higher greenness exposure and lower HOMA-IR in adolescents might thus be attributable mainly to the lower co-exposure to traffic-related air pollution.

CITATION

Thiering E, Markevych I, Brüske I, Fuertes E, Kratzsch J, Sugiri D, Hoffmann B, von Berg A, Bauer CP, Koletzko S, Berdel D, Heinrich J. 2016. Associations of residential long-term air pollution exposures and satellite-derived greenness with insulin resistance in German adolescents. Environ Health Perspect 124:1291-1298; http://dx.doi.org/10.1289/ehp.1509967.

Quantile Regression Analysis of the Distributional Effects of Air Pollution on Blood Pressure, Heart Rate Variability, Blood Lipids, and Biomarkers of Inflammation in Elderly American Men: The Normative Aging Study

BACKGROUND

Previous studies have observed associations between air pollution and heart disease. Susceptibility to air pollution effects has been examined mostly with a test of effect modification, but little evidence is available whether air pollution distorts cardiovascular risk factor distribution.

OBJECTIVES

This paper aims to examine distributional and heterogeneous effects of air pollution on known cardiovascular biomarkers.

METHODS

A total of 1,112 men from the Normative Aging Study and residents of the greater Boston, Massachusetts, area with mean age of 69 years at baseline were included in this study during the period 1995-2013. We used quantile regression and random slope models to investigate distributional effects and heterogeneity in the traffic-related responses on blood pressure, heart rate variability, repolarization, lipids, and inflammation. We considered 28-day averaged exposure to particle number, PM2.5 black carbon, and PM2.5 mass concentrations (measured at a single monitor near the site of the study visits).

RESULTS

We observed some evidence suggesting distributional effects of traffic-related pollutants on systolic blood pressure, heart rate variability, corrected QT interval, low density lipoprotein (LDL) cholesterol, triglyceride, and intercellular adhesion molecule-1 (ICAM-1). For example, among participants with LDL cholesterol below 80 mg/dL, an interquartile range increase in PM2.5 black carbon exposure was associated with a 7-mg/dL (95% CI: 5, 10) increase in LDL cholesterol, while among subjects with LDL cholesterol levels close to 160 mg/dL, the same exposure was related to a 16-mg/dL (95% CI: 13, 20) increase in LDL cholesterol. We observed similar heterogeneous associations across low versus high percentiles of the LDL distribution for PM2.5 mass and particle number.

CONCLUSIONS

These results suggest that air pollution distorts the distribution of cardiovascular risk factors, and that, for several outcomes, effects may be greatest among individuals who are already at high risk.

CITATION

Bind MA, Peters A, Koutrakis P, Coull B, Vokonas P, Schwartz J. 2016. Quantile regression analysis of the distributional effects of air pollution on blood pressure, heart rate variability, blood lipids, and biomarkers of inflammation in elderly American men: the Normative Aging Study. Environ Health Perspect 124:1189-1198; http://dx.doi.org/10.1289/ehp.1510044.

Chemical constituents and sources of ambient particulate air pollution and biomarkers of endothelial function in a panel of healthy adults in Beijing, China

BACKGROUND

Exposure to ambient air pollution has been associated with endothelial dysfunction as reflected by short-term alterations in circulating biomarkers, but the chemical constituents and pollution sources behind the association has been unclear.

METHODS

We investigated the associations between various ambient air pollutants including gases and 31 chemical constituents and seven sources of fine particles (PM2.5) and biomarkers of endothelial function, including endothelin-1 (ET-1), E-selectin, soluble intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1), based on 462 repeated measurements in a panel of 40 college students who were followed for three study periods before and after relocating from a suburban area to an urban area in Beijing, China in 2010-2011. Air pollution data were obtained from central air-monitoring stations. Linear mixed-effects models were used to estimate the changes in biomarkers associated with exposures.

RESULTS

Total PM2.5 mass showed few appreciable associations with examined biomarkers. However, several PM2.5 constituents and related sources showed significant associations with examined biomarkers. PM2.5 from dust/soil and several crustal and transition metals, including strontium, iron, titanium, cobalt and magnesium, were significantly associated with increases in ET-1 at 1-day average; manganese and potassium were significantly associated with increases in ICAM-1 at 2-day average; and PM2.5 from industry and metal cadmium were significantly associated with decreases in VCAM-1 at 1-day average. In addition, carbon monoxide was significantly associated with increasing ICAM-1 at 1-day and 2-day averages, whereas nitric oxide was significantly associated with decreasing ICAM-1 at 1-day and 3-day averages.

CONCLUSIONS

Our results suggest that certain PM2.5 metal constituents were more closely associated with circulating biomarkers of endothelial function than PM2.5, and therefore highlight the research necessity to examine pollution chemical constituents in future studies.

A structured review of panel studies used to investigate associations between ambient air pollution and heart rate variability

INTRODUCTION

Dysfunction of the autonomic nervous system is one of the postulated pathways linking short-term exposure to air pollution to adverse cardiovascular outcomes. A hypothesis is that exposure to air pollution decreases heart rate variability, a recognized independent predictor of poorer cardiovascular prognosis.

METHODS

We conducted a structured review of panel studies published between 1946 and July 2015 of the association between ambient air pollution and parameters of heart rate variability reflecting autonomic nervous function. We focused on exposure to mass concentrations of fine particles (PM2.5), nitrogen dioxide (NO2), and ozone (O3), and four commonly used indices of heart rate variability (HRV): standard deviation of all normal-to-normal intervals (SDNN); root mean square of successive differences in adjacent normal-to-normal intervals (RMSSD); high frequency power (HF); and low frequency power (LF). We searched bibliographic databases and references of identified articles and abstracted characteristics of their design and conduct, and synthesized the quantitative findings in graphic form according to health condition of the study population and the functional form of the HRV indices used in the regression analyses.

RESULTS

A total of 33 panel studies were included: 31, 12, and 13 studies were used to investigate ambient exposure to PM2.5, NO2 and O3, respectively. We found substantial variation across studies in terms of design characteristics and statistical methodologies, and we identified some studies that may have had methodological and statistical issues. Because many panel studies were not comparable to each other, meta-analyses were not generally possible, although we were able to pool the results obtained amongst older adults who had cardiovascular disease for the 24-h average concentrations of PM2.5 prior to the heart rate variability measurements. In studies of PM2.5 among older adults with cardiovascular disease, logarithmic transformations of the HRV indices were used in ten studies. Negative associations across all HRV indices were found in 60-86% of these studies for periods of exposures ranging from 5-min to 5-days. The pooled percent changes for an increase of 10μg/m(3) in the 24-h prior to the measurements of HRV were: -2.11% for SDNN (95% confidence interval (95%CI): -4.00, -0.23%), -3.29% for RMSSD (95%CI: -6.32, -0.25%), -4.76% for LF (95%CI: -12.10, 2.58%), and -1.74% for HF (95%CI: -7.79, 4.31%). No transformations were used in seven studies of PM2.5 among older adults with cardiovascular disease, and we found for absolute differences pooled changes in the HRV indices, for an increase of 10μg/m(3), of -0.31ms for SDNN (95%CI: -1.02, 0.41ms) and -1.22ms for RMSSD (95%CI: -2.37; -0.07ms). For gaseous pollutants, negative associations over periods of exposure ranging from 5-min or to 5-days prior to the heart rate variability measurements were reported in 71-83% of studies of NO2 and 57-100% of studies of O3, depending of the indices of heart rate variability. However, many of these studies had statistical or methodological issues, and in the few studies without these issues the confidence intervals were relatively wide and mostly included the null.

CONCLUSIONS AND DISCUSSION

We were not persuaded by the results that there was an association between PM2.5 and any of the four indices of heart rate variability. For NO2 and O3 the number of high-quality studies was insufficient to draw any definite conclusions. Further panel studies with improved design and methodologies are needed to help establish or refute an association between ambient exposure to air pollution and heart rate variability.

Fine particles, genetic pathways, and markers of inflammation and endothelial dysfunction: Analysis on particulate species and sources

Studies have found associations between PM2.5 and cardiovascular events. The role of different components of PM2.5 is not well understood. We used linear mixed-effects models with the adaptive LASSO penalty to select PM2.5 species and source(s), separately, that may be associated with markers of inflammation and endothelial dysfunction, with adjustment for age, obesity, smoking, statin use, diabetes mellitus, temperature, and season as fixed effects in a large longitudinal cohort of elderly men. We also analyzed these associations with source apportionment models and examined genetic pathway-air pollution interactions within three relevant pathways (oxidative stress, metal processing, and endothelial function). We found that independent of PM2.5 mass vanadium (V) was associated with intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). An IQR increase (3.2 ng/m(3)) in 2-day moving average V was associated with a 2.5% (95% CI: 1.2-3.8%) change in ICAM-1 and a 3.9% (95% CI: 2.2-5.7%) change in VCAM-1, respectively. In addition, an oil combustion source rich in V was linked to these adhesion molecules. People with higher allelic risk profiles related to oxidative stress may have greater associations (P-value of interaction=0.11). Our findings suggest that particles derived from oil combustion may be associated with inflammation and endothelial dysfunction, and it is likely that oxidative stress plays a role in the associations.

Cross-sectional association between exposure to particulate matter and inflammatory markers in the Japanese general population: NIPPON DATA2010

A suggestive mechanism behind the association between particulate matter and cardiovascular disease is inflammatory response. Earlier population-based studies investigating the association between particulate matter and inflammatory biological markers, in particular C-reactive protein (CRP), showed inconsistent results. In addition, evidence from the Asian population, in which CRP levels are typically lower than those observed in Western populations, was sparse. We examined the cross-sectional association between short- and long-term exposure to particulate matter and inflammatory markers, including high-sensitivity CRP (hs-CRP) and white blood cell (WBC) count, in a representative population of Japanese community dwellers (NIPPON DATA2010). We analysed data from 2360 participants (1002 men and 1358 women), aged 20 years or older, who resided in 300 randomly selected districts (222 public health centre areas) throughout Japan. We used background concentrations of suspended particulate matter (SPM, defined as particles with a 100% cut-off level at 10 μm aerodynamic diameter) and co-pollutants within the public health centre area. A logistic regression model was applied to estimate odds ratios (ORs) of elevated hs-CRP (> 0.3 mg/dl) or WBC (> 9000/μl). Since smoking is an important confounding factor, we firstly included this in the models, and additionally conducted the analyses after excluding current smokers. The one-month average concentration of SPM was positively associated with hs-CRP (OR per 10 μg/m(3) increase in SPM = 1.42, 95% confidence interval = 1.00-2.04), and high exposure to SPM on the day of blood draw was associated with increased WBC count, after excluding current smokers (OR = 1.13, 1.01-1.28). Similar association patterns were observed for ozone. In conclusion, exposure to particulate matter was associated with inflammatory markers in the general Japanese population. Systemic inflammation may play a role in the link between particulate matter and cardiovascular disease.

The relationship of exposure to air pollutants in pregnancy with surrogate markers of endothelial dysfunction in umbilical cord

BACKGROUND

This study aims to investigate the association of exposure to ambient air pollution during pregnancy with cord blood concentrations of surrogate markers of endothelial dysfunction.

METHODS

This population-based cohort was conducted from March 2014 to March 2015 among 250 mother-neonate pairs in urban areas of Isfahan, the second large and air-polluted city in Iran. We analyzed the association between the ambient carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), particular matter 10 (PM10), and air quality index (AQI) with cord blood levels of endothelin-1, vascular adhesion molecule (VCAM), and intercellular adhesion molecule (ICAM). Multiple regression analysis was conducted after adjustment for potential confounding factors and covariates. The regression coefficient (beta), standard error of the estimate (SE), and 95% confidence intervals for each regression coefficient (95% CI) are reported.

RESULTS

Data of 233 mother-neonate pairs were complete, and included in the analysis. Multiple regression analyses showed that AQI, CO and O3 had significant correlation with cord blood ICAM-1 [Beta (SE), 95%CI: 2.93 (0.72), 1.33,5.54; 2.28(1.44), 1.56,5.12; and 2.02(0.01), 1.03,2.04, respectively] as well as with VCAM-1 [2.78(0.91), 1.69,4.57; 2.47(1.47), 1.43,5.37; and 2.01(0.01),1.07,2.04, respectively]. AQI, PM10, and SO2 were significantly associated with Endothelin-1 concentrations [Beta (SE), 95%CI: 10.16(5.08),7.61,14.28; 9.70(3.46), 2.88,16.52; and 1.07(0.02), 1.03,2.11, respectively].

CONCLUSIONS

The significant associations of air pollutants with markers of endothelial dysfunction during fetal period may provide another evidence on the adverse health effects of air pollutants on early stages of atherosclerosis from fetal period. Our findings underscore the importance of considering environmental factors in primordial prevention of chronic diseases.

Increases in ambient particulate matter air pollution, acute changes in platelet function, and effect modification by aspirin and omega-3 fatty acids: A panel study

Increased particulate matter (PM) air pollutant concentrations have been associated with platelet activation. It was postulated that elevated air pollutant concentrations would be associated with increases in measures of platelet function and that responses would be blunted when taking aspirin and/or fish oil. Data from a sequential therapy trial (30 subjects with type 2 diabetes mellitus), with 4 clinic visits (first: no supplements, second: aspirin, third: omega-3 fatty acid supplements, fourth: aspirin and omega-3 fatty acids) per subject, were utilized. Using linear mixed models, adjusted for relative humidity, temperature, visit number, and season, changes in three platelet function measures including (1) aggregation induced by adenosine diphosphate (ADP), (2) aggregation induced by collagen, and (3) thromboxane B2 production were associated with interquartile range (IQR) increases in mean concentrations of ambient PM2.5, black carbon, ultrafine particles (UFP; 10-100 nm), and accumulation mode particles (AMP; 100-500 nm) in the previous 1-96 h. IQR increases in mean UFP and AMP concentrations were associated with significant decreases in platelet response, with the largest being a -0.43 log(pg/ml) decrease in log(thromboxane B2) (95% CI = -0.8, -0.1) associated with each 582-particles/cm(3) increase in AMP, and a -1.7 ohm reduction in collagen-induced aggregation (95% CI = -3.1, -0.3) associated with each 2097-particles/cm(3) increase in UFP in the previous 72 h. This UFP effect on thromboxane B2 was significantly muted in diabetic subjects taking aspirin (-0.01 log[pg/ml]; 95% CI = -0.4, 0.3). The reason for this finding remains unknown, and needs to be investigated in future studies.

Metabolomic changes in murine serum following inhalation exposure to gasoline and diesel engine emissions

The adverse health effects of environmental exposure to gaseous and particulate components of vehicular emissions are a major concern among urban populations. A link has been established between respiratory exposure to vehicular emissions and the development of cardiovascular disease (CVD), but the mechanisms driving this interaction remain unknown. Chronic inhalation exposure to mixed vehicle emissions has been linked to CVD in animal models. This study evaluated the temporal effects of acute exposure to mixed vehicle emissions (MVE; mixed gasoline and diesel emissions) on potentially active metabolites in the serum of exposed mice. C57Bl/6 mice were exposed to a single 6-hour exposure to filtered air (FA) or MVE (100 or 300 μg/m(3)) by whole body inhalation. Immediately after and 18 hours after the end of the exposure period, animals were sacrificed for serum and tissue collection. Serum was analyzed for metabolites that were differentially present between treatment groups and time points. Changes in metabolite levels suggestive of increased oxidative stress (oxidized glutathione, cysteine disulfide, taurine), lipid peroxidation (13-HODE, 9-HODE), energy metabolism (lactate, glycerate, branched chain amino acid catabolites, butrylcarnitine, fatty acids), and inflammation (DiHOME, palmitoyl ethanolamide) were observed immediately after the end of exposure in the serum of animals exposed to MVE relative to those exposed to FA. By 18 hours post exposure, serum metabolite differences between animals exposed to MVE versus those exposed to FA were less pronounced. These findings highlight complex metabolomics alterations in the circulation following inhalation exposure to a common source of combustion emissions.

A common functional variant on the pro-inflammatory Interleukin-6 gene may modify the association between long-term PM10 exposure and diabetes

BACKGROUND

Air pollutants have been linked to type 2 diabetes (T2D), hypothesized to act through inflammatory pathways and may induce interleukin-6 gene (IL6) in the airway epithelium. The cytokine interleukin-6 may impact on glucose homeostasis. Recent meta-analyses showed the common polymorphisms, IL6 -572G > C and IL6 -174G > C to be associated with T2D risk. These IL6 variants also influence circulatory interleukin-6 levels. We hypothesize that these common functional variants may modify the association between air pollutants and T2D.

METHODS

We cross-sectionally studied 4410 first follow-up participants of the Swiss Cohort Study on Air Pollution and Lung and Heart Diseases (SAPALDIA), aged 29 to 73 years who had complete data on genotypes, diabetes status and covariates. We defined diabetes as self-reported physician-diagnosed, or use of diabetes medication or non-fasting glucose >11.1 mmol/L or HbA1c > 0.065. Air pollution exposure was 10-year mean particulate matter <10 μm in diameter (PM10) assigned to participants' residences using a combination of dispersion modelling, annual trends at monitoring stations and residential history. We derived interaction terms between PM10 and genotypes, and applied mixed logistic models to explore genetic interactions by IL6 polymorphisms on the odds of diabetes.

RESULTS

There were 252 diabetes cases. Respective minor allele frequencies of IL6 -572G > C and IL6 -174G > C were 7 and 39 %. Mean exposure to PM10 was 22 μg/m(3). Both variants were not associated with diabetes in our study. We observed a significant positive association between PM10 and diabetes among homozygous carriers of the pro-inflammatory major G-allele of IL6 -572G > C [Odds ratio: 1.53; 95 % confidence interval (1.22, 1.92); P interaction (additive) = 0.003 and P interaction (recessive) = 0.006]. Carriers of the major G-allele of IL6 -174G > C also had significantly increased odds of diabetes, but interactions were statistically non-significant.

CONCLUSIONS

Our results on the interaction of PM10 with functionally well described polymorphisms in an important pro-inflammatory candidate gene are consistent with the hypothesis that air pollutants impact on T2D through inflammatory pathways. Our findings, if confirmed, are of high public health relevance considering the ubiquity of the major G allele, which puts a substantial proportion of the population at risk for the development of diabetes as a result of long-term exposure to air pollution.

Ozone exposure and systemic biomarkers: Evaluation of evidence for adverse cardiovascular health impacts

The US Environmental Protection Agency (EPA) recently concluded that there is likely to be a causal relationship between short-term (< 30 days) ozone exposure and cardiovascular (CV) effects; however, biological mechanisms to link transient effects with chronic cardiovascular disease (CVD) have not been established. Some studies assessed changes in circulating levels of biomarkers associated with inflammation, oxidative stress, coagulation, vasoreactivity, lipidology, and glucose metabolism after ozone exposure to elucidate a biological mechanism. We conducted a weight-of-evidence (WoE) analysis to determine if there is evidence supporting an association between changes in these biomarkers and short-term ozone exposure that would indicate a biological mechanism for CVD below the ozone National Ambient Air Quality Standard (NAAQS) of 75 parts per billion (ppb). Epidemiology findings were mixed for all biomarker categories, with only a few studies reporting statistically significant changes and with no consistency in the direction of the reported effects. Controlled human exposure studies of 2 to 5 hours conducted at ozone concentrations above 75 ppb reported small elevations in biomarkers for inflammation and oxidative stress that were of uncertain clinical relevance. Experimental animal studies reported more consistent results among certain biomarkers, although these were also conducted at ozone exposures well above 75 ppb and provided limited information on ozone exposure-response relationships. Overall, the current WoE does not provide a convincing case for a causal relationship between short-term ozone exposure below the NAAQS and adverse changes in levels of biomarkers within and across categories, but, because of study limitations, they cannot not provide definitive evidence of a lack of causation.

The Role of the Epigenome in Translating Neighborhood Disadvantage Into Health Disparities

The possible causal role of the environment in health disparities is not well understood, even though it has been a national priority for many years. Progress to investigate the relationship between genetics, environmental exposures, and health outcomes has been hampered by the lack of analytical tools to quantify the combined or cumulative effect of multiple chemical and non-chemical stressors on gene expression. The studies cited here provide a strong rationale for using epigenomic analysis to assess cumulative risk from multiple environmental exposures over the life course. The environment-specific "imprints" on the genome, coupled with transcriptomics and metabolomics, can be used to advance our understanding of the relationship between neighborhood disadvantage and health disparities.

Epigenetic Signatures as Biomarkers of Exposure

To advance our knowledge of the influence of environmental exposures on human health and disease, robust studies are needed. However, for many exposures, robust studies are not feasible due to limitations with current ascertainment methods and/or study designs. Epigenetics, the study of mitotically heritable, reversible information that regulates critical cell processes, has gained much attention because it offers a potential mechanism to explain how exposures can influence cell states. Therefore, most studies have focused on epigenetics as a mechanism for disease. However, emerging evidence also suggests that epigenetic marks may also serve as biomarkers of exposure. Here, we highlight findings showing that the epigenome is labile to the environment and that these exposure-associated changes show long-term stability, are specific, are detectable in accessible tissues, can predict exposure status, and can be practically implemented, thus supporting the potential for epigenetic patterns to serve as robust measures of environmental exposure.

DNA Methylation in Whole Blood: Uses and Challenges

Due to its convenience, the blood is commonly used in epigenomic studies, but its heterogeneous nature leads to interpretation difficulties, given the now widely recognized potential for confounding by cell composition effects. Many recent publications have reported significant associations between DNA methylation and a variety of health conditions or exposures. In this review, we summarize many of these recent publications, highlighting the findings in the context of potential cell composition effects, particularly findings that are indicative of immune response or inflammation. While there is substantial evidence for confounding by cell composition, there is nevertheless also evidence for differential DNA methylation suggestive of processes that are not cell mediated. We conclude that important biological insights still may be gained from studying DNA methylation in whole blood, either by investigating the cell composition effects themselves or processes that demonstrate associations even after adjusting for cell composition effects.

Influence of residential environment and lifestyle on multiple primary malignancies in Taiwan

BACKGROUND

Multiple primary malignancies (MPM) have become increasingly prevalent worldwide. This investigation was aimed at establishing the clinicopathological characteristics of MPM patients and evaluating the impact of the living environment on MPM in the Taiwanese population.

MATERIALS AND METHODS

From January 2009 to December 2013, a total of 8,268 cancer patients were identified in our institutional center. Of these, 125 were diagnosed as MPM and thus enrolled. Data for clinicopathological features and treatment approaches for these MPM patients living in urban or suburb zone were obtained. Findings for the air pollution status in Taiwan were also collected.

RESULTS

The most common cancer match of MPM was esophageal cancer with hypopharyngeal cancer (12.8%), followed by colorectal cancer with gastric cancer (6.4%) and colorectal cancer with breast cancer (5.6%). The air quality was significantly worse in the urban than in the suburban zone and there was a remarkably higher portion of MPM patients in the urban zone suffering from grade III and IV post-chemotherapeutic neutropenia (30.8% vs 15.1%, P=0.036).

CONCLUSIONS

The tumor frequency and site distribution should be taken into the clinical evaluation because there is a relatively high risk of developing MPM. This study also highlighted the potential influence of environmental factors on post-chemotherapeutic neutropenia for patients with MPM.

DNA methylation of oxidative stress genes and cancer risk in the Normative Aging Study

Oxidative stress (OS) is a primary mechanism of carcinogenesis, and methylation of genes related to it may play a role in cancer development. In this study, we examined the prospective association between blood DNA methylation of four oxidative stress genes and cancer incidence. Our study population included a total of 582 participants in the Normative Aging Study (NAS) who had blood drawn during 1-4 visits from 1999-2012 (mean follow up 9.0 years). Promoter DNA methylation of CRAT, iNOS, OGG1 and GCR in blood leukocytes was measured using pyrosequencing. We used Cox regression models to examine prospective associations between cancer incidence and both methylation at the baseline visit and methylation rate of changes over time. Baseline OGG1 methylation was associated with higher risk of all-cancer (HR: 1.43, 95% CI: 1.15-1.78) and prostate cancer (HR: 1.52, 95% CI: 1.03-2.25) incidence. Compared with participants remaining cancer-free, those who eventually developed cancer had significantly accelerated CRAT methylation (p = 0.04) and decelerated iNOS methylation (p<0.01) over time prior to cancer diagnosis. Accelerated CRAT methylation was associated with higher all-cancer incidence (HR: 3.88, 95% CI: 1.06-14.30), whereas accelerated iNOS methylation was associated with lower all-cancer incidence (HR: 0.08, 95% CI 0.02-0.38). Our results suggest that methylation and its dynamic change over time in OS-related genes, including OGG1, CRAT and iNOS, may play an important role in carcinogenesis. These results can potentially facilitate the development of early detection biomarkers and new treatments for a variety of cancers.

The Role of DNA Methylation in Cardiovascular Risk and Disease: Methodological Aspects, Study Design, and Data Analysis for Epidemiological Studies

Epidemiological studies have demonstrated that genetic, environmental, behavioral, and clinical factors contribute to cardiovascular disease development. How these risk factors interact at the cellular level to cause cardiovascular disease is not well known. Epigenetic epidemiology enables researchers to explore critical links between genomic coding, modifiable exposures, and manifestation of disease phenotype. One epigenetic link, DNA methylation, is potentially an important mechanism underlying these associations. In the past decade, there has been a significant increase in the number of epidemiological studies investigating cardiovascular risk factors and outcomes in relation to DNA methylation, but many gaps remain in our understanding of the underlying cause and biological implications. In this review, we provide a brief overview of the biology and mechanisms of DNA methylation and its role in cardiovascular disease. In addition, we summarize the current evidence base in epigenetic epidemiology studies relevant to cardiovascular health and disease and discuss the limitations, challenges, and future directions of the field. Finally, we provide guidelines for well-designed epigenetic epidemiology studies, with particular focus on methodological aspects, study design, and analytical challenges.

Causal mediation analysis for longitudinal data with exogenous exposure

Mediation analysis is a valuable approach to examine pathways in epidemiological research. Prospective cohort studies are often conducted to study biological mechanisms and often collect longitudinal measurements on each participant. Mediation formulae for longitudinal data have been developed. Here, we formalize the natural direct and indirect effects using a causal framework with potential outcomes that allows for an interaction between the exposure and the mediator. To allow different types of longitudinal measures of the mediator and outcome, we assume two generalized mixed-effects models for both the mediator and the outcome. The model for the mediator has subject-specific random intercepts and random exposure slopes for each cluster, and the outcome model has random intercepts and random slopes for the exposure, the mediator, and their interaction. We also expand our approach to settings with multiple mediators and derive the mediated effects, jointly through all mediators. Our method requires the absence of time-varying confounding with respect to the exposure and the mediator. This assumption is achieved in settings with exogenous exposure and mediator, especially when exposure and mediator are not affected by variables measured at earlier time points. We apply the methodology to data from the Normative Aging Study and estimate the direct and indirect effects, via DNA methylation, of air pollution, and temperature on intercellular adhesion molecule 1 (ICAM-1) protein levels. Our results suggest that air pollution and temperature have a direct effect on ICAM-1 protein levels (i.e. not through a change in ICAM-1 DNA methylation) and that temperature has an indirect effect via a change in ICAM-1 DNA methylation.

Association of exposure to particulate matter (PM2.5) air pollution and biomarkers of cardiovascular disease risk in adult NHANES participants (2001-2008)

BACKGROUND AND OBJECTIVES

Exposure to particulate matter (PM2.5) has been associated with increased cardiovascular outcomes, mediated by a hypothesized biological mechanism of systemic inflammation and oxidation. Although PM10 has been linked to inflammatory markers in a nationally representative sample (NHANES) using data from earlier cycles (1989-1994); no study has considered these relationships for PM2.5 in more recent time periods. We examined the association of ambient PM2.5 exposure and inflammatory markers in adult NHANES participants for cycles 2001-2008.

METHODS

We linked each of the adult NHANES participant's address with meteorological and modeled air pollution data for each census tract in conterminous United States. The effects of short and long term PM2.5 on C-reactive protein, white blood cells, fibrinogen and homocysteine were analyzed using multiple linear regression, adjusting for cardiovascular risk factors, temperature and ozone. SAS SURVEYREG was used to account for the complex survey design of NHANES.

RESULTS

In the overall population, no significant positive associations were noted for either short or long term PM2.5 exposures for any of the biomarkers after controlling for confounders. However, stronger associations were found among obese, diabetics, hypertensive and smokers. For every 10μg/m(3) increase in PM2.5, there was an increase of (a) 36.9% (95% CI: 0.1%, 87.2%) in CRP at annual average PM2.5 (adjusting for short term exposure) among diabetics (b) 2.6% (95% CI: 0.1%, 5.1%) in homocysteine at lag 0 among smokers.

CONCLUSIONS

In a nationally representative sample of individuals we noted no overall association between PM2.5 and biomarkers of cardiovascular risk. However, sensitive subgroups manifested increases in these markers to PM2.5 exposure. Further studies should concentrate on the impact of PM2.5 on these biomarkers in those with multiple cardiovascular risk factors.

Exposure to Elemental Carbon, Organic Carbon, Nitrate, and Sulfate Fractions of Fine Particulate Matter and Risk of Preterm Birth in New Jersey, Ohio, and Pennsylvania (2000-2005)

BACKGROUND

Particulate matter ≤ 2.5 μm in aerodynamic diameter (PM2.5) has been consistently associated with preterm birth (PTB) to varying degrees, but roles of PM2.5 species have been less studied.

OBJECTIVE

We estimated risk differences (RD) of PTB (reported per 106 pregnancies) associated with change in ambient concentrations of elemental carbon (EC), organic carbon (OC), nitrates (NO3), and sulfates (SO4).

METHODS

From live birth certificates from three states, we constructed a cohort of singleton pregnancies at or beyond 20 weeks of gestation from 2000 through 2005 (n = 1,771,225; 8% PTB). We estimated mean species exposures for each week of gestation from monitor-corrected Community Multi-Scale Air Quality modeling data. RDs and 95% confidence intervals (CIs) for four PTB categories were estimated for each exposure using linear regression, adjusted for maternal race/ethnicity, marital status, education, age, smoking, maximum temperature, ozone, and season of conception. We also adjusted for other species in multi-species models.

RESULTS

RDs varied by exposure window and outcome period. EC was positively associated with PTB after 27 and before 35 weeks of gestation. For example, for a 0.25-μg/m(3) increase in EC exposure during gestational week 9, RD = 96 (95% CI: -20, 213) and RD = 145 (95% CI: -50, 341) for PTB during weeks 28-31 and 32-34, respectively. Associations with OCs were null or negative. RDs for NO3 were elevated with exposure in early weeks of gestation, and null in later weeks. RDs for SO4 exposure were positively associated with PTB, though magnitude varied across gestational weeks. We observed effect measure modification for associations between EC and PTB by race/ethnicity and smoking status.

CONCLUSION

EC and SO4 may contribute to associations between PM2.5 and PTB. Associations varied according to the timing of exposure and the timing of PTB.

Alterations in DNA methylation corresponding with lung inflammation and as a biomarker for disease development after MWCNT exposure

Use of multi-walled carbon nanotubes (MWCNT) is growing which increases occupational exposures to these materials. Their toxic potential makes it important to have an in-depth understanding of the inflammation and disease that develops due to exposure. Epigenetics is one area of interest that has been quickly developing to assess disease processes due to its ability to change gene expression and thus the lung environment after exposure. In this study, promoter methylation of inflammatory genes (IFN-γ and TNF-α) was measured after MWCNT exposure using the pyrosequencing assay and found to correlate with initial cytokine production. In addition, methylation of a gene involved in tissue fibrosis (Thy-1) was also altered in a way that matched collagen deposition. In addition to using epigenetics to better understand disease processes, it has also been used as a biomarker of exposure and disease. In this study, global methylation was determined in the lung to ascertain whether MWCNT alter global methylation at the site of exposure and if those alterations coincide with disease development. Then, global methylation levels were determined in the blood to ascertain whether global methylation could be used as a biomarker of exposure in a more easily accessible tissue. Using the LuUminometric Methylation Assay (LUMA) and 5-Methylcytosine (5-mC) Quantification assay, we found that MWCNT lead to DNA hypomethylation in the lung and blood, which coincided with disease development. This study provides initial data showing that alterations in gene-specific methylation correspond with an inflammatory response to MWCNT exposure. In addition, global DNA methylation in the lung and blood coincides with MWCNT-induced disease development, suggesting its potential as a biomarker of both exposure and disease development.

Environmental pollution and DNA methylation: carcinogenesis, clinical significance, and practical applications

Environmental pollution is one of the main causes of human cancer. Exposures to environmental carcinogens result in genetic and epigenetic alterations which induce cell transformation. Epigenetic changes caused by environmental pollution play important roles in the development and progression of environmental pollution-related cancers. Studies on DNA methylation are among the earliest and most conducted epigenetic research linked to cancer. In this review, the roles of DNA methylation in carcinogenesis and their significance in clinical medicine were summarized, and the effects of environmental pollutants, particularly air pollutants, on DNA methylation were introduced. Furthermore, prospective applications of DNA methylation to environmental pollution detection and cancer prevention were discussed.

Air pollution and public health: emerging hazards and improved understanding of risk

Despite past improvements in air quality, very large parts of the population in urban areas breathe air that does not meet European standards let alone the health-based World Health Organisation Air Quality Guidelines. Over the last 10 years, there has been a substantial increase in findings that particulate matter (PM) air pollution is not only exerting a greater impact on established health endpoints, but is also associated with a broader number of disease outcomes. Data strongly suggest that effects have no threshold within the studied range of ambient concentrations, can occur at levels close to PM2.5 background concentrations and that they follow a mostly linear concentration-response function. Having firmly established this significant public health problem, there has been an enormous effort to identify what it is in ambient PM that affects health and to understand the underlying biological basis of toxicity by identifying mechanistic pathways-information that in turn will inform policy makers how best to legislate for cleaner air. Another intervention in moving towards a healthier environment depends upon the achieving the right public attitude and behaviour by the use of optimal air pollution monitoring, forecasting and reporting that exploits increasingly sophisticated information systems. Improving air quality is a considerable but not an intractable challenge. Translating the correct scientific evidence into bold, realistic and effective policies undisputedly has the potential to reduce air pollution so that it no longer poses a damaging and costly toll on public health.

Beyond the Mean: Quantile Regression to Explore the Association of Air Pollution with Gene-Specific Methylation in the Normative Aging Study

BACKGROUND

Air pollution has been related to mean changes in outcomes, including DNA methylation. However, mean regression analyses may not capture associations that occur primarily in the tails of the outcome distribution.

OBJECTIVES

In this study, we examined whether the association between particulate air pollution and DNA methylation differs across quantiles of the methylation distribution. We focused on methylation of candidate genes related to coagulation and inflammation: coagulation factor III (F3), intercellular adhesion molecule 1 (ICAM-1), interferon gamma (IFN-γ), interleukin-6 (IL-6), and toll-like receptor 2 (TRL-2).

METHODS

We measured gene-specific blood DNA methylation repeatedly in 777 elderly men participating in the Normative Aging Study (1999-2010). We fit quantile regressions for longitudinal data to investigate whether the associations of particle number, PM2.5 (diameter ≤ 2.5 μm)black carbon, and PM2.5 mass concentrations (4-week moving average) with DNA methylation [expressed as the percentage of methylated cytosines over the sum of methylated and unmethylated cytosines at position 5 (%5mC)] varied across deciles of the methylation distribution. We reported the quantile regression coefficients that corresponded to absolute differences in DNA methylation (expressed in %5mC) associated with an interquartile range increase in air pollution concentration.

RESULTS

Interquartile range increases in particle number, PM2.5 black carbon, and PM2.5 mass concentrations were associated with significantly lower methylation in the lower tails of the IFN-γ and ICAM-1 methylation distributions. For instance, a 3.4-μg/m3 increase in PM2.5 mass concentration was associated with a 0.18%5mC (95% CI: -0.30, -0.06) decrease on the 20th percentile of ICAM-1 methylation, but was not significantly related to the 80th percentile (estimate: 0.07%5mC, 95% CI: -0.09, 0.24).

CONCLUSIONS

In our study population of older men, air pollution exposures were associated with a left shift in the lower tails of the IFN-γ and ICAM-1 methylation distributions.

Epidemiology of air pollution and diabetes

Air pollution affects a large proportion of the global population. Air pollutants are hypothesized to exert their effects via impaired endothelial function, elevated systemic inflammation, mitochondrial dysfunction, and oxidative stress, all of which are hallmarks of type 2 diabetes (T2D). Here we review epidemiological studies aimed at answering whether diabetes patients are more vulnerable to ambient (outdoor) air pollution exposure and whether air pollution is associated with diabetes development or other predisposing conditions for T2D. Current evidence suggests an association between air pollution exposure and T2D, but more critical analysis is warranted. Understanding the associations between air pollution exposure and the development of T2D is critical in our efforts to control sources of air pollution and their impact on the disease.

Response of biomarkers of inflammation and coagulation to short-term changes in central site, local, and predicted particle number concentrations

PURPOSE

Previous studies have reported acute (hours-28 days) associations between ambient ultrafine particles (UFP; diameter <0.1) and biomarkers of cardiovascular health using central site data. We evaluated particle number concentration (a proxy measure for UFP) measured at a central site, a local near-highway site and predicted residential concentrations with response of biomarkers of inflammation and coagulation in a near-highway population.

METHODS

Participants provided two blood samples for analysis of interleukin-6 (IL-6), high-sensitivity C-reactive protein (hs-CRP), tumor necrosis factor-α receptor II, and fibrinogen. Mixed effect models were used to evaluate the association between PNC levels on the same day, prior 2 days, and moving averages of 3 to 28 days.

RESULTS

Estimated effects on biomarkers of a 5000 unit increase in central site PNC generally increased with longer averaging times for IL-6, hs-CRP, and fibrinogen. Effect estimates were highest for a 28-day moving average, with 91% (95% confidence interval [CI]: 9, 230) higher IL-6 levels, 74% (95% CI: -7, 220) higher hs-CRP levels, and 59% (95% CI: -13, 130) higher fibrinogen levels. We observed no clear trend between near-highway or predicted residential PNC and any of the biomarkers.

CONCLUSIONS

Only central site PNC increased blood markers of inflammation while near-highway and predicted residential values did not. We cannot fully explain this result, although differing PNC composition is a possibility. Future studies would assist in understanding these findings.

Weight-of-evidence evaluation of short-term ozone exposure and cardiovascular effects

There is a relatively large body of research on the potential cardiovascular (CV) effects associated with short-term ozone exposure (defined by EPA as less than 30 days in duration). We conducted a weight-of-evidence (WoE) analysis to assess whether it supports a causal relationship using a novel WoE framework adapted from the US EPA's National Ambient Air Quality Standards causality framework. Specifically, we synthesized and critically evaluated the relevant epidemiology, controlled human exposure, and experimental animal data and made a causal determination using the same categories proposed by the Institute of Medicine report Improving the Presumptive Disability Decision-making Process for Veterans ( IOM 2008). We found that the totality of the data indicates that the results for CV effects are largely null across human and experimental animal studies. The few statistically significant associations reported in epidemiology studies of CV morbidity and mortality are very small in magnitude and likely attributable to confounding, bias, or chance. In experimental animal studies, the reported statistically significant effects at high exposures are not observed at lower exposures and thus not likely relevant to current ambient ozone exposures in humans. The available data also do not support a biologically plausible mechanism for CV effects of ozone. Overall, the current WoE provides no convincing case for a causal relationship between short-term exposure to ambient ozone and adverse effects on the CV system in humans, but the limitations of the available studies preclude definitive conclusions regarding a lack of causation. Thus, we categorize the strength of evidence for a causal relationship between short-term exposure to ozone and CV effects as "below equipoise."

Interaction effects of temperature and ozone on lung function and markers of systemic inflammation, coagulation, and fibrinolysis: a crossover study of healthy young volunteers

BACKGROUND

Trends in climate suggest that extreme weather events such as heat waves will become more common. High levels of the gaseous pollutant ozone are associated with elevated temperatures. Ozone has been associated with respiratory diseases as well as cardiovascular morbidity and mortality and can reduce lung function and alter systemic markers of fibrinolysis. The interaction between ozone and temperature is unclear.

METHODS

Sixteen healthy volunteers were exposed in a randomized crossover study to 0.3 ppm ozone and clean air for 2 hr at moderate (22°C) temperature and again at an elevated temperature (32.5°C). In each case lung function was performed and blood taken before and immediately after exposure and the next morning.

RESULTS

Ozone exposure at 22°C resulted in a decrease in markers of fibrinolysis the next day. There was a 51.8% net decrease in PAI-1 (plasminogen activator inhibitor-1), a 12.1% net decrease in plasminogen, and a 17.8% net increase in D-dimer. These significantly differed from the response at 32.5°C, where there was a 44.9% (p = 0.002) and a 27.9% (p = 0.001) increase in PAI-1 and plasminogen, respectively, and a 12.5% (p = 0.042) decrease in D-dimer. In contrast, decrements in lung function following ozone exposure were comparable at both moderate and elevated temperatures (forced expiratory volume in 1 sec, -12.4% vs. -7.5%, p > 0.05). No changes in systemic markers of inflammation were observed for either temperature.

CONCLUSION

Ozone-induced systemic but not respiratory effects varied according to temperature. Our study suggests that at moderate temperature ozone may activate the fibrinolytic pathway, while at elevated temperature ozone may impair it. These findings provide a biological basis for the interaction between temperature and ozone on mortality observed in some epidemiologic studies.

The relation between past exposure to fine particulate air pollution and prevalent anxiety: observational cohort study

OBJECTIVE

To determine whether higher past exposure to particulate air pollution is associated with prevalent high symptoms of anxiety.

DESIGN

Observational cohort study.

SETTING

Nurses' Health Study.

PARTICIPANTS

71,271 women enrolled in the Nurses' Health Study residing throughout the contiguous United States who had valid estimates on exposure to particulate matter for at least one exposure period of interest and data on anxiety symptoms.

MAIN OUTCOME MEASURES

Meaningfully high symptoms of anxiety, defined as a score of 6 points or greater on the phobic anxiety subscale of the Crown-Crisp index, administered in 2004.

RESULTS

The 71,271 eligible women were aged between 57 and 85 years (mean 70 years) at the time of assessment of anxiety symptoms, with a prevalence of high anxiety symptoms of 15%. Exposure to particulate matter was characterized using estimated average exposure to particulate matter <2.5 μm in diameter (PM2.5) and 2.5 to 10 μm in diameter (PM2.5-10) in the one month, three months, six months, one year, and 15 years prior to assessment of anxiety symptoms, and residential distance to the nearest major road two years prior to assessment. Significantly increased odds of high anxiety symptoms were observed with higher exposure to PM2.5 for multiple averaging periods (for example, odds ratio per 10 µg/m(3) increase in prior one month average PM2.5: 1.12, 95% confidence interval 1.06 to 1.19; in prior 12 month average PM2.5: 1.15, 1.06 to 1.26). Models including multiple exposure windows suggested short term averaging periods were more relevant than long term averaging periods. There was no association between anxiety and exposure to PM2.5-10. Residential proximity to major roads was not related to anxiety symptoms in a dose dependent manner.

CONCLUSIONS

Exposure to fine particulate matter (PM2.5) was associated with high symptoms of anxiety, with more recent exposures potentially more relevant than more distant exposures. Research evaluating whether reductions in exposure to ambient PM2.5 would reduce the population level burden of clinically relevant symptoms of anxiety is warranted.

Effects of temperature and relative humidity on DNA methylation

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Cardiac autonomic dysfunction: particulate air pollution effects are modulated by epigenetic immunoregulation of Toll-like receptor 2 and dietary flavonoid intake

Background

Short‐term fine particles (PM_2.5) exposure is associated with reduced heart rate variability, a strong predictor of cardiac mortality among older people. Identifying modifiable factors that confer susceptibility is essential for intervention. We evaluated whether Toll‐like receptor 2 (TLR2) methylation, a reversible immune‐epigenetic process, and its dietary modulation by flavonoids and methyl nutrients, modify susceptibility to heart rate variability effects following PM_2.5 exposure.

Methods and Results

We measured heart rate variability and PM_2.5 repeatedly over 11 years (1275 total observations) among 573 elderly men from the Normative Aging Study. Blood TLR2 methylation was analyzed using pyrosequencing. Daily flavonoid and methyl nutrients intakes were assessed through the Food Frequency Questionnaire (FFQ). Every 10 μg/m³ increase in 48‐hour PM_2.5 moving average was associated with 7.74% (95% CI: −1.21% to 15.90%; P=0.09), 7.46% (95% CI: 0.99% to 13.50%; P=0.02), 14.18% (95% CI: 1.14% to 25.49%; P=0.03), and 12.94% (95% CI: −2.36% to 25.96%; P=0.09) reductions in root mean square of successive differences, standard deviation of normal‐to‐normal intervals, low‐frequency power, and high‐frequency power, respectively. Higher TLR2 methylation exacerbated the root mean square of successive differences, standard deviation of normal‐to‐normal intervals, low‐frequency, and high‐frequency reductions associated with heightened PM_2.5 (P_interaction=0.006, 0.03, 0.05, 0.04, respectively). Every interquartile‐range increase in flavonoid intake was associated with 5.09% reduction in mean TLR2 methylation (95% CI: 0.12% to 10.06%; P=0.05) and counteracted the effects of PM_2.5 on low frequency (P_interaction=0.05). No significant effect of methyl nutrients on TLR2 methylation was observed.

Conclusions

Higher TLR2 methylation may confer susceptibility to adverse cardiac autonomic effects of PM_2.5 exposure in older individuals. Higher flavonoid intake may attenuate these effects, possibly by decreasing TLR2 methylation.

Clinical applications of epigenetics in cardiovascular disease: the long road ahead

Epigenetic processes, defined as heritable changes in gene expression that occur without changes to the DNA sequence, have emerged as a promising area of cardiovascular disease research. Epigenetic information transcends that of the genotype alone and provides for an integrated etiologic picture of cardiovascular disease pathogenesis because of the interaction of the epigenome with the environment. Epigenetic biomarkers, which include DNA methylation, histone modifications, and RNA-based mechanisms, are both modifiable and cell-type specific, which makes them not only responsive to the environment, but also an attractive target for drug development. However, the enthusiasm surrounding possible applications of cardiovascular epigenetics currently outpaces available evidence. In this review, the authors synthesize the evidence linking epigenetic changes with cardiovascular disease, emphasizing the gap between the translational potential and the clinical reality of cardiovascular epigenetics.

Environmental NO2 level is associated with 2-year mortality in patients undergoing peritoneal dialysis

An ongoing issue related to global urbanization is the association of air pollution with increased incidences of morbidity and mortality. However, no in-depth study has investigated this issue focusing on peritoneal dialysis (PD) patients. Therefore, this study assessed the effects of traffic-related air pollutants and other important mortality-associated factors on 2-year mortality in PD patients.A total of 160 PD patients were recruited in this 2-year retrospective observational study. Differences in air quality were analyzed with respect to the patients' living areas. The PD patients were categorized into 2 groups according to high (n = 65) and low (n = 95) nitrogen dioxide (NO2) exposure. Demographic, hematological, nutritional, inflammatory, biochemical, air pollutants, and dialysis-related data were analyzed. Univariate and multivariate Cox regression analyses were used for 2-year mortality analysis.A total of 160 PD patients (38 men and 122 women) were enrolled. Fourteen patients (8.8%) died within 2 years; among them, the causes of death were infection (n = 10), malignancy (n = 1), and cardiovascular events (n = 3). Among the 10 patients who died from infection, 5, 4, and 1 died from pneumonia, PD-related peritonitis, and sepsis of unknown origin, respectively. All patients who died from pneumonia were living in high environmental NO2 exposure areas. Multivariate Cox regression analysis showed that age (hazard ratio [HR] 1.073, 95% confidence interval [CI] [1.013-1.137]; P = 0.017), white blood cell count (HR 1.41, 95% CI [1.116-1.781]; P = 0.004), log normalized protein nitrogen appearance (HR 0.0001, 95% CI [0-0.073]; P = 0.005), high cardiothoracic ratio (HR 14.28, 95% CI [1.778-114.706]; P = 0.012), and high environmental NO2 exposure (HR 3.776, 95% CI [1.143-12.47]; P = 0.029) were significantly associated with 2-year mortality.PD patients with high environmental NO2 exposure had a higher 2-year mortality rate than those with low exposure. Therefore, air pollution may be associated with 2-year mortality in such patients.

The cardiopulmonary effects of ambient air pollution and mechanistic pathways: a comparative hierarchical pathway analysis

Previous studies have investigated the associations between exposure to ambient air pollution and biomarkers of physiological pathways, yet little has been done on the comparison across biomarkers of different pathways to establish the temporal pattern of biological response. In the current study, we aim to compare the relative temporal patterns in responses of candidate pathways to different pollutants. Four biomarkers of pulmonary inflammation and oxidative stress, five biomarkers of systemic inflammation and oxidative stress, ten parameters of autonomic function, and three biomarkers of hemostasis were repeatedly measured in 125 young adults, along with daily concentrations of ambient CO, PM2.5, NO2, SO2, EC, OC, and sulfate, before, during, and after the Beijing Olympics. We used a two-stage modeling approach, including Stage I models to estimate the association between each biomarker and pollutant over each of 7 lags, and Stage II mixed-effect models to describe temporal patterns in the associations when grouping the biomarkers into the four physiological pathways. Our results show that candidate pathway groupings of biomarkers explained a significant amount of variation in the associations for each pollutant, and the temporal patterns of the biomarker-pollutant-lag associations varied across candidate pathways (p<0.0001) and were not linear (from lag 0 to lag 3: p = 0.0629, from lag 3 to lag 6: p = 0.0005). These findings suggest that, among this healthy young adult population, the pulmonary inflammation and oxidative stress pathway is the first to respond to ambient air pollution exposure (within 24 hours) and the hemostasis pathway responds gradually over a 2-3 day period. The initial pulmonary response may contribute to the more gradual systemic changes that likely ultimately involve the cardiovascular system.

Environmental effects on immune responses in patients with atopy and asthma

Despite attempts and some successes to improve air quality over the decades, current US national trends suggest that exposure to outdoor and indoor air pollution remains a significant risk factor for both the development of asthma and the triggering of asthma symptoms. Emerging science also suggests that environmental exposures during the prenatal period and early childhood years increase the risk of asthma. Multiple mechanisms mediate this risk because a wide range of deleterious air pollutants contribute to the pathogenesis of asthma across a variety of complex asthma phenotypes. In this review we will consider the role of altered innate and adaptive immune responses, gene-environment interactions, epigenetic regulation, and possibly gene-environment-epigene interactions. Gaining a greater understanding of the mechanisms that underlie the effect of exposure to air pollution on asthma, allergies, and other airway diseases can identify targets for therapy. Such interventions will include pollutant source reduction among those most exposed and most vulnerable and novel pharmaceutical strategies to reduce asthma morbidity.

Environmental carbon monoxide level is associated with the level of high-sensitivity C-reactive protein in peritoneal dialysis patients

Inflammation is highly prevalent among peritoneal dialysis (PD) patients. High-sensitivity C-reactive protein (hs-CRP) is the most widely used inflammatory marker in clinical medicine and is correlated with mortality in PD patients. Air pollution is associated with systemic inflammation. The aim of this cross-sectional study was to assess the role of air pollutants and other clinical variables on hs-CRP values in PD patients.We recruited a total of 175 patients who had been undergoing continuous ambulatory PD or automated PD for at least 4 months and regularly followed up. Air pollution levels were recorded by a network of 27 monitoring stations near or in the patients' living areas throughout Taiwan. The 12-month average concentrations of particulate matter (PM) with an aerodynamic diameter of <10 and <2.5 μm (PM10 and PM2.5), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3) were included.In stepwise linear regression, after adjustment for related factors, white blood cell count (β: 0.27, 95% confidence interval [CI] [0.71, 2.11]) and CO level (β: 0.17, 95% CI [2.5, 21.32]) were positively associated with hs-CRP and serum albumin levels (β: -0.25, 95% CI [-13.69, -3.96]) and normalized protein nitrogen appearance (β: -0.18, 95% CI [-17.7, -2.51]) was negatively associated with hs-CRP. However, serum indoxyl sulfate and p-cresyl sulfate levels were not significantly associated with hs-CRP (P > 0.05).In PD patients, the environmental CO level was positively correlated with hs-CRP level.

Ambient Air Pollution and Hypertensive Disorders of Pregnancy: A Systematic Review and Meta-analysis

Hypertensive disorders of pregnancy (HDP, including gestational hypertension, preeclampsia, and eclampsia) have a substantial public health impact. Maternal exposure to high levels of air pollution may trigger HDP, but this association remains unclear. The objective of our report is to assess and quantify the association between maternal exposures to criteria air pollutants (ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, and particulate matter ≤ 10, 2.5 μm) on HDP risk. PubMed, EMBASE, MEDLINE, Current Contents, Global Health, and Cochrane were searched (last search: September, 2013). After a detailed screening of 270 studies, 10 studies were extracted. We conducted meta-analyses if a pollutant in a specific exposure window was reported by at least four studies. Using fixed- and random-effects models, odds ratios (ORs) and 95% CIs were calculated for each pollutant with specific increment of concentration. Increases in risks of HDP (OR per 10 ppb = 1.16; 95% CI, 1.03-1.30) and preeclampsia (OR per 10 ppb = 1.10; 95% CI, 1.03-1.17) were observed to be associated with exposure to NO2 during the entire pregnancy, and significant associations between HDP and exposure to CO (OR per 1 ppm = 1.79; 95% CI, 1.31-2.45) and O3 (OR per 10 ppb = 1.09; 95% CI, 1.05-1.13) during the first trimester were also observed. Our review suggests an association between ambient air pollution and HDP risk. Although the ORs were relatively low, the population-attributable fractions were not negligible given the ubiquitous nature of air pollution.

Environmental risk factors for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) remains a major cause of morbidity and mortality in critically ill patients. Over the past several decades, alcohol abuse and cigarette smoke exposure have been identified as risk factors for the development of ARDS. The mechanisms underlying these relationships are complex and remain under investigation but are thought to involve pulmonary immune impairment and alveolar epithelial and endothelial dysfunction. This review summarizes the epidemiologic data supporting links between these exposures and ARDS susceptibility and outcomes and highlights key mechanistic investigations that provide insight into the pathways by which each exposure is linked to ARDS.

Genome-wide investigation of DNA methylation marks associated with FV Leiden mutation

In order to investigate whether DNA methylation marks could contribute to the incomplete penetrance of the FV Leiden mutation, a major genetic risk factor for venous thrombosis (VT), we measured genome-wide DNA methylation levels in peripheral blood samples of 98 VT patients carrying the mutation and 251 VT patients without the mutation using the dedicated Illumina HumanMethylation450 array. The genome-wide analysis of 388,120 CpG probes identified three sites mapping to the SLC19A2 locus whose DNA methylation levels differed significantly (p<3 10-8) between carriers and non-carriers. The three sites replicated (p<2 10-7) in an independent sample of 214 individuals from five large families ascertained on VT and FV Leiden mutation among which 53 were carriers and 161 were non-carriers of the mutation. In both studies, these three CpG sites were also associated (2.33 10-110.05). In conclusion, our work clearly illustrates some promises and pitfalls of DNA methylation investigations on peripheral blood DNA in large epidemiological cohorts. DNA methylation levels at SLC19A2 are influenced by SNPs in LD with FV Leiden, but these DNA methylation marks do not explain the incomplete penetrance of the FV Leiden mutation.

Ambient Air Pollution and Pregnancy-Induced Hypertensive Disorders

Pregnancy-induced hypertensive disorders can lead to maternal and perinatal morbidity and mortality, but the cause of these conditions is not well understood. We have systematically reviewed and performed a meta-analysis of epidemiological studies investigating the association between exposure to ambient air pollution and pregnancy-induced hypertensive disorders including gestational hypertension and preeclampsia. We searched electronic databases for English language studies reporting associations between ambient air pollution and pregnancy-induced hypertensive disorders published between December 2009 and December 2013. Combined risk estimates were calculated using random-effect models for each exposure that had been examined in ≥4 studies. Heterogeneity and publication bias were evaluated. A total of 17 articles evaluating the impact of nitrogen oxides (NO 2 , NO X ), particulate matter (PM 10 , PM 2.5 ), carbon monoxide (CO), ozone (O 3 ), proximity to major roads, and traffic density met our inclusion criteria. Most studies reported that air pollution increased risk for pregnancy-induced hypertensive disorders. There was significant heterogeneity in meta-analysis, which included 16 studies reporting on gestational hypertension and preeclampsia as separate or combined outcomes; there was less heterogeneity in findings of the 10 studies reporting solely on preeclampsia. Meta-analyses showed increased risks of hypertensive disorders in pregnancy for all pollutants except CO. Random-effect meta-analysis combined odds ratio associated with a 5-µg/m 3 increase in PM 2.5 was 1.57 (95% confidence interval, 1.26–1.96) for combined pregnancy-induced hypertensive disorders and 1.31 (95% confidence interval, 1.14–1.50) for preeclampsia. Our results suggest that exposure to air pollution increases the risk of pregnancy-induced hypertensive disorders.

Effect of particulate air pollution and passive smoking on surrogate biomarkers of endothelial dysfunction in healthy children

BACKGROUND

This study aimed to determine the association of ambient particulate matter (PM) on surrogate markers of endothelial function and inflammation in healthy children with or without exposure to second-hand smoke.

METHODS

This cross-sectional study was conducted in 2011 in Isfahan, which is the second largest and second most air-polluted city in Iran. The areas of the city with lowest and highest air pollution were determined, and in each area, 25 pre-pubescent boys with or without exposure to daily tobacco smoke at home were selected, i.e. 100 children were studied in total. Serum levels of C-reactive protein (CRP) and nitric oxide (NO) were measured.

RESULTS

Mean (SD) NO concentration was 7·87 (2·18) and 7·75 (2·04) μmol/L for participants not exposed and exposed to passive smoking, respectively, which is not statistically significant. The corresponding figures for CRP concentrations were 1·69 (0·89) and 2·13 (1·19) μg/ml (P = 0·04). Mean (SD) CRP concentration was significantly higher in children living in the highly polluted area than in those in the area of low pollution [2·11 (1·91) vs 1·60 (1·43) μg/ml, respectively, P = 0·02]. This difference was not significant for NO concentration. The regression analysis that examined the association between PM concentration (as independent variable) and CRP and NO levels (as dependent variables) in children not exposed to passive smoking demonstrated that increased PM was associated with a decrease in NO and an increase in CRP concentration. This finding shows that, regardless of passive smoking, PM10 concentration has a significant independent association with serum CRP and is inversely associated with NO levels.

CONCLUSION

The findings suggest that in healthy children PM concentration has a significant independent association with biomarkers of endothelial dysfunction and inflammation.

Inhalation of ultrafine carbon particles alters heart rate and heart rate variability in people with type 2 diabetes

BACKGROUND

Diabetes may confer an increased risk for the cardiovascular health effects of particulate air pollution, but few human clinical studies of air pollution have included people with diabetes. Ultrafine particles (UFP, ≤100 nm in diameter) have been hypothesized to be an important component of particulate air pollution with regard to cardiovascular health effects.

METHODS

17 never-smoker subjects 30-60 years of age, with stable type 2 diabetes but otherwise healthy, inhaled either filtered air (0-10 particles/cm3) or elemental carbon UFP (~107 particles/cm3, ~50 ug/m3, count median diameter 32 nm) by mouthpiece, for 2 hours at rest, in a double-blind, randomized, crossover study design. A digital 12-lead electrocardiogram (ECG) was recorded continuously for 48 hours, beginning 1 hour prior to exposure.

RESULTS

Analysis of 5-minute segments of the ECG during quiet rest showed reduced high-frequency heart rate variability with UFP relative to air exposure (p = 0.014), paralleled by non-significant reductions in time-domain heart rate variability parameters. In the analysis of longer durations of the ECG, we found that UFP exposure increased the heart rate relative to air exposure. During the 21- to 45-hour interval after exposure, the average heart rate increased approximately 8 beats per minute with UFP, compared to 5 beats per minute with air (p = 0.045). There were no UFP effects on cardiac rhythm or repolarization.

CONCLUSIONS

Inhalation of elemental carbon ultrafine particles alters heart rate and heart rate variability in people with type 2 diabetes. Our findings suggest that effects may occur and persist hours after a single 2-hour exposure.

Association between source-specific particulate matter air pollution and hs-CRP: local traffic and industrial emissions

BACKGROUND

Long-term exposures to particulate matter air pollution (PM2.5 and PM10) and high traffic load have been associated with markers of systemic inflammation. Epidemiological investigations have focused primarily on total PM, which represents a mixture of pollutants originating from different sources.

OBJECTIVE

We investigated associations between source-specific PM and high-sensitive C-reactive protein (hs-CRP), an independent predictor of cardiovascular disease.

METHODS

We used data from the first (2000-2003) and second examination (2006-2008) of the Heinz Nixdorf Recall study, a prospective population-based German cohort of initially 4,814 participants (45-75 years of age). We estimated residential long-term exposure to local traffic- and industry-specific fine particulate matter (PM2.5) at participants' residences using a chemistry transport model. We used a linear mixed model with a random participant intercept to estimate associations of source-specific PM and natural log-transformed hs-CRP, controlling for age, sex, education, body mass index, low- and high-density lipoprotein cholesterol, smoking variables, physical activity, season, humidity, and city (8,204 total observations).

RESULTS

A 1-μg/m3 increase in total PM2.5 was associated with a 4.53% increase in hs-CRP concentration (95% CI: 2.76, 6.33%). hs-CRP was 17.89% (95% CI: 7.66, 29.09%) and 7.96% (95% CI: 3.45, 12.67%) higher in association with 1-μg/m3 increases in traffic- and industry-specific PM2.5, respectively. RESULTS for PM10 were similar.

CONCLUSIONS

Long-term exposure to local traffic-specific PM (PM2.5, PM10) was more strongly associated with systemic inflammation than total PM. Associations of local industry-specific PM were slightly stronger but not significantly different from associations with total PM.

An evidence-based appraisal of global association between air pollution and risk of stroke

BACKGROUND

The aim of this study was to evaluate the transient effects of air pollutants on stroke morbidity and mortality using the meta-analytic approach.

METHODS

Three databases were searched for case-crossover and time series studies assessing associations between daily increases in particles with diameter<2.5 μm (PM2.5) and diameter<10 μm (PM10), sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide (NO2), ozone, and risks of stroke hospitalizations and mortality. Risk estimates were combined using random-effects model.

RESULTS

A total of 34 studies were included in the meta-analysis. Stroke hospitalizations or mortality increased 1.20% (95%CI: 0.22-2.18) per 10 μg/m3 increase in PM2.5, 0.58% (95%CI: 0.31-0.86) per 10 μg/m3 increase in PM10, 1.53% (95%CI: 0.66-2.41) per 10 parts per billion (ppb) increase in SO2, 2.96% (95%CI: 0.70-5.27) per 1 ppm increase in CO, and 2.24% (95%CI: 1.16-3.33) per 10ppb increase in NO2. These positive associations were the strongest on the same day of exposure, and appeared to be more apparent for ischemic stroke (for all 4 gaseous pollutants) and among Asian countries (for all 6 pollutants). In addition, an elevated risk (2.45% per 10 ppb; 95%CI: 0.35-4.60) of ischemic stroke associated with ozone was found, but not for hemorrhagic stroke.

CONCLUSION

Our study indicates that air pollution may transiently increase the risk of stroke hospitalizations and stroke mortality. Although with a weak association, these findings if validated may be of both clinical and public health importance given the great global burden of stroke and air pollution.

Effects of short-term exposure to inhalable particulate matter on DNA methylation of tandem repeats

There is compelling evidence that particulate matter (PM) increases lung cancer risk by triggering systemic inflammation, and leukocyte DNA hypomethylation. However, previous investigations focused on repeated element sequences from LINE-1 and Alu families. Tandem repeats, which display a greater propensity to mutate, and are often hypomethylated in cancer patients, have never been investigated in individuals exposed to PM. We measured methylation of three tandem repeats (SATα, NBL2, and D4Z4) by polymerase chain reaction-pyrosequencing on blood samples from truck drivers and office workers (60 per group) in Beijing, China. We used lightweight monitors to measure personal PM2.5 (PM with aerodynamic diameter ≤2.5 µm) and elemental carbon (a tracer of PM from vehicular traffic). Ambient PM10 data were obtained from air quality measuring stations. Overall, an interquartile increase in personal PM2.5 and ambient PM10 levels was associated with a significant covariate-adjusted decrease in SATα methylation (-1.35% 5-methyl cytosine [5mC], P = 0.01; and -1.33%5mC; P = 0.01, respectively). Effects from personal PM2.5 and ambient PM10 on SATα methylation were stronger in truck drivers (-2.34%5mC, P = 0.02; -1.44%5mC, P = 0.06) than office workers (-0.95%5mC, P = 0.26; -1.25%5mC, P = 0.12, respectively). Ambient PM10 was negatively correlated with NBL2 methylation in truck drivers (-1.38%5mC, P = 0.03) but not in office workers (1.04%5mC, P = 0.13). Our result suggests that PM exposure is associated with hypomethylation of selected tandem repeats. Measuring tandem-repeat hypomethylation in easy-to-obtain blood specimens might identify individuals with biological effects and potential cancer risk from PM exposure.

A novel genetic score approach using instruments to investigate interactions between pathways and environment: application to air pollution

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 (p(interaction) = 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 (p(interaction) = 0.12), CRP (p(interaction) = 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.