Placental DNA hypomethylation in association with particulate air pollution in early life.

BACKGROUND: There is evidence that altered DNA methylation is an important epigenetic mechanism in prenatal programming and that developmental periods are sensitive to environmental stressors. We hypothesized that exposure to fine particles (PM2.5) during pregnancy could influence DNA methylation patterns of the placenta. METHODS: In the ENVIRONAGE birth cohort, levels of 5'-methyl-deoxycytidine (5-mdC) and deoxycytidine (dC) were quantified in placental DNA from 240 newborns. Multiple regression models were used to study placental global DNA methylation and in utero exposure to PM2.5 over various time windows during pregnancy. RESULTS: PM2.5 exposure during pregnancy averaged (25th-75th percentile) 17.4 (15.4-19.3) µg/m3. Placental global DNA methylation was inversely associated with PM2.5 exposures during whole pregnancy and relatively decreased by 2.19% (95% confidence interval [CI]: -3.65, -0.73%, p = 0.004) for each 5 µg/m3 increase in exposure to PM2.5. In a multi-lag model in which all three trimester exposures were fitted as independent variables in the same regression model, only exposure to PM2.5 during trimester 1 was significantly associated with lower global DNA methylation (-2.13% per 5 µg/m3 increase, 95% CI: -3.71, -0.54%, p = 0.009). When we analyzed shorter time windows of exposure within trimester 1, we observed a lower placental DNA methylation at birth during all implantation stages but exposure during the implantation range (6-21d) was strongest associated (-1.08% per 5 µg/m3 increase, 95% CI: -1.80, -0.36%, p = 0.004). CONCLUSIONS: We observed a lower degree of placental global DNA methylation in association with exposure to particulate air pollution in early pregnancy, including the critical stages of implantation. Future studies should elucidate genome-wide and gene-specific methylation patterns in placental tissue that could link particulate exposure during in utero life and early epigenetic modulations.

Host and environmental predictors of exhaled breath temperature in the elderly.

BACKGROUND: Exhaled breath temperature has been suggested as a new method to detect and monitor pathological processes in the respiratory system. The putative mechanism of this approach is based upon changes in the blood flow. So far potential factors that influence breath temperature have not been studied in the general population. METHODS: The exhaled breath temperature was measured in 151 healthy non-smoking elderly (aged: 60-80 years) at room temperature with the X-halo device with an accuracy of 0.03°C. We related exhaled breath temperature by use of regression models with potential predictors including: host factors (sex, age) and environmental factors (BMI, physical activity, and traffic indicators). RESULTS: Exhaled breath temperature was lower in women than in men and was inversely associated with age, physical activity. BMI and daily average ambient temperature were positively associated with exhaled breath temperature. Independent of the aforementioned covariates, exhaled breath temperature was significantly associated with several traffic indicators. Residential proximity to major road was inversely associated with exhaled breath temperature: doubling the distance to the nearest major intense road was observed a decrease of 0.17°C (95% CI: -0.33 to -0.01; p=0.036). CONCLUSIONS: Exhaled breath temperature has been suggested as a noninvasive method for the evaluation of airway inflammation. We provide evidence that several factors known to be involved in proinflammatory conditions including BMI, physical activity and residential proximity to traffic affect exhaled breath temperature. In addition, we identified potential confounders that should be taken into account in clinical and epidemiological studies on exhaled breath temperature including sex, age, and ambient temperature.

Child's buccal cell mitochondrial DNA content modifies the association between heart rate variability and recent air pollution exposure at school.

BACKGROUND: Studies investigating short-term exposure to ambient air pollution and heart rate variability (HRV) suggest that particulate matter (PM) exposure is associated with reductions in measures of HRV. Mitochondria are sensitive to PM exposure and may represent a biologically relevant underlying mechanism. However, evidence in children is lacking. OBJECTIVES: Here we examine whether PM has an influence on children's HRV and evaluate whether mitochondrial DNA content (mtDNAc) reflects individual susceptibility. METHODS: Within a panel study in primary school children (aged 9-12 years), we measured HRV in a subset of 60 children on three different days during school-time using four indicators: normal-to-normal intervals (SDNN), square root of mean squared difference of normal-to-normal intervals (rMSSD), high frequency (HF), and low frequency (LF). This resulted in a total number of 150 visits (median number of visits per child: 2.5/child). MtDNAc was measured using qPCR in buccal cells. We measured recent PM exposure at the school. Residential 24-hour mean exposure to PM was modelled with a high resolution spatial temporal model. Mixed-effects models were used to estimate the association between HRV and recent PM exposure and potential effect-modification by mtDNAc. RESULTS: Children were on average [SD] 9.9 [1.2] years and comprised 39 girls. Median [25th-75th] recent outdoor PM2.5 and PM10 exposure at school was 6.20 [2.8-12.8] µg/m3 and 29.3 [24.7-42.0] µg/m3, respectively. In children with low mtDNAc (25th percentile), we observed for each 10 µg/m3 increment in recent PM2.5 exposure a lowering in the LF parameter with 9.76% (95% CI: -16.9 to -1.99%, p = 0.02; pint = 0.007). Children with high mtDNAc did not show this association. For PM10 exposure, we observed an inverse association with three HRV indicators in children with low mtDNAc: -2.24% (95% CI: -4.27 to -0.16%; p = 0.04; pint = 0.02) for SDNN, -5.67% (95% CI: -10.5 to -0.59%; p = 0.03; pint = 0.04) for HF and -6.64% (95% CI: -10.7 to -2.38%; p = 0.003; pint = 0.005) for LF. CONCLUSIONS: HRV is inversely associated with recent PM air pollution, especially in children with low mtDNAc. Our data revealed that mtDNAc determines susceptibility to adverse autonomic effects of recent PM exposure in children.

Biomolecular Markers within the Core Axis of Aging and Particulate Air Pollution Exposure in the Elderly: A Cross-Sectional Study.

BACKGROUND: Telomere length and mitochondrial DNA (mtDNA) content are markers of aging and aging-related diseases. There is inconclusive evidence concerning the mechanistic effects of airborne particulate matter (PM) exposure on biomolecular markers of aging. OBJECTIVE: The present study examines the association between short- and long-term PM exposure with telomere length and mtDNA content in the elderly and investigates to what extent this association is mediated by expression of genes playing a role in the telomere-mitochondrial axis of aging. METHODS: Among 166 nonsmoking elderly participants, we used qPCR to measure telomere length and mtDNA content in leukocytes and RNA from whole blood to measure expression of SIRT1, TP53, PPARGC1A, PPARGC1B, NRF1, and NFE2L2. Associations between PM exposure and markers of aging were estimated using multivariable linear regression models adjusted for sex, age, BMI, socioeconomic status, statin use, past smoking status, white blood cell count, and percentage of neutrophils. Mediation analysis was performed to explore the role of age-related markers between the association of PM exposure and outcome. Annual PM2.5 exposure was calculated for each participant's home address using a high-resolution spatial-temporal interpolation model. RESULTS: Annual PM2.5 concentrations ranged from 15 to 23 µg/m3. A 5-µg/m3 increment in annual PM2.5 concentration was associated with a relative decrease of 16.8% (95% CI: -26.0%, -7.4%, p = 0.0005) in telomere length and a relative decrease of 25.7% (95% CI: -35.2%, -16.2%, p < 0.0001) in mtDNA content. Assuming causality, results of the mediation analysis indicated that SIRT1 mediated 19.5% and 22.5% of the estimated effect of PM2.5 exposure on telomere length and mtDNA content, respectively. CONCLUSIONS: Our findings suggest that the estimated effects of PM2.5 exposure on the telomere-mitochondrial axis of aging may play an important role in chronic health effects of PM2.5. CITATION: Pieters N, Janssen BG, Dewitte H, Cox B, Cuypers A, Lefebvre W, Smeets K, Vanpoucke C, Plusquin M, Nawrot TS. 2016. Biomolecular markers within the core axis of aging and particulate air pollution exposure in the elderly: a cross-sectional study. Environ Health Perspect 124:943-950; http://dx.doi.org/10.1289/ehp.1509728.

Prenatal Ambient Air Pollution, Placental Mitochondrial DNA Content, and Birth Weight in the INMA (Spain) and ENVIRONAGE (Belgium) Birth Cohorts.

BACKGROUND: Mitochondria are sensitive to environmental toxicants due to their lack of repair capacity. Changes in mitochondrial DNA (mtDNA) content may represent a biologically relevant intermediate outcome in mechanisms linking air pollution and fetal growth restriction. OBJECTIVE: We investigated whether placental mtDNA content is a possible mediator of the association between prenatal nitrogen dioxide (NO2) exposure and birth weight. METHODS: We used data from two independent European cohorts: INMA (n = 376; Spain) and ENVIRONAGE (n = 550; Belgium). Relative placental mtDNA content was determined as the ratio of two mitochondrial genes (MT-ND1 and MTF3212/R3319) to two control genes (RPLP0 and ACTB). Effect estimates for individual cohorts and the pooled data set were calculated using multiple linear regression and mixed models. We also performed a mediation analysis. RESULTS: Pooled estimates indicated that a 10-µg/m3 increment in average NO2 exposure during pregnancy was associated with a 4.9% decrease in placental mtDNA content (95% CI: -9.3, -0.3%) and a 48-g decrease (95% CI: -87, -9 g) in birth weight. However, the association with birth weight was significant for INMA (-66 g; 95% CI: -111, -23 g) but not for ENVIRONAGE (-20 g; 95% CI: -101, 62 g). Placental mtDNA content was associated with significantly higher mean birth weight (pooled analysis, interquartile range increase: 140 g; 95% CI: 43, 237 g). Mediation analysis estimates, which were derived for the INMA cohort only, suggested that 10% (95% CI: 6.6, 13.0 g) of the association between prenatal NO2 and birth weight was mediated by changes in placental mtDNA content. CONCLUSION: Our results suggest that mtDNA content can be one of the potential mediators of the association between prenatal air pollution exposure and birth weight. CITATION: Clemente DB, Casas M, Vilahur N, Begiristain H, Bustamante M, Carsin AE, Fernández MF, Fierens F, Gyselaers W, Iñiguez C, Janssen BG, Lefebvre W, Llop S, Olea N, Pedersen M, Pieters N, Santa Marina L, Souto A, Tardón A, Vanpoucke C, Vrijheid M, Sunyer J, Nawrot TS. 2016. Prenatal ambient air pollution, placental mitochondrial DNA content, and birth weight in the INMA (Spain) and ENVIRONAGE (Belgium) birth cohorts. Environ Health Perspect 124:659-665; http://dx.doi.org/10.1289/ehp.1408981.

Telomere length, cardiovascular risk and arteriosclerosis in human kidneys: an observational cohort study.

BACKGROUND: Replicative senescence, associated with telomere shortening, plays an important role in aging and cardiovascular disease. The relation between telomere length, cardiovascular risk, and renal disease is unknown. METHODS: Our study consisted of a cohort of 257 kidney donors for transplantation, divided into a test and a validation cohort. We used quantitative RT-PCR to measure relative telomere length (log T/S ratio) in peripheral blood leucocytes, and in kidney biopsies performed prior to implantation. The association between leucocyte and intrarenal telomere length, cardiovascular risk factors, and renal histology, was studied using multiple regression models, adjusted for calendar age, gender and other donor demographics. RESULTS: Subjects with intrarenal arteriosclerosis had significantly shorter leucocyte telomere length compared with patients without arteriosclerosis (log T/S ratio -0.3±0.4 vs. 0.1±0.2 with vs. without arteriosclerosis; p=0.0008). Intrarenal arteriosclerosis was associated with shorter telomere length, independent of gender, calendar age, history of hypertension and history of cardiovascular events. For each increase of one standard deviation of the log T/S ratio, the odds for intrarenal arteriosclerosis decreased with 64% (Odds ratio 0.36; 95% CI 0.17-0.77; p=0.02). In accordance with leucocyte telomere length, shorter intrarenal telomere length associated significantly with the presence of renal arteriosclerosis (log T/S ratio -0.04±0.06 vs. 0.08±0.01 with vs. without arteriosclerosis, p=0.007), and not with other histological lesions. INTERPRETATION: We demonstrate that arteriosclerosis in smaller intrarenal arteries is associated with shorter telomere length. Our study suggests a central role of replicative senescence in the progression of renovascular disease, independent of calendar age.

Blood Pressure and Same-Day Exposure to Air Pollution at School: Associations with Nano-Sized to Coarse PM in Children.

BACKGROUND: Ultrafine particles (UFP) may contribute to the cardiovascular effects of particulate air pollution, partly because of their relatively efficient alveolar deposition. OBJECTIVE: In this study, we assessed associations between blood pressure and short-term exposure to air pollution in a population of schoolchildren. METHODS: In 130 children (6-12 years of age), blood pressure was determined during two periods (spring and fall 2011). We used mixed models to study the association between blood pressure and ambient concentrations of particulate matter and ultrafine particles measured in the schools' playground. RESULTS: Independent of sex, age, height, and weight of the child, parental education, neighborhood socioeconomic status, fish consumption, heart rate, school, day of the week, season, wind speed, relative humidity, and temperature on the morning of examination, an interquartile range (860 particles/cm3) increase in nano-sized UFP fraction (20-30 nm) was associated with a 6.35 mmHg (95% CI: 1.56, 11.14; p = 0.01) increase in systolic blood pressure. For the total UFP fraction, systolic blood pressure was 0.79 mmHg (95% CI: 0.07, 1.51; p = 0.03) higher, but no effects on systolic blood pressure were found for the nano-sized fractions with a diameter > 100 nm, nor PM2.5, PMcoarse, and PM10. Diastolic blood pressure was not associated with any of the studied particulate mass fractions. CONCLUSION: Children attending school on days with higher UFP concentrations (diameter < 100 nm) had higher systolic blood pressure. The association was dependent on UFP size, and there was no association with the PM2.5 mass concentration.

Molecular responses in the telomere-mitochondrial axis of ageing in the elderly: a candidate gene approach.

Experimental evidence shows that telomere shortening induces mitochondrial damage but so far studies in humans are scarce. Here, we investigated the association between leukocyte telomere length (LTL) and mitochondrial DNA (mtDNA) content in elderly and explored possible intermediate mechanisms by determining the gene expression profile of candidate genes in the telomere-mitochondrial axis of ageing. Among 166 non-smoking elderly, LTL, leukocyte mtDNA content and expression of candidate genes: sirtuin1 (SIRT1), tumor protein p53 (TP53), peroxisome proliferator-activated receptor γ-coactivator1α (PGC-1α), peroxisome proliferator-activated receptor γ-coactivator1ß (PGC-1ß), nuclear respiratory factor 1 (NRF1) and nuclear factor, erythroid 2 like 2 (NRF2), using a quantitave real time polymerase chain assay (qPCR). Statistical mediation analysis was used to study intermediate mechanisms of the telomere-mitochondrial axis of ageing. LTL correlated with leukocyte mtDNA content in our studied elderly (r = 0.23, p = 0.0047). SIRT1 gene expression correlated positively with LTL (r = 0.26, p = 0.0094) and leukocyte mtDNA content (r = 0.43, p < 0.0001). The other studied candidates showed significant correlations in the telomere-mitochondrial interactome but not independent from SIRT1. SIRT1 gene expression was estimated to mediate 40% of the positive association between LTL and leukocyte mtDNA content. The key finding of our study was that SIRT1 expression plays a pivotal role in the telomere-mitochondrial interactome.

Decreased mitochondrial DNA content in association with exposure to polycyclic aromatic hydrocarbons in house dust during wintertime: from a population enquiry to cell culture.

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants that are formed in combustion processes. At the cellular level, exposure to PAHs causes oxidative stress and/or some of it congeners bind to DNA, which may interact with mitochondrial function. However, the influence of these pollutants on mitochondrial DNA (mtDNA) content remains largely unknown. We determined whether indoor exposure to PAHs is associated with mitochondrial damage as represented by blood mtDNA content. Blood mtDNA content (ratio mitochondrial/nuclear DNA copy number) was determined by real-time qPCR in 46 persons, both in winter and summer. Indoor PAH exposure was estimated by measuring PAHs in sedimented house dust, including 6 volatile PAHs and 8 non-volatile PAHs. Biomarkers of oxidative stress at the level of DNA and lipid peroxidation were measured. In addition to the epidemiologic enquiry, we exposed human TK6 cells during 24 h at various concentrations (range: 0 to 500 µM) of benzo(a)pyrene and determined mtDNA content. Mean blood mtDNA content averaged (± SD) 0.95 ± 0.185. The median PAH content amounted 554.1 ng/g dust (25(th)-75(th) percentile: 390.7-767.3) and 1385 ng/g dust (25(th)-75(th) percentile: 1000-1980) in winter for volatile and non-volatile PAHs respectively. Independent for gender, age, BMI and the consumption of grilled meat or fish, blood mtDNA content decreased by 9.85% (95% CI: -15.16 to -4.2; p = 0.002) for each doubling of non-volatile PAH content in the house dust in winter. The corresponding estimate for volatile PAHs was -7.3% (95% CI: -13.71 to -0.42; p = 0.04). Measurements of oxidative stress were not correlated with PAH exposure. During summer months no association was found between mtDNA content and PAH concentration. The ability of benzo(a)pyrene (range 0 µM to 500 µM) to lower mtDNA content was confirmed in vitro in human TK6 cells. Based on these findings, mtDNA content can be a target of PAH toxicity in humans.

An epidemiological appraisal of the association between heart rate variability and particulate air pollution: a meta-analysis.

OBJECTIVE: Studies on the association between short-term exposure to ambient air pollution and heart rate variability (HRV) suggest that particulate matter (PM) exposure is associated with reductions in measures of HRV, but there is heterogeneity in the nature and magnitude of this association between studies. The authors performed a meta-analysis to determine how consistent this association is. DATA SOURCE: The authors searched the Pubmed citation database and Web of Knowledge to identify studies on HRV and PM. STUDY SELECTION: Of the epidemiologic studies reviewed, 29 provided sufficient details to be considered. The meta-analysis included 18667 subjects recruited from the population in surveys, studies from patient groups, and from occupationally exposed groups. DATA EXTRACTION: Two investigators read all papers and computerised all relevant information. RESULTS: The authors computed pooled estimates from a random-effects model. In the combined studies, an increase of 10 µg/m(3) in PM(2.5) was associated with significant reductions in the time-domain measurements, including low frequency (-1.66%, 95% CI -2.58% to -0.74%) and high frequency (-2.44%, 95% CI -3.76% to -1.12%) and in frequency-domain measurements, for SDNN (-0.12%, 95% CI -0.22% to -0.03%) and for rMSSD (-2.18%, 95% CI -3.33% to -1.03%). Funnel plots suggested that no publication bias was present and a sensitivity analysis confirmed the robustness of our combined estimates. CONCLUSION: The meta-analysis supports an inverse relationship between HRV, a marker for a worse cardiovascular prognosis, and particulate air pollution.

Placental mitochondrial DNA content and particulate air pollution during in utero life.

BACKGROUND: Studies emphasize the importance of particulate matter (PM) in the formation of reactive oxygen species and inflammation. We hypothesized that these processes can influence mitochondrial function of the placenta and fetus. OBJECTIVE: We investigated the influence of PM10 exposure during pregnancy on the mitochondrial DNA content (mtDNA content) of the placenta and umbilical cord blood. METHODS: DNA was extracted from placental tissue (n = 174) and umbilical cord leukocytes (n = 176). Relative mtDNA copy numbers (i.e., mtDNA content) were determined by real-time polymerase chain reaction. Multiple regression models were used to link mtDNA content and in utero exposure to PM10 over various time windows during pregnancy. RESULTS: In multivariate-adjusted analysis, a 10-µg/m³ increase in PM10 exposure during the last month of pregnancy was associated with a 16.1% decrease [95% confidence interval (CI): -25.2, -6.0%, p = 0.003] in placental mtDNA content. The corresponding effect size for average PM10 exposure during the third trimester was 17.4% (95% CI: -31.8, -0.1%, p = 0.05). Furthermore, we found that each doubling in residential distance to major roads was associated with an increase in placental mtDNA content of 4.0% (95% CI: 0.4, 7.8%, p = 0.03). No association was found between cord blood mtDNA content and PM10 exposure. CONCLUSIONS: Prenatal PM10 exposure was associated with placental mitochondrial alterations, which may both reflect and intensify oxidative stress production. The potential health consequences of decreased placental mtDNA content in early life must be further elucidated.