Nicky Pieters

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/m3 in PM2.5 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.

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 (25th–75th percentile: 390.7–767.3) and 1385ng/g dust (25th–75th 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.

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

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. Citation Pieters N, Koppen G, Van Poppel M, De Prins S, Cox B, Dons E, Nelen V, Int Panis L, Plusquin M, Schoeters G, Nawrot TS. 2015. Blood pressure and same-day exposure to air pollution at school: associations with nano-sized to coarse PM in children. Environ Health Perspect 123:737–742; http://dx.doi.org/10.1289/ehp.1408121

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

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-coactivator1β (PGC-1β), 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.

Effects of broccoli sprouts intake on oxidative stress, inflammation, microalbuminuria and platelet function in human volunteers: a cross-over study

Broccoli sprouts contain a high content of glucosinolates (1) . These substances induce phase 2 enzymes, known for their protection against carcinogenesis (2) , mutagenesis and other forms of toxicity of electrophiles and reactive forms of oxygen. We investigated the effects of the intake of broccoli sprouts on inflammation, microalbuminuria, platelet function and oxidative DNA damage. The study included 23 patients aged between 22 and 35 years who had no history of chronic illnesses or other harmful diseases. They were randomised in a cross-over study with two treatments: 20 g broccoli sprouts or no broccoli sprouts for 4 d. The two groups were crossed after 2 weeks. Platelet function was measured ex vivo with the PFA-100 platelet function analyser, which simulates a damaged blood vessel; we analysed the function of platelets in primary haemostasis under high shear conditions. Total and differential blood leucocytes were counted and oxidative DNA damage measured (8-hydroxy-2-deoxyguanosine [8-OH-2dG]) in urine from healthy volunteers. Baseline values were: lymphocytes (1000 ml 1 ) 2.130.44; monocytes (%) 5.901.07; 8-OH-2dG/creatinine (mg/g) 1.090.28 and microalbumine/creatinine (mg/g) 0.550.29. These variations induced by broccoli sprout intake showed a 8.9 % reduction (P = 0.029) in the amount of lymphocytes, a 11.9 % reduction (P = 0.0093) in the percentage of monocytes, a 34.5 % reduction (P = 0.016) in microalbumine/creatinine concentration and a 16.7% increase (P = 0.012) in 8-OH-2dG/creatinine concentration. The intake of broccoli sprouts did not significantly influence platelet function action. Non-significant results were found in the assessment of blood and urine content in the control group. Broccoli sprouts intake showed a significant reduction of lymphocytes, monocytes and microalbuminuria and a significant increase of 8-OH-2dG. Whether the increase in urinary 8-OH-2dG reflects enhanced DNA repair or more repair because of increased oxidative DNA damage by broccoli sprouts must be further elucidated.

Telomere Length, Cardiovascular Risk and the Discrepancy Between Baseline and Post-Transplant Renal Allograft Histology.: Abstract# A259

[De Vusser, K.; Kuypers, D.; Naesens, M.] UZ Leuven, Dept Nephrol, Leuven, Belgium. [Pieters, N.; Janssen, B.; Nawrot, T.] Univ Hasselt, Dept Toxicol, Diepenbeek, Belgium. [Lerut, E.] UZ Leuven, Dept Pathol, Leuven, Belgium.