Traffic-Related Air Pollution and Telomere Length in Children and Adolescents Living in Fresno, CA: A Pilot Study

Aging in chronic lung disease: Will anti-aging therapy be the key to the cure?

Chronic lung disease is the third leading cause of death globally, imposing huge burden of death, disability and healthcare costs. However, traditional pharmacotherapy has relatively limited effects in improving the cure rate and reducing the mortality of chronic lung disease. Thus, new treatments are urgently needed for the prevention and treatment of chronic lung disease. It is particularly noteworthy that, multiple aging-related phenotypes were involved in the occurrence and development of chronic lung disease, such as blocked proliferation, telomere attrition, mitochondrial dysfunction, epigenetic alterations, altered nutrient perception, stem cell exhaustion, chronic inflammation, etc. Consequently, senescent cells induce a series of pathological changes in the lung, such as immune dysfunction, airway remodeling, oxidative stress and regenerative dysfunction, which is a critical issue that needs special attention in chronic lung diseases. Therefore, anti-aging interventions may bring new insights into the treatment of chronic lung diseases. In this review, we elaborate the involvement of aging in chronic lung disease and further discuss the application and prospects of anti-aging therapy.

Children exposed to salt-dust emission from Urmia Lake have short telomere length: a case-control pilot study

This study aimed to measure telomere length in healthy children living next to Urmia Lake, Iran, which is exposed to salt dust from a drying lakebed. In this case-control pilot study, we recruited 39 sex- and age-matched healthy children from two different geographic regions to study the relative telomere lengths using qPCR. We categorized the study samples into high-impact and low-impact areas based on wind direction, aerosol particle level, and distance from the lake. Our main results revealed that children living in high-impact areas have shorter telomeres than those living in low-impact areas. Furthermore, according to our statistical model, parental age significantly affected telomere length in children, but inversely. When the father's age impact was positive, the mother had a negative effect. Based on our results, to prevent Urmia Lake from dying out completely, national and international organizations should implement comprehensive visions and strategies for its restoration.

Cellular senescence-Related genes define the immune microenvironment and molecular characteristics in severe asthma patients

Recent studies have shown that cellular senescence is involved in the pathogenesis of severe asthma (SA). The objective of this study was to investigate the role of cellular senescence-related genes (CSGs) in the pathogenesis of SA. Here, 54 differentially expressed CSGs were identified in SA patients compared to healthy control individuals. Among the 54 differentially expressed CSGs, 3 CSGs (ETS2, ETS1 and AURKA) were screened using the LASSO regression analysis and logistic regression analysis to establish the CSG-based prediction model to predict severe asthma. Moreover, we found that the protein expression levels of ETS2, ETS1 and AURKA were increased in the severe asthma mouse model. Then, two distinct senescence subtypes of SA with distinct immune microenvironments and molecular biological characteristics were identified. Cluster 1 was characterized by increased infiltration of immature dendritic cells, regulatory T cells, and other cells. Cluster 2 was characterized by increased infiltration levels of eosinophils, neutrophils, and other cells. The molecular biological characteristics of Cluster 1 included aerobic respiration and oxidative phosphorylation, whereas the molecular biological characteristics of Cluster 2 included activation of the immune response and immune receptor activity. Then, we established an Random Forest model to predict the senescence subtypes of SA to guide treatment. Finally, potential drugs were searched for each senescence subgroup of SA patients via the Connectivity Map database. A peroxisome proliferator-activated receptor agonist may be a potential therapeutic drug for patients in Cluster 1, whereas a tachykinin antagonist may be a potential therapeutic drug for patients in Cluster 2. In summary, CSGs are likely involved in the pathogenesis of SA, which may lead to new therapeutic options for SA patients.

Gender-specific associations between mixture of polycyclic aromatic hydrocarbons and telomere length

Evidence shows the relationships of individual environmental PAHs by their urinary metabolites with relative telomere length (RTL), which may be affected by biological gender differences. Since plasma parent PAHs are not metabolized, it may reflect human exposure to PAHs more realistically in daily life. Thus, exploring joint associations between plasma parent PAHs and RTL is urgent, which may identify the major contributor to its adverse effect. In this study, 2577 participants were obtained from the Henan Rural Cohort. The level of PAHs in blood samples was detected by gas chromatography coupled with tandem mass spectrometry. RTL in blood samples was detected by quantitative polymerase chain reaction. Generalized linear models or quantile g-computation were performed to evaluate the associations between the individual or a mixture of PAHs and RTL. Results from generalized linear models showed that each unit increment in BghiP value corresponded to a 0.098 (95%CI: 0.067, 0.129) increment in RTL for men; each unit increment in BaP, BghiP and Flu value corresponded to a 0.041 (95%CI: 0.014, 0.068), 0.081 (95%CI: 0.055, 0.107) and 0.016 (95%CI: 0.005, 0.027) increment in RTL for women. Results from quantile-g computation revealed that each one-quantile increment in the mixture of 10 PAHs corresponded to a 0.057 (95%CI: 0.021, 0.094) and 0.047 (95%CI: 0.003, 0.091) increment in RTL values of women and men, but these associations were mainly ascribed to three PAHs for women (BaP, Flu and BghiP) and men (BaP, BghiP and Pyr), respectively. Similar results were found in smoking men and cooking women without smoking. Our study found that exposure to 10 PAHs mixture was positively associated with RTL across gender, mainly attributed to Flu, BaP and BghiP, implicating that gender-specific associations may be ascribed to tobacco and cooking smoke pollution. The findings provided clues for effective measures to control PAHs pollutants-related aging disease.Clinical trial registration The Henan Rural Cohort Study has been registered at the Chinese Clinical Trial Register (Registration number: ChiCTR-OOC-15006699). Date of registration: 06 July 2015. http://www.chictr.org.cn/showproj.aspx?proj=11375 .

Impact of air pollution on cardiovascular aging

The world population is aging rapidly, and by some estimates, the number of people older than 60 will double in the next 30 years. With the increase in life expectancy, adverse effects of environmental exposures start playing a more prominent role in human health. Air pollution is now widely considered the most detrimental of all environmental risk factors, with some studies estimating that almost 20% of all deaths globally could be attributed to poor air quality. Cardiovascular diseases are the leading cause of death worldwide and will continue to account for the most significant percentage of non-communicable disease burden. Cardiovascular aging with defined pathomechanisms is a major trigger of cardiovascular disease in old age. Effects of environmental risk factors on cardiovascular aging should be considered in order to increase the health span and reduce the burden of cardiovascular disease in older populations. In this review, we explore the effects of air pollution on cardiovascular aging, from the molecular mechanisms to cardiovascular manifestations of aging and, finally, the age-related cardiovascular outcomes. We also explore the distinction between the effects of air pollution on healthy aging and disease progression. Future efforts should focus on extending the health span rather than the lifespan.

Association between mixed exposure of polycyclic aromatic hydrocarbons and telomere length in general population: NHANES 2001-2002

Although an association between single polycyclic aromatic hydrocarbons (PAHs) adult exposure and telomere length has been reported, the evidence of mixed PAHs (1-napthol, 2-napthol, 3-fluorene, 2-fluorene, 3-phenanthrene, 1-phenanthrene, 2-phenanthrene, and 1-pyrene) exposure and telomere length in the adult general population is still not clear. A total of 1460 adults over the age of 20 years provided urine information on 8 PAHs and selected covariates from the 2001-2002 National Health and Nutrition Examination Survey (NHANES). Bayesian nuclear machine regression (BKMR) was conducted to analyze these associations of telomere length in multiple PAH-exposed environments. Linear regression is mainly used for correlation analysis of PAHs with selected covariate adjustments. Restricted cubic spline (RCS) is used to estimate the correlation between selected PAHs and telomere length. After adjusting for potential covariates, PAHs mixed exposure was negatively associated with telomere length. The linear regression results showed that 2-napthol and 2-fluorene were negatively correlated with telomere length. Telomere length decreased by 1.0% in the fully adjusted model per increment of one unit in the base-10-logarithm-transformed 2-napthol and 2-fluorene concentrations (P = 0.030 and 0.049, respectively). However, the other 6 PAH metabolites were not significantly different. In addition, RCS results showed that 2-napthol has a marginal dose effect relationship with telomere length. Our present study suggested that PAHs are negatively associated with telomere length in the general population of the USA. Considering that the low level of PAHs exposure in the general population can also induce reduced telomere length and potential health risks, future research is needed to explore potential mechanisms.

Children's exposure to polycyclic aromatic hydrocarbon (PAHs): a review on urinary 1-hydroxypyrene and associated health effects

This article reviewed the published studies on the environmental exposure to polycyclic aromatic hydrocarbons (PAHs) among children and assessed the urinary 1-hydroxypyrene (1-OHP) level as a biomarker of exposure to PAHs. The current knowledge of the potential health effects of increased 1-OHP in children was reviewed. Additionally, the influence of genetic polymorphism on the urinary 1-OHP level was discussed in this review. The assembled data showed that children who are attending schools or living close to industrial and polluted urban areas might have greater exposure to higher concentrations of PAHs with a higher level of urinary 1-OHP when compared to those children living in rural areas. Urinary 1-OHP may be a reliable biomarker for determining the genotoxic effects, oxidative stress and inflammation caused by exposure to PAHs. Strong research evidence indicated that the total body burden of PAHs should be evaluated by biomonitoring of 1-OHP in line with other urinary PAHs metabolites (with 2-3 rings) to evaluate recent total exposure to PAHs. Overall, the study suggests implementing a mitigation plan to combat air pollution to provide a cleaner environment for children.

Effects of air pollution on telomere length: Evidence from in vitro to clinical studies

Air pollution remains the major environmental problem globally. There is extensive evidence showing that the variety of air pollutants from environmental and occupational exposures cause adverse effects to our health. The clinical symptoms of those effects may present at a late stage, so surveillance is difficult to manage. Several biomarkers have been used for the early detection of health issues following exposure to air pollution, including the use of telomere length which indicates cellular senescence in response to oxidative stress. Oxidative stress is one of the most plausible mechanisms associated with exposure to air pollutants. Some specific contexts including age groups, gender, ethnicity, occupations, and health conditions, showed significant alterations in telomere length after exposure to air pollutants. Several reports demonstrated both negative and positive associations between telomere length and air pollution, the studies using different concentrations and exposure times to air pollution on the study of telomere lengths. Surprisingly, some studies reported that low levels of exposure to air pollutants (lower than regulated levels) caused the alterations in telomere length. Those findings suggest that telomere length could be one of most practical biomarkers in air pollution surveillance. Therefore, this review aimed to summarize and discuss the relationship between telomere length and exposure to air pollution. The knowledge from this review will be beneficial for the planning of public health to reduce health problems in the general population, particularly in vulnerable people, who still live in areas with high air pollution.

Gestational exposure to NO2 aggravates placental senescence

Placental senescence is a normal physiological process of placenta, while premature placental senescence has been confirmed to be associated with some adverse pregnancy complications. Epidemiological studies indicate that NO₂ exposure can aggravate placental senescence which is represented by fibrosis and abnormal telomere homeostasis, etc. In this study, pregnant C57BL/6 mice were exposed to NO₂ (2.5 ppm, 5 h/day) daily in a dynamic exposure chamber throughout the gestation period, and were sacrificed at embryonic day 13.5 (E13.5), E15.5 and E18.5. Placenta were harvested and conducted for histopathological examination and telomere evaluation. Our results showed that gestational NO₂ exposure significantly aggravated placental fibrosis and calcification, and up-regulated the related bio-markers (connective tissue growth factor (Ctgf) and transforming growth factor-β1 (Tgf-β1)) at E18.5. In addition, gestational exposure to NO₂ also activated senescence related pathway (p53/p21) at E18.5. Furthermore, gestational NO₂ exposure significantly shortened telomere length at E18.5, and the expression of telomere homeostasis regulation genes telomeric repeat binding factor 1 (Trf1), protection of telomeres 1a (Pot1a) and Pot1b were significantly increased while telomerase reverse transcriptase (Tert) was suppressed after NO₂ exposure at E13.5 or E18.5, respectively. Importantly, DNA methylation status of the 22^nd at E13.5 and 32^nd at E18.5 site in sub-telomeric region of chromosome 1 was significantly altered. Based on the above results, our present study indicated that gestational NO₂ exposure could lead to premature placental senescence during the late trimester of pregnancy via aggravation of fibrosis and telomere length shortening regulated by telomere regulatory enzyme and DNA methylation.

Development in the European flounder (Platichthys flesus) of a q-PCR assay for the measurement of telomere length, a potential biomarker of pollutant effects for biomonitoring studies

Telomeres protect the coding sequence of chromosome ends and Telomere Length (TL) has been proposed as a biomarker of cellular aging, cumulative stress exposure and life-span in humans. With the aim to propose new biomarkers, a q-PCR protocol was adapted for the measurement of TL in the European flounder Platichthys flesus. The protocol was then applied in 2-year-old flounders from the Seine Estuary. The absolute TL in the flounder is 54 ± 13 kbp per genome (mean ± standard error). Considering relative or absolute TL, no correlation was observed with DNA damage and any of the measured contaminant concentrations (trace elements, metabolites of polycyclic aromatic hydrocarbons, polychlorobiphenyls, organochlorinated pesticides, polybrominated diphenyl ethers, perfluoroalkyl substances). Because sampling was limited, further investigations are required to state a possible impact of chemical pollution on flatfish telomeres. This is motivated by correlations observed with organochlorinated compounds when decreasing statistical significance (p ≤ 0.10).

Different epigenetic signatures of newborn telomere length and telomere attrition rate in early life

Telomere length (TL) and telomere shortening are biological indicators of aging, and epigenetic associates have been found for TL in adults. However, the role of epigenetic signatures in setting newborn TL and early life telomere dynamics is unknown. In the present study, based on 247 participating newborns from the ENVIRONAGE birth cohort, whole-genome DNA methylation, profiled on the Illumina MethylationEPIC BeadChip microarray, and TL were measured in cord blood. In a follow-up visit at a mean age of 4.58 years, leukocyte TL was evaluated. We combined an epigenome-wide association study and a statistical learning method with re-sampling to select CpGs and their two-way interactions to model baseline (cord blood) TL and early-life telomere attrition rate, where distinct epigenetic signatures were identified for the two outcomes. In addition, a stronger epigenetic regulation was suggested in setting newborn TL than that of telomere dynamics in early life: 47 CpGs and 7 between-CpG interactions explained 76% of the variance in baseline TLs, while 72% of the total variance in telomere attrition rate was explained by 31 CpGs and 5 interactions. Functional enrichment analysis based on the selected CpGs in the two models revealed GLUT4 translocation and immune cell signaling pathways, respectively. These CpGs and interactions, as well as the cellular pathways, are potential novel targets of further investigation of telomere biology and aging.

Polycyclic aromatic hydrocarbons exposures and telomere length: A cross-sectional study on preschool children

Exposure to polycyclic aromatic hydrocarbons (PAHs) has been associated with shorter telomere length (TL), a marker of ageing at cellular level. However, the available evidence on this association among children is still scarce. We therefore aimed to assess, the relationship between urinary 1-hydroxipayrene (1-OHP), a marker of exposure to PAHs, and relative leukocyte TL (LTL) in children at preschool age. Our study was based on 200 children enrolled from 27 randomly-selected kindergartens in the city of Sabzevar, Iran (2017). 1-OHP levels in the participants' urine samples were measured using solid phase extraction (SPE) method and high-performance liquid chromatography (HPLC). Moreover, real-time PCR was used to measure the LTL in the participants' blood samples. Linear mixed effects models, controlled for relevant covariates, were applied to investigate the association of 1-OHP concentration and LTL. The median (interquartile range (IQR)) of relative LTL and urinary 1-OHP were 0.83 (0.7) and 257 (375.5) ng/L, respectively. In the fully adjusted model, an IQR increase in urinary 1-OHP was related to -0.05 (95% confidence interval (CI): 0.09, -0.01, P-value = 0.02) decrease in relative LTL. This association was similar among boys and girls; however, we observed indications for a stronger association for those children whose parents had university education. Our study suggested an inverse relationship between urinary 1-OHP and LTL in children at preschool age. However, further longitudinal research with repeated measures of PAHs and LTL are needed to confirm these findings.

Airway hyperresponsiveness development and the toxicity of PM2.5

Airway hyperresponsiveness (AHR) is characterized by excessive bronchoconstriction in response to nonspecific stimuli, thereby leading to airway stenosis and increased airway resistance. AHR is recognized as a key characteristic of asthma and is associated with significant morbidity. At present, many studies on the molecular mechanisms of AHR have mainly focused on the imbalance in Th1/Th2 cell function and the abnormal contraction of airway smooth muscle cells. However, the specific mechanisms of AHR remain unclear and need to be systematically elaborated. In addition, the effect of air pollution on the respiratory system has become a worldwide concern. To date, numerous studies have indicated that certain concentrations of fine particulate matter (PM2.5) can increase airway responsiveness and induce acute exacerbation of asthma. Of note, the concentration of PM2.5 does correlate with the degree of AHR. Numerous studies exploring the toxicity of PM2.5 have mainly focused on the inflammatory response, oxidative stress, genotoxicity, apoptosis, autophagy, and so on. However, there have been few reviews systematically elaborating the molecular mechanisms by which PM2.5 induces AHR. The present review separately sheds light on the underlying molecular mechanisms of AHR and PM2.5-induced AHR.

Child buccal telomere length and mitochondrial DNA content as biomolecular markers of ageing in association with air pollution

BACKGROUND

Pro-inflammatory conditions such as air pollution might induce biological ageing. However, the available evidence on such an impact in children is still very scarce. We studied in primary schoolchildren the association of ambient residential air pollution exposure with telomere length (TL) and mitochondrial DNA content (mtDNAc), two important targets of the core axis of ageing.

METHODS

Between 2012 and 2014, buccal TL and mtDNAc were repeatedly assessed using qPCR in 197 Belgian primary schoolchildren (mean age 10.3 years) as part of the COGNAC study. At the child's residence, recent (week), sub-chronic (month) and chronic (year) exposure to nitrogen dioxide (NO₂), particulate matter ≤ 2.5 µm (PM_2.5) and black carbon (BC) were estimated using a high resolution spatiotemporal model. A mixed-effects model with school and subject as random effect was used while adjusting for a priori chosen covariates.

RESULTS

An interquartile range (IQR) increment (1.9 µg/m³) in chronic PM_2.5 exposure was associated with a 8.9% (95% CI: -15.4 to -1.9%) shorter TL. In contrast to PM_2.5, chronic exposure to BC and NO₂ was not associated with TL but recent exposure to BC and NO₂ showed significant inverse associations with TL: an IQR increment in recent exposure to BC (0.9 µg/m³) and NO₂ (10.2 µg/m³) was associated with a 6.2% (95% CI: -10.6 to -1.6%) and 6.4% (95% CI: -11.8 to -0.7%) shorter TL, respectively. Finally, an IQR increment in chronic PM_2.5 exposure was associated with a 12.7% (95% CI: -21.7 to -2.6%) lower mtDNAc. However, no significant associations were seen for NO₂ and BC or for other exposure windows.

CONCLUSION

Chronic exposure to PM_2.5 below the EU threshold was associated with child's shorter buccal TL and lower mtDNAc, while traffic-related pollutants (BC and NO₂) showed recent effects on telomere biology. Our data add to the literature on air pollution-induced effects of TL and mtDNAc, two measures part of the core axis of cellular ageing, from early life onwards.

Long-term ozone exposure is positively associated with telomere length in critically ill patients

RATIONALE

Chronic air pollutant exposure has been associated with development of Acute Respiratory Distress Syndrome (ARDS) in patients at risk, particularly from severe trauma. We recently reported that shorter peripheral blood leukocyte (PBL) telomere length (TL) was associated with worse outcomes and higher severity of ARDS in critically ill patients. Since most major air pollutants are potent oxidants that can induce cellular oxidative stress, and oxidative stress can accelerate telomere shortening, we hypothesized that higher levels of chronic air pollutant exposure would be associated with shorter telomere length in critically ill patients including patients with ARDS.

METHODS

PBL-TL was measured in genomic DNA collected on the morning of ICU day 2 in 772 critically ill patients enrolled in a prospective observational study. Exposures to air pollutants including ozone (warm-season only), particulate matter < 2.5 µm (PM_2.5), particulate matter < 10 µm (PM₁₀), CO, NO₂ and SO₂, were estimated by weighted average of daily levels from all monitors within 50 km of each patient's residential address for the 3 years prior to admission. Associations of each air pollutant exposure and PBL-TL were investigated by multivariable linear regression models adjusting for age, ethnicity, sex, smoking history, alcohol abuse, insurance status, median household income, history of malignancy and APACHE II.

RESULTS

Contrary to our hypothesis, TL increased across exposure quartiles in both ozone and PM_2.5 analyses (p < 0.05). In a regression model controlling for potential confounders, long term ozone exposure was significantly associated with an increase in TL in the entire cohort (0.31 kb per 10 ppb), as well as in subgroups with sepsis, trauma and ARDS (all p < 0.05). In multivariable models, entire-year exposure to PM_2.5, PM₁₀, CO, NO₂ and SO₂ was not associated with TL after adjustment for potential confounders. In an analysis restricted to warm-season levels to assess the effect of seasonality, higher warm-season PM_2.5 and CO exposures were independently associated with longer TL.

CONCLUSIONS

Long-term exposure to ozone is associated with longer peripheral blood TL in critically ill patients. Further studies are needed to investigate the potential underlying mechanisms for this unexpected positive association between telomere length and air pollution exposure in critical illness.

Association of exposure to air pollution and telomere length in preschool children

Exposure to air pollution is associated with adverse health effects; however, the available evidence of its association with telomere length (TL), an early marker of ageing, in children is still scarce with no study available for preschool children. This study aimed to investigate the association of exposure to air pollution and traffic indicators at home and kindergarten with relative leukocyte TL (LTL) in preschool children. This cross-sectional study included 200 preschool children (5-7 years old) recruited from 27 kindergartens in Sabzevar, Iran (2017). Outdoor annual average levels PM₁, PM_2.5, and PM₁₀ at residential address and kindergartens were estimated applying land use regression (LUR) models. Moreover, indoor levels of PMs at kindergartens were measured for four days in each season resulting in a total of 16 days of measurements for each kindergarten. Total streets length in different buffers and distance to major road were calculated as traffic indicators at residential address and kindergartens. We applied quantitative real-time polymerase chain reaction (qRT-PCR) to measure relative LTL in blood samples obtained from children. Mixed linear regression models were developed with qPCR plate and kindergarten as random effects, to estimate association of each pollutant and traffic indicator with LTL, controlled for relevant covariates. Higher concentrations of outdoor PM₁, PM_2.5, and PM₁₀, at home and kindergartens were associated with shorter relative LTL. Similarly, increase in indoor PM_2.5 concentrations at kindergartens was associated with shorter relative LTL (β = -0.18, 95% CI: -0.36, -0.01, P-value < 0.01). Moreover, higher total street length in 100 m buffer around residence and lower residential distance to major roads were associated with shorter relative LTL (β = -0.25, 95% CI: -0.37, -0.13, P-value < 0.01, and 0.32, 95% CI: 0.20, 0.44, P-value < 0.01, respectively). Overall, our study suggested that higher exposure to air pollution and traffic at kindergarten and residential home were associated with shorter relative LTL in preschool children.

Associations of telomere length with anthropometric and glucose changes after a lifestyle intervention in abdominal obese children

BACKGROUND AND AIMS

In lifestyle intervention studies, we demonstrated that changes in telomere length (TL) were associated with changes in anthropometric indices. Therefore, our new hypothesis is that TL could be a predictor of changes in anthropometric or metabolic measures in children with abdominal obesity. The aim of the study was to evaluate the association between anthropometric and biochemical measurements with TL before and after an 8-week lifestyle intervention in children with abdominal obesity (7-16 years old).

METHODS AND RESULTS

We assessed anthropometric and biochemical outcomes at baseline and after 8-week lifestyle intervention in 106 children with abdominal obesity (11.30 ± 2.49 years old, 63% girls). TL was measured by monochrome multiplex real-time quantitative PCR. After the lifestyle intervention, anthropometric parameters and glucose metabolism indicators significantly improved in the participants. TL did not change after the intervention in participants. Significant negative correlations between baseline TL and anthropometric measures (BMI, body weight and waist circumference) were observed. Furthermore, baseline TL was a predictor for changes in blood glucose levels after the lifestyle intervention.

CONCLUSIONS

An inverse correlation between TL and obesity traits was observed in children with abdominal obesity. Interestingly, we found that baseline TL could predict changes in blood glucose levels.

CLINICAL TRIAL

NCT03147261. Registered 10 May 2017.

A genome-wide by PM10 interaction study identifies novel loci for lung function near BICD1 and IL1RN-IL1F10 genes in Korean adults

Although several genome-wide interaction studies (GWIS) have been performed in specific European populations to understand the missing link between genetic and environmental factors for lung function, GWIS of Asian samples remain rare. Therefore, we performed a GWIS of exposure to air pollution to identify loci for lung function in Korean adult men. A total of 1826 adult men recruited from two health check-up centers were included in the analysis and the annual mean concentrations of ambient particulate matter with an aerodynamic diameter ≤10 μm (PM₁₀) were used. In case of forced vital capacity (FVC), one SNP (rs12312730) that passed our genome-wide threshold of pint < 1 × 10-5 was detected in the intronic region of the BICD1 gene on chromosome 12. In addition, we found two variants (rs6743376 and rs17042888) located near the IL1RN-IL1F10 gene that were involved in the inflammatory response and associated with decreased FVC via interaction with PM₁₀ exposure. A stratified association analysis according to these SNP genotypes showed that PM₁₀ concentrations in subjects with one or two of the risk alleles, compared with those with the non-risk allele, were significantly correlated with a reduction in FVC. This pattern was replicated in another 892 Korean adult samples. The current study reports the first GWIS discovery in an Asian population: the BICD1 and IL1RN-IL1F10 genes may contribute to the decrease in FVC levels by interacting with PM₁₀ exposure.

Organophosphate insecticide exposure and telomere length in U.S. adults

BACKGROUND

Organophosphate insecticides have been widely used for >30 years, and are reported to be associated with various age-related chronic diseases. While shortening of telomere length has been considered as a marker of cellular aging, only a few small studies have been conducted to examine any difference of telomere length in workers exposed to organophosphates versus controls. Epidemiologic studies of the dose-response associations between environmental organophosphate exposure and telomere length in the general population are few.

OBJECTIVE

This study aimed to evaluate the association between levels of organophosphate insecticide exposure and telomere length in the general population.

METHODS

We analyzed data for 1724 participants aged 20 years or more from the National Health and Nutrition Examination Survey 1999-2002. Organophosphate insecticide exposure was estimated using measures of urinary concentrations for 3,5,6-trichloro-2-pyridinol (TCPY) and six non-specific dialkyl phosphate metabolites, e.g., diethyl thiophosphate (DETP). Multiple linear regression was conducted to assess the association between organophosphate exposure and telomere length.

RESULTS

After controlling for sociodemographic and physical factors and urinary creatinine, participants in the second quartile for urinary TCPY had 0.06 (95% CI: 0.02-0.10) T/S ratio shorter telomere length than those in the lowest quartile. By contrast, participants in the second and third tertiles of urinary DETP had 0.08 (95% CI: 0.02-0.14) and 0.06 (95% CI, 0.01-0.11) T/S ratio longer telomere length than those in the lowest tertile. For other five metabolites, there was no association with telomere length.

CONCLUSIONS

Levels of environmental exposures to certain organophosphate insecticides may be linked to altered telomere length in adults in the general population. Although our findings may need to be replicated, we provide the first evidence that environmental exposure to organophosphates may contribute to the alteration of telomere length, which is potentially related to biological aging and to the development of various chronic diseases.

Potential Role of Cellular Senescence in Asthma

Cellular senescence is a complicated process featured by irreversible cell cycle arrest and senescence-associated secreted phenotype (SASP), resulting in accumulation of senescent cells, and low-grade inflammation. Cellular senescence not only occurs during the natural aging of normal cells, but also can be accelerated by various pathological factors. Cumulative studies have shown the role of cellular senescence in the pathogenesis of chronic lung diseases including chronic obstructive pulmonary diseases (COPD) and idiopathic pulmonary fibrosis (IPF) by promoting airway inflammation and airway remodeling. Recently, great interest has been raised in the involvement of cellular senescence in asthma. Limited but valuable data has indicated accelerating cellular senescence in asthma. This review will compile current findings regarding the underlying relationship between cellular senescence and asthma, mainly through discussing the potential mechanisms of cellular senescence in asthma, the impact of senescent cells on the pathobiology of asthma, and the efficiency and feasibility of using anti-aging therapies in asthmatic patients.

Effect of combustion-derived particles on genotoxicity and telomere length: A study on human cells and exposed populations

Particulate matter (PM) from combustion processes has been associated with oxidative stress to DNA, whereas effects related to telomere dysfunction are less investigated. We collected air-borne PM from a passenger cabin of a diesel-propelled train and at a training facility for smoke diving exercises. Effects on oxidative stress biomarkers, genotoxicity measured by the comet assay and telomere length in PM-exposed A549 cells were compared with the genotoxicity and telomere length in peripheral blood mononuclear cells (PBMCs) from human volunteers exposed to the same aerosol source. Although elevated levels of DNA strand breaks and oxidatively damaged DNA in terms of Fpg-sensitive sites were observed in PBMCs from exposed humans, the PM collected at same locations did not cause genotoxicity in the comet assay in A549 cells. Nevertheless, A549 cells displayed telomere length shortening after four weeks exposure to PM. This is in line with slightly shorter telomere length in PBMCs from exposed humans, although it was not statistically significant. In conclusion, the results indicate that genotoxic potency measured by the comet assay of PM in A549 cells may not predict genotoxicity in exposed humans, whereas telomere length measurements may be a novel indicator of genotoxic stress in cell cultures and humans.

Seasonal modification of the associations of exposure to polycyclic aromatic hydrocarbons or phthalates of cellular aging

Exposure to polycyclic aromatic hydrocarbons (PAHs) and phthalates link to oxidative stress and inflammatory response, which exert cellular aging. However, modification effect of seasonal factor on the association of PAHs or phthalates exposure with relative telomere length (RTL) or mitochondrial DNA copy number (mtDNA-CN) has remained unclear. In this pilot study, 106 subjects were from an urban population (n = 1240) who lived in the two districts in Wuhan city, China. Participants completed physical examinations and provided 191 blood samples for RTL and mtDNA-CN analysis and 627 urine samples for monohydroxylated-PAHs (OH-PAHs) and phthalate metabolites measurements in the winter and summer seasons. We assessed the associations of urinary OH-PAHs or phthalates metabolites with RTL or mtDNA-CN by linear regression analysis and linear mixed-effect models. We found that urinary OH-PAHs were positively associated with mtDNA-CN at lag 2 day and 3-day moving average, but negatively related to RTL at lag 0, lag 1 and lag 2 day and 3-day moving average (p < 0.05). Urinary phthalate metabolites were negatively associated with mtDNA lag 0, lag 1 and lag 2 day and 3-day moving average, but positively related to RTL at lag 0 day (p < 0.05). Seasonal factor modified the association of urinary OH-PAHs with mtDNA-CN as well as urinary phthalate metabolites with RTL. In vitro experiment showed that under certain conditions, benzo[a]pyrene increased mtDNA-CN at 48 h and di (2-ethylhexyl) phthalate did RTL at 24 h in HepG2 cells. Seasonal variations in the metabolisms of PAHs or phthalates in human body may affect the relation of PAHs or phthalates exposure with cellular aging.

Telomere dynamic in humans and animals: Review and perspectives in environmental toxicology

Telomeres (TLs) play major roles in stabilizing the genome and are usually shortened with ageing. The maintenance of TLs is ensured by two mechanisms involving telomerase (TA) enzyme and alternative lengthening telomeres (ALT). TL shortening and/or TA inhibition have been related to health effects on organisms (leading to reduced reproductive lifespan and survival), suggesting that they could be key processes in toxicity mechanisms (at molecular and cellular levels) and relevant as an early warning of exposure and effect of chemicals on human health and animal population dynamics. Consequently, a critical analysis of knowledge about relationships between TL dynamic and environmental pollution is essential to highlight the relevance of TL measurement in environmental toxicology. The first objective of this review is to provide a survey on the basic knowledge about TL structure, roles, maintenance mechanisms and causes of shortening in both vertebrates (including humans) and invertebrates. Overall, TL length decreases with ageing but some unexpected exceptions are reported (e.g., in species with different lifespans, such as the nematode Caenorhabditis elegans or the crustacean Homarus americanus). Inconsistent results reported in various biological groups or even between species of the same genus (e.g., the microcrustacean Daphnia sp.) indicate that the relation usually proposed between TL shortening and a decrease in TA activity cannot be generalized and depends on the species, stage of development or lifespan. Although the scientific literature provides evidence of the effect of ageing on TL shortening, much less information on the relationships between shortening, maintenance of TLs, influence of other endogenous and environmental drivers, including exposure to chemical pollutants, is available, especially in invertebrates. The second objective of this review is to connect knowledge on TL dynamic and exposure to contaminants. Most of the studies published on humans rely on correlative epidemiological approaches and few in vitro experiments. They have shown TL attrition when exposed to contaminants, such as polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), pesticides and metallic elements (ME). In other vertebrates, the studies we found deals mainly with birds and, overall, report a disturbance of TL dynamic consecutively to exposure to chemicals, including metals and organic compounds. In invertebrates, no data are available and the potential of TL dynamic in environmental risk assessment remains to be explored. On the basis of the main gaps identified some research perspectives (e.g., impact of endogenous and environmental drivers, dose response effects, link between TL length, TA activity, longevity and ageing) are proposed to better understand the potential of TL and TA measurements in humans and animals in environmental toxicology.

Ambient air pollution, asthma drug response, and telomere length in African American youth

BACKGROUND

Telomere length (TL) can serve as a potential biomarker for conditions associated with chronic oxidative stress and inflammation, such as asthma. Air pollution can induce oxidative stress. Understanding the relationship between TL, asthma, and air pollution is important for identifying risk factors contributing to unhealthy aging in children.

OBJECTIVES

We sought to investigate associations between exposures to ambient air pollutants and TL in African American children and adolescents and to examine whether African ancestry, asthma status, and steroid medication use alter the association.

METHODS

Linear regression was used to examine associations between absolute telomere length (aTL) and estimated annual average residential ozone (O3) and fine particulate matter with a diameter of 2.5 μm or less (PM2.5) exposures in a cross-sectional analysis of 1072 children in an existing asthma case-control study. African ancestry, asthma status, and use of steroid medications were examined as effect modifiers.

RESULTS

Participants' aTLs were measured by using quantitative PCR. A 1-ppb and 1 μg/m3 increase in annual average exposure to O3 and PM2.5 were associated with a decrease in aTL of 37.1 kilo-base pair (kb; 95% CI, -66.7 to -7.4 kb) and 57.1 kb (95% CI, -118.1 to 3.9 kb), respectively. African ancestry and asthma were not effect modifiers; however, exposure to steroid medications modified the relationships between TL and pollutants. Past-year exposure to O3 and PM2.5 was associated with shorter TLs in patients without steroid use.

CONCLUSION

Exposure to air pollution was associated with shorter TLs in nonasthmatic children and adolescents. This was not the case for asthmatic children as a group, but those receiving steroid medication had less shortening than those not using steroids. Reduced exposure to air pollution in childhood might help to preserve TL.

Prenatal and Childhood Traffic-Related Air Pollution Exposure and Telomere Length in European Children: The HELIX Project

BACKGROUND

Telomere length is a molecular marker of biological aging.

OBJECTIVE

Here we investigated whether early-life exposure to residential air pollution was associated with leukocyte telomere length (LTL) at 8 y of age.

METHODS

In a multicenter European birth cohort study, HELIX (Human Early Life Exposome) ([Formula: see text]), we estimated prenatal and 1-y childhood exposure to nitrogen dioxide ([Formula: see text]), particulate matter with aerodynamic diameter [Formula: see text] ([Formula: see text]), and proximity to major roads. Average relative LTL was measured using quantitative real-time polymerase chain reaction (qPCR). Effect estimates of the association between LTL and prenatal, 1-y childhood air pollution, and proximity to major roads were calculated using multiple linear mixed models with a random cohort effect and adjusted for relevant covariates.

RESULTS

LTL was inversely associated with prenatal and 1-y childhood [Formula: see text] and [Formula: see text] exposures levels. Each standard deviation (SD) increase in prenatal [Formula: see text] was associated with a [Formula: see text] (95% CI: [Formula: see text], [Formula: see text]) change in LTL. Prenatal [Formula: see text] was nonsignificantly associated with LTL ([Formula: see text] per SD increase; 95% CI: [Formula: see text], 0.6). For each SD increment in 1-y childhood [Formula: see text] and [Formula: see text] exposure, LTL shortened by [Formula: see text] (95% CI: [Formula: see text], [Formula: see text]) and [Formula: see text] (95% CI: [Formula: see text], 0.1), respectively. Each doubling in residential distance to nearest major road during childhood was associated with a 1.6% (95% CI: 0.02, 3.1) lengthening in LTL.

CONCLUSION

Lower exposures to air pollution during pregnancy and childhood were associated with longer telomeres in European children at 8 y of age. These results suggest that reductions in traffic-related air pollution may promote molecular longevity, as exemplified by telomere length, from early life onward. https://doi.org/10.1289/EHP4148.

Effects of maternal exposure to ambient air pollution on newborn telomere length

BACKGROUND

Telomere length (TL) is considered as a surrogate of biological aging and has been related to aging-related diseases. The initial setting of newborn TL has important implications for telomere dynamics in adulthood, and is affected by the intrauterine environment. However, the effects of prenatal air pollution exposure on the initial setting of newborn TL are poor understood.

OBJECTIVES

We aimed to explore the trimester-specific relationships between maternal air pollution exposure and newborn TL.

METHODS

Between November 2013 and March 2015, a total of 762 mother-newborn pairs were recruited in a birth cohort study in Wuhan, China. Relative cord blood TL was assessed using quantitative real-time polymerase chain reaction. Maternal exposures to PM_2.5, PM₁₀, SO₂, CO, and NO₂, were determined using spatial-temporal land use regression models. Multiple informant models were applied to explore the trimester-specific associations of maternal air pollution exposure with cord blood TL.

RESULTS

In single-pollutant models, a 10 μg/m³ increase in PM_2.5, PM₁₀, SO₂, and a 100 μg/m³ increase in CO during the third trimester were related to 3.71% (95% confidence interval [CI]: -6.06%, -1.30%), 3.24% (95% CI: -5.29%, -1.14%), 11.07% (95% CI: -18.86%, -2.53%), and 3.67% (95% CI: -6.27%, -1.00%) shorter cord blood TL, respectively. The inverse relationships between exposures to PM_2.5, PM₁₀, SO₂, and CO during the third trimester and cord blood TL were more evident in male infants. In multi-pollutant models, exposures to PM_2.5 and PM₁₀ during the third trimester were both related to shorter cord blood TL, but not SO₂ and CO.

CONCLUSION

This study suggested that maternal exposures to PM_2.5, PM₁₀, CO, and SO₂ during the third trimester were related to shorter newborn TL, which highlights the importance of improving air quality in favor of subsequent health in later life of newborns.

Urinary levels of 1-hydroxypyrene and health risk assessment in children living in Mexican communities with a high risk of contamination by polycyclic aromatic hydrocarbons (PAHs)

Health complications have been associated with polycyclic aromatic hydrocarbons (PAHs) exposure, a widespread environmental pollutants family. Therefore, the objective of this investigation was to develop a probabilistic health risk evaluation (using Monte-Carlo simulation) in an infantile population living in areas with a high risk of pollution by PAHs (indoor wood combustion, brick kiln industry, municipal landfill, and low and high vehicular traffic) in Mexico. Urine samples were obtained from Mexican children (n = 135) and urinary 1-OHP concentrations (used as a PAHs biomarker) were quantified. Highest urinary 1-OHP concentrations were detected in children living in areas that use wood combustion as the principal indoor fuel (3.50 ± 0.95 µg/L). Nevertheless, estimated hazard quotients (HQ) lower than 1 were found in all assessed sites after Monte-Carlo analysis. Although HQ <1.0 (a toxic effect is not expected), more data are necessary to determine the real impact of PAHs exposure on children health status.

Genetic Determinants of Telomere Length in African American Youth

Telomere length (TL) is associated with numerous disease states and is affected by genetic and environmental factors. However, TL has been mostly studied in adult populations of European or Asian ancestry. These studies have identified 34 TL-associated genetic variants recently used as genetic proxies for TL. The generalizability of these associations to pediatric populations and racially diverse populations, specifically of African ancestry, remains unclear. Furthermore, six novel variants associated with TL in a population of European children have been identified but not validated. We measured TL from whole blood samples of 492 healthy African American youth (children and adolescents between 8 and 20 years old) and performed the first genome-wide association study of TL in this population. We were unable to replicate neither the 34 reported genetic associations found in adults nor the six genetic associations found in European children. However, we discovered a novel genome-wide significant association between TL and rs1483898 on chromosome 14. Our results underscore the importance of examining genetic associations with TL in diverse pediatric populations such as African Americans.

Air pollution and telomere length: a systematic review of 12,058 subjects

Background

Over recent decades, adverse effects of ambient air pollution on the cardiovascular system have been clearly demonstrated. However, the underlying mechanisms are not fully elucidated. Air pollution may accelerates biological aging and thereby the susceptibility to cardiovascular diseases (CVDs). Telomeres are tandem repetitive DNA complexes that play a critical role in maintaining chromosome stability. There are, however, heterogeneities among the reported effects of air pollution on telomere. This study sought to evaluate the existing literature on the association between air pollution and telomere length (TL).

Methods

Two reviewers independently searched on electronic databases including PUBMED, EMBASE, SCOPUS, WEB OF SCIENCE and Ovid. The key terms were "air pollution" and "telomere" without language restriction. Articles relating to tobacco smoke were excluded.

Results

A total of 12,058 subjects from 25 articles remained for final review. All were observational studies: 14 cross-sectional, 6 cohort and 5 case-control studies. Nineteen (76%) assessed leukocyte telomere length (LTL) of which 15 found associations between air pollution and shorter TL, 2 with longer TL, 1 had mixed results, and a study of patients with type 2 diabetes found non-significant associations with TL. One found longer TL from saliva. The remaining studies were of placental cells, buccal cells or sperm and all reported shorter TL associated with air pollution. Particulate matter (PM) was investigated in 8 articles, and the remainder assessed black carbon (BC), benzene, lead, cadmium and polycyclic aromatic hydrocarbon (PAH). Geographically, 11 studies were conducted in Europe, with 10 in Asia and 4 in North America. While all followed Cawthon's protocol for TL assessment, discordance in the reporting formats did not allow us to perform a quantitative meta-analysis.

Conclusions

Most of the studies support the association of shorter TL with air pollution. Uniform reporting format would be warranted for future studies to estimate true effect size of air pollution on TL.

2-Naphthol Levels and Allergic Disorders in Children

Background: The measurement of polycyclic aromatic hydrocarbons (PAH) in ambient air is quite difficult to perform. Using urine biomarkers of PAH such as 2-naphthol is one approach to this problem. This study explored the association between urine 2-naphthol levels and allergic diseases. The associations between 2-naphthol levels and oxidative stress biomarkers for the possible disease pathogenesis were also investigated. Method: A total of 453 kindergarten children from the (Childhood Environment and Allergic Diseases Study) CEAS cohort with urine samples were recruited. Urine 2-naphthol levels were measured by high-performance liquid chromatography mass spectrometry (HPLC-MS/MS) and markers of oxidative stress (8OHdG) were measured by enzyme-linked immunosorbent assays (ELISA). Information on environmental risk factors and allergic diseases were also collected. The association between 2-naphthol levels, 8OHdG levels, IgE, and allergic diseases were evaluated by multivariate linear regression and logistic regression. Results: Levels of 2-naphthol were positively correlated with 8OHdG levels. A one ln-unit increase in the 2-naphthol level was positively associated to 8OHdG levels (per ln-unit: β = 100.61, p < 0.001). When dividing 2-naphthol levels into quartiles, asthma was significantly associated with 2-naphthol levels at a concentration of >1.60 ng/mL (adjusted OR: 3.14, 95% CI 1.34–7.35). Conclusion: Urine 2-naphthol levels are associated with markers of oxidative stress and the risk of allergic diseases in young children.

Ageing at the level of telomeres in association to residential landscape and air pollution at home and work: a review of the current evidence

Studies suggest that leukocyte telomere length is an index of systemic ageing. Here, we discuss telomere length as a marker of biological ageing in relation to residential landscape (greenness), residential air pollution and work-related exposures. Telomere lengths are memories of cumulative oxidative and inflammatory stress, and show to have inverse associations with the risk of non-communicable diseases. For this reason, telomeres are considered as markers of biological ageing. Studies at birth, in children, young adulthood, and elderly show that residential green space, lower traffic exposure and long-term lower exposure to particulate air pollution are associated with longer telomeres. Work-related exposures including exposure to toxic metals, polycyclic aromatic hydrocarbons and particulate matter are associated with shorter telomeres for a given age. In contrast to chronic exposures, evidence is present of the observation that recent exposure is associated with longer telomeres. Our overview shows that the magnitude of residential and work-related environmental factors on telomere length are often as important as many classical lifestyle factors.

Shorter telomere length in cord blood associated with prenatal air pollution exposure: Benefits of intervention

BACKGROUND

To examine the molecular benefits of the government action to close the local coal burning power plant in Tongliang County, Chongqing Municipality, we compared biologic markers and health outcomes in two successive birth cohorts enrolled before and after the plant was shut down. In this city, polycyclic aromatic hydrocarbons (PAH) were primarily emitted by the coal burning facility. We previously reported that cord blood levels of PAH-DNA adducts (a biomarker of exposure) and various adverse health outcomes were reduced in the second cohort, whereas levels of brain-derived neurotrophic factor/BDNF (a protein involved in neuronal growth) were increased. Here we assessed telomere length (TL), which has been associated with risk of certain chronic diseases, early mortality, aging and cognitive decline in adults.

OBJECTIVES

The goals of the present study were to determine whether TL differed between the two cohorts and whether prenatal PAH exposure, estimated by PAH-DNA adducts in cord white blood cells of newborns in China, were predictive of shorter TL in cord blood, suggesting the potential accrual of risk of certain chronic diseases during the prenatal period. We explored relationships of TL with BDNF and neurodevelopmental outcomes, each previously associated with PAH-DNA adducts in these cohorts, as well as the potential mediating role of TL in the associations between adducts and neurodevelopmental outcomes.

METHODS

We analyzed TL in cord blood of 255 newborns who also had data on PAH-DNA adducts, BDNF, and relevant covariates. Multiple regression analysis was carried out to test associations between adducts and TL and between TL and BDNF, adjusting for relevant covariates. In the subset with developmental quotient (DQ) scores from Gesell testing at age 2 (N = 210), we explored whether TL was a mediator of the relationship between PAH-DNA adducts and DQ scores by first examining the associations between cord adducts and DQ, cord adducts and TL, and TL and DQ, adjusting for the same covariates.

RESULTS

As hypothesized, the mean TL was significantly higher in the second cohort compared to the first cohort. Overall, PAH-DNA cord adducts were significantly and inversely correlated with TL. Multiple regression analysis showed a significant association between adducts and TL, after adjusting for key covariates: β (effect size per standard deviation adducts) = -0.019, p = .003. The regression coefficient of TL on (Ln) BDNF was also significant (β = 0.167, p < .001). Exploratory analysis, regressing TL on Gesell developmental scores, showed generally inverse, but not significant associations. TL was not, therefore, deemed to be a potential mediator of the association between adducts and developmental scores at age two.

CONCLUSION

This study provides the first evidence that prenatal PAH exposure from coal burning may adversely affect TL, with potential implications for future risk of chronic diseases including cardiovascular disease. The improvement in TL in the second cohort and the observed correlation between increased TL and higher levels of BDNF indicate direct benefits to the health and development of children resulting from the government's closure of the power plant.

The impact of prenatal exposure to air pollution on childhood wheezing and asthma: A systematic review

BACKGROUND AND OBJECTIVES

There has been no clear consensus about whether prenatal exposure to air pollution contributes to the development of wheezing and asthma in children. We conducted a systematic review to analyze the association between exposure to different pollutants during pregnancy and the development of childhood wheezing and asthma.

METHODS

We systematically reviewed epidemiological studies published through June 6, 2017 available in the MEDLINE and Web of Science databases. We included studies that examined the association between prenatal exposure to any air pollutants except tobacco smoke and the incidence or prevalence of "wheezing" or "asthma" from birth to 14 years of age. We extracted key characteristics of each included study using a template of predefined data items. We used the Critical Appraisal Skills Programme checklists to assess the validity of each included study. We conducted overall and subgroup meta-analyses for each summary exposure-outcome association. Pooled odds ratios (OR) with 95% confidence intervals (CI) were estimated by using a random effects model.

RESULTS

Eighteen studies met our eligibility criteria. There was notable variability in exposure assessment methods. The overall random effects risk estimates (95% CI) of different pollutants were 1.04 (0.94-1.15) aromatic hydrocarbons (PAH), 1.04 (1.01-1.07) NO₂, 1.4 (0.97-2.03) PM_2.5 for childhood wheeze and 1.07 (1.01-1.14) NO₂, 1 (0.97-1.03) PM_2.5, 1.02 (0.98-1.07) SO₂, 1.08 (1.05-1.12) PM₁₀ for childhood asthma. Minimal heterogeneity was seen for PAH and SO₂, while some heterogeneity was observed for PM₁₀, PM_2.5 and NO₂.

CONCLUSIONS

The overall and subgroup risk estimates from the meta-analyses showed statistically significant associations between prenatal exposures to NO₂, SO₂, and PM₁₀ and the risk of wheezing and asthma development in childhood. There is insufficient evidence to show an effect of prenatal exposure to BC, CO, and O₃ on childhood wheezing and asthma. Further studies are needed to examine the individual compounds' effects.