Epigenetic regulation: the interface between prenatal and early-life exposure and asthma susceptibility

Health effects of exposure to indoor volatile organic compounds from 1980 to 2017: A systematic review and meta-analysis

Exposure to volatile organic compounds (VOCs) indoors is thought to be associated with several adverse health effects. However, we still lack concentration-response (C-R) relationships between VOC levels in civil buildings and various health outcomes. For this paper, we conducted a systematic review and meta-analysis of observational studies to summarize related associations and C-R relationships. Four databases were searched to collect all relevant studies published between January 1980 and December 2017. A total of 39 studies were identified in the systematic review, and 32 of these were included in the meta-analysis. We found that the pooled relative risk (RR) for leukemia was 1.03 (95% CI: 1.01-1.05) per 1 μg/m³ increase of benzene and 1.25 (95%CI: 1.14-1.37) per 0.1 μg/m³ increase of butadiene. The pooled RRs for asthma were 1.08 (95% CI: 1.02-1.14), 1.02 (95% CI: 1.00-1.04), and 1.04 (95% CI: 1.02-1.06) per 1 μg/m³ increase of benzene, toluene, and p-dichlorobenzene, respectively. The pooled RR for low birth weight was 1.12 (95% CI: 1.05-1.19) per 1 μg/m³ increase of benzene. Our findings provide robust evidence for associations between benzene and leukemia, asthma, and low birth weight, as well as for health effects of some other VOCs.

Air pollution and children's health-a review of adverse effects associated with prenatal exposure from fine to ultrafine particulate matter

BACKGROUND

Particulate matter (PM), a major component of ambient air pollution, accounts for a substantial burden of diseases and fatality worldwide. Maternal exposure to PM during pregnancy is particularly harmful to children's health since this is a phase of rapid human growth and development.

METHOD

In this review, we synthesize the scientific evidence on adverse health outcomes in children following prenatal exposure to the smallest toxic components, fine (PM_2.5) and ultrafine (PM_0.1) PM. We highlight the established and emerging findings from epidemiologic studies and experimental models.

RESULTS

Maternal exposure to fine and ultrafine PM directly and indirectly yields numerous adverse birth outcomes and impacts on children's respiratory systems, immune status, brain development, and cardiometabolic health. The biological mechanisms underlying adverse effects include direct placental translocation of ultrafine particles, placental and systemic maternal oxidative stress and inflammation elicited by both fine and ultrafine PM, epigenetic changes, and potential endocrine effects that influence long-term health.

CONCLUSION

Policies to reduce maternal exposure and health consequences in children should be a high priority. PM_2.5 levels are regulated, yet it is recognized that minority and low socioeconomic status groups experience disproportionate exposures. Moreover, PM_0.1 levels are not routinely measured or currently regulated. Consequently, preventive strategies that inform neighborhood/regional planning and clinical/nutritional recommendations are needed to mitigate maternal exposure and ultimately protect children's health.

Atopy risk among school-aged children in relation to early exposures to a farm environment: A systematic review

BACKGROUND AND OBJECTIVES

Childhood atopy is a complex condition with both a genetic and an environmental component. This systematic review will explore the current understanding of the importance of early life exposures to a farm in the development of atopy measured by objective markers of skin prick testing, and specific IgE measurements in school age children.

METHODS

A systematic review was performed.

RESULTS

Among 7285 references identified, 14 studies met the inclusion criteria (13 cross-sectional studies and 1 case-control study). The results were fairly consistent in that early farm-related exposures can protect children from becoming atopic at school age. In general, there was heterogeneity in the assessment of outcomes and exposures.

CONCLUSIONS

Early-life farm exposures are associated with a protective effect on childhood atopy as assessed by objective markers. Future work should focus on understanding specific farm exposures that may important in these associations between atopy and farm exposures in children.

The Role of Short-Chain Fatty Acids in the Interplay between a Very Low-Calorie Ketogenic Diet and the Infant Gut Microbiota and Its Therapeutic Implications for Reducing Asthma

Gut microbiota is well known as playing a critical role in inflammation and asthma development. The very low-calorie ketogenic diet (VLCKD) is suggested to affect gut microbiota; however, the effects of VLCKD during pregnancy and lactation on the infant gut microbiota are unclear. The VLCKD appears to be more effective than caloric/energy restriction diets for the treatment of several diseases, such as obesity and diabetes. However, whether adherence to VLCKD affects the infant gut microbiota and the protective effects thereof on asthma remains uncertain. The exact mechanisms underlying this process, and in particular the potential role of short chain fatty acids (SCFAs), are still to be unravelled. Thus, the aim of this review is to identify the potential role of SCFAs that underlie the effects of VLCKD during pregnancy and lactation on the infant gut microbiota, and explore whether it incurs significant implications for reducing asthma.

Understanding Root Causes of Asthma. Perinatal Environmental Exposures and Epigenetic Regulation

A common explanation for the origins and rising prevalence of asthma is that they involve complex interactions between hereditary predispositions and environmental exposures that are incompletely understood. Yet, emerging evidence substantiates the paradigm that environmental exposures prenatally and during very early childhood induce epigenetic alterations that affect the expression of asthma genes and, thereby, asthma itself. Here, we review much of the key evidence supporting this paradigm. First, we describe evidence that the prenatal and early postnatal periods are key time windows of susceptibility to environmental exposures that may trigger asthma. Second, we explain how environmental epigenetic regulation may explain the immunopathology underlying asthma. Third, we outline specific evidence that environmental exposures induce epigenetic regulation, both from animal models and robust human epidemiological research. Finally, we review some emerging topics, including the importance of coexposures, population divergence, and how epigenetic regulation may change over time. Despite all the inherent complexity, great progress has been made toward understanding what we still consider reversible asthma risk factors. These, in time, may impact patient care.

The etiologic origins for chronic obstructive pulmonary disease

COPD, characterized by long-term poorly irreversible airway limitation and persistent respiratory symptoms, has resulted in enormous challenges to human health worldwide, with increasing rates of prevalence, death, and disability. Although its origin was thought to be in the interactions of genetic with environmental factors, the effects of environmental factors on the disease during different life stages remain little known. Without clear mechanisms and radical cure for it, early screening and prevention of COPD seem to be important. In this review, we will discuss the etiologic origins for poor lung function and COPD caused by specific adverse effects during corresponding life stages, as well as try to find new insights and potential prevention strategies for this disease.

Environmental exposures during pregnancy: Mechanistic effects on immunity

In human studies, it is well established that exposures during embryonic and fetal development periods can influence immune health. Coupled with genetic predisposition, these exposures can alter lifetime chronic and infectious disease trajectory, and, ultimately, life expectancy. Fortunately, as research advances, mechanisms governing long-term effects of prenatal exposures are coming to light and providing the opportunity for intervention and risk reduction. For instance, human association studies have provided a foundation for the association of prenatal exposure to particulate matter with early immunosuppression and later allergic disease in the offspring. Only recently, the mechanisms mediating this response have been revealed and there is much we have yet to discover. Although cellular immune response is understood for many exposure scenarios, molecular pathways are still unidentified. This review will provide commentary and synthesis of the current literature regarding environmental exposures during pregnancy and mechanisms determining immune outcomes. Shared mechanistic features and current gaps in the state of the science are identified and discussed. To such purpose, we address exposures by their immune effect type: immunosuppression, autoimmunity, inflammation and tissue damage, hypersensitivity, and general immunomodulation.

Methylation analysis for multiple gene promoters in non-small cell lung cancers in high indoor air pollution region in China

AIM

The prevalence and mortality rates of lung cancer in Xuanwei, Yunnan, China, are the highest in the world. The severe indoor air pollution caused by smoky coals with high benzo (a)pyrene (BaP) and quartz levels is the main environmental factor. The aim of this study was to investigate methylation profiles of promoters in eight genes in primary non-small cell lung cancers (NSCLC) exposed to smoky coals.

MATERIALS AND METHODS

Candidate genes including CDKN2A, DLEC1, CDH1, DAPK, RUNX3, APC, WIF1 and MGMT were determined for the promoter methylation status using Nested methylation-specific PCR (nMSP) in primary 23NSCLC tissues and in circulating tumor DNA (ctDNA) isolated from 42plasma samples (9matched to tissues) as well as 10healthy plasma samples, using Sanger sequencing to verify the results.

RESULTS

Seven of the 8genes, except MGMT, had relatively high methylation frequencies ranging from 39%-74% in tissues. Moreover, methylation frequencies in five genes identified in lung cancer plasma were 45% for CDKN2A, 48% for DLEC1, 76% for CDH1, 14% for DAPK, 29% for RUNX3, with a relatively good concordance of methylation among 9 tissues and paired plasma. However, the genes from all healthy plasma showed no methylation.

CONCLUSIONS

A panel of genes including CDKN2A, DLEC1, CDH1, DAPK and RUNX3 may be used as potential epigenetic biomarkers for early lung cancer detection. CDH1 promoter methylation was associated with lung cancer metastasis in areas of air pollution from buring of smoky coals. DLEC1 and CDH1 exhibited specific high methylation frequencies, different from previous reports.

Air pollutants and early origins of respiratory diseases

Air pollution is a global health threat and causes millions of human deaths annually. The late onset of respiratory diseases in children and adults due to prenatal or perinatal exposure to air pollutants is emerging as a critical concern in human health. Pregnancy and fetal development stages are highly susceptible to environmental exposure and tend to develop a long-term impact in later life. In this review, we briefly glance at the direct impact of outdoor and indoor air pollutants on lung diseases and pregnancy disorders. We further focus on lung complications in later life with early exposure to air pollutants. Epidemiological evidence is provided to show the association of prenatal or perinatal exposure to air pollutants with various adverse birth outcomes, such as preterm birth, lower birth weight, and lung developmental defects, which further associate with respiratory diseases and reduced lung function in children and adults. Mechanistic evidence is also discussed to support that air pollutants impact various cellular and molecular targets at early life, which link to the pathogenesis and altered immune responses related to abnormal respiratory functions and lung diseases in later life.

Pregnancy and perinatal conditions and atopic disease prevalence in childhood and adulthood

BACKGROUND

Previous studies showed controversial results for the influence of pregnancy-related and perinatal factors on subsequent respiratory and atopic diseases in children. The aim of this study was to assess the association between perinatal variables and the prevalence of asthma, bronchial hyperreactivity (BHR), flexural eczema (FE), allergic rhinitis, and sensitization in childhood and early adulthood.

METHODS

The studied population was first examined in Munich and Dresden in 1995/1996 at age 9-11 years. Participants were followed until age 19-24 years using questionnaires and clinical examinations. Associations between perinatal data and subsequent atopic diseases were examined using logistic regression analyses adjusting for potential confounders.

RESULTS

Cesarean section was statistically significantly associated with BHR in early adulthood (odds ratio 4.8 [95% confidence interval 1.5-15.2]), while assisted birth was associated with presence of asthma symptoms in childhood (2.2 [1.2-3.9]), FE symptoms (2.2 [1.2-4.3]) and doctor's diagnosis of atopic dermatitis (1.9 [1.0-3.4]) in childhood, and sensitization in early adulthood (2.2 [1.1-4.3]). Lower birth length (1.9 [1.1-3.2]), lower birthweight (0.5 [0.3-0.9]), and higher birthweight (0.6 [0.4-1.0]) were predictive of sensitization in early adulthood compared to average birth length and birthweight, respectively. None of the other perinatal factors showed statistically significant associations with the outcomes.

CONCLUSIONS

Our results indicate that children who are born by cesarean section and especially by assisted birth, might be at greater risk for developing asthma, FE, and sensitization and should hence be monitored. Prenatal maternal stress might partly explain these associations, which should be further investigated.

Prenatal fine particulate exposure associated with reduced childhood lung function and nasal epithelia GSTP1 hypermethylation: Sex-specific effects

Background

In utero exposure to particulate matter with an aerodynamic diameter of less than 2.5 μm (PM_2.5) has been linked to child lung function. Overlapping evidence suggests that child sex and exposure timing may modify effects and associations may be mediated through glutathione S-transferase P1 (GSTP1) methylation.

Methods

We prospectively examined associations among prenatal PM_2.5 exposure and child lung function and GSTP1 methylation in an urban pregnancy cohort study. We employed a validated satellite-based spatiotemporally resolved prediction model to estimate daily prenatal PM_2.5 exposure over gestation. We used Baysian distributed lag interaction models (BDLIMs) to identify sensitive windows for prenatal PM_2.5 exposure on child lung function and nasal epithelia GSTP1 methylation at age 7 years, and to examine effect modification by child sex.

Results

BDLIMs identified a sensitive window for prenatal PM_2.5 exposure at 35–40 weeks gestation [cumulative effect estimate (CEE) = − 0.10, 95%CI = − 0.19 to − 0.01, per μg/m³ increase in PM_2.5] and at 36–40 weeks (CEE = − 0.12, 95%CI = − 0.20 to − 0.01) on FEV₁ and FVC, respectively, in boys. BDLIMs also identified a sensitive window of exposure at 37–40 weeks gestation between higher prenatal PM_2.5 exposure and increased GSTP1 percent methylation. The association between higher GSTP1 percent methylation and decreased FEV1 was borderline significant in the sample as a whole (β = − 0.37, SE = 0.20, p = 0.06) and in boys in stratified analyses (β = − 0.56, SE = 0.29, p = 0.05).

Conclusions

Prenatal PM_2.5 exposure in late pregnancy was associated with impaired early childhood lung function and hypermethylation of GSTPI in DNA isolated from nasal epithelial cells. There was a trend towards higher GSTP1 percent methylation being associated with reduced FEV1. All findings were most evident among boys.

Reduced mouse allergen is associated with epigenetic changes in regulatory genes, but not mouse sensitization, in asthmatic children

Chronic exposure to mouse allergen may contribute greatly to the inner-city asthma burden. We hypothesized that reducing mouse allergen exposure may modulate the immunopathology underlying symptomatic pediatric allergic asthma, and that this occurs through epigenetic regulation. To test this hypothesis, we studied a cohort of mouse sensitized, persistent asthmatic inner-city children undergoing mouse allergen-targeted integrated pest management (IPM) vs education in a randomized controlled intervention trial. We found that decreasing mouse allergen exposure, but not cockroach, was associated with reduced FOXP3 buccal DNA promoter methylation, but this was unrelated to mouse specific IgE production. This finding suggests that the environmental epigenetic regulation of an immunomodulatory gene may occur following changing allergen exposures in some highly exposed cohorts. Given the clinical and public health importance of inner-city pediatric asthma and the potential impact of environmental interventions, further studies will be needed to corroborate changes in epigenetic regulation following changing exposures over time, and determine their impact on asthma morbidity in susceptible children.

Reduced PRF1 enhancer methylation in children with a history of severe RSV bronchiolitis in infancy: an association study

Background

Acute lower respiratory tract infection is the commonest disease affecting children under five worldwide. Respiratory syncytial virus (RSV) is among the most common causative pathogens. Epidemiological data suggest an association between severe viral respiratory infections in infancy and increased incidence of childhood wheeze and asthma. DNA methylation is involved in immune cell differentiation and identity. It provides an avenue for environmental influences on the genome and therefore has potential as a marker for sustained effects of infectious insults. In this study we investigated the association between DNA methylation patterns in the perforin gene (PRF1) in childhood and a history of hospitalisation for severe RSV disease in the first two years of life.

Methods

In this retrospective study, we explored patterns of whole blood DNA methylation at a methylation sensitive region of the proximal PRF1 enhancer in a group of children with a record of hospitalisation for severe RSV disease during infancy (n = 43) compared to healthy controls matched for age and sex with no similar hospitalisation history, no allergy and no persistent wheeze (n = 43). Univariate and bivariate conditional logistic regression analyses were conducted to test the association between PRF1 enhancer methylation and record of hospitalisation for RSV disease.

Results

Children with a record of hospitalisation for severe RSV bronchiolitis demonstrated markedly lower levels of DNA methylation at two cytosine-phosphate-guanine dinucleotide (CpG) loci of the PRF1 proximal enhancer, corresponding to a signal transducer and activator of transcription 5 (STAT5) responsive element, compared to controls, adjusted odds ratios of 0.82 (95% confidence interval [CI] 0.71, 0.94) and 0.73 (95% CI 0.58, 0.92) for each 1% increase in DNA methylation. Smoking in the household showed a significant influence on DNA methylation at the assayed positions.

Conclusions

Our findings support an association between childhood DNA methylation patterns in PRF1 and a record of severe RSV infection in infancy. Longitudinal studies are required to establish the utility of PRF1 methylation as a marker of severe RSV disease.

Epigenome-Wide Meta-Analysis of Methylation in Children Related to Prenatal NO2 Air Pollution Exposure

BACKGROUND

Prenatal exposure to air pollution is considered to be associated with adverse effects on child health. This may partly be mediated by mechanisms related to DNA methylation.

OBJECTIVES

We investigated associations between exposure to air pollution, using nitrogen dioxide (NO2) as marker, and epigenome-wide cord blood DNA methylation.

METHODS

We meta-analyzed the associations between NO2 exposure at residential addresses during pregnancy and cord blood DNA methylation (Illumina 450K) in four European and North American studies (n = 1,508) with subsequent look-up analyses in children ages 4 (n = 733) and 8 (n = 786) years. Additionally, we applied a literature-based candidate approach for antioxidant and anti-inflammatory genes. To assess influence of exposure at the transcriptomics level, we related mRNA expression in blood cells to NO2 exposure in 4- (n = 111) and 16-year-olds (n = 239).

RESULTS

We found epigenome-wide significant associations [false discovery rate (FDR) p < 0.05] between maternal NO2 exposure during pregnancy and DNA methylation in newborns for 3 CpG sites in mitochondria-related genes: cg12283362 (LONP1), cg24172570 (3.8 kbp upstream of HIBADH), and cg08973675 (SLC25A28). The associations with cg08973675 methylation were also significant in the older children. Further analysis of antioxidant and anti-inflammatory genes revealed differentially methylated CpGs in CAT and TPO in newborns (FDR p < 0.05). NO2 exposure at the time of biosampling in childhood had a significant impact on CAT and TPO expression.

CONCLUSIONS

NO2 exposure during pregnancy was associated with differential offspring DNA methylation in mitochondria-related genes. Exposure to NO2 was also linked to differential methylation as well as expression of genes involved in antioxidant defense pathways. Citation: Gruzieva O, Xu CJ, Breton CV, Annesi-Maesano I, Antó JM, Auffray C, Ballereau S, Bellander T, Bousquet J, Bustamante M, Charles MA, de Kluizenaar Y, den Dekker HT, Duijts L, Felix JF, Gehring U, Guxens M, Jaddoe VV, Jankipersadsing SA, Merid SK, Kere J, Kumar A, Lemonnier N, Lepeule J, Nystad W, Page CM, Panasevich S, Postma D, Slama R, Sunyer J, Söderhäll C, Yao J, London SJ, Pershagen G, Koppelman GH, Melén E. 2017. Epigenome-wide meta-analysis of methylation in children related to prenatal NO2 air pollution exposure. Environ Health Perspect 125:104-110; http://dx.doi.org/10.1289/EHP36.

Exposure to outdoor air pollution during trimesters of pregnancy and childhood asthma, allergic rhinitis, and eczema

BACKGROUND

Mounting evidence suggests that exposure to ambient air pollution is associated with the development of childhood allergic diseases, but the effect of prenatal exposure to air pollution on the risk of childhood asthma and allergy is unclear.

OBJECTIVES

We evaluated the association between maternal exposure to outdoor air pollution during different trimesters of pregnancy and incidence of asthma, allergic rhinitis, and eczema in 2598 preschool children aged 3-6 years in China.

METHODS

Children's lifetime incidence of allergic diseases was obtained using questionnaire. Individual exposure to outdoor air pollutants during trimesters of pregnancy was estimated by an inverse distance weighted (IDW) method based on the measured concentrations at monitoring stations. We used multiple logistic regression method to estimate the odds ratio (OR) of asthma, allergic rhinitis, and eczema for per interquartile range (IQR) increase in the exposure to air pollutant in each trimester, which was adjusted for the effect of other air pollutants and its effect in other trimesters by a multi-pollutant/trimester model.

RESULTS

Incidence of asthma (6.8%), allergic rhinitis (7.3%), and eczema (28.6%) in children was associated with maternal exposure to traffic-related pollutant NO2 during entire pregnancy with OR (95% confidence interval [CI]) respectively 1.63 (0.99-2.70), 1.69 (1.03-2.77), and 1.37 (1.04-1.80). After adjustment for other pollutants and trimesters, we found the association was significant only in specific trimester: the first trimester for eczema (1.54, 1.14-2.09), the second trimester for asthma (1.72, 1.02-2.97), and the third trimester for allergic rhinitis (1.77, 1.09-2.89). Sensitivity analysis indicated that the trimester sensitive to the development of allergic diseases was stable.

CONCLUSION

Maternal exposure to traffic-related air pollutant NO2 during pregnancy, especially in specific trimesters, is associated with an increased risk of developing asthma, rhinitis, and eczema in children. Our results support the hypothesis that childhood allergic diseases originate in fetal life and are triggered by traffic-related air pollution in sensitive trimesters.

Prenatal exposures and DNA methylation in newborns: a pilot study in Durban, South Africa

The in utero environment has the potential to influence epigenetic programming and subsequently the health of offspring. Even though pregnant women living in urban Africa are exposed to multiple chemicals and infectious agents that may impact their developing children, the neonatal epigenome has not been studied in these regions. We assessed whether prenatal exposures to air pollution and maternal human immunodeficiency virus (HIV) are associated with changes to DNA methylation throughout the epigenome using a pilot sample from the Mother and Child Environmental (MACE) birth cohort, of which 36% of the mothers are HIV positive. Families living in a high air pollution region (south Durban, n = 11) and a low air pollution region (north Durban, n = 11) with comparable socioeconomic characteristics were selected for analysis. DNA methylation was quantified in cord blood plasma DNA at >430 000 CpG sites using the Infinium HumanMethylation450 BeadChip. Sites associated with living in south Durban or maternal HIV infection (p < 0.001) were more likely to be hypomethylated and located in CpG islands. Top differentially methylated sites by region of Durban were enriched in pathways related to xenobiotic metabolism, oxygen and gas transport, and sensory perception of chemical stimuli when performing gene set enrichment testing with LRpath. Differentially methylated sites by maternal HIV status were enriched in cytochrome P450s, pathways involved in detection of chemical stimuli, metabolic processes, and viral regulation and processing. Given the small sample size of the study, future work examining the impact of prenatal exposures to air pollution, maternal infection, and antiviral treatment on the epigenome and downstream health implications is merited in Sub-Saharan African populations.

Increased Risk of Asthma in Children with ADHD: Role of Prematurity and Maternal Stress during Pregnancy

OBJECTIVE

ADHD and asthma are prevalent conditions in childhood, with complex pathophysiology involving genetic-environmental interplay. The study objective is to examine the prevalence of asthma in our ADHD population and explore factors that may increase the risk of developing asthma in children with ADHD.

METHODS

We retrospectively analyzed the presence of maternal stress during pregnancy and history of asthma in 201 children diagnosed with ADHD.

RESULTS

Chi-square analysis indicated significant higher presence of asthma in our ADHD sample compared to Quebec children, χ(2)(1, N = 201) = 15.37, P<0.001. Only prematurity and stress during pregnancy significantly predicted asthma in a logistic regression model, χ(2)(2)=23.70, P<0.001, with odds ratios of 10.6 (95% CI: 2.8-39.5) and 3.2 (95% CI: 1.4-7.3), respectively.

CONCLUSION

Children with ADHD have a higher prevalence of asthma than the general Quebec pediatric population. Children with ADHD born prematurely and/or those whose mothers experienced stress during pregnancy have a significantly increased risk of developing asthma. The study highlights the importance of potentially offering social and psychological support to mothers who experienced stress during pregnancy and/or are at risk of delivering prematurely.

Inter- and transgenerational epigenetic inheritance: evidence in asthma and COPD?

Evidence is now emerging that early life environment can have lifelong effects on metabolic, cardiovascular, and pulmonary function in offspring, a concept also known as fetal or developmental programming. In mammals, developmental programming is thought to occur mainly via epigenetic mechanisms, which include DNA methylation, histone modifications, and expression of non-coding RNAs. The effects of developmental programming can be induced by the intrauterine environment, leading to intergenerational epigenetic effects from one generation to the next. Transgenerational epigenetic inheritance may be considered when developmental programming is transmitted across generations that were not exposed to the initial environment which triggered the change. So far, inter- and transgenerational programming has been mainly described for cardiovascular and metabolic disease risk. In this review, we discuss available evidence that epigenetic inheritance also occurs in respiratory diseases, using asthma and chronic obstructive pulmonary disease (COPD) as examples. While multiple epidemiological as well as animal studies demonstrate effects of 'toxic' intrauterine exposure on various asthma-related phenotypes in the offspring, only few studies link epigenetic marks to the observed phenotypes. As epigenetic marks may distinguish individuals most at risk of later disease at early age, it will enable early intervention strategies to reduce such risks. To achieve this goal further, well designed experimental and human studies are needed.

Risk and protective factors for the development of childhood asthma

Childhood asthma prevalence worldwide has been increasing markedly over several decades. Various theories have been proposed to account for this alarming trend. The disease has a broad spectrum of potential determinants ranging from genetics to lifestyle and environmental factors. Epidemiological observations have demonstrated that several important lifestyle and environmental factors including obesity, urban living, dietary patterns such as food low in antioxidants and fast food, non-breastfeeding, gut flora imbalance, cigarette smoking, air pollution, and viral infection are associated with asthma exacerbations in children. However, only environmental tobacco smoke has been associated with the development of asthma. Despite epidemiological studies indicating that many other factors are probably associated with the development of asthma, the relationships are not considered causal due to the inadequate evidence and inconsistent results from recent studies. This may highlight that sufficient data and exact mechanisms of causality are still in need of further study.

An update on epigenetics and childhood respiratory diseases

Epigenetic mechanisms, defined as changes in phenotype or gene expression caused by mechanisms other than changes in the underlying DNA sequence, have been proposed to constitute a link between genetic and environmental factors that affect complex diseases. Recent studies show that DNA methylation, one of the key epigenetic mechanisms, is altered in children exposed to air pollutants and environmental tobacco smoke early in life. Several candidate gene studies on epigenetics have been published to date, but it is only recently that global methylation analyses have been performed for respiratory disorders such as asthma and chronic obstructive pulmonary disease. However, large-scale studies with adequate power are yet to be presented in children, and implications for clinical use remain to be evaluated. In this review, we summarize the recent advances in epigenetics and respiratory disorders in children, with a main focus on methodological challenges and analyses related to phenotype and exposure using global methylation approaches.

New problems arising from old drugs: second-generation effects of acetaminophen

Acetaminophen (APAP)/paracetamol is one of the most commonly used over-the-counter drugs taken worldwide for treatment of pain and fever. Although considered as safe when taken in recommended doses not higher than 4 g/day, APAP overdose is currently the most important cause of acute liver failure (ALF). ALF may require liver transplantation and can be fatal. The reasons for APAP-related ALF are mostly intentional (suicidal) or unintentional overdose. However, results from large scale epidemiological studies provide increasing evidence for second generation effects of APAP, even when taken in pharmacological doses. Most strikingly, APAP medication during pregnancy has been associated with health problems including neurodevelopmental and behavioral disorders such as attention deficit hyperactivity disorder and increase in the risk of wheezing and incidence of asthma among offspring. This article reviews the epidemiological findings and aims to shed light into the molecular and cellular mechanisms responsible for APAP-mediated prenatal risk for asthma.