Atopic dermatitis: Interaction between genetic variants of GSTP1, TNF, TLR2, and TLR4 and air pollution in early life

Air pollution and global healthcare use for atopic dermatitis: A systematic review

Increasing air pollution is common around the world, but the impacts of outdoor air pollution exposure on atopic dermatitis (AD) are unclear. We synthesized the current global epidemiologic evidence for air pollution exposure and associated medical visits for AD among adults and children. This review followed PRISMA guidelines, and searches were conducted on PubMed, MEDLINE, Web of Science and EMBASE databases. The searches yielded 390 studies, and after screening, 18 studies around the world assessing at least 5,197,643 medical visits for AD in total were included for the final analysis. We found that exposure to particulate matter ≤2.5 μm in diameter (PM2.5 ) [(10/11) of studies], particulate matter ≤10 μm in diameter (PM10 ) (11/13), nitrogen dioxide (NO2 ) (12/14) and sulfur dioxide (SO2 ) (10/13) was positively associated with AD visits. Results were equivocal for ozone [(4/8) of studies reported positive association] and limited for carbon monoxide [(1/4) of studies reported positive association]. When stratifying results by patient age, patient sex and season, we found that the associations with particulate matter, NO2 and O3 may be affected by temperature. Exposure to selected air pollutants is associated with AD visits, and increasingly poor worldwide air quality may increase global healthcare use for AD.

Critical role of epigenetic modification in the pathogenesis of atopic dermatitis

Atopic dermatitis is a chronic inflammatory skin disease characterised by recurrent eczema-like lesions and severe pruritus, along with drying and decrustation of skin. Current research relates the pathogenesis of atopic dermatitis mainly to genetic susceptibility, abnormal skin barrier function, immune disorders, Staphylococcus aureus colonisation, microbiological dysfunction and vitamin D insufficiency. Epigenetic modifications are distinct genetic phenotypes resulting from environment-driven changes in chromosome functions in the absence of nuclear DNA sequence variation. Classic epigenetic events include DNA methylation, histone protein modifications and non-coding RNA regulation. Increasing evidence has indicated that epigenetic events are involved in the pathogenesis of atopic dermatitis by their effects on multiple signalling pathways which in turn influence the above factors. This review primarily analyses the function of epigenetic regulation in the pathogenesis of atopic dermatitis. In addition, it tries to make recommendations for personalised epigenetic treatment strategies for atopic dermatitis in the future.

The immunological and structural epidermal barrier dysfunction and skin microbiome in atopic dermatitis-an update

Atopic dermatitis (AD) is a common, chronic and relapsing inflammatory skin disease with various clinical presentations and combinations of symptoms. The pathophysiology of AD is complex and multifactorial. There are several factors involved in the etiopathogenesis of AD including structural and immunological epidermal barrier defect, imbalance of the skin microbiome, genetic background and environmental factors. Alterations in structural proteins, lipids, proteases, and their inhibitors, lead to the impairment of the stratum corneum which is associated with the increased skin penetration and transepidermal water loss. The elevated serum immunoglobulin E levels and blood eosinophilia have been shown in the majority of AD patients. Type 2 T-helper cell immune pathway with increased expression of interleukin (IL)-4, IL-5, and IL-13, has an important role in the etiopathogenesis of AD. Both T cells and keratinocytes contribute to epidermal barrier impairment in AD via a dynamic interaction of cytokines and chemokines. The skin microbiome is another factor of relevance in the etiopathogenesis of AD. It has been shown that during AD flares, Staphylococcus aureus (S. aureus) colonization increased, while Staphylococcus epidermidis (S. epidermidis) decreased. On the contrary, S. epidermidis and species of Streptococcus, Corynebacterium and Propionibacterium increased during the remision phases. However, it is not clear whether skin dysbiosis is one of the symptoms or one of the causes of AD. There are several therapeutic options, targeting these pathways which play a critical role in the etiopathogenesis of AD. Although topical steroids are the mainstay of the treatment of AD, new biological therapies including IL-4, IL-13, and IL-31 inhibitors, as well as Janus kinase inhibitors (JAKi), increasingly gain more importance with new advances in the therapy of AD. In this review, we summarize the role of immunological and structural epidermal barrier dysfunction, immune abnormalities, impairment of lipids, filaggrin mutation and skin microbiome in the etiopathogenesis of AD, as well as the therapeutic options for AD and their effects on these abnormalities in AD skin.

Association of air pollution and genetic risks with incidence of elderly-onset atopic dermatitis: A prospective cohort study

BACKGROUND

Elderly-onset atopic dermatitis (AD) is a remarkable subtype and has been put on the agenda owing to its difficulty to control. Understanding the influence of genetic and environmental exposures is crucial to preventing elderly-onset AD.

OBJECTIVES

To explore the association between genes and air pollution on incident elderly-onset AD.

MATERIAL AND METHODS

This study was based on UK Biobank that recruited over 500,000 participants. The genetic risks were categorized into low, intermediate, and high groups according to tertiles of polygenic risk scores. Mixed exposure to various air pollutants was assessed using the weighted quantile sum (WQS) and also categorized based on tertiles. Within each genetic risk group, whether air pollutant mixture was associated with incident elderly-onset AD was estimated.

RESULTS

337,910 participants were included in the final analysis, and the mean age was 57.1. The median years for follow-up were 12.0, and the incident cases of AD were 2545. The medium and high air pollution mixture was significantly associated with incident AD compared with the low pollution group, with HRs of 1.182 (P = 0.003) and 1.359 (P < 0.001), respectively. In contrast, HR for medium and high genetic susceptibility was only 1.065 (P = 0.249) and 1.153 (P = 0.008). The population-attributable fraction of air pollution and genetic risk was 15.5 % (P < 0.001) and 6.4 % (P = 0.004). Additionally, compared with low genetic risk and low air pollution, high genetic risk and high air pollution was significantly associated with the incidence of elderly-onset AD with a HR of up to 1.523 (P < 0.001). There were no interactive effects between each group of genetic risks and air pollution. When grouped by sex, females could observe a stronger effect by genetic and air pollutant mixture exposure.

CONCLUSION

Air pollution and genetics both independently enhance the risk of newly developed AD, and the effect of air pollutants is stronger than the investigated genes.

Air Pollution and Atopic Dermatitis, from Molecular Mechanisms to Population-Level Evidence: A Review

Atopic dermatitis (AD) has increased in prevalence to become the most common inflammatory skin condition globally, and geographic variation and migration studies suggest an important role for environmental triggers. Air pollution, especially due to industrialization and wildfires, may contribute to the development and exacerbation of AD. We provide a comprehensive, multidisciplinary review of existing molecular and epidemiologic studies on the associations of air pollutants and AD symptoms, prevalence, incidence, severity, and clinic visits. Cell and animal studies demonstrated that air pollutants contribute to AD symptoms and disease by activating the aryl hydrocarbon receptor pathway, promoting oxidative stress, initiating a proinflammatory response, and disrupting the skin barrier function. Epidemiologic studies overall report that air pollution is associated with AD among both children and adults, though the results are not consistent among cross-sectional studies. Studies on healthcare use for AD found positive correlations between medical visits for AD and air pollutants. As the air quality worsens in many areas globally, it is important to recognize how this can increase the risk for AD, to be aware of the increased demand for AD-related medical care, and to understand how to counsel patients regarding their skin health. Further research is needed to develop treatments that prevent or mitigate air pollution-related AD symptoms.

Ambient air pollutants increase the risk of immunoglobulin E-mediated allergic diseases: a systematic review and meta-analysis

Immunoglobulin E (IgE)-mediated allergic diseases, including eczema, atopic dermatitis (AD), and allergic rhinitis (AR), have increased prevalence in recent decades. Recent studies have proved that environmental pollution might have correlations with IgE-mediated allergic diseases, but existing research findings were controversial. Thus, we performed a comprehensive meta-analysis from published observational studies to evaluate the risk of long-term and short-term exposure to air pollutants on eczema, AD, and AR in the population (per 10-μg/m3 increase in PM2.5 and PM10; per 1-ppb increase in SO2, NO2, CO, and O3). PubMed, Embase, and Web of Science were searched to identify qualified literatures. The Cochran Q test was used to assess heterogeneity and quantified with the I2 statistic. Pooled effects and the 95% confidence intervals (CIs) were used to evaluate outcome effects. A total of 55 articles were included in the study. The results showed that long-term and short-term exposure to PM10 increased the risk of eczema (PM10, RRlong = 1.583, 95% CI: 1.328, 1.888; RRshort = 1.006, 95% CI: 1.003-1.008) and short-term exposure to NO2 (RRshort = 1.009, 95% CI: 1.008-1.011) was associated with eczema. Short-term exposure to SO2 (RRshort: 1.008, 95% CI: 1.001-1.015) was associated with the risk of AD. For AR, PM2.5 (RRlong = 1.058, 95% CI: 1.014-1.222) was harmful in the long term, and short-term exposure to PM10 (RRshort: 1.028, 95% CI: 1.008-1.049) and NO2 (RRshort: 1.018, 95% CI: 1.007-1.029) were risk factors. The findings indicated that exposure to air pollutants might increase the risk of IgE-mediated allergic diseases. Further studies are warranted to illustrate the potential mechanism for air pollutants and allergic diseases.

Manipulating Microbiota to Treat Atopic Dermatitis: Functions and Therapies

Atopic dermatitis (AD) is a globally prevalent skin inflammation with a particular impact on children. Current therapies for AD are challenged by the limited armamentarium and the high heterogeneity of the disease. A novel promising therapeutic target for AD is the microbiota. Numerous studies have highlighted the involvement of the skin and gut microbiota in the pathogenesis of AD. The resident microbiota at these two epithelial tissues can modulate skin barrier functions and host immune responses, thus regulating AD progression. For example, the pathogenic roles of Staphylococcus aureus in the skin are well-established, making this bacterium an attractive target for AD treatment. Targeting the gut microbiota is another therapeutic strategy for AD. Multiple oral supplements with prebiotics, probiotics, postbiotics, and synbiotics have demonstrated promising efficacy in both AD prevention and treatment. In this review, we summarize the association of microbiota dysbiosis in both the skin and gut with AD, and the current knowledge of the functions of commensal microbiota in AD pathogenesis. Furthermore, we discuss the existing therapies in manipulating both the skin and gut commensal microbiota to prevent or treat AD. We also propose potential novel therapies based on the cutting-edge progress in this area.

Association of Toll-like receptors 4 (TLR-4) gene expression and polymorphisms in patients with severe asthma

Innate immunity plays a central role in the pathogenesis of severe asthma, and it is closely linked to elevated IgE and Toll-like receptor 4 (TLR-4) levels. However, there is a scarcity of information about the association of the TLR-4 receptor polymorphism in the pathogenesis of severe asthma. This study highlights the level of gene expression of different alleles in asthmatic patients compared to healthy control individuals. This was a randomized control trial, which included 150 patients with asthma (with high serum levels of IgE) with a matching 150 healthy control individuals. Participants had a series of blood tests to measure various immune parameters: interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor (TNF), intercellular adhesion molecule-1 (ICAM1) and detect allele type and gene expression of the TLR-4 gene. Patients with asthma had significantly higher levels of IL-8 when compared to the healthy control participants. In addition, in the rs91 genotyping, there were significant differences in the levels of IL-8 and TNF between CC and TT genotyping. While in rs90 TLR-4, TNF levels were significantly higher in AA vs. AG and GG genotypes among the asthmatic patients when compared to the control group. The results showed that in TLR-4, rs4986791 were significantly associated with asthma risk. Polymorphisms in TLRs play essential roles in asthma.

Allergy Prevalence in France and Skin Impact - Epidemiological Survey of a Representative Sample of French Adults

Background

Increased allergy frequency may have a significant impact on the skin, one of the largest targeted organs for allergic and immunological responses.

Methods

An online survey of 2036 adults as a representative sample of the French general population was conducted to evaluate the prevalence of self-reported allergies, the populations who report allergies and the skin conditions related to allergies.

Results

In general, 20.2% of French adults (average age 45 ± 15.8 years) reported allergies. These allergies were respiratory allergies (55.3%), skin allergies (48.8%) and food allergies (27.9%), and 78.9% indicated that their reported allergies were diagnosed by a doctor. In addition, 53.2% of individuals reporting an allergy also indicated that they experienced associated skin reactions. In comparison to those who did not report an allergy, these individuals were 1.5 to 4 times more likely to have a skin disease and 3 times more likely to have sensitive skin or skin reactions when using skincare products.

Conclusion

It is estimated that over 10 million French adults have allergies. These data will help increase awareness among the allergic population and healthcare professionals about the burden associated with allergies and the need for management to reduce their health impact.

Gut Microbiota, Probiotics, and Their Interactions in Prevention and Treatment of Atopic Dermatitis: A Review

Atopic dermatitis (AD) is a public health concern and is increasing in prevalence in urban areas. Recent advances in sequencing technology have demonstrated that the development of AD not only associate with the skin microbiome but gut microbiota. Gut microbiota plays an important role in allergic diseases including AD. The hypothesis of the “gut-skin” axis has been proposed and the cross-talk mechanism between them has been gradually demonstrated in the research. Probiotics contribute to the improvement of the intestinal environment, the balance of immune responses, regulation of metabolic activity. Most studies suggest that probiotic supplements may be an alternative for the prevention and treatment of AD. This study aimed to discuss the effects of probiotics on the clinical manifestation of AD based on gut microbial alterations. Here we reviewed the gut microbial alteration in patients with AD, the association between gut microbiota, epidermal barrier, and toll-like receptors, and the interaction of probiotics and gut microbiota. The potential mechanisms of probiotics on alleviating AD via upregulation of epidermal barrier and regulation of immune signaling had been discussed, and their possible effective substances on AD had been explored. This provides the supports for targeting gut microbiota to attenuate AD.

The role of epigenetics in allergy and asthma development

PURPOSE OF REVIEW

Epigenetic mechanisms are known to play a crucial role in the pathogenesis of asthma, allergic rhinitis, atopic dermatitis, food allergy, and other allergic disorders, especially through mediating the effects of the environmental factors, well recognized allergy-risk modifiers. The aim of this work was to provide a concise but comprehensive review of the recent progress in the epigenetics of allergic diseases.

RECENT FINDINGS

Recent few years have substantially expanded our knowledge on the role of epigenetics in the pathogenesis and clinical picture of allergies. Specifically, it has been shown that epigenetic marks, especially DNA methylation, possess a diagnostic potential for atopic sensitization, asthma, allergic rhinitis, and food allergy. DNA methylation can be a predictor of clinical responses in controlled allergen challenges, including oral food challenges. Furthermore, direct or indirect targeting epigenetic mechanisms, this time especially histone modifications, was able to favorably affect expression of the genes underlying allergies and generally improve airway biology in allergic diseases or their animal models.

SUMMARY

Further studies are needed to explore the diagnostic and therapeutic potential of epigenetic modifications in allergies and to develop respective clinical tools.

Onset and remission of eczema at pre-school age in relation to prenatal and postnatal air pollution and home environment across China

We investigated associations between prenatal and postnatal environmental factors and onset and remission of preschool childhood eczema across China. The study population was preschoolers in randomized day care centers in seven cities (N = 39,782). Data on eczema and prenatal and postnatal indoor and outdoor environment were obtained from a cross-sectional questionnaire sent to parents or other guardians. Reports on eczema in the first 2 years and in the past year was used to retrospectively calculate onset and remission (changes of reported eczema). Prenatal and postnatal outdoor temperature, NO₂ and PM₁₀ were modelled from official air pollution data. Associations were estimated by two-level logistic regression. Calculated onset rate was 3.2%/y and remission rate 29.2%/y. Exposure to NO₂ during pregnancy was associated with onset of eczema, similarly for all trimesters. Postnatal PM₁₀ and NO₂ were related to decreased remission. Postnatal outdoor temperature was associated with onset of eczema. Pre-natal and current redecoration or buying new furniture, and perinatal as well as current dampness and indoor mould, were associated with increased onset and decreased remission. Cockroaches in current home was another indoor risk factors. Prenatal exposure to farm environment and large family size were all negatively associated with eczema. In conclusion, a warmer climate and prenatal NO₂ can be associated with increased onset of eczema in Chinese preschoolers. Postnatal PM₁₀ and NO₂ can be associated with reduced remission. Perinatal and current dampness, indoor mould and cockroaches may increase onset and decrease remission. Exposure to chemical emissions from indoor materials after first year of life may increase onset. Prenatal exposure to farm environment and large family size could be protective.

Impact of airborne particulate matter on skin: a systematic review from epidemiology to in vitro studies

BACKGROUND

Air pollution is killing close to 5 million people a year, and harming billions more. Air pollution levels remain extremely high in many parts of the world, and air pollution-associated premature deaths have been reported for urbanized areas, particularly linked to the presence of airborne nano-sized and ultrafine particles.

MAIN TEXT

To date, most of the research studies did focus on the adverse effects of air pollution on the human cardiovascular and respiratory systems. Although the skin is in direct contact with air pollutants, their damaging effects on the skin are still under investigation. Epidemiological data suggested a correlation between exposure to air pollutants and aggravation of symptoms of chronic immunological skin diseases. In this study, a systematic literature review was conducted to understand the current knowledge on the effects of airborne particulate matter on human skin. It aims at providing a deeper understanding of the interactions between air pollutants and skin to further assess their potential risks for human health.

CONCLUSION

Particulate matter was shown to induce a skin barrier dysfunction and provoke the formation of reactive oxygen species through direct and indirect mechanisms, leading to oxidative stress and induced activation of the inflammatory cascade in human skin. Moreover, a positive correlation was reported between extrinsic aging and atopic eczema relative risk with increasing particulate matter exposure.

An update on immunologic mechanisms in the respiratory mucosa in response to air pollutants

Every day, we breathe in more than 10,000 L of air that contains a variety of air pollutants that can pose negative consequences to lung health. The respiratory mucosa formed by the airway epithelium is the first point of contact for air pollution in the lung, functioning as a mechanical and immunologic barrier. Under normal circumstances, airway epithelial cells connected by tight junctions secrete mucus, airway surface lining fluid, host defense peptides, and antioxidants and express innate immune pattern recognition receptors to respond to inhaled foreign substances and pathogens. Under conditions of air pollution exposure, the defenses of the airway epithelium are compromised by reductions in barrier function, impaired host defense to pathogens, and exaggerated inflammatory responses. Central to the mechanical and immunologic changes induced by air pollution are activation of redox-sensitive pathways and a role for antioxidants in normalizing these negative effects. Genetic variants in genes important in epithelial cell function and phenotype contribute to a diversity of responses to air pollution in the population at the individual and group levels and suggest a need for personalized approaches to attenuate the respiratory mucosal immune responses to air pollution.

Antioxidant genes and susceptibility to air pollution for respiratory and cardiovascular health

Oxidative stress occurs when antioxidant defences, which are regulated by a complex network of genes, are insufficient to maintain the level of reactive oxygen species below a toxic threshold. Outdoor air pollution has long been known to adversely affect health and one prominent mechanism of action common to all pollutants is the induction of oxidative stress. An individual's susceptibility to the effects of air pollution partly depends on variation in their antioxidant genes. Thus, understanding antioxidant gene-pollution interactions has significant potential clinical and public health impacts, including the development of targeted and cost-effective preventive measures, such as setting appropriate standards which protect all members of the population. In this review, we aimed to summarize the latest epidemiological evidence on interactions between antioxidant genes and outdoor air pollution, in the context of respiratory and cardiovascular health. The evidence supporting the existence of interactions between antioxidant genes and outdoor air pollution is strongest for childhood asthma and wheeze, especially for interactions with GSTT1, GSTM1 and GSTP1, for lung function in both children and adults for several antioxidant genes (GSTT1, GSTM1, GSTP1, HMOX1, NQO1, and SOD2) and, to a more limited extent, for heart rate variability in adults for GSTM1 and HMOX1. Methodological challenges hampering a clear interpretation of these findings and understanding of true potential heterogeneity are discussed.

Genetics and Epigenetics of Atopic Dermatitis: An Updated Systematic Review

BACKGROUND

Atopic dermatitis is a common inflammatory skin disorder that affects up to 15-20% of the population and is characterized by recurrent eczematous lesions with intense itching. As a heterogeneous disease, multiple factors have been suggested to explain the nature of atopic dermatitis (AD), and its high prevalence makes it necessary to periodically compile and update the new information available. In this systematic review, the focus is set at the genetic and epigenetic studies carried out in the last years.

METHODS

A systematic literature review was conducted in three scientific publication databases (PubMed, Cochrane Library, and Scopus). The search was restricted to publications indexed from July 2016 to December 2019, and keywords related to atopic dermatitis genetics and epigenetics were used.

RESULTS

A total of 73 original papers met the inclusion criteria established, including 9 epigenetic studies. A total of 62 genes and 5 intergenic regions were described as associated with AD.

CONCLUSION

Filaggrin (FLG) polymorphisms are confirmed as key genetic determinants for AD development, but also epigenetic regulation and other genes with functions mainly related to the immune system and extracellular matrix, reinforcing the notion of skin homeostasis breakage in AD.

Recent advances in atopic dermatitis

The prevalence and disease burden of atopic dermatitis (AD) is substantial. AD causes significant impairment in quality of life. It is also associated with mental disorders as well as cardiovascular diseases. Many factors including race, environment, skin barrier dysfunction, immune regulatory abnormalities, and microbiome have been reported to affect the pathophysiology of AD. A variety of cell types including Th2, Th17, Th22, and type 2 innate lymphoid cells contribute to AD. Cytokines from these immune cells cause abnormal epidermal differentiation and skin barrier dysfunction. Moreover, microbial dysbiosis and deficiency of antimicrobial peptides result in Staphylococcus aureus infection. Recently, new drugs have been successfully launched to target polarized immune pathways that lead to moderate-to-severe AD.

A study on the relationship between air pollution and pulmonary tuberculosis based on the general additive model in Wulumuqi, China

OBJECTIVE

This study aimed to explore the impact of atmospheric pollutants on the incidence of tuberculosis (TB), and provide new ideas for the prevention and control of TB in the future.

METHODS

It explored the relationship between air pollutants and meteorological factors, as well as between air pollutants and heating through Spearman correlation analysis and rank sum test. Additionally, it analyzed the relationship between air pollutants and TB incidence using the general additive model. Statistical analysis results at the p<0.05 level were considered significant.

RESULTS

Three months after exposure to air pollutants (PM_2.5, SO₂, NO₂, and CO) TB incidence increased. However, TB incidence increased 9 months after exposure to PM₁₀. The single pollutant model showed when concentrations of PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃ increased by 1μg/m³ (or 1mg/m³), the number of TB cases increased by 0.09%, 0.08%, 0.58%, 0.42%, 6.9%, and 0.57%, respectively. The optimal multi-pollutant model was a two-factor model (PM₁₀+NO₂).

CONCLUSION

Air pollutants including PM_2.5, PM₁₀, SO₂, NO₂, CO, and O₃ increased the risk of TB. Few studies have been conducted in this area of research, especially regarding the mechanism. The results of this study should contribute to the understanding of TB incidence and prompt additional research.

Associations between air pollution and pediatric eczema, rhinoconjunctivitis and asthma: A meta-analysis of European birth cohorts

BACKGROUND

Uncertainly continues to exist regarding the role of air pollution on pediatric asthma and allergic conditions, especially as air pollution levels have started to decrease in recent decades.

OBJECTIVE

We examined associations of long-term air pollution levels at the home address with pediatric eczema, rhinoconjunctivitis and asthma prevalences in five birth cohorts (BIB, EDEN, GASPII, RHEA and INMA) from seven areas in five European countries.

METHODS

Current eczema, rhinoconjunctivitis and asthma were assessed in children aged four (N = 6527) and eight years (N = 2489). A multi-morbidity outcome (≥2 conditions versus none) was also defined. Individual outdoor levels of nitrogen dioxide (NO₂), nitrogen oxides, mass of particulate matter with an aerodynamic diameter <10 μm (PM₁₀), 10-2.5 μm (PM_coarse) and <2.5 μm (PM_2.5), and PM_2.5 absorbance were assigned to the birth, four- and eight-year home addresses using highly defined spatial air pollution exposure models. Cohort-specific cross-sectional associations were assessed using logistic regression models adjusted for demographic and environmental covariates and combined in a random effects meta-analysis.

RESULTS

The overall prevalence of pediatric eczema, rhinoconjunctivitis and asthma at four years was 15.4%, 5.9% and 12.4%. We found no increase in the prevalence of these outcomes at four or eight years with increasing air pollution exposure. For example, the meta-analysis adjusted odds ratios (95% confidence intervals) for eczema, rhinoconjunctivitis and asthma at four years were 0.94 (0.81, 1.09), 0.90 (0.75, 1.09), and 0.91 (0.74, 1.11), respectively, per 10 μg/m³ increase in NO₂ at the birth address, and 1.00 (0.81, 1.23), 0.70 (0.49, 1.00) and 0.88 (0.54, 1.45), respectively, per 5 μg/m³ increase in PM_2.5 at the birth address.

DISCUSSION

In this large meta-analysis of five birth cohorts, we found no indication of adverse effects of long-term air pollution exposure on the prevalence of current pediatric eczema, rhinoconjunctivitis or asthma.

Oxidative Stress and Atopic Dermatitis

Atopic dermatitis is a common chronic/chronically relapsing inflammatory skin disease, with increasing worldwide prevalence. Etiopathogenesis is complex and multifactorial, with a mix of genetic, immunological and environmental aspects. Like in other chronic inflammatory diseases, oxidative stress plays an important pathogenetic role. We reviewed in vivo research studies on humans about oxidative stress and atopic dermatitis. Although sometimes contrasting, overall, they suggest that oxidative stress may have a significant role in atopic dermatitis, but our understanding is still incomplete, at least concerning in vivo data, because of limitations of available literature. Research consists of 33 papers published in 28 years, was not always performed on large study populations, represents a limited number of countries and ethnicities-not always in proportion to their size-and is scattered over multiple papers that, in the majority of cases, cannot be pooled and/or compared because many biomarkers were studied, in different tissues and with different methods. Further, larger studies appear warranted and necessary to shed more light on this aspect of atopic dermatitis, which is important not only to improve our understanding of this disease, but also for potential clinical and therapeutic implications.

Recent findings in the genetics and epigenetics of asthma and allergy

In asthma and allergy genetics, a trend towards a few main topics developed over the last 2 years. First, a number of studies have been published recently which focus on overlapping and/or very specific phenotypes: within the allergy spectrum but also reaching beyond, looking for common genetic traits shared between different diseases or disease entities. Secondly, an urgently needed focus has been put on asthma and allergy genetics in populations genetically different from European ancestry. This acknowledges that the majority of new asthma patients today are not white and asthma is a truly worldwide disease. In epigenetics, recent years have seen several large-scale epigenome-wide association studies (EWAS) being published and a further focus was on the interaction between the environment and epigenetic signatures. And finally, the major trends in current asthma and allergy genetics and epigenetics comes from the field of pharmacogenetics, where it is necessary to understand the susceptibility for and mechanisms of current asthma and allergy therapies while at the same time, we need to have scientific answers to the recent availability of novel drugs that hold the promise for a more individualized therapy.

The impact of airborne pollution on atopic dermatitis: a literature review

The increasing prevalence of atopic dermatitis (AD) parallels a global rise in industrialization and urban living over recent decades. This shift in lifestyle is accompanied by greater cutaneous exposure to environmental pollutants during the course of daily activities. The objectives of this review are to highlight the effects of airborne pollution on epidermal barrier function, examine evidence on the relationship between pollutants and AD, synthesize a proposed mechanism for pollution-induced exacerbation of AD, and identify potential methods for the reduction and prevention of pollutant-induced skin damage. The literature review was done by searching the PubMed, Embase and Google Scholar databases. Inclusion criteria were in vitro and animal studies, clinical trials and case series. Non-English-language publications, review articles and case reports were excluded. Pollutants induce cutaneous oxidative stress and have been shown to damage skin barrier integrity by altering transepidermal water loss, inflammatory signalling, stratum corneum pH and the skin microbiome. AD represents a state of inherent barrier dysfunction, and both long- and short-term pollutant exposure have been linked to exacerbation of AD symptoms and increased AD rates in population studies. Airborne pollutants have a detrimental effect on skin barrier integrity and AD symptoms, and appear to pose a multifaceted threat in AD through several parallel mechanisms, including oxidative damage, barrier dysfunction, immune stimulation and propagation of the itch-scratch cycle. Future research is needed to elucidate specific mechanisms of pollution-induced epidermal barrier dysfunction and to identify efficacious methods of skin barrier repair and protection against pollutant-driven damage.

Methodological challenges in constructing DNA methylation risk scores

Polygenic approaches often access more variance of complex traits than is possible by single variant approaches. For genotype data, genetic risk scores (GRS) are widely used for risk prediction as well as in association and interaction studies. Recently, interest has been growing in transferring GRS approaches to DNA methylation data (methylation risk scores, MRS), which can be used 1) as biomarkers for environmental exposures, 2) in association analyses in which single CpG sites do not achieve significance, 3) as dimension reduction approach in interaction and mediation analyses, and 4) to predict individual risks of disease or treatment success. Most GRS approaches can directly be transferred to methylation data. However, since methylation data is more sensitive to confounding, e.g. by age and tissue, it is more complex to find appropriate external weights. In this review, we will outline the adaption of current GRS approaches to methylation data and highlight occurring challenges.

[Air pollution and atopic eczema : Systematic review of findings from environmental epidemiological studies]

BACKGROUND

Among the many risk factors for the development of atopic eczema (AE), the influence of air pollution has recently been discussed more often. A systematic review about this topic however is lacking.

AIMS

Which effects of outdoor air pollution (particles, nitric oxides, sulfur dioxide, ozone or general traffic exhaust emissions) on AE can be demonstrated in a systematic analysis of available environmental epidemiologic studies?

METHODS

All environmental epidemiologic studies on AE and air pollution found in the literature database PubMed were identified. The most important key figures of these studies were tabulated, the quality of evidence was graded and the studies described.

RESULTS

A total of 57 studies were identified. Only one of the 15 cross-sectional studies with a large-scale exposure assessment found a significant association between AE and air pollution. In contrast 23 of 30 studies with small-scale exposure assessment found a significant association between AE and traffic related emissions-especially from trucks. Of the 30 studies, 14 were cohort studies (1 adult, 13 birth cohorts). The sole adult cohort found an association with intrinsic AE. In the East Asian cohorts (all published since 2015), an association between maternal exposure to traffic-related pollution and incidence of AE in the offspring was found. This was less clear in cohorts from Europe/US or simply not investigated. In 5/5 panel studies (all from South Korea), symptom severity of AE was found to be significantly and positively related to outdoor air pollution.

CONCLUSIONS

In a systematic analysis of environmental epidemiologic studies about air pollution and AE rather good evidence was found that, based on small-scale exposure measurements, especially truck traffic emissions increased AE prevalence, while large-scale exposure to larger particles (PM10) or SO₂ was without effect. Considering pathophysiologic aspects traffic exhaust emissions seem to affect both skin barrier function and activation of immune responses.

The "envirome" and what the practitioner needs to know about it

OBJECTIVE

This review on the "envirome" focuses on pollution, microbial, and social stressor elements of the environment that may impact development or expression of allergic diseases.

DATA SOURCES

Peer-reviewed publications on the impact of environmental factors indexed in PubMed were the primary data source for this review.

STUDY SELECTIONS

The primary search strategy for this review employed cross-referencing asthma, atopic dermatitis, and immunoglobulin E (IgE) against pollution (ozone, particulate matter, nitrogen oxides, tobacco smoke), microbial exposures (farm exposure, microbiome, infection, antibiotic use) and psychosocial stressors, with emphasis on results in the past 5 years, with inclusion of key seminal articles or comprehensive reviews.

RESULTS

Air pollution is a clear cause of allergic disease exacerbation, with increasing recognition that pollutant exposure increases risk of allergic disease. Microbial exposures and maternal and child stress also modulate development and expression of allergic disease. Early life exposures are especially critical periods during which all of these factors have notable impacts on allergic disease.

CONCLUSION

Nonallergenic environmental factors are important modulators and adjuvants for development of allergic disease, with early life exposures being especially important. Development and validation of interventions directed toward these factors during early life is a significant opportunity for primary prevention of allergic disease.

Xenobiotic Receptors and Their Mates in Atopic Dermatitis

Atopic dermatitis (AD) is the most common inflammatory skin disease worldwide. It is a chronic, relapsing and pruritic skin disorder which results from epidermal barrier abnormalities and immune dysregulation, both modulated by environmental factors. AD is strongly associated with asthma and allergic rhinitis in the so-called 'atopic march.' Xenobiotic receptors and their mates are ligand-activated transcription factors expressed in the skin where they control cellular detoxification pathways. Moreover, they regulate the expression of genes in pathways involved in AD in epithelial cells and immune cells. Activation or overexpression of xenobiotic receptors in the skin can be deleterious or beneficial, depending on context, ligand and activation duration. Moreover, their impact on skin might be amplified by crosstalk among xenobiotic receptors and their mates. Because they are activated by a broad range of endogenous molecules, drugs and pollutants owing to their promiscuous ligand affinity, they have recently crystalized the attention of researchers, including in dermatology and especially in the AD field. This review examines the putative roles of these receptors in AD by critically evaluating the conditions under which the proteins and their ligands have been studied. This information should provide new insights into AD pathogenesis and ways to develop new therapeutic interventions.

TLR4 in skin cancer: From molecular mechanisms to clinical interventions

The health and economic burden imposed by skin cancer is substantial, creating an urgent need for the development of improved molecular strategies for its prevention and treatment. Cutaneous exposure to solar ultraviolet (UV) radiation is a causative factor in skin carcinogenesis, and TLR4-dependent inflammatory dysregulation is an emerging key mechanism underlying detrimental effects of acute and chronic UV exposure. Direct and indirect TLR4 activation, upstream of inflammatory signaling, is elicited by a variety of stimuli, including pathogen-associated molecular patterns (such as lipopolysaccharide) and damage-associated molecular patterns (such as HMGB1) that are formed upon exposure to environmental stressors, such as solar UV. TLR4 involvement has now been implicated in major types of skin malignancies, including nonmelanoma skin cancer, melanoma and Merkel cell carcinoma. Targeted molecular interventions that positively or negatively modulate TLR4 signaling have shown promise in translational, preclinical, and clinical investigations that may benefit skin cancer patients in the near future.

Vitamins A and E during Pregnancy and Allergy Symptoms in an Early Childhood-Lack of Association with Tobacco Smoke Exposure

Epidemiological studies have suggested an association between maternal antioxidant levels during pregnancy and development of allergic diseases in their offspring. The aim of the study was to determine plasma vitamins A and E concentration in the 1st trimester of pregnancy, at delivery and in cord blood and to search for a relationship with allergy in up to 2-year-old children who were prenatally exposed or not exposed to tobacco smoke. The study participants included 252 mother-child pairs from Polish Mother and Child Cohort. Vitamin concentrations were measured using the HPLC-UV method, smoking status&mdash;as saliva cotinine level using the HPLC-MS/MS technique. Children&rsquo;s health status was assessed using a questionnaire and pediatricians/allergists examination. Cord plasma vitamin concentrations were significantly lower than their levels in maternal plasma in the 1sttrimester and at delivery (p < 0.001). Significantly higher concentrations of vitamin E have been shown to occur during the 1st trimester of pregnancy in plasma of the women who have actively/passively smoked cigarettes compared to the non-smokers (p < 0.02). Multivariate analysis with inclusion of a variety of confounding factors have not indicated any statistically significant associations between &beta;-carotene, vitamins A and E and the risk of food allergy, atopic dermatitis and wheezing in their children up to 2 years of age. The interaction between smoking during pregnancy and vitamins levels on the risk of allergy was not statistically significant (p < 0.4). The relationship between plasma concentration of vitamins A and E, and the risk of allergy in their young children has not been demonstrated.