Genetic aspects of pulmonary responses to inhaled pollutants

Genetic susceptibility to airway inflammation and exposure to short-term outdoor air pollution

BACKGROUND

Air pollution is a large environmental health hazard whose exposure and health effects are unequally distributed among individuals. This is, at least in part, due to gene-environment interactions, but few studies exist. Thus, the current study aimed to explore genetic susceptibility to airway inflammation from short-term air pollution exposure through mechanisms of gene-environment interaction involving the SFTPA, GST and NOS genes.

METHODS

Five thousand seven hundred two adults were included. The outcome measure was fraction of exhaled nitric oxide (FeNO), at 50 and 270 ml/s. Exposures were ozone (O₃), particulate matter < 10 µm (PM₁₀), and nitrogen dioxide (NO₂) 3, 24, or 120-h prior to FeNO measurement. In the SFTPA, GST and NOS genes, 24 single nucleotide polymorphisms (SNPs) were analyzed for interaction effects. The data were analyzed using quantile regression in both single-and multipollutant models.

RESULTS

Significant interactions between SNPs and air pollution were found for six SNPs (p < 0.05): rs4253527 (SFTPA1) with O₃ and NO_x, rs2266637 (GSTT1) with NO₂, rs4795051 (NOS2) with PM₁₀, NO₂ and NO_x, rs4796017 (NOS2) with PM₁₀, rs2248814 (NOS2) with PM₁₀ and rs7830 (NOS3) with NO₂. The marginal effects on FeNO for three of these SNPs were significant (per increase of 10 µg/m³):rs4253527 (SFTPA1) with O₃ (β: 0.155, 95%CI: 0.013-0.297), rs4795051 (NOS2) with PM₁₀ (β: 0.073, 95%CI: 0.00-0.147 (single pollutant), β: 0.081, 95%CI: 0.004-0.159 (multipollutant)) and NO₂ (β: -0.084, 95%CI: -0.147; -0.020 (3 h), β: -0.188, 95%CI: -0.359; -0.018 (120 h)) and rs4796017 (NOS2) with PM₁₀ (β: 0.396, 95%CI: 0.003-0.790).

CONCLUSIONS

Increased inflammatory response from air pollution exposure was observed among subjects with polymorphisms in SFTPA1, GSTT1, and NOS genes, where O₃ interacted with SFTPA1 and PM10 and NO₂/NO_x with the GSTT1 and NOS genes. This provides a basis for the further exploration of biological mechanisms as well as the identification of individuals susceptible to the effects of outdoor air pollution.

Susceptibility Variations in Air Pollution Health Effects: Incorporating Neuroendocrine Activation

Diverse host factors/phenotypes may exacerbate or diminish biological responses induced by air pollutant exposure. We lack an understanding of biological indicators of environmental exposures that culminate in a physiological response versus those that lead to adversity. Variations in response phenotype might arise centrally and/or at the local tissue level. In addition to genetic differences, the current evidence supports the roles of preexisting cardiopulmonary diseases, diabetes, diet, adverse prenatal environments, neurobehavioral disorders, childhood infections, microbiome, sex, and psychosocial stressors in modifying the susceptibility to air pollutant exposures. Animal models of human diseases, obesity, nutritional inadequacies, and neurobehavioral conditions have been compared with healthy controls to understand the causes of variations in susceptibility. Although psychosocial stressors have been associated with increased susceptibility to air pollutant effects, the contribution of neuroendocrine stress pathways in mediating these effects is just emerging. The new findings of neuroendocrine activation leading to systemic metabolic and immunological effects of air pollutants, and the potential contribution to allostatic load, emphasize the consideration of these mechanisms into susceptibility. Variations in susceptibility to air pollution health effects are likely to underlie host genetic and physiological conditions in concert with disrupted neuroendocrine circuitry that alters physiological stability under the influence of stressors.

Genetic susceptibility to toxicologic lung responses among inbred mouse strains following exposure to carbon nanotubes and profiling of underlying gene networks

The risk of human exposure to fiber nanoparticles has risen in recent years due to increases in the manufacture and utilization of carbon nanotubes (CNTs). CNTs are present as airborne particulates in occupational settings and their hazard potential has been demonstrated in experimental lung exposure studies using inbred mouse strains. However, it is not known whether different inbred strains differ in lung responses to CNTs by virtue of their genetics. In this work, common inbred strains (BALB/c, C57Bl/6, DBA/2, and C3H/He) were exposed to CNTs via oropharyngeal aspiration and lung histology and bronchoalveolar lavage (BAL) samples were evaluated over 28days with the objective of evaluating sensitivity/resistance among strains. C57Bl/6 mice developed significantly more extensive type II pneumocyte (T2P) hyperplasia and alveolar infiltrate compared to DBA/2 mice, which were resistant. Surprisingly, DBA/2 but not C57Bl/6 mice were extremely sensitive to increases in leukocytes recovered in BAL fluid. Underlying global gene expression patterns in the two strains were compared using mRNA sequencing to investigate regulatory networks associated with the different effects. The impact of exposure on gene networks regulating various aspects of immune response and cell survival was limited in DBA/2 mice compared to C57Bl/6. Investigation of B6D2F1 (C57Bl/6×DBA/2 hybrid) mice demonstrated inheritance of sensitivity to CNT exposures in regard to toxicologic lung pathology and BAL leukocyte accumulations. These findings demonstrate a genetic basis of susceptibility to CNT particle exposures and both inform the use of inbred mouse models and suggest the likelihood of differences in genetic susceptibility among humans.

The Role of Matrix Metalloproteinases in Development, Repair, and Destruction of the Lungs

Normal gas exchange after birth requires functional lung alveolar units that are lined with epithelial cells, parts of which are intricately fused with microvascular capillaries. A significant phase of alveolar lung development occurs in the perinatal period, continues throughout early stages in life, and requires activation of matrix-remodeling enzymes. Failure to achieve an optimum number of alveoli during lung maturation can cause several untoward medical consequences including disabling obstructive and/or restrictive lung diseases that limit physiological endurance and increase mortality. Several members of the matrix metalloproteinase (MMP) family are critical in lung remodeling before and after birth; however, their resurgence in response to environmental factors, infection, and injury can also compromise lung function. Therefore, temporal expression, regulation, and function of MMPs play key roles in developing and maintaining adequate oxygenation under steady state, as well as in diseased conditions. Broadly, with the exception of MMP2 and MMP14, most deletional mutations of MMPs fail to perturb lung development; however, their individual absence can alter the pathophysiology of respiratory diseases. Specifically, under stressed conditions such as acute respiratory infection and allergic inflammation, MMP2 and MMP9 can play a protective role through bacterial clearance and production of chemotactic gradient, while loss of MMP12 can protect mice from smoke-induced lung disease. Therefore, better understanding of the expression and function of MMPs under normal lung development and their resurgence in response respiratory diseases could provide new therapeutic options in the future.

Pulmonary function reductions among potentially susceptible subgroups of agricultural workers in Colorado and Nebraska

OBJECTIVE

Organic dust inhalation has been associated with adverse respiratory responses among agricultural workers. We evaluated factors that may confer increased susceptibility to these health effects.

METHODS

We quantified personal work shift exposures to inhalable dust, endotoxin, and its 3-hydroxy fatty acid constituents, and evaluated changes in pulmonary function among 137 grain elevator, cattle feedlot, dairy, and corn farm workers.

RESULTS

Increased dust exposure was associated with work shift reductions in lung function. Although interpretation is limited because of small samples, a suggestion of stronger exposure-response relationships was observed among smokers, as well as workers reporting pesticide/herbicide application, asthma, or allergies, and those with genetic polymorphisms (TLR4) (Pinteraction ≤ 0.05).

CONCLUSIONS

A better understanding of factors leading to increased susceptibility of adverse respiratory outcomes is needed to optimize exposure reduction strategies and develop more comprehensive wellness programs.

Role of GSTM1 in resistance to lung inflammation

Lung inflammation resulting from oxidant/antioxidant imbalance is a common feature of many lung diseases. In particular, the role of enzymes regulated by the NF-E2-related factor 2 transcription factor has recently received increased attention. Among these antioxidant genes, glutathione S-transferase Mu 1 (GSTM1) has been most extensively characterized because it has a null polymorphism that is highly prevalent in the population and associated with increased risk of inflammatory lung diseases. Present evidence suggests that GSTM1 acts through interactions with other genes and environmental factors, especially air pollutants. Here, we review GSTM1 gene expression and regulation and summarize the findings from epidemiological, clinical, animal, and in vitro studies on the role played by GSTM1 in lung inflammation. We discuss limitations in the existing knowledge base and future perspectives and evaluate the potential of pharmacologic and genetic manipulation of the GSTM1 gene to modulate pulmonary inflammatory responses.

Genomics and the respiratory effects of air pollution exposure

Adverse health effects from air pollutants remain important, despite improvement in air quality in the past few decades. The exact mechanisms of lung injury from exposure to air pollutants are not yet fully understood. Studying the genome (e.g. single-nucleotide polymorphisms (SNP) ), epigenome (e.g. methylation of genes), transcriptome (mRNA expression) and microRNAome (microRNA expression) has the potential to improve our understanding of the adverse effects of air pollutants. Genome-wide association studies of SNP have detected SNP associated with respiratory phenotypes; however, to date, only candidate gene studies of air pollution exposure have been performed. Changes in epigenetic processes, such DNA methylation that leads to gene silencing without altering the DNA sequence, occur with air pollutant exposure, especially global and gene-specific methylation changes. Respiratory cell line and animal models demonstrate distinct gene expression signatures in the transcriptome, arising from exposure to particulate matter or ozone. Particulate matter and other environmental toxins alter expression of microRNA, which are short non-coding RNA that regulate gene expression. While it is clearly important to contain rising levels of air pollution, strategies also need to be developed to minimize the damaging effects of air pollutant exposure on the lung, especially for patients with chronic lung disease and for people at risk of future lung disease. Careful study of genomic responses will improve our understanding of mechanisms of lung injury from air pollution and enable future clinical testing of interventions against the toxic effects of air pollutants.

Glutathione-S-transferase M1 regulation of diesel exhaust particle-induced pro-inflammatory mediator expression in normal human bronchial epithelial cells

Background

Diesel exhaust particles (DEP) contribute substantially to ambient particulate matter (PM) air pollution in urban areas. Inhalation of PM has been associated with increased incidence of lung disease in susceptible populations. We have demonstrated that the glutathione S-transferase M1 (GSTM1) null genotype could aggravate DEP-induced airway inflammation in human subjects. Given the critical role airway epithelial cells play in the pathogenesis of airway inflammation, we established the GSTM1 deficiency condition in primary bronchial epithelial cells from human volunteers with GSTM1 sufficient genotype (GSTM1+) using GSTM1 shRNA to determine whether GSTM1 deficiency could exaggerate DEP-induced expression of interleukin-8 (IL-8) and IL-1β proteins. Furthermore, the mechanisms underlying GSTM1 regulation of DEP-induced IL-8 and IL-1β expression were also investigated.

Methods

IL-8 and IL-1β protein levels were measured using enzyme-linked immunosorbent assay. GSTM1 deficiency in primary human bronchial epithelial cells was achieved using lentiviral GSTM1 shRNA particles and verified using real-time polymerase chain reaction and immunoblotting. Intracellular reactive oxygen species (ROS) production was evaluated using flow cytometry. Phosphorylation of protein kinases was detected using immunoblotting.

Results

Exposure of primary human bronchial epithelial cells (GSTM1+) to 25-100 μg/ml DEP for 24 h significantly increased IL-8 and IL-1β protein expression. Knockdown of GSTM1 in these cells further elevated DEP-induced IL-8 and IL-1β expression, implying that GSTM1 deficiency aggravated DEP-induced pro-inflammatory response. DEP stimulation induced the phosphorylation of extracellular signal-regulated kinase (ERK) and Akt, the downstream kinase of phosphoinositide 3-kinase (PI3K), in GSTM1+ bronchial epithelial cells. Pharmacological inhibition of ERK kinase and PI3K activity blocked DEP-induced IL-8 and IL-1β expression. DEP-induced ERK and Akt phosphorylation could be increased by GSTM1 knockdown. In addition, pretreatment of HBEC with the antioxidant N-acetyl cysteine significantly inhibited DEP-induced ERK and Akt phosphorylation, and subsequent IL-8 and IL-1β expression.

Conclusion

GSTM1 regulates DEP-induced IL-8 and IL-1β expression in primary human bronchial epithelial cells by modulation of ROS, ERK and Akt signaling.

Evolutionary conservation of metabolism explains howDrosophila nutrigenomics can help us understand human nutrigenomics

While large populations in the third world are enduring famine, much of the developed world is undergoing an obesity epidemic. In addition to reflecting an unbalanced distribution of food, the "epidemic of overabundance" is ironically leading to a decrease in the health and longevity of the obese and improperly nourished in the first world. International consortia, such as the European Nutrigenomics Organization (NuGO), are increasing our knowledge of nutrientgene interactions and the effects of diet and obesity on human health. In this review, we summarize both previous and ongoing nutrigenomics studies in Drosophila and we explain how these studies can be used to provide insights into molecular mechanisms underlying nutrigenomics in humans. We will discuss how quantitative trait locus (QTL) experiments have identified genes that affect triglyceride levels in Drosophila, and how microarray analyses show that hundreds of genes have altered gene expression under different dietary conditions. Finally, we will discuss ongoing combined microarray-QTL studies, termed "genetical genomics," that promise to identify "master modulatory loci" that regulate global responses of potentially hundreds of genes under different dietary conditions. When "master modulatory loci" are identified in Drosophila, then experiments in mammalian models can be used to determine the relevance of these genes to human nutrition and health.

Unusual ciliary abnormalities in three 9/11 response workers

After the 9/11 terrorist attacks on the World Trade Center in New York in 2001, thousands of response workers were exposed to complex mixtures of toxins, pollutants, and carcinogens. Many developed illnesses involving the respiratory tract. We report unusual ultrastructural ciliary abnormalities in 3 response workers that corresponded to their respiratory and ciliary functional abnormalities. Each patient had respiratory cilia biopsies that were evaluated for motility and ultrastructural changes. Impaired ciliary motility was seen in 2 of the 3 patients. Each of the patients showed monomorphic ultrastructural abnormalities. Two of the patients showed identical triangular disarray of axonemal microtubules with peripheral doublets 1,4, and 7 forming the corners of the triangle and doublet 9 always more medially displaced than doublets 2, 3, 5, 6, and 8. Two workers had cilia in which axonemes were replaced by homogeneously dense cores. One of these also had cilia with triangular axonemes as previously described. The other had cilia with a geometric triangular to pentagonal shape. The ciliary abnormalities described here may represent a new class of primary ciliary dyskinesia in which abnormalities may have a genetic basis and a phenotypic expression that is prompted at the cellular level by local environmental conditions.

The influence of traffic-related pollution on individuals' life-style: results from the BRFSS

This paper employs the Behavioral Risk Factor Surveillance System (2001) data in conjunction with the Environmental Protection Agency's Air Quality System data to investigate how air pollution caused by motor vehicle emissions affects the likelihood of good health and the amount of health investments. Models are estimated using three different measures of overall health: a measure of self-assessed health and two health outcome indicators (asthma and blood pressure). A multivariate probit approach is used to estimate recursive systems of equations for self-assessed health, health outcomes and life-styles. The most interesting result concerns the influence of pollution on health-improving life-style choices: only if traffic pollution is in the 'satisfactory range' (AQI level at or below 100), individuals will have incentive to invest in health.

Differential zinc accumulation and expression of human zinc transporter 1 (hZIP1) in prostate glands

Zinc (Zn) is essential for a very large number and variety of cellular functions but is also potentially toxic. Zn homeostasis is therefore dynamically maintained by a variety of transporters and other proteins distributed in distinct cellular and subcellular compartments. Zn transport is mediated by two major protein families: the Zip family, which mediates Zn influx, and the ZnTs which are primarily linked to Zn sequestration into intracellular compartments and are, thereby, involved in lowering cytoplasmic Zn free ion concentrations. In the prostate epithelial cell, the accumulation of high cellular zinc is a specialized function that is necessary for these cells to carry out the major physiological functions of production and secretion of prostatic fluids. The loss of Zn accumulation is the most consistent and persistent characteristic of prostate malignancy. Currently, there are no direct methods to determine the relative Zn levels in various cell types of prostate gland (i.e. stroma, glandular epithelia, acini, and muscular) and no reliable ways to compare the Zn in normal versus malignant areas of the gland. Here we report a new method to show a differential Zn staining method that correlates with various stages of prostate cancer development in situ and expression of a human Zn transporter1-hZIP1 -in situ by in situ reverse transcriptase-polymerase chain reaction hybridization (ISRTPCR) that correlate with the relative Zn levels determined by the differential Zn staining method. By utilizing these methods, we show for the first time that: (1) the relative Zn levels are very low to absent in the malignant glands, (2) normal glands show high Zn levels in both glandular epithelia as well as in stromal tissues, (3) the Zn levels begin to decrease in pre-malignant glands and precedes the development of malignancy, and (4) the expression of human Zn transporter1 (hZIP1) appears to correlate with the Zn levels in the prostate glands and may be the major Zn regulator in this organ.

Air pollution as a potential contributor to the 'epidemic' of autoimmune disease

There has been remarkable progress over the past 20 years in pushing forward our understanding of many facets of autoimmune disease. Indeed, knowledge of the genetic basis of autoimmunity and the molecular and cellular pathways involved in its pathogenesis has reached an unprecedented level. Yet this knowledge has not served to prevent autoimmune disease nor to curtail the dramatic rise in its incidence over the same interval. Population-level genetic changes cannot explain this trend; thus, environmental factors are strongly implicated. Among the possible environmental contributors to autoimmune disease, air pollution exposure has received very little attention. Although there is only a small amount of published data directly examining a possible causal relationship between air pollution exposure and autoimmunity, data from related fields suggests that it could facilitate autoimmunity as well. If correct, this hypothesis could prove to have sizeable public health implications.

Deducing in vivo toxicity of combustion-derived nanoparticles from a cell-free oxidative potency assay and metabolic activation of organic compounds

BACKGROUND

The inhalation of combustion-derived nanoparticles (CDNPs) is believed to cause an oxidative stress response, which in turn may lead to pulmonary or even systemic inflammation.

OBJECTIVE AND METHODS

In this study we assessed whether the in vivo inflammatory response--which is generally referred to as particle toxicity-of mice to CDNPs can be predicted in vitro by a cell-free ascorbate test for the surface reactivity or, more precisely, oxidative potency (OxPot) of particles.

RESULTS

For six types of CDNPs with widely varying particle diameter (10-50 nm), organic content (OC; 1-20%), and specific Brunauer, Emmett, and Teller (BET) surface area (43-800 m2/g), OxPot correlated strongly with the in vivo inflammatory response (pulmonary polymorphonuclear neutrophil influx 24 hr after intratracheal particle instillation). However, for CDNPs with high organic content, OxPot could not explain the observed inflammatory response, possibly due to shielding of the OxPot of the carbon core of CDNPs by an organic coating. On the other hand, a pathway-specific gene expression screen indicated that, for particles rich in polycyclic aromatic hydrocarbon (PAHs), cytochrome P450 1A1 (CYP1A1) enzyme-mediated biotransformation of bio-available organics may generate oxidative stress and thus enhance the in vivo inflammatory response.

CONCLUSION

The compensatory nature of both effects (shielding of carbon core and biotransformation of PAHs) results in a good correlation between inflammatory response and BET surface area for all CDNPs. Hence, the in vivo inflammatory response can either be predicted by BET surface area or by a simple quantitative model, based on in vitro OxPot and Cyp1a1 induction.

Vulnerability to air pollution health effects

INTRODUCTION

Ambient air pollution can have adverse effects on the health of exposed populations, but individuals or groups are not equally vulnerable, and pollution reduction benefits are likely to be unevenly distributed within a population. While the use of total-population risks is a valid approach for public health protection, it is increasingly recognized that more attention on vulnerable groups is necessary. This paper describes population vulnerability to the health effects of air pollutants using risk analysis concepts and based on available evidence.

METHODS

Publications reporting air pollution health risks for specific sub-populations, or more conceptual discussions of vulnerability, were selected following a literature search of the PubMed database. Only studies in the context of developed countries were included. Information on population characteristics and factors that can influence risk was assessed from the perspective of the vulnerability framework, and was used to outline interactions with biological susceptibility, exposure, and social coping.

RESULTS

Population characteristics encompass several factors that interact and confer vulnerability. Age, for example, regarded as significant mostly in terms of physiology, also relates to exposure through behaviours and activities that can be more amenable to prevention. Children are recognized as a high-risk group but their vulnerability may differ by childhood stage, while pregnant women are not explicitly identified as a vulnerable group despite growing evidence for reproductive risks. Social-economic factors have received little attention, although they can affect coping capacity as well as interact with susceptibility and exposure to air pollution.

CONCLUSIONS

Evidence for vulnerability components often lies in different fields of study and has not been evaluated in an integrated manner. Better understanding of population vulnerability can improve the scientific basis to assess risks and develop policies or other health protection initiatives to reduce the impacts of air pollution.

Genetic susceptibility to late normal tissue injury

The outcome of all cancer therapies, including radiation, has greatly improved in the last 25 years, resulting in a doubling of the number of long-term cancer survivors. However, a subset of these survivors incurs adverse chronic side effects in unavoidably irradiated normal tissues, persisting long after treatment and compromising the quality of life of these patients. Interpatient variability in normal tissue radiation response is well documented and suggested to be under genetic control. Fibrosis, a clinically significant late effect in many irradiated tissues that results in tissue remodeling and loss of function, is a complex genetic trait making identification of the underlying genes difficult. Current clinical and animal studies are providing information on the genetics and molecular basis of late normal tissue injury in the radiation therapy setting, bringing us closer to our dual goal of individualizing treatment by genetic profiling and improving the quality of life of long-term survivors.

Gene-environmental interaction in asthma

PURPOSE OF REVIEW

Asthma is likely to result from the effects of environmental stimuli in genetically susceptible individuals. This review summarizes recent studies of gene-environmental interaction in the pathogenesis of asthma, focusing on study designs.

RECENT FINDINGS

Studies using genetic epidemiology, in-vitro and ex-vivo models and in-vivo model organisms demonstrate that gene-environmental interaction in involved in the development of asthma. Genetic association studies show a reduced risk of asthma and atopy with early life exposure to farming environments and house dust endotoxin, and increased risk with environmental tobacco smoke. These associations are modified by CD14 genotype. In people with a specific genotype, high environmental exposure may have the opposite effect of low exposure, possibly explaining some of the inconsistencies in previous studies. In-vitro and ex-vivo cell culture experiments show gene-environmental interactions with Toll-like receptor agonists, viruses and tobacco smoke. Interactions between innate immunity genes and exposure to endotoxin and air pollution have been observed in in-vivo mouse models.

SUMMARY

The expanding evidence for gene-environmental interaction in asthma indicates the importance of measuring environmental factors in genetic studies of asthma. Understanding gene-environmental interaction would facilitate risk prognostication, improve preventive strategies and develop targeted interventions in people with asthma.

Environmental factors and developmental outcomes in the lung

The developing lung is highly susceptible to damage from exposure to environmental toxicants particularly due to the protracted maturation of the respiratory system, extending from the embryonic phase of development in utero through to adolescence. The functional organization of the lungs requires a coordinated ontogeny of critical developmental processes that include branching morphogenesis, cellular differentiation and proliferation, alveolarization, and maturation of the pulmonary immune, vasculature, and neural systems. Therefore, exposure to environmental pollutants during crucial periods of prenatal and/or postnatal development may determine the course of lung morphogenesis and maturation. Depending on the timing of exposure and pathobiological response of the affected tissue, exposure to environmental pollutants can potentially result in long-term alterations that affect the structure and function of the respiratory system. Besides an immature respiratory system at birth, children possess unique differences in their physiology and behavioral characteristics compared to adults that are believed to augment the vulnerability of their developing lungs to perturbations by environmental toxins. Furthermore, an interaction between genetic predisposition and increased opportunity for exposure to chemical and infectious disease increase the hazards and risks for infants and children. In this article, the evidence for perturbations of lung developmental processes by key ambient pollutants (environmental tobacco smoke [ETS], ozone, and particulate matter [PM]) are discussed in terms of biological factors that are intrinsic to infants and children and that influence exposure-related lung development and respiratory outcomes.