Phase II Enzymes Induction Blocks the Enhanced IgE Production in B Cells by Diesel Exhaust Particles

Impact of particulate air pollution on airway injury and epithelial plasticity; underlying mechanisms

Air pollution plays an important role in the mortality and morbidity of chronic airway diseases, such as asthma and chronic obstructive pulmonary disease (COPD). Particulate matter (PM) is a significant fraction of air pollutants, and studies have demonstrated that it can cause airway inflammation and injury. The airway epithelium forms the first barrier of defense against inhaled toxicants, such as PM. Airway epithelial cells clear airways from inhaled irritants and orchestrate the inflammatory response of airways to these irritants by secreting various lipid mediators, growth factors, chemokines, and cytokines. Studies suggest that PM plays an important role in the pathogenesis of chronic airway diseases by impairing mucociliary function, deteriorating epithelial barrier integrity, and inducing the production of inflammatory mediators while modulating the proliferation and death of airway epithelial cells. Furthermore, PM can modulate epithelial plasticity and airway remodeling, which play central roles in asthma and COPD. This review focuses on the effects of PM on airway injury and epithelial plasticity, and the underlying mechanisms involving mucociliary activity, epithelial barrier function, airway inflammation, epithelial-mesenchymal transition, mesenchymal-epithelial transition, and airway remodeling.

Diesel exhausts particles: Their role in increasing the incidence of asthma. Reviewing the evidence of a causal link

Exposure to air pollutants has been correlated with an increase in the severity of asthma and in the exacerbation of pre-existing asthma. However, whether or not environmental pollution can cause asthma remains a controversial issue. The present review analyzes the current scientific evidence of the possible causal link between diesel exhaust particles (DEP), the solid fraction of the complex mixture of diesel exhaust, and asthma. The mechanisms that influence the expression and development of asthma are complex. In children prolonged exposure to pollutants such as DEPs may increase asthma prevalence. In adults, this causal relation is less clear, probably because of the heterogeneity of the studies carried out. There is also evidence of physiological mechanisms by which DEPs can cause asthma. The most frequently described interactions between cellular responses and DEP are the induction of pulmonary oxidative stress and inflammation and the activation of receptors of the bronchial epithelium such as toll-like receptors or increases in Th2 and Th17 cytokines, which generally orchestrate the asthmatic response. Others support indirect mechanisms through epigenetic changes, pulmonary microbiome modifications, or the interaction of DEP with environmental antigens to enhance their activity. However, in spite of this evidence, more studies are needed to assess the harmful effects of pollution - not only in the short term in the form of increases in the rate of exacerbations, but in the medium and long term as well, as a possible trigger of the disease.

Sulforaphane improves the bronchoprotective response in asthmatics through Nrf2-mediated gene pathways

Background

It is widely recognized that deep inspiration (DI), either before methacholine (MCh) challenge (Bronchoprotection, BP) or after MCh challenge (Bronchodilation, BD) protects against this challenge in healthy individuals, but not in asthmatics. Sulforaphane, a dietary antioxidant and antiinflammatory phytochemical derived from broccoli, may affect the pulmonary bronchoconstrictor responses to MCh and the responses to DI in asthmatic patients.

Methods

Forty-five moderate asthmatics were administered sulforaphane (100 μmol daily for 14 days), BP, BD, lung volumes by body-plethsmography, and airway morphology by computed tomography (CT) were measured pre- and post sulforaphane consumption.

Results

Sulforaphane ameliorated the bronchoconstrictor effects of MCh on FEV₁ significantly (on average by 21 %; p = 0.01) in 60 % of these asthmatics. Interestingly, in 20 % of the asthmatics, sulforaphane aggravated the bronchoconstrictor effects of MCh and in a similar number was without effect, documenting the great heterogeneity of the responsiveness of these individuals to sulforaphane. Moreover, in individuals in whom the FEV₁ response to MCh challenge decreased after sulforaphane administration, i.e., sulforaphane was protective, the activities of Nrf2-regulated antioxidant and anti-inflammatory genes decreased. In contrast, individuals in whom sulforaphane treatment enhanced the FEV₁ response to MCh, had increased expression of the activities of these genes. High resolution CT scans disclosed that in asthmatics sulforaphane treatment resulted in a significant reduction in specific airway resistance and also increased small airway luminal area and airway trapping modestly but significantly.

Conclusion

These findings suggest the potential value of blocking the bronchoconstrictor hyperresponsiveness in some types of asthmatics by phytochemicals such as sulforaphane.

[Genetic and biochemical mechanisms of involvement of antioxidant defense enzymes in the development of bronchial asthma]

In the present review we have analyzed and summarized recent literature data on genetic and biochemical mechanisms responsible for involvement of antioxidant defense enzymes in the etiology and pathogenesis of bronchial asthma. It has been shown that the mechanisms of asthma development are linked with genetically determined abnormalities in the functioning of antioxidant defense enzymes. These alterations are accompanied by a systemic imbalance between oxidative and anti-oxidative reactions with the shift of the redox state toward increased free radical production and oxidative stress, a key element in the pathogenesis of bronchial asthma.

Interplay of air pollution and asthma immunopathogenesis: a focused review of diesel exhaust and ozone

Controlled human exposure experiments with diesel exhaust particles (DEPs) and ozone serve to illustrate the important role pollutants play in modulating both allergic mechanisms and immune responses to affect the immunopathogenesis of airway diseases such as asthma. For DEP, evidence is stronger for the exacerbation of existing asthma rather than for the development of new disease. To the extent that this enhancement occurs, the augmentation of Th2-type immunity seems to be a common element. For ozone, neutrophilic inflammation, altered immune cell phenotype and function and oxidative stress are all marked responses that likely contribute to underlying immune-inflammatory features of asthma. Evidence is also emerging that unique gene signatures and epigenetic control of immune and inflammatory-based genes are playing important roles in the magnitude of the impact ozone is having on respiratory health. Indeed, the interplay between air pollutants such as DEP and ozone and asthma immunopathogenesis is an ongoing concern in terms of understanding how exposure to these agents can lead to worsening of disease. To this end, asthmatics may be pre-disposed to the deleterious effects of pollutants like ozone, having constitutively modified host defense functions and gene signatures. Although this review has utilized DEP and ozone as example pollutants, more research is needed to better understand the interplay between air pollution in general and asthma immumopathogenesis.

Cigarette smoking is associated with human semen quality in synergy with functional NRF2 polymorphisms

Although cigarette smoking is considered a major risk factor for several human diseases, the effects of smoking on male fertility are controversial. Studies on the consequences of smoking, which also take into account genetic background, may facilitate understanding of the interactions between genes and smoking and their effects on male fertility. In this study, genetic variants of two functional polymorphisms of erythroid 2-related factor 2 (NRF2), mRNA expression levels of the antioxidant gene NRF2, catalase (CAT), superoxide dismutase isoenzyme-2 (SOD2), glutathione S-transferase-M1 (GSTM1), and seminal SOD activities were compared in 314 heavy smokers and 314 matched nonsmokers. The NRF2 rs6721961 TT genotype was found to be associated with low semen quality in heavy smokers (OR [95% CI] = 2.370 [1.106-5.081]). This variant genotype was found more frequently in heavy smokers with low semen quality than in those with high semen quality (P = 0.011). Heavy smokers with this genotype had significantly lower sperm concentrations and sperm counts (P < 0.05) when compared with those without this genotype. Smoking was also significantly associated with decreased seminal SOD activity (P < 0.05) and reduced NRF2 and SOD2 mRNA expression in heavy smokers with this variant genotype. These results were specific to heavy smokers with the NRF2 rs6721961 TT genotypes, but did not apply to nonsmokers or heavy smokers that did not carry this genotype. This study suggests an association between cigarette smoking in heavy smokers with NRF2 rs6721961 TT genotype and a decrease in semen quality.

Low NRF2 mRNA expression in spermatozoa from men with low sperm motility

Antioxidant genes and enzymes play important roles in human spermatogenesis. Although low levels of antioxidant enzyme expression are associated with poor sperm quality, it is not clear whether mRNA expression of antioxidant genes is lower in these men than in normozoospermic men. In this study, 55 asthenozoospermic and oligoasthenozoospermic patients and 65 controls were recruited. Quantitative real-time reverse transcription PCR was performed and the abundance of mRNA of four antioxidant genes known to be important to spermatogenesis were evaluated. These genes were nuclear factor erythroid 2-related factor 2 (NRF2), catalase (CAT), glutathione S-transferase Mu 1 (GSTM1), and superoxide dismutase isoenzyme 2 (SOD2). Results showed the level of NRF2 mRNA expression to be significantly lower in patients than in controls (P < 0.001), but no statistically significant difference in the level of SOD2, CAT, or GSTM1 gene expression was observed between the two groups. A significant correlation was observed between the level of NRF2 mRNA expression and specific sperm function parameters, including concentration, progressive motility, immotility, vitality, and morphology (all P < 0.01). NRF2 expression was also found to be associated with seminal SOD activity and mRNA levels of the CAT and SOD2 genes (all P < 0.05). Therefore, our data demonstrated that the level of NRF2 mRNA expression is significantly lower in human males with low sperm motility and correlated with specific sperm function parameters. This suggests that NRF2 is important to spermatogenesis and may serve as a useful biomarker in the prediction of male infertility.

Novel concepts of broccoli sulforaphanes and disease: induction of phase II antioxidant and detoxification enzymes by enhanced-glucoraphanin broccoli

Consumption of broccoli has long been considered to play a role in a healthy diet. Broccoli accumulates significant amounts of the phytonutrient glucoraphanin (4-methylsulfinylbutyl glucosinolate), which is metabolized in vivo to the biologically active sulforaphane. The preponderance of evidence available from in vitro, animal, and human studies supports the association of sulforaphane with phase II enzyme induction. This has provided impetus for developing varieties of broccoli, both sprouts and whole heads, that are rich in glucoraphanin. The cancer-preventive properties of cruciferous vegetables, especially broccoli, have been studied for decades. However, evidence of broccoli directly affecting cancer incidence or progression is ambiguous, in part because of the presence of substantial polymorphisms in enzymes that metabolize sulforaphane. Since broccoli sulforaphane is one of the most potent inducers of phase II enzymes, exploration into broccoli's impact on other areas of human health, such as cardiovascular health and upper airway immunity, has been suggested. This review provides an update on evidence supporting phase II enzyme induction by sulforaphanes, with implications for breeding broccoli varieties with enhanced amounts of glucoraphanin. Early-stage human studies of consumption of broccoli with enhanced glucoraphanin are also discussed.

The effect of environmental oxidative stress on airway inflammation

PURPOSE OF REVIEW

Asthma is an inflammatory respiratory condition with significantly associated morbidity and mortality that is increasing in prevalence. Air pollution is an important factor in both the development of asthma and in asthma exacerbations. Oxidative stress as a result of exposure to air pollution and underlying genetic polymorphisms that may play a role in susceptibility to this oxidative stress are the subject of current investigation. This article reviews the data regarding the effects of air pollution on the innate immune response and potential clinical and treatment implications of how genetic polymorphisms affect this response.

RECENT FINDINGS

Recent investigation reveals how pollutant-induced oxidative stress impacts airway inflammatory responses. Work by our study group demonstrates that asthmatic patients have an exaggerated inflammatory response to air pollution-induced oxidative stress. New trials investigating antioxidants as potential therapeutic interventions may target this specific issue.

SUMMARY

Air pollution plays a critical role in asthma and may affect certain patients more than others. Further investigation into the genetic polymorphisms that affect inflammatory responses may help target patient populations at greatest risk for air pollution-induced asthma and may provide new therapeutic options for these patient populations.

Divergent effects of urban particulate air pollution on allergic airway responses in experimental asthma: a comparison of field exposure studies

BACKGROUND

Increases in ambient particulate matter of aerodynamic diameter of 2.5 μm (PM2.5) are associated with asthma morbidity and mortality. The overall objective of this study was to test the hypothesis that PM2.5 derived from two distinct urban U.S. communities would induce variable responses to aggravate airway symptoms during experimental asthma.

METHODS

We used a mobile laboratory to conduct community-based inhalation exposures to laboratory rats with ovalbumin-induced allergic airways disease. In Grand Rapids exposures were conducted within 60 m of a major roadway, whereas the Detroit was located in an industrial area more than 400 m from roadways. Immediately after nasal allergen challenge, Brown Norway rats were exposed by whole body inhalation to either concentrated air particles (CAPs) or filtered air for 8 h (7:00 AM - 3:00 PM). Both ambient and concentrated PM2.5 was assessed for mass, size fractionation, and major component analyses, and trace element content. Sixteen hours after exposures, bronchoalveolar lavage fluid (BALF) and lung lobes were collected and evaluated for airway inflammatory and mucus responses.

RESULTS

Similar CAPs mass concentrations were generated in Detroit (542 μg/m3) and Grand Rapids (519 μg/m3). Exposure to CAPs at either site had no effects in lungs of non-allergic rats. In contrast, asthmatic rats had 200% increases in airway mucus and had more BALF neutrophils (250% increase), eosinophils (90%), and total protein (300%) compared to controls. Exposure to Detroit CAPs enhanced all allergic inflammatory endpoints by 30-100%, whereas inhalation of Grand Rapids CAPs suppressed all allergic responses by 50%. Detroit CAPs were characterized by high sulfate, smaller sized particles and were derived from local combustion sources. Conversely Grand Rapids CAPs were derived primarily from motor vehicle sources.

CONCLUSIONS

Despite inhalation exposure to the same mass concentration of urban PM2.5, disparate health effects can be elicited in the airways of sensitive populations such as asthmatics. Modulation of airway inflammatory and immune responses is therefore dependent on specific chemical components and size distributions of urban PM2.5. Our results suggest that air quality standards based on particle speciation and sources may be more relevant than particle mass to protect human health from PM exposure.

Genetic variation in the Nrf2 promoter associates with defective spermatogenesis in humans

Defective spermatogenesis, which severely impairs male fertility, can be caused by excessive reactive oxygen species (ROS). Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates transcription of genes encoding enzymes important for protection against ROS. In human seminal plasma and spermatozoa, superoxide dismutase isoenzymes (SOD) and glutathione S-transferases (GST) are key antioxidant enzymes. We hypothesized that decreased function of the Nrf2-antioxidant response element (ARE) pathway might predispose individuals to male infertility. In this study, we identified three functional single nucleotide polymorphisms (SNPs) in the Nrf2 promoter regions of 196 idiopathic asthenozoospermic patients, 140 idiopathic oligoasthenozoospermic patients, and 295 controls. We found that two of the Nrf2 SNPs (-617 G > T and -653 T > C) were associated with oligoasthenozoospermia (p = 0.001) and individuals with 617 TT and 653 TT genotypes had higher risk of oligoasthenozoospermia (p = 0.006 and p = 0.002). Four haplotypes of Nrf2 promoters were identified, and two of them (GCC and TCT) had different frequencies in oligoasthenozoospermic patients than in controls (p = 0.019 and p = 0.011). In vitro reporter assay indicated that oligoasthenozoospermia associated genotypes of Nrf2 had significantly decreased transcriptional capabilities. The GCC and TCT haplotypes both showed lower Nrf2 mRNA expression in spermatozoa than GCT. TCT also showed decreased levels of antioxidant gene GSTM1 and SOD2 mRNA. Analysis of total seminal SOD activity elucidated that oligoasthenozoospermic patients had less SOD activity than controls. This study is the first to demonstrate a strong association between functional polymorphisms in Nrf2 promoters with defective spermatogenesis in humans.

Prenatal negative life events increases cord blood IgE: interactions with dust mite allergen and maternal atopy

BACKGROUND

Prenatal exposure to both stress and aeroallergens (dust mite) may modulate the fetal immune system. These exposures may interact to affect the newborn immune response. We examined associations between prenatal maternal stress and cord blood total IgE in 403 predominately low-income minority infants enrolled in the Asthma Coalition on Community, Environment, and Social Stress (ACCESS) project. We also examined potential modifying effects of maternal atopy and maternal dust mite exposure.

METHODS

The Crisis in Family Systems survey was administered to mothers prenatally, and a negative life event domain score was derived to characterize stress. Dust mite allergen was quantified in dust from pregnant mothers' bedrooms. Cord blood was analyzed for total IgE. Using linear regression, we modeled the relationship of stress with cord blood IgE and interactions of stress with dust mite and/or maternal atopy, adjusting for potential confounders.

RESULTS

Higher prenatal maternal stress (β = 0.09; P = 0.01) was associated with increased cord blood IgE. The interactive effects between stress and dust mite groups (high vs low) were significantly different for children of atopic vs nonatopic mothers (P for three-way interaction = 0.005). Among children of atopic mothers, the positive association between stress and IgE was stronger in the high dust mite group. In children of mothers without a history of atopy, the positive association between stress and IgE was most evident in the low allergen group.

CONCLUSIONS

Prenatal stress was independently associated with elevated cord blood IgE. Mechanisms underlying stress effects on fetal immunomodulation may differ based on maternal atopic status.

The role of oxidative stress and innate immunity in O(3) and endotoxin-induced human allergic airway disease

Ozone (O(3)) and endotoxin are common environmental contaminants that cause asthma exacerbation. These pollutants have similar phenotype response characteristics, including induction of neutrophilic inflammation, changes in airway macrophage immunophenotypes, and ability to enhance response to inhaled allergen. Evoked phenotyping studies of volunteers exposed to O(3) and endotoxin were used to identify the response characteristics of volunteers to these pollutants. New studies support the hypotheses that similar innate immune and oxidant processes modulate response to these agents. These include TLR4 and inflammasome-mediated signaling and cytokine production. Innate immune responses are also impacted by oxidative stress. It is likely that continued discovery of common molecular processes which modulate response to these pollutants will occur. Understanding the pathways that modulate response to pollutants will also allow for discovery of genetic and epigenetic factors that regulate response to these pollutants and determine risk of disease exacerbation. Additionally, defining the mechanisms of response will allow rational selection of interventions to examine. Interventions focused on inhibition of Toll-like receptor 4 and inflammasome represent promising new approaches to preventing pollutant-induced asthma exacerbations. Such interventions include specific inhibitors of innate immunity and antioxidant therapies designed to counter the effects of pollutants on cell signaling.

Antioxidant components of naturally-occurring oils exhibit marked anti-inflammatory activity in epithelial cells of the human upper respiratory system

BACKGROUND

The upper respiratory tract functions to protect lower respiratory structures from chemical and biological agents in inspired air. Cellular oxidative stress leading to acute and chronic inflammation contributes to the resultant pathology in many of these exposures and is typical of allergic disease, chronic sinusitis, pollutant exposure, and bacterial and viral infections. Little is known about the effective means by which topical treatment of the nose can strengthen its antioxidant and anti-inflammatory defenses. The present study was undertaken to determine if naturally-occurring plant oils with reported antioxidant activity can provide mechanisms through which upper respiratory protection might occur.

METHODS

Controlled exposure of the upper respiratory system to ozone and nasal biopsy were carried out in healthy human subjects to assess mitigation of the ozone-induced inflammatory response and to assess gene expression in the nasal mucosa induced by a mixture of five naturally-occurring antioxidant oils--aloe, coconut, orange, peppermint and vitamin E. Cells of the BEAS-2B and NCI-H23 epithelial cell lines were used to investigate the source and potential intracellular mechanisms of action responsible for oil-induced anti-inflammatory activity.

RESULTS

Aerosolized pretreatment with the mixed oil preparation significantly attenuated ozone-induced nasal inflammation. Although most oil components may reduce oxidant stress by undergoing reduction, orange oil was demonstrated to have the ability to induce long-lasting gene expression of several antioxidant enzymes linked to Nrf2, including HO-1, NQO1, GCLm and GCLc, and to mitigate the pro-inflammatory signaling of endotoxin in cell culture systems. Nrf2 activation was demonstrated. Treatment with the aerosolized oil preparation increased baseline levels of nasal mucosal HO-1 expression in 9 of 12 subjects.

CONCLUSIONS

These data indicate that selected oil-based antioxidant preparations can effectively reduce inflammation associated with oxidant stress-related challenge to the nasal mucosa. The potential for some oils to activate intracellular antioxidant pathways may provide a powerful mechanism through which effective and persistent cytoprotection against airborne environmental exposures can be provided in the upper respiratory mucosa.

Environmental pollution and lung effects in children

PURPOSE OF REVIEW

Studies over the last 2 years have added important new information on the relationship between air pollution and asthma incidence and severity.

RECENT FINDINGS

Outdoor air pollution has been associated with asthma exacerbations, including emergency department visits and hospitalizations, as well as with the onset of asthma. Possible mechanisms mediating both incidence and severity effects include the induction of oxidative stress, and/or allergic sensitization, as well as increased susceptibility to viral infections. Some of these mechanisms may be occurring in utero including epigenetic changes that may increase risk for development of asthma. Factors related to increased susceptibility for air pollution-related asthma severity include age, season and genetic polymorphisms related to antioxidant enzymes.

SUMMARY

Ambient pollution levels may be associated with both asthma incidence and severity. Susceptibility to air pollution may be higher in children with genetic polymorphisms related to the 'oxidant stress pathways'. Potential interventions for susceptible children at risk for asthma development and/or severity include decreased exposure on high air pollution days, especially in the summer months, and antioxidant supplementation. On the population level, changes in school and home zoning to increase distance from busy roadways may help reduce both asthma incidence and severity.

Air pollution and circulating biomarkers of oxidative stress

Chemical components of air pollutant exposures that induce oxidative stress and subsequent inflammation may be partly responsible for associations of cardiovascular morbidity and mortality with airborne particulate matter and combustion-related pollutant gasses. However, epidemiologic evidence regarding this is limited. An exposure-assessment approach is to measure the oxidative potential of particle mixtures because it is likely that hundreds of correlated chemicals are involved in overall effects of air pollution on health. Oxidative potential likely depends on particle composition and size distribution, especially ultrafine particle concentration, and on transition metals and certain semivolatile and volatile organic chemicals. For health effects, measuring systemic oxidative stress in the blood is one feasible approach, but there is no universal biomarker of oxidative stress and there are many potential target molecules (lipids, proteins, DNA, nitric oxide, etc.), which may be more or less suitable for specific study goals. Concurrent with the measurement of oxidative stress, it is important to measure gene and/or protein expression of endogenous antioxidant enzymes because they can modify relations between oxidative stress biomarkers and air pollutants. Conversely, the expression and activities of these enzymes are modified by oxidative stress. This interplay will likely determine the observed effects of air pollutants on systemic inflammatory and thrombotic mediators and related clinical outcomes. Studies are needed to assess the reliability and validity of oxidative stress biomarkers, evaluate differences in associations between oxidative stress biomarkers and various pollutant measurements (mass, chemical components, and oxidative potential), and evaluate impacts of antioxidant responses on these relations.

The effects of oxidative stress induced by prolonged low-dose diesel exhaust particle exposure on the generation of allergic airway inflammation differ between BALB/c and C57BL/6 mice

We have recently reported that airway inflammatory responses to the oxidative stress induced by prolonged low-dose diesel exhaust particle (DEP) exposure differ markedly between BALB/c and C57BL/6 mice. In the present study, the effects of genetic differences in the response to prolonged low-dose DEP exposure on the generation of ovalbumin-induced allergic airway inflammation were further explored using the same mouse strains. In BALB/c mice, eosinophils and mucous goblet cells in histopathological pulmonary specimens increased significantly after DEP exposure, and were more marked than in C57BL/6 mice. Interleukin (IL)-5 and IL-13 levels in bronchoalveolar lavage (BAL) fluid were increased significantly by DEP exposure only in BALB/c mice. The DEP-induced increases in peribronchial eosinophils and mucous goblet cells in the lung tissues, and of IL-5 and IL-13 in the BAL fluid, were significantly attenuated by the antioxidant N-acetylcysteine. Thus, the effects of prolonged low-dose DEP exposure on the generation of allergic airway inflammation differed markedly between the mouse strains. These differences may be caused by different antioxidant responses to the oxidative stress induced by DEP exposure. Our results contribute more information to the search for genetic susceptibility factors in the response to DEP, and may thus assist in the discovery of new biomarkers for DEP-related disease.

Novel antioxidant approaches to the treatment of upper airway inflammation

PURPOSE OF REVIEW

Current understanding of the role of oxidative stress in airway inflammation suggests that antioxidant therapy may be important to optimize the treatment. This review summarizes recent investigations of novel antioxidant agents for upper airway inflammation, with selected studies focused on lower airway disease as additional candidate therapeutics.

RECENT FINDINGS

Recently investigated antioxidant therapies for airway inflammation may be broadly grouped into three categories: endogenous metabolic agents, vitamins/nutrients, and botanical extracts. Studies examining effects in upper airway inflammation are limited and primarily consist of in-vitro human and in-vivo animal models. More extensive studies have investigated the benefits of antioxidants in lower airway conditions such as allergic asthma. Existing evidence identifies antioxidant agents with potential therapeutic value, although human studies suggest that subpopulations affected by specific genetic, environmental, dietary factors, or all are most likely to benefit from antioxidant therapy.

SUMMARY

Oxidative stress plays a causative role in upper airway inflammation, and novel strategies to mitigate cellular injury with antioxidant therapy may ameliorate disease in target populations. Preclinical studies demonstrate evidence of anti-inflammatory effects for a number of promising antioxidant agents. Well designed interventional human studies of the upper airway, which account for complex gene-environment-diet interactions, will be necessary to adequately examine the potential clinical benefit of antioxidant therapies for rhinosinusitis.

Effects of atmospheric pollutants on the Nrf2 survival pathway

BACKGROUND, AIM, AND SCOPE

Atmospheric pollution is a worldwide problem. Exposure to atmospheric pollutants causes toxic cellular effects. One of the mechanisms of toxicity by these pollutants is the promotion of oxidative stress. Several signaling pathways control cellular redox homeostasis. In this respect, nuclear factor erythroid 2-related factor 2 (Nrf2) is a crucial transcription factor in the cell's response to oxidative stress.

MAIN FEATURES

In cellular animal models, exposure to atmospheric pollutants activates Nrf2, attenuating its toxic and even its carcinogenic effects. Therefore, we have reviewed the scientific literature in order to indicate that air pollutants, such as particulate matter, polycyclic aromatic hydrocarbons, and gaseous matter, are Nrf2 pathway inductors, triggering self-defense through the establishment of proinflammatory and antioxidant responses.

RESULTS AND DISCUSSION

Exposure to reactive molecules as atmospheric pollutants causes the activation of Nrf2 and the subsequent regulation of the expression of cytoprotective and detoxifying enzymes, as well as antioxidants. Moreover, induction of Nrf2 prior to exposure reduces the harmful effects of pollutants. The present article discusses the protective role of the Nrf2 pathway against different atmospheric pollutant insults.

CONCLUSIONS

Nrf2 regulates the expression of numerous cytoprotective genes that function to detoxify reactive species produced during atmospheric pollutant metabolic reactions. From the papers highlighted in this review, we conclude that Nrf2 has an important role in the defense against atmospheric pollutant-induced toxicity.

PERSPECTIVES

Further studies are needed to understand the signaling events that turn on the system in response to atmospheric pollutant stress. This could allow for the possibility of targeting the pathway for prevention benefits in the near future.

Outdoor air pollution, genetic susceptibility, and asthma management: opportunities for intervention to reduce the burden of asthma

Outdoor air pollution at levels occurring in many urban areas around the world has substantial adverse effects on health. Children in general, and children with asthma in particular, are sensitive to the adverse effects of outdoor air pollutants, including ozone, nitrogen oxides, and respirable particulate matter. A growing number of studies also show that children living in environments near traffic have increased risks of new-onset asthma, asthma symptoms, exacerbations, school absences, and asthma-related hospitalizations. The large population of children exposed to high levels of outdoor air pollutants and the substantial risks for adverse health effects present unexploited opportunities to reduce the burden of asthma. Because the evidence indicates significant adverse effects of air pollution at current levels, there is clearly a need to reduce levels of regulated pollutants such as ozone, as well as unregulated pollutants in tailpipe emissions from motor vehicles. Achieving this long-term goal requires the active involvement of physicians and medical providers to ensure that the health of children is at the top of the list of competing priorities for regulatory policy decision-making. Clinical approaches include treatment to control asthma and patient education to reduce adverse effects of the disease. Reduction in exposures also can be approached at a policy level through changes in schools and school bus operations. Beyond clinical and public health approaches to reduce exposure, another strategy to be used before clean air goals are met is to decrease the susceptibility of children to air pollution. Emerging research indicates that dietary supplementation for individuals with low antioxidant levels is one promising approach to reducing susceptibility to air pollution. A second approach involves induction of enzymatic antioxidant defenses, especially for individuals with at-risk genetic variants of key antioxidant enzymes.

Oral sulforaphane increases Phase II antioxidant enzymes in the human upper airway

BACKGROUND

Cellular oxidative stress is an important factor in asthma and is thought to be the principle mechanism by which oxidant pollutants such as ozone and particulates mediate their pro-inflammatory effects. Endogenous Phase II enzymes abrogate oxidative stress through the scavenging of reactive oxygen species and metabolism of reactive chemicals.

OBJECTIVE

We conducted a placebo-controlled dose escalation trial to investigate the in vivo effects of sulforaphane, a naturally occurring potent inducer of Phase II enzymes, on the expression of glutathione-s-transferase M1 (GSTM1), glutathione-s-transferase P1 (GSTP1), NADPH quinone oxidoreductase (NQO1), and hemoxygenase-1 (HO-1) in the upper airway of human subjects.

METHODS

Study subjects consumed oral sulforaphane doses contained in a standardized broccoli sprout homogenate (BSH). RNA expression for selected Phase II enzymes was measured in nasal lavage cells by RT-PCR before and after sulforaphane dosing.

RESULTS

All subjects tolerated oral sulforaphane dosing without significant adverse events. Increased Phase II enzyme expression in nasal lavage cells occurred in a dose-dependent manner with maximal enzyme induction observed at the highest dose of 200 g broccoli sprouts prepared as BSH. Significant increases were seen in all sentinel Phase II enzymes RNA expression compared to baseline. Phase II enzyme induction was not seen with ingestion of non-sulforaphane containing alfalfa sprouts.

CONCLUSION

Oral sulforaphane safely and effectively induces mucosal Phase II enzyme expression in the upper airway of human subjects. This study demonstrates the potential of antioxidant Phase II enzymes induction in the human airway as a strategy to reduce the inflammatory effects of oxidative stress.

CLINICAL IMPLICATIONS

This study demonstrates the potential of enhancement of Phase II enzyme expression as a novel therapeutic strategy for oxidant induced airway disease.

CAPSULE SUMMARY

A placebo-controlled dose escalation trial demonstrated that naturally occurring sulforaphane from broccoli sprouts can induce a potent increase in antioxidant Phase II enzymes in airway cells.

Oral sulforaphane increases Phase II antioxidant enzymes in the human upper airway

BACKGROUND

Cellular oxidative stress is an important factor in asthma and is thought to be the principle mechanism by which oxidant pollutants such as ozone and particulates mediate their pro-inflammatory effects. Endogenous Phase II enzymes abrogate oxidative stress through the scavenging of reactive oxygen species and metabolism of reactive chemicals.

OBJECTIVE

We conducted a placebo-controlled dose escalation trial to investigate the in vivo effects of sulforaphane, a naturally occurring potent inducer of Phase II enzymes, on the expression of glutathione-s-transferase M1 (GSTM1), glutathione-s-transferase P1 (GSTP1), NADPH quinone oxidoreductase (NQO1), and hemoxygenase-1 (HO-1) in the upper airway of human subjects.

METHODS

Study subjects consumed oral sulforaphane doses contained in a standardized broccoli sprout homogenate (BSH). RNA expression for selected Phase II enzymes was measured in nasal lavage cells by RT-PCR before and after sulforaphane dosing.

RESULTS

All subjects tolerated oral sulforaphane dosing without significant adverse events. Increased Phase II enzyme expression in nasal lavage cells occurred in a dose-dependent manner with maximal enzyme induction observed at the highest dose of 200 g broccoli sprouts prepared as BSH. Significant increases were seen in all sentinel Phase II enzymes RNA expression compared to baseline. Phase II enzyme induction was not seen with ingestion of non-sulforaphane containing alfalfa sprouts.

CONCLUSION

Oral sulforaphane safely and effectively induces mucosal Phase II enzyme expression in the upper airway of human subjects. This study demonstrates the potential of antioxidant Phase II enzymes induction in the human airway as a strategy to reduce the inflammatory effects of oxidative stress.

CLINICAL IMPLICATIONS

This study demonstrates the potential of enhancement of Phase II enzyme expression as a novel therapeutic strategy for oxidant induced airway disease.

CAPSULE SUMMARY

A placebo-controlled dose escalation trial demonstrated that naturally occurring sulforaphane from broccoli sprouts can induce a potent increase in antioxidant Phase II enzymes in airway cells.

Functional polymorphism of detoxification gene NQO1 predicts intensity of empirical treatment of childhood asthma

The management of moderate to severe childhood asthma remains empirical. Genotypic variation has been proposed as a way to tailor specific pharmaceutical regimens to individual patients. The objective of this study was to determine the factors associated with asthma treatment progression, including functional polymorphisms of phase II detoxification enzymes, demographics, and environmental factors. In a study of 120 asthmatic children cared for in a single pediatric pulmonary practice, intensity of medical treatment over the year prior was modeled as a function of null mutations of glutathione S transferase (GST) M1 and T1, ile105val variant of GSTP1, and pro187ser variant of NAD(P)H:quinone oxidoreductase 1 (NQO1). The model included demographics, medical information, and environmental factors obtained via questionnaire analyzed with multivariate logistic regression and artificial neural networks. Multivariate logistic regression with bootstrapped validation identified a polymorphic variant of NQO1 as significantly contributing to increasing the odds of receiving more aggressive medical therapy (odds ratio, 11.56; p=0.0001). Parent income and education inversely correlated with medical treatment (odds ratio, 1.50; p=0.001 and odds ratio, 0.375; p=0.002, respectively). Age and reporting restricted physical activity due to asthma also impacted medical treatment (odds ratio, 0.63; p=0.0001 and odds ratio, 5.90; p=0.004, respectively). The optimism-adjusted discriminative ability (c-index) of the model was 0.881 (close to Bayes optimum of 0.902) with 80% overall classification accuracy. Our study supports the role of NQO1 polymorphism as an important factor determining the intensity of medical therapy in asthmatic children after adjusting for significance relating to parental income and education level, age, and restricted physical activity. Asthmatic children with a functional polymorphism of NQO1 may require more intensive pharmaceutical treatment to effectively control their asthma.

The effect of air pollution on asthma and allergy

Air pollution exposure is associated with increased asthma and allergy morbidity and is a suspected contributor to the increasing prevalence of allergic conditions. Observational studies continue to strengthen the association between air pollution and allergic respiratory disease, whereas recent mechanistic studies have defined the prominent role of oxidative stress in the proallergic immunologic effects of particulate and gaseous pollutants. The identification of common genetic polymorphisms in key cytoprotective responses to oxidative stress has highlighted the importance of individual host susceptibility to pollutant-induced inflammation. Future therapy to reduce the adverse effects of air pollution on allergic respiratory disease will likely depend on targeting susceptible populations for treatment that reduces oxidative stress, potentially through enhancement of phase 2 enzymes or other antioxidant defenses.

Importance of oxidative stress in the pathogenesis and treatment of asthma

PURPOSE OF REVIEW

The purpose of the current review is to summarize recent evidence demonstrating the important role of oxidative stress in asthma pathogenesis. The therapeutic implications of these findings will be presented.

RECENT FINDINGS

Mechanistically, the effect of oxidative stress on dendritic cells has been demonstrated to have a potent effect on Th1/Th2 skewing of the immune response. Investigations of gene-environment interactions have identified genetic polymorphisms associated with individual susceptibility to pollutant-induced respiratory oxidative stress. The effects of current asthma therapy on oxidative stress are currently unclear, but previous trials using conventional antioxidant therapy in asthma have been largely ineffective. Recent investigations have identified two promising broad-based therapeutic approaches: Nrf2 pathway activation and the use of thiol precursors. Preliminary data suggest that fullerene nanomaterials and dietary interventions may also have potential benefits in asthma.

SUMMARY

Our current understanding of the role of oxidative stress in asthma suggests that antioxidant therapy may be important in optimizing asthma treatment and prevention. The future success of antioxidant asthma therapy will require strategies with broad effects on airway redox equilibrium and the selection of appropriate target populations.

Complex issues with examining diesel exhaust toxicity: is the task getting easier or harder?

Petroleum diesel exhaust (DE) exposure has been linked to several health effects including lung cancer. The role of DE in the cardiopulmonary effects associated with particulate matter (PM) exposures is unclear; this uncertainty drives current research efforts to better understand how the DE exerts toxicity. Several issues present complexities to the design of DE health effects research. One issue is to better establish the health effects and biological responses from DE exposure. Lung responses have been examined with variable findings with controlled exposures, but to date relatively little is known about cardiovascular responses. Additionally, induction of other health effects from DE exposure has been examined mainly through either controlled nonhuman animal model exposures or epidemiological approaches. Due to changing regulations and technology to achieve compliance with regulatory standards, DE from more modern emissions contains less PM and certain gases, making comparisons to older emissions complicated. In addition, the gas phase contains proportionally more mass than the PM phase, presenting technological problems in terms of the collection of the DE for future studies and across-laboratory comparison. Therefore, in order to study the toxicity of DE, whole exhaust (PM and gases) exposures should ideally be performed, at least as part of establishing the role that the PM or gases may play in the biological responses being examined.

The role of oxidative stress in ambient particulate matter-induced lung diseases and its implications in the toxicity of engineered nanoparticles

Ambient particulate matter (PM) is an environmental factor that has been associated with increased respiratory morbidity and mortality. The major effect of ambient PM on the pulmonary system is the exacerbation of inflammation, especially in susceptible people. One of the mechanisms by which ambient PM exerts its proinflammatory effects is the generation of oxidative stress by its chemical compounds and metals. Cellular responses to PM-induced oxidative stress include activation of antioxidant defense, inflammation, and toxicity. The proinflammatory effect of PM in the lung is characterized by increased cytokine/chemokine production and adhesion molecule expression. Moreover, there is evidence that ambient PM can act as an adjuvant for allergic sensitization, which raises the possibility that long-term PM exposure may lead to increased prevalence of asthma. In addition to ambient PM, rapid expansion of nanotechnology has introduced the potential that engineered nanoparticles (NP) may also become airborne and may contribute to pulmonary diseases by novel mechanisms that could include oxidant injury. Currently, little is known about the potential adverse health effects of these particles. In this communication, the mechanisms by which particulate pollutants, including ambient PM and engineered NP, exert their adverse effects through the generation of oxidative stress and the impacts of oxidant injury in the respiratory tract will be reviewed. The importance of cellular antioxidant and detoxification pathways in protecting against particle-induced lung damage will also be discussed.

Antioxidant enzyme induction: a new protective approach against the adverse effects of diesel exhaust particles

Exposure to airborne particulate pollutants such as diesel exhaust particles (DEPs) has been associated with allergic respiratory disorders, including asthma and allergic rhinitis. In this communication, we review recent advances in the mechanism by which DEPs elicit their harmful effects and the protective role of antioxidants. Reactive oxidative species (ROS) are believed to play a key role in cellular damage after exposure to DEPs. Numerous reports demonstrate that both proinflammatory and anti-inflammatory products are induced by DEPs via the activation of transcription factors. DEPs trigger multiple signaling pathways, which lead to DNA damage and cell apoptosis, inflammatory response, and antioxidant defense. Recent studies both in vitro and in mice show that antioxidants could alleviate the allergic inflammatory effects of DEPs. Human in vivo models suggest that the important phase II enzymes GSTM1 and GSTP1 modify the adjuvant effect of diesel exhaust particles on allergic inflammation. We have shown that the induction of phase II enzymes by the chemical sulforaphane can block DEP-induced enhanced immunoglobulin (Ig) E production in B cells and DEP-induced proinflammatory cytokine production in epithelial cells. These findings suggest that overexpression of antioxidant enzymes could constitute a powerful potential chemopreventive approach against adverse effects induced by oxidant pollutants such as DEPs.

[Air pollution and allergic airway diseases]

In the last decades, many studies have shown an increase in the prevalence of allergic rhinitis and asthma mainly in urban communities, especially in industrialized countries. Airborne pollutants such as diesel exhaust particles, ozone, nitrogen dioxide and sulphur dioxide have been implicated in the initiation and exacerbation of allergic airway diseases. Epidemiologic studies have shown clear associations between air pollution and allergic diseases, in vivo and in vitro studies have provided biologic link and potential molecular mechanisms. Particulate and gaseous pollutants can act both on the upper and lower airways to initiate and exacerbate cellular inflammation through interaction with the innate immune system. As a consequence, increased non-specific airway hyper-responsiveness and airway resistance have been observed in man. Diesel exhaust particles can both induce and exacerbate in vivo allergic responses. They can also modify the immune system's handling of the allergen. The effects of gaseous pollutants on immune responses to allergens are not fully understood. We review the different mechanisms involved in the enhancement of allergic inflammation by urban air pollutants, including effects on cytokine and chemokine production, as well as activation of different immune cells. We discuss the hypothesis that pollutants' effects on the immune system involve hierarchical oxidative stress. Susceptibility genes to air pollution inducing allergic diseases are also discussed.