Oxidative stress in asthma and COPD: antioxidants as a therapeutic strategy

Cells, mediators and Toll-like receptors in COPD

Chronic obstructive pulmonary disease (COPD) is a global health problem. Being a progressive disease characterized by inflammation, it deteriorates pulmonary functioning. Research has focused on airway inflammation, oxidative stress, and remodelling of the airways. Macrophages, neutrophils and T cells are thought to be important key players. A number of new research topics received special attention in the last years. The combined use of inhaled corticosteroids and long-acting beta(2)-adrenoceptor agonists produces better control of symptoms and lung function than that of the use of either compound alone. Furthermore, collagen breakdown products might be involved in the recruitment and activation of inflammatory cells by which the process of airway remodelling becomes self-sustaining. Also, TLR (Toll-like receptor)-based signalling pathways seem to be involved in the pathogenesis of COPD. These new findings may lead to new therapeutic strategies to stop the process of inflammation and self-destruction in the airways of COPD patients.

Cellular responses to reactive oxygen species-induced DNA damage and aging

Oxidative stress in cells and tissues can occur during pathophysiological developments, e.g., during inflammatory and allergic diseases or during ischemic or toxic and hyperglycemic conditions via the generation of reactive oxygen species (ROS). Moreover, ROS can be generated by radiation (UV, X-rays) and pharmacologically, e.g., by anthracyclins as chemotherapeutic compounds for treatment of a variety of tumors to induce 'stress or aberrant signaling-inducing senescence' (STASIS). Although STASIS is distinguished from intracellular replicative senescence, a variety of cellular mechanisms appear similar in both aging pathways. It is generally accepted that oxidative stress and ROS eventually cause DNA damage, whereby insufficient cellular repair mechanisms may contribute to premature aging and apoptosis. Conversely, ROS-induced imbalances of the signaling pathways for metabolic protein turnover may also result in opposite effects to recruit malfunctioning aberrant proteins and compounds that trigger tumorigenic processes. Consequently, DNA damage plays a role in the development of carcinogenesis, but is also associated with an aging process in cells and organisms.

Targeting systemic inflammation: novel therapies for the treatment of chronic obstructive pulmonary disease

The increasing evidence that inflammation in the lungs leads to the structural changes observed in chronic obstructive pulmonary disease, whereas extrapulmonary symptoms and comorbidities may be systemic manifestations of these inflammatory processes, highlights an urgent need to discover novel, effective anti-inflammatory treatments for this disease. Some studies are suggesting that, by decreasing dynamic hyperinflation, bronchodilators might reduce systemic inflammation; inhaled corticosteroids and their combination with long-acting beta2-agonists might contribute to this goal. Even so, the opinion that suppression of the inflammatory response might improve systemic complications is stimulating a search for novel anti-inflammatory therapies. Many drugs include those that inhibit the recruitment and activation of inflammatory cells and/or antagonise their products. However, many of these therapeutic strategies are not specific for neutrophilic inflammation because they affect other cell types, thus, it is difficult to interpret whether any clinical benefit observed is a result of a reduction in airway neutrophils. In any case, there is some evidence that drugs used to treat a co-morbid condition, such as statins, angiotensin converting enzyme (ACE) inhibitors and angiontensin II type 1 (AT1) receptor blockers as well as glycosaminoglycans and peroxisome proliferator-activated receptor (PPAR) agonists, might benefit chronic obstructive pulmonary disease patients because they deal with the extrapulmonary, systemic component of chronic obstructive pulmonary disease.

Inhibition of NADPH oxidase by apocynin inhibits lipopolysaccharide (LPS) induced up-regulation of arginase in rat alveolar macrophages

Reactive oxygen species participate in the pathogenesis of inflammatory airway diseases, in which increased arginase may play a role by interfering with nitric oxide (NO) synthesis and providing substrate for collagen synthesis. Therefore a modulatory role of reactive oxygen species for arginase was explored in alveolar macrophages using the NADPH oxidase inhibitor apocynin. The effects of lipopolysacharides (LPS) and apocynin on nitrite accumulation, arginase activity and mRNA for inducible NO synthase (iNOS), arginase I and II were determined. Superoxide anion (O(2)(-)) release was analysed by the iodonitrotetrazolium (INT) formazan assay. LPS (1 microg/ml) caused a 55%, transient increase in INT formation, i.e. O(2)(-) release which was inhibited by apocynin (500 microM). LPS caused a 2 fold increase in arginase activity and a marked increase in mRNA encoding arginase I, the predominant isoenzyme. Both effects were largely attenuated by apocynin. Apocynin did not affect the stability of arginase I mRNA, but accelerated the decline of arginase activity when protein synthesis was inhibited by cycloheximide. Apocynin also reduced LPS-induced nitrite accumulation (by 30%) and iNOS mRNA expression, but the magnitude of these effects was smaller than that on arginase I. Arginase I mRNA was also increased following exposure to hydrogen peroxide (H(2)O(2), 200 muM). In conclusion, inhibition of NADPH oxidase in alveolar macrophages causes down-regulation of arginase, indicating that reactive oxygen species exert stimulatory effects on arginase. Enhanced transcription of arginase mRNA and prolongation of the life time of the active enzyme appear to contribute to the enhanced arginase activity.

Treating systemic effects of COPD

The emerging recognition that chronic obstructive pulmonary disease (COPD) is a complex disorder, characterized not only by local pulmonary inflammation, but also by systemic inflammation that might have an adverse impact on various extrapulmonary organs, such as the blood vessels and the heart, among others, emphasizes the need for new and more effective forms of therapy for this debilitating disorder. Fortunately, many of the 'standard' therapeutic options used to treat COPD have the potential to influence systemic inflammation. Moreover, several new therapeutic strategies aimed at controlling the underlying inflammatory processes of COPD more specifically are under development. Unfortunately, we still do not know whether treatment of lung inflammation decreases, for example, the risk of acute cardiac events, progression of atherosclerosis or thrombotic events. It is also unclear whether, alternatively, treatment of heart disease can affect the progression of lung disease. Nonetheless, initial data seem to indicate that drugs, such as statins, ACE inhibitors, AT1 receptor blockers and PPAR agonists, used to treat a co-morbid condition have the potential to benefit COPD patients.

Azithromycin suppresses activation of nuclear factor-kappa B and synthesis of pro-inflammatory cytokines in tracheal aspirate cells from premature infants

Nuclear factor-kappaB (NF-kappaB) plays a central role in regulating key proinflammatory mediators. The activation of NF-kappaB is increased in tracheal aspirate (TA) cells from premature infants developing bronchopulmonary dysplasia (BPD). We studied the effect of azithromycin (AZM) on the suppression of NF-kappaB activation and the synthesis of pro-inflammatory cytokines IL-6 and IL-8 by TA cells obtained from premature infants. Tracheal aspirate cells were stimulated with tumor necrosis factor-alpha (TNF-alpha) and incubated with AZM. The nuclear NF-kappaB-DNA binding activity, the levels of inhibitory kappaB-alpha (IkappaB-alpha) in the cytoplasmic fraction and IL-6 and IL-8 release in the cell culture media were measured. Stimulation of TA cells by TNF-alpha increased the activation of NF-kappaB, which was suppressed by the addition of AZM. Increased activation of NF-kappaB was also associated with increased levels of pro-inflammatory cytokines (IL-6 and IL-8). AZM significantly reduced the IL-6 and IL-8 production to the levels similar to control. TNF-alpha stimulation also increased the degradation of IkappaB-alpha, which was restored with the addition of AZM. Our data suggest that AZM therapy may be an effective alternative to steroids in reducing lung inflammation and prevention of BPD in ventilated premature infants.

Elevated plasma glutathione peroxidase concentration in acute severe asthma: comparison with plasma glutathione peroxidase activity, selenium and malondialdehyde

OBJECTIVE

To investigate plasma glutathione peroxidase concentration, glutathione peroxidase activity, plasma selenium and oxidative stress in acute severe asthma.

MATERIAL AND METHODS

The study was case-control in design, with cases presenting to the emergency department with acute severe asthma and controls randomly selected from a larger cross-sectional study. Plasma malondialdehyde (MDA) was used as a measure of oxidative stress and plasma selenium was measured using ICP-MS. Glutathione peroxidase (GPx) activity was analysed using a colorimetric GPx assay and plasma GPx level was measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Fifteen cases [mean (range) predicted peak expiratory flow rate (PEFR) of 43% (20-69)] and 15 matched controls were recruited. MDA levels (mean+/-SD) were higher in acute asthma subjects (1.30+/-0.56 micromol/L) than in controls (0.86+/-0.53 micromol/L; p<0.05). There were no differences between cases and controls for selenium (99+/-34 microg/L versus 109+/-17 microg/L) or for GPx activity (39+/-25 nmol min(-1) mL(-1) versus 38+/-24 nmol min(-1) mL(-1)), however, GPx plasma levels measured by ELISA were higher in cases than controls (22.5+/-10.8 mg/L versus 13.8+/-7.3 mg/L; p<0.05).

CONCLUSIONS

Patients with acute severe asthma demonstrated increased MDA levels but no differences in plasma selenium levels or GPx activity. GPx levels measured by ELISA were elevated in severe asthma. These results are consistent with an adaptive up-regulation of GPx to protect against oxidative stress.

Oxidative stress in smokers and non-smokers

Oxidative stress plays an important role in the pathogenesis of some diseases such as lung cancer, chronic obstructive pulmonary disease, and atheroscleorosis. Smoking may enhance oxidative stress not only through the production of reactive oxygen radicals in smoke but also through weakening of the antioxidant defense systems. In this study, we investigated the effects of smoking on lipid peroxidation and paraoxonase activity in a healthy population. The study consisted of (n = 30) smokers and (n = 30) nonsmokers. The age of the population which is studied was 44.74 +/- 10.59 yr. The levels of serum malondialdehyde (MDA) and paraoxonase (PON1) activities were measured by the modified Buege method and the Eckerson method, respectively. Student's t-test was used to analyze the data. The serum MDA levels were significantly higher (p < .05) and serum PON1 activities were significantly lower (p < .001) in smokers than in nonsmokers. Thus, increased levels of serum MDA and decreased PON1 activities may be important in determining the oxidant/antioxidant imbalance in smokers.

An imbalance in antioxidant enzymes and stress proteins in childhood asthma

OBJECTIVES

The study was undertaken to examine antioxidant status and level of the major intracellular heat shock proteins (Hsps) in healthy children and children with mild and moderate asthma.

DESIGN AND METHODS

Native gel assays were performed to estimate activities of copper/zinc (CuZn) and manganese (Mn) superoxide dismutase (SOD), and catalase (CAT) in peripheral blood mononuclear cells (PBMC) of healthy and asthmatic children. Hsp70 and Hsp90 protein levels in PBMCs were assessed by Western blot analysis.

RESULTS

Moderate asthmatics displayed higher CuZnSOD/CAT activity ratio compared to healthy children, and increased Hsp90 level compared to mild asthmatics and healthy children.

CONCLUSIONS

With regard to the imbalance in the antioxidant enzyme activities children with moderate asthma differ from healthy children, while an increased Hsp90 expression could be associated with the disease severity, as well.

Severe asthma in adults: what are the important questions?

The term severe refractory asthma (SRA) in adults applies to patients who remain difficult to control despite extensive re-evaluation of diagnosis and management following an observational period of at least 6 months by a specialist. Factors that influence asthma control should be recognized and adequately addressed prior to confirming the diagnosis of SRA. This report presents statements according to the literature defining SRA in order address the important questions. Phenotyping SRA will improve our understanding of mechanisms, natural history, and prognosis. Female gender, obesity, and smoking are associated with SRA. Atopy is less frequent in SRA, but occupational sensitizers are common inducers of new-onset SRA. Viruses contribute to severe exacerbations and can persist in the airways for long periods. Inflammatory cells are in the airways of the majority of patients with SRA and persist despite steroid therapy. The T(H)2 immune process alone is inadequate to explain SRA. Reduced responsiveness to corticosteroids is common, and epithelial cell and smooth muscle abnormalities are found, contributing to airway narrowing. Large and small airway wall thickening is observed, but parenchymal abnormalities may influence airway limitation. Inhaled corticosteroids and bronchodilators are the mainstay of treatment, but patients with SRA remain uncontrolled, indicating a need for new therapies.

Oxidative stress, chronic disease, and muscle wasting

Underlying the pathogenesis of chronic disease is the state of oxidative stress. Oxidative stress is an imbalance in oxidant and antioxidant levels. If an overproduction of oxidants overwhelms the antioxidant defenses, oxidative damage of cells, tissues, and organs ensues. In some cases, oxidative stress is assigned a causal role in disease pathogenesis, whereas in others the link is less certain. Along with underlying oxidative stress, chronic disease is often accompanied by muscle wasting. It has been hypothesized that catabolic programs leading to muscle wasting are mediated by oxidative stress. In cases where disease is localized to the muscle, this concept is easy to appreciate. Transmission of oxidative stress from diseased remote organs to skeletal muscle is thought to be mediated by humoral factors such as inflammatory cytokines. This review examines the relationship between oxidative stress, chronic disease, and muscle wasting, and the mechanisms by which oxidative stress acts as a catabolic signal.

Changes of antioxidant enzyme activity and heat shock protein content in lymphocytes of children with asthma

The aim of the present study was to examine whether changes in the antioxidant status and expression of major intracellular stress proteins are associated with pathophysiology of childhood asthma and severity of the disease. The activities of copper/zinc (CuZn) and manganese (Mn) superoxide dismutase (SOD) and catalase (CAT) in peripheral blood mononuclear cells (PBMCs) of 28 stable pediatric patients (11 mild persistent and 17 moderate persistent asthmatics) and 12 healthy children were assessed by native gel assays. The levels of two heat shock proteins (HSPs), Hsp70 and Hsp90, were examined by quantitative Western blot analysis. Moderate asthmatics, in comparison to healthy children, displayed higher activity of CuZnSOD, while differences of MnSOD and CAT activity between the groups of patients were not found. The levels of Hsp90 and the inducible isoform of Hsp70 were increased in moderate asthmatics as compared to mild asthmatics and healthy children. The results demonstrate an imbalance in cellular antioxidant and stress response systems that may contribute to pathogenesis of childhood asthma, but are not necessarily related to severity of the disease.

Differential effects of cigarette smoke on oxidative stress and proinflammatory cytokine release in primary human airway epithelial cells and in a variety of transformed alveolar epithelial cells

Background

Cigarette smoke mediated oxidative stress and inflammatory events in the airway and alveolar epithelium are important processes in the pathogenesis of smoking related pulmonary diseases. Previously, individual cell lines were used to assess the oxidative and proinflammatory effects of cigarette smoke with confounding results. In this study, a panel of human and rodent transformed epithelial cell lines were used to determine the effects of cigarette smoke extract (CSE) on oxidative stress markers, cell toxicity and proinflammatory cytokine release and compared the effects with that of primary human small airway epithelial cells (SAEC).

Methods

Primary human SAEC, transformed human (A549, H1299, H441), and rodent (murine MLE-15, rat L2) alveolar epithelial cells were treated with different concentrations of CSE (0.2–10%) ranging from 20 min to 24 hr. Cytotoxicity was assessed by lactate dehydrogenase release assay, trypan blue exclusion method and double staining with acridine orange and ethidium bromide. Glutathione concentration was measured by enzymatic recycling assay and 4-hydroxy-2-nonenal levels by using lipid peroxidation assay kit. The levels of proinflammatory cytokines (e.g. IL-8 and IL-6) were measured by ELISA. Nuclear translocation of the transcription factor, NF-κB was assessed by immunocytochemistry and immunoblotting.

Results

Cigarette smoke extract dose-dependently depleted glutathione concentration, increased 4-hydroxy-2-nonenal (4-HNE) levels, and caused necrosis in the transformed cell lines as well as in SAEC. None of the transformed cell lines showed any significant release of cytokines in response to CSE. CSE, however, induced IL-8 and IL-6 release in primary cell lines in a dose-dependent manner, which was associated with the nuclear translocation of NF-κB in SAEC.

Conclusion

This study suggests that primary, but not transformed, lung epithelial cells are an appropriate model to study the inflammatory mechanisms in response to cigarette smoke.

Regulation of inflammation and redox signaling by dietary polyphenols

Reactive oxygen species (ROS) play a key role in enhancing the inflammation through the activation of NF-kappaB and AP-1 transcription factors, and nuclear histone acetylation and deacetylation in various inflammatory diseases. Such undesired effects of oxidative stress have been found to be controlled by the antioxidant and/or anti-inflammatory effects of dietary polyphenols such as curcumin (diferuloylmethane, a principal component of turmeric) and resveratrol (a flavonoid found in red wine). The phenolic compounds in fruits, vegetables, tea and wine are mostly derivatives, and/or isomers of flavones, isoflavones, flavonols, catechins, tocopherols, and phenolic acids. Polyphenols modulate important cellular signaling processes such as cellular growth, differentiation and host of other cellular features. In addition, they modulate NF-kappaB activation, chromatin structure, glutathione biosynthesis, nuclear redox factor (Nrf2) activation, scavenge effect of ROS directly or via glutathione peroxidase activity and as a consequence regulate inflammatory genes in macrophages and lung epithelial cells. However, recent data suggest that dietary polyphenols can work as modifiers of signal transduction pathways to elicit their beneficial effects. The effects of polyphenols however, have been reported to be more pronounced in vitro using high concentrations which are not physiological in vivo. This commentary discusses the recent data on dietary polyphenols in the control of signaling and inflammation particularly during oxidative stress, their metabolism and bioavailability.