Cells and mediators in bronchoalveolar lavage of asthmatic patients: the example of eosinophilic inflammation

Oxidative stress in asthma: Part of the puzzle

An imbalance between the production of reactive oxygen species and the capacity of antioxidant defense mechanisms favoring oxidants is called oxidative stress and is implicated in asthmatic inflammation and severity. Major reactive oxygen species that are formed endogenously include hydrogen peroxide, superoxide anion, hydroxyl radical, and hypohalite radical; and the major antioxidants that fight against the endogenous and environmental oxidants are superoxide dismutase, catalase, and glutathione. Despite the well-known presence of oxidative stress in asthma, studies that target oxidative burden using a variety of nutritional, pharmacological, and environmental approaches have generally been disappointing. In this review, we summarize the current knowledge on oxidative stress and antioxidant imbalance in asthma. In addition, we focus on possible biomarkers of oxidative stress in asthma and on current and future treatment strategies using the modulation of oxidative stress to treat asthma patients.

New Insights in Oxidant Biology in Asthma

Research over the past 30 years has identified mechanistic biochemical oxidation pathways that contribute to asthma pathophysiology. Redox imbalance is present in asthma and strongly linked to the pathobiology of airflow obstruction, airway hyperreactivity, and remodeling. High levels of reactive oxygen species, reactive nitrogen species, and oxidatively modified proteins in the lung, blood, and urine provide conclusive evidence for pathologic oxidation in asthma. Concurrent loss of antioxidants, such as superoxide dismutases and catalase, is attributed to redox modifications of the enzymes, and further amplifies the oxidative injury in the airway. The presence of high levels of urine bromotyrosine, an oxidation product of eosinophil peroxidase, identifies activated eosinophils, and shows promise for use as a noninvasive biomarker of poor asthma control.

Effects of supportive treatment such as antioxidant or leukotriene receptor antagonist drugs on inflammatory and respiratory parameters in asthma patients

In this study, prospectively, we aimed to determine the effects of the different treatment alternatives on the oxidant system and inflammatory and clinic determinants during the stable period of 1 month following an asthmatic attack. Thirty-one patients (22 female, nine male) were randomly divided into three groups following the stabilization of an acute asthma attack. The control group that is an additional group to the three patient groups consisted of 10 healthy volunteers (five female, five male). The following protocols were used for 4 weeks: Group I: short-acting inhaler beta2 mimetic as required (treatment A)+800 mug inhaler budesonide (treatment B)+leukotriene receptor antagonist; Group II: treatment A and B; Group III: treatment A and B+vitamin E. The serum levels before and after treatment of eosinophilic cationic protein (ECP), leukotriene E4 (LTE(4)), and malondialdehyde (MDA) were determined. The values before and after treatment were statistically compared both with each other and control values. Pretreatment ECP, LTE(4), and MDA levels for the three groups were significantly higher compared with post-treatment levels (P<0.05 to P<0.001) and the control levels (P<0.01 to P<0.001). However, when post-treatment levels were compared with those of the control group, no significant differences were found (P>0.05). Lack of significant variation was observed when the pre- and post-treatment differences in the three groups were compared for each one of ECP, LTE(4), and MDA levels (P>0.05). Leukotriene receptor antagonist or antioxidant agents added to standard asthma treatment did not make a significant contribution on ECP, LTE(4), and MDA levels and respiratory parameters such as spirometric function tests. Etiologic factors and/or the possible changes in different pathogenetic ways of the inflammation process may have been responsible for nonsignificant intertreatment difference in the biomarker levels. The result confirms that suppressing the inflammation in asthma enables the entire inflammatory pathologic process to be controlled.

Oxidative and nitrosative events in asthma

Asthma affects over 15 million individuals in the United States, with over 1.5 million emergency room visits, 500,000 hospitalizations, and 5500 deaths each year, many of which are children. Airway inflammation is the proximate cause of the recurrent episodes of airflow limitation in asthma. Research applying molecular biology, chemistry, and cell biology to human asthma and model systems of asthma over the last decade has revealed that numerous biologically active proinflammatory mediators lead to increased production of reactive oxygen species (ROS) and the gaseous molecule nitric oxide (NO). Persistently increased ROS and NO in asthma lead to reactive nitrogen species (RNS) formation and subsequent oxidation and nitration of proteins, which may cause alterations in protein function that are biologically relevant to airway injury/inflammation. Eosinophil peroxidase and myeloperoxidase, leukocyte-derived enzymes, amplify oxidative events and are another enzymatic source of NO-derived oxidants and nitrotyrosine formation in asthma. Concomitant with increased generation of oxidative and nitrosative molecules in asthma, loss of protective antioxidant defense, specifically superoxide dismutase (SOD), contributes to the overall toxic environment of the asthmatic airway. This review discusses the rapidly accruing data linking oxidative and nitrosative events as critical participants in the acute and chronic inflammation of asthmatic airways.

Serum eosinophil derived neurotoxin may reflect more strongly disease severity in childhood atopic dermatitis than eosinophil cationic protein

Serum levels of eosinophil cationic protein (ECP) have been shown to be a good parameter of the disease severity of patients with atopic dermatitis (AD). However, the relationship between the disease severity and the eosinophil derived neurotoxin (EDN) has not been established in AD patients. The purpose of this study is to examine serum ECP and EDN levels in relation to the disease severity in AD children. Serum ECP and EDN levels were assessed in relation to the skin scores in 34 AD children (18 boys and 16 girls; age 0.6 to 7years: mean+/-S.D. 2.2+/-1.9) and six non-atopic control children (three boys and three girls; age 1 to 3years: mean+/-S.D. 1.7+/-0.9). Serum ECP and EDN levels of the patients with AD were significantly increased compared with the non-atopic controls. Serum EDN levels of the patients were also related to the disease severity. The skin scores were more significantly correlated with serum EDN levels than ECP levels. We concluded that serum EDN may reflect more strongly disease severity as eosinophilic activation in AD children than serum ECP.

Serum eosinophil cationic protein (ECP) and eosinophil protein X (EPX) in childhood asthma: the influence of atopy

The purpose of this study was to determine the value of serum measurements of eosinophil cationic protein (ECP) and eosinophil protein X (EPX) in diagnosing asthma in children, and to investigate the influence of concomitant allergic diseases and atopic sensitization, assessed by skin prick tests (SPT), on these markers. ECP and EPX were determined in 36 children with asthma, in 33 children with other symptoms from lower airways disease (OSLA), and in 166 control children. Sixteen children with asthma but no anti-inflammatory therapy had significantly higher concentrations of ECP and EPX (ECP: 27.5 microg/L, P < 0.001; EPX: 59.9 microg/L, P < 0.001) than the control children (ECP: 11.2 microg/L; EPX: 26.2 microg/L). In the 20 children on anti-inflammatory therapy, ECP values were similar to those of controls. The children with OSLA (ECP: 13.6 microg/L, P < 0.01; EPX: 47.2 microg/L, P < 0.001) differed significantly from controls. When using the value of 24.7 microg/L (97.5 percentile in the 68 non-atopic controls) as a pathologic upper limit for ECP, 10 (63%) of the 16 asthmatic children on no maintenance medication, two (10%) of the 20 asthmatics on maintenance therapy, and 11 (33%) of the 33 children with OSLA had high ECP; the same figure was only 18 (11%) in the 166 control children. Both ECP and EPX had a significant association with allergic disorders and with SPT reactivity. In multivariate logistic regression analysis, an elevated ECP was significantly associated with asthma (OR 2.3, 95%CI 1.1-4.9) and atopic dermatitis (2.9, 1.2-6.9), and an elevated EPX was significantly associated with asthma (2.61, 1.19-5.74) and allergic rhinoconjunctivitis (5.23, 1.46-18.73). We conclude that serum concentrations of both ECP and EPX are higher in asthmatic than in healthy children. However, other allergic diseases, such as allergic rhinoconjunctivitis, atopic dermatitis, and allergic skin sensitization also raise the concentrations of these markers. This limits their usefulness in the diagnosis of childhood asthma.

An in vivo mammary infusion model for tissue migration of leucocytes during inflammation

Infusion of LPS or nematode larvae into the mammary glands of sheep induces recruitment of neutrophils or eosinophils respectively. While neutrophil recruitment required only a single infusion of LPS, repeated infusions of parasite larvae were required to induce significant eosinophil migration into the lumen of the glands. Eosinophil recruitment was accompanied by a distinct population of lymphocytes consisting mainly of activated (MHC class II and CD25+) T cells. L-selectin was expressed at reduced levels on both neutrophils and eosinophils collected from the mammary gland compared with cells present in the blood of the same sheep. In addition, VLA-4 and beta 1-integrin were down-regulated or negative in mammary eosinophils compared with strong expression in the blood while neutrophils were negative for these markers in both mammary washes and blood. Eosinophils in blood and mammary glands were negative for MHC class II, CD25 and CD4. Mast cells and lymphocyte aggregates were present in the tissue of glands chronically stimulated with parasite larvae while eosinophils were only present if the gland had been recently stimulated. These studies show that detailed in vivo analysis of leucocyte migration can be easily performed in the sheep mammary infusion model which allows non-invasive and repeated sampling of inflammatory cells before and after tissue migration.

Measurement of serum levels of eosinophil cationic protein to monitor patients with seasonal respiratory allergy induced by Parietaria pollen (treated and untreated with specific immunotherapy)

This trial studied the behavior of a marker of eosinophilic inflammation, eosinophil cationic protein (ECP), in the peripheral blood of two groups of subjects with seasonal allergic respiratory symptoms (rhinitis and mild bronchial asthma) induced by pollen allergens of Parietaria judaica (P.j.) (one group treated and another untreated with specific immunotherapy [SIT]), to determine what contribution these serial measurements might provide, in comparison with various other tools now available for pollinosis monitoring. In a previously randomized order, we selected 25 patients with monosensitization to P.j. pollen allergens; among them, 12 had started SIT with a P.j. extract in autumn 1993. As a control group, 13 patients were untreated. All patients were studied with various tests at four different times: time I-November 1993; time II-February 1994; time III-end of May 1994; and time IV-September 1994. Blood samples for determination of serum ECP were collected at each time. Methacholine challenge tests were performed at times I and III. A pollen count was also carried out. A statistically significant difference (P < 0.05) was observed in mean ECP levels at times I and III in SIT treated and untreated patients. The interaction between groups and time was not significant. No statistically significant difference was found between PD20 FEV1 values at times I and III in either group. After 1 year of treatment, we did not find any effect of SIT on bronchial hyperresponsiveness or on ECP serum values.

Sequential appearance of inflammatory mediators in rat bronchoalveolar lavage fluid after oleic acid-induced lung injury

The oleic acid (OA) model of rat lung injury was originally developed as a model of fat embolism syndrome. A single intravenous dose of pure OA causes an acute diffuse lung injury, which, in its initial stages, histologically and physiologically resembles human ARDS. Rat lungs acutely injured by intravenous OA manifest increased levels of ICAM-1 within 30-60 min. This study shows that human umbilical vein endothelial cells (HUVEC) can be used in a bioassay to reveal some of the adhesion molecule stimulating activities present in bronchoalveolar lavage fluid (BALF) from post-OA-injected rats: (1) There is an as yet unidentified ICAM-1 and ELAM (E Selectin) inducing activity in BALF within 15 min of OA injection that is not TNF alpha; there is very little measurable tumor necrosis factor-alpha (TNF alpha) in 15 min BALF (BALF15). (2) BALF15 also stimulates cultured macrophage derived from BALF of normal rat lungs to produce TNF alpha. (3) By 60 min after OA injection, 50-75% of the ICAM-1 and ELAM inducing activity in BALF (BALF60) is TNF alpha; BALF60 contains about 250-280 pg/mL TNF alpha. The other 25-50% adhesion molecule-inducing activity in BALF60 is unidentified. (4) The ICAM-1-inducing activity of pure TNF alpha was equal to that of BALF60 containing equivalent concentrations of TNF alpha. The ELAM inducing activity of pure TNF alpha, however, was about 1/2 that of BALF60 containing equivalent concentrations of TNF alpha. The time courses for ICAM and ELAM stimulation with pure TNF alpha or BALF60 containing equivalent levels of TNF alpha were the same. The identity of the mediators in BALF15 and BALF60 that are not TNF alpha and the mechanisms by which OA injection stimulates cytokine production remain to be elucidated.