Bronchial asthma is a chronic, complex, heterogeneous disease of the airways, which includes the activation of many inflammatory and structural cell populations that release numerous inflammatory mediators, giving rise to the physiopathological changes that are characteristic of the disease.1 Environmental and genetic factors play a role in its onset, although the exact mechanisms of their actions have not been fully determined. The lungs are continually exposed to oxidants generated endogenously from the mitochondria, phagocytes and other cells, or exogenously from air pollutants and cigarette smoke. They have the largest endothelial surface area of any organ, which makes the lung tissue the principal target for circulating oxidants and xenobiotics. Asthmatic patients produce a variety of mediators, including reactive oxygen species (ROS).2 An increase in oxidative damage can contribute to both the origin and development of respiratory diseases, including bronchial asthma. Lung lesions due to ROS are related with the oxidation of deoxyribonucleic acid (DNA), proteins and lipids. These oxidized biomolecules can induce various responses and a cascade of events, such as airway hyperreactivity, increase in the generation of chemoattractants, release of tachykinins and neurokinins, and an increase in the release of mediators which ultimately aggravate the oxidative damage.1 The lungs can use non-enzymatic antioxidants, such as vitamins, uric acid, glutathione, sulfhydryl groups (proteins, peptides and amino acids) and various enzymatic antioxidants, such as superoxide dismutase, catalase (CAT) and glutathione peroxidase as a defense against oxidative damage and ROS.

CAT (EC 1.11.1.6) is a common antioxidant enzyme responsible for controlling the hydrogen peroxide concentrations in cells. It is ubiquitous in most aerobic cells also detected in the lungs (macrophages, fibroblasts and pneumocytes).3 As an intracellular antioxidant enzyme, CAT catalyses the breakdown of two hydrogen peroxide molecules into one oxygen molecule and two water molecules; its activity is determined genetically. The CAT gene is located on chromosome 11p13; it is 34kb long, contains 13 exons and 12 introns and codes a 256-amino acid protein.4,5 Various polymorphisms of this enzyme have been described and characterized, both in the coding6,7 and non-coding region.7–11 A common polymorphism in the CAT gene promoter region is the substitution of T for C in position T -262 in the 5′ region,9 which is considered to lead to a decrease in enzyme activity. The CAT TT genotype could be responsible for a reduction in the antioxidant defense and a subsequent increase in oxidative damage.

Since oxidative damage plays a role in the pathogenesis of asthma, and CAT is critical for protecting cells against ROS, we hypothesized that the polymorphisms in the CAT gene that influence its enzyme activity contribute substantially to the onset of the disease. This study aimed to evaluate CAT polymorphism -262 C/T in asthmatic children. We sought to determine markers of oxidative damage, and to analyze a possible association between the CAT genotype and oxidative damage of proteins and lipids in asthmatic and healthy children.

Bronchial asthma is a complex immunological disease, affected by environmental and genetic factors and their interactions, which are probably key in its pathogenesis and prognosis. Asthma belongs to a group of disorders in which oxidative damage and an imbalance between pro-oxidant and antioxidant substances play an important role. We observed a higher prevalence of the TT genotype of the antioxidant enzyme CAT and an increase in the oxidative damage of proteins and lipids associated with bronchial asthma. We also found that in asthmatic children with the CAT TT genotype, there was greater oxidative damage compared with the other genetic variation of CAT -262 C/T. As far as the authors are aware, this is the first study on the association of genetic polymorphism and oxidative damage in Slovakian children or adults with asthma.

Polymorphism of the genes involved in oxidative stress pathways, NAD(P)H:quinone oxidoreductase16 and glutathione transferases M1 and P1,17,18 have been associated with bronchial asthma.16,17 CAT is one of the essential antioxidant enzymes and, therefore, CAT is a candidate gene for many diseases that are potentially related with oxidative damage and exogenous/endogenous oxidative stress. In this study, the frequency of the CAT TT genotype was 0.226 in asthmatic children and 0.048 in healthy children (P<.001). The frequency of CAT genotype -262 C/T was comparable to that described in other European Studies (English, German, Polish and Turkish).18–21 Analysis according to sex showed similar results to the analysis of the total population, and the homozygous variant was associated with bronchial asthma. We have demonstrated that polymorphism in the CAT gene may be associated with a predisposition to bronchial asthma. The homozygous variant CAT -262 C/T was associated with asthma in white children of Hispanic origin but not in children of other origins.22 Polonikov et al. (2009) did not observe differences in the frequencies or genotype of CAT gene polymorphism -262 C/T between asthmatic adults and healthy controls.23 However, an association was observed between CAT gene polymorphism -21A/T and bronchial asthma, and it was found that the risk of asthma in carriers of the -21AA genotype depends on exposure to both oxidants and antioxidants. The contradictory results with respect to the relationship between the CAT gene polymorphism and bronchial asthma may be explained by the influence of the ethnicity. In our selected population of Slovakian children, the TT genotype was associated with bronchial asthma. This genetic variation of the CAT gene could be responsible for oxidative damage, as we observed an increase particularly in asthmatic children who were carriers of the TT genotype. A decrease has been observed in CAT activity in the TT genotype in various studies.11,24,25 However, Forsberg et al.9 found a higher level of CAT in the CAT gene TT genotype. The higher risk of asthma could be a result of the decreased CAT activity in the TT genotype, and the subsequent increase in the oxidative damage of the biomolecules. We observed an increase in protein and lipid oxidative damage in children with bronchial asthma. Chronic inflammation is associated with higher production of ROS and an increase in oxidative stress in the lung. Higher levels of hydrogen peroxide, superoxide radical27 and lipid peroxidation27,28 have been found in children with bronchial asthma. In the asthmatic population in the present study, we observed an increase in nitric oxide29 and eCO. These markers are characterized by a higher concentration in the TT genotype of asthmatic children compared with the CC and CT genotypes (results not published). It has been shown that the combination of the heterozygous variant with the homozygous variant is positive. A C allele could be sufficient for CAT to function, but further genetic studies are required to determine the activity and function of CAT in different genotypes, not only for this polymorphism. In healthy children with a variant of the CAT genotype, other enzymatic antioxidants (such as heme oxygenase, superoxide dismutase, glutathione peroxidase and glutathione transferase) are detected in the normal homozygous form, which protect them against oxidative damage. Moreover, healthy children do not show the increased ROS values detected in asthmatic children. The relationship between oxidative damage and chronic inflammation in asthmatics is probably two-way. Oxidative stress can exacerbate existing inflammation and can contribute to airway remodeling and conversely, continuous chronic inflammation may result in increased production of ROS and greater oxidative damage. In the control group, comparison of the concentration of oxidative damage markers according to the CAT genotype did not reveal significant differences. In this study, the higher lipid peroxidation and protein modification detected could be a result of excessive ROS production or reduced capacity of the antioxidant defense system in asthmatics. The antioxidants in food help endogenous antioxidants to prevent oxidative damage and represent a possible therapeutic option. Antioxidant treatment could enhance reference asthma treatment and be an adjuvant, especially in asthmatic patients with antioxidant enzyme risk genotypes. Interactions between genes and environmental factors may influence CAT activity in the different genotypes. We did not analyze these effects, but it has been shown that exposure to smoke and the consumption of fruit and vegetables affect the activity of CAT in the CC, CT and TT genotypes of the CAT gene.24–26,28

Bronchial asthma is a complex, multifactor disease in which genetic factors, environmental factors and oxidative damage are responsible for its onset, modulation and progression. The results of this study show that polymorphisms of the CAT gene may be associated with bronchial asthma in children, and could participate in greater oxidative damage. The genetic variation in CAT, which protects the cells against ROS, may affect the asthmatic process. In summary, asthma is not an individual disease, but a group of diseases associated with an increase in oxidative stress, followed by the accumulation of oxidative damage. This could be an important factor that contributes to the development and persistence of airway inflammation in asthmatic children. Greater oxidative damage may be a consequence of cross reactions between polymorphism of the CAT gene and environmental factors, as well as polymorphism of the CAT gene and other genetic factors that may modify the risk of disease. However, further studies on the interactions between polymorphism of the CAT gene and additional polymorphisms in genes related with asthma are required, as they could help to improve our understanding of the complex disease that is bronchial asthma.

This study was funded with a grant from the Ministry of Health 2007/47-UK-12, and by the Ministry of Education, Science, Research and Sports of the Slovak Republic, VEGA 1/0071/11.

None of the authors have declared any conflict of interests.