Measurement of oxidative stress and antioxidant status in acute lymphoblastic leukemia patients

Abstract

Objectives

To evaluate the oxidative status and antioxidant defense in patients with acute lymphoblastic leukemia (ALL).

Design and methods

We measured concentrations of plasmatic thiobarbituric acid reactive substances (TBARS), serum protein carbonylation, whole blood catalase (CAT) and superoxide dismutase (SOD) activities, as well as the plasmatic and erythrocyte thiol levels and serum vitamin E concentration. This study was performed on 80 children with ALL divided into 4 groups: just diagnosed, remission induction, remission maintenance and out-of-treatment.

Results

TBARS levels and serum protein carbonylation were higher in ALL patients than in controls and reduced levels of antioxidants were found in these patients.

Conclusion

These findings may indicate a possible link between decreased antioxidants and increased levels of cells alterations due to oxidative damage, supporting the idea that there is a persistence of oxidative stress in acute lymphoblastic leukemia.

Introduction

Leukemias originate from hematopoietic stem cells that lose the capacity to differentiate normally in mature blood cells at different stages of their maturation and differentiation [1], [2]. Acute lymphoblastic leukemia (ALL) is the most common cancer found in the pediatric population and it accounts for more than 50% of the hematopoietic malignancies in this age group [3], [4]. In contrast, ALL is a relatively rare leukemia subtype in adults, accounting for only 2–3% of hematopoietic malignancies [4].

ALL is a disease characterized by uncontrolled proliferation and maturation arrest of lymphoid progenitor cells in bone marrow resulting in an excess of malignant cells [5]. The lymphoblasts replace the normal marrow elements, resulting in a marked decrease in the production of normal blood cells. ALL is a disorder caused by an abnormal expression of genes, which is usually a result of chromosomal translocations [6].

The disease can be originated from lymphoid cells of different lineages, giving rise to B- or T-cell leukemias or sometimes mixed-lineage leukemia [7]. It is a curable disease with an expected long term survival rate of at least 70%, when treated with modern therapeutic regimens. In general, ALL standard treatment protocols consist of induction and maintenance remission with chemotherapeutic drugs [8].

It is well recognized that oxidants play a role in several stages of carcinogenesis [9]. Production of reactive oxygen species (ROS) is an inevitable result in cells that use aerobic metabolism for energy production [10]. ROS are known to play a dual role in biological systems, since they may be either harmful or beneficial to living systems. Furthermore, oxidative stress may inhibit or promote apoptosis and until necrosis, depending on the intensity of the stimulation. Beneficial effects of ROS involve physiological roles in cellular responses to noxia, as for example in the defense against infectious agents and in the function of a number of cellular signaling systems [11]. In contrast, at high concentrations, ROS can be important mediators of damage to biomolecules such as DNA, proteins, and lipids, leading to cellular dysfunction and cell death. Accumulation of such molecules causes noxious effects on individuals, resulting in diseases such as hematopoietic malignancies [12]. The first biological molecules for oxidative damage in cells are proteins and their side chains can be carbonylated by reactive carbonyl compounds [13]. In addition, oxidative damage in lipids leads to the formation of products such as malondialdehyde (MDA) [14].

The effect of reactive species is balanced by the antioxidant action of non-enzymatic antioxidants, as well as by antioxidant enzymes. Antioxidant defenses are extremely important as they represent the direct removal of free radicals (pro-oxidants), providing maximal protection for biological sites [11].

The most efficient enzymatic antioxidants involve superoxide dismutase (SOD) and catalase (CAT). SOD is an antioxidant enzyme that catalyzes the dismutation of O₂⁻ to O₂ and to the less-reactive species hydrogen peroxide (H₂O₂) protecting cells from injury induced by free radicals [15]. Additionally, the enzyme CAT very efficiently promotes the conversion of H₂O₂ to water and molecular oxygen [14]. Non-enzymatic antioxidants include thiol antioxidants and vitamin E. Non-protein thiols have a variety of functions in bioreduction and detoxification processes [16]. The main antioxidant function of vitamin E is the protection against lipid peroxidation [17].

Information about the activities of antioxidant enzymes is conflicting in patients with cancer and studies on leukemia patients are rare [18]. Moreover, the levels of oxidative damage and antioxidant defenses have not been investigated in children just diagnosed with ALL as compared to those in the different stages of treatment and after therapy. In this work, we studied the oxidative profile in ALL patients in these groups, through the verification of main enzymatic antioxidant defenses (CAT and SOD) and non-enzymatic antioxidants (thiols and vitamin E). Moreover, we determined the intensity of biological damage caused by free radicals in lipid and protein through the measurement of lipid peroxidation and the levels of protein carbonylation.