الفهرس 
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Abstract
Acute lymphoblastic leukemia (ALL) is a more prevalent problem, and has a better prognosis in children. This disease was diagnosed on the basis of clinical history, physical examination and complete blood hemogram. Patients with ALL can have a high, normal or also low white blood cell count. The lymphoblasts replace the normal marrow elements, resulting in a marked decrease in the production of normal blood cells.
It is well recognized that oxidants play a role in several stages of carcinogenesis. Production of reactive oxygen species (ROS) is an inevitable result in cells that use aerobic metabolism for energy production; they play different or even opposing roles during different cellular process. At high level, they are toxic to the cell. Free radicals (FR) are highly reactive and present a challenge to the cellular morphological and function integrity of the cell. They have been implicated in the pathogenesis of many diseases since they initiate lipid peroxidation and DNA damage leading to mutagenesis, carcinogenesis and cell death, if the antioxidant system is impaired.
Antioxidants are natural or synthetic molecules preventing the uncontrolled formation of ROS or inhibiting their action. They may be enzymatic and non enzymatic.
Selenium is an important element and the diet represents the only source of Se in human. Dietary Se is important to provide the Se containing co factor for GPX enzyme which is an important selenoprotein. It catalyzes the oxidation of reduced glutathione and allows the reduction of H2O2 and ROOH, thereby preventing lipid peroxidation and cellular damage.
Information about the activities of antioxidant enzymes is conflicting in patients with cancer and studies on leukemia patients are rare. Moreover, the levels of oxidative damage and antioxidant defense have not been investigated in children just diagnosed with ALL as compared to those after treatment therapy.
The aim of the present study is to examine the prevalence of oxidative stress and the role of antioxidant defense in leukemic patients before and after induction chemotherapy.
This study included ten patients with newly diagnosed acute lymphoblastic leukemia treated in Haematological Department, the same ten patients after induction chemotherapy, and ten control healthy subjects of comparable age and sex. They subjected to careful history taking, thorough clinical examination and hematological investigation including complete blood picture, bone marrow examination, and biochemical determination of MDA, GPX activity and serum selenium level.
The results showed non significant increase in the level of serum MDA in patients group as compared with control group, indicating its involvement in the pathogenesis of the disease, while after chemotherapy the level of MDA decline, but still higher than the control group.
GPH-Px activity was significantly decreased in patients at diagnosis and after chemotherapy induction as compared with control. This indicates a disturbance of the protective role of this enzyme against FR in ALL.
After treatment the activity of GSH-Px is slightly increased this may represent an adaptation mechanism against H2O2 and other peroxides formed in tumor cells.
The decreased GSH-Px activity and the increased MDA levels give the evidence of significant alteration of pro-oxidants and antioxidant of cancer patients.
Serum selenium level was significantly decreased at diagnosis while after treatment it increased when compared with control group, this decrease of selenium level at diagnosis might be due to disease mediated dietary changes and Se tends to concentrate in neoplastic tissues.
After chemotherapy, the level of Se increase due to release of Se into blood from neoplastic tissues
It is concluded that, the present study highlight that oxidant-antioxidant imbalance may be one of the major factors responsible for the development of cancer. Se supplementation may be given to improve the antioxidant enzymes activity in patients with ALL. More studies are necessary to confirm whether these alteration in oxidant-antioxidant levels are the cause or the consequence of carcinogenesis.