Oxidative damage and cell signaling transduction in patients of chronic myeloid leukemia.

Abstract

Chronic myeloid leukemia (CML) was the first human malignancy shown to be consistently associated with a chromosomal abnormality, the Philadelphia chromosome. At the gene level, the Philadelphia chromosome is the result of breaks on chromosomes 9 and 22 with a reciprocal translocation of the distal genetic material. This translocation forms the new hybrid BCR-ABL oncogene, an abnormal 8.5-kb RNA that encodes a 210-kDa fusion protein, which, presumably through its increased tyrosine kinase activity, changes normal hematopoietic cells into CML cells [1]. Oxidative stress is a biochemical condition that occurs when intracellular antioxidants are unable to neutralize pro-oxidants such as reactive oxidant species (ROS). These ROS damage membranes, DNA, lipids, proteins, and carbohydrates, eventually causing cell injury and death. ROS contribute to several cellular functions, including the regulation of signal transduction, gene expression, and cell proliferation [2]. Nuclear factor kappa B (NF-κB) is a redox-sensitive transcription factor that is mostly cytoplasmic and maintained in the cytoplasm by interaction with its inhibitor IκB-α. NF-κB pathway plays an important role in the control of cell proliferation, differentiation, apoptosis, stress response, cell signaling transduction, and other physiological processes [3]. ROS can activate NF-κB signal transduction pathways, which in turn lead to the transcription of genes involved in cell growth regulatory pathways. A number of somatic mutations have been identified in cancer, like transversion mutations of p53. These key genes have been linked to cancer progression, and the mutations found in them can be produced by ROS. Although the direct link between ROS modification of DNA and mutations of these genes remains to be established, they should be considered important candidates for the induced carcinogenesis because mutations in these genes could be responsible for tumor initiation as well as progression. ROS have also been shown to increase the production of the angiogenic factor such as vascular endothelial growth factor (VEGF) in tumor cells resulting in carcinogenesis. In an attempt to explore the possibility that cellular redox status may up-regulate NF-κB signaling, the present study was designed to correlate the alterations in the pro-oxidant/antioxidant status with the up-regulation of the nuclear transcription factor NF-κB, pro-inflammatory cytokine VEGF, and tumor suppressor gene p53 in the development/progression of CML. Case control study consisted of 40 clinically diagnosed CML patients from the Department of Medicine, University Hospital, Banaras Hindu University (Varanasi, India), with cytogenetic analysis to confirm the presence of Philadelphia (Ph) chromosome. Exclusion criteria for enrolment in the study group were patients with clinical or pathologic evidence of cancer at any other site or having received any type of neo-adjuvant therapy along with the presence of liver dysfunction, diabetes mellitus, heart failure, or renal failure. The mean age of the CML patients was 36.7 ± 11.9 years. The mean leukocyte count was 80,410 per mm. Themean spleen size of patients measured by ultrasonography was 21.1 ± 3.5 cm, and was found to be significantly larger than controls. The Philadelphia chromosomewas present in all of 40 patients with CML, which confirmed the BCR/ABL translocation. Forty age and sex-matched healthy volunteers having socioeconomic status similar to that of patients served as controls. None of the patients and controls was under antioxidant supplementation. The venous blood was drawn from patients and healthy volunteers in sterile tubes for various biochemical and hematologic investigations. The study protocol was approved by the ethical committee of the Institute of Medical Sciences, Banaras Hindu University. Informed consent of each patient and healthy volunteers was obtained purely for research purpose. The oxidative stress parameters 8-hydroxydeoxyguanosine (8-OHdG), protein carbonyl (PC), and total antioxidant status (TAS) were measured [4–6]. NF-κB p65 subunit DNA-binding activity, VEGF, and p53 levels were estimated to correlate the up-regulation of nuclear transcription factor/cytokine level with increased oxidative stress so as to determine the role of oxidative microenvironment in the progression of disease. All the data were expressed as the mean ± standard error of the mean (SEM). Data were analyzed statistically by independent Student’s t-test for comparison of parametric variables. Either linear or nonlinear regression analysis was applied for association studies. All statistical analyses were two-tailed and a value of Acta Biochim Biophys Sin, 2015, 47(6), 474–476 doi: 10.1093/abbs/gmv029 Advance Access Publication Date: 28 April 2015 New Phenomenon