Chronic Lymphocytic Leukemia: Correlations Between Oxidative Stress Metabolism and Cytogenetic Subgroups

The chronic lymphocytic leukemia (B cell-CLL) is a heterogeneous lymphoproliferative disorder susceptible to oxidative stress. The excessive production of reactive oxygen intermediates above the capability of naturally produced antioxidants may result in the instability of essential macromolecules, and represents the molecular basis of many diseases including cancer. Highly reactive radicals interact with DNA inducing a multitude of oxidative modifications, and are implicated in mutagenesis due to misreplication of the damaged base 8-oxo-2′-deoxiguanosine (8-oxo-dG). Furthermore, protooncogene activation and/or tumor suppressor gene inhibition has been reported as a consequence of oxygen radical-induced DNA modification. Even though their molecular alterations involving different genes as TP53 (17p13.1) and ATM (11q22-23) in B-cells CLL has been well established, the role of oxidative stress is still poorly understood and a matter of our interest. The aim of the present study was to analyze the correlations between oxidative stress status and the most common genetic subgroups in B-CLL.

Patients and methods: We analyzed peripheral blood and urine from 86 untreated patients with B-CLL, and 39 normal controls. DNA damage was measured assessing the levels of 8-oxo-dG by HPLC-EC. Lipid peroxidation was studied quantifying the levels of malondialdehyde (MDA) and 8-isoprostane by HPLC-EC and enzyme immunoassay, respectively. The activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were examined by spectrophotometric methods; and the oxidative stress marker oxidized/reduced glutathione ratio (GSSG/GSH) was measured by HPLC. Genetic abnormalities were analyzed by fluorescence in situ hybridization (FISH) technique with LSI D13S19, LSI ATM, LSI P53 and CEP 12 probes (Abbott Molecular Inc, Des Plaines, IL, USA).

Results: With regard to antioxidant enzyme activities, there was a significantly decrease of SOD (range: 1.53–13.19 vs 11.88±3.25, p<0.001) and CAT (15.27–68.42 vs 47.15±16.45, p<0.05) levels in all B-CLL cytogenetic subgroups as compared with control subjects. On the contrary, GPx activity increased significantly among patients with del(13q) (31.22±16.53 vs 13.60±5.72, p<0.05). There was also a general increase of GSH (0.64–13.69 vs 0.45±0.51, p<0.001) and GSSG (14.41–67.47 vs 21.12±3.50, p<0.001) content in lymphocytes of CLL patients. As a consequence, the GSSG/GSH x 100 ratio (1.34–43.78 vs 1.95±1.94, p<0.001) increased indicating that the thiol redox status is elevated in CLL lymphocytes. In addition, there was an extensive lipid peroxidation as indicated by the increase of MDA and 8-isoprostane, especially among cases with ATM (MDA/8-isoprostane: 1.98±1.61/118.87±25.96 vs 0.21±0.10/74.64±33.94, p<0.001 and p<0.05) and TP53 (MDA: 2.09±0.78 vs 0.21±0.10, p<0.001) deletions. Finally, DNA damage was also enhanced in B-CLL. The mutagenic base 8-oxo-dG was found to be significantly increased in the lymphocytes DNA and urine of CLL patients (CLL lymphocytes: 13.20–92.64 vs 12.99±18.30, p<0.001 and urine 1.19–85.05 vs 7.43±2.63, p<0.001).

Conclusion: Several oxidative stress parameters could relate to the prognostic role of some chromosomal abnormalities, as the favorable increase of GPx in patients with del(13q), the low oxidative damage among cases of trisomy 12, or the DNA and lipid deterioration of patients with ATM and TP53 deletions.