en Radiation Biology Radiation Biology تحقيق بديع Original Research <div style="text-align: justify;"><span style="font-size:10pt"><span style="text-justify:newspaper"><span style="text-kashida-space:50%"><span style="line-height:119%"><span style="font-family:Calibri"><span style="color:black"><span lang="en-US" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:#1f497d"><span style="font-style:italic"><span style="font-weight:bold"><span style="language:en-US">Background:</span></span></span></span></span></span> <span lang="en-GB" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:black"><span style="language:en-GB">The use of radioprotectors to ameliorate the deleterious effects of radiation could be an option to reduce normal tissue radiotoxicity. In this study, melatonin as an efficient naturally occurring antioxidant was used to explore its modulating effects on radiation induced cytogenetic damages at G0 and G2-lymphocytes of control and breast cancer (BC) patients. </span></span></span></span><span lang="en-GB" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:#1f497d"><span style="font-style:italic"><span style="font-weight:bold"><span style="language:en-GB">Materials and Methods: </span></span></span></span></span></span><span lang="en-GB" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:black"><span style="language:en-GB">Whole blood samples were collected from 20 BC patients, and also 10 healthy individuals. Lymphocyte culture was initiated, irradiation was applied in G0-lymphocytes 1 hour before culture initiation using a 6 MV linear accelerator at dose of 3Gy and 4 hours before harvesting for G2-lymphocytes at a dose of 1Gy in the presence or absence of melatonin (800 &micro;g/ml). Cytogenetic damages were assessed using cytochalasin-B blocked micronucleus (CBMN) assay and chromosomal aberrations were analyzed using G2-assay according to standard methods. Data were statistically analyzed and P-value <0.05 was considered as significant difference. </span></span></span></span><span lang="en-GB" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:#1f497d"><span style="font-style:italic"><span style="font-weight:bold"><span style="language:en-GB">Results: </span></span></span></span></span></span><span lang="en-GB" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:black"><span style="language:en-GB">Results obtained for G0-irradiated lymphocytes in the presence of melatonin, showed a profound reduction in the frequency of CBMN in both lymphocytes of normal control and BC patients compared to radiation alone (p<0.05). Conversely, a significant increase in the frequency of radiation induced chromosomal aberrations was observed in both groups (p<0.05). </span></span></span></span><span lang="en-GB" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:#1f497d"><span style="font-style:italic"><span style="font-weight:bold"><span style="language:en-GB">Conclusion: </span></span></span></span></span></span><span lang="en-GB" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:black"><span style="language:en-GB">Apparently melatonin exerts its modifying effect on radiation induced cytogenetic damages in a cell-cycle dependent manner. It acts as a radioprotector when lymphocytes have been irradiated in G0-phase of the cell cycle. Conversely it acts as radiosensitizer when used for lymphocytes exposed at G2-phase of the cell cycle.</span></span></span></span></span></span></span></span></span></span></div> Breast cancer, lymphocytes, antioxidants, ionizing radiation, radioprotector, radiosensitizer, cell cycle. 251 257 http://ijrr.com/browse.php?a_code=A-10-1-1483&slc_lang=en&sid=1 H. Mozdarani mozdarani@modares.ac.ir 7900319475328460033005 7900319475328460033005 Yes Department of Medical Genetics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran S. Mozdarani 7900319475328460033006 7900319475328460033006 No Department of Cytogenetics, Cytogenome Medical Genetics laboratory, Ale-Ahmad High way, Chamran Medical Building, Tehran, Iran E. Samei 7900319475328460033007 7900319475328460033007 No Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran S. Mozdarani 7900319475328460033008 7900319475328460033008 No Department of Cytogenetics, Cytogenome Medical Genetics laboratory, Ale-Ahmad High way, Chamran Medical Building, Tehran, Iran F. Pakniat 7900319475328460033009 7900319475328460033009 No Department of Medical Physics, Shahid Beheshti University of Medical Sciences, Tehran, Iran H. Nosrati 7900319475328460033010 7900319475328460033010 No Cancer Institute, Department of Radiotherapy, Tehran, Iran