Aberrations of Genetic Material as Biomarkers of Ionizing Radiation Effects

Ionizing radiation is the most powerful mutagen in environmental and working conditions. The result of genotoxic effect of radiation is the development of chromosome aberrations. The structural chromosome aberrations in peripheral blood lymphocytes are dicentric, ring, acentric fragment. The observation of chromosome aberration frequency in lymphocyte karyotype is the conclusive method to assess the absorbed dose of ionizing radiation. Our study compared the incidence of chromosome aberrations in occupationally exposed healthy medical workers and in nonexposed healthy population. We analyzed the effect of working place, dose by thermo luminescence personal dosimeter (TLD), duration of occupational exposure (DOE) and age to the sum of aberrant cells and aberrations. Four-year study included 462 subjects, mean-aged 42.3 years, who were occupational exposed to ionizing radiation and 95 subjects, mean-aged 35,2 years, who were not exposed to ionizing radiation, during the same time period and from the same territory. All of them possess thermo luminescence personal dosimeter (TLD) which is read by scanner for thermo luminescence dosimeters. Modified Moorhead’s micro method for peripheral blood lymphocytes and conventional cytogenetic technique of chromosome aberration analysis were used for analysis of chromosome aberrations. Stained preparations (Giemsa) are observed in immersion by light microscope. The karyotype of 200 lymphocytes in metaphase is analyzed the most characteristic aberration: dicentric, then the ring and acentric fragments. The increased incidence of chromosome aberrations was found to be 21.6% in the exposed group and 2.1% in the controls, while the “findings within the limits” (non-specific chromosome lesions – gaps, breaks, elongations, and exchanges) were equal in both groups (22%). Among occupationally exposed medical workers, the highest incidence was found in nuclear medicine workers (42.6%), then in orthopedists (27.08%). There is highly significant difference of the number of aberrant cells and the sum of chromosome aberrations between the exposed and control groups (t-test; p<0.001). The sum of chromosome aberrations and the number of aberrant cells was in positive correlation with the duration of exposure (p< 0.001), and to a less degree of probability with the age (p< 0.05) in the exposed workers. In the controls, this correlation was negative and insignificant. The group of subjects with the duration of occupational exposure up to 15 years had significantly less number of aberrant cells and chromosome aberrations in comparison to the subjects with longer duration of occupational exposure, over 15 years. Long-term occupational exposure to low doses had the effect to the development and frequency of chromosome aberrations, especially unstable ones (dicentric), but it varied in relation to different working places in public health system. The majority of subjects had no genetic modifications affected by low doses, arguing for the significance of individual variability’s in radio sensitivity and genetic predisposition.