Analysis of chromosome aberrations by FISH and Giemsa assays in lymphocytes of cancer patients undergoing whole-body irradiation: comparison of in vivo and in vitro irradiation.

PURPOSE: To study the cytogenetic effects of fractionated radiotherapy in peripheral blood lymphocytes of five cancer patients. In vitro experiments were performed in parallel using the same dose range and a comparison was made of the induced frequencies of stable and unstable chromosome aberrations. The object was to clarify the use of an in vitro calibration curve for immediate and retrospective dosimetry in cases of radiation accidents. MATERIALS AND METHODS: Patients were exposed to 60Co gamma-rays at a single dose of 11.5 cGy each day up to a total dose of 57.5 cGy, given in 5 days. For measurement of chromosome aberrations, blood was collected from patients before irradiation and after each exposure. Blood taken before treatment was used as a control and for in vitro irradiation experiments in the dose range 8-50 cGy. Chromosome aberration frequency (stable as well as unstable) was determined using fluorescence in situ hybridization (FISH) assay with specific DNA libraries for chromosomes 1, 4 and 8 and a pancentromertic probe for the whole genome. Giemsa-stained preparations were used to score unstable aberrations following in vivo and in vitro exposure. RESULTS: A linear dose-response curve was determined for both dicentrics and translocations. The in vivo frequency of translocations was higher than for dicentrics. Dose-response curves generated for translocations following in vivo and in vitro irradiation yielded similar frequencies. In contrast, for dicentrics, in vitro irradiation yielded a higher frequency when compared with data generated following in vivo exposure. CONCLUSIONS: For dose reconstruction purposes, translocations frequency seems to be a more adequate end-point than the scoring of dicentrics. The established in vitro calibration curve for dicentrics may underestimate absorbed radiation dose in cases of protracted exposure.

An investigation of the age-dependency of chromosome abnormalities in human populations exposed to low-dose ionising radiation.

Among various cytogenetic changes stable chromosome aberrations (SCHA) seem to be the most significant for ageing and carcinogenesis. Being nonlethal they can persist through cell divisions and accumulate in time. We studied the age response of SCHA (translocations and insertions) in normal and radiation exposed human populations. Two cohorts of people at the age range of 3--72 years were studied: control (43 persons) and exposed to low doses of accidental irradiation due to Chernobyl accident and atomic bomb testing in Semipalatinsk (67 persons). FISH method was used for visualisation of chromosome aberrations. Metaphases from cultured lymphocytes were hybridised with biotinilated whole chromosome specific DNA probes for 1, 4 and 12 chromosomes, and with pancentromeric probe labelled with digoxigenin. The frequency of SCHA in lymphocytes increased as a quadratic function of donor age in both populations studied, being higher in exposed cohort as compared with control one. No age dependence for dicentrics was observed. The frequency of SCHA is a reliable biomarker of ageing in humans. Quadratic model of their age-response gives reasons to suggest that their increase is due to lower level of DNA repair or/and the genomic instability in older people. The exposure of people to low doses of ionising radiation accelerates the age-related increase of SCHA frequency.