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Studies on Radiation-induced Chromosome Aberrations in Mammalian Cells. 2) Applied Aspects

Objective


A) Cortés-Benavides et al. (Univ. Sevilla) reported the use of the cytokinesis-block micronucleus method to evaluate the AR as a good alternative to the single fixation method and scoring of chromosomal aberrations at metaphase for the study of the AR in human lymphocyes. With this method they observed a significant decrease in the yield of micronuclei in binucleate cells conditioned with various doses of peroxide and irradiated with either 1.5 or 3.0 Gy of X-rays later on. They also show a clear AR in binucleated cells conditioned with H(2)O(2), while for low dose-irradiated cells the adaptation observed seems to depend upon the dose rate and never reached the extent observed in cells pretreated with peroxide.
At the Univ. of Rome, esperiments were carried out with human lymphocytes to test the effect of low-dosage X-ray irradiation (2 cGy) on cell-cycle kinetics and on the mitotic delay induced by a subsequent challenge treatment.
Dr. Kalina (Univ. Safarikis) followed adpative response in lymphocytes of patients with Down syndrome and in homozygous and heterozygous ataxia telangiectasia patients.

B) Whole blood cultures of human lymphocytes were exposed to various doses of fission neutrons or X-rays and treated post-irradiation during the last 2.45 h before harvesting with 5 mM caffeine, 5 mM Hu and 0.05 mM ara-C.
The presence of caffeine and HU strongly potentiate the yield of chromatid-type aberrations induced by both neutrons and X-rays. No potentiating effect, except at the highest dose of neutrons, was observed when irradiated cells were subsequently treated with ara-C. Since ara-C strongly potentiated the frequency of chromatid aberrations induced in G(2) lymphocytes by X-rays, the results obtained indicate that fission neutrons produce a smaller proportion of lesions, the repair of which can be inhibited by ara-C compared with the number produced by X-rays.

C) An investigation of the quantification of chromatid-type aberrations was carried out. Three approaches were used:

a) The use of BrdU cell marking techniques which enable to pin-point the position of a cell at the time of radiation, and also to classify the kinds of aberrations present with increased accuracy.
b) The mitigation of induced mitotic delay by chemical, like Caffeine, and so to isolate and assess its effect upon observed yield.
c) Computer modelling of cell cycle perturbation effects on observed aberration yield.

All three approaches were successful. The newly introduced technique for chromosome painting (FISH) was showing up also for chromosome-type exchanges anomalous patterns which were readily interpretable as resulting from Complex exchanges. Dr. Savage et al developed a new classification scheme ("the CAB system"), and expanded all the possible break interaction possibilities for up to 5 breaks in 5 chromosomes, and the painting patterns that will be derived from them. This data base has gained International recognition, and has already proved invaluable for modelling and predicting several facets of aberration theory.
This proposal comprises studies on: A) low-dose, low-dose-rate radiation effects and the adaptive response; B) G2 radiosensentivity and inter-indivi dual variability; C) cell kinetic perturbation and evaluation of radiation-induced cytogenetic damage.
There is now a considerable body of evidence that exposure of celles to Very low doses of ionizing radiation can ''condition'' or ''adapt'' them su that they show a reduced response to a subsequent higher dose. However, recent experimentation has shown that there is interindividual variability in the response and that the demonstration of the response is very dependent upon a variety of cultural and cell-kinetic factors and there is need to establish standardised conditions so that effect can be properly evaluated and confounding artefacts identified.
It is known that inter-individual variability in human exists for respon se to the induction of chromosomal aberrations by ionizing radiations. This individual radiosensitivity is becoming more interesting for radiation protection and radiotherapy, and because of the possibility that differential G2 radiosensitivity may be used to identify cancer prone individuals. The six-participants in this proposal will concentrate on various aspects and problems of chromatid-type aberration production (and.their product micrônuclei) in G2 and S cells, both as regards investigating adaptive response and the possible enhanced G2 radiosensitivity of cells from cancer prone individuals. Studies at point A) will be mostly done by Rome, Seville and Stockolm groups; at point B) by Viterbo and Liege groups; at point C) by Harwell. Nevertheless, is should be noted that there are several collaborative links in the six projects and a large complementarity in the materials and methods that will be used.
This proposal forms one segment of a two-part programme, the other part of wich is concerned with ''basic'' aspects of chromosome aberration formation (coordinator prof. A.T. Natarajan).

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

UNIVERSITY OF ROME "LA SAPIENZA"
Address
Piazzale Aldo Moro 5
00185 Roma
Italy

Participants (3)

SWEDISH RADIATION PROTECTION INSTITUTE
Sweden
Address

171 16 Solna
UNIVERSITÀ DEGLI STUDI DELLA TUSCIA
Italy
Address
Via S. Camillo De Lellis
01100 Viterbo
Universidad de Sevilla
Spain
Address
Av. Reina Mercedes
41012 Sevilla