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Biomedical subjects

N V Luchnik

Publications and source records attributed to N V Luchnik.

At least 37 records · Page 2Linked to original sources
PubMed1979

[Cytogenetic effects induced by neutrons in human peripheral blood lymphocytes in vitro. I. Dose-effect relationship for different types of chromosome aberrations when exposed to neutrons with different energies].

Human lymphocytes were irradiated in vitro during G0 stage by graded doses of thermal neutrons and of neutrons with mean energy of 0.04; 0.09; 0.35; 0.85 and 14.7 MeV as well as by 60Co gamma-rays. The data were fitted to the linear and linear-quadratic relations. The neutrons of low and intermediate energies showed the linear dependence on the dose, 14.7 MeV neutrons and gamma-rays--a linear-quadratic one, whereas the data obtained with 0.85 MeV neutrons fitted well the both models. Terminal and interstitial deletions produced by both gamma-rays and neutrons showed different dependencies upon the dose. Some qualitative pecularities of aberration spectra were found in the experiments with neutrons as compared with the data on gamma-irradiation: the ratio of exchanges to fragments was greater, and aberrations of chromatid type were produced. The specially designed experiments and calculations showed that the last effect was not connected with induced radioactivity.

Cells, Cultured↗
PubMed1977

Isolabelling is a radiation-induced phenomenon.

Human lymphocytes were incubated during two mitotic cycles in the presence of 5-bromodeoxyuridine and differentiation between chromatids was obtained with combined "Hoechst 33258" and azur-eosine staining. Analysis of non-irradiated cells revealed numerous sister chromatid exchanges (SCE) and no abnormalities of "harlequine" appearance of chromosomes. When, however, the cells were irradiated, an identical staining (IS, isostaining) of some chromosomes or chromosome segments were observed. Production of IS was accompanied by decrease of the frequency of SCE, the total frequency of SCE+IS remained, however, the same as in control. An antagonism between SCE and IS was established: the frequency of SCE decreased in the cells with multiple IS, and chromosomes with both SCE and IS were only rarely observed. Thus, IS is neither an artifact nor a physiologic event but a phenomenon induced by radiation. The reliable existence of IS is considered as an evidence for binemic structure of chromatid. It is suggested that some mechanism of lateral spread of genetic information is involved in the production of SCE. If delayed by radiation, the spread could be restricted only to a fraction of chromosome cross-section resulting in IS.

Azure Stains↗
PubMed1977

[Effect of gamma-irradiation on human chromosomes. VIII. Cytogenetic effect of low doses during in vitro irradiation].

Cultures of human lymphocytes obtained from blood of healthy adult donors were irradiated at different doses of gamma-rays (60Co), and irradiated cells were analysed at metaphase in 50 hours after the irradiation. The effect (total yield of aberrations of chromosome type, or total yield of exchange type aberrations) produced by the lowest dose (5 r) appears to be statistically significant in a sample of 1500 cells. Within usual dose-range (25--400 r) both parabolic and linear-quadratic equations give a satisfactory fit of experimental data (dicentrics, fragments, or all aberration of the chromosome type). Low doses of gamma-rays produce, however, more aberrations than expected, if one extrapolates dose-effect curves from higher doses. Both equations should be considered therefore just as empirical equations. Dicentrics show a plateau at low doses (10--30 r) which appear to be statistically significant. Some indications are obtained that the total number of chromosome-type aberrations is a more reliable criterion of cytogenetic damage than usually accepted yield of dicentrics and rings.

Cells, Cultured↗
PubMed1976

Critical periods of the mitotic cycle: influence of aminopterin and thymidine on production of chromosomal aberrations by radiation in Crepis capillaris.

The influence of aminopterin (AP), tritiated thymidine ([3H] TdR) and "cold" thymidine (TdR) on production of chromosomal aberrations in meristematic cells of Crepis capillaris irradiated in different stages of the mitotic cycle with 300 rad of 63Co gamma-rays was studied. All the chemical treatments increased most of all the frequency of aberrations induced during two "critical periods" localized before the stage of DNA synthesis (fixation 9 h after irradiation) and before that of mitosis (4 h). Treatments with TdR and [3H]TdR increased most of all the frequency of chromatid aberrations when irradiation was performed in G1, and the frequency of gaps when irradiated in G2. Treatment with AP increased the yield of different types of aberration more uniformly. The modifying effect of the chemicals tested appeared to be independent of replicative synthesis. The "critical periods" are suggested to be the stages when regular "proof reading" and correction of spontaneous errors takes place [9,13]. In addition to this regular mechanism, radiation induces an "emergency" mechanism of repair. AP inhibits the mechanism of regular repair; in addition TdR and [3H] TdR suppress the lateral spread of primary injuries across the chromosome.

Aminopterin↗
PubMed1976

Radiation-induced chromosomal aberrations in human lymphocytes. I. Dependence on the dose of gamma-rays and an anomaly at low doses.

Cultures of human lymphocytes obtained from blood of healthy adult donors were irradiated with different doses of 60Co gamma-rays and the irradiated cells were analysed in metaphase 50 h after irradiation. The effect (total yield of aberrations of chromosome type, or total yield of exchange type aberrations) produced by the lowest dose (5 rad) appears to be statistically significant in a sample of 1500 cells. In the usual dose range (25-400 rad), both parabolic and linear-quadratic equations give a satisfactory fit of experimental data (dicetrics, fragments, or all aberrations of chromosome type). Low doses of gamma-rays, however, produced more aberrations than expected, if one extrapolates dose-effect curves from higher doses. Both relations should be considered, therefore, merely as empirical equations. Dicentrics show at low doses (10-30 rad) a plateau which appears to be statistically significant. Some indications are obtained that the total number of chromosome-type aberrations is a more reliable criterion of cytogenetic damage than the usually accepted yield of dicentrics and rings.

Cells, Cultured↗
PubMed1975

Do one-hit chromosome exchanges exist? Dose-response relation for irradiated human lymphocytes.

It is demonstrated that the expectation of a quadratic dose-response relation for two-hit aberrations is not correct. In fact the theoretical curve is changed from near-quadratic to near-linear when the dose increases and fits well the experimental data on production of exchanges in human lymphocytes by radiation. The commonly used relation y = alphaD + betaD2 shows systematic deviations from the observed frequencies. Therefore, no reason exists to postulate some fraction of exchanges to be produced by a one-hit mechanism.

Chromosome Aberrations↗
PubMed1975

Does repair or stage sensitivity determine the shape of time-effect curves in radiation mutagenesis?

Seedlings of Crepis capillaris were irradiated after pulse-labelling with tritiated thymidine ([3-H]TdR), and both chromosomal aberrations and presence of silver grains were recorded in the same metaphase cells at various intervals throughout the whole mitotic cycle. The following results were obtained: (a) irradiated roots were homogeneous with respect to the number of aberrations, and heterogenous with respect to labelling index (LI); (b) time--effect curves for labelled (L) and unlabelled (U) cells showed no significant difference from one another; (c) no significant quantitative difference of aberration spectra produced in S and G2 stages was found. These results support the view that the major factor which determines both quantitative and qualitative variation in the production of chromosomal aberrations by radiation is the time lapse between irradiation and fixation rather than relation of the time of irradiation to the time of DNA synthesis. In addition, it was found that labelling with [3-H]TdR modifies the effect of radiation on chromosomes.

Chromosome Aberrations↗