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N V Luchnik

Publications and source records attributed to N V Luchnik.

At least 19 recordsLinked to original sources
PubMed2002

[Phenomenon of pseudomutagenesis: experiments with modifiers of cell metabolism in human lymphocytes].

The term "pseudomutagens" is suggested for factors that increase the spontaneous mutation level not by induction of DNA molecule changes but as a result of inhibition of the repair of spontaneous pre-mutation lesions. The expected regularities of pseudomutagen effects, which are suitable as criteria for their identification, are considered. The experimental results on the effects of six modifiers of cell metabolism in human lymphocytes are analyzed. Four of the modifiers (5-fluorodeoxyuridine, sodium cyanide, sodium fluoride and monoiodoacetic acid) behaved as pseudomutagens according to all the criteria applied. 2,4-Dinitrophenol proved to be a true mutagen. Adenosine diphosphate revealed unusual properties: it inhibited the repair of spontaneous lesions but decreased the frequency of structural mutations induced by radiation. The significance of the phenomenon of the pseudomutagenesis for the problem of environmental mutagens/carcinogens is discussed.

2,4-Dinitrophenol↗
PubMed1990

[Effect of free 5-bromodeoxyuridine on induction of SCE in human lymphocytes gamma-irradiated at the presynthetic stage of primary and secondary mitotic cycles].

Formation of SCE was studied in lymphocytes irradiated by 60Co gamma-rays at the G1 stage of the first or second mitotic cycles. The yield of SCEs induced by irradiation in the presence of 5-bromodeoxyuridine (BrdU) proved to be significantly higher than that obtained in the absence of BrdU. The enhancing influence of BrdU on SCE induction depends on neither replication cycle nor the molecular constitution of chromosomes under irradiation. Direct modification of chromosomal radiosensitivity by BrdU is excluded. The results obtained suggest the interference of free BrdU present in culture medium with processes of DNA reparation at the G1 stage.

Bromodeoxyuridine↗
PubMed1990

[Changes in radiosensitivity of chromosomes at the presynthetic stage of the mitotic cycle: role of single-stranded segments of DNA].

Formation of single-stranded DNA regions was investigated during the presynthetic stage of human lymphocyte cell cycle. Two peaks of single-stranded region production were found in about the middle and near the end of the G1 stage. Both the peaks appeared some hours earlier in gamma-irradiated cells than in control. Experiments showed that the periods of the peak formation coincided with the terms when time-effect dependence for gamma-induced chromosomal aberrations changed its character. The interpretation of the results supposes existence of inherent for the G1 stage process of genetic material correction.

Chromosome Aberrations↗
PubMed1988

[Chromosome radiosensitivity in 2 successive mitotic cycles of human lymphocytes].

A culture of human lymphocytes was irradiated with gamma-quanta (0.5 Gy) after incubation during different time intervals, i.e. at different relative frequencies of cells in the first and second mitotic cycle. The frequency of aberrations produced in the G2 stage was analysed. The total yield of aberrations gradually increased with the increase of time lapse between the onset of cultivation and irradiation. If, however, the relative frequencies of the first and second mitoses are taken into account, it could be concluded that radiosensitivity of chromosomes remains constant in each cycle and independent from its duration. Besides, radiosensitivity of chromosomes during the second cycle is one and half times stronger, as compared to the first cycle. In accordance with the data of other authors, 5-bromodeoxyuridine has been found to significantly increase radiosensitivity.

Bromodeoxyuridine↗
PubMed1987

[Effect of radiation on the formation of isolabels in the late replicating regions of the Chinese hamster genome].

The cells synchronized in the G1 stage were incubated in a medium containing 5-bromodeoxyuridine, and chromosomes were analysed after two rounds of replication Iso-labels (IL) were observed in the late-replicating (heterochromatic) segments. The frequency of IL increased after irradiation during the G2 stage of the second cycle. Moreover, IL were observed in euchromatic segments (not recorded in control cells), whereas the frequency of sister chromatid exchanges decreased. Formation of IL in heterochromatin follows the statistical regularities: IL were only observed in some fraction of cells and, as a rule, involved not all heterochromatic segments. The regularities established witness against the uninemic model of chromosome.

Animals↗
PubMed1986

[Statistical patterns of the anomalous staining of 5-bromodeoxyuridine-substituted chromosomes].

Five large chromosome segments showing sometimes an abnormal staining were found in the genome of Chinese hamster (clone 237). Three types of abnormal staining were recorded. After one round of replication in the presence of BrdUrd these segments showed a hetero-staining, whereas after two rounds of replication the same segments showed iso-dark or iso-light staining. Pulse labeling with 3H-thymidine showed that all these segments were the late-replicating ones. The labeling proceeded according to all-or-none principle; in a given cell all five segments showed either presence or absence of the label. On the contrary, the abnormal staining was statistically distributed among these segments. These results are in disagreement with the current view that the abnormal staining is associated with asymmetrical distribution of thymine among two strands of DNA duplex. The above regularities are considered as an argument for the two-stranded model of chromosome.

Animals↗
PubMed1985

[Appearance of single-stranded regions in DNA molecules in the G1 stage and the formation od structural mutations].

Single-stranded DNA regions in the nuclei of human lymphocytes were detected by means of fluorescent antibody technique. The frequency of fluorescent nuclei increased with the onset of the S stage, as expected. Also, a clear peak of the fluorescent nuclei amount was observed in about the middle of the G1 stage. The appearance of this peak correlated with some regularities of production of structural mutations by radiation. The suggestion is made that the maximum discovered might reflect the beginning of the recombinational repair of double-stranded breaks.

Cells, Cultured↗
PubMed1985

[Effect of cell respiration inhibitors on the formation of structural mutations in human lymphocytes irradiated at different stages of the mitotic cycle].

Human lymphocytes were irradiated by 60Co gamma-rays after 0, 10, 20, 35, 45, 48 and 49.5 h of incubation. Immediately after irradiation sodium cyanide, sodium fluoride or monoiodoacetic acid was given for 2.5 h. Non-irradiated cells were subjected to the same treatments. Chromosomal aberrations were analysed in metaphase cells of the first mitosis. When administered alone, all chemicals increased the frequency of chromatid aberrations. The special analysis showed that these chemicals were not mutagens in a strict sense, as the observed increase of aberration frequency was due to inhibition of repair processes, which increased the probability of manifestation of spontaneous changes (so-called "pseudomutagenesis"). The same chemicals increased the frequency of radiation-induced aberrations during two periods of the mitotic cycle, namely, in the end of the G1 stage and in the G2 stage. It has been recently shown that the inhibitor of DNA synthesis, 5-fluorodeoxyuridine, increased the frequency of radiation-induced aberrations during the same periods. It follows that the process of repair proceeding during these periods requires both DNA synthesis and energy supply.

Chromosome Aberrations↗
PubMed1983

[Effect of 5-bromodeoxyuridine concentration on sister chromatid exchange frequency in consecutive replication cycles].

A yield of single and twin sister chromatid exchanges (SCE) in Chinese hamster cells incubated at different concentrations of 5'-bromodeoxyuridine (BrdUrd) has been studied. The ratio of SCEs formed in the second and in the first cycle has been discovered to be dependent on the dose of BrdUrd; it is 1.5:1 for the high concentration of BrdUrd and 1:1 for the lowest one. The authors arrived at a conclusion that the observed level of SCEs--0.1 per chromosome per cycle for the lowest concentration is spontaneous.

Animals↗
PubMed1983

[Mechanism of formation of chromatid exchanges].

Chinese hamster cells with different patterns of distribution of 5-bromodeoxyuridine (BrdUrd) between chromosome subunits were subjected, during the G2 stage, to UV irradiation, which only produced breaks in BrdUrd substituted DNA. The frequency of chromatid and subchromatid interchanges as well as isochromatid aberrations was estimated. It was found that only BrdUrd containing chromatids were involved into aberrations; this result challenges the so called "molecular theory" for aberration production proposed by Leenhouts and Chadwick. A very small increase of the aberration yield in chromosomes without BrdUrd may be connected with the action of UV on the frequency of recombination. The observed frequency of interchanges was not proportional to the BrdUrd content in chromosomes and depended on the time of its incorporation: more exchanges were induced in the chromatids incorporating BrdUrd during the last round of replication. These regularities may be connected with some molecular peculiarities of chromosome structure and function.

Animals↗
PubMed1982

[Effect of irradiation at different stages of the mitotic cycle on the formation of sister chromatid exchanges in a Chinese hamster cell culture].

Cultured Chinese hamster cells (line 237) grown in a medium containing 5-bromo-deoxyuridine were irradiated with 1 Gy of 60Co gamma-rays and fixed at different times there after 1-18 hours. Sister chromatid exchanges (SCE) were analysed in harlequine-stained cells. It was established that SCE may occur involving only part hitherto only recorded in plant cells. Radiation produced 18 fold increase of the frequency of SsCE, whereas the increase of usual SCE was less than two fold. The shape of stage-effect curves for induces SCE and SsCE was the same; the maximal yield was observed in the middle of the S stage, and no exchanges were produced in the G2 stage. It is concluded that SsCE is nothing other than minute intercalary SCE produced by the single-hit mechanism.

Animals↗
PubMed1981

[Formation of chromosome aberrations in human lymphocytes to the action of 5-fluorodeoxyuridine used separately and in combination with gamma irradiation: changes in the effect in the course of the mitotic cycle].

Human lymphocytes were treated after different times of incubation, either by 60Co gamma-rays (1 Gy) followed by 5-fluorodeoxyuridine (FUdR, 2.10-7 M during 2,5 h) or by radiation and FUdR, separately. Chromosomal aberrations were studied after 51 h of incubation. When administered alone, FUdR increased the frequency of chromatid aberrations and gaps over the spontaneous level. This increase took place mainly during two periods of the mitotic cycle, namely, on the borderline between G1 and S stages and at the end of the G2 stage. FudR barely affected the frequency of chromosomal aberrations. THe effect did not depend upon the concentration of FUdR. Irradiation during the G1 stage produced chromatid aberrations and gaps with the same frequency as FUdR, whereas the frequency of chromosome aberrations was much higher. When administered after irradiation, FUdR increased the frequency of all types of aberrations; the periods of mitotic cycle when this increase was statistically significant correspond to those of "mutagenic" action of FUdR mentioned above. This pattern may be easily explained if one postulates that in our experiments FUdR exhibited the features of a "pseudomutagen" i.e. the factor which suppresses repair of primary lesions (spontaneous or radiation-induced) without giving rise to new mutational changes.

Cells, Cultured↗
PubMed1981

[Frequency of aberrations in uni- and biliary 5-bromodeoxyuridine-substituted chromatids].

Chinese hamster cells and human lymphocytes were incubated with BrdUrd during two cycles of replication and stained using the "harlequine" technique. The G2 cells were irradiated with 1 Gy of gamma-rays from the 60 Co source. The frequency of breaks in light (i.e. bifiliary substituted) chromatids was significantly lower, as compared with dark (i.e. unifiliary substituted) ones. The comparison of these data with the previously published suggests that the relative frequency of breaks in uni- and bifiliary substituted chromatids depends on the energy of quanta. A hypothesis is discussed that a resonance absorption of energy by Br atoms and an increased interaction between BrdUrd-substituted structures, which favours the repair of double-strand breaks, can explain the noted regularity.

Animals↗