scholarly journals Indications of Repair of Radon-Induced Chromosome Damage in Human Lymphocytes: An Adaptive Response Induced by Low Doses of X-Rays

1993 ◽  
Vol 101 ◽  
pp. 73 ◽  
Author(s):  
Sheldon Wolff ◽  
Veena Afzal ◽  
Rick F. Jostes ◽  
John K. Wiencke
Keyword(s):  
Adaptive Response ◽  
Human Lymphocytes ◽  
Chromosome Damage ◽  
Low Doses ◽  
X Rays

Chromosomal Aberrations in Human Lymphocytes Inducedin Vitroby Very Low Doses of X-rays

1992 ◽  
Vol 61 (3) ◽  
pp. 335-343 ◽  
Author(s):  
D.C. Lloyd ◽  
A.A. Edwards ◽  
A. Leonard ◽  
G.L. Deknudt ◽  
L. Verschaeve ◽  
...  
Keyword(s):  
Chromosomal Aberrations ◽  
Human Lymphocytes ◽  
Low Doses ◽  
X Rays

Statistical analysis of adaptive response in sister chromatid exchanges in human lymphocytes after treatment with very low and extremely low doses of N-methyl-N′-nitro-N-nitrosoguanidine using a study design to control variability

1999 ◽  
Vol 88 (01) ◽  
pp. 7-16 ◽  
Author(s):  
D Anderson ◽  
AJ Edwards ◽  
P Fisher ◽  
DP Lovell
Keyword(s):  
Quality Assurance ◽  
Protective Effect ◽  
Sister Chromatid ◽  
Adaptive Response ◽  
Statistical Power ◽  
Human Lymphocytes ◽  
Sister Chromatid Exchanges ◽  
Power Calculation ◽  
Low Doses ◽  
Chromatid Exchanges

AbstractPrevious studies have been interpreted as suggesting that low concentrations of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) have an adaptive effect in the cultured lymphocytes of responsive donors (that is, the cells are protected against the mutagenic effects of a subsequent challenge with a higher concentration of MNNG). The objectives of the present study were to investigate, under stringent experimental conditions, whether a protective effect exists at very low and extremely low doses of MNNG (10−8 and 10−24M, respectively).Peripheral blood lymphocytes from a donor considered responsive in a previous study were stimulated to divide and were cultured under standard conditions. Pre-adaptive treatments with dilutions of MNNG were added to the cultures repeatedly before a challenge treatment with MNNG. Bromodeoxyuridine was added at the same time as the challenge treatment and, following mitotic arrest, cells were differentially stained so that the number of sister chromatid exchanges (SCEs) could be counted. The study was designed to address potential criticisms of earlier studies which did not include replicate cultures. Samples of blood were divided into two identical batches for independent processing. Five replicate cultures were prepared for each combination of pre-adaptive and challenge treatments in each batch. The complete experiment was repeated to provide a further test of the consistency of results. Five replicates per treatment combination were chosen in an attempt to provide an experiment of adequate statistical power. Considerable precautions were taken to minimise the effect of factors outside experimental control on the results. Scoring was done by three scorers. In order to minimise inter-scorer variation, 240 cells were scored at each treatment observation (five cells per scorer, three scorers per culture, four cultures per batch, two batches per experiment and two experiments). The study was designed in this way to take account of the sources of variability to ensure that any response obtained would exceed that obtainable by experimental variability alone. A high level of quality assurance monitoring was undertaken throughout the investigation. Two measures of SCE induction were used: (i) the mean frequency of SCEs; (ii) proportion of cells with at least 20 SCEs. In both experiments, the challenge concentration of MNNG significantly increased SCE frequency. There were, however, highly significant differences between the two experiments. The proportion of high frequency cells (HFCs) in Experiment 1 was increased significantly; the proportion of HFCs was also increased in Experiment 2, but the increase was not statistically significant. The pre-adaptive concentrations of MNNG included an extremely low dilution of 6.8 × 10−24 M and a very low dilution of 6.8 × 10−8 M in Experiment 1 and 1.4 × 10−7 M in Experiment 2. The various pre-adaptive concentrations used had no consistent protective effect against the SCE-inducing capacity of the challenge concentration of MNNG of 6.8 × 10−6 M.It is concluded that an adaptive response to the alkylating agent MNNG could not be demonstrated in cultured human lymphocytes. Neither a very low nor an extremely low dilution of MNNG elicited an adaptive response in terms of SCE induction (measured either as SCE frequency or as proportion of HFCs). This is in contradiction to previous reports published by us and other groups. This study was carefully designed with large numbers of replicates, a preliminary statistical power calculation, predefined comparisons and extensive quality assurance at each treatment administration. Despite these precautions the variability between scorers and between batches was much larger than anticipated. This resulted in some statistically significant differences, but these are likely to be false positives. Our findings indicate the need for such methodological refinement in human cell adaptive response studies.

Studies of the 'Adaptive' Repair Response in Human Lymphocytes and V79 Cells after Treatment with MNNG and MNU

1988 ◽  
Vol 7 (4) ◽  
pp. 337-341 ◽  
Author(s):  
D. Anderson ◽  
P. Fisher ◽  
P.C. Jenkinson ◽  
B.J. Phillips
Keyword(s):  
Adaptive Response ◽  
Mammalian Cells ◽  
Tritiated Thymidine ◽  
Human Lymphocytes ◽  
Alternative Methods ◽  
X Rays ◽  
V79 Cells ◽  
Repair Mechanisms ◽  
Experimental Protocols ◽  
Mutagenic Effects

In bacteria, there is evidence that a damage inducible repair response system known as the adaptive response exists since pretreatment with low doses of a simple monofunctional alkylating agent leads to a decrease in both the lethal and mutagenic effects of a subsequent challenge dose of the agent. The evidence for an analagous system in mammalian cells has proved to be inconsistent to date. The induction of chromosome repair mechanisms in human cells by low-dose radiation from tritiated thymidine has been shown to make the cells refractory to the induction of chromosome aberrations by X-rays. The present communication investigates the induction of an adaptive response in human lymphocytes from four donors and V79 cells using SCE and mutation as endpoints and MNNG and MNU for the adapting and challenging treatment. It is clear that a reproducible model of the adaptive response in human lymphocytes is difficult to establish because of the variability between different donors and different culture times. In V79 cells, assays with much larger cell numbers are required to detect a reproducible response with such small changes in mutant frequency. To demonstrate an adaptive response conclusively in mammalian cells will probably require the use of more sensitive experimental protocols and alternative methods of administration of adaptive doses of mutagen.

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