Kinetics of the Formation of Chromosome Aberrations in X-Irradiated Human Lymphocytes: Analysis by Premature Chromosome Condensation with Delayed Fusion

Abstract

Human lymphocytes irradiated with graded doses of up to 5 Gy of 150 kV X rays were fused with mitotic CHO cells after delay times ranging from 0 to 14 h after irradiation. The yields of dicentrics seen under PCC conditions, using C-banding for centromere detection, and of excess acentric fragments observed in the PCC experiment were determined by image analysis. At 4 Gy the time course of the yield of dicentrics shows an early plateau for delay times up to 2 h, then an S-shaped rise and a final plateau which is reached after a delay time of about 8 to 10 h. Whereas the dose-yield curve measured at zero delay time is strictly linear, the shape of the curve obtained for 8 h delay time is linear-quadratic. The linear yield component, alpha D, is formed entirely in the fast process manifested in the early plateau, while component beta D2 is developed slowly in the subsequent hours. Analysis of the kinetics of the rise of the S-shaped curve for yield as a function of time leads to the postulate of an "intermediate product" of pairwise DNA lesion interaction, still fragile when subjected to the stress of PCC, but gradually processed into a stable dicentric chromosome. It is concluded that the observed difference in the kinetics of the alpha and beta components explains a number of earlier results, especially the disappearance of the beta component at high LET, and opens possibilities for chemical and physical modification of the beta component during the extended formation process after irradiation observed here.

Review: Proximity effects in the production of chromosome aberrations by ionizing radiation

“…One PCC study reported dicentrics developing so rapidly after irradiation that the process is virtually completed with < 1 h (Vyas et al 1991), but most indicate a more gradual rise for part or all of the dicentric yield (e.g. Greinert et al 1995, Evans et al 1996.…”

On the formation kinetics of radiation-induced chromosome exchanges in human lymphocytes

“…Moiseenko et al think that this lack of a detectable difference was the reason why Vyas et al did not increase the delay time further. However, in our subsequent study [3] at a dose of 4 Gy, a significant additional yield contribution solely ascribable to the βD 2 component was observed at longer delay times up to 14 h [3]. This contrast is interesting, especially with regard to the design of further experiments, because of the great influence of the chosen dose level upon the detectability of the delayed yield increase.…”

“…It is worth noting that the linear term at t D = 8 h is only about two-thirds of that seen at t D = 0 h [3], a reduction of opposite tendency to the increase of the dose-squared term with increasing delay time. This partial compensation contributes to the difficulties in detecting any yield differences at smaller doses.…”

“…It is true that at D = 2 Gy and even at D = 3 Gy, statistical limits of uncertainty may prevent the detection of any yield difference between the observation at t D = 0 h and the two other conditions. However, at D = 4 Gy, where we studied the change of the dicentric yield with fusion delay time [3], the yield difference cannot be masked by measurement uncertainty, and it would be even more prominent in an experiment performed at 5 Gy. We conclude that the yield of radiation-induced dicentrics seen under PCC conditions at long fusion delay times closely resembles the yield seen in first metaphase, while the yield for short delay times is significantly smaller at doses exceeding 3 Gy.…”

“…1 the dose-dependent yield of dicentrics seen under PCC conditions for fusion delay times t D of 0 and 8 h (taken from [3]) and the yields observed in the first metaphase after PHA stimulation (taken from [4] and new unpublished data, R. P. Virsik-Peuckert). It is true that at D = 2 Gy and even at D = 3 Gy, statistical limits of uncertainty may prevent the detection of any yield difference between the observation at t D = 0 h and the two other conditions.…”