Assessment of the integrity and reparative capabilities of lymphocytes during 21-day head-down bed rest

Abstract

The head-down bed rest (HDBR) used in studies of physiological changes similar to those caused by weightlessness can be considered as a condition on f transient dysregulation.

Aim: To evaluate the effect of HDBR on the integrity and reparative capabilities of the genetic material of peripheral blood lymphocytes from volunteers.

Methods. The study included 6 male volunteers exposed to HDBR for 21 days. The total lymphocyte count was determined on a DYMIND DF50 hematological analyzer. The degree of damage to the lymphocyte DNA was assessed by electrophoresis of single cells: at the beginning of the experiment (day 0) and on days 6 and 21 in native lymphocytes (background), in cells after a 2-h incubation in a phosphate-salt buffer supplemented with 1% autologous serum (recovery), and after additional UV irradiation (irradiation).

Results. On day 6, the total number of lymphocytes was unchanged whereas by day 21, all subjects showed an increase in the lymphocyte count. Evaluation of the degree of damage to the lymphocyte DNA showed that by the 6th day, the number of undamaged cells increased, apparently, as a result of activated reparative processes. By the end of HDBR, the number of normal lymphocytes returned to the background values. However, among the cells with damaged DNA, the percentage of cells with completely destroyed DNA (type IV comet cells) was increased. The 2-h incubation in phosphate-buffered saline supplemented with 1% autologous serum showed that the ability to eliminate damaged cells was weakened already on the 6th day and remained at a reduced level until the end of the experiment. UV irradiation slightly increased the proportion of damaged cells at the beginning of the experiment, mainly due to an increased contribution of type I comets. On the 6th day, the difference in the proportion of damaged cells in the background group and the irradiation group became significant. However, by the end of HDBR, the ratios of different types of comets in the background and the irradiation groups no longer differed.

Conclusions. The simulated microgravity modeled with HDBR caused the activation of adaptive mechanisms in the first week of the experiment. However, by the end of the experiment, the mechanisms for eliminating damaged cells begin increasing.