[The Chernobyl Disaster Consequences from the -Distance of 30 Years].

There are 2 most important questions regarding studies of the Chernobyl disaster: to what degree the opportunities to decrease injuries of the people affected by the disaster were realized and how the study of the con- sequences of the disaster impacted elucidation of low level radiation damage to human health. It can be as- sumed that not all scientific elaborations were realized to a proper degree (the use of iodine prophylaxis, radioprotectors). It was associated with impoper fulfillment of instructions by executive organs of radiation safety and medical emergency aid. However, the stationary medical treatment of patients with acute radiation disease was well organized. Insufficient consideration was given to non- radiological factors having an effect or,the psycho-emotional state of the people. Harmful effects of small doses on human health were not be found. The adverse delayed consequences (thyroid cancer, leucosis, and solid cancers) were found in the case of exceeding dose limit of 250 mGy. The upper border of low harmless.radiation doses could not be detected in those studies because of poor radiation dosimetry of liquidators, inadequate models of risk evaluation and ignoring influence of non-radiological factors on human health.

[Searching Radiation Countermeasures using the Model of Prolonged Irradiation of Mice with Low Dose Rate and Evaluation of Their Influence on Heat Shock Protein Genes Expression].

Different radiomodificators (cytokine betaleukine, antioxidant phenoxan, antigipoksant limontar and nucleoside riboxin) were investigated on mice for evaluating their radiation protective capacity against prolonged (21 h) exposure at a dose of 12.6 Gy at a low dose rate of 10 mGy/min. Bone marrow cellularity and endogenic CFUs were used as evaluation criteria 9 days after exposure. Simultaneously, expression of the heat shock proteins of 25, 70 and 90 kDa in unexposed mice bone marrow was studied 2, 24 and 48 h after injections. Betaleukine only had a positive significant effect in both tests in the variants of 50 mcg/kg and 3 mcg/kg when administered 2 h and 22 h before exposure, correspondingly. Effects of betaleukine HSPs on expression were both stimulating and inhibiting, that was in contradiction with a constant positive effect in 5 experiments on exposed mice for each betaleukine variant. It argues against the vital role of HSPs in the betaleukine antiradiation effect. In 2 experiments with high temperatures betaleukine administered at a dose of 50 mcg/kg evoked a very high HSP-70 gene expression after 24 h, and mice exposed to irradiation at that time in a parallel experiment showed an increased radiation effect. It corresponds to the idea that HSPs serve a stress indicator.

The phenomenology and possible mechanisms of a new experimental method for accelerating postirradiation restoration of hemopoietic stem cell potential.

Extraction of bone marrow from one or several bones immediately after irradiation, with or without subsequent incubation for a short period under suitable conditions, and subsequent reimplantation into the same organism can reduce the lethal effect of irradiation in a number of species. Extraction plus a period of incubation is referred to as the reimplantation method. The effectiveness is roughly relative to the amount of bone marrow extracted and transplanted. This effect has been demonstrated by assays of 30-45-day survival and of hemopoietic stem cell potential. The effectiveness of the reimplantation method has been tested in a dose range of 6.5 to 8.5 Gy and was found to be 1.2-1.06 in terms of dose reduction factors assayed by bone marrow row cellularity 9 days after exposure and 1.18-1.09 for survival of bone marrow colony-forming units. The favorable effect of incubating irradiated bone marrow with cycloheximide on the stem cell potential has been proven by experiments using a donor-recipient method. The positive effect of the reimplantation procedure and the partial extraction procedure on the stem cell potential in irradiated mice can be shown as soon as 2 h after exposure and the procedures. The results suggest that ther exist some reserves that can be stimulated to accelerate hemopoietic restoration in a heavily irradiated organism. The recruitment of these reserves seems to be related to the response of the structures producing cytokines after lethal irradiation. In addition, repair processes may be involved in the rescue of lethally irradiated hemopoietic stem cells.