DNA quaternary structure in the radiation sensitivity of human lymphocytes--a proposed role of copper.

On challenging with 2M NaCl, the nuclei of human lymphocytes yield an aggregate of DNA-protein material. The density of the material is less when isolated from irradiated cells than when isolated from unirradiated cells. The density of this material, designated histone-free-DNA (HF-DNA), from irradiated cells returns to that from unirradiated cells if the irradiated cells are allowed time at 37 degrees C in nutrient conditions. Lymphocyte HF-DNA from patients who have exhibited hypersensitivity to radiotherapy exhibit slower repair characteristics than lymphocyte HF-DNA from the average normal subjects. Neutrons are more effective than X-rays in producing density changes. Misonidazole and the ADPRT inhibitor 3-AAB substantially inhibit return to unirradiated densities. The oer for the initial effect is between 2 and 3. These properties of this DNA material from human lymphocytes suggest that alterations in the configuration of such material by the loss and re-establishment of relatively weak cellular bonds are closely related to the well-known changes observed in classical cell survival experiments. Where the proliferation of human lymphocytes has been observed by concanavalin A stimulation, oer, RBE and chemical modification has been of the same order as the measured density changes. Additionally, we have found that the density of HF-DNA is heavily dependent upon Cu content. This has led us to propose that cell killing or malfunction at the nuclear level caused by ionizing radiation is caused by the conversion CuII----CuI and also by specific .OH attack on DNA or proteins at a Cu site.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitivity to X-irradiation of peripheral blood lymphocytes from ageing donors.

The proliferation of human blood lymphocytes from ageing donors, responding to concanavalin A, showed greater sensitivity to inhibition by X-rays than similar cells from younger donors. This increased sensitivity was associated with deficiency in repair of X-ray-induced damage to nuclear material, as measured by density in sucrose gradients, and with increased incidence of chromosomal damage following exposure of freshly isolated lymphocytes. There was also an increased frequency of spontaneous chromosomal aberrations in ageing subjects whose lymphocytes were deficient in repair of DNA damage.

Radiosensitivity of peripheral blood lymphocytes in autoimmune disease.

The proliferation of peripheral blood lymphocytes, cultured with Con A, can be inhibited by ionizing radiation. Lymphocytes from patients with conditions associated with autoimmunity, such as rheumatoid arthritis, systemic lupus erythematosus and polymyositis, are more radiosensitive than those from healthy volunteers or patients with conditions not associated with autoimmunity. The nuclear material isolated from the lymphocytes of patients with autoimmune diseases is, on average, lighter in density than the nuclear material from most healthy controls. This difference in density is not related to increased sensitivity to ionizing radiation but the degree of post-irradiation change in density (lightening) is proportional to the initial density, i.e. more dense nuclear material always shows a greater upward shift after radiation. The recovery of preirradiation density of nuclear material, 1 h after radiation exposure, taken as an indication of DNA repair, correlates with the radiosensitivity of lymphocyte proliferation (Con A response); failure to return to pre-irradiation density being associated with increased sensitivity of proliferative response. These results require extension but, taken with previously reported studies of the effects of DNA methylating agents, support the idea that DNA damage and its defective repair could be important in the aetio-pathogenesis of autoimmune disease.

Subcellular lesions: the current position.

There continues to be an oversimplification of the approach to correlate cellular lesions with radiation induced cell death. Both in the prokaryotic and eukaryotic cell the relationship between vital macromolecules such as DNA, RNA, membrane and proteins is not yet fully understood either in a structural or functional sense. These macromolecules are often closely associated and interdependent. In spite of these recognised relationships much work is still devoted to measuring relatively early changes induced only in the DNA molecule. However, at the present time the quaternary structure of DNA and its closely neighbouring macromolecules is becoming better defined, and disturbances in these vital interrelationships may prove to be the most important radiation lesions. In the attempts to relate identifiable radiation damage to cell malfunction several criteria must be applied. For instance, the measured lesions must exhibit sensitization, protection and shoulder changes in response to the variety of agents and conditions which produce these phenomena at cellular level. In addition the radiation doses employed to produce measurable change must be within the same dose range as those used to study cellular and tissue effects. In much of the published work these criteria have not been applied.