Radiation and Environmental Biophysics

Rakvin, B.; Herak, J.; Voit, K.; Huttermann, J.

doi: 10.1007/BF01211360pmid: 3035602

In single crystals of the DNA nucleotide 2′deoxyguanosine-5′phosphate (5′dGMP) X- orγ-irradiated at 4.2 K or 15 K, two primary radical species can be discriminated and assigned to the cation and anion of the guanine base,G(+) andG(−). Both species are unstable.G(−) partially transforms into a secondary radical at 4.2 K, the latter being the precursor to the dominant 300 K species formed by netH-addition to carbonC8. The secondary radical, together with another intermediate appearing at 77 K and perhaps connected with the anion decay could not be structurally identified. The guanine cationG(+) transforms upon annealing to temperatures above 77 K into a more stable species by deprotonation at positionN1.

Mee, Lorna; Adelstein, S.

doi: 10.1007/BF01211361pmid: 3588834

Strand breaks have been determined by sedimentation on sucrose gradients in the DNA of chromatin irradiated after isolation from Chinese hamster lung fibroblasts. The yields of double-strand and single-strand breaks are similar to those found in the DNA of irradiated mammalian cells. Irradiation of isolated chromatin in the presence of the radical scavenger tertiary butanol indicates that at least 65% of single-strand breaks and 56% of double-strand breaks can be attributed to the action of hydroxyl radicals. The results indicate the influence of chromosomal proteins in modifying radiation damage to DNA and suggest that the mechanisms for the induction of strand breaks in the DNA of isolated chromatin may be comparable to those operating in the intact cell.

Lett, J.; Kengl, P.; Bergtold, D.; Howard, J.

doi: 10.1007/BF01211362pmid: 3588835

Excised retinas from New Zealand white (NZW) rabbits were irradiated at 0° C with 9–260 Gy (depending on the type of radiation) of 300 kVp X-rays, or the first 5 cm (range: ∼ 14 cm in water) of 365 MeV/u Ne ions or 530 MeV/u Ar ions (LET∞'s : ∼ 1, 35 ± 3 and 90 ± 5 keV/µm, respectively). Other positions (LET∞'s) in the Ne-ion beam (Bragg curve) were employed in more limited experiments. The retinas were frozen and stored in liquid nitrogen until analysis.

Ianzini, F.; Yatvin, M.

doi: 10.1007/BF01211363pmid: 3588836

The effect of ferrous ion-ascorbate and X-radiation on multilamellar liposomes, composed of either completely saturated, unsaturated or a mixture of saturated and unsaturated fatty acids, is reported. Lipid composition is shown to be of critical importance in determining the extent to which peroxidation occurs. Liposomes composed of the mixture of saturated and unsaturated fatty acids are peroxidized to a lesser extent by ferrous ion-ascorbate. The reduced peroxidation is apparently the result of an inhibition mechanism shown by the saturated lipid component. In contrast, liposomes composed of mixed lipids do not reduce the level of peroxidation induced by ionizing radiation.

Iliakis, G.; Wright, Eva; Ngo, F.

doi: 10.1007/BF01211364pmid: 3588837

OH mouse 10 T1/2 cells showing strong inhibition of growth at confluency were grown under daily refeeding in the presence of BrdUrd (from 0 to 1 µM) and exposed toγ-rays either while exponentially growing or in the plateau phase. An increase in radiosensitivity was observed in both growth conditions mainly reflected by a reduction in Dq. Greater radiosensitization was observed in exponentially growing than in plateau-phase cells, and 3–4 times higher BrdUrd concentrations were required in plateau-phase cells for similar potentiation in killing. This effect could not be entirely attributed to a reduction in BrdUrd incorporation since measurements with3H-BrdUrd showed reductions in incorporation between only 17–47% in plateau-phase cells. The rate of repair of potentially lethal damage (PLD) as demonstrated by delayed plating was not affected by the incorporation of BrdUrd, but the amount of repair (measured as the relative increase in cell survival) was higher for BrdUrd-containing cells. Post-irradiation treatment of cells in the plateau-phase (no BrdUrd) with 9-β-d-arabinofuranosyladenine (araA) caused fixation of radiation-induced PLD. AraA treatment of cells grown in the presence of various amounts of BrdUrd also caused fixation of PLD, but resulted in survival levels similar to those observed with cells growing in BrdUrd-free medium. This result indicates that BrdUrd mediated radiosensitization cannot be observed when cells are prevented from repairing PLD by postirradiation incubation with araA. Based on these findings we propose that the mechanism of radiosensitization by BrdUrd incorporation might be, by increasing probability of fixation, mediated by the postirradiation progression of cells through the cycle, of a sector of PLD also sensitive to post-irradiation treatment with araA. For this sector of PLD the term α-PLD has been proposed.

Sontag, W.

doi: 10.1007/BF01211365pmid: 3588838

A cell survival model with saturable repair has been developed. The model is based on the assumption that after irradiation the cell can be in one of the following three states: In state A the viable cells have no lesions, in state C cells carry lethal lesions and in state B cells exhibit potentially lethal lesions which can be repaired by a saturable enzymatic repair system or which are converted to lethal lesions. The model incorporates five parameters. The applicability of the model has been demonstrated by fitting 11 experimental data sets obtained with different cell lines, different kinds of radiation and variable repair times simulated by liquid holding recovery or inhibition of repair processes by different agents. The model and the results obtained are discussed in relation to published results.

Sportelli, L.; Rosi, A.; Bonincontro, A.; Cametti, C.

doi: 10.1007/BF01211366pmid: 3035603

The influence of ionizing radiation on the membrane of human normal erythrocytes has extensively been studied and a variety of effects including changes in the cation fluxes [3, 9] or in non-electrolytes permeability [5, 6, 11], in membrane fluidity, in peroxidation of unsaturated lipids as well as chemical composition or structural modifications [4, 7, 8] has been observed.