Effects of ionizing radiation on dried spores of Osmunda regalis III. 35 GHz e.s.r. study.

The use of 35 GHz microwave frequency has greatly simplified the separation of overlapping signals in dried irradiated fern spores. While in general confirming the conclusions previously drawn from X-band spectra, the use of Q-band has clarified several assignments of radical groups and allowed the recognition of additional radical groups or sub-groups.     

Effects of storage conditions on survival and free radical populations in dried irradiated spores ofosmunda regalis

Radiation and Environmental Biophysics - Spores of the fernOsmunda regalis were irradiated and stored for 8 weeks in N2, NO, H2S and O2. They were examined at increasing times after irradiation...     

Effects of scavengers of reactive oxygen and radical species on cell survival following photodynamic treatment in vitro: comparison to ionizing radiation

The effects of various scavengers of reactive oxygen and/or radical species on cell survival in vitro of EMT6 and CHO cells following photodynamic therapy (PDT) or gamma irradiation were compared. None of the agents used exhibited major direct cytotoxicity. Likewise, none interfered with cellular porphyrin uptake, and none except tryptophan altered singlet oxygen production during porphyrin illumination. The radioprotector cysteamine (MEA) was equally effective in reducing cell damage in both modalities. In part, this protection seems to have been induced by oxygen consumption in the system due to MEA autoxidation under formation of H2O2. The addition of catalase, which prevents H2O2 buildup, reduced the effect of MEA to the same extent in both treatments. Whether the remaining protection was due to MEA's radical-reducing action or some remaining oxygen limitation is unclear. The protective action of MEA was not mediated by a doubling of cellular glutathione levels, since addition of buthionine sulfoximine, which prevented glutathione increase, did not diminish the observed MEA protection. The hydroxyl radical scavenger mannitol also afforded protection in both kinds of treatment, but it was approximately twice as effective in gamma irradiation as in PDT. This is consistent with the predominant role of OH radicals in ionizing radiation damage and their presumed minor involvement in PDT damage. Superoxide dismutase, a scavenger of O2, acted as a radiation protector but was not significantly effective in PDT. Catalase, which scavenges H2O2, was ineffective in both modalities. Tryptophan, an efficient singlet oxygen scavenger, reduced cell death through PDT by several orders of magnitude while being totally ineffective in gamma irradiation. These data reaffirm the predominant role of 1O2 in the photodynamic cell killing but also indicate some involvement of free radical species.     

Modification of rat thymocyte membrane properties by hyperthermia and ionizing radiation.

Thymocytes are one the most widely used cell models for the study of radiation-induced interphase death. This cell-type was chosen for the study of hyperthermic and radiation effects on two membrane-related processes implicated in the interphase death of cells: Na+-dependent 2-aminoisobutyric acid (AIB) transport and cyclic 3'-5' adenosine monophsophate formation. The response of AIB transport to heat is dose-dependent, but the biphasic thermal response curve (AIB uptake versus time) differs fom the sigmoidal radiation response curve. Heating thymocytes for 20-30 min at 43 degrees C stimulates AIB uptake. Additional heating at 43 degrees C, however, markedly reduces AIB uptake. Despite the immediate stimulating effect of heat (30 min at 43 degrees C), the thymocyte has already developed irrepairable impairments, as demonstrated by the fractionated heating experiments. The heat-induced impairment of AIB uptake is mainly on the Na+-dependent component of neutral amino-acid transport, affecting primarily the maximal rate of uptake, i.e. Vmax. Additional evidence for heat-induced plasma membrane damage is the alteration in cAMP levels. Heating thymocytes for 30 min or longer at 43 degrees C causes a massive rise in cAMP level within the cell. This differs from thymocytes exposed to radiation where no rise in cAMP is observed.     

The action of ionizing radiation on protein: radical formation in L-histidine crystals.

Radicals produced at temperatures between 77 K and 300 K by X-irradiation of L-histidine.2HC1 crystals have been analysed by electron spin resonance spectroscopy. The results are compared with previous findings with L-histidine and L-histidine.HC1.H2O crystals. In these three crystals we have identified three main species, which, depending on the molecular environment, are stabilized at different temperatures and produced in different concentrations. These findings are discussed in connection with the observations made on irradiated aqueous solutions of amino acids. It is concluded that our results corroborate the mechanism for the action of ionizing radiation on dry protein proposed by Platzman and Franck (1958),     

Effects of ionizing radiation and partial hepatectomy on messenger RNA synthesis.

Newly synthesized messenger RNA, as measured by a 40 min uptake of the radioactive precursor (6-14C) orotic acid, was studied in the regenerating livers of non-irradiated and gamma-irradiated (1800 rad) adrenal-intact and adrenalectomized rats 24 aand 48 hours after partial hepatectomy. Two groups of rats, one with and one without adrenal glands, were each divided into four subgroups: (1) control rats, (2) irradiated rats, (3) partially hepatectomized rats and (4) irradiated, partially hepatectomized rats. The radioactive profile of polyribosome formation and distribution was determined by sucrose density gradient centrifugation (10--40 per cent). The result of this study indicates that ionizing radiation decreases the synthesis of newly formed messenger RNA in re generating livers of adrenal-intact rats. However, adrenalectomy largely abolished that inhibition. These data suggest that the decrease in messenger RNA synthesis may be explained by the disturbance of adrenal hormones induced by partial hepatectomy and ionizing radiation.     

Effects of ionizing radiation on cyclin expression in HeLa cells.

The levels of cyclin B mRNA and protein rise rapidly in G2 + M phase, and fall at the end of mitosis. The studies described here were initiated to determine the effects of ionizing radiation on the level of cyclin B bearing in mind that the division delay induced by ionizing radiation might be influenced by the expression of cyclin B. After irradiation in S phase, the cyclin B mRNA in HeLa cells was measured as the cells proceeded through the cell cycle. Instead of the usual rise, after irradiation cyclin B mRNA levels remained low during the G2 delay. After irradiation in G2 phase, cyclin B mRNA was readily detectable although at slightly lower levels than in the controls. However, cyclin B protein was markedly decreased in amount.     

Effects of sparsely and densely ionizing radiation on plants

One of the main purposes leading botanists to investigate the effects of ionizing radiations is to understand plant behaviour in space, where vegetal systems play an important role for nourishment, psychological support and functioning of life support systems. Ground-based experiments have been performed with particles of different charge and energy. Samples exposed to X- or γ-rays are often used as reference to derive the biological efficiency of different radiation qualities. Studies where biological samples are exposed directly to the space radiation environment have also been performed. The comparison of different studies has clarified how the effects observed after exposure are deeply influenced by several factors, some related to plant characteristics (e.g. species, cultivar, stage of development, tissue architecture and genome organization) and some related to radiation features (e.g. quality, dose, duration of exposure). In this review, we report main results from studies on the effect of ionizing radiations, including cosmic rays, on plants, focusing on genetic alterations, modifications of growth and reproduction and changes in biochemical pathways especially photosynthetic behaviour. Most of the data confirm what is known from animal studies: densely ionizing radiations are more efficient in inducing damages at several different levels, in comparison with sparsely ionizing radiation.     

Action of hypoxic sensitizers on the survival of haplont yeasts irradiated with ionizing radiation

A study was made of the oxygen effect and the radiosensitizing action of metronidazole and misonidazole on hypoxic cells of irradiated yeast haplonts. It was shown that metronidazole did not increase the radiosensitivity of all the strains under study while the sensitizing effectiveness of oxygen and misonidazole approximated the values characteristic of different repair-deficient rad-mutants. Possible causes of the radiosensitizing effects observed are discussed.     

Theory of survival of bacteria exposed to ionizing radiation. I. X and gamma rays

A new model for the survival of bacteria exposed to ionizing radiation is constructed in the framework of a target theory based on microdosimetric concepts, where single- and double-strand breaks of DNA and their repair in vivo can be described consistently in terms of the microdosimetric quantity j (number of effective primary events per track per target). In this model, the ability of cells to repair DNA damage is taken into consideration in terms of the repair capacities for single- and double-strand breaks of DNA, xi 1 and xi 2 (0 less than or equal to xi 1, xi 2 less than or equal to 1). To apply this model to Escherichia coli K-12 strains with different repair abilities, values of the repair capacity for single-strand breaks, xi 1, were derived from experimental survival curves. The theoretical survival curves for 60Co gamma rays were found to be effectively insensitive to the value of xi 2. Experimental survival curves for the wild-type, uvr, and rec strains of E. coli K-12 were well reproduced in this model. From these results, it is concluded that the theoretical formulation for the survival fraction of bacteria can afford a quantitative method for analysis of the repair process for radiation-induced single-strand breaks in DNA in vivo.     

Effects of ionizing radiation on nitric oxide myoglobin. Part 2. Effects on the globin moiety

Irradiation of nitric oxide myoglobin (NOMb) induces changes in the haem as well as protein moiety of NOMb, especially at doses of 400-800 krad. The changes in the protein include: Conformational changes, with apparent partial denaturation of globin alpha-helix as evidenced by circular dichroism. Preferential scission of the polypeptide chain and dimerization via covalent bond(s) as evidenced by SDS-polyacrylamide gel electrophoresis. Products with a spectrum of hydrodynamic volumes between those of the monomer and the dimer are also formed. The shift of NOMb pIs toward more acidic pHs (probably due to modification and/or destruction of basic amino acid residues by water radiolytic products) as evidenced by isoelectric focusing.