DNA sequence dependence of closely opposed cyclobutyl pyrimidine dimers induced by UV radiation

Treatment of UV-irradiated DNAs with Micrococcus luteus pyrimidine dimer-DNA glycosylase results in the formation of double-strand breaks due to cleavage at closely opposed pyrimidine dimers. To determine if the induction of closely opposed dimers is significantly affected by DNA nucleotide sequence, end-labeled DNA fragments of known nucleotide sequence were UV irradiated, incubated with pyrimidine dimer-DNA glycosylase, and analyzed by electrophoresis through nondenaturing polyacrylamide gels. Distinct bands of increased electrophoretic mobility were observed, indicating that bifilar cleavage had occurred with greater probability at specific sites in each DNA sequence. In vitro enzymatic photoreactivation of dimers prior to treatment with pyrimidine dimer-DNA glycosylase prevented the appearance of bands. DNA sequence analysis revealed the presence of closely opposed runs of pyrimidines at sites of more frequent bifilar cleavage. Our results indicate that the induction of closely opposed dimers occurs with greater probability at specific sites in DNA sequences and that such sites are characterized by the presence of closely opposed pyrimidine runs.     

Repair of DNA damage induced by gamma radiation and UV and gamma mimetics in virus-infected human cells

The method of chromatography of cell lysates on the columns with hydroxyapatite (HAP) and the method of ultracentrifugation of cell lysates in neutral sucrose gradient were used to study the mutagen-induced repair activity of human cells HEp-2 noninfected and chronically infected with measles and rubella viruses in order to determine the sedimentation properties of complexes containing DNA. Gamma-radiation, bleomycin, 4-nitroquinoline-1-oxide, and mitomycin C were used as DNA damaging agents. It was shown that the chronic infectious process inhibited repair of DNA damages induced by 4-nitroquinoline-1-oxide and mitomycin C and did not influence repair of DNA lesions caused by gamma-radiation and bleomycin.     

Modification of radiation damage of bacteria by folic acid antagonists

Pittillo, Robert F. (Southern Research Institute, Birmingham, Ala.), Mary Lucas, Robert T. Blackwell, and Carolyn Woolley. Modification of radiation damage of bacteria by folic acid antagonists. J. Bacteriol. 90:1548-1551. 1965.-The folic acid analogues, 2,4-diamino-6-methylpteridine, amethopterin, and aminopterin, have been found to sensitize certain bacteria, especially Escherichia coli, to the lethal action of ionizing irradiation. Data are presented which indicate that (i) the compounds must be present during the irradiation period for maximal sensitization to be observed, (ii) the sensitizing effect can be nullified by cysteine or cysteamine, (iii) the sensitizing effect occurs in a number of diverse bacterial genera, and (iv) folic acid neither sensitizes bacteria to irradiation nor prevents the sensitization caused by these antifolic agents.     

Wavelength dependence of inactivation and membrane damage to Saccharomyces cerevisiae cells by monochromatic synchrotron vacuum-uv radiation (145-190 nm)

Using an electron storage ring as a source of radiation, the wavelength dependence of inactivation and membrane damage in yeast cells (Saccharomyces cerevisiae) was investigated in the range from 145 to 254 nm, with special reference to the effects of vacuum-uv radiation. The cells were irradiated on a Millipore filter in a moist chamber filled with water vapor (deoxygenated) at saturation pressure. Fluence-survival curves taken at 5-nm intervals were generally sigmoidal. Action spectra of the two types of effects were nearly identical in shape. The maximum occurred in both spectra at 160 nm, decreasing sharply toward 180 nm. The spectra remarkably resembled the calculated absorption spectrum of (liquid) water in the range from 145 to 170 nm; the spectra had no similarity at all to the absorption spectra of DNA, proteins, or lipids. These data support the theory that inactivation of wet cells by vacuum-uv radiation may be attributable to damage in the cell membrane initiated by the absorption of water molecules. Above 210 nm the spectrum for inactivation paralleled the absorption of DNA. Genetic changes (induction of gene conversion) were also observed above 210 nm. Photoreversion for the induced convertants was detectable only above 220 nm. These characteristics are consistent with the expectation that above 210 nm the site of major lethal damage shifts to DNA.     

Application of the comet assay to measure DNA damage induced by UV radiation in the hydrophyte, Spirodela polyrhiza

The single-cell gel electrophoresis or comet assay is now widely used to detect DNA damage in animal cells induced by radiation or chemicals. Here, we apply the comet assay to measure ultraviolet (UV)-B-induced DNA damage in plant cells. The accepted animal cell protocol for the comet assay was modified to adapt it to plant cells. The major modifications were conversion of the plant cells to protoplasts and the use of T4 endonuclease V. As a positive control hydrogen peroxide was applied. Significant DNA damage was detected at 100 μ M H₂O₂. This type of DNA damage was not affected by T4 endonuclease V treatment, which implies that the mechanism of H₂O₂-induced DNA damage was different from UV-B-induced DNA damage. Our results also indicate that both UV-A and UV-B radiation can induce DNA single-strand breaks in plant cells, while UV-B was more effective than UV-A for inducing pyrimidine dimer formation.     

Photoreactivation of damage induced by ionizing radiation in yeast cells

Summary Experimental data on photoreactivation of damage induced by ionizing radiation in yeast cells are presented. The value of photoreactivation was found to be the highest for the following conditions predicted by us as optimum ones: large volume of irradiated suspension, hypoxia and high energy sparsely ionizing radiation. A comparison of data for yeast and bacterial cells shows that Cerenkov emission from ionizing radiation may produce photoreactivated pyrimidine dimers in both prokaryotic and eukaryotic cell systems.     

Membrane oxidative damage induced by ionizing radiation detected by fluorescence polarization

Effects of ionizing radiation on biological membranes include alterations in membrane proteins, peroxidation of unsaturated lipids accompanied by perturbations of the lipid bilayer polarity. We have measured radiation-induced membrane modifications using two fluorescent lipophilic membrane probes (TMA-DPH and DPH) by the technique of fluorescence polarization on two different cell lines (Chinese hamster ovary CHO-K1 and lymphoblastic RPMI 1788 cell lines). γ-Irradiation was performed using a ⁶⁰Co source with dose rates of 0.1 and 1 Gy/min for final doses of 4 and 8 Gy. Irradiation induced a decrease of fluorescence intensity and anisotropy of DPH and TMA-DPH in both cell lines, which was dose-dependent but varied inversely with the dose rate. Moreover, the fluorescence anisotropy measured in lymphoblastic cells using TMA-DPH was found to decrease as early as 1 h after irradiation, and remained significantly lower 24 h after irradiation. This study indicates that some alterations of membrane fluidity are observed after low irradiation doses and for some time thereafter. The changes in membrane fluidity might reflect oxidative damage, thus confirming a radiation-induced fluidization of biological membranes. The use of membrane fluidity changes as a potential biological indicator of radiation injury is discussed. Received: 14 May 1996 / Accepted in revised form: 30 September 1996     

Selenomethionine protects against adverse biological effects induced by space radiation

Ionizing radiation-induced adverse biological effects impose serious challenges to astronauts during extended space travel. Of particular concern is the radiation from highly energetic, heavy, charged particles known as HZE particles. The objective of the present study was to characterize HZE particle radiation-induced adverse biological effects and evaluate the effect of D-selenomethionine (SeM) on the HZE particle radiation-induced adverse biological effects. The results showed that HZE particle radiation can increase oxidative stress, cytotoxicity, and cell transformation in vitro, and decrease the total antioxidant status in irradiated Sprague-Dawley rats. These adverse biological effects were all preventable by treatment with SeM, suggesting that SeM is potentially useful as a countermeasure against space radiation-induced adverse effects. Treatment with SeM was shown to enhance ATR and CHK2 gene expression in cultured human thyroid epithelial cells. As ionizing radiation is known to result in DNA damage and both ATR and CHK2 gene products are involved in DNA damage, it is possible that SeM may prevent HZE particle radiation-induced adverse biological effects by enhancing the DNA repair machinery in irradiated cells.     

Numerical analysis of the thermochemical tooth damage induced by laser radiation

A numerical model is developed to predict zones of thermochemical tooth damage induced by laser radiation. Particular attention is devoted to pulp denaturation, enamel fracture and caries sterilization treatment dependence on laser energy and other beam parameters.     

Vicia faba chromosome damage induced by low doses of gamma radiation

The rate of radiation damage to chromosomes by low doses of gamma rays (0.01-0.30 Gy) was studied in the root tips ofVicia faba. As criteria of the effect of ionizing radiation, the frequency of sister chromatid exchanges (SCEs), incidence of chromosomal aberrations and the number of micronuclei were evaluated and compared in irradiated cells. The results obtained confirmed that the analysis of SCEs did not represent an efficient indicator of radiation damage to chromosomes. On the contrary, the formation of chromosomal aberrations and micronuclei was effectively stimulated by low radiation doses, there being linear dose-effect relationships in the low doses region used.     

Modification of radiation induced damage in mouse intestine by WR-2721

Intestinal protection in mice against radiation injury by WR-2721 (300 mg/kg body wt, i.p., 30 min before irradiation) was studied after whole body gamma irradiation (0.5, 1.5, 3.0, 4.5, or 6.0 Gy). Crypt survival and induction of apoptosis, and abnormal mitoses in crypt cells in the jejunum were studied on day 1, 3 and 7 after irradiation. Irradiation produced a significant decrease in crypt survival, whereas apoptosis and abnormal mitoses showed a significant increase from sham-treated control animals. Maximum changes in all the parameters were observed on day 1 after irradiation and the effect increased linearly with radiation dose. There was recovery at later intervals, which was inversely related to radiation dose. WR-2721 pre-treatment resulted in a significant increase in the number of surviving crypts, whereas the number of apoptotic cells in the crypts showed a significant decrease from respective irradiated controls on day 1 after exposure. The recovery was also faster in WR-2721 pre- treated animals. It is concluded that WR-2721 protects against gastrointestinal death by reducing radiation induced cell death, thereby maintaining a higher number of stem cells in the proliferating compartment.     

Influence of superinfection on the photoreversible phase of UV induced lysogenic bacteria

Summary Bombyx mori L. ribosomal proteins have been analyzed by four related two-dimensional polyacrylamide gel electrophoretic systems (Madjar et al. 1977a). In the small and large subunits are present 32 and 45 proteins, respectively, whose numbering is proposed. No significant differences in composition or migration could be detected between proteins in membranebound ribosomes and free ribosomes. The molecular weights of the proteins vary from 60,000 to less than 10,000. In vivo phosphorylation was investigated by labeling with ³²P-orthophosphate. Autoradiograms of four two dimensional gels unambiguously show five labeled ribosomal proteins: S1, S7, L6, L29, and L40.     

Microcalorimetric studies on cell survival and repair after UV induced damage

Rate of heat production during cell proliferation following UV-irradiation of respiratory-deficient yeast cells was measured as a function of time (p-t curve) in a batch microcalorimeter. Following observations were made: (a) All growing cell cultures showed 3 distinct phases of heat production namely lag, exponential and declining phases of rate of heat production. (b) Duration of the lag phase is inversely proportional to the number of cells capable of proliferation. (c) After UV-irradiation, lag phase increased in a dose dependent manner. (d) Liquid-holding reactivation increased the surviving fraction and reduced the lag phase in p-t curves. Presence of 2-deoxy-D-glucose during liquid-holding prevented the reduction in lag phase due to the inhibition of repair processes.     

Wavelength dependence of bilirubin photoreactivity

The rates and products of the self-sensitized photoreactions of bilirubin IXα vary with excitation wavelength, solvent and the presence or absence of oxygen. Radical or Type I photooxidation reactions of bilirubin are implicated in degassed chloroform or methanol. Quantum yields for the disappearance of bilirubin vary from 10^?2 to 10^?4 with excitation wavelengths of 440, 340 and 280 nm and with the higher quantum yield generally appearing in chloroform solvent and/or excitation at 280 nm. Bilirubin is stable in degassed chloroform to irradiation at 440 nm.