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Misura del danno ossidativo radioindotto su matrici lipidiche per mezzo della fluorometria
No full textAlteration in erytrocyte membrane lipids induced by low doses of ionizing radiation as revealed by 1,6-diphenil-1,3,5-hexatriene fluorescence lifetime
No full textDamage in membrane lipids induced by low doses of ionizing radiation in the presence of oxygen has been detected in rabbit erythrocyte ghosts labelled with 1,6-diphenyl-1,3,5-hexatriene (DPH). Multifrequency phase and modulation fluorometry was used to measure DPH fluorescence lifetime. This technique is particularly suited for the observation of heterogeneous fluorescence decays. DPH decay in erythrocyte membranes is described by a two-component continuous distribution of lifetimes. The value of the distribution width of the long-lived component is found to be affected by radiation-induced membrane lipid damage at doses as low as 0.5 Gy, well within the dose range used to measure cell survival. The width of the DPH lifetime distribution decreases when the ghosts are irradiated in the presence of oxygen. Such a decrease is a linear function of the logarithm of the dose. After a dose of 110 Gy and above, the fractional intensity of the short-lived component of the DPH decay increases linearly, indicating severe membrane damage. Experiments performed in the absence of oxygen do not show any change in the fluorescence parameters up to a dose of 550 Gy. The molecular identification of the produced damage has not been accomplished, but the necessity of oxygen to observe the damage suggests that hydroperoxides and lipids crosslinks are produced
Tecniche di fluorescenza per l’osservazione di danni ossidativi prodotti da basse dosi di radiazioni ionizzanti su lipidi di membrana
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Human cell membrane oxidative damage induced by single and fractionated doses of ionizing radiation: a fluorescence spectroscopy study
No full textPurpose: To investigate the production and repair of lipid oxidative damage in two human cell lines exposed to acute and fractionated dose of ionizing radiation. Radiation dose was in the range from 0.1 to 44 Gy. Materials and Methods: K562 and HL60 human cell lines have been used, 24 and 96 h after seeding. Membrane lipid oxidative damage has been detected by the measurement of the fluorescence decay of 1,6-diphenyl-1,3,5-hexatriene (DPH), its polarization value and the conjugated dienes concentration. The modification of DPH decay has been previously reported to be directly related to the lipid hydroperoxide concentration. Results: A modification of the DPH decay has been observed as a linear function of the logarithm of the radiation dose and only when the irradiation was performed in the presence of oxygen. The amount of the damage is related to the time after the cell medium change. By exposing the cells to fractionated radiation doses for several days (10 cGy day(-1)), the oxidative damage has been found to be cumulative. After a single acute dose, evidence of repair of the lipid oxidative damage was not obtained. Conclusions: Following a previously developed method, the membrane damage was attributed to the production of hydroperoxide residues in the lipid acyl chains with the consequence of water penetration into the external portion of the bilayer, from the aqueous environment to the position of hydroperoxides. This damage is not repaired. The results obtained by measuring the DPH fluorescence decay have been compared with those obtained using other current optical and biochemical methods. None of these techniques could detect membrane oxidative damage at doses <10Gy. Finally, the different sensitivity of 'young' and 'old' cells to the oxidative damage can be related to different cholesterol concentrations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Radiation induced membrane oxidative damage in human cells at low and high dose-rate: production and repair.
No full textA human promyelocitic cell line, HL60, has been used to study the production and repair of membrane oxidative damage after exposure to acute and fractionated doses of ionising radiation. The oxidative damage is detected at doses as low as 0.1 Gy . The dose response curve is not linear with the dose and most of the damage is produced at doses 10Gy. After exposure to an acute dose of 10 Gy cells were incubated in the growth conditions but evidences of repair were not obtained for incubation times up to 4 hours. Cells daily exposed to low doses, namely 0.1 Gy or 0.1 Gy followed by 10 hours incubation and then a second dose of 0.1 Gy, show an additive increase of the damage. In summary: (i) membrane oxidative damage can be observed after very low doses of ionizing radiation; (ii) the damage produced by fractionated doses is additive; (iii) oxidative damage is not repaired both after acute or fractionated exposures
Time–resolved experiments in the frequency domain using syncrotron radiation
No full textPLASTIQUE is the only synchrotron radiation beam line in the world that performs time‐resolved fluorescence experiments in frequency domain. These experiments are extremely valuable sources of information on the structure and the dynamics of molecules. This technique measures fluorescence lifetimes with picosecond resolution in the near UV spectral range. Such accurate measurements are rendered possible by taking phase and modulation data, and by the advantages of the cross‐correlation technique. A successful experiment demonstrated the radiation damage induced by low doses of radiation on rabbit blood cell membrane
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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