[en] In this paper we describe the alpha-particle irradiator that has been set up at the Istituto Superiore di Sanita (ISS) for controlled exposure of cultured mammalian cells. It can be equipped with two different sources, namely 2'4'4'Cm and 2'4'1'Am, allowing irradiation at different dose-rates (typically 1-100 mGy/min). The irradiator has dimensions small enough to be inserted into a standard cell culture incubator to perform irradiation of cultured cells in physiological conditions. The dose uniformity is such that the variations in the irradiation area are less than ± 12% of the average dose value on different irradiation areas up to ∼ 25 cm'2. Moreover, in the framework of the FP6 Euratom Integrated Project Non-targeted effects of ionizing radiation (NOTE), Petri dishes were realized for housing permeable membrane insert(s) to be used in co-culture experiments. Aluminium shields were also realized for half shield irradiation experiments. The alpha-particle irradiator of the ISS has been successfully used for studying DNA damage, namely double strand breaks (DSB, as measured by the γ-H2AX assay), in directly hit and in bystander primary human fibroblasts

[en] The specific pattern of energy deposition at cellular level by protons and HZE particles (the components of space radiation of major concern) is believed to produce spatially correlated damage in the DNA which is critical for radiobiological effects. AG1522 human fibroblasts were irradiated with low-energy protons (0.88 MeV) at the Laboratori Nazionali di Legnaro (Padova, Italy), with 1 and 5 GeV/u Fe ions at the Brookhaven National Laboratory (USA) and with 414 and 115 MeV/u Fe ions at the National Institute for Radiological Sciences (Chiba, Japan). Gamma-rays were used as reference radiation. The DNA fragmentation patterns have been investigated using calibrated Pulsed Field Gel Electrophoresis (PFGE) in the size range 23 kbp - 5.7 Mbp. The results until now obtained show linear, or almost linear, increases of DSB with the dose. DSB yields are in the following increasing order: gamma-rays, 115 MeV/u Fe ions, then protons and 414 MeV/u Fe ions very close each other, and then 1 and 5 GeV/u Fe ions, also very close each other. When the same data were considered as a function of particle fluence, the order is different with 115 MeV/u Fe ions being the most effective particles per unit fluence. The total number of fragments per particle, in the size range considered, increases with LET. Fragmentation spectra shows that the frequency distributions of fragments induced by charged particles are shifted towards smaller sizes with respect to that induced by comparable doses of gamma-rays. A more detailed analysis is given in 'DNA fragmentation in AG1522 human cells irradiated with gamma-rays and charged particles: theoretical analysis' by Belli et al (presentation at this meeting)

[en] Mammalian cells were cultured in parallel at the Instituto Superiore di Sanita', in the presence of standard radiation background, and at the INFN-Gran Sasso underground Laboratory, exposed to low radiation background. Both cultures were grown up to six months and periodically tested to check for the onnset of metabolic changes and different sensitivity to genotoxic damage caused by ionizing and UV radiation, as well as by chemical agents. These tests include measurements of enzyme activities protecting from oxidative cell damage, induction of opoptosis and mutation

[en] Investigation of the mechanisms underlying the biological effects induced by densely ionizing radiation has relevant implications in both radiation protection and therapy. In particular, the possible advantages of hadrontherapy with respect to conventional radiotherapy in terms of high conformal tumor treatment and sparing of healthy tissues are well known. Further improvements are limited by lack of radiobiological knowledge, particularly about the specific cellular response to the damage induced by particles of potential interest for tumor treatment. This study compares early and late effects induced in AG01522 normal human primary fibroblasts by γ-rays and C-ions having E ∼ 45 MeV/u at the cell entrance, corresponding to LET (in water) ∼ 49 keV/μm. Different end points have been investigated, namely: cell killing and lethal mutation, evaluated as early and delayed reproductive cell death, respectively; chromosome damage, as measured by micronuclei induction (MN); DNA damage, in terms of DSB induction and repair, as measured by the H2AX phosphorylation/dephosphorylation kinetics. Linear dose-response relationships were found for cell killing and induction of lethal mutations, with RBEs of about 1.3 and 1.6 respectively, indicating that the presence of genomic instability is greater in the progeny of C-ions irradiated cells. H2AX phosphorylation/dephosphorylation kinetics have shown a maximum foci number at 30 min after irradiation, higher for γ-rays than for C-ions. However, in the first 12 h the fraction of residual γ-H2AX foci was higher for C-ions irradiated cells, indicating a lower removal rate, possibly related to multiple/more complex damage along the particle track, with respect to the sparse lesions produced by γ-rays. MN induction, observed after 72 h from irradiation, was also greater for C-ions. Overall, these data indicate a more severe DNA damage induced by 45 MeV/u C-ions with respect to γ-rays, likely responsible of an increased cellular misrepair, leading to the greater observed levels of chromosome damage and, eventually, of genomic instability. They give strong support to the idea that higher damage severity at molecular level, determined by the typical deposition pattern of densely ionizing radiation, is the earliest relevant factor for the more severe late effects at cellular level

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