Chelation of lysosomal iron protects against ionizing radiation.

Ionizing radiation causes DNA damage and consequent apoptosis, mainly due to the production of hydroxyl radicals (HO•) that follows radiolytic splitting of water. However, superoxide (O2•-) and H2O2 also form and induce oxidative stress with resulting LMP (lysosomal membrane permeabilization) arising from iron-catalysed oxidative events. The latter will contribute significantly to radiation-induced cell death and its degree largely depends on the quantities of lysosomal redox-active iron present as a consequence of autophagy and endocytosis of iron-rich compounds. Therefore radiation sensitivity might be depressed by lysosome-targeted iron chelators. In the present study, we have shown that cells in culture are significantly protected from ionizing radiation damage if initially exposed to the lipophilic iron chelator SIH (salicylaldehyde isonicotinoyl hydrazone), and that this effect is based on SIH-dependent lysosomal stabilization against oxidative stress. According to its dose-response-modifying effect, SIH is a most powerful radioprotector and a promising candidate for clinical application, mainly to reduce the radiation sensitivity of normal tissue. We propose, as an example, that inhalation of SIH before each irradiation session by patients undergoing treatment for lung malignancies would protect normally aerated lung tissue against life-threatening pulmonary fibrosis, whereas the sensitivity of malignant lung tumours, which usually are non-aerated, will not be affected by inhaled SIH.

Different G2/M accumulation in M059J and M059K cells after exposure to DNA double-strand break-inducing agents.

PURPOSE: To investigate and compare the cell cycle progression in relation to cell death in the human glioma cell lines, M059J and M059K, after exposure to DNA double-strand break-inducing agents. METHODS AND MATERIALS: The M059J and M059K cells, deficient and proficient in the catalytic subunit of the DNA-dependent protein kinase, respectively, were exposed to 1 and 4 Gy of photons or accelerated nitrogen ions. In addition, M059J and M059K cells were treated with 10 and 40 mug/mL of bleomycin for 30 min, respectively. Cell cycle progression, monitored by DNA flow cytometry, was measured up to 72 h after treatment. RESULTS: M059J, but not M059K, cells displayed G(2)/M accumulation after low linear energy transfer irradiation. High linear energy transfer radiation exposure however, resulted in a substantial increase of M059K cells in the G(2)/M phase detected at 48 h. At 72 h, the number of cells in the G(2)/M phase was equivalent to its control. M059J cells accumulated mainly in S phase after high linear energy transfer irradiation. In contrast to M059K, M059J cells were still blocked at 72 h. Bleomycin induced G(2)/M accumulation for both M059J and M059K cells detected 24 h after treatment. At 48 h, the percentage of bleomycin-treated M059J cells in G(2)/M phase remained high, and the number of M059K cells had decreased to control levels. Neither cell line showed cell cycle arrest (< or =10 h) after exposure to these agents. CONCLUSION: Distinct cell cycle block and release is dependent on the complexity of the induced DNA damage and the presence of the DNA-dependent protein kinase catalytic subunit.

Radiation-induced cell cycle response in lymphocytes is not related to clinical side-effects in breast cancer patients.

BACKGROUND: We examined whether development of radiation-induced lung injury after irradiation for breast cancer correlates with lymphocyte radiosensitivity (LRS) in vitro. MATERIALS AND METHODS: Patients were selected from a cohort of 177 patients, who were treated with adjuvant postoperative radiotherapy (RT) for loco-regional breast cancer, and included 14 patients who had severe early lung injury measured as respiratory symptoms caused by RT and treated with corticosteroids (i.e. "cases") and a corresponding 14 control patients without such symptoms. LRS was measured as the postirradiation fraction of mitogen-stimulated blood lymphocytes in S- and G2-phase. Plasma levels of TGF-beta 1 and thiols, both suggested to be involved in the pathogenesis of radiation-induced lung injury, were also analysed. RESULTS: The result showed that cells from the controls responded to a higher extent to mitogen stimulation than cells from the cases (p < 0.05). Analysis of the fraction of S- and G2-phase cells after irradiation showed no significant difference between the two groups (p = 0.57 and 0.31, respectively). There was no difference in plasma levels of TGF-beta 1 and thiols in patients who did or did not develop pulmonary injury after RT. Tamoxifen administered before or at RT did not influence the incidence of pulmonary reactions. CONCLUSION: No differences in LRS were found between breast cancer patients with lung complications after RT and matched control patients without complications.

X-ray-induced DNA double-strand breaks in mouse l1210 cells: a new computational method for analyzing neutral filter elution data.

The aim of this article is to present a method for studying the shape of the dose and repair responses for X-ray-induced double-strand breaks (DSBs) as measured by neutral filter elution (NFE). The approach is closely related to a method we developed for the use of specific molecular size markers and used for determination of the absolute number of randomly distributed radiation-induced DSBs by pulsed-field gel electrophoresis (PFGE). Mouse leukemia L1210 cells were X-irradiated with 0-50 Gy. Samples were then evaluated both with PFGE and with NFE. Assuming that with both migration (PFGE) and elution (NFE), a heterogeneous population of double-stranded DNA fragments will start with the smallest fragments and proceed with increasingly larger fragments, it is possible to match the migration behavior of fractions of fragments smaller than a certain size to the fraction eluted at a specific time. This assumption does not exclude the possibility of DNA being sheared in the NFE filter. The yield, as determined by the size markers in PFGE, was used to find the corresponding elution times in the NFE experiment. These experimentally used elution times could then reversely be interpreted as size markers which finally were used to calculate DSBs/Mbp as a function of X-ray dose. The resulting lines were almost straight. The data were also plotted as relative elution and showed that, as expected, the dose response then appears with a more pronounced sigmoid shape.