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- Slater, AFG, et al.
(författare)
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Constitutive nuclear NF kappa B/rel DNA-binding activity of rat thymocytes is increased by stimuli that promote apoptosis, but not inhibited by pyrrolidine dithiocarbamate
- 1995
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Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 312312 ( Pt 3), s. 833-838
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Tidskriftsartikel (refereegranskat)abstract
- Rat thymocytes spontaneously undergo apoptotic death in cell culture, and are also sensitive to the induction of apoptosis by various stimuli. We show that unstimulated thymocytes constitutively express a p50-containing nuclear factor kappa B (NF kappa B)/rel DNA-binding activity in their nuclei. When the cells were fractionated by density-gradient centrifugation this activity was found to be most pronounced in immature CD4+8+ thymocytes, the cell population that undergoes selection by apoptosis in vivo and that is most sensitive to external inducers of apoptosis in vitro. The intensity of the NF kappa B/rel protein-DNA complex was significantly enhanced 30 min after exposing thymocytes to methylprednisolone or etoposide, two agents well known to induce apoptosis in these cells. Expression of this DNA-binding activity therefore correlates with the subsequent occurrence of apoptosis. By analogy to other systems, it has been suggested that antioxidants such as pyrrolidine dithiocarbamate (PDTC) inhibit thymocyte apoptosis by preventing the activation of an NF kappa B/rel transcription factor. However, we have found that etoposide induces a very similar enhancement of the NF kappa B/rel DNA-binding activity in the presence or absence of PDTC, despite a pronounced inhibition of apoptotic DNA fragmentation in the former situation. Dithiocarbamates therefore do not exert their anti-apoptotic activity in thymocytes by inhibiting the activation of this transcription factor.
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- SLATER, AFG, et al.
(författare)
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Nitrone spin traps and a nitroxide antioxidant inhibit a common pathway of thymocyte apoptosis
- 1995
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Ingår i: The Biochemical journal. - : Portland Press Ltd.. - 0264-6021 .- 1470-8728. ; 306306 ( Pt 3), s. 771-778
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Tidskriftsartikel (refereegranskat)abstract
- Oxidative stress has recently been suggested to be a mediator of apoptotic cell death [Buttke and Sandstrom (1994) Immunology Today 15, 7-10], although evidence that this phenomenon is a widespread component of apoptosis is lacking. When rat thymocytes were exposed to the glucocorticoid methylprednisolone (MPS), a progressive increase in intracellular peroxides and a decrease in glutathione (GSH) were observed to accompany the onset of apoptosis. Using Percoll density gradients to isolate subpopulations of thymocytes at different stages of apoptosis, the increase in peroxide content was found to be restricted to apoptotic cells, while a significant depletion of GSH and reduced protein thiol was detected in both pre-apoptotic and fully apoptotic cells. To investigate the biological significance of these redox changes, the free radical spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and 3,3,5,5-tetramethyl-1-pyrroline-1-oxide (TMPO), and the related nitroxide-radical antioxidant 2,2,6,6-tetramethyl-1-piperidinyl-1-oxyl (TEMPO) were tested as inhibitors of thymocyte apoptosis. The cell shrinkage and DNA fragmentation induced by four different initiators of apoptosis were reduced by each compound. TEMPO inhibition of both etoposide- and MPS-induced thymocyte DNA fragmentation was also found to correlate with an increase in intracellular GSH, providing support for the proposal that its antioxidant properties were responsible for the observed protective activity. We conclude that some form of intracellular oxidation (here measured indirectly by changes in intracellular GSH and peroxide levels) is required during thymocyte apoptosis even when this process is initiated by an agent that does not exert a direct oxidant action.
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- Vatnitsky, S, et al.
(författare)
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Proton dosimetry intercomparison based on the ICRU report 59 protocol
- 1999
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Ingår i: Radiotherapy and Oncology. - 0167-8140 .- 1879-0887. ; 51:3, s. 273-279
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND PURPOSE:A new protocol for calibration of proton beams was established by the ICRU in report 59 on proton dosimetry. In this paper we report the results of an international proton dosimetry intercomparison, which was held at Loma Linda University Medical Center. The goals of the intercomparison were, first, to estimate the level of consistency in absorbed dose delivered to patients if proton beams at various clinics were calibrated with the new ICRU protocol, and second, to evaluate the differences in absorbed dose determination due to differences in 60Co-based ionization chamber calibration factors.MATERIALS AND METHODS:Eleven institutions participated in the intercomparison. Measurements were performed in a polystyrene phantom at a depth of 10.27 cm water equivalent thickness in a 6-cm modulated proton beam with an accelerator energy of 155 MeV and an incident energy of approximately 135 MeV. Most participants used ionization chambers calibrated in terms of exposure or air kerma. Four ionization chambers had 60Co-based calibration in terms of absorbed dose-to-water. Two chambers were calibrated in a 60Co beam at the NIST both in terms of air kerma and absorbed dose-to-water to provide a comparison of ionization chambers with different calibrations.RESULTS:The intercomparison showed that use of the ICRU report 59 protocol would result in absorbed doses being delivered to patients at their participating institutions to within +/-0.9% (one standard deviation). The maximum difference between doses determined by the participants was found to be 2.9%. Differences between proton doses derived from the measurements with ionization chambers with N(K)-, or N(W) - calibration type depended on chamber type.CONCLUSIONS:Using ionization chambers with 60Co calibration factors traceable to standard laboratories and the ICRU report 59 protocol, a distribution of stated proton absorbed dose is achieved with a difference less than 3%. The ICRU protocol should be adopted for clinical proton beam calibration. A comparison of proton doses derived from measurements with different chambers indicates that the difference in results cannot be explained only by differences in 60Co calibration factors.
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