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Cytoplasmic irradiation: Biological consequences and role of oxyradicals
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P-5
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DUAL ROLE OF THIOLS IN RADIATION-INDUCED APOPTOSIS. Kathrvn D. Held Yvonne L. McCarey and John E. Biaglow, Massachusetts General HospitaliHarvard Medical School, Boston, MA 02114 and University of Pennsylvania, Philadelphia, PA 19104 In some cell types, particularly cells of hematopoietic origin, ionizing radiation is very effective at inducing apoptosis. The amount of apoptosis after irradiation depends on many factors, including radiation dose, time at which the apoptosis is assayed, cell type and status of genes such as ~53 and bcl-2. Thiols are generally good antioxidants and radioprotectors, yet thev can be two faced. In some circumstances. e.g.. in the presence of traces of transition metals, some anti&idants become pro-oxidants, causing cell killing. Thus, in some cells, added thiols can decrease rachation-induced apoptosis and clonogenic cell death, but in other cells or under other circumstances thiols themselves cause apoptosis. Thiol-induced auontosis is comulex and deuends on the thiol used. its concentration, the drug exposure time, the cell type, etc. In human leukemia HL-60 cells, for example, dithiothreitol (DTT) or several other thiols cause maximal apoptosis 5-6 h after cells are treated with 1-5 mM drug for at least an hour. Although D’IT oxidation can produce hydrogen peroxide and OH radicals, based on studies with antioxidants it is unclear whether thiol-induced apoptosis occurs via this oxidative stress pathway. On the other hand, depleting thiols, particularly glutathione, can cause auootosis in some cell tvues and can enhance radiation-induckd*apoptosis, even in the absence of thiol depletion-induced apoptosis. Some published data suggest there may be an interdependence between bcl-2 expression&d glutathione levels for radiation-induced apoptosis, but it remains unclear whether this is true for all cell types,
CYTOPLASMIC IRRADIATION: BIOLOGICAL CONSEQUENCES AND ROLE OF OXYRADICALS. Tom, Lijun Wu, and Gerhard Randers-Pehrson, Center for Radiological Research, Columbia University, New York, NY., 10032. The radiobiological effects of cy-toplasmic irradiation are unknown. Using the microbeam at the Radiological Research Accelerator Facility, we examine lethality, mutation induction and the role of oxyradicals in human-hamster hybrid (AL) cells traversed by an exact number of alpha particles (150 keV/pm) through cellular cytoplasm. Dual fluorochrome dyes and an image analysis system were used to determine the irradiation positions off the long ends of each cell. In comparison to nuclear irradiation (Hei et al., Proc. Natl. Acad. Sci. 94: 3765,1997), cytoplasmic irradiation induced minimal toxicity. While cytoplasmic traversal with either one or two particles induced few Sl- mutants in AL cells, those irradiated with 4 or more particles had an induced mutant fraction that was 2.5 fold higher than the background incidence. In contrast to the multilocus deletions induced predominately by nuclear traversals, Sl* mutants induced by cytoplasmic irradiation involved mostly small alterations similar to those of spontaneous origin. Pretreatment of cells with either DMSO or BSO significantly reduced or enhanced, respectively, the mutagenic potential of cytoplaamic irradiation. Our results show that cytoplasmic traversal of mammalian cells by a-particles is mutagenic via a mechanism different from that of nuclear traversal and likely to involve oxyradicals.
OXYGEN
’ 9
8
P-5
I
DUAL ROLE OF THIOLS IN RADIATION-INDUCED APOPTOSIS. Kathrvn D. Held Yvonne L. McCarey and John E. Biaglow, Massachusetts General HospitaliHarvard Medical School, Boston, MA 02114 and University of Pennsylvania, Philadelphia, PA 19104 In some cell types, particularly cells of hematopoietic origin, ionizing radiation is very effective at inducing apoptosis. The amount of apoptosis after irradiation depends on many factors, including radiation dose, time at which the apoptosis is assayed, cell type and status of genes such as ~53 and bcl-2. Thiols are generally good antioxidants and radioprotectors, yet thev can be two faced. In some circumstances. e.g.. in the presence of traces of transition metals, some anti&idants become pro-oxidants, causing cell killing. Thus, in some cells, added thiols can decrease rachation-induced apoptosis and clonogenic cell death, but in other cells or under other circumstances thiols themselves cause apoptosis. Thiol-induced auontosis is comulex and deuends on the thiol used. its concentration, the drug exposure time, the cell type, etc. In human leukemia HL-60 cells, for example, dithiothreitol (DTT) or several other thiols cause maximal apoptosis 5-6 h after cells are treated with 1-5 mM drug for at least an hour. Although D’IT oxidation can produce hydrogen peroxide and OH radicals, based on studies with antioxidants it is unclear whether thiol-induced apoptosis occurs via this oxidative stress pathway. On the other hand, depleting thiols, particularly glutathione, can cause auootosis in some cell tvues and can enhance radiation-induckd*apoptosis, even in the absence of thiol depletion-induced apoptosis. Some published data suggest there may be an interdependence between bcl-2 expression&d glutathione levels for radiation-induced apoptosis, but it remains unclear whether this is true for all cell types,
CYTOPLASMIC IRRADIATION: BIOLOGICAL CONSEQUENCES AND ROLE OF OXYRADICALS. Tom, Lijun Wu, and Gerhard Randers-Pehrson, Center for Radiological Research, Columbia University, New York, NY., 10032. The radiobiological effects of cy-toplasmic irradiation are unknown. Using the microbeam at the Radiological Research Accelerator Facility, we examine lethality, mutation induction and the role of oxyradicals in human-hamster hybrid (AL) cells traversed by an exact number of alpha particles (150 keV/pm) through cellular cytoplasm. Dual fluorochrome dyes and an image analysis system were used to determine the irradiation positions off the long ends of each cell. In comparison to nuclear irradiation (Hei et al., Proc. Natl. Acad. Sci. 94: 3765,1997), cytoplasmic irradiation induced minimal toxicity. While cytoplasmic traversal with either one or two particles induced few Sl- mutants in AL cells, those irradiated with 4 or more particles had an induced mutant fraction that was 2.5 fold higher than the background incidence. In contrast to the multilocus deletions induced predominately by nuclear traversals, Sl* mutants induced by cytoplasmic irradiation involved mostly small alterations similar to those of spontaneous origin. Pretreatment of cells with either DMSO or BSO significantly reduced or enhanced, respectively, the mutagenic potential of cytoplaamic irradiation. Our results show that cytoplasmic traversal of mammalian cells by a-particles is mutagenic via a mechanism different from that of nuclear traversal and likely to involve oxyradicals.
OXYGEN
’ 9
8