Effect of caffeine on radiation-induced apoptosis in TK6 cells.
Apoptosis has been measured in cells of the human TK6 lymphoblastoid cell line by recording the release of endonuclease-digested DNA from affected cells using flow cytometry. In asynchronously dividing cells, DNA degradation characteristic of apoptosis was first seen 12 h after irradiation as a defined DNA fluorescent peak of sub-G1-phase content, reaching a maximum of 30-50% of the population by 24-72 h. Treating cells with 2 mM caffeine either before or up to 3 h after irradiation eliminated the degradation of DNA entirely. In addition, the percentage of cells in which apoptosis could be detected microscopically decreased from 62.4 +/- 0.95% to 16.7 +/- 1.5% 72 h after caffeine treatment. Delaying caffeine treatment for 12 h after irradiation reduced DNA degradation by approximately 50% compared to cells receiving radiation alone. DNA degradation induced by serum deprivation was unaffected by caffeine treatment. These data support the contention that irradiation of TK6 cells produces a long-lived cellular signal which triggers apoptosis. Apoptosis produced by serum deprivation does not operate through the same pathway.
Department of Radiotherapy, Loyola University Chicago, Maywood, Illinois 60153.
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D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects*; D001769:Blood; D002110:Caffeine / Q000494:pharmacology*; D002460:Cell Line; D003470:Culture Media; D004247:DNA / Q000187:drug effects; D004307:Dose-Response Relationship, Radiation; D016195:G2 Phase / Q000187:drug effects / Q000528:radiation effects; D006801:Humans
D003470:Culture Media; D002110:Caffeine; D004247:DNA