Effect of environment pH on heat-induced apoptosis after irradiation

초록

The purpose of this study was to investigate how environment acidity influences hyperthermia-induced apoptosis in cancer cells. RKO human colorectal cancer cells in pH 7.5 or pH 6.6 medium were heated at 42℃ FOR 1H. The cells were then incubated at 37℃ in the same medium or after replacing the pH 6.6 medium with pH 7.5 medium and apoptosis was determined with flow cytomety and agarose electrophoresis of DNA extracts. At 96h after heating, 20-25% of the cells heated in pH 7.5 and then incubated in the same medium (pH 7.5 →7.5) and those heated in pH 6.6 medium and then incubated in the same medium (pH 6.6 →6.6) were in apoptosis while 60% of the cells heated in pH 6.6 medium and then incubated in pH 7.5 medium(pH 6.6 →7.5) were in apoptosis. Western blot analysis indicated that the heat-induced cleavage of PARP, a central step in apoptotic pathway, was most extensive in the pH 6.6 →7.5 group and least extensive in the pH 6.6 →6.6 group. The level of Bcl-2 and Bax proteins did not change by the heating in all three different pH groups. It is concluded that heating in acidic pH medium followed by incubation in neutral pH medium is most effective in inducing apoptosis(This work was supported by NCl grant number CA44114.)