Apoptosis induced by hyperthermia in Dunn osteosarcoma cell line in vitro

The effect of hyperthermia at 43.5 degrees C for Ih on Dunn osteosarcoma ce lls was studied. With sham-heated cells (37 degrees C, Ih) as the control, the hyperthermia treated cells were divided into five groups. Time 0 group was the cells that were harvested immediately after heated at 43.5 degrees C for 1 h, Whereas time 3, 6, 12, and 24h groups were the cells that were c ollected respectively after reincubation at 37 degrees C for the above diff erent time periods. The appearance of hyperthermia-induced apoptosis of Dun n osteosarcoma cells was demonstrated to be time dependent. With the confoc al microscopic study and TUNEL staining, the morphological characteristics of apoptosis, condensed nuclei and fragmented nuclei were obvious when rein cubated at 37 degrees C for 6h after hyperthermic treatment. This hyperther mia-induced apoptosis was further confirmed by how cytometric analysis on D NA contents. The sub-G(1) region that was proposed as a marker of apoptotic cells was most significantly elevated at 6 h after hyperthermic treatment and, thereafter, decreased to the levels of control values by 24 h, as the apoptotic cells underwent secondary necrosis and degraded to debris. The DN A strand breaks, considered as the key biochemical event of apoptosis, were detected by the TUNEL assay. This study indicated that hyperthermia (43.5 degrees C for 1 h) can induce apoptotic changes on osteosarcoma cells in vi tro very rapidly (within 6h after treatment), and its occurrence might not be detected if the samples are not taken at several early time points after hyperthermia.