Reactive oxygen species producing site in radiation-induced apoptosis of human peripheral T cells: Involvement of lysosomal membrane destabilization

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In our previous studies, we have partly elucidated the mechanism of radiation-induced apoptosis of human peripheral T cells. The exact site of the ROS (reactive oxygen species) formation induced by irradiation has been so far unknown. Therefore, in this study, we investigated the site of ROS formation by utilizing MitoCapture H2DCFDA (succinimidyl ester of dichlorodihydrofluorescein diacetate), DAPI, and Lysosensor. Our results showed that ROS formation apparently originated in the mitochondria and/or lysosomes instead of in the neclei of irradiated T cells. Moreover, lysosomal swelling and deformity, possibly revealing lysosomal membrane instability, were observed at 1 h after 5 Gy irradiation of T cells. At 4 h after irradiatronof 5 Gy, increase of fluorescence around the lysosomes, possibly revealing lysosomal ruputure, was seen. Based on the above results, we concluded the possible existence of a new apoptotic cascade involving early lysosomal membrane destabilization in radiation-induced apoptotsis of human peripheral T cells. Therefore, possible involvement of lysosomal protease leakage caused by hydroxyl radical formation in lysosomes (possibly resulting in mitochondrial membrane destabilization) is considered to play an important role in radiation induced T cell apoptosis.