Expression of Bax and Bcl-2 in Apoptosis of the Rat Cochlea Induced by Acute Cisplatin Ototoxicity

Kim, Chong Sun; Song, Byeong Ho; Koo, Ja Won; Lim, Duk Whan

Abstract

BACKGROUND AND OBJECTIVES
Cisplatin is an ototoxic agent commonly used for the treatment of solid tumors. Recently, it has been recognized to cause apoptosis in tumor cells, kidney and cochlea. The Bcl-2 family are specific proteins which are a well-known group of death modulating factors. The aims of this study was to analyze the expression of Bcl-2 family for the time course after cisplatin injection.
MATERIALS AND METHODS
Sprague-Dawley (SD) rats were injected intraperitoneally wtih either 20 mg/kg of cisplatin, or the same amount of saline water to be used as control. Cochleae were harvested 6, 12 and 24 hours after injection and compared to those of the control ones. TUNEL staining was performed to observe apoptotic cells. Immunohistochemistry and Western blotting were performed to investigate the expression of Bax and Bcl-2.
RESULTS
Positively TUNEL-labeled nuclei were observed mainly in the outer hair cells (OHCs), inner hair cells (IHCs), supporting cells and marginal cells. Bax and Bcl-2 immunoreactivity was observed in stria vascularis, OHCs, IHCs and Deiter's cells in the groups harvested at 6 h and 12 h. Bax was expressed most highly at 6 h and Bcl-2 at 12 h. The western blotting method showed that in the group harvested at 24 h, the intensity of Bax and Bcl-2 expression showed no difference compared with those of the control group.
CONCLUSION
The present results suggest that apoptotic mechanism in which Bax and Bcl-2 play an important role begins before 6 h and terminates within 24 h after a single injection of high dose cisplatin.