Salicylate Initiates Apoptosis in the Spiral Ganglion Neuron of Guinea Pig Cochlea by Activating Caspase-3

• Published in: Neurochemical research 2011-06, Vol.36 (6), p.1108-1115
• Main Authors: Feng, Hao, Yin, Shi-Hua, Tang, An-Zhou, Tan, Song-Hua
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis - drug effects; Biochemistry; Biomedical and Life Sciences; Biomedicine; Caspase 3 - metabolism; Cell Biology; Cochlea - drug effects; Cochlea - enzymology; Cochlea - metabolism; Ganglia, Spinal - cytology; Ganglia, Spinal - enzymology; Ganglia, Spinal - metabolism; Guinea Pigs; Neurochemistry; Neurology; Neurosciences; Original Paper; Salicylic Acid - pharmacology
• ISSN: 0364-3190; 1573-6903
• DOI: 10.1007/s11064-011-0455-9

Salicylate-induced ototoxicity leading to sensorineural hearing loss (SNHL) and tinnitus is well documented. However, the exact mechanisms are poorly defined. Caspase-3 is a member of the class of effector caspases and has been activated in nearly every model of apoptosis. To examine its role in salicylate-induced injury, we subjected guinea pigs to treatment with a specific inhibitor zDEVD-FMK via the round window niche (RWN) followed by a systemic injection of salicylate at a dose of 200 mg·kg −1 ·d −1 i.p. for 10 consecutive days. For those animals administered with salicylate, immunohistochemical studies revealed that caspase-3 was activated in the spiral ganglion neurons (SGNs) and method of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) to identify neuronal apoptosis showed that fragmented nuclei were distributed in Rosenthal’s canal. Topical administration of the zDEVD-FMK at a concentration of 500 mM blocked caspase-3 activation and had an effect in reducing the number of TUNEL-positive auditory neurons. In contrast, the inhibitor at a concentration of 125 or 250 mM caused no variation in the expression of activated caspase-3, or in the ratio of TUNEL-positive neurons. These results indicate that caspase-3 is a crucial mediator of apoptosis induced by salicylate in the primary auditory neuron in vivo, and suggest that the specific inhibitor at a relatively high concentration may be therapeutically beneficial in salicylate-induced apoptosis.