Some ototoxic drugs destroy cochlear support cells before damaging sensory hair cells

Abstract

A wide variety of ototoxic drugs are capable of damaging the sensory hair cells in the mammalian cochlea resulting in permanent hearing. However, the toxic properties of these drugs suggest that some could potentially damage cochlear support cells as well. To test the hypothesis, we treated postnatal day three rat cochlear cultures with toxic doses of gentamicin, cisplatin, mefloquine and cadmium. Gentamicin primarily destroyed the hair cells and disrupted the intercellular connection with the surrounding support cells. Gentamicin-induced hair cell death was initiated through the caspase-9 intrinsic apoptotic pathway followed by activation of downstream executioner caspase-3. In contrast, cisplatin, mefloquine and cadmium initially damaged the support cells and only later damaged the hair cells. Support cells death was initiated through the caspase-8 extrinsic apoptotic pathway followed later by downstream activation of caspase-3. Cisplatin, mefloquine and cadmium significantly reduced the expression of actin and laminin, in the extracellular matrix, leading to significant disarray of the sensory epithelium.