Outer hair cells as potential targets of inflammatory mediators

Inner ear sequelae with temporary or permanent sensorineural hearing loss can result from inflammatory processes in the middle ear. Loss of outer hair cells in the base of the cochlea has been noted in otitis media, but it is not known how this damage occurs. Evidence supports the permeability of the round window membrane to substances mediating inflammation in the middle ear, and the presence of white blood cells has been reported in the perilymph. In the present study, the potential cytotoxic effects of two representative inflammatory mediators, endotoxin and free radicals, have been evaluated by use of short-term culture of isolated outer hair cells from the guinea pig cochlea model. Incubation with endotoxins from two gram-negative pathogens increased the rate of hair cell death fourfold to sixfold. Free radicals (generated by exposure of cells to UV light or by excitation of intracellular fluorescent dyes) produced morphologic damage to hair cells within 60 seconds. These latter effects were delayed by addition of free-radical scavengers. It is concluded that inflammatory mediators are cytotoxic to hair cells and therefore are potentially ototoxic if permeating the round window membrane.