Cathepsin D activity in otosclerotic bone and perilymph

Otosclerotic bone and perilymph samples obtained during stapedectomy operations from patients suffering from pure conductive hearing loss of at least 40 dBs air-bone gap at 500 Hz. Control perilymph samples derived from patients suffering from round window membrane rupture or Meniere's disease. Enzyme activities were determined using a synthetic fluorogenic substrate by fluorescence spectrophotometry. No significant differences have been found between the protein content of otosclerotic and normal or non-otosclerotic perilymph samples. Cathepsin D activity was significantly higher (p less than 0.001) in the otosclerotic perilymph samples. Otosclerotic stapes footplate contained more activity than normal meatal cortical bone as well, though the difference was not significant. Biological significance of the elevated Cathepsin D activity must be considered.