calpain and Hearing-Loss--Noise-Induced

Our previous studies demonstrated that intense noise-induced hearing loss might be at least in part due to an oxidative stress-induced decrease in the level of gap junction-composing protein connexins in the spiral ligament (SL) of the cochlear lateral wall structures in mice. Further, an in vivo exposure of mice to intense noise activates calpain in the cochlear SL. Based on these studies, we sought to determine whether a calpain inhibitor would prevent an intense noise exposure from causing hearing loss, disruption of gap junction-mediated intercellular communication (GJIC) in the SL. An exposure of mice to intense noise (8-Hz octave band noise, 110-dB sound pressure level, 1h) produced permanent hearing loss and cochlear hair cell death. The results of an ex vivo assay using gap-fluorescence recovery after photobleaching of dissected lateral wall structures revealed that the intense noise disrupted GJIC in the cochlear SL at day-7 post exposure. A prior intracochlear injection of the calpain inhibitor PD150606 significantly abolished this noise-induced hearing loss on days 5 and 7 post exposure. Similarly, PD150606 prevented noise-induced hair cell death and the GJIC disruption on day-7 post exposure. The intense noise temporarily enhanced the gene expression of calpain subtypes Capn1 and Capn2 immediately after exposure. Taken together, our data suggest that calpain inhibitor alleviated the noise-induced hearing loss, at least in part, by preventing disruption of GJIC in the cochlear SL. It possible that calpain inhibitors would be useful as a candidate of therapeutic drugs for sudden sensorineural hearing loss.

Topics: Acrylates; Animals; Calpain; Cell Communication; Cell Death; Gap Junctions; Hair Cells, Auditory; Hearing Loss, Noise-Induced; Male; Mice; Permeability; Protease Inhibitors; Spiral Ligament of Cochlea

Free radical and calcium buffering mechanisms are implicated in cochlear cell damage that has been induced by sound trauma. Thus in this study we evaluated the therapeutic effect of a novel dual inhibitor of calpains and of lipid peroxidation (BN 82270) on the permanent hearing and hair cell loss induced by sound trauma. Perfusion of BN 82270 into the scala tympani of the guinea pig cochlea prevented the formation of calpain-cleaved fodrin, translocation of cytochrome c, DNA fragmentation and hair cell degeneration caused by sound trauma. This was confirmed by functional tests in vivo, showing a clear dose-dependent reduction of permanent hearing loss (ED50 = 4.07 microM) with almost complete protection at 100 microM. Furthermore, BN82270 still remained effective even when applied onto the round window membrane after sound trauma had occurred, within a therapeutic window of 24 h. This indicates that BN 82270 may be of potential therapeutic value in treating the cochlea after sound trauma.

Topics: Action Potentials; Animals; Apoptosis; Calpain; Carrier Proteins; Cochlea; Cysteine Proteinase Inhibitors; Cytochromes c; Dipeptides; DNA Fragmentation; Electrophysiology; Female; Guinea Pigs; Hair Cells, Auditory; Hearing Loss, Noise-Induced; Immunohistochemistry; Lipid Peroxidation; Microfilament Proteins; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Round Window, Ear; Tympanic Membrane

The purpose of this study was to evaluate the long-term safety of administering leupeptin (1 mg/ml in Hank's Balanced Salt Solution) to the round window membrane by investigating its effects on cochlear blood flow, auditory sensitivity (i.e., auditory brainstem response), and cochlear histology. A comparison of baseline and posttreatment measurements of cochlear blood flow and mean arterial blood pressure in guinea pigs revealed no significant changes. Auditory brainstem response measurements revealed no significant changes in auditory threshold shifts when compared to controls at the 2-, 4-, 6-, and 8-week time points. Furthermore, poststudy surface preparations of the organs of Corti and cytocochleograms from leupeptin-treated ears and controls revealed no significant hair cell losses. These data suggest that the prolonged administration of leupeptin (1 mg/ml at a rate of 0.5 microliter/hr for 8 weeks) to the round window membrane is not ototoxic. This study may serve as a basis for future clinical trials of leupeptin administration for the prevention or treatment of noise-induced hearing loss and the management of tinnitus.

Topics: Animals; Calpain; Cochlea; Evoked Potentials, Auditory, Brain Stem; Guinea Pigs; Hearing Loss, Noise-Induced; Leupeptins; Male; Neuroprotective Agents; Protease Inhibitors; Random Allocation; Regional Blood Flow; Tinnitus

Calpains, a family of calcium activated proteases, promote the breakdown of cellular proteins, kinases, phosphatases and transcription factors. Calpain inhibitors attenuate some neurodegenerative processes in certain cell types. Here we show that leupeptin, a potent calpain inhibitor, protects the sensory hair cells in the inner ear from acoustic overstimulation (48 h, 100 or 105 dB SPL, octave band noise at 4 kHz). Acoustic overstimulation caused a significant increase in calpain immunolabeling in the sensory epithelium suggesting a possible role in noise-induced cochlear degeneration. Infusion of leupeptin into the inner ear significantly reduced the amount of sensory cell loss from acoustic overstimulation. However, leupeptin did not protect against hair cell loss from the ototoxic drug, carboplatin.

Topics: Animals; Antineoplastic Agents; Calpain; Carboplatin; Chinchilla; Enzyme Inhibitors; Hair Cells, Auditory; Hearing Disorders; Hearing Loss, Noise-Induced; Immunohistochemistry; Leupeptins; Organ of Corti