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Laryngoscope. 2013 Mar;123 Suppl 1:S1-14. doi: 10.1002/lary.23902. Epub 2013 Feb 4.

Molecular mechanisms involved in cochlear implantation trauma and the protection of hearing and auditory sensory cells by inhibition of c-Jun-N-terminal kinase signaling.

Author information

1
University of Miami Hearing Research Laboratory, Department of Otolaryngology, University of Miami Miller School of Medicine, Miami, Florida 33136-1015, USA. aeshraghi@med.miami.edu

Abstract

OBJECTIVES/HYPOTHESIS:

To investigate the molecular mechanisms involved in electrode insertion trauma (EIT) and to test the otoprotective effect of locally delivered AM-111.

STUDY DESIGN:

An animal model of cochlear implantation.

METHODS:

Guinea pigs' hearing thresholds were measured by auditory brainstem response (ABR) before and after cochlear implantation in four groups: EIT; pretreated with hyaluronate gel 30 minutes before EIT (EIT+Gel); pretreated with hyaluronate gel/AM-111 30 minutes before EIT (EIT+AM-111); and unoperated contralateral ears as controls. Neurofilament, synapsin, and fluorescein isothiocyanate (FITC)-phalloidin staining for hair cell counts were performed at 90 days post-EIT. Immunostaining for 4-hydroxy-2-nonenal (HNE), activated caspase-3, CellROX, and phospho-c-Jun were performed at 24 hours post-EIT.

RESULTS:

ABR thresholds increased post-EIT in the cochleae of EIT only and EIT+Gel treated animals. There was no significant increase in hearing thresholds in cochleae from either EIT+AM-111 treated or unoperated control ears. AM-111 protection of organ of Corti sensory elements (i.e., hair cells [HCs], supporting cells [SCs], nerve fibers, and synapses) was documented at 3 months post-EIT. Immunostaining of 24-hour post-EIT specimens demonstrated increased levels of HNE in HCs and SCs; increased levels of CellROX and activation of caspase-3 was observed only in SCs, and phosphorylation of c-Jun occurred only in HCs of the EIT-only and EIT+Gel specimens. There was no immunostaining for either HNE, CellROX, caspase-3, or phospho-c-Jun in the organ of Corti specimens from AM-111 treated cochleae.

CONCLUSIONS:

Molecular mechanisms involved in programmed cell death of HCs are different than the ones involved in programmed cell death of SCs. Local delivery of AM-111 provided a significant level of protection against EIT-induced hearing losses, HC losses, and damage to neural elements.

PMID:
23382052
DOI:
10.1002/lary.23902
[Indexed for MEDLINE]

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