Development of a safe dexamethasone-eluting electrode array for cochlear implantation

Abstract

Objectives

Cochlear implantation can result in trauma leading to increased tissue response and loss of residual hearing. A single intratympanic application of the corticosteroid dexamethasone is sometimes used clinically during surgery to combat the potential effect of trauma on residual hearing. This project looked at the safety and efficacy of dexamethasone eluted from an intracochlear array in vivo.

Methods

Three trials were conducted using normal hearing adult guinea pigs implanted with successive iterations of dexamethasone-eluting (DX1, DX2, and DX3) or non-eluting (control) intracochlear electrode arrays. The experimental period for each animal was 90 days during which hearing tests were performed at multiple time points.

Results

There was no significant difference between matched control array and dexamethasone array groups in terms of spiral ganglion neuron density, organ of Corti condition, or fibrosis and ossification. A cochleostomy seal was present in all implanted cochleae. There were no differences in the degree of hearing threshold shifts between DX1 and DX3 and their respective control arrays. Cochleae implanted with DX2 arrays showed less hearing loss and marginally better spiral ganglion neuron survival than their control array counterparts. Post-explant inspection of the DX2 and DX3 arrays revealed a difference in pore density following dexamethasone elution.

Conclusion

The dexamethasone doses used were safe in the guinea pig cochlea. Dexamethasone did not inhibit formation of a cochleostomy seal. The level of hearing protection afforded by dexamethasone eluting from an intracochlear array may depend upon the degree of elution and level of trauma inflicted.

Keywords:

• Cochlear implantation
• Dexamethasone
• Corticosteroid
• Drug delivery
• Guinea pig
• Hearing loss

Acknowledgements

We acknowledge the financial support of the HEARing CRC, established and supported under the Australian Government's Cooperative Research Centres Programme. The Igor Pro ABR analysis package was created by, and used with permission from, Robert Shepherd's research group currently funded by the National Institutes of Health contract NIDCD HHS-N-263-2007-0053c. We would like to thank James Fallon, Helen Feng, Rodney Millard, Elisa Borg, Sue Pierce, and the staff of the Biological Research Centre. We also thank Andrew Chang, Hayden Eastwood, Jacqueline Andrew, Ricki Minter, Brianna Flynn, Leon Heffer, and Leon Winata for their valued contribution to this work.