Radical Scavenging of Nanoceria in Minimizing the Oxidative Stress‑Induced Loss of Residual Hearing: A Review

Abstract

Among the several unresolved issues, profound/total loss of
low-frequency residual hearing after cochlear implant fixation is the most
frequent event. Even after several attempts such as modifications in the
design of electrodes, improvement in the surgical procedures and use
of protective drugs to minimize the trauma and its after-effects, residual
hearing has been retained in less than 50% patients only. Surgical procedure
and mechanical trauma at the electrode insertion site are thought
to be responsible for excess generation of reactive oxygen species
(ROS) following initiation of inflammatory cytokines resulting into loss of
residual hearing due to programmed cell death of essential inner ear
structures. Though very recent studies have reported the use of conventional
antioxidants to preserve the residual hearing, they have their own
limitations. With the emerging need of better and effective antioxidants,
nanoceria has spurred immense research interest on utilizing its unique
catalytic characteristics for ROS-associated diseases. Nanoceria has
shown effective protection against several ROS-induced damages compared to conventional antioxidants such as vitamin C and vitamin E. The objective of the present work is to develop an understanding about the underlying mechanism of loss of residual hearing and propose a novel method based on delivery of nanoceria to minimize it. The first part of the article highlights the failure of cochlear implants, nature of failures
and revised surgeries due to loss of residual hearing. Subsequently, the
article explores the relation among surgical/mechanical trauma, excess
generation of ROS at electrode insertion site, progressive death of hair
cells and loss of residual hearing. Finally, effectiveness of radical scavenging characteristics of nanoceria along with controlling parameters
and involved mechanisms has been reviewed. The present work also
focuses on the limitations and challenges of nanoceria in clinical applications. Based on the literature review, it is hypothesized that the residual hearing loss is associated with excess generation of ROS and it is proposed that the delivery of effective antioxidants/radical scavengers
having a good longevity and regenerative ability is expected to reduce
the excess level of ROS and retain the residual hearing.