Comparison of the protective efficacy of neurotrophins and antioxidants for vibration-induced trauma

Advances and Challenges in Pharmaceutical Therapies to Prevent and Repair Cochlear Injuries From Noise

Noise induces a broad spectrum of pathological injuries to the cochlea, reflecting both mechanical damage to the delicate architecture of the structures of the organ of Corti and metabolic damage within the organ of Corti and lateral wall tissues. Unlike ototoxic medications, the blood-labyrinth barrier does not offer protection against noise injury. The blood-labyrinth barrier is a target of noise injury, and can be weakened as part of the metabolic pathologies in the cochlea. However, it also offers a potential for therapeutic intervention with oto-protective compounds. Because the blood-labyrinth barrier is weakened by noise, penetration of blood-borne oto-protective compounds could be higher. However, systemic dosing for cochlear protection from noise offers other significant challenges. An alternative option to systemic dosing is local administration to the cochlea through the round window membrane using a variety of drug delivery techniques. The review will discuss noise-induced cochlear pathology, including alterations to the blood-labyrinth barrier, and then transition into discussing approaches for delivery of oto-protective compounds to reduce cochlear injury from noise.

Reactive oxygen species in human inner ear perilymph

CONCLUSIONS

The results reported here provide the first evidence of the production of superoxide, a biologically relevant reactive oxygen species (ROS), in human inner ear perilymph (hIP) in pathological conditions, by the activity of the xanthine dehydrogenase/xanthine oxidase (XA/XO) enzyme system.

OBJECTIVE

To investigate the presence of ROS in hIP.

METHODS

Since damage and apoptosis of inner ear hair cells may occur as a result of ROS-mediated injury, we investigated the presence and production of ROS in 105 hIP samples; 98 collected from patients affected by profound sensorineural hearing loss, during surgery for cochlear implantation, and 7 controls, collected from patients affected by otosclerosis, in case of spontaneous leakage after stapedotomy. ROS production was investigated by spectrophotometric analysis and polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

In hIP samples tested by cytochrome c reduction kinetics, the average superoxide production was 27.34 mumoles per mg of total protein, against 0.36 in controls. Some of these hIP samples, analyzed by cytochrome c reduction kinetics in the presence of xanthine, were found to be positive for ROS-producing XA/XO enzyme. These results were supported by SDS-PAGE analysis.

Soft cochlear implantation: rationale for the surgical approach

Recent advances in cochlear implant technology have focused renewed attention on the preservation of residual hearing. The focus on preservation of residual hearing is driven by the concept of electroacoustic stimulation. This option depends on the insertion of a short cochlear implant electrode into the basal region of the cochlea while preserving native function in the apical region. The desire to preserve residual hearing has led to the development of the soft-surgery cochlear implantation technique. Here, the authors evaluate its various components. Avoiding entry of blood into the cochlea and the use of hyaluronate seem to be reasonably supported, whereas the use of topical steroids is unlikely to be beneficial. The site of entry into the cochlea, the use of contoured or straight devices, and the depth of insertion are also evaluated. The authors highlight the importance of systematic recording of outcomes and surgical events.

Intratympanic treatment of hearing loss with novel and traditional agents

As knowledge of the cellular and molecular pathophysiology behind otopathologies expands, the possibility exists of preventing sensorineural hearing loss and perhaps reversing the loss. Cellular and molecular mechanisms seem to be similar in hearing loss secondary to aging, drug ototoxicity, noise, or other mechanisms. A final common pathway may hinge upon apoptosis. It is likely that anti-apoptotic factors will increasingly be realized as an important intervention strategy for sensorineural hearing loss. Furthermore, it is also possible that mounting a staged attack at the various regions in the pathway leading to cellular damage using a combination of several protective substances such as steroids, antioxidants, neurotrophic factors, anti-apoptotic compounds, and mitochondrial enhancers may prevent hearing loss and even reverse it in some situations. This article has presented some of the molecular and cellular mechanisms for hearing loss and potential ways of treating them. In theory, the delivery of these medications to the inner ear transtympanically would decrease systemic side effects and be more target specific. Because most of the studies conducted to date have been animal studies, randomized, double-blind, placebo-controlled clinical trials would be necessary before the use of these therapies becomes common practice.