[Experiments on the medicamental treatment of the noise-induced cochlear damage. Part I. The effect of dipyridamol and allopurinol on the RMP of the cochlea (guinea pig) after noise (author's transl)]

Protection and treatment of sensorineural hearing disorders caused by exogenous factors: experimental findings and potential clinical application

During the last decade, there have been numerous interesting findings regarding the roles of neurotrophins, nitric oxide, reactive oxygen species, glutamate receptors, and shock protein in the auditory system. These findings have provided a scientific basis for the development of techniques to protect the auditory system against trauma as well as for the treatment of peripheral hearing disorders. This review focuses on recent advances in experimental prevention and treatment of hearing impairment which are expected to be of clinical value in the near future. Viral vector and non-viral vector gene therapy and transplantation of stem cells are discussed as potential treatments of irreversible sensorineural inner ear damage.

Direct effects of reactive oxygen species on cochlear outer hair cell shape in vitro

Reactive oxygen species (ROS) have been implicated in the ototoxicity of various agents. This study examines the effects of superoxide anion (O2), hydroxyl radical (OH.) and hydrogen peroxide (H2O2), on isolated cochlear outer hair cell (OHC) morphology. OHCs were superfused with artificial perilymph (AP) or AP containing a specific ROS scavenger, and then with AP, ROS system or scavenger plus ROS system for 90 min. The generation of ROS as well as the scavenging properties of other agents were confirmed by specific biochemical assays. Control cells decreased 4.8% in mean length, and showed no obvious membrane damage. Generation of O2. or OH. resulted in high rates (85.7 and 42.9%, respectively) of bleb formation at the synaptic pole, and decreased (O2., 15.2%; OH., 17.3%) mean cell length. Length change and bleb formation rate were H2O2 concentration-dependent. 20 mM H2O2 led to 33.3% decreased mean cell length, and only 20% bleb formation; 0.1 mM H2O2 led to 83.3% bleb formation, with no length decrease. Superoxide dismutase, deferoxamine and catalase protected against O2., OH. and H2O2 effects, respectively. Bleb formation and diminished cell length likely represent differential lipid peroxidative outcomes at supra- and infranuclear membranes, and are consistent with effects of certain ototoxicants.

The protective effects of allopurinol and superoxide dismutase-polyethylene glycol on ischemic and reperfusion-induced cochlear damage

The purpose of this study was to assess the protective effects of allopurinol, a blocker of free oxygen radical (FOR) formation, and superoxide dismutase-polyethylene glycol (SOD-PEG), a scavenger of FORs, on ischemic and reperfusion-induced cochlear damage. Fifteen Wistar Kyoto rats (WKY) were randomly assigned to three groups: (1) a control group (5 animals) that was exposed to 15 minutes of cochlear ischemia by clamping the anterior inferior cerebellar artery (AICA), followed by 15 minutes of reperfusion as documented by laser Doppler flowmetry; (2) a drug-treated group (5 animals) that received allopurinol before ischemia/reperfusion; and (3) a drug-treated group (5 animals) that received SOD-PEG before ischemia/reperfusion. In the control group, the tone burst-evoked compound action potential (CAP) recorded from the round window (RW) of the cochlea was abolished, and the cochlear microphonic (CM) was reduced after ischemia. In contrast, both allopurinol and SOD-PEG-treated animals showed post-reperfusion sensitivity in CAP and CM measures. We interpret these results to indicate that damage to the cochlear from ischemia and subsequent reperfusion can be attenuated by pretreatment with allopurinol or SOD-PEG. This provides indirect evidence that FORs may be partially responsible for cochlear damage resulting from ischemic conditions.