The hearing loss from exposure to noise and ototoxic drugs share a number of audiological and pathological similarities. Recent research has shown that reactive oxygen species (ROS) may be a common factor in both noise- and drug-induced hearing loss. This review describes three experiments that point to ROS as a causative factor in both noise- and drug-induced hearing loss and antioxidants as a protective agent. In the first experiment, the ears of chinchillas were treated with R-N6-phenylisopropyladenoisine (R-PIA) and exposed to 150-dB impulse noise. The treated ears developed substantially less permanent hearing loss (PTS) and hair cell loss than the untreated ears. One interpretation of this experiment is that R-PIA increases the availability of glutathione (GSH). In the second experiment, the role of GSH was specifically examined. The ears of chinchillas were treated with glutathione monoethylester (GEE), a pro-GSH drug that has been shown to readily cross cell membranes and increase GSH levels. The GEE-treated ears had significantly less PTS and hair-cell loss than the nontreated ear. Previous research has shown that moderate levels of noise exposure can increase a subject's resistance to noise, and also increase the availability of antioxidant enzymes in the cochlea. In the third experiment, chinchillas were given a series of "toughening" exposures (i.e., 6 h of a 0.5-kHz OB noise at 95 dB for 10 days). After the series of "toughening" exposures, the subjects were treated with carboplatin, a drug that causes massive inner-hair-cell lesions in the chinchilla. The animals receiving the 10-day toughening exposure developed less PTS and hair-cell loss than the control animals.
Hydroxyl terminated polybutadiene bound 2,2-methylenebis (4-methyl-6-tert-butylphenol) (HTPB–IPDI–MPH) was prepared by binding 2,2-methylenebis (4-methyl-6-tert-butylphenol) (MPH) onto hydroxyl terminated polybutadiene (HTPB) using isophorone diisocyanate (IPDI) as bridging agent. The structure of HTPB–IPDI–MPH was characterised by Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, 13C NMR spectroscopy and gel permeation chromatography. The thermal stability of HTPB–IPDI–MPH was studied by thermal gravity analysis (TGA). The thermo-oxidative aging resistance of HTPB–IPDI–MPH for natural rubber (NR) vulcanizates was investigated by mechanical properties, cross-link density assessment and TGA, and then, possible mechanism of thermo-oxidative aging resistance of HTPB–IPDI–MPH for NR was proposed. The results showed that HTPB–IPDI–MPH had better thermal stability than the corresponding low molecular antioxidant MPH. The thermo-oxidative aging resistance and thermo-oxidative degradation of NR vulcanizates containing HTPB–IPDI–MPH were better than that of NR vulcanizates containing MPH obviously, indicating that the synergetic effect of phenolic –OH and –NHCOO– groups existed in HTPB–IPDI–MPH, which could enhance ability to scavenge free radical.
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