The detrimental effects of potassium bromate and thioglycolate on auditory brainstem response of guinea pigs

Potassium bromate (KBrO3) is known to be an oxidizing agent that is used not only as a food additive, mainly in the bread-making process, but also as a neutralizer in thioglycolate containing hair curling set. Although it has been shown that bromate poisoning could cause severe and irreversible sensorineural hearing loss as well as renal failure, the action mechanism of bromate-induced otoneurotoxicity especially its combination with thioglycolate remains to be studied. In this study, we attempted to investigate the toxic effects of KBrO3 in combination with or without thioglycolate on the auditory brainstem response (ABR) system in the guinea-pigs which was claimed to be very susceptible to the xenobiotics. In a preliminary test, we have found that after consecutive 2 weeks administration, KBrO3 caused a significant prolongation of wave I-III and the interwave latencies of ABR as well as significantly elevated the threshold of hearing, suggesting that the conduction velocity of the peripheral auditory nerve was delayed. By contrast, the absolute latency of wave IV/V and the interwave latency of wave III-V were not significantly prolonged, suggesting that KBrO3 had no effect on the brainstem. This oto-neurotoxic effect of KBrO3 was markedly enhanced by combining with thioglycolate. Our data also indicated that KBrO3 combined with thioglycolate but not KBrO3 alone prominantly caused a decrease of body weight. However, enzymatic activities (including Na+/K+-ATPase and Ca2+-ATPase) and the level of nitric oxide (NO) was significantly affected in the brainstem. Based on these findings, we tentatively conclude that whether KBrO3 alone or KBrO3 combined with thioglycolate induced oto-neurotoxicity majorly through the peripheral auditory nerve rather than via the central brainstem intoxication.