Toxic Effects of Potassium Bromate and Thioglycolate on Vestibuloocular Reflex Systems of Guinea Pigs and Humans

Abstract

Potassium bromate (KBrO3) and thioglycolate are two components of hair curling solution. The neurotoxic effects of KBrO3 and thioglycolate on the vestibuloocular reflex (VOR) system have not been elucidated. In this paper, we report the adverse effects of KBrO3 and thioglycolate on the VOR system of Hartley-strain guinea pigs. The function of the VOR system was evaluated by caloric test coupled with the electronystagmographic recordings after subcutaneous injection of 20 or 50 mg/kg KBrO3 or 15 mg/kg thioglycolate, either alone or in combination once daily for 14 consecutive days. The results showed that KBrO3 produced abnormal caloric responses in a concentration-dependent manner and thioglycolate enhanced this abnormality. Our clinical patients, 10 female hairdressers exposed to the hair curling solution for 10–30 years revealed a similar dysfunction in the caloric test. The possible mechanism of this adverse effect was studied: the cerebellar-regulated functions such as motor equilibrium performance and spontaneous locomotor activity of guinea pigs were reduced, the enzymatic Na+/K+-ATPase and Ca2+-ATPase activities of cerebellar tissues were significantly decreased, and the loss of Purkinje cells as well as the derangement of the granular cell layer of the cerebellar cortex was revealed after treatment with KBrO3 plus thioglycolate. These findings imply that KBrO3 plus thioglycolate is toxic to the VOR system, mediated by, at least in part, the dysfunction of a higher cerebellar regulatory mechanism. We suggest that the caloric test is a noninvasive method for monitoring the consequences of hazardous exposure of hair curling solution in humans. Our clinical findings together with the animal study imply that clinicians should be alert to the risk of bromate exposure in hairdressers, especially those with vertigo, tinnitus, or hearing loss.