Bromate is frequently detected in tap water and bottled water, since it is an inorganic oxyhalide disinfection by-product, which is formed when drinking water supplies undergo ozonation, an advanced wastewater treatment technique. 1,2) Potassium bromate (KBrO 3 ) is a renal carcinogen and is classified as a group 2B (possibly carcinogenic to humans) by the International Agency for Research on Cancer, 3,4) as are bleomycin and carbon tetrachloride, etc. However, KBrO 3 is generally used as an oxidizing agent for the treatment of wheat flour and as a constituent in cold-wave hair solutions. Acute exposure to KBrO 3 causes not only kidney failure 5,6) but also neuropathological disorder, such as vertigo, tinnitus, and hearing loss. 7,8) Potassium bromate is known to cause oxidative modification of lipid, protein and DNA bases in the kidney, which has usually been thought to contribute to its renal carcinogenic properties.9,10) Methaemoglobinemia and cyanosis in the incipient stage of renal damage are also known to be caused by KBrO 3 .11) Acquired but not heritable methaemoglobinemia is thought to be caused by the oxidative modification of haemoglobin (Hb) by certain chemicals, such as amyl nitrite and acetanilide, since the iron in the haem rings of Hb is in the Fe 2ϩ state and Hb oxidation is speeded up by the presence of nitrite or certain transition metal ions, especially copper.12) So far, KBrO 3 has been regarded as the direct oxidant of Hb as chlorate 13) but no details of KBrO 3 -induced elevation of methaemoglobin (MetHb) concentration in blood have been examined. Previously KBrO 3 -induced renal oxidative stress and kidney damage were reported to be mainly attributable to the reduction of cytoplasmic glutathione peroxidase (GPx) activity, probably caused by the enhanced production of NO and peroxynitrite (ONOO Ϫ ).14) Therefore, it is possible that KBrO 3 -induced methaemoglobinemia is also related to the change in GPx activity resulting from the enhancement of NO production in blood vessels. In this report, the effects of the GPx mimic ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) on the elevation of MetHb concentration, the enhancement of NO production and the attenuation of GPx activity by KBrO 3 are examined to clarify the significant impact of NO on KBrO 3 -induced methaemoglobinemia. In addition, the effect of ebselen on KBrO 3 -induced renal oxidative stress and kidney damage was comparatively investigated.
MATERIALS AND METHODS
ChemicalsGlutathione reductase from bakers yeast (EC 1.6.4.2), nitrate reductase from aspergillus species (EC 1.6.6.2), Hb, MetHb, reduced glutathione (GSH) and oxidized glutathione were purchased from Sigma Chemical Co. (St. Louis, MO, U.S.A.). 2,4-Dinitrophenylhydrazine (DNPH) was obtained from Tokyo Chemical Industry Co. (Tokyo, Japan). KBrO 3 , potassium cyanide, sodium hydrosulfite and ebselen were purchased from Wako Pure Chemical Industries (Osaka, Japan). 1-Hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene (NOC-7), 3-(4-morpholinyl) sydnonimine hydroc...