title: Effects of oximes on mitochondrial oxidase activity.
abstract: Oximes, including 2-pyridinealdoxime methiodide (2-PAM), are reactivators of acetylcholinesterase (AChE) inhibited by organophosphate poisoning. Unfortunately, their clinical use has been limited by their toxicity. To investigate the mechanism of this toxicity, the effects of oximes on the enzymes choline oxidase (ChOD) and cytochrome c oxidase (CyCOD) of the respiratory chain in mitochondria were examined. The oximes 2-PAM, obidoxime, and diacetylmonoxime significantly (P<0.01) inhibited ChOD activity, and the extent of inhibition correlated with the ability to reactivate inhibited AChE. When ChOD activity in mitochondrial extracts was tested, 2-PAM inhibited the activity by 75%, obidoxime and diacetylmonoxime did not significantly inhibit it, and 4-[(hydroxy-imino)methyl]-1-decylpyridinium bromide (4-PAD), which has greater toxicity, increased the amount of product generated in the assay to approximately 200% of normal levels. Similarly, 2-PAM inhibited the activity of CyCOD in mitochondrial extracts whereas obidoxime and diacetylmonoxime did not. One explanation for these findings is that, in addition to their inhibition of mitochondrial oxidases, the oximes may produce excessive reactive oxygen species such as H(2)O(2) in the mitochondrial fraction, which may account for some of their toxicity. This is a preliminary report related to the toxicities of oximes that may participate in the inactivation of mitochondrial oxidase enzymes. This hypothesis should be further investigated by in vivo study, including kinetic determination and free radical work.
authors.affiliation: National Research Institute of Police Science, 6-3-1, Kashiwanoha, Kashiwa, Chiba 277-0882, Japan. sakurada@nrips.go.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Sakurada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ikegaya
authors.forename: Hikoto
authors.initials: H
authors.lastname: Ohta
authors.forename: Hisayo
authors.initials: H
authors.lastname: Fukushima
authors.forename: Tomoko
authors.initials: T
authors.lastname: Akutsu
authors.forename: Ken
authors.initials: K
authors.lastname: Watanabe
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D000818:Animals; D002800:Cholinesterase Inhibitors / Q000633:toxicity; D002801:Cholinesterase Reactivators / Q000737:chemistry / Q000633:toxicity*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000201:enzymology*; D010091:Oximes / Q000737:chemistry / Q000633:toxicity*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002800:Cholinesterase Inhibitors; D002801:Cholinesterase Reactivators; D010091:Oximes; D000255:Adenosine Triphosphate; D000429:Alcohol Oxidoreductases; C019888:choline oxidase; D003576:Electron Transport Complex IV