title: Hydrolysis of an acetylthiocholine by pralidoxime iodide (2-PAM).
abstract: Pralidoxime iodide (2-PAM), an antidote approved for the reactivation of inhibited acetylcholinesterase (AChE) in organophosphate poisoning, dose-dependently hydrolyzed an acetylthiocholine iodide (ASCh). The AChE (0.3 U) activity inhibited by VX analog (ENMP, 0.1 microM) increased to approximately 200% of normal levels after a dosage of 5 mM 2-PAM (control 0.132+/-0.012 U/ml, 5 mM 0.253+/-0.026 U/ml). This result indicates that 2-PAM produced a thiocholine from the ASCh by hydrolysis. High-performance liquid chromatography (HPLC) analysis was then performed to further clarify the hydrolysis of ASCh with 2-PAM. It was clear that 2-PAM was converted to acetylated 2-PAM with acetic acid produced from ASCh by hydrolysis. Next, we tried to compare this esterase-like activity of 2-PAM with that of obidoxime, which is known as a strong reactivator of inhibited AChE, and with diacetylmonoxime, known as a weak reactivator. All of these oximes showed esterase-like activity, and their strengths were consistent with those of known reactivators of inhibited AChE. These results indicate that a great deal of the data obtained previously with ASCh relating to the effects of oximes must be rechecked. It is clear that oximes easily hydrolyze ASCh. We therefore strongly caution that the method of determining AChE activity with ASCh is not suitable for examining the effects of oximes.
authors.affiliation: National Research Institute of Police Science, 6-3-1, Kashiwanoha, Kashiwa, Chiba, 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: Tomoko
authors.initials: T
authors.lastname: Akutsu
authors.forename: Takehiko
authors.initials: T
authors.lastname: Takatori
mesh_terms: D000110:Acetylcholinesterase / Q000097:blood / Q000378:metabolism; D000122:Acetylthiocholine / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D000931:Antidotes / Q000737:chemistry* / Q000494:pharmacology; D002417:Cattle; D002801:Cholinesterase Reactivators / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004912:Erythrocytes / Q000201:enzymology; D006868:Hydrolysis; D009768:Obidoxime Chloride / Q000494:pharmacology; D010091:Oximes / Q000737:chemistry; D011220:Pralidoxime Compounds / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D000931:Antidotes; D002801:Cholinesterase Reactivators; D010091:Oximes; D011220:Pralidoxime Compounds; D009768:Obidoxime Chloride; D000122:Acetylthiocholine; D000110:Acetylcholinesterase