Hydrolysis of an acetylthiocholine by pralidoxime iodide (2-PAM).

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 (0.3U) activity inhibited by VX analog (ENMP, 0.1μM) increased to approximately 200% of normal levels after a dosage of 5mM 2-PAM (control 0.132±0.012U/ml, 5mM 0.253±0.026U/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.