Targeting Cholinesterase Inhibitor Poisoning with a Novel Blocker Against Both Nicotinic and Muscarinic Receptors

Oxime reactivators and their in vivo and in vitro effects on nicotinic receptors

Current treatment of organophosphorus poisoning, resulting in overstimulation and desensitization of muscarinic and nicotinic receptors by acetylcholine (ACh), consists of the administration of atropine and oxime reactivators. However, no versatile oxime reactivator has been developed yet and some mortality still remains after application of standard atropine treatment, probably due to its lack of antinicotinic action. In our study, we focused on the interesting non-acetylcholinesterase property of oximes, i.e. antinicotinic effect of reactivators. Two standard reactivators (HI-6, obidoxime) and two new compounds (K027 and K203) were chosen for in vitro (patch clamp) and in vivo (nerve-evoked muscle contraction) testings. Both examinations showed antinicotinic effects of the reactivators. In vitro inhibition of acetylcholine-evoked currents by obidoxime, HI-6 and K203 was equivalent while K027 was less potent. Similar order of potency was observed by the in vivo examinations. We thus confirm previous in vitro results, which describe antinicotinic effects of oxime reactivators, and furthermore, we show in vivo antagonism of oxime reactivators exerted by the inhibition of ACh effect on the nicotinic receptor in the neuromuscular junction. Taking together, the effects of tested oxime reactivators indicate an antagonism on both embryonic and adult form of the muscle nicotinic receptors.

Toxicity of tetramethylammonium hydroxide: Review of two fatal cases of dermal exposure and development of an animal model

To document two cases of patients who were fatally exposed to tetramethylammonium hydroxide (TMAH) on the skin and to establish a rat model to investigate the effects of dermal exposure to TMAH. The charts of two workers who died from occupational accidental exposure to TMAH were reviewed. The 4-hour lethal dose (LD50) of TMAH was determined by applying solutions mimicking the two most common industrially used concentrations (2.38% and 25%) of TMAH to the skin of Sprague-Dawley rats. Exposure of the rat’s skin to 2.38% or 25% TMAH generated LD 50 values of 85.9 mg/kg and 28.7 mg/kg, respectively. Application of either concentration of TMAH to the skin produced a rapid, significant increase in the rate of respiration. The serum concentrations of tetramethylammonium (TMA) also changed significantly with time of exposure to both concentrations of TMAH. The level of blood urea nitrogen decreased significantly in rats exposed to the 2.38% TMAH, and rats exposed to the 25% solution had a significant decrease in the serum concentration of sodium. Injection of atropine after 5 minutes of exposure did not significantly overcome any of the toxic effects observed with either solution of TMAH. The preliminary results in the rat model indicated that the lethality of TMAH cannot be fully explained by the severity of the patients’ chemical burns, and the physiologic effects on respiratory and kidney functions were probably involved.