Ingrid Nordgren

Stereoselectivity of enzymes involved in toxicity and detoxification of soman

The fate of the four stereoisomers of soman [0-(1,2,2-trimethylpropyl)-methyl-fluoro phosphonate] has been studied a) in vivo in mouse blood and liver after IP injection of 0.75 × LD50 Rc- and Sc-soman respectively, and b) in vitro upon incubation wih acetyl- und pseudocholinesterase, aliesterase and phosphorylphosphatase. The analytical method used is based on gas chromatography — mass spectrometry with deuterated internal standard.Most soman disappeared very rapidly from blood and liver. In liver, SCRP and RCRP, the two isomers that preferentially react with cholinesterase, could be detected. The level of SCRP, which was higher than that of RCRP, could be followed for 17–18 h. In blood only SCRP could be detected. The amounts found were fairly constant during the time period 2 min to 4h, and it could even be detected 17–18 h after soman administration.

Analysis of Succinylcholine in Tissues and Body Fluids by Ion-Pair Extraction and Gas Chromatography-Mass Spectrometry

The neuromuscular blocking agent succinylcholine (SCh) has been identified and quantitated in biological material using gas chromatography-mass spectrometry. The bisquaternary ammonium compound SCh is extracted from tissue homogenates or body fluids into dichloromethane as an ion pair with hexanitrodiphenylamine (DPA). The evaporated ion pair residue is demethylated with sodium benzenethiolate to form the corresponding tertiary amine which is identified and quantitated by gas chromatography-mass spectrometry using a glass capillary column coated with SE 52. In the quantitative analysis deuterated SCh is used as internal standard. The instrument is focussed on m/z 58 for demethylated SCh and m/z 62 or 64 for the internal standard. Concentrations as low as 5 ng SCh iodide/g tissue or body fluid are easily detected.

Quantitation of Metrifonate and Dichlorvos in Blood and Tissues by Gas Chromatography - Mass Spectrometry

Metrifonate (0,0-dimethyl-(1-hydroxy-2,2,2-trichloroethyl)-phosphonate) is an organophosphorus compound where there are excellent possibilities to make studies in man. Metrifonate and its rearrangement product dichlorvos (2,2-dichlorovinyl dimethyl phosphate, DDVP) were studied in human blood from schistosomiasis patients treated with Bilarcil. A mass fragmentographic technique was employed. Deuterium labelled variants of the substances were used, both as internal standards and to compensate for DDVP formed during the workup procedure. The amount of DDVP in plasma was about 1% of the amount of metrifonate. In erythrocytes the corresponding amount of DDVP in percent of metrifonate was half or less. Both compounds reached peak levels within two hours and were detectable for at least eight hours. The results were compared to erythrocyte and plasma cholinesterase determinations. Levels of metrifonate and DDVP, together with cholinesterase activity, have also been studied in mouse brain, liver and kidney. It is proposed that metrifonate acts as a slow release formulation for DDVP. Clearance of metrifonate in man occurs primarily via DDVP. Mild vertigo subsiding in a few hours was the most common side-effect.

Distribution and Elimination of the Stereoisomers of Soman and Their Effect on Brain Acetylcholine

The four stereoisomers of soman (O-(1,2,2-trimethylpropyl)-methyl-fluorophosphonate) have been analyzed in vivo in mouse blood and tissues after administration of doses corresponding to 0.75 X LD50 of the two diastereoisomeric pairs of soman (Sc- and Rc-soman). The disappearance of the four isomers has been studied in vitro in the presence of enzymes involved in the toxicity and detoxification of soman, e.g., acetyl- and pseudocholinesterase, aliesterase, and phosphorylphosphatase. The effect of Sc- and Rc-soman on brain acetylcholine was studied in the mouse. The analytical methods used are based on gas chromatography-mass spectrometry with deuterated internal standards. Rc-Rp- and ScRp-soman, the two isomers that preferentially react with acetylcholinesterase, were found in blood and liver. In liver the concentration of ScRp was higher than that of RcRp and could be followed for 18 hr. In blood only ScRp could be found. Its presence there could be followed during 18 hr. The levels were, however, lower than in liver. The results indicate that the liver might be a depot for soman and that ScRp might be responsible for the delayed intoxication noted after treatment with antidotes. Rc-soman was found to have a more pronounced effect on the acetylcholine synthesizing system than has Sc-soman, which might explain its higher in vivo toxicity.

Toxicological Limitations to Cholinomimetic Therapy

Within the amount of space available, it is not possible to deal with all cholinomimetic agents. We have therefore limited ourselves to two compounds, THA (tetrahydroaminoacridine) and metrifonate. Due to its use in AD, a considerable number of clinical papers exist concerning THA, but basic toxicology data seem to be largely missing. With regard to metrifonate, a considerable number of both clinical and toxicological data exist due to its use as an insecticide and in the therapy of schistosomiasis. A short review of this compound was given at the last symposium on AD (Giacobini E and Becker R, 1988) and metrifonate was suggested as a possible treatment in AD. So far, only one publication has appeared in this particular field (Becker et al., 1990). This review will focus mainly on toxicological data in review papers. It also includes a section on butonate that can possibly be of use to achieve a prolonged cholinesterase inhibition (ChEI).

Succinylcholine — Clinical and Toxicological Aspects

The history of succinylcholine (SCh) from 1906 up to date has been well documented by Dorkins (1982). It was introduced as a muscle relaxant by several groups around 1950. Its short lasting effect made it ideal for intubation before surgery. For prolonged muscle relaxation it has been largely superseded by other synthetic compounds. Untoward effects have been noted, such as prolonged apnea, cardiovascular effects and muscle fasciculations. In 1954 SCh was introduced in veterinary medicine as a casting agent for large animals (Hansson and Edlund, 1954; Hansson, 1958).