Levels of metrifonate and dichlorvos in plasma and erythrocytes during treatment of schistosomiasis with Bilarcil

A method for the simultaneous quantitation of metrifonate (0,0-dimethyl-(1-hydroxy-2,2,2-trichloroethyl)-phosphonate) and dichlorvos (2,2-dichlorovinyl dimethyl phosphate, DDVP) in human blood has been worked out. It is based upon multiple labelling of the compounds with deuterium and gas phase analysis using the mass spectrometer as a selective detector. The amount of DDVP in plasma is about 1% of the amount of metrifonate. In erythrocytes the corresponding amount of DDVP is 0.5% or less of metrifonate. Both compounds reach peak levels in blood within two hours after oral dosing and are detectable for at least eight hours. Cholinesterase activity in plasma reaches zero levels within 15 min. and remains inhibited for more than eight hours. Red blood cell cholinesterase is inhibited only 60-80%. According to kinetic calculations, clearance of metrifonate occurs primarily via dichlorvos. If dichlorvos is the only active component, which in all likelihood it is, it's slow release may be important in the schistosomicidal effect. Clinical data in seven metrifonate treated patients revealed that mild vertigo subsiding in a few hours was the most common side effect.

Liver tumour promoting activity of 3,4,5,3',4'-pentachlorobiphenyl and its interaction with 2,3,7,8-tetrachlorodibenzo-p-dioxin

This study was undertaken to compare the tumour promoting effects induced by 3,4,5,3',4'-pentachlorobiphenyl (PCB 126) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In addition, interactive effects in rats treated with combinations of PCB 126 and TCDD were studied. Partially hepatectomized female Sprague-Dawley rats were initiated with nitrosodiethylamin. After 5 weeks of recovery the promotion treatment started and continued for 20 weeks. The results from the present study demonstrate that PCB 126 elicit approximately 10% of TCDD's tumour promoting activity measured as enhancement of the development of gamma-glutamyl-transpeptidase-positive altered hepatic foci in the liver. The factor required for the PCB to match the response of TCDD was adopted as a toxic equivalency factor and was in this case 0.1, which is the same as the factor suggested by Ahlborg et al. (1994). In the groups treated with a mixture of PCB 126 and TCDD the tumour promoting effect indicated an additive response. This result suggests that PCB 126 and TCDD act by the same mechanistical pathway, which in turn, supports that the toxic equivalency factor-concept can be used for TCDD-like tumour promoters.

Relative tumour promoting activity of three polychlorinated biphenyls in rat liver

The relative tumour promoting activity of three structurally and toxicologically diverse polychlorinated biphenyls (3,4,5,3',4'-penta- 2,3,4,3',4'-penta- and 2,4,5,2',4',5'-hexachlorobiphenyl) was measured in an initiation/promotion assay in nitrosodiethylamine-initiated female Sprague-Dawley rats. The congeners under study were administered by once-weekly subcutaneous injections for 20 weeks. Evaluation of the development of gamma-glutamyl transpeptidase (GGT)- and glutation transferase P (GST-P)-positive hepatic foci showed that all congeners promoted altered hepatic foci, although 3,4,5,3',4'-pentachlorobiphenyl was far more potent. The volume fraction of the liver occupied by GGT-positive tissue in the 3,4,5,3',4'-pentachlorobiphenyl-treated animals (100 micrograms/kg per week) was 23%, while the volume fractions of altered liver tissue in the rats treated with 2,3,4,3',4'-pentachlorobiphenyl (5000 micrograms/kg per week) and 2,4,5,2',4',5'-hexaCB (20,000 micrograms/kg per week) were 1.2 and 2.3, respectively. The enhancement of GGT- and GST-P-positive foci was accompanied by an increased incidence of histological changes in the livers.

Metrifonate and tacrine: a comparative study on their effect on acetylcholine dynamics in mouse brain

Tetrahydroaminoacridine (THA) and metrifonate are cholinesterase inhibitors used in the treatment of Alzheimer's disease. In experimental animals they inhibit acetylcholinesterase activity and have been reported to increase levels of brain acetylcholine. This paper presents results from studies of their effect at two dose levels on the dynamics of acetylcholine in mouse brain. Metrifonate at two doses (10 and 30 mg/kg intraperitoneally), known to cause cholinesterase inhibition, had no effect on levels of acetylcholine or choline or on the rate of synthesis of acetylcholine. THA (3 mg/kg intraperitoneally) had no effect on levels of acetylcholine and choline but had a shortlasting decreasing effect on the synthesis rate of acetylcholine. THA (10 mg/kg intraperitoneally) increased levels of acetylcholine and choline and markedly decreased the synthesis rate of acetylcholine. At this dose, the animals showed severe cholinergic effects, e.g. tremor and salivation. It is suggested that a moderate cholinesterase inhibition in brain facilitates cholinergic nerve transmission which is obtained at a broader dose range for metrifonate than for THA.

Intoxications with anticholinesterases: effect of different combinations of antidotes on the dynamics of acetylcholine in mouse brain

Intoxications with organophosphorus compounds are normally treated with a mixture of atropine and an enzyme regenerating oxime. The addition of diazepam to the conventional drug therapy is reported to greatly improve the antidotal effect. The implication of the cholinergic system in such intoxications prompted us to study the effect of different combinations of antidotes on the acetylcholine (ACh) synthesizing system in mouse brain in vivo. The antidotes studied in this paper are diazepam, HI-6 and 1-hyoscyamine, the active enantiomer of atropine. Diazepam decreases the synthesis rate of ACh both when administered separately and in combination with 1-hyoscyamine and HI-6. This is in contrast to 1-hyoscyamine which, in addition to blocking muscarinic receptors, also increases the release and rate of synthesis of ACh, which probably is an unfavourable effect of the antidote. This might at least partly explain the advantage of combining 1-hyoscyamine and an oxime with diazepam in intoxications with anticholinesterases. Mice administered soman (0.75 x LD50), after pretreatment with the three-drug combination of antidotes, show no cholinergic symptoms despite a 50% increase in endogenous ACh. The rate of synthesis of ACh in these mice is in the same range as in animals administered diazepam alone. Mice administered the same dose of soman with no antidotal pretreatment suffer from severe tremor and salivation, and have a strongly reduced synthesis rate of ACh.

Relative liver tumour promoting activity and toxicity of some polychlorinated dibenzo-p-dioxin- and dibenzofuran-congeners in female Sprague-Dawley rats

The polychlorinated dibenzo-p-dioxins/dibenzofurans 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) were studied for liver tumour promoting activity in a medium-term altered foci assay in nitrosamine-initiated female Sprague-Dawley rats. The congeners under study were administered by weekly subcutaneous injections at three dose levels for 20 weeks. Evaluation of gamma-glutamyltranspeptidase (GGT+), altered hepatic foci development, showed that all congeners studied acted as potent promoters of hepatocarcinogenesis. TCDD and PeCDD were virtually equipotent as enhancers of foci development while PeCDF displayed approximately ten per cent of the activity of the dioxins. Analysis of the dioxin- and furan-congeners by gas chromatography/mass spectroscopy (GC/MS) technique showed that the retention of PeCDD and PeCDF in liver tissue was approximately 7 and 20 times, respectively, as high as the retention of TCDD. Based on the concentration of the respective congener in liver tissue, PeCDD and PeCDF were 0.14 and 0.007 times as active as TCDD as promoters of foci development. The dose related enhancement of GGT+ foci development induced by the PCDD/PCDF congeners was accompanied by an increased incidence of histological changes in the liver.

Quantitative determination of arsenocholine and acetylarsenocholine in aquatic organisms using pyrolysis and gas chromatography/mass spectrometry

A method for qualitative and quantitative analysis of trace amounts of quaternary organoarsenicals such as arsenocholine and acetylarsenocholine has been developed. The method is based on pyrolysis, gas chromatography/mass spectrometry and use of deuterium-labelled internal standards. Arsenocholine and acetylarsenocholine have been estimated in fish from arsenic-polluted brackish water and compared with the same species of fish from unpolluted water. The investigation also includes some fish and crustacea from marine water. The presence of arsenocholine and acetylarsenocholine in different aquatic organisms indicate the existence of a general metabolic pathway for these compounds in aquatic ecosystems.

Effects of diazepam on muscarinic acetylcholine receptor binding in vivo and on oxotremorine-induced tremor and hypothermia in mice

Diazepam has previously been shown to affect the acetylcholine synthesizing system in mouse brain. This paper reports studies on the effect of diazepam on muscarinic receptor density and on pharmacological effects of oxotremorine. The receptor density was studied using a new technique that allows such studies to be performed in vivo under physiological conditions. The method is based on the fact that L-hyoscyamine, the active antipode of atropine, binds specifically to muscarinic receptors in the brain, and can be measured with high sensitivity by gas chromatography--mass spectrometry. Diazepam was found to modify the binding properties of muscarinic receptors in CNS, thereby decreasing the functional receptor pool. It also prevented tremor induced by the muscarinic agonist oxotremorine. Diazepam could however not prevent the hypothermia induced, but rather accentuated this effect of oxotremorine. It is concluded that diazepam, directly or indirectly, influences the effect of cholinergic stimulators by modulating the size of the muscarinic receptor pool.

Effects of diazepam on blood choline and acetylcholine turnover in brain of mice

The effect of diazepam on the acetylcholine (ACh) synthesizing system has been studied in mouse brain in vivo. ACh and choline (Ch) were analyzed by gas chromatography - mass spectrometry using deuterated internal standards. Turnover of ACh was studied by following the incorporation of Ch into ACh after an intravenous injection of [2H6]-Ch. The mice were killed by focussed microwave irradiation on the head. Diazepam was found to increase the endogenous level of Ch, while the concentration of [2H6]-Ch was only half of that of the controls. The incorporation of [2H6]-Ch into [2H6]-ACh was decreased, while the endogenous level of ACh was slightly increased. The turnover rate of ACh was decreased, consistent with a decrease in neuronal excitability induced by diazepam. The elevated endogenous Ch-level and the lower concentration of [2H6]-Ch in the brain, might be explained by an effect of diazepam on the Ch-transport across the blood-brain barrier. This theory is supported by experiments where levels of endogenous and [2H6]-labelled Ch were analyzed in blood following an intravenous injection of [2H6]-Ch. The [2H6]-Ch was found to be eliminated faster in blood from diazepam treated mice. The increased blood level of endogenous Ch, induced by the [2H6]-Ch injection also returned more rapidly to normal in these animals. This is consistent with peripheral Ch being eliminated faster when the central Ch supply is decreased.

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.

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 X LD50 RC- and SC-soman respectively, and b) in vitro upon incubation with 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.

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.

Plasma levels of metrifonate and dichlorvos during treatment of schistosomiasis with bilarcil

Metrifonate (0,0-dimethyl-[1-hydroxy-2,2,2-trichloroethyl]-phosphonate), and its rearrangement product dichlorvos (2,2-dichlorovinyl dimethyl phosphate) (DDVP), were studied in plasma from two patients with schistosomiasis who were treated with Bilarcil. A mass fragmentographic technique was used. Isotopic variants of the substances were used as internal standards and to compensate for DDVP formed during the workup procedure. The results were related to erythrocyte and plasmacholinesterase determinations. The method described makes it possible to study pharmacokinetics in man and to relate this information to therapeutic effects. It is proposed that metrifonate acts as a slow release formulation for DDVP.

Metrifonate. Summary of toxicological and pharmacological information available

The organophosphorus compound 0,0-dimethyl-(1-hydroxy-2,2,2-trichloroethyl)-phosphonate was introduced as an insecticide, trichlorfon, in 1952 (Lorenz et al., 1955) and as a drug, metrifonate, in the treatment of schistosomiasis in 1960 (Lebrun and Cerf, 1960). This organophosphorus compound is unique in that it has been claimed not to be a direct acting cholinesterase inhibitor but being transformed nonenzymatically into an active component dichlorvos, 2, 2-dichlorovinyl dimethyl phosphate (DDVP). The evidence for this transformation has mostly been indirect. Recently it has been proved chemically and quantitatively that this transformation occurs in the animal body (Nordgren et al., 1978). Metrifonate is the sole organophosphorus compound currently studied clinically in schistosomiasis. A substantial therapeutic effect is obtained only in Schistosoma haematobium infections. In this review on available data of metrifonate it is suggested that further more detailed studies of both S. haematobium and S. mansoni are necessary. This should include studies of the enzymic properties of the worms and the reaction of their esterases towards both metrifonate and DDVP as well as the pharmacokinetics of these compounds in man. In addition there are still unsolved discrepancies reported regarding organ toxicity of the compound which may, however, be due to different grades of parity of the test material.

Transformation and action of metrifonate

Chemical formation of dichlorvos (2, 2-dichlorovinyl dimethyl phosphate) was found to occur in mouse brain after i.p. injection of metrifonate (2, 2, 2-trichloro-1-hydroxyethyl dimethyl phosphonate). A mass fragmentographic technique was used. Different isotopic variants were used both as internal standards and to compensate for dichlorvos formed during the workup procedure. The dichlorvos formed in vivo was found to have its maximal concentration a few minutes after the maximum of the metrifonate itself. The effect of metrifonate and dichlorvos on acetylcholine levels, acetylcholinesterase activity and synthesis rate of acetylcholine in mouse brain was also studied. In all three cases the effect of metrifonate was found to be prolonged and delayed as compared to the effect of dichlorvos. It is concluded that metrifonate acts as a slow release formulation in the body giving rise to dichlorvos nonenzymatically. This circumstance at least partly explains its efficacy in the treatment of schistosomiasis.