Effects of administration of an organo-phosphorus compound as an antibilharzial agent, with special reference to plasma cholinesterase

Effects of trichlorfon on progesterone production in cultured human granulosa-lutein cells

Trichlorfon, a widely used organophophorus pesticide, has been reported to disrupt reproductive function in human and animal. However, the mechanisms have not been clearly elucidated. In the present study, the effects of trichlorfon on the biosynthesis of progesterone in the primary human granulosa-lutein cells (hGLCs) and the related pathway were investigated. Results showed that progesterone production in hGLCs treated with trichlorfon decreased significantly while cell viability was not affected. Trichlorfon also inhibited FSH-stimulated progesterone production, and this inhibition could not be reversed by 8-bromo-cAMP. However, trichlorfon did not affect the intracellular cAMP contents in the basal and FSH-stimulated conditions. These results suggested that the site in the steroid biosynthesis pathway affected by trichlorfon occurred downstream of PKA activation in hGLCs. Furthermore, our results found that 22(R)-hydroxycholesterol (22R-HC) could remove the inhibitory action of trichlorfon on progesterone biosynthesis, indicating that trichlorfon caused a disruption of cholesterol transport across mitochondrial membranes, which was further confirmed by the observation that trichlorfon dose-dependently inhibited the mRNA level of the steroidogenic acute regulatory protein (StAR). These results suggested that trichlorfon inhibited steroidogenesis in hGLCs by reducing StAR gene expression, which may further contribute to the pathogenesis of trichlorfon-induced reproductive dysfunction.

Sister-chromatid exchange frequencies induced by metrifonate in mammalian in vivo and in vitro systems

Metrifonate is a drug widely used to cure several helminthiases in man including cysticercosis. In this study we determine its capacity to induce SCEs in vivo and in vitro using the fluorescence-plus-Giemsa technique. In the human lymphocyte system we tested 10, 20, 30, 40, 50 and 60 micrograms/ml added at 24 h of culture with a duration of 72 h. The results showed a SCE inducing effect with the exception of the first tested dose (10 micrograms/ml), but without a dose-response expression. A cell cycle progression delay was seen with the three highest dosages. In the mouse bone marrow we tested 30, 60 and 120 mg/kg in a 24-h experiment, and the results indicated an SCE increase only with the highest dose. No modification of the cell proliferation kinetics was observed.

Field trial of the efficacy of a simplified and standard metrifonate treatments of Schistosoma haematobium

In a randomized double-blind study, the percentage egg reduction and cure rate after the standard schedule of metrifonate treatment of Schistosoma haematobium (3 doses of 7.5 mg.kg-1 at two-weekly intervals; A) and an abbreviated regimen (3 doses of 5 mg.kg-1 in one day; B) were compared in five villages in Somalia. 300 patients who were excreting 20 or more eggs of S. haematobium in 10 ml urine were recruited. The patients were classified according to their home villages and were then, randomly allocated to treatment A or B. They had similar ages, weights and egg output. Each patient received 3 doses of metrifonate and 2 doses of identical appearing placebo. Group A received metrifonate on the 1st, 4th and 5th dosing occasions and placebo on the 2nd and 3rd times. Group B received metrifonate on the 1st, 2nd and 3rd dosing times and placebo on the 4th and 5th times. Two hundred and one patients were followed up from 1 to 6 months. The remaining 99 (33%) patients either did not complete treatment or were lost during follow up. Egg reduction in the groups 1, 2, 3 and 6 months after treatment were 97, 97, 95 and 93% in Group A and 96, 96, 94 and 92% in Group B (NS). Corresponding cure rates for Group A were 52, 50, 48 and 44%, and in Group B they were 47, 48, 43 and 40% (NS). Seven patients from Group A and 9 from Group B complained of minor side-effects.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Evaluation of schistosomicides against experimentally established Schistosoma mansoni infections in mice and hamsters

The procedures employed at the Sterling Winthrop Research Institute for the maintenance of Schistosoma mansoni, method of infection, and measurement of efficacy are discussed. Data are presented illustrating the activities of a number of known antischistosomal agents in mice and hamsters against a Puerto Rican strain of the parasite with a well-documented origin.

Safety evaluation of chemicals in food: toxicological data profiles for pesticides. 1. Carbamate and organophosphorus insecticides used in agriculture and public health

The sources of the scientific information used over the past several years by the Joint FAO/WHO Meetings on Pesticide Residues in carrying out toxicological evaluations are classified systematically according to compound and subject for the first time in this paper. It is hoped that those engaged in the toxicological assessment of pesticide chemicals, for the purpose of standardizing pesticide tolerances or for developing criteria of acceptability, will profit from this classification.

Inhibition by metrifonate and dichlorvos of cholinesterases in schistosomes

1. No species differences between Schistosoma haematobium and Schistosoma mansoni were detected when the I50 of metrifonate for the acetylcholinesterases (AChE) and the cholinesterases (ChE) of these two trematodes were determined in isolated enzyme preparations or following exposure of the intact worms to this drug in vitro.2. S. haematobium appeared to be more affected by AChE inhibition because, after administration of metrifonate to hamsters, a hepatic shift of the parasites was observed with a dose of metrifonate (150 mg (0.6 mmol) per kg) which produced no shift of S. mansoni, although AChE inhibition was comparable in both species.3. Administration of a possible metabolite of metrifonate, dichlorvos, to hamsters resulted in a greater inhibition of AChE and ChE activities of S. haematobium than those of S. mansoni. Furthermore, when schistosomes were incubated with dichlorvos, inhibition of AChE activity of female S. haematobium was significantly greater (P<0.005) than that of both sexes of S. mansoni and of male S. haematobium.4. The discrepancy between the lack of a significant chemotherapeutic effect of metrifonate in hamsters infected with S. haematobium and the clinical results obtained with this organophosphorus compound in human schistosomiasis haematobium is discussed, and the need to conduct similar studies in primates is pointed out.

Effect of metrifonate on blood cholinesterases in children during the treatment of schistosomiasis

In a controlled clinical trial, Tanzanian schoolchildren with urinary schistosomiasis, many of whom had coexisting hookworm infection, were randomly allocated to one of three groups that were treated with doses of 7.5, 10.0, and 12.5 mg per kg of body weight, respectively, of metrifonate, orally, up to 3 times at 14-day intervals. No serious side effects were observed during or after the administration of single or repeated doses. A few hours after medication, plasma cholinesterase was almost completely inhibited, regardless of the dose given, while erythrocyte cholinesterase was almost completely inhibited, regardless of the dose given, while erythrocyte cholinesterase was inhibited down to 40-60% of the pretreatment level, depending on the dose. Plasma cholinesterase was inhibited to a greater extent than erythrocyte cholinesterase but showed a more rapid recovery of activity. A moderate accumulation of unreactivated erythrocyte cholinesterase occurred at all dose levels with this regime. Four weeks after the last dose of drug, plasma cholinesterase activity was nearly normal in all the treated children. Erythrocyte cholinesterase activity returned to normal 8-15 weeks after the last dose. The therapeutic results confirmed the efficacy of metrifonate against Schistosoma haematobium. There was an additional though less striking effect against hookworm.

Metrifonate in urinary schistosomiasis

This paper describes the effect of oral metrifonate, an organophosphorus cholinesterase inhibitor, on Schistosoma haematobium infections.The methodology of initial studies in hospital patients and 3 field trials in schoolchildren, using spaced doses ranging from 5 mg to 15 mg per kg of body-weight is detailed.The expected fall in plasma cholinesterase was confirmed. No major side-effects were encountered and minor symptoms were associated with high doses only.The optimum dose was 7.5 mg per kg, given once every 14 days or once monthly to a maximum of 3 doses if necessary. About two-thirds of patients were cured after 1 or 2 doses, but some 10% of these relapsed within 6 months of treatment. In 2 trials of this dose, cure rates of 71% and 79% were obtained.The authors conclude that metrifonate is a useful addition to oral schistosomicides for the treatment of S. haematobium infections in children, but suggest that more trials with spaced dose regimes are indicated and that further experimental studies are needed to define its mode of action.