Praziquantel binds Schistosoma mansoni adult worm actin.

Praziquantel (PZQ) is widely used for the treatment of schistosomiasis. It induces worm muscle contractions and tegumental disruption, followed by exposure of parasite surface membrane antigens to the host immunological defence mechanisms. It may be assumed that PZQ, like cholesterol, is too hydrophobic to traverse the schistosome outer lipid bilayers by passive diffusion and probably requires binding to a surface membrane protein carrier for distribution throughout the worm. However, the PZQ binding site on the schistosome surface and the precise mechanism of action are not yet known. The Claisen condensation reaction was used to bind PZQ on cellulose acetate membranes. Triton-insoluble surface membrane antigens of Schistosoma mansoni adult worms were allowed to bind to the PZQ column. The identity of the bound molecules was examined by amino acid microsequencing and immunogenicity in outbred and inbred mice. The PZQ column was found to bind molecules of 45 kDa selectively from the Triton-insoluble surface membrane antigens of S. mansoni adult worms. Amino acid microsequencing revealed that the 45 kDa species consist predominantly of schistosome actin. This finding was supported by the poor immunogenicity of the 45 kDa molecules in outbred and inbred mice. PZQ was also shown to bind bovine actin but not bovine serum albumin. However, pre-incubation with bovine actin did not impair the effect of PZQ on adult worms in vitro. The study represents an attempt to understand how PZQ distributes across schistosome outer lipid bilayers.

Investigation of the stereoselective metabolism of praziquantel after incubation with rat liver microsomes by capillary electrophoresis and liquid chromatography-mass spectrometry.

Two different separation methods for the antischistosomal drug praziquantel and its metabolites by capillary electrophoresis are described. Achiral separation was obtained by micellar electrokinetic capillary chromatography using sodium dodecyl sulfate as micelle-forming surfactant. On the other hand, the negatively charged sulfobutylether-beta-cyclodextrin as a chiral selector enabled the separation of the drug and its metabolites as well as their enantioseparation. Based on this separation, the enantioselectivity of the metabolism of praziquantel was studied by incubation of the drug with rat liver microsomes. Whereas trans- and cis-4-hydroxypraziquantel were mainly formed from the R-(-)-enantiomer, another, different monohydroxylated metabolite was only formed from the S-(+)-enantiomer. Information about the structure of these metabolites was obtained, using LC-MS.

Avermectins and milbemycins against Fasciola hepatica: in vivo drug efficacy and in vitro receptor binding.

Few studies have examined activity against trematodes for the avermectin/milbemycin class of anthelmintics. To gain insight into this, 12 different members of the avermectin/milbemycin mode of action class were tested against juvenile Fasciola hepatica in a mouse model. The compounds chosen were Avermectin A1, Avermectin A2, Avermectin B1, Avermectin B2, Ivermectin, Ivermectin monosaccharide, Ivermectin aglycone, 13-deoxy ivermectin aglycone, Moxidectin, 13-O-methoxyethoxymethyl ivermectin aglycone, 4"-deoxy-4"-epi-methylamino avermectin B1, and 4"-deoxy-4"-epi-acetylamino avermectin B1 5-oxime. Each of these compounds was administered orally to 4 mice at 2.0 mg kg-1. These mice had been administered 3 metacercariae of F. hepatica 14 days prior to treatment and all mice were necropsied 4 days after treatment. At necropsy, none of the individual avermectin or milbemycin-treated groups showed any significant activity (P > 0.05) against juvenile F. hepatica relative to a vehicle-treated control. In a receptor binding study, adult F. hepatica that had been obtained from sheep were homogenized, their membranes incubated in the presence of 3H-ivermectin, and then measured for high affinity binding sites. The same was done with the free-living nematode, Caenorhabditis elegans. While the C. elegans membranes displayed high affinity 3H-ivermectin binding sites over the range of ivermectin concentrations tested (5-100 nM), no significant 3H-ivermectin binding sites were detected in the F. hepatica membranes. Based on these data, it seems unlikely that any avermectin or milbemycin will show activity against F. hepatica, and certainly makes one pessimistic about possible activity of this mode of action class against trematodes in general.

Metabolic detoxication of bis-(2-hydroxy-3, 5-dichlorophenyl)-sulfoxide in man.

The metabolic detoxication of bis(2-hydroxy-3, 5-dichlorophenyl)sulfoxide (BTS) in man was investigated. Bis(2-hydroxy-3, 5-dichlorophenyl)sulfide (BT) was identified in beta-glucuronidase treated urine following the administration of BTS by thin-layer chromatography, gas chromatography, ultraviolet spectrum and quantitative analysis. No other metabolites were detectable. BT-glucuronide was also identified in urine. It was assumed that BTS was reduced to BT and successively conjugated with glucuronide in man, and excreted as BT-glucuronide in the urine.

[Residue determinations in milk following application of the fasciolicides rafoxanide and hexachloro-p-xylene]. / Rückstandsuntersuchungen bei Milch nach Anwendung der Fasziolizide Rafoxanid und Hexachlor-p-xylol.

The control of Fasciola hepatica in dairy cattle may lead to considerable residue problems in dairying. In the GDR, a hexachloro-p-xylene-based fasciolicide has been approved till recently, and another, rafoxanide-based fasciolicide has been on trial. The investigations have shown that the two active principles are excreted in the milk for a prolonged period, rafoxamide being found more suitable. Their marked lipophil behaviour leads to accumulation in the fat phase and, thus, in high-fat milk products.