The pharmacokinetics and tissue distribution of gomphoside in Wistar rats.

The excretion and tissue distribution of [3H]-gomphoside was studied after i.p. and i.v. administration of the cardiac glycoside (1 micrograms/g) to male Wistar rats. Following an intraperitoneal dosage of [3H]-gomphoside, most of the radioactivity (greater than 80%) had been excreted from the body by the end of 48 hours. Biliary excretion played a major role in elimination of [3H]-gomphoside with 90 +/- 15% of radioactivity being collected in 24 hours. Renal excretion formed a minor route of elimination of the cardiac glycoside; only 6 +/- 2% being excreted over 6 days. The distribution of radioactivity to tissues after an intravenous dose was rapid; most of the dose was located in the liver (32%), and the skeletal muscle (31%) 3 minutes after injection. The pharmacokinetics of [3H]-gomphoside could be described by a two-compartment open model with an average elimination half-life of 3.7 hours, and a large volume of distribution (2.3 +/- 0.3 ml/g body weight) characteristic of the commonly used cardiac glycosides (1).

Quantification of leukotriene B4 in synovial fluid by gas chromatography/tandem mass spectrometry.

A procedure for the quantification of leukotriene B4 (LTB4) in synovial fluid has been developed using gas chromatography/tandem mass spectrometry based on selected reaction monitoring of the elimination of t-butyldimethylsilanol from the ions of m/z 431 and 438 in the negative ion chemical ionization mass spectra of the di-t-butyldimethylsilyl/pentafluorobenzyl derivatives of leukotriene B4 and the internal standard (2H8)leukotriene B4. The detection limit (approximately 10 pg ml-1) is sufficiently low to permit determination of LTB4 concentration in the synovial fluid of patients with various arthropathies. Single-stage mass spectrometry was found not to be selective enough to permit quantification of LTB4 in synovial fluid.

In vitro metabolism of the cardiotonic steroids gomphogenin and calactin.

The metabolism of gomphogenin and calactin was studied in vitro using respectively microsomes and the S9 fraction of homogenates from rat liver. These two substrates were previously shown to be in vitro and in vivo metabolites of gomphoside, a cardiotonic steroid belonging to a class of 5 alpha-cardenolide glycosides with doubly-linked hexosulose sugars. Structures of new metabolites were elucidated using 400 MHz 1H-NMR and chemical ionization mass spectrometry, while known compounds were identified by direct comparison. The major metabolite isolated from gomphogenin (2 alpha-hydroxyuzarigenin) metabolism was the oxidation product 2-oxo-uzarigenin which was further oxidized metabolically to 4 alpha-hydroxy-2-oxo-uzarigenin. Other metabolites were 2 alpha-hydroxyuzarigenone and its reduction product 3-epigomphogenin. Calactin was oxidized in vitro to 10-carboxyl-19-norgomphoside, the predominant metabolite, and underwent cleavage of the doubly-linked sugar to yield calotropagenin.

The disposition of biphenylacetic acid following topical application.

Plasma and synovial fluid concentrations of biphenylacetic acid were determined following application of 3 g of 3% biphenylacetic acid gel to one knee of patients suffering from rheumatoid arthritis. The mean peak plasma concentration was 34 ng/ml. Synovial fluid concentrations tended to follow plasma concentrations but at a somewhat lower level, the mean peak synovial fluid concentration was 21 ng/ml. The average ratio of synovial fluid AUC (0-24 h) to plasma AUC (0-24 h) was 0.58, r = 0.97. Where patients had bilateral effusions, the concentration in the ipsilateral knee at each time point examined was not significantly different to that in the contralateral knee, suggesting that absorption was initially into the plasma and subsequently into the synovium.

In vivo and in vitro metabolism of gomphoside, a cardiotonic steroid with doubly-linked sugar.

The metabolism of gomphoside, a cardiotonic steroid glycoside with doubly-linked 4,6-dideoxyhexosulose sugar was studied in vivo in rats, and in vitro using rat liver microsomes. The biliary excretion of metabolites, following intraperitoneal administrative of [3H]gomphoside, was rapid with 68% of radioactivity being collected over 8 h. The metabolites in the bile were principally a water-soluble glucuronide conjugate of gomphoside, and a small amount of chloroform-soluble metabolites. Conversion of [3H]gomphoside to metabolites by microsomes at 37 degrees C reached a maximum of 16% under optimum conditions, producing the same set of metabolites as those in the chloroform-soluble fraction of the bile. The major chloroform-soluble metabolite was the aglycone of gomphoside, viz. gomphogenin or 2 alpha,3 beta, 14-trihydroxy-5 alpha-card-20(22)-enolide. The other major component was recovered gomphoside. Other metabolites were calactin, calotropin, and 2 alpha-hydroxyuzarigenin 3-(4,6-dideoxy-beta-D-arabino-hexopyranoside). Another metabolite, which is a new cardenolide was shown to be 3-epi-gomphogenin or 2 alpha,3 alpha, 14-trihydroxy-5 alpha-card-20(22)-enolide. Gomphoside glucuronide was shown spectroscopically to have the glucuronide residue attached to position 3' of the hexosulose sugar. It was cleaved by beta-D-glucuronidase to gomphoside, and is thus gomphoside 3'-beta-D-glucuronide. The metabolic transformations of gomphoside are summarized in Fig. 5.

Comparison of inhibition of polymerisation of mammalian tubulin and helminth ovicidal activity by benzimidazole carbamates.

The correlation between the inhibition of hatching of Haemonchus contortus eggs and inhibition of mammalian tubulin polymerisation by benzimidazole carbamates has been investigated. The hatching process was observed to be independent of the biomass (eggs plus debris) over a 6-fold range and the early (E1-E3) stages of egg development, but was dependent on the concentration of co-solvent (DMSO) and time of incubation. Benzimidazole carbamates with strong inhibitory activity against mammalian tubulin were potent inhibitors of egg hatch, while non-inhibitors failed to prevent hatching. It is postulated that the primary mode of action of these drugs on nematode eggs is the inhibition of microtubule-dependent processes within the developing egg. The implications and limitations of this correlation are discussed.

Cardenolide connection between overwintering monarch butterflies from Mexico and their larval food plant,Asclepias syriaca.

The majority (85%) of 394 monarch butterflies sampled from overwintering sites in Mexico contain the same epoxy cardenolide glycosides, including most conspicuously a novel polar glycoside with a single genin-sugar bridge (aspecioside), as occur in the milkweedsAsclepias speciosa andA. syriaca. This cardenolide commonality was established by isolating aspecioside and syriobioside from the wings of overwintering monarchs and the two plant species, and comparing Chromatographie and NMR spectrometric characteristics of the isolates. When combined with the migratory pattern of monarchs and the distribution of these two milkweed species, this chemical evidence lends strong support to the hypothesis thatA. syriaca is the major late summer food plant of monarchs in eastern North America. This finding may be of ecological importance, forA. syriaca contributes less cardenolide and cardenolides of lower emetic potency to monarchs than most milkweeds studied to date.

Conformational factors in cardiac glycoside activity.

Gomphoside, a 5 alpha-H cardiac glycoside isolated from Asclepias fructicosa, has an unique double glycosidic linkage to the aglycon through oxygen atoms at 2 alpha and 3 beta of the steroid. The 3'-axial hydroxyl of its conformationally rigid sugar residue appears to be the functional group responsible for its potent inotropic activity. With use of gomphoside as the model compound, the conformation of the flexible glycosidic linkage of the 5 beta-H cardenolides, digitoxigenin alpha-L-rhamnoside and digitoxigenin beta-D-digitoxoside, and the 5 alpha-H cardenolides, uzarigenin alpha-L-rhamnoside and uzarigenin beta-D-6-deoxyalloside, were investigated with the aid of computer graphics and conformational potential energy calculations. The relative inotropic potencies of these cardenolides can be accounted for by considering their active binding conformations with their potential energy distributions. The conformational distribution of the glycosidic moiety was postulated to be the major determinant of the biological activity of these cardenolides.

Structure-activity relationships of benzimidazole carbamates as inhibitors of mammalian tubulin, in vitro.

The structure-activity relationships of thirty-two methyl (5(6)-substituted benzimidazol-2yl) carbamates as inhibitors of the rate of polymerisation of mammalian tubulin have been investigated. The size or some colinear physico-chemical characteristic of the substituent in the 5 (or 6)-position has a profound effect on potency. The presence of branching with or without a commensurate increase in the polarity of the 5(6)-substituent adjacent to the benzimidazole ring (alpha-position) resulted in a loss of activity. The nature of the overall site, as reflected by the quantitative models, could relate to either the hydrophobicity or molar volume of the 5 (or 6)-substituents.

The pharmacokinetics and bioavailability of a tracer dose of [3H]-mebendazole in man.

Five volunteers, whose ages ranged between 37 and 64 years, took part in a crossover study to determine the pharmacokinetics and bioavailability of mebendazole in man following intravenous and oral administration of a tracer dose of [3H]-mebendazole. Following intravenous administration, the average distribution half-life, elimination half-life and rate of clearance were 0.20 h, 1.12 h, and 1.063 min respectively. After oral administration of the solution, the average elimination half-life was 0.93 h, the apparent rate of clearance was 0.846 l/min, the average time to peak plasma concentration was 0.42 h, and the bioavailability of mebendazole was 22%. Comparison of metabolite area under the plasma concentration vs time data from each route of administration indicates that absorption of mebendazole from the gastrointestinal tract at this dose level is almost complete. The low bioavailability observed following oral administration at this dose level is postulated to be due to high first pass elimination. Approximately half of the administered dose of radioactivity following intravenous and oral administration was detected in the urine, and the major unconjugated metabolite of mebendazole was found to be 2-amino-5(6) [alpha-hydroxybenzyl]benzimidazole (IV), not 2-amino-5(6)benzoylbenzimidazole (II), as previously reported.

The effect of dose form on the bioavailability of mebendazole in man.

Four different dose forms of mebendazole were administered to human volunteers, and urine was collected and assayed for mebendazole and unconjugated metabolites of mebendazole. Oral administration of mebendazole as an oily suspension slightly enhances the bioavailability of the drug, however mebendazole is not absorbed following rectal administration. The major urinary metabolite of mebendazole in humans is 2-amino-5(6)[alpha-hydroxybenzyl]benzimidazole (IV), not 2-amino-5(6) benzoylbenzimidazole (II), as previously reported.

Three new contaminants detected in postmortem blood samples.

Three contaminants were identified during drug screening of postmortem blood samples which had been stored in glass bottles with a black rubber seal. Two of these contaminants, cyanoethyl dimethyldithiocarbamate and N-phenyl-2-naphthylamine, were found to come from the rubber seal of some bottles. The third contaminant was not a single compound but rather a mixture of aryl phosphates with a composition very similar to technical grade tritolyl phosphate. The origin of these phosphates is at present unknown.

Cyst and host tissue concentrations of mebendazole in patients undergoing surgery for hydatid disease.

Mebendazole levels were assayed by high performance liquid chromatographic assay in plasma, host tissues, and hydatid material taken from four patients who underwent surgery for hydatid disease. The drug was absorbed and had penetrated both into the host and into the parasite material. The levels of the drug in viable hydatid cysts were much lower than those in dead cysts. The possibility of exclusion or detoxification of the drug by viable hydatid cysts is raised.

The metabolic and pharmacokinetic disposition of mebendazole in the rat.

The metabolism and pharmacokinetics of mebendazole was studied in rats using [2'-3H]-mebendazole (biologically stable; specific activity 383.9 (mCi/mMol) and [2-14C]-mebendazole (specific activity 2.57 mCi/mMol). Analyses were performed by high pressure liquid chromatography and liquid scintillation spectrometry. About 85% of an intravenous dose was eliminated with the bile and the remainder with the urine. The majority of the dose was recovered as conjugated metabolites. The major metabolite (methyl-5(6)-(alpha-hydroxybenzyl)-2-benzimidazole carbamate) accounted for about 77% of the total recovered and 99% of it was conjugated. Anaerobic metabolism studies conducted in vitro with intestinal microorganisms obtained from rats indicated that metabolism of mebendazole did not occur in the gut, but that the intestinal microflora was able to hydrolyse conjugated metabolites which were eliminated with the bile. Mebendazole was found to have a biphasic elimination profile after intravenous administration. Its terminal plasma elimination half-life was 3.2 hours and its re-distribution half-life was 0.4 hour. After oral administration, as a solution in aqueous dimethyl sulphoxide, a bioavailability of 53% was obtained.

4-Amino-3-(3'-methoxycarbonyl-2'-thioureido)benzophenone, a prodrug of mebendazole.

The compound 4-amino-3-(3'-methoxycarbonyl-2'-thioureido) benzophenone has shown promise as a prodrug of the anthelmintic mebendazole. The compound is stable in acid and neutral media and is rapidly hydrolysed in base. An HPLC assay procedure for mebendazole, the prodrug and their known or expected metabolites and degradation products in aqueous media and rat blood has been developed. The prodrug administrated orally to rats is rapidly converted to mebendazole. The area under the blood level versus time curve of mebendazole, in rats dosed with the prodrug, is more than twice that obtained after dosing rats with an equimolar amount of mebendazole. Only the prodrug, mebendazole and known metabolites of mebendazole are detected in rats dosed with the prodrug.