Species differences in the biotransformation of the antiemetic tropisetron, a potent 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist, were evident in liver slice incubates of human, rat and dog, and reflected the species differences observed in vivo with respect to the relative importance of individual pathways. The dominant biotransformation pathway of tropisetron (10 microM) in human liver slices was formation of 6-hydroxy-tropisetron, whereas in rat liver slices it was 5-hydroxy-tropisetron, and in dog liver slices N-oxide formation. Initial rates of tropisetron metabolite formation in the liver slices (8 mm in diameter, 200 +/- 25 microns thickness) of human (83 +/- 61 pmol/h/mg slice protein), rat (413 +/- 98 pmol/h/mg slice protein) and dog (426 +/- 38 pmol/h/mg slice protein) would predict less of a first-pass effect in humans compared to the rat or the dog. For human and rat, the prediction matched well with the species ranking of tropisetron bioavailability; however, for dog the in vitro data overestimated the apparent first-pass effect. The jejunum is not expected to contribute to the first-pass effect in humans, since human jejunum microsomes did not metabolize tropisetron. The major organ of excretion for tropisetron and its metabolites is the kidney, but the contribution of the kidney to the overall metabolism of tropisetron would be small. Species independent N-oxide formation (2-12 pmol/h/mg slice protein) was the major pathway in human, rat and dog kidney slices, and was comparable to N-oxide formation in the rat and human liver slices but was 1/10 the rate in dog liver slices. This study has demonstrated that the liver is the primary site of tropisetron biotransformation, and the usefulness of organ slices to characterize cross species differences in the dominant biotransformation pathways.

Administration, Oral↗

PubMedDate not supplied

[Example of a diagnostic trap in juvenile anorexia nervosa apropos of 3 cases of cardiospasm].

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Anorexia Nervosa↗

PubMedDate not supplied

Pharmacokinetics and metabolism of the 5-hydroxytryptamine antagonist tropisetron after single oral doses in humans.

Tropiestron is a potent and selective antagonist of 5-hydroxytryptamine receptors. Tropisetron was developed for the indication of cancer chemotherapy-induced emesis. The pharmacokinetic and metabolic dispositions of tropisetron were studied in 12 healthy male volunteers receiving a single oral dose of 62 or 312 mumol (20 or 100 mg) of [14C]tropisetron. Serial plasma samples and complete urine and feces were collected for 120 hr postdose. Whereas the absorption of oral doses of 62-312 mumol tropisetron was rapid and complete, bioavailability was estimated to be only 66% for the 312 mumol dose and 52% for the 62 mumol dose, apparently because of saturable first-pass metabolism. Maximal concentrations of tropisetron averaged 87 and 608 nM after doses of 62 and 312 mumol, respectively, and the parent drug accounted for 21 and 36% of the radioactivity in AUC0-24 hr pools. Approximately 90% of the drug was metabolized before excretion, and approximately 70% of the dose was recovered in the urine. Following both the 62 and 312 mumol doses, the terminal half-life of tropisetron averaged 6-7 hr and that of total radioactivity was 10-11 hr. Tropisetron and its metabolites in plasma and urine were separated by gradient elution reversed-phase HPLC. Structures of eight metabolites were assigned on the bases of NMR and MS data. Tropisetron was metabolized by oxidative hydroxylation of the indole ring at positions 5, 6, and 7. The hydroxylated derivatives are further conjugated with glucuronic acid and sulfate. N-Oxygenation and oxidative N-demethylation at the tropinyl nitrogen also occur in trace amounts.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

PubMedDate not supplied

Cyclosporin A metabolism in human liver, kidney, and intestine slices. Comparison to rat and dog slices and human cell lines.

This study assesses the contribution of cyclosporin A (CsA) metabolism at sites of CsA-induced toxicity: kidney and liver, and a site of absorption, the intestine. With organ slice cultures (8 mm phi), it has been possible to demonstrate that the extrahepatic metabolism of CsA is significant. Both human kidney and colonic mucosal tissue metabolize CsA (1 microM, 24 hr) as analyzed by HPLC. The major metabolite M17 was formed in the kidney at an initial rate of 3 pmol/hr/mg slice protein, which was comparable to M17 formation in the liver slices (5 pmol/hr/mg slice protein). The rate of total CsA metabolism by human kidney slices represents about 42% the rate in liver slices. The metabolism of CsA to M17 was the same in the human kidney cell line 293; however, CsA metabolism was not detectable using human kidney microsomes, nor was metabolism clearly evident in either rat or dog kidney slice cultures. The metabolism of CsA by human colonic mucosal slices to at least three metabolites and the metabolism of CsA by the human intestinal cell line FHs74 Int indicates that the intestinal metabolism of CsA contributes to the first-pass effect of the drug. The liver proved to be the major site of CsA biotransformation in terms of the complexity of metabolites produced, whereas the human liver HepG2 cell line proved not to be a suitable model for CsA metabolism. A time course revealed that the first metabolites formed in the liver slice cultures were the monohydroxylated, M1 and M17, and N-demethylated, M21, followed by the secondary metabolites (including M8, M13, and M18).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Metabolism of the tropine indole-3-carboxylate ICS 205-930 by differentiated rat and human hepatoma cells.

The metabolism of the tropine indole-3-carboxylate ICS 205-930 (ICS), a highly potent and selective antagonist of 5-HT3 receptors, was investigated in continuous cell lines derived from rat or human liver and compared to the in vivo metabolism in rat and human. The well-differentiated rat hepatoma line 2sFou extensively metabolized ICS by hydroxylation of the indole moiety and subsequent conjugation to form the corresponding glucuronides and sulfates. The 2sFou cells also oxidized ICS at the tropinyl moiety to form both N-demethyl and N-oxide derivatives. The relative amount of the various metabolites was dependent on the substrate concentration. Pretreatment of the cells with dexamethasone increased the rate of metabolism for all pathways, while benz[a]anthracene caused an increase in hydroxylation at the indole moiety at the expense of N-oxidation. Phenobarbital pretreatment had no effect on ICS metabolism. The pattern of metabolites formed in 2sFou cells was qualitatively similar to that formed in rat urine. The human hepatoma line HepG2 metabolized ICS only to a small extent. The HepG2 cells failed to form detectable amounts of ICS conjugates found in human urine. The N-oxide-ICS was not found in HepG2 cells or in human urine. Virtually no ICS metabolites were found in human lung adenocarcinoma lines NCI-H358 or NCI-H322. The results suggest that continuous cell lines such as the differentiated rat hepatoma cells 2sFou might be used to mimic the metabolism of xenobiotics in rat and to clarify their complex metabolic pathways.

Adolescent↗

PubMedDate not supplied

Cyclosporine A nephrotoxicity studied by the combined application of kidney cell lines, hepatocytes, and endothelial-platelet cocultures.

Established renal epithelial cell lines of human, pig, and dog origin (293, LLC-PK1, MDCK) were examined in terms of nephrotoxicity and ability to biotransform cyclosporine A (CsA). All three cell lines exhibited a comparable concentration dependent cytotoxicity to CsA treatment. Alterations in cell function included a decreased transport of lysine, an inhibition of growth, and an activation of lysosomal and mitochondrial activity as indicated by the increased uptake of neutral red (NR) and increased reduction of the tetrazolium dye MTT at 1-6 microM CsA. Increased leakage of lactic dehydrogenase and activities of gamma-glutamyl transpeptidase (GGT) and N-acetyl-beta-D-hexosaminidase were observed at 48 h and 12 microM CsA. A discrimination between CsA and the less nephrotoxic cyclosporine-(CsH) was shown for DNA synthesis and NR uptake. The contribution of extrarenal parameters on kidney cell function was studied by the addition of medium from hepatocytes exposed to CsA to the kidney cell lines. A more potent inhibition of DNA synthesis and enhanced reduction of MTT resulted than by addition of equimolar CsA directly to the kidney cells. These data indicate that hepatocyte constituents present in the medium due to CsA treatment affect kidney cell function; additionally, the presence of CsA metabolites may contribute to the CsA-induced nephrotoxicity. The vascular nephrotoxicity induced by CsA, an increased deposition of platelets in the renal arterioles, was mimicked by cocultures of endothelial cell monolayers and platelets. CsA increased the aggregability and adherence of platelets to the endothelial cell monolayers, whereas CsH had no effect.

Animals↗

PubMedDate not supplied

[Coping with disease and personality: on the psychotherapeutic modification of illness denial strategies in stroke patients].

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Adaptation, Psychological↗

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The polymorphic cytochrome P-4502D6 is involved in the metabolism of both 5-hydroxytryptamine antagonists, tropisetron and ondansetron.

Tropisetron and ondansetron, which are potent and selective 5-hydroxytryptamine (5-HT3) receptor antagonists, were both metabolized by human liver microsomes to several metabolites. These metabolites include the major metabolites found in humans, which are the 5-, 6-, and 7-hydroxy tropisetron and the 7- and 8-hydroxy ondansetron. The cytochrome P-450 (CYP) 2D6 inhibitor quinidine (1 microM) reduced the hydroxylation of tropisetron (67%) and ondansetron (18%). Confirmation of CYP2D6 involvement in the hydroxylation of tropisetron and ondansetron was obtained by the formation of these metabolites in recombinant V79 cells expressing human CYP2D6. The CYP3A substrate/inhibitor, cyclosporine A (CsA) had little effect on tropisetron hydroxylation (< 10%), whereas CsA and triacetyloleandomycin reduced ondansetron 7- and 8-hydroxylation up to 27%. Substrates for CYP1A (phenacetin and acetanilide), CYP2C (mephenytoin), and CYP2E (chlorzoxazone) had negligible inhibitory effects on the hydroxylation of either tropisetron or ondansetron. For the CYP2D6-dependent O-demethylation of dextromethorphan, tropisetron and ondansetron were competitive inhibitors with Ki values of 14 and 29 microM, respectively. The CYP3A specific metabolism of CsA was also competitively inhibited by tropisetron (Ki = 2.1 mM) and ondansetron (Ki = 31 microM). Other metabolites, which are only minor in vivo were also inhibited by CsA, 47-60% for tropisetron metabolism and 43% for ondansetron metabolism. To summarize, this study has identified the involvement of CYP2D6 in the formation of the hydroxylated metabolites of tropisetron and ondansetron and in addition of CYP3A in ondansetron hydroxylation. Because these are the major pathways in vivo, coadministration of drugs competing for CYP2D6 and possibly CYP3A4 could influence the human kinetics of tropisetron and ondansetron.

Animals↗

PubMedDate not supplied

[Invasive diagnosis, transcatheter and surgical treatment of acute coronary syndromes].

On the basis of long-term personal experiences and critical evaluation of the present literatury sources authors described the role of invasive diagnostic methods and transcathetral and cardiosurgical possibilities in the recognition and therapy of acute coronary syndromes. These techniques are, and in the forthcoming year shall be available only in specialized institutions. The paper describes the indication for these aggressive techniques as well as their limitations and complications. The goal of the presented article is to inform both the cardiological and frequently broad physicians' societies about the possibilities of diaventional cardiology and cardiosurgery which will be gradually more applied in the care of the patients with acute coronary syndromes. (Ref. 39, Tab. 2, Fig. 3.)

Acute Disease↗