Evaluation of animal models for intestinal first-pass metabolism of drug candidates to be metabolized by CYP3A enzymes via in vivo and in vitro oxidation of midazolam and triazolam.

1. To search an appropriate evaluation methodology for the intestinal first-pass metabolism of new drug candidates, grapefruit juice (GFJ)- and vehicle (tap water)-pretreated mice or rats were orally administered midazolam (MDZ) or triazolam (TRZ), and blood levels of the parent compounds and their metabolites were measured by liquid chromatography/MS/MS. A significant effect of GFJ to elevate the blood levels was observed only for TRZ in mice. 2. In vitro experiments using mouse, rat and human intestinal and hepatic microsomal fractions demonstrated that GFJ suppressed the intestinal microsomal oxidation of MDZ and especially TRZ. Substrate inhibition by MDZ caused reduction in 1'-hydroxylation but not 4-hydroxylation in both intestinal and hepatic microsomal fractions. The kinetic profiles of MDZ oxidation and the substrate inhibition in mouse intestinal and hepatic microsomal fractions were very similar to those in human microsomes but were different from those in rat microsomes. Furthermore, MDZ caused mechanism-based inactivation of cytochrome P450 3A-dependent TRZ 1'-hydroxylation in mouse, rat and human intestinal microsomes with similar potencies. 3. These results are useful information in the analysis of data obtained in mouse and rat for the evaluation of first-pass effects of drug candidates to be metabolized by CYP3A enzymes.

Separate evaluation of intestinal and hepatic metabolism of three benzodiazepines in rats with cannulated portal and jugular veins: comparison with the profile in non-cannulated mice.

Pharmacokinetic analyses of three kinds of benzodiazepines--midazolam (MDZ), triazolam (TRZ) and alprezolam (APZ)--were performed in rats with cannulated portal and jugular veins. Each drug was administered to the double-cannulated rats, and pharmacokinetic data for the parent drugs and their 1'- and 4-hydroxylated metabolites were compared with those obtained in non-cannulated mice. In bioavailability, the drugs ranked APZ >> TRZ = MDZ in rats, and APZ > TRZ >> MDZ in mice, with the values for MDZ remarkably different between rats and mice (19% in rats versus 2.3% in mice). In contrast, hepatic availability (Fh) was similar (APZ > TRZ > MDZ) in both species. Highly significant relationships were found between the ratio of the area under the plasma concentration-time curve (AUC) for the parent drugs in portal blood (AUC(por)) to that in systemic blood (AUC(sys)) and Fh in rats and mice. The double-cannulated rat is useful for estimating the hepatic availability of drug candidates by determining the AUC values for the parent drugs in portal and systemic blood samples.

N3-phenacyluridine, a novel hypnotic compound, interacts with the benzodiazepine receptor.

N3-Phenacyluridine (3-phenacyl-1-beta-D-ribofuranosyluracil) has potent sedative and hypnotic activities following intracerebroventricular injection in mice. To study the mechanism of action of N3-phenacyluridine, the interaction of this compound with the benzodiazepine receptor has been investigated. Results obtained showed that this compound inhibited specific binding of [3H]flunitrazepam to synaptic membranes of bovine cortex in a concentration-dependent fashion (IC50 = 129 microM). Scatchard analysis of [3H]flunitrazepam binding revealed that N3-phenacyluridine interacted with the ligand at the benzodiazepine receptor binding site in a competitive manner. Ro15-1788 (8-fluoro-3-carboethoxy-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5a ]1, 4-benzodiazepine), a benzodiazepine receptor antagonist, also inhibited the specific binding of [3H]flunitrazepam in the presence of the compound. The results suggest that the pharmacological activity of N3-phenacyluridine may be partially mediated through the benzodiazepine receptor.

Central nervous system depressant effects of N3-substituted derivatives of deoxyuridine in mice.

N3-Substituted derivatives of deoxyuridine (1) were synthesized and their pharmacological effects were evaluated by intracerebroventricular (i.c.v.) injection in mice. Eleven derivatives, including the methyl (2), ethyl (3), propyl (4), allyl (5), butyl (6), benzyl (7), o, m and p-xylyls (8, 9, 10), alpha-phenylethyl (11) and phenacyl (12) derivatives, of 1 were prepared and their pharmacological effects were evaluated by using hypnotic activity, pentobarbital-induced sleep prolongation, spontaneous activity and motor incoordination as indices of central nervous system (CNS) depressant effects. At a dose of 2.0 mumol/mouse, the values of mean sleeping time induced by 7, 8, 9 and 10 were 23, 35, 29 and 30 min, respectively. Although the alkyl (2-6) derivatives did not cause any hypnotic activity, some derivatives tested (3, 5, 6, 8-12) significantly prolonged the pentobarbital-induced sleeping time. When the CNS depressant effects of phenacyl substituted 1 were compared to that of other oxopyrimidine nucleosides, N3-phenacyluridine (13), N3-phenacylthymidine (14), N3-phenacyl-6-azauridine (15), compounds 12, 13 and 14 (1.0 mumol/mouse, i.c.v.) significantly decreased mouse spontaneous activity. Furthermore, 12-15 (1.0 mumol/mouse, i.c.v.) caused mouse motor incoordination. These results indicate that deoxyuridine derivatives have generally central depressant activity, and the benzyl and xylyl derivatives, but not alkyl derivatives, possess hypnotic activity.

The potent depressant effects of N3-phenacyluridine in mice.

The hypnotic activity of N3-phenacyluridine in 2.0 mumol/mouse by intracerebroventricular (i.c.v.) injection was 20 times stronger than that of known N3-benzyluridine. In 0.5 mumol/mouse, i.c.v., this compound strongly potentiated both pentobarbital- and diazepam-induced sleep as compared to N3-substituted uridines, including N3-benzyluridine. Furthermore, the compound caused motor incoordination as well as decreasing spontaneous activity in the same dose. These results indicate that among the N3-substituted uridines and related compounds previously reported, N3-phenacyluridine possesses potent depressant effects.

Sedative and hypnotic activities of pyrimidine nucleoside derivatives.

N3-Substituted pyrimidine nucleoside and their related compounds were synthesized. The central nervous system (CNS) depressant effect of the compounds such as hypnotic activity and synergistic effect with pentobarbital have been evaluated. N3-Phenacyl derivatives of uridine (2), thymidine (3), deoxyuridine (4), 6-azauridine (5) and arabinofuranosyluracil (6) exhibited the hypnotic activity, whereas N3-phenacyl-2',3'-O-isopropylideneuridine did not. Compound 2, 3, 4 and 6 significantly enhanced pentobarbital-induced sleep. The results indicate that CNS depressant effect of pyrimidine nucleoside derivatives might relate to functional group at the N3-position on oxopyrimidine ring and stereospecificity of sugar moiety at the N1-position.

The nucleoside derivatives possessing sedative and hypnotic effects.

N3-Substituted oxopyrimidines and their related compounds were synthesized. The central nervous system (CNS) depressant activities of the compounds such as hypnotic activity and barbiturate-induced narcosis have been evaluated. N3-Benzyl, o,m,p-xylyl, alpha-phenylethyl, phenacyl substituted and related oxopyrimidine nucleosides exhibited potent hypnotic activity by intracerebroventricular (i.c.v.) administration to mice. The results indicate that hypnotic action of oxopyrimidine nucleoside derivatives might relate to functional group at the N3 position on oxopyrimidine ring and stereospecificity of sugar moiety.