Effect of aluminium ion on bioavailability of levofloxacin following oral administration of cilexetil ester of levofloxacin as prodrug in rats.

A prodrug of levofloxacin (LVFX), cilexetil ester of LVFX (LVFX-CLX), was synthesized to examine whether the prodrug can avoid chelate formation with metal cations in the gastrointestinal tract. LVFX-CLX exhibited a 10-times higher partition coefficient than LVFX. In vitro, LVFX was precipitated by 76.1% in the presence of a 10-times higher concentration of aluminium chloride (Al3+), but LVFX-CLX was not. LVFX-CLX was rapidly hydrolyzed enzymatically by rat plasma, intestinal mucosal and liver homogenates at 37 °C, but not by pancreatic enzymes and luminal fluid. The minimum inhibitory concentration values of LVFX-CLX against S. aureus, E. coli and P. aeruginosa were far higher than that of LVFX. In rats, area under the plasma concentration-time curve from zero to 4 h (AUC0-4h) of LVFX after oral administration of LVFX-CLX was 1.34-fold higher than that after LVFX, though it did not reach significance level. Co-administration of Al3+ with LVFX and LVFX-CLX in rats decreased AUC0-4h of plasma LVFX by 75% and 60%, respectively, however, the AUC0-4h of plasma LVFX after co-administration of LVFX-CLX and Al3+ was 2.2-times higher than that after co-administration of LVFX and Al3+. These results suggested that the use of LVFX-CLX may reduce the modulation of intestinal microflora caused by LVFX and the suppressive effect of Al3+ on intestinal absorption of LVFX.

High affinity binding of [3H]6-nitroquipazine to cortical membranes in the rat: inhibition by 5-hydroxytryptamine and 5-hydroxytryptamine uptake inhibitors.

[3H]6-Nitroquipazine is a new, suitable radioligand for studying the uptake system for 5-hydroxytryptamine (5-HT; serotonin). In the present study, inhibition by drugs of the binding of [3H]6-nitroquipazine to uptake sites for 5-HT in the cerebral cortex of the rat was investigated. The inhibition of 5-HT and several inhibitors of the uptake of 5-HT (paroxetine, clomipramine, citalopram, Z-norzimelidine, fluoxetine, imipramine, desipramine and 5-methoxytryptoline) against the binding of [3H]6-nitroquipazine to membranes from the cortex of the rat were the same and competition curves indicated a single population of binding sites. The addition of 5-HT and the tricyclic inhibitors of the uptake of 5-HT, imipramine, clomipramine and desipramine, all produced changes in the apparent dissociation constant (Kd), without changes in the number of binding sites (Bmax). Also, the non-tricyclic inhibitors of the uptake of 5-HT, paroxetine, citalopram, fluoxetine and Z-norzimelidine, and 5-methoxytryptoline, all produced changes in Kd values without changes in the Bmax. These results suggest that all the drugs used in this experiment exhibited competitive interactions with the binding of [3H]6-nitroquipazine to uptake sites for 5-HT in the brain of the rat. These drugs may bind to common binding sites, which are likely to represent the substrate recognition sites for the uptake of 5-HT.

4-Bromo-6-nitroquipazine: a new ligand for studying 5-hydroxytryptamine uptake sites in vivo.

The present study was undertaken to evaluate 2 bromo-derivatives (4-bromo-6-nitroquipazine and 6-bromoquipazine) of quipazine as potential ligands for studying 5-hydroxytryptamine (5-HT; serotonin) uptake sites in the brain in vivo. The inhibition experiments of [3H]5-HT uptake into synaptosomes from rat brain and of the binding of [3H]6-nitroquipazine to membranes of rat brain showed that 4-bromo-6-nitroquipazine and 6-bromoquipazine were very potent and selective inhibitors of 5-HT uptake in vitro, very close to that of 6-nitroquipazine. Furthermore, 4-bromo-6-nitroquipazine was about a 2-fold more potent inhibitor of specific binding of [3H]6-nitroquipazine in vivo in the hypothalamus of mouse brain than 6-bromoquipazine. Thus, 4-bromo-6-nitroquipazine seems to be superior to 6-bromoquipazine, as a potential ligand for in vivo imaging of 5-HT uptake sites in the brain.

Reduction of in vivo binding of [3H]paroxetine in mouse brain by 3,4-methylenedioxymethamphetamine.

The effects of 3,4-methylenedioxymethamphetamine (MDMA) on the in vivo binding of [3H]paroxetine, a potent and selective 5-hydroxytryptamine (5-HT; serotonin) uptake inhibitor, in the brain of the mouse were studied. The distribution of radioactivity in the brain of the mouse, after intravenous administration of [3H]paroxetine, was significantly altered by pretreatment with MDMA (15 mg/kg, i.p., 3 hr before). The hypothalamus/cerebellum and cerebral cortex/cerebellum ratios, as a function of time, were significantly decreased after the pretreatment with MDMA, indicating that the in vivo binding of [3H]paroxetine to uptake sites for 5-HT in the brain of the mouse was significantly decreased by MDMA. These ratios could reflect those of the total binding, to the non-specific binding and free ligand, since the cerebellum has very low levels of binding for [3H]paroxetine. Furthermore, these ratios decreased after pretreatment with MDMA, in a dose-dependent manner. However, the binding of [3H]paroxetine to membranes from the brain of the mouse in vitro was not altered by treatment with MDMA. The discrepancy between the in vivo binding and in vitro binding of [3H]paroxetine in the brain of the mouse is discussed.

High-affinity [3H]6-nitroquipazine binding to the 5-hydroxytryptamine transport system in rat lung.

[3H]6-Nitroquipazine bound to rat lung membranes at 37 degrees with a dissociation constant (Kd) of 0.310 +/- 0.13 nM and a maximal number of binding sites (Bmax) of 1752 +/- 334 fmol/mg protein (mean +/- SD, N = 4). The binding was saturable, of high affinity and sodium dependent. Drug inhibition studies indicated that [3H]6-nitroquipazine binding in the lung is similar to that already reported in the rat brain and human platelets. Scatchard analysis indicated that 5-hydroxytryptamine (5-HT) inhibited [3H]6-nitroquipazine binding to rat lung membranes in a competitive manner. The present results suggest that [3H]6-nitroquipazine binding sites in the rat lung are associated with the uptake system of 5-HT.

Effects of benzylpiperazine derivatives on the neurotoxicity of 3,4-methylenedioxymethamphetamine in rat brain.

The neurotoxicity of 3,4-methylenedioxymethamphetamine (MDMA) in rat brain was attenuated significantly by coadministration of several benzylpiperazines (p-nitrobenzylpiperazine, p-chlorobenzylpiperazine and 1-piperonylpiperazine), which were weak inhibitors for [3H]6-nitroquipazine binding to the 5-hydroxytryptamine (5-HT) transporter in rat brain. These results suggest that these benzylpiperazines may inhibit the MDMA-induced neurotoxicity by a novel neuropharmacological effect other than 5-HT uptake inhibition.

High-affinity binding of [3H]6-nitroquipazine to 5-hydroxytryptamine transporter in human platelets.

The characteristics of the binding [3H]6-nitroquipazine, a very potent and selective inhibitor of 5-hydroxytryptamine (5-HT; serotonin) uptake, to human platelet membranes were studied at a physiological temperature of 37 degrees C. The presence of a single saturable high-affinity binding component for [3H]6-nitroquipazine was demonstrated Non-specific binding was estimated in the presence of 1 microM paroxetine. Scatchard analysis revealed an apparent equilibrium dissociation constant (Kd) of 0.450 +/- 0.04 nM and a maximal number of binding sites (Bmax) of 2508 +/- 360 fmol/mg protein (mean +/- S.D., n = 4). The kinetically derived dissociation constant (Kd) was 0.431 nM. [3H]6-Nitroquipazine binding was inhibited selectively by 5-HT uptake inhibitors, and the potency of various drugs to inhibit [3H]6-nitroquipazine binding closely correlated with their inhibitory effects on [3H]5-HT uptake into synaptosome. Moreover, Ki values for drug inhibition of [3H]6-nitroquipazine binding to human platelet membranes were significantly correlated with the corresponding Ki values for inhibition of [3H]paroxetine binding at 37 degrees C. The present results suggest that the binding sites for [3H]6-nitroquipazine are associated with the 5-HT transporter in human platelets.

High-affinity [3H]6-nitroquipazine binding sites in rat brain.

6-Nitroquipazine is a very potent and selective inhibitor of neuronal 5-hydroxytryptamine (5-HT; serotonin) uptake. We have characterized the specific binding of [3H]6-nitroquipazine to rat brain membranes at 22 degrees C. The present results indicate the presence of a single saturable high-affinity binding component for [3H]6-nitroquipazine. Scatchard analysis revealed an apparent equilibrium dissociation constant (Kd) of 93.0 +/- 2.23 pM, and a maximal number of binding sites (Bmax) of 831.7 +/- 18.7 fmol/mg protein (mean +/- S.D., n = 4). The kinetically derived dissociation constant was 74.5 pM. [3H]6-Nitroquipazine binding was inhibited selectively by 5-HT uptake inhibitors, and a good correlation was demonstrated between the potency of various drugs to inhibit [3H]6-nitroquipazine binding and [3H]5-HT uptake. The highest densities of [3H]6-nitroquipazine binding were obtained in the hypothalamus and midbrain, intermediate binding was observed in the striatum, hippocampus, medulla oblongata and cortex, and the lowest binding was observed in the cerebellum. Lesioning of 5-HT neurons with p-chloroamphetamine resulted in a 72% reduction in [3H]6-nitroquipazine binding compared to controls. These results indicate that the binding site specifically labelled by [3H]6-nitroquipazine is associated with the neuronal 5-HT transporter complex. [3H]6-Nitroquipazine is an excellent radioligand for the study of the 5-HT uptake system.

Antagonism of 3,4-methylenedioxymethamphetamine-induced neurotoxicity in rat brain by 1-piperonylpiperazine.

The effects of 1-piperonylpiperazine and N,alpha-dimethylpiperonylamine, which are weak inhibitors for [3H]5-hydroxytryptamine (5-HT) uptake, on 3,4-methylenedioxymethamphetamine (MDMA)-induced neurotoxicity were examined. The reductions of serotonergic parameters in the rat cerebral cortex produced by multiple administration of MDMA (10 mg/kg) were attenuated significantly by coadministration of 6-nitroquipazine (10 mg/kg), paroxetine (10 mg/kg) or 1-piperonylpiperazine (20 mg/kg), but not by N,alpha-dimethylpiperonylamine (20 mg/kg). The present data suggest that 1-piperonylpiperazine might inhibit the MDMA-induced neurotoxicity by effect(s) other than 5-HT uptake inhibition.

Drug effects on distribution of [3H]3,4-methylenedioxymethamphetamine in mice.

The present study was undertaken to examine the drug interactions between 3,4-methylenedioxymethamphetamine (MDMA) and paroxetine or several compounds including the 3,4-methylenedioxybenzyl (piperonyl) group in mice. The time course of radioactivity in the mouse brain after i.v. administration of the tracer amount (approximately 70 ng/kg) of [3H]MDMA was altered significantly by coinjection of carrier MDMA (15 mg/kg) or by pretreatment with paroxetine (10 mg/kg, i.p., 5 min). Furthermore, the radioactivity in the brain 60 min after injection of [3H]MDMA was increased significantly by pretreatment with paroxetine, but not by pretreatment with 6-nitroquipazine, fluoxetine, clomipramine, GBR 12909 or desipramine, indicating that paroxetine-induced alteration of the brain radioactivity was not due to the inhibitory effect of 5-hydroxytryptamine (5-HT) uptake of paroxetine. The radioactivity in the brain 60 min after injection of [3H]MDMA was increased significantly by pretreatment with 3,4-methylenedioxyamphetamine (MDA), MDMA, 1-piperonylpiperazine and N, alpha-dimethylpiperonylamine, but not by pretreatment with piperonylacetone, piperonyl butoxide and piperonyl isobutyrate. HPLC analyses indicated that the alteration of brain radioactivity 60 min after injection of [3H]MDMA was, in part, due to inhibition in the metabolism of [3H]MDMA to radioactive metabolite(s). The present results suggest that a specific mechanism for the 3,4-methylenedioxyphenyl group which rapidly alters the disposition and metabolism of [3H]MDMA may exist in brain and peripheral organs of mice.

Reduction of [3H]6-nitroquipazine-labelled 5-hydroxytryptamine uptake sites in rat brain by 3,4-methylenedioxymethamphetamine.

3,4-Methylenedioxymethamphetamine (MDMA; Ecstasy) is a known neurotoxin to 5-hydroxytryptamine (5-HT; serotonin) nerve terminals. It has recently been demonstrated that [3H]6-nitroquipazine is a new radioligand for studying the 5-HT transport system in brain. Therefore, we examined the effects of repeated systemic administration (10 mg/kg ip, twice daily for 3 d) of MDMA on [3H]6-nitroquipazine-labelled 5-HT uptake sites in rat brain. Marked reductions in the concentrations of 5-HT and its major metabolite 5-hydroxyindoleacetic acid (5-HIAA) were observed in the cerebral cortex 1 week after the last injection of MDMA. In addition, the density of [3H]6-nitroquipazine-labelled 5-HT uptake sites was significantly decreased by MDMA. Furthermore, the reduction of 5-HT and 5-HIAA content and the density of [3H]6-nitroquipazine-labelled 5-HT uptake sites by MDMA were significantly prevented by co-administration of 6-nitroquipazine (5 mg/kg), a very potent and selective 5-HT uptake inhibitor. The present results indicate that the 5-HT uptake carrier plays an important role in the neurotoxic action of MDMA.

Studies on drug metabolism by use of isotopes XXVII: urinary metabolites of rutin in rats and the role of intestinal microflora in the metabolism of rutin.

Analysis of urinary metabolites of orally administered rutin (I) labeled with deuterium [( 2',5',6'-2H]rutin, rutin-d) was carried out by GLC-MS. In rat urine, 3-hydroxyphenylacetic acid (III), 3-methoxy-4-hydroxyphenylacetic acid (IV), 3,4-dihydroxyphenylacetic acid (V), 3,4-dihydroxytoluene (VI), and 3-(m-hydroxyphenyl)propionic acid (VIII) were identified as rutin metabolites and were differentiated from the corresponding endogeneous compounds. Unchanged I and quercetin (II) were not present in the urine. Rutin-d was injected intraperitoneally in rats, administered orally to neomycin-treated rats, and incubated in vitro with the intestinal contents of rats. The experiments suggested the involvement of intestinal microflora in the metabolism of orally administered I.

Use of stable isotopes in the study of pharmacokinetics of drugs by mass fragmentography II: Detailed examination of pharmacokinetics of a single oral dose of phenytoin in humans.

To study the pharmacokinetics of phenytoin in detail, a mass fragmentographic method was applied for the precise, sensitive, and specific analysis of phenytoin, 5-(4-hydroxyphenyl)-5-phenylhydantoin, and 5-(4-hydroxyphenyl)-5-phenylhydantoin glucuronide in plasma and urine after administration of a single oral dose of phenytoin to two healthy volunteers. Salivary phenytoin concentrations also were measured. Phenytoin and 5-(4-hydroxyphenyl)-5-phenylhydantoin were analyzed after the addition of deuterium-labeled internal standards and conversion to volatile methyl derivatives for mass fragmentographic analysis. The lower limit of detection was approximately 10 ng/ml. The simultaneous pharmacokinetic analysis of the plasma levels and urinary excretion data of phenytoin and its major metabolite, 5-(4-hydroxyphenyl)-5-phenylhydantoin, yielded detailed information about the pharmacokinetics of phenytoin.

[Isotopic fractionation of iproniazid and isopropylhydrazine from their deuterated analogues and application for isotope dilution analysis by capillary gas chromatography].

Quantitative analyses of iproniazid (IPN) and deuterated analogue (IPN-d6) and of isopropylhydrazine (IP-Hy) and deuterated analogue (IP-Hy-d6) after conversion to pyrazole derivatives (IDP) were carried out by gas chromatography. The complete separation of protio- from deutero-forms of IPN and IDP was achieved by using a fused-silica CBP1 capillary column (50 m). The resolution coefficients between two isotopic molecules were 1.10 for IPN and 1.62 for IDP, respectively. The present isotopic fractionation procedure was applied to the isotope dilution analyses of IPN and IP-Hy. By the measurement of the samples prepared by the addition of known amounts of IPN and IPN-d6 to the control plasma and urine of rat, a linear relationship between peak height ratio and added amount ratio was observed. The correlation coefficients obtained by regression analysis were 0.9990 for the plasma and 0.9999 for the urine, respectively. In the case of IP-Hy, a linear relationship was also observed, and the correlation coefficients were 0.9998 for the plasma and 0.9997 for the urine, respectively. The present method was compared with the gas chromatography-mass spectrometry method in urinary samples from rats treated with IPN. The results of these parallel determinations were comparable.

[Effects of ascorbic acid on the metabolic fate and the free radical formation of iproniazid].

The effects of ascorbic acid (AA) on the metabolic fate of iproniazid (IPN) and on the free radical intermediates derived from IPN were investigated in rats. After oral administration of IPN with or without AA, the plasma concentration and the urinary excretion of IPN and its metabolites were determined by gas chromatography-mass spectrometry using stable isotope labeled compounds as internal standards. In the excretion of IPN and its metabolites except hydrazine (Hy), the differences between co-administration and single administration were not observed. The excretion of Hy, which is a known hepatotoxic metabolite, decreased clearly in the co-administration of IPN and AA. When IPN and AA were co-administered orally, the profiles of plasma levels of IPN and its metabolites were almost similar after the administration of IPN alone. Furthermore, no differences between i.v. co-administration and i.v. administration alone were observed. These results indicated that AA did not affect both absorption and metabolism of IPN. By the electron spin resonance (ESR) spectroscopy and spin-trapping technique, the ESR signals due to the alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN) adducts induced by isopropylhydrazine (IP-Hy) were two-fold higher than those by IPN in microsomal systems. The free radical formations of IPN and IP-Hy were significantly inhibited by AA in a dose dependent manner. The 4-POBN-trapped radical species generated from IPN and IP-Hy were presumed to be an isopropyl radical by the results of mass spectrometry.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effects of ascorbic acid on the free radical formations of isoniazid and its metabolites].

By the use of electron spin resonance (ESR) spectroscopy and of spin-trapping technique, the effects of ascorbic acid on the formation of the free radical intermediates due to isoniazid (INAH) and its metabolites were investigated with a microsomal system. When alpha-(4-pyridyl 1-oxide)-N-tert butylnitrone (4-POBN) was used as a spin trapping agent, the ESR signal due to hydrazine (Hy) was formed to be most intensive among others. Therefore, it was presumed that Hy is a potent intermediate to cause an INAH-induced hepatic injury. In the presence of ascorbic acid (AA), the free radical formation of Hy, INAH and acetyl hydrazine was significantly inhibited, suggesting that AA may affect the INAH-hepatitis. By the addition of inhibitors of cytochrome P-450 like metyrapone and CO, the generation of the radical from Hy decreased, confirming that the radical is formed by the cytochrome P-450 dependent microsome systems. The 4-POBN-trapped radical species generated from Hy was presumed to be the hydrazyl radical by the results of mass spectrometry.

[Evaluation of 3H-paroxetine as a radiopharmaceutical for lung function].

The potential of 3H-paroxetine as a radiotracer for in vivo study of the function in mouse lung was examined. A high accumulation of radioactivity in the mouse lung was observed after intravenous administration of 3H-paroxetine. However, the distributions of radioactivity in the mouse lung were not significantly decreased by treatment with paroxetine or other monoamine uptake inhibitors (6-nitroquipazine, desipramine and GBR 12909). It was found that the radioactivity in the mouse lung at 1 hr after intravenous administration of 3H-paroxetine was due to unmetabolized 3H-paroxetine from TLC and HPLC analyses. Furthermore, 3H-paroxetine exhibits both saturable and high affinity binding sites in mouse lung with a maximal number of binding sites (Bmax) of 303 fmoles/mg protein and a dissociation constant (Kd) of 92.2 pM. These results suggest that 3H-paroxetine would be a suitable radiopharmaceutical for in vivo study of the function of lung as a metabolic organ of serotonin.