Trospium Chloride Transport by Mouse Drug Carriers of the Slc22 and Slc47 Families

Background: The muscarinic receptor antagonist trospium chloride (TCl) is used for pharmacotherapy of the overactive bladder syndrome. TCl is a hydrophilic positively charged drug. Therefore, it has low permeability through biomembranes and requires drug transporters for distribution and excretion. In humans, the organic cation transporters OCT1 and OCT2 and the multidrug and toxin extrusion MATE1 and MATE2-K carriers showed TCl transport. However, their individual role for distribution and excretion of TCl is unclear. Knockout mouse models lacking mOct1/mOct2 or mMate1 might help to clarify their role for the overall pharmacokinetics of TCl. Method: In preparation of such experiments, TCl transport was analyzed in HEK293 cells stably transfected with the mouse carriers mOct1, mOct2, mMate1, and mMate2, respectively. Results: Mouse mOct1, mOct2, and mMate1 showed significant TCl transport with Km values of 58.7, 78.5, and 29.3 µM, respectively. In contrast, mMate2 did not transport TCl but showed MPP⁺ transport with Km of 60.0 µM that was inhibited by the drugs topotecan, acyclovir, and levofloxacin. Conclusion: TCl transport behavior as well as expression pattern were quite similar for the mouse carriers mOct1, mOct2, and mMate1 compared to their human counterparts.

Propiverine-induced accumulation of nuclear and cytosolic protein in F344 rat kidneys: isolation and identification of the accumulating protein

Male and female F344 rats but not B6C3F1 mice exposed for 104 weeks to propiverine hydrochloride (1-methylpiperid-4-yl 2,2-diphenyl-2-(1-propoxy)acetate hydrochloride), used for treatment of patients with neurogenic detrusor overactivity (NDO) and overactive bladder (OAB), presented with an accumulation of proteins in the cytosol and nuclei of renal proximal tubule epithelial cells, yet despite this, no increased renal tumor incidence was observed. In order to provide an improved interpretation of these findings and a better basis for human health risk assessment, male and female F344 rats were exposed for 16 weeks to 1000 ppm propiverine in the diet, the accumulating protein was isolated from the kidneys via cytosolic and nuclear preparations or laser-capture microdissection and analyzed using molecular weight determination and mass spectrometry. The accumulating protein was found to be d-amino acid oxidase (DAAO), an enzyme involved in amino and fatty acid metabolism. Subsequent reanalysis of kidney homogenate and nuclear samples as well as tissue sections using western blot and DAAO-immunohistochemistry, confirmed the presence and localization of DAAO in propiverine-treated male and female F344 rats. The accumulation of DAAO only in rats, and the limited similarity of rat DAAO with other species, including humans, suggests a rat-specific mechanism underlying the drug-induced renal DAAO accumulation with little relevance for patients chronically treated with propiverine.

Effects of three metabolites of propiverine on voltage-dependent L-type calcium currents in human atrial myocytes

The non-selective muscarinic receptor antagonist propiverine impairs L-type Ca(2+) currents (I(Ca,L)) in human detrusor smooth muscle cells and atrial cardiomyocytes. Here, we have investigated the effects of three metabolites of propiverine on human cardiac I(Ca,L). Propiverine reduced I(Ca)(,L) with a -logIC(50) [M] value of 4.1, M-5 only showed minor effect on I(Ca)(,L) at high concentrations, M-6 did not influence I(Ca)(,L) at all. Like the parent compound M-14 also reduced I(Ca)(,L) (-logIC(50) [M]=4.6). We conclude, that propiverine and M-14 reduce cardiac I(Ca)(,L) at higher concentrations than in detrusor cells and therefore preferentially reduce I(Ca)(,L) in the urinary bladder than in the heart.

Anesthesia increases in vivo N-([18F]fluoroethyl)piperidinyl benzilate binding to the muscarinic cholinergic receptor

The in vivo binding of N-[18F]fluoroethyl-piperidinyl benzilate ([18F]FEPB) to the muscarinic cholinergic receptor was measured in awake and anesthetized rats. Studies were done using an equilibrium infusion technique to provide estimates of specific binding as distribution volume ratios. Anesthesia with either isoflurane or sodium pentobarbital produced a significant (65-90%) increase of radiotracer binding in receptor-rich brain regions (striatum, cortex, hippocampus) relative to awake controls. Pretreatment of anesthetized animals with the acetylcholinesterase inhibitor phenserine produced no further increases in radioligand binding, in contrast to the large (>70%) increases previously observed in awake animals following drug treatment. These studies demonstrate that anesthesia can produce significant changes in baseline biochemical measures that can obscure even very large effects of pharmacological challenges.

[Pharmacological evaluation of efficacy and safety of propiverine hydrochloride in patients of overactive bladder--relationship between urodynamic observation and propiverine pharmacokinetics--]

PURPOSE

The clinical benefit of propiverine hydrochloride against overactive bladder was evaluated, and the relationships between urinary voiding functions and the pharmacokinetics were investigated by means of clinical pharmacology with PK/PD approach.

PATIENTS AND METHODS

Total 7 patients suffering urgency with urinary frequency and incontinence received propiverine hydrochloride in doses of 10 mg qd or 20 mg qd for 4 weeks, and then the doses were switched in cross-over manner to continue the treatment for further 4 weeks. The urodynamic measurements as well as pharmacokinetic samplings were done before the medication, 4 weeks and 8 weeks after the starting medication, to examine the dose-response and concentration-response relationships.

RESULTS

The volume at first desire to void increased according to dose increased, and the volume at first involuntary contraction tended to increase according to both dose and drug concentration in plasma. However, no apparent dose-response relationships were observed for maximum urinary flow rate and the detrusor pressure at the maximum urinary flow rate. The PK/PD analysis using Emax model suggested that, approximately 75 ng/mL of the propiverine concentration in plasma allowed the increase in the volume at first involuntary contraction for 50%. The urinary residual volume increased in dose-dependent manner only in the patients with severe grade of lower urinary tract obstruction, but scarcely increased in the patients with moderate grade or below.

CONCLUSION

Propiverine hydrochloride improved the urinary voiding functions with a tendency to depend on both dose and concentration in plasma. After the administration of propiverine hydrochloride, the concentration in plasma will immediately reach the level at which the drug can increase in the volume at first involuntary contraction for 50%, and then the concentration level will sustain the effect ranging from 10% to 50% increase in bladder volume. Furthermore, the lower urinary tract obstruction will be a predictor of increase in urinary residual volume.

Binding kinetics of11c-n-methyl piperidyl benzilate (11c-nmpb) in a rhesus monkey brain using the cerebellum as a reference region

The binding kinetics of 11C-N-methyl piperidyl benzilate (11C-NMPB) in rhesus monkey brain were studied using animal positron emission tomography (PET) (SHR2000). This study is intended to assess the validity of the method using the cerebellum as a reference region, and to evaluate the effects of anesthesia on 11C-NMPB binding. Two monkeys, anesthetized with ketamine, received intravenous 11C-NMPB alone (370-760 MBq, < 1 microg/kg) or mixed with varying doses of nonradioactive NMPB (3 microg/kg, 10 microg/kg, 30 microg/kg) and were subjected to PET scans for 60 minutes. Regions of interest (ROI) were drawn on reconstructed PET images and a time-activity curve was obtained for each region. 11C-NMPB accumulated densely in the striatum and cerebral cortex with time. In contrast, the tracer accumulation significantly decreased with increased doses of nonradioactive NMPB. In the cerebellum, on the other hand, the accumulation of 11C-NMPB remained low and the tracer was slowly eliminated from the brain following the injection. 11C-NMPB binding in the cerebellum was barely affected by the increased dose of nonradioactive NMPB. We thus concluded that the specific 11C-NMPB binding was negligible in the cerebellum, and performed simplified evaluation of 11C-NMPB binding in each brain region by a graphical method using the cerebellum as a reference region. PET was conducted 26 times, in total both in ketamine-anesthetized and awake monkeys (n = 3 each). Measurements of 11C-NMPB binding showed good run-to-run reproducibility within individual animals. When 11C-NMPB binding was compared between ketamine-treated and awake animals, a significant increase in 11C-NMPB binding was observed in the striatum but not in other brain regions of ketamine-treated animals.

Pharmacodynamics of propiverine and three of its main metabolites on detrusor contraction

1. Besides its antimuscarinic effects, propiverine may possess an additional mode of action. We compared the effects of propiverine, three of its metabolites (M-5, M-6, M-14) and atropine in human, pig and mouse urinary bladder preparations in order to elucidate the nature of a possible additional mode of action. 2. Like the parent compound, M-5, M-6 and M-14 reduced to variable degrees the contractions elicited by electric field stimulation (EFS) of isolated, urothelium-denuded detrusor strips. In mouse the atropine-resistant and therefore the nonadrenergic, noncholinergic component of contractile response to EFS was reduced by M-5, M-14 and propiverine, but was hardly affected by M-6. 3. Atropine, propiverine and M-6 significantly shifted the cumulative concentration-response curves for carbachol (CCh) to higher concentrations. Atropine and M-6 did not affect the maximum tension induced by CCh. Propiverine, M-5 and M-14 reduced the maximum CCh effect, suggesting at least one additional mode of action. This pattern of response was observed in all the three species, albeit with some differences in sensitivity to the various agents. 4. In freshly isolated human detrusor smooth muscle cells, propiverine and M-14 inhibited the nifedipine-sensitive L-type calcium current (I(Ca)) in a concentration-dependent manner. In contrast, the effects of M-5 and M-6 on I(Ca) were insignificant in the concentration range examined. 5. The investigated responses to propiverine and its metabolites suggest that impairment of maximum CCh-induced contractions is due to strong effect on I(Ca) and that this may be associated with the presence of the aliphatic side chain.

Sensitivity of [11C]N-methylpyrrolidinyl benzilate ([11C]NMPYB) to endogenous acetylcholine: PET imaging vs tissue sampling methods

Administration of phenserine, an acetylcholinesterase inhibitor, raises endogenous brain acetylcholine levels and has been previously shown to reduce in vivo binding of the muscarinic cholinergic receptor antagonist [(11)C]N-methylpyrrolidinyl benzilate ([(11)C]NMPYB) in the awake rat brain. In this study, phenserine pretreatment was studied in both awake and isoflurane-anesthetized rats using the techniques of ex vivo dissection or in vivo microPET imaging. In ex vivo dissection experiments, a statistically significant 10% inhibition of [(11)C]NMPYB binding could be demonstrated in both awake and anesthetized animals after phenserine pretreatment, showing no deleterious effect of using isoflurane anesthesia. However, microPET imaging in anesthetized animals failed to successfully demonstrate inhibition of [(11)C]NMPYB binding following the identical phenserine treatment protocol. These results demonstrate that in small numbers of subjects ex vivo dissection may be a more sensitive experimental method for determining small changes of in vivo radiotracer binding in this model of neurotransmitter competition for brain receptor sites.

Validation of a simple liquid chromatography–tandem mass spectrometric method for the determination of propiverine hydrochloride and its N-oxide metabolite in human plasma

A simple high-performance liquid chromatography (HPLC)-tandem mass spectrometric method has been developed for determination of propiverine hydrochloride and its metabolite, propiverine N-oxide (M-1) in human plasma using stable isotopes, propiverine hydrochloride-d10 and M-1-d10, as internal standards. The analytes were extracted with dichloromethane from 0.2 ml of plasma in neutral condition (pH 7.0) and separated by HPLC on a C18 reversed-phase column using methanol-1% acetic acid (50:50) as a mobile phase, and detected using positive electrospray ionization in selected reaction monitoring (SRM) mode. The method was validated over a concentration range of 2-500 ng/ml for propiverine hydrochloride and 4-1000 ng/ml for M-1 using 0.2 ml of human plasma per assay. The method developed was successfully applied to analysis of propiverine hydrochloride and M-1 in clinical studies.

Pharmacokinetics and bioavailability of denaverine hydrochloride in healthy subjects following intravenous, oral and rectal single doses

The neurotropic-musculotropic spasmolytic agent denaverine hydrochloride is used mainly in the treatment of smooth muscle spasms of the gastrointestinal and urogenital tract. Despite its commercial availability as a solution for intravenous or intramuscular administration (ampoule) and as a suppository formulation, no pharmacokinetic data in man was available to date. Therefore, the objectives of this clinical trial were to determine the basic pharmacokinetic parameters of denaverine after intravenous administration, to assess the feasibility of using the oral route of administration and to characterise the bioavailability of the suppository formulation. To achieve this, healthy subjects received 50 mg denaverine hydrochloride intravenously, orally and rectally in aqueous solutions and rectally as suppository in an open, randomised crossover design. Total body clearance, volume of distribution at steady-state and half-life of denaverine are 5.7 ml/min per kg, 7.1 l/kg and 33.8 h, respectively. The absolute bioavailability after oral administration of an aqueous solution is 37%. First-pass metabolism leading to the formation of N-monodemethyl denaverine was found to be one reason for the incomplete bioavailability after oral administration. Rectal administration of an aqueous solution of denaverine hydrochloride resulted in a decreased rate (median of C(max) ratios: 26%, difference in median t(max) values: 1.9 h) and extent (31%) of bioavailability compared to oral administration. Using the suppository formulation led to a further reduction in rate (median of C(max) ratios: 30%, difference in median t(max) values: 3 h) and extent (42%) of bioavailability compared to the rectal solution.

(R)-N-[11C]methyl-3-pyrrolidyl benzilate, a high-affinity reversible radioligand for PET studies of the muscarinic acetylcholine receptor

We recently reported the synthesis and binding affinity of ligands for the muscarinic acetylcholine receptor (mAChR) based on both the pyrrolidyl and piperidyl benzilate scaffold. One of these, (R)-3-pyrrolidyl benzilate, was successfully radiolabeled with [(11)C]methyl triflate and the resulting compound, (R)-N-[(11)C]methyl-3-pyrrolidyl benzilate (3-[(11)C]NMPYB), was evaluated as a reversible, acetylcholine-sensitive tracer for the mAChR (K(i) of unlabeled 3-NMPYB is 0.72 nM). This compound displayed high, receptor-mediated retention in regions of the mouse and rat brain known to have high concentrations of mAChRs. Moreover, bolus studies in a pigtail monkey showed that this compound had superior clearance from the brain when compared to muscarinic radiotracers previously employed in human PET studies. Infusion studies in the same monkey revealed that it was possible to achieve equilibrium of radiotracer distribution for 3-[(11)C]NMPYB in both the striatum and cortex. Sensitivity to endogenous acetylcholine levels was evaluated by injecting phenserine (5 mg/kg) into rats prior to administration of 3-[(11)C]NMPYB in an equilibrium infusion protocol. This pretreatment produced a modest, statistically significant decrease (9-11%) in the distribution volume ratios for muscarinic receptor rich regions of the rat brain as compared to controls.

Age differences in muscarinic cholinergic receptors assayed with (+)N-[(11)C]methyl-3-piperidyl benzilate in the brains of conscious monkeys

Age-related changes in muscarinic cholinergic receptors were evaluated with the novel ligand (+)N-[(11)C]methyl-3-piperidyl benzilate ((+)3-MPB) in the living brains of young (5.9 +/- 1.8 years old) and aged (19.0 +/- 3.3 years old) monkeys (Macaca mulatta) in the conscious state using high-resolution positron emission tomography (PET). For quantitative analysis of receptor binding in vivo, metabolite-corrected arterial plasma radioactivity curves were obtained as an input function into the brain, and kinetic analyses using the three-compartment model and graphical Logan plot analysis were applied. Kinetic analyses of [(11)C](+)3-MPB indicated a regionally specific decrease in the receptor binding in vivo determined as binding potential (BP) = k(3)/k(4) in aged animals compared with young animals. Thus, the frontal and temporal cortices as well as the striatum showed age-related reduction of muscarinic cholinergic receptors in vivo, reflecting the reduced receptor density (B(max)) determined by Scatchard plot analysis in vivo. In the hippocampus, although BP of [(11)C](+)3-MPB indicated no significant age-related changes, it showed an inverse correlation with individual cortisol levels in plasma. When the graphical Logan plot analysis was applied, all regions assayed showed significant age-related decrease of [(11)C](+)3-MPB binding. These results demonstrate the usefulness of kinetic three-compartment model analysis of [(11)C](+)3-MPB with metabolite-corrected arterial plasma input as an indicator for the aging process of the cortical muscarinic cholinergic receptors in vivo as measured by PET.

Evaluation of PET ligands (+)N-[(11)C]ethyl-3-piperidyl benzilate and (+)N-[(11)C]propyl-3-piperidyl benzilate for muscarinic cholinergic receptors: a PET study with microdialysis in comparison with (+)N-[(11)C]methyl-3-piperidyl benzilate in the conscious monkey brain

We developed PET ligands (+)N-[(11)C]ethyl-3-piperidyl benzilate ([(11)C](+)3-EPB) and (+)N-[(11)C]propyl-3-piperidyl benzilate ([(11)C](+)3-PPB) for cerebral muscarinic cholinergic receptors. The distribution and kinetics of the novel ligands were evaluated for comparison with the previously reported ligand (+)N-[(11)C]methyl-3-piperidyl benzilate ([(11)C](+)3-MPB) in the monkey brain (Macaca mulatta) in the conscious state using high-resolution positron emission tomography (PET). At 60-91 min postinjection, regional distribution patterns of these three ligands were almost identical, and were consistent with the muscarinic receptor density in the brain as previously reported in vitro. However, the time-activity curves of [(11)C](+)3-EPB and [(11)C](+)3-PPB showed earlier peak times of radioactivity and a faster clearance rate than [(11)C](+)3-MPB in cortical regions rich in the receptors. Kinetic analysis using the three-compartment model with time-activity curves of radioactivity in metabolite-corrected arterial plasma as input functions revealed that labeling with longer [(11)C]alkyl chain length induced lower binding potential (BP = k(3)/k(4)), consistent with the rank order of affinity of these ligands obtained by an in vitro assay using rat brain slices and [(3)H]QNB. The cholinesterase inhibitor Aricept administered at doses of 50 and 250 microg/kg increased acetylcholine level in extracellular fluid of the frontal cortex and the binding of [(11)C](+)3-PPB with the lowest affinity to the receptors was displaced by the endogenous acetylcholine induced by cholinesterase inhibition, while [(11)C](+)3-MPB with the highest affinity was not significantly affected. Taken together, these observations indicate that the increase in [(11)C]alkyl chain length could alter the kinetic properties of conventional receptor ligands for PET by reducing the affinity to receptors, which might make it possible to assess the interaction between endogenous neurotransmitters and ligand-receptor binding in vivo as measured by PET.

A validated high-performance liquid chromatographic assay for the simultaneous determination of denaverine and its N-monodemethyl metabolite in human plasma

An isocratic reversed-phase high-performance liquid chromatographic method for the simultaneous determination of denaverine and its N-monodemethyl metabolite (MD 6) in human plasma is described. The assay involves the extraction with an n-heptane-2-propanol mixture (9:1, v/v) followed by back extraction into 12.5% (w/w) phosphoric acid. The analytes of interest and the internal standard were separated on a Superspher RP8 column using a mobile phase of acetonitrile-0.12 M NH4H2PO4-tetrahydrofuran (24:17.2:1, v/v), adjusted to pH 3 with 85% (w/w) phosphoric acid. Ultraviolet detection was used at an operational wavelength of 220 nm. The retention times of MD 6, denaverine and the internal standard were 5.1, 6.3 and 10.2 min, respectively. The assay was validated according to international requirements and was found to be specific, accurate and precise with a linear range of 2.5-150 ng/ml for denaverine and MD 6. Extraction recoveries for denaverine and MD 6 ranged from 44 to 49% and from 42 to 47%, respectively. The stability of denaverine and MD 6 in plasma was demonstrated after 24 h storage at room temperature, after three freeze-thaw cycles and after 7 months frozen storage below -20 degrees C. The stability of processed samples in the autosampler at room temperature was confirmed after 24 h storage. The analytical method has been applied to analyses of plasma samples from a pharmacokinetic study in man.

Evaluation of novel PET ligands (+)N-[11C]methyl-3-piperidyl benzilate ([11C](+)3-MPB) and its stereoisomer [11C](-)3-MPB for muscarinic cholinergic receptors in the conscious monkey brain: a PET study in comparison with

The novel muscarinic cholinergic ligands (+)N-[11C]methyl-3-piperidyl benzilate ([11C](+)3-MPB) and its stereoisomer [11C](-)3-MPB were evaluated in comparison with [11C]4-MPB in the brains of conscious monkeys (Macaca mulatta) using high-resolution positron emission tomography (PET). The regional distribution patterns of [11C](+)3-MPB and [11C]4-MPB at 60-91 min postinjection were almost identical: highest in the striatum and occipital cortex; intermediate in the temporal and frontal cortices, cingulate gyrus, hippocampus, and thalamus; lower in the pons; and lowest in the cerebellum. The uptake of [11C](+)3-MPB in all regions was higher and the dynamic range of regional uptake differences of [11C](+)3-MPB was better than those of [11C]4-MPB. The levels of [11C](-)3-MPB were much lower in all regions of the brain than [11C](+)3-MPB and [11C]4-MPB. Administration of scopolamine, a muscarinic cholinergic antagonist, at a dose of 50 microg/kg reduced the radioactivity of [11C](+)3-MPB and [11C]4-MPB in all regions except the cerebellum. Time-activity curves of [11C](+)3-MPB peaked in all regions, while those of [11C]4-MPB showed gradual increases with time in all regions except the thalamus, pons, and cerebellum. Two graphical analyses (Logan plot and Patlak plot) with plasma radioactivity as an input function into the brain were applied to evaluate receptor binding in vivo. [11C](+)3-MPB showed linear regression curves on Logan plot analysis and nonlinear curves on Patlak plot in all regions, suggesting that [11C](+)3-MPB bound reversibly to the muscarinic receptors. The in vivo binding parameters as well as uptake at 60-91 min postinjection of [11C](+)3-MPB were consistent with muscarinic receptor density in the brain as reported in vitro.

Propiverine-induced Parkinsonism: a case report and a pharmacokinetic/pharmacodynamic study in mice

PURPOSE

We present a case report of propiverine-induced Parkinsonism. We previously reported the induction of catalepsy by amiodarone, aprindine and procaine, which possess a diethylaminomethyl moiety and demonstrated selective blockade of dopamine D2 receptors by these drugs in mice. We hypothesized that drugs possessing a diethylaminomethyl structure may generally induce Parkinsonism and/or catalepsy.

METHODS

Thus, we performed a study to examine whether oxybutynin, pentoxyverine and etafenone, as well as propiverine, induce catalepsy in mice.

RESULTS

The intensity of drug-induced catalepsy was in the order: haloperidol > etafenone > pentoxyverine > propiverine > oxybutynin. In vivo occupancy of dopamine D1, D2 and mACh receptors in the striatum was also examined. The in vitro binding affinities to the D1, D2 and mACh receptors in the striatum synaptic membrane were within the ranges of 2.4-140 microM, 380-4,200 nM, and 1.2-2,800 nM, respectively.

CONCLUSIONS

These results support the idea that any drug possessing a diethylaminomethyl moiety may contribute to the induction of catalepsy, possibly by occupying dopamine receptors.

Quantitative autoradiography with short-lived positron emission tomography tracers: a study on muscarinic acetylcholine receptors with N-[(11)C]methyl-4-piperidylbenzilate

The present work demonstrates quantitative autoradiography by using positron emission tomography tracers and storage phosphorimaging plates. The uptake and association of [(11)C]N-methyl-4-piperidylbenzilate was measured in rat brain tissue cryosections of various thicknesses. The signal increased with increasing section thickness, but only in 10-micrometer-thick sections did the binding reach the steady state during a 50-min observation time. This violation of the equilibrium condition, potentially combined with perfusion limitations, leads to erroneous increased binding-site density and decreased affinity in the 25- and 50-micrometer-thick sections. For better imaging of receptor distribution it is reasonable to use thicker sections. For quantitative analysis of receptor-binding parameters, the specific properties of ligands at different thicknesses of cryosections need to be considered. Evidence is provided that the nonselective muscarinic antagonist N-methyl-4-piperidylbenzilate binds preferentially to the M(4) subtype of muscarinic acetylcholine receptors.

Using single photon emission tomography (SPECT) and positron emission tomography (PET) to trace the distribution of muscarinic acetylcholine receptor (MACHR) binding radioligands

Two [18F] labeled ligands for the mAChR were prepared and evaluated in rodents and nonhuman primates. The properties of both compounds, one an agonist and the other an antagonist, were consistent with M2 subtype specificity.

Muscarinic cholinergic receptors in human narcolepsy: a PET study

OBJECTIVES

To investigate the function of the muscarinic cholinergic receptor (mAchR) in narcolepsy and the effects of pharmacotherapy on mAchRs.

BACKGROUND

Muscarinic neural transmission serves as the main executive system in REM sleep. Studies in canine narcolepsy reported an increase in mAchRs in the pons.

METHODS

The mAchRs of 11 drug naive/free patients with narcolepsy and 21 normal controls were investigated using PET with [11C]N-methyl-4-piperidylbenzilate ([11C]NMPB). Measurements were done in the pons, thalamus, striatum, and cerebral cortex. Seven of the 11 patients also underwent additional PET scans after the alleviation of symptoms by pharmacotherapy.

RESULTS

There were no differences in [11C]NMPB binding between the control and drug naive/free patients in all areas analyzed. At the time of on-medication PET scan, [11C]NMPB binding in the thalamus was decreased, but only to a small degree compared with that by anticholinergic drugs.

CONCLUSION

The present results do not support the notion that the mAchR is the main site of action of pharmacotherapy in the marked clinical improvement of human cataplexy.

Pharmacokinetics and safety of propiverine in patients with fatty liver disease

OBJECTIVE

The present study was designed to assess the pharmacokinetics of propiverine after single and multiple dosing in patients with and without fatty liver disease.

METHODS

The serum concentration-time curves of propiverine and its main metabolite propiverine-N-oxide were investigated in 12 patients with mild to moderate impairment of liver function (mean antipyrine clearance 26.0 ml x min(-1)) and in 12 controls (antipyrine clearance 42.8 ml x min(-1)). Subjects were treated orally with propiverine hydrochloride (Mictonorm) for 5 days (15 mg t. i. d.) to reach steady state.

RESULTS

No significant differences were observed for propiverine and its main metabolite with regard to peak serum concentration (Cmax), area under the serum concentration-time curve (AUC) and elimination half-life (t1/2). Adverse events were reported by 12 patients. Five patients with fatty liver disease and seven patients with normal liver function complained of dry mouth and/or blurred vision. All adverse events reported were transient and mild.

CONCLUSION

No pharmacokinetic differences relevant for safety were observed, comparing patients with and without fatty liver disease following repeated oral administration of propiverine. Thus there seems to be no need to adjust the dose in patients with mild to moderate impairment of liver function.

Comparison of the in vitro skin penetration of propiverine with that of terodiline

This study was designed to clarify the relationship between the properties of propiverine and skin penetration, and to compare the in vitro penetration characteristics of propiverine and terodiline through rat skin. Propiverine in both hydrochloride and free forms penetrated across the skin extremely slowly, with a 2.6 times higher flux in the hydrochloride than that in the free base, in the absence of enhancers. Various enhancers failed to enhance the penetration of propiverine hydrochloride, whereas the same agents slightly increased the flux of the free form, these being due to the slow release rate of the free form from the gel formulations, an extremely high lipophilicity (log Poct/water > 4.97), much less solubility (0.141 mg/ml) and a large partition capacity of the drug to skin components. Terodiline in both forms was able to rapidly penetrate through the skin, even in the absence of enhancers, with 20.2 and 9.8 times higher fluxes respectively, than the corresponding forms of propiverine. The high penetration characteristics of terodiline would be due to a suitable lipophilicity, low binding property as well as the structural masking from the binding to the epidermal components. Propiverine hydrochloride penetrated through the stratum corneum 4.4 times and viable skin 3.1 times higher than through full-thickness skin, while the fluxes of terodiline through the stratum corneum and viable skin were similar to each other, with high penetration rates for each form.

Synthesis, in vivo biodistribution and dosimetry of [11C]N-methylpiperidyl benzilate ([11C]NMPB), a muscarinic acetylcholine receptor antagonist

4-N-Methylpiperidyl benzilate (NMPB), a high affinity antagonist for the muscarinic cholinergic receptor, has been synthesized in carbon-11-labeled form through the N-[11C]methylation of 4-piperidylbenzilate. The product was isolated by HPLC, and obtained in yields (> 100 mCi) and specific activities (500-3000 Ci/mmol) sufficient for in vivo evaluation in small animals. Time-dependent regional brain distributions in rats and mice showed high radiotracer uptake and retention in striatum and cortex, and low in cerebellum, consistent with muscarinic cholinergic receptor distributions. Radiotracer retention in tissues could be significantly reduced by pretreatment of animals with a large dose of a competing antagonist, quiniclidinyl benzilate. Whole body biodistribution in rats was used to calculate the expected human internal radiation dosimetry for this new radiopharmaceutical. These animal experiments formed the basis for subsequent introduction of [11C]NMPB into human use with positron emission tomography.

An acute effect of triazolam on muscarinic cholinergic receptor binding in the human brain measured by positron emission tomography

An acute effect of triazolam, a potent benzodiazepine agonist, on cholinergic receptor binding in the human brain was measured by PET (positron emission tomography) using [11C]N-methyl-4-piperidylbenzilate ([11C]NMPB), a potent muscarinic cholinergic receptor antagonist. Two PET scans were performed in each subject: (1) control scan; (2) after oral administration of 0.5 mg triazolam or placebo. The previously discussed amnestic effect of triazolam was measured by immediate and delayed recall of meaningful and meaningless syllables. A compartment model employing the radioactivity in the cerebellum as an input function was used for the quantification of receptor binding. The binding parameter, k3, was decreased after triazolam administration in all measured regions, whereas no change was observed after placebo treatment. The reduction compared to the control study varied from 8.6 +/- 3.7% in the temporal cortex to 16.3 +/- 6.3% in the thalamus. Triazolam administration impaired both immediate and delayed recall of syllables, whereas placebo administration had no effects. Benzodiazepine agonists are reported to decrease the cortical acetylcholine release. The decrease of acetylcholine release in the synaptic cleft might be the explanation for the decreased binding of [11C]NMPB.

Kinetics of propiverine as assessed by radioreceptor assay in poor and extensive metabolizers of debrisoquine

A pharmacokinetic study with 30 mg propiverine p.o. was performed in healthy volunteers (10 males, 6 females, age 36-56 years, body weight 55-100 kg, body height 162-184 cm, Broca index 0.96-1.19). 8 of them were poor and 8 extensive metabolizers of the debrisoquine type hydroxylation polymorphism. The total anticholinergic activity of the parent compound and active metabolites was measured with a radioreceptor assay calibrated with the metabolite M2. The affinity of this metabolite to the muscarinic receptors was similar to that of atropine. The urinary excretion of 3 major metabolites was determined with TLC and densitometry. Arterial blood pressure, heart rate, diameter of pupils, accommodation and parotic salivary flow were also measured. The concentrations of anticholinergic equivalents of propiverine were below 1 ng/ml of M2. 1.4-6.0% of the dose were excreted as N-oxidized metabolites into the urine. The poor and extensive metabolizers of debrisoquine did not differ significantly with regard to the concentration time behaviour of the active drug components, pattern of major metabolites, adverse drug reactions or any pharmacodynamic parameters measured.

In vitro and ex vivo evaluation of cyclic aminoalkyl benzilates as potential emission tomography ligands for the muscarinic receptor

A series of muscarinic antagonists were screened as potential receptor imaging agents. (+)2 alpha-tropanyl benzilate (TRB), N-methyl-4-piperidyl benzilate (NMPB) and several analogs amenable to labeling with positron emitting isotopes were evaluated for muscarinic binding to mouse brain tissue in vitro and ex vivo using [3H]quinuclidinyl benzilate as the probe. The in vitro assay directly compared the innate binding affinities of the compounds. The rank order of binding (IC50) was TRB (0.7 nm), QNB (0.8 nm), scopolamine (1.3 nm) and NMPB (1.6 nm). The ex vivo assay was used to gain information regarding the pharmacokinetics and brain penetration of the compounds in live animals. Ex vivo results demonstrated that TRB was rapidly taken up into the brain and was equipotent with QNB in occupying muscarinic binding sites at early time points, but TRB binding decreased twice as fast over time as QNB binding. The results suggest TRB would be a good candidate for radiolabeling and further study.

[Biotransformation of denaverin (Spasmalgan) in the rat]

After oral application of denaverine hydrochloride to rats (200-250 mg/kg) 12 metabolites have been detectecd in urine. Besides the unchanged drug, 8 metabolites were identified by MS as 2,2-diphenyl-(2-dimethylaminoethyl) acetate (3), diphenylacetic (5) and benzilic acid (6); methyl-and ethyl [2-(2-ethylbutoxy)-2,2-diphenyl]acetate (7, 11), methylbenzilate (10), N-demethyl-1 (12) and 3,3-diphenyl-morpholin-2-one (13). 6 and the metabonate 13 represent the main metabolic products. Compounds 7 and 11 indicate the metabolic pathway about an alkoxybenzilic acid (4). Phenols resp. conjugates were not detected.

On the pharmacokinetics and metabolism of propiverine in man

The pharmacokinetics of 14C-propiverine was studied in 13 volunteers and in 2 patients after a single i.v. injection of 5 mg or after oral administration of 15 mg. To each dose 1.11 MBq 14C-propiverine was added. The radioactivity measured in plasma, urine (and bile fluid), and the metabolites were estimated by an extraction procedure together with TLC and radiochromatography. Propiverine was eliminated from the plasma with a half-life time (t0.5) of 4.1 h (i.v. and per os), while the plasma radioactivity decreased with a t0.5 of 21.2 (i.v.) or 10.4 h (per os). Within 4 days, 84.5 (i.v.) or 53.5% (per os) of the administered radioactivity was excreted in urine. The absorption of radioactivity of propiverine amounted to 84.5%, while the amount of available propiverine was only 48.9%. In two patients with cannulated ductus choledochus, 21.5 or 14.7% of the administered radioactivity was excreted within 2 days. The metabolic pattern of plasma, urine and bile fluid mainly consisted of amine oxides, substances oxidized in the propyl side chain, desalkylated metabolites, substances with a N-demethylated piperidino group or with ester cleavage, and glucuronide conjugates. Unchanged propiverine appeared in plasma, urine and bile at about 6 to 8% of the administered dose.

[The biotransformation of propiverin hydrochloride (Mictonorm)]

Propiverine hydrochloride [1; hydrochloride of O-n-Propyl-(N-methylpiperidinyl-4)-benzilate; Mictonorm] is metabolized after p.o. application of 25 mg/kg on rats almost completely. Besides of small amounts of unchanged 1 in urine were detected the phase-I metabolites N-methylpiperidinyl(4)-benzilate (2), 2,2-diphenyl-5-methyl-1, 4-dioxan-3-on (3), N-oxide of 2 (4), benzilic acid (5) and O-n-propylbenzilic acid (6) using ms, dc and hplc comparison of the isolated compounds with authentic samples. The structure of further metabolites, i.e. monohydroxy-benzophenone (7), acetoxy-1-derivatives (8) and ethylbenzilate (9) were elucidated by high resolution MS.