Shuji Maruyama

Effects of Ginkgo Biloba Extract on Pharmacokinetics and Pharmacodynamics of Tolbutamide and Midazolam in Healthy Volunteers

This study was undertaken to clarify the influence of repeated oral administration of Ginkgo biloba extract (GBE) on CYP2C9 and CYP3A4. CYP2C9 probe (tolbutamide, 125 mg) and CYP3A4 probe (midazolam, 8 mg) were orally administered to 10 male healthy volunteers before and after GBE intake (360 mg/d) for 28 days, and they received 75 g glucose after the dosing of tolbutamide. Plasma drug concentrations and blood glucose levels were measured. The area under concentration versus time curve (AUC0–∞) for tolbutamide after GBE intake was slightly but significantly (16%) lower than that before GBE intake. Concomitantly, GBE tended to attenuate AUC0–2 of blood glucose—lowering effect of tolbutamide. AUC0–∞ for midazolam was significantly (25%) increased by GBE intake and oral clearance was significantly (26%) decreased. Thus, it is suggested that the combination of GBE and drugs should be cautious in terms of the potential interactions, especially in elderly patients or patients treated with drugs exerting relatively narrow therapeutic windows.

Human Muscarinic Receptor Binding Characteristics of Antimuscarinic Agents to Treat Overactive Bladder

PURPOSE We characterized the binding affinities of several antimuscarinic agents in human muscarinic receptors. MATERIALS AND METHODS Competitive inhibitory effects of antimuscarinic agents on specific NMS [H] (PerkinElmer Life Sciences, Boston, Massachusetts) binding were examined in human tissue homogenates and in CHO-K1 cell membranes expressing human muscarinic receptor subtypes. RESULTS Oxybutynin, propiverine, tolterodine, the respective metabolites DEOB, DPr-P-4(N-->O) and 5-HM, and darifenacin inhibited in concentration dependent fashion specific [(3)H]NMS binding in homogenates of the human bladder and parotid gland as well as in membranes of CHO-K1 cell lines expressing human muscarinic M(1) to M(5) receptor subtypes. Based on inhibition constant values the inhibitory effects of tolterodine, 5-HM and DPr-P-4(N-->O) were 1.4 to 1.7 times greater in the bladder than in the parotid gland, whereas the inhibitory effects of oxybutynin, DEOB, propiverine and darifenacin were 2 to 10 times greater in the parotid gland. Consequently tolterodine, 5-HM and DPr-P-4(N-->O) compared with oxybutynin, DEOB, propiverine and darifenacin were found to show 3 to 4 times greater affinity to muscarinic receptors in the human bladder than in the parotid gland. Tolterodine and 5-HM were 2-fold more potent for inhibiting specific [(3)H]NMS binding at cell membranes expressing the M(2) vs the M(3) subtype. Conversely oxybutynin, DEOB, propiverine, DPr-P-4(N-->O) and darifenacin showed 2 to 22 times higher affinity to the M(3) than to the M(2) subtype. CONCLUSIONS Compared with oxybutynin, tolterodine, 5-HM and DPr-P-4(N-->O) may bind more selectively to muscarinic receptors in the human bladder than in the parotid gland.

In Vivo Quantitative Autoradiographic Analysis of Brain Muscarinic Receptor Occupancy by Antimuscarinic Agents for Overactive Bladder Treatment

We evaluated the effects of five clinically used antimuscarinic agents for overactive bladder (OAB) treatment on in vivo muscarinic receptor binding in rat brain by quantitative autoradiography. There was a dose-related decrease in in vivo specific (+)N-[11C]methyl-3-piperidyl benzilate ([11C](+)3-MPB) binding in each brain region of rats 10 min after i.v. injection of oxybutynin, propiverine, solifenacin, and tolterodine. Rank order of the i.v. dose for 50% receptor occupancy (RO50) of antimuscarinic agents in rat brain regions was propiverine > solifenacin > tolterodine, oxybutynin. There was a good linear relationship between in vivo (pRO50 values in the rat hippocampus) and in vitro (pKi values in human M1 receptors) receptor binding activities of propiverine, solifenacin, and tolterodine. The observed RO50 value of oxybutynin was approximately five times smaller than the predicted in vitro Ki value. The dose ratios of antimuscarinic agents for the brain receptor occupancy (RO50) to the inhibition of carbachol- and volume-induced increases in intravesical pressure (ID50), which reflects in vivo selectivity for the urinary bladder over the brain, were greater for solifenacin, tolterodine, and propiverine than oxybutynin. Darifenacin displayed only a slight decrease in specific [11C](+)3-MPB binding in the rat brain regions, and it was not dose-related. In conclusion, in vivo quantitative autoradiographic analysis of brain muscarinic receptor occupancy may provide fundamental basis for managing central nervous system (CNS) side effects in antimuscarinic therapy for OAB. It is suggested that in the treatment of OAB, CNS side effects can be avoided by antimuscarinic agents with high selectivity for the urinary bladder over the brain.

Noninvasive evaluation of brain muscarinic receptor occupancy of oxybutynin, darifenacin and imidafenacin in rats by positron emission tomography.

AIMS The current study was conducted to evaluate, by the noninvasive positron emission tomography (PET), the binding of antimuscarinic agents used to treat overactive bladder (OAB) to muscarinic receptors in rat brain. MAIN METHODS Muscarinic receptor occupancy in the rat brain after the intravenous (i.v.) injection of oxybutynin, darifenacin and imidafenacin was evaluated by using a small animal PET system, and compared with the results by ex vivo autoradiographic and ex vivo radioligand binding experiments. KEY FINDINGS In PET study, the i.v. injection of oxybutynin but not darifenacin or imidafenacin at pharmacological doses decreased significantly binding potential (BP) of (+)N-[(11)C]methyl-3-piperidyl benzilate ([(11)C](+)3-MPB) in the rat cerebral cortex and corpus striatum in a dose-dependent manner. Similarly, in the in vivo autoradiographic experiment, oxybutynin dose-dependently reduced binding of [(11)C](+)3-MPB in the brain, whereas darifenacin and imidafenacin did not. Following the i.v. injection of oxybutynin, darifenacin and imidafenacin, there was a similar degree of binding to muscarinic receptors in the bladder as demonstrated by a significant increase in apparent dissociation constant (K(d)) values for specific [N-methyl-(3)H]scopolamine methyl chloride ([(3)H]NMS) binding. Significant binding of muscarinic receptors in the brain was observed after the injection of oxybutynin but not darifenacin or imidafenacin. SIGNIFICANCE Oxybutynin but not darifenacin or imidafenacin has potential side effects on the central nervous system (CNS) in patients with OAB. The results reveal the noninvasive characterization of brain receptor occupancy by PET to be a powerful tool for precise evaluation of adverse CNS effects of antimuscarinic agents in pre-clinical and clinical evaluations.

Effect of oxybutynin and imidafenacin on central muscarinic receptor occupancy and cognitive function: a monkey PET study with [(11)C](+)3-MPB.

Although antimuscarinic agents are widely used to treat overactive bladder (OAB), they have been shown to induce side effects including dry mouth and cognitive impairment. The present study was aimed to investigate the effects of antimuscarinic agents, oxybutynin and imidafenacin, on temporal changes in cognitive function and central mAChR occupancy in conscious monkeys (Macaca mulatta). Three conscious monkeys underwent positron emission tomography (PET) scans with a mAChR radioligand N-[(11)C]methyl-3-piperidyl benzilate ([(11)C](+)3-MPB). The scan sequence was pre, and 1, 4, and 24h post oral administration of oxybutynin (0.1-1.0mg/kg) or imidafenacin (0.01-0.1mg/kg). Maximum cognitive impairment was observed 1h post-oxybutynin at oral doses of 0.3 and 1.0mg/kg, in a dose-dependent manner, and oxybutynin produced significant positive correlations between mAChR occupancy and cognitive impairment in the cortices, thalamus, brainstem, and striatum. The most significant correlation was observed in the brainstem, and then cortices. In contrast, imidafenacin did not induce discernible cognitive impairment, despite having obtained some lesser occupancy in cortices and brainstem. We propose that the thresholds of mAChR occupancy to produce cognitive impairment by antimuscarinic agents are ca. 30-40% in cortices and ca. 20-30% in brainstem, and a desirable drug for OAB treatment should not occupy central mAChR above these thresholds.

Pharmacological effects and lung-binding characteristics of a novel VIP analogue, [R15, 20, 21, L17]-VIP-GRR (IK312532).

A novel VIP derivative, [R15, 20, 21, L17]-VIP-GRR (IK312532), relaxed potently the carbachol-induced contraction of guinea-pig isolated trachea with longer duration than that induced by VIP. IK312532 competed with [125I]VIP for the binding sites in the rat lung in a concentration-dependent manner. There was considerable decrease in specific [125I]VIP binding in each lobe of right and left lung 0.5 h after the intratracheal administration of IK312532 (50 microg/rat) as dry powder inhaler (DPI). Rosenthal analysis revealed that the administration of IK312532 (50 and 100 microg/rat)-DPI brought about a significant decrease of maximal number of binding sites (Bmax) for specific [125I]VIP binding in anterior and posterior lobes of rat right lung, suggesting a significant occupancy of lung VIP receptors. This effect by IK312532 in the posterior lobe of the right lung was dose-dependent and lasted until at least 2 h after the intratracheal administration. Furthermore, the antigen-evoked infiltration of granulocytes in the rat bronchiolar mucosa was markedly suppressed by the intratracheal administration of IK312532 (50 microg/rat)-DPI. In conclusion, the present study has shown that IK312532 exhibits long-lasting relaxation of tracheal smooth muscles and that the intratracheal administration of this peptide exerts a significant occupancy of lung VIP receptors as well as a suppression of the antigen-evoked infiltration of granulocytes in the bronchiolar mucosa. Thus, the formulation of IK312532 as DPI may be a pharmacologically useful drug delivery system for the therapy of pulmonary diseases such as asthma.

Urodynamics and bladder muscarinic receptors in rats with cerebral infarction and bladder outlet obstruction.

We characterized muscarinic receptor binding and urodynamic parameters in rats with cerebral infarction and chronic bladder outlet obstruction as models of detrusor overactivity. Bladder weight showed little significant difference between the cerebral-infarcted and sham rats, but the bladder weight was about three times greater in the bladder outlet-obstructed rats. Bladder capacity and voided volume were significantly lower (36.7 and 55.1%, respectively) in the cerebral-infarcted than in the sham rats. Involuntary contractions before micturition were seen in the bladder outlet-obstructed rats but not in sham rats. The bladder outlet-obstructed rats showed significant increases (2.65 and 2.57 times, respectively) in bladder capacity and voided volume, compared with those in sham rats. Bmax values for specific [N-methyl-3H]scopolamine ([3H]NMS) binding in the bladder were significantly (34%) increased in the cerebral-infarcted rats compared with sham rats, whereas Kd was unaffected by infarction. On the other hand, there was little significant change in Kd and Bmax for specific [3H]NMS binding in the bladder-obstructed rats compared with sham rats. In conclusion, the present study shows that cerebral infarction but not bladder outlet obstruction in rats causes up-regulation of bladder muscarinic receptors, and that such regulation of bladder muscarinic receptors may be at least partly associated with the symptoms of detrusor overactivity subsequent to cerebral infarction.

In vivo characterization of muscarinic receptors in peripheral tissues: evaluation of bladder selectivity of anticholinergic agents to treat overactive bladder

The present study was undertaken to characterize in vivo muscarinic receptors in peripheral tissues (urinary bladder, submaxillary gland, colon, stomach, heart) of mice, and further to evaluate bladder-selectivity of anticholinergic agents to treat overactive bladder. Following i.v. injection of [3H]QNB in mice, the radioactivity in peripheral tissues was exclusively detected as the unchanged form. The in vivo specific [3H]QNB binding in particulate fraction of tissue homogenates of mice showed a pharmacological specificity which characterized muscarinic receptors. Binding parameters (Kd and Bmax) for in vivo specific [3H]QNB binding differed between mouse tissues. Oral administration of oxybutynin attenuated significantly in vivo specific [3H]QNB binding in all tissues of mice. From ratios of AUCurinary bladder/AUCother tissues of time-dependent muscarinic receptor occupancy, oral oxybutynin has been shown to exert little urinary bladder selectivity. Following oral administration of propiverine, there was a significant reduction of in vivo specific [3H]QNB binding in the urinary bladder, colon and submaxillary gland, but not in the stomach and heart. From the ratios of AUCurinary bladder to AUCsubmaxillary gland or AUC heart, it has been shown that oral propiverine exerts higher selectivity to muscarinic receptors in the urinary bladder than in the submaxillary gland and heart. Similarly, tolterodine displayed high selectivity to muscarinic receptors in the urinary bladder than in the submaxillary gland. Thus, the present study has demonstrated that [3H]QNB may be a useful ligand for in vivo characterization of muscarinic receptor binding of anticholinergic agents to treat overactive bladder. Propiverine and tolterodine have exhibited in vivo selectivity of muscarinic receptor in the mouse urinary bladder rather than in the submaxillary gland, and such receptor binding specificity may be the reason of lower incidence of dry mouth.