Masayuki Nadai

Dysfunction of Cholinergic and Dopaminergic Neuronal Systems in β-Amyloid Protein-Infused Rats

Abstract: Accumulations of β‐amyloid protein are characteristic and diagnostic features of the brain of Alzheimers disease patients; however, the physiological role of this protein in CNS is unknown. We have previously reported that continuous infusion of β‐amyloid protein into rat cerebral ventricle impairs learning ability and decreases choline acetyltransferase activity, a marker enzyme of cholinergic neuron. In this study, the effects of β‐amyloid protein infusion on the release of neurotransmitters in cholinergic and dopaminergic neuronal systems were investigated by using an in vivo brain microdialysis method. Nicotine‐stimulated release of acetylcholine and dopamine in these animals was significantly lower than that in vehicle‐infused rats. Further, dopamine release induced by high‐K stimulation was decreased in β‐amyloid protein‐infused rats compared with vehicle‐infused rats. These results suggest that the release of the two transmitters, acetylcholine and dopamine, was decreased by β‐amyloid protein and that learning deficits observed in the β‐amyloid protein‐infused rats are partly due to the impairment of neurotransmitter release. Furthermore, continuous infusion of β‐amyloid protein may be a useful method to produce the animal model of Alzheimers disease.

Possible Involvement of the Drug Transporters P Glycoprotein and Multidrug Resistance-Associated Protein Mrp2 in Disposition of Azithromycin

ABSTRACT P glycoprotein and multidrug resistance-associated protein 2 (Mrp2), ATP-dependent membrane transporters, exist in a variety of normal tissues and play important roles in the disposition of various drugs. The present study seeks to clarify the contribution of P glycoprotein and/or Mrp2 to the disposition of azithromycin in rats. The disappearance of azithromycin from plasma after intravenous administration was significantly delayed in rats treated with intravenous injection of cyclosporine, a P-glycoprotein inhibitor, but was normal in rats pretreated with intraperitoneal injection erythromycin, a CYP3A4 inhibitor. When rats received an infusion of azithromycin, cyclosporine and probenecid, a validated Mrp2 inhibitor, significantly decreased the steady-state biliary clearance of azithromycin to 5 and 40% of the corresponding control values, respectively. However, both inhibitors did not alter the renal clearance of azithromycin, suggesting the lack of renal tubular secretion of azithromycin. Tissue distribution experiments showed that azithromycin is distributed largely into the liver, kidney, and lung, whereas both inhibitors did not alter the tissue-to-plasma concentration ratio of azithromycin. Significant reduction in the biliary excretion of azithromycin was observed in Eisai hyperbilirubinemic rats, which have a hereditary deficiency in Mrp2. An in situ closed-loop experiment showed that azithromycin was excreted from the blood into the gut lumen, and the intestinal clearance of azithromycin was significantly decreased by the presence of cyclosporine in the loop. These results suggest that azithromycin is a substrate for both P glycoprotein and Mrp2 and that the biliary and intestinal excretion of azithromycin is mediated via these two drug transporters.

Involvement of the Drug Transporters P Glycoprotein and Multidrug Resistance-Associated Protein Mrp2 in Telithromycin Transport

ABSTRACT The present study aims to investigate the role of P glycoprotein and multidrug resistance-associated protein (Mrp2) in the transport of telithromycin, a newly developed ketolide antibiotic, in vitro and in vivo. The in vitro experiments revealed that the intracellular accumulation of telithromycin in adriamycin-resistant human chronic myelogenous leukemia cells (K562/ADR) overexpressing P glycoprotein was significantly lower than that in human chronic myelogenous leukemia cells (K562/S) not expressing P glycoprotein. Cyclosporine significantly increased the intracellular accumulation of telithromycin in K562/ADR cells. When telithromycin was coadministered intravenously with cyclosporine in Sprague-Dawley (SD) rats, cyclosporine significantly delayed the disappearance of telithromycin from plasma and decreased its systemic clearance to 60% of the corresponding control values. Hepatobiliary excretion experiments revealed that cyclosporine almost completely inhibited the biliary clearance of telithromycin, suggesting that telithromycin is a substrate of P glycoprotein and a potential substrate of Mrp2. Moreover, the biliary clearance of telithromycin was significantly decreased by 80% in Eisai hyperbilirubinemic mutant rats with a hereditary deficiency in Mrp2, indicating that Mrp2, as well as P glycoprotein, plays an important role in the biliary excretion of telithromycin. When the effect of telithromycin on the biliary excretion of doxorubicin, a substrate of P glycoprotein and Mrp2, was examined in SD rats, telithromycin significantly decreased the biliary clearance of doxorubicin by 80%. Results obtained from this study indicate that telithromycin is a substrate of both P glycoprotein and Mrp2, and these transporters are involved in the hepatobiliary transport of telithromycin.

Time-dependent effects of Klebsiella pneumoniae endotoxin on hepatic drug-metabolizing enzyme activity in rats

The time‐dependent effects of Klebsiella pneumoniae endotoxin on hepatic cytochrome P450‐dependent drug‐metabolizing capacity (cytochrome P450 and b5 content, activity of aminopyrine N‐demethylase, p‐nitroanisole O‐demethylase, aniline hydroxylase and benzphetamine N‐demethylase) and on the pharmacokinetics of antipyrine have been determined in rats. Measurement of enzyme activity and antipyrine (after intravenous injection of 20 mgkg−1) were performed 2, 24 and 96 h after a single intraperitoneal injection of endotoxin (1 mgkg−1) and after repeated doses (once daily for 4 days). The contribution of tumour necrosis factor α (TNFα) to the endotoxin‐induced changes was also examined in rats pretreated with granulocyte colony‐stimulating factor (G‐CSF).

The Possible Mechanism of Interaction between Xanthines and Quinolone

Abstract— To clarify the mechanism of interaction between theophylline and enoxacin, the effects of enoxacin and its metabolite, 4‐oxo‐enoxacin, on the disposition of new xanthine derivatives, 1‐methyl‐3‐propylxanthine (MPX) and 3‐propylxanthine (enprofylline), as models of theophylline have been investigated in rats. Pretreatment with enoxacin significantly delayed the elimination of MPX from plasma. No significant change in the volume of distribution of MPX was observed in the presence of enoxacin, but the total body clearance of MPX was significantly decreased by approximately 60 and 80% after pretreatment with 25 and 100 mg kg−1 of enoxacin, respectively. The amount of the decrease in total body clearance depended on the dose of enoxacin. 4‐Oxo‐enoxacin had little or no effect on MPX disposition. A newly developed quinolone, NY‐198, which does not affect the disposition of theophylline, also did not affect the disposition of MPX. Enoxacin also had no effect on the disposition of enprofylline. These results indicate that the mechanism for decrease in theophylline clearance induced by enoxacin may not be due to its metabolite, 4‐oxo‐enoxacin, but to enoxacin itself, and that enoxacin does not inhibit solely the elimination process depending on cytochrome P450 isoenzyme for N‐demethylation. It is likely that enoxacin has no influence on the renal excretion of xanthines.

Alterations in pharmacokinetics and protein binding behavior of cefazolin in endotoxemic rats.

The possible alterations in the pharmacokinetics and protein binding behavior of the beta-lactam antibiotic cefazolin (CEZ) were investigated in endotoxemic rats induced by Klebsiella pneumoniae O3 lipopolysaccharide (LPS). LPS (250 micrograms/kg of body weight) was infused for 20 to 30 min 2 h before an intravenous administration of CEZ (20 mg/kg). Significant decreases in systemic clearance and renal clearance of CEZ were observed in LPS-treated rats without any changes in fraction of urinary excretion in unchanged CEZ (> 0.8). The volume of distribution at steady state showed a tendency to increase. The protein binding parameters of CEZ, the binding capacity, and number of binding sites on the albumin molecule were decreased by LPS, whereas the dissociation constant did not change. Significant decreases in systemic and renal clearances for unbound CEZ were observed in LPS-treated rats. The glomerular filtration rate estimated as inulin clearance was also decreased by LPS. The ratio of renal clearance of unbound CEZ to glomerular filtration rate (clearance ratio) dropped to 70% of that in control rats, and the net tubular secretion of CEZ was also dramatically reduced. The present study suggests that LPS has an effect on the pharmacokinetics of CEZ by changes which occur in renal handling and protein binding.

Interspecies differences and scaling for the pharmacokinetics of xanthine derivatives

Abstract— Pharmacokinetic characteristics of the new xanthine bronchodilators, enprofylline and 1‐methyl‐3‐propylxanthine (MPX), were investigated in mice, rats, guinea‐pigs, rabbits and dogs. The possibility of an interspecies pharmacokinetic scale was also evaluated. The concentration of these two drugs in plasma and urine was determined by HPLC. Pharmacokinetic parameters were calculated using model‐independent methods. The disappearance curves of the two drugs from plasma varied markedly among animal species. Interspecies differences in the plasma protein binding of each drug were observed for all animals in the study. Differences in the biotransformation of enprofylline and MPX were also confirmed among the various animal species: enprofylline is mainly excreted in an unchanged form in urine while MPX follows a non‐renal route of elimination. In all animals, the renal clearance for enprofylline was greater than the glomerular filtration rate, indicating active tubular secretion. Significant allometric relationships were seen between the values of total body clearance and steady state volume of distribution for both total and unbound enprofylline and species body weight, but similar correlations could not be recognized for MPX. Renal clearance of enprofylline was also closely correlated with species body weight, suggesting no interspecies difference with relation to affinity and/or capacity for the active tubular secretion mechanism of enprofylline. Our findings suggest that xanthine derivatives, including enprofylline, are mainly eliminated via the kidney, and an estimate of the basic pharmacokinetics in man can be obtained from data in experimental animals.

Possible Involvement Of P-Glycoprotein In The Biliary Excretion Of Grepafloxacin

1. In the present study, we have examined the effects of the quinolones norfloxacin (NFLX), enoxacin (ENX), ofloxacin (OFLX), tosufloxacin (TFLX), lomefloxacin (LFLX), sparfloxacin (SPFX) and grepafloxacin (GPFX) on the efflux of doxorubicin from mouse leukaemia P388/ADR cells expressing P‐glycoprotein. The relationship between their partition coefficients (hydrophobicity) and effluxing potencies was also elucidated.

Changes in absorptive function of rat intestine injured by methotrexate.

1. Methotrexate (MTX), an anticancer drug, has been shown to induce acute injury in the small intestine. The present study was designed to investigate the in vivo absorptive function of the small intestine injured by MTX using an amino‐β‐lactam antibiotic cephalexin (CEX). Time‐dependent changes in diamine oxidase (DAO) and alkaline phosphatase (ALP) activity in the small intestine and histopathological findings were also measured in rats treated with MTX (20 mg/kg).

Effect of a new quinolone, sparfloxacin, on the pharmacokinetics of theophylline in asthmatic patients.

Recently, it has become evident that some quinolones affect the processing of theophylline in the human system. The effect of a new quinolone, sparfloxacin, on the pharmacokinetics and metabolism of theophylline was investigated in six asthmatic patients receiving chronic theophylline therapy (a sustained-release theophylline tablet formulation of 200 to 300 mg twice daily at 12-h intervals). To these patients, sparfloxacin (200 mg once daily) was coadministered for 1 week. Plasma and urine samples were analyzed by high-performance liquid chromatography for theophylline and its metabolites. Plasma theophylline concentration-time curves and the urinary excretion of theophylline and its major metabolites before and after coadministration of sparfloxacin were compared. The total body clearance of theophylline after coadministration of sparfloxacin, 42.81 +/- 6.64 ml/h/kg (mean +/- standard error of the mean), was not significantly different from that after the administration of theophylline alone, 47.11 +/- 7.61 ml/h/kg. Also, no significant change in the urinary excretion of theophylline and its metabolites was observed for subjects receiving or not receiving sparfloxacin. These findings indicate that a once-daily dose of 200 mg of sparfloxacin has no significant effect on the pharmacokinetics and metabolism of theophylline and that it would be safe to coadminister this quinolone to asthmatic patients receiving chronic theophylline therapy.