Yusuke Tanigawara

P-glycoprotein-mediated transcellular transport of MDR-reversing agents

Understanding of the interactions between P‐glycoprotein and multidrug resistance (MDR) reversing agents is important in designing more effective MDR modulators. We examined transcellular transport of several MDR modulators by using a drug‐sensitive epithelial cell line, LLC‐PK1 and its transformant cell line, LLC‐GA5‐COL300, which expresses human P‐glycoprotein on the apical surface. Basal‐to‐apical transports of azidopine and diltiazem across the LLC‐GA5‐COL300 monolayer were increased and apical‐to‐basal transports were decreased compared to those across the LLC‐PK1 monolayer, indicating that P‐glycoprotein transports azidopine and diltiazem. Movements of nitrendipine and staurosporine across the epithelial monolayer were not affected by P‐glycoprotein. These results suggests that some MDR modulators exert their inhibitory effect not only by blocking the initial binding of anticancer drugs but throughout the course of the transport process.

Genotyping of N‐acetylation polymorphism and correlation with procainamide metabolism

We studied the genotypes of polymorphic N‐acetyltransferase (NAT2) in 145 Japanese subjects by the polymerase chain reaction‐restriction fragment length polymorphism method. The rapid‐type NAT2*4 was expressed at a higher frequency (68.6%) than the slow‐type genes with specific point mutations (NAT2*6A, 19.3%; NAT2*7B, 9.7%; NAT2*5B, 2.4%). The frequency of NAT2* genotypes consisted of 44% of a homozygote of NAT2*4, 49% of a heterozygote of NAT2*4 and mutant genes, and 7% of a combination of mutant genes. The metabolic activity for procainamide to N‐acetylprocainamide was measured in 11 healthy subjects whose genotype had been determined. Although the acetylation activity substantially varied interindividually, the variability was considerably reduced after classification according to the genotype. The N‐acetylprocainamide/procainamide ratio in urinary excretion was 0.60 ± 0.17 (mean ± SD) for those with NAT2*4/ *4, 0.37 ± 0.06 for NAT2*4/ *6A, 0.40 ± 0.03 for NAT2*4/ *7B, and 0.17 for NAT2*6A/ *7B. The results indicated that the NAT2* genotype correlates with acetylation of procainamide.

Effect of cyclosporin analogues and FK506 on transcellular transport of daunorubicin and vinblastine via P-glycoprotein.

AbstractPurpose. P-glycoprotein-mediated transcellular transport of anticancer agents and the inhibitory effect of cyclosporin analogs and FK506 were investigated.nMethods. The transcellular transport of daunorubicin and vinblastine by monolayers of LLC-GA5-COL150 cells which overexpressed P-glycoprotein was measured in the presence and absence of cyclosporins or FK506.nResults. Cyclosporins and FK506 inhibited P-glycoprotein-mediated transport of daunorubicin and vinblastine in the order of cyclosporin D, dihydrocyclosporin D > cyclosporin A > FK506 > cyclosporin C, dihydrocyclosporin C. The intracellular accumulation of the anticancer agents was highly associated with the transporting function of P-glycoprotein. The inhibitory effect of cyclosporin D was concentration-dependent. The inhibitory effect of the modulators on P-glycoprotein was not correlated with the immunosuppressive activity, but was correlated with their lipophilicity.nConclusions. In the transcellular transport system, lipophilicity may be one of the determinants for the inhibitory effect of various multidrug resistance modulators on the P-glycoprotein-mediated transport.

Cross-reactivity of TDX and OPUS immunoassay systems for serum digoxin determination

The properties of the widely used TDX Analyzer and recently developed OPUS Immunoassay System were compared using 403 serum specimens taken from patients who did or did not take digoxin. Of the 210 specimens from patients not treated with digoxin, a false- positive digoxin concentration was detected in 15 specimens (7%) by TDX and in only 2 specimens (1%) by OPUS because of the cross-reactivity with structurally similar drugs. Potassium canrenoate, digitoxin, deslanoside, and methyldigoxin exhibited marked concentration-dependent cross-reactivity in the TDX assay method, whereas deslanoside and methyldigoxin only showed cross-reactivity with the antibody used in the OPUS method. Although a poor correlation was observed between these two methods for the determination of 193 samples from patients treated with digoxin, the correlation was remarkably improved (r = 0.914) and the slope approximated unity when excluded the data from patients who were treated concurrently with the cross-reactive compounds. In routine TDM of digoxin, the authors experienced two cases in which cross-reactivity of the assay system caused a clinical problem. Concurrent administration of intravenous canrenoate apparently interfered with the digoxin assay by TDX, but this problem was solved by using the OPUS system. The authors found OPUS more useful for monitoring serum digoxin concentrations in patients because of its superior specificity.

Predictive performance of the Bayesian analysis: Effects of blood sampling time, population parameters, and pharmacostatistical model

The present paper reports theoretical equations for the predictive performance of the Bayesian forecasting method. The precision of parameter estimates and predicted concentrations for an individual was described by general equations with the aid of a variance-covariance matrix of parameter estimates that involved the Bayes theorem. The equations were applied to assess the predictive performance of the one-point Bayesian method in association with blood sampling time, the population parameters, and the pharmacostatistical model. The simulation study showed that the prediction error in parameter estimates essentially depended upon the sampling time but the magnitude of dependency was affected by the size of inter-and intraindividual variances. With a smaller value of interindividual variance, the dependency on sampling time was less apparent. Effects of sampling time were further examined using clinical data obtained from 20 patients taking theophylline, and the results were in good agreement with the theoretical consideration. The present general equations are useful to investigate the sampling strategy as well as structural and variance modeling on the predictive performance of the Bayesian method.

Moment analysis of drug disposition in kidney. V: In vivo transepithelial transport of p-aminohippurate in rat kidney.

A new method that can assess the kinetics of in vivotransepithelial transport in rat kidney has been established. The method is based upon a multiple-indicator dilution experiment and the moment analysis theory. After simultaneous bolus injections of p-aminohippurate (PAH) and inulin into the right renal artery, blood samples were taken from the carotid artery and urine was separately collected from right and left ureters. The characteristic response for the first passage of drugs through the right kidney was evaluated by taking blood circulation into consideration. To determine the mean artery-tovein transit time and the extraction ratio in the kidney, an intravenous injection was also performed as a reference experiment for deconvolution. The urinary excretion curve corresponding to the first passage was obtained as the difference between both kidneys. The mean artery-tolumen transit time (mean transepithelial transit time, ¯Tcell)was computed by subtracting the mean urinary transit time of inulin from that of secreted PAH. Sinc transport across the luminal membrane into the lumen from tubular epithelial cells can influence the cellular residence time of drugs, ¯ Tcelland the single-pass mean residence time in epithelial cells (¯Tcell.sp)can be thought of describing luminal membrane transport. The value of ¯Tcell obtained for 0. t mM PAH was 22 sec and it was prolonged to 61 sec in the presence of probenecid, suggesting an inhibitory effect on transport across the luminal membrane. On the other hand, antiluminal membrane transport into cells from blood is characterized by the volume of distribution in the kidney (VdPAH). VdPAH was remarkably decreased by treatment with probenecid, indicating an inhibitory effect on antiluminal membrane transport. The effects of probenecid on both sides of epithelial cell membrane transport were first demonstrated in vivo.The present method is useful for the analysis of in vivotransepithelial transport including antiluminal and luminal membrane transport for drugs excreted via tubular secretion.

Moment analysis of drug disposition in kidney. VI: Assessment of in vivo transmembrane transport of p-aminohippurate in tubular epithelium

This paper describes a novel method to assess the antiluminal membrane (ALM) and luminal membrane (LM) transport in vivo across renal tubular epithelial cells. The method is based upon a noncompartmental moment analysis of the plasma concentration and urinary excretion rate curves following renal artery injection. Quantitative relationships are represented between the noncompartmental parameters (clearance, volume of distribution, and the mean transit time) and the first-order rate constants associated with transmembrane transport processes. The in vivo transepithelial transport of [14C]p -aminohippurate (PAH) was examined using the rat kidney in the absence or presence of various plasma concentrations of unlabeled PAH, cefazolin, and methotrexate. The tubular secretion intrinsic clearance was reduced with an increase in the plasma concentration of concurrent unlabeled organic onions. The distribution volume of PAH in the kidney decreased in association with a decrease in the amount of PAH secreted, whereas the mean transepithelial (artery-to-lumen) transit time (¯Tcell) remained constant. These findings indicate that ALM transport is a capacity-limited process determining the amount of tubular secretion, and that LM transport is linear over the concentration range examined and independent of the amount of secretion. The contribution of ALM and LM transport to transcellular transport was first clarified in vivo. The present method will be useful for analyzing the transmembrane transport processes in vivo for highly diffusible substances in the kidney.

Pharmacokinetics of Adriamycin and cisplatin for anhepatic chemotherapy during liver transplantation

Abstract We investigated the pharmacokinetics of cytotoxic anticancer agents administered under anhepatic conditions. Beagle dogs underwent either a sham operation consisting of laparotomy only (control group, nu2009=u200911) or a laparotomy and total hepatectomy under venovenous bypass (anhepatic group, nu2009=u200912). Each dog received a bolus intravenous injection of either Adriamycin (1u2009mg/kg) or cisplatin (1u2009mg/kg). The plasma and urine concentrations of each drug were measured at intervals for up to 2u2009h after drug injection. The dogs given Adriamycin were then sacrificed to determine tissue drug concentrations in the liver (controls only), spleen, kidney, heart, lung, skeletal muscle and small intestine. The control and anhepatic groups showed similar Adriamycin profiles during the initial 5u2009min after drug injection. However, subsequently, the plasma Adriamycin concentrations remained persistently higher in the anhepatic dogs than in the controls, yielding a two-fold elevation of the mean area under the concentration-time curve in the anhepatic group (P<0.01 vs controls). The renal clearance values did not significantly differ between the two groups. The tissue Adriamycin concentrations in all measured organs, excluding the liver, were higher in the anhepatic group than in the controls. In a second set of experiments with cisplatin, the plasma platinum concentrations did not significantly differ between the two groups throughout the time course. However, the renal clearance of platinum in the anhepatic dogs showed a fourfold increase compared with that in the controls (P<0.01). These pharmacokinetic data suggest that Adriamycin carries the risk of increased systemic toxicities, while cisplatin may be associated with increased renal toxicity when administered during the anhepatic period of liver transplantation.