Functional characteristics of a renal H+/lipophilic cation antiport system in porcine LLC-PK1 cells and rats.

We have recently found an H+/quinidine (a lipophilic cation, QND) antiport system in Madin-Darby canine kidney (MDCK) cells. The primary aim of the present study was to evaluate whether the H+/lipophilic cation antiport system is expressed in porcine LLC-PK1 cells. That is, we investigated uptake and/or efflux of QND and another cation, bisoprolol, in LLC-PK1 cells. In addition, we studied the renal clearance of bisoprolol in rats. Uptake of QND into LLC-PK1 cells was decreased by acidification of the extracellular pH or alkalization of the intracellular pH. Cellular uptake of QND from the apical side was much greater than from the basolateral side. In addition, apical efflux of QND from LLC-PK1 cells was increased by acidification of the extracellular pH. Furthermore, lipophilic cationic drugs significantly reduced uptake of bisoprolol in LLC-PK1 cells. Renal clearance of bisoprolol in rats was approximately 7-fold higher than that of creatinine, and was markedly decreased by alkalization of the urine pH. The present study suggests that the H+/lipophilic cation antiport system is expressed in the apical membrane of LLC-PK1 cells. Moreover, the H+/lipophilic cation antiport system may be responsible for renal tubular secretion of bisoprolol in rats.

The true distribution volume and bioavailability of mizoribine in children with chronic kidney disease.

BACKGROUND: Mizoribine (MZR) is used kidney transplant and various kidney diseases. However, few studies reported the association between pharmacokinetics and pharmacodynamics. The Pharmacokinetics Study Group for Pediatric Kidney Disease (PSPKD) used population pharmacokinetics (PPK) analysis and Bayesian analysis to investigate the usefulness of MZR. In this study, the fact that almost all MZR are excreted unchanged in urine was used to calculate its bioavailability (F) and true distribution volume (V d), and analyzed these correlation with age. METHODS: Ishida et al. reported a PPK analysis by the PSPKD. In the present study, 71 samples extracted from their study population of 105 pediatric chronic kidney disease patients aged between 1 and 20 years were investigated. The bioavailability was calculated by measuring total excreted MZR in 24 h urine samples, and this was compared to the oral dosage. The apparent distribution volume (V d/F) obtained from Bayesian analysis was then used to calculate true distribution volume (V d), and the correlation of each parameter with age was investigated. RESULTS: The median dose of MZR per weight was 5.17 mg/kg/day. Median bioavailability was 32.02%. Median V d per weight was 0.46 L/kg. There was a significant, weakly positive correlation between bioavailability and age (p = 0.026). There was also a significant, weakly negative correlation between V d per weight and age (p = 0.003). CONCLUSION: Bioavailability and V d per weight tended to decrease depending on age. The younger patient required larger dose required to obtain the maximum effect from MZR, and this is important for immunosuppressive therapy.

Presence of an H+/Quinidine Antiport System in Madin-Darby Canine Kidney Cells.

BACKGROUND AND OBJECTIVES: We have recently found an H+/quinidine antiport system in human kidney HEK 293 cells. The aim of the present study was to evaluate whether the H+/quinidine antiport system is expressed in Madin-Darby canine kidney (MDCK) cells. METHODS: We investigated the uptake and efflux of quinidine in MDCK cells. RESULTS: The uptake of 100 µM quinidine into MDCK cells was decreased by acidification of extracellular pH or alkalization of intracellular pH. In addition, the uptake of quinidine was highly temperature sensitive, but was extracellular Na+ and membrane potential independent. Furthermore, tetraethylammonium, a typical substrate of renal organic cation transporters, did not inhibit the uptake of quinidine in MDCK cells. On the other hand, lipophilic cationic drugs, such as clonidine, bisoprolol, diphenhydramine, pyrilamine, and imipramine, significantly decreased the uptake of quinidine in MDCK cells. The uptake of quinidine was saturable, and the Michaelis-Menten constant was estimated to be approximately 0.5 mM. In addition, the efflux of quinidine from MDCK cells was increased by the acidification of extracellular pH, suggesting that the transport system mediates not only the uptake, but also secretion of quinidine. CONCLUSIONS: The present findings suggested that the renal new antiport system is involved in the bidirectional membrane transport of quinidine in MDCK cells.

Population pharmacokinetics of mizoribine in pediatric patients with kidney disease.

BACKGROUND: The present study aimed to obtain information enabling optimisation of the clinical effect of mizoribine (MZR) in pediatric patients with kidney disease. METHODS: A total of 105 pediatric patients with kidney disease treated at our institutions were enrolled. Kidney transplant patients were excluded. Population pharmacokinetic analysis of MZR was performed based on serum concentration data. Area under the curve from time zero to infinity (AUC∞) and maximal concentration (C max) were calculated by Bayesian analysis. RESULTS: In children, the appearance of MZR in the blood tended to be slower and the subsequent rise in blood concentration tended to be more sluggish, compared to healthy adults. Apparent volume of distribution and oral clearance were also higher in children compared to adults. A significant positive correlation was observed between patient age and AUC∞. There were significant differences of AUC∞ and C max by age group. No relationship was observed between the administration method of MZR and serum concentration. CONCLUSION: The pharmacokinetics of MZR was different in children compared to adults. To obtain the expected clinical efficacy, the regular MZR dosage schedule (2-3 mg/kg/day) might be insufficient for pediatric patients. In particular, younger patients might require a higher dosage of MZR per unit body weight.

Membrane transport mechanisms of choline in human intestinal epithelial LS180 cells.

The aim of the present study was to investigate the membrane transport mechanisms of choline using human intestinal epithelial LS180 cells. The mRNA of choline transporter-like proteins (CTLs) was expressed significantly in LS180 cells, and the rank order was CTL1 > CTL4 > CTL3 > CTL2 > CTL5. In contrast, the mRNA expression of other choline transporters, organic cation transporter (OCT) 1, OCT2 and high-affinity choline transporter 1 (CHT1), was considerably lower in LS180 cells. Five mm unlabelled choline, hemicolinium-3 and guanidine, but not tetraethylammonium, inhibited the cellular uptake of 100 µm choline in LS180 cells. The uptake of choline into LS180 cells was virtually Na(+)-independent. The uptake of choline was significantly decreased by acidification of the extracellular pH; however, it was not increased by alkalization of the extracellular pH. In addition, both acidification and alkalization of intracellular pH decreased the uptake of choline, indicating that the choline uptake in LS180 cells is not stimulated by the outward H(+) gradient. On the other hand, the uptake of choline was decreased by membrane depolarization along with increasing extracellular K(+) concentration. In addition, the Na(+)-independent uptake of choline was saturable, and the Km value was estimated to be 108 µm. These findings suggest that the uptake of choline into LS180 cells is membrane potential-dependent, but not outward H(+) gradient-dependent.

Pharmacokinetic variability of flecainide in younger Japanese patients and mechanisms for renal excretion and intestinal absorption.

The aims of the present study were to evaluate the variability of pharmacokinetics of flecainide in young Japanese patients and to investigate the mechanisms of renal excretion and intestinal absorption of the drug using cultured epithelial cells. First the plasma concentration data of flecainide was analysed in 16 Japanese patients aged between 0.07 and 18.30 years using a one-compartment model. Considerable interindividual variability was observed in the oral clearance (CL/F) and the apparent volume of distribution (V/F) of flecainide in the young patients. Flecainide was transported selectively in the basolateral-to-apical direction in P-glycoprotein-expressing renal epithelial LLC-GA5-COL150 cell monolayers. The uptake of flecainide into intestinal epithelial LS180 cells was decreased significantly by acidification of the extracellular medium, and was inhibited by tertiary amines, such as diphenhydramine and quinidine. These findings in the present study suggest that flecainide is excreted by P-glycoprotein in the renal tubule and is taken up by the postulated H(+)/tertiary amine antiporter in the intestine, and that functional variability of not only the hepatic drug-metabolizing enzymes, but also the transporters in the kidney and intestine, may be responsible for the interindividual variability of systemic clearance (CL) and/or the bioavailability (F) of flecainide.

Variability of bioavailability and intestinal absorption mechanisms of metoprolol.

We previously reported that aging and/or cytochrome P450 2D6 polymorphism are responsible for the interindividual variability in the systemic clearance (CL) and bioavailability (F) of metoprolol. The aim of the present study was to evaluate the residual variability of F of metoprolol in routinely treated Japanese patients and to investigate the intestinal absorption mechanism of the drug using human intestinal epithelial LS180 cells. We first re-analyzed the blood concentration data for metoprolol in 34 Japanese patients using a nonlinear mixed effects model. The oral clearance (CL/F) of metoprolol was positively correlated with the apparent volume of distribution (V/F), suggesting the residual variability of F. The uptake of metoprolol into LS180 cells was significantly decreased by the acidification of extracellular medium pH, and was dependent on temperature and intracellular pH. Furthermore, the cellular uptake of metoprolol was saturable, and was significantly decreased in the presence of hydrophobic cationic drugs such as diphenhydramine, procainamide, bisoprolol, and quinidine. These findings indicate that residual variability of F is one of the causes of the interindividual pharmacokinetic variability of metoprolol, and that the interindividual variability of not only presystemic first-pass metabolism, but also intestinal absorption, may be responsible for the variable F of the drug.

Effect of chronic hypoxic hypoxia on oxidation and glucuronidation of carvedilol in rats.

Heart failure is accompanied with tissue (circulatory) hypoxia, and the metabolism of several drugs has been reported to be reduced in heart failure. The aim of this study was to investigate the effect of another type of respiratory hypoxia, hypoxic hypoxia (FiO2 15 % for 24 h followed by FiO2 10 % for 9 days) on the metabolism of carvedilol enantiomers in rats. Oxidation of carvedilol in rat liver microsomes was evaluated in the presence of reduced nicotinamide adenine dinucleotide phosphate, whereas glucuronidation was evaluated in the presence of UDP-glucuronic acid. Both oxidation and glucuronidation activities for two carvedilol enantiomers in hypoxic rat liver microsomes were similar to those in control rat liver microsomes. We also performed pharmacokinetic analysis of carvedilol enantiomers following intraportal infusion in control and hypoxic rats. The mean (±S.E.) portal clearance value of R- and S-carvedilol in control rats was 72 ± 16 and 156 ± 31 ml/min/kg, respectively, whereas that of the R- and S-enantiomers in hypoxic rats was 68 ± 8 and 113 ± 14 ml/min/kg, respectively. These findings indicated that the metabolism of carvedilol enantiomers was not significantly diminished in rats with chronic hypoxic hypoxia, and that other factor(s) besides hypoxia may be responsible for the reduced drug metabolism in heart failure.

Variability of bioavailability and intestinal absorption characteristics of bisoprolol.

We previously reported that renal function is partly responsible for the interindividual variability of the pharmacokinetics of bisoprolol. The aim of the present study was to examine the variability of bioavailability (F) of bisoprolol in routinely treated Japanese patients and intestinal absorption characteristics of the drug. We first analyzed the plasma concentration data of bisoprolol in 52 Japanese patients using a nonlinear mixed effects model. We also investigated the cellular uptake of bisoprolol using human intestinal epithelial LS180 cells. The oral clearance (CL/F) of bisoprolol in Japanese patients was positively correlated with the apparent volume of distribution (V/F), implying variable F. The uptake of bisoprolol in LS180 cells was temperature-dependent and saturable, and was significantly decreased in the presence of quinidine and diphenhydramine. In addition, the cellular uptake of bisoprolol dissolved in an acidic buffer was markedly less than that dissolved in a neutral buffer. These findings suggest that the rate/extent of the intestinal absorption of bisoprolol is another cause of the interindividual variability of the pharmacokinetics, and that the uptake of bisoprolol in intestinal epithelial cells is highly pH-dependent and also variable.

Effect of salt intake on bioavailability of mizoribine in healthy Japanese males.

Bioavailability of mizoribine in subjects with the concentrative nucleoside transporter 1 (CNT1, SLC28A1) 565-A/A allele is significantly lower than that in subjects with the SLC28A1 565-G/G allele. The aims of the present study were to investigate the cellular uptake of mizoribine in CNT1- and CNT2-expressing Madin-Darby canine kidney type II (MDCKII) cells, and to evaluate the effect of salt intake on bioavailability of mizoribine in healthy Japanese volunteers with SLC28A1 565-A/A and -G/A alleles. Eight healthy males participated in the present study, and took 150 mg mizoribine concomitantly with/without 300 mg salt. Bioavailability of mizoribine was estimated by total cumulative urinary excretion of the drug. Mizoribine was taken up Na(+)-dependently into not only CNT1-expressing but also CNT2-expressing MDCKII cells, indicating that mizoribine is a substrate for both CNT1 and CNT2. Mean bioavailability of mizoribine taken with salt (83.8%) was significantly higher than that taken without salt (73.0%). These findings suggest that the salt intake is expected to improve the bioavailability of mizoribine in patients with insufficient intestinal absorption.

Population pharmacokinetics of mizoribine in pediatric recipients of renal transplantation.

BACKGROUND: An immunosuppressive agent, mizoribine, is excreted predominantly in the urine. The aim of this study was to investigate the pharmacokinetic variability of mizoribine in pediatric recipients of renal transplantation. METHODS: Pharmacokinetic data for population analysis were collected from 51 recipients (32 males and 19 females) treated with oral administration of mizoribine (0.83-5.56 mg/day/kg). The population pharmacokinetic parameters of mizoribine were estimated using a nonlinear mixed effects model program. RESULTS: The pharmacokinetics of mizoribine in pediatric recipients of renal transplantation was well described by a one-compartment model with first-order absorption. The mean value of the absorption lag time (ALAG) and absorption rate constant (K (A)) was estimated to be 0.363 h and 0.554 h(-1), respectively. Apparent volume of distribution (V/F) was modeled as a function of body weight (WT), and the mean value was estimated to be 1.03 · WT L. Oral clearance (CL/F) was modeled as a function of creatinine clearance (CL(cr)), and the mean value was estimated to be 2.81 · CL(cr) · 60/1000 L/h. In addition, there was a positive correlation between CL(cr)-corrected CL/F and WT-corrected V/F in the pediatric recipients, indicating large interindividual variability in the bioavailability (F) of mizoribine. CONCLUSION: The present findings indicated that the rate of renal excretion and also the extent of intestinal absorption of mizoribine are responsible for the large interindividual pharmacokinetic variability of the drug.

Effect of genetic polymorphisms of SLC28A1, ABCG2, and ABCC4 on bioavailability of mizoribine in healthy Japanese males.

The aim of the present study was to investigate the genetic factors responsible for the interindividual variability in the bioavailability of mizoribine. Thirty healthy Japanese men aged 20-49 years and weighing 53-75 kg participated in the present study and took 150 mg of mizoribine. Urine samples were collected periodically for 12 h after the dose, and the bioavailability of mizoribine was calculated from the estimated total urinary excretion from time zero to infinity. The bioavailability of mizoribine in the 30 subjects ranged from 60.3% to 99.4%. The mean bioavailability of mizoribine in subjects with the concentrative nucleoside transporter 1 (SLC28A1) 565-A/A allele (75.4%) was significantly lower than that in subjects with the SLC28A1 565-G/G allele (90.1%). On the other hand, the bioavailability of mizoribine was not affected by polymorphisms of breast cancer resistance protein (ABCG2) C421A and multidrug resistance-associated protein 4 (ABCC4) G2269A. The findings in the present prospective study suggested that the genetic test for the SLC28A1 G565A polymorphism is promising for predicting the Japanese subjects with lower bioavailability of mizoribine.

Population pharmacokinetics of mizoribine in adult recipients of renal transplantation.

BACKGROUND: The aim of the present study was to estimate the population pharmacokinetic parameters of mizoribine in adult recipients of renal transplantation using a nonlinear mixed effects model (NONMEM) program. METHODS: Pharmacokinetic data for population analysis were retrospectively collected from 114 recipients (66 males and 48 females) routinely treated with oral administration of mizoribine (25-450 mg/day). The range of creatinine clearance (CL(cr)) was 7.6-136.1 mL/min (mean 49.2 mL/min). RESULTS: The pharmacokinetics of mizoribine in adult recipients of renal transplantation was well described by a 1-compartment model with first-order absorption. The mean value of the absorption lag time (ALAG) and absorption rate constant (KA) was estimated to be 0.581 and 0.983 h(-1), respectively. Apparent volume of distribution (V/F) was modeled as a function of body weight (WT), and the mean value was estimated to be 0.858 × WT L. Oral clearance (CL/F) was modeled as a function of creatinine clearance (CL(cr)), and the mean value was estimated to be 1.80 × CL(cr) × 60/1000 L/h. In addition, there was a strong correlation between CL(cr)-corrected CL/F and WT-corrected V/F in the adult recipients, indicating large interindividual variability in bioavailability (F) of mizoribine. CONCLUSION: The present findings suggested that not only the rate of renal excretion but also the extent of intestinal absorption of mizoribine is responsible for the large interindividual pharmacokinetic variability of the drug.

Mechanisms for membrane transport of metformin in human intestinal epithelial Caco-2 cells.

The aim of the present study was to investigate the mechanisms for membrane transport of metformin in human intestinal epithelial Caco-2 cells. The mRNA of not only organic cation transporter (OCT) 3, but also OCT1 and OCT2, was expressed in Caco-2 cells. The uptake of 100 µm metformin at the apical membrane of Caco-2 cells grown on porous filter membrane was significantly greater than that at the basolateral membrane. The apical uptake of 100 µm metformin in Caco-2 cells grown on plastic dishes was inhibited significantly by 1 mm unlabeled metformin, quinidine and pyrilamine, indicating that a specific transport system is involved in the apical uptake of metformin in Caco-2 cells. The apical uptake of 100 µm metformin in Caco-2 cells was decreased by acidification of the medium, but not increased by alkalization. In addition, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (a protonophore) had no effect on the apical uptake of metformin in Caco-2 cells at apical medium pH 8.4. These findings suggested that the apical uptake of metformin in Caco-2 cells is mediated at least partly by OCTs, but that the postulated H(+) /tertiary amine antiport system is not responsible for the apical uptake of metformin.

Pharmacokinetics of bosentan in routinely treated Japanese pediatric patients with pulmonary arterial hypertension.

We evaluated the pharmacokinetics of routinely administered bosentan in 46 Japanese pediatric patients with pulmonary arterial hypertension. Plasma samples were taken twice at times corresponding to the peak and trough concentrations following repetitive oral administration. The population pharmacokinetic parameters of bosentan were estimated by use of the NONMEM program, in which a one-compartment model with repetitive bolus dosing was parameterized in terms of the oral clearance (CL/F) and elimination rate constant (k). Polymorphisms of CYP3A5, SLCO1B1, SLCO1B3, and SLCO2B1 had no significant effect on the disposition of bosentan. In addition, the pharmacokinetics of bosentan was not altered by heart failure or coadministration of sildenafil. In contrast, weight (WT)-normalized values of CL/F were correlated negatively with age (AGE). The final population mean values of CL/F and k were estimated to be 0.409 · (1 - 0.0377 · (AGE - 3.81)) · WT L/h and 0.175 h(-1), respectively.

Effect of the VKORC1 genotype on warfarin dose requirements in Japanese pediatric patients.

The primary aim of the present study was to evaluate the effect of the genotype of vitamin K epoxide reductase complex 1 (VKORC1) on warfarin dose requirements in Japanese pediatric patients. Forty-eight pediatric patients (0.42-19.25 years old) in whom stable anticoagulation was achieved by warfarin were enrolled in this study, and the polymorphic alleles of VKORC1 and CYP2C9 were determined for each subject. The relative impact of covariates on the anticoagulant effect of warfarin was evaluated by multiple regression analysis. It was found that VKORC1 genotype and age were major factors affecting the relationship between the weight-normalized warfarin dose and the therapeutic prothrombin time-international normalized ratio (PT-INR). Because only one patient had the CYP2C9*3 allele, we could not evaluate the effect of CYP2C9 polymorphisms on the anticoagulant effect of warfarin. In contrast, the anticoagulant effect of warfarin in patients with the VKORC1 1173CT or 1173CC genotype was 52.3% of that in patients with the 1173TT genotype. In addition, the anticoagulant effect of warfarin was shown to increase by 10.5% per year in Japanese pediatric patients. In conclusion, genotyping of VKORC1 will be useful in establishing individual anticoagulant therapy with warfarin, and it should be noted that a higher weight-normalized dose of warfarin is required in younger pediatric patients.

Evaluation of limited sampling designs to estimate maximal concentration and area under the curve of mizoribine in pediatric patients with renal disease.

The aim of this study was to evaluate limited sampling designs to estimate the maximal concentration (C(max)) and area under the curve (AUC) of mizoribine in pediatric patients with renal disease. We utilized 48 serum mizoribine concentration profiles obtained from the full (6-point) sampling pharmacokinetic test, and estimated 48 individual C(max) and AUC values accurately with Bayesian analysis using the full sampling data. We then developed limited sampling models (LSM) for C(max) and AUC using 1-4 serum mizoribine concentration data points. The C(max) and AUC estimation performance of the Bayesian and LSM analysis was fairly good in the 3-point (2, 3, and 6 hr after the dose) sampling design. In addition, the C(max) estimation performance of the Bayesian and LSM analysis deteriorated only marginally even in the 1-point (3 hr) sampling design. On the other hand, the AUC estimation performance seemed to be inadequate in the 1-point (3 hr) sampling design; however, it improved markedly in the 2-point (3 and 6 hr) sampling design. These findings suggested that the 1-point (3 hr) sampling design is promising for approximate C(max) estimation, but that the 2-point (3 and 6 hr) sampling design is preferable to estimate the AUC of mizoribine.

Membrane transport mechanisms of quinidine and procainamide in renal LLC-PK1 and intestinal LS180 cells.

The aim of the present study was to compare the membrane transport mechanisms of procainamide with those of quinidine using renal epithelial LLC-PK(1) and intestinal epithelial LS180 cells. In LLC-PK(1) cells, the transcellular transport of 10 microM quinidine in the basolateral-to-apical direction was similar to that in the opposite direction, and 1 mM tetraethylammonium (TEA) did not affect the transcellular transport of the drug. On the other hand, the transcellular transport of 10 microM TEA and procainamide in LLC-PK(1) cells was directional from the basolateral side to the apical side. In addition, this directional transcellular transport of procainamide was diminished in the presence of 1 mM TEA. In LS180 cells, the temperature-dependent cellular uptake of 100 microM quinidine and procainamide was markedly increased by alkalization of the apical medium, and was inhibited significantly by 1 mM several hydrophobic cationic drugs, but not by TEA. The rank order of the inhibitory effects of hydrophobic cationic drugs on the uptake of procainamide in LS180 cells was imipramine>quinidine>diphenhydramine asymptotically equal topyrilamine>procainamide, which was consistent with that on the uptake of quinidine. These findings suggested that procainamide (but not quinidine) was transported by cation transport systems in renal epithelial cells, but that both procainamide and quinidine were taken up by another cation transport system in intestinal epithelial cells.

Inhibitory and stimulative effects of amiodarone on metabolism of carvedilol in human liver microsomes.

It was reported that coadministration of amiodarone with carvedilol increased the serum concentration to dose (C/D) ratio of S-carvedilol in patients with heart failure, but not of R-carvedilol. The aim of the present study was to investigate the effect of amiodarone and its metabolite on the metabolism of R- and S-carvedilol in human liver microsomes (HLM). Oxidation of carvedilol in HLM was evaluated in the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH), whereas glucuronidation was evaluated in the presence of uridine 5'-diphosphate (UDP)-glucuronic acid. The oxidation and glucuronidation activities of HLM for S-carvedilol were approximately 2- and 4-fold greater, respectively, than those for R-carvedilol. In the presence of amiodarone (50 microM) and/or desethylamiodarone (25 microM), the oxidation activity for R- and S-carvedilol decreased significantly. In contrast, the glucuronidation activity for R-carvedilol was increased 1.6- and 1.4-fold by amiodarone and desethylamiodarone, respectively, whereas the glucuronidation of S-carvedilol was only slightly changed by amiodarone and desethylamiodarone. These results suggested that inhibition of S-carvedilol oxidation by amiodarone and/or desethylamiodarone is implicated in the increased C/D ratio of S-carvedilol associated with coadministration of amiodarone. On the other hand, the stimulative effect of amiodarone and/or desethylamiodarone on the glucuronidation of R-carvedilol may compensate for the inhibitory effect of those on R-carvedilol oxidation.

Temperature-dependent specific transport of levofloxacin in human intestinal epithelial LS180 cells.

It was reported previously that specific levofloxacin uptake in Caco-2 cells was inhibited by nicotine, enalapril, L-carnitine and fexofenadine. The aim of the present study was to characterize the cellular uptake of levofloxacin using another human intestinal cell line, LS180. Levofloxacin uptake in LS180 cells was temperature-dependent and optimal at neutral pH, but was Na(+)-independent. The rank order of inhibitory effects of the four compounds on [(14)C] levofloxacin uptake in LS180 cells was nicotine>enalapril>L-carnitine>fexofenadine, which is consistent with that in Caco-2 cells. The mRNA levels of OATP1A2, 1B1, 1B3 and 2B1 in LS180 cells were markedly different from those in Caco-2 cells, and OATP substrates/inhibitors had no systematic effect on the levofloxacin uptake. The mRNA levels of OCTN1 and 2 in LS180 cells were similar to those in Caco-2 cells. However, the inhibitory effect of nicotine on L-[(3)H]carnitine uptake was much less potent than that of unlabeled L-carnitine. These results indicate that the specific uptake system for levofloxacin in LS180 cells is identical/similar to that in Caco-2 cells, but that OATPs and OCTNs contribute little to levofloxacin uptake in the human intestinal epithelial cells.