Relationship Between Clozapine and Non-Hematological Malignant Tumors: A Pharmacovigilance Analysis Using the FDA Adverse Event Reporting System Database

BACKGROUND AND OBJECTIVES

Clozapine shows higher efficacy against treatment-resistant schizophrenia than other antipsychotics. This study aimed to investigate whether clozapine is associated with the risk of non-hematological malignant tumors, utilizing the US Food and Drug Administration (FDA) Adverse Event Report System (FAERS) database.

METHODS

The records from the first quarter of 2004 to the third quarter of 2012 were used for disproportionality analysis, and patients who developed non-hematological malignant tumors were identified by the Standardized Medical Dictionary for Regulatory Activities Queries (SMQ).

RESULTS

Of the 3,641,281 patients with 12,401,586 reports of adverse drug events, 151,904 reports belonged to non-hematological malignant tumors (SMQ). We identified 1668 reports of non-hematological malignant tumors (SMQ) in clozapine users, and the reporting odds ratio (ROR) was calculated to be 1.28 (95% confidence interval (CI): 1.22-1.34). ROR (95% CI) for the relationship between clozapine and the risk of testis cancer was calculated as 10.94 (6.99-17.12), 9.87 (7.42-13.15) for gastrointestinal carcinoma, 7.48 (5.57-10.05) for metastatic lung cancer, 6.71 (4.52-9.97) for throat cancer, 6.12 (4.56-8.21) for metastases to the spine, 5.97 (5.30-6.72) for lung malignant neoplasm, 5.07 (3.69-6.95) for esophageal carcinoma, 1.88 (1.43-2.47) for colon cancer, and 1.65 (1.24-2.21) for metastases to the liver. Colon cancer, esophageal carcinoma, and throat cancer were predominantly reported in males, and metastases to the spine and liver were in females.

CONCLUSION

This study detected signals indicating a relationship between clozapine and certain non-hematological malignant tumors, utilizing the FAERS database. Despite the database relying on spontaneous reporting, the current results justify further investigation.

Data Mining for Risks of Clozapine Side Effects, Including Neutropenia, Associated with Lithium Carbonate Administration: Analysis Using the Japanese Adverse Drug Event Report Database

BACKGROUND AND OBJECTIVE

Clozapine use is associated with development of neutropenia, and lithium carbonate may be co-administered to reduce this risk; however, this has not yet been adequately investigated. The present study examined whether lithium administration is associated with the risks of clozapine side effects, including neutropenia.

METHODS

Data on patients taking clozapine, extracted from the Japanese Adverse Drug Event Report (JADER) database, were analyzed. Patients who developed clozapine side effects were identified by the Standardized Medical Dictionary for Regulatory Activities Queries. The relationship between the use of lithium and risk of clozapine side effects was examined using logistic regression analysis.

RESULTS

The use of lithium was reported in 530 out of 2,453 clozapine users. Hematopoietic leukopenia, convulsion, and noninfectious myocarditis/pericarditis developed in 109, 87, and seven lithium-treated patients, and in 335, 173, and 62 untreated patients, respectively. Univariate analysis showed no relationship between lithium administration and the risks of hematopoietic leukopenia (adjusted odds ratio (aOR) 1.11; 95% confidence interval (CI) 0.98-1.25), and the association with the risks of convulsion (aOR 1.41; 95% CI 1.23-1.62) and noninfectious myocarditis/pericarditis (aOR 0.63; 95% CI 0.43-0.94). Multivariate analysis revealed that lithium use was independently associated with the risks of convulsion (aOR 1.40; 95% CI 1.21-1.60) and noninfectious myocarditis/pericarditis (aOR 0.62; 95% CI 0.41-0.91).

CONCLUSION

The risks of seizure and myocarditis, but not of neutropenia, in clozapine-treated patients may be altered by lithium. Although the JADER database is based on spontaneous reporting, the present results warrant further study.

Risk factors for suicidal behavior/ideation and hostility/aggression in patients with bipolar disorders: An analysis using the Japanese Adverse Drug Event Report database

The present study attempted to identify risk factors for suicidality and hostility/aggression in patients with bipolar disorders. Data on 3521 patients were extracted from the Japanese Adverse Drug Event Report (JADER) database. There were 134 reports regarding suicidal behavior/ideation, and 129 patients were judged to have it. Standardized Medical Dictionary for Regulatory Activities queries indicated that 248 adverse drug events pertained to hostility/aggression, and 218 patients were considered to show hostility/aggression. A multiple logistic regression analysis revealed the association of the risk for suicidal behavior/ideation with bipolar II disorder [adjusted odds ratio (aOR): 4.55, 95% confidence interval (CI): 1.90-10.9], male sex (aOR: 1.23, 95% CI: 1.02-1.48), age <50 years (aOR: 1.75, 95% CI: 1.43-2.15), the administration of aripiprazole (aOR: 1.27, 95% CI: 1.00-1.60), and akathisia (aOR: 3.05, 95% CI: 1.80-5.18), while lithium carbonate decreased its odds (aOR: 0.664, 95% CI: 0.537-0.821). The risk of hostility/aggression was associated with male sex (aOR: 1.22, 95% CI: 1.06-1.40), lithium carbonate (aOR: 0.823, 95% CI: 0.710-0.953), and carbamazepine (aOR: 0.693, 95% CI: 0.500-0.961). No association between suicidal behavior/ideation and hostility/aggression was recognized. The present study proposes factors related with suicidal behavior/ideation and hostility/aggression in patients with bipolar disorders using the JADER database. Lithium carbonate appeared to decrease the risks of suicidal behavior/ideation and hostility/aggression in patients with bipolar disorders, and akathisia may be associated with the former risk. Further studies are required to evaluate the identified signals.

Analysis of adverse drug events in patients with bipolar disorders using the Japanese Adverse Drug Event Report database

The aim of the present study was to survey adverse drug events (ADEs) in patients with bipolar disorders and identify risk factors using the Japanese Adverse Drug Event Report (JADER) database, a spontaneous reporting system. Data on patients with bipolar disorders were extracted from the JADER database. The Medical Dictionary for Regulatory Activities (MedDRA) preferred terms (PT) and standardized MedDRA queries (SMQ) were used to define ADEs. A multiple logistic regression analysis was performed to identify risk factors for ADEs. A total of 8653 reports of 1108 types of ADEs (PT) were registered in data collected on 3521 patients with bipolar disorders. Rash (PT) was the most frequently reported in 549 patients, followed by drug eruption (PT) in 387, fever (PT) in 364, toxicity to various agents (PT) in 291, and Stevens-Johnson syndrome (PT) in 261. Among 24 ADEs (PT) that were reported in more than 50 patients, lamotrigine was associated with increased risks of 13 ADEs (PT), followed by carbamazepine with increased risks of 8 ADEs (PT). The majority of these ADEs belonged to hypersensitivity (SMQ) or hepatic disorder (SMQ). Lithium carbonate was associated with increased risks of rash (PT), drug interaction (PT), and tubulointerstitial diseases (SMQ). All antipsychotics increased the adjusted odds ratio for neuroleptic malignant syndrome (PT). The risk of hyperglycemia/new onset diabetes mellitus (SMQ) was increased by olanzapine, quetiapine fumarate, and risperidone. We are presenting the profiles of ADEs in patients with bipolar disorders using the JADER database, and propose risk factors for 19 ADEs (PT) and 4 ADEs (SMQ).

Relationship between lithium carbonate and the risk of Parkinson-like events in patients with bipolar disorders: A multivariate analysis using the Japanese adverse drug event report database

The present study attempted to identify risk factors for Parkinson-like events using the Japanese adverse drug event report database. A total of 3521 patients with bipolar disorders were extracted from the database, and Parkinson-like events were detected in 111 (3.15%) using the standardized Medical Dictionary for Regulatory Activities queries. A multiple logistic regression analysis identified age ≥50 years and the use of sodium valproate or aripiprazole as risk factors. Lithium carbonate was not associated with an increased risk of Parkinson-like events, but was related to these events in patients taking sodium valproate.

Surveillance of drug overdose and identification of its risk factors by a multivariate analysis using the Japanese Adverse Drug Event Report database

BACKGROUND

Limited information is currently available on drug overdose in Japan. Therefore, the present study examined drug overdose using the Japanese Adverse Drug Event Report (JADER) database.

METHODS

The records of drug overdose in patients were extracted from the JADER database. Risk factors for drug overdose in patients with bipolar disorders were examined using a multiple logistic regression analysis.

RESULTS

Overdoses of 1327 medicines in 784 patients were registered in the JADER database. An overdose of lithium carbonate was the most frequently reported in 144 patients, followed by zolpidem tartrate in 88, and then quetiapine fumarate, sodium valproate, risperidone, and paroxetine hydrochloride hydrate. The number of overdoses was higher in females, and peaked in patients aged with 30-39 years. The dosages of overdosed lithium carbonate ranged between 1800 and 60,000 mg, with a median of 8400 mg, while those of overdosed zolpidem tartrate ranged between 15 and 600 mg, with a median of 105 mg. Forty-one drug overdose cases were registered in 3521 patients with bipolar disorder, bipolar I disorder, or bipolar II disorder in the JADER database. A multivariate analysis of these cases identified female sex, an age younger than 50 years, and the use of lithium carbonate as risk factors for drug overdose. Lamotrigine reduced its odds, and no relationship was observed with aripiprazole or sodium valproate.

CONCLUSION

The present study represented a surveillance of drug overdose, and identified risk factors in patients with bipolar disorders by a multivariate analysis using the JADER database.

Analysis of sex difference in the tubular reabsorption of lithium in rats

Lithium is used in the treatment of bipolar disorder. We previously demonstrated that two types of transporters mediate the tubular reabsorption of lithium in rats, and suggested that sodium-dependent phosphate transporters play a role in lithium reabsorption with high affinity. In the present study, we examined sex differences in lithium reabsorption in rats. When lithium chloride was infused at 60 µg/min, creatinine clearance and the renal clearance of lithium were lower, and the plasma concentration of lithium was higher in female rats. These values reflected the higher fractional reabsorption of lithium in female rats. In rats infused with lithium chloride at 6 µg/min, the pharmacokinetic parameters of lithium examined were all similar in both sexes. The fractional reabsorption of lithium was decreased by foscarnet, a representative inhibitor of sodium-dependent phosphate transporters, in male and female rats when lithium chloride was infused at the low rate. Among the candidate transporters mediating lithium reabsorption examined herein, the mRNA expression of only PiT2, a sodium-dependent phosphate transporter, exhibited sexual dimorphism. The present results demonstrated sex differences in the tubular reabsorption of lithium with low affinity in rats.

Effect of Experimental Fanconi Syndrome on Tubular Reabsorption of Lithium in Rats

Lithium, administered to patients of bipolar disorders, is mainly excreted into urine, and tubular reabsorption at the proximal tubule is involved in the renal handling of lithium. In this study, we examined the renal excretion of lithium in rats with Fanconi syndrome, characterized by defects of transports of various compounds at the proximal tubules, induced by maleic acid. After maleic acid was intravenously injected, mannitol and lithium chloride were infused in turn. Using samples of plasma and bladder urine during the mannitol infusion, renal parameters were determined. Pharmacokinetic parameters of lithium were obtained using samples during the lithium chloride infusion. Maleic acid decreased creatinine clearance and increased the fractional excretion of glucose and phosphate, suggesting the induction of Fanconi syndrome. In rats with Fanconi syndrome, plasma concentration of lithium was increased, and its renal clearance was decreased. No effect on the fractional excretion of lithium was exhibited. This study represents that the tubular reabsorption of lithium was impaired to the same degree with glomerular filtration in rats with experimental Fanconi syndrome and that the dysfunction of the tubular reabsorption of glucose and phosphate was more severe. It is possible that Fanconi syndrome inhibited the reabsorption of lithium at the proximal tubule and facilitated the reabsorption of lithium from the loop of Henle to the collecting duct.

Potent Inhibition of Biphasic Tubular Reabsorption of Lithium by Acetazolamide and Foscarnet in Rats

Lithium is mainly excreted into urine, and a large fraction of lithium filtered through glomeruli is reabsorbed in the proximal tubule. However, the mechanisms responsible for lithium reabsorption remain unclear. We previously reported that the reabsorption of lithium was biphasic in rats, and that foscarnet inhibited lithium reabsorption with a high affinity type. We herein evaluated the effects of acetazolamide and foscarnet on the renal excretion of lithium in rats treated with lithium chloride at 2 doses. In rats intravenously injected with a bolus of 25 mg/kg lithium chloride, acetazolamide facilitated the urinary excretion of lithium, and increased the fractional excretion of lithium from 0.446 to 0.953, near the theoretically maximum value. At a dose of 2.5 mg/kg lithium chloride, the fractional excretion of lithium was 0.241 in control rats, 0.420 in rats administered acetazolamide, and 0.976 in rats administered acetazolamide and foscarnet. These results showed the potent inhibition of lithium reabsorption by acetazolamide and foscarnet in rats. And, it was exhibited that the effects of acetazolamide on lithium reabsorption differed with the dosages of lithium administered.

Citrus auraptene induces drug efflux transporter P-glycoprotein expression in human intestinal cells

P-glycoprotein (encoded by MDR1) is a membrane transport protein expressed in the intestine, liver, kidney, placenta, and blood-brain barrier. It excludes various clinically important drugs from cells, such as verapamil, digoxin, tacrolimus, and vinblastine. Therefore, human P-glycoprotein plays important roles in drug absorption, distribution, and excretion. We reported previously that auraptene, a natural compound occurring widely in citrus fruit (e.g., grapefruit), inhibited P-glycoprotein-mediated drug transport. In this study, we investigated the effects of auraptene and other phenylpropanoids on P-glycoprotein expression using human intestinal epithelial LS174T cells and a reporter plasmid expressing 10.2 kbp of the upstream regulatory region of MDR1. Auraptene (7-geranyloxycoumarin), a prenylated coumarin, and several phenylpropanoids, such as 3-(4'-geranyloxy-3'-methoxyphenyl)-2-trans propenoic acid, derricidin [2'-hydroxy-4'-(prenyloxy)chalcone], and 3-(4'-geranyloxyphenyl)-propanoic acid, induced MDR1 promoter activity in LS174T cells. Overexpression of the nuclear receptor human pregnane X receptor gene (NR1I2) enhanced auraptene-induced MDR1 activation. Nuclear factor-kappaB inhibitors, Bay11-7082 and JSH-23, repressed MDR1 activation by auraptene. Western blot analyses showed the induction of P-glycoprotein expression in the auraptene-treated LS174T cells. The citrus phytochemical auraptene can induce the drug efflux transporter P-glycoprotein in human intestinal cells, and thus has the potential to cause food-drug interactions.

Investigation of Fluorescent Substrates and Substrate-Dependent Interactions of a Drug Transporter Organic Anion Transporting Polypeptide 2B1 (OATP2B1)

PURPOSE

In this study, we investigated organic anion transporting polypeptide 2B1 (OATP2B1)-mediated uptake of fluorescent anions to better identify fluorescent substrates for in vitro OATP2B1 assays. The OATP2B1 is involved in the intestinal absorption and one of the pharmacokinetic determinants of orally administered drugs.

METHODS

A microplate reader was used to determine the cellular accumulation of the fluorescent compounds into the OATP2B1 or the empty vector-transfected HEK293 cells.

RESULTS

Two types of derivatives were found to be OATP2B1 substrates: heavy halogenated derivatives, such as 4',5'-dibromofluorescein (DBF), and carboxylated derivatives, such as 5-carboxyfluorescein (5-CF). The DBF and 5-CF were transported in a time and concentration-dependent manner. The DBF was transported at a broad pH (pH 6.5-8.0) while 5-CF was transported at an acidic pH (pH 5.5-6.5). The K_m values were 0.818 ± 0.067 μM at pH 7.4 for DBF and 8.56 ± 0.41 μM at pH 5.5 for 5-CF. The OATP2B1 inhibitors, including atorvastatin, bromosulfophthalein, glibenclamide, sulfasalazine, talinolol, and estrone 3-sulfate, inhibited the DBF and the 5-CF transport. Contrastively, testosterone, dehydroepiandrosterone sulfate, and progesterone inhibited the DBF transport but stimulated the 5-CF transport. Natural flavonoid aglycones, such as naringenin and baicalein, also exhibited substrate-dependent effects in this manner.

CONCLUSION

We found two fluorescein analogs, DBF and 5-CF as the OATP2B1 substrates that exhibited substrate-dependent interactions.

Microtubule-targeting anticancer drug eribulin induces drug efflux transporter P-glycoprotein

This study examined the effects of microtubule-targeting anticancer drugs (paclitaxel, cabazitaxel, and eribulin) on the expression of drug efflux transporter P-glycoprotein, which is encoded by MDR1. Paclitaxel and eribulin induced MDR1 promoter activity in a concentration-dependent manner, while cabazitaxel had little effect in human intestinal epithelial LS174T cells. Overexpression of the nuclear receptor pregnane X receptor (PXR) gene (NR1I2) enhanced paclitaxel- and eribulin-induced MDR1 activation, but expression of the nuclear receptor co-repressor silencing mediator for retinoid and thyroid receptors (SMRT) gene (NCOR2) repressed MDR1 activation. Eribulin increased the mRNA and protein expression of P-glycoprotein in LS174T cells. Cellular uptake of rhodamine 123 and calcein-acetoxymethyl ester (calcein-AM), P-glycoprotein substrates, decreased in paclitaxel- or eribulin-treated LS174T cells. Eribulin also increased MDR1 promoter activity in human breast cancer MCF7 cells. The results suggest that the microtubule-targeting anticancer drug eribulin can induce the drug efflux transporter P-glycoprotein via PXR in human intestinal and breast cancer cells and thus influence the efficacy of anticancer drugs.

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Eribulin activates the P-glycoprotein gene (MDR1) promoter in human intestinal LS174T and breast cancer MCF7 cells.

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Eribulin increases mRNA and protein expression of P-glycoprotein in human intestinal LS174T cells.

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Eribulin can induce P-glycoprotein and modulate the efficacy of anticancer drugs.

Effect of acetazolamide on lithium reabsorption and lithium-induced GSK3β phosphorylation in rat kidney

Lithium promotes the phosphorylation of glycogen synthase kinase-3β (GSK3β), and this reaction protects against acute kidney injury mediated by renal apoptosis. Lithium is considered to be reabsorbed by sodium-phosphate cotransporters and sodium-proton exchanger NHE3. This study evaluated the relation between the lithium reabsorption and the phosphorylation of GSK3β, by using acetazolamide, an NHE3 inhibitor. In rats infused with lithium chloride, the plasma concentration of lithium was 4.77 mEq/l, and the renal clearance of lithium and its fractional excretion were calculated to be 2.29 ml/min/kg and 0.405, respectively. Coadministration of acetazolamide decreased creatinine clearance and the reabsorption rate of lithium, increased the fractional excretion of lithium, and did not affect its plasma concentration. Western blot analysis exhibited the facilitation of GSK3β phosphorylation in the kidney cortex by lithium infusion, and acetazolamide inhibited the lithium-induced phosphorylation of GSK3β. Lithium did not affect GSK3β phosphorylation in the liver and did not affect Akt in the kidney cortex and liver. These data show that lithium reabsorption contributes to GSK3β phosphorylation in the kidney cortex.

Effect of renal ischemia on urinary excretion of lithium in rats

Lithium, administered to patients with bipolar disorders, is mainly excreted in the urine, and tubular reabsorption is involved. This study characterized the renal excretion of lithium in rats subjected to renal ischemia for 60 min or 90 min. After intravenous injection of lithium chloride at 25 mg/kg, the pharmacokinetic parameters of lithium were determined. In sham-operated rats, the renal clearance of lithium was calculated to be 1.49 ml/min/kg, and its ratio to creatinine clearance (fractional excretion) was 43.4%. Renal ischemia inhibited the renal excretion of lithium, and did not affect its fractional excretion. The urinary pH of rats with renal ischemia for 90 min was significantly higher than those of the other groups, and the linear regression with the fractional excretion of lithium in rats with renal ischemia showed a moderate correlation (r = 0.650, p = 0.00193). This study demonstrated the effect of renal ischemia on the renal excretion of lithium in rats. It was suggested that not only glomerular filtration but also the reabsorption of lithium was impaired by renal ischemia.

Effects of Natural Polyphenols on the Expression of Drug Efflux Transporter P-Glycoprotein in Human Intestinal Cells

The drug efflux transporter P-glycoprotein, which is encoded by MDR1 (ABCB1), plays important roles in drug absorption, distribution, and elimination. We previously reported that dietary polyphenols such as quercetin, curcumin, honokiol, magnolol, caffeic acid phenetyl ester (CAPE), xanthohumol, and anacardic acid inhibit P-glycoprotein-mediated drug transport. In the present study, we investigated the effects of polyphenols on the expression of P-glycoprotein using human intestinal epithelial LS174T cells and a reporter plasmid expressing 10.2 kbp of the upstream regulatory region of MDR1. Honokiol, magnolol, CAPE, xanthohumol, and anacardic acid activated the MDR1 promoter in LS174T cells, and the cellular uptake of rhodamine 123 and calcein-AM, fluorescent substrates of P-glycoprotein, decreased in polyphenol-treated LS174T cells. These results suggest that dietary natural polyphenols can induce the drug efflux transporter P-glycoprotein and have the potential to promote food-drug interactions.

Nonlinear disposition of lithium in rats and saturation of its tubular reabsorption by the sodium-phosphate cotransporter as a cause

We previously reported the contribution of sodium-phosphate cotransporter to the tubular reabsorption of lithium in rats. In the present study, the dose dependency of the renal handling of lithium was examined in rats. When lithium chloride at 1.25 mg/kg, 2.5 mg/kg and 25 mg/kg was intravenously injected as a bolus, the areas under the plasma concentration-time curve of lithium until 60 minutes were calculated to be 6.23 mEq·min/l, 8.77 mEq·min/l and 64.6 mEq·min/l, respectively. The renal clearance of lithium and its fractional excretion increased with increments in the dose administered. The renal clearance of lithium strongly correlated with the urinary excretion rate of phosphate in the 1.25 mg/kg group (r = 0.840) and 2.5 mg/kg group (r = 0.773), whereas this correlation was weak in the 25 mg/kg group (r = 0.306). The infusion of foscarnet, a typical inhibitor of sodium-phosphate cotransporter, decreased the fractional reabsorption of lithium in rats administered lithium chloride at 2.5 mg/kg, but did not affect it in rats administered 25 mg/kg. These results demonstrate the nonlinearity of the renal excretion of lithium in rats, with the saturation of lithium reabsorption by the sodium-phosphate cotransporter potentially being involved.

D-Malate decreases renal content of α-ketoglutarate, a driving force of organic anion transporters OAT1 and OAT3, resulting in inhibited tubular secretion of phenolsulfonphthalein, in rats

d-Malate inhibits a Krebs cycle enzyme and the tubular transport of α-ketoglutarate, an intermediate of the Krebs cycle and the driving force for rat organic anion transporter 1 (rOAT1) and rOAT3 in the kidney. This study examined the effects of d-malate on the rat organic anion transport system. The uptake of 6-carboxyfluorescein by HEK293 cells expressing rOAT1 or rOAT3 was not affected by d-malate and l-malate. Up to 60 min after the intravenous injection of phenolsulfonphthalein (PSP), a typical substrate of the renal organic anion transporters, as a bolus to rats, 47.1% of the dose was recovered in the urine, and its renal clearance was estimated to be 8.60 ml/min/kg. d-Malate but not l-malate interfered with its renal excretion, resulting in the delayed elimination of PSP from plasma. No effect of d-malate was recognized on creatinine clearance or the expression level of rOAT3 in the kidney cortex. d-Malate increased the plasma concentration of α-ketoglutarate. In addition, the compound greatly stimulated the renal excretion of α-ketoglutarate, implying that d-malate inhibited its reabsorption. The content of α-ketoglutarate was significantly decreased in the kidney cortex of rats administered d-malate. Collectively, this study shows that d-malate abrogates the tubular secretion of PSP, and the reduction of the renal content of α-ketoglutarate was proposed to be one of the mechanisms. A relationship between the reabsorption of α-ketoglutarate and the basolateral uptake of organic anion in the kidney is suggested.

Enantioselective Effect of Flurbiprofen on Lithium Disposition in Rats

AIMS

Lithium is administered for treating bipolar disorders and is mainly excreted into urine. Nonsteroidal anti-inflammatory drugs inhibit this process. In this study, we examined the enantioselective effect of flurbiprofen on the disposition of lithium in rats.

METHODS

Pharmacokinetic experiments with lithium were performed.

RESULTS

Until 60 min after the intravenous administration of lithium chloride at 30 mg/kg as a bolus, 17.8% of lithium injected was recovered into the urine. Its renal clearance was calculated to be 1.62 mL/min/kg. Neither creatinine clearance (Ccr) nor pharmacokinetics of lithium was affected by the simultaneous injection of (R)-flurbiprofen at 20 mg/kg. (S)-flurbiprofen impaired the renal function and interfered with the urinary excretion of lithium. The ratio of renal clearance of lithium to Ccr was decreased by the (S)-enantiomer.

CONCLUSION

This study clarified that the (S)-flurbiprofen but not (R)-flurbiprofen inhibited the renal excretion of lithium in rats.

Foscarnet, an inhibitor of the sodium-phosphate cotransporter NaPi-IIa, inhibits phosphorylation of glycogen synthase kinase-3β by lithium in the rat kidney cortex

Lithium, which is used in the treatment of and prophylaxis for bipolar disease, inhibits glycogen synthase kinase-3β (GSK3β) by producing its phosphorylated form (p-GSK3β). GSK3β plays a role in apoptosis and some kinds of acute kidney injuries, and the formation of p-GSK3β is considered to contribute to protection against acute kidney injury. We previously reported that the sodium-phosphate cotransporter NaPi-IIa (SLC34A1) mediated the reabsorption of lithium in the rat kidney. In the present study, the phosphorylation status of GSK3β in the kidney cortex of rats administered lithium chloride and foscarnet, a typical inhibitor of NaPi-IIa, was examined using Western blotting. Under a 2-h infusion of lithium chloride, the plasma concentration of lithium was 1.06 mEq/l, and its renal clearance was calculated as 1.18 ml/min/kg, which was 29.6% of creatinine clearance. The abundance of p-GSK3β in the kidney cortex was augmented by the administration of lithium. The simultaneous infusion of foscarnet increased the renal clearance of lithium and its ratio to creatinine clearance as well as the urinary excretion of phosphate. Foscarnet also inhibited the lithium-induced phosphorylation of GSK3β. These results suggest that the reabsorption of lithium by NaPi-IIa triggers the phosphorylation of GSK3β in the rat kidney cortex.

Minor contribution of biliary excretion in lithium elimination in rats

BACKGROUND

Lithium, which is often used for the treatment of bipolar disorders, is mainly recovered into urine after being orally administered. Due to the fact that it is completely absorbed via the gastrointestinal tract, it remains unknown whether biliary excretion is involved in the lithium disposition. In this study, we examined biliary excretion of lithium in rats and compared these with renal excretion.

MATERIALS AND METHODS

After the injection of lithium chloride to femoral vein, plasma levels and excretion into urine and bile of lithium were evaluated.

RESULTS

After its intravenous administration as a bolus, the plasma concentration of lithium decreased time-dependently. Until 60 min, 6.47% and 0.694% of injected lithium were excreted into urine and bile, respectively. The biliary clearance of lithium was calculated to be 0.0779 mL/min/kg, and this was 11.3% of the renal clearance.

CONCLUSIONS

These findings suggest the low ability of the liver to eliminate lithium from plasma in comparison with the kidney in rats.

Sodium-phosphate cotransporter mediates reabsorption of lithium in rat kidney

Lithium, used for the treatment of bipolar disorders, is reabsorbed via sodium-transport system in the proximal tubule. This step causes intra-/inter-individual difference of lithium disposition, and it has not been unclear which transporter contributes. In this study, we examined effect of foscarnet and parathyroid hormone (PTH), inactivators for sodium-phosphate cotransporter, and phlorizin, a typical inhibitor for sodium-glucose cotransporter, on the disposition of lithium in rats. Their intravenous administration stimulated urinary excretion of phosphate or glucose. After the intravenous injection of lithium chloride as a bolus, plasma concentration of lithium decreased time-dependently. The renal clearance of lithium was calculated to be 0.740 ml/min/kg in control rats, and this was 26.7% of creatinine clearance. Foscarnet and PTH significantly increased the renal clearance of lithium and its ratio to creatinine clearance, suggesting that they prevented the reabsorption of lithium. No effect of phlorizin on the renal handling of lithium was recognized. In control rats, the renal clearance of lithium showed a strong correlation with the renal excretion rate of phosphate, compared with creatinine clearance. These findings suggest that sodium-phosphate cotransporter reabsorbs lithium in the rat kidney. Furthermore, its contribution was estimated to be more than 65.9% in the lithium reabsorption. And, this study raised the possibility that therapeutic outcome of lithium is related with the functional expression of sodium-phosphate cotransporter in the kidney.

Diuresis by intravenous administration of xanthurenic acid in rats, and inhibition by probenecid

The conjugates with sulfate and glucoside of xanthurenic acid, a tryptophan metabolite, were reported to show natriuresis. Sulfotransferase for xanthurenic acid works in the renal proximal tubule to produce the sulfate of xanthurenic acid as well as the liver, and we recently found that xanthurenic acid is a substrate of renal organic anion transporter OAT1. The purpose of this study was to examine relationship between the transport by OAT1 and diuresis related with xanthurenic acid. Drug transport experiment using Xenopus laevis oocytes represented that probenecid inhibited xanthurenic acid uptake by rat OAT1 (rOAT1). Although no diuresis was recognized by the intravenous injection of xanthurenic acid as a bolus in rats, the addition of its infusion exhibited natriuresis. Simultaneous administration of probenecid significantly decreased the urine volume and excreted amounts of sodium into urine. These findings showed the diuresis by the xanthurenic acid administration, and it was probenecid-sensitive. The rOAT1-mediated transport of xanthurenic acid might, at least in part, contribute to its diuretic effect.

Transport of Kynurenic Acid by Rat Organic Anion Transporters rOAT1 and rOAT3: Species Difference between Human and Rat in OAT1

A tryptophan catabolite, kynurenic acid, is involved in schizophrenia and uremia; there is little information on the mechanism of its disposition. Recently, our laboratory showed that kynurenic acid is a good substrate of human organic anion transporters hOAT1 and hOAT3. In this study, we performed uptake experiment using Xenopus laevis oocytes to characterize the transport of kynurenic acid by rat homologs of the transporters, rOAT1, and rOAT3. These transporters stimulated the uptake of kynurenic acid into oocytes, and transport by rOAT3 was marked. The Km values of the transport were estimated to be 8.46 μM for rOAT1 and 4.81 μM for rOAT3, and these values are comparable to their human homologs. The transport activity of kynurenic acid by rOAT1 was about one quarter of that of p-aminohippurate, although they were at the similar levels in hOAT1. A comparative experiment with hOAT1 was added in this study, showing that uptake amounts of kynurenic acid by hOAT1-expressing oocytes were 4 times greater than rOAT1-expressing oocytes. rOAT3 transported kynurenic acid as efficiently as estrone sulfate; this phenomenon was also observed in hOAT3. In conclusion, transport of kynurenic acid by rOAT1 and rOAT3 was shown. The characteristics of rOAT3 were similar to hOAT3, but low transport activity of kynurenic acid by rOAT1 was exhibited compared with hOAT1.

Stereoselective inhibitory effect of flurbiprofen, ibuprofen and naproxen on human organic anion transporters hOAT1 and hOAT3

Nonsteroidal anti-inflammatory drugs (NSAIDs) delay the renal excretion of antifolate methotrexate by inhibiting human organic anion transporters hOAT1 (SLC22A6) and hOAT3 (SLC22A8). In this study, uptake experiments were performed using Xenopus laevis oocytes to assess stereoselectivity in the inhibitory characteristics of flurbiprofen, ibuprofen and naproxen against hOAT1 and hOAT3. Uptake of p-aminohippurate by hOAT1 was inhibited by each enantiomer of the three NSAIDs, and the inhibitory effect was superior in each (S)-enantiomer around 10 µM. The apparent 50% inhibitory concentrations were estimated to be 0.615 µM for (S)-flurbiprofen, 2.84 µM for (S)-ibuprofen and 1.93 µM for (S)-naproxen, and these values were significantly lower than those of the respective (R)-enantiomers [(R)-flurbiprofen: 2.35 µM, (R)-ibuprofen: 6.14 µM, (R)-naproxen: 5.26 µM]. Furthermore, the (S)-NSAIDs at 3 µM reduced methotrexate accumulation in hOAT1-expressing oocytes more strongly than the corresponding (R)-enantiomers. All enantiomers inhibited hOAT3-mediated transport of estrone sulfate and methotrexate, but there was no difference between both enantiomers of each NSAID in the inhibitory potencies. Eadie-Hofstee plot analysis showed that (S)-flurbiprofen and (R)-flurbiprofen inhibited hOAT1 and hOAT3 in a competitive manner. These findings represent the stereoselective inhibitory potencies of flurbiprofen, ibuprofen and naproxen on hOAT1, and the (S)-enantiomers are greater. In contrast, stereoselectivity was not recognized in their inhibitory effect on hOAT3.

Inhibitory effect of selective cyclooxygenase-2 inhibitor etoricoxib on human organic anion transporter 3 (hOAT3)

It is well known that nonsteroidal anti-inflammatory drugs (NSAIDs) delay the elimination of methotrexate. One of the mechanisms is thought to be inhibition of methotrexate uptake via human organic anion transporter 3 (hOAT3, SLC22A8) in the renal proximal tubule by NSAIDs. In this study, we evaluated the inhibitory effects of selective cyclooxygenase-2 inhibitor etoricoxib on hOAT3 by uptake experiments using Xenopus laevis oocytes. The injection of hOAT3 cRNA stimulated the uptake of methotrexate into the oocytes, and its transport was inhibited by etoricoxib. Etoricoxib inhibited estrone sulfate uptake by hOAT3 dose dependently, and the 50% inhibitory concentration was estimated to be 9.8 µM. Eadie-Hofstee plot analysis showed that etoricoxib inhibited hOAT3 in a competitive manner. These findings show that etoricoxib has inhibitory effect on hOAT3, and that the potential is comparable to that of traditional NSAIDs.

Inhibitory effect of selective cyclooxygenase-2 inhibitor lumiracoxib on human organic anion transporters hOAT1 and hOAT3

Nonsteroidal anti-inflammatory drugs (NSAIDs) delay renal excretion of antifolate methotrexate by inhibiting human organic anion transporters hOAT1 (SLC22A6) and hOAT3 (SLC22A8). In this study, we performed uptake experiments using Xenopus laevis oocytes to assess the inhibitory effect of selective cyclooxygenase-2 inhibitors on hOAT1 and hOAT3. The uptake of methotrexate into oocytes was increased by the injection of hOAT1 and hOAT3 cRNA, and transport was strongly inhibited by lumiracoxib. The apparent 50% inhibitory concentrations of lumiracoxib were estimated to be 3.3 µM and 1.9 µM for uptake of p-aminohippurate by hOAT1 and of estrone sulfate by hOAT3, respectively. Eadie-Hofstee plot analysis showed that lumiracoxib inhibited hOAT1 and hOAT3 in a competitive manner. For other cyclooxygenase-2 inhibitors celecoxib, etoricoxib, rofecoxib and valdecoxib, slight to moderate inhibition of hOAT3 only was observed. These findings show that lumiracoxib has inhibitory potential toward hOAT1 and hOAT3, comparable to that of nonselective NSAIDs.

Transport of aminopterin by human organic anion transporters hOAT1 and hOAT3: Comparison with methotrexate

The transport of antifolate aminopterin by human organic anion transporters hOAT1 (SLC22A6) and hOAT3 (SLC22A8) was characterized using Xenopus laevis oocytes and was compared with that of methotrexate. Although hOAT1 and hOAT3 transported both aminopterin and methotrexate, uptake of methotrexate was greater in hOAT3-expressing oocytes than in hOAT1-expressing oocytes, and aminopterin was transported by hOAT1 more efficiently. The apparent 50% inhibitory concentration (IC(50)) of aminopterin for p-aminohippurate uptake by hOAT1 was lower than that of methotrexate (methotrexate: 998 microM, aminopterin: 160 microM). On the other hand, IC(50) values of these antifolates for estrone sulfate transport by hOAT3 were comparable (methotrexate: 61.5 microM, aminopterin: 59.2 microM). The Michaelis-Menten constant and maximum velocity of aminopterin transport by hOAT1 were calculated to be 226 microM and 72.5 pmol/ oocyte/2 hr, respectively. Probenecid and non-steroidal anti-inflammatory drugs strongly inhibited the transport. These findings show that both aminopterin and methotrexate are substrates of hOAT1 and hOAT3, and that there are differences between the antifolates in terms of their transport characteristics.

Interaction and transport characteristics of mycophenolic acid and its glucuronide via human organic anion transporters hOAT1 and hOAT3

The immunosuppressant mycophenolate mofetil (MMF) is frequently administered with calcineurin inhibitors and corticosteroids to recipients of organ transplantations. However, the renal handling of the active metabolite mycophenolic acid (MPA) and 7-O-MPA-glucuronide (MPAG) has been unclear. The purpose of the present study was to assess the interaction of MPA and MPAG with the human renal organic anion transporters hOAT1 (SLC22A6) and hOAT3 (SLC22A8), by conducting uptake experiments using HEK293 cells stably expressing these transporters. MPA and MPAG inhibited the time-dependent uptake of p-[(14)C]aminohippurate by hOAT1 and that of [(3)H]estrone sulfate by hOAT3. The apparent 50% inhibitory concentration (IC(50)) of MPA for hOAT1 and hOAT3 was estimated at 10.7 and 1.5 microM, respectively. In the case of MPAG, the IC(50) values were calculated at 512.3 microM for hOAT1 and 69.1 microM for hOAT3. Eadie-Hofstee plot analyses showed that they inhibited hOAT1 noncompetitively and hOAT3 competitively. No inhibitory effects of tacrolimus, cyclosporin A and azathioprine on transport of p-[(14)C]aminohippurate by hOAT1 and of [(3)H]estrone sulfate by hOAT3 were observed. No transport of MPA by these transporters was observed. On the other hand, the uptake of MPAG into cells was stimulated by the expression of hOAT3, but not hOAT1. These findings propose the possibility that the administration of MMF decreases the renal clearance of drugs which are substrates of hOAT1 and hOAT3. Present data suggest that hOAT3 contributes to the renal tubular secretion of MPAG.

Renal Transport of Adefovir, Cidofovir, and Tenofovir by SLC22A Family Members (hOAT1, hOAT3, and hOCT2)

PURPOSE

The nephrotoxicity of the nucleotide antivirals adefovir, cidofovir and tenofovir is considered to depend on the renal tubular transport of them. Although it is known that the antivirals are substrates of the human renal organic anion transporter hOAT1 (SLC22A6), there is no information available on other organic ion transporters. The aim of the present study was to investigate whether the other renal organic anion transporter hOAT3 (SLC22A8) and organic cation transporter hOCT2 (SLC22A2) transport the antivirals.

MATERIALS AND METHODS

Uptake experiments were performed using HEK293 cells transfected with cDNA of the organic ion transporters.

RESULTS

The uptake of adefovir, cidofovir and tenofovir in monolayers stably expressing hOAT3 increased time-dependently, compared with control. Probenecid, a typical inhibitor of organic anion transporters, completely inhibited their transport. The amounts of the antivirals taken up by hOAT3 were much lower than those by hOAT1. The transient expression of hOCT2 did not increase uptake of the antivirals.

CONCLUSION

These results indicate that adefovir, cidofovir and tenofovir are substrates of hOAT3 as well as hOAT1, but that quantitatively hOAT1 is the major renal transporter for these drugs.

Different transport properties between famotidine and cimetidine by human renal organic ion transporters (SLC22A)

Histamine H2 receptor antagonist famotidine and cimetidine are commonly used for treatment of gastrointestinal ulcer diseases. Inasmuch as these drugs are mainly secreted by renal tubules, dosages have been adjusted according to renal function. Although many studies have been performed on the molecular mechanisms of renal handling of cimetidine, little is known about that of famotidine. In this study, to examine the recognition and transport of famotidine by human organic anion transporters (OATs; hOAT1, hOAT3) and human organic cation transporter (OCT; hOCT2), the uptake studies using Xenopus laevis oocytes were performed in comparison with cimetidine. The half-maximal inhibitory concentrations of famotidine for [3H]estrone sulfate transport by hOAT3 and [14C]tetraethylammonium transport by hOCT2 (300 microM and 1.8 mM, respectively) were higher than those of cimetidine (53 and 67 microM, respectively). While cimetidine inhibited p-[14C]aminohippurate transport by hOAT1 in a concentration dependent manner, famotidine did not affect it at 5 mM. In addition, hOAT3 mediated famotidine uptake, but hOAT1 and hOCT2 did not show famotidine transport. These results indicate that there are marked differences between famotidine and cimetidine in the recognition and transport by organic ion transporters and that hOAT3 contributes to the renal tubular secretion of famotidine. Present findings should be useful information to understand the renal handling of famotidine and cimetidine.

Methotrexate-Loxoprofen Interaction: Involvement of Human Organic Anion Transporters hOAT1 and hOAT3

Human organic anion transporters hOAT1 (SLC22A6) and hOAT3 (SLC22A8) are responsible for renal tubular secretion of an antifolic acid methotrexate, and are considered to be involved in drug interaction of methotrexate with nonsteroidal anti-inflammatory drugs (NSAIDs). In our hospital, a delay of methotrexate elimination was experienced in a patient with Hodgkin's disease, who took loxoprofen, a commonly used NSAID in Japan, which suggested a cause. In this study, we examined the drug interaction via hOAT1 and hOAT3, using Xenopus laevis oocytes. hOAT1 and hOAT3 mediated the methotrexate transport with low affinity (K(m) of 724.0 muM) and high affinity (K(m) of 17.2 muM), respectively. Loxoprofen and its trans-OH metabolite, an active major metabolite, markedly inhibited the methotrexate transport by both transporters. Their inhibition concentrations (IC(50)) were in the range of the therapeutic levels. These findings suggest that loxoprofen retards the elimination of methotrexate, at least in part, by inhibiting hOAT1 and hOAT3.

Common single nucleotide polymorphisms of the MDR1 gene have no influence on its mRNA expression level of normal kidney cortex and renal cell carcinoma in Japanese nephrectomized patients

In this study, we have quantified the mRNA expression levels of multidrug resistance gene 1 (MDR1) in the normal kidney cortex and renal cell carcinoma (RCC) segments from 24 Japanese nephrectomized patients by real-time polymerase chain reaction (PCR). The mRNA expression level of MDR1 in RCC segments was significantly decreased in comparison with each normal segment (P=0.0042, by Student's paired t-test). In addition, the ten common single nucleotide polymorphisms (SNPs) of the MDR1 gene in the patients were assessed using the PCR-restriction enzyme fragment length polymorphism method to investigate the influence of these SNPs on its mRNA expression levels. The allele frequencies of these SNPs were comparable with our previous report in the Japanese recipients of living-donor liver transplantation (Goto et al., Pharmacogenetics 12:451-457; 2002). MDR1 expression levels in the normal kidney cortex were independent on the five SNPs, which were polymorphic in the Japanese population. Furthermore, the effect of the SNPs on expression levels of MDR1 mRNA in RCC segments was not recognized. These findings suggest that the common SNPs in the MDR1 gene have no influence on the expression of its transcript in RCC segments as well as in the normal kidney cortex.

Organic anion transporter oatp2-mediated interaction between digoxin and amiodarone in the rat liver

PURPOSE

The interaction between amiodarone and digoxin has been known to increase serum concentrations of digoxin in humans and rats. In this study, we assessed the molecular mechanism(s) of that drug interaction, focusing on digoxin transport mediated by P-glycoprotein (Pgp) and by rat liver organic anion transporter (oatp2).

METHODS

Digoxin transport by Pgp and oatp2 was assessed using Pgp-overexpressing transfectant LLC-GA5-COL150 monolayers and oatp2-expressing Xenopus oocytes, respectively. The digoxin uptake into the isolated rat hepatocytes was also examined.

RESULTS

Amiodarone (10 microM) inhibited slightly the transcellular transport of digoxin in LLC-GA5-COL150 monolayers, whereas itraconazole (10 microM), a potent Pgp inhibitor, markedly blocked the transport. The digoxin uptake by the isolated rat hepatocytes and by the oatp2-expressing Xenopus oocytes was decreased markedly in the presence of amiodarone but not in the presence of itraconazole. In addition, amiodarone inhibited the oatp2-mediated digoxin uptake in a competitive manner with an apparent inhibition constant value of 1.8 microM.

CONCLUSION

These findings suggest that rat oatp2 rather than Pgp may be one of the interaction sites for digoxin and amiodarone in the liver.

Rat Renal Organic Anion Transporter rOAT1 Mediates Transport of Urinary-Excreted Cephalosporins, but not of Biliary-Excreted Cefoperazone

Most cephalosporin antibiotics are excreted into urine via glomerular filtration and active tubular secretion by renal organic anion transporters. In this study, we investigated the interaction of cephalosporins with rat organic anion transporter rOAT1, mainly expressed at the basolateral membrane of the renal proximal tubules, using Xenopus laevis oocytes, to assess the roles of rOAT1 in renal excretion of cephalosporin antibiotics. The expression of rOAT1 significantly stimulated the uptake of cefazolin, cefotiam and cephalexin into oocytes, but not of cefoperazone. The inhibition constants of these cephalosporins to rOAT1-mediated p-aminohippurate (PAH) uptake were 72 microM for cefazolin, 298 microM for cefoperazone, 718 microM for cefotiam and 6 mM for cephalexin. Eadie-Hofstee plot analysis revealed that cefoperazone as well as cefotiam inhibited rOAT1-mediated PAH uptake competitively. These results suggest that rOAT1 mediates basolateral uptake of cephalosporin antibiotics in the renal tubules. Furthermore, it is suggested that a minor contribution of the kidney to cefoperazone excretion could be related to the finding that cefoperazone is a poor substrate of rOAT1.

Interaction between methotrexate and nonsteroidal anti-inflammatory drugs in organic anion transporter

The antifolate drug methotrexate is mainly eliminated from the body by renal tubular secretion via organic anion transporters. In clinical situations, severe methotrexate toxicity, due to an increase in serum concentrations, was observed after coadministration with nonsteroidal anti-inflammatory drugs (NSAIDs) or probenecid. In this study, we examined the effects of NSAIDs and probenecid on methotrexate transport via the rat renal organic anion transporter rOAT1, using Xenopus laevis oocytes. [3H]Methotrexate uptake was markedly stimulated in the rOAT1 cRNA-injected oocytes, and this uptake was inhibited by probenecid and various NSAIDs, whereas the influence of salicylate was less. The Dixon plots showed that probenecid, indomethacin and salicylate competitively inhibited rOAT1 with apparent K(i) values of 15.8 microM, 4.2 microM and 1.0 mM, respectively. These findings demonstrate that rOAT1 is the major site of the transporter-mediated interaction between methotrexate and NSAIDs and/or probenecid, leading to a decrease in renal excretion of methotrexate.

Interaction and transport of thiazide diuretics, loop diuretics, and acetazolamide via rat renal organic anion transporter rOAT1

The renal tubular secretion of thiazides and loop diuretics via the organic anion transport system in renal tubules is required for them to reach their principal sites of action. Similarly, acetazolamide, a diuretic clinically administered for glaucoma, is excreted from the kidney by glomerular filtration and tubular secretion. In this study, we investigated the interaction and transport of these diuretics via the rat renal organic anion transporter rOAT1 by using Xenopus laevis oocyte expression system. p-[(14)C]Aminohippurate (PAH) uptake by rOAT1-expressing oocytes was inhibited in the presence of a thiazide (chlorothiazide, cyclothiazide, hydrochlorothiazide), a loop diuretic (bumetanide, ethacrynic acid, furosemide), or a carbonic anhydrase inhibitor (acetazolamide, ethoxzolamide, methazolamide). Dixon plot analysis demonstrated that the inhibition constant (K(i)) value was 1.1 mM for acetazolamide, 150 microM for hydrochlorothiazide, 9.5 microM for furosemide, and 5. 5 microM for bumetanide. Kinetic analysis revealed that acetazolamide inhibited rOAT1 competitively and that inhibition style of furosemide was a mixture of competitive and noncompetitive. [(14)C]PAH efflux was significantly enhanced when the rOAT1-expressing oocytes were incubated in the presence of unlabeled PAH, alpha-ketoglutarate, acetazolamide, chlorothiazide, or hydrochlorothiazide. rOAT1 stimulated acetazolamide uptake, which was inhibited by probenecid. Although the loop diuretics had little trans-stimulation effect on [(14)C]PAH efflux via rOAT1, the rOAT1-mediated furosemide uptake was observed. These findings suggest that rOAT1 contributes, at least in part, to the renal tubular secretion of acetazolamide, thiazides, and loop diuretics.

Inhibitory effect of anti-diabetic agents on rat organic anion transporter rOAT1

The interactions of sulfonylureas and a novel anti-diabetic drug, nateglinide, with rat renal organic anion transporter (rOAT1) expressed in Xenopus laevis oocytes were studied. Uptake of p-aminohippurate via rOAT1 was markedly inhibited by glibenclamide and nateglinide, and moderately by chlorpropamide and tolbutamide. The inhibition constant values (K(i)) for chlorpropamide, glibenclamide, tolbutamide and nateglinide were 39.5, 1.6, 55.5 and 9.2 microM, respectively. Kinetic analysis showed that the inhibition of p-aminohippurate uptake by glibenclamide was competitive. Sulfonylureas examined and nateglinide did not show a trans-stimulation effect on [14C]p-aminohippurate efflux from rOAT1-expressing oocytes. There was no stimulation of [3H]glibenclamide uptake via rOAT1. These findings suggested that sulfonylureas and nateglinide interact with rOAT1, but these drugs are not translocated via the transporter.

Functional characterization of the rat multispecific organic anion transporter OAT1 mediating basolateral uptake of anionic drugs in the kidney

The functional characteristics of rat organic anion transporter OAT1 were investigated using Xenopus laevis oocytes. Uptake of p-aminohippurate (PAH) by the oocytes expressing OAT1 was markedly inhibited by glutarate, alpha-ketoglutarate and probenecid, moderately inhibited by folate and methotrexate, but not inhibited by taurocholate or tetraethylammonium. Methotrexate and folate were transported by OAT1, but probenecid, a typical inhibitor of organic anion transporter, was not transported. Inhibition of PAH uptake by aliphatic dicarboxylates with various alkyl chain lengths was maximal at 5 (glutarate) and 6 (adipate) carbon atoms. OAT1-mediated PAH uptake was markedly inhibited by phorbol 12-myristate 13-acetate (PMA), phorbol 12,13-dibutyrate and mezerein, but not by 4alpha-phorbol 12,13-didecanoate. The inhibitory effect of PMA was attenuated in the presence of staurosporine, suggesting that OAT1 is regulated by protein kinase C. These results suggest that the substrate recognition of OAT1 is comparable to that of renal basolateral organic anion transporter, and the transport activity is regulated by protein kinase C.

Genetic polymorphism of the CYP2C subfamily and its effect on the pharmacokinetics of phenytoin in Japanese patients with epilepsy

OBJECTIVE

To examine the genetic polymorphism of CYP2C9 and CYP2C19 and its effect on the pharmacokinetics of phenytoin among 44 Japanese patients with epilepsy.

METHODS

Polymerase chain reaction tests with leukocyte deoxyribonucleic acid were used to detect the mutations for the amino acid substitution (Arg144-->Cys and Ile359-->Leu) in CgammaP2C9 and for the defective allele (m1 and m2) in CgammaP2C19. The pharmacokinetic parameters of phenytoin in individual patients were estimated by means of empirical bayesian analysis, in which the prior information was the population parameters for Japanese patients with epilepsy.

RESULTS

Of the 44 patients, none had the CgammaP2C9 mutation for the Cys144 allele, whereas six patients were heterozygous for the wild-type (wt) and Leu359 allele (wt/Leu359) in cgammaP2C9. The maximal elimination rate (Vmax) of phenytoin among patients with heterozygous wt/Leu359 in CgammaP2C9 was 33% lower than that among patients with normal CgammaP2C9. A total of 21 patients were heterozygous for the CgammaP2C19 mutation (wt/m1 or wt/m2), and five patients had the homozygous or heterozygous mutations in CgammaP2C19 (m1/m1 or m1/m2). The Vmax values of phenytoin were slightly decreased (up to 14%) among patients with CgammaP2C19 mutations compared with patients with normal CgammaP2C19.

CONCLUSION

The findings indicated that the genetic polymorphisms of CYP2C isozymes play an important role in the pharmacokinetic variability of phenytoin and that the mutation in CYP2C9 proteins (Ile359-->Leu) is a determinant of impaired metabolism of the drug among Japanese persons.