Inhibitory effects of Kampo medicines, Keishibukuryogan and Shakuyakukanzoto, on the substrate uptake activities of solute carrier organic anion transporters.

The aim of this study was to assess the effects of Keishibukuryogan (K-06) and Shakuyakukanzoto (TJ-68), commercial herbal medicines, on the substrate uptake activities of renal organic anion transporters. We performed transporter uptake and cell viability assays in Xenopus oocytes and HEK293 human kidney embryonic cells treated with K-06 or TJ-68. K-06 and TJ-68 markedly inhibited the substrate uptake activities of URAT1, OAT1, and OAT3, while they did not exhibit non-cytotoxic effects. Our findings demonstrated that K-06 and TJ-68 inhibited the substrate uptake activities of renal transporters, suggesting their mechanism of action as nephroprotective agents.

Different transport activity of human triallelic MDR1 893Ala/Ser/Thr variant and its association with herb extracts.

Individual pharmacokinetic differences for herb-drug interaction have been associated with genetic variations of the multidrug resistance (MDR) gene. A high level expression of MDR protein increases cellular efflux and might decrease drug sensitivity. This study investigated the drug efflux activity difference of human MDR1 triallelic variant 2677G/T/A (rs2032582), as a nonsynonymous 893Ala/Ser/Thr, using Xenopus laevis oocytes and MDR1 overexpressing LLC-PK1 cells. Two MDR1 variants (2667T/893Ser and 2667A/893Thr) were generated using human MDR1 cDNA (2677G/893Ala). No significant difference in the expression of MDR1 893Ala/Ser/Thr was found in X. laevis oocytes. However, the MDR1 2667A/893Thr variant interestingly showed a significant decrease of efflux activity for both digoxin and daunorubicin compared with those of 893Ala and 893Ser variants. In further investigation assessing the inhibitory effects of three herbal extracts on MDR1, 893Ala and 893Ser showed significant decreases of efflux activities in treatments with P. cocos (p = 0.005 for 893Ser) and D. dasycarpus (p = 0.0009 for 893Ala; p = 0.002 for 893Ser) in X. laevis oocytes. The results in this study suggest that herbal medicines could interact with other drugs and change the therapeutic effects depending on the genetic polymorphisms of individuals.

Establishment and characterization of Mardin-Darby canine kidney cells stably expressing human organic anion transporters.

Organic anion transporters (OATs) play essential roles in the renal elimination of clinically important anionic drugs. The purpose of this study was to establish an efficient in vitro assay system to screen the transport characteristics of drugs and to examine drug interaction potentials of drugs with OATs. First, we established Mardin-Darby canine kidney (MDCK) cells stably expressing OAT1, OAT3, and OAT4 (MDCK-OAT1, -OAT3, and -OAT4, respectively). To characterize these cells, [(14)C]para-aminohippuric acid and [(3)H]estrone-3-sulfate transport properties were measured, and these corresponded to the results of the mRNA expression and localization of respective transporters using RT-PCR and immunofluorescence staining assay. Additionally, we screened three herbal medicines, Woohwangcheongsimwon, Hawangyeonhaedoktang, and Aristolochiae fructus extracts, which have been widely used in Korea or reported for nephrotoxicity, in our MDCK-OAT1, -OAT3, and -OAT4 cells. Aristolochiae fructus extracts strongly inhibited organic anion uptake by OAT1, OAT3, and OAT4, whereas Woohwangcheongsimwon only interacted with OAT1, and Hawangyeonhaedoktang with OAT1 and OAT3, suggesting drug interaction potential with OATs-mediated renal eliminating drugs. In conclusion, we established and characterized MDCK cells stably expressing OAT1, OAT3, and OAT4 for the elucidation of substrates or inhibitors of respective transporters as high-throughput screening tools.

Effect of silymarin supplement on the pharmacokinetics of rosuvastatin.

OBJECTIVES: To evaluate the effect of silymarin on the pharmacokinetics of rosuvastatin in systems overexpressing OATP1B1 or BCRP transporters and in healthy subjects. MATERIALS AND METHODS: The concentration-dependent transport of rosuvastatin and the inhibitory effect of silymarin were examined in vitro in OATP1B1-expressing oocytes and MDCKII-BCRP cells. For in vivo assessment, eight healthy male volunteers, divided into two groups, were randomly assigned to receive placebo or silymarin (140 mg) three times per day for 5 days. On day 4, all subjects received rosuvastatin (10 mg, 8 AM: ) 1 h after the placebo or silymarin administration. A series of blood samples were collected for 72 h, and the plasma concentration of rosuvastatin was determined using LC-MS/MS. RESULTS: Based on the concentration dependency of rosuvastatin transport in the OATP1B1 and BCRP overexpression systems, rosuvastatin is a substrate for both transporters. Silymarin inhibited both OATP1B1- and BCRP-mediated rosuvastatin transport in vitro (K (i) 0.93 microM and 97 microM, respectively). However, no significant changes in AUC, half-life, Vd/F, or Cl/F of rosuvastatin were observed in human subjects following pretreatment with silymarin. CONCLUSIONS: Silymarin does not appear to affect rosuvastatin pharmacokinetics in vivo, suggesting that silymarin, administered according to a recommended supplementation regimen, is not a potent modulator of OATP1B1 or BCRP in vivo.

Novel single nucleotide polymorphisms of organic cation transporter 1 (SLC22A1) affecting transport functions.

Organic cation transporter OCT1 (SLC22A1) plays an essential role in absorption, distribution, and excretion of various xenobiotics including therapeutically important drugs. In the present study, we analyzed the functional properties of the single nucleotide polymorphisms (SNPs) in SLC22A1 gene found in Japanese control individuals. Four mutations resulting in the amino acid changes (F160L, P283L, R287G, and P341L) were functionally characterized in Xenopus oocyte expression system. Two new SNPs, identified in Japanese population, P283L and R287G exhibited no uptake of both [14C]TEA and [3H]MPP+, although their protein expressions were detected in the plasma membrane of the oocytes injected with their cRNAs. Uptake of [14C]TEA by P341L was reduced to 65.1% compared to wild type, whereas F160L showed no significant change in its transport activity. This study suggests that the newly found OCT1 variants will contribute to inter-individual variations leading to the differences in cationic drug disposition and perhaps certain disease processes.

Molecular identification of a novel carnitine transporter specific to human testis. Insights into the mechanism of carnitine recognition.

l-Carnitine is an essential component of mitochondrial fatty acid beta-oxidation and plays a pivotal role in the maturation of spermatozoa within the male reproductive tract. Epididymal plasma contains the highest levels of l-carnitine found in the human body, and initiation of sperm motility occurs in parallel to l-carnitine increase in the epididymal lumen. Using a specific carrier, epididymal epithelium secretes l-carnitine into the lumen by an active transport mechanism; however, the structure-activity relationship comprising the carnitine-permeation pathway is poorly understood. We discovered a novel carnitine transporter (CT2) specifically located in human testis. Analyzing the primary structure of CT2 revealed that it is phylogenetically located between the organic cation transporter (OCT/OCTN) and anion transporter (OAT) families. Hence, CT2 represents a novel transporter family. When expressed in Xenopus oocytes, CT2 mediates the high affinity transport of l-carnitine but does not accept mainstream OCT/OCTN cationic or OAT anionic substrates. We synthesized and tested various carnitine-related compounds and investigated the physicochemical properties of substrate recognition by semi-empirical computational chemistry. The data suggest that the quaternary ammonium cation bulkiness and relative hydrophobicity be the most important factors that trigger CT2-substrate interactions. Immunohistochemistry showed that the CT2 protein is located in the luminal membrane of epididymal epithelium and within the Sertoli cells of the testis. The identification of CT2 represents an interesting evolutionary link between OCT/OCTNs and OATs, as well as provides us with an important insight into the maturation of human spermatozoa.