Effects of nonsteroidal anti-inflammatory drugs on the expression and function of P-glycoprotein/MDR1 in Caco-2 cells.

The aim of this study was to examine the effects of 16 kinds of nonsteroidal anti-inflammatory drugs (NSAIDs) on P-glycoprotein/MDR1 in Caco-2 cells as an intestinal epithelial cell model. Cells were treated with NSAIDs for 24 hours, and then, the expression of MDR1 mRNA was evaluated by reverse-transcriptase polymerase chain reaction. The function of MDR1 in cells pretreated with NSAIDs for 48 hours was evaluated by measuring the cellular amount of rhodamine123, which is a substrate of MDR1. The expression of MDR1 mRNA was increased by diclofenac, fenbufen, indomethacin, and nimesulide and the tended to be increased by meloxicam, mepirizole, and sulindac. However, pretreatment for 48 hours with diclofenac, indomethacin, or nimesulide, but not fenbufen, resulted in a significant increase in the amount of rhodamine123 accumulated. Although NSAIDs without effects on the expression of MDR1 mRNA altered the accumulation of rhodamine123 significantly, the efflux of rhodamine123 from cells was unchanged. In conclusion, the expression of MDR1 mRNA in Caco-2 cells was demonstrated to be increased by treatment with some NSAIDs, although the transport function of MDR1 was unchanged. These findings imply that the NSAIDs did not cause the drug interaction via MDR1 induction.

Effects of alpha-adrenoceptor antagonist doxazosin on MDR1-mediated multidrug resistance and transcellular transport.

The purpose of this study is to examine the effects of doxazosin, an alpha-adrenoceptor antagonist, on P-glycoprotein/MDR1-mediated multidrug resistance (MDR) and the transport of anticancer drugs. The effects of doxazosin, prazosin, and terazosin on MDR1-mediated MDR were assessed in human cervical carcinoma HeLa cells and the MDR1-overexpressing derivative Hvrl00-6, established by stepwise increases of the vinblastine concentration in the culture medium. The effects of doxazosin on the transcellular transport and intracellular accumulation of [3H]vinblastine, [3H]daunorubicin, and [3H]digoxin, all MDR1 substrates, were evaluated using LLC-GA5-COL150 cell monolayers, established by transfection of human MDR1 cDNA into porcine kidney epithelial LLC-PK1 cells. The sensitivity to vinblastine and paclitaxel of Hvrl00-6 cells was increased at 3.4- and 17.5-fold, respectively, by the addition of 1 microM doxazosin, whereas prazosin and terazosin had weaker or no such effects. Prazosin at 1 microM had a reversal effect on the sensitivity to vinblastine, whereas terazosin had no effect. In transport experiments, doxazosin concentration dependently increased the apical-to-basal transport of radiolabeled drugs in LLC-GA5-COL150 cells, but did not show remarkable effects on the basal-to-apical transport. In addition, doxazosin restored the intracellular accumulation in a concentration-dependent manner in LLC-GA5-COL150 cells. Doxazosin may partly reverse MDR by inhibiting MDR1-mediated transport, making it a candidate lead compound in the development of a reversing agent for MDR.

Molecular changes to HeLa cells on continuous exposure to SN-38, an active metabolite of irinotecan hydrochloride.

It is important to clarify the molecular characteristics of tumor cells showing multidrug resistance (MDR) and to identify the novel targets or biomarkers for chemotherapy. The aim of this study is to establish resistant HeLa sublines through exposure to SN-38, an active metabolite of irinotecan hydrochloride, and to investigate their molecular changes. HeLa cells were exposed to SN-38 at 1, 10, or 100 nM, and resistant clones were isolated and named HeLa/SN1, HeLa/SN10, and HeLa/SN100, respectively. Their cellular changes were examined based on growth inhibition assays, the function of ABCG2/BCRP, and a RT-PCR analysis of MDR-related protein. The sublines showed a decrease in sensitivity to not only SN-38 but also other chemotherapeutic agents as compared with HeLa cells. mRNA and protein levels of ABCG2/BCRP were increased, and the transport activity of ABCG2/BCRP was enhanced, in the resistant cells. In addition, the expression levels of ABCC1/MRP1, ABCC3/MRP3, and ABCC5/MRP5 were higher than in HeLa cells. The mRNA levels of GGT1 encoding a gamma-glutamyl transferase, but not GCS encoding a gamma-glutamyl cysteine synthetase, were also higher. Other factors examined, i.e., topoisomerase, SLCO1B1, and apoptosis-regulating factors, were comparable among the cells. The overexpression of ABCG2/BCRP was involved in the mechanism of resistance in SN-38-tolerant cells, and ABCC1/MRP1, ABCC3/MRP3, ABCC5/MRP5, and GGT1 may also have participated.

Effects of Agaricus blazei Murill extract on sensitivity to chemotherapeutic agents in HeLa cells and its resistant sublines.

Agaricus blazei Murill (ABM; Japanese name: Kawahiratake or Agarikusutake) extract is a widely used dietary supplement. However, limited information is available on the effects of the extract on the effectiveness of the chemotherapeutic agents. In this study, we examined the effects of ABM extract (Kyowa Wellness Co., Ltd.) on sensitivity to chemotherapeutic agents, paclitaxel and doxorubicin as MDR1/P-glycoprotein substrates, and cisplatin and 5-fluorouracil as non-substrates, in human cervical carcinoma HeLa cells, and paclitaxel-resistant and cisplatin-resistant derivatives (HeLa/TXL and HeLa/CDDP, respectively). The extract had no growth inhibitory effects on HeLa and the resistant cells at concentrations ranging from 7.6 × 10(-4) µ g/ml to 8.0 × 10(2)µ g/ml, indicating no remarkable cytotoxic activity in vitro. In the presence of 0.1, 0.5, and 1 µ g/ml of ABM extract, sensitivity to paclitaxel, cisplatin and 5-fluorouracil did not change in HeLa, HeLa/TXL and HeLa/CDDP cells. However, the extract reduced sensitivity to doxorubicin in HeLa/TXL and HeLa/CDDP cells in a concentration-dependent manner. In conclusion, the concomitant use of ABM extract minimally affected sensitivity to various chemotherapeutic agents in HeLa cells and resistant sublines in vitro.

Effects of turmeric extract on the pharmacokinetics of nifedipine after a single oral administration in healthy volunteers.

The effects of turmeric extracts on the pharmacokinetics of nifedipine were examined in 10 healthy volunteers. An open-label and randomized crossover study was performed at 2-week intervals. In the control experiment, after a 10 h overnight fast, 10 mg of nifedipine (Adalat® capsule) was administered orally and blood was collected at 0, 0.5, 1, 2, 3, 4, 5, 6, and 8 h. In the combination experiment, the volunteers were orally administered 10 mg of nifedipine together with six tablets containing concentrated turmeric extract (480 mg of curcuminoid per six tablets), which is the general daily dose, and blood was sampled as above. The time profile of the plasma concentration of nifedipine in the control was comparable to that in combination with turmeric extract, as were the pharmacokinetic parameters: that is, the mean ratio of turmeric extract/control group (90% confidence interval: CI); C(max), 0.98 (0.95, 1.01) and AUC(0 - ∞) 1.00 (0.98, 1.02). In addition, the volunteers all completed the study without any serious adverse events. Consumption of the turmeric extract did not affect the pharmacokinetics of nifedipine after a single oral administration.

Effects of Sairei-to on the pharmacokinetics of nifedipine in rats.

Sairei-to is a traditional herbal medicine used to complement, and as an alternative to, Western drugs. The aim of this study was to evaluate the pharmacokinetic interactions between Sairei-to and nifedipine (NFP), a substrate for CYP3A, in rats. NFP-oxidizing activity and the pharmacokinetics of NFP were examined after a single or 1-week of administration of Sairei-to (EK-114). NFP-oxidizing activity was enhanced transiently around 24 h after a single administration of EK-114 (1400 mg/kg). In vivo, the first-pass metabolism of NFP increased in the small intestine at 24 h after the administration of EK-114, and this effect disappeared at 72 h. Co-administration of EK-114 tended to inhibit the metabolism of NFP. On the other hand, when EK-114 was given at a high dose (1400 mg/kg) for 1 week, the oxidation of NFP in the small intestine was inhibited, and Cmax and AUC after the oral administration of NFP increased. In addition, a clinical dose of EK-114 (140 mg/kg) did not alter the pharmacokinetics of NFP, regardless of the administration schedule. EK-114 was suggested to affect the metabolism of NFP. However, the CYP3A-mediated pharmacokinetic interaction on the concomitant use of EK-114 may not be clinically significant.

Effects of propolis extract on sensitivity to chemotherapeutic agents in HeLa and resistant sublines.

The effects of a propolis extract obtained by supercritical fluid extraction on sensitivity to chemotherapeutic agents were examined in HeLa cells and resistant sublines thereof. In addition, the actions of propolis and caffeic acid phenethyl ester (CAPE), a constituent of propolis, on the multidrug efflux transporter P-glycoprotein/MDR1, were evaluated in paclitaxel-resistant HeLa/TXL cells (MDR1-overexpressing cells). In HeLa cells, the sensitivity to paclitaxel and doxorubicin, substrates of MDR1, was unchanged in the presence of propolis. In HeLa/TXL cells, propolis increased sensitivity to these MDR1 substrates. The accumulation of Rhodamine123, also a substrate for MDR1, by HeLa/TXL cells increased in the presence of 50 microg/mL, but not 10 microg/mL, of the extract. However, the growth inhibition of HeLa/TXL cells by paclitaxel was not changed by CAPE, although the accumulation of Rhodamine123 increased significantly in the presence of 100 microm, but not 1 nM or 1 microm, CAPE. Collectively, the extract was suggested to inhibit the function of MDR1 and to increase the sensitivity to MDR1 substrates in HeLa/TXL cells, effects likely to be caused by constituents other than CAPE.

Molecular changes to HeLa cells on continuous exposure to cisplatin or paclitaxel.

OBJECTIVE: To achieve a reversal of multidrug resistance (MDR) in cancer chemotherapy, it is crucial to clarify the characteristics of MDR cells generated by various types of chemotherapeutic agents and to find novel targets. METHODS: Cisplatin- and paclitaxel-resistant HeLa sublines (HeLa/CDDP and HeLa/TXL, respectively) were established by continuous exposure and their cellular changes were examined based on growth inhibition assays, the transport activity of P-glycoprotein/MDR1, and a RT-PCR analysis of MDR-related factors. RESULTS: HeLa/CDDP cells showed cross-resistance to platinum derivatives, whereas HeLa/TXL cells were resistant to a variety of MDR1 substrates. Transport activity of MDR1 was reduced in HeLa/CDDP cells and the expression of MDR1 was significantly accelerated in HeLa/TXL cells, compared with HeLa cells. In addition, the expression levels of MDR-related transporters (MRP1-5 or BCRP), betatubulin which is a target for taxanes, and apoptosis-regulated factors were comparable among the three cell lines. On the other hand, the mRNA levels of gamma-glutamyl transferase, but not gamma-glutamyl cysteine synthetase, were higher in HeLa/CDDP cells than in HeLa and HeLa/TXL cells. CONCLUSIONS: HeLa/CDDP cells showed decreased activity and expression of MDR1 and overexpression of gamma-GT but not gamma-GCS whereas the activity of MDR1 in HeLa/TXL cells was significantly enhanced. Thus, the molecular changes to HeLa cells caused by continuous exposure to cisplatin or paclitaxel were in part clarified, and therefore an understanding of the cellular changes induced by chemotherapeutic agents will be necessary to establish a strategy for reversing MDR.

Effects of 19 herbal extracts on the sensitivity to paclitaxel or 5-fluorouracil in HeLa cells.

The popularity of traditional herbal medicine (THM) being used as complementary medicines or alternative medicines is increasing. On the other hand, the development of multidrug resistance (MDR) remains a major hurdle to successful cancer chemotherapy. Some THMs capable of reversing MDR may contribute to the improvement of clinical outcomes in cancer chemotherapy. Herein, 19 kinds of herb were chosen from the ingredients of major THMs, and their effects on the sensitivity to anticancer drugs of tumor cells were investigated using the human cervical carcinoma HeLa cells. Focusing on the major mechanism for MDR, i.e., MDR1/P-glycoprotein, the effects of herbal extracts on its transport function were also examined using a MDR1 substrate Rhodamine123. Glycyrrhizae Radix, Rhei Rhizoma, Scutellariae Radix, Poria, Zizyphi Fructus, Zingiberis Rhizoma (dry), Coptidis Rhizoma, Ephedrae Herba and Asiasari Radix significantly enhanced the sensitivity to a MDR1 substrate paclitaxel, whereas none of the herbal extracts used had any effect on the sensitivity to 5-fluorouracil, which is not a substrate for MDR1. Rhodamine123 uptake was significantly increased by Rhei Rhizoma, Poria or Ephedrae Herba among nine herbal extracts sensitized to paclitaxel. This suggests that the increase in paclitaxel sensitivity by Glycyrrhizae Radix, Rhei Rhizoma, Poria or Ephedrae Herba was caused, in part, by the inhibition of MDR1 function, and the change in paclitaxel sensitivity by the other herbal extracts was not always dependent on this. Collectively, these findings indicate that the combination of anticancer drugs with some herbal extracts contributes to the enhancement of clinical outcomes in cancer chemotherapy.

Studies on interactions between functional foods or dietary supplements and medicines. IV. Effects of ginkgo biloba leaf extract on the pharmacokinetics and pharmacodynamics of nifedipine in healthy volunteers.

The effects of Ginkgo biloba leaf extract (GBE), a widely used herbal dietary supplement in Japan, on the pharmacokinetics and pharmacodynamics of nifedipine (NFP), a calcium-channel blocker, were studied using 8 healthy volunteers. Simultaneous oral ingestion of GBE (240 mg) did not significantly affect any of the mean pharmacokinetic parameters of either NFP or dehydronifedipine, a major metabolite of NFP, after oral administration of NFP (10 mg). However, the maximal plasma NFP concentrations in 2 subjects were approximately doubled by GBE, and they had severer and longer-lasting headaches with GBE than without GBE, with dizziness or hot flushes in combination with GBE. The mean heart rate after oral administration of NFP with GBE tended to be faster than that without GBE at every time point. Accordingly, it was concluded that GBE and NFP should not be simultaneously ingested as much as possible, and careful monitoring is needed when administering NFP concomitantly with GBE to humans.

Studies on interactions between functional foods or dietary supplements and medicines. III. Effects of ginkgo biloba leaf extract on the pharmacokinetics of nifedipine in rats.

The effects of Ginkgo biloba leaf extract (GBE), one of the most widely used herbal dietary supplements in Japan and the United States, on the pharmacokinetics of nifedipine (NFP), a typical probe of P450 (CYP) 3A, but not a substrate of the multidrug transporter P-glycoprotein (P-gp), were studied using rats. Simultaneous oral treatment with GBE (20 mg/kg) did not affect the pharmacokinetics after intravenous administration of NFP (2.5 mg/kg). However, the maximal plasma NFP concentration, the area under the concentration-time curve and absolute bioavailability after oral administration of NFP (5 mg/kg) were significantly increased by simultaneous oral treatment with GBE, approximately 1.6-fold, 1.6-fold and 2.1-fold, respectively. These results suggest that the concomitant oral use of GBE appeared to reduce the first-pass metabolism of orally administered NFP, by inhibiting CYP3A, possibly but not P-gp, in rats.

Interactions between medicines and functional foods or dietary supplements.

Recently, the demand for supplements has steadily been increasing with the diffusion of alternative and supplemental medicines throughout the world. Therefore, the supplements have frequently been taken with many drugs. Here, we have introduced the pharmacokinetic and pharmacological interactions between them.

Effect of rabeprazole on MDR1-mediated transport of Rhodamine 123 in Caco-2 and Hvr100-6 cells.

The aim of our study was to investigate the effects of rabeprazole, a proton pump inhibitor, on MDR1 expressed on human colon carcinoma cell line, Caco-2, and MDR1-overexpressing human cervical carcinoma cell line, HeLa cells selected by exposure to 100 nM vinblastine (Hvr100-6 cells). Inhibitory effects of rabeprazole on MDR1-mediated transport of Rhodamine123 were examined in these cells. A thousand micro molar rabeprazole increased Rhodamine 123 uptakes in Caco-2 and Hvr100-6 cells by 68% and 185%, respectively. No significant effects of rabeprazole were observed at the concentration of 1-100 microM. Since rabeprazole did not show any effects on Rhodamine 123 transport via MDR1 at the plasma levels (approximately 1 microM), it was considered that the drug interaction with MDR1 substrates would be minimal even though the interaction occurred in the patients with rabeprazole treatment.

Expression profiles of drug-metabolizing enzyme CYP3A and drug efflux transporter multidrug resistance 1 subfamily mRNAS in small intestine.

The purpose of this study is to examine the expression profiles of CYP3A1, CYP3A2, CYP3A9, and CYP3A18 mRNAs as well as multidrug resistance (mdr)1a and mdr1b mRNAs in the liver and small intestine of normal male Wistar rats using a reverse transcription-polymerase chain reaction (PCR). In the rat liver, the PCR products for CYP3A1, CYP3A2, and CYP3A18 were readily detectable, whereas CYP3A9 was slightly and mdr1a and mdr1b barely detected. Surprisingly, no PCR products for CYP3A1 and CYP3A2 were detected in the small intestine, but those for CYP3A9, CYP3A18, and mdr1a were readily detectable, and a faint band for mdr1b was also observed. Both CYP3A9 and CYP3A18 levels were found to be high in the duodenum and decreased from the top to bottom of the gut, indicating regional differences in both CYP3A9 and CYP3A18 expression in the small intestine. In contrast, mdr1a expression increased gradually from the upper to lower intestine. Consequently, it was suggested that drug metabolism in the small intestine of normal rats was mediated by CYP3A9 and CYP3A18 rather than CYP3A1 and CYP3A2. Also, regional differences of CYP3A9, CYP3A18, and mdr1a expression were found in the small intestine. The distributions of CYP3A9 and CYP3A18 were different from the distribution of mdr1a, suggesting the cooperative action of drug clearance pathways. This information is important to drug metabolism research based on ex vivo and in vivo studies using rats.

Studies on interactions between functional foods or dietary supplements and medicines. I. Effects of Ginkgo biloba leaf extract on the pharmacokinetics of diltiazem in rats.

The effects of Ginkgo biloba leaf extract (GBE), one of the most widely used herbal dietary supplements in Japan, on the pharmacokinetics of diltiazem (DTZ), a typical probe of cytochrome P450 (CYP) 3A, were examined in rats. The simultaneous addition of GBE to small intestine and liver microsomes inhibited the formation of N-demethyl DTZ (MA), an active metabolite of DTZ produced by CYP3A, in a concentration-dependent manner, with an IC(50) of about 50 and 182 microg/ml, respectively. This inhibition appeared to be caused, at least in part, by a mechanism-based inhibition. Both the rate of formation of MA and total amount of CYP in intestinal or hepatic microsomes after a single oral pretreatment with GBE (20 mg/kg) decreased transiently. The pretreatment significantly decreased the terminal elimination rate constant and increased the mean residence time, after intravenous administration of DTZ (3 mg/kg). Furthermore, it significantly increased the area under the concentration-time curve and absolute bioavailability after oral administration of DTZ (30 mg/kg). These results indicated that the concomitant use of GBE in rats increased the bioavailability of DTZ by inhibiting both intestinal and hepatic metabolism, at least in part, via a mechanism-based inhibition for CYP3A.

Effects of continuous exposure to digoxin on MDR1 function and expression in Caco-2 cells.

The Caco-2 cell line has been used widely for studying intestinal permeability and several transport functions, and express the multidrug resistance transporter MDR1/P-glycoprotein. Previously, the transient exposure to digoxin for 24 h was found to induce MDR1 mRNA in Caco-2 cells. Here, a digoxin-tolerant Caco-2 subline (Caco/DX) was newly established by the continuous exposure of Caco-2 cells to digoxin, and the effects of continuous exposure to digoxin on MDR1 were examined. The 50% growth inhibitory concentration (IC(50)) values for digoxin in Caco-2 and Caco/DX cells were 17.2 and 81.4 nM, respectively. The IC(50) values for paclitaxel, an MDR1 substrate, were 1.0 and 547 nM, respectively, whereas the cytotoxicity of 5-fluorouracil was comparable in both cells. The uptake and efflux of Rhodamine123, an MDR1 substrate, in Caco/DX cells were significantly less and greater, respectively, than those in Caco-2 cells, and these transports were affected by the addition of ciclosporin. The expression of MDR1 mRNA in Caco/DX cells was approximately 2- and 1.7-fold compared with Caco-2 cells and Caco-2 cells treated with 100 nM digoxin for 24 h, respectively. On the other hand, MRP1 mRNA in Caco/DX cells was unchanged. These observations confirmed that the continuous exposure to digoxin, as well as the transient exposure, induced MDR1 in Caco-2 cells.

Digoxin up-regulates multidrug resistance transporter (MDR1) mRNA and simultaneously down-regulates steroid xenobiotic receptor mRNA.

A steroid xenobiotic receptor (SXR) is involved in the induction of MDR1/P-glycoprotein. MDR1 up-regulation by digoxin was previously demonstrated in human colon adenocarcinoma Caco-2 cells, but the participation of SXR remains unclear. Herein, the participation of SXR in MDR1 up-regulation was examined using reverse transcription-polymerase chain reaction in Caco-2 cells, and digoxin-tolerant cells (Caco/DX) as well as human colon carcinoma LS180 cells, which expressed SXR. MDR1 mRNA expression in Caco-2 or LS180 cells was increased by exposure to 1 microM digoxin for 24h, in a concentration-dependent manner, but SXR mRNA decreased concentration-dependently and was undetectable or significantly lower at 1 microM digoxin, indicating antithetical changes in MDR1 and SXR mRNA expression. Moreover, the MDR1 mRNA level was higher in Caco/DX cells than Caco-2 cells, whereas the SXR mRNA level was lower in Caco/DX cells. Consequently, digoxin was demonstrated to up-regulate MDR1 mRNA and simultaneously down-regulate SXR mRNA expression.

Up-regulation of MDR1 function and expression by cisplatin in LLC-PK1 cells.

To examine whether cisplatin affects the multidrug transporter MDR1/P-glycoprotein in the kidneys, the effects of cisplatin on cell sensitivity to an anticancer drug, MDR1 function and expression were examined by assessing the growth inhibition by the MDR1 substrate paclitaxel, the uptake and efflux of the MDR1 substrate Rhodamine123 and the level of MDR1 mRNA, respectively. Porcine kidney epithelial LLC-PK1 cells were used, as they have a structure and function similar to those of renal proximal tubular cells and physiologically express low levels of MDR1. The growth inhibitory curve of LLC-PK1 cells by paclitaxel was shifted to a higher concentration range by pretreatment with 1 micro M cisplatin for 48 h. The uptake and efflux of Rhodamine123 were significantly reduced and enhanced, respectively, by pretreatment with 1 micro M cisplatin for 48 h. This enhanced efflux was suppressed by the representative MDR1 substrate/inhibitor ciclosporin. The expression of MDR1 mRNA was increased by the existence of cisplatin for 48 h. These observations taken together suggested that the transient exposure to cisplatin could cause the up-regulation of MDR1 in LLC-PK1 cells.

Studies on interactions between traditional herbal and western medicines. V. effects of Sho-saiko-to (Xiao-Cai-hu-Tang) on the pharmacokinetics of carbamazepine in rats.

The possibility of pharmacokinetic interactions between Sho-saiko-to extract powder (TJ-9), the most widely used traditional Chinese herbal (Kampo) medicine in Japan, and carbamazepine (CBZ), an important anti-epileptic drug, was examined in rats. There was no significant difference in the protein binding of CBZ in serum obtained before and after the single oral administration of TJ-9. The addition of TJ-9 to normal hepatic microsomes inhibited CBZ-10,11-epoxylase activity in a concentration-dependent manner. Liver weight, amounts of P450 and cytochrome b(5) in hepatic microsomes and the formation of carbamazepine-10,11-epoxide (CBZ-E), an active metabolite of CBZ, by microsomes were not influenced by 2-week repeated oral pretreatment with TJ-9 (1 g/kg/d), although pretreatments with phenobarbital (80 mg/kg/d, i.p.) significantly increased these parameters. The simultaneous oral administration of TJ-9 (1 g/kg) significantly decreased the peak plasma concentration of CBZ and the area under the concentration-time curve of CBZ-E, and lengthened the time to reach the peak concentration of CBZ after oral administration of CBZ. Two-week repeated oral pretreatment with TJ-9, however, did not affect the plasma concentration-time profile or any pharmacokinetic parameter of CBZ or CBZ-E. Also, a single oral administration of TJ-9 (1 g/kg) significantly delayed gastric emptying. These results indicated that the simultaneous oral administration of TJ-9 with CBZ to rats decreased the gastrointestinal absorption of CBZ, at least in part, by delaying gastric emptying, without affecting the metabolism of CBZ.

Monocarboxylate transporter mediates uptake of lovastatin acid in rat cultured mesangial cells.

To clarify the uptake mechanism(s) for statins, we examined whether monocarboxylate transporter (MCT) contributed to the uptake of lovastatin acid by rat cultured mesangial cells. Expression of mRNAs for MCT1, 2, and 4 was confirmed in mesangial cells. The uptake of lovastatin acid by mesangial cells increased with decreasing extracellular pH. There was clear overshooting in lovastatin acid uptake by the ATP-depleted cells in the presence, but not in the absence, of an inwardly directed H(+)-gradient. The representative MCT substrates/inhibitors inhibited the lovastatin acid uptake. In particular, the inhibition of lovastatin acid uptake by L-lactic acid at the concentration of 80 mM reached 70%, and L-lactic acid and valproic acid inhibited the uptake competitively. On preloading of mesangial cells with L-lactic acid or valproic acid, the lovastatin acid uptake was significantly stimulated. The inhibition constant of L-lactic acid for the lovastatin acid uptake was 32 mM, and this value is comparable to the Michaelis constant (>20 mM) of L-lactic acid for MCT4 described elsewhere. These results demonstrate that lovastatin acid was largely taken up by mesangial cells via MCT, and suggest that MCT4 might contribute to lovastatin acid uptake in the cells.