Secretory transport of p-aminohippuric acid across intestinal epithelial cells in Caco-2 cells and isolated intestinal tissue

The Possible Role of Nitric Oxide Pathway in Pentylenetetrazole Preconditioning Against Seizure in Mice

Preconditioning is defined as an induction of adaptive response in organs against lethal stimulation provoked by subsequent mild sublethal stress. Several chemical agents have been demonstrated to cause brain tolerance through preconditioning. The aim of the present study is to test the hypothesis that preconditioning with pentylenetetrazole (PTZ) may have protective effect against seizure induced by i.v. infusion of PTZ. Mice were preconditioned by low-dose administration of PTZ (25 mg/kg) for 5 consecutive days, and the threshold of seizure elicited by i.v. infusion of PTZ was measured. To investigate the possible role of nitric oxide, NOS inhibitor enzymes, including L-NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) (10 mg/kg), aminoguanidine (AG) (50 mg/kg), 7-nitroindazole (7-NI) (15 mg/kg), and L-arginine (L-arg) (60 mg/kg), were administered concomitantly with PTZ in both acute and chronic phases. Determination of seizure threshold revealed significant enhancement after preconditioning with low dose of PTZ. While the protective effect of PTZ preconditioning was enhanced after the administration of L-arg, it was reversed following administration of L-NAME and 7NI, suggesting the involvement of nitric oxide pathway as an underlying mechanism of PTZ-induced preconditioning. Preconditioning with PTZ led to brain tolerance and adaptive response in animal model of PTZ-induced seizure. This effect is in part due to the involvement of nitric oxide pathway.

Development of a Dynamic Physiologically Based Mechanistic Kidney Model to Predict Renal Clearance

Renal clearance is usually predicted via empirical approaches including quantitative structure activity relationship and allometric scaling. Recently, mechanistic prediction approaches using in silico kidney models have been proposed. However, empirical scaling factors are typically used to adjust for either passive diffusion or active secretion, to acceptably predict renal clearances. The goal of this study was to establish a renal clearance simulation tool that allows prediction of renal clearance (filtration and pH-dependent passive reabsorption) from in vitro permeability data. A 35-compartment physiologically based mechanistic kidney model was developed based on human physiology. The model was verified using 46 test compounds, including neutrals, acids, bases, and zwitterions. The feasibility of incorporating active secretion and pH-dependent bidirectional passive diffusion into the model was demonstrated using para-aminohippuric acid (PAH), cimetidine, memantine, and salicylic acid. The developed model enables simulation of renal clearance from in vitro permeability data, with predicted renal clearance within twofold of observed for 87% of the test drugs.

Effects of 2-Deoxyglucose on ischemic brain injuries in rats

OBJECTIVES

In vivo and in vitro studies have shown that 2-deoxyglucose (2-DG) administration enhances tolerance and exerts neuroprotection against ischemic injury or oxidative stress. In this study, we investigated the effects of 2-DG on ischemic brain injuries in rats and determined whether the effects are related to sublethal endoplasmic reticulum (ER) stress.

METHODS

2-DG was administered systemically 7 d before the rats were subjected to focal cerebral ischemia (2 h) followed by reperfusion. Neurological score and infarct volume were evaluated, and protein expression of ER molecular chaperone glucose-regulated protein 78 (GRP78) and X-box protein-1 (XBP-1) was determined at different time points after reperfusion.

RESULTS

2-DG pretreatment significantly decreased neurological scores after reperfusion for 3 h, 6 h, 12 h, and 24 h, reduced infarct volume at 24 h after reperfusion compared to the corresponding control groups. ER molecular chaperone GRP78 and XBP-1 increased in 2-DG pretreatment group as compared to the control.

CONCLUSION

Pretreatment with 2-DG improves the neurological function after cerebral ischemia-reperfusion injury. Increased expression of ER chaperone GRP78 and activation of XBP-1 may contribute to the protective effect of 2-DG against brain injury.

Proteomic analysis of the mice hippocampus after preconditioning induced by N-methyl-D-aspartate (NMDA)

Preconditioning induced by N-methyl-D-aspartate (NMDA) has been used as a therapeutic tool against later neuronal insults. NMDA preconditioning affords neuroprotection against convulsions and cellular damage induced by the NMDA receptor agonist, quinolinic acid (QA) with time-window dependence. This study aimed to evaluate the molecular alterations promoted by NMDA and to compare these alterations in different periods of time that are related to the presence or lack of neuroprotection. Putative mechanisms related to NMDA preconditioning were evaluated via a proteomic analysis by using a time-window study. After a subconvulsant and protective dose of NMDA administration mice, hippocampi were removed (1, 24 or 72 h) and total protein analyzed by 2DE gels and identified by MALDI-TOF. Differential protein expression among the time induction of NMDA preconditioning was observed. In the hippocampus of protected mice (24 h), four proteins: HSP70(B), aspartyl-tRNA synthetase, phosphatidylethanolamine binding protein and creatine kinase were found to be up-regulated. Two other proteins, HSP70(A) and V-type proton ATPase were found down-regulated. Proteomic analysis showed that the neuroprotection induced by NMDA preconditioning altered signaling pathways, cell energy maintenance and protein synthesis and processing. These events may occur in a sense to attenuate the excitotoxicity process during the activation of neuroprotection promoted by NMDA preconditioning.

Contribution of multidrug resistance-associated protein 2 to secretory intestinal transport of organic anions

Various mechanisms can influence the intestinal absorption and oral bioavailability of drugs. The barrier effects of efflux transporters may be one of the critical factors limiting the bioavailability of certain drugs. It has been reported that multidrug resistance-associated protein 2 (Mrp2) is expressed in the mucosal membrane of the epithelium of the small intestine and secretes various drugs into the jejunum lumen. However, it is possible that total intestinal secretion of Mrp2 substrates is accounted for the contribution of Mrp2 and other transporter(s) to the intestinal secretion of Mrp2 substrates. In this study, we found that phenolsulfonphthalein and pravastatin, both Mrp2 substrates, are transported by different transport systems in the intestine. These results suggest that contribution of transporters to the drug transport may be a critical factor affecting drug disposition and drug-drug interaction. In addition to evaluating the substrate specificity of a transporter, it is important to be aware of the contribution of a transporter to drug disposition.

NO-induced neuroprotection in ischemic preconditioning stimulates mitochondrial Mn-SOD activity and expression via RAS/ERK1/2 pathway

To identify the transductional mechanisms responsible for the neuroprotective effect of nitric oxide (NO) during ischemic preconditioning (IPC), we investigated the effects of this gaseous mediator on mitochondrial Mn-superoxide dismutase (Mn-SOD) expression and activity. In addition, the possible involvement of Ras/extracellular-regulated kinase (ERK) ERK1/2 pathway in preserving cortical neurons exposed to oxygen and glucose deprivation (OGD) followed by reoxygenation was also examined. Ischemic preconditioning was obtained by exposing neurons to a 30-min sublethal OGD (95% N(2) and 5% CO(2)). Then, after a 24-h interval, neurons were exposed to 3 h of OGD followed by 24 h of reoxygenation (OGD/Rx). Our results revealed that IPC reduced cytochrome c (cyt c) release into the cytosol, improved mitochondrial function, and decreased free radical production. Moreover, it induced an increase in nNOS expression and NO production and promoted ERK1/2 activation. These effects were paralleled by an increase in Mn-SOD expression and activity that persisted throughout the following OGD phase. When the neurons were treated with L-NAME, a well known NOS inhibitor, the increase in Mn-SOD expression occurring during IPC was reduced and, as a result, IPC-induced neuroprotection was prevented. Similarly, when ERK1/2 was inhibited by its selective inhibitor PD98059, the increase in Mn-SOD expression observed during IPC was almost completely abolished. As a result, its neuroprotective effect on cellular survival was thwarted. The present findings indicate that during IPC the increase in Mn-SOD expression and activity are paralleled by NO production. This suggests that NO neuroprotective role occurs through the stimulation of Mn-SOD expression and activity. In particular, NO via Ras activation stimulates downstream ERK1/2 cascade. This pathway, in turn, post-transcriptionally activates Mn-SOD expression and activity, thus promoting neuroprotection during preconditioning.

[Novel formulations of a liver protection drug glycyrrhizin]

In Japan, glycyrrhizin injections have been used as a therapeutic drug for allergy inflammation since 1948 and for chronic hepatitis since 1979. A 20 ml injection of glycyrrhizin contains 53 mg of monoammonium glycyrrhizinate (40 mg as glycyrrhizin acid), 400 mg of glycine, and 20 mg of L-cysteine. Patients receiving glycyrrhizin injections two or three times per week are forced to accept a decline in quality of life. Because administering glycyrrhizin by injection has some disadvantages, many researchers have systematically searched for novel glycyrrhizin formulations that can be administered through oral, rectal, intranasal, and subcutaneous routes. There are two problems, however, in developing new formulations: (1) glycyrrhizin has low membrane permeability and is thus poorly absorbed, and (2) highly concentrated glycyrrhizin readily forms gels in aqueous solutions. Here, we describe the utility of glycyrrhizin formulations prepared in safe solubility agents and absorption-enhancing agents, as assessed in animal experiments. We also discuss pharmaceutical issues in developing various glycyrrhizin formulations. In the near future, convenient pharmaceutical preparations of glycyrrhizin will be developed for chronic hepatitis patients who require glycyrrhizin therapy.

[Pharmacokinetic study of cancer chemotherapy]

We reported that the rate of conversion of lactone to carboxylate forms of irinotecan (CPT-11) and its metabolites plays a major role in the biliary excretion of these compounds. Sulfobromophthalein partially inhibited the secretion of SN-38-glucronide into the gastrointestinal lumen, whereas little change was seen in that of active metabolite SN-38. Co-administration of sulphobromophthalein with CPT-11 might lower the late-onset gastrointestinal toxicity observed during treatment with CPT-11 without lowering anticancer activity. In the ileum, the level of transport in the direction form the serosal layer to mucosal layer was significantly greater than that in the direction form the mucosal layer to serosal layer, whereas a significant difference was not observed in the jejunum. This secretory transport required metabolic energy was diminished by sulfobromophthalein. A specific transport system plays a major role in the secretion of SN-38 and that this secretory transport system predominantly exists in the ileum. Uptake of SN-38 was significantly reduced at 4 degrees C. Baicalin inhibited the uptake of SN-38. A specific transport system mediates the uptake of SN-38 across the apical membrane in Caco-2 cells. Inhibition of this transporter would be a useful means for reducing late-onset diarrhea.

Ischemic preconditioning ameliorates excitotoxicity by shifting glutamate/gamma-aminobutyric acid release and biosynthesis

Excitotoxicity is recognized to play a major role in cerebral ischemia-induced cell death. The main goal of the present study was to define whether our model of ischemic preconditioning (IPC) promotes a shift from excitatory to inhibitory neurotransmission during the test ischemia to diminish metabolic demand during the reperfusion phase. We also determined whether gamma-aminobutyric acid (GABA) played a role in IPC-induced neuroprotection. Ten minutes of cerebral ischemia was produced by tightening the carotid ligatures bilaterally following hypotension. Samples of microdialysis perfusate, representing extracellular fluid, were analyzed for amino acid content by HPLC. IPC promoted a robust release of GABA after lethal ischemia compared with control rats. We also observed that the activity of glutamate decarboxylase (the predominant pathway of GABA synthesis in the brain) was higher in the IPC group compared with control and ischemic groups. Because GABAA receptor up-regulation has been shown to occur following IPC, and GABAA receptor activation has been implicated in neuroprotection against ischemic insults, we tested the hypothesis that GABAA or GABAB receptor activation was neuroprotective during ischemia or early reperfusion by using an in vitro model (organotypic hippocampal slice culture). Administration of the GABAB agonist baclofen during test ischemia and for 1 hr of reperfusion provided significant neuroprotection. We concluded that increased GABA release in preconditioned animals after ischemia might be one of the factors responsible for IPC neuroprotection. Specific activation of GABAB receptor contributes significantly to neuroprotection against ischemia in organotypic hippocampal slices.

Characterization of secretory intestinal transport of phenolsulfonphthalein

It is known that secretory transport limits the oral bioavailability of certain drugs. However, there is little information on the secretion of anionic compounds in the intestine. Phenolsulfonphthalein (PSP) and p-aminohippuric acid (PAH) have been used widely as substrates for organic anion transport systems. PAH is transported in the secretory direction in the intestine. It is possible that PSP and PAH share the same transport system at the mucosal membrane. The purpose of this study was to characterize the transport system for PSP in the intestine. In the jejunum, the serosal-to-mucosal permeation rate of PSP was significantly reduced in an ATP-depleted condition, whereas a significant difference was not observed in the ileum. Some multidrug resistance-associated protein 2 (Mrp2) inhibitors inhibited PSP permeation in the jejunum. However, pravastatin, a substrate of Mrp2, did not inhibit the PSP permeation. The jejunal secretory transport of pravastatin was significantly reduced in an ATP-depleted condition and by addition of probenecid, but PSP did not affect the jejunal permeation of pravastatin. These results suggest that PSP is secreted into the intestinal lumen by Mrp2-like transporter and that two Mrp2 substrates, PSP and pravastatin, are likely to be transported by different transport systems at the mucosal membrane.

Secretory transport of irinotecan metabolite SN-38 across isolated intestinal tissue

PURPOSE

The purpose of this study was to investigate the transport mechanisms of transporters that contribute to the intestinal efflux of 7-ethyl-10-hydroxycamptothecin (SN-38).

METHODS

The intestinal transport of SN-38 was studied in rat intestinal tissue mounted in Ussing chambers.

RESULTS

In the ileum, the level of transport from the serosal layer to the mucosal layer was significantly greater than that from the mucosal layer to the serosal layer, whereas a significant difference was not observed in the jejunum. This secretory transport required metabolic energy and was diminished by sulfobromophthalein. However, mitoxantrone, an inhibitor of breast cancer resistance protein (BCRP), did not affect the ileal secretion of SN-38.

CONCLUSIONS

The results suggest that a specific transport system, which is distinct from BCRP, plays a major role in the secretion of SN-38 and that this secretory transport system predominantly exists in the ileum.

NMDA preconditioning protects against seizures and hippocampal neurotoxicity induced by quinolinic acid in mice

PURPOSE

N-methyl D-aspartate (NMDA) preconditioning has been used to prevent cellular death induced by glutamate or NMDA in cultured neurons. Quinolinic acid (QA)-induced seizures are used to average NMDA receptors-evoked neurotoxicity in animal models. The purpose of this study was to investigate the potential neuroprotective effects of NMDA preconditioning against QA-induced seizures and hippocampal damage in vivo.

METHODS

Mice were pretreated with nonconvulsant doses of NMDA for different times before i.c.v. QA infusion and observed for the occurrence of seizures. Hippocampal slices from mice were assayed to measure cellular viability.

RESULTS

NMDA preconditioning presented 53% protection against QA-induced seizures, as well as QA-induced cellular death in the hippocampus. The NMDA receptor antagonist, MK-801, prevented the protection evoked by NMDA preconditioning. The adenosine A1 receptor antagonist, CPT, prevented the protection evoked by NMDA preconditioning against QA-induced seizures, but not against QA-induced hippocampal cellular damage. The adenosine A1 receptor agonist, CPA, did not mimic the NMDA preconditioning-evoked protective effects.

CONCLUSIONS

These results suggest that in vivo preconditioning with subtoxic doses of NMDA protected mice against seizures and cellular hippocampal death elicited by QA, probably through mechanisms involving NMDA receptors operating with adenosine A1 receptors.

Putative endogenous mediators of preconditioning-induced ischemic tolerance in rat brain identified by genomic and proteomic analysis

In brain, a brief ischemic episode induces protection against a subsequent severe ischemic insult. This phenomenon is known as preconditioning-induced neural ischemic tolerance. An understanding of the molecular mechanisms leading to preconditioning helps in identifying potential therapeutic targets for preventing the post-stroke brain damage. The present study conducted the genomic and proteomic analysis of adult rat brain as a function of time following preconditioning induced by a 10-min transient middle cerebral artery (MCA) occlusion. GeneChip analysis showed induction of 40 putative neuroprotective transcripts between 3 to 72 h after preconditioning. These included heat-shock proteins, heme oxygenases, metallothioneins, signal transduction mediators, transcription factors, ion channels and apoptosis/plasticity-related transcripts. Real-time PCR confirmed the GeneChip data for the transcripts up-regulated after preconditioning. Two-dimensional gel electrophoresis combined with MALDI-TOF analysis showed increased expression of HSP70, HSP27, HSP90, guanylyl cyclase, muskelin, platelet activating factor receptor and beta-actin at 24 h after preconditioning. HSP70 protein induction after preconditioning was localized in the cortical pyramidal neurons. The infarct volume induced by focal ischemia (1-h MCA occlusion) was significantly smaller (by 38 +/- 7%, p < 0.05) in rats subjected to preconditioning 3 days before the insult. Preconditioning also prevented several gene expression changes induced by focal ischemia.

Technique for expanding the donor liver pool: heat shock preconditioning in a rat fatty liver model

Fatty liver is a common predisposing risk factor for postoperative liver failure and accounts for most discarded livers during triage of donors. We investigated the effect of heat shock preconditioning (HPc) on recipient survival in a rat fatty liver transplantation model. Fatty liver donor rats were exposed to brief whole-body hyperthermia (10 minutes at 42.5 degrees C) and allowed to recover. HPc induced heat shock proteins (HSPs) (HSP72, HSP90, and heme oxygenase [HO]-1) in donor livers, with levels peaking 12 to 48 hours after HPc. Subsequently, donor livers were harvested 24 hours after HPc, placed in cold storage for 10 hours, and transplanted into normal rats. At 3 hours posttransplantation, HPc reduced serum liver enzymes in the recipients and almost completely suppressed the release of tumor necrosis factor (TNF)-alpha and interleukin (IL)-10. Histologic evaluation 3 and 24 hours after transplantation showed that HPc significantly reduced hepatic inflammation and hepatocellular necrosis without affecting the steatotic appearance of hepatocytes. One week after transplantation, control non-heat-shocked and heat-shocked fatty liver recipients exhibited survival rates of less than 10% and more than 80%, respectively. The evaluation of the survival of recipients receiving fatty livers at different times after HPc showed that the protective effect of HPc was significant when donor livers were transplanted 3 to 48 hours after HPc, with the maximum effect seen 6 to 48 hours after HPc. In conclusion, HPc is a promising avenue to salvage rejected donor fatty livers and enhance the survival rate of fatty liver recipients. We estimate that this technique could increase the annual donor pool by 600 livers.

Choline uptake in human intestinal Caco-2 cells is carrier-mediated

The objective of the current investigation was to examine the transport characteristics of choline, an endogenous quaternary ammonium compound, into human intestinal Caco-2 cells; the transport of choline has not been characterized in human intestine. The cellular accumulation of choline was independent of an inwardly directed Na(+) gradient and demonstrated temperature dependence and saturability. Using the initial uptake rates, choline accumulation was best characterized by a Michaelis-Menten equation and a diffusion component with a K(m) and V(max) of 110 +/- 3 micro mol/L and 2800 +/- 250 pmol/(mg protein. 10 min), respectively. Choline uptake was significantly inhibited by an excess of choline itself and by hemicholinium-3, a structural analog of choline. However other hydrophilic organic cations, such as tetraethylammonium (TEA) and N-methylnicotinamide (NMN), did not affect choline uptake in Caco-2 cells. Additionally, two typical p-glycoprotein substrates, daunomycin and verapamil, both inhibited choline accumulation. However the opposite was not true: choline did not inhibit DNM accumulation in Caco-2 cells. These results indicate the presence of a carrier-mediated transport system for choline in Caco-2 cells. The substrate specificity of this carrier is unlike that seen in the rat intestinal epithelium, and the human transport protein is distinct from those for TEA and NMN. P-glycoprotein substrates may inhibit choline uptake through specific or nonspecific interactions with the choline transporter.

Arbekacin is actively secreted in the rat intestine via a different efflux system from P-glycoprotein

This study was undertaken to examine the secretory transport of arbekacin, an aminoglycoside antibiotic, in the rat small intestine and to compare it with those in Caco-2 and LLC-PK1 cells. In vitro permeation of arbekacin was examined using an Ussing chamber technique. Serosal-to-mucosal (secretory)/mucosal-to-serosal (absorptive) permeation ratios of 0.5 mM arbekacin were 2.8 in the jejunum and 7.0 in the ileum, respectively, indicating that arbekacin permeation was highly secretory-oriented. In the ileum, the ratios became smaller with increase in arbekacin concentration applied. When D-glucose was replaced with 3-o-methyl-D-glucose in the experimental medium, the directionality of the arbekacin permeation disappeared almost completely. Absorptive permeation of arbekacin was not significantly influenced by verapamil, cyclosporin A, or probenecid. On the other hand, when gentamicin sulfate was added to the serosal medium, secretory transport of arbekacin was significantly inhibited. The results of this study strongly suggest that a specialized efflux system other than P-glycoprotein and multidrug resistance proteins was involved in the secretory transport of arbekacin in the rat intestine. There was no directionality in arbekacin permeation across Caco-2 cell monolayers, suggesting the absence or very slight expression of the secretory system for arbekacin in this cell line.

[Biopharmaceutical studies on molecular mechanisms of membrane transport]

By incorporating the transporter-mediated or receptor-mediated transport process in physiologically based pharmacokinetic models, we succeeded in the quantitative prediction of plasma and tissue concentrations of beta-lactam antibiotics, insulin, pentazocine, quinolone antibacterial agents, and inaperizone and digoxin. The author's research on transporter-mediated pharmacokinetics focuses on the molecular and functional characteristics of drug transporters such as oligopeptide transporter, monocarboxylic acid transporter, anion antiporter, organic anion transporters, organic cation/carnitine transporters (OCTNs), and the ATP-binding cassette transporters P-glycoprotein and MRP2. We have successfully demonstrated that these transporters play important roles in the influxes and/or effluxes of drugs in intestinal and renal epithelial cells, hepatocytes, and brain capillary endothelial cells that form the blood-brain barrier. In the systemic carnitine deficiency (SCD) phenotype mouse model, juvenile visceral steatosis (jvs) mouse, a mutation in the OCTN2 gene was found. Furthermore, several types of mutation in human SCD patients were found, demonstrating that OCTN2 is a physiologically important carnitine transporter. Interestingly, OCTNs transport carnitine in a sodium-dependent manner and various cationic drugs transport it in a sodium-independent manner. OCTNs are thought to be multifunctional transporters for the uptake of carnitine into tissue cells and for the elimination of intracellular organic cationic drugs.

Involvement of multidrug resistance-associated protein 2 in intestinal secretion of grepafloxacin in rats

We investigated the contribution of multidrug resistance-associated protein 2 (MRP2) to the secretory transport of grepafloxacin and compared its functional role with that of P-glycoprotein (P-gp) by using Sprague-Dawley rats (SDRs) and Eisai hyperbilirubinemic rats (EHBRs), in which MRP2 is hereditarily defective. In intestinal tissue from SDRs mounted in Ussing chambers, the level of transport in the direction from the serosal layer to the mucosal layer was twofold greater than that in the direction from the mucosal layer to the serosal layer. This secretory transport of grepafloxacin was diminished by both probenecid, an MRP2 inhibitor, and cyclosporine, a P-gp inhibitor. In intestinal tissue from EHBRs, the secretory transport of grepafloxacin was lower than that in intestinal tissue from SDRs and was inhibited by cyclosporine but not by probenecid. The absorption of grepafloxacin from intestinal loops in SDRs was in the order of duodenum > jejunum > ileum and was increased by cyclosporine but not by probenecid. The absorption in EHBRs was not higher than that in SDRs. The intestinal secretory clearance in SDRs after intravenous administration of grepafloxacin was shown to be greater for the ileum than for the duodenum, which is in good agreement with the previously reported regional expression profile of MRP2 mRNA. The intestinal secretory clearance was lower in EHBRs than in SDRs. Accordingly, in addition to P-gp, MRP2 might play a role in the secretory transport of grepafloxacin. The function of MRP2 in facilitating grepafloxacin transport in the secretory direction is more pronounced both in vitro and in vivo, while the restriction of entry from the lumen into the cell by MRP2 seems to be negligible, compared with that by P-gp, in the case of grepafloxacin.

Active intestinal secretion of new quinolone antimicrobials and the partial contribution of P-glycoprotein

Transport of quinolone antimicrobials and the contribution of the secretory transporter P-glycoprotein were studied in-vivo and in-vitro. In rat intestinal tissue (Ussing chambers method) and human Caco-2 cells (Transwell method), grepafloxacin showed secretory-directed transport. In both experimental systems, the secretory-directed transport was decreased by ciclosporin A, an inhibitor of P-glycoprotein, and probenecid, an inhibitor of anion transport systems. This suggested the contribution of P-glycoprotein and anion-sensitive transporter(s). The involvement of P-glycoprotein was investigated by using a P-glycoprotein over-expressing cell line, LLC-GA5-COL150, and P-glycoprotein-gene-deficient mice (mdr1a(-/-)/1b(-/-) mice). LLC-GA5-COL150 cells showed secretory-directed transport of grepafloxacin, while the parent cell line, LLC-PK1, did not. The secretory-directed transport of sparfloxacin and levofloxacin was also detected in LLC-GA5-COL150 cells. In the mdr1a(-/-)/1b(-/-) mice, the intestinal secretory clearance was smaller than that in wild-type mice after intravenous administration of grepafloxacin. Moreover, the absorption from an intestinal loop in mdr1a(-/-)/1b(-/-) mice was larger than that in wild-type mice. Accordingly, it appears that some quinolones are transported by secretory transporters, including P-glycoprotein. The involved transporters function in-vivo not only to transport grepafloxacin from blood to intestine but also to limit its intestinal absorption.