Biomedical subjects

Akira Tsuji

Publications and source records attributed to Akira Tsuji.

At least 37 records · Page 2Linked to original sources

PubMed2005

OCTN2-mediated transport of carnitine in isolated Sertoli cells.

Carnitine is extensively accumulated in epididymis. Carnitine is also accumulated in testis at higher concentration than in the plasma and is used in spite of the presence of the blood-testis barrier. In this study, we examined the characteristics of carnitine transport in primary-cultured rat Sertoli cells, which constitute a part of the blood-testis barrier. Uptake of [3H]carnitine (11.4 nM) from the basal side of Sertoli cells was Na+-dependent and was significantly decreased in the presence of 10 microM (48.0 +/- 7.4% of control) or 100 microM unlabeled carnitine (14.6 +/- 5.7% of control). Furthermore, the uptake was significantly inhibited in the presence of 100 microM acetyl-L-carnitine, 100 microM gamma-butyrobetaine or 500 microM quinidine. In RT-PCR analysis, the high-affinity carnitine transporter OCTN2 was detected in rat whole testis tissue and primary-cultured Sertoli cells. In contrast, the low-affinity carnitine transporter ATB(0,+) was detected in rat whole testis tissue, but not in primary cultured Sertoli cells. These results demonstrate that OCTN2 mediates carnitine supply to Sertoli cells from the circulation.

Animals↗

PubMed2005

Carnitine/organic cation transporter OCTN2-mediated transport of carnitine in primary-cultured epididymal epithelial cells.

Carnitine is essential for the acquisition of motility and maturation of spermatozoa in the epididymis, and is accumulated in epididymal fluid. In this study, carnitine transport into primary-cultured rat epididymal epithelial cells was characterized to clarify the nature of the transporter molecules involved. Uptake of carnitine by primary-cultured epididymal epithelial cells was time, Na(+) and concentration dependent. Kinetic analysis of carnitine uptake by the cells revealed the involvement of high- and low-affinity transport systems with Km values of 21 microM and 2.2 mM respectively. The uptake of carnitine by the cells was significantly reduced by inhibitors of carnitine/organic cation transporter (OCTN2), such as carnitine analogues and cationic compounds. In RT-PCR analysis, OCTN2 expression was detected. These results demonstrated that the high-affinity carnitine transporter OCTN2, which is localized at the basolateral membrane of epididymal epithelial cells, mediates carnitine supply into those cells from the systemic circulation as the first step of permeation from blood to spermatozoa.

Acetylcarnitine↗

PubMed2005

Small molecular drug transfer across the blood-brain barrier via carrier-mediated transport systems.

Because of the physiological nature of the blood-brain barrier (BBB), transport of chemical compounds between blood and brain has been widely believed to occur by means of passive diffusion, depending upon the lipophilicity of the compounds. However, discrepancies exist between the lipophilicity and apparent BBB permeation properties in many cases, and these discrepancies can be ascribed to the existence of multiple mechanisms of drug transport through the BBB. Molecular identification and functional analysis of influx transport proteins (from blood to brain) and efflux transport proteins (from brain to blood) have progressed rapidly. Therefore, the BBB is now considered to be a dynamic interface that controls the influx and efflux of a wide variety of substances, including endogenous nutrients and exogenous compounds such as drugs, to maintain a favorable environment for the CNS. This review focuses on the role of transport systems in the uptake of xenobiotics, including organic anionic/cationic and neutral drugs, across the BBB into the brain, as well as on strategies to increase drug delivery into the brain by blocking efflux transport protein function, or to reduce CNS side effects by modulating BBB transport processes.

Animals↗

PubMed2005

Na+/H+ exchanger 3 affects transport property of H+/oligopeptide transporter 1.

Oligopeptide transporter PEPT1 is thought to be involved in the intestinal absorption and renal reabsorption of peptides and therapeutic agents. The driving force of PEPT1 is H+ gradient, a part of which is supplied by Na+/H+ exchanger (NHE) expressed on the apical surface of the epithelium although molecular identification of NHE has not yet been fully clarified. Here we examined the effect of NHE3 coexpression on the function of PEPT1 to support the hypothesis that NHE3 regulates PEPT1 function by supplying its driving force. HEK293 cells expressing PEPT1 alone exhibited Na+-independent but pH-dependent uptake of glycylsarcosine (GlySar), whereas those coexpress PEPT1 and NHE3 showed an increase in GlySar uptake and conferred Na+-dependence on the uptake of GlySar. The increase in GlySar transport by PEPT1 depended on the expression level of NHE3 and was found at various levels of PEPT1 expression. Kinetic analysis of GlySar uptake in HEK293 cells expressing both PEPT1 and NHE3 or those expressing PEPT1 alone revealed an approximately 3 times increase in the transport capacity in the presence of NHE3, as normalized by PEPT1 mRNA expression. Confocal microscopy indicated that both PEPT1 and NHE3 are colocalized on the cell-surface of HEK293 cells. Thus, the present findings are the first to specify that NHE3 exerts post-transcriptional stimulation of PEPT1-mediated transport and can affect cellular uptake of the substrates by PEPT1 expressed on apical membranes in the body.

Antibodies, Monoclonal↗

PubMed2004

Role of organic anion transporter OATP1B1 (OATP-C) in hepatic uptake of irinotecan and its active metabolite, 7-ethyl-10-hydroxycamptothecin: in vitro evidence and effect of single nucleotide polymorphisms.

Irinotecan hydrochloride (CPT-11) is a potent anticancer drug that is converted to its active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), and other metabolites in liver. The disposition and gastrointestinal toxicity of irinotecan exhibit a wide interpatient variability. Here, we examined the contribution of an organic anion-transporting polypeptide, OATP1B1 (OATP-C), which transports a variety of drugs and their metabolites from blood to liver in humans, to the hepatic disposition of irinotecan, SN-38, and its glucuronide conjugate (SN-38G) by using HEK293 cells stably transfected with SLCO1B1*1a (OATP-C*1a) coding wild-type OATP1B1. We further examined the effect of single nucleotide polymorphisms in OATP1B1 by measuring uptake activity in Xenopus oocytes expressing OATP1B1*1a and three common variants. In all cases, transport activity for SN-38 was observed, whereas irinotecan and SN-38G were not transported. Moreover, SN-38 exhibited a significant inhibitory effect on OATP1B1-mediated uptake of [(3)H]estrone-3-sulfate. Among the variants examined, OATP1B1*15 (N130D and V174A; reported allele frequency 10-15%) exhibited decreased transport activities for SN-38 as well as pravastatin, estrone-3-sulfate, and estradiol-17beta-glucuronide. This study is the first to yield evidence that OATP1B1 is involved in the hepatic disposition of SN-38 and that genetic polymorphisms of OATP1B1 may contribute to the known interpatient variability in disposition of irinotecan.

Animals↗

PubMed2004

PDZK1 directly regulates the function of organic cation/carnitine transporter OCTN2.

Urinary excretion of cationic xenobiotics is believed to be mediated by organic cation transporter (OCT and OCTN) families expressed on both basolateral and brush-border membranes of renal tubules, although the molecular mechanisms for targeting of these transporters to each membrane are poorly understood. Here, to examine the regulatory mechanisms for cell-surface expression and function of these transporters, we evaluated the interaction of these transporters with several PDZ proteins. A pull-down study using recombinant C-terminal proteins of OCTs and OCTNs identified a specific interaction of apical transporters OCTN1 and OCTN2, but not basolateral transporters OCT1 and OCT2, with PDZK1, intestinal and kidney-enriched PDZ protein, and Na+/H+ exchanger regulatory factor 2 (also called E3KARP, SIP-1, or TKA-1). Both yeast two-hybrid and pull-down studies suggested a requirement of the last four amino acids in OCTN1 and OCTN2 for the interaction. The interaction of PDZK1 with the C terminus of OCTN2 was also confirmed in a pull-down study using kidney brush-border membrane vesicles. Immunohistochemical analysis revealed that both PDZK1 and OCTN2 are colocalized in brush-border membranes of the kidney. Finally, double transfection of OCTN2 with PDZK1 stimulated the uptake by OCTN2 of its endogenous substrate carnitine, and this increase could be accounted for by the 6-fold increase in transport capacity. Such an increase was not observed for OCTN2 with deletion of the last four amino acids. Biotinylation study of surface proteins revealed minimal effect of PDZK1 on cell-surface expression of OCTN2. The present findings are the first to identify PDZK1 as a functional regulator of OCTN2 through direct interaction with the C terminus.

Amino Acid Sequence↗

PubMed2004

Possible involvement of P-glycoprotein in renal excretion of pazufloxacin in rats.

The present study aims to investigate whether pazufloxacin, a new quinolone antimicrobial agent, is a substrate for P-glycoprotein in vitro, and whether it is excreted from kidney by P-glycoprotein and/or multidrug resistance-associated protein (Mrp2) in vivo. The in vitro experiments showed that the intracellular accumulation of pazufloxacin in adriamycin-resistant human chronic myelogenous leukemia cells (K562/ADR) overexpressing P-glycoprotein was significantly lower than that in human chronic myelogenous leukemia cells (K562/S) not expressing P-glycoprotein. When rats received an intravenous injection of pazufloxacin in combination with or without cyclosporine, cyclosporine significantly delayed the disappearance of pazufloxacin from plasma and decreased the systemic clearance and volume of distribution at steady state of pazufloxacin to 50% and 70% of the corresponding control values, respectively. Renal handling experiments revealed that the renal clearance of pazufloxacin was 75% of that corresponding to the systemic clearance, suggesting that the main route of pazufloxacin elimination is the kidney. Cyclosporine significantly increased the steady-state concentration of pazufloxacin in plasma by decreasing the tubular secretion clearance and glomerular filtration rate. These results suggest the possibility that pazufloxacin is excreted into the urine via P-glycoprotein. No significant differences in the renal and tubular secretion clearances of pazufloxacin were observed between normal rats and Eisai hyperbilirubinemic rats (EHBR), which have a hereditary deficiency in Mrp2, indicating the lack of the involvement of Mrp2 in the renal excretion of pazufloxacin. Sparfloxacin, a P-glycoprotein substrate, also significantly decreased the renal and tubular secretion clearances of pazufloxacin, suggesting that pazufloxacin and sparfloxacin share the same transporters, including P-glycoprotein. The present study at least suggests that pazufloxacin is excreted into the urine via P-glycoprotein and some active drug transporters other than Mrp2.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2004

Involvement of estrone-3-sulfate transporters in proliferation of hormone-dependent breast cancer cells.

Although circulating estrone-3-sulfate is a major precursor of biologically active estrogen, permeation across the plasma membrane is unlikely to occur by diffusion because of the high hydrophilicity of the molecule. The object of this study was to clarify the involvement of specific transporter(s) in the supply of estrone-3-sulfate to human breast cancer-derived T-47D cells, which grow in an estrogen-dependent manner. The proliferation of T-47D cells was increased by the addition of estrone-3-sulfate, or estradiol, to the cultivation medium. The initial uptake rate of estrone-3-sulfate kinetically exhibited a single saturable component, with Km and Vmax values of 7.6 microM and 172 pmol/mg of protein/min, respectively. The replacement of extracellular Na+ with Li+, K+, or N-methylglucamine+ had no effect on the uptake of [3H]estrone-3-sulfate. The uptake was strongly inhibited by sulfate conjugates of steroid hormones, but not by estradiol-17beta-glucuronide. Taurocholate and sulfobromophthalein inhibited the uptake, whereas other tested anionic and cationic compounds did not. The expression of organic anion transporting polypeptides, OATP-D and OATP-E, which are candidate transporters of estrone-3-sulfate, was detected by reverse transcription-polymerase chain reaction analysis, although their actual involvement in the uptake of estrogen remains to be clarified. In conclusion, the uptake of estrone-3-sulfate by T-47D cells was mediated by a carrier-mediated transport mechanism, suggesting that the estrogen precursor is actively imported by estrogen-dependent breast cancer cells.

Breast Neoplasms↗

PubMed2004

Transporter-mediated drug delivery: recent progress and experimental approaches.

A comprehensive list of drug transporters has recently become available as a result of extensive genome analysis, as well as membrane physiology and molecular biology studies. This review covers recent progress in identification and characterization of drug transporters, illustrative cases of successful drug delivery to, or exclusion from, target organs via transporters, and novel experimental approaches to therapeutics using heterologously transduced transporters in tissues. We aim to provide clues that could lead to efficient strategies for the use of transporters to deliver drugs and/or to optimize lead compounds.

ATP-Binding Cassette Transporters↗

PubMed2004

Involvement of OCTN1 (SLC22A4) in pH-dependent transport of organic cations.

OCTN1 (SLC22A4) transports cationic compounds such as tetraethylammonium in a pH-sensitive and sodium-independent manner in cultured cells, and is expressed in wide variety of tissues, including kidney, muscle, placenta, heart, and others. This study focused on the clarification of its subcellular distribution in kidney and on its driving force to throw light on the pharmacological and physiological roles of OCTN1. Uptake of [14C]tetraethylammonium by membrane vesicles prepared from HEK293 cells stably transfected with human OCTN1 cDNA was osmolarity-sensitive, and the Km of tetraethylammonium was 1.28 mM at intravesicular and extravesicular pH values of 6.0 and 7.4, respectively. Tetraethylammonium uptake was pH-dependent, and overshoot uptake was observed in the presence of an outwardly directed proton gradient. A protonophore and membrane potential affected the overshoot uptake. Furthermore, preloading tetraethylammonium in the vesicles significantly increased the rate of uptake of [14C]tetraethylammonium. In mouse kidney, OCTN1 was expressed predominantly at the apical membrane of cortical proximal tubular epithelial cells. It was concluded that OCTN1 is involved in renal excretion of organic cations across the apical membrane in a pH-dependent, membrane potential-sensitive manner and is affected significantly by the organic cations on the trans side, showing counter transport activity.

Biological Transport↗

PubMed2004

Transporter-mediated renal handling of nafamostat mesilate.

Nafamostat mesilate (NM) is a serine-protease inhibitor that is rapidly eliminated from the circulation and accumulated in the kidney. This study was conducted to characterize the mechanism of NM transport in the kidney because a serious side effect of NM-induced hyperkalemia may be related to accumulation of NM in the kidney. Measurements of uptake of NM in vivo by the kidney uptake index (KUI) method and of transport in an in vitro-cultured LLC-PK1 cell system suggested the involvement of an organic cation transporter (OCT). To clarify the involvement of OCTs located in the basolateral membrane of proximal tubules, we evaluated NM transport by OCTs expressed in Xenopus laevis oocytes. The IC(50) values of NM on [(14)C]TEA ([(14)C]tetraethylammonium) uptake by rOCT1, rOCT2, and hOCT2 were 50, 0.5, and 20 microM, respectively, and NM was concluded to be a substrate of OCTs. To investigate the transport of NM across the brush-border membrane, we examined the uptake of NM into brush-border membrane vesicles (BBMVs) isolated from rat renal cortex. NM was taken up into the BBMVs, and the uptake was decreased by unlabeled NM and temperature, implying that a transporter(s) is also involved in NM transport across the apical membrane. NM was not a substrate of hOCTN1, hOCTN2, or P-gp, implying the involvement of some unknown transporter(s). Thus, renal accumulation of NM can be explained by the involvement of the basolateral OCTs, though the influence of the apical membrane transporter remains to be clarified.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2004

Characterization of renal excretion mechanism for a novel diuretic, M17055, in rats.

M17055 was developed as a novel diuretic that inhibits both Na(+), K(+), and 2Cl(-) cotransport at the thick ascending Henle's loop and Na(+) reuptake at the distal tubule. It is secreted at the renal proximal tubules. The purpose of the present study was to characterize the renal excretion mechanism of M17055. We used the renal cortical slices and brush border membrane vesicles (BBMVs) to investigate the transport mechanisms across the basolateral and brush border membranes, respectively. M17055 uptake by rat renal slices increased with time and was saturable. Several organic anions including probenecid, para-aminohippurate (PAH), and estrone-3-sulfate, decreased M17055 uptake. The uptake of M17055 was also observed into HEK293 cells expressing rat OAT1, and was inhibited by PAH. M17055 uptake by BBMVs was time-dependent, saturable, osmolarity-sensitive, and inhibited by several organic anions, but not by PAH. These results suggest that plural organic anion transport systems are involved in M17055 transport via both basolateral and brush border membranes of proximal tubule epithelial cells, a part of the renal uptake being mediated by OAT1.

Animals↗

PubMed2004

Functional characterization of human organic cation transporter OCTN1 single nucleotide polymorphisms in the Japanese population.

The organic cation transporter OCTN1 (SLC22A4) is expressed ubiquitously, with strong expression in kidney, trachea, bone marrow, and fetal liver, and it mediates transport of organic cations in a pH-dependent manner. Recent studies have identified single nucleotide polymorphisms (SNPs) of OCTN1 in the Japanese population. Two SNPs present in the exon regions, c1063t and g1531a, cause amino acid mutation, Thr306Ile (T306I) and Gly462Glu (G462E), respectively. We examined the influence of these SNPs on the intracellular localization, protein expression, and transport activity of OCTN1. Immunocytochemical analysis showed similar localizations of OCTN1 in cellular membranes of HEK293 cells transiently transfected with an expression plasmid DNA for OCTN1 or its SNP allelic variants. The Km and Vmax values for tetraethylammonium (TEA) uptake by T306I were similar to those of the wild-type even when the Vmax value was normalized for the expression level of OCTN1 protein. In contrast, G462E had almost negligible transport activity, although the protein expression level of G462E was equivalent to that of the wild-type. We conclude that the SNP that causes the single amino acid mutation T306I does not affect TEA transport activity, whereas the mutation G462E abrogates the TEA transport activity, presumably affecting the physiological function of OCTN1 and/or the pharmacological characteristics of its substrates.

Asian People↗

PubMed2004

Expression of organic cation transporter OCTN1 in hematopoietic cells during erythroid differentiation.

OBJECTIVE: Organic cation/carnitine transporter, OCTN1 (SLC22A4) shows a relatively broad tissue distribution and transports organic cations in a pH-dependent manner. However, its physiological role remains to be clarified. To understand the physiological role of OCTN1, tissue expression of OCTN1 in human and mice was characterized. METHODS: Expression of OCTN1 in various tissues and blood cells was examined by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and flow cytometry analysis. RESULTS: Mouse OCTN1 mRNA was detected in kidney, smooth muscle, and hematopoietic tissues, such as spleen and bone marrow, by RT-PCR analysis. Further study focused on expression of OCTN1 in various types of blood cells. OCTN1 mRNA was detected in myeloid cells in mouse bone marrow, but not in lymphoid cells. Bone marrow nuclear cells positive for TER119, an erythrocyte marker, showed strong expression of OCTN1. Similarly, OCTN1 was strongly expressed in glycophorin A-positive erythroid cells obtained from human cord blood. In Western blot analysis, OCTN1 protein was detected in isolated mouse mature peripheral erythrocytes. Further analysis by RT-PCR and flow cytometry showed OCTN1 was expressed in both glycophorin A-positive and negative erythroid cells after cultivation. These findings suggested that OCTN1 transports compound(s) that are required for erythroid differentiation, maturation, and/or growth. CONCLUSION: The present study demonstrated that OCTN1 is associated with myeloid cells rather than lymphoid cells, and especially with erythroid-lineage cells at the transition stage from immature erythroid cells to peripheral mature erythrocytes.

Animals↗

PubMed2004

Screening of the interaction between xenobiotic transporters and PDZ proteins.

PURPOSE: Xenobiotic transporters have been proposed to be involved in membrane penetration of various therapeutic agents. As little information is available on molecular mechanism of their functional regulation, we have attempted to clarify the protein-protein interactions of such transporters as a first step to identify their regulators. METHODS: Yeast two-hybrid screening was performed to examine the interaction between carboxylic terminus of various xenobiotic transporters and PDZ (PSD95, D1g and ZO1) domain-containing proteins. The interaction and functional regulation were also evaluated in pull-down, immunoprecipitation and transport studies. RESULTS: Specific interaction with PDZ proteins was identified for several xenobiotic transporters including PEPT1, PEPT2, OCT3, OCTN1, OCTN2, OAT4, OATP-A, OATP-D, and OATP-F. The potent interaction was observed between PEPT2 and PDZK1, and deletion of the last four amino acids of the PEPT2 C-terminus almost completely abrogated such interaction. Recombinant PEPT2 C-terminus fusion protein can bind to purified His6-tagged PDZK1, confirming the involvement of two of four PDZ domains within PDZK1 in the interaction. Alanine-scanning mutation in PEPT2 revealed the presence of a consensus sequence (-T-X-L) that is responsible for the PDZK1 interaction. Transfection of PDZK1 increased the uptake of glycylsarcosine by PEPT2, whereas such stimulation was not observed for PEPT2 with the last four amino acids deleted. CONCLUSIONS: These results first identified the interaction between PDZ proteins and the cytosolic tail of various xenobiotic transporters. PDZK1 directly interacts with PEPT2, exerting functional regulation of its transporting activity. The current findings imply the localization of PEPT2 within a protein network constructed from PDZK1 and other transporter proteins.

Carrier Proteins↗

PubMed2004

Role of anion exchange transporter PAT1 (SLC26A6) in intestinal absorption of organic anions.

Mouse PAT1 (putative anion transporter, CEFX, slc26a6), an orthologue of human SLC26A6, was recently identified at the intestinal brush-border membrane and shown to transport organic anions such as formate and oxalate, as well as inorganic ions. In this study, we conducted functional characterization of the uptake of formate by HEK293 cells transfected with PAT1. The uptake of formate by PAT1 was increased in the presence of an outwardly-directed Cl gradient, whereas Na had no effect, and the uptake was independent of pH. The Km of PAT1 for formate was 3.75 mM. Various organic acids exhibited a cis-inhibitory effect on the uptake of formate by PAT1. Furthermore, the uptake was increased by preloading with -lactate, nicotinate, valproate and short-and medium-chain fatty acids, showing a trans-stimulatory effect. Thus, it was suggested that PAT1 transports organic acids as well as inorganic anions, demonstrating that it is involved in the intestinal absorption of anionic organic weak acids in the small intestine.

Amino Acid Transport Systems↗

PubMed2004

Involvement of organic anion transporting polypeptides in the transport of troglitazone sulfate: implications for understanding troglitazone hepatotoxicity.

Troglitazone is a thiazolidinedione insulin sensitizer drug that is metabolized mainly to a sulfate conjugate (M-1) in humans. It was reported to cause hepatotoxicity, although the cause has not been fully clarified. The objective of this study was to identify whether organic anion transporting polypeptide (OATP) transporters expressed at the basolateral membrane of human hepatocytes participate in troglitazone-associated hepatotoxicity. When OATP-B, OATP-C, or OATP8 was expressed in Xenopus oocytes, the transporter-mediated uptake into oocytes of troglitazone sulfate conjugate and the inhibitory effects of thiazolidinediones and the metabolites of troglitazone on estrone-3-sulfate transport were measured. M-1 was transported well by OATP-C but was not transported by OATP-B. OATP8 showed weak, but not statistically significant, transport of M-1. M-1 exhibited a strong inhibitory effect on estrone-3-sulfate transport by OATP-C and OATP8, suggesting a higher affinity than other thiazolidinediones and the metabolites of troglitazone, glucuronide conjugate and quinone metabolite. In conclusion, the sulfate conjugate of troglitazone has a higher affinity for OATPs than troglitazone itself or other metabolites. Since OATP transporters are important in the hepatic handling of bile acids, bilirubin, and other endogenous anionic compounds, M-1 may disturb the hepatic influx and efflux transport of these endogenous molecules across the basolateral membranes. Moreover, OATP-C may be involved in the hepatic toxicity of troglitazone through the inhibitory action of M-1.

Biological Transport, Active↗

PubMed2004

Does the well-stirred model assess the intestinal first-pass effect well?

The pre-systemic intestinal extraction ratio (E(g)) has been estimated by an equation based on the well-stirred model, which does not have a term of membrane transport. In this report, we have identified the application limitations of the well-stirred model equation to assess the pre-systemic intestinal extraction ratio. The E(g) of metoprolol (CYP2D6 substrate) was assessed by three methods. Intrinsic clearances for metoprolol metabolism in hepatic and gastrointestinal microsomes were from a published report. Method 1 (model-independent method): the E(g) of 0.228 was obtained according to the equation, F = F(f) x (1 - E(g)) x F(h), where F, F(f) and F(h) were the bioavailability, the fraction entering the intestinal tissue and the hepatic availability, respectively. Method 2: the E(g) of 0.0071 was calculated according to the well-stirred model equation, and was much lower than the value of 0.228. Method 3: the E(g) of 0.213 was obtained by the transport-metabolism-flow (TMF) model equation, and was much closer to the value of 0.228 obtained by the model-independent method than the E(g) of 0.0071 calculated by the well-stirred model equation. Therefore, we propose that the factor of membrane transport process be incorporated into the pharmacokinetic model for the assessment of the pre-systemic intestinal extraction ratio.

Intestinal Absorption↗