Kinetic and time-dependent features of sustained inhibitory effect of myricetin on folate transport by proton-coupled folate transporter.

Myricetin is a flavonoid that has recently been suggested to induce sustained inhibition of proton-coupled folate transporter (PCFT/SLC46A1), which operates for intestinal folate uptake. The present study was conducted to characterize the inhibitory effect in more detail, using human PCFT stably expressed in Madin-Darby canine kidney II cells, to gain information to cope with problems potentially arising from that. The kinetics of saturable folate transport was first assessed in the absence of myricetin in the cells pretreated with the flavonoid for 60 min.

Sustained inhibition of proton-coupled folate transporter by myricetin.

Myricetin is a flavonoid that has recently been suggested to interfere with the intestinal folate transport system. To examine that possibility, focusing on its sustained inhibitory effect on proton-coupled folate transporter (PCFT), the uptake of folate was examined in Caco-2 cells, in which PCFT is known to be in operation, in the absence of myricetin in the medium during uptake period after preincubation of the cells with the flavonoid (100 μM) for 1 h. This pretreatment induced an extensive and sustained reduction in the carrier-mediated component of folate uptake, which was attributable to a reduction in the maximum transport rate (Vmax).

Noncompetitive inhibition of proton-coupled folate transporter by myricetin.

Myricetin is a flavonoid that has recently been suggested to interfere with the intestinal folate transport system. The present study was conducted to examine that possibility, focusing on its inhibitory effect on proton-coupled folate transporter (PCFT) as the molecular entity of the transport system. The uptake transport of folate was first examined in the Caco-2 cell as an intestinal epithelial cell model, and its carrier-mediated component, of which the Michaelis constant (Km) was 0.

Transcriptional regulation of PCFT by KLF4, HNF4α, CDX2 and C/EBPα: implication in its site-specific expression in the small intestine.

Proton-coupled folate transporter (PCFT), which is responsible for the intestinal uptake of folates and analogs, is expressed only in the proximal region in the small intestine. The present study was to examine its transcriptional regulation, which may be involved in such a unique expression profile and potentially in its alteration, using dual-luciferase reporter assays in human embryonic kidney (HEK) 293 cells. The luciferase activity derived from the reporter construct containing the 5'-flanking sequence of -1695/+96 of the human PCFT gene was enhanced most extensively by the introduction of Krüppel-like factor 4 (KLF4).

Predictors of home death of home palliative cancer care patients: a cross-sectional nationwide survey.

Objectives: To identify factors influencing the place of death among home palliative cancer care patients, focusing on the role of nurses in terms of pre- and post-discharge from hospital to home care settings.

Design, Settings And Participants: A cross-sectional nationwide questionnaire survey was conducted at 1000 randomly selected homecare agencies in Japan. The questionnaires were completed by primary community nurses of home palliative patients just after their discharge.

Late referrals to home palliative care service affecting death at home in advanced cancer patients in Japan: a nationwide survey.

Background: To identify factors influencing place of death among home palliative care patients with advanced cancer, focusing on the timing of referrals from hospital to home care settings.

Methods: A cross-sectional nationwide questionnaire survey was conducted on home palliative care patients at 1000 randomly selected home care agencies in Japan. A total of 568 responses were analyzed (effective response rate, 69%).

Molecular and functional characteristics of proton-coupled folate transporter.

Proton-coupled folate transporter (PCFT) has recently been identified as the molecular entity of the carrier-mediated intestinal folate transport system. PCFT has been demonstrated to be most abundantly expressed in the upper small intestine, localizing at the brush border membrane of epithelial cells, transport folate and its analogs more efficiently at lower (acidic) pH by a H(+)-coupled cotransport mechanism, and have a high affinity for folate with a Michaelis constant (K(m)) of a few microM at pH 5.5 and somewhat lower affinities for reduced folates and methotrexate (MTX).

Effect of glycerol-related compounds on carrier-mediated glycerol uptake in HCT-15 human colon cancer cell line.

The effect of several compounds, which are structurally analogous to glycerol, on carrier-mediated glycerol uptake was examined in HCT-15 cells to help clarifying the functional characteristics of the glycerol transport system. The carrier-mediated uptake of glycerol conformed to the Michaelis-Menten kinetics with a Michaelis constant of 21.1 microM and the tested compounds were all suggested to inhibit it competitively with the values of the inhibition constant (K(i)) in the increasing order as follows: monobutyrin (41.

Functional characterization of PCFT/HCP1 as the molecular entity of the carrier-mediated intestinal folate transport system in the rat model.

Proton-coupled folate transporter/heme carrier protein 1 (PCFT/HCP1) has recently been identified as a transporter that mediates the translocation of folates across the cellular membrane by a proton-coupled mechanism and suggested to be the possible molecular entity of the carrier-mediated intestinal folate transport system. To further clarify its role in intestinal folate transport, we examined the functional characteristics of rat PCFT/HCP1 (rPCFT/HCP1) expressed in Xenopus laevis oocytes and compared with those of the carrier-mediated folate transport system in the rat small intestine evaluated by using the everted tissue sacs. rPCFT/HCP1 was demonstrated to transport folate and methotrexate more efficiently at lower acidic pH and, as evaluated at pH 5.

Enhanced uptake of glycerol by butyrate treatment in HCT-15 human colon cancer cell line.

The HCT-15 human colon cancer cell line has a Na(+)-dependent carrier-mediated transport system for the uptake of glycerol. A similar transport system has been suggested to be present also in the small intestine and is of interest with regard to its role in the absorption of glycerol and possibly some structurally related compounds. To help clarifying functional characteristics of such glycerol transport systems, we examined the effect of butyrate, an agent known to facilitate the differentiation of cells, on glycerol uptake in HCT-15 cells.

Effect of Lactobacillus casei on the absorption of nifedipine from rat small intestine.

Lactobacillus casei Shirota strain (L. casei) has a modulating effect on the production of cytokines, which often play important roles in drug metabolism, in the inflamed intestinal mucosa. We evaluated the effect of L.

Functional characterization of human proton-coupled folate transporter/heme carrier protein 1 heterologously expressed in mammalian cells as a folate transporter.

The functional characteristics of human proton coupled folate transporter (hPCFT)/heme carrier protein (HCP) 1 were investigated. hPCFT/HCP1 expressed transiently in human embryonic kidney 293 cells mediated the transport of folate at an acidic extracellular pH of 5.5 in a manner independent of Na(+) and insensitive to membrane potential, but its transport activity was absent at near-neutral pH.

Molecular identification and functional characterization of rat multidrug and toxin extrusion type transporter 1 as an organic cation/H+ antiporter in the kidney.

We have cloned and functionally characterized the rat ortholog of multidrug and toxin extrusion type transporter 1 (rMATE1). The mRNA of rMATE1 was strongly expressed in kidney and detectable in the various tissues such as brain, stomach, colon, lung, liver, spleen, skeletal muscle, and prostate. When stably expressed in HEK293 cells, rMATE1 could mediate the transport of tetraethylammonium (TEA) and cimetidine under the condition where the membrane potential was disrupted by a high concentration of potassium ion and intracellular pH was reduced by NH(4)Cl pretreatment.

Carrier-mediated transport of glycerol in the perfused rat small intestine.

Studies using the closed loop and everted sacs of the rat small intestine recently prompted us to suggest that carrier-mediated transport is involved in the intestinal absorption of glycerol. Although it could be mediated by a novel carrier system, little information is available. The aim of the present study was to kinetically characterize carrier-mediated glycerol transport in the perfused rat small intestine to help in identifying the carrier involved and to explore the possibility that the carrier might be used as a pathway for oral drug delivery and a target for drug development.

Glycerol uptake in HCT-15 human colon cancer cell line by Na(+)-dependent carrier-mediated transport.

It has recently been suggested that an Na(+)-dependent carrier-mediated transport system is involved in intestinal glycerol absorption. Such a transport system is of general interest as a possible pathway of drug delivery and a target of drug development. However, the Na(+)-dependent mechanism of cellular glycerol uptake has not been fully clarified in the small intestine or in any other organ.

Glycerol absorption by Na+-dependent carrier-mediated transport in the closed loop of the rat small intestine.

The absorption of glycerol was examined using the closed loop of the rat small intestine in situ to clarify the transport mechanism. The absorption of glycerol, evaluated by its disappearance from the intestinal lumen, was saturable and reduced under the Na(+)-free conditions, suggesting the involvement of an Na(+)-dependent carrier-mediated transport system. Furthermore, glycerol absorption was selectively inhibited by several alcohols, among which 1,3-propanediol caused the greatest inhibition, and also by glycerol-3-phosphate and voglibose, which are alcohol-related compounds analogous to glycerol.

Absorption and metabolic extraction of diltiazem from the perfused rat small intestine.

The metabolic extraction of diltiazem was examined in conjunction with its absorption, using rat small intestine perfused in situ by the single-pass method, to clarify its intestinal metabolism. This is a topic of increasing interest which has not been fully clarified, particularly as far as the extent of metabolic extraction and the enzymes involved (cytochrome P450 (CYP) 3A and/or others) are concerned. The intestinal availability (Fi) of diltiazem was evaluated at steady-state by dividing the fraction absorbed into the mesenteric venous blood (Fa,b) by the fraction that disappeared from the intestinal lumen (Fa).

Metabolic extraction of nifedipine during absorption from the rat small intestine.

Nifedipine is one of drugs that have been suggested to undergo significant first-pass metabolism by cytochrome P450 (CYP) 3A in the intestine, based mainly on pharmacokinetic analyses of in vivo observations. To further substantiate this suggestion, we examined the metabolic extraction of nifedipine from the rat small intestine, using intestine perfused in situ by a single-pass technique and microsomes in vitro. When the intestinal lumen was perfused with nifedipine solution (30 microM) at the flow rate of 0.

Functional characterization of the carrier-mediated transport system for glycerol in everted sacs of the rat small intestine.

The mechanism of intestinal glycerol transport was investigated by using the in vitro everted sac method involving the rat small intestine. The uptake of glycerol into everted sacs was saturable with a Michaelis constant (K(m)) of 0.77 mM and a maximum transport rate (J(max)) of 11.

Dose adjustment strategy for oral microemulsion formulation of cyclosporine: population pharmacokinetics-based analysis in kidney transplant patients.

The present study aims to determine the population pharmacokinetic parameters of cyclosporine (CsA) after multiple oral administration of the microemulsion formulation, Neoral, in kidney transplant patients and to propose a limited sampling strategy to predict AUC(0-4h) using them and the Bayesian method. The AUC(0-4h) is a parameter that has recently been recommended as an index for the dose adjustment in therapeutic drug monitoring of CsA. Blood samples were obtained at the trough level and at hourly intervals up to 5 hours from 125 patients (78 male and 47 female) who were receiving Neoral twice daily, and whole-blood concentrations of CsA were measured.

Saturable absorption of glycerol in the rat intestine.

The permeability of glycerol, a small hydrophilic solute, across the intestinal membrane would be low, if passive diffusion restricted to the paracellular route is the principal transport mechanism as generally assumed for this class of solutes. However, in the present study using a closed loop of rat small intestine in situ, we found that the absorption of glycerol was faster than that of urea, a probe solute widely assumed to permeate exclusively via the paracellular route. This finding is inconsistent with the paracellular permeation hypothesis, which predicts that the absorption of glycerol, which is larger than urea in terms of molecular size, could not be faster than that of urea.

Kinetic characterization of carrier-mediated transport systems for D-glucose and taurocholate in the everted sacs of the rat colon.

The present study was aimed at kinetically characterizing the carrier-mediated transport systems for D-glucose and taurocholate in the rat colon, compared with their respective counterparts in the small intestine. The transport of these compounds was evaluated by measuring the initial uptake into everted intestinal tissue sacs. The uptake of both D-glucose and taurocholate was highly saturable, conforming to Michaelis-Menten kinetics without an appreciable nonsaturable transport component.

Search for carrier-mediated transport systems in the rat colon.

Several nutrients and drugs, which are known to be absorbed by specific carrier-mediated transport systems in the small intestine, had their transport investigated in the rat colon, by measuring uptake into everted sacs, to find if carrier-mediated transport systems may also be present in the colon. Among those transported by Na+-dependent carriers in the small intestine, D-glucose and taurocholate were found to be transported in an Na+-dependent manner in the colon, while 5-fluorouracil and ascorbate were not. It was also found that the colonic transports of D-glucose and taurocholate were saturable.

Uptake of FH by two types of scavenger-like receptors in rat liver parenchymal cells in primary culture.

Several anionic proteins that are known to be substrates of scavenger receptors documented in the literature were selected and tested for their effects on the uptake of fractionated heparin (FH), an anionic macromolecular drug. The tests were made in rat liver parenchymal cells to characterize scavenger-like receptors involved in FH uptake, probing into substrate recognition characteristics in comparison with those of scavenger receptors. Although the uptake of FH was completely inhibited by dextran sulfate, a typical substrate of scavenger receptors, suggesting that scavenger-like receptors that have affinity for some anionic macromolecules are responsible for the uptake, it was not inhibited by acetylated low density lipoprotein (Ac-LDL), another typical substrate.

Variability in cimetidine absorption and plasma double peaks following oral administration in the fasted state in humans: correlation with antral gastric motility.

The role of gastrointestinal motility and pH in determining cimetidine bioavailability as well as double peaks in plasma profiles following oral administration, in the quiescent or active phase of antral motility, to humans in the fasted state was examined. Plasma cimetidine-time curves did not show the presence of double peaks in any subject following intravenous administration. The incidence of double peaks was 73% following oral administration and was independent of antral migrating motility complex phase.