Biomedical subjects

Anna-Lena Ungell

Publications and source records attributed to Anna-Lena Ungell.

9 recordsLinked to original sources

PubMed2006

Presentation of a structurally diverse and commercially available drug data set for correlation and benchmarking studies.

A multivariate analysis of drugs on the Swedish market was the basis for the selection of a small, physicochemically diverse set of 24 drug compounds. Factors such as structural diversity, commercial availability, price, and a suitable analytical technique for quantification were considered in the selection. Lipophilicity, pKa, solubility, and permeability across human Caco-2 cell monolayers were measured for the compiled data set. The results show that, by use of a physicochemically diverse data set, experimental responses over a wide range were obtained. The paper also shows how experimental difficulties due to the diversity of the data set can be overcome. We anticipate that this data set can serve as a benchmark set for validation of new experimental techniques or in silico models. It can also be used as a diverse starting data set for the development of new computational models.

Caco-2 Cells↗

PubMed2006

Variability in mRNA expression of ABC- and SLC-transporters in human intestinal cells: comparison between human segments and Caco-2 cells.

The Caco-2 cell monolayer model is widely used as a tool for evaluating human intestinal permeability and interaction with transporters. Therefore, we determined mRNA levels for 15 of the most frequently studied uptake and efflux transporters (MDR1, MRP2-3, BCRP, OCTN2, PepT1, OATP-B, OATP8, OCT1-3, OAT1-3, MCT1) using real-time PCR in Caco-2 cells and in human jejunum and colon. The expression levels in the Caco-2 cells did not significantly vary between different passages (p29-43) and batches for any of the genes measured. However, levels increased with culture time (1-5 weeks) for PepT1, MDR1, MRP2, OATP-B and BCRP. The general rank order of the gene expression levels in Caco-2 cells was established as follows: MRP2>OATP-B>PepT1>>MDR1>MCT1 approximately MRP3 approximately BCRP approximately OCTN2>>OCT3>OCT1>OAT2. Four genes were absent: OATP8, OCT2, OAT1, and OAT3. Ranking of 11 expressed genes showed a significant correlation between human jejunum and 2-5-week-old Caco-2 cells. The expression profile in colon was, however, very different compared to both Caco-2 cells and jejunum. We conclude that the Caco-2 cells in our hands express similar transporters as the human jejunum, but are different from colon, indicating their usefulness for obtaining small intestinal transport data. In addition, we also suggest that cells with a well-defined range of culture ages should be used to minimize variability in data from experiments and even erroneous conclusions.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2006

Impact of extracellular protein binding on passive and active drug transport across Caco-2 cells.

AIM: The objective of the study is to evaluate the mechanism behind alterations in passive and active transport of drugs in the presence of basolaterally applied extracellular protein using the Caco-2 cell model. METHODS: The permeation across Caco-2 monolayers of two groups of compounds, transported either solely by passive diffusion or partly also by active transport in the secretory direction, was studied at two donor concentrations in the absence or presence of bovine serum albumin (BSA, 0-4%). Each group contained compounds with high or low protein binding (PB) capabilities and high or low absorption in humans (fraction absorbed, f(a)). The unbound fraction (f(u)) of each compound was determined by ultrafiltration. RESULTS: The transport rate of the passively permeating compounds was the same in both apical-to-basolateral (absorptive) and basolateral-to-apical (secretory) directions in the absence of BSA. Basolaterally applied BSA increased the transport rate in the absorptive direction and decreased it in the secretory direction for all compounds, in direct proportion to the extent of PB. The efflux ratios for the actively transported compounds were reduced in the presence of BSA. CONCLUSIONS: Basolaterally applied BSA, which mimics in vivo PB, alters both passive and active drug transport in the Caco-2 cell model. Using C(u) in the calculations of transport rate allowed elucidation of the different mechanisms behind these alterations. Our data also suggest that active secretory transport for highly protein-bound compounds might have less effect in vivo than predicted from traditional Caco-2 cell models (without BSA).

Algorithms↗

PubMed2005

pH-Dependent passive and active transport of acidic drugs across Caco-2 cell monolayers.

The aim of this study was to investigate pH-dependent passive and active transport of acidic drugs across Caco-2 cells. Therefore, the bidirectional pH-dependent transport of two acidic drugs, indomethacin and salicylic acid, across Caco-2 cells was studied in the physiological pH range of the gastrointestinal tract. The transport of both drugs decreased with increased pH, as expected from the pH-partition hypothesis. Net absorption occurred when the basolateral pH exceeded the apical pH. Concentration dependence and transporter inhibition studies indicated passive transport for indomethacin and a mixture of pH-dependent passive and active influx for salicylic acid. Unexpectedly, active and passive drug transport results were indistinguishable in temperature dependency studies. The transport of salicylic acid (apical pH 5.0; basolateral pH 7.4) was partly blocked by inhibitors of the proton-dependent transporters MCT1 (SLC16A1) and OATP-B (SLC21A9, SLCO2B1). This study shows that the asymmetry in bidirectional transport of acidic drugs is affected by both passive and active components in the presence of pH gradients across Caco-2 cells. Thus, combined studies of concentration-dependency and transport-inhibition are preferred when acidic drug transport is studied in a pH gradient. The findings of this in vitro study can be extrapolated to in vivo situations involving an acidic microclimate.

Biological Transport, Active↗

PubMed2003

Surface descriptors for protein-ligand affinity prediction.

Molecular descriptors calculated by the VolSurf program have been extensively used to model pharmacokinetic properties, e.g., passive permeability through the gastrointestinal tract or through the blood-brain barrier. These descriptors quantify steric, hydrophobic, and hydrogen bond interactions between model compounds and different environments. Since these interactions are the same as those involved in the ligand-receptor binding, VolSurf descriptors could potentially be relevant in modeling this process as well. We obtained a significant model (r(2) = 0.85, q(2) = 0.75) using VolSurf descriptors derived from the ligand, the protein, and the ligand-protein complex for a diverse set of 38 structures previously used in the VALIDATE (ref 23) training set. Furthermore, a statistically significant model (r(2) = 0.94, q(2) = 0.89) was obtained using the same type of descriptors for a homogeneous set of glycogen phosphorylase inhibitors (ref 25). Using the VolSurf computational framework, both ligand-receptor binding and the ligand's pharmacokinetic behavior can be modeled simultaneously during the preclinical aspects of drug discovery.

Ligands↗

PubMed2003

pH-dependent bidirectional transport of weakly basic drugs across Caco-2 monolayers: implications for drug-drug interactions.

PURPOSE: The purpose of this study was to investigate the pH-dependent passive and active transport of weakly basic drugs across the human intestinal epithelium. METHODS: The bidirectional pH-dependent transport of weak bases was studied in Caco-2 cell monolayers in the physiologic pH range of the gastrointestinal tract. RESULTS: A net secretion of atenolol and metoprolol was observed when a pH gradient was applied. However, the bidirectional transport of both compounds was equal in the nongradient system. Hence, at lower apical than basolateral pH a change in passive transport caused by an imbalance in the concentration of the uncharged drug species resulted in a "false" asymmetry (efflux ratio). Furthermore, a mixture of pH-dependent passive and active efflux was found for the P-glycoprotein (P-gp, MDR1, ABCB1) substrates, talinolol and quinidine, but not for the neutral drug, digoxin. However, the clinically important digoxin-quinidine interaction depended on the presence of a pH gradient. Hence, the degree of interaction depends on the amount of quinidine available at the binding site of the P-gp. CONCLUSIONS: Active efflux of weak bases can only be accounted for when the fraction of unionized drug species is equal in all compartments because the transport is biased by a pH-dependent passive component. However, this component may take part in vivo and contribute to drug-drug interactions involving P-gp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2002

Influence of hydrodynamics and particle size on the absorption of felodipine in labradors.

PURPOSE: To study the influence of GI hydrodynamics and drug particle size on felodipine absorption in the dog. METHODS: Labradors fistulated at midjejunum were used to selectively study the influence of hydrodynamics and particle size on the in vivo dissolution and absorption of the poorly soluble, lipophilic drug felodipine. A combination of infusion and oral administration of either normal saline or a 5% glucose solution was used to maintain "fasted" and establish "fed" state motility patterns, respectively. The absorption characteristics of both a micronized (8 microm) and a coarse fraction (125 micom) of felodipine were subsequently studied under these two motility patterns. RESULTS: A reduction in particle size led up to an approximate 22-fold increase in maximum plasma concentration and up to an approximate 14-fold increase in area under the curve, with a commensurate decrease in the time at which the maximum plasma concentration occurred. Although the absorption of felodipine from the solution and micronized suspension was not influenced by a change in the hydrodynamics, felodipine was absorbed from the coarse suspension almost twice as well in the "fed" state as under "fasted" conditions. CONCLUSIONS: Absorption from coarse suspensions of felodipine was sensitive to luminal hydrodynamics, whereas micronized suspensions were not. However, the particle size seems to have a much more important influence on the bioavailability of felodipine than the hydrodynamics per se.

Administration, Oral↗

PubMedDate not supplied

Pharmacokinetically based mapping device for chemical space navigation.

ChemGPS, the chemical global positioning system, is a tool that combines rules (equivalent to dimensions) and objects (chemical structures) to provide a consistent chemical space map (Oprea, T. I.; Gottfries, J. J. Comb. Chem. 2001, 3, 157-166.). Rules included, initially, general properties such as size, lipophilicity, and hydrogen bond capacity, while objects include "satellites", intentionally placed outside the druglike space, as well as "core" objects, mostly orally available drugs. ChemGPS molecules (objects) were used in conjunction with the VolSurf (http://www.moldiscovery.com) descriptors (rules), which are relevant for ADME (absorption, distribution, metabolism, and excretion) properties. The combination of ChemGPS and VolSurf, GPSVS, was investigated with respect to the biopharmaceutics classification system, which is recommended by the Food and Drug Administration (FDA) (http://www.fda.gov/cder/OPS/BCS_guidance.htm), in particular with respect to permeability and solubility. The first GPSVS principal component correlates, with no further training, to passive transcellular permeability, as illustrated for the Caco-2, ghost erythrocyte, and blood-brain barrier datasets, respectively. The second GPSVS principal component correlates, without prior training, to solubility, as shown for the octanol-water partition and intrinsic solubility datasets, respectively. Although derived from principal component analysis, the two property axes rotate and form an angle of approximately 43 degrees, thus being no longer orthogonal. GPSVS can be used to map the chemical space with respect to permeability and solubility, as recommended by FDA's biopharmaceutics classification system.

Journal Article↗

PubMedDate not supplied

Regional intestinal absorption and biliary excretion of fluvastatin in the rat: possible involvement of mrp2.

The first purpose of this study was to investigate the in vivo absorption, biliary secretion, and first-pass effect of fluvastatin following regional intestinal dosing in the rat. We also examined the membrane transport mechanisms and made in silico predictions of the relative importance of various intestinal regions to the human absorption of fluvastatin. Fluvastatin was administered intravenously (2, 10, and 20 micromol/kg) and into the duodenum (1.46, 2.92, 7.32, and 14.6 micromol/kg), jejunum (14.6 micromol/kg), ileum (1.46 and 14.6 mciromol/kg), and colon (1.46 and 14.6 micromol/kg) as a solution to conscious rats. In a separate group of rats, bile was collected after an i.v. dose of fluvastatin (2 micromol/kg). In the Caco-2 model the bidirectional transport of fluvastatin (16 microM) was investigated with and without various efflux inhibitors (verapamil, vinblastine, probenecid, and indomethacin, 160 microM). The human in vivo absorption of fluvastatin from an oral immediate release tablet and that from an oral extended release tablet (both 40 mg) were simulated in GastroPlus. Neither the dose nor the intestinal region influenced the bioavailability of fluvastatin significantly. The rate of absorption was, however, affected by both the dose and the site of administration; duodenum = jejunum > colon > ileum, and higher following the high dose. Increasing the i.v. dose from 2 to 20 micromol/kg decreased the clearance (26 +/- 3 to 12 +/- 1 mL/min/kg), the hepatic extraction (66 +/- 8 to 30 +/- 2%), and the volume of distribution (7.3 +/- 0.3 to 2.1 +/- 0.7 L/kg) for fluvastatin (p < 0.05). Neither bile cannulation nor bile sampling affected the pharmacokinetics. Fluvastatin was secreted into the bile, probably by active transport. The in vitro permeability for fluvastatin was high (>10 x 10(-6) cm/s). Indomethacin, but not the other inhibitors, affected the transport in both directions suggesting mrp2 to be involved. In silico, 93% of the dose was absorbed from the small intestine and 6% from the colon when given as an immediate release formulation. The corresponding values for an extended release formulation were 21% and 74%, respectively. In conclusion, fluvastatin exhibits dose-dependent pharmacokinetics in the rat. The rate of absorption (Cmax, Tmax, and Cmax/AUC(lqc)) from the intestinal tract is both region and dose-dependent in the rat. This may be due to the involvement of mrp2 in the intestine and/or in the liver. These absorption properties have to be considered in the development of an extended release formulation of fluvastatin.

Administration, Oral↗