Biomedical subjects

Albin Kristl

Publications and source records attributed to Albin Kristl.

9 recordsLinked to original sources

PubMed2006

Fluorescein transport properties across artificial lipid membranes, Caco-2 cell monolayers and rat jejunum.

Membrane transport characteristics of a paracellular permeability marker fluorescein were evaluated using artificial membrane, Caco-2 cell monolayers and rat jejunum, all mounted in side-by-side diffusion cells. Modified Ringer buffers with varied pH values were applied as incubation salines on both sides of artificial membrane, cell culture monolayers or rat jejunum. Passive transport according to pH partition theory was determined using all three permeability models. In addition to that, active transport of fluorescein in the M-S (mucosal-to-serosal) direction through rat jejunum was observed. The highest M-S P(app) values regarding the active transport through the rat jejunum were observed in incubation saline with pH 6.5. Fluorescein transport through the rat jejunum was inhibited by DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) and alpha-CHC (alpha-cyano-4-hydroxycinnamic acid). Thus, we assume that two pH-dependent influx transporters could be involved in the fluorescein membrane transport through the intestinal (jejunal) epithelium. One is very likely an MCT (monocarboxylic acid cotransporter) isoform, inhibited by specific MCT inhibitor alpha-CHC, while the involvement of the second one with overlapping substrate/inhibitor specificities (most probably a member of the organic anion-transporting polypeptide family, inhibited at least partially by DIDS) could not be excluded.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed2006

Ciprofloxacin permeability and its active secretion through rat small intestine in vitro.

The biopharmaceutical aspect of the fluoroquinolones-metal cations interaction, which reduces antibacterial agents bioavailability and the mechanism of the fluoroquinolone intestinal efflux are still poorly understood. The purpose of this work was to gain further insights into these two issues by measuring the permeability of ciprofloxacin through the rat small intestine in side-by-side diffusion chambers using different incubation media and transport inhibitors. The permeability of ciprofloxacin from the mucosal to the serosal side was low. It was not influenced by the different concentrations of Ca(2+) and Mg(2+) in the donor solution. The active efflux of ciprofloxacin was the highest in the region of the rat small intestine excised proximal to the ileo-caecal junction or when the pH value of the incubation saline was slightly acidic. Thus ciprofloxacin appears to be transported in its cationic or in its zwitterionic form. The efflux was not inhibited by verapamil, benzbromarone or quinidine, which were added to the mucosal side of the intestinal tissue. It was however inhibited by quinidine added to the serosal side. The active secretion is therefore most probably a consequence of the organic cation transporter 1 activity at the basolateral membrane of enterocytes.

Animals↗

PubMed2006

Permeability characteristics of novel aldose reductase inhibitors using rat jejunum in vitro.

The aim of this study was to estimate in vivo permeability and bioavailability of epalrestat and newly synthesized compounds with possible therapeutic activity as aldose enzyme inhibitors (ARIs). For this purpose permeability in vitro using rat jejunum mounted in side-by-side diffusion cells was determined. Tested substances were found to be low and moderately permeable and some of them were also substrates for efflux transporters. It was shown, that the higher efflux for some derivatives was due to MRP-2, but not Pgp involvement. Tested ARIs do not share the same efflux transporter with epalrestat, the only ARI currently on the market in Japan. The most permeable compound, a 2,6-difluoro-4-pyrrol-1ylphenol derivative, is not a substrate for efflux transporters and would therefore be the most promising lead compound for further investigation of potent ARIs.

Aldehyde Reductase↗

PubMed2005

The effect of clodronate on the integrity and viability of rat small intestine in vitro-a comparison with EDTA.

Although substances, which can increase the paracellular permeability of intestinal mucosa, could be very helpful for increasing the bioavailability of hydrophilic drugs, they are not used therapeutically due to the possibilities of acute or long-term toxicity (intestinal inflammations due to penetration of bacterial fragments into subepithelial spaces). In this paper the abilities of a calcium chelator EDTA and clodronate (a first generation bisphosphonate) to increase the paracellular permeability were assessed using rat jejunum in side-by-side diffusion chambers while the viability of the tissue was monitored by transepithelial potential difference. Although clodronate is less potent than EDTA in depleting calcium from the intestinal tissue, it significantly increased the paracellular permeability of viable rat jejunum "in vitro" when tested at 15 mM and higher concentrations (the highest therapeutic dose dissolved in 250 ml gives a 22 mM solution of clodronate). This effect was reversible under "high-calcium" conditions. Since clodronate therapy does not have any long-term consequences it was concluded that a safe, transient increase of small intestinal permeability is possible. However, the acute gastrointestinal undesired effects, which can develop during the therapy with high doses of clodronate, might also occur after oral applications of paracellular permeability enhancers. Namely, 30 mM and higher concentrations of clodronate caused a loss of the tissue viability in all rat jejunal segments tested in "in vitro" conditions. A similar effect was observed with much lower concentrations of EDTA.

Animals↗

PubMed2004

The influence of buffer composition on tissue integrity during permeability experiments "in vitro".

A well-balanced incubation saline is necessary for permeability experiments with the rat jejunal tissue in the diffusion chambers. At the same time the investigated substance must be chemically stable and sufficiently soluble in this incubation saline. To investigate whether the absence of some ions in incubation salines influences the tissue viability and integrity or the diffusional characteristics of the epithelial membrane the electrical parameters were monitored and the permeability of fluorescein and acyclovir was evaluated during the experiments in side-by-side diffusion chambers. Our results show that the tissue integrity and viability are seriously impaired when Ca(2+) and Mg(2+)-free conditions are applied on both sides of the diffusion chambers, but not when only mucosal or only serosal side is Ca(2+) and Mg(2+)-free. Bicarbonate-free incubation salines can also alter the measured apparent permeability coefficients even though the tissue viability and integrity do not change. This change in the apparent permeability is most likely due to a change in the pH of the mucosal surface and can be prevented if the buffer capacity of the incubation saline is increased.

Acyclovir↗

PubMed2004

D-glucose triggers multidrug resistance-associated protein (MRP)-mediated secretion of fluorescein across rat jejunum in vitro.

PURPOSE: To examine the transport characteristics of the multidrug resistance-associated protein (MRP) substrate fluorescein across the isolated rat small intestinal segments. METHODS: The transport of fluorescein was studied in side-by-side diffusion chambers under short-circuited conditions at physiological pH. RESULTS: The serosal-to-mucosal permeability of fluorescein significantly exceeded the permeability in the opposite direction in the jejunum, but not in the ileum. This asymmetry in transport in the jejunum was observed only when D-glucose was present at the mucosal side of the tissue, and not in the presence of D-galactose or D-mannitol. In the presence of D-glucose at the mucosal side, serosal-to-mucosal permeability of fluorescein in the jejunum can be divided into an active (Michaelis-Menten constant, KM = 1.07 mM; maximum flux of the substrate. Jmax = 14.0 nmol/h x cm2) and a passive component (passive permeability, Ppas = 2.51 x 10(-6) cm/s). The polarization of fluorescein transport was almost completely abolished by MRP inhibitor, benzbromarone (50 or 100 microM, applied apically), and by MRP/P-glycoprotein inhibitor, verapamil (200 microM, applied apically). CONCLUSIONS: D-glucose at the mucosal side activates fluorescein secretion across rat jejunum by an apical MRP, most probably by isoform 2 (MRP2), which could have an impact on the intestinal absorption of MRP substrates.

Animals↗

PubMed2003

pH and energy dependent transport of ketoprofen across rat jejunum in vitro.

The aim of this study was to elucidate transport mechanisms of ketoprofen (monocarboxylic acid with pK(a) 4.6) across rat jejunum in vitro using side-by-side diffusion cells. When the tissue was incubated on the mucosal and serosal sides with buffer of pH 7.51 (pH of the mucosal surface was 7.08), ketoprofen permeated faster in the mucosal-to-serosal than in the opposite direction. No asymmetry in transport was observed when 2 mM mucus disrupting agent 1,4-dithio-DL-threitol (pH of the mucosal surface increased to 7.21) was added to the mucosal side. Mucosal-to-serosal permeability of ketoprofen increased three times when the pH of the incubation medium was changed from 8.06 (pH of the mucosal surface was 7.34) to 6.07 (pH of the mucosal surface was 5.95), while no pH dependence was found under ATP-depletion caused by sodium azide. In the ketoprofen concentration range from 0.125 to 5 mM no saturation of transport was observed. Moreover, ketoprofen transport was not changed in the presence of 2 mM benzoate, 10 and 20 mM acetate, 20 mM L-lactate (substrates for monocarboxylate transporter 1, MCT1) and 1 mM alpha-cyano-4-hydroxy-cinnamic acid (an inhibitor of MCT1). These results indicate that ketoprofen is transported across rat jejunum in vitro by pH and energy dependent transport mechanisms, and most probably not by MCT1.

Adenosine Triphosphate↗

PubMed2003

Factors affecting the microclimate pH of the rat jejunum in ringer bicarbonate buffer.

General characteristics of the microclimate layer on the mucosal surface of the rat jejunum incubated in bicarbonate buffers were investigated in vitro using pH sensitive flat membrane microelectrode. Jejunal surface microclimate (JSM) pH changed from 7.30+/-0.03 to 5.83+/-0.04 when the incubation buffer pH decreased from 8.03+/-0.02 to 6.12+/-0.01. Treatment of the mucosal side with mucolytic substances L-cysteine (1% (wt/v)) and 1,4-dithio-DL-threitol (2 mM) significantly (p<0.01) increased JSM pH. Respiratory chain inhibitor, sodium azide (10 mM) also significantly (p<0.05) increased JSM pH. D-Glucose (10 mM) at the mucosal side markedly (p<0.05) decreased JSM pH, which was attenuated by Na(+)/H(+) exchange inhibitor, amiloride (1 mM). Amiloride had no effect on JSM pH when D-glucose was not present at the mucosal side. In contrast to previous observations using bicarbonate free incubation buffers, we have demonstrated that JSM pH is not a constant value, but is dependent on pH of the incubation buffer. Additionally, Na(+)/H(+) exchanger does not contribute to acidic properties of JSM, when there is no D-glucose in the bicarbonate incubation buffer at the mucosal side of the tissue. In conclusion, we suggest that the bicarbonate buffers which are more close to in vivo situation than bicarbonate free buffers should be preferable incubation media when examining JSM.

Amiloride↗

PubMed2002

Ketoprofen-induced intestinal permeability changes studied in side-by-side diffusion cells.

It is known that non-steroidal anti-inflammatory drugs (NSAIDs) increase intestinal permeability. Increased intestinal permeability is believed to result from the opening of tight junctions because of NSAID-induced reduction of prostaglandin synthesis and/or energy-depletion. In this study, ketoprofen-induced changes in intestinal permeability were evaluated by measuring tissue electrical parameters, namely tissue electrical resistance (TER), short circuit current (I(sc)) and transepithelial potential difference (PD), and the transport of a paracellular marker, fluorescein, across rat jejunum in-vitro. Ketoprofen, added to the mucosal side of the tissue, decreased TER and increased fluorescein transport in a concentration-dependent manner. I(sc) values and the active transport of D-glucose were not affected at ketoprofen concentrations of less than 5 mM. Higher ketoprofen concentrations decreased I(sc) values and diminished active transport of D-glucose, while transport of fluorescein increased markedly. Similar effects on intestinal properties were observed when the metabolic inhibitor sodium azide was added to the incubation medium. The results of this study suggest that the increased intestinal permeability observed at lower ketoprofen concentrations (< 5 mM) is most probably a consequence of reduced prostaglandin tight junction control, whereas at higher concentrations, ATP depletion caused by ketoprofen seems to be the major mechanism for increased intestinal permeability.

Algorithms↗