Biomedical subjects

Igor Legen

Publications and source records attributed to Igor Legen.

6 recordsLinked to original sources

PubMed2005

The evaluation of some pharmaceutically acceptable excipients as permeation enhancers for amoxicillin.

The aim of the present study was to evaluate different pharmaceutically acceptable excipients as permeation enhancers for a low permeability drug, amoxicillin. As a model for the intestinal epithelium excised rat jejunum, mounted in side-by-side diffusion cells, was used. Amoxicillin was actively transported across the intestine in the serosal-to-mucosal direction, but only if glucose was present at the mucosal side. This effect of glucose was abolished by a multridrug resistance associated protein (MRP) inhibitor benzbromarone (0.04 mM), but not by verapamil (0.2 mM). Among the tested pharmaceutically acceptable excipients only sodium lauryl sulfate (0.2 mg/ml) increased the permeability of amoxicillin in the mucosal-to-serosal direction, which was accompanying with the abolishment of the secretory oriented transport of amoxicillin. Other excipients (0.07 2mg/ml Pluronic F68, 0.2 mg/ml Lutrol F127, 0.2 mg/ml Cremophor EL or 0.2 mg/ml Carbopol 934) have no influence on the permeability of amoxicillin. The effect of sodium lauryl sulfate on the active secretion of amoxicillin was mainly attributed to the reversible cellular ATP depletion. We concluded that sodium lauryl sulfate can be considered as a relatively safe permeation enhancer for amoxicillin in drug delivery systems intended to improve oral bioavailability of this drug.

Amoxicillin↗

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↗