Bisphosphonates increase tight junction permeability in the human intestinal epithelial (Caco-2) model

The SK3/K(Ca)2.3 potassium channel is a new cellular target for edelfosine

BACKGROUND AND PURPOSE

The 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (edelfosine) is an ether-linked phospholipid with promising anti-cancer properties but some side effects that preclude its full clinical therapeutic exploitation. We hypothesized that this lipid could interact with plasma membrane ion channels and modulate their function.

EXPERIMENTAL APPROACH

Using cell migration-proliferation assays, patch clamp, spectrofluorimetry and ¹²⁵I-Apamin binding experiments, we studied the effects of edelfosine on the migration of breast cancer MDA-MB-435s cells, mediated by the small conductance Ca²(+) -activated K(+) channel, SK3/K(Ca)2.3.

KEY RESULTS

Edelfosine (1 µM) caused plasma membrane depolarization by substantially inhibiting activity of SK3/K(Ca)2.3 channels, which we had previously demonstrated to play an important role in cancer cell migration. Edelfosine did not inhibit ¹²⁵I-Apamin binding to this SK(Ca) channel; rather, it reduced the calcium sensitivity of SK3/K(Ca)2.3 channel and dramatically decreased intracellular Ca²(+) concentration, probably by insertion in the plasma membrane, as suggested by proteinase K experiments. Edelfosine reduced cell migration to the same extent as known SK(Ca) channel blockers. In contrast, K+ channel openers prevented edelfosine-induced anti-migratory effects. SK3 protein knockdown decreased cell migration and totally abolished the effect of edelfosine on MDA-MB-435s cell migration. In contrast, transient expression of SK3/K(Ca)2.3 protein in a SK3/K(Ca)2.3-deficient cell line increased cell migration and made these cells responsive to edelfosine.

CONCLUSIONS AND IMPLICATIONS

Our data clearly establish edelfosine as an inhibitor of cancer cell migration by acting on SK3/K(Ca)2.3 channels and provide insights into the future development of a new class of migration-targeted, anti-cancer agents.

Specific permeability modulation of intestinal paracellular pathway by chitosan-poly(isobutylcyanoacrylate) core-shell nanoparticles

This work is focused on the evaluation of the in vitro permeation modulation of chitosan and thiolated chitosan (chitosan-TBA) coated poly(isobutylcyanoacrylate) (PIBCA) nanoparticles as drug carriers for mucosal administration. Core-corona nanoparticles were obtained by radical emulsion polymerisation of isobutylcyanoacrylate (IBCA) with chitosan of different molecular weights and different proportions of chitosan/chitosan-TBA. In this work, the effect of these nanoparticles on the paracellular permeability of intestinal epithelium was investigated using the Ussing chamber technique, by adding nanoparticle suspensions in the mucosal side of rat intestinal mucosa. Results showed that permeation of the tracer [14C]mannitol and the reduction of transepithelial electrical resistance (TEER) in presence of nanoparticles were more pronounced in those formulations prepared with intermediate amounts of thiolated polymer. This effect was explained thanks to the high diffusion capacity of those nanoparticles through the mucus layer that allowed them to reach the tight junctions in higher extent. It was concluded that, although a first contact between nanoparticles and mucus was a mandatory condition for the development of a permeation enhancement effect, the optimal effect depended on the chitosan/chitosan-TBA balance and the conformational structure of the particles shell.

Trimethylated chitosan as polymeric absorption enhancer for improved peroral delivery of peptide drugs

The absorption enhancing effects of chitosan and its derivatives have been intensively studied in recent years. It has been shown that these compounds are potent absorption enhancers. Chitosan is only soluble in acidic environments and is therefore incapable of enhancing absorption in the small intestine, the main absorption area in the gastrointestinal tract. Special emphasis has been placed on the absorption enhancing properties of N-trimethyl chitosan chloride (TMC), a partially quaternised derivative of chitosan, due to its solubility in neutral and basic environments. TMC is prepared by the reductive methylation of chitosan. The degree of quaternisation can be altered by increasing the number of reaction steps or by increasing the reaction time. Although the molecular weight of the polymer increases with addition of the methyl groups, a net decrease in the molecular weight is observed due to a decrease in the chain length of the polymer. TMC, like chitosan, possesses mucoadhesive properties. In vitro studies performed on Caco-2 cell monolayers showed a pronounced reduction in the transepithelial electrical resistance (TEER). TMC is also able to increase the permeation of hydrophilic compounds such as [14C]-mannitol and [14C] polyethylene glycol 4000 ([14C] PEG 4000, MW4000) across the cell monolayers. It was also shown that the degree of quaternisation of the polymer plays an important role on its absorption enhancing properties, especially in neutral environments where chitosan is ineffective as an absorption enhancer. The reduction in TEER is an indication of the opening of the tight junctions located between epithelial cells. Opening of the tight junctions will result in enhancement of absorption via the paracellular route. Confocal laser scanning microscopy confirmed transport of large hydrophilic compounds via the paracellular route as well as the mechanism of action of the polymer in which redistribution of the cytoskeletal F-actin is provoked, which leads to the opening of the tight junctions. Various in vivo studies in different animal models confirmed the ability of TMC to increase the absorption of the peptide drugs buserelin and octreotide after intraduodenal or -jejunal administration. However, TMC has always been administered as a solution in these studies. The impracticality of administering a solution, as well as the fact that most peptides are unstable in the presence of water, have led to the need for a solid oral dosage form with which TMC can be administered together with peptide drugs. Recent studies have focused on the development and in vivo evaluation of solid oral dosage forms.

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.

In vitro–in vivo evaluation of supercritical processed solid dispersions: Permeability and viability assessment in Caco‐2 cells

In this study improvement in the bioavailability of carbamazepine (CBZ) prepared as solid dispersions by conventional solvent evaporation and supercritical fluid (SCF) processing methods was assessed, along with the elucidation of the mechanism of improved absorption. Solid dispersions of CBZ in polyethylene glycol (PEG) with either Gelucire 44/14 or vitamin E-TPGS (TPGS) were evaluated by intrinsic dissolution. Directional transport through Caco-2 cell monolayers was determined in the presence and absence of TPGS. Cell viability in presence of various concentrations of amphiphilic carriers was seen. In vivo oral bioavailability was determined in rats. The apparent intrinsic dissolution rates (IDR) of both conventional- and SCF-CBZ/PEG 8000/TPGS solid dispersions were increased by 13- and 10.6-fold, respectively, relative to neat CBZ. CBZ was not a substrate of P-glycoprotein. Higher CBZ permeability was seen in presence of 0.1% TPGS. Cell viability studies showed significant cytotoxicity only at or above 0.1% amphiphilic carrier. Supercritical treated formulation (without amphiphilic carrier) displayed oral bioavailability on par with those conventional solid dispersions augmented with amphiphilic carriers. An in vitro-in vivo correlation was seen between IDR and the AUC of the various CBZ solid dispersions. Bioavailability of CBZ was more a function of dissolution as opposed to membrane effects. Although bioavailability from SCF processed dispersions was better than conventionally processed counterparts (except for one formulation containing Gelucire 44/14), an interaction of processing method and inclusion of an amphiphilic carrier, rather by one factor alone contributed to optimal absorption, thus giving contradictory results for Gelucire 44/14 and TPGS formulations.

Effects of various absorption enhancers on transport of clodronate through Caco-2 cells

The major disadvantage concerning clinical use of bishosphonate drugs, like clodronate, is their poor and variable absorption after oral administration. The objective of this study was to assess the effects of four different absorption enhancers-palmitoyl carnitine chloride (PCC), N-trimethyl chitosan chloride (TMC), sodium caprate (C10), and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-on the transport of clodronate using Caco-2 cell culture model. The transport experiments were performed in a normal (1.3mM) and in a minimum-calcium concentration (apically calcium-free medium and basolaterally 100 microM calcium concentration). In the normal calcium concentration, a strong enhancement in clodronate permeation was observed with the enhancers: EGTA (2.5mM), TMC (1.5% w/v), and PCC (0.2mM) increased the transport of 1mM clodronate 190-, 20-, and 10-fold, respectively, and the transport of 10mM clodronate 130-, 70-, and 35-fold. In the minimum-calcium concentration, the effects of the absorption enhancers on the transport of clodronate were not so potent: TMC, PCC, and EGTA caused 2- to 20-fold enhancement in clodronate permeation whereas C10 (10mM) was without any effect. According to the results, the permeation of clodronate through Caco-2 cells could be significantly promoted by the absorption enhancers, which cause widening of the tight junctions and, thus, increase the permeability of the paracellular route.

Tight junctional changes upon microwave and x-ray irradiation

Tight junctions (zonulae occludentes, ZO) are cellularly regulated dynamic structures sensitive to environmental stress agents including ionizing radiation. Radiation induced pathological alterations of the small intestine (gastrointestinal radiation syndrome) are related to altered ZO-mediated paracellular transport. We carried out a quantitative morphological evaluation of the murine jejunal epithelial tight junctional structure in freeze fracture replicas as changed upon whole body X-ray irradiation and low energy microwave exposition. X-ray treatment (4 Gy, 1, 24 h) brought about a partial dearrangement of the ZO strand network which regenerated only partially by 24 h. This observation is in line with data on paracellular permeability increases and ZO-bound calcium drop caused by X-ray irradiation. On the other hand, microwave treatment (16 Hz-modulated 2.45 GHz wave, 1 mW/cm2 power density, I h exposition, samples at I and 3 h after exposition) did not cause dearrangement but, rather an increase in the integration of thight junctional structure, which is in agreement with an increase in cytochemically detectable ZO-bound calcium.

Analytical method for monitoring concentrations of cyclosporin and lovastatin in vitro in an everted rat intestinal sac absorption model

Cyclosporin A (CSA) and lovastatin (LV) are lipophilic drugs, which show poor and erratic absorption when administered perorally. The permeability of these compounds can be increased transiently by altering the membrane characteristics of the absorptive epithelium by the use of sorption promoters (SPs). In the present work a simple validated HPLC method utilizing an isocratic mobile phase with short retention times for CSA and LV was developed in order to monitor their concentrations in Kreb's Ringer bicarbonate (KRB) solution in vitro in intestinal sac absorption model. The same method was utilized to determine the apparent permeability coefficients and absorption profiles of CSA and LV by a modified Wilson-Wiseman method. Drugs were analysed by a reversed-phase HPLC method using a Shim-pack C18 column. An isocratic mobile phase containing acetonitrile and water in the proportions 70:30 and 80:20 was used for the HPLC analysis of CSA and LV, respectively. The flow-rate was 2 ml/min and quantitative determinations were carried out at 215 nm at 70 degrees C for CSA. In the case of LV the flow-rate was 1 ml/min and detection was done at 238 nm at 25 degrees C. The method was found to be specific as none of the proposed SPs, components of KRB or intestinal sac artefacts interfered with the drug peaks. Recovery studies and intra- and inter-day variations were within statistical limits. The limits of detection were 250 and 10 ng/ml and the limits of quantitation were 400 and 30 ng/ml for CSA and LV, respectively. The calibration curve was found to be linear in concentration range of 0.5-6 microg/ml for CSA and 0.05-0.4 microg/ml for LV. The proposed method was found to be rapid and selective and hence can be applied for continuous monitoring of CSA and LV in vitro in intestinal sac absorption studies.

Chitosan for enhanced intestinal permeability: prospects for derivatives soluble in neutral and basic environments

In this study the effects of two chitosan salts, namely chitosan hydrochloride and chitosan glutamate (0.5 and 1.5% w/v), on the transepithelial electrical resistance (TEER) and permeability of Caco-2 cell monolayers, using the radioactive marker [14C]-mannitol, were investigated in a slightly acidic (pH 6.2) and neutral (pH 7.4) environment. Both salts are soluble in acidic conditions up to a concentration of 1.5% w/v and solutions of this strength, at a pH of 6.2, caused a pronounced lowering in the TEER of Caco-2 cell monolayers in the order of 70+/-1% (chitosan glutamate) and 77+/-3% (chitosan hydrochloride), 20 min after incubation started. In agreement with the TEER results the transport of the radioactive marker, [14C]-mannitol, was increased 25-fold (chitosan glutamate) and 36-fold (chitosan hydrochloride), respectively, at this pH. However, at a pH of 7.4 both salts are insoluble and prove to be ineffective since no reduction in the TEER values or increase in the transport of [14C]-mannitol were found. The results show that these chitosan salts are potent absorption enhancers in acidic environments. We conclude that there is a need for chitosan derivatives with increased solubility, especially at neutral and basic pH values, for use as absorption enhancers aimed at the delivery of therapeutic compounds in the more basic environment of the large intestine and colon.

Comparison of the effect of different chitosan salts and N-trimethyl chitosan chloride on the permeability of intestinal epithelial cells (Caco-2)

A partially quaternized chitosan derivative, N-trimethyl chitosan chloride (TMC) (degree of quaternization 12.28%), was synthesized and the effects of this novel polymer on the permeability of intestinal epithelial cells, using Caco-2 cell monolayers, were investigated and compared with those of chitosan hydrochloride and chitosan glutamate. Transepithelial electrical resistance (TEER) measurements at pH 6.20 revealed that all these polymers (0.25-1.5% w/v) caused an immediate and pronounced lowering in TEER values in the order chitosan hydrochloride (84% reduction after 2 h incubation) > chitosan glutamate (60% reduction) > TMC (24% reduction) at 0.25% w/v concentrations. At higher concentrations (up to 2.5% w/v), TMC was able to decrease the TEER further. Similar results were obtained in transport studies, using the hydrophilic radioactive markers, [14C]-mannitol (MW 182.2) and [14C]-polyethylene glycol 4000 (PEG-4000, MW 4000). Large increases in the permeation of these markers were found. The transport of [14C]-mannitol was increased 34-fold (chitosan hydrochloride), 25-fold (chitosan glutamate) and 11-fold (TMC) at 0.25% w/v concentrations. Further increases in the permeation of both markers were found at higher concentrations of TMC. Due to its quaternary structure, TMC is better soluble than the other chitosan salts, and its higher solubility may compensate for its lesser effectivity at similar concentrations. It is also soluble at pH 7.40, where the chitosan salts are insoluble and therefore ineffective. No deleterious effects to the cells could be demonstrated with trypan blue exclusion studies and confocal laser scanning microscopy (CLSM). CLSM confirmed that these polymers increase the transport of large hydrophilic compounds (using the fluorescent markers FD-4, MW 4400 and FD-20, MW 19,600) through opening of tight junctions to allow for paracellular transport. It is concluded from this study that the charge, charge density and the structural features of chitosans and chitosan derivatives are important factors determining their potential use as absorption enhancers.