Targeting polymerised liposome vaccine carriers to intestinal M cells

Due to their transcytotic capability, intestinal M cells may represent an efficient potential route for oral vaccine delivery. We previously demonstrated that the lectin Ulex europaeus agglutinin 1 (UEA1, specific for alpha-L-fucose residues) selectively binds to mouse Peyer's patch M cells and targets 0.5 microm polystyrene microparticles to these cells. Using a gut loop model we now demonstrate that covalently-membrane-bound UEA1 similarly targets polymerised liposomes (Orasomes, approximately 200 nm diameter), potential biocompatable oral vaccine delivery vehicles, to mouse M cells. Targeting was inhibited by alpha-L-fucose while the co-entrapped adjuvant, monophosphoryl Lipid A (MPL), failed to exert any detrimental effect on UEA1-mediated M cell targeting. Lectin-mediated M cell targeting may thus permit the efficacy of mucosal vaccines to be enhanced if cellular relationship between particle binding and immune outcome can be established.

Expression of specific markers and particle transport in a new human intestinal M-cell model

The aim of this work was to establish a new, simplified in vitro model of the human M-cell. Cocultures of physically separated human intestinal epithelial Caco-2 cells and B-cell lymphoma Raji cells were established. The cocultures were characterized under the criteria of morphology, integrity, expression of M-cell markers and cell adhesion molecules (CAMs), and altered particle transport. Using this construct, the epithelial cells were transformed to cells with an M-cell-like morphology and had altered expression of potential human M-cell markers (alkaline phosphatase down-regulation and Sialyl Lewis A antigen up-regulation). The expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule was altered and there was an increased binding of lectins wheat germ agglutinin and peanut agglutinin with a 40-fold increase in microparticle transport. The particle transport was size-dependent and could be inhibited at 4 degrees C or by replacing the Raji B-cells with Jurkat T-cells. This new coculture model will enable controlled studies of M-cell development and function in vitro.

Evaluation of the Caco-2 monolayer as a model epithelium for iontophoretic transport

PURPOSE

To assess the Caco-2 monolayer as a model for iontophoresis of drugs across a model epithelium.

METHODS

The apparent permeability co-efficient (Papp) of mannitol, thyrotrophin releasing hormone (TRH), dexamethasone and a range of sizes of fluorescein isothiocyanate (FITC) dextrans across Caco-2 monolayers was measured under passive and electrically stimulated conditions. Trans-epithelial electrical resistance (TEER) was determined throughout. Transmission electron micrographs (TEM) of the monolayers were taken. Confocal laser scanning microscopy (CLSM) was used to visualize the iontophoretic transport route of FITC-Dextran (MW = 20 kDa) across a Caco-2 monolayer.

RESULTS

Application of 14.3 micro-Eq x cm(-2) across the monolayer evoked a transient drop in TEER. The drop in TEER was accompanied by statistically significant increases in fluxes of all the agents in the mucosal to serosal direction except for FD-70. TEM of test samples exhibited tight junction dilatation, in addition to intracellular vacuolisation. The iontophoresis of FD-20 was visualised with confocal laser scanning microscopy and was localised in paracellular spaces of the monolayer.

CONCLUSIONS

The fluxes of mannitol, TRH, dexamethasone, FD-4, FD-10 and FD-20 across the Caco-2 monolayer were significantly enhanced when electric field was applied. The iontophoretic effect appeared to be directly upon tight junctions

Binding and uptake of biodegradable poly-DL-lactide micro- and nanoparticles in intestinal epithelia

The use of biodegradable particles as oral delivery vehicles for macromolecular drugs was investigated. We evaluated the binding, uptake and absorption of poly-dl-lactide (PLA) micro- and nanoparticles in Caco-2 monolayers and in ileal tissue and gut associated lymphoid tissue (GALT) of anaesthetised rats and rabbits. Using a range of experimental techniques, we found that approximately 10% of administered micro- and nanoparticles were adsorbed to the apical membranes of each of the five intestinal models. Nanoparticles were found to be absorbed better than microparticles. Overall, little discrimination in uptake patterns was evident between Peyer's patch (PP) and non-PP tissue while rat ileum showed a greater uptake capacity than rabbit. Our results show that uptake of PLA particles was low capacity, size-dependent and predominantly transcellular in all systems. A low proportion of the apically-bound particles was absorbed, with uptake exclusion evident for particles >4microm. The affinity of PLA particles for intestinal epithelia and GALT needs to be greatly enhanced in order to achieve improved oral bioavailability of macromolecules.

Heparin absorption across the intestine: effects of sodium N-[8-(2-hydroxybenzoyl)amino]caprylate in rat in situ intestinal instillations and in Caco-2 monolayers

PURPOSE

The effects of sodium N-[8-(2-hydroxybenzoyl)amino]caprylate (SNAC) on heparin intestinal absorption were studied using rat in situ ileal and colonic instillations and Caco-2 monolayers.

METHODS

The flux of heparin was tested in the following groups: i) heparin alone, ii) heparin in the presence of SNAC, iii) heparin in the presence of propylene glycol (PG), and iv) heparin in the presence of SNAC and PG. Heparin absorption was measured by the APTT assay in the in situ models and by the anti-Factor Xa assay in Caco-2. SNAC and [3H]-SNAC fluxes were assessed by HPLC and by scintillation counting respectively.

RESULTS

In the rat ileal and colonic in situ instillations SNAC (17-35 mg) promoted heparin absorption in the presence and absence of PG without damaging the tissue. PG alone did not alter heparin absorption in situ, but it amplified the effect of SNAC. In Caco-2, enhanced heparin fluxes were variable in the presence of non-cytotoxic concentrations of SNAC (< 10 mg/ml) and these effects could not be discriminated from those of PG. Papp values for SNAC alone were 2.2 x 10(-5) cm/s and 2.0 x 10(-5) cm/s in the mucosal-to-serosal and serosal-to-mucosal directions respectively, suggesting a substantial passive transcellular flux. Transport of SNAC was significantly reduced in the presence of heparin and/or PG, perhaps indicating physical association between the agents.

CONCLUSIONS

SNAC augmented heparin absorption alone and in combination with PG in the rat in situ models without causing toxicity. Caco-2 had limitations for testing increased heparin absorption due to cytotoxic effects of high concentrations of SNAC and PG. However, SNAC itself was well absorbed across Caco-2 and its mechanism of permeation was determined.