Permeability polycarbonate filters

Epithelial barrier models for the skin [48,49], respiratory tract [50], BBB, and intestine [39] are constructed to study and predict the absorption, penetration, and metabolism of drugs or environmental toxins through these barriers. All the models are physically tight structures, and generally involve cells cultured at the air-liquid interface on porous membrane support, such as a porous polycarbonate filter. The use of a permeable support allows cells to be grown in a polarized state under more natural conditions promote Cell differentiation and enhance cell functions. 

Efforts to stabilize BLMs by the use of polymerizable lipids have been successful, but the electrochemical properties of these membranes were greatly compromised and ion channel phenomena could not be observed [21]. Microfiltration and polycarbonate filters, polyimide mesh, and hydrated gels have been used successfully as stabilizing supports for the formation of black lipid films [22-25] and these systems were observed to retain their electrical and permeability characteristics [24]. Poly(octadec-l-ene-maleic anhydride) (PA-18) was found to be an excellent intermediate layer for interfacing phospholipids onto solid substrates, and is sufficiently hydrophilic to retain water for unimpeded ion transfer at the electrode-PA-18 interface [26]. Hydrostatic stabilization of solventless BLMs has been achieved by the transfer of two lipid monolayers onto the aperture of a closed cell compartment however, the use of a system for automatic digital control of the transmembrane pressure difference was necessary [27]. 

In order to analyse which lipidic compounds are involved in the altered membrane permeability, liposome studies were undertaken Large unilamellar vesicles (80-90 nm LUV) were prepared from purified pollen lipids, employing the technique of repeated extrusion at 500 psi through polycarbonate filters (0 1 /jm pore diameter). The fluorescent dye, 5(6)carboxy-fluorescein (CF), was entrapped during... 

Under prevalidation (ECVAM) we find the transepithelial resistance (TER) and para-ceUular permeability (PCP) in two renal cell lines (LLC-PKl, epithelial proximal tubular cells and MDCK, epithelial distal cells). TER measuranent and the transepithelial transport of uncharged small molecules like FlTC-inulin (PCP) are reliable parameters for characterising the intactness of an epithelial barrier. Cells are seeded onto 24-weU polycarbonate filter plates and then exposed to test substances. Barrier damage is measured for TER assessment and with fluorescence measuranent in the base plate for PCP (Duffet al.,2002). 

In the same way, o-nitrophenyl octyl ether (o-NPOE) was immobilized on polycarbonate (PC) filters and the apparent permeability measured after 5 h incubation time was correlated to log Pnpoe for a series of reference compounds (log Pnpoe ranging from —1 to 3.6) [90]. Lipophilicity values in the alkane/water system were also determined using PAMPA with hexadecane-PC coated filters [89]. In this case, a correlation was found between intrinsic permeability (log Pq, permeability corrected for ionization and for unstirred water layer contribution, which particularly affects permeability of lipophilic compounds) and log P ik. However, log Pq is obtained from the knowledge of the pJC, value(s) and the permeability pH profile and therefore requires the full permeability pH profile to be measured for each compound, which negatively impacts the assay throughput. 

Different filter supports have been tested nitrocellulose (NC), polycarbonate (PC), aluminium oxide (AO), polyethylenterephtalate (PET). NC filters have shown reduced non-specific binding compared to AO filters but seem to interact with marker PEG and steroids (Nicklin et al. 1992). AO filters displayed only half of permeability of PC for taurocholic acid. Reproducibility of binding and transport experiments was improved with PC filters (Hidalgo et al. 1989). Pore size is an important factor which needs to be considered and tested CACO-2 cells migrate through pores > 1 xm (Tucker et al. 1992 Hilgers et al. 1990). PET filters are translucent and allow microscopic observation as well as staining procedures. 

In vitro reconstituted models of the BBB from different mammalian species have been used since the late 1970s. However, their comparison is difficult because of the different species and methods used for isolation, culture, coculture, and characterization of the models. Lundquist et al. (2002) confirmed that the epithelial cells might not represent a valid and reliable in vitro BBB model, because results obtained on epithelial monolayers correlated poorly with in vivo BBB permeability values. Bowman et al. (1983) introduced the first in vitro BBB filter model. The insert was made of nylon mesh and polycarbonate tubing, and bovine brain endothelial cells were seated on it for stud5ung the effect of calcium-free medium and osmotic shock on sucrose flux. Since then, a variety of... 

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