TR146 CELLS GROWN ON FILTERS AS A MODEL FOR HUMAN BUCCAL EPITHELIUM .1. MORPHOLOGY, GROWTH, BARRIER PROPERTIES, AND PERMEABILITY

The characterization and functional application of filter-grown TR146 cells are presented. TR146 is a continued cell line of human buccal ep ithelial origin. Growth parameters indicated a saturation density in t he order of 2 x 10(5) cells/cm(2) and a doubling time ranging from 33 to 49 h dependent on type of support. Phase-contrast microscopy of the filter-grown TR146 cells showed morphologically epithelial-like cells . Transmission electron microscopy (TEM) of the TR146 cells, grown far 10 days (day of confluence) and until day 50 in culture, revealed a s tratified epithelium of 4-7 cell layers. The surface cells were flatte ned and clearly distinct from cells in the lower layers. Filter-grown TR146 cells express ultrastructural characteristics of normal human bu ccal epithelium, e.g., intermediate filaments, microvilli-like process es, no tight junctions, multilaminar bodies considered equivalent to m embrane coating granules, and absence of complete keratinization. The TEM of TR146 cells delineated an increasing number of organelles and d esmosomes with the advancing age of the culture. The maximum integrity of the cell layers was reached at around day 30 in culture, and was a ssessed by measuring the transepithelial electrical resistance (TEER) (55-120 Omega cm(2), n = 92), and by conducting permeability studies. The apparent permeability coefficient (P-app) of mannitol, a hydrophil ic marker of the paracellular transport pathway, declined until about day 30 in culture (P-app similar to 4 x 10(-6) cm/s). The permeability of the lipophilic marker testosterone did not alter from the time of confluence to day 50 in culture (P-app -2 x 10(-5) cm/s). An estimatio n of the thickness of the unstirred water layer (h(aq)) adjacent to th e filter with and without TR146 cells was conducted using testosterone and various agitation rates. At the highest agitation rate, 163 rpm, the h(aq) was approx. 1450 mu m (cellular permeability coefficient (P- c) of testosterone similar to 4 x 10(-4) cm/s). The TEER and P-app of mannitol and testosterone showed significant inter-passage variations (p < 0.05). The P-app values of testosterone and mannitol were not rel ated to postfeeding time, were independent of the initial drug concent ration, and were slightly dependent on the transport direction. The fu nctional application of the filter-grown TR146 cells testing the perme ability of various beta-adrenoceptor antagonists showed a positive cor relation between the P-c and the lipophilicity. The findings of this s tudy indicate that filter-grown TR146 cells has a potential to model t he human buccal epithelial permeation of drugs.