An in vitro mucosal model predictive of bioadhesive agents in the oral cavity.

The formulation of a drug/carrier complex that can be distributed and retained for extended periods within the oral cavity would be advantageous in the treatment of local conditions. In this study, an in vitro system was developed to investigate the binding of bioadhesive macromolecules to buccal epithelial cells, without having to alter their physicochemical properties by the addition of 'marker' entities. In this innovative approach a lectin binding inhibition technique, involving an avidin-biotin complex and a colourmetric detection system, was used to evaluate polymer binding. 0.5% w/v polymer solutions in saline (pH 7.6) were left in contact with a standardized number of freshly collected human buccal cells for 15 min. The cells were then exposed to 10 mg L(-1) biotinylated lectin from Canavalia ensiformis followed by 5 mg L(-1) streptavidin peroxidase. The inhibition of lectin binding (i.e. by 'masking' of the binding site on the cell surface by the attached bioadhesive polymer) was measured and expressed as a percentage reduction in the rate of o-phenylenediamine oxidation over 1 min. From the wide range of polymer solutions screened, chitosan gave the greatest inhibition of lectin binding to the surface of buccal cells, while methylcellulose, gelatin, Carbopol 934P and polycarbophil also produced a substantial reduction. Lectin binding inhibition was also observed for a selected number of polymer solutions when screened at pH 6.2. The presence of bound chitosan, polycarbophil and Carbopol 934P on the buccal cell surface was confirmed using direct staining techniques. It was concluded that this assay can be used to detect polymer binding to the cells present on the buccal mucosa, and the information gained used in the development of retentive drug/polymer formulations.