Epithelium, buccal mucosa

Keywords Buccal mucosa Permeability barrier Passive diffusion Excised tissue Nonkeratinized epithelium Diffusion chamber... 

The buccal mucosa, which lines the inside of the cheek, has been investigated as an alternative route for drug delivery, especially for proteins and peptides. There are many advantages associated with the use of the buccal mucosa as a site for the delivery of drugs into the systemic circulation. Since blood flow from the buccal epithelium drains directly into the internal jugular... 

Because of the possible effects of active and carrier-mediated processes and metabolic biotransformation, the issue of tissue viability is important for in vitro buccal mucosal experiments. The barrier nature of the buccal mucosa resides in the upper layers of the epithelium, where unlike in the stratum corneum, the cells contain a variety of functional organelles [119, 122, 125, 150], and so tissue viability may be an important component of the barrier function of the tissue. Various methods have been employed to assess the viability of excised buccal mucosa, including measurement of biochemical markers, microscopic methods, and linearity of transport data [42], While biochemical methods, including measurement of adenosine 5 -triphosphate (ATP) levels and utilization of glucose, provide information on the metabolic activity of the tissue, this does not necessarily relate to the barrier function of the tissue. In excised rabbit buccal mucosa, levels of ATP were measured and found to decline by 40% in 6 h, and this correlated well with transmission electron microscopic evaluation of the tissue (intact superficial cells) [32], In addition, the permeability of a model peptide was unaltered up to 6 h postmortem, but at 8 h, a significant change in permeability was observed [32], These investigators therefore claimed that excised rabbit buccal mucosa could be used for diffusion studies for 6 h. 

In our laboratory, the viability of excised porcine buccal mucosa was assessed using histological evaluation and a 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) biochemical assay which has previously been used in assessing the viability of excised buccal mucosa and cornea [49, 50], Histological evaluation of tissue demonstrated that the buccal epithelium appeared viable up to 9 h postmortem, and this was supported by the MTT biochemical assay, which indicated that viability was maintained for up to 12 h [80], Therefore, we recommend that all permeation experiments using porcine buccal mucosa be performed within 9-12 h of animal death. 

Nielsen HM, Rassing MR (2000b) TR146 cells grown on filters as a model of human buccal epithelium IV. Permeability of water, mannitol, testosterone and P-adrenoceptor antagonists. Comparison to human, monkey and porcine buccal mucosa. Int J Pharm 194 155-167... 

Figure 7.4 Correlation analysis for Tapp values across cultured human buccal epithelium and freshly isolated human buccal mucosa of Lucifer yellow, enalaprilat, atenolol, caffeine, sumatriptan, and fentanyl. Results from internal study by Absorption Systems Company.

Agarwal V, Habib W, and Moe D (2005) Effervescent mediated transmucosal enhancement of fentanyl permeability Comparison across ex vivo porcine buccal mucosa and in vitro cultured human buccal epithelium test. American Association Pharm. Sci. Abs. T2126. 

Landay, M.A., and H.E. Schroeder. 1979. Differentiation in normal human buccal mucosa epithelium. J Anat 128 31. 

The thickness of the buccal epithelium varies from 10 to about 50 cell layers in different regions because of serrations in connective tissue. In fact, the thickness of buccal mucosa has been observed to be 580 pm, the hard palate 310 pm, the epidermis 120 pm, and the floor of mouth mucosa 190 pm. 

The cross-sectional structure of the buccal mucosa is shown in Fig. 2.7. The buccal mucosa consists of the epithelium and the underlying connective tissue, the lamina propria, separated by a basement membrane. 

The permeability of the oral mucosal epithelium is intermediate between that of the skin epithelium, which is highly specialized for a barrier function (see Section 8.1) and the gut, which is highly specialized for an absorptive function. Within the oral cavity, the buccal mucosa is less permeable than the sublingual mucosa. 

A rich blood supply and lymphatic network in the lamina propria serve the oral cavity, thus drag moieties which traverse the oral epithelium are readily absorbed into the systemic circulation. The blood flow in the buccal mucosa is 2.4 mL min 1 cm 2 whereas that to the sublingual mucosa is 0.97 mL min-1 cm 2. 

The human vaginal epithelium is composed of noncomified, stratified squamous cells, similar to those of the buccal mucosa (see Section 7.2.1) and somewhat similar to the skin epithelium (see Section 8.2.1). The vaginal epithelium is composed of five different cell layers ... 

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