Rabbits buccal

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. 

Dowty ME, Knuth KE, Irons BK, Robinson JR (1992) Transport of thyrotropin releasing hormone in rabbit buccal mucosa in vitro. Pharm Res 9 1113-1122... 

Gandhi R.B., and J.R. Robinson. 1991. Permselective characteristics of rabbit buccal mucosa. Pharm Res 8 1199. 

Gandhi, R.B. Some Permselectivity and Permeability Characteristics of Rabbit Buccal Mucosa. Ph.D. thesis. University of Wisconsin Madison, 1990. 

Yamamoto et al. [4] showed that 0.01% aprotinin (a serine protease inhibitor) reduced the metabolism of insulin and proinsuHn in homogenates of albino rabbit buccal mucosa, which otherwise would have occurred at 70-80% within 2.5 hours. Moreover, Lehr et al. suggest that polycar-bophil, a bioadhesive polymer, may protect some peptides from proteolysis, though the mechanism of this is unknown [5]. Others [6] have developed a series of pro-dmgs for peptides, with the aim of overcoming the metabohc barrier imposed by different peptidases. Stable prodrugs proved to be N-hydroxymethylated derivatives of the assessed dipeptides Gly-L-Leu and Gly-L-Ala [6]. 

Shin SC, Bum JP, and Choi JS (2000) Enhanced bioavailability by buccal administration of triamcinolone acetonide from the bioadhesive gels in rabbits. Int. J. Pharm. 209 37—43. 

Similarly, the 4-methoxy-2-naphthylamides of Leu, Ala, Arg, and Glu (6.1, R=side chain of amino acid, R =MeO) were used to assess the type and activity of aminopeptidase in homogenates of conjunctival, nasal, buccal, duodenal, ileal, rectal, and vaginal tissues from rabbits. This systematic comparison afforded a better understanding of the role of the aminopeptidase barrier in peptide absorption from oral vs. non-oral routes [18]. In a comparable manner, the y-glutamyltranspeptidase and dipeptidase activities were investigated in mammary tissue with the 4-nitroanilides of Leu, Met, Lys, Glu, and Asp (6.2, R=side chain of amino acid) [19]. 

FIG. 3. The force of detachment from excised rabbit intestinal mucosa for directly compressed buccal tablets which contained 40 mg CPM (chlorpheniramine maleate) and 0, 2, 12, 22, and 32 mg Hakea applied to the mucosa with a force of 5 N (— —), 10 N (—0—), 15 N (—O—), and 20 N (—A—). All data points represent the mean value standard deviation of ten experiments. Lines through mean values are included to illustrate the trend and represent a mathematical fit of the data as well (from Ref. 29). 

In vitro permeation studies employ a glass diffusion cell with the buccal tissue mounted between the two halves of the eell whieh may be filled with constantly stirred buffer solutions. The bueeal mueosa is exeised from the eanine, porcine, or rabbit eheek immediately after saerifiee. Permeation studies may provide meaningful results on the simultaneous proeesses of drug transport and metabolism in the tissue... 

Tannins derive their name from their ability to tan (i.e. they combine with protein). They render plants less palatable and impair digestion by binding with the buccal mucosa, dietaiy proteins, and digestive enzymes of the animal. Tannins are thought to bind to proteins upon destruction of plant tissue by herbivores. This reduces the nutritive value of the plant to the herbivore. Some tannins such as oak gallotannins, are even toxic to livestock and rabbits (Meyer and Karasov, 1991). However, Martin and Martin (1983) have questioned the role of tannins as plant defense against herbivores. 

Transmucosal delivery of salmon calcitonin (sCT) via the buccal route was studied using a mucoadhesive bilayer thin-film composite (TFC) [104], In vitro studies showed that over 80% of sCT was released from the TFCs within 240 min. The relative bioavailability for rabbits treated with the film composites was 43.8% + 10.9% as compared to intravenous injection. 

Cui, Z., and R.J. Mumper. 2002. Bilayer films for mucosal (genetic) immunization via the buccal route in rabbits. Pharm Res 19 947. 

Li, C., et al. 1997. Transmucosal delivery of oxytocin to rabbits using a mucoadhesive buccal patch. Pharm Dev Technol 2 265. 

FIGURE 22.6 Permeability and permselectivity of vaginal and buccal epithelia in the rabbit, (a) Flux of 6-carboxyfluoroscein, a hydrophilic molecule, by in vitro perfusion studies steady-state flux ( xg/cm2/h x 106), (b) resistance (fl cm2 x 10 2), (c) thickness (p,m x 10-2), and (d) ratio of potassium transport number to chloride transport number, which is calculated from electrical measurements, used as indicative of the epithelium selectivity for positively charged molecules. (Modified from Sayani, A.P. and Chien, Y.W., Crit. Rev. Ther. Drug Carrier Syst. 13, 85, 1996.)... 

Figure 1. Buccal Mucosa of the Rat - epidermis covered by thick keratinized layer lining the cheek. This type of cheek pouch lining was seen in all rodents studied, including mouse, guinea pig, rat and rabbit.

Human oral mucosa consists of different cell types including keratinized and non-keratinized striated epithelial, but the buccal mucosa is composed predominately of the latter. In selecting an appropriate animal model care was taken to ensure that the mucosal structure in the selected species matched that in man as closely as possible. Based on histological examinations all the rodent species (rat, guinea pig, hamster and rabbit) would constitute poor models because of extensive keratinization of their buccal mucosa. Of the other possibilities, the dog appeared to be the best choice. 

In addition, the buccal delivery of insulin in rabbits has been shown to be increased from approximately 3-5% by co-administration of edetate (least effective), sodium dextransulfate, sodium methoxysalicylate, sodium deoxycholate, sodium lauryl sulfate, sodium taurocholate and Brij 35 (most effective) with Brij 35 increasing the bioavailability of insulin to 12% by this route. 

The buccal mucosae from monkeys, apes, dogs, pigs, and rabbits possess physiology very similar to that of human buccal mucosa. 

Extent of Damage to Mucosal Cells. Permeation enhancement implies possible alteration of the protective permeability barrier either by 1) an increase in the fludity of intercellular lipids (relatively non-toxic) and/ or 2) extraction of intercellular lipids or denaturation of cellular proteins (much more damaging/toxic). Therefore, it is imperative that the permeation enhancer 1) exert a reversible effect 2) not be systemically absorbed and 3) not cause cumulative toxicity or permanent changes in the barrier properties. Application of up to 1% sodium lauryl sulfate or cetylpyridinium chloride to the ventral surface of the tongue of dogs resulted in desquamation, widening and separation of keratin.f The buccal mucosa of rabbits treated with... 

Dali, M.M. Heran, C.L. Kaeppeli, M. Stetsko, P.I. Smith, R.L. Intra-oral (buccal/sublingual) bioavailablity of propranolol in conscious rabbits as a function of PH and dosing variables. Proceedings of the American Association of Pharmaceutical Scientists Annual Meeting, New Orleans, LA Nov 19-23, 1999,1394 Abstract Number 2559. 

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