Optimization of an Ex Vivo Method for Bioadhesion Quantification

An ex vivo method for quantification of the bioadhesion between a polymer of acrylic acid (Carbopol® 934) and a piece of bovine sublingual mucosa is described. The procedure uses a tensile tester coupled with a data acquisition system and relies upon the principle of a peel test. Mucoadhesion has been evaluated by the work of elongation of the mucosal sample during the detachment of the tablet. The reproducibility of the result obtained depends primarily upon the thickness of the tissue and the hydration conditions.Eine ex vivo-Methode zur Quantifizierung der Bioadhäsion von Polyacrylaten (Carbopol® 934) auf sublingualen Schleimhautstücken von Rindern wird beschrieben. Die Prüfungsmethode verwendet ein Tensiometer, das mit einem Datenverarbeitungssystem verbunden ist. Die Methode beruht auf dem Prinzip eines Abschältests. Die Mucoadhäsion wird durch die Bestimmung der Verlangerungsarbeit des Schleimhautstückes während der Ablösung der Tablette definiert. Die Reproduzierbarkeit der Ergebnisse hängt primär von der Dicke der Schleimhaut und dem Grad ihrer Hydratation ab

An investigation of the physical behaviour of moisture-activated mucoadhesive hydrogels upon contact with biological and non-biological substrates

The physical behaviour of moisture-activated mucoadhesive hydrogels in contact with a Plexiglas® plate or artificial mucin gels was investigated using an adapted tensile tester fitted with force and displacement transducers. Our study of the ‘Plexiglas®-hydrogel’ interface showed that the intrinsic mechanical response of most poly(acrylic acid) polymers is quite different from that exhibited by cellulose derivatives. The former exert an attractive interaction towards the substrate in contrast to the latter where the interaction is essentially repulsive. The interfacial forces developed by pure mucin were closely related to those of poly(acrylic acid) polymers. Similar results were observed when the Plexiglas® was replaced by artificial mucin gels. A correlation was found between the attractive force developed by poly(acrylic acid) hydrogels towards the inert substrate and their in vitro mucoadhesive joint strength. Therefore, a non-specific physical interaction occurs during the initial adhesive process, whatever the nature of the substrate. Besides the water absorption capacity and swelling properties of the candidate materials, it seems that their initial mucoadhesiveness depends more on their mechanical response to hydration and less on the extent of molecular interactions at the adhesive interface

Synthesis and characterization of an acylated di-peptide (Myr-Trp-Leu) with modified transmucosal transport properties

In order to improve the buccal absorption of a dipeptide model compound, Tryptophan-Leucine (Trp-Leu), we have synthesised a lipophilic derivative by myristoylation of the N- terminal amino group of Trp-Leu. The acylated peptide (Myr-Trp-Leu) was characterized by HPTLC, purified and isolated by chromatography on a silica gel column. Its structure was confirmed by (13)C and (1)H NMR and mass spectroscopy. The increased lipophilicity of the Myr-Trp-Leu was compared to that of the native peptide by chromatography and by its partition coefficient between n-octanol and saline phosphate buffer. In addition, the sensitivity towards hydrolytic enzymes was studied. The interaction of Trp-Leu with liposomes as model membranes was also studied. The phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) was lowered in the presence of Myr-Trp-Leu, while it was increased in the presence of native parent peptide. Permeation experiments performed in vitro with pig buccal mucosa showed that the Myr-Trp-Leu accumulated in the tissue at the various concentrations tested. In contrast, the native peptide was able to pass through the membrane at all concentrations used. Lipophilic modification of the peptide by acylation drastically changes its behaviour towards tissue systems

Factors and strategies for improving buccal absorption of peptides

Peptides and polypeptides have important pharmacological properties but only a limited number (e.g. insulin, oxytocin, vasopressin) have been exploited as therapeutics because of problems related to their delivery. The buccal mucosa offers an alternative route to conventional, parenteral administration. Peptides are generally not well absorbed through mucosae because of their molecular size, hydrophilicity and the low permeability of the membrane. Peptide transport across buccal mucosa occurs via passive diffusion and is often accompanied by varying degrees of metabolism. This review describes various approaches to improve the buccal absorption of peptides including the use of penetration enhancers to increase membrane permeability and/or the addition of enzyme inhibitors to increase their stability. Other strategies including molecular modification with bioreversible chemical groups or specific formulations such as bioadhesive delivery systems are also discussed

Lipid extracting effect of ethanol on keratinized oral mucosa

Ethanol has been widely used as a percutaneous penetration enhancer and its action on the cutaneous barrier has been well studied. Ethanol may have a "tluidisation" effect on the intercellular lipids of the stratum comeum, the insertion of ethanol between endogenous lipid provokes an increase in structural disorder. This effect has been reported to occur at low ethanol concentrations (25% v/v) (1) and has been compared to the effect of increasing skin temperature (2). An increasing extraction of epidermal lipids with increasing ethanol concentrations, has also been reported as the major mechanism by which alkanols promote transdermal penetration (3). It has been observed that very high alkanol concentrations (> 75% ), result in significant lipid extraction and with 100% ethanol treatment, full thickness skin appears to be devoid of its barrier and even behaves like stripped skin ( 1,4 ). Bath contact time and ethanol concentration influence whether or not the effects of ethanol treatment are reversible (1,3-5). As in the skin, the action of ethanol on oral mucosa depends upon the amount of alcohol in contact with the membrane and the contact time (6). As the ethanol concentration is increased, there is a greater lipid extraction, accompanied by a reorganization of the intercellular lipids. Therefore, one can expect that treatment with high ethanol levels for long periods, will produce a greater perturbation of the membrane. Based on the evidence described above, in this study we have addressed the following objectives: (a) To determine the action of ethanol as a lipid extracting solvent, on keratinized oral mucosa. (b) To separate, identify and quantify the Iipids present in the hydroalcoholic treating solutions. (c) To determine the relative importance of ethanol concentration and contact time on lipid extraction

Permeation of a myristoylated dipeptide across the buccal mucosa: topological distribution and evaluation of tissue integrity

The ex vivo permeation of an acylated model dipeptide, Myristoyl-Tryptophan-Leucine (Myr-Trp-Leu) was studied using pig buccal mucosa. Myr-Trp-Leu, being lipophilic, did not readily penetrate across the membrane. Rather, it accumulated in the epithelial and connective tissue of the mucosal barrier. The topological distribution of Myr-Trp-Leu across the mucosa, following its application in ethanol/phosphate buffer (30/70 pH 7.4), was determinated by thin-sectioning of the tissue, extraction of the peptide, and high performance thin layer chromatography (HPTLC). The concentration profile depended, of course, on the duration of the experiment and appeared to be dependent upon the presence of sufficient ethanol in order that the peptide could be solubilized. This important role for ethanol then raised the question of the solvent's effect on tissue integrity. Light microscopic examination of the mucosa was, therefore, undertaken, under identical conditions to those used in the permeation experiments, to evaluate any perturbation induced by the ethanolic vehicle. No obvious effects were observed

Comparison of the ex-vivo oral mucosal permeation of tryptophan-leucine (Trp-Leu) and its myristoyl derivative

The ex vivo permeation of a model peptide, tryptophan-leucine (Trp-Leu), was studied using two different regions of pig oral mucosa, the hard palate and the cheek. In order to increase the mucosal absorption of Trp-Leu, a lipophilic derivative was synthesized by acylation of the N-terminal amino group of Trp-Leu with myristic acid. The purified Trp-Leu derivative (Myr-Trp-Leu) was more lipophilic than the parent Trp-Leu as observed by HPTLC (Rf's values of 0.41 and 0.81, respectively). Measurement of partition coefficients in n-octanol/phosphate buffer pH 7.4, gave Kp values of −0.68 and 1.04 for Trp-Leu and Myr-Trp-Leu, respectively. The native Trp-Leu was unable to pass through the keratinized layer of palatal mucosa, and after 24 h only 12% had passed through the buccal mucosa to the receptor compartment. The higher lipophilicity of the acylated peptide, meant that it was not easily transported across the oral mucosal barrier but accumulated in the tissue, founding 25 and 70% of the original amount in the palatal and buccal mucosae, respectively. Both, Trp-Leu and Myr-Trp-Leu were found to be stable in palatal and buccal mucosae