Development and evaluation of a novel mucus diffusion test system approved by self-nanoemulsifying drug delivery systems.

The aim of this study was the development of a novel mucus diffusion model and the approval thereof by self-nanoemulsifying drug delivery systems (SNEDDSs). For diffusion experiments, various SNEDD formulations were developed, spiked with fluorescein diacetate, and evaluated for their mucus diffusion behavior through an intestinal mucus layer within the novel setup. In brief, SNEDD formulations resulting in particle sizes of 12.0 nm produced 70.3% of diffused model drug through the mucus layer. In comparison, SNEDDSs with particle sizes of 455.5 nm led to a permeation of 8.3% only. Apart from this size dependence, two SNEDDS excipients namely Cremophor RH 40 and triacetin were identified to strongly affect the permeation through mucus. Hence, it could be demonstrated that particle size and single excipients can positively influence mucus diffusion of SNEDDSs. Furthermore, it could be shown that the developed mucus diffusion model is a promising tool for pharmaceutical research in comparison with already established systems as it allows an easy handling coupled with the possibility to test different kinds of mucus in parallel within one setup.

Preactivated thiomers for vaginal drug delivery vehicles.

It was the purpose of this study to design and evaluate a chitosan derivative as mucoadhesive excipient for vaginal drug delivery systems. The chemical modification of chitosan was achieved by conjugation of thioglycolic acid (TGA) resulting in 1594 µmol thiol groups per gram of polymer followed by the linkage of mercaptonicotinic acid (MNA) to the immobilized thiol groups via disulfide bonding leading to 702 µmol ligand per gram of preactivated polymer. The mucoadhesive properties of these polymers within newly designed vaginal formulations (Chitosan-TGA and Chitosan-TGA-MNA) and commercially available vaginal formulations (Candibene®, Daktarin®, Dalacin®, GynoPevaryl®) were tested over a time period of 24 h via a mucoadhesion test system simulating vaginal conditions, tensile studies and mucus polymer interaction studies via viscosity measurements. Within the vaginal test system simulating vaginal in situ conditions, a 1.5-fold increase in mucoadhesion could be observed for preactivated thiomer formulations after 24 h in comparison to commercially available formulations. Similar results were achieved for tensile studies, as the chitosan-TGA-MNA containing formulation resulted in a 4.9-fold increase in total work of adhesion (TWA) in comparison to Candibene which showed the highest TWA value of all tested commercial formulations. Also in terms of rheology investigations of mucus/formulation mixtures, a 5.8-fold increase in dynamic viscosity for chitosan-TGA-MNA containing mixtures could be observed in comparison to the mucus-free control. In contrast, commercially available formulations achieved a maximum enhancement of 1.9-fold. These outcomes confirm that the newly developed polymer is a promising tool for vaginal drug delivery likely providing a prolonged vaginal residence time due to its comparatively high mucoadhesive properties.

Synthesis and in vitro characterization of a preactivated thiomer via polymerization reaction.

The objective of this study was to synthesize 6-(2-acryloylamino-ethyldisulfanyl)-nicotinic acid (ACENA) for subsequent copolymerization with acrylic acid (AA) as a new method for synthesis of preactivated thiomers. Copolymerization reactions of ACENA and AA with different molar ratios were performed and the molecular weight (M(w)) values of the resulting copolymers were calculated and reported from 3046 to 3271 Da. The disulfide bond content values in the polymer chain were determined from 400 to 544 µmol disulfide bond per gram polymer. The transport enhancement ratio for 0.5% (m/v) solution of poly(acrylic acid) (PAA) was 1.1 using sodium fluorescein (Na-Flu) as model drug, in Ussing-type chambers, whereas it was over 1.9 for 0.5% (m/v) solution of ACENA and AA copolymers. Resazurin cell-viability test showed no significant toxicity for the polymers. Copolymerization of AA and disulfide-bond-containing monomers can open new horizons for the preparation of preactivated thiomers taking the better controllability and the huge variety of available monomers and combinations thereof into account.

In vivo evaluation of an oral drug delivery system for peptides based on S-protected thiolated chitosan.

The aim of the present study was the development and evaluation in vitro as well as in vivo of an oral delivery system based on a novel type of thiolated chitosan, so-called S-protected thiolated chitosan, for the peptide drug antide. The sulfhydryl ligand thioglycolic acid (TGA) was covalently attached to chitosan (CS) in the first step of modification. In the second step, these thiol groups of thiolated chitosan were protected by disulfide bond formation with the thiolated aromatic residue 6-mercaptonicotinamide (6-MNA). Absorptive transport studies of antide were evaluated ex vivo using rat intestinal mucosa. Matrix tablets of each polymer sample were prepared and their effect on the absorption of antide evaluated in vivo in male Sprague-Dawley rats. In addition, tablets were examined in terms of their disintegration, swelling and drug release behavior. The resulting S-protected thiomer (TGA-MNA) exhibited 840µmol of covalently linked 6-MNA per gram thiomer. Based on the implementation of this hydrophobic ligand on the thiolated backbone, the disintegration behavior was reduced greatly and a controlled release of the peptide could be achieved. Furthermore, permeation studies with TGA-MNA on rat intestine revealed a 4.5-fold enhanced absorptive transport of the peptide in comparison to antide in solution. Additional in vivo studies confirmed the potential of this novel conjugate. Oral administration of antide in solution led to only very small detectable quantities in plasma with an absolute and relative bioavailability (BA) of 0.003 and 0.03%, only. In contrast, with antide incorporated in TGA-MNA matrix tablets an absolute and relative BA of 1.4 and 10.9% could be reached, resulting in a 421-fold increased area under the plasma concentration time curve (AUC) compared to the antide solution. According to these results, S-protected thiolated chitosan as oral drug delivery system might be a valuable tool for improving the bioavailability of peptides.

S-protected thiolated chitosan for oral delivery of hydrophilic macromolecules: evaluation of permeation enhancing and efflux pump inhibitory properties.

The objective of this study was the investigation of permeation enhancing and P-glycoprotein (P-gp) inhibition effects of a novel thiolated chitosan, the so-named S-protected thiolated chitosan. Mediated by a carbodiimide, increasing amounts of thioglycolic acid (TGA) were covalently bound to chitosan (CS) in the first step of modification. In the second step, these thiol groups of thiolated chitosan were protected by disulfide bond formation with the thiolated aromatic residue 6-mercaptonicotinamide (6-MNA). Mucoadhesive properties of all conjugates were evaluated in vitro on porcine intestinal mucosa based on tensile strength investigations. Permeation enhancing effects were evaluated ex vivo using rat intestinal mucosa and in vitro via Caco-2 cells using the hydrophilic macromolecule FD(4) as the model drug. Caco-2 cells were further used to show P-gp inhibition effects by using Rho-123 as P-gp substrate. Apparent permeability coefficients (P(app)) were calculated and compared to values obtained from each buffer control. Three different thiolated chitosans were generated in the first step of modification, which displayed increasing amounts of covalently attached free thiol groups on the polymer backbone. In the second modification step, more than 50% of these free thiol groups were covalently linked with 6-MNA. Within 3 h of permeation studies on excised rat intestine, P(app) values of all S-protected chitosans were at least 1.3-fold higher compared to those of corresponding thiomers and more than twice as high as that of unmodified chitosan. Additional permeation studies on Caco-2 cells confirmed these results. Because of the chemical modification and higher amount of reactive thiol groups, all S-protected thiolated chitosans exhibit at least 1.4-fold pronounced P-gp inhibition effects in contrast to their corresponding thiomers. These features approve S-protected thiolated chitosan as a promising excipient for various drug delivery systems providing improved permeation enhancing and efflux inhibition effects.