Flavia Laffleur

Thiolated chitosan nanoparticles for the nasal administration of leuprolide: Bioavailability and pharmacokinetic characterization

The purpose of this study was to develop thiolated nanoparticles to enhance the bioavailability for the nasal application of leuprolide. Thiolated chitosan-thioglycolic acid (chitosan-TGA) and unmodified chitosan nanoparticles (NPs) were developed via ionic gelation with tripolyphosphate (TPP). Leuprolide was incorporated during the formulation process of NPs. The thiolated (chitosan-TGA) NPs had a mean size of 252 ± 82 nm, a zeta potential of +10.9 ± 4 mV, and payload of leuprolide was 12 ± 2.8. Sustained release of leuprolide from thiolated NPs was demonstrated over 6h, which might be attributed to inter- and/or intramolecular disulfide formation within the NPs network. Ciliary beat frequency (CBF) study demonstrated that thiolated NPs can be considered as suitable additives for nasal drug delivery systems. Compared to leuprolide solution, unmodified NPs and thiolated NPs provoked increased leuprolide transport through porcine nasal mucosa by 2.0 and 5.2 folds, respectively. The results of a pharmacokinetic study in male Sprague-Dawley rats showed improved transport of leuprolide from thiolated NPs as compared to leuprolide solution. Thiolated NPs had a 6.9-fold increase in area under the curve, more than 4-fold increase in elimination half-life, and a ∼3.8-fold increase in maximum plasma concentration compared to nasal solution alone. The relative nasal bioavailability (versus s.c. injection) of leuprolide thiolated NPs calculated on the basis of AUC((0-6)) was about 19.6% as compared to leuprolide solution 2.8%. The enhanced bioavailability of leuprolide is likely due to facilitated transport by thiolated NPs rather than improved release.

In vivo evaluation of an oral self-microemulsifying drug delivery system (SMEDDS) for leuprorelin

The objective of this study was to develop a self-microemulsifying drug delivery system (SMEDDS) for the model peptide drug leuprorelin to prove a protective effect against luminal enzymatic metabolism. In order to incorporate leuprorelin into microemulsion droplets (o/w), the commercially available hydrophilic leuprolide acetate was modified by hydrophobic ion paring with sodium oleate. The obtained hydrophobic leuprolide oleate was dissolved in the SMEDDS formulation (30% (m/m) Cremophor EL, 30% (m/m) Capmul MCM, 10% (m/m) propylene glycol and 30% (m/m) Captex 355) in a concentration of 4 mg/g showing a mean droplet size of 50.1 nm when dispersed in a concentration of 1% (m/v) in phosphate buffer pH 6.8. The microemulsion was able to shield leuprolide oleate from enzymatic degradation by trypsin and α-chymotrypsin, so that after 120 min 52.9% and 58.4%, respectively, of leuprolide oleate were still intact. Leuprolide acetate dissolved in an aqueous control solution was completely metabolized by trypsin within 60 min and by α-chymotrypsin within 5 min. Moreover, an in vivo study in rats showed a 17.2-fold improved oral bioavailability of leuprolide oleate SMEDDS compared to a leuprolide acetate control solution. This is the first time, to our knowledge, that hydrophobic ion pairing is utilized in order to incorporate a peptide drug in SMEDDS and evidence of a protective effect of oil-in-water (o/w) microemulsion droplets against enzymatic degradation of a peptide drug was provided. According to these results, the system could be likely a novel platform technology to improve the oral bioavailability of peptide drugs.

Mucoadhesive polymers for buccal drug delivery

Abstract Raising the concept of mucoadhesion in the 1980s, the use of mucoadhesive polymers for buccal drug delivery has been the subject of interest. Buccal route is one of the non-invasive routes comprising several advantages such as targeting the specific tissue (I), bypassing the first-pass effect (II) as well as higher patient compliance (III) and higher bioavailability (IV) have rendered administration route feasible for a variety of drugs. This review highlights the use of mucoadhesive polymers in buccal drug delivery. An overview of the oral mucosa’s anatomy, theories of mucoadhesion as well as mucoadhesive polymers is given within this review. Furthermore, recent advantages in mucoadhesive polymers according to the variety of drug delivery forms are presented.

Development and in vitro evaluation of slippery nanoparticles for enhanced diffusion through native mucus

AIM The aim of this study was to investigate the mucus-penetrating properties of neutral nanoparticles comprising poly(acrylic acid) (PAA) and poly(allylamine) (PAM). MATERIALS & METHODS PAA and PAM nanoparticles were prepared on the basis of ionic interactions between the two polymers. Nanoparticles were characterized by particle size as well as surface charge. The cytotoxicity was examined via resazurin and lactate dehydrogenase assays. Using a modified Ussing chamber with mucus, the diffusion properties of obtained neutral nanoparticles were compared with control particles. RESULTS The obtained PAA-PAM nanoparticles demonstrated no significant cytotoxicity and displayed smooth and spherical surfaces, a particle size range of 200 nm and ζ-potential of 0.9 mV. The diffusion efficiency of neutral nanoparticles was 2.5- and 1.8-fold higher than PAM and PAA nanoparticles, respectively. CONCLUSION Taking enhanced mucus-penetrating properties into account, neutral nanoparticles were shown to be very promising in drug delivery via mucus membranes of different cavities.

Thiomers: promising platform for macromolecular drug delivery

The application of macromolecules as therapeutic agents holds great promise for several major disorders such as cancer and cardiovascular disease. However, their use is limited by the lack of efficient, safe and specific delivery strategies. A promising strategy to overcome these challenges might be the use of thiolated polymers or designated thiomers. Thiomers are synthesized by immobilization of sulfhydryl bearing ligands on a polymeric backbone of well-established polymers. These multifunctional polymeric excipients show advantages in mucoadhesion, enzyme and efflux pump inhibition in comparison to unmodified polymers. One obstacle in the use of thiomers is that they are prone to oxidation at lower pH but this could be solved by introducing a completely new generation of thiomers, namely, the preactivated thiomer generation. Preactivated thiomers are mixed disulfides, which exhibit oxidation resistance and, beyond that, improved thiomer features. This review summarizes recent findings of polymeric excipients for macromolecular drug delivery as well as their synthesis and distinctive features.

Strategies for improving mucosal drug delivery

Within this review we will provide a comprehensive understanding in order to improve existing strategies and to develop new systems to lower the barrier for improving mucosal drug delivery. Mucosal administration of drugs achieves a therapeutical effect as the permeation of significant amounts of a drug is permitted through the absorption membrane. The absorption membrane relies on the mucosal layer and the epithelial tissue. In order to overcome barriers, drug delivery systems have to exhibit various functions and features, such as mucoadhesive and protective activity, solubility improving, permeation and uptake enhancing, and drug release controlling properties. This review also aims to provide an insight of well-distinguished strategies to date, as well as provide a focus on the enhancement of membrane permeability. Furthermore, since the development and functions of drug delivery systems exert a high influence on the ability of drug permeation through membrane, these considerations will also be discussed in this review.

HEC-cysteamine conjugates: influence of degree of thiolation on efflux pump inhibitory and permeation enhancing properties.

Within the present study hydroxyethyl cellulose-cysteamine conjugates are investigated regarding biocompatibility, in situ gelling, permeation enhancing and efflux pump inhibitory properties. For this purpose, a series of concentrations of sodium periodate was prepared to oxidize HEC leading to ring opening of glucose subunits. The resulting polymers showing varying degrees of oxidation (DO) were then conjugated with cysteamine stabilized via reductive amination. Consequently, HEC-cysteamine conjugates with increasing degree in thiolation were obtained. Since the conjugates are positively charged, potency of cytotoxicity was tested by resazurin assay. In situ gelling properties of the conjugates were studied to investigate change of their viscosity due to inter- and/or intramolecular crosslinking via disulfide bonds. The influence of the presence of the conjugates on transport of rhodamine 123 and fluoresceinisothiocyanate-dextran 4 (FD4) representing model compounds for P-glycoprotein (P-gp) inhibition and permeation enhancing studies, respectively, across Caco-2 cell monolayers was determined. The conjugates showed a degree of thiolation in the range of 316-2158 μmol/g. Within 30 min, dynamic viscosity of the conjugate with the lowest degree of thiolation 0.5% (m/v) increased up to 300-fold. The conjugates showed a degree of thiolation-dependent increase in cytotoxicity but they all were found comparatively low cytotoxic. The addition of the conjugate with thiol group content of 1670 μmol/g resulted in the highest improvement in the transport of both rhodamine 123 and FD4 as compared to buffer control. Accordingly, the degree of thiolation strongly influences the properties of the conjugates and the modulation of the degree of thiolation could be exploited for development of various drug delivery systems.

Enzymatic degradation of thiolated chitosan

The objective of this study was to evaluate the biodegradability of thiolated chitosans in comparison to unmodified chitosan. Mediated by carbodiimide, thioglycolic acid (TGA) and mercaptonicotinic acid (MNA) were covalently attached to chitosan via formation an amide bond. Applying two different concentrations of carbodiimide 50 and 100 mM, two chitosan TGA conjugates (TGA A and TGA B) were obtained. According to chitosan solution (3% m/v) thiomer solutions were prepared and chitosanolytic enzyme solutions were added. Lysozyme, pectinase and cellulase were examined in chitosan degrading activity. The enzymatic degradability of these thiomers was investigated by viscosity measurements with a plate–plate viscometer. The obtained chitosan TGA conjugate A displayed 267.7 µmol and conjugate B displayed 116.3 µmol of immobilized thiol groups. With 325.4 µmol immobilized thiol groups, chitosan MNA conjugate displayed the most content of thiol groups. In rheological studies subsequently the modification proved that chitosan TGA conjugates with a higher coupling rate of thiol groups were not only degraded to a lesser extent by 20.9–26.4% but also more slowly. Chitosan mercaptonicotinic acid was degraded by 31.4–50.1% depending the investigated enzyme and even faster than unmodified chitosan. According to these results the biodegradability can be influenced by various modifications of the polymer which showed in particular that the rate of biodegradation is increased when MNA is the ligand, whereas the degradation is hampered when TGA is used as ligand for chitosan.

Preactivated hyaluronic acid: A potential mucoadhesive polymer for vaginal delivery

The objective of this study was to develop mucoadhesive polymeric excipients for vaginal drug delivery systems. Hyaluronic acid was thiolated and subsequently preactivated with 6-mercaptonicotinamide (HA-CYS-MNA) to enhance stability and mucoadhesive properties on vaginal mucosa. After determination of the thiol group content, disintegration studies and in vitro mucoadhesion studies (rotating cylinder and tensile) were performed. Furthermore, swelling behavior and cytotoxicity studies were performed in comparison with corresponding polymers. Both, disintegration and in vitro mucoadhesive studies revealed that modifying HA-CYS with MNA resulted in higher stability (3.6-fold prolonged disintegration time compared to unmodified hyaluronic acid) and prolonged mucoadhesion time. MTT assay and LDH revealed no toxicity for the polymeric excipients and safe for their use. Disintegration and swelling results conducted more pronounced stability of the preactivated thiomers compared to corresponding unmodified ones. According to these results preactivated hyaluronic acid might be a useful tool for vaginal delivery systems.

Chemical Modification of Hyaluronic Acid for Intraoral Application

This study was aimed to investigate chemical preactivated thiomers for their potential use in mucosal drug delivery. Thiomers--thiolated polymers--are mucoadhesive polymers with sulfhydryl group-bearing side chains. Thiomers are synthesized by covalent attachment of low molecular mass compounds bearing sulfhydryl group to the polymeric backbone of well-established polymers. Hyaluronic acid-cysteine ethyl ester-mercaptonicotinamide conjugates (HA-CYS-MNA) were synthesized by the oxidative S-S coupling of HA-CYS with 6-MNA. Conjugates were compressed into test discs to investigate cohesive properties, cytotoxicity assays, and mucoadhesion studies. Because of the immobilization of MNA, the HA-CYS-MNA conjugates exhibit comparatively higher swelling properties and cohesive properties corresponding unmodified HA. On the rotating cylinder, discs based on HA-CYS-MNA conjugates displayed fourfold improved mucoadhesion time compared with thiolated polymers. Tensile study results were found in good agreement with rotating cylinder results. Moreover, preactivated thiomers showed higher stability. All polymers were found nontoxic over Caco-2 cells. On the basis of achieved results, the preactivated thiomeric therapeutic agent seems to represent a promising generation of mucoadhesive polymers that are safe to use for a prolonged residence time to target the mucosa requested for intraoral application.