Tailoring the properties of chitosan by grafting with 2-mercaptobenzoic acid to improve mucoadhesion: in silico studies, synthesis and characterization.

Mucoadhesive polymers improve oral bioavailability of drugs by prolonging the duration of adhesion of drugs with mucosa. Various methods could be employed to address the problems of mucoadhesive polymers like weak adhesion forces. Chemical modification of polymers, such as the addition of a thiol group or thiolation, is another way for improving the polymers' mucoadhesive properties that is studied in present research work. A novel thiomer of chitosan was prepared by attaching 2-mercaptobenzoic acid, a hydrophobic ligand onto it. The docking of thiomer and chitosan with mucin structure showed higher binding energy for former. The prepared thiomer was subjected to X-ray diffraction and DSC which established reduction in crystallinity and formation of a new compound through changes in glass transition, melting point and change in diffraction pattern. The NMR studies established conjugation of 2-mercapto benzoic acid to chitosan. The increased mucoadhesion in thiomer behaviour (2-3 fold) was confirmed through mucus glycoprotein assay as well as through texture analysis. The permeation enhancing the property of thiomer was established by demonstrating the permeation of phenol red across thiomer treated intestinal membrane. An in vitro cell toxicity assay was done to establish toxicity of chitosan and thiolated chitosan. Finally, the reduced water uptake of thiomer over chitosan proved that the increase in mucoadhesion is not contributed by swelling. Thus, a thiomer with improved mucoadhesion and enhanced permeation properties was prepared and characterized. Hence, all these properties render the newly synthesized polymer a better alternative to chitosan as an excipient for mucoadhesive drug delivery systems.

Preparation and detailed characterization of the thiomer chitosan-cysteine as a suitable mucoadhesive excipient for nasal powders.

The therapeutic application of nasal powders requires the development of novel mucoadhesive excipients. Thiolated polymers exhibit significant potential for this purpose based on their increased mucoadhesion attributable to the formation of disulfide bonds between the polymer and mucus surface. A chitosan-cysteine (chit-cyst) conjugate was synthesized using 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide in aqueous solution. The synthetic yield and synthesis conditions were optimized, and the efficiency of the reaction was evaluated. Rheological measurements revealed that the polymer derivative exhibited increased mucoadhesive properties in comparison to chitosan powder. To characterize the polymer, a novel purity investigation method was developed and verified to investigate the residual l-cysteine content. The results revealed that l-cysteine was not detectable in the resultant polymer matrix. Based on the cytotoxicity studies, chit-cyst was found to be safe for nasal application. Thereafter, nasal powder formulations were prepared using the polymer and the antiparkinsonian drug levodopa methyl ester hydrochloride by freeze-drying to investigate their nasal applicability. Based on the in vitro studies, these powders might be suitable for reducing the off periods of Parkinson's disease because of their expected higher in vivo mucoadhesion.

Synthesis and Characterization of a Cationic Thiomer Based on Ethyl Cellulose for Realization of Mucoadhesive Tablets and Nanoparticles.

Purpose: Ethyl cellulose (EC) based nanoparticles are being extensively studied for their ability to achieve prolonged drug release and improve drug stability. Within this study, the thiolation of unmodified EC using cysteamine as a ligand was carried out to design nanoparticles with mucoadhesive properties and comparatively strong lipophilic properties. Methods: The thiolation was performed via oxidation and reductive amination, whereas the nanoparticles were generated via the ionic gelation followed by the precipitation method. Results: The number of free thiol groups on EC-cysteamine was in the range of 210-261 µmol per gram of polymer. Tablets based on EC-cysteamine demonstrated mucoadhesive properties 16.7-fold improved compared with those comprising unmodified EC. The mean diameter of the particles was in the range of 94-123 nm and the zeta potential was determined to be -7.97 to -14.70 mV. The nanoparticles remained attached to porcine intestinal mucosa for up to 36% after 3 h of incubation. The formation of nanoparticles improved the stability of EC-cysteamine conjugate against cellulase and provided a zero-order release. Moreover, both EC-cysteamine and the nanoparticles did not show any pronounced cytotoxicity. Conclusion: Accordingly, EC-cysteamine nanoparticles could be a specific type of nanoparticulate delivery system with mucoadhesive properties. The amount of free thiol groups within EC-cysteamine nanoparticles together with their lipophilic properties could be further modified and modulated for a desired release behavior.

SEDDS-loaded mucoadhesive fiber patches for advanced oromucosal delivery of poorly soluble drugs.

To date, buccal administration of lipophilic drugs is still a major challenge due to their poor solubility in saliva and limited penetration into mucosal tissues. To overcome these limitations, we developed electrospun patches combining the benefits of mucoadhesive fibers and self-emulsifying drug delivery systems (SEDDS). The fiber system comprises a combination of mucoadhesive thiolated polyacrylic acid fibers and SEDDS-loaded fibers fabricated by parallel electrospinning. The resulting mucoadhesive electrospun SEDDS patches were systemically investigated for fiber characteristics, self-emulsification, mucoadhesion, drug penetration into porcine buccal tissue and biocompatibility. The patches showed high encapsulation efficiency for SEDDS without causing fiber defects or leakage. SEDDS incorporation enhanced the spinning process and reduced the fiber diameter and fiber size distribution. Hydration-dependent self-emulsification provided a controlled release of curcumin being encapsulated in nano-scaled o/w emulsion for over 3 h. Due to the thiolated polyacrylic acid fibers, the buccal residence time of patches was 200-fold prolonged. Further, they promoted a significantly increased drug penetration into buccal tissue compared to fiber patches without SEDDS. Finally, biocompatibility and improved therapeutic effects of curcumin-loaded patches on human keratinocytes and fibroblasts were confirmed. Mucoadhesive electrospun SEDDS patches represent a promising approach to overcome current challenges in the oromucosal delivery of lipophilic drugs to unlock their full therapeutic potential.

Thiolated pectins: In vitro and ex vivo evaluation of three generations of thiomers.

In recent decades, three generations of thiomers have been developed with the main purpose of obtaining enhanced interactions with mucosal tissues. Therefore, many different types of thiolated ligands have been generated and attached to polymeric backbones. The aim of this study was to synthesize all three generations of thiomers and to directly compare their properties regarding mucus penetration and mucoadhesion. Starting from pectin, the unprotected thiomer pectin-cysteine (Pec-Cys), the preactivated S-protected thiomer pectin-cysteine-mercaptonicotinic acid (Pec-Cys-MNA) and the less reactive S-protected thiomer pectin-cysteine-glutathione (Pec-Cys-GSH) were synthesized and characterised by FT-IR, NMR, and colorimetric studies. The polymers were evaluated regarding their cytotoxicity, swelling behaviour, viscosity after mixing with mucus, mucus diffusion, penetration into mucosa, and mucoadhesion. The amount of the three ligands (Cys, Cys-MNA and Cys-GSH) bound to the polymer was determined to be in the range of 193-196 µmol/g. All polymers showed no cytotoxicity. Viscosity of the mixture of Pec-Cys-MNA and Pec-Cys-GSH with mucus increased 21.5- and 26.7-fold, respectively, compared to the unmodified polymer within 3 hours. Swelling, mucoadhesion, interpenetration and mucus diffusion were increased in the following rank order: Pec-Cys < Pec-Cys-MNA < Pec-Cys-GSH. Results of mucoadhesion study indicated a 7.4 and 8.1-fold increase of Pec-Cys-MNA and Pec-Cys-GSH, respectively, compared to the unmodified polymer. As the less reactive S-protected thiomer exhibited higher mucoadhesive properties than the other thiomers, this study provides evidence for the superior mucoadhesion of 3rd generation thiomers. STATEMENT OF SIGNIFICANCE: Three generations of thiolated polymers have been developed bearing different types of thiol ligands with the main purpose of enhancing mucus interactions. In this study, all generations were synthesized on the polymeric backbone of pectin for the first time to directly compare their mucus penetrating and mucoadhesive properties. 1st generation exhibited covalently bound L-cysteine moieties. For 2nd generation, thiols of cysteines were S-protected with 2-mercaptonicotinic acid (MNA), resulting in high reactive disulfide bonds. 3rd generation was synthesized by a thiol/disulfide exchange of glutathione with MNA, producing a less reactive disulfide bond. Mucus penetrating and mucoadhesive properties were found to be increased as follows: 1st generation < 2nd generation < 3rd generation. According to these results, the thiomer of 3rd generation represents a promising excipient with strong mucoadhesion.

Synthesis and in vitro characterization of a preactivated thiolated acrylic acid/acrylamide-methylpropane sulfonic acid copolymer as a mucoadhesive sprayable polymer.

AIM: Development of a preactivated thiomer as sprayable excipient for mucoadhesive formulations. METHODS: CG4500 (acrylic acid/acrylamide-methyl propane sulfonic acid copolymer) was thiolated by conjugation with L-cysteine and preactivated by further modification with 2-mercaptonicotinic acid (MNA) in a two-step synthesis and characterized regarding degree of modification and cytotoxicity on Caco-2 cells. The mucoadhesive properties of this novel thiomer were evaluated via rheological synergism, tensile and mucosal residence time studies. Furthermore, the sprayability of the thiomer was evaluated. RESULTS: The newly synthesized derivatives CG4500-SH and CG4500-S-S-MNA showed mean coupling rates of 651 µmol thiol groups and 264 µmol MNA per gram polymer, respectively. Even for the unmodified polymer a rheological synergism was observed with isolated porcine intestinal mucus, which was 2.81-fold higher in case of the preactivated thiomer. Mucoadhesion studies on freshly excised porcine intestinal mucosa confirmed these results via a 2.43-fold higher total work of adhesion and a 2.31-fold higher mucosal residence time of the preactivated thiomer. In sprayability tests it was shown that solutions of the preactivated thiomer could be sprayed in concentrations up to 12% (m/V). CONCLUSION: The novel polymer CG4500-S-S-MNA is a promising sprayable excipient for mucoadhesive formulations.

Inhibitory activity of biofunctionalized silver-capped N-methylated water-soluble chitosan thiomer for microbial and biofilm infections.

One of the most important self-defense strategies employed by bacteria to resist the action of antibiotics is a biofilm formation upon the infected surface. Thus, there is an urgent need to explore novel candidates that have potent antibacterial and anti-biofilm effects to tackle this challenge. In this endeavor, we have transformed shrimp shell wastes to N-methylated water-soluble chitosan thiomer (MWSCT) which was used as either a chelating agent or bio-reductant and capping agent for Ag(I) ions in the preparation of a Ag(I)MWSCT complex or silver nanocomposite (Ag(0)MWSCT), for targeting antibacterial and anti-biofilm applications. The antibacterial and anti-biofilm performance of the new methylated chitosan thiomer (MWSCT) and its silver architectures (Ag(I)MWSCT, Ag(0)MWSCT) were assessed in vitro against E. coli and S. aureus. These new materials have significant capacities to synergistically inhibit the proliferation of the targeted bacterial cells and biofilm formation, in a structure- and species-dependent manner. Ag(0)MWSCT emerged as the most potent compound in inhibiting the growth of bacterial strains (MICE. coli/ MICS. aureus = 0.05/ 0.34 µg/mL, 1.6-/ 2.5-times lower than that recorded for the clinical drug (ciprofloxacin, Cipro). Also, this nanocomposite showed the highest anti-biofilm effects (only 1.7% E. coli biofilm growth; 11.8% staphylococcal biofilm growth).

N-Hydroxysulfosuccinimide Esters versus Thiomers: A Comparative Study Regarding Mucoadhesiveness.

The objective of the study was to compare poly(acrylic acid)- N-hydroxysulfosuccinimide reactive esters (PAA-Sulfo-NHS) and poly(acrylic acid)-cysteine conjugates (PAA-Cys) regarding their mucoadhesiveness. Polymer conjugates were synthesized in a water free environment and characterized by UV-vis spectroscopy and FTIR. Water uptake studies were performed, and the polymers were further examined for their mucoadhesive properties and cohesiveness using the rotating cylinder method. Tensile force measurements were conducted to define the strength of adhesion to porcine intestinal mucosa. Additionally, polymer-mucus mixtures were assessed for rheological synergism by measuring the increase in dynamic viscosity. Both modifications led to a prolonged adhesion time compared to unmodified PAA. Fast dissolution of PAA-Sulfo-NHS derivatives was monitored, whereas PAA-Cys tended to extensively swell while exhibiting high cohesive properties. Measurements of tensile force revealed up to 2.7-fold (PAA-Sulfo-NHS) and 2.3-fold (PAA-Cys) enhancement of the maximum detachment force and 7.6-fold (PAA-Sulfo-NHS) and 3.6-fold (PAA-Cys) increase in the total work of adhesion. Formation of a gel network between polymer and mucus was confirmed by a 10.8-fold (PAA-Sulfo-NHS) and 20.8-fold (PAA-Cys) increase in viscosity. Both types of polymers show high mucoadhesive properties due to the formation of covalent bonds with the mucus. As thiolated polymers are capable of forming stabilizing disulfide bonds within their polymeric network, they are advantageous over PAA-Sulfo-NHS.

A chitosan-thiomer polymer for highly efficacious adsorption of mercury.

Thiomers have recently attracted attention as effective adsorbents for Hg2+. In the present study a chitosan- thiobarbituric acid based thiomer(CTG) was investigated as a potential adsorbent for elemental mercury (Hg°), inorganic mercury (Hg2+) and methyl mercury (CH3Hg+). CTG was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Adsorption experiments were performed to optimize the parameters for maximum removal of Hg°, Hg2+ and CH3Hg+. The experimental data fitted well to Freundlich isotherm and pseudo second order kinetic models with high R2 and minimal error function values. The maximum adsorption capacities were determined to be 1367 ± 96.9, 2493 ± 174.6 and 2531 ± 178.4 mg/g for Hg°, Hg2+ and CH3Hg+ respectively. Quantitative desorption of Hg°, Hg2+ and CH3Hg+ from CTG could be performed using 0.01 N thiourea, 0.01 N HClO4 and 0.2 N NaCl respectively.

S-preactivated thiolated glycol chitosan useful to combine mucoadhesion and drug delivery.

This work describes S-preactivated N-acetylcysteine (NAC)- and glutathione (GSH)-glycol chitosan (GC) polymer conjugates engineered as potential mucoadhesive platform. Preactivated thiomers (GC-NAC-MNA, GC-GSH-MNA) were synthesized by bond formation between GC-NAC or GC-GSH and 2-mercaptonicotinic acid (MNA) used as ligand. The presence of protected thiol moieties on this new class of thiolated GC made them not subject to oxidation. The structural modifications of the resulting derivatives were confirmed by proton Nuclear Magnetic Resonance (1H NMR) and Size Exclusion Chromatography (SEC). The conjugates displayed 91.2% and 90.1% of S-preactivation for GC-NAC-MNA and GC-GSH-MNA, respectively. The polymers were tested in ex-vivo and in vitro for their mucoadhesive properties and toxicity. The results showed that the preactivation of GC-NAC and GC-GSH increased their mucoadhesive abilities compared to their thiolated precursors by 1.4-, 4.4-fold in time of adhesion evaluated using rotating cylinder method, 1.6-, 1.5-fold in total work of adhesion (TWA) and 2.0-, 1.3-fold in maximum detachment force (MDA) determined using tensile studies, respectively. Moreover, water-uptake studies showed an improved in weight indicating water-uptake strongly dependent on derivations, before erosion occurred, whereas disintegration took place for the thiolated polymers within the first hour. The S-preactivated modification did not affect the cell viability of Caco2 cells exposed to the polymers. The release of the model drug sodium naproxen from tablets prepared with a lyophilized mixture of drug and polymer was studied via dissolution apparatus revealing that the preactivation on GC-GSH and GC-NAC involves a slowdown in the drug release rate. The results shown that the novel preactivated thiolated GC-derivatives can be considered promising excipients for the development of mucoadhesive drug delivery systems.

S-protected thiolated cyclodextrins as mucoadhesive oligomers for drug delivery.

AIM: The purpose of this study was to develop a novel mucoadhesive thiolated and S-protected gamma cyclodextrin (γ-CD) with an intact ring backbone to assure a prolonged residence time at specific target sites. METHOD: Thiolated γ-CD was generated through bromine substitution of its hydroxyl groups followed by replacement to thiol groups using thiourea. In the second step, thiol groups were protected by disulfide bond formation with 2-mercaptonicotinic acid (2-MNA). RESULT: Thiolated γ-CD displayed 1385 ±â€¯84 µmol thiol groups per gram of oligomer and the amount of MNA determined in the S-protected oligomer was 1153 ±â€¯41 µmol per gram of oligomer. In-vitro screening of mucoadhesive properties of thiolated and S-protected γ-CD was done by two methods. Rheological investigation revealed the conjugates non-mucolytic with only a slight increase in viscosity of thiolated and S-protected γ-CD as compared to unmodified γ-CD, whereas mucoadhesive properties of the new thiolated and S-protected γ-CD performed on freshly excised porcine intestinal mucosa showed 44.4- and 50.9-fold improvement in mucoadhesion, respectively. The new conjugates did not show any cytotoxicity to Caco-2 cells even at a concentration of 1% (m/v) for 24 h. In addition, in-vitro studies of α-amylase degradation of γ-CD, γ-CD-SH and γ-CD-SS-MNA confirmed that all conjugates are biodegradable. CONCLUSION: These outcomes predict that these new conjugates of γ-CD might provide a new favorable tool for drug delivery providing a prolonged residence time on mucosal surfaces.

New perspectives of starch: Synthesis and in vitro assessment of novel thiolated mucoadhesive derivatives.

AIM: The purpose of this study was to develop a novel thiolated starch polymer with improved mucoadhesive properties by conjugation of cysteamine to starch as a natural polymer of restricted mucoadhesive properties. METHODS: Aldehyde substructures were integrated into starch via oxidative cleavage of vicinal diols by increasing amounts of sodium periodate followed by covalent attachment of cysteamine to oxidized starch via reductive amination. Thiol groups were quantified via Ellman's reaction and their impact on mucoadhesion was analyzed by rheological investigations, the rotating cylinder method and tensile studies on porcine mucosa. RESULTS: The total amount of immobilized thiol groups revealed a correlation between degree of oxidation and thiolation. Modified starch demonstrated an up to 1.66-fold increase in water uptake in comparison to native starch. Modification of starch resulted in greatly improved cohesive properties and improvement in mucoadhesion. Rheological investigations revealed a 2- to 4-fold rise in viscosity of mucus. Tensile studies revealed a linear correlation between degree of oxidation/thiolation and enhancement of maximum detachment force and total work adhesion. CONCLUSION: In terms of these results, thiolated starch is a new, promising, polymer in the field of mucoadhesive drug delivery systems.

Solidification/stabilization of ASR fly ash using Thiomer material: Optimization of compressive strength and heavy metals leaching.

Optimization studies of a novel and eco-friendly construction material, Thiomer, was investigated in the solidification/stabilization of automobile shredded residue (ASR) fly ash. A D-optimal mixture design was used to evaluate and optimize maximum compressive strength and heavy metals leaching by varying Thiomer (20-40wt%), ASR fly ash (30-50wt%) and sand (20-40wt%). The analysis of variance was utilized to determine the level of significance of each process parameters and interactions. The microstructure of the solidified materials was taken from a field emission-scanning electron microscopy and energy dispersive X-ray spectroscopy that confirmed successful Thiomer solidified ASR fly ash due to reduced pores and gaps in comparison with an untreated ASR fly ash. The X-ray diffraction detected the enclosed materials on the ASR fly ash primarily contained sulfur associated crystalline complexes. Results indicated the optimal conditions of 30wt% Thiomer, 30wt% ASR fly ash and 40wt% sand reached a compressive strength of 54.9MPa. For the optimum results in heavy metals leaching, 0.0078mg/LPb, 0.0260mg/L Cr, 0.0007mg/LCd, 0.0020mg/L Cu, 0.1027mg/L Fe, 0.0046mg/L Ni and 0.0920mg/L Zn were leached out, being environmentally safe due to being substantially lower than the Korean standard leaching requirements. The results also showed that Thiomer has superiority over the commonly used Portland cement asa binding material which confirmed its potential usage as an innovative approach to simultaneously synthesize durable concrete and satisfactorily pass strict environmental regulations by heavy metals leaching.

Preactivated thiolated glycogen as mucoadhesive polymer for drug delivery.

The purpose of this study was to synthesize and characterize a novel thiolated glycogen, so-named S-preactivated thiolated glycogen, as a mucosal drug delivery systems and the assessment of its mucoadhesive properties. In this regard, glycogen-cysteine and glycogen-cysteine-2-mercaptonicotinic acid conjugates were synthesized. Glycogen was activated by an oxidative ring opening with sodium periodate resulting in reactive aldehyde groups to which cysteine was bound via reductive amination. The obtained thiolated polymer displayed 2203.09±200µmol thiol groups per gram polymer. In a second step, the thiol moieties of thiolated glycogen were protected by disulfide bond formation with the thiolated aromatic residue 2-mercaptonicotinic acid (2MNA). In vitro screening of mucoadhesive properties was performed on porcine intestinal mucosa using different methods. In particular, in terms of rheology investigations of mucus/polymer mixtures, the S-preactivated thiolated glycogen showed a 4.7-fold increase in dynamic viscosity over a time period of 5h, in comparison to mucus/Simulated Intestinal Fluid control. The S-preactivated polymer remained attached on freshly excised porcine mucosa for 45h. Analogous results were obtained with tensile studies demonstrating a 2.7-fold increase in maximum detachment force and 3.1- fold increase in total work of adhesion for the S-preactivated polymer compared to unmodified glycogen. Moreover, water-uptake studies showed an over 4h continuing weight gain for the S-preactivated polymer, whereas disintegration took place for the unmodified polymer within the first hour. Furthermore, even in the highest tested concentration of 2mg/ml the new conjugates did not show any cytotoxicity on Caco-2 cell monolayer using an MTT assay. According to these results, S-preactivated glycogen represents a promising type of mucoadhesive polymers useful for the development of various mucosal drug delivery systems.

In vitro evaluation of glycol chitosan based formulations as oral delivery systems for efflux pump inhibition.

Recently, we have reported that glycol chitosan (GCS) was able to reverse the P- glycoprotein (P-gp) efflux pump. The objective of the present study was to evaluate the potential of two GCS-based dosage forms (aqueous solution or nanoparticle suspension) for oral administration of the P-gp substrate Rho-123. A further aim of the present study was to assess the effect of the glycol chitosan-4-thiobutylamidine thiomer (GCS-TBA) on P-gp activity considering that the corresponding thiomer of chitosan series is a well-known P-gp inhibitor. Pre-treatment of Caco-2 cell monolayer with a GCS solution or GCS-based nanoparticles increased the absorptive transport of Rho-123 across the monolayer of 1.43-fold. The modification of GCS with 2-iminothiolane led to GCS-TBA conjugate which did not show any P-gp inhibitory activity. Therefore, GCS polymer and corresponding dosage forms may contribute to increase the oral bioavailability of Pgp-substrate drugs, while GCS-TBA cannot be used for the same purpose.

Natural dendrimers: Synthesis and in vitro characterization of glycogen-cysteamine conjugates.

The aim of this study was to synthesize, characterize and evaluate the mucoadhesive properties of the first thiolated hyperbranched natural polysaccharide with biodegradability and biocompatibility features. In detail, glycogen-cysteamine conjugates were synthesized through a first step of oxidative ring opening applying increasing concentrations of sodium periodate, to obtain polymers with different degrees of oxidation, and a second step of reductive amination with a constant amount of cysteamine. The obtained glycogen-cysteamine conjugates were characterized regarding their content of free and total thiol groups by Ellman's assay, biocompatibility, swelling/erosion behavior, rheological synergism and mucoadhesive properties in comparison to the unmodified glycogen. The higher the concentration of periodate was, the higher was the content of total thiol groups being in the range of 255.7±12-1194.5±82µmol/g, biocompatibility remained unaffected by these structural changes. On the contrary, the mucoadhesive properties, evaluated by tensile, rheological synergism and rotating cylinder studies, appear to be influenced by the thiol groups concentration on the glycogen. In particular the glycogen-cysteamine conjugate exhibiting the highest degree of thiolation showed a 79-fold increase in viscosity over a time period of 8h, as well as, remained attached on freshly excised porcine mucosa 32-fold longer than the unmodified polymer. The higher was the amount of conjugated thiol groups, the higher was the water absorption capacity of glycogen-cysteamine tablets in Simulated Intestinal Fluid pH 6.8 (SIF). The introduction of thiol moieties on polymer changed the characteristics of the polysaccharide by improving mucoadhesion properties. Therefore, this work represents the first study describing thiolated natural dendrimers as potential platform useful to realize appropriate mucoadhesive nanocarrier systems suitable to prolong mucosal residence time.

Combination of SEDDS and Preactivated Thiomer Technology: Incorporation of a Preactivated Thiolated Amphiphilic Polymer into Self-Emulsifying Delivery Systems.

PURPOSE: The aim of the study was to create novel mucoadhesive drug delivery systems by incorporating amphiphilic hydrophobically modified, thiolated and preactivated polymers (preactivated thiomers) into self-emulsifying drug delivery systems (SEDDS). METHODS: L-Cysteine methyl ester was covalently attached to the polymeric backbone of Pemulen TR-2 and preactivated using 2-mercaptonicotinic acid (2-MNA). These thiomers were incorporated in a concentration of 0.3% (w/v) into SEDDS. The size distribution and the zeta potential of the emulsions were evaluated by dynamic light scattering. Mucoadhesive properties of thiomers-SEDDS spiked with FDA (fluorescein diacetate) were examined utilizing rheological measurement, permeation studies and in vitro residence time study on porcine mucosa. Cell viability tests were additionally performed. RESULTS: 734 ± 58 µmol L-Cysteine methyl ester and 562 ± 71 µmol 2-MNA could be attached per gram polymer of Pemulen TR-2. Emulsions exhibited a droplet size range between 180 and 270 nm. Blank SEDDS possessed a zeta potential value between -5.7 and -8.6 mV, whereas thiomers-SEDDS between -14.6 and -17.2 mV. Viscous modulus of thiomer and preactivated thiomer containing SEDDS-mucus mixture was 8-fold and 11-fold increased in comparison to reference. The amount of FDA permeated the mucus layer was 2-fold lower in case of thiomers-SEDDS compared to blank SEDDS. A prolonged residence time was observed for thiomers-SEDDS over 45 min. During cell viability studies no severe toxic effects were detected. CONCLUSION: The novel developed SEDDS with incorporated thiomers might be a promising tool for mucoadhesive oral drug delivery.

In Vitro and Ex Vivo Evaluation of Novel Curcumin-Loaded Excipient for Buccal Delivery.

This study aimed to develop a mucoadhesive polymeric excipient comprising curcumin for buccal delivery. Curcumin encompasses broad range of benefits such as antioxidant, anti-inflammatory, and chemotherapeutic activity. Hyaluronic acid (HA) as polymeric excipient was modified by immobilization of thiol bearing ligands. L-Cysteine (SH) ethyl ester was covalently attached via amide bond formation between cysteine and the carboxylic moiety of hyaluronic acid. Succeeded synthesis was proved by H-NMR and IR spectra. The obtained thiolated polymer hyaluronic acid ethyl ester (HA-SH) was evaluated in terms of stability, safety, mucoadhesiveness, drug release, and permeation-enhancing properties. HA-SH showed 2.75-fold higher swelling capacity over time in comparison to unmodified polymer. Furthermore, mucoadhesion increased 3.4-fold in case of HA-SH and drug release was increased 1.6-fold versus HA control, respectively. Curcumin-loaded HA-SH exhibits a 4.4-fold higher permeation compared with respective HA. Taking these outcomes in consideration, novel curcumin-loaded excipient, namely thiolated hyaluronic acid ethyl ester appears as promising tool for pharyngeal diseases.

Enhancing the efficiency of thiomers: Utilizing a highly mucoadhesive polymer as backbone for thiolation and preactivation.

The objective of this study was to develop a novel thiomer with enhanced mucoadhesive properties using a highly mucoadhesive polymeric backbone. Fixomer™ A-30 (poly(methacrylic acid-co-sodium acrylamidomethyl propane sulfonate)), exhibiting a mucoadhesive strength superior to that of all other polymers, was thiolated by conjugation with l-cysteine and furthermore preactivated with 2-mercaptonicotinic acid (MNA). The resulting derivatives Fix-SH and Fix-S-MNA exhibited coupling rates of 755µmol thiol groups and 304µmol MNA per gram polymer, respectively. The mucoadhesive profile was evaluated with three different methods: tensile studies, rotating cylinder and rheological synergism. In tensile studies, a total work of adhesion of above 500µJ was determined for the unmodified polymer that increased to around 750µJ after thiolation and around 1500µJ after preactivation. The adhesion time of Fix-SH on the rotating cylinder was 3.7-fold and that of Fix-S-MNA 6.8-fold longer compared to the unmodified polymer. A rheological synergism was observed for the unmodified polymer as well as the derivatives with a non-significant difference for Fix-SH but a 5.44-fold improvement for Fix-S-MNA. Fix-S-MNA showed a significantly improved swelling behavior with a water-uptake up to the 30-fold of its initial weight over >50h whereas thiolation showed only slight improvements. Derivatization had no significant influence on cell viability. According to the results, Fix-S-MNA seems to be a suitable polymer for mucoadhesive drug delivery systems.

Preactivated thiolated pullulan as a versatile excipient for mucosal drug targeting.

AIM: The purpose of the present study was to generate a novel mucoadhesive thiolated pullulan with protected thiol moieties and to evaluate its suitability as mucosal drug delivery system. METHODS: Two different synthetic pathways: bromination-nucleophilic substitution and reductive amination including periodate cleavage were utilized to synthesize such thiolated pullulans. The thiomer (pullulan-cysteamine) with the highest amount of free thiol groups was further enrolled in a reaction with 6-mercaptonicotinamide and its presence in pullulan structure was confirmed via NMR analysis. Furthermore, unmodified, thiolated and preactivated thiolated pullulan were investigated in terms of mucoadhesion via rotating cylinder studies and rheological synergism method as well as their toxicity potential over Caco-2 cells. RESULTS: Comparing both methods the reductive amination seems to be the method of choice resulting in comparatively higher coupling rates. Using this procedure pullulan-cysteamine conjugate displayed 1522±158µmol immobilized thiol groups and 280±70µmol free thiol groups per gram polymer. Furthermore, 82% of free thiol groups on this conjugate were linked with 6-mercaptonicotinamide (6-MNA). The adhesion time on the rotating cylinder was up to 46-fold prolonged in case of the thiolated polymer and up to 75-fold in case of the preactivated polymer. Rheological measurements of modified pullulan samples showed 98-fold and 160-fold increase in dynamic viscosity upon the addition of mucus within 60min, whereas unmodified pullulan did not show an increase in viscosity at all. Both conjugates had a minor effect on Caco-2 cell viability. CONCLUSION: Because of these features preactivated thiolated pullulan seems to represent a promising type of mucoadhesive polymers for the development of various mucosal drug delivery systems.