Evaluation of modified hyaluronic acid in terms of rheology, enzymatic degradation and mucoadhesion.

PURPOSE: This study aimed to investigate the properties of modified hyaluronic acid in terms of rheological properties, enzymatic degradation and mucoadhesiveness. METHODS: Hyaluronic acid (HA) was chemically modified with sulfhydryl ligand cysteine ethyl ester (C) in order to immobilize sulfhydryl groups on the polymeric backbone. MTT assay was performed to evaluate the safety of hyaluronic acid-cysteine ethyl ester (HAC). Rheological and enzymatic degradation studies were accomplished by preparing hydrogels of HA and HAC, respectively. HA served as control. Enzymes such as lysozyme, amylase and hyaluronidase were chosen to perform degradation studies. To study mucoadhesiveness, hydrogels of HA and HAC, respectively, were mixed with mucus and evaluated by rheology. RESULTS: MTT assay indicated no toxicity at all. The rheological assay showed 2.2-fold increase in gelling properties in case of HAC in comparison to HA. Furthermore, it could be shown that HAC was degraded by amylase to a lesser extent of 11.5-fold than HA. After 2 h, HA showed a higher degradation by lysozyme with 67.97% than HAC. Adhesion studies exhibited a 2.17-fold higher mucoadhesion of HAC with mucus compared to HA. CONCLUSION: These results will open the door for high efficient drug delivery systems based on hydrogels for mucosal application.

Comparison of mucoadhesive and cohesive features of poly(acrylic acid)-conjugates respective their molecular mass.

OBJECTIVES: This study aimed to assess the impact of molecular mass as well as the differences between poly(acrylic acid)-thiol-conjugates (PAA100,250,450KDa) on their mucoadhesive and cohesive qualities. METHODS: Covalent attachment of cysteine (CYS), cysteamine (CYSM) and l-gluthathione (GSH) to poly(acrylic acid) was achieved by formation of amide bonds between primary amino group of the amino acid (in the case of cysteine and glutathione), respectively the amino group of the aminothiol cysteamine and carboxylic acid group of the polymer. Obtained polymer conjugates were evaluated in regard to their safety profile, mucoadhesive properties on the buccal mucosa by rotating cylinder, tensile strength and rheological investigations, respectively. Furthermore, stability, cohesive and water uptake studies were performed. KEY FINDINGS: Mucoadhesive studies revealed that maximum detachment force of PAACYS450 was 24.3-fold higher in comparison to the respective controls. Stability studies revealed for PAACYS450 a 50.2-fold higher stability compared to controls. CONCLUSION: Taken together, among all polymers tested, PAACYS450 evinced the most favorable qualities regarding mucoadhesion and cohesion, followed by PAACYSM450 and PAACYS250.

Self-emulsifying drug delivery systems (SEDDS): Proof-of-concept how to make them mucoadhesive.

AIM: The objective of this study was to provide a proof-of-concept that self-emulsifying drug delivery systems can be made mucoadhesive by the incorporation of hydrophobic mucoadhesive polymers. METHODS: In order to obtain such a hydrophobic mucoadhesive polymer, Eudragit® S100 was thiolated by covalent attachment of cysteamine. After determination of the thiol group content, in vitro mucoadhesion studies (rotating cylinder and rheological measurements) were performed. Then, synthesized conjugate was incorporated into self-emulsifying drug delivery systems (SEDDS) and their toxic potential as well as that of unmodified and thiolated Eudragit® S100 was examined on Caco-2 cell line. Lastly, the mucoadhesiveness of developed SEDDS on porcine intestinal mucosa was determined. RESULTS: Generated thiolated Eudragit® S100 displaying 235±14µmol of free thiol groups and 878±101µmol of disulfide bonds per gram polymer showed a great improvement in both: dynamic viscosity with mucus and adhesion time on mucosal tissue compared to the unmodified polymer. Resazurin assay revealed that unmodified and thiolated polymers and also SEDDS dispersions were non-toxic over Caco-2 cells. Furthermore, the incorporation of 1.5% (w/w) of such thiomer into SEDDS led to remarkably improved mucoadhesiveness. Blank SEDDS were completely removed from the mucosa within 15min, whereas >60% of SEDDS containing thiolated Eudragit® S100 were still attached to it. CONCLUSION: These results provide evidence that SEDDS can be made mucoadhesive by the incorporation of hydrophobic mucoadhesive polymers.

Thiolated polymers: evaluation of their potential as dermoadhesive excipients.

The objective of this study was to evaluate and compare four different thiolated polymers regarding their dermoadhesive potential. Therefore, three hydrophilic polymers (poly(acrylic acid), Carbopol 971 and carboxymethylcellulose) and a lipophilic polymer (silicone oil) were chosen to generate thiolated polymers followed by characterization. The total work of adhesion (TWA) and the maximum detachment force (MDF) of formulations containing modified and unmodified polymers were investigated on skin obtained from pig ears using a tensile sandwich technique. The synthesis of thiolated polymers provided 564 µmol, 1079 µmol, 482 µmol and 217 µmol thiol groups per gram poly(acrylic acid), Carbopol 971, carboxymethylcellulose and silicone oil, respectively. Hydrogels containing poly(acrylic acid)-cysteine, Carbopol 971-cysteine, and carboxymethylcellulose-cysteamine exhibited a 6-fold, 25-fold and 9-fold prolonged adhesion on porcine skin than the hydrogel formulations prepared from the corresponding unmodified polymers, respectively. Furthermore, thiolation of silicone oil with thioglycolic acid led to a 5-fold improvement in adhesion compared to the unmodified silicone oil. A comparison between the four thiolated polymer formulations showed a clear correlation between the amount of coupled thiol groups and the TWA. According to these results thiomers might also be useful excipients to provide a prolonged dermal resistance time of various formulations.

Preactivated silicone oil as potential long-term vitreous replacement with nonemulsifying properties.

AIM: Assessment of preactivated and thiolated silicone oils as potential long-term vitreous replacement. METHODS: Thioglycolic acid (TGA) and 3-mercaptopropionic acid (MPA) were covalently coupled to amino-modified silicone oil and subsequently preactivated with 2-mercaptonicotinic acid (2-MNA). Each silicone thiomer was evaluated in view of oxidation, reductive reliquefaction, emulsification, and cytotoxicity. RESULTS: Both thiol ligands were coupled in almost quantitative yield to the silicone oils' backbone with a total amount of thiol groups of 223 ± 25 and 219 ± 11 µmol/g for silicone-TGA and silicone-MPA, respectively. A following preactivation with 2-MNA of around 50% of all thiol groups could be achieved. Preactivated silicones showed a protection against oxidation as the viscosity of silicone-TGA and silicone-MPA after iodine treatment were two- and fourfold higher than the preactivated counterparts, respectively. The percentage of emulsification was below 8% for both preactivated silicones in comparison to control with 100% emulsification. Silicone-TGA-MNA and silicone-MPA-MNA could be aspired via a 20 G needle within 35 s and showed a reversible sol-gel transition. CONCLUSION: Preactivated silicone oils tackle the shortcomings of currently available silicone oils as they unite suitable handling qualities with a resistance against emulsification, which renders them promising for long-term vitreous replacement. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2015. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 551-559, 2017.

Development, in vitro and in vivo evaluation of a self-emulsifying drug delivery system (SEDDS) for oral enoxaparin administration.

AIM: The aim of this study was to develop SEDDS for oral enoxaparin administration and evaluate it in vitro and in vivo. METHODS: The emulsifying properties of SEDDS composed of long chain lipids (LC-SEDDS), medium chain lipids (MC-SEDDS), short chain lipids (SC-SEDDS) and no lipids (NL-SEDDS) were evaluated. Thereafter, enoxaparin was incorporated via hydrophobic ion pairing in the chosen SEDDS, which were evaluated regarding their mucus permeating properties, stability towards pancreatic lipase, drug release profile and cytotoxicity. Finally, in vivo performance of SEDDS was evaluated. RESULTS: The average droplet size of chosen LC-SEDDS, MC-SEDDS and NL-SEDDS ranged between 30 and 40nm. MC-SEEDS containing 30% Captex 8000, 30% Capmul MCM, 30% Cremophor EL and 10% propylene glycol and NL-SEDDS containing 31.5% Labrafil 1944, 22.5% Capmul PG-8, 9% propylene glycol, 27% Cremophor EL and 10% DMSO exhibited 2-fold higher mucus diffusion than LC-SEDDS and were therefore chosen for further studies. The enoxaparin-dodecylamine complex (ENOX/DOA) was incorporated in a payload of 2% (w/w) into MC-SEDDS and NL-SEDDS. After 90min 97% of MC-SEDDS and 5% of NL-SEDDS were degraded by pancreatic lipase. Both MC-SEDDS and NL-SEDDS showed sustained in vitro enoxaparin release. Furthermore, orally administrated MC-SEDDS and NL-SEDDS yielded an absolute enoxaparin bioavailability of 2.02% and 2.25%, respectively. CONCLUSION: According to the abovementioned findings, SEDDS could be considered as a potential oral LMWH delivery system.

Preactivated thiomers for intranasal delivery of apomorphine: In vitro and in vivo evaluation.

The purpose of this study was to synthesize preactivated thiomers with different degrees of preactivation and to evaluate their potential as novel excipient for nasal apomorphine administration. The thiomer (PAA-cys) was synthesized by addition of thiol groups on poly(acrylic acid) with various molecular mass including 100, 250and450kDafollowed by immobilization of 2-mercaptonicotinic acid (2MNA) to thiol groups by disulfide bond formation resulting in PAA-cys-2MNA. These thiomers (PAA100-cys, PAA250-cys and PAA450-cys) were in the next step preactivated by 56.3, 59.5 and 46.5% (medium degree), and 80.1, 81.6 and 87% (high degree), respectively. Apomorphine permeation across porcine nasal mucosa in the presence of PAA100-cys-2MNA, PAA250-cys-2MNA and PAA450-cys-2MNA with high degree of preactivation was 3.1-, 4.4- and 4.1-fold, while 2.7-, 3.4- and 3.0-fold higher than control for medium degree of preactivation, respectively. Administration of apomorphine in the presence of PAA250-cys-2MNA showed in rats 9 and ∼2-fold improvement of relative bioavailability compared with oral and intranasal administration of apomorphine solution, respectively. Because of the pronounced improvement among other polymers, PAA250-cys-2MNA with high degree of preactivation could be considered as promising excipient for nasal delivery of apomorphine.

Thiolated graphene oxide as promising mucoadhesive carrier for hydrophobic drugs.

The aim of this study was to improve the mucoadhesive properties of graphene by conjugating thiol ligands, in order to formulate an oral delivery system for hydrophobic drugs showing long mucus residence time. Graphene oxide was obtained by oxidation of graphite and then was thiolated following two synthetic paths. On the one hand, the hydroxyl groups were conjugated with thiourea passing through the formation of a brominated intermediate. On the other hand, the carboxylic acid groups were conjugated with cysteamine via carbodiimide chemistry. The mucoadhesive properties of thiolated graphene were evaluated by rheological measurements and by residence time assay. Then, valsartan was loaded on thiolated graphene and the release profile was evaluated in simulated intestinal fluid. Following both synthetic paths it was possible to obtain thiolated graphene bearing 215-302µmol SH/g product. Both products induced after 1h incubation an increase of mucus viscosity of about 22-33-fold compared to unmodified graphite. The residence time assay confirmed that 60% of thiolated graphene could be retained on intestinal mucosa after 4h incubation, whereas just 20% of unmodified graphite could be retained. Valsartan could be loaded with a drug loading of about 31±0.3% and a sustained release profile was observed for both formulations. According to the presented data, the thiolation of graphene could improve its mucoadhesive properties. Therefore, thiolated graphene represents a promising platform for oral delivery of hydrophobic drugs, possessing a long residence time on intestinal mucosa which allows the release of the loaded drug close to the adsorptive epithelium.

Mucoadhesive polymers in the treatment of dry X syndrome.

Mucoadhesive polymers are an essential tool in the treatment of diseases where dry mucosal surfaces are involved. In this review, we focus on the application of mucoadhesive polymers in the context of dry eye, dry mouth, and dry vagina syndrome, collectively named 'dry X syndrome'. With a prolonged residence time on mucosal membranes, mucoadhesive materials are as targeted treatment option, with the mucosa as an intended site of action. Thus, mucoadhesive polymers are able to ease local irritation or itching, alleviate chewing difficulties, improve tear-film break-up time, and help to restore physiological conditions. Here, we discuss the different classes of mucoadhesive material and their performance in the treatment of dry X syndrome.

Development and in vitro evaluation of an oral SEDDS for desmopressin.

CONTEXT: Self-emulsifying drug delivery systems (SEDDS) are among most promising tools for improving oral peptide bioavailability. OBJECTIVE: In this study, in vitro protective effect of SEDDS containing desmopressin against presystemic inactivation by glutathione and α-chymotrypsin was evaluated. MATERIALS AND METHODS: The partitioning coefficient (log P) of desmopressin was increased via hydrophobic ion pairing using anionic surfactants. Solubility studies were performed to select the appropriate solvents for SEDDS preparation. Subsequently, droplet size and emulsification properties of 22 SEDDS formulations were evaluated. Moreover, the peptide-surfactant complex was dissolved in two chosen SEDDS formulations. Finally, SEDDS containing desmopressin were characterized regarding lipase stability, toxicity, and in vitro protective effect toward glutathione and α-chymotrypsin. RESULTS: Desmopressin log P was increased from initial -6.13 to 0.33 using sodium docusate. The resulting desmopressin docusate complex (DES/AOT) was incorporated in two different SEDDS formulations, containing Capmul 907 P as main solvent. DES/AOT-SEDDS-F4 (containing 0.07% w/w DES/AOT) was composed of 50% Capmul 907P, 40% Cremophor RH40, and 10% Transcutol. The comparatively more hydrophilic formulation DES/AOT-SEDDS-F15 (containing 0.25% w/w DES/AOT) consisted of 20% Capmul 907P, 40% Acconon MC8-2, and 40% Tween 20. Both formulations were stable toward digestion by lipase and protected desmopressin toward α-chymotrypsin degradation. Moreover, DES/AOT-SEDDS-F4 also protected the peptide from thiol/disulfide exchange reactions with glutathione and was not cytotoxic at a concentration of 0.375% (w/w). CONCLUSION: DES/AOT-SEDDS-F4 protected desmopressin from in vitro glutathione and α-chymotrypsin degradation. DES/AOT-SEDDS-F4 was metabolically stable and nontoxic. Therefore, it could be considered as a potential delivery system for oral desmopressin administration.

Development and in vitro characterisation of an oral self-emulsifying delivery system for daptomycin.

It was the aim of this study to develop an oral self-emulsifying drug delivery system (SEDDS) for the peptide drug daptomycin exhibiting an anionic net charge. Drug lipophilicity was increased by hydrophobic ion pairing with cationic surfactant dodecylamine hydrochloride in molar ratio of surfactant to peptide 5:1. Log P (octanol/water) of -5.0 was even raised to +4.8 due to complexation with dodecylamine hydrochloride. Various SEDDS formulations were developed and characterised regarding emulsification properties, droplet size, polydispersity index and zeta potential. When the daptomycin dodecylamine complex (DAP/DOA) was dissolved in a formulation containing 35% Dermofeel MCT, 30% Capmul MCM and 35% Cremophor RH40, a maximum payload of even 8.0% (w/w) corresponding to 5.5% pure daptomycin was achieved. The formulation was degraded by lipase within 90min. Release studies of daptomycin from this formulation emulsified in 50mM phosphate buffer pH6.8 demonstrated a sustained drug release for at least six hours. Moreover, SEDDS exhibited also mucus permeating properties as well as a protective effect towards drug degradation by α-chymotrypsin. According to these results, SEDDS containing 8% DAP/DOA complex may be considered as a new potential oral delivery system for daptomycin.

Mucus permeating thiolated self-emulsifying drug delivery systems.

CONTEXT: Mucus represents a critical obstacle for self-emulsifying drug delivery systems (SEDDS) targeting the epithelial membrane site. OBJECTIVE: The aim of the study was the development of a novel SEDDS to overcome the mucus barrier. MATERIALS AND METHODS: Two novel conjugates N-dodecyl-4-mercaptobutanimidamide (thiobutylamidine-dodecylamine, TBA-D) and 2-mercapto-N-octylacetamide (thioglycolicacid-octylamine, TGA-O) were synthesized, incorporated into SEDDS and analyzed for stability, cytotoxicity and physico-chemical characteristics using dynamic light scattering. Mucus interaction studies were performed using in vitro assays based on multiple particle tracking, rotational silicone tubes and rheology. RESULTS AND DISCUSSION: TBA-D was synthesized using dodecylamine and iminothiolane as thiol precursor (yield=55 ± 5%). TGA-O was obtained via crosslinking of octylamine with SATA ((2,5-dioxopyrrolidin-1-yl) 2-acetylsulfanylacetate) (yield=70 ± 6%). The chemical structure of target compounds was confirmed via NMR analysis. The thiol-conjugates were incorporated in an amount of 3% (m/m) into SEDDS (Cremophor EL 30%, Capmul MCM 30%, Captex 355 30% and propylene glycol 10%), namely thiolated SEDDS leading to a droplet size around 50 nm and zeta potential close to 0 mV. Thiolated SEDDS with an effective diffusion coefficient 〈Deff〉 of up to 0.871 ± 0.122 cm(2) s(-1) × 10(-9) were obtained. Rotational silicone studies show increased permeation of the thiolated SEDDS A in comparison with unthiolated control. Rheological studies confirmed the mucolytic activity of the thiol-conjugates which differed only by 3% from DTT (dithiothreitol) serving as positive control. CONCLUSION: Low molecular weight thiol-conjugates were identified to improve the mucus permeation, leading to highly efficient mucus permeating SEDDS, which were superior to conventional SEDDS and might thus be a new carrier for lipophilic drug delivery.

Evaluation of thiolated silicone oil as advanced mucoadhesive antifoaming agent.

CONTEXT: Silicone oils, such as dimethicone, are commonly administered against gastrointestinal gas accumulation and are attributed with mucoprotective features. OBJECTIVE: Evaluation of thiolated silicone oil as advanced antiflatulence with a prolonged retention on small intestinal mucosa as an intended site of action. MATERIALS AND METHODS: 3-Mercaptopropionic acid (MPA) as a thiol ligand was covalently attached to silicone oil. This thiomer was assessed with regard to foam inhibiting action, droplet size of a suitable self-emulsifying system, mucoadhesion and cytotoxicity. RESULTS: Antifoaming activity of silicone-MPA was complying with United States Pharmacopeia (USP) requirements for simethicone as standard antiflatulence. Another antifoaming test performed on porcine mucosa supported silicone-MPA's outstanding foam destruction, as this thiomer was superior in comparison to non-thiolated silicone oil and dimethicone with 14.7 ± 2.1 versus 73.3 ± 9.1 and 66.3 ± 7.5 s, respectively. A significantly enhanced mucoadhesiveness (p < 0.02) with 26.2 ± 7.1% silicone formulation remaining on small intestinal mucosa after 8 h was evident for the thiomer without any toxic effect. CONCLUSION: Thiolated silicone oil was found to exhibit excellent antifoaming and superior mucoadhesive features. The prolonged residence time of thiolated silicone oil promises to be beneficial in the treatment of flatulence, aerophagy and inflammation throughout the whole gastrointestinal tract.

Thiolated silicone oil: synthesis, gelling and mucoadhesive properties.

The aim of this study was the development of novel thiolated silicone oils and their evaluation with regard to gelling and mucoadhesive properties. A thiol coupling of 220 ± 14 and 127 ± 33 µmol/g polymer for 3-mercaptopropionic acid (MPA)- and cysteine-coupled silicone oil was determined, respectively. The dynamic viscosity of MPA-silicone raised significantly (p<0.000001) after oxidation with iodine to a maximum of 523-fold within 1h. During tensile studies, MPA-silicone showed both the highest results for total work of adhesion (TWA) and maximum detachment force (MDF) with a 3.8- and 3.4-fold increase, respectively, compared to the control. As far as the residence time on small intestinal mucosa is concerned, both silicone conjugates were detectable in almost the same quantities for up to 8h with 56.9 ± 3.3 and 47.8 ± 8.9% of the initially applied conjugated silicone oil. Thiolated silicone oils can be regarded superior in comparison to commonly used silicone oils due to a prolonged retention time in the small intestine as site of action. Gelling and mucoadhesive features are advantageous for antiflatulent as well as mucoprotective biomaterials. Thus, these novel thiomers seem promising for an upgrade of currently available products for the treatment of dyspepsia, reflux oesophagitis and even inflammatory bowel diseases such as ulcerative colitis or Crohn's disease.