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

Thiolation of non-ionic surfactants for the development of lipid-based mucoadhesive drug delivery systems

The aim of this study was to develop thiolated self-emulsifying drug delivery systems (SEDDS) and nanostructured lipid carriers (NLCs) with improved mucoadhesive properties. Two non-ionic surfactants bearing a short and long PEG chain, namely polyoxyethylene (10) stearyl ether (PSE₁₀) and polyoxyethylene (100) stearyl ether (PSE₁₀₀), were thiolated for the first time by substituting the terminal hydroxyl group with a thiol group. The synthesis was confirmed by FT-IR, NMR and Ellman's test. SEDDS and NLCs containing these thiolated compounds were investigated for size, polydispersity index (PDI) and ζ potential. Subsequently, mucus diffusion studies, rheological evaluations after mixing the nanocarriers with mucus and mucoadhesion studies on porcine intestinal mucosa were performed. All nanocarriers had a size less than 250 nm, a maximum PDI of 0.3 and a ζ potential < -9.0 mV. Mucus diffusion studies resulted in the rank order of increasing diffusivity: PSE₁₀-SH < PSE₁₀₀-SH < PSE₁₀-OH < PSE₁₀₀-OH for NLCs and PSE₁₀-OH < PSE₁₀₀-OH < PSE₁₀₀-SH < PSE₁₀-SH for SEDDS. The mucoadhesive properties and increase in viscosity of SEDDS and NLCs ranked: PSE₁₀₀-OH < PSE₁₀-OH < PSE₁₀₀-SH < PSE₁₀-SH. In addition, the short chain PSE₁₀-SH showed higher mucus interactions than the long chain PSE₁₀₀-SH for both SEDDS and NLCs. The thiolated PSE surfactants appeared to be promising excipients for the design of highly mucoadhesive drug delivery systems.

Targeting mucus barrier in respiratory diseases by chemically modified advanced delivery systems

Mucus gel constitutes of heavily cross-linked mucin fibers forming a viscoelastic, dense porous network that coats all the exposed epithelia not covered with the skin. The layer provides protection to the underlying gastrointestinal, respiratory, and female reproductive tracts, in addition to the organs such as the surface of eye by trapping the pathogens, irritants, environmental fine particles, and potentially hazardous foreign matter. However, this property of mucus gel poses a substantial challenge for realizing the localized and sustained drug delivery across the mucosal surfaces. The mucus permeating particles that spare the protective properties of mucus gel improve the therapeutic potency of the drugs aimed at the management of diseases, including sexually transmitted infections, lung cancer, irritable bowel disease, degenerative eye diseases and infections, and cystic fibrosis. As such, the mucoadhesive materials conjugated with drug molecules display a prolonged retention time in the mucosal gel that imparts a sustained release of the deliberated drug molecules across the mucosa. The contemporarily developed mucus penetrating materials for drug delivery applications comprise of a finer size, appreciable hydrophilicity, and a neutral surface to escape the entrapment within the cross-inked mucus fibers. Pertaining to the mucus secretion as a first line of defence in respiratory tract in response to the invading physical, chemical, and biological pathogens, the development of mucus penetrating materials hold promise as a stalwart approach for revolutionizing the respiratory drug delivery paradigm. The present review provides an epigrammatic collation of the mucus penetrating/mucoadhesive materials for achieving a controlled/sustained release of the cargo pharmaceutics and drug molecules across the respiratory mucus barrier.

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 3^rd 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. 1^st generation exhibited covalently bound L-cysteine moieties. For 2^nd generation, thiols of cysteines were S-protected with 2-mercaptonicotinic acid (MNA), resulting in high reactive disulfide bonds. 3^rd 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: 1^st generation < 2^nd generation < 3^rd generation. According to these results, the thiomer of 3^rd generation represents a promising excipient with strong mucoadhesion.

Synthesis of Thiol-Modified Hemicellulose, Its Biocompatibility, Studies, and Appraisal as a Sustained Release Carrier of Ticagrelor

Background: Nature has always been considered as the primary source of pharmaceutical ingredients. A variety of hemicelluloses, as well as their modified forms, have been under investigation. Herein, a study was designed to explore the biocompatibility of hemicellulose and its modified form (thiolated hemicellulose) as well as its potential as a pharmaceutical excipient. Method: For thiol modification thiourea was used as the thiol donor, HCl as the catalytic reagent, and methanol was used for washing purposes. Modified polymers were characterized for physicochemical characteristics, including surface morphology, the amorphous or crystalline nature of the particles, modification of polymer by FTIR, and biocompatibilities. For acute oral toxicity study, a single dose of 2 g/kg was administered to albino rats of 200 g average weight (n = 3). Polymers were evaluated as pharmaceutical excipients by preparing compressed tablets of antiplatelet drug (Ticagrelor), followed by various quality control tests, such as swelling index, thickness and diameter, disintegration, and in-vitro drug release. Results: From the results, it was observed that thiol modification has been successfully accomplished as characteristic peaks belonging to -SH group appeared at 2667.7691 cm-1 in FTIR scan. The modified polymer was found safe in the use concentration range, confirming their safe use for in vivo analysis. No significant effect has been observed in the behavior, biological fluid (blood), or on vital organs. Thiolated hemicellulose was found to be an excellent drug retarding polymer as 8 h of dissolution studies showed that 67.08% of the drug has been released. Conclusion: Conclusively, incorporation of thiol moiety made the polymer more mucoadhesive with, and a worthy carrier of, the drug with good biocompatibilities.

Synthesis and Evaluation of Thiol-Conjugated Poloxamer and Its Pharmaceutical Applications

The current study was designed to convert the poloxamer (PLX) into thiolated poloxamer (TPLX), followed by its physicochemical, biocompatibilities studies, and applications as a pharmaceutical excipient in the development of tacrolimus (TCM)-containing compressed tablets. Thiolation was accomplished by using thiourea as a thiol donor and hydrochloric acid (HCl) as a catalyst in the reaction. Both PLX and TPLX were evaluated for surface morphology based on SEM, the crystalline or amorphous nature of the particles, thiol contents, micromeritics, FTIR, and biocompatibility studies in albino rats. Furthermore, the polymers were used in the development of compressed tablets. Later, they were also characterized for thickness, diameter, hardness, weight variation, swelling index, disintegration time, mucoadhesion, and in vitro drug release. The outcomes of the study showed that the thiolation process was accomplished successfully, which was confirmed by FTIR, where a characteristic peak was noticed at 2695.9968 cm-1 in the FTIR scan of TPLX. Furthermore, the considerable concentration of the thiol constituents (20.625 µg/g of the polymer), which was present on the polymeric backbone, also strengthened the claim of successful thiolation. A mucoadhesion test illustrated the comparatively better mucoadhesion strength of TPLX compared to PLX. The in vitro drug release study exhibited that the TPLX-based formulation showed a more rapid (p < 0.05) release of the drug in 1 h compared to the PLX-based formulation. The in vivo toxicity studies confirmed that both PLX and TPLX were safe when they were administered to the albino rats. Conclusively, the thiolation of PLX made not only the polymer more mucoadhesive but also capable of improving the dissolution profile of TCM.

Strategies for improved hair binding: Keratin fractions and the impact of cationic substructures

Keratin extracts and hydrolysates from varying sources, their chemical modifications and compositions thereof have shown potential in the restoration of hair properties. Within this study on reactivity of thiol groups and the shielding effect of anionic charges the binding of keratin-associated proteins (KAP) and α-keratins (Ker) extracted from human hair to natural and permed hair fibers was evaluated. Selectively extracted KAP and Ker were preactivated with 6-mercaptonicotinamide in a quantity of 194 ± 21 μmol/g for KAP and 169 ± 27 μmol/g for Ker resulting in 1.9- and 1.4-fold enhanced binding to natural hair, respectively. The amount of accumulated Ker on hair fibers was furthermore increased by 1.7-fold in presence of 25 mM L-arginine. Perming of hair impaired binding characteristics of Ker with negligible effects for preactivation, whereas unmodified and preactivated KAP showed results comparable to natural hair. Strongly enhanced penetrability after perming was reflected by the mean penetration depth for fluorescein of 25 μm compared to 5 μm for natural fibers.

Oral delivery and enhanced efficacy of antimonal drug through macrophage-guided multifunctional nanocargoes against visceral Leishmaniasis

The present study aimed on the site specific delivery and enhanced in-vivo efficacy of antimonial drugs against the visceral leishmaniasis via macrophage targeted mannose anchored thiomer based nanoparticles. Mannose anchored thiolated nanoformulation [M-(CS-g-PEI)-TGA] was developed and evaluated in terms particle size, zeta-potential and entrapment efficacy. The TEM and EDX analysis was carried out to evaluate the morphology and successful entrapment of antimonial drug. Mucodhesion, permeation enhancement, oral pharmacokinetics, and in-vivo anti-leishmanial activity were carried out. The M-(CS-g-PEI)-TGA were found to be spherical having particle size of 287 ± 20 nm. Ex-vivo permeation indicated a 7.39-fold enhanced permeation of Meglumine Antimoniate with M-(CS-g-PEI)-TGA across Caco-2 cells compared to the Glucantime. Evaluation of in-vitro reduction in the parasitic burden via flow cytometric analysis indicated a 5.7-fold lower IC₅₀ for M-(CS-g-PEI)-TGA compared to Glucantime. A 6.1-fold improvement in the oral bioavailability and 5.2-fold reduced parasitic burden in the L. donovani infected BALB/c mice model was observed with M-(CS-g-PEI)-TGA compared to Glucantime. The results encouraged the concept of M-(CS-g-PEI)-TGA nanoformulations as a promising strategy for oral therapy against visceral leishmaniasis.

A gellan gum derivative as in-situ gelling cationic polymer for nasal drug delivery

The aim of the present study was the development of a novel gellan gum derivative exhibiting mucoadhesive properties for nasal application. Accomplishing this, amino groups have been introduced to the polymeric backbone. The resulting synthesis products were characterized in terms of the amount of attached amino groups, regarding hydration, zeta potential and gel characteristics. Mucoadhesiveness was assessed studying rheological synergism, by rotating cylinder and regarding tensile studies. Next to erythrocyte-/cytotoxicity evaluation, the impact on ciliary beat frequency of nasal epithelial cells was investigated. Results revealed coupling rates up to 1259.50 ± 75.98 μmol/g polymer as well as accelerated hydration of the derivatives. Comparing aminated with unmodified gellan, enhanced mucoadhesion was verified by a 32-fold increase in viscosity of polymer/mucus mixtures and by a 14-fold extended mucosal adhesion time. Tensile studies demonstrated a 9-fold higher total work of adhesion and a 3.75-fold elevated maximum detachment force. Cellular membrane was not seriously impaired. CBF studies proved a reversible inhibition due to the application of the novel derivative. According to the outlined findings, aminated gellan gum can be considered as a promising excipient for nasal dosage forms improving drug bioavailability by superior adhesive features.

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.

Thiolated polymers: Bioinspired polymers utilizing one of the most important bridging structures in nature

Thiolated polymers designated "thiomers" are obtained by covalent attachment of thiol functionalities on the polymeric backbone of polymers. In 1998 these polymers were first described as mucoadhesive and in situ gelling compounds forming disulfide bonds with cysteine-rich substructures of mucus glycoproteins and crosslinking through inter- and intrachain disulfide bond formation. In the following, it was shown that thiomers are able to form disulfides with keratins and membrane-associated proteins exhibiting also cysteine-rich substructures. Furthermore, permeation enhancing, enzyme inhibiting and efflux pump inhibiting properties were demonstrated. Because of these capabilities thiomers are promising tools for drug delivery guaranteeing a strongly prolonged residence time as well as sustained release on mucosal membranes. Apart from that, thiomers are used as drugs per se. In particular, for treatment of dry eye syndrome various thiolated polymers are in development and a first product has already reached the market. Within this review an overview about the thiomer-technology and its potential for different applications is provided discussing especially the outcome of studies in non-rodent animal models and that of numerous clinical trials. Moreover, an overview on product developments is given.

Rheological analysis and mucoadhesion: A 30 year-old and still active combination

At the end of 80s and in the early 90s, an increasing interest in the development of mucoadhesive formulations occurred in the pharmaceutical field. Such formulations, prolonging the drug permanence on the mucosa of action/absorption, improve drug availability/bioavailability and therefore its therapeutic effectiveness. Among the various methods reported in the literature for the evaluation of the mucoadhesive properties of polymers, in the early 1990s, the study of the rheological variation of the polymer solutions after mixing with a mucin solution/dispersion has been proposed as an approach to measure the strength of the mucoadhesive joint. Even today, both viscosity and viscoelastic measurements are used to evaluate the ability of polymers and formulations to adhere to the mucosa of application/action. This review aims at providing an overview of the rheological approaches employed in the development and characterization of mucoadhesive formulation, highlighting their advantages and disadvantages. To do this the scientific path that, since the beginning of the 90s, has led to the affirmation of the rheological analysis as a useful tool for the evaluation of the strength of the mucoadhesive bond is retraced.

Synthesis of thiolated arabinoxylan and its application as sustained release mucoadhesive film former

The present work aimed to synthesize thiolated arabinoxylan (TAX), and to evaluate its mucoadhesive potential. Synthesis of TAX was accomplished by esterification of arabinoxylan (AX) with thioglycolic acid (TGA). The appearance of a characteristic peak at 2516 cm^-1 in the FTIR spectrum of TAX, and presence of 6.01 ± 1.03 m moles of thiol per gram of the polymer confirmed successful thiolation of AX. The incorporation of the thiol group considerably promoted mucoadhesive strength of the polymer-viz. 3.99-fold. Moreover, in vivo safety analysis in albino rats revealed TAX to be safe in the concentration range of 750-1000 mg kg^-1 body weight. Synthesized TAX was utilized to prepare Tizanidine HCl (TZN HCl) loaded sustained release (SR) mucoadhesive buccal films using a solvent casting technique. Results proved that the prepared films were of uniform thickness, good mechanical strength (with folding endurance >300), acceptable moisture contents (5%-7%) and surface pH (6.23 ± 0.81 to 6.43 ± 0.49) compatible to that of the buccal cavity. Presence of greater that 90% of drug contents indicated the excellent drug loading ability of the prepared films. Results of in vitro dissolution studies and ex vivo permeation studies conducted respectively by USP dissolution apparatus II and Franz diffusion cell indicated that sustained effect of TAX was achieved for 8 h. These results have conclusively proven that TAX has the potential to improve the bioavailability of TZN HCl due to enhanced mucoadhesion in buccal cavity, hence signifying its suitability as a mucoadhesive buccal film former.