Thiomers and their potential applications in drug delivery

Thiolated dextrin nanoparticles for curcumin delivery: Stability, in vitro release, and binding mechanism

To achieve the effective loading and delivery of curcumin, novel disulfide-crosslinked nanoparticles based on modified dextrin were developed for the encapsulation of curcumin. Thiolated dextrin (Dt-SH) was obtained via sodium periodate oxidation and cysteamine grafting. The Dt-SH exhibited a rough, flake-like morphology, was classified as an amorphous material and demonstrated enhanced enzyme resistance. Subsequently, spherical nanoparticles with sizes ranging from 92.52 to 157.12 nm and zeta potentials between +23.59 and + 29.90 mV were self-assembled in an aqueous solution. Thiol modification promoted interconnection and aggregation of the nanoparticles. These nanoparticles exhibited pH-dependent size variations. Taking curcumin as a hydrophobic model, nanoparticles showed intestinal targeted release in vitro. Fluorescence spectroscopy and thermodynamic analysis indicated that curcumin bound to Dt-SH nanoparticles primarily through hydrogen bonding and van der Waals forces, with hydrophobic interactions contributing. These findings supported the potential of thiolated dextrin nanoparticles in the effective delivery of hydrophobic compounds.

Thiolated pectin-chitosan composites: Potential mucoadhesive drug delivery system with selective cytotoxicity towards colorectal cancer

Mucoadhesive drug delivery systems (DDS) may promote safer chemotherapy for colorectal cancer (CRC) by maximizing local drug distribution and residence time. Carbohydrate polymers, e.g. pectin (P) and chitosan (CS), are potential biomaterials for CRC-targeted DDS due to their gelling ability, mucoadhesive property, colonic digestibility, and anticancer activity. Polymer mucoadhesion is augmentable by thiolation, e.g. pectin to thiolated pectin (TP). Meanwhile, P-CS polyelectrolyte complex has been shown to improve structural stability. Herein, we fabricated, characterized, and evaluated 5-fluorouracil-loaded primary DDS combining TP and CS as a composite (TPCF) through triple crosslinking actions (calcium pectinate, polyelectrolyte complex, disulfide). Combination of these crosslinking yields superior mucoadhesion property relative to single- or dual-crosslinked counterparts, with comparable drug release profile and drug compatibility. PCF and TPCF exhibited targeted cytotoxicity towards HT29 CRC cells with milder cytotoxicity towards HEK293 normal cells. In conclusion, TP-CS composites are promising next-generation mucoadhesive and selectively cytotoxic biomaterials for CRC-targeted DDS.

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.

Naturally Occurring Polyelectrolytes and Their Use for the Development of Complex-Based Mucoadhesive Drug Delivery Systems: An Overview

Biopolymers have several advantages for the development of drug delivery systems, since they are biocompatible, biodegradable and easy to obtain from renewable resources. However, their most notable advantage may be their ability to adhere to biological tissues. Many of these biopolymers have ionized forms, known as polyelectrolytes. When combined, polyelectrolytes with opposite charges spontaneously form polyelectrolyte complexes or multilayers, which have great functional versatility. Although only one natural polycation-chitosan has been widely explored until now, it has been combined with many natural polyanions such as pectin, alginate and xanthan gum, among others. These polyelectrolyte complexes have been used to develop multiple mucoadhesive dosage forms such as hydrogels, tablets, microparticles, and films, which have demonstrated extraordinary potential to administer drugs by the ocular, nasal, buccal, oral, and vaginal routes, improving both local and systemic treatments. The advantages observed for these formulations include the increased bioavailability or residence time of the formulation in the administration zone, and the avoidance of invasive administration routes, leading to greater therapeutic compliance.

Thiol- and Disulfide-Based Stimulus-Responsive Soft Materials and Self-Assembling Systems

Properties and applications of synthetic thiol- and disulfide-based materials, principally polymers, are reviewed. Emphasis is placed on soft and self-assembling materials in which interconversion of the thiol and disulfide groups initiates stimulus-responses and/or self-healing for biomedical and non-biomedical applications.

A Review: Uses of Chitosan in Pharmaceutical Forms

Chitosan is a natural polysaccharide widespread in nature. It has many unique and attractive properties for the pharmaceutical field: it is biodegradable, safe, hypoallergenic, biocompatible with the body, free of toxicity, with proven anticholesterolemic, antibacterial, and antimycotic action. In this review we highlighted the physical, chemical, mechanical, mucoadhesive, etc. properties of chitosan to be taken into account when obtaining various pharmaceutical forms. The methods by which the pharmaceutical forms based on chitosan are obtained are very extensive, and in this study only the most common ones were presented.

Thiolation of Biopolymers for Developing Drug Delivery Systems with Enhanced Mechanical and Mucoadhesive Properties: A Review

Biopolymers are extensively used for developing drug delivery systems as they are easily available, economical, readily modified, nontoxic, biodegradable and biocompatible. Thiolation is a well reported approach for enhancing mucoadhesive and mechanical properties of polymers. In the present review article, for the modification of biopolymers different thiolation methods and evaluation/characterization techniques have been discussed in detail. Reported literature on thiolated biopolymers with enhanced mechanical and mucoadhesive properties has been presented conspicuously in text as well as in tabular form. Patents filed by researchers on thiolated polymers have also been presented. In conclusion, thiolation is an easily reproducible and efficient method for customization of mucoadhesive and mechanical properties of biopolymers for drug delivery applications.

Thiolated Chitosans: A Multi-talented Class of Polymers for Various Applications

Various properties of chitosan can be customized by thiolation for very specific needs in a wide range of application areas. Since the discovery of thiolated chitosans, many studies have proven their advantageous characteristics, such as adhesion to biological surfaces, adjustable cross-linking and swelling behavior, controllable drug release, permeation as well as cellular uptake enhancement, inhibition of efflux pumps and enzymes, complexation of metal ions, antioxidative properties, and radical scavenging activity. Simultaneously, these polymers remain biodegradable without increased toxicity. Within this Review, an overview about the different possibilities to covalently attach sulfhydryl ligands to the polymeric backbone of chitosan is given, and the resulting versatile physiochemical properties are discussed in detail. Furthermore, the broad spectrum of applications for thiolated chitosans in science and industry, ranging from their most advanced use in pharmaceutical and medical science over wastewater treatment to the impregnation of textiles, is addressed.

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.

Therapeutic medications against diabetes: What we have and what we expect

Diabetes has become one of the largest global health and economic burdens, with its increased prevalence and high complication ratio. Stable and satisfactory blood glucose control are vital to reduce diabetes-related complications. Therefore, continuous attempts have been made in antidiabetic drugs, treatment routes, and traditional Chinese medicine to achieve better disease control. New antidiabetic drugs and appropriate combinations of these drugs have increased diabetes control significantly. Besides, novel treatment routes including oral antidiabetic peptide delivery, nanocarrier delivery system, implantable drug delivery system are also pivotal for diabetes control, with its greater efficiency, increased bioavailability, decreased toxicity and reduced dosing frequency. Among these new routes, nanotechnology, artificial pancreas and islet cell implantation have shown great potential in diabetes therapy. Traditional Chinese medicine also offer new options for diabetes treatment. Our paper aim to overview these therapeutic methods for diabetes therapy. Proper combinations of these existing anti-diabetic medications and searching for novel routes are both necessary for better diabetes control.

Intestinal absorption of S-nitrosothiols: Permeability and transport mechanisms

S-Nitrosothiols, a class of NO donors, demonstrate potential benefits for cardiovascular diseases. Drugs for such chronic diseases require long term administration preferentially through the oral route. However, the absorption of S-nitrosothiols by the intestine, which is the first limiting barrier for their vascular bioavailability, is rarely evaluated. Using an in vitro model of intestinal barrier, based on human cells, the present work aimed at elucidating the mechanisms of intestinal transport (passive or active, paracellular or transcellular pathway) and at predicting the absorption site of three S-nitrosothiols: S-nitrosoglutathione (GSNO), S-nitroso-N-acetyl-l-cysteine (NACNO) and S-nitroso-N-acetyl-d-penicillamine (SNAP). These S-nitrosothiols include different skeletons carrying the nitroso group, which confer different physico-chemical characteristics and biological activities (antioxidant and anti-inflammatory). According to the values of apparent permeability coefficient, the three S-nitrosothiols belong to the medium class of permeability. The evaluation of the bidirectional apparent permeability demonstrated a passive diffusion of the three S-nitrosothiols. GSNO and NACNO preferentially cross the intestinal barrier though the transcellular pathway, while SNAP followed both the trans- and paracellular pathways. Finally, the permeability of NACNO was favoured at pH 6.4, which is close to the pH of the jejunal part of the intestine. Through this study, we determined the absorption mechanisms of S-nitrosothiols and postulated that they can be administrated through the oral route.