Thiomers: potential excipients for non-invasive peptide delivery systems

Dress me an outfit: advanced probiotics hybrid systems for intelligent IBD therapy

Inflammation bowel disease (IBD) has emerged as a public health challenge worldwide; with high incidence and rapid prevalence, it has troubled billions of people and further induced multitudinous systemic complications. Recent decade has witnessed the vigorous application of food-borne probiotics for IBD therapy; however, the complicated and changeable environments of digestive tract have forced probiotics to face multiple in vivo pressures, consequently causing unsatisfied prophylactic or therapeutic efficacy attributed to off-targeted arrival, damaged viability, insufficient colonization efficiency, etc. Fortunately, arisen hybrid technology has provided versatile breakthroughs for the targeted transplantation of probiotics. By ingeniously modifying probiotics to form probiotics hybrid systems (PHS), the biological behaviors of probiotics in vivo could be mediated, the interactions between probiotics with intestinal components can be facilitated, and diverse advanced probiotic-based therapies for IBD challenge can be developed, which attribute to the intelligent response to microenvironment of PHS, and intelligent design of PHS for multiple functions combination. In this review, various PHS were categorized and their intestinal behaviors were elucidated systematically, their therapeutic effects and intrinsic mechanism were further analyzed. Besides, shortages of present PHS and the corresponding solutions have been discussed, based on which the future perspectives of this field have also been proposed. The undeniable fact is that PHS show an incomparable future to bring the next generation of advanced food science.

Tannic acid-coated cellulose nanocrystals with enhanced mucoadhesive properties for aquaculture

Mucoadhesion can be exploited as a strategy to target drug and nutrient delivery to the outer mucosal layers of fish in aquaculture farms. Cellulose nanocrystals (CNC) derived from cellulose pulp fibers can interact with the mucosal membranes via hydrogen bonding, however, their mucoadhesive properties are weak and should be enhanced. In this study, CNC were coated with tannic acid (TA), a plant polyphenol with excellent wet-resistant bioadhesive properties, to strengthen their mucoadhesive capability. The optimal CNC:TA mass ratio was determined to be 20:1. The modified CNCs were 190 ± 40 nm in length and 21 ± 4 nm wide and displayed excellent colloidal stability, with a zeta potential of -35 mV. Turbidity titrations and rheological measurements revealed that the modified CNC possessed superior mucoadhesive properties compared to pristine CNC. Modification with tannic acid introduced additional functional groups for stronger hydrogen bond formation and hydrophobic interactions with mucin, which was confirmed by a large reduction in viscosity enhancement values in the presence of chemical blockers (urea and Tween80). The enhanced mucoadhesion of the modified CNC could be utilized for the fabrication of a mucoadhesive drug delivery system to promote sustainable aquaculture practices.

Challenges and opportunities in delivering oral peptides and proteins

INTRODUCTION

Rapid advances in bioengineering enable the use of complex proteins as therapeutic agents to treat diseases. Compared with conventional small molecule drugs, proteins have multiple advantages, including high bioactivity and specificity with low toxicity. Developing oral dosage forms with active proteins is a route to improve patient compliance and significantly reduce production costs. However, the gastrointestinal environment remains a challenge to this delivery path due to enzymatic degradation, low permeability, and weak absorption, leading to reduced delivery efficiency and poor clinical outcomes.

AREAS COVERED

This review describes the barriers to oral delivery of peptides and complex proteins, current oral delivery strategies utilized and the opportunities and challenges ahead to try and circumvent these barriers. Oral protein drugs on the market and clinical trials provide insights and approaches for advancing delivery strategies.

EXPERT OPINION

Although most current studies on oral protein delivery rely on in vitro and in vivo animal data, the safety and limitations of the approach in humans remain uncertain. The shortage of clinical data limits the development of new or alternative strategies. Therefore, designing appropriate oral delivery strategies remains a significant challenge and requires new ideas, innovative design strategies and novel model systems.

Nanostructured steady-state nanocarriers for nutrients preservation and delivery

Food bioactives possess specific physiological benefits of preventing certain diet-related chronic diseases or maintain human health. However, the limitations of the bioactives are their poor stability, lower water solubility and unacceptable bioaccessibility. Structure damage or degradation is often found for the bioactives under certain environmental conditions like high temperature, strong light, extreme pH or high oxygen concentration during food processing, packaging, storage and absorption. Nanostructured steady-state nanocarriers have shown great potential in overcoming the drawbacks for food bioactives. Various delivery systems including solid form delivery system, liquid form delivery system and encapsulation technology have been developed. The embedded food nutrients can largely decrease the loss and degradation during food processing, packaging and storage. The design and application of stimulus and targeted delivery systems can improve the stability, bioavailability and efficacy of the food bioactives upon oral consumption due to enzymatic degradation in the gastrointestinal tract. The food nutrients encapsulated in the smart delivery system can be well protected against degradation during oral administration, thus improving the bioavailability and releazing controlled or targeted release for food nutrients. The encapsulated food bioactives show great potential in nutrition therapy for sub-health status and disease. Much effort is required to design and prepare more biocompatible nanostructured steady-state nanocarriers using food-grade protein or polysaccharides as wall materials, which can be used in food industry and maintain the human health.

Mucoadhesive drug delivery systems: a promising noninvasive approach to bioavailability enhancement. Part II: formulation considerations

INTRODUCTION

Mucoadhesive drug delivery systems (MDDS) are specifically designed to interact and bind to the mucosal layer of the epithelium for localized, prolonged, and/or targeted drug delivery. Over the past 4 decades, several dosage forms have been developed for localized as well as systemic drug delivery at different anatomical sites.

AREAS COVERED

The objective of this review is to provide a detailed understanding of the different aspects of MDDS. Part II describes the origin and evolution of MDDS, followed by a discussion of the properties of mucoadhesive polymers. Finally, a synopsis of the different commercial aspects of MDDS, recent advances in the development of MDDS for biologics and COVID-19 as well as future perspectives are provided.

EXPERT OPINION

A review of the past reports and recent advances reveal MDDS as highly versatile, biocompatible, and noninvasive drug delivery systems. The rise in the number of approved biologics, the introduction of newer highly efficient thiomers, as well as the recent advances in the field of nanotechnology have led to several excellent applications of MDDS, which are predicted to grow significantly in the future.

Thiolated Polymeric Hydrogels for Biomedical Applications: A Review

Hydrogels are a three-dimensional (3D) network of hydrophilic polymers. The physical and chemical crosslinking of polymeric chains maintains the structure of the hydrogels even when they are swollen in water. They can be modified with thiol by thiol epoxy, thiol-ene, thiol-disulfide, or thiol-one reactions. Their application as a matrix for protein and drug delivery, cellular immobilization, regenerative medicine, and scaffolds for tissue engineering was initiated in the early 21st century. This review focuses on the ingredients, classification techniques, and applications of hydrogels, types of thiolation by different thiol-reducing agents, along with their mechanisms. In this study, different applications for polymers used in thiolated hydrogels, including dextran, gelatin, polyethylene glycol (PEG), cyclodextrins, chitosan, hyaluronic acid, alginate, poloxamer, polygalacturonic acid, pectin, carrageenan gum, arabinoxylan, carboxymethyl cellulose (CMC), gellan gum, and polyvinyl alcohol (PVA) are reviewed.

Low-cost luminescent scaffolds-based on thiol chitosans by microwave radiation for vertebral disc repair/theragnostic

This study introduces a new 3D scaffold based on thiolated chitosans with luminescence by microwave radiation using cysteine (Chi_CT_Cys) and 11-mercaptoundecanoic acid (Chi_CT_MUA) for vertebral disc regeneration/theragnostic. These scaffolds were characterized by Raman, PL spectroscopy, swelling, gel-fraction, and morphologies. Cytocompatibility and mechanical behavior were evaluated. Raman showed that disulfide bonds improved the grafting degree (Chi_CT_Cys (1072 ± 136) μmol·g^-1 and Chi_CT_MUA (3245 ± 105) μmol·g^-1). Morphologies showed interesting characteristics. Swelling behavior showed that Chi_CT_MUA presented a slight minor swelling (2101 ± 251) % compared to Chi_CT_Cys (2589 ± 188) %. Differently, gel-fraction showed that the chemical stability of Chi_CT_Cys was worse (29 ± 4) % than Chi_CT_MUA (15 ± 3) %. PL showed a possibility to use theragnostic evaluation of points of greater compression in a vertebral disc. The mechanical behavior of Chi_CT_MUA presented better results ((70 ± 3) MPa) than Chi_CT_Cys ((37 ± 3) MPa). Cytocompatible showed that the scaffolds presented cell viability >90%. Thusly, these 3D scaffolds presented an incredible potential for tissue engineering applications.

Augmentation of Antidiabetic Activity of Glibenclamide Microspheres Using S-Protected Okra Powered by QbD: Scintigraphy and In Vivo Studies

Successful drug delivery by mucoadhesive systems depends on the polymer type, which usually gets adherent on hydration. The intended polymers must sustain the association with biomembranes and preserve or accommodate the drug for an extended time. The majority of hydrophilic polymers tend to make weak interactions like noncovalent bonds, which hampers the positioning of dosage forms at the required target sites, leading to inefficient therapeutic outcomes. It is possible to overcome this by functionalizing the natural polymers with thiol moiety. Further, considering that S-protected thiomers can benefit by improving thiol stability at a broad range of pH and enhancing the residence period at the required target, 2-mercapto-nicotinic acid (MA) was utilized in this present study to shield the free thiol groups on thiolated okra (TO). S-protected TO (STO) was synthesized and characterized for various parameters. Glibenclamide-loaded microspheres were formulated using STO (G-STO-M), and the process was optimized. The optimized formulation has shown complete and controlled release of the loaded drug at the end of the dissolution study. Cell viability assay indicated that the thiolated S-protected polymers gelated very well, and the formulated microspheres were safe. Further, G-STO-M showed considerable in vivo mucoadhesion strength. The glucose tolerance test confirmed the efficacy of STO formulation in minimizing the plasma glucose level. These results favor S-protection as an encouraging tool for improving the absorption of poorly aqueous soluble drugs like glibenclamide.

An Updated Overview of the Emerging Role of Patch and Film-Based Buccal Delivery Systems

Buccal mucosal membrane offers an attractive drug-delivery route to enhance both systemic and local therapy. This review discusses the benefits and drawbacks of buccal drug delivery, anatomical and physiological aspects of oral mucosa, and various in vitro techniques frequently used for examining buccal drug-delivery systems. The role of mucoadhesive polymers, penetration enhancers, and enzyme inhibitors to circumvent the formulation challenges particularly due to salivary renovation cycle, masticatory effect, and limited absorption area are summarized. Biocompatible mucoadhesive films and patches are favored dosage forms for buccal administration because of flexibility, comfort, lightness, acceptability, capacity to withstand mechanical stress, and customized size. Preparation methods, scale-up process and manufacturing of buccal films are briefed. Ongoing and completed clinical trials of buccal film formulations designed for systemic delivery are tabulated. Polymeric or lipid nanocarriers incorporated in buccal film to resolve potential formulation and drug-delivery issues are reviewed. Vaccine-enabled buccal films have the potential ability to produce both antibodies mediated and cell mediated immunity. Advent of novel 3D printing technologies with built-in flexibility would allow multiple drug combinations as well as compartmentalization to separate incompatible drugs. Exploring new functional excipients with potential capacity for permeation enhancement of particularly large-molecular-weight hydrophilic drugs and unstable proteins, oligonucleotides are the need of the hour for rapid advancement in the exciting field of buccal drug delivery.

The progress on sulfhydryl modified polymers with regard to synthesis, characterization and mucoadhesion

The concepts of mucoadhesion and mucoadhesive polymers were introduced in the 20th century, leading to several advantages. These included enhanced drug absorption and extended residence at specific site of action. Polymeric excipients underwent chemical modification with sulfhydryl groups on the polymeric backbone so as to improve mucoadhesive features as well as potential. This modification resulted in compounds mimicking the nature of secreted mucus glycoproteins. Thus, these thiol group-bearing excipients presented the ability to attach covalently to the mucosa by the disulfide bonding. Nevertheless, the first generation of these thiol-modified polymers, named thiomers, presented disadvantages such as low stability in aqueous media and/or the high susceptibility towards oxidation along with the drawback of low sufficient reactive functional moieties on the polymeric backbone at lower pH. Therefore, in the 21st century, a second generation of preactivated or S-protected polymers with protected thiol moieties were developed, as well as a third generation of thiomers, solving some of the previously described problems. This review article aimed to highlight the progess on a potent sulfhydryl modification during the last decades and the posterior characterization and in vitro/ex vivo/in vivo mucoadhesiveness.

Advanced materials for drug delivery across mucosal barriers

Mucus is a viscoelastic gel that traps pathogens and other foreign particles to limit their penetration into the underlying epithelium. Dosage forms containing particle-based drug delivery systems are trapped in mucosal layers and will be removed by mucus turnover. Mucoadhesion avoids premature wash-off and prolongs the residence time of drugs on mucus. Moreover, mucus penetration is essential for molecules to access the underlying epithelial tissues. Various strategies have been investigated to achieve mucoadhesion and mucus penetration of drug carriers. Innovations in materials used for the construction of drug-carrier systems allowed the development of different mucoadhesion and mucus penetration delivery systems. Over the last decade, advances in the field of materials chemistry, with a focus on biocompatibility, have led to the expansion of the pool of materials available for drug delivery applications. The choice of materials in mucosal delivery is generally dependent on the intended therapeutic target and nature of the mucosa at the site of absorption. This review presents an up-to-date account of materials including synthesis, physical and chemical modifications of mucoadhesive materials, nanocarriers, viral mimics used for the construction of mucosal drug delivery systems.

An Update on Pharmaceutical Strategies for Oral Delivery of Therapeutic Peptides and Proteins in Adults and Pediatrics

While each route of therapeutic drug delivery has its own advantages and limitations, oral delivery is often favored because it offers convenient painless administration, sustained delivery, prolonged shelf life, and often lower manufacturing cost. Its limitations include mucus and epithelial cell barriers in the gastrointestinal (GI) tract that can block access of larger molecules including Therapeutic protein or peptide-based drugs (TPPs), resulting in reduced bioavailability. This review describes these barriers and discusses different strategies used to modify TPPs to enhance their oral bioavailability and/or to increase their absorption. Some seek to stabilize the TTPs to prevent their degradation by proteolytic enzymes in the GI tract by administering them together with protease inhibitors, while others modify TPPs with mucoadhesive polymers like polyethylene glycol (PEG) to allow them to interact with the mucus layer, thereby delaying their clearance. The further barrier provided by the epithelial cell membrane can be overcome by the addition of a cell-penetrating peptide (CPP) and the use of a carrier molecule such as a liposome, microsphere, or nanosphere to transport the TPP-CPP chimera. Enteric coatings have also been used to help TPPs reach the small intestine. Key efficacious TPP formulations that have been approved for clinical use will be discussed.

Ecofriendly multifunctional thiolated carboxymethyl chitosan-based 3D scaffolds with luminescent properties for skin repair and theragnostic of tissue regeneration

Luminescent biopolymers, namely carboxymethyl chitosan, have become a target of attention due to their potential for biomedical applications. In this context, biomaterials capable of improving theragnostic tissue regeneration and provide a tissue repair remain a challenge. This study introduces a new 3D scaffold based on two innovative thiolated carboxymethyl chitosan with cysteine (CMCCys) and 11-mercaptoundecanoic acid (CMCMerc) resulting in enhanced fluorescence of CMC for repair and theragnostic of tissue regeneration. Those thiolated CMCs were intensively characterized by spectroscopy techniques (FTIR, NMR), swelling degree, chemical stability (Gel-fraction, GF) and morphological analysis (SEM, microtomography, BET). In addition, the photoluminescence properties were evaluated and cytocompatibility was performed via in vitro bioassays. The results demonstrated that those scaffolds presented interconnected 3D porous (porosity > 80%), a great GF, and a high degree of thiolation (2%-11%). Furthermore, the spectroscopy analysis elucidated a significant disulfide bond formation, which guaranteed mechanical stability for applications in tissue engineering (elastic modulus, (22 ± 3) kPa and (35 ± 2) kPa, for CMCCys and CMCMerc, respectively). Additionally, the incorporation of thiol group improved the fluorescence of CMC and they presented cytocompatibility > 90%. Thus, for the first time, a multifunctional 3D CMC thiomer was produced for applications in repair and theragnostic of tissue regeneration.

Okra-Thioglycolic Acid Conjugate—Synthesis, Characterization, and Evaluation as a Mucoadhesive Polymer

The success of mucoadhesive drug delivery systems relies on the type of polymer used, which becomes adhesive naturally upon hydration. Intended polymers should be able to maintain prolonged contact with biological membranes, and to protect or cater the drug to a prolonged period. Most of the hydro polymers form weak non-covalent bonds, that hinder localization of dosage forms at specific sites resulting in therapeutic inefficiency. This can be overcome by the thiol functionalization of natural polymers. In the present study, natural okra gum (OG) was extracted, followed by thiolation (TOG) and evaluated for mucoadhesion property and its role in enhancing the efficacy of repaglinide as a model drug (short-acting Type II antidiabetic drug). The thiol functionalization of OG (TOG) was confirmed by a Fourier-transform infrared spectroscopy (FTIR) study that showed a polyhedral to a spherical shape that had a rougher surface. Differential scanning calorimetry (DSC) and X-Ray Diffraction (XRD) studies of TOG indicated a decline in endothermic transition temperature and high crystallinity, respectively, in comparison to OG. CSFR (Crushing Strength: Friability Ratio), weight and thickness variations of repaglinidetablets formulated using TOG were >80% and <2.5% respectively. The highest swelling index (107.89 ± 1.99%) and strong mucoadhesion due to high disulfide bonds were observed for repaglinide TOG tablets in comparison to RG OG tablets. In-vitro release studies indicated a controlled drug release from thiolated formulations proportional to the concentration of thiomers that have a good correlation with in-vivo studies. Pharmacokinetic studies indicated higher AUC (area under the curve), longer t1/2 with thiomers. and Level A IVIV (in vitro in vivo) correlation was established from the bioavailability and dissolution data. Consequently, all the obtained results suggest that thiomers based formulations can be promising drug delivery systems, even in targeting onerous mucosal surfaces like nasal, ocular or vaginal.

Development of Microspheres Based on Thiol-Modified Sodium Alginate for Intestinal-Targeted Drug Delivery

Bioactive peptide drugs are mostly delivered by parenteral administration, which brings great pain and risks to patients. Oral administration is an acceptable alternative form. However, peptide drugs are extremely sensitive to the strong acidic environment in the stomach after oral administration. They would be degraded by pepsin and trypsin in the gastrointestinal tract. Herein, we present microspheres for intestinal-targeted peptides drug delivery through oral administration. Sodium alginate was reacted with l-cysteine to bring it into thiol groups. Then sodium alginate-l-cysteine conjugates were mixed with native sodium alginate and emulsified by an improved method. Ca²⁺ was used to fix the emulsion to get the microspheres. Bovine serum albumin was used as the simulating drug to assess the feasibility of microspheres as intestinal delivery carriers. The results showed that the microspheres exhibited spherical properties and narrow size distribution. The drug-loading capacity of microspheres was not compromised after thiol-modification. It is interesting that the microspheres can maintain structural integrity and hold drugs in the strong acidic environment in the stomach. Conversely, the microspheres presented sustained intestinal-targeted drugs release ability as expected. Moreover, thiol-modification further improved the adherence ability of microspheres on the inner walls of the small intestine, which is good for enhancing drug permeability. In sum, the microspheres based on thiol-modified sodium alginate have promising applications as intestinal-targeted macromolecular drug carriers.

Recent advances in oral delivery of biologics: nanomedicine and physical modes of delivery

INTRODUCTION

Research into oral delivery of biologics has a long and rich history but has not produced technologies used in the clinic. The area has evolved in terms of strategies to promote oral biologics delivery from early chemical absorption enhancers to nanomedicine to devices. Continued activity in this area is justifiable considering the remarkable proliferation of biologics.

AREAS COVERED

The article discusses some physiological barriers to oral delivery of biologics, with a special focus on less characterized barriers such as the basement membrane. Recent progress in oral delivery of biologics via nanomedicine is subsequently covered. Finally, the emerging field of device-mediated gastrointestinal delivery of biotherapeutics is discussed

EXPERT OPINION

Oral delivery of biologics is considered a 'panacea' in drug delivery. Almost century-old approaches of utilizing chemical absorption enhancers have not produced clinically translated technologies. Nanomedicine for oral biologics delivery has demonstrated potential, but the field is relatively new, and technologies have not progressed to the clinic. Device-mediated oral biologics delivery (e.g. ultrasound or microneedles) is in its infancy. However, this space is likely to intensify owing to advances in electronics and materials, as well as the challenges and history related to clinical translation of alternative approaches.

Challenges in the local delivery of peptides and proteins for oral mucositis management

Oral mucositis, a common inflammatory side effect of oncological treatments, is a disorder of the oral mucosa that can cause painful ulcerations, local motor disabilities, and an increased risk of infections. Due to the discomfort it produces and the associated health risks, it can lead to cancer treatment restrains, such as the need for dose reduction, cycle delays or abandonment. Current mucositis management has low efficiency in prevention and treatment. A topical drug application for a local action can be a more effective approach than systemic routes when addressing oral cavity pathologies. Local delivery of growth factors, antibodies, and anti-inflammatory cytokines have shown promising results. However, due to the peptide and protein nature of these novel agents, and the several anatomic, physiological and environmental challenges of the oral cavity, their local action might be limited when using traditional delivering systems. This review is an awareness of the issues and strategies in the local delivery of macromolecules for the management of oral mucositis.

N-acetyl-L-cysteine functionalized nanostructured lipid carrier for improving oral bioavailability of curcumin: preparation, in vitro and in vivo evaluations

The application of orally administered nanoparticles in the circulation system is limited by the secretion and shedding of intestinal tract mucous layer. In order to enhance mucoadhesion and mucus penetration of curcumin (Cur)-loaded nanostructured lipid carrier (NLC) after oral administration, a new multifunctional conjugate, N-acetyl-L-cysteine-polyethylene glycol (100)-monostearate (NAPG), was synthesized. Functionalized nanocarriers (Cur-NAPG-NLC) modified by different amounts of NAPG (the amounts of NAPG were 20, 50, and 100 mg) were prepared and investigated for in vitro and in vivo behavior. Mean particle sizes of 89-141 nm with negative zeta potential (-15 to -11 mV) and high encapsulation efficiency (EE, >90%) possessing spherical and stable nanocarriers were observed. Sustained drug release was also observed for the NAPG-NLC. In situ intestinal perfusion studies showed that with increasing the amount of NAPG increase absorption of Cur. In vivo oral pharmacokinetic evaluation suggested that the bioavailability of Cur in rats was proportional to the degree of functionalization of NLCs with NAPG. AUC0-t of Cur-NAPG100-NLC was improved by 499.45 and 116.89 folds as compared to that of Cur solution and unmodified Cur-NLC, respectively. In conclusion, NAPG modified NLC could be a promising drug delivery system for improving oral performance of BCS class IV drugs.

Overviews on the cellular uptake mechanism of polysaccharide colloidal nanoparticles

Nanoparticulate drug/gene carriers have gained much attention in the past decades because of their versatile and tunable properties. However, efficacy of the therapeutic agents can be further enhanced using naturally occurring materials-based nanoparticles. Polysaccharides are an emerging class of biopolymers; therefore, they are generally considered to be safe, non-toxic, biocompatible and biodegradable. Considering that the target of nanoparticle-based therapeutic strategies is localization of biomedical agents in subcellular compartments, a detailed understanding of the cellular mechanism involved in the uptake of polysaccharide-based nanoparticles is essential for safe and efficient therapeutic applications. Uptake of the nanoparticles by the cellular systems occurs with a process known as endocytosis and is influenced by the physicochemical characteristics of nanoparticles such as size, shape and surface chemistry as well as the employed experimental conditions. In this study, we highlight the main endocytosis mechanisms responsible for the cellular uptake of polysaccharide nanoparticles containing drug/gene.

Multifunctional adhesive polymers: Preactivated thiolated chitosan-EDTA conjugates

AIM

The aim of this study was to synthesis preactivated thiolated chitosan-EDTA (Ch-EDTA-cys-2MNA) conjugates exhibiting in particular high mucoadhesive, cohesive and chelating properties.

METHODS

Thiol groups were coupled with chitosan by carbodiimide reaction and further preactivated by attachment with 2-mercaptonicotinic acid (2MNA) via disulfide bond formation. Determinations of primary amino and sulfhydryl groups were performed by TNBS and Ellman's tests, respectively. Cytotoxicity was screened by resazurin assay in Caco-2 cells. Mucoadhesive properties and bivalent cation binding capacity with Mg²⁺ and Ca²⁺ in comparison to chitosan-EDTA (Ch-EDTA) and thiolated Ch-EDTA (Ch-EDTA-cys) were evaluated.

RESULTS

Determination of 2MNA and total sulfhydryl groups indicated that 80% of thiol groups were preactivated. The results from cytotoxicity studies demonstrated that Ch-EDTA-cys and Ch-EDTA-cys-2MNA were not toxic to the cells at the polymer test concentration of 0.25% (w/v) while cell viability decreased by increasing the concentration of Ch-EDTA. Although EDTA molecule was modified by thiolation and preactivation, approximately 50% of chelating properties of the conjugates were maintained compared to Ch-EDTA. Ch-EDTA-cys-2MNA adhered on freshly excised porcine intestinal mucosa up to 6h while Ch-EDTA adhered for just 1h.

CONCLUSION

According to the combination of mucoadhesive and chelating properties of the conjugates synthesized in this study, Ch-EDTA-cys-2MNA might be useful for various mucosal drug delivery systems.

Spray-dried mucoadhesives for intravesical drug delivery using N-acetylcysteine- and glutathione-glycol chitosan conjugates

This work describes N-acetylcysteine (NAC)- and glutathione (GSH)-glycol chitosan (GC) polymer conjugates engineered as potential platform useful to formulate micro-(MP) and nano-(NP) particles via spray-drying techniques. These conjugates are mucoadhesive over the range of urine pH, 5.0-7.0, which makes them advantageous for intravesical drug delivery and treatment of local bladder diseases. NAC- and GSH-GC conjugates were generated with a synthetic approach optimizing reaction times and purification in order to minimize the oxidation of thiol groups. In this way, the resulting amount of free thiol groups immobilized per gram of NAC- and GSH-GC conjugates was 6.3 and 3.6mmol, respectively. These polymers were completely characterized by molecular weight, surface sulfur content, solubility at different pH values, substitution and swelling degree. Mucoadhesion properties were evaluated in artificial urine by turbidimetric and zeta (ζ)-potential measurements demonstrating good mucoadhesion properties, in particular for NAC-GC at pH 5.0. Starting from the thiolated polymers, MP and NP were prepared using both the Büchi B-191 and Nano Büchi B-90 spray dryers, respectively. The resulting two formulations were evaluated for yield, size, oxidation of thiol groups and ex-vivo mucoadhesion. The new spray drying technique provided NP of suitable size (<1μm) for catheter administration, low degree of oxidation, and sufficient mucoadhesion property with 9% and 18% of GSH- and NAC-GC based NP retained on pig mucosa bladder after 3h of exposure, respectively.

STATEMENT OF SIGNIFICANCE

The aim of the present study was first to optimize the synthesis of NAC-GC and GSH-GC, and preserve the oxidation state of the thiol moieties by introducing several optimizations of the already reported synthetic procedures that increase the mucoadhesive properties and avoid pH-dependent aggregation. Second, starting from these optimized thiomers, we studied the feasibility of manufacturing MP and NP by spray-drying techniques. The aim of this second step was to produce mucoadhesive drug delivery systems of adequate size for vesical administration by catheter, and comparable mucoadhesive properties with respect to the processed polymers, avoiding thiolic oxidation during the formulation. MP with acceptable size produced by spray-dryer Büchi B-191 were compared with NP made with the apparatus Nano Büchi B-90.

Thiomers and their potential applications in drug delivery

INTRODUCTION

Thiomers are the product of the immobilization of sulfhydryl-bearing ligands onto the polymer backbone of a conventional polymer, which results in a significant improvement in mucoadhesion; in situ gelation and efflux inhibition compare with unchanged polymers. Because of thiol groups, thiomers have more reactivity and enhanced protection against oxidation. Since the late 1990s, extensive work has been conducted on these promising polymeric excipients in the pharmaceutical field. Areas covered: This review covers thiomers, their classification and their different properties. Various techniques for the synthesis, purification and characterization of thiomers are described in detail. This review also encompasses their various properties such as mucoadhesion, permeation enhancement, in situ gelation and efflux inhibition, as well as different formulations based on thiomers. In addition to the use of thiomers as multifunctional excipients, this review also encompasses their use as drugs. Expert opinion: The synthesis is realized by linkage of sulfhydryl-bearing ligands but reported methods give low yields. Higher degrees of modification are not necessary and would probably lead to extreme changes in properties. Nevertheless, an accurate characterization of the final product is important. The scale-up procedure for industrial manufacturing has been adapted to produce GMP materials; Lacrimera® eye drops have already entered the European market.

Nasal immunization with mannan-decorated mucoadhesive HPMCP microspheres containing ApxIIA toxin induces protective immunity against challenge infection with Actinobacillus pleuropneumoiae in mice

The development of subunit mucosal vaccines requires an appropriate delivery system or an immune modulator such as an adjuvant to improve antigen immunogenicity. The nasal route for vaccine delivery by microparticles has attracted considerable interest, although challenges such as the rapid mucociliary clearance in the respiratory mucosa and the low immunogenicity of subunit vaccine still remain. Here, we aimed to develop mannan-decorated mucoadhesive thiolated hydroxypropylmethyl cellulose phthalate (HPMCP) microspheres (Man-THM) that contain ApxIIA subunit vaccine - an exotoxin fragment as a candidate for a subunit nasal vaccine against Actinobacillus pleuropneumoniae. For adjuvant activity, mucoadhesive thiolated HPMCP microspheres decorated with mannan could be targeted to the PRRs (pathogen recognition receptors) and mannose receptors (MR) of antigen presenting cells (APCs) in the respiratory immune system. The potential adjuvant ability of Man-THM for intranasal immunization was confirmed by in vitro and in vivo experiments. In a mechanistic study using APCs in vitro, it was found that Man-THM enhanced receptor-mediated endocytosis by stimulating the MR of APCs. In vivo, the nasal vaccination of ApxIIA-loaded Man-THM in mice resulted in higher levels of mucosal sIgA and serum IgG than mice in the ApxIIA and ApxIIA-loaded THM groups due to the specific recognition of the mannan in the Man-THM by the MRs of the APCs. Moreover, ApxIIA-containing Man-THM protected immunized mice when challenged with strains of A. pleuropneumoniae serotype 5. These results suggest that mucoadhesive Man-THM may be a promising candidate for a nasal vaccine delivery system to elicit systemic and mucosal immunity that can protect from pathogenic bacteria infection.

Poly(thioacrylate)s: expanding the monomer toolbox of functional polymers

A facile method for synthesizing thioacrylate monomers and their RAFT polymerization have been demonstrated for the first time.

The Potential of Silk and Silk-Like Proteins as Natural Mucoadhesive Biopolymers for Controlled Drug Delivery

Drug delivery across mucus membranes is a particularly effective route of administration due to the large surface area. However, the unique environment present at the mucosa necessitates altered drug formulations designed to (1) deliver sensitive biologic molecules, (2) promote intimate contact between the mucosa and the drug, and (3) prolong the drug's local residence time. Thus, the pharmaceutical industry has an interest in drug delivery systems formulated around the use of mucoadhesive polymers. Mucoadhesive polymers, both synthetic and biological, have a history of use in local drug delivery. Prominently featured in the literature are chitosan, alginate, and cellulose derivatives. More recently, silk and silk-like derivatives have been explored for their potential as mucoadhesive polymers. Both silkworms and spiders produce sticky silk-like glue substances, sericin and aggregate silk respectively, that may prove an effective, natural matrix for drug delivery to the mucosa. This mini review will explore the potential of silk and silk-like derivatives as a biocompatible mucoadhesive polymer matrix for local controlled drug delivery.

Engineered in-situ depot-forming hydrogels for intratumoral drug delivery

Chemotherapy is the traditional treatment for intermediate and late stage cancers. The search for treatment options with minimal side effects has been ongoing for several years. Drug delivery technologies that result in minimal or no side effects with improved ease of use for the patients are receiving increased attention. Polymer drug conjugates and nanoparticles can potentially offset the volume of drug distribution while enhancing the accumulation of the active drug in tumors thereby reducing side effects. Additionally, development of localized drug delivery platforms is being investigated as another key approach to target tumors with minimal or no toxicity. Development of in-situ depot-forming gel systems for intratumoral delivery of immuno-oncology actives can enhance drug bioavailability to the tumor site and reduce systemic toxicity. This field of drug delivery is critical to develop given the advent of immunotherapy and the availability of novel biological molecules for treating solid tumors. This article reviews the advances in the field of engineered in-situ gelling platforms as a practical tool for local delivery of active oncolytic agents to tumor sites.

Mannan-decorated thiolated Eudragit microspheres for targeting antigen presenting cells via nasal vaccination

Mucosal vaccination of protein as an antigen requires appropriate delivery or adjuvant systems to deliver antigen to mucosal immune cells efficiently and generate valid immune responses. For successful nasal immunization, the obstacles imposed by the normal process of mucociliary clearance which limits residence time of applied antigens and low antigen delivery to antigen presenting cells (APCs) in nasal associated lymphoid tissue (NALT) need to be overcome for the efficient vaccination. Here, we prepared mucoadhesive and mannan-decorated thiolated Eudragit microspheres (Man-TEM) as a nasal vaccine carrier to overcome the limitations. Mucoadhesive thiolated Eudragit (TE) were decorated with mannan for targeting mannose receptors (MR) in antigen presenting cells (APCs) to obtain efficient immune responses. The potential adjuvant ability of Man-TEM for intranasal immunization was confirmed by in vitro and in vivo experiments. In mechanistic study using APCs in vitro, we obtained that Man-TEM enhanced the receptor-mediated endocytosis by stimulating the MR receptors of APCs. The nasal vaccination of OVA-loaded Man-TEM in mice showed higher levels of serum IgG and mucosal sIgA than the soluble OVA group due to the specific recognition of MR of APCs by the mannan in the Man-TEM. These results suggest that mucoadhesive and Man-TEM may be a promising candidate for nasal vaccine delivery system to elicit systemic and mucosal immunity.

Permeation enhancement via thiolation: in vitro and ex vivo evaluation of hyaluronic acid-cysteine ethyl ester

It was the aim of this study to evaluate the permeation-enhancing effect of synthesized thiolated hyaluronic acid (HA). HA, a naturally found polysaccharide, was chemically modified with l-cysteine ethyl ether (C) via amide bond formation. In vitro permeation enhancement was tested on Caco-2 cells with two compounds, sulforhodamine (SR) and fluorescein isothiocyanate-dextran (FD4). Cytotoxicity assays as lactate dehydrogenase and thiazolyl blue tetrazolium bromide (MTT) were performed on colon carcinoma cell line. Transepithelial electrical resistance (TEER) measurements were conducted. Ex vivo evaluation was accomplished on rat intestinal mucosa in order to predict the permeation enhancing effect with SR, sodium fluorescein (SF), and FD4, respectively. The MTT as well as lactate dehydrogenase revealed no toxicity over time periods of 3 and 12 h, respectively. The bioconjugate is biocompatible and safe to use. Furthermore, TEER measurements showed the integrity of tight junctions. The in vitro permeation studies on cell studies exhibit 1.28-fold enhancement for SR and 1.47-fold enhancement for FD4 with hyaluronic acid-cysteine ethyl ester (HAC) in comparison to unmodified one. The ex vivo transport studies exhibit 1.9-fold enhancement for SF, 1.31-fold enhancement for Rhodamine123, and 1.3-fold enhancement for FD4 with HAC in comparison to unmodified one, respectively. Thus, the promising results encourage further investigations and exploitation of this versatile polysaccharide.

Evaluation of functional characteristics of preactivated thiolated chitosan as potential therapeutic agent for dry mouth syndrome

PURPOSE

The objective of this study was to investigate preactivated thiomers for their potential in the treatment of dry mouth syndrome.

METHODS

Chitosan-thioglycolic-mercaptonicotinamide conjugates (chitosan-TGA-MNA) were synthesized by the oxidative S-S coupling of chitosan-thioglycolic acid (chitosan-TGA) with 6-mercaptonicotinamide (MNA). Test disks were compressed out of unmodified chitosan, chitosan-TGA (thiomers) and chitosan-TGA-MNA conjugates to investigate cohesive properties, cytotoxicity assays and mucoadhesion studies.

RESULTS

Immobilizing the MNA achieved higher swelling and cohesive properties of chitosan-TGA-MNA conjugates compared to unmodified chitosan. Rotating cylinder studies displayed a 3.1-fold improvement of mucoadhesiveness of chitosan-TGA-MNA conjugates compared to thiolated polymers. Findings in tensile strength were in good agreement with rotating cylinder ones. Furthermore, preactivated thiomers exhibit higher stability. All conjugates were found non-toxic against Caco-2 cells.

CONCLUSION

Preactivated thiolated chitosan could be a promising system for the treatment of dry mouth syndrome where mucosa requires lubrication and mucoadhesiveness.

In vitro and ex vivo evaluation of biomaterials' distinctive properties as a result of thiolation

Background: Polysaccharide hyaluronic acid (HA) was chemically modified with cysteine ethyl ester (CYS). By immobilization of the thiol-bearing ligand on the polymeric backbone the thiolated bioconjugate HA-CYS was obtained. Methodology & Results: Mucoadhesion, permeation enhancement effect and stability was tested. Furthermore mechanical, physicochemical properties as well as mucoadhesive strength, swelling index and residence time on the mucosa were investigated. The developed thiolated bioconjugate displayed 1.5-fold improved mucoadhesiveness on buccal mucosa as well as an enhanced permeation behavior and 2.5-fold higher polymer stability. The near neutral pH and 2.49±0.49% cytotoxicity over 12-h studies indicated their non-irritability and biocompatible nature with biological tissues. Further, the model drug sulforhodamine 101 was incorporated to determine its drug release profiles, which revealed a 2.8-fold controlled release of HA-CYS in comparison to unmodified HA. Conclusion: Thus, the promising results encourage further investigations and exploitation of this versatile polysaccharide.

Nano-carrier systems: Strategies to overcome the mucus gel barrier

The present review provides an overview of nanotechnology-based strategies to overcome various mucus gel barriers including the intestinal, nasal, ocular, vaginal, buccal and pulmonary mucus layer without destroying them. It focuses on the one hand on strategies to improve the mucus permeation behavior of particles and on the other hand on systems avoiding the back-diffusion of particles out of the mucus gel layer. Nanocarriers with improved mucus permeation behavior either exhibit a high density of positive and negative charges, bearing mucolytic enzymes such as papain and bromelain on their surface or display a slippery surface due to PEG-ylation. Furthermore, self-nanoemulsifying-drug-delivery-systems (SNEDDS) turned out to exhibit comparatively high mucus permeating properties. Strategies in order to avoid back-diffusion are based on thiolated polymers reacting to a higher extent with cysteine subunits of the mucus at pH 7 in deeper mucus regions than at pH 5 being prevalent in luminal mucus regions of the intestinal and vaginal mucosa. Furthermore, particles changing their zeta potential from negative to positive once they have reached the epithelium seem to be promising carriers. The summarized knowledge should provide a good starting point for further developments in this field.

Thiomers: A Blessing to Evaluating Era of Pharmaceuticals

Thiomers are the polymers modified for the mucoadhesive properties and other additive properties by incorporating thiol moieties in the backbone of the unmodified polymeric chain by substitution reactions or simple oxidation reactions. Drugs that are less soluble and permeable can be complexed with thiomers for their increased absorption through the mucosal membranes by increase in contact time and prolonged stay in body due to mucoadhesion. Immobilization of thiol group therefore increases the mucoadhesive properties of the modified polymer by 2–140-folds. The prepared thiomers are characterized and made stable by different techniques. Thiomers also give the controlled delivery of the active pharmaceutical ingredients in the body. Different polymers that are modified by thiolation are chitosan, polyacrylic acid, sodium alginate, sodium carboxy methyl cellulose, guar gum, and so forth. Thiomeric formulations are a challenge to deliver drugs with low therapeutic compatibility. Micro- and nanopreparations containing thiomers can be prepared by different techniques such as covalent crosslinking, in situ gelation, radical emulsion polymerization, and emulsification. Nowadays thiomers have wide range of applications as a promising pharmaceutical excipient in the evaluating era of pharmaceutical technology.

Buccal drug delivery: A challenge already won?

The main obstacles that drugs meet when administered via the buccal route derive from the limited absorption area and the barrier properties of the mucosa. The effective physiological removal mechanisms of the oral cavity that take the formulation away from the absorption site are the other obstacles that have to be considered. The strategies studied to overcome such obstacles include the employment of new materials that, possibly, combine mucoadhesive, enzyme inhibitory and penetration enhancer properties and the design of innovative drug delivery systems which, besides improving patient compliance, favor a more intimate contact of the drug with the absorption mucosa.: