Pectin-cysteine conjugate: synthesis and in-vitro evaluation of its potential for drug delivery

Sustainable Chemical Modification of Natural Polysaccharides: Mechanochemical, Solvent-Free Conjugation of Pectins and Hyaluronic Acid Promoted by Microwave Radiations

The modern chemistry has the main focus of saving resources and developing synthetic strategies characterized by intrinsic efficiency, ease and safety in operation, short reaction time, reduced energy, and waste. Natural polysaccharides are largely distributed in plant/animal cells; in other words, they are often provided by renewable sources. This characteristic makes them suitable compounds to be investigated for their employment as biodegradable material. In addition, natural polysaccharides have been proven to have a wide range of applications, and this prompted researchers to investigate their chemical modifications in order to modulate their properties. Herein we discuss the development of conjugation strategies of some polysaccharides with natural substrates and the effects of the structural modification on their bioactivities. Finally, this work intends to provide suggestions and perspectives on the development of safe and sustainable synthetic processes on polysaccharides.

Quantitative analysis of loxoprofen sodium loaded microspheres comprising pectin and its thiolated conjugates: In-vivo evaluation of their sustained release behavior

Continuous use of oral NSAIDs can damage mucosal membrane, which results in decreased bioavailability and non-compliance with the therapy. But the use of sustained release drug delivery systems might offer a solution. Objective was to synthesize mucoadhesive SR microspheres by using different combinations of pectin (PEC) and its thiolated derivative (T-PEC3100) for improved loxoprofen (LS) permeation. Thiolated pectin (T-PEC) was synthesized by the esterification method using thioglycolic acid. Thiolation was confirmed by thiol group quantification and charring point determination. Further characterization was done by Fourier Transform Infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM). Ex-vivo mucoadhesion study was performed to confirm the improved characteristics. Microspheres (MS) were prepared using different ratios of PEC/T-PEC by solvent evaporation method and their particle size and surface morphology were evaluated. Mucus permeation study was carried out using the trans-well plate method. Sustained release behavior of prepared microspheres was investigated through the edema inhibition method in albino rats. T-PEC3100 was considered the optimum formulation for further evaluation and contained maximum thiol group content. FTIR spectra showed a characteristic peak of -SH and charring point was also changed considerably confirming the successful thiolation of PEC. SEM results showed spherical microspheres in the size range of 2-10 μm. Thiol-rich formulation of MS exhibited more than 80 % release after 12 h and maximum absorbable dose (MAD) was calculated as 400 μg % inhibition of edema in MS treated group was slowly attained initially but the reduction in inflammation was detected even after 24 h as compared to control group. Promising results from In-vivo edema inhibition study suggest the possible use of these thiolated MS in formulating sustained release formulation for arthritis.

Gelling properties of lysine-amidated citrus pectins: The key role of pH in both amidation and gelation

The amidation of pectin by amino acids has been widely applied due to its safety and excellent gelling properties. This study systematically examined the effects of pH on the gelling properties of lysine-amidated pectin during amidation and gelation. Pectin was amidated over the range of pH 4-10, and the amidated pectin obtained at pH 10 showed the highest degree of amidation (DA, 27.0 %) due to the de-esterification, electrostatic attraction, and the stretching state of pectin. Moreover, it also exhibited the best gelling properties due to its greater numbers of calcium-binding regions (carboxyl groups) and hydrogen bond donors (amide groups). During gelation, the gel strength of CP (Lys 10) at pH 3-10 first increased and then decreased, with the highest gel strength at pH 8, which was due to the deprotonation of carboxyl groups, protonation of amino groups, and β-elimination. These results show that pH plays a key role in both amidation and gelation, with distinct mechanisms, and would provide a basis for the preparation of amidated pectins with excellent gelling properties. This will facilitate their application in the food industry.

Design and evaluation of propranolol hydrochloride loaded thiolated Zein/PEO electrospun fibrous matrix for transmucosal drug delivery

Thiolated polymers have garnered wide attention from researchers on mucoadhesive drug delivery. This work explores the thiolation of zein protein using cysteine amino acid via the EDC crosslinker. The optimization of thiolation and purification have been done and confirmed using Ellman's assay and Raman spectra. The thiolated Zein/PEO polymer blend has been appraised for electrospinning to fabricate fibrous matrices. The extent of thiol modification augmented the mechanical properties and adhesion in rabbit intestinal mucosa. In vitro cytotoxicity evaluations such as direct contact assay, MTT assay, and live dead assay performed in RPMI 2650 cells corroborated the non-cytotoxicity of the fabricated matrices with and without propranolol hydrochloride (PL). Detailed drug release studies were conducted in PBS. Drug release in PBS followed the Korsmeyer Peppas model of release. On treating RPMI 2650 cells with the matrix, F-actin and adherens junctional proteins retained integrity, and consequently, drug permeation would proceed through the transcellular transport mechanism. Transepithelial electrical resistance (TEER) measurement of the RPMI 2650 cell monolayer also supported the transcellular transport mechanism. Ex vivo permeation study through porcine buccal mucosa showed 41.26 ± 0.56% PL permeation within 24 h of study. It validated the competence of the electrospun thiolated Zein/PEO matrix for transmucosal drug delivery.

Recent developments in natural biopolymer based drug delivery systems

Targeted delivery of drug molecules to diseased sites is a great challenge in pharmaceutical and biomedical sciences. Fabrication of drug delivery systems (DDS) to target and/or diagnose sick cells is an effective means to achieve good therapeutic results along with a minimal toxicological impact on healthy cells. Biopolymers are becoming an important class of materials owing to their biodegradability, good compatibility, non-toxicity, non-immunogenicity, and long blood circulation time and high drug loading ratio for both macros as well as micro-sized drug molecules. This review summarizes the recent trends in biopolymer-based DDS, forecasting their broad future clinical applications. Cellulose chitosan, starch, silk fibroins, collagen, albumin, gelatin, alginate, agar, proteins and peptides have shown potential applications in DDS. A range of synthetic techniques have been reported to design the DDS and are discussed in the current study which is being successfully employed in ocular, dental, transdermal and intranasal delivery systems. Different formulations of DDS are also overviewed in this review article along with synthesis techniques employed for designing the DDS. The possibility of these biopolymer applications points to a new route for creating unique DDS with enhanced therapeutic qualities for scaling up creative formulations up to the clinical level.

Ca2+-Responsive Glyco-insulin

Chemical modification of peptides and proteins, such as PEGylation and lipidation, creates conjugates with new properties. However, they are typically not dynamic or stimuli-responsive. Self-assembly controlled by a stimulus will allow adjusting properties directly. Here, we report that conjugates of oligogalacturonic acids (OGAs), isolated from plant-derived pectin, are Ca²⁺-responsive. We report the conjugation of OGA to human insulin (HI) to create new glyco-insulins. In addition, we coupled OGA to model peptides. We studied their self-assembly by dynamic light scattering, small-angle X-ray scattering, and circular dichroism, which showed that the self-assembly to form nanostructures depended on the length of the OGA sequence and Zn²⁺ and Ca²⁺ concentrations. Subcutaneous administration of OGA12-HI with Zn²⁺ showed a stable decrease in blood glucose over a longer period of time compared to HI, despite the lower receptor binding affinity.

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.

Structure and Applications of Pectin in Food, Biomedical, and Pharmaceutical Industry: A Review

Pectin is a biocompatible polysaccharide with intrinsic biological activity, which may exhibit different structures depending on its source or extraction method. The extraction of pectin from various industrial by-products presents itself as a green option for the valorization of agro-industrial residues by producing a high commercial value product. Pectin is susceptible to physical, chemical, and/or enzymatic changes. The numerous functional groups present in its structure can stimulate different functionalities, and certain modifications can enable pectin for countless applications in food, agriculture, drugs, and biomedicine. It is currently a trend to use pectin to produce edible coating to protect foodstuff, antimicrobial bio-based films, nanoparticles, healing agents, and cancer treatment. Advances in methodology, use of different sources of extraction, and knowledge about structural modification have significantly expanded the properties, yields, and applications of this polysaccharide. Recently, structurally modified pectin has shown better functional properties and bioactivities than the native one. In addition, pectin can be used in conjunction with a wide variety of biopolymers with differentiated properties and specific functionalities. In this context, this review presents the structural characteristics and properties of pectin and information on the modification of this polysaccharide, its respective applications, perspectives, and future challenges.

Self-Assembled Folic Acid-Targeted Pectin-Multi-Arm Polyethylene Glycol Nanoparticles for Tumor Intracellular Chemotherapy

Ursolic acid is widely used as an effective anticancer drug for the treatment of various cancers. However, its poor water solubility, short circulation time in vivo, and lack of targeting have made it a burden for clinical applications. We report a self-assembled folate-modified pectin nanoparticle for loading ursolic acid (HCPT@F-Pt-PU NPs) and embed the anticancer drug hydroxycamptothecin to achieve synergistic treatment with ursolic acid. In addition, the galactose residue of the pectin molecule can be recognized by the asialoglycoprotein receptor on the surface of the liver cancer cell, promoting the rapid penetration and release of HCPT@F-Pt-PU NPs intracellularly. In particular, the introduction of multiarm polyethylene glycol can improve the uniformity (106 nm) and concealment of the nanoparticles and avoid the early release of the drug or the toxicity to normal cells. HCPT@F-Pt-PU NPs have a high drug loading (7.27 wt %) and embedding efficiency (19.84 wt %) and continuous circulation up to 80 h, leading to more apoptosis (91.61%). HCPT@F-Pt-PU NP intracellular drug delivery will be a promising strategy.

Hybrid Acrylated Chitosan and Thiolated Pectin Cross-Linked Hydrogels with Tunable Properties

We developed and characterized a new hydrogel system based on the physical and chemical interactions of pectin partially modified with thiol groups and chitosan modified with acrylate end groups. Gelation occurred at high pectin thiol ratios, indicating that a low acrylated chitosan concentration in the hydrogel had a profound effect on the cross-linking. Turbidity, Fourier transform infrared spectroscopy, and free thiol determination analyses were performed to determine the relationships of the different bonds inside the gel. At low pH values below the pKa of chitosan, more electrostatic interactions were formed between opposite charges, but at high pH values, the Michael-type addition reaction between acrylate and thiol took place, creating harder hydrogels. Swelling experiments and Young’s modulus measurements were performed to study the structure and properties of the resultant hydrogels. The nanostructure was examined using small-angle X-ray scattering. The texture profile analysis showed a unique property of hydrogel adhesiveness. By implementing changes in the preparation procedure, we controlled the hydrogel properties. This hybrid hydrogel system can be a good candidate for a wide range of biomedical applications, such as a mucosal biomimetic surface for mucoadhesive testing.

Fundamental Concepts of Hydrogels: Synthesis, Properties, and Their Applications

In the present review, we focused on the fundamental concepts of hydrogels-classification, the polymers involved, synthesis methods, types of hydrogels, properties, and applications of the hydrogel. Hydrogels can be synthesized from natural polymers, synthetic polymers, polymerizable synthetic monomers, and a combination of natural and synthetic polymers. Synthesis of hydrogels involves physical, chemical, and hybrid bonding. The bonding is formed via different routes, such as solution casting, solution mixing, bulk polymerization, free radical mechanism, radiation method, and interpenetrating network formation. The synthesized hydrogels have significant properties, such as mechanical strength, biocompatibility, biodegradability, swellability, and stimuli sensitivity. These properties are substantial for electrochemical and biomedical applications. Furthermore, this review emphasizes flexible and self-healable hydrogels as electrolytes for energy storage and energy conversion applications. Insufficient adhesiveness (less interfacial interaction) between electrodes and electrolytes and mechanical strength pose serious challenges, such as delamination of the supercapacitors, batteries, and solar cells. Owing to smart and aqueous hydrogels, robust mechanical strength, adhesiveness, stretchability, strain sensitivity, and self-healability are the critical factors that can identify the reliability and robustness of the energy storage and conversion devices. These devices are highly efficient and convenient for smart, light-weight, foldable electronics and modern pollution-free transportation in the current decade.

A novel self-assembled nanoparticle platform based on pectin-eight-arm polyethylene glycol-drug conjugates for co-delivery of anticancer drugs

The application of non-toxic carriers to increase drug loading, multi-drug delivery, and extremely small size of nano-drugs to construct a tremendous transmission system is the goal for all researchers to be pursued. The proposal of natural pectin nano-platform for delivery of multiple drugs is critical for biomedical research, especially a particle size of below 100nm with high yield. Here we design a new core-shell structure pectin-eight-arm polyethylene glycol-ursolic acid/hydrooxycampothecin nanoparticle (Pec-8PUH NPs) through a special self-assembly method for stabilizing and dispersing particles, improving water-solubility, and achieving drug controlled release. The obtained Pec-8PUH NPs possessed appropriate size (~91nm), drug-loaded efficiency and encapsulation efficiency through the regulation of eight-arm polyethylene glycol. In addition, Pec-8PUH NPs could enhance cell cytotoxicity, shorten blood retention time (7.3-fold UA, 7.2-fold HCPT) and more effective cellular uptake than free drugs, which exhibited an obvious synergistic effect of UA and HCPT by the co-delivery. 4T1 tumor-bearing mice also showed a higher survival rate than free UA and free HCPT. The result further shows that this novel drug delivery system has a promising potential for anti-cancer combination therapy.

Thiolated citrus low-methoxyl pectin: Synthesis, characterization and rheological and oxidation-responsive gelling properties

In the present study, citrus low-methoxyl pectin was modified by conjugating cysteine via amide bonds, and the resultant polymer (CYS-PEC) was characterized. CYS-PEC conjugates with thiol contents varying from 77.8μmol/g to 296μmol/g were synthesized, and the successful conjugation was evidenced by elemental, and FT-IR analyses. The sulfur in CYS-PEC is predominately in the thiol form, with a minor fraction forming disulfide bonds (∼15%), which occur when thiol/disulfide interchange interrupts the intended thiolation. Both native and modified pectin dispersions exhibited strong pseudoplastic properties, and the frequency sweeps revealed them to be dispersions containing microgel particles. Dynamic viscoelastic analysis was used to determine the oxidation-response gelling capacities of polymer dispersions containing H₂O₂, especially those that are highly thiolated and have cross-linked gel properties. For oxidation-induced CYS-PEC gels, their gelation time, hardness, viscosity and elastic moduli and swelling-disintegration ratio are dependent on the thiol group content, H₂O₂ concentration and polymer concentration.

Modified biomolecule as potential vehicle for buccal delivery of doxepin

Aim: Doxepin is a traditional tricyclic antidepressant with analgesic and anesthetic properties when applied topically to the mucosa. Doxepin is one approach in treating insomnia and depression in Parkinson's disease. Patients with Parkinson's disease suffer difficulties in swallowing. Therefore, it was the aim of this study to develop a buccal-adhesive delivery system. Methods: Pectin was modified with cysteine. Stability assays in form of disintegration assay according to the Ph.Eur were performed. Furthermore, bioadhesiveness on buccal mucosa was investigated incorporating the drug doxepin. Results: The adhesiveness was improved 1.4-fold and revealed a sustained release over 3 h. Conclusion: Taking these findings into account, the modifications render this designed excipient fruitful for buccal delivery.

Design, modification and in vitro evaluation of pectin's bucco-adhesiveness

Aim: It was the aim of this study to synthesize pectin (PEC) with sulfhydryl groups and evaluate its suitability in buccal application. Materials & methods: Native PEC was chemically modified by covalent attachment of sulfhydryl-bearing cysteine (CYS). Stability assays in form of water uptake behavior and erosion study were performed. Additionally, mucoadhesive study on buccal mucosa was performed. Results: Pectin–cysteine (PECCYS) was successfully synthesized as proved by IR and Ellman's assay exhibiting 436.59 ± 127.87 µmol thiol groups per gram polymer. Stability assay showed that PECCYS revealed a 2.27-fold improved water uptake and mucoadhesiveness augmented 3.75-fold in comparison to unmodified PEC. Conclusion: PECCYS might be a future suitable excipient for buccal adhesive application.

Oral delivery of nanoparticles containing anticancer SN38 and hSET1 antisense for dual therapy of colon cancer

An oral delivery system intended for treatment of colon cancer in HT29 cancerous cells was investigated by encapsulating hSET1 antisense and SN38 anticancer in nanoparticles based on cysteine trimethyl chitosan (cysTMC) and carboxymethyl dextran (CMD). Studies have shown hSET1 as the main type of histone methyltransferase (HMT) complex, is significantly overexpressed in malignant cells. In this study, hSET1 antisense was employed to inhibit gene expression. Additionally, SN38 was incorporated into nanoparticles to enhance the efficiency of the system by inhibition of topoisomerase 1. CysTMC was synthetized and characterized by (1)H NMR and FTIR. Nanoparticles were prepared through complexation of CMD and cysTMC. Particle size and surface charge was 100-150 nm and 17-21 mV respectively with drug content of around 2.6%. Gel electrophoresis assay proved the stability of antisense in simulated gastric and intestinal fluids. Nanoparticles showed high mucoadhesion and glutathione responsive release. Cellular uptake was observed by confocal microscopy and quantified by flow cytometry. Cytotoxicity of NPs was assessed using MTT assay. Results showed hSET1/SN38 nanoparticles had significantly higher cytotoxicity against HT29 cells compared with nanoparticles containing SN38, free SN38 or naked hSET1. Therefore, present system could be considered an effective combination therapy of highly hydrophobic SN38 and hSET1.

Is the antioxidative effectiveness of a bilberry extract influenced by encapsulation?

BACKGROUND

Bilberries (Vaccinium myrtillus L.) have been suggested to have preventive properties against diseases associated with oxidative stress such as colon cancer or inflammatory bowel diseases. Therefore the gastrointestinal tract is regarded as a potential target for prevention. In this study the antioxidative properties of a commercially available anthocyanin-rich bilberry extract (BE) were investigated in comparison with four different BE-loaded microcapsule systems. As markers to describe the antioxidant status in this cellular system, intracellular reactive oxygen species (ROS) levels, oxidative DNA damage and total glutathione (tGSH) levels were monitored.

RESULTS

Incubations with the BE-loaded capsule systems showed an increase in cellular glutathione levels and reduction of ROS levels at high BE concentrations (100-500 µg mL(-1) ) and a positive effect on the formation of DNA strand breaks (5-10 µg mL(-1) BE). The biological properties of BE-loaded pectin amide core-shell capsules, whey protein matrix capsules and coated apple pectin matrix capsules were comparable to those of the non-encapsulated BE.

CONCLUSION

Overall, the BE and the encapsulated BE types tested have antioxidative activity under the studied assay conditions in terms of the prevention of oxidative DNA damage, the reduction of intracellular ROS and the enhancement of cellular tGSH.

Synthesis and in vitro characterization of entirely S-protected thiolated pectin for drug delivery

The study was aimed to synthesize a thiolated polymer (thiomer) that is resistant to oxidation in solutions above pH 5. In order to protect a pectin-cysteine conjugate against premature oxidation, the thiomer was S-protected by a disulfide connected leaving group. Therefore, 2-mercaptonicotinic acid was first coupled to L-cysteine by a disulfide exchange reaction and the purified product was subsequently attached to pectin by a carbodiimide mediated amid bond formation. The obtained fully S-protected thiolated pectin was in vitro characterized with respect to co- and mucoadhesive properties and stability toward oxidation. The results indicated a 1.8-fold and 2.3-fold enhanced disintegration time at pH 6.8 of the S-protected thiolated pectin (Pec-Cys-MNA) compared to thiolated pectin (Pec-Cys) and unmodified pectin (Pec). Moreover, rheological measurements of polymer/mucus mixtures showed a 1.6-fold (compared to Pec-Cys) and 6.7-fold (compared to Pec) increased dynamic viscosity of Pec-Cys-MNA. On the other hand, in the presence of a strong oxidizing agent such as H2O2 (0.3% v/v), no increase in viscosity of Pec-Cys-MNA could be observed. A 6-month experiment also demonstrated the long-term stability of a liquid formulation based on Pec-Cys-MNA. Further investigations proved that the first time all thiol groups on a thiolated polymer could be protected owing to the novel synthesis. Accordingly, these features may help to develop thiomer based liquid or gel formulations targeting mucosal surfaces such as nasal, ocular or vaginal drug delivery systems.

Preactivated thiomers: evaluation of gastroretentive minitablets

The object of this study was to evaluate the potential of a recently developed preactivated thiolated pectin derivative as mucoadhesive excipient in drug delivery to the gastric cavity. Pectin (Pec) was chemically modified with L-cysteine (Cys). The free thiol groups of resulting thiomer were activated with 2-mercaptonicotinic acid (MNA) in order to improve stability and reactivity of attached thiol groups over a broad pH range. Multiunit dosage form properties of the resulting conjugate (Pec-Cys-MNA) were compared to unmodified pectin and the intermediate thiolated using rosuvastatin calcium as a model drug in loaded minitablets. Obtained results were compared with unmodified pectin and the intermediate thiolated pectin. Approximately half of attached thiol groups (507 μmol/g polymer) have been preactivated. Minitablets were evaluated regarding mucoadhesive properties, hardness, disintegration behavior, swelling characteristics and release of rosuvastatin calcium. Mediated by covalent bonds between the polymer and cysteine-rich subdomains in mucus, total work of adhesion increased more than 5-fold. The modification had no impact on hardness of compressed tablets but implementation of the aromatic ligand went along with reduction in hydrophilic properties. Disintegration time was prolonged more than 2-fold while water uptake capacity increased. Weight gain for Pec-Cys-MNA was at least 16-fold. Further, a sustained release of rosuvastatin calcium over 36 h was determined. Neither biodegradability nor CaCo-2 cell viability was affected. The study shows that Pec-Cys-MNA is a promising excipient for the development of mucoadhesive gastric dosage form.

Thiomers and thiomer-based nanoparticles in protein and DNA drug delivery

INTRODUCTION

Thanks to advances in biotechnology, more and more highly efficient protein- and DNA-based drugs have been developed. Unfortunately, these kinds of drugs underlie poor non-parental bioavailability. To overcome hindrances like low mucosal permeability and enzymatic degradation polymeric excipients are utilized as drug carrier whereat thiolated excipients showed several promising qualities in comparison to the analogical unmodified polymer.

AREAS COVERED

The article deals with the comparatively easy modification of well-established polymers like chitosan or poly(acrylates) to synthesize thiomers. Further, the recently developed "next generation" thiomers e.g. preactivated or S-protected thiomers are introduced. Designative properties like mucoadhesion, uptake and permeation enhancement, efflux pump inhibition and protection against enzymatic degradation will be discussed and differences between first and next generation thiomers will be pointed out. Additionally, nanoparticles prepared with thiomers will be dealt with regarding to protein and DNA drug delivery as thiomers seem to be a promising approach to avoid parenteral application.

EXPERT OPINION

Properties of thiomers per se and results of in vivo studies carried out so far for peptide and DNA drugs demonstrate their potential as multifunctional excipients. However, further investigations and optimizations have to be done before establishing a carrier system ready for clinical approval.

Thiomers: influence of molar mass on in situ gelling properties

The aim of this study was to investigate the influence of molar mass of thiolated polymers (thiomers) on their in situ gelling properties. Chitosan-thioglycolic acid (chitosan-TGA) and pectin-cysteine (pectin-Cys) of increasing molar mass were chosen to produce in situ gels in combination with carbamide peroxide. Low molar mass chitosan (~2 kDa) was prepared by oxidative degradation with NaNO(2), whereas pectin was depolymerized by heat treatment. Thiomers, displaying 1271-1616 μmol (chitosan-TGA) and 305-403 μmol (pectin-Cys) free thiol groups per gram polymer, were synthesized via amide bond formation mediated by a carbodiimide. The results showed that a reduction of molar mass combined with increased concentrations of both cationic chitosan-TGA and anionic pectin-Cys leads to higher final viscosities and to a higher relative increase in viscosity within 60 min and 180 min, respectively. Using this method, the dynamic viscosity of a very low molar mass chitosan-TGA (~2 kDa) could be increased 100,000-fold within 60 min and 390,000-fold within 180 min. In view of these in situ gelling properties carbohydrate thiomers might be useful for various pharmaceutical applications such as vehicle for drug delivery or as wound dressing material.

Polyanionic carbohydrate doxorubicin-dextran nanocomplex as a delivery system for anticancer drugs: in vitro analysis and evaluations

This study deals with the preparation and investigation of a nanoscale delivery system for the anticancer drug doxorubicin (DOX) using its complexation with polyanionic carbohydrate dextran sulfate (DS). Dynamic light scattering, SEM, and zeta potential determination were used to characterize nanocomplexes. DOX-DS complexation was studied in the presence of ethanol as a hydrogen-bond disrupting agent, NaCl as an electrostatic shielding agent, and chitosan as a positively charged polymer. Thermodynamics of DOX-DS interaction was studied using isothermal titration calorimetry (ITC). A dialysis method was applied to investigate the release profile of DOX from DOX-DS nanocomplexes. Spherical and smooth-surfaced DOX-DS nanocomplexes (250–500 nm) with negative zeta potential were formed at a DS/DOX (w/w) ratio of 0.4–0.6, with over 90% drug encapsulation efficiency. DOX when complexed with DS showed lower fluorescence emission and 480 nm absorbance plus a 15 nm bathometric shift in its visible absorbance spectrum. Electrostatic hydrogen bonding and π-π stacking interactions are the main contributing interactions in DOX-DS complexation. Thermal analysis of DOX-DS complexation by ITC revealed that each DOX molecule binds with 3 DS glycosyl monomers. Drug release profile of nanocomplexes showed a fast DOX release followed by a slow sustained release, leading to release of 32% of entrapped DOX within 15 days. DOX-DS nanocomplexes may serve as a drug delivery system with efficient drug encapsulation and also may be taken into consideration in designing DOX controlled-release systems.

Application of pectin in oral drug delivery

INTRODUCTION

Biopolymers have been used extensively in the pharmaceutical field. Pectin, a biopolymer, has several unique properties that enable it to be used as an excipient or carrier for oral drug delivery systems. Accordingly, several investigators have identified the benefits of pectin-based delivery systems for oral drug administration.

AREAS COVERED

This review first describes the chemical structure, source and production, degree of esterification and gel formation properties of pectin. The application of pectin in various oral drug delivery platforms is also discussed, that is, controlled release systems, gastro-retentive systems, colon-specific delivery systems and mucoadhesive delivery systems.

EXPERT OPINION

Pectin from different sources provides different gelling abilities, due to variations in molecular size and chemical composition. Like other natural polymers, a major problem with pectin is inconsistency in reproducibility between samples, which may result in poor reproducibility in delivery characteristics. Scintigraphic studies and in vivo studies, in both animals and human volunteers, demonstrate the successful development of a pectin-based colon-specific drug delivery system. Pectin-based controlled release systems, gastro-retentive systems and mucoadhesive systems present promising approaches for increasing the bioavailability of drugs, but are in their infancy. A lack of direct correlation between in vitro release and in vivo absorption studies is a major concern with these systems.

Novel pectin-4-aminothiophenole conjugate microparticles for colon-specific drug delivery

Within this study metronidazole-containing microparticles based on a pectin-4-aminothiophenol (Pec-ATP) conjugate were developed and investigated regarding their potential for colon-specific drug delivery. Microparticles were produced by spray-drying and subsequent processing. Posteriorly, they were investigated regarding their disintegration behavior, particle size, drug load, release behavior and impact on viability of Caco-2 cells. Microparticles with a mean diameter of 5.16+/-2.41 microm and a drug load of 1.15+/-0.03% metronidazole were prepared. Disintegration studies revealed that the stability of Pec-ATP microparticles was significantly improved compared to control microparticles based on unmodified pectin. In vitro release studies without potential colonic release-inducers revealed that 34.4-fold more metronidazole is retarded in Pec-ATP microparticles within 6h compared to control particles. It could be demonstrated that the retarded amount of metronidazole can be released rapidly under the influence of pectinolytic enzymes or a reducing agent, simulating the colonic environment. Cell viability studies did not reveal a significant difference between native and modified pectin, neither as a solution nor as microparticle suspension. From the improved stability, the described release features and the low toxicity of the investigated microparticles can be concluded that these particles are a promising carrier for colon-specific drug delivery.

Hydrophobic thiolation of pectin with 4-aminothiophenol: synthesis and in vitro characterization

The aim of this study was to modify pectin by covalent attachment of the water-insoluble ligand 4-aminothiophenol to its polymeric backbone. 4-Aminothiophenol is a ligand which is highly prone to oxidation. Therefore, this ligand allows oxidative cross-linking of pectin under mild oxidative conditions. Additionally, hydrophobization of pectin can be achieved by the mentioned modification which offers certain advantages over highly hydrophilic native pectins. 4-Aminothiophenol was covalently attached to pectin via amide bond formation between carboxylic moieties of pectin and the amino-group of 4-aminothiophenol. Two different pectin-4-aminothiophenol conjugates were synthesized and investigated regarding the amount of coupled ligand, rheological behavior under oxidative conditions, swelling behavior, and cytotoxic effects. Within this study, 557.3 +/- 49.0 and 158.8 +/- 23.1 micromol 4-aminothiophenol have been coupled per gram pectin. Within both conjugates, around 75% of the bound ligand appeared in its reduced form. Within rheological studies, a 500-fold increase in viscosity was achieved by addition of hydrogen peroxide as an oxidizing agent. Investigations on the swelling behavior revealed that this hydrophobic modification of pectin results in decelerated water uptake on the one hand and improved cohesive properties after oxidation of thiol groups to disulfide bonds on the other hand. Thereby, the maximum amount of water which can be uptaken by pectin matrices could be increased. According to these results, Pec-ATP conjugates could be valuable tools for several pharmaceutical applications due to the established method of gelation and the altered swelling and disintegration behavior.