Thiolated α-Cyclodextrin: The Invisible Choice to Prolong Ocular Drug Residence Time

Mucoadhesive Budesonide Solution for the Treatment of Pediatric Eosinophilic Esophagitis

Eosinophilic Esophagitis is an antigen-mediated inflammatory disease characterized by thickening of the esophageal wall, leading to dysphagia, vomiting, reflux, and abdominal pain. This disease can be treated with a therapeutic approach ranging from diet to pharmacological therapy. Jorveza® (budesonide) and Dupixent® (dupilumab) are treatments for Eosinophilic Esophagitis approved by the European Medicines Agency in adults but not in children. Budesonide-based extemporaneous oral liquid suspensions could be prepared for pediatric use. The main limit of this formulation is that budesonide needs a longer residence time on the esophageal mucosa to solubilize and diffuse in it to exert its local anti-inflammatory effect. Herein, we propose the development of an extemporaneous mucoadhesive oral budesonide solution for the pediatric population. A liquid vehicle containing hydroxypropyl-beta-cyclodextrin as a complexing agent and carboxymethylcellulose sodium as a mucoadhesive excipient was used to prepare budesonide-based formulations. A stable solution at a concentration of 0.7 mg/mL was successfully prepared and characterized. The formulation showed rheological and mucoadhesive properties suitable for an Eosinophilic Esophagitis local prolonged treatment. In this way, pharmacists can prepare stable budesonide-based mucoadhesive solutions, providing both patients and physicians with a new therapeutic option for Eosinophilic Esophagitis pediatric treatment.

Cyclodextrins and derivatives in drug delivery: New developments, relevant clinical trials, and advanced products

Cyclodextrins (CD) and derivatives are functional excipients that can improve the bioavailability of numerous drugs. Because of their drug solubility improving properties they are used in many pharmaceutical products. Furthermore, the stability of small molecular drugs can be improved by the incorporation in CDs and an unpleasant taste and smell can be masked. In addition to well-established CD derivatives including hydroxypropyl-β-CD, hydroxypropyl-γ-CD, methylated- β-CD and sulfobutylated- β-CD, there are promising new derivatives in development. In particular, CD-based polyrotaxanes exhibiting cellular uptake enhancing properties, CD-polymer conjugates providing sustained drug release, enhanced cellular uptake, and mucoadhesive properties, and thiolated CDs showing mucoadhesive, in situ gelling, as well as permeation and cellular uptake enhancing properties will likely result in innovative new drug delivery systems. Relevant clinical trials showed various new applications of CDs such as the formation of CD-based nanoparticles, stabilizing properties for protein drugs or the development of ready-to-use injection systems. Advanced products are making use of various benefical properties of CDs at the same time. Within this review we provide an overview on these recent developments and take an outlook on how this class of excipients will further shape the landscape of drug delivery.

Development and Characterization of Thiolated Cyclodextrin-Based Nanoparticles for Topical Delivery of Minoxidil

PURPOSE

The aim of this research was to prepare adhesive nanoparticles for the topical application of Minoxidil (MXD).

METHODS

Thiolated β-CDs were prepared via conjugation of cysteamine with oxidized CDs. MXD was encapsulated within thiolated and unmodified β-CDs. Ionic gelation method was used to prepare nanoparticles (Thio-NP and blank NP) of CDs with chitosan. Nanoparticles were analyzed for size and zetapotential. Inclusion complexes were characterized via FTIR. Drug dissolution studies were carried out. An in vitro adhesion study over human hair was performed. An in vivo skin irritation study was performed. Ex vivo drug uptake was evaluated by using a Franz diffusion cell.

RESULTS

Thiolated β-CDs presented 1804.68 ± 25 μmol/g thiol groups and 902.34 ± 25 μmol/g disulfide bonds. Nanoparticles displayed particle sizes within a range of 231 ± 07 nm to 354 ± 13 nm. The zeta potential was in the range of -8.1 ± 02 mV, +16.0 ± 05 mV. FTIR analyses confirmed no interaction between the excipients and drug. Delayed drug release was observed from Thio-NP. Thio-NP retained over hair surfaces for a significantly longer time. Similarly, drug retention was significantly improved. Thio-NP displayed no irritation over rabbit skin.

CONCLUSION

Owing to the above results, nanoparticles developed with MXD-loaded thiolated β-CDs might be a potential drug delivery system for topical scalp diseases.

Mucoadhesive, Fluconazole-Loaded Nanogels Complexed with Sulfhydryl-β-cyclodextrin for Oral Thrush Treatment

The objective of this study was to generate fluconazole-loaded mucoadhesive nanogels to address the problem of hydrophobicity of fluconazole (FL). An inclusion complex was formulated with sulfhydryl-β-CD (SH-β-CD) followed by nanogels formation by a Schiff base reaction of carbopol 940 (CA-940) and gelatin (GE). For characterization, PXRD, FT-IR analysis, drug content, and phase solubility studies were performed. Similarly, nanogels were assessed for particle size, zeta potential, organoleptic, and spreadability studies. Moreover, drug contents, rheological, in vitro drug permeation, release kinetics, toxicity, and stability studies of nanogels were performed. Furthermore, mucoadhesive characteristics over the buccal mucosal membrane of the goat were evaluated. The nanogels formulated with a higher amount of CA-940 and subsequently loaded with the inclusion complexes of FL showed promising results. PXRD and FT-IR analysis confirmed the physical complexes by displaying a reduction in the intensity of peaks of FL. The average particle size of nanogels was in the range of 257 to 361 nm. The highest drug content of 88% was encapsulated within the FL-SH-β-CD complex. All formulations at 0.5-1% concentration displayed no toxicity to the Caco-2 cell lines. Nanogels loaded with FL-SH-β-CD complexes showed 18-fold improved mucoadhesion on the buccal mucous membrane of the goat when compared to simple nanogels. The in vitro permeation study exhibited significantly enhanced permeation and first-order concentration-dependent drug release was observed. On the bases of these findings, we can conclude that a mucoadhesive nanogel-based drug delivery system can be an ideal therapy for candidiasis.

Advancements in Nanogels for Enhanced Ocular Drug Delivery: Cutting-Edge Strategies to Overcome Eye Barriers

Nanomedicine in gel or particle formation holds considerable potential for enhancing passive and active targeting within ocular drug delivery systems. The complex barriers of the eye, exemplified by the intricate network of closely connected tissue structures, pose significant challenges for drug administration. Leveraging the capability of engineered nanomedicine offers a promising approach to enhance drug penetration, particularly through active targeting agents such as protein peptides and aptamers, which facilitate targeted release and heightened bioavailability. Simultaneously, DNA carriers have emerged as a cutting-edge class of active-targeting structures, connecting active targeting agents and illustrating their potential in ocular drug delivery applications. This review aims to consolidate recent findings regarding the optimization of various nanoparticles, i.e., hydrogel-based systems, incorporating both passive and active targeting agents for ocular drug delivery, thereby identifying novel mechanisms and strategies. Furthermore, the review delves into the potential application of DNA nanostructures, exploring their role in the development of targeted drug delivery approaches within the field of ocular therapy.

Thiolated cyclodextrins: A comparative study of their mucoadhesive properties

AIM

The aim of this study was the comparison of the mucoadhesive properties of nonionic, negatively, and positively charged thiolated cyclodextrins (CDs), including α-, β-, and γ-CDs of low and high degree of thiolation.

METHODS

Native α-, β-, and γ-CDs were thiolated with phosphorous pentasulfide in sulfolane (CD-SH) (i), via reductive amination with cysteamine after oxidative ring opening (CD-Cya) (ii), and via esterification with mercaptosuccinic acid (CD-MSA) (iii). These thiolated CDs were characterized via ¹H NMR and Ellman's test. Cytotoxicity was determined via resazurin and hemolysis assay. Mucoadhesive properties were evaluated via rheological studies with freshly isolated porcine mucus, as well as residence time studies on porcine small intestinal mucosa.

RESULTS

The structure of thiolated CDs was confirmed via ¹H NMR. The degree of thiolation was in the range of 594-1034 µmol/g for low and 1360-3379 µmol/g for high CD-SH, whereas thiolated CD-Cya and thiolated CD-MSA exhibited a degree of thiolation of 1142-3242 µmol/g and 243-1227 µmol/g, respectively. Just cationic CDs showed cytotoxicity. Nonionic highly thiolated α-CD-SH, α-CD-Cya, and α-CD-MSA exhibited with mucus 5.6-, 15.7- and 2.8-fold improved dynamic viscosity, while improvement was 7.7-, 6.1-, and 5.4-fold for the corresponding thiolated β-CDs and 12.3-, 15.4- and 17.8-fold for the corresponding thiolated γ-CDs compared with native CDs, respectively. A prolonged mucosal residence time following the rank order γ > β > α was observed for all thiolated CDs, whereby γ-CD-Cya, nonionic highly thiolated β-CD-SH and α-CD-Cya showed the highest mucoadhesive properties.

CONCLUSION

A high degree of thiolation and the introduction of cationic charges are mainly responsible for high mucoadhesive properties of CDs.

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

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

Emerging technologies to increase gastrointestinal transit times of drug delivery systems

Apart from already established technologies to increase gastrointestinal transit times, including devices rapidly increasing in size once they have reached the stomach in order to retard the passage through the pylorus, formulations that float on gastric fluids and mucoadhesive drug delivery systems adhering to the gastrointestinal mucosa, there are new technologies emerging that might be game changing. They include mucus permeating nanocarriers that are able to diffuse deeply into the mucus gel layer of the gastric and intestinal mucosa remaining there for a prolonged time period (i), charge-converting nanocarriers that shift their zeta potential from negative to positive within the mucus gel layer providing strong ionic bonds with anionic mucus glycoproteins (ii) and thiolated nanocarriers and cyclodextrins form even covalent bonds with cysteine-rich subdomains of mucus glycoproteins (iii). Within this review we will provide an overview about these emerging new technologies and will critically discuss their potential and shortcomings.

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.

Formulation and Optimization of Sodium Alginate Polymer Film as a Buccal Mucoadhesive Drug Delivery System Containing Cetirizine Dihydrochloride

Currently, pharmaceutical companies are working on innovative methods, processes and products. Oral mucoadhesive systems, such as tablets, gels, and polymer films, are among these possible products. Oral mucoadhesive systems possess many advantages, including the possibility to be applied in swallowing problems. The present study focused on formulating buccal mucoadhesive polymer films and investigating the physical and physical–chemical properties of films. Sodium alginate (SA) and hydroxypropyl methylcellulose (HPMC) were used as film-forming agents, glycerol (GLY) was added as a plasticizer, and cetirizine dihydrochloride (CTZ) was used as an active pharmaceutical ingredient (API). The polymer films were prepared at room temperature with the solvent casting method by mixed two-level and three-level factorial designs. The thickness, tensile strength (hardness), mucoadhesivity, surface free energy (SFE), FTIR, and Raman spectra, as well as the dissolution of the prepared films, were investigated. The investigations showed that GLY can reduce the mucoadhesivity of films, and CTZ can increase the tensile strength of films. The distribution of CTZ proved to be homogeneous in the films. The API could dissolve completely from all the films. We can conclude that polymer films with 1% and 3% GLY concentrations are appropriate to be formulated for application on the buccal mucosa as a drug delivery system.

Thiolated cyclodextrins: Mucoadhesive and permeation enhancing excipients for ocular drug delivery

Thiolated β-cyclodextrin (β-CD) has the potential to enhance mucoadhesive and permeation enhancing properties on ocular mucosa. Thiolated β-CD was synthesized via replacement of all primary hydroxyl groups on β-CD backbone by halogen followed by substitution with thiol groups. The structure was confirmed by FT-IR and ¹H NMR spectroscopy. Thiolated CD was characterized for hemolytic effect, ocular irritation, solubility enhancement, viscoelastic behavior and mucoadhesive properties. Moreover, the permeation enhancing effect of thiolated oligomer on different ocular tissues including conjunctiva, sclera and cornea was evaluated with sodium fluorescein (Na-Flu) as a marker. Thiolated β-CD displayed 5360 ± 412 µmol/g thiol groups. The newly synthesized oligomer did not show any hemolytic effect on red blood cells at a concentration of 0.5% (m/v) for an incubation period of 3 h and minimal corneal irritation effects without any inflammation within 72 h. Thiolated β-CD exhibited a 5.3-fold improved aqueous solubility as compared to the unmodified β-CD. Thiolated oligomer (0.5% m/v) enhanced the viscosity of mucus up to 6.2-fold within 4 h and provided a 26-fold prolonged ocular residence time due to mucoadhesion. Moreover, 0.5% (m/v) thiolated β-CD enhanced the permeation of Na-Flu 9.6-, 7.1- and 5.3-fold on conjunctiva, sclera and cornea, respectively. Based on these findings, thiolated β-CD might be a promising auxiliary agent for ocular drug delivery.

Strategies to prolong the residence time of drug delivery systems on ocular surface

Ocular diseases may be treated via different routes of administration, such as topical, intracameral, intravitreal, oral and parenteral. Among them the topical route is most accepted by patients, although it provides in many cases the lowest bioavailability. Indeed, when a topical formulation reaches the precorneal area, i.e., the drug absorption and/or action site, it is rapidly eliminated due to eye protection mechanisms such as blinking, basal and reflex tearing, and naso-lacrimal draining. To avoid this and to reduce the frequency of dosing, various strategies have been developed to prolong drug residence time after topical administration. These strategies include the use of viscosity increasing and mucoadhesive excipients as well as combinations thereof. From the drug delivery system point of view, liquid and semisolid formulations are preferred over solid formulations such as ocular inserts and contact lenses. Furthermore, liquid and semisolid formulations can contain nano- and microcarrier systems that contribute to a prolonged residence time. Within this review an overview about the different types of excipients and formulations as well as their performance in valid animal models and clinical trials is provided.

Challenges for cysteamine stabilization, quantification, and biological effects improvement

The aminothiol cysteamine, derived from coenzyme A degradation in mammalian cells, presents several biological applications. However, the bitter taste and sickening odor, chemical instability, hygroscopicity, and poor pharmacokinetic profile of cysteamine limit its efficacy. The use of encapsulation systems is a good methodology to overcome these undesirable properties and improve the pharmacokinetic behavior of cysteamine. Besides, the conjugation of cysteamine to the surface of nanoparticles is generally proposed to improve the intra-oral delivery of cyclodextrin-drug inclusion complexes, as well as to enhance the colorimetric detection of compounds by a gold nanoparticle aggregation method. On the other hand, the detection and quantification of cysteamine is a challenging mission due to the lack of a chromophore in its structure and its susceptibility to oxidation before or during the analysis. Derivatization agents are therefore applied for the quantification of this molecule. To our knowledge, the derivatization techniques and the encapsulation systems used for cysteamine delivery were not reviewed previously. Thus, this review aims to compile all the data on these methods as well as to provide an overview of the various biological applications of cysteamine focusing on its skin application.

Per-6-Thiolated Cyclodextrins: A Novel Type of Permeation Enhancing Excipients for BCS Class IV Drugs

The purpose of the study was to develop a per-6-thiolated α-cyclodextrin (α-CD) by substituting all primary hydroxyl groups of α-CD with thiol groups and to assess its solubility-improving and permeation-enhancing properties for a BCS Class IV drug in vitro as well as in vivo. The primary hydroxyl groups of α-CD were replaced by iodine, followed by substitution with -SH groups. The structure of per-6-thiolated α-CD was approved by FT-IR and ¹H NMR spectroscopy. The per-6-thiolated was characterized for thiol content, -SH stability, cytotoxicity, and solubility-improving properties by using the model BCS Class IV drug furosemide (FUR). The mucoadhesive properties of the thiolated oligomer were investigated via viscoelastic measurements with porcine mucus, whereas permeation-enhancing features were evaluated on the Caco-2 cell monolayer and rat gut mucosa. Furthermore, oral bioavailability studies were performed in rats. The per-6-thiolated α-CD oligomer displayed 4244 ± 402 μmol/g thiol groups. These -SH groups were stable at pH ≤ 4, exhibiting a pK_a value of 8.1, but subject to oxidation at higher pH. Per-6-thiolated α-CD was not cytotoxic to Caco-2 cells in 0.5% (m/v) concentration within 24 h. It improved the solubility of FUR in the same manner as unmodified α-CD. The addition of per-6-thiolated α-CD (0.5% m/v) increased the mucus viscosity up to 5.8-fold at 37 °C within 4 h. Because of the incorporation in per-6-thiolated α-CD, the apparent permeability coefficient (P_app) of FUR was 6.87-fold improved on the Caco-2 cell monolayer and 6.55-fold on the intestinal mucosa. Moreover, in vivo studies showed a 4.9-fold improved oral bioavailability of FUR due to the incorporation in per-6-thiolated α-CD. These results indicate that per-6-thiolated α-CD would be a promising auxiliary agent for the mucosal delivery of, in particular, BCS Class IV drugs.

Cyclodextrins in Drug Delivery Systems and Their Effects on Biological Barriers

Cyclodextrins are widely used excipients, composed of glucopyranose units with a cyclic structure. One of their most important properties, is that their inner cavity is hydrophobic, while their surface is hydrophilic. This enables them for the complex formation with lipophilic molecules. They have several applications in the pharmaceutical field like solubility enhancers or the building blocks of larger drug delivery systems. On the other hand, they have numerous effects on cells or biological barriers. In this review the most important properties of cyclodextrins and cyclodextrin-based drug delivery systems are summarized with special focus on their biological activity.

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.

Mucoadhesive hydrogels for buccal drug delivery: In vitro-in vivo correlation study

AIM

It was the aim of this study to assess in vitro methods for the characterization of mucoadhesive hydrogels for their potential to predict the residence time on human buccal mucosa.

METHODS

Mixtures of hydrogels comprising hydroxyethyl cellulose (HEC), sodium carboxymethyl cellulose (CMC), xanthan gum (XTGM), hyaluronic acid sodium salt (HA), sodium alginate (ALG), carbopol (CP) as well as polycarbophil (PCP) and porcine mucus were analysed for relative rheological synergism. Furthermore, hydrogels were characterized for their texture and mechanical properties. For the assessment of mucoadhesive strength of formulations tensile studies were performed on porcine buccal mucosa. To facilitate a direct comparability of data the residence time of stained hydrogels was determined ex vivo on porcine buccal mucosa and in the oral cavity of volunteers.

RESULTS

The extent of relative rheological synergism was in good agreement with data from in vivo residence time studies. Results of tensile studies were further effected by textural properties of hydrogels leading to a restricted correlation with data from the in vivo experiment. The resistance towards removal by artificial saliva flow ex vivo revealed the highest correlation to the in vivo experiment with increasing mucosal residence time in the rank order CP < HEC, HA, ALG, PCP < CMC < XTGM.

CONCLUSIONS

This overview of measurement principles to predict the residence time of hydrogels for buccal application in humans may be a potent tool for the development of semisolid intraoral formulations.

Crossing biological barriers with nanogels to improve drug delivery performance

The current limitations in the use of nanocarriers to treat constantly evolving diseases call for the design of novel and smarter drug delivery systems (DDS). Nanogels (NGs) are three-dimensional crosslinked polymers with dimensions on the nanoscale and with a great potential for use in the biomedical field. Particular interest focuses on their application as DDS to minimize severe toxic effects and increase the therapeutic index of drugs. They have recently gained attention, since they can include responsive modalities within their structure, which enable them to excerpt a therapeutic function on demand. Their bigger sizes and controlled architecture and functionality, when compared to non-crosslinked polymers, make them particularly interesting to explore novel modalities to cross biological barriers. The present review summarizes the most significant developments of NGs as smart carriers, with focus on smart modalities to cross biological barriers such as cellular membrane, tumor stroma, mucose, skin, and blood brain barrier. We discuss the properties of each barrier and highlight the importance that the NG design has on their capability to overcome them and deliver the cargo at the site of action.

S-protected thiolated cyclodextrins as mucoadhesive oligomers for drug delivery

AIM

The purpose of this study was to develop a novel mucoadhesive thiolated and S-protected gamma cyclodextrin (γ-CD) with an intact ring backbone to assure a prolonged residence time at specific target sites.

METHOD

Thiolated γ-CD was generated through bromine substitution of its hydroxyl groups followed by replacement to thiol groups using thiourea. In the second step, thiol groups were protected by disulfide bond formation with 2-mercaptonicotinic acid (2-MNA).

RESULT

Thiolated γ-CD displayed 1385 ± 84 µmol thiol groups per gram of oligomer and the amount of MNA determined in the S-protected oligomer was 1153 ± 41 µmol per gram of oligomer. In-vitro screening of mucoadhesive properties of thiolated and S-protected γ-CD was done by two methods. Rheological investigation revealed the conjugates non-mucolytic with only a slight increase in viscosity of thiolated and S-protected γ-CD as compared to unmodified γ-CD, whereas mucoadhesive properties of the new thiolated and S-protected γ-CD performed on freshly excised porcine intestinal mucosa showed 44.4- and 50.9-fold improvement in mucoadhesion, respectively. The new conjugates did not show any cytotoxicity to Caco-2 cells even at a concentration of 1% (m/v) for 24 h. In addition, in-vitro studies of α-amylase degradation of γ-CD, γ-CD-SH and γ-CD-SS-MNA confirmed that all conjugates are biodegradable.

CONCLUSION

These outcomes predict that these new conjugates of γ-CD might provide a new favorable tool for drug delivery providing a prolonged residence time on mucosal surfaces.

Non-ionic thiolated cyclodextrins - the next generation

Introduction

The current study was aimed at developing a novel mucoadhesive thiolated cyclodextrin (CD) without ionizable groups and an intact ring backbone for drug delivery.

Materials and methods

Thiolated beta CD (β-CD) was prepared through bromine substitution of its hydroxyl groups followed by replacement to thiol groups using thiourea. The thiolated β-CD was characterized in vitro via dissolution studies, cytotoxicity studies, mucoadhesion studies on freshly excised porcine intestinal mucosa, and inclusion complex formation with miconazole nitrate.

Results

Thiolated β-CDs namely β-CD-SH₆₀₀ and β-CD-SH₁₂₀₀ displayed 558.66 ± 78 and 1,163.45 ± 96 µmol thiol groups per gram of polymer, respectively. Stability constant (Kc) of 190 M^-1 confirmed the inclusion complex formation of miconazole nitrate with β-CD-SH. Inclusion complexes of β-CD-SH₆₀₀ and β-CD-SH₁₂₀₀ resulted in 157- and 257-fold increased solubility of miconazole nitrate, respectively. In addition, more than 80% of thiol groups were stable even after 6 hours at pH 5. Both β-CD-SH compounds showed at least 1.3-fold improved solubility in water. In contrast to cationic thiolated CDs of the first generation, both thiomers showed no significant cytotoxicity. The mucoadhesive properties of the new thiolated CDs were 39.73- and 46.37-fold improved, respectively.

Conclusion

These results indicate that β-CD-SH might provide a new favorable tool for delivery of poorly soluble drugs providing a prolonged residence time on mucosal surfaces.

Novel drug delivery systems for ocular therapy: With special reference to liposomal ocular delivery

Delivery of drugs to eyes is a great challenge to researchers because of a number of barriers in the eye preventing the actual dose from reaching the site. A number of ophthalmic delivery systems have been developed in the past couple of years that are not only new but also safe and reliable and help to overcome all those barriers in the eye which are responsible for the very less bioavailability of drugs. In this review, we tried to focus on current research in ocular delivery of drug substances giving special emphasis to liposomal delivery system. A brief analysis of other novel ocular delivery systems, ocular physiology, and microbial sources of disease are also highlighted herein. We analyzed the various research findings for churning a general idea for novel ocular delivery system and its future use. The novel formulations may overcome the addressed problems of ophthalmic medication and comply with the quality assurance issues. The liposomal delivery is advantageous as they have the ability to entrap both hydrophobic and hydrophilic drugs and are suitable for delivery to both the anterior and posterior segment of the eye. Therefore, the use of this alternative approach is quite a necessity.

New perspectives of starch: Synthesis and in vitro assessment of novel thiolated mucoadhesive derivatives

AIM

The purpose of this study was to develop a novel thiolated starch polymer with improved mucoadhesive properties by conjugation of cysteamine to starch as a natural polymer of restricted mucoadhesive properties.

METHODS

Aldehyde substructures were integrated into starch via oxidative cleavage of vicinal diols by increasing amounts of sodium periodate followed by covalent attachment of cysteamine to oxidized starch via reductive amination. Thiol groups were quantified via Ellman's reaction and their impact on mucoadhesion was analyzed by rheological investigations, the rotating cylinder method and tensile studies on porcine mucosa.

RESULTS

The total amount of immobilized thiol groups revealed a correlation between degree of oxidation and thiolation. Modified starch demonstrated an up to 1.66-fold increase in water uptake in comparison to native starch. Modification of starch resulted in greatly improved cohesive properties and improvement in mucoadhesion. Rheological investigations revealed a 2- to 4-fold rise in viscosity of mucus. Tensile studies revealed a linear correlation between degree of oxidation/thiolation and enhancement of maximum detachment force and total work adhesion.

CONCLUSION

In terms of these results, thiolated starch is a new, promising, polymer in the field of mucoadhesive drug delivery systems.

Chlorophyll a in cyclodextrin supramolecular complexes as a natural photosensitizer for photodynamic therapy (PDT) applications

Chlorophyll a (Chl a), an amphipathic porphyrin, was employed as natural photosensitizer for photodynamic therapy applications. Due to its lacking solubility in water and high tendency to aggregate, Chl a was included into different modified cyclodextrins (CDs) to form stable water-soluble supramolecular complexes. To achieve this aim, 2-Hydroxypropyl-β-cyclodextrin (2-HP-β-CD), 2-Hydroxypropyl-γ-cyclodextrin (2-HP-γ-CD), Heptakis(2,6-di-o-methyl)-β-cyclodextrin (DIMEB) and Heptakis(2,3,6-tri-o-methyl)-β-cyclodextrin (TRIMEB) were used. The chemical physical properties of Chl a/CD complexes in cellular medium were studied by means of UV-Vis absorption spectroscopy. Results demonstrated the good aptitude of 2-HP-γ-CD, and more particularly of 2-HP-β-CD, to solubilize the Chl a in cell culture medium in monomeric and photoactive form. Then, Chl a/2-HP-β-CD and Chl a/2-HP-γ-CD complexes were evaluated in vitro on human colorectal adenocarcinoma HT-29 cell line, and cytotoxicity and intracellular localization were respectively assessed. Further tests, such as phototoxicity, ROS generation, intracellular localization and mechanism of cell death were then focused exclusively on Chl a/2-HP-β-CD system. This complex exhibited no dark toxicity and a high phototoxicity toward HT-29 cells inducing cell death via necrotic mechanism. Therefore, it is possible to affirm that Chl a/2-HP-β-CD supramolecular complex could be a promising and potential formulation for applications in photodynamic therapy.

Cyclodextrin-Based Formulations: A Non-Invasive Platform for Targeted Drug Delivery

Cyclodextrins (CDs) are recognized as promising pharmaceutical excipients due to their unique ability to form water-soluble inclusion complexes with various poorly soluble compounds. The numerous investigations on CDs and their use in nanomedicine have received considerable attention in the last three decades, leading to the rapid development of new CD-containing formulations that significantly facilitate targeted drug delivery and controlled drug release, with consequent improvements in drug bioavailability. This MiniReview highlights the efficacy and recent uses of CDs for non-invasive drug delivery. Using ophthalmic and nasal drug delivery as examples, an overview of chemical properties, mechanisms of CDs on drug solubilization, stabilization and permeation, along with their toxicological profiles relevant to nasal and ocular administration, are provided and discussed. The recent development and application of CD-based nanocarrier systems for targeted drug delivery are summarized.