Cyclodextrin nanosystems in oral drug delivery: A mini review

Sculpturing the future of water-soluble cyclodextrin branched polymers in pharmaceutical applications

Water-soluble polymers of cyclodextrins (CyD) can be easily obtained in alkaline media following polycondensation of the naturally occurring monomers in the presence of a crosslinking agent. They can be further modified to customize specifically functionalized architectures. Compared to other macromolecules natural and not, the CyD polymers are endowed with a unique feature, the cone-shaped cavities where they can host guests of various nature. This element has sollicited interest in this class of molecules for a wide range of applications including the biomedical field, in particular drug delivery. The CyD polymers display excellent behavior in terms of water solubility and solubilizing power towards drugs and therapeutic agents that are incompatible with biological fluids. Moreover, they can load more than one type of therapeutic agent in a single system thus allowing to implement combination therapy. In spite of some very promising results as delivery systems, their potentialities remain limited by some intrinsic hurdles. Herein, we comment on their limits mainly related to the production process and the possible solutions to overcome them, giving an outlook on their assets for innovation in disease treatment.

Surface modification of carbon dots with cyclodextrins as potential biocompatible photoluminescent delivery/bioimaging nanoplatform

BACKGROUND

Cyclodextrins are a well-established system which form inclusion complexes with many guest molecules. This property can be easily exploited to develop drug delivery systems. Additionally, carbon dots (CD) are a low-toxic photoluminescent product which have been used as luminescent tags. The combination of cyclodextrins and carbon dots allows obtaining a new nanoplatform, a biocompatible material, with both capabilities, increasing as well the internalization by the cells of the CD, induced by the cyclodextrins.

RESULTS

In the present work, we have modified the surface of carbon dots obtained from citric acid and glutathione with β and γ cyclodextrins. After a morphological and spectroscopic characterization, we concluded that the luminescence quantum yield and absorption molar coefficient of the derivatized and unmodified carbon dots was the same. These findings, together with the spectroscopic detection of active cyclodextrins, those bond to the CD able to interact with a guest molecule, allowed determination of the ratios: cyclodextrins/CD, active cyclodextrins/CD and an estimation of the CD molecular mass. Furthermore, the biocompatibility of the new materials was evaluated through cytotoxicity and cell-penetrance assays revealing that the materials were non cytotoxic up to 0.1 mg/mL. Moreover, the biocompatible developed nanoplatform penetrates in the cells maintaining the material's intrinsic fluorescence, thus constituting an adequate photoluminescent-tag with high-contrast for in vitro cell imaging.

SIGNIFICANCE

This work provides a new and easy method to combine cyclodextrins and carbon dots into a biocompatible material which can be used as nanoplatform both as drug delivery system and as photoluminescent tag in cell imaging. Likewise, this paper shows how to characterize the number of cyclodextrins and active cyclodextrins per CD, having an average stoichiometric relation of 1:1 for guest molecule - CD. Additionally, the minimum molecular mass of the unmodified CD was indirectly obtained, yielding about 1.6-1.9 kDa.

Cyclodextrins and their potential applications for delivering vitamins, iron, and iodine for improving micronutrient status

Cyclodextrins (CDs) have been investigated as potential biopolymeric carriers that can form inclusion complexes with numerous bioactive ingredients. The inclusion of micronutrients (e.g. vitamins or minerals) into cyclodextrins can enhance their solubility and provide oxidative or thermal stability. It also enables the formulation of products with extended shelf-life. The designed delivery systems with CDs and their inclusion complexes including electrospun nanofibers, emulsions, liposomes, and hydrogels, show potential in enhancing the solubility and oxidative stability of micronutrients while enabling their controlled and sustained release in applications including food packaging, fortified foods and dietary supplements. Nano or micrometer-sized delivery systems capable of controlling burst release and permeation, or moderating skin hydration have been reported, which can facilitate the formulation of several personal and skin care products for topical or transdermal delivery of micronutrients. This review highlights recent developments in the application of CDs for the delivery of micronutrients, i.e. vitamins, iron, and iodine, which play key roles in the human body, emphasizing their existing and potential applications in the food, pharmaceuticals, and cosmeceuticals industries.

Pharmacokinetics and pharmacodynamics of cyclodextrin-based oral drug delivery formulations for disease therapy

Oral drug administration has become the most common and preferred mode of disease treatment due to its good medication adherence and convenience. For orally administered drugs, the safety, efficacy, and targeting ability requirements have grown as disease treatment research advances. It is difficult to obtain prominent efficacy of traditional drugs simply via oral administration. Numerous studies have demonstrated that cyclodextrins (CDs) can improve the clinical applications of certain orally administered drugs by enhancing their water solubility and masking undesirable odors. Additionally, deeper studies have discovered that CDs can influence disease treatment by altering the drug pharmacokinetics (PK) or pharmacodynamics (PD). This review highlights recent research progress on the PK and PD effects of CD-based oral drug delivery in disease therapy. Firstly, the review describes the characteristics of current drug delivery modes in oral administration. Besides, we minutely summarized the different CD-containing drugs, focusing on the impact of CD-based alterations in PK or PD of orally administered drugs in treating diseases. Finally, we deeply discussed current challenges and future opportunities with regard to PK and PD of CD-based oral drug delivery formulations.

Chitosan and Cyclodextrins-Versatile Materials Used to Create Drug Delivery Systems for Gastrointestinal Cancers

Gastrointestinal cancers are characterized by a frequent incidence, a high number of associated deaths, and a tremendous burden on the medical system and patients worldwide. As conventional chemotherapeutic drugs face numerous limitations, researchers started to investigate better alternatives for extending drug efficacy and limiting adverse effects. A remarkably increasing interest has been addressed to chitosan and cyclodextrins, two highly versatile natural carbohydrate materials endowed with unique physicochemical properties. In this respect, numerous studies reported on fabricating various chitosan and cyclodextrin-based formulations that enabled prolonged circulation times, improved cellular internalization of carried drugs, preferential uptake by the targeted cells, reduced side effects, enhanced apoptosis rates, and increased tumor suppression rates. Therefore, this paper aims to briefly present the advantageous properties of these oligo- and polysaccharides for designing drug delivery systems, further focusing the discussion on nanocarrier systems based on chitosan/cyclodextrins for treating different gastrointestinal cancers. Specifically, there are reviewed studies describing promising solutions for colorectal, liver, gastric, pancreatic, and other types of cancers of the digestive system towards creating an updated framework of what concerns anticancer chitosan/cyclodextrin-based drug delivery systems.

Supercritical Antisolvent Precipitation of Corticosteroids/β-Cyclodextrin Inclusion Complexes

In this study, corticosteroid-β-cyclodextrin (β-CD) inclusion complexes were prepared by using supercritical antisolvent (SAS) precipitation to enhance the dissolution rate of dexamethasone (DEX) and prednisolone (PRED), which are poorly water soluble drugs. The processing of the active principles in the absence of a carrier led to their almost complete extraction (the small amount of obtained material precipitates in the form of crystals). The coprecipitation of the ingredients in the presence of β-CD was investigated at different concentrations, pressures, and molar ratios. For both the corticosteroids, the optimized operating conditions were 40 °C, 120 bar, an equimolar ratio, and a concentration in DMSO of 20 mg/mL; these conditions led to the attainment of microparticles with mean diameters equal to 0.197 ± 0.180 μm and 0.131 ± 0.070 μm in the case of DEX and PRED, respectively. Job's method confirmed the formation of inclusion complexes with a 1/1 mol/mol ratio. Compared to the pure ingredients, the obtained powders have an improved release rate, which is about three times faster in both cases. The release curves obtained under the best operating conditions were fitted using different models. The best fitting was obtained using the Weibull model, whose parameters are compatible with a combined release mechanism involving Fickian diffusion and controlled release.

Cyclodextrin-based metal-organic framework materials: Classifications, synthesis strategies and applications in variegated delivery systems

Metal-organic frameworks (MOFs) are coordination compounds that possess an adjustable structure and controllable function. Despite their wide applications in various industries, the use of MOFs in the fields of food and biomedicine is limited mainly due to their potential biological toxicity. Researchers have thus focused on developing biocompatible MOFs to address this issue. Among them, cyclodextrin-based metal-organic frameworks (CD-MOFs) have emerged as a promising alternative. CD-MOFs are novel MOFs synthesized using naturally carbohydrate cyclodextrin and alkali metal cations, and possess renewable, non-toxic, and edible characteristics. Due to their high specific surface area, controllable porosity, great biocompatibility, CD-MOFs have been widely used in various delivery systems, such as encapsulation of nutraceuticals, flavors, and antibacterial agents. Although the field of CD-MOF materials is still in its early stages, they provide a promising direction for the development of MOF materials in the delivery field. This review describes classification and structural characteristics, followed by an introduction to formation mechanism and commonly used synthetic methods for CD-MOFs. Additionally, we discuss the status of the application of various delivery systems based on CD-MOFs. Finally, we address the challenges and prospects of CD-MOF materials, with the aim of providing new insights and ideas for their future development.

Vitamin C fortification: need and recent trends in encapsulation technologies

The multifaceted role of vitamin C in human health intrudes several biochemical functions that are but not limited to antioxidant activity, homoeostasis, amino acid synthesis, collagen synthesis, osteogenesis, neurotransmitter production and several yet to be explored functions. In absence of an innate biosynthetic pathway, humans are obligated to attain vitamin C from dietary sources to maintain its optimal serum level (28 μmol/L). However, a significant amount of naturally occurring vitamin C may deteriorate due to food processing, storage and distribution before reaching to the human gastrointestinal tract, thus limiting or mitigating its disease combating activity. Literature acknowledges the growing prevalence of vitamin C deficiency across the globe irrespective of geographic, economic and population variations. Several tools have been tested to address vitamin C deficiency, which are primarily diet diversification, biofortification, supplementation and food fortification. These strategies inherit their own advantages and limitations. Opportunely, nanotechnology promises an array of delivery systems providing encapsulation, protection and delivery of susceptible compounds against environmental factors. Lack of clear understanding of the suitability of the delivery system for vitamin C encapsulation and fortification; growing prevalence of its deficiency, it is a need of the hour to develop and design vitamin C fortified food ensuring homogeneous distribution, improved stability and enhanced bioavailability. This article is intended to review the importance of vitamin C in human health, its recommended daily allowance, its dietary sources, factors donating to its stability and degradation. The emphasis also given to review the strategies adopted to address vitamin c deficiency, delivery systems adopted for vitamin C encapsulation and fortification.

Insights into recent preclinical studies on labelled cyclodextrin-based imaging probes: towards a novel oncological era

As malignancies remain one of the major health concerns worldwide, increasing focus has been centered around the application of cyclodextrins (CDs) in cancer imaging and therapy due to their outstanding inclusion forming capability. Albeit the physicochemical properties of CDs were intensively elucidated, the spread of their clinical application is limited by the relative paucity of knowledge about their pharmacokinetic profile, especially biodistribution. Studies applying fluorescently- CDs, or CD-based MRI contrast agents revealed much about pharmacokinetics and diagnostic applications; however, derivatives labelled with positron emitters seem superior molecular probes in the investigation of the route of CDs in biological niche. In vivo imaging based on preclinical tumor-bearing model systems are well-suited to evaluate the whole-body distribution of the two most frequently assessed CDs: randomly methylated β-cyclodextrin (RAMEB), and hydroxypropyl-β-cyclodextrin (HPBCD). Exploiting the firm signaling interaction between cancer-related cyclooxygenase-2, prostaglandin E2 (PGE2) and RAS oncoprotein, radioconjugated, PGE2-affine CDs project the establishment of novel imaging probes and therapeutic agents. Currently, we provide an overview of the preclinical studies on CD pharmacokinetics highlighting the significance of the integration of translational discoveries into human patient care.

Supramolecular assembly of benzocaine bearing cyclodextrin cavity via host-guest complexes on polyacrylonitrile as an electrospun nanofiber

Nanofibers (NFs) can be encapsulated with cyclodextrins (CDs) based host-guest complexes (HCs) in order to enable many biological applications. Here, benzocaine (BNZ) forms HCs with β-cyclodextrin (β-CD) that are co-precipitated and further added to polyacrylonitrile (PAN) solution for making BNZ:β-CD-HCs/PAN NFs material with the aid of electrospinning technique. The marginal increase in absorbance and fluorescence intensity along with the shift in spectral maxima of BNZ in the presence of β-CD suggested the host-guest interaction between BNZ and β-CD. NFs showed a uniform and clean morphology in SEM images and interestingly, the ICs revealed that significantly thinner in terms of average fiber diameter (AFD) than those of free BNZ on PAN medium. BNZ molecule is completely included in the PAN surface as the result of NFs and thus, the original sharp peaks for the BNZ have vanished and the peaks are much broader for the BNZ and BNZ:β-CD-HCs. BNZ is also found to be a good candidate for anti-inflammatory, anti-oxidant, and anti-diabetic. The results showed an improved activity when it is in the form of HCs on a PAN medium. Making HCs of drugs could be significant in biological applications.

Preparation and Characterization of Clopidogrel Bisulfate-hydroxypropyl-β-Cyclodextrin Mixed Inclusion Complex for Improved Intestinal Solubility and Anti-Thrombotic Efficacy

The study aimed to increase the intestinal solubility and absorption of orally bioavailable clopidogrel-bisulfate (CPB) by complexing with hydroxypropyl-β-cyclodextrin (HCD) to form a binary inclusion complex that was stabilized by Tween 80 (T80) resulting into mixed inclusion complex. The results of phase solubility studies and molecular docking of CPB with β-cyclodextrin (β-CD) and HCD suggested higher solubility and binding energy of the stable CPB: HCD complex in the presence of T80 as compared to the CPB: β-CD complex. The D-Optimal mixture design was used to optimize the formulation containing the CPB: HCD: T80 mixed inclusion complex. The results suggest the enhanced stability of the CPB: HCD inclusion complex in the presence of T80. The spectral attributes confirmed the inclusion complexation and pointed out the central position of CPB in a hydrophilic cavity of HCD. Further, the prepared soft gelatin capsule successfully confirmed the importance of obliterating the intestinal precipitation associated problem of CPB through an in-vitro release study. The anticoagulant activity in rabbits confirmed that soft gelatin capsules showed 1.2 folds and 1.3 folds increase in clotting time, 1.2 fold and 1.5 folds increase in bleeding time when compared to marketed formulation and pure drug, respectively. Conclusively, soft gelatin capsules exhibit the potential to enhance the oral bioavailability of CPB, leading to reduction of the dose and dose-related side effects.

Cyclodextrin-Based Delivery Systems and Hydroxycinnamic Acids: Interactions and Effects on Crucial Parameters Influencing Oral Bioavailability-A Review

Hydroxycinnamic acids (HCAs) are a subclass of phenolic acids presenting caffeic acid (CA), chlorogenic acid (CGA), coumaric acid (COA) isomers, ferulic acid (FA), and rosmarinic acid (RA) as the major representants, being broadly distributed into vegetal species and showing a range of biological potentials. Due to the low oral bioavailability of the HCAs, the development of delivery systems to promote better administration by the oral route is demanding. Among the systems, cyclodextrin (CD)-based delivery systems emerge as an important technology to solve this issue. Regarding these aspects, in this review, CD-based delivery systems containing HCAs are displayed, described, and discussed concerning the degree of interaction and their effects on crucial parameters that affect the oral bioavailability of HCAs.

Cyclodextrin nanoparticles for diagnosis and potential cancer therapy: A systematic review

Cancer is still one of the world’s deadliest health concerns. As per latest statistics, lung, breast, liver, prostate, and cervical cancers are reported topmost worldwide. Although chemotherapy is most widely used methodology to treat cancer, poor pharmacokinetic parameters of anticancer drugs render them less effective. Novel nano-drug delivery systems have the caliber to improve the solubility and biocompatibility of various such chemical compounds. In this regard, cyclodextrins (CD), a group of natural nano-oligosaccharide possessing unique physicochemical characteristics has been highly exploited for drug delivery and other pharmaceutical purposes. Their cup-like structure and amphiphilic nature allows better accumulation of drugs, improved solubility, and stability, whereas CDs supramolecular chemical compatibility renders it to be highly receptive to various kinds of functionalization. Therefore combining physical, chemical, and bio-engineering approaches at nanoscale to specifically target the tumor cells can help in maximizing the tumor damage without harming non-malignant cells. Numerous combinations of CD nanocomposites were developed over the years, which employed photodynamic, photothermal therapy, chemotherapy, and hyperthermia methods, particularly targeting cancer cells. In this review, we discuss the vivid roles of cyclodextrin nanocomposites developed for the treatment and theranostics of most important cancers to highlight its clinical significance and potential as a medical tool.

Investigation of the Drug Carrier Properties of Insoluble Cyclodextrin Polymer Microspheres

The investigation of the usability of solid insoluble β-cyclodextrin polymers (βCDP) in micro-sized, controlled drug delivery systems has only recently attracted interest. Our aim was to form complexes with poorly soluble active pharmaceutical ingredients (APIs) with two types of βCDP for drug delivery applications. Solid insoluble cyclodextrin polymer of irregular shape (βCDPIS) and cyclodextrin microbeads (βCDPB) were used in the experiments. Morphology, surface area, size distribution and swelling capacity of carriers were investigated. We created complexes with two APIs, curcumin and estradiol, and applied powder X-ray diffraction, FTIR and thermal analysis (TGA/DSC) to prove the complexation. Finally, the dissolution, biocompatibility and permeation of APIs on Caco-2 cells were investigated. The size of the beads was larger than 100 µm, their shape was spherical and surfaces were smooth; while the βCDPIS particles were around 4 µm with irregular shape and surface. None of the polymers showed any cytotoxic effect on Caco-2 cells. Both carriers were able to extract curcumin and estradiol from aqueous solutions, and the dissolution test showed prolonged estradiol release. Caco-2 permeability tests were in accordance with the complexation abilities and dissolution of the complexes. This study offers useful data for further pharmaceutical applications of insoluble cyclodextrin polymers.

Implementation of Water-Soluble Cyclodextrin-Based Polymers in Biomedical Applications: How Far are we?

Cyclodextrin-based polymers can be prepared starting from the naturally occurring monomers following green and low-cost procedures. They can be selectively derivatized pre- or post-polymerization allowing to fine-tune functionalities of ad hoc customized polymers. Preparation nowadays has reached the 100 g scale thanks also to the interest of industries in these extremely versatile compounds. During the last 15 years these macromolecules have been the object of intense investigations in view of possible biomedical applications as the ultimate goal and large amounts of scientific data are now available. Compared to their monomeric models, already used in the formulation of various therapeutic agents, they display superior behavior in terms of their solubility in water and solubilizing power towards drugs incompatible with biological fluids. Moreover, they allow the combination of more than one type of therapeutic agent in the polymeric system. In this review we provide a complete state-of-the-art on the knowledge and potentialities of water-soluble cyclodextrin-based polymers as therapeutic agents as well as carrier systems for different types of therapeutics to implement combination therapy. Finally, we give a perspective on their assets for innovation in disease treatment as well as their limits that still need to be addressed. This article is protected by copyright. All rights reserved.

Vitamin A fortification: Recent advances in encapsulation technologies

Vitamin A is an essential micronutrient whose deficiency is still a major health concern in many regions of the world. It plays an essential role in human growth and development, immunity, and vision, but may also help prevent several other chronic diseases. The total amount of vitamin A in the human diet often falls below the recommended dietary allowance of approximately 900-1000 μ $ \umu $ g/day for a healthy adult. Moreover, a significant proportion of vitamin A may be degraded during food processing, storage, and distribution, thereby reducing its bioactivity. Finally, the vitamin A in some foods has a relatively low bioavailability, which further reduces its efficacy. The World Health Organization has recommended fortification of foods and beverages as a safe and cost-effective means of addressing vitamin A deficiency. However, there are several factors that must be overcome before effective fortified foods can be developed, including the low solubility, chemical stability, and bioavailability of this oil-soluble vitamin. Consequently, strategies are required to evenly disperse the vitamin throughout food matrices, to inhibit its chemical degradation, to avoid any adverse interactions with any other food components, to ensure the food is palatable, and to increase its bioavailability. In this review article, we discuss the chemical, physical, and nutritional attributes of vitamin A, its main dietary sources, the factors contributing to its current deficiency, and various strategies to address these deficiencies, including diet diversification, biofortification, and food fortification.

Bio-enabling strategies to mitigate the pharmaceutical food effect: a mini review

The concomitant administration of oral drugs with food can result in significant changes in bioavailability, leading to variable pharmacokinetics and considerable clinical implications, such as over- or under-dosing. Consequently, there is increasing demand for bio-enabling formulation strategies to reduce variability in exposure between the fasted and fed state and/or mitigate the pharmaceutical food effect. The current review critically evaluates technologies that have been implemented to overcome the positive food effects of pharmaceutical drugs, including, lipid-based formulations, nanosized drug preparations, cyclodextrins, amorphisation and solid dispersions, prodrugs and salts. Additionally, improved insight into preclinical models for predicting the food effect is provided. Despite the wealth of research, this review demonstrates that application of optimal formulation strategies to mitigate the positive food effects and the evaluation in preclinical models is not a universal approach, and improved standardisation of models to predict the food effects would be desirable. Ultimately, the successful reformulation of specific drugs to eliminate the food effect provides a panoply of advantages for patients with regard to clinical efficacy and compliance.

Development of oral curcumin based on pH-responsive transmembrane peptide-cyclodextrin derivative nanoparticles for hepatoma

Herein, a pH-responsive cyclodextrin derivative (R6H4-CMβCD) with cell-penetrating ability was successfully synthesized, and curcumin-loaded nanoparticles (R6H4-CMβCD@CUR NPs, RCCNPs) were developed to improve its efficacy in hepatoma. RCCNPs could improve the cell uptake compared with CMβCD@CUR NPs (CCNPs) and were internalized into cells mainly through endocytosis mediated by reticulin and macropinocytosis. Furthermore, the accumulation of RCCNPs in hepatoma cells at pH 6.4 was higher than that at pH 7.4, indicating a pH-responsive uptake. Additionally, RCCNPs could escape from the lysosomes via the "proton sponge effect", and a high apoptosis rate was detected. Importantly, in vivo experiments revealed that orally administered RCCNPs could exert excellent anti-cancer effects in tumor-bearing mice. Hematoxylin-eosin staining did not show significant histological changes in the major organs. Thus, our findings indicate the potential of R6H4-CMβCD as a nanopharmaceutical material, and RCCNPs as an effective delivery system for oral curcumin in cancer management.

Nano-molecularly imprinted polymers (nanoMIPs) as a novel approach to targeted drug delivery in nanomedicine

Molecularly imprinted polymers - MIPs - denote synthetic polymeric structures that selectively recognize the molecule of interest against which MIPs are templated. A number of works have demonstrated that MIPs can exceed the affinity and selectivity of natural antibodies, yet operating by the same principle of "lock and key". In contrast to antibodies, which have certain limitations related to the minimal size of the antigen, nanoMIPs can be fabricated against almost any target molecule irrespective of its size and low immunogenicity. Furthermore, the cost of MIP production is much lower compared to the cost of antibody production. Excitingly, MIPs can be used as nanocontainers for specific delivery of therapeutics both in vitro and in vivo. The adoption of the solid phase synthesis rendered MIPs precise reproducible characteristics and, as a consequence, improved the controlled release of therapeutic payloads. These major breakthroughs paved the way for applicability of MIPs in medicine as a novel class of therapeutics. In this review, we highlight recent advances in the fabrication of MIPs, mechanisms of controlled release from the MIPs, and their applicability in biomedical research.

Inclusion Scenarios and Conformational Flexibility of the SSRI Paroxetine as Perceived from Polymorphism of β-Cyclodextrin–Paroxetine Complex

Depression, a global mental health problem, is prevalent during the coronavirus disease 2019 (COVID-19) pandemic and can be efficiently treated by selective serotonin reuptake inhibitors (SSRIs). Our study series aims at forwarding insights on the β-cyclodextrin (β-CD)–SSRI inclusion complexes by X-ray crystallography combined with density functional theory (DFT) calculation. Here, we report a new crystal form (II) of the 1:1 β-CD–paroxetine (PXT) complex, which is inspired by the reported 2:1 β-CD–PXT complex (crystal form I), reflecting an elusive phenomenon of the polymorphism in CD inclusion complexes. The β-CD–PXT polymorphism stems from the PXT conformational flexibility, which is defined by torsion angles κ, ε around the -CH2–O- group bridging the A- and C–D-rings, of which those of PXT in I and II are totally different. While PXT (II) in an open V-shaped conformation that has the B-ring shallowly inserted in the β-CD cavity, PXT (I) in a closed U-shaped structure is mostly entirely embedded in the β-CD dimeric cavity, of which the A-ring is deeply inserted in the main β-CD cavity. However, PXT molecules in both crystal forms are similarly maintained in the CD cavity via host–guest N–H···O5/O6 H-bonds and C/O–H···π(B/C) interactions and β-CDs have similar 3D arrangements, channel (II) vs. screw-channel (I). Further theoretical explorations on the β-CD–PXT thermodynamic stabilities and the PXT conformational stabilities based on their potential energy surfaces (PESs) have been completed by DFT calculations. The 2:1 β-CD–PXT complex with the greater presence of dispersion interactions is more energetically favorable than the unimolar complex. Conversely, whereas free PXT, PXT (II) and PXT in complex with serotonin transporter are more energetically stable, PXT (I) is least stable and stabilized in the β-CD cavity. As SSRIs could lessen the COVID-19 severity, the CD inclusion complexation not only helps to improve the drug bioavailability, but also promotes the use of antidepressants and COVID-19 medicines concurrently.

Cyclodextrin-Modified Nanomaterials for Drug Delivery: Classification and Advances in Controlled Release and Bioavailability

In drug delivery, one widely used way of overcoming the biopharmaceutical problems present in several active pharmaceutical ingredients, such as poor aqueous solubility, early instability, and low bioavailability, is the formation of inclusion compounds with cyclodextrins (CD). In recent years, the use of CD derivatives in combination with nanomaterials has shown to be a promising strategy for formulating new, optimized systems. The goals of this review are to give in-depth knowledge and critical appraisal of the main CD-modified or CD-based nanomaterials for drug delivery, such as lipid-based nanocarriers, natural and synthetic polymeric nanocarriers, nanosponges, graphene derivatives, mesoporous silica nanoparticles, plasmonic and magnetic nanoparticles, quantum dots and other miscellaneous systems such as nanovalves, metal-organic frameworks, Janus nanoparticles, and nanofibers. Special attention is given to nanosystems that achieve controlled drug release and increase their bioavailability during in vivo studies.

Advancing insights on β-cyclodextrin inclusion complexes with SSRIs through lens of X-ray diffraction and DFT calculation

Depression-the global crisis hastened by the coronavirus outbreak, can be efficaciously treated by the selective serotonin reuptake inhibitors (SSRIs). Cyclodextrin (CD) inclusion complexation is a method of choice for reducing side effects and improving bioavailability of drugs. Here, we investigate in-depth the β-CD encapsulation of sertraline (STL) HCl (1) and fluoxetine (FXT) HCl (2) by single-crystal X-ray diffraction and DFT complete-geometry optimization, in comparison to the reported complex of paroxetine (PXT) base. X-ray analysis unveiled the 2:2 β-CD-STL/FXT complexes with two drug molecules inserting their halogen-containing aromatic ring in the β-CD dimeric cavity, which are stabilized by the interplay of intermolecular O2-H⋯N1-H⋯O3 H-bonds, C3/C5-H⋯π and halogen⋯halogen interactions. Similarly, the 1:1 β-CD-tricyclic-antidepressant (TCA) complexes have an exclusive inclusion mode of the aromatic ring, which is maintained by C3/C5-H⋯π interactions. By contrast, the 2:1 β-CD-PXT complex has a total inclusion that is stabilized by host-guest O6-H⋯N1-H⋯O5 H-bonds and C3-H⋯π interactions. The inherent stabilization energies of 1 and 2 evaluated using DFT calculation suggested that the improved thermodynamic stabilities via CD encapsulation facilitates the reduction of drug side effects. Moreover, the SSRI conformational flexibilities are thoroughly discussed for understanding of their pharmacoactivity.

Cyclodextrins: promising scaffolds for MRI contrast agents

Magnetic resonance imaging (MRI) is a powerful tool for non-invasive, high-resolution three-dimensional medical imaging of anatomical structures such as organs and tissues. The use of contrast agents based on gadolinium chelates started in 1988 to improve the quality of the image, since researchers and industry focused their attention on the development of more efficient and stable structures. This review is about the state of the art of MRI contrast agents based on cyclodextrin scaffolds. Chemical engineering strategies are herein reported including host-guest inclusion complexation and covalent linkages. It also offers descriptions of the MRI properties and in vitro and in vivo biomedical applications of these emerging macrostructures. It highlights that these supramolecular associations can improve the image contrast, the sensitivity, and the efficiency of MRI diagnosis by targeting cancer tumors and other diseases with success proving the great potential of this natural macrocycle.

Cyclodextrin-based Pickering emulsions: functional properties and drug delivery applications

Cyclodextrins (CDs) are biocompatible, cyclic oligosaccharides that are widely used in various industrial applications and have intriguing interfacial science properties. While CD molecules typically have low surface activity, they are capable of stabilizing emulsions by inclusion complexation of oil-phase components at the oil/water interface, which results in Pickering emulsion formation. Such surfactant-free formulations have gained considerable attention in recent years, owing to their enhanced physical stability, improved tolerability, and superior environmental compatibility compared to conventional, surfactant-based emulsions. In this review, we critically describe the latest insights into the molecular mechanisms involved in CD stabilization of Pickering emulsions, including covering practical aspects such as methods to prepare CD-based Pickering emulsions, lipid encapsulation, and relevant stability issues. In addition, the rheological and textural features of CD-based Pickering emulsions are discussed and particular attention is focused on promising examples for drug delivery, cosmetic, and nutraceutical applications. The functionality of currently developed CD-based Pickering emulsions is also summarised, including examples such as antifungal uses, and we close by discussing emerging possibilities to utilize the molecular encapsulation of CD-based emulsions for translational medicine applications in the antiviral and antibacterial spaces.

Supercritical Carbon Dioxide as a Green Alternative to Achieve Drug Complexation with Cyclodextrins

Cyclodextrins are widely used in pharmaceutics to enhance the bioavailability of many drugs. Conventional drug/cyclodextrin complexation techniques suffer from many drawbacks, such as a high residual content of toxic solvents in the formulations, the degradation of heat labile drugs and the difficulty in controlling the size and morphology of the product particles. These can be overcome by supercritical fluid technology thanks to the outstanding properties of supercritical CO₂ (scCO₂) such as its mild critical point, its tunable solvent power, and the absence of solvent residue after depressurization. In this work the use of scCO₂ as an unconventional medium to achieve the complexation with native and substituted cyclodextrins of over 50 drugs, which belong to different classes, are reviewed. This can be achieved with different approaches such as the “supercritical solvent impregnation” and “particle-formation” techniques. The different techniques are discussed to point out how they affect the complexation mechanism and efficiency, the physical state of the drug as well as the particle size distribution and morphology, which finally condition the release kinetics and drug bioavailability. When applicable, the results obtained for the same drug with various cyclodextrins, or different complexation techniques are compared with those obtained with conventional approaches.

History of cyclodextrin-based polymers in food and pharmacy: a review

Cyclodextrins are glucose macrocycles whose inclusional capabilities towards non-polar solutes can be modulated with the help of other macrostructures. The incorporation of cyclodextrin moieties into larger structures produces five types of new materials: crosslinked networks, functionalized chains, amphiphilic cyclodextrins, polyrotaxanes and nanocomposites. This review presents crosslinking and grafting to prepare covalently-attached cyclodextrins, and applications in the food and pharmaceutical sectors, from an historical point of view. In food science, applications include debittering of juices, retention of aromas and release of preservatives from packaging. In biomedical science, cyclodextrin polymers are applied classically to drug release, and more recently to gene delivery and regenerative medicine. The remarkable points are: 1) epichlorohydrin and diisocyanates have been extensively used as crosslinkers since the 1960s, but during the last two decades more complex cyclodextrin polymeric structures have been designed. 2) The evolution of cyclodextrin polymers matches that of macromolecular materials with regard to complexity, functionality and capabilities. 3) The use of cyclodextrin polymers as sorbents in the food sector came first, but smart packaging is now an active challenge. Cyclodextrins have also been recently used to design treatments against the coronavirus disease 2019 (COVID-19).

Fate of β-Carotene within Loaded Delivery Systems in Food: State of Knowledge

Nanotechnology has opened new opportunities for delivering bioactive agents. Their physiochemical characteristics, i.e., small size, high surface area, unique composition, biocompatibility and biodegradability, make these nanomaterials an attractive tool for β-carotene delivery. Delivering β-carotene through nanoparticles does not only improve its bioavailability/bioaccumulation in target tissues, but also lessens its sensitivity against environmental factors during processing. Regardless of these benefits, nanocarriers have some limitations, such as variations in sensory quality, modification of the food matrix, increasing costs, as well as limited consumer acceptance and regulatory challenges. This research area has rapidly evolved, with a plethora of innovative nanoengineered materials now being in use, including micelles, nano/microemulsions, liposomes, niosomes, solidlipid nanoparticles, nanostructured lipids and nanostructured carriers. These nanodelivery systems make conventional delivery systems appear archaic and promise better solubilization, protection during processing, improved shelf-life, higher bioavailability as well as controlled and targeted release. This review provides information on the state of knowledge on β-carotene nanodelivery systems adopted for developing functional foods, depicting their classifications, compositions, preparation methods, challenges, release and absorption of β-carotene in the gastrointestinal tract (GIT) and possible risks and future prospects.

Oral Drug Delivery: Conventional to Long Acting New-Age Designs

The Oral route of administration forms the heartwood of the ever-growing tree of drug delivery technology. It is one of the most preferred dosage forms among patients and controlled release community. Despite the high patient compliance, the deliveries of anti-cancerous drugs, vaccines, proteins, etc. via the oral route are limited and have recorded a very low bioavailability. The oral administration must overcome the physiological barriers (low solubility, permeation and early degradation) to achieve efficient and sustained delivery. This review aims at highlighting the conventional and modern-age strategies that address some of these physiological barriers. The modern age designs include the 3D printed devices and formulations. The superiority of 3D dosage forms over conventional cargos is summarized with a focus on long-acting designs. The innovations in Pharmaceutical organizations (Lyndra, Assertio and Intec) that have taken giant steps towards commercialization of long-acting vehicles are discussed. The recent advancements made in the arena of oral peptide delivery are also highlighted. The review represents a comprehensive journey from Nano-formulations to micro-fabricated oral implants aiming at specific patient-centric designs.

Curcumin Encapsulated in Crosslinked Cyclodextrin Nanoparticles Enables Immediate Inhibition of Cell Growth and Efficient Killing of Cancer Cells

The efficiency of anti-cancer drugs is commonly determined by endpoint assays after extended incubation times, often after days. Here we demonstrate that curcumin encapsulated in crosslinked cyclodextrin nanoparticles (CD-NP) acts extremely rapidly on cell metabolism resulting in an immediate and complete inhibition of cell growth and in efficient cancer-cell killing only few hours after incubation. This early onset of anti-cancer action was discovered by live-cell high-throughput fluorescence microscopy using an environmental stage. To date, only very few examples of covalently crosslinked nanoscale CD-based (CD-NP) drug carriers exist. Crosslinking cyclodextrins enables the adsorption of unusually high payloads of hydrophobic curcumin (762 µg CC/mg CD-NP) reflecting a molar ratio of 2.3:1 curcumin to cyclodextrin. We have investigated the effect of CD-NP encapsulated curcumin (CD-CC-NP) in comparison to free, DMSO-derived curcumin nanoparticles (CC-NP) on 4 different cell lines. Very short incubations times as low as 1 h were applied and cell responses after medium change were subsequently followed over two days. We show that cell proliferation is inhibited nearly immediately in all cell lines and that a cell- and concentration dependent cancer-cell killing occurs. Anti-cancer effects were similar with free and encapsulated curcumin, however, encapsulation in CD-NP drastically extends the long-term photostability and anti-cancer activity of curcumin. Curcumin-sensitivity is highest in HeLa cells reaching up to 90% cell death under these conditions. Sensitivity decreased from HeLa to T24 to MDA MB-231 cells. Strikingly, the immortalized non-cancerous cell line MCF-10A was robust against curcumin concentrations that were highly toxic to the other cell lines. Our results underline the potential of curcumin as gentle and yet effective natural anti-cancer agent when delivered solvent-free in stabilizing and biocompatible drug carriers such as CD-NP that enable efficient cellular delivery.

Advances in applied supramolecular technologies

Supramolecular chemistry has successfully built a foundation of fundamental understanding. However, with this now achieved, we show how this area of chemistry is moving out of the laboratory towards successful commercialisation.

Cyclodextrin-Based Contrast Agents for Medical Imaging

Cyclodextrins (CDs) are naturally occurring cyclic oligosaccharides consisting of multiple glucose subunits. CDs are widely used in host–guest chemistry and biochemistry due to their structural advantages, biocompatibility, and ability to form inclusion complexes. Recently, CDs have become of high interest in the field of medical imaging as a potential scaffold for the development of a large variety of the contrast agents suitable for magnetic resonance imaging, ultrasound imaging, photoacoustic imaging, positron emission tomography, single photon emission computed tomography, and computed tomography. The aim of this review is to summarize and highlight the achievements in the field of cyclodextrin-based contrast agents for medical imaging.

Physical formulation approaches for improving aqueous solubility and bioavailability of ellagic acid: A review

Ellagic acid (EA) is a polyphenolic active compound with antimalarial and other promising therapeutic activities. However, its solubility and its permeability are both low (BCS IV). These properties greatly compromise its oral bioavailability and clinical utilizations. To overcome these limitations of the physicochemical parameters, several formulation approaches, including particle size reduction, amorphization and lipid-based formulations, have been used. Although these strategies have not yet led to a clinical application, some of them have resulted in significant improvements in the solubility and bioavailability of EA. This critical review reports and analyses the different formulation approaches used by scientists to improve both the biopharmaceutical properties and the clinical use of EA.

Self-assembling Peptides in Current Nanomedicine: Versatile Nanomaterials for Drug Delivery

BACKGROUND

The development of modern nanomedicine greatly depends on the involvement of novel materials as drug delivery system. In order to maximize the therapeutic effects of drugs and minimize their side effects, a number of natural or synthetic materials have been widely investigated for drug delivery. Among these materials, biomimetic self-assembling peptides (SAPs) have received more attention in recent years. Considering the rapidly growing number of SAPs designed for drug delivery, a summary of how SAPs-based drug delivery systems were designed, would be beneficial.

METHOD

We outlined research works on different SAPs that have been investigated as carriers for different drugs, focusing on the design of SAPs nanomaterials and how they were used for drug delivery in different strategies.

RESULTS

Based on the principle rules of chemical complementarity and structural compatibility, SAPs such as ionic self-complementary peptide, peptide amphiphile and surfactant-like peptide could be designed. Determined by the features of peptide materials and the drugs to be delivered, different strategies such as hydrogel embedding, hydrophobic interaction, electrostatic interaction, covalent conjugation or the combination of them could be employed to fabricate SAPs-drug complex, which could achieve slow release, targeted or environment-responsive delivery of drugs. Furthermore, some SAPs could also be combined with other types of materials for drug delivery, or even act as drug by themselves.

CONCLUSION

Various types of SAPs have been designed and used for drug delivery following various strategies, suggesting that SAPs as a category of versatile nanomaterials have promising potential in the field of nanomedicine.

Cyclodextrin Encapsulated pH Sensitive Dyes as Fluorescent Cellular Probes: Self-Aggregation and In Vitro Assessments

We have designed and synthesized a series of novel, supramolecular, long-lived fluorescent probes based on the host-guest inclusion complexes formation between fluorescent indolizinyl-pyridinium salts and β-cyclodextrin. Fluorescence and electrospray ionisation mass spectrometry experiments, supported by theoretical molecular docking studies, were utilized in the monitoring of the inclusion complexes formation, evidencing the appearance of corresponding 1:1 and 1:2 species. Additionally, the influence of the guest molecule over the aggregation processes of the cyclodextrin inclusion complexes was investigated by transmission electron microscopy. The absence of cytotoxicity, cellular permeability, long-lived intracellular fluorescence, and in time specific accumulation within acidic organelles identified the investigated supramolecular entities as remarkable candidates for intracellular fluorescence probes. Co-staining experiments using specific organelle markers revealed the fact that, after a 24-h incubation period, the inclusion complexes accumulate predominantly in lysosomes rather than in mitochondria. This study opens new possibilities for a broad range of fluorescent dyes with solubility and high toxicity issues, able to form inclusion complexes with β-cyclodextrin, to be tested as intracellular fluorescence probes.

The Lord of the NanoRings: Cyclodextrins and the battle against SARS-CoV-2

A handful of singular structures and laws can be observed in nature. They are not always evident but, once discovered, it seems obvious how to take advantage of them. In chemistry, the discovery of reproducible patterns stimulates the imagination to develop new functional materials and technological or medical applications. Two clear examples are helical structures at different levels in biological polymers as well as ring and spherical structures of different size and composition. Rings are intuitively observed as holes able to thread elongated structures. A large number of real and fictional stories have rings as inanimate protagonists. The design, development or just discovering of a special ring has often been taken as a symbol of power or success. Several examples are the Piscatory Ring wore by the Pope of the Catholic Church, the NBA Championship ring and the One Ring created by the Dark Lord Sauron in the epic story The Lord of the Rings. In this work, we reveal the power of another extremely powerful kind of rings to fight against the pandemic which is currently affecting the whole world. These rings are as small as ~1 nm of diameter and so versatile that they are able to participate in the attack of viruses, and specifically SARS-CoV-2, in a large range of different ways. This includes the encapsulation and transport of specific drugs, as adjuvants to stabilize proteins, vaccines or other molecules involved in the infection, as cholesterol trappers to destabilize the virus envelope, as carriers for RNA therapies, as direct antiviral drugs and even to rescue blood coagulation upon heparin treatment.

“One ring to rule them all. One ring to find them. One ring to bring them all and in the darkness bind them.” J. R. R. Tolkien.

Carboxymethyl β-cyclodextrin grafted carboxymethyl chitosan hydrogel-based microparticles for oral insulin delivery

This study was aimed at utilizing polysaccharides for the development of effective hydrogel microparticles for oral insulin delivery that has a controlled, and sustained release to enhance paracellular transcellular absorption. Carboxymethyl β-cyclodextrin grafted carboxymethyl chitosan hydrogels (CMCD-g-CMCs) were prepared from carboxymethyl β-cyclodextrin (CMCD) and carboxymethyl chitosan (CMC) using a water-soluble carbodiimide as a crosslinker in the presence of N-hydroxysuccinimide. After synthesis, the hydrogel structures were determined via FT-IR and XRD analyses. The porous structure of hydrogels was confirmed by SEM observations and swelling behaviours. The insulin release behaviours were found to betriggered by pH in vitro. Results showed that insulin was successfully retained inside the hydrogels in the gastric environment and slowly released following passage to intestinal conditions. The stability of the secondary structure of insulin was studied by dichroism circular (CD) and fluorescence (FL) spectrophotometer measurement. There was no significant difference in the secondary structure between the native and released insulin. In vitro studies revealed that the hydrogel microparticles exhibited non-cytotoxicity and were transported across the Caco-2 cell monolayers mainly via the paracellular pathway. In order to examine the effectiveness of hydrogel-based sustained release microparticles in delivering insulin in vivo, we administered different insulin-loaded hydrogel microparticles to diabetic mice. In these studies, we found that the insulin-loaded hydrogel microparticles provided a significant and sustained (ranging from 6 h to 12 h) reduction in the blood glucose levels of diabetic mice compared with subcutaneous injection. Overall, these findings demonstrate that CMCD-g-CMCs may be a promising protein carrier for use in oral drug delivery.

In vitro and in vivo evaluation of didymin cyclodextrin inclusion complexes: characterization and chemosensitization activity

Didymin is a dietary flavonoid that first found in citrus fruits, and possesses antioxidant properties. Our preliminary experiments first discovered that didymin was able to sensitize the resistant cancer cells against chemotherapeutics and combat multidrug resistance. However, its poor aqueous solubility and resultant low bioavailability limit its potentials as an adjuvant phytochemical drug for chemotherapy. Thus, this study prepared the inclusion complex of didymin with β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin to improve its bioavailability and then evaluate their chemosensitization effects. The didymin inclusion complexes formulation was prepared and their host-guest structure was characterized by FT-IR, PXRD, DSC, and SEM techniques. In vitro/in vivo results demonstrated that didymin inclusion complex enhanced its water solubility and orally bioavailability. Furthermore, didymin inclusion complex exerted considerable chemosensitivity potency, and improve the anti-tumor effects of chemotherapeutics in vivo. Therefore, didymin inclusion complex could provide a safe, effective, economical, and adjuvant drug for future treatment of chemoresistant cancers.

Cyclodextrin as a magic switch in covalent and non-covalent anticancer drug release systems

Cancer has been a threat to human health, so its treatment is a huge challenge to the present medical field. One of commonly used methods is the controlled release of anticancer drug to reduce the dose for patients, increase the stability of drug treatment and minimize side effects. Cyclodextrin is a kind of cyclic oligosaccharide produced by amylase hydrolysis. Because cyclodextrin contains a cavity structure and active hydroxyl groups, it has a positive effect on the study of the controlled release of anticancer drugs. This article reviews the controlled release of current anticancer drugs based on cyclodextrins as a "flexible switch", and discusses the classification of different types of release systems, highlighting their role in cancer treatment. Moreover, the opportunities and challenges of cyclodextrin as a magic switch in the controlled release of anticancer drugs are discussed.

Pyromellitic dianhydride crosslinked soluble cyclodextrin polymers: Synthesis, lopinavir release from sub-micron sized particles and anti-HIV-1 activity

We report the synthesis of water soluble cyclodextrin (CD) polymers prepared by crosslinking pyromellitic dianhydride (PMDA) with two CD derivatives (methyl-β-CD - MβCD and (2-hydroxy)propyl-β-CD - HPβCD) and their evaluation as functional sub-micron sized carriers in the development of antiretroviral drug delivery systems. Using the protease inhibitor lopinavir (LPV) as model drug, LPV loaded CD polymers (pHPβCD and pMβCD) were prepared and fully characterized. The physicochemical characterization and in vitro drug release confirmed the successful synthesis of pHPβCD and pMβCD, the formation of sub-micron sized particles and a 12-14 fold increase in LPV solubility. Cytotoxicity assays indicated that both pHPβCD and pMβCD were able to improve the safety profile of LPV while the viral infectivity assay revealed a concentration independent anti-HIV-1 effect for both pHPβCD and pMβCD with a maximum percentage inhibition (MPI) of 79 and 91% respectively. After LPV loading, the antiviral profile of pHPβCD was reversed to the sigmoidal dose-response profile of LPV, while pMβCD maintained its dose-independent profile followed by a LPV mediated increase in viral inhibition. Overall, both pHPβCD and pMβCD demonstrated anti-HIV-1 activity, while drug loaded pMβCD indicated its potential as functional sub-micron sized drug delivery polymers for achieving synergistic anti-HIV activity.

Probing inclusion complexes of 2-hydroxypropyl-β-cyclodextrin with mono-amino mono-carboxylic acids: physicochemical specification, characterization and molecular modeling

Density (ρ), viscosity (η) and surface tension (γ) of three amino acids (valine, alanine, and glycine) have been measured at a different mass fraction (0.002 - 0.009) of aqueous hydroxypropyl-β-cyclodextrin (HPβCD) mixtures and different temperatures (278.15 - 295.15 K). The formation of inclusion complexes has been analyzed via evaluating the amounts of apparent and limiting apparent molar volumes, limiting apparent molar expansibilities, activation energy, kinematic, relative, intrinsic, spatial, and dynamic viscosities. The surface tension studies indicated that the inclusion complexes have been formed with 1:1 stoichiometry and mediated by hydrophobic effects and electrostatic forces. Additionally, the ρ and η parameters were evaluated by molecular modeling experiments to provide more details on the mechanisms of the complexation.

Cyclodextrin Based Nanoparticles for Drug Delivery and Theranostics

Colloidal nanoparticulate technology has been described in the literature as a versatile drug delivery system. But it possesses some inherent lacunae in their formulation. Cyclodextrins (CDs) have been extensively reported for the solubility enhancement of poorly water-soluble drugs. The CDs can cause intervention in aspects related to nanoparticles (NPs) that include improving drug loading in nano-system, improving stability, site-specific/targeted drug delivery, improving solubility profile and absorption of the drug in nanosystem with consequent improvement in bioavailability, with the possibility of controlled release, safety and efficacy. They find application in for simultaneous diagnosis and therapeutics for better treatment procedures. The current communication is focused on the application of CDs to overcome troubles in nanoparticulate formulation and enhancement of their performance. It also envisages the theranostic aspects of CDs.