"Back to the Future": A New Look at Hydroxypropyl Beta-Cyclodextrins

Solving the puzzle of 2-hydroxypropyl β-cyclodextrin: Detailed assignment of the substituent distribution by NMR spectroscopy

2-Hydroxypropyl-β-cyclodextrin (HPBCD) is one of the most important cyclodextrin derivatives, finding extensive applications in the pharmaceutical sector. Beyond its role as an excipient, HPBCD achieved orphan drug status in 2015 for Niemann-Pick type C disease treatment, prompting research into its therapeutic potential for various disorders. However, the acceptance of HPBCD as an active pharmaceutical ingredient may be impeded by its complex nature. Indeed, HPBCD is not a single entity with a well-defined structure, instead, it is a complex mixture of isomers varying in substituent positions and the degree of hydroxypropylation, posing several challenges for unambiguous characterization. Pharmacopoeias' methods only address the average hydroxypropylation extent, lacking a rapid approach to characterize the substituent positions on the CD scaffold. Recognizing that the distribution of substituents significantly influences the complexation ability and overall activity of the derivative, primarily by altering cavity dimensions, we present a straightforward and non-destructive method based on liquid state NMR spectroscopy to analyze the positions of the hydroxypropyl sidechains. This method relies on a single set of routine experiments to establish quantitative assignment and it provides a simple yet effective tool to disclose the substitution pattern of this complex material, utilizing easily accessible (400 MHz NMR) instrumentation.

Synthesis and Inclusion Properties of a β-Cyclodextrin Heptaphosphoramidate

In this study, we report a novel per-6-substituted β-cyclodextrin (4) featuring seven phosphoramidate moieties as an innovative host for inclusion. This structurally well-defined host has remarkable water solubility and was isolated in pure form. Analytical techniques such as NMR and ITC were used to probe the molecular interactions with different drug molecules. Our investigations revealed that host 4 can form 2:1 inclusion complexes with various drugs. Further studies showed that the inclusions of drugs by β-CD host (4) are mostly enthalpy driven, highlighting the potential roles played by the phosphoramidate functionalities of the host. Comparatively, a per-O2, O3-acetylated analog (6) of compound 4 was also obtained, which also shows unusual water solubility but diminished inclusion capability.

Facile synthesis of 2-hydroxy-β-cyclodextrin/polyacrylamide/carbazole hydrogel and its application for the treatment of infected wounds in a murine model

This work aimed to synthesize hydrogels by combining carbazole (Carb) with 2-hydroxy, β-cyclodextrin (HPβCD)/polyacrylamide (PAA) hybrid complexes. The hydrogels were then evaluated for their potential use in treating infected wounds. The physicochemical structures of the preparations were evaluated using several characterization methods including FTIR, FESEM, EDX, XRD, pH sensitivity, and TGA. Moreover, In vitro release, toxicity, antibacterial activity and in vivo infected wound healing activity were evaluated. Physicochemical testing verified the effective synthesis of the preparations and the timely release of Carb. The P(AA-co-AM)/HPβCD material exhibited an open structure characterized by macroscopic voids, whereas the hydrogels displayed surfaces that were not uniform. The FTIR analysis revealed the creation of a novel polymeric hydrogel composed of HPβCD as the main polymer structure. The hydrogels exhibited good reversible swelling and recoverable deformation, with an optimal swelling ratio of 30.12 achieved at pH 7.4. The antibacterial and safety of the formulations were validated by in vitro studies. β.Dex/PAA/Carb hydrogels have been shown to effectively expedite the healing of infected wounds by promoting the production of CD31, FGF-2, and COL1A, while reducing the levels of ROS, CD68, COX-2, and NF-κB. Overall, the combination of Carb, β.Dex, and PAA molecules had a synergistic impact on the healing process of infected wounds.

The counteracting influence of 2-hydroxypropyl substitution and the presence of a guest molecule on the shape and size of the β-cyclodextrin cavity

The aqueous solubility of β-cyclodextrin (β-CD), a cyclic carbohydrate comprising seven α-D-glucose molecules, is enhanced by 2-hydroxypropyl (2-HP) substitution of the hydroxyl groups at the CD rims. Our thorough analysis of the structural and solvation properties with different degrees of 2-hydroxypropyl substitution on β-CD using molecular dynamics simulations reveals that the solubility is enhanced at the cost of the structural distortion of the CD cyclic structure. Substitution at the secondary rim predominantly enhances the favourable interactions between CD and water by decreasing CD-CD hydrogen bonding and promoting CD-water hydrogen bonding. However, the effect of substitution at the primary rim on the CD-water interactions is minimal; the hydrogen bonds between water and the primary hydroxyl group in native CD merely get replaced by those between water and 2-HP, since the substitution makes the primary hydroxyl oxygen (O6 atom) inaccessible to water. In contrast, substitution at the primary rim maintains the structural integrity of CD, while substitution at the secondary rim results in structural distortion due to the disruption of the intramolecular hydrogen bond belt, even leading to cavity closure. Certain strategic substitutions of the primary hydroxyl groups can help in the reduction of structural distortion, depending upon the degree of substitution at the secondary hydroxyl rim. A detailed inspection of the simulation trajectory revealed that the tilting of glucose units with the primary hydroxyl oxygen (O6) pointing inward is the primary driver for cavity closure. Even though the dynamics of glucose tilting can influence the kinetics of host-guest complex formation, once the guest is well incorporated into the cavity, glucose tilting is inhibited and the cavity opens up as in native β-CD.

Cyclodextrins permeabilize DPPC liposome membranes: a focus on cholesterol content, cyclodextrin type, and concentration

Cyclodextrins (CDs) are known for their ability to extract lipid components from synthetic and biological membranes and therefore to induce an increase of membrane permeability. However, the effect of cholesterol (CHOL) content in the membrane on the CD permeabilizing effect was not considered yet. Given that an increase in CHOL content reduces the membrane permeability, the aim of this work was to reveal how CHOL would modulate the CDs effect on the membrane. Hence, liposomes made of dipalmitoyl phosphatidylcholine (DPPC) and various CHOL contents (DPPC/CHOL 100:10, 100:25, 100:50, and 100:100) encapsulating the hydrophilic fluorophore, sulforhodamine B (SRB), were prepared and exposed to the native CDs (α-CD, β-CD, γ-CD) and four β-CD derivatives: the randomly methylated-β-CD (RAMEB), the low methylated-β-CD (CRYSMEB), the hydroxypropyl-β-CD (HP-β-CD) and the sulfobutyl ether-β-CD (SBE-β-CD) at different CD/DPPC molar ratios (1:1, 10:1, and 100:1). The membrane permeability was monitored following the release of SRB with time. The results demonstrated that the CDs effect on the membrane depends on the CD type, CD concentration, and membrane CHOL content. The investigated CDs exhibited an instantaneous permeabilizing effect promoting vesicle leakage of SRB from the various membranes; this effect increased with CDs concentration. Among the studied CDs, α-CD, β-CD, and RAMEB were the most permeabilizing CDs on the different membranes. Similar modifications of SRB release from the various liposomal formulations were obtained with HP-β-CD, CRYSMEB, and SBE-β-CD. γ-CD was the less potent CD in affecting the membrane permeability. The CDs effect also depended on the CHOL content: at the CD/DPPC molar ratio (100:1), RAMEB and β-CD considerably permeabilized the membrane of high CHOL content (50%, 100%) while the remaining CDs showed a decreasing permeabilizing effect upon CHOL content membrane increase.

Different solubilizing ability of cyclodextrin derivatives for cholesterol in Niemann-Pick disease type C treatment

BACKGROUND

Niemann-Pick disease type C (NPC) is a fatal neurodegenerative disorder caused by abnormal intracellular cholesterol trafficking. Cyclodextrins (CDs), the most promising therapeutic candidates for NPC, but with concerns about ototoxicity, are cyclic oligosaccharides with dual functions of unesterified cholesterol (UC) shuttle and sink that catalytically enhance the bidirectional flux and net efflux of UC, respectively, between the cell membrane and the extracellular acceptors. However, the properties of CDs that regulate these functions and how they could be used to improve treatments for NPC are unclear.

METHODS

We estimated CD-UC complexation for nine CD derivatives derived from native α-, β-, and γ-CD with different cavity sizes, using solubility and molecular docking analyses. The stoichiometry and complexation ability of the resulting complexes were investigated in relation to the therapeutic effectiveness and toxicity of each CD derivative in NPC experimental models.

FINDINGS

We found that shuttle and sink activities of CDs are dependent on cavity size-dependent stoichiometry and substituent-associated stability of CD-UC complexation. The ability of CD derivatives to form 1:1 and 2:1 complexes with UC were correlated with their ability to normalize intracellular cholesterol trafficking serving as shuttle and with their cytotoxicity associated with cellular UC efflux acting as sink, respectively, in NPC model cells. Notably, the ability of CD derivatives to form an inclusion complex with UC was responsible for not only efficacy but ototoxicity, while a representative derivative without this ability negligibly affected auditory function, underscoring its preventability.

CONCLUSIONS

Our findings highlight the importance of strategies for optimizing the molecular structure of CDs to overcome this functional dilemma in the treatment of NPC.

Anomalous Properties of Cyclodextrins and Their Complexes in Aqueous Solutions

Cyclodextrins (CDs) are cyclic oligosaccharides that emerged as industrial excipients in the early 1970s and are currently found in at least 130 marketed pharmaceutical products, in addition to numerous other consumer products. Although CDs have been the subject of close to 100,000 publications since their discovery, and although their structure and properties appear to be trivial, CDs are constantly surprising investigators by their unique physicochemical properties. In aqueous solutions, CDs are solubilizing complexing agents of poorly soluble drugs while they can also act as organic cosolvents like ethanol. CDs and their complexes self-assemble in aqueous solutions to form both nano- and microparticles. The nanoparticles have diameters that are well below the wavelength of visible light; thus, the solutions appear to be clear. However, the nanoparticles can result in erroneous conclusions and misinterpretations of experimental results. CDs can act as penetration enhancers, increasing drug permeation through lipophilic membranes, but they do so without affecting the membrane barrier. This review is an account of some of the unexpected results the authors have encountered during their studies of CDs as pharmaceutical excipients.

Antibacterial drugs and cyclodextrin inclusion complexes: a patent review

INTRODUCTION

Bacterial antibiotic resistance occurs when bacteria mutate and escape the effect of antibiotics, which makes the antibiotics no longer effective in treating infections. New solutions for bacterial infections are a persistent need including the identification of drugs with better pharmacological profiles, more potent, and safer. Cyclodextrins inclusion complexes have been able to improve the physicochemical and pharmacological properties of the formulation molecules, resulting in new alternatives with better efficacy.

AREAS COVERED

The patents analyzed in the review used treatments based on antibiotics already on the market, natural products, and synthesized molecules composed of the formulation with cyclodextrins. The combination between cyclodextrin and nanostructures also were presented in the patents review process. Moreover, inclusion complexes have been an alternative in developing treatment mainly in China by the pharmaceutical industries in several countries such as Germany, Hungary, the United States of America, Japan and China.

EXPERT OPINION

This review is broad and complete since it considers the first patent involving cyclodextrins and antibacterial drugs. Therefore, the various inclusion complexes and antibacterial drugs alternatives presented in this review offer therapeutic options to fight bacterial infections. If shown to be effective, these drugs may be extremely important in the current clinical practice.

Mass Spectrometry of Esterified Cyclodextrins

Cyclodextrins are cyclic oligosaccharides that have received special attention due to their cavity-based structural architecture that imbues them with outstanding properties, primarily related to their capacity to host various guest molecules, from low-molecular-mass compounds to polymers. Cyclodextrin derivatization has been always accompanied by the development of characterization methods, able to unfold complicated structures with increasing precision. One of the important leaps forward is represented by mass spectrometry techniques with soft ionization, mainly matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI). In this context, esterified cyclodextrins (ECDs) benefited also from the formidable input of structural knowledge, thus allowing the understanding of the structural impact of reaction parameters on the obtained products, especially for the ring-opening oligomerization of cyclic esters. The current review envisages the common mass spectrometry approaches such as direct MALDI MS or ESI MS analysis, hyphenated liquid chromatography-mass spectrometry, and tandem mass spectrometry, employed for unraveling the structural features and particular processes associated with ECDs. Thus, the accurate description of complex architectures, advances in the gas phase fragmentation processes, assessment of secondary reactions, and reaction kinetics are discussed in addition to typical molecular mass measurements.

First Synthesis of DBU-Conjugated Cationic Carbohydrate Derivatives and Investigation of Their Antibacterial and Antifungal Activity

The emergence of drug-resistant bacteria and fungi represents a serious health problem worldwide. It has long been known that cationic compounds can inhibit the growth of bacteria and fungi by disrupting the cell membrane. The advantage of using such cationic compounds is that the microorganisms would not become resistant to cationic agents, since this type of adaptation would mean significantly altering the structure of their cell walls. We designed novel, DBU (1,8-diazabicyclo[5.4.0]undec-7-ene)-derived amidinium salts of carbohydrates, which may be suitable for disturbing the cell walls of bacteria and fungi due to their quaternary ammonium moiety. A series of saccharide-DBU conjugates were prepared from 6-iodo derivatives of d-glucose, d-mannose, d-altrose and d-allose by nucleophilic substitution reactions. We optimized the synthesis of a d-glucose derivative, and studied the protecting group free synthesis of the glucose-DBU conjugates. The effect of the obtained quaternary amidinium salts against Escherichia coli and Staphylococcus aureus bacterial strains and Candida albicans yeast was investigated, and the impact of the used protecting groups and the sugar configuration on the antimicrobial activity was analyzed. Some of the novel sugar quaternary ammonium compounds with lipophilic aromatic groups (benzyl and 2-napthylmethyl) showed particularly good antifungal and antibacterial activity.

Fine-tuned cholesterol solubilizer, mono-6-O-α-D-maltosyl-γ-cyclodextrin, ameliorates experimental Niemann-Pick disease type C without hearing loss

Niemann-Pick disease type C (NPC) is a fatal disorder with abnormal intracellular cholesterol trafficking resulting in neurodegeneration and hepatosplenomegaly. A cyclic heptasaccharide with different degrees of substitution of 2-hydroxypropyl groups, 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), acts as a strong cholesterol solubilizer and is under investigation for treating this disease in clinical trials, but its physicochemical properties and ototoxicity remain a concern. Here, we evaluated the potential of mono-6-O-α-maltosyl-γ-CD (G2-γ-CD), a single-maltose-branched cyclic octasaccharide with a larger cavity than HP-β-CD, for treating NPC. We identified that G2-γ-CD ameliorated NPC manifestations in model mice and showed lower ototoxicity in mice than HP-β-CD. To investigate the molecular mechanisms of action behind the differential ototoxicity of these CDs, we performed cholesterol solubility analysis, proton nuclear magnetic resonance spectroscopy, and molecular modeling, and estimated that the cholesterol inclusion mode of G2-γ-CD maintained solely the 1:1 inclusion complex, whereas that of HP-β-CD shifted to the highly-soluble 2:1 complex at higher concentrations. We predicted the associations of these differential complexations of CDs with cholesterol with the profile of disease attenuation and of the auditory cell toxicity using specific cell models. We proposed that G2-γ-CD can serve as a fine-tuned cholesterol solubilizer for treating NPC, being highly biocompatible and physicochemically suitable for clinical application.

Comparative Interaction Studies of Quercetin with 2-Hydroxyl-propyl-β-cyclodextrin and 2,6-Methylated-β-cyclodextrin

Quercetin (QUE) is a well-known natural product that can exert beneficial properties on human health. However, due to its low solubility its bioavailability is limited. In the present study, we examine whether its formulation with two cyclodextrins (CDs) may enhance its pharmacological profile. Comparative interaction studies of quercetin with 2-hydroxyl-propyl-β-cyclodextrin (2HP-β-CD) and 2,6-methylated cyclodextrin (2,6Me-β-CD) were performed using NMR spectroscopy, DFT calculations, and in silico molecular dynamics (MD) simulations. Using T1 relaxation experiments and 2D DOSY it was illustrated that both cyclodextrin vehicles can host quercetin. Quantum mechanical calculations showed the formation of hydrogen bonds between QUE with 2HP-β-CD and 2,6Μe-β-CD. Six hydrogen bonds are formed ranging between 2 to 2.8 Å with 2HP-β-CD and four hydrogen bonds within 2.8 Å with 2,6Μe-β-CD. Calculations of absolute binding free energies show that quercetin binds favorably to both 2,6Me-β-CD and 2HP-β-CD. MM/GBSA results show equally favorable binding of quercetin in the two CDs. Fluorescence spectroscopy shows moderate binding of quercetin in 2HP-β-CD (520 M⁻¹) and 2,6Me-β-CD (770 M⁻¹). Thus, we propose that both formulations (2HP-β-CD:quercetin, 2,6Me-β-CD:quercetin) could be further explored and exploited as small molecule carriers in biological studies.

Developing Novel Hydroxypropyl-β-Cyclodextrin-Based Nanosponges as Carriers for Anticancer Hydrophobic Agents: Overcoming Limitations of Host–Guest Complexes in a Comparative Evaluation

This study aimed to design and fabricate novel hydroxypropyl-β-cyclodextrin-based hypercrosslinked polymers, called nanosponges, as carriers for anticancer hydrophobic agents and compare them with host–guest complexes of hydroxypropyl-β-cyclodextrin, a remarkable solubilizer, to investigate their application in improving the pharmaceutical properties of the flavonoid naringenin, a model hydrophobic nutraceutical with versatile anticancer effects. For this purpose, three new nanosponges, crosslinked with pyromellitic dianhydride, citric acid, and carbonyldiimidazole, were fabricated. The carbonate nanosponge synthesized by carbonyldiimidazole presented the highest naringenin loading capacity (≈19.42%) and exerted significantly higher antiproliferative effects against MCF-7 cancer cells compared to free naringenin. Additionally, this carbonate nanosponge formed a stable nanosuspension, providing several advantages over the naringenin/hydroxypropyl-β-cyclodextrin host–guest complex, including an increase of about 3.62-fold in the loading capacity percentage, sustained released pattern (versus the burst pattern of host–guest complex), and up to an 8.3-fold increase in antiproliferative effects against MCF-7 cancer cells. Both naringenin-loaded carriers were less toxic to L929 murine fibroblast normal cells than MCF-7 cancer cells. These findings suggest that hydroxypropyl-β-cyclodextrin-based carbonate nanosponges could be a good candidate as a drug delivery system with potential applications in cancer treatment.

Cholecalciferol complexation with hydroxypropyl-β-cyclodextrin (HPBCD) and its molecular dynamics simulation

The focus of the current study is to investigate cholecalciferol (vitamin D3) solubilization by hydroxypropyl-β-cyclodextrin (HPBCD) complexation through experimental and computational studies. Phase solubility diagram of vitamin D3 (completely insoluble in water) has an A_P profile revealing a deviation from a linear regression with HPBCD concentration increase. Differential scanning calorimetry (DSC) is the best tool to confirm complex formation by disappearance of cholecalciferol exothermic peak in cholecalciferol-HPBCD complex thermogram, due to its amorphous state by entering HPBCD inner hydrophobic cavity, similarly validated by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). A_P solubility diagram profile can be associated with cholecalciferol-HPBCD complex instability in liquid phase requiring spray drying to bring it to a solid dispersion state (always more stable) illustrated by scanning electron microscopy (SEM). Computational studies led to a deeper understanding and clarification, at molecular level, of the interactions within cholecalciferol-HPBCD complex. Thermodynamics and geometry of the complex were investigated by molecular dynamics (MD) simulation.

Cyclodextrin-Oligocaprolactone Derivatives—Synthesis and Advanced Structural Characterization by MALDI Mass Spectrometry

Cyclodextrins have previously been proven to be active in the catalysis of cyclic ester ring-opening reactions, hypothetically in a similar way to lipase-catalyzed reactions. However, the way they act remains unclear. Here, we focus on β-cyclodextrin’s involvement in the synthesis and characterization of β-cyclodextrin-oligocaprolactone (CDCL) products obtained via the organo-catalyzed ring-opening of ε-caprolactone. Previously, bulk or supercritical carbon dioxide polymerizations has led to inhomogeneous products. Our approach consists of solution polymerization (dimethyl sulfoxide and dimethylformamide) to obtain homogeneous CDCL derivatives with four monomer units on average. Oligomerization kinetics, performed by a matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) optimized method in tandem with 1H NMR, revealed that monomer conversion occurs in two stages: first, the monomer is rapidly attached to the secondary OH groups of β-cyclodextrin and, secondly, the monomer conversion is slower with attachment to the primary OH groups. MALDI MS was further employed for the measurement of the ring-opening kinetics to establish the influence of the solvents as well as the effect of organocatalysts (4-dimethylaminopyridine and (–)-sparteine). Additionally, the mass spectrometry structural evaluation was further enhanced by fragmentation studies which confirmed the attachment of oligoesters to the cyclodextrin and the cleavage of dimethylformamide amide bonds during the ring-opening process.

Cyclodextrin and its derivatives as effective excipients for amorphous ulipristal acetate systems

Many efforts have been devoted to screening new solid-state forms of poorly soluble drugs in the pharmaceutical industry, thus modulating the drug properties without changing the pharmacological nature. It is a wise strategy to prepare amorphous series with cyclodextrin (CD) and its derivatives as excipients to enhance the aqueous solubility, dissolution, and bioavailability of water-insoluble drugs. In this study, four binary amorphous mixtures of ulipristal acetate (UPA) with CDs (β-CD, γ-CD, dimethyl-β-CD, hydroxypropyl-β-CD) were prepared by the co-milling method and characterized in the solid-state. According to powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC), UPA existed in the noncrystalline form in the four binary amorphous mixtures. Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) indicated that UPA interacted with the four CDs, which was also verified by molecular docking. Compared with the crystalline and amorphous UPA, the solubility, dissolution, and stability of the drug in the four amorphous UPA systems were significantly improved, so they were considered potentially advantageous solid forms. Our research shows that CDs can be used as new effective excipients in amorphous systems for active pharmaceutical ingredients (API).

Enhancing the water-solubility of curcuminoids-rich extract using a ternary inclusion complex system: Preparation, characterization, and anti-cancer activity

Curcuminoids are known to exert diverse pharmacological effects and used in some pharmaceutical formulations. This study describes the preparation, characterization, and enhancement in the solubility and anticancer activity of a curcuminoids-rich extract (CRE) using a ternary inclusion complex system. CRE containing 88.9% w/w curcuminoids was prepared using a 'green' microwave extraction coupled with fractionation on a column of hydrophobic adsorbent resin. The ternary complex consisting of CRE, hydroxylpropyl-β-cyclodextrin and polyvinylpyrrolidone K30 was prepared using the solvent evaporation method and thoroughly characterized using Fourier-transform infrared spectroscopy, powder X-ray diffractograms, differential scanning calorimetry and scanning electron microscopy. The ternary complex of CRE improved the water-solubility of curcuminoids (up to 70.3 µg/mL) as well as the dissolution rate when compared to those of CRE (0 µg/mL). In addition, the ternary complex exhibited significantly stronger anticancer activity against human lung adenocarcinoma (A-549), human cervical adenocarcinoma (HeLa) and human colon adenocarcinoma (HT-29) cell lines than CRE.

The Role of Cyclodextrins in the Design and Development of Triterpene-Based Therapeutic Agents

Triterpenic compounds stand as a widely investigated class of natural compounds due to their remarkable therapeutic potential. However, their use is currently being hampered by their low solubility and, subsequently, bioavailability. In order to overcome this drawback and increase the therapeutic use of triterpenes, cyclodextrins have been introduced as water solubility enhancers; cyclodextrins are starch derivatives that possess hydrophobic internal cavities that can incorporate lipophilic molecules and exterior surfaces that can be subjected to various derivatizations in order to improve their biological behavior. This review aims to summarize the most recent achievements in terms of triterpene:cyclodextrin inclusion complexes and bioconjugates, emphasizing their practical applications including the development of new isolation and bioproduction protocols, the elucidation of their underlying mechanism of action, the optimization of triterpenes’ therapeutic effects and the development of new topical formulations.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Computational Insights Into the Influence of Substitution Groups on the Inclusion Complexation of β-Cyclodextrin

Cyclodextrins (CDs) and their derivatives have good prospects in soil remediation application due to their ability to enhance the stability and solubility of low water-soluble compounds by inclusion performance. To investigate the effect of different structural properties of cyclodextrin and its derivatives on the inclusion complexation, molecular dynamic (MD) simulations were performed on the inclusion complexes formed by three kinds of CDs with polycyclic aromatic hydrocarbons (PAHs). Based on neutral β-CD, the other two CDs were modified by introducing substitutional groups, including 2-hydroxypropyl and sulfonated butyl (SBE) functional groups in the ring structure, called HP-CD and SBE-CD. MD results show that PAH can merely enter into the cavity of SBE–β-CD from its wide rim. The substitutional groups significantly affect the structure of CDs, which may also cause the flipping of the glucose units. However, the substitutional groups can also enlarge the volume of the hydrophobic cavity, resulting in a tight combination with the guest molecules.

Molecular Structure of Cefuroxime Axetil Complexes with α-, β-, γ-, and 2-Hydroxypropyl-β-Cyclodextrins: Molecular Simulations and Raman Spectroscopic and Imaging Studies

The formation of cefuroxime axetil+cyclodextrin (CA+CD) complexes increases the aqueous solubility of CA, improves its physico-chemical properties, and facilitates a biomembrane-mediated drug delivery process. In CD-based tablet formulations, it is crucial to investigate the molecular details of complexes in final pharmaceutical preparation. In this study, Raman spectroscopy and mapping were applied for the detection and identification of chemical groups involved in α-, β-, γ-, and 2-hydroxypropyl-β-CD (2-HP- β-CD)+CA complexation process. The experimental studies have been complemented by molecular dynamics-based investigations, providing additional molecular details of CA+CD interactions. It has been demonstrated that CA forms the guest–host type inclusion complexes with all studied CDs; however, the nature of the interactions is slightly different. It seems that both α- and β-CD interact with furanyl and methoxy moieties of CA, γ-CD forms a more diverse pattern of interactions with CA, which are not observed in other CDs, whereas 2HP-β-CD binds CA with the contribution of hydrogen bonding. Apart from supporting this interpretation of the experimental data, molecular dynamics simulations allowed for ordering the CA+CD binding affinities. The obtained results proved that the molecular details of the host–guest complexation can be successfully predicted from the combination of Raman spectroscopy and molecular modeling.

Development of an LC-MS/MS method for simultaneous quantitative analysis of macromolecular pharmaceutical adjuvant 2-hydroxypropyl-β-cyclodextrin and active pharmaceutical ingredients butylphthalide in rat plasma

Hydroxypropyl-β-cyclodextrin, which possesses a high water solubility and low hemolycity, is widely used as a solubilizer and an excipient. It had also been reported that hydroxypropyl-β-cyclodextrin has the activity of regulating lipid homeostasis. In order to further understand the metabolism, the primary focus was to establish a quantitative method for hydroxypropyl-β-cyclodextrin. The analytes were extracted from plasma by protein precipitation with methanol and then carried out on a Waters CORTECS T3 column in the gradient elution of pure water and methanol. Finally, liquid chromatography-tandem mass spectrometry was applied in multiple reaction monitoring mode to complete the quantitative analysis of hydroxypropyl-β-cyclodextrin. This validated method had been successfully applied to investigate the interaction between hydroxypropyl-β-cyclodextrin and butylphthalide in vivo by optimizing the extraction reagent, simplifying the experimental procedure, and improving the sensitivity while considering the difference of drug chemical properties. Results showed that the inclusion of hydroxypropyl-β-cyclodextrin with butylphthalide significantly improved the pharmacokinetic behavior of free body hydroxypropyl-β-cyclodextrin and 3-n-butylphthalide in vivo. It had been implied that the metabolism of hydroxypropyl-β-cyclodextrin and the drug active ingredients could impact each other. It will help better application of hydroxypropyl-β-cyclodextrin and the developed method might lay the foundation for development of hydroxypropyl-β-cyclodextrin as a treatment drug for brain diseases.

Cyclodextrin dimers: A versatile approach to optimizing encapsulation and their application to therapeutic extraction of toxic oxysterols

We have developed a novel class of specifically engineered, dimerized cyclodextrin (CD) nanostructures for the encapsulation of toxic biomolecules such as 7-ketocholesterol (7KC). 7KC accumulates over time and causes dysfunction in many cell types, linking it to several age-related diseases including atherosclerosis and age-related macular degeneration (AMD). Presently, treatments for these diseases are invasive, expensive, and show limited benefits. CDs are cyclic glucose oligomers utilized to capture small, hydrophobic molecules. Here, a combination of in silico, in vitro, and ex vivo methods is used to implement a synergistic rational drug design strategy for developing CDs to remove atherogenic 7KC from cells and tissues. Mechanisms by which CDs encapsulate sterols are discussed, and we conclude that covalently linked head-to-head dimers of βCDs have substantially improved affinity for 7KC compared to monomers. We find that inclusion complexes can be stabilized or destabilized in ways that allow the design of CD dimers with increased 7KC selectivity while maintaining an excellent safety profile. These CD dimers are being developed as therapeutics to treat atherosclerosis and other debilitating diseases of aging.

HP-β-CD for the formulation of IgG and Ig-based biotherapeutics

The main challenge to develop HCF for IgG and Ig-based therapeutics is to achieve essential solubility, viscosity and stability of these molecules in order to maintain product quality and meet regulatory requirement during manufacturing, production, storage, shipment and administration processes. The commonly used and FDA approved excipients for IgG and Ig -based therapeutics may no longer fulfil the challenge of HCF development for these molecules to certain extent, especially for some complex Ig-based platforms. 2-Hydroxypropyl beta-cyclodextrin (HP-β-CD) is one of the promising excipients applied recently for HCF development of IgG and Ig-based therapeutics although it has been used for formulation of small synthesized chemical drugs for more than thirty years. This review describes essential aspects about application of HP-β-CD as excipient in pharmaceutical formulation, including physico-chemical properties of HP-β-CD, supply chain, regulatory, patent landscape, marketed drugs with HP-β-CD, analytics and analytical challenges, stability and control strategies, and safety concerns. It also provides an overview of different studies, and outcomes thereof, regarding formulation development for IgGs and Ig-based molecules in liquid and solid (lyophilized) dosage forms with HP-β-CD. The review specifically highlights the challenges for formulation manufacturing of IgG and Ig-based therapeutics with HP-β-CD and identifies areas for future work in pharmaceutical and formulation development.

Functionalization of Gold Nanostars with Cationic β-Cyclodextrin-Based Polymer for Drug Co-Loading and SERS Monitoring

Gold nanostars (AuNSs) exhibit modulated plasmon resonance and have a high SERS enhancement factor. However, their low colloidal stability limits their biomedical application as a nanomaterial. Cationic β-cyclodextrin-based polymer (CCD/P) has low cytotoxicity, can load and transport drugs more efficiently than the corresponding monomeric form, and has an appropriate cationic group to stabilize gold nanoparticles. In this work, we functionalized AuNSs with CCD/P to load phenylethylamine (PhEA) and piperine (PIP) and evaluated SERS-based applications of the products. PhEA and PIP were included in the polymer and used to functionalize AuNSs, forming a new AuNS-CCD/P-PhEA-PIP nanosystem. The system was characterized by UV–VIS, IR, and NMR spectroscopy, TGA, SPR, DLS, zeta potential analysis, FE-SEM, and TEM. Additionally, Raman optical activity, SERS analysis and complementary theoretical studies were used for characterization. Minor adjustments increased the colloidal stability of AuNSs. The loading capacity of the CCD/P with PhEA-PIP was 95 ± 7%. The physicochemical parameters of the AuNS-CCD/P-PhEA-PIP system, such as size and Z potential, are suitable for potential biomedical applications Raman and SERS studies were used to monitor PhEA and PIP loading and their preferential orientation upon interaction with the surface of AuNSs. This unique nanomaterial could be used for simultaneous drug loading and SERS-based detection.

2D DOSY NMR: A Valuable Tool to Confirm the Complexation in Drug Delivery Systems

Many bioactive substances face the problem of limited bioavailability, mainly due to low aqueous solubility and poor metabolic stability. Their complexation with drug delivery systems offers a more optimum pharmacological profile. Some of these drug delivery systems that have promising potential form complexes with bioactive compounds such as cyclodextrins and calixarenes. The monitoring of the success and the type of the complexation are of great importance and two-dimensional diffusion-ordered NMR spectroscopy (2D DOSY) is a valuable tool for the studying of these complexes and described as "NMR chromatography." Herein we report the procedure for the complexation of the natural product quercetin in 2-hydroxypropyl-β-cyclodextrin and the anticancer drug temozolomide in p-sulfonatocalix[4]arene and the determination of the complexation with 2D DOSY spectroscopy.

The Budesonide-Hydroxypropyl-β-Cyclodextrin Complex Attenuates ROS Generation, IL-8 Release and Cell Death Induced by Oxidant and Inflammatory Stress. Study on A549 and A-THP-1 Cells

Synthetic glucocorticoids such as budesonide (BUD) are potent anti-inflammatory drugs commonly used to treat patients suffering from chronic inflammatory diseases. A previous animal study reported a higher anti-inflammatory activity with a 2-hydroxypropyl-β-cyclodextrin (HPβCD)-based formulation of BUD (BUD:HPβCD). This study investigated, on cellular models (A549 and A-THP-1), the effect of BUD:HPβD in comparison with BUD and HPβCD on the effects induced by oxidative and inflammatory stress as well as the role of cholesterol. We demonstrated the protective effect afforded by BUD:HPβCD against cytotoxicity and ROS generation induced by oxidative and inflammatory stress. The effect observed for BUD:HPβCD was comparable to that observed with HPβCD with no major effect of cholesterol content. We also demonstrated (i) the involvement of the canonical molecular pathway including ROS generation, a decrease in PI3K/Akt activation, and decrease in phosphorylated/unphosphorylated HDAC2 in the effect induced by BUD:HPβCD, (ii) the maintenance of IL-8 decrease with BUD:HPβCD, and (iii) the absence of improvement in glucocorticoid insensitivity with BUD:HPβCD in comparison with BUD, in conditions where HDAC2 was inhibited. Resulting from HPβCD antioxidant and anticytotoxic potential and protective capacity against ROS-induced PI3K/Akt signaling and HDAC2 inhibition, BUD:HPβCD might be more beneficial than BUD alone in a context of concomitant oxidative and inflammatory stress.

Investigation of Cytotoxicity and Cell Uptake of Cationic Beta-Cyclodextrins as Valid Tools in Nasal Delivery

Cyclodextrin polymers have high applicability in pharmaceutical formulations due to better biocompatibility, solubility enhancement, loading capacity and controlled drug release than their parent, cyclodextrins. The cytotoxicity and cell uptake of new cationic beta-cyclodextrin monomers and polymers were evaluated as suitable materials for nasal formulations and their protective effects on cells exposed to hydrogen peroxide were studied. PC12 and CACO-2 cells were selected as the neuronal- and epithelial-type cells, respectively, to mimic the structure of respiratory and olfactory epithelia of the nasal cavity. All cationic beta-cyclodextrin polymers tested showed dose- and time-dependent toxicity; nevertheless, at 5 µM concentration and 60 min of exposure, the quaternary-ammonium-beta-cyclodextrin soluble polymer could be recognized as nontoxic. Based on these results, a fluorescently labelled quaternary-ammonium-beta-cyclodextrin monomer and polymer were selected for uptake studies in CACO-2 cells. The monomeric and polymeric beta-cyclodextrins were internalized in the cytoplasm of CACO-2 cells; the cationic monomer showed higher permeability than the hydroxypropyl-beta-cyclodextrin, employed as comparison. Therefore, these cationic beta-cyclodextrins showed potential as excipients able to improve the nasal absorption of drugs. Furthermore, amino-beta-cyclodextrin and beta-cyclodextrin soluble polymers were able to reduce oxidative damage in PC12 and CACO-2 cells and thus could be studied as bioactive carriers or potential drugs for cell protection against oxidative stress.

Conformational preferences of TEMPO type radicals in complexes with cyclodextrins revealed by a combination of EPR spectroscopy, induced circular dichroism and molecular modeling

Electron paramagnetic resonance (EPR) spectroscopy is the main tool for evidencing the formation of inclusion complexes of cyclodextrins with paramagnetic guests, based on changes in the EPR parameters. In-depth information on complexation can only be obtained by a combination of physico-chemical methods. Herein we report on the interaction of three TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl) type radicals with cyclodextrins by collecting and analysing data provided experimentally by EPR and circular dichroism spectroscopies and theoretically by density functional theory and molecular docking. The study focused on the pH influence on the complexation of three paramagnetic probes with cyclodextrins. The EPR spectra revealed that the type and protonation state of the substituent linked to the TEMPO structure influences the affinity of the paramagnetic group for the cyclodextrin cavity. Neutral radical species favour stronger association with cyclodextrins and inclusion of the nitroxide group into the cavity, especially in the case of 4-carboxy-TEMPO. Induced circular dichroism signals of neutral species varied in sign and intensity as a function of substituent and cyclodextrin type. Density functional theory and molecular docking results supported the experimental data regarding the conformational preferences of TEMPO radicals in complexes with cyclodextrins.

Cyclodextrin Ameliorates the Progression of Atherosclerosis via Increasing High-Density Lipoprotein Cholesterol Plasma Levels and Anti-inflammatory Effects in Rabbits

To investigate the therapeutic effects of cyclodextrin on the development of atherosclerosis in rabbits, we evaluated the effects of (2-hydroxypropyl)-β-cyclodextrin (HPβCD) therapy on the organ coefficient, lipid profiles, inflammatory cytokines, and atherosclerotic plaques in rabbits fed a high-fat diet. Our results demonstrated that HPβCD therapy reduced plasma triglyceride levels and inflammatory cytokine levels but increased plasma high-density lipoprotein cholesterol levels. HPβCD therapy produced a significant decrease in the atherosclerotic lesion area and reduced macrophage and collagen content in the lesions. The expression levels of inflammatory genes in aortic plaques were significantly reduced by HPβCD treatment, but the expression of ATP-binding cassette (ABC) transporters A1 (ABCA1) and G1 (ABCG1) in aortic plaques and livers increased significantly. HPβCD therapy may produce additional antiatherosclerotic benefits likely via increasing high-density lipoprotein cholesterol levels.

Charting the structural and thermodynamic determinants in phenolic acid natural product - cyclodextrin encapsulations

Cyclodextrins are pliable platforms that have served to optimize the pharmaceutic profile of numerous compounds and to enhance the stability of natural food additives. Caffeic and rosmarinic acid are natural products with proven health benefits, though their full therapeutic potential has not been exploited. To enhance their pharmaceutic profile, we developed cyclodextrin-based formulates and unveiled their thermodynamic and structural principles. The complexes' stoichiometry was determined by ESI-MS. Solid-state and liquid NMR spectroscopy revealed the interactions and the topographical location of the caffeic and rosmarinic acid inside the cyclodextrin cavity. The theoretically analyzed HP-β-CD's degree of substitution (DS) of caffeic and rosmarinic acids can explain the intensities obtained by 2D NOESY experiments. The thermodynamics and the affinity of the complexes were evaluated through isothermal titration calorimetry. In addition, the rosmarinic and caffeic acids as, also, their complexes showed considerable antimicrobial activity against common food spoilage and pathogenic bacteria. The generated data could provide the basis to understand the structural and thermodynamic determinants implicated in natural products - CD recognition and to develop platforms for the optimization of their pharmaceutical and stability profiles in order to be utilized as safe and stable natural antimicrobial food additives.Communicated by Ramaswamy H. Sarma.

Molecular structure study of a heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin complex of cholesterol

Heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (2) and cholesterol form a water-soluble complex 3. We performed several NMR studies, particularly ¹H, ¹³C, 2D NOESY and DOSY, at various temperatures on 500 and 950 MHz instruments. We discovered that the complex 3 is unstable above 57 °C in heavy water, while it is kinetically stable enough to be studied by NMR in detail at 1 °C. We demonstrated the formation of a face-to-face 2:1 complex with a binding constant of approximately 2.2 × 10⁶ M^-2.

Pharmacokinetic Properties of Fluorescently Labelled Hydroxypropyl-Beta-Cyclodextrin

2-Hydroxypropyl-beta-cyclodextrin (HPBCD) is utilized in the formulation of pharmaceutical products and recently orphan designation was granted for the treatment of Niemann–Pick disease, type C. The exact mechanism of HPBCD action and side effects are not completely explained. We used fluorescently labelled hydroxypropyl-beta-cyclodextrin (FITC-HPBCD) to study its pharmacokinetic parameters in mice and compare with native HPBCD data. We found that FITC-HPBCD has fast distribution and elimination, similar to HPBCD. Interestingly animals could be divided into two groups, where the pharmacokinetic parameters followed or did not follow the two-compartment, first-order kinetic model. Tissue distribution studies revealed, that a significant amount of FITC-HPBCD could be detected in kidneys after 60 min treatment, due to its renal excretion. Ex vivo fluorescent imaging showed that fluorescence could be measured in lung, liver, brain and spleen after 30 min of treatment. To model the interaction and cellular distribution of FITC-HPBCD in the wall of blood vessels, we treated human umbilical vein endothelial cells (HUVECs) with FITC-HPBCD and demonstrated for the first time that this compound could be detected in the cytoplasm in small vesicles after 30 min of treatment. FITC-HPBCD has similar pharmacokinetic to HPBCD and can provide new information to the detailed mechanism of action of HPBCD.

Effect of cyclodextrin additives on azithromycin in aqueous solution and insight into the stabilization mechanism by sulfobutyl ether-β-cyclodextrin

The stability of azithromycin in buffered aqueous solution at pH 6.7 was investigated in the presence of different cyclodextrin (CD) additives by HPLC monitoring of the drug concentration over time. In the presence of γ-CDs, either in native or derivatized form, the long-term stability of azithromycin was sensibly decreased with respect to the reference sample without any additives, whereas the opposite effect was observed with all the three tested β-CDs. The most effective stabilization of the drug was obtained by using sulfobutyl ether-β-cyclodextrin, which allowed a concentration of azithromycin in solution at 99% up to 6 months at room temperature. The positive action of sulfobutyl ether-β-cyclodextrin was mainly exerted through the suppression of a degradation pathway leading to the opening of lactone ring of azithromycin. The formation of dynamic inclusion complexes in solution was ruled out by NMR data and stabilization of azithromycin by the amphiphilic sulfobutyl ether-β-cyclodextrin through surfactant-like effects was proposed on the basis of the strict similarity, either in the degradation profiles and in the NMR data, with a solution of the drug in the presence of sodium hexylsulphonate as surfactant.

Cavity Closure of 2-Hydroxypropyl-β-Cyclodextrin: Replica Exchange Molecular Dynamics Simulations

2-Hydroxypropyl-β-cyclodextrin (HPβCD) has unique properties to enhance the stability and the solubility of low water-soluble compounds by inclusion complexation. An understanding of the structural properties of HPβCD and its derivatives, based on the number of 2-hydroxypropyl (HP) substituents at the α-d-glucopyranose subunits is rather important. In this work, replica exchange molecular dynamics simulations were performed to investigate the conformational changes of single- and double-sided HP-substitution, called 6-HPβCDs and 2,6-HPβCDs, respectively. The results show that the glucose subunits in both 6-HPβCDs and 2,6-HPβCDs have a lower chance of flipping than in βCD. Also, HP groups occasionally block the hydrophobic cavity of HPβCDs, thus hindering drug inclusion. We found that HPβCDs with a high number of HP-substitutions are more likely to be blocked, while HPβCDs with double-sided HP-substitutions have an even higher probability of being blocked. Overall, 6-HPβCDs with three and four HP-substitutions are highlighted as the most suitable structures for guest encapsulation, based on our conformational analyses, such as structural distortion, the radius of gyration, circularity, and cavity self-closure of the HPβCDs.

β-Cyclodextrin and oleic acid increase levels of dopamine and potentiates oxidative damage in young and adult rat brain

Background

Cyclodextrins are active pharmaceutical ingredients to treat neurological diseases by reducing neurotoxicity. The aim of this study was to test if combined consumption of β-cyclodextrin (BCD) and Oleic acid (OA) potentiates brain antioxidant protection.

Methods

Four groups of young Wistar rats, grouped in 6 animals each, were treated as follows: Group (G) 1, saline solution 0.9% (control); G2, BCD (0.7 g/kg); G3, OA (15 ml/kg); G4, BCD + OA. The same design was assayed for groups of adult rats. Treatments were daily administered by oral means for five consecutive days. On the last day of administration, brains of the animals were extracted to measure dopamine, 5-HIAA, glutathione (GSH), ATPase, Lipoperoxidation and H₂O_2.

Results

Oleic acid and β-cyclodextrin upgraded the levels of dopamine, 5-HIAA and lipid peroxidation and downgraded the concentrations of GSH and H₂O₂ in cortex, hemispheres (striatum) and cerebellum/medulla oblongata regions.

Conclusions

The results of the present study suggest that combined use of oleic acid and β-cyclodextrin may increase oxidative damage in brain regions and promote alteration in dopamine and 5-HIAA amines and hence, constitutes health risks among age of subjects.