Host–guest system of taxifolin and native cyclodextrin or its derivative: Preparation, characterization, inclusion mode, and solubilization

Metabolism, tissue distribution and excretion of taxifolin in rat

The metabolism, tissue distribution and excretion of taxifolin in rat after oral administration of taxifolin encapsulated zein-caseinate Nanoparticles (TZP) were studied. The isomerization of taxifolin in rat small intestine and colon was found. Besides isomers, 16 metabolites of taxifolin were identified in rat feces, plasma and urine by UPLC-QTOF-MS. In colon, taxifolin underwent the metabolism of hydration, dehydration and ring-fission through the gut microflora. The main metabolites of taxifolin found in plasma and urine were its sulfated, glucuronidated, and/or methylated products. The dynamic variation of taxifolin and its metabolites in tissues and urine were quantified by UPLC-QqQ-MS/MS. Taxifolin and its metabolites could be quickly absorbed and distributed in the tissues, and relatively low concentrations were found in the heart and brain. The feces excretion of taxifolin was determined by HPLC. The total excretion during 24 h was 2.83 ± 0.80% to its given does, and the maximum excretion was found during 8-10 h post administration. Compared with feces, the excretion of taxifolin and its metabolites in urine was much faster, and the total excretion was 1.96 ± 0.23% during 12 h.

Alginate enriched with phytic acid for hydrogels preparation. Therapeutic applications

In the last decade, numerous innovative strategies have been used to obtain highly efficient synthetic or semi-synthetic biomaterials. Between these innovative biomaterials, hydrogels occupy a distinct place due to their superior biological and physico-chemical characteristics. Alginate is a natural linear polysaccharide with important physico-chemical and biological properties. Recently, we obtained a new hydrogel based on alginate and phytic acid with improved physico-chemical properties. In the present study, the hydrogels previously obtained were tested in terms of their biological properties and possibilities of use in the biomedical field. For this purpose, the hydrogels were loaded with norfloxacin (NRF), an antibacterial compound utilised in the treatment against Gram-negative and Gram-positive organisms. Unfortunately, NRF has low solubility and permeability. In order to provide protection against loss, but also for enhanced bioavailability, and controlled-release of norfloxacin, a drug inclusion complex with cyclodextrin was realized. The effect of complexation on the release profile was highlighted. The addition of NRF to the hydrogel matrices greatly improved the antibacterial activity of the tested compounds. The presence of CD did not affect the homogeneity of the drug distribution. Changes in the polymeric matrix structure were registered after the incorporation of the drug, which were attributed to the relaxation of the network subsequently to the penetration and diffusion of the drug solution simultaneously with the swelling process. The release of NRF from Alg_PA polymeric network has been successfully modulated by the use of CD as a host molecule.

Exploring Taxifolin Polymorphs: Insights on Hydrate and Anhydrous Forms

Taxifolin, also known as dihydroquercetin, possesses several interesting biological properties. The purpose of the study was to identify polymorphs of taxifolin prepared using crystallization in different solvents. Data from X-ray powder diffraction, differential scanning calorimetry, and thermogravimetry enabled us to detect six different crystalline phases for taxifolin. Besides the already known fully hydrated phase, one partially hydrated phase, one monohydrated phase, two anhydrous polymorphs, and one probably solvated phase were obtained. The unit cell parameters were defined for three of them, while one anhydrous polymorph was fully structurally characterized by X-ray powder diffraction data. Scanning electron microscopy and hot stage microscopy were also employed to characterize the crystallized taxifolin powders. The hydrate and anhydrous forms showed remarkable stability in drastic storage conditions, and their solubility was deeply evaluated. The anhydrous form converted into the hydrate form during the equilibrium solubility study and taxifolin equilibrium solubility was about 1.2 mg/mL. The hydrate taxifolin intrinsic dissolution rate was 56.4 μg cm^-2 min^-1. Using Wood's apparatus, it was not possible to determine the intrinsic dissolution rate of anhydrous taxifolin that is expected to solubilize more rapidly than the hydrate form. In view of its high stability, its use can be hypothesized.

PLGA encapsulated γ-cyclodextrin-meropenem inclusion complex formulation for oral delivery

Meropenem (MER) is one of the last resort antibiotics used to treat resistant bacterial infections. However, the clinical effectiveness of MER is hindered due to chemical instability in aqueous solution and gastric pH, and short plasma half-life. Herein, a novel multi-material delivery system based on γ-cyclodextrin (γ-CD) and poly lactic-co-glycolic acid (PLGA) is demonstrated to overcome these challenges. MER showed a saturated solubility of 14 mg/100 mL in liquid CO₂ and later it was loaded into γ-CD to form the inclusion complex using the liquid CO₂ method. The γ-CD and MER inclusion complex (MER-γ-CD) was encapsulated into PLGA by the well-established double emulsion solvent evaporation method. The formation of the inclusion complex was confirmed using FTIR, XRD, DSC, SEM, and ¹H NMR and docking study. Further, MER-γ-CD loaded PLGA nanoparticles (MER-γ-CD NPs) were characterized by SEM, DLS, and FTIR. The drug loading and entrapment efficiency for MER-γ-CD were 21.9 and 92. 2% w/w, respectively. However, drug loading and entrapment efficiency of MER-γ-CD NPs was significantly lower at up to 3.6 and 42.1% w/w, respectively. In vitro release study showed that 23.6 and 27.4% of active (non-degraded drug) and total drug (both degraded and non-degraded drug) were released from MER-γ-CD NPs in 8 h, respectively. The apparent permeability coefficient (Papp) (A to B) for MER, MER-γ-CD, and MER-γ-CD NPs were 2.63 × 10^-6 cm/s, 2.81 × 10^-6 cm/s, and 2.92 × 10^-6 cm/s_, respectively. For secretory transport, the Papp (B to A) were 1.47 × 10^-6 cm/s, 1.53 × 10^-6 cm/s, and 1.58 × 10^-6 cm/s for MER, MER-γ-CD and MER-γ-CD NPs_, respectively. Finally, the MER-γ-CD inclusion complex and MER-γ-CD NPs retained MER's antibacterial activities against Staphylococcus aureus and Pseudomonas aeruginosa. Overall, this work demonstrates the significance of MER-γ-CD NPs to protect MER from gastric pH with controlled drug release, while retaining MER's antibacterial activity.

Physical and Chemical Stability of Formulations Loaded with Taxifolin Tetra-octanoate

Chemically stable ester derivatives of taxifolin have become a focus of interest for their role in the satisfactory effects on human health. Accordingly, the aim of this study was to evaluate the physical and chemical stability of different formulations containing 0.02% taxifolin tetra-octanoate, which was proved to possess higher inhibitory effect on tyrosinase activity compared with taxifolin in a cell-free system. In the studies of physical stability, a Brookfield viscometer was used to determine rheological behavior of formulations containing taxifolin tetra-octanoate, and a portable pH meter was used to determine pH change. Moreover, chemical stability was determined by HPLC with UV detection. Formulations were evaluated for 12 weeks stored at 25 and 40°C. Results showed that storage time had no significant influence on viscosity of the formulations containing taxifolin tetra-octanoate, and pH value was relatively stable, which was within the limits of normal skin pH range. In the chemical stability studies, taxifolin tetra-octanoate in the essence formulation was most unstable at 40°C with about 81% degradation in 12 weeks of storage, however, the percentage of remaining taxifolin tetra-octanoate in cream formulation stored for 12 weeks at 25°C was the highest, about 93%. The results in this study may contribute to the development of more stable formulations containing taxifolin tetra-octanoate.

Amorphous Metal-Free Room-Temperature Phosphorescent Small Molecules with Multicolor Photoluminescence via a Host-Guest and Dual-Emission Strategy

Metal-free room-temperature phosphorescence (RTP) materials offer unprecedented potentials for photoelectric and biochemical materials due to their unique advantages of long lifetime and low toxicity. However, the achievements of phosphorescence at ambient condition so far have been mainly focused on ordered crystal lattice or on embedding into rigid matrices, where the preparation process might bring out poor repeatability and limited application. In this research, a series of amorphous organic small molecular compounds were developed with efficient RTP emission through conveniently modifying phosphor moieties to β-cyclodextrin (β-CD). The hydrogen bonding between the cyclodextrin derivatives immobilizes the phosphors to suppress the nonradiative relaxation and shields phosphors from quenchers, which enables such molecules to emit efficient RTP emission with decent quantum yields. Furthermore, one such cyclodextrin derivative was utilized to construct a host-guest system incorporating a fluorescent guest molecule, exhibiting excellent RTP-fluorescence dual-emission properties and multicolor emission with a wide range from yellow to purple including white-light emission. This innovative and universal strategy opens up new research paths to construct amorphous metal-free small molecular RTP materials and to design organic white-light-emitting materials using a single supramolecular platform.

Research on Characteristics, Antioxidant and Antitumor Activities of Dihydroquercetin and Its Complexes

Dihydroquercetin is a kind of dihydroflavonol compounds with antioxidant, antitumor, antivirus and radioresistance activities. This study attempted to produce the dihydroquercetin complexes with lecithin and β-cyclodextrin, and research their characteristics and bioactivities via ultraviolet spectrum (UV), infrared spectroscopy (IR), scanning electron microscope (SEM), differential scanning calorimetry (DSC), X-ray diffraction spectrum (XRD), and MTT assay. Results showed that the complexes with lecithin and β-cyclodextrin could improve the solubility and dissolution rate, and remove the characteristic endothermic peak of dihydroquercetin. IR spectra proved their interaction, and results of SEM and XRD showed the amorphous characteristics of the dihydroquercetin compounds. These results indicated that dihydroquercetin was combined by lecithin or β-cyclodextrin with better physical and chemical properties, which would effectively improve the application value in the food and drug industries.

Analysis of Molecular Interaction of Drugs within β-Cyclodextrin Cavity by Solution-State NMR Relaxation

The prime focus of the present study is to employ NMR relaxation measurement to address the intermolecular interactions, as well as motional dynamics, of drugs, viz., paracetamol and aspirin, encapsulated within the β-cyclodextrin (β-CD) cavity. In this report, we have attempted to demonstrate the applicability of nonselective (R₁^ns), selective (R₁^se), and bi-selective (R₁^bs) spin-lattice relaxation rates to infer dynamical parameters, for example, the molecular rotational correlation times (τ_c) and cross-relaxation rates (σ_ij) of the encapsulated drugs. Molecular rotational correlation times of the free drugs were calculated using the selective relaxation rate in the fast molecular motion time regime (ω_H²τ_c² ≪ 1 and R₁^ns/R₁^se ≈ 1.500), whereas that of the 1:1 complexed drugs were found from the ratio of R₁^ns/R₁^se in the intermediate motion time regime (ω_H²τ_c² ∼ 1 and R₁^ns/R₁^se ≈ 1.054), and these values were compared with each other to confirm the formation of inclusion complexes. Furthermore, the cross-relaxation rates were used to evaluate the intermolecular proton distances. Also, density functional theory calculations were performed to determine the minimum energy geometry of the inclusion complexes and the results compared with those from experiments. The report, thus, presents the possibility of utilizing NMR relaxation data, a more cost-effective experiment, to calculate internuclear distances in the case of drug-supramolecule complexes that are generally obtained by extremely time consuming two-dimensional nuclear Overhauser enhancement-based methods. A plausible mode of insertion of the drug molecules into the β-CD cavity has also been described based on experimental NMR relaxation data analysis.

Synthesis, characterization, solubilization, cytotoxicity and antioxidant activity of aminomethylated dihydroquercetin

A dihydroquercetin derivative (DHQA) was prepared through aminomethylation to overcome the low water solubility and bioavailability of dihydroquercetin (DHQ). DHQA was characterized through HPLC, nuclear magnetic resonance, scanning electron microscopy, X-ray diffraction, and thermogravimetric analyses. DHQA was converted into the amorphous form, but the major structure of DHQ remained unchanged. Solubilization and dissolution tests were also performed. Results showed that the solubility and dissolution rates of DHQA were approximately 16.28 and 6.31 times higher than those of DHQ, respectively. The MTT assay of DHQA showed a non-toxic effect against non-cancerous HEK-293T cells (EC₅₀ = 820.00 μM), and potent inhibitory activity against cancerous Hela cells (EC₅₀ = 138.17 μM). Finally, the antioxidant activity of DHQA was confirmed in vitro through DPPH and ABTS radical scavenging activity assays. DHQA displayed high antioxidant activities with low IC₅₀ values (0.043 and 0.042 mM, respectively). Reducing Fe³⁺ power assay indicated that DHQA exhibited higher reducing power than DHQ and ascorbic acid.

Characterization and Antioxidant Activity of Flash-Assisted Extracted Dihydroquercetin from Wood Sawdust of Larix gmelinii Using a Response Surface Methodology

We investigate a flash-assisted extraction of dihydroquercetin (DHQ) from wood sawdust of Larix gmelinii by response surface methodology. Box–Behnken design optimized the extraction conditions, and the highest DHQ yield (6.15 %) was obtained under optimal extraction conditions: FAE time (3 min), extraction time (3 h), solid-to-liquid (g/mL) ratio (1:15), and ethanol concentration (75 %). After purification, the DHQ purity was 96 % as determined by HPLC and was further characterized by FTIR. Purified DHQ’s antioxidant activities were confirmed in vitro by determining DPPH and ABTS radical scavenging activities and reducing Fe3+ power. In the DPPH and ABTS radical scavenging activity assays, DHQ displayed prominent antioxidant activities with low IC50 values (11.568 and 12.475 μg/mL, respectively). In reducing Fe3+ power assay, high DHQ absorbance values showed that DHQ had higher reducing power than butylated hydroxyl toluene and had nearly the same consistent power as ascorbic acid at the same doses.

Preparation, characterisation and antitumour activity of β-, γ- and HP-β-cyclodextrin inclusion complexes of oxaliplatin

Three water-soluble oxaliplatin complexes were prepared by inclusion complexation with β-cyclodextrin (β-CD), γ-CD and HP-β-CD. The structures of oxaliplatin/CDs were confirmed by NMR, FTIR, TGA, XRD as well as SEM analysis. The results show that the water solubility of oxaliplatin was increased in the complex with CDs in 1:1 stoichiometry inclusion modes, and the cyclohexane ring of oxaliplatin molecule was deeply inserted into the cavity of CDs. Moreover, the stoichiometry was established by a Job plot and the water stability constant (Kc) of oxaliplatin/CDs was calculated by phase solubility studies, all results show that the oxaliplatin/β-CD complex is more stable than free oxaliplatin, oxaliplatin/HP-β-CD and oxaliplatin/γ-CD. Meanwhile, the inclusion complexes displayed almost twice as high cytotoxicity compared to free oxaliplatin against HCT116 and MCF-7 cells. This satisfactory water solubility and higher cytotoxic activity of the oxaliplatin/CD complexes will potentially be useful for their application in anti-tumour therapy.

Investigation of β-cyclodextrin-norfloxacin inclusion complexes. Part 1. Preparation, physicochemical and microbiological characterization

INTRODUCTION

Drugs classified as class IV by the Biopharmaceutical Classification System present significant problems in relation to effective oral administration. In the case of antibiotics, the subsequently high doses required can enhance the emergence of microorganism resistance and lead to a low rate of patient treatment adherence.

OBJECTIVE

In an attempt to improve physicochemical properties and microbiological activity of norfloxacin, the aim of this study was to investigate different methods (coevaporation, kneading followed by freeze-drying or spray-drying) to obtain complexes of norfloxacin and different cyclodextrins.

METHODS

Guest-host interactions were investigated through a complete physical-chemical characterization and the dissolution profile and microbiological activity were determined.

RESULTS

The formation of a complex of norfloxacin and β-cyclodextrin (1:1), obtained by kneading followed by freeze drying, led to increased drug solubility, which could maximize the oral drug absorption.

CONCLUSION

Moreover, the microbiological activity was enhanced by around 23.3%, demonstrating that the complex formed could represent an efficient drug delivery system.

Analytical techniques for characterization of cyclodextrin complexes in the solid state: A review

Cyclodextrins are cyclic oligosaccharides able to form inclusion complexes with a variety of hydrophobic guest molecules, positively modifying their physicochemical properties. A thorough analytical characterization of cyclodextrin complexes is of fundamental importance to provide an adequate support in selection of the most suitable cyclodextrin for each guest molecule, and also in view of possible future patenting and marketing of drug-cyclodextrin formulations. The demonstration of the actual formation of a drug-cyclodextrin inclusion complex in solution does not guarantee its existence also in the solid state. Moreover, the technique used to prepare the solid complex can strongly influence the properties of the final product. Therefore, an appropriate characterization of the drug-cyclodextrin solid systems obtained has also a key role in driving in the choice of the most effective preparation method, able to maximize host-guest interactions. The analytical characterization of drug-cyclodextrin solid systems and the assessment of the actual inclusion complex formation is not a simple task and involves the combined use of several analytical techniques, whose results have to be evaluated together. The objective of the present review is to present a general prospect of the principal analytical techniques which can be employed for a suitable characterization of drug-cyclodextrin systems in the solid state, evidencing their respective potential advantages and limits. The applications of each examined technique are described and discussed by pertinent examples from literature.

A 5,7-dimethoxyflavone/hydroxypropyl-β-cyclodextrin inclusion complex with anti-butyrylcholinesterase activity

This study aimed to improve the water solubility of 5,7-dimethoxyflavone (5,7-DMF) isolated from Kaempferia parviflora by complexation with 2-hydroxypropyl-β-cyclodextrin (HPβ-CD). The phase solubility profile of 5,7-DMF in the presence of HPβ-CD was classified as AL-type and indicated a 1:1 mole ratio. Differential scanning colorimetry, X-ray diffraction, NMR and SEM analyses supported the formation of a 5,7-DMF/HPβ-CD inclusion complex involving the A ring of 5,7-DMF inside the HPβ-CD cavity. This is the first example of CD inclusion with the A ring of non-hydroxyl flavones. The stability and binding constants of the complexes were determined using the phase solubility and UV-vis absorption spectroscopy, respectively. The water solubility of 5,7-DMF was increased 361.8-fold by complexation with HPβ-CD and overcame the precipitation problem observed in aqueous buffers, such as during in vitro anti-butyrylcholinesterase activity assays. The 1:1 mole ratio of the 5,7-DMF/HPβ-CD complex showed a 2.7-fold higher butyrylcholinesterase inhibitory activity (in terms of the IC50 value) compared to the non-complexed compound.

Enhanced stability of a naringenin/2,6-dimethyl β-cyclodextrin inclusion complex: molecular dynamics and free energy calculations based on MM- and QM-PBSA/GBSA

The structure, dynamic behavior and binding affinity of the inclusion complexes between naringenin and the two cyclodextrins (CDs), β-CD and its 2,6-dimethyl derivative (DM-β-CD), were theoretically studied by multiple molecular dynamics simulations and free energy calculations. Naringenin most likely prefers to bind with CDs through the phenyl ring. Although a lower hydrogen bond formation of naringenin with the 3-hydroxyl group of DM-β-CD (relative to β-CD) was observed, the higher cavity could encapsulate almost the whole naringenin molecule. In contrast for the naringenin/β-CD complex, the phenyl ring feasibly passed through the primary rim resulting in the chromone ring binding inside instead. MM-PBSA/GBSA and QM-PBSA/GBSA binding free energies strongly suggested a greater stability of the naringenin/DM-β-CD inclusion complex. Van der Waals force played an important role as the key guest-host interaction for the complexation between naringenin and each cyclodextrin.

Effect of pH on the complexation of kaempferol-4'-glucoside with three β-cyclodextrin derivatives: isothermal titration calorimetry and spectroscopy study

The utilization of kaempferol and its glycosides in food and pharmaceutical industries could be improved by the formation of inclusion complexes with cyclodextrins at different pH. This study explores the complexation of kaempferol-4'-glucoside with sulfobutyl ether-β-cyclodextrin (SBE-β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and methylated-β-cyclodextrin (M-β-CD) in phosphate buffer solutions of different pH using isothermal titration calorimetry, UV-vis absorption and proton nuclear magnetic resonance spectroscopy at 298.2 K. Experimental results showed that kaempferol-4'-glucoside binds with the three β- cyclodextrins in the same 1:1 stoichiometry. The rank order of stability constants is SBE-β-CD > HP-β-CD > M-β-CD at the same pH level and pH 6.0 > pH 7.4 > pH 9.0 for the same cyclodextrin. The binding of kaempferol-4'-glucoside with the three β-cyclodextrin derivatives is synergistically driven by enthalpy and entropy at pH 6.0 and enthalpy-driven at pH 7.4 and 9.0. The possible inclusion mode was that in the cavity of β-CD is included the planar benzopyranic-4-one part of the kaempferol-4'-glucoside.

Cyclodextrins as encapsulation agents for plant bioactive compounds

Plants possess a wide range of molecules capable of improve healing: fibre, vitamins, phytosterols, and further sulphur-containing compounds, carotenoids, organic acid anions and polyphenolics. However, they require an adequate level of protection from the environmental conditions to prevent losing their structural integrity and bioactivity. Cyclodextrins are cyclic oligosaccharides arising from the degradation of starch, which can be a viable option as encapsulation technique. Cyclodextrins are inexpensive, friendly to humans, and also capable of improving the biological, chemical and physical properties of bioactive molecules. Therefore, the aim of this review is to highlight the use of cyclodextrins as encapsulating agents for bioactive plant molecules in the pharmaceutical field.