Exploring oral drug delivery: In vitro release and mathematical modeling of hydrophobic drug (Na-L-thyroxine) and its cyclodextrin inclusion complex in chitosan microparticles

Na-l-Thyroxine (Na-l-Thy) is a frequently prescribed synthetic hormone for hypothyroidism treatment. Despite its efficacy, its hydrophobic nature poses a challenge for achieving optimal bioavailability. To address this, researchers explored various delivery methods, including micro-formulations and nano-formulations, for precise and prolonged release of hydrophobic and hydrophilic drugs. In this study, we developed micro-formulations with cyclodextrin and chitosan. Docking studies identified γ-cyclodextrin as the preferred option for forming a stable complex with Na-l-Thyroxine compared to α, and β-cyclodextrins. Two micro-formulations were prepared compared: Na-l-Thyroxine loaded on chitosan (CS + Na-l-Thy) and Na-l-Thyroxine and γ-cyclodextrin inclusion complex (IC) loaded on chitosan (CS + IC). CS + IC exhibited superior encapsulation efficiency (91.25 %) and loading capacity (18.62 %) compared to CS + Na-l-Thy (encapsulation efficiency: 70.24 %, loading capacity: 21.18 %). Characterization using FTIR, SEM, and TGA validated successful encapsulation of Na-l-Thy in spherical microparticles with high thermal stability. In-vitro release studies at pH 1.2 and 7.4 showed that the CS + IC microparticles displayed gradual, consistent drug release compared to CS + Na-l-Thy -Thy. Both formulations showed faster release at pH 1.2 than at pH 7.4. Reaction kinetics analysis of release studies of CS + Na-l-Thy and CS + IC were best described by Higuchi kinetic model and Korsemeyer-Peppas kinetic model respectively. This study suggests that the CS + IC microparticles are an effective and stable delivery system for sustained release of hydrophobic Na-l-Thy.

Carboxymethyl potato starch hydrogels encapsulated cyclodextrin metal-organic frameworks for enantioselective loading of S-naproxen and its programmed release

A natural polysaccharide-based vehicle is facilely prepared for enantioselective loading of S-naproxen (S-NPX) and its programmed release. Cyclodextrin metal-organic frameworks (CD-MOF) are synthesized through the coordination of K+ with γ-cyclodextrin (γ-CD). Compared with R-NPX, the CD-MOF preferably combines with S-NPX, which can be confirmed by the thermodynamic calculations. The S-NPX loaded CD-MOF (CD-MOF-S-NPX) is grafted with disulfide bond (-S-S-) to improve its hydrophobicity, and the loaded S-NPX is further encapsulated in the chiral cavity of γ-CD by carboxymethyl potato starch (CPS) hydrogels. The intermolecular hydrogen bonding of the CPS hydrogels is prone to be destroyed in mildly basic media (∼pH 8.0), resulting in the swelling of the hydrogels; the -S-S- linkage in the vehicle can be cleaved in the presence of glutathione (GSH), leading to the collapse of the CD-MOF. Therefore, the programmed release of S-NPX can be achieved. Also in this work, the release kinetics is investigated, and the results indicate that the release of S-NPX is controlled by the Higuchi model.

Enhanced stability of anthocyanins by cyclodextrin-metal organic frameworks: Encapsulation mechanism and application as protecting agent for grape preservation

Anthocyanins are promising naturally occurring food preservatives for enhancing the quality of food products due to their excellent antioxidant properties. However, their low stability hinders their food packaging application. Here, we propose a facile strategy to achieve the improved stability of anthocyanins encapsulated in γ-cyclodextrin metal-organic frameworks (CD-MOFs) with an in-depth exploration of their structure-property relationships. The adsorbed anthocyanins in CD-MOFs are stabilized by multiple cooperative non-covalent interactions including hydrogen bonding and van der Waals (vdW) interactions as demonstrated by density functional theory (DFT) calculations and spectroscopy analysis. Particularly, by ion-exchange of acetate ions into the pores of CD-MOFs, the resulting CD-MOFs (CD-MOF_OAc) shows a higher anthocyanins adsorption rate with a maximum loading capacity of 83.7 % at 1 min. Besides, CD-MOF_OAc possesses the more effective protecting effect on anthocyanins with at least two-fold enhancement of stability in comparison of free anthocyanins under heating and light irradiation. The anthocyanins encapsulated CD-MOFs films for fruit freshness was validated by the Kyoho experiment. This novel encapsulation system provides a new possibility for the potential use of CD-MOFs as the encapsulating material for anthocyanins in fruit preservation.

Increased bioavailability of diosmetin-7-glucoside-γ-cyclodextrin inclusion complex compared with diosmin in Sprague-Dawley rats

Diosmin (DSN) is found mainly in citrus fruits, and has potent antioxidant effects. This study aimed to evaluate pharmacokinetics of diosmetin-7-glucoside-γ-cyclodextrin (DIOSG-CD) inclusion complex. The area under the curve values from AUC0-24 of DIOSG-CD, prepared by reacting DSN and naringinase with γ-CD, were approximately 800-fold higher than those of DSN following their administration in Sprague-Dawley rats.

Preformulation studies of dovitinib free base: Solubility, lipophilicity and stability

Dovitinib has been investigated as an anti-tumor drug due to its ability to inhibit multiple receptor tyrosine kinases. Dovitinib free base has a poor water solubility leading to poor absorption. Salts and lipid-based formulations have been used to improve drug availability. Here, we investigated the physiochemical properties of the dovitinib free base in the presence of some pharmaceutical excipients. We sought to study the effect of acidic counterions on the aqueous solubility and lipophilicity of dovitinib and how pH, buffer species, and cyclodextrin (CD) influenced dovitinib stability. pH-solubility studies were performed by titration against five different acids. Aqueous solubility of dovitinib salt depended on the counterion. Lactic acid greatly increased the aqueous solubility of dovitinib. The counterion effect on the solubility was also investigated in the aqueous complexing media. Unexpected synergistic solubilization was found with γ-CD/phosphoric acid and γ-CD/maleic acid. The counterion did not affect the lipophilicity of dovitinib at physiological pH. Accelerated degradation of dovitinib was carried out at high temperature. Stability was studied across a range of pH values, buffer species and in the presence of two CDs. Dovitinib was most stable at pH 4 in the phosphate buffer species. γ-CD stabilized the drug at relatively low pH.

Gamma cyclodextrin glycosyltransferase from evansella caseinilytica: production, characterization and product specificity

Alkalohalophilic Evansella caseinilytica produced an extracellular cyclodextrin glycosyltransferase (CGTase) with cyclization activity of 43.5 ± 4.4 U/L in M1 medium containing 1% starch and 6% NaCl in nutrient broth at 37 ºC, pH 9.0, after 48 h. This is the first report of CGTase from this bacterium. 0.1% starch was found to induce CGTase, and further optimization using one variable at a time approach followed by statistical optimization led to 5.5-fold enhancement resulting in 240.5 ± 5.46 U/L. Six parameters were identified as positive signals using Plackett-Burman (PB). Of these, yeast extract, MgSO4 and tryptone were taken further for Response Surface Methodology (RSM) by disposing beef extract and fixing starch and soya peptone. The optimized M4 medium consisted of tryptone (0.1%, w/v), yeast extract (0.25%, w/v), MgSO4 (8 mM, w/v), potato starch (0.1%, w/v) and soya peptone (0.2%, w/v). CGTase was further purified with 6.44-fold purification and 19.32% yield employing starch affinity. It was found to be monomeric, corresponding to a size of 68 kDa as estimated by SDS-PAGE and was further confirmed to be 65 kDa by size exclusion chromatography. γ-Cyclodextrins were produced as the major product with a conversion of 5% soluble starch into 20.38% γ-cyclodextrins after 24 h reaction, as determined by HPLC. Peptide fingerprint after LC-MS analysis matched with IPT/TIG domain-containing protein within the genome of E. caseinilytica. Further blastp analysis revealed the closest homology with γ-CGTase from an alkalophilic E. clarkii, thereby confirming CGTase from E. caseinilytica as γ-CGTase.

Nanopore sensing of γ-cyclodextrin induced host-guest interaction to reverse the binding of perfluorooctanoic acid to human serum albumin

Perfluorooctanoic acid (PFOA) has been one of the most common perfluorochemicals, which are globally pervasive contaminants that are persistent, bioaccumulative, toxic, and have adverse impacts on human health. The highest concentration of PFOA occurs in the blood, where it strongly binds to human serum albumins (HSA). Thus, a method to reverse the HSA-PFOA binding is critical to help facilitate the faster elimination of PFOA from the body to minimize its toxicological effects. Inspired by the remediation effect of cyclodextrin (CD) to PFOA through host-guest interactions, herein, by elucidating inter-molecular interactions using a nanopore sensor, we demonstrated in vitro reversal of the binding of PFOA to HSA using γ-cyclodextrin (γ-CD). The competition behavior for the complexation of PFOA between HSA and γ-CD was discussed in combination with in situ nanopore current recording and nuclear magnetic resonance (NMR) characterization. The present work not only demonstrates the potential therapeutic application of γ-CD for PFOA removal from human blood, but also provides an emerging method for investigating interactions between organic compounds and proteins.

Enrofloxacin/florfenicol loaded cyclodextrin metal-organic-framework for drug delivery and controlled release

We presented an antibiotic-loaded γ-cyclodextrin metal-organic framework that delivered antibiotics suitable for the treatment of bacterial infections. The γ-cyclodextrin metal-organic framework was developed using γ-cyclodextrin and potassium ion via the ultrasonic method. The antibiotic (florfenicol and enrofloxacin) was primarily encapsulated into the pore structures of γ-CD-MOF, which allowed the sustained release of antibiotics over an extended period of time in vitro and in vivo. Notably, antibiotics-loaded γ-CD-MOF showed much superior activity against bacteria than free antibiotics (lower MIC value) and displayed better long-lasting activity (longer antibacterial time). The antibiotics-loaded γ-CD-MOF showed nontoxic and perfect biocompatibility to mammalian cells and tissues both in vitro and in vivo. These materials thus represent a novel drug-delivery device suitable for antibiotic therapy. This research is of great significance for reducing the generation of bacterial resistance and providing new ideas for the application of γ-CD-MOF.

Novel γ-cyclodextrin-metal-organic frameworks for encapsulation of curcumin with improved loading capacity, physicochemical stability and controlled release properties

A safe and biodegradable γ-cyclodextrin-metal-organic-frameworks (γ-CD-MOFs) was successfully synthesized by using an improved hydrothermal method. In this study, curcumin (Cur) was chosen for testing the encapsulation stability and release performance of γ-CD-MOFs. Results of the crystal structure measurement indicated that the encapsulated curcumin within γ-CD-MOFs via van der Waals forces, hydrophobic interactions and hydrogen bonding was failed to disturb the inherent microtopography and crystallinity of γ-CD-MOFs. Compared to individual γ-CD, the γ-CD-MOFs exhibited improved loading capacity, physicochemical stability as well as controlled-release property in simulated digestion, and hence can be regarded as effective carriers for curcumin. Curcumin-loaded γ-CD-MOFs with a Cur : γ-CD-MOFs mass ratio of 2:3 (Cur-CD-MOFs/3), which showed the highest encapsulation efficiency (67.31 ± 2.25%), improved physicochemical stability and controlled-release performance, was selected for further research and industrialization. Our results demonstrate that γ-CD-MOFs can be regarded as a promising novel carrier for the delivery of curcumin or other hydrophobic nutraceuticals.

Engineering CGTase to improve synthesis of alkyl glycosides

Alkyl glycoside surfactants with elongated carbohydrate chains are useful in different applications due to their improved biocompatibility. Cyclodextrin glucanotransferases can catalyze the elongation process through the coupling reaction. However, due to the presence of a hydrophobic tail, the interaction between an alkyl glycoside acceptor and the active site residues is weaker than the interaction with maltooligosaccharides at the corresponding site. Here we report the mutations of F197, G263 and E266 near the acceptor subsites in the CGTase CspCGT13 from Carboxydocella sp. The results showed that substitutions of both F197 and G263 were important for the binding of acceptor substrate dodecyl maltoside during coupling reaction. The double mutant F197Y/G263A showed enhanced coupling activity and displayed a 2-fold increase of the primary coupling product using γ-cyclodextrin as donor when compared to wildtype CspCGT13. Disproportionation activity was also reduced, which was also the case for another double mutant (F197Y/E266A) that however not showed the corresponding increase in coupling. A triple mutant F197Y/G263A/E266A maintained the increase in primary coupling product (1.8-fold increase) using dodecyl maltoside as acceptor, but disproportionation was approximately at the same level as in the double mutants. In addition, hydrolysis of starch was slightly increased by the F197Y and G263A substitutions, indicating that interactions at both positions influenced the selectivity between glycosyl and alkyl moieties.

Effect of porcine pancreatic α-amylase on dexamethasone release from aqueous solution containing natural γ-cyclodextrin

Dexamethasone release from natural γ-cyclodextrin (γCD) complexes was investigated in presence of porcine pancreatic α-amylase (PPA). The phase-solubility of dexamethasone in aqueous γCD solutions was determined, PPA degradation of γCD was investigated, and permeation studies were performed in simulated tear fluid. The phase-solubility profile was of B_s type and the stability constant (K_1:1) of the dexamethasone/γCD complex determined from the initial linear section of the profile was relatively high or 12887 M^-1. The high K_1:1 value indicates that dexamethasone has high affinity for γCD under the test condition. From the PPA catalyzed γCD degradation studies the Michaelis-Menten constant (K_m) and V_max were determined to be 3.24 mM and 9.79 × 10^-3 mM/min, respectively. The permeation studies performed at low γCD concentrations, showed that dexamethasone is released from the complex solutions at faster rate when PPA was present than when no PPA was present.

Honeycomb-like pH-responsive γ-cyclodextrin electrospun particles for highly efficient tumor therapy

We report here the tumor-implantable microparticles with a honeycomb-like porous structure. These microparticles were prepared by electrospinning using γ-cyclodextrin (γ-CD) conjugated with 3-(diethylamino)propylamine (DEAP, as a pH-responsive moiety), named γ-CD-DEAP. The resulting microparticles had pore channels (constructed using γ-CD-DEAP) extending into the deep compartment of the microparticles and allowing efficient paclitaxel (PTX, as a chemotherapeutic model drug) entrapment by a simple hole-filling encapsulation process. Importantly, the hydrophobic DEAP (at pH 7.4) in the γ-CD-DEAP microparticles changed to hydrophilic DEAP (at pH 6.8) because of its acidic pH-induced protonation. This phenomenon resulted in an acidic pH-activated particle destruction by a charge-charge repulsion between the protonated DEAP moieties and allowed a pH-triggered release of the encapsulated PTX from the collapsed microparticles. Consequently, γ-CD-DEAP microparticles implanted at the tumor site caused a significant enhancement of the in vitro/in vivo tumor cell ablation, suggesting their significant potential as a chemotherapeutic implant for tumor therapy.

Application of cyclodextrinase in non-complexant production of γ-cyclodextrin

The production of γ-cyclodextrin usually includes the utilization of organic complexants. However, the non-complexant production of γ-cyclodextrin is always being explored due to the defects of organic complexants. However, in non-complexant production, the separation of γ-cyclodextrin from α- and β-cyclodextrin is still a challenge. Here, the selective hydrolysis ability of a cyclodextrinase designated PpCD (cyclodextrinase from Palaeococcus pacificus) on α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin was proved. The k_cat /K_m values of PpCD for α-cyclodextrin and β-cyclodextrin were roughly 12-fold and 5-fold higher than that of γ-cyclodextrin. It was proved that PpCD had selective hydrolysis ability and its γ-cyclodextrin purification performance was apparent on various simulated cyclodextrin mixtures with reported proportions derived from different CGTases. Besides, the hydrolysis temperature was optimized and it could be seen that 85°C was appropriate for the production of γ-cyclodextrin. In addition, the production of γ-cyclodextrin was achieved by using PpCD in the γ-CGTase reaction products.

γ-Cyclodextrin

γ-Cyclodextrin (γCD) is a cyclic oligosaccharide formed by bacterial digestion of starch and used as solubilizing agent and stabilizer in a variety of pharmaceutical and food products. γCD is a large (molecular weight 1297Da) hydrophilic molecule that does not readily permeate biological membranes and is rapidly digested by bacteria in the gastrointestinal tract. In humans γCD is metabolized by α-amylase that is found in, for example, saliva, bile fluid and tears. Thus, bioavailability of γCD is negligible. Also, γCD is readily excreted unchanged in the urine after parenteral administration. Like other cyclodextrins, γCD can form water-soluble inclusion complexes with many poorly-soluble compounds. In comparison with the natural αCD and βCD, γCD has the largest hydrophobic cavity, highest water solubility and the most favorable toxicological profile. The focus of this review is production, physiochemical properties, pharmacokinetics, toxicity and applications of γCD and its derivatives. Also, the aggregation behavior of γCD in aqueous media is discussed.

Encapsulation of curcumin in cyclodextrin-metal organic frameworks: Dissociation of loaded CD-MOFs enhances stability of curcumin

Curcumin has been successfully encapsulated in cyclodextrin-metal organic frameworks (CD-MOFs) without altering their crystallinity. The interaction between curcumin and CD-MOFs is strong through hydrogen bond type interaction between the OH group of cyclodextrin of CD-MOFs and the phenolic hydroxyl group of the curcumin. Interestingly, dissolving the curcumin loaded CD-MOFs crystals in water results in formation of a unique complex between curcumin, γCD and potassium cations. In fact, the initial interaction between curcumin and CD-MOF is crucial for the formation of the latter. This new complex formed in alkaline media at pH 11.5 has maximum absorbance at 520nm and emittance at 600nm. Most importantly, the stability of curcumin in this complex was enhanced by at least 3 orders of magnitude compared to free curcumin and curcumin:γ-CD at pH 11.5. These results suggest a promising benign system of CD-MOFs, which can be used to store and stabilize curcumin for food applications.

Enantioseparation of dansyl amino acids and dipeptides by chiral ligand exchange capillary electrophoresis based on Zn(II)-L-hydroxyproline complexes coordinating with γ-cyclodextrins

A chiral ligand exchange capillary electrophoresis (CLE-CE) method using Zn(II) as the central ion and L-4-hydroxyproline as the chiral ligand coordinating with γ-cyclodextrin (γ-CD) was developed for the enantioseparation of amino acids (AAs) and dipeptides. The effects of various separation parameters, including the pH of the running buffer, the ratio of Zn(II) to L-4-hydroxyproline, the concentration of complexes and cyclodextrins (CDs) were systematically investigated. After optimization, it has been found that eight pairs of labeled AAs and six pairs of labeled dipeptides could be baseline-separated with a running electrolyte of 100.0mM boric acid, 5.0mM ammonium acetate, 3.0mM Zn(II), 6.0mM L-hydroxyproline and 4.0mM γ-CD at pH 8.2. The quantitation of AAs and dipeptides was conducted and good linearity (r(2)≥0.997) and favorable repeatability (RSD≤3.6%) were obtained. Furthermore, the proposed method was applied in determining the enantiomeric purity of AAs and dipeptides. Meanwhile, the possible enantiorecognition mechanism based on the synergistic effect of chiral metal complexes and γ-CD was explored and discussed briefly.

Ligation-rolling circle amplification combined with γ-cyclodextrin mediated stemless molecular beacon for sensitive and specific genotyping of single-nucleotide polymorphism

A novel approach for highly sensitive and selective genotyping of single-nucleotide polymorphism (SNP) has been developed based on ligation-rolling circle amplification (L-RCA) and stemless molecular beacon. In this approach, two tailored DNA probes were involved. The stemless molecular beacon, formed through the inclusion interactions of γ-cyclodextrin (γ-CD) and bis-pyrene labeled DNA fragment, was served as signal probe. In the absence of mutant target, the two pyrene molecules were bound in the γ-CD cavity to form an excimer and showed a strong fluorescence at 475 nm. It was here named γ-CD-P-MB. The padlock DNA probe was designed as recognition probe. Upon the recognition of a point mutation DNA targets, the padlock probe was ligated to generate a circular template. An RCA amplification was then initiated using the circular template in the presence of Phi29 polymerase and dNTPs. The L-RCA products, containing repetitive sequence units, subsequently hybridized with the γ-CD-P-MB. This made pyrene molecules away from γ-CD cavity and caused a decrease of excimer fluorescence. As a proof-of-concept, SNP typing of β-thalassemia gene at position -28 was investigated using this approach. The detection limit of mutated target was determined to be 40 fM. In addition, DNA ligase offered high fidelity in distinguishing the mismatched bases at the ligation site, resulting in positive detection of mutant target even when the ratio of the wildtype to the mutant is 999:1. Given these attractive characteristics, the developed approach might provide a great genotyping platform for pathogenic diagnosis and genetic analysis.

Molecule-binding dependent assembly of split aptamer and γ-cyclodextrin: a sensitive excimer signaling approach for aptamer biosensors

A highly sensitive and selective fluorescence aptamer biosensors for the determination of adenosine triphosphate (ATP) was developed. Binding of a target with splitting aptamers labeled with pyrene molecules form stable pyrene dimer in the γ-cyclodextrin (γ-CD) cavity, yielding a strong excimer emission. We have found that inclusion of pyrene dimer in γ-cyclodextrin cavity not only exhibits additive increases in quantum yield and emission lifetime of the excimer, but also facilitates target-induced fusion of the splitting aptamers to form the aptamer/target complex. As proof-of-principle, the approach was applied to fluorescence detection of adenosine triphosphate. With an anti-ATP aptamer, the approach exhibits excimer fluorescence response toward ATP with a maximum signal-to-background ratio of 32.1 and remarkably low detection limit of 80 nM ATP in buffer solution. Moreover, due to the additive fluorescence lifetime of excimer induced by γ-cyclodextrin, time-resolved measurements could be conveniently used to detect as low as 0.5 μM ATP in blood serum quantitatively.