Cyclodextrins as hosts for poorly water-soluble compounds in enzyme catalysis

Advances and Classification of Cyclodextrin-Based Polymers for Food-Related Issues

Cyclodextrins (CDs) are a good alternative to reduce or enhance different biomolecule characteristics and have demonstrated great results in food science. However, CDs present intrinsic limitations that can be solved by derivative synthesis. This review represents a survey of the state of the art of CD-based materials and their uses in food science. A deep review of the structure is carried out and different groups for ordination are suggested. After that, different applications such as cholesterol complexation or its use as sensors are reviewed. The derivatives show novel and promising activities for the industry. A critical perspective of the materials suggests that they might not present toxicity, although more studies are required. These points suggest that the research in this field will be increased in the following years.

A physicochemical, thermodynamical, structural and computational evaluation of kynurenic acid/cyclodextrin complexes

In this work, the interaction between Kynurenic acid (KYNA) and several natural and modified cyclodextrins (CDs) is carried out. Among all the CD tested, HPβ-CD showed the strongest complexation constant (K_F), with a value of 270.94 ± 29.80 M^-1. Between natural (α- and β-) CDs, the complex of KYNA with β-CD was the most efficient. The inclusion complex of KYNA with CDs showed a strong influence of pH and temperature. The K_F value decreased at high pH values, when the pK_a was passed. Moreover, an increase of the temperature caused a decrease in the K_F values. The thermodynamic parameters of the complexation (ΔH°, ΔS° and ΔG°) were studied with negative entropy, enthalpy and spontaneity of the process at 25 °C. Moreover, the inclusion complex was also characterized using FTIR and TGA. Finally, molecular docking calculations provided different interactions and their influence in the complexation constant.

Detection of anabolic steroids via cyclodextrin-promoted fluorescence modulation

Reported herein is the detection of anabolic steroids through the use of cyclodextrin-promoted interactions between the analyte of interest and a high quantum yield fluorophore, which lead to measurable, analyte-specific changes in the fluorophore emission signal. By using a variety of β-cyclodextrin derivatives (unmodified β-cyclodextrin, methyl-β-cyclodextrin, and 2-hydroxypropyl-β-cyclodextrin) in combination with high quantum yield fluorophore rhodamine 6G, we detected five anabolic steroid analytes with 100% differentiation between structurally similar analytes and micromolar level limits of detection. Overall, these results show significant potential in the development of practical, fluorescence-based steroid detection devices.

A Way to Increase the Bioaccesibility and Photostability of Roflumilast, a COPD Treatment, by Cyclodextrin Monomers

Roflumilast is an orally available inhibitor of phosphodiesterase (PDE) type 4, which is widely used in chronic obstructive pulmonary diseases. However, it has low solubility and adverse effects include diarrhea and nausea. Since its solubilization may improve treatment and, dismissing any adverse effects, its interaction with cyclodextrins (CDs) was studied. The Higuchi-Connors method was used to determine the complexation constant with different CDs, pH values and temperatures. Molecular docking was used to predict interaction between the complexes. An in vitro digestion experiment was carried out to test roflumilast protection. Finally, the photostability of the complex was evaluated. The complex formed with β-CD had the highest K₁₁ value (646 ± 34 M⁻¹), although this value decreased with increasing temperature. Similarly, K₁₁ decreased as the pH increased. In vitro digestion showed that CDs protect the drug during digestion and even improve its bioaccessibility. Finally, CDs reduced the drug’s extreme photosensitivity, originating a fluorescence signal, which is described for first time. The kinetic parameters of the reaction were obtained. This study not only completes the complexation study of roflumilast-CD, but also points to the need to protect roflumilast from light, suggesting that tablets containing the drug might be reformulated.

The inclusion complex of oxyresveratrol in modified cyclodextrins: A thermodynamic, structural, physicochemical, fluorescent and computational study

The interaction between oxyresveratrol (a type of stilbene with high biological activity) and modified cyclodextrins (CDs) was studied. Using HPLC-RP, was seen to form a 1:1 complex with all the CDs tested. The best CD in this respect was MβCD (K_F=606.65±30.18M^-1), the complexation showing a strong dependence on pH and temperature: The complexation constant (K_F) decreased as the pH and temperature increased. The thermodynamic parameters studied (ΔH°, ΔS° and ΔG°) showed negative entropy, enthalpy and Gibbs free energy change at 25°C. In addition, fluorescence signal of oxyresveratrol increased when MβCD was added. The oxyresveratrol emission and excitation spectra were obtained for first time. A ¹H NMR was carried out to study the structure of the complex and, DSC studied demonstrated the complexation. A computational study by molecular docking was made to complement the structural study.

Encapsulation of piceatannol, a naturally occurring hydroxylated analogue of resveratrol, by natural and modified cyclodextrins

In this work, an in-depth study of the interaction between piceatannol (a type of stilbene with high biological activity) and different natural and modified cyclodextrins (CDs) is made, using steady state fluorescence. This bioactive molecule forms a 1 : 1 complex with all the natural (α-CD, β-CD and γ-CD) and modified (HP-β-CD, HE-β-CD and M-β-CD) CDs tested. Among natural CDs, the interaction of piceatannol with β-CD was the most efficient. However, the modified CDs showed higher encapsulation constants (KF) than β-CD, except M-β-CD; the highest KF being found for HP-β-CD (14 048 ± 702 M(-1)). The encapsulation of piceatannol in the internal cavity of CDs showed a strong dependence on pH and temperature. The interaction between HP-β-CD and piceatannol was less effective in the pH region where the stilbene begins to suffer the deprotonation of its hydroxyl group. Moreover, the values of KF decreased as the system temperature increased. To obtain information on the mechanism involved in the piceatannol affinity for CD, the thermodynamic parameters of the complexation (ΔH°, ΔS° and ΔG°) were studied, the results showed a negative entropy (-3.7 ± 0.2 J mol(-1) K(-1)), enthalpy (-24.6 ± 1.2 kJ mol(-1)) and Gibbs free energy change at 25 °C (-23.5 ± 1.2 J mol(-1)). Finally, molecular docking calculations provided further insights into how the different interactions influence the complexation constant. A high degree of correlation was observed between the computed scores and experimental values.

Diadenosine triphosphate is a novel factor which in combination with cyclodextrins synergistically enhances the biosynthesis of trans-resveratrol in Vitis vinifera cv. Monastrell suspension cultured cells

Dinucleoside polyphosphates are considered as signal molecules that may evoke response of plant cells to stress. Other compounds whose biological effects have been recognized are cyclodextrins. They are cyclic oligosaccharides that chemically resemble the alkyl-derived pectic oligosaccharides naturally released from the cell walls during fungal attack, and they act as true elicitors, since, when added to plant cell culture, they induce the expression of genes involved in some secondary metabolism pathways. Previously, we demonstrated that some dinucleoside polyphosphates triggered the biosynthesis of enzymes involved in the phenylpropanoid pathway in Arabidopsis thaliana. In Vitis vinifera suspension cultured cells, cyclodextrins were shown to enhance the accumulation of trans-resveratrol, one of the basic units of the stilbenes derived from the phenylpropanoid pathway. Here, we show that diadenosine triphosphate, applied alone or in combination with cyclodextrins to the grapevine suspension-cultured cells, increased the transcript level of genes encoding key phenylpropanoid-pathway enzymes as well as the trans-resveratrol production inside cells and its secretion into the extracellular medium. In the latter case, these two compounds acted synergistically. However, the accumulation of trans-resveratrol and its glucoside trans-piceid inside cells were stimulated much better by diadenosine triphosphate than by cyclodextrins.

Physicochemical study of the complexation of pterostilbene by natural and modified cyclodextrins

In this paper, the interaction between pterostilbene and cyclodextrins (CDs) is described for the first time using steady-state fluorescence. It was seen that pterostilbene forms a 1:1 complex with all of the natural (alpha-, beta-, and gamma-CDs) and modified (HP-beta-CD, methyl-beta-CD, and ethyl-beta-CD) CDs tested. Among natural CDs, the interaction of pterostilbene with beta-CD was the most efficient. However, all of the modified CDs showed higher complexation constants (K(F)) than beta-CD. The highest K(F) was found for HP-beta-CD (17520 +/- 981 M(-1)), in which its value showed a strong dependence upon pH in the region where the pterostilbene begins the deprotonation of its hydroxyl group. Moreover, the values of K(F) decreased as the system temperature increased. To obtain information on the mechanism of pterostilbene affinity for CD, the thermodynamic parameters of the complexation (DeltaH degrees , DeltaS degrees , and DeltaG degrees ) were studied. Finally, a comparison of the K(F) values obtained for three types of stilbenes revealed that both the stoichiometry and the K(F) values of the complex are dependent upon the structure of the guest molecule. While the trans-resveratrol-HP-beta-CD and pterostilbene-HP-beta-CD complexes showed a 1:1 stoichiometry with a higher K(F) value for the trans-resveratrol-HP-beta-CD complexes, trans-stilbene showed a 1:2 stoichiometry.

Effect of protonation and aggregation state of (E)-resveratrol on its hydroperoxidation by lipoxygenase

The protonation and aggregation states of (E)-resveratrol were used as tools to investigate the kinetic properties of lipoxygenase (LOX). It was found that the deprotonation of the 4'-hydroxyl group at pH values higher than the pK(a1) of (E)-resveratrol produced an increase in the LOX activity, with an optimum pH of 8.5. Moreover, the results show how LOX activity is strongly affected by the aggregation state of (E)-resveratrol. When the enzyme uses monomers of (E)-resveratrol as substrate, LOX shows a Michaelian behavior and the K(m) value can be determined (44.39 microM). However, when (E)-resveratrol concentration is increased to values higher than the critical concentration determined by fluorescence methods (35 microM at pH 8.5), LOX shows strong inhibition. These results can be interpreted as a previously unreported aggregate-induced enzyme inhibition, which can be modified by the use of different modulators of the aggregation state of (E)-resveratrol, such as cyclodextrins or ethanol. Finally, when the reaction was kinetically characterized in the optimum conditions of both aggregation and protonation state, a typical induction period was observed, along with a dependence of the hydroperoxidation rate with the hydrogen peroxide concentration.

Candida rugosa Lipase-Catalyzed Intramolecular O- to N-Transacylation of Butyryl Propranolol in the Presence of Cyclodextrins

In the present paper, a novel enzymatic reaction between (R,S)-O-butyryl propranolol (O-BP) and lipase from Candida rugosa in the presence of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) is described. Under the used condition, lipase catalyzed the intramolecular transacylation of O-BP into N-butyryl propranolol (N-BP). Propranolol, the product of the expected hydrolysis reaction, was not detected in the reaction medium. A chiral analysis of the reaction product indicated that lipase showed a preference for (R)-O-butyryl propranolol since it first transformed the (R)-enantiomer and then the corresponding (S)-enantiomer. The influence of different reaction conditions on the initial rate is also studied.

Enhanced production of hydroperoxides by immobilized lipoxygenase in the presence of cyclodextrins

The advantages of the presence of cyclodextrins in a reaction catalyzed by immobilized lipoxygenase at neutral pH are reported for the first time. The steady-state rate in the presence of beta-cyclodextrins was seven times higher than in control experiments using the same concentration of linoleic acid; furthermore the percentage of substrate conversion (and product accumulation) obtained in the presence of beta-cyclodextrins was higher than in the control assays. The optimum concentration of free linoleic acid coincided with the critical micellar concentration for linoleic acid at neutral pH. The operational stability of the immobilized enzyme increased in the presence of beta-cyclodextins, while an increase in the percentage of 13-HPOD was also observed.

Lipase-catalyzed preparation of S-propranolol in presence of hydroxypropyl β-cyclodextrins

A simple method for the preparation of S-propranolol catalyzed by a Rhizopus niveus lipase in an aqueous medium is described. Hydroxypropyl-beta-cyclodextrin was used for the first time to increase the solubility of (R,S)-O-butyryl propranolol thus permitting the reaction to be carried out in water. The formation of an inclusion complex between (R,S)-O-butyryl propranolol and hydroxypropyl-beta-cyclodextrin was studied and a stoichiometry of 1:1 was determined. The influences of the hydroxypropyl-beta-cyclodextrin concentration, pH and percentage of ethanol on the enzymatic activity were also investigated. Under the conditions presented in this paper, values of ee(s) of 90% and E=48 were obtained.