Stilbenes: Characterization, bioactivity, encapsulation and structural modifications. A review of their current limitations and promising approaches.

Stilbenes are phenolic compounds naturally synthesized as secondary metabolites by the shikimate pathway in plants. Research on them has increased in recent years due to their therapeutic potential as antioxidant, antimicrobial, anti-inflammatory, anticancer, cardioprotective and anti-obesity agents. Amongst them, resveratrol has attracted the most attention, although there are other natural and synthesized stilbenes with enhanced properties. However, stilbenes have some physicochemical and pharmacokinetic problems that need to be overcome before considering their applications. Human clinical evidence of their bioactivity is still controversial due to this fact and hence, exhaustive basis science on stilbenes is needed before applied science. This review gathers the main physicochemical and biological properties of natural stilbenes, establishes structure-activity relationships among them, emphasizing the current problems that limit their applications and presenting some promising approaches to overcome these issues: the encapsulation in different agents and the structural modification to obtain novel stilbenes with better features. The bioactivity of stilbenes should move from promising to evident.

Molecular encapsulation and bioactivity of gnetol, a resveratrol analogue, for use in foods.

BACKGROUND: Gnetol is a stilbene whose characterization and bioactivity have been poorly studied. It shares some bioactivities with its analogue resveratrol, such as anti-inflammatory, anti-thrombotic, cardioprotective and anti-cancer activities. However, the low solubility of stilbenes may limit their potential applications in functional foods. Encapsulation in cyclodextrins could be a solution. RESULTS: The antioxidant activity of gnetol was evaluated by 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation and ferric reducing antioxidant power methods (Trolox equivalents 13.48 µmol L-1 and 37.08 µmol L-1 respectively at the highest concentration) and it was higher than that of resveratrol, and depending on the method, similar or higher to that of oxyresveratrol. Spectrophotometric and spectrofluorimetric characterization of gnetol is published for the first time. Moreover, its water solubility was determined and improved almost threefold after its molecular encapsulation in cyclodextrins, as well as its stability after storage for a week. A physicochemical and computational study revealed that cyclodextrins complex gnetol in a 1:1 stoichiometry, with better affinity for like 2-hydroxypropyl-ß-cyclodextrin (KF  = 4542.90 ± 227.15 mol-1  L). Temperature and pH affected the encapsulation constants. CONCLUSION: These results could increase interest of gnetol as an alternative to the most studied stilbene, resveratrol, as well as aid in the development of more stable inclusion complexes that improve its aqueous solubility and stability so that it can be incorporated into functional foods. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Improvement of the Physicochemical Limitations of Rhapontigenin, a Cytotoxic Analogue of Resveratrol against Colon Cancer.

It has been argued that methoxylated stilbenes are better candidates for oral administration than hydroxylated stilbenes, including resveratrol, as they share many biological activities but have better bioavailability. By contrast, they have a disadvantage to consider, i.e., their lower hydrophilic character that leads to precipitation issues in the final product. In this work, we analysed and compared the growth inhibition of colorectal cancer cells of the methoxylated stilbene rhapontigenin and some analogues and overcame potential problems in the development of fortified products by designing inclusion complexes. Among several cyclodextrins, we found the one that best fit the molecule by physicochemical and bioinformatics assays. The stoichiometry and the encapsulation constants with natural and modified cyclodextrins were determined by fluorescence spectroscopy. The most promising complexes were analysed at different temperature and pH conditions, determining the thermodynamic parameters, to discover the optimal conditions for the preparation and storage of the products. The results showed that rhapontigenin solubility and stability were significantly improved, achieving a sevenfold increase in water solubility and maintaining more than 73% of the stilbene after three months. These findings could be of great interest for industries that aim to deliver novel bioactive compounds with higher solubility and lower degradation.

Antiproliferative Effects in Colorectal Cancer and Stabilisation in Cyclodextrins of the Phytoalexin Isorhapontigenin.

Isorhapontigenin has been proposed as a better alternative for oral administration than the famous resveratrol, as it shares many biological activities, but with a structure that could make its delivery easier. Although this hydrophobic structure could enhance bioavailability, it could also be a disadvantage in the development of products. In this research, we study the antiproliferative activity of this stilbene against colorectal cancer and overcome its limitations through molecular encapsulation in cyclodextrins. The cytotoxic activity against human colorectal cancer cells of isorhapontigenin was similar to that of resveratrol or piceatannol, supporting its use as a bioactive alternative. The study of the encapsulation through fluorescence spectroscopy and molecular docking revealed that the complexation satisfies a 1:1 stoichiometry and that HP-ß-CD is the most suitable CD to encapsulate this stilbene. Through a spectrophotometric assay, it was observed that this CD could double the basal water solubility, exceeding the solubility of other hydroxylated stilbenes. The stability of these inclusion complexes was higher at a pH below 9 and refrigeration temperatures. Moreover, the use of CDs retained more than 78% of isorhapontigenin after storage for 12 weeks, compared to 15% in free form. Overall, these findings could help design novel formulations to better deliver isorhapontigenin.

The use of cyclodextrins as solubility enhancers in the ORAC method may cause interference in the measurement of antioxidant activity.

The ability of cyclodextrins to enhance the water solubility of lipophilic compounds is used to modify the water-based Oxygen Radical Absorbance Capacity (ORAC) method to measure antioxidant activity in vitro. However, the use of these solubility enhancers may alter fluorescent readings, which has led to contradictory results being described in the literature. The low specificity of these oligosaccharides and their controlled release effect can result in cyclodextrins forming inclusion complexes with other reagents in the assay, changing the kinetics. In this study, the cause of cyclodextrins' interference in the ORAC method is evaluated through a physicochemical and computational approach. Cyclodextrins showed a clear increase in the fluorescent signal both in the presence and absence of the antioxidant oxyresveratrol, the precise effect being dependent on the type and concentration of cyclodextrin. Although the glucidic nature of cyclodextrins could play a minimal role in this effect, it seems that the main cause was the encapsulation of other substrates in the reaction, fluorescein and AAPH.

Development if healthy milk and yogurt products for reducing metabolic diseases using cyclodextrin and omega-3 fatty acids from fish oil.

The food industry is constantly attempting to develop better products that will have a positive effect on health. Feiraco® and Clesa®, expressed their intention to create novel products using UNICLA® milk as a matrix to develop functional foods. In this respect, ß-cyclodextrin (ß-CD) at 1% was able to reduce the cholesterol concentration in Feiraco-UNICLA® milk products by around 87-85%. Products were fortified with omega-3 from fish oil with α- and ß-CD acting as carriers. It was possible to add around 50% of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) Recommended Dietary Allowances (RDA), with a high diet proportion of fibre and similar organoleptic properties to commercial omega-3 products. 80% of a sensory panel found our formulations satisfactory. The final product was stable, and the bioaccessibilty of the fatty acids added to the milk was around 74%. These results as a whole satisfy the aid of Feiraco® and Clesa® to develop improved products.

Study of the fluorescence and interaction between cyclodextrins and neochlorogenic acid, in comparison with chlorogenic acid.

Neochlorogenic acid, a less-studied isomer of chlorogenic acid, has been seen to posses antioxidant, antifungal, anti-inflammatory and anticarcinogenic effects, which makes it an interesting candidate for incorporation in functional foods. However, its poor solubility in water and susceptibility to oxidation make such a task difficult. To overcome that, its encapsulation in cyclodextrins (CDs) is proposed. The fluorescence of neochlorogenic acid in different pH conditions was analyzed, and caffeic acid was proved to be the fluorescent moiety in the molecule. An encapsulation model whereby the ligand poses two potential complexation sites (caffeic and D-(-)-quinic moieties), showed that α-CD and HP-ß-CD formed the best inclusion complexes with neochlorogenic acid, followed by M-ß-CD, ß-CD and γ-CD. Molecular docking with the two best CDs gave better scores for α-CD, despite HP-ß-CD providing stabilization through H-bonds. The encapsulation of chlorogenic acid led to a similar CD order and scores, although constants were higher for α-CD, ß-CD and M-ß-CD, lower for HP-ß-CD, and negligible for γ-CD. The protonation state affected these results leading to a different order of CD preference. The solubility and the susceptibility to oxidation of neochlorogenic acid improved after complexation with α-CD and HP-ß-CD, while the antioxidant activity of both isomers was maintained.

Cyclodextrins as Anti-inflammatory Agents: Basis, Drugs and Perspectives.

Inflammation is a biological response of the immune system to harmful stimuli. Importantly, inflammation is also a hallmark of several human diseases such as cancer or diabetes. Novel drugs to treat this response are constantly researched, but the formulation is usually forgotten. Cyclodextrins (CDs) are a well-known excipient for complexing and drug delivery. Anti-inflammatory drugs and bioactive compounds with similar activities have been favored from these CD processes. CDs also illustrate anti-inflammatory activity per se. This review tried to describe the capacities of CDs in this field, and is divided into two parts: Firstly, a short description of the inflammation disease (causes, symptoms, treatment) is explained; secondly, the effects of different CDs alone or forming inclusion complexes with drugs or bioactive compounds are discussed.

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.

Recent advances in the treatment of Niemann pick disease type C: A mini-review.

Niemann Pick disease Type C (NPC) is a recessive rare disease caused by the mutation on NPC1 and/or NPC2 genes changing the processing of the Low-density proteins (LDL) resulting in an accumulation of lipids in the cells. Until today there is not a cure, the current treatment is based on palliative affairs to reduce the symptoms and prevent its appearance. Among all the treatments proposed the use of cyclodextrins (CDs), nanocarriers which can complex cholesterol, is one of the most useful alternatives. Indeed, for several years 2-hydroxypropyl-ß-CD (HPß-CD) is approved as orphan drug for FDA and EMA to the treatment. However, different CDs based materials are created each year to improve the cholesterol uptake. This review is focused on the novelty of CD based materials for NPC treatment.

Evaluation of the properties of the essential oil citronellal nanoencapsulated by cyclodextrins.

In this work we used natural and modified cyclodextrins (ß-CD and HP-ß-CD) as encapsulating agents to improve citronellal properties. Using fluorimetric techniques, its aggregation behavior was studied for the first time. Its critical micellar concentration was seen to vary with the presence of cyclodextrins, which form 1:1 stoichiometry complexes with citronellal. The encapsulation constants and the scores obtained by Molecular Docking were correlated. Chromatographic (GC-MS) and sensory analysis confirmed that cyclodextrins improve the persistence of the aroma. Finally, the antimicrobial effect of citronellal against Escherichia coli and Bacillus subtilis in the presence and absence of cyclodextrins was studied. A combinatorial effect of citronellal, HP-ß-cyclodextrin and Glucobay® as an antimicrobial mixture was observed. The results of this study not only demonstrated the potential of CD mixtures, but also that the growth caused by CD digestion may sometimes be greater that the antimicrobial effect of the agents used in this study.

Ellagic acid-borax fluorescence interaction: application for novel cyclodextrin-borax nanosensors for analyzing ellagic acid in food samples.

The food industry needs cheap, fast and sensitive methods to increase the number of analyses that are routinely carried out; for this reason, new methods are constantly being sought. This paper describes a novel fluorescent nanosensor based on cyclodextrin (CD) to determine ellagic acid (EA). The encapsulation of EA in the presence of borax was studied. Firstly, the complexation of EA-borax was tested. The stoichiometry of the EA-borax complex showed a 1 : 2 complex, with KF1 = 2548 ± 127 M-1 and KF2 = 302 ± 15 M-1. Different CDs were used to obtain a 1 : 1 : 1 CD-EA-borax complex with γ-CD providing the best complexation constant (KF3 = 364 ± 18 M-1). Furthermore, when the accuracy and sensitivity of the nanosensor were tested using a crude blueberry extract, the CD/borax mixture provided an 18 times stronger signal than with the crude extract alone and 7 times stronger than that obtained using borax alone.