Rafts making and rafts braking: how plant flavonoids may control membrane heterogeneity

Specific ABA-independent tomato transcriptome reprogramming under abiotic stress combination

Crops often have to face several abiotic stresses simultaneously, and under these conditions, the plant's response significantly differs from that observed under a single stress. However, up to the present, most of the molecular markers identified for increasing plant stress tolerance have been characterized under single abiotic stresses, which explains the unexpected results found when plants are tested under real field conditions. One important regulator of the plant's responses to abiotic stresses is abscisic acid (ABA). The ABA signaling system engages many stress-responsive genes, but many others do not respond to ABA treatments. Thus, the ABA-independent pathway, which is still largely unknown, involves multiple signaling pathways and important molecular components necessary for the plant's adaptation to climate change. In the present study, ABA-deficient tomato mutants (flacca, flc) were subjected to salinity, heat, or their combination. An in-depth RNA-seq analysis revealed that the combination of salinity and heat led to a strong reprogramming of the tomato transcriptome. Thus, of the 685 genes that were specifically regulated under this combination in our flc mutants, 463 genes were regulated by ABA-independent systems. Among these genes, we identified six transcription factors (TFs) that were significantly regulated, belonging to the R2R3-MYB family. A protein-protein interaction network showed that the TFs SlMYB50 and SlMYB86 were directly involved in the upregulation of the flavonol biosynthetic pathway-related genes. One of the most novel findings of the study is the identification of the involvement of some important ABA-independent TFs in the specific plant response to abiotic stress combination. Considering that ABA levels dramatically change in response to environmental factors, the study of ABA-independent genes that are specifically regulated under stress combination may provide a remarkable tool for increasing plant resilience to climate change.

Resurrection Plants-A Valuable Source of Natural Bioactive Compounds: From Word-of-Mouth to Scientifically Proven Sustainable Use

Resurrection plant species are a group of higher plants whose vegetative tissues are able to withstand long periods of almost full desiccation and recover quickly upon rewatering. Apart from being a model system for studying desiccation tolerance, resurrection plant species appear to be a valuable source of metabolites, with various areas of application. A significant number of papers have been published in recent years with respect to the extraction and application of bioactive compounds from higher resurrection plant species in various test systems. Promising results have been obtained with respect to antioxidative and antiaging effects in various test systems, particularly regarding valuable anticancer effects in human cell lines. Here, we review the latest advances in the field and propose potential mechanisms of action of myconoside-a predominant secondary compound in the European members of the Gesneriaceae family. In addition, we shed light on the possibilities for the sustainable use of natural products derived from resurrection plants.

Investigation of the Membrane Localization and Interaction of Selected Flavonoids by NMR and FTIR Spectroscopy

In this report, we discuss the effects of undescribed flavone derivatives, HZ4 and SP9, newly isolated from the aerial parts of Hottonia palustris L. and Scleranthus perennis L. on membranes. Interaction of flavonoids with lipid bilayers is important for medicinal applications. The experiments were performed with FTIR and NMR techniques on liposomes prepared from DPPC (dipalmitoylphosphatidylcholine) and EYPC (egg yolk phosphatidylcholine). The data showed that the examined polyphenols incorporate into the polar head group region of DPPC phospholipids at both 25 °C and 45 °C. At the lower temperature, a slight effect in the spectral region of the ester carbonyl group is observed. In contrast, at 45 °C, both compounds bring about the changes in the spectral regions attributed to antisymmetric and symmetric stretching vibrations of CH2 and CH3 moieties. Similarly, as in DPPC lipids, the tested compounds interact with the fingerprint region of the polar head groups of the EYPC lipids and cause its reorganization. The outcomes obtained by NMR analyses confirmed the localization of both flavonoids in the polar heads zone. Unraveled effects of HZ4 and SP9 in respect to lipid bilayers can partly determine their biological activities and are crucial for their usability in medicine as disease-preventing phytochemicals.

Activity of Na+/K+- and Ca2+-ATPases in human erythrocyte membranes: Protocol improvement, relation to cholesterol content, and effects of polyphenols

It is known that the activities of Na+/K+- and Ca2+-ATPases in the plasma membrane with an excess of cholesterol are compromised. Our main goal was to find out whether quercetin, resveratrol, or caffeic acid, in the nano- and low micromolar concentration ranges, can improve the ATPase activity in human erythrocyte membranes with excess cholesterol. These molecules belong to different chemical classes of polyphenols and are widely present in plant foods. Also, due to some variations in the protocol for determining the ATPase activity, we first analyzed several key parameters of the protocol to improve the accuracy of the results. The activities of Na+/K+- and Ca2+-ATPases were reduced in membranes with moderate and high cholesterol levels compared to membranes from normocholesterolemic subjects (p < 0.01). All three polyphenols affected the ATPase activity in a similar biphasic manner. Namely, the ATPase activity gradually increased with increasing polyphenol concentration up to 80-200 nM, and then gradually decreased with further increase in polyphenol concentration. Moreover, the stimulating effect of the polyphenols was highest in membranes with high cholesterol content, making ATPase activity values close/equal to those in normal cholesterol membranes. In other words, quercetin, resveratrol, and caffeic acid at nanomolar concentrations were able to improve/restore the functioning of Na+/K+- and Ca2+-ATPases in erythrocyte membranes with high cholesterol levels. This suggests a common membrane-mediated mechanism of action for these polyphenols, related to the content of membrane cholesterol.

Analysis of the Polyphenolic Composition of Vaccinium L. Extracts and Their Protective Effect on Red Blood Cell Membranes

The blueberry fruit of the genus Vaccinium, including high blueberry, low blueberry, and wild bilberry, is consumed for its flavor and medicinal properties. The purpose of the experiments was to investigate the protective effect and mechanism of the interaction of blueberry fruit polyphenol extracts with the erythrocytes and their membranes. The content of polyphenolic compounds in the extracts was determined using the chromatographic UPLC-ESI-MS method. The effects of the extracts on red blood cell shape changes, hemolysis and osmotic resistance were examined. Changes in the order of packing and fluidity of the erythrocyte membrane and the lipid membrane model caused by the extracts were identified using fluorimetric methods. Erythrocyte membrane oxidation was induced by two agents: AAPH compound and UVC radiation. The results show that the tested extracts are a rich source of low molecular weight polyphenols that bind to the polar groups of the erythrocyte membrane, changing the properties of its hydrophilic area. However, they practically do not penetrate the hydrophobic part of the membrane and do not damage its structure. Research results suggest that the components of the extracts can defend the organism against oxidative stress if they are delivered to the organism in the form of dietary supplements.

Natural products in digestive tract tumors metabolism: Functional and application prospects

Digestive tract diseases are presently the hotspot of clinical diagnosis and treatment, and the incidence of digestive tract tumor is increasing annually. Surgery remains the main therapeutic schedule for digestive tract tumor. Though benefits were brought by neoadjuvant chemotherapy, a part of patients lose the chance of surgery because of late detection or inappropriate intervention. Therefore, the treatment of inoperable patients has become an urgent need. At the same time, tumor metabolism is an extremely complex and diverse process. Natural products are confirmed effective to inhibit the development of tumors in vitro and in vitro. There are many kinds of natural products and their functions remain not clear. However, some natural products such as polyphenols have been proven to have definite anti-cancer effects, and some terpenoids have definite anti-inflammatory, anti-ulcer, anti-tumor, and other effects. Therefore, the anti-tumor characteristics of natural products should arouse our high attention. Although there are many obstacles to study the activities of natural products in tumor, including the difficulty in detection or distinguishing each component due to their low levels in tumor tissue, etc., the emergence of highly sensitive and locatable spatial metabolomics make the research and application of natural products a big step forward. In this review, natural products such as phenols, terpenoids and biotinoids were summarized to further discuss the development and therapeutic properties of natural metabolites on digestive tract tumors.

Polar localization of new flavonoids from aerial parts of Scleranthus perennis and Hottonia palustris and their modulatory action on lipid membranes properties

The aim of this study was to characterize, for the first time, the interactions, location, and influence of flavonoids isolated from aerial parts of Scleranthus perennis (Caryophyllaceae) and Hottonia palustris (Primulaceae) on the properties of model lipid membranes prepared from dipalmitoylphosphatidylcholine (DPPC) and egg yolk phosphatidylcholine (EYPC). The tested compounds incorporated into liposomes into the region of the polar heads or at the water/membrane interface of DPPC phospholipids. Spectral effects accompanying the presence of polyphenols revealed their effect on ester carbonyl groups apart from SP8. All polyphenols brought about reorganization of the polar zone of liposomes as it was observed by FTIR technique. Additionally, fluidization effect was noted in the region of symmetric and antisymmetric stretching vibrations of the CH₂ and CH₃ groups with exception to HZ2 and HZ3. Similarly, in EYPC liposomes, they interacted mainly with the regions of the choline heads of the lipids and had various effects on the carbonyl ester groups with exception to SP8. The region of polar head groups is restructured due to the presence of the additives in liposomes. The outcomes obtained using the NMR technique confirmed the locations of all of the tested compounds in the polar zone and indicated a flavonoid-dependent modifying effect towards lipid membranes. HZ1 and SP8 raised motional freedom in this region whereas opposite effect was revealed for HZ2 and HZ3. In the hydrophobic region restricted mobility was noted. In this report we discuss the mechanism of previously undescribed flavonoids in terms of their actions on membranes.

Antimicrobial Activity of Quercetin, Naringenin and Catechin: Flavonoids Inhibit Staphylococcus aureus-Induced Hemolysis and Modify Membranes of Bacteria and Erythrocytes

Search for novel antimicrobial agents, including plant-derived flavonoids, and evaluation of the mechanisms of their antibacterial activities are pivotal objectives. The goal of this study was to compare the antihemolytic activity of flavonoids, quercetin, naringenin and catechin against sheep erythrocyte lysis induced by α-hemolysin (αHL) produced by the Staphylococcus aureus strain NCTC 5655. We also sought to investigate the membrane-modifying action of the flavonoids. Lipophilic quercetin, but not naringenin or catechin, effectively inhibited the hemolytic activity of αHL at concentrations (IC₅₀ = 65 ± 5 µM) below minimal inhibitory concentration values for S. aureus growth. Quercetin increased the registered bacterial cell diameter, enhanced the fluidity of the inner and surface regions of bacterial cell membranes and raised the rigidity of the hydrophobic region and the fluidity of the surface region of erythrocyte membranes. Our findings provide evidence that the antibacterial activities of the flavonoids resulted from a disorder in the structural organization of bacterial cell membranes, and the antihemolytic effect of quercetin was related to the effect of the flavonoid on the organization of the erythrocyte membrane, which, in turn, increases the resistance of the target cells (erythrocytes) to αHL and inhibits αHL-induced osmotic hemolysis due to prevention of toxin incorporation into the target membrane. We confirmed that cell membrane disorder could be one of the direct modes of antibacterial action of the flavonoids.

Flavonoids as new regulators of mitochondrial potassium channels: contribution to cardioprotection

Objectives

Acute myocardial ischemia is one of the major causes of illness in western society. Reduced coronary blood supply leads to cell death and loss of cardiomyocyte population, resulting in serious and often irreversible consequences on myocardial function. Mitochondrial potassium (mitoK) channels have been identified as fine regulators of mitochondrial function and, consequently, in the metabolism of the whole cell, and in the mechanisms underlying the cardioprotection. Interestingly, mitoK channels represent a novel putative target for treating cardiovascular diseases, particularly myocardial infarction, and their modulators represent an interesting tool for pharmacological intervention. In this review, we took up the challenge of selecting flavonoids that show cardioprotective properties through the activation of mitoK channels.

Key findings

A brief overview of the main information on mitoK channels and their participation in the induction of cytoprotective processes was provided. Then, naringenin, quercetin, morin, theaflavin, baicalein, epigallocatechin gallate, genistein, puerarin, luteolin and proanthocyanidins demonstrated to be effective modulators of mitoK channels activity, mediating many beneficial effects.

Summary

The pathophysiological role of mitoK channels has been investigated as well as the impact of flavonoids on this target with particular attention to their potential role in the prevention of cardiovascular disorders.

Hitchhiking into a cell: flavonoids may produce complexes with transition metals for transmembrane translocation

Flavonoids are a group of food polyphenols that are delivered to the human body with plant foods. In recent years, these substances have attracted the attention of researchers due to their effectiveness in preventing a wide variety of diseases, including neurodegenerative, oncological, autoimmune, and cardiovascular. Similar pathologies may also occur with a lack of some first-row transition metals, including Cu(II), Zn(II), Mn(II), Fe(II/III). It is noteworthy that flavonoids are known as transition metal chelators. When a complex with these metals is formed, the therapeutic effect of flavonoids can be enhanced, assuming the possibility of synergy. Molecular models have shown that the lipophilicity of flavonoid-metal complexes can vary significantly depending on their binding stoichiometry. Therefore, a unique process of translocation of flavonoid-metal complexes of various lipophilicity through cell membranes is assumed, based on the possibility of their sequential association and dissociation, called "hitchhiking". It is expected that studies of the interaction of flavonoids with metals will improve the effectiveness of drugs based on flavonoids.

The role of catechin in electroporation of pancreatic cancer cells - Effects on pore formation and multidrug resistance proteins

Catechin is a bioflavonoid known for its anti-cancer properties. In the present study, we combined theoretical and experimental approaches to reveal the potential of catechin application in the electroporation (EP) or electrochemotherapy (ECT) of pancreatic cancer cells. The molecular dynamics simulations were implemented to examine the interactions of catechin with a model of a membrane, its influence on the membrane's thickness, and the impact of the catechin-membrane interaction on the pore formation. The data were confronted with experimental measurement of the threshold electric field required for permeabilization of pancreatic cancer cells to a fluorescent dye YO-PRO-1. Further, we examined the influence of catechin on cell viability following electroporation with cisplatin or calcium ions. Finally, we investigated the catechin impact on four proteins associated with multidrug resistance: P-glycoprotein, MRP1, BCRP, and LRP. We demonstrated that catechin may boost the effects of electroporation through various mechanisms: i) increasing the cell permeability prior to electroporation ii) increasing the electroporation threshold iii) sensitization of cells to chemotherapeutic compounds. We showed that catechin incubation influences mRNA levels and mitigates the immunoreactivity of Pgp, MRP1, BCRP, and LRP but these changes did not translate to the efficacy of electrochemotherapy.

Insights into Polyphenol-Lipid Interactions: Chemical Methods, Molecular Aspects and Their Effects on Membrane Structures

Plant polyphenols have many potential applications, for example, in the fields of chemical ecology and human and animal health and nutrition. These biological benefits are related to their bioavailability, bioaccessibility and interactions with other biomolecules, such as proteins, lipids, fibers and amino acids. Polyphenol-protein interactions are well-studied, but less is known about their interactions with lipids and cell membranes. However, the affinity of polyphenols for lipid bilayers partially determines their biological activity and is also important from the usability perspective. The polyphenol-lipid interactions can be studied with several chemical tools including, among others, partition coefficient measurements, calorimetric methods, spectroscopic techniques and molecular dynamics simulation. Polyphenols can variably interact with and penetrate lipid bilayers depending on the structures and concentrations of the polyphenols, the compositions of the lipids and the ambient conditions and factors. Polyphenol penetrating the lipid bilayer can perturb and cause changes in its structure and biophysical properties. The current studies have used structurally different polyphenols, diverse model lipids and various measuring techniques. This approach provides detailed information on polyphenol-lipid interactions, but there is much variability, and the results may even be contradictory, for example, in relation to the locations and orientations of the polyphenols in the lipid bilayers. Nevertheless, by using well-characterized model polyphenols and lipids systematically and combining the results obtained with several techniques within a study, it is possible to create a good overall picture of these fascinating interactions.

Multimodal Investigation into the Interaction of Quinacrine with Microcavity-Supported Lipid Bilayers

Quinacrine is a versatile drug that is widely recognized for its antimalarial action through its inhibition of the phospholipase enzyme. It also has antianthelmintic and antiprotozoan activities and is a strong DNA binder that may be used to combat multidrug resistance in cancer. Despite extensive cell-based studies, a detailed understanding of quinacrine's influence on the cell membrane, including permeability, binding, and rearrangement at the molecular level, is lacking. Herein, we apply microcavity-suspended lipid bilayers (MSLBs) as in vitro models of the cell membrane comprising DOPC, DOPC:Chol(3:1), and DOPC:SM:Chol(2:2:1) to investigate the influence of cholesterol and intrinsic phase heterogeneity induced by mixed-lipid composition on the membrane interactions of quinacrine. Using electrochemical impedance spectroscopy (EIS) and surface-enhanced Raman spectroscopy (SERS) as label-free surface-sensitive techniques, we have studied quinacrine interaction and permeability across the different MSLBs. Our EIS data reveal that the drug is permeable through ternary DOPC:SM:Chol and DOPC-only bilayer compositions. In contrast, the binary cholesterol/DOPC membrane arrested permeation, yet the drug binds or intercalates at this membrane as reflected by an increase in membrane impedance. SERS supported the EIS data, which was utilized to gain structural insights into the drug-membrane interaction. Our SERS data also provides a simple but powerful label-free assessment of drug permeation because a significant SERS enhancement of the drug's Raman signature was observed only if the drug accessed the plasmonic interior of the pore cavity passing through the membrane. Fluorescent lifetime correlation spectroscopy (FLCS) provides further biophysical insight, revealing that quinacrine binding increases the lipid diffusivity of DOPC and the ternary membrane while remarkably decreasing the lipid diffusivity of the DOPC:Chol membrane. Overall, because of its adaptability to multimodal approaches, the MSLB platform provides rich and detailed insights into drug-membrane interactions, making it a powerful tool for in vitro drug screening.

Quercetin induces lipid domain-dependent permeability

Quercetin is a polyphenolic molecule with a broad spectrum of biological activities derived from its antioxidant property. Its mechanism of action has been explained by its binding and/or interference with enzymes, receptors, transporters and signal transduction systems. Since these important mechanisms generally occur in membrane environments, within and through lipid bilayers, investigating the biophysical properties related to the diversity of lipid compositions of cell membranes may be the key to understanding the role of cell membrane in these processes. In this work, we explored the interaction of quercetin with model membranes of different lipid compositions to access the importance of lipid phases and bilayer homogeneity to the action of quercetin and contribute to the understanding of quercetin multiple activities. Analysis of the influence of quercetin on the morphology and permeability of GUVs, the rigidity of LUVs and affinity to these vesicles showed that quercetin strongly partitions to the more homogeneous environments, but significantly permeates and modifies the more heterogeneous where liquid-disordered, liquid-ordered and solid phases coexist. Our findings support the condensing effect of quercetin, which is observed through a significant rigidifying of bilayers containing 40% cholesterol, but much less evidenced when it is reduced to 20% or in its absence. Nevertheless, the presence of sphingomyelin in the ternary system led to a more heterogeneous bilayer with the formation of micrometric and probably also nanometric domains, which coalesce in the presence of quercetin. This observation together with increased permeability points to an insertion effect.

Hydrolysable tannins change physicochemical parameters of lipid nano-vesicles and reduce DPPH radical - Experimental studies and quantum chemical analysis

Tannins belong to plant secondary metabolites exhibiting a wide range of biological activity. One of the important aspects of the realization of the biological effects of tannins is the interaction with lipids of cell membranes. In this work we studied the interaction of two hydrolysable tannins: 1,2,3,4,6-penta-O-galloyl-β-d-glucose (PGG) and 1,2-di-O-galloyl-4,6-valoneoyl-β-d-glucose (T1) which had the same number of both aromatic rings (5) and hydroxyl groups (15) but differing in flexibility due to the presence of valoneoyl group in the T1 molecule with DMPC (dimyristoylphosphatidylcholine) lipid nano-vesicles (liposomes). Tannins-liposomes interactions were investigated using fluorescence spectroscopy, differential scanning calorimetry, laser Doppler velocimetry, dynamic light scattering and Fourier Transform Infra-Red spectroscopy. It was shown that more flexible PGG molecules stronger decreased the microviscosity of the liposomal membranes and increased the values of negative zeta potential in comparison with the more rigid T1. Both compounds diminished the phase transition temperature of DMPC membranes, interacted with liposomes via PO groups of head of phospholipids and their hydrophobic regions. These tannins neutralized DPPH free radicals with the stoichiometry of the reaction equal 1:1. The effects of the studied compounds on liposomes were discussed in relation to tannin quantum chemical parameters calculated by molecular modeling.

Novel Nanoliposome Codelivered DHA and Anthocyanidin: Characterization, In Vitro Infant Digestibility, and Improved Cell Uptake

There are still many challenges in understanding the absorption and transport mechanism of liposomes in the gastrointestinal tract of infants, especially for liposome-coentrapped two or more substances. In this study, novel docosahexaenoic acid (DHA)-anthocyanidin-codelivery liposomes (DA-LPs) were fabricated and characterized, and their digestive and absorptive behaviors were evaluated using the in vitro infant digestive method combined with the Caco-2 cell model. The liposomal bilayer structure remained intact with the particles aggregated in simulated infant gastric fluid, while their phospholipid membrane underwent enzymatic lipolysis under simulated intestinal conditions. Compared to single substance-loaded liposomes (DHA- or anthocyanidin-loaded liposomes), the digested DA-LPs showed better cell viability, higher cellular uptake and membrane fluidity, and lower reactive oxygen species (ROS). It can be concluded that DA-LPs are promising carriers for simultaneously transporting hydrophobic and hydrophilic molecules and may be beneficial for improving nutrient absorption and alleviating intestinal stress oxidation.

Interaction of drugs with lipid raft membrane domains as a possible target

Introduction

Plasma membranes are not the homogeneous bilayers of uniformly distributed lipids but the lipid complex with laterally separated lipid raft membrane domains, which provide receptor, ion channel and enzyme proteins with a platform. The aim of this article is to review the mechanistic interaction of drugs with membrane lipid rafts and address the question whether drugs induce physicochemical changes in raft-constituting and raft-surrounding membranes.

Methods

Literature searches of PubMed/MEDLINE and Google Scholar databases from 2000 to 2020 were conducted to include articles published in English in internationally recognized journals. Collected articles were independently reviewed by title, abstract and text for relevance.

Results

The literature search indicated that pharmacologically diverse drugs interact with raft model membranes and cellular membrane lipid rafts. They could physicochemically modify functional protein-localizing membrane lipid rafts and the membranes surrounding such domains, affecting the raft organizational integrity with the resultant exhibition of pharmacological activity. Raft-acting drugs were characterized as ones to decrease membrane fluidity, induce liquid-ordered phase or order plasma membranes, leading to lipid raft formation; and ones to increase membrane fluidity, induce liquid-disordered phase or reduce phase transition temperature, leading to lipid raft disruption.

Conclusion

Targeting lipid raft membrane domains would open a new way for drug design and development. Since angiotensin-converting enzyme 2 receptors which are a cell-specific target of and responsible for the cellular entry of novel coronavirus are localized in lipid rafts, agents that specifically disrupt the relevant rafts may be a drug against coronavirus disease 2019.

Effect of Hydrolyzable Tannins on Glucose-Transporter Expression and Their Bioavailability in Pig Small-Intestinal 3D Cell Model

Intestinal transepithelial transport of glucose is mediated by glucose transporters, and affects postprandial blood-glucose levels. This study investigates the effect of wood extracts rich in hydrolyzable tannins (HTs) that originated from sweet chestnut (Castanea sativa Mill.) and oak (Quercus petraea) on the expression of glucose transporter genes and the uptake of glucose and HT constituents in a 3D porcine-small-intestine epithelial-cell model. The viability of epithelial cells CLAB and PSI exposed to different HTs was determined using alamarBlue^®. qPCR was used to analyze the gene expression of SGLT1, GLUT2, GLUT4, and POLR2A. Glucose uptake was confirmed by assay, and LC–MS/ MS was used for the analysis of HT bioavailability. HTs at 37 µg/mL were found to adversely affect cell viability and downregulate POLR2A expression. HT from wood extract Tanex at concentrations of 4 µg/mL upregulated the expression of GLUT2, as well as glucose uptake at 1 µg/mL. The time-dependent passage of gallic acid through enterocytes was influenced by all wood extracts compared to gallic acid itself as a control. These results suggest that HTs could modulate glucose uptake and gallic acid passage in the 3D cell model.

Natural compounds as inhibitors of SARS-CoV-2 endocytosis: A promising approach against COVID-19

BACKGROUND AND AIM

The recent COVID-19 pandemic caused by SARS-CoV-2 affected more than six million people and caused thousands of deaths. The lack of effective drugs or vaccines against SARS-CoV-2 further worsened the situation. This review is focused on the identification of molecules that may inhibit viral entry into host cells by endocytosis.

METHODS

We performed the literature search for these natural compounds in the articles indexed in PubMed.

RESULTS

Natural products against viral infections have been gaining importance in recent years. Specific natural compounds like phytosterols, polyphenols, flavonoids, citrus, galangal, curcuma and hydroxytyrosol are being analyzed to understand whether they could inhibit SARS-CoV-2.

CONCLUSIONS

We reviewed natural compounds with potential antiviral activity against SARS-CoV-2 that could be used as a treatment for COVID-19.

Lipid rafts as potential mechanistic targets underlying the pleiotropic actions of polyphenols

Polyphenols have attracted a lot of global attention due to their diverse biological actions against cancer, obesity, and cardiovascular diseases. Although extensive research has been carried out to elucidate the mechanisms of pleiotropic actions of polyphenols, this remains unclear. Lipid rafts are distinct nanodomains enriched in cholesterol and sphingolipids, present in the inner and outer leaflets of cell membranes, forming functional platforms for the regulation of cellular processes and diseases. Recent studies focusing on the interaction between polyphenols and cellular lipid rafts shed new light on the pleiotropic actions of polyphenols. Polyphenols are postulated to interact with lipid rafts in two ways: first, they interfere with the structural integrity of lipid rafts, by disrupting their structure and clustering of the ordered domains; second, they modulate the downstream signaling pathways mediated by lipid rafts, by binding to receptor proteins associated with lipid rafts, such as the 67 kDa laminin receptor (67LR), epidermal growth factor receptor (EGFR), and others. This study aims to elaborate the mechanism of interaction between polyphenols and lipid rafts, and describe pleiotropic preventive effects of polyphenols.

Flavonoids modulate liposomal membrane structure, regulate mitochondrial membrane permeability and prevent erythrocyte oxidative damage

In the present work, we investigated the interaction of flavonoids (quercetin, naringenin and catechin) with cellular and artificial membranes. The flavonoids considerably inhibited membrane lipid peroxidation in rat erythrocytes treated with tert-butyl hydroperoxide (700 μM), and the IC₅₀ values for prevention of this process were equal to 9.7 ± 0.8 μM, 8.8 ± 0.7 μM, and 37.8 ± 4.4 μM in the case of quercetin, catechin and naringenin, respectively, and slightly decreased glutathione oxidation. In isolated rat liver mitochondria, quercetin, catechin and naringenin (10-50 μM) dose-dependently increased the sensitivity to Ca²⁺ ions - induced mitochondrial permeability transition. Using the probes TMA-DPH and DPH we showed that quercetin rather than catechin and naringenin strongly decreased the microfluidity of the 1,2-dimyristoyl-sn-glycero-3-phosphocholine liposomal membrane bilayer at different depths. On the contrary, using the probe Laurdan we observed that naringenin transfer the bilayer to a more ordered state, whereas quercetin dose-dependently decreased the order of lipid molecule packing and increased hydration in the region of polar head groups. The incorporation of the flavonoids, quercetin and naringenin and not catechin, into the liposomes induced an increase in the zeta potential of the membrane and enlarged the area of the bilayer as well as lowered the temperature and the enthalpy of the membrane phase transition. The effects of the flavonoids were connected with modification of membrane fluidity, packing, stability, electrokinetic properties, size and permeability, prevention of oxidative stress, which depended on the nature of the flavonoid molecule and the nature of the membrane.

Apigenin produced by maize flavone synthase I and II protects plants against UV-B-induced damage

Flavones, one of the largest groups of flavonoids, have beneficial effects on human health and are considered of high nutritional value. Previously, we demonstrated that maize type I flavone synthase (ZmFNSI) is one of the enzymes responsible for the synthesis of O-glycosyl flavones in floral tissues. However, in related species such as rice and sorghum, type II FNS enzymes also contribute to flavone biosynthesis. In this work, we provide evidence that maize has both one FNSI and one FNSII flavone synthases. Arabidopsis transgenic plants expressing each FNS enzyme were generated to validate the role of flavones in protecting plants against UV-B radiation. Here, we demostrate that ZmCYP93G7 (FNSII) has flavone synthase activity and is able to complement the Arabidopsis dmr6 mutant, restoring the susceptibility to Pseudomonas syringae. ZmFNSII expression is controlled by the C1/PL1 + R/B anthocyanin transcriptional complexes, and both ZmFNSI and ZmFNSII are regulated by UV-B. Arabidopsis transgenic plants expressing ZmFNSI or ZmFNSII that accumulate apigenin exhibit less UV-B-induced damage than wild-type plants. Together, we show that maize has two FNS-type enzymes that participate in the synthesis of apigenin, conferring protection against UV-B radiation.

Effect of Different Anthocyanidin Glucosides on Lutein Uptake by Caco-2 Cells, and Their Combined Activities on Anti-Oxidation and Anti-Inflammation In Vitro and Ex Vivo

The interactive effects on anti-oxidation and anti-inflammation of lutein combined with each of the six common anthocyanidin glucosides were studied in both chemical and cellular systems. The combined phytochemicals showed an antagonism in the inhibition of lipid oxidation in a liposomal membrane, but showed an additive effect on cellular antioxidant activity in Caco-2 cells. Lutein was an active lipoxygenase inhibitor at 2–12 μM while anthocyanins were inactive. The concentration of lutein when it was used in combination with anthocyanins was 25–54% higher than when lutein was used alone (i.e., IC₅₀ = 1.2 μM) to induce 50% of lipoxygenase inhibition. Only the combination of lutein with malvidin-3-glucoside showed anti-inflammatory synergy in the suppression of interleukin-8, and the synergy was seen at all three ratios tested. Some mixtures, however, showed anti-inflammatory antagonism. The presence of anthocyanins (5–7.5 μM) did not affect lutein uptake (2.5–5 μM) by Caco-2 cells.

Ion Channels Induced by Antimicrobial Agents in Model Lipid Membranes are Modulated by Plant Polyphenols Through Surrounding Lipid Media

The potential therapeutic applications of plant polyphenols in various neurological, cardiovascular, metabolic and malignant disorders determine the relevance of studying the molecular mechanisms of their action on the cell membranes. Here, the quantitative changes in the physical parameters of model bilayer lipid membranes upon the adsorption of plant polyphenols were evaluated. It was shown that butein and naringenin significantly decreased the intrinsic dipole potential of cholesterol-free and cholesterol-enriched membranes. Cardamonin, 4'-hydroxychalcone, licochalcone A and liquiritigenin demonstrated the average efficiency, while resveratrol did not characterized by the ability to modulate the bilayer electrostatics. At the same time, the tested polyphenols affected melting of phospholipids with saturated acyl chains. The effects were attributed to the lipid disordering and a promotion of the positive curvature stress. According to DSC data and results of measurements of the threshold voltages that cause bilayer breakdown licochalcone A is the most effective agent. Furthermore, the role of the polyphenol induced changes in the electric and elastic properties of lipid host in the regulation of reconstituted ion channels was examined. The ability of the tested polyphenols to decrease the conductance of single ion channels produced by the antifungal cyclic lipopeptide syringomycin E was in agreement with their effects on the dipole potential of the lipid bilayers. The greatest effect of licochalcone A on the steady-state membrane conductance induced by the antifungal polyene macrolide antibiotic nystatin correlated with its greatest efficacy to induce the positive curvature stress. We also found that butein and naringenin bind specifically to a single pore formed by α-hemolysin from Staphylococcus aureus.

Differential targeting of membrane lipid domains by caffeic acid and its ester derivatives

Phenolic acids have been associated to a wide range of important health benefits underlain by a common molecular mechanism of action. Considering that significant membrane permeation is prevented by their hydrophilic character, we hypothesize that their main effects result from the interplay with cell membrane surface. This hypothesis was tested using the paradigmatic caffeic acid (CA) and two of its ester derivatives, rosmarinic (RA) and chlorogenic (CGA) acids, for which we predict, based on molecular dynamics simulations, a shallow location in phospholipid bilayers dependent on the protonation-state. Using complementary experimental approaches, an interaction with the membrane was definitely revealed for the three compounds, with RA exhibiting the highest lipid bilayer partition, and the redox signals of membrane-bound RA and CA being clearly detected. Cholesterol decreased the compounds bilayer partition, but not their ability to lower membrane dipole potential. In more complex membrane models containing also sphingomyelin, with liquid disordered (ld)/ liquid ordered (lo) phases coexistence, mimicking domains in the external leaflet of human plasma membrane, all compounds were able to affect nanodomains lateral organization. RA, and to a lesser extent CGA, decreased the size of lo domains. The most significant effect of CA was the possible formation of a rigid gel-like phase, enriched in sphingomyelin. In addition, all phenolic acids decreased the order of lo domains. In sum, phenolic acid effects on the membrane are enhanced in cholesterol-rich lo phases, which predominate in the outer leaflet of human cell membranes and are involved in many key cellular processes.

Combination of EPA with Carotenoids and Polyphenol Synergistically Attenuated the Transformation of Microglia to M1 Phenotype Via Inhibition of NF-κB

Microglia activation toward the M1 phenotype has been reported to contribute to the neurodegenerative processes and cognition alterations due to the release of pro-inflammatory mediators and cytokines. The aim of the present research was to assess the effectiveness of free fatty acids omega-3 preparations: eicosapentaenoic acid (EPA) or/and docosahexaenoic acid (DHA), carotenoids and phenolics combinations, in inhibiting the release of inflammatory mediators from activated microglia. Preincubation of BV-2 microglia cells with each of the FFAs omega-3 preparations in a range of 0.03-2 μM together with Lyc-O-mato^® (0.1 μM), Carnosic acid (0.2 μM) with or without Lutein (0.2 μM), 1 h before addition of lipopolysaccharide (LPS) for 16 h caused a synergistic inhibition of nitric oxide (NO) production with a rank order of EPA > Ropufa (EPA/DHA 2/1) > Krill (EPA/DHA 1.23/1). The optimal inhibitory combinations of EPA (0.125 μM) with the phytonutrients caused a synergistic inhibition of prostaglandin E₂ (PGE₂) release, IL-6 secretion, superoxide and NO production and prevention of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) upregulation and elevated CD40 expression in microglia exposed to LPS or interferon-γ (IFN-γ), representing infection or inflammation, respectively. The presence of the combination caused a synergistic increase in the release of the anti-inflammatory cytokine IL-10. The inhibitory effects by the combinations of EPA with the phytonutrients were mediated by the inhibition of the redox-sensitive NF-κB activation and detected by its phosphorylated p-65 on serine 536 in microglia stimulated by either LPS or IFN-γ. In addition, phosphorylated CREB on serine 133 which was shown to be involved in the induction of iNOS was inhibited by the combinations in stimulated cells. In conclusion, the results suggest that low concentrations of EPA with the phytonutrients are very efficient in inhibiting the transformation of microglia to M1 phenotype and may prevent cognition deficit.

Biomolecular Interactions of Tannin Isolated from Oenothera gigas with Liposomes

We have examined the interaction between hydrolysable tannin 1-O-galloyl-4,6-hexahydroxydiphenoyl-β-D-glucose (OGβDG) with neutral liposomes as a model of cell membranes composed of three lipids: lecithin, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at different mass ratios. OGβDG in the concentration range 0.5-15 µg/ml (0.4-12 µM) strongly interacts with liposomal membranes by changing their structure, surface charge and fluidity. Used OGβDG molecules decrease and increase the rigidity of hydrophilic surface and hydrophobic parts of liposomes, respectively. At higher concentrations of tannin (>15 µM), liposomes are aggregated. Fourier Transform Infra-Red (FTIR) analysis showed that mainly -OH groups from OGβDG and also PO(2-) groups from phospholipids are responsible for the interaction. Obtained data indicate the importance of membrane lipid composition in interactions between tannins and cells.

Effects of Dipole Potential Modifiers on Heterogenic Lipid Bilayers

In this work, we examine the ability of dipole modifiers, flavonoids, and RH dyes to affect the dipole potential (φ d) and phase separation in membranes composed of ternary mixtures of POPC with different sphingolipids and sterols. Changes in the steady-state conductance induced by cation-ionophore complexes have been measured to evaluate the changes in dipole potential of planar lipid bilayers. Confocal fluorescence microscopy has been employed to investigate lipid segregation in giant unilamellar vesicles. The effects of flavonoids on φ d depend on lipid composition and dipole modifier type. The effectiveness of RH dyes to increase φ d depends on sphingolipid type but is not influenced by sterol content. Tested modifiers lead to partial or complete disruption of gel domains in bilayers composed of POPC, sphingomyelin, and cholesterol. Substitution of cholesterol to ergosterol or 7-dehydrocholesterol leads to a loss of fluidizing effects of modifiers except phloretin. This may be due to various compositions of gel domains. The lack of influence of modifiers on phase scenario in vesicles composed of ternary mixtures of POPC, cholesterol, and phytosphingosine or sphinganine is related to an absence of gel-like phase. It was concluded that the membrane lateral heterogeneity affects the dipole-modifying abilities of the agents that influence the magnitude of φ d by intercalation into the bilayer and orientation of its own large dipole moments (phloretin and RH dyes). The efficacy of modifiers that do not penetrate deeply and affect φ d through water adsorption (phlorizin, quercetin, and myricetin) is not influenced by lateral heterogeneity of membrane.

Properties of Langmuir and solid supported lipid films with sphingomyelin

Biological cell membranes play a crucial role in various biological processes and their functionality to some extent is determined by the hydrophilic/hydrophobic balance. A significant progress in understanding the membrane structure was the discovery of laterally segregated lipid domains, called the lipid rafts. These raft domains are of ordered lamellar liquid-crystalline phase, while rest of the membrane exists in a relatively disordered lamellar liquid-crystalline phase. Moreover, the chemical constitution of the lipid rafts consists of a higher content (up to 50%) of cholesterol (Chol) and sphingomyelin (SM). Sphingomyelin also plays a significant role in the red cells of blood and nerves, in some diseases, as a precursor to ceramides, and other sphingolipid metabolites. In this paper properties of Langmuir and solid supported mixed lipid films of DPPC/SM, DOPC/SM, and Chol/SM are described. Special attention has been paid to wetting properties (hydrophobic/hydrophilic balance) of these films transferred onto a hydrophilic glass surface. To our knowledge such results have not yet been published in the literature. The properties were determined via contact angle measurements and then calculation of the films' apparent surface free energy. The films' wettability and their apparent surface free energy strongly depend on their composition. The energy is affected by both the structure of hydrocarbon chains of glycerophospholipids (DPPC and DOPC) and their interactions with SM. Properties of mixed Chol/SM monolayer depend also on the film stoichiometry. At a low Chol content (XChol=0.25) the interactions between SM and Chol are strong and hence the formation of binary complex is possible. This is accompanied by a decrease in the film surface free energy in comparison to that of pure SM monolayer, contrary to a higher Chol content where the monolayer energy increases. This suggests that cholesterol is excluded from the membrane thus increasing the film hydrophilicity. These results are consistent with the literature data and somehow confirm the hypothesis of lipid raft formation. The roughness of the investigated monolayer surfaces was also determined using optical profilometry. The roughness parameters of the DPPC, SM, and mixed DPPC/SM generally correlate with the changes of their apparent surface free energy, i.e. with the decreasing roughness the apparent surface free energy also decreases. However, this is not the case for mixed DOPC/SM monolayers. Although the roughness increases with SM content the apparent surface free energy decreases. Therefore some other factors, like the presence of unsaturated bonds in the DOPC molecule, influence the film phase state and the energy too. More experiments are needed to explain this hypothesis.

The Evaluation of Antioxidant Interactions among 4 Common Vegetables using Isobolographic Analysis

Isobolographic analysis was used to assess the antioxidant interactions (synergism, addition, and antagonism) of 4 common vegetables (tomato [T], carrot [C], eggplant [E], and purple potato [P]). The lipophilic (L) extracts of T and C (main carotenoids), the hydrophilic (H) extracts of E and P (main phenolics) were mixed by the certain ratios (1:9, 3:7, 1:1, 7:3, 9:1, w/w) and their antioxidant activities were investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radical scavenging assays, respectively. Most of the binary mixtures (LC-HE, LC-HP, HE-HP, LT-HE, and LT-HP combinations) showed the synergistic antioxidant effects. In DPPH assay, the greatest antioxidant activity of vegetable combinations was 1:9 LT-HP (EC50 : 2.45 ± 0.13 mg/mL), followed by 9:1 HE-HP (EC50 : 3.62 ± 0.12 mg/mL) and 1:9 LC-HE (EC50 : 3.74 ± 0.47 mg/mL). In ABTS assay, the greatest antioxidant activity of vegetable combinations was 9:1 HE-HP (EC50 : 4.20 ± 0.10 mg/mL), followed by 7:3 HE-HP (EC50 : 4.41 ± 0.63 mg/mL) and 1:1 HE-HP (EC50 : 5.35 ± 0.85 mg/mL). Among these combinations, 1:1 LC-HE combination showed the highest synergistic antioxidant effects in DPPH assay (synergistic rate: 87.4%), and 7:3 LC-HE combination showed the highest synergistic antioxidant effects in ABTS assay (synergistic rate: 87.0%). The mixtures of phenolics and carotenoids with suitable ratios in vegetables effectively enhanced the synergistic antioxidant effects.

Modifiers of membrane dipole potentials as tools for investigating ion channel formation and functioning

Electrostatic fields generated on and within biological membranes play a fundamental role in key processes in cell functions. The role of the membrane dipole potential is of particular interest because of its powerful impact on membrane permeability and lipid-protein interactions, including protein insertion, oligomerization, and function. The membrane dipole potential is defined by the orientation of electric dipoles of lipid headgroups, fatty acid carbonyl groups, and membrane-adsorbed water. As a result, the membrane interior is several hundred millivolts more positive than the external aqueous phase. This potential decrease depends on the lipid, and especially sterol, composition of the membrane. The adsorption of certain electroneutral molecules known as dipole modifiers may also lead to significant changes in the magnitude of the potential decrease. These agents are widely used to study the effects of the dipole potential on membrane transport. This review presents a critical analysis of a variety of data from studies dedicated to ion channel formation and functioning in membranes with different dipole potentials. The types of ion channels found in cellular membranes and pores formed by antimicrobial agents and toxins in artificial lipid membranes are summarized. The mechanisms underlying the influence of the membrane dipole potential on ion channel activity, including dipole-dipole and charge-dipole interactions in the pores and in membranes, are discussed. A hypothesis, in which lipid rafts in both model and cellular membranes also modulate ion channel activity by virtue of an increased or decreased dipole potential, is also considered.

Influence of resveratrol and dihydroquercetin inclusion into phospholipid nanopatricles on their bioavailability and specific activity

The effects of natural polyphenols, resveratrol (RES) and dihydroquercetin (DHQ), included in phospholipid nanoparticles, have been compared with free substances of RES and DHQ in in vitro and in vivo experiments. Preincubation of healthy donor plasma low density lipoproteins (LDL) with RES or DHQ included in phospholipid nanoparticles caused a more pronounced decrease in Cu2+ induced lipid oxidation compared with the free substances, and reduced the formation of lipid peroxides products. Bioavailabilities of RES and DHQ in phospholipid formulations after oral administration in rats were increased by 1.5-2 times. In an acute hypoxia model in mice prophylactic two-week administration of RES or DHQ phospholipid formulations resulted in 25% increase in survival and 1.5-fold increase in catalase activity in brain homogenates compared to free substances. Using the model of endothelial dysfunction in rats induced by L-NAME it was shown, that RES markedly attenuated the inhibition effect of L-NAME on NO synthesis. RES in phospholipid nanoparticles had the same action at a dose 10 times lower compared to free RES. Load test with resistance (clamping of the ascending aorta for 30 sec) showed that phospholipid formulation of RES possessed more pronounced protective effect due to the stimulation of endothelial NO-synthase.

Influence of membrane lipid composition on flavonoid-membrane interactions: Implications on their biological activity

The membrane interactions and localization of flavonoids play a vital role in altering membrane-mediated cell signaling cascades as well as influence the pharmacological activities such as anti-tumour, anti-microbial and anti-oxidant properties of flavonoids. Various techniques have been used to investigate the membrane interaction of flavonoids. These include partition coefficient, fluorescence anisotropy, differential scanning calorimetry, NMR spectroscopy, electrophysiological methods and molecular dynamics simulations. Each technique will provide specific information about either alteration of membrane fluidity or localization of flavonoids within the lipid bilayer. Apart from the diverse techniques employed, the concentrations of flavonoids and lipid membrane composition employed in various studies reported in literature also are different and together these variables contribute to diverse findings that sometimes contradict each other. This review highlights different techniques employed to investigate the membrane interaction of flavonoids with special emphasis on erythrocyte model membrane systems and their significance in understanding the nature and extent of flavonoid-membrane interactions. We also attempt to correlate the membrane localization and alteration in membrane fluidity with the biological activities of flavonoids such as anti-oxidant, anti-cancer and anti-microbial properties.

Polyphenols and the modulation of gene expression pathways: can we eat our way out of the danger of chronic disease?

Plant-derived dietary polyphenols may improve some disease states and promote health. Experimental evidence suggests that this is partially attributable to changes in gene expression. The rational use of bioactive food components may therefore present an opportunity to activate or repress selected gene expression pathways and, consequently, to manage or prevent disease. It remains to be determined whether this use of bioactive food components can be done safely. This article reviews the associated controversies and limitations of polyphenol therapy. There is a paucity of clinical data on the rational use of polyphenols, including a lack of knowledge on effective dosage, actual chemical formulations, bioavailability, distribution in tissues, the effect of genetic variations, differences in gut microflora, the synergistic (or antagonistic) effects observed in extracts, and the possible interaction between polyphenols and lipid domains of cell membranes that may alter the function of relevant receptors. The seminal question of why plants make substances that benefit humans remains unanswered, and there is still much to learn in terms of correlative versus causal effects of human exposure to various nutrients. The available data strongly suggest significant effects at the molecular level that represent interactions with the epigenome. The advent of relatively simple technologies is helping the field of epigenetics progress and facilitating the acquisition of multiple types of data that were previously difficult to obtain. In this review, we summarize the molecular basis of the epigenetic regulation of gene expression and the epigenetic changes associated with the consumption of polyphenols that illustrate how modifications in human nutrition may become relevant to health and disease.

Membrane dipole modifiers modulate single-length nystatin channels via reducing elastic stress in the vicinity of the lipid mouth of a pore

The polyene antifungal antibiotic nystatin confers its biological activity by forming pores in the membranes of target cells. Exposure of only one side of the membrane to nystatin is more relevant than two-side exposure because in vivo antibiotic molecules initially interact with cell membrane from the exterior side. The effect of flavonoids and styryl dyes on the steady-state conductance induced by a cis-side addition of nystatin was investigated by using electrophysiological measurements on artificial membranes. The assessment of changes in membrane dipole potential by dipole modifiers was carried out by their influence on K(+)-nonactin (K(+)-valinomycin) current. The alterations of the phase segregation scenario induced by nystatin and flavonoids were observed via confocal fluorescence microscopy. The introduction of phloretin, phlorizin, biochanin A, myricetin, quercetin, taxifolin, genistin, genistein, and RH 421 leads to a significant increase in the nystatin-induced steady-state transmembrane current through membranes composed of a mixture of DOPC, cholesterol and sphingomyelin (57:33:10 mol%). Conversely, daidzein, catechin, trihydroxyacetophenone, and RH 237 do not affect the transmembrane current. Three possible mechanisms that explain the observed results are discussed: changes in the membrane dipole potential, alterations of the phase separation within the lipid bilayer, and influences of the dipole modifiers on the formation of the lipid mouth of the polyene pore. Most likely, changes in the monolayer curvature in the vicinity of trans-mouth of a nystatin single-length channel prevail over alterations of dipole potential of membrane and the phase segregation scenarios induced by dipole modifiers.

Agomelatine strongly interacts with zwitterionic DPPC and charged DPPG membranes

Depression is one of the most common psychiatric diseases in the population. Agomelatine is a novel antidepressant drug with melatonin receptor agonistic and serotonin 5-HT2C antagonistic properties. Furthermore, being a melatonergic drug, agomelatine has the potential of being used in therapeutic applications like melatonin as an antioxidant, anti-inflammatory and antiapoptotic drug. The action mechanism of agomelatine on the membrane structure has not been clarified yet. In the present study, we aimed to investigate the interaction of agomelatine with model membranes of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylgylcerol (DPPG) by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). We found that agomelatine interacts with the head group in such a manner that it destabilizes the membrane architecture to a large extent. Thus, agomelatine causes alterations in the order, packing and dynamics of the DPPC and DPPG model membranes. Our results suggest that agomelatine strongly interacts with zwitterionic and charged membrane phospholipids. Because lipid structure and dynamics may have influence on the structure of membrane bound proteins and affect the signal transduction systems of membranes, these effects of agomelatine may be important in its action mechanism.

Channel-forming activity of cecropins in lipid bilayers: effect of agents modifying the membrane dipole potential

Cecropin A (CecA) and cecropin B (CecB) added to one side of a bilayer formed from equimolar mixtures of DOPS and DOPE, DPhPS and DPhPE, or DOPS, DOPE, and Chol leads to the formation of well-defined and well-reproducible ion channels of different conductance levels while cecropin P1 (CecP1) does not induce pore formation at micromolar concentrations. We found three populations of CecA channels: pores with weak cationic selectivity, pores with weak anionic selectivity, and pores that were nonselective. The dipole modifiers, flavonoids and styryl dyes, were used to modulate the channel-forming activity of CecA and CecB. The mean conductance of single CecA channels is affected by the influence of dipole modifiers on the lipid packing in the membrane. A decrease in the membrane dipole potential is accompanied by a decrease in the steady-state transmembrane current induced by CecA and CecB in cholesterol-free and cholesterol-containing bilayers. The observed changes in the channel-forming activity might be caused by an increase in the energy barrier for the interfacial accumulation of cecropin monomers. This finding indicates that the negative pole of the cecropin dipole is inserted into the membrane.

Flavonoid-membrane interactions: involvement of flavonoid-metal complexes in raft signaling

Flavonoids are polyphenolic compounds produced by plants and delivered to the human body through food. Although the epidemiological analyses of large human populations did not reveal a simple correlation between flavonoid consumption and health, laboratory investigations and clinical trials clearly demonstrate the effectiveness of flavonoids in the prevention of cardiovascular, carcinogenic, neurodegenerative and immune diseases, as well as other diseases. At present, the abilities of flavonoids in the regulation of cell metabolism, gene expression, and protection against oxidative stress are well-known, although certain biophysical aspects of their functioning are not yet clear. Most flavonoids are poorly soluble in water and, similar to lipophilic compounds, have a tendency to accumulate in biological membranes, particularly in lipid rafts, where they can interact with different receptors and signal transducers and influence their functioning through modulation of the lipid-phase behavior. In this study, we discuss the enhancement in the lipophilicity and antioxidative activity of flavonoids after their complexation with transient metal cations. We hypothesize that flavonoid-metal complexes are involved in the formation of molecular assemblies due to the facilitation of membrane adhesion and fusion, protein-protein and protein-membrane binding, and other processes responsible for the regulation of cell metabolism and protection against environmental hazards.

Molecular promiscuity of plant polyphenols in the management of age-related diseases: far beyond their antioxidant properties

The use of plant-derived polyphenols for the management of diseases has been under debate in the last decades. Most studies have focused on the specific effects of polyphenols on particular targets, while ignoring their pleiotropic character. The multitargeted character of polyphenols, a plausible consequence of their molecular promiscuity, may suppose an opportunity to fight multifactorial diseases. Therefore, a wider perspective is urgently needed to elucidate whether their rational use as bioactive food components may be valid for the management of diseases. In this chapter, we discuss the most likely targets of polyphenols that may account for their salutary effects from a global perspective. Among these targets, the modulation of signalling and energy-sensitive pathways, oxidative stress and inflammation-related processes, mitochondrial functionality, epigenetic machinery, histone acetylation and membrane-dependent processes play central roles in polyphenols' mechanisms of action.Sufficient evidence on polyphenols has accumulated for them to be considered a serious option for the management of non-communicable diseases, such as cancer and obesity, as well as infectious diseases. The remaining unresolved issues that must be seriously addressed are their bioavailability, metabolite detection, specific molecular targets, interactions and toxicity. The Xenohormesis hypothesis, which postulates that polyphenols are the product of plant evolutive adaptation to stress and conferee their resistance to mammals, offers a reasonable explanation to justify the beneficial and non-toxic effects of plant mixtures, but do not fully meet expectations. Hence, future research must be supported by the use of complex polypharmacology approaches and synergic studies focused on the understanding of the pleiotropic effects of polyphenols. Revisiting polyphenol mechanisms of action with the help of these techniques may allow for the improvement of human health and wellness by using intelligent nutritional intervention.