The effects and mechanism of flavonoid-rePON1 interactions. Structure-activity relationship study

Role of Fisetin in Selected Malignant Neoplasms in Women

A promising therapeutic window and cost-effectiveness are just two of the potential advantages of using naturally derived drugs. Fisetin (3,3',4',7-tetrahydroxyflavone) is a natural flavonoid of the flavonol group, commonly found in fruit and vegetables. In recent years, fisetin has gained wide attention across the scientific community because of its broad spectrum of pharmacological properties, including cytotoxic activity against most abundant cancers. By stimulating or inhibiting selected molecular targets or biochemical processes, fisetin could affect the reduction of metastasis or cancer progression, which indicates its chemotherapeutic or chemopreventive role. In this review, we have summarized the results of studies on the anticancer effects of fisetin on selected female malignancies, both in in vitro and in vivo tests, i.e., breast, cervical, and ovarian cancer, published over the past two decades. Until now, no article dedicated exclusively to the action of fisetin on female malignancies has appeared. This review also describes a growing number of nanodelivery systems designed to improve the bioavailability and solubility of this natural compound. The reported low toxicity and activity of fisetin on cancer cells indicate its valuable potential, but large-scale clinical trials are urgently needed to assess real chemotherapeutic efficacy of this flavonoid.

Catechins and Proanthocyanidins Involvement in Metabolic Syndrome

Recent studies on natural antioxidant compounds have highlighted their potentiality against various pathological conditions. The present review aims to selectively evaluate the benefits of catechins and their polymeric structure on metabolic syndrome, a common disorder characterized by a cluster of three main risk factors: obesity, hypertension, and hyperglycemia. Patients with metabolic syndrome suffer chronic low inflammation state and oxidative stress both conditions effectively countered by flavanols and their polymers. The mechanism behind the activity of these molecules has been highlighted and correlated with the characteristic features present on their basic flavonoidic skelethon, as well as the efficient doses needed to perform their activity in both in vitro and in vivo studies. The amount of evidence provided in this review offers a starting point for flavanol dietary supplementation as a potential strategy to counteract several metabolic targets associated with metabolic syndrome and suggests a key role of albumin as flavanol-delivery system to the different target of action inside the organism.

Synthesis, enzyme inhibition, and molecular docking studies of a novel chalcone series bearing benzothiazole scaffold

This study reports the facile synthesis of a novel series of benzothiazole-chalcones, in addition to their inhibitory profile on important metabolic enzymes including human carbonic anhydrases (hCA-I, hCA-II) and paraoxonase (PON-1). The inhibition parameters, IC₅₀ (concentration for 50% inhibition) and Ki (dissociation constant) values, toward the title enzymes were determined for the studied compounds. As a result, IC₅₀ values of hydratase activity were in the range 4.15-5.47 and 2.56-4.58 μM for hCA-I and hCA-II, respectively. At the same time, IC₅₀ values of esterase activity were in the range 24.91-104.00 and 35.25-97.00 μM, while Ki values were in the range 14.43-59.66 and 26.65-73.34 μM for hCA-I and hCA-II, respectively. In addition, PON-1 enzyme inhibition results showed interesting inhibitory effects, with IC₅₀ values between 13.28 and 16.68 μM. Finally, a comprehensive approach was established for the synthesized compounds based on theoretical calculations, which have been done using B3LYP, PBE0 theories and SVP, TVZP, TVZPP basis sets, followed by docking studies by which the outputs proved the harmonically flows with the experimental results.

Destroying the Shield of Cancer Stem Cells: Natural Compounds as Promising Players in Cancer Therapy

In a scenario where eco-sustainability and a reduction in chemotherapeutic drug waste are certainly a prerogative to safeguard the biosphere, the use of natural products (NPs) represents an alternative therapeutic approach to counteract cancer diseases. The presence of a heterogeneous cancer stem cell (CSC) population within a tumor bulk is related to disease recurrence and therapy resistance. For this reason, CSC targeting presents a promising strategy for hampering cancer recurrence. Increasing evidence shows that NPs can inhibit crucial signaling pathways involved in the maintenance of CSC stemness and sensitize CSCs to standard chemotherapeutic treatments. Moreover, their limited toxicity and low costs for large-scale production could accelerate the use of NPs in clinical settings. In this review, we will summarize the most relevant studies regarding the effects of NPs derived from major natural sources, e.g., food, botanical, and marine species, on CSCs, elucidating their use in pre-clinical and clinical studies.

Halogenated Flavonoid Derivatives Display Antiangiogenic Activity

Antiangiogenic agents attenuate tumours' growth and metastases and are therefore beneficial as an adjuvant or standalone cancer regimen. Drugs with dual antiproliferative and antiangiogenic activities can achieve anticancer efficacy and overcome acquired resistance. In this study, synthetic flavones (5a,b) with reported anticancer activity, and derivatives (4b and 6a), exhibited significant inhibition of endothelial cell tube formation (40-55%, 12 h) at 1 µM, which is comparable to sunitinib (50% inhibition at 1 µM, 48 h). Flavones (4b, 5a,b and 6a) also showed 25-37% reduction in HUVECs migration at 10 µM. In a Western blotting assay, 5a and 5b subdued VEGFR2 phosphorylation by 37% and 57%, respectively, suggesting that VEGFR2 may be their main antiangiogenic target. 5b displayed the best docking fit with VEGFR2 in an in silico study, followed by 5a, emphasizing the importance of the 7-hydroxyl group accompanied by a 4-C=S for activity. Conversely, derivatives with a 4-carbonyl moiety fitted poorly into the target's binding pocket, suggesting that their antiangiogenic activity depends on a different target. This study provides valuable insight into the Structure Activity Relationships (SAR) and modes of action of halogenated flavones with VEGFR2 and highlights their therapeutic potential as antiangiogenic/anticancer lead compounds.

Hepatoprotective Effect of Bee Bread in Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD) Rats: Impact on Oxidative Stress and Inflammation

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a pathological accumulation of hepatic lipid closely linked with many metabolic disorders, oxidative stress and inflammation. We aimed to evaluate the hepatoprotective effect of bee bread on oxidative stress and inflammatory parameters in MAFLD rats. Twenty-eight male Sprague-Dawley rats were assigned into four groups (n = 7/group): normal control (NC), high-fat diet (HFD), bee bread (HFD + Bb, HFD + 0.5 g/kg/day bee bread) and orlistat (HFD + Or, HFD + 10 mg/kg/day orlistat) groups. After 12 weeks, the HFD group demonstrated significantly higher body weight gain, serum levels of lipids (TG, TC, LDL), liver enzymes (AST, ALT, ALP) and adiponectin, liver lipids (TG, TC) and insulin resistance (HOMA-IR). Furthermore, the HFD group showed significantly decreased antioxidant enzyme activities (GPx, GST, GR, SOD, CAT) and GSH level, and increased liver oxidative stress (TBARS, NO), translocation of Nrf2 to the nucleus, Keap1 expression and inflammation (TNF-α, NF-κβ, MCP-1) together with histopathological alterations (steatosis, hepatocyte hypertrophy, inflammatory cell infiltration, collagen deposition), which indicated the presence of non-alcoholic steatohepatitis (NASH) and fibrosis. Bee bread significantly attenuated all these changes exerted by HFD feeding. In conclusion, our results suggest that bee bread might have antioxidant, anti-inflammatory, anti-steatotic and anti-fibrotic effects that are beneficial in protecting liver progression towards NASH and fibrosis.

Natural Products Targeting Cancer Stem Cells for Augmenting Cancer Therapeutics

Cancer stem cells (CSC) have been identified in several types of solid tumors. In some cases, CSC may be the source of all the tumor cells, the cause of the tumor's resistance to chemotherapeutic agents, and the source of metastatic cells. Thus, a combination therapy targeting non-CSC tumor cells as well as specifically targeting CSCs holds the potential to be highly effective. Natural products (NPs) have been a historically rich source of biologically active compounds and are known for their ability to influence multiple signaling pathways simultaneously with negligible side effects. In this review, we discuss the potential of NPs in targeting multiple signaling pathways in CSC and their potential to augment the efficacy of standard cancer therapy. Specifically, we focus on the anti-CSC activities of flavonoids, FDA-approved drugs originating from natural sources. Additionally, we emphasize the potential of NPs in targeting microRNA-mediated signaling, given the roles of microRNA in the maintenance of the CSC phenotype.

Protein Adducts and Protein Oxidation as Molecular Mechanisms of Flavonoid Bioactivity

There are tens of thousands of scientific papers about flavonoids and their impacts on human health. However, despite the vast amount of energy that has been put toward studying these compounds, a unified molecular mechanism that explains their bioactivity remains elusive. One contributing factor to the absence of a general mechanistic explanation of their bioactivity is the complexity of flavonoid chemistry in aqueous solutions at neutral pH. Flavonoids have acidic protons, are redox active, and frequently auto-oxidize to produce an array of degradation products including electrophilic quinones. Flavonoids are also known to interact with specificity and high affinity with a variety of proteins, and there is evidence that some of these interactions may be covalent. This review summarizes the mechanisms of flavonoid oxidation in aqueous solutions at neutral pH and proposes the formation of protein-flavonoid adducts or flavonoid-induced protein oxidation as putative mechanisms of flavonoid bioactivity in cells. Nucleophilic residues in proteins may be able to form covalent bonds with flavonoid quinones; alternatively, specific amino acid residues such as cysteine, methionine, or tyrosine in proteins could be oxidized by flavonoids. In either case, these protein-flavonoid interactions would likely occur at specific binding sites and the formation of these types of products could effectively explain how flavonoids modify proteins in cells to induce downstream biochemical and cellular changes.

An Untargeted Metabolomics Approach for Correlating Pulse Crop Seed Coat Polyphenol Profiles with Antioxidant Capacity and Iron Chelation Ability

Pulse crop seed coats are a sustainable source of antioxidant polyphenols, but are typically treated as low-value products, partly because some polyphenols reduce iron bioavailability in humans. This study correlates antioxidant/iron chelation capabilities of diverse seed coat types from five major pulse crops (common bean, lentil, pea, chickpea and faba bean) with polyphenol composition using mass spectrometry. Untargeted metabolomics was used to identify key differences and a hierarchical analysis revealed that common beans had the most diverse polyphenol profiles among these pulse crops. The highest antioxidant capacities were found in seed coats of black bean and all tannin lentils, followed by maple pea, however, tannin lentils showed much lower iron chelation among these seed coats. Thus, tannin lentils are more desirable sources as natural antioxidants in food applications, whereas black bean and maple pea are more suitable sources for industrial applications. Regardless of pulse crop, proanthocyanidins were primary contributors to antioxidant capacity, and to a lesser extent, anthocyanins and flavan-3-ols, whereas glycosylated flavonols contributed minimally. Higher iron chelation was primarily attributed to proanthocyanidin composition, and also myricetin 3-O-glucoside in black bean. Seed coats having proanthocyanidins that are primarily prodelphinidins show higher iron chelation compared with those containing procyanidins and/or propelargonidins.

Flavonoids-Macromolecules Interactions in Human Diseases with Focus on Alzheimer, Atherosclerosis and Cancer

Flavonoids, a class of polyphenols, consumed daily in our diet, are associated with a reduced risk for oxidative stress (OS)-related chronic diseases, such as cardiovascular disease, neurodegenerative diseases, cancer, and inflammation. The involvement of flavonoids with OS-related chronic diseases have been traditionally attributed to their antioxidant activity. However, evidence from recent studies indicate that flavonoids' beneficial impact may be assigned to their interaction with cellular macromolecules, rather than exerting a direct antioxidant effect. This review provides an overview of the recent evolving research on interactions between the flavonoids and lipoproteins, proteins, chromatin, DNA, and cell-signaling molecules that are involved in the OS-related chronic diseases; it focuses on the mechanisms by which flavonoids attenuate the development of the aforementioned chronic diseases via direct and indirect effects on gene expression and cellular functions. The current review summarizes data from the literature and from our recent research and then compares specific flavonoids' interactions with their targets, focusing on flavonoid structure-activity relationships. In addition, the various methods of evaluating flavonoid-protein and flavonoid-DNA interactions are presented. Our aim is to shed light on flavonoids action in the body, beyond their well-established, direct antioxidant activity, and to provide insights into the mechanisms by which these small molecules, consumed daily, influence cellular functions.

Antiangiogenic Activity of Flavonoids: A Systematic Review and Meta-Analysis

Abstract: An imbalance of angiogenesis contributes to many pathologies such as cancer, arthritis and retinopathy, hence molecules that can modulate angiogenesis are of considerable therapeutic importance. Despite many reports on the promising antiangiogenic properties of naturally occurring flavonoids, no flavonoids have progressed to the clinic for this application. This systematic review and meta-analysis therefore evaluates the antiangiogenic activities of a wide range of flavonoids and is presented in two sections. The first part of the study (Systematic overview) included 402 articles identified by searching articles published before May 2020 using ScienceDirect, PubMed and Web of Science databases. From this initial search, different classes of flavonoids with antiangiogenic activities, related pathologies and use of in vitro and/or in/ex vivo angiogenesis assays were identified. In the second part (Meta-analysis), 25 studies concerning the antiangiogenic evaluation of flavonoids using the in vivo chick chorioallantoic membrane (CAM) assay were included, following a targeted search on articles published prior to June 2020. Meta-analysis of 15 out of the 25 eligible studies showed concentration dependent antiangiogenic activity of six compared subclasses of flavonoids with isoflavones, flavonols and flavones being the most active (64 to 80% reduction of blood vessels at 100 µM). Furthermore, the key structural features required for the antiangiogenic activity of flavonoids were derived from the pooled data in a structure activity relationship (SAR) study. All in all, flavonoids are promising candidates for the development of antiangiogenic agents, however further investigations are needed to determine the key structural features responsible for their activity.

Effects of Moringa oleifera Leaf Extract on Diabetes-Induced Alterations in Paraoxonase 1 and Catalase in Rats Analyzed through Progress Kinetic and Blind Docking

In our study, we aimed to evaluate the effects of Moringa oleifera leaves extract on rat paraoxonase 1 (rPON1) and catalase (rCAT) activities in alloxan-induced diabetic rats. Our study included three groups; group C (control, n = 5); group D (diabetic, n = 5); and group DM (M. oleifera extract-supplemented diabetic rats, n = 5). Daily oral administration of M. oleifera extract at 200 mg/kg doses produced an increase in endogenous antioxidants. Serum rPON1 (lactonase) and liver cytosol catalase activities were determined by a spectrophotometric assay using progress curve analysis. We found a decrease in the Vm value of rPON1 in diabetic rats, but dihydrocoumarin (DHC) affinity (Km) was slightly increased. The value of Vm for the DM group was found to be reduced approximately by a factor of 3 compared with those obtained for group C, whereas Km was largely changed (96 times). Catalase activity was significantly higher in the DM group. These data suggest that the activation of rPON1 and rCAT activities by M. oleifera extracts may be mediated via the effect of the specific flavonoids on the enzyme structure. In addition, through molecular blind docking analysis, rPON1 was found to have two binding sites for flavonoids. In contrast, flavonoids bound at four sites in rCAT. In conclusion, the data suggest that compounds from M. oleifera leaves extract were able to influence the catalytic activities of both enzymes to compensate for the changes provoked by diabetes in rats.

Flavonoids Restore Platinum Drug Sensitivity to Ovarian Carcinoma Cells in a Phospho-ERK1/2-Dependent Fashion

Ovarian cancer (OC) is the second most common type of gynecological malignancy; it has poor survival rates and is frequently (>75%) diagnosed at an advanced stage. Platinum-based chemotherapy, with, e.g., carboplatin, is the standard of care for OC, but toxicity and acquired resistance to therapy have proven challenging. Despite advances in OC diagnosis and treatment, approximately 85% of patients will experience relapse, mainly due to chemoresistance. The latter is attributed to alterations in the cancer cells and is also mediated by tumor microenvironment (TME). Recently, we reported the synthesis of a platinum (IV) prodrug that exhibits equal potency toward platinum-sensitive and resistant OC cell lines. Here, we investigated the effect of TME on platinum sensitivity. Co-culture of OC cells with murine or human mesenchymal stem cells (MS-5 and HS-5, respectively) rendered them resistant to chemotherapeutic agents, including platinum, paclitaxel and colchicine. Platinum resistance was also conferred by co-culture with differentiated murine adipocyte progenitor cells. Exposure of OC cells to chemotherapeutic agents resulted in activation of phospho-ERK1/2. Co-culture with MS-5, which conferred drug resistance, was accompanied by blockage of phospho-ERK1/2 activation. The flavonoids fisetin and quercetin were active in restoring ERK phosphorylation, as well as sensitivity to platinum compounds. Exposure of OC cells to cobimetinib-a MEK1 inhibitor that also inhibits extracellular signal-regulated kinase (ERK) phosphorylation-which resulted in reduced sensitivity to the platinum compound. This suggests that ERK activity is involved in mediating the function of flavonoids in restoring platinum sensitivity to OC co-cultured with cellular components of the TME. Our data show the potential of combining flavonoids with standard therapy to restore drug sensitivity to OC cells and overcome TME-mediated platinum drug resistance.

Lyso-diacylglyceryltrimethylhomoserine (lyso-DGTS) isolated from Nannochloropsis microalgae improves high-density lipoprotein (HDL) functions

Many population studies have shown that blood concentrations of high-density lipoprotein (HDL) cholesterol are inversely correlated with risk of cardiovascular disease (CVD). However, in recent studies, increasing blood HDL cholesterol concentrations failed to reduce CVD events. On the other hand, studies suggest that improving HDL quality can be a more efficient tool for assessing atherosclerotic risk than simply measuring blood HDL cholesterol concentration. Thus, improving HDL activity using natural substances might be a useful therapeutic approach to reducing CVD risk. We previously isolated a novel active compound from Nannochloropsis microalgae termed lyso-diacylglyceryltrimethylhomoserine (lyso-DGTS), which increased activity of paraoxonase 1, the main antioxidant enzyme associated with HDL. Here we examined the effect of lyso-DGTS on HDL quality and function. Tryptophan-fluorescence-quenching assay showed that lyso-DGTS interacts spontaneously with the entire HDL lipoprotein and with apolipoprotein A1 (ApoA1), the major structural and functional HDL protein, with high affinity (K_a = 2.17 × 10⁴  M^-1 at 37°C). Lyso-DGTS added to HDL and to ApoA1 increased cholesterol efflux from macrophage cells, the main antiatherogenic function of HDL, dose-dependently, and significantly increased HDL's ability to induce nitric oxide production from endothelial cells. In-vivo supplementation of lyso-DGTS to the circulation of mice fed a high-fat diet via osmotic mini-pumps implanted subcutaneously enhanced HDL anti-inflammatory effect significantly as compared to controls. Our findings suggest that lyso-DGTS may have a beneficial effect in decreasing atherosclerosis risk by interacting with HDL particles and improving their quality and antiatherogenic functions.

Genome-wide localization of the polyphenol quercetin in human monocytes

BACKGROUND

Quercetin is a polyphenol of great interest given its antioxidant activity and involvement in the immune response. Although quercetin has been well studied at the molecular level as a gene regulator and an activator of specific cellular pathways, not much attention has been given to its mechanism of action at the genome-wide level. The present study aims to characterize quercetin's interaction with cellular DNA and to show its subsequent effect on downstream transcription.

RESULTS

Two massive parallel DNA-sequencing technologies were used: Chem-seq and RNA-seq. We demonstrate that upon binding to DNA or genome-associated proteins, quercetin acts as a cis-regulatory transcription factor for the expression of genes that are involved in the cell cycle, differentiation and development.

CONCLUSIONS

Such findings could provide new and important insights into the mechanisms by which the dietary polyphenol quercetin influences cellular functions.

Inhibition of VEGFR-2 Phosphorylation and Effects on Downstream Signaling Pathways in Cultivated Human Endothelial Cells by Stilbenes from Vitis Spp

Stilbenes are phenolic compounds present in different higher plant families that have shown different biological activities, such as antioxidant properties and antitumoral and anti-atherosclerotic effects, among others. Angiogenesis is a key process involved in both cancer and cardiovascular diseases, the vascular endothelial growth factor (VEGF) and its receptor VEGFR-2 being the main triggers. Certain polyphenol compounds, such as flavonoids, have shown a potent capacity to inhibit VEGF and, consequently, angiogenesis. The present work, therefore, aims to evaluate the potential effect of stilbenes on inhibiting VEGF and their subsequent effect on the downstream signaling pathway (PLCγ1, Akt, and eNOS). VEGFR-2 activation was studied through an ELISA assay in the HUVEC line, while the phosphorylation of intracellular downstream proteins PLCγ1, Akt, and eNOS was tested by Western blot. Student's t test was used to determine significant differences between samples. On the one hand, astringin, pallidol, and ω-viniferin showed the lowest IC₅₀ values (2.90 ± 0.27, 4.42 ± 0.67, and 6.10 ± 1.29 μM, respectively) against VEGFR-2 activation. Additionally, VEGF-induced PLCγ1 phosphorylation was significantly inhibited by ε-viniferin, astringin, and ω-viniferin. However, ε-viniferin and pallidol simultaneously enhanced eNOS activation, proving to be via Akt activation in the case of ε-viniferin. For the first time, these data suggest that stilbenes such as astringin, pallidol, ω-viniferin, and ε-viniferin have a potential anti-angiogenic effect and they could be further considered as anti-VEGF ingredients in food and beverages. In addition, ε-viniferin and pallidol significantly allowed eNOS activation and could likely prevent the side effects caused by anti-VEGF hypertension drugs.

Structural Determination of Antioxidant and Anticancer Flavonoid Rutin in Solution through DFT Calculations of 1H NMR Chemical Shifts

As the knowledge of the predominant molecular structure of antioxidant and anticancer flavonoid rutin in solution is very important for understanding the mechanism of action, a quantum chemical investigation of plausible rutin structures including solvent effects is of relevance. In this work, DFT calculations were performed to find possible minimum energy structures for the rutin molecule. ¹H NMR chemical shift DFT calculations were carried out in DMSO solution using the polarizable continuum model (PCM) to simulate the solvent effect. Analysis of the experimental and theoretical ¹H NMR chemical shift profiles offers a powerful fingerprint criterion to determine the predominant molecular structure in solution. Therefore, our aim is to find the best match between experimental (in DMSO‐d) and theoretical (PCM–DMSO) ¹H NMR spectrum profiles. Among 34 optimized structures located on the potential energy surface, we found that structure 32, with a B‐ring deviated 30° from a planar configuration (geometry usually assumed for polyphenols), showed an almost perfect agreement with experimental the ¹H NMR pattern when compared to the corresponding fully optimized planar geometry. This structure is also predicted as the global minimum based on room‐temperature Gibbs free energy calculations in solution and, therefore, should be experimentally observed. This is new and valuable structural information regarding structure–activity relationship studies, and such information is hard to obtain by experimentalists without the aid of the X‐ray diffraction technique.

Punicalagin Decreases Serum Glucose Levels and Increases PON1 Activity and HDL Anti-Inflammatory Values in Balb/c Mice Fed a High-Fat Diet

Polyphenols are consumed daily in the human diet and are associated with reduced risk of a number of chronic diseases, including cancer, cardiovascular disease, and diabetes. Traditionally, the health benefits of polyphenols have been attributed to their antioxidant activity, but many studies might be hampered by oral administration and insignificant bioavailability. Rather than exerting a direct antioxidant effect, the mechanisms by which polyphenols express their beneficial effect seem to involve their interaction with proteins. The present study is aimed at broadening and confirming our recently published in vitro results showing that polyphenols may reduce atherosclerosis risk via interaction with proteins and lipoproteins related to atherosclerosis. The biological functions of punicalagin and quercetin in relation to glucose and lipid levels, paraoxonase 1 (PON1) activity, and inflammation were examined in vivo. Mice were fed a high-fat diet (HFD) for 12 weeks, and during the last 4 weeks, they received subcutaneous treatments via implanted minipumps, which released physiological concentrations of punicalagin, quercetin, or atorvastatin (as a positive control) daily into the serum. The HFD reduced serum PON1 activity, whereas punicalagin administration restored PON1 activity to the level of mice fed a normal diet. In addition, punicalagin significantly reduced glucose levels in HFD mice and improved HDL anti-inflammatory properties. In conclusion, beyond antioxidant activity, the mechanisms by which polyphenols exert their beneficial properties appear to involve their interaction with serum proteins that mediate HDL function and lipid-glucose state in the circulation.

Lyso-DGTS lipid isolated from microalgae enhances PON1 activities in vitro and in vivo, increases PON1 penetration into macrophages and decreases cellular lipid accumulation

High-density lipoprotein (HDL) plays an important role in preventing atherosclerosis. The antioxidant effect of HDL is mostly associated with paraoxonase 1 (PON1) activity. Increasing PON1 activity using nutrients might improve HDL function and quality and thus, decrease atherosclerotic risk. We previously isolated and identified a novel active compound, lyso-DGTS (C20:5,0) from Nannochloropsis sp. ethanol extract. In the present study, its effect on PON1 activities was examined and the mechanism by which the compound affects PON1 activity was explored. Lyso-DGTS elevated recombinant PON1 (rePON1) lactonase and esterase activities in a dose- and time-responsive manner, and further stabilized and preserved rePON1 lactonase activity. Incubation of lyso-DGTS with human serum for 4 h at 37 °C also increased PON1 lactonase activity in a dose-responsive manner. Using tryptophan-fluorescence-quenching assay, lyso-DGTS was found to interact with rePON1 spontaneously with negative free energy (ΔG = -22.87 kJ mol^-1 at 25 °C). Thermodynamic parameters and molecular modeling calculations showed that the main interaction of lyso-DGTS with the enzyme is through a hydrogen bond with supporting van der Waals interactions. Furthermore, lyso-DGTS significantly increased rePON1 influx into macrophages and prevented lipid accumulation in macrophages stimulated with oxidized low-density lipid dose-dependently. In vivo supplementation of lyso-DGTS to the circulation of mice fed a high-fat diet via osmotic mini-pumps implanted subcutaneously significantly increased serum PON1 lactonase activity and decreased serum glucose concentrations to the level of mice fed a normal diet. Our findings suggest a beneficial effect of lyso-DGTS on increasing PON1 activity and thus, improving HDL quality and atherosclerotic risk factors. © 2018 BioFactors, 44(3):299-310, 2018.

Bioactive flavonoids in medicinal plants: Structure, activity and biological fate

Flavonoids, a class of polyphenol secondary metabolites, are presented broadly in plants and diets. They are believed to have various bioactive effects including anti-viral, anti-inflammatory, cardioprotective, anti-diabetic, anti-cancer, anti-aging, etc. Their basic structures consist of C₆-C₃-C₆ rings with different substitution patterns to produce a series of subclass compounds, and correlations between chemical structures and bioactivities have been studied before. Given their poor bioavailability, however, information about associations between structure and biological fate is limited and urgently needed. This review therefore attempts to bring some order into relationships between structure, activity as well as pharmacokinetics of bioactive flavonoids.

Punicalagin Induces Serum Low-Density Lipoprotein Influx to Macrophages

High levels of circulating low-density lipoprotein (LDL) are a primary initiating event in the development of atherosclerosis. Recently, the antiatherogenic effect of polyphenols has been shown to be exerted via a mechanism unrelated to their antioxidant capacity and to stem from their interaction with specific intracellular or plasma proteins. In this study, we investigated the interaction of the main polyphenol in pomegranate, punicalagin, with apolipoprotein B-100 (ApoB100) that surrounds LDL. Punicalagin bound to ApoB100 at low concentrations (0.25–4 μM). Upon binding, it induced LDL influx to macrophages in a concentration-dependent manner, up to 2.5-fold. In contrast, another polyphenol which binds to ApoB100, glabridin, did not affect LDL influx. We further showed that LDL influx occurs specifically through the LDL receptor, with LDL then accumulating in the cell cytoplasm. Taken together with the findings of Aviram et al., 2000, that pomegranate juice and punicalagin induce plasma LDL removal and inhibit macrophage cholesterol synthesis and accumulation, our results suggest that, upon binding, punicalagin stimulates LDL influx to macrophages, thus reducing circulating cholesterol levels.

Molecular structure-function relationship of dietary polyphenols for inhibiting VEGF-induced VEGFR-2 activity

Scope

We recently reported potent inhibition of VEGF signalling by two flavanols at sub‐micromolar concentrations, mediated by direct binding of the flavanols to VEGF. The aim of this study was to quantify the inhibitory potency and binding affinity of a wide range of dietary polyphenols and determine the structural requirements for VEGF inhibition.

Methods and results

The concentration of polyphenol required to cause 50% inhibition (IC₅₀) of VEGF‐dependent VEGFR‐2 activation in HUVECS was determined after pretreating VEGF with polyphenols at various concentations. Binding affinities and binding sites on VEGF were predicted using in‐silico modelling. Ellagic acid and 15 flavonoids had IC₅₀ values ≤10 μM while 28 other polyhenols were weak/non‐inhibitors. Structural features associated with potent inhibition included 3‐galloylation, C‐ring C2=C3, total OH, B‐ring catechol, C‐ring 3‐OH of flavonoids. Potency was not associated with polyphenol hydrophobicity. There was a strong correlation between potency of inhibition and binding affinities, and all polyphenols were predicted to bind to a region on VEGF involved in VEGFR‐2 binding.

Conclusion

Specific polyphenols bind directly to a discrete region of VEGF and inhibit VEGF signalling, and this potentially explains the associations between consumption of these polyphenols and CVD risk.

Anti-atherogenic properties of date vs. pomegranate polyphenols: the benefits of the combination

MPM cholesterol content was not significantly affected by consumption of PJ or date seed extract alone. In contrast, consumption of Hallawi date fruit extract or a combination of PJ together with date fruit and date seeds extract significantly decreased macrophage cholesterol content by 12% or 28%, respectively.

Quercetin and quercetin-3-O-glucoside interact with different components of the cAMP signaling cascade in human retinal pigment epithelial cells

AIMS

The ability of the plant flavonol quercetin and its conjugated form quercetin-3-glucoside, compared to that of the anthocyanin cyanidin-3-glucoside, to interfere with 3',5'-cyclic adenosine monophosphate (cAMP) efflux was investigated in cultured human retinal pigment epithelial (HRPE) cells.

MAIN METHODS

HRPE cells were stimulated for a time course with 1 μM adrenaline, in the presence and absence of increasing concentrations of anthocyanins or flavonols, then intracellular and extracellular cAMP levels obtained from whole cells and cAMP synthetized by the activity of adenylate cyclase in cell membrane fractions were determined by radiochemical assay.

KEY FINDINGS

The treatment with either compound caused a significant lowering in extracellular cAMP concentrations deriving from a time course cell stimulation with 1 μM epinephrine. As to quercetin, the effect was shown to rely on the inhibition of cAMP efflux transporters. In the case of the glycoside, it was found to depend on the contrary on a reduction in the extent of epinephrine stimulation. Consistently, quercetin-3-glucoside inhibited the epinephrine-stimulated activity of adenylyl cyclase in membrane preparations, while quercetin was ineffective. The anthocyanin cyanidin-3-glucoside exerted similar effects as quercetin-3-glucoside.

SIGNIFICANCE

Results strengthen the diverse effect of the glucosides versus the corresponding aglycones. Since differently from flavonols, anthocyanins are present in human plasma in their glycosylated form, the aglycone or glycoside forms of these plant secondary metabolites might therefore be utilized as synergistic regulators of cAMP homeostasis for therapeutical purposes.

HDL3 stimulates paraoxonase 1 antiatherogenic catalytic and biological activities in a macrophage model system: in vivo and in vitro studies

We analyzed in-vivo and in-vitro high density lipoprotein (HDL) effects on paraoxonase 1 (PON1) antiatherogenic properties in serum and in macrophages. Intraperitoneal injection to C57BL/6 mice of recombinant PON1 (rePON1) + HDL, in comparison to HDL or to rePON1 alone, significantly increased serum PON1 arylesterase activity (by 20%), and serum-mediated cholesterol efflux from J774A.1 macrophages (by 18%). Similarly, in peritoneal macrophages (MPM) harvested from mice injected with HDL + rePON1 versus rePON1 alone, we observed reduction in oxidative stress (by 11%), increase in cellular PON1 activity (by 14%) and in HDL-mediated cholesterol efflux (by 38%). Incubation of serum or HDL with rePON1, substantially increased PON1 arylesterase activity, two-fold more than the expected additive values. HDL2 and HDL3 increased PON1 activity by 199% or 274%, respectively. Macrophage (J774A.1) cholesterol efflux rate significantly increased by HDL3 + rePON1 versus HDL3 alone (by 19%), but not by HDL2 + rePON1 versus HDL2 alone. Oxidation of HDL3 reduced its ability to induce macrophage cholesterol efflux, and abolished HDL3 stimulatory effects on rePON1. Addition of exogenous polyphenol quercetin (60 µM), but not phosphatidylcholine or apolipoprotein A1, to HDL + rePON1 increased PON1 activity (by 404%), increased the ability to reduce oxidative stress in J774A.1 macrophages (by 53%) and to stimulate macrophage cholesterol efflux (by 14%). Upon adding the hypocholesterolemic drug simvastatin (15 µg/mL) to HDL + rePON1, PON1 activity and the ability to induce macrophage cholesterol efflux increased, in comparison to HDL + rePON1. We thus concluded that HDL (mostly HDL3), stimulates PON1 antiatherogenic activities in macrophages, and these PON1 activities were further stimulated by quercetin, or by simvastatin.

HDL and cognition in neurodegenerative disorders

High-density lipoproteins (HDLs) are a heterogeneous group of lipoproteins composed of various lipids and proteins. HDL is formed both in the systemic circulation and in the brain. In addition to being a crucial player in the reverse cholesterol transport pathway, HDL possesses a wide range of other functions including anti-oxidation, anti-inflammation, pro-endothelial function, anti-thrombosis, and modulation of immune function. It has been firmly established that high plasma levels of HDL protect against cardiovascular disease. Accumulating evidence indicates that the beneficial role of HDL extends to many other systems including the central nervous system. Cognition is a complex brain function that includes all aspects of perception, thought, and memory. Cognitive function often declines during aging and this decline manifests as cognitive impairment/dementia in age-related and progressive neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. A growing concern is that no effective therapy is currently available to prevent or treat these devastating diseases. Emerging evidence suggests that HDL may play a pivotal role in preserving cognitive function under normal and pathological conditions. This review attempts to summarize recent genetic, clinical and experimental evidence for the impact of HDL on cognition in aging and in neurodegenerative disorders as well as the potential of HDL-enhancing approaches to improve cognitive function.

Oxidative stress and antioxidant status in beta-thalassemia heterozygotes

BACKGROUND

Several studies have evaluated the oxidant and antioxidant status of thalassemia patients but most focused mainly on the severe and intermediate states of the disease. Moreover, the oxidative status has not been evaluated for the different beta-thalassemia mutations.

OBJECTIVE

To evaluate lipid peroxidation and Trolox equivalent antioxidant capacity in relation to serum iron and ferritin in beta thalassemia resulting from two different mutations (CD39 and IVS-I-110) compared to individuals without beta-thalassemia.

METHODS

One hundred and thirty subjects were studied, including 49 who were heterozygous for beta-thalassemia and 81 controls. Blood samples were subjected to screening tests for hemoglobin. Allele-specific polymerase chain reaction was used to confirm mutations for beta-thalassemia, an analysis of thiobarbituric acid reactive species was used to determine lipid peroxidation, and Trolox equivalent antioxidant capacity evaluations were performed. The heterozygous beta-thalassemia group was also evaluated for serum iron and ferritin status.

RESULTS

Thiobarbituric acid reactive species (486.24 ± 119.64 ng/mL) and Trolox equivalent antioxidant capacity values (2.23 ± 0.11 mM/L) were higher in beta-thalassemia heterozygotes compared to controls (260.86 ± 92.40 ng/mL and 2.12 ± 0.10 mM/L, respectively; p-value < 0.01). Increased thiobarbituric acid reactive species values were observed in subjects with the CD39 mutation compared with those with the IVS-I-110 mutation (529.94 ± 115.60 ng/mL and 453.39 ± 121.10 ng/mL, respectively; p-value = 0.04). However, average Trolox equivalent antioxidant capacity values were similar for both mutations (2.20 ± 0.08 mM/L and 2.23 ± 0.12 mM/L, respectively; p-value = 0.39). There was no influence of serum iron and ferritin levels on thiobarbituric acid reactive species and Trolox equivalent antioxidant capacity values.

CONCLUSION

This study shows an increase of oxidative stress and antioxidant capacity in beta-thalassemia heterozygotes, mainly in carriers of the CD39 mutation.