The relationship between standard reduction potentials of catechins and biological activities involved in redox control

Mussel-inspired chitosan and its applications in the biomedical field

Chitosan (CS) has physicochemical properties including solubility, crystallinity, swellability, viscosity, and cohesion, along with biological properties like biocompatibility, biodegradation, antioxidant, antibacterial, and antitumor effects. However, these characteristics of CS are greatly affected by its degree of deacetylation, molecular weight, pH and other factors, which limits the application of CS in biomedicine. The modification of CS with catechol-containing substances inspired by mussels can not only improve these properties of CS, but also endow it with self-healing property, providing an environmentally friendly and sustainable way to promote the application of CS in biomedicine. In this paper, the properties of CS and its limitation in the biomedical filed are introduced in detail. Then, the modification methods and properties of substances with catechol groups inspired by mussels on CS are reviewed. Finally, the applications of modified CS in the biomedical field of wound healing, drug delivery, anticancer therapy, biosensor and 3D printing are further discussed. This review can provide valuable information for the design and exploitation of mussel-inspired CS in the biomedical field.

The Interplay between Endogenous and Foodborne Pro-Oxidants and Antioxidants in Shaping Redox Homeostasis

Oxidative stress has been known about in biological sciences for several decades; however, the understanding of this concept has evolved greatly since its foundation. Over the past years, reactive oxygen species, once viewed as solely deleterious, have become recognized as intrinsic components of life. In contrast, antioxidants, initially believed to be cure-all remedies, have failed to prove their efficacy in clinical trials. Fortunately, research on the health-promoting properties of antioxidants has been ongoing. Subsequent years showed that the former assumption that all antioxidants acted similarly was greatly oversimplified. Redox-active compounds differ in their chemical structures, electrochemical properties, mechanisms of action, and bioavailability; therefore, their efficacy in protecting against oxidative stress also varies. In this review, we discuss the changing perception of oxidative stress and its sources, emphasizing everyday-life exposures, particularly those of dietary origin. Finally, we posit that a better understanding of the physicochemical properties and biological outcomes of antioxidants is crucial to fully utilize their beneficial impact on health.

Development of New Resolvin D1 Analogues for Osteoarthritis Therapy: Acellular and Computational Approaches to Study Their Antioxidant Activities

In osteoarthritis (OA), oxidative stress plays a crucial role in maintaining and sustaining cartilage degradation. Current OA management requires a combination of pharmaceutical and non-pharmacological strategies, including intraarticular injections of hyaluronic acid (HA). However, several lines of evidence reported that HA oxidation by reactive oxygen species (ROS) is linked with HA cleavage and fragmentation, resulting in reduced HA viscosity. Resolvin D1 (RvD1) is a lipid mediator that is biosynthesized from omega-3 polyunsaturated fatty acids and is a good candidate with the potential to regulate a panoply of biological processes, including tissue repair, inflammation, oxidative stress, and cell death in OA. Herein, newly designed and synthesized imidazole-derived RvD1 analogues were introduced to compare their potential antioxidant properties with commercially available RvD1. Their antioxidant capacities were investigated by several in vitro chemical assays including oxygen radical absorbance capacity, 2,2-diphenyl-1-picrylhydrazyl radical scavenging, ferric ion reducing antioxidant power, hydroxyl radical scavenging, and HA fragmentation assay. All results proved that imidazole-derived RvD1 analogues showed excellent antioxidant performance compared to RvD1 due to their structural modifications. Interestingly, they scavenged the formed reactive oxygen species (ROS) and protected HA from degradation, as verified by agarose gel electrophoresis and gel permission chromatography. A computational study using Gaussian 09 with DFT calculations and a B3LYP/6-31 G (d, p) basis set was also employed to study the relationship between the antioxidant properties and chemical structures as well as calculation of the molecular structures, frontier orbital energy, molecular electrostatic potential, and bond length. The results showed that the antioxidant activity of our analogues was higher than that of RvD1. In conclusion, the findings suggest that imidazole-derived RvD1 analogues can be good candidates as antioxidant molecules for the treatment of oxidative stress-related diseases like OA. Therefore, they can prolong the longevity of HA in the knee and thus may improve the mobility of the articulation.

Amelioration of Functional, Metabolic, and Morphological Deterioration in the Retina following Retinal Detachment by Green Tea Extract

Retinal detachment (RD) can result in the loss of photoreceptors that cause vision impairment and potential blindness. This study explores the protective effects of the oral administration of green tea extract (GTE) in a rat model of RD. Various doses of GTE or epigallocatechin gallate (EGCG), the most active ingredient in green tea catechins, were administered to Sprague Dawley (SD) rats with experimentally induced retinal detachment. The rats received sub-retinal injections of hyaluronic acid (0.1%) to induce RD and were given different doses of GTE and EGCG twice daily for three days. Notably, a low dose of GTE (142.9 mg/kg) caused significantly higher signal amplitudes in electroretinograms (ERGs) compared to higher GTE doses and any doses of EGCG. After administration of a low dose of GTE, the outer nuclear layer thickness, following normalization, of the detached retina reduced to 82.4 ± 8.2% (Mean ± SEM, p < 0.05) of the thickness by RD treatment. This thickness was similar to non-RD conditions, at 83.5 ± 4.7% (Mean ± SEM) of the thickness following RD treatment. In addition, the number of TUNEL-positive cells decreased from 76.7 ± 7.4 to 4.7 ± 1.02 (Mean ± SEM, p < 0.0001). This reduction was associated with the inhibition of apoptosis through decreased sphingomyelin levels and mitigation of oxidative stress shown by a lowered protein carbonyl level, which may involve suppression of HIF-1α pathways. Furthermore, GTE showed anti-inflammatory effects by reducing inflammatory cytokines and increasing resolving cytokines. In conclusion, low-dose GTE, but not EGCG, significantly alleviated RD-induced apoptosis, oxidative stress, inflammation, and energy insufficiency within a short period and without affecting energy metabolism. These findings suggest the potential of low-dose GTE as a protective agent for the retina in RD.

Silver(I) complexes containing antifungal azoles: significant improvement of the anti-Candida potential of the azole drug after its coordination to the silver(I) ion

Inspired by the emergence of resistance to currently available antifungal therapy and by the great potential of metal complexes for the treatment of various diseases, we synthesized three new silver(I) complexes containing clinically used antifungal azoles as ligands, [Ag(ecz)2]SbF6 (1, ecz is econazole), {[Ag(vcz)2]SbF6}n (2, vcz is voriconazole), and [Ag(ctz)2]SbF6 (3, ctz is clotrimazole), and investigated their antimicrobial properties. The synthesized complexes were characterized by mass spectrometry, IR, UV-vis and 1H NMR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction analysis. In the mononuclear complexes 1 and 3 with ecz and ctz, respectively, the silver(I) ion has the expected linear geometry, in which the azoles are monodentately coordinated to this metal center through the N3 imidazole nitrogen atom. In contrast, the vcz-containing complex 2 has a polymeric structure in the solid state in which the silver(I) ions are coordinated by four nitrogen atoms in a distorted tetrahedral geometry. DFT calculations were done to predict the most favorable structures of the studied complexes in DMSO solution. All the studied silver(I) complexes have shown excellent antifungal and good to moderate antibacterial activities with minimal inhibitory concentration (MIC) values in the ranges of 0.01-27.1 and 2.61-47.9 μM on the selected panel of fungi and bacteria, respectively. Importantly, the complexes 1-3 have exhibited a significantly improved antifungal activity compared to the free azoles, with the most pronounced effect observed in the case of complex 2 compared to the parent vcz against Candida glabrata with an increase of activity by five orders of magnitude. Moreover, the silver(I)-azole complexes 2 and 3 significantly inhibited the formation of C. albicans hyphae and biofilms at the subinhibitory concentration of 50% MIC. To investigate the impact of the complex 3 more thoroughly on Candida pathogenesis, its effect on the adherence of C. albicans to A549 cells (human adenocarcinoma alveolar basal epithelial cells), as an initial step of the invasion of host cells, was studied.

Comparative Analysis of Phytochemical Profiles and Selected Biological Activities of Various Morphological Parts of Ligustrum vulgare

Ligustrum vulgare (LV), widely cultivated in Europe and often used in hedges, has been historically recognized in folk medicine for its potential health benefits. This study focused on exploring the untargeted identification of secondary metabolites in ethanol extracts (70% v/v) from different morphological parts (young shoots, leaves, flowers and fruits) of LV at various stages of plant development, using ultra-high-performance liquid chromatography with high-resolution mass spectrometry (UHPLC-HRMS). Additionally, the selected biological activities (antioxidant activity, cyclooxygenase-2 inhibition (COX-2), α-amylase inhibition and cytotoxicity) of the tested extracts were determined. Untargeted metabolomics showed that LV extracts were a rich source of phenylethanoid compounds, flavonoids, iridoids and their derivatives. The flowers of LV had the highest content of oleuropein (33.43 ± 2.48 mg/g d.w.). The lowest antioxidant activity was obtained for ripe and post-seasonal fruits, while in the case of other samples, the activity was at a similar level. All tested extracts showed α-amylase and COX-2 inhibitory activity. In addition, LV extracts showed strong antiproliferative properties in colorectal (HT29) and liver (HepG2) cancer cell lines. The obtained results show the difference in the content of bioactive compounds in various morphological parts of Ligustrum vulgare. These differences may influence the multifaceted medicinal potential of this plant.

Hypericum alpestre extract exhibits in vitro and in vivo anticancer properties by regulating the cellular antioxidant system and metabolic pathway of L-arginine

Conventional treatment methods are not effective enough to fight the rapid increase in cancer cases. The interest is increasing in the investigation of herbal sources for the development of new anticancer therapeutics. This study aims to investigate the antitumor capacity of Hypericum alpestre (H. alpestre) extract in vitro and in vivo, either alone or in combination with the inhibitors of the  l-arginine/polyamine/nitric oxide (NO) pathway, and to characterize its active phytochemicals using advanced chromatographic techniques. Our previous reports suggest beneficial effects of the arginase inhibitor NG-hydroxy-nor- l-arginine and NO inhibitor NG-nitro-Larginine methyl ester in the treatment of breast cancer via downregulation of polyamine and NO synthesis. Here, the antitumor properties of H. alpestre and its combinations were explored in vivo, in a rat model of mammary gland carcinogenesis induced by subcutaneous injection of 7,12-dimethylbenz[a]anthracene. The study revealed strong antiradical activity of H. alpestre aerial part extract in chemical (DPPH/ABTS) tests. In the in vitro antioxidant activity test, the H. alpestre extract demonstrated pro-oxidant characteristics in human colorectal (HT29) cells, which were contingent upon the hemostatic condition of the cells. The H. alpestre extract expressed a cytotoxic effect on HT29 and breast cancer (MCF-7) cells measured by the MTT test. According to comet assay results, H. alpestre extract did not exhibit genotoxic activity nor possessed antigenotoxic properties in HT29 cells. Overall, 233 substances have been identified and annotated in H. alpestre extract using the LC-Q-Orbitrap HRMS system. In vivo experiments using rat breast cancer models revealed that the H. alpestre extract activated the antioxidant enzymes in the liver, brain, and tumors. H. alpestre combined with chemotherapeutic agents attenuated cancer-like histological alterations and showed significant reductions in tumor blood vessel area. Thus, either alone or in combination with Nω -OH-nor- l-arginine and Nω -nitro- l-arginine methyl ester, H. alpestre extract exhibits pro- and antioxidant, antiangiogenic, and cytotoxic effects.

Phytochemical screening and biological evaluation of Greek sage (Salvia fruticosa Mill.) extracts

This study explores the influence of extraction solvents on the composition and bioactivity of Salvia fruticosa extracts. Ultrasound-assisted extraction with water, ethanol and their mixtures in variable proportions was used to produce four different extracts. An untargeted UPLC/MS‑based metabolomics was performed to discover metabolites profile variation between the extracts. In the analyzed samples, 2704 features had been detected, of which 95 were tentatively identified. The concentrations of the important metabolites, namely, caffeic acid, carnosic acid, carnosol, rosmarinic acid, salvianolic acid B and scutellarin, were determined, using UPLC-PDA methods. Rosmarinic acid was the dominant metabolite and antioxidant in all tested extracts, except the aqueous extract, in which scutellarin was the most abundant compound. The extracts and standards were examined for antioxidant activity and xanthine oxidase (XO) inhibitory activity. The most diverse in terms of chemical composition and rich in antioxidant compounds was 70% ethanolic extract and the strongest antioxidant was caffeic acid. All analyzed extracts showed the ability to inhibit XO activity, but the highest value was recorded for 30% ethanolic extract. Among tested standards, the most potent XO inhibitor was caffeic acid. The results suggest that the leaves of Greek sage are a source of natural XO inhibitors and may be an alternative to drugs produced by chemical synthesis.

Post-Chromatographic Derivatization Coupled with Mass Spectrometry as a Method of Profiling and Identification of Antioxidants; Ligustrum vulgare Phytocomplex as an Example

High-performance liquid chromatography (HPLC) and high-performance thin-layer chromatography (HPTLC) coupled with radical scavenging assays, such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) can be both used for the detection of the antioxidants in plant extracts. In this study, the ethanolic (70% v/v) extracts from different morphological parts of Ligustrum vulgare collected at different stages of maturity were used as the source of antioxidants. The final identification of antioxidants was performed using high-resolution mass spectroscopy (HRMS). As a result, 19 compounds with antioxidant properties detected with HPLC-ABTS assay and 10 compounds detected with HPTLC-DPPH/ABTS assay were identified, mostly from the group of iridoids, phenylethanoids, and flavonoids. When comparing different L. vulgare samples, it was found that the extracts obtained from leaves contained the greatest number of antioxidants. The results of this study suggest that HPTLC-DPPH/ABTS as well as HPLC-ABTS derivatization coupled with the HRMS can be successfully used for profiling and identification of antioxidants from natural sources. Planar chromatography is more suitable for screening multiple samples because of its simplicity, whereas more challenging liquid chromatography provides more detailed information and is therefore better for a selected set of samples.

The comparison of antioxidant properties and nutrigenomic redox-related activities of vitamin C, C-vitamers, and other common ascorbic acid derivatives

The term 'vitamin C' describes a group of compounds with antiscorbutic activity of l-ascorbic acid (AA). Despite AA's omnipresence in plant-derived foods, its derivatives have also been successfully implemented in the food industry as antioxidants, including the D-isomers, which lack vitamin C activity. This study aimed to determine the relationship between redox-related activities for five derivatives of AA using electrochemical, chemical, and biological approaches. Here we report that AA, C-vitamers, and other commonly consumed AA derivatives differ in their redox-related activities. As long as the physiological range of concentrations was maintained, there was no simple relationship between their redox properties and biological activity. Clear distinctions in antioxidant activity were observed mostly at high concentrations, which were strongly correlated with electrochemical and kinetic parameters describing redox-related properties of the studied compounds. Despite obvious similarities in chemical structures and antioxidant activity, we showed that C-vitamers may exhibit different nutrigenomic effects. Together, our findings provide a deeper insight into so far underinvestigated area combining chemical properties with biological activities of commonly applied AA derivatives.

Relationship between Chemical Structure and Biological Activity Evaluated In Vitro for Six Anthocyanidins Most Commonly Occurring in Edible Plants

Numerous studies have provided evidence that diets rich in anthocyanins show a broad spectrum of health benefits. Anthocyanins in nature are usually found in the form of glycosides. Their aglycone forms are called anthocyanidins. The chemical structure of anthocyanins is based on the flavylium cation, but they differ in the position and number of substituents. However, the bioactives and foods that contain them are frequently treated as a uniform group of compounds exhibiting the same biological activity, without paying attention to the structural differences between individual anthocyanidins. The aim of this study was to find out how structural differences impact the biological activity of the six most common dietary anthocyanidins, i.e., delphinidin (Dp), petunidin (Pt), cyanidin (Cd), malvidin (Mv), pelargonidin (Pg) and peonidin (Po). The study concentrated on redox-related phenomena and compared the following parameters: antioxidant activity (measured using various methods: spectrophotometric tests (ABTS, DPPH), ORAC assay and CAA test (cellular antioxidant activity)), the ability to inhibit growth of human colon cancer cells (HT29; determined using MTT assay), and the ability of studied compounds to protect DNA from oxidative damage (comet assay). Based on the obtained results, the relationship between the structure of studied anthocyanidins and their biological activity was assessed. The obtained results revealed that the number and position of the hydroxyl and methoxy groups in the anthocyanidin structure strongly influenced not only the color of anthocyanidins but most of all their antioxidant and biological activities.

Green Tea Catechins as Therapeutic Antioxidants for Glaucoma Treatment

Glaucoma is the leading cause of irreversible blindness and visual impairment, affecting more than 80 million individuals worldwide. Oxidative stress and inflammation-induced neurodegenerative insults to retinal ganglion cells are the main pathogenesis of glaucoma. Retinal ganglion cells, the retinal neurons transmitting the visual signals to the visual cortex in the brain, have very limited regeneration or recovery capacity after damages. Apart from intraocular pressure-lowering treatments, there is still no clinically effective treatment to rescue the degeneration of retinal ganglion cells in glaucoma. Dietary antioxidants are easily accessible and can be applied as supplements assisting in the clinical treatments. Catechins, a chemical family of flavonoids, are the phenolic compounds found in many plants, especially in green tea. The anti-oxidative and anti-inflammatory properties of green tea catechins in vitro and in vivo have been well proven. They could be a potential treatment ameliorating retinal ganglion cell degeneration in glaucoma. In this review, the chemistry, pharmacokinetics, and therapeutic properties of green tea catechins were summarized. Research updates on the biological effects of green tea catechins in cellular and animal experimental glaucoma models were reviewed. In addition, clinical potentials of green tea catechins for glaucoma treatment were also highlighted.

The Synergy between Glutathione and Phenols-Phenolic Antioxidants Repair Glutathione: Closing the Virtuous Circle-A Theoretical Insight

Glutathione (GSH) and phenols are well-known antioxidants, and previous research has suggested that their combination can enhance antioxidant activity. In this study, we used Quantum Chemistry and computational kinetics to investigate how this synergy occurs and elucidate the underlying reaction mechanisms. Our results showed that phenolic antioxidants could repair GSH through sequential proton loss electron transfer (SPLET) in aqueous media, with rate constants ranging from 3.21 × 10⁶ M^-1 s^-1 for catechol to 6.65 × 10⁸ M^-1 s^-1 for piceatannol, and through proton-coupled electron transfer (PCET) in lipid media with rate constants ranging from 8.64 × 10⁶ M^-1 s^-1 for catechol to 5.53 × 10⁷ M^-1 s^-1 for piceatannol. Previously it was found that superoxide radical anion (O₂^•-) can repair phenols, thereby completing the synergistic circle. These findings shed light on the mechanism underlying the beneficial effects of combining GSH and phenols as antioxidants.

Beyond Antioxidant Activity: Redox Properties of Catechins May Affect Changes in the DNA Methylation Profile—The Example of SRXN1 Gene

The role of catechins in the epigenetic regulation of gene expression has been widely studied; however, if and how this phenomenon relates to the redox properties of these polyphenols remains unknown. Our earlier study demonstrated that exposure of the human colon adenocarcinoma HT29 cell line to these antioxidants affects the expression of redox-related genes. In particular, treatment with (−)-epigallocatechin (EGC) downregulated transcription of gene encoding sulfiredoxin-1 (SRXN1), the peroxidase involved in the protection of cells against hydrogen peroxide-induced oxidative stress. The aim of this study was to investigate whether the observed SRXN1 downregulation was accompanied by changes in the DNA methylation level of its promoter and, if so, whether it was correlated with the redox properties of catechins. The impact on DNA methylation profile in HT29 cells treated with different concentrations of five catechins, varying in chemical structures and standard reduction potentials as well as susceptibility to oxidation, was monitored by a methylation-sensitive high-resolution melting technique employing the SRXN1 promoter region as a model target. We demonstrated that catechins, indeed, are able to modulate DNA methylation of the SRXN1 gene in a redox-related manner. The nonlinear method in the statistical analysis made it possible to fish out two parameters (charge transfer in oxidation process Qox and time of electron transfer t), whose strong interactions correlated with observed modulation of DNA methylation by catechins. Based on these findings, we present a proof-of-concept that DNA methylation, which limits SRXN1 expression and thus restricts the multidirectional antioxidant action of SRXN1, may represent a mechanism protecting cells against reductive stress caused by particularly fast-reacting reductants such as EGC and (−)-epicatechin gallate (ECG) in our study.

Anti-cancer effect of Rumex obtusifolius in combination with arginase/nitric oxide synthase inhibitors via downregulation of oxidative stress, inflammation, and polyamine synthesis

Cancer continues to be a leading cause of death worldwide, making the development of new treatment methods crucial in the fight against it. With cancer incidence rates increasing worldwide, ongoing research must focus on identifying new and effective ways to prevent and treat the disease. The combination of herbal extracts with chemotherapeutic agents has gained much interest as a novel strategy to combat cancer. Rumex obtusifolius L. is a wild plant known for its medicinal properties and is widely distributed worldwide. Our preclinical evaluations suggested that R. obtusifolius seed extracts possessed cancer-inhibiting properties and we also evaluated the beneficial effects of the arginase inhibitor NG-hydroxy-nor-L-arginine and nitric oxide inhibitor NG-nitro-L-arginine methyl ester in the treatment of breast cancer. The current study aimed to combine these observations and evaluate the antioxidant and antitumor properties of R. obtusifolius extracts alone and in combination with the arginase and nitric oxide synthase inhibitors. Metabolic characterization of the plant extract using a liquid chromatography/high-resolution mass spectrometry advanced system revealed the presence of 240 phenolic compounds many of which possess anticancer properties, according to the literature. In vitro studies revealed a significant cytotoxic effect of the R. obtusifolius extracts on the human colon (HT29) and breast cancer (MCF-7) cell lines. Thus, a new treatment approach of combining R. obtusifolius bioactive phytochemicals with the arginase and nitric oxide synthase inhibitors NG-nitro-L-arginine methyl ester and/or NG-hydroxy-nor-L-arginine, respectively, was proposed and could potentially be an effective way to treat breast cancer. Indeed, these combinations showed immunostimulatory, antiproliferative, antioxidant, anti-inflammatory, and antiangiogenic properties in a rat breast cancer model.

Gut microbiota-mediated metabolism of green tea catechins and the biological consequences: An updated review

Multiple beneficial effects have been attributed to green tea catechins (GTCs). However, the bioavailability of GTCs is generally low, with only a small portion directly absorbed in the small intestine. The majority of ingested GTCs reaches the large intestinal lumen, and are extensively degraded via biotransformation by gut microbiota, forming many low-molecular-weight metabolites such as phenyl-γ-valerolactones, phenolic acids, butyrate, and acetate. This process not only improves the overall bioavailability of GTC-derived metabolites but also enriches the biological activities of GTCs. Therefore, the intra- and inter-individual differences in human gut microbiota as well as the resulting biological contribution of microbial metabolites are crucial for the ultimate health benefits. In this review, the microbial degradation of major GTCs was characterized and an overview of the in vitro models used for GTC metabolism was summarized. The intra- and inter-individual differences of human gut microbiota composition and the resulting divergence in the metabolic patterns of GTCs were highlighted. Moreover, the potential beneficial effects of GTCs and their gut microbial metabolites were also discussed. Overall, the microbial metabolites of GTCs with higher bioavailability and bioactive potency are key factors for the observed beneficial effects of GTCs and green tea consumption.

Epigallocatechin Gallate: pH-Dependent Redox Properties and Effect on Respiration, Photosynthesis, and Cell Death in Pea Plants

In vitro redox properties of the green tea component epigallocatechin gallate (EGCG) and its effect on pea plant cells were investigated. EGCG was found to exhibit both pro- and antioxidant properties. In solutions, EGCG was oxidized by oxygen at physiological (slightly alkaline) pH values with the generation of O2-• and H2O2, the reaction being slowed down by a decrease in the medium pH. On the other hand, EGCG functioned as an electron donor for peroxidase, resulting in the H2O2 utilization. EGCG suppressed respiration, reduced mitochondrial transmembrane potential difference and inhibited electron transfer in the photosynthetic electron transport chain in pea leaf cells (leaf cuttings and epidermis). Among components of the photosynthetic redox chain, Photosystem II was the least sensitive to the EGCG action. In the epidermis, EGCG reduced the rate of reactive oxygen species formation that was induced by NADH. EGCG at the concentrations from 10 μM to 1 mM suppressed the KCN-induced death of guard cells in the epidermis, which was determined from the destruction of cell nuclei. EGCG at a concentration of 10 mM disrupted the barrier function of the guard cell plasma membrane, increasing its permeability to propidium iodide.

Effect of oxidation and in vitro intestinal hydrolysis on phospholipid toxicity towards HT29 cell line serving as a model of human intestinal epithelium

Oxidation of food-derived phospholipids (PLs) can influence nutrient digestion and induce oxidative stress in gastrointestinal epithelium. In this study, hen egg yolk PL fraction was used to evaluate the effect of lipoxygenase (LOX)-induced PL oxidation on the rate of PL hydrolysis catalyzed by pancreatic phospholipase A₂ (PLA₂) in the presence of bile salts (BSs). Then, PL/BS solutions containing native or oxidized PLs were used in in vitro intestinal digestion to assess the effect of PL oxidation and hydrolysis on the toxicity towards HT29 cell line. Based on the obtained results, we suggest that hexanal and (E)-2-nonenal, formed by the decomposition of PL hydroperoxides, inhibited PLA₂ activity. The cell exposure to simulated intestinal fluid (SIF) containing BSs decreased HT29 cell viability and significantly damaged cellular DNA. However, the genotoxic effect was reversed in the presence of all tested PL samples, while the protective effect against the BS-induced cytotoxicity was observed for native non-hydrolyzed PLs, but was not clearly visible for other samples. This can result from an overlap of other toxic effects such as lipotoxicity or disturbance of cellular redox homeostasis. Taking into account the data obtained, it was proposed that the PLA₂ activity decline in the presence of PL oxidation products may be a kind of protective mechanism against rapid release of oxidized FAs characterized by high cytotoxic effect towards intestinal epithelium cells.

The Gut Microbial Metabolite Pyrogallol Is a More Potent Inducer of Nrf2-Associated Gene Expression Than Its Parent Compound Green Tea (-)-Epigallocatechin Gallate

(-)-Epigallocatechin gallate (EGCG) has been associated with multiple beneficial effects. However, EGCG is known to be degraded by the gut microbiota. The present study investigated the hypothesis that microbial metabolism would create major catechol-moiety-containing microbial metabolites with different ability from EGCG to induce nuclear factor-erythroid 2-related factor 2 (Nrf2)-mediated gene expression. A reporter gene bioassay, label-free quantitative proteomics and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) were combined to investigate the regulation of Nrf2-related gene expression after exposure of U2OS reporter gene or Hepa1c1c7 cells in vitro to EGCG or to its major microbial catechol-moiety-containing metabolites: (-)-epigallocatechin (EGC), gallic acid (GA) and pyrogallol (PG). Results show that PG was a more potent inducer of Nrf2-mediated gene expression than EGCG, with a 5% benchmark dose (BMD₅) of 0.35 µM as compared to 2.45 µM for EGCG in the reporter gene assay. EGC and GA were unable to induce Nrf2-mediated gene expression up to the highest concentration tested (75 µM). Bioinformatical analysis of the proteomics data indicated that Nrf2 induction by PG relates to glutathione metabolism, drug and/or xenobiotics metabolism and the pentose phosphate pathway. Taken together, our findings demonstrate that the microbial metabolite PG is a more potent inducer of Nrf2-associated gene expression than its parent compound EGCG.

Mechanistic Insight into the Design of Chemical Tools to Control Multiple Pathogenic Features in Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia and is characterized by memory loss and cognitive decline. Approximately 50 million people worldwide are suffering from AD and related dementias. Very recently, the first new drug targeting amyloid-β (Aβ) aggregates has been approved by the United States Food and Drug Administration, but its efficacy against AD is still debatable. Other available treatments temporarily relieve the symptoms of AD. The difficulty in discovering effective therapeutics for AD originates from its complicated nature, which results from the interrelated pathogenic pathways led by multiple factors. Therefore, to develop potent disease-modifying drugs, multiple pathological features found in AD should be fully elucidated.Our laboratory has been designing small molecules as chemical tools to investigate the individual and interrelated pathologies triggered by four pathogenic elements found in the AD-affected brain: metal-free Aβ, metal-bound Aβ, reactive oxygen species (ROS), and acetylcholinesterase (AChE). Aβ peptides are partially folded and aggregate into oligomers, protofibrils, and fibrils. Aβ aggregates are considered to be neurotoxic, causing membrane disruption, aberrant cellular signaling, and organelle dysfunction. In addition, highly concentrated metal ions accumulate in senile plaques mainly composed of Aβ aggregates, which indicates that metal ions can directly interact with Aβ. Metal binding to Aβ affects the aggregation and conformation of the peptide. Moreover, the impaired homeostasis of redox-active Fe(II/III) and Cu(I/II) induces the overproduction of ROS through Fenton chemistry and Fenton-like reactions, respectively. Dysregulated ROS prompt oxidative-stress-damaging biological components such as lipids, proteins, and nucleic acids and, consequently, lead to neuronal death. Finally, the loss of cholinergic transmission mediated by the neurotransmitter acetylcholine (ACh) contributes to cognitive deficits observed in AD.In this Account, we illustrate the design principles for small-molecule-based chemical tools with reactivities against metal-free Aβ, metal-bound Aβ, ROS, and AChE. More importantly, mechanistic details at the molecular level are highlighted with some examples of chemical tools that were developed by our group. The aggregation of metal-free Aβ can be modulated by modifying amino acid residues responsible for self-assembling Aβ or disassembling preformed fibrils. To alter the aggregation and cytotoxicity profiles of metal-bound Aβ, ternary complexation, metal chelation, and modifications onto metal-binding residues can be effective tactics. The presence and production of ROS are able to be controlled by small molecules with antioxidant and metal-binding properties. Finally, inhibiting substrate access or substrate binding at the active site of AChE can diminish its activity, which restores the levels of ACh. Overall, our rational approaches demonstrate the feasibility of developing small molecules as chemical tools that can target and modulate multiple pathological factors associated with AD and can be useful for gaining a greater understanding of the multifaceted pathology of the disease.

Conjugation of Diclofenac with Novel Oleanolic Acid Derivatives Modulate Nrf2 and NF-κB Activity in Hepatic Cancer Cells and Normal Hepatocytes Leading to Enhancement of Its Therapeutic and Chemopreventive Potential

Combining NSAIDs with conventional therapeutics was recently explored as a new strategy in cancer therapy. Our earlier studies showed that novel oleanolic acid oximes (OAO) conjugated with aspirin or indomethacin may enhance their anti-cancer potential through modulation of the Nrf2 and NF-κB signaling pathways. This study focused on the synthesis and biological evaluation of four diclofenac (DCL)–OAO derivative conjugates in the context of these pathways’ modification and hepatic cells survival. Treatment with the conjugates 4d, 3-diclofenacoxyiminoolean-12-en-28-oic acid morpholide, and 4c, 3-diclofenacoxyiminoolean-12-en-28-oic acid benzyl ester significantly reduced cell viability in comparison to the DCL alone. In THLE-2, immortalized normal hepatocytes treated with these conjugates resulted in the activation of Nrf2 and increased expression in SOD-1 and NQO1, while the opposite effect was observed in the HepG2 hepatoma cells. In both cell lines, reduced activation of the NF-κB and COX-2 expression was observed. In HepG2 cells, conjugates increased ROS production resulting from a reduced antioxidant defense, induced apoptosis, and inhibited cell proliferation. In addition, the OAO morpholide derivative and its DCL hybrid reduced the tumor volume in mice bearing xenografts. In conclusion, our study demonstrated that conjugating diclofenac with the OAO morpholide and a benzyl ester might enhance its anti-cancer activity in HCC.

Interactions between polyphenolic antioxidants quercetin and naringenin dictate the distinctive redox-related chemical and biological behaviour of their mixtures

Food synergy concept is suggested to explain observations that isolated antioxidants are less bioactive than real foods containing them. However, mechanisms behind this discrepancy were hardly studied. Here, we demonstrate the profound impact of interactions between two common food flavonoids (individual: aglycones quercetin-Q and naringenin-N- or their glycosides rutin-R and naringin-N+ vs. mixed: QN- and RN+) on their electrochemical properties and redox-related bioactivities. N- and N+ seemed weak antioxidants individually, yet in both chemical and cellular tests (DPPH and CAA, respectively), they increased reducing activity of mixtures synergistically. In-depth measurements (differential pulse voltammetry) pointed to kinetics of oxidation reaction as decisive factor for antioxidant power. In cellular (HT29 cells) tests, the mixtures exhibited properties of a new substance rather than those of components. Pure flavonoids did not influence proliferation; mixtures stimulated cell growth. Individual flavonoids tended to decrease global DNA methylation with growing concentration; this effect was more pronounced for mixtures, but not concentration-dependent. In nutrigenomic studies, expression of gene set affected by QN- differed entirely from common genes modulated by individual components. These results question the current approach of predicting bioactivity of mixtures based on research with isolated antioxidants.

Comparative evaluation of different methods for determining phytochemicals and antioxidant activity in products containing betalains - Verification of beetroot samples

This study presents methods that can be used to assess the health quality of products containing betalains. The paper compares and verifies data on the phytochemical composition of three different pigmented beetroot cultivars using spectrophotometric, HPLC-DAD, HPTLC and LC-Q-Orbitrap-HRMS techniques. Additionally, we compared the total antioxidant activity in both the cell-free and cellular systems. Betalain contribution to antioxidant activity was also determined using post-column derivatization and it was found that in the case of red beetroot it is about 50%. Photometric measurements are recommended for a simple and inexpensive analysis of the total betacyanin and betaxanthin content. Liquid chromatography techniques produced more precise information on phytochemical composition in the tested samples. The combination of liquid chromatography with high-resolution mass spectrometry produced the largest amount of quantitative and qualitative data; in beetroot samples sixty-four phytochemicals have been identified therefore, this approach is recommended for more detailed metabolomics studies.

Synergistic, additive, and antagonistic antioxidant effects in the mixtures of curcumin with (-)-epicatechin and with a green tea fraction containing (-)-epicatechin

The combinations of curcumin with green tea flavan-3-ols produce various synergistic biological effects. This study aimed to verify the antioxidant effects in mixtures of curcumin with (-)-epicatechin (EC) or with EC fraction from green tea in a non-polar lipid system (triacylglycerol autoxidation) and in a polar conditions (ABTS assay). Curcumin was 2.5-2.6 and 2.9-3.6 times weaker antioxidant than EC and EC fraction, respectively. The synergism was found in mixtures using the isobologram analysis of ABTS^•+ scavenging activity results. The strongest effect with a combination index of 0.751 was in the equimolar mixture of pure compounds. In the lipid system, antagonism occurred for curcumin and EC fraction combination. However, an additive effect was found between curcumin and EC. In conclusion, the antioxidant effects in the curcumin and EC mixtures depended on the polarity of the assay media, the ratio of antioxidants, and presence other phenolics in the system.

Anti-aging Effects of Mangosteen Peel Extract and Its Phytochemical Compounds: Antioxidant Activity, Enzyme Inhibition and Molecular Docking Simulation

Skin aging is a complex natural process characterised by gradual diminishment of structural integrity and physiological imbalance of the skin tissue. Since the oxidative stress is tightly corelated to the skin aging process, the usage of antioxidant may serve as favourable strategies for slowing down the skin aging process. Mangosteen is an important fruit commodity and its extract had been extensively studied and revealing various biological activities. Present study aimed to assess the antioxidant and antiaging activity of mangosteen peel extract (MPE) and its phytochemical compounds. MPE and its compounds were subjected to ferric reducing antioxidant power (FRAP), hydroperoxide (H₂O₂) scavenging, anti-collagenase, anti-elastase, anti-hyaluronidase and anti-tyrosinase assay. MPE has the highest FRAP 116.31 ± 0.60 μM Fe(II) μg⁻¹ extract, IC₅₀ of MPE on H₂O₂ scavenging activity was 54.61 μg mL⁻¹. MPE also has the highest anti elastase activity at IC₅₀ 7.40 μg mL⁻¹. Alpha-mangostin showed potent anti-collagenase activity (IC₅₀ 9.75 μg mL⁻¹). While gamma-mangostin showed potent anti-hyaluronidase (IC₅₀ 23.85 μg mL⁻¹) and anti-tyrosinase (IC₅₀ 50.35 μg mL⁻¹). MPE and its compounds were evaluated in vitro for antioxidant and antiaging activities. Current findings may provide scientific evidence for possible usage of mangosteen extract and its compounds as antioxidant and antiaging agent.

Voltammetric Behaviour of Drug Molecules as a Predictor of Metabolic Liabilities

Electron transfer plays a vital role in drug metabolism and underlying toxicity mechanisms. Currently, pharmaceutical research relies on pharmacokinetics (PK) and absorption, distribution, metabolism, elimination and toxicity (ADMET) measurements to understand and predict drug reactions in the body. Metabolic stability (and toxicity) prediction in the early phases of the drug discovery and development process is key in identifying a suitable lead compound for optimisation. Voltammetric methods have the potential to overcome the significant barrier of new drug failure rates, by giving insight into phase I metabolism events which can have a direct bearing on the stability and toxicity of the parent drug being dosed. Herein, we report for the first time a data-mining investigation into the voltammetric behaviour of reported drug molecules and their correlation with metabolic stability (indirectly measured via t½), as a potential predictor of drug stability/toxicity in vivo. We observed an inverse relationship between oxidation potential and drug stability. Furthermore, we selected and prepared short- (<10 min) and longer-circulation (>2 h) drug molecules to prospectively survey the relationship between oxidation potential and stability.

Roles and action mechanisms of herbs added to the emulsion on its lipid oxidation

Quality of food emulsions is mainly determined by their physicochemical stability such as lipid oxidation, and herbs as antioxidative food materials are added to improve their quality and shelf-life. Despite the extensive researches, the chemistry and implications of herb addition in the lipid oxidation of emulsions are still confusing. This review intended to provide the information on the roles and action mechanisms of herbs in the lipid oxidation of food emulsions, with focuses on polyphenols. Polyphenols act as antioxidants mainly via reactive oxygen species scavenging and metal chelating; however, their oxidation products and reducing capacity to more reactive metal ions increase the lipid oxidation. Factors such as structure, concentration, and distribution determine their anti- or prooxidant role. Interactions, synergism and antagonism, among polyphenol compounds and the effects of tocopherols derived from oil on the antioxidant activity of herbs were also described with the involving action mechanisms.

Interactions between bioactive components determine antioxidant, cytotoxic and nutrigenomic activity of cocoa powder extract

Numerous studies have shown, rather disappointingly, that isolated bioactive phytochemicals are not as biologically effective as natural plant products. Such a discrepancy may be explained by the concept of food synergy, which was verified in this research for cocoa extract versus its major components with regard to cancer chemoprevention. The evaluation embraced the relationship between redox properties evaluated in cell-free systems with the aid of free radicals scavenging method and differential pulse voltammetry, and redox associated anticarcinogenic activities (cellular antioxidant activity, cytotoxicity, nutrigenomic activity) in human colon adenocarcinoma cell line exposed to either cocoa powder extract or artificial mixtures of cocoa bioactives at matching concentrations. In contrast to expectations, our results showed that the stepwise enrichment with antioxidants caused no gradual increase in the antioxidant activity of the model mixtures; also, these model mixtures did not reach the reducing potential of cocoa in the cell-free systems or cellular model employed. Further, the biological activities examined in colon adenocarcinoma cells did not alter in a stepwise manner that could reflect the gradual changes in composition of bioactive ingredients. In conclusion, the experiments presented here showed that the growing complexity of a mixture of phytochemicals seems to create a new redox bioactive substance rather than enrich the mixture with new activities, characteristic of the compound added. It follows that no simple, predictable relationship can be expected between the chemopreventive potential and the composition of real food items containing a complicated set of non-toxic redox active ingredients. Our observations suggest that the interactions between different bioactive compounds and food matrix components are cooperating factors determining the final bioactivity of foods.

Quantification of Polyphenols and Metals in Chinese Tea Infusions by Mass Spectrometry

Chemical compounds within tea (Camellia sinensis) are characterized by an extensive heterogeneity; some of them are crucial for their protective and defensive role in plants, and are closely connected to the benefits that the consumption of tea can provide. This paper is mainly focused on the characterization of polyphenols (secondary metabolites generally involved in defense against ultraviolet radiation and aggression by pathogens) and metals, extracted from nine Chinese tea samples, by integrating different mass spectrometry methodologies, LC-MS/MS in multiple reaction monitoring (MRM) and inductively coupled plasma mass spectrometry (ICP-MS). Our approach allowed to identify and compare forty polyphenols differently distributed in tea infusions at various fermentation levels. The exploration of polyphenols with nutraceutical potential in tea infusions can widely benefit especially tea-oriented populations. The worldwide consumption of tea requires at the same time a careful monitoring of metals released during the infusion of tea leaves. Metal analysis can provide the identification of many healthy minerals such as potassium, sodium, calcium, magnesium, differently affected by the fermentation of leaves. Our results allowed us: (i) to draw up a polyphenols profile of tea leaves subjected to different fermentation processes; (ii) to identify and quantify metals released from tea leaves during infusion. In this way, we obtained a molecular fingerprint useful for both nutraceutical applications and food control/typization, as well as for frauds detection and counterfeiting.

MicroRNA-based regulatory mechanisms underlying the synergistic antioxidant action of quercetin and catechin in H2O2-stimulated HepG2 cells: Roles of BACH1 in Nrf2-dependent pathways

The microRNA-based mechanisms underlying the antioxidant action(s) of co-existing flavonoids in response to oxidative stress are of high interest. This study aimed to extend the existing knowledge and provide insights into the potential regulatory network in response to oxidative stress and the co-presence of quercetin and catechin antioxidants, via a preclinical approach using H₂O₂-stimulated HepG2 cells. It was confirmed that BACH1 serves as an essential and direct negative regulator of the Keap1-Nrf2 signaling pathway and the antioxidant synergism between quercetin and catechin. BACH1 promoted reactive oxygen species (ROS) accumulation while inhibiting cell growth, which could be reversed by the synergistic action of let-7a-5p and miR-25-3p in the co-presence of quercetin and catechin. Both let-7a-5p and miR-25-3p could directly regulate the expression and function of BACH1 (e.g. upregulation of the two miRNAs could rescue largely overexpression of BACH1). Although these molecular interactions likely represented only some aspects of the overall regulatory network, this research confirms the feasibility of the combined uses of dietary flavonoids with chemopreventive properties in synergy during multiple-target interactions and multiple-pathway regulation.

Quantitative Detection of the Disappearance of the Antioxidant Ability of Catechin by Near-Infrared Absorption and Near-Infrared Photoluminescence Spectra of Single-Walled Carbon Nanotubes

We succeeded in quantitatively detecting the disappearance of catechin antioxidant ability as a function of time using near-infrared (NIR) absorbance and NIR photoluminescence (PL) spectra of single-walled carbon nanotubes (SWNTs) wrapped with DNA molecules (DNA-SWNT hybrids). When 15 μg/mL of catechin was added to the oxidized hybrid suspension, the absorbance of SWNTs increased, according to the antioxidant ability of catechin, and the effect was maintained at least for 30 min. When catechin concentrations were less than 0.3 μg/mL, SWNT absorbance gradually decreased, although it increased when catechin is added. The results revealed that disappearance of the catechin effects could be quantitatively detected by NIR absorbance spectra. When NIR PL was employed, the disappearance of PL intensity was also observed in the case of low catechin concentrations. However, time-lapse measurement of the disappearance was difficult because the PL intensity was rapidly quenched. In addition, the optical responses were different due to different chirality of SWNTs. Our results suggested that both NIR absorbance and PL can detect disappearance of catechin antioxidant effects; in particular, slow response of NIR absorbance was effective to detect time dependence of the disappearance of the catechin effects. Contrarily, PL revealed huge and rapid responses in contrast to NIR absorbance. PL might be effective for reversible use of DNA-SWNT hybrids as a nanobiosensor.