Redox reactions of heme proteins with flavonoids

(-)-Epigallocatechin gallate as an inhibitor of hemoglobin-catalyzed lipid oxidation: molecular mechanism of action and nutritional application

Hemoglobin (Hb) is effective inducer for lipid oxidation and protein-polyphenol interaction is a well-known phenomenon. The effects of the interaction of (-)-epigallocatechin gallate (EGCG) with Hb on lipid oxidation were rarely elucidated. The detailed interaction between bovine Hb and EGCG was systematically explored by experimental and theoretical approaches, to illustrate the molecular mechanisms by which EGCG influenced the redox states and stability of Hb. EGCG would bind to the central pocket of protein with one binding site to form Hb-EGCG complex. The binding constant for Hb-EGCG complex was 0.34 × 104 M-1 at 277 K, and thermodynamic parameters (ΔH > 0, ΔS > 0 and ΔG < 0) revealed the participation of hydrophobic forces in the binding process. The binding of EGCG would increase the compactness of protein molecule and diminish the crevice near the heme cavity, which was responsible for the reduction of met-Hb to oxy-Hb and inhibition of hemin release from met-Hb. Moreover, EGCG efficiently suppressed Hb-caused lipid oxidation in liposomes and cod muscles, which was possibly attributed to the reduction to oxy-Hb state and declined hemin dissociation from met-Hb. Altogether, our results provide significant insights into the binding of EGCG to redox-active Hb, which represents a novel mechanism for the anti-oxidant capacity of EGCG in human health and is favorable to the applications of natural EGCG in the good quality of Hb-containing products.

USP7 promotes cardiometabolic disorders and mitochondrial homeostasis dysfunction in diabetic mice via stabilizing PGC1β

Diabetic cardiomyopathy (DCM) is a major complication of diabetes and is characterized by left ventricular dysfunction. Currently, there is a lack of effective treatments for DCM. Ubiquitin-specific protease 7 (USP7) plays a key role in various diseases. However, whether USP7 is involved in DCM has not been established. In this study, we demonstrated that USP7 was upregulated in diabetic mouse hearts and NMCMs co-treated with HG+PA or H9c2 cells treated with PA. Abnormalities in diabetic heart morphology and function were reversed by USP7 silencing through conditional gene knockout or chemical inhibition. Proteomic analysis coupled with biochemical validation confirmed that PCG1β was one of the direct protein substrates of USP7 and aggravated myocardial damage through coactivation of the PPARα signaling pathway. USP7 silencing restored the expression of fatty acid metabolism-related proteins and restored mitochondrial homeostasis by inhibiting mitochondrial fission and promoting fusion events. Similar effects were also observed in vitro. Our data demonstrated that USP7 promoted cardiometabolic metabolism disorders and mitochondrial homeostasis dysfunction via stabilizing PCG1β and suggested that silencing USP7 may be a therapeutic strategy for DCM.

Chronic cypermethrin induced toxicity and molecular fate assessment within common carp (Cyprinus carpio) using multiple biomarkers approach and its novel therapeutic detoxification

Cypermethrin (CYP) is a chemical of emerging concern which has persistent and bioaccumulating impacts as it can be found extensively in freshwater ecosystem and agricultural products. It has exposure risk and toxic effects over human edible fish, as common carp. Four groups were designed for toxicity assessment and detoxification approach: control group (CL), CYP exposure group (CYP), CYP + 10% M. oleifera leaves and 10% M. oleifera seeds (CMO group), 10% M. oleifera leaves and 10% M. oleifera seeds (MO group). Trial period was forty days during which cohort of 240 fish in CYP and CMO group was exposed to 1/5 of 96h LC50 of CYP (0.1612 μg/L). CYP-exposed carp exhibited lower growth parameters, but carp fed with 10% M. oleifera seeds and leaves showed significant improvement in growth rate (SGR, RGR) and weight gain (WG) as compared to the control group. CYP exposure negatively affected haemato-biochemical parameters. Moreover, CYP exposure also led to oxidative stress, damaged immunological parameters, genotoxicity and histopathological damage in liver and intestinal cells. Whereas, M. oleifera supplementation has ameliorated these conditions. Thereby, supplementation with M. oleifera is potential and novel therapeutic detoxication approach for common carp and human health against persistent and bioaccumulating emerging chemicals.

Binding of Quercetin to Hemoglobin Reduced Hemin Release and Lipid Oxidation

The interactions between quercetin and bovine (or human) hemoglobin (Hb) were systematically investigated by fluorescence, UV-vis absorption spectroscopy, and molecular docking to demonstrate the structural mechanism by which quercetin affected the Hb redox state and stability. Quercetin could interact with the central cavity of the Hb molecule with one binding site to generate an Hb-quercetin complex, and the hydrophobic interaction played an important role in the formation of the complex. The binding constant for the Hb-quercetin complex at 298 K was observed to be 1.25 × 10⁴ M^-1. In addition, quercetin effectively inhibited Hb-induced lipid oxidation in liposomes or washed muscles, which was ascribed to the conversion to oxy-Hb and decreased hemin dissociation from met-Hb. Consistent with its lower abilities to bind Hb and scavenge free radicals, rutin (i.e., quercetin-3-rhamnosylglucsoside) did not significantly influence the redox state of Hb nor reduce hemin release from Hb, and subsequently, it less effectively inhibited Hb-induced lipid oxidation than quercetin. Altogether, the results herein provide novel insights into the antioxidant mechanism for quercetin and are beneficial to the application of natural quercetin in Hb-containing foods.

Recent insights into oxidative metabolism of quercetin: catabolic profiles, degradation pathways, catalyzing metalloenzymes and molecular mechanisms

Quercetin is the most abundant polyphenolic flavonoid (flavonol subclass) in vegetal foods and medicinal plants. This dietary chemopreventive agent has drawn significant interest for its multiple beneficial health effects ("polypharmacology") largely associated with the well-documented antioxidant properties. However, controversies exist in the literature due to its dual anti-/pro-oxidant character, poor stability/bioavailability but multifaceted bioactivities, leaving much confusion as to its exact roles in vivo. Increasing evidence indicates that a prior oxidation of quercetin to generate an array of chemical diverse products with redox-active/electrophilic moieties is emerging as a new linkage to its versatile actions. The present review aims to provide a comprehensive overview of the oxidative conversion of quercetin by systematically analyzing the current quercetin-related knowledge, with a particular focus on the complete spectrum of metabolite products, the enzymes involved in the catabolism and the underlying molecular mechanisms. Herein we review and compare the oxidation pathways, protein structures and catalytic patterns of the related metalloenzymes (phenol oxidases, heme enzymes and specially quercetinases), aiming for a deeper mechanistic understanding of the unusual biotransformation behaviors of quercetin and its seemingly controversial biological functions.

Deletion of cox7c Results in Pan-Azole Resistance in Aspergillus fumigatus

In Aspergillus fumigatus, the most prevalent resistance to azoles results from mutational modifications of the azole target protein Cyp51A, but there are non-cyp51A mutants resistant to azoles, and the mechanisms underlying the resistance of these strains remain to be explored. Here, we identified a novel cytochrome c oxidase, cox7c (W56*), nonsense mutation in the laboratory and found that it caused reduced colony growth and resistance to multiantifungal agents. Meanwhile, we revealed that cold storage is responsible for increased tolerance of conidia to itraconazole (ITC) stress, which further advances azole-resistant mutations (cryopreservation→ITC tolerance→azole resistance). The deletion or mutation of cox7c results explicitly in resistance to antifungal-targeting enzymes, including triazoles, polyenes, and allylamines, required for ergosterol synthesis, or resistance to fungal ergosterol. A high-performance liquid chromatography (HPLC) assay showed that the cox7c knockout strain decreased intracellular itraconazole concentration. In addition, the lack of Cox7c resulted in the accumulation of intracellular heme B. We validated that an endogenous increase in, or the exogenous addition of, heme B was capable of eliciting azole resistance, which was in good accordance with the phenotypic resistance analysis of cox7c mutants. Furthermore, RNA sequencing verified the elevated transcriptional expression levels of multidrug transport genes. Additionally, lower itraconazole-induced reactive oxygen species generation in mycelia of a cox7c-deletion strain suggested that this reduction may, in part, contribute to drug resistance. These findings increase our understanding of how A. fumigatus’s direct responses to azoles promote fungal survival in the environment and address genetic mutations that arise from patients or environments.

Mutations that alter Arabidopsis flavonoid metabolism affect the circadian clock

Flavonoids are a well-known class of specialized metabolites that play key roles in plant development, reproduction, and survival. Flavonoids are also of considerable interest from the perspective of human health, as both phytonutrients and pharmaceuticals. RNA sequencing analysis of an Arabidopsis null allele for chalcone synthase (CHS), which catalyzes the first step in flavonoid metabolism, has uncovered evidence that these compounds influence the expression of genes associated with the plant circadian clock. Analysis of promoter-luciferase constructs further showed that the transcriptional activity of CCA1 and TOC1, two key clock genes, is altered in CHS-deficient seedlings across the day/night cycle. Similar findings for a mutant line lacking flavonoid 3'-hydroxylase (F3'H) activity, and thus able to synthesize mono- but not dihydroxylated B-ring flavonoids, suggests that the latter are at least partially responsible; this was further supported by the ability of quercetin to enhance CCA1 promoter activity in wild-type and CHS-deficient seedlings. The effects of flavonoids on circadian function were also reflected in photosynthetic activity, with chlorophyll cycling abolished in CHS- and F3'H-deficient plants. Remarkably, the same phenotype was exhibited by plants with artificially high flavonoid levels, indicating that neither the antioxidant potential nor the light-screening properties of flavonoids contribute to optimal clock function, as has recently also been demonstrated in animal systems. Collectively, the current experiments point to a previously unknown connection between flavonoids and circadian cycling in plants and open the way to better understanding of the molecular basis of flavonoid action.

Crosstalk between Heme Oxygenase-1 and Iron Metabolism in Macrophages: Implications for the Modulation of Inflammation and Immunity

Heme oxygenase-1 (HO-1) is an enzyme that catalyzes the degradation of heme, releasing equimolar amounts of carbon monoxide (CO), biliverdin (BV), and iron. The anti-inflammatory and antioxidant properties of HO-1 activity are conferred in part by the release of CO and BV and are extensively characterized. However, iron constitutes an important product of HO-1 activity involved in the regulation of several cellular biological processes. The macrophage-mediated recycling of heme molecules, in particular those contained in hemoglobin, constitutes the major mechanism through which living organisms acquire iron. This process is finely regulated by the activities of HO-1 and of the iron exporter protein ferroportin. The expression of both proteins can be induced or suppressed in response to pro- and anti-inflammatory stimuli in macrophages from different tissues, which alters the intracellular iron concentrations of these cells. As we discuss in this review article, changes in intracellular iron levels play important roles in the regulation of cellular oxidation reactions as well as in the transcriptional and translational regulation of the expression of proteins related to inflammation and immune responses, and therefore, iron metabolism represents a potential target for the development of novel therapeutic strategies focused on the modulation of immunity and inflammation.

Redox Activity of Flavonoids: Impact on Human Health, Therapeutics, and Chemical Safety

The cost-effectiveness of presently used therapies is a problem in overall redox-based management, which is posing a significant financial burden on communities across the world. As a result, sophisticated treatment models that provide notions of predictive diagnoses followed by targeted preventive therapies adapted to individual patient profiles are gaining global acclaim as being beneficial to patients, the healthcare sector, and society as a whole. In this context, natural flavonoids were considered due to their multifaceted antioxidant, anti-inflammatory, and anticancer effects as well as their low toxicity and ease of availability. The aim of this review is to focus on the capacity of flavonoids to modulate the responsiveness of various diseases and ailments associated with redox toxicity. The review will also focus on the flavonoids' pathway-based redox activity and the advancement of redox-based therapies as well as flavonoids' antioxidant characteristics and their influence on human health, therapeutics, and chemical safety. Research findings indicated that flavonoids significantly exhibit various redox-based therapeutic responses against several diseases such as inflammatory, neurodegenerative, cardiovascular, and hepatic diseases and various types of cancer by activating the Nrf2/Keap1 transcription system, suppressing the nuclear factor κB (NF-κB)/IκB kinase inflammatory pathway, abrogating the function of the Hsp90/Hsf1 complex, inhibiting the PTEN/PI3K/Akt pathway, and preventing mitochondrial dysfunction. Some flavonoids, especially genistein, apigenin, amentoflavone, baicalein, quercetin, licochalcone A, and biochanin A, play a potential role in redox regulation. Conclusions of this review on the antioxidant aspects of flavonoids highlight the medicinal and folk values of these compounds against oxidative stress and various diseases and ailments. In short, treatment with flavonoids could be a novel therapeutic invention in clinical trials, as we hope.

The effect of Luteolin on DNA damage mediated by a copper catalyzed Fenton reaction

Luteolin has been reviewed as a flavonoid possessing potential cardioprotective, anti-inflammatory, anti-cancer activities. Having multiple biological effects, luteolin may act as either an antioxidant or a pro-oxidant. In this work, the protective role of copper(II)-chelation by luteolin on DNA damage via the Cu-Fenton reaction was studied. EPR and UV-vis spectroscopic data demonstrated that the luteolin, lacking 3-OH group, chelates to Cu(II) via the 5-OH and 4-CO groups, respectively. EPR spin trapping experiments using DMPO spin trap confirmed that the coordination of luteolin to Cu(II) significantly suppressed formation of hydroxyl and superoxide radicals (by 80%) in a Cu-Fenton system. Absorption titrations showed that the chelation of Cu(II) by luteolin slightly increased the mild intercalation strength of its interaction with DNA, as compared with free luteolin. Comparison with kaempferol and quercetin revealed, that the strength of the interaction between the free flavonoids/Cu-flavonoid complexes with DNA is only mildly affected by the presence/absence of 3-OH group. Due to the differences in the sensitivities of absorption titrations and viscometry, the latter confirmed weaker DNA intercalating efficiency of Cu-luteolin complex than does free luteolin. A dose dependent protective effect of luteolin against ROS-induced DNA damage was observed using gel electrophoresis. This effect was more pronounced compared to quercetin and kaempferol. In conclusion, the administration of luteolin to patients suffering from oxidative stress-related diseases with disturbed Cu-metabolism such as Alzheimer's diseases (antioxidant effect) and certain cancers (prooxidant effect) may have several health benefits.

The α-melanocyte-stimulating hormone/melanocortin-1 receptor interaction: A driver of pleiotropic effects beyond pigmentation

Melanocortin-1 Receptor (MC1R), when stimulated by alpha-melanocyte-stimulating hormone (α-MSH), is a driver of eumelanogenesis. Brown/black eumelanin is an effective filter against ultraviolet radiation (UVR) and is a scavenger of free radicals. Several polymorphic variants of MC1R are frequent in red-head people. These polymorphisms reduce the ability of MC1R to promote eumelanogenesis after its activation and spontaneous pheomelanogenesis take place. Since pheomelanin can act as an endogenous photosensitizer, people carrying MC1R polymorphisms are more susceptible to skin cancer. Here, we summarize current knowledge on the biology of MC1R beyond its ability to drive eumelanogenesis. We analyze its capacity to cope with oxidative insult and consequent DNA damage. We describe its ability to transduce through different pathways. We start from the canonical pathway, the cAMP/protein kinase A (PKA) pathway mainly involved in promoting eumelanogenesis, and protection from oxidative damage, and we then move on to describe more recent knowledge concerning ERK pathways, phosphoinositide 3-kinase (PI3K) pathway/AKT, and α-MSH/Peroxisome proliferators activated receptor-γ (PPAR-γ) connection. We describe MC1R polymorphic variants associated with melanoma risk which represent an open window of clinical relevance.

Iron Complexes of Flavonoids-Antioxidant Capacity and Beyond

Flavonoids are common plant natural products able to suppress ROS-related damage and alleviate oxidative stress. One of key mechanisms, involved in this phenomenon is chelation of transition metal ions. From a physiological perspective, iron is the most significant transition metal, because of its abundance in living organisms and ubiquitous involvement in redox processes. The chemical, pharmaceutical, and biological properties of flavonoids can be significantly affected by their interaction with transition metal ions, mainly iron. In this review, we explain the interaction of various flavonoid structures with Fe(II) and Fe(III) ions and critically discuss the influence of chelated ions on the flavonoid biochemical properties. In addition, specific biological effects of their iron metallocomplexes, such as the inhibition of iron-containing enzymes, have been included in this review.