The Substituent Effect on the Radical Scavenging Activity of Apigenin

Computational Chemistry Strategies to Investigate the Antioxidant Activity of Flavonoids-An Overview

Despite several decades of research, the beneficial effect of flavonoids on health is still enigmatic. Here, we focus on the antioxidant effect of flavonoids, which is elementary to their biological activity. A relatively new strategy for obtaining a more accurate understanding of this effect is to leverage computational chemistry. This review systematically presents various computational chemistry indicators employed over the past five years to investigate the antioxidant activity of flavonoids. We categorize these strategies into five aspects: electronic structure analysis, thermodynamic analysis, kinetic analysis, interaction analysis, and bioavailability analysis. The principles, characteristics, and limitations of these methods are discussed, along with current trends.

Defense mechanisms of alfalfa against cyclic tetramethylene tetranitramine (HMX) stress

Much attention has been paid to the environmental toxicity and ecological risk caused by cyclic tetramethylene tetranitramine (HMX) pollution in military activity sites. In this study, the response mechanism of alfalfa plants to HMX was analyzed from the aspects of the photosynthetic system, micromorphology, antioxidant enzyme system, mineral metabolism, and secondary metabolism, in order to improve the efficiency of plant restoration. Exposure to 5 mg·L-1 HMX resulted in a significant increase in leaf N content and a significant increase and drift of the Fourier transform infrared protein peak area. Transmission electron microscopy images revealed damage to the root system subcellular morphology, but the plant leaves effectively resisted HMX pressure, and the photosynthetic parameters essentially maintained steady-state levels. The root proline content decreased significantly by 23.1-47.2 %, and the root reactive oxygen species content increased significantly by 1.66-1.80 fold. The roots regulate the transport/absorption of many elements that impart stress resistance, and Cu, Mn, and Na uptake is significantly associated with secondary metabolism. The metabolism of roots was upregulated in general by HMX exposure, with the main differences appearing in the content of lipids and lipid-like molecules, further confirming damage to the root biofilm structure. HMX causes an imbalance in the energy supply from oxidative phosphorylation in roots and generates important biomarkers in the form of pyrophosphate and dihydrogen phosphate. Interestingly, HMX had no significant effect on basic metabolic networks (i.e., glycolysis/gluconeogenesis and the tricarboxylic acid cycle), confirming that alfalfa has good stress resistance. Alfalfa plants apparently regulate multiple network systems to resist/overcome HMX toxicity. These findings provide a scientific basis for improving plant stress tolerance and understanding the HMX toxicity mechanism.

Graphene oxide and flavonoids as potential inhibitors of the spike protein of SARS-CoV-2 variants and interaction between ligands: a parallel study of molecular docking and DFT

Nanocarriers allow the connection between biomolecules and other structures to enhance the treatment efficacy, through the biomolecule's properties to an existing drug, or to allow a better and specific delivery. Apigenin and orientin are biomolecules with excellent therapeutic properties that are proposed in the fight against COVID-19. Besides that, graphene oxide is a nanomaterial that exhibits antiviral activity and is used as a nanocarrier of several drugs. We evaluated in this work, through molecular docking, the binding affinity between these structures to the receptor-binding domain of spike protein of two coronavirus variants, Delta and Omicron. The results indicate that all the structures exhibit affinity with the two protein targets, with binding affinity values of -11.88 to -6.65 kcal/mol for the Delta variant and values of -9.58 to -13.20 kcal/mol for the Omicron variant, which is a successful value as found in the literature as a potential inhibitor of SARS-CoV-2 infection. Also, through first-principles calculations based on Density Functional Theory, the interaction of graphene oxide with the biomolecules apigenin and orientin occurred. The results exhibit weak binding energy, which indicates that physical adsorption occurs, with better results when the biomolecule is set in parallel to the nanomaterial due to attractive π-π staking. These results are conducive to the development of a nanocarrier.

Quantum-mechanical characteristics of apigenin: Antiradical, metal chelation and inhibitory properties in physiologically relevant media

Density functional theory was used to examine the antioxidant activity of apigenin. All protonated species that are present in a non-negligible population at physiological pH were considered in the study. The ability to scavenge the hydroperoxide radical was evaluated in lipid and aqueous environments. The capacity to halt the Fenton reaction by chelating Fe(III) and Cu(II) ions was also investigated, as was the ability to inhibit xanthine oxidase. The results indicate that these activities may be particularly important in describing the beneficial effects of apigenin, especially because of its lower anti-•OOH potential than Trolox or vitamin C. The findings underscore the significant role of dianion in the antiradical and chelating properties, despite its presence in much lower molar fractions than other ions.

Upregulation of Nrf2/HO-1 Signaling and Attenuation of Oxidative Stress, Inflammation, and Cell Death Mediate the Protective Effect of Apigenin against Cyclophosphamide Hepatotoxicity

Liver injury is among the adverse effects of the chemotherapeutic agent cyclophosphamide (CP). This study investigated the protective role of the flavone apigenin (API) against CP-induced liver damage, pointing to the involvement of Nrf2/HO-1 signaling. Rats were treated with API (20 and 40 mg/kg) for 15 days and received CP (150 mg/kg) on day 16. CP caused liver damage manifested by an elevation of transaminases, alkaline phosphatase (ALP), and lactate dehydrogenase (LDH), and histological alterations, including granular vacuolation, mononuclear cell infiltration, and hydropic changes. Hepatic reactive oxygen species (ROS), malondialdehyde (MDA), and nitric oxide (NO) were increased and glutathione (GSH) and antioxidant enzymes were decreased in CP-administered rats. CP upregulated the inflammatory markers NF-κB p65, TNF-α, IL-6, and iNOS, along with the pro-apoptotic Bax and caspase-3. Pre-treatment with API ameliorated circulating transaminases, ALP, and LDH, and prevented histopathological changes in CP-intoxicated rats. API suppressed ROS, MDA, NO, NF-κB p65, iNOS, inflammatory cytokines, oxidative DNA damage, Bax, and caspase-3 in CP-intoxicated rats. In addition, API enhanced hepatic antioxidants and Bcl-2 and boosted the Nrf2 and HO-1 mRNA abundance and protein. In conclusion, API is effective in preventing CP hepatotoxicity by attenuating oxidative stress, the inflammatory response, and apoptosis. The hepatoprotective efficacy of API was associated with the upregulation of Nrf2/HO-1 signaling.

Current Trends in Computational Quantum Chemistry Studies on Antioxidant Radical Scavenging Activity

The antioxidative nature of chemicals is now routinely studied using computational quantum chemistry. Scientists are constantly proposing new approaches to investigate those methods, and the subject is evolving at a rapid pace. The goal of this review is to collect, consolidate, and present current trends in a clear, methodical, and reference-rich manner. This paper is divided into several sections, each of which corresponds to a different stage of elaborations: preliminary concerns, electronic structure analysis, and general reactivity (thermochemistry and kinetics). The sections are further subdivided based on methodologies used. Concluding remarks and future perspectives are presented based on the remaining elements.

Remodeling the Epigenetic Landscape of Cancer-Application Potential of Flavonoids in the Prevention and Treatment of Cancer

Epigenetics, including DNA methylation, histone modification, and noncoding RNA regulation, are physiological regulatory changes that affect gene expression without modifying the DNA sequence. Although epigenetic disorders are considered a sign of cell carcinogenesis and malignant events that affect tumor progression and drug resistance, in view of the reversible nature of epigenetic modifications, clinicians believe that associated mechanisms can be a key target for cancer prevention and treatment. In contrast, epidemiological and preclinical studies indicated that the epigenome is constantly reprogrammed by intake of natural organic compounds and the environment, suggesting the possibility of utilizing natural compounds to influence epigenetics in cancer therapy. Flavonoids, although not synthesized in the human body, can be consumed daily and are common in medicinal plants, vegetables, fruits, and tea. Recently, numerous reports provided evidence for the regulation of cancer epigenetics by flavonoids. Considering their origin in natural and food sources, few side effects, and remarkable biological activity, the epigenetic antitumor effects of flavonoids warrant further investigation. In this article, we summarized and analyzed the multi-dimensional epigenetic effects of all 6 subtypes of flavonoids (including flavonols, flavones, isoflavones, flavanones, flavanols, and anthocyanidin) in different cancer types. Additionally, our report also provides new insights and a promising direction for future research and development of flavonoids in tumor prevention and treatment via epigenetic modification, in order to realize their potential as cancer therapeutic agents.

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.

Investigation of HMG-CoA reductase inhibitory and antioxidant effects of various hydroxycoumarin derivatives

Cardiovascular diseases are one of the primary causes of deaths worldwide, and the development of atherosclerosis is closely related to hypercholesterolemia. As the reduction of the low-density lipoprotein cholesterol level is critical for treating these diseases, the inhibition of 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase, which is essentially responsible for cholesterol biosynthesis, stands out as a key solution to lower plasma cholesterol levels. In this study, we synthesized several dihydroxycoumarins and investigated their antioxidant and in vitro HMG-CoA reductase inhibitory effects. Furthermore, we carried out in silico studies and examined the quantum-chemical properties of the coumarin derivatives. We also performed molecular docking experiments and analyzed the binding strength of each coumarin derivative. Our results revealed that compound IV displayed the highest HMG-CoA reductase inhibitory activity (IC₅₀  = 42.0 µM) in vitro. Cupric-reducing antioxidant capacity and ferric-reducing antioxidant power assays demonstrated that coumarin derivatives exhibit potent antioxidant activities. Additionally, a close relationship was found between the lowest unoccupied molecular orbital energy levels and the antioxidant activities.

Apigenin, flavonoid component isolated from Gentiana veitchiorum flower suppresses the oxidative stress through LDLR-LCAT signaling pathway

Flower of Gentiana veitchiorum has traditionally been used as an herbal medicine in Tibet for treatment of variola, respiratory infection, and pneumonia. However, the effective components contained in flower are not identified yet, and the underlying mechanisms for anti-inflammatory, antibacterial, and antioxidative activities remain to be elucidated. Here, we first extracted the flavonoid mixture from G. veitchiorum flower. The mixture was then further isolated and the within compounds was identified through the high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The results showed that apigenin (4',5,7-trihydroxyflavone) was the most abundant flavonoid in G. veitchiorum flower. We next examined the antioxidative activity of the extracted apigenin using the ferric reducing/antioxidant power (FRAP), the 1,1-diphenyl-2-picrylhydrazyl (DPPH), and the 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) assays and found that a positive correlation between apigenin concentration and reactive oxygen species (ROS) scavenging rate. The biochemical assays further revealed that the levels of total cholesterol (TC), triglyceride (TG), and malondialdehyde (MDA) were reduced, while the activity of superoxide dismutase (SOD) was increased after apigenin treatment in hyperlipidemic rats. Moreover, we performed histopathological investigations and found that the lipidic deposition patterns were recovered and the amount of lipid vacuoles was significantly reduced in apigenin-treated hyperlipidemic rat liver. Western blotting assay showed that the expression of low-density lipoprotein receptor (LDLR) and lecithin-cholesterol acyltransferase (LCAT) were up-regulated in the apigenin-treated samples. Overall, our results demonstrated that the apigenin isolated from G. veitchiorum flower exhibited radical scavenging activities, and reversed the high fat diet-induced oxidative damage in rats. Its antioxidative activities are probably achieved via LDLR-LCAT signaling pathway.

Computational Study of Ortho-Substituent Effects on Antioxidant Activities of Phenolic Dendritic Antioxidants

Antioxidants are an important component of our ability to combat free radicals-an excess of which leads to oxidative stress, which is related to aging and numerous human diseases. Oxidative damage also shortens the shelf-life of foods and other commodities. Understanding the structure-activity relationship of antioxidants and their mechanisms of action is important for designing more potent antioxidants for potential use as therapeutic agents as well as preservatives. We report the first computational study on the electronic effects of ortho-substituents in dendritic tri-phenolic antioxidants, comprising a common phenol moiety and two other phenol units with electron-donating or electron-withdrawing substituents. Among the three proposed antioxidant mechanisms, sequential proton loss electron transfer (SPLET) was found to be the preferred mechanism in methanol for the dendritic antioxidants based on calculations using Gaussian 16. We then computed the total enthalpy values by cumulatively running SPLET for all three rings to estimate electronic effects of substituents on overall antioxidant activity of each dendritic antioxidant and establish their structure-activity relationships. Our results show that the electron-donating o-OCH3 group has a beneficial effect while the electron-withdrawing o-NO2 group has a negative effect on the antioxidant activity of the dendritic antioxidant. The o-Br and o-Cl groups did not show any appreciable effects. These results indicate that electron-donating groups such as o-methoxy are useful for designing potent dendritic antioxidants while the nitro and halogens do not add value to the radical scavenging antioxidant activity. We also found that the half-maximal inhibitory concentration (IC50) values of 2,2-diphenyl-1-picrylhydrazyl (DPPH) better correlate with the second step (electron transfer enthalpy, ETE) than the first step (proton affinity, PA) of the SPLET mechanism, implying that ETE is the better measure for estimating overall radical scavenging antioxidant activities.

A Theoretical and Experimental Study for Screening Inhibitors for Styrene Polymerization

Styrene is one of the most important monomers utilized in the synthesis of various polymers. Nevertheless, during distillation, storage, and transportation of ST, undesired polymer (i.e., UP) formation can take place. Thus, the control of undesired polymerization of styrene is a challenging issue facing industry. To tackle the mentioned issue, the antipolymer and antioxidant activity of stable nitroxide radicals (i.e., SNRs) and phenolics in styrene polymerization were studied by density functional theory (DFT) calculation and experimental approach. The electrophilicity index and growth percentage have been determined by DFT calculation and experimental approach, respectively. It is depicted that 2,6-di-tert-butyl-4-methoxyphenol (DTBMP) and 2,6-di-tert-butyl-4-methylphenol (BHT) from phenolics, and 4-hydroxy-2,2,6,6-tetramethyl piperidine 1-Oxyl (4-hydroxy-TEMPO) and 4-oxo-2,2,6,6-tetramethylpiperidine 1-Oxyl (4-oxo-TEMPO) from stable nitroxide radicals were the most effective inhibitors. Also, the growth percentage of DTMBP, BHT, 4-hydroxy-TEMPO, and 4-oxo-TEMPO after 4 h were 16.40, 42.50, 24.85, and 46.8, respectively. In addition, the conversion percentage of DTMBP, BHT, 4-hydroxy-TEMPO, and 4-oxo-TEMPO after 4 h were obtained to be 0.048, 0.111, 0.065, and 0.134, respectively. Furthermore, the synergistic effect of these inhibitors was investigated experimentally, indicating that DTMBP/4-hydroxy-TEMPO exerted the best synergistic effects on the inhibition of polymerization. The optimum inhibition effect was observed at the blend of 4-hydroxy-TEMPO (25 wt.%) and DTMBP (75 wt.%,) corresponding to 6.8% polymer growth after 4 h.

Niosomal Nanocarriers for Enhanced Skin Delivery of Quercetin with Functions of Anti-Tyrosinase and Antioxidant

This study aimed to screen an effective flavonoid with promising whitening and antioxidant capacities, and design flavonoid-loaded niosomes to improve its solubility, stability, and penetration. In vitro anti-tyrosinase and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging experiments were conducted to investigate the whitening and antioxidant capacities of several flavonoids, including quercetin, morin, festin, myricetin, rutin, and breviscapine. The conductivity, viscosity, and particle size of Span60-RH40-based formulation of nonionic surfactant vesicles (niosomes) with different mass ratios were studied to determine the most appropriate formulation. Drug-loaded niosomes were characterized for size, zeta potential, morphology, and entrapment efficiency. The photostability, solubility, release behavior, ex vivo drug penetration, and skin retention were also studied. The results showed that quercetin has considerable whitening and antioxidant capacities and Span60-RH40 at a mass ratio of 9:11 forms spherical or oval niosomes of 97.6 ± 3.1 nm with a zeta potential range of 31.1 ± 0.9 mV, and drug entrapment efficiency as high as 87.3 ± 1.6%. Niosomes remarkably improved the solubility and photostability of quercetin. Furthermore, compared to quercetin solution, quercetin-niosomes had the advantages of sustained release and improved transdermal penetration, with skin retention 2.95 times higher than quercetin solution.