The prooxidant, rather than antioxidant, acts of daidzein in vivo and in vitro: Daidzein suppresses glutathione metabolism

Dietary Polyphenols: Review on Chemistry/Sources, Bioavailability/Metabolism, Antioxidant Effects, and Their Role in Disease Management

Polyphenols, as secondary metabolites ubiquitous in plant sources, have emerged as pivotal bioactive compounds with far-reaching implications for human health. Plant polyphenols exhibit direct or indirect associations with biomolecules capable of modulating diverse physiological pathways. Due to their inherent abundance and structural diversity, polyphenols have garnered substantial attention from both the scientific and clinical communities. The review begins by providing an in-depth analysis of the chemical intricacies of polyphenols, shedding light on their structural diversity and the implications of such diversity on their biological activities. Subsequently, an exploration of the dietary origins of polyphenols elucidates the natural plant-based sources that contribute to their global availability. The discussion extends to the bioavailability and metabolism of polyphenols within the human body, unraveling the complex journey from ingestion to systemic effects. A central focus of the review is dedicated to unravelling the antioxidant effects of polyphenols, highlighting their role in combating oxidative stress and associated health conditions. The comprehensive analysis encompasses their impact on diverse health concerns such as hypertension, allergies, aging, and chronic diseases like heart stroke and diabetes. Insights into the global beneficial effects of polyphenols further underscore their potential as preventive and therapeutic agents. This review article critically examines the multifaceted aspects of dietary polyphenols, encompassing their chemistry, dietary origins, bioavailability/metabolism dynamics, and profound antioxidant effects. The synthesis of information presented herein aims to provide a valuable resource for researchers, clinicians, and health enthusiasts, fostering a deeper understanding of the intricate relationship between polyphenols and human health.

Comparison of the effect of quercetin and daidzein on production performance, anti-oxidation, hormones, and cecal microflora in laying hens during the late laying period

This study aims to compare the effect of quercetin and daidzein on production performance, anti-oxidation, hormones, and cecal microflora in laying hens during the late laying period. A total of 360 53-week-old healthy Hyline brown laying hens were randomly divided into 3 groups (control, 0.05% quercetin, and 0.003% daidzein). Diets were fed for 10 wk, afterwards 1 bird per replicate (6 replicates) were euthanized for sampling blood, liver and cecal digesta. Compared with the control, quercetin significantly increased laying rate and decreased feed-to-egg weight ratio from wk 1 to 4, wk 5 to 10, and wk 1 to 10 (P < 0.05). Quercetin significantly increased the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and decreased catalase (CAT) activity and malondialdehyde (MDA) content in serum and liver (P < 0.05) and increased content of total antioxidant capacity (T-AOC) in liver (P < 0.05). Quercetin increased content of estradiol (E₂), luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), insulin-like growth factor 1 (IGF-1), triiodothyronine (T₃) and thyroxine (T₄) in serum (P < 0.05). Quercetin significantly decreased the relative abundance of Bacteroidaceae and Bacteroides (P < 0.01) and significantly increased the relative abundance of Lactobacillaceae and Lactobacillus (P < 0.05) at family and genus levels in cecum. Daidzein did not significantly influence production performance from wk 1 to 10. Daidzein significantly increased SOD activity and decreased CAT activity and MDA content in serum and liver (P < 0.05), and increased T-AOC content in liver (P < 0.05). Daidzein increased content of FSH, IGF-1, T₃ in serum (P < 0.05). Daidzein increased the relative abundance of Rikenellaceae RC9 gut group at genus level in cecum (P < 0.05). Quercetin increased economic efficiency by 137.59% and 8.77%, respectively, compared with daidzein and control. In conclusion, quercetin improved production performance through enhancing antioxidant state, hormone levels, and regulating cecal microflora in laying hens during the late laying period. Quercetin was more effective than daidzein in improving economic efficiency.

Unveiling the Pharmacological and Nanotechnological Facets of Daidzein: Present State-of-the-Art and Future Perspectives

Herbal drugs have been attracting much scientific interest in the last few decades and nowadays, phytoconstituents-based research is in progress to disclose their unidentified medicinal potential. Daidzein (DAI) is the natural phytoestrogen isoflavone derived primarily from leguminous plants, such as the soybean and mung bean, and its IUPAC name is 4',7-dihydroxyisoflavone. This compound has received great attention as a fascinating pharmacophore with remarkable potential for the therapeutic management of several diseases. Certain pharmacokinetic properties of DAI such as less aqueous solubility, low permeability, and poor bioavailability are major obstacles restricting the therapeutic applications. In this review, distinctive physicochemical characteristics and pharmacokinetics of DAI has been elucidated. The pharmacological applications in treatment of several disorders like oxidative stress, cancer, obesity, cardiovascular, neuroprotective, diabetes, ovariectomy, anxiety, and inflammation with their mechanism of action are explained. Furthermore, this review article comprehensively focuses to provide up-to-date information about nanotechnology-based formulations which have been investigated for DAI in preceding years which includes polymeric nanoparticles, solid lipid nanoparticles, nanostructured lipid carrier, polymer-lipid nanoparticles, nanocomplexes, polymeric micelles, nanoemulsion, nanosuspension, liposomes, and self-microemulsifying drug delivery systems.

Potential Protective Effects of Equol (Soy Isoflavone Metabolite) on Coronary Heart Diseases-From Molecular Mechanisms to Studies in Humans

Equol, a soy isoflavone-derived metabolite of the gut microbiome, may be the key cardioprotective component of soy isoflavones. Systematic reviews have reported that soy isoflavones have no to very small effects on traditional cardiovascular disease risk factors. However, the potential mechanistic mode of action of equol on non-traditional cardiovascular risk factors has not been systematically reviewed. We searched the PubMed through to July 2021 by using terms for equol and each of the following markers: inflammation, oxidation, endothelial function, vasodilation, atherosclerosis, arterial stiffness, and coronary heart disease. Of the 231 records identified, 69 articles met the inclusion criteria and were summarized. Our review suggests that equol is more lipophilic, bioavailable, and generally more potent compared to soy isoflavones. Cell culture, animal, and human studies show that equol possesses antioxidative, anti-inflammatory, and vasodilatory properties and improves arterial stiffness and atherosclerosis. Many of these actions are mediated through the estrogen receptor β. Overall, equol may have a greater cardioprotective benefit than soy isoflavones. Clinical studies of equol are warranted because equol is available as a dietary supplement.

Role of natural plant products against Alzheimer's disease

Alzheimer's disease (AD) is one of the major neurodegenerative disorder. Deposition of amyloid fibrils and tau protein are associated with various pathological symptoms. Currently limited medication is available for AD treatment. Most of the drugs are basically cholinesterase inhibitors and associated with various side effects. Natural plant products have shown potential as a therapeutic agent for the treatment of AD symptoms. Variety of secondary metabolites like flavonoids, tannins, terpenoids, alkaloids and phenols are used to reduce the progression of the disease. Plant products have less or no side effect and are easily available. The present review gives a detailed account of the potential of natural plant products against the AD symptoms.

Role of Plant-Derived Flavonoids and Their Mechanism in Attenuation of Alzheimer's and Parkinson's Diseases: An Update of Recent Data

Neurodegeneration is a progressive loss of neuronal cells in certain regions of the brain. Most of the neurodegenerative disorders (NDDs) share the communal characteristic such as damage or reduction of various cell types typically including astrocytes and microglial activity. Several compounds are being trialed to treat NDDs but they possess solitary symptomatic advantages along with copious side effects. The finding of more enthralling and captivating compounds to suspend and standstill the pathology of NDDs will be considered as a hallmark of present times. Phytochemicals possess the potential to alternate the synthetic line of therapy against NDDs. The present review explores the potential efficacy of plant-derived flavonoids against most common NDDs including Alzheimer's disease (AD) and Parkinson's disease (PD). Flavonoids are biologically active phytochemicals which possess potential pharmacological effects, including antiviral, anti-allergic, antiplatelet, anti-inflammatory, anti-tumor, anti-apoptotic and anti-oxidant effects and are able to attenuate the pathology of various NDDs through down-regulating the nitric oxide (NO) production, by reducing the tumor necrosis factor-α (TNF-α), by reducing the excitotoxicity of superoxide as well as acting as tyrosine kinase (TK) and monoamine oxidase (MAO) inhibiting enzyme.

In vitro antioxidant/prooxidant effects of combined use of flavonoids

The present study was undertaken to investigate the individual and combined antioxidant or prooxidant effects of genistein, daidzein and quercetin in human erythrocytes and rat microsomes in vitro. Their reducing potential against oxidation of a redox sensitive fluorescent probe, their protective effect against H₂O₂-induced membrane lipid peroxidation and their inhibitory effect on AAPH-induced hemolysis were evaluated. Genistein and daidzein were prooxidant in erythrocytes but antioxidant in microsomes where their metabolites might have been formed which suggests the importance of metabolic capacity in in vitro models to predict the physiological situation. Quercetin showed antioxidant effects in all models and conditions. Prooxidant effect of 'genistein-daidzein mixture', at their concentrations reflecting the real life, was suppressed by addition of quercetin to the mixture. Our study shows that flavonoids can exert prooxidant effects depending on the conditions, but the mixture effect should be considered while assessing their effects and safety in humans.

The antioxidant activity of daidzein metabolites, O‑desmethylangolensin and equol, in HepG2 cells

Daidzein and its glycoside form daidzin, are known to have potential health benefits and are metabolized to O‑desmethylangolensin (O‑DMA) and equol following consumption. In the current study, the antioxidant activity and cytotoxicity of O‑DMA, equol, daidzein and daidzin was investigated and their effects on HepG2 human hepatocelluar carcinoma cells were compared. For cytotoxicity assays, lactose dehydrogenase (LDH) release and 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide‑based cell viability, cells were exposed to various concentrations of each compound (5‑200 µM) for 24, 48 or 72 h. O‑DMA and equol did not affect LDH release, but higher concentrations (<75 µM) showed inhibition of cell growth. By contrast, daidzein and daidzin (200 µM) increased LDH release and cell growth. All compounds stimulated catalase and total superoxide dismutase (SOD) (CuZn‑ and Mn‑SOD) activity, and mRNA and protein expression. This phenomenon was most pronounced for O‑DMA and equol, as their effects were similar. These data suggested that O‑DMA and equol possess greater antioxidant properties compared with daidzein and may, thus, be beneficial for human health.

A potential daidzein derivative enhances cytotoxicity of epirubicin on human colon adenocarcinoma Caco-2 cells

In this study, we evaluated the effects of 8-hydroxydaidzein (8HD), an isoflavone isolated from fermented soy germ koji, and epirubicin (Epi), an antineoplastic agent, on the production of reactive oxygen species (ROS). We subsequently correlated the ROS levels to the anticancer mechanisms of Epi and 8HD in human colon adenocarcinoma Caco-2 cells. 8HD enhanced cytotoxicity of Epi and generated a synergistic effect. Epi and/or 8HD treatments increased the hydrogen peroxide and superoxide levels. Combined treatment markedly decreased mRNA expression levels of multidrug resistance protein 1 (MDR1), MDR-associated protein (MRP) 1, and MRP2. 8HD significantly intensified Epi intracellular accumulation in Caco-2 cells. 8HD and/or Epi-induced apoptosis, as indicated by the reduced mitochondrial membrane potential and increased sub-G1 phase in cell cycle. Moreover, 8HD and Epi significantly enhanced the mRNA expressions of Bax, p53, caspases-3, -8, and -9. To our best knowledge, this study verifies for the first time that 8HD effectively circumvents MDR in Caco-2 cells through the ROS-dependent inhibition of efflux transporters and p53-mediated activation of both death receptor and mitochondrial pathways of apoptosis. Our findings of 8HD shed light on the future search for potential biotransformed isoflavones to intensify the cytotoxicity of anticancer drugs through simultaneous reversal of pump and nonpump resistance.

Effects of various polyphenolics on hydrogen peroxide-induced p53 activity in NIH3T3 cells

A cell-based assay system was developed to evaluate the potential antioxidant and pro-oxidant effects of various dietary polyphenolic compounds based on the induction of p53 activity by hydrogen peroxide. A p53-luciferase reporter vector was stably transfected into NIH3T3 cells. Individual clones were isolated, and one clone (number 33) was selected that showed the highest induction levels with different generators of free radicals. Clone 33 was preincubated for 1 hour with 0, 0.1, 1.0, 10, 50, and 100 microM genistein, resveratrol, naringenin, quercetin, epicatechin gallate, and epigallocatechin-3-gallate and then treated with 40 microM hydrogen peroxide or left untreated for 4 hours. Cell lysates were prepared and assayed for luciferase activity. Results show that the effects on p53 activity by the different polyphenolics varied depending on the compound and concentration. Quercetin and genistein reduced p53 activity at 1.0 microM, whereas the other four compounds did not attenuate p53 activity. With the exception of naringenin, the other compounds increased p53 at the higher (50 microM or 100 microM) amounts, without added hydrogen peroxide, suggesting that these compounds can act as pro-oxidants or possibly stimulate p53 activity by another mechanism.

Genistein and daidzein prevent low potassium-dependent apoptosis of cerebellar granule cells

We have investigated the ability of certain dietary flavonoids, known to exert beneficial effects on the central nervous system, to affect neuronal apoptosis. We used cerebellar granule cells undergoing apoptosis due to potassium deprivation in a serum-free medium in either the absence or presence of the flavonoids genistein and daidzein, which are present in soy, and of catechin and epicatechin, which are present in cocoa. These compounds were used in a blood dietary concentration range. We found that genistein and daidzein, but not catechin and epicatechin, prevented apoptosis, with cell survival measured 24h after the induction of apoptosis being higher than that of the same cells incubated in flavonoid free medium (80% and 40%, respectively); there was no effect in control cells. A detailed investigation of the effect of these compounds on certain mitochondrial events that occur in cells en route to apoptosis showed that genistein and daidzein prevented the impairment of glucose oxidation and mitochondrial coupling, reduced cytochrome c release, and prevented both impairment of the adenine nucleotide translocator and opening of the mitochondrial permeability transition pore. Interestingly, genistein and daidzein were found to reduce the levels of reactive oxygen species, which are elevated in cerebellar granule cell apoptosis. These findings strongly suggest that the prevention of apoptosis depends mainly on the antioxidant properties of genistein and daidzein. This could lead to the development of a flavonoid-based therapy in neuropathies.

Evaluation of equol function on anti- or prooxidant status in vivo

The present study was performed to investigate the effects of equol on oxidative stress and the antioxidant defense system in the livers of mice. Mice were orally administered equol at either 5 or 25 mg/kg body weight/day for 1, 3, or 7 wk. Equol administration significantly inhibited biomarkers of oxidative stress (thiobarbituric acid-reactive substances value, carbonyl content, and serum 8-OH-dG) at all doses and for all durations of administration, and this phenomenon was most pronounced at 3 wk. Moreover, catalase and total superoxide dismutase (SOD) activities and their mRNA expression were significantly increased by equol. Although equol increased the glutathione peroxidase (GSH-px) activity in mice treated with equol for 1 wk, long-term administration of equol (7 wk) caused a decrease in the ratio of reduced/oxidized glutathione (GSH/GSSG) and the activities of GSH-px and glutathione reductase (GR). Taken together, these results suggest that equol may act as an antioxidant through an inhibition of oxidative stress and stimulation of catalase and SOD, but can also cause prooxidant effects such as reduction of the GSH/GSSG ratio, depending on the treatment period.

Daidzein causes cell cycle arrest at the G1 and G2/M phases in human breast cancer MCF-7 and MDA-MB-453 cells

We examined the mechanisms by which daidzein inhibits the growth of breast cancer cells. First, we investigated its antiproliferative effects in MCF-7 and MDA-MB-453 cells exposed to 1-100 microM daidzein for 24, 48, or 72 h. Daidzein significantly inhibited cell proliferation in a dose- and time-dependent manner (p<0.05) and resulted in significant cell cycle arrest in the G1 and G2/M phases after 72 h of treatment at concentrations over 5 and 10 microM in MCF-7 and MDA-MB-453 cells, respectively (p<0.05). In addition, daidzein caused the accumulation of cells in sub-G0 phase in a dose-dependent manner in MDA-MB-453 (p<0.05), but not MCF-7, cells. As another biomarker of apoptosis induction, caspase-9 activity was significantly increased by daidzein in both cells. To investigate the effects of daidzein on the proteins regulating cell cycle arrest, cells were treated with 100 microM daidzein for 72 h. Similar changes in the expression of regulatory proteins were detected in both cells. Daidzein treatment resulted in decreases in cyclin D, CDK2, and CDK4, whereas the expression of CDK6 and cyclin E was unchanged. The protein expression of CDK1 related to the G2/M phase decreased markedly with daidzein treatment, whereas slight expression of cyclins A and B occurred. Daidzein treatment increased the expression of the CDK inhibitors p21(Cip1) and p57(Kip2), but not that of p27(Kip1). Thus, daidzein exerts its anticancer effects in human breast cancer cells via cell cycle arrest at the G1 and G2/M phases.

Effect of Chronic N-Acetyl Cysteine Administration on Oxidative Status in the Presence and Absence of Induced Oxidative Stress in Rat Striatum

Antioxidants have possible therapeutic value in neurodegenerative disorders, although they may have pro-oxidant effects under certain conditions. Glutathione (GSH) is a key free radical scavenger. N-acetylcysteine (NAC) bolsters GSH and intracellular cysteine and also has effective free radical scavenger properties. The effects of chronic NAC administration (50 mg/kg/day, 500 mg/kg/day, 1500 mg/kg/day x 21 days) on cellular markers of oxidative status was studied in striatum of healthy male Sprague-Dawley rats as well as in animals with apparent striatal oxidative stress following chronic haloperidol treatment (1.5 mg/kg/day x 3 weeks). In non-haloperidol treated animals, NAC 50 and 500 mg/kg did not affect oxidative status, although NAC 1,500 mg/kg significantly increased striatal superoxide levels, decreased lipid peroxidation and increased consumption of reduced glutathione (GSH). Haloperidol alone evoked a significant increase in superoxide and lipid peroxidation. All NAC doses blocked haloperidol induced increases in superoxide levels, while NAC 500 mg/kg and 1,500 mg/kg prevented haloperidol-associated lipid peroxidation levels and also increased the GSSG/GSH ratio. NAC may protect against conditions of striatal oxidative stress, although possible pro-oxidative actions at high doses in otherwise healthy individuals, e.g. to offset worsening of neurodegenerative illness, should be viewed with caution.

Metabolism of dietary soy isoflavones to equol by human intestinal microflora--implications for health

Soy isoflavones have received considerable attention. Individuals with isoflavones-rich diets have significantly lower occurrences of cardiovascular disease, osteoporosis, and some cancers. The clinical effectiveness of soy isoflavones may be a function of the ability to biotransform soy isoflavones to the more potent estrogenic metabolite, equol, which may enhance the actions of soy isoflavones, owing to its greater affinity for estrogen receptors, unique antiandrogenic properties, and superior antioxidant activity. However, not all individuals consuming daidzein produce equol. Only approximately one-third to one-half of the population is able to metabolize daidzein to equol. This high variability in equol production is presumably attributable to interindividual differences in the composition of the intestinal microflora, which may play an important role in the mechanisms of action of isoflavones. But, the specific bacterial species in the colon involved in the production of equol are yet to be discovered. Therefore, future researches are aimed at identifying the specific bacterial species and strains that are capable of converting daidzein to equol or increasing equol production.