Chemical features of flavonols affecting their genotoxicity. Potential implications in their use as therapeutical agents

Kaempferol, a potential neuroprotective agent in neurodegenerative diseases: From chemistry to medicine

Neurodegenerative diseases (NDDs) encompass a range of conditions that involve progressive deterioration and dysfunction of the nervous system. Some of the common NDDs include Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). Although significant progress has been made in understanding the pathological mechanisms of NDDs in recent years, the development of targeted and effective drugs for their treatment remains challenging. Kaempferol is a flavonoid whose derivatives include kaempferol-O-rhamnoside, 3-O-β-rutinoside/6-hydroxykaempferol 3,6-di-O-β-d-glucoside, and kaempferide. Emerging studies have suggested that kaempferol and its derivatives possess neuroprotective properties and may have potential therapeutic benefits in NDDs. Here, we aimed to provide a theoretical basis for the use of kaempferol and its derivatives in the clinical treatment of NDDs. We systematically reviewed the literature in the PubMed, Web of Science, and Science Direct databases until June 2022 using the search terms "kaempferol," "kaempferol derivatives," "NDDs," "pharmacokinetics," and "biosynthesis" according to the reporting items for systematic review (PRISMA) standard. Based on combined results of in vivo and in vitro studies, we summarize the basic mechanisms and targets of kaempferol and its derivatives in the management of AD, PD, HD, and ALS. Kaempferol and its derivatives exert a neuroprotective role mainly by preventing the deposition of amyloid fibrils (such as Aβ, tau, and α-synuclein), inhibiting microglia activation, reducing the release of inflammatory factors, restoring the mitochondrial membrane to prevent oxidative stress, protecting the blood-brain barrier, and inhibiting specific enzyme activities (such as cholinesterase). Kaempferol and its derivatives are promising natural neuroprotective agents. By determining their pharmacological mechanism, kaempferol and its derivatives may be new candidate drugs for the treatment of NDDs.

Flavonoids regulate tumor-associated macrophages - From structure-activity relationship to clinical potential (Review)

In recent years, the strategy for tumor therapy has changed from focusing on the direct killing effect of different types of therapeutic agents on cancer cells to the new mainstream of multi-mode and -pathway combined interventions in the microenvironment of the developing tumor. Flavonoids, with unique tricyclic structures, have diverse and extensive immunomodulatory and anti-cancer activities in the tumor microenvironment (TME). Tumor-associated macrophages (TAMs) are the most abundant immunosuppressive cells in the TME. The regulation of macrophages to fight cancer is a promising immunotherapeutic strategy. This study covers the most comprehensive cognition of flavonoids in regulating TAMs so far. Far more than a simple list of studies, we try to dig out evidence of crosstalk at the molecular level between flavonoids and TAMs from literature, in order to discuss the most relevant chemical structure and its possible relationship with the multimodal pharmacological activity, as well as systematically build a structure-activity relationship between flavonoids and TAMs. Additionally, we point out the advantages of the macro-control of flavonoids in the TME and discuss the potential clinical implications as well as areas for future research of flavonoids in regulating TAMs. These results will provide hopeful directions for the research of antitumor drugs, while providing new ideas for the pharmaceutical industry to develop more effective forms of flavonoids.

Modulatory effect of myricitrin against chromosome instability and cytostasis induced by bleomycin and oxaliplatin in CHO-K1 cells

Myricitrin (MYR), a flavonol consumed in the leaves and fruits of plants of the Myrtaceae family, presents anti-proliferative, anti-inflammatory, anti-diabetic, and antioxidant properties in humans. However, there are few studies regarding the cyto-genotoxicity and the chemopreventive potential of MYR. Using the in vitro Micronucleus test, the cytostasis, mutagenicity, and modulatory effect of MYR in CHO-K1 cells were assessed. The concentrations of 39 and 78 µg/mL (p < 0.001.) of MYR decrease the cytokinesis-block proliferation index (CBPI) in the short exposure treatment (4 h), while in the extended treatment (24 h), concentrations of 4.8, 9.7, 19.5, 39 and 78 µg/mL (p < 0.001.) decreased the CBPI. MYR associated with oxaliplatin decreased CBPI at all tested concentrations in the pre-(p < 0.001) and post-treatments (p < 0.001), but there was no decrease when associated with bleomycin. As for chromosome instability, MYR did not increase the frequency of micronuclei (MNi), nucleoplasmic bridges (NPBs), or nuclear buds (NBUDs) in the 4 h exposure time, however, in the 24 h treatment, MYR increased the frequency of MNi and NPBs at concentration 19.5 µg/mL (p < 0.001). As for the modulatory effect, MYR associated with bleomycin decreased the frequency of MNi, NPBs, and NBUDs at all concentrations in the pretreatment (MNi and NPBs p < 0.001, NBUDs p < 0.05) and simultaneously (MNi, NPBs and NBUDs p < 0.001). When associated with oxaliplatin, the simultaneous treatment decreased the frequency of MNi (p < 0.001) and NBUDs (p < 0.01) at all concentrations, however, in the post-treatment, MYR increased MNi (p < 0.001) and NPBs p < 0.05) in CHO-K1 cells, when compared to oxaliplatin alone. The results demonstrated that MYR could modulate the mutagenic and cytostatic actions of bleomycin and oxaliplatin, demonstrating distinct behaviors, depending on the mechanism of action of the chemotherapeutic agent.

A novel extraction method enhanced the osteogenic and anti-osteoporosis effect of tea extract without any hepatotoxicity in ovariectomized rats

Tea (Camellia sinensis) has several reported health benefits, including that on bone health attributed to catechins of which the most abundant is epigallocatechin-3-gallate (EGCG). However, several preclinical and clinical studies raise safety concerns about EGCG in tea extract causing acute liver failure. Tea also contains kaempferol, albeit scanty, and it has hepatoprotective and osteogenic effects. Here, we utilized a novel extraction procedure of acid hydrolysis to enhance the osteogenic effect of tea extract while reducing its hepatotoxicity. The resultant extract (USKECSE) has a ~40-fold increase in kaempferol and a 2.5-fold reduction in EGCG content compared with the hydroethanolic extract (USCSE). In a female Sprague Dawley (SD) rat femur osteotomy model, USKECSE (100 mg/kg) but not USCSE promoted bone regeneration. In a rat postmenopausal osteoporosis model induced by bilateral ovariectomy (OVX), USKECSE through an osteogenic mechanism maintained bone mass, strength, and microarchitecture to the levels of ovary-intact rats with no hepatotoxic effect. After a single oral dose (100 mg/kg) of USKECSE to adult rats, kaempferol was detectable for 48 hours, suggesting its significant absorption and distribution in plasma. Peak kaempferol concentration in plasma (C_max) was 483 ng/ml (2 μM), and at this concentration, kaempferol induces osteoblast differentiation. USKECSE had no genotoxicity, and its safety index assessed by preclinical toxicity studies, including safety pharmacology, was >20-fold. Taken together, we report a novel extraction process that enhanced the osteogenicity and concomitantly reduced hepatotoxicity of tea extract with significant kaempferol bioavailability and a favorable systemic safety profile. Based on these data, we propose assessing the USKECSE effect for postmenopausal osteoporosis treatment.

Polyphenols as anticancer agents: Toxicological concern to healthy cells

Polyphenols are a group of diverse chemical compounds present in a wide range of plants. Various biological properties such as antiallergic, antiviral, antibacterial, anticarcinogenic, antiinflammatory, antithrombotic, vasodilatory, and hepatoprotective effect of different polyphenols have been reported in the scientific literature. The major classes of polyphenols are flavonoids, stilbenoids, lignans, and polyphenolic acids. Flavonoids are a large class of food constituents comprising flavones, isoflavanones, flavanones, flavonols, catechins, and anthocyanins sub-classes. Even with seemingly broad biological activities, their use is minimal clinically. Among the other concurrent problems such as limited bioavailability, rapid metabolism, untargeted delivery, the toxicity associated with these polyphenols has been a topic of concern lately. These polyphenols have been reported to result in different forms of toxicity that include organ toxicity, genotoxicity, mutagenicity, cytotoxicity, etc. In the present article, we have tried to unravel the toxicological aspect of these polyphenols to healthy cells. Further high-quality studies are needed to establish the clinical efficacy and toxicology concern leading to further exploration of these polyphenols.

Mutational spectra induced by flavonoid extracts from pepper tree (Schinus terebinthifolius, Raddi) stem bark

Flavonoids are a diverse family of plant compounds that are involved in pigmentation, protection, and endogenous regulation. Flavonoids also have medicinal applications, suggesting that they may exert chemoprotective effects. However, some studies have shown, that some plant flavonoids have oxidative and toxic effects, including those produced by Schinus terebinthifolius. In Brazil, extracts of this plant are widely used for medical purposes. In this study, we analyzed the mutagenic potential of two flavonoid-enriched fractions from Brazilian pepper tree stem bark using Escherichia coli CC strains deficient and proficient in enzymes involved in the DNA repair of oxidative lesions. The highest mutagenic response was detected in the CC104mutMmutY strain but CC104mutY showed a higher mutation frequency than CC104mutM. The spectrum of mutations induced in plasmid DNA is composed of mutations typically caused by oxidative lesions. However, a new type of lesion must be occurred to explain the cytotoxicity, higher mutation rates in the CC104mutY strain, and the rare A:T → T:A and G:C → C:G transversions found in this work.

Redox reactions of heme proteins with flavonoids

Proteins containing heme groups perform a variety of important functions in living organisms. The heme groups are involved in catalyzing oxidation/reduction reactions, in electron transfer, and in binding small molecules, like oxygen or nitric oxide. Flavonoids, low molecular weight plant polyphenols, are ubiquitous components of human diet. They are also components of many plant extracts used in herbal medicine as well as of food supplements. Due to their relatively low reduction potential, flavonoids are prone to oxidation. This paper provides a review of redox reactions of various heme proteins, including catalase, some peroxidases, cytochrome P450, cytochrome c, myoglobin, and hemoglobin with flavonoids. Potential biological significance of these reactions is discussed, in particular when flavonoids are delivered to the body at pharmacological doses.

Genotoxic and cytotoxic properties of two medical plants (Teucrium arduini L.and Teucrium flavum L.) in relation to their polyphenolic contents

A large number of species belonging to the genus Teucrium are used in pharmacy and traditional medicine for the treatment of different diseases. This study aimed to evaluate the polyphenolic composition as well as genotoxic and cytotoxic effects of methanolic extracts from T. arduini and T. flavum, two native species found in Montenegro. We determined the total phenolic and flavonoid contents of these plants using spectrophotometric methods; the qualitative content of polyphenolic compounds was investigated by high-performance liquid chromatography (HPLC). Genotoxicity in cultured human lymphocytes was measured in the cytokinesis-block micronucleus assay (CBMN) and comet assay in the range between 125 and 1000 μg/mL. Cytotoxicity was assessed by the MTT viability assay in normal human MRC-5 fibroblasts and MDA-MB-231 breast carcinoma cells. The content of total phenolics and flavonoids in T. arduini extract was higher than in T. flavum (200.35 mg GA/g vs. 171.08 mg GA/g; 96.32 mg RU/g vs. 78.14 mg RU/g). The polyphenolic composition of both extracts was qualitatively similar and eight phenol compounds were identified. The most commonly present phenol was caffeic acid and among four flavonoids, the most common was quercetin. Both plant extracts were genotoxic in both the CBMN and comet assays at concentrations of 250, 500 and 1000 μg/mL. After 72 h of exposure, the extracts of T. arduini and T. flavum were found to induce cytotoxicity in MRC-5 fibroblasts but not in MDA-MB-231 breast cancer cells. The results suggest that the constituents of both plant species are genotoxic and cytotoxic, therefore these extracts warrant additional evaluation to be safely applied in humans.

Cytotoxic and genotoxic action of Tagetes patula flower methanol extract and patuletin using the Allium test

Tagetes patula is used to treat cancer patients in alternative healthcare systems. However, its cytotoxic and genotoxic effects have not been reported. Therefore, themethanol extract of T. patula flower, the ethyl acetate fraction, and the pure compound patuletin were evaluatedusing the Allium test.The methanol extract and fraction contained ~3% and ~36% patuletin, respectively, with ~98% purity. The methanol extract caused inhibition of Allium root growth displaying an IC₅₀ value of ~500 µg/mL, while the fraction and patuletin were more potent by ~2 and ~5 times, respectively. The Allium root tips demonstrated a decline in prophase, metaphase, anaphase, and telophase stages with concomitant decrease in percent mitotic index in the methanol extract (~5.64), fraction, and patuletin (~4) as compared to the control (~7.61). However, in only methanol extract-treated root tips, an increase in metaphase stage was noted. In addition, the methanol extract predominantly induced c-type, misaligned, and multipolar chromosomal abnormalities while the fraction and patuletin displayed fragments and sticky chromosomes. The fraction and patuletin also produced micronuclei (~2%). In conclusion, T. patula flower methanol extract and ethyl acetate fraction are cytotoxicand genotoxic, which most likely could be due to the patuletin. Further preclinical and clinical studies are required to justify its clinical use.

A personally guided tour on some of our data with the Ames assay-A tribute to Professor Bruce Ames

In contributing to this Special Issue of Mutation Research dedicated to Professor Bruce N. Ames in recognition of his 90^th birthday in December 2018, we intend to portray the importance not only of the Ames Salmonella/mammalian-microsome mutagenicity assay in some of our studies over the years, but also the importance of the insight that Bruce Ames brought to the field of genetic toxicology.

Polyphenolic contents of Teucrium polium L. and Teucrium scordium L. associated with their protective effects against MMC-induced chromosomal damage in cultured human peripheral blood lymphocytes

Teucrium species have been used in traditional medicine for treatment of different diseases. The aim of this study was to investigate polyphenolic contents by high-performance liquid chromatography (HPLC), and the genotoxic effect of methanolic extracts of Teucrium polium and Teucrium scordium using the cytokinesis-block micronucleus (CBMN) assay on human peripheral blood lymphocytes (PBLs) from healthy donors. The HPLC  analysis  showed that extracts consist of phenolic acid (gallic, vanillic, caefic, chlorogenic, p-coumaric, sinapic) and flavonoids (catechin, rutin, myricetin, luteolin, quercetin and apigenin). Cultures were treated with extracts of both plants separately and in combinations with mitomycin C (MMC). In separate treatments, both herbal extracts significantly induced micronucleus (MN) frequency only at the highest concentrations. All concentrations of T. scordium , except the lowest, and all concentrations of T. polium extracts in combined treatment with MMC significantly reduced the frequency of MN. The extract of T. polium did not significantly aefct the nuclear division index (NDI), whereas T. scordium in higher concentrations, separately and in combined treatment with MMC, significantly decreased the NDI value. Our results suggest that both herbal extracts in combination with MMC have antimutagenic (T. polium) and proapoptotic effects (T. scordium), which indicates their protective effects in PBLs.

(Anti)mutagenic and immunomodulatory properties of quercetin glycosides

BACKGROUND

Quercetin-3-O-β-D-glucopyranoside (isoquercitrin) and quercetin-3-O-rutinoside (rutin) are common components of a normal human diet and are increasingly used in food supplements. Here their effect on mutagenesis and immunity is shown.

RESULTS

The in vitro (anti)mutagenic potential was compared with that of quercetin using the Ames test in Salmonella typhimurium His(-) strains TA100, TA98 and TA102. Isoquercitrin only slightly increased the number of revertants, while rutin was totally non-mutagenic. On the other hand, all compounds displayed dose-dependent protective activity against H2O2 - and tert-butyl hydroperoxide-induced oxidative damage to the TA102 strain and at 75 µmol L(-1) inhibited H2O2/Fe(2+)-induced formation of the open circular and linear forms of the DNA plasmid pBSIISK(-). In mice, none of the flavonols (0.86 µmol day(-1), 34 days) induced harmful effects. In immunized animals, all compounds enhanced ex vivo B cell proliferation; quercetin stimulated lymphocyte basal proliferation and increased the number of IgM-producing lymphocytes. Rutin promoted NK cytotoxic activity, supported T cells and enhanced gut epithelium renewal. No effect on IgG-forming cells was found.

CONCLUSION

Isoquercitrin displayed negligible and rutin no mutagenicity, but both showed significant antimutagenic and DNA-protective effects against oxidative damage. In vivo, they supported the readiness of the immune system for specific humoral immune response.

Low-energy electron interaction with retusin extracted from Maackia amurensis: towards a molecular mechanism of the biological activity of flavonoids

The antioxidant isoflavone retusin efficiently attaches low-energy electrons in vacuo, generating fragment species via dissociative electron attachment (DEA), as has been shown by DEA spectroscopy. According to in silico results obtained by means of density functional theory, retusin is able to attach solvated electrons and could be decomposed under reductive conditions in vivo, for instance, near the mitochondrial electron transport chain, analogous to gas-phase DEA. The most intense decay channels of retusin temporary negative ions were found to be associated with the elimination of H atoms and H2 molecules. Doubly dehydrogenated fragment anions were predicted to possess a quinone structure. It is thought that molecular hydrogen, known for its selective antioxidant properties, can be efficiently generated via electron attachment to retusin in mitochondria and may be responsible for its antioxidant activity. The second abundant species, i.e., quinone bearing an excess negative charge, can serve as an electron carrier and can return the captured electron back to the respiration cycle. The number of OH substituents and their relative positions are crucial for the present molecular mechanism, which can explain the radical scavenging activity of polyphenolic compounds.

Design, Synthesis, and Biological Evaluation of Quercetagetin Analogues as JNK1 Inhibitors

The recent discovery of c-Jun NH2-terminal kinase JNK1 suppression by natural quercetagetin (1) is a promising lead for the development of novel anticancer agents. Using both X-ray structure and docking analyses we predicted that 5'-hydroxy- (2) and 5'-hydroxymethyl-quercetagetin (3) would inhibit JNK1 more actively than the parent compound 1. Notably, our drug design was based on the active enzyme-ligand complex as opposed to the enzyme's relatively open apo structure. In this paper we test our theoretical predictions, aided by docking-model experiments, and report the first synthesis and biological evaluation of quercetagetin analogues 2 and 3. As calculated, both compounds strongly suppress JNK1 activity. The IC50 values were determined to be 3.4 μM and 12.2 μM, respectively, which shows that 2 surpasses the potency of the parent compound 1 (IC50 =4.6 μM). Compound 2 was also shown to suppress matrix metalloproteinase-1 expression with high specificity after UV irradiation.

Kaempferol and inflammation: From chemistry to medicine. Pharmacol Res. 2015;99:1-10. [PMID: 25982933 DOI: 10.1016/j.phrs.2015.05.002]

Inflammation is an important process of human healing response, wherein the tissues respond to injuries induced by many agents including pathogens. It is characterized by pain, redness and heat in the injured tissues. Chronic inflammation seems to be associated with different types of diseases such as arthritis, allergies, atherosclerosis, and even cancer. In recent years natural product based drugs are considered as the novel therapeutic strategy for prevention and treatment of inflammatory diseases. Among the different types of phyto-constituents present in natural products, flavonoids which occur in many vegetable foods and herbal medicines are considered as the most active constituent, which has the potency to ameliorate inflammation under both in vitro and in vivo conditions. Kaempferol is a natural flavonol present in different plant species, which has been described to possess potent anti-inflammatory properties. Despite the voluminous literature on the anti-inflammatory effects of kaempferol, only very limited review articles has been published on this topic. Hence the present review is aimed to provide a critical overview on the anti-inflammatory effects and the mechanisms of action of kaempferol, based on the current scientific literature. In addition, emphasis is also given on the chemistry, natural sources, bioavailability and toxicity of kaempferol.

In Vitro and In Vivo Cytogenotoxic Effects of Hot Aqueous Extract of Achyrocline satureioides (Lam.) DC

In this work we extend the toxicological studies of hot aqueous extract of A. satureioides (As-HAE) evaluating cytotoxic and apoptotic effects on human peripheral blood mononuclear cells (PBMCs). We also determine genotoxic action of this extract in vivo. In addition, the extract was chemically characterized. Finally, we established a comparison with previous data of cold aqueous extract. The As-HAE induced cytotoxicity on PBMCs determined by trypan blue dye exclusion (CC50 = 653 μg/mL) and MTT (CC50 = 588 μg/mL) assays being more toxic than cold extract. However, As-HAE as well as cold extract did not induce apoptosis measured by Hoechst 33258 staining, TUNEL assay, and DNA fragmentation analysis. The in vivo micronucleus test showed that As-HAE exerted cytogenotoxic effects on bone marrow of mice, contrary to what was observed with cold extract. The chemical study of As-HAE allowed identifying the flavonoids found in cold extract: luteolin, quercetin, and 3-O-methylquercetin, but at higher concentrations. We suggest that toxic effects induced by As-HAE could be due to high concentrations of these flavonoids. Given that As-HAE is the most used in folkloric medicine, its administration should be controlled in order to prevent potential cell damage.

Protective role of quercetin against cisplatin-induced hair cell damage in zebrafish embryos

BACKGROUND AND OBJECTIVES

The aim of this study was to evaluate the protective effects of quercetin on cisplatin-induced hair cell damage in transgenic zebrafish embryos.

MATERIALS AND METHODS

Five days postfertilization zebrafish embryos were exposed to 1 mM cisplatin and quercetin at 10, 50, 100, or 200 μM for 4 h. Hair cells within neuromasts of the supraorbital, otic, and occipital lateral lines were analyzed by fluorescent microscopy (n = 10). Survival of hair cells was calculated as the average number of hair cells in the control group that were not exposed to cisplatin. Ultrastructural changes were evaluated using scanning electron microscopy.

RESULTS

Hair cell damage in neuromasts was decreased by co-treatment of quercetin and cisplatin (quercetin 100 μM: 8.6 ± 1.1 cells; 1 mM cisplatin only: 5.0 ± 0.5 cells; n = 10, p < 0.05); apoptosis of hair cells examined by special stain was also decreased by quercetin. The ultrastructure of hair cells within neuromasts was preserved in zebrafish by the combination of quercetin (100 μM) and cisplatin (1 mM).

CONCLUSION

In conclusion, quercetin showed protective effects against cisplatin-induced toxicity in a zebrafish model. The results of this study suggest the possibility of a protective role of quercetin against cisplatin-induced apoptotic cell death in zebrafish.

Flavonoid-induced conversion of catalase to its inactive form--Compound II

Flavonoids (FlaOHs), plant polyphenols, are ubiquitous components of human diet and are known as antioxidants. However, their prooxidant activity has also been reported. We have recently found that FlaOHs inhibit catalase, the heme enzyme which catalyzes the decomposition of hydrogen peroxide (H2O2) into water and molecular oxygen. The catalytic cycle proceeds with the formation of the intermediate, Compound I (Cpd I), an oxoferryl porphyrin π-cation radical, the two-electron oxidation product of a heme group. Under conditions of low H2O2 fluxes and in the presence of an appropriate substrate, Cpd I can undergo one-electron reduction to inactive Compound II (Cpd II), oxoferryl derivative without radical site. Here we show that in vitro, under low fluxes of H2O2, FlaOHs reduce Cpd I to inactive Cpd II. Measurable amounts of Cpd II can be formed even in the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH) at concentration comparable with the investigated FlaOHs. Possible mechanisms of electron transfer from FlaOH molecule to the heme are discussed.

Differences in the hydroxylation pattern of flavonoids alter their chemoprotective effect against direct- and indirect-acting mutagens

The antimutagenicity of ten flavonoids, differing in their hydroxylation patterns against direct-acting and indirect-acting mutagens, namely 4-nitro-o-phenylenediamine, sodium azide, mitomycin C, benzo[a]pyrene, aflatoxin B1 and 2-aminofluorene, were compared with the aim of investigating how the hydroxyl groups in their structures govern the biological activity of flavonoids, by the Ames test, with Salmonella typhimurium strains TA98, TA100 and TA102. The flavonoids tested were: quercetin, kaempferol, luteolin, fisetin, chrysin, galangin, flavone, 3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone. In these tests, all compounds were shown to be antimutagenic in more than one strain and various mechanisms of action were demonstrated. The results suggested that the number and position of hydroxyl groups may increase or decrease the protective effect, depending on the type and concentration of flavonoids and mutagen used. These studies contribute to clarifying the mechanisms by which these flavonoids act in protecting DNA from damage. This is required before they can be widely used.

Effects of a Mangifera indica L. stem bark extract and mangiferin on radiation-induced DNA damage in human lymphocytes and lymphoblastoid cells

OBJECTIVES

Mangifera indica L. (mango) stem bark aqueous extract (MSBE) that has antioxidant, anti-inflammatory and immunomodulatory properties, can be obtained in Cuba. It is rich in polyphenols, where mangiferin is the main component. In this study, we have tested DNA damage and protection effects of MSBE and mangiferin on primary human lymphocytes and lymphoblastoid cells.

MATERIAL AND METHODS

Cell suspensions were incubated with the products (50-1000 μg/ml) for experiments on damage induction, and evaluation of any potential protective effects (5-100 μg/ml) for 60 min at 37 °C. Irradiation was performed using a γ-ray source, absorbed dose 5 Gy. At the end of exposure, DNA damage, protection and repair processes were evaluated using the comet assay.

RESULTS

MSBE (100-1000 μg/ml) induced DNA damage in a concentration dependent manner in both cell types tested, primary cells being more sensitive. Mangiferin (200 μg/ml) only induced light DNA damage at higher concentrations. DNA repair capacity was not affected after MSBE or mangiferin exposure. On the other hand, MSBE (25 and 50 μg/ml) and mangiferin (5-25 ug/ml) protected against gamma radiation-induced DNA damage.

CONCLUSIONS

These results show MSBE has protector or harmful effects on DNA in vitro depending on the experimental conditions, which suggest that the extract could be acting as an antioxidant or pro-oxidant product. Mangiferin was involved in protective effects of the extract.

Evaluation of estrogenic potential of flavonoids using a recombinant yeast strain and MCF7/BUS cell proliferation assay

Phytoestrogens are of interest because of their reported beneficial effects on many human maladies including cancer, neurodegeneration, cardiovascular disease and diabetes. Furthermore, there is a search for compounds with estrogenic activity that can replace estrogen in hormone replacement therapy during menopause, without the undesirable effects of estrogen, such as the elevation of breast cancer occurrence. Thus, the principal objective of this study was to assess the estrogenic activity of flavonoids with different hydroxylation patterns: quercetin, kaempferol, luteolin, fisetin, chrysin, galangin, flavone, 3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone via two different in vitro assays, the recombinant yeast assay (RYA) and the MCF-7 proliferation assay (E-screen), since the most potent phytoestrogens are members of the flavonoid family. In these assays, kaempferol was the only compound that showed ERα-dependent transcriptional activation activity by RYA, showing 6.74±1.7 nM EEQ, besides acting as a full agonist for the stimulation of proliferation of MCF-7/BUS cells. The other compounds did not show detectable levels of interaction with ER under the conditions used in the RYA. However, in the E-screen assay, compounds such as galangin, luteolin and fisetin also stimulated the proliferation of MCF-7/BUS cells, acting as partial agonists. In the evaluation of antiestrogenicity, the compounds quercetin, chrysin and 3-hydroxyflavone significantly inhibited the cell proliferation induced by 17-β-estradiol in the E-screen assay, indicating that these compounds may act as estrogen receptor antagonists. Overall, it became clear in the assay results that the estrogenic activity of flavonoids was affected by small structural differences such as the number of hydroxyl groups, especially those on the B ring of the flavonoid.

Modulation of radiation-induced and mitomycin C-induced chromosome damage by apigenin in human lymphocytes in vitro

Apigenin (APG), a flavone, is known to exhibit antioxidant, antimutagenic and antitumorigenic activity, both in vivo and in vitro. The aim of this study is to investigate the modulatory effects of APG on human lymphocytes after irradiation with gamma rays (3 Gy) or treatment with the antineoplastic agent, mitomycin C (MMC), in vitro. Cytogenetic biomarkers such as chromosome aberrations (CAs), sister chromatid exchanges (SCEs) and cytochalasin-B blocked micronuclei (CBMN), were studied in blood lymphocytes treated with radiation, or antineoplastic agent (MMC), and APG. Whole blood lymphocytes were cultured in vitro using a standard protocol. No significant differences were found in the frequency of CAs or micronuclei (MN) in human peripheral blood lymphocytes irradiated with gamma rays (3 Gy) and then post-treated with APG. There was an increase in the frequency of SCEs per cell in APG-treated samples compared with the controls. Lymphocytes treated with MMC in the presence of APG exhibited a significant decrease (P < 0.01) in the frequency of SCEs compared with MMC treatment alone. The data for the MN test indicated that APG treatment significantly reduced (P < 0.01) the frequency of MMC-induced MN.

Gas-phase dissociative electron attachment to flavonoids and possible similarities to their metabolic pathways

The gas-phase empty-level structures and formation of anion states via resonance attachment of low-energy electrons to the flavonoids naringenin (III), quercetin (IV) and myricetin (V) and the smaller reference molecules chromone (I) and flavone (II) are investigated experimentally for the first time. Dissociative electron attachment spectroscopy (DEAS) is used to measure the fragment anion currents generated through dissociative decay channels of the molecular anions of compounds I–V, detected with a mass filter as a function of the incident electron energy in the 0–14 eV energy range. Due to the insufficient volatility of flavonoids III–V, the energies of vertical electron attachment associated with temporary occupation of the lower-lying virtual orbitals are measured with electron transmission spectroscopy (ETS) only in the smaller reference molecules I and II. The experimental findings are interpreted with the support of appropriate density functional theory calculations with the B3LYP functional. The experimental vertical electron attachment energies measured in the ET spectra of I and II are compared with the orbital energies of the neutral molecules scaled using an empirically calibrated linear equation. The vertical and adiabatic electron affinities are evaluated at the B3LYP/6-31+G(d) level as the anion/neutral total energy difference. The latter theoretical method is also used for evaluation of the most stable conformers of the neutral molecules, O–H bond dissociation energies and thermodynamic energy thresholds for production of the anion fragments observed in the DEA spectra. A possible role played by loss of an H(2) molecule from the parent molecular anion in vivo in the mitochondrial respiratory chain is briefly discussed.

Evaluation of genotoxic and cytotoxic effects of antileishmanial extract from Julocroton triqueter (Euphorbiaceae)

Julocroton triqueter extracts have antileishmanial activity; however, the effect on genetic stability has not been studied. We evaluated genotoxic and cell death induction potential (in vitro and in vivo) of J. triqueter var. triqueter hydroalcoholic extracts, as well as their antigenotoxic potential in vivo. The in vitro genotoxic studies were performed using human leukocytes at four different concentrations. For the in vivo tests, Swiss mice were treated with 125, 250 or 500 mg/kg of extract injected intraperitoneally. Antigenotoxic effects of the extract were measured before and after cyclophosphamide treatment. An absence of genotoxic effects was observed both in vitro and in vivo. In the antigenotoxic studies, no significant difference was observed between the treatments and the positive control, indicating that the extracts did not protect against damage caused by cyclophosphamide. Hydroalcoholic extracts of J. triqueter did not provoke DNA damage at concentrations and doses normally used for antileishmanial treatment; however, they reduced apoptotic cell death and induced necrotic cell death.

Tricin biosynthesis during growth of wheat under different abiotic stresses

In plants, O-methylation is mediated by an enzyme family of O-methyltransferases (OMTs) that transfer the methyl groups from the methyl donor, S-adenosyl-L-methionine (AdoMet) to suitable phenolic acceptor molecules. In a previous study [1], a flavonoid OMT (TaOMT2) was isolated and characterized from wheat (Triticum aestivum L.) leaves. Its novel gene product catalyzes three sequential O-methylations of the flavone tricetin (5,7,3',4',5'-pentahydroxyflavone) to its 3'-monomethyl-(selgin)→3',5'-dimethyl-(tricin)→3',4',5'-trimethyl (TMT) ether derivatives, with tricin being the major product of the reaction. In this report, the biological significance of tricetin methylation was investigated by measuring the OMT activity, its expression level, and the accumulation of its major product (tricin) at different stages of development of wheat plants exposed to different abiotic stresses such as cold, salt and drought. The results showed that tricin accumulates mostly in wheat inflorescences under normal conditions compared to leaves and other developmental stages. Tricin accumulation was associated with increased TaOMT2 expression level and its enzyme activity, suggesting a possible de novo synthesis of the enzyme at this important developmental stage. This phenomenon may be attributed to the putative role of tricin in protecting seeds against biotic and abiotic stresses. The functions of tricin during growth and development of wheat and the importance of tricetin methylation during abiotic stresses are discussed.

Estragole: a weak direct-acting food-borne genotoxin and potential carcinogen

We evaluated the genotoxicity of the food-flavouring agent estragole in V79 cells using the sister chromatid exchange (SCE) assay and the alkaline comet assay. Unexpectedly, we observed an increase in SCE without an exogenous biotransformation system (S9) and a decrease in its presence. Positive results were also observed in the alkaline comet assay without S9, indicating DNA strand breakage. To ascertain repair of damage, we performed the comet assay in V79 cells after two hours of recovery, and observed a reduction of the genotoxic response. Estragole did not produce strand breaks in plasmid DNA in vitro. We then evaluated the formation of DNA adducts in V79 cells by use of the (32)P-postlabelling assay and detected a dose-dependent formation of DNA adducts, which may be responsible for its genotoxicity. We then assayed estragole in the comet assay with two CHO cell lines, a parental AA8 cell line, and an XRCC1-deficient cell line, EM9. Results confirmed the genotoxicity of estragole without biotransformation in both cell lines, although the genotoxicity in EM9 cells compared with that in AA8 cells was not significantly different, suggesting that the XRCC1 protein is not involved in the repair of estragole-induced lesions. Estragole induces apoptosis, but only with high doses (2000μM), and after long treatment periods (24h). Overall, our results suggest that estragole, besides being metabolized to genotoxic metabolites, is a weak direct-acting genotoxin that forms DNA adducts.

Mutagenicity of flavonoids assayed by bacterial reverse mutation (Ames) test

The mutagenicity of ten flavonoids was assayed by the Ames test, in Salmonella typhimurium strains TA98, TA100 and TA102, with the aim of establishing hydroxylation pattern-mutagenicity relationship profiles. The compounds assessed were: quercetin, kaempferol, luteolin, fisetin, chrysin, galangin, flavone, 3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone. In the Ames assay, quercetin acted directly and its mutagenicity increased with metabolic activation. In the presence of S9 mix, kaempferol and galangin were mutagenic in the TA98 strain and kaempferol showed signs of mutagenicity in the other strains. The absence of hydroxyl groups, as in flavone, only signs of mutagenicity were shown in strain TA102, after metabolization and, among monohydroxylated flavones (3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone), the presence of hydroxyl groups only resulted in minor changes. Luteolin and fisetin also showed signs of mutagenicity in strain TA102. Finally, chrysin, which has only two hydroxy groups, at the 5-OH and 7-OH positions, also did not induce mutagenic activity in any of the bacterial strains used, under either activation condition. All the flavonoids were tested at concentrations varying from 2.6 to 30.7 nmol/plate for galangin and 12.1 to 225.0 nmol/plate for other flavonoids. In light of the above, it is necessary to clarify the conditions and the mechanisms that mediate the biological effects of flavonoids before treating them as therapeutical agents, since some compounds can be biotransformed into more genotoxic products; as is the case for galangin, kaempferol and quercetin.

Mikania glomerata Sprengel (Asteraceae) influences the mutagenicity induced by doxorubicin without altering liver lipid peroxidation or antioxidant levels

As shown in numerous studies, natural compounds may exert adverse effects, mainly when associated with some drugs. The hydroalcoholic extract of Mikania glomerata is the pharmaceutical form present in commercially available syrup used for the treatment of respiratory diseases in popular Brazilian medicine. The objective of the present investigation was (1) to evaluate the preventive effects of standardized hydroalcoholic extract of M. glomerata (MEx) against antitumoral drug doxorubicin (DXR)-induced micronucleated polychromatic erythrocytes (MNPCE) in a subchronic assay in mice, and (2) to determine the liver content of malondialdehyde (MDA) and the antioxidants glutathione (GSH) and vitamin E (VE). Male Swiss mice were treated for 30 d with MEx added to drinking water, combined or not with DXR (90 mg/kg body weight) injected intraperitoneally (ip) 24 h before analysis. The results demonstrated that MEx produced no genotoxic damage, but significantly increased the frequency of MNPCE induced by DXR, indicating a drug-drug interaction. This rise was not accompanied by lipid peroxidation or antioxidants level reduction, as measured by MDA, GSH, and VE. Despite the presence of coumarin (a known antioxidant), MEx may exert adverse effects probably in association with mutagenic compounds, although this effect on DNA damage did not involve oxidative stress.

Structural characteristics for superoxide anion radical scavenging and productive activities of green tea polyphenols including proanthocyanidin dimers

The purpose of this paper is to report structural characteristics for superoxide anion radical (O(2(-))) scavenging and productive activities of green tea polyphenols. (-)-Epicatechin 3-O-gallate (5), (-)-epigallocatechin (6), (-)-epigallocatechin 3-O-gallate (7), (+)-gallocatechin-(4alpha-->8')-epigallocatechin (8), and (-)-epigallocatechin-(2beta-->O-->7', 4beta-->8')-epicatechin 3'-O-gallate (9) were isolated from the tea plant Camellia sinensis L. (+)-Epigallocatechin-(2beta-->O-->7, 4beta-->8')-epicatechin (10) was prepared by hydrolyzing 9. The polyphenols, as well as commercially available pyrogallol (1), methyl gallate (2), (+)-catechin (3), (-)-epicatechin (4), and the flavonol myricetin (11), produced O(2(-)) in descending order 1, 6 asymptotically equal to11 asymptotically equal to8, 7, 10, 2 asymptotically equal to9, 5 asymptotically equal to4. In the polyphenols with the pyrogallol-type B-ring and/or galloyl group, electron-withdrawing substituents (carbonyl and ketal carbons) and/or intramolecular hydrogen bonding constituted structural characteristics against the autoxidation reaction. The O(2(-))-productive activity partially counteracted O(2(-))-scavenging activity. However, such structural characteristics appeared to enhance the scavenging activity, accordingly the polyphenols in effect served as O(2(-))-scavengers in descending order 9 asymptotically equal to7, 2, 11, 8, 10, 3 asymptotically equal to4. On the other hand, 6, having no such structural characteristic, acted as a O(2(-))-generator, as well as 1. Further assessments covering tannins (e.g., A-type proanthocyanidin dimer 9) are needed to identify which green tea polyphenols are the most desirable chemopreventive agents.

Potential genotoxicity of plant extracts used in Ethiopian traditional medicine

AIM OF THE STUDY

Although traditional herbal medicines are widely used in Ethiopia, no information is available on their potential genotoxicity. In the present study, hydroalcoholic extracts of Glinus lotoides, Plumbago zeylanica, Rumex steudelii and Thymus schimperi were evaluated for their DNA damaging effects using the comet assay.

MATERIAL AND METHODS

Mouse lymphoma L5178Y cells were exposed to different concentrations of the extracts for 3h with and without metabolic activation (S9-mix) using 4-nitroquinoline-N-oxide and benzo(a)pyrene as positive controls, and vehicles as negative controls.

RESULTS

In the absence of S9, all extracts were found to induce significant DNA damage without affecting the cell viability. T. schimperi and R. steudelii were the most potent DNA-damaging extracts, and G. lotoides and P. zeylanica the least potent. The addition of S9 had different effects on the DNA damage induced by the extracts: it lowered the DNA damaging effect of P. zeylanica, did not affect the DNA damaging effect of T. schimperi, and increased the DNA damaging effects of R. steudelii and G. lotoides.

CONCLUSION

The findings of the present study suggest that all extracts evaluated have a genotoxic potential in vitro which needs to be substantiated by further studies.

Health effects of quercetin: from antioxidant to nutraceutical. Eur J Pharmacol. 2008;585:325-337. [PMID: 18417116 DOI: 10.1016/j.ejphar.2008.03.008]

Quercetin, a member of the flavonoids family, is one of the most prominent dietary antioxidants. It is ubiquitously present in foods including vegetables, fruit, tea and wine as well as countless food supplements and is claimed to exert beneficial health effects. This includes protection against various diseases such as osteoporosis, certain forms of cancer, pulmonary and cardiovascular diseases but also against aging. Especially the ability of quercetin to scavenge highly reactive species such as peroxynitrite and the hydroxyl radical is suggested to be involved in these possible beneficial health effects. Consequently, numerous studies have been performed to gather scientific evidence for these beneficial health claims as well as data regarding the exact mechanism of action and possible toxicological aspects of this flavonoid. The purpose of this review is to evaluate these studies in order to elucidate the possible health-beneficial effects of the antioxidant quercetin. Firstly, the definitions as well as the most important aspects regarding free radicals, antioxidants and oxidative stress will be discussed as background information. Subsequently, the mechanism by which quercetin may operate as an antioxidant (tested in vitro) as well as the potential use of this antioxidant as a nutraceutical (tested both ex vivo and in vivo) will be discussed.

Antioxidant Activity of Fruits toward Iron under Gastrointestinal Conditions

The objectives of this study were to determine the antioxidant activity of fruits containing polyphenolics, namely anthocyanins, and their capacity to reduced Fe (III) to Fe (II) under simulated gastrointestinal conditions. The antioxidant capacity of fruits against prooxidant iron was determined using an in vitro assay. All the fruits exhibited variable antioxidant activity to iron in comparison to the control, both in the presence and absence of digestive enzymes and bile salts. For the fruits containing anthocyanins it was possible to obtain a positive correlation between total ferrous iron and anthocyanins content. There are strong negative correlations between phenolic compounds and dialyzable ferrous iron.

Flavonoid effects on DNA oxidation at low concentrations relevant to physiological levels

Flavonoids, which are abundant in fruits and vegetables, are known to have many beneficial health effects. Antioxidant activity is likely to be a main function but has been mostly studied at high flavonoid concentrations which are not feasible at the intracellular level. In this experiment, several flavonoids (e.g., catechin, quercetin, myricetin, luteolin, morin and cyanidin) were examined at low physiologically relevant concentrations. Calf thymus DNA was treated with different flavonoids at concentrations of 0.1, 1, 10 and 100 microM using Fenton conditions to induce oxidation and several oxidative adducts including 8-hydroxy guanine (7,8-dihydro-8-oxo-2'-deoxyguanosine; 8-OH guanine) were analyzed using gas chromatography-mass spectrometry-selective ion monitoring (GC-MS-SIM). Catechin, quercetin and cyanidin inhibited 8-OH guanine formation by 92%, 33% and 45%, respectively, at low concentrations (0.1 microM). In addition catechin and quercetin showed antioxidant activities on 8-OH guanine formation over all concentrations. When the oxidative DNA adduct 4,6-diamino-5-formamidopyrimidine (fapy-adenine) was measured, however, the highest concentrations of catechin and quercetin actually increased adduct formation. These results indicate that flavonoids can act as antioxidants at low concentrations relevant to physiological levels. However measuring only one oxidative DNA adduct as a biomarker may result in misleading conclusions regarding antioxidant activities of natural products.

Genotoxic effects of tanshinones from Hyptis martiusii in V79 cell line

The genotoxic effect of two tanshinones isolated from roots of Hyptis martiussi Benth (Labiatae) was studied using V79 (Chinese hamster lung) cells by the alkaline comet assay and micronucleus test. Tanshinones were incubated with the cells at concentrations of 1, 3, 6 and 12 microg/mL for 3 h. Tanshinones were shown to be quite strongly genotoxic against V79 cells at all tested concentrations. The data obtained provide support to the view that tanshinones has DNA damaging activity in cultured V79 cells under the conditions of the assays.

Base excision repair pathway is involved in the repair of lesions generated by flavonoid-enriched fractions of pepper tree (Schinus terebinthifolius, Raddi) stem bark

Cell-free and bacterial assays indicate that flavonoid-enriched fractions and the flavonoids of pepper tree stem bark from Schinus terebinthifolius Raddi have genotoxic rather than antigenotoxic properties. In the present report, we have examined the ability of flavonoid-enriched fractions to damage plasmid DNA and the repair pathways involved in the recognition of these DNA lesions. High concentrations of two flavonoid-enriched fractions were able to break phosphodiester bonds in DNA. In addition, studies using bacterial strains deficient in nucleotide excision repair and base excision repair (BER) enzymes indicated that the flavonoid-enriched fractions generated lesions that were substrates for enzymes belonging to the BER pathway. In addition, in vitro studies indicated that the DNA damage produced by the flavonoid-enriched fractions was also a substrate for exonuclease III and that the phosphodiester breakage was amplified by copper ions. These results indicate that flavonoids from the pepper tree (Schinus terebinthifolius, Raddi) generate lesions on DNA that are potential targets of FPG and MutY glycosylase from the BER pathway. Chromatographic and spectral analyses helped to support the hypothesis that the flavonoids of the Brazilian pepper tree bark are the main factors involved in the fraction's damage potential. The isolated flavonoids from Fraction II were also tested in vitro and support the oxidative damage potential of these flavonoids.

Complex mixtures that may contain mutagenic and/or genotoxic components: a need to assess in vivo target-site effect(s) associated with in vitro-positive(s)

A battery of short-term in vitro assays and/or in vivo protocols to evaluate single-agent mutagenicity and/or genotoxicity is available. However, a protocol to assess the effect(s) of complex mixtures in vivo following a positive test finding in vitro remains difficult. Complex interactions may occur in vivo because component pharmacokinetics increases the unpredictability of pharmacodynamic outcomes. The question arises as to whether in vitro mutagenic component(s) of a complex mixture, probably unidentified, reach target organ(s) in vivo at a sufficient concentration. To address the issue of an in vitro positive, standard in vivo chromosome damage assays to test both mixtures and fractions could be conducted but, to assess site-of-contact effects, the alkaline single cell-gel electrophoresis ("comet") assay or DNA reactivity (e.g., (32)P-postlabelling of DNA adducts) might be employed. A newer approach may be the derivation of a "biochemical-cell fingerprint" of potential target sites using infrared microspectroscopy. There is interest in platforms such as gene expression, proteomics, epigenomics or metabolomics as biomarkers of signature genotoxic or non-genotoxic mechanisms. One still needs to address whether a mutagenic and/or genotoxic component reaches a target organ. An approach to track levels of target-organ exposure may be to radio-label components with a short-lived positron-emitting radionuclide. The parent compound retains its physicochemical properties whilst allowing non-invasive in vivo tissue-specific imaging. However, determining target-organ concentration(s) and effect(s) in vivo remains a difficult challenge.