Antioxidation mechanism studies of caffeic acid: identification of antioxidation products of methyl caffeate from lipid oxidation

Chlorogenic acid as an indispensible partner of caffeic acid in coffee via selective regulation of prooxidative actions of caffeic acid

Chlorogenic acid (CGA) and caffeic acid (CA) are two major phenolic acids in coffee. Though the International Agency for Research on Cancer has classified CA as a Group2B carcinogen, coffee consumption seems generally safe within the usual levels of intake and is more likely to benefit health than to harm it. We thus speculated that CGA may effectively suppress the carcinogenic potential of CA. In a molar ratio achievable in vivo, this study shows that CGA can inhibit (i) copper reduction caused by CA, (ii) CA oxidation caused by copper, (iii) the formation of hydroxyl radicals by CA and copper, and (iv) DNA damage induced by CA, quercetin or (-)-epigallocatechin-3-gallate in the presence of copper. CA tends to undergo autoxidation to produce hydrogen peroxide and quinone, which further reacts with proteins to form quinoproteins. This autoxidation at a tolerable level normally induces beneficial adaptive responses. This study shows that CGA is less efficient than CA in producing hydrogen peroxide and quinoprotein; however, together they synergistically produce hydrogen peroxide and quinoprotein in vitro at a molar ratio achievable in vivo. In conclusion, CGA can selectively regulate the prooxidant activities of CA depending on whether copper is involved or not. CGA could be viewed as an indispensable partner of CA in coffee, given its dual role in suppressing the carcinogenic potential of CA and boosting CA autoxidation which is beneficial for disease prevention.

Boosting caffeic acid performance as antioxidant and monoamine oxidase B/catechol-O-methyltransferase inhibitor

Increased oxidative stress (OS) and depletion of nigrostriatal dopamine (DA) are closely linked to the neurodegeneration observed in Parkinson's Disease (PD). Caffeic acid (CA)-based antioxidants were developed, and their inhibitory activities towards monoamine oxidases (MAOs) and catechol O-methyltransferases (COMT) were screened. The results showed that the incorporation of an extra double bond maintained or even boosted the antioxidant properties of CA. α-CN derivatives displayed redox potentials (E_p) similar to CA (1) and inhibited hMAO-B with low μM IC₅₀ values. Moreover, catechol amides acted as MB-COMT inhibitors, showing IC₅₀ values within the low μM range. In general, CA derivatives presented safe cytotoxicity profiles at concentrations up to 10 μM. The formation of reactive oxygen species (ROS) induced by CA derivatives may be underlying the cytotoxic effects observed at higher concentrations. Catechol amides 3-6, 8-11 at 10 μM protected cells against oxidative damage. Compounds 3 and 8 were predicted to cross the blood-brain barrier (BBB) by passive diffusion. In summary, we report for the first time BBB-permeant CA-based multitarget lead compounds that may restore DAergic neurotransmission (dual hMAO-B/MB-COMT inhibition) and prevent oxidative damage. The data represents a groundbreaking advancement towards the discovery of the next generation of new drugs for PD.

A caffeic acid electrochemical sensor amplified with GNR/CoFe2O4@NiO and 1-Ethyl-3-methylimidazolium acetate; a new perspective for food analysis

Determining Caffeic acid is important as an antioxidant compound in food. In this study, caffeic acid (CA) was measured using a carbon paste electrode modified with GNR/CoFe₂O₄@NiO and 1-Ethyl-3-methylimidazolium acetate (EMIM Ac) as ion liquid. A simple sensor showed a higher current than a bare carbon paste; thus, it can be said that the modified electrode has a higher sensitivity for detecting CA. The linear range of this sensor and its detection limit was equal to 0.01-100.0 μM and 0.01 μM, respectively. Moreover, the developed electrode indicated outstanding selectivity in the presence of several interferences, high sensitivity, reproducibility, and long-term stability. The percentage recovery of CA obtained with the developed sensor affirmed its reliability for CA determination in real samples. The modified sensor's accuracy was confirmed to identify this analyte according to the results.

Evaluation of Toxicity, Bacteriostatic, Analgesic, Anti-Inflammatory, and Antipyretic Activities of Huangqin-Honghua-Pugongying-Jinyinhua Extract

The extensive use of antibiotics has caused the global spread of multidrug-resistant bacteria and genes, seriously reducing antibiotic efficacy and threatening animal and human health. As an alternative, traditional Chinese veterinary medicine (TCVM) was used in this study for its lack of drug resistance and low toxicity. Huangqin-honghua-pugongying-jinyinhua extract (HHPJE), a novel TCVM, consists of the extracts of Huangqin (Scutellaria baicalensis), Honghua (Carthami Flos), Pugongying (Taraxacum) and Jinyinhua (Lonicerae Japonicae Flos), and was developed to treat bovine mastitis. In this study, we evaluated the toxicity, bacteriostatic, analgesic, anti-inflammatory, and antipyretic activities of HHPJE. Our results show that HHPJE did not show any acute oral toxicity and can be considered safe for oral administration. Additionally, HHPJE possessed a dose-dependent antibacterial effect on Staphylococcus aureus, Escherichia coli, Streptococcus agalactiae and Streptococcus dysgalactiae. HHPJE (60, 30 and 15 g/kg) can reduce the abdominal pain by 44.83 ± 7.69%, 43.15 ± 9.50% and 26.14 ± 4.17%, respectively. The percentages of anti-inflammation inhibition (60, 30 and 15 g/kg) were 35.34 ± 2.17%, 22.29 ± 2.74% and 12.06 ± 3.61%, respectively. The inhibition rates (60, 30 and 15 g/kg) of antipyretic activity were 82.05%, 65.71% and 52.80%, respectively. The evaluation of pharmacodynamics and toxicity indicate that HHPJE possesses significant bacteriostatic, analgesic, anti-inflammatory and antipyretic potential, and also that it is safe for acute oral toxicity, which means it has potential value for treating bovine mastitis in future and alleviating clinical symptoms with no drug resistance or side effects.

Enzymatic glucosylation of polyphenols using glucansucrases and branching sucrases of glycoside hydrolase family 70

Polyphenols exhibit various beneficial biological activities and represent very promising candidates as active compounds for food industry. However, the low solubility, poor stability and low bioavailability of polyphenols have severely limited their industrial applications. Enzymatic glycosylation is an effective way to improve the physicochemical properties of polyphenols. As efficient transglucosidases, glycoside hydrolase family 70 (GH70) glucansucrases naturally catalyze the synthesis of polysaccharides and oligosaccharides from sucrose. Notably, GH70 glucansucrases show broad acceptor substrate promiscuity and catalyze the glucosylation of a wide range of non-carbohydrate hydroxyl group-containing molecules, including benzenediol, phenolic acids, flavonoids and steviol glycosides. Branching sucrase enzymes, a newly established subfamily of GH70, are shown to possess a broader acceptor substrate binding pocket that acts efficiently for glucosylation of larger size polyphenols such as flavonoids. Here we present a comprehensive review of glucosylation of polyphenols using GH70 glucansucrase and branching sucrases. Their catalytic efficiency, the regioselectivity of glucosylation and the structure of generated products are described for these reactions. Moreover, enzyme engineering is effective for improving their catalytic efficiency and product specificity. The combined information provides novel insights on the glucosylation of polyphenols by GH70 glucansucrases and branching sucrases, and may promote their applications.

Supramolecular Caffeic Acid and Bortezomib Nanomedicine: Prodrug Inducing Reactive Oxygen Species and Inhibiting Cancer Cell Survival

Phenolics from plant materials have garnered attention in nanomedicine research, due to their various medicinal properties. Caffeic acid, a phenolic compound that is abundant in coffee beans, has been proven to have anticancer effects, due to its reactive oxygen species (ROS)-inducing properties. Here, a supramolecular nanomedicine was designed using caffeic acid molecule and the synthetic anticancer drug bortezomib, via catechol–boronic acid conjugation and Fe(III) ion crosslinking. Bortezomib is a proteasome-inhibiting drug and its boronic acid functional group can bind to caffeic acid’s catechol moiety. By having a nanoparticle formulation that can deliver bortezomib via intracellular endocytosis, the catechol–boronic acid conjugation can be dissociated, which liberates the boronic acid functional group to bind to the 26S proteasome of the cell. The ROS-inducing property of caffeic acid also complements the bortezomib payload, as the latter suppresses the survival mechanism of the cell through NF-κB inhibition.

Synthesis of Lipophilic Caffeoyl Alkyl Ester Using a Novel Natural Deep Eutectic Solvent

In this work, a novel method for lipophilic caffeoyl alkyl ester production was developed using a natural deep eutectic solvent (DES) consisting of choline chloride and caffeic acid (CA) as the caffeoyl donor. Cation-exchange resins were used as the catalyst to catalyze the esterification of fatty alcohols with the DES. Effects of the caffeoyl donor and reaction variables were investigated. Reaction thermodynamics were also analyzed. The results showed that the lipophilic caffeoyl alkyl ester production can be enhanced using the DES as the caffeoyl donor, and cation-exchange resin A-35 showed the best catalytic activity for the reaction. Under the optimized conditions (85 °C, stearyl alcohol/CA 8:1 (mol/mol), A-35 load 5% and 24 h), the maximum octodecyl caffeate (OC) yield (90.69 ± 2.71%) and CA conversion (95.17 ± 2.76%) were obtained with the DES as the caffeoyl donor, which were much higher than those obtained with solid CA as the caffeoyl donor (OC yield 40.97 ± 2.37% and CA conversion 44.26 ± 1.69%). The activation energy of CA conversion (67.57 kJ/mol) with the DES was lower than that with solid CA (90.19 kJ/mol). In addition, the mass transfer limitation can be decreased with the DES. Compared with solid CA as the caffeoyl donor, a fast reaction rate and low mass transfer limitation were obtained using the DES as the caffeoyl donor.

Metabolome Profiling Supports the Key Role of the Spike in Wheat Yield Performance

Although the relevance of spike bracts in stress acclimation and contribution to wheat yield was recently revealed, the metabolome of this organ and its response to water stress is still unknown. The metabolite profiles of flag leaves, glumes and lemmas were characterized under contrasting field water regimes in five durum wheat cultivars. Water conditions during growth were characterized through spectral vegetation indices, canopy temperature and isotope composition. Spike bracts exhibited better coordination of carbon and nitrogen metabolisms than the flag leaves in terms of photorespiration, nitrogen assimilation and respiration paths. This coordination facilitated an accumulation of organic and amino acids in spike bracts, especially under water stress. The metabolomic response to water stress also involved an accumulation of antioxidant and drought tolerance related sugars, particularly in the spikes. Furthermore, certain cell wall, respiratory and protective metabolites were associated with genotypic outperformance and yield stability. In addition, grain yield was strongly predicted by leaf and spike bracts metabolomes independently. This study supports the role of the spike as a key organ during wheat grain filling, particularly under stress conditions and provides relevant information to explore new ways to improve wheat productivity including potential biomarkers for yield prediction.

Synergistic effects of cisplatin-caffeic acid induces apoptosis in human cervical cancer cells via the mitochondrial pathways

Cervical cancer (CxCa) is a major health problem globally and is associated with the presence of human papillomavirus infection. Cisplatin (CDDP) is a platinum-based chemotherapeutic agent. Owing to its side effects and drug-resistance, novel anticancer agents with lower toxicity, including caffeic acid (CFC), are of interest. However, the effects of CDDP and CFC in combination are, to the best of our knowledge, uninvestigated. The present study investigated the effectiveness of CDDP and CFC in combination and its mechanism of action on four human cervical cancer cell lines, which were compared with the Chlorocebus sabaeus normal kidney Vero cell line. Cell viability was evaluated using a sulforhodamine B assay. Caspase-Glo assay kits, measuring the activity of caspases-3, -7, -8 and -9, were used to detect caspase activation in HeLa and CaSki cell lines in response to CDDP and CFC in combination. The results revealed that CDDP and CFC alone reduced the proliferation of HeLa, CaSki, SiHa and C33A cell lines. Treatment with CFC exhibited no significant cytotoxicity towards Vero cells. In addition, CDDP-CFC significantly inhibited cell growth of HeLa and CaSki cell lines. In HeLa and CaSki cell lines, a combination index <1 for CDDP and CFC indicated the synergistic growth inhibition; the combination of the two also significantly increased expression of caspase-3, -7 and -9. In conclusion, CFC may be a candidate anticancer agent that, when use in combination, may increase the therapeutic efficacy of CDDP.

Synthesis and Functional Characterization of Caffeic Acid Glucoside Using Leuconostoc mesenteroides Dextransucrase

Caffeic acid was modified via transglucosylation using sucrose and dextransucrase from Leuconostoc mesenteroides B-512FMCM. Following enzymatic modification, a caffeic acid glucoside was isolated by butanol separation, silica gel chromatography, and preparative HPLC. The synthesized caffeic acid glucoside had a molecular mass-to-charge ratio of 365 m/z, and its structure was identified as caffeic acid-3-O-α-d-glucopyranoside. The production of this caffeic acid-3-O-α-d-glucopyranoside at a concentration of 153 mM was optimized using 325 mM caffeic acid, 355 mM sucrose, and 650 mU mL^-1 dextransucrase in the synthesis reaction. In comparison with the caffeic acid, the caffeic acid-3-O-α-d-glucopyranoside displayed 3-fold higher water solubility, 1.66-fold higher antilipid peroxidation effect, 15% stronger inhibition of colon cancer cell growth, and 11.5-fold higher browning resistance. These results indicate that this caffeic acid-3-O-α-d-glucopyranoside may be a suitable functional component of food and pharmaceutical products.

Inhibitory mechanism against oxidative stress of caffeic acid

The purpose of this article is to summarize the reported antioxidant activities of a naturally abundant bioactive phenolic acid, caffeic acid (CA, 3,4-dihydroxycinnamic acid), so that new avenues for future research involving CA can be explored. CA is abundantly found in coffee, fruits, vegetables, oils, and tea. CA is among the most potential and abundantly found in nature, hydroxycinnamic acids with the potential of antioxidant behavior. Reactive oxygen species produced as a result of endogenous processes can lead to pathophysiological disturbances in the human body. Foods containing phenolic substances are a potential source for free radical scavenging; these chemicals are known as antioxidants. This review is focused on CA’s structure, availability, and potential as an antioxidant along with its mode of action. A brief overview of the literature published about the prooxidant potential of caffeic acid as well as the future perspectives of caffeic acid research is described. CA can be effectively employed as a natural antioxidant in various food products such as oils.

Identification of a potent xanthine oxidase inhibitor from oxidation of caffeic acid

Inhibitory activity of Fe-ion-catalyzed radical oxidation products from 22 types of phenolic compounds toward xanthine oxidase (XO) was investigated. Phenols are readily oxidizable compounds in nature and, thus, showed potent antioxidant activities. Among the phenols screened in this study, noticeable activity was observed in the oxidation product of caffeic acid, whereas almost no XO-inhibitory activity of caffeic acid was observed. Assay-guided purification of the oxidation product of caffeic acid afforded a highly potent XO inhibitor, with an IC50 value that was calculated to be 60 nmol L(-1), which indicated XO-inhibitory activity much stronger than that of allopurinol (IC50 = 1 μmol L(-1)), a potent XO inhibitor and excellent medicine for the treatment of gout. The chemical structure of this new XO inhibitor was investigated by one- and two-dimensional NMR and HR-ESI-MS analyses, and the unique tetracyclic structure was confirmed by synthesis starting from commercially available 1,2,4-trimethoxybenzene and 3,4-dimethoxylbenzoyl chloride.

The effects of bioactive compounds from plant foods on mitochondrial function: a focus on apoptotic mechanisms

Mitochondria are essential organelles for cellular integrity and functionality maintenance and their imparement is implicated in the development of a wide range of diseases, including metabolic, cardiovascular, degenerative and hyperproliferative pathologies. The identification of different compounds able to interact with mitochondria for therapeutic purposes is currently becoming of primary importance. Indeed, it is well known that foods, particularly those of vegetable origin, present several constituents with beneficial effects on health. This review summarizes and updates the most recent findings concerning the mechanisms through which different dietary compounds from plant foods affect mitochondria functionality in healthy and pathological in vitro and in vivo models, paying particular attention to the pathways involved in mitochondrial biogenesis and apoptosis.

An electrocatalytic oxidation and voltammetric method using a chemically reduced graphene oxide film for the determination of caffeic acid

The present work describes the characterization of a chemically reduced graphene oxide (CRGO) modified glassy carbon electrode (GCE) for electrochemical investigation of caffeic acid (CA). Cyclic voltammetry (CV), differential pulse voltammetry (DPV), amperometry, and electrochemical impedance spectroscopy (EIS) techniques were used to characterize the properties of the electrode. There was an obvious enhancement of the current response and a decreased over potential for the oxidation of CA. The interfacial electron transfer rate of CA was studied by EIS. Under optimal conditions, the CRGO displayed a linear response range of 1×10(-8) to 8×10(-4) M and the detection limit was 2×10(-9) M (S/N=3), with a sensitivity of 192.21 μA mM(-1) cm(-2) at an applied potential of +0.2V (vs. Ag/AgCl reference), which suggests that the CRGO is a promising sensing materials for the electrochemical investigation of CA. The results showed the good sensitivity, selectivity and high reproducibility of the CRGO modified electrode. Moreover, this modified electrode was further applied to investigate the CA in real samples of wine with satisfactory results.

An antioxidant bioinspired phenolic polymer for efficient stabilization of polyethylene

The synthesis, structural characterization and properties of a new bioinspired phenolic polymer (polyCAME) produced by oxidative polymerization of caffeic acid methyl ester (CAME) with horseradish peroxidase (HRP)-H2O2 is reported as a new sustainable stabilizer toward polyethylene (PE) thermal and photo-oxidative degradation. PolyCAME exhibits high stability toward decarboxylation and oxidative degradation during the thermal processes associated with PE film preparation. Characterization of PE films by thermal methods, photo-oxidative treatments combined with chemiluminescence, and FTIR spectroscopy and mechanical tests indicate a significant effect of polyCAME on PE durability. Data from antioxidant capacity tests suggest that the protective effects of polyCAME are due to the potent scavenging activity on aggressive OH radicals, the efficient H-atom donor properties inducing free radical quenching, and the ferric ion reducing ability. PolyCAME is thus proposed as a novel easily accessible, eco-friendly, and biocompatible biomaterial for a sustainable approach to the stabilization of PE films in packaging and other applications.

Electrochemical oxidation of wine polyphenols in the presence of sulfur dioxide

Electrochemical oxidation of three representative wine polyphenols (catechin, caffeic acid, and quercetin) in the presence of sulfur dioxide in a model wine solution (pH = 3.3) was investigated. The oxidation was undertaken using chronoamperometry at a rotating glassy carbon rod electrode, and the reaction products were characterized by HPLC-MS. The mechanism of electrochemical oxidation of polyphenols in the presence of sulfur dioxide was proposed to be an ECEC mechanism. The polyphenols first underwent a one-electron oxidation to a semiquinone radical, which can be reduced back to the original polyphenol by sulfur dioxide, or further oxidized to the quinone form. In the cases of caffeic acid and catechin, the quinone combined with sulfur dioxide and produced new derivatives. The quercetin quinone underwent further chemical transformations, producing several new compounds. The proposed mechanisms were confirmed by digital simulation of cyclic voltammograms.

Chemical interaction between polyphenols and a cysteinyl thiol under radical oxidation conditions

Chemical interaction between polyphenols and thiols was investigated under radical oxidation conditions using a model cysteinyl thiol derivative, N-benzoylcysteine methyl ester. The radical oxidation was carried out with a stoichiometric amount of 2,2-diphenyl-1-picrylhydrazyl (DPPH), and the decreases in the amounts of polyphenols and the thiol were measured by HPLC analysis. Cross-coupling products between various polyphenols and the thiol were examined by LC-MS in reactions that showed decreases in both the polyphenols and the thiol. The LC-MS results indicated that three phenolic acid esters (methyl caffeate, methyl dihydrocaffeate, and methyl protocatechuate) and six flavonoids (kaempferol, myricetin, luteolin, morin, taxifolin, and catechin) gave corresponding thiol adducts, whereas three polyphenols (methyl ferulate, methyl sinapate, and quercetin) gave only dimers or simple oxidation products without thiol substituents. Thiol adducts of the structurally related compounds methyl caffeate and methyl dihydrocaffeate were isolated, and their chemical structures were determined by NMR analysis. The mechanism for the thiol addition was discussed on the basis of the structures of the products.

Coffee components inhibit amyloid formation of human islet amyloid polypeptide in vitro: possible link between coffee consumption and diabetes mellitus

Global epidemic studies have suggested that coffee consumption is reversely correlated with the incidence of type 2 diabetes mellitus (T2DM), a metabolic disease. The misfolding of human islet amyloid polypeptide (hIAPP) is regarded as one of the causative factors of T2DM. Coffee extracts have three major active components: caffeine, caffeic acid (CA), and chlorogenic acid (CGA). In this study, the effects of these major coffee components, as well as dihydrocaffeic acid (DHCA) (a major metabolite of CGA and CA), on the amyloidogenicity of hIAPP were investigated by thioflavin-T based fluorescence emission, transmission electronic microscopy, circular dichroism, light-induced cross-linking, dynamic light scattering, and MTT-based cell viability assays. The results suggest that all components show varied inhibitory effects on the formation of toxic hIAPP amyloids, in which CA shows the highest potency in delaying the conformational transition of the hIAPP molecule with the most prolonged lag time, whereas caffeine shows the lowest potency. At a 5-fold excess molar ratio of compound to hIAPP, all coffee-derived compounds affect the secondary structures of incubated hIAPP as suggested by the circular dichroism spectra and CDPro deconvolution analysis. Further photoinduced cross-linking based oligomerization and dynamic light scattering studies suggested CA and CGA significantly suppressed the formation of hIAPP oligomers, whereas caffeine showed no significant effect on oligomerization. Cell protection effects were also observed for all three compounds, with the protection efficiency being greatest for CA and least for CGA. These findings suggest that the beneficial effects of coffee consumption on T2DM may be partly due to the ability of the major coffee components and metabolites to inhibit the toxic aggregation of hIAPP.

Caffeic acid induces apoptosis in human cervical cancer cells through the mitochondrial pathway

OBJECTIVE

The anti-proliferation effect of caffeic acid (3,4-dihydroxycinnamic acid), isolated from Ocimum gratissimum Linn, on human cervical cancer cells (HeLa cells) was examined to elucidate the associated mechanism and death mode.

MATERIALS AND METHODS

Flow cytometry showed that caffeic acid treatment results in dramatically increased apoptosis of HeLa cells. Western blot analysis revealed that caffeic acid activates various processed caspases.

RESULTS

Caffeic acid significantly reduced proliferation of HeLa cells in a concentration-dependent manner. Morphological evidence of apoptosis, including nuclei fragmentation was clearly observed 24 and 48 hours after exposure to caffeic acid (1 mM and 10 mM) by flow cytometry. Time-dependent inhibition was also observed. Caffeic acid decreased levels of uncleaved caspase-3 and Bcl-2, and induced cleaved caspase-3 and p53.

CONCLUSION

Caffeic acid induces apoptosis by inhibiting Bcl-2 activity, leading to release of cytochrome c and subsequent activation of caspase-3, indicating that caffeic acid induces apoptosis via the mitochondrial apoptotic pathway. This also suggests that caffeic acid has a strong anti-tumor effect and may be a promising chemopreventive or chemotherapeutic agent.

Tyrosine-lipid peroxide adducts from radical termination: para coupling and intramolecular Diels-Alder cyclization

Free radical co-oxidation of polyunsaturated lipids with tyrosine or phenolic analogues of tyrosine gave rise to lipid peroxide-tyrosine (phenol) adducts in both aqueous micellar and organic solutions. The novel adducts were isolated and characterized by 1D and 2D NMR spectroscopy as well as by mass spectrometry (MS). The spectral data suggest that the polyunsaturated lipid peroxyl radicals give stable peroxide coupling products exclusively at the para position of the tyrosyl (phenoxy) radicals. These adducts have characteristic (13)C chemical shifts at 185 ppm due to the cross-conjugated carbonyl of the phenol-derived cyclohexadienone. The primary peroxide adducts subsequently undergo intramolecular Diels-Alder (IMDA) cyclization, affording a number of diastereomeric tricyclic adducts that have characteristic carbonyl (13)C chemical shifts at ~198 ppm. All of the NMR HMBC and HSQC correlations support the structure assignments of the primary and Diels-Alder adducts, as does MS collision-induced dissociation data. Kinetic rate constants and activation parameters for the IMDA reaction were determined, and the primary adducts were reduced with cuprous ion to give a phenol-derived 4-hydroxycyclohexa-2,5-dienone. No products from adduction of peroxyls at the phenolic ortho position were found in either the primary or cuprous reduction product mixtures. These studies provide a framework for understanding the nature of lipid-protein adducts formed by peroxyl-tyrosyl radical-radical termination processes. Coupling of lipid peroxyl radicals with tyrosyl radicals leads to cyclohexenone and cyclohexadienone adducts, which are of interest in and of themselves since, as electrophiles, they are likely targets for protein nucleophiles. One consequence of lipid peroxyl reactions with tyrosyls may therefore be protein-protein cross-links via interprotein Michael adducts.

A novel ring-expanded product with enhanced tyrosinase inhibitory activity from classical Fe-catalyzed oxidation of rosmarinic acid, a potent antioxidative Lamiaceae polyphenol

The iron-ion catalyzed oxidation of the ethanol solution of rosmarinic acid, a potent antioxidant polyphenol of Lamiaceae (Labiatae) plants, afforded a highly tyrosinase-inhibitory active product. The structure of the active product in the oxidation product mixture was determined using extensive NMR spectroscopy to have a novel oxygen-containing seven-membered ring system. The formation mechanism of the unique ring structure from the catechol part of the rosmarinic acid was proposed.

Identification of cytotoxic dimers in oxidation product from sesamol, a potent antioxidant of sesame oil

Phytophenols of edible plants have recently attracted much attention as potent antioxidants and related bioactive substances. These antioxidative phytophenols are very oxidizable due to their chemical properties, and their oxidation products must accumulate in the oxidizing foods when they are contained as active ingredients. In this investigation, several phytophenols, which are well known as potent antioxidants in food science, were oxidized by oxygen in the presence of a catalytic amount of Ferric ion. Caffeic acid, catechin, chlorogenic acid, rosmarinic acid, and sesamol were quickly oxidized, whereas eugenol, resveratrol, rutin, and quercetin were not under the stated conditions. The oxidation product mixtures of the quickly oxidized phytophenols were next subjected to a cytotoxic assay using normal cells. Among the products, the oxidation product from sesamol showed a remarkably high cytotoxic activity. To clarify the cytotoxic principle of the oxidation products, an assay-guided fractionation and subsequent isolation of the oxidation compound of sesamol was carried out. Structure analysis of the isolated compounds revealed that they are new dimeric compounds (2-5) of sesamol. The cytotoxic activity of the dimers was evaluated from the population of dead cells by a flow cytometric analysis of rat thymocytes in the presence of 100 μM of each compound. Compound 2 showed the most potent cytotoxic activity among them. Compound 2 has a typical conjugated carbonyl moiety and the moiety possibly contributes to its high toxicity from a structure-activity point of view.

(E)-1-(3,4-dihydroxyphenethyl)-3-styrylurea inhibits proliferation of MCF-7 cells through G1 cell cycle arrest and mitochondria-mediated apoptosis

Growing interest in the beneficial effects of antioxidants has inspired the synthesis of new phenolic acid phenethyl ureas (PAPUs) with enhanced antioxidant potential. We have previously shown the capacity of one PAPU compound, (E)-1-(3,4-dihydroxyphenethyl)-3-styrylurea (PAPU1), to induce caspase-dependent apoptosis in melanoma cells. In the present study, we examined the anti-proliferative effects of PAPU compounds on MCF-7 human breast cancer cells and determined the molecular mechanisms involved. Treatment with PAPU compounds inhibited predominantly proliferation in these cells, where the PAPU1 was the most efficient form. Flow cytometric analysis showed that PAPU1 blocked cell cycle progression in the G(0)/G(1) phase, and reduced the proportion of cells in G(2)/M phase. This was related to the inhibition of cell cycle regulatory factors, including cyclin D/E and cyclin-dependent kinase (CDK) 2/4, through induction of p21(Cip1). PAPU1 also induced the mitochondrial-mediated and caspase-dependent apoptosis in MCF-7 cells. This was evidenced by cellular changes in the levels of Bcl-2 and Bax, loss of the mitochondrial membrane potential, release of cytochrome c into the cytosol, and caspase-9 activation. Collectively, our results suggest that G(1) cell cycle regulatory proteins and mitochondrial pathways are the crucial targets of PAPU1 in the chemoprevention of breast cancer cells.