Oxidation of dietary polyphenolics by hydroperoxidase activity of lipoxygenase

Lipoxygenase, in the presence of hydrogen peroxide, produces the oxidative decomposition of quercetin, naringenin, and resveratrol, known antioxidant molecules. Quercetin was the molecule more efficiently oxidized, followed by resveratrol and naringenin. When this molecule was incubated in the presence of GSH, a quinoid derivative was produced. This compound was not obtained in the presence of naringenin or resveratrol, suggesting that in the presence of hydrogen peroxide and lipoxygenase, quercetin may be oxidized to a prooxidant species. When hydrogen peroxide was substituted by hydroperoxy linoleic acid, the same oxidative process was observed. This means that in food products in which lipoxygenase and linoleic acid are presents, quercetin may be oxidized to prooxidant species; in contrast, naringenin and resveratrol may constitute a valid additive for the prevention of the oxidative degradation of foods.     

Oxidation of resveratrol catalyzed by soybean lipoxygenase

In this work the oxidative degradation of resveratrol catalyzed by lipoxygenase-1 (LOX-1) has been studied. The process has been characterized by spectroscopic and polarographic measurements. The oxidation of resveratrol was dependent on the concentration of resveratrol and the enzyme. When resveratrol was incubated in the presence of lipoxygenase at pH 9.0, the reaction displayed a k(M) value of 18.6 x 10(-)(6) M and a catalytic efficiency (k(cat)/k(M)) of 4.3 x 10(4) s(-)(1) M(-)(1). These values are close to those shown by the enzyme when linoleic acid is used as the substrate. The effect of lipoxygenase inhibitors on the lipoxygenase-catalyzed resveratrol oxidation was also evaluated. The rate of resveratrol oxidation was markedly decreased by the presence of NDGA in the incubation mixture. From HPLC measurements, it can be deduced that resveratrol is oxidatively decomposed to a complex mixture of products similar to those obtained when the molecule is oxidized by hydrogen peroxide.     

Computer simulation of the structure and dynamics of phenol in sodium montmorillonite hydrates

Monte Carlo and molecular dynamics computer simulations have been used to study the structure and dynamics of phenol‐water solutions in the bulk and confined within the interlayer pores of sodium montmorillonite clays, as a function of pressure and temperature. Conditions have been chosen to mimic those encountered at burial depths of up to 6 km, thereby enabling us to shed light on subsurface processes including groundwater contamination and oil and gas migration. The structural data show that the phenol molecules are able to form a donor hydrogen bond to the clay surface. In addition, the phenolic –OH group is solvated by approximately three water molecules, and is also able to coordinate directly to an interlayer sodium cation. The phenolic aromatic ring is surrounded by approximately 25 water molecules in the bulk, compared to 18 in the compacted clay. Interlayer diffusion increases by an order of magnitude as temperature is increased from 275 K to 460 K. However, diffusion decreases by a factor of 2–4 as we move from the bulk into a clay hydrate of layer spacing ∼17 Å. For example, at 275 K the diffusion coefficient of phenol is 8.3 × 10⁻¹⁰ m² s⁻¹ in bulk solution, compared to 2.5 × 10⁻¹⁰ m² s⁻¹ in the clay.     

Effects of structure on radical-scavenging abilities and antioxidative activities of tea polyphenols: NMR analytical approach using 1,1-diphenyl-2-picrylhydrazyl radicals

Tea (Camellia sinensis) leaves contain various antioxidants such as ascorbic acid (1) and polyphenols. This study tries to clarify the molecular mechanisms underlying the antioxidative and radical-scavenging activities of these antioxidants, and the reactivities of each antioxidant have been compared against that of the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH, 2) using nuclear magnetic resonance (NMR) analysis. Catechol (3) and (+)-taxifolin (4) were oxidized to o-quinone by 2. However, ethyl protocatechuate (5) and quercetin (6) were not oxidized to o-quinone, even though they possess a catechol structure. The radical-scavenging ability of o-dihydroxyl phenolic compounds with a conjugated olefinic double bond (e.g., 6) was superior to that of compounds without this bond (e.g., 4), whereas the ability of o-dihydroxyl phenolic compounds possessing a conjugated carbonyl bond (5) was inferior to that of compounds lacking this bond (3). Vicinal trihydroxyl phenolic compounds with a conjugated olefinic double bond [e.g., myricetin (7)] had an inferior scavenging ability as compared with compounds lacking this bond [e.g., pyrogallol (8)], but 7 was a better scavenger than compounds with a conjugated carbonyl double bond [e.g., ethyl gallate (9)]. In addition, vicinal trihydroxyl phenolic compounds (e.g., 9) were superior to o-dihydroxyl phenolic compounds (e.g., 6). Finally, 1 scavenged radicals more quickly than 8.     

Polyphenol glucosylating activity in cell suspensions of grape (Vitis vinifera)

Stilbenes are phenolic molecules that have antifungal effects in the plant and antioxidant and anti-cancer effects when consumed in the human diet. Glycosylation of stilbenes increases their solubility and may make them more easily absorbed by the intestine. We have found an activity in extracts of cultured cells of Vitis vinifera (cv. Gamay Freaux) that glucosylates the stilbene resveratrol to form piceid. The Km for UDP-Glucose was 1.2 mM, and the Km for resveratrol was 0.06 mM, values similar to those of other phenolic glucosyltransferases. We investigated the resveratrol glucosylating activity of the enzyme extracted from cells grown under different light treatments (dark, visible light, light + ultraviolet (UVC) radiation) and found the activity to be unaffected or slightly reduced. In contrast, UVC light strongly stimulated extractable quercetin glucosyltransferase activity. These results, combined with analysis of phenolic compounds extracted from the differently treated cells, suggest that the resveratrol glucosyltransferase is distinct from the glucosyltransferase(s) active on other phenolics.     

Crystal and molecular structure of piceatannol; scavenging features of resveratrol and piceatannol on hydroxyl and peroxyl radicals and docking with transthyretin

The mechanism by which the naturally occurring polyphenolic compounds resveratrol (RES), C(14)H(12)O(3), and its metabolite piceatannol (PIC), C(14)H(12)O(4), scavenge free radicals is studied using experimental and density functional theory (DFT) methods. PIC's crystal structure shows a strong intermolecular hydrogen bond network, which, through a concerted motion of the hydroxyl hydrogen atoms, can produce a second hydrogen bond chain. This reorganization offers a low-energy pathway for the transfer of hydrogen atoms and is a contributing factor to PIC's biological activity. Additionally, DFT calculations describing the entire reaction mechanism of RES, PIC, and 3,3',4',5,5'-pentahydroxystilbene with hydroxyl and peroxyl radicals agree with experimental results, showing that increased hydroxylation aids in scavenging activity. PIC is more efficient than RES because (i) by sharing its 3'-OH hydrogen atom with its adjacent neighbor, O-4', the abstraction and transfer of the 4'-H atom to the free radical becomes easier and (ii) the resulting PIC semiquinone radical is more stable. As a result of the reaction with OH(*), both RES and PIC form water; with the peroxyl radical, both RES and PIC form hydrogen peroxide. Also, docking of PIC onto the protein transthyretin suggests better performance than RES and confirms its possible application in neurodegenerative conditions such as Alzheimer's disease.     

High molecular weight coffee melanoidins are inhibitors for matrix metalloproteases

High molecular (above 10 kDa) melanoidins isolated from coffee beans of varying roasting degree were found to be efficient inhibitors for the zinc-containing matrix metalloproteases MMP-1, MMP-2, and MMP-9 with IC(50) values ranging between 0.2 and 1.1 mg/mL in vitro. The inhibitory potential increased with roasting degree. No or only slight inhibition of other zinc-containing peptidases closely related to MMPs, namely, Clostridium histolyticum collagenase and angiotensin converting enzyme, was found, indicating specific structural features of melanoidins to be responsible for the interaction with MMPs. A continuous increase on the apparent molecular weight of melanoidins as well as incorporation of phenolic substances into the melanoidin structure with progress of roasting was observed, concomitant with a significant increase in the carbon/nitrogen of the melanoidins. This suggests that the melanoidins are mainly formed by incorporation of carbohydrates and phenolic compounds onto a proteinaceous backbone. As MMP-1, MMP-2, and MMP-9 play a pivotal role in pathogenesis of colorectal cancer, studies on possible physiological effects of melanoidins are mandatory.     

Fulvic acids: structure and metal binding. I. A random molecular model

We have investigated a model of fulvic acid based on randomized positioning of functional groups and aromatic rings which can be used to deduce the types of metal chelating sites and provide statistical estimates of their concentrations. A FORTRAN program ‘RANDOM’ has been written which generates random molecules of fulvic acid. For each molecule generated the program also searches for and counts 14 types of binding site and calculates average concentrations over one thousand such molecules. A formula relating percentage aromatic carbon to the molar hydrogen/carbon ratio is also derived. The results show that the predominant bidentate sites are likely to be phthalate- and salicylate-type sites with a significant proportion of aromatic carboxyl and phenolic hydroxyl not participating in chelating sites.     

Structure-activity relationships of (1'S)-1'-acetoxychavicol acetate, a major constituent of a southeast Asian condiment plant Languas galanga, on the inhibition of tumor-promoter-induced Epstein-Barr virus activation

The structure-activity relationships of (1'S)-1'-acetoxychavicol acetate (ACA), a cancer chemopreventive agent of food origin, were investigated in an inhibitory test of tumor promoter teleocidin B-4-induced Epstein-Barr virus (EBV) activation in Raji cells. Through a test of 16 derivatives, the structural factors regulating activity were found to be as follows: (1) the absolute configuration at the 1'-position does not affect activity; (2) hydrogenation of the terminal methylene group abolishes activity; (3) both the phenolic and alcoholic hydroxyl groups are compulsorily acetylated, and it is necessary that the former is oriented only at the position para to the side chain; (4) an additional acetoxyl group is allowed to locate at the ortho or meta position; and (5) substitution of the hydrogen atom at the 1'-position by a methyl group reduces activity. Upon esterase blockade in Raji cells, (1'R,S)-ACA suppressed EBV activation, the extent of which was the same as tested in the control, suggesting that ACA bearing two acetoxyl groups is an intracellular structure prerequisite for activity exhibition. The present study suggests that nucleophilic attack to the 3'-position is important and involved in the interaction of ACA with an unidentified target molecule(s) participating in the process of EBV activation.     

Low molecular weight melanoidins in coffee brew

Analysis of low molecular weight (LMw) coffee brew melanoidins is challenging due to the presence of many non-melanoidin components that complicate analysis. This study focused on the isolation of LMw coffee brew melanoidins by separation of melanoidins from non-melanoidin components that are present in LMw coffee brew material. LMw coffee fractions differing in polarity were obtained by reversed-phase solid phase extraction and their melanoidin, sugar, nitrogen, caffeine, trigonelline, 5-caffeoylquinic acid, quinic acid, caffeic acid, and phenolic groups contents were determined. The sugar composition, the charge properties, and the absorbance at various wavelengths were investigated as well. The majority of the LMw melanoidins were found to have an apolar character, whereas most non-melanoidins have a polar character. The three isolated melanoidin-rich fractions represented 56% of the LMw coffee melanoidins and were free from non-melanoidin components. Spectroscopic analysis revealed that the melanoidins isolated showed similar features as high molecular weight coffee melanoidins. All three melanoidin fractions contained approximately 3% nitrogen, indicating the presence of incorporated amino acids or proteins. Surprisingly, glucose was the main sugar present in these melanoidins, and it was reasoned that sucrose is the most likely source for this glucose within the melanoidin structure. It was also found that LMw melanoidins exposed a negative charge, and this negative charge was inversely proportional to the apolar character of the melanoidins. Phenolic group levels as high as 47% were found, which could be explained by the incorporation of chlorogenic acids in these melanoidins.     

Resveratrol and other phenolics from the bark of Yucca schidigera roezl

Five phenolic constituents have been identified in Yucca schidigera bark, and their structures were established by spectral (FABMS and NMR) experiments. These included two known stilbenes, trans-3,4',5-trihydroxystilbene (resveratrol) and trans-3,3',5,5'-tetrahydroxy-4'-methoxystilbene, as well as three novel compounds, yuccaols A, B, and C, with spiro-structures rarely occurring in the plant kingdom. It is suggested that yuccaols A-C are biosynthethized via attachment of a stilbenic derivative to the carbocationic intermediate of the oxidative flavanone-flavonol conversion.     

初级芳香胺的高分辨质谱裂解规律研究

为探究初级芳香胺类化合物的质谱裂解规律,本研究采用超高效液相色谱-四极杆/静电场轨道阱高分辨质谱法,在电喷雾正离子模式下采集数据,根据一、二级质谱离子的精确质荷比推导14种初级芳香胺类化合物可能的裂解途径。结果表明,由于分子结构中存在氨基基团,因此初级芳香胺类化合物极易被质子化,更易形成[M+H]⁺。断裂过程主要发生NH₃中性碎片的丢失,产生[M+H-NH₃]⁺特征碎片离子,在此基础上,氯代苯胺类化合物发生碳正离子重排后,丢失氯原子形成[·M+H-NH₃-Cl]⁺碎片离子。甲氧基取代苯胺类化合物可丢失CH₃O基团产生碎片离子[M+H-NH₃-CH₃O]⁺,或发生碳正离子转移重排至苯甲基,进一步丢失CH₃和CH₃O基团。甲基或甲氧基取代的联苯胺类化合物还会发生CN键断裂形成[M+H-NH]⁺,继而丢失NH₃中性碎片形成[M+H-NH-NH₃]⁺。偶氮苯类化合物中高键能的偶氮键不易断裂,碎片离子主要通过两侧的CN键断裂形成。本研究提出的最佳电离方式和质谱裂解规律为初级芳香胺类化合物的快速鉴定提供了重要依据。     

Phenolic antioxidants and the protection of low density lipoprotein from peroxynitrite-mediated oxidations at physiologic CO2

Dietary phenolic antioxidants have been shown to prevent LDL modifications mediated by several physiologic oxidants including peroxynitrite. However, more recent data demonstrated that CO(2) affected the fate of peroxynitrite in biological fluids and significantly reduced peroxynitrite scavenging by polyphenols, raising doubts concerning their antioxidant activity. We found that the oxidation of LDL lipids mediated by peroxynitrite decreased in the presence of bicarbonate, while Trp oxidation and 3-nitroTyr formation increased, suggesting a redirection of peroxynitrite reactivity toward the protein moiety. We therefore evaluated the protective activity of some phenolic antioxidants (quercetin, oleuropein, resveratrol, (+)-catechin, (-)-epicatechin, tyrosol, alpha- and gamma-tocopherol, ascorbate) on peroxynitrite-mediated oxidation of LDL aromatic residues. Some of these phenols protected LDL Trp from oxidation better than ascorbate or alpha-tocopherol, although protection at 100 microM did not exceed 30-40%. However, the same phenolic antioxidants were more active in inhibiting 3-nitroTyr formation and those with a catechin structure provided significant protection (IC(50%) 40-50 microM). Red wine, a polyphenol-rich beverage, showed a protective effect comparable to that of the most active phenolic antioxidants. Direct EPR studies showed that bicarbonate significantly increased the peroxynitrite-dependent formation of O-semiquinone radicals in red wine, supporting the hypothesis that polyphenols are efficient scavengers of radicals formed by peroxynitrite/CO(2). Ascorbate was a poor inhibitor of peroxynitrite/CO(2)-induced LDL tyrosine nitration, but the simultaneous addition to the most active polyphenols halved their IC(50%). In conclusion, although cooperation with other antioxidants can further decrease the IC(50%) of polyphenolics, as demonstrated for ascorbate, their antioxidant activity appears to occur at concentrations at least 1 order of magnitude higher than their bioavailability.     

Phenolic composition of the Brazilian seedless table grape varieties BRS Clara and BRS Morena

The detailed phenolic composition (anthocyanins, flavonols, hydroxycinnamic acid derivatives, stilbenes, and flavan-3-ols) in the skin and flesh of the new BRS Clara and BRS Morena seedless table grapes has been studied using HPLC-DAD-ESI-MS/MS. The two grapes, especially BRS Morena, contained high amounts of phenolic compounds, mainly located in their skins and qualitatively not different from those found in Vitis vinifera grapes. In addition, BRS Morena (a teinturier variety) showed qualitatively different phenolic compositions in its skin and flesh, mainly affecting the anthocyanin and flavonol profiles. Consistent with high phenolic contents, high antioxidant capacity values were registered for both grape varieties, especially for BRS Morena. Proanthocyanidins and hydroxycinnamoyl-tartaric acids were the major phenolic compounds found in BRS Clara and were also important in BRS Morena, although anthocyanins were the main phenolic compounds in the latter case. These results suggest that the entire grapes, including the skin, may potentially possess properties that are beneficial to human health. In this context, the BRS Morena grape can be considered as a high resveratrol producer.     

Piceid (resveratrol glucoside) synthesis in stilbene synthase transgenic apple fruit

A stilbene synthase gene along with the selectable marker gene bar for herbicide resistance was transferred via Agrobacterium tumefaciens mediated transformation into apple (Malus domesticaBorkh.) cvs. 'Elstar' and 'Holsteiner Cox'. The stilbene synthase catalyzes the conversion of 1 molecule of p-coumaroyl-CoA and 3 molecules of malonyl-CoA into 3,4',5-trihydroxystilbene, commonly known as resveratrol. This phytoalexin has implications in both phytopathology and human health. Greenhouse-grown transgenic and nontransformed control plants were grafted onto dwarfing rootstock M27. Flowering and fruiting occurred within the following years, offering the opportunity to analyze transgenic apple fruit and fertility of transgenic plants as well as inheritance of the transgenes into the seedling progeny. Molecular analysis revealed that the stilbene synthase is expressed in transgenic plants and in the skin and flesh of transgenic apple fruit. After formation, resveratrol is modified by the addition of a hexose sugar. The resulting component was characterized as piceid. With the aim of characterizing the influence of the novel biosynthetic pathway on the accumulation of other phenolic compounds naturally present in apple fruit, the amounts of flavanols, flavonols, phloretin derivatives and hydroxycinnamic acids in wild type and transgenic fruit were determined by HPLC. In all investigated transformed lines that accumulated piceid, no negative correlation between levels of piceid and the above-mentioned compounds was observed, except for the flavonol contents, which slightly decreased. Inheritance of the transgenes was confirmed in the seedling progeny, which were obtained after pollination of transgenic plants with nontransgenic pollen and vice versa after pollination of nontransgenic plants with pollen obtained from transgenic plants. The fertility of stilbene synthase transgenic plants was demonstrated. To the authors' knowledge this is the first time that data are available on piceid synthesis in transgenic apple fruit and the effects of its accumulation on levels of other phenolic compounds present in the fruit.     

Estimation and decomposition pattern of the lignin component in forest humus layers

Lignin is one of the most abundant polymeric organic constituents of forest litter. Due to its molecular structure and heterogeneity the isolation of lignin in an unchanged form and its exact determination in forest humus have not proved possible. The oxidative degradation with CuO provides a specific method for the characterization of intact lignin structures in forest humus layers. The sum of phenolic CuO oxidation products gives an overall pattern of lignin decomposition. The degree of alteration of the remnant lignin is described by the acid-to-aldehyde ratio (Ac:Al) of syringyl and vanillyl units for angiosperm and gymnosperm lignin and the ratio of syringyl-to-vanillyl units (S:V) for angiosperm lignin.The lignin component of three different forest humus layers investigated was partly decomposed. The residual lignin fraction had undergone extensive modification during microbial decomposition. The chemical changes occurring in the lignin molecule during decomposition in forest humus layers suggest similar mechanisms of lignin degradation (“white-rot”) are shared by wood and forest litter.     

Molecular binding of black tea theaflavins to biological membranes: relationship to bioactivities

Molecular dynamics simulations were used to study the interactions of three theaflavin compounds with lipid bilayers. Experimental studies have linked theaflavins to beneficial health effects, some of which are related to interactions with the cell membrane. The molecular interaction of theaflavins with membranes was explored by simulating the interactions of three theaflavin molecules (theaflavin, theaflavin-3-gallate, and theaflavin-3,3'-digallate) with a mixed bilayer composed of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) and 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE). The simulations show that the theaflavins evaluated have an affinity for the lipid bilayer surface via hydrogen bonding. The molecular structure of theaflavins influenced their configuration when binding to the bilayer surface, as well as their ability to form hydrogen bonds with the lipid headgroups. The theaflavin-bilayer interactions studied here help to define structure-function relationships of the theaflavins and provide a better understanding of the role of theaflavins in biological processes. The significance of the results are discussed in the context of black tea composition and bioactivity.     

木质素对木质纤维素降解性能的影响

木质素影响木质纤维素降解性能,明确木质素影响木质纤维素降解的程度和机理,对于植物基因改造、纤维素酶基因改造/筛选、预处理工艺优化均具有重大意义。但是由于木质素和木质纤维素结构的复杂性,木质素对木质纤维素影响的程度和机理尚无定论。该文综述了关于目前研究主要集中在木质素的含量和结构对木质纤维素降解性能的影响上,初始木质素含量和残留木质素含量对同物种和不同物种木质纤维素降解性能的影响;木质素单体比例(syringyl units/guaiacyl units)、键连方式、官能团对木质纤维素降解性能的影响;纯化木质素对木质纤维素降解性能的影响。该文为木质素对纤维素降解性能的影响的相关研究工作提供指导。     

A preliminary study of fungal melanin by infrared spectroscopy

Infrared spectra of melanin and methylated melanin have been interpreted to show the existence of carboxyl groups in two different environments in the melanin structure. In one, there are a small number of carboxyl groups with an absorption band at about 1700 cm^?1; these are relatively free and are capable of interaction with alkali to produce carboxylate in the normal way. In the other environment, the carboxyl groups, absorbing at 1615 cm^?1, are conjugated and strongly hydrogen bonded to presumably phenolic hydroxyl groups, and cannot be neutralized with alkali. They do, however, react with diazomethane, as do the free carboxyls, to produce methyl ester absorbing at 1728 cm^?1.The significance of these conclusions for the survival of melanin in soil and its reactions therein, is briefly discussed.     

Grapes and human health: a perspective

Grapes are a valuable source of numerous phytonutrients, including the intensively studied constituent, resveratrol. A question worth addressing is the potential of dietary grape consumption to positively modulate human health. Many studies have suggested cardiovascular benefits, and some work has indicated cancer chemopreventive activity. Data are particularly compelling in the area of skin cancer prevention. With financial support provided by the California Table Grape Commission, novel and exciting preliminary data are emerging from independent research suggesting beneficial activity against other less prevalent but devastating illnesses, such as Alzheimer's disease and urinary bladder dysfunction. It is further suggested that some of the copious amounts of data obtained with resveratrol may be relevant to grape consumption, especially responses that can be mediated by low concentrations of the substance. Whether future specific health claims will be sought from or allowed by regulatory authorities is not known, but based on existing data, it is clear that grapes should be considered an integral component of fruit and vegetable enriched diets that are recommended by health authorities and widely accepted as beneficial for human health and disease prevention.