Structure-antioxidant activity relationships of flavonoids and phenolic acids

The recent explosion of interest in the bioactivity of the the flavonoids of higher plants is due, at least in part, to the potential health benefits of these polyphenolic components of major dietary constituents. This review article discusses the biological properties of the flavonoids and focuses on the relationship between their antioxidant activity, as hydrogen donating free radical scavengers, and their chemical structures. This culminates in a proposed hierarchy of antioxidant activity in the aqueous phase. The cumulative findings concerning structure-antioxidant activity relationships in the lipophilic phase derive from studies on fatty acids, liposomes, and low-density lipoproteins; the factors underlying the influence of the different classes of polyphenols in enhancing their resistance to oxidation are discussed and support the contention that the partition coefficients of the flavonoids as well as their rates of reaction with the relevant radicals define the antioxidant activities in the lipophilic phase.     

Interactions of retroviral structural proteins with single-stranded nucleic acids

We have studied the interactions of single-stranded polyribonucleotides with murine leukemia virus structural proteins p10, p10' (a p10 variant), and Pr65gag, as well as Rous sarcoma virus (RSV) pp12 (a p10 analog). Two quantitative assays have been used to monitor protein-RNA association: the fluorescence enhancement of polyethenoadenylic acid) poly(epsilon A) upon binding protein, and tryptophan fluorescence quenching upon binding to poly(U). With each assay p10 was shown to bind stoichiometrically to single-stranded RNA, covering a length of nucleic acid chain (occluded site size, n) of about 6 residues. RSV pp12 was also shown to bind to poly(epsilon A), with n = 5 +/- 1. Addition of NaCl to fully titrated MuLV p10-nucleic acid mixtures effected nearly complete restoration of poly(epsilon A) or MuLV p10 fluorescence. Under conditions of 0.06 M NaCl, p10 bound noncooperatively to poly(epsilon A) with an intrinsic association constant, K = 2.3 X 10(6) M-1. K and n determined in this study were shown to relate to Kapp determined by other methods, by the approximation Kapp approximately NK, where N is the number of binding sites along the polynucleotide chain ((nucleotides/chain)/n). Chemical modifications of the p10 cysteine residues did not alter the affinity for poly(epsilon A). The affinity of Pr65gag for poly(epsilon A) appears to be higher than that of p10.     

Interactions between model proteins and deoxyribonucleic acids.

Interactions between DNA and model proteins, poly(L-Lys(m)L-Ala(n)), where m + n = 100%, have been investigated using thermal denaturation and circular dichroism (CD). All complexes of DNA with these proteins precipitate in a small range of input ratios, protein to DNA, with the midpoints of all precipitation curves close to a 1:1 ratio of lysine to phosphate. The melting temperature of model protein-bound DNA regions decreases slightly as the alanine content of the model protein is increased, which can be explained as a result of insufficient charge neutralization of phosphates by lysine residues in the model proteins. In the free state, these model proteins possess varying amounts of alpha helix, random coil, or a mixture of these two, depending upon the relative lysine/alanine content. When bound to DNA, the CD of the complex shows a substantial increase in alpha-helical structure for those model proteins with 40-60% alanine, while there is no significant change in alpha-helical structure when the percent alanine is either substantially higher or lower (i.e., 81 or 19% alanine). Only those complexes formed with model proteins having 40-60% alanine undergo a drastic transition from a B-type CD to an A-type in the presence of intermediate ionic strength (0.2 M NaCl, for example). Poly(Lys19Ala81)-DNA complexes show a slight transition toward A-type CD at 0.4 M NaCl or higher. Apparently other factors, in addition to alanine and alpha-helical content, must be responsible for this B leads to A transition. At the other extreme of lysine/alanine ratio, with high lysine content, poly(Lys81Ala19) or polylysine, the presence of NaCl produces a B leads to psi transition. The possible significance of these differences in response to the binding of these model proteins is discussed.     

Mitochondriotropic action and DNA protection: Interactions between phenolic acids and enzymes

The protective action of caffeic (CA) and syringic (SA) acids on the genotoxicity exercised by snake venoms was investigated in this study. Molecular interactions between phenolic acids and the enzyme succinate dehydrogenase were also explored. In the electrophoresis assay, SA did not inhibit the genotoxicity induced by the venom. However, CA partially inhibited DNA degradation. In the comet assay, SA and CA exerted an inhibitory effect on the venom‐induced fragmentation. Succinate dehydrogenase presented, in computational analyzes, favorable energies to the molecular bond to both the malonic acid and the phenolic compounds evaluated. In the enzymatic activity assays, SA inhibited succinate dehydrogenase and interfered in the interaction of malonic acid. Meanwhile, CA potentiated the inhibition exerted by the malonic acid. The results suggest transient interactions between toxins present in venoms and phenolic acids, mainly by hydrogen interactions, which corroborate with the data from previous works.     

Interactions of phenolic acids, metallic ions and chelating agents on auxin-induced growth

By growth experiments in indoleacetic acid-1-¹⁴C (IAA), and determination of the ¹⁴CO₂ evolved, it has been shown directly that polyphenols synergize IAA-induced growth by counteracting IAA decarboxylation. Sinapic and ferulic acids act like polyphenols. Endogenous polyphenols doubtless exert the same influence in intact plants. Monophenols stimulate the decarboxylation of IAA under conditions where they depress growth. When Mn⁺⁺ is present as well, this effect is enhanced. All these growth effects are paralleled by effects on the isolated IAA oxidizing enzyme of Avena.     

Interactions of cyclic and non-cyclic naphthalene diimide derivatives with different nucleic acids

Recently, strategy based on stabilization of G-quadruplex telomeric DNA by small organic molecule has been realized by naphthalene diimide derivatives (NDIs). At the same time NDIs bind to DNA duplex as threading intercalators. Here we present cyclic derivative of naphthalene diimide (ligand 1) as DNA-binding ligand with ability to recognition of different structures of telomeric G-quadruplexes and ability to bis-intercalate to double-stranded helixes. The results have been compared to non-cyclic derivative (ligand 2) and revealed that preferential binding of ligands to nucleic acids strongly depends on their topology and structural features of ligands.     

In vitro effects of some flavonoids and phenolic acids on human pyruvate kinase isoenzyme M2

Pyruvate kinase isoenzyme M2 (PKM2) is one of the most important control point enzyme in glycolysis pathway. Hence, its inhibitors and activators are currently considered as the potential anticancer agents. The effect of 28 polyphenolic compounds on the enzyme activity was investigated in vitro. Among these compounds, neoeriocitrin, (?)-catechin gallate, fisetin, (±)-taxifolin and (?)-epicatechin have the highest inhibition effect with IC₅₀ value within 0.65–1.33?µM range. Myricetin and quercetin 3-β-d-glucoside exhibited the highest activation effect with 0.51 and 1.34?µM AC₅₀ values, respectively. Twelve of the compounds showed inhibition effect within 7–38?µM range of IC₅₀ value. Sinapinic acid and p-coumaric acid showed an activation effect with 26.2 and 22.2?µM AC₅₀ values, respectively. The results propose that the polyphenolics may be the potential PKM2 inhibitors/activators, and they may be used as lead compounds for the synthesis of new inhibitors or activators of this enzyme.     

不同间隔年限地黄土壤的自毒作用和酚酸类物质含量

分别取2、4、6、8年前种植过地黄的土壤进行大田再植生物测试,并采用HPLC检测再植地黄土壤中与化感现象密切相关的5种酚酸（阿魏酸、对羟基苯甲酸、香草酸、香豆酸和丁香酸）的含量。结果表明：随着土壤间隔年限的增加,大田再植地黄的块根干质量、体积和叶片干质量依次增加,且从地黄苗期就开始表现出这种变化趋势;地黄土壤中5种酚酸的含量也依次降低, 间隔2、4、6、8年的再植地黄土壤中5种一元酚酸总含量分别为1.503、1.323、0.700和0.340 μg·g^-1。间隔2、4、6、8年的再植地黄土壤水提液中阿魏酸、对羟基苯甲酸和香豆酸含量与地黄大田生物测试结果呈显著或极显著负相关。从整体看,地黄生育的前期和中期应当是地黄化感作用的重点时期。     

Interaction of hydrated electron with dietary flavonoids and phenolic acids: rate constants and transient spectra studied by pulse radiolysis.

The reaction rate constants and transient spectra of 11 flavonoids and 4 phenolic acids reacting with e(aq)- at neutral pH were measured. Absorption bands of the transients of e(aq)- reacting with the above compounds all located at a wavelength shorter than 400 nm. The e(aq)- scavenging abilities were divided into three groups: (+)catechin ((1.2 +/-0.1) x 10(8) M(-1)s(-1)) < 4-chromanol ((4.4 +/- 0.4) x 10(8) M(-1)s(-1)) < genistein ((6.2+/-0.4) x 10(9) M (-1) s(-1) approximately genistin ((8 +/- 1) x 10(9) M(-1)s(-1)) approximately rutin ((7.6 +/- 0.4) x M(-1)s(-1) approximately caffeic acid ((8.3 +/- 0.5) x 10(9)M(-1)s(-1)) < transcinnamic acid((1.1 +/- 0.1) x 10(10) M(-1)s(-1)) approximately p-coumaric acid ((1.1 +/- 0.1) x 10(10) M(-1)s(-1) approximately 2,4,6-trihydroxylbenzoic acid((1.1 +/- 0.1) x 10(10) M(-1)s(-1)) approximately baicalein ((1.1 +/- 0.5) x 10(10) M(-1)s(-1)) approximately baicalin((1.3 + 0.1) X 10(10) M(-1)s(-1)) approximately naringenin ((1.2 +/- 0.1) x 10(10) M(-1)s(-1)) approximately naringin ((1.0 +/- 0.1) x 10(10) M(-1)s(-1)) approximately gossypin((1.2 +/- 0.1) x 10(10) M(-1)s(-1)) approximately quercetin((1.3 +/- 0.5) x 10(10) M(-1)s(-1)). These results suggested that C4 keto group is the active site for e(aq)- to attack on flavonoids and phenolic acids, whereas the o-dihydroxy structure in B ring, the C2,3 double bond, the C3-OH group, and glucosylation, which are key structures that influence the antioxidant activities of flavonoids and phenolic acids, have little effects on the e(aq)- scavenging activities.     

Bioavailability of phenolic acids

Two large classes of phenolic acids were comprised in this review: benzoic acid derivatives and cinnamic acid derivatives. They have been found to be very extended in fruits and vegetables at different concentrations. For example, hydroxycinnamic acids concentration was higher than that found for hydroxybenzoic acids. Concerning their consumption, hydroxycinnamic acids provide larger contributions to the total polyphenol intake than benzoic acid derivatives or flavonoids. This phenolic acid intake is led by the coffee intake since it has very rich concentrations in hydroxycinnamic acids. Moreover, several experimental and epidemiological studies report the protection of phenolic acids against various degenerative diseases. However, despite all these interesting attributions and even if phenolic acids are the main polyphenols consumed, their bioavailability has not received as attention as that flavonoids. This concept is an essential step to understand the health-promoting properties of phenolic acids and to serve as tool to design in vivo and in vitro experiments to know their biological properties. Therefore, a compilation of bioavailability data of phenolic acids have been presented here paying attention to the two types of phenolic acid bioavailability, direct and indirect derived from the direct phenolic acid and flavonoid consumption, respectively. Then, a new relevant concept which may be named as total bioavailability of phenolic acids includes the direct absorption and metabolism of phenolic acids from food consumption and phenolic acids bioavailability as a result of the cleavage on the main skeleton ring of flavonoids by the gut microflora.     

Solubility of soy lipophilic proteins: comparison with other soy protein fractions

Solubility of soy lipophilic proteins (LP) was studied as compared with that of other soy protein fractions. LP, β-conglycinin, glycinin, and soy protein isolate (N-SPI) were prepared under the condition to avoid heat denaturation. Solubility of LP was lower than that of other soy protein fractions under all the tested conditions varying in pH values and ionic strength. The solubility of LP was increased constantly by elevating temperature until 90 °C, whereas that of β-conglycinin and glycinin dropped at high temperature. Temperature-dependent change in solubility of N-SPI might reflect the balance among that of glycinin, β-conglycinin and LP. Based on the results of SDS-PAGE, determination of phospholipid content and Fourier Transform Infrared spectroscopy, we discussed the solubilization behavior of LP relating to its origin and composition.     

Interactions of amidated acids with heparin

Raman and NMR studies are performed to characterize the solution structures of complexes between heparin and a group of amidated acids, which act as delivery agents that facilitate the gastrointestinal absorption of orally administered heparin. At concentrations typically employed for the oral drug delivery of heparin, the contact points between heparin complexed with the delivery agents include points near the OH groups of heparin. The results suggest that heparin interacts rather nonspecifically with the amidated acids as monomers and with self-associated complexes of the delivery agents. It is also found that the carboxyl groups of at least one of the bioactive delivery agents easily protonates when it forms complexes with itself or heparin. This attribute may be one reason why this class of compounds is effective in the oral delivery of heparin.     

Interactions of porphyrins with nucleic acids

The interactions of nucleic acids with water-soluble porphyrins and metalloporphyrins have been investigated by stopped-flow and temperature-jump techniques. Both natural DNA (calf thymus) and synthetic homopolymers [poly(dG-dC) and poly(dA-dT)] have been employed. The porphyrins studied belong to the tetrakis(4-N-methylpyridyl)porphine (H2TMpyP-4) series and can be divided into two groups: (i) those which have no axial ligands when bound to nucleic acids [e.g., Ni(II), Cu(II), and the nonmetallic derivatives] and (ii) those which maintain axial ligands upon binding [e.g., Mn(III), Fe(III), Co(III), and Zn(II) derivatives]. The reaction of both axially and nonaxially liganded porphyrins at AT sites is too rapid to be measured by the kinetic methods utilized, whereas at GC sites the interaction of the nonaxially liganded porphyrins is in the millisecond time range and can be monitored by both stopped-flow and temperature-jump techniques. These results corroborate previous static studies, utilizing visible spectroscopy and circular dichroism, which indicate that the formation of an intercalated complex occurs only at GC base pair sites with porphyrins which do not possess axial ligands. With all the porphyrins investigated, the complexes formed at AT sites are envisioned as being of an "external" type involving some degree of overlap between the porphyrin and the bases of the duplex. In relaxation experiments of poly-(dG-dC) with H2TMpyP-4, a large, reproducible effect is observed which can be analyzed as a single exponential. Rate constants for association and dissociation of the H2TMpyP-4/poly(dG-dC) complex are 3.7 X 10(5) M-1 s-1 and 1.8 s-1, respectively. Relaxation studies of mixtures of poly(dA-dT) and poly(dG-dC) with H2TMpyP-4 indicate that the transfer of the porphyrin from one homopolymer to another occurs via a mechanism involving dissociation rather than direct transfer.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tea prepared from Anastatica hirerochuntica seeds contains a diversity of antioxidant flavonoids, chlorogenic acids and phenolic compounds

HPLC-PDA-MS(2) was used to identify phenolic and polyphenolic compounds in an herbal tea made from seeds of Anastatica hirerochuntica, a plant found in the Sahara-Arabian deserts and used to treat a variety of ailments. Twenty compounds comprising a series of flavone C- and O-linked glycosides, phenolic acids, chlorogenic acids and flavonols were identified or partially identified on the basis of co-chromatography with reference compounds and MS(2) and MS(3) fragmentation patterns. The flavones were the principal components, occurring as luteolin, apigenin and diosmetin conjugates. The antioxidant potential of individual compounds in Anastatica was assessed using HPLC with an on-line ABTS·(+) detection system. This revealed that 14 compounds exhibited antioxidant activity. The highest contribution to the antioxidant capacity of the tea, 56%, came from 3,4-dihydroxybenzoic acid and caffeoyl- and dicaffeoylquinic acids while 6-C-glucosides of luteolin and apigenin contributed 41%.