Antioxidant Properties of Ethyl Vanillin in Vitro and in Vivo

We systematically evaluated the antioxidant activity of ethyl vanillin, a vanillin analog, as compared with the activities of vanillin and other vanillin analogs using multiple assay systems. Ethyl vanillin and vanillin exerted stronger antioxidant effects than did vanillyl alcohol or vanillic acid in the oxygen radical absorbance capacity (ORAC) assay, although the antioxidant activities of vanillyl alcohol and vanillic acid were clearly superior to those of ethyl vanillin and vanillin in the three model radical assays. The antioxidant activity of ethyl vanillin was much stronger than that of vanillin in the oxidative hemolysis inhibition assay, but was the same as that of vanillin in the ORAC assay. Oral administration of ethyl vanillin to mice increased the concentration of ethyl vanillic acid, and effectively raised antioxidant activity in the plasma as compared to the effect of vanillin. These data suggest that the antioxidant activity of ethyl vanillin might be more beneficial than has been thought in daily health practice.     

Simultaneous Detection of the Antioxidant and Pro-oxidant Activity of Dietary Polyphenolics in a Peroxidase System

The ability to reduce the peroxidase (myeloglobin/H²O²)-generated ABTS^?+ [2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) radical cation] has been used to rank the antioxidant activity of various agents including dietary flavonoids and chalcones. Surprisingly, we found that in the presence of catalytic concentrations of the phenol B-ring containing flavonoids, apigenin, naringenin and the chalcone phloretin, the formation of the ABTS^?+ was initially increased. The enhanced formation of the ABTS^?+ was attributed to the peroxidase/H²O² mediated generation of polyphenolic phenoxyl radicals that were able to co-oxidize ABTS. The relative ABTS^?+ generating ability of these dietary polyphenolics correlated with their ability to co-oxidize NADH to the NAD* radical with the resultant generation of superoxide. This pro-oxidant activity was not observed for either luteolin or eriodyctiol, which are B-ring catecholic analogues of apigenin and naringenin, respectively, suggesting that these antioxidants are incapable of the transition metal-independent generation of reactive oxygen species. This pro-oxidant activity of the polyphenolics therefore needs to be taken into account when quantifying antioxidant activity.     

Oxidation of galactomannan by laccase plus TEMPO yields an elastic gel

Chemical modifications of galactomannans are applied to improve and/or modify their solubility, rheological and functional properties, but have limited specificity and are often difficult to control. Enzymatic reactions, catalyzed under mild process conditions, such as depolymerization, debranching and oxidation, represent a viable and eco-friendly alternative. In this study, we describe oxidation of guar galactomannan primary hydroxyl groups by a fungal laccase using the stable radical TEMPO as mediator. Four fungal laccases were investigated from: Trametes versicolor, Myceliophthora thermophila, Thielavia arenaria, Cerrena unicolor. The laccase from T. versicolor was found to efficiently oxidize TEMPO and to be free of mannanase side activity. Oxidation of galactomannan with this enzyme plus TEMPO brought about a ten-fold increase in viscosity of a guar galactomannan solution and altered its rheological profile, by converting a viscous polysaccharide solution into an elastic gel. This structural modification is presumably due to formation of inter-chain hemiacetalic bonds between newly generated carbonyl groups and free OH groups, yielding a cross-linked gel. These findings could be of practical importance, considering that polysaccharides with high viscosity, gelling and elastic properties can find interesting and novel applications as thickeners, viscosifiers and emulsion stabilizers in several industrial applications such as: personal care, oil operations, paper coating, paints, construction and mining.     

A chloride tolerant laccase from the plant pathogen ascomycete Botrytis aclada expressed at high levels in Pichia pastoris

Fungal laccases from basidiomycetous fungi are thoroughly investigated in respect of catalytic mechanism and industrial applications, but the number of reported and well characterized ascomycetous laccases is much smaller although they exhibit interesting catalytic properties. We report on a highly chloride tolerant laccase produced by the plant pathogen ascomycete Botrytis aclada, which was recombinantly expressed in Pichia pastoris with an extremely high yield and purified to homogeneity. In a fed-batch fermentation, 495 mg L⁻¹ of laccase was measured in the medium, which is the highest concentration obtained for a laccase by a yeast expression system. The recombinant B. aclada laccase has a typical molecular mass of 61,565 Da for the amino acid chain. The pI is approximately 2.4, a very low value for a laccase. Glycosyl residues attached to the recombinant protein make up for approximately 27% of the total protein mass. B. aclada laccase exhibits very low K_M values and high substrate turnover numbers for phenolic and non-phenolic substrates at acidic and near neutral pH. The enzyme's stability increases in the presence of chloride ions and, even more important, its substrate turnover is only weakly inhibited by chloride ions (I₅₀ = 1.4 M), which is in sharp contrast to most other described laccases. This high chloride tolerance is mandatory for some applications such as implantable biofuel cells and laccase catalyzed reactions, which suffer from the presence of chloride ions. The high expression yield permits fast and easy production for further basic and applied research.     

Production of lactose-free galacto-oligosaccharide mixtures: comparison of two cellobiose dehydrogenases for the selective oxidation of lactose to lactobionic acid

Galacto-oligosaccharides, complex mixtures of various sugars, are produced by transgalactosylation from lactose using beta-galactosidase and are of great interest for food and feed applications because of their prebiotic properties. Most galacto-oligosaccharide preparations currently available in the market contain a significant amount of monosaccharides and lactose. The mixture of galacto-oligosaccharides (GalOS) in this study produced from lactose using recombinant beta-galactosidase from Lactobacillus reuteri contains 48% monosaccharides, 26.5% lactose and 25.5% GalOS. To remove efficiently both monosaccharides and lactose from this GalOS mixture containing significant amounts of prebiotic non-lactose disaccharides, a biocatalytic approach coupled with subsequent chromatographic steps was used. Lactose was first oxidised to lactobionic acid using fungal cellobiose dehydrogenases, and then lactobionic acid and monosaccharides were removed by ion-exchange and size-exclusion chromatography. Two different cellobiose dehydrogenases (CDH), originating from Sclerotium rolfsii and Myriococcum thermophilum, were compared with respect to their applicability for this process. CDH from S. rolfsii showed higher specificity for the substrate lactose, and only few other components of the GalOS mixture were oxidised during prolonged incubation. Since these sugars were only converted once lactose oxidation was almost complete, careful control of the CDH-catalysed reaction will significantly reduce the undesired oxidation, and hence subsequent removal, of any GalOS components. Removal of ions and monosaccharides by the chromatographic steps gave an essentially pure GalOS product, containing less than 0.3% lactose and monosaccharides, in a yield of 60.3%.     

Structural insights into rice BGlu1 beta-glucosidase oligosaccharide hydrolysis and transglycosylation

The structures of rice BGlu1 β-glucosidase, a plant β-glucosidase active in hydrolyzing cell wall-derived oligosaccharides, and its covalent intermediate with 2-deoxy-2-fluoroglucoside have been solved at 2.2 Å and 1.55 Å resolution, respectively. The structures were similar to the known structures of other glycosyl hydrolase family 1 (GH1) β-glucosidases, but showed several differences in the loops around the active site, which lead to an open active site with a narrow slot at the bottom, compatible with the hydrolysis of long β-1,4-linked oligosaccharides. Though this active site structure is somewhat similar to that of the Paenibacillus polymyxa β-glucosidase B, which hydrolyzes similar oligosaccharides, molecular docking studies indicate that the residues interacting with the substrate beyond the conserved -1 site are completely different, reflecting the independent evolution of plant and microbial GH1 exo-β-glucanase/β-glucosidases. The complex with the 2-fluoroglucoside included a glycerol molecule, which appears to be in a position to make a nucleophilic attack on the anomeric carbon in a transglycosylation reaction. The coordination of the hydroxyl groups suggests that sugars are positioned as acceptors for transglycosylation by their interactions with E176, the catalytic acid/base, and Y131, which is conserved in barley BGQ60/β-II β-glucosidase, that has oligosaccharide hydrolysis and transglycosylation activity similar to rice BGlu1. As the rice and barley enzymes have different preferences for cellobiose and cellotriose, residues that appeared to interact with docked oligosaccharides were mutated to those of the barley enzyme to see if the relative activities of rice BGlu1 toward these substrates could be changed to those of BGQ60. Although no single residue appeared to be responsible for these differences, I179, N190 and N245 did appear to interact with the substrates.     

Stereoselective synthesis of enantiopure N-substituted pyrrolidin-2,5-dione derivatives by 1,3-dipolar cycloaddition and assessment of their in vitro antioxidant and antibacterial activities

1,3-Dipolar cycloaddition between a chiral nitrone and N-substituted maleimides afforded unprecedented enantiopure spiro-fused heterocycles in good yields with a high enantio- and diastereoselectivity. The reaction was taking place on the less hindered face of the nitrone. The obtaining heterocycles were screened for their in vitro antioxidant properties and the results revealed that the potent antioxidant activity was generally recorded to compounds (3g) and (3e). The in vitro antibacterial activities of these two compounds were also investigated and the results demonstrated the strongest potential of compound (3g) against all the tested bacteria. Molecular properties were analyzed and showed good oral drug candidate like properties and that could be exploited as a potential antioxidant and antimicrobial agent. Finally, the preliminary results obtained from this investigation attempted to clarify if the structurally different side chains of active compounds interfere with their biological properties.     

Synthesis,structural characterization and biological activity of novel Knoevenagel condensates on DLD-1 human colon carcinoma

Biologically active Knoevenagel condensates (1–14) of diarylheptanoids: 1,7-bis(3-methoxy-4-hydroxyphenyl)hepta-1,7-diene-3,5-dione and 1,7-bis(3-ethoxy-4-hydroxyphenyl)hepta-1,7-diene-3,5-dione, were synthesized and structurally characterized. Compounds 1–14 exhibited cytotoxicity against colon carcinoma cells, and their antiproliferative effect was associated with a significant decrease of multidrug resistance proteins. One of the underlying mechanisms of these effects is the reduction of intracellular and extracellular SOD enzymes by compounds 1, 12 and 14, which render the tumor cells more vulnerable to oxidative stress.     

Antimicrobial and antioxidant activities of methanol extracts of <Emphasis Type="Italic">Evax pygmaea</Emphasis> (Asteraceae) growing wild in Tunisia

Antimicrobial activity of methanolic extracts obtained from the aerial parts of Evax pygmaea was tested against five bacteria and two strains of phytopathogenic fungi using the agar diffusion and broth microdilution methods. Antioxidant properties were evaluated through the ability of the different fractions to scavenge the stable ABTS (2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH (1,1-diphenyl-2-picrylhydrazyl) radicals. The TEAC (Trolox Equivalent Antioxidant Capacity) and IC₅₀ values of the fractions were calculated and compared. The experimental data indicated that all fractions exhibit moderate to appreciable antibacterial activities against all Gram-positive cocci and Gram-negative rods except Pseudomonas aeruginosa, but no antifungal activity was observed. Ethyl acetate and methanol fractions were found to cause significant free radical-scavenging effects in both assays. These results may suggest that E. pygmaea could be used as a natural preservative ingredient in the food and/or pharmaceutical industries.