Preparation and antioxidant activity of alpha-pyridoin and its derivatives

Focusing on alpha-pyridoin (1, 1,2-di(2-pyridyl)-1,2-ethenediol) as the lead compound of the novel antioxidative enediol, we synthesized 5,5'- or 6,6'-bis-substituted derivatives of 1 from disubstituted pyridines. The antioxidant activity of 1 and its synthetic derivatives 2-7 was evaluated by DPPH (1,1-diphenyl-2-picrylhydrazyl radical) scavenging assay and inhibition of lipid peroxidation. In the DPPH assay, 1 exhibited an activity stronger than that of ascorbic acid, and 5,5'-dimethyl-(5) or 5,5'-dimethoxy-substituted derivatives (6) exhibited more potent activity than 1. The DPPH scavenging activities of alpha-pyridoins were correlated with their oxidation potential and thus the electron density of enediol. 5 and 6 effectively inhibited lipid peroxidation in the rat liver microsome/tert-butyl hydroperoxide system. Therefore, 5 and 6 serve as good candidates for a pharmacologically useful enediol antioxidant.     

Hydroxylated chalcones with dual properties: Xanthine oxidase inhibitors and radical scavengers

In this study, we evaluated the abilities of a series of chalcones to inhibit the activity of the enzyme xanthine oxidase (XO) and to scavenge radicals. 20 mono- and polyhydroxylated chalcone derivatives were synthesized by Claisen–Schmidt condensation reactions and then tested for inhibitory potency against XO, a known generator of reactive oxygen species (ROS). In parallel, the ability of the synthesized chalcones to scavenge a stable radical was determined. Structure–activity relationship analysis in conjunction with molecular docking indicated that the most active XO inhibitors carried a minimum of three hydroxyl groups. Moreover, the most effective radical scavengers had two neighboring hydroxyl groups on at least one of the two phenyl rings. Since it has been proposed previously that XO inhibition and radical scavenging could be useful properties for reduction of ROS-levels in tissue, we determined the chalcones’ effects to rescue neurons subjected to ROS-induced stress created by the addition of β-amyloid peptide. Best protection was provided by chalcones that combined good inhibitory potency with high radical scavenging ability in a single molecule, an observation that points to a potential therapeutic value of this compound class.     

Light-dependent orientation responses in animals can be explained by a model of compass cue integration

The magnetic compass sense of animals is currently thought to be based on light-dependent processes like the proposed radical pair mechanism. In accordance, many animals show orientation responses that depend on light. However, the orientation responses depend on the wavelength and irradiance of monochromatic light in rather complex ways that cannot be explained directly by the radical pair mechanism. Here, a radically different model is presented that can explain a vast majority of the complex observed light-dependent responses. The model put forward an integration process consisting of simple lateral inhibition between a normal functioning, light-independent magnetic compass (e.g. magnetite based) and a vision based skylight color gradient compass that misperceives compass cues in monochromatic light. Integration of the misperceived color compass cue and the normal magnetic compass not only explains most of the categorically different light-dependent orientation responses, but also shows a surprisingly good fit to how well the animals are oriented (r-values) under light of different wavelength and irradiance. The model parsimoniously suggests the existence of a single magnetic sense in birds (probably based on magnetic crystals).     

The Positive Correlations Between the Activity of Superoxide Dismutase and Dehydration Tolerance in Wheat Seedlings

Damage to crops by drought is still a serious problem in large areas of the world. Considerable research has been undertaken to discover the mechanisms of drought injury and drought resistance of plants. However, the critical features of drought injury have not yet been identified. In the past ten years a free radical hypothesis has been suggested to account for subcellular damage caused by severe environments. Superoxide (oxygen radical) is normally produced in hydrated tissues. It is controlled by free radical scavenging reactions. One such scavenger is the enzyme superoxide dismutase (SOD). Under water stress, production of excess free radicals may occur in dehydrated plant tissues and this probably damages the membranes by causing peroxidation of the lipid components. So far few studies have been done to determine if drought injury is correlated with the free radical mechanism. In the present study, the SOD activities in wheat seedlings under water stress have been investigated by measuring the photoreduction of nitro blue tetrazolium using a spectrometric method. Meanwhile, the viabilities of wheat seedlings during drying were followed by tetrazolium test. These results provided information on the relationship between SOD activity and the dehydration tolerance of the plant. Results indicated that SOD activity changed with the time after germination. The activity of SOD of 24 h seedlings was 1.9 times higher than those of 72 h seedlings based on fresh weight. SOD activity in shoot was also higher than in root. These results were consistent with the results obtained from rating of the viabilities of seedlings during drying. The 24h seedlings were more tolerant of dehydration than 72 h seedlings and root were more sensitive of drought than shoot. In addition, shoot and root tips showed the higher SOD activities than non-tip region and they also showed a higher survival ability upon dehydration. In dehydration and subsequent rehydration, SOD activity, different from many other enzymes in plants, increased rather than declined during drying. After rehydration SOD activity returned to nearly the original level. Therefore, the positive correlations were found to exist between SOD activity and dehydration tolerance. It is reasonable to suggest that SOD enzyme may play a protective role against damage caused by free radicals which may be produced excessively during dehydration in wheat seedling.     

A spectroscopic characterization of a phenolic natural mediator in the laccase biocatalytic reaction

Multi-frequency ESR combined with NALDI-TOF MS has been used for the characterization of 3,5-dimethoxy-4-hydroxyacetophenone radical intermediate and by-products formed during the Coriolopsis gallica laccase catalytic reaction. A stable radical species is formed and an intense and well-structured ESR spectrum was detected and fully characterized at S-, X- and W-bands. The presence of by-products generated as the result of by-reactions has been investigated and analyzed through NALDI-TOF MS, performing the experiments versus time. The superior radical stability of such phenoxy radical, due to steric hindrance in ortho to the phenol group and the great delocalization of the unpaired electron on the acetyl substituent, makes acetosyringone particularly interesting for biotechnological applications. This represents a good example for the development of new stable laccase mediator molecules.     

Quinones as Free-radical Fragmentation Inhibitors in Biologically Important Molecules

Effects of a number of quinones and diphenols of various structures on free-radical fragmentation processes taking place in &#102 -diols, glycerol, 2-aminoethanol, glycero-1-phosphate, ethylene glycol monobutyrate, maltose, and some lipids were investigated. Quinone additions have been found to change the direction of free-radical transformations of the compounds cited above by inhibiting formation of the respective fragmentation products owing to oxidation of radicals of the starting compounds. The results obtained and literature data available allow a suggestion to be made that the system quinone/diphenol is able to not only deactivate or generate such active species as O 2 &#148 &#109 but also control the realization probability of free-radical processes of peroxidation and fragmentation in biologically important molecules.     

Microwave hydrodiffusion and gravity processing of Sargassum muticum

An aqueous based extraction process was developed to obtain soluble fractions from Sargassum muticum. Microwave hydrodiffusion and gravity (MHG) and subsequent rehydration and extraction stages (MHG-W) in an open system, hot pressurized water extraction or autohydrolysis (A) and enzyme aided extraction (E) were selected on the basis of their simplicity and the possibility of using water as solvent. The performance of these combined technologies using biorenewable solvents to extract antioxidants was compared. A preliminary selection of MHG extraction conditions suggested that 600 W was the optimal irradiation power. A multistage process based on an initial solvent free MHG stage followed by a sequence of water extraction stages (MHG-W) proved suited to selectively obtain phenolic compounds in shorter times than conventional processes. The yield of total solubles was lower than with conventional solvent extraction, but the phenolic content of the extracts and their ABTS radical scavenging properties were enhanced. The microscopic observations of extracted tissues confirmed the impact of the microwave and hot pressurized water processes on the algal cell wall integrity.     

Radical scavenging capacity and cytoprotective effect of enzymatic digests of <Emphasis Type="Italic">Ishige okamurae</Emphasis>

In order to obtain natural antioxidants of good quality from a marine bioresource, we selected the brown marine alga, Ishige okamurae, which is an abundant and unutilized source of biomass and grows near Jeju Island, South Korea. An enzymatic extraction technique was used in order to determine the antioxidant effects of I. okamurae using commercially available food-grade digestive enzymes. In the evaluation of the radical scavenging capacity of the enzymatic extracts from I. okamurae using an electron spin resonance (ESR) spectrophotometer, all of the enzymatic extracts showed profound dose-dependent radical scavenging abilities. The majority of enzymatic extracts generated by proteases (except for Neutrase) had stronger hydrogen peroxide scavenging effects than the carbohydrase extract. In particular, the cytoprotective effects of the Kojizyme extract against H₂O₂ - induced DNA damage increased significantly with increasing extract concentrations in our comet assay tests. These results showed that I. okamurae may prove to be a valuable natural source of antioxidants.     

An aromatic amide C-glycoside and a cyclitol derivative from stem barks of Piper guineense Schum and Thonn (Piperaceae)

Two new compounds, an aromatic amide C-glycoside, 4-C-β-D-glucopyranosyl-3,5-dihydroxy-2-methoxybenzamide (1) and a cyclitol derivative, 4-O-caffeoyl-2-C-methoxycarbonyl-1-C-methyl-2,3,6-trihydroxycyclohexanecarboxylic acid (2), were isolated from the methanol soluble extract of the stem barks of Piper guineense Schum and Thonn, together with four known quinic acids derivatives including 3-O-caffeoyl-1-methylquinic acid (3), 3-O-feruloylquinic acid (4), ethyl-4-O-feruloylquinate (5), and 5-caffeoylquinic acid (6). Their structures were established on the basis of detailed spectroscopic analysis. The radical scavenging activity of the isolates were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay. Five of them were found to have significant radical scavenging activities, while compounds 2 and 3 displayed the highest activities with IC₅₀ values of 8.35 and 7.06 μM, respectively.     

Structural characterization of laminaran and galactofucan extracted from the brown seaweed Saccharina longicruris

Brown seaweed contains several polysaccharides like laminaran, fucoidan and alginate. Laminaran is a β-glucan that has shown anti-apoptotic and anti-tumoral activities, while galactofucan (fucoidan) is a sulfated polysaccharide that has displayed anticoagulant, anti-tumor, anti-thrombosis, anti-inflammatory and antiviral properties. In this study, crude laminaran and galactofucan (fucoidan) were extracted from the brown seaweed Saccharina longicruris at four harvest periods (M05, A05, N05 and J06). The galactofucan M05 and N05 fractions were depolymerized (RDP) over 2 or 4 h to give 4 RDP fractions (M05 RDP 2H, M05 RDP 4H, N05 RDP 2H and N05 RDP 4H) whose molecular weights, monosaccharide compositions and glycosidic linkages were determined by GC-MS. The laminaran fraction gave a molecular weight range from 2900 to 3300 Da and contained between 50.6% and 68.6% d-glucose and an average of 1.3% d-mannitol. The presence of a β-(1,3) linkage between d-glucose in the main chain was observed, with branching at positions 6 and 2. The M05 fraction contained less branching than other laminaran fractions, which might have influenced its conformation in solution and thus its activity. The crude galactofucan fractions displayed a molecular weight range from 638 to 1529 kDa, whereas the RDP fractions had molecular weights <30 kDa. The structure of the galactofucan fractions remained complex after depolymerization, with these also being more sulfated (30-39%) than the crude fractions (13-20%). The crude and RDP fractions contained 3-linked fucopyranose 4-sulfate and 6-linked galactopyranose 3-sulfate moieties, although the galactofucans isolated from M05 and J06 contained less 6-linked galactopyranose 3-sulfate than the A05 and N05 fractions.