Synthesis and antioxidant properties of dendritic polyphenols

Three dendritic polyphenols (generation 1) were synthesized: a syringaldehyde-based dendrimer (1), a vanillin-based dendrimer (2), and an iodinated vanillin-based dendrimer (3). They all showed strong antioxidant activity according to the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay. The syringaldehyde dendrimer was twice and 10 times stronger than quercetin and Trolox, respectively. The vanillin-based dendrimer and its more hydrophobic iodinated derivative were also more potent antioxidants than quercetin and Trolox. The DPPH order of potency was 1 > 2, 3 > quercetin > Trolox. All three dendrimers also protected human LDL from free radical attack in a dose-dependent manner. Their order of free radical scavenging was 1 > 3 > 2 > quercetin > Trolox. The increased hydrophobic nature of the iodinated derivative may have contributed to its better LDL protection than 2. Protection of linoleic acid oxidation was studied by the β-carotene–linoleate assay. Dendrimer 1 was clearly superior to the other antioxidants in protecting the fatty acid. In case of DNA protection against free radical damage, the order of activity was 1 > quercetin > 2 > 3, Trolox. Pro-oxidant effect on copper-induced DNA oxidation showed the following order: quercetin, Trolox > 1 > 2 > 3. Results of the study show that dendritic antioxidants, even at the generation 1 level, provide promising antioxidant properties for their potential use as drug candidates for diseases associated with oxidative stress.     

Stage-specific induction of systemic acquired resistance by fruit extracts of Azadirachta indica

In the present study, the efficacy of aqueous fruit extract of Azadirachta indica A. Juss. (Neem) on induction of systemic acquired resistance (SAR) in tomato against Pseudomonas syringae pv. tomato through enhancement in the activity of polyphenol oxidase (PPO) at different ages was studied. Plants at 6, 8, 10 and 12?weeks of age were selected. A single leaf at the third node from the base of each plant was treated either singly or with different combinations of the pathogen and Neem fruit extract. Samples were collected from the non-treated leaves at an interval of 24?h up to five?days for enzyme assay and after two?weeks for disease development from both treated and untreated plants. The results demonstrate that the neem fruit extract could induce additional PPO isoforms both locally as well as systemically. The PPO activity was observed to be elevated in both the treated and non-treated leaves leading to induction of SAR. The induction of SAR enhances with the increase in the age of the plant.     

Relationship Between Ethylene Release,Membrane Permeability and Activity of Polyphenol Oxidase Changes of Duck (Pears Pyrus bretschnideri Rehder) During Low Temperature Storage

Duck pear (Pyrus bretschneideri Rehder) tends to develop browning core after 55 to 60 days storage at low temperature (0℃). Following physiological changes of the duck pear during storage at different temperature were investigated: (1) As compared with 20℃, ethylene release is obviously decreased and its peak is retarded for 15 days at 0℃. Levels of internal ethylene are variant at different individuals harvested at same time. Concentrations of internal ethylene are in accord with ethylene release. The higher internal ethylene is, the easier the pear core becomes brown. (2) At 0℃, activity of polyphenol oxidase in the core increases with ethylene release enhancement. After ethylene peak passes, its activity is lower than before. (3) The electric conductivity of cores is higher at 0℃ than at 20℃. During post climacteric period, the electric conductivity increases irreversibly, then browning core occurs. From above results, it is concluded that interactions between two factors induce the browrang core of the duck pears at low temperature. One is chilling injury caused by low temperature, another is ethylene function. They stimulate the activity of polyphenol oxidase and enhance the membrane permeability.     

Overexpression of the laccase gene,lcc1, in Lentinula edodes using the pChG vector

Lentinula edodes secretes laccase (Lcc: EC 1.10.3.2), an industrially useful enzyme. In this study, we introduced and expressed the L. edodes Lcc gene, lcc1, driven by L. edodes glyceraldehyde-3-phosphate dehydrogenase gene promoter into L. edodes. The resulting transformants showed 2-fold Lcc activity than that of the host strain, and expression of the recombinant lcc1 was confirmed by RT-PCR.     

Extraction, structural characterisation and evaluation of hydroxycinnamate esters of orchard grass (Dactylis glomerata) as substrates for polyphenol oxidase

Polyphenol oxidase (PPO) activity has been reported in orchard grass (Dactylis glomerata); however, to date, no endogenous substrates have been identified. In the present study, we report the isolation and structural elucidation of PPO substrates in this species. The free phenol fraction was extracted, separated by reverse-phase chromatography and six potential substrates, including two hydroxycinnamate esters, were identified by UV spectrometry, electrospray ionisation-tandem mass spectrometry (LC-ESI-MSⁿ) and 1D and 2D NMR analyses (¹H NMR, ¹³C NMR, DEPT, COSY, HMQC and HMBC). Furthermore, three caffeoylquinic acids (3-CQA, 4-CQA and 5-CQA) were identified by comparison of their spectral data (ESI-MS) with those of known compounds and literature data. Five of these compounds were demonstrated to be substrates for orchard grass PPO.     

Biotransformation of tea catechins into theaflavins with immobilized polyphenol oxidase

Theaflavins, an active antioxidant, a natural pigment and pharmacologically active molecule obtained from black tea were bioprocessed on an immobilized tea polyphenol oxidase (PPO) system by the conversion of tea catechins extracted from green tea leaves with an overall conversion efficiency of 85% about 14-fold increase over maximum achievable in normal black teas. The immobilized enzyme (IE) system consists of activated cellulose matrix on to which the freshly extracted tea leaf polyphenol oxidase was covalently linked. Cellulose as a matrix of choice was considered primarily for its non-toxic nature, natural origin, low cost and easy availability. The kinetic parameters of the IE system were; protein loading capacity 11.8 mg/g; pH optimum 5.9; temperature optimum 37.5 °C; K_m 4.76 ± 0.08 mM; V_max 20 ± 1.80 nmol/min; enzyme activity retention (83.58%) and number of batches per turnover without loss of activity was 14. The product from IE system was identified by HPLC and ESI-QTOF-MS spectrometry.     

Hydrolyzable tannins of tamaricaceous plants. IV: Micropropagation and ellagitannin production in shoot cultures of Tamarix tetrandra

Shoot cultures of Tamarix tetrandra on Linsmaier–Skoog (LS) agar medium with 30 g l⁻¹ sucrose, 2.13 mg l⁻¹ indoleacetic acid and 2.25 mg l⁻¹ benzyl adenine produced ellagitannins found in intact plants of the Tamaricaceae. This was demonstrated by the isolation of 14 monomeric–tetrameric ellagitannins from the aq. Me₂CO extract of the cultured tissues. This is the first report on the production of ellagitannin tetramers by plant tissue culture. The effects of light and certain medium constituents on tissue growth and ellagitannin production were examined. The contents of representative tannins of different types [i.e., tellimagrandin II (monomer), hirtellin A (linear GOG-type dimer), hirtellin B (hellinoyl-type dimer), hirtellin C (macrocyclic-type dimer), and hirtellin T1 (linear GOG-type trimer)] in the resultant tissues in response to these factors were estimated by HPLC, and the optimal condition for production of these tannins were established. Shoots cultured on LS hormone-free medium promoted root development, and regenerated plants could adapt to ordinary soil and climate. Acclimatized and intact T. tetrandra plants that were collected in November and May, respectively, demonstrated seasonal differences in individual ellagitannin contents. HPLC comparison of individual ellagitannin contents in different plant materials (i.e., leaves, stems, and roots) of intact T. tetrandra plants is also reported. The results are discussed with respect to cellular deposition and biosynthetic relationship of tannins.     

Tannins in plant-herbivore interactions

Tannins are the most abundant secondary metabolites made by plants, commonly ranging from 5% to 10% dry weight of tree leaves. Tannins can defend leaves against insect herbivores by deterrence and/or toxicity. Contrary to early theories, tannins have no effect on protein digestion in insect herbivores. By contrast, in vertebrate herbivores tannins can decrease protein digestion. Tannins are especially prone to oxidize in insects with high pH guts, forming semiquinone radicals and quinones, as well as other reactive oxygen species. Tannin toxicity in insects is thought to result from the production of high levels of reactive oxygen species. Tannin structure has an important effect on biochemical activity. Ellagitannins oxidize much more readily than do gallotannins, which are more oxidatively active than most condensed tannins. The ability of insects to tolerate ingested tannins comes from a variety of biochemical and physical defenses in their guts, including surfactants, high pH, antioxidants, and a protective peritrophic envelope that lines the midgut. Most work on the ecological roles of tannins has been correlative, e.g., searching for negative associations between tannins and insect performance. A greater emphasis on manipulative experiments that control tannin levels is required to make further progress on the defensive functions of tannins. Recent advances in the use of molecular methods has permitted the production of tannin-overproducing transgenic plants and a better understanding of tannin biosynthetic pathways. Many research areas remain in need of further work, including the effects of different tannin types on different types of insects (e.g., caterpillars, grasshoppers, sap-sucking insects).     

Naturally occurring polyphenolic inhibitors of amyloid beta aggregation

Alzheimer’s disease is the most common neurodegenerative disease and is one of the main causes of death in developed countries. Consumption of foods rich in polyphenolics is strongly correlated with reduced incidence of Alzheimer’s disease. Our study has investigated the biological activity of previously untested polyphenolic compounds in preventing amyloid β aggregation. The anti-aggregatory potential of these compounds was assessed using the Thioflavin-T assay, transmission electron microscopy, dynamic light scattering and size exclusion chromatography. Two structurally related compounds, luteolin and transilitin were identified as potent inhibitors of Aβ fibril formation. Computational docking studies with an X-ray derived oligomeric structure offer a rationale for the inhibitory activity observed and may facilitate development of improved inhibitors of Aβ aggregation and toxicity.