Effect of ellagic acid on gastric damage induced in ischemic rat stomachs following ammonia or reperfusion

We examined the effect of ellagic acid (EA), one of the polyphenols that are abundantly contained in whisky as a nonalcoholic component, on gastric lesions induced by ammonia plus ischemia or ischemia/reperfusion in rats, in relation to the antioxidative system. Under urethane anesthesia, a rat stomach was mounted in an ex vivo chamber, and the following two experiments were performed; 1) a stomach was made ischemic (1.5 ml/100 g body weight) for 20 min, followed by reperfusion for 15 min in the presence of 100 mM HCl; 2) a stomach was made ischemic by bleeding from the carotid artery (1 ml/100 g body weight), followed by intragastric application of ammonia (NH4OH: 120 mM). EA (0.1-10 mg/ml) was applied in the chamber 30 min before the onset of ischemia. Gastric potential difference (PD) and mucosal blood flow (GMBF) were measured before, during and after 20 min of ischemia. Ischemia/reperfusion caused a profound drop in GMBF followed by a return, and resulted in hemorrhagic lesions in the stomach in the presence of 100 mM HCI. These lesions were dose-dependently prevented by EA with suppression of lipid peroxidation but no effect on GMBF, and the effect at 6 mg/ml was almost equivalent to that of superoxide dismutase (SOD: 15000 unit/kg/hr) infused i.v. during a test-period. On the other hand, application of NH4OH to the ischemic stomach produced a marked reduction in PD, resulting in severe hemorrhagic lesions. These changes were prevented with both EA and SOD. In addition, EA had a potent scavenging action against monochloramine in vitro. These results suggest that EA exhibits gastric protective action against gastric lesions induced by NH4OH or reperfusion in the ischemic stomach, probably due to its anti-oxidative activity. This property of EA partly explains the less damaging effect of whisky in the stomach and may be useful as the prophylactic for Helicobacter pylori-associated gastritis.     

Brazilin Removes Toxic Alpha-Synuclein and Seeding Competent Assemblies from Parkinson Brain by Altering Conformational Equilibrium

Alpha-synuclein (α-syn) fibrils, a major constituent of the neurotoxic Lewy Bodies in Parkinson’s disease, form via nucleation dependent polymerization and can replicate by a seeding mechanism. Brazilin, a small molecule derived from red cedarwood trees in Brazil, has been shown to inhibit the fibrillogenesis of amyloid-beta (Aβ) and α-syn as well as remodel mature fibrils and reduce cytotoxicity. Here we test the effects of Brazilin on both seeded and unseeded α-syn fibril formation and show that the natural polyphenol inhibits fibrillogenesis of α-syn by a unique mechanism that alters conformational equilibria in two separate points of the assembly mechanism: Brazilin preserves the natively unfolded state of α-syn by specifically binding to the compact conformation of the α-syn monomer. Brazilin also eliminates seeding competence of α-syn assemblies from Parkinson’s disease patient brain tissue, and reduces toxicity of pre-formed assemblies in primary neurons by inducing the formation of large fibril clusters. Molecular docking of Brazilin shows the molecule to interact both with unfolded α-syn monomers and with the cross-β sheet structure of α-syn fibrils. Our findings suggest that Brazilin has substantial potential as a neuroprotective and therapeutic agent for Parkinson’s disease.     

Chemical constituents from the stems of Dendrotrophe frutescens

Phytochemical investigation of Dendrotrophe frutescens (Benth.) Danser led to the isolation of eight compounds (1–8), including a furan-2-carbonyl C-glycoside together with a series of polyphenols and their glycosides. The structures were elucidated on the basis of spectroscopic analysis, including 1D and 2D-NMR experiments and by comparison with data in the literature. This is the first report of the isolation of compounds 1–6 from the family Santalaceae, while compound 7 was isolated from the genus Dendrotrophe for the first time.     

Identification of free radical species derived from caffeic acid and related polyphenols

Polyphenols are widely distributed in various fruits, vegetables and seasonings. It is well known that they have several physiological effects due to their antioxidative activities. Their activities depend on structural characteristics that favour the formation of their corresponding stable radicals. During the examination at which pH values, the polyphenol radicals are stabilized, we confirmed that polyphenol radicals were stabilized in NaHCO₃/Na₂CO₃ buffer (pH 10) rather than in physiological pH region. Then, we measured electron spin resonance (ESR) spectra at pH 10 to examine the characteristics of free radical species derived from caffeic acid (CA) with an unsaturated side chain, dihydrocaffeic acid (DCA) with a saturated side chain, chlorogenic acid (ChA) and rosmarinic acid (RA). In analyzing the radical structures, ESR simulation, determinations of macroscopic and microscopic acid dissociation constants and molecular orbital (MO) calculation were performed. In CA, the monophenolate forms were assumed to participate in the formation of free radical species, while in DCA, the diphenol form and the monophenolate forms were presumed to contribute to the formation of free radical species. On the basis of the results, we propose the possible structures of the free radical species formed from polyphenols under alkaline conditions.     

Purification and characterization of polyphenol oxidase from nettle (Urtica dioica L.) and inhibitory effects of some chemicals on enzyme activity

Polyphenol oxidase (PPO) of nettle (Urtica dioica L.) was extracted and purified through (NH₄)₂SO₄ precipitation, dialysis, and CM-Sephadex ion-exchange chromatography and was used for its characterization. The PPO showed activity to catechol, 4-methylcatechol, L-3,4-dihydroxyphenylalanine (L-DOPA), L-tyrosine, p-cresol, pyrogallol, catechin and trans-cinnamic acid. For each of these eight substrates, optimum conditions such as pH and temperature were determined and L-tyrosine was found to be one of the most suitable substrates. Optimum pH and temperature were found at pH 4.5 and 30°C respectively and K_m and V_max values were 7.90?×?10^?4?M, and 11290?EU/mL for with L-tyrosine as substrate. The inhibitory effect of several inhibitors, L-cysteine chloride, sodium azide, sodium cyanide, benzoic acid, salicylic acid, L-ascorbic acid, glutathione, thiourea, sodium diethyl dithiocarbamate, β-mercaptoethanol and sodium metabisulfite were tested. The most effective was found to be sodium diethyl dithiocarbamate which acted as a competitive inhibitor with a K_i value of 1.79?×?10^?9?M. In addition one isoenzyme of PPO was detected by native polacrylamide slab gel electrophoresis.     

Combined application of botanical formulations and biocontrol agents for the management of Fusarium oxysporum f. sp. cubense (Foc) causing Fusarium wilt in banana

Plant products along with biocontrol agents were tested against Fusarium wilt of banana caused by Fusarium oxysporum f. sp. cubense (Foc). Of the 22 plant species tested, the leaf extract of Datura metel (10%) showed complete inhibition of the mycelial growth of Foc. Two botanical fungicides, Wanis 20 EC and Damet 50 EC along with selected PGPR strains with known biocontrol activity, Pseudomonas fluorescens 1, Pf1 and Bacillus subtilis, TRC 54 were tested individually and in combination for the management of Fusarium wilt under greenhouse and field conditions. Combined application of botanical formulation and biocontrol agents (Wanis 20 EC + Pf1 + TRC 54) reduced the wilt incidence significantly under greenhouse (64%) and field conditions (75%). Reduction in disease incidence was positively correlated with the induction of defense-related enzymes peroxidase (PO) and polyphenol oxidase (PPO). Three antifungal compounds (two glycosides and one ester) in D. metel were separated and identified using TLC, RP-HPLC (Reverse Phase-High Pressure Liquid Chromatography) and mass spectrometry. In this study it is clear that combined application of botanical formulations and biocontrol agents can be very effective in the management of Fusarium wilt of banana.     

Polyphenol biosensor based on laccase immobilized onto silver nanoparticles/multiwalled carbon nanotube/polyaniline gold electrode

Laccase purified from Ganoderma sp. was immobilized covalently onto electrochemically deposited silver nanoparticles (AgNPs)/carboxylated multiwalled carbon nanotubes (cMWCNT)/polyaniline (PANI) layer on the surface of gold (Au) electrode. A polyphenol biosensor was fabricated using this enzyme electrode (laccase/AgNPs/cMWCNT/PANI/Au electrode) as the working electrode, Ag/AgCl as the reference electrode, and platinum (Pt) wire as the auxiliary electrode connected through a potentiostat. The biosensor showed optimal response at pH 5.5 (0.1 M acetate buffer) and 35 °C when operated at a scan rate of 50 mV s⁻¹. Linear range, response time, and detection limit were 0.1–500 μM, 6 s, and 0.1 μM, respectively. The sensor was employed for the determination of total phenolic content in tea, alcoholic beverages, and pharmaceutical formulations. The enzyme electrode was used 200 times over a period of 4 months when stored at 4 °C. The biosensor has an advantage over earlier enzyme sensors in that it has no leakage of enzyme during reuse and is unaffected by the external environment due to the protective PANI microenvironment.     

Enzymatic synthesis of a catecholic polyphenol product with excellent antioxidant activity

Abstract

Polyphenols, especially catecholic stilbene derivatives, have attracted much attention due to the huge pharmacological effects and promising health benefits. However, their chemical synthesis via regioselective ortho-hydroxylation on aromatic rings is highly challenging. In this study, 3′-hydroxypterostilbene (HPS) is taken as a model product due to its strong potential as an antitumor agent. One-step enzymatic synthesis of HPS from pterostilbene (PS) was explored, with immobilised tyrosinase as catalyst. The impact of solvent, pH, temperature, oxygen and reductant concentration on the reaction was investigated, and the conversion was optimised by employing the response surface methodology (RSM). Finally, a high yield of 77.9% was obtained in 2.7?h. This study demonstrates the first successful use of a biotechnological strategy to synthesise HPS. The antioxidant activities of both PS and HPS were evaluated by using the DPPH assay, demonstrating that HPS is more potent than PS as a radical scavenger.     

Syntheses of procyanidin B2 and B3 gallate derivatives using equimolar condensation mediated by Yb(OTf)3 and their antitumor activities

Synthesis of procyanidin B2 and B3 gallate derivatives, 3-O-gallate, 3″-O-gallate, and 3,3″-di-O-gallate, were synthesized using equimolar condensation mediated by Yb(OTf)₃. Synthesized compounds showed significant antitumor effects against human prostate PC-3 cell lines. Their activities were weaker than well-known EGCG and prodelphinidin B3.     

Antioxidant and prooxidant effects of polyphenol compounds on copper-mediated DNA damage

Inhibition of copper-mediated DNA damage has been determined for several polyphenol compounds. The 50% inhibition concentration values (IC₅₀) for most of the tested polyphenols are between 8 and 480 μM for copper-mediated DNA damage prevention. Although most tested polyphenols were antioxidants under these conditions, they generally inhibited Cu^I-mediated DNA damage less effectively than Fe^II-mediated damage, and some polyphenols also displayed prooxidant activity. Because semiquinone radicals and hydroxyl radical adducts were detected by EPR spectroscopy in solutions of polyphenols, Cu^I, and H₂O₂, it is likely that weak polyphenol-Cu^I interactions permit a redox-cycling mechanism, whereby the necessary reactants to cause DNA damage (Cu^I, H₂O₂, and reducing agents) are regenerated. The polyphenol compounds that prevent copper-mediated DNA damage likely follow a radical scavenging pathway as determined by EPR spectroscopy.