Amplification of antioxidant activity of catechin by polycondensation with acetaldehyde

Catechin exhibits numerous biological and pharmacological effects attributed to antioxidant action. The synthetic poly(catechin)s condensed through acetaldehyde with different molecular weights were assessed in terms of antioxidant activity and enzyme inhibitory activity on the basis of a catechin repeating unit and compared with monomeric catechin. The poly(catechin)s showed great amplification of superoxide scavenging activity, xanthine oxidase (XO) inhibitory activity, and inhibition effects on human low-density lipoprotein oxidation initiated by 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) as a radical generator on the catechin unit level, compared to monomeric catechin: these activities were proportional to their molecular weights. The reducing power of the polymer was lower than that of monomeric catechin, which decreased with increasing the molecular weight. The polymer also protected endothelial cells from oxidative injury induced by AAPH, with a greater effect expressed on a catechin unit basis than that of the monomer. These results demonstrate that the poly(catechin)s are more potent antioxidant agents and enzyme inhibitors.     

Amplification of inhibitory activity of catechin against disease-related enzymes by conjugation on poly(epsilon-lysine)

A new inhibitor against disease-related enzymes, collagenase, hyaluronidase, and xanthine oxidase, has been developed by the laccase-catalyzed conjugation of catechin on poly(epsilon-lysine). The resulting poly(epsilon-lysine)-catechin conjugate showed greatly improved inhibition effects on activity of these enzymes, whereas the catechin monomer showed very low inhibition activity. The kinetic analysis on the inhibition of collagenase exhibited that the conjugate was a mixed-type inhibitor. The amplified activities might offer high potential as a therapeutic agent for prevention of various enzyme-related diseases.     

Antioxidant properties of catechins and proanthocyanidins: Effect of polymerisation, galloylation and glycosylation

A range of catechins and oligomeric procyanidins was purified by high performance liquid chromatography (HPLC) from grape seed, apple skin, lentil and almond flesh. Catechins, galloylated epicatechin, glycosylated catechin, procyanidin dimers, galloylated dimers, trimer, and tetramer species were all identified, purified and quantified by HPLC, LC-MS and NMR. The antioxidant properties of these compounds were assessed using two methods: (a) inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine liposomes; (b) scavenging of the radical cation of 2,2'-azinobis(3-ethyl-benzothiazoline-6-sulphonate) (ABTS) relative to the water-soluble vitamin E analogue Trolox C (expressed as Trolox C equivalent antioxidant capacity, TEAC). Antioxidant activity in the lipid phase decreased with polymerisation in contrast with antioxidant action in the aqueous phase which increased from monomer to trimer and then decreased from trimer to tetramer. Galloylation of catechin and dimeric procyanidins decreased lipid phase and increased aqueous phase antioxidant activity. Glycosylation of catechin demonstrated decreased activity in both phases.     

Antioxidant properties of catechins and proanthocyanidins: Effect of polymerisation,galloylation and glycosylation

A range of catechins and oligomeric procyanidins was purified by high performance liquid chromatography (HPLC) from grape seed, apple skin, lentil and almond flesh. Catechins, galloylated epicatechin, glycosylated catechin, procyanidin dimers, galloylated dimers, trimer, and tetramer species were all identified, purified and quantified by HPLC, LC-MS and NMR. The antioxidant properties of these compounds were assessed using two methods: (a) inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine liposomes; (b) scavenging of the radical cation of 2,2′-azinobis(3-ethyl-benzothiazoline-6-sulphonate) (ABTS) relative to the water-soluble vitamin E analogue Trolox C (expressed as Trolox C equivalent antioxidant capacity, TEAC). Antioxidant activity in the lipid phase decreased with polymerisation in contrast with antioxidant action in the aqueous phase which increased from monomer to trimer and then decreased from trimer to tetramer. Galloylation of catechin and dimeric procyanidins decreased lipid phase and increased aqueous phase antioxidant activity. Glycosylation of catechin demonstrated decreased activity in both phases.     

Contribution of phenolic compounds to the antioxidant potential and type II diabetes related enzyme inhibition properties of Pongamia pinnata L. Pierre seeds

The methanolic extract of Pongamia pinnata L. Pierre (locally called as karanja) seed materials, an underutilized food legume collected from India was analyzed for antioxidant and type II diabetes related enzyme inhibition properties. The methanolic extract of raw seeds contained total free phenolic content of 14.85 ± 0.32 g catechin equivalent/100 g extract DM. Encouraging levels of ferric reducing/antioxidant power (FRAP, 1179 mmol Fe[II]/mg extract), inhibition of β-carotene degradation (41.13%) and radical scavenging activity against DPPH (54.64%) and superoxide (54.53%) were exhibited by the raw sample. Further, it also recorded 77.92% of α-amylase and 86.50% of α-glucosidase enzyme inhibition characteristics under in vitro starch digestion bioassay. Sprouting + oil-frying caused a apparent increase on the total free phenolic content and also significant improvement on the antioxidant and free radical scavenging capacity of P. pinnata seeds, while soaking + cooking as well as open-pan roasting treatments showed diminishing effects. Moreover, inhibition of α-amylase and α-glucosidase enzyme activities was declined to 24.24 and 45.14%, respectively during sprouting + oil-frying treatment, which are more desirable for the dietary management of type II diabetic patients.     

Superoxide anion scavenging and xanthine oxidase inhibition of (+)-catechin-aldehyde polycondensates. Amplification of the antioxidant property of (+)-catechin by polycondensation with aldehydes

In this study, the antioxidant property of (+)-catechin-aldehyde polycondensates has been examined. Superoxide anions are one of the most typical reactive oxygen species (ROS) and generated by xanthine oxidase (XO). The measurements of the superoxide anion scavenging and XO inhibition activity showed that catechin had pro-oxidant properties in lower concentrations and little XO inhibition. On the other hand, the polycondensates exhibited much higher effects compared to the catechin monomer, and their physiological activities were greatly affected by the structure of polycondensates. Steady-state analysis of the inhibition against XO showed that the inhibition type of the polycondensate was uncompetitive. Furthermore, the results of the circular dichroism and UV-visible measurements of a mixture of the polycondensate and XO were in good agreement with that of the steady-state analysis; the spectral changes due to the chelation of the polycondensate onto the Fe/S and/or the FAD center of XO were observed. These data strongly suggest that the polycondensates possess a great potential as antioxidant for various applications.     

Antioxidant Activity and α-Glucosidase Inhibitory Activities of the Polycondensate of Catechin with Glyoxylic Acid

In order to investigate polymeric flavonoids, the polycondensate of catechin with glyoxylic acid (PCG) was prepared and its chemically antioxidant, cellular antioxidant (CAA) and α-glucosidase inhibitory activities were evaluated. The DPPH and ABTS radical scavenging activities and antiproliferative effect of PCG were lower than those of catechin, while PCG had higher CAA activity than catechin. In addition, PCG had very high α-glucosidase inhibitory activities (IC₅₀ value, 2.59 μg/mL) in comparison to catechin (IC₅₀ value, 239.27 μg/mL). Inhibition kinetics suggested that both PCG and catechin demonstrated a mixture of noncompetitive and anticompetitive inhibition. The enhanced CAA and α-glucosidase inhibitor activities of PCG could be due to catechin polymerization enhancing the binding capacity to the cellular membrane and enzymes.     

Isolation and characterization of a novel flavonoid possessing a 4,2'-glycosidic linkage from green mature acerola (Malpighia emarginata DC.) fruit

The novel flavonoid, leucocyanidin-3-O-beta-D-glucoside, possessing a 4,2'-glycosidic linkage was isolated from green mature acerola (Malpighia emarginata DC.) puree and given the trivial name "aceronidin." To examine the functions of aceronidin, its antioxidative activity and both its alpha-glucosidase and alpha-amylase inhibition activities, as a potential inhibitor of the sugar catabolic enzyme, were evaluated against those of taxifolin, catechin, isoquercitrin and quercitrin which each have a similar structure. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical quenching activity of aceronidin was stronger than that of alpha-tocopherol and comparable to that of flavonoids. In the yeast alpha-glucosidase inhibitory assay, aceronidin showed significantly greater inhibition than the other flavonoids tested. In the human salivary alpha-amylase inhibitory assay, aceronidin showed inhibition activity. Taken together, these results indicate aceronidin to be a potent antioxidant that may be valuable as an inhibitor of sugar catabolic enzymes.     

Egyptian propolis: 3. Antioxidant,antimicrobial activities and chemical composition of propolis from reclaimed lands

The free radical scavenging effect of two propolis samples collected from reclaimed land, Egypt as well as of vitamin C and caffeic acid in 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical system was determined. The antimicrobial (Staphylococcus aureus; Escherichia coli and Candida albicans) activity was also investigated. The results of the free radical scavenging effect of El-Saff and Ismailia propolis showed a concentration-dependent activity. The antioxidant activity was varied according to the examined material. It was obvious that caffeic acid and vitamin C showed the highest activity if compared with the propolis samples. El- Saff propolis had a higher antioxidant activity than Ismailia propolis, it showed a higher antibacterial activity against Staphylococcus aureus and a higher anti-fungal activity against Candida albicans. While the Ismailia propolis had a higher antibacterial activity against Escherichia coli, than El-Saff propolis. The chemical composition of propolis samples was investigated by GC/MS, where 75 compounds were identified, 22 being new for propolis. The Ismailia propolis was characterized by the presence of a highly significant amount of aromatic acid esters (47.3%) and triterpenoids (17.3%), while El-Saff propolis contained 3% and 1.9% respectively. The new esters belonged to 4-methoxyhydrocinnamic acid, hydroferulic acid and ferulic acid. El-Saff propolis had a very high significant amount (27%) of 2,6-bis-(pentanyloxy)-4-pentanylphenethanol, which is also a new compound for propolis.     

Stable free radical scavenging and antiperoxidative properties of resveratrol compared in vitro with some other bioflavonoids

Stable free radical scavenging and antiperoxidative activities of resveratrol, a component of grapes and red wine, were evaluated and compared with some other known bioflavonoids (quercetin, catechin, kaempferol, myricetin, fisetin, ellagic acid and naringenin) widely present in the plant kingdom. Free radical scavenging activity was measured in an in vitro chemical system (DPPH assay), while for antiperoxidative activity, biological system comprising of hepatic and pulmonary homogenates was employed. Antiradical activity assay showed quercetin and myricetin to be stronger antiradical agents than resveratrol. Structure-activity study revealed that O-dihydroxy group on ring B of flavonoid plays a crucial role. A double bond at 2-3 position conjugated with a 4-oxo function and hydroxy groups at positions 3 and 5 also contribute towards antiradical activity of flavonoids. Resveratrol exhibited stronger antiradical activity than kaempferol and naringenin and was also more efficient than alpha-tocopherol, a known strong endogenous non-flavonoid antioxidant, used for comparison. In vitro antiperoxidative assay showed fisetin as the strongest and kaempferol as the weakest antioxidant. Resveratrol was found to be stronger antioxidant than catechin, myricetin, kaempferol and naringenin, but was weaker than quercetin, fisetin and alpha-tocopherol. Antiradical and antiperoxidative activities of resveratrol may explain its beneficial effects in disease states. Assays exhibited no direct correlation between antiradical and antiperoxidative activities of the phenolics.     

Cyanidin and cyanidin 3-O-β-D-glucoside as DNA cleavage protectors and antioxidants

Anthocyanins, colored flavonoids, are water-soluble pigments present in the plant kingdom; in fact they are secondary plant metabolites responsible for the blue, purple, and red color of many plant tissues. Present in beans, fruits, vegetables and red wines, considerable amounts of anthocyanins are ingested as constituents of the human diet (180-215 mg daily). There is now increasing interest in the in vivo protective function of natural antioxidants contained in dietary plants against oxidative damage caused by free radical species. Recently, the antioxidant activity of phenolic phytochemicals, has been investigated. Since the antioxidant mechanism of anthocyanin pigments is still controversial, in the present study we evaluated the effects of cyanidin and cyanidin 3-O-beta-D-glucoside on DNA cleavage, on their free radical scavenging capacity and on xanthine oxidase activity. Cyanidin and cyanidin 3-O-beta-D-glucoside showed a protective effect on DNA cleavage, a dose-dependent free radical scavenging activity and significant inhibition of XO activity. These effects suggest that anthocyanins exhibit interesting antioxidant properties, and could therefore represent a promising class of compounds useful in the treatment of pathologies where free radical production plays a key role.     

Enzymatic synthesis and antioxidant properties of poly(rutin)

Rutin, quercetin-3-rutinoside, is one of the most famous glycosides of flavonoid and widely present in many plants. In this study, we performed an oxidative polymerization of rutin using Myceliophthora laccase as catalyst in a mixture of methanol and buffer to produce a flavonoid polymer and evaluated antioxidant properties of the resultant polymer. Under selected conditions, the polymer with molecular weight of several thousands was obtained in good yields. The resulting polymer was readily soluble in water, DMF, and DMSO, although rutin monomer showed very low water solubility. UV measurement showed that the polymer had broad transition peaks around 255 and 350 nm in water, which were red-shifted in an alkaline solution. Electron spin resonance (ESR) measurement showed the presence of a radical in the polymer. The polymer showed greatly improved superoxide scavenging activity and inhibition effects on human low-density lipoprotein (LDL) oxidation initiated by 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH), compared with the rutin monomer. The polymer also protected endothelial cells from oxidative injury induced by AAPH as a radical generator with a much greater effect than the rutin monomer.     

Differential antioxidant properties of red wine in water soluble and lipid soluble peroxyl radical generating systems

Red wine and its components have been shown to possess cardioprotective and anti-atherogenic effects. Additionally, red wine and many of its components like catechin, epicatechin, rutin, transresveratrol and quercetin possess antioxidant properties. Oxidized low density lipoprotein (LDL) is involved in the development of an atherosclerotic lesion. Red wine, therefore, may be anti-atherogenic because of its antioxidant effects on LDL modification. This study examined the antioxidant effects of catechin, epicatechin, rutin, transresveratrol, quercetin and Merlot wines on LDL oxidation. Merlot was chosen because although other red wines have been tested, limited information exists for this variety. Oxidation was carried out with AAPH (2,2-Azo-bis(2-amidinopropane) dihydrochloride) and AMVN (2,2-Azo-bis(2,4-dimethylvaleronitrile)), as water and lipid soluble peroxyl radical generating systems (FRGS), respectively. This allowed us to determine the lipophilic antioxidant characteristics of the wine and its components. Conjugated diene assays were used to measure LDL oxidation over 6 hrs. In an AAPH system, all polyphenolic compounds except transresveratrol displayed an antioxidant effect. LDL oxidation by AAPH was also inhibited by aliquots of Merlot wine. No antioxidant effects were observed in an AMVN environment except for a mild antioxidant effect by quercetin. Surprisingly, incubation of LDL with Merlot wine strongly protected against oxidation by AMVN. In summary, the five phenolic compounds displayed antioxidant effects in a water soluble free radical generating system, but only quercetin showed this in a lipid soluble one. However, red wine inhibited LDL oxidation by both water and lipid soluble free radical generating systems. Our data suggest, therefore, that red wines contain unidentified antioxidants that provide protection against LDL oxidation within a lipid soluble environment. (Mol Cell Biochem 263: 211–215, 2004)     

Antioxidant Properties of Fruits and Vegetables Shots and Juices: An Electron Paramagnetic Resonance Study

The antioxidant activity of some commercially available fruit and vegetable juices was evaluated with regard to their radical scavenging activity against the stable free radical 4-hydroxy-2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPOL) monitored by electron paramagnetic resonance (EPR) spectroscopy. TEMPOL is a stable nitroxide free radical characterized by a well-defined EPR spectrum consisting of three peaks. The integral intensity of the EPR spectra of TEMPOL was decreased upon juice addition, and the decrease was dose dependent. EPR spectroscopy using stable free radicals provides a simple, rapid, and sensitive method for the determination of antioxidant activity of fruit and vegetable juices. The method was standardized by using the standard antioxidant compound Trolox, and the antioxidant activity of the juices was expressed as Trolox equivalents. When concentrated juices of fruits and vegetables (shots) were considered, the evaluated antioxidant activity was almost twofold higher than that of the conventional, non-concentrated ones. Fruits and vegetables shots also showed very good stability during storage. This finding indicates that natural antioxidant compounds contained in commercially available concentrated juices are not eliminated or inactivated when the juices are kept refrigerated according to the instructions of the manufacturer.     

Free radical scavenging potential of Picrorhiza kurrooa Royle ex Benth

For assessing free radical scavenging potential of P. kurrooa, the antioxidant activity of P. kurrooa extract was studied by lipid peroxidation assay using rat liver homogenate. The extract (1 mg/ml) showed marked protection (up to 66.68%) against peroxidation of liver phospholipids. Besides, reduced glutathione showed very encouraging activity. The extract also exhibited significant scavenging activity. Thus augmenting the wide use of plant in the indigenous system of medicine, which may partly be due to antioxidant and free radical scavening activity of the extract.     

Enzymatic synthesis and antioxidant property of gelatin-catechin conjugates

Gelatin-catechin conjugate was synthesized by the laccase-catalyzed oxidation of catechin in the presence of gelatin. The conjugate had a good scavenging activity against superoxide anion radicals. Moreover, the conjugate showed an amplified inhibition effect on human low density lipoprotein oxidation initiated by 2,2'-azobis(2-amidinopropane)dihydrochloride as a radical generator.     

Inhibition effects of (+)-catechin-aldehyde polycondensates on proteinases causing proteolytic degradation of extracellular matrix

Inhibition effects of (+)-catechin-aldehyde polycondensates against the activity of proteinases, Clostridium histolyticum collagenase (ChC) and human neutrophil elastase (HNE) causing proteolytic degradation of extracellular matrix (ECM), have been investigated. In normal tissues, a balance is reached between the formation and destruction of ECM, leading to a state of homeostasis. However, uncontrolled destruction of ECM contributes to tumor invasion and metastasis. In the measurement of the inhibition activity on ChC and HNE, the polycondensates exhibited superior effects compared to the catechin monomer. Kinetic assays of ChC and HNE inhibition by the polycondensate clearly showed a mixed-type inhibition. These data demonstrate that the polycondensates are a new class of proteinase inhibitors useful for a potent therapeutic agent.     

Antioxidant activity of oligomeric acylphloroglucinols from Myrtus communis L

The use of myrtle (Myrtus communis L.) as a culinary spice and as a flavoring agent for alcoholic beverages is widespread in the Mediterranean area, and especially in Sardinia. Myrtle contains unique oligomeric non-prenylated acylphloroglucinols, whose antioxidant activity was investigated in various systems. Both semimyrtucommulone (1) and myrtucommulone A (2) showed powerful antioxidant properties, protecting linoleic acid against free radical attack in simple in vitro systems, inhibiting its autoxidation and its FeCl3- and EDTA-mediated oxidation. While both compounds lacked pro-oxidant activity, semimyrtucommulone was more powerful than myrtucommulone A, and was further evaluated in rat liver homogenates for activity against lipid peroxidation induced by ferric-nitrilotriacetate, and in cell cultures for cytotoxicity and the inhibition of TBH- or FeCl3-induced oxidation. The results of these studies established semimyrtucommulone as a novel dietary antioxidant lead.     

Antioxidant properties and protective effects of a standardized extract of Hypericum perforatum on hydrogen peroxide-induced oxidative damage in PC12 cells

Free radical scavenging and antioxidant activities of a standardized extract of Hypericum perforatum (SHP) were examined for inhibition of lipid peroxidation, for hydroxyl radical scavenging activity and interaction with 1,1-diphenyl-2-picrylhydrazyl stable free radical (DPPH). Concentrations between 1 and 50 microg/ml of SHP effectively inhibited lipid peroxidation of rat brain cortex mitochondria induced by Fe2+/ascorbate or NADPH system. The results showed that SHP scavenged DPPH radical in a dose-dependent manner and also presented inhibitory effects on the activity of xanthine oxidase. In contrast, hydroxyl radical scavenging occurs at high doses. The protective effect of the standardized extract against H2O2-induced oxidative damage on the pheochromocytoma cell line PC 12 was investigated by measuring cell viability via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH) assays, caspase-3-enzyme activity and accumulation of reactive oxygen species [2',7'-dichlorofluorescin (DCF) assay]. Following 8-h cell exposure to H2O2 (300 microM), a marked reduction in cell survival was observed, which was significantly prevented by SHP (pre-incubated for 24 h) at 1-100 microg/ml. In a separate experiment, different concentrations of the standardized extract (0.1-100 microg/ml) also attenuated the increase in caspase-3 activity and suppressed the H2O2 -induced reactive oxygen species generation. Taken together, these results suggest that SHP shows relevant antioxidant activity both in vitro and in a cell system, by means of inhibiting free radical generation and lipid peroxidation.     

Thyroxine induced stress and its possible prevention by catechin

Free radicals are all known to damage cell components. The present study was designed to evaluate the free radical generation in the testis and liver and also to determine the testicular and hepatic antioxidant enzyme activities with and without catechin administration in thyroxine induced male Sprague-Dawley rats. The experimental animals were divided into four groups, six on each division. L-thyroxine (T4) (0.3 mg/kg body weight) was administered to experimental groups for 15 days. Another group (CAT-T4) was administered with L-thyroxine (T4) in the dose as mentioned and catechin (100 mg/kg of body weight/day) simultaneously. Third group was administered only with catechin, and the remaining group was kept as control. Lipid peroxidation level (LPO) increased in L-thyroxine treated rats as compared to control, while LPO level was almost normal in L-thyroxine (T4) and catechin (CAT-T4) treated group. Superoxide dismutase (SOD) and catalase activities were increased in L-thyroxine (T4) treated rats as compared to control, where as there were almost at normal level in L-thyroxine (T4) and catechin (CAT-T4) treated groups. The results show that, thyroxine administration develops oxidative stress; the organism defends it against the effects of oxidative stress by increasing SOD and catalase activities as a protective mechanism and catechin, being an antioxidant, normalizes lipid peroxidation in testis and liver including SOD and catalase activities.