Comparison of the protective effect of various flavonoids against lipid peroxidation of erythrocyte membranes (induced by cumene hydroperoxide)

In silico identification of potential inhibitors of key SARS-CoV-2 3CL hydrolase (Mpro) via molecular docking, MMGBSA predictive binding energy calculations, and molecular dynamics simulation

The incidence of 2019 novel corona virus (SARS-CoV-2) has created a medical emergency throughout the world. Various efforts have been made to develop the vaccine or effective treatments against the disease. The discovery of crystal structure of SARS-CoV-2 main protease has made the in silico identification of its inhibitors possible. Based on its critical role in viral replication, the viral protease can prove to be a promising “target” for antiviral drug therapy. We have systematically screened an in-house library of 15,754 natural and synthetic compounds, established at International Center for Chemical and Biological Sciences, University of Karachi. The in silico search for potential viral protease inhibitors resulted in nine top ranked ligands (compounds 1–9) against SARS-CoV-2 main protease (PDB ID: 6LU7) based on docking scores, and predictive binding energies. The in silico studies were updated via carrying out the docking, and predictive binding energy estimation, with a recently reported crystal structure of main protease (PDB ID: 6Y2F) at a better resolution i.e., 1.95 Å. Compound 2 (molecular bank code AAA396) was found to have highest negative binding energy of −71.63 kcal/mol for 6LU7. While compound 3 (molecular bank code AAD146) exhibited highest negative binding energy of -81.92 kcal/mol for 6Y2F. The stability of the compounds- in complex with viral protease was analyzed by Molecular Dynamics simulation studies, and was found to be stable over the course of 20 ns simulation time. Compound 2, and 3 were predicted to be the significant inhibitors of SARS-CoV-2 3CL hydrolase (Mpro) among the nine short listed compounds.

Interaction of Catechins with Human Erythrocytes

The aim of this study was to characterize the interaction of chosen catechins ((+)-catechin, (−)-epigallocatechin (EGC), and (−)-epigallocatechin gallate (EGCG)) with human erythrocytes and their protective effects against oxidative damage of erythrocytes. Uptake of the catechins by erythrocytes was studied by fluorimetry, their interaction with erythrocyte membrane was probed by changes in erythrocyte osmotic fragility and in membrane fluidity evaluated with spin labels, while protection against oxidative damage was assessed by protection against hemolysis induced by permanganate and protection of erythrocyte membranes against lipid peroxidation and protein thiol group oxidation. Catechin uptake was similar for all the compounds studied. Accumulation of catechins in the erythrocyte membrane was demonstrated by the catechin-induced increase in osmotic resistance and rigidification of the erythrocyte membrane detected by spin labels 5-doxyl stearic acid and 16-doxyl stearic acid. (−)-Epigallocatechin and EGCG inhibited erythrocyte acetylcholinesterase (mixed-type inhibition). Catechins protected erythrocytes against permanganate-induced hemolysis, oxidation of erythrocyte protein thiol groups, as well as membrane lipid peroxidation. These results contribute to the knowledge of the beneficial effects of catechins present in plant-derived food and beverages.

Distribution of betalain pigments in red blood cells after consumption of cactus pear fruits and increased resistance of the cells to ex vivo induced oxidative hemolysis in humans

Betalain pigments are bioavailable phytochemicals recently acknowledged as natural radical scavengers. This work, which extends previous research on the postabsorbitive fate of dietary betalains, investigated the distribution of betanin and indicaxanthin in red blood cells (RBCs) isolated from healthy volunteers (n = 8), before and during the 1-8 h interval after a cactus pear fruit meal, and the potential antioxidative activity of the pigments in these cells. A peak concentration of indicaxanthin (1.03 +/- 0.2 microM) was observed in RBCs isolated at 3 h after fruit feeding, whereas the concentration at 5 h was about half, and even smaller amounts were measured at 8 h. Indicaxanthin was not detected at 1 h. Betanin (30.0 +/- 5.2 nM) was found only in RBCs isolated at 3 h from fruit feeding. In comparison with homologous RBCs before fruit ingestion, a significant delay (P < 0.05) of the onset of an ex vivo cumene hydroperoxide (cumOOH)-induced hemolysis was evident in the RBCs isolated at 3 h (33.0 +/- 4.5 min) and at 5 h (16.0 +/- 2.0 min). Neither vitamins C and E nor GSH was modified in the RBCs at any time point. Blood collected from the same volunteers after a 12-h fasting was incubated with the purified betalains in the range of 5-25 microM, to enrich the erythrocytes with either betanin or indicaxanthin, and then the cells were exposed to cumOOH. When compared to the relevant nonenriched cells, the betalain-enriched erythrocytes exhibited an enhanced resistance to the cumOOH-induced hemolysis, which was positively correlated (r (2) = 0.99) to the amount of the incorporated compound. On a micromolar basis, betanin and indicaxanthin showed a comparable effectiveness. Taken together, these findings provide evidence that human RBCs incorporate dietary betalains and support the concept that these phytochemicals may offer antioxidative protection to the cells.

Naringin supplementation lowers plasma lipids and enhances erythrocyte antioxidant enzyme activities in hypercholesterolemic subjects

BACKGROUND AND AIMS

Preliminary studies have shown that naringin has a potent lipid-lowering effect and antioxidant capacity in high-cholesterol diet fed animals. Accordingly, the present study was conducted to investigate the effect of naringin on hypercholesterolemic subjects.

METHODS

A hypercholesterolemic group (n=30) and healthy control group (n=30) were established based on the plasma cholesterol levels in the subjects, then all subjects received naringin (400mg/capsule/day) with regular meals for a period of 8 weeks.

RESULTS

In the hypercholesterolemic subjects, naringin supplementation was found to lower the plasma total cholesterol by 14% and low-density lipoprotein cholesterol concentrations by 17%, while the plasma triglyceride and high-density lipoprotein cholesterol concentrations remained unaffected. The apolipoprotein B levels in the hypercholesterolemic subjects were significantly lowered after naringin treatment, yet no change was observed in the apolipoprotein A-1 levels. The erythrocyte superoxide dismutase and catalase activities in the hypercholesterolemic group were significantly increased, whereas the glutathione peroxidase activity and plasma TBARS levels were not different from the baseline measurements. Meanwhile, naringin supplementation had no affect on plasma lipids, apolipoproteins, and TBARS levels or antioxidant enzyme activities in the control group.

CONCLUSIONS

Therefore, these data suggest that naringin may play an important role in lowering plasma cholesterol and regulating the antioxidant capacity in hypercholesterolemic subjects.

The grapefruit flavanone naringin protects against the radiation-induced genomic instability in the mice bone marrow: a micronucleus study

The effect of various doses, viz. 0, 0.5, 1, 2, 4, 6 and 8 mg/kg body weight of naringin (NIN) (a citrus flavanone) was studied on the alteration in the radiation-induced micronucleated polychromatic (MPCE) and normochromatic (MNCE) erythrocytes in mouse bone marrow exposed to 2 Gy of 60Co gamma-radiation. The treatment of mice with various doses of NIN before exposure to 2 Gy resulted in a significant decline in the frequency of MPCE when compared to the non-drug-treated irradiated control. However, the greatest reduction in MPCE was observed for 2mg/kg body weight NIN, accompanied by a highest PCE/NCE ratio when compared with the non-drug-treated irradiated control. Therefore, further studies were carried out using this dose of NIN, where the animals were administered with 2mg/kg body weight of NIN before exposure to 0, 0.5, 1, 2, 3 and 4 Gy of gamma-radiation. The frequency of MPCE and MNCE increased in a dose-dependent manner in both the non-drug-treated irradiated control and NIN-pretreated irradiated groups up to a dose of 2 Gy, while a further increase in the irradiation dose resulted in a significant decline in MPCE and MNCE frequencies in both groups. Pretreatment of mice with 2mg/kg body weight of NIN resulted in a significant decline in the frequencies of MPCE and MNCE. NIN treatment not only reduced the frequency of MPCE with one micronucleus, but also of MPCE with multiple micronuclei (MN), indicating its ability to reduce complex chromosome aberrations. Conversely, the PCE/NCE ratio declined in a dose-dependent manner in both groups. The treatment of mice with NIN before exposure to different doses of gamma-radiation resulted in the inhibition in this decline in the PCE/NCE ratio. Our study demonstrates that NIN is able to protect mouse bone marrow cells against the radiation-induced DNA damage and decline in the cell proliferation as observed by a reduction in the micronucleus frequency and an increase in PCE/NCE ratio, respectively, in the NIN-pretreated irradiated group.

Naringin has an antiatherogenic effect with the inhibition of intercellular adhesion molecule-1 in hypercholesterolemic rabbits

Naringin, a bioflavonoid found in citrus fruit peel, is known to have an antioxidative effect, but its effect on atherosclerosis has not been studied. This study evaluated the effect of naringin on blood lipid levels and aortic fatty streaks, and its action mechanism in hypercholesterolemic rabbits. Male New Zealand white rabbits were fed a 0.25% cholesterol diet and divided into an untreated group (n = 4), a naringin-treated group (n = 5; 500 mg/kg per day), and a lovastatin-treated group (n = 5; 20 mg/kg per day). After 8 weeks, blood was sampled and analyzed biochemically. Aorta and liver were harvested and examined histologically. Cholesterol level in rabbits fed the 0.25% cholesterol diet reached 17 times normal and decreased in the rabbits fed naringin and lovastatin, whose effects were not statistically significant (p > 0.05). However, both naringin and lovastatin effectively decreased the area of fatty streak in thoracic aorta on macroscopic analysis (p < 0.05) and significantly reduced subintimal foam cell infiltration on microscopic morphometry (p < 0.05). These foam cells were macrophages on immunohistochemical analysis. Naringin treatment inhibited hypercholesterolemia-induced intercellular adhesion molecule-1 (ICAM-1) expression on endothelial cells. Hypercholesterolemia caused fatty liver and elevation of liver enzymes, which was prevented by naringin but not by lovastatin. Naringin significantly reduced fatty streak formation and neointimal macrophage infiltration and also inhibited the expression of ICAM-1 in endothelial cells, suggesting that suppression of ICAM-1 contributed to the antiatherogenic effect. Naringin, unlike lovastatin, has a hepatoprotective action.

Effect of a bioflavonoid dietary supplement on acetaminophen-induced oxidative injury to feline erythrocytes

OBJECTIVE

To determine the effect of a commercial bioflavonoid antioxidant on acetaminophen-induced oxidative injury to feline erythrocytes.

DESIGN

Randomized controlled study.

ANIMALS

45 healthy age-matched cats.

PROCEDURE

Cats were assigned to 3 experimental groups. Groups 1 and 3 received a bioflavonoid antioxidant (10 mg/d) orally for 2 weeks. Groups 2 and 3 received an oxidative challenge with acetaminophen (90 mg/kg [41 mg/lb] of body weight, PO) on day 7. Packed cell volume, percentage of erythrocytes with Heinz bodies, blood methemoglobin concentration, and blood reduced and oxidized glutathione concentrations were determined at various times during the 2-week study period.

RESULTS

Adverse effects were not associated with bioflavonoid antioxidant administration alone. Acetaminophen administration resulted in a significant increase in methemoglobin concentration in groups 2 and 3; differences were not detected between these groups. Heinz body concentrations in groups 2 and 3 increased after acetaminophen administration; however, the increase in cats that received the antioxidant was significantly less than in group-2 cats. Total blood glutathione concentrations did not change significantly in groups 2 and 3 after acetaminophen administration; however, ratio of reduced to oxidized glutathione concentration increased significantly after administration in group-2 cats, compared with group-3 cats.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of bioflavonoid antioxidants to cats at risk for oxidative stress may have a beneficial effect on their ability to resist oxidative injury to erythrocytes.

Prevention of toxin-induced cytoskeletal disruption and apoptotic liver cell death by the grapefruit flavonoid, naringin

The protein phosphatase-inhibitory algal toxins, okadaic acid and microcystin-LR, induced overphosphorylation of keratin and disruption of the keratin cytoskeleton in freshly isolated rat hepatocytes. In hepatocyte cultures, the toxins elicited DNA fragmentation and apoptotic cell death within 24 h. All these toxin effects could be prevented by the grapefruit flavonoid, naringin. The cytoprotective effect of naringin was apparently limited to normal hepatocytes, since the toxin-induced apoptosis of hepatoma cells, rat or human, was not prevented by the flavonoid.

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.

Effect of donor age on the susceptibility of erythrocytes and erythrocyte membranes to cumene hydroperoxide-induced oxidative stress

A comparative study on erythrocytes and erythrocyte membranes of healthy elderly and young adults was carried out to understand how the antioxidant defense capacity is effected by aging. The levels of endogenous malondialdehyde and Ca(2+)-ATPase activity were taken as indices of oxidative damage. In addition, chemiluminescence measurements were performed on intact erythrocytes. The susceptibility of these parameters to in vitro cumene hydroperoxide, under low oxidant level that does not induce hemolysis, was also taken as an age-related indicator of the endogenous peroxidative potential of the erythrocytes. Our data showed that the content of malondialdehyde and Ca(2+)-ATPase activity did not change with age. Furthermore, the susceptibility of intact erythrocytes to oxidative stress did not change in the elderly group. However, under the same conditions erythrocyte membranes were more susceptible to oxidative damage in the elderly than young adults. Our results also showed that antioxidant defenses were overwhelmed in intact erythrocytes of the elderly at high concentrations of cumene hydroperoxide.

Pharmacological effects of selected flavonoids on rat isolated ileum: structure-activity relationship

1. Eleven selected flavonoids were studied to evaluate their effects on the rat isolated ileum and to determine their structure-activity relationships. 2. The flavonoids rutin and 3',5,7-trihydroxy-4' methoxyflavone-7-rutinoside, which have a sugar moiety (O-rha-glu), had no significant effect on the ileum, indicating that the presence of sugar substitution reduces the biological activity of the flavonoids. 3. Nine other flavonoids caused inhibition of tonic and phasic contractions of the ileum with the following order of potency from highest to lowest: galangin, quercetin, chrysin, xanthomicrol, flavone, naringenin, fisetin, morin, and flavanone. 4. Flavones were more potent than flavanones, indicating that the double bond at carbon 2-3 increases the potency of the flavonoid. 5. Galangin, quercetin, chrysin, and xanthomicrol, which have hydroxyl substituents on carbon 3 and/or 5, showed higher potency than flavone, indicating that such hydroxyl groups are essential for the activity. 6. Galangin was more potent than quercetin, morin, and fisetin, suggesting that the hydroxyl substituents on ring B attenuate the potency. 7. Quercetin caused more potent relaxation of the ileum than morin, suggesting that the presence of a hydroxyl group at C-2' of ring B attenuates the myolytic activity.

Morin hydrate inhibits azo-initiator induced oxidation of human low density lipoprotein

We demonstrated that the flavonoid morin hydrate at 75-100 microM protects against the oxidation of low density lipoprotein (LDL) by free radicals produced by 2,2'-azo-bis(2-amidinopropane) dihydrochloride. Morin hydrate reduces the relative electrophoretic mobility, malondialdehyde equivalents and lipid peroxide level of oxidized LDL. On the other hand, Trolox (an analogue of vitamin E) showed less protective effect in the present system. Since free radical mediated oxidation of LDL is implicated to be a cause of atherogenesis, morin hydrate may be a candidate chemotherapeutic agent herein.

Antioxidation of human low density lipoprotein by morin hydrate

Oxidative modification of low density lipoprotein (LDL) has been suggested to be a risk factor for the development of atherosclerosis. Agents which can protect LDL from oxidation may be useful in preventing atherogenesis. Here, we found that morin hydrate, at 100 microM concentration, effectively inhibits Cu(2+)-induced oxidation of LDL. The oxidation of LDL was assessed by agarose gel electrophoresis. This was further studied by measuring the increased values of the malondialdehyde equivalents and the decreased numbers of reactive amino groups on oxidized LDL. Trolox, at equimolar concentrations, exhibit similar effects in preventing oxidation of LDL.

alpha-Tocopherol, ascorbic acid, and rutin inhibit synergistically the copper-promoted LDL oxidation and the cytotoxicity of oxidized LDL to cultured endothelial cells

Low-density lipoproteins (LDL) mildly oxidized by copper ions or UV radiations exhibit a cytotoxic effect to cultured endothelial cells. Rutin, a polyphenolic flavonoid, ascorbic acid, and alpha-tocopherol were able to inhibit the peroxidation of LDL and their subsequent cytotoxicity. The mixture of the three compounds (rutin/ascorbic acid/alpha-tocopherol, 4/4/1) exhibited a supra-additive antioxidant effect. The inhibition of the cytotoxic effect was well correlated with that of TBARS formation. Another important conclusion is that these antioxidants were able to prevent directly at the cellular level the cytotoxic effect of oxidized LDL, since cells preincubated with them were protected against the cytotoxic effect of previously oxidized LDL. The protective effect of antioxidants was limited because of their own toxicity. The antioxidant mixture permitted a maximal cytoprotective effect with relatively lower concentrations to be obtained and the cytotoxicity of high concentrations to be avoided. In conclusion, rutin, ascorbic acid, and alpha-tocopherol constitute two lines of defense in protecting cells against injury owing to oxidation of LDL (1) at the LDL level, by inhibiting the LDL oxidation and the subsequent cytotoxicity, and (2) at the cellular level, by protecting the cells directly, i.e., by increasing their resistance against the cytotoxic effect of oxidized LDL.

A novel antioxidant flavonoid (IdB 1031) affecting molecular mechanisms of cellular activation

In searching for new drug candidates which could help bridge the gaps between free radical oxidations, pathophysiological responses, and pharmacological treatment, a series of flavonoids was screened. The most interesting compound emerging from this screening, the flavone 3'-hydroxyfarrerol (IdB 1031), is presented in this article. This compound is a good inhibitor of microsomal lipid peroxidation induced by either iron-adenosine 5'-diphosphate (ADP) or carbon tetrachloride. The elevated rate constant for the interaction with peroxyl radicals, analysed by the kinetics of inhibition of crocin bleaching in the presence of a diazo initiator, gives an account for the observed antioxidant capacity. When tested on human neutrophils activated by fMLP, IdB 1031 inhibits (ID50:20 microM) respiratory burst. This effect, which is possibly linked to the observed inhibition of protein-kinase C (ID50:50 microM), seems rather specific since IdB 1031 does not inhibit tyr-kinases and casein-kinase-2, while Quercetin and other flavonoids inhibit unspecifically all these enzymes. These effects, as a whole, depict this compound as a drug candidate for diseases in which peroxidative damage is associated with the induction of inflammatory responses and specifically with activation of a respiratory burst of leucocytes.

Morin: a wood pigment that protects three types of human cells in the cardiovascular system against oxyradical damage

Morin is a yellowish pigment extractable from the wood of Chlorophora tinctoria. In the present study, we have determined that morin protects three types of human cells--ventricular myocytes, saphenous vein endothelial cells, and erythrocytes--against damage by oxyradicals generated in situ. In myocytes and endothelial cells, morin prolonged substantially and in a concentration-dependent manner the survival of cells exposed to either xanthine oxidase-generated oxyradicals or superoxide radicals produced with menadione. Morin protected erythrocytes from lytic attack by peroxyl radicals generated with 2,2'-azo-bis (2-amidinopropane) dihydrochloride. In all three types of human cells, the protective effect of morin clearly excelled that displayed by Trolox (a vitamin E analog), ascorbate, or mannitol, which are water-soluble antioxidants of similar molecular size. Chemically, we verified that morin behaves as an antioxidant by diminishing markedly the amount of malondialdehyde (lipid peroxidation product) found in human cardiocytes despite their exposure to oxyradicals. In agreement with related reports, we also observed that morin is non-toxic in rats even when used at concentrations 2-3 orders of magnitude higher than those in our in vitro studies. Thus, morin acts as a broad-spectrum and non-toxic antioxidant.

Effects of phenolic compounds on bromobenzene-mediated hepatotoxicity in mice

1. The hepatic protective effects of the phenolic compounds 7,8-dihydroxyflavone, morin, silymarin, caffeic acid and chlorogenic acid on bromobenzene-induced toxicity in mice were studied. 2. Morin, caffeic acid and chlorogenic acid at an oral dose of 200 mg/kg failed to influence hepatotoxicity in vivo, while 7,8-dihydroxyflavone exhibited efficacy and potency higher than those of the reference compound silymarin. 3. 7,8-Dihydroxyflavone, an antioxidant and hepatoprotective agent in vitro, decreased serum glutamate-pyruvate transaminase levels (SGPT) in a dose-related manner, and at 200 mg/kg inhibited bromobenzene-induced glutathione depletion in liver.

Antioxidant and iron-chelating activities of the flavonoids catechin, quercetin and diosmetin on iron-loaded rat hepatocyte cultures

The cytoprotective effect of three flavonoids, catechin, quercetin and diosmetin, was investigated on iron-loaded hepatocyte cultures, considering two parameters: the prevention of iron-increased lipid peroxidation and the inhibition of intracellular enzyme release. These two criteria of cytoprotection allowed the calculation of mean inhibitory concentrations (IC50) which revealed that the effectiveness of these flavonoids could be classified as follows: catechin > quercetin > diosmetin. These IC50 values have been related to structural characteristics of the flavonoids tested. Moreover, the investigation of the capacity of these flavonoids to remove iron from iron-loaded hepatocytes revealed a good relationship between this iron-chelating ability and the cytoprotective effect. The cytoprotective activity of catechin, quercetin and diosmetin could thus be ascribed to their widely known antiradical property but also to their iron-chelating effectiveness. These findings increase further the prospects for the development and clinical application of these potent antioxidants.

Morin hydrate is a plant-derived and antioxidant-based hepatoprotector

Morin hydrate, or simply morin, is shown here to be an effective hepatoprotector in vitro and in vivo. Between 0.25-2.0 mM, morin prolongs survival of rat hepatocytes against free radical damage triggered by xanthine oxidase-hypoxanthine, and substantially better than equimolar concentrations of Trolox (a vitamin E analogue), mannitol, and ascorbate. In a rat model of 80 min ischemia-24 h reperfusion in the liver, infusion of morin at 2.5, 5.0 and 10 mumol/Kg body weight before reperfusion reduces liver necrosis in the placebo control by 51.48 +/- 9.94%, 66.55 +/- 2.18%, and 79.37 +/- 11.03%, respectively, for n = 6 per group. Mechanistically, morin acts in a two-pronged manner: as a preventive antioxidant by partially inhibiting xanthine oxidase and partly as a curative antioxidant by scavenging oxyradicals. The role of morin as an effective free radical scavenger is further evidenced by its ability to protect human red cell membrane from peroxidative attack better than ascorbate, Trolox, and mannitol. Collectively, our data demonstrate that morin is an effective hepatoprotector, both in cultured cells and in hepatic ischemia-reperfusion.

Antioxidant action of benzylisoquinoline alkaloids

The antioxidant action of a series of benzylisoquinoline alkaloids has been investigated. Laudanosoline, protopapaverine, anonaine, apomorphine, glaucine, boldine, bulbocapnine, tetrahydroberberine and stepholidine produced a dose-dependent inhibition of microsomal lipid peroxidation induced by Fe2+/ascorbate, CCl4/NADPH or by Fe3+ ADP/NADPH. Apomorphine exerted the highest inhibitory effects in the three systems of induction used, with a potency higher than propyl gallate. Laudanosoline was particularly effective in the first system, while bulbocapnine and anonaine were more potent when CCl4/NADPH or Fe3(+)-ADP/NADPH were used as inducers. Laudanosoline, protopapaverine, apomorphine, tetrahydroberberine and stepholidine were also potent inhibitors of nitroblue tetrazolium (NBT) reduction. The presence of a free hydroxyl group or preferably of a catechol group is a feature relevant for inhibition of lipid peroxidation and NBT reduction, nevertheless the antioxidant activity of benzylisoquinoline alkaloids cannot be only ascribed to the formation of phenoxy radicals and other free radical species may be formed during aporphine and tetrahydroprotoberberine oxidation. The influence of this series of compounds on the time course of lipid peroxidation suggests that some of them, like apomorphine and boldine act as chain-breaking antioxidants.

Thermal behavior and elastic properties of phospholipid bilayers under the effect of a synthetic flavonoid derivative, LEW-10

We have investigated the effect on phospholipidic bilayers of LEW-10, a synthetic flavonoid, derivative of diosmin. Two optical techniques, Quasi-elastic Light Scattering (QLS) and Fourier Transform Infrared Spectroscopy (FT-IR) were used. The results show that in the presence of LEW-10, the phase transition of the bilayers is lowered and that the elastic modulus is decreased. The FT-IR results indicate interactions in the aqueous interface regions of the bilayers. We also discuss LEW-10 comparatively with another derivative, LEW-7/S1, whose effect has been previously studied.

Effects of baicalein and alpha-tocopherol on lipid peroxidation, free radical scavenging activity and 12-O-tetradecanoylphorbol acetate-induced ear edema

The effects of baicalein, a flavonoid, and alpha-tocopherol (vitamin E) on lipid peroxidation in rat forebrain homogenates, on free radical scavenging action against diphenyl-p-picrylhydrazyl (DPPH), and on 12-O-tetradecanoylphorbol acetate (TPA)-induced ear edema in mice were studied. Baicalein inhibited lipid peroxidation in forebrain homogenates, DPPH-induced free radical and TPA-induced ear edema as potently as did quercetin and nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, and more potently than BW755C, a mixed cyclooxygenase and lipoxygenase inhibitor. Lipid peroxidation in forebrain homogenates, DPPH-induced free radical and TPA-induced ear edema were also inhibited by alpha-tocopherol. Flavone showed no reaction. These results suggest that lipid peroxidation may play an important role in the pathogenesis of TPA-induced ear edema in mice.

Effect of hydroxyethyl rutosides and related compounds on lipid peroxidation and free radical scavenging activity. Some structural aspects

Four hydroxyethyl rutosides, 7,3',4'-trihydroxyethyl quercetin, quercetin and a commercial standardized mixture of hydroxyethyl rutosides were investigated on non-enzymatic lipid peroxidation, for hydroxyl radical scavenging activity and interaction with 1,1-diphenyl-2-picrylhydrazyl stable free radical (DPPH). It was found that the tested compounds exhibited a considerable inhibition of microsomal lipid peroxidation. They were less active than the reference compound quercetin, and this was attributed to their structural characteristics. They were also found to be potent hydroxyl radical scavengers and to interact with DPPH. As hydroxyl radical scavengers, they were more potent than the scavengers mannitol and dimethyl sulphoxide. These properties could be considered as a useful and exploitable combination.

Ultraviolet-treated lipoproteins as a model system for the study of the biological effects of lipid peroxides on cultured cells. III. The protective effect of antioxidants (probucol, catechin, vitamin E) against the cytotoxicity of oxidized LDL occurs in two different ways

Comparison of the protective effect of three antioxidants (from three different chemical classes) against cell injury due to LDL oxidation, allowed us to clearly discriminate between two different lines of defence. The ultraviolet-induced lipid peroxidation of LDL was strongly inhibited by 10 mumol/l catechin and 25 mumol/l probucol, but only poorly by 100 mumol/l vitamin E. The ultraviolet-treated LDL protected by catechin or probucol (i.e. LDL irradiated by ultraviolet in the presence of effective concentrations of antioxidants inhibiting the lipid peroxidation) were much less 'cytotoxic' than unprotected ultraviolet-treated LDL. In contrast, LDL treated by ultraviolet in the presence of 100 mumol/l vitamin E were 'cytotoxic' similarly to unprotected LDL. The level of 'cytotoxicity' of LDL treated by ultraviolet in the presence of antioxidants (protected ultraviolet-treated LDL) was well correlated with their content in lipid peroxidation markers. Therefore these markers can be useful for predicting the 'cytotoxicity' of oxidized LDL and subsequently the protective effect of the tested antioxidants. The 'cytotoxicity' of unprotected ultraviolet-treated LDL (i.e. LDL irradiated by ultraviolet in the absence of exogenous antioxidant) can be effectively blocked by preincubation of the cells with antioxidants. Catechin (10 mumol/l) and vitamin E (100 mumol/l) are very effective cytoprotective agents, whereas probucol (up to 50 mumol/l) was completely ineffective under these experimental conditions. The cytoprotective effect of vitamin E was associated to a complete inhibition of the cellular TBARS formation induced by ultraviolet-treated LDL, whereas the cytoprotective effect of catechin was relatively independent on the TBARS inhibition. All these results showed that: (1) probucol (25 mumol/l) is very effective to prevent lipid peroxidation of LDL and their subsequent 'cytotoxicity', but it cannot protect cells against the 'cytotoxicity' of previously oxidized LDL; (2) vitamin E (100 mumol/l) prevents poorly the ultraviolet-induced lipid peroxidation of LDL, but is able to block simultaneously the cellular oxidative stress and the 'cytotoxicity' induced by previously oxidized LDL; and (3) catechin (10 mumol/l) exhibited two types of protective effects: it inhibits the lipid peroxidation of LDL (and their subsequent 'cytotoxicity') and very effectively protects the cells against 'toxicity' of previously oxidized LDL (with only little inhibition of the cellular oxidative stress).(ABSTRACT TRUNCATED AT 400 WORDS)

Structure-activity relationships of polymethoxyflavones and other flavonoids as inhibitors of non-enzymic lipid peroxidation

Polymethoxylated flavones and C-glycosyl derivatives isolated from medicinal plants besides other flavonoid compounds were studied for their influence on lipid peroxidation induced by FeSO4+ cysteine in rat liver microsomes. A number of hydroxyflavones (e.g. luteolin); C-glycosyl-flavones (e.g. orientin); methoxyflavones (e.g. gardenin D) and flavonols (e.g. datiscetin), as well as the flavanol leucocyanidol and the biflavone amentoflavone behaved as inhibitors of non-enzymic lipid peroxidation. Structure-activity relationships were established and it was observed that the structural features for active polyhydroxylated compounds were different from those of polymethoxylated flavones, antiperoxidative flavonoids possessing a high lipophilicity.