Inhibition Of Microsomal Lipid Peroxidation Research Articles

Inhibition of Microsomal Lipid Peroxidation and Protein Oxidation by Carica papaya (L) Leaf against Carbon Tetrachloride-Induced Hepatic Injury in Wistar Albino Rats

Inhibition of Microsomal Lipid Peroxidation and Protein Oxidation by Carica papaya (L) Leaf against Carbon Tetrachloride-Induced Hepatic Injury in Wistar Albino Rats

Flavonolignan 2,3-dehydroderivatives: Preparation, antiradical and cytoprotective activity

The protective constituents of silymarin, an extract from Silybum marianum fruits, have been extensively studied in terms of their antioxidant and hepatoprotective activities. Here, we explore the electron-donor properties of the major silymarin flavonolignans. Silybin (SB), silychristin (SCH), silydianin (SD) and their respective 2,3-dehydroderivatives (DHSB, DHSCH and DHSD) were oxidized electrochemically and their antiradical/antioxidant properties were investigated. Namely, Folin–Ciocalteau reduction, DPPH and ABTS+ radical scavenging, inhibition of microsomal lipid peroxidation and cytoprotective effects against tert-butyl hydroperoxide-induced damage to a human hepatocellular carcinoma HepG2 cell line were evaluated. Due to the presence of the highly reactive C3-OH group and the C-2,3 double bond (ring C) allowing electron delocalization across the whole structure in the 2,3-dehydroderivatives, these compounds are much more easily oxidized than the corresponding flavonolignans SB, SCH and SD. This finding was unequivocally confirmed not only by experimental approaches, but also by density functional theory (DFT) calculations. The hierarchy in terms of ability to undergo electrochemical oxidation (DHSCH~DHSD>DHSB>>SCH/SD>SB) was consistent with their antiradical activities, mainly DPPH scavenging, as well as in vitro cytoprotection of HepG2 cells. The results are discussed in the context of the antioxidant vs. prooxidant activities of flavonolignans and molecular interactions in complex biological systems.

Antimutagenic and antioxidant activity of Ficus benghalensis stem bark and Moringa oleifera root extract

Objective: To investigate antimutagenic and antioxidant potency of the aqueous heat treated Ficus benghalensis stem bark (FBH) extract and Moringa oleifera root (MRH) extract against sodium azide in TA100 tester strains of Salmonella typhimurium and their inhibition of microsomal lipid peroxidation (LPO). Methods: Mutagenicity was assayed by the standard Ames test (standard plate incorporation assay) and antioxidant potency was investigated by employing ex vivo inhibition of lipid peroxidation in liver Microsomes. Results: Both FBH and MRH showed strong antimutagenic effect on S. typhimurium TA100 strains against sodium azide (NaN3). IC50 values of aqueous extract of FBH and MRH extracts were 70.24 mg/ml and 99.20 mg/ml respectively. FBH extract showed maximum inhibition of microsomal lipid peroxidation responses than MRH. IC50 values of aqueous extract of FBH and MRH extracts were 80.24 mg/ml and 92 mg/ml respectively. FBH and MRH exhibited a dose dependent antioxidant activity. Conclusion: The aqueous heat-treated FBH and MRH have antimutagenic as well as antioxidant activity. Further studies are in progress to evaluate the effect of both extracts by other antioxidant and antimutagenic assays and to identify the factors responsible for these activities.

Synthesis and antioxidant evaluation of novel indole-3-acetic acid analogues

Indole-3-acetic acid ( 1 ) on reaction with thionyl chloride, afforded 2-(1 H -indol-3-yl)acetyl chloride ( 2 ), which was further treated with aniline and various substituted anilines through base condensation reaction to obtain respected indole-3-acetic acid derivatives ( 3 - 9 ). The structures of all new compounds were elucidated by elemental analysis, Mass, IR, 1 H NMR and 13 C NMR and spectroscopic techniques. All the compounds were screened for their antioxidant activities by applying in vitro methods like 2,2-diphenyl-1-picryl hydrazyl (DPPH) free radical scavenging assay and inhibition of microsomal lipid peroxidation (LPO) assay. Butylated hydroxy anisole (BHA) was used as a reference antioxidant compound and the comparative study with newly synthesized compounds was also done. Among the analogues, compound 9 bearing electron donating methoxy substituent in addition to the phenolic moiety showed predominant activity. It is conceivable from these studies that the coupling of aniline and substituted anilines is the most important feature for the significant antioxidant activity of indole-3-acetic acid analogues studied.

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.

Evaluation of Antioxidant Activity of Medicinal Plant Extracts Produced for Commercial Purpose

The antioxidant potential of some herbal plant extracts (commercial products) was measured using variousin vitroassays. Among the extracts fromCurcuma longa, Caffea arabica, Tribulus terrestris, Bacopa monnieriandTrigonella foenum- graecum, theCurcuma longaand coffee bean extract (Caffea Arabica) showed greater antioxidant activity measured as scavenging of DPPH, superoxide radicals, reducing power and inhibition of microsomal lipid peroxidation.

Antihepatotoxic and Antioxidant Activities of Methanol Extract and Isolated Compounds fromFicus Chlamydocarpa

Free radicals, in particular radical oxygen species (ROS), play an important role in the aetiology and pathogenesis of various diseases. Current research in many countries focuses on the use of local medicinal plants as a promising source of liver protective agents. This paper describes the hepatoprotective effects of the methanol extract and four isolated compounds from Ficus chlamydocarpa on CCl4-induced liver damage, as well as the possible antioxidant mechanisms involved in this protection. The DPPH test, along with the beta-Carotene-Linoleic Acid Model System and Ferric-Reducing Antioxidant Power assays, as well as the inhibition of microsomal lipid peroxidation were used to measure radical-scavenging and antioxidant activities. Pretreatment of rats with the methanol extract of F. chlamydocarpa before CCl4 administration, significantly prevented serum increase of hepatic enzyme markers, glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT), in a dose-dependent manner. The hepatoprotection was also associated with a significant enhancement in hepatic reduced glutathione (GSH) and a marked decrease of liver malondialdehyde (MDA). Among the four compounds 1-4, isolated from the methanol extract, alpha-amyrin acetate (1) and luteolin (4) showed a significant hepatoprotective activity, as indicated by their ability to prevent liver cell death and lactate dehydrogenase (LDH) leakage during CCl4 intoxication.

Free Radical Scavenging Activity of Aqueous and Ethanolic Extract of Brassica oleracea L. var. italica

In this study, antioxidant activities of aqueous and ethanolic extracts of Brassica oleracea L. var. italica were investigated. The antioxidant properties of both extracts of Brassica oleracea L. var. italica were evaluated using different antioxidant tests, including 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, superoxide radical scavenging, inhibition of microsomal lipid peroxidation, reduction of power, and metal ion chelating activities. Inhibition of superoxide scavenging by aqueous and ethanolic extracts showed an IC50 of 0.93 and 0.25 mg/ml, respectively. Metal ion chelation showed an IC50 of 0.35 mg/ml of both the extracts and was equipotent to positive control, ethylenediamine tetra-acetic acid. The ethanolic extract of Brassica oleracea L. var. italica exhibited higher antioxidant activity in DPPH radical and superoxide anion scavenging than that of aqueous extract. The results obtained in the in vitro models clearly suggest that, Brassica oleracea L. var. italica is a natural source for antioxidants, which could serve as a nutraceutical with potential applications in reducing the level of oxidative stress and related health benefits. However, comprehensive studies need to be conducted to ascertain the in vivo safety of such extracts in experimental animal models.

Inhibition of microsomal lipid peroxidation and protein oxidation by extracts from plants used in Bamun folk medicine (Cameroon) against hepatitis.

The antioxidant activities of 53 medicinal plants used in Bamun folk medicine for the management of jaundice and hepatitis were investigated. The studies were done using rat hepatic microsomes for lipid peroxidation and bovine serum albumin (BSA) for carbonyl group formation. Silymarine was used as reference compound. Fifteen different extracts were effective at a dose of 200 microg/ml in both experiments. Specifically, 25 extracts inhibited lipid peroxidation initiated non-enzymatically by ascorbic acid while 18 inhibited peroxidation as determined by reduced Nicotinamide Adenine Dinucleotide Phosphate (NADPH). The inhibitory concentration 50 (IC(50)) of 23 different plant extracts was lower than 200 microg/ml in the microsomal lipid peroxidation inhibition study. Fifteen of the 23 extracts were active in preventing protein oxidation by inhibiting the formation of the carbonyl group on BSA with an IC(50) value less than 200 microg/ml. The results suggest that the antioxidant activity of the extracts, may be due to their ability to scavenge free radicals involved in microsomal lipid peroxidation or in protein oxidation. These biochemical processes are involved in the aetiology of toxic hepatitis.

Antioxidant, antiinflammatory and antiinvasive activities of biopolyphenolics

A large number of polyphenolic and heterocyclic compounds, i.e. 4-methylcoumarins, 4methylthionocoumarins, xanthones, pyrazoles, pyrazolylacrylonitriles, flavones and isoflavones have been tested for their antioxidant activity towards NADPH-catalysed liver-microsomal lipid peroxidation with a view to establish their structure-activity relationship. Inhibition of microsomal lipid peroxidation by 7,8-dihydroxy-4-methylcoumarin (DHMC, 2) and 7,8diacetoxy-4-methylcoumarin (DAMC, 3) was intriguing. We also found that dihydroxy and diacetoxy derivatives of 4-methylthionocoumarin were more potent in comparison to the corresponding coumarin derivatives in inhibiting TNF-α induced expression of ICAM-1. The effect of nine different xanthones has been examined on the modulation of cytokine-induced expression of ICAM-1 in human endothelial cells. 1,4-Dihydroxyxanthone (10) showed enhanced antioxidant activity as well as the inhibition of the expression of cell adhesion molecules, such as ICAM-1, VCAM-1 and E-selectin on endothelial cells in a concentration and time dependent manner. Antioxidant activity of different pyrazoles and pyrazolylacrylonitriles and antiinvasive activity of flavones and isoflavones against solid tumors have also been studied.

Antioxidant activity of South African red and white cultivar wines and selected phenolic compounds: In vitro inhibition of microsomal lipid peroxidation

In vitro inhibition of microsomal lipid peroxidation (MLP) by the major South African red (Cabernet Sauvignon, Ruby Cabernet, Pinotage, Shiraz, Merlot) and white (Sauvignon blanc, Chenin blanc, Chardonnay, Colombard) commercial cultivar wines is presented for the first time. Of the red wines, Merlot was the most effective MLP inhibitor, with Ruby Cabernet and Pinotage being the least effective. Of the white wines, Chenin blanc and Chardonnay were the least and most effective MLP inhibitor, respectively. The mean antioxidant potencies (AP) of the red and white wine total phenols were 14.25 and 4.19, respectively. Ascorbic acid, present in some white wines, counteracted their ability to inhibit MLP. Inhibition of MLP significantly ( P<0.001) correlated with the total phenol content of red ( r=0.90) and white ( r=0.73) wines, as well as the flavanol content ( r=0.88) of red wines and the flavanol ( r=0.79) and tartaric acid ester ( r=0.73) contents of white wines. The MLP inhibitory activities of selected flavonoids were in the order: Quercetin > procyanidin B3 > malvidin > cyanidin ≈ (−)-epicatechin > (+)-catechin ≈ delphinidin.

Decreased oxidative stress in patients with ulcerative colitis supplemented with fish oil ω-3 fatty acids

Objective The potential pathogenicity of free radicals may have a pivotal role in ulcerative colitis. Fish oil ω-3 fatty acids exert anti-inflammatory effects on patients with ulcerative colitis (UC), but the precise mechanism of the action of fish oil on oxidative stress is still controversial. The aim of the present work was to verify the blood oxidative stress in patients with UC and determine whether the association of sulfasalazine to fish oil ω-3 fatty acids is more effective than isolated use of sulfasalazine to reduce the oxidative stress. Methods Nine patients (seven female and two male; mean age = 40 ± 11 y) with mild or moderate active UC were studied in a randomized crossover design. In addition to their usual medication (2 g/d of sulfasalazine), they received fish oil ω-3 fatty acids (4.5 g/d) or placebo for 2-mo treatment periods that were separated by 2 mo, when they only received sulfasalazine. Nine healthy individuals served as control subjects to study the oxidative stress status. Disease activity was assessed by laboratory indicators (C-reactive protein, α 1-acid glycoprotein, α 1-antitrypsin, erythrocyte sedimentation rate, albumin, hemoglobin, and platelet count), sigmoidoscopy, and histology scores. Analysis of oxidative stress was assessed by plasma chemiluminescence and erythrocyte lipid peroxidation, both induced by tert butyl hydroperoxide (t-BuOOH) and by plasma malondialdehyde. Antioxidant status was assayed by total plasma antioxidant capacity (TRAP) and microsomal lipid peroxidation inhibition (LPI). Superoxide dismutase (SOD) and catalase erythrocyte enzymatic activities were also determined. Results No significant changes were observed in any laboratory indicator or in the sigmoidoscopy or histology scores, with the exception of erythrocyte sedimentation rate, which decreased with both treatments. Oxidative stress was demonstrated by significant decreases in TRAP and LPI levels, increased chemiluminescence induced by t-BuOOH, and higher SOD activity in patients with UC. Treatment with fish oil ω-3 fatty acids reverted the chemiluminescence induced by t-BuOOH and LPI to baseline levels but that did not occur when patients received only sulfasalazine. Levels of plasma malondialdehyde, erythrocyte lipid peroxidation, and catalase were not different from those in the control group. Conclusions The results indicated that plasma oxidative stress occurs in patients with UC, and there was a significant decrease when the patients used sulfasalazine plus fish oil ω-3 fatty acids. However, there was no improvement in most laboratory indicators, sigmoidoscopy, and histology scores. The results suggested that ω-3 fatty acids may act as free radical scavengers protecting the patients against the overall effect of oxidative stress.

Inhibition of Rat Liver Microsomal NADPH Cytochrome P450 Reductase by Glutathione and Glutathione Disulfide

Previously we have demonstrated inhibition of lipid peroxidation by reduced glutathione (GSH) in rat liver microsomes that is dependent upon the presence of α-tocopherol (α-TH) in the membranes. Glutathione disulfide (GSSG) potentiated the inhibitory effect of GSH in an enzymatic (NADPH-dependent) lipid peroxidation system in rat liver microsomes; however, inhibition by GSH + GSSG is independent of α-TH. When we repeated these experiments with a non-enzymatic system (ascorbate/ADP) to stimulate lipid peroxidation, GSSG did not potentiate the inhibitory effect of GSH. To delineate the mechanism of inhibition of microsomal lipid peroxidation by GSH + GSSG, we examined the effects of these compounds on cytochrome P-450 reductase (EC 1.6.2.4), an important component of the NADPH-dependent enzymatic lipid peroxidation system. It was observed that GSH alone caused about 25% and 21% inhibition of reductase activity in crude microsomes and partially purified enzyme preparations, respectively. There was no inhibition of reductase activity by GSSG alone in either crude microsomes or partially purified enzyme preparations. However, when added together, GSH and GSSG enhanced the inhibition of reductase activity in crude microsomes and partially purified enzyme by 39% and 56%, respectively. We speculate that one possible mechanism for the inhibition of NADPH-dependent lipid peroxidation by GSH + GSSG is, in part, due to inhibition of NADPH cytochrome P-450 reductase, thus affecting the initiation phase of lipid peroxidation.

Inhibition of microsomal lipid peroxidation by baicalein: a possible formation of an iron-baicalein complex.

Baicalein decreased the production of thiobarbituric acid reactive substances, the rate of oxygen consumption and iron reduction in the reaction system of ascorbic acid with FeCl3. Superoxide dismutase, catalase and hydroxyl radical scavengers had no significant effect. Iron-chelators had an inhibitory effect similar to that of baicalein. The production of thiobarbituric acid reactive substances of baicalein-treated microsomes obtained by centrifugation after incubation with baicalein was not observed in the reaction system, but was stimulated by adding iron with increases in concentration. The amount of bound iron to microsomal membranes increased by increasing both the concentration of baicalein and iron. The amount of baicalein bound to microsomal membranes increased with increasing concentration of added baicalein. These results suggest that baicalein bound to microsomal membranes inhibits lipid peroxidation by formating an iron-baicalein complex.

The effects of glutathione on protein thiols and α-tocopherol in rat liver microsomes following storage and during NADPH-dependent lipid peroxidation

Liver microsomes from rats fed a diet supplemented with vitamin E (+E) were stored at 2°C in Tris buffers containing 5.0 mM reduced glutathione (GSH), GSH + 2.5 mM glutathione disulfide (GSSG) or no additions for up to 4 days. Thoroughly washed microsomes were then subjected to NADPH-dependent lipid peroxidation assays containing glutathione in combinations of its reduced and oxidized forms. These experiments demonstrated the presence of at least two glutathione-dependent factors in the inhibition of microsomal lipid peroxidation in rat liver. The first was quite labile and required GSH for its expression. The second factor was comparatively stable and showed a marked potentiation of GSH by GSSG. Changes in membrane protein thiols (PrSH) and α-tocopherol (α-TH) were also determined during storage of the microsomes in the various buffers and during assays of lipid peroxidation. Total membrane PrSH was higher in native (freshly prepared) liver microsomes from +E rats than in microsomes from rats fed a diet deficient in vitamin E (−E). The addition of GSH or GSH + GSSG diminished the extent of PrSH depletion during storage in both +E and −E microsomes, but the protective effect was greater for the +E microsomes. The loss of α-TH was also reduced in microsomes stored in buffers containing either GSH or GSH + GSSG compared to Tris buffer alone. Changes in PrSH during lipid peroxidation were pronounced in the absence of GSH or GSH + GSSG and were independent of the α-TH content of the membranes. Addition of either GSH or GSH + GSSG to the assays markedly reduced the depletion of PrSH during lipid peroxidation. For +E microsomes, the depletion of PrSH and α-TH in the presence or absence of GSH were parallel. The rate and extent of this depletion, however, were much greater in the absence of GSH. These data demonstrated that membrane α-TH was not essential in maintaining PrSH in the absence of GSH once lipid peroxidation was initiated. It also appeared that the potentiating effect of GSH by GSSG on the inhibition of rat liver microsomal lipid peroxidation, which was also resistant to inactivation during storage, was not through selective maintenance of α-TH or general sparing of PrSH.

In vitro and in vivo inhibition of microsomal lipid peroxidation by MA-631

Excess free radicals are linked to many diseases, including aging, atherosclerosis, and cancer. Previously, we have shown that MA-631 (a complex herbal mixture) inhibits human low-density lipoprotein (LDL) oxidation and may play a role in prevention of atherosclerosis. In this study we further evaluated the in vivo and in vitro antioxidant activity of MA-631. Both the alcoholic and aqueous extracts of MA-631 inhibited enzymatic- and nonenzymatic-induced rat liver microsomal lipid peroxidation in a concentration-dependent manner. The thiobarbituric acid-reactive substances (TBARS) values (nmol malondialdehyde (MDA)/mg microsomal protein) were 1.43 ± 0.18 for microsomes alone (baseline for enzymatic system), 19.63 ± 2.50 for microsomes + reduced nicotinamide adenine dinucleotide phosphate (NADPH) (oxidation without inhibitor), 9.89 ± 1.41 for heated microsomes (baseline for nonenzymatic system), and 27.15 ± 0.08 for microsomes + ascorbate (oxidation without inhibitor). The concentrations (μg/2 ml) of MA-631 which produced 50% inhibition (IC 50) of enzymatic- and non-enzymatic-induced lipid peroxidation were 15.2 ± 2.0 and 17.0 ± 2.6, respectively for the aqueous extract, and 4.3 ± 0.8 and 6.4 ± 1.2, respectively, for the alcoholic extract. A 2% MA-631 (w : w) supplemented diet fed to rats for three weeks inhibited in vivo, toluene-induced microsomal lipid peroxidation in the brain, kidney, liver, and heart. These results imply that MA-631 may be useful in the prevention of free radical-linked diseases.

Inhibition of in vitro lipid peroxidation by 21-aminosteroids evidence for differential mechanisms

In a previous report (Ryan and Petry, Arch Biochem Biophys 300: 699–704, 1993), the effects of two 21-aminosteroids (U-74500A and U-74006F) on the oxidation and reduction of iron in a buffer/organic solvent system were investigated. In those studies, U-74500A was found to be an efficient iron reductant and potential iron chelator, whereas U-74006F had little effect on iron redox chemistry. As an extension of those studies, we now report the effects of U-74006F and U-74500 A on lipid peroxidation in systems that are dependent upon iron oxidation/reduction. In liposomes, U-74500A inhibited ADP:Fe(II)-dependent lipid peroxidation in a concentration-dependent manner, whereas U-74006F was minimally effective in this system. The mechanism of U-74500A-dependent inhibition probably involved interactions with iron, as iron oxidation was inhibited in the presence of this compound. No effects on iron oxidation were observed in the presence of U-74006F. Addition of Ferrozine® to liposomal incubation mixtures indicated that at least two iron pools were present in samples containing U-74500A, one immediately bound by Ferrozine®, and another that was bound more slowly. Furthermore, ADP:Fe(III)/ascorbate-dependent lipid peroxidation was blocked completely by U-74500A, presumably by formation of a redox inert complex upon reduction of the iron. U-74500A partially protected ADP:Fe(II) from oxidation by H 2O 2 and lipid hydroperoxides, indicating that the U-74500A:iron complex was stable in the presence of biologically relevant oxidants. U-74006F did not markedly affect iron oxidation or reduction when incorporated into phospholipid liposomes. In microsomal lipid peroxidation systems containing ADP:Fe(III) and NADPH, both U-74500A and U-74006F inhibited lipid peroxidation. U-74006F-dependent inhibition of microsomal lipid peroxidation was dependent on both NADPH and Fe(III). Further, it was enhanced when U-74006F was allowed to preincubate in this system prior to iron addition. Preincubation of U-74006F with microsomes, NADPH, and ADP:Fe(III) produced several metabolites detectable by HPLC. These results suggest that U-74500A inhibits lipid peroxidation by directly affecting iron redox chemistry, whereas U-74006F-mediated inhibition is enhanced by preincubation with a metabolically competent microsomal system.

Involvement of vitamin E and protein thiols in the inhibition of microsomal lipid peroxidation by glutathione.

Iron-ascorbate stimulated lipid peroxidation in rat liver microsomes can be inhibited by glutathione (GSH). The role of protein thiols and vitamin E in this process was studied in liver microsomes isolated from rats fed diets either sufficient or deficient in vitamin E and incubated at 37 degrees C under 100% O2. Lipid peroxidation was induced by adding 400 microM adenosine 5'-triphosphate, 2.5 to 20 microM FeCl3, and 450 microM ascorbic acid. One mL of the incubation mixture was removed at defined intervals for the measurement of thiobarbituric acid reactive substances (TBARS), protein thiols and vitamin E. In vitamin E sufficient microsomes, the addition of GSH enhanced the lag time prior to the onset of maximal TBARS accumulation and inhibited the loss of vitamin E. Treatment of these microsomes with the protein thiol oxidant diamide resulted in a 56% loss of protein thiols, but did not significantly change vitamin E levels. However, diamide treatment abolished the GSH-mediated protection against TBARS formation and loss of vitamin E during ascorbate-induced peroxidation. Liver microsomes isolated from rats fed a vitamin E deficient diet contained 40-fold less vitamin E and generated levels of TBARS similar to vitamin E sufficient microsomes at a 4-fold lower concentration of iron. GSH did not affect the lag time prior to the onset of maximal TBARS formation in vitamin E deficient microsomes although total TBARS accumulation was inhibited. Similar to what was previously found in vitamin E sufficient microsomes [Palamanda and Kehrer, (1992) Arch. Biochem. Biophys. 293, 103-109], GSH prevented the loss of protein thiols in vitamin E deficient microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Antioxidant effect of manganese

The antioxidant effects of manganese and other transition metals were studied as the inhibition of microsomal lipid peroxidation and crocin bleaching by peroxyl radicals. The peroxyl radical scavenging capacity was measured by competition kinetics analysis. While Zn(II), Ni(II), and Fe(II) were almost completely ineffective, Mn(II) and Co(II) showed a free radical scavenging capacity, exhibiting relative rate constant ratios respectively of 0.513 and 0.287. This indicates that Mn(II) is by far the most active. Therefore, the chain-breaking antioxidant capacity of Mn(II) seems to be related to the rapid quenching of peroxyl radicals according to the reaction R-OO · + Mn(II) + H + → ROOH + Mn(III). The antioxidant mechanism is discussed considering the different reduction potentials of the examined cations.