Antioxidant activities of cultured Armillariella mellea

This study aimed to evaluate the antioxidant activities of a cultured medicinal fungus--Armillariella mellea (Vahl. ex Fr.) Karst. (AM). Three antioxidant assay systems, namely cytochrome c, xanthine oxidase inhibition and FeCl2-ascorbic acid stimulated lipid peroxidation in rat tissue homogenate tests, were used. Total flavonoid and phenol contents of AM extracts were also analyzed. Results showed that both aqueous (AM-H2O) and ethanolic (AM-EtOH) extracts of solid state cultured AM showed antioxidant activities in a concentration-dependent manner. At concentrations 1-100 microg/ml, the free radical scavenging activity was 73.7-92.1% for AM-H2O, and 60.0-90.8% for AM-EtOH. These extracts also showed an inhibitory effect on xanthine oxidase activity, but with a lesser potency (IC50 - 9.17 microg/ml for AM-H2O and 7.48 microg/ml for AM-EtOH). In general, AM-H2O showed a stronger anti-lipid peroxidation activity on different rat's tissues than AM-EtOH. However, both AM extracts displayed a weak inhibitory effect on lipid peroxidation in plasma. Interestingly, the anti-lipid peroxidation activity of AM-H2O (IC50 - 6.66 microg/ml) in brain homogenate was as good as alpha-tocopherol (IC50 - 5.42 microg/ml). AM-H2O (80.0 mg/g) possessed a significant higher concentration of total flavonoids than AM-EtOH (30.0 mg/g), whereas no difference was noted in the total phenol content between these two extracts. These results conclude that AM extracts possess potent free radical scavenging and anti-lipid peroxidation activities, especially the AM-H20 in the brain homogenate.     

Design and synthesis of 2,6-diprenyl-4-iodophenol TX-1952 with a novel and potent anti-peroxidative activity

The structure-based elucidation of 2,4,6-tri-substituted phenols for their antioxidative and anti-peroxidative effects has been investigated using TX-1952 (2,6-diprenyl-4-iodophenol), TX-1961, TX-1980, BTBP and BHT. In the inhibition of mitochondrial lipid peroxidation, the inhibitory activity of 2,6-di-tert-butyl-4-bromophenol (BTBP) (IC(50)=0.17 microM) was twice as high as that of 2,6-di-tert-butyl-4-methylphenol (BHT) (IC(50)=0.31 microM). This result shows that the 4-halogen group increases inhibitory activity for mitochondrial lipid peroxidation. Besides, TX-1952 (IC(50)=0.60 microM) was the highest inhibitor among 2,6-diprenyl-4-halophenols, followed by TX-1961 (IC(50)=0.93 microM) and TX-1980 (IC(50)=1.2 microM). In 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging experiments, the activity of TX-1952 (IC(0.200)=53.1 microM) was lower than that of BHT (IC(0.200)=33.7 microM) and BTBP (IC(0.200)=16.0 microM), but TX-1952 and BHT showed the same HOMO energy (-8.991 eV). These results suggest that the two prenyl groups at ortho position hinder the phenolic hydrogen abstraction by DPPH radical. These findings demonstrated that TX-1952 was a novel and potent inhibitor for lipid peroxidation.     

Structural requirements of flavonoids for inhibition of antigen-Induced degranulation,TNF-alpha and IL-4 production from RBL-2H3 cells

To clarify the structure-activity relationships of flavonoids for antiallergic activity, the inhibitory effects of various flavonoids on the release of beta-hexosaminidase, as a marker of degranulation of RBL-2H3 cells, were examined. Among them, luteolin (IC(50)=3.0 microM), diosmetin (2.1 microM), and fisetin (3.0 microM) were found to show potent inhibitory activity, and the results suggested the following structural requirements of flavonoids: (1) the 2-3 double bond of flavones and flavonols is essential for the activity; (2) the 3- or 7-glycoside moiety reduced the activity; (3) as the hydroxyl groups at the 3'-, 4'-, 5-, 6-, and 7-positions increased in number, the inhibitory activities become stronger; (4) the flavonols with a pyrogallol type moiety (the 3',4',5'-trihydroxyl groups) at the B ring exhibited less activity than those with a phenol type moiety (the 4'-hydroxyl group) or catechol type moiety (the 3',4'-dihydroxyl groups) at the B ring; (5) the activities of flavones were stronger than those of flavonols; and (6) methylation of flavonols at the 3-position reduced the activity. However, (7) several flavones and flavonols with the 4'- and/or 7-methoxyl groups did not obey rules (3), (4), and (5). In addition, several flavonoids, that is apigenin, luteolin, diosmetin, fisetin, and quercetin, inhibited the antigen-IgE-mediated TNF-alpha and IL-4 production from RBL-2H3 cells, both of which participate in the late phase of type I allergic reactions.     

Quantitative structure toxicity relationships for phenols in isolated rat hepatocytes

Quantitative structure toxicity relationship (QSTR) equations were obtained to predict and describe the cytotoxicity of 31 phenols using logLD(50) as a concentration to induce 50% cytotoxicity of isolated rat hepatocytes in 2 h and logP as octanol/water partitioning: logLD(50) (microM)=-0.588(+/-0.059)logP+4.652(+/-0.153) (n=27, r(2)=0.801, s=0.261, P<1 x 10(-9)). Hydroquinone, catechol, 4-nitrophenol, and 2,4-dinitrophenol were outliers for this equation. When the ionization constant pK(a) was considered as a contributing factor a two-parameter QSTR equation was derived: logLD(50) (microM)=-0.595(+/-0.051)logP+0.197(+/-0.029)pK(a)+2.665(+/-0.281) (n=28, r(2)=0.859, s=0.218, P<1 x 10(-6)). Using sigma+, the Brown variation of the Hammet electronic constant, as a contributing parameter, the cytotoxicity of phenols towards hepatocytes were defined by logLD(50) (microM)=-0.594(+/-0.052)logP-0.552(+/-0.085)sigma+ +4.540(+/-0.132) (n=28, r(2)=0.853, s=0.223, P<1 x 10(-6)). Replacing sigma+ with the homolytic bond dissociation energy (BDE) for (X-PhOH+PhO.-->X-PhO.+PhOH) led to logLD(50) (microM)=-0.601(+/-0.066)logP-0.040(+/-0.018)BDE+4.611(+/-0.166) (n=23, r(2)=0.827, s=0.223, P<0.05). Hydroquinone, catechol and 2-nitrophenol were outliers for the above equations. Using redox potential and logP led to a new correlation: logLD(50) (microM)=-0.529(+/-0.135)logP+2.077(+/-0.892)E(p/2)+2.806(+/-0.592) (n=15, r(2)=0.561, s=0.383, P<0.05) with 4-nitrophenol as an outlier. Our findings indicate that phenols with higher lipophilicity, BDE, or sigma+ values or with lower pK(a) and redox potential were more toxic towards hepatocytes. We also showed that a collapse of hepatocyte mitochondrial membrane potential preceded the cytotoxicity of most phenols. Our study indicates that one or a combination of mechanisms; i.e. mitochondrial uncoupling, phenoxy radicals, or phenol metabolism to quinone methides and quinones, contribute to phenol cytotoxicity towards hepatocytes depending on the phenol chemical structure.     

Characterization of the phenolic constituents in Mauritian endemic plants as determinants of their antioxidant activities in vitro

The phenolic constituents of Mauritian endemic plants from the Rubiaceae and Myrtaceae family were assessed and correlated with their potential antioxidant activities in vitro. The antioxidant activities of the plant extracts ranged from 0.27 to 1.49mmol Trolox equivalent/g FW and from 0.20 to 1.39mmol Fe(II) equivalent/g FW in the TEAC and FAP assays, respectively, with Syzygium commersonii showing the highest activity in these two systems. Eugenia orbiculata and all the Syzygium species were effective scavengers of hypochlorous acid while Monimiastrum acutisepalum was the most potent inhibitor of deoxyribose degradation. The plant extracts inhibited microsomal lipid peroxidation with low IC(50)s ranging from 0.02 to 1.75mgFW/mL when reaction was initiated with Fe(3+)/ascorbate and from 0.093 to 1.55mgFW/mL in the AAPH-dependent lipid peroxidation. The potential prooxidant nature of the plant extracts was compared with ascorbate (250microM) using copper-phenanthroline assay. The plant extracts at concentrations up to 5gFW/L were not prooxidant. However, Myonima nitens, Syzygium commersonii, Syzygium glomeratum and Syzygium mauritianum at concentrations of 10gFW/L had potency approaching 50% of the prooxidant activity of ascorbic acid in vitro, suggesting relative safeties. The total phenolics influenced the antioxidant activities in the TEAC, FRAP and HOCl scavenging assays whereas a negative correlation was observed with the deoxyribose assay. The high levels of polyphenolic compounds and the significant antioxidant activities of these Rubiaceae and Myrtaceae plant family make them suitable candidates as prophylactic agent.     

Novel 4,5-diaryl-3-hydroxy-2(5H)-furanones as anti-oxidants and anti-inflammatory agents

In order to study the effect of phenol moieties on biological activities of ascorbic acid derivatives, we synthesized 13 novel 4,5-diaryl-3-hydroxy-2(5H)-furanones 5a-m with various substitution patterns. Compound 5 g bearing a 2,3-dihydroxy phenyl ring on the 5-position of the heterocycle appeared to be the most powerful anti-oxidant furanone with reducing activity against DPPH (IC(50)=10.3 microM), superoxide anion quenching capacity (IC(50)=0.187 mM) and lipid peroxidation inhibitory effect (IC(50)=0.129 mM). To ascertain determinant molecular features for anti-oxidant activities, structure-activity relationships were studied. Lipophilicity and molecular parameters related to electron distribution and structure (difference in heats of formation between the compound and its radical or its cation radical, energy of the highest occupied molecular orbital, HOMO) were found to correlate with the anti-oxidant action of compounds 5 in the different tests used. Oxygen-derived free radicals are known to contribute to inflammatory disorders; therefore we have investigated effects of compounds 5 in two models of inflammation: phorbol ester-induced ear edema in mice (TPA-test) and carrageenan-induced paw edema in rat. At 100 mg/kg ip in the TPA-test, the anti-inflammatory activity of compounds 5 was potent compared with that of indomethacin and ketorolac and all the results suggested a cyclooxygenase inhibition in the emergence of such properties. The combined pharmacological actions of compounds 5 associated with a favorable therapeutic index prompt with interesting perspectives for their use in heart and brain disorders as well as in inflammatory diseases.     

Novel inhibitors of neuronal nitric oxide synthase with potent antioxidant properties

A series of hybrid compounds possessing an nNOS pharmacophore linked to an antioxidant fragment has been synthesized. Among them, compound 8d, a propofol derivative, displayed the greatest dual potencies against nNOS (IC(50)=0.12 microM) and lipid peroxidation (IC(50)=0.4 microM) accompanied with e/nNOS selectivity (67.5). This shows that nNOS was able to accommodate very bulky groups such as di-tert-butyl or di-iso-propyl phenol in its active site.     

Biosensor for the determination of phenols based on cross-linked enzyme crystals (CLEC) of laccase

Cross-linked enzyme crystals (CLECs) are a versatile form of biocatalyst that can also be used for biosensor application. Laccase from Trametes versicolor (E.C.1.10.3.2) was crystallized, cross-linked and lyophilized with beta-cyclodextrin. The CLEC laccase was found to be highly active towards phenols like 2-amino phenol, guaiacol, catechol, pyrogallol, catechin and ABTS (non-phenolic). The CLEC laccase was embedded in 30% polyvinylpropylidone (PVP) gel and mounted into an electrode to make the sensor. The biosensor was used to detect the phenols in 50-1000 micromol concentration level. Phenols with lower molecular weight such as 2-amino phenol, catechol and pyrogallol gave a short response time where as the higher molecular weight substrates like catechin and ABTS had comparatively a long response time. The optimum pH of the analyte was 5.5-6.0 when catechol was used as substrate. The CLEC laccase retained good activity for over 3 months.     

Antioxidant properties of di-tert-butylhydroxylated flavonoids

Epidemiological evidence suggests an inverse relationship between dietary intake of flavonoids and cardiovascular risk. The biological activities of flavonoids are related to their antioxidative effects, but they also can be mutagenic, due to the prooxidant activity of the catechol pattern. To prevent these problems, we synthesized new flavonoids where one or two di-tert-butylhydroxyphenyl (DBHP) groups replaced catechol moiety at position 2 of the benzopyrane heterocycle. Two DBHP moieties can also be arranged in an arylidene structure or one DBHP fixed on a chalcone structure. Position 7 on the flavone and arylidene or position 4 on the chalcone was substituted by H, OCH(3), or OH. New structures were compared with quercetin and BHT in an LDL oxidation system induced by Cu(II) ions. Arylidenes and chalcones had the best activities (ED(50) = 0.86 and 0.21) compared with vitamin E, BHT, and quercetin (ED(50) = 10.0, 7. 4, and 2.3 microM). Activity towards stable free radical 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) was measured by log Z and ECR(50) parameters. Synthesized flavones proved to be poor DPPH radical scavengers, the activity increasing with the number of DBHP units. In contrast, arylidenes and chalcones were stronger DPPH radical scavengers (log Z > 3, 0.3 < ECR(50) < 2.12) than BHT (log Z = 0.75, ECR(50) = 12.56) or quercetin (log Z = 2.76, ECR(50) = 0.43). Unlike quercetin, synthesized compounds neither chelated nor reduced copper, proving that these new flavonoids had no prooxidant activity in vitro.     

Substituted N-(3,5-dichlorobenzenesulfonyl)-L-prolyl-phenylalanine analogues as potent VLA-4 antagonists

A series of substituted N-(3,5-dichlorobenzenesulfonyl)-L-prolyl- and alpha-methyl-L-prolyl-phenylalanine derivatives was prepared as VLA-4/VCAM antagonists. The compounds showed excellent potency with a wide variety of neutral, polar, electron withdrawing or donating groups on the phenylalanine ring (IC50 approximately 1 nM). Heteroaryl ring substitution for phenylalanine was also well tolerated. Pharmacokinetic studies in rat were performed on a representative set of compounds in both series.     

Cinnamophilin as a novel antiperoxidative cytoprotectant and free radical scavenger

The antioxidant properties of cinnamophilin were evaluated by studying its ability to react with relevant reactive oxygen species, and its protective effect on cultured cells and biomacromolecules under oxidative stress. Cinnamophilin concentration-dependently suppressed non-enzymatic iron-induced lipid peroxidation in rat brain homogenates with an IC50 value of 8.0+/-0.7 microM and iron ion/ADP/ascorbate-initiated rat liver mitochondrial lipid peroxidation with an IC50 value of 17.7+/-0.2 microM. It also exerted an inhibitory activity on NADPH-dependent microsomal lipid peroxidation with an IC50 value of 3.4+/-0.1 microM without affecting microsomal electron transport of NADPH-cytochrome P-450 reductase. Both 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azo-bis(2-amidinopropane) dihydrochloride-derived peroxyl radical tests demonstrated that cinnamophilin possessed marked free radical scavenging capacity. Cinnamophilin significantly protected cultured rat aortic smooth muscle cells (A7r5) against alloxan/iron ion/H2O2-induced damage resulting in cytoplasmic membranous disturbance and mitochondrial potential decay. By the way, cinnamophilin inhibited copper-catalyzed oxidation of human low-density lipoprotein, as measured by fluorescence intensity and thiobarbituric acid-reactive substance formation in a concentration-dependent manner. On the other hand, it was reactive toward superoxide anions generated by the xanthine/xanthine oxidase system and the aortic segment from aged spontaneously hypertensive rat. Furthermore, cinnamophilin exerted a divergent effect on the respiratory burst of human neutrophil by different stimulators. Our results show that cinnamophilin acts as a novel antioxidant and cytoprotectant against oxidative damage.     

Protective effect of unsymmetrical dichalcogenide, a novel antioxidant agent, in vitro and an in vivo model of brain oxidative damage

Unsymmetrical dichalcogenides, a class of organoselenium compounds, were screened for antioxidant activity in rat brain homogenates in vitro. Unsymmetrical dichalcogenides (1-3) were tested against lipid peroxidation induced by sodium nitroprusside (SNP) or malonate, and reactive species (RS) production induced by sodium azide in rat brain homogenates. Compounds 1 (without a substituent at the phenyl group), 2 (chloro substituent at the phenyl group bounded to the sulfur atom) and 3 (chloro substituent at the phenyl group bounded to the selenium atom) protected against lipid peroxidation induced by SNP. The IC50 values followed the order 3<2<1. Lipid peroxidation induced by malonate was also reduced by dichalcogenides 1, 2 and 3. The IC50 values were 3相似文献   

Purification and characterization of antioxidant peptide from hoki (Johnius belengerii) frame protein by gastrointestinal digestion

To extract antioxidant peptide from hoki frame protein hydrolysate (APHPH), we employed six proteases (pepsin, trypsin, papain, alpha-chymotrypsin, Alcalase and Neutrase) for enzymatic hydrolysis, and the antioxidant activities of their hydrolysates were investigated using both lipid peroxidation inhibition assay and free radical scavenging assay by electron spin resonance spin-trapping technique. Among hydrolysates, peptic hydrolysate, having the highest antioxidant activity, further separated into four groups using ultrafiltration membranes and purified consecutive chromatographic methods. Finally, the purified peptide had a molecular mass of 1801 Da, and amino acid sequence was identified as Glu-Ser-Thr-Val-Pro-Glu-Arg-Thr-His-Pro-Ala-Cys-Pro-Asp-Phe-Asn. APHPH inhibited lipid peroxidation higher than that of alpha-tocopherol as positive control and efficiently quenched different sources of free radical: 1,1-diphenyl-2-pycryl-hydrazyl (IC(50)=41.37 microM), hydroxyl (IC(50)=17.77 microM), peroxyl (IC(50)=18.99 microM) and superoxide radicals (IC(50)=172.10 microM). Furthermore, APHPH decreased t-butylhydroperoxide-induced cytotoxicity on human embryonic lung fibroblasts and efficiently protected free-radical-induced DNA damage.     

Structural requirements of flavonoids for nitric oxide production inhibitory activity and mechanism of action

To clarify the structure-activity relationships of flavonoids for nitric oxide (NO) production inhibitory activity, we examined the inhibitory effects of 73 flavonoids on NO production in lipopolysaccharide-activated mouse peritoneal macrophages. Among those flavonoids, apigenin (IC(50)=7.7 microM), diosmetin (8.9 microM), and tetra-O-methylluteolin (2.4 microM), and hexa-O-methylmyricetin (7.4 microM) were found to show potent inhibitory activity, and the results suggested the following structural requirements of flavonoids: (1) the activities of flavones were stronger than those of corresponding flavonols; (2) the glycoside moiety reduced the activity; (3) the activities of flavones were stronger than those of corresponding flavanones; (4) the flavones and flavonols having the 4'-hydroxyl group showed stronger activities than those lacking the hydroxyl group at the B ring and having the 3',4'-dihydroxyl group; (5) the flavonols having the 3',4'-dihydroxyl group (catechol type) showed stronger activities than those having the 3',4',5'-trihydroxyl group (pyrogallol type); (6) the 5-hydroxyl group tended to enhance the activity; (7) methylation of the 3-, 5-, or 4'-hydroxyl group enhanced the activity; (8) the activities of isoflavones were weaker than those of corresponding flavones; (9) methylation of the 3-hydroxyl group reduced the cytotoxicity. In addition, potent NO production inhibitors were found to inhibit induction of inducible nitric oxide synthase (iNOS) without iNOS enzymatic inhibitory activity.     

Synthesis,structure-activity relationship and in vitro evaluation of coelenterazine and coelenteramine derivatives as inhibitors of lipid peroxidation

Coelenterazine (2-p -hydroxybenzyl-6-(3'-hydroxyphenyl)-8-benzyl-3,7-dihydroimidazolo[1,2-a]pyrazin-3-one, CLZn) and coelenteramine (2-amino-3-benzyl-5-(4'-hydroxyphenyl)-1,4-pyrazine CLM), first described as luciferin and etioluciferin, respectively, of bioluminescent systems in marine organisms are endowed with antioxidant properties. This study was aimed at understanding the structural basis of their chain-breaking properties and at designing new compounds with improved antioxidative properties. For this, a series of 2-amino-1,4-pyrazine derivatives and their related imidazolopyrazinones were synthesised and examined for their capacity to inhibit lipid peroxidation in linoleate micelles subjected to the peroxidizing action of AAPH. Structure-activity relationship studies indicated that the reduction of the peroxidation rate by CLM is mainly determined by the concomitant presence of 5-p-hydroxyphenyl and 2-amino groups in para position. The lipophilic character of substituents also affected this effect. All imidazolopyrazinones induced a lag-time before the onset of the peroxidation process. The hetero-bicyclic imidazolopyrazinone moiety appears as the main contributor to this activity while phenol groups play little role in it. On the other hand, phenol groups were required for the reduction of the peroxidation rate after the lag-phase. The introduction of a supplementary p-hydroxyphenyl substituent at C₈ position did not increase chain-breaking properties. The substitution of the C₅-p-hydroxyphenyl with a catechol moiety or the introduction of a second amino group on the pyrazine ring yielded the most active compounds, superior to imidazolopyrazinones and reference antioxidants like epigallocatechin gallate, vitamin E and trolox. The strong antioxidant properties of 2,6-diaminopyrazines are not dependent on the presence of hydroxyl groups indicating that their reaction mechanism differs from that of 2-amino-1,4-pyrazine derivatives.     

Free radical scavenging activity of a novel antioxidative peptide purified from hydrolysate of bullfrog skin, Rana catesbeiana Shaw

In the present study, a peptide having antioxidant properties was isolated from bullfrog skin protein, Rana catesbeiana Shaw. Bullfrog skin protein was hydrolyzed using alcalase, neutrase, pepsin, papain, alpha-chymotrypsin and trypsin. Antioxidant activities of respective hydrolysates were evaluated using lipid peroxidation inhibition assay and direct free radical scavenging activity by using electron spin resonance (ESR) spectrometer. Among hydrolysates, alcalase derived hydrolysate exhibited the highest antioxidant activities than those of other enzyme hydrolysates. In order to purity a peptide having potent antioxidant properties, alcalase hydrolysate was separated using consecutive chromatographic methods on a Hiprep 16/10 DEAE FF anion exchange column, Superdex Peptide 10/300 GL gel filtration column and highan octadecylsilane (ODS) C18 reversed phase column. Finally, a potent antioxidative peptide was isolated and its sequence was identified to be LEELEEELEGCE (1487 Da) by Q-TOF ESI mass spectroscopy. This antioxidant peptide from bullfrog skin protein (APBSP) inhibited lipid peroxidation higher than that of alpha-tocopherol as positive control and efficiently quenched different sources of free radicals: DPPH radical (IC(50)=16.1 microM), hydroxyl radical (IC(50)=12.8 microM), superoxide radical (IC(50)=34.0 microM) and peroxyl radical (IC(50)=32.6 microM). Moreover, MTT assay showed that this peptide does not exert any cytotoxicity on human embryonic lung fibroblasts cell line (MRC-5).     

Initiation of membranal lipid peroxidation by activated metmyoglobin and methemoglobin

The interaction of hydrogen peroxide (H2O2) with metmyoglobin (MetMb) led very rapidly to the generation of an active species which could initiate lipid peroxidation. The activity of this prooxidant decreased rapidly during the first minutes, but 50% of its activity remained stable for more than 30 min. In this model system, it was found that small amounts of H2O2 (1-10 microM) could activate MetMb for significant lipid peroxidation. The incubation of the sarcosomal lipids with activated MetMb caused oxygen absorption. No absorption of oxygen was determined in the presence of membrane with MetMb or H2O2 alone. Methemoglobin (MetHb) was also found to be activated by H2O2 and to initiate lipid peroxidation. Membranal lipid peroxidation initiated by activated MetMb was inhibited by several reducing compounds and antioxidants. However, several hydroxyl radical scavengers and catalase failed to inhibit this reaction.     

Melanogenesis inhibitory effects of methanolic extracts of Umbilicaria esculenta and Usnea longissima

The primary objective of this study was to assess the in vitro melanogenesis inhibitory effects of methanolic extracts of the edible and medicinal lichens, Umbilicaria (Gyrophora) esculenta and Usnea longissima. The quantities of the total phenolic compounds of methanolic extract of the two lichen extracts were determined to be 1.46% and 2.62%, respectively. In order to evaluate the antioxidative effects of the extracts, we also measured electron donating abilities (EDA) and lipid peroxidation rates. The EDA values measured by the reduction of 1.1'-diphenyl-2-picrylhydrazyl (DPPH) were 72.8% and 80.7% for the extracts, with SC50 (median scavenging concentration) values of 1.29+/-0.05 mg/ml and 1.03+/-0.06 mg/ml, respectively. The rates of inhibition of lipid peroxidation using linoleic acid were 92.1% and 97.3% for the extracts, with IC50 (median inhibitory concentration) values of 0.57+/-0.05 mg/ml and 0.53+/-0.06 mg/ml, respectively. The inhibitory rates of the extracts against tyrosinase were 67.4% and 84.8%, respectively. The extracts were shown to reduce melanin formation in human melanoma cells. Melanin contents in the samples treated with 0.01% and 0.1% U. esculenta were 47.1% and 31.2%, respectively, and those treated with 0.01% and 0.1% Usnea longissima were 51.1% and 34.9%, respectively, whereas a value of 54.0% was registered when ascorbic acid was utilized as a positive control. In addition to direct tyrosinase inhibition, it was determined that the lichen extracts affected the activity of tyrosinase via the inhibition of tyrosinase glycosylation. As a result, the methanolic extracts of U. esculenta and Usnea longissima evidenced melanogenesis inhibitory effects, which occurred via multiple routes.     

Metalloporphyrins are potent inhibitors of lipid peroxidation

The objectives of these studies were to determine whether metalloporphyrins could inhibit lipid peroxidation, characterize factors that influence their potency and compare their potency to prototypical antioxidants. Lipid peroxidation was initiated with iron and ascorbate in rat brain homogenates and the formation of thiobarbituric acid reactive species was used as an index of lipid peroxidation. Metalloporphyrins were found to be a novel and potent class of lipid peroxidation inhibitors. Inhibition of lipid peroxidation by metalloporphyrins was dependent on the transition metal ligated to the porphyrin, indicating that metal centered redox chemistry was important to the mechanism of their antioxidant activities. Manganese porphyrins with the highest superoxide dismutase (SOD) activities, MnOBTM-4-PyP and MnTM-2-PyP (charges are omitted throughout text for clarity), were the most potent inhibitors of lipid peroxidation with calculated IC50s of 1.3 and 1.0 microM, respectively. These manganese porphyrins were 2 orders of magnitude more potent than either trolox (IC50 = 204 microM) or rutin (IC50 = 112 microM). The potencies of the manganese porphyrins were related not only to their redox potentials and SOD activities, but also to other factors that may contribute to their ability to act as electron acceptors. The broad array of antioxidant activities possessed by metalloporphyrins make them attractive therapeutic agents in disease states that involve the overproduction of reactive oxygen species.