Quinone formation from carcinogenic benzo[a]pyrene mediated by lipid peroxidation in phosphatidylcholine liposomes

Exploring micromycetes biodiversity for screening benzo[a]pyrene degrading potential

Twenty-five strains of filamentous fungi, encompassing 14 different species and belonging mainly to Ascomycetes, were tested for their ability to degrade benzo[a]pyrene (BaP) in mineral liquid medium. The most performing isolates for BaP degradation (200 mg l(-1)) in mineral medium were Cladosporium sphaerospermum with 29 % BaP degradation, i.e., 82.8 μg BaP degraded per day (day(-1)), Paecilomyces lilacinus with 20.5 % BaP degradation, i.e., 58.5 μg BaP day(-1), and Verticillium insectorum with 22.3 % BaP degradation, i.e., 64.3 μg BaP day(-1), after only 7 days of incubation. Four variables, e.g., biomass growth on hexadecane and glucose, BaP solubilization, activities of extracellular- and mycelium-associated peroxidase, and polyethylene glycol degradation, were also studied as selective criteria presumed to be involved in BaP degradation. Among these variables, the tests based on polyethylene glycol degradation and on fungal growth on hexadecane and glucose seemed to be the both pertinent criteria for setting apart isolates competent in BaP degradation, suggesting the occurrence of different mechanisms presumed to be involved in pollutant degradation among the studied micromycetes.

Antioxidant properties of gingerol related compounds from ginger

Ginger (Zingiber officinale Roscoe) shows an antioxidant activity, and we have been engaging to determine the structures of more than 50 antioxidants isolated from the rhizomes of ginger. The isolated antioxidants are divided into two groups; gingerol related compounds and diarylheptanoids. In this study, structure-activity relationship of gingerol related compounds was evaluated. Gingerol related compounds substituted with an alkyl group bearing 10-, 12- or 14-carbon chain length were isolated from the dichloromethane extract of rhizomes using repeated chromatographic techniques. The antioxidant activities of these compounds were evaluated by the following measurements; 1) 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, 2) inhibitory effect on oxidation of methyl linoleate under aeration and heating by the Oil Stability Index (OSI) method, and 3) inhibitory effect on oxidation of liposome induced by 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH). These results suggested that the substituents on the alkyl chain might contribute to both radical scavenging effect and inhibitory effect of autoxidation of oils, while inhibitory effects against the AAPH-induced peroxidation of liposome was somewhat influenced by the alkyl chain length; the antioxidant activity might be due to not only radical scavenging activity of antioxidants but also their affinity of the antioxidants to the substrates.

Antioxidative polyphenols from berries of Pimenta dioica

The ethyl acetate-soluble part of allspice, berries of Pimenta dicica, showed strong antioxidant activity and radical-scavenging activity against 1,1diphenyl-2-picrylhydrazl (DPPH) radical. From the ethyl acetate-soluble part, two new compounds, 5-galloyloxy-3-4-dihydroxypentanoic acid and 5-(5-carboxmethyl-2-oxocyclopenty)3Z-penteny 6-O-galloy-beta-D-glucoside were isolated together with 11 known polyphenols by repeated column chromatography. Their structures were elucidated on the basis of MS and various NMR spectroscopic data. All isolated compounds were evaluated for antioxidative effects on oxidation of methyl linoleate under aeration and heating, anf on peroxidation of liposome induced by 2-2'-azobis-(2-amidinopropane)dihydrocloride (AAPH) as water-soluble initiator along with their radical-scavenging activity against DPPH. Quercetin and its glycoside showed remarkable activity for scavenging DPPH radical and inhibiting peroxidation of liposome. Two new compounds also exhibited strong DPPH radical-scavenging activity and inhibitory effect on the peroxidation od liposome as myricetin.

Antioxidant compounds from the leaves of Peucedanum japonicum thunb

Seventeen compounds were isolated from the n-butanol soluble fraction of the leaves of Peucedanum japonicum Thunb. On the basis of MS and various NMR spectroscopic techniques, the structures of the isolated compounds were determined as isoquercitrin (1), rutin (2), 3-O-caffeoylquinic acid (3), 4-O-caffeoylquinic acid (4), 5-O-caffeoylquinic acid (5), cnidioside A (6), praeroside II (7), praeroside III (8), apterin (9), esculin (10), (R)-peucedanol (11), (R)-peucedanol 7-O-beta-d-glucopyranoside (12), l-tryptophan (13), uracil (14), guanosine (15), uridine (16), and thymidine (17). All compounds except 11 and 12 were isolated for the first time from P. japonicum. Several isolated compounds were quantified by high-performance liquid chromatography analysis. In addition, all isolated compounds were examined for radical scavenging on 1,1-diphenyl-2-picrylhydrazyl radical and for inhibition of oxidation of liposome induced by 2,2'-azobis(2-amidinopropane)dihydrochloride. Compounds 2-5 were found to be the major potent constituents, which contribute to the antioxidant activity of P. japonicum leaves.

Sex-specific biotransformation and detoxification after xenobiotic exposure of primary cultured hepatocytes of European flounder (Platichthys flesus L.)

Sex-specific effects of sublethal concentrations of known effective pro-oxidants such as 100,200 and 400 microM benzo[a]pyrene (B[a]p), 50 microM nitrofurantoin (NF) and 100 microM hydrogen peroxide (H2O2) on biotransformation pathways were studied in isolated hepatocytes of immature female and male European flounder (Platichthys flesus L.). Cell responses were assessed at the level of: (1) stress induction as measured by formation of reactive oxygen species (ROS), mainly superoxide radicals, and induction of cytochrome P450 (CYP450) biotransformation activity; (2) cellular antioxidant defences, both non-enzymatic (reduced glutathione) and enzymatic (DT-diaphorase (DTD) or quinone oxidoreductase, EC 1.6.99.2); (3) detoxification (aldehyde dehydrogenase (ALDH), EC 1.2.1.3); and (4) cellular damage as measured by reduced lysosomal membrane stability and cell death. As there is increasing evidence that 17-beta-estradiol interferes with certain pathways of xenobiotic biotransformation, we additionally tested the effects of different concentrations of 17-beta-estradiol (0.2-10 microM) alone and 17-beta-estradiol (1 microM) in combination with 100 microM B[a]p. Parameters were monitored after 1 and 9 days of exposure by quantitative image analysis of chromogenic or fluorogenic reaction products. Our study revealed sex-dependent differences in cellular stress responses. In hepatocytes of female flounder, biotransformation was slower and the capacity of non-enzymatic antioxidant defences and detoxification of toxic aldehydes was lower than in males. Additional administration of 17-beta-estradiol enlarged these differences between the sexes with respect to biotransformation activity and antioxidant defence in xenobiotic-induced injury. These findings may explain the higher susceptibility of female flounder to toxic and carcinogenic compounds in the marine environment.

Sex-related responses to oxidative stress in primary cultured hepatocytes of European flounder (Platichthys flesus L.)

Effects of oxidative stress induced by xenobiotic compounds were studied in primary cultures of isolated hepatocytes of immature European flounder (Platichthys flesus L.) of both sexes caught in a relatively unpolluted area of the German Bight (North Sea). Cells were exposed to oxidative stressors such as 100 microM hydrogen peroxide (H2O2), 100 microM benzo[a]pyrene (B[a]p) and 50 microM nitrofurantoin (N-(5-nitro-2-furfurylidene)-1-aminohydantoin; NF) for 2 and 24 h. Cell mortality was determined with the use of the fluorescent ethidium homodimer-1 and calcein. Oxidative stress response was assessed by quantitative analysis of (1) intracellular reactive oxygen species (ROS) formation with dihydrorhodamine 123, (2) lipid peroxidation on the basis of concentrations of lipid hydroperoxides and the lipid peroxidation products malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) and (3) cellular total oxidant-scavenging capacity (TOSC) using the TOSC assay (Winston et al., 1998). An increase in ROS formation was detected as early as 2 h after exposure to H2O2, B[a]p and NF. After 24 h, stress responses were lower, except following exposure to NF. The pattern of responses differed with the different oxidative stressors. Lipid peroxidation and the capacity to scavenge ROS were increased significantly in both sexes only after exposure to H2O2, whereas B[a]p and NF provoked sex-dependent responses. B[a]p-induced lipid peroxidation and increase in scavenging capacity were observed only in hepatocytes of females, whereas NF initiated these responses only in cells of males. Sex differences in oxidative stress response only after exposure to pro-oxidants that require enzymatic activation infer the importance of biotransformation pathways in stress responses. Because of their sensitivity to oxidative stress, flounder hepatocytes provide a useful model for early risk assessment of xenobiotics.

Antioxidant activity of a novel vitamin E derivative, 2-(alpha-D glucopyranosyl)methyl-2,5,7,8-tetramethylchroman-6-ol

A novel vitamin E derivative, 2-(alpha-D-glucopyranosyl)methyl-2,5,7,8-tetramethylchroman-6-ol (TMG), has excellent water-solubility (> 1 x 10[3] mg/ml). The antioxidant activity of TMG was investigated. Kinetic studies of the inhibition of radical-chain reaction of methyl linoleate in solution demonstrated that the peroxyl radical-scavenging activity was not changed by the replacement of phytiyl side chain of vitamin E to glucosyl group. TMG acted as an effective inhibitor on lipid peroxidation of egg yolk phosphatidylcholine (PC)-liposomal suspension induced by a water-soluble and a lipid-soluble radical generator, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). Its effectiveness was higher than that of ascorbic acid (AsA) when liposomal suspension was exposed to a lipid-soluble radical generator, AMVN. TMG also showed an excellent antioxidant activity on cupric ion-induced lipid peroxidation of PC-liposomal suspension, and suppressed the oxidation of rat brain homogenate which contained trace level of iron ion. On the other hand, AsA acted as a prooxidant on both the cupric ion-induced liposomal peroxidation and the oxidation of rat brain homogenate. When human plasma was exposed to either AAPH or AMVN, the accumulation of cholesteryl ester hydroperoxides was retarded by the addition of TMG.

A study of uric acid pretreatment for the protection of rat gastric mucosa against toxic damage

Uric acid was evaluated for its potential to protect the gastric mucosa against the injuries caused by 80% ethanol, 0.6 m-HCl and 0.2 M-NaOH in rats. Uric acid at doses of 50, 100 or 300 mg/kg body weight provided dose-dependent protection against the ulcerogenic effects of all three agents. Other effects caused by ethanol only were studied. Serum uric acid concentrations were statistically significantly increased by both uric acid and ethanol treatments. Treatments of rats by gavage with 1 ml 80% ethanol was found to cause depletion of stomach-wall mucus, to lower the concentrations of protein, nucleic acids and non-protein sulphydryl groups in the stomach wall, and to cause histopathological lesions, including necrosis, erosions, congestion and haemorrhage, of the stomach wall. Treatment with uric acid, at doses of 50, 100 or 300 mg/kg body weight, by gavage, provided some measure of protection against all of these effects, and the protection was generally dose dependent. The protective effects of uric acid against damage to the gastric-wall mucosa may be mediated through its effects on mucus production and non-protein sulphydryl concentrations, and/or its free-radical scavenging properties.

Linoleate-dependent co-oxygenation of benzo(a)pyrene and benzo(a)pyrene-7,8-dihydrodiol by rat cytosolic lipoxygenase

1. Co-oxygenation of 14C-labelled benzo(a)pyrene and benzo(a)pyrene-7,8-dihydrodiol was studied in rat lung cytosol, using linoleic acid as a co-substrate. Covalently bound and soluble metabolites were quantified by radiometry and h.p.l.c., respectively. 2. The co-oxygenation resulted in the production of reactive metabolites capable of protein binding as well as a series of soluble derivatives. 3. Co-oxygenation of benzo(a)pyrene yielded primarily a significant amount of benzo(a)pyrene-6,12-dione while benzo(a)pyrene-7,8-dihydrodiol led to a significant amount of benzo(a)pyrene-trans-anti-tetrol. 4. Their production was abolished by addition of 25 microM of the lipoxygenase inhibitor and antioxidant NDGA. 5. It is postulated that the linoleic acid peroxyl radicals, formed by rat lung lipoxygenase, initiate the one-electron oxidation of benzo(a)pyrene to its quinones, and epoxidation of benzo(a)pyrene-7,8-diol to the ultimate carcinogenic benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide.

Uric acid as an inhibitor of biochemical changes induced by cyclophosphamide in mice

The biochemical changes induced by uric acid, cyclophosphamide and uric acid plus cyclophosphamide were evaluated in Swiss albino male mice. Uric acid dissolved in water was administered orally in different doses for 7 days. Some mice from each group were injected intraperitoneally with cyclophosphamide (25 mg/kg) and sacrificed after 30 h. The blood of all animals was analyzed for uric acid levels. Uric acid was found not to affect the biosynthesis of nucleic acids and proteins in liver, testes and brain at 10-100 mg/kg/d. Pretreatment with uric acid provided significant protection against cyclophosphamide-induced impairment of DNA, RNA and protein biosynthesis.

Uric acid as an inhibitor of cyclophosphamide-induced micronuclei in mice

Swiss albino male mice, 6-8 weeks old, were treated orally with different doses of uric acid dissolved in water for 7 days. Some of the mice in each group were injected i.p. with cyclophosphamide (25 mg/kg) and killed after 30 h. The blood of all animals was analyzed for uric acid levels. The femoral cells of the mice in different groups were collected and studied. Uric acid was found to be devoid of mitodepressant or clastogenic activity at 10-100 mg/kg/day. Pretreatment with uric acid was found to provide significant protection against cyclophosphamide-induced bone marrow depression and micronucleated polychromatic erythrocytes.

Antioxidant activity of 6-phosphatidyl-L-ascorbic acid

The antioxidant activity of 6-phosphatidyl-L-ascorbic acid was investigated in a homogeneous solution and a liposomal suspension. In an apolar solvent, one molecule of 6-phosphatidyl-L-ascorbic acid could trap one peroxyl radical. When 6-phosphatidyl-L-ascorbic acid was included in multilamellar liposomes of egg yolk phosphatidylcholine, it could retard more effectively the aqueous peroxyl-induced peroxidation of phosphatidylcholine than L-ascorbic acid.

Lipid peroxidation-coupled co-oxygenation of benzo(a)pyrene and benzo(a)pyrene-7,8-dihydrodiol in human term placental microsomes

The link between lipid peroxidation and benzo(a)pyrene activation was studied in microsomes isolated from human term placenta. Lipid peroxidation was initiated in the presence of NADPH by partially chelated iron. Covalently bound and free metabolites of benzo(a)pyrene or benzo(a)pyrene-7,8-diol were quantitated by radiometry and/or HPLC. Peroxidative conditions increased the amounts of benzo(a)pyrene-trans-anti-tetrol produced from benzo(a)pyrene-7,8-diol, benzo(a)pyrene-diones from benzo(a)pyrene, and protein bound metabolites from both. A reactive oxo-iron complex is proposed as an ultimate species initiating hydrogen abstraction and lipid peroxidation. It is suggested that partially chelated iron catalyzes co-oxygenation of benzo(a)pyrene and benzo(a)pyrene-7,8-diol by peroxyl radical in placental microsomes. This peroxidative reaction may be crucial for bioactivation of benzo(a)pyrene in human term placenta.

Quinone formation from benzo[a]pyrene by free radicals: effects of antioxidants

Liposomes comprising dimyristoylphosphatidylcholine and benzo[a]pyrene (B[a]P) were incubated at 37 degrees C in the presence of a water-soluble azo initiator. B[a]P 1,6-, 3,6- and 6,12-quinone were formed with the generation of peroxyl radicals by the thermal decomposition of the initiator in an aqueous phase of the suspension. Vitamin E showed little inhibitory effect on B[a]P quinone formation. Uric acid was found to suppress B[a]P quinone formation completely at a concentration lower than that of vitamin C, indicating that uric acid in an aqueous phase traps peroxyl radicals more effectively.