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PubMed1987

R-goitrin- and BHA-induced modulation of aflatoxin B1 binding to DNA and biliary excretion of thiol conjugates in rats.

Previous studies have shown that dietary R-goitrin is a potent inducer of hepatic glutathione S-transferase (GST) and epoxide hydrolase activities but has no effect on components of the mixed function oxidase system (ethoxycoumarin O-deethylase and cytochrome P-450). In the present work effects of dietary R-goitrin (200 p.p.m.) or butylated hydroxyanisole (BHA) (7500 p.p.m.) on GST activity, binding of aflatoxin B1 (AFB1) to DNA, in vivo, and biliary excretion of thiol conjugates of AFB1 in rats were studied. Increases of GST activities (1.9- and 2.1-fold) were accompanied by reductions in AFB1-DNA binding (43% and 85%) and increases (1.7- and 2.2-fold) in biliary excretion of AFB1-thiol conjugates in R-goitrin and BHA groups, respectively. Microsomal aflatoxin 8,9-epoxidase activities were not increased in either treatment group. The role of GST induction in the carcinogenesis of AFB1 and the anticarcinogenic potential of R-goitrin are discussed.

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PubMed2001

[Proportion of aflatoxin B1 contaminated kernels and its concentration in imported peanut samples].

Moldy and split peanut kernels were separated from peanuts exported from Brazil, Sudan, India and Taiwan by visual inspection. The remaining peanuts from Brazil, Sudan and India were roasted lightly and the skins were removed. Stained peanuts were separated from the others. Aflatoxin was detected in moldy and stained peanuts. There was a positive correlation between % of aflatoxin-contaminated peanut kernels and aflatoxin B1 concentration in whole samples. Aflatoxin concentration of moldy peanuts was higher than that of stained peanut kernels.

Aflatoxin B1↗
PubMed1998

Ability of dairy strains of lactic acid bacteria to bind a common food carcinogen, aflatoxin B1.

This study was conducted to examine the ability of selected dairy strains of lactic acid bacteria to remove aflatoxin B1 (AFB1) from liquid media. Both Lactobacillus rhamnosus strain GG (LBGG) and L. rhamnosus strain LC-705 (LC705) can significantly (P > 0.05) remove AFB1 when compared with that by other strains of either Gram-positive or Gram-negative bacteria. Removal of AFB1 by LBGG and LC705 was a rapid process with approximately 80% AFB1 removed at 0 hr. Removal of AFB1 by these two strains was both temperature and bacterial concentration dependent.

Aflatoxin B1↗
PubMed1985

Different responses to phenobarbital promotion in the development of gamma-glutamyltranspeptidase-positive foci in the liver of rats initiated with diethylnitrosamine, N-hydroxy-2-acetyl-aminofluorene and aflatoxin B1.

The promoting activities of phenobarbital (PB) on the development of gamma-glutamyl-transpeptidase-positive (gamma-GT+) foci in rat liver with three different initiating agents were compared in a short-term system (8 weeks). Male F344 rats were initiated by a single application of 200 mg/kg of diethylnitrosamine (DEN), 30 mg/kg of N-hydroxy-2-acetylaminofluorene (N-OH-AAF), 1.0 or 0.5 mg/kg of aflatoxin B1 (AFB1) or the vehicles alone. Two weeks after the initiation, animals were placed on a 0.05% PB diet for 6 weeks. Partial hepatectomy was performed at the end of the third week of the experiment. As a positive control, some animals were fed diet containing 0.06% 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) after the initiation. The number and area of gamma-GT+ foci in the liver were quantified. All three initiators showed a summation effect with 3'-Me-DAB on the appearance of gamma-GT+ foci. Promotion by PB, however, was observed only in DEN-initiated rats and not in N-OH-AAF- or AFB1-initiated rats. It is apparent from the present experimental data that the promoting potential of PB on liver carcinogenesis depends on the initiating agent.

Aflatoxin B1↗
PubMed1979

Distribution of aflatoxins B1 and M1 in contaminated calf and pig livers.

The determination of aflatoxins B1 and M1 in multiple sections of livers from 4 calves and 1 pig exposed to high levels of aflatoxins showed a uniform distribution of the aflatoxins in each liver, within the precision of the analytical method used. The thin layer chromatographic method has an expected within-laboratory coefficient of variation of 15%.

Aflatoxins↗
PubMed1999

Semecarpus anacardium L. nut extract administration induces the in vivo antioxidant defence system in aflatoxin B1 mediated hepatocellular carcinoma.

The antioxidant defence system which plays a critical role in carcinogenesis is severely altered in aflatoxin B1 induced hepatocellular carcinoma conditions. In order to assess the antitumour activity of Semecarpus anacardium nut extract, a flavonoid containing drug, non-enzymic antioxidant levels were analysed in control and experimental animals. Plasma was analysed for uric acid, vitamin E and vitamin C. Glutathione, total thiols, non-protein thiols, vitamin E, vitamin C and cytochrome P450 were estimated in liver and kidney homogenates. Depletion of all these antioxidants were recorded in cancer conditions. These deleterious effects are controlled by the administration of Semecarpus anacardium nut extract. Following drug administration, there was a marked increase in antioxidant levels and a dramatic elevation in cytochrome P450 content. It can be concluded that the observed anticancer property of Semecarpus anacardium nut extract may also be explained by its strong antioxidant capacity and capability to induce the in vivo antioxidant system.

Aflatoxin B1↗
PubMed1985

[Morphological characteristics and physiological properties of aflatoxin B1 producing and non-producing Aspergillus flavus strains].

Comparison between about 80 strains of Aspergillus flavus, belonging to the series flavus and oryzae, obtained from international collections but also isolated from French or African substrates revealed the following observations: 1. Cultural and morphological characteristics of toxicogenic and atoxicogenic strains of A. flavus are similar. However, the former produce a diffusible yellow pigment in 83% of isolates. 2. The two groups of conidiospores have the same resistance to UV irradiation (254 nm, 5 and 10 min). All the strains are equally sensitive to 4 antifungal antibiotics: nystatine, ketoconazole, clotrimazole and amphotericine. 3. A difference was seen in the capacity to produce enzymes as alpha-galactosidase, beta-galactosidase and beta-glucosidase, implicated in the glucid metabolism. The specific hydrolytic activity has been confirmed by the characterization of a large amount of beta-galactosidase and by a diauxic growth on glucose medium supplemented by lactose. Possible relationship between these characters and aflatoxin B1 production by A. flavus strains is discussed.

Aflatoxin B1↗
PubMed1992

The effect of aflatoxin B1 exposure on serotonin metabolism: response to a tryptophan load.

Semi-chronic exposure of ICR male Mice to Aflatoxin B1 (AFB1) in non-toxic doses decreased brain serotonin (5-hydroxytryptamine, 5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA) and catecholamines without altering tryptophan (TRP) or tyrosine (TYR) levels. A TRP load (300 mg/kg, i.p. x 2 hours) slightly increased brain TRP levels while causing a slight decrease in 5-HT and 5-HIAA in control animals. A TRP load in AFB1 treated mice increased brain 5-HT and 5-HIAA. The TRP load caused a further reduction in brain catecholamines without altering TYR levels. Exposure to AFB significantly increased lung TRP levels without altering 5-HT or 5HIAA levels. TRP loading increased lung TRP concentrations in control mice. However, in AFB1 treated mice the increase was not significantly elevated above the level caused by AFB1 treatment alone. Lung 5-HT or 5-HIAA levels in control or AFB1 treated mice are not significantly altered by TRP loading. These experiments demonstrate that AFB1 alters brain and lung TRP metabolism.

Aflatoxin B1↗
PubMed1993

An ethoxyquin-inducible aldehyde reductase from rat liver that metabolizes aflatoxin B1 defines a subfamily of aldo-keto reductases.

Protection of liver against the toxic and carcinogenic effects of aflatoxin B1 (AFB1) can be achieved through the induction of detoxification enzymes by chemoprotectors such as the phenolic antioxidant ethoxyquin. We have cloned and sequenced a cDNA encoding an aldehyde reductase (AFB1-AR), which is expressed in rat liver in response to dietary ethoxyquin. Expression of the cDNA in Escherichia coli and purification of the recombinant enzyme reveals that the protein exhibits aldehyde reductase activity and is capable of converting the protein-binding dialdehyde form of AFB1-dihydrodiol to the nonbinding dialcohol metabolite. We show that the mRNA encoding this enzyme is markedly elevated in the liver of rats fed an ethoxyquin-containing diet, correlating with acquisition of resistance to AFB1. AFB1-AR represents the only carcinogen-metabolizing aldehyde reductase identified to date that is induced by a chemoprotector. Alignment of the amino acid sequence of AFB1-AR with other known and putative aldehyde reductases shows that it defines a subfamily within the aldo-keto reductase superfamily.

Aflatoxin B1↗
PubMed2005

Protection against aflatoxin-B1-induced liver mutagenesis by Scutellaria baicalensis.

We have measured the inhibition of the mutagenicity of the mycotoxin aflatoxin-B(1) in the liver of the rat by plant material of Scutellaria baicalensis, or Huang-qin. The addition of one percent dried Huang-qin to the feed of the animals reduced the mutant frequency of a subsequent administration of aflatoxin-B1 by approximately 60 and 77%, respectively, for two different batches of the plant material. The addition of Huang-qin also increased the expression of the gene for glutathione S-transferase A5 subunit by 2.5-3.0-fold, and decreased expression of P450 cytochrome 3A2 by 1.8-2.0-fold. The greater increase of the expression of the GST gene may result in the protection shown by Huang-qin. The sensitivity of the hepatic mitochondria to swelling, a measure of the mitochondrial permeability transition, is increased significantly in animals that are on a diet containing Huang-qin. This may lead to increased sensitivity to apoptosis on treatment with toxic compounds. The two batches of Huang-qin material show differences in both chemical composition and preventive potential. This study demonstrates how a combination of generating and analysis of plant varieties together with a mammalian assay for efficacy may improve the search for better plant-based prevention of cancer initiation.

Aflatoxin B1↗
PubMed1982

Quantitative forward-mutation specificity of mono-functional alkylating agents, ICR-191, and aflatoxin B1 in mouse lymphoma cells.

We have analyzed forward-mutation specificity in S49 mouse T lymphoma cells. Our criteria of specificity were based upon relative mutabilities of a panel of 3 genetic markers: resistance to 6-thioguanine (6TGr), dibutyryl cAMP (bt2cAMPr), and ouabain (OUAr). We tested 2 monofunctional alkylating agents, ethyl methane-sulfonate (EMS) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and 2 heterocyclic compounds, ICR-191 and aflatoxin B1 (AFb1). AFB1 was activated with rat-liver microsomal S9 plus cofactors. Expression-time lags of each genetic marker ranged from 2 days of OUAr mutations to 6 and 8 days for bt2cAMPr and 6TGr cells, with stable induced mutant fractions thereafter. The relative activity of each agent for each marker was assessed on the basis of its mutagenic efficiency at equitoxic doses. Specificity differences between the agents were determined by taking ratios of mutagenic efficiencies (RME) for the 3 possible pairs of markers. From these quantitative correlations and other data we conclude that both MNNG and EMS induce ouabain resistance (and probably bt2cAMPr and 6TGr) by similar mechanisms, almost certainly base substitutions. In contrast, ICR-191 and AFB1 are respectively less than 2 and 3% as efficient as MNNG for OUAr mutant induction relative to the activity of each agent for 6TGr mutagenesis. We infer that ICR-191 and AFB1 very rarely cause base substitutions in S49 cells, but that their activities are consistent with production of deletions, insertions or chromosomal aberrations. S49 cells demonstrate an unusually high specificity of mutagenesis at the OUAr locus compared to several other rodent cell lines. Thus, this panel of markers in S49 cells can be used as a sensitive, reliable screening system for mutagen detection and to discriminate among major classes of mutagenic mechanisms.

Aflatoxin B1↗
PubMed2004

Low hepatic glutathione S-transferase and increased hepatic DNA adduction contribute to increased tumorigenicity of aflatoxin B1 in newborn and partially hepatectomized mice.

Low levels of hepatic glutathione S-transferase and increased formation of aflatoxin B1 (AFB1)-DNA adducts correlate with hepatocyte proliferation and increased hepatocarcinogenesis in both newborn mice and partially hepatectomized adult mice, as compared to normal, adult C57BL/6J mice. Newborn mice, which are highly susceptible to the hepatocarcinogenic effects of AFB1, have active proliferation of hepatocytes until 3 weeks of age, when hepatocyte proliferation abruptly ceases. At about this time, the mice become highly resistant to AFB1. In adult mice, AFB1 carcinogenicity is increased after stimulation of liver proliferation by partial hepatectomy. To become carcinogenic, AFB1 is activated in the liver by the P450 enzyme system to electrophilic intermediates, some of which form DNA adducts believed to be responsible for mutations leading to cancer. The most carcinogenic intermediate, AFB(1)-8,9-epoxide, is detoxified by glutathione S-transferase-mediated conjugation to glutathione. Glutathione levels, glutathione S-transferase levels, and AFB1-DNA adduct formation were measured at 4, 10, 30, 120, 245 and 365 days of age in C57BL/6J mice. There was a 5-fold increase in hepatic glutathione S-transferase levels and 13-fold decrease in hepatic AFB1-DNA adduct formation over these ages. Induction of hepatocyte proliferation following partial hepatectomy of 120-day-old mice lowered hepatic glutathione S-transferase levels and increased the extent of hepatic AFB1-DNA formation to levels similar to those measured in 4-day-old mice. These results indicate that increased susceptibility to AFB1 hepatocarcinogenesis in newborn mice, and in adult mice following partial hepatectomy, is due to decreased GST and increased adduct formation in proliferating liver.

Aflatoxin B1↗
PubMed1981

A comparison of the effects of pretreatment with phenobarbitone and 3-methylcholanthrene on the metabolism of aflatoxin B1 by rat liver microsomes and isolated hepatocytes in vitro.

In agreement with previous reports (Neal and Colley, Biochem. J., 174 (1978) 839; Gurtoo and Dave, Cancer Res., 35 (1975) 382) the capacity of isolated hepatic microsomes to metabolise aflatoxin B1 (AFB1) is enhanced by pretreatment in vivo with phenobarbitone. Microsomes isolated from rats pretreated with 3-methylcholanthrene also exhibit increased metabolism of AFB1. The levels of metabolism are increased in proportion to the increased levels of cytochromes P-450 and P-448 indicating similar overall efficiencies of the two cytochromes to metabolise AFB1. However, the qualitative aspects of the metabolism induced by the two compounds are very different. In agreement with the previous data (Neal and Colley, Biochem J., 174 (1978) 839) the formation of aflatoxins Q1, M1 and B1-dihydrodiol are enhanced by pretreatment with phenobarbitone whereas pretreatment with 3-methylcholanthrene, while not affecting the production of aflatoxin Q1 and slightly lowering AFB1-dihydrodiol formation, increases the production of aflatoxin M1 greater than 10-fold. Covalent binding of AFB1 to microsomal protein in vitro is increased by pretreatment in vivo with phenobarbitone, but decreased by pretreatment with 3-methylcholanthrene. The changes in the level of protein binding in vitro brought about by these pretreatments are quantitatively similar to the relative changes in AFB1-dihydrodiol tris complex production induced by the two compounds indicating a role for this metabolite in protein binding. Covalent binding of AFB1 to DNA in vitro is also increased by pretreatment in vivo with phenobarbitone, but not by 3-methylcholanthrene and the total level of binding of AFB1 to DNA in the in vitro system is greater than binding to microsomal protein. The possible mechanisms for binding AFB1 to microsomal protein and DNA are discussed. In contrast to the microsomal incubations, only low levels of aflatoxins Q1 and M1 are present after 2 h incubation AFB1 with intact hepatocytes isolated from control, methylcholanthrene or phenobarbitone pretreated rats. Pretreatment with either phenobarbitone or 3-methylcholanthrene induces the formation of polar metabolites, presumably conjugates, emphasising the predominant role of phase 2 metabolism in intact cellular systems.

Aflatoxin B1↗
PubMed1984

Inhibition of aflatoxin B1 carcinogenesis in rainbow trout by flavone and indole compounds.

Several compounds such as flavonoids, selenium, antioxidants and retinoids reportedly reduce the induction of cancer in experimental animals, and some have been suggested to function by affecting the mixed-function oxidase (MFO) system. The following compounds: 50 and 500 p.p.m. beta-naphthoflavone (BNF), 1000 p.p.m. flavone, 1000 p.p.m. of a tangeretin - nobilitin mixture, 1000 p.p.m. beta- ionone , 1000 p.p.m. indole-3-carbinol ( I3C ) and 2000 p.p.m. quercetin were examined for protection against aflatoxin B1 (AFB1) hepatocarcinogenesis, induction of the MFO system and metabolism of AFB1 in rainbow trout. These compounds were fed to fingerling rainbow trout for 8 weeks. At that time the activity of several MFO enzymes and cytochrome P450 content were measured and the trout were exposed for 2 weeks to 20 p.p.b. AFB1 in the same diets. After feeding the test diets without AFB1 for another 6 weeks and basal diet for another 52 weeks, the tumor incidence was determined. The effect of BNF and I3C on in vivo binding of AFB1 to DNA was also measured in separate groups of trout. BNF induced the trout MFO system in a dose-dependent manner, tangeretin - nobilitin was less effective and I3C did not induce. BNF showed significant alterations in the metabolism of AFB1 to aflatoxicol and aflatoxin M1 using cell fractions from pretreated fish. None of the other compounds, including I3C showed such an effect. Despite the apparent lack of in vitro effect of I3C , both BNF and I3C reduced AFB1 - DNA binding in vivo. I3C and BNF provided marked protection against AFB1-induced hepatocarcinogenesis, while the other compounds were less effective. The 58 weeks tumor incidences were 4% for 1000 p.p.m. I3C , 6% for 500 p.p.m. BNF and 18% for 50 p.p.m. BNF, compared to 38% for the AFB1-positive control. These data demonstrate that gross induction of the MFO system was not necessarily required for alterations in DNA adduct formation in vivo or protection against AFB1 carcinogenesis. Both BNF and I3C provided marked protection but only BNF induced the MFO system.

Aflatoxin B1↗
PubMed2003

Aflatoxin residues in eggs of laying Japanese quail after long-term administration of rations containing low levels of aflatoxin B1.

The aim was to evaluate the excretion of residues of aflatoxin B(1) (AFB(1)), aflatoxin M(1) (AFM(1)), aflatoxin B(2a) (AFB(2a)) and aflatoxicol (AFL) in eggs of laying Japanese quail fed rations with low levels of aflatoxin B(1) for 90 days. The quail were randomly assigned into four experimental groups and given prepared rations containing either 0 (controls), 25, 50 or 100 microg AFB(1) kg(-1) feed. Thirty-two eggs per treatment were collected on days 1-7, 10, 20, 30, 60 and 90 of the aflatoxin treatment period, and submitted to aflatoxin analysis by high-performance liquid chromatography. Average egg production and feed consumption were not affected ( p > 0.05) by AFB(1). Egg weight was significantly lower ( p<0.05) only for groups exposed to 100 microg AFB(1) kg(-1). Residues of aflatoxins were detected in eggs at levels that ranged from 0.01 to 0.08 microg kg(-1) (AFB(1)), 0.03-0.37 microg kg(-1) (AFM(1)), 0.01-1.03 microg kg(-1)(AFB(2a)) and 0.01-0.03 microg kg(-1) (AFL). Results indicate that the excretion of aflatoxin residues in quail eggs might occur at relatively low concentrations under conditions of long-term exposure of quail to low levels of AFB(1).

Aflatoxin B1↗
PubMed1984

Synthesis and degradation of aflatoxins by Aspergillus parasiticus. I. Synthesis of aflatoxin B1 by young mycelium and its subsequent degradation in aging mycelium.

Aflatoxin production and degradation were examined in three isolates of A. parasiticus. Maximum yields were present after incubation for 14 days and these declined gradually as the culture aged. Young mycelia (4 days old) synthesized the greatest amounts of aflatoxin, but aging mycelia (14 days old) were mainly responsible for degradation. Addition of cycloheximide to young cultures and removal of mycelia from aging cultures both prevented further aflatoxin degradation. Intramycelial substances released from fragmented or homogenized mycelium were capable of degrading aflatoxins, and their concentration increased as the mycelium aged. When 14C-labelled aflatoxin was added to a 2-day-old culture and further incubated, 75% of the radioactivity at 12 days was intramycelial, but at 20 days, most radioactivity was in the filtrate.

Aflatoxin B1↗
PubMed1988

Mechanisms of anti-carcinogenesis by indole-3-carbinol: detailed in vivo DNA binding dose-response studies after dietary administration with aflatoxin B1.

Several recent reports have described inhibitor-mediated reductions in the covalent binding of various carcinogens to DNA in vivo. The majority of these studies show inhibitory effects after testing at one inhibitor and one carcinogen dose level only. Consequently, the detailed relationships between inhibitor dose, carcinogen dose, and in vivo inhibitory potency have not been clearly delineated in any species. To systematically determine these relationships in vivo, rainbow trout (Salmo gairdneri) were exposed to a range of carcinogen (aflatoxin B1, AFB1) and inhibitor (indole-3-carbinol, I3C) doses by concomitant dietary exposure. Inhibitory potencies were then assessed using in vivo covalent binding of AFB1 to hepatic DNA as an end-point. Linear increases in DNA binding occurred with increasing dose of AFB1 and with time of inhibitor/carcinogen co-treatment, at each I3C dose level. Successive increases in inhibitor dose resulted in corresponding dose-related decreases in AFB1--DNA binding such that a series of curves of decreasing slope was produced. AFB1--DNA binding was suppressed by almost 95% at the highest I3C dose tested. These studies describe for the first time such a degree of inhibition by I3C on covalent binding of AFB1 to DNA in vivo, where inhibitor and carcinogen are covariables administered repeatedly in the diet. Moreover, the linear inhibitory response observed at low I3C doses indicates the possible absence of any significant threshold for I3C protection against AFB1--DNA binding. Thus, even at low levels I3C may offer some protection against chemically-induced neoplasia.

Aflatoxin B1↗
PubMed1982

Toxicology of aflatoxin B1, warfarin, and cadmium in young pigs: metal residues and pathology.

The effects of feeding dietary cadmium (83 micrograms/g of diet) to young pigs on the distributions of copper, iron, and zinc in urine samples and in kidney, liver, and muscle tissues was determined. The diet with added Cd resulted in renal and hepatic tissue concentrations of 42.90 +/- 10.57 micrograms/g and 7.90 +/- 2.37 micrograms/g, respectively, at the 40th day of the experiment. Iron was found to decrease at the same time, which predisposed to the anemic condition of these pigs. The feeding of dietary CD to pigs prevented extensive fatty hepatocytic infiltration and severe jaundice, but not hydropic degeneration induced by aflatoxin B1. Cadmium increased the toxicity of warfarin with severe lameness, subcutaneous hematomas in the ventral surface of the neck, and death.

Aflatoxin B1↗