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PubMed1975

Excretion of carbon-14-labeled aflatoxin B1 via bile, urine, and intestinal contents of the chicken.

Carbon-14-labeled aflatoxin B1 was prepared by growing Aspergillus parasiticus in medium containing sucrose-14-C as the sole carbon source. The 14-C-labeled aflatoxin B1 was extracted with chloroform and purified by thin-layer chromatography (TLC) followed by precipitation from solution and washing. The 14-C-labeled aflatoxin B1 was intravenously given to anesthetized dwarf White Leghorn or Rhode Island Red hens with cannulated ureters and bile ducts. The 14-C had a calculated plasma half-life of 1.5 minutes and rapidly appeared in the bile. The 14-C concentration in the bile reached values approximately 7 times maximum for plasma, and most could no longer be extracted with chloroform. This finding indicated that metabolites of the 14-C-labeled aflatoxin B1 had been excreted against a concentration gradient into the bile. The quantities of 14-C excreted via bile, urine, and intestinal contents remained at a fairly constant ratio of 70:15:15, respectively, over the 315-minute experimental period. Six major chloroform-soluble compounds containing 14-C were isolated. Three of these were tentatively identified as aflatoxin B1, B2, and M1. A 4th was believed to be aflatoxin B2a. None of the early chloroform-soluble metabolites were as cytotoxic as aflatoxin B1.

Aflatoxins↗

PubMed1993

Metabolic activation of aflatoxin B1 by human placental microsomes.

The metabolic activation of aflatoxin B1 by human placental microsomes was studied. Aflatoxin B1 showed relatively high mutagenic activity in Ames test when incubated with human placental microsomes. Addition of alpha-naphthoflavone or aminoglutethimide, known inhibitors of cytochrome P450 1A and P450 19, respectively, into the test system partially inhibited the mutagen-producing activity. It was suggested that the activation of aflatoxin B1 in human placental microsomes is mediated by at least these two forms of cytochrome P450.

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PubMed1991

Effect of aflatoxin B1 on human platelet protein kinase C.

1. Aflatoxin B1 serves as an activator for protein kinase C (PKC). 2. Following activation, the enzyme translocates from the cytosol to the particulate fraction. 3. Aflatoxin B1 leads to rapid and extensive phosphorylation of the known substrate of the enzyme. 4. Aflatoxin B1 causes rapid hydrolysis of phosphatidylinositol-4,5-biphosphate to diacylglycerol and inositol-1,4,5-triphosphate.

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PubMed1983

Influence of selenium on aflatoxin B1 or crotalaria toxicity in turkey poults.

This research compared the toxic effects of aflatoxin B1 and monocrotaline, the active principle of Crotalaria spectabilis, and the additive effect between aflatoxin B1 and monocrotaline in turkey poults. It was of interest whether selenium fed at dosage levels of 0.1, 5, or 10 micrograms/g of feed would protect against the toxic effect of aflatoxin and/or monocrotaline, and whether the toxicants would result in detectable residues in poult tissues. A total of 180 healthy 1-day-old male turkey poults was assigned at random to 12 treatment groups (15 birds/group). Body and liver weight losses, and low serum concentrations in total protein (TP), albumin (A), alpha-globulin (alpha G), and beta-globulin (beta G), as well as high values in gamma-globulin (gamma G), were produced in the groups fed crotalaria. Pathologic changes were induced by monocrotaline with no protection afforded by the added selenium. Low values in TP, A, alpha G, and beta G and in body and liver weights were observed in groups given the combination of aflatoxin plus crotalaria. Gross lesions were associated with an additive toxic effect and a lack of protective effect of selenium against this combination. However, higher values in TP, A, alpha G, and beta G, and liver weights in groups fed aflatoxin B1 plus selenium indicated that selenium had a protective effect against aflatoxin toxicity. Residues of aflatoxin B1 and aflatoxin M1 were found in the kidneys of poults fed aflatoxin B1; also, dehydroretronecine (the metabolite of monocrotaline) was detected in livers of poults fed Crotalaria spectabilis seeds.

Aflatoxins↗

PubMed1999

Production and characterization of monoclonal antibodies for aflatoxin B1.

Hybridomas that secreted antibodies for aflatoxin B1 were selected using two immunization protocols referred to as A and B. Protocol A is a standard immunization method and resulted in the selection of only two clones that produced monoclonal antibodies against aflatoxin B1. In protocol B a unique immunization schedule which resulted in the generation of 10 hybridomas is described. Of the 10, one antibody was highly specific to B1, four antibodies reacted equally strongly with B1, G1 and weakly with B2. Another four reacted strongly with B1 and weakly with B2 and G1. One clone reacted equally strongly with B1, G1 and B2. Interestingly all the 10 antibodies showed little or no cross-reaction with G2.

Aflatoxin B1↗

PubMed1976

Some studies of the effects of aflatoxin B1 in vivo and in vitro on nucleic acid synthesis in rat and mouse.

The mouse compared with the rat, is more resistent to the acute toxic action of aflatoxin B1 and is refractory to its hepatocarcinogenic properties. Aflatoxin B1 inhibits DNA synthesis more strongly than RNA synthesis in the rat, and both nucleic acid syntheses more strongly in rat than in the mouse. Mouse hepatic microsomes, like those of the rat, are capable of metabolizing aflatoxin B1 in vitro in the presence of NADPH, to an active form which binds to DNA both in solution and in intact nuclei and also inhibits nuclear RNA synthesis. Non NADPH-dependent binding of aflatoxin B1 to nuclei is not effective in inhibiting RNA polymerase and is largely removed by washing with lipid solvents. Mouse nuclear RNA polymerases particularly Mn 2+ (NH4)2SO4 primed acitivity are more resistant to inhibition in vitro by activated aflatoxin B1 than are the corresponding enzyme activities in rat liver nuclei. This would appear to be due to the bound aflatoxin B1 being less efficient in the case of the mouse nucleus, in inhibiting RNA synthesis. Mouse liver slices exhibit a much lesser degree of inhibition of RNA synthesis by aflatoxin B1 than do rat liver slices. Accompanying this is a lower level of binding of aflatoxin B1 to subcellular particulate fractions in the mouse liver slice compared to the rat, this disparity being most marked in the case of the nuclear fraction. The suggestion is made that the resistance of RNA synthesis in the mouse liver, to aflatoxin B1, and perhaps also resistance to its toxicity, is dependent, not on a lower capacity to activate the toxin, but (a) on a less efficient inhibition of RNA synthesis by nuclear bound toxin, and (b) a detoxifying mechanism at least partially situated in the cytosol fraction.

Aflatoxins↗

PubMed1982

Detoxification of aflatoxin B1 by acidogenous yoghurt.

Serial concentrations of aflatoxin B1 ranged from 200 to 1000 p.p.b. were assayed for detoxification by acidogenous yoghurt. Thin-layered chromatography analysis revealed a complete transformation of 800 p.p.b. of aflatoxin B1 to a new fluorescing compound corresponding to aflatoxin B2a which is referred as hydroxydihydroaflatoxin B1. Partial conversion was present in yoghurt sample containing 1000 p.p.b. Toxicity test on chicken, confirmed Ciegler findings.

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PubMed1984

Fluorometric studies on the binding of aflatoxin B1 to bovine serum albumin.

The quenching of dansylated BSA fluorescence by Aflatoxin B1 at the dansyl emission peak provided a useful method to study Aflatoxin B1 - BSA interaction, making evident one binding site with hydrophobic characteristics. The Ka = 4.0 X 10(4) M-1 at 18 degrees C could assing to this site a role in Aflatoxin B1 transport, but not in storage in the systemic circulation. Evidence supporting the presence of more binding sites, probably of similar characteristics as the former, was obtained from the study of the displacement of ANS bound to BSA by Aflatoxin B1, in spite of the fact that this interaction cannot be explained as a simple competition between ligands.

Aflatoxin B1↗

PubMedDate not supplied

Interaction of aflatoxin B1 and cyclopiazonic acid toxicities.

Toxic properties of the mycotoxins cyclopiazonic acid and aflatoxin B1 have been analyzed separately and in combination by monitoring their effects on luminescence in the marine bacterium Photobacterium phosphoreum, Strain NCMB 844. Genotoxicity was analyzed with a dark mutant of this organism whose reversion to the bioluminescent condition is stimulated by compounds attacking guanine sites in deoxyribonucleic acids. In this assay, cyclopiazonic acid, unlike aflatoxin B1, is not enhanced by cyclopiazonic acid when the two mycotoxins are assayed in combination. Cytotoxicity was assessed by the diminution of bioluminescence in a separate assay system with strain NRRLB-1177 of P. phosphoreum. Cyclopiazonic acid is more cytotoxic than aflatoxin B1, and concentrations of cyclopiazonic acid required for cytotoxicity decreases with time, whereas aflatoxin B1 cytotoxic expression does not change significantly with time under most assay conditions. Aflatoxin B1 and cyclopiazonic acid assayed as a dose pair indicate that these mycotoxins elicit their effects by independent modes of action.

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PubMed1992

Aflatoxin B1 DNA adducts in smeared tumor tissue from patients with hepatocellular carcinoma.

Aflatoxins are well-known animal hepatocarcinogens, but the association between aflatoxins and human hepatocellular carcinoma remains to be elucidated. A study method consisting of indirect immunofluorescence assay combined with densitometry was developed to quantitate aflatoxin B1 DNA adducts in smeared liver tissue obtained at the time of biopsy for diagnosis in 50 hepatocellular carcinoma patients in Taiwan. Monoclonal antibody 6A10, generated against the persistent form of the major N7 guanine adduct of aflatoxin B1, was used for detection of adduct. Thirty-five (70%) of the hepatocellular carcinoma samples had detectable levels of aflatoxin B1 DNA adducts (> or = 1/10(6) nucleotides). The detection rate was slightly lower in men (69%) than in women (75%), and younger patients had a significantly higher rate of adducts (83%) than did older ones (58%). Carriers of both HBsAg and HBeAg, carriers of HBsAg only and noncarriers had different rates of detection: 29%, 74% and 82%, respectively. Patients with family histories of hepatocellular carcinoma had a higher detection rate (100%) than did those patients without such histories (67%). No association was found between aflatoxin B1 DNA adducts in liver tissue and Child's score for severity of liver disease. The results suggest that aflatoxin B1 may be involved in the pathogenesis of hepatocellular carcinoma in Taiwan. Our immunohistochemical method for analysis of adducts in small numbers of cells from the target organ should improve results of monitoring for the biologically effective dose of aflatoxin.

Adult↗

PubMed1999

Anticancer potency of the milk extract of Semecarpus anacardium Linn. nuts against aflatoxin B1 mediated hepatocellular carcinoma bearing Wistar rats with reference to tumour marker enzymes.

Aflatoxin B1 is an important consideration in the aetiology of human and animal hepatocellular carcinoma. The influence of the drug, Semecarpus anacardium Linn. nut extract, on hepatocarcinogenicity of aflatoxin B1 was evaluated in adult albino male Wistar rats. Aflatoxin B1 was administered intraperitoneally to induce hepatocellular carcinoma. These cancer bearing animals were treated with Semecarpus anacardium Linn. nut extract (200 mg/kg body weight/day) in sunflower oil orally for 14 days. The plasma and the liver tumour tissue were investigated biochemically for lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and gamma-glutamyl transpeptidase. The elevation of plasma concentration of these enzymes were indicative of the persistent deteriorating effect of aflatoxin B1 in cancer bearing animals. Lactate dehydrogenase and aminotransferases levels were decreased in liver, whereas alkaline phosphatase and gamma-glutamyl transpeptidase were increased in cancer conditions. These enzyme levels were reversed to near normal control values in drug treated animals. The analysis of marker enzyme activities clearly indicates the antitumour efficacy of Semecarpus anacardium Linn. nut extract on aflatoxin B1 induced hepatocellular carcinoma.

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PubMed1981

Studies on the mechanism of aflatoxin B1 inhibition of rat liver nucleolar RNA synthesis.

In an earlier report, it was shown that aflatoxin B1 treatment strongly inhibits rat liver nucleolar RNA synthesis (Yu, F. L. (1977) J. Biol. Chem. 252, 3245-3251). The present paper is an attempt to elucidate the mechanism of this inhibition. Two h after aflatoxin B1 injection (0.3 mg/100 g body weight), rat liver nucleolar RNA synthesis, in vitro, was inhibited by an average of 90%. This inhibition could result from (a) inhibited RNA polymerase I activity per se, (b) impaired nucleolar DNA template, or (c) impaired nucleolar chromatin. Earlier studies found that the total RNA polymerase I activity was not affected by aflatoxin B1 treatment. In the present work the total nucleolar DNAs from control and from aflatoxin B1-treated groups were isolated and compared for template efficiencies in directing RNA synthesis with solubilized RNA polymerase I from the control group. No difference was found. However, when nucleolar chromatin function was analyzed, it was found that aflatoxin B1 treatment resulted in a dramatic reduction in the RNA chain elongation rate to only 13% of the control. The chain number, which is a measure of the number of engaged enzymes transcribing the nucleolar chromatin initiated in vivo, was only slightly reduced (33%). Furthermore since it was found that aflatoxin B1 treatment did not increase RNase activity in the treated nucleoli, the dramatic decrease in RNA chain elongation is therefore believed to be the major mechanism of aflatoxin B1 inhibition of rat liver nucleolar RNA synthesis. DNase I digestion of the nucleolar chromatin suggests that aflatoxin B1 treatment may have altered the conformation of the transcriptionally active regions of the nucleolar chromatin.

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PubMed2000

Hepatocurative effect of picroliv and silymarin against aflatoxin B1 induced hepatotoxicity in rats.

Single doses of aflatoxin B1 (2 mg/kg, i.p.) caused significant increases in the activities of tau-glutamyl transpeptidase, 5'-nucleotidase, acid phosphatase and acid ribonuclease, and decreases in the activities of succinate dehydrogenase and glucose-6-phosphatase in liver, after 8 weeks. The level of lipid peroxides, DNA, RNA, and cholesterol increased while glycogen decreased. It also increased the serum level of transaminases, sorbitol dehydrogenase, glutamate dehydrogenase, lactate dehydrogenase, acid phosphatase, alkaline phosphatase, and bilirubin. Oral administration of picroliv (25 mg/kg/day for 15 days), a standardised iridoid glycoside fraction of Picrorhiza kurroa, 6 weeks after aflatoxin B1 toxication, significantly prevented the biochemical changes induced in liver and serum of aflatoxin B1 treated rats. The hepatocurative effect of picroliv and silymarin, a plant based standard hepatoprotective are comparable.

Aflatoxin B1↗

PubMedDate not supplied

Effect of aflatoxin B1 on egg production.

Laying pullets dosed with aflatoxin B1 showed a significant decrease in egg production at aflatoxin levels of 0.7 mg per kg body weight per day or higher. When the dose was 5 mg/kg, production ceased after three days. At 1.0 or 0.7 mg/kg, no effect on production was apparent until four to five weeks after the 14-day dosing period. No aflatoxin B1 could be detected chemically in eggs during dosing or for 10 weeks following dosing.

Aflatoxin B1↗

PubMedDate not supplied

Effects of aflatoxin B1 on chicken chondrocytes in culture.

In vitro effects of aflatoxin B1 on DNA and proteoglycan synthesis were assessed by measuring tritiated thymidine and radiosulfate incorporation by chicken chondrocyte cultures. Chondrocytes were harvested from the growth-plate cartilage of a 35-day-old chicken, cultured in triplicate, and treated with 0, 1, 5, 10, or 25 micrograms aflatoxin B1/ml of culture medium. The cultures were then spiked separately with [3H]thymidine or [35S]sulfate. After the cells, matrix, and medium were harvested, radioactivity was measured by a scintillation counter. Aflatoxin B1 resulted in a dose-dependent inhibition of DNA synthesis, as measured by tritiated thymidine incorporation by chicken chondrocytes: 54.6%, 30.9%, 25.9%, and 5.9% of control in cultures treated with 1, 5, 10, and 25 micrograms aflatoxin B1/ml of culture medium, respectively (P < 0.05). Sulfated proteoglycan synthesis, as measured by radiosulfate incorporation in chondrocyte cultures, was decreased in the media and intercellular matrix by all aflatoxin B1 levels. Compared with controls, 21% less (P < 0.05) radiosulfate was incorporated into non-matrix macromolecules of the medium fraction from chondrocytes exposed to 1 microgram aflatoxin B1/ml. However, 5 micrograms aflatoxin B1/ml was necessary to produce a significant decrease in radiosulfate incorporation in proteoglycans of intercellular matrix (34% less than controls). The ratios of the means of radiosulfate incorporation into intercellular macromolecules to the means of tritiated thymidine incorporation indicated that aflatoxin B1 inhibited DNA synthesis more than proteoglycan synthesis.

Aflatoxin B1↗

PubMed2000

Effects of dietary oltipraz and ethoxyquin on aflatoxin B1 biotransformation in non-human primates.

Following aflatoxin B1 (AFB) exposure, rats readily develop liver tumors. However, treatment of rats with a variety of compounds, including the synthetic dithiolthione oltipraz and the antioxidant ethoxyquin, protects these rodents from AFB-induced hepatocarcinogenesis. Several epidemiological studies strongly suggest that AFB is also a causative agent of liver cancer in humans. However, relatively little is known about the efficacy of cancer chemoprevention in human and non-human primates. To this end, we examined the effects of chemopreventive agents on AFB metabolism in non-human primates. Hepatic aflatoxin B1 metabolism profiles of macaque (Macaca nemestrina) and marmoset (Callithrix jacchus) monkeys were determined and compared to humans. Quantitatively, the oxidative metabolism of this mycotoxin was similar in the three primate species. In contrast to macaques, both humans and marmosets lacked AFB-glutathione conjugating activity. It was concluded that marmosets resembled human AFB metabolism more closely than the macaques, and therefore, marmoset monkeys were chosen for this study. Eleven adult male marmosets were randomly assigned to three groups. Animals received the synthetic dithiolthione oltipraz, the antioxidant ethoxyquin, or vehicle only. In addition, two single doses of AFB were also administered orally before and after animals were treated with aforementioned compounds. Both oltipraz and ethoxyquin induced aflatoxin B1-glutathione conjugating activity in the livers of some but not all marmosets. In addition, 10 microM oltipraz inhibited cytochrome P450-mediated activation of AFB to the ultimate carcinogenic metabolite, aflatoxin B1-8,9-epoxide, in vitro, up to 51%. Furthermore, animals treated in vivo with oltipraz, but not ethoxyquin, exhibited a significant reduction (53% average) in AFB-DNA adduct formation relative to the control animals (p < 0.05). Together, our data suggest that chemoprevention is also effective in primates; however, most likely to a lesser degree than in rodents.

Aflatoxin B1↗

PubMed1980

Different tissue responses of mixed function oxidases and detoxifying enzymes to aflatoxin B1 administration in the rat.

The carcinogenic effects of aflatoxin B1 have been related to the formation of an active intermediate metabolite, an epoxide produced via the cytochrome P-450-mediated mixed function oxidase. The toxicity of this intermediate is dependent on metabolic transformations by enzymes such as aryl hydrocarbon hydroxylase, glutathione S-transferase and glutathione peroxidase. Like the mixed function oxygenase, these enzymes are inducible, and dependent on the action of specific drugs and inducers. The present study describes the effect of a single sublethal i.p. dose (6 mg/kg body wt) of aflatoxin B1 on the specific activities of microsomal demethylases, aryl hydrocarbon hydroxylase (AHH), glutathione S-transferase and glutathione peroxidase in rat liver, kidney, lung, brain and adrenals. The enzymes were assayed 24 h after the toxin treatment. Among the different tissues, only liver AHH showed an induction on toxin treatment whereas those of kidney and brain declined. Microsomal demethylase was also high in liver and low in kidney. However, no significant alteration was induced by aflatoxin B1 on glutathione S-transferase and glutathione peroxidase activities in the various tissues examined except the adrenals, which showed a significant increase. The present study revealed that the reaction sequence for metabolic transformation of aflatoxin B1 is more complex than foreseen from the activities of these inducible metabolite-transforming enzymes.

Aflatoxins↗

PubMed1977

[Degradation of aflatoxin b1 by various microorganisms (author's transl)].

The degradation of aflatoxin B1 by various representatives of bacteria, yeasts and moulds in growing and resting cultures was investigated. We found that growing cultures of Corynebacterium rubrum degraded the added aflatoxin nearly quantitatively. -- Growing cultures of anascosporogenous yeasts degraded most of aflatoxin B1 while no degradation of this substance by ascosporogenous yeasts could be stated. Moulds degraded aflatoxin B1 to a high extent. -- With regard to the course of degradation three types can be distinguished. -- In the cultures of moulds two blue fluorescing compounds were found beside aflatoxin B1.

Aflatoxins↗