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PubMed1975

[Spectrophotometric investigations on aflatoxin B1 and aflatoxin G1 (author's transl)].

UV-spectrophotometric and fluorescence-spectrophotometric investigations have been performed on the aflatoxins B1 and G1 with the aim of their unequivocal identification and quantitative estimation in the routine examination. The lower limits of the quantitative and semiquantitative estimations have been found to be 0,4 ng (thin layer chromatography, semiquantitative), Imug/ml (UV-spectroscopy) and 10 ng/ml (fluorescence spectroscopy) for the aflatoxin B1 and 0,3 ng (TLC, semiquantitative), 1 mug/ml (UV-spectroscopy) and 1 ng/ml (fluorescence spectroscopy). Quinine sulfate in 0.1 n sulfuric acid was successfully utilized as a convenient standard substance for quantitative fluorescence spectroscopic estimations of the aflatoxins B1 and G1. In an extensive series of estimations the fluorescence intensity of aflatoxin B1 in chloroform in the range of 0,01-10 mug/ml has been compared with that of equally concentrated solutions of quinine sulfate in sulfuric acid. The ratio of the intensities was 0.5 : 1(0.509 : 1). Similar comparative estimations of aflatoxin G1 in chloroform in the range of 0.001 bis 1 mug/ml and quinine sulfate in sulfuric acid resulted in a ratio of 5 : 1 (4.99 : 1). These ratios have been found using a fluorescence spectrophotometer Beckman SF 1078.

Aflatoxins↗

PubMed1992

Effect of soil on aflatoxin tissue retention in chicks when added to aflatoxin-contaminated poultry rations.

The effects of silty clay loam soil on aflatoxin B1 (AFB1) absorption were investigated when added to the diets of chicks fed aflatoxin-contaminated rations. Sixty 1-d-old White Leghorn chicks were fed a control ration (< 5 ng AFB1/g), a low aflatoxin-contaminated ration (55 ng AFB1/g), a high aflatoxin-contaminated ration (4,488 ng AFB1/g), or high aflatoxin-contaminated rations (4,488 ng AFB1/g) + 25% or 50% soil. Livers in each group were pooled and analyzed for AFB1 and metabolites. The addition of soil significantly reduced the levels of AFB1 in the livers, although the reduction was less when 25% soil was fed compared with the 50% soil feeding.

Aflatoxins↗

PubMed1992

Distribution of aflatoxin-producing moulds and aflatoxins in dairy cattle feed and raw milk.

Distribution of aflatoxigenic moulds and aflatoxin B1 in Yugoslav dairy cattle feeds as well as the presence of aflatoxin B1 and M1 in raw milk, was tested. The experiments were carried out through three years (in all seasons). Samples were taken from state and private farms in Vojvodina. Feeds were contaminated in 83-100% with moulds. Fungi of farms in Vojvodina. Feeds were contaminated in 83-100% with moulds. Fungi of Aspergillus flavus-oryzae group were present permanently and the highest incidence of them was noticed during the third research year. Aflatoxin B1 was not found in the first year, but malt spent grains used for cows' feeding in summer of the second research year was contaminated with it (50.0 micrograms/kg). The same feed and pelleted sugar beet pulp were contaminated with aflatoxin B1 in winter, spring and summer of the third research year (5.0 to 16.0 micrograms/kg). Aflatoxin B1 and M1 were not found in raw milk through three-years investigations.

Aflatoxin B1↗

PubMedDate not supplied

Effects of dietary aflatoxin and ammonia-inactivated aflatoxin on Newcastle disease antibody titers in layer-breeders.

Corn containing aflatoxin and the same corn ammoniated to inactivate aflatoxin was incorporated into layer diets to supply 500 ppb and 2.3 ppb aflatoxin, respectively, to determine whether such diets interfere with immunity to Newcastle disease vaccination. Control diets containing uncontaminated corn, both with and without ammoniation, were also fed. A trial 3 months long with 12 birds per treatment was conducted. Vaccination treatments included no vaccination, a single vaccination at the initiation of each trial, and monthly vaccinations for three months. Serum samples, for determination of Newcastle disease hemagglutination-inhibition titers by the microtiter method, were collected just before vaccination and seven days postvaccination, as well as at trial termination. Birds receiving a single initial vaccination and fed a diet containing 500 ppb aflatoxin showed a significant (P less than 0.05) decrease in HI titers, whereas birds similarly vaccinated and fed a diet containing inactivated (ammoniated) aflatoxin showed no reduction in titers regardless of dietary treatment.

Aflatoxins↗

PubMed1982

The comparative metabolism and toxic potency of aflatoxin B1 and aflatoxin M1 in primary cultures of adult-rat hepatocytes.

Both aflatoxin B1 (AFB1) and a hydroxylated metabolite, aflatoxin M1 (AFM1), were potent cytotoxins and genotoxins to primary cultures of rat hepatocytes. However, AFB1 stimulated the release of lactate dehydrogenase into the culture medium and the loss of viable cells from the monolayer at lower doses than did AFM1. The lowest toxic doses of AFB1 and AFM1 were 0.05-01 and 0.6 microgram/culture, respectively. Genotoxicity, determined by an assay for stimulation of DNA repair, was apparent at lower doses than was cytotoxicity. AFB1 was again more potent than AFM1, stimulating DNA repair at 0.025 microgram/culture, compared to the lowest genotoxic dose of AFM1 of 0.05 microgram/culture. At higher doses (1.2-2.4 microgram/culture) the responses due to both aflatoxins in the cytotoxicity and DNA-repair assays were approximately equal. The metabolism of a low dose (c. 0.17 microgram/culture) of [14C]AFB1 and [3H]AFM1 by cultured hepatocytes differed significantly. After 1 hr, 50% of the [14C]AFB1 remained unchanged in the culture medium, whereas about 18 hr were required for the same amount of [3H]AFM1 metabolism to occur [14C]AFB1 was metabolized to AFM1, to polar metabolites recovered in the aqueous phase after chloroform extraction, and to metabolites covalently bound to hepatocyte macromolecules. [3H]AFM1 was also metabolized to polar metabolites and to forms bound to macromolecules. The degree of covalent binding of the aflatoxins correlated with their cytotoxicity and genotoxicity at lower doses. After a 24-hr incubation, 12.5% of the dose of [14C]AFB1 was covalently bound to macromolecules compared to 1.5% of [3H]AFM1. Although AFM1 was less potent than AFB1 in cytotoxicity, DNA-repair and covalent-binding assays using primary cultures of hepatocytes, AFM1 was still active at relatively low doses and therefore is probably a potent hepatotoxin in vivo.

Aflatoxin B1↗

PubMedDate not supplied

Aflatoxins B1, M1 and aflatoxicol in tissues and urine of calves receiving aflatoxin.

Liver and kidney tissues and urine from calves chronically or acutely intoxicated by aflatoxin were surveyed to detect the presence of aflatoxins B1, M1 (AFB1, AFM1) and aflatoxicol (AFL). Aflatoxins B1, M1, and aflatoxicol were not found in the liver, kidney or urine from animals intoxicated by chronic forms. However in a calf that received a single dose of 0.8 mg of AFB1/kg of live weight and one submitted to a single dose of 1.8 mg of AFB1/kg of live weight detectable levels of aflatoxins occurred in tissues and urine.

Aflatoxin B1↗

PubMed1988

Comparative metabolism and DNA binding of aflatoxin B1, aflatoxin M1, aflatoxicol and aflatoxicol-M1 in hepatocytes from rainbow trout (Salmo gairdneri).

DNA binding and metabolism patterns of 3H-labeled aflatoxin B1 (AFB1) and its phase I metabolites, aflatoxicol (AFL), aflatoxin M1 (AFM1), and aflatoxicol-M1 (AFL-M1), were compared in freshly prepared rainbow trout (Salmo gairdneri) hepatocytes. Aflatoxins were incubated with hepatocytes for periods up to 1 h, cellular DNA was isolated and specific activities determined by scintillation counting and Burton analysis. Data for (pmol bound aflatoxin/micrograms DNA)/(mumol dose) versus time fit a linear function (P less than 0.002) passing nearly through the origin for each aflatoxin. DNA binding at 1 h relative to AFB1 was: AFL, 0.53 +/- 0.07; AFM1, 0.81 +/- 0.20 AFL-M1, 0.83 +/- 0.24. Statistical analysis indicated that binding of AFL, AFM1 and AFL-M1 were significantly less than that of AFB1. HPLC analysis of the cellular supernatants indicated that the major metabolites were AFL, AFB1, AFL-M1, and AFM1 from AFB1, AFL, AFM1 and AFL-M1 substrates, respectively. Small quantities of hydroxylated metabolites and glucuronides also were detected in some of the incubations. The time-course data suggested that initial formation of major metabolites was rapid and that, by 20-30 min, net changes in metabolite levels decreased or approached zero. Because the four compounds possess a 8,9-double bond, DNA binding could be due to activation of the parent substrates as well as of their phase I metabolites. Based on current mutagenicity data and limited carcinogenicity studies, AFM1 and AFL-M1 have binding levels which are higher than expected compared to AFB1 and AFL.

Aflatoxin B1↗

PubMed1982

Aflatoxicol and aflatoxins B1 and M1 in the tissues of pigs receiving aflatoxin.

Aflatoxicol (AFL) and aflatoxins B1 and M1 were found in tissues (kidney, liver, and muscle) of feeder pigs given an estimated LD50 oral dose of B1 (1.0 mg/kg body weight) provided as a rice culture of Aspergillus flavus and of market-weight pigs fed a naturally contaminated feed, containing aflatoxin B1 at a level of 400 ng/g from corn, for 14 days. The residues in all tissues decreased with time after treatment in both groups, with no detectable residues (approximate detection limits, ng/g, B1 0.03, M1 0.05, AFL 0.01) in pig tissues from the feeding experiment 24 h after withdrawal of aflatoxin-contaminated feed. B1 and M1, when found in the feeding experiment, were at about the same levels in all tissues except the kidney, in which M1 was the dominant aflatoxin. The level of AFL, when detected, was about 10% of the B1 level.

Aflatoxin B1↗

PubMed1987

Human aflatoxin B1 metabolism: an investigation of the importance of aflatoxin Q1 as a metabolite of hepatic post-mitochondrial fraction.

The metabolism of aflatoxin B1 by the post-mitochondrial fraction of human autopsy or biopsy liver and monkey necropsy liver was investigated. Aflatoxin Q1, a hydroxy metabolite of B1, was produced by 18 of 22 human liver samples and by 5 of 7 species of non-human primates investigated. Human specimens from both sexes, ages 20-80 years, with a variety of hepatic histological and historical influences produced this metabolite. Aflatoxin Q1 was of variable quantitative importance. Yields seldom exceeded 10% of initial B1. However, based upon its persistent formation in vitro, these studies identify the need to clarify the role of Q1 in aflatoxin epidemiology.

Adult↗

PubMed2003

Identification of aflatoxin M1-N7-guanine in liver and urine of tree shrews and rats following administration of aflatoxin B1.

Epidemiological studies have shown that exposure to aflatoxin B(1) (AFB(1)) and concurrent infection with hepatitis B lead to a multiplicative risk of developing liver cancer. This chemical-viral interaction can be recapitulated in the tree shrew (Tupia belangeri chinensis). As an initial characterization of this model, the metabolism of AFB(1) in tree shrews has been examined and compared to a sensitive bioassay species, the rat. Utilizing LC/MS/MS, an unreported product, aflatoxin M(1)-N(7)-guanine (AFM(1)-N(7)-guanine), was detected in urine and hepatic DNA samples 24 h after administration of 400 microg/kg AFB(1). In hepatic DNA isolated from tree shrews, AFM(1)-N(7)-guanine was the predominant adduct, 0.74 +/- 0.14 pmol/mg DNA, as compared to 0.37 +/- 0.07 pmol/mg DNA of AFB(1)-N(7)-guanine. Conversely, in rat liver, 6.56 +/- 2.41 pmol/mg DNA of AFB(1)-N(7)-guanine and 0.42 +/- 0.13 pmol/mg DNA of AFM(1)-N(7)-guanine were detected. Rats excreted 1.00 +/- 0.21 pmol AFB(1)-N(7)-guanine/mg creatinine and 0.29 +/- 0.10 pmol AFM(1)-N(7)-guanine/mg creatinine as compared to 0.60 +/- 0.12 pmol AFB(1)-N(7)-guanine/mg creatinine and 0.69 +/- 0.16 pmol AFM(1)-N(7)-guanine/mg creatinine excreted by the tree shrew. Furthermore, tree shrew urine contained 40 times more of the hydroxylated metabolite, AFM(1), than was excreted by rats. In vitro experiments confirmed this difference in oxidative metabolism. Hepatic microsomes isolated from tree shrews failed to produce aflatoxin Q(1) or aflatoxin P(1) but formed a significantly greater amount of AFM(1) than rat microsomes. Bioassays indicated that the tree shrew was considerably more resistant than the rat to AFB(1) hepatocarcinogenesis, which may reflect the significant differences in metabolic profiles of the two species.

Administration, Oral↗

PubMed2001

Quantification and validation of enzyme immunoassay for urinary aflatoxin B1-N7-guanine adduct for biological monitoring of aflatoxins.

The aflatoxin B1-N7-guanine (AFB1-N7-guanine) adduct has been established as one of the relevant biomarkers of dietary aflatoxin (AFB1) exposure. Measurement of this adduct is potentially a useful dosimeter in molecular epidemiological studies. This paper reports the application and evaluation of a sensitive indirect competitive enzyme-linked immunosorbent assay (ELISA) for the detection and quantification of urinary AFB1-N7-guanine adduct in high risk populations exposed to dietary aflatoxin. Earlier, we had reported a simple and rapid indirect ELISA method for AFB1-N7-guanine adduct in the urine and liver tissues using polyclonal antibodies specific to AFB1-N7-guanine adduct. The method was evaluated using a rodent model (Fischer 344), exposed to 1 mg kg-1 body mass of AFB1 and human urine samples obtained from a maize eating population, environmentally exposed to AFB1 through their diet. The levels of AFB1-N7-guanine adduct in rat and human urine ranged from 6.42 to 20.16 micrograms mg-1 creatinine and from 9.30 to 13.43 ng mg-1 creatinine, respectively. The level of AFB1 in the diet as estimated by ELISA ranged from 1000 to 3600 ng d-1. The interesting observation in these studies is that the females (in both rodents and human subjects) are more efficient than males at excreting the adduct. Total adduct (DNA bound adduct and guanine adduct excreted in urine) was found to be similar in male and female rats. However, 63% of the total adduct was accounted for in urine of female rats, whereas male rats excreted 47% of the total adduct in their urine. The present method may find wide application as a biochemical tool in molecular epidemiological studies with respect to human exposure to dietary aflatoxins.

Aflatoxin B1↗

PubMed1988

Biosynthetic origin of aflatoxin G1: confirmation of sterigmatocystin and lack of confirmation of aflatoxin B1 as precursors.

The origin of aflatoxin G1 was studied using mutant strains of Aspergillus parasiticus blocked early in the pathway and by tracing 14C-labelled aflatoxin B1 (AFB1) in wild-type A. flavus and A. parasiticus strains. Sterigmatocystin (ST) was a precursor of AFB1, AFG1 and AFG2 in the four mutants examined. The identity of AFG1 was confirmed by mass spectrometry. No evidence for conversion of AFB1 to AFG1 was found. A rigorously controlled study of conversions of radioactivity based on preparative thin-layer chromatography of aflatoxins demonstrated that low levels of aflatoxin interconversions previously reported in the literature might actually be artifacts.

Aflatoxin B1↗

PubMed1983

Genetic expression of aflatoxin metabolism. Effects of 3-methylcholanthrene and beta-naphthoflavone on hepatic microsomal metabolism and mutagenic activation of aflatoxins.

The effects of pretreatment with 3-methylcholanthrene (MC) and beta-naphthoflavone (beta NF) on the hepatic microsome-mediated mutagenesis of aflatoxin B1 (AFB1) and benzo[a]pyrene, and on the metabolism of aflatoxins B1 and B2, were investigated in inbred mouse strains. The inbred strains of mice studied included Ah nonresponsive strains (DBA/2Ha, AKR/Sn and RF/J), which were also nonresponsive to the induction of the metabolism of AFB1 to AFM1 (AFB1-4-hydroxylase activity), and Ah responsive strains (C57BL/6Ha, ICR/Ha, C3H/St, A/St, Balb/cCr, C57e/Ha and CBA/Pi), which were also responsive to the induction of AFB1-4-hydroxylase activity. The hepatic microsome-mediated enzyme activities studied included: mutagenic activation of AFB1 and benzo[a]pyrene in the Ames Salmonella typhimurium TA-98 system; metabolism of AFB1 and AFB2 to AFM1 and AFM2, respectively; and benzo[a]pyrene metabolism measured as the formation of fluorescent phenolic metabolites, i.e. aryl hydrocarbon hydroxylase (AHH) activity. Time-course and dose-response studies in C57BL/6Ha mice revealed that the metabolism of aflatoxin B1/B2 to aflatoxin M1/M2 (AFB1/B2-4-hydroxylase activity) was induced by both MC and beta NF. In the nonresponsive strains studied, pretreatment with MC or beta NF produced essentially little alteration of AFB1-4-hydroxylase activity or AHH activity or the mutagenic activation of AFB1 and benzo[a]pyrene. On the other hand, AFB1-4-hydroxylase activity in the responsive strains was induced 4- to 10-fold by MC (60 mg/kg) and 2.5- to 7-fold by beta NF (150 mg/kg). Also in the responsive strains, induction of AFB1-4-hydroxylase activity was strongly associated with (a) the depression of the mutagenic activation of AFB1, and (b) with the induction of both AHH and the mutagenic activation of benzo[a]pyrene. In summary, the results described in this report suggest that: (a) induction of AFB1-4-hydroxylase activity by MC (or beta NF) is associated with the depression of AFB1 mutagenesis and with the induction of benzo[a]pyrene mutagenesis; and (b) induction by MC (or beta NF) of AHH activity, AFB1-4-hydroxylase activity and AFB2-4-hydroxylase activity is controlled by either the same or closely linked genetic factors.

Aflatoxins↗

PubMed1978

Urinary excretion of aflatoxin M1 after administration of aflatoxin B1 in sucrose- or starch-rich diets.

1. Male Sprague--Dawley rats were given 630 g/kg sucrose or starch with 2 mg/kg aflatoxin b1 for periods of 75, 145 and 200 d, and the 24 h urinary excretion of aflatoxin M1 was measured. 2. Less aflatoxin M1 was excreted by the rats fed on the sucrose-rich diet compared to those fed on the starch-rich diet. This difference was especially marked when expressed per g metabolizing tissue. 3. It is concluded that sucrose probably decreases the activity of aflatoxin B1 metabolism in a similar way to its previously found effect on the drug-metabolizing enzyme.

Aflatoxins↗

PubMed1995

Physical and transcriptional map of an aflatoxin gene cluster in Aspergillus parasiticus and functional disruption of a gene involved early in the aflatoxin pathway.

Two genes involved in aflatoxin B1 (AFB1) biosynthesis in Aspergillus parasiticus, nor-1 and ver-1, were localized to a 35-kb region on one A. parasiticus chromosome and to the genomic DNA fragment carried on a single cosmid, NorA. A physical and transcriptional map of the 35-kb genomic DNA insert in cosmid NorA was prepared to help determine whether other genes located in the nor-1-ver-1 region were involved in aflatoxin synthesis. Northern (RNA) analysis performed on RNA isolated from A. parasiticus SU1 grown in aflatoxin-inducing medium localized 14 RNA transcripts encoded by this region. Eight of these transcripts, previously unidentified, showed a pattern of accumulation similar to that of nor-1 and ver-1, suggesting possible involvement in AFB1 synthesis. To directly test this hypothesis, gene-1, encoding one of the eight transcripts, was disrupted in A. parasiticus CS10, which accumulates the aflatoxin precursor versicolorin A, by insertion of plasmid pAPNVES4. Thin-layer chromatography revealed that gene-1 disruptant clones no longer accumulated versicolorin A. Southern hybridization analysis of these clones indicated that gene-1 had been disrupted by insertion of the disruption vector. These data confirmed that gene-1 is directly involved in AFB1 synthesis. The predicted amino acid sequence of two regions of gene-1 showed a high degree of identity and similarity with the beta-ketoacyl-synthase and acyltransferase functional domains of polyketide synthases, consistent with a proposed role for gene-1 in polyketide backbone synthesis.

Aflatoxin B1↗

PubMed2001

Effects of aflastatin A, an inhibitor of aflatoxin production, on aflatoxin biosynthetic pathway and glucose metabolism in Aspergillus parasiticus.

Aflastatin A inhibits aflatoxin production by Aspergillus parasiticus via an unknown mechanism. We found that aflastatin A clearly inhibited production of norsolorinic acid, an early biosynthetic intermediate of aflatoxin, at a concentration of 0.25 microg/ml. Reverse-transcriptase polymerase chain reaction (RT-PCR), and real-time quantitative PCR (TaqMan PCR) experiments indicated that the transcription of genes encoding aflatoxin biosynthetic enzymes (pksA, ver-1, and omtA) and a gene encoding a regulatory protein for expression of the biosynthetic enzymes (aflR) were significantly reduced by the addition of aflastatin A. We also found that aflastatin A elevated the glucose consumption and ethanol accumulation by A. parasiticus, and repressed transcription of genes involved in ethanol utilization. These results suggest that aflastatin A inhibits a very early step in aflatoxin biosynthesis prior to the transcription of aflR and can influence glucose metabolism in the fungus.

Aflatoxins↗

PubMed1977

Aflatoxin B1-2,3-oxide as a probable intermediate in the covalent binding of aflatoxins B1 and B2 to rat liver DNA and ribosomal RNA in vivo.

Administration of[3H]aflatoxin B2 (2,3-dihydroaflatoxin B1)(AFB2) to male rats resulted in levels of hepatic DNA- and ribosomal(r)RNA-aflatoxin adducts that were about 1% of those for rats given [3H]aflatoxin B1(AFB1). The levels of hepatic protein-aflatoxin adducts were 35 to 70% as great for AFB2-treated as compared to AFB1-treated rats...

Aflatoxins↗

PubMed1990

Distribution of aflatoxins in tissues of growing pigs fed an aflatoxin-contaminated diet amended with a high affinity aluminosilicate sorbent.

The effect of hydrated sodium calcium aluminosilicate (HSCAS) added to the diet of swine fed an aflatoxin-contaminated diet on tissue aflatoxin levels was investigated. Pigs were fed control (less than 10 ng/g B1 + B2), contaminated (500-600 ng/g B1 + B2), and contaminated +0.5% HSCAS diets. Tissues analyzed for the presence of aflatoxin B1, B2, and M1 residues included liver, muscle, kidney, and adipose. Addition of HSCAS to the contaminated diet significantly reduced the amount of M1 in liver, kidney, and muscle tissue. Aflatoxin B1 was not reduced in liver or kidney, but was decreased in muscle.

Aflatoxins↗