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PubMed1975

Reduction of aflatoxins B1 and B2 with sodium borohydride.

Reduction of aflatoxin B1 and aflatoxin B2 with sodium borohydride quantitatively yielded new fluorescent derivatives, designated as aflatoxin RB1 and aflatoxin RB2. Mass spectrometric data showed that RB1 and RB2 were trihydroxy derivatives of B1 and B2, respectively. Nuclear magnetic resonance analysis revealed that new chemical shifts were present in aflatoxins RB1 and RB2 in addition to those of the parent aflatoxins. The new compounds had lower melting points and different ultraviolet and infrared spectra compared to aflatoxins B1 and B2 and the monohydroxy derivative aflatoxicol. They were lses toxic to chick embryos than the parent toxins. Since the reduction yields were quantitative and since the reduction products could be detected at low levels comparable to those for B1 and B2, the reduction reaction could be used as a confirmatory test for both aflatoxins B1 and B2. Preliminary results obtained from gas-liquid chromatography (GLC) analysis of the trimethylsilyl derivatives of aflatoxins RB1 and RB2 indicated that these compounds could furnish the basis for developing an analytical GLC method for aflatoxins B1 and B2.

Aflatoxins↗
PubMed1992

Sensitivity and single-strand DNA break repair in Chinese hamster mutants exposed to the carcinogen aflatoxin B1 epoxide and its dichloride model.

Aflatoxin B1 (AFB1) is a potent carcinogen and mutagen. It requires metabolic activation to be converted to the DNA-binding product aflatoxin B1 epoxide (AFB1-epoxide). A model of this epoxide is aflatoxin B1 dichloride (AFB1Cl2). Both react at the N7 position of guanine to form large adducts. The major adduct formed can either be rapidly removed to leave an apurinic site or can undergo ring opening of the imidazole ring to form a chemically stable adduct. A number of Chinese hamster DNA repair-deficient mutants have been screened for their sensitivity to AFB1-epoxide and AFB1Cl2. Some of the mutants screened belong to different UV complementation groups. Human genes involved in nucleotide excision-repair correct deficiencies found in these complementation groups. The mutants which were found to be most sensitive to AFB1 (V-C4 and V-H1) were further investigated. Alkaline elution was used to measure AFB1-induced DNA single-strand break repair in the mutants. V-H1 repaired completely in 24 h whereas V-C4 displayed only partial repair.

Aflatoxin B1↗
PubMed1982

Enhanced hepatotoxicity of aflatoxin B1 by pretreatment of rats with ethanol.

Hepatotoxicity of aflatoxin B1 (2.0 and 4.0 mg/kg i.p.) as determined by plasma enzyme activities (GPT and GOT), liver triglycerides and histopathologic changes was enhanced in rats pretreated with four oral doses of ethanol (4.0 g/kg each) at 48, 45, 24 and 21 hrs prior to aflatoxin B1 administration. Pretreatment with ethanol (4.0 g/kg) slightly increased liver weight without changing hepatic microsomal protein contents. Also it caused an increase in microsomal aniline hydroxylase but a decrease in p-nitroanisole-o-demethylase, 48 hrs after the first ethanol dose. In the rats pretreated with ethanol, aflatoxin B1 was metabolized at a higher extent to aflatoxins M1 and Q1. These results suggest that an increased hepatotoxicity of aflatoxin B1 after pretreatment with ethanol may presumably due to an increase in microsomal formation of active aflatoxin B1 metabolite.

Aflatoxin B1↗
PubMedDate not supplied

A study on the inhibition of aflatoxin B1 induced hepatocarcinogenesis by the Rhizopus delemar.

The effect of Rhizopus delemar on the carcinogenicity in rats of Aflatoxin B1 was studied. The Aflatoxin B1 was administered in free drinks to each male wistar rat at 126 micrograms per week such that a total dose of 3.40 mg was given over a period of 27 weeks. The culture abstract of Rhizopus delemar was added simultaneously to a group of these rats by mixing the Aflatoxin B1 solution. Animals were killed separately during 18th, 30th, 38th and 52nd week. Liver cell altered foci and neoplasms were qualified by using light microscopic and electromicroscopic morphology, by the morphometry and by the enzymic reactions. In the group of Aflatoxin B1 the incidence of hepatocellular carcinoma was 71%. In the group receiving Rhizopus delemar together with Aflatoxin B1, the hyperplastic foci and pathological enzymic foci were decreased at all times pointed and atd at termination, and in none of the rats had liver neoplasms appeared. The result of this experiment showed that the Rhizopus delemar has intensive capacity in inhibiting the toxic damage and carcinogenicity of the liver by the Aflatoxin B1, because it is not only able to postpone the appearance of altered foci and to control their development but also to accelerate their withdraw in advance. The Rhizopus delemar can be used as a feasible and efficacious means to control the intoxication of Aflatoxin B1.

Aflatoxin B1↗
PubMed1997

Synthesis and characterization of aflatoxin B1 mercapturic acids and their identification in rat urine.

Biologic effects of the hepatocarcinogenic mycotoxin aflatoxin B1 are principally induced by one of its metabolites, the exo-aflatoxin B1 epoxide which produces both DNA and protein adducts in vivo. Detoxication of the exo-aflatoxin B1 epoxide can be mediated in part by glutathione S-transferases whose induction could be important in chemoprotection interventions. Thus, biomarkers of the enzymatic conjugation of exo-aflatoxin B1 epoxide with glutathione may be important indices of protection against the toxic effects of this agent. Since glutathione conjugates undergo further metabolic processing in vivo to yield mercapturic acids, increased urinary excretion of exo-aflatoxin B1 mercapturate could be expected during chemoprotection intervention. To determine if this mercapturic acid could be used as a biomarker, techniques for its specific measurement were developed using monoclonal antibody immunoaffinity chromatography and reverse phase high-performance liquid chromatography with ultraviolet absorbance and mass spectral detection. First, a synthetic exo-aflatoxin B1 mercapturate was characterized using mass spectrometry, ultraviolet absorbance, circular dichroism spectrometry, and chemical derivatization. In vivo metabolite characterization was then facilitated by comparison with the synthetically prepared exo-aflatoxin B1 mercapturate and both aflatoxin B1-glutathione conjugate diastereoisomers. In rats, 1% of the aflatoxin dose was excreted as exo-aflatoxin B1 mercapturate within 24 h. The finding that exo-aflatoxin B1 mercapturate was excreted in urine in a dose-dependent manner provides the basis for investigating its applicability as a biomarker of glutathione S-transferase status in aflatoxin chemoprotection studies.

Acetylcysteine↗
PubMed1984

Effect of aflatoxin B1 and major metabolites on phytohemeagglutinin-stimulated lymphoblastogenesis of bovine lymphocytes.

Effects of aflatoxin B1 and three of its metabolites on cellular immune response were assessed with an assay based on inhibition of tritiated thymidine uptake by phytohemeagglutinin stimulated lymphocytes. In this in vitro system aflatoxin B1 and aflatoxin Q1 were strongly inhibitory (more than 50% inhibition) at concentrations of 10 mu/ml, whereas aflatoxicol and aflatoxin B2 alpha exhibited little inhibition at 10 micrograms/ml and only 45 to 50% inhibition at 25 micrograms/ml. Contrasts with single degrees of freedom and orthogonal polynomial analysis revealed that the pair of aflatoxin B1 and aflatoxin Q1 differed linearly and quadratically from the pair of aflatoxin B2 alpha and aflatoxicol, but within each pair there were no differences. Limited data with aflatoxin M1 revealed that it was slightly more active than aflatoxicol in the assay, but minimal replication prevented rigorous statistical testing. It may be theorized that the moderate to strong inhibition of blastogenesis by aflatoxin B1 and its metabolites could inhibit T lymphocyte functions, such as killer, helper, effector, or other immune processes, and thus compromise the immunological surveillance mechanism.

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↗
PubMed1977

Hepatic cell loss and proliferation induced by N-2-fluorenylacetamide, diethylnitrosamine, and aflatoxin B1 in relation to hepatoma induction.

Three hepatic carcinogens (aflatoxin B1, diethylnitrosamine (DEN) and N-2-fluorenylacetamide (FAA)) were compared for carcinogenicity, early cell toxicity and parenchymal cell proliferation. The carcinogens were administered to rats for 15 weeks as follows: aflatoxin B1, 1 in 10(6) in pelleted food; DEN, 2 in 10(5) in drinking water; FAA, 3 in 10(4) in pelleted food. The loss of prelabelled DNA and the [H3] TdR pulse-labelling indices (LI) of parenchymal and nonparenchymal cells were determined at various times during the period of carcinogen availability. On a molar basis, aflatoxin B1 was 90 times as carcinogenic as FAA and 24 times as carcinogenic as DEN. However, for about equal magnitudes of hepatic cell proliferation and loss, aflatoxin B1 was the least potent carcinogen. For a given level of carcinogenicity, FAA was more potent than DEN in causing loss of hepatic DNA and in increasing the parenchymal cell labelling index. DEN and aflatoxin B1 produced about the same degree of DNA loss and parenchymal cell labelling, but the former was a more potent carcinogen. When carcinogenicity was compared for approximately equal levels of early hepatic cell destruction and proliferation, the 3 chemicals in the present study could be ranked in descending order of potency as DEN, FAA and aflatoxin B1.

2-Acetylaminofluorene↗
PubMed1978

Toxic effects of aflatoxin B1 on Bacillus brevis.

At a concentration of 50 microgram/ml and below, aflatoxin B1 inhibited Bacillus brevis (2611) bacteristatically, but at a concentration of 100 microgram/ml the inhibition was bactericidal. Bactericidal inhibition was further studied by determining the mean single survivor times of the bacterium in 100 microgram/ml aqueous solutions of aflatoxin B1 (18.2 mins.) and phenol (16.6 mins.). Further study on the bacteriostatic inhibition within the bacteriostatic concentration limit of 50 microgram/ml shows that the doubling time of B. brevis exposed to 5 microgram/ml aflatoxin B1 is approximately half that of the bacterium exposed to 10 microgram/ml. At the molecular level, 50 microgram/ml aflatoxin B1 inhibited the synthesis of DNA (78%), RNA (15%) and Protein (18%) in B. brevis. The strength of the affinity of subcellular fractions of B. brevis for aflatoxin B1 during inhibition was studied by assessing the resistance of aflatoxin B1 bound to cell fractions to removal by water. 66% (w/w) of the aflatoxin B1 bound to B. brevis after six successive washes in 50 ml distilled water, remained bound to the cell membrane fraction. The implication of this preferential strong binding to cell membrane was studied by investigating its effect on oxygen uptake. Results of inhibition of oxygen uptake is compatible with aflatoxin B1 binding to cell membrane. Vitamin k, however, reversed this inhibition.

Aflatoxins↗
PubMed1994

[Changes of anaphylactic sensitivity to some food proteins and aflatoxin B1 in guinea pigs].

The study was made of aflatoxin B1 effect on guinea pig alimentary anaphylaxis to chicken ovalbumin (CO) and pasteurized cow milk (PCM), of CO-specific IgG antibody levels, some serum indices, sensitivity of the animals to LD50 histamine. In response to aflatoxin B1 alimentary anaphylaxis both to CO and PCM became more severe, lethality of the anaphylaxis to CO being in logarithmic relation to aflatoxin B1 dose (p < 0.05); specific IgG-antibodies to CO grew in number; serum total protein increased against unchanged levels of albumins; the activity of gamma-glutamyltransferase inhibited; histamine shock gained severity, its lethality being logarithmically related to the aflatoxin B1 dose. The discussion covers mechanisms underlying the animal allergic reactivity responses to aflatoxin B1.

Aflatoxin B1↗
PubMed1983

Fate of aflatoxins in tissues, fluids, and excrements from cows dosed orally with aflatoxin B1.

A study was conducted to determine aflatoxins in tissues and non-tissues of 2 Holstein cows given oral doses of 0.35 mg of purified aflatoxin B1/kg of body weight/day for 3 consecutive days. Cow 1 was slaughtered 24 hours after the 3rd dose, and cow 2, after day 3, was fed aflatoxin-free rations for 7 additional days before slaughter. Tissue samples of brain, gallbladder and bile, heart, intestine, kidney, liver, lung, mammary gland, skeletal muscle, spleen, supramammary lymph nodes, thymus, and tongue, and nontissue samples of blood, feces, milk, rumen content, and urine were examined. Aflatoxins B1 and M1 were found in all samples of cow 1, except the thymus. Kidney, liver, and mammary gland had the highest concentrations of total aflatoxins (57.9, 13.2, and 25.1 ng/g, respectively), with the aflatoxin M1 concentration 40 times more than the aflatoxin B1 level in kidney. Aflatoxin residues were present (0.02 to 0.11 ng/g) only in kidney, liver, and intestine of the tissues from cow 2 (fed aflatoxin-free feed for 7 additional days). Aflatoxin B1 was not present in nontissue samples, but aflatoxin M1 (0.10 and 1.5 ng/ml) was found in the last milk and urine samples from the same cow. Urine assays are a possible way to monitor the presence of aflatoxin residues in meat tissues.

Aflatoxins↗
PubMed1998

The role of trace metal ions in aflatoxin B1 degradation by Flavobacterium aurantiacum.

Flavobacterium aurantiacum NRRL B-184 possesses the ability to degrade aflatoxin B1 in solution and in several food items. Aflatoxin B1 is a potent carcinogen that causes significant economic losses to the agricultural and food industry. The role of trace metal ions (Cu2+, Mn2+, Zn2+, and Co2+) were studied in an effort to understand the enzymatic system involved in aflatoxin B1 degradation by F aurantiacum. The effect of divalent chelators (EDTA and 1,10-phenanthroline [OPT]) in the presence of the trace metal ions was studied as well. Aflatoxin B1 (10 microg/ml) was added to 72-h cultures of F aurantiacum that had been washed and resuspended in phosphate buffer (pH 7.0). HPLC was used to determine aflatoxin B1 concentration in these cultures. Incubating cells at 30 degrees C with 1 and 10 mM Cu2+, Mn2+, and Zn2+ significantly decreased aflatoxin B degradation after 4 and 24 h (P < 0.05). Decreased degradation was also observed with 1 and 10 mM Cu2+ and Zn2+ after 48 h and with 0.1 mM Cu2+ after 24 and 48 h. Co2+ did not have a significant effect on aflatoxin B1 degradation. EDTA and OPT did not counter the inhibition in the presence of Cu2+. The addition of 1 mM EDTA countered the inhibition by 1 mM Mn2+ after 4 and 24 h, but 1 mM OPT did not counter the inhibition by 10 mM Mn2+ after 4 and 24 h. OPT countered the inhibition by 1 mM Zn2+ after 4 and 48 h. These trace elements inhibit aflatoxin B1 degradation by F aurantiacum. In addition, their presence necessitates higher concentrations (>1 mM) of EDTA and OPT for the removal of their inhibitory effect.

Aflatoxin B1↗
PubMed2002

Aflatoxin B1 content in patients with hepatic diseases.

Aflatoxins are toxic metabolites of some Aspergillus flavus, A. parasiticus and A. nomius strains that occur in many foods and feeds. There are four major natural occurring aflatoxins: B1, B2, G1 and G2. These toxins can cause illness in human beings and animals. Aflatoxin B1 is the most abundant and toxic member of the family, and it is also the most potent hepatocarcinogen known. In order to estimate the potential human health risk of AFB1, it is useful to measure blood concentration. The presence of aflatoxin B1 in patients was evaluated by high-performance liquid chromatography, in serum samples, obtained from 20 patient volunteers with hepatic disease. Out of the 20 patients, the presence of AFB1 was detected in only one of them, in a concentration of 0.47 ng/cm3. Nevertheless, this result should draw the attention of control organizations in Argentina to the need for a thorough food and feed inspection.

Adult↗
PubMed1979

The detoxication of aflatoxin B1 with glutathione in the rat.

1. The deactivation of aflatoxin B1 by glutathione (GSH) has been investigated in rat. Binding of metabolites of aflatoxin B1 to [3H]glutathione in vitro with rat liver microsomes is insignificant. Incubation with rat liver 10 000 g supernatant results in increased binding. Under identical conditions, benzo(a)pyrene metabolites are bound to [3H]glutathione much more than is aflatoxin B1. 2. Pre-treatment of rats with aflatoxin 1 (2 mg/kg) caused depletion in GSH of rat liver with a minimum at 6 h but returning to above normal at 24 h. GSH S-transferase activity was marginally increased at 6 h also and returned to normal at 24 h. 3. Kidney GSH was not significantly decreased, but kidney GSH S-transferase activity showed a sudden increase in 6 h, returning to almost normal at 24 h. 4. Pre-treatment with benzo(a)pyrene (2 mg/kg) caused greater depletion of hepatic GSH than occurred with aflatoxin B1 but did not show any effect on kidney GSH. 5. Hepatic and kidney GSH S-transferase in benzo(a)pyrene-treated rats showed greatest activity at 2 h followed by a gradual fall through 24 h. 6. GSH was therefore a less efficient nucleophile for aflatoxin B1 metabolites than for benzo(a)pyrene metabolites.

Aflatoxins↗
PubMedDate not supplied

[Comparative characteristics of immunoreagents based on aflatoxin B1 hemiacetals and sterigmatocystine].

Aflatoxin B1 and sterigmatocystine hemiacetal derivatives were synthesized, and their conjugation to albumins and gelatin and also spectral and immunochemthe specificity and analytical properties of the antibodies produced by immunization with conjugated antigens. The possible mechanism of hemiacetal interaction with proteins is discussed. Based on immune reagents to sterigmatocystine hemiacetal, a test system was developed for determination of sterigmatocystine at the sensitivity of 0.1 ng/ml.

Aflatoxin B1↗
PubMed1998

Assessing airborne aflatoxin B1 during on-farm grain handling activities.

The presence of aflatoxin in corn and corn dust during relatively normal years and the increased risk of Aspergillus flavus infestation during drought conditions suggest that airborne agricultural exposures should be of considerable concern. Liquid extraction, thin layer chromatography, and high pressure liquid chromatography were used for the analysis of aflatoxin B1 in grain dust and bulk corn samples. A total of 24 samples of airborne dust were collected from 8 farms during harvest, 22 samples from 9 farms during animal feeding, and 14 sets of Andersen samples from 11 farms during bin cleaning. A total of 14 samples of settled dust and 18 samples of bulk corn were also collected and analyzed. The airborne concentration of aflatoxin B1 found in dust collected during harvest and grain unloading ranged from 0.04 to 92 ng/m3. Higher levels of aflatoxin B1 were found in the airborne dust samples collected from enclosed animal feeding buildings (5-421 ng/m3) and during bin cleaning (124-4849 ng/m3). Aflatoxin B1 up to 5100 ng/g were detected in settled dust collected from an enclosed animal feeding building; however, no apparent correlation was found between the airborne concentration of aflatoxin B1 and its concentration in settled dust or bulk corn. The data demonstrate that farmers and farm workers may be exposed to potentially hazardous concentrations of aflatoxin B1, particularly during bin cleaning and animal feeding in enclosed buildings.

Aflatoxin B1↗
PubMed1981

Inhibition of rat liver aminoacyl-tRNA synthetases in vitro after acute and chronic aflatoxin B1 administration in vivo.

In a cell-free system the influence of acute aflatoxin B1 administration on the fractions of the hepatic microsomal translation complex of female rats was examined and compared with the influence of chronic aflatoxin B1 treatment. Polypeptide synthesis determined by [14C]leucine incorporation with the postmitochondrial supernatant was inhibited by 80% 24 h after acute aflatoxin B1 administration whereas inhibition was only 17% in animals 30 weeks after chronic treatment. After acute aflatoxin B1 administration inhibition of protein synthesis was by 67%, mainly on the polysomal level, whereas inhibition with the pH 5 enzyme was only by 22%. After chronic aflatoxin B1 administration inhibition was by 18%, mainly with the pH 5 enzyme and by only 6% on the polysomes. The inhibition by pH 5 enzyme was further investigated with regard to aminoacyl-tRNA synthetases, components of pH 5 enzyme. Leucine-specific aminoacyl-tRNA synthesis was inhibited by 20% 24 h after acute and by 12% 30 weeks after chronic aflatoxin B1 treatment. Aminoacyl-tRNA synthetase activities in a crude synthetase preparation tested with 5 amino acids were found to be noncompetitively inhibited. It is concluded that the inhibition of protein synthesis after acute and chronic aflatoxin B1 administration is in part due to decreased aminoacyl-tRNA levels caused by inhibited aminoacyl-tRNA synthetases.

Aflatoxin B1↗