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PubMed1985

Differential sensitivity of Ah-responsive mice to beta-naphthoflavone-induced metabolism and mutagenesis of benzo[a]pyrene and aflatoxin B1.

Effects of the administration to C57BL/6ha (Ah-responsive) mice of a low (10 mg/kg) and a high dose (150 mg/kg) of beta-naphthoflavone (BNF) on the hepatic microsome-mediated mutagenesis and metabolism of benzo[a]pyrene (BP) and aflatoxin B1 (AFB1) were studied. Hepatic microsome-mediated mutagenesis of benzo[a]pyrene was not enhanced by the low dose (10 mg/kg) but at the high dose (150 mg/kg) the mutagenic activation was enhanced several fold relative to control (corn oil-treated). Mutagenic activity of aflatoxin B1 was however depressed by both the low and the high doses of beta NF. These results are consistent with the effects of beta NF administration on hepatic microsome-mediated metabolism of BP to its phenolic products and on the metabolism of aflatoxin B1 to aflatoxin M1 catalyzed by aflatoxin B1-4-hydroxylase. Relative to control, pretreatment of the mice with 10 mg/kg beta NF did not induce aryl hydrocarbon hydroxylase activity (a measure of BP metabolism), however, the same pretreatment induced the metabolism of AFB1 to AFM1 by 2.7 to 4.7-fold. Microsomal preparations from 150 mg/kg beta NF-pretreated mice showed a 3-fold induction of aryl hydrocarbon hydroxylase activity and a 6.8-fold induction of AFB1-4-hydroxylase activity. These results suggest that two different enzyme systems are involved in the metabolism of BP and the metabolism of AFB1 to AFM1.

Aflatoxin B1↗
PubMed1989

Differential changes in rat brain tryptophan, serotonin and tyrosine levels following acute aflatoxin B1 treatment.

Female Sprague-Dawley rats were treated acutely (12-h) with aflatoxin B1 (100 micrograms/kg i.p.) or vehicle (10% acetone in 0.9% NaCl) and regional brain levels of tryptophan, serotonin and tyrosine were assayed. Brainstem but not cerebellar or cortical tyrosine levels were decreased in aflatoxin B1-treated rats. Brain tryptophan was increased in all 3 brain regions by acute aflatoxin B1 treatment, while serotonin levels were unaltered in the cerebellum and cortex and decreased in the brainstem. These experiments indicate that acute aflatoxin B1 treatment differentially alters brain amino acids and serotonin and that changes in brain tryptophan, the serotonin precursor, do not parallel changes in brain serotonin.

Aflatoxin B1↗
PubMed1988

Substances with affinity to a monoclonal aflatoxin B1 antibody in Danish urine samples.

Using a competitive enzyme immunoassay, one or more substances recognized by a monoclonal antibody against aflatoxin B1 were detected in human urine samples collected in Denmark. The concentration of urinary aflatoxin-like substances was equivalent to 0.0-6.5 ng aflatoxin B1/mg creatinine. A truly competitive interaction in the immunoassay was found between aflatoxin-like substances and aflatoxin B1. Aflatoxin-like substances could be isolated in small quantities from urine by affinity chromatography. The quantity of urinary aflatoxin-like compounds in the samples collected showed a skewed normal distribution (80 individuals). In order to explain the seemingly high level of aflatoxin-like material in urine samples from people living in a cold temperate climate, the source of aflatoxin-like compounds was investigated. In a dietary restriction study, potential dietary factors leading to excretion of aflatoxin-like compounds were investigated. Our data indicate that the excretion of these compounds by healthy Danes depends mainly on the food ingested 24-48 hr before urine samples were collected. In particular, the excretion of aflatoxin-like substances was increased when diets include beer, dairy products or meat. A map of the epitope recognized by the antibody was constructed from the results of competition studies with several AFB1 analogues. The epitope map was used to draw chemical structures representing the minimal requirements for antibody recognition. An on-line search was conducted among the 98.2 x 10(6) structures in the Chemical Abstracts and Registry Databases (STN, Columbus, OH) and provided strong evidence that only aflatoxins or aflatoxin derivatives are recognized by the antibody. The possible chemical structures of the aflatoxin-like substances are discussed.

Aflatoxin B1↗
PubMed1976

The effect of pre-treatment with phenobarbitone on the activation of aflatoxin B1 by rat liver.

Microsomes prepared from rats pre-treated with phenobarbitone are more effective in activating aflatoxin B1 in vitro to a metabolite which inhibits RNA polymerase than are microsomes obtained from control animals. This result is in contrast with the situation in vivo where pre-treatment with phenobarbitone protects against inhibition of RNA synthesis by aflatoxin B1. The hypothesis is advanced that, in vivo, the activation of aflatoxin B1 which is significant in terms of inhibition of nucleic acid synthesis largely occurs on the outer nuclear membrane, and that by increasing activation by the microsomes, phenobarbitone pre-treatment reduces the amount of aflatoxin B1 available for the nuclear activation.

Aflatoxins↗
PubMed1985

Experimental combined aflatoxin B1 and ochratoxin A intoxication in pigs.

Twenty-one pigs weighing approximately 18 kg were placed in 7 groups of 3 and given diets containing respectively aflatoxin B1 alone at 0.375 and 0.0750 mg/kg, ochratoxin A alone at 1 and 2 mg/kg, 0.375 mg/kg of aflatoxin B1 plus 1 mg/kg of ochratoxin A and 0.750 mg/kg aflatoxin B1 and 2 mg/kg of ochratoxin A. The remaining group served as untreated control. At the respective dose levels, pigs receiving similar doses of ochratoxin A alone or in combination with aflatoxin B1, were similarly affected, the clinical effects of aflatoxin having been mostly obscured by those due to ochratoxin A. Mild degenerative hepatic changes typical of aflatoxicosis were observed in pigs fed this toxin alone or in combination with ochratoxin A. In kidneys of pigs fed diet containing 1 and 2 mg of ochratoxin A alone changes included interstitial fibrosis of the vortex and dystrophy and degeneration of the tubular epithelium. Similar lesions but less pronounced fibrosis were found in kidneys of pigs receiving both toxins. The respective lower dose levels of mycotoxins selected were judged to be about the no-effect levels for each dosed separately under the conditions of the trial. Such levels have been found not infrequently on mould affected grain and stock foods. The result highlights the difficulties that may be experienced in the recognition of such multimycotoxicoses as they are likely to occur in the field and indicate the need for toxicological analysis as well as pathological investigation in establishing a diagnosis.

Aflatoxin B1↗
PubMed2006

Survey of breakfast and infant cereals for aflatoxins B1, B2, G1 and G2.

Three hundred and forty-nine breakfast and infant cereal samples were collected at retail level across Canada from 2002 to 2005. They included rice-, soy-, barley-based and mixed-grain infant cereals, corn-, wheat-, rice-based and mixed-grain breakfast cereals, and were analysed for aflatoxins B1, B2, G1 and G2 using a modified AOAC International official method. An immunoaffinity column was used for the cleanup and purification of extracts. Determination of aflatoxins was by LC using post-column derivatization with pyridinium hydrobromide perbromide and fluorescence detection. Results indicated that 50% of both breakfast and infant cereals had detectable levels (limit of detection = 0.002 ng g-1) of aflatoxin B1, which is the most toxic of the four toxins. The levels found varied from 0.002 to 1.00 ng g-1 for aflatoxin B1, from 0.002 to 0.14 ng g-1 for aflatoxin B2, from 0.008 to 0.27 ng g-1 for aflatoxin G1, and from 0.008 to 0.048 ng g-1 for aflatoxin G2. Only 4% of the breakfast cereals and 1% of the infant cereals had aflatoxin B1 levels exceeding 0.1 ng g-1, which is the European Union maximum limit for aflatoxin B1 in baby foods and processed cereal-based foods for infants and young children.

Aflatoxin B1↗
PubMed1983

Efficacy of activated charcoal and other agents in the reduction of hepatotoxic effects of a single dose of aflatoxin B1 in chickens.

Liver injury caused by a toxic dose of aflatoxin B1 (AFB1) (6 mg/kg, p.o.) in experimental chickens was measured by observing changes in hepatic microsomal cytochrome P-450 and the activity of microsomal benzphetamine N-demethylase and serum glutamic oxaloacetic transaminase (SGOT). However, simultaneous administration of activated charcoal, reduced glutathione (GSH), cysteine, selenium, beta-carotene or fisetin with aflatoxin B1 considerably reduced the toxic injury to liver as measured by the above parameters.

Aflatoxin B1↗
PubMed1988

Gene-specific differences in the aflatoxin B1 adduction of chicken erythrocyte chromatin.

Mature and immature chicken erythrocyte nuclei were treated with activated aflatoxin B1 (2,3-dichloroaflatoxin B1), producing covalently bound DNA adducts. This reaction produces alkali-labile sites in the DNA which can be identified by using a variation of the Maxam-Gilbert sequencing procedure. We determined the aflatoxin B1 accessibility of defined regions of the erythroid genome by using different specific probes and monitoring the disappearance of similar-sized fragments generated by restriction enzyme digestion. The genes studied were the erythroid-specific beta-globin and histone H5 genes, which are potentially active in mature erythroid nuclei and transcriptionally active in immature erythrocytes, and the vitellogenin and ovalbumin genes, which are both transcriptionally inactive in these cells. The beta-globin and histone H5 genes were more accessible than the repressed vitellogenin and ovalbumin genes to aflatoxin B1 modification in mature and immature erythroid chromatin. Micrococcal nuclease was used to probe the nucleosomal organization of active (beta-globin and histone H5) and repressed (vitellogenin and ovalbumin) genes in chicken erythrocytes. The vitellogenin and ovalbumin genes show a canonical nucleosome repeat pattern in mature and immature chicken erythrocyte nuclei. In contrast, the beta-globin and histone H5 genes lack a distinct nucleosomal repeat pattern in these cells. These results support the hypothesis that transcriptionally active genes are preferentially accessible to carcinogen modification because of their disrupted chromatin structure.

Aflatoxin B1↗
PubMedDate not supplied

The development of five animal feed reference materials, certified for their aflatoxin B1 content.

The development of three peanut meal and two compound feed reference materials and the certification of their aflatoxin B1 content is described. The materials were prepared and certified within the Measurements and Testing Programme of the Commission of the European Communities as part of a broad activity to improve accuracy and agreement of results of measurements on food and agriculture. RM 262 (peanut meal) was prepared from uncontaminated peanut products. RM 263 and RM 264 (peanut meals) were prepared from naturally contaminated peanuts which were blended with uncontaminated ones, to achieve the desired aflatoxin B1 mass fractions. RM 375 and RM 376 (compound feeds) were made by blending decontaminated dairy feed together with commercial feed ration and contaminated dairy feed with several feed compounds, respectively. Details are given of the preparation and the investigations to verify homogeneity and stability of the materials. The certification exercise was carried out by 17 laboratories using a variety of extraction and clean-up procedures. Most laboratories used liquid chromatography as the determinative step, although operating under a variety of chromatographic conditions. A few laboratories applied thin layer chromatography with densitometric quantification. Peanut meal RM 262 was certified as containing aflatoxin B1 at a mass fraction of < 3 micrograms/kg, RM 263 at 43.3 +/- 2.1 micrograms/kg and RM 264 at 204 +/- 10 micrograms/kg. Compound feed RM 375 was certified as containing aflatoxin B1 at a mass fraction of < 1 micrograms/kg and RM 376 at 9.2 +/- 0.5 micrograms/kg. The materials can be employed either to establish or confirm a calibration curve, or to check the performance of a method.

Aflatoxin B1↗
PubMedDate not supplied

Determination of aflatoxin B1 in pistachio kernels and shells.

A method was developed for accurate measurement of aflatoxin B1 in the edible portion of pistachio nuts. Twenty-nine samples of kernels with and without their shells were slurried with a Mega Ultra Turrax. A subsample of the homogenate was extracted with water-methanol, defatted with petroleum ether, purified with a silica solid-phase extraction column, and redissolved in methanol. After separation on an octadecyl column and postcolumn reaction with on-line electrochemically generated bromine, the aflatoxin B1 derivative was detected fluorometrically. The shells contained less than 1% of the aflatoxin B1 found in the edible kernel, and they accounted for 41.7-46.8% of the weight of the whole pistachio. These observations indicate it is possible to analyze an entire sample, up to 25 kg, as a whole and still be able to judge whether it meets the legal tolerance limit of 5 micrograms aflatoxin B1/kg edible part, as set by the Dutch Food Act.

Aflatoxin B1↗
PubMed2001

Mechanism of removal of aflatoxin B1 by a resistant bacterium.

A bacterium resistant to aflatoxin B1 isolated from the soil was shown to remove a maximum 26% of toxin at 3 microg ml(-1). A comparison of spectrophotometric and radioisotope methods showed that a maximum of 48 hr was sufficient to remove the toxin. Radioisotope analysis showed that the radioactivity decreased in the chloroform phase while it increased in the aqueous phase during the time course of the experiment. An analysis of the supernatant of culture medium showed that the bacterium had converted aflatoxin B1 to water soluble compounds with lambda(max) of 338 and 374.

Aflatoxin B1↗
PubMed1987

Mechanisms of frameshift mutagenesis by aflatoxin B1-2,3-dichloride.

In order to characterize frameshift mutagenesis by aflatoxin B1-2,3-dichloride (AFB1Cl2), we have introduced a +1 (BK8) or a -1 (HS8) frameshift within the lacZ alpha gene segment contained in the phage M13mp8 to obtain lacZ alpha- derivatives. BK8 or HS8 replicative form DNA was modified with AFB1Cl2 in vitro, transfected into appropriate Escherichia coli hosts and lacZ alpha+ revertants scored and defined by DNA sequencing. The -1 frameshift (BK8) results suggest the following. (1) The E. coli recA gene is not absolutely required for AFB1Cl2-induced frameshift mutagenesis; however, in recA+ cells, ultraviolet light (SOS) induction enhances AFB1Cl2 mutagenesis, but such ultraviolet induction is not required. The plasmid pGW270 (mucAB+) significantly enhances the AFB1Cl2-induced frameshift mutagenesis. The uvrABC+ excision system plays a major role in the repair of AFB1Cl2-induced damage. (2) Sequence analysis reveals that AFB1Cl2 induces two classes of -1 frameshift mutations: the simple class in which the frameshift is due to the loss of one base-pair, and the complex class in which the loss of a base-pair is coupled to a vicinal base substitution. Both types of mutations occur predominantly at G.C runs, which are hotspots for AFB1Cl2 damage. The complex mutations appear to be concerted events targeted by a single AFB1Cl2 adduct. The frequency of these complex mutations is significantly enhanced by mucAB activity. In this system, recA activity is required for generation of significant levels of complex mutations. An analysis of the +1 frameshifts (HS8) reveals that AFB1Cl2 induces +1 frameshifts with an efficiency comparable to that for -1 frameshifts. Most +1 frameshifts occur by the addition of a base, and a third of the additions are complex mutations because they are accompanied by at least one base substitution. All simple additions occur at G.C runs; however, in a striking contrast to spontaneous insertions, a majority of the induced events introduce an A.T pair at these sites. Our data suggest a model for the generation of base substitution as well as simple and complex frameshift mutations induced by AFB1Cl2. To the extent determined, the frameshift specificity of aflatoxin B1 activated by metabolic enzymes is similar to that of AFB1Cl2.

Aflatoxin B1↗
PubMed1983

Changes in preneoplastic response to aflatoxin B1 in rats fed green beans, beets or squash.

Weanling male Fischer rats were fed diets containing 25% freeze-dried green beans, beets or squash either with or without 1 ppm aflatoxin B1 for 8 wk. Plasma alpha-foetoprotein concentrations were determined weekly from wk 4 to 7. During wk 8 the animals were killed and hepatic sections were stained for gamma-glutamyl transpeptidase. All three vegetable diets, as compared to the basal semi-purified diet, enhanced both aflatoxin-B1-induced elevation of plasma alpha-foetoprotein and aflatoxin-B1-induced emergence of hepatic cell foci of gamma-glutamyl transpeptidase. The data suggest that these vegetables contain natural factors that enhance aflatoxin B1 carcinogenicity.

Aflatoxin B1↗
PubMed1997

Individual and combined genotoxic response of boric acid and aflatoxin B1 in Escherichia coli PQ37.

The genotoxic potentials of boric acid in Escherichia coli PQ37 was assessed along in the presence of aflatoxin B1 using SOS chromotest. Boric acid induced beta-galactosidase synthesis on the tester bacteria both on the presence and absence of S9 activation mixture. Therefore, the inorganic acid may not require metabolic activation to be genotoxic for this bacteria. When present together with aflatoxin B1 in the assay medium, boric acid increased the degree of beta-galactosidase synthesis induced by the maximal inducing concentration of aflatoxin B1 before the toxin's activation. However, the degree of enzyme synthesis induced was significantly decreased when boric acid was present after aflatoxin activation. This suggests that boric acid may not interfere with nor block the expoxidation of aflatoxin B1. It may however interact with the expoxide thereby inhibiting its activity. Boric acid may be a genotoxin and could possibly act as a syngenotoxic and/or a cogenotoxic agent.

Aflatoxin B1↗
PubMed2001

Effect of aflatoxin B1 on phosphoinositide signal transduction pathway during regeneration of liver cells following partial hepatectomy.

Aflatoxin B1 (AFB1) when administered to partially hepatectomised rats 4 hr prior to sacrifice, activated the signalling pathway in regenerating rat liver. The activity of phosphatidylinositol (PI) kinase was found decreased at 30 min but increased at 24 hr and returned to normal at 48 hr. At 30 min, inositol-1,4,5-triphosphate (IP3) level increased significantly whereas diacylglycerol (DAG) level dropped. However, at 24 hr and 48 hr, DAG and IP3 showed the same trend i.e. an increase in their levels. Phosphatidylinositol-4-phosphate levels were found to increase at 24 hr. Protein kinase C (PKC), activity from the particulate fraction was significantly inhibited at 30 min, followed by increase in activity at 24 hr and return to normal at 48 hr. Cytosolic PKC showed a decrease at 24 hr and a significant increase at 48 hr. At the peak of DNA synthesis (24 hr) following partial hepatectomy, all these signalling steps had earlier been found to be inhibited, but the present study shows that aflatoxin B1 administration 4 hr prior to sacrifice reverses the action. Activation of PKC by aflatoxin B1, during regeneration of liver cells when PKC in normally inhibited, may possibly create conditions conducive to carcinogenesis.

Aflatoxin B1↗
PubMed1975

A comparative study of the effects of aflatoxin B1, alpha-amanitin and actinomycin-D on RNA synthesis by rat liver.

The effect of different combinations of aflatoxin B1, alpha-amanitin and actinomycin-D on the incorporation of orotic acid-6-14C into RNA was investigated using rat liver slices. The results support the view that the mode of action of aflatoxin B1 and alpha-amanitin are similar in some respects, and that aflatoxin B1 and actinomycin-D act according to different mechanisms. Evidence was also obtained about the formation of an active metabolite of aflatoxin B1 in this system.

Aflatoxins↗
PubMed1977

Comparison of the genetic activity of aflatoxins B1 and G1 in Escherichia coli and Saccharomyces cerevisiae.

The ability of aflatoxins B1 and G1 to induce back mutations to arg+ in Escherichia coli K-12/343/113 was compared with the induction of mitotic gene conversion to ade+ in the diploid yeast strain Saccharomyces cerevisiae D4, ade-2. In analogy to previous results with other microorganisms, the compounds were not genetically active per se, indicating that under the experimental conditions employed none of the tester strains were able to activate the compounds to mutagenic products. In experiments using liver homogenates (S-9 fraction) of male Golden Syrian hamsters previously treated with phenobarbital, aflatoxin B1 exhibited strong genetic activity both in E. coli and in S. cerevisiae, whereas the mutagenic activity of aflatoxin G1 was markedly lower and could be detected only in the E. coli tester strain. These results correlate the findings that aflatoxin G1 is a less potent carcinogen and mutagen than aflatoxin B1.

Aflatoxins↗