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PubMed1981

Temporal patterns of covalent DNA adducts in rat liver after single and multiple doses of aflatoxin B1.

We examined patterns of covalent modifications of DNA produced in rat liver after exposure to single and multiple doses of aflatoxin B1. The principal product, previously identified as 2,3-dihydro-3-hydroxy(N7-guanyl) aflatoxin B1, was removed rapidly from liver DNA in vivo after a 0.6-mg/kg dose was administered i.p. to male Fischer rats. This lesion had an apparent half-life of 7.5 hr. Similar kinetics of disappearance was seen for two other aflatoxin adducts, one of which was previously identified as an N7-guanine adduct of aflatoxin P1. The kinetics of formation and disappearance differed for two other products believed to be produced by scission of the imidazole ring of the 7-substituted guanine moiety of the principal adduct in the DNA molecule. These adducts were removed slowly, if at all, during the 72-hr period studied. Approximately 20% of the principal N7 adduct initially formed was converted to these products in 24 hr, at which time they were the predominant lesions in DNA. Administration of multiple doses of aflatoxin B1, using a regimen shown to produce a high incidence of hepatocellular carcinoma, caused accumulation of these persistent products in liver DNA over a 14-day period.

Aflatoxins↗
PubMedDate not supplied

Enzyme-linked immunosorbent assay of total aflatoxins B1, B2, and G1 in corn: follow-up collaborative study.

A direct competitive enzyme-linked immunosorbent assay screening method for aflatoxins at 20 ng/g in corn was studied by 15 collaborating laboratories. Test samples of corn were extracted by blending with methanol-water (8 + 2). The extracts were filtered and the filtrates were diluted with buffer to a final methanol concentration of < 30%. Each diluted filtrate was applied to a test device containing a filter with immobilized polyclonal antibodies specific to aflatoxins B1, B2, and G1. Aflatoxin B1-peroxidase conjugate was added, the test device was washed with water, and a mixture of hydrogen peroxide and tetramethylbenzidine was added. A test sample was judged to contain > or = 20 ng aflatoxins/g when, after exactly 1 min, no color was observed on the filter; if a blue or gray color developed, the test sample was judged to contain < 20 ng aflatoxins/g. All laboratories correctly identified naturally contaminated corn test samples. Only one false positive was found for controls containing no aflatoxins. The correct responses for positive test samples spiked at levels of 10, 20, and 30 ng aflatoxins/g (the ratio of B1:B2:G1 was 15:1:3) were 67, 97, and 100%, respectively. This method was adopted first action by AOAC INTERNATIONAL as a change in method for 990.34 for screening for aflatoxins B1, B2, and G1 in corn at total aflatoxin concentrations of > or = 20 ng/g.

Aflatoxin B1↗
PubMed2001

Immunosuppressive effects of aflatoxin B1 in Indian major carp (Labeo rohita).

Aflatoxin B1 (AFB1) is a potent immunomodulator in endotherms. The experiment was carried out to study the immunosuppressive nature of AFB1 in one ectothermic species of Indian major carp. Graded levels (0, 1.25, 5.00 mg/kg of body weight) of purified AFB1 were intraperitoneally (i.p.) injected into rohu (Labeo rohita) fingerlings weighing 30-50 g, and the fish were observed for a period of 90 days. At the end of the trial, blood samples were collected from the control group as well as the AFB1 injected fish and were screened for nitroblue tetrazolium (NBT) assay, serum total protein, albumin, globulin, albumin-globulin ratio (A:G), serum bactericidal activity and bacterial agglutination titre against Edwardsiella tarda. The aflatoxin-treated fish revealed a reduction of total protein, globulin levels, bacterial agglutination titre, NBT and serum bactericidal activities, as well as an enhanced A:G ratio without change in albumin concentration, irrespective of dose levels of toxin treatment, when compared to the control group. Thus, AFB1 proved to be immunosuppressive in rohu even at the lowest dose (1.25 mg/kg body weight) of toxin treatment. This could be of economic significance in intensive culture systems of rohu.

Aflatoxin B1↗
PubMed1994

Role of human microsomal and human complementary DNA-expressed cytochromes P4501A2 and P4503A4 in the bioactivation of aflatoxin B1.

The metabolism of the carcinogenic mycotoxin aflatoxin B1 (AFB1) was examined in microsomes derived from human lymphoblastoid cell lines expressing transfected CYP1A2 or CYP3A4 complementary DNAs and in microsomes prepared from human liver donors (n = 4). Lymphoblast microsomes expressing only CYP1A2 activated AFB1 to AFB1-8,9-epoxide (AFB1-8,9-epoxide trapped as the glutathione, conjugate) at both 16 microM and 128 microM AFB1 concentrations, whereas activation of AFB1 to the epoxide in lymphoblast microsomes expressing only CYP3A4 was detected only at high substrate concentrations (128 microM AFB1). AFB1 epoxidation was strongly inhibited in CYP1A2 but not CYP3A4 lymphoblast microsomes pretreated with furafylline, a specific mechanism-based CYP1A2 inhibitor, whereas troleandomycin (TAO), a specific CYP3A inhibitor, strongly inhibited AFB1 epoxidation in CYP3A4 but not CYP1A2 microsomes. Formation of the hydroxylated metabolite aflatoxin M1 (AFM1) was observed only in the CYP1A2 microsomes whereas aflatoxin Q1 (AFQ1) production was observed exclusively in the CYP3A4 microsomes. Treatment of individual human liver microsomes (HLM) with TAO resulted in an average 20% inhibition of AFB1-8,9-epoxide formation at 16 microM AFB1, whereas incubation of HLM with furafylline at 16 microM AFB1 resulted in an average 72% inhibition of AFB1-8,9-epoxide formation at 16 microM AFB1. TAO was slightly more effective than furafylline in inhibiting AFB1 epoxidation at 128 microM AFB1 (46% inhibition by TAO, 32% inhibition by furafylline) in HLM. AFB1-8,9-epoxide formation was inhibited by 89% at low substrate concentration and 85% at high substrate concentrations when HLM were inhibited with a furafylline/TAO mixture. AFM1 formation was strongly inhibited by furafylline, whereas AFQ1 formation was strongly inhibited by TAO, in all HLM regardless of substrate concentration. Analysis of R-6- and R-10-hydroxywarfarin activities (respective markers of CYP1A2 and CYP3A4 activities) in the complementary DNA-expressed microsomes demonstrated that TAO was less effective than furafylline as a selective P450 isoenzyme inhibitor (60% inhibition of CYP3A4 by TAO as compared to 99% inhibition of CYP1A2 by furafylline). The rates of AFB1 epoxidation and AFQ1 formation in HLM were increased 7- and 18-fold, respectively, at high versus low substrate concentrations. These results are consistent with the hypothesis that CYP1A2 is the high-affinity P450 enzyme principally responsible for the bioactivation of AFB1 at low substrate concentrations associated with dietary exposure. CYP3A4 appears to have a relatively low affinity for AFB1 epoxidation and is primarily involved in AFB1 detoxification through AFQ1 formation in HLM.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1995

[In vitro study of the metabolic conversion of aflatoxin B1 into its epoxide].

The conversion of aflatoxin B1 into its epoxide was evaluated in vitro by two different approaches based on HPLC analysis: the quantitative estimation of the tris(OH)AFB1 addition product resulting from the indirect reaction of AFB1-epoxide with tris buffer (hydroxymethyl) aminomethane and on the other hand by the quantification of the formation of the glutathione conjugate (AFB1-SG). The tris(OH)AFB1 is more sensitive than AFB1-SG in fluorescence detection. The AFB1-SG obtained (5.42 +/- 0.42 microgram) is weakly less than the quantity of tris(OH)AFB1 (6.00 +/- 0.72) obtained in the same experimental conditions.

Aflatoxin B1↗
PubMed1992

[Effects of harman and norharman on aflatoxin B1 and aminopyrine metabolism by phenobarbital and 3-methylcholanthrene-induced rat liver microsomes].

Harman and norharman are two beta-carboline derivatives known to be present in certain foods and are formed during pyrolysis of amino-acids. Their effects on the metabolism of aflatoxin B1 and aminopyrine by 3-methylcholanthrene and phenobarbital-induced rat liver microsomes were studied. Both harman and norharman markedly inhibited the metabolism of aflatoxin B1 to its hydroxylated derivative, aflatoxin M1. However, only norharman showed an inhibitory effect on aminopyrine N-demethylation; harman had no effect. Harman and norharman inhibited aflatoxin B1 binding to DNA, mediated by hepatic microsomes in vitro.

Aflatoxin B1↗
PubMedDate not supplied

Production of aflatoxins B1, B2, G1, and G2 in pure and mixed cultures of Aspergillus parasiticus and Aspergillus flavus.

Production of aflatoxins B1, B2, G1, and G2 in pure and mixed cultures of Aspergillus parasiticus and aspergillus flavus were compared. Differing percentages of A. parasiticus (NRRL 2999) and A. flavus (NRRL 5520) conidia were used as inoculum and allowed to grow in static liquid culture for 10 days. The pure and mixed cultures of A. parasiticus/A. flavus were extracted and the aflatoxins partially purified. High-performance liquid chromatography was then used to determine aflatoxin concentrations. The maximal decreases of G1 and G2 production occurred when the inocula went from 0 to 12.5% or 25% A. flavus. Aflatoxins G1 and G2 comprised less than 10% of the total aflatoxins when the A. parasiticus/A. flavus inocula contained greater than 25% A. flavus. Production of aflatoxins B1 and B2 increased slightly as the percentage of A. flavus in the A. parasiticus/A. flavus mixed inoculum increased. A. flavus is apparently capable of suppressing accumulation of aflatoxins G1 and G2 by A. parasiticus when these fungi are grown in mixed culture.

Aflatoxin B1↗
PubMed1998

Regulation of rat glutathione S-transferase A5 by cancer chemopreventive agents: mechanisms of inducible resistance to aflatoxin B1.

The rat can be protected against aflatoxin B1 (AFB1) hepatocarcinogenesis by being fed on a diet containing the synthetic antioxidant ethoxyquin. Evidence suggests that chemoprotection against AFB1 is due to increased detoxification of the mycotoxin by one or more inducible drug-metabolising enzymes. The glutathione S-transferase (GST) isoenzymes in rat liver that contribute to ethoxyquin-induced chemoprotection against AFB1 have been identified by protein purification. This approach resulted in the isolation of several heterodimeric class alpha GST, all of which contained the A5 subunit and possessed at least 50-fold greater activity towards AFB1-8,9-epoxide than previously studied transferases. Molecular cloning and heterologous expression of rat GSTA5-5 has led to the demonstration that it exhibits substantially greater activity for AFB1-8,9-epoxide than other rat transferases. The A5 homodimer can also catalyse the conjugation of glutathione with other epoxides, such as trans-stilbene oxide and 1,2-epoxy-3-(4'-nitrophenoxy)propane, and possesses high catalytic activity for the reactive aldehyde 4-hydroxynonenal. Western blotting has shown that the A5 subunit is not only induced by ethoxyquin but that it is also induced by other cancer chemopreventive agents, such as butylated hydroxyanisole, oltipraz, benzyl isothiocyanate, indole-3-carbinol and coumarin. In addition to GSTA5, we have identified a novel aflatoxin-aldehyde reductase (AFAR) that is similarly induced by ethoxyquin. However, immunoblotting has shown that GSTA5 and AFAR are not always co-ordinately regulated by chemoprotectors. In order to gain a better understanding of the mechanisms responsible for the induction of GSTA5 protein, the GSTA5 gene has been cloned. It was isolated on two overlapping bacteriophage lambda clones and found to be approximately 12 kb in length. The transcriptional start site of GSTA5 has been identified 228 bp upstream from the ATG translational initiation codon. Computer-assisted analysis of the upstream sequence has indicated the presence of a putative antioxidant responsive element (located between -421 and -429 bp) which may be responsible for the induction of GSTA5 by chemopreventive agents.

Aflatoxin B1↗
PubMed1993

Genotoxic evaluation of ammonium inactivated aflatoxin B1 in mice fed with contaminated corn.

Aflatoxin B1 (AFB1) is a major contaminant in different agricultural products including maize. In an attempt to reduce this problem and the hazards to human health, an AFB1 inactivating system with ammonia has been developed. In this work we evaluated the efficiency of the system in mice using micronucleus (MN) and sister chromatid exchange (SCE) analysis. Four groups of animals were fed during 8 weeks with a special diet mainly composed of maize: (1) uncontaminated; (2) uncontaminated/inactivated; (3) contaminated/inactivated; and (4) contaminated. We evaluated MN at weekly intervals in peripheral blood, and in weeks 4 and 8 SCE frequencies were quantified in bone marrow cells. The results showed that animals fed with AFB1 contaminated/inactivated maize had a 45% lower level of induced cytogenetic damage than those animals fed with AFB1 contaminated, but not inactivated maize. A residual amount of AFB1 after the inactivating treatment and the reconversion back to AFB1 in the organism may account for the remaining increased levels of SCE and MN.

Aflatoxin B1↗
PubMed1992

Alterations in the growth and cycling status of granulocyte-monocyte colony-forming units (CFU-GM) in rats injected single doses of aflatoxin B1.

To determine the toxic effect of aflatoxin B1 (AFB1) on granulopoiesis in vitro, cultures of myeloid progenitor cells for granulocytes and macrophages CFU-GM in semisolid agar medium were used to evaluate colony formation and tritiated thymidine suicide technique for analysis of cycling status of CFU-GM. Male Fischer rats, 5 to 6 weeks old, were given a single i.p. injection of 1 mg/kg or 0.1 mg/kg of AFB1 which were approximately 1/5 or 1/50, respectively, of LD50 dose of AFB1. The administration of either dose of AFB1 caused a significant reduction of the number of CFU-GM derived colonies on the first and the second day after injection. This reduction was followed by a strong enhancement in CFU-GM colony formation on the third day, and by restoration to the normal level on the fourth day. The increase in percentage of CFU-GM in S-phase preceded one day the peak in CFU-GM colony formation. The two different doses of AFB1 exerted similar effects on the growth and cycling status of CFU-GM. Our data outline an early suppressive effect exerted by AFB1 to the rat granulopoiesis in vivo.

Aflatoxin B1↗
PubMed1992

Alterations in the structural gene and the expression of p53 in rat liver tumors induced by aflatoxin B1.

Rat hepatocellular carcinomas (HCCs) induced by aflatoxin B1 (AFB) treatment were examined for changes in the p53 tumor suppressor gene and in p53 suppressor gene expression. A high proportion of HCCs (nine of 11 tumors in six of eight animals) exhibited new p53 restriction fragments, indicating genomic alterations of one of the p53 alleles. Each tumor with an altered p53 restriction-fragment pattern exhibited a new fragment in one of two size classes (3 kb or 7 kb with EcoRI digestion) that were missing portions of the 3' end of the p53 gene. These findings indicate that apparently similar genomic rearrangements or deletions occurred independently in AFB-induced tumors. When compared with nontumor liver tissue from the same animal, the tumors with p53 gene alterations showed dramatically reduced levels of p53 mRNA and protein and greatly increased levels of histone H2B and retinoblastoma tumor suppressor (Rb) mRNA. In two HCCs showing no evidence of p53 restriction-fragment alterations, mutant p53 protein was detected. Mutant protein was also detected in two liver samples containing an adenoma and altered foci. These data suggest that alterations of the p53 tumor suppressor gene are involved in the induction of rat HCC by AFB.

Aflatoxin B1↗
PubMed2006

Kinetics of the oxidoreductase involved in the conversion of O-methylsterigmatocystin to aflatoxin B1.

Among the enzymatic steps in the aflatoxin biosynthetic pathway, the conversion of O-methylsterigmatocystin (OMST) to the potent environmental carcinogen aflatoxin B1 (AFB1), has been proposed to be catalysed by an oxidoreductase (OR) that requires a cytochrome P-450 type of oxidoreductase activity. This enzyme displays relative specificity towards OMST homologues in fungal whole cells. These studies were extended to the action of a cell-free enzyme system (CFES), on five OMST homologues, with a view to establish the kinetics. In the current study a CFES, containing an oxidoreductase, was derived from a blocked mutant of Aspergillus parasiticus (Wh1-11-105). The key experimental steps involved rapid concentration and efficient dialysis by membrane filtration to remove small biomolecules (MW<10,000), co-factors, primary and secondary metabolites. The kinetic parameters of the enzyme-substrate reactions indicated that the reaction follows a Michealis-Menten kinetics and OR activity decreased in the order: O-butylsterigmatocystin>O-propylsterigmatocystin>O-ethylsterigmatocystin>O-methylsterigmatocystin>O-acetylsterigmatocystin>O-benzoylsterigmatocystin. The 7-O-alkyl homologues were the best substrate for the CFES, thereby substantially supporting that the 7-O-methyl group of OMST is preferred for OR catalytic activity in the absence of any other alkylating groups in vitro. The Km was calculated as 5.65 microM for this CFES and varied marginally among the OMST homologues studied.

Aflatoxin B1↗
PubMed1997

An intercalation inhibitor altering the target selectivity of DNA damaging agents: synthesis of site-specific aflatoxin B1 adducts in a p53 mutational hotspot.

Aflatoxin B1 (AFB1) is a potent human carcinogen implicated in the etiology of hepatocellular carcinoma. Upon metabolic activation to the reactive epoxide, AFB1 forms DNA adducts primarily at the N7 position of guanines. To elucidate more fully the molecular mechanism of AFB1-induced mutagenesis, an intercalation inhibitor was designed to probe the effects of intercalation by AFB1 epoxide on its reaction with DNA. DNA duplexes were prepared consisting of a target strand containing multiple potentially reactive guanines and a nontarget strand containing a cis-syn thymidine-benzofuran photoproduct. Because the covalently linked benzofuran moiety physically occupies an intercalation site, we reasoned that such a site would be rendered inaccessible to AFB1 epoxide. By strategic positioning of this intercalation inhibitor in the intercalation site 5' to a specific guanine, the adduct yield at that site was greatly diminished, indicating that intercalation by AFB1 epoxide contributes favorably to adduct formation. Using this approach it has been possible to simplify the production of site-specifically modified oligonucleotides containing AFB1 adducts in the sequence context of a p53 mutational hotspot. Moreover, we report herein isolation of site-specifically AFB1-modified oligonucleotides in sequences containing multiple guanines. Use of intercalation inhibitors will facilitate both investigation of the ability of other carcinogens to intercalate into DNA and the synthesis of specific carcinogen-DNA adducts.

Aflatoxin B1↗
PubMed2000

Mutations in the p53 tumor suppressor gene in tree shrew hepatocellular carcinoma associated with hepatitis B virus infection and intake of aflatoxin B1.

Infection with hepadnaviruses and exposure to aflatoxin B1 (AFB1) are considered to be major risk factors in the development of hepatocellular carcinoma (HCC) in humans. A high rate of p53 mutations at codon 249 has been reported in these tumors. The tree shrew (Tupaia belangeri chinensis) is a useful animal model for the development of HCC after human hepatitis B virus (HBV) infection or AFB1 treatment. Therefore, it was of particular interest to determine whether the p53 gene in tree shrew HCCs associated with HBV infection and/or with exposure to AFB1 is affected in the same manner as in human HCCs. We determined the tree shrew p53 wild-type nucleotide sequences by RT-PCR and automatic DNA-sequencing. Tree shrew wild-type p53 sequence showed 91.7 and 93.4% homologies with human p53 nucleotide and amino acids sequences, respectively, while it showed 77.2 and 73.7% homologies in mice. One HCC and normal liver tissue from AFB1 treated and one HCC from AFB1- and HBV-treated tree shrew showed no change in p53 sequences, while three HCCs from AFB1- and HBV-treated tree shrews showed point mutations in p53 sequences. One HCC showed point mutations at codon 275, which is on the DNA-binding domain of p53 gene, which might be a cause of gain-of-function during the development of HCC. As a result, our finding indicates that tree shrews exposed to AFB1 and/or HBV had neither codon 249 mutations nor significant levels of other mutations in the p53 gene, as is the case with humans.

Aflatoxin B1↗
PubMed2005

Effects of aflatoxin B1 on embryo fetal development in rabbits.

Aflatoxin B1 (AFB1), is a food borne mycotoxin produced by fungal species of the genera Aspergillus. To elucidate the teratogenic effects, AFB1 was dissolved in corn oil and given orally to New Zealand White rabbits during 6-18 days of gestation with the dose levels of 0.025, 0.05 and 0.1 mg/kg body weight. To assess pathomorphological features of the anomalies induced by AFB1, the fetal serial sections were histologically examined. There was no maternal mortality in any group. There was non-significant decrease in percent of live fetuses and increase in the percent resorptions and post-implantation losses at 0.1 mg/kg dose group as compared with those of controls. The mean crown to rump lengths of 0.05 and 0.1 mg/kg dose groups were significantly reduced than that of the control. The mean fetal weights were significantly reduced in 0.1 mg/kg dose group than that of other treated groups. The gross anomalies observed included wrist drop and enlarged eye socket whereas, skeletal anomalies were agenesis of caudal vertebrae, incomplete ossification of skull bones and bent metacarpals. The visceral anomalies of microphthalmia and cardiac defects were seen at 0.1 mg/kg dose group. The characteristic histological findings of fetal tissues were distortion of normal hepatic cord pattern and reduced megakaryocytes in liver, fusion of auriculo-ventricular valves, mild degenerative changes in myocardial fibers, microphthalmic eyes and lenticular degeneration. The results of this study indicated that AFB1 was found to be teratogenic in rabbits when given by oral route during gestation days 6-18 and the dose of 0.1 mg/kg could be considered as the minimum oral teratogenic dose. The histological examination of the fetal tissues indicated its importance in identifying the visceral anomalies which were otherwise not visible.

Administration, Oral↗
PubMed1988

The significance of glutathione conjugation for aflatoxin B1 metabolism in rainbow trout and coho salmon.

Rainbow trout are known to be more susceptible to aflatoxin B1 (AFB1) hepatocarcinogenesis than coho salmon, or trout pre-fed the carcinogenesis inhibitors beta-naphthoflavone (beta NF), Aroclor 1254 or indole-3-carbinol. The study reported here examined the relationship between AFB1-glutathione (GSH) conjugation and AFB1 carcinogenesis in salmon, trout and trout pre-fed the three inhibitors. The AFB1-glutathione (AFB1-SG) conjugate was not detected in salmon bile and was present in trout bile in amounts representing less than 0.2% of the administered dose 24 hr after injection of [3H]AFB1. The major conjugates were glucuronides of aflatoxicol and aflatoxicol M1. In incubations of isolated liver cell fractions, less than 0.5% of the original AFB1 dose was recovered as AFB1-SG in salmon and trout preparations, compared to 25% in mouse-liver cell preparations. The GSH concentration in livers of the control trout was higher than that for coho salmon but lower than that for trout pre-fed beta NF. Liver GSH-transferase activity in control trout livers was much higher than in the control salmon livers, but was only 62% of that found for trout fed beta NF. There was no apparent relationship among the various groups between liver GSH concentrations, liver GSH-transferase activity, or biliary GSH conjugate, and the degree of carcinogenic response of AFB1. Thus current evidence does not indicate a major role for aflatoxin B1 epoxide-GSH detoxification in coho salmon, or rainbow trout fed any of the three anticarcinogens tested. These results in salmonid fish are contrary to those which suggest AFB1-SG conjugation as a major determinant of AFB1 carcinogenesis and its dietary modulation in rodent models.

Aflatoxin B1↗
PubMedDate not supplied

Food restriction and short-term effects of aflatoxin B1 feeding on putative preneoplastic biochemical markers.

The susceptibility of experimental rats to Aflatoxin B1, a well known hepatocarcinogen, during chronic food restriction was studied, using a few putative preneoplastic biochemical markers. Gamma-Glutamyl transpeptidase was the most sensitive among the various enzymes studied, at the dose of 10 micrograms/day/100 gm body weight of Aflatoxin B1 fed over a period of three weeks after a twelve chronic food restriction in experimental rats. It was significantly elevated in the underfed untreated group, thus suggesting that preneoplastic changes may be precipitated during chronic undernutrition and carcinogen exposure.

Aflatoxin B1↗
PubMed1987

Averufanin is an aflatoxin B1 precursor between averantin and averufin in the biosynthetic pathway.

Wild-type Aspergillus parasiticus produces, in addition to the colorless aflatoxins, a number of pigmented secondary metabolites. Examination of these pigments demonstrated that a major component was an anthraquinone, averufanin. Radiolabeling studies with [14C]averufanin showed that 23% of the label was incorporated into aflatoxin B1 by the wild type and that 31% of the label was incorporated into O-methylsterigmatocystin by a non-aflatoxin-producing isolate. In similar studies with blocked mutants of A. parasiticus the 14C label from averufanin was accumulated in averufin (72%) and versicolorin A (54%) but not averantin. The results demonstrate that averufanin is a biosynthetic precursor of aflatoxin B1 between averantin and averufin.

Aflatoxin B1↗