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PubMed1991

DNA binding, adduct characterisation and metabolic activation of aflatoxin B1 catalysed by isolated rat liver parenchymal, Kupffer and endothelial cells.

In vitro studies with rat liver parenchymal, Kupffer and endothelial cells isolated from male Sprague-Dawley rats were undertaken to investigate cell-specific bioactivation of aflatoxin B1, DNA binding and adduct formation. In the mutagenicity studies, using homogenates of all three separated liver cell populations (co-incubated with NADP+ and glucose-6-phosphate as cofactors for the cytochrome P-450 monooxygenase system) parenchymal, Kupffer and endothelial cells were able to activate aflatoxin B1 to a metabolite mutagenic to Salmonella typhimurium TA 98. In the case of nonparenchymal cells (i.e. Kupffer and endothelial cells) 10-fold higher concentrations of aflatoxin B1 had to be used to obtain a similar number of revertants to that observed with parenchymal cells. Induction studies with Aroclor 1254 led to a striking decrease in the activation of aflatoxin B1 in parenchymal cells, whereas nonparenchymal cells had a slightly enhanced metabolic activation capacity for aflatoxin B1. Metabolism studies with microsomes from induced and noninduced cells using testosterone as substrate revealed comparable results: after induction with Aroclor 1254, parenchymal cells showed a 60% decrease in the formation rate of 2 alpha-hydroxytestosterone, whereas the formation rate of this metabolite remained unchanged in nonparenchymal cells; 2 alpha-hydroxytestosterone is specifically formed by cytochrome P-450 IIC11, which also catalyses the activation of aflatoxin B1 to its epoxide. When freshly isolated, intact cells were incubated with tritiated aflatoxin B1, a dose-dependent aflatoxin B1 binding to DNA in parenchymal and nonparenchymal cells was observed. HPLC analysis of DNA acid hydrolysates of all three cell types showed the major adduct to be 8,9-dihydro-8-(N7-guanyl)-9-hydroxy-aflatoxin B1.

Aflatoxin B1↗

PubMed2005

Antioxidant enzymes stimulation in Aspergillus parasiticus by Lentinula edodes inhibits aflatoxin production.

Biosynthesis of aflatoxins, toxic metabolites produced by Aspergillus parasiticus, is correlated to the fungal oxidative stress and cell ageing. In this paper, the mechanism underlying the aflatoxin-inhibiting effect of the Lentinula edodes culture filtrates was studied by analysing their anti-oxidant activity and beta-glucan content. Mushroom beta-glucans are pharmacologically active compounds stimulating anti-oxidant responses in animal cells. L. edodes lyophilised filtrates stimulate A. parasiticus anti-oxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase) and aflatoxin inhibition was better correlated with beta-glucan content than with anti-oxidant activity of the filtrates. RT-PCR analyses on treated mycelia showed a delay in the activation of aflR, and norA, genes of aflatoxin cluster and a synchronous activation of hsf2-like, a homologue of a yeast transcription factor involved in oxidative stress responses. The first evidence of hsf2-like in A. parasiticus and its activation during aflatoxin biosynthesis is reported. L. edodes filtrates could play a role as external stimulus affecting the anti-oxidant status in the fungal cell that, in turn, leads to aflatoxin inhibition. In the fungal cell, beta-glucans present in the filtrates could stimulate the activation of transcription factors related to anti-oxidant response and anti-oxidant enzyme activity with a contemporaneous delay of aflatoxin genes transcription, which led to a marked reduction of aflatoxin production. This research suggests new perspectives to set suitable strategies against aflatoxins and L. edodes could be considered a promising tool.

Aflatoxins↗

PubMed2000

Genes encoding cytochrome P450 and monooxygenase enzymes define one end of the aflatoxin pathway gene cluster in Aspergillus parasiticus.

The identification of overlapping cosmids resulted in the discovery of the aflatoxin biosynthetic pathway gene cluster in Aspergillus flavus and A. parasiticus. This finding led to the cloning and characterization of one regulatory and 16 structural genes involved in aflatoxin biosynthesis, including the most recent report on the gene, ordA, which has been identified to be involved in the formation of four aflatoxins (B1, B2, G1 and G2). However, these genes do not account for all the identified chemical/biochemical steps in aflatoxin synthesis and efforts are underway to identify the genes controlling the other steps. We are also attempting to define the outer boundaries of the aflatoxin pathway gene cluster in the Aspergillus genome. For this goal, we extended sequencing in both directions from the existing (60 kb) aflatoxin pathway gene cluster, beyond the pksA gene at one end and the omtA gene at the other. Within the 25-kb genomic DNA sequence determined at the omtA end of the cluster, several new gene sequences were identified. The recently reported genes, vbs and ordA, were found within this 25-kb region. Two additional genes were also found in this region, a cytochrome P450 monooxygenase encoding gene, tentatively named cypX, and a monooxygenase encoding gene, tentatively named moxY, and these are also reported in this study. The sequence beyond these genes showed a 5-kb non-coding region of DNA followed by the presence of a cluster of genes probably involved in sugar metabolism. Northern blot analysis and reverse transcriptase-polymerase chain reaction (RT-PCR) studies demonstrated that the genes, cypX and moxY, are expressed concurrently with genes involved in aflatoxin biosynthesis. Therefore, the two putative aflatoxin pathway genes cypX and moxY followed by a 5-kb non-coding region of DNA define one end of the boundary of the aflatoxin pathway gene cluster in A. parasiticus.

Aflatoxins↗

PubMed2006

Understanding the genetics of regulation of aflatoxin production and Aspergillus flavus development.

Aflatoxins are polyketide-derived, toxic, and carcinogenic secondary metabolites produced primarily by two fungal species, Aspergillus flavus and A. parasiticus, on crops such as corn, peanuts, cottonseed, and treenuts. Regulatory guidelines issued by the U.S. Food and Drug Administration (FDA) prevent sale of commodities if contamination by these toxins exceeds certain levels. The biosynthesis of these toxins has been extensively studied. About 15 stable precursors have been identified. The genes involved in encoding the proteins required for the oxidative and regulatory steps in the biosynthesis are clustered in a 70 kb portion of chromosome 3 in the A. flavus genome. With the characterization of the gene cluster, new insights into the cellular processes that govern the genes involved in aflatoxin biosynthesis have been revealed, but the signaling processes that turn on aflatoxin biosynthesis during fungal contamination of crops are still not well understood. New molecular technologies, such as gene microarray analyses, quantitative polymerase chain reaction (PCR), and chromatin immunoprecipitation are being used to understand how physiological stress, environmental and soil conditions, receptivity of the plant, and fungal virulence lead to episodic outbreaks of aflatoxin contamination in certain commercially important crops. With this fundamental understanding, we will be better able to design improved non-aflatoxigenic biocompetitive Aspergillus strains and develop inhibitors of aflatoxin production (native to affected crops or otherwise) amenable to agricultural application for enhancing host-resistance against fungal invasion or toxin production. Comparisons of aflatoxin-producing species with other fungal species that retain some of the genes required for aflatoxin formation is expected to provide insight into the evolution of the aflatoxin gene cluster, and its role in fungal physiology. Therefore, information on how and why the fungus makes the toxin will be valuable for developing an effective and lasting strategy for control of aflatoxin contamination.

Aflatoxins↗

PubMed2006

A USA-Africa collaborative strategy for identifying, characterizing, and developing maize germplasm with resistance to aflatoxin contamination.

Aflatoxin contamination of maize by Aspergillus flavus poses serious potential economic losses in the US and health hazards to humans, particularly in West Africa. The Southern Regional Research Center of the United States Department of Agriculture, Agricultural Research Service (USDA-ARS-SRRC) and the International Institute of Tropical Agriculture (IITA) initiated a collaborative breeding project to develop maize germplasm with resistance to aflatoxin accumulation. Resistant genotypes from the US and selected inbred lines from IITA were used to generate backcrosses with 75% US germplasm and F(1) crosses with 50% IITA and 50% US germplasm. A total of 65 S(4) lines were developed from the backcross populations and 144 S(4) lines were derived from the F(1) crosses. These lines were separated into groups and screened in SRRC laboratory using a kernel-screening assay. Significant differences in aflatoxin production were detected among the lines within each group. Several promising S(4) lines with aflatoxin values significantly lower than their respective US resistant recurrent parent or their elite tropical inbred parent were selected for resistance-confirmation tests. We found pairs of S(4) lines with 75-94% common genetic backgrounds differing significantly in aflatoxin accumulation. These pairs of lines are currently being used for proteome analysis to identify resistance-associated proteins and the corresponding genes underlying resistance to aflatoxin accumulation. Following confirmation tests in the laboratory, lines with consistently low aflatoxin levels will be inoculated with A. flavus in the field in Nigeria to identify lines resistant to strains specific to both US and West Africa. Maize inbred lines with desirable agronomic traits and low levels of aflatoxin in the field would be released as sources of genes for resistance to aflatoxin production.

Aflatoxins↗

PubMed1976

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

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

Aflatoxins↗

PubMed1992

Urinary aflatoxin biomarkers and risk of hepatocellular carcinoma.

Aflatoxins have long been suspected to be human hepatic carcinogens but no direct study was feasible until assays to measure individual aflatoxin exposure became available. We have used assays for urinary aflatoxin B1, its metabolites AFP1 and AFM1, and DNA-adducts (AFB1-N7-Gua) to assess the relation between aflatoxin exposure and liver cancer, as part of an ongoing prospective study of 18,244 middle-aged men in Shanghai, People's Republic of China. After 35,299 person-years of follow-up, 22 cases of liver cancer had been identified. For each case, 5 or 10 controls were randomly selected from cohort members without liver cancer on the date the disorder was diagnosed in the case and matched to within 1 year for age, within 1 month for sample collection, and for neighbourhood of residence. Subjects with liver cancer were more likely than were controls to have detectable concentrations of any of the aflatoxin metabolites (relative risk 2.4, 95% confidence interval 1.0-5.9). The highest relative risk was for aflatoxin P1 (6.2, 1.8-21.5). In an analysis adjusting for the effects of hepatitis B surface antigen seropositivity, level of education, cigarette smoking, and alcohol consumption, the relative risk for the presence of aflatoxin metabolites was 3.8 (1.2-12.2). There was a strong interaction between serological markers of chronic hepatitis B infection and aflatoxin exposure in liver-cancer risk. Reduction of aflatoxin exposure may be a useful intermediate goal in prevention of liver cancer, since the benefits of wide-scale hepatitis B vaccination will not be apparent for many years.

Aflatoxins↗

PubMed1994

Activation of aflatoxin B1 by mouse CYP2A enzymes and cytotoxicity in recombinant yeast cells.

The ability of three highly homologous mouse liver CYP2A enzymes to activate aflatoxin B1 was studied by expressing them in recombinant AH22 Saccharomyces cerevisiae yeast cells. The reconstituted monooxygenase complex with CYP2A5 purified from yeast cell microsomes produced epoxide at a rate of 17.2 nmol/min per nmol P450 in the presence of 50 microM aflatoxin B1 while CYP2A4 had about 10% and P4507 alpha only 1.5% of this activity. However, Km values were 530 and 10 microM and Vmax values 12.5 and 14.3 nmol/min per nmol P450 for CYP2A4 and CYP2A5, respectively. When recombinant yeast cells were exposed to aflatoxin B1 LC50 concentrations were 7.5 +/- 5.5 microM for CYP2A4, 0.45 +/- 0.10 microM for CYP2A5 and > 320 microM for P4507 alpha expressing yeast cells. Aflatoxin B1-DNA adduct levels in the same yeast cells were 50, 890 pmol/mg DNA and below detection limit when 3.0 microM aflatoxin B1 was used in the incubation mixture. Coumarin an inhibitor for CYP2A4 and a substrate for CYP2A5 diminished the toxicity of aflatoxin B1 in a dose-dependent manner for these recombinant yeast cells. These data demonstrate that (1) highly homologous mouse CYP2A enzymes activate aflatoxin B1 in a different manner and (2) that recombinant yeast cells expressing mammalian CYP enzymes are a useful and inexpensive system to test the role of different enzymes in aflatoxin B1 toxicity. The data also indicate that mouse CYP2A5 and its counterpart in other species could have a significant role in aflatoxin B1 toxicity in organs where it is expressed at high levels.

Aflatoxin B1↗

PubMed2005

Ameliorative effects of black tea extract on aflatoxin-induced lipid peroxidation in the liver of mice.

We have evaluated the ameliorative effect of black tea extract on aflatoxin-induced lipid peroxidation in the liver of mice. Adult male albino mice were orally administered with 25 and 50 microg of aflatoxin in 0.2 ml olive oil/animal/day for 30 days. Results revealed dose-dependent and significantly (p<0.05) higher lipid peroxidation in the liver of aflatoxin-treated mice than that of vehicle control. As compared with vehicle control, the levels of non-enzymatic antioxidants such as glutathione and ascorbic acid, as well as the enzymatic antioxidants such as superoxide dismutase, glutathione peroxidase and catalase were significantly (p<0.05) lowered in the liver of aflatoxin-treated mice. Oral administration of two percent aqueous black tea extract along with aflatoxin for 30 days (groups 6 and 7) caused significant (p<0.05) amelioration in aflatoxin-induced lipid peroxidation by increasing significantly (p<0.05) the activities of enzymatic (superoxide dismutase, glutathione peroxidase, catalase) and contents of non-enzymatic (glutathione and ascorbic acid) antioxidants in the liver of mice as compared with those given aflatoxin alone (groups 4 and 5). Thus, oral administration of black tea along with aflatoxin significantly (p<0.05) ameliorates aflatoxin-induced lipid peroxidation in the liver of mice.

Administration, Oral↗

PubMed2006

Nonaflatoxigenic Aspergillus flavus TX9-8 competitively prevents aflatoxin accumulation by A. flavus isolates of large and small sclerotial morphotypes.

Aflatoxins are a family of highly toxic and carcinogenic toxins produced by several Aspergillus species. Aflatoxin contamination of agricultural commodities both pre- and postharvest is a serious food safety issue and a significant economic concern. Using nonaflatoxigenic A. flavus isolates to competitively exclude toxigenic A. flavus isolates in agricultural fields has become an adopted approach to reduce aflatoxin contamination. From screening subgroups of nonaflatoxigenic A. flavus, we identified an A. flavus isolate, TX9-8, which competed well with three A. flavus isolates producing low, intermediate, and high levels of aflatoxins, respectively. TX9-8 has a defective polyketide synthase gene (pksA), which is necessary for aflatoxin biosynthesis. Co-inoculating TX9-8 at the same time with large sclerotial (L strain) A. flavus isolates at a ratio of 1:1 or 1:10 (TX9-8:toxigenic) prevented aflatoxin accumulation. The intervention of TX9-8 on small sclerotial (S strain) A. flavus isolates varied and depended on isolate and ratio of co-inoculation. At a ratio of 1:1 TX9-8 prevented aflatoxin accumulation by A. flavus CA28 and reduced aflatoxin accumulation 10-fold by A. flavus CA43. No decrease in aflatoxin accumulation was apparent when TX9-8 was inoculated 24 h after toxigenic L- or S strain A. flavus isolates started growing. The competitive effect likely is due to TX9-8 outgrowing toxigenic A. flavus isolates.

Aflatoxins↗

PubMed1999

Mutations associated with in vivo aflatoxin B1-induced carcinogenesis need not be present in the in vitro transformations by this toxin.

Ingestion of aflatoxin B1 is implicated in the high incidence of human liver cancers in several developing countries. An association has been detected between human exposure to aflatoxins, and mutations in the third base of codon 249 of the p53 gene in hepatomas. In vitro experiments using human cell line cells and aflatoxin B1 have demonstrated the induction of p53 mutations in codon 249 and adjacent codons. It was therefore of interest to see if this correlation between the in vivo and in vitro situations held for other species. The present study examined a rat liver-derived cell line, transformed in vitro with aflatoxin B1, for the presence of mutations associated with in vivo aflatoxin-induced hepatocarcinogenesis. In an in vivo rodent model systems using the aflatoxin B1-sensitive male F344 rat, previous studies have shown that hepatocarcinogenesis is accompanied by significant incidences of codon 12 mutations in K-ras and codon 13 mutations in N-ras genes, but in contrast to the human, apparently not by mutations in codon 243 of the p53 gene (which corresponds to codon 249 in the human gene). In contrast to the situation in humans, mutation in the third base of codon 243 in the rat would not result in any changes in amino acid sequence, but mutations in codon 250, as seen in in vitro human systems, would be expressed in the rat p53 protein. In the present study, an immortalised, non-transformed liver epithelial cell line derived from a male F344 rat was transformed in vitro by aflatoxin B1 as demonstrated by tumour formation in nude mice. The transformation was dependent on metabolic activation of the aflatoxin B1. Transfection of DNA, extracted from these tumours, into NIH 3T3 fibroblasts conferred a stable, malignant transforming capacity. However, no mutations in codon 12 of the K-ras or codon 13 of the N-ras genes were detected in any of these tumours. These results indicate that in vitro transformation does not necessarily involve the same mutations, as those observed in vivo. Also, no mutations in codon 243 or adjacent codons of the p53 gene, paralleling those observed in the human cell line treated with aflatoxin B1, were detected. The results serve to emphasise the in vivo and in vitro variation in the oncogene activation in the same target organ or cell lines derived from that organ, even when using a single carcinogen activated by a known metabolic pathway.

3T3 Cells↗

PubMed2003

Effect of intraspecific competition by Aspergillus flavus on aflatoxin formation in suspended disc culture.

The ability of two non-aflatoxin producing strains of Aspergillus flavus to interfere with aflatoxin production by a toxigenic A. flavus strain was examined using a replacement series with suspended disc culture method. Individual glass fiber discs, affixed to a pin suspended from the caps of scintillation vials, were inoculated with medium containing A. flavus conidial mixtures in different proportions (aflatoxin producer:non-producer = 100:0, 80:20, 60:40, 20:80 and 0:100 by vol) at a constant total density (1 x 10(5) spores ml(-1)). Reductions in the total conidial density of these strains when grown alone, had little effect on fungal growth (mycelium dry weight) or aflatoxin production. Significant (P < 0.0001) reductions in aflatoxin B1 were recorded when non-toxigenic strains represented any proportion of the inoculum mixture. Aflatoxin yield values were less than (P < 0.0001) expected from the input ratios for toxigenic vs. non-toxigenic conidial inoculum within the replacement series. Aflatoxin yields were also reduced (P < 0.001), with a corresponding increase in fungal growth (P < 0.001), when conidia from aflatoxin producing strains were mixed in equal proportions. This suggests that the substantial inhibition of aflatoxin yield for inoculum mixtures results from the failure of spore germlings to establish a cooperative mycelial network.

Aflatoxin B1↗

PubMed2002

Development of a fluorescence polarization assay for the determination of aflatoxins in grains.

Aflatoxins produced by Aspergillus flavus are commonly found in human and animal foods including grains, cereals, peanut products, sorghum, and soy seeds. Exposure to aflatoxins has been associated with carcinogenicity. This paper reports a simple, portable, and rapid fluorescence polarization (FP) assay for aflatoxin determination in grains. This immunoassay is field portable, homogeneous, and without any washing and cleaning steps. The assay is based upon the competition between free aflatoxin and an aflatoxin-fluorescein tracer for an aflatoxin-specific monoclonal antibody in solution. A series of naturally contaminated corn, sorghum, peanut butter, and peanut paste samples were analyzed by FP and compared with HPLC results. Similarly, spiked popcorn samples were analyzed by FP. FP results of naturally contaminated samples correlated well with HPLC (r (2) = 0.97). FP analysis of spiked popcorn samples (with a mixture of B(1)/B(2)/G(1)/G(2), 7/1/3/1, w/w) gave a good correlation with spiked values (r (2) = 0.99). However, FP consistently underestimated the aflatoxin contents. This was perhaps due to low cross-reactivity of the antibody used toward B(2), G(1), and G(2) aflatoxins. These results combined with the portability and simplicity of the assay suggest that the assay can be used for screening total aflatoxin in grains.

Aflatoxins↗

PubMed2006

Effect of pressure cooking on aflatoxin B1 in rice.

The effect of pressure cooking on aflatoxin residues in polished rice was conducted to determine reduction of aflatoxin and mutagenic potentials. Three rice lots consisting of naturally contaminated, A. parasiticus-infested, and aflatoxin-spiked rice were steamed by ordinary and pressure cookers after they were washed with water. They were chemically analyzed for aflatoxins using a silica solid phase extraction tube and high-performance liquid chromatography (HPLC)-fluorescence detection (FD), and the presence of aflatoxin residues was confirmed using HPLC-electrospray ionization (ESI)-mass spectrometry (MS). An in vitro mutagenicity test with Salmonella typhimurium TA100 was employed to verify the results based on chemical analyses. The aflatoxin loss (78-88%) was notable after pressure cooking, and the reduction of aflatoxin-induced mutagenic potential (68-78%) was in good agreement with the HPLC results. It can be concluded that Koreans are safe from the aflatoxin-related risk if a pressure cooker is employed for cooking rice. The average Korean daily intake of aflatoxin through the consumption of staple rice would fall to 0.15 ng/kg bw/day, which would not exceed the established tolerable daily intake (0.40 ng/kg bw/day).

Aflatoxin B1↗

PubMed2000

Protective effect of ebselen on aflatoxin B1-induced cytotoxicity in primary rat hepatocytes.

Recent studies have shown that aflatoxin B1 enhances reactive oxygen species formation and causes oxidative damage, which may ultimately contribute to the cytotoxicity and carcinogenic effect of aflatoxin B1. Ebselen, 2-phenyl-1,2-benzoisoseleazol-3(H)-one, a synthetic seleno-organic compound has been shown to possess glutathione peroxidase-like activity and free radical scavenging ability. Thus present study was designed to investigate the protective effect of ebselen on aflatoxin B1-induced cytotoxicity in primary rat hepatocytes. Aflatoxin B1-induced cytotoxicity and lipid peroxidation were determined by lactate dehydrogenase leakage and malondialdehyde generation, respectively. Intracellular reactive oxygen species level was measured using the fluorescent probe 2',7'-dichlorofluorescin diacetate, and the intracellular reduced glutathione concentration was determined with a fluorometric method. Ebselen was found to display a dose-dependent protective effect on lactate dehydrogenase leakage and malondialdehyde generation caused by aflatoxin B1 exposure. The results also demonstrate that ebselen efficiently inhibits the intracellular reactive oxygen species formation in aflatoxin B1-treated hepatocytes in a dose and time-dependent manner. It was also noted that ebselen was able to increase the intracellular reduced glutathione concentration, both in the control and in aflatoxin B1-treated hepatocytes. The protection of ebselen against aflatoxin B1 cytotoxicity, however, was not affected by lowering the concentration of intracellular reduced glutathione. The overall data indicate that ebselen possesses a potent protective effect against aflatoxin B1-induced cytotoxicity, and the main mechanism involved in the protection may be its strong capability in inhibiting intracellular reactive oxygen species formation and preventing oxidative damage.

Aflatoxin B1↗

PubMed2003

Substrate-induced lipase gene expression and aflatoxin production in Aspergillus parasiticus and Aspergillus flavus.

AIMS: To establish a relationship between lipase gene expression and aflatoxin production by cloning the lipA gene and studying its expression pattern in several aflatoxigenic and nontoxigenic isolates of Aspergillus flavus and A. parasiticus. METHODS AND RESULTS: We have cloned a gene, lipA, that encodes a lipase involved in the breakdown of lipids from aflatoxin-producing A. flavus, A. parasiticus and two nonaflatoxigenic A. flavus isolates, wool-1 and wool-2. The lipA gene was transcribed under diverse media conditions, however, no mature mRNA was detected unless the growth medium was supplemented with 0.5% soya bean or peanut oil or the fungus was grown in lipid-rich medium such as coconut medium. The expression of the lipase gene (mature mRNA) under substrate-induced conditions correlated well with aflatoxin production in aflatoxigenic species A. flavus (SRRC 1007) and A. parasiticus (SRRC 143). CONCLUSIONS: Substrate-induced lipase gene expression might be indirectly related to aflatoxin formation by providing the basic building block 'acetate' for aflatoxin synthesis. No direct relationship between lipid metabolism and aflatoxin production can be ascertained, however, lipase gene expression correlates well with aflatoxin formation. SIGNIFICANCE AND IMPACT OF THE STUDY: Lipid substrate induces and promotes aflatoxin formation. It gives insight into genetic and biochemical aspects of aflatoxin formation.

Aflatoxins↗

PubMed2005

Consumers' ability to discriminate aflatoxin-contaminated Brazil nuts.

The objectives of the study were to investigate the extent to which consumers can separate nuts with a high content of aflatoxin from sound nuts, and whether sorting results can be improved by information or whether they are affected by certain factors. A test panel consisting of 100 subjects was asked to crack 300 g Brazil nuts and to sort the nuts into those they considered edible and inedible. The test showed that consumers can, on current behaviour, discriminate aflatoxin-contaminated Brazil nuts to a significant extent. The median and the 95th percentile of the total concentrations of aflatoxins (B1, B2, G1, G2) in the samples before sorting were 1.4 and 557 microg kg(-1), respectively, and in the edible fractions after sorting 0.4 and 56 microg kg(-1), respectively. Given that levels of aflatoxins before sorting exceed either 2 microg aflatoxin B1 kg(-1) or totally 4 microg aflatoxins kg(-1), there was no effect of aflatoxin concentrations before sorting on the probability of exceeding these thresholds in the edible fraction. This means that similar sorting results were obtained for samples with aflatoxin levels exceeding either of the two thresholds, irrespective of if the thresholds were exceeded with a few microg kg(-1) or up to more than 1000 microg kg(-1). None of the tested factors (such as sex, age, level of education, ethnic background or knowledge of mycotoxins) had any effects on the probability of exceeding either of the two aflatoxin thresholds.

Adult↗

PubMedDate not supplied

Aflatoxin in betel nut and its control by use of food preservatives.

The occurrence of aflatoxins in market betel nut samples was studied. It was observed that several betel nut samples were infested with aflatoxin-producing fungus, Aspergillus flavus. Out of 32 samples collected from various places, 12 were positive for aflatoxin. Aflatoxin B1 was detected in all the positive samples. Other aflatoxins were also detected in some samples. Boric acid, propionic acid and potassium metabisulphite were used for the control of aflatoxin B1 on betel nuts. Propionic acid was most effective in inhibiting aflatoxin production on betel nut after intervals of 2 (62%) and 4 (85%) weeks. Controlling the occurrence of aflatoxin could safeguard the users from the health hazards of aflatoxins.

Aflatoxins↗