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PubMed1989

Production and characterization of antibodies cross-reactive with major aflatoxins.

Antibodies cross-reactive with 4 major aflatoxins were demonstrated three weeks after immunization of rabbits with an immunogen which was prepared by conjugating aflatoxin B3 to bovine serum albumin. Aflatoxin B3 was first converted to its hemisuccinate before conjugation to the protein. Tritiated aflatoxin B1 (AFB1) was used as the marker ligand both for antibody titer determination as well as for analysis of antibody specificity. Competitive RIA revealed that the antibodies have good cross-reactivity with aflatoxins B1, B2, G1, and G2 when tritiated AFB1 was used as the marker ligand. The concentrations causing 50% inhibition of binding of 3H-AFB1 to the antibodies by unlabeled aflatoxins B1, B2, G1, G2 and B3 were found to be 0.25, 3.34, 0.32, 4.0 and 0.53 ng/assay, respectively. The antibodies could be used for simultaneous analysis of aflatoxins B1 and G1, two of the most important toxic metabolites produced by Aspergillus flavus and A. parasiticus.

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↗

PubMed1985

Uptake and vascular transport of ingested aflatoxin.

The uptake and vascular transport of abomasally instilled aflatoxin B1 (AFB1) was investigated in sheep. Aflatoxin uptake was compared with that of palmitate, a water-insoluble oil known to be absorbed into the intestinal lymphatic drainage which bypasses the liver to enter the peripheral vascular circulation via the thoracic duct. After instillation into the abomasum, aflatoxin was detected in inferior vena cava blood within 30 min, while palmitate was not detected in vena cava blood at any time. Palmitate was detected in thoracic duct lymph after about 2 h. More than 95% of the palmitate in lymph was associated with the chylomicron fraction, while aflatoxin in either plasma or lymph was not detectably associated with any of the circulating lipoproteins. In addition, aflatoxin did not partition into plasma or lymph lipoproteins in vitro. Toxic lipophilic xenobiotics, such as benzo(a)pyrene and polychlorinated biphenyls (PCBs) do partition into lipoproteins, are absorbed into the intestinal lymphatic drainage, bypassing the liver to enter the peripheral vascular circulation directly, and are not specifically hepatotoxic. These data suggest that the mode of aflatoxin absorption from the gastrointestinal system results in its immediate transport to the liver, which may contribute to aflatoxin hepatotoxicity.

Aflatoxin B1↗

PubMed2001

Aflatoxins and fumonisins in corn from the high-incidence area for human hepatocellular carcinoma in Guangxi, China.

A comparative study on the natural occurrence of aflatoxins and Fusarium toxins was conducted with corn samples from high- and low-incidence areas for human primary hepatocellular carcinoma (PHC) in Guangxi, China. In samples from the high-risk area, aflatoxin B(1) was the predominant toxin detected in terms of quantity and frequency, with its concentration ranging between 9 and 2496 microg/kg and an 85% incidence of contamination. Among the samples, 13 (76%) exceeded the Chinese regulation of 20 microg/kg for aflatoxin B(1) in corn and corn-based products intended for human consumption. Significant differences in aflatoxin B(1), B(2), and G(1) and total aflatoxin concentrations in corn between the areas were found (P < 0.05). The average daily intake of aflatoxin B(1) from corn in the high-risk area was 184.1 microg, and the probable daily intake is estimated to be 3.68 microg/kg of body weight/day, 3.20 times the TD(50) in rats. Corn samples from both areas were simultaneously contaminated with fumonisins B(1), B(2), and B(3). Aflatoxin B(1) may play an important role in the development of PHC in Guangxi.

Aflatoxin B1↗

PubMed1981

In vitro reactions of aflatoxin B1-adducted DNA.

The chemical stability of aflatoxin B1 bound to calf thymus DNA was studied over a 48-hour exposure to phosphate buffers at pH 6.8-8.0 (37 degrees C). During this time, aliquots of the aflatoxin B1-modified DNA were acid-hydrolyzed and analyzed for the presence of 2,3-dihydro-2-(N7-guanyl)-3-hydroxyflatoxin B1, 2,3-dihydro-2,3-dihydroxy-aflatoxin B1, and the tentatively identified, 2,3-dihydro-2-(N5-formyl-2',5',6'-triamino-4'-oxo-N5-pyrimidyl-3-hydroxyflatoxin B1 and 2,3-dihydro-2-(8,9-dihydro-8-hydroxy-N7-guanyl)-3-hydroxyaflatoxin B1. Initial experiments determined the stability of 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 in DNA at levels of modification of one residue per 60 and 1500 nucleotides. The acid-hydrolysis products obtained from these modified nucleic acids were qualitatively similar, but their proportional concentrations were different. These quantitative differences were dependent upon both pH and the initial level of modification of the DNA. During the first 6 hr of incubation, under all conditions examined, the formation of 2,3-dihydro-2,3-dihydroxyaflatoxin B1 was responsible for the initial decrease of the 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 adduct in DNA. After 48 hr of incubation at pH 7.0, the major reaction of the modified DNA was depurination of the 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 adduct. However, at pH 8.0, the predominant reaction product formed in 48 hr was the putative 2,3-dihydro-2-(N5-formyl-2',5',6'-triamino-4'-oxo-N5-pyrimidyl)-3-hydroxy-aflatoxin B1. The putative DNA-bound products resulting from the elimination of the positive charge in the imidazole ring of the aflatoxin-N7-guanine adduct [2,3-dihydro-2-(N5-formyl-2',5',6'-triamino-4'-oxo-N5-pyrimidyl)-3-hydroxy-aflatoxin B1 and 2,3-dihydro-2-(8,9-dihydro-8-hydroxy-N7-guanyl)-3-hydroxyaflatoxin B1] were found to be stable in DNA for at least 24 hr at both pH 6.8 and 7.4. Taken together with observed patterns of stability of aflatoxin B1 adducts in vivo, these observations strongly suggest the involvement of enzymatic repair processes in removal of the N7-guanyl adduct and also emphasize the possible biological significance of the stable imidazole ring-opened adduct.

Aflatoxin B1↗

PubMed2006

Aflatoxins, patulin and ergosterol contents of dried figs in Turkey.

Dried figs of three different categories, palatable, fluorescent, and cull, were investigated for their contents of aflatoxins (B(1), B(2), G(1) and G(2)), patulin, and ergosterol. Samples were obtained from four fig processing plants located in a major fig producing area in the Aegean Region in Turkey. Affinity column clean-up methods were employed for aflatoxins. All aflatoxins, patulin, and ergosterol were determined using high performance liquid chromatography. Palatable figs contaminated with trace amounts of aflatoxins, patulin, and ergosterol, so they posed no risk for the consumer when national and/or international regulatory limits were considered. Fluorescent figs were contaminated with high (117.9-471.9 ppb) aflatoxin levels and cull figs with high patulin (39.3-151.6 ppb) and ergosterol (4.5-18 ppm) levels. The total aflatoxins content was significantly correlated with the patulin content (r(2) = 0.813, p < 0.002) and the ergosterol content (r(2) = 0.920, p < 0.002) only in fluorescent figs. However there was no significant correlation between patulin and ergosterol contents of fluorescent figs. Furthermore, there were no significant correlations between the contents of any two of the three substances in cull figs. This is the first report on the presence of patulin and its co-occurrence with aflatoxin in dried figs.

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↗

PubMed1984

Aflatoxins in human breast milk.

Breast milk from 99 Sudanese mothers was analysed for aflatoxins. Aflatoxins M1 and/or M2 were detected in 37 of the milks. No other aflatoxin was detected. M1 occurred alone in 13 milks, (mean 19.0 pg/ml), M2 in 11 milks (mean 12.2 pg/ml), and in 13 samples both M1 and M2 were detected. There appeared to be a linear relationship between M1 and M2 where both were excreted. No aflatoxin was detected in subcutaneous abdominal wall fat removed during Caesarian section from 15 women, but was present in three out of 14 bloods taken during anaesthesia. The presence of aflatoxins in mothers' milk showed no correlation with duration of lactation, the infants' nutrition, presence of aflatoxin in mothers' blood, or the infant's blood and urine. It is concluded that some Sudanese women excrete aflatoxins in breast-milk at levels similar to or higher than those considered safe in animal milk, for human consumption.

Adipose Tissue↗

PubMed1990

The aflatoxin-lysine adduct quantified by high-performance liquid chromatography from human serum albumin samples.

Aflatoxin B1 (AFB1) exposure from the diet is a major risk factor for the development of liver cancer in people living in regions of China and Africa. Rapid methods to assess the exposure status of these individuals to genotoxic damage imparted by AFB1 will be very important for cancer prevention strategies. Serum albumin is a readily accessible target protein for AFB1 and we report here the development of an accurate and sensitive method to quantitate the major AFB1 serum albumin adduct, aflatoxin-lysine, from less than 100 microliters of serum by combined immunoaffinity chromatography/high-performance liquid chromatography (IAC/HPLC) with fluorescence detection. For this method, serum is digested with Pronase and the adducts are purified by monoclonal antibody IAC and quantified by HPLC. Analysis of human serum samples obtained from an exposed population revealed a highly significant correlation coefficient (up to 0.82 for male samples) between aflatoxin-lysine adduct levels and AFB1 consumption. These data suggest that aflatoxin-lysine is an excellent molecular dosimeter for exposure assessment. To determine whether the liver is the sole site of aflatoxin-albumin adduct formation, preliminary experiments with isolated perfused rat liver were done. These data showed that AFB1 metabolites covalently react not only with albumin in the hepatocyte, but also with circulating proteins in the perfusate. This suggests that a reactive aflatoxin metabolite secreted by the liver may form serum albumin adducts in circulating blood. Taken together, the analysis of aflatoxin-lysine could prove a very useful tool for epidemiological studies.

Aflatoxin B1↗

PubMed1983

Excision of aflatoxin B1-imidazole ring opened guanine adducts from DNA by formamidopyrimidine-DNA glycosylase.

This investigation has confirmed the earlier reports that when aflatoxin B1-DNA adducts are stored under physiological conditions some aflatoxin B1-guanine adducts are converted to a secondary product in which fission of the imidazole ring of the adduct guanine has occurred. Incubation of DNA containing aflatoxin B1-guanine adducts for an increasing number of hours under physiological conditions resulted in a progressive increase in the number of adducts in which the imidazole rings of guanines underwent fission. It was shown that the Escherichia coli enzyme, formamidopyrimidine-DNA glycosylase exercises from the 6-day incubated DNA, an amount of imidazole ring opened guanines equivalent to 40% of the aflatoxin B1-guanine adducts present in the DNA. The enzymatic excision of imidazole ring opened aflatoxin B1-guanine adducts is inhibited by Cibacron Blue F3GA a strong inhibitor of formamidopyrimidine-DNA glycosylase. Treatment of aflatoxin B1-DNA with mild alkali (pH 9.6), resulted in a 2-fold increase in the amount of aflatoxin B1-guanines with opened imidazole rings; this was revealed by enzyme assays using this alkaline treated DNA substrate as well as by analysis of acid hydrolysates of the alkaline treated DNA.

Aflatoxin B1↗

PubMed1981

Precursor recognition by kinetic pulse-labeling in a toxigenic aflatoxin B1-producing strain of Aspergillus.

Kinetic pulse-labeling of aflatoxin pathway compounds was carried out in Aspergillus parasiticus, beginning with radioactive acetate. Norsolorinic acid, averufin, versicolorin A, and sterigmatocystin (all known as compounds which can be incorporated into the aflatoxin molecule) were radiotraced to follow their order of appearance. Aflatoxin species B1, B2, G1, and G2 were included. Norsolorinic acid and averufin appeared as early transient intermediates followed in order by versicolorin A, aflatoxins, and sterigmatocystin. To date, a mutually confirming array of results has been obtained with established precursors in wild-type strains of A. parasiticus and A. versicolor (as well as with an aflatoxin pathway mutant of A. parasiticus), which together establish a practical methodology for recognition of new pathway intermediates. The kinetic of pulse-labeling for sterigmatocystin in relation to aflatoxins suggests that duel branchlets may exist to flatoxins; i.e., sterigmatocystin may not be an obligatory aflatoxin precursor.

Aflatoxin B1↗

PubMed1991

Mold flora and aflatoxin contamination of stored and cooked samples of pearl millet in the Paharia tribal belt of Santhal paragana, Bihar, India.

Stored and cooked samples of pearl millet (Pennesetum typhoides), which is regularly consumed as food by the Paharia tribe in the hilly regions of Santhal Pargana, Bihar State, India, that were harvested in January 1989 were analyzed for mold flora, natural occurrence of Aspergillus flavus and A. parasiticus, and incidence and levels of aflatoxin B1. Of the 22 fungal species isolated, A. flavus and A. parasiticus were the predominant species (63.8%) during the rainy season, followed by other species of Aspergillus, Penicillium, Fusarium, Rhizopus, Helminthosporium, and Curvularia. Screening of 169 A. flavus and A. parasiticus strains showed that 59 of them were toxigenic, producing various combinations of aflatoxins B1, B2, G1, and G2. The amounts of aflatoxin B1 ranged between 4 and 30 mg/100 ml of liquid medium. Analysis of stored and cooked samples also revealed a high incidence and alarming levels of naturally produced aflatoxin B1. Forty-nine of 75 stored and 16 of 38 cooked samples contained various combinations of aflatoxins. The levels of aflatoxin B1 ranged between 17 and 2,110 ppb in stored samples and 18 and 549 ppb in cooked samples. The correlation of insect damage with A. flavus and A. parasiticus incidence and quantity of aflatoxin B1 was found to be insignificant.

Aflatoxin B1↗

PubMed1998

Characterization of the critical amino acids of an Aspergillus parasiticus cytochrome P-450 monooxygenase encoded by ordA that is involved in the biosynthesis of aflatoxins B1, G1, B2, and G2.

The conversion of O-methylsterigmatocystin (OMST) and dihydro-O-methylsterigmatocystin to aflatoxins B1, G1, B2, and G2 requires a cytochrome P-450 type of oxidoreductase activity. ordA, a gene adjacent to the omtA gene, was identified in the aflatoxin-biosynthetic pathway gene cluster by chromosomal walking in Aspergillus parasiticus. The ordA gene was a homolog of the Aspergillus flavus ord1 gene, which is involved in the conversion of OMST to aflatoxin B1. Complementation of A. parasiticus SRRC 2043, an OMST-accumulating strain, with the ordA gene restored the ability to produce aflatoxins B1, G1, B2, and G2. The ordA gene placed under the control of the GAL1 promoter converted exogenously supplied OMST to aflatoxin B1 in Saccharomyces cerevisiae. In contrast, the ordA gene homolog in A. parasiticus SRRC 2043, ordA1, was not able to carry out the same conversion in the yeast system. Sequence analysis revealed that the ordA1 gene had three point mutations which resulted in three amino acid changes (His-400-->Leu-400, Ala-143-->Ser-143, and Ile-528-->Tyr-528). Site-directed mutagenesis studies showed that the change of His-400 to Leu-400 resulted in a loss of the monooxygenase activity and that Ala-143 played a significant role in the catalytic conversion. In contrast, Ile-528 was not associated with the enzymatic activity. The involvement of the ordA gene in the synthesis of aflatoxins G1, and G2 in A. parasiticus suggests that enzymes required for the formation of aflatoxins G1 and G2 are not present in A. flavus. The results showed that in addition to the conserved heme-binding and redox reaction domains encoded by ordA, other seemingly domain-unrelated amino acid residues are critical for cytochrome P-450 catalytic activity. The ordA gene has been assigned to a new cytochrome P-450 gene family named CYP64 by The Cytochrome P450 Nomenclature Committee.

Aflatoxin B1↗

PubMed1981

Inhibitory effect of molybdenum and vanadium salts on aflatoxin B1 synthesis by Aspergillus flavus.

The effects of the elements zinc, manganese, iron, copper, molybdenum, and vanadium, added in various salt forms, on mycelial weights and aflatoxin B1 accumulation in the mycelium of Aspergillus flavus were investigated in liquid shake cultures. Ammonium heptamolybdate, when added to a complete medium at concentrations of 50-100 mg/L, appreciably reduced aflatoxin B1 accumulation without affecting growth of the fungus. Sodium molybdate and sodium monovanadate also reduced aflatoxin B1 yields without affecting mycelial growth but to a lesser extent. The addition of zinc sulphate stimulated aflatoxin B1 production in all media used. The influence of the other trace elements on aflatoxin production depended on the level of trace elements present in the basal medium. In general, manganese chloride had a stimulatory effect, whereas copper sulphate depressed yields. Mycelial levels of aflatoxin had peaked and then declined before mycelial dry weights had reached maximum. High yields of aflatoxin B1 were obtained in media having a final pH as low as pH 2.8.

Aflatoxin B1↗

PubMed1983

Factors influencing the inhibition of aflatoxin production in corn by Aspergillus niger.

Aspergillus niger, a mold commonly associated with Aspergillus flavus in damaged corn, interferes with the production of aflatoxin when grown with A. flavus on autoclaved corn. The pH of corn-meal disks was adjusted using NaOH-HCl, citric acid-sodium citrate, or a water extract of A. niger fermented corn. Aflatoxin formation was completely inhibited below pH 2.8-3.0, irrespective of the system used for pH adjustment. When grown in association with A. flavus NRRL 6432 on autoclaved corn kernels, A. niger NRRL 6411 lowered substrate pH sufficiently to suppress aflatoxin production. The biodegradation of aflatoxin B1 or its conversion to aflatoxin B2a were eliminated as potential mechanisms by which A. niger reduces aflatoxin contamination. A water extract of corn kernels fermented with A. niger caused an additional inhibition of aflatoxin formation apart from the effects of pH.

Aflatoxin B1↗

PubMed1993

Does aflatoxin exposure in the United Kingdom constitute a cancer risk?

Although the aflatoxins were discovered more than 30 years ago, there is still considerable controversy surrounding their human health effects. Most countries have introduced legislation to control the level of aflatoxins in food, but it is not known if these permitted levels still pose a significant cancer risk. Furthermore, it is unlikely that all the sources of human aflatoxin exposure have been discovered, nor if the liver is the only, or indeed, major target organ for aflatoxin-induced cancer in man. In our laboratory we have used both immunological and HPLC methods to examine human DNA from a variety of tissues and organs to identify and quantify aflatoxin DNA-adducts. We have already detected aflatoxin B1 (AFB1)-DNA adducts in formalin-fixed tissue from an acute poisoning incident in Southeast Asia. Here we have examined human colon and rectum DNA from normal and tumorous tissue obtained from cancer patients and colon, liver, pancreas, breast, and cervix DNA from autopsy specimens. AFB1-DNA adducts were detected in all tissue types examined and ranged from 0-60 adducts/10(6) nucleotides. Where sample size allowed, the adduct levels were confirmed by HPLC analysis. Tumor tissues tended to have higher adduct levels than normal tissue from the same individual, and levels generally increased with patient age. In samples analyzed by HPLC, the adducts present had the chromatographic properties of [8,9-dihydro-8-(N5-formyl)-2',5',6'-triamino-4'-oxo-(N5-pyramidyl) -9- hydroxy-aflatoxin B1, the ring-opened form of the AFB1-guanine adduct.(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxin B1↗

PubMedDate not supplied

[Inactivation of aflatoxin B1 and aflatoxicol through traditional "nixtamalización" of corn and their regeneration by acidification of corn dough].

OBJECTIVE: To ratify the effect of traditional "nixtamalización" upon aflatoxin in corn, to identify the residual compound in dough, to evaluate its toxicity, and to verify the effect of acidic treatment on the regeneration of aflatoxin. MATERIAL AND METHODS: Corn with and without aflatoxin was treated separately with lime and heat to obtain two types of dough. Aflatoxin and the residual compound were quantified by high pressure liquid chromatography (HPLC) and toxicity was evaluated in eight day old chicks. RESULTS: "Nixtamalización" destroyed AFBI (96%) and aflatoxicol (70%). The residual compound was identified as AFBI. Experimental animals died by ingestion of 260 microg of AFBI Dough containing residual aflatoxin was not toxic. Acidic treatment did not increase aflatoxin concentration,nor aflatoxicol. CONCLUSIONS: The results support the use of traditional "nixtamalización" as a means to inactivate aflatoxin in corn and that acidic treatment prevents its regeneration in dough.

Aflatoxin B1↗

PubMed1981

Effect of aflatoxin B1 on hepatic drug-metabolizing enzymes in female rats. Interaction with a contraceptive agent.

1. The effect of a contraceptive on aflatoxin B1 toxicity has been studied in female rats treated for 15 consecutive days with repeated doses of aflatoxin (0.40 mg/kg/day), norethindrone (0.60 mg/kg/day) and ethynylestradiol (0.012 mg/kg/day). 2. Increases occurred in hepatic microsomal cytochrome P-450 content (31%), and in the activities of epoxide hydrase (77%), UDP-glucuronyltransferase (67%) and gamma-glutamyltransferase (78%). 3. Aflatoxin alone caused a 22% increase in GSH S-epoxide transferase activity, whereas the contraceptive given alone or combined with aflatoxin increased the hepatic reduced glutathione. 4. The effect of aflatoxin plus contraceptive was not additive. 5. The effects caused by aflatoxin and the contraceptive were similar, and the contraceptive (depending on its progestogen/estrogen ratio), may modify aflatoxin toxicity by increasing the drug-metabolizing enzyme activities and the concentration of hepatic glutathione.

Aflatoxin B1↗