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PubMedDate not supplied

Oxidation of aflatoxins and sterigmatocystin by human liver microsomes: significance of aflatoxin Q1 as a detoxication product of aflatoxin B1.

Aflatoxin Q1 8,9-oxide was synthesized and found to yield lower levels of N7-guanyl adducts than obtained from aflatoxin B1 8,9-oxide when mixed with calf thymus DNA or Salmonella typhimurium TA 98 cells. However, when S. typhimurium TA 98 was treated with the (analogous) epoxides of aflatoxin B1, aflatoxin G1, aflatoxin Q1, or sterigmatocystin, the ratios of revertants to N7-guanyl DNA adducts were similar. Aflatoxin Q1 and aflatoxin B1 8,9-oxide (trapped here as the glutathione conjugate) are the major oxidative products formed from aflatoxin B1 at all substrate concentrations in human liver microsomes, and cytochrome P-450 (P-450) 3A4 appears to be the dominant enzyme involved in both oxidations, as judged by studies involving correlation of activities in different liver samples, chemical inhibition, immunoinhibition, and reconstitution with purified hepatic and yeast recombinant P-450 3A4. Aflatoxin Q1 is not appreciably oxidized in human liver microsomes and is not very genotoxic. The postulated formation of both aflatoxin Q1 and aflatoxin 8,9-oxide from aflatoxin B1 can be rationalized by a model in which P-450 3A4 binds the substrate in either of two different configurations. This is further demonstrated by the dichotomous effect of 7,8-benzoflavone--this flavone stimulates 8,9-epoxidation while inhibiting the 3 alpha-hydroxylation reaction to form aflatoxin Q1. Thus, the 3 alpha-hydroxylation of aflatoxin B1 to aflatoxin Q1 is viewed as a potentially significant detoxication pathway.

Aflatoxin B1↗
PubMed2003

Reduction of aflatoxins by Korean soybean paste and its effect on cytotoxicity and reproductive toxicity--Part 3. Inhibitory effects of Korean soybean paste (doen-jang) on aflatoxin toxicity in laying hens and aflatoxin accumulation in their eggs.

This study was conducted to determine the effects of Korean soybean paste (doen-jang [dwen-jahng]) (at concentrations of 0.5, 1, and 5%) on the toxicity of 500 ppb of aflatoxin in the diets of 60 laying hens (Isa Brown) divided into five groups and treated from week 15 to week 67. The aflatoxin-treated hens exhibited many deleterious effects, including reduced body weight; increased relative organ weights; decreased egg production; aflatoxin accumulation in eggs; decreased serum calcium, phosphorus, and alanino amonotransferase (ALT) levels; increased serum gammaglutamil transferase and lactic dehydrogenase levels; and, most significantly, severely altered cell foci and sinusoid dilatation in the liver, relative to control hens. The feeding of 1% soybean paste to hens reduced the adverse effects of aflatoxin on body weight, relative organ weights, egg production, and aflatoxin accumulation in eggs and improved serum calcium and ALT levels and the histopathological lesions of the liver. The feeding of 5% soybean paste to hens resulted in higher levels of the same types of improvements, especially with regard to the histopathological findings for the liver. On the basis of these results, it was suggested that a diet including 5% (and in some cases only 1%) Korean soybean paste protected laying hens and their eggs from the major deleterious effects of 500 microg of aflatoxin per kg of diet and from aflatoxin accumulation. These results indicate that dietary supplementation with Korean soybean paste reduces aflatoxin toxicity in laying hens that ultimately produce human foods such as eggs and poultry.

Aflatoxins↗
PubMed2005

Mannanoligosaccharides and aflatoxin B1 in feed for laying hens: effects on egg quality, aflatoxins B1 and M1 residues in eggs, and aflatoxin B1 levels in liver.

Ninety-six laying hens were allocated to 4 groups and fed diets (control diet (0-0), diet supplemented with 2.5 ppm aflatoxin B1 (0-AF); diet supplemented with 0.11% mannanoligosaccharide (MOS-0); diet supplemented with 0.11% MOS and 2.5 ppm aflatoxin B1 (MOS-AF) for 4 wk to evaluate the effect of aflatoxin B1 (AFB1), mannanoligosaccharide (MOS), or both on egg quality and the in vivo efficacy of MOS to interact with an oral administration of AFB1. After 2 and 3 wk, egg weight decreased (P < 0.05) in the group fed MOS-0 versus groups on 0-0 and 0-AF. Egg shell weight was lower (P < 0.05) in the group fed 0-AF. Aflatoxin influenced color parameters, which were probably related to interference of AFB1 with lipid metabolism and pigmentary substances deposition in yolk. MOS appeared to increase protein percentage in albumen. No AFB1 or aflatoxin M1 (AFM1; a polar metabolite of AFB1) residues were found in eggs of the experimental groups. Livers from groups 0-0 and MOS-0 always tested negative for AFB1 and AFM1. Differences (P < 0.01) were found between AFB1 hepatic levels of group 0-AF (mean +/- SD: 4.13 +/- 1.95 ppb) and group MOS-AF (mean +/- SD: 2.21 +/- 1.37 ppb). The data demonstrated the ability of MOS to adsorb and degrade AFB1, reducing gastrointestinal absorption of AFB1 and its levels in tissues.

Aflatoxin B1↗
PubMed1984

Effects of chronic exposure to aflatoxin B1 and aflatoxin M1 on the in vivo covalent binding of aflatoxin B1 to hepatic macromolecules.

Induction of resistance to aflatoxin B1 (AFB1) binding to cellular macromolecules in the rat by chronic exposure to AFB1 and aflatoxin M1 (AFM1) was investigated. The binding of [14C]AFB1 to liver macromolecules was measured in F-344 rats fed 0.5 ppb or 50 ppb AFM1 or 50 ppb AFB1 for 41 wk. The animals then received an intragastric dose of [14C]AFB1 at 5 micrograms/kg and were sacrificed 6 h later. Hepatic DNA, RNA, and protein were isolated by chloroform-phenol extraction and hydroxylapatite chromatography. In animals preexposed to 50 ppb AFB1, labeled AFB1 binding to DNA, RNA, and protein was decreased by 72%, 74%, and 61%, respectively. Preexposure to AFM1 resulted in a small reduction in binding to nucleic acids. Glutathione transferase activity was increased by 133% in animals fed 50 ppb AFB1, by 48% in those preexposed to 50 ppb AFM1, and remained at control values in rats fed 0.5 ppb AFM1. These results suggest that the induction of detoxification enzymes following chronic exposure to aflatoxin might contribute to the reduction in covalent binding of AFB1 to macromolecules.

Aflatoxin B1↗
PubMed1988

Serum albumin adducts in the molecular epidemiology of aflatoxin carcinogenesis: correlation with aflatoxin B1 intake and urinary excretion of aflatoxin M1.

Aflatoxin-serum albumin adducts in the blood of 42 residents of Guangxi Province, People's Republic of China, were determined and compared with intake of aflatoxin B1 (AFB1) and excretion of aflatoxin M1 (AFM1) in urine. Blood specimens were obtained during the same period that urine was collected and that diet was sampled. Serum albumin was isolated from blood by affinity chromatography on Reactive Blue 2-Sepharose and subjected to enzymatic proteolysis using Pronase. Immunoreactive products were purified by immunoaffinity chromatography and quantified by competitive radioimmunoassay. A highly significant correlation (r = 0.60, P less than 0.00003) of adduct level with AFM1 excretion was observed. An equally highly significant correlation of adduct level with intake (r = 0.69, P less than 0.000001) was also observed. From the slope of the regression line for adduct level as a function of intake, it was calculated that 1.4-2.3% of ingested AFB1 becomes covalently bound to serum albumin, a value very similar to that observed when rats are administered AFB1.

Aflatoxin B1↗
PubMed2004

Aflatoxin binders II: reduction of aflatoxin M1 in milk by sequestering agents of cows consuming aflatoxin in feed.

Sequestering agents bind dietary aflatoxin B1 (AFB1) and reduce absorption from an animal's gastrointestinal tract. As a result, they protect an animal from the toxic effects of AFB1 and reduce transfer of the metabolite, aflatoxin M1 (AFM1), into milk. Three experiments, using late-lactation Holstein cows fed AFB1-contaminated feed, were conducted to evaluate several potential sequestering agents for their abilities to prevent or reduce the transmission of AFM1 into milk. Six agents previously tested in our laboratory for AFB1 binding in vitro were evaluated in these experiments. These were: SA-20, an activated carbon (AC-A); Astra-Ben-20, a sodium bentonite (AB-20); MTB-100, an esterified glucomannan (MTB-100); Red Crown, a calcium bentonite (RC); Flow Guard, a sodium bentonite (FG); and Mycrosorb, a sodium bentonite (MS). Five of the six sequestering agents significantly (P < 0.01) reduced AFM1 contamination of milk (AB-20, 61%; FG, 65%; MS, 50%; MTB-100, 59%; and RC, 31%); whereas, AC-A, activated carbon, had no effect on AFM1 transmission at 0.25% of feed. By the first milking (1 day after cows consumed contaminated feed), AFM1 appeared in milk, then reached maximum levels after three days, and was absent from milk within four days after AFB1 was removed from the feed. Sodium bentonites at 1.2% of feed showed good potential as AFB1 binders; MTB-100, a yeast cell wall product, was equally effective at 0.05% in feed. Potential AFB1 binding agents should be evaluated experimentally to demonstrate efficacy. Our data show that sequestering agents can reduce AFM1 in milk of cows fed AFB1-contaminated feed.

Aflatoxin B1↗
PubMed1992

Molecular dosimetry in rat urine of aflatoxin-N7-guanine and other aflatoxin metabolites by multiple monoclonal antibody affinity chromatography and immunoaffinity/high performance liquid chromatography.

The development of molecular dosimetry methods will simplify the identification of people at high risk for cancer. A combined monoclonal antibody immunoaffinity chromatography/high performance liquid chromatography method has been devised to isolate and quantify aflatoxin-DNA adducts and other metabolites in rat urine samples. We report the production of 11 different monoclonal antibodies recognizing aflatoxin B1, aflatoxin Q1, aflatoxin G1, aflatoxicol, and aflatoxin M1 and the application of these antibodies to a multiple monoclonal antibody affinity chromatography technique. Using the multiple monoclonal antibody affinity column with rat urines obtained from dosed animals, between 90 and 95% of total aflatoxin metabolites can be bound to the column and isolated. Analytical immunoaffinity chromatography/high performance liquid chromatography analysis of these isolated aflatoxins reveals that more than 55% of the aflatoxins in rat urine are aflatoxin-dihydrodiol, aflatoxin-N7-guanine, aflatoxin Q1, aflatoxin M1, aflatoxin P1, and aflatoxin B1, accounting for 1.5, 9.6, 1.8, 34.5, 8.0, and 1.0% of the total aflatoxins, respectively. Further, a perchloric acid digestion of the aflatoxin-N7-guanine peak was used to confirm its identity by its conversion to guanine. The measurement of aflatoxin-N7-guanine excretion in rat urine was examined to assess its utility as a marker of DNA adduct formation in the liver, and a dose-dependent excretion in urine was found with a correlation coefficient of 0.99. A comparison of the dose-dependent residual levels of aflatoxin binding to liver DNA with the amount of aflatoxin-N7-guanine excreted in urine showed a correlation coefficient of 0.98. Besides the nucleic acid adduct excretion data, aflatoxin M1 and aflatoxin P1 were evaluated as molecular dosimeters in the urine. Aflatoxin M1 was found to be an excellent marker, whereas no linear relationship between dose and aflatoxin P1 excretion in urine was found.

Aflatoxin B1↗
PubMed2005

Effect of dietary calcium propionate on performance, hepatic enzyme activities and aflatoxin residues in broilers fed a diet containing low levels of aflatoxin B1.

This study was undertaken to the study toxic effects of aflatoxins and reducing toxic effects of calcium propionate on performance, hepatic enzyme activities and aflatoxin residues in broilers. Two hundred and seventy 1-day-old hybrid Arbor Acor broiler chickens were fed conventional feed for 3 days. Broilers were then randomly divided into nine groups of 30 birds each. The nine dietary treatments consisted of (1) conventional feed as a negative control diet, (2) 0.25% calcium propionate, (3) 0.5% calcium propionate, (4) 50 ppb aflatoxin B1, (5) 50 ppb aflatoxin B1 plus 0.25% calcium propionate, (6) 50 ppb aflatoxin B1 plus 0.5% calcium propionate, (7) 100 ppb aflatoxin B1, (8) 100 ppb aflatoxin B1 plus 0.25% calcium propionate, (9) 100 ppb aflatoxin B1 plus 0.5% calcium propionate. Test diets were offered for 6 weeks continuously and the birds were sacrificed. Decreased body weight gain, feed consumption and feed conversion ratio were observed in aflatoxin treated groups whereas aflatoxin B1-calcium propionate supplemented diet groups increased, in comparison to the control group. Significant difference was observed after 4 weeks of feeding. Serum samples were tested for gamma glutamyl transferase (gamma-GGT), aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Gamma-GGT, AST and ALT were significantly increased in aflatoxin treated groups, in comparison among the dietary treated groups. Muscle and liver tissues were analyzed for aflatoxin residues. The residual levels of aflatoxin B1 and aflatoxin M1 were significantly higher in liver than in muscle. The levels in the liver and the muscle were highest in the aflatoxin B1-supplemented groups and lower in the aflatoxin B1-calcium propionate supplemented groups. Results of this study indicate that addition of calcium propionate to diets containing aflatoxin B1 appears to be effective in reducing toxicity. Aflatoxin contamination in broiler feed may cause economic losses by lowering body weight gain. Therefore, lower levels of aflatoxin B1 in the chicken feeds should be required if all acceptable risk is to be avoided. Additionally, the risk of aflatoxins in broiler as a food appears to remain very low, although the levels of aflatoxins in human foods should be kept as low as possible to reduce the incidence of hepatic cancer.

Aflatoxin B1↗
PubMed1999

Enzymatic formation of G-group aflatoxins and biosynthetic relationship between G- and B-group aflatoxins.

We detected biosynthetic activity for aflatoxins G(1) and G(2) in cell extracts of Aspergillus parasiticus NIAH-26. We found that in the presence of NADPH, aflatoxins G(1) and G(2) were produced from O-methylsterigmatocystin and dihydro-O-methylsterigmatocystin, respectively. No G-group aflatoxins were produced from aflatoxin B(1), aflatoxin B(2), 5-methoxysterigmatocystin, dimethoxysterigmatocystin, or sterigmatin, confirming that B-group aflatoxins are not the precursors of G-group aflatoxins and that G- and B-group aflatoxins are independently produced from the same substrates (O-methylsterigmatocystin and dihydro-O-methylsterigmatocystin). In competition experiments in which the cell-free system was used, formation of aflatoxin G(2) from dihydro-O-methylsterigmatocystin was suppressed when O-methylsterigmatocystin was added to the reaction mixture, whereas aflatoxin G(1) was newly formed. This result indicates that the same enzymes can catalyze the formation of aflatoxins G(1) and G(2). Inhibition of G-group aflatoxin formation by methyrapone, SKF-525A, or imidazole indicated that a cytochrome P-450 monooxygenase may be involved in the formation of G-group aflatoxins. Both the microsome fraction and a cytosol protein with a native mass of 220 kDa were necessary for the formation of G-group aflatoxins. Due to instability of the microsome fraction, G-group aflatoxin formation was less stable than B-group aflatoxin formation. The ordA gene product, which may catalyze the formation of B-group aflatoxins, also may be required for G-group aflatoxin biosynthesis. We concluded that at least three reactions, catalyzed by the ordA gene product, an unstable microsome enzyme, and a 220-kDa cytosol protein, are involved in the enzymatic formation of G-group aflatoxins from either O-methylsterigmatocystin or dihydro-O-methylsterigmatocystin.

Aflatoxin B1↗
PubMedDate not supplied

Estimating aflatoxin in farmers' stock peanut lots by measuring aflatoxin in various peanut-grade components.

Five, 2 kg test samples were taken from each of 120 farmers' stock peanut lots contaminated with aflatoxin. Kernels from each 2 kg sample were divided into the following grade components: sound mature kernels plus sound splits (SMKSS), other kernels (OK), loose shelled kernels (LSK), and damaged kernels (DAM). Kernel mass, aflatoxin mass, and aflatoxin concentration were measured for each of the 2400 component samples. For 120 lots tested, average aflatoxin concentrations in SMKSS, OK, LSK, and DAM components were 235, 2543, 11,775, and 69,775 ng/g, respectively. Aflatoxins in SMKSS, OK, LSK, and DAM components represented 6.9, 7.9, 33.3, and 51.9% of the total aflatoxin mass, respectively. Cumulatively, 3 aflatoxin risk components--OK, LSK, and DAM--accounted for 93.1% of total aflatoxin, but only 18.4% percent of test sample mass. Correlation analysis suggests that the most accurate predictor of aflatoxin concentration in the lot is the cumulative aflatoxin mass in the high 3 risk components OK + LSK + DAM (correlation coefficient, r = 0.996). If the aflatoxin in the combined OK + LSK + DAM components is expressed in concentration units, r decreases to 0.939. Linear regression equations relating aflatoxin in OK + LSK + DAM to aflatoxin concentration in the lot were developed. The cumulative aflatoxin in the OK + LSK + DAM components was not an accurate predictor (r = 0.539) of aflatoxin in the SMKSS component. Statistical analyses of 3 other data sets published previously yielded similar results.

Aflatoxins↗
PubMedDate not supplied

Alteration of the aflatoxin cyclopentenone ring to a delta-lactone reduces intercalation with DNA and decreases formation of guanine N7 adducts by aflatoxin epoxides.

The regio- and stereospecificity exhibited by reaction of aflatoxin B1 8,9-epoxide with DNA as well as the efficiency of reaction are remarkable and suggests that a specific orientation of bound epoxide facilitates formation of the transition state leading to guanine N7 adducts. We have compared aflatoxins B1 and B2 with aflatoxins G1 and G2 as to their binding with calf thymus DNA, d(ATGCAT)2, d(GCATGC)2, and plasmid pBR322. Aflatoxins B1 and B2 contain a cyclopentenone ring fused to the lactone ring of the coumarin. They have similar DNA association constants and intercalate with B-DNA, as demonstrated by NMR analysis of association with d(ATGCAT)2 and d(GCATGC)2, alteration of pBR322 electrophoretic mobility, and flow dichroism using linearly oriented calf thymus DNA. The less planar delta-lactone ring of aflatoxins G1 and G2 reduces DNA binding affinity by approximately 1 order of magnitude. Nevertheless, binding studies with d(ATGCAT)2 and d(GCATGC)2 suggest that aflatoxins G1 and G2 also bind B-DNA by intercalation. To establish the existence of a relationship between the association of these aflatoxins with DNA and adduct formation induced by aflatoxin epoxides, we compared the yield of guanine N7 adduct from aflatoxin B1 8,9-epoxide and from aflatoxin G1 9,10-epoxide at three concentrations of calf thymus DNA. As DNA concentration is decreased, two observations are made: (1) the number of adducts formed by either aflatoxin B1 8,9-epoxide or aflatoxin G1 9,10-epoxide is reduced with a concomitant increase in formation of the respective dihydrodiols, and (2) the ratio of adducts formed by aflatoxin G1 9,10-epoxide to those formed by an equivalent concentration of aflatoxin B1 8,9-epoxide decreases.(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxin B1↗
PubMed1995

Retention and distribution of aflatoxin in tissues of chicks fed aflatoxin-contaminated poultry rations amended with soil.

The effects of silty clay loam on aflatoxin B1 (AFB1) retention and distribution were investigated when added to diets of chicks fed aflatoxin-contaminated rations. One hundred 14-d-old White Leghorn chicks were fed a control ration (clean corn), a low aflatoxin-contaminated ration (120 ng AFB1/g), a high aflatoxin-contaminated ration (700 ng AFB1/g), or a high aflatoxin-contaminated ration (700 ng AFB1/g) + 10% or 25% soil. Livers, crops and breast muscles in each group were pooled and analyzed for AFB1 and metabolites. The addition of soil significantly reduced the AFB1 levels in the livers, although the reduction was less when 10% soil was fed compared with the 25% soil feeding. AFB1 concentrations in the crops of chicks fed high aflatoxin-contaminated ration without soil was statistically indistinguishable from the chicks in the other groups. AFB1 concentrations were significantly reduced in the breast muscles of chicks fed 10% or 25% soil compared to chicks fed the high aflatoxin-contaminated ration without soil. Aflatoxin B2 was detected only in livers, crops and breast muscles from chicks fed aflatoxin-contaminated ration without soil. Aflatoxin M1 (AFM1) was detected only in livers and crops of chicks fed aflatoxin-contaminated ration without soil and only in breast muscles of chicks fed the low aflatoxin-contaminated ration and high aflatoxin-contaminated ration + 25% soil. AFM1 concentration was significantly higher in the crops of chicks fed high aflatoxin-contaminated ration without soil.

Aflatoxin B1↗
PubMedDate not supplied

Performance of sampling plans to determine aflatoxin in farmers' stock peanut lots by measuring aflatoxin in high-risk-grade components.

Five 2 kg test samples were taken from each of 120 farmers' stock peanut lots contaminated with aflatoxin. Kernels from each 2 kg sample were divided into the following U.S. Department of Agriculture grade components: sound mature kernels plus sound splits (SMKSS), other kernels (OK), loose shelled kernels (LSK), and damaged kernels (DAM). The kernel mass (g), aflatoxin mass (ng), and aflatoxin concentration (ng of aflatoxin/g of peanuts) were measured for each of the 2400 component samples. The variabilities associated with measuring aflatoxin mass (ng) in OK + LSK + DAM, or A(OLD)ng, and in LSK + DAM, or A(LD)ng, and aflatoxin concentration (ng/g) in OK + LSK + DAM, or A(OLD)ng/g, and in LSK + DAM, or A(LD)ng/g, were determined. The variance associated with measuring aflatoxin in each of the 4 combinations of components increased with aflatoxin, and functional relationships were developed from regression analysis. The variability associated with estimating the lot concentration from each of the 4 combinations of components was also determined. The coefficients of variation (CV) associated with estimating the aflatoxin for a lot with aflatoxin at 100 ng/g were 90, 86, 94 and 96% for aflatoxin masses A(OLD)ng and A(LD)ng and aflatoxin concentrations A(OLD)ng/g and A(LD)ng/g, respectively. The performance of aflatoxin sampling plans using the combination of aflatoxin masses in OK + LD + DAM and LD + DAM components was evaluated with a 2 kg test sample and a 50 ng/g accept/reject limit.

Aflatoxins↗
PubMed1983

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

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

Aflatoxins↗
PubMed1987

Comparative binding and sequence interaction specificities of aflatoxin B1, aflatoxicol, aflatoxin M1, and aflatoxicol M1 with purified DNA.

The covalent binding of the activated forms of several aflatoxins to N-7 of guanine residues on purified DNA has been studied. The aflatoxins include aflatoxin B1 (AFB1) and two human metabolites, aflatoxicol and aflatoxin M1, along with aflatoxicol M1, a rabbit and trout metabolite. DNA binding studies using tritiated [3H]aflatoxins indicate that equimolar solutions of each aflatoxin upon activation with chloroperoxybenzoic acid readily react to produce covalently bound adducts. These reactions produce alkali-labile sites which can be identified using a simple variation of the Maxam-Gilbert sequencing procedure. Two DNA fragments were exposed to each aflatoxin, and the reaction intensities at 33 guanine residues were determined. As much as 10-fold variation in reaction intensities was observed for various guanyl sites. Data indicate that none of the aflatoxins had identical reaction profiles, although AFB1 and aflatoxicol M1 were similar, as were aflatoxicol and aflatoxin M1. Hence, the frequency with which the various aflatoxin epoxides might damage specific sites critical for tumor initiation in vivo would not be predictable from total covalent binding indices. The frequency of occurrence of modifications at particular sites for AFB1 was also compared with the empirical "rules" established for AFB1 by Misra et al. (Misra, R. P., Muench, K. F., and Humayun, M. Z. (1983) Biochemistry 22, 3351-3359). Identical sites within fragments were compared for each aflatoxin, and the data showed that the attacking frequency for some such sites varied significantly. These results indicate that binding intensity rules based on nearest neighbor nucleotides do not reliably predict guanyl-AFB1 binding frequencies.

Aflatoxin B1↗
PubMed2005

Taxonomic comparison of three different groups of aflatoxin producers and a new efficient producer of aflatoxin B1, sterigmatocystin and 3-O-methylsterigmatocystin, Aspergillus rambellii sp. nov.

Accumulation of the carcinogenic mycotoxin aflatoxin B, has been reported from members of three different groups of Aspergilli (4) Aspergillus flavus, A. flavus var. parvisclerotigenus, A. parasiticus, A. toxicarius, A. nomius, A. pseudotamarii, A. zhaoqingensis, A. bombycis and from the ascomycete genus Petromyces (Aspergillus section Flavi), (2) Emericella astellata and E. venezuelensis from the ascomycete genus Emericella (Aspergillus section Nidulantes) and (3) Aspergillus ochraceoroseus from a new section proposed here: Aspergillus section Ochraceorosei. We here describe a new species, A. rambellii referable to Ochraceorosei, that accumulates very large amounts of sterigmatocystin, 3-O-methylsterigmatocystin and aflatoxin B1, but not any of the other known extrolites produced by members of Aspergillus section Flavi or Nidulantes. G type aflatoxins were only found in some of the species in Aspergillus section Flavi, while the B type aflatoxins are common in all three groups. Based on the cladistic analysis of nucleotide sequences of ITS1 and 2 and 5.8S, it appears that type G aflatoxin producers are paraphyletic and that section Ochraceorosei is a sister group to the sections Flavi, Circumdati and Cervini, with Emericella species being an outgroup to these sister groups. All aflatoxin producing members of section Flavi produce kojic acid and most species, except A. bombycis and A. pseudotamarii, produce aspergillic acid. Species in Flavi, that produce B type aflatoxins, but not G type aflatoxins, often produced cyclopiazonic acid. No strain was found which produce both G type aflatoxins and cyclopiazonic acid. It was confirmed that some strains of A. flavus var. columnaris produce aflatoxin B2, but this extrolite was not detected in the ex type strain of that variety. A. flavus var. parvisclerotigenus is raised to species level based on the specific combination of small sclerotia, profile of extrolites and rDNA sequence differences. A. zhaoqingensis is regarded as a synonym of A. nomius, while A. toxicarius resembles A. parasiticus but differs with at least three base pair differences. At least 10 Aspergillus species can be recognized which are able to biosynthesize aflatoxins, and they are placed in three very different clades.

Aflatoxin B1↗