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PubMed2002

Determinants of formation of aflatoxin-albumin adducts: a seven-township study in Taiwan.

Dietary exposure to aflatoxins is one of the major risk factors for hepatocellular carcinoma. Individual susceptibility to aflatoxin-induced hepatocarcinogenesis may be modulated by both genetic and environmental factors affecting metabolism. A cross-sectional study was performed to evaluate determinants of the formation of aflatoxin covalently bound to albumin (AFB1-albumin adducts). A total of 474 subjects who were free of liver cancer and cirrhosis and were initially selected as controls for previous case-control studies of aflatoxin-induced hepatocarcinogenesis in Taiwan, were employed in this study. Aflatoxin-albumin adducts were determined by competitive enzyme-linked immunosorbent assay, hepatitis B surface antigen and antibodies to hepatitis C virus by enzyme immunoassay, as well as genotypes of glutathione S-transferase M1-1 and T1-1 by polymerase chain reaction. The detection rate of AFB1-albumin adducts was significantly higher in males (42.5%) than in females (21.6%) (multivariate-adjusted odds ratio=2.6, 95% confidence interval=1.4-5.0). The formation of detectable albumin adducts was moderately higher in hepatitis B surface antigen carriers (42.8%) than in non-carriers (36.6%) (multivariate-adjusted odds ratio=1.4, 95% confidence interval=1.0-2.1). In addition, the detection rate of AFB1-albumin adducts tended to increase with the increasing number of null genotypes of glutathione S-transferase M1-1 and glutathione S-transferase T1-1. In conclusion, this cross-sectional study has assessed the relative contributions of environmental exposure and host susceptibility factors in the formation of AFB1-albumin adducts in a well characterised Chinese adult population. This study further emphasises the necessity to reduce aflatoxin exposure in people living in an area endemic for chronic hepatitis B virus infection.

Adult↗

PubMed1983

Some mass-spectral and n.m.r. analytical studies of a glutathione conjugate of aflatoxin B1.

A system for the formation of an aflatoxin B1-reduced glutathione conjugate in vitro was developed, capable of yielding 80% conversion of aflatoxin B1 into the conjugate. A reverse-phase high-pressure-liquid-chromatography system was also devised that not only facilitates improved resolution of the compound but that, by manipulation of the pH, is also capable of an extensive purification of the compound from other aflatoxin B1 metabolites in a single step. Material produced by these techniques, after further purification, has been used in 1H-n.m.r. and mass-spectroscopic studies. Results were obtained that support the proposed linkage of the aflatoxin B1 to reduced glutathione in a 1:1 molar ratio via a thioether linkage. Amino acid analyses were also consistent with this structure. The absence of a Schiff-base linkage of aflatoxin B1 8,9-dihydrodiol to glutamate was further demonstrated by the presence of a gamma-glutamyltransferase-catalysed-transferable glutamate moiety. These data are consistent with the structure 8,9-dihydro-8-(S-glutathionyl)-9-hydroxy-aflatoxin B1.

Aflatoxin B1↗

PubMed1990

Five of 12 forms of vaccinia virus-expressed human hepatic cytochrome P450 metabolically activate aflatoxin B1.

Twelve forms of human hepatic cytochrome P450 were expressed in hepatoma cells by means of recombinant vaccinia viruses. The expressed P450s were analyzed for their abilities to activate the potent hepatocarcinogen aflatoxin B1 to metabolites having mutagenic or DNA-binding properties. Five forms, P450s IA2, IIA3, IIB7, IIIA3, and IIIA4, activated aflatoxin B1 to mutagenic metabolites as assessed by the production of His revertants of Salmonella typhimurium in the Ames test. The same P450s catalyzed conversion of aflatoxin B1 to DNA-bound derivatives as judged by an in situ assay in which the radiolabeled carcinogen was incubated with cells expressing the individual P450 forms. Seven other human P450s, IIC8, IIC9, IID6, IIE1, IIF1, IIIA5, and IVB1, did not significantly activate aflatoxin B1 as measured by both the Ames test and the DNA-binding assay. Moreover, polyclonal anti-rat liver P450 antibodies that crossreact with individual human P450s IA2, IIA3, IIIA3, and IIIA4 each inhibited aflatoxin B1 activation catalyzed by human liver S-9 extracts. Inhibition ranged from as low as 10% with antibody against IIA3 to as high as 65% with antibody against IIIA3 and IIIA4. These results establish that metabolic activation of aflatoxin B1 in human liver involves the contribution of multiple forms of P450.

Aflatoxin B1↗

PubMed1982

The effects of gum arabic, wheat offal and various of its fractions on the metabolism of 14C-labelled aflatoxin B1 in the male weanling rat.

1. Male weanling rats were given for extended periods diets containing gum arabic or wheat offal or various offal fractions. The fractions included two lipid fractions, a water-soluble extract and a modified-acid-detergent (MAD)-fibre extract. The diets contained either low concentrations of aflatoxin B1 (induced rats) or were free from this source of aflatoxin (non-induced rats). The distribution of 14C was then studied after the rats received 14C-labelled aflatoxin B1 in their feed. Blood plasma concentrations of triglycerides, and total cholesterol were also measured. 2. Gum arabic and wheat offal accelerated the rate of passage of 14C through the small intestine and wheat offal very considerably decreased retention time in the large intestine. Both fibre sources increased faecal bulk. However, only wheat offal decreased liver and urinary accumulation of 14C and the effect could be explained entirely by the MAD-fibre fraction of wheat offal. 3. The possible induction of either microsomal enzymes unrelated to the production of mutagenic aflatoxin metabolites, or of extramicrosomal enzymes is discussed; but it is concluded that the main effect brought about by wheat offal on the toxicity and carcinogenicity of aflatoxin can be attributed to a direct influence of the MAD fibre fraction of wheat offal on the intestinal absorption of aflatoxin B1. 4. The relevance of these conclusions to drug safety studies is discussed, because comparable studies may yield differing results, despite a use of diets having the same nutrient composition but differing ingredient composition.

Aflatoxin B1↗

PubMed2001

Occurrence of aflatoxins B1, B2, G1 and G2 in cooked food components of whole meals marketed in fast food outlets of the city of São Paulo, SP, Brazil.

Samples of cooked components of regular meals served at fast food outlets of the city of São Paulo, Brazil were analysed for aflatoxins B1, B2, G1 and G2. The 322 samples were composed of prepared traditional Brazilian and ethnic foods in which aflatoxins might be present. Thin-layer chromatography was used for separation of the compounds and their determination was achieved by both long wave UV light and fluorodensitometry. Aflatoxins were detected in 30 samples (9.31% of the total) in a range of 2.80 to 1323 ng/g for B1 + B2 + G1 + G2 with 90th percentiles of 158 (B1 + G1) and 258 (B1 + B2 + G1 + G2). Aflatoxin B1 was detected in all contaminated samples. The contamination levels and frequency of aflatoxins B1 and G1 in positive samples above 20 ng/g in this study are high, indicating that there is a certain degree of exposure of the population to the carcinogenic aflatoxin.

Aflatoxin B1↗

PubMedDate not supplied

A survey of the occurrence of aflatoxin B1 in peanut butters by enzyme-linked immunosorbent assay.

A survey was carried out in 1986 for the occurrence of aflatoxin B1 in peanut butters (129 samples) obtained from specialist Health Food outlets. The results showed that 6.2% of the samples exceeded 10 micrograms/kg of aflatoxin, 8% contained between 2.5 and 10 micrograms/kg, and in the remainder (86%) aflatoxin could not be detected at a limit of 2.5 micrograms/kg. These results show a lower contamination by aflatoxin than found in these products in previous surveys (1982-1984). An aflatoxin B1-specific enzyme-linked immunosorbent assay (ELISA) was employed for the first time in these analyses; and to make an assessment of its performance positive aflatoxin results, together with a random selection of those below the ELISA limit of detection, were additionally analysed by conventional extraction and clean-up followed by HPLC. The ELISA technique offered a significant improvement in speed of analysis over conventional approaches, enabling a six-fold increase in sample throughput compared to that required for conventional analysis, together with other advantages.

Aflatoxin B1↗

PubMedDate not supplied

EC-collaborative study on the determination of aflatoxin B1 in animal feeding stuffs.

A collaborative study was conducted to test a method, proposed in the European Community (EC) as a candidate-official method for the determination of aflatoxin B1 in compounded feeding stuffs. The study was undertaken on behalf of the European Commission's Community Bureau of Reference (BCR). It involved 25 laboratories from 11 EC countries. The method, based on chloroform extraction and Sep-Pak Florisil and C18 cartridge clean-up, offered either reverse-phase high performance liquid chromatography (HPLC) with iodine post-column derivatization, or two-dimensional thin-layer chromatography (TLC) as determinative steps. In the study, 22 laboratories applied HPLC, three laboratories applied TLC. The study involved six unknown samples. These consisted of blind duplicate samples of compounded feeding stuff, with target concentrations of aflatoxin B1 at less than 2, 8 and and 14 micrograms/kg. Statistical analysis of the HPLC data was carried out according to ISO 5725. For the less than 2 micrograms/kg sample, all reported aflatoxin concentrations were less than 2 micrograms/kg. At the 8 and 14 micrograms/kg level (pooled), repeatability (r) and reproducibility (R), expressed as ratios, were 1.4 and 1.7 respectively, and within-laboratory and between-laboratory coefficients of variation were 11% and 18% respectively. The study revealed that admittance of daylight in the laboratory caused losses of aflatoxin B1 and must be avoided. New glassware coming into contact with aqueous solutions containing aflatoxin B1 was found to be a potential cause of loss of aflatoxin B1. The method has been recommended to the European Commission to be considered for adoption in EC regulations.

Aflatoxin B1↗

PubMed1988

Aflatoxin B1 carcinogenesis and its relation to DNA adduct formation and adduct persistence in sensitive and resistant salmonid fish.

Rainbow trout (Salmo gairdneri) and coho salmon (oncorhynchus kisutch) were exposed to aflatoxin B1 (AFB1) either by passive embryo uptake or by dietary treatment after hatching and feeding onset. Trout exposed as embryos to an aqueous solution of 0.5 p.p.m. AFB1 for 15 min showed a 62% tumor incidence 12 months later, whereas coho salmon exposed to a similar solution for 30 min showed only a 9% incidence. The difference between salmon and trout response was even greater by dietary AFB1 treatment. Trout exposed for 4 weeks to 20 p.p.b. dietary AFB1 had a 62% tumor response 12 months later, whereas salmon exposed to 40 p.p.b. dietary AFB1 for 4 weeks failed to develop tumors. A 5% tumor incidence was observed in salmon 12 months after 3 weeks exposure to 5000 p.p.b. dietary AFB1, a lethal dose for trout. In addition to a lower tumor incidence when compared to trout, the neoplastic response of salmon to AFB1 is to produce benign hepatic adenomas in contrast to the malignant hepatocellular carcinomas seen in trout. AFB1 metabolism, DNA adduct formation, adduct persistence in vivo and in vitro and cytochrome P-450 isozyme composition were compared in livers of trout and salmon to understand the role of metabolism and initiation in this species difference. AFB1-DNA binding was 7-56 times greater in trout than salmon liver at various times after AFB1 injection, 20 times greater in embryos or in freshly isolated trout hepatocyte preparations after a 1 h incubation with aflatoxin B1, and 18 times greater in trout liver after a three week dietary (80 p.p.b.) exposure. The major AFB1-DNA adduct was 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 in both species. Persistence of AFB1-DNA adducts in vivo in liver was high compared to mammalian systems, implying that active enzymatic removal of bulky DNA adducts is low in both species and probably not a factor in their differential response to aflatoxin. Species differences in other phase I and phase II metabolism pathways and in AFB1 elimination were, overall, much less striking than those previously observed for trout fed inhibitors of aflatoxin carcinogenesis. Rates of bile elimination of AFB1 detoxication products, and total excretion of aflatoxins into water after AFB1 exposure, were not significantly different between trout and salmon. Since detoxication differences were not observed, the species difference in AFB1-DNA binding appears to reflect less efficient cytochrome P-450 metabolism of aflatoxin to the reactive 8,9-epoxide in salmon, compared to trout.(ABSTRACT TRUNCATED AT 400 WORDS)

Aflatoxin B1↗

PubMed1983

Production of aflatoxin by an Aspergillus flavus isolate cultured under a limited oxygen supply.

In a previous experiment on the preservation of hay of high moisture content with formic acid, among other agents, aflatoxin was formed in the hay, and aflatoxin-forming strains of Aspergillus flavus were isolated from this hay after incubation in air as well as in an anaerobic jar. One isolate from the anaerobic jar was cultivated in a chemostat (Bioflo model C 30; New Brunswick Scientific Co.) in a defined medium with added B vitamins, yeast extract, or formic acid, with or without gas flow (air or nitrogen). In all cases where spore germination occurred, aflatoxin was formed in the cultures with gas flow, and small quantities of aflatoxins B1 and B2 occurred even in an atmosphere of nitrogen. Addition of B vitamins and supply of traces of air gave an approximately 15-fold increase in the amount of aflatoxin in 2 days. Carbon dioxide enrichment hindered aflatoxin formation on the defined medium even in the presence of B vitamins, but when formic acid was added, small quantities (5 to 15 micrograms/liter) were formed, and this low level remained constant until the gas flow was started.

Aflatoxin B1↗

PubMed1996

Aflatoxin destruction by microwave heating.

Microwaves were used in the present work in order to destroy pure aflatoxins (model system), and yellow corn and peanuts containing aflatoxins (food system). Pure aflatoxins (B1, B2, G1 and G2) were individually coated on a silica gel and exposed to microwaves at various power settings and periods. The same technique was adopted for peanuts and yellow corn deliberately infected by Aspergillus flavus. The aflatoxins were extracted, fractionated by thin-layer chromatographic technique and quantitatively determined by spectrodensitometry. In all cases, the content of different aflatoxins in the deliberately infected yellow corn was in the decreasing order B1 = G1 > B2 > G2. Infected peanuts were characterized by the highest B1 level, being approximately 3, 2, and 4.4 times as great as that in B2, G1 and G2, respectively. The rate of aflatoxin destruction of model and food systems increased with the increase of microwave oven power setting (low, moderate and high) and exposure time to microwaves.

Aflatoxin B1↗

PubMed1982

Some effects of phenobarbital dosing of dairy cattle on aflatoxin M1 and fat in milk.

Eight Holstein cows were selected randomly to determine effects of phenobarbital on the fate of orally administered aflatoxin B1, milk fatty acid profiles, total milk fat, and milk production. Animals were grouped in pairs for one of four treatments: 1) control, 2) oral dosing with sodium phenobarbital for 5 days, 3) dosing with sodium phenobarbital followed by oral dosing with aflatoxin B1, and 4) oral dosing with aflatoxin B1 for 5 days. Daily composite raw milk samples were taken and assayed for aflatoxin M1 by thin-layer chromatography, and milk fatty acid profiles were measured by gas-liquid chromatography. Milk production for all treatments was less than that of controls. Total milk fat was not affected. Both aflatoxin B1 and phenobarbital affected fatty acid distribution, suppressing the amount of fatty acids carbons 8 through 14 while increasing the amount of 16-carbon fatty acids. No treatment effect was significant for the short chain fatty acids of 4 and 6 carbons and the 18-carbon acids oleic, stearic, and linoleic. Pretreatment with phenobarbital resulted in a significant difference between treated and untreated difference between treated and untreated animals. A greater than 50% reduction in the amount of aflatoxin B1 excreted as M1 in the milk was realized.

Aflatoxin M1↗

PubMed1986

Use of ultraviolet energy to degrade aflatoxin M1 in raw or heated milk with and without added peroxide.

Raw whole milk was artificially contaminated to contain 1 ppb aflatoxin M1. A thin layer of milk (.1 cm) was irradiated with ultraviolet energy. In the first experiment, milk was held at 90 degrees C for 10 min, cooled to 20 degrees C, and irradiated for 30 min. Amount of aflatoxin M1 decreased equally (56.2 vs. 53.9%) in raw or preheated milk, suggesting no involvement of milk enzymes in degrading aflatoxin M1 by ultraviolet energy. Data obtained when raw milk containing aflatoxin M1 was exposed to ultraviolet energy for 15 to 60 min suggest first order kinetics for the degradation reaction. In another experiment, milk was held at 5, 25, or 65 degrees C while it was being irradiated. Aflatoxin M1 was degraded at all temperatures. Amount of toxin decreased nonlinearly when temperature at which milk was held was increased. Presence in milk of benzoyl peroxide at .002% did not change the extent to which aflatoxin M1 was degraded by irradiation. Amount of toxin, however, decreased by 89.1% in milk containing .05% H2O2 as compared with 60.7% for H2O2-free milk when both were exposed to ultraviolet irradiation for 20 min at 25 degrees C.

Aflatoxin M1↗

PubMed1993

Application of a diphasic dialysis technique to the extraction of aflatoxins in dairy products.

A new method is described for the extraction of aflatoxins from milk and milk products based on a diphasic dialysis technique, followed by detection and quantification of aflatoxins by TLC. Recovery was 65 to 99% for aflatoxins B1, G1, and M1, and the detection limit in milk and yogurt was .01 to .02 ppb for all aflatoxins studied. In cheese, the detection limit was .03 to .04 ppb for aflatoxins B1 and G1 and .1 ppb for aflatoxin M1. The main advantages of this technique are its simplicity; sensitivity; very economical use of reagents, thereby minimizing environmental pollution; efficiency, allowing the quick processing of a high number of samples; use by laboratories with little equipment; and a sensitivity comparable with that of much more sophisticated techniques.

Aflatoxin M1↗

PubMed2001

Aflatoxin levels in corn available as wild turkey feed in Georgia.

Samples of corn available as wildlife feed from retailers throughout Georgia (USA) were collected during April 1997 and analyzed for aflatoxin to determine if levels harmful to wild turkeys (Meleagris gallopavo) were present. Three of 31 (10%) samples collected from a 40-country area were positive. An enzyme-linked immunosorbent assay qualitatively determined that two samples contained from 0 to 20 ppb aflatoxin. A chromatography analysis of a third sample measured 380 ppb total aflatoxin. A small percentage of our sample of wildlife feed collected during one season contained levels of aflatoxin that may cause harm to turkeys, especially poults. However, because aflatoxin levels ranging from 100 to 400 ppb may cause liver dysfunction and immunosuppression in turkey poults and other wildlife, grains known to be contaminated with aflatoxin at levels unacceptable for domestic animal feeds (> or =100 ppb) should not be sold as wildlife feed. Further analyses of grains sold as wildlife feed should be conducted to address this potential problem.

Aflatoxins↗

PubMed1979

[Appearance of aflatoxin M1 during the manufacture of Camembert cheese].

Several classic cheese making of camembert are made from raw milk spiked with Aflatoxin M1. Three Aflatoxin levels 7.5 microgram/l, 3 microgram/l are used. In respective curds 35.6, 47.1 and 57.7% of Aflatoxin M1 are recovered and 64.4, 52.9 and 42.3% in respective whey. During the first 15 days of storage the Aflatoxin M1 content of different cheeses decrease respectively 25, 55, 75%. A similar experience is made with a milk contamined in Aflatoxin M1 C14 labelled. Same results are recovered, except about behaviour of Aflatoxin M1 in cheese: a same C14 activity is recovered during storage for 30 days.

Aflatoxin M1↗

PubMedDate not supplied

[Stability of B1 and G2 aflatoxins after routine water chlorination].

Stability of aflatoxin B1 and G2 as water pollutants in the presence of active chlorine was examined. One liter of demineralized water was polluted with 0.5 mg of aflatoxin B1 and with 0.5 mg of aflatoxin G2. Routine chlorination with Pantacide tablets was applied afterwards. Initial aflatoxin concentrations and those after chlorination were measured by fluorescence high-pressure liquid chromatography (HPLC). Residual chlorine was parallely measured. It was found that aflatoxin B1 was almost completely degraded in the presence of active chlorine after a half of an hour which concentration was instantly lowered but aflatoxin G2 concentration was not significantly changed even after several days.

Aflatoxin B1↗

PubMedDate not supplied

Behavior of 14C aflatoxin M1 during camembert cheese making.

Camembert cheeses are made from raw milk spiked with aflatoxin M1. Three aflatoxin M1 levels (7.5 micrograms/L, 3 micrograms/L, and 0.3 micrograms/L) are used. In curds 35.6, 47.1, and 57.7% of aflatoxin M1, respectively, are recovered, and in wheys 64.4, 52.9, and 42.3%, respectively, are recovered. During the first 15 days of storage, the aflatoxin M1 content of different cheeses decreases 25, 55, and 75%, respectively. A similar experiment is made with milk contaminated with 14C labeled aflatoxin M1. The same results are obtained, except for the behavior of aflatoxin M1 in cheese; the same 14C activity is recovered during storage for 30 days.

Aflatoxin M1↗

PubMed1987

Killing and mutation of human lymphoblast cells by aflatoxin B1: evidence for an inducible repair response.

Diploid human lymphoblast cells exhibit apparent saturation of mutation induced by exposure to aflatoxin B1, despite a linear increase in the amount and proportion of the aflatoxin-DNA adducts formed. The saturation is neither a cell cycle phenomenon nor a result of a genetically heterozygous population. Examination of the biphasic nature of aflatoxin-DNA adduct loss in vivo shows initial, rapid removal of all adduct species, followed by a slow loss of the aflatoxin-N7-guanine adduct alone. We hypothesize that these data reveal two modes of adduct loss in these cells. The first is an inducible, error-free system that is short-lived, turning off as adduct levels fall below the induction threshold of some 1000 total adducts/cell. The second loss is slower and results from spontaneous depurination of remaining aflatoxin-N7-guanines. Our data are in agreement with the possibility that apurinic sites thus generated are responsible for the mutation observed. A major paradox arises from the fact that aflatoxin-related premutagenic depurinations are estimated to be only 10% of the number of spontaneous depurinations estimated by others to occur in human cells in a 1-h period.

Aflatoxin B1↗