Density Functional Theory Study on the Interaction between Aflatoxin B1/M1 and Gold Substrate

Aflatoxin M1 (AFM1) and its precursor, Aflatoxin B1 (AFB1), are highly pathogenic and mutagenic substances, making the detection and sensing of AFB1/M1 a long-standing focus of researchers. Among various detection techniques, surface-enhanced Raman spectroscopy (SERS) is considered an ideal method for AFB1/M1 detection due to its ability not only to enhance characteristic frequencies but also to detect shifts in these frequencies with high repeatability. Therefore, we employed density functional theory in conjunction with surface-enhanced Raman spectroscopy to investigate the interaction between AFB1/M1 and a Au substrate in the context of the SERS effect for the first time. To predict the potential binding sites of AFB1/M1 and Au within the SERS effect, we performed calculations on the molecular electrostatic potential of AFB1/M1. Considering the crucial role of the binding energy in molecular docking studies, we computed the binding energy between two molecules interacting with Au at different binding sites. The molecular frontier orbitals and related chemical parameters of AFB1/M1 and "molecular-Au" complexes were computed to elucidate the alterations in AFB1/M1 molecules under the SERS effect. Subsequently, the theoretical Raman spectra of AFB1/M1 and the complexes were compared and analyzed, enabling determination of the adsorption conformation of AFB1/M1 on the gold surface based on SERS surface selection rules. These findings not only provide a deeper understanding of the interaction mechanism between molecules and substrates in the SERS effect but also offer theoretical support for developing novel aflatoxin SERS sensors.

Aflatoxin M1 Analysis in Urine of Mill Workers in Bangladesh: A Pilot Study

Presence of aflatoxin B1 (AFB1) in food and feed is a serious problem, especially in developing countries. Human exposure to this carcinogenic mycotoxin can occur through dietary intake, but also through inhalation or dermal contact when handling and processing AFB1-contaminated crops. A suitable biomarker of AFB1 exposure by all routes is the occurrence of its hydroxylated metabolite aflatoxin M1 (AFM1) in urine. To assess mycotoxin exposure in mill workers in Bangladesh, we analyzed AFM1 levels in urine samples of this population group who may encounter both dietary and occupational AFB1 exposure. In this pilot study, a total of 76 participants (51 mill workers and 25 controls) were enrolled from the Sylhet region of Bangladesh. Urine samples were collected from people who worked in rice, wheat, maize and spice mills and from controls with no occupational contact to these materials. A questionnaire was used to collect information on basic characteristics and normal food habits of all participants. Levels of AFM1 in the urine samples were determined by a competitive enzyme linked immunosorbent assay. AFM1 was detected in 96.1% of mill workers' urine samples with a range of LOD (40) of 217.7 pg/mL and also in 92% of control subject's urine samples with a range of LOD of 307.0 pg/mL). The mean level of AFM1 in mill workers' urine (106.5 ± 35.0 pg/mL) was slightly lower than that of the control group (123.3 ± 52.4 pg/mL), whilst the mean AFM1 urinary level adjusted for creatinine was higher in mill workers (142.1 ± 126.1 pg/mg crea) than in the control group (98.5 ± 71.2 pg/mg crea). Yet, these differences in biomarker levels were not statistically significant. Slightly different mean urinary AFM1 levels were observed between maize mill, spice mill, rice mill, and wheat mill workers, yet biomarker values are based on a small number of individuals in these subgroups. No significant correlations were found between the study subjects' urine AFM1 levels and their consumption of some staple food items, except for a significant correlation observed between urinary biomarker levels and consumption of groundnuts. In conclusion, this pilot study revealed the frequent presence of AFM1 in the urine of mill workers in Bangladesh and those of concurrent controls with dietary AFB1 exposure only. The absence of a statistical difference in mean biomarker levels for workers and controls suggests that in the specific setting, no extra occupational exposure occurred. Yet, the high prevalence of non-negligible AFM1 levels in the collected urines encourage further studies in Bangladesh regarding aflatoxin exposure.

Assessment of Aflatoxin M1 in human breast and powdered milk in Tehran, Iran

AIM AND BACKGROUND

Aflatoxins, produced by Aspergillus flavus and Aspergillus parasiticus, are among the most toxic mycotoxins. Aflatoxin M1 (AFM1) is a hydroxylated metabolite of aflatoxin B1 (AFB1), found in milk and dairy products from animals fed AFB1-contaminated feed. Consumption of AFM1 has related adverse effects on human health. Breast milk can be a source of contamination for infants due to the presence of AFM. AFM1 can also contaminate powdered milk, a significant product of the milk industry. Consequently, monitoring dairy products for these toxins is imperative.

STUDY METHOD

A total of 50 samples (25 samples of breast milk and 25 samples of powdered infant milk formula) were collected in Tehran from December 2021 to February 2022. HPLC method was used for the determination of AFM1 in samples.

RESULTS

and Discussion: AFM1 was detected in 72% of breast milk samples and 96% of powdered milk samples. AFM1 levels varied significantly between the two sample types (p < 0.05). The average amount of AFM1 in breast milk samples was 25.82 ± 4.72 ng/kg, while the average amount in powdered milk samples was 40.59 ± 7.76 ng/kg. Moreover, 44% of the breast and 68% of powdered milk samples exceeded the AFM1 content limit of the European Union and the Iranian national standard. This study concludes that given the importance of breast milk and formula to maternal and infant health, monitoring and regulating the toxin levels in these products in Tehran is crucial.

Triple strategy-enhanced immunochromatographic assay based on APCB and AIEFM for the ultrasensitive detection of AFM1

Aflatoxin M1 (AFM1) is highly toxic, widely distributed, and difficult to monitor, posing a serious threat to human health. Therefore, a highly sensitive, rapid, convenient, and low-cost detection method must be urgently established. In this study, a triple strategy-enhanced immunochromatographic assay (ICA) was developed to satisfy these detection requirements. First, a turn-on signal output mode of the fluorescence quenching ICA substituted the turn-off mode of the traditional ICA for sensitive response to trace AFM1, with the limit of detection (LOD) reduced by approximately 4.9-fold. Then, a novel Au and polydopamine (PDA) cogrowth chrysanthemum-like blackbody was prepared as the quenching probe to reduce the background signal. This probe combined the excellent properties of Au nanoparticles with PDA. Thus, its fluorescence quenching constant was higher than that of single Au and PDA nanoparticles by 25.8- and 4.9-fold, respectively. Furthermore, an aggregation-induced emission fluorescence microsphere with a 5.7-fold higher relative quantum yield than a commercial fluorescence microsphere was selected as the signal output carrier to improve the signal-to-noise ratio. The integration of the above triple strategies established a 53.4-fold sensitivity-enhanced fluorescence quenching ICA (LOD = 0.9 pg/mL) for detecting AFM1 in milk, providing a strong technical guarantee for the safety monitoring of milk products.

Novel Porphyrinic Covalent Organic Polymer with Polarity-Switchable Dual Wavelength for Accurate and Sensitive Photoelectrochemical Sensing

Herein, we synthesized a novel porphyrinic covalent organic polymer (TPAPP-PTCA PCOP) for constructing a polarity-switchable dual-wavelength photoelectrochemical (PEC) biosensor with ferrocene (Fc) and hydrogen peroxide (H2O2) as regulator and amplifier simultaneously. Interestingly, this new PCOP possessed both n-type and p-type semiconductor characteristics, which thus enabled the appearance of a dual-polarity photocurrent at two different excitation wavelengths. Furthermore, Fc and H2O2 could readily switch the photocurrent of PCOP to the cathode and anode stemming from its efficient electron collection and donation function, respectively. Based on these, a PCOP-based PEC biosensor skillfully integrating dual wavelengths with reliable accuracy and polarity switch with high sensitivity was instituted. As a result, the developed PEC biosensor exhibited a low detection limit down to 0.089 pg mL-1 for the most powerful natural carcinogen aflatoxin M1 (AFM1) assay. Impressively, the target exhibited a completely opposite photocurrent difference to the interfering substances, and the linear correlation coefficient of the assay was improved compared to single-wavelength detection. The PEC sensing platform not only provided a basis for exploring multicharacteristic photoactive material but also innovatively developed the detection mode of the PEC biosensor.

Detoxification of aflatoxin M1 in different milk types using probiotics

The aim of this study, research the potential use of probiotics in reducing the toxic effect of Aflatoxin M1 in cow milk, goat milk, sheep milk, and Phosphate-buffered saline (PBS). Milk and Phosphate-buffered saline were contaminated with Aflatoxin M1 at a concentration of 100 ppt. Then, various study groups were formed by adding Lactobacillus acidophilus DSMZ 20079, Lactobacillus rhamnosus GG, and Bifidobacterium bifidum DSMZ 20456 probiotic bacteria at a density of 108 CFU/ml. Then, working groups were stored for 1 day and Aflatoxin M1 levels were analyzed by an Enzyme-Linked Immunosorbent Assay kit. The binding level of Aflatoxin M1 by probiotic bacteria varies between 2.32-12.52% in Phosphate-buffered saline, 9.08-40.14% in cow milk, 15.01-38.01% in goat milk, and 32.49-42.90% in sheep milk. The highest binding level of Aflatoxin M1 was detected in sheep milk and the lowest in Phosphate-buffered saline. The binding ability of Aflatoxin M1 is ranked from highest to lowest in sheep milk, cow milk, and goat milk. The data obtained from this study is important because it is the first study to show that if sheep and goat milk is enriched with probiotics, it can reduce AFM1 exposure.

A survey of aflatoxin M1 in cow milk in Southern Iran

The competitive enzyme-linked immunosorbent assay technique was used to evaluate aflatoxin M1 (AFM1) levels in 168 samples of raw milk (135 samples and 33 samples from bulk tanks of farms and milk collection centers, respectively) and 12 samples of pasteurized milk in Fars province, Southern Iran. AFM1 was found in 55.56% of the samples with a mean concentration of 21.31 ng/L. The concentration of AFM1 in raw milk samples from farms was significantly (p < 0.05) lower than that in samples from collection centers and pasteurized milk. The concentration of AFM1 was not influenced by season, location, or type of farm. The concentrations of AFM1 in all samples were lower than the Iranian national standard limit (100 ng/L), but in 30% of raw cow milk samples they were higher than the maximum tolerance limit accepted by the European Union (50 ng/L); therefore, more effort is needed to control AFM1 levels in milk produced in Southern Iran.

Assessment of exposure of Egyptian infants to aflatoxin M1 through breast milk

BACKGROUND

Mothers are exposed to many toxins that can reach their infants through breast milk. One of these toxins is aflatoxins, produced by Aspergillus fungus. Aspergillus colonizes grains, especially in tropical regions where there is high temperature and humidity. Aflatoxins are highly toxic, mutagenic, teratogenic, and carcinogenic. One of these is aflatoxin B1 that is excreted in breast milk as aflatoxin M1 (AFM1).

MATERIALS AND METHODS

This is a cross-sectional study in which 150 mother-infant dyads were included. All the infants were exclusively breastfed. Infant weights' standard deviation scores were documented at birth and at 6 months. At 6 months, before starting weaning, AFM1 was measured in breast milk by enzyme-linked immunosorbent assay and by liver enzymes; alanine aminotransferase (ALT) and aspartate aminotransferase (AST) for all mothers and infants.

RESULTS

Ninety-eight mothers (65.3%) had AFM1-positive breast milk samples (AFM1>0.05 μg/l according to the European Community and Codex Alimentarius). AFM1 levels ranged between 0.2 and 19.0 μg/l (mean: 7.1±5.0 μg/l). In cases considered negative, AFM1 levels ranged between 0.01and 0.05 μg/l (mean: 0.04±0.01 μg/l). Infants of AFM1-positive mothers had lower weight standard deviation scores at birth and at 6 months (P=0.04 and 0.0001). ALT and aspartate aminotransferase of mothers and ALT of infants were significantly higher in dyads having AFM1-positive breast milk (P=0.0001, 0.0001, and 0.03, respectively).

CONCLUSION

Aflatoxins represent a real threat in Egypt. The higher liver enzymes in AFM1-positive cases might represent an alarm toward future development of hepatocellular carcinoma.

RECOMMENDATIONS

Cooperation of ministries is recommended to combat this problem. The public should be educated about proper food storage and about the hazards of aflatoxin ingestion.

Rapid immunochemical screening method for aflatoxin B1 in human and animal urine

A method has been developed to determine the presence of aflatoxin B1 in the urine of animals (including humans) by utilizing commercial immunochemical kits that can be used in the field. Urine is treated with diatomaceous earth and filtered to clarify the sample; 2-3 ppb aflatoxin B1, corresponding to about 300 ppb in the ingested feed/food, can be detected in the filtered urine without further purification. To improve sensitivity, the urine filtrate is passed through a C18 solid phase column to extract the aflatoxin. The column is washed with acetonitrile-water (15 + 85) and water, aflatoxin B1 is eluted with methanol-water (7 + 3), and water is added to the eluate, which is then tested for aflatoxin with the test kit. The limit of detection is 0.2 ppb, reflecting consumption of 40 ppb or more aflatoxin in the feed/food. When the initial sample volume is adequate, purification through the C18 column step is usually sufficient. For limited sample volumes, the eluate from the C18 column is mixed with water, added to an immunosorbent affinity column, and washed with water to remove excess sample matrix and impurities. Aflatoxin B1 is eluted with acetonitrile. The extract is evaporated under nitrogen and the residue is redissolved in methanol-water (25 + 75). At this purification stage, the limit of detection is reduced to 0.05 ppb.

Biological reactive intermediates of bisfuranoid mycotoxins

Based on the mode of action of AFB1 and the activities of its biologically active intermediates, one may conclude that: 1. The mode of toxic action of the bisfuranoid mycotoxin is through epoxidation of the vinyl ether double bond of their dihydrobisfuran functionality. 2. The DNA and plasma albumin adducts formed in vivo may be useful in the molecular dosimetry of these environmental carcinogens. 3. Monitoring of these adducts of AFB1 in biological samples so far indicates that aflatoxin is likely involved in the etiology of human liver cancer.

Robotic analysis of aflatoxin M1 in milk

An automated aflatoxin M1 assay system capable of performing multiple unattended extractions and chromatographic analyses has been developed. A six-axis anthropomorphic laboratory robot and a flexible computer system are combined to operate a sample turntable, a multisolvent dispensing facility, a solid-phase extraction station, a vacuum manifold, an automatic HPLC sample preconcentration unit, an HPLC, a fluorescence detector and a computing integrator. The system is capable of handling bulk milk samples and can determine aflatoxins at the sub-micrograms/kg level with an accuracy and precision comparable to those of the manual methods of analysis. Time of analysis is reduced. The system can be run in an unattended mode of operation.

Automated liquid chromatographic determination of aflatoxin M1 in milk using on-line dialysis for sample preparation

A procedure has been developed for the automated isolation of aflatoxin M1 from decreamed milk. The method uses on-line stopped flow dialysis and subsequent trace enrichment on a reverse-phase column. After a back-flush to the analytical liquid chromatography column, aflatoxin M1 is determined with fluorescence detection. Fully automated analysis is possible with reproducible dialysis recoveries above 50% (CV = 7.5%, n = 25 at the 50 ng/kg level) and determination levels of 20 ng/kg within 20 min.

Biotransformation of aflatoxin B1 in rabbit lung and liver microsomes

Aflatoxin B1 (AFB1) is a potent hepatotoxic and hepatocarcinogenic mycotoxin that requires bioactivation to AFB1-2,3-oxide for activity. In addition to epoxidation, microsomal monooxygenases biotransform AFB1 to the less toxic metabolites, aflatoxin M1 (AFM1) and aflatoxin Q1 (AFQ1). The lung is at risk from AFB1 both via inhalation and via the circulation. In the present study, we have characterized rabbit lung and liver microsomal AFB1-DNA binding (an index of AFB1-2,3-oxide formation), AFM1 formation and AFQ1 formation. Vmax values for AFB1-DNA binding were not different between lung and liver when expressed per mg microsomal protein (1.06 +/- 0.13 and 2.12 +/- 1.30 nmol/mg/h for lung and liver respectively), but lung values were greater than liver when expressed per nmol cytochrome P450 (3.64 +/- 0.31 and 1.29 +/- 0.70 nmol/nmol P450/h for lung and liver respectively). Km values for this reaction were not different between lung and liver. Vmax values for AFM1 formation in liver microsomes were greater than in lung when expressed per mg protein, but not when expressed per nmol P450. No differences were detected for the Km for AFM1 formation between lung and liver microsomes. For AFQ1 formation, no differences were detected between Vmax values of lung and liver, regardless of whether results were expressed per mg protein or per nmol P450, while the Km for AFQ1 formation was lower in liver. SKF-525A inhibited these reactions by 63-74% in lung microsomes and 90-96% in liver microsomes. These results indicate that the lung is capable of activating AFB1, and that rabbit lung microsomes contain high activity for this reaction. Furthermore, little AFM1 and AFQ1 are formed in lung microsomes, leading to minimal shunting of AFB1 from the activation pathway.

Two-dimensional chromatographic method for determination of aflatoxins in liver; occurrence of aflatoxins in animal liver

A thin-layer chromatographic method is described for the analysis of aflatoxins in animal liver. Liver samples are extracted with chloroform and phosphoric acid. After filtration, an aliquot is evaporated and defatted by liquid-liquid partitioning. The extract is submitted to silica gel minicolumn cleanup and the final extract is concentrated and submitted to two-dimensional thin-layer chromatography (TLC). The identity of aflatoxins B1 and M1 is confirmed with trifluoroacetic acid (TFA) carried out on the thin-layer plate used for quantitation of these aflatoxins. The method permits the detection and confirmation of aflatoxins in liver in concentrations as low as 0.05 micrograms/kg. Average recoveries for aflatoxin M1 and aflatoxin B1 at spiking levels of 0.2 micrograms/kg were found to be 65% and 85%, respectively. With this method, 73 samples of bovine liver, 70 samples of porcine liver, and 56 samples of chicken liver taken from different slaughterhouses were investigated. In one sample of bovine liver, aflatoxins B1, B2, and M1 could be detected in concentrations of 0.10, 0.03, and 0.08 micrograms/kg, respectively.

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 excretion in children with kwashiorkor or marasmic kwashiorkor--a clinical investigation

A group of five children with kwashiorkor, seven with marasmic kwashiorkor and one underweight child were given an aflatoxin-free diet consisting of maize meal and milk powder. Blood specimens were collected on admission; on day 4 and 10, 24 hour urine and stool samples were collected for the first ten days. Serum, urine and stool samples were analysed for aflatoxins using high performance liquid chromatography with fluorescent detection, after various extraction and clean-up procedures. The children with kwashiorkor and marasmic kwashiorkor excreted aflatoxins in stools for up to 9 and 6 days after admission respectively. No aflatoxins were detected in the stools or urine of the underweight child. In kwashiorkor, urinary excretion ceased after 2 days, while in marasmic kwashiorkor urinary excretion persisted for 4 days. In stools, B1 was the type of aflatoxin detected most frequently in kwashiorkor and least frequently in marasmic kwashiorkor. Aflatoxin M2 was frequently detected in the stools of both groups of children. Estimates of the total amount of aflatoxin excreted by kwashiorkor and marasmic kwashiorkor indicate that these children were harbouring up to 4 micrograms/kg body weight at the time of admission. These findings establish that aflatoxins accumulate in body fluids and tissues in kwashiorkor and marasmic kwashiorkor which is only slowly eliminated.

A new method for the quantitation of aflatoxin M1 in urine by high performance liquid chromatography and its application to the etiologic study of hepatoma

A high performance liquid chromatographic (HPLC) method for the analysis of aflatoxin M1 (AFM1) in urine is described. Urine samples were treated with saturated lead acetate and AFM1 was extracted with chloroform. After washing with water to remove impurities the compound was derivatized with trifluoroacetic acid and the AFM1 derivative was analyzed quantitatively by HPLC. The sample pretreatment is simple and more selective. A good line correlation between AFM1 peak height and its concentration was obtained when AFM1 content was in the range of 50-400 pg. The ratio of recovery was 87.42%. Sensitivity is 0.01 ppb. The method is applicable to trace analysis. Results in urine of residents who live in the high/low liver cancer incidence area in Fushui county were the same as that of previous epidemiological investigation.

Effects of injection solvent and mobile phase on efficiency in reverse-phase liquid chromatographic determination of aflatoxin M1

The effects of injection solvent and mobile phase composition on the reverse-phase liquid chromatographic determination of aflatoxin M1 (M1) were examined. M1 was converted to the more highly fluorescent derivative aflatoxin M2a (M2a). Using a C-18 column and a mobile phase of H2O-MeCN-MeOH (60 + 20 + 20) (MP-A), M2a was dissolved in various ratios of MeCN-H2O prior to injection. Chromatographic efficiency for the M2a peak varied from ca 2000 theoretical plates when injected in 30% aqueous MeCN to ca 9000 plates when injected in water alone. However, using the same C-18 column but with a mobile phase of H2O-IPA-MeCN (80 + 12 + 8) (MP-B), the M2a peak exhibited 25,000 plates when injected in 30% aqueous MeCN and 10,000 plates when injected in water alone.

2(3)-tert-butyl-4-hydroxyanisole inhibits oxidative metabolism of aflatoxin B1 in isolated rat hepatocytes

Previous studies indicate that dietary administration of phenolic antioxidants, 2(3)-tert-butyl-4-hydroxyanisole (BHA) and 3,5-di-tert-butyl-4-hydroxytoluene, inhibits the carcinogenic effect of a number of chemical carcinogens including aflatoxin B1 (AFB1). Induction of hepatic enzymes, such as glutathione S-transferase, UDP-glucuronyltransferase, and epoxide hydrolase, has been shown to be responsible for the reduction of AFB1 cytotoxic and carcinogenic effects. The effect of BHA on AFB1 activation was examined in vitro utilizing isolated rat hepatocytes and liver microsomes. In hepatocytes, the total AFB1 content and bound form of AFB1 were 3.4 and 1.4 pmol/10(6) cells, respectively. In the cell-free microsomal activating system, 2.2 pmol were activated per mg of microsomal protein during 60 min of incubation. BHA (0.1-0.5 mM) inhibited AFB1 activation and binding in both systems in a dose-dependent manner; in hepatocytes, 90% inhibition was observed at 0.5 mM. Analyzing various AFB1 adducts, BHA (0.25 mM)-treated hepatocytes contained a significantly reduced amount of AFB1 macromolecular adducts. The antioxidant neither stimulated nor inhibited the cytosolic glutathione S-transferase and microsomal UDP-glucuronyltransferase activities. Analysis of various hydroxylated (aflatoxins M1 and Q1 (AFM1 and AFQ1] and demethylated (aflatoxin P1 (AFP1] metabolites of AFB1 in both the conjugated and unconjugated form indicated that there was a 30-50% reduction of unconjugated AFP1, AFQ1, and AFM1, whereas AFB1 was increased 3-fold. There was no significant change of conjugated metabolites. The effect of BHA on AFB1 activation in hepatocytes was compared with that of other cytochrome P-450 inhibitors; the ED50 values of SKF 525A, BHA, and metyrapone were 9 microM, 40 microM, and 280 microM, respectively. In the cell-free microsomal system, biotransformation of AFB1 to AFP1, AFM1, and AFQ1 was also inhibited. Kinetic analysis of p-nitroanisole O-demethylase activity of rat liver microsomes demonstrated that BHA inhibited noncompetitively with an apparent Ki of 90 microM. In the absence of enzyme induction, the phenolic antioxidant, BHA, blocks the oxidative biotransformation of AFB1 in isolated hepatocytes.

Replication blocks and sequence interaction specificities in the codon 12 region of the c-Ha-ras proto-oncogene induced by four carcinogens in vitro

We have examined the region surrounding codon 12 in the human c-Ha-ras proto-oncogene in vitro to determine the reaction intensities at the guanine nucleotides after exposure to the mycotoxin aflatoxin B1, to one of its human metabolites aflatoxin M1, to dimethyl sulfate, and to the major ultimate carcinogen of benzo(a)pyrene, benzo(a)pyrene diol-epoxide. Among the adducts produced, those at N-7-guanyl sites are alkali-labile and can be identified using a variation of the Maxam-Gilbert sequencing procedure. Data indicate that the guanine nucleotides of codon 12 have above average potential for adduct formation by the genotoxins when compared to other guanine sites, but were not the strongest sites. This codon 12 region has been inserted into single-stranded M13 phage, exposed to several of the genotoxins, and used as a template for DNA synthesis in vitro. There is a sequence-specific variation in polymerase inhibition at various adducted nucleotide sites, but replication blocks are not preferentially seen at the carcinogen-adducted guanines of codon 12. These results indicate that the predominance of point mutations which are detected in vivo at codon 12 do not reflect sequence-mediated preferential susceptibility of these sites to initial DNA adduction or to replication errors. The mechanisms controlling these sequence effects are not currently understood, and attempts to predict relative alkylation or termination frequencies based solely on local DNA sequence are not reliable.

Variations in the levels of aflatoxin in cows milk consumed in the city of São Paulo, Brazil

One hundred samples of commercially available cows milk, collected in the state of São Paulo, from July 1979 to September 1981, were analysed to determine the levels of aflatoxins M1 and M2 by the method of the AOAC. This investigation was also undertaken in 50 samples of cows milk from two farms located in the Médio Vale do Paraiba, from animals which had ingested stored feed. Aflatoxin M1 was detected in only one sample of commercially available cows milk, while those from the farms were found to contain a minimum of 0.1 microgram/l and a maximum of 1.68 microgram/l.

Methods for determination of aflatoxin M1 in milk and milk products--a review of performance characteristics

Among numerous methods that have been published for determination of aflatoxin M1 in milk and milk products, the following have been selected for review of performance characteristics: methods for which interlaboratory testing has been carried out, methods proposed in support of national (Swiss) regulations following inclusion in check sample series, and methods that report detection limits for milk of less than or equal to 5 ng/l (less than or equal to 0.005 microgram/l) or less than or equal to 10 ng/kg (less than or equal to 0.01 microgram/kg) for cheese. It is practical to determine aflatoxin M1 in milk with good accuracy and precision down to low ng/l concentrations using thin-layer chromatography, high-performance liquid chromatography or enzyme-linked immunosorbent assay for quantitation. However, measurement at such low levels has not been tested by a true collaborative study. Confirmation of identity of aflatoxin M1 at low ng/l levels has also been reported. Recent evidence suggests that consideration should be given to inclusion of aflatoxin M4 in methods for aflatoxin M1.

Development of milk powder reference materials certified for aflatoxin M1 content (Part II): Certification of milk powder RM 283

The development of a full cream milk powder reference material, certified for its aflatoxin M1 content (target concentration: 0.1 microgram/kg), is described. The material (RM 283) was prepared and certified within the Reference Material Programme of the Community Bureau of Reference, along with other members of a series of milk powder reference materials. Homogeneity, evaluated by determining the aflatoxin M1 content of 30 units, was found to be acceptable (coefficient of variation of analysis results: 9.1%); stability has been demonstrated in a long-term study. The certification exercise involved 7 laboratories. Calibration, control of recoveries, blank values, and independence of the replicate measurements were emphasized. All sets of results of the certification exercise were accepted for statistical evaluation. A certified value for the aflatoxin M1 content: 0.09(+0.04)(-0.02) micrograms/kg was derived. The certification of RM 283 completes the series of 4 milk powder reference materials having certified aflatoxin M1 contents.

The genetics of aflatoxin B1 metabolism. Association of the induction of aflatoxin B1-4-hydroxylase with the transcriptional activation of cytochrome P3-450 gene

The association between murine cytochrome P3-450 and hepatic aflatoxin B1-4-hydroxylase, a cytochrome P-450-dependent enzyme which converts aflatoxin B1 (AFB1) to aflatoxin M1 (AFM1), was examined by (a) purification of the cytochrome P-450 which preferentially metabolizes AFB1 to AFM1; (b) isolation of the specific cDNA clone; and (c) correlating induction of transcriptional activation of the specific message with the enzyme activity in the hepatic microsomes. Isolation of cytochromes P-450 from C57BL/6 mice, an Ah-responsive strain, pretreated with a 150 mg/kg dose of beta-naphthoflavone resulted in the partial purification of the cytochrome P-450 with preference for the metabolism of AFB1 to AFM1. Antibodies raised against this cytochrome P-450 were used to enrich hepatic mRNA for cDNA cloning. A cDNA library screened with a rat cytochrome P-450c gene probe yielded only two types of cDNA clones that contained inserts corresponding to cytochrome P1-450 and cytochrome P3-450. Specific restriction fragments of near full-length P1-450 cDNA and full-length P3-450 cDNA, hybridizing only with their respective messages, were isolated and used to assess transcriptional activation of these messages in liver and extrahepatic tissues from C57BL/6 mice treated with 3-methylcholanthrene, beta-naphthoflavone, indolylacetonitrile, and Aroclor-1254. Dose-dependent induction of the two messenger RNAs, when compared with the induction of specific enzyme activities, demonstrated the association of cytochrome P1-450 with aryl hydrocarbon hydroxylase activity and the association of cytochrome P3-450 with AFB1-4-hydroxylase activity. This supports our earlier hypothesis that AFB1-4-hydroxylase and aryl hydrocarbon hydroxylase, although regulated by the Ah locus, are the products of two separate genes (Gurtoo, H.L., Dahms, R.P., Kanter, P., and Vaught, J.B. (1978) J. Biol. Chem. 253, 3952-3961).

Cytochrome P3-450 cDNA encodes aflatoxin B1-4-hydroxylase

Aflatoxin B1 (AFB1), a potent hepatocarcinogen and ubiquitous dietary contaminant in some countries, is detoxified to aflatoxin M1 (AFM1) via cytochrome P-450-mediated AFB1-4-hydroxylase. Genetic studies in mice have demonstrated that the expression of AFB1-4-hydroxylase is regulated by the aryl hydrocarbon locus and suggested that different cytochrome P-450 isozymes catalyze AFB1-4-hydroxylase and aryl hydrocarbon hydroxylase activities. We have now examined lysates from mammalian cells infected with recombinant vaccinia viruses containing expressible cytochrome P1-450 or P3-450 cDNAs for their ability to metabolize AFB1 to AFM1. Our results show that cytochrome P3-450 cDNA specifies AFB1-4-hydroxylase. This is the first direct assignment of a specific cytochrome P-450 to an AFB1 detoxification pathway. This finding may have relevance to the dietary modulation of AFB1 hepatocarcinogenesis.

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.

Presence of aflatoxin M1 in commercial ultra-high-temperature-treated milk

Forty-seven samples of commercial ultra-high-temperature-treated milk from a dairy facility in the northwest part of Spain were analyzed for the presence of aflatoxin M1. A total of 14 samples (29.8%) were positive for aflatoxin M1 (4 in May, 3 in November, 3 in December, 1 in January, 1 in April, 1 in July, and 1 in August), 29 (61.7%) were negative, and 4 (8.5%) were doubtful, i.e., they showed trace quantities of aflatoxin M1. The range of aflatoxin M1 content was 0.02 to 0.1 ng/ml.

Aflatoxin M1 occurrence in dairy products marketed in Italy

In 1984, 313 samples of imported liquid milk and 159 samples of imported cheese were checked for aflatoxin M1; 225 of the milk samples came from FR Germany and 88 from France, while 82 of the cheese samples came from France, 34 from FR Germany and 43 from the Netherlands. The number of positive samples was small both for German (13.8%) and for French (12.5%) milks, and the contamination levels were very low (maximum 23 ng/l). As regards the cheeses, aflatoxin M1 was detected in 19.5, 26.5 and 53.5% of the French, German and Dutch samples respectively, but only 2 French samples exceeded 250 ng/kg, the limit set by Swiss law. In 1985, two surveys were carried out on 276 milk samples mostly obtained from individual farms and on 416 cheese samples taken from all parts of the country. As regards the milk samples, 70 (25.3%) contained aflatoxin M1, but generally at very low levels; in fact only 7 (2.5%) of the samples exceeded 50 ng/l. Aflatoxin M1 was found in 130 (31.3%) of the cheese samples, but here again only 9 (2.2%) exceeded 250 ng/kg. There was no significant difference in aflatoxin M1 levels between Italian, German and French cheese samples but these were significantly lower (P less than 0.01) than in Dutch samples.

Interactive effects of duration of storage and addition of formaldehyde on levels of aflatoxin M1 in milk

Spray-dried skim milk, naturally contaminated with aflatoxin M1, was added to either raw or pasteurized whole milk to a final concentration of 1.1 microgram aflatoxin M1/L milk. Formalin (37% w/w) was added to the milk solutions to final concentrations of 0, 0.025, 0.05, and 0.1% formaldehyde. Samples were stored in the dark at 21 degrees C in plastic and glass containers and were analyzed for aflatoxin M1 at 0, 1, 2, 3, and 4 weeks. This experiment was repeated using only raw milk and glass containers. Aflatoxin M1 analyses were done at 0, 1, and 2 weeks. Aflatoxin M1 losses increased over time and with increased formaldehyde concentration. With both experiments, aflatoxin M1, levels after 2 weeks were less than 0.05 micrograms/L in samples containing 0.1% formaldehyde.

Comparative metabolism and DNA binding of aflatoxin B1, aflatoxin M1, aflatoxicol and aflatoxicol-M1 in hepatocytes from rainbow trout (Salmo gairdneri)

DNA binding and metabolism patterns of 3H-labeled aflatoxin B1 (AFB1) and its phase I metabolites, aflatoxicol (AFL), aflatoxin M1 (AFM1), and aflatoxicol-M1 (AFL-M1), were compared in freshly prepared rainbow trout (Salmo gairdneri) hepatocytes. Aflatoxins were incubated with hepatocytes for periods up to 1 h, cellular DNA was isolated and specific activities determined by scintillation counting and Burton analysis. Data for (pmol bound aflatoxin/micrograms DNA)/(mumol dose) versus time fit a linear function (P less than 0.002) passing nearly through the origin for each aflatoxin. DNA binding at 1 h relative to AFB1 was: AFL, 0.53 +/- 0.07; AFM1, 0.81 +/- 0.20 AFL-M1, 0.83 +/- 0.24. Statistical analysis indicated that binding of AFL, AFM1 and AFL-M1 were significantly less than that of AFB1. HPLC analysis of the cellular supernatants indicated that the major metabolites were AFL, AFB1, AFL-M1, and AFM1 from AFB1, AFL, AFM1 and AFL-M1 substrates, respectively. Small quantities of hydroxylated metabolites and glucuronides also were detected in some of the incubations. The time-course data suggested that initial formation of major metabolites was rapid and that, by 20-30 min, net changes in metabolite levels decreased or approached zero. Because the four compounds possess a 8,9-double bond, DNA binding could be due to activation of the parent substrates as well as of their phase I metabolites. Based on current mutagenicity data and limited carcinogenicity studies, AFM1 and AFL-M1 have binding levels which are higher than expected compared to AFB1 and AFL.

Comparative study of aflatoxins M1 and B1 production in solid-state and shaking liquid cultures

Production of aflatoxins M1 (AFM) and B1 (AFB) by Aspergillus flavus NRRL 3251 in solid-state and shaking liquid cultures using rice as the carbon source was compared. In general, solid-state cultures produced more aflatoxins than shaking liquid cultures on an equal rice weight basis. Solid-state cultures with continuous shaking yielded higher levels of toxins than those with intermittent shaking. However, intermittent shaking is a feasible replacement for the continuous shaking method for AFM production. A typical solid rice culture supplemented with yeast extract produced 30 and 2600 mg per kg rice of AFM and AFB, respectively, in 8 days at 29 degrees C. The optimal culture conditions for toxin production in a shaking liquid culture were also studied. Parameters under consideration included the amount of carbon (rice) and nitrogen source, initial medium pH, and aeration rate. At optimum conditions, a representative shaking liquid culture produced 18 and 1680 mg per kg rice of AFM and AFB, respectively, in 5 days at 29 degrees C. This shaking liquid culture appears feasible for scaling up and routine production of AFM and AFB for toxicological investigations.

Effects of ammoniation on the 'carry-over' of aflatoxins into bovine milk

Two experiments were performed using lactating cows fed various treated and non-treated commodities from AFB1 contaminated peanut cakes. Treatment with ammonia gas by an autoclaving process was used for detoxification. Two methods were used for AFM1 determination in every milk sample: a TLC procedure recognized by AOAC and IDF and an HPLC method with a detection limit of 0.100 and 0.010 microgram/l, respectively. In a first experiment, lactating cows were fed treated and untreated meals during periods separated by uncontaminated soya meals phases. The total excreted AFM1 was 2.6% of the total ingested AFB1 from untreated feed contaminated at 1100 micrograms/kg. During periods receiving treated meals in the diet, AFM1 contents in milk were below 0.1 microgram/l. However, by using AFM1 data obtained using the HPLC method, an AFM1/AFB1 ratio of 4.6% was found from treated feed contaminated at 40 micrograms AFB1/kg. In a second experiment, a herd of 50 lactating cows was used for a long term (16 months) feeding of mixed commodities containing 30% ammoniated peanut cakes. AFB1 residues in the treated diet were below 10 micrograms/kg, the EEC action level, and no AFM1 residue was found up to 0.1 microgram/l in collected milk throughout this experiment.

Optimum conditions for formation of aflatoxin M1-trifluoroacetic acid derivative

Because thin-layer chromatographic (TLC) confirmation of identity and reverse-phase liquid chromatographic (LC) determination with fluorescence detection of aflatoxin M1 both require the derivative formed in the reaction of M1 and trifluoroacetic acid (TFA), various reaction conditions were studied to obtain complete derivative formation. Of the various organic solvents tested, the reaction between M1 and TFA proceeded best in the nonpolar solvents hexane and isooctane. Other parameters investigated were reaction temperature and time, aflatoxin M1 concentration, and solvent volume. The following procedure is considered optimum: 200 microL each of hexane and trifluoroacetic acid are mixed with M1 standard in a silylated glass vial or with milk residue in a regular glass vial with a Teflon-lined screw cap and heated 10 min at 40 degrees C. The mixture is evaporated to dryness under N2, and the derivative is saved for TLC or LC. No unreacted aflatoxin M1 was detected by reverse-phase LC after this procedure was incorporated for analysis of milk samples.

Odontogenic tumors in Fischer rats

The formation of odontogenic tumors in rats is rare unless they are treated with known carcinogens. In this study, male Fischer rats were continuously fed aflatoxins M1, B1, or control diets, then killed at 1, 6, 10, 16, 17, 19 and 21 months. Of the 186 rats fed aflatoxin M1 at 3 concentrations, 12 developed odontogenic tumors; 7 of 63 rats fed an agar-based diet also developed odontogenic tumors in 17-21 months. The purpose of this study is to describe these tumors. All the tumors were located in the upper jaw associated with the incisor teeth. The tumors developed in the periodontal ligament area and were composed mainly of highly cellular fibrous connective tissue. The fibroblastic nuclei were clustered in poorly defined swirls in areas and were evenly scattered in a myxomatous stroma in other areas. Within this tissue were ovoid sometimes coalescing, calcified bodies resembling cementum. Occasional inclusions of solid epithelial cell nests were present. Scattered nests were composed of ovoid epithelial ghost cells. Acellular cementum-like material surrounded many of these nests. An inductive phenomenon was present around occasional epithelial nests. Rare structures composed of globular dentin with irregular tubules were also observed. These tumors caused distortion of the facial areas and disruption of incisor tooth development. No metastatic lesions were noted but other neoplastic lesions occurred in these animals.

Development of milk powder reference materials certified for aflatoxin M1 content (Part I)

The development of 3 full-cream milk powder reference materials, certified for their aflatoxin M1 content, is described. The materials were prepared and certified within the Reference Material Programme of the Community Bureau of Reference (BCR). The 3 reference materials, RMs 282, 284, and 285, contain aflatoxin M1 at concentrations of less than 0.05, 0.31 +/- 0.06, and 0.76 +/- 0.05 micrograms/kg, respectively. The preparation, testing for homogeneity, stability of the reference materials, and the certification exercise, which was preceded by 2 intercomparisons of methods, are discussed. Particular emphasis was placed on the independence of the measurements in the certification exercise and the control of errors associated with extraction efficiency and the aflatoxin M1 calibrant. Finally, some guidance is given on avoiding the principal sources of errors in the determination of aflatoxin M1. Details concerning the supply of the reference materials will be provided by BCR on request.

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.

Correlation of dietary aflatoxin B1 levels with excretion of aflatoxin M1 in human urine

Corn and peanut oil (total, 253 samples) were collected from 32 households in Fushui county of the Guangxi autonomous region of the People's Republic of China, where high liver cancer incidence has been reported, every day over a period of 1 week and analyzed for aflatoxin B1 (AFB). A total of 252 urine samples were collected simultaneously from the residents in the households which were shown to have consumed AFB and were analyzed for aflatoxin M1 (AFM) by a competitive direct enzyme-linked immunosorbent assay. A good correlation between total dietary AFB intake and total AFM excretion in human urine was observed during a 3-day study. A regression equation of 0.143 plus 0.0135 multiplied by the amount of AFB consumed was observed. Between 1.23 and 2.18% of dietary AFB was found to be present as AFM in human urine. A good correlation was also observed between the AFB concentration in corn and the AFM concentration in human urine. The results suggest that analysis of AFM in urine by enzyme-linked immunosorbent assay could be used as an index for human exposure of AFB in an extensive epidemiological study.

Carcinogenicity of dietary aflatoxin M1 in male Fischer rats compared to aflatoxin B1

Aflatoxin M1 (AFM), an hydroxy metabolite of the potent carcinogenic mycotoxin aflatoxin B1 (AFB) is frequently found in milk and other dairy products. Sufficient amounts of AFM were produced to study the carcinogenicity of this compound. AFM was fed to male Fischer rats starting at 7 weeks up to 21 months of age. Agar-based semisynthetic diets contained 0.0, 0.5, 5.0, and 50.0 micrograms/kg of AFM or 50 micrograms/kg of AFB. Hepatocellular carcinomas were detected in two of 37 rats and neoplastic nodules were found in six of 37 rats fed 50 micrograms/kg AFM between 19 and 21 months. No nodules or carcinomas were observed in the lower AFM dose groups. Nineteen of 20 rats fed a diet containing 50 micrograms/kg of AFB developed hepatocellular carcinomas by 19 months of age. Carcinogenic potency of the aflatoxins was reflected by morphometric quantitation of foci detected in hematoxylin and eosin stained sections. Three rats fed the diet containing 50 micrograms/kg AFM developed intestinal carcinomas. None were observed in other groups. Under the conditions of this experiment AFM was found to be a weak hepatic carcinogen compared to AFB and to possess intestinal carcinogenicity.

Distribution and clearance of aflatoxins B1 and M1 in turkeys fed diets containing 50 or 150 ppb aflatoxin from naturally contaminated corn

Turkeys were fed a diet containing 50 or 150 ppb aflatoxin for 11 or 13 weeks or fed these diets for 11 weeks and then the control diet for 1 or 2 weeks. Aflatoxins B1 and M1 were found in liver, kidney, gizzard, and feces of poults fed the diets for 11 or 13 weeks. However, in turkeys fed the control diet for 1 or 2 weeks after the 11-week feeding trial, no residues of aflatoxin were found in the feces or tissues, except for some aflatoxin B1 remaining in detectable amounts in the gizzard. No mortality was attributable to aflatoxin, and there were no notable differences among groups in weight gains, feed conversion, or histopathologic changes in selected tissues. The response to a second inoculation with sheep erythrocytes was significantly lower in poults given dietary aflatoxin than in controls. This reduced antibody response was not observed when a Pasteurella multocida vaccine was administered.

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.

Thin layer chromatographic confirmation of aflatoxin M1 extracted from milk

Aflatoxin M1 can be confirmed directly on a thin layer plate by reacting the toxin with a mixture of reagents containing p-anisaldehyde. This confirmatory procedure requires only 2 elutions in the same direction using 2 different solvents. The mixture containing p-anisaldehyde is overspotted on M1 after the plate has been developed in toluene-ethyl acetate-ethyl ether-formic acid (25 + 35 + 40 + 5). The plate is heated at 110 degrees C for 10 min and then developed in hexane-acetone-chloroform (15 + 50 + 35). The Rf value of the green fluorescent derivative is less than that of the M1 standard. This confirmatory procedure requires only one-dimensional TLC, so several sample extracts and the standard can be run simultaneously. The minimum detectable quantity of aflatoxin M1 on the TLC plate with this test is 0.3 ng. p-Anisaldehyde reagent solution may also be used as a spray reagent for the confirmation of aflatoxin M1. The procedures described were satisfactory for confirming the mycotoxin in spiked samples of powdered and liquid milk.

Rapid liquid chromatographic determination of aflatoxins M1 and M2 in artificially contaminated fluid milks: collaborative study

An international collaborative study involving 14 collaborators from 5 different countries was conducted to test a rapid liquid chromatographic (LC) method for detecting aflatoxins M1 and M2 in fluid milk. Each collaborator prepared artificially contaminated milk samples (0.078-1.31 ng M1/mL and 0.030-0.13 ng M2/mL) by adding solutions containing various concentrations of aflatoxins M1 and M2 to fresh milk. Recoveries ranged from 85.2 to 102.5% (av. 93.7%) for aflatoxin M1 and from 99.5 to 126.7% (av. 109.8%) for aflatoxin M2. Coefficients of variation averaged 21.4% (M1) and 35.9% (M2). An analysis of variance was calculated from combined data to determine variance components. The within-laboratory variations (So) (repeatability) were 27.9% (M1) and 23.9% (M2), and the among-laboratory variations (Sx) (reproducibility) were 44.5% (M1) and 64.7% (M2). No visual differences were determined between normal or reverse phase LC for contaminated samples; however, there were an insufficient number of collaborators using normal phase to give meaningful separate statistical data. For 26 observations of uncontaminated milk, 3 false M1 positives were reported for normal phase LC determinations and 2 false M1 positives were reported for reverse phase LC determinations. Three normal phase and 11 reverse phase false M2 positives were reported for 104 observations in uncontaminated milk. The reverse phase LC method for determination of aflatoxins M1 and M2 in fluid milk has been adopted official first action.

[Aflatoxin M1 in type B milk solid in the municipality of São Paulo, SP (Brazil)]

No leite tipo "B", comercializado no Município de São Paulo, SP (Brasil), foi pesquisada a presença de aflatoxina M1. As amostras de leite analisadas foram provenientes das quatro marcas de maior consumo pela população, coletadas no período de julho a outubro de 1982. A aflatoxina M1, embora em baixos níveis e em pequena proporção (1,8%), fez-se presente nas quatro marcas.

Clinical and pathologic changes in acute bovine aflatoxicosis: rumen motility and tissue and fluid concentrations of aflatoxins B1 and M1

Effects of aflatoxin on bovine rumen motility were determined by radiotelemetric techniques. Aflatoxin altered amplitude and/or frequency of rumen contractions in steers given dosages of 0.2, 0.4, 0.6, or 0.8 mg of aflatoxin/kg of body weight. Effects of aflatoxin on rumen motility were dose dependent. An increase in elimination time of aflatoxin from rumen contents was observed in steers given the aflatoxin dosages of 0.4 to 0.8 mg/kg. The increase in elimination time of this toxin facilitates diagnostic capabilities for detecting bovine aflatoxicosis by obtaining rumen contents for analysis for aflatoxin. Aflatoxin M1 was detected in rumen contents from steers at 2 hours after aflatoxin was administered. Thus, intraruminal metabolism of aflatoxin B1 to M1 may occur.

Mechanisms of anti-carcinogenesis: the distribution and metabolism of aflatoxin B1 in rainbow trout fed aroclor 1254

Polychlorinated biphenyls (PCBs) have previously been shown to be inhibitors of carcinogenesis in trout. The mechanism of this inhibition was investigated by studying the effects of PCBs on aflatoxin B1 (AFB1) distribution, metabolism and DNA adduct formation, both in vivo and in vitro. A 24 h distribution study of injected tritiated AFB1 showed more radioactivity in blood, liver and bile in fish fed PCBs, but less in residual carcass. The metabolites of AFB1 found in vivo in blood plasma and liver homogenates were shifted by PCB pretreatment towards greater production of the polar metabolite aflatoxin M1 (AFM1) and glucuronide conjugates. The major metabolite in bile of PCB fish was the glucuronide of aflatoxicol M1 (AFL-M1), which was enhanced 15-fold over controls. Levels of aflatoxicol (AFL) glucuronide, the major conjugate in controls, were unaltered by PCBs. The pattern of AFB1 metabolism in isolated hepatocytes from PCB-prefed fish was consistent with in vivo metabolism. AFB1--DNA adduct formation in a 1 h assay was similar in hepatocytes from PCB-fed and control fish. However, the total rate of AFB1 metabolism was significantly elevated in hepatocytes from PCB-fed fish such that the degree of AFB1--DNA adduct formed per unit AFB1 metabolized was 42% lower than control. Similarly, adduct formation in vivo during the first 24 h post-AFB1 injection in PCB fish was not significantly different from controls. However, over a longer 21 day period, adduct levels in PCB fish were only 48-69% of controls (P less than 0.005, analysis of variance), once peak adduct formation was reached. Thus, initial rates of adduct formation may be misleading in the absence of further information on rates of carcinogen metabolism in vitro and/or pharmacokinetics of peak adduct formation in vivo. These results indicate that PCB inhibition of AFB1 carcinogenesis in trout involves dramatic initial changes in carcinogen distribution, metabolism and elimination which, over time, results in a net reduction of DNA adduct formation.

Production and isolation of aflatoxin M1 for toxicological studies

One hundred mg aflatoxin M1 was produced and purified for toxicological studies. Aspergillus flavus NRRL 3251 was cultured on rice to produce aflatoxins B1, B2, M1, and M2, B1 and B2 were separated from M1 and M2 by a normal phase low pressure liquid chromatography (LC) column. M1 was then separated from M2 by a reverse phase low pressure LC column. Recoveries of aflatoxins from the LC columns were about 90%. The purified M1 was confirmed by ultraviolet-visible spectrometry, mass spectrometry, nuclear magnetic resonance spectrometry, optical rotation, and its mutagenicity to Salmonella typhimurium TA98.