Biotransformation Of Aflatoxin B1 Research Articles

Biotransformation of aflatoxin B1 by a novel strain Brevundimonas sp. LF-1

Aflatoxin B1 (AFB1) is a potent mycotoxin and a common source of food and feed contamination, posing risks to both human and animal health. The biotransformation of AFB1 has been proven to be a promising approach to control AFB1 contamination. In this study, Brevundimonas sp. LF-1 capable of degrading AFB1 was isolated from a corn-planted soil sample. Strain LF-1 could degrade 86.90% of 2 mg L−1 AFB1 after incubation in Luria-Bertani (LB) medium at 30 °C for 72 h and exhibited high performance when exposed to up to 10.0 mg L−1 AFB1. The optimum pH and temperature were 7.0–10.0 and 30 °C, respectively. The results of the in vitro cytotoxicity assay showed that the degradation products had considerably (p < 0.05) less harmful effects than the parent AFB1. Additionally, strain LF-1 possessed the bioremediation potential of AFB1 contamination for biocontrol strategies in animal fodder. Two putative novel AFB1-degrading enzymes, peroxiredoxin 1 and peroxiredoxin 2, were identified in the genome of strain LF-1. Comparative genomics indicated that the peroxiredoxin enzyme was widely distributed in the genus Brevundimonas. The comprehensive examination of strain LF-1 has outstanding potential for the development of detoxifying agents for AFB1 in the food and feed industries.

Bile Acids Promote Hepatic Biotransformation and Excretion of Aflatoxin B1 in Broiler Chickens.

Aflatoxin B1 (AFB1) is a hazardous mycotoxin that often contaminates animal feed and may potentially induce severe liver damage if ingested. The liver is the primary organ responsible for AFB1 detoxification through enzyme-catalyzed xenobiotic metabolism and bile acid (BA)-associated excretion. In this study, we sought to investigate whether exogenous BA improves hepatic AFB1 detoxification to alleviate AFB1-induced liver injury in broiler chickens. Five-day-old broiler chicks were randomly assigned to three groups. CON and AFB1 received a basal diet; AFB1 + BA received a basal diet with 250 mg/kg BA for 20 days. After a 3-day pre-feed, AFB1 and AFB1 + BA were daily gavaged with 250 μg/kg BW AFB1, while CON received gavage solvent for AFB1 treatment. Dietary BA supplementation protected chickens from AFB1-induced hepatic inflammation and oxidative stress. The hepatic biotransformation of AFB1 to its metabolite AFBO was improved, with accelerated excretion to the gallbladder and cecum. Accordantly, AFB1-induced down-regulation of detoxification genes, including cytochrome P450 enzymes, glutathione S-transferases, and the bile salt export pump, was rescued by BA supplementation. Moreover, liver X receptor α, suppressed by AFB1, was enhanced in BA-treated broiler chickens. These results indicate that dietary BA supplementation improves hepatic AFB1 detoxification and excretion through LXRα-involved regulation of xenobiotic enzymes.

Bio-based material-edible rosemary induced biodegradation of aflatoxin B1 via altering endogenous protective enzymes signatures in animal-derived foods

Aflatoxin B1 (AFB1) is the most hazardous mycotoxin, posing risks to public health. Utilization of bio-based materials to biodegrade AFB1 is a green strategy to overcome this issue. The investigation aimed to screen for endogenous protective enzymes in bio-based material-edible rosemary based on ultra-high performance liquid chromatography coupled to hybrid quadrupole-Orbitrap high-resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS)-proteomics and ascertain their impacts on the biodegradation and biotransformation of AFB1, and the trade-offs of multilevel metabolism of the animal-derived foods through untargeted metabolomics. The proteomics results verified that bio-based material-edible rosemary (0.20%, w/w) significantly up-regulated glutathione S-transferase and stimulated the down-regulation of cytochrome P450 1A2 levels via activating AhR nuclear translocation in rosemary-pickled AFB1-contaminated goat meat. Metabolomics results demonstrated that edible rosemary substantially increased histidine and glutathione implicated in the antioxidant status of goat meat. More importantly, edible rosemary with high endogenous protective enzyme content could efficiently biodegrade AFB1 in goat meat. We first unveiled that rosemary could not only efficiently biodegrade AFB1 up to 90.20% (20.00–1.96 μg kg−1) but also elevate the bio-ingestion quality of goat meat. These findings suggest that the bio-based material-rosemary is an efficient and environmentally friendly approach for biodegrading AFB1 and elevating the bio-ingestion composition of goat meat.

Exposure and Health Risk Assessment of Aflatoxin M1 in Raw Milk and Cottage Cheese in Adults in Ethiopia.

Aflatoxin M1 (milk toxin) found in milk is formed from the hepatic biotransformation of AFB1 (aflatoxin B1) and poses a risk to human health when consumed. The risk assessment of AFM1 exposure due to milk consumption is a valuable way to assess health risk. The objective of the present work was to determine an exposure and risk assessment of AFM1 in raw milk and cheese, and it is the first of its kind in Ethiopia. Determination of AFM1 was conducted using an enzyme-linked immunosorbent assay (ELISA). The results indicated that AFM1 was positive in all samples of milk products. The risk assessment was determined using margin of exposure (MOE), estimated daily intake (EDI), hazard index (HI), and cancer risk. The mean EDIs for raw milk and cheese consumers were 0.70 and 0.16 ng/kg bw/day, respectively. Our results showed that almost all mean MOE values were <10,000, which suggests a potential health issue. The mean HI values obtained were 3.50 and 0.79 for raw milk and cheese consumers, respectively, which indicates adverse health effects for large consumers of raw milk. For milk and cheese consumers, the mean cancer risk was 1.29 × 10-6 and 2.9 × 10-6 cases/100,000 person/year, respectively, which indicates a low risk for cancer. Therefore, a risk assessment of AFM1 in children should be investigated further as they consume more milk than adults.

Zanthoxylum bungeanum as a natural pickling spice alleviates health risks in animal-derived foods via up-regulating glutathione S-transferase, down-regulating cytochrome P450 1A

Endogenous aflatoxin B1 (AFB1) was quantified in five hundred and forty Hengshan goat meat samples (0.00 ± 23.09 μg kg−1). Zanthoxylum bungeanum (Z. bungeanum), as a natural pickling spice, can ameliorate the flavor of animal-derived food (goat meat). Yet, considering the direct administration of Z. bungeanum in AFB1-contaminated goat meat, the degradation mechanisms of AFB1 remain elusive. Here, UHPLC-Q-Orbitrap HRMS-based integrative metabolomics (LOQ: 1.74–59.54 μg kg−1) and proteomics analyses were executed to determine the effects of Z. bungeanum in the biotransformation of AFB1. Z. bungeanum (1.50 %, w/w) application mediated the metabolism of xenobiotics by cytochrome P450, significantly down-regulated cytochrome P450 1A and stimulated the up-regulation of glutathione S-transferase levels in AFB1-contaminated goat meat, leading to degradation of AFB1 (20.00–3.39 μg kg−1). Metabolomics assays indicated that Z. bungeanum up-regulated l-histidine (1.43–2.21 mg kg−1) and l-arginine, manifesting potential applications for the contribution of Z. bungeanum to the nutritional value of goat meat.

Progress on the detoxification of aflatoxin B1 using natural anti-oxidants.

Aflatoxins are toxic secondary metabolites produced by Aspergillus fungi. The most toxic among them is Aflatoxin B1 (AFB1) which is known to have genotoxic, immunotoxic, teratogenic, carcinogenic, and mutagenic toxic effects (amongst others). The mechanisms responsible for its toxicity include the induction of oxidative stress, cytotoxicity, and DNAdamage. Studies have found that natural anti-oxidants can reduce the damage that AFB1 inflicts on the body by alleviating oxidative stress and inhibiting the biotransformation of AFB1. Therefore, this review outlines the latest progress in research on the use of natural anti-oxidants as antidotes to aflatoxin poisoning and their detoxification mechanisms. It also considers the problems that may possibly arise from their use and their application prospects. Our aim is to provide a useful reference for the prevention and treatment of AFB1 poisoning.

Antagonistic role of barley against bioaccumulation and oxidative stress of aflatoxin B1 in male rats

BackgroundThis study aims to evaluate the protective effect of barley against the bioaccumulation and oxidative stress of aflatoxin B1 (AFB1) in male rats. The lethality percentile doses (LDs: LD1 to LD99 at 24, 48, 72, and 96 h) were measured. To achieve these goals during subacute treatments, one hundred rats were divided into five groups, each with twenty rats. The groups I, II, III, IV, and V throughout 21 days were daily given drinking water, DMSO, 2.0 g of barley/kg, and 7.49 mg/kg of AFB1 alone or in combination with 2.0 g of barley/kg, respectively.ResultsThe results revealed that AFB1 was detected only in the liver, kidney, and serum of groups IV, in which the accumulated AFB1 exhibited a significant direct relationship with the experimental periods with a marked positive correlation coefficient. Additionally, the concentrations of AFB1 residue in the serum of rats given AFB1 alone exhibited a significant inverse relationship with the levels of GSH, activity of CAT, SOD, and GR, whereas the levels of MDA showed a significant positive relationship. In the serum of rats given AFB1 plus barley, all parameters were mostly recovered and didn’t correlate with either the experimental periods or AFB1 in the serum.ConclusionsThe present data concluded that barley accelerated the biotransformation of AFB1 to a hydrophilic metabolite that is easily eliminated outside the body, leading to the recovery of all studied parameters to normal levels.

Dietary aflatoxin B1 caused the growth inhibition, and activated oxidative stress and endoplasmic reticulum stress pathway, inducing apoptosis and inflammation in the liver of northern snakehead (Channa argus)

The purpose of this study was to investigate the effects of dietary aflatoxin B1 (AFB1) on growth performance and AFB1 biotransformation, and hepatic oxidative stress, endoplasmic reticulum (ER) stress, apoptosis, and inflammation in northern snakehead (Channa argus). A total of 600 northern snakeheads (7.52 ± 0.02 g) were divided into five groups (three replicates/group) and fed the diets with AFB1 at concentrations of 0, 50, 100, 200, and 400 ppb for 8 weeks. The results demonstrated that dietary AFB1 (≥ 200 ppb) reduced FBW, WG, and SGR. 100, 200, and 400 ppb AFB1 treatment groups significantly decreased the PER, CRP, C3, C4, IgM, and LYS levels in northern snakehead, while FCR was significant increased. Moreover, dietary AFB1 (100, 200, and 400 ppb) increased cyp1a, cyp1b (except 400 ppb), and cyp3a mRNA expression levels, while reducing the GST enzymatic activity and mRNA expression levels in northern snakehead. Furthermore, AFB1 (≥ 100 ppb) increased ROS, MDA, and 8-OHdG levels, and grp78, ire1, perk, jnk, chop, and traf2 mRNA expression levels, and decreased SOD, CAT, GSH-Px, and GSH (except 100 ppb) levels and the gene expression levels of cat, gsh-px (except 100 ppb), and Cu/Zn sod. In addition, AFB1 (100, 200, and 400 ppb) up-regulated the cyt-c, bax, cas-3, and cas-9 mRNA levels in the liver, while down-regulating the bcl-2 expression levels. Meanwhile, the expression levels of nf-κb, tnf-α (except 100 ppb), il-1β, and il-8 in the liver were up-regulated in AFB1 treatment groups (≥ 100 ppb), while the iκbα mRNA levels were down-regulated. In summary, dietary AFB1 reduced growth performance and humoral immunity in northern snakehead. Meanwhile, the cyclic occurrence of oxidative stress and ER stress, and induced apoptosis and inflammation, is one of the main reasons for AFB1-induced liver injury in the northern snakehead, which will provide valuable information and a fresh perspective for further research into AFB1-induced liver injury in fish.

In Vivo Kinetics and Biotransformation of Aflatoxin B1 in Dairy Cows Based on the Establishment of a Reliable UHPLC-MS/MS Method.

The in vivo kinetics of aflatoxin B1 (AFB1) and its carry-over as aflatoxin M1 (AFM1) in milk as well as the toxin loads in the tissue of dairy cows were assessed through a repetitive feeding trial of an AFB1-contaminated diet of 4 μg kg−1 body weight (b.w.) for 13 days. This was followed by a clearance period that ended with a single dose trial of an AFB1-contaminated diet of 40 μg kg−1 b.w. An ultra-high performance liquid chromatography tandem mass spectrometry method was developed and successfully validated by the determination of linearity (R 2 ≥ 0.990), sensitivity (lower limit of quantification, 0.1–0.2 ng ml−1), recovery (79.5–111.2%), and precision relative standard deviation (RSD) ≤14.7%) in plasma, milk, and various tissues. The repetitive ingestion of AFB1 indicated that the biotransformation of AFB1 to AFM1 occurred within 48 h, and the clearance period of AFM1 in milk was not more than 2 days. The carry-over rate of AFM1 in milk during the continuous ingestion experiment was in the range of 1.15–2.30% at a steady state. The in vivo kinetic results indicated that AFB1 reached a maximum concentration of 3.8 ± 0.9 ng ml−1 within 35.0 ± 10.2 min and was slowly eliminated from the plasma, with a half-life time (T1/2) of 931.1 ± 30.8 min. Meanwhile, AFM1 reached a plateau in plasma (0.5 ± 0.1 ng ml−1) at 4 h after the ingestion. AFB1 was found in the heart, spleen, lungs, and kidneys at concentrations of 1.6 ± 0.3, 4.1 ± 1.2, 3.3 ± 0.9 and 5.6 ± 1.4 μg kg−1, respectively. AFM1 was observed in the spleen and kidneys at concentrations of only 0.7 ± 0.2 and 0.8 ± 0.1 μg kg−1, respectively. In conclusion, the in vivo kinetics and biotransformation of AFB1 in dairy cows were determined using the developed UHPLC-MS/MS method, and the present findings could be helpful in assessing the health risks to consumers.

An overview of aflatoxin B1 biotransformation and aflatoxin M1 secretion in lactating dairy cows.

Milk is considered a perfect natural food for humans and animals. However, aflatoxin B1 (AFB1) contaminating the feeds fed to lactating dairy cows can introduce aflatoxin M1 (AFM1), the main toxic metabolite of aflatoxins into the milk, consequently posing a risk to human health. As a result of AFM1 monitoring in raw milk worldwide, it is evident that high AFM1 concentrations exist in raw milk in many countries. Thus, the incidence of AFM1 in milk from dairy cows should not be underestimated. To further optimize the intervention strategies, it is necessary to better understand the metabolism of AFB1 and its biotransformation into AFM1 and the specific secretion pathways in lactating dairy cows. The metabolism of AFB1 and its biotransformation into AFM1 in lactating dairy cows are drawn in this review. Furthermore, recent data provide evidence that in the mammary tissue of lactating dairy cows, aflatoxins significantly increase the activity of a protein, ATP-binding cassette super-family G member 2 (ABCG2), an efflux transporter known to facilitate the excretion of various xenobiotics and veterinary drugs into milk. Further research should focus on identifying and understanding the factors that affect the expression of ABCG2 in the mammary gland of cows.

Biotransformation of aflatoxin B1 by Lactobacillus helviticus FAM22155 in wheat bran by solid-state fermentation

Lactobacillus helveticus FAM22155 was the most efficient among five lactic acid bacteria at removing aflatoxin B1 (AFB1) during solid-state fermentation on wheat bran substrate. The mechanism of removal was explored by comparing different fermentation modes. Liquid fermentation had little effect on the breakdown of AFB1. However, a protein extract from the fermented bran was equally effective at degrading aflatoxin B1 as living cell digestion. After treatment with heat and protease K, the degrading capacity of the protein extract was significantly reduced. Taken together, the observed biotransformation of AFB1 was mainly associated with proteins produced during bran fermentation. Four products of U-[13C17]-AFB1 were found by mass spectrometry, including Ⅱ-1 (C11H10O4), Ⅱ-2 (C11H10O4), III (C15H12O5), and IV (C14H10O4). These products all lack the lactone ring indicating lower toxicity than aflatoxin B1.

Exploration of biodegradation mechanism by AFB1-degrading strain Aspergillus niger FS10 and its metabolic feedback

Significant progress has been made in the biological degradation of aflatoxin B1 (AFB1), which is the most toxic and carcinogenic mycotoxin commonly found in food and feed products; however, research in this area has currently focused on the effective methods for detoxifying AFB1 and the mechanisms underlying the degradation process. The relationship between AFB1 biotransformation and the metabolic feedback by the AFB1-degrading strain has rarely been reported. This study investigated the biotransformation pathway of AFB1 in a highly efficient degrading strain, Aspergillus niger FS10, and the metabolic regulation of FS10 during AFB1 degradation. We analyzed the AFB1 metabolic degradation products and evaluated its toxicity based on its structures by triple quadrupole-linear ion trap-mass spectrometry (Q-Trap-MS) coupled with LightSight™ Software. Four metabolic degradation products were obtained: Product 1 (C17H14O6), Product 2 (C17H14O7), Product 3 (C16H12O5), and Product 4 (C27H31N3O13, AFB2-GOH). Two biotransformation pathways were proposed based on the structures of these degradation products. Metabolomics data revealed that FS10 exhibited different degrees of bioremediation under low-, medium- and high- dose AFB1. The results also suggested the significant involvement of glutathione, a metabolite, in the AFB1 biotransformation pathway and its formation of AFB2-GOH with AFB1. The four products could probably be less toxic than AFB1, as reflected by changes in the AFB1 toxicity site. Therefore, the AFB1-degrading strain FS10 exhibits great potential for application in the detoxification of AFB1 in food and feed products.

Antimutagenic constituents from Monanthotaxis caffra (Sond.) Verdc.

Monanthotaxis caffra (Sond.) Verdc. (Annonaceae) has been reported to possess antitumoural properties. Preliminary screening showed that the crude methanolic leaf extract had strong antimutagenic effects against aflatoxin B1 -induced mutagenicity. The aim of this study was to isolate and evaluate the antimutagenic properties of the active constituents from M. caffra. Different chromatographic, spectroscopic and spectrometric techniques were used for the isolation and identification of the antimutagenic constituents. The antimutagenic effect of the extract and compounds was evaluated using Ames, Vitotox and Comet assays. Bioassay-guided fractionation of the methanolic leaf extract yielded two antimutagenic compounds identified as (+)-crotepoxide and 5,6-diacetoxy1-benzoyloxymethyl-1,3-cyclohexadiene. Crotepoxide had strong antimutagenicity in the Vitotox assay with an IC50 value of 131 μg/ml. 5,6-Diacetoxy-1-benzoyloxymethyl-1,3-cyclohexadiene showed strong antimutagenic activity in the Ames assay with an IC50 value of 348.9 μg/plate and no antimutagenic activity in the Vitotox test. Furthermore, the compound was able to inhibit, block or prevent biotransformation of aflatoxin B1 by repressing the proteins involved in transcription. Crotepoxide and 5,6-diacetoxy-1-benzoyloxymethyl-1,3-cyclohexadiene have the potential to mitigate the risks arising from consumption of aflatoxin B1 -contaminated food and feed.

Incidence of aflatoxin M1 in fresh milk from small farms

Abstract The objective of this work was to determine aflatoxin M1 in fresh milk from fifty-two small farms in the city of Concordia - SC, Brazil. Samples from the cooling tanks of each property were collected from November 2014 to January 2015. The QuEChERS method was used for the extraction of aflatoxin M1, and quantification was performed in UHPLC-FL. 40.4% of the analyzed samples (eg, 21 samples) showed contamination levels by aflatoxin M1 above the maximum limit allowed by the Brazilian regulation, which is 0.5 μg L-1. These results suggest the importance of implementing Good Practices in obtaining feed for dairy cows, since the contamination of milk by aflatoxin M1 occurs through the biotransformation of aflatoxin B1, after the ingestion of feed or silage contaminated by the animals, posing risk to the animals themselves, as well as to consumers of milk and dairy products.

Current Immunoassay Methods for the Rapid Detection of Aflatoxin in Milk and Dairy Products.

The presence of mycotoxins in foodstuff causes serious health problems to consumers and economically affects the food industry. Among the mycotoxins, aflatoxins are very toxic and highly carcinogenic contaminants which affect the safety of many foods, and therefore endanger human health. Aflatoxin M1 (AFM1 ) found in milk results from the biotransformation of aflatoxin B1 . Many efforts have been made to control the source of AFM1 from farmers to dairy product companies. However, AFM1 escapes ordinary methods of food treatment such as cooking, sterilization, and freezing, hence it appears in milk and dairy products. The presence of high levels of AFM1 constitutes an alarming threat as milk and dairy products contain essential nutrients for human health, especially for infants and children. For this reason, there is a pressing need for developing a fast and reliable screening method for detecting trace aflatoxins in food. Several analytical methods based on high-performance liquid chromatography (HPLC) and mass spectroscopy have been used for aflatoxin detection; however, they are expensive, time-consuming, and require many skills. Recently, immunoassay methods, including enzyme-linked immunosorbent assay (ELISA), immunosensors, and lateral flow immunoassay (LFIA), have been preferred for food analysis because of their improved qualities such as high sensitivity, simplicity, and capability of onsite monitoring. This paper reviews the new developments and applications of immunoassays for the rapid detection of AFM1 in milk.

Detoxification of Aflatoxin B₁ by Zygosaccharomyces rouxii with Solid State Fermentation in Peanut Meal.

Aflatoxins are highly carcinogenic, teratogenetic, and morbigenous secondary metabolites of Aspergillus flavus and A. parasiticus that can contaminate multiple staple foods, such as peanut, maize, and tree nuts. In this study, Zygosaccharomyces rouxii was screened out and identified from fermented soy paste—one kind of traditional Chinese food—to detoxify aflatoxin B1 (AFB1) by aerobic solid state fermentation in peanut meal. The optimal degradation condition was chosen from single factor experiment, and the most effective detoxification rate was about 97%. As for liquid fermentation, we tested the binding ability of Z. rouxii, and the highest binding rate reached was 74.3% (nonviable cells of Z. rouxii) in phosphate-buffered saline (PBS). Moreover, the biotransformation of AFB1 through fermentation of Z. rouxii in peanut meal was further verified by liquid chromatography/mass spectrometry (LC/MS). According to TIC scan, after fermentation by Z. rouxii, the AFB1 in peanut meal was prominently degraded to the lowering peaks of AFB1. Additionally, m/s statistics demonstrated that AFB1 may be degraded to some new products whose structural properties may be different from AFB1, or the degradation products may be dissolved in the aqueous phase rather than the organic phase. As far as we know, this is the first report indicating that the safe strain of Z. rouxii has the ability to detoxify AFB1.

Biotransformation of aflatoxin B1 and aflatoxin G1 in peanut meal by anaerobic solid fermentation of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus

The purpose of this study was to explore the ability of anaerobic solid fermentation of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus to biotransform aflatoxins in peanut meal. The pH of the peanut meal was adjusted above 10, and then heated for 10min at 100°C, 115°C and 121°C. The S. thermophilus and L. delbrueckii subsp. bulgaricus were precultured together in MRS broth for 48h at 37°C. The heated peanut meal was mixed with precultured MRS broth containing 7.0×108CFU/mL of S. thermophilus and 3.0×103CFU/mL of L. delbrueckii subsp. bulgaricus with the ratio of 1 to 1 (weight to volume) and incubated in anaerobic jars at 37°C for 3days. The aflatoxin content in the peanut meal samples was determined by HPLC. The results showed that the peanut meal contained mainly aflatoxin B1 (AFB1) (10.5±0.64μg/kg) and aflatoxin G1 (AFG1) (18.7±0.55μg/kg). When heat treatment was combined with anaerobic solid fermentation, the biotransformation rate of aflatoxins in peanut meal could attain 100%. The cytotoxicity of fermented peanut meal to L929 mouse connective tissue fibroblast cells was determined by MTT assay and no significant toxicity was observed in the fermented peanut meal. Furthermore, heat treatment and anaerobic solid fermentation did not change the amino acid concentrations and profile in peanut meal.

Occurrence and estimative of aflatoxin M1 intake in UHT cow milk in Paraná State, Brazil

Aflatoxin M1 (AFM1) is a product of aflatoxin B1 biotransformation when ingested by lactating animals and humans. Its introduction in the diet occurs mainly through the cow milk intake. This study aimed to assess the seasonal occurrence of AFM1 in ultra-high-temperature (UHT) milk commercially available in Maringá, Paraná State, Brazil and to estimate the exposure of the population to mycotoxin. A total of 152 samples of UHT whole cow milk were collected. AFM1 was determined by high performance liquid chromatography using a previous validated method with immunoaffinity column clean-up. The 87.5% of the samples were contaminated with an average of 19.6 ng/L of AFM1 and 2.6% exhibited AFM1 levels above the limit established by the European Community (50 ng/L). The highest value for probable daily intake (0.07 ng/kg b.w/day) was observed in the autumn. Toxin concentrations were different between samples collected in different seasons, thus indicating an influence of climatic conditions.

Aflatoxins upregulate CYP3A4 mRNA expression in a process that involves the PXR transcription factor

Pregnane X receptor (PXR) is a member of the nuclear hormone receptor (NHR) superfamily, which regulates xenobiotic and endobiotic metabolism in the liver. This transcription factor is activated by structurally diverse ligands, including drugs and environmental pollutants. PXR regulates the expression of numerous genes that function in biotransformation and the disposition of xenobiotics upon binding to an AG(G/T)TCA DNA motif in target promoter regions. We performed a screen of mycotoxins that pose a known environmental threat to human and animal health for the ability to activate PXR function in a human hepatocyte cell line, HepG2. We found that aflatoxins B1, M1, and G1 activated PXR. This activation was associated with upregulation of CYP3A4 expression and increased occupancy of PXR protein on the CYP3A4 promoter. Using a microarray approach, we also found that aflatoxin B1 upregulated the expression of multiple genes involved in xenobiotic metabolism, including genes known to be regulated in a PXR-dependent fashion. We also observed an effect of aflatoxin B1 on the expression in other functional groups of genes, including the downregulation of genes involved in cholesterologenesis. The results of this study indicate that aflatoxin B1 is able to activate PXR, a known regulator of liver xenobiotic metabolism, in human hepatocytes, and it can upregulate the expression of PXR-dependent genes responsible for aflatoxin B1 biotransformation, including CYP3A4.

Microsomal and cytosolic biotransformation of aflatoxin B1 in four poultry species

1. This research evaluated differences in hepatic in vitro metabolism of aflatoxin B1 (AFB1) on selected avian species. 2. Microsomal and cytosolic liver fractions were obtained from chickens, ducks, quails and turkeys; eight males and eight females of each. 3. All microsomes studied produced AFB1-8,9-exo-epoxide (AFBO), a metabolite regarded as the active product of AFB1. Turkey microsomes produced 1·8 and 3·5 times more AFBO than quails and chickens microsomes, respectively. 4. Males from evaluated birds produced more AFBO than females, but statistically-significant differences between genders were observed only in ducks and turkeys. 5. The cytosolic fraction from all four species produced aflatoxicol (AFL). Turkey and duck hepatic cytosol produced more AFL than from quail and chickens. 6. It is known that turkeys are very sensitive to AFB1, quails are intermediate and chickens are particularly resistant; the differences in AFBO production shown in our study may help to explain the different in vivo responses among turkeys, quail and chickens. 7. Moreover, AFL may be related to AFB1 toxicity; it was produced in larger amounts by hepatic cytosol from the more susceptible species. 8. Because AFBO production by microsomes in ducks was relatively low, it is possible that other toxicity mechanisms are involved in this highly susceptible species.