Chicken CYP1A5 is able to hydroxylate aflatoxin B1 to aflatoxin M1

Aflatoxin B1 (AFB1), a naturally-occurring mycotoxin, can cause severe toxicological and carcinogenic effects in livestock and humans. Given that the chicken is one of the most important food-producing animals, knowledge regarding AFB1 metabolism and enzymes responsible for AFB1 transformation in the chicken has important implications for chicken production and food safety. Previously, we have successfully expressed chicken CYP1A5 and CYP3A37 monooxygenases in E. coli, and reconstituted them into a functional CYP system consisting of CYP1A5 or CYP3A37, CPR and cytochrome b5. In this study, we aimed to investigate the roles of CYP1A5 and CYP3A37 in the bioconversion of AFB1 to AFM1. Our results showed that chicken CYP1A5 was able to hydroxylate AFB1 to AFM1. The formation of AFM1 followed the typical Michaelis-Menten kinetics. The kinetics parameters of Vmax and Km were determined as 0.83 ± 0.039 nmol/min/nmol P450 and 26.9 ± 4.52 μM respectively. Docking simulations further revealed that AFB1 adopts a "side-on" conformation in chicken CYP1A5, facilitating the hydroxylation of the C9a atom and the production of AFM1. On the other hand, AFB1 assumes a "face-on" conformation in chicken CYP3A37, leading to the displacement of the C9a atom from the heme iron and explaining the lack of AFM1 hydroxylation activity. The results demonstrate that chicken CYP1A5 possesses efficient hydroxylase activity towards AFB1 to form AFM1.

Diverse mycotoxin threats to safe food and feed cereals

Toxigenic fungi, including Aspergillus and Fusarium species, contaminate our major cereal crops with an array of harmful mycotoxins, which threaten the health of humans and farmed animals. Despite our best efforts to prevent crop diseases, or postharvest spoilage, our cereals are consistently contaminated with aflatoxins and deoxynivalenol, and while established monitoring systems effectively prevent acute exposure, Aspergillus and Fusarium mycotoxins still threaten our food security. This is through the understudied impacts of: (i) our chronic exposure to these mycotoxins, (ii) the underestimated dietary intake of masked mycotoxins, and (iii) the synergistic threat of cocontaminations by multiple mycotoxins. Mycotoxins also have profound economic consequences for cereal and farmed-animal producers, plus their associated food and feed industries, which results in higher food prices for consumers. Climate change and altering agronomic practices are predicted to exacerbate the extent and intensity of mycotoxin contaminations of cereals. Collectively, this review of the diverse threats from Aspergillus and Fusarium mycotoxins highlights the need for renewed and concerted efforts to understand, and mitigate, the increased risks they pose to our food and feed cereals.

CYP1A2, 2A13, and 3A4 network and interaction with aflatoxin B1

Aspergillus fungi are known to produce aflatoxins, among which aflatoxin B1 (AFB1) is the most potent carcinogen that is metabolised by cytochrome P450 (CYP450). In the liver, AFB1 is metabolised into exo-8,9-epoxide by the CYP1A2 enzymes. The resulting epoxide can react with guanine to cause DNA damage. Natural inhibitors are being identified. However, the modes of action are poorly understood. In the current study, we have investigated the mode of action of AFB1 with CYP1A2, CYP3A4 and CYP2A13 using molecular dynamic simulation (MD simulation) approaches. The interaction network and paths among CYP1A2, CYP3A4, and CYP2A13 have been investigated using the STRING database and PathLinker plugin of Cytoscape. CYP3A4 is the most active protein involved in interactions with AFB1 during its metabolism. Residues 362ARG, 445SER, 450LEU and 451PHE of CYP1A2 are important, interacting with AFB1 and converting it to toxic exo-AFB1-8,9-epoxide (AFBEX). The pathway shows that microsomal epoxide hydrolase (EPHX1) may acts as initiator in the signalling pathway where CYP1A2, CYP3A4 and CYP2A13 interact in a sequential order. The interaction network shows there to be a strong association in expression among CYP1A2, CYP3A4 and CYP2A13 along with other metabolising enzymes. The complex of AFB1 and CYP1A2 was found to be stable during the MD simulation. This study provides a better understanding of the mode of action between AFB1 and CYP1A2, CYP3A4 and CYP2A13 which relates to the effective management of AFB1 toxicity. EPHX1 in the protein network may be an ideal target when designing inhibitors to prevent the toxin’s activation. Peptide inhibitors may be designed to block the substrate site residues of CYP1A2 in order to prevent the conversion from AFB1 into AFBEX. This would either neutralise or reduce its toxicity.

Determination of aflatoxin biomarkers in excreta and ileal content of chickens

Aflatoxins are carcinogenic secondary metabolites frequently detected in food and feed stuff based on maize and other crops susceptible to infection with the fungal pathogen Aspergillus flavus. We investigated the metabolization of aflatoxins in chickens by analyzing excreta and ileal content and developed and validated a biomarker method for detection of aflatoxins and their metabolites in these matrices. Analysis of ileal content served to distinguish between urinary and fecal excretion combined in the excreta samples. During a 3-wk animal trial, one hundred sixty-eight 1-day-old chicks were randomly allocated to 24 pens with 7 chicks per pen and subjected to different feed regimens with: A) toxin-free feed, B) feed supplemented with 18 ng of total aflatoxins/g, and C) feed supplemented with 515 ng of total aflatoxins/g. Chicken excreta and ileal content were sampled after 7, 14, and 21 D. An analytical method based on liquid chromatography coupled to tandem mass spectrometry was validated for the determination of aflatoxin B1, B2, G1, G2, M1, P1, Q1, and aflatoxin B1-N7-guanine (AFB1-N7-Gua) in chicken's samples. Comparing chicken excreta, which contain urine and feces, to ileal content, which contains no urine, we explored the secretion pathway of aflatoxin metabolites. The AFB1-N7-Gua was only detected in excreta, whereas aflatoxin M1 (AFM1) was detected both in ileal content and excreta. Aflatoxin M1 was detected in excreta in concentrations 5 times higher than in ileal content, suggesting primary excretion via urine. Although chickens are relatively resistant to aflatoxins, contamination of feed can lead to adverse effects and thus economic losses in farming. Therefore, a biomarker method to estimate the exposure of chickens to aflatoxins can play an important role to monitor the animals' health.

A Limited Survey of Aflatoxins in Poultry Feed and Feed Ingredients in Guyana

A study was conducted to determine the presence of aflatoxins in finished poultry feed from manufacturing companies, feed ingredients, and poultry feed at the point of sale. Two collections were made. In the first collection, samples of the finished feed and feed ingredients were analyzed by high-performance liquid chromatography (HPLC). For the second collection, all samples were analyzed by ELISA while a subset was analyzed by HPLC. Of the 27 samples of finished feed, five samples had aflatoxin concentrations greater than the United States Food and Drug Administration (USFDA) and European Union Commission (EUC) maximum tolerable limit of 20 µg/kg, while for the feed ingredients, three of the 30 samples of feed ingredients exceeded the limit. Of the 93 samples of finished feed purchased from retailers, five samples had aflatoxin concentrations greater than the maximum tolerable limit. This survey indicates that most of the samples were below the maximum regulatory limit and maintained quality up to the point of sale for 2015 and 2016. However, given that some samples were above the limit, there is a need to monitor the production and marketing chain to ensure that the quality of the finished feed is not compromised.

Validation of a liquid chromatography/tandem mass spectrometry method for the detection of aflatoxin B1 residues in broiler liver

Aflatoxin B₁ is a carcinogenic and mutagenic mycotoxin produced mainly by Aspergillus flavus and Aspergillus parasiticus. It is the predominant mycotoxin found in raw materials used for the manufacture of broiler feeds. The aim of the present study was to develop a new and optimized method for the detection and quantification of aflatoxin B₁ (AFB₁) residues in broiler liver using solid phase extraction (SPE) clean-up and liquid chromatography-electrospray ionization/tandem mass spectrometry (LC-ESI-MS/MS) detection. The method was validated for linearity, accuracy, precision, limit of detection (LOD) and limit of quantification (LOQ). The validation parameters indicated satisfactory linearity (r²>0.99), accuracy and precision (4.57% intra-day RSD; 14.65% inter-day RSD) a very high recovery (99±13%) and high sensitivity achieved for AFB₁ in animal samples (LOD=0.017 and LOQ=0.050ng/g). The method was effective for the detection and quantification of AFB₁ residues in broiler liver and could also be potentially used for detecting AFB₁ in other edible animal tissues after natural or experimental AFB₁ exposure with high sensitivity and precision.