Methods for chemical preparation of aflatoxin B1adducts, AFB1-N7-guanine and AFB1-lysine

Comparative metabolism of aflatoxin B1 in mouse, rat and human primary hepatocytes using HPLC-MS/MS

Aflatoxin B1 (AFB1) is a highly hepatotoxic and carcinogenic mycotoxin produced by Aspergillus species. The compound is mainly metabolized in the liver and its metabolism varies between species. The present study quantified relevant AFB1- metabolites formed by mouse, rat, and human primary hepatocytes after treatment with 1 µM and 10 µM AFB1. The use of liquid chromatographic separation coupled with tandem mass spectrometric detection enabled the selective and sensitive determination of phase I and phase II metabolites of AFB1 over incubation times of up to 24 h. The binding of AFB1 to macromolecules was also considered. The fastest metabolism of AFB1 was observed in mouse hepatocytes which formed aflatoxin P1 as a major metabolite and also its glucuronidated form, while AFP1 occurred only in traces in the other species. Aflatoxin M1 was formed in all species and was, together with aflatoxin Q1 and aflatoxicol, the main metabolite in human cells. Effective epoxidation led to high amounts of DNA adducts already 30 min post-treatment, especially in rat hepatocytes. Lower levels of DNA adducts and fast DNA repair were found in mouse hepatocytes. Also, protein adducts arising from reactive intermediates were formed rapidly in all three species. Detoxification via glutathione conjugation and subsequent formation of the N-acetylcysteine derivative appeared to be similar in mice and in rats and strongly differed from human hepatocytes which did not form these metabolites at all. The use of qualitative reference material of a multitude of metabolites and the comparison of hepatocyte metabolism in three species using advanced methods enabled considerations on toxification and detoxification mechanisms of AFB1. In addition to glutathione conjugation, phase I metabolism is strongly involved in the detoxification of AFB1.

Simplified Synthesis and Stability Assessment of Aflatoxin B1-Lysine and Aflatoxin G1-Lysine

Aflatoxins B₁ (AFB₁) and G₁ (AFG₁) are carcinogenic mycotoxins that contaminate crops such as maize and groundnuts worldwide. The broadly accepted method to assess chronic human aflatoxin exposure is by quantifying the amount of aflatoxin adducted to human serum albumin. This has been reported using ELISA, HPLC, or LC-MS/MS to measure the amount of AFB₁-lysine released after proteolysis of serum albumin. LC-MS/MS is the most accurate method but requires both isotopically labelled and unlabelled AFB₁-lysine standards, which are not commercially available. In this work, we report a simplified synthetic route to produce unlabelled, deuterated and ¹³C₆ ¹⁵N₂ labelled aflatoxin B₁-lysine and for the first-time aflatoxin G₁-lysine. Additionally, we report on the stability of these compounds during storage. This simplified synthetic approach will make the production of these important standards more feasible for laboratories performing aflatoxin exposure studies.