Long-term stability of human aflatoxin B₁ albumin adducts assessed by isotope dilution mass spectrometry and high-performance liquid chromatography-fluorescence

The measurement of the aflatoxin B₁-lysine serum albumin adduct in human blood samples is the most facile biomarker for the assessment of chronic exposure to aflatoxin B₁. Many technologies have been developed for the measurement of this protein adduct including immunoassays, high-performance liquid chromatography (HPLC) with fluorescence detection, and a newly developed isotope-dilution mass spectrometry method. Irrespective of the technology used to determine this adduct level, an important question remains about the long-term stability of this damage product in stored samples. To address this issue, 19 human serum samples that had been previously analyzed for the aflatoxin B₁-lysine adduct by high-performance liquid chromatography-fluorescence in 1989 were re-analyzed by isotope dilution mass spectrometry after storage at -80°C. The adduct concentrations measured by these two techniques were identical within 4% over the range 5 to 100 pg of aflatoxin B₁-lysine/mg albumin. In addition, the specific chemical structure of the aflatoxin B₁-lysine adduct in human samples was confirmed for the first time by collision-induced dissociation full scan mass spectrometry analysis of the protonated adduct molecular ion. These results illustrate that the aflatoxin B₁-lysine serum albumin adduct can be stable in human serum stored at -80°C since 1989, and this provides confidence for the measurement of this biomarker in repository samples from epidemiologic investigations.