Quantitative analysis and chronic dosimetry of the aflatoxin B-1 plasma albumin adduct Lys-AFB(1) in rats by isotope dilution mass spectrometry

Aflatoxin B-1 (AFB(1)) is a major risk factor in the pathogenesis of liver cancer in Asia and sub-Saharan Africa. Biomarkers reflecting exposure will facilitate disease risk assessment and the efficacy of protective interventions in these populations. The Lys-AFB(1) adduct in plasma albumin is a candidate biomarker for this role. Although aflatoxin albumin adducts are most frequently measured in epidemiological studies using an enzyme-linked immunosorbent assay, a more specific and 10-fold more sensitive isotopic dilution mass spectrometric assay for Lys-AFB(1) has recently become available. Here, the dosimetry of chronically administered AFB(1) at lower doses than have been previously studied was explored using this assay. AFB(1) was administered to rats for nine consecutive days at eight dose levels ranging from 50 pg to 55 mu g/kg body wt. Plasma samples were enzymatically digested and processed by solid phase extraction. Lys-AFB(1) was isolated by HPLC and detected via selected reaction monitoring. The dose-response relationship was linear-quadratic exhibiting upward curvature at higher doses. The adduct yield [(pg Lys-AFB(1)/mg albumin)/(mu g AFB(1)/kg body wt)] increased nonlinearly with the dose by 6-fold between the 0.05 and 55 mu g AFB(1)/kg body wt groups and exhibited the onset of saturation in the highest dose group where the adduct yield was approximately 2%. Incomplete knowledge of the timing of exposure and the complexity of the underlying biology confound the precise determination of prior AFB(1) exposures in humans; however, the dosimetry of AFB(1) observed in chronically dosed rats conceptually suggests that measurements in humans may underestimate exposure if a constant fraction of the AFB(1) dose, approximately 2%, is assumed to be converted to Lys-AFB(1) without regard to the dose.