Quantitative Analysis and Chronic Dosimetry of the Aflatoxin B_1 Plasma Albumin Adduct Lys-AFB_1 in Rats by Isotope Dilution Mass Spectrometry

摘要

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.