Quantitative Comparison of Aflatoxin B1 Serum Albumin Adducts in Humans by Isotope Dilution Mass Spectrometry and ELISA

Abstract

Metabolic activation of the hepatocarcinogenic mycotoxin aflatoxin B 1 (AFB 1 ) results in the covalent attachment of AFB 1 to serum albumin. Digestion of adducted albumin releases AFB 1 -lysine, a biomarker of exposure status. AFalbumin adducts have been most frequently measured in precipitated serum albumin using an immunoassay (ELISA); however, a sensitive and specific isotope dilution mass spectrometric (IDMS) assay for measurement of AFB 1 -lysine in serum has recently been developed. The ELISA and IDMS methods were compared using 20 human sera collected in Guinea, West Africa, where AF exposure is endemic. Measurement of AFB 1 -lysine adduct concentrations by IDMS in serum and albumin precipitated from the same sample revealed that precipitation has no effect on the measured adduct levels. The concentration of AF-albumin adducts measured by ELISA and AFB 1 -lysine measured by IDMS in 2 mg of albumin were well correlated (R = 0.88, P < 0.0001); however, AF-albumin adduct concentrations measured by ELISA were on average 2.6-fold greater than those of the AFB 1 -lysine adduct. Although these data suggest that the ELISA is measuring other AF adducts in addition to AFB 1 -lysine, these biomarkers are comparable in their ability to assess AF exposure at AF-albumin concentrations z3 pg AFB 1 -lysine equivalents/mg albumin. Identification of other adducts may clarify the mechanistic basis for using AFprotein biomarkers to assess exposure status in future epidemiologic studies of liver cancer. (Cancer Epidemiol Biomarkers Prev 2006;15(4):823 -6)

Human Aflatoxin Albumin Adducts Quantitatively Compared by ELISA, HPLC with Fluorescence Detection, and HPLC with Isotope Dilution Mass Spectrometry

“…Because the present study represents an extreme range of adduct levels, the curve was truncated to ELISA concentrations of 500 pg/mg albumin for the purpose of comparison and the regression analysis was repeated (n = 39). The slope of this line was 2.53 with a correlation coefficient of 0.86 and an intercept of 0.014 ng/mg albumin, within experimental error of the slope obtained previously (16).…”

“…In addition, the AF-lys levels were again far lower in the earlier study (17). The higher response of the ELISA method relative to chromatographic methods has been reported previously (16)(17)(18). The chromatographic methods are expected to measure only the concentration of AF-lys.…”

Long-term Stability of Human Aflatoxin B1 Albumin Adducts Assessed by Isotope Dilution Mass Spectrometry and High-Performance Liquid Chromatography–Fluorescence

“…Aflatoxin-albumin adduct concentrations measured by ELISA are well correlated with AFB 1 -lys concentrations measured by HPLC-fluorescence and IDMS, albeit the levels obtained in a recent study found that values using an ELISA were 2.6-fold higher than those measured in the same samples by IDMS (12,13). The AFB 1 -lys adduct has been shown to be present in rat albumin by full scan and tandem mass spectrometry, such confirmatory spectra have not been reported for human albumin samples collected in exposed populations (8,13).…”

“…Immunoassays, high-performance liquid chromatography (HPLC) with fluorescence detection, and isotope dilution mass spectrometry (IDMS) have been used to measure serum albumin adduct concentrations and assess aflatoxin exposure status in epidemiologic studies (9)(10)(11)(12). Aflatoxin-albumin adduct concentrations measured by ELISA are well correlated with AFB 1 -lys concentrations measured by HPLC-fluorescence and IDMS, albeit the levels obtained in a recent study found that values using an ELISA were 2.6-fold higher than those measured in the same samples by IDMS (12,13).…”

Aflatoxins and Their Impact on Human and Animal Health: An Emerging Problem

“…Many different analytical methods are now available for quantitation of chemical adducts in biological samples, each with unique specificity and sensitivity (Santella, 1999;Poirier, 2004;Wogan et. al., 2004;Scholl et. al., 2006).…”