Is correction for protein concentration appropriate for protein adduct dosimetry? Hypothesis and clues from an aflatoxin B1‐exposed population

Abstract

Protein adducts are useful biomarkers for assessing exposure, metabolism and risk of carcinogens. Aflatoxin B1-albumin adducts (AAA) and protein carbonyl content (PCC) have long been used for assessing aflatoxin exposure and oxidative stress to proteins, and the quantitative data are almost exclusively expressed per mg protein. Given the large variation in protein concentrations in plasma among populations, this may not be the most appropriate method. The objective was to test the hypothesis that AAA and PCC should be expressed per mL plasma in population studies. AAA and PCC were analyzed among 402 subjects from three regions of China with a gradient in hepatocellular carcinoma (HCC) mortality ranging from 21 to 97 per 100 000. When biomarker values were expressed per mL plasma, the AAA level was significantly associated with plasma PCC (r = 0.262, P < 0.001), and adjusted levels of AAA and PCC paralleled HCC mortalities in the three regions, suggesting a role for aflatoxin-related oxidative stress in hepatocarcinogenesis in this population. In addition, there were statistically significant associations between both protein biomarkers, expressed per mL plasma, and the levels of alanine aminotransferase and aspartate aminotransferase in hepatitis B virus-infected subjects, suggesting roles for aflatoxin exposure, oxidative stress and hepatitis B virus infection in the development of HCC. The present data suggest that interindividual variation in plasma protein concentration may influence the dosimetry and relevant interpretation of protein biomarkers. (Cancer Sci 2007; 98: 140-146) E nvironmental chemicals are possible etiological agents for a number of human cancers, (1) and the development of quantitative risk assessment methodologies has emphasized the need for chemical-specific biomarkers as molecular dosimeters of individual exposure.(2) The adducts formed by the covalent binding of genotoxic chemicals with proteins are useful biomarkers for assessing exposure, metabolism and risk in molecular epidemiology.(3) Unlike DNA adducts, protein adducts are not repaired. Therefore, protein adducts form a stable repository of accumulated exposure to carcinogens over the lifetime of the protein.(4) The levels of stable protein adducts can be used to evaluate exposure if the dose-response relationship is known.(3) Further, formation of biomarkers of carcinogenesis may be important biological events that take place between exposure to external or endogenous carcinogens and the subsequent development of cancer.(4) Thus, protein adducts in blood may serve as useful surrogates for those in the target organ in animal or human population studies. The 40 years of investigation of aflatoxin exposures probably provides one of the most extensive data sets in molecular epidemiology.(6) Aflatoxins are highly carcinogenic agents, and the role of exposure to AFB1 in the development of HCC has long been documented in animal and human studies.(7) AFB1 is metabolized by constitutive cellular enzymes, during which there is formation of...

Hepatitis B virus infection contributes to oxidative stress in a population exposed to aflatoxin B1 and high-risk for hepatocellular carcinoma

“…Comparison of protein adducts levels among subjects from the three regionsSimilar to our previous analysis of a smaller sample size [19], there were significant differences in AAA and PCC levels among the populations from the three different regions, in accordant with their HCC incidences (data not shown).…”

“…It is not surprising to see a significantly lower concentration of plasma proteins in HCC cases and HBsAg(+) control subjects. However, this leads to concerns on protein adduct dosimetry in these special populations [19]. Determining the influence of protein concentration on protein adduct dosimetry in a mal-nourished animal model might provide supportive data addressing this issue.…”

“…Details on recruitment have been described elsewhere and AFB1-Albumin-Adducts and Protein carbonyl content data on a subset of 404 subjects in this analysis has been reported previously [19]. In brief, a total of 695 healthy subjects (530 males, 165 females, age 36.6 ± 15.6 yrs) were recruited from three regions of P.R.…”

“…The minimum level of AAA among these subjects was 32.6 fmol/mg albumin, above the limit of sensitivity of this assay (10 fmol/mg albumin) and quality control measures were taken as described previously [20]. PCC was determined by a noncompetitive ELISA as described previously that involves derivatization of carbonyl groups with dinitrophenylhydrazine (DNP) followed by detection of the DNP group with a commercial antibody [19]. PCC values were first normalized by TP (nmol/mg TP) and then normalized by TP concentration in plasma (nmol/ml plasma).…”

The Effect on Oxidative Stress of Aflatoxin and Protective Effect of Lycopene on Aflatoxin Damage

“…By its capacity to generate ROS, AFB1 can promote the ROS-mediated oxidative damages in proteins (Figure 6) [79].…”