The hemoglobin adduct N-(2,3-dihydroxypropyl)-valine as biomarker of dietary exposure to glycidyl esters: a controlled exposure study in humans

Abstract

Fatty acid esters of glycidol (glycidyl esters) are heat-induced food contaminants predominantly formed during industrial deodorization of vegetable oils and fats. After consumption, the esters are digested in the gastrointestinal tract, leading to a systemic exposure to the reactive epoxide glycidol. The compound is carcinogenic, genotoxic and teratogenic in rodents, and rated as probably carcinogenic to humans (IARC group 2A). Assessment of exposure from occurrence and consumption data is difficult, as lots of different foods containing refined oils and fats may contribute to human exposure. Therefore, assessment of the internal exposure using the hemoglobin adduct of glycidol, N-(2,3-dihydroxypropyl)-valine (2,3-diHOPr-Val), may be promising, but a proof-of-principle study is needed to interpret adduct levels with respect to the underlying external exposure. A controlled exposure study was conducted with 11 healthy participants consuming a daily portion of about 36 g commercially available palm fat with a relatively high content of ester-bound glycidol (8.7 mg glycidol/kg) over 4 weeks (total amount 1 kg fat, individual doses between 2.7 and 5.2 µg/kg body weight per day). Frequent blood sampling was performed to monitor the 2,3-diHOPr-Val adduct levels during formation and the following removal over 15 weeks, using a modified Edman degradation and ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/ MS). Results demonstrated for the first time that the relatively high exposure during the intervention period was reflected in corresponding distinct increases of 2,3-diHOPr-Val levels in all participants, following the expected slope for hemoglobin adduct formation and removal over time. The mean adduct level increased from 4.0 to 12.2 pmol 2,3-diHOPr-Val/g hemoglobin. By using a nonlinear mixed model, values for the adduct level/dose ratio (k, mean 0.082 pmol 2,3-diHOPr-Val/g hemoglobin per µg glycidol/kg body weight) and the adduct lifetime (τ, mean 104 days, likely the lifetime of the erythrocytes) were determined. Interindividual variability was generally low. 2,3-DiHOPr-Val was therefore proven to be a biomarker of the external dietary exposure to fatty acid esters of glycidol. From the background adduct levels observed in our study, a mean external glycidol exposure of 0.94 µg/kg body weight was estimated. This value is considerably higher than current estimates for adults using occurrence and consumption data of food. Possible reasons for this discrepancy are discussed (other oral or inhalational glycidol sources, endogenous formation, exposure to other chemicals also forming the adduct 2,3-diHOPr-Val). Further research is necessary to clarify the issue. KeywordsGlycidol · Edman degradation · Protein adduct · Biomarker · Exposure study Abbreviations DHP-Val-FTH N-(2,3-Dihydroxypropyl)-valine fluorescein thiohydantoin 2,3-diHOPr-Val N-(2,3-Dihydroxypropyl)-valine FITC Fluorescein-5-isothiocyanate FTH Fluorescein thiohydantoin Hb Hemoglogin MRM Multiple reaction monitoring T 25Dose...

Mode of action-based risk assessment of genotoxic carcinogens

“…From this increase, a mathematical model was used to calculate the external exposure in the group of participants in the 4 months prior to the start of the controlled exposure study. Of course, this approach seems only possible if the interindividual variations of bioactivation and detoxification of the substance in question are relatively small (Abraham et al 2019).…”

Internal Doses of Glycidol in Children and Estimation of Associated Cancer Risk

“…To perform this calculation, the relation between the adduct level (or in vivo dose) and administered dose of glycidol is required. We used the results recently published by Abraham et al, who studied the relation between glycidol-induced diHOPrVal adduct levels and administered dose of glycidol from palm fat in human subjects [22]. The adduct increment in their study was calculated to be 82 pmol/g Hb per mg glycidol/kg body weight (b.w.).…”

“…The relation between adduct level and intake of glycidol in humans was obtained from a recently published human exposure study by Abraham et al, which involved a good number of persons (11) with intake of palm fat oil over 4 weeks corresponding to a mean daily intake of glycidol of 4.3 µg/kg b.w. [22]. The methods for measurement of the diHOPrVal adducts used by Abraham et al and by us are not inter-calibrated, which might contribute to some uncertainty in this calculation, just like the figure on a mean lifetime of erythrocytes of 126 days (cf., Mitlyng et al [33] and Abraham et al [22]).…”

“…[22]. The methods for measurement of the diHOPrVal adducts used by Abraham et al and by us are not inter-calibrated, which might contribute to some uncertainty in this calculation, just like the figure on a mean lifetime of erythrocytes of 126 days (cf., Mitlyng et al [33] and Abraham et al [22]).…”

Does External Exposure of Glycidol-Related Chemicals Influence the Forming of the Hemoglobin Adduct, N-(2,3-dihydroxypropyl)valine, as a Biomarker of Internal Exposure to Glycidol?

“…A total of eleven healthy participants consumed a daily portion of about 36 g of commercially available palm fat (8.7 mg glycidol/kg) over 4 weeks. The mean daily glycidol exposure, as estimated from the adduct levels of the participants before the intervention period (background levels of diHOPrVal), was 0.94 µg/kg body weight [15]. Additionally, diHOPrVal levels were used to estimate a continuous exposure of 1.4 µg/kg/day of glycidol in 50 children aged approximately 12 years old [16].…”