Integrating PBPK modeling and tobacco biomarkers to interpret N-(2-hydroxyethyl)valine (HEV) hemoglobin adducts in the U.S. population

Abstract

Background

Ethylene oxide (EtO) is a human carcinogen, and cigarette smoke is the leading source of exposure in the general population. In blood, EtO alkylates the N-terminal valine of hemoglobin to form N-(2-hydroxyethyl)valine (HEV), a stable biomarker. Yet HEV levels vary widely, even among smokers. This variability reflects differences in nicotine intake, smoking behavior, endogenous ethylene oxidation, and demographic factors.

Objective

We estimated the contribution of cigarette smoking to HEV levels and evaluated whether combining HEV with nicotine-derived and other tobacco biomarkers improves exposure assessment.

Methods

We analyzed adults from the National Health and Nutrition Examination Survey (NHANES) 2013–2014, the only cycle with both HEV and supplemental smoking biomarkers. Cigarette consumption was estimated from serum cotinine and entered into a physiologically based pharmacokinetic (PBPK) model to predict HEV formation from cigarette-derived EtO. Predicted values were compared with measured HEV levels. Survey-weighted regression examined how demographic factors and other biomarkers contributed to variability.

Results

HEV and other biomarkers were highest in active smokers, followed by passive smokers, and lowest in non-smokers. Predicted HEV matched observed patterns but was consistently 20–30 pmol/g globin lower than measured values. Body weight was a major source of variability, while age and others contributed less. Serum cotinine showed the strongest link with HEV. 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and 2-hydroxyethyl mercapturic acid (2-HEMA) added complementary information across different exposure windows.

Conclusions

Cigarette smoking is the primary source of HEV in the U.S. Using PBPK modeling alongside tobacco biomarkers helps explain variability and supports exposure assessment.