Compound-Specific Isotope Analysis of Human Hair: Predicting Behaviors and Biometrics beyond Dietary Factors

Abstract

This study describes the use of amino acid quantitation and amino-acid-specific isotope ratio analysis of scalp hair of American individuals to predict soft biometric traits about the donors. The scalp hair of each donor was washed, dried, homogenized and acid hydrolyzed before analysis using liquid chromatography-isotope ratio mass spectrometry (LC-IRMS). A variety of statistical tests examined the relationships between the amino acid variables and biometric questionnaire responses, the latter of which could be assessed as continuous variablesin the case of age or body mass index (BMI)or as categorical variables in the case of sex and alcohol consumption. Correlations between biometric factors and amino acid δ 13C values were more significant after controlling for the extent of 13C in the subjects’ diets. Multivariate analysis revealed that the sex of a donor could be correctly predicted with cross-validated accuracies of 80% using the isotope ratios and 89% using amino acid quantities. Using amino acid δ 13C values or quantities, the age of a subject could only be predicted with an accuracy of ±27 years (95% CI). Hair treatments, such as chemical straitening and dying, did not have any measurable effect on the isotope ratios or quantities of amino acids in the hair. Unexpectedly, the δ 13C values of sulfur-containing amino acids were significantly different between teetotalers and subjects who consumed alcohol daily. Further refinement of this study, including larger cohorts with controlled behavioral states or genetic factors, could provide helpful investigative leads in forensic casework.

Reconstructing Hominin Diets with Stable Isotope Analysis of Amino Acids: New Perspectives and Future Directions

“… 2021 ), researchers are also investigating the extent δ 13 C amino acid values can inform about biometric traits, such as body mass index, age, and sex (Jackson et al. 2015 , Matos and Jackson 2020 ). More feeding experiments on pigs and other mammalian model species are needed to improve contextualization of omnivore-specific δ 13 C amino acid patterns (Edgar Hare et al.…”

Longitudinal isotope ratio variations in human hair and nails

“…Determination of element concentrations and their isotopic compositions in keratinized tissues, such as hair and nails, is increasingly used for a variety of purposes in bioarchaeology, forensics, the environmental sciences, toxicology and medicine (e.g. Oyoo-Okoth et al, 2012;Thompson et al, 2013;Pozebon et al, 2017;Zhao et al, 2018;Amais et al, 2020;Chesson et al, 2020;Matos and Jackson, 2020). This approach owes its popularity to several reasons; the non-invasive nature of the sampling, ease of sample collection, ease of transport and storage, as well as the possibility for obtaining time-resolved information via spatially resolved analysis.…”

“…Most stable isotope ratio studies in keratinized tissues to date have been focusing on the structural elements, such as C, H, O, N and S, and to a significantly lesser extent, on trace elements with radiogenic isotopes, such as Sr and Pb (e.g. Rodushkin and Axelsson, 2000b;Santamaria-Fernandez et al, 2009;Petzke et al, 2010;Neuberger et al, 2013;Reitsema, 2013;Lehn et al, 2015a;2015b;Mancuso and Ehleringer, 2018;Bataille et al, 2020a;Chesson et al, 2020;Hu et al, 2020;Matos and Jackson, 2020). Other biologically relevant stable isotope systems, such as Zn, Fe, Cu, Mg and Cd, have to date remained mostly unexplored in these matrices, probably as a reflection of their relatively low concentrations, combined with the limited amount of hair and nails often available for analysis, which complicates the sample preparation.…”