Mercury contamination in Amazon traditional populations: Metalloproteomic study associated with exposure frequency

Mercury (Hg) contamination in humans in the Amazon has been reported for decades. However, studies reporting a proteomic approach to this topic are limited. Thus, herein, we report a study on Hg contamination in plasma samples from the traditional population of the Brazilian Amazon, employing a sampling process using Noviplex™ cards and metalloproteomic strategies, which are procedures that were previously unheard of in this context. After the plasma elution process from the Noviplex™ card sampling disks, the protein fraction was separated from the eluates via precipitation using cold acetone. Total Hg (HgT) determinations were conducted using graphite furnace absorption atomic spectrometry on the protein pellets allowed the assembly of four groups of seven volunteers with increasing concentrations of HgT: group 1 (HgT = 270 ± 3.50 µg kg-1), group 2 (HgT = 360 ± 3.26 µg kg-1), group 3 (HgT = 1100 ± 17.4 µg kg-1), and group 4 (HgT = 3030 ± 39.8 µg kg-1). Protein abundance analysis using shotgun - liquid chromatography coupled with tandem mass spectrometry of the plasma proteome across the four groups of volunteers identified 132 proteins with fold changes and/or unique proteins, considering the comparison between groups g2-g4 and group g1. Notably, immunoglobulin kappa was expressed as a unique protein in g3 and g4 and ceruloplasmin showed a positive fold change in g4. Given that, these proteins have coordination sites with soft-base characteristics capable of interacting with Hg species they may act as potential Hg exposure biomarkers in traditional populations of the Amazon.