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 (Hg_T) 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 Hg_T: group 1 (Hg_T = 270 ± 3.50 µg kg^-1), group 2 (Hg_T = 360 ± 3.26 µg kg^-1), group 3 (Hg_T = 1100 ± 17.4 µg kg^-1), and group 4 (Hg_T = 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.