Results obtained from rat studies indicate that, even at low concentrations, mercurial species cause harmful effects on the kidneys, by inducing the nephrotic oxidative stress response. In the present work, Hg-associated proteins were identified as possible mercury-exposure biomarkers in rat kidneys exposed to low mercury chloride concentrations for 30 days (Hg-30) and 60 days (Hg-60), using metalloproteomic strategies. The renal proteomic profile was fractioned by two-dimensional electrophoresis and the mercury determinations in kidney samples, protein pellets and protein spots were performed using graphite furnace atomic absorption spectrometry. The characterization of Hg-associated protein spots and the analysis of differentially expressed proteins were performed by liquid chromatography, coupled with tandem mass spectrometry. Eleven Hg-associated protein spots with a concentration range of 79 ± 1 to 750 ± 9 mg kg⁻¹ in the Hg-60 group were identified. The characterization and expression analyses allowed the identification of 53 proteins that were expressed only in the Hg-60 group, 13 “upregulated” proteins (p > 0.95) and 47 “downregulated” proteins (p < 0.05). Actin isoforms and hemoglobin subunits were identified in protein spots of the Hg-60 group, with mercury concentrations in the range of 138 to 750 mg kg⁻¹, which qualifies these proteins as potential mercury-exposure biomarkers.

This paper reports the results of a mercury (Hg) and selenium (Se) metallomic study in the liver tissues of Psectrogaster amazonica and Raphiodon vulpinus from the Brazilian Amazon. Two-dimensional electrophoresis, graphite furnace atomic absorption spectrometry, and liquid chromatography-tandem mass spectrometry were performed. Hg and Se determinations allowed the calculation of Hg:Se and Se:Hg molar ratio and Se values for health benefits (Se HBVs). The Se:Hg values were >1 for both fish species, whereas the Se HBVs were >5 for P. amazonica and >10 for R. vulpinus, indicating that both possess Se reserves to control Hg toxicity. The metallomic data allowed the identification of 11 Hg/Se-associated protein spots in the two fish species, with concentrations in the range of 9.70 ± 0.14 and 28.44 ± 0.31 mg kg⁻¹ of Hg and 16.15 ± 0.21 and 43.12 ± 0.51 mg kg⁻¹ of Se. Five metal binding proteins (MBP) in the Hg/Se-associated protein spots in the liver proteome of P. amazonica and eight in R. vulpinus were identified, indicating the possible formation of Hg/Se complexes on the MBP structures. The activities analysis of catalase, superoxide dismutase, GPx enzymes, and lipoperoxide concentrations demonstrated that Hg-induced oxidative stress did not occur, possibly because both fish species possess Se reserves necessary to inhibit the Hg’s deleterious effects.

The chapter reports the use of metalloproteomics strategies to identify the protein abundance in muscle tissue of Psectrogaster amazonica and Raphiodon vulpinus from Madeira River/Brazil exposed to mercury (Hg), with the aim of investigating possible Hg:Se interactions. Metalloproteomic results allowed the calculation of selenium values for health benefits (SeHBVs) that showed positive values for both fish species, suggesting that fish have Se reserves in their muscle tissue necessary to control the Hg toxic effects. Protein abundance analysis (PAA) showed that the few proteins and/or enzymes with up- and/or downregulated expression were expressed in the groups with higher Hg and Se concentrations. Therefore, it can be inferred that Se could be attenuating the Hg negative action on the functions of these proteins and/or enzymes through the formation of Se-Hg complexes in the structures of these macromolecules. The catalase, glutathione peroxidase and superoxide dismutase activity analysis, as well as that of lipoperoxides concentration, did not indicate that Hg concentrations present in muscle tissue of both fish species could trigger an oxidative stress state, corroborating with PAA results. The preliminary results obtained in the present chapter provide new insights into studies of the Se mitigating effect on the Hg toxicity in fish.