Characterization of molecular biomarkers of mercury exposure to muscle tissue of Plagioscion squamosissimus and Colossoma macropomum from the Amazon region

The effects of mercury exposure on Amazonian fishes: An investigation of potential biomarkers

Exposure to mercury can interfere with the expression of proteins and enzymes, compromise important pathways, such as apoptosis and glucose metabolism, and even induce the expression of metallothioneins. In this study, analytical techniques were used to determine the concentration of total mercury (THg) in muscle and liver tissue, protein pellets, and spots [using graphite furnace atomic absorption spectrometry (GFAAS)], and molecular techniques were used to identify metalloproteins present in mercury-associated protein spots. Thirty individuals from three different fish species, Cichla sp. (n = 10), Brachyplatystoma filamentosum (n = 10), and Semaprochilodus sp. (n = 10) from the Brazilian Amazon were used. Oxidative stress indicators [such as glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD), a marker of lipid peroxidation (LPO)] and the possible expression of metallothioneins in muscle and liver tissues were investigated. The two piscivorous species, Cichla sp. and B. filamentosum, presented the highest concentrations of mercury in their hepatic tissue, 1219 ± 15.00 and 1044 ± 13.6 μg kg^-1, respectively, and in their muscle tissue, 101 ± 1.30 μg kg^-1 and 87.4 ± 0.900 μg kg^-1, respectively. The non-carnivorous species Semaprochilodus sp. had comparatively low concentrations of mercury in both its hepatic (852 ± 11.1 μg kg^-1) and muscle (71.4 ± 0.930 μg kg^-1) tissues. The presence of mercury was identified in 24 protein spots using GFAAS; concentrations ranged from 11.5 to 787 μg kg^-1, and mass spectrometry identified 21 metal-binding proteins. The activities of GSH-Px, CAT, and SOD, related to oxidative stress, decreased proportionally as tissue Hg concentrations increased, while the levels of LPO markers increased, indicating the presence of stress. Our study results demonstrate possible mercury interference in oxidative stress markers (GSH-Px, CAT, SOD, and LPO), in addition to the identification of 21 metal-binding proteins as possible biomarkers of mercury exposure in fish.

Metalloproteomic approach to liver tissue of rats exposed to mercury

The aims of this study were to identify mercury-associated protein spots in the liver tissue of rats exposed to low concentrations of mercury and to elucidate the physiological and functional aspects of the proteins identified in the protein spots. Therefore, proteomic analysis of the liver tissue of Wistar rats exposed to mercury chloride (4.60 μg kg^-1 in Hg²⁺) was performed for thirty days (Hg-30 group) and sixty days (Hg-60 group). The proteomic profile of the liver tissue of the rats was obtained by two-dimensional electrophoresis (2D-PAGE), and the determinations of total mercury in the liver tissue, pellets and protein spots were performed by graphite furnace atomic absorption spectrometry (GFAAS). ImageMaster 2D Platinum 7.0 software was used to identify the differentially expressed mercury-associated protein spots, which were then characterized by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The determinations by GFAAS indicated a total mercury bioaccumulation of 2812% in the Hg-30 group and 3298% in the Hg-60 group and 10 mercury-associated protein spots with a concentration range of 51 ± 1.0 to 412 ± 6.00 mg kg^-1 in the 2D PAGE gels from the liver tissue of the Hg-60 group. The LC-MS/MS analyses allowed the identification of 11 metal binding proteins in mercury-associated protein spots that presented fold change with upregulation >1.5, downregulation < -1.7 or that were expressed only in the Hg-60 group. Using the FASTA sequences of the proteins identified in the mercury-associated protein spots, bioinformatics analyses were performed to elucidate the physiological and functional aspects of the metal binding proteins, allowing us to infer that enzymes such as GSTM2 presented greater mercury concentrations and downregulation < -3; Acaa2 and Bhmt, which showed expression only in the Hg-60 group, among others, may act as potential mercury exposure biomarkers.

Mercury metalloproteomic profile in muscle tissue of Arapaima gigas from the Brazilian Amazon

Metalloproteomics is an innovative methodology for identifying of protein-associated mercury. Thus, we analyzed the muscle proteome of Arapaima gigas (pirarucu), collected in the Madeira River of the Brazilian Amazon, to identify protein-associated mercury, with the aim of identifying possible mercury biomarkers in fish muscle tissue. After obtaining the protein pellet, we conducted two-dimensional electrophoresis (2D PAGE) to fractionate the muscle proteome. Total mercury in muscle tissue and protein pellets and mapping of mercury content in protein spots of the 2D PAGE gels was determined using graphite furnace atomic absorption spectrometry (GFAAS). The protein-associated mercury identification was performed using liquid chromatography coupled with sequence mass spectrometry (LC‒MS/MS). Total mercury determinations by GFAAS indicated concentrations on the order of 153 ± 1.90 mg kg^-1 and 142 ± 1.50 mg kg^-1 (total precipitation of protein fraction) and 139 ± 1.45 mg kg^-1 (fractional precipitation of protein fraction) in muscle tissue and protein pellets, respectively. Mercury concentrations in the range of 48 ± 0.90 to 165 ± 3.00 mg kg^-1 were found in twelve protein spots. Among the 2D PAGE protein spots, eleven Hg-binding proteins were identified using LC‒MS/MS, which showed characteristics of mercury exposure biomarkers for important metabolic functions, such as five parvalbumin isoforms, triosephosphate isomerase, cofilin 2 (muscle), and fructose-bisphosphate aldolases.

Investigation of Protein Biomarkers and Oxidative Stress in Pinirampus pirinampu Exposed to Mercury Species from the Madeira River, Amazon-Brazil

In recent decades, the scientific community has widely debated the contamination of fish in the Amazon region by mercury species. As the diet of riverside populations in the Amazon region is based mainly on fish, these populations are exposed to mercurial species that can cause serious and irreversible damage to their health. The risks of consuming fish exposed to mercurial species in the Amazon region have motivated toxicological investigations. However, the effect of mercurial species on protein and enzyme levels is still controversial. In this work, analytical and bioanalytical techniques Two-dimensional polyacrylamide gel electrophoresis [2D-PAGE] Graphite Furnace Atomic Absorption Spectrometry [GFAAS], and Mass Spectrometry in Sequence with Electrospray Ionization [ESI-MS/MS] were used to identify proteins associated with mercury (metal-binding protein) in muscle and liver tissues of the fish species Pinirampus pirinampu from the Madeira River, in the Brazilian Amazon. Enzymatic and lipid peroxidation analyses were also used to assess changes related to oxidative stress. Determinations of total mercury by GFAAS indicated higher concentrations in liver tissue (555 ± 19.0 µg kg^-1) when compared to muscle tissue (60 ± 2.0 µg kg^-1). The fractionation process of tissue proteomes by 2D-PAGE and subsequent mapping of mercury by GFAAS in the protein spots of the gels identified the presence of mercury in three spots of the liver tissue (concentrations in the range of 0.800 to 1.90 mg kg^-1). The characterization of protein spots associated with mercury by ESI-MS/MS identified the enzymes triosephosphate isomerase A, adenylate kinase 2 mitochondrial, and glyceraldehyde-3-phosphate dehydrogenase as possible candidates for mercury exposure biomarkers. The muscle tissue did not show protein spots associated with mercury. Enzymatic activity decreased proportionally to the increase in mercury concentrations in the tissues.

Metalloproteomic Strategies for Identifying Proteins as Biomarkers of Mercury Exposure in Serrasalmus rhombeus from the Amazon Region

This manuscript describes the results of a metalloproteomic study of mercury in samples of muscle and liver tissue of the species Serrasalmus rhombeus, popularly known as black piranha and characterised as the most voracious and aggressive predator in the Brazilian Amazon. The metalloproteomic study involved using two-dimensional electrophoresis (2D PAGE) to fractionate the proteome of the muscle and liver tissue samples, along with atomic absorption spectrometry in a graphite furnace (GFAAS) to identify mercury associated with protein SPOTs and mass spectrometry with electrospray ionisation (ESI-MS/MS) to characterise the mercury-binding proteins. The protein SPOTs characterised showed concentrations in the order of 156 mg kg^-1, which ranks as the highest concentrations of mercury determined so far in metalloproteomic studies involving fish species in the Amazon region. Based on FASTA sequences of proteins characterised by ESI-MS/MS, bioinformatics studies were performed that allowed identifying nine proteins with characteristics of biomarkers of mercury exposure. Of those proteins, glutathione peroxidase stands out as an enzyme of great importance in the antioxidant defence of organisms subjected to oxidative stress caused by xenobiotics.

Characterization of the mercury-binding proteins in tuna and salmon sashimi: Implications for health risk of mercury in food

Fish consumption is one of the major ways through which humans receive exposure to mercury (Hg). The existing forms of Hg in food, particularly Hg bound to proteins, may affect the absorption of Hg by humans and subsequently its potentially toxic effects. However, the knowledge regarding Hg-binding proteins in edible fish muscle is scarce. In the present study, salmon and tuna fish muscles, collected from seven different regions and countries, were analyzed using metallomics- and proteomics-based techniques. The concentration of Hg in sashimi samples ranged from 4.4 to 317.4 ng/g. Size exclusion chromatography (SEC) coupled with inductively coupled plasma mass spectrometer (ICP-MS) showed that beta-actin was a novel Hg-binding protein from the fish muscles, and this protein could also bind bismuth (Bi), silver (Ag), and copper (Cu). Hg bound to beta-actin accounted for approximately 30.2-37.6% of the total Hg in the tuna muscles and was significantly correlated to total Hg in the fish muscles (r = 0.98, p < 0.01) and in the fraction of soluble proteins (r = 0.94, p < 0.01). These findings suggest that proteins act as the main Hg accumulation sites in edible fish; thus, increasing human exposure to Hg following gastrointestinal digestion.

Parvalbumin and Ubiquitin as Potential Biomarkers of Mercury Contamination of Amazonian Brazilian Fish

Recent studies have demonstrated the association of mercury (Hg) with some fish proteins, milk, and hair from individuals exposed to the element in the Amazon. However, few studies involve identifying biomarkers of mercury exposure. Therefore, the present study aimed to identify potential biomarkers of Hg exposure in fish. For this, the muscular tissues of two species of fish (Prochilodus lineatus and Mylossoma duriventre) that feed the Amazonian human population were analyzed. Through the analyses obtained by graphite furnace atomic absorption spectrometry (GFAAS), it was possible to identify four protein SPOTS where mercury was present. These SPOTS, identified by mass spectrometry (ESI-MS/MS), included parvalbumin and ubiquitin-40S ribosomal protein S27a, and these being metalloproteins with biomarker characteristics. In addition, the results show the intense Hg/protein ratio observed in the two proteins, which makes metalloproteins strong candidates for biomarkers of mercury exposure. Graphical Abstract.

Metalloproteomic approach of mercury-binding proteins in liver and kidney tissues of Plagioscion squamosissimus (corvina) and Colossoma macropomum (tambaqui) from Amazon region: Possible identification of mercury contamination biomarkers

Fish is an important source of protein, vitamins, and minerals. However, this food is also a major source of human exposure to toxic contaminants such as mercury. Thus, this paper aimed to evaluate mercury-binding proteins for possible application as biomarkers of mercury contamination in hepatic and renal tissues of Plagioscion squamosissimus (carnivorous fish) and Colossoma macropomum (omnivorous fish) from the Amazon region using metalloproteomic approach. The proteome of hepatic and renal tissues of fish species was separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), and the mercury concentrations in protein spots were determined by graphite furnace atomic absorption spectrometry (GFAAS). Finally, the protein spots associated to mercury were characterized by electrospray ionization mass spectrometry (ESI-MS/MS). The activity of antioxidant enzymes (SOD, CAT, GPx, and GST) and lipid peroxidation (LPO) were also determined. The results showed that the highest concentrations of mercury were found in the carnivorous species (P. squamosissimus) and that the accumulation pattern of this metal was higher in hepatic tissues than in renal tissues for both species. A tendency was observed for greater enzymatic activity in the hepatic and renal tissues of P. squamosissimus, the species with the highest concentration of mercury. Only GPx activity in the kidney and GST in the liver were lower for the P. squamosissimus species, and this finding can be explained by the interaction of mercury with these enzymes. The data obtained by ESI-MS/MS allowed for the characterization of the protein spots associated to mercury, revealing proteins involved in energy metabolism, biomolecules transport, protein synthesis and degradation, cell differentiation, gene regulation, and the antioxidant system. The results obtained in the present study can contribute to understanding the physiological processes underlying mercury toxicity and have provided new perspectives on possible candidates for mercury contamination biomarkers in fish.

Physiological and functional aspects of metal-binding protein associated with mercury in the liver tissue of pirarucu (Arapaima gigas) from the Brazilian Amazon

High concentrations of mercury found in soils, sediments, fish, and humans of the Amazon region have gained prominence in scientific studies during the last decade. However, studies related to the elucidation of mercury toxicity mechanisms in ichthyofauna at the molecular and metallomic levels that seek to elucidate physiological and functional aspects, as well as the search for biomarkers of mercury exposure, are still sparse. In the search for these answers, the present study analyzed the hepatic tissue proteome of the Arapaima gigas (pirarucu) fish species collected in the Jirau hydroelectric power plant reservoir in the state of Rondônia state, Brazil, in order to identify mercury-related metal-binding proteins and to elucidate their physiological and functional aspects. The proteomic profile of the hepatic tissue of Arapaima gigas was obtained by two-dimensional electrophoresis (2D-PAGE) and the presence of mercury was mapped in the protein SPOTS by graphite furnace atomic absorption spectrometry(GFAAS). Mercury was detected in 18 protein SPOTS with concentrations ranging from 0.13 ± 0.003 to 131.00 ± 3 mg kg^-1. The characterization of the protein SPOTS associated with mercury was performed by electrospray ionisation tandem mass spectrometry (ESI-MS/MS), and 10 proteins were identified. Bioinformatics analyses showed that most of the proteins found linked to mercury were involved in cellular component processes and biological processes. For the most part, protein sequences have cellular functions comprising catalytic, binding, sense of localization, and metabolic processes.

Study of proteins with mercury in fish from the Amazon region

The high concentrations of mercury found in Amazon have been intensively studied by the scientific community in the last decades. These mercurial species bind preferentially to proteins. Therefore, this work proposal sought to obtain the fractionation, identification and study of mercury - bound proteins present in samples of muscular and hepatic tissue from fish collected in the reservoir of the Jirau Hydroelectric Power Plant - on the Madeira River. Two-dimensional electrophoresis (2D-PAGE) for protein fractionation, graphite furnace atomic absorption spectrometry (GFAAS) for the quantification of mercury and Mass Spectrometry (ESI-MS/MS) were used for the identification of proteins. Concluding the work with analysis of graphics from the Blast2go program. Two mercury - bound proteins were identified as triosephosphate isomerase A and Protein FAM45A. The data generated by the bioinformatics programs confirm the tendency of these proteins to be linked to mercury and elucity the possibles existing physiological and cellular interactions.

Proteomic analysis of the fast-twitch muscle of pacu (Piaractus mesopotamicus) after prolonged fasting and compensatory growth

Protocols that improve growth performance in fish while assuring product quality are important for aquaculture. Fasting followed by refeeding may promote compensatory growth, thus optimizing growth performance. During fasting and refeeding, fast-twitch muscle, which comprises most of fish fillet, undergoes intense plasticity. In this work, we studied the proteome of pacu (Piaractus mesopotamicus) fast-twitch muscle after 30 days of fasting (D30), 30 days of refeeding (D60) and 60 days of refeeding (D90) with two-dimensional electrophoresis, mass spectrometry and bioinformatics. Body mass, growth rate and muscle histology were also assessed. At D30, fish presented muscle catabolism and decreased growth. Proteomic analysis showed that metabolism proteins were the most affected, up and downregulated. Cytoskeleton and amino acid biosynthesis proteins were downregulated, while nuclear and regulatory proteins were upregulated. At D60, fish showed accelerated growth, despite the body mass not completely recovering. Metabolism proteins were still the most affected. Amino acid biosynthesis proteins became upregulated, while cytoskeleton proteins remained downregulated. At D90, the fish presented total compensatory growth. Many metabolic proteins were up or downregulated. Few cytoskeleton proteins remained differentially expressed. Amino acid biosynthesis proteins were mostly upregulated, but less than at D60. Prolonged fasting followed by refeeding also led to the regulation of possible meat quality biomarkers, such as antioxidant enzymes. This fact suggests possible consequences of this protocol on fish meat quality. Our work also enriches our knowledge on proteomic changes during muscle plasticity that occur during fasting and refeeding diet protocols.