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.

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.

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.

Changes in energy metabolism induced by fluoride: Insights from inside the mitochondria

The mechanisms involved in changes in energy metabolism caused by excessive exposure to fluoride (F) are not completely understood. The present study employed proteomic tools to investigate the molecular mechanisms underlying the dose- and time-dependency of the effects of F in the rat liver mitochondria. Thirty-six male Wistar rats received water containing 0, 15 or 50 mgF/L (as NaF) for 20 or 60 days. Rat liver mitochondria were isolated and the proteome profiles were examined using label-free quantitative nLC-MS/MS. PLGS software was used to detect changes in protein expression among the different groups. The bioinformatics analysis was done using the software CYTOSCAPE^® 3.0.7 (Java^®) with the aid of ClueGo plugin. The dose of 15 mgF/L, when administered for 20 days, reduced glycolysis, which was counterbalanced by an increase in other energetic pathways. At 60 days, however, an increase in all energy pathways was observed. On the other hand, the dose of 50 mgF/L, when administered for 20 days, reduced the enzymes involved in all energetic pathways, indicating a lower rate of energy production, with less generation of ROS and consequent reduction of antioxidant enzymes. However, when the 50 mgF/L dose was administered for 60 days, an increase in energy metabolism was seen but in general no changes were observed in the antioxidant enzymes. Except for the group treated with 50 mgF/L for 20 days, all the other groups had alterations in proteins in attempt to maintain calcium homeostasis and avoid apoptosis. The results suggest that the organism seems to adapt to the effects of F over time, activating pathways to reduce the toxicity of this ion. Ultimately, our findings corroborate the safety of the use of fluoride for caries control.

Proposed mechanism for understanding the dose- and time-dependency of the effects of fluoride in the liver

Fluoride (F) can induce changes in the expression of several liver proteins. It is suggested that these changes are dose- and time-dependent. The objective of this study was to analyze the effect of different F concentrations and exposure times to this ion on the pattern of protein expression in the liver of rats. Thirt-six 21-day-old male Wistar rats were divided into 2 groups (n = 18) according to the treatment duration (20 or 60 days). Each of these groups was then divided into 3 subgroups (n = 6) according to the concentration of F administered in drinking water, as follows: 0 mg/L (control), 15 mg/L or 50 mg/L. After the experiment periods, the animals were anesthetized and the liver and blood were collected. F was analyzed in plasma and liver. Part of the liver was fixed for histological analysis. Liver proteins were extracted and prepared for quantitative label-free mass spectrometry analysis. F concentrations in plasma and liver were significantly higher in the group treated with 50 mg /L in comparison with control, regardless the time of exposure. Histological alterations in the liver were more evident in the subgroups treated for 20 days. The proteomic analysis revealed changes in proteins related to endoplasmic reticulum and mitochondrial oxidative stress, mitochondrial alteration, apoptosis and cellular respiration upon exposure to F. The results reinforce previous findings showing that the effects of F in the liver are dose- and time-dependent and provide the molecular basis for understanding the evolution of these effects.

Fluoride affects bone repair differently in mice models with distinct bone densities

We grouped mice [strains: C57BL/6J (n=32) and C3H/HeJ (n=32)] to address the influence of bone density on fluoride's (F's) biological effects. These animals received low-fluoride food and water containing 0 (control group) or 50ppm of F for up to 28days. The upper left central incisor was extracted, and the left maxilla was collected at 7, 14, 21, and 28days for histological and histomorphometric analysis to estimate bone neoformation. Our results showed bone neoformation in all of the evaluated groups, with the presence of bone islets invading the center of the alveoli when replacing the existing connective tissue. Curiously, this biological phenomenon was more evident in the C57BL/6J strain. The histomorphometric analysis confirmed the histological findings in relation to the amount of new bone tissue and showed a decrease in C3H/HeJ mice (control group). Altogether, our results showed differential effects of fluoride bone metabolism, confirming a genetic component in susceptibility to the effects of fluoride.

Absence of DNA damage in multiple organs (blood, liver, kidney, thyroid gland and urinary bladder) after acute fluoride exposure in rats

Fluoride has been widely used in dentistry as a caries prophylactic agent. However, there has been some speculation that excess fluoride could cause an impact on genome integrity. In the current study, the potential DNA damage associated with exposure to fluoride was assessed in cells of blood, liver, kidney, thyroid gland and urinary bladder by the single cell gel (comet) assay. Male Wistar rats aging 75 days were distributed into seven groups: Groups 1 (control), 2, 3, 4, 5, 6 and 7 received 0 (deionized water), 10, 20, 40, 60, 80 and 100 mgF/Kg body weight from sodium fluoride (NaF), respectively, by gastrogavage. These groups were killed at 2 h after the administration of the fluoride doses. The level of DNA strand breaks did not increase in all organs evaluated and at all doses of NaF tested, as depicted by the mean tail moment. Taken together, our results suggest that oral exposure to NaF did not result in systemic genotoxic effect in multiple organs related to fluoride toxicity. Since DNA damage is an important step in events leading to carcinogenesis, this study represents a relevant contribution to the correct evaluation of the potential health risk associated with chemical exposure. Human & Experimental Toxicology ( 2007) 26, 435—440