A brain proteome profile in rats exposed to methylmercury or thimerosal (ethylmercury).

Exposure to organomercurials has been associated with harmful effects on the central nervous system (CNS). However, the mechanisms underlying organomercurial-mediated neurotoxic effects need to be elucidated. Exposure to toxic elements may promote cellular modifications such as alterations in protein synthesis in an attempt to protect tissues and organs from damage. In this context, the use of a "proteomic profile" is an important tool to identify potential early biomarkers or targets indicative of neurotoxicity. The aim of this study was to investigate potential modifications in rat cerebral cell proteome following exposure to methylmercury (MeHg) or ethylmercury (EtHg). For MeHg exposure, animals were administered by gavage daily 140 µg/kg/d of Hg (as MeHg) for 60 d and sacrificed 24 h after the last treatment. For EtHg exposure, 800 µg/kg/d of Hg (as EtHg) was given intramuscularly (im) in a single dose and rats were sacrificed after 4 h. Control groups received saline either by gavage or im. After extraction of proteins from whole brain samples and separation by two-dimensional electrophoresis (2-DE), 26 differentially expressed proteins were identified from exposed animals by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF/TOF). Both MeHg and EtHg exposure induced an overexpression of calbindin, a protein that acts as a neuroprotective agent by (1) adjusting the concentration of Ca(2+) within cells and preventing neurodegenerative diseases and (2) decreasing expression of glutamine synthetase, a crucial protein involved in regulation of glutamate concentration in synaptic cleft. In contrast, expression of superoxide dismutase (SOD), a protein involved in antioxidant defense, was elevated in brain of MeHg-exposed animals. Taken together, our data provide new valuable information on the possible molecular mechanisms associated with MeHg- and EtHg-mediated toxicity in cerebral tissue. These observed protein alterations may be considered as biomarkers candidates for biological monitoring of organomercurial poisoning.

Genetic Effects of eNOS Polymorphisms on Biomarkers Related to Cardiovascular Status in a Population Coexposed to Methylmercury and Lead.

The aim of the present study was to evaluate possible effects of endothelial nitric oxide synthase (eNOS) polymorphisms on systolic (SBP) and diastolic blood pressure (DBP) and on nitrite levels in plasma (NitP) in a population coexposed to methylhemoglobin (MeHg) and lead (Pb) in the Amazonian region, Brazil. Plasmatic levels of hemoglobin Hg (HgP) and Pb (PbP) were determined by inductively coupled plasma-mass spectrometry, whereas NitP were quantified by chemiluminescence. Genotyping was performed by conventional and restriction fragment length polymorphism-polymerase chain reaction assay. The population age ranged from 18 to 87 years (mean 40 ± 16), and the distribution between the sexes was homogenous (63 men and 50 women). Mean HgP and PbP were 7.1 ± 6.1 and 1.1 ± 1.1 µg L(-1), respectively. PbP was correlated to SBP and DBP, whereas no effects were observed for HgP on blood pressure. Subjects carrying the 4b allele in intron 4 presented greater SBP and DBP compared with those who had the 4a4a genotype. In addition, interactions between alcohol consumption and the -786 T/C polymorphism were observed on NitP, i.e., individuals carrying the polymorphic allele and drinkers had lower NitP. Taken together, our data give new insights concerning the genetic effects of eNOS polymorphisms on biomarkers related to cardiovascular status in populations coexposed to Hg and Pb.

Polymorphisms in glutathione-related genes modify mercury concentrations and antioxidant status in subjects environmentally exposed to methylmercury.

Methylmercury (MeHg) toxicity may vary widely despite similar levels of exposure. This is hypothetically related to genetic differences in enzymes metabolizing MeHg. MeHg causes oxidative stress in experimental models but little is known about its effects on humans. The aims of the present study was to evaluate the effects of polymorphisms in glutathione (GSH)-related genes (GSTM1, GSTT1, GSTP1 and GCLM) on Hg concentrations in blood and hair, as well as MeHg-related effects on catalase (CAT) and glutathione-peroxidase (GPx) activity and GSH concentrations. Study subjects were from an Amazonian population in Brazil chronically exposed to MeHg from fish. Hg in blood and hair were determined by ICP-MS, CAT, GPx and GSH were determined by spectrophotometry, and multiplex PCR (GSTM1 and GSTT1) and TaqMan assays (GSTP1 and GCLM) were used for genotyping. Mean Hg concentrations in blood and hair were 48±36 µg/L and 14±10 µg/g. Persons with the GCLM-588 TT genotype had lower blood and hair Hg than did C-allele carriers (linear regression for Hg in blood ß=-0.32, p=0.017; and hair ß=-0.33; p=0.0090; adjusted for fish intake, age and gender). GSTM1*0 homozygous had higher blood (ß=0.20; p=0.017) and hair Hg (hair ß=0.20; p=0.013). Exposure to MeHg altered antioxidant status (CAT: ß=-0.086; GSH: ß=-0.12; GPx: ß=-0.16; all p<0.010; adjusted for gender, age and smoking). Persons with GSTM1*0 had higher CAT activity in the blood than those with GSTM1. Our data thus indicate that some GSH-related polymorphisms, such as GSTM1 and GCLM may modify MeHg metabolism and Hg-related antioxidant effects.

Evaluation of glutathione S-transferase GSTM1 and GSTT1 polymorphisms and methylmercury metabolism in an exposed Amazon population.

Over the last decades, the presence of methylmercury (MeHg) in the Amazon region of Brazil and its adverse human health effects have given rise to much concern. The biotransformation of MeHg occurs mainly through glutathione (GSH) in the bile mediated by conjugation with glutathione S-transferases (GST). Epidemiological evidence has shown that genetic polymorphisms may affect the metabolism of MeHg. The aim of this study was to evaluate the association between GST polymorphisms, GSH, and Hg levels in blood (B-Hg) and in hair (H-Hg) of an Amazon population chronically exposed to the metal through fish consumption. Blood and hair samples were collected from 144 volunteers (71 men, 73 women). B-Hg and H-Hg levels were determined by inductively coupled plasma-mass spectrometry, and GSH levels were evaluated by a spectrophotometric method. GSTM1 and T1 genotyping evaluation were carried out by multiplex polymerase chain reaction (PCR). Mean levels of B-Hg and H-Hg were 37.7 ± 24.5 µg/L and 10.4 ± 7.4 µg/g, respectively; GSH concentrations ranged from 0.52 to 2.89 µM/ml of total blood. Distributions for GSTM1/T1, GSTM1/GSTT1*0, GSTM1*0/T1, and GSTM1*0/GSTT1*0 genotypes were 35.4, 22.2, 25.0, and 17.4%, respectively. GSTT1 genotype carriers presented lower levels of B-Hg and H-Hg when compared to other genotypes carriers. In addition, GSTM1*0/GSTT1*0 individuals presented higher Hg levels in blood and hair than subjects presenting any other genotypes. There appeared to be no evidence of an effect of polymorphisms on GSH levels. Therefore, our data suggest that GST polymorphisms may be associated with MeHg detoxification.

Intron 4 polymorphism of the endothelial nitric oxide synthase (eNOS) gene is associated with decreased NO production in a mercury-exposed population.

Nitric oxide (NO), produced by endothelial nitric oxide synthase (eNOS), is a potent vasodilator and plays a prominent role in regulating the cardiovascular system. Decreased basal NO release may predispose to cardiovascular diseases. Evidence suggests that the 27 nt repeat polymorphism of the intron 4 in the eNOS gene may regulate eNOS expression. On the other hand, some recent reports strongly suggest an association between methylmercury (MeHg) exposures and altered NO synthesis. In the present study, we investigate the contribution of the 27-pb tandem repeat polymorphism on nitric oxide production, which could enhance susceptibility to cardiovascular disease in the MeHg-exposed study population. Two-hundred-two participants (98 men and 104 women), all chronically exposed to MeHg through fish consumption were examined. Mean blood Hg concentration and nitrite plasma concentration were 50.5 ± 35.4 µg/L and 251.4 ± 106.3n M, respectively. Mean systolic and diastolic blood pressure were 120.1 ± 19.4mm Hg and 72.0 ± 10.6mm Hg, respectively. Mean body mass index was 24.5 ± 4.3 kg/m(2) and the mean heart rate was 69.8 ± 11.8 bpm. There were no significant differences in age, arterial blood pressure, body mass index or cardiac frequency between genotype groups (all P>0.05). However, we observed different nitrite concentrations in the genotypes groups, with lower nitrite levels for the 4a4a genotype carriers. Age, gender and the presence of intron 4 polymorphism contributed to nitrite reduction as a result of blood Hg concentration. Taken together, our results show that the 27 nt repeat polymorphism of the intron 4 in the eNOS gene increases susceptibility to cardiovascular diseases after MeHg exposure by modulating nitric oxide levels.

Determination of the effects of eNOS gene polymorphisms (T-786C and Glu298Asp) on nitric oxide levels in a methylmercury-exposed population.

Nitric oxide (NO) is a potent vasodilator with multiple protective effects involved in the regulation of cardiovascular functions. Endothelial NO synthase (eNOS) gene polymorphisms and environmental factors, such as mercury (Hg) exposure, may influence NO levels and increase the risk of cardiovascular damage. The aim of this study was to determine the role of the T-786C and Glu298Asp polymorphisms of the eNOS gene on nitrite concentrations following Hg exposure in humans. It was postulated that Hg exposure might decrease circulating nitrite concentrations and that variants in the eNOS gene might enhance the adverse effects of Hg resulting in increased risk of cardiovascular disease. Blood samples were collected from 202 volunteers exposed to methylmercury (MeHg) following fish consumption. Blood Hg concentrations (BHg) were determined by inductively coupled plasma-mass spectrometry and nitrite plasma concentration by a chemiluminescent method. The mean Hg concentration was 50.5 ± 35.4 µg/L and mean nitrite concentration was 251.4 ± 106.3 nM. There were no significant differences in age, arterial blood pressure, body mass index, heart rate, and concentrations of Hg and nitrite concentrations between the genotype groups . When data were grouped together (TC + CC and TT group), there were still no marked differences. A multiple regression model indicated that decreased NO production was predominantly due to Hg, age, and gender. Polymorphisms did not seem to influence this effect. Our findings suggest that eNOS gene polymorphisms (T-786C and Glu298Asp) are not associated with an increased risk for cardiovascular diseases in MeHg-exposed subjects.

Environmental exposure to methylmercury is associated with a decrease in nitric oxide production.

Some studies have recently suggested that mercury (Hg)-exposed populations face increased risks of cardiovascular diseases, and experimental data indicate that such risks might be due to reductions in nitric oxide bioavailability. However, no previous study has examined whether Hg exposure affects plasma nitrite concentrations in humans as an indication of nitric oxide production. Here, we investigated whether there is an association between circulating nitrite and Hg concentrations in whole blood, plasma and hair from an exposed methylmercury (MeHg) population. Hair and blood samples were collected from 238 persons exposed to MeHg from fish consumption. Hg concentrations in plasma (PHg), whole blood (BHg) and hair Hg (HHg) were determined by inductively coupled plasma-mass spectrometry. Mean BHg content was 49.8 +/- 35.2 microg/l, mean PHg was 7.8 +/- 6.9 microg/l and HHg 14.6 +/- 10.6 microg/g. Mean plasma nitrite concentration was 253.2 +/- 105.5 nM. No association was found between plasma nitrite concentration and BHg or HHg concentrations in a univariate model. However, multiple regression models adjusted for gender, age and fish consumption showed a significant association between plasma nitrite and plasma Hg concentration (beta = -0.1, p < 0.001). Our findings constitute preliminary clinical evidence that exposure to MeHg may cause inhibitory effects on the production of endothelial nitric oxide.