The influence of methylmercury on the nitric oxide production of alveolar macrophages

Changes in the renal function after acute mercuric chloride exposure in the rat are associated with renal vascular endothelial dysfunction and proximal tubule NHE3 inhibition

Mercury is an environmental pollutant and a threat to human health. Mercuric chloride (HgCl₂)-induced acute renal failure has been described by several reports, but the mechanisms of renal dysfunction remain elusive. This study tested the hypothesis that HgCl₂ directly impairs renal vascular reactivity. Additionally, due to the mercury toxicity on the proximal tubule, we investigated whether the HgCl₂-induced natriuresis is accompanied by inhibition of Na⁺/H⁺ exchanger isoform-3 (NHE3). We found that 90-min HgCl₂ infusion (6.5 μg/kg i.v.) remarkably increased urinary output, reduced GFR and renal blood flow, and increased vascular resistance in rats. "In vitro" experiments of HgCl₂ infusion in isolated renal vascular bed demonstrated an elevation of perfusion pressure in a concentration- and time-dependent manner, associated with changes on the endothelium-dependent vasodilatation and the flow-pressure relationship. Moreover, by employing "in vivo" stationary microperfusion of the proximal tubule, we found that HgCl₂ inhibits NHE3 activity and increases the phosphorylation of NHE3 at serine 552 in the renal cortex, in line with the HgCl₂-induced diuresis. Changes in renal proximal tubular function induced by HgCl₂ were parallel to increased urinary markers of proximal tubular injury. Besides, atomic spectrometry showed that mercury accumulated in the renal cortex. We conclude that acute HgCl₂ exposure causes renal vasoconstriction that is associated with reduced endothelial vasodilator agonist- and flow-mediated responses and inhibition of NHE3-mediated sodium reabsorption. Thus, our data suggest that HgCl₂-induced acute renal failure may be attributable at least in part by its direct effects on renal hemodynamics and NHE3 activity.

A Hypothesis and Evidence That Mercury May be an Etiological Factor in Alzheimer's Disease

Mercury is one of the most toxic elements and causes a multitude of health problems. It is ten times more toxic to neurons than lead. This study was created to determine if mercury could be causing Alzheimer's disease (AD) by cross referencing the effects of mercury with 70 factors associated with AD. The results found that all these factors could be attributed to mercury. The hallmark changes in AD include plaques, beta amyloid protein, neurofibrillary tangles, phosphorylated tau protein, and memory loss-all changes that can be caused by mercury. Neurotransmitters such as acetylcholine, serotonin, dopamine, glutamate, and norepinephrine are inhibited in patients with Alzheimer's disease, with the same inhibition occurring in mercury toxicity. Enzyme dysfunction in patients with Alzheimer's disease include BACE 1, gamma secretase, cyclooxygenase-2, cytochrome-c-oxidase, protein kinases, monoamine oxidase, nitric oxide synthetase, acetyl choline transferase, and caspases, all which can be explained by mercury toxicity. Immune and inflammatory responses seen in patients with Alzheimer's disease also occur when cells are exposed to mercury, including complement activation, cytokine expression, production of glial fibrillary acid protein antibodies and interleukin-1, transforming growth factor, beta 2 microglobulins, and phosphodiesterase 4 stimulation. Genetic factors in patients with Alzheimer's disease are also associated with mercury. Apolipoprotein E 4 allele increases the toxicity of mercury. Mercury can inhibit DNA synthesis in the hippocampus, and has been associated with genetic mutations of presenilin 1 and 2, found in AD. The abnormalities of minerals and vitamins, specifically aluminum, calcium, copper, iron, magnesium, selenium, zinc, and vitamins B1, B12, E, and C, that occur in patients with Alzheimer's disease, also occur in mercury toxicity. Aluminum has been found to increase mercury's toxicity. Likewise, similar biochemical factors in AD are affected by mercury, including changes in blood levels of homocysteine, arachidonic acid, DHEA sulfate, glutathione, hydrogen peroxide, glycosamine glycans, acetyl-L carnitine, melatonin, and HDL. Other factors seen in Alzheimer's disease, such as increased platelet activation, poor odor identification, hypertension, depression, increased incidences of herpes virus and chlamydia infections, also occur in mercury exposure. In addition, patients diagnosed with Alzheimer's disease exhibit higher levels of brain mercury, blood mercury, and tissue mercury in some studies. The greatest exogenous sources of brain mercury come from dental amalgams. Conclusion: This review of the literature strongly suggests that mercury can be a cause of Alzheimer's Disease.

Methylmercury induces oxidative stress and subsequent neural hyperactivity leading to cell death through the p38 MAPK-CREB pathway in differentiated SH-SY5Y cells

Methylmercury (MeHg) induces site-specific cerebrocortical neuronal cell death. In our previous study using an in vivo mouse model, we reported that MeHg-induced cerebrocortical neuronal cell death may be due to neural hyperactivity triggered by activation of kinase pathways. However, the detailed molecular mechanism remained to be completely understood. In this study, we analyzed detailed signaling pathways for MeHg-induced neuronal cell death using all-trans-retinoic acid (RA) differentiated SH-SY5Y cells, which show neuron-like morphological changes and express neuron/synapse markers for cerebrocortical neurons. Time course studies revealed that MeHg-induced upregulation of c-fos, a marker of neural activation, preceded neuronal cell death. These results were similar to those observed in a MeHg-intoxicated mouse model. We observed early expression of the oxidative stress marker thymidine glycol followed by activation of p44/42 mitogen-activated protein kinase (MAPK) and p38 MAPK, and an increase in cAMP response element binding protein (CREB). Investigation of the effects of specific kinase inhibitors revealed that SB203580, a specific inhibitor for p38 MAPK, significantly blocked the upregulation of c-fos and the subsequent neuronal cell death. In contrast, PD98059 and U0126, specific inhibitors for p44/p42 MAPK, showed no effects on MeHg-induced neurotoxicity. Furthermore, the antioxidants Trolox and edaravone significantly suppressed MeHg-induced thymidine glycol expression, p38 MAPK-CREB pathway activation, and neurotoxicity. Altogether, these results suggest that MeHg-induced oxidative stress and subsequent activation of the p38 MAPK-CREB pathway contribute to cerebrocortical neuronal hyperactivity and subsequent neuronal cell death.

Delayed neurochemical effects of prenatal exposure to MeHg in the cerebellum of developing rats

Human fetuses and neonates are particularly vulnerable to methylmercury (MeHg)-induced brain damage and are sensitive even to low exposure levels. Previous work of our group evidence that prenatal exposure to MeHg causes cognitive and behavioral alterations and disrupt hippocampus signaling. The current study aimed to investigate the effect of gestational exposure of rats to MeHg at low doses (1 or 2 mg/kg) on parameters of redox imbalance and key signaling pathways in the cerebellum of their offspring. Pregnant females received MeHg (treated group) or 0.9% saline water (control group) by gavage in alternated days from gestational day 5 (GD5) until parturition and analyzes were proceed in the cerebellum of 30-day-old pups. We found increased lipid peroxidation and protein carbonylation levels as well as decreased SH content in pups prenatally exposed to 2 mg/kg MeHg. In addition, misregulated SOD/catalase activities supported imbalanced redox equilibrium. We found decreased GSK3β(Ser9) phosphorylation, suggesting activation of this enzyme and dephosphorylation/inhibition of ERK1/2 and JNK pathways. Increased PKAα catalytic subunit could be upstream of hyperphosphorylated c-Raf(Ser259) and downregulated MAPK pathway. In addition, we found raised levels of the Ca²⁺-dependent protein phosphatase 2 B (PP2B). We also found preserved immunohistochemical staining for both glial fibrillary acidic protein (GFAP) and NeuN in MeHg-exposed pups. Western blot analysis showed unaltered levels of BAX/BCL-XL, BAD/BCL-2 and active caspase 3. Together, these findings support absence of reactive astrocytes, neuronal damage and apoptotic cell death in the cerebellum of MeHg treated pups. The present study provides evidence that prenatal exposure to MeHg leads to later redox imbalance and disrupted signaling mechanisms in the cerebellum of 30-day-old pups potentially predisposing them to long-lasting neurological impairments in CNS.

Lead hepatotoxicology: a study in an animal model

The increasing use of lead (Pb) for industrial purposes has resulted in the significant increase in environmental contamination of our planet especially in concern to water and food. In this study using the electron scanning microscopy (SEM), the authors showed the effects of this metal as a result of a chronic and cumulative process. As a primary method of detection of Pb in situ, SEM was chosen, coupled with a detection system Noran Voyager of basic microanalysis X-ray (SEM-XRM), with detection system energy dispersive spectrometry. Mice BALB/c was used as a study model. An animal model of inflammation was used, that consisted in the formation of a subcutaneous pocket of air. It was observed that 75% of Pb stock was captured by the liver, the main target organ in the capture of the metal, the kidney was the second organ to capture the Pb stock and the third was the spleen. It was verified that a low deposition of Pb was found in the lungs and the brain. The main results of this study showed how Pb is captured by different organs. We also demonstrated the vulnerability to inflammation of this metal.