Neurological changes in cats following long-term diet of mercury contaminated tuna

Mercury-induced toxicity: Mechanisms, molecular pathways, and gene regulation

Mercury is a well-known neurotoxicant for humans and wildlife. The epidemic of mercury poisoning in Japan has clearly demonstrated that chronic exposure to methylmercury (MeHg) results in serious neurological damage to the cerebral and cerebellar cortex, leading to the dysfunction of the central nervous system (CNS), especially in infants exposed to MeHg in utero. The occurrences of poisoning have caused a wide public concern regarding the health risk emanating from MeHg exposure; particularly those eating large amounts of fish may experience the low-level and long-term exposure. There is growing evidence that MeHg at environmentally relevant concentrations can affect the health of biota in the ecosystem. Although extensive in vivo and in vitro studies have demonstrated that the disruption of redox homeostasis and microtube assembly is mainly responsible for mercurial toxicity leading to adverse health outcomes, it is still unclear whether we could quantitively determine the occurrence of interaction between mercurial and thiols and/or selenols groups of proteins linked directly to outcomes, especially at very low levels of exposure. Furthermore, intracellular calcium homeostasis, cytoskeleton, mitochondrial function, oxidative stress, neurotransmitter release, and DNA methylation may be the targets of mercury compounds; however, the primary targets associated with the adverse outcomes remain to be elucidated. Considering these knowledge gaps, in this article, we conducted a comprehensive review of mercurial toxicity, focusing mainly on the mechanism, and genes/proteins expression. We speculated that comprehensive analyses of transcriptomics, proteomics, and metabolomics could enhance interpretation of "omics" profiles, which may reveal specific biomarkers obviously correlated with specific pathways that mediate selective neurotoxicity.

Pets, Genuine Tools of Environmental Pollutant Detection

In a shared environment, our companion animals became unintended sentinels for pollutant exposure consequences, developing even earlier similar conditions to humans. This review focused on the human-pet cohabitation in an environment we all share. Alongside other species, canine and feline companions are veritable models in human medical research. The latency period for showing chronic exposure effects to pollutants is just a few years in them, compared to considerably more, decades in humans. Comparing the serum values of people and their companion animals can, for example, indicate the degree of poisonous lead load we are exposed to and of other substances as well. We can find 2.4 times higher perfluorochemicals from stain- and grease-proof coatings in canine companions, 23 times higher values of flame retardants in cats, and 5 times more mercury compared to the average levels tested in humans. All these represent early warning signals. Taking these into account, together with the animal welfare orientation of today's society, finding non-invasive methods to detect the degree of environmental pollution in our animals becomes paramount, alongside the need to raise awareness of the risks carried by certain chemicals we knowingly use.

Mercury concentration in the tissues of the Eurasian otter: a seasonal dependance in Slovakia

The river otter is considered to be an important bioindicator of water clarity. This study focuses on mercury contamination within this species. Throughout the study, individuals from habitats in the foothills and surroundings of the Liptovská Mara reservoir were analyzed. Twenty-three samples of liver tissue, and twenty-two samples of hair and kidney tissue were collected. Of these samples, the average mercury concentration detected in tissues was 10.6 mg/kg in guard hairs; 12.9 mg/kg in under hairs; 3.3 mg/kg in kidney tissue; and 4.3 mg/kg in liver tissue. Analysis of certified reference material (ERM-BB186-Pig Kidney) was used to assist in the development of an accurate method for total mercury determination in animal tissues, to check the quality of measurements, and to validate the measurement method. Our method represented a high average percentage of recovery (> 95%) in the standard reference material matrix and a relative standard deviation (RSD) of 5% or less. Seasonality was determined to be a significant factor influencing the level of contamination of a given individual, both through mercury methylation within the aquatic environment and through fish ingestion by this apex semi-aquatic predator (guard hairs (p = 0.01); underfur (p = 0.04); kidney (p = 0.03); liver (p = 0.03)). Sex, location, and body size were not found to have a significant influence on heavy metal concentrations in river otters sampled in terms of season.

Nutritional Evaluation and Risk Assessment of the Exposure to Essential and Toxic Elements in Dogs and Cats through the Consumption of Pelleted Dry Food: How Important Is the Quality of the Feed?

Dry feed for pets lacks specific legislation regarding maximum residue limits for inorganic elements. The aim of the present study was to determine the content of 43 inorganic elements in dog and cat feed, studying whether there were differences according to the supposed quality of the food and performing the risk assessment for health. Thirty-one and thirty packages of pelleted dry food for cats and dogs, respectively, were analyzed. After acidic microwave-assisted digestion, elements were detected and quantified by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). In general, we did not observe important differences in the content of elements according to the supposed quality of the brand. Among trace elements, selenium and manganese are above the dietary reference value. Arsenic and mercury showed the highest acute hazard indexes, which make them risk factors for the health of dogs and cats. Aluminum, uranium, antimony and vanadium contents were above the toxic reference value and showed the highest acute hazard indexes. It is necessary to improve the legislation regarding the food safety of pets, for their health and to protect the rights of consumers.

What is in commercial cat and dog food? The case for mercury and ingredient testing

Commercial pet foods should be safe for long-term feeding. However, recent recalls and lawsuits have eroded public trust in pet food companies and products. Recent studies have identified high concentrations of mercury, a potent neurotoxin, in pet food products. Here we posit that pet food products require independent testing to verify safety and compliance with developed Food and Drug Administration and Association of American Feed Control Officials standards, and initiate a discussion as to why including quantification of mercury and methylmercury, as well as the identification of adulteration, are important to such testing protocols. The outcomes of these discussions will be multi-faceted: initiating the impetus to investigate the quality and label accuracy of pet foods; ensuring product safety; promoting transparency within the pet food industry; informing veterinary practices regarding pet food recommendations; providing data for evidence-based policy and regulatory enforcement; and working toward fulfilling the National Research Council's call for research that identifies levels of contaminants in animal feeds and residues in human foods.

Immunotoxicity of mercury: Pathological and toxicological effects

Mercury (Hg) is toxic and hazardous metal that causes natural disasters in the earth's crust. Exposure to Hg occurs via various routes; like oral (fish), inhalation, dental amalgams, and skin from cosmetics. In this review, we have discussed the sources of Hg and its potential for causing toxicity in humans. In addition, we also review its bio-chemical cycling in the environment; its systemic, immunotoxic, genotoxic/carcinogenic, and teratogenic health effects; and the dietary influences; as well as the important considerations in risk assessment and management of Hg poisoning have been discussed in detail. Many harmful outcomes have been reported, which will provide more awareness.

Mercury in bats from the northeastern United States

This study examines mercury exposure in bats across the northeast U.S. from 2005 to 2009. We collected 1,481 fur and 681 blood samples from 8 states and analyzed them for total Hg. A subset (n = 20) are also analyzed for methylmercury (MeHg). Ten species of bats from the northeast U.S. are represented in this study of which two are protected by the Endangered Species Act (ESA 1973) and two other species are pending review. There are four objectives in this paper: (1) to examine correlates to differences in fur-Hg levels among all of the sampling sites, including age, sex, species, and presence of a Hg point source; (2) define the relationship between blood and fur-Hg levels and the factors that influence that relationship including age, sex, species, reproductive status, and energetic condition; (3) determine the relationships between total Hg and MeHg in five common eastern bat species; and (4) assess the distribution of Hg across bat populations in the northeast. We found total blood and fur mercury was eight times higher in bats captured near point sources compared to nonpoint sources. Blood-Hg and fur-Hg were well correlated with females on average accumulating two times more Hg in fur than males. On average fur MeHg accounted for 86 % (range 71-95 %) of the total Hg in bat fur. Considering that females had high Hg concentrations, beyond that of established levels of concern, suggests there could be negative implications for bat populations from high Hg exposure since Hg is readily transferred to pups via breast milk. Bats provide an integral part of the ecosystem and their protection is considered to be of high priority. More research is needed to determine if Hg is a stressor that is negatively impacting bat populations.

Inorganic mercury exposure in prairie voles (Microtus ochrogaster) alters the expression of toll-like receptor 4 and activates inflammatory pathways in the liver in a sex-specific manner

Environmental exposure to mercury can cause a number of adverse effects in humans including the disruption of endocrine function that may result in sex-specific effects. The present study was designed to characterize sex-specific effects of chronic inorganic mercury exposure on toll-like receptor (TLR) 2 and TLR4 and inflammatory signaling in the liver of prairie voles (Microtus ochrogaster). Following 10 weeks of exposure to mercury via drinking water, effects on protein expression levels of TLR2 and TLR4 and the downstream p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor-kappa (NF-κB) signaling pathways were assessed. Using immunoblot analysis, we found that mercury exposure significantly enhanced the expression of TLR4 and activated p38 MAPK and NF-κB pathways in vole livers. This is the first report indicating that TLR4 may serve as a sensor for chronic mercury exposure in the liver. Further, compared to females, mercury-treated male voles exhibited significant increases in activated p38 MAPK and a greater extent of liver damage. Together, these findings establish sex-specific liver immunomodulation and cellular signaling following chronic inorganic mercury exposure. Furthermore, this study also supports the use of voles as biomarkers of environmental mercury contamination and offers a promising in vivo tool to test various therapeutic strategies for mercury detoxification.

Total mercury and methylmercury residues in river otters (Lutra canadensis) from Wisconsin

The Wisconsin Department of Natural Resources (WDNR) collected trapper-caught river otter (Lutra canadensis) from 3 distinct areas of Wisconsin (north, central, and south). Otter carcasses were collected from a total of 12 counties during the trapping seasons of 2003 and 2004. Liver, kidney, muscle, brain, and fur tissue was collected for mercury (Hg) analysis. Analysis of variance identified collection zone as the significant factor for differences in tissue Hg levels, with a pattern of decreasing Hg concentrations from north to south (p < 0.0001). This trend was apparent in all tissue types analyzed. Strong relationships were observed between Hg concentrations in all tissues. Likewise, highly significant (p < 0.0001) relationships were found to exist between Hg concentrations in otter fur and Hg concentrations of internal organs (brain, muscle, kidney, and liver). Although these data suggest that Hg concentrations are related among tissues, they do not suggest uniform distribution of Hg throughout the tissues. The results suggest that Hg accumulates at higher concentrations in fur followed by liver, kidney, muscle, and brain. Analysis of a subset of samples for methylmercury (MeHg) revealed that MeHg made up a greater percentage of total Hg in brain and muscle compared to liver and kidney tissue. Although a gradient in tissue concentrations was observed from north to south, none of the tissue concentrations reached levels known to cause toxicity in either otter or mink.

Factors in fish modifying methylmercury toxicity and metabolism

We report here some results of a long-term (19 month) study with cats fed methylmercury (MeHg) in nutritionally balanced diets based on fish. By using either freshwater pike (low in Se) or canned tuna (high in Se) as the major protein source, basal diets with low levels of MeHg were prepared having different Se content, all Se being of natural origin. The basal diets produced no signs of toxicity or pathological changes over the l9-month period. In cats fed basal diets spiked with medium or high levels of MeHg, evidence for delayed onset of toxic effects from the added MeHg was observed with the tuna diets compared to pike diets. In brain, muscle, and blood, the activity of GSH peroxidase, a selenoenzyme, was decreased by Hg. In liver, substantial accumulation of Hg with Se occured (molar Hg/Se ratio approximately 1.4 to 1.8) but GSH peroxidase activity was unaffected. We suggest that the coaccumulation of Hg and Se in liver measures the extent to which MeHg has been metabolically transformed by metabolism to Hg++, and inactivated by deposition as a Hg/Se complex of low bioavailability. The accumulation of Hg and Se in liver was much greater in cats fed tuna compared to pike, out of proportion to the relatively small differences in Hg and Se content of the tuna and pike basal diets. Some mechanisms are described by which selenium, vitamin E, and other factors might facilitate MeHg breakdown to inorganic Hg during long term low level exposure to MeHg.

Organic mercury compounds: human exposure and its relevance to public health

Humans may be exposed to organic forms of mercury by either inhalation, oral, or dermal routes, and the effects of such exposure depend upon both the type of mercury to which exposed and the magnitude of the exposure. In general, the effects of exposure to organic mercury are primarily neurologic, while a host of other organ systems may also be involved, including gastrointestinal, respiratory, hepatic, immune, dermal, and renal. While the primary source of exposure to organic mercury for most populations is the consumption of methylmercury-contaminated fish and shellfish, there are a number of other organomercurials to which humans might be exposed. The antibacterial and antifungal properties of organomercurials have resulted in their long use as topical disinfectants (thimerosal and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Phenylmercury has been used in the past in paints, and dialkyl mercurials are still used in some industrial processes and in the calibration of certain analytical laboratory equipment. The effects of exposure to different organic mercurials by different routes of exposure are summarized in this article.

Determination of a site-specific reference dose for methylmercury for fish-eating populations

Environmental risk-management decisions in the U.S. involving potential exposures to methylmercury currently use a reference dose (RfD) developed by the U.S. Environmental Protection Agency (USEPA). This RfD is based on retrospective studies of an acute poisoning incident in Iraq in which grain contaminated with a methylmercury fungicide was inadvertently used in the baking of bread. The exposures, which were relatively high but lasted only a few months, were associated with neurological effects in both adults (primarily paresthesia) and infants (late walking, late talking, etc.). It is generally believed that the developing fetus represents a particularly sensitive subpopulation for the neurological effects of methylmercury. The USEPA derived an RfD of 0.1 microg/kg/day based on benchmark dose (BMD) modeling of the combined neurological endpoints reported for children exposed in utero. This RfD included an uncertainty factor of 10 to consider human pharmacokinetic variability and database limitations (lack of data on multigeneration effects or possible long-term sequelae of perinatal exposure). Alcoa signed an Administrative Order of Consent for the conduct of a remedial investigation/feasibility study (RI/FS) at their Point Comfort Operations and the adjacent Lavaca Bay in Texas to address the effects of historical discharges of mercury-containing wastewater. In cooperation with the Texas Natural Resource Conservation Commission and USEPA Region VI, Alcoa conducted a baseline risk assessment to assess potential risk to human health and the environment. As a part of this assessment. Alcoa pursued the development of a site-specific RfD for methylmercury to specifically address the potential human health effects associated with the ingestion of contaminated finfish and shellfish from Lavaca Bay. Application of the published USEPA RfD to this site is problematic; while the study underlying the RfD represented acute exposure to relatively high concentrations of methylmercury, the exposures of concern for the Point Comfort site are from the chronic consumption of relatively low concentrations of methylmercury in fish. Since the publication of the USEPA RfD, several analyses of chronic exposure to methylmercury in fish-eating populations have been reported. The purpose of the analysis reported here was to evaluate the possibility of deriving an RfD for methylmercury, specifically for the case of fish ingestion, on the basis of these new studies. In order to better support the risk-management decisions associated with developing a remediation approach for the site in question, the analysis was designed to provide information on the distribution of acceptable ingestion rates across a population, which could reasonably be expected to be consistent with the results of the epidemiological studies of other fish-eating populations. Based on a review of the available literature on the effects of methylmercury, a study conducted with a population in the Seychelles Islands was selected as the critical study for this analysis. The exposures to methylmercury in this population result from chronic, multigenerational ingestion of contaminated fish. This prospective study was carefully conducted and analyzed, included a large cohort of mother-infant pairs, and was relatively free of confounding factors. The results of this study are essentially negative, and a no-observed-adverse-effect level (NOAEL) derived from the estimated exposures has recently been used by the Agency for Toxic Substances and Disease Registry (ATSDR) as the basis for a chronic oral minimal risk level (MRL) for methylmercury. In spite of the fact that no statistically significant effects were observed in this study, the data as reported are suitable for dose-response analysis using the BMD method. Evaluation of the BMD method used in this analysis, as well as in the current USEPA RfD, has demonstrated that the resulting 95% lower bound on the 10% benchmark dose (BMDL) represents a conservative estimate of the traditional NOAEL, and that it is superior to the use of "average" or "grouped" exposure estimates when dose-response information is available, as is the case for the Seychelles study. A more recent study in the Faroe Islands, which did report statistically significant associations between methylmercury exposure and neurological effects, could not be used for dose-response modeling due to inadequate reporting of the data and confounding from co-exposure to polychlorinated biphenyls (PCBs). BMD modeling over the wide range of neurological endpoints reported in the Seychelles study yielded a lowest BMDL for methylmercury in maternal hair of 21 ppm. This BMDL was then converted to an expected distribution of daily ingestion rates across a population using Monte Carlo analysis with a physiologically based pharmacokinetic (PBPK) model to evaluate the impact of interindividual variability. The resulting distribution of ingestion rates at the BMDL had a geometric mean of 1.60 microg/kg/day with a geometric standard deviation of 1.33; the 1st, 5th, and 10th percentiles of the distribution were 0.86, 1.04, and 1.15 microg/kg/day. In place of the use of an uncertainty factor of 3 for pharmacokinetic variability, as is done in the current RfD, one of these lower percentiles of the daily ingestion rate distribution provides a scientifically based, conservative basis for taking into consideration the impact of pharmacokinetic variability across the population. On the other hand, it was felt that an uncertainty factor of 3 for database limitations should be used in the current analysis. Although there can be high confidence in the benchmark-estimated NOAEL of 21 ppm in the Seychelles study, some results in the New Zealand and Faroe Islands studies could be construed to suggest the possibility of effects at maternal hair concentrations below 10 ppm. In addition, while concerns regarding the possibility of chronic sequelae are not supported by the available data, neither can they be absolutely ruled out. The use of an uncertainty factor of 3 is equivalent to using a NOAEL of 7 ppm in maternal hair, which provides additional protection against the possibility that effects could occur at lower concentrations in some populations. Based on the analysis described above, the distribution of acceptable daily ingestion rates (RfDs) recommended to serve as the basis for site-specific risk-management decisions at Alcoa's Point Comfort Operations ranges from approximately 0.3 to 1.1 microg/kg/day, with a population median (50th percentile) of 0.5 microg/kg/day. By analogy with USEPA guidelines for the use of percentiles in applications of distributions in exposure assessments, the 10th percentile provides a reasonably conservative measure. On this basis, a site-specific RfD of 0.4 microg/kg/day is recommended.

Interactions of vitamin E and selenium with mercury and silver

It is well established that the toxicity of silver and methylmercury is suppressed by the presence of low levels of vitamin E or selenium in the diet, but little is known of the mechanisms involved. Silver induces a conditioned deficiency of selenium in rats, as shown by its effects on tissue levels of selenium and glutathione peroxidase (a selenoprotein), but methylmercury does not. Supplements of selenium do not decrease mercury levels in tissues of animals given methylmercury, and animals given selenium plus methylmercury may accumulate high levels of mercury without signs of toxicity. Although an equimolar accumulation of selenium and mercury in tissues sometimes occurs and could lead to mutual detoxification, such a coaccumulation is not always linked to protection. The only known functions of vitamin E and selenium are related to the prevention of oxidative damage. It is possible that their protective effects against heavy metals may involve such functions, thus accounting for the protection afforded by low levels of the nutrients against high levels of the metal toxicants.

Is the solitary dark neuron a manifestation of postmortem trauma to the brain inadequately fixed by perfusion?

Dark neurons, classified as solitary because of their sparse occurrence, were discerned in the transitional zones between gray and white matter in various species of laboratory animals fixed by perfusion. These neurons, histologically indistinguishable from dark neurons in immersion fixed material, tended to develop when the saline perfusion was delayed or slow, the amount of the Bouin fixative was excessive, or the autopsy was performed shortly after the perfusion. Under these conditions, the white matter manifested a softer consistency and a paler color than the gray matter. These observations suggest that, as the consequence of regional differences in intensity and speed of fixation, distortion during extraction of the brain may activate a stress force in the transitional zones where incompletely fixed neurons become affected and acquire an abnormal affinity for aniline dyes and silver.