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The relationship of the toxic effects of mercury to exacerbation of the medical condition classified as Alzheimer's disease
Abstract
Mercury(II) or Hg 2+ , is neurotoxic. When exposed to normal brain tissue homogenates, neurons in culture, Hg 2+ (mercury(II) or mercuric mer-cury) is capable of causing many of the same biochemical aberrancies found in Alzheimer's diseased (AD) brain. Also, rats exposed to mercury(0), metallic mercury, vapor show some of these same abnormalities in their brain tissue. Specifically, the rapid inactivation of the brain thiol-sensitive enzymes (tubulin, creatine kinase and glutamine synthetase) occurs after: (a) the addition of low micromolar levels of Hg 2+ , (b) exposure to mercury vapor (Hg 0) or (c) the addition of Thimerosal (ethylmercurythiosalicylate sodium salt). Moreover, these same enzymes are significantly inhibited in the AD brain. Further, exposure of neurons in culture to nanomolar levels of Hg 2+ has been shown to produce three of the widely accepted pathologi-cal diagnostic hallmarks of AD. These AD hallmarks are elevated amyloid protein, hyper-phosphorylation of Tau, and formation of neurofibillary tangles (NFTs). This paper proposes the hypothesis that elemental mercury, organic mercury compounds, and other blood-brain permeable toxicants, which have enhanced specificity for thiol-sensitive enzymes, are the etiological source of AD. Included in this category are other heavy metals such as lead and cadmium that act synergistically to enhance, by many-fold, the toxicity of metallic mercury and organic-mercury(II) compounds, like Thimerosal. This hypothesis also explains the genetic susceptibility to AD that is expressed through the APO-E geneotype. Specifically, a reduction of APO-E gene type that contains two cysteines decreases the one of the innate detoxification capabilities of APO-E, the removal of mercury and other thiol-reactive toxicants from the central nervous system. This increases brain exposure to thiol-reactive toxicants and elevates the risk of AD. Also, the increased exposure to mercury through breathing the mercury vapor emanating from mercury amalgam dental fillings can have a deleterious effect on olfactory capability. This effect may explain the high correlation between the loss of sense of smell and the subsequent development of AD.
... Mercury toxicity has been shown to have almost identical biochemical similarities to that of ADZ as seen in brain tissue studies. Mercury is a naturally occurring element within diet and is at increased levels in diets rich in certain fish and shellfish [3][4][5]. Modern medical science has been attempting for many years to link the dietary impact of mercury with that of neurological pathological change with varying results. It is currently understood that mercury at certain levels will ultimately destroy brain tissue, however mercury has been proven to be extensive in certain fish and shellfish which also have important dietary values. ...
... This is somewhat of a dichotomy, as it has been suggested that a large contributor to the progression of the dementias is due to lack of protein synthesis due to inadequate nutritional intake. The levels at which mercury is deemed toxic in the human varies from text to text with pharmacological chelation being the chosen medical course of treatment at acutely toxic levels only [3][4][5]. ...
... For the purpose of this work, the Tau and Neurovascular hypothesis will be the only two studied in reference to ADZ progression with consideration of methylmercury toxicity. The Tau Hypothesis (Th) proposes that the tau protein abnormalities initiate ADZ disease progression via hyperphosphorylation of the tau protein with other threads of tau, culminating in the formation of neurofibrillary tangles inside nerve cell bodies, resulting in the destruction of the microtubules and leading to the destruction of the cell's cytoskeleton [3][4][5]. ...
... However, with the exception of a few chemicals, the role of environmental toxins and dietary proteins in association with AD has largely been neglected [19]. Toxic metals such as aluminum [20][21][22][23][24], mercury [25][26][27] and lead [28,29] are among the few that are known to cause toxicity to the brain and other organs and have been linked to numerous neurodegenerative disorders, including AD. ...
... Mercury is another chemical which extensive epidemiological and demographical studies have reported to have a strong association with AD [25]. In fact, according to one review article, some autopsy studies found increased levels of mercury in the brain tissues of AD patients but not in the blood, urine, hair or cerebrospinal fluid [25]. ...
... Mercury is another chemical which extensive epidemiological and demographical studies have reported to have a strong association with AD [25]. In fact, according to one review article, some autopsy studies found increased levels of mercury in the brain tissues of AD patients but not in the blood, urine, hair or cerebrospinal fluid [25]. Furthermore, in in vitro and animal studies it was demonstrated that mercury causes tau protein phosphorylation, and the increased formation of amyloid-β protein [25]. ...
Objective: The aim of our study was to examine immunoreactivity between AβP-42, toxic chemicals, and food proteins that could be involved in AD. Methods: We applied monoclonal anti-AβP-42 to a variety of chemicals bound to human serum albumin (HSA) and 208 different food extracts. Results: We found that anti-AβP-42 reacts from moderately to strongly with mercury-HSA, dinitrophenyl-HSA (DNP-HSA), phthalate-HSA, and aluminum-HSA, but not to many other tested chemicals bound to HSA nor to HSA alone. This antibody also reacted with 19 out of the 208 food antigens used in the assay. One example of a food that reacted strongly with anti-AβP-42 in our study was canned tuna, although raw tuna reacted only moderately. Conclusion: Based on these results, we hypothesized that reaction between AβP-42 antibody with chemicals bound to HSA and numerous food antigens might play a role in Alzheimer’s disease (AD). These anti-AβP antibodies could be derived from protein misfolding similar to β-amyloid, or from antibodies to various food antigens that cross-react with AβP-42. Removal of toxic chemicals and food items that share a homology with β-amyloid may be recommended at least for patients in the early stages of AD. Therefore, the role of AβP-42 cross-reactive foods and chemicals bound to HSA in neurodegeneration should be investigated further.
... • Dental plaque (Lyttle and Bowden 1993 ) • Selenium levels (Raymond and Ralston 2004 ) • Exposure to lead (Pb) (Haley 2005(Haley , 2007Ingalls 1983 ;Schubert et al. 1978 ) • Consumption of milk (Kostial et al. 1979 ;Mata et al. 1997 ) • Consumption of alcohol (Hursh et al. 1980 ) Obviously, other circumstances can also play a role in each person's unique response to mercury. ...
... Dr. Boyd Haley concluded that mercury and other blood-brain permeable toxicants with enhanced specifi city for thiol-sensitive enzymes are the etiological source of AD (Haley 2007 ). Included in this category are other heavy metals such as lead and cadmium that act synergistically to enhance the toxicity of mercury and organicmercury compounds (Haley 2007 ). ...
... Dr. Boyd Haley concluded that mercury and other blood-brain permeable toxicants with enhanced specifi city for thiol-sensitive enzymes are the etiological source of AD (Haley 2007 ). Included in this category are other heavy metals such as lead and cadmium that act synergistically to enhance the toxicity of mercury and organicmercury compounds (Haley 2007 ). The involvement of these other metals explains why mercury levels alone and severity of AD-like brain damage has not been exhibited in other studies. ...
All dental amalgam fillings contain approximately 50 % elemental mercury by weight. Concerns about health risks due to continual emissions of mercury vapor from this tooth restorative material have been addressed by dentists, scientists, and government authorities worldwide and have resulted in a range of recommended practices and regulations. By reviewing articles collected by a literature search of the International Academy of Oral Medicine and Toxicology (IAOMT) database and the PubMed database, we identify health risks associated with dental mercury amalgam. We present the science of potential harm as applicable to the general population, pregnant women, fetuses, children, and dental professionals. We specifically address genetic predispositions, mercury allergies, Alzheimer’s disease, multiple sclerosis, amyotrophic lateral sclerosis, and other health conditions pertinent to dental mercury exposure. We conclude that reviews and studies of dental amalgam mercury risk should assess biocompatibility with special consideration for all populations and all risk factors.
... Some scientists try to argue that results gained by animal or cell testing are overestimated and not comparable to the situation of the human body. However, in contrast to test animals in experiments, humans are exposed to many other toxins simultaneously, thus the effects add up or are even synergistic [101,102]. For example, it has been proven that the combination of the Lethal Dose 1% of mercury (LD1 Hg ) together with the LD1 of lead (Pb) results in the death of all animals, so the following toxicological equation can be assumed: LD1 (Hg) + LD1 (Pb) = LD 100 [101]. ...
... SCENIHR questioned that mercury may contribute to the development of AD. As a proof of this statement they cited only one study [41] published in the trade journal of the world-wide leading American Dental Association (ADA) [102]. In contrast, other studies have shown that mercury play a major pathogenetic role in AD [108,109,169,170]. ...
... APO-E4 is known to be the major genetic risk factor for Alzheimer's disease, whereas APO-E2 decreases the risk. It has been postulated that this is due to the difference in capacity to remove heavy metals from the cerebrospinal fluid [44,92,102,124,231,234,244]. APO-E2 possesses two cysteines with metal binding sulfhydryl-groups whereas APO-E4 does not have any cysteine residues. ...
It was claimed by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR)) in a report to the EU-Commission that "....no risks of adverse systemic effects exist and the current use of dental amalgam does not pose a risk of systemic disease..." [1, available from: http://ec.europa.eu/health/ph_risk/committees/04_scenihr/docs/scenihr_o_016.pdf].
SCENIHR disregarded the toxicology of mercury and did not include most important scientific studies in their review. But the real scientific data show that:
(a) Dental amalgam is by far the main source of human total mercury body burden. This is proven by autopsy studies which found 2-12 times more mercury in body tissues of individuals with dental amalgam. Autopsy studies are the most valuable and most important studies for examining the amalgam-caused mercury body burden.
(b) These autopsy studies have shown consistently that many individuals with amalgam have toxic levels of mercury in their brains or kidneys.
(c) There is no correlation between mercury levels in blood or urine, and the levels in body tissues or the severity of clinical symptoms. SCENIHR only relied on levels in urine or blood.
(d) The half-life of mercury in the brain can last from several years to decades, thus mercury accumulates over time of amalgam exposure in body tissues to toxic levels. However, SCENIHR state that the half-life of mercury in the body is only "20-90 days".
(e) Mercury vapor is about ten times more toxic than lead on human neurons and with synergistic toxicity to other metals.
(f) Most studies cited by SCENIHR which conclude that amalgam fillings are safe have severe methodical flaws.
... Anaerobic bacteria from periodontal diseases produce hydrogen sulfide (H 2 S) and methyl mercaptan (CH 3 SH) are responsible for gingivitis [59]. These sulfur compounds react with the mercury amalgam to produce a black gum tissue called "amalgam tattoos", consisting of mercuric sulfide (HgS) [60]; mercuric sulfide is extremely toxic causing oral and systemic diseases [58]. ...
... A correlation has been established between sulfhydryl (HS) groups on the surface of the APO-E protein (binds Hg 2+ ions) and the removal of mercury from the brain. The increased risk of acquiring the Alzheimer's disease may be up to 80% greater if the APO-E4 form predominates over the APO-E2 form [60]. Since these housekeeping APO-E proteins are involved in removing toxic metals (including mercury), as well as oxidized lipids, this condition may exacerbate in genetically sensitive people [85]. The levels of mercury in the brain of Alzheimer's-affected subjects need to be evaluated in accordance to genetic susceptibility of previously discussed genes and the pathological conditions. ...
Abstract: Mercury (Hg) has been identified as one of the most toxic non-radioactive material known to man. Although mercury is a naturally occurring element, anthropogenic mercury is now a major worldwide concern and is an international priority toxic pollutant. It also comprises one of the primary constituents of dental amalgam fillings. Even though dental mercury amalgams have been used for almost two centuries, its safety has never been tested or proven in the United States by any regulatory agency. There has been an on-going debate regarding the safety of its use since 1845, and many studies conclude that its use exposes patients to troublesome toxicity. In this review, we present in an objective way the danger of dental amalgam to human health based on current knowledge. This dilemma is addressed in terms of an integrated toxicological approach by focusing on four mayor issues to show how these interrelate to create a composite picture: 1) the irrefutable constant release of mercury vapor from dental amalgams which is responsible for individual chronic exposure, 2) the evidence of organic mercury formation from dental amalgam in the oral cavity, 3) the effect of mercury exposure on gene regulation in human cells which supports the intrinsic genetic susceptibility to toxicant, and finally 4) the availability of recent epidemiological data supporting the link of dental amalgams to pathological diseases such as Alzheimer and Parkinson.
... Inorganic Hg damages nervous system and produces pathological changes similar to AD (Mutter et al., 2010;Haley, 2007). Hg exposure helps to form "neurofibrillar tangles" inside brain cells that are one of the two diagnostic markers for Alzheimer's disease (http:// articles.mercola.com/sites/articles/archive/2001/04/07/alzheimersmercury.aspx). ...
... Low level inorganic Hg exposure damages nerve cell (like AD). Whereas, other metals (zinc, aluminium, copper, cadmium, manganese, iron, and chromium) aggravate the toxic effects of Hg inside nerve cell (Thompson et al., 1987;Deibel et al., 1996;Haley, 2007). Markesbery (1997) has reported that increasing Hg exposure can generate free radical and produce oxidative stress in brains. ...
... These sulfur compounds react with the mercury amalgam to produce a black pigment on the gum tissue (amalgam tattoo), consisting of HgS, which is extremely toxic and can cause oral and systemic diseases. (38) According to Paknahad et al., (39) amalgam fillings in patients who are exposed to Wi-Fi wave emissions release more mercury than those in patients not exposed. Leszek et al. (40) reported the deposition of mercury in various parts of the body within 29 days after the placement of amalgam restorations. ...
The purpose of this study was to determine the levels of mercury in hard tissue from dental amalgam fillings under in vitro conditions. Methods and Results: The study included 30 human teeth that were extracted for various clinical reasons. The teeth were stored in a physiological solution until they were used. The teeth were divided into 3 experimental groups: Group 1 (n=10) – occlusal surface cavity preparation (class I according to Black); Group 2 (n=10) – proximal-occlusal surface cavity preparation (class II); and Group 3 (n=10) – mesio-occlusal-distal [MOD] surface cavity preparation. Each of these groups was divided into 2 subgroups: subgroup 1 (n=5) – amalgam fillings were not polished, and subgroup 2 (n=5) amalgam fillings were polished. The teeth were filled with amalgam, and those in subgroups 2 were polished after 24 hours. The amount of mercury released from the amalgam fillings was determined 9 months after the teeth were filled. Before chemical analysis, the teeth were irrigated 4 times over a period of 10 minutes in an ultrasonic bath. From each tooth, 250mg of the powder was mineralized with royal water (HCl+HNO3 in a ratio of 1:3) in a microwave oven, for 54 minutes. After mineralization, the samples were filtered and analyzed with inductively coupled plasma optical emission spectrometry. The average mercury level after polishing the amalgam filling was significantly smaller (P=0.032) only in Group 1. The average mercury levels in the 3 groups revealed significant differences between both the unpolished samples (one-way ANOVA F = 69.54, P < 0.001) and the polished samples (one-way ANOVA F = 110.54, P < 0.001). Group 3 with MOD surface cavity preparation was characterized by the highest mercury levels. Conclusion: The teeth with an MOD amalgam restoration are characterized by the highest mercury levels. The more mercury is released from unpolished amalgam fillings than from polished amalgam fillings in teeth with occlusal surface cavity preparation (class I according to Black).
... Both selenium and mercury have been linked to the development and pathogenesis of AD, however, the clinical relevance and connections have been conflicting [76,[86][87][88][89][90][91]. The many similarities between mercury toxicity and AD pathology have recently been emphasized by Siblerud et al. [92] and Bjørklund et al. [86]. ...
Methylmercury (MeHg) is a well-known environmental contaminant, particularly harmful to the developing brain. The main human dietary exposure to MeHg occurs through seafood consumption. However, seafood also contains several nutrients, including selenium, which has been shown to interact with MeHg and potentially ameliorate its toxicity. The aim of this study was to investigate the combined effects of selenium (as selenomethionine; SeMet) and MeHg on mercury accumulation in tissues and the effects concomitant dietary exposure of these compounds exert on the hippocampal proteome and transcriptome in mice. Adolescent male BALB/c mice were exposed to SeMet and two different doses of MeHg through their diet for 11 weeks. Organs, including the brain, were sampled for mercury analyses. Hippocampi were collected and analyzed using proteomics and transcriptomics followed by multi-omics bioinformatics data analysis. The dietary presence of SeMet reduced the amount of mercury in several organs, including the brain. Proteomic and RNA-seq analyses showed that both protein and RNA expression patterns were inversely regulated in mice receiving SeMet together with MeHg compared to MeHg alone. Several pathways, proteins and RNA transcripts involved in conditions such as immune responses and inflammation, oxidative stress, cell plasticity and Alzheimer’s disease were affected inversely by SeMet and MeHg, indicating that SeMet can ameliorate several toxic effects of MeHg in mice.
... This results in increased levels of Aβ in the hippocampus and decreased levels in the CSF region advocating that removal of a pathogenic peptide from the brain gets reduced (Kim et al. 2014). The structural integrity of neurons and neurites is completely distorted by Hg ions besides the binding of guanosine triphosphate (GTP) to β tubulin also gets inhibited which in turn reduces the biological activity causing microtubule degeneration as exhibited in AD brain homogenates (Leong et al. 2001;Haley 2007). In human nutrition, arsenic (As) represents an essential element; however, at higher doses, it affects both cognitive and neurodevelopmental functions (Nielsen 2000;Tyler and Allan 2014). ...
Neurodegenerative disorders are commonly erratic influenced by various factors including lifestyle, environmental, and genetic factors. In recent observations, it has been hypothesized that exposure to various environmental factors enhances the risk of Alzheimer’s disease (AD). The exact etiology of Alzheimer’s disease is still unclear; however, the contribution of environmental factors in the pathology of AD is widely acknowledged. Based on the available literature, the review aims to culminate in the prospective correlation between the various environmental factors and AD. The prolonged exposure to the various well-known environmental factors including heavy metals, air pollutants (particulate matter), pesticides, nanoparticles containing metals, industrial chemicals results in accelerating the progression of AD. Common mechanisms have been documented in the field of environmental contaminants for enhancing amyloid-β (Aβ) peptide along with tau phosphorylation, resulting in the initiation of senile plaques and neurofibrillary tangles, which results in the death of neurons. This review offers a compilation of available data to support the long-suspected correlation between environmental risk factors and AD pathology.
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... Conversely, numerous studies have found no significant difference in the blood (Fung et al. 1995;Homme et al. 2014) and urine Hg levels between patients with AD and healthy controls (Chakraborty 2017;Pigatto et al. 2018). Moreover, there is an association between the loss of sense of smell and subsequent development of AD, which may indicate a subclinical equivalent of Hg toxicity (Haley 2007). It is also presumed that Hg pollution may play an important role in AD epidemics in India (Chakraborty 2017). ...
Mercury (Hg), which is a non-essential element, is considered a highly toxic pollutant for biological systems even when present at trace levels. Elevated Hg exposure with the growing release of atmospheric pollutant Hg and rising accumulations of mono-methylmercury (highly neurotoxic) in seafood products have increased its toxic potential for humans. This review aims to highlight the potential relationship between Hg exposure and Alzheimer's disease (AD), based on the existing literature in the field. Recent reports have hypothesized that Hg exposure could increase the potential risk of developing AD. Also, AD is known as a complex neurological disorder with increased amounts of both extracellular neuritic plaques and intracellular neurofibrillary tangles, which may also be related to lifestyle and genetic variables. Research reports on AD and relationships between Hg and AD indicate that neurotransmitters such as serotonin, acetylcholine, dopamine, norepinephrine, and glutamate are dysregulated in patients with AD. Many researchers have suggested that AD patients should be evaluated for Hg exposure and toxicity. Some authors suggest further exploration of the Hg concentrations in AD patients. Dysfunctional signaling pathways in AD and Hg exposure appear to be interlinked with some driving factors such as arachidonic acid, homocysteine, dehydroepiandrosterone (DHEA) sulfate, hydrogen peroxide, glucosamine glycans, glutathione, acetyl-L carnitine, melatonin, and HDL. This evidence suggests the need for a better understanding of the relationship between AD and Hg exposure, and potential mechanisms underlying the effects of Hg exposure on regional brain functions. Also, further studies evaluating brain functions are needed to explore the long-term effects of subclinical and untreated Hg toxicity on the brain function of AD patients.
... Many studies reveal the toxic effect of metals released in the environment on human health (Picot, 2003;Sasha, 2009;Lauwerys et al., 1984;Exley, 2013;Boyd, 2007). Screening the presence of toxic elements and their concentration levels allows assessing the potential hazards resulting from their consumption. ...
... Many studies reveal the toxic effect of metals released in the environment on human health (Picot, 2003;Sasha, 2009;Lauwerys et al., 1984;Exley, 2013;Boyd, 2007). Screening the presence of toxic elements and their concentration levels allows assessing the potential hazards resulting from their consumption. ...
The weight fractions of the nutrients and toxic elements have been determined in environmental and foodstuff samples in the oil bearing Bakassi Peninsula. This study is highly justified by the occurrence of many offshore production platforms in the peninsula that could lead to the environmental pollution. The use of a Quant´X EDXRF spectrometer and the Fundamental Parameter approach for quantification of the results enabled us to increase sensitivity and accuracy in the analysis of soil and foodstuffs. The results obtained for soil samples exhibit a predominance of iron and the presence of lead. Mercury and cadmium are below the detection limit. The analysis of foodstuffs shows a high content of potassium and calcium. Concerning water, the analysis also shows a high content of iron (Fe) (2.18±0.04) mg/L in tap water, 10 times above the accepted limit value. Concentrations of lead (2.58±0.01) mg/L in tap water and (0.30±0.01) mg/L in rain water have been determined. No cadmium has been detected in tap water but its presence (0.80±0.01) mg/L in rain water is probably due to the atmospheric deposition.
... Animal and in vitro studies have demonstrated that mercury causes tau protein hyperphosphorylation, and the increased formation of amyloid-β protein [56]. Hg ions disrupt membrane structural integrity of neurites and neuron growth cones [57] and also inhibit binding of guanosine triphosphate (GTP) to β-tubulin reducing the biological activity, causing abnormal partition and ultimately microtubule degeneration as shown in AD brain homogenates [58]. ...
Alzheimer's disease (AD) is a leading cause of mortality in the developed world with 70% risk attributable to genetics. The remaining 30% of AD risk may be hypothesized to include environmental factors and human lifestyle patterns. Environmental factors possibly include inorganic and organic hazards, exposure to toxic metals (aluminium, copper), pesticides (organochlorine and organophosphate insecticides), industrial chemicals (flame retardants) and air pollutants (particulate matter). Long term exposures to these environmental contaminants together with bioaccumulation over an individual's life-time are speculated to induce neuroinflammation and neuropathology paving the way of developing AD. Epidemiologic associations between environmental contaminant exposures and AD are still limited. However, many in vitro and animal studies have identified toxic effects of environmental contaminants at the cellular level, revealing alterations of pathways and metabolisms associated with AD that warrant further investigations. This review provides an overview of in vitro, animal and epidemiological studies on the etiology of AD, highlighting available data supportive of the long hypothesized link between toxic environmental exposures and development of AD pathology.
... Hence, why much of the research involving genetics and autism involves looking at how genetics has a role in susceptibility to toxins and the autoimmune dysfunction, again the link back to vaccines (Haley, 2005). Haley (2007), of the University of Kentucky, has spent many years studying the effect of mercury on the body. He has researched one possible genetic risk factor in autistics. ...
Autism is the fastest growing disability ever. With the growth comes a lot of questions as to the etiologies and treatment of this condition, often putting parents, schools, and traditional medical personnel at odds with what treatments have efficacy. As the popularity of alternative treatments increase, so does the need for research.
Hyperbaric oxygen therapy is one alternative treatment parents are seeking for their child with autism. When one looks at the science behind hyperbaric oxygen therapy and the physical condition of a child with autism the rationale behind the treatment becomes clear. Research has shown that children with autism have decreased cerebral blood flow, neurological and gastrointestinal inflammation, reduction of purkinje cells, poor immune systems, increase of heavy metals, and deficits with their myelination. When these conditions are compared to the benefits one receives in hyperbarics a correlation is noted, and an understanding of why a child functioning improves.
This research was a study of five children with school diagnosis of autism that were doing hyperbaric oxygen therapy. Both the parents and the child's teacher filled out a pre and post evaluation of the child using ATEC evaluation tool. The evaluation tool assessed improvements in the area of speech/language/communication, sociability, sensory/cognitive awareness, health/physical/behavior of a child with autism.The results were assessed with the SPSS (Statistical Package for the Social Sciences Personal Computer) software using t-test with Paired Samples Statistics data analysis to compare the pretest and posttest scores.
All areas showed improvements. In speech/language/communication the parents reported a 6.33 percentage of improvements and the teachers reported a 10.34 percentage of improvements. In sociability the parents reported a 10.53 percentage of improvements and the teachers reported a 3.96 percentage of improvements. In sensory/cognitive awareness the parents reported a 4.11 percentage of improvements and the teachers reported a 14.29 percentage of improvements. Lastly, in health/physical/behavior the parents reported a 17.61 percentage of improvements and the teachers reported a 10.22 percentage of improvements.
Overall, the study concluded that further research with a larger sample size is warranted to see if hyperbaric oxygen therapy can help benefit children with autism.
... 62 Furthermore, work by Dr. Boyd Haley and other have pointed to a possible link between dental amalgams and Alzheimer's disease and other brain disorders. 59,63,64 It is interesting to note that, while Alzheimers has never been linked directly to Minamata Disease, there are several shared neurological symptoms, and both illnesses do involve severe neurological damage. 28 The differences could arise from the slightly different reactivity in the body between mercury vapor (Hg 0 ) and methylmercury (Hg II ). ...
Mercury has been an element of great industrial importance since early times.This wide utilization of the element has led to pervasive mercury contamination in theglobal environment. Due to mercury's high toxicity, this is a matter of great concern. Anumber of methods, includ ing phytoremediation, filtration, and precipitation/chelation,have been investigated to remove mercury from the environment. Unfortunately, thesemethods are not entirely satisfactory for the in-situ remediation of mercury from aqueousenvironments.The hypothesis of this dissertation is that this can best be accomplished by theaddition of a large and flexible sulfur-based chelate, that will bind mercury in atetracoordinate and presumably tetrahedral environment, to mercury-contaminatedwaters. Although this proved difficult due to the tendency of these ligands to decomposeinto smaller, sulfur-containing rings, the synthesis and characterization of such a chelatewas achieved. Several potential mercury-binding ligands were eventually synthesizedsignificant amounts of mercury (91-100%) from the contaminated solutions, in one caselowering the mercury levels in the water to below the CVAF detection limits. Theresulting solids lost little (andlt;15 ppb) of their mercury during leaching studies.This work demonstrates the use of tetradentate chelates in precipating Hg2+ fromwater to produce stable mercury- ligand precipitates. A calculation for the quantification ofthe geometry of a four-coordinate compound was also developed and applied to aluminum,gallium, and mercury compounds. This calculation could also be applied to the mercurycompounds described in this thesis once X-ray structures become available
Alzheimer's disease (AD) is the most common form of dementia, which causes progressive memory loss and cognitive decline. Effective strategies to treat or prevent remains one of the most challenging undertakings in the medical field. AD is a complex and multifactorial disease that involves several risk factors. Aging and genetic factors both play important roles in the onset of the AD, however; certain environmental factors have been reported to increase the risk of AD. Chronic exposure to toxins has been seen as an environmental factor that may increase the risk of developing a neurodegenerative disease such as AD. Exposure to metals and biotoxins produced by bacteria, molds, and viruses may contribute to the cognitive decline and pathophysiology associated with AD. Toxins may contribute to the pathology of the disease through various mechanisms such as deposition of amyloid-beta (Aβ) plaques and tangles in the brain, induction of apoptosis, inflammation, or oxidative damage. Here, we will review how toxins affect brain physiology with a focus on mechanisms by which toxins may contribute to the development and progression of AD. A better understanding of these mechanisms may help contribute towards the development of an effective strategy to slow the progression of AD.
Methylmercury, a pollutant produced by various industrial activities, is a potent neurotoxin that has now caused serious contamination issues within our oceans. As a fat-soluble molecule, methylmercury enters the food chain and accumulates in the flesh of the fish that then may end up in our supermarkets. Consuming larger, longer living fish on a regular basis is now known to pose a serious health hazard, especially for children and pregnant women who are consequently advised to limit (or even avoid) the intake of some species such as fresh tuna or marlin.
Large autism epidemics have recently been reported in the United States and the United Kingdom. Emerging epidemiologic evidence and biologic plausibility suggest an association between autistic spectrum disorders and mercury exposure. This study compares mercury excretion after a three-day treatment w ith a n o ral c helating a gent, m eso-2,3- dimercaptosuccinic acid (DMSA), in children with autistic spectrum disorders and a matched control population. Overall, urinary mercury concentrations were significantly higher in 221 children with autistic spectrum disorders than in 18 normal controls (Relative Increase (RI)=3.15; P < 0.0002). Additionally, vaccinated cases showed a significantly higher urinary mercury concentration than did vaccinated controls (RI=5.94; P < 0.005). Similar urinary mercury concentrations were observed among matched vacci- nated and unvaccinated controls, and no association was found between urinary cadmium or lead concentrations and autistic spectrum disorders. The observed urinary concentrations of mercury could plausibly have resulted from thimerosal in childhood vaccines, although other environmental sources and thimerosal in Rh (D) immune globulin administered to mothers may be contributory. Regardless of the mechanism by which children with autistic spectrum disorders have high urinary mercury concentrations, the DMSA treatment described in this study might be useful to diag- nose their present burden of mercury.
Using gamma-32P-labeled 8-azidopurine nucleotide photoaffinity probes of GTP and ATP, the respective purine ring binding domain peptides of tubulin have been identified. First, the location of the GTP-specific binding site was shown to be on the beta-subunit, whereas the major ATP-specific binding site was on the alpha-subunit. Using a combination of anion-exclusion and immobilized Al3+ column chromatography, the respective photolabeled tryptic peptides of both nucleotide binding sites were isolated, further purified by reverse phase high performance liquid chromatography (HPLC) and sequenced. Chymotryptic peptides were also generated for the GTP binding site. High retention of the photoinserted radiolabel was observed with many of the peptides on reverse phase HPLC at low flow rates. The stability of the photoinserted radiolabel to HPLC varied with different peptides. However, certain peptides were easily distinguished as being within the base binding domains of the GTP and ATP binding sites of tubulin. Two beta-tubulin peptides containing the majority of photoinserted [gamma-32P]8-azidoguanosine 5'-triphosphate corresponded to N-terminal beta-tubulin amino acid residues 3EIVHIQAGQCGNQIGAK19 and 20FWEVISDEHGIDPTGS35. The peptide containing the majority of photoinserted [gamma-32P]8-azidoadenosine 5'-triphosphate corresponded to the C-terminal alpha-tubulin sequence 431DYEEVGVDSVEGEGEEEGEE450.
Minute amounts of mercury vapor are released from dental amalgams. Since mercury vapor is known to be associated with adverse health effects from occupationally exposed persons, questions regarding the margin of safety for exposure to mercury vapor in the general population continue to be raised. To address this issue, one needs information regarding exposure to mercury vapor from dental amalgam fillings and its possible consequences for health in the general population. The NIDR Amalgam Study is designed to obtain precise information on amalgam exposure and health outcomes for a non-occupationally-exposed population of US adults. One hypothesis was that in a generally healthy population a significant association between amalgam exposure and Hg levels in urine and/or whole blood could be detected. The cohort investigated was an adult military population of 1127 healthy males. Their average age was 52.8 years, and their ages varied from 40 to 78 years. Ninety-five percent of the study participants were white males, and slightly over 50% had some college education. Five percent were edentulous. The dentate participants, on average, had 25 natural teeth, 36.9 decayed or filled surfaces (DFS), and 19.9 surfaces exposed to amalgam, with amalgam exposure varying from 0 to 66 surfaces. Their average total and inorganic urinary mercury concentrations were 3.09 microg/L and 2.88 microg/L. The average whole-blood total and inorganic mercury concentrations were 2.55 microg/L and 0.54 microg/L. Significant correlations were detected between amalgam exposure and the total (r = 0.34, p < 0.001) and inorganic 0.34 (r = 0.34, p < 0.001) urinary mercury concentrations on the original scale. Stronger correlations were found for total (r = 0.44, p < 0.001) and inorganic (r = 0.41, p < 0.001) urinary Hg on the log scale, as well as for creatinine-corrected total (r = 0.43, p < 0.001) and inorganic (r = 0.43, p < 0.001) urine concentrations. In whole blood, statistically significant, but biologically weak, correlations were detected for total (r = 0.09, p = 0.005) and inorganic (r = 0.15, p < 0.001) Hg concentrations, respectively. Based on these cross-sectional data, it is estimated that, on average, each ten-surface increase in amalgam exposure is associated with an increase of 1 microg/L mercury in urine concentration.
This study evaluated the predictive utility of olfactory identification deficits in patients with mild cognitive impairment for follow-up diagnosis of probable Alzheimer's disease.
Ninety outpatients with mild cognitive impairment were examined at 6-month intervals. Matched healthy comparison subjects (N=45) were examined annually. The University of Pennsylvania Smell Identification Test was given at baseline.
Olfaction scores were lower in patients with mild cognitive impairment than in healthy comparison subjects. Seventy-seven patients were followed up; 19 were diagnosed with Alzheimer's disease by 2 years. Patients with low olfaction scores (< or =34 of 40), and patients with low olfaction scores who reported no subjective problems smelling, were more likely to develop Alzheimer's disease than other patients. In a Cox proportional hazards model adjusted for age, sex, modified Mini-Mental State score, and education, low olfaction scores did not predict time until development of Alzheimer's disease, but low olfaction scores accompanied by lack of awareness of olfactory deficits predicted time to development of Alzheimer's disease. This effect remained when attention or memory measures replaced modified Mini-Mental State score in the model. In patients with high Mini-Mental State scores (> or =27 of 30), low olfaction with lack of awareness remained a significant predictor of Alzheimer's disease. Olfaction scores of 30-35 showed moderate to strong sensitivity and specificity for diagnosis of Alzheimer's disease at follow-up.
In patients with mild cognitive impairment, olfactory identification deficits, particularly with lack of awareness of olfactory deficits, may have clinical utility as an early diagnostic marker for Alzheimer's disease.
Reported rates of autism have increased sharply in the United States and the United Kingdom. One possible factor underlying these increases is increased exposure to mercury through thimerosal-containing vaccines, but vaccine exposures need to be evaluated in the context of cumulative exposures during gestation and early infancy. Differential rates of postnatal mercury elimination may explain why similar gestational and infant exposures produce variable neurological effects. First baby haircut samples were obtained from 94 children diagnosed with autism using Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM IV) criteria and 45 age- and gender-matched controls. Information on diet, dental amalgam fillings, vaccine history, Rho D immunoglobulin administration, and autism symptom severity was collected through a maternal survey questionnaire and clinical observation. Hair mercury levels in the autistic group were 0.47 ppm versus 3.63 ppm in controls, a significant difference. The mothers in the autistic group had significantly higher levels of mercury exposure through Rho D immunoglobulin injections and amalgam fillings than control mothers. Within the autistic group, hair mercury levels varied significantly across mildly, moderately, and severely autistic children, with mean group levels of 0.79, 0.46, and 0.21 ppm, respectively. Hair mercury levels among controls were significantly correlated with the number of the mothers' amalgam fillings and their fish consumption as well as exposure to mercury through childhood vaccines, correlations that were absent in the autistic group. Hair excretion patterns among autistic infants were significantly reduced relative to control. These data cast doubt on the efficacy of traditional hair analysis as a measure of total mercury exposure in a subset of the population. In light of the biological plausibility of mercury's role in neurodevelopmental disorders, the present study provides further insight into one possible mechanism by which early mercury exposures could increase the risk of autism.
Methylation events play a critical role in the ability of growth factors to promote normal development. Neurodevelopmental toxins, such as ethanol and heavy metals, interrupt growth factor signaling, raising the possibility that they might exert adverse effects on methylation. We found that insulin-like growth factor-1 (IGF-1)- and dopamine-stimulated methionine synthase (MS) activity and folate-dependent methylation of phospholipids in SH-SY5Y human neuroblastoma cells, via a PI3-kinase- and MAP-kinase-dependent mechanism. The stimulation of this pathway increased DNA methylation, while its inhibition increased methylation-sensitive gene expression. Ethanol potently interfered with IGF-1 activation of MS and blocked its effect on DNA methylation, whereas it did not inhibit the effects of dopamine. Metal ions potently affected IGF-1 and dopamine-stimulated MS activity, as well as folate-dependent phospholipid methylation: Cu(2+) promoted enzyme activity and methylation, while Cu(+), Pb(2+), Hg(2+) and Al(3+) were inhibitory. The ethylmercury-containing preservative thimerosal inhibited both IGF-1- and dopamine-stimulated methylation with an IC(50) of 1 nM and eliminated MS activity. Our findings outline a novel growth factor signaling pathway that regulates MS activity and thereby modulates methylation reactions, including DNA methylation. The potent inhibition of this pathway by ethanol, lead, mercury, aluminum and thimerosal suggests that it may be an important target of neurodevelopmental toxins.
Autism is a complex neurodevelopmental disorder that usually presents in early childhood and that is thought to be influenced by genetic and environmental factors. Although abnormal metabolism of methionine and homocysteine has been associated with other neurologic diseases, these pathways have not been evaluated in persons with autism.
The purpose of this study was to evaluate plasma concentrations of metabolites in the methionine transmethylation and transsulfuration pathways in children diagnosed with autism.
Plasma concentrations of methionine, S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), adenosine, homocysteine, cystathionine, cysteine, and oxidized and reduced glutathione were measured in 20 children with autism and in 33 control children. On the basis of the abnormal metabolic profile, a targeted nutritional intervention trial with folinic acid, betaine, and methylcobalamin was initiated in a subset of the autistic children.
Relative to the control children, the children with autism had significantly lower baseline plasma concentrations of methionine, SAM, homocysteine, cystathionine, cysteine, and total glutathione and significantly higher concentrations of SAH, adenosine, and oxidized glutathione. This metabolic profile is consistent with impaired capacity for methylation (significantly lower ratio of SAM to SAH) and increased oxidative stress (significantly lower redox ratio of reduced glutathione to oxidized glutathione) in children with autism. The intervention trial was effective in normalizing the metabolic imbalance in the autistic children.
An increased vulnerability to oxidative stress and a decreased capacity for methylation may contribute to the development and clinical manifestation of autism.
We previously described a polymorphism in exon 4 of the gene encoding the heme biosynthetic pathway enzyme, coproporphyrinogen oxidase (CPOX4), which significantly modifies the effect of mercury exposure on urinary porphyrin excretion in humans. Here, we examined potential consequences of this polymorphism (“CPOX4”) on performance within neurobehavioral domains, symptoms, and mood that are known to be affected by elemental mercury (Hg°) exposure in human subjects. A behavioral test battery was administered on the day of urine and buccal cell collections for 194 male dentists (DDs) and 233 female dental assistants (DAs) occupationally exposed to Hg° for an average of 19 and 10 years, respectively. Subjects had no history of health disorders and were employed for a minimum of 5 years in the dental profession. Respective mean urinary mercury (HgU) levels in DDs and DAs were 3.32 (4.87) μg/l and 1.98 (2.29) μg/l. Corresponding indices of chronic occupational Hg° exposure, weighted for historical exposure, were 27.1 (20.6) and 15.2 (12.3). The frequencies of the homogygous common (A/A), heterozygous (A/C), and homozygous polymorphic (C/C) genotypes were 75%, 23% and 2% for DDs and 73%, 25%, and 2% for DAs, respectively. DDs and DAs were evaluated separately. Regression analyses controlled for age, premorbid intelligence, alcohol consumption, and education.
Reported rates of autism have increased sharply in the United States and the United Kingdom. One possible factor underlying these increases is increased exposure to mercury through thimerosal-containing vaccines, but vaccine exposures need to be evaluated in the context of cumulative exposures during gestation and early infancy. Differential rates of postnatal mercury elimination may explain why similar gestational and infant exposures produce variable neurological effects. First baby haircut samples were obtained from 94 children diagnosed with autism using Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM IV) criteria and 45 age- and gender-matched controls. Information on diet, dental amalgam fillings, vaccine history, Rho D immunoglobulin administration, and autism symptom severity was collected through a maternal survey questionnaire and clinical observation. Hair mercury levels in the autistic group were 0.47 ppm versus 3.63 ppm in controls, a significant difference. The mothers in the autistic group had significantly higher levels of mercury exposure through Rho D immunoglobulin injections and amalgam fillings than control mothers. Within the autistic group, hair mercury levels varied significantly across mildly, moderately, and severely autistic children, with mean group levels of 0.79, 0.46, and 0.21 ppm, respectively. Hair mercury levels among controls were significantly correlated with the number of the mothers' amalgam fillings and their fish consumption as well as exposure to mercury through childhood vaccines, correlations that were absent in the autistic group. Hair excretion patterns among autistic infants were significantly reduced relative to control. These data cast doubt on the efficacy of traditional hair analysis as a measure of total mercury exposure in a subset of the population. In light of the biological plausibility of mercury's role in neurodevelopmental disorders, the present study provides further insight into one possible mechanism by which early mercury exposures could increase the risk of autism.
There is increasing evidence to support a role for both the amyloid beta-protein precursor (A beta PP) and its proteolytic fragment, amyloid beta (A beta), in metal ion homeostasis. Furthermore, metal ions such as zinc and copper can interact with both A beta PP and A beta to potentiate Alzheimer's disease by participating in the aggregation of these normal cellular proteins and in the generation of reactive oxygen species. In addition, metal ions may interact on several other AD-related pathways, including those involved in neurofibrillary tangle formation, secretase cleavage of A beta PP and proteolytic degradation of A beta. As such, a dysregulation of metal ion homeostasis, as occurs with both aging and in AD, may foster an environment that can both precipitate and accelerate degenerative conditions such as AD. This offers a broad biochemical front for novel therapeutic interventions.
The release of both Aβ 1-40 and Aβ 1-42 into the culture medium was increased by exposure of SHSY5Y cells to mercury. Melatonin preincubation resulted in a significant decrease in Aβ release. The mercury-induced increase in Aβ release may be caused through mercury’s deleterious action on essential kinase enzymes involved in the α-secretase pathway of APP metabolism. The result could be that cells are pushed toward the β-secretase pathway of APP metabolism, resulting in an increase in Aβ release. Mercury has previously been shown to be a potent inhibitor of enzymes, especially those containing sulfhydryl groups (Edstrom and Mattsson, 1976). Protein kinase C activity in vitro and in brain tissue is markedly reduced in a concentration-dependent manner by mercury (Rajanna et al., 1995). Phorbol ester binding to protein kinase C is also inhibited by micromolar concentrations of mercury (Rajanna et al., 1995). It is thus possible that increased levels of mercury reduce protein kinase C-mediated α-secretase activity with the consequence of increased Aβ formation because protein kinase C mediates activation of the α-secretase pathway. Mercury induces both Aβ production and oxidative stress; thus, the chelation of mercury by melatonin could shift the APP metabolism back toward the α-secretase pathway, reducing Aβ production and the concomitant oxidative stress-inducing effects of mercury and Aβ. Aβ-Fibrillogenesis is also inhibited by melatonin, thereby potentially reducing the toxic buildup of Aβ 1-40 and Aβ 1-42 fibrils (Pappolla et al., 1998). Furthermore, melatonin has been shown to reduce the release of soluble APP from cells in culture and to reduce the levels of APP mRNA and other housekeeping protein mRNAs (Song and Lahiri, 1997). These data suggest that melatonin may be involved in metabolic mechanisms regulating APP and other essential cellular protein production, over and above its antioxidant capacity.
Mercury toxicity and intoxication (poisoning) are realities that every American needs to face. Both the Environmental Protection Agency and National Academy of Science state that between 8 to 10% of American women have mercury levels that would render any child they gave birth to neurological disorders. One of six children in the USA have a neurodevelopmental disorder according to the Centers for Disease Control and Preven- tion. Yet our dentistry and medicine continue to expose all patients to mercury. This article discusses the obvious sources of mercury exposures that can be easily prevented. It also points out that genetic susceptibility and exposures to other materials that synergistically enhance mercury and ethyl- mercury toxicity need to be evaluated, and that by their existence prevent the actual determination of a "safe level" of mercury exposure for all. The mercury sources we consider are from dentistry and from drugs, mainly vaccines, that, in today's world are not only unnecessary sources, but also sources that are being increasingly recognized as being significantly deleterious to the health of many. © Copyright 2005, Pearblossom Private School, Inc.-Publishing Division.
AimsIt is now well established that there are abnormalities in the sense of smell in patients suffering from Alzheimer's disease (AD). They have both raised olfactory thresholds and impaired odour identification. The situation in vascular dementia is unclear. We used the University of Pennsylvania Smell Identification Test (UPSIT), a 40-item, forced choice, cued, ‘scratch-and- sniff’ test, to examine olfactory identification in vascular dementia and to determine whether it would differentiate the disorder from AD and normal elderly.Methods
We investigated three matched subject groups: 13 people having a Cambridge Examination for Mental Disorders in the Elderly (CAMDEX) diagnosis of definite senile dementia of Alzheimer type, 13 having a CAMDEX diagnosis of definite vascular dementia and 13 non-cognitively impaired controls. The subjects were then tested with the UPSIT in their own home by an independent blind researcher to see if the test could distinguish the different diagnostic groups in this setting.ResultsThe median UPSIT score was 30 (out of a maximum of 40) for controls, 12 for the vascular group and 15 for the AD group. The difference was significant (p = 0.05) between both demented groups and the normal controls. Similarly there was a significant difference in the UPSIT score between the AD group and controls (p = 0.001) and between the vascular dementia group and controls (p = 0.001), but there was no significant difference between the AD group and the vascular dementia group. The UPSIT score correlated strongly with the degree of cognitive impairment as measured by the CAMCOG (rs = 0.683, p = 0.01)Conclusions
Patients with vascular dementia had a similar degree of olfactory impairment to those with AD. The UPSIT successfully differentiated between dementia patients and normal elderly British subjects tested in their own homes. The UPSIT did not differentiate between those with AD and vascular dementia. Copyright © 2001 John Wiley & Sons, Ltd
Objectives:
We sought to investigate the possible pathogenetic role of myocardial trace elements (TE) in patients with various forms of cardiac failure.
Background:
Both myocardial TE accumulation and deficiency have been associated with the development of heart failure indistinguishable from an idiopathic dilated cardiomyopathy.
Methods:
Myocardial and muscular content of 32 TE has been assessed in biopsy samples of 13 patients (pts) with clinical, hemodynamic and histologic diagnosis of idiopathic dilated cardiomyopathy (IDCM), all without past or current exposure to TE. One muscular and one left ventricular (LV) endomyocardial specimen from each patient, drawn with metal contamination-free technique, were analyzed by neutron activation analysis and compared with 1) similar surgical samples from patients with valvular (12 pts) and ischemic (13 pts) heart disease comparable for age and degree of LV dysfunction; 2) papillary and skeletal muscle surgical biopsies from 10 pts with mitral stenosis and normal LV function, and 3) LV endomyocardial biopsies from four normal subjects.
Results:
A large increase (>10,000 times for mercury and antimony) of TE concentration has been observed in myocardial but not in muscular samples in all pts with IDCM. Patients with secondary cardiac dysfunction had mild increase (< or = 5 times) of myocardial TE and normal muscular TE. In particular, in pts with IDCM mean mercury concentration was 22,000 times (178,400 ng/g vs. 8 ng/g), antimony 12,000 times (19,260 ng/g vs. 1.5 ng/g), gold 11 times (26 ng/g vs. 2.3 ng/g), chromium 13 times (2,300 ng/g vs. 177 ng/g) and cobalt 4 times (86,5 ng/g vs. 20 ng/g) higher than in control subjects.
Conclusions:
A large, significant increase of myocardial TE is present in IDCM but not in secondary cardiac dysfunction. The increased concentration of TE in pts with IDCM may adversely affect mitochondrial activity and myocardial metabolism and worsen cellular function.
A testing procedure is described for the assessment of the toxicological response (e.g., acute toxicity or mutagenicity) of any combination and number of chemical, physical, and biological agents, with no more effort for a particular combination than for a single agent. The method provides a simple, sensitive, and quantitative index of synergism, antagonism, and additivity, and it has been demonstrated experimentally in rats by determining the acute lethality of combinations of cadmium, mercury, and lead salts. In a combination of two metal salts, the dose of one metal of the pair was fixed at or near the no-effect level while the dose of the second metal was increased until the entire dose-response curve was obtained. To evaluate interactions of the three metals, the previous pair of metals were kept fixed at their combined extrapolated LD1 level, and the third metal was increased. The statistical treatment of the data employed a computer program that did not involve probit transformations, but rather the approximate linear relationship between the fractional response and the logarithm of the dose. A particular combination could be synergistic, antagonistic, or additive, depending on the relative doses employed. Generally, a combination was synergistic when the most toxic member was present at or near its LD1 dose in the presence of the much less toxic member; the same combination was protective when the least toxic member was present at or near its LD1 dose. The results clarify apparently contradictory reports regarding the biological effects of metal combinations. The application of the testing procedure to combinations of mutagens is described, and an example is cited involving, for a particular bacterial mutagen, a combination of N-methyl-N'-nitro-N-nitrosoguanidine with ethylmethanesulfonate.
In this report, 8- and 2-azidoadenosine 5'-[gamma-32P]triphosphate were used to examine cerebrospinal fluid (CSF) samples for the presence of an ATP binding protein unique to individuals with Alzheimer disease (AD). A 42-kDa ATP binding protein was found in the CSF of AD patients that is not observed in CSF from normal patients or other neurological controls. The photolabeling is saturated with 30 microM 2-azidoadenosine 5'-[gamma-32P]triphosphate. Photoinsertion can be totally prevented by the addition of 25 microM ATP. Photoinsertion of 2-azidoadenosine 5'-triphosphate into the protein is only weakly protected by other nucleotides such as ADP and GTP, indicating that this is a specific ATP binding protein. A total of 83 CSF samples were examined in a blind manner. The 42-kDa protein was detected in 38 of 39 AD CSF samples and in only 1 of 44 control samples. This protein was identified as glutamine synthetase [GS; glutamate-ammonia ligase; L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2] based on similar nucleotide binding properties, comigration on two-dimensional gels, reaction with a polyclonal anti-GS antibody, and the presence of significant GS enzyme activity in AD CSF. In brain, GS plays a key role in elimination of free ammonia and also converts the neurotransmitter and excitotoxic amino acid glutamate to glutamine, which is not neurotoxic. The involvement of GS, if any, in the onset of AD is unknown. However, the presence of GS in the CSF of terminal AD patients suggests that this enzyme may be a useful diagnostic marker and that further study is warranted to determine any possible role for glutamate metabolism in the pathology of AD.
The hazards of mercury from dental amalgams have long been recognized. This study examined the mercury release from a "non-mercury-releasing" dental amalgam, Composil, over a 104-week period. Four cylindrical specimens were incubated in 10 ml of purified water at 37 degrees C. The incubate was changed at the end of each 24-hour period and assayed for its mercury content at biweekly intervals. Mercury estimation was carried out using cold-vapor, atomic absorption spectrophotometry over a 104-week period. Results showed that the overall mean release of mercury was 43.5 +/- 3.2 micrograms/cm2/24 hr, and the amount of mercury released remained fairly constant during the duration of the experiment. This study showed that Composil releases mercury in quantities that far exceed those detected in other amalgam systems.
Guanosine triphosphate (GTP) is an absolute requirement for tubulin polymerization in situ. The nucleotide photoaffinity probe 8-azidoguanosine 5'-triphosphate (8N3GTP) has been shown to be a biological mimic of GTP in this system and, also, an effective active site probe of the exchangeable GTP binding site. Using [32P]8N3GTP we demonstrate that the exchangeable GTP site of the beta subunit of tubulin is available to added guanine nucleotide in normal aged brain homogenates, whereas it is variably unavailable in Alzheimer's diseased brain. Inability of 8N3GTP to photolabel beta tubulin appears to be associated with neurofibrillary tangle density. These results support the hypothesis that microtubule formation is abnormal in brains affected by Alzheimer's disease.
Alzheimer's disease (AD) brain trace-element imbalances in the amygdala, hippocampus and nucleus basalis of Meynert (nbM) are found in most cases to be consistent with those previously reported in samples derived principally from AD cerebral cortex (Ehmann et al., 1986). The elevation of mercury in AD nbM, as compared to age-matched controls, is the largest trace-element imbalance observed to date in AD brain. In addition to the general confirmation of imbalances for Cs, Hg, N, Na, P, and Rb noted previously in cerebral cortex samples, imbalances for Fe, K, Sc, and Zn were observed in two regions and one region also exhibited imbalances for both Co and Se. Persistent imbalances for the univalent cations Na, K, Rb and Cs support arguments for a membrane abnormality in AD. The data presented here also provide the first comprehensive simultaneous multi-element determinations in both control and AD nbM.
The 8-azidopurine analogs of adenosine and guanine nucleotides have proved to be very useful probes for nucleotide-binding sites. In most systems they have proved to be effective mimics of the natural compounds with 1) both 8-azidoadenosine-3',5'-monophosphate and 8-azidoguanosine-3',5'-monophosphate activating their respective kinases, 2) 8-azidoguanosine-5'-triphosphate effecting tubulin polymerization and activation of adenylate cyclase, and 3) 8-azidoadenosine-5'-triphosphate appearing to be a substrate for a large number of ATPases and several kinases. As photoprobes they have been used to 1) isolate and study active site peptides; 2) determine the membrane sidedness and cellular location of binding sites; 3) detect the availability of various nucleotide-binding sites as cells progress through development, maturation, infectious stages, etc.; 4) study membrane-soluble partitioning of binding sites relative to nucleotide regulation of a biochemical process; 5) detect nucleotide-binding sites exposed by small molecules such as Ca2+ and calmodulin; and 6) detect potential catalytic and regulatory subunits of protein kinases found in preparations that actively phosphorylate endogenous substrates. The difference between the gamma-32P-labeled 8-azidopurine nucleotide triphosphate and the alpha-32P-labeled species has been used to study the in situ hydrolysis of the nucleotides on specific protein receptors and determine the fate of the produced nucleotide diphosphate. Such factors are important in studying the molecular dynamics of such systems as tubulin polymerization, G-actin to F-actin conversions, and GTP activation of adenylate cyclase. A review of techniques used and data obtained with these probes is presented.
The effect of intestinal flora on the absorption and dispositon of mercury in tissues was investigated using conventional rats, and rats treated with antibiotics to eliminate their gut flora. Antibiotic-treated rats given [203Hg]-labeled methylmercuric chloride orally had significantly more mercury in their tissues, especially in kidney, brain, lung, blood, and skeletal muscle, and also excreted less mercury in the feces than conventional rats. Furthermore, in the kidneys of the antibiotic-treated rats, the proportion of mercury present as organic mercury was greater than in the kidneys of the conventional rats. The results suppport the hypothesis that the metabolism of methylmercuric chloride by the gut flora reduces the tissue content of mercury. When rats were administered 10 mg methylmercuric chloride/kg . day for 6 days, four of five of those given antibiotics developed neurological symptoms of toxicity, whereas only one of five conventional rats given methylmercuric chloride was affected.
An in vitro screening test was used to compare the cytotoxicity and elemental release from mercury- and gallium-based dental restorative materials.
The test employed three sequential extractions of the samples into cell-culture medium which were then used to evaluate the cytotoxicity of the samples and the release of elements from the samples. Cytotoxicity was measured by placing the extract in contact with Balb/c mouse fibroblasts for 24 h and measuring the succinic dehydrogenase activity of the cells. The release of elements was measured by means of atomic absorption spectrophotometry.
Samples of Tytin (Kerr) showed no cytotoxicity compared to Teflon controls. Dispersalloy (Johnson and Johnson) was severely cytotoxic initially when Zn release was greatest, but was less toxic between 48 and 72 h as Zn release decreased. Gallium Alloy GF (Tokuriki Honten) was moderately cytotoxic after 8 h, and increased in cytotoxicity thereafter, which correlated with a substantial and persistent release of Ga from this material.
The results of the current study concurred with in vivo assessments of these materials, and the use of sequential extractions was useful in determining trends in the cytotoxicity and elemental release from these materials.
For more than 160 years dentistry has used silver amalgam, which contains approximately 50% Hg metal, as the preferred tooth filling material. During the past decade medical research has demonstrated that this Hg is continuously released as vapor into mouth air; then it is inhaled, absorbed into body tissues, oxidized to ionic Hg, and finally covalently bound to cell proteins. Animal and human experiments demonstrate that the uptake, tissue distribution, and excretion of amalgam Hg is significant, and that dental amalgam is the major contributing source to Hg body burden in humans. Current research on the pathophysiological effects of amalgam Hg has focused upon the immune system, renal system, oral and intestinal bacteria, reproductive system, and the central nervous system. Research evidence does not support the notion of amalgam safety.
The long-term urinary mercury excretion was determined in 17 28- to 55-year-old persons before and at varying times (up to 14 months) after removal of all (4-24) dental amalgam fillings. Before removal the urinary mercury excretion correlated with the number of amalgam fillings. In the immediate post-removal phase (up to 6 days after removal) a mean increase of 30% was observed. Within 12 months the geometric mean of the mercury excretion was reduced by a factor of 5 from 1.44 micrograms/g (range: 0.57-4.38 micrograms/g) to 0.36 microgram/g (range: 0.13-0.88 microgram/g). After cessation of exposure to dental amalgam the mean half-life was 95 days. These results show that the release of mercury from dental amalgam contributes predominantly to the mercury exposure of non-occupationally exposed persons. The exposure from amalgam fillings thus exceeds the exposure from food, air and beverages. Within 12 months after removal of all amalgam fillings the participants showed substantially lower urinary mercury levels which were comparable to those found in subjects who have never had dental amalgam fillings. A relationship between the urinary mercury excretion and adverse effects was not found. Differences in the frequency of effects between the pre- and the post-removal phase were not observed.
We have found that EDTA and EGTA complexes of Hg2+, which conventional wisdom has assumed are biologically inert, are potentially injurious to the neuronal cytoskeleton. Tubulin, a major protein component of the neuronal cytoskeleton, is the target of multiple toxicants, including many heavy metal ions. Among the mercurials, inorganic mercuric ion (Hg2+) is one of the most potent inhibitors of microtubule polymerization both in vivo and in vitro. In contrast to other heavy metals, the capacity of Hg2+ to inhibit microtubule polymerization or disrupt formed microtubules cannot be prevented by the addition of EDTA and EGTA, both of which bind Hg2+ with very high affinity. To the contrary, the addition of these two chelating agents potentiates Hg2+ inhibition of tubulin polymerization. Results herein show that HgEDTA and HgEGTA inhibit tubulin polymerization by disrupting the interaction of GTP with the E-site of brain beta-tubulin, an obligatory step in the polymerization of tubulin. Both HgEDTA and HgEGTA, but not free Hg2+, prevented binding of [32P]8N3GTP, a photoaffinity nucleotide analog of GTP, to the E-site and displaced bound [32P]8N3GTP at low micromolar concentrations. This complete inhibition of photoinsertion into the E-site occurred in a concentration- and time-dependent fashion and was specific for Hg2+ complexes of EDTA and EGTA, among the chelating agents tested. Given the ubiquity of Hg2+ in the environment and the widespread use of EDTA in foodstuffs and medicine, these mercury complexes may pose a potentially serious threat to human health and play a role in diseases of the neuronal cytoskeleton.
Porphyrins are formed as intermediates in the biosynthesis of heme. In humans and other mammals, porphyrins with eight, seven, six, five, and four carboxyl groups are excreted in the urine in a well‐established pattern. Mercury selectively alters porphyrin metabolism in kidney proximal tubule cells, leading to an altered urinary porphyrin excretion pattern. Previous studies in rats have shown that changes in the urinary porphyrin profile during exposure to mercury as methylmercury hydroxide are uniquely characterized by highly elevated (20‐ to 30‐fold) levels of four‐ and five‐carboxyl porphyrins and by the excretion of an atypical porphyrin (“precoproporphyrin”), which elutes on high performance liquid chromatography (HPLC) approximately midway between penta‐ and coproporphyrins. Changes in the urinary porphyrin profile are highly correlated with the dose and duration of mercury exposure and persist for up to 20 wk following cessation of mercury treatment. In the present studies, the utility of urinary porphyrin profile changes as a biomarker of mercury exposure in human subjects was evaluated. Urinary porphyrin concentrations were measured in dentists participating in the Health Screening Programs conducted during the 1991 and 1992 annual meetings of the American Dental Association and compared with urinary mercury levels measured in the same subjects. Among dentists with no detectable urinary mercury, mean concentrations of urinary porphyrins were within the established normal ranges for male human subjects.
Copper (Cu), iron (Fe), and zinc (Zn) levels in five different brain regions (amygdala, hippocampus, inferior parietal lobule, superior and middle temporal gyri, and cerebellum) were determined by instrumental neutron activation analysis (INAA) in samples from Alzheimer's disease (AD) patients and age-matched control subjects. A significant decrease in Cu, and significant increases in Zn and Fe were found in AD hippocampus and amygdala, areas showing severe histopathologic alterations in AD. None of these elements were significantly imbalanced in the cerebellum which is minimally affected in AD.
The activity of the astrocytic enzyme glutamine synthetase (GS) is decreased in the Alzheimer's disease brain, which may have relevance to mechanisms of chronic excitotoxicity. The molecular perturbation(s) that results in GS inactivation is not known, although oxidative lesioning of the enzyme is one likely cause. To assess structural perturbation induced in GS by metal-catalyzed oxidation, a series of spin-labeling studies were undertaken. Ovine GS was oxidized by exposure to iron/hydrogen peroxide and subsequently labeled with the thiol-specific nitroxide probe MTS [(1-oxyl-2,2,5,5-tetramethyl-pyrroline-3-methyl)methanethiosulfonate]. The reaction of MTS with cysteine residues within GS was monitored in real time by electron paramagnetic resonance spectrometry. Structural perturbation of GS, manifested as decreased thiol accessibility, was inferred from an apparent decrease in the rate constant for the second-order reaction of MTS with protein thiols. A subsequent spin-labeling study was undertaken to compare the structural integrity of GS purified and isolated from Alzheimer's disease-afflicted brain (AD-GS) with that of GS isolated from nondemented, age-matched control brain (C-GS). The rate constant for reaction of MTS with AD-GS was markedly decreased relative to that for the reaction of spin label with C-GS. The kinetic data were partially corroborated by spectroscopic data obtained from circular dichroism analysis of control and peroxide-treated ovine GS. In an adjunct experiment, the interaction of GS with a synthetic analogue of the Alzheimer's-associated beta-amyloid peptide, known to induce free radical oxidative stress, indicated strong interaction of the enzyme with the peptide as reflected by a decrease in the rate constant for MTS binding to reactive protein thiols.
Hg2+ interacts with brain tubulin and disassembles microtubules that maintain neurite structure. Since it is well known that Hg vapor (Hg0) is continuously released from "silver" amalgam tooth fillings and is absorbed into brain, rats were exposed to Hg0 4h/day for 0, 2, 7, 14 and 28 d at 250 or 300 micrograms Hg/m3 air, concentrations present in mouth air of some humans with many amalgam fillings. Average rat brain Hg concentrations increased significantly (11-47 fold) with duration of Hg0 exposure. By 14 d Hg0 exposure, photoaffinity labelling on the beta-subunit of the tubulin dimer with [alpha 32P] 8N3 GTP in brain homogenates was decreased 41-74%, upon analysis of SDS-PAGE autoradiograms. The identical neurochemical lesion of similar or greater magnitude is evident in Alzheimer brain homogenates from approximately 80% of patients, when compared to human age-matched neurological controls. Total tubulin protein levels remained relatively unchanged between Hg0 exposed rat brains and controls, and between Alzheimer brains and controls. Since the rate of tubulin polymerization is dependent upon binding of GTP to tubulin dimers, we conclude that chronic inhalation of low-level Hg0 can inhibit polymerization of brain tubulin essential for formation of microtubules.
The report shows that Alzheimer's disease (AD) brain creatine kinase (CK) is modified such that the nucleotide binding site of CK is blocked and that abnormal partitioning of CK between the soluble and pellet fractions occurs. First, CK activity was 86% decreased in AD brain homogenates in comparison to age-matched controls. Secondly, over a 23.5 fold greater 32P photoincorporation of [alpha 32P]8N3ATP was observed into CK of control vs. AD samples. Also, a 7.4-fold increase of enzyme induced 32P incorporation was observed in controls vs. AD samples by incubation with [gamma 32P]ATP. Thirdly, Western blot analysis showed that CK copy numbers in the AD homogenate were decreased by less than 14% in comparison to controls. However, analysis showed that control supernatant and pellet fractions contained 10.3 and 0.4 times the CK copy number found in the corresponding AD fractions. 32P incorporation by both photolabeling and enzyme catalyzed incorporation of radiolabel followed CK activity and not CK copy number. Further, [alpha 32P]ADP and [gamma 32P]ATP incorporated 32P into control brain and purified brain CK equally well, indicating that a mechanism different from gamma-phosphoryl transfer is involved in the enzymatic incorporation of radiolabel. Also, the level of abnormal partitioning of CK into AD brain pellet correlated with the decreased [32P]8N3GTP photolabeling and abnormal partitioning of beta-tubulin, a protein known to be aberrantly modified in the AD brain. This indicates that a common chemistry is affecting both CK and tubulin in AD.
Alzheimer's disease (AD) is a common neurodegenerative disorder that leads to dementia and death. In addition to several genetic parameters, various environmental factors may influence the risk of getting AD. In order to test whether blood levels of the heavy metal mercury are increased in AD, we measured blood mercury concentrations in AD patients (n = 33), and compared them to age-matched control patients with major depression (MD) (n = 45), as well as to an additional control group of patients with various non-psychiatric disorders (n = 65). Blood mercury levels were more than two-fold higher in AD patients as compared to both control groups (p = 0.0005, and p = 0.0000, respectively). In early onset AD patients (n = 13), blood mercury levels were almost three-fold higher as compared to controls (p = 0.0002, and p = 0.0000, respectively). These increases were unrelated to the patients' dental status. Linear regression analysis of blood mercury concentrations and CSF levels of amyloid beta-peptide (A beta) revealed a significant correlation of these measures in AD patients (n = 15, r = 0.7440, p = 0.0015, Pearson type of correlation). These results demonstrate elevated blood levels of mercury in AD, and they suggest that this increase of mercury levels is associated with high CSF levels of A beta, whereas tau levels were unrelated. Possible explanations of increased blood mercury levels in AD include yet unidentified environmental sources or release from brain tissue with the advance in neuronal death.
Ingestion of fish or grain contaminated with methylmercury resulted in epidemics of severe neurotoxicity and death in Japan in the 1950s and 1960s1 and in Iraq in 1972.2 The World Health Organization and other organizations have warned of the dangers of methylmercury compounds to the environment and to scientific researchers.1,3–6 Dimethylmercury may be even more dangerous than methylmercury compounds. The physical properties of dimethylmercury permit transdermal absorption, and the volatility of this liquid permits toxic exposure through inhalation. Since dimethylmercury is lethal at a dose of approximately 400 mg of mercury (equivalent to a few drops, or about . . .
The mercury concentration in 70 breast milk samples (Hg-M) from 46 mothers, collected within the first 7 days after delivery, was determined by cold vapour atomic absorption spectrometry. For comparison, 9 formula milk samples (reconstituted with Hg-free water) were investigated. The Hg-M in the human milk samples ranged from < 0.2 to 6.86 micrograms/L (median 0.37), in the formula milk samples from 0.4 to 2.5 micrograms/L (median 0.76). The Hg-M in the breast milk samples correlates positively with the number of maternal teeth with dental amalgam. The mean Hg-M of amalgam-free mothers was < 0.2 microgram/L, while milk from mothers with 1-4 amalgam fillings contained 0.57 microgram/L, with 5-7 fillings 0.50 microgram/L and with more than 7 fillings 2.11 micrograms/L. Hg-M correlated negatively to the day after delivery. Frequency of fish consumption tends to influence Hg-M positively, while the age of the mother shows no significant correlation. In the first 2 to 3 days after delivery some colostrum samples with Hg-M higher than in formula milk were found. Later on, the Hg-concentration in the breast milk was equal or even lower to that in formula milk. The higher Hg burden of infants' tissues from mothers with dental amalgam, as reported previously, must be explained (1) by a prenatal transfer of Hg from the mother's fillings through the placenta to the fetus, followed by a redistribution of this Hg in the body of the newborn, and (2) an additional burden via breast milk. Nevertheless, the comparison of Hg-M in breast and formula milk, the relatively moderate Hg burden in both kinds of milk, and the multiple manifest advantages of breast feeding speak against any limitation of nursing, even for mothers with a large number of dental amalgam fillings.
Apolipoprotein E (APOE) is a true susceptibility polymorphism of the common form of Alzheimer's disease (AD). There are three APOE alleles (ɛ2, ɛ3, ɛ4) that are universally distributed in the population with some variation in allele frequency due to racial and ethnic differences, and are associated with different risks and age of onset distributions. In multiple studies, the positive predictive value for symptomatic possible or probable AD patients who carry at least one ɛ4 allele was consistently >95%. Thus, early in the clinical course of dementia, when diagnoses are only 60-70% accurate, the presence of an ɛ4 allele raises the diagnostic accuracy of AD to >95%. With the anticipation of a second major late-onset AD susceptibility locus on chromosome 12, a matrix of relative susceptibility risks in the population raises many ethical and social questions associated with preclinical prediction.
The metabolism of apoE (protein) in the brain is a new and exciting area of neurobiology research made relevant by the association with AD. We have constructed transgenic animals using large human genomic fragments containing human APOE on an APOE-deficit mouse background as well as homologous recombination experiments replacing mouse APOE with human APOE promoter elements. The APOE tissue elements, NOT the human APOE gene coding sequence, is associated with the human pattern of intraneuronal apoE immunoreactivity.
Mercury, or Hg, is a neurotoxin that has been speculated to play a role in the pathogenesis of Alzheimer's disease, or AD. Dental amalgam releases low levels of Hg vapor and is a potential source of Hg for a large segment of the adult population.
The authors studied 68 subjects with AD and 33 control subjects without AD to determine Hg levels in multiple brain regions at autopsy and to ascertain the subjects' dental amalgam status and history. The subjects were from central Kentucky and Elm Grove, Wis. The authors conducted dental amalgam assessments during the lives of the majority of subjects and in some subjects at the time of autopsy only. The authors also determined three dental amalgam index scores--Event (placement, repair or removal of amalgam), Location and Time In Mouth--in addition to the numbers of and surface area of occlusal amalgam restorations. The authors determined Hg levels in multiple brain regions and performed full neuropathologic evaluations to confirm the normal status of the brain or the presence of AD.
The authors found no significant association of AD with the number, surface area or history of having dental amalgam restorations. They also found no statistically significant differences in brain Hg level between subjects with AD and control subjects.
Hg in dental amalgam restorations does not appear to be a neurotoxic factor in the pathogenesis of AD. The authors found that brain Hg levels are not associated with dental amalgam, either from existing amalgam restorations or according to subjects' dental amalgam restoration history.
Dental amalgam restorations, regardless of number, occlusal surface area or time, do not relate to brain Hg levels.
To determine whether the glutamine synthetase (GS) level in cerebrospinal fluid (CSF) is a useful biochemical marker in the diagnosis of Alzheimer disease (AD), and to assess the source of GS (brain vs. blood derived) in CSF.
Sandwich enzyme immunoassay and immunoblotting were applied to detect GS in CSF and in serum from neurologically healthy control subjects and patients with neurodegenerative diseases, including AD. The origin of GS was estimated by the concentration gradients of CSF to serum and ventricular to lumbar CSF. In addition, postmortem brain tissue from controls and patients with AD was analyzed using immunohistochemistry for expression of GS.
Levels of GS were significantly increased in lumbar CSF from patients with AD (20+/-12 pg/mL; P = .01) and to a lesser extent in patients with vascular dementia and amyotrophic lateral sclerosis. In CSF of controls, GS levels were 4+/-3 pg/mL. The GS concentration gradients were less than 1:10 for CSF to serum and 2:1 for ventricular to lumbar CSF. Immunoreactivity of GS was most prominent in astrocytes from temporal neocortex of patients with AD, suggesting a relationship between astrocyte reactions and increased GS levels in CSF.
Level of GS in lumbar CSF of patients with AD is increased significantly but nonspecifically, probably related to the strong astrogliosis in brain. Glutamine synthetase in lumbar CSF is mainly brain derived.
A considerable body of evidence indicates that the activity of glutamine synthetase is decreased in the cerebral cortices of brains affected by Alzheimer's disease. It is difficult to discern the reason for this decrease because it is not known whether the cellular distribution of glutamine synthetase is altered in Alzheimer's disease. Therefore the present study has used immunocytochemistry to compare the cellular distributions of glutamine synthetase in the inferior temporal cortices of six Alzheimer's diseased brains and six age-matched, non-demented brains. Double-label immunocytochemistry has been used to examine whether the distribution of cellular glutamine synthetase is influenced by the distribution of senile plaques. It was found that glutamine synthetase expression in astrocytes is diminished in Alzheimer's disease, particularly in the vicinity of senile plaques. The most striking finding of the present study was that glutamine synthetase was expressed in a subpopulation of pyramidal neurons in all six Alzheimer's diseased brains, whereas glutamine synthetase was not observed in any neurons from control brains. The changed expression of glutamine synthetase may be triggered by toxic agents in senile plaques, a reduced noradrenergic supply to the cerebral cortex, and increased brain ammonia levels. That such dramatic changes occur in the distribution of this critical, and normally stable enzyme, suggests that the glutamate-glutamine cycle is profoundly impaired in Alzheimer's disease. This is significant because impairments of the glutamate-glutamine cycle are known to cause alterations of mood and behaviour, disturbance of sleeping patterns, amnesia, confusion and reduced awareness. Since these behavioural changes are also seen in Alzheimer's disease, it is speculated that they might be attributable to the reduced expression of glutamine synthetase or to impairments of the glutamate-glutamine cycle.
Thimerosal is an important preservative in vaccines and ophthalmologic preparations. The substance is known to be a type IV sensitizing agent. High sensitization rates were observed in contact-allergic patients and in health care workers who had been exposed to thimerosal-preserved vaccines. There is evidence for the involvement of the glutathione system in the metabolism of thimerosal or its decomposition products (organomercury alkyl compounds). Thus detoxification by polymorphically expressed glutathione S-transferases such as GSTT1 and GSTM1 might have a protective effect against sensitization by these substances.
To address this question, a case control study was conducted, including 91 Central European individuals with a positive patch-test reaction to thimerosal. This population was compared with 169 healthy controls and additionally with 114 individuals affected by an allergy against para-substituted aryl compounds. The latter population was included in order to test whether possible associations were due to substance-specific effects, or were a general feature connected with type IV immunological diseases. Homozygous deletions of GSTT1 and GSTM1 were determined by polymerase chain reaction.
Glutathione S-transferase M1 deficiency was significantly more frequent among patients sensitized to thimerosal (65.9%, P = 0.013) compared with the healthy control group (49.1%) and the "para-compound" group (48%, P = 0.034). Glutathione S-transferase T1 deficiency in the thimerosal/mercury group (19.8%) was barely elevated versus healthy controls (16.0%) and the "para-compound" group (14.0%). The combined deletion (GSTT1-/GSTM1-) was markedly more frequent among thimerosal-sensitized patients than in healthy controls (17.6% vs. 6.5%, P = 0.0093) and in the "para-compound" group (17.6% vs. 6.1%, P =0.014), revealing a synergistic effect of these enzyme deficiencies (healthy controls vs. thimerosal GSTM1 negative individuals, OR = 2.0 [CI = 1.2-3.4], GSTT1-, OR = 1.2 [CI = 0.70-2.1], GSTM1/T1-, OR = 3.1 [CI = 1.4-6.5]).
Since the glutathione-dependent system was repeatedly shown to be involved in the metabolism of thimerosal decomposition products, the observed association may be of functional relevance.
In Alzheimer's disease (AD), neurofibrillary tangles spread from the entorhinal cortex to the limbic system, then to neocortical areas, according to the Braak's stages. Olfaction is impaired in early stages of AD. The aim of this study was to describe the pathology of the cortical olfactory centres in relation to Braak's stages determining the earliest site of pathology. We examined 15 control and 15 AD cases. The primary olfactory cortices were involved in more advanced Braak's stages, while olfactory bulbs were damaged in very early (i.e. Braak's stage 0 or 1) stages. These results are supporting the fact that olfaction might be an early marker in AD and argues against the hypothesis that AD pathology is spreading through the olfactory system.
Inhalation of mercury vapor (Hg0) inhibits binding of GTP to rat brain tubulin, thereby inhibiting tubulin polymerization into microtubules. A similar molecular lesion has also been observed in 80% of brains from patients with Alzheimer disease (AD) compared to age-matched controls. However the precise site and mode of action of Hg ions remain illusive. Therefore, the present study examined whether Hg ions could affect membrane dynamics of neurite growth cone morphology and behavior. Since tubulin is a highly conserved cytoskeletal protein in both vertebrates and invertebrates, we hypothesized that growth cones from animal species could be highly susceptible to Hg ions. To test this possibility, the identified, large Pedal A (PeA) neurons from the central ring ganglia of the snail Lymnoea stagnalis were cultured for 48 h in 2 ml brain conditioned medium (CM). Following neurite outgrowth, metal chloride solution (2 microl) of Hg, Al, Pb, Cd, or Mn (10(-7) M) was pressure applied directly onto individual growth cones. Time-lapse images with inverted microscopy were acquired prior to, during, and after the metal ion exposure. We demonstrate that Hg ions markedly disrupted membrane structure and linear growth rates of imaged neurites in 77% of all nerve growth cones. When growth cones were stained with antibodies specific for both tubulin and actin, it was the tubulin/microtubule structure that disintegrated following Hg exposure. Moreover, some denuded neurites were also observed to form neurofibrillary aggregates. In contrast, growth cone exposure to other metal ions did not effect growth cone morphology, nor was their motility rate compromised. To determine the growth suppressive effects of Hg ions on neuronal sprouting, cells were cultured either in the presence or absence of Hg ions. We found that in the presence of Hg ions, neuronal somata failed to sprout, whereas other metalic ions did not effect growth patterns of cultured PeA cells. We conclude that this visual evidence and previous biochemical data strongly implicate Hg as a potential etiological factor in neurodegeneration.
Methyl mercury (MeHg) and metallic Hg are well known as neurotoxic agents. Dental amalgam contributes significantly to elemental Hg vapour exposure in the general population. There is little information about Hg concentration in human amniotic fluid (AF) of pregnant women and its potential toxic effect on the fetuses.
Primary to assess the relationship between the presence of detectable mercury (Hg) concentration in human AF, number and surface areas of amalgam fillings of pregnant women; secondary to analyse their obstetric history and perinatal complications.
Seventy-two pregnant women took part in this prospective study. One dentist recorded the dental status, presence, number and surface areas of amalgam fillings. Total Hg concentration in AF was determined in digested samples using automatic cold vapour atomic absorption equipment. The detection limit of Hg in AF, determined from blank readings, was 0.08 ng/ml. To estimate the dependence of the explanatory variables (such as number and surface areas of amalgam fillings, fish consumption, presence of liver or neurological diseases and smoking habits) on mercury concentration several linear regression models were built up. Stepwise logistic regression procedures were running on total sample and on patients with at least one amalgam filling (Positive Filling group = PF). Principal component analysis (PCA) provided two factors, which explained for more the 60% of the variance among the variables.
The overall mean Hg concentration in AF among all patients was 0.37+/-0.49 ng/ml. Nineteen (26.4%) women had a Hg concentration <0.08 ng/ml (Hg negative group). In 53 (73.6%) patients, with a concentration > or = 0.08 ng/ml (Hg positive group), the mean value of Hg was 0.49+/-0.52 ng/ml. The average number of amalgam fillings was 2.26 +/- 3.19 in the Hg negative group and 5.32+/-3.03 in the Hg positive group (ANOVA one-way p=0.04). A dependence of mercury concentration on number of amalgam fillings (p=0.03), surface area of the amalgam fillings (p=0.04) and fish consumption (p=0.04) was observed but not at a significant level. In stepwise logistic procedure the number of amalgam fillings gave a contribution to the model (p=0.04), although null value was included in the confidence intervals. We observed no statistically significant differences (chi2 test) among the patients with a Hg concentration <0.08 ng/ml (n=19) and those with a concentration > or = 0.08 (n=53) with regard to obstetric history and perinatal complications.
Number and surface areas of amalgam fillings influenced positively Hg concentration in AF but not at a significant level. Moreover Hg levels detected in AF were low and no adverse outcomes were observed through pregnancies and in the newborns.
Dental amalgam, which has been used for over 150 years in dental practice, consists of about 50% metallic mercury. Studies on animal and humans show that mercury is continuously released from dental amalgam and absorbed by several body tissues. It is widely accepted that the main source of mercury vapor is dental amalgam and it contributes substantially to mercury load in human body tissues. There is still a controversy about the consequences of this additional mercury exposure from amalgam to human health. Many studies were performed to evaluate possible adverse effects. In this comment, these studies were analyzed with regard to their methodical quality by considering the newest findings on mercury toxicity and metabolism. In sum, a number of studies are methodically flawed drawing inaccurate conclusions as to the safety of dental amalgam.
Thimerosol is an antiseptic containing 49.5% ethyl mercury that has been used for years as a preservative in many infant vaccines and in flu vaccines. Environmental methyl mercury has been shown to be highly neurotoxic, especially to the developing brain. Because mercury has a high affinity for thiol (sulfhydryl (-SH)) groups, the thiol-containing antioxidant, glutathione (GSH), provides the major intracellular defense against mercury-induced neurotoxicity. Cultured neuroblastoma cells were found to have lower levels of GSH and increased sensitivity to thimerosol toxicity compared to glioblastoma cells that have higher basal levels of intracellular GSH. Thimerosal-induced cytotoxicity was associated with depletion of intracellular GSH in both cell lines. Pretreatment with 100 microM glutathione ethyl ester or N-acetylcysteine (NAC), but not methionine, resulted in a significant increase in intracellular GSH in both cell types. Further, pretreatment of the cells with glutathione ethyl ester or NAC prevented cytotoxicity with exposure to 15 microM Thimerosal. Although Thimerosal has been recently removed from most children's vaccines, it is still present in flu vaccines given to pregnant women, the elderly, and to children in developing countries. The potential protective effect of GSH or NAC against mercury toxicity warrants further research as possible adjunct therapy to individuals still receiving Thimerosal-containing vaccinations.
Patients having immune cytopenias produce antibodies that target hematopoietic cells resulting in their phagocytosis and intracellular destruction. Early reports suggested that phagocytosis could be inhibited by interfering with membrane thiol (SH) groups on phagocytes. Thus, whether chemical compounds that interact with SH or disulfide (SS) groups on mononuclear phagocytes can inhibit phagocytosis of antibody-coated cells was examined.
A monocyte monolayer assay (MMA), which examines the in vitro monocyte-macrophage (Mphi) interaction with anti-Rh(D)-coated red cells (RBCs), was used to study the ability of different SH and SS chemicals to inhibit the Fc receptor-mediated phagocytosis of sensitized RBCs. The compounds examined included thimerosal, dithiothreitol (DTT), pentane-1-thiol, and two recently described SH and two SS chemicals that have been synthesized.
All compounds were found to be able to inhibit phagocytosis to varying degrees correlating to the structure of the molecule. In general, those compounds that interact with free SH groups to inhibit phagocytosis were found better than SH-containing compounds that interact with SSs. Thimerosal and p-nitrophenyl methyl disulfide were the most effective compounds inhibiting phagocytosis. Both chemicals showed greater than 50 percent inhibition at concentrations as low as 10(-9) mol per L. DTT was the least effective compound tested. Only thimerosal showed significant toxicity, as determined by decreased cell viability and increased apoptosis, but only at concentrations of 10(-8) mol per L. The effect of chemical treatment was on attachment rather than on phagocytosis itself. Fcgamma receptor-independent endocytosis was not affected by the chemical treatment.
These studies indicate that pharmacologic strategies that target SH groups on mononuclear phagocytes may have future efficacy for the treatment of immune cytopenias.
Potential cognitive and motor effects from exposure to elemental mercury (Hg0) were examined in the presence and absence of a polymorphism (Val66Met) in brain-derived neurotrophic factor (BDNF). A group of 194 male dentists (DDs) and 233 female dental assistants (DAs) were occupationally exposed to mercury and had no history of kidney or nervous system disorders. Acute exposure was measured using spot urinary Hg (HgU) concentrations (average 3.32 and 1.98 μg/l, respectively) and indices of chronic occupational exposure (26.3 and 14.9 years, respectively, weighted for historical exposures). The BDNF status was 68% and 66% wild type, 26% and 30% single substitution, and 5% and 4% full mutation for DDs and DAs, respectively. DDs and DAs were evaluated separately. Regression analyses controlled for age, premorbid intelligence, alcohol consumption, and education.
Eighteen cadavers from routine autopsy casework were subject to a study of tissue levels of total mercury in brain, thyroid, and kidney samples by atomic absorption. On these same cadavers, all dental amalgam fillings (the most important source of inorganic mercury exposure in the general population, according to the World Health Organization (WHO) were charted. Total mercury levels were significantly higher in subjects with a greater number of occlusal amalgam surfaces (>12) compared with those with fewer occlusal amalgams (0-3) in all types of tissue (all P < or = 0.04). Mercury levels were significantly higher in brain tissues compared with thyroid and kidney tissues in subjects with more than 12 occlusal amalgam fillings (all P < or = 0.01) but not in subjects with 3 or less occlusal amalgams (all P > or = 0.07).