Lead content of brain tissue in diffuse neurofibrillary tangles with calcification (DNTC): the possibility of lead neurotoxicity

Lead Acetate Exposure and Cerebral Amyloid Accumulation: Mechanistic Evaluations in APP/PS1 Mice

BACKGROUND

The role of environmental factors in Alzheimer's disease (AD) pathogenesis remains elusive. Mounting evidence suggests that acute and past exposure to the environmental toxicant lead (Pb) is associated with longitudinal decline in cognitive function, brain atrophy, and greater brain β -amyloid (A β ) deposition. However, the nature of Pb-induced amyloid deposition and how it contributes to AD development remain unclear.

OBJECTIVES

This study investigates the role of Pb in the pathogenesis of cerebral amyloid angiopathy (CAA) and whether plasminogen activator inhibitor-1 (PAI-1) contributes to this process in the APP/PS1 mouse model.

METHODS

Female APP/PS1 mice at 8 wk of age were administered either 50 mg / kg Pb-acetate (PbAc) (i.e., 27 mg   Pb / kg ) or an equivalent molar concentration of sodium acetate (NaAc) via oral gavage once daily for 8 wk. Amyloid deposition and vascular amyloid were determined by immunostaining. In addition, A β perivascular drainage, vascular binding assay, and microglial endocytosis were examined to determine underlying mechanisms. Furthermore, magnetic resonance imaging demyelination imaging was performed in vivo measure the level of demyelination. Finally, Y-maze and Morris water maze tests were assessed to evaluate the cognitive function of mice.

RESULTS

APP/PS1 mice (an AD mice model) exposed to PbAc demonstrated more vascular amyloid deposition less neocortical myelination, and lower cognitive function, as well as greater vascular binding to A β 40 , higher A β 40 / A β 42 ratios, strikingly lower A β 40 levels in the perivascular drainage, and microglial endocytosis. Importantly, exposure to a specific PAI-1 inhibitor, tiplaxtinin, which previously was reported to lower CAA pathology in mice, resulted in less CAA-related outcomes following PbAc exposure.

DISCUSSION

Our findings suggest that PbAc induced CAA/AD pathogenesis via the PAI-1 signaling in the APP/PS1 mouse model, and the inhibition of PAI-1 could be a potential therapeutic target for PbAc-mediated CAA/AD disorders. https://doi.org/10.1289/EHP14384.

Trace Elements in Alzheimer's Disease and Dementia: The Current State of Knowledge

Changes in trace element concentrations are being wildly considered when it comes to neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease. This study aims to present the role that trace elements play in the central nervous system. Moreover, we reviewed the mechanisms involved in their neurotoxicity. Low zinc concentrations, as well as high levels of copper, manganese, and iron, activate the signalling pathways of the inflammatory, oxidative and nitrosative stress response. Neurodegeneration occurs due to the association between metals and proteins, which is then followed by aggregate formation, mitochondrial disorder, and, ultimately, cell death. In Alzheimer's disease, low Zn levels suppress the neurotoxicity induced by β-amyloid through the selective precipitation of aggregation intermediates. High concentrations of copper, iron and manganese cause the aggregation of intracellular α-synuclein, which results in synaptic dysfunction and axonal transport disruption. Parkinson's disease is caused by the accumulation of Fe in the midbrain dopaminergic nucleus, and the pathogenesis of multiple sclerosis derives from Zn deficiency, leading to an imbalance between T cell functions. Aluminium disturbs the homeostasis of other metals through a rise in the production of oxygen reactive forms, which then leads to cellular death. Selenium, in association with iron, plays a distinct role in the process of ferroptosis. Outlining the influence that metals have on oxidoreduction processes is crucial to recognising the pathophysiology of neurodegenerative diseases and may provide possible new methods for both their avoidance and therapy.

Developmental Pb exposure increases AD risk via altered intracellular Ca2+ homeostasis in hiPSC-derived cortical neurons

Exposure to environmental chemicals such as lead (Pb) during vulnerable developmental periods can result in adverse health outcomes later in life. Human cohort studies have demonstrated associations between developmental Pb exposure and Alzheimer's disease (AD) onset in later life which were further corroborated by findings from animal studies. The molecular pathway linking developmental Pb exposure and increased AD risk, however, remains elusive. In this work, we used human iPSC-derived cortical neurons as a model system to study the effects of Pb exposure on AD-like pathogenesis in human cortical neurons. We exposed neural progenitor cells derived from human iPSC to 0, 15, and 50 ppb Pb for 48 h, removed Pb-containing medium, and further differentiated them into cortical neurons. Immunofluorescence, Western blotting, RNA-sequencing, ELISA, and FRET reporter cell lines were used to determine changes in AD-like pathogenesis in differentiated cortical neurons. Exposing neural progenitor cells to low-dose Pb, mimicking a developmental exposure, can result in altered neurite morphology. Differentiated neurons exhibit altered calcium homeostasis, synaptic plasticity, and epigenetic landscape along with elevated AD-like pathogenesis markers, including phosphorylated tau, tau aggregates, and Aβ42/40. Collectively, our findings provide an evidence base for Ca dysregulation caused by developmental Pb exposure as a plausible molecular mechanism accounting for increased AD risk in populations with developmental Pb exposure.

High affinity of β-amyloid proteins to cerebral capillaries: implications in chronic lead exposure-induced neurotoxicity in rats

Lead (Pb) is a known environmental risk factor in the etiology of Alzheimer's disease (AD). The existing reports suggest that Pb exposure increases beta-amyloid (Aβ) levels in brain tissues and cerebrospinal fluid (CSF) and facilitates the formation of amyloid plaques, which is a pathological hallmark for AD. Pb exposure has long been associated with cerebral vasculature injury. Yet it remained unclear if Pb exposure caused excessive Ab buildup in cerebral vasculature, which may damage the blood-brain barrier and cause abnormal Ab accumulation. This study was designed to investigate the impact of chronic Pb exposure on Aβ accumulation in cerebral capillary and the expression of low-density lipoprotein receptor protein-1 (LRP1), a critical Aβ transporter, in brain capillary and parenchyma. Sprague-Dawley rats received daily oral gavage at doses of 0, 14 (low-dose), and 27 (high-dose) mg Pb/kg as Pb acetate, 5 d/wk, for 4 or 8 wks. At the end of Pb exposure, a solution containing Aβ40 was infused into the brain via the cannulated internal carotid artery. Data by ELISA showed a strikingly high affinity of Ab to cerebral vasculature, which was approximately 7-14 times higher than that to the parenchymal fractions collected from control brains. Pb exposure further aggravated the Aβ accumulation in cerebral vasculature in a dose-dependent manner. Western blot analyses revealed that Pb exposure decreased LRP1 expression in cortical capillaries and hippocampal parenchyma. Immunohistochemistry (IHC) studies further revealed a disrupted distribution of LRP1 alongside hippocampal vasculature accompanied with a decreased expression in hippocampal neurons by Pb exposure. Taken together, the current study demonstrated that the cerebral vasculature naturally possessed a high affinity to Aβ present in circulating blood. Pb exposure significantly increased Aβ accumulation in cerebral vasculature; such an increased Aβ accumulation was due partly to the diminished expression of LRP1 in response to Pb in tested brain regions. Perceivably, Pb-facilitated Ab aggravation in cerebral vasculature may contribute to Pb-associated amyloid alterations.

Pb Induces MCP-1 in the Choroid Plexus

Lead (Pb) is an environmental element that has been implicated in the development of dementia and Alzheimer's disease (AD). Additionally, innate immune activation contributes to AD pathophysiology. However, the mechanisms involved remain poorly understood. The choroid plexus (CP) is not only the site of cerebrospinal fluid (CSF) production, but also an important location for communication between the circulation and the CSF. In this study, we investigated the involvement of the CP during Pb exposure by evaluating the expression of the monocyte chemoattractant protein-1 (MCP-1). MCP-1 is highly expressed in the CP compared to other CNS tissues. MCP-1 regulates macrophage infiltration and is upregulated in AD brains. Our study revealed that Pb exposure stimulated MCP-1 expression, along with a significantly increased macrophage infiltration into the CP. By using cultured Z310 rat CP cells, Pb exposure stimulated MCP-1 expression in a dose-related fashion and markedly activated both NF-κB and p38 MAP kinase. Interestingly, both SB 203580, a p38 inhibitor, and BAY 11-7082, an NF-κB p65 inhibitor, significantly blocked Pb-induced MCP-1 expression. However, SB203580 did not directly inhibit NF-κB p65 phosphorylation. In conclusion, Pb exposure stimulates MCP-1 expression via the p38 and NF-κB p65 pathways along with macrophage infiltration into the CP.

Childhood Lead Exposure and Adult Neurodegenerative Disease

Millions of Americans now entering midlife and old age were exposed to high levels of lead, a neurotoxin, as children. Evidence from animal-model and human observational studies suggest that childhood lead exposure may raise the risk of adult neurodegenerative disease, particularly dementia, through a variety of possible mechanisms including epigenetic modification, delayed cardiovascular and kidney disease, direct degenerative CNS injury from lead remobilized from bone, and lowered neural and cognitive reserve. Within the next ten years, the generation of children with the highest historical lead exposures, those born in the 1960s, 1970s, and 1980s, will begin to enter the age at which dementia symptoms tend to emerge. Many will also enter the age in which lead stored in the skeleton may be remobilized at greater rates, particularly for women entering menopause and men and women experiencing osteoporosis. Should childhood lead exposure prove pro-degenerative, the next twenty years will provide the last opportunities for possible early intervention to forestall greater degenerative disease burden across the aging lead-exposed population. More evidence is needed now to characterize the nature and magnitude of the degenerative risks facing adults exposed to lead as children and to identify interventions to limit long-term harm.

Trace metal concentrations in hair and nails from Alzheimer's disease patients: Relations with clinical severity

BACKGROUND AND OBJECTIVES

Metals, especially transition metals, seem to be important in the pathogenesis of Alzheimer disease. This study aims to determine the relationship of trace metal elements to the pathogenesis and/or course of Alzheimer Disease in terms of clinical severity.

METHODS

The hair and nail trace metal levels of 62 Alzheimer Disease patients at different clinical stages (21 mild, 20 moderate, 21 severe) and 60 healthy control subjects were measured by using inductively coupled plasma-mass spectrometry. The statistical comparisons were performed with regards to the study groups, clinical stages, disease duration and age.

RESULTS

The patient and control groups were significantly different from each other in regards to Mn, Fe, Cu, Cd, Hg (p<0.001), Zn (p<0.01) in nail concentrations and, Na, Al, Pb, Co (p<0.001), Fe, Mn (p=0.001), Hg, Cu, Cd, K in hair concentrations (p<0.01). No difference was detected in the levels of Mg and Ca. Nail Na level showed differences among different clinical stages of the disease (p<0.01). In comparing the mild degree Alzheimer patients to the control group; significant differences were detected in nail Mn, Fe, Cu, Co (p<0.001), Hg, Zn (p<0.01) and, hair Pb, Al (p<0.001), Na, K levels (p<0.01).

CONCLUSIONS

Our results have shown that transition and posttransition metals are especially important metals for the disease process. The relation of nail Na level with clinical stages of AD is an interesting new finding, making someone to think that alkali metals may be important in the progression of the disease.

Diffuse neurofibrillary tangles with calcification (Kosaka-Shibayama disease) in Japan

Diffuse neurofibrillary tangles with calcification (DNTC) is a rare, pre-senile type of dementia. The term 'DNTC' was initially proposed by Kosaka in 1994. Although 26 autopsies and 21 clinical patients with DNTC have been described in Japan to date, DNTC has rarely been reported in the European and North American published work. We speculate that DNTC has been overlooked in other countries. Herein, we review all known reports of DNTC in Japan and propose clinical diagnostic criteria for DNTC.

Serum trace metal levels in Alzheimer's disease and normal control groups

OBJECTIVE

To determine whether serum trace metals are related to abnormal cognition in Alzheimer's disease (AD).

METHODS

We studied serum lead (Pb), cadmium (Cd), mercury (Hg), and arsenic(As) in 89 patients with AD and in 118 cognitively normal individuals. We analyzed the results of the blood tests and the food intake.

RESULTS

Serum Pb levels correlated with word list recall (P = .039) and word list recognition (P = .037). Without age adjustment, serum Cd levels (P = .044) were significantly higher in the AD group. After stratified age adjustment, the levels of selected trace metals did not differ significantly between AD and normal individuals. Food intakes regarding selected trace metals were not significantly different between the 2 groups.

CONCLUSIONS

In this study, serum Pb, Cd, Hg, and As levels were not directly related to abnormal cognition in AD. Serum Pb levels were significantly negatively correlated with verbal memory scores.

Environmental and dietary risk factors in Alzheimer’s disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects millions in the aging population worldwide and will affect millions more in the next 20 years. Over 90% of all cases are sporadic, with genetics playing a minor role in the etiology of AD. Therefore, it is crucial to investigate the environment and diet as primary risk factors in AD pathology. This review considers epidemiologic case control studies, and in vitro and in vivo research to investigate the potential of environmental exposure to metals, air pollution and pesticides as well as diet as risk factors for AD. In some cases, the role of genetic mutations and environmental risk is discussed. The evidence examined in this review provides a brief overview of the current literature on selected, significant risk factors in promoting amyloid-beta accumulation and aggregation, thus contributing to neurodegeneration.

Fibrillization of human tau is accelerated by exposure to lead via interaction with His-330 and His-362

BACKGROUND

Neurofibrillary tangles, mainly consisted of bundles of filaments formed by the microtubule-associated protein Tau, are a hallmark of Alzheimer disease. Lead is a potent neurotoxin for human being especially for the developing children, and Pb(2+) at high concentrations is found in the brains of patients with Alzheimer disease. However, it has not been reported so far whether Pb(2+) plays a role in the pathology of Alzheimer disease through interaction with human Tau protein and thereby mediates Tau filament formation. In this study, we have investigated the effect of Pb(2+) on fibril formation of recombinant human Tau fragment Tau(244-372) and its mutants at physiological pH.

METHODOLOGY/PRINCIPAL FINDINGS

As revealed by thioflavin T and 8-anilino-1-naphthalene sulfonic acid fluorescence, the addition of 5-40 µM Pb(2+) significantly accelerates the exposure of hydrophobic region and filament formation of wild-type Tau(244-372) on the investigated time scale. As evidenced by circular dichroism and Fourier transform infrared spectroscopy, fibrils formed by wild-type Tau(244-372) in the presence of 5-40 µM Pb(2+) contain more β-sheet structure than the same amount of fibrils formed by the protein in the absence of Pb(2+). However, unlike wild-type Tau(244-372), the presence of 5-40 µM Pb(2+) has no obvious effects on fibrillization kinetics of single mutants H330A and H362A and double mutant H330A/H362A, and fibrils formed by such mutants in the absence and in the presence of Pb(2+) contain similar amounts of β-sheet structure. The results from isothermal titration calorimetry show that one Pb(2+) binds to one Tau monomer via interaction with His-330 and His-362, with sub-micromolar affinity.

CONCLUSIONS/SIGNIFICANCE

We demonstrate for the first time that the fibrillization of human Tau protein is accelerated by exposure to lead via interaction with His-330 and His-362. Our results suggest the possible involvement of Pb(2+) in the pathogenesis of Alzheimer disease and provide critical insights into the mechanism of lead toxicity.

Strio-pallido-dentate calcinosis: a diagnostic approach in adult patients

Familial idiopathic bilateral strio-pallido-dentate calcinosis is a rare autosomal dominant disorder characterized by massive symmetric calcification, detectable by CT, into the globus pallidus and striatum, with or without the involvement of the dentate nucleus, thalamus and white matter in the absence of alterations of calcium metabolism. Clinically, it has been associated with movement and/or neuropsychiatric disorders with age at onset typically in the fourth or fifth decade. Other sporadic or familial diseases can be responsible for brain calcifications with a similar anatomic strio-pallidal or strio-pallido-dentate pattern and, a restricted number of them, for neurological symptoms with onset in adulthood. Moreover, physiological age-related basal ganglia calcifications are often incidentally found, although with a far different CT aspect, in elderly patients with movement disorders. Indentifying familial and idiopathic cases may offer the opportunity to study the molecular mechanisms underlying this minerals deposition.

Lead-induced accumulation of beta-amyloid in the choroid plexus: role of low density lipoprotein receptor protein-1 and protein kinase C

The choroid plexus (CP), constituting the blood-cerebrospinal fluid barrier, has the capacity to remove beta-amyloid (Abeta) from the cerebrospinal fluid. Our previous work indicates that exposure to lead (Pb) results in Abeta accumulation in the CP by decreasing the expression of low density lipoprotein receptor protein-1 (LRP1), a protein involved in the transport and clearance of Abeta. The current study was designed to explore the relationship between Abeta accumulation, protein kinase C (PKC) activity, and LRP1 status in the CP following Pb exposure. Confocal microscopy revealed that LRP1 was primarily localized in the cytosol of the CP in control rats and migrated distinctly towards the apical surface and the microvilli following acute Pb exposure (27 mg Pb/kg, i.p., 24h). Co-immunostaining revealed a co-localization of both PKC-delta and LRP1 in the cytosol of control rats, with a distinct relocalization of both towards the apical membrane following Pb exposure. Preincubation of the tissues with PKC-delta inhibitor rottlerin (2 microM) prior to Pb exposure in vitro, resulted in abolishing the Pb-induced relocalization of LRP1 to the apical surface. Importantly, a significant elevation in intracellular Abeta levels (p<0.01) was observed in the cytosol of the CP following Pb exposure, which was abolished following preincubation with rottlerin. In addition, rottlerin caused a relocalization of Abeta from the cytosol to the nucleus in both Pb-treated and control CP tissues. Finally, co-immunoprecipitation studies revealed a strong protein-protein interaction between LRP1 and PKC-delta in the CP. These studies suggest that Pb exposure disrupts Abeta homeostasis at the CP, owing partly to a Pb-induced relocalization of LRP1 via PKC-delta.

Increased beta-amyloid levels in the choroid plexus following lead exposure and the involvement of low-density lipoprotein receptor protein-1

The choroid plexus, a barrier between the blood and cerebrospinal fluid (CSF), is known to accumulate lead (Pb) and also possibly function to maintain brain's homeostasis of Abeta, an important peptide in the etiology of Alzheimer's disease. This study was designed to investigate if Pb exposure altered Abeta levels at the blood-CSF barrier in the choroid plexus. Rats received ip injection of 27 mg Pb/kg. Twenty-four hours later, a FAM-labeled Abeta (200 pmol) was infused into the lateral ventricle and the plexus tissues were removed to quantify Abeta accumulation. Results revealed a significant increase in intracellular Abeta accumulation in the Pb-exposed animals compared to controls (p<0.001). When choroidal epithelial Z310 cells were treated with 10 microM Pb for 24 h and 48 h, Abeta (2 microM in culture medium) accumulation was significantly increased by 1.5 fold (p<0.05) and 1.8 fold (p<0.05), respectively. To explore the mechanism, we examined the effect of Pb on low-density lipoprotein receptor protein-1 (LRP1), an intracellular Abeta transport protein. Following acute Pb exposure with the aforementioned dose regimen, levels of LRP1 mRNA and proteins in the choroid plexus were decreased by 35% (p<0.05) and 31.8% (p<0.05), respectively, in comparison to those of controls. In Z310 cells exposed to 10 microM Pb for 24 h and 48 h, a 33.1% and 33.4% decrease in the protein expression of LRP1 was observed (p<0.05), respectively. Knocking down LRP1 resulted in even more substantial increases of cellular accumulation of Abeta, from 31% in cells without knockdown to 72% in cells with LRP1 knockdown (p<0.05). Taken together, these results suggest that the acute exposure to Pb results in an increased accumulation of intracellular Abeta in the choroid plexus; the effect appears to be mediated, at least in part, via suppression of LRP1 production following Pb exposure.

Involvement of insulin-degrading enzyme in the clearance of beta-amyloid at the blood-CSF barrier: Consequences of lead exposure

Background

Alzheimer's disease (AD) is characterized by the deposition of beta-amyloid (Aβ) peptides in the brain extracellular matrix, resulting in pathological changes and neurobehavioral deficits. Previous work from this laboratory demonstrated that the choroid plexus (CP) possesses the capacity to remove Aβ from the cerebrospinal fluid (CSF), and exposure to lead (Pb) compromises this function. Since metalloendopeptidase insulin-degrading enzyme (IDE), has been implicated in the metabolism of Aβ, we sought to investigate whether accumulation of Aβ following Pb exposure was due to the effect of Pb on IDE.

Methods

Rats were injected with a single dose of Pb acetate or an equivalent concentration of Na-acetate; CP tissues were processed to detect the location of IDE by immunohistochemistry. For in vitro studies, choroidal epithelial Z310 cells were treated with Pb for 24 h in the presence or absence of a known IDE inhibitor, N-ethylmaleimide (NEM) to assess IDE enzymatic activity and subsequent metabolic clearance of Aβ. Additionally, the expression of IDE mRNA and protein were determined using real time PCR and western blots respectively.

Results

Immunohistochemistry and confocal imaging revealed the presence of IDE towards the apical surface of the CP tissue with no visible alteration in either its intensity or location following Pb exposure. There was no significant difference in the expressions of either IDE mRNA or protein following Pb exposure compared to controls either in CP tissues or in Z310 cells. However, our findings revealed a significant decrease in the IDE activity following Pb exposure; this inhibition was similar to that seen in the cells treated with NEM alone. Interestingly, treatment with Pb or NEM alone significantly increased the levels of intracellular Aβ, and a greater accumulation of Aβ was seen when the cells were exposed to a combination of both.

Conclusion

These data suggest that Pb exposure inhibits IDE activity but does not affect its expression in the CP. This, in turn, leads to a disrupted metabolism of Aβ resulting in its accumulation at the blood-CSF barrier.

JEM spotlight: metal speciation related to neurotoxicity in humans

Improved living conditions have led to a steady increase in the life expectancy of humans in most countries. However, this is accompanied by an increased probability of suffering from neurodegenerative diseases like Alzheimer's disease or Parkinson's disease. Unfortunately, the therapeutic possibilities for curing these diseases are very limited up to now. Many studies indicate that a variety of environmental factors contribute to the initiation and promotion of neurodegenerative diseases. For example, the role of metal exposure and disturbance of metal homeostasis in the brain is discussed in this respect. However, most studies focus on the neurological and toxicological aspects but not on a detailed characterisation of the species of the involved metals. Therefore, this review summarizes the neurotoxic effects of selected metals on humans and focuses on contributions from trace element speciation analysis with relevance to neuroscientific research. In spite of the advance in instrumentation and methodology of speciation analysis there are few applications for matrices like cerebrospinal fluid which is due to limited access to these samples and analytical challenges caused by matrix interferences, low concentrations and limited stability of many trace element species of interest. The most relevant neurotoxic metals aluminium, lead, manganese and mercury are reviewed in detail while further metals like cadmium, arsenic, bismuth and tin are briefly discussed. Current results indicate that knowledge on trace element speciation can contribute to a better understanding of the transport of metals across the neural barriers and potentially of their role in diseased human brains.

Very low lead exposures and children's neurodevelopment

PURPOSE OF REVIEW

We remain far from achieving the goal of eliminating lead-associated neurodevelopmental morbidities in children. New evidence regarding the blood lead levels at which morbidities occur have led to calls for the Centers for Disease Control and Prevention to reduce the current screening guideline of 10 microg/dl. The review evaluates the basis for these calls.

RECENT FINDINGS

Adverse outcomes, such as reduced intelligence quotient and academic deficits, occur at levels below 10 microg/dl. Some studies suggest that the rate of decline in performance is greater at levels below 10 microg/dl than above 10 microg/dl, although a plausible mechanism has not been identified. Increased exposure is also associated with neuropsychiatric disorders such as attention deficit hyperactivity disorder and antisocial behavior. Functional imaging studies are beginning to provide insight into the neural substrate of lead's neurodevelopmental effects. Current protocols for chelation therapy appear ineffective in preventing such effects, although environmental enrichment might do so.

SUMMARY

No level of lead exposure appears to be 'safe' and even the current 'low' levels of exposure in children are associated with neurodevelopmental deficits. Primary prevention of exposure provides the best hope of mitigating the impact of this preventable disease.

Diffuse neurofibrillary tangles with calcification (DNTC): Kosaka-Shibayama disease in America

Alzheimer's disease and Pick's disease are representative dementias. Cases which do not fit prototypes are termed unclassifiable dementias. New dementia subtypes are identified when a conglomerate of clinical, radiologic and pathologic findings are consistently identified. One such variant is diffuse neurofibrillary tangles with calcification (DNTC), which has been reported almost exclusively from Japan. Significant pathological advances in this decade have established DNTC as a distinct entity. Although initially the diagnosis was neuropathologic, increasing knowledge about DNTC has made it possible for a clinical diagnosis to be made. We report a clinical case of DNTC in a Caucasian American. The diagnosis of DNTC was based on his atypical senile dementia, anomia, apathy and parkinsonian features, normal serum biochemistry, and evidence of basal ganglia and cerebellar calcification with predominant temporal lobe atrophy on neuroimaging. To the best of our knowledge, this is the first clinical description of DNTC from the United States.

The environment, epigenetics and amyloidogenesis

Alzheimer's Disease (AD) is a progressive, irreversible neurodegenerative disease. Despite several genetic mutations (Haass et al., J. Biol. Chem. 269:17741-17748, 1994; Ancolio et al., Proc. Natl. Acad. Sci. USA 96:4119-4124, 1999; Munoz and Feldman, CMAJ 162:65-72, 2000; Gatz et al., Neurobiol. Aging 26:439-447, 2005) found in AD patients, more than 90% of AD cases are sporadic (Bertram and Tanzi, Hum. Mol. Genet. 13:R135-R141, 2004). Therefore, it is plausible that environmental exposure may be an etiologic factor in the pathogenesis of AD. The AD brain is characterized by extracellular beta-amyloid (Abeta) deposition and intracellular hyperphosphorylated tau protein. Our lab has demonstrated that developmental exposure of rodents to the heavy metal lead (Pb) increases APP (amyloid precursor protein) and Abeta production later in the aging brain (Basha et al., J. Neurosci. 25:823-829, 2005a). We also found elevations in the oxidative marker 8-oxo-dG in older animals that had been developmentally exposed to Pb (Bolin et al., FASEB J. 20:788-790, 2006) as well as promotion of amyloidogenic histopathology in primates. These findings indicate that early life experiences contribute to amyloidogenesis in old age perhaps through epigenetic pathways. Here we explore the role of epigenetics as the underlying mechanism that mediates this early exposure-latent pathogenesis with a special emphasis on alterations in the methylation profiles of CpG dinucleotides in the promoters of genes and their influence on both gene transcription and oxidative DNA damage.

Axonal degeneration with unusual lesions of the myelin in an occupational neuropathy

A 35-year-old man had prolonged occupational exposure to lead carboxylate, triethylbenzene, xylene, and dichloromethane, when he developed a subacute predominantly sensory neuropathy. Ultrastructural examination of a peripheral nerve biopsy showed axonal degeneration and unusual lesions of the myelin, with Schwann cell sequestration of vesicular and lamellar debris. Biochemical analysis of lead in a frozen peripheral nerve specimen revealed no significant difference between the propositus and a control. The authors were unable to find any similar peripheral nerve lesions in the literature dealing with neurotoxic chemicals. Any of the several organic solvents could have equally caused the neuropathy and may have been potentialized by the other chemicals.

Distribution of cerebral cortical lesions in diffuse neurofibrillary tangles with calcification: a clinicopathological study of four autopsy cases showing prominent parietal lobe involvement

We investigated clinicopathologically four Japanese autopsy cases of diffuse neurofibrillary tangles with calcification (DNTC), which has been believed to be characterized by temporal or temporofrontal circumscribed lobar atrophy, and examined the distribution of their cerebral cortical lesions using hemisphere specimens. The lesions were classified into three categories (slight, moderate, and severe). Severe lesions were present in the temporal lobes and insular gyri of all four cases, consistent with the studies reported to date. In contrast, severe lesions were encountered in the parietal lobe of case 1 and moderate lesions were found in the parietal lobes of cases 2-4. Furthermore, moderate lesions of the precentral gyrus were present in cases 2-4, and moderate lesions of the postcentral gyrus were encountered in all four cases. We postulate that the distribution of cerebral cortical lesions in DNTC is more widespread than previously assumed. Our data also indicate that the unusual clinical signs of DNTC reported by several Japanese researchers, including parietal signs such as apraxia and agnosia, are roughly consistent with the topographic distribution of cerebral cortical lesions in DNTC elucidated in this study.

Can dementia be prevented? Brain aging in a population-based context

As a consequence of global aging of the human population, the occurrence of cognitive impairment and dementia is rapidly becoming a significant burden for medical care and public health systems. By the year 2020, the WHO predicts there will be nearly 29 million demented people in both developed and developing countries. Primary and secondary prevention of dementia through individual and population-level interventions could reduce this imminent risk. Vascular risk factors such as type 2 diabetes, hypertension, dietary fat intake, high cholesterol, and obesity have emerged as important influences on the risk of both vascular and Alzheimer's dementia. Understanding the reasons for differences between populations in genetic vulnerability and environmental exposures may help to identify modifiable risk factors that may lead to effective prevention of vascular and Alzheimer's dementia.