Possible factors in the etiology of Alzheimer's disease

Temperature controlled ionic liquid-based dispersive micro-extraction using two ligands, for determination of aluminium in scalp hair samples of Alzheimer's patients: a multivariate study

A green and sensitive temperature controlled dispersive liquid-liquid microextraction (TIL-DLLME) methodology based on the application of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [C4mim][PF6], as an extractant solvent was proposed for the preconcentration of trace levels of aluminium (Al(3+)) in scalp hair samples of Alzheimer's (AD) patients, prior to analyzing by flame atomic absorption spectrometry (FAAS). The Al(3+) was complexed with 8-hydrooxyquinoline (oxine) (L1) and 3,5,7,2'-4' pentahydroxy flavone (morin) (L2) separately and then extracted by IL at temperature (50±2.0°C). Some effective factors that influence the TIL-DLLME efficiency such as pH, ligands concentrations, volume of IL, ionic strength, and incubation time were investigated and optimized by multivariate analysis. In the optimum experimental conditions, the limit of detection (3s) and enhancement factor were 0.56 μg L(-1), 0.64 μg L(-1) and 85, 73 for both ligands, respectively. The relative standard deviation (RSD) for six replicate determinations of 100 μg L(-1) Al(3+) complexed with oxine and morin were found to be 3.88% and 4.74%, respectively. The developed method was validated by the analysis of certified reference material of human hair (NCSZC81002).and applied satisfactorily to the determination of Al(3+) in acid digested scalp hair samples of AD patients and healthy controls. The resulted data shows significant higher level in scalp hair samples of AD male patients with related to referents of same age and socioeconomic status.

Amyloid and tau pathology of familial Alzheimer's disease APP/PS1 mouse model in a senescence phenotype background (SAMP8)

The amyloid precursor protein/presenilin 1 (APP/PS1) mouse model of Alzheimer's disease (AD) has provided robust neuropathological hallmarks of familial AD-like pattern at early ages, whereas senescence-accelerated mouse prone 8 (SAMP8) has a remarkable early senescence phenotype with pathological similarities to AD. The aim of this study was the investigation and characterization of cognitive and neuropathological AD markers in a novel mouse model that combines the characteristics of the APP/PS1 transgenic mouse model with a senescence-accelerated background of SAMP8 mice. Initially, significant differences were found regarding amyloid plaque formation and cognitive abnormalities. Bearing these facts in mind, we determined a general characterization of the main AD brain molecular markers, such as alterations in amyloid pathway, neuroinflammation, and hyperphosphorylation of tau in these mice along their lifetimes. Results from this analysis revealed that APP/PS1 in SAMP8 background mice showed alterations in the pathways studied in comparison with SAMP8 and APP/PS1, demonstrating that a senescence-accelerated background exacerbated the amyloid pathology and maintained the cognitive dysfunction present in APP/PS1 mice. Changes in tau pathology, including the activity of cyclin-dependent kinase 5 (CDK5) and glycogen synthase kinase 3 β (GSK3β), differs, but not in a parallel manner, with amyloid disturbances.

Fluoride in the media: a review of newspaper articles from 1999 to 2009

The effects of fluoride are regularly discussed in newspapers. This paper reviews this coverage over a ten-year period and compares the content with contemporary scientific evidence. The reporting used in a sample of daily newspapers when the subject of fluoride and its effects were mentioned was analysed and factual statements within the articles were compared with contemporary scientific studies, to assess the accuracy of reporting.

CLINICAL RELEVANCE

Practitioners may face questions from patients regarding the evidence base for the safety and efficacy of the use of fluoride in dentistry.

Accumulation of nuclear DNA damage or neuron loss: molecular basis for a new approach to understanding selective neuronal vulnerability in neurodegenerative diseases

According to a long-standing hypothesis, aging is mainly caused by accumulation of nuclear (n) DNA damage in differentiated cells such as neurons due to insufficient nDNA repair during lifetime. In line with this hypothesis it was until recently widely accepted that neuron loss is a general consequence of normal aging, explaining some degree of decline in brain function during aging. However, with the advent of more accurate procedures for counting neurons, it is currently widely accepted that there is widespread preservation of neuron numbers in the aging brain, and the changes that do occur are relatively specific to certain brain regions and types of neurons. Whether accumulation of nDNA damage and decline in nDNA repair is a general phenomenon in the aging brain or also shows cell-type specificity is, however, not known. It has not been possible to address this issue with the biochemical and molecular-biological methods available to study nDNA damage and nDNA repair. Rather, it was the introduction of autoradiographic methods to study quantitatively the relative amounts of nDNA damage (measured as nDNA single-strand breaks) and nDNA repair (measured as unscheduled DNA synthesis) on tissue sections that made it possible to address this question in a cell-type-specific manner under physiological conditions. The results of these studies revealed a formerly unknown inverse relationship between age-related accumulation of nDNA damage and age-related impairment in nDNA repair on the one hand, and the age-related, selective, loss of neurons on the other hand. This inverse relation may not only reflect a fundamental process of aging in the central nervous system but also provide the molecular basis for a new approach to understand the selective neuronal vulnerability in neurodegenerative diseases, particularly Alzheimer's disease.

Aluminium blunts the proliferative response and increases apoptosis of cultured human cells: putative relationship to Alzheimer's disease

Aluminium (Al) has been investigated as a neurotoxic substance. Al ranks among the potential environmental risk factors for Alzheimer's disease (AD). Epidemiological studies tested the relationship between Al in drinking water and AD, showing a significant correlation between elevated levels of monomeric Al in water and AD, although data to date remain inconclusive with respect to total Al. The aim of this study was to test whether or not Al exacerbates cellular toxicity mediated by the amyloid beta (Abeta) peptide. We evaluated the role of Al in modulating programmed cell death (apoptosis) in human cell cultures. We used the osteosarcoma cell line monolayer (SaOs-2) to demonstrate that treatment of SaOs-2 cultures with the Abeta peptide mid-fragment (25 to 35) at nano M, followed by co-incubation with physiological concentrations of aluminium chloride, which release monomeric Al in solution, led to marked expression of caspase 3, but not caspase 9, key markers of the apoptotic process. The same experimental conditions were shown to blunt significantly the proliferative response of normal human peripheral blood mononuclear cells (PBMC) to phytohemagglutinin (PHA) stimulation. Our observations support the hypothesis that Al significantly impairs certain cellular immune responses, and confirm that Al-mediated cell toxicity may play an important role in AD.

The aging brain: Accumulation of DNA damage or neuron loss?

Age-related molecular and cellular alterations in the central nervous system are known to show selectivity for certain cell types and brain regions. Among them age-related accumulation of nuclear (n) DNA damage can lead to irreversible loss of genetic information content. In the present study on the aging mouse brain, we observed a substantial increase in the amount of nDNA single-strand breaks in hippocampal pyramidal and granule cells as well as in cerebellar granule cells but not in cerebellar Purkinje cells. The reverse pattern was found for age-related reductions in total numbers of neurons. Only the total number of cerebellar Purkinje cells was significantly reduced during aging whereas the total numbers of hippocampal pyramidal and granule cells as well as of cerebellar granule cells were not. This formerly unknown inverse relation between age-related accumulation of nDNA damage and age-related loss of neurons may reflect a fundamental process of aging in the central nervous system.

Localization and role of metallothioneins in the olfactory pathway after exposure to mercury vapor

We have investigated the localization and physiological roles of metallothioneins (MTs) in the olfactory pathway after exposure to mercury (Hg0) vapor. Male MT-null and wild-type mice were examined for the distribution of mercury, MT immunoreactivity and MT-III mRNA expression. There were no signs of histological changes in MT-null or wild-type mice. Light and electron microscopy of the samples stained with autometallography demonstrated chronological transfer of exposed mercury granules to the olfactory bulb by way of the olfactory tract. Basal expression of MT-I and -II immunoreactivity was observed in supporting cells, basal cells and acinar cells of the Bowman's gland of the olfactory mucosa in wild-type mice even without mercury exposure. In situ hybridization showed that signals for MT-III mRNA dominated in the olfactory cells of the olfactory mucosa, neurons in the olfactory bulb and those of brain in MT-null and wild-type mice. No difference in these findings was observed between samples taken at any interval after mercury exposure.

Neurodegenerative memory disorders: a potential role of environmental toxins

The hypothesis that neurotoxins may play a role in neurodegenerative disorders remains an elusive one, given that epidemiologic studies often provide conflicting results. Although these conflicting results may result from methodological differences within and between studies, the complexity of chemical disruption of the central nervous system cannot be ignored in attempts to evaluate this hypothesis in different neurodegenerative disorders. Spencer provides a detailed review of the complex processes involved in defining the neurotoxic potential of naturally occurring and synthetic agents. Even concepts such as exposure and dose, as often reported in studies attempting to evaluate the risk imparted by a potential compound, can be deceptive. For example, although dose reflects "that amount of chemical transferred to the exposed subject", factors such as time and concentration in the organism, the ability to access the central nervous system, and how a compound reaches the central nervous system (routes of administration) or secondarily affects other organ systems leading to central nervous system disruption are clearly important to the concept of neurotoxic risk in neurodegenerative disorders. These factors would appear to explain the observed disagreements between studies using animal or neuronal models of neurotoxicity and population-based studies in humans. The importance of these factors and how a potential neurotoxin is investigated are clearly seen in the data on AD and aluminum. In contrast, the impact of MTPT on the central nervous system is more direct and compelling. Added complexity in the study of neurotoxins in human neurodegeneration is derived from data showing that agents may have additive, potentiating, synergistic, or antagonistic effects. Therefore, data from studies evaluating EMF risks could be readily confounded by the presence or absence of heavy metals (eg, arc welding). Other factors that may conceal neurotoxic causes for a given disorder focus on additional features such as genetic predispositions, physiologic changes that occur in aging, and even nutritional status that can support or hinder the affect of a given agent on the central nervous system. Finally, many studies that investigate exposure risk do not readily incorporate the five criteria proposed by Schaumburg for establishing causation. For example, if we apply Schaumburg's first criterion, epidemiologic studies often determines the presence of an agent through history, yet they cannot readily confirm exposure based on environmental or clinical chemical analyses to fulfill this criterion for causation. Additional limitations in research design along with the populations and methods that are sued to study neurotoxins in human neurodegenerative disorders often fail to meet other criteria such as linking the severity and onset with duration and exposure level. Therefore, although studies of agents such as MTPT provide compelling models of neurotoxins and neurodegeneration in humans, disorders such as ALS, PD, and particularly AD will require additional effort if research is to determine the contribution (presence or absence) of neurotoxins to these neurologic disorders.

Perinatal exposure to aluminum alters neuronal nitric oxide synthase expression in the frontal cortex of rat offspring

Disturbance of the neuronal nitric oxide signaling pathway by chronic exposure to aluminum (Al) in drinking water may be a causal factor of neurological disorders in offspring. In order to investigate the relationship between Al administration and expression of neuronal nitric oxide synthase (nNOS), the numbers and distribution patterns of nNOS-immunoreactive neurons were examined in the frontal cortex of offspring after exposure to 0, 5, and 10 mM of Al in drinking water during prenatal and neonatal periods. At the bregma 0.20 level, the number of nNOS-positive neurons was significantly increased (10%) and decreased (17%) following exposure to 5 and 10 mM of Al in drinking water, respectively. The change was more severe in the upper layer than in deep layer of the cortex. In contrast, at the bregma -2.80 level, the number and distribution pattern was not significantly changed following exposure to Al. These data suggest that Al toxicity may be mediated through disturbances to the nitric oxide signaling pathway and exhibits a biphasic effect, especially in the frontal area of the cortex. In addition, the results suggest that impaired expression of nNOS plays an important role in the development of neurological syndrome caused by an exposure to Al during the early developmental stage.

Neurotoxic effects of aluminium among foundry workers and Alzheimer's disease

BACKGROUND

In a cross-sectional case-control study conducted in northern Italy, 64 former aluminium dust-exposed workers were compared with 32 unexposed controls from other companies matched for age, professional training, economic status, educational and clinical features. The findings lead the authors to suggest a possible role of the inhalation of aluminium dust in pre-clinical mild cognitive disorder which might prelude Alzheimer's disease (AD) or AD-like neurological deterioration.

METHODS

The investigation involved a standardised occupational and medical history with particular attention to exposure and symptoms, assessments of neurotoxic metals in serum: aluminium (Al-s), copper (Cu-s) and zinc (Zn-s), and in blood: manganese (Mn-b), lead (Pb-b) and iron (Fe-b). Cognitive functions were assessed by the Mini Mental State Examination (MMSE), the Clock Drawing Test (CDT) and auditory evoked Event-Related Potential (ERP-P300). To detect early signs of mild cognitive impairment (MCI), the time required to solve the MMSE (MMSE-time) and CDT (CDT-time) was also measured.

RESULTS

Significantly higher internal doses of Al-s and Fe-b were found in the ex-employees compared to the control group. The neuropsychological tests showed a significant difference in the latency of P300, MMSE score, MMSE-time, CDT score and CDT-time between the exposed and the control population. P300 latency was found to correlate positively with Al-s and MMSE-time. Al-s has significant effects on all tests: a negative relationship was observed between internal Al concentrations, MMSE score and CDT score; a positive relationship was found between internal Al concentrations, MMSE-time and CDT-time. All the potential confounders such as age, height, weight, blood pressure, schooling years, alcohol, coffee consumption and smoking habit were taken into account.

CONCLUSIONS

These findings suggest a role of aluminium in early neurotoxic effects that can be detected at a pre-clinical stage by P300, MMSE, MMSE-time, CDT-time and CDT score, considering a 10 micrograms/l cut-off level of serum aluminium, in aluminium foundry workers with concomitant high blood levels of iron. The authors raise the question whether pre-clinical detection of aluminium neurotoxicity and consequent early treatment might help to prevent or retard the onset of AD or AD-like pathologies.

The amyloid peptide induces early genotoxic damage in human preneuron NT2

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the extracellular deposition of amyloid beta-peptide (Abeta) in the brain. Abeta is involved in the pathogenesis of AD but the molecular mechanisms of its neurotoxicity are unknown. Here, we report that Abeta exposure on human preneuronal NT2 cells provoked a strong and early up-regulation of growth arrest and DNA damage inducible gene (Gadd45 mRNA), an indicator of DNA damage and DNA excision-repair processes, strongly suggesting that Abeta causes an early DNA strand breakage leading to a cellular DNA repair response. Comet assay clearly demonstrated that both full-length Abeta (1-42), and its minimal cytotoxic fragment Abeta (25-35), caused DNA breakage as early as 3h after the start of Abeta exposure. This extensive DNA damage provoked by Abeta constitutes an early event in the pathogenic cascade leading to neuronal death which could contribute to the neuropathogenesis of AD.

Fibril formation and neurotoxicity by a herpes simplex virus glycoprotein B fragment with homology to the Alzheimer's A beta peptide

Despite significant progress in the elucidation of the genetic basis of early-onset familial Alzheimer's disease (AD), the etiology of sporadic cases remains elusive. Although certain genetic loci play a role in conferring susceptibility in some sporadic AD cases, it is likely that the etiology is multifactorial; hence, the majority of cases cannot be attributed to genetic factors alone, indicating that environmental factors may modulate the onset and/or progression of the disease. Head injury and infectious agents are environmental factors that have been periodically implicated, but no plausible mechanisms have been clearly identified. With regard to infectious agents, speculation has often centered on the neurotropic herpes viruses, with herpes simplex virus 1 (HSV1) considered a likely candidate. We report that an internal sequence of HSV1 glycoprotein B (gB) is homologous to the carboxyl-terminal region of the A beta peptide that accumulates in diffuse and neuritic plaques in AD. Synthetic peptides were generated and the biophysical and biological properties of the viral peptide compared to those of A beta. Here we show that this gB fragment forms beta-pleated sheets, self-assembles into fibrils that are thioflavin-positive and ultrastructurally indistinguishable from A beta, accelerates the formation of A beta fibrils in vitro, and is toxic to primary cortical neurons at doses comparable to those of A beta. These findings suggest a possible role for this infectious agent in the pathophysiology of sporadic cases of AD.

Herpes simplex virus type 1 and Alzheimer's disease

Until recently, the only risk factors implicated in noninherited cases of Alzheimer's disease were increasing age, Down's syndrome, and probably, head injury. Having found that herpes simplex type 1 virus (HSV1) is present in the brain of many elderly people, we discovered that it is a risk factor for Alzheimer's disease when in the central nervous system of APOE-epsilon4 allele carriers. On the basis of this result and our finding that apoE-epsilon4 is a risk factor for herpes labialis, we suggested that the combination of virus and genetic factor is particularly damaging in the nervous system. The present review describes 1) the search for HSV1 in human brain; 2) HSV1 infection of the peripheral nervous system; 3) HSV1 infection of the central nervous system; 4) how APOE genotype might influence HSV1 infection; 5) possible APOE genotype effect on viral latency and its reactivation; 6) interactions of viruses with lipoproteins, their components, and lipoprotein receptors; 7) the role of APOE in repair; 8) pathological processes in AD and their relationship to prior damage; and 9) implications for the prevention or treatment of Alzheimer's disease.

[18F]fluoroethoxy-benzovesamicol, a PET radiotracer for the vesicular acetylcholine transporter and cholinergic synapses

Loss of cholinergic transmission in the cortex and hippocampus is a characteristic feature of Alzheimer's disease, and visualization of functional cholinergic synapses in the brain with PET could be a useful method for studying this degenerative condition in living humans. We investigated [18F]fluoroethoxybenzovesamicol, (-)-[18F] FEOBV,(-)-(2R,3R)-trans-2-hydroxy-3-(4-phenylpiperidino)-5-(2-[18F ]fluoroethoxy)-1,2,3,4-tetralin, a high affinity positron emitting ligand for the vesicular acetylcholine transporter, as a potential in vivo cholinergic synapse mapping agent. Rodent biodistribution, dosimetry, stereospecificity of biological effects, pharmacologic blocking studies, in vivo rodent brain autoradiography and metabolites were examined. (-)-[18F]FEOBV brain uptake following intravenous injection was robust, with 2.65% dose/brain in mice at 5 min, and the regional localization matched the known distributions of presynaptic cholinergic markers at later times. Both the cholinergic localization and curare-like effects of FEOBV were associated with the "(-)"-enantiomer exclusively. (-)-[18F]FEOBV regional brain distribution in rodents was changed little by pretreatment with haloperidol, (+)-3-PPP, or E-2020, indicating FEOBV, unlike other vesamicol analogs, did not interact in vivo with dopamine or sigma receptor systems. Autoradiography of rat brain 3 h following i.v. injection of (-)-[18F]FEOBV showed high localization in brain areas rich in presynaptic cholinergic elements. Metabolic defluorination in rodents was modest, and analysis of brain tissue following tracer administration found FEOBV as the only extractable radioactive species. (-)-[18F]FEOBV dosimetry calculated from rat data estimate 10 mCi doses can be given to humans. These studies show FEOBV maps cholinergic areas with high specificity in vivo, and may provide a noninvasive means to safely and accurately gauge the functional integrity of cholinergic synapses in man using PET.

Establishing the limits of normal cerebral ageing and senile dementias

Cognitive deterioration is so commonly observed in the elderly that it is considered by many to be an inevitable feature of the ageing process. Some researchers have proposed that the senile dementias are the inevitable end-point of this process, should the person live long enough. The differentiation of normal cerebral ageing from disease process is important in the selection of control groups for research, and also for clinical decision-making. In the latter context it is important to ask at what level of dysfunction intervention should occur, and whether this should be active or palliative. Cognitive change in the elderly is here considered from biological, neuropsychological and epidemiological viewpoints. Current research suggests that senile dementia is the result of the interplay of genetically determined disease processes, ageing-related decline which may be regulated at a cellular level, and neuronal repair and compensation mechanisms. Therefore, to debate whether dementia is simply an extension of a normal ageing process or not is probably too simplistic an approach.

Chronic administration of aluminum-fluoride or sodium-fluoride to rats in drinking water: alterations in neuronal and cerebrovascular integrity

This study describes alterations in the nervous system resulting from chronic administration of the fluoroaluminum complex (AlF3) or equivalent levels of fluoride (F) in the form of sodium-fluoride (NaF). Twenty seven adult male Long-Evans rats were administered one of three treatments for 52 weeks: the control group was administered double distilled deionized drinking water (ddw). The aluminum-treated group received ddw with 0.5 ppm AlF3 and the NaF group received ddw with 2.1 ppm NaF containing the equivalent amount of F as in the AlF3 ddw. Tissue aluminum (Al) levels of brain, liver and kidney were assessed with the Direct Current Plasma (DCP) technique and its distribution assessed with Morin histochemistry. Histological sections of brain were stained with hematoxylin & eosin (H&E), Cresyl violet, Bielschowsky silver stain, or immunohistochemically for beta-amyloid, amyloid A, and IgM. No differences were found between the body weights of rats in the different treatment groups although more rats died in the AlF3 group than in the control group. The Al levels in samples of brain and kidney were higher in both the AlF3 and NaF groups relative to controls. The effects of the two treatments on cerebrovascular and neuronal integrity were qualitatively and quantitatively different. These alterations were greater in animals in the AlF3 group than in the NaF group and greater in the NaF group than in controls.

Aggregation of amyloid beta-protein as function of age and apolipoprotein E in normal and Alzheimer's serum

We compared the effect of serum from (a) 26 Alzheimer's disease (AD) patients and 22 age-matched non-demented controls (CO) with apolipoprotein E 4/4, 3/3 or 3/2 phenotypes, and (b) 17 normal young (aged 15-41 years) and 21 normal elderly (aged 64-83 years) people on in vitro aggregation of synthetic amyloid beta-protein (A beta) 1-40 by Thioflavin T fluorescence spectroscopy. A beta 1-40 aggregation in presence of serum from the normal elderly group was significantly higher as compared to the normal young group (correlation coefficient between age and A beta aggregation=0.73). However, no difference in A beta aggregation was observed in the presence of serum from AD patients and non-demented controls. There was a positive correlation between serum apo E concentrations and A beta aggregation, while there was no significant difference between different apo E phenotypes. The correlation coefficient in the AD 4/4 (0.65) was higher than the CO 4/4 group (0.04), while it was lower in the AD 3/3 group (-0.12) than in the CO 3/3 (0.39) group. These results suggest that the apo E4 allele alone may not be responsible for A beta fibril formation in AD; other factors may be involved in increasing risk for AD pathogenesis in those having the apo E4 allele. The severity of dementia and serum albumin levels also did not correlate with A beta aggregation. We propose that the age of an individual may be an important factor in determining the degree of A beta aggregation/fibrillization, and that mechanism of sequestration of A beta in serum may not be defective in AD.

Current concepts in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) affects a large proportion of the increasingly aging population of this country, with prevalence rates as high as 47% for those >85 years old and a total annual cost approaching $70 billion. There is no currently validated test for detection of dementia of the Alzheimer type (DAT). Because of this and the insidious onset of the disease, the diagnosis may be missed by primary care physicians. Cerebral extracellular beta-amyloid deposition as senile plaques and intraneuronal neurofibrillary tangles appear to represent critical processes in the development of AD; however, whether and the extent to which these may also occur in nondemented aging is uncertain. Tangles occur primarily in medial temporal lobe structures (hippocampus, entorhinal cortex, and amygdala), and tangle density correlates with dementia severity. Plaques are diffusely distributed throughout the cerebral cortex, and are the neuropathologic hallmark of the disease. Aging is the primary risk factor for AD. After controlling for differential life expectancy, female sex still appears to be an additional risk factor. There may be a genetic component, in some cases based on family and twin studies. Allelic variation in the apolipoprotein E (Apo E) gene located on chromosome 19 represents another important risk factor. However, the diversity of gene mutations apparently responsible for the various forms of AD suggest that the disease is genetically heterogeneous. AD may be conceptualized as an imbalance between neuronal injury and repair. Oxygen free radicals may be involved in the cross-linking process of beta-amyloid aggregation, and antioxidants may represent a potential intervention. There may be a role for heavy metals in the pathogenesis of AD, but this remains controversial. Work continues toward possibly a cure or prevention, but more likely palliation, of AD, and the results of trials of anti-inflammatory agents, estrogen, and antioxidant therapy are anticipated in the near future.

Neurotropic viruses and Alzheimer's disease: a search for varicella zoster virus DNA by the polymerase chain reaction

BACKGROUND

In studies on the possible role of viruses in the aetiopathogenesis of Alzheimer's disease, herpes simplex virus type 1 (HSV1) DNA was detected by the polymerase chain reaction (PCR) in a high proportion of normal elderly people and of patients with Alzheimer's disease. The combination of HSV1 and a host factor, the type 4 allele of the gene for apolipoprotein E, is a strong risk factor for the disease.

METHODS

Brain specimens were examined for another herpes virus, varicella zoster (VZV), which, like HSV1, is neurotropic, has a predilection for residing latently in the peripheral nervous system, and can reactivate.

RESULTS

Using primers for sequences in the VZV origin of replication gene or thymidine kinase gene, VZV DNA was not found in any of 24 samples (18 HSV1 positive), from 17 patients with Alzheimer's disease, nor in 20 samples (12 HSV1 positive from 12 aged normal people. Hybridisation of the PCR products with a radiolabelled oligonucleotide probe capable of detecting less than 10 copies of the target sequence, confirmed the absence of VZV DNA.

CONCLUSION

The presence of one neurotropic virus--HSV1--and the absence of another--VZV--in aged human brains is consistent with a role for HSV1 in the aetiology of Alzheimer's disease.

Herpes simplex virus type 1 in brain and risk of Alzheimer's disease

BACKGROUND

The apolipoprotein E epsilon 4 (APOE-epsilon 4) allele is a risk factor for Alzheimer's disease (AD), but it is neither essential nor sufficient for development of the disease. Other factors-genetic or environmental-must therefore have a role. By means of a PCR we have detected herpes simplex virus type 1 (HSV1) in latent form in brains of elderly people with and without AD. We have postulated that limited reactivation of the virus causes more damage in AD patients than in elderly people without AD because of a difference in the hosts. We now report the APOE genotypes of AD patients and non-AD sufferers with and without HSV1 in brain.

METHODS

DNA was extracted from 84 samples of brain from 46 AD patients (39 temporal lobe, 39 frontal lobe, three hippocampus) and from 75 samples of brain from 44 non-AD elderly people (33 temporal lobe, 36 frontal lobe, six hippocampus). PCR amplification was used to detect HSV1 thymidine kinase gene and the host APOE gene.

FINDINGS

By multiple logistic regression, the APOE-epsilon 4 allele frequency was significantly higher in the patients positive for HSV1 in brain than in the HSV1-negative AD group, the HSV1-positive non-AD group, or the HSV1-negative non-AD group (52.8% vs 10.0%, 3.6%, and 6.3%, respectively). The odds ratio for APOE-epsilon 4 in the HSV1-positive AD group compared with HSV1-negative non-AD group was 16.8 (95% CI 3.61-77.8) and in the HSV1-negative AD group, 1.67 (0.21-13.4). We also compared APOE genotypes of 40 people who had recurrent cold sores and 33 non-sufferers; the APOE-epsilon 4 allele frequencies were 36% and 9%, respectively (p < 0.0001).

INTERPRETATION

These findings suggest that the combination of HSV1 in brain and carriage of an APOE-epsilon 4 allele is a strong risk factor for AD, whereas either of these features alone does not increase the risk of AD. The findings in people with cold sores support our hypothesis that APOE-epsilon 4 and HSV1 together are damaging in the nervous system.

Neurotropic viruses and Alzheimer disease. Interaction of herpes simplex type 1 virus and apolipoprotein E in the etiology of the disease

Infectious agents have been proposed as possible etiological factors in sporadic cases of Alzheimer disease (AD), herpes simplex type 1 virus (HSV1) being a likely candidate. We have detected laten HSV1 in brain from AD patients and from aged normal individuals, using polymerase chain reaction (PCR), in the regions most affected in the disease. In contrast, we have not detected another neurotropic herpes virus, varicella zoster (VZV), in any brains. We have postulated that HSV1 reactivates periodically, and that a host or viral characteristic determines the degree of damage caused by the resulting acute infection-with much greater damage in the case of AD patients. We have therefore examined a host factor-the apolipoprotein E (apoE) genotype, since the E4 allele is a known risk factor in the disease. We have found that the risk of developing AD is much greater in those who are HSV1-positive in brain and who possess an apoE4 allele than for those with only one of these factors.

beta-Amyloid toxicity in organotypic hippocampal cultures: protection by EUK-8, a synthetic catalytic free radical scavenger

Oxygen free radicals have been proposed to mediate amyloid peptide (beta-AP)-induced neurotoxicity. To test this hypothesis, we evaluated the effects of EUK-8, a synthetic catalytic superoxide and hydrogen peroxide scavenger, on neuronal injury produced by beta-AP in organotypic hippocampal slice cultures. Cultures of equivalent postnatal day 35 (defined as mature) and 14 (defined as immature) were exposed to various concentrations of beta-AP (1-42 or 1-40) in the absence or presence of 25 microM EUK-8 for up to 72 hours. Neuronal injury was assessed by lactate dehydrogenase release and semiquantitative analysis of propidium iodide uptake at various times after the initiation of beta-AP exposure. Free radical production was inferred from the relative increase in dichlorofluorescein fluorescence, and the degree of lipid peroxidation was determined by assaying thiobarbituric acid-reactive substances. Treatment of mature cultures with beta-AP (50-250 microg/ml) in serum-free conditions resulted in a reproducible pattern of damage, causing a time-dependent increase in neuronal injury accompanied with formation of reactive oxygen species. However, immature cultures were entirely resistant to beta-AP-induced neurotoxicity and also demonstrated no dichlorofluorescein fluorescence or increased lipid peroxidation after beta-AP treatment. Moreover, mature slices exposed to beta-AP in the presence of 25 microM EUK-8 were significantly protected from beta-AP-induced neurotoxicity. EUK-8 also completely blocked beta-AP-induced free radical accumulation and lipid peroxidation. These results not only support a role for oxygen free radicals in beta-AP toxicity but also highlight the therapeutic potential of synthetic radical scavengers in Alzheimer disease.