Documented head injury in early adulthood and risk of Alzheimer's disease and other dementias

Detangling Alzheimer's Disease

Alzheimer's disease afflicts 4.5 million people in the United States, and the number is expected to rise to 16 million by the year 2050, as the population ages. Researchers are scrambling to find genetic risk factors, decipher disease mechanisms, and develop reliable diagnostic tests that detect the illness at its earliest, potentially most treatable stage. Using these findings, they hope to devise new therapeutic approaches. Current clinical trials are assessing novel techniques that stall or reverse Alzheimer-like neuropathology in mice.

Apolipoprotein e4 decreases whereas apolipoprotein e3 increases the level of secreted amyloid precursor protein after closed head injury

Apolipoprotein E (apoE4) and head trauma are important genetic and environmental risk factors for Alzheimer's disease. Furthermore, apoE4 increases both the acute and chronic consequences of head trauma. The latter are associated with the deposition of amyloid-beta, which is particularly elevated in apoE4 subjects. The short-term effects of head injury are associated with transiently increased metabolism of amyloid precursor protein (APP) and its secreted fragment, APPs. In the present study, we examined the possibility that the acute, short-term pathological effects of apoE4 following head trauma and the corresponding neuroprotective effects of apoE3 are related to isoform-specific effects of apoE on APP metabolism. Accordingly, male transgenic mice expressing human apoE3 or apoE4 on a null mouse apoE background and apoE-deficient and control mice were subjected to closed head injury (CHI). The resulting effects on brain APP, and on its secreted products, APPs and secreted product of the alpha-cleavage of APP (APPsalpha) were then determined 24 h following injury. Immunoblotting revealed no significant differences between the basal APP, APPs and APPsalpha levels of the hippocampus or the cortex of the control and the apoE3 and ApoE4 transgenic mice. The apoE-deficient mice also had similar cortical basal levels of APP and its metabolites, whereas their corresponding basal hippocampal APP and APPs levels were lower than those of the other groups. CHI lowered the hipppocampal APPs and APPsalpha levels of the apoE4 transgenic mice, whereas those of the apoE3 transgenic mice and of the control and apoE-deficient mice were not affected by this insult. In contrast, CHI raised the cortical APP and APPs levels of the apoE3 transgenic mice but had no significant effect on those of the other mice groups. These animal model findings suggest that the acute, short-term pathological effects of apoE4 following CHI and the corresponding neuroprotective effects of apoE3 may be mediated by their opposing effects on the expression and cleavage of cortical and hippocampal APP. Similar isoform-specific interactions between apoE and APP may play a role in the acute, short-term effects of head trauma in humans.

Synergistic dopaminergic neurotoxicity of MPTP and inflammogen lipopolysaccharide: relevance to the etiology of Parkinson's disease

Parkinson's disease (PD) is a profound movement disorder resulting from progressive degeneration of the nigrostriatal dopaminergic pathway. Although its etiology remains unknown, increasing evidence suggests the involvement of multiple factors such as environmental toxins and genetic susceptibilities in the pathogenesis of PD. In this study using mesencephalic neuron-glia cultures as an in vitro PD model, we demonstrated that the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 0.1-0.5 microM) and an inflammogen lipopolysaccharide (LPS, 0.5 ng/ml) synergistically induced a progressive and selective degeneration of dopaminergic neurons. The synergistic neurotoxicity was observed when both agents were applied either simultaneously or in tandem. The synergistic neurotoxicity was more prominent when lower doses of both agents were applied for a longer period of time. Mechanistically, microglial NADPH oxidase-mediated generation of reactive oxygen species played a pivotal role in the synergistic neurotoxicity: MPTP and LPS synergistically stimulated the NADPH oxidase-mediated release of superoxide free radical; pharmacological inhibition and genetic inactivation of NADPH oxidase prevented superoxide production and the synergistic neurotoxicity. Additionally, inhibition of nitric oxide synthase afforded significant neuroprotection, suggesting the involvement of nitric oxide in the synergistic neurotoxicity. This study lends strong support for a multifactorial etiology of PD and provides clues for therapeutic interventions.

Long term neuropsychological outcome after head injury: relation to APOE genotype

BACKGROUND

Existing evidence suggests that some patients who sustain a head injury suffer cognitive decline many years later, and that head injury and possession of the APOE epsilon 4 allele are each risk factors for Alzheimer's disease.

OBJECTIVE

To determine whether late cognitive decline after head injury is more prevalent among carriers of APOE epsilon 4.

METHODS

A database of head injured patients was used. Initial assessment was at the time of their injury, between 1968 and 1985, and outcome data at six months were available. Their ages at the time of injury ranged between 2 and 70 years. A cohort of 396 subjects was reassessed at a mean of 18 years later, with determination of APOE genotype and detailed neuropsychological testing.

RESULTS

Judging by the Glasgow outcome scale, twice as many patients had deteriorated as improved between six months after injury and the late assessment; 22.2% of APOE epsilon 4 carriers had a good late outcome compared with 30.5% of non-carriers (95% confidence interval for the difference, -0.7% to 17.2%; p = 0.084). There were no clear differences between epsilon 4 carriers and non-carriers in detailed neuropsychological assessments.

CONCLUSIONS

Although this study provides additional evidence that a late decline may occur after head injury, there was no clear relation to APOE genotype. Despite the follow up interval of 15 to 25 years, the cohort is still too young (mean age 42.1 years) to assess the risk of Alzheimer's disease.

Head injury as a risk factor for Alzheimer's disease: the evidence 10 years on; a partial replication

OBJECTIVE

To determine, using a systematic review of case-control studies, whether head injury is a significant risk factor for Alzheimer's disease. We sought to replicate the findings of the meta-analysis of Mortimer et al (1991).

METHODS

A predefined inclusion criterion specified case-control studies eligible for inclusion. A comprehensive and systematic search of various electronic databases, up to August 2001, was undertaken. Two independent reviewers screened studies for eligibility. Fifteen case-control studies were identified that met the inclusion criteria, of which seven postdated the study of Mortimer et al.

RESULTS

We partially replicated the results of Mortimer et al. The meta-analysis of the seven studies conducted since 1991 did not reach significance. However, analysis of all 15 case-control studies was significant (OR 1.58, 95% CI 1.21 to 2.06), indicating an excess history of head injury in those with Alzheimer's disease. The finding of Mortimer et al that head injury is a risk factor for Alzheimer's disease only in males was replicated. The excess risk of head injury in those with Alzheimer's disease is only found in males (males: OR 2.29, 95% CI 1.47 to 2.06; females: OR 0.91, 95% CI 0.56 to 1.47).

CONCLUSIONS

This study provides support for an association between a history of previous head injury and the risk of developing Alzheimer's disease.

Parkinson's disease and exposure to infectious agents and pesticides and the occurrence of brain injuries: role of neuroinflammation

Idiopathic Parkinson's disease (PD) is a devastating movement disorder characterized by selective degeneration of the nigrostriatal dopaminergic pathway. Neurodegeneration usually starts in the fifth decade of life and progresses over 5-10 years before reaching the fully symptomatic disease state. Despite decades of intense research, the etiology of sporadic PD and the mechanism underlying the selective neuronal loss remain unknown. However, the late onset and slow-progressing nature of the disease has prompted the consideration of environmental exposure to agrochemicals, including pesticides, as a risk factor. Moreover, increasing evidence suggests that early-life occurrence of inflammation in the brain, as a consequence of either brain injury or exposure to infectious agents, may play a role in the pathogenesis of PD. Most important, there may be a self-propelling cycle of inflammatory process involving brain immune cells (microglia and astrocytes) that drives the slow yet progressive neurodegenerative process. Deciphering the molecular and cellular mechanisms governing those intricate interactions would significantly advance our understanding of the etiology and pathogenesis of PD and aid the development of therapeutic strategies for the treatment of the disease.

Genetic vulnerability following traumatic brain injury: the role of apolipoprotein E

Apolipoprotein E (APOE) is thought to be responsible for the transportation of lipids within the brain, maintaining structural integrity of the microtubule within the neurone, and assisting with neural transmission. Possession of the APOE epsilon4 allele has also been shown to influence neuropathological findings in patients who die from traumatic brain injury, including the accumulation of amyloid beta protein. Previous clinical studies reporting varying outcome severities of traumatic brain injury, including cognitive and functional recovery, all support the notion that APOE epsilon4 allele possession is associated with an unfavourable outcome. Evidence from experimental and clinical brain injury studies confirms that APOE plays an important role in the response of the brain to injury.

Interleukin-10 promoter polymorphism in sporadic Alzheimer's disease

Proinflammatory cytokines and acute-phase proteins play an important role in Alzheimer's disease (AD) neurodegeneration, and common polymorphisms of genes controlling their high production have been shown to be associated with AD. Thus, AD patients display a proinflammatory genotype and the control of inflammation might play a protective role in AD development. By sequence-specific probes, we have evaluated the role of anti-inflammatory cytokine interleukin(IL)-10 in AD, by analysing in 132 AD patients and 213 healthy controls the prevalence of three different haplotypes, involving three single-nucleotide polymorphisms (SNPs) at -1082 (G-->A), -819 (C-->T) and -592 (C-->A) nucleotides of IL-10 promoter, associated with different IL-10 production. The percentage of -1082A carrier subjects was significantly increased among AD patients, and this increase was mainly due to the increase of ATA haplotype. Analysing these results according to the well-known genetic risk factor APOE-e4 allele, no significant differences were observed in SNP IL-10 allele distribution between AD patients carrying the genotype or not. So we may conclude that the presence of -1082A allele and in particular of -1082A/-819T/-592A haplotype, associated with a low production of anti-inflammatory cytokine IL-10, may be considered as an additive and independent genetic risk factor for AD.

Synergistic dopaminergic neurotoxicity of the pesticide rotenone and inflammogen lipopolysaccharide: relevance to the etiology of Parkinson's disease

Parkinson's disease (PD) is characterized by a progressive degeneration of the nigrostriatal dopaminergic pathway resulting in movement disorders. Although its etiology remains unknown, PD may be the final outcome of interactions among multiple factors, including exposure to environmental toxins and the occurrence of inflammation in the brain. In this study, using primary mesencephalic cultures, we observed that nontoxic or minimally toxic concentrations of the pesticide rotenone (0.5 nm) and the inflammogen lipopolysaccharide (LPS) (0.5 ng/ml) synergistically induced dopaminergic neurodegeneration. The synergistic neurotoxicity of rotenone and LPS was observed when the two agents were applied either simultaneously or in tandem. Mechanistically, microglial NADPH oxidase-mediated generation of reactive oxygen species appeared to be a key contributor to the synergistic dopaminergic neurotoxicity. This conclusion was based on the following observations. First, inhibition of NADPH oxidase or scavenging of free radicals afforded significant neuroprotection. Second, rotenone and LPS synergistically stimulated the NADPH oxidase-mediated release of the superoxide free radical. Third and most importantly, rotenone and LPS failed to induce the synergistic neurotoxicity as well as the production of superoxide in cultures from NADPH oxidase-deficient animals. This is the first demonstration that low concentrations of a pesticide and an inflammogen work in synergy to induce a selective degeneration of dopaminergic neurons. Findings from this study may be highly relevant to the elucidation of the multifactorial etiology of PD and the discovery of effective therapeutic agents for the treatment of the disease.

Expanding the association between the APOE gene and the risk of Alzheimer's disease: possible roles for APOE promoter polymorphisms and alterations in APOE transcription

Alzheimer's disease (AD) is the most commonly diagnosed form of dementia in the elderly. Predominantly this disease is sporadic in nature with only a small percentage of patients exhibiting a familial trait. Early-onset AD may be explained by single gene defects; however, most AD cases are late onset (> 65 years) and, although there is no known definite cause for this form of the disease, there are several known risk factors. Of these, the epsilon4 allele of the apolipoprotein E (apoE) gene (APOE) is a major risk factor. The epsilon4 allele of APOE is one of three (epsilon2 epsilon3 and epsilon4) common alleles generated by cysteine/arginine substitutions at two polymorphic sites. The possession of the epsilon 4 allele is recognized as the most common identifiable genetic risk factor for late-onset AD across most populations. Unlike the pathogenic mutations in the amyloid precursor or those in the presenilins, APOE epsilon4 alleles increase the risk for AD but do not guarantee disease, even when present in homozygosity. In addition to the cysteine/arginine polymorphisms at the epsilon2/epsilon3/epsilon4 locus, polymorphisms within the proximal promoter of the APOE gene may lead to increased apoE levels by altering transcription of the APOE gene. Here we review the genetic and biochemical evidence supporting the hypothesis that regulation of apoE protein levels may contribute to the risk of AD, distinct from the well known polymorphisms at the epsilon2/epsilon3/epsilon4 locus.

Zinc takes the center stage: its paradoxical role in Alzheimer's disease

There is compelling evidence that the etiology of Alzheimer's disease (AD) involves characteristic amyloid-beta (Abeta) deposition, oxidative stress, and anomalous metal-Abeta protein interaction. New studies have implicated redox active metals such as copper, iron, and zinc as key mediating factors in the pathophysiology of Alzheimer's disease. There is also evidence that drugs with metal chelating properties could produce a significant reversal of amyloid-beta plaque deposition in vitro and in vivo. This paper reviews current observations on the etiologic role of zinc in AD. We also discuss the interactions of zinc and copper with Abeta, a factor that purportedly facilitates disease processes. Finally, we review the protective role of zinc against Abeta cytotoxicity and hypothesize how the apparent effect of zinc on AD pathology may be paradoxical, The Zinc Paradox. Indeed, complex pathologic stressors inherent to the Alzheimer's diseased brain dictate whether or not zinc will be neuroprotective or neurodegenerative. Further research on the zinc paradox in AD is needed in order to elucidate the exact role zinc plays in AD pathogenesis.

Apolipoprotein E4 influences amyloid deposition but not cell loss after traumatic brain injury in a mouse model of Alzheimer's disease

The epsilon4 allele of apolipoprotein E (APOE) and traumatic brain injury (TBI) are both risk factors for the development of Alzheimer's disease (AD). These factors may act synergistically, in that APOE4+ individuals are more likely to develop dementia after TBI. Because the mechanism underlying these effects is unclear, we questioned whether APOE4 and TBI interact either through effects on amyloid-beta (Abeta) or by enhancing cell death/tissue injury. We assessed the effects of TBI in PDAPP mice (transgenic mice that develop AD-like pathology) expressing human APOE3 (PDAPP:E3), human APOE4 (PDAPP:E4), or no APOE (PDAPP:E-/-). Mice were subjected to a unilateral cortical impact injury at 9-10 months of age and allowed to survive for 3 months. Abeta load, hippocampal/cortical volumes, and hippocampal CA3 cell loss were quantified using stereological methods. All of the groups contained mice with Abeta-immunoreactive deposits (56% PDAPP:E4, 20% PDAPP:E3, 75% PDAPP:E-/-), but thioflavine-S-positive Abeta (amyloid) was present only in the molecular layer of the dentate gyrus in the PDAPP:E4 mice (44%). In contrast, our previous studies showed that in the absence of TBI, PDAPP:E3 and PDAPP:E4 mice have little to no Abeta deposition at this age. After TBI, all of the Abeta deposits present in PDAPP:E3 and PDAPP:E-/- mice were diffuse plaques. In contrast to the effect of APOE4 on amyloid, PDAPP:E3, PDAPP:E4, and PDAPP:E-/- mice did not differ in the amount of brain tissue or cell loss. These data support the hypothesis that APOE4 influences the neurodegenerative cascade after TBI via an effect on Abeta.

Vascular basis of Alzheimer's pathogenesis

Considerable evidence now indicates that Alzheimer's disease (AD) is primarily a vascular disorder. This conclusion is supported by the following evidence: (1) epidemiologic studies linking vascular risk factors to cerebrovascular pathology that can set in motion metabolic, neurodegenerative, and cognitive changes in Alzheimer brains; (2) evidence that AD and vascular dementia (VaD) share many similar risk factors; (3) evidence that pharmacotherapy that improves cerebrovascular insufficiency also improves AD symptoms; (4) evidence that preclinical detection of potential AD is possible from direct or indirect regional cerebral perfusion measurements; (5) evidence of overlapping clinical symptoms in AD and VaD; (6) evidence of parallel cerebrovascular and neurodegenerative pathology in AD and VaD; (7) evidence that cerebral hypoperfusion can trigger hypometabolic, cognitive, and degenerative changes; and (8) evidence that AD clinical symptoms arise from cerebromicrovascular pathology. The collective data presented in this review strongly indicate that the present classification of AD is incorrect and should be changed to that of a vascular disorder. Such a change in classification would accelerate the development of better treatment targets, patient management, diagnosis, and prevention of this disorder by focusing on the root of the problem. In addition, a theoretical capsule summary is presented detailing how AD may develop from chronic cerebral hypoperfusion and the role of critically attained threshold of cerebral hypoperfusion (CATCH) and of vascular nitric oxide derived from endothelial nitric oxide synthase in triggering the cataclysmic cerebromicrovascular pathology.

Thinking preventively about dementia: a review

BACKGROUND

The dementias of late life now constitute a major public health challenge to our society.

OBJECTIVE

To examine the contributions of neuroscience, clinical treatment and health-care policy to the building of a national programme for preventive approaches to dementia.

METHOD

Critical review of the literature, making use of international databases (Medline, Embase, Psychlit) and British official publications.

RESULTS

Recent developments in a number of research fields afford prospects for advances in primary and secondary prevention. These include findings from case-control and cohort studies of associations with earlier head injury and vascular disease, possibilities of pharmacological protection for persons at high risk for Alzheimer's disease, and the use of more effective anti-dementia drugs in the mild to moderate stages of severity. Research aimed at tertiary prevention is lagging behind, but there are some indications that the worst features of late-stage decline could already be mitigated by improvements in community support services and nursing-home care.

CONCLUSIONS

Containment of the growing social and economic burdens of dementia calls for a national policy to ensure that new research findings can be translated into practice and applied to the benefit of all old people who stand in need. For this purpose the most appropriate conceptual framework is supplied by a preventive model, broadly similar to those already developed for some other forms of chronic degenerative disease.

Microglial activation-mediated delayed and progressive degeneration of rat nigral dopaminergic neurons: relevance to Parkinson's disease

The etiology of sporadic Parkinson's disease (PD) remains unknown. Increasing evidence has suggested a role for inflammation in the brain in the pathogenesis of PD. However, it has not been clearly demonstrated whether microglial activation, the most integral part of the brain inflammatory process, will result in a delayed and progressive degeneration of dopaminergic neurons in substantia nigra, a hallmark of PD. We report here that chronic infusion of an inflammagen lipopolysaccharide at 5 ng/h for 2 weeks into rat brain triggered a rapid activation of microglia that reached a plateau in 2 weeks, followed by a delayed and gradual loss of nigral dopaminergic neurons that began at between 4 and 6 weeks and reached 70% by 10 weeks. Further investigation of the underlying mechanism of action of microglia-mediated neurotoxicity using rat mesencephalic neuron-glia cultures demonstrated that low concentrations of lipopolysaccharide (0.1-10 ng/mL)-induced microglial activation and production of neurotoxic factors preceded the progressive and selective degeneration of dopaminergic neurons. Among the factors produced by activated microglia, the NADPH oxidase-mediated release of superoxide appeared to be a predominant effector of neurodegeneration, consistent with the notion that dopaminergic neurons are particularly vulnerable to oxidative insults. This is the first report that microglial activation induced by chronic exposure to inflammagen was capable of inducing a delayed and selective degeneration of nigral dopaminergic neurons and that microglia-originated free radicals play a pivotal role in dopaminergic neurotoxicity in this inflammation-mediated model of PD.

Deciphering the 4 D's: cognitive decline, delirium, depression and dementia--a review

PURPOSE

The purpose of this paper is to assist advanced practice nurses to recognize, identify, and diagnose cognitive change in older adults.

BACKGROUND/RATIONALE

Optimal cognitive function is important for continued independence, and yet changes in cognition are frequently unrecognized among older adults. Cognitive change in older adults can be observed due to age-related cognitive decline, the development of acute confusion (delirium), depression, dementia and/or a combination of these. When the aetiological source for alterations in cognitive function is delirium or depression, the potential for reversibility mandates that the reason for the cognitive change be identified with steps taken to remedy the situation. Also, early recognition of dementia is an important factor in obtaining timely and appropriate care. These conditions can exist concurrently and may fluctuate making deciphering the reason for the cognitive change problematic.

CONCLUSIONS

It is essential to understand how the 4 'D's' are expressed and to recognize the potential contributing factors to an observable change in cognitive function for diagnosis and treatment. Recommendations for obtaining a person's history are included.

Persistent accumulation of cyclooxygenase-1-expressing microglial cells and macrophages and transient upregulation by endothelium in human brain injury

OBJECT

Secondary damage after central nervous system (CNS) injury is driven in part by oxidative stress and CNS inflammation and is substantially mediated by cyclooxygenases (COXs). To date, the rapidly inducible COX-2 isoform has been primarily linked to inflammatory processes, whereas expression of COX-1 is confined to physiological functions. The authors report the differential localization of COX-1 in human traumatic brain injury (TBI).

METHODS

Differential cellular COX-1 protein expression profiles were analyzed following TBI in 31 patients and compared with neuropathologically unaltered control brains by using immunohistochemistry. In these patients with TBI, a significant increase of COX-1 protein expression by vessel endothelial and smooth-muscle cells and CD68+ microglia/macrophages was observed to be strictly confined to the lesion. Accumulation of COX-1+ microglia/macrophages in the lesion was already evident 6 hours postinjury, reaching maximal levels after several weeks and remaining elevated at submaximal levels for several months after injury. Furthermore, COX-1+ cell clusters were located in the Virchow-Robin space during the leukocyte infiltration period from Days 4 to 8 after TBI. Double-labeling experiments confirmed coexpression of COX-1 by CD68+ microglia/macrophages. The numbers of COX-1+ vessel endothelial and smooth-muscle cells increased from Day 1, remaining at submaximal levels for months after injury.

CONCLUSIONS

The prolonged accumulation of COX- 1+ microglia/macrophages that were restricted to perilesional areas affected by the acute inflammatory response points to a role of COX-1 in secondary injury. The authors have identified localized, accumulated COX- I expression as a potential pharmacological target following TBI. Their results challenge the current paradigms of a selective COX-2 role in the postinjury inflammatory response.

Caspase-3-mediated cleavage of amyloid precursor protein and formation of amyloid Beta peptide in traumatic axonal injury

Immunohistochemical studies demonstrate accumulation of the beta-amyloid precursor protein (APP) within injured axons following traumatic brain injury (TBI). Despite such descriptions, little is known about the ultimate fate of accumulating APP at sites of traumatic axonal injury (TAI). Recently, caspase-3-mediated cleavage of APP and subsequent Abeta deposition was linked to apoptotic neuronal death pathways in hippocampal neurons following ischemic and excitotoxic brain injury. Given that (1) APP is known to accumulate within traumatically injured axons, (2) caspase-3 activation has been demonstrated in traumatic axonal injury (TAI), and (3) recent studies have identified a caspase-3 cleavage site within APP, we initiated the current investigation to determine whether caspase-3-mediated cleavage of APP occurs in TAI. We further assessed whether these events were found in relation to Abeta peptide formation. To this end, we employed antibodies targeting APP, the caspase-3-mediated breakdown product of APP proteolysis, and the Abeta peptide. Rats were subjected to impact acceleration TBI (6 h to 10 days survival), and their brains were processed for single-label bright field and multiple double-label immunofluorescent paradigms using the above antibodies. By 12 h postinjury, caspase-3-mediated APP proteolysis (CMAP) was demonstrated within the medial lemniscus (ML) and medial longitudinal fasciculus (MLF) in axons undergoing TAI, identified by their concomitant APP accumulation. Immunoreactivity for CMAP persisted up to 48 h postinjury in the ML and MLF, but was notably reduced by 10 days following injury. Further, CMAP was colocalized with Abeta formation in foci of TAI. The current study demonstrates that caspase-3 cleavage of APP occurs in TAI and is associated with formation of Abeta peptide. These findings are of interest given recent epidemiological studies supporting an association between TBI and later risk for AD development.

Physical disorders and causes of death in relatives of Alzheimer's disease patients

BACKGROUND

Genetic risk factors are important in Alzheimer's disease (AD). These risk factors might also predispose for other disorders. This might lead to a familial coaggregation of AD and other disorders, e.g. Down's syndrome or Parkinson's disease. In the present study the risk of physical disorders in relatives of AD patients, of depressed patients and of control subjects were compared.

METHODS

Family history and, if possible, interview information on physical disorders and causes of death in relatives of 146 patients with AD, 168 patients with major depression (MD) and 136 controls was collected. Statistical comparisons were performed using chi-square tests and, if necessary, logistic regression analysis accounting for age, gender and interview status.

RESULTS

In contrast to our hypotheses, there was no increased risk of cerebrovascular disease, Down's syndrome, haematological malignancies or Parkinson's disease in relatives of AD patients compared with relatives of patients with MD and of controls. The explorative analysis revealed that congenital malformations, i.e. malformations of the heart or of the extremities, were slightly increased in relatives of AD patients. Relatives of patients with AD or MD were at increased risk of dying as a result of accidents, in most cases falls in advanced age, and relatives of patients with MD were at slightly increased risk of dying from gastroenterologic diseases, in most cases complications of peptic ulcers.

CONCLUSION

The results do not support a major overlap between the genetic risk of AD and the genetic risk of cerebrovascular disease, Down's syndrome, haematological malignancies or Parkinson's disease. The finding of an increased risk of congenital malformations in relatives of AD patients needs further replication before it can be stated. The increased risk of dementia or depression with cognitive impairment in elderly relatives of patients with AD or MD increases the risk of accidents like falls. The genetic risk of depression in relatives of patients with MD could have a negative influence on the prognosis of peptic ulcera.

Ageing of the brain

The brains of individuals who are cognitively normal show age-related changes that include an overall reduction in the brain volume and weight and enlargement of the brain ventricles. These changes are partly the result of nerve cell loss but accurate estimates of neuronal loss are notoriously difficult to make. There is loss of synapses and dendritic pruning in the aged brain but in selected areas rather than globally. Neurofibrillary tangles and senile plaques are the neuropathological hallmark of Alzheimer's disease in which they are more abundant and widespread than in the brains of intellectually intact elderly people. Alzheimer's disease has, therefore, been regarded as accelerated brain ageing, however, since there is a strong genetic contribution to developing the disease it implies that it may not be the inevitable, even if frequent, consequence of old age. The interplay between genetic and environmental factors probably determines the degree of pathological brain ageing and whether or not individuals develop dementia.

Alzheimer disease as a vascular disorder: nosological evidence

BACKGROUND

The main stumbling block in the clinical management and in the search for a cure of Alzheimer disease (AD) is that the cause of this disorder has remained uncertain until now.

SUMMARY OF REVIEW

Evidence that sporadic (nongenetic) AD is primarily a vascular rather than a neurodegenerative disorder is reviewed. This conclusion is based on the following evidence: (1) epidemiological studies showing that practically all risk factors for AD reported thus far have a vascular component that reduces cerebral perfusion; (2) risk factor association between AD and vascular dementia (VaD); (3) improvement of cerebral perfusion obtained from most pharmacotherapy used to reduce the symptoms or progression of AD; (4) detection of regional cerebral hypoperfusion with the use of neuroimaging techniques to preclinically identify AD candidates; (5) presence of regional brain microvascular abnormalities before cognitive and neurodegenerative changes; (6) common overlap of clinical AD and VaD cognitive symptoms; (7) similarity of cerebrovascular lesions present in most AD and VaD patients; (8) presence of cerebral hypoperfusion preceding hypometabolism, cognitive decline, and neurodegeneration in AD; and (9) confirmation of the heterogeneous and multifactorial nature of AD, likely resulting from the diverse presence of vascular risk factors or indicators of vascular disease.

CONCLUSIONS

Since the value of scientific evidence generally revolves around probability and chance, it is concluded that the data presented here pose a powerful argument in support of the proposal that AD should be classified as a vascular disorder. According to elementary statistics, the probability or chance that all these findings are due to an indirect pathological effect or to coincidental circumstances related to the disease process of AD seems highly unlikely. The collective data presented in this review strongly support the concept that sporadic AD is a vascular disorder. It is recommended that current clinical management of patients, treatment targets, research designs, and disease prevention efforts need to be critically reassessed and placed in perspective in light of these important findings.

Repetitive mild brain trauma accelerates Abeta deposition, lipid peroxidation, and cognitive impairment in a transgenic mouse model of Alzheimer amyloidosis

Traumatic brain injury (TBI) increases susceptibility to Alzheimer's disease (AD), but it is not known how TBI contributes to the onset or progression of this common late life dementia. To address this question, we studied neuropathological and behavioral consequences of single versus repetitive mild TBI (mTBI) in transgenic (Tg) mice (Tg2576) that express mutant human Abeta precursor protein, and we demonstrate elevated brain Abeta levels and increased Abeta deposition. Nine-month-old Tg2576 and wild-type mice were subjected to single (n = 15) or repetitive (n = 39) mTBI or sham treatment (n = 37). At 2 d and 9 and 16 weeks after treatment, we assessed brain Abeta deposits and levels in addition to brain and urine isoprostanes generated by lipid peroxidation in these mice. A subset of mice also was studied behaviorally at 16 weeks after injury. Repetitive but not single mTBI increased Abeta deposition as well as levels of Abeta and isoprostanes only in Tg mice, and repetitive mTBI alone induced cognitive impairments but no motor deficits in these mice. This is the first experimental evidence linking TBI to mechanisms of AD by showing that repetitive TBI accelerates brain Abeta accumulation and oxidative stress, which we suggest could work synergistically to promote the onset or drive the progression of AD. Additional insights into the role of TBI in mechanisms of AD pathobiology could lead to strategies for reducing the risk of AD associated with previous episodes of brain trauma and for preventing progressive brain amyloidosis in AD patients.

Traumatic brain injury as a risk factor for Alzheimer disease. Comparison of two retrospective autopsy cohorts with evaluation of ApoE genotype

BACKGROUND AND PURPOSE

The impact of traumatic brain injury (TBI) on the pathogenesis of Alzheimer disease (AD) is still controversial. The aim of our retrospective autopsy study was to assess the impact of TBE and ApoE allele frequency on the development of AD.

MATERIAL AND METHODS

We examined 1. the incidence of AD pathology (Braak stageing, CERAD, NIA-Reagan Institute criteria) in 58 consecutive patients (mean age +/- SD 77.0 +/- 6.8 years) with residual closed TBI lesions, and 2. the frequency of TBI residuals in 57 age-matched autopsy proven AD cases. In both series, ApoE was evaluated from archival paraffin-embedded brain material.

RESULTS

1. TBE series: 12.1 % showed definite and 10.3% probable AD (mean age 77.6 and 75.2 years), only 2/13 with ApoEepsilon3/4. From 45 (77.6%) non-AD cases (mean age 78.2 years), 3 had ApoEepsilon3/4. The prevalence of 22.4% AD in this small autopsy cohort was significantly higher than 3.3% in a recent large clinical series and 14% in the general population over age 70. 2. In the AD cohort with ApoEepsilon4 allele frequency of 30% similar to other AD series, residuals of closed TBI were seen in 4 brains (7%) (mean age +/- SD 78.2 +/- 6.4), all lacking the ApoEepsilon4 allele. TBI incidence was slightly lower than 8.5% in the clinical MIRAGE study.

CONCLUSIONS

The results of this first retrospective autopsy study of TBI, ApoEepsilon allele frequency, and AD confirm clinical studies suggesting severe TBI to be a risk factor for the development AD higher in subjects lacking ApoEepsilon4 alleles. Further studies in larger autopsy series are needed to elucidate the relationship between TBI, genetic predisposition, and AD.

A review and rationale for the use of genetically engineered animals in the study of traumatic brain injury

The mechanisms underlying secondary cell death after traumatic brain injury (TBI) are poorly understood. Animal models of TBI recapitulate many clinical and pathologic aspects of human head injury, and the development of genetically engineered animals has offered the opportunity to investigate the specific molecular and cellular mechanisms associated with cell dysfunction and death after TBI, allowing for the evaluation of specific cause-effect relations and mechanistic hypotheses. This article represents a compendium of the current literature using genetically engineered mice in studies designed to better understand the posttraumatic inflammatory response, the mechanisms underlying DNA damage, repair, and cell death, and the link between TBI and neurodegenerative diseases.

Effects of closed traumatic brain injury and genetic factors on the development of Alzheimer's disease

In order to assess the impact of traumatic brain injury (TBI) and Apolipoprotein E (ApoE) allele frequency on the development of Alzheimer's disease (AD), we examined: (i) the incidence of AD pathology in 55 consecutive autopsy cases (mean age +/- SD 77.6 +/- 7.3 years) with residual closed TBI lesions and (ii) the frequency of TBI residuals in 53 age-matched autopsy proven AD cases. In both series, ApoE was evaluated from archival paraffin-embedded brain material. The results were as follows: (i) In the TBI series, 12.7% showed Consortium to Establish a Registry for Alzheimer's disease (CERAD) definite and 9.1% probable AD, only one with ApoEepsilon4. From the remaining 43 non-AD cases, three had ApoEepsilon4. The prevalence of 21.8% AD in this small autopsy cohort was significantly higher than 3.3% in a recent large clinical series and 14% in the general population over the age of 70. (ii) In the AD cohort with ApoEepsilon4 allele frequency of 30% similar to other AD series, residuals of TBI were seen in 4 brains (7.5%), all lacking the ApoEepsilon4 allele. TBI incidence was slightly higher than 8.5% in the clinical MIRAGE study. The results of this first retrospective autopsy study of TBI, ApoE allele frequency, and AD confirms clinical studies suggesting severe TBI to be a risk factor for the development of AD particularly in subjects lacking ApoEepsilon4.

Preventing dementia

Primary prevention will become increasingly important as dementia prevalence increases and effective retardive therapies are developed. To date, only one randomized controlled trial (involving treatment of systolic hypertension) has demonstrated that the incidence of dementia can be reduced. Physicians should remain alert to possible secondary causes of dementia and correct these whenever possible. Primary and secondary prevention of stroke should reduce dementia related to cerebrovascular disease either directly or as a comorbid factor in Alzheimer's disease (AD). Epidemiological studies have revealed a number of risk factors for AD including genetic mutation, susceptibility genes, positive family history, Down's syndrome, age, sex, years of education, head trauma and neurotoxins. In case-control studies non-steroidal anti-inflammatory medication and estrogen replacement therapy appear to decrease the relative risk of developing AD. Further research to develop and test preventative therapies in AD and other dementias should be strongly encouraged.