Early detection of Alzheimer's disease by combining apolipoprotein E and neuroimaging

Mitochondria as a target for neuroprotection: implications for Alzheimer´s disease

INTRODUCTION

Alzheimer's disease (AD), the most common form of dementia, is marked by progressive loss of memory and impairment of cognitive ability. Despite decades of intensive research and scientific advances, the intricate pathogenic mechanisms of AD are still not fully understood and, consequently, an effective treatment is yet to be developed. As widely accepted, the alterations of mitochondrial function are actively engaged in a plethora of neurodegenerative diseases, including AD. With growing interest in the mitochondria as a potential target for understanding AD, it has even been hypothesized that deficits in these organelles may be at the heart of the progression of AD itself. Areas covered: The purpose of this review is to summarize relevant studies that suggest a role for mitochondrial (dys)function in AD and to provide a survey on latest developments regarding AD-related mitochondrial therapeutics. Expert commentary: As outlined in a plethora of studies, there is no doubt that mitochondria play a major role in several stages of AD progression. Even though more in-depth studies are needed before pharmaceutical industry can apply such knowledge to human medicine, the continuous advances in AD research field will certainly facilitate and accelerate the development of more effective preventive or therapeutic strategies to fight this devastating disease.

Exercise, but not antioxidants, reversed ApoE4-associated motor impairments in adult GFAP-ApoE mice

Motor dysfunction has been found to be predictive of cognitive dysfunction in Alzheimer's disease and to occur earlier than cognitive impairments. While apolipoprotein (Apo) E4 has been associated with cognitive impairments, it remains unclear whether it also increases risk for motor dysfunction. Exercise and antioxidants are often recommended to reduce cognitive declines, however it is unclear whether they can successfully improve motor impairments. This study was designed to determine the extent of the impact of apolipoprotein genotype on motor function, and whether interventions such as exercise and antioxidant intake can improve motor function. This study is the first to identify the nature of the interaction between antioxidant intake and exercise using a mouse model expressing either the human ApoE3 or ApoE4 isoforms under glial fibrillary acid protein promoter (GFAP-ApoE3 and GFAP-ApoE4 mice). The mice were fed either a control diet or the control diet supplemented with vitamins E and C (1.12 IU/g diet α-tocopheryl acetate and 1.65mg/g ascorbic acid). Each genotype/diet group was further divided into a sedentary group or a group that followed a 6 days a week exercise regimen. After 8 weeks on their respective treatment, the mice were administered a battery of motor tests to measure reflexes, strength, coordination and balance. GFAP-ApoE4 mice exhibited impaired motor learning and diminished strength compared to the GFAP-ApoE3 mice. Exercise alone was more efficient at improving motor function and reversing ApoE4-associated impairments than antioxidants alone, even though improvements were rather subtle. Contrarily to expected outcomes, combination of antioxidants and exercise did not yield further improvements of motor function. Interestingly, antioxidants antagonized the beneficial effects of exercise on strength. These data suggest that environmental and genetic factors influence the outcome of interventions on motor function and should be investigated more thoroughly and taken into consideration when implementing changes in lifestyles.

Emerging concepts in Alzheimer's disease

Alzheimer's disease/senile dementia of the Alzheimer type (AD/SDAT) is the most common neuropathologic substrate of dementia. It is characterized by synapse loss (predominantly within neocortex) as well as deposition of certain distinctive lesions (the result of protein misfolding) throughout the brain. The latter include senile plaques, composed mainly of an amyloid (Aβ) core and a neuritic component; neurofibrillary tangles, composed predominantly of hyperphosphorylated tau; and cerebral amyloid angiopathy, a microangiopathy affecting both cerebral cortical capillaries and arterioles and resulting from Aβ deposition within their walls or (in the case of capillaries) immediately adjacent brain parenchyma. In this article, I discuss the hypothesized role these lesions play in causing cerebral dysfunction, as well as CSF and neuroimaging biomarkers (for dementia) that are especially relevant as immunotherapeutic approaches are being developed to remove Aβ from the brain parenchyma. In addition, I address the role of neuropathology in characterizing the sequelae of new AD/SDAT therapies and helping to validate CSF and neuroimaging biomarkers of disease. Comorbidity of AD/SDAT and various types of cerebrovascular disease is a major theme in dementia research, especially as cognitive impairment develops in the oldest old, who are especially vulnerable to ischemic and hemorrhagic brain lesions.

New applications of disease genetics and pharmacogenetics to drug development

TOMMORROW is a Phase III delay of onset clinical trial to determine whether low doses of pioglitazone, a molecule that induces mitochondrial doubling, delays the onset of MCI-AD in normal subjects treated with low dose compared to placebo. BOLD imaging studies in rodents and man were used to find the dose that increases oxygen consumption at central regions of the brain in higher proportion than activation of large corticol regions. The trial is made practical by the use of a pharmacogenetic algorithm based on TOMM40 and APOE genotypes and age to identify normal subjects at high risk of MCI-AD between the ages of 65-83 years within a five year follow-up period.

Ushering in the study and treatment of preclinical Alzheimer disease

Researchers have begun to characterize the subtle biological and cognitive processes that precede the clinical onset of Alzheimer disease (AD), and to set the stage for accelerated evaluation of experimental treatments to delay the onset, reduce the risk of, or completely prevent clinical decline. In this Review, we provide an overview of the experimental strategies, and brain imaging and cerebrospinal fluid biomarker measures that are used in early detection and tracking of AD, highlighting at-risk individuals who could be suitable for preclinical monitoring. We discuss how advances in the field have contributed to reconceptualization of AD as a sequence of biological changes that occur during progression from preclinical AD, to mild cognitive impairment and finally dementia, and we review recently proposed research criteria for preclinical AD. Advances in the study of preclinical AD have driven the recognition that efficacy of at least some AD therapies may depend on initiation of treatment before clinical manifestation of disease, leading to a new era of AD prevention research.

Insulin in central nervous system: more than just a peripheral hormone

Insulin signaling in central nervous system (CNS) has emerged as a novel field of research since decreased brain insulin levels and/or signaling were associated to impaired learning, memory, and age-related neurodegenerative diseases. Thus, besides its well-known role in longevity, insulin may constitute a promising therapy against diabetes- and age-related neurodegenerative disorders. More interestingly, insulin has been also faced as the potential missing link between diabetes and aging in CNS, with Alzheimer's disease (AD) considered as the "brain-type diabetes." In fact, brain insulin has been shown to regulate both peripheral and central glucose metabolism, neurotransmission, learning, and memory and to be neuroprotective. And a future challenge will be to unravel the complex interactions between aging and diabetes, which, we believe, will allow the development of efficient preventive and therapeutic strategies to overcome age-related diseases and to prolong human "healthy" longevity. Herewith, we aim to integrate the metabolic, neuromodulatory, and neuroprotective roles of insulin in two age-related pathologies: diabetes and AD, both in terms of intracellular signaling and potential therapeutic approach.

Alzheimer's Prevention Initiative: a plan to accelerate the evaluation of presymptomatic treatments

There is an urgent need to find effective presymptomatic Alzheimer's disease (AD) treatments that reduce the risk of AD symptoms or prevent them completely. It currently takes too many healthy people, too much money and too many years to evaluate the range of promising presymptomatic treatments using clinical endpoints. We have used brain imaging and other measurements to track some of the earliest changes associated with the predisposition to AD. We have proposed the Alzheimer's Prevention Initiative (API) to evaluate investigational amyloid-modifying treatments in healthy people who, based on their age and genetic background, are at the highest imminent risk of developing symptomatic AD using brain imaging, cerebrospinal fluid (CSF), and cognitive endpoints. In one trial, we propose to study AD-causing presenilin 1 [PS1] mutation carriers from the world's largest early-onset AD kindred in Antioquia, Colombia, close to their estimated average age at clinical onset. In another trial, we propose to study apolipoprotein E (APOE) ε4 homozygotes (and possibly heterozygotes) close to their estimated average age at clinical onset. The API has several goals: 1) to evaluate investigational AD-modifying treatments sooner than otherwise possible; 2) to determine the extent to which the treatment's brain imaging and other biomarker effects predict a clinical benefit-information needed to help qualify biomarker endpoints for use in pivotal prevention trials; 3) to provide a better test of the amyloid hypothesis than clinical trials in symptomatic patients, when these treatments may be too little too late to exert their most profound effect; 4) to establish AD prevention registries needed to support these and other presymptomatic AD trials; and 5) to give those individuals at highest imminent risk of AD symptoms access to the most promising investigational treatments in clinical trials.

Pathologic lesions in neurodegenerative diseases

This chapter will discuss two of the most widely used approaches to assessing brain structure: neuroimaging and neuropathology. Whereas neuropathologic approaches to studying the central nervous system have been utilized for many decades and have provided insights into morphologic correlates of dementia for over 100 years, accurate structural imaging techniques "blossomed" with the development and refinement of computerized tomographic scanning and magnetic resonance imaging (MRI), beginning in the late 1970s. As Alzheimer disease progresses over time, there is progressive atrophy of the hippocampus and neocortex--this can be quantified and regional accentuation of the atrophy can be evaluated using quantitative MRI scanning. Furthermore, ligands for amyloid proteins have recently been developed--these can be used in positron emission tomography studies to localize amyloid proteins, and (in theory) study the dynamics of their deposition (and clearance) within the brain over time. Neuropathologic studies of the brain, using highly specific antibodies, can demonstrate synapse loss and the deposition of proteins important in AD progression--specifically ABeta and phosphor-tau. Finally, neuropathologic assessment of (autopsy) brain specimens can provide important correlation with sophisticated neuroimaging techniques.

Insulin-resistant brain state: the culprit in sporadic Alzheimer's disease?

Severe abnormalities in brain glucose/energy metabolism and insulin signaling have been documented to take a pivotal role in early sporadic Alzheimer's disease (sAD) pathology. Indeed, the "insulin-resistant brain state" has been hypothesized to form the core of the neurodegenerative events that occur in sAD. In this vein, intracerebroventricular administration of subdiabetogenic doses of streptozotocin (STZ) in rats can induce an insulin-resistant brain state, which is proposed as a suitable experimental model of sAD. This review highlights the involvement of disturbed brain insulin metabolism in sAD etiopathogenesis. Furthermore, current knowledge demonstrates that central STZ administration produces brain pathology and behavioral changes that resemble changes found in sAD patients. The STZ-intracerebroventricularly treated rat represents a promising experimental tool in this field by providing new insights concerning early brain alterations in sAD, which can be translated in novel etiopathogenic and therapeutic approaches in this disease.

Oxidative stress and transcriptional regulation in Alzheimer disease

Alzheimer disease (AD) is defined by progressive impairments in memory and cognition and by the presence of extracellular neuritic plaques and intracellular neurofibrillary tangles. However, oxidative stress and impaired mitochondrial function always accompany AD. Mitochondria are a major site of production of free radicals [ie, reactive oxygen species (ROS)] and primary targets of ROS. ROS are cytotoxic, and evidence of ROS-induced damage to cell membranes, proteins, and DNA in AD is overwhelming. Nevertheless, therapies based on antioxidants have been disappointing. Thus, alternative strategies are necessary. ROS also act as signaling molecules including for transcription. Thus, chronic exposure to ROS in AD could activate cascades of genes. Although initially protective, prolonged activation may be damaging. Thus, therapeutic approaches based on modulation of these gene cascades may lead to effective therapies. Genes involved in several pathways including antioxidant defense, detoxification, inflammation, etc, are induced in response to oxidative stress and in AD. However, genes that are associated with energy metabolism, which is necessary for normal brain function, are mostly down-regulated. Redox-sensitive transcription factors such as activator protein-1, nuclear factor-kappaB, specificity protein-1, and hypoxia-inducible factor are important in redox-dependent gene regulation. Peroxisome proliferators-activated receptor-gamma coactivator (PGC-1alpha) is a coactivator of several transcription factors and is a potent stimulator of mitochondrial biogenesis and respiration. Down-regulated expression of PGC-1alpha has been implicated in Huntington disease and in several Huntington disease animal models. PGC-1alpha role in regulation of ROS metabolism makes it a potential candidate player between ROS, mitochondria, and neurodegenerative diseases. This review summarizes the current progress on how oxidative stress regulates the expression of genes that might contribute to AD pathophysiology and the implications of the transcriptional modifications for AD. Finally, potential therapeutic strategies based on the updated understandings of redox state-dependent gene regulation in AD are proposed to overcome the lack of efficacy of antioxidant therapies.

Autophagocytosis of Mitochondria Is Prominent in Alzheimer Disease

Mitochondrial abnormalities are prominent in Alzheimer disease. In this study, 2 mitochondrial markers, cytochrome oxidase-1 and lipoic acid, a sulfur-containing cofactor required for the activity of several mitochondrial enzyme complexes, were compared using light and electron microscopic analyses and immunoblot assays. Both lipoic acid and cytochrome oxidase-1 immunoreactivity are increased in the cytoplasm of pyramidal neurons in Alzheimer disease compared with control cases. Of significance, lipoic acid was found to be strongly associated with granular structures, and ultrastructure analysis showed localization to mitochondria, cytosol, and, importantly, in organelles identified as autophagic vacuoles and lipofuscin in Alzheimer disease but not control cases. Cytochrome oxidase-1 immunoreactivity was limited to mitochondria and cytosol in both Alzheimer and control cases. These data suggest that mitochondria are key targets of increased autophagic degradation in Alzheimer disease. Whether increased autophagocytosis is a consequence of an increased turnover of mitochondria or whether the mitochondria in Alzheimer disease are more susceptible to autophagy remains to be resolved.

Biomarkers in the diagnosis of Alzheimer's disease: are we ready?

Although clinical manifestations of cognitive dysfunction and impairments of activities of daily living are the current standard measures for the diagnosis of Alzheimer's disease, biomarkers are receiving increasing attention in research centers as possible early diagnostic measures or as surrogate measures of the ongoing pathology. In preparation for the upcoming development of the Diagnostic and Statistical Manual of Mental Disorders (5th ed; DSM-V) nosology, the American Psychiatric Association has sponsored an effort to reassess the current approaches to diagnosis in dementia in general and Alzheimer's disease in particular. This article focuses on the potential use of biomarkers in the diagnosis of Alzheimer's disease, in the monitoring of mild cognitive impairment, and as possible prognostic markers in normal controls at risk for dementia. Most advanced information is available with the biomarkers found in the cerebrospinal fluid, but there are many other potential biomarkers using blood, brain imaging, or a combination. The current biomarker approaches to diagnosis are reviewed along with a special emphasis on near-term recommendations and further research directions.

Neuropsychological and neuroimaging changes in preclinical Alzheimer's disease

Alzheimer's disease (AD) is a common, devastating form of dementia. With the advent of promising symptomatic treatment, the importance of recognizing AD at its very earliest stages has increased. We review the extant neuropsychological and neuroimaging literature on preclinical AD, focusing on longitudinal studies of initially nondemented individuals and cross-sectional investigations comparing at-risk with normal individuals. We systematically reviewed 91 studies of neuropsychological functioning, structural neuroimaging, or functional neuroimaging in preclinical AD. The neuropsychological studies indicated that preclinical AD might be characterized by subtle deficits in a broad range of neuropsychological domains, particularly in attention, learning and memory, executive functioning, processing speed, and language. Recent findings from neuroimaging research suggest that volume loss and cerebral blood flow or metabolic changes, particularly in the temporal lobe, may be detected before the onset of dementia. There exist several markers of a preclinical period of AD, in which specific cognitive and biochemical changes precede the clinical manifestations. The preclinical indicators of AD reflect early compromise of generalized brain integrity and temporal lobe functioning in particular.

The (un)balance between metabolic and oxidative abnormalities and cellular compensatory responses in Alzheimer disease

Compelling evidence supports the importance of metabolic abnormalities in Alzheimer disease pathogenesis. Indeed, that oxidative mechanisms are involved in the neuropathology associated with Alzheimer disease is evidenced by the large number of metabolic signs of oxidative stress as well as by specific markers of oxidative damage. However, in the initial stages of disease development, neurons adapt to the oxidative environment through the development of compensatory responses resulting in a shift of neuronal priority from normal function to basic survival.

Apolipoprotein E and alpha brain rhythms in mild cognitive impairment: A multicentric Electroencephalogram study

OBJECTIVE

Relationships between the apolipoprotein E epsilon4 allele and electroencephalographic (EEG) rhythmicity have been demonstrated in Alzheimer's disease (AD) patients but not in the preclinical stage prodromic to it, namely, mild cognitive impairment (MCI). The present multicentric EEG study tested the hypothesis that presence of epsilon4 affects sources of resting EEG rhythms in both MCI and AD subjects.

METHODS

We enrolled 89 MCI subjects (34.8% with epsilon4) and 103 AD patients (50.4% with epsilon4). Resting eyes-closed EEG data were recorded for all subjects. EEG rhythms of interest were delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13Hz), beta 1 (13-20 Hz), and beta 2 (20-30 Hz). EEG cortical sources were estimated by low-resolution brain electromagnetic tomography.

RESULTS

Results showed that amplitude of alpha 1 and 2 sources in occipital, temporal, and limbic areas was lower in subjects carrying the epsilon4 allele than in those not carrying the epsilon4 allele (p < 0.01). This was true for both MCI and AD. For the first time to our knowledge, a relationship was shown between ApoE genotype and global neurophysiological phenotype (ie, cortical alpha rhythmicity) in a preclinical AD condition, MCI, in addition to clinically manifest AD.

INTERPRETATION

Such a demonstration motivates future genotype-EEG phenotype studies for the early prediction of AD conversion in individual MCI subjects.

Neuropsychology in Alzheimer's disease and other dementia research

PURPOSE OF REVIEW

This review describes a variety of neuropsychological dementia studies published between January 2004 and June 2005. In selecting articles for description in the present paper, our goal was not a comprehensive review of what is an enormous and growing literature, but rather to select and describe individual interesting studies from a sufficient range of dementia-related topics to permit illustration of some of the important questions for which a neuropsychological perspective aids in the understanding of dementias.

RECENT FINDINGS

Findings in the studies reviewed include a variety of different topics. Some of the themes include the following: (a) Alzheimer's disease is the most common cause of dementia, but a large body of research documents that there are important cognitive differences among various types of dementia, (b) the emerging research is also important in demonstrating the need for more sensitive clinical screening measures, (c) cognitive data are strongly predictive of functional decline, and (d) subtle declines in verbal learning appear to precede clinical Alzheimer's disease.

SUMMARY

Neuropsychological data are key to progress in understanding and developing more effective treatments for Alzheimer's disease and other dementia. For instance, efforts to identify early markers of dementia will be a key component to development of early intervention strategies.

The use of biomarkers in the elderly: current and future challenges

Biomarkers are hypothesized but not frequently used in research with the elderly because of a general paucity of supportive scientific data. However, there is an obvious need for greater diagnostic specificity and sensitivity across many diagnoses in the elderly, as well as good targets for therapeutic trials. The authors reviewed the available information in this field as part of a general review of geriatric research for the . Potential biomarkers with pathophysiologic significance have been studied in the field of Alzheimer disease research with some success, especially in the area of genetic markers (apolipoprotein E [APOE] epsilon4 allele), neuroimaging, and cerebrospinal fluid markers (beta-amyloid and tau). While some progress has been made in the search for adequate biomarkers in the elderly, in particular with Alzheimer disease, much more work is needed before these potential biomarkers can be reliably used in clinical practice.

Eyeblink Classical Conditioning to Auditory and Olfactory Stimuli: Performance Among Older Adults With and Without the Apolipoprotein E ε4 Allele

Patients with Alzheimer's disease (AD) demonstrate slowed acquisition of the conditioned response (CR) in eyeblink classical conditioning paradigms (EBCC), although it is unknown how early in the course of the disease CR acquisition is affected. This study investigated whether changes in the rate of CR acquisition were apparent in nondemented older adults at greater genetic risk for developing AD (i.e., carriers of the apolipoprotein E [APOE] epsilon 4 allele). Both epsilon 4+ and epsilon 4- participants demonstrated CR acquisition to auditory and olfactory CSs; however, rate of acquisition to the olfactory CS was significantly slower in epsilon 4+ persons. Both groups acquired the CR to an auditory CS at the same rate. Results support olfactory compromise in the earliest stages of the AD disease process. ((c) 2005 APA, all rights reserved).

Diagnosis of suspected Alzheimer's disease is improved by automated analysis of regional cerebral blood flow

PURPOSE

Accurate diagnosis of Alzheimer's disease (AD), the most common form of dementia, remains difficult. In order to assess whether fully automated stereotactic surface projection (3D-SSP) presentation contributes to the diagnosis of AD by single-photon emission computed tomography (SPECT), we investigated the diagnostic accuracy of transaxial display with and without 3D-SSP analysis as well as the correlation between cerebral perfusion in different cortical areas and the mini mental score (MMS).

METHODS

Seventy-two patients referred because of cognitive impairment were included in the study. According to the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) and the Alzheimer's disease and Related Disorders Association (ADRDA) criteria, 27 patients were diagnosed as having probable AD while 45 were classified as non-AD patients. 3D-SSP was used to quantify the regional cerebral blood flow (rCBF) acquired from SPECT imaging.

RESULTS

Compared with the transaxial section presentation alone, 3D-SSP presentation improved the area under the receiver operating curve (p<0.05) as well as intra-observer (k=0.73 vs 0.88) and inter-observer (k=0.50 vs 0.84) reproducibility. Upon normalisation of regional to thalamic activity, multiple regression analysis revealed a strong correlation between the MMS and rCBF in the right parietal cortex (p=0.002).

CONCLUSION

Addition of 3D-SSP to the transaxial section display of ECD-SPECT studies improves the reproducibility and the diagnostic performance in respect of AD in patients with cognitive impairment and provides a valid tool for assessment of the severity of cortical perfusion abnormalities in such patients.

Imaging Alzheimer's disease: clinical applications

Extensive PET imaging research on AD has been conducted since PET scanners became available in the early 1980s. PET imaging using FDG, now commercially available, can detect early metabolic changes in AD and differential metabolic features of various dementing disorders. Image analysis techniques have also advanced in the field of functional brain imaging and permit accurate and consistent scan interpretation. PET studies that involve autopsy-confirmed cases suggest that the PET diagnosis of AD is no worse or may even be better than clinical diagnosis. Limited prospective studies demonstrated the effects of PET imaging in dementia management, which precludes the approval of FDG PET for more widespread, reimbursable use. Further evidence for the efficacy of PET imaging through well-organized clinical studies, as well as continuing efforts in technologic development and basic research to characterize functional alterations in dementing disorders in living patients, are equally important to achieve the goal of better dementia care.

Comparative biology and pathology of oxidative stress in Alzheimer and other neurodegenerative diseases: beyond damage and response

In this review, we consider comparative aspects of the biology and pathology of oxygen radicals in neurodegenerative disease and how these findings have influenced our concept of oxidative stress. The common definition of oxidative stress is a breach of antioxidant defenses by oxygen radicals leading to damage to critical molecules and disrupted physiology. Inherent in this definition is that oxidative stress is an unstable situation, for if there is net damage, viability of the system decreases with time, leading to disequilibria and death. While this circumstance defines acute conditions, such as stroke and head trauma which result in dysfunction and death, it does not fit physiological situations or chronic diseases closely aligned to normal physiology. Therefore, we propose that oxidative modifications in Alzheimer disease may actually serve as a homeostatic response to stress resulting in a shift of neuronal priority from normal function to basic survival. This phenomenon is comparable to normal physiological conditions of metabolic decrease, such as those seen in hibernation and estivation. Thus, Alzheimer disease could be seen as part of normal aging that includes additional pathology due to inadequate homeostatic response.

Functional neuroimaging in Alzheimer's type dementia

This article aims to review the role of the functional neuroimaging modality of positron emission tomography (PET) in the early diagnosis of Alzheimer's disease (AD). Clinical diagnosis in the early disease stages is difficult and treatments are emerging which rather than reversing structural damage are likely to slow or halt the disease process. While currently no routine diagnostic test confirms AD presence, imaging techniques are an important expanding field in biological neuropsychiatry. The challenge for neuroimaging methods is to achieve high specificity and sensitivity in early disease stages. Glucose metabolic PET imaging with fluorodeoxyglucose (FDG) has the potential to detect very early neocortical dysfunction before even abnormal neuropsychological testing is obtainable. The implications are for the identification of minimally symptomatic patients that could benefit most from treatment strategies, as well as the monitoring of treatment response and possible therapeutic deceleration of the disease. FDG PET correlates with AD neuropathology and is able to indicate disease progression or severity, meeting both functional neuroimaging prerequisites in diagnosing AD. A combination of functional neuroimaging with different techniques should be able to provide highest diagnostic specificity in diagnosing dementia. This may even lead to a new classification of dementias according to differences in the causative aetiology.

Natural history of Alzheimer's disease

Alzheimer's disease (AD) is the principal cause of dementia in the elderly, and affects about 15 million people worldwide. The earliest symptom is usually an insidious impairment of memory. As the disease progresses, there is increasing impairment of language and other cognitive functions. Problems occur with naming and word-finding, and later with verbal and written comprehension and expression. Visuospatial, analytic and abstract reasoning abilities, judgment, and insight become affected. Behavioral changes may include delusions, hallucinations, irritability, agitation, verbal or physical aggression, wandering, and disinhibition. Ultimately, there is loss of self-hygiene, eating, dressing, and ambulatory abilities, and incontinence and motor dysfunction. Before diagnosis of AD, individuals may have memory complaints, which represent a period of mild cognitive impairment (MCI). Before MCI, there is a prodromal, ill-defined presymptomatic period of disease ('pre-MCI"). In this review, we particularly focus on these earliest stages. We also discuss the more advanced stages of AD, and address factors that may influence disease course. Understanding the natural history of AD will allow better targeting of the disease-modifying treatments that are on the horizon.

Early diagnosis of Alzheimer disease with positron emission tomography

The emergence of drugs that may slow progression of Alzheimer disease, if administered early during its course, has necessitated early diagnosis of the disease itself. Among the functional imaging methods that could assist in early diagnosis, positron emission tomography has an important role in providing quantitative measures of various aspects of brain function affected by the disease. Positron emission tomography studies in patients with Alzheimer disease have revealed a typical pattern of metabolic deficits in the temporal and parietal lobes. Additionally, converging evidence from numerous studies indicates that a similar pattern of deficits can be observed in nondemented subjects who are at risk of developing the disease, such as those with recognized genetic traits such as familial Alzheimer disease with mutations in chromosomes 21 and 14, Down syndrome, subjects with the epsilon4 allele of the apolipoprotein E gene, and individuals with mild cognitive impairment. These findings might have implications for the selection of patients for clinical trials, defining the outcome measures and evaluation of treatment efficacy and responder characteristics, but should be confirmed by prospective studies comprising larger samples and include clinicopathologic correlations.

Oxidative stress and a key metabolic enzyme in Alzheimer brains, cultured cells, and an animal model of chronic oxidative deficits

Oxidative stress and diminished metabolism occur in several neurodegenerative disorders. Brains from Alzheimer's disease (AD) patients exhibit several indicators of oxidative stress and have reduced activities of the alpha-ketoglutarate dehydrogenase complex (KGDHC), a key mitochondrial enzyme. Whether these abnormalities are secondary to neurodegenerative processes or are inherent properties of the cells cannot be determined in autopsy brain. Studies in cultured fibroblasts suggest that AD-related differences in oxidative stress and KGDHC reflect inherent properties of AD cells. KGDHC is sensitive to oxidative stress whether the enzyme is studied in cells, in purified mitochondria, or as an isolated protein. Reductions of brain KGDHC in living rodents lead to oxidative stress and selective cell death. The results suggest that KGDHC participates in a deleterious cascade of events related to oxidative stress that are critical in selective neuronal loss in neurodegenerative diseases.

The prognosis of mild cognitive impairment in the elderly

PURPOSE

To determine whether or not subtypes of intellectual functioning are suitable to predict further cognitive decline in individuals with mild cognitive impairment.

DESIGN

Naturalistic longitudinal study (mean interval 2.7 years).

PATIENTS

41 subjects with mild cognitive impairment who attended a memory clinic.

METHODS

SIDAM, CT, SPECT, and ApoE genotype.

RESULTS

At follow-up, 8 out of 41 patients (19.5%) with MCI had progressed to dementia, 8 patients (19.5%) had improved to normal levels of cognitive functioning, 25 patients (61%) had remained stable within the MCI group. At baseline the two prognostic groups differed significantly with regard to age, memory functions, orientation, and the degree of atrophy of the left medial temporal lobe on CT scan.

CONCLUSION

The majority of MCI patients in this study remained cognitively stable within the observation period. Patients with older age, poorer test performance on memory tasks and orientation deficits are at higher risk of progressive decline to dementia. CT measures of medial temporal lobe atrophy may be a sensitive parameter of group discrimination.

Early diagnostic indices for the prevention of Alzheimer's disease

Recent progress in our understanding of the pathophysiology of Alzheimer's disease (AD) has made it clear that it is a heterogeneous disorder to which both genetic and environmental factors contribute. Therefore, it is unlikely that a single test for the diagnosis of this disease will be developed. Possible candidates for early diagnostic indices have been identified, in addition to biological markers, in the fields of neuropsychology, genetics and neuroimaging. Many studies have indicated that low scores in tests assessing delayed recall predict dementia already years before the actual criteria of dementia are fulfilled. Molecular genetic studies have confirmed that the epsilon4 allele of the apolipoprotein E (APOE) is also a definite risk factor for AD, and other susceptibility genes will probably be identified and confirmed in the near future. Evaluation of the hippocampal atrophy by magnetic resonance imaging (MRI) scans has been reported to be a sensitive and possible specific indicator of mild AD, while possibilities of using functional MRI are currently being explored. A combination of low scores in tests assessing delayed recall, small size of the hippocampus on MRI and APOE epsilon4 might point to a high risk of developing AD. We need extensive follow-up studies to identify which combination of molecular genetic factors and memory test scores supplemented with neuroimaging will prove to be most efficient in diagnosing AD in its preclinical phase, as this is the phase which offers the most promising therapeutic options.

Apolipoprotein E, a gene with complex biological interactions in the aging brain

Age-dependent neurodegeneration in Alzheimer disease (AD) may be viewed as a complex interaction among: (i) susceptibility polymorphisms, (ii) somatic mutations or alterations that occur over extended periods of time, and (iii) environmental interactions. Putative "sporadic" diseases appear to have a much stronger genetic component than had been considered previously. For example, in Alzheimer disease, apolipoprotein E is a major susceptibility locus that accounts for approximately half the heritability. Specific APOE genotypes are associated with different relative risks and age of onset distributions. Disease may be expressed as a confluence of several genetic risk factors, superimposed upon the age-dependent increments of somatic mitochondrial mutations, and environmental determinants such as head injury, stroke, or hypoxia. A matrix involving each of these complex factors may influence the age of onset of AD in a particular individual. With careful clinically based family and epidemiological studies, it is now possible to tease out the relevant genetic contributions from the confluence of other factors leading to complex disease affecting specific sets of neurons. The highly intricate maze of contributing factors provides many potential unanticipated opportunities to design rational therapeutic and preventative strategies.