Severe cardiovascular disease and Alzheimer's disease: senile plaque formation in cortical areas

The independent impact of dementia in patients undergoing percutaneous coronary intervention for acute myocardial infarction

BACKGROUND

Although age and frailty are associated with worse prognoses for patients who undergo percutaneous coronary intervention (PCI), little is known regarding the independent impact of dementia.

HYPOTHESIS

The aim of this study was to evaluate the association between dementia and outcomes for patients with acute myocardial infarction (AMI).

METHODS

Consecutive patients with ST-elevation or non-ST elevation MI who had undergone PCI as part of our AMI registry were included in this study. We compared outcomes within the 1-year period of their PCI, including death and major adverse cardiac events (MACE) and corrected for confounders using Cox regression.

RESULTS

Of 28 274 patients, 9167 patients who had undergone PCI for AMI were included in this study, 250 with dementia; Mean age (77.4 ± 9.4 in the dementia group vs. 63.6 ± 12.7 in the control), female gender (32.4 vs. 24.2%, p = .003), diabetes mellitus (54.0 vs. 42.4%, p < .001) and chronic kidney disease (44.4 vs. 19.3%, p < .001) were higher. At 12 months, unadjusted rates of death (25.5 vs. 9.8%, p < .001) and MACE (33.8 vs. 17.6%, p < .001) were higher for patients with dementia. After standardizing for confounding variables, dementia remained an independent risk factor for death (HR 1.90; CI 1.37-2.65; p < .001) and MACE (HR 1.73; CI 1.30-2.31; p < .001), as well as in propensity score matched analysis (HR 1.54; CI: 1.03-2.28; p < .001 and HR 1.49; CI: 1.09-2.02; p < .001, respectively).

CONCLUSIONS

Dementia is an independent predictor of worse outcomes in patients undergoing PCI for AMI. Future intervention and specialized healthcare measures to mitigate this risk is warranted.

Influence of mild cognitive impairment on activities of daily living in patients with cardiovascular disease

Activities of daily living (ADL) are maintained in patients with mild cognitive impairment (MCI), but, in patients with cardiovascular disease, ADL may have already declined. MCI combined with cardiac disease may accentuate the decline of ADL in these patients. Because the relationship between MCI and ADL in patients with cardiovascular disease is unclear, we examined the associations between MCI and ADL in these patients. We conducted a cross-sectional study of 114 patients with cardiovascular disease but without probable dementia. MCI was estimated with the Japanese version of the Montreal Cognitive Assessment (MoCA-J). We classified patients into the normal cognitive group and MCI group, and compared their clinical characteristics, physical function [Short Physical Performance Battery (SPPB), gait speed, handgrip strength, and knee extensor muscle strength], and ADL [via the Functional Independence Measure (FIM)]. We used logistic regression analysis to evaluate the specific association between MCI and ADL. The incidence of MCI was 36.0%. Significant differences between the two groups were identified for age, body mass index, estimated glomerular filtration rate, albumin, dyslipidemia, educational background, SPPB, gait speed, handgrip strength, and FIM. However, after adjustment for covariates, only FIM was significantly associated with MCI (odds ratio 0.74, 95% confidence interval 0.65-0.84, p < 0.001). ADL was the only independent factor significantly associated with MCI in patients with cardiovascular disease. ADL may be hindered in these patients, even at an early stage of MCI. Therefore, early intervention is necessary to prevent ADL decline from the time of MCI onset or before.

Oligomeric and fibrillar amyloid beta 42 induce platelet aggregation partially through GPVI

The effects of the Alzheimer's disease (AD)-associated Amyloid-β (Aβ) peptides on platelet aggregation have been previously assessed, but most of these studies focused on Aβ40 species. It also remains to be determined which distinct forms of Aβ peptides exert differential effects on platelets. In AD, oligomeric Aβ42 species is widely thought to be a major contributor to the disease pathogenesis. We, therefore, examine the ability of oligomeric and fibrillary Aβ42 to affect platelet aggregation. We show that both forms of Aβ42 induced significant platelet aggregation and that it is a novel ligand for the platelet receptor GPVI. Furthermore, a novel binding peptide that reduces the formation of soluble Aβ42 oligomers was effective at preventing Aβ42-dependent platelet aggregation. These results support a role for Aβ42 oligomers in platelet hyperactivity.

Cerebral hypoperfusion induces cortical watershed microinfarcts which may further aggravate cognitive decline in Alzheimer's disease

Increasing number of data, including the existence of common risk factors, indicate an association between cerebrovascular disease and Alzheimer's disease (AD). AD is known to be often associated with cerebral hypoperfusion. Recent histopathological evidence showed a significant association between watershed cortical microinfarcts and AD indicating that cerebral hypoperfusion induces not only white matter damage, known as leuko-araiosis, but cortical border zone infarcts as well, further aggravating the degenerative process and worsening dementia. In late stages of Alzheimer's disease--in cases with neuropathologically confirmed definite AD--the occurrence of watershed cortical microinfarcts was ten times higher than in aged matched control cases. Congophilic angiopathy and perturbed hemodynamic factors were found to be important factors in the genesis of watershed microinfarcts. To consider the vulnerability of the cerebral blood flow and the perturbed cortical vascular network in AD is important. Neuroleptic and sedative treatments frequently employed in AD may further accentuate cerebral hypoperfusion by decreasing blood pressure. Therefore, to treat and prevent arterial hypotension and maintain cerebral perfusion at an appropriate level in AD is essential.

Heart disease as a risk factor for dementia

As life expectancy lengthens, dementia is becoming a significant human condition in terms of its prevalence and cost to society worldwide. It is important in that context to understand the preventable and treatable causes of dementia. This article exposes the link between dementia and heart disease in all its forms, including coronary artery disease, myocardial infarction, atrial fibrillation, valvular disease, and heart failure. This article also explores the cardiovascular risk factors and emphasizes that several of them are preventable and treatable. In addition to medical therapies, the lifestyle changes that may be useful in retarding the onset of dementia are also summarized.

The Basic Biology of BACE1: A Key Therapeutic Target for Alzheimer's Disease

Alzheimer’s disease (AD) is an intractable, neurodegenerative disease that appears to be brought about by both genetic and non-genetic factors. The neuropathology associated with AD is complex, although amyloid plaques composed of the β-amyloid peptide (Aβ) are hallmark neuropathological lesions of AD brain. Indeed, Aβ plays an early and central role in this disease. β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the initiating enzyme in Aβ genesis and BACE1 levels are elevated under a variety of conditions. Given the strong correlation between Aβ and AD, and the elevation of BACE1 in this disease, this enzyme is a prime drug target for inhibiting Aβ production in AD. However, nine years on from the initial identification of BACE1, and despite intense research, a number of key questions regarding BACE1 remain unanswered. Indeed, drug discovery and development for AD continues to be challenging. While current AD therapies temporarily slow cognitive decline, treatments that address the underlying pathologic mechanisms of AD are completely lacking. Here we review the basic biology of BACE1. We pay special attention to recent research that has provided some answers to questions such as those involving the identification of novel BACE1 substrates, the potential causes of BACE1 elevation and the putative function of BACE1 in health and disease. Our increasing understanding of BACE1 biology should aid the development of compounds that interfere with BACE1 expression and activity and may lead to the generation of novel therapeutics for AD.

Vascular basis for brain degeneration: faltering controls and risk factors for dementia

The integrity of the vascular system is essential for the efficient functioning of the brain. Aging-related structural and functional disturbances in the macro- or microcirculation of the brain make it vulnerable to cognitive dysfunction, leading to brain degeneration and dementing illness. Several faltering controls, including impairment in autoregulation, neurovascular coupling, blood-brain barrier leakage, decreased cerebrospinal fluid, and reduced vascular tone, appear to be responsible for varying degrees of neurodegeneration in old age. There is ample evidence to indicate vascular risk factors are also linked to neurodegenerative processes preceding cognitive decline and dementia. The strongest risk factor for brain degeneration, whether it results from vascular or neurodegenerative mechanisms or both, is age. However, several modifiable risks such as cardiovascular disease, hypertension, dyslipidemia, diabetes, and obesity enhance the rate of cognitive decline and increase the risk of Alzheimer's disease in particular. The ultimate accumulation of brain pathological lesions may be modified by genetic influences, such as the apolipoprotein E ε4 allele and the environment. Lifestyle measures that maintain or improve cardiovascular health, including consumption of healthy diets, moderate use of alcohol, and implementation of regular physical exercise are important factors for brain protection.

Statin use and the risk of Alzheimer's disease: the MIRAGE study

BACKGROUND

The aim of this study was to examine the association between statin use before the onset of Alzheimer's disease (AD) symptoms and risk of having AD, and to explore the potential impact of APOE genotype and race on this association.

METHODS

Data were collected through standardized, validated questionnaires from 895 subjects with probable or definite AD by research criteria, and 1,483 of their nondemented relatives in this family-based, case-control study of AD patients and their relatives enrolled at 15 research centers from 1996 through 2002. To minimize temporal and prescription biases, exposure to statin use within each family was ignored in the one year before the first appearance of AD symptoms in that family's affected member. Associations were estimated using generalized estimating equations for a logistic model, adjusting for age, sex, race, education, history of heart disease, stroke, diabetes, smoking and APOE genotype.

RESULTS

Statin use was associated with lowered odds of having AD (adjusted odds ratio [OR], 0.61; 95% confidence interval [CI], 0.38 to 0.98). Nonstatin cholesterol-lowering medications were not associated significantly with lowered odds of having had AD (adjusted OR, 1.7; 95% CI, 0.61 to 5.0).

CONCLUSIONS

Statin medications were associated with lowered risk of AD in this population. Neither African-American race, nor the presence of the APOE 4 allele modified the statin-AD association.

Carotid artery ultrasound and echocardiography testing to lower the prevalence of Alzheimer's disease

The use of two clinic office techniques, carotid artery ultrasound and echocardiography (CAUSE), to detect deficient brain blood flow delivery in the healthy, cognitively normal, older individual is proposed. Evidence indicates that persistent heart-to-brain blood flow deficit involving low cardiac output or low ejection fraction and carotid artery narrowing can promote cognitive impairment and that such impairment may lead to Alzheimer's disease (AD) or vascular dementia (VaD). A number of independent epidemiologic studies reported cardiovascular and cerebrovascular disease to be risk factors to AD and VaD. The clinical rationale for CAUSE is to detect and prevent progression of cognitive dysfunction in elderly persons and is based on the general understanding that mild cognitive impairment is a preclinical threshold to AD or VaD with high conversion rates to either dementia. The use of CAUSE is anticipated to prevent or attenuate, by appropriate clinical management, mild cognitive impairment arising from persistent brain hypoperfusion, a condition implicated in the promotion of cognitive impairment in the elderly and a common preclinical feature seen in AD and VaD. As detection of lowered cerebral perfusion from cardiac and carotid artery pathology is achieved using these cost-effective, noninvasive, and relatively accurate ultrasound procedures, a significant reduction in the number of new AD and VaD cases would be anticipated after appropriate patient treatment. In this context, a brief summary is presented outlining recent medical and surgical treatments that may improve cerebral blood flow insufficiency. The merit of CAUSE in screening and treating mentally healthy elderly persons who are identified as being at risk of cognitive decline is that it could blunt the soaring socioeconomic impact that will hammer the health care system of many nations by the mounting dementia prevalence rate expected in the next 25 years. A 5- year delay in the onset of AD could reduce the prevalence of AD by 50%. We are making preparations to test the merit of CAUSE in a clinical study of a cognitively healthy elderly population.

Preventing dementia: role of vascular risk factors and cerebral emboli

INTRODUCTION OR BACKGROUND

Dementia, Alzheimer's disease and vascular dementia being two main causes, is major and growing health problem. Vascular risk factors are thought to be involved in the causation of both dementias.

SOURCES OF DATA

A review of the literature was conducted using MedLine to identify current evidence for role of vascular risk factors as potential targets in preventing dementia. Cross-references were hand searched.

AREAS OF AGREEMENT

The evidence from prospective epidemiological studies suggests that optimizing the control of vascular risk factors such as hypertension, high cholesterol, diabetes, smoking and heart disease may prevent dementia. However, this has been proven in randomized placebo-controlled trials (RCT) for only hypertension.

AREAS OF CONTROVERSY

Dementia is a secondary outcome in most RCTs and it is not known if there is a therapeutic time window between mid- and late-life when interventions are most effective. Also, we do not know precise mechanisms by which interventions for vascular risk factors offer brain protection.

GROWING POINTS

Our research suggests that asymptomatic cerebral emboli, which are preventable, may be involved in the causation of dementia.

AREAS TIMELY FOR DEVELOPING RESEARCH

There is a need for RCT targeting multiple vascular risk factors in patients at high risk of dementia such as those with mild cognitive impairment.

The Alzheimer's disease beta-secretase enzyme, BACE1

The pathogenesis of Alzheimer's disease is highly complex. While several pathologies characterize this disease, amyloid plaques, composed of the β-amyloid peptide are hallmark neuropathological lesions in Alzheimer's disease brain. Indeed, a wealth of evidence suggests that β-amyloid is central to the pathophysiology of AD and is likely to play an early role in this intractable neurodegenerative disorder. The BACE1 enzyme is essential for the generation of β-amyloid. BACE1 knockout mice do not produce β-amyloid and are free from Alzheimer's associated pathologies including neuronal loss and certain memory deficits. The fact that BACE1 initiates the formation of β-amyloid, and the observation that BACE1 levels are elevated in this disease provide direct and compelling reasons to develop therapies directed at BACE1 inhibition thus reducing β-amyloid and its associated toxicities. However, new data indicates that complete abolishment of BACE1 may be associated with specific behavioral and physiological alterations. Recently a number of non-APP BACE1 substrates have been identified. It is plausible that failure to process certain BACE1 substrates may underlie some of the reported abnormalities in the BACE1-deficient mice. Here we review BACE1 biology, covering aspects ranging from the initial identification and characterization of this enzyme to recent data detailing the apparent dysregulation of BACE1 in Alzheimer's disease. We pay special attention to the putative function of BACE1 during healthy conditions and discuss in detail the relationship that exists between key risk factors for AD, such as vascular disease (and downstream cellular consequences), and the pathogenic alterations in BACE1 that are observed in the diseased state.

Alzheimer's disease: cholesterol, membrane rafts, isoprenoids and statins

Alzheimer's disease (AD) is a heterogeneous neurodegenerative disorder and the most prevalent form of dementia worldwide. AD is characterized pathologically by amyloid-β plaques, neurofibrillary tangles and neuronal loss, and clinically by a progressive loss of cognitive abilities. At present, the fundamental molecular mechanisms underlying the disease are unclear and no treatment for AD is known. Epidemiological evidence continues to mount linking vascular diseases, such as hypertension and diabetes, and hypercholesterolaemia with an increased risk for developing AD. A growing amount of evidence suggests a mechanistic link between cholesterol metabolism in the brain and the formation of amyloid plaques in AD development. Cholesterol and statins clearly modulate β-amyloid precursor protein (βAPP) processing in cell culture and animal models. Statins not only reduce endogenous cholesterol synthesis but also exert other various pleiotrophic effects, such as the reduction in protein isoprenylation. Through these effects statins modulate a variety of cellular functions involving both cholesterol (and membrane rafts) and isoprenylation. Although clearly other factors, such as vascular inflammation, oxidative stress and genetic factors, are intimately linked with the progression of AD, this review focuses on the present research findings describing the effect of cholesterol, membrane rafts and isoprenylation in regulating βAPP processing and in particular γ-secretase complex assembly and function and AD progression, along with consideration for the potential role statins may play in modulating these events.

Isoprenoids and Alzheimer's disease: a complex relationship

Cholesterol metabolism has been linked to Alzheimer's disease (AD) neuropathology, which is characterized by amyloid plaques, neurofibrillary tangles and neuroinflammation. Indeed, the use of statins, which inhibit cholesterol and isoprenoid biosynthesis, as potential AD therapeutics is under investigation. Whether statins offer benefit for AD will be determined by the outcome of large, placebo-controlled, randomized clinical trials. However, their use as pharmacological tools has delineated novel roles for isoprenoids in AD. Protein isoprenylation regulates multiple cellular and molecular events and here we review the complex roles of isoprenoids in AD-relevant processes and carefully evaluate isoprenoid pathways as potential AD therapeutic targets.

Small hippocampal size in cognitively normal subjects with coronary artery disease

OBJECTIVE

Hippocampal size reduction detected by three-dimensional structural magnetic resonance imaging (3D-MRI) represents an important hallmark of Alzheimer's disease (AD). Recently, epidemiological and neuropathological studies have associated coronary artery disease (CAD) and cardiovascular risk factors with AD. The present study aimed to assess whether small hippocampal size is also a feature of CAD.

METHODS

Hippocampal volumes were assessed in 20 men with CAD and 20 healthy matched control subjects by use of 3D-MRI. Subjects with a history of neurological or psychiatric disorder, or signs of cognitive impairment were rigorously excluded.

RESULTS

Compared with controls, subjects with CAD had significantly smaller (-14%) hippocampal volumes. Cardiovascular risk factors were not related to hippocampal volumes of CAD subjects.

CONCLUSIONS

Our results demonstrate small hippocampal size in CAD subjects without any cognitive impairment. Future studies should clarify whether the annual rate of hippocampal volume loss of persons with CAD is greater than that of healthy individuals and predicts later cognitive decline or dementia.

Atherosclerosis, vascular amyloidosis and brain hypoperfusion in the pathogenesis of sporadic Alzheimer's disease

We postulate that severe atherosclerotic occlusion of the circle of Willis and leptomeningeal arteries is an important factor in the pathogenesis of some sporadic Alzheimer's disease (AD) cases. These arterial stenoses are complicated by an overwhelming amyloid accumulation in the walls of leptomeningeal and cortical arteries resulting in a significant decrease in perfusion pressure and consequent ischemia/hypoxia of the brain tissue. We also propose that the distal areas of the white matter (WM) will be the first affected by a lack of oxygen and nutrients. Our hypotheses are supported by the following observations: (1) the number of stenoses is more frequent in AD than in the control population (p = 0.008); (2) the average index of occlusion is greater in AD than in the control group (p < 0.00001); (3) the index of stenosis and the total number of stenoses per case are positively correlated (R = 0.67); (4) the index of stenosis correlates with the neuropathological lesions of AD and with the MMSE psychometric test; (5) the number and degree of atherosclerosis of the anterior, middle and posterior cerebral arteries is more severe in cases of AD than in the control population; (6) atherosclerosis severity is apparently associated with the severity of the vascular amyloidosis; (7) the WM rarefaction correlates with the severity of the atherosclerosis and vascular amyloidosis; (8) the total cell count and microvessel count in the areas of WM rarefaction correlate with the neuropathological lesions of AD and with the MMSE score. Our data strongly suggest that severe hemodynamic disturbances contribute to sporadic AD and support the numerous observations indicating cardiovascular system participation in the pathogenesis of these dementias.

A beta, aging, and Alzheimer's disease: a tale, models, and hypotheses

In this paper we explore the potential functional role of the A beta peptides in the context of Alzheimer's disease (AD). We begin by defining the morphology of the amyloid deposits in relation to surrounding glial cells and, more importantly, in relation to the brain vasculature. Amyloid accumulation in the brain's microvasculature causes disturbances in the blood-brain barrier (BBB), and in larger arteries, impairment in control of regional cerebral blood flow due to myocyte degeneration. We postulate that the deposition of vascular amyloid may represent a hydrophobic protein plaster to seal leaks in the BBB, occasionally observed in aging and catastrophically common in AD. The vasoconstrictive activity of A beta may also be related to leaky vessels whereby decreasing the arterial diameter may also help to control breaches in the BBB. The admission of plasma neurotoxic proteins into the brain may be controlled by activation of microglia elicited by soluble A beta peptides creating a subtle, but permanent brain inflammatory reaction. We also delve into the influence that cholesterol metabolism may have in membrane topology and A beta production, and the close correlations that exist between cardiovascular disease and AD. Finally, we speculate about the possibility of a peripheral source of A beta that may, by crossing the BBB, contribute to the vascular and parenchymal deposits of A beta in the AD brain.

Circle of willis atherosclerosis is a risk factor for sporadic Alzheimer's disease

OBJECTIVE

We conducted a quantitative investigation of brain arterial atherosclerotic damage and its relationship to sporadic Alzheimer's disease (AD).

METHODS AND RESULTS

Fifty-four consecutive autopsy cases, 32 AD and 22 nondemented control subjects, were examined to establish the degree of arterial stenosis. Vessel external and lumenal area measurements were taken from 3-mm arterial cross-sections to calculate a stenosis index. AD patient circle of Willis arteries possessed a significant degree of stenosis as a consequence of multiple and severe atherosclerotic lesions. These lesions were significantly more severe in AD cases than in age-matched controls (P<0.0001), and the number of stenoses and the index of occlusion (R=0.67; P<0.00001) were positively correlated. In addition, the index of stenosis significantly correlated with the following measures of AD neuropathological lesions: total plaque score, neuritic plaque score, neurofibrillary tangle score, Braak stage score, and white matter rarefaction score.

CONCLUSIONS

Our study reveals an association between severe circle of Willis atherosclerosis and sporadic AD that should be considered a risk factor for this dementia. These observations strongly suggest that atherosclerosis-induced brain hypoperfusion contributes to the clinical and pathological manifestations of AD.

Vascular disorder in Alzheimer's disease: role in pathogenesis of dementia and therapeutic targets

It is not clear whether Alzheimer's Disease (AD) is primarily a neurodegenerative disorder or not. A body of evidence suggests that vascular disorder in brains of individuals with AD contributes to the extremes of this disease. This raises a question whether Alzheimer's dementia is secondary to vascular dysfunction in the central nervous system (CNS) and, therefore, the neurodegeneration that follows is a consequence of inadequate cerebral blood flow, altered brain metabolism and failure in physiological functions of brain endothelium which represents a site at the blood-brain barrier (BBB). In this paper the evidence for a primary role of the CNS vascular system in pathogenesis of Alzheimer's dementia is reviewed to show how alterations in transport across the BBB contribute to development of cerebral beta-amyloidosis in AD. In addition, vascularly-based therapeutic strategies to limit the development of beta-amyloidosis and to remove amyloid and plaques from the CNS of AD individuals are discussed.

Cerebral hypoperfusion generates cortical watershed microinfarcts in Alzheimer disease

BACKGROUND AND PURPOSE

The watershed cortical areas are the first to be deprived of sufficient blood flow in the event of cerebral hypoperfusion and will be the sites of watershed microinfarcts. Cerebral hypoperfusion is associated with Alzheimer disease (AD), but information regarding the occurrence of watershed cortical infarcts in AD is lacking.

METHODS

Brains of 184 autopsy cases (105 definite AD cases and 79 age-matched controls) were selected and analyzed by histochemical and immunohistochemical techniques. The 3-dimensional reconstruction of the whole cerebrum, with 3-mm spaced serial sections, was performed in 6 AD cases to study the intrahemispheric and interhemispheric distribution of the cortical microinfarcts.

RESULTS

A significant association (P=0.001) was found between the occurrence of watershed cortical infarcts and AD (32.4% versus 2.5% in controls). The microinfarcts were restricted to the watershed cortical zones. Congophilic angiopathy was revealed to be an important risk factor. Perturbed hemodynamic factors (eg, decreased blood pressure) may play a role in the genesis of cortical watershed microinfarcts.

CONCLUSIONS

In AD, cerebral hypoperfusion induces not only white matter changes but cortical watershed microinfarcts as well, further aggravating the degenerative process and worsening dementia. To prevent the formation of watershed cortical microinfarcts in AD, monitoring blood pressure and treating arterial hypotension are essential.

Is pharmacological prevention of Alzheimer's a realistic goal?

A growing body of evidence suggests that several classes of drugs marketed for other indications may be effective in the prevention of Alzheimer's disease. Among the most promising of these are nonsteroidal anti-inflammatory agents, oestrogens (oestrogen replacement therapy) and antioxidant vitamins. Other less well-established candidates include histamine H(2) receptor antagonists (H(2) blockers) and 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins). For each of these, we discuss possible mechanisms for their postulated neuroprotective effects and review the studies suggesting their benefits in Alzheimer's disease. We conclude that nonsteroidal anti-inflammatory drugs and oestrogen replacement therapies may be effective in preventing Alzheimer's disease only if taken during the latent phase of the disease several years prior to the appearance of disturbances. Antioxidants may also prevent Alzheimer's disease, but unlike nonsteroidal anti-inflammatory drugs and oestrogen replacement therapies, they may continue to have beneficial effects even after the clinical onset of the disease. The only way to demonstrate the efficacy of these agents will be through randomised, controlled prevention trials. Such trials are currently underway but conclusive results may not be available for several years. Although intriguing, more studies on the neuroprotective effects of statins and H(2) blockers are needed before trials of these agents are initiated. Finally, there are other classes of pharmacological compounds emerging on the horizon, including folic acid, anti-beta-sheet conformational agents, secretase inhibitors and vaccines, that may soon prove to be effective for the prevention of Alzheimer's disease.

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.

The clinical implications of cognitive impairment in elderly patients with chronic heart failure

The purpose of this study was to examine whether cognitive dysfunction was associated with poor participation in an outpatient treatment program for patients with chronic heart failure and if it was related to specific patient characteristics. Cognitive function was measured with the Mini Mental State Examination (MMSE). Twenty-three of 78 (29%) patients randomized to structured care did not participate in this program and nonparticipation during 6-month follow-up was associated with an MMSE score below the median and a low calculated creatinine clearance (CrCl) (R2=0.15, p=0.0025) at entry. In the entire group long duration of heart failure and low blood hemoglobin concentration were independently associated with an MMSE score below the median at entry (R2=0.14, p < 0.0001). Among elderly patients hospitalized with moderate-severe chronic heart failure, judged to be eligible for a nurse-directed outpatient program after discharge, a low MMSE score predicted nonparticipation in such a program. Cognitive dysfunction, which was related to the duration of heart failure, should be evaluated in the treatment of patients with chronic heart failure.

Vascular aspects in Alzheimer's disease

Alzheimer's disease is a primary degenerative dementia and is not considered to be of vascular origin. Furthermore, severe cerebrovascular diseases are generally exclusionary for the clinical diagnosis. During recent years both epidemiological and neuropathological studies have suggested an association between Alzheimer's disease and several vascular risk factors, such as hypertension, inheritance of the apolipoprotein E epsilon4 allele, coronary heart disease, diabetes mellitus, ischaemic white matter lesions and generalised atherosclerosis. These findings may reflect an overdiagnosis of Alzheimer's disease in individuals with silent cerebrovascular disease or that cerebrovascular disease may affects the clinical expression of Alzheimer's disease. Further possibilities include that Alzheimer's disease may increase the risk of vascular disease or that vascular disease may stimulate the Alzheimer's disease process. Similar mechanisms may also be involved in the pathogenesis of both disorders, such as disturbances in the renin-angiotensin system, apoptosis, and psychological stress.

Status of risk factors for vascular dementia

The two most common causes of vascular dementia (VAD) are dementia evolving in connection with multiple small or large strokes and dementia related to ischemic white-matter lesions (WMLs) of the brain. The knowledge about risk factors for these disorders is still scarce. Besides sharing risk factors with stroke, dementia with multiple small or large brain infarcts is also associated with non-vascular risk factors such as high alcohol consumption, psychological stress in early life, lower formal education, blue collar occupation, and occupational exposures. Risk factors for dementia in stroke victims include stroke-related and non-stroke related risk factors. Non-stroke-related factors are similar to those found in Alzheimer's disease. The main risk factors for ischemic WMLs are hypertension or increased blood pressure, but WMLs have also been associated with a number of other vascular risk factors. In recent years, Alzheimer's disease (AD) has also been reported to be associated with vascular risk factors, including hypertension, coronary heart disease, atrial fibrillation, diabetes mellitus, and WMLs. Although these associations may reflect an overdiagnosis of AD in cases with silent cerebrovascular disease, or that cerebrovascular disease increases the possibility that individuals with Alzheimer lesions will express a dementia syndrome, there are also alternative explanations. AD and cerebrovascular disease may for instance share similar risk factors or etiologic pathways. The pathogenetic implications for the association between AD and vascular factors need to be further explored. There is also a need for more studies on risk factors for VAD and risk factors for dementia in stroke samples, as well as studies on non-vascular risk factors for ischemic WMLs.

Link between heart disease, cholesterol, and Alzheimer's disease: a review

Increased prevalence of Alzheimer's disease-like beta-amyloid deposits in the neuropil and within neurons occurs in the brains of non-demented individuals with heart disease. Heart disease is a prevalent finding in Alzheimer's disease, and may be a forerunner to the dementing disorder. In the cholesterol-fed rabbit model of human coronary heart disease there is production and accumulation of beta-amyloid in the brain. This accumulation of beta-amyloid can be reversed by removing cholesterol from the rabbits' diet. In culture cells, a cholesterol challenge has been shown to increase production of beta-amyloid, and dramatic reductions of cholesterol produced by HMG Co-A reductase inhibitors decrease production of beta-amyloid. Increased beta-amyloid production is also produced by dietary cholesterol in a number of transgenic mouse models of Alzheimer's disease. Administration of HMG Co-A reductase inhibitors may block beta-amyloid production caused by dietary cholesterol in rabbits. Clinical trials testing the benefit of HMG Co-A reductase inhibitors in the treatment of Alzheimer's disease are underway.

Alterations of Alzheimer's disease in the cholesterol-fed rabbit, including vascular inflammation. Preliminary observations

We determined the levels of endothelial inflammation using MECA-32 antibody and alpha 4 nicotinic receptor subunit densities employing [3H]epibatidine binding in the brains of Alzheimer's disease (AD) patients, cholesterol-fed rabbits, and appropriate controls. We also assessed rabbit brain for beta-amyloid levels and immunohistochemical localization, and for evidence of blood-brain barrier breach using normally-excluded Evans Blue dye. Dietary cholesterol induced a twofold increase in beta-amyloid concentration in rabbit hippocampal cortex, which may be related to the appearance of beta-amyloid immunoreactivity in the neuropil. Epibatidine binding was significantly decreased in AD superior frontal cortex, but unchanged in the superior frontal cortex of cholesterol-fed rabbits. Increased vascular MECA-32 immunoreactivity occurred in AD and cholesterol-fed rabbit brain. Evans Blue dye could be found in the parenchyma of cholesterol-fed rabbits only, and appeared as pockets of dye surrounding small blood vessels. The data suggest that vascular inflammation can lead to breach of the blood-brain barrier, which may produce biochemical derangements in surrounding brain tissue that are conducive to production of beta-amyloid.

Neuropathology of mitral valve prolapse in man and cardiopulmonary bypass (CPB) surgery in adolescent Yorkshire pigs

We investigated the brains of non-demented individuals with mitral valve prolapse (MVP) and found evidence of Alzheimer-like lesions. This neuropathology consisted of premature presence of beta-amyloid-containing senile plaques (SP) without increased prevalence of neurofibrillary tangles. Low levels of SP occurred in 20 to 45- year-old subjects with MVP, and much greater densities were observed in subjects between 45 and 62 years of age. We also investigated the brains of adolescent Yorkshire pigs undergoing cardiopulmonary bypass surgery and likewise found evidence of Alzheimer-like neuropathology. This took the form of intraneuronal accumulation of beta-amyloid immunoreactivity and increasing numbers of Alz-50 immunoreactive neurons with reduced recovery of cardiac efficiency after the surgery. Based on prevailing concepts in Alzheimer's disease, it is feasible to hypothesize that cognitive dysfunction occurring after cardiopulmonary bypass surgery with coronary artery grafting or valve repair/replacement is a functional sequela of AD-like neuropathology. This postulate is based on the premise that an individual seeking such surgery would have pre-existing, elevated AD-like neuropathology to start with. It is further coupled with the probability that these forms of cardiovascular surgery exacerbate the extent and progression of AD-like neuropathology.

Histochemically-reactive zinc in amyloid plaques, angiopathy, and degenerating neurons of Alzheimer's diseased brains

Excess brain zinc has been implicated in Alzheimer's neuropathology. Here we evaluated that hypothesis by searching the brains of Alzheimer's patients for abnormal zinc deposits. Using histochemical methods, we found vivid Zn2+ staining in the amyloid deposits of dense-core (senile) plaques, in the amyloid angiopathy surrounding diseased blood vessels, and in the somata and dendrites of neurons showing the characteristic neurofibrillary tangles (NFT) of Alzheimer's. In contrast, brains from age-matched, non-demented subjects showed only occasional staining for Zn2+ in scattered neurons and possible plaques. A role of abnormal zinc metabolism in Alzheimer's neuropathology is suggested.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Elevated low-density lipoprotein in Alzheimer's disease correlates with brain abeta 1-42 levels

Sera obtained in the immediate postmortem from 100 individuals, 64 neuropathologically diagnosed Alzheimer's disease (AD) cases and 36 nondemented controls, were analyzed for cholesterol, lipoproteins, apolipoproteins (Apo), and triglycerides. All individuals were ApoE genotyped, and the amounts of Abeta (N-40 and N-42) in cerebral cortex of AD and control subjects were determined. When compared to controls, AD individuals had significantly higher LDL cholesterol (P = 0.006), ApoB (P = 0.018), Abeta N-40 (P = 0.024) and Abeta N-42 (P < 0.001), and significantly lower HDL cholesterol (P = 0.040). There were positive correlations between the levels of serum total cholesterol (r = 0.359, P = 0.004), LDL cholesterol (r = 0.328, P = 0.008), and ApoB (r = 0.395, P = 0.001) to the amount of Abeta N-42 in AD brains, but not to Abeta N-40. These correlations were independent of ApoE genotype and were not seen in the control group. The present results suggest for the first time that elevated serum cholesterol, especially in the form of LDL, influences the expression of AD-related pathology.

The relationship between blood pressure and dementia: a review

Hypertension has been related to the development of dementia, including Alzheimer's disease, and cognitive dysfunction in middle-aged and elderly populations. One possible explanation is that hypertension is a risk factor for cerebral infarcts and ischaemic subcortical white-matter lesions. Hypertension may also give rise to a blood-brain barrier dysfunction, which has been suggested to be involved in the aetiology and pathogenesis of Alzheimer's disease. Other possible explanations for the association are shared risk factors, such as psychological stress, and the formation of free oxygen radicals. Low blood pressure has also been hypothesized to give rise to brain damage and dementia. However, the brain is involved in blood pressure regulation and dementia disorders may therefore influence the blood pressure. The findings of an association between hypertension and dementia may have implications for prevention and treatment.