Neurotoxicity of A beta amyloid protein in vitro is not altered by calcium channel blockade

Verapamil and Alzheimer's Disease: Past, Present, and Future

Verapamil is a phenylalkylamine class calcium channel blocker that for half a century has been used for the treatment of cardiovascular diseases. Nowadays, verapamil is also considered as a drug option for the treatment of several neurological and psychiatric disorders, such as cluster headache, bipolar disorders, epilepsy, and neurodegenerative diseases. Here, we review insights into the potential preventive and therapeutic role of verapamil on Alzheimer’s disease (AD) based on limited experimental and clinical data. Pharmacological studies have shown that verapamil has a wide therapeutic spectrum, including antihypertensive, anti-inflammatory, and antioxidative effects, regulation of the blood-brain barrier function, due to its effect on P-glycoprotein, as well as adjustment of cellular calcium homeostasis, which may result in the delay of AD onset or ameliorate the symptoms of patients. However, the majority of the AD individuals are on polypharmacotherapy, and the interactions between verapamil and other drugs need to be considered. Therefore, for an appropriate and successful AD treatment, a personalized approach is more than necessary. A well-known narrow pharmacological window of verapamil efficacy may hinder this approach. It is therefore important to note that the verapamil efficacy may be conditioned by different factors. The onset, grade, and brain distribution of AD pathological hallmarks, the time-sequential appearances of AD-related cognitive and behavioral dysfunction, the chronobiologic and gender impact on calcium homeostasis and AD pathogenesis may somehow be influencing that success. In the future, such insights will be crucial for testing the validity of verapamil treatment on animal models of AD and clinical approaches.

The changing landscape of voltage-gated calcium channels in neurovascular disorders and in neurodegenerative diseases

It is a common belief that voltage-gated calcium channels (VGCC) cannot carry toxic amounts of Ca²⁺ in neurons. Also, some of them as L-type channels are essential for Ca²⁺-dependent regulation of prosurvival gene-programs. However, a wealth of data show a beneficial effect of drugs acting on VGCCs in several neurodegenerative and neurovascular diseases. In the present review, we explore several mechanisms by which the “harmless” VGCCs may become “toxic” for neurons. These mechanisms could explain how, though usually required for neuronal survival, VGCCs may take part in neurodegeneration. We will present evidence showing that VGCCs can carry toxic Ca²⁺ when: a) their density or activity increases because of aging, chronic hypoxia or exposure to β-amyloid peptides or b) Ca²⁺-dependent action potentials carry high Ca²⁺ loads in pacemaker neurons. Besides, we will examine conditions in which VGCCs promote neuronal cell death without carrying excess Ca²⁺. This can happen, for instance, when they carry metal ions into the neuronal cytoplasm or when a pathological decrease in their activity weakens Ca²⁺-dependent prosurvival gene programs. Finally, we will explore the role of VGCCs in the control of nonneuronal cells that take part to neurodegeneration like those of the neurovascular unit or of microglia.

Neuroprotective actions of noradrenaline: effects on glutathione synthesis and activation of peroxisome proliferator activated receptor delta

The endogenous neurotransmitter noradrenaline (NA) can protect neurons from the toxic consequences of various inflammatory stimuli, however the exact mechanisms of neuroprotection are not well known. In the current study, we examined neuroprotective effects of NA in primary cultures of rat cortical neurons. Exposure to oligomeric amyloid beta (Abeta) 1-42 peptide induced neuronal damage revealed by increased staining with fluorojade, and toxicity assessed by LDH release. Abeta-dependent neuronal death did not involve neuronal expression of the inducible nitric oxide synthase 2 (NOS2), since Abeta did not induce nitrite production from neurons, LDH release was not reduced by co-incubation with NOS2 inhibitors, and neurotoxicity was similar in wildtype and NOS2 deficient neurons. Co-incubation with NA partially reduced Abeta-induced neuronal LDH release, and completely abrogated the increase in fluorojade staining. Treatment of neurons with NA increased expression of gamma-glutamylcysteine ligase, reduced levels of GSH peroxidase, and increased neuronal GSH levels. The neuroprotective effects of NA were partially blocked by co-treatment with an antagonist of peroxisome proliferator activated receptors (PPARs), and replicated by incubation with a selective PPARdelta (PPARdelta) agonist. NA also increased expression and activation of PPARdelta. Together these data demonstrate that NA can protect neurons from Abeta-induced damage, and suggest that its actions may involve activation of PPARdelta and increases in GSH production.

Abeta ion channels. Prospects for treating Alzheimer's disease with Abeta channel blockers

The main pathological features in the Alzheimer's brain are progressive depositions of amyloid protein plaques among nerve cells, and neurofibrillary tangles within the nerve cells. The major components of plaques are Abeta peptides. Numerous reports have provided evidence that Abeta peptides are cytotoxic and may play a role in the pathogenesis of AD. An increasing number of research reports support the concept that the Abeta-membrane interaction event may be followed by the insertion of Abeta into the membrane in a structural configuration which forms an ion channel. This review summarizes experimental procedures which have been designed to test the hypothesis that the interaction of Abeta with a variety of membranes, both artificial and natural, results in the subsequent formation of Abeta ion channels We describe experiments, by ourselves and others, that support the view that Abeta is cytotoxic largely due to the action of Abeta channels in the cell membrane. The interaction of Abeta with the surface of the cell membrane may results in the activation of a chain of processes that, when large enough, become cytotoxic and induce cell death by apoptosis. Remarkably, the blockage of Abeta ion channels at the surface of the cell absolutely prevents the activation of these processes at different intracellular levels, thereby preserving the life of the cells. As a prospect for therapy for Alzheimer's disease, our findings at cellular level may be testable on AD animal models to elucidate the potential role and the magnitude of the contribution of the Abeta channels for induction of the disease.

Glutamate and amyloid beta-protein rapidly inhibit fast axonal transport in cultured rat hippocampal neurons by different mechanisms

Impairment of axonal transport leads to neurodegeneration and synapse loss. Glutamate and amyloid beta-protein (Abeta) have critical roles in the pathogenesis of Alzheimer's disease (AD). Here we show that both agents rapidly inhibit fast axonal transport in cultured rat hippocampal neurons. The effect of glutamate (100 microm), but not of Abeta25-35 (20 microm), was reversible, was mimicked by NMDA or AMPA, and was blocked by NMDA and AMPA antagonists and by removal of extracellular Ca2+. The effect of Abeta25-35 was progressive and irreversible, was prevented by the actin-depolymerizing agent latrunculin B, and was mimicked by the actin-polymerizing agent jasplakinolide. Abeta25-35 induced intracellular actin aggregation, which was prevented by latrunculin B. Abeta31-35 but not Abeta15-20 exerted effects similar to those of Abeta25-35. Full-length Abeta1-42 incubated for 7 d, which specifically contained 30-100 kDa molecular weight assemblies, also caused an inhibition of axonal transport associated with intracellular actin aggregation, whereas freshly dissolved Abeta1-40, incubated Abeta1-40, and fresh Abeta1-42 had no effect. These results suggest that glutamate inhibits axonal transport via activation of NMDA and AMPA receptors and Ca2+ influx, whereas Abeta exerts its inhibitory effect via actin polymerization and aggregation. The ability of Abeta to inhibit axonal transport seems to require active amino acid residues, which is probably present in the 31-35 sequence. Full-length Abeta may be effective when it represents a structure in which these active residues can access the cell membrane. Our results may provide insight into the early pathogenetic mechanisms of AD.

Abeta(25-35) and Abeta(1-40) act on different calcium channels in CA1 hippocampal neurons

The acute effects of beta-amyloid (25-35) and (1-40) on high voltage activated calcium channels were compared in CA1 pyramidal cells of adult mouse hippocampal slices using the whole-cell patch-clamp recording. Bath application of oligomeric beta-amyloid (25-35) reversibly increased the barium current (I(Ba)) to 1.61 (normalized amplitude), while oligomeric beta-amyloid (1-40) reversibly enhanced the I(Ba) to 1.74. Reverse-sequence beta-amyloid [(35-25) and (40-1)] had no effect. The effect of beta-amyloid (25-35) was blocked by nifedipine, a selective antagonist of L-type calcium channels. In contrast, the effect of beta-amyloid (1-40) was not blocked by nifedipine and I(Ba) was enhanced to 4.96. It is concluded that these oligomeric peptides may act through different types of calcium channels and/or receptors. The toxicity of Abeta(25-35) implicates a potentiation of L-type calcium channels while the one of Abeta(1-40) is related to an increase of non-L-type calcium channels, which may involve an increase in transmitter release.

Amyloid beta protein forms ion channels: implications for Alzheimer's disease pathophysiology

Amyloid beta protein (AbetaP) is the major constituent of senile plaques associated with Alzheimer's disease (AD). However, its mechanistic role in AD pathogenesis is poorly understood. Globular and nonfibrillar AbetaPs are continuously released during normal metabolism. Using techniques of atomic force microscopy, laser confocal microscopy, electrical recording, and biochemical assays, we have examined the molecular conformations of reconstituted globular AbetaPs as well as their real-time and acute effects on neuritic degeneration. Atomic force microscopy (AFM) of AbetaP1-42 shows globular structures that do not form fibers in physiological-buffered solution for up to 8 h of continuous imaging. AFM of AbetaP1-42 reconstituted in a planar lipid bilayer reveals multimeric channel-like structures. Consistent with these AFM resolved channel-like structures, biochemical analysis demonstrates that predominantly monomeric AbetaPs in solution form stable tetramers and hexamers after incorporation into lipid membranes. Electrophysiological recordings demonstrate the presence of multiple single channel currents of different sizes. At the cellular level, AbetaP1-42 allows calcium uptake and induces neuritic abnormality in a dose- and time-dependent fashion. At physiological nanomolar concentrations, rapid neuritic degeneration was observed within minutes; at micromolar concentrations, neuronal death was observed within 3-4 h. These effects are prevented by zinc (an AbetaP channel blocker) and by the removal of extracellular calcium, but are not prevented by antagonists of putative AbetaP cell surface receptors. Thus, AbetaP channels may provide a direct pathway for calcium-dependent AbetaP toxicity in AD.

Mechanisms of prion-induced modifications in membrane transport properties: implications for signal transduction and neurotoxicity

Prion-related encephalopathies are associated with the conversion of a normal cellular isoform of prion protein (PrP(c)) to an abnormal pathologic scrapie isoform (PrP(Sc)). The conversion of this single polypeptide chain involves a reduction in the alpha-helices and an increase in beta-sheet content. This change in the content ratio of alpha-helices to beta-sheets may explain the diversity in the proposed mechanisms of action. Many of the pathogenic properties of PrP(Sc), such as neurotoxicity, proteinase-resistant properties and induction of hypertrophy and proliferation of astrocytes, have been attributed to the peptide fragment corresponding to residues 106-126 of prion (PrP[106-126]). In particular, the amyloidogenic and hydrophobic core AGAAAAGA has been implicated in modulation of neurotoxicity and the secondary structure of PrP[106-126]. Because of some similarities between the properties of PrP[106-126] and PrP(Sc), the former is used as a useful tool to characterize the pharmacological and biophysical properties of PrP(Sc) in general and of that domain in particular, by various laboratories. However, it is important to note that by no means can PrP[106-126] be considered a complete equivalent to PrP(Sc) in function. Several hypotheses have been proposed to explain prion-induced neurodegenerative diseases. These non-exclusive hypotheses include: (i) changes in the membrane microviscosity; (ii) changes in the intracellular Ca(2+) homeostasis; (iii) superoxide dismutase and Cu(2+) homeostasis; and (iv) changes in the immune system. The prion-induced modification in Ca(2+) homeostasis is the result of: (1) prion interaction with intrinsic ion transport proteins, e.g. L-type Ca(2+) channels in the surface membrane, and IP(3)-modulated Ca(2+) channels in the internal membranes, and/or (2) formation of cation channels. These two mechanisms of action lead to changes in Ca(2+) homeostasis that further augment the abnormal electrical activity and the distortion of signal transduction causing cell death. It is concluded that the hypothesis of the interaction of PrP[106-126] with membranes and formation of redox-sensitive and pH-modulated heterogeneous ion channels is consistent with: (a) PrP-induced changes in membrane fluidity and viscosity; (b) PrP-induced changes in Ca(2+) homeostasis (and does not exclude changes in endogenous Ca(2+) transport pathways and Cu(2+) homeostasis); (c) PrP role as an antioxidant; and (d) the PrP structural properties, i.e. beta sheets, protein aggregation, hydrophobicity, functional significance of specific amino acids (e.g. methionine, histidine) and regulation with low pH.

Mechanisms of amyloid beta protein-induced modification in ion transport systems: implications for neurodegenerative diseases

1. Alzheimer's disease (AD) is a neurodegenerative disorder that affects the cognitive function of the brain. Pathological changes in AD are characterized by the formation of amyloid plaques and neurofibrillary tangles as well as extensive neuronal loss. Abnormal proteolytic processing of amyloid precursor protein (APP) is the central step that leads to formation of amyloid plaque, neurofibrillary tangles, and neuronal loss. 2. The plaques, which accumulate extracellularly in the brain, are composed of aggregates and cause direct neurotoxic effects and/or increase neuronal vulnerability to excitotoxic insults. The aggregates consist of soluble pathologic amyloid beta peptides AbetaP[1-42] and AbetaP[1-43] and soluble nonpathologic AbetaP[1-40]. Both APP and AbetaP interact with ion transport systems. AbetaP induces a wide range of effects as the result of activating a cascade of mechanisms. 3. The major mechanisms proposed for AbetaP-induced cytotoxicity involve the loss of Ca2+ homeostasis and the generation of reactive oxygen species (ROS). The changes in Ca2+ homeostasis could be the result of (1) changes in endogenous ion transport systems, e.g. Ca2+ and K+ channels and Na+/K+-ATPase, and membrane receptor proteins, such as ligand-driven ion channels and G-protein-driven releases of second messengers, and (2) formation of heterogeneous ion channels. 4. The consequences of changes in Ca2+-homeostasis-induced generation of ROS are (a) direct modification of intrinsic ion transport systems and their regulatory mechanisms, and (b) indirect effects on ion transport systems via peroxidation of phospholipids in the membrane, inhibition of phosphorylation, and reduction of ATP levels and cytoplasmic pH. 5. We propose that in AD, AbetaP with its different conformations alters cell regulation by modifying several ion transport systems and also by forming heterogeneous ion channels. The changes in membrane transport systems are proposed as early steps in impairing neuronal function preceding plaque formation. We conclude that these changes damage the membrane by compromising its integrity and increasing its ion permeability. This mechanism of membrane damage is not only central for AD but also may explain other malfunctioned protein-processing-related pathologies.

Nicotine and its interaction with beta-amyloid protein: a short review

Two features of Alzheimer's disease (AD) are beta-amyloid protein (betaAP) deposition and a severe cholinergic deficit. beta-Amyloid protein is a 39- to 43-amino acid transmembrane fragment of a larger precursor molecule, amyloid precursor protein. It is a major constituent of senile plaque, a neuropathologic hallmark of AD, and has been shown to be neurotoxic in vivo and in vitro. The cholinergic neurotransmission system is seen as the primary target of AD. However, other systems are also found to show functional deficit. An association between cholinergic deficit and betaAP is suggested by a negative correlation between cigarette smoking and AD. Evidence hitherto suggests that betaAP causes neuronal death possibly via apoptosis by disrupting calcium homeostasis, which may involve direct activation or enhancement of ligand-gated or voltage-dependent calcium channels. Selective second messengers such as protein kinases are triggered that signal neuronal death. Nicotine or acetylcholinesterase inhibitors can partially prevent the neurotoxicity of betaAP in vivo and in vitro. However, the exact mechanism by which nicotine provides its protective effects is not fully understood, but clearly there are protective roles for nicotine. Here, some aspects of betaAP neurotoxicity and nicotinic intervention as a protective agent are discussed.

cAMP delays beta-amyloid (25-35) induced cell death in rat cortical neurons

Beta-amyloid (A beta) accumulation is believed to contribute to neuronal cell death in Alzheimer's disease. To understand the role of cAMP in the regulation of A beta induced cell death, we used 8-chlorophenylthio-cAMP (8-CPT-cAMP, a cAMP analog) to raise intracellular cAMP levels. Exposure of rat cortical neurons to A beta(25-35) resulted in a gradual increase in lactate dehydrogenase (LDH) over 48 h, which was preceded by a transient elevation in caspase-3-like activity. In the presence of 8CPT-cAMP, both caspase-3 activity and LDH release was significantly reduced. These data suggest that elevation of intracellular cAMP levels attenuate A beta-induced neurotoxicity and may delay or prevent the onset of A beta-induced neurodegeneration.

Fresh and globular amyloid beta protein (1-42) induces rapid cellular degeneration: evidence for AbetaP channel-mediated cellular toxicity

Amyloid beta peptides (AbetaP) deposit as plaques in vascular and parenchymal areas of Alzheimer's disease (AD) tissues and Down's syndrome patients. Although neuronal toxicity is a feature of late stages of AD, vascular pathology appears to be a feature of all stages of AD. Globular and nonfibrillar AbetaPs are continuously released during normal cellular metabolism, form calcium-permeable channels, and alter cellular calcium level. We used atomic force microscopy, laser confocal microscopy, and calcium imaging to examine the real-time and acute effects of fresh and globular AbetaP(1-42), AbetaP(1-40), and AbetaP(25-35) on cultured endothelial cells. AbetaPs induced morphological changes that were observed within minutes after AbetaP treatment and led to eventual cellular degeneration. Cellular morphological changes were most sensitive to AbetaP(1-42). AbetaP(1-42)-induced morphological changes were observed at nanomolar concentrations and were accompanied by an elevated cellular calcium level. Morphological changes were prevented by anti-AbetaP antibody, AbetaP-channel antagonist zinc, and the removal of extracellular calcium, but not by tachykinin neuropeptide, voltage-sensitive calcium channel blocker cadmium, or antioxidants DTT and Trolox. Thus, nanomolar fresh and globular AbetaP(1-42) induces rapid cellular degeneration by elevating intracellular calcium, most likely via calcium-permeable AbetaP channels and not by its interaction with membrane receptors or by activating oxidative pathways. Such rapid degeneration also suggests that the plaques, and especially fibrillar AbetaPs, may not have a direct causative role in AD pathogenic cascades.

Blockage of amyloid beta peptide-induced cytosolic free calcium by fullerenol-1, carboxylate C60 in PC12 cells

Amyloid beta protein (Abeta) alters signal transduction systems, including increases in the cytosolic free calcium ([Ca2+]i) response which have pathophysiological significance in Alzheimer's disease (AD). The purposes of this study were to elucidate the mechanism involved in Abeta's effect on the Ca2+ signal and to evaluate the effect of fullerenol-1, a water-soluble hydroxyl and superoxide radical scavenger, on the Abeta-induced Ca2+ response. Both Abeta and bradykinin (BK) dose-dependently elevated [Ca2+]i in PC12 cells. Fullerenol-1, at a concentration range between 100 nM and 1 microM, dose-dependently reduced the Abeta-induced [Ca2+]i response, but did not alter the subsequent BK-mediated process. Thapsigargin, an inhibitor of Ca2+-ATPase, released Ca2+ from the internal store and diminished the BK-mediated calcium spike but did not affect the Abeta-induced Ca2+ response. In the absence of extracellular calcium, the Abeta-induced, but not BK-induced, calcium spike was completely abolished. The Ca induced by Abeta did not enter through the voltage-dependent calcium channels or ligand gated calcium channels, because the peak of Abeta-evoked Ca2+ was not significantly altered by various Ca2+ channel blockers or a NMDA receptor antagonist MK801. In addition, neither cholera toxin nor pertussis toxin altered the Abeta-induced Ca response. The results demonstrated that Abeta-stimulated [Ca2+]i increase is due to Ca influx from an extracellular source rather than from the intracellular store. Alteration of the membrane lipid structure and permeability by free radicals generated by Abeta may be a major cause of Ca -influx. Furthermore, fullerenol-1, a novel antioxidant, may provide therapeutic benefits in neurodegenerative diseases such as AD.

Beta-amyloid-induced calcium influx induces apoptosis in culture by oxidative stress rather than tau phosphorylation

Beta-amyloid (betaA) toxicity in culture is accompanied by multiple events culminating in apoptosis. Calcium influx may represent the initial event, since calcium chelation prevents all subsequent events, while subsequent events include increased generation of reactive oxygen species (ROS) and hyperphosphorylation of tau. In the present study, we undertook to determine whether ROS generation or tau hyperphosphorylation mediate betaA-induced apoptosis. The anti-oxidant vitamin E or the kinase inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenslfonamide (W7) was added following brief treatment of differentiated SH-SY-5Y human neuroblastoma cells with 22 microM betaA. Under these conditions, vitamin E prevented ROS generation and apoptosis, but did not prevent intracellular calcium accumulation or tau phosphorylation. W7 prevented tau phosphorylation but did not block betaA-induced calcium influx, ROS generation or apoptosis. While these studies do not address the long-term consequences of PHF formation, they indicate that ROS generation, rather than tau hyperphosphorylation, leads to apoptosis following betaA-induced calcium influx into cultured cells.

Neuroprotective approaches in experimental models of beta-amyloid neurotoxicity: relevance to Alzheimer's disease

1. beta-Amyloid peptides (A beta s) accumulate abundantly in the Alzheimer's disease (AD) brain in areas subserving information acquisition and processing, and memory formation. A beta fragments are produced in a process of abnormal proteolytic cleavage of their precursor, the amyloid precursor protein (APP). While conflicting data exist in the literature on the roles of A beta s in the brain, and particularly in AD, recent studies have provided firm experimental evidence for the direct neurotoxic properties of A beta. 2. Sequence analysis of A beta s revealed a high degree of evolutionary conservation and inter-species homology of the A beta amino acid sequence. In contrast, synthetic A beta fragments, even if modified fluorescent or isotope-labeled derivatives, are pharmacological candidates for in vitro and in vivo modeling of their cellular actions. During the past decade, acute injection, prolonged mini-osmotic brain perfusion approaches or A beta infusions into the blood circulation were developed in order to investigate the effects of synthetic A beta s, whereas transgenic models provided insight into the distinct molecular steps of pathological APP cleavage. 3. The hippocampus, caudate putamen, amygdala and neocortex all formed primary targets of acute neurotoxicity screening, but functional consequences of A beta infusions were primarily demonstrated following either intracerebroventricular or basal forebrain (medial septum or magnocellular basal nucleus (MBN)) infusions of A beta fragments. 4. In vivo investigations confirmed that, while the active core of A beta is located within the beta(25-35) sequence, the flanking peptide regions influence not only the folding properties of the A beta fragments, but also their in vivo neurotoxic potentials. 5. It has recently been established that A beta administration deranges neuron-glia signaling, affects the glial glutamate uptake and thereby induces noxious glutamatergic stimulation of nerve cells. In fact, a critical role for N-methyl-D-aspartate (NMDA) receptors was postulated in the neurotoxic processes. Additionally, A beta s might become internalized, either after their selective binding to cell-surface receptors or after membrane association in consequence of their highly lipophilic nature, and induce free radical generation and subsequent oxidative injury. Ca(2+)-mediated neurotoxic events and generation of oxygen free radicals may indeed potentiate each other, or even converge to the same neurotoxic events, leading to cell death. 6. Neuroprotection against A beta toxicity was achieved by both pre- and post-treatment with NMDA receptor channel antagonists. Moreover, direct radical-scavengers, such as vitamin E or vitamin C, attenuated A beta toxicity with high efficacy. Interestingly, combined drug treatments did not necessarily result in additive enhanced neuroprotection. 7. Similarly to the blockade of NMDA receptors, the neurotoxic action of A beta s could be markedly decreased by pharmacological manipulation of voltage-dependent Ca(2+)-channels, serotonergic IA or adenosine A1 receptors, and by drugs eliciting membrane hyperpolarization or indirect blockade of Ca(2+)-mediated intracellular consequences of intracerebral A beta infusions. 8. A beta neurotoxicity might be dose-dependently modulated by trace metals. In spite of the fact that zinc (Zn) may act as a potent inhibitor of the NMDA receptor channel, high Zn doses accelerate A beta fibril formation, stabilize the beta-sheet conformation and thereby potentiate A beta neurotoxicity. Combined trace element supplementation with Se, Mn, or Mg, which prevails over the expression of detoxifying enzymes or counteracts intracellular elevations of Ca2+, may reduce the neurotoxic impact of A beta s. 9. Alterations in the regulatory functions of the hypothalamo-pituitary-adrenal axis may contribute significantly to neurodegenerative changes in the brain. Furthermore, AD patients exhibit substantially increased circadia

Rate of medial temporal lobe atrophy in typical aging and Alzheimer's disease

OBJECTIVES

To determine the annual rates of volumetric change of the hippocampus and temporal horn in cognitively normal elderly control subjects and individually matched patients with AD, and to test the hypothesis that these rates were different.

BACKGROUND

Cross-sectional studies consistently reveal cerebral atrophy in elderly nondemented subjects compared with healthy young adults, and greater atrophy in patients with AD relative to elderly control subjects. However, rates of atrophy are estimated most accurately by performing serial measurements in the same individuals.

METHODS

MRI-based volumetric measurements of the hippocampi and temporal horns were performed in 24 cognitively normal subjects aged 70 to 89 years who were individually matched with respect to gender and age with 24 patients with AD. Each subject underwent an MRI protocol twice, separated by 12 months or more.

RESULTS

The mean annual rate of hippocampal volume loss among control subjects was -1.55+/-1.38% and the temporal horns increased in volume by 6.15+/-7.69% per year. These rates were significantly greater among AD patients: hippocampus, -3.98+/-1.92% per year, p < 0.001; temporal horn, 14.16+/-8.47% per year, p = 0.002.

CONCLUSION

A statistically significant yearly decline in hippocampal volume and an increase in temporal horn volume was identified in elderly control subjects who represent typical aging individuals. These rates were approximately 2.5 times greater in patients with AD than in individually age- and gender-matched control subjects.

CSF tau is related to apolipoprotein E genotype in early Alzheimer's disease

We quantified microtubule-associated protein tau in CSF (CSF tau) using ELISA assay in 168 subjects: 81 patients with clinically diagnosed early Alzheimer's disease (AD), 43 patients with other dementia, 11 Down's syndrome patients, and 33 nondemented neurologic control subjects. Multivariate ANOVA showed an effect of diagnostic group (p < 0.01) and apolipoprotein E (apoE) allele (p < 0.005) on CSF tau. Comparison between diagnostic groups showed higher CSF tau levels in AD than in the control group (p < 0.001). However, CSF tau values in the non-AD dementia group did not differ significantly from those of AD patients or neurologic control subjects. Tau levels were increased (p < 0.005) in AD patients with apolipoprotein E epsilon4 allele, a well-characterized risk factor of AD, compared with AD patients without epsilon4 allele, and the highest values were found in AD patients with two epsilon4 alleles. These increased levels of CSF tau may indicate pronounced neuronal degeneration and neurofibrillar pathology at the early stage of AD in patients carrying the epsilon4 allele. This study shows that the current ELISA test for CSF tau is not sensitive and specific enough to distinguish early AD from other dementias and indicates that in the interpretation of CSF tau analysis as a diagnostic tool, the apoE genotype should also be taken into account.

Alzheimer's disease: a re-examination of the amyloid hypothesis

Alzheimer's disease (AD) is a neurodegenerative disorder of the brain characterized by the presence of neuritic amyloid plaques and neurofibrillary tangles. Although it most frequently occurs in the elderly, this disorder also afflicts younger patients. The majority of AD cases are late in onset, lack an obvious genetic etiology and are characterized as sporadic, whereas a small percentage of cases are early in onset and segregate strongly within families (FAD), suggesting a genetic etiology. During the past decade it has become evident that the clinical and histopathological phenotypes of this disease are caused by heterogeneous genetic, and probably environmental, factors. Indeed, several genes have been identified that together appear to cause most of the familial forms of the disease, whereas the epsilon4 allele of the apolipoprotein E (apoE) gene has been shown to be a significant risk factor for the late onset forms of AD. Despite this evidence of heterogeneity, it has been suggested that all of these factors work through a common pathway by triggering the deposition of amyloid in the brain, which is ultimately responsible for the neuronal degeneration of AD. This is a controversial theory, however, primarily because there is a poor correlation between the concentrations and distribution of amyloid depositions in the brain and several parameters of AD pathology, including degree of dementia, loss of synapses, loss of neurons and abnormalities of the cytoskeleton.

Medial temporal atrophy on MRI in normal aging and very mild Alzheimer's disease

Magnetic resonance imaging (MRI)-based volumetric measurements of medial temporal lobe (MTL) structures can discriminate between normal elderly control subjects and patients with Alzheimer's disease (AD) of moderate to advanced severity. In terms of clinical utility, however, a more important issue concerns the ability of the technique to differentiate between normal elderly control subjects and AD patients with the very mildest form of the disease. We performed MRI-based volumetric measurements of the hippocampus, parahippocampal gyrus, and amygdala in 126 cognitively normal elderly control subjects and 94 patients with probable AD. The diagnosis of AD was made according to NINDS/ADRDA criteria, and disease severity was categorized by Clinical Dementia Rating (CDR) scores. Patients with CDR 0.5 were classified as very mild, CDR 1 as mild, and CDR 2 as moderate disease severity. Volumes of each structure declined with increasing age in control subjects and did so in parallel for men and women. The volume of each measured MTL structure also declined with age in patients with AD. The volume of each MTL structure was significantly smaller in AD patients than control subjects (p < 0.001). Of the several MTL measures, the total hippocampal volumetric measurements were best at discriminating control subjects from AD patients. The mean hippocampal volumes for AD patients relative to control subjects by severity of disease were as follows: very mild AD (CDR 0.5) -1.75 SD below the control mean, mild AD (CDR 1) -1.99 SD, and moderate AD (CDR 2) -2.22 SD. Age- and gender-adjusted, normalized MRI-based hippocampal volumetric measurements provide a sensitive marker of the MTL neuroanatomic degeneration in AD early in the disease process.

Effects of apolipoprotein E on dementia and aging in the Shanghai Survey of Dementia

We investigated the status of the apolipoprotein E allele in 538 participants in the incidence phase of the ongoing Shanghai Survey of Dementia, including 103 demented subjects, 72 with mild cognitive impairment and 363 cognitively normal. The apo E epsilon 4 allele was present in 10.2% of control subjects and the allelic frequency did not change between ages 60 to 96 years. The apo E epsilon 4 allelic frequency was increased both in those wiht Alzheimer's disease (AD) (25.4%) and those with vascular dementia (VaD) (22.2%), but not in those with other dementing illnesses or the cognitively impaired. All of the subjects homozygous for apo E epsilon 4 were demented, three were diagnosed as having AD, and three met NINDS/AIREN criteria for VaD. The increased apo E epsilon 4 allelic frequency in clinically diagnosed VaD patients suggests that some of the infarcts are secondary to congophilic angiopathy. The adjusted odds ratio of developing AD in this community-derived study for persons with at least one apo E epsilon 4 allele was 4.1 (95% CI: 2.2, 7.7). Thus, the apo E epsilon 4 risk of developing AD in this Chinese cohort is similar to that in western community studies.

Risk of Alzheimer's disease and duration of NSAID use

In a longitudinal study of 1,686 participants in the Baltimore Longitudinal Study of Aging, we examined whether the risk of Alzheimer's disease (AD) was reduced among reported users of aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs). In addition, we examined use of acetaminophen, a pain-relief medication with little or no anti-inflammatory activity, to assess the specificity of the association between AD risk and self-reported medications. Information on use of medications was collected during each biennial examination between 1980 and 1995. The relative risk (RR) for AD decreased with increasing duration of NSAID use. Among those with 2 or more years of reported NSAID use, the RR was 0.40 (95% confidence interval [CI]: 0.19-0.84) compared with 0.65 (95% CI: 0.33-1.29) for those with less than 2 years of NSAID use. The overall RR for AD among aspirin users was 0.74 (95% CI: 0.46-1.18), and no trend of decreasing risk of AD was observed with increasing duration of aspirin use. No association was found between AD risk and use of acetaminophen (RR = 1.35; 95% CI: 0.79-2.30), and there was no trend of decreasing risk with increasing duration of use. These findings are consistent with evidence from cross-sectional studies indicating protection against AD risk among NSAID users and with evidence suggesting that one stage of the pathophysiology leading to AD is characterized by an inflammatory process.

Ionic effects of the Alzheimer's disease beta-amyloid precursor protein and its metabolic fragments

Alzheimer's disease is a progressive dementia characterized in part by deposition of proteinaceous plaques in various areas of the brain. The main plaque protein component is beta-amyloid, a metabolic product of the beta-amyloid precursor protein. Substantial evidence has implicated beta-amyloid (and other amyloidogenic fragments of the precursor protein) with the neurodegeneration observed in Alzheimer's disease. Recently, beta-amyloid precursor protein and its amyloidogenic metabolic fragments have been shown to alter cellular ionic activity, either through interaction with existing channels or by de novo channel formation. Such alteration in ionic homeostasis has also been linked with cellular toxicity and might provide a molecular mechanism underlying the neurodegeneration seen in Alzheimer's disease.

Beta-amyloid peptide blocks the fast-inactivating K+ current in rat hippocampal neurons

Deposition of beta-amyloid peptide (A beta) in senile plaques is a hallmark of Alzheimer disease neuropathology. Chronic exposure of neuronal cultures to synthetic A beta is directly toxic, or enhances neuronal susceptibility to excitotoxins. Exposure to A beta may cause a loss of cellular calcium homeostasis, but the mechanism by which this occurs is uncertain. In this work, the acute response of rat hippocampal neurons to applications of synthetic A beta was measured using whole-cell voltage-clamp techniques. Pulse application of A beta caused a reversible voltage-dependent decrease in membrane conductance. A beta selectively blocked the voltage-gated fast-inactivating K+ current, with an estimated KI < 10 microM. A beta also blocked the delayed rectifying current, but only at the highest concentration tested. The response was independent of aggregation state or peptide length. The dynamic response of the fast-inactivating current to a voltage jump was consistent with a model whereby A beta binds reversibly to closed channels and prevents their opening. Blockage of fast-inactivating K+ channels by A beta could lead to prolonged cell depolarization, thereby increasing Ca2+ influx.

Ion channel hypothesis for Alzheimer amyloid peptide neurotoxicity

1. Alzheimer's disease (AD) is a chronic dementia and neurodegenerative disorder affecting the oldest portions of the population. Brains of AD patients accumulate large amount of the A beta P peptide in amyloid plaques. 2. The A beta P[1-40] peptide is derived by proteolytic processing from a much larger amyloid precursor protein (APP), and has been circumstantially identified as the toxic principle causing cell damage in the disease. 4. The A beta P[1-40] peptide is able to form quite characteristic calcium channels in planar lipid bilayers. These channels have conductances in the nS range, and can dissipate ion gradients quickly. The peptide can also cause equivalent cation conductances in cells. 5. We suggest that amyloid channel blocking agents might be therapeutically useful in Alzheimer's Disease, and have constructed molecular models of the channels to aid in the design of such compounds.

Amyloid beta protein (25-35) stimulation of phospholipases A, C and D activities of LA-N-2 cells

[3H]Myristic acid prelabeled LA-N-2 cells were exposed to varying concentrations of amyloid beta protein (25-35), from 20 to 250 micrograms/ml, and the activation of phospholipases A and D estimated. A progressive increase in phosphatidylethanol formation, a measure of phospholipase D activity, and of free fatty acid release, a measure of phospholipase A activity, was observed over a time-course of 60 min. [3H]Inositol prelabeled LA-N-2 cells were exposed to varying concentrations of A beta P, from 20 to 125 micrograms/ml, and phospholipase C activation was measured. There was an increased release of inositol phosphates in the presence of amyloid beta protein as a function of incubation time. The effects of adrenergic, metabotropic amino acid and bombesin antagonists on the A beta P mediated stimulation of phospholipase C activity was investigated. Propranolol, a beta adrenergic antagonist, 7-chloro-kynurenic acid, a metabotropic amino acid antagonist, and [Tyr4-D-Phe12]bombesin, a bombesin antagonist, blunted the A beta P stimulation of phospholipase C activity in [3H]inositol prelabeled LA-N-2 cells. This suggests that amyloid beta protein activation of phospholipase C may be receptor mediated. The phospholipase C inhibitor U 71322 prevented the activation of phospholipase C by A beta P. However, this activation was not effected by tocopherol, propylgallate, or vitamin C.