Aqueous dissolution of Alzheimer's disease Abeta amyloid deposits by biometal depletion

Metal binding and oxidation of amyloid-beta within isolated senile plaque cores: Raman microscopic evidence

Alzheimer's disease (AD) is characterized by the deposition of amyloid plaques in the parenchyma and vasculature of the brain. Although previous analytical studies have provided much information about the composition and structure of synthetic amyloid-beta fibrils, there is, surprisingly, a dearth of data on intact amyloid plaques from AD brain. Therefore, to elucidate the structure and detailed composition of isolated amyloid plaque cores, we utilized a high-resolution, nondestructive technique, Raman microscopy. The data are of very high quality and contain detailed information about protein composition and conformation, about post-translational modification, and about the chemistry of metal binding sites. Remarkably, spectra obtained for senile plaque (SP) cores isolated from AD brain are essentially identical both within and among brains. The Raman data show for the first time that the SP cores are composed largely of amyloid-beta and confirm inferences from X-ray studies that the structure is beta-sheet with the additional possibility that this may be present as a parallel beta-helix. Raman bands characteristic of methionine sulfoxide show that extensive methionine oxidation has occurred in the intact plaques. The Raman spectra also demonstrate that Zn(II) and Cu(II) are coordinated to histidine residues in the SP cores, at the side chains' N(tau) and N(pi) atoms, respectively. Treatment of the senile plaques with the chelator ethylenediaminetetraacetate reverses Cu binding to SP histidines and leads to a broadening of amide features, indicating a "loosening" of the beta-structure. Our results indicate that Abeta in vivo is a metalloprotein, and the loosening of the structure following chelation treatment suggests a possible means for the solubilization of amyloid deposits. The results also reveal a direct chemical basis for oxidative damage caused by amyloid-beta protein in AD.

In vitro fibrillogenesis of the amyloid beta 1-42 peptide: cholesterol potentiation and aspirin inhibition

Understanding the formation of extracellular amyloid neurofibrillar bundles/senile plaques and their role in the development of Alzheimer's disease is of considerable interest to neuroscientists and clinicians. Major components of the extracellular neurofibrillar bundles are polymerized amyloid beta (Abeta) peptides (1-40), (1-42) and (1-43), derived in vivo from the soluble amyloid precursor protein (sAPP) by proteolytic (beta- and gamma-secretase) cleavage. The Abeta(1-42) peptide is widely considered to be of greatest significance in relation to the pathogenesis of Alzheimer's disease. A well-defined ultrastructural characteristic within Alzheimer dense plaques is the presence of helical fibrils that are believed to consist of polymerized amyloid beta, together with other associated proteins such as the serum amyloid P protein, apolipoprotein E isoform epsilon 4, alpha1-anti-chymotrypsin, catalase, glycoproteins, proteoglycans, cholesterol and other lipids. The spontaneous in vitro fibrillogenesis of chemically synthesized Abeta(1-42) peptide (rat sequence), following 20h incubation at 37 degrees C, has been assessed from uranyl acetate negatively stained specimens studied by transmission electron microscopy (TEM). Amyloid beta(1-42) peptide fibrillogenesis in the presence of cholesterol has been investigated using aqueous suspensions of microcrystalline cholesterol and cholesteryl acetate, globular particles of cholesteryl oleate, a soluble (micellar) cholesterol derivative (polyoxyethyl cholesteryl sebacate/cholesteryl PEG 600 sebacate), cholesterol-sphingomyelin liposomes and sphingomyelin liposomes. In all these cases, with the exception of cholesteryl oleate, considerable potentiation of long smooth helical fibril formation occurred, compared to 20h 37 degrees C control samples containing the Abeta(1-42) peptide alone. The binding of polyoxyethyl cholesteryl sebacate micelles to helical Abeta fibrils/filaments and the binding of fibrils to the surface of cholesterol and cholesteryl acetate microcrystals, and to a lesser extent on cholesteryl oleate globules, indicates an affinity of the Abeta peptide for cholesterol. This potentiation of Abeta(1-42) polymerization is likely to be mediated at the molecular level via hydrophobic interaction between the amino acid side chains of the peptide and the tetracyclic sterol nucleus. Addition of cupric sulphate (0.1mM) to the Abeta solution produced large disorganized fibril aggregates. Inclusion of 1mM aspirin (sodium acetylsalicylate) in the Abeta peptide alone and as an addition to Abeta peptide solution containing cholesterol, cholesteryl acetate, soluble cholesterol, sphingomyelin and sphingomyelin-cholesterol liposomes, and to 0.1mM cupric sulphate solution, completely inhibited fibrillogenesis. Instead, only non-crystalline diffuse, non-filamentous microaggregates of insoluble Abeta particles were found, free and attached to the sterol particles. The in vitro system presented here provides a way to rapidly monitor at the structural/TEM level other compounds (e.g. chelating agents, drugs, beta-sheet breaking peptides and anti-oxidants) for their effects on amyloid beta peptide fibrillogenesis (and on preformed fibril disassembly) in parallel with in vitro biochemical studies and in vivo studies using animal models of Alzheimer's disease as well as studies on man.

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

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

Genetic and environmental factors in cancer and neurodegenerative diseases

The aim of this review is to summarise the recent findings in the fields of carcinogenesis and neurodegenerative diseases, the both disorders are characterised by the contribution of different factors including the inheritance of mutated genes, and the exposure to endogenous or exogenous agents during the life. We first analysed the causative genes until now discovered in both processes, then we focused our attention on the role of environmental exposure, susceptibility factors, oxidative stress, apoptosis and aging to the development of such disorders. The genotype at a particular locus may account for an inter-individual susceptibility that can both increase or decrease the risk to develop the pathology especially after the exposure to environmental agents. The mechanism of apoptosis, that is an excellent strategy in order to eliminate damaged cells, seems to be lost during carcinogenesis, while it seems to be involved in the neuronal death in a lot of neurodegenerative disorders. Oxidative stress can both lead to DNA mutations or to the formation of damaged proteins, so being an important risk factor for the initiation and the progression of a disease: in fact it may be one of the causes or can arise as a consequence of a damage caused by other factors increasing then the first damage. It is well established that carcinogenesis is a multi-step process caused by series of successive mutations occurring into a cell and conferring to this cell a growth advantage, so that age is the largest risk factor for cancer in humans. Pathophysiology of neurodegenerative diseases is complex and likely involves multiple overlapping and perhaps redundant pathways of neuronal damage, characterised by the generation of anomalous proteins, often due to mutations in the corresponding gene, and by their subsequent accumulation into or outside specific areas of the brain.

Overexpression of Alzheimer's disease amyloid-beta opposes the age-dependent elevations of brain copper and iron

Increased brain metal levels have been associated with normal aging and a variety of diseases, including Alzheimer's disease (AD). Copper and iron levels both show marked increases with age and may adversely interact with the amyloid-beta (Abeta) peptide causing its aggregation and the production of neurotoxic hydrogen peroxide (H(2)O(2)), contributing to the pathogenesis of AD. Amyloid precursor protein (APP) possesses copper/zinc binding sites in its amino-terminal domain and in the Abeta domain. Here we demonstrate that overexpression of the carboxyl-terminal fragment of APP, containing Abeta, results in significantly reduced copper and iron levels in transgenic mouse brain, while overexpression of the APP in Tg2576 transgenic mice results in significantly reduced copper, but not iron, levels prior to the appearance of amyloid neuropathology and throughout the lifespan of the mouse. Concomitant increases in brain manganese levels were observed with both transgenic strains. These findings, complemented by our previous findings of elevated copper levels in APP knock-out mice, support roles for APP and Abeta in physiological metal regulation.

Metal complexing agents as therapies for Alzheimer's disease

Modern research approaches into drug development for Alzheimer's disease (AD) target beta-amyloid (Abeta) accumulation in the brain. The main approaches attempt to prevent Abeta production (secretase inhibitors) or to clear Abeta (vaccine). However, there is now compelling evidence that Abeta does not spontaneously aggregate, but that there is an age-dependent reaction with excess brain metal (copper, iron and zinc), which induces the protein to precipitate into metal-enriched masses (plaques). The abnormal combination of Abeta with Cu or Fe induces the production of hydrogen peroxide, which may mediate the conspicuous oxidative damage to the brain in AD. We have developed metal-binding compounds that inhibit the in vitro generation of hydrogen peroxide by Abeta, as well as reverse the aggregation of the peptide in vitro and from human brain post-mortem specimens. Most recently, one of the compounds, clioquinol (CQ; a USP antibiotic) was given orally for 9 weeks to amyloid-bearing transgenic mice, and succeeded in markedly inhibiting Abeta accumulation. On the basis of these results, CQ is being tested in clinical trials.

Metalloenzyme-like activity of Alzheimer's disease beta-amyloid. Cu-dependent catalytic conversion of dopamine, cholesterol, and biological reducing agents to neurotoxic H(2)O(2)

Beta-amyloid (Abeta) 1-42, implicated in the pathogenesis of Alzheimer's disease, forms an oligomeric complex that binds copper at a CuZn superoxide dismutase-like binding site. Abeta.Cu complexes generate neurotoxic H(2)O(2) from O(2) through Cu(2+) reduction, but the reaction mechanism has been unclear. We now report that Abeta1-42, when binding up to 2 eq of Cu(2+), generates the H(2)O(2) catalytically by recruiting biological reducing agents as substrates under conditions where the Cu(2+) or reducing agents will not form H(2)O(2) themselves. Cholesterol is an important substrate for this activity, as are vitamin C, L-DOPA, and dopamine (V(max) for dopamine = 34.5 nm/min, K(m) = 8.9 microm). The activity was inhibited by anti-Abeta antibodies, Cu(2+) chelators, and Zn(2+). Toxicity of Abeta in neuronal culture was consistent with catalytic H(2)O(2) production. Abeta was not toxic in cell cultures in the absence of Cu(2+), and dopamine (5 microm) markedly exaggerated the neurotoxicity of 200 nm Abeta1-42.Cu. Therefore, microregional catalytic H(2)O(2) production, combined with the exhaustion of reducing agents, may mediate the neurotoxicity of Abeta in Alzheimer's disease, and inhibitors of this novel activity may be of therapeutic value.

Coordination of copper(II) ions by the 11-20 and 11-28 fragments of human and mouse beta-amyloid peptide

A potentiometric and spectroscopic (UV-vis, CD and EPR) study of Cu(II) binding to the (11-20), (11-28), (Ac-11-20H) and (Ac-11-28) fragments of human (H) and mouse (M) beta-amyloid peptide was carried out. The values of the protonation constants of the two lysine side chain amino groups for the (11-28) and (Ac-11-28) fragments of beta-amyloid peptide differ noticeably suggesting considerable interactions between the two residues. The N-terminal amino acid sequence Xaa-Yaa-His for the (11-20H) and (11-28H) fragments determines the coordination ability of the fragments studied to copper(II) ions. Addition of the (17-20) and (17-28) sequences to the (11-16) fragment of human and mouse beta-amyloid peptide does not change the coordination mode, and the stabilities of the complexes formed are comparable to those of the (11-16) peptide, although 1N complexes of the (11-28) fragments are stabilized by about one order of magnitude compared to those of the (11-16) peptides. The (Ac-11-28) peptides form complexes with the same coordination mode as those for the (Ac-11-16) fragments. The stability of the complexes for the (Ac-11-28H) fragment is one or two orders of magnitude higher compared to those of the (Ac-11-16H) fragment. This stabilization may result from structural organization of a peptide in copper(II) complexes.

Evidence for a copper-binding superfamily of the amyloid precursor protein

The amyloid precursor protein (APP) copper-binding domain (CuBD) has been shown to reduce Cu(II) to Cu(I) and to mediate copper-induced oxidation in vitro. However, little is known about copper binding to the homologous domains of APP and APP family paralogs and orthologs (including amyloid precursor-like proteins from Drosophila melanogaster, Xenopus laevis, and Caenorhabditis elegans) and their effects on Cu-induced oxidation and Cu(I) formation. Here, we show that APP homologues with and without conserved histidine residues at positions 147, 149, and 151 all bind Cu(II). Oxidized peptides were the kinetically favored products of the redox reaction of CuBDs promoting the reduction of Cu(II) to Cu(I). These results reveal a molecular phylogeny-based divergence that has taken place between the ancestral Drosophila APPL and C. elegans APL-1 and the recently evolved APP lineage of CuBDs. Whereas higher species CuBDs have a decreased affinity for Cu(II) and high Cu(II) reducing activities, ancestral CuBDs form very tight binding sites for Cu(II) ions and have low Cu(II) reducing activities. Thus, the APP lineage displays a gain in activity toward promoting Cu(II) reduction and Cu(I) release. The findings suggests that the Cu(II)-binding equilibrium at the phylogenetic stage of Drosophila APPL and C. elegans APL-1 is shifted from the exchangeable Cu(II) pool to the tightly bound, nonexchangeable pool and that ancestral CuBDs may exert antioxidation activities in vivo. The more recently evolved homologues of human APP appear to take advantage of unique redox properties for yet unknown biological functions.

The role of iron and copper in the aetiology of neurodegenerative disorders: therapeutic implications

Abnormalities in the metabolism of the transition metals iron and copper have been demonstrated to play a crucial role in the pathogenesis of various neurodegenerative diseases. Metal homeostasis as it pertains to alterations in brain function in neurodegenerative diseases is reviewed in this article in depth. While there is documented evidence for alterations in the homeostasis, redox-activity and localisation of transition metals, it is also important to realise that alterations in specific copper- and iron-containing metalloenzymes appear to play a crucial role in the neurodegenerative process. These changes provide the opportunity to identify pathways where modification of the disease process can occur, potentially offering opportunities for clinical intervention. As understanding of disease aetiology evolves, so do the tools with which diseases are treated. In this article, we examine not only the possible mechanism of disease but also how pharmaceuticals may intervene, from direct and indirect antioxidant therapy to strategies involving gene therapy.

Senile plaque composition and posttranslational modification of amyloid-beta peptide and associated proteins

Amyloid deposits are primarily composed of the amyloid-beta protein, although other proteins (and metal ions) also have been colocalized to these lesions. The pattern of oxidative modifications in amyloid plaques is very different to that associated with neurofibrillary tangles and neuronal cell bodies, likely reflecting the different composition of these structures, accessibility of oxidants, the generation of oxidants in and around these structures and the intrinsic antioxidant defense systems to protect these structures. Future studies directed at understanding Abeta interactions with other amyloid components, the role of oxidative modifications in stabilizing amyloid deposits and the determination of protease cleavage sites on Abeta may provide mechanistic insights regarding both amyloid formation and removal.

Novel therapeutic strategies provide the real test for the amyloid hypothesis of Alzheimer's disease

The amyloid and tangle cascade hypothesis is the dominant explanation for the pathogenesis of Alzheimer's disease (AD). A complete knowledge of the metabolic pathways leading to beta-amyloid (A beta) production and clearance in vivo and of the pathological events that lead to fibril formation and deposition into plaques is crucial for the development of an 'anti-amyloid' therapeutic strategy. Important advances in this respect have been achieved recently, revealing new candidate drug targets. Among the most promising potential treatments are beta- and gamma-secretase inhibitors, A beta vaccination, Cu-Zn chelators, cholesterol-lowering drugs and non-steroidal anti-inflammatory drugs. Now, the major question is whether these drugs will work in the clinic.

Possible mechanisms of APP-mediated oxidative stress in Alzheimer's disease

Oxidative stress was presented to play an important role in the pathogenesis of Alzheimer's disease (AD), especially in the early evolution of AD amyloidogenesis and not only as a consequence thereof. The effect of oxidative stress catalysed by transition metals appears to have a critical relevance in AD. Metal-ion homeostasis is severely dysregulated in AD and it was found that experimentally induced disturbances in the homeostasis of Zn(II) and Cu(II) affect the amyloid precursor protein (APP) metabolism. APP itself binds Zn(II) and Cu(II) at nanomolar concentrations and an altered APP metabolism or expression level is believed to result in neurotoxic processes.

Biogenesis and metabolism of Alzheimer's disease Abeta amyloid peptides

Biochemical and genetic evidence indicates the balance of biogenesis/clearance of Abeta amyloid peptides is altered in Alzheimer's disease. Abeta is derived, by two sequential cleavages, from the receptor-like amyloid precursor protein (APP). The proteases involved are beta-secretase, identified as the novel aspartyl protease BACE, and gamma-secretase, a multimeric complex containing the presenilins (PS). Gamma-secretase can release either Abeta40 or the more aggregating and cytotoxic Abeta42. Secreted Abeta peptides become either degraded by the metalloproteases insulin-degrading enzyme (IDE) and neprilysin or metabolized through receptor uptake mediated by apolipoprotein E. Therapeutic approaches based on secretase inhibition or amyloid clearance are currently under development.

Lipid peroxidation in neurodegeneration: new insights into Alzheimer's disease

Imbalances of oxidative homeostasis and lipid peroxidation have been revealed as important factors involved in neurodegenerative disorders such as Alzheimer's disease. The brains of patients with Alzheimer's disease contain increased levels of lipid-peroxidation products such as 4-hydroxy-2-nonenal or acrolein, and enhanced lipid peroxidation can also be detected in cerebrospinal fluid and plasma from such patients. Recent research revealed that the interplay of transition metals, amyloid-beta peptide and lipid peroxidation might be responsible for increased oxidative stress and cell damage in this disease. In particular, the contrasting roles of amyloid-beta peptide, as a possible transition metal-chelating antioxidant for lipoproteins and a pro-oxidant when aggregated in brain tissue, has been the focus of discussion recently. In this context, lipid peroxidation has to be seen as an important part of the pathophysiological cascade in Alzheimer's disease, and its measurement in body fluids might serve as a therapy control for Alzheimer's disease and other neurodegenerative diseases.

Physiopathological modulators of amyloid aggregation and novel pharmacological approaches in Alzheimer's disease

The biological mechanisms underlying the neuropathology of Alzheimer's disease (AD) are complex, as several factors likely contribute to the development of the disease. Therefore, it is not surprising that a number of different possible therapeutic approaches addressing distinct aspects of this disease are currently being investigated. Among these are ways to prevent amyloid aggregation and/or deposition, to prevent neuronal degeneration, and to increase brain neurotransmitter levels. Here, we discuss possible roles of endogenous modulators of Abeta aggregation in the physiopathology of AD and some of the strategies currently under consideration to interfere with brain levels of beta-amyloid, its aggregation and neurotoxicity.

Hohenheim consensus workshop: copper

Copper (Cu) is an essential trace element with many physiological functions. Homeostatic mechanisms exist to allow Cu to act as a cofactor in enzymatic processes and to prevent accumulation of Cu to toxic levels. The aim of this commentary is to better understand the role of dietary Cu supply in deficiency and under physiological and pathological conditions. The essentiality of Cu can be attributed to its role as a cofactor in a number of enzymes that are involved in the defence against oxidative stress. Cu, however, has a second face, that of a toxic compound as it is observed with accumulating evidence in hepatic, neurodegenerative and cardiovascular diseases. The destructive potential of Cu can be attributed to inherent physico-chemical properties. The main property is its ability to take part in Fenton-like reactions in which the highly reactive and extremely deleterious hydroxyl radical is formed. Diseases caused by dietary Cu overload could be based on a genetic predisposition. Thus, an assessment of risk-groups, such as infants with impaired mechanisms of Cu homeostasis regarding detoxification, is of special interest, as their Cu intake with resuspended formula milk may be very high. This implies the need for reliable diagnostic markers to determine the Cu status. These topics were introduced at the workshop by the participants followed by extensive group discussion. The consensus statements were agreed on by all members. One of the conclusions is that a re-assessment of published data is necessary and future research is required.

Reduction of amyloid load and cerebral damage in a transgenic mouse model of Alzheimer's disease by treatment with a beta-sheet breaker peptide

Genetic, neuropathological, and biochemical studies have provided strong evidence for a central role of amyloid in the pathogenesis of Alzheimer's disease (AD). We have proposed previously that peptides designed as beta-sheet breakers may be useful in preventing the formation of amyloid plaques. In this study, we describe a modified beta-sheet breaker peptide with improved pharmacological properties, a high rate of penetration across the blood-brain barrier, and the ability to induce a dramatic reduction in amyloid deposition in two different transgenic AD models. In addition, we report for the first time a significant increase in neuronal survival and a decrease in brain inflammation associated with the reduction of amyloid plaques. These results demonstrate that the process of amyloid deposition is one of the causes of neurodegeneration in AD. Moreover, our findings indicate that beta-sheet breaker peptides provide a valuable tool for evaluating further the importance of amyloid in the etiology of AD and suggest that these peptides or some of their derivatives might be good candidates for AD treatment.

Contribution by synaptic zinc to the gender-disparate plaque formation in human Swedish mutant APP transgenic mice

Endogenous metals may contribute to the accumulation of amyloid plaques in Alzheimer's disease. To specifically examine the role of synaptic zinc in the plaque accumulation, Tg2576 (also called APP2576) transgenic mice (hAPP(+)) expressing cerebral amyloid plaque pathology were crossed with mice lacking zinc transporter 3 (ZnT3(-/-)), which is required for zinc transport into synaptic vesicles. With aging, female hAPP(+):ZnT3(+/+) mice manifested higher levels of synaptic zinc, insoluble amyloid beta, and plaques than males; these sex differences disappeared in hAPP(+):ZnT3(-/-) mice. Both sexes of hAPP(+):ZnT3(-/-) mice had markedly reduced plaque load and less insoluble amyloid beta compared with hAPP(+):ZnT3(+/+) mice. Hence, of endogenous metals, synaptic zinc contributes predominantly to amyloid deposition in hAPP(+) mice.

Scavenger receptor class B type I expression and elemental analysis in cerebellum and parietal cortex regions of the Alzheimer's disease brain

Metal ions play an important role in health and disease by influencing cellular biochemical pathways. The increased concentrations of some metal ions may have cytotoxic effects through their ability to oxidatively modify biomolecules, which may cause oxidative stress-induced brain cell death leading to neurodegenerative disorders observed in Alzheimer's disease (AD). We therefore performed elemental analysis of human brain tissues by a sophisticated method of inductively coupled plasma mass spectrometry (ICP-MS) in two regions of the AD brain, the parietal cortex and cerebellum, and compared them with the age-matched control. Our analysis shows the differential distribution of some metal ions in the two regions of the brain. Most importantly, Si, Sn, Al and Mn showed significantly higher levels in the parietal cortex of the AD brain compared to the control. The other metal ions showing moderate increases in the parietal cortex were Na, Te, Cr, Fe and B. Since these metal ions can modify lipoproteins in the brain and modified lipoproteins are taken up by scavenger receptors class B type I (SR-BI), we also determined the presence of SR-BI in the parietal cortex and cerebellum regions of the control and AD brains using a sensitive method, the reverse transcriptase-polymerase chain reaction. Our results suggest that SR-BI are present in the parietal cortex as well as in the cerebellum of the control and AD brains, suggesting that the presence of SR-BI may be involved in the uptake of oxidatively modified lipoproteins and beta-amyloid (Abeta) protein complexed with apoE, suggesting implications in the progression of late onset AD and other neurodegenerative disorders characterized by the deposition of insoluble aggregates observed in the AD brain.

Role of free radicals in the neurodegenerative diseases: therapeutic implications for antioxidant treatment

Free radicals and other so-called 'reactive species' are constantly produced in the brain in vivo. Some arise by 'accidents of chemistry', an example of which may be the leakage of electrons from the mitochondrial electron transport chain to generate superoxide radical (O2*-). Others are generated for useful purposes, such as the role of nitric oxide in neurotransmission and the production of O2*- by activated microglia. Because of its high ATP demand, the brain consumes O2 rapidly, and is thus susceptible to interference with mitochondrial function, which can in turn lead to increased O2*- formation. The brain contains multiple antioxidant defences, of which the mitochondrial manganese-containing superoxide dismutase and reduced glutathione seem especially important. Iron is a powerful promoter of free radical damage, able to catalyse generation of highly reactive hydroxyl, alkoxyl and peroxyl radicals from hydrogen peroxide and lipid peroxides, respectively. Although most iron in the brain is stored in ferritin, 'catalytic' iron is readily mobilised from injured brain tissue. Increased levels of oxidative damage to DNA, lipids and proteins have been detected by a range of assays in post-mortem tissues from patients with Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis, and at least some of these changes may occur early in disease progression. The accumulation and precipitation of proteins that occur in these diseases may be aggravated by oxidative damage, and may in turn cause more oxidative damage by interfering with the function of the proteasome. Indeed, it has been shown that proteasomal inhibition increases levels of oxidative damage not only to proteins but also to other biomolecules. Hence, there are many attempts to develop antioxidants that can cross the blood-brain barrier and decrease oxidative damage. Natural antioxidants such as vitamin E (tocopherol), carotenoids and flavonoids do not readily enter the brain in the adult, and the lazaroid antioxidant tirilazad (U-74006F) appears to localise in the blood-brain barrier. Other antioxidants under development include modified spin traps and low molecular mass scavengers of O2*-. One possible source of lead compounds is the use of traditional remedies claimed to improve brain function. Little is known about the impact of dietary antioxidants upon the development and progression of neurodegenerative diseases, especially Alzheimer's disease. Several agents already in therapeutic use might exert some of their effects by antioxidant action, including selegiline (deprenyl), apomorphine and nitecapone.

'...and C is for Clioquinol' - the AbetaCs of Alzheimer's disease

Alzheimer's disease (AD) is a devastating age-related neurodegenerative disorder that has been intensively studied over the last several years. In vitro and in vivo studies have led to an understanding of some of the physico-chemical properties of amyloid, a well-characterized hallmark of AD. Clioquinol is a drug that acts on amyloid by perturbing amyloid's metallo-chemistry, and Clioquinol treatment has been shown to be beneficial in a mouse model of AD. This short review examines the recent studies relating to Clioquinol and AD, and anticipates the imminent results of a Phase II trial of Clioquinol in AD, due in March 2002.

Carbonic anhydrase gating of attention: memory therapy and enhancement

Enhancement of memory acquisition and recall represents an important pharmacological goal in the treatment of cognitive disorders. In addition to its involvement in pH regulation, HCO3- reabsorption and CO2 expiration, carbonic anhydrase plays a crucial role in signal processing, long-term synaptic transformation and attentional gating of memory storage. Carbonic anhydrase dysfunction impairs cognition and is associated with mental retardation, Alzheimer's disease and aging. The pharmacological profile of carbonic anhydrase has been refined and specific activators have been developed. In this article, an integrated view of the involvement of carbonic anhydrase activity in synaptic plasticity and cognition will be presented, with particular focus on attentional gating of spatial learning and memory.

Contrasting, species-dependent modulation of copper-mediated neurotoxicity by the Alzheimer's disease amyloid precursor protein

The amyloid precursor protein (APP) of Alzheimer's disease (AD) has a copper binding domain (CuBD) located in the N-terminal cysteine-rich region that can strongly bind copper(II) and reduce it to Cu(I) in vitro. The CuBD sequence is similar among the APP family paralogs [amyloid precursor-like proteins (APLP1 and APLP2)] and its orthologs (including Drosophila melanogaster, Xenopus laevis, and Caenorhabditis elegans), suggesting an overall conservation in its function or activity. The APP CuBD is involved in modulating Cu homeostasis and amyloid beta peptide production. In this paper, we demonstrate for the first time that Cu-metallated full-length APP ectodomain induces neuronal cell death in vitro. APP Cu neurotoxicity can be induced directly or potentiated through Cu(I)-mediated oxidation of low-density lipoprotein, a finding that may have important implications for the role of lipoproteins and membrane cholesterol composition in AD. Cu toxicity induced by human APP, Xenopus APP, and APLP2 CuBDs is dependent on conservation of histidine residues at positions corresponding to 147 and 151 of human APP. Intriguingly, APP orthologs with different amino acid residues at these positions had dramatically altered Cu phenotypes. The corresponding C. elegans APL-1 CuBD, which has tyrosine and lysine residues at positions 147 and 151, respectively, strongly protected against Cu-mediated lipid peroxidation and neurotoxicity in vitro. Replacement of histidines 147 and 151 with tyrosine and lysine residues conferred this neuroprotective Cu phenotype to human APP, APLP2, and Xenopus APP CuBD peptides. Moreover, we show that the toxic and protective CuBD phenotypes are associated with differences in Cu binding and reduction. These studies identify a significant evolutionary change in the function of the CuBD in modulating Cu metabolism. Our findings also suggest that targeting of inhibitors to histidine residues at positions 147 and 151 of APP could significantly alter the oxidative potential of APP.

Amyloid-beta: an antioxidant that becomes a pro-oxidant and critically contributes to Alzheimer's disease

Elevated production of amyloid-beta (A beta) as a preventive antioxidant for brain lipoproteins under the action of increased oxidative stress in aging is postulated to represent a major event in the development of Alzheimer's disease (AD). Increase in A beta production is followed by chelation of transition metal ions by A beta, accumulation of A beta-metal lipoprotein aggregates, production of reactive oxygen species and neurotoxicity. Chelation of copper by A beta is proposed to be a most important part of this pathway, because A beta binds copper stronger than other transition metals and because copper is a more efficient catalyst of oxidation than other metals. This amyloid-binds-copper (ABC) model does not remove A beta peptide from its central place in our current thinking of AD, but rather places additional factors in the center of discussion. Most importantly, they embrace pathological mechanisms known to develop in aging (which is the major risk factor for AD), such as increased production of reactive oxygen species by mitochondria, that are positioned upstream relative to the generation of A beta.

New insights on how metals disrupt amyloid beta-aggregation and their effects on amyloid-beta cytotoxicity

Amyloid-beta protein (A beta) aggregates in the brain to form senile plaques. By using thioflavin T, a dye that specifically binds to fibrillar structures, we found that metals such as Zn(II) and Cu(II) normally inhibit amyloid beta-aggregation. Another method for detecting A beta, which does not distinguish the types of aggregates, showed that these metals induce a non-beta-sheeted aggregation, as reported previously. Secondary structural analysis and microscopic studies revealed that metals induced A beta to make non-fibrillar aggregates by disrupting beta-sheet formation. These non-fibrillar A beta aggregates displayed much weaker Congo Red birefringence, and in separate cell culture experiments, were less toxic than self beta-aggregates, as demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. The toxicity of soluble A beta was enhanced in the presence of Cu(II), which suggests the previously hypothesized role of A beta in generating oxidative stress. Finally, under an acidic condition, similar to that in the inflammation associated with senile plaques, beta-aggregation was robustly facilitated at one specific concentration of Zn(II) in the presence of heparin. However, because a higher concentration of Zn(II) virtually abolished this abnormal phenomenon, and at normal pH any concentrations strongly inhibit beta-aggregation and its associated cytotoxicity, including its anti-oxidative nature we suggest that Zn(II) has an overall protective effect against beta-amyloid toxicity.

Zinc enhances synthesis of presenilin 1 in mouse primary cortical culture

Whether zinc interacts with presenilin 1 (PS1), one of the causative genes of familial Alzheimer's disease (AD), is not known. Here we report that zinc modulates the synthesis of PS1. Exogenous zinc enhanced the amount of C-terminal fragments of PS1 (PS1-CTF) in neonatal mouse cortical cultures in a dose-dependent manner. Zinc also induced cell death in a dose-dependent manner. These effects of zinc were not mimicked by calcium, copper, or iron, and were blocked by a zinc-specific chelator, TPEN. Experiments using metabolic labeling and cycloheximide treatment revealed that zinc increased PS1-CTF by elevating the de novo synthesis of PS1. Time course experiments revealed that cell death commenced sooner (0.5-1 h) than enhancement of PS1-CTF (1-2 h) following zinc treatment. However, the amount of PS1-CTF remained unchanged during etoposide- or H(2)O(2)-induced cell death, suggesting that enhancement of PS1 synthesis is specifically correlated with zinc-induced cell death.

Copper and zinc binding modulates the aggregation and neurotoxic properties of the prion peptide PrP106-126

The abnormal form of the prion protein (PrP) is believed to be responsible for the transmissible spongiform encephalopathies. A peptide encompassing residues 106-126 of human PrP (PrP106-126) is neurotoxic in vitro due its adoption of an amyloidogenic fibril structure. The Alzheimer's disease amyloid beta peptide (Abeta) also undergoes fibrillogenesis to become neurotoxic. Abeta aggregation and toxicity is highly sensitive to copper, zinc, or iron ions. We show that PrP106-126 aggregation, as assessed by turbidometry, is abolished in Chelex-100-treated buffer. ICP-MS analysis showed that the Chelex-100 treatment had reduced Cu(2+) and Zn(2+) levels approximately 3-fold. Restoring Cu(2+) and Zn(2+) to their original levels restored aggregation. Circular dichroism showed that the Chelex-100 treatment reduced the aggregated beta-sheet content of the peptide. Electron paramagnetic resonance spectroscopy identified a 2N1S1O coordination to the Cu(2+) atom, suggesting histidine 111 and methionine 109 or 112 are involved. Nuclear magnetic resonance confirmed Cu(2+) and Zn(2+) binding to His-111 and weaker binding to Met-112. An N-terminally acetylated PrP106-126 peptide did not bind Cu(2+), implicating the free amino group in metal binding. Mutagenesis of either His-111, Met-109, or Met-112 abolished PrP106-126 neurotoxicity and its ability to form fibrils. Therefore, Cu(2+) and/or Zn(2+) binding is critical for PrP106-126 aggregation and neurotoxicity.

Alzheimer's disease amyloid-beta binds copper and zinc to generate an allosterically ordered membrane-penetrating structure containing superoxide dismutase-like subunits

Amyloid beta peptide (Abeta) is the major constituent of extracellular plaques and perivascular amyloid deposits, the pathognomonic neuropathological lesions of Alzheimer's disease. Cu(2+) and Zn(2+) bind Abeta, inducing aggregation and giving rise to reactive oxygen species. These reactions may play a deleterious role in the disease state, because high concentrations of iron, copper, and zinc have been located in amyloid in diseased brains. Here we show that coordination of metal ions to Abeta is the same in both aqueous solution and lipid environments, with His(6), His(13), and His(14) all involved. At Cu(2+)/peptide molar ratios >0.3, Abeta coordinated a second Cu(2+) atom in a highly cooperative manner. This effect was abolished if the histidine residues were methylated at N(epsilon)2, indicating the presence of bridging histidine residues, as found in the active site of superoxide dismutase. Addition of Cu(2+) or Zn(2+) to Abeta in a negatively charged lipid environment caused a conformational change from beta-sheet to alpha-helix, accompanied by peptide oligomerization and membrane penetration. These results suggest that metal binding to Abeta generated an allosterically ordered membrane-penetrating oligomer linked by superoxide dismutase-like bridging histidine residues.

Treatment with a copper-zinc chelator markedly and rapidly inhibits beta-amyloid accumulation in Alzheimer's disease transgenic mice

Inhibition of neocortical beta-amyloid (Abeta) accumulation may be essential in an effective therapeutic intervention for Alzheimer's disease (AD). Cu and Zn are enriched in Abeta deposits in AD, which are solubilized by Cu/Zn-selective chelators in vitro. Here we report a 49% decrease in brain Abeta deposition (-375 microg/g wet weight, p = 0.0001) in a blinded study of APP2576 transgenic mice treated orally for 9 weeks with clioquinol, an antibiotic and bioavailable Cu/Zn chelator. This was accompanied by a modest increase in soluble Abeta (1.45% of total cerebral Abeta); APP, synaptophysin, and GFAP levels were unaffected. General health and body weight parameters were significantly more stable in the treated animals. These results support targeting the interactions of Cu and Zn with Abeta as a novel therapy for the prevention and treatment of AD.

Copper in disorders with neurological symptoms: Alzheimer's, Menkes, and Wilson diseases

Copper is an essential element for the activity of a number of physiologically important enzymes. Enzyme-related malfunctions may contribute to severe neurological symptoms and neurological diseases: copper is a component of cytochrome c oxidase, which catalyzes the reduction of oxygen to water, the essential step in cellular respiration. Copper is a cofactor of Cu/Zn-superoxide-dismutase which plays a key role in the cellular response to oxidative stress by scavenging reactive oxygen species. Furthermore, copper is a constituent of dopamine-beta-hydroxylase, a critical enzyme in the catecholamine biosynthetic pathway. A detailed exploration of the biological importance and functional properties of proteins associated with neurological symptoms will have an important impact on understanding disease mechanisms and may accelerate development and testing of new therapeutic approaches. Copper binding proteins play important roles in the establishment and maintenance of metal-ion homeostasis, in deficiency disorders with neurological symptoms (Menkes disease, Wilson disease) and in neurodegenerative diseases (Alzheimer's disease). The Menkes and Wilson proteins have been characterized as copper transporters and the amyloid precursor protein (APP) of Alzheimer's disease has been proposed to work as a Cu(II) and/or Zn(II) transporter. Experimental, clinical and epidemiological observations in neurodegenerative disorders like Alzheimer's disease and in the genetically inherited copper-dependent disorders Menkes and Wilson disease are summarized. This could provide a rationale for a link between severely dysregulated metal-ion homeostasis and the selective neuronal pathology.

The amyloid-beta peptide and its role in Alzheimer's disease

Amyloid formation plays a central role in the cause and progression of Alzheimer's disease. The major component of this amyloid is the amyloid-beta (A beta) peptide, which is currently the subject of intense study. This review discusses some recent studies in the area of A beta synthesis, purification and structural analysis. Also discussed are proposed mechanisms for A beta-induced neurotoxicity and some recent advances in the development of A beta-related therapeutic strategies.

Metal chelation as a potential therapy for Alzheimer's disease

Alzheimer's disease is a rapidly worsening public health problem. The current lack of effective treatments for Alzheimer's disease makes it imperative to find new pharmacotherapies. At present, the treatment of symptoms includes use of acetylcholinesterase inhibitors, which enhance acetylcholine levels and improve cognitive functioning. Current reports provide evidence that the pathogenesis of Alzheimer's disease is linked to the characteristic neocortical amyloid-beta deposition, which may be mediated by abnormal metal interaction with A beta as well as metal-mediated oxidative stress. In light of these observations, we have considered the development of drugs that target abnormal metal accumulation and its adverse consequences, as well as prevention or reversal of amyloid-beta plaque formation. This paper reviews recent observations on the possible etiologic role of A beta deposition, its redox activity, and its interaction with transition metals that are enriched in the neocortex. We discuss the effects of metal chelators on these processes, list existing drugs with chelating properties, and explore the promise of this approach as a basis for medicinal chemistry in the development of novel Alzheimer's disease therapeutics.

Homocysteine potentiates copper- and amyloid beta peptide-mediated toxicity in primary neuronal cultures: possible risk factors in the Alzheimer's-type neurodegenerative pathways

Oxidative stress may have an important role in the progression of neurodegenerative disorders such as Alzheimer's disease (AD) and prion diseases. Oxidative damage could result from interactions between highly reactive transition metals such as copper (Cu) and endogenous reducing and/or oxidizing molecules in the brain. One such molecule, homocysteine, a thiol-containing amino acid, has previously been shown to modulate Cu toxicity in HeLa and endothelial cells in vitro. Due to a possible link between hyperhomocysteinemia and AD, we examined whether interaction between homocysteine and Cu could potentiate Cu neurotoxicity. Primary mouse neuronal cultures were treated with homocysteine and either Cu (II), Fe (II or III) or Zn (II). Homocysteine was shown to selectively potentiate toxicity from low micromolar concentrations of Cu. The toxicity of homocysteine/Cu coincubation was dependent on the ability of homocysteine to reduce Cu (II) as reflected by the inhibition of toxicity with the Cu (I)-specific chelator, bathocuproine disulphonate. This was supported by data showing that homocysteine reduced Cu (II) more effectively than cysteine or methionine but did not reduce Fe (III) to Fe (II). Homocysteine also generated high levels of hydrogen peroxide in the presence of Cu (II) and promoted Abeta/Cu-mediated hydrogen peroxide production and neurotoxicity. The potentiation of metal toxicity did not involve excitotoxicity as ionotropic glutamate receptor antagonists had no effect on neurotoxicity. Homocysteine alone also had no effect on neuronal glutathione levels. These studies suggest that increased copper and/or homocysteine levels in the elderly could promote significant oxidant damage to neurons and may represent additional risk factor pathways which conspire to produce AD or related neurodegenerative conditions.

Standardization of measurement of beta-amyloid(1-42) in cerebrospinal fluid and plasma

The standardization and clinical validation of the measurement of beta-amyloid(1-42) (Abeta42) in cerebrospinal fluid (CSF), plasma and urine is described using a commercially available sandwich-type ELISA with 21F12 and 3D6 as monoclonal antibodies. The INNOTEST beta-amyloid(1-42) allows the specific and reliable measurement of(1-42) amyloid peptides in CSF and plasma. The Abeta42 concentrations in serum and urine were below the detection limit. In plasma, no differences were found in Abeta42 levels between controls and patients with different neurodegenerative disorders (Alzheimer's disease (AD), Lewy body disease (LBD), others). In contrast, CSF-Abeta42 concentrations were lower in AD and LBD patients as compared to controls. No correlation was found in AD patients between CSF and plasma concentrations of Abeta42 or between CSF Abeta42 levels and blood-brain-barrier function. The quantitative outcome of the test is in part dependent on confounding factors such as tube type, freeze/thaw cycles, temperature of incubation, standard preparation protocol, and antibody selection. Notwithstanding these aspects, it emerged that Abeta42 is a useful biochemical marker for the diagnosis of AD patients, but there is a need for an international Abeta standard, a universally accepted protocol for CSF preparation, and a thorough evaluation of assay performance in function of the boundary conditions.

Examining the zinc binding site of the amyloid-beta peptide

The amyloid beta-peptide (Abeta) is a principal component of insoluble amyloid plaques which are characteristic neuropathological features of Alzheimer's disease. Abeta also exists as a normal soluble protein that undergoes a pathogenic transition to an aggregated, fibrous form. This transition can be affected by extraneous proteinaceous and nonproteinaceous elements, such as zinc ions, which may promote aggregation and/or stabilization of the fibrils. Protein chelation of zinc is typically mediated by histidines, cysteines and carboxylates. Previous studies have demonstrated that the Abeta-Zn2+ binding site is localized within residues 6-28 and that histidines may serve as the principal sites of interaction. To localize key residues within this region, a series of Abeta peptides (residues 1-28) were synthesized that contained systematic His/Ala substitutions. Circular dichroism and electron microscopy were used to monitor the effects of Zn2+ on the peptide beta-sheet conformation and fibril aggregation. Our results indicate that substitution of either His13 or His14 but not His6 eliminates the zinc-mediated effects. These observations indicate a specific zinc binding site within Abeta that involves these central histidine residues.

Zn(2+): a novel ionic mediator of neural injury in brain disease

Zn(2+) is the second most prevalent trace element in the body and is present in particularly large concentrations in the mammalian brain. Although Zn(2+) is a cofactor for many enzymes in all tissues, a unique feature of brain Zn(2+) is its vesicular localization in presynaptic terminals, where its release is dependent on neural activity. Although the physiological significance of synaptic Zn(2+) release is little understood, it probably plays a modulatory role in synaptic transmission. Furthermore, several lines of evidence support the idea that, upon excessive synaptic Zn(2+) release, its accumulation in postsynaptic neurons contributes to the selective neuronal loss that is associated with certain acute conditions, including epilepsy and transient global ischaemia. More speculatively, Zn(2+) dis-homeostasis might also contribute to some degenerative conditions, including Alzheimer's disease. Further elucidation of the pathological actions of Zn(2+) in the brain should result in new therapeutic approaches to these conditions.

Characterization of copper interactions with alzheimer amyloid beta peptides: identification of an attomolar-affinity copper binding site on amyloid beta1-42

Cu and Zn have been shown to accumulate in the brains of Alzheimer's disease patients. We have previously reported that Cu(2+) and Zn(2+) bind amyloid beta (Abeta), explaining their enrichment in plaque pathology. Here we detail the stoichiometries and binding affinities of multiple cooperative Cu(2+)-binding sites on synthetic Abeta1-40 and Abeta1-42. We have developed a ligand displacement technique (competitive metal capture analysis) that uses metal-chelator complexes to evaluate metal ion binding to Abeta, a notoriously self-aggregating peptide. This analysis indicated that there is a very-high-affinity Cu(2+)-binding site on Abeta1-42 (log K(app) = 17.2) that mediates peptide precipitation and that the tendency of this peptide to self-aggregate in aqueous solutions is due to the presence of trace Cu(2+) contamination (customarily approximately 0.1 microM). In contrast, Abeta1-40 has much lower affinity for Cu(2+) at this site (estimated log K(app) = 10.3), explaining why this peptide is less self-aggregating. The greater Cu(2+)-binding affinity of Abeta1-42 compared with Abeta1-40 is associated with significantly diminished negative cooperativity. The role of trace metal contamination in inducing Abeta precipitation was confirmed by the demonstration that Abeta peptide (10 microM) remained soluble for 5 days only in the presence of high-affinity Cu(2+)-selective chelators.

Prion disease: A loss of antioxidant function?

Prion disease, a neurodegenerative disorder, is widely believed to arise when a cellular prion protein (PrP(C)) undergoes conformational changes to a pathogenic isoform (PrP(Sc)). Recent data have shown PrP(C) to be copper binding and that it acquires antioxidant activity as a result. This enzymatic property is dependent mainly on copper binding to the octarepeats region. In normal human brain and human prion disease, there is a population of brain-derived PrP that has been truncated at the N-terminal which encompassed the octarepeats region. Increasing evidences have suggested imbalances of metal-catalyzed reactions to be the common denominator for several neurodegenerative diseases. Therefore, we propose that one of the causative factors for prion disease could be due to the imbalances in metal-catalyzed reactions resulting in an alteration of the antioxidant function. These result in an increase level of oxidative stress and, as such, trigger the neurodegenerative cascade.

Evidence that the beta-amyloid plaques of Alzheimer's disease represent the redox-silencing and entombment of abeta by zinc

Abeta binds Zn(2+), Cu(2+), and Fe(3+) in vitro, and these metals are markedly elevated in the neocortex and especially enriched in amyloid plaque deposits of individuals with Alzheimer's disease (AD). Zn(2+) precipitates Abeta in vitro, and Cu(2+) interaction with Abeta promotes its neurotoxicity, correlating with metal reduction and the cell-free generation of H(2)O(2) (Abeta1-42 > Abeta1-40 > ratAbeta1-40). Because Zn(2+) is redox-inert, we studied the possibility that it may play an inhibitory role in H(2)O(2)-mediated Abeta toxicity. In competition to the cytotoxic potentiation caused by coincubation with Cu(2+), Zn(2+) rescued primary cortical and human embryonic kidney 293 cells that were exposed to Abeta1-42, correlating with the effect of Zn(2+) in suppressing Cu(2+)-dependent H(2)O(2) formation from Abeta1-42. Since plaques contain exceptionally high concentrations of Zn(2+), we examined the relationship between oxidation (8-OH guanosine) levels in AD-affected tissue and histological amyloid burden and found a significant negative correlation. These data suggest a protective role for Zn(2+) in AD, where plaques form as the result of a more robust Zn(2+) antioxidant response to the underlying oxidative attack.

Chelation and intercalation: complementary properties in a compound for the treatment of Alzheimer's disease

Selective application of metal chelators to homogenates of human Alzheimer's disease (AD) brain has led us to propose that the architecture of aggregated beta-amyloid peptide, whether in the form of plaques or soluble oligomers, is determined at least in part by high-affinity binding of transition metals, especially copper and zinc. Of the two metals, copper is implicated in reactive oxygen species generating reactions, while zinc appears to be associated with conformational and antioxidant activity. We tested the copper chelators trientine, penicillamine, and bathophenanthroline for their ability to mobilize brain Abeta as measured against our benchmark compound bathocuproine (BC). All of these agents were effective in solubilizing brain Abeta, although BC was the most consistent across the range of AD brain tissue samples tested. Similarly, all of the copper chelators depleted copper in the high-speed supernatants. BC alone had no significant effect upon zinc levels in the soluble fraction. BC extraction of brain tissue from C100 transgenic mice (which express human Abeta but do not develop amyloid) revealed SDS-resistant dimers as Abeta was mobilized from the sedimentable to the soluble fraction. NMR analysis showed that, in addition to its copper chelating properties, BC interacts with Abeta to form a complex independent of the presence of copper. Such hybrid copper chelating and "chain breaking" properties may form the basis of a rational design for a therapy for Alzheimer's disease.

Metals and neuroscience

Data are now rapidly accumulating to show that metallochemical reactions might be the common denominator underlying Alzheimer's disease, amyotrophic lateral sclerosis, prion diseases, cataracts, mitochondrial disorders and Parkinson's disease. In these disorders, an abnormal reaction between a protein and a redox-active metal ion (copper or iron) promotes the formation of reactive oxygen species or radicalization. It is especially intriguing how the powerful catalytic redox activity of antioxidant Cu/Zn-superoxide dismutase can convert into a pro-oxidant activity, a theme echoed in the recent proposal that Abeta and PrP, the proteins respectively involved in Alzheimer's disease and prion diseases, possess similar redox activities.

Cu(II) potentiation of alzheimer abeta neurotoxicity. Correlation with cell-free hydrogen peroxide production and metal reduction

Oxidative stress markers as well as high concentrations of copper are found in the vicinity of Abeta amyloid deposits in Alzheimer's disease. The neurotoxicity of Abeta in cell culture has been linked to H(2)O(2) generation by an unknown mechanism. We now report that Cu(II) markedly potentiates the neurotoxicity exhibited by Abeta in cell culture. The potentiation of toxicity is greatest for Abeta1-42 > Abeta1-40 >> mouse/rat Abeta1-40, corresponding to their relative capacities to reduce Cu(II) to Cu(I), form H(2)O(2) in cell-free assays and to exhibit amyloid pathology. The copper complex of Abeta1-42 has a highly positive formal reduction potential ( approximately +500-550 mV versus Ag/AgCl) characteristic of strongly reducing cuproproteins. These findings suggest that certain redox active metal ions may be important in exacerbating and perhaps facilitating Abeta-mediated oxidative damage in Alzheimer's disease.

Soluble pool of Abeta amyloid as a determinant of severity of neurodegeneration in Alzheimer's disease

Genetic evidence strongly supports the view that Abeta amyloid production is central to the cause of Alzheimer's disease. The kinetics, compartmentation, and form of Abeta and its temporal relation to the neurodegenerative process remain uncertain. The levels of soluble and insoluble Abeta were determined by using western blot techniques, and the findings were assessed in relation to indices of severity of disease. The mean level of soluble Abeta is increased threefold in Alzheimer's disease and correlates highly with markers of disease severity. In contrast, the level of insoluble Abeta (also a measure of total amyloid load) is found only to discriminate Alzheimer's disease from controls, and does not correlate with disease severity or numbers of amyloid plaques. These findings support the concept of several interacting pools of Abeta, that is, a large relatively static insoluble pool that is derived from a constantly turning over smaller soluble pool. The latter may exist in both intracellular and extracellular compartments, and contain the basic forms of Abeta that cause neurodegeneration. Reducing the levels of these soluble Abeta species by threefold to levels found in normal controls might prove to be a goal of future therapeutic intervention.