Clioquinol Treatment in Familiar Early Onset of Alzheimer’s Disease

Alzheimer's Drug PBT2 Interacts with the Amyloid β 1-42 Peptide Differently than Other 8-Hydroxyquinoline Chelating Drugs

Although Alzheimer's disease (AD) was first described over a century ago, it remains the leading cause of age-related dementia. Innumerable changes have been linked to the pathology of AD; however, there remains much discord regarding which might be the initial cause of the disease. The "amyloid cascade hypothesis" proposes that the amyloid β (Aβ) peptide is central to disease pathology, which is supported by elevated Aβ levels in the brain before the development of symptoms and correlations of amyloid burden with cognitive impairment. The "metals hypothesis" proposes a role for metal ions such as iron, copper, and zinc in the pathology of AD, which is supported by the accumulation of these metals within amyloid plaques in the brain. Metals have been shown to induce aggregation of Aβ, and metal ion chelators have been shown to reverse this reaction in vitro. 8-Hydroxyquinoline-based chelators showed early promise as anti-Alzheimer's drugs. Both 5-chloro-7-iodo-8-hydroxyquinoline (CQ) and 5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline (PBT2) underwent unsuccessful clinical trials for the treatment of AD. To gain insight into the mechanism of action of 8HQs, we have investigated the potential interaction of CQ, PBT2, and 5,7-dibromo-8-hydroxyquinoline (B2Q) with Cu(II)-bound Aβ(1-42) using X-ray absorption spectroscopy (XAS), high energy resolution fluorescence detected (HERFD) XAS, and electron paramagnetic resonance (EPR). By XAS, we found CQ and B2Q sequestered ∼83% of the Cu(II) from Aβ(1-42), whereas PBT2 sequestered only ∼59% of the Cu(II) from Aβ(1-42), suggesting that CQ and B2Q have a higher relative Cu(II) affinity than PBT2. From our EPR, it became clear that PBT2 sequestered Cu(II) from a heterogeneous mixture of Cu(II)Aβ(1-42) species in solution, leaving a single Cu(II)Aβ(1-42) species. It follows that the Cu(II) site in this Cu(II)Aβ(1-42) species is inaccessible to PBT2 and may be less solvent-exposed than in other Cu(II)Aβ(1-42) species. We found no evidence to suggest that these 8HQs form ternary complexes with Cu(II)Aβ(1-42).

Longitudinal Consumption of Ergothioneine Reduces Oxidative Stress and Amyloid Plaques and Restores Glucose Metabolism in the 5XFAD Mouse Model of Alzheimer's Disease

Background: Ergothioneine (ERGO) is a unique antioxidant and a rare amino acid available in fungi and various bacteria but not in higher plants or animals. Substantial research data indicate that ERGO is a physiological antioxidant cytoprotectant. Different from other antioxidants that need to breach the blood-brain barrier to enter the brain parenchyma, a specialized transporter called OCTN1 has been identified for transporting ERGO to the brain. Purpose: To assess whether consumption of ERGO can prevent the progress of Alzheimer's disease (AD) on young (4-month-old) 5XFAD mice. Methods and materials: Three cohorts of mice were tested in this study, including ERGO-treated 5XFAD, non-treated 5XFAD, and WT mice. After the therapy, the animals went through various behavioral experiments to assess cognition. Then, mice were scanned with PET imaging to evaluate the biomarkers associated with AD using [¹¹C]PIB, [¹¹C]ERGO, and [¹⁸F]FDG radioligands. At the end of imaging, the animals went through cardiac perfusion, and the brains were isolated for immunohistology. Results: Young (4-month-old) 5XFAD mice did not show a cognitive deficit, and thus, we observed modest improvement in the treated counterparts. In contrast, the response to therapy was clearly detected at the molecular level. Treating 5XFAD mice with ERGO resulted in reduced amyloid plaques, oxidative stress, and rescued glucose metabolism. Conclusions: Consumption of high amounts of ERGO benefits the brain. ERGO has the potential to prevent AD. This work also demonstrates the power of imaging technology to assess response during therapy.

Cortical iron mediates age-related decline in fluid cognition

Brain iron dyshomeostasis disrupts various critical cellular functions, and age-related iron accumulation may contribute to deficient neurotransmission and cell death. While recent studies have linked excessive brain iron to cognitive function in the context of neurodegenerative disease, little is known regarding the role of brain iron accumulation in cognitive aging in healthy adults. Further, previous studies have focused primarily on deep gray matter regions, where the level of iron deposition is highest. However, recent evidence suggests that cortical iron may also contribute to cognitive deficit and neurodegenerative disease. Here, we used quantitative susceptibility mapping (QSM) to measure brain iron in 67 healthy participants 18-78 years of age. Speed-dependent (fluid) cognition was assessed from a battery of 12 psychometric and computer-based tests. From voxelwise QSM analyses, we found that QSM susceptibility values were negatively associated with fluid cognition in the right inferior temporal gyrus, bilateral putamen, posterior cingulate gyrus, motor, and premotor cortices. Mediation analysis indicated that susceptibility in the right inferior temporal gyrus was a significant mediator of the relation between age and fluid cognition, and similar effects were evident for the left inferior temporal gyrus at a lower statistical threshold. Additionally, age and right inferior temporal gyrus susceptibility interacted to predict fluid cognition, such that brain iron was negatively associated with a cognitive decline for adults over 45 years of age. These findings suggest that iron may have a mediating role in cognitive decline and may be an early biomarker of neurodegenerative disease.

Trace element alterations in Alzheimer's disease: A review

Dyshomeostasis of trace elements have been implicated in the progression of Alzheimer's disease (AD), which is characterized by amyloid-β (Aβ) plaques. Trace elements are particularly associated with the Aβ plaques. Metal-protein attenuating compounds have been developed to inhibit metals from binding to Aβ proteins, which result in Aβ termination, in the hope of improving cognitive functioning. However, there are still some contradicting reports. This review aims to first establish which trace elements are increased or decreased in the brains of Alzheimer's patients, and secondly, to review the effectiveness of clinical trials with metal-protein attenuating compounds for AD. Studies have consistently reported unchanged or increased iron, contradicting reports for zinc, decreased copper, unchanged or decreased manganese, inconsistent results for calcium, and magnesium seems to be unaffected. However, varied results have been reported for all trace elements. Clinical trials using metal-protein attenuating compounds to treat AD have also reported varied results. Copper chelators have repeatedly been used in clinical trials, even though few studies report increased brain copper levels in AD patients. Homeostasis of copper levels is important since copper has a vital role in several enzymes, such as cytochrome c, Cu/Zn superoxide dismutase and ceruloplasmin. Dyshomeostasis of copper levels can lead to increased oxidative stress and neuronal loss. Future studies should assess a variety of trace element levels in moderately and severely affected AD patients since there are contradicting reports. This review thus provides some insight into trace element alterations in the brains of individuals with AD.

Copper(II) Binding to PBT2 Differs from That of Other 8-Hydroxyquinoline Chelators: Implications for the Treatment of Neurodegenerative Protein Misfolding Diseases

PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) is a small Cu(II)-binding drug that has been investigated in the treatment of neurodegenerative diseases, namely, Alzheimer's disease (AD). PBT2 is thought to be highly effective at crossing the blood-brain barrier and has been proposed to exert anti-Alzheimer's effects through the modulation of metal ion concentrations in the brain, specifically the sequestration of Cu(II) from amyloid plaques. However, despite promising initial results in animal models and in clinical trials where PBT2 was shown to improve cognitive function, larger-scale clinical trials did not find PBT2 to have a significant effect on the amyloid plaque burden compared with controls. We propose that the results of these clinical trials likely point to a more complex mechanism of action for PBT2 other than simple Cu(II) sequestration. To this end, herein we have investigated the solution chemistry of Cu(II) coordination by PBT2 primarily using X-ray absorption spectroscopy (XAS), high-energy-resolution fluorescence-detected XAS, and electron paramagnetic resonance. We propose that a novel bis-PBT2 Cu(II) complex with asymmetric coordination may coexist in solution with a symmetric four-coordinate Cu(II)-bis-PBT2 complex distorted from coplanarity. Additionally, PBT2 is a more flexible ligand than other 8HQs because it can act as both a bidentate and a tridentate ligand as well as coordinate Cu(II) in both 1:1 and 2:1 PBT2/Cu(II) complexes.

Solution Chemistry of Copper(II) Binding to Substituted 8-Hydroxyquinolines

8-Hydroxyquinolines (8HQs) are a family of lipophilic metal ion chelators that have been used in a range of analytical and pharmaceutical applications over the last 100 years. More recently, CQ (clioquinol; 5-chloro-7-iodo-8-hydroxyquinoline) and PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) have undergone clinical trials for the treatment of Alzheimer's disease and Huntington's disease. Because CQ and PBT2 appear to redistribute metals into cells, these compounds have been redefined as copper and zinc ionophores. Despite the attention surrounding the clinical trials and the clear link between 8HQs and metals, the fundamental solution chemistry of how these compounds bind divalent metals such as copper and zinc, as well as their mechanism(s) of action in mammalian systems, remains poorly understood. In this study, we used a combination of X-ray absorption spectroscopy (XAS), high-energy resolution fluorescence detected (HERFD) XAS, electron paramagnetic resonance (EPR), and UV-visible absorption spectroscopies to investigate the aqueous solution chemistry of a range of 8HQ derivatives. To circumvent the known solubility issues with 8HQ compounds and their complexes with Cu(II), and to avoid the use of abiological organic solvents, we have devised a surfactant buffer system to investigate these Cu(II) complexes in aqueous solution. Our study comprises the first comprehensive investigation of the Cu(II) complexes formed with many 8HQs of interest in aqueous solution, and it provides the first structural information on some of these complexes. We find that halogen substitutions in 8HQ derivatives appear to have little effect on the Cu(II) coordination environment; 5,7-dihalogenated 8HQ conformers all have a pseudo square planar Cu(II) bound by two quinolin-8-olate anions, in agreement with previous studies. Conversely, substituents in the 2-position of the 8HQ moiety appear to cause significant distortions from the typical square-planar-like coordination of most Cu(II)-bis-8HQ complexes, such that the 8HQ moieties in the Cu(II)-bis-8HQ complex are rotated approximately 30-40° apart in a "propeller-like" arrangement.

Synthesis and Cytoprotective Characterization of 8-Hydroxyquinoline Betti Products

The 8-hydroxyquinoline pharmacophore scaffold has been shown to possess a range of activities as metal chelation, enzyme inhibition, cytotoxicity, and cytoprotection. Based on our previous findings we set out to optimize the scaffold for cytoprotective activity for its potential application in central nervous system related diseases. A 48-membered Betti-library was constructed by the utilization of formic acid mediated industrial-compatible coupling with sets of aromatic primary amines such as anilines, oxazoles, pyridines, and pyrimidines, with (hetero)aromatic aldehydes and 8-hydroxiquinoline derivatives. After column chromatography and re-crystallization, the corresponding analogues were obtained in yields of 13–90%. The synthesized analogs were optimized with the utilization of a cytoprotection assay with chemically induced oxidative stress, and the most active compounds were further tested in orthogonal assays, a real time cell viability method, a fluorescence-activated cell sorting (FACS)-based assay measuring mitochondrial membrane potential changes, and gene expression analysis. The best candidates showed potent, nanomolar activity in all test systems and support the need for future studies in animal models of central nervous system (CNS) disorders.

Metal ions influx is a double edged sword for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a common form of dementia in aged people, which is defined by two pathological characteristics: β-amyloid protein (Aβ) deposition and tau hyperphosphorylation. Although the mechanisms of AD development are still being debated, a series of evidence supports the idea that metals, such as copper, iron, zinc, magnesium and aluminium, are involved in the pathogenesis of the disease. In particular, the processes of Aβ deposition in senile plaques (SP) and the inclusion of phosphorylated tau in neurofibrillary tangles (NFTs) are markedly influenced by alterations in the homeostasis of the aforementioned metal ions. Moreover, the mechanisms of oxidative stress, synaptic plasticity, neurotoxicity, autophagy and apoptosis mediate the effects of metal ions-induced the aggregation state of Aβ and phosphorylated tau on AD development. More importantly, imbalance of these mechanisms finally caused cognitive decline in different experiment models. Collectively, reconstructing the signaling network that regulates AD progression by metal ions may provide novel insights for developing chelators specific for metal ions to combat AD.

New Hydroxyquinoline-Based Derivatives as Potent Modulators of Amyloid-β Aggregations

Copper and zinc have been found to contribute to the burden of amyloid-β (Aβ) aggregations in neurodegenerative Alzheimer's disease (AD). Dysregulation of these metals leads to the generation of reactive oxygen species (ROS) and eventually results in oxidative damage and accumulation of the Aβ peptide, which are the key elements of the disease. Aiming to pursue the discovery of new modulators for the disease, we here rationally focused on conjugating the core hydroxyquinoline of the metal-protein attenuating compound PBT2 and the N-methylanilide analogous moiety of the Aβ imaging agent to build a new type of multi-target modulators of Aβ aggregations. We found that the N,N-dimethylanilinyl imines 7a, 8a, and the corresponding amines 7b, 8b exerted efficient inhibition of Cu(2+) - or Zn(2+) -induced Aβ aggregations and significant disassembly of metal-mediated Aβ aggregated fibrils. Further, 7a and 7b also exhibited significant ROC scavenging effects compared to PBT2. The results suggested that 7a and 7b are promising lead compounds for the development of a new therapy for AD.

Targeting Metal-Aβ Aggregates with Bifunctional Radioligand [11C]L2-b and a Fluorine-18 Analogue [18F]FL2-b

Interest in quantifying metal-Aβ species in vivo led to the synthesis and evaluation of [¹¹C]L2-b and [¹⁸F]FL2-b as radiopharmaceuticals for studying the metallobiology of Alzheimer’s disease (AD) using positron emission tomography (PET) imaging. [¹¹C]L2-b was synthesized in 3.6% radiochemical yield (nondecay corrected, n = 3), >95% radiochemical purity, from the corresponding desmethyl precursor. [¹⁸F]FL2-b was synthesized in 1.0% radiochemical yield (nondecay corrected, n = 3), >99% radiochemical purity, from a 6-chloro pyridine precursor. Autoradiography experiments with AD positive and healthy control brain samples were used to determine the specificity of binding for the radioligands compared to [¹¹C]PiB, a known imaging agent for β-amyloid (Aβ) aggregates. The K_d for [¹¹C]L2-b and [¹⁸F]FL2-b were found to be 3.5 and 9.4 nM, respectively, from those tissue studies. Displacement studies of [¹¹C]L2-b and [¹⁸F]FL2-b with PiB and AV-45 determined that L2-b binds to Aβ aggregates differently from known radiopharmaceuticals. Finally, brain uptake of [¹¹C]L2-b was examined through microPET imaging in healthy rhesus macaque, which revealed a maximum uptake at 2.5 min (peak SUV = 2.0) followed by rapid egress (n = 2).

Therapeutic options in Alzheimer’s disease

Alzheimer's disease (AD) places an enormous burden on individuals, families and society. Consequently, a tremendous effort is being devoted to the development of drugs that prevent or delay neurodegeneration. Current pharmacological treatments are based on the use of acetylcholinesterase inhibitors or memantine, a N-methyl-D-aspartate channel blocker. However, new therapeutic approaches, including those more closely targeted to the pathogenesis of the disease, are being developed. These potentially disease-modifying therapeutics include secretase inhibitors, cholesterol-lowering drugs, amyloid-beta immunotherapy, nonsteroidal anti-inflammatory drugs, hormonal modulation and the use of antioxidants. The possibility that oxidative stress is a primary event in AD indicates that antioxidant-based therapies are perhaps the most promising weapons against this devastating neurodegenerative disorder.

Metallostasis in Alzheimer's disease

2012 has been another year in which multiple large-scale clinical trials for Alzheimer's disease (AD) have failed to meet their clinical endpoints. With the social and financial burden of this disease increasing every year, the onus is now on the field of AD researchers to investigate alternative ideas to deliver outcomes for patients. Although several major clinical trials targeting Aβ have failed, three smaller clinical trials targeting metal interactions with Aβ have all shown benefit for patients. Here we review the genetic, pathological, biochemical, and pharmacological evidence that underlies the metal hypothesis of AD. The AD-affected brain suffers from metallostasis, or fatigue of metal trafficking, resulting in redistribution of metals into inappropriate compartments. The metal hypothesis is built upon a triad of transition elements: iron, copper, and zinc. The hypothesis has matured from early investigations showing amyloidogenic and oxidative stress consequences of these metals; recently, disease-related proteins, APP, tau, and presenilin, have been shown to have major roles in metal regulation, which provides insight into the pathway of neurodegeneration in AD and illuminates potential new therapeutic avenues.

Zinc diet and Alzheimer's disease: a systematic review

OBJECTIVES

This paper reviews evidence of an association between zinc (Zn) nutrition and Alzheimer's disease (AD) or age-associated cognitive decline. The involvement of zinc in the pathology of AD has been reported hundreds of times. It is, however, still a matter of debate whether the disease progression can be influenced by modifying zinc in the diet.

METHODS

We searched Medline, Embase, Biosis, ALOIS, the Cochrane central register of controlled trials, the Cochrane database of systematic reviews, and different publisher databases, and included studies that dealt with zinc in the diet and AD or cognitive decline in elderly subjects.

RESULTS

Fifty-five studies met the inclusion criteria. Neither randomized-controlled trials nor observational studies provide conclusive evidence whether Zn in the diet is associated with cognitive decline or AD. Case-control and autopsy studies suggest decreased systemic and increased brain Zn levels, respectively.

DISCUSSION

The current state of evidence does not allow conclusions to be drawn on whether supplementation of Zn is beneficial for the prevention or treatment of AD, although a subclinical deficiency appears common in the elderly and subjects with AD. Dietary studies with animals suggest that the impact of dietary Zn on cognitive performance depend on additional nutrients. Further studies are necessary to determine whether Zn deficiency is a risk factor for AD in general terms or under certain dietary circumstances only.

Clioquinol inhibits zinc-triggered caspase activation in the hippocampal CA1 region of a global ischemic gerbil model

Background

Excessive release of chelatable zinc from excitatory synaptic vesicles is involved in the pathogenesis of selective neuronal cell death following transient forebrain ischemia. The present study was designed to examine the neuroprotective effect of a membrane-permeable zinc chelator, clioquinol (CQ), in the CA1 region of the gerbil hippocampus after transient global ischemia.

Methodology/Principal Findings

The common carotid arteries were occluded bilaterally, and CQ (10 mg/kg, i.p.) was injected into gerbils once a day. The zinc chelating effect of CQ was examined with TSQ fluorescence and autometallography. Neuronal death, the expression levels of caspases and apoptosis inducing factor (AIF) were evaluated using TUNEL, in situ hybridization and Western blotting, respectively. We were able to show for the first time that CQ treatment attenuates the ischemia-induced zinc accumulation in the CA1 pyramidal neurons, accompanied by less neuronal loss in the CA1 field of the hippocampus after ischemia. Furthermore, the expression levels of caspase-3, -9, and AIF were significantly decreased in the hippocampus of CQ-treated gerbils.

Conclusions/Significance

The present study indicates that the neuroprotective effect of CQ is related to downregulation of zinc-triggered caspase activation in the hippocampal CA1 region of gerbils with global ischemia.

Current therapeutic targets for the treatment of Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disease for which no cure exists. There is a substantial need for new therapies that offer improved symptomatic benefit and disease-slowing capabilities. In recent decades there has been substantial progress in understanding the molecular and cellular changes associated with Alzheimer's disease pathology. This has resulted in identification of a large number of new drug targets. These targets include, but are not limited to, therapies that aim to prevent production of or remove the amyloid-beta protein that accumulates in neuritic plaques; to prevent the hyperphosphorylation and aggregation into paired helical filaments of the microtubule-associated protein tau; and to keep neurons alive and functioning normally in the face of these pathologic challenges. We provide a review of these targets for drug development.

Challenges associated with metal chelation therapy in Alzheimer's disease

A close association between brain metal dishomeostasis and the onset and/or progression of Alzheimer's disease (AD) has been clearly established in a number of studies, although the underlying biochemical mechanisms remain obscure. This observation renders chelation therapy an attractive pharmacological option for the treatment of this disease. However, a number of requirements must be fulfilled in order to adapt chelation therapy to AD so that the term "metal targeted strategies" seems now more appropriate. Indeed, brain metal redistribution rather than brain metal scavenging and removal is the major goal of this type of intervention. The most recent developments in metal targeted strategies for AD will be discussed using, as useful examples, clioquinol, curcumin, and epigallocatechin, and the future perspectives will also be outlined.

Prevention of age-associated dementia

The advancement of medical sciences during the last century has resulted in a considerable increase in life expectancy. As more people live to old age, one of the most fundamental questions of the 21st century is whether the number of individuals suffering from dementia will also continue to increase. Alzheimer's disease (AD) accounts for the majority of cases of dementia in the elderly, but there is currently no curative treatment available. Several strategies have been introduced for treatment, the most recent strategy of which was the immunization of patients using antibodies against Abeta, which is a naturally occurring, even though misfolded peptide in the AD brain. Both active and passive immunization routes have been shown to reduce the pathology associated with Abeta accumulation in brains of genetically designed animal models. However, despite tremendous efforts, no unequivocal proof of therapeutic efficacy could be shown in AD patients. Particularly, the persistence of the neurofibrillary tangles in immunized brains and the issue of inducing cerebral amyloid angiopathy are major limiting factors of antibody therapy. Furthermore, physical activity, a healthy immune system and nutritional habits are suggested to protect against the onset of age-associated dementia. Thus, accumulative evidence suggests that an early integrated strategy, combining pharmacological, immunological, nutritional and life-style factors, is the most pragmatic approach to delay the onset and progression of age-associated dementia.

The anti-neurodegeneration drug clioquinol inhibits the aging-associated protein CLK-1

The development of neurodegenerative diseases such as Alzheimer, Parkinson, and Huntington disease is strongly age-dependent. Discovering drugs that act on the high rate of aging in older individuals could be a means of combating these diseases. Reduction of the activity of the mitochondrial enzyme CLK-1 (also known as COQ7) slows down aging in Caenorhabditis elegans and in mice. Clioquinol is a metal chelator that has beneficial effects in several cellular and animal models of neurodegenerative diseases as well as on Alzheimer disease patients. Here we show that clioquinol inhibits the activity of mammalian CLK-1 in cultured cells, an inhibition that can be blocked by iron or cobalt cations, suggesting that chelation is involved in the mechanism of action of clioquinol on CLK-1. We also show that treatment of nematodes and mice with clioquinol mimics a variety of phenotypes produced by mutational reduction of CLK-1 activity in these organisms. These results suggest that the surprising action of clioquinol on several age-dependent neurodegenerative diseases with distinct etiologies might result from a slowing down of the aging process through action of the drug on CLK-1. Our findings support the hypothesis that pharmacologically targeting aging-associated proteins could help relieve age-dependent diseases.

Zinc and copper modulate Alzheimer Abeta levels in human cerebrospinal fluid

Abnormal interaction of beta-amyloid 42 (Abeta42) with copper, zinc and iron induce peptide aggregation and oxidation in Alzheimer's disease (AD). However, in health, Abeta degradation is mediated by extracellular metalloproteinases, neprilysin, insulin degrading enzyme (IDE) and matrix metalloproteinases. We investigated the relationship between levels of Abeta and biological metals in CSF. We assayed CSF copper, zinc, other metals and Abeta42 in ventricular autopsy samples of Japanese American men (N=131) from the population-based Honolulu Asia Aging Study. There was a significant inverse correlation of CSF Abeta42 with copper, zinc, iron, manganese and chromium. The association was particularly strong in the subgroup with high levels of both zinc and copper. Selenium and aluminum levels were not associated to CSF Abeta42. In vitro, the degradation of synthetic Abeta substrate added to CSF was markedly accelerated by low levels (2microM) of exogenous zinc and copper. While excessive interaction with copper and zinc may induce neocortical Abeta precipitation in AD, soluble Abeta degradation is normally promoted by physiological copper and zinc concentrations.

Membrane permeability of redox active metal chelators: an important element in reducing hydroxyl radical induced NAD+ depletion in neuronal cells

There is substantial evidence implicating increased production of the hydroxyl radical and oxidative stress in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). Significant amounts of hydroxyl radicals will be produced in the presence of hydrogen peroxide and redox active iron via Fenton chemistry. Increased iron levels within the cytoplasm of vulnerable neurons suggest that this may also be an important site of oxidative activity. We investigated the likelihood that intracellular, rather than extracellular chelation of ferrous or ferric iron may be more effective in reducing hydroxyl radical induced cell damage and preserving NAD(+) levels and cell viability. Using intracellular NAD(H) measurements as an indicator of cell viability we found that membrane permeable ferrous chelators were most efficient in preserving cellular NAD(+) levels. Hydrophilic, ferrous or ferric chelators and lipophilic ferric chelators were essentially ineffective in preventing cellular NAD(+) depletion when added at physiological concentrations. We propose that lipophilic ferrous chelators, due to their actions inside the cell, are effective agents for moderating neuronal damage in conditions such as AD where intracellular oxidative stress plays a significant role in disease pathology.

Molecular mechanisms for Alzheimer's disease: implications for neuroimaging and therapeutics

Alzheimer's disease is a progressive neurodegenerative disorder characterised by the gradual onset of dementia. The pathological hallmarks of the disease are beta-amyloid (Abeta) plaques, neurofibrillary tangles, synaptic loss and reactive gliosis. The current therapeutic effort is directed towards developing drugs that reduce Abeta burden or toxicity by inhibiting secretase cleavage, Abeta aggregation, Abeta toxicity, Abeta metal interactions or by promoting Abeta clearance. A number of clinical trials are currently in progress based on these different therapeutic strategies and they should indicate which, if any, of these approaches will be efficacious. Current diagnosis of Alzheimer's disease is made by clinical, neuropsychologic and neuroimaging assessments. Routine structural neuroimaging evaluation with computed tomography and magnetic resonance imaging is based on non-specific features such as atrophy, a late feature in the progression of the disease, hence the crucial importance of developing new approaches for early and specific recognition at the prodromal stages of Alzheimer's disease. Functional neuroimaging techniques such as functional magnetic resonance imaging, magnetic resonance spectroscopy, positron emission tomography and single photon emission computed tomography, possibly in conjunction with other related Abeta biomarkers in plasma and CSF, could prove to be valuable in the differential diagnosis of Alzheimer's disease, as well as in assessing prognosis. With the advent of new therapeutic strategies there is increasing interest in the development of magnetic resonance imaging contrast agents and positron emission tomography and single photon emission computed tomography radioligands that will permit the assessment of Abeta burden in vivo.

Radioiodinated clioquinol as a biomarker for beta-amyloid: Zn complexes in Alzheimer's disease

Neocortical beta-amyloid (Abeta) aggregates in Alzheimer's disease (AD) are enriched in transition metals that mediate assembly. Clioquinol (CQ) targets metal interaction with Abeta and inhibits amyloid pathology in transgenic mice. Here, we investigated the binding properties of radioiodinated CQ ([(125)I]CQ) to different in vitro and in vivo Alzheimer models. We observed saturable binding of [(125)I]CQ to synthetic Abeta precipitated by Zn(2+) (K(d)=0.45 and 1.40 nm for Abeta(1-42) and Abeta(1-40), respectively), which was fully displaced by free Zn(2+), Cu(2+), the chelator DTPA (diethylene triamine pentaacetic acid) and partially by Congo red. Sucrose density gradient of post-mortem AD brain indicated that [(125)I]CQ concentrated in a fraction enriched for both Abeta and Zn, which was modulated by exogenous addition of Zn(2+) or DTPA. APP transgenic (Tg2576) mice injected with [(125)I]CQ exhibited higher brain retention of tracer compared to non-Tg mice. Autoradiography of brain sections of these animals confirmed selective [(125)I]CQ enrichment in the neocortex. Histologically, both thioflavine-S (ThS)-positive and negative structures were labeled by [(125)I]CQ. A pilot SPECT study of [(123)I]CQ showed limited uptake of the tracer into the brain, which did however, appear to be more rapid in AD patients compared to age-matched controls. These data support metallated Abeta species as the neuropharmacological target of CQ and indicate that this drug class may have potential as in vivo imaging agents for Alzheimer neuropathology.