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.

The cortical deposition of A␤ is an event that occurs in Alzheimer's disease, Down's syndrome, head injury, and normal aging. Previously, in appraising the effects of different neurochemical factors that impact upon the solubility of A␤, we observed that Zn 2؉ was the predominant bioessential metal to induce the aggregation of soluble A␤ at pH 7.4 in vitro and that this reaction is totally reversible with chelation. We now report that unlike other biometals tested at maximal biological concentrations, marked Cu 2؉ -induced aggregation of A␤ 1-40 emerged as the solution pH was lowered from 7.4 to 6.8 and that the reaction was completely reversible with either chelation or alkalinization. (20), amyloid Pcomponent (21), and apolipoprotein E (22, 23), A␤ is found in the brains of individuals affected by AD and Down's syndrome (DS) as dense extracellular deposits of twisted ␤-pleated sheet fibrils in the neuropil (senile plaques) and within cerebral blood vessels (amyloid congophilic angiopathy; see Refs. 4 and 5). The deposition of A␤, however, is not confined to the brain parenchyma, having been detected in amyloid diseases of the muscle (24 -26), blood vessels (27, 28), and in the kidneys, lungs, skin, subcutaneous tissue, and intestine of AD patients (29,30). Cerebral A␤ deposition occurs in other aged mammals that have the human A␤ sequence (31) but is not a feature of aged rats (32, 33). Although soluble A␤ 1-40 is produced by rat neuronal tissue (34), it contains three amino acid substitutions (Arg 3 Gly, Tyr 3 Phe, and His 3 Arg at positions 5, 10, and 13, respectively (32)) that appear to alter the physicochemical properties of the peptide preventing it from precipitating in the neocortex.A␤ accumulates in the brain in AD and DS in forms that can be resolubilized in water (35, 36) but also in forms that require harsher conditions to extract and exhibit associated SDS-resistant polymerization on polyacrylamide gel electrophoresis (35, 37). A␤ 1-40 is the predominant soluble species in biological fluids, whereas A␤ 1-42 , a minor species of A␤ that is more insoluble in vitro, is the predominant species found in plaques and deposits associated with .We have pursued studies of the physicochemical properties of synthetic A␤ peptides in order to appraise the potential of various neurochemical environments to induce A␤ deposition. To this end, we had previously found that A␤ is strikingly precipitated by certain metals in vitro, in particular Zn 2ϩ (42)(43)(44)(45). This is important since zinc and other biometals are concentrated in the brain neocortical parenchyma. A recent study, using micro particle-induced x-ray emission analyses of the cortical and accessory basal nuclei of the amygdala, demonstrated that levels of Zn 2ϩ , Fe 3ϩ , and Cu 2ϩ are significantly elevated within AD neuropil compared with control neuropil and that these metal ions are significantly further concentrated within the core and periphery of plaque deposits (46). We have also found that the extraction of A␤ deposits from brain tissue int...

Blast exposure is associated with traumatic brain injury (TBI), neuropsychiatric symptoms, and long-term cognitive disability. We examined a case series of postmortem brains from U.S. military veterans exposed to blast and/or concussive injury. We found evidence of chronic traumatic encephalopathy (CTE), a tau protein–linked neurodegenerative disease, that was similar to the CTE neuropathology observed in young amateur American football players and a professional wrestler with histories of concussive injuries. We developed a blast neurotrauma mouse model that recapitulated CTE-linked neuropathology in wild-type C57BL/6 mice 2 weeks after exposure to a single blast. Blast-exposed mice demonstrated phosphorylated tauopathy, myelinated axonopathy, microvasculopathy, chronic neuroinflammation, and neurodegeneration in the absence of macroscopic tissue damage or hemorrhage. Blast exposure induced persistent hippocampal-dependent learning and memory deficits that persisted for at least 1 month and correlated with impaired axonal conduction and defective activity-dependent long-term potentiation of synaptic transmission. Intracerebral pressure recordings demonstrated that shock waves traversed the mouse brain with minimal change and without thoracic contributions. Kinematic analysis revealed blast-induced head oscillation at accelerations sufficient to cause brain injury. Head immobilization during blast exposure prevented blast-induced learning and memory deficits. The contribution of blast wind to injurious head acceleration may be a primary injury mechanism leading to blast-related TBI and CTE. These results identify common pathogenic determinants leading to CTE in blast-exposed military veterans and head-injured athletes and additionally provide mechanistic evidence linking blast exposure to persistent impairments in neurophysiological function, learning, and memory.

Oxidative stress markers characterize the neuropathology both of Alzheimer's disease and of amyloid-bearing transgenic mice. The neurotoxicity of amyloid A beta peptides has been linked to peroxide generation in cell cultures by an unknown mechanism. We now show that human A beta directly produces hydrogen peroxide (H2O2) by a mechanism that involves the reduction of metal ions, Fe(III) or Cu(II), setting up conditions for Fenton-type chemistry. Spectrophotometric experiments establish that the A beta peptide reduces Fe(III) and Cu(II) to Fe(II) and Cu(I), respectively. Spectrochemical techniques are used to show that molecular oxygen is then trapped by A beta and reduced to H2O2 in a reaction that is driven by substoichiometric amounts of Fe(II) or Cu(I). In the presence of Cu(II) or Fe(III), A beta produces a positive thiobarbituric-reactive substance (TBARS) assay, compatible with the generation of the hydroxyl radical (OH.). The amounts of both reduced metal and TBARS reactivity are greatest when generated by A beta 1-42 >> A beta 1-40 > rat A beta 1-40, a chemical relationship that correlates with the participation of the native peptides in amyloid pathology. These findings indicate that the accumulation of A beta could be a direct source of oxidative stress in Alzheimer's disease.

BackgroundThe amyloid β-protein (Aβ) is believed to be the key mediator of Alzheimer's disease (AD) pathology. Aβ is most often characterized as an incidental catabolic byproduct that lacks a normal physiological role. However, Aβ has been shown to be a specific ligand for a number of different receptors and other molecules, transported by complex trafficking pathways, modulated in response to a variety of environmental stressors, and able to induce pro-inflammatory activities.Methodology/Principal FindingsHere, we provide data supporting an in vivo function for Aβ as an antimicrobial peptide (AMP). Experiments used established in vitro assays to compare antimicrobial activities of Aβ and LL-37, an archetypical human AMP. Findings reveal that Aβ exerts antimicrobial activity against eight common and clinically relevant microorganisms with a potency equivalent to, and in some cases greater than, LL-37. Furthermore, we show that AD whole brain homogenates have significantly higher antimicrobial activity than aged matched non-AD samples and that AMP action correlates with tissue Aβ levels. Consistent with Aβ-mediated activity, the increased antimicrobial action was ablated by immunodepletion of AD brain homogenates with anti-Aβ antibodies.Conclusions/SignificanceOur findings suggest Aβ is a hitherto unrecognized AMP that may normally function in the innate immune system. This finding stands in stark contrast to current models of Aβ-mediated pathology and has important implications for ongoing and future AD treatment strategies.

The amyloid-β peptide (Aβ) is a key protein in Alzheimer's disease (AD) pathology. We previously reported in vitro evidence suggesting that Aβ is an antimicrobial peptide. We present in vivo data showing Aβ expression protects against fungal and bacterial infections in mouse, nematode, and cell culture models of AD. We show that Aβ oligomerization, a behavior traditionally viewed as intrinsically pathological, may be necessary for the antimicrobial activities of the peptide. Collectively, our data are consistent with a model in which soluble Aβ oligomers bind to microbial cell wall carbohydrates via a heparin-binding domain. Developing protofibrils inhibit pathogen adhesion to host cells. Propagating β-amyloid fibrils mediate agglutination and final entrapment of microbes.. Consistent with our model, Salmonella Typhimurium bacteria infections of the brains of transgenic 5XFAD mice resulted in rapid seeding and accelerated β-amyloid deposition, which closely co-localized with the invading bacteria. Our findings raise the intriguing possibility that β-amyloid may play a protective role in innate immunity and infectious or sterile inflammatory stimuli may drive amyloidosis. These data suggest a dual protective/damaging role for Aβ, as has been described for other antimicrobial peptides.

Summary Alzheimer’s Disease (AD) is complicated by pro-oxidant intraneuronal Fe2+ elevation as well as extracellular Zn2+ accumulation within amyloid plaque. We found that the AD β-amyloid protein precursor (APP) possesses ferroxidase activity mediated by a conserved H-ferritin-like active site, which is inhibited specifically by Zn2+. Like ceruloplasmin, APP catalytically oxidizes Fe2+, loads Fe3+ into transferrin, and has a major interaction with ferroportin in HEK293T cells (that lack ceruloplasmin) and in human cortical tissue. Ablation of APP in HEK293T cells and primary neurons induces marked iron retention, whereas increasing APP695 promotes iron export. Unlike normal mice, APP−/− mice are vulnerable to dietary iron exposure, which causes Fe2+ accumulation and oxidative stress in cortical neurons. Paralleling iron accumulation, APP ferroxidase activity in AD post-mortem neocortex is inhibited by endogenous Zn2+, which we demonstrate can originate from Zn2+-laden amyloid aggregates and correlates with Aβ burden. Abnormal exchange of cortical zinc may link amyloid pathology with neuronal iron accumulation in AD.

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