MINIREVIEW Therapeutic approaches for prion and Alzheimer’s diseases Thomas Wisniewski1,2,3 and Einar M Sigurdsson2,3 Department of Neurology, New York University School of Medicine, NY, USA Department of Pathology, New York University School of Medicine, NY, USA Department of Psychiatry, New York University School of Medicine, NY, USA Keywords Alzheimer’s disease; metals; mucosal vaccination; prion; vaccine Correspondence T Wisniewski, New York University School of Medicine, Departments of Neurology, Psychiatry and Pathology, Millhauser Laboratories, Room HN419, 560 First Avenue, New York, NY 10016, USA Fax: +1 212 263 7528 Tel: +1 212 263 7993 E-mail: thomas.wisniewski@med.nyu.edu (Received March 2007, revised May 2007, accepted May 2007) doi:10.1111/j.1742-4658.2007.05919.x Alzheimer’s and prion diseases belong to a category of conformational neurodegenerative disorders [Prusiner SB (2001) N Eng J Med 344, 1516–1526; Sadowski M & Wisniewski T (2007) Curr Pharm Des 13, 1943–1954; Beekes M (2007) FEBS J 274, 575] Treatments capable of arresting or at least effectively modifying the course of disease not yet exist for either one of these diseases Alzheimer’s disease is the major cause of dementia in the elderly and has become an ever greater problem with the aging of Western societies Unlike Alzheimer’s disease, prion diseases are relatively rare Each year only approximately 300 people in the USA and approximately 100 people in the UK succumb to various forms of prion diseases [Beekes M (2007) FEBS J 274, 575; Sigurdsson EM & Wisniewski T (2005) Exp Rev Vaccines 4, 607–610] Nevertheless, these disorders have received great scientific and public interest due to the fact that they can be transmissible among humans and in certain conditions from animals to humans The emergence of variant Creutzfeld–Jakob disease demonstrated the transmissibility of the bovine spongiform encephalopathy to humans [Beekes M (2007) FEBS J 274, 575] Therefore, the spread of bovine spongiform encephalopathy across Europe and the recently identified cases in North America have put a large human population at risk of prion infection It is estimated that at least several thousand Britons are asymptomatic carriers of prion infections and may develop variant Creutzfeld–Jakob disease in the future [Hilton DA (2006) J Pathol 208, 134–141] This delayed emergence of human cases following the near elimination of bovine spongiform encephalopathy in the UK may occur because prion disease have a very prolonged incubation period, ranging from months to decades, which depends on the amount of inoculum, the route of infection and the genetic predisposition of the infected subject [Hilton DA (2006) J Pathol 208, 134– 141] Therefore, there is a great need for effective therapies for both Alzheimer’s disease and prion diseases Introduction Alzheimer’s disease (AD) and prion disease belong to a category of conformational disorders showing sub- stantial overlap in pathologic mechanism [1–3] The basic pathomechanism in both disorders is related to a conformational change of normally expressed proteins: amyloid-b (Ab) in AD and the prion protein (PrP) in Abbreviations ACT, a1-antichymotrypsin; AD, Alzheimer’s disease; Ab, amyloid-b; apoE, apolipoprotein E; BBB, blood–brain barrier; BSE, bovine spongiform encephalopathy; CAA, congophilic amyloid angiopathy; CNS, central nervous system; CWD, chronic wasting disease; DC, dendritic cell; GSSS, Gerstmann–Strausler–Scheinker syndrome; PrP, prion protein; sAb, soluble Ab; sCJD, sporadic CJD; ă Tg, transgenic; vCJD, variant Creutzfeld–Jakob disease 3784 FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS T Wisniewski and E M Sigurdsson Therapy for prion disease and AD prion disease (Fig 1) [4,5] This occurs without an alteration in the amino-acid sequence of the proteins Ab is a 40–43 amino acid peptide, which, in AD, selfassembles into toxic oligomers and fibrils that accumulate in the brain, forming plaques and deposits in the walls of meningocephalic vessels [6,7] The same peptide can be detected in most physiological fluids, such as serum or cerebrospinal fluid, where it is called soluble Ab (sAb) [7] PrPC (C-cellular) is a 209 amino acid, cell membrane anchored protein expressed at highest levels by neurons and follicular dendritic cells of the immune system In the setting of prion disease, this protein undergoes a transformation to toxic PrPSc (Sc-scrapie) [8–10] Fibrillar Ab and PrPSc have a high b-sheet content which renders them insoluble, resistant to proteolytic degradation and toxic to neurons Neurological symptoms in AD and prion disease are directly related to loss of neurons and synaptic connections Oligomeric and fibrillar Ab can be directly neurotoxic and ⁄ or can promote formation of neurofibrillary tangles [7] Both fibrillar Ab and PrPSc are capable of forming amyloid deposits The presence of amyloid deposits is necessary for making the diagnosis CONFORMATIONAL DISORDERS Alzheimer’s Disease Mainly Random Coil Monomers Non-Toxic PrPC Aβ Plaque Neurofibrillary Tangle Pathological Chaperones Protofibrils Fibrils Increased Metals Prionoses Neuronal loss Spongiform changes Aggregated Toxic PrPSc Fig Conversion of sAb peptide or PrPC to their pathological b-sheet conformers is a key step in the pathogenesis of AD and prionoses, respectively In AD, these b-sheet rich structures consist of oligomers, protofibrils and fibrils that form plaques within the brain parenchyma or deposit in the cerebrovasculature A comparable entity in prion diseases consists of the proteinase K resistant scrapie form of the prion protein (PrPSc) that, in certain prion diseases, fibrillizes and deposits as plaques within the brain This process is facilitated by various pathological chaperones as well as several metals The aim of most therapeutic interventions for these conformational disorders is to reduce the amount of the substrate (sAb, PrPC) and ⁄ or its availability for this structural alteration; interfere with the conversion either directly or indirectly (via the pathological chaperones or metals); and promote removal of the disease-associated conformers of AD [11,12] Abundant amyloid deposits composed of PrPSc (full length or fragments) are a neuropathological hallmark of variant CreutzfeldJakob disease (vCJD), GerstmannStrauslerScheinker syndrome ă (GSS), and kuru [13] They are also present in 10% of sporadic CJD (sCJD) cases [9] A number of proteins may actively promote the conformational transformation of these disease specific proteins and stabilize their abnormal structure Examples of such proteins in AD include apolipoprotein E (apoE), especially its E4 isoform [13,14], a1-antichymotrypsin (ACT) [15] or C1q complement factor [16,17] (Fig 1) In their presence, the formation of Ab fibrils in a solution of sAb is much more efficient [13,15] These ‘pathological chaperone’ proteins have been found histologically and biochemically in association with fibrillar Ab deposits [18] but not in preamyloid aggregates, which are not associated with neuronal loss [19] Similarly, in prion disease, extensive data points toward the existence of an unidentified protein X actively involved in the conversion of PrPC into PrPSc [20] AD and prion diseases exist as sporadic and inherited illnesses In addition, prion disease can be transmitted from one subject to another In experimental model settings, some evidence also exists for the infectivity of AD [21,22] An important event in the pathomechanism of AD is thought to be reaching a critical concentration of sAb and ⁄ or chaperone proteins in the brain, at which point the conformational change occurs [23] This leads to the formation of Ab aggregates, initiating a neurodegenerative cascade In sporadic AD, this occurs due to an age-associated overproduction of Ab, impaired clearance from the brain, and ⁄ or influx into the central nervous system (CNS) of sAb circulating in the serum [24] Inherited forms of AD are associated with various genetic defects, resulting in overproduction of total sAb, or more fibrillogenic Ab 1–42 species [25] Sporadic prionoses like sCJD are thought to result from the spontaneous conversion of PrPC into PrPSc [26] The mechanisms that stabilize PrPC structure are largely unknown but, once PrPSc assumes its pathological conformation, it can bind to PrPC and induce a conformation change This starts a self-perpetuating vicious cycle allowing PrPSc to replicate without DNA, using the host cell’s PrPC as a template [9,26] Most inherited prionoses such as GSS or inherited forms of CJD are the result of a point mutation in PrPC that increases the propensity for it to assume an abnormal conformation Virtually all genetic defects implicated in familial forms of AD and prionoses are inherited in an autosomal dominant fashion Unlike AD, prionoses can be easily transmitted between subjects of the same FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS 3785 Therapy for prion disease and AD T Wisniewski and E M Sigurdsson species Transmissibility of prionoses between different species is generally ineffective due to differences in the PrP sequence The phenomenon protecting one species from acquiring a prion disease from another is called ‘the species barrier’ Therefore, scrapie (a prionosis affecting sheep) is not transmissible to humans The species barrier does not provide absolute protection; therefore, transmission of scrapie to cattle and transmission of bovine spongiform encephalopathy (BSE) from cattle to humans results in the emergence of vCJD In transmissible prionoses, exogenous PrPSc present in the inoculum is responsible for the conformational transformation of host PrPC Upon entering an organism, PrPSc initially replicates within the lymphoreticular organs, including the spleen, lymph nodes and tonsils, for months to years prior to neuroinvasion and the onset of neurological symptoms Therefore, infected but asymptomatic individuals are a reservoir of infectious material This occurs because PrPC is expressed by follicular dendritic cells and other lymphoid cells [27] Accumulation of PrPSc in the lymphatic organs of presymptomatic humans infected with BSE has been demonstrated by immunohistochemistry [28] PrPSc replication is possible because it does not elicit an immune response [29] This is related to the inability of the immune system to distinguish between PrPC and PrPSc Vaccination approaches for AD Vaccination was the first treatment approach demonstrated to have genuine impact on disease process, at least in animal models of AD Vaccination of AD transgenic (Tg) mice with Ab1–42 or Ab homologous peptides coinjected with Freund’s adjuvant prevented the formation of Ab deposition and, as a consequence, eliminated the behavioral impairments that are related to Ab deposition [30–35] Similar effects on Ab load and behavior have been demonstrated in AD Tg mice by peripheral injections of anti-Ab monoclonal serum indicating that the therapeutic effect of the vaccine is based primarily on eliciting a humoral response [36,37] The striking biological effect of the vaccine in preclinical testing and the apparent lack of side-effects in AD Tg mice encouraged Elan ⁄ Wyeth to launch clinical trials with a vaccine designated as AN1792 which contained preaggregated Ab1–42 and QS21 as an adjuvant This type of vaccine design was aimed to induce a strong cell-mediated immune response because QS21 is known to be a strong inducer of Th-1 lymphocytes [38] The initial safety testing of AN1792 in phase I of the trial did not demonstrate any adverse effects The phase II of the trial was prematurely terminated when 3786 6% of vaccinated patients manifested symptoms of acute meningoencephalitis [38,39] An autopsy performed on one of the affected patients revealed an extensive cytotoxic T-cell reaction surrounding some cerebral vessels; however, analysis of the Ab load in the brain cortex suggested that Ab clearance had occurred [40] It appeared that the immune reaction triggered by AN1792 was a double-edge sword, where the benefits of a humoral response against Ab were overshadowed in some individuals by uncontrolled cytotoxicity [41] Not all patients who received AN1792 responded with antibody production The majority mounted a humoral response and showed a modest but statistically significant cognitive benefit demonstrated as an improvement on some cognitive testing scales compared to baseline and a slowed rate of disease progression compared to patients who did not form antibodies [42] The follow-up data from the ‘Zurich’s cohort’, who are a subset of the Elan ⁄ Wyeth trial followed by Dr Nitsch’s group [42,43], indicated that the vaccination approach may be beneficial for human AD patients but that the concept of the vaccine has to be redesigned It appears that a humoral response elicited by the vaccine has at least two mechanisms of action and both of these are thought to be involved in amyloid clearance [44,45] Conformational selective anti-Ab serum may target Ab deposits in the brain [43] leading to their disassembly [46,47] and elicit Fc mediated phagocytosis by microglia cells The second mechanism by which anti-Ab serum likely prevents Ab deposition is the creation of a ‘peripheral sink’ effect, where the removal of excess sAb circulating in the blood stream leads to sAb being drawn out from the brain [31,34, 47,48] This peripheral sink mechanism is likely to be the dominant means of reducing Ab peptides in the brain The cause(s) for the toxicity in 6% of the Elan trial patients are not entirely known; however, from the available clinical and limited autopsy data, it is thought that an excessive Th-1 cell-mediated response within the brain was to blame [49] The concept of a redesigned AD vaccine puts emphasis on avoiding this cell-mediated response in the following ways: (a) avoiding stimulation of Th-1 lymphocytes so the vaccine could potentially elicit a purely humoral response; (b) using nontoxic and nonfibrillogenic Ab homologous peptides, so that the immunogen can not produce any direct toxicity; and (c) enhancing the peripheral sink effect rather than central action Passive transfer of exogenous anti-Ab monoclonal serum appears to be the easiest way to fulfill the goal of providing anti-Ab serum without risk of uncontrolled Th-1 mediated autoimmunity AD Tg model mice FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS T Wisniewski and E M Sigurdsson treated this way had a significantly reduced Ab level and demonstrated cognitive benefit [36,37] The major drawbacks of this approach are the high cost, limited half-life of monoclonal antibodies (2–21 days depending on class and isoform) and the potential for inducing serum sickness with resultant complications such as renal failure or lymphomas Nevertheless, clinical trials for passive immunization trials are underway Alternative approaches for passive immunization which are less likely to be associated with toxicity, are use of Fv fragments or mimetics of the active antibody binding site Another potential source of toxicity in association with passive immunization is cerebral hemorrhage The mechanism of this hemorrhage is thought to be inflammation in association with cerebral amyloid deposits (congophilic amyloid angiopathy; CAA) that weakens the blood vessel wall Several reports have shown an increase in microhemorrhages in different AD mouse models following passive intraperitoneal immunization with different monoclonal antibodies with high affinity for Ab plaques and CAA [50–52] The risk of microhemorrhage following active immunization in animal models has not been fully assessed It has not been a problem in our own active immunization studies [34,35], but has been reported in one study [53] Furthermore, the clinical trial data from the limited number of autopsied cases suggests that vascular amyloid was not being cleared and that hemorrhage may have been increased [54–56] In one of these autopsies, numerous cortical bleeds, which are typically rare in AD patients, were evident [55] In addition, the association of T lymphocytosis and cuffing with the cerebral vessel Ab in these autopsies suggests a potential role of CAA and an excessive Th-1 response in the genesis of the inflammatory sideeffects [57] This is an important issue because CAA is present in virtually all AD cases, with approximately 20% of AD patients having ‘severe’ CAA [58] Furthermore CAA is present in approximately 33% of cognitively normal elderly, control populations [59–61] Understanding the antigenic profile of Ab peptide, allows engineering of modifications that favor a humoral response and reduce the potential for a Th-1 mediated response This approach has been termed altered peptide ligands Computer models have predicted that Ab1–42 has one major antibody binding site located on its N-terminus and two major T-cell epitopes located at the central and C-terminal hydrophobic regions encompassing residues 17–21 and 29–42, respectively [62–64] Therefore, their elimination or modification provides a double gain by eliminating toxicity, as well as the potential for T-cell stimulation Sigurdsson et al [34] immunized AD Tg mice with Therapy for prion disease and AD K6Ab1–30[E18E19], a nontoxic Ab-homologous peptide, where the first above mentioned T-cell epitope was modified and the second removed Polyamino acid chains coupled to its N-terminus aimed to increase the immunogenicity and solubility of the peptide AD Tg mice vaccinated with this peptide produced mainly an IgM class antibodies and low or absent IgG titer These animals showed behavioral improvement and a partial reduction of Ab deposits [34,35] One of the advantages of this design is that IgM, with a molecular mass of 900 kDa, does not penetrate the blood–brain barrier (BBB) and therefore is unlikely to be associated with any immune reaction in the brain Like passive immunization, this type of vaccine focuses its mechanism of action on the peripheral sink Furthermore, the IgM response is reversible because it is T-cell independent; hence memory T-cells that could maintain the immune response are not generated Therefore, this vaccine method may potentially be safer than typical active immunization Mucosal vaccination can be an alternative way to achieve a primarily humoral response This mechanism is based on the presence of lymphocytes in the mucosa of the nasal cavity and of the gastrointestinal tract This type of response produces primarily S-IgA antibodies but, when the antigen is coadministrated with adjuvants such as cholera toxin subunit B or heat-labile Escherichia coli enterotoxin, significant IgG titer in the serum may be achieved [65,66] A marked reduction of Ab burden in AD Tg mice immunized this way using Ab as an antigen has been already demonstrated [66,67] Interestingly, this type of mucosal immunization has recently been shown to be highly effective for prion infection [68,69,70] This promising approach requires further exploration, especially using nonfibrillar and nontoxic Ab homologous peptides as an antigen Mucosal immunization offers a great potential advantage in that a more limited humoral immune response can be obtained, with little or no cell-mediated immunity Inhibition of Ab fibrillization Formation of Ab fibrils and deposition of Ab in the brain parenchyma or in the brain’s vessels occurs in the setting of increased local Ab peptide concentrations [71] Initially, conditions not favor aggregation of fibrils; however, once a critical nucleus has been formed, aggregation with fast kinetics is favored Any available monomer can then become entrapped in an aggregate or fibril Several compounds, such as Congo red [71], anthracycline [73], rifampicin [74], anionic sulphonates [75], or melatonin [76], can interact with Ab and prevent its aggregation into fibrils FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS 3787 Therapy for prion disease and AD T Wisniewski and E M Sigurdsson in vitro, thereby reducing toxicity It has been further identified that certain nonfibrillogenic, Ab homologous peptides can bind to Ab and break the formation of b-sheet structure [77–80] Therefore, these peptides were termed b-sheet breakers Several modifications were used to extend serum half-life and increase BBB permeability of these peptides Permanne et al [81], using a BBB permeable five amino-acid long peptide (iAb5), were able to demonstrate a reduction of Ab load in AD Tg mice that received this peptide compared with age-matched control group which received placebo Of interest, a similar concept of b-sheet breakers has been shown to be applicable to prion disease [82] Extensive evidence suggests that the most toxic forms of Ab are oligomeric aggregates [83] There is also evidence implicating oligomeric aggregates in the mediation of PrPSc toxicity and infectivity [84,85] Recently, compounds and antibodies have been developed that specifically target Ab oligomers [86–88] Similar approaches are being developed for prion oligomers Ab homologous peptides can aggregate and form fibrils spontaneously in vitro; however, in vivo this process appears more dependant on the presence of Ab pathological chaperones This group of proteins promotes conformational transformation at certain concentrations by increasing the b-sheet content of these disease specific proteins and stabilizes their abnormal structure [89,90] Examples of such proteins in AD include apoE, especially its E4 isoform [18,91], ACT [20] or C1q complement factor [21,22] In their presence, the formation of Ab fibrils in a solution of sAb monomers becomes much more efficient [18,20] These ‘pathological chaperone’ proteins have been found histologically and biochemically in association with fibrillar Ab deposits [23,89,92,93] but not in preamyloid aggregates that are not associated with neuronal toxicity [24,94] Inheritance of the apoE4 isoform has been identified as the major identified genetic risk factor for sporadic, late-onset AD [95] and correlates with an earlier age of onset and greater Ab deposition, in an allele-dose-dependent manner [19,95,96] In vitro, all apoE isoforms can propagate the b-sheet content of Ab peptides promoting fibril formation [92], with apoE4 being the most efficient [18] The critical dependence of Ab deposition in plaques on the presence of apoE has also been confirmed in AD Tg APPV717F ⁄ apoE– ⁄ – mice which have a delayed onset of Ab deposition, a reduced Ab load, and no fibrillar Ab deposits Compared to APPV717F ⁄ apoE+ ⁄ + Tg mice, APPV717F ⁄ apoE+ ⁄ – mice demonstrate an intermediate level of pathology [97–100] Neutralization of the chaperoning effect of apoE would therefore potentially have a mitigating 3788 effect on Ab accumulation ApoE hydrophobically binds to the 12–28 amino acid sequence of Ab, forming SDS insoluble complexes [101–103] Ma et al [104] have demonstrated that a synthetic peptide homologous to 12–28 amino-acid sequence of Ab can be used as a competitive inhibitor of the binding of full length Ab to apoE, resulting in reduced fibril formation in vitro and increased survival of cultured neurons The introduction of several modifications to Ab12–28 by replacing a valine for proline in position 18, making this peptide nontoxic and nonfibrillogenic, as well as end-protection by amidation and and acetylation of the C- and N-termini, respectively, to increase serum half-life, have allowed us to use this peptide therapeutically in the APPK670N ⁄ M671L ⁄ PS1M146L double Tg mice model Tg mice treated with Ab12–28P for month demonstrated a 63.3% reduction in Ab load in the cortex (P ¼ 0.0043) and a 59.5% (P ¼ 0.0087) reduction in the hippocampus comparing to agematched control Tg mice that received placebo [105,106] The treated Tg mice also had a cognitive benefit [105,106] No antibodies against Ab were detected in sera of treated mice; therefore, the observed therapeutic effect of Ab12–28P cannot be attributed to an antibody clearance response This experiment demonstrates that compounds blocking the interaction between Ab and its pathological chaperones may be beneficial for treatment of Ab accumulation in AD [14,105,106] Whether similar approaches can be used for prion disease remains to be determined Prion disease Interest in prion disease has greatly increased subsequent to the emergence of BSE in England and the resulting appearance of vCJD in human populations BSE arose from the feeding of cattle with prion contaminated meat and bone meal products, whereas vCJD developed following entry of BSE into the human food chain [107,108] Since the original report in 1995, a total of 201 probable or confirmed cases of vCJD have been diagnosed, 165 in Great Britain, 21 in France, four in Ireland, three in the USA, two in the Netherlands and one each in Italy, Canada, Japan, Saudi Arabia, Portugal and Spain Most of the patients from these countries resided in the UK during a key exposure period of the UK population to the BSE agent It has proven difficult to predict the expected future numbers of vCJD Mathematical analysis has given a range from 1000 to approximately 136 000 individuals who will eventually develop the disease This broad range reflects a lack of knowledge regarding the time of incubation and the number of patients FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS T Wisniewski and E M Sigurdsson who could be infected from a given dosage of BSE agent Because the vCJD agent is present at high levels in the lymphatic tissue, screening for PrPSc was performed on sections from lymph nodes, tonsils, and appendices archives in the UK Three out of 12 674 randomly selected cases showed evidence of subclinical infection, leading to a prediction that approximately 4000 vCJD further cases may occur in the UK [109] However, there is much uncertainty about such a prediction because it is not known whether all subclinical infections will progress and also whether such screening of lymphoid tissue would capture all subclinical cases The initially predicted epidemic of vCJD does not seem to be materializing because the number of cases in the UK has declined from a peak of 28 in 2000 to five cases in 2006 [107] A complicating factor for estimating future numbers of vCJD is the documentation of several transfusion associated cases These occurred after incubation periods of 6–8 years One of these disease associated donations was made more than years before the donor became symptomatic, suggesting that vCJD can be transmitted from silently infected individuals [110] The estimated risk for new cases of vCJD in other European countries looks more optimistic In the UK, 200 000 cases of BSE were reported (it is estimated that four times this number entered the food chain), compared to approximately 5600 BSE cases in other European countries (with the highest numbers being 1590, 1030 and 986 in Ireland, Portugal and Frances, respectively) This suggests a significantly lower exposure of these populations to BSE prions A few cases of BSE have also been reported in other parts of the world, such as Japan, the USA and Canada Of greater concern in North America is chronic wasting disease (CWD) This disease is now endemic in Colorado, Wyoming and Nebraska and continues to spread to other parts in the USA, initially in the Midwest but now detected as far East as New York State [111,112] Most vulnerable to CWD infection are white tailed deer and the disease is now found in areas with a large population of these animals, which indicates that its prevalence can be expected to increase substantially in the future The occurrence of CJD among three young deer hunters from this same region raised the speculation of transmission of the CWD to humans [113] However, autopsy of these three subjects did not reveal the extensive amyloidosis characteristic of vCJD and CWD [114] However like BSE, CWD is transmissible to nonhuman primates and transgenic mice expressing human PrPC [115,116] Therefore, the possibility of such transmission needs to be closely monitored CWD is similar to BSE in that the peripheral titers of the prion Therapy for prion disease and AD agent are high PrPSc has been detected in both muscle and saliva of CWD infected deer [117,118] Vaccination as a therapeutic approach for prionoses The prion protein is a self-antigen; hence, prion infection is not known to elicit a classical immune response In fact, the immune system is involved in the peripheral replication of the prion agent and its ultimate access to the CNS [29,68] This involvement is further supported by the observation that immune suppression with, for example, splenectomy or immunosuppressive drugs, increases the incubation period This interval, during which time the prion agent replicates peripherally, without producing any symptoms, is quite long, lasting many months in experimental animals and up to 56 years in documented human cases associated with cannibalistic exposure to the prion agent [119] Lymphatic organs such as the spleen, tonsils, lymph nodes or gut associated lymphoid tissue contain high concentrations of PrPSc long before PrPSc replication starts in the brain [27,120,121] Cells found to be particularly important for peripheral PrPSc replication are the follicular dendritic cells (DC) and the migratory bone-marrow derived DC [121,122] DC from infected animals are capable of spreading the disease [122] An emerging therapeutic approach for prion infection is immunomodulation [68,70,123] Currently, there is no treatment that would arrest and ⁄ or reverse progression of prion disease in nonexperimental settings, although many approaches have been tried [124] Partly due to the success in AD models discussed above, similar experiments with anti-PrP serum were initiated in prion infectivity culture models as well as active and passive immunization studies in rodent models Earlier in vivo studies showed that infection with a slow strain of PrPSc blocked expression of a more virulent fast strain of PrP, mimicking vaccination with a live attenuated organism [125] In tissue culture studies, anti-PrP serum and antigen binding fragments directed against PrP were shown to inhibit prion replication [126–128] Although we first demonstrated that active immunization with recombinant PrP delayed the onset of prion disease in wild-type mice, the therapeutic effect was relatively modest and, eventually, all the mice succumbed to the disease [129] This limited therapeutic effect may be explained by the observation that antibodies generated against prokaryotic PrP often not have a high affinity towards PrPC [130], although, in our studies, the increase in the incubation period correlated well with the antibody FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS 3789 Therapy for prion disease and AD T Wisniewski and E M Sigurdsson titers against PrPC Our follow-up passive anti-PrP immunization study confirmed the importance of the humoral response, showing that anti-PrP serum is able to prolong the incubation period [131] Subsequently, other investigators, using a much higher antibody dosage, were able to completely prevent disease onset in mice exposed to PrPSc provided that passive immunization was initiated within month of exposure [132] This type of approach could be used immediately following accidental exposure in humans to prevent future infection However, passive immunization has not been found to be effective closer to the clinically symptomatic stages of prion infection Also, passive immunization would be an approach that is too costly for animal prion diseases In the development of immunotherapeutic approaches targeting a self-antigen, designing a vaccine avoiding auto-immune related toxicity is a major concern The emerging data from AD targeting immunization is that toxicity is due to excessive cell-mediated immunity within the CNS, whereas the therapeutic response is linked to humoral immunity In addition, toxicity could be partially related to the immunogen and ⁄ or to the adjuvant used; in the human AD vaccination trial, fibrillar Ab1–42 was used as an immunogen This peptide is well characterized to be toxic Hence, we have been promoting the use of nonamyloidogenic derivatives as immunogens for protein conformational disorders, including AD and prion disease [31,34,38] How significant an issue direct toxicity of the immunogen may be for prion vaccination remains unclear Unlike the Ab peptide used for vaccination in AD models, direct application of recombinant PrP has not been shown to be toxic However, this issue has not been investigated as thoroughly as in the Alzheimer’s field and remains controversial Several lines of evidence suggest that intracellular accumulations of PrPSc promote neurodegeneration [133] A potential ideal means of using immunomodulation to prevent prion infection is by mucosal immunization One important reason for this is that the gut is the major route of entry for many prion diseases such as CWD, BSE and vCJD Furthermore, mucosal immunization can be designed to induce primarily a humoral immune response, avoiding the cell-mediated toxicity that was seen in the human AD vaccine trial In addition, mucosal vaccination has the advantage that it is unlikely to induce significant immune response within the brain Although it has been shown that reduced levels or absence of CNS PrPC by, for example, conditional ablation by genetic manipulation of neuronal PrPC [134] can prevent clinical prion infection, it is likely that the immunological targeting of neuronal 3790 PrP would be associated with inflammatory toxicity Recently, we have been developing prion vaccines that target gut associated tissue, the main site of entry of the prion agent One of our approaches is to express PrP in attenuated Salmonella strains as a live vector for oral vaccination, which has resulted in prevention or significant delay of prion disease in mice [69] Live attenuated strains of Salmonella enterica have been used for many years as vaccines against salmonellosis and as a delivery system for the construction of multivalent vaccines with a broad application in human and veterinary medicine [135] A main advantage for this system is that the safety of human administration of live attenuated Salmonella has been extensively confirmed in humans and animals [136,137] Ruminants and other veterinary species can be effectively immunized by the oral route using attenuated Salmonella, to induce humoral mucosal responses [138,139] We are currently exploring ways to increase the efficacy even further In these studies, the mucosal IgA anti-PrP titer correlates well with the delay or prevention of prion infection, further supporting the importance of the humoral response for the therapeutic effect Salmonella target M-cells, antigen sampling cells in the intestines, which may also be important for uptake of PrPSc [27,68,121] Hence, this approach is more targeted than prior vaccination studies, likely explaining the improved efficacy By exploring other strains of attenuated Salmonella, using different bacteria or oral adjuvants, and ⁄ or by altering the expression levels or sequence of the PrP antigen, it is likely that the percentage of uninfected animals can be improved Our recent work utilizing this approach indicates that complete protection to clinical prion infection via an oral route is possible Overall, this approach holds great promise as an inexpensive prophylactic immunotherapy to prevent the spread of prion disease, particularly in animals at risk and perhaps eventually in certain high risk human populations Metal chelation for prion and AD Metal chelation is emerging as an important therapeutic approach for AD, which is currently in clinical trial [140,141] This approach for AD is reviewed elsewhere in this minireview series Importantly, modulation of metal levels, in particular copper, has been shown to be important for the conversion of PrPC to PrPSc, highlighting another similarity between AD and prion diseases [10] Copper binding is thought to be part of the normal function of PrPC [142–144] The binding of copper to PrPC gives the complex antioxidant activity [145,146]; hence, it has been suggested that the reduced FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS T Wisniewski and E M Sigurdsson copper binding of PrPSc with a consequent reduction of antioxidant activity is part of the pathogenesis of prion disease [147] This hypothesis has been supported by the finding that copper is reduced up to 50% in the brains of sporadic CJD patients [148] How copper binding influences the PrPC to PrPSc conversion is complex [10,149] We were the first to show that, similar to studies in AD Tg models, metal chelation can be used therapeutically [150] in prion infection Our studies indicated that penicillamine, a copper chelator, prolongs the incubation period of scrapie in mice [150] Consistent with this observation, the presence of copper has also been shown to stabilize the PrPSc conformation using preformed fibrils [151–158], as well as to induce aggregation of the prion peptide 106–126 [159] Some tissue culture studies of prion infection have also suggested that copper chelators are suitable candidates for antiprion drugs [160] However, there are conflicting reports indicating that the interaction between copper and PrP is likely to be quite complex For example, copper has been shown to inhibit the in vitro conversion of recombinant PrP into amyloid fibrils but, also in contrast, to enhance the proteinase K resistance of preformed fibrils [157] These findings indicate that copper may have a dual and opposite effect on prion propagation It may both inhibit prion replication and prevent clearance of potentially infectious forms of the prion protein Furthermore, copper treatment has also been shown to inhibit PrPSc amplification in reactions where brain derived PrPC was used as a seed [161], as well as delaying the onset of clinical disease in scrapie infected hamsters [162] In addition, it has been shown that physiological levels of copper promote internalization of PrPC [163] The interaction between PrPC and copper was found to be the overriding factor in stimulating the internalization response with other metals showing no effect The decrease in detectable levels of PrPC at the cell surface following copper treatment was found to be the result of internalization rather than loss into the surrounding environment [163] Such internalization would limit the exposure of PrPC to conversion from exogenous PrPSc; however, because cytoplasmic forms of PrP have been linked to neurodegeneration [133], increased internalization could also be deleterious in some settings Copper has also been shown to have immunomodulatory effects [164] and, as discussed earlier, the immune system can have profound effects on prion infection Hence, it appears that the deleterious or beneficial role of copper in prion infection might vary depending on which function predominates under the distinct experimental conditions being used Nevertheless, it is clear that a Therapy for prion disease and AD greater understanding of the role of metal binding in prion infection presents a therapeutic opportunity Conclusions Immunization appears to be an effective therapeutic method for prevention of Ab deposition and cognitive decline in AD, provided that cell-mediated autoimmune toxicity can be avoided The second generation AD vaccines, which are under development, are based on nontoxic and nonfibrillar Ab homologous peptides that are modified to eliminate the potential for inducing cellular immunity, and elicit primarily a humoral response Other related approaches include direct administration of antibodies that target Ab These interventions would likely favor a peripheral sink effect, clearing soluble Ab from the blood stream and inducing efflux of Ab from the brain Additional potentially synergistic therapeutic approaches for AD would include blocking the interaction of Ab with its ‘pathological chaperones’ such as apoE, as well as use of b-sheet breaker compounds Immunization approaches could be used for sporadic AD, familial AD, and AD associated with Down’s syndrome The effectiveness of treatment would depend on its initiation early in the disease course Therefore, such a treatment needs to coincide with the development of a procedure for the detection and monitoring of Ab deposits Both active and passive immunization appear to be effective in prevention of prion infections in animal models Further studies are needed to develop specific protocols applicable for human use Active immunization, using especially mucosal immunization could be used to prevent spread of BSE through the oral route, whereas passive immunization protocols would be more appropriate for subjects accidentally infected with prion contaminated material (e.g blood transfusion or organ transplant) Effective immunization for prion infections works through prevention of entry of PrPSc via the gut and ⁄ or neutralization of PrPSc replicating in the peripheral lymphoreticular system Metal chelation is another promising therapeutic approach for AD, which is currently undergoing clinical trials Similar approaches are just emerging for prion diseases However, a greater understanding of the role of copper and other metals in the PrPC to PrPSc conversion is needed before this therapeutic strategy can be effectively harnessed for prion infection Acknowledgements This manuscript is supported by NIH grants: AG15408, AG20245, AG20197 and the Alzheimer’s Association FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS 3791 Therapy for prion disease and AD T Wisniewski and E M Sigurdsson References Prusiner SB (2001) Neurodegenerative diseases and prions N Eng J Med 3444, 1516–1526 Wisniewski T, Sigurdsson EM, Aucouturier P & Frangione B (2001) Conformation as a therapeutic target in the prionoses and other neurodegenerative conditions In Molecular and Cellular Pathology in Prion Disease (Baker HF, ed.), pp 223–236 Humana Press, Totowa, NJ DeArmond SJ (1993) Alzheimer’s disease and Creutzfeldt-Jakob disease: overlap of pathogenic mechanisms Curr Opin Neurol 6, 872–881 Sadowski M & Wisniewski T (2004) Vaccines for conformational disorders Exp Rev Vaccines 3, 89–100 Sigurdsson EM (2006) Immunotherapy for conformational disorders Curr Pharm Des 12, 2569–2585 Small DH & Cappai R (2006) Alois Alzheimer and Alzheimer’s disease: a centennial perspective J Neurochem 99, 708–710 Walsh DM & Selkoe DJ (2007) Abeta oligomers ) a decade of discovery J Neurochem 101, 1172–1184 DeArmond SJ & Prusiner SB (1995) Etiology and pathogenesis of prion diseases Am J Pathol 146, 785–811 Sadowski M, Verma A & Wisniewski T, (2007) Prion diseases In Neurology in Clinical Practice, 5th edn Butterworth-Heinemann., Philadelphia, PA 10 Caughey B & Baron GS (2006) Prions and their partners in crime Nature 443, 803–810 11 Mirra SS, Gearing M & Nash F (1997) Neuropathologic assessment of Alzheimer’s disease Neurology 49, S14–S16 12 Wisniewski HM, Bancher C, Barcikowska M, Wen GY & Currie J (1989) Spectrum of morphological appearance of amyloid deposits in AD Acta Neuropathol 78, 337–347 13 Wisniewski T, Castano EM, Golabek AA, Vogel T & ˜ Frangione B (1994) Acceleration of Alzheimer’s fibril formation by apolipoprotein E in vitro Am J Pathol 145, 1030–1035 14 Sadowski M & Wisniewski T (2006) Apolipoproteins in different amyloidoses In Protein Misfolding, Aggregation and Conformational Diseases (Uversky VN, ed.) Springer, New York, NY 15 Ma J, Yee A, Brewer HB Jr, Das S & Potter H (1994) Amyloid-associated proteins alpha 1-antichymotrypsin and apolipoprotein E promote assembly of Alzheimer beta-protein into filaments Nature 372, 92–94 16 Johnson LV, Leitner WP, Rivest AJ, Staples MK, Radeke MJ & Anderson DH (2002) The Alzheimer’s A beta-peptide is deposited at sites of complement activation in pathologic deposits associated with aging and age-related macular degeneration Proc Natl Acad Sci USA 99, 11830–11835 3792 17 Boyett KW, DiCarlo G, Jantzen PT, Jackson J, O’Leary C, Wilcock D, Morgan D & Gordon MN (2003) Increased fibrillar beta-amyloid in response to human C1q injections into hippocampus and cortex of APP+PS1 transgenic mice Neurochem Res 28, 83–93 18 Wisniewski T, Lalowski M, Golabek AA, Vogel T & Frangione B (1995) Is Alzheimer’s disease an apolipoprotein E amyloidosis? Lancet 345, 956–958 19 Wisniewski HM, Sadowski M, Jakubowska-Sadowska K, Tarnawski M & Wegiel J (1998) Diffuse, lake-like amyloid-beta deposits in the parvopyramidal layer of the presubiculum in Alzheimer disease J Neuropathol Exp Neurol 57, 674–683 20 Telling GC, Haga T, Torchia M, Tremblay P, DeArmond SJ & Prusiner SB (1996) Interactions between wild-type and mutant prion proteins modulate neurodegeneration transgenic mice Genes Dev 10, 1736–1750 21 Meyer-Luehmann M, Coomaraswamy J, Bolmont T, Kaeser S, Schaefer C, Kilger E, Neuenschwander A, Abramowski D, Frey P, Jaton AL et al (2006) Exogenous induction of cerebral beta-amyloidogenesis is governed by agent and host Science 313, 1781–1784 22 Walker LC, LeVine H III, Mattson MP & Jucker M (2006) Inducible proteopathies Trends Neurosci 29, 438–443 23 Wisniewski T, Ghiso J & Frangione B (1994) Alzheimer’s disease and soluble Ab Neurobiol Aging 15, 143–152 24 Shibata M, Yamada S, Kumar S, Calero M, Bading J, Frangione B, Holtzman D, Miller CA, Strickland DK, Ghiso J et al (2000) Clearance of Alzheimer’s amyloidB 1–40 peptide from brain by LDL receptor-related protein-1 at the blood–brain barrier J Clin Invest 106, 1489–1499 25 Hardy J (2006) A hundred years of Alzheimer’s disease research Neuron 52, 3–13 26 Beekes M (2007) Prions and prion diseases FEBS J 274, 575 27 Beekes M & McBride PA (2007) The spread of prions through the body in naturally acquired transmissible spongiform encephalopathies FEBS J 274, 588–605 28 Hilton DA, Ghani AC, Conyers L, Edwards P, McCardle L, Penney M, Ritchie D & Ironside JW (2002) Accumulation of prion protein in tonsil and appendix: review of tissue samples Br Med J 325, 633–634 29 Aucouturier P, Carp RI, Carnaud C & Wisniewski T (2000) Prion diseases and the immune system Clin Immunol 96, 79–85 30 Schenk D, Barbour R, Dunn W, Gordon G, Grajeda H, Guido T, Hu K, Huang J, Johnson-Wood K, Khan K et al (1999) Immunization with amyloid-B attenuates Alzheimer disease-like pathology in the PDAPP mice Nature 400, 173–177 FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS T Wisniewski and E M Sigurdsson 31 Sigurdsson EM, Scholtzova H, Mehta P & Frangione B & Wisniewski T (2001) Immunization with a non-toxic ⁄ non-fibrillar amyloid-B homologous peptide reduces Alzheimer’s disease associated pathology in transgenic mice Am J Pathol 159, 439–447 32 Morgan D, Diamond DM, Gottschall PE, Ugen KE, Dickey C, Hardy J, Duff K, Jantzen P, DiCarlo G, Wilcock D et al (2001) Ab peptide vaccination prevents memory loss in an animal model of Alzheimer’s disease Nature 408, 982–985 33 Janus C, Pearson J, McLaurin J, Mathews PM, Jiang Y, Schmidt SD, Chishti MA, Horne P, Heslin D, French J et al (2000) Ab peptide immunization reduces behavioural impairment and plaques in a model of Alzheimer’s disease Nature 408, 979–982 34 Sigurdsson EM, Knudsen EL, Asuni A, Sage D, Goni F, Quartermain D, Frangione B & Wisniewski T (2004) An attenuated immune response is sufficient to enhance cognition in an Alzheimer’s disease mouse model immunized with amyloid-B derivatives J Neurosci 24, 6277–6282 35 Asuni A, Boutajangout A, Scholtzova H, Knudsen E, Li Y, Quartermain D, Frangione B, Wisniewski T & Sigurdsson EM (2006) Ab derivative vaccination in alum adjuvant prevents amyloid deposition and does not cause brain microhemorrhages in Alzheimer’s model mice Eur J Neurosci 24, 2530–2542 36 Bard F, Cannon C, Barbour R, Burke RL, Games D, Grajeda H, Guido T, Hu K, Huang J, Johnson-Wood K et al (2000) Peripherally administered antibodies against amyloid beta-peptide enter the central nervous system and reduce pathology in a mouse model of alzheimer disease Nat Med 6, 916–919 37 DeMattos RB, Bales KR, Cummins DJ, Dodart JC, Paul SM & Holtzman DM (2001) Peripheral anti-A beta antibody alters CNS and plasma A beta clearance and decreases brain A beta burden in a mouse model of Alzheimer’s disease Proc Natl Acad Sci USA 98, 8850–8855 38 Wisniewski T & Frangione B (2005) Immunological and anti-chaperone therapeutic approaches for Alzheimer’s disease Brain Pathol 15, 72–77 39 Wisniewski T (2005) Practice point commentary on ‘Clinical effects of Ab immunization (AN1792) in patients with AD in an interupted trial Nat Clin Pract Neurol 1, 84–85 40 Nicoll JAR, Wilkinson D, Holmes C, Steart P, Markham H & Weller RO (2003) Neuropathology of human Alzheimer disease after immunization with amyloidbeta peptide: a case report Nat Med 9, 448–452 41 Sadowski M & Wisniewski T (2007) Disease modifying approaches for Alzheimer’s pathology Curr Pharm Des 13, 1943–1954 42 Hock C, Konietzko U, Straffer JR, Tracy J, Signorell A, Muller-Tillmanns B, Lemke U, Henke K, Moritz E, Garcia E et al (2003) Antibodies against B-amyloid Therapy for prion disease and AD 43 44 45 46 47 48 49 50 51 52 53 54 slow cognitive decline in Alzheimer’s disease Neuron 38, 547–554 Hock C, Konietzko U, Paspassotiropoulos A, Wollmer A, Streffer J, von Rotz RC, Davey G, Moritz E & Nitsch RM (2002) Generation of antibodies specific for B-amyloid by vaccination of patients with Alzheimer disease Nat Med 8, 1270–1276 Golde TE (2006) Disease modifying therapy for AD? J Neurochem 99, 689–707 Kennedy GJ, Golde TE, Tariot PN & Cummings JL (2007) Amyloid-based interventions in Alzheimer’s disease CNS Spectr 12, 1–14 Bacskai BJ, Kajdasz ST, Christie RH, Carter C, Games D, Seubert P, Schenk D & Hyman BT (2001) Imaging of amyloid-B deposits in brains of living mice permits direct observation of clearance of plaques with immunotherapy Nat Med 7, 369–372 Solomon B, Koppel R, Frankel D & Hanan-Aharon E (1997) Disaggregation of Alzheimer beta-amyloid by site-directed mAb Proc Natl Acad Sci USA 94, 4109– 4112 Sigurdsson EM, Wisniewski T & Frangione B (2002) A safer vaccine for Alzheimer’s disease? Neurobiol Aging 23, 1001–1008 Robinson SR, Bishop GM, Lee HG & Munch G (2004) Lessons from the AN 1792 Alzheimer vaccine: lest we forget., Neurobiol Aging 25, 609–615 Pfeifer M, Boncristiano S, Bondolfi L, Stalder A, Deller T, Staufenbiel M, Mathews PM & Jucker M (2002) Cerebral hemorrhage after passive anti-Ab immunotherapy Science 298, 1379–1380 Wilcock DM, Rojiani A, Rosenthal A, Subbarao S, Freeman MJ, Gordon MN & Morgan D (2004) Passive immunization against Abeta in aged APP-transgenic mice reverses cognitive deficits and depletes parenchymal amyloid deposits in spite of increased vascular amyloid and microhemorrhage J Neuroinflammation 1, 24 Racke MM, Boone LI, Hepburn DL, Parsadanian M, Bryan MT, Ness DK, Piroozi KS, Jordan WH, Brown DD, Hoffman WP et al (2005) Exacerbation of cerebral amyloid angiopathy-associated microhemorrhages in amyloid precursor protein transgenic mice by immunotherapy is dependent on antibody recognition of deposited forms of amyoid beta J Neurosci 25, 629– 636 Wilcock DM, Jantzen PT, Li Q, Morgan D & Gordon MN (2007) Amyloid-beta vaccination, but not nitrononsteroidal anti-inflammatory drug treatment, increases vascular amyloid and microhemorrhage while both reduce parenchymal amyloid, Neuroscience 144, 950– 960 Nicoll JA, Wilkinson D, Holmes C, Steart P, Markham H & Weller RO (2005) Neuropathology of human Alzheimer disease after immunization with amyloid-beta peptide: a case report Nat Med 9, 448–452 FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS 3793 Therapy for prion disease and AD T Wisniewski and E M Sigurdsson 55 Ferrer I, Boada RM, Sanchez Guerra ML, Rey MJ & Costa-Jussa F (2004) Neuropathology and pathogenesis of encephalitis following amyloid-beta immunization in Alzheimer’s disease Brain Pathol 14, 11–20 56 Masliah E, Hansen L, Adame A, Crews L, Bard F, Lee C, Seubert P, Games D, Kirby L & Schenk D (2005) Ab vaccination effects on plaque pathology in the absence of encephalitis in Alzheimer disease Neurology 64, 129–131 57 Gandy S & Walker L (2004) Toward modeling hemorrhagic and encephalitic complications of Alzheimer amyloid-B vaccination in nonhuman primates Curr Opin Immunol 16, 607–615 58 Jellinger KA (2002) Alzheimer disease and cerebrovascular pathology: an update J Neural Transm 109, 813–836 59 Jellinger KA & Attems J (2005) Prevalence and pathogenic role of cerebrovascular lesions in Alzheimer disease J Neurol Sci 229–230, 37–41 60 Fernando MS & Ince PG (2004) Vascular pathologies and cognition in a population-based cohort of elderly people J Neurol Sci 226, 13–17 61 Zhang-Nunes SX, Maat-Schieman ML, Van Duinen SG, Roos RA, Frosch MP & Greenberg SM (2006) The cerebral beta-amyloid angiopathies: hereditary and sporadic Brain Pathol 16, 30–39 62 Jameson BA & Wolf H (1988) The antigenic index: a novel algorithm for predicting antigenic determinants Comput Appl Biosci 4, 181–186 63 Singh H & Raghava GP (2001) ProPred: prediction of HLA-DR binding sites Bioinformatics 17, 1236–1237 64 Singh H & Raghava GP (2003) ProPred1: prediction of promiscuous MHC class-I binding sites Bioinformatics 19, 1009–1014 65 Lemere CA, Maron R, Selkoe DJ & Weiner HL (2001) Nasal vaccination with beta-amyloid peptide for the treatment of Alzheimer’s disease DNA Cell Biol 20, 705–711 66 Zhang J, Wu X, Qin C, Qi J, Ma S, Zhang H, Kong Q, Chen D, Ba D & He W (2003) A novel recombinant adeno-associated virus vaccine reduces behavioral impairment and beta-amyloid plaques in a mouse model of Alzheimer’s disease Neurobiol Dis 14, 365– 379 67 Weiner HL, Lemere CA, Maron R, Spooner ET, Grenfell TJ, Mori C, Issazadeh S, Hancock WW & Selkoe D (2000) Nasal administration of amyloid-B peptide decreases cerebral amyloid burden in a mouse model of Alzheimer’s disease Ann Neurol 48, 567–579 68 Sigurdsson EM & Wisniewski T (2005) Promising developments in prion immunotherapy Exp Rev Vaccines 4, 607–610 69 Goni F, Knudsen EL, Schreiber F, Scholtzova H, Pankiewicz J, Carp RI, Meeker HC, Brown DR, Chabalgoity JA, Sigurdsson EM et al (2005) Mucosal 3794 70 71 72 73 74 75 76 77 78 79 80 81 vaccination delays or prevents prion infection via an oral route Neuroscience 133, 413–421 Wisniewski T, Chabalgoity JA & Goni F (2007) Is vaccination against transmissible spongiform encephalopathy feasible? Rev Sci tech Off int Epiz 26(1), 243–251 Barrow CJ, Yasuda A, Kenny PT & Zagorski MG (1992) Solution conformations and aggregational properties of synthetic amyloid beta-peptides of Alzheimer’s disease Analysis of circular dichroism spectra J Mol Biol 225, 1075–1093 Lorenzo A & Yankner BA (1994) Beta-amyloid neurotoxicity requires fibril formation and is inhibited by congo red Proc Natl Acad Sci USA 91, 12243–12247 Merlini G, Ascari E, Amboldi N, Bellotti V, Arbustini E, Perfetti V, Ferrari M, Zorzoli I, Marinone MG & Garini P (1995) Interaction of the anthracycline 4¢-iodo-4¢-deoxydoxorubicin with amyloid fibrils: inhibition of amyloidogenesis Proc Natl Acad Sci USA 92, 2959–2963 Tomiyama T, Shoji A, Kataoka K, Suwa Y, Asano S, Kaneko H & Endo N (1996) Inhibition of amyloid B protein aggregation and neurotoxicity by rifampicin ) its possible function as a hydroxyl radical scavenger J Biol Chem 271, 6839–6844 Kisilevsky R, Lemieux LJ, Fraser PE, Kong X, Hultin PG & Szarek WA (1995) Arresting amyloidosis in vivo using small-molecule anionic sulphonates or sulphates: implications for Alzheimer’s disease Nat Med 1, 143– 148 Pappolla M, Bozner P, Soto C, Shao H, Robakis NK, Zagorski M, Frangione B & Ghiso J (1998) Inhibition of Alzheimer beta-fibrillogenesis by melatonin J Biol Chem 273, 7185–7188 Hilbich C, Kisters-Woike B, Reed J, Masters CL & Beyreuther K (1992) Substitutions of hydrophobic amino acids reduce the amyloidogenicity of Alzheimer’s disease bA4 peptides J Mol Biol 228, 1–14 Soto C, Kindy MS, Baumann M & Frangione B (1996) Inhibition of Alzheimer’s amyloidosis by peptides that prevent B-sheet conformation Biochem Biophys Res Commun 226, 672–680 Soto C, Sigurdsson EM, Morelli L, Kumar A, Castano ˜ EM & Frangione B (1998) B-sheet breaker peptides inhibit fibrillogenesis in a rat brain model of amyloidosis: Implications for Alzheimer’s therapy Nat Med 4, 822–826 Sigurdsson EM, Permanne B, Soto C, Wisniewski T & Frangione B (2000) In vivo reversal of amyloid B lesions in rat brain J Neuropath Exp Neurol 59, 11–17 Permanne B, Adessi C, Saborio GP, Fraga S, Frossard MJ, Van Dorpe J, Dewachter I, Banks WA, Van Leuven F & Soto C (2002) Reduction of amyloid load and cerebral damage in a transgenic mouse model of Alzheimer’s disease by treatment with a B-sheet breaker peptide FASEB J 16, 860–862 FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS T Wisniewski and E M Sigurdsson 82 Soto C, Kascsak RJ, Saborio GP, Aucouturier P, Wisniewski T, Prelli F, Kascsak R, Mendez E, Harris DA, Ironside J et al (2000) Reversion of prion protein conformational changes by synthetic B-sheet breaker peptides Lancet 355, 192–197 83 Walsh DM & Selkoe DJ (2007) Abeta oligomers ) a decade of discovery J Neurochem 101, 1172–1184 84 Demuro A, Mina E, Kayed R, Milton SC, Parker I & Glabe CG (2005) Calcium dysregulation and membrane disruption as a ubiquitous neurotoxic mechanism of soluble amyloid oligomers J Biol Chem 280, 17294– 17300 85 Novitskaya V, Bocharova OV, Bronstein I & Baskakov IV (2006) Amyloid fibrils of mammalian prion protein are highly toxic to cultured cells and primary neurons J Biol Chem 281, 13828–13836 86 Townsend M, Cleary JP, Mehta T, Hofmeister J, Lesne S, O’Hare E, Walsh DM & Selkoe DJ (2006) Orally available compound prevents deficits in memory caused by the Alzheimer amyloid-beta oligomers Ann Neurol 60, 668–676 87 Kayed R & Glabe CG (2006) Conformation-dependent anti-amyloid oligomer antibodies Methods Enzymol 413, 326–344 88 Necula M, Kayed R, Milton S & Glabe CG (2007) Small molecule inhibitors of aggregation indicate that amyloid beta oligomerization and fibrillization pathways are independent and distinct J Biol Chem 282, 10311–10324 89 Wisniewski T & Frangione B (1992) Apolipoprotein E: a pathological chaperone protein in patients with cerebral and systemic amyloid Neurosci Lett 135, 235–238 90 Quinn J (2003) Vascular dementia J Am Med Dir Assoc 4, S155–S161 91 Sanan DA, Weisgraber KH, Russell SJ, Mahley RW, Huang D, Saunders A, Schmechel D, Wisniewski T, Frangione B, Roses AD et al (1994) Apolipoprotein E associates with beta amyloid peptide of Alzheimer’s disease to form novel monofibrils Isoform apoE4 associates more efficiently than apoE3 J Clin Invest 94, 860–869 92 Golabek AA, Soto C, Vogel T & Wisniewski T (1996) The interaction between apolipoprotein E and Alzheimer’s amyloid B-peptide is dependent on B-peptide conformation J Biol Chem 271, 10602–10606 93 Permanne B, Perez C, Soto C, Frangione B & Wisniewski T (1997) Detection of apolipoprotein E dimeric soluble amyloid B complexes in Alzheimer’s disease brain supernatants Biochem Biophys Res Commun 240, 715– 720 94 Kida E, Golabek AA, Wisniewski T & Wisniewski KE (1994) Regional differences in apolipoprotein E immunoreactivity in diffuse plaques in Alzheimer’s disease brain Neurosci Lett 167, 73–76 95 Schmechel DE, Saunders AM, Strittmatter WJ, Crain BJ, Hulette CM, Joo SH, Pericak-Vance MA, Therapy for prion disease and AD 96 97 98 99 100 101 102 103 104 105 Goldgaber D & Roses AD (1993) Increased amyloid beta-peptide deposition in cerebral cortex as a consequence of apolipoprotein E genotype in late-onset Alzheimer disease Proc Natl Acad Sci USA 90, 9649– 9653 Rebeck GW, Reiter JS, Strickland DK & Hyman BT (1993) Apolipoprotein E in sporadic Alzheimer’s disease: allelic variation and receptor interactions Neuron 11, 575–580 Bales KR, Verina T & Dodel RC, Du YS, Altstiel L, Bender M, Hyslop P, Johnstone EM, Little SP, Cummins DJ et al (1997) Lack of apolipoprotein E dramatically reduces amyloid B-peptide deposition Nat Genet 17, 263–264 Bales KR, Verina T & Cummins DJ, Du Y, Dodel RC, Saura J, Fishman CE, DeLong CA, Piccardo P, Petegnief V et al (1999) Apolipoprotein E is essential for amyloid deposition in the APPV717F transgenic mouse model of Alzheimer’s disease Proc Natl Acad Sci USA 96, 15233–15238 Holtzman DM, Bales KR, Wu S, Bhat P, Parsadanian M, Fagan AM, Chang LK, Sun Y & Paul SM (1999) Expression of human apolipoprotein E reduces amyloid-beta deposition in a mouse model of Alzheimer’s disease J Clin Invest 103, R15–R21 Holtzman DM, Bales KR, Tenkova T, Fagan AM, Parsadanian M, Sartorius LJ, Mackey B, Olney J, McKeel D, Wozniak D et al (2000) Apolipoprotein E isoform-dependent amyloid deposition and neuritic degeneration in a mouse model of Alzheimer’s disease Proc Natl Acad Sci USA 97, 2892–2897 Strittmatter WJ, Saunders AM, Schmechel D, PericakVance M, Enghild J, Salvesen GS & Roses AD (1993) Apolipoprotein E: high-avidity binding to beta-amyloid and increased frequency of type allele in late-onset familial Alzheimer disease Proc Natl Acad Sci USA 90, 1977–1981 Wisniewski T, Golabek AA, Matsubara E, Ghiso J & Frangione B (1993) Apolipoprotein E: binding to soluble Alzheimer’s beta-amyloid Biochem Biophys Res Commun 192, 359–365 Naslund J, Thyberg J, Tjernberg LO, Wernstedt C, Karlstrom AR, Bogdanovic N, Gandy SE, Lannfelt L, Terenius L & Nordstedt C (1995) Characterization of stable complexes involving apolipoprotein E and the amyloid beta peptide in Alzheimer’s disease brain Neuron 15, 219–228 Ma J, Brewer BH, Potter H & Brewer HB Jr (1996) Alzheimer Ab neurotoxicity: promotion by antichymotrypsin, apoE4; inhibition by Ab-related peptides Neurobiol Aging 17, 773–780 Sadowski M, Pankiewicz J, Scholtzova H, Ripellino JA, Li Y, Schmidt SD, Mathews P, Fryer JD, Holtzman DM, Sigurdsson EM et al (2004) Blocking the apolipoprotein E ⁄ B–amyloid interaction reduces FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS 3795 Therapy for prion disease and AD 106 107 108 109 110 111 112 113 114 115 116 117 118 119 T Wisniewski and E M Sigurdsson B-amyloid toxicity and decreases B-amyloid load in transgenic mice Am J Pathol 165, 937–948 Sadowski M, Pankiewicz J, Scholtzova H, Mehta P, Prelli F & Quartermain D & Wisniewski T (2006) Blocking the apolipoproteinE ⁄ amyloid B interaction reduces the parenchymal and vascular amyloid-B deposition and prevents memory deficit in AD transgenic mice Proc Natl Acad Sci USA 103, 18787– 18792 Manson JC, Cancellotti E, Hart P, Bishop MT & Barron RM (2006) The transmissible spongiform encephalopathies: emerging and declining epidemics Biochem Soc Trans 34, 1155–1158 Butler R (2006) Prion diseases in humans: an update Br J Psychiatry 189, 295–296 Hilton DA (2006) Pathogenesis and prevalence of variant Creutzfeldt-Jakob disease J Pathol 208, 134–141 Brown P, Brandel JP, Preese M & Sato T (2006) Iatrogenic Creutzfeldt-Jakob disease: the waning of an era Neurology 67, 389–393 Williams ES (2005) Chronic wasting disease Vet Pathol 42, 530–549 Aguzzi A & Sigurdson CJ (2004) Antiprion immunotherapy: to suppress or to stimulate? Nat Rev Immunol 4, 725–736 Belay ED, Maddox RA, Williams ES, Miller MW, Gambetti P & Schonberger LB (2004) Chronic wasting disease and potential transmission to humans Emerg Infect Dis 10, 977–984 Liberski PP, Guiroy DC, Williams ES, Walis A & Budka H (2001) Deposition patterns of disease-associated prion protein in captive mule deer brains with chronic wasting disease Acta Neuropathol 102, 496– 500 Marsh RF, Kincaid AE, Bessen RA & Bartz JC (2005) Interspecies transmission of chronic wasting disease prions to squirrel monkeys (Saimiri sciureus) J Virol 79, 13794–13796 Tamguney G, Giles K, Bouzamondo-Bernstein E, Bosque PJ, Miller MW, Safar J, DeArmond SJ & Prusiner SB (2006) Transmission of elk and deer prions to transgenic mice J Virol 80, 9104–9114 Angers RC, Browning SR, Seward TS, Sigurdson CJ, Miller MW, Hoover EA & Telling GC (2006) Prions in skeletal muscles of deer with chronic wasting disease Science 311, 1117 Mathiason CK, Powers JG, Dahmes SJ, Osborn DA, Miller KV, Warren RJ, Mason GL, Hays SA, HayesKlug J, Seelig DM et al (2006) Infectious prions in the saliva and blood of deer with chronic wasting disease Science 314, 133–136 Collinge J, Whitfield J, McKintosh E, Beck J, Mead S, Thomas DJ & Alpers MP (2006) Kuru in the 21st century ) an acquired human prion disease with very long incubation periods Lancet 367, 2068–2074 3796 120 Brown KL, Ritchie DL, McBride PA & Bruce ME (2000) Detection of PrP in extraneural tissues Microsc Res Tech 50, 40–45 121 Mabbott NA & MacPherson GG (2006) Prions and their lethal journey to the brain Nat Rev Microbiol 4, 201–211 122 Aucouturier P, Geissmann F, Damotte D, Saborio GP, Meeker HC, Kascsak R, Kascsak R, Carp RI & Wisniewski T (2001) Infected dendritic cells are sufficient for prion transmission to the CNS in mouse scrapie J Clin Invest 108, 703–708 123 Sasson J, Sadowski M, Wisniewski T & Brown DR (2005) Therapeutics and prion disease: can immunization or drugs be effective? Mini Rev Med Chem 5, 361–366 124 Trevitt CR & Collinge J (2006) A systematic review of prion therapeutics in experimental models Brain 129, 2241–2265 125 Manuelidis L (1998) Vaccination with an attenuated Creutzfeldt-Jakob disease strain prevents expression of a virulent agent Proc Natl Acad Sci USA 95, 2520–2525 126 Enari M, Flechsig E & Weissmann C (2001) Scrapie prion protein accumulation by scrapie-infected neuroblastoma cells abrogated by exposure to a prion protein antibody Proc Natl Acad Sci USA 98, 9295–9299 127 Peretz D, Williamson RA, Kaneko K, Vergara J, Leclerc E, Schmitt-Ulms G, Mehlhorn IR, Legname G, Wormald MR, Rudd PM et al (2001) Antibodies inhibit prion propagation and clear cell cultures of prion infectivity Nature 412, 739–743 128 Pankiewicz J, Prelli F, Sy MS, Kascsak RJ, Kascsak RB, Spinner DS, Carp RI, Meeker HC, Sadowski M & Wisniewski T (2006) Clearance and prevention of prion infection in cell culture by anti-PrP antibodies Eur J Neurosci 24, 2635–2647 129 Sigurdsson EM, Brown DR, Daniels M, Kascsak RJ, Kascsak R, Carp RI, Meeker HC, Frangione B & Wisniewski T (2002) Vaccination delays the onset of prion disease in mice Am J Pathol 161, 13–17 130 Polymenidou M, Heppner FL, Pellicioli EC, Urich E, Miele G, Braun N, Wopfner F, Schatzl HM, Becher B & Aguzzi A (2004) Humoral immune response to native eukaryotic prion protein correlates with antiprion protection Proc Natl Acad Sci USA 101, 14670–14676 131 Sigurdsson EM, Sy MS, Li R, Scholtzova H, Kascsak RJ, Kascsak R, Carp RI, Meeker HC, Frangione B & Wisniewski T (2003) Anti-PrP antibodies for prophylaxis following prion exposure in mice Neurosci Lett 336, 185–187 132 White AR, Enever P, Tayebl M, Mushens R, Linehan J, Brandner S, Anstee D, Collinge J & Hawke S (2003) Monoclonal antibodies inhibit prion replication and delay the development of prion disease Nature 422, 80–83 FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS T Wisniewski and E M Sigurdsson 133 Tatzelt J & Schatzl HM (2007) Molecular basis of cerebral neurodegeneration in prion diseases FEBS J 274, 606–611 134 Mallucci GR, White MD, Farmer M, Dickinson A, Khatun H, Powell AD, Brandner S, Jefferys JG & Collinge J (2007) Targeting cellular prion protein reverses early cognitive deficits and neurophysiological dysfunction in prion-infected mice Neuron 53, 325–335 135 Mastroeni P, Chabalgoity JA, Dunstan SJ, Maskell DJ & Dougan G (2001) Salmonella: immune responses and vaccines Vet J 161, 132–164 136 Tacket CO, Sztein MB, Wasserman SS, Losonsky G, Kotloff KL, Wyant TL, Nataro JP, Edelman R, Perry J, Bedford P et al (2000) Phase clinical trial of attenuated Salmonella enterica serovar typhi oral live vector vaccine CVD 908-htrA in US volunteers Infect Immun 68, 1196–1201 137 Kirkpatrick BD, McKenzie R, O’Neill JP, Larsson CJ, Bourgeois AL, Shimko J, Bentley M, Makin J, Chatfield S, Hindle Z et al (2006) Evaluation of Salmonella enterica serovar typhi (Ty2 aroC-ssaV-) M01ZH09, with a defined mutation in the Salmonella pathogenicity island 2, as a live, oral typhoid vaccine in human volunteers Vaccine 24, 116–123 138 Villarreal-Ramos B, Manser J, Collins RA, Dougan G, Chatfield SN & Howard CJ (1998) Immune responses in calves immunised orally or subcutaneously with a live Salmonella typhimurium aro vaccine Vaccine 16, 45–54 139 Chabalgoity JA, Moreno M, Carol H, Dougan G & Hormaeche CE (2000) A dog-adapted Salmonella typhimurium strain as a basis for a live oral Echinococcus granulosus vaccine Vaccine 19, 460–469 140 Doraiswamy PM & Finefrock AE (2004) Metals in our minds: therapeutic implications for neurodegenerative disorders Lancet Neurol 3, 431–434 141 Crouch PJ, Barnham KJ, Bush AI & White AR (2006) Therapeutic treatments for Alzheimer’s disease based on metal bioavailability Drug News Perspect 19, 469–474 142 Brown DR, Qin K, Herms JW, Madlung A, Manson J, Strome R, Fraser PE, Kruck T, von Bohlen A, SchulzSchaeffer W et al (1997) The cellular prion protein binds copper in vivo Nature 390, 684–687 143 Brown DR (2002) Copper and prion diseases Biochem Soc Trans 30, 742–745 144 Cheng F, Lindqvist J, Haigh CL, Brown DR & Mani K (2006) Copper-dependent co-internalization of the prion protein and glypican-1 J Neurochem 98, 1445–1457 145 Brown DR, Nicholas RS & Canevari L (2002) Lack of prion protein expression results in a neuronal phenotype sensitive to stress J Neurosci Res 67, 211–224 146 Brown DR, Wong B-S, Hafiz F, Clive C, Haswell SJ & Jones IM (2001) Normal prion protein has an Therapy for prion disease and AD 147 148 149 150 151 152 153 154 155 156 157 158 159 activity like that of superoxide dismutase Biochem J 344, 1–5 Brown DR (2001) Prion and prejudice: normal protein and the synapse Trends Neurosci 24, 85–90 Wong BS, Chen SG, Colucci M, Xie Z, Pan T, Liu T, Li R, Gambetti P, Sy MS & Brown DR (2001) Aberrant metal binding by prion protein in human prion disease J Neurochem 78, 1400–1408 Varela-Nallar L, Gonzalez A & Inestrosa NC (2006) Role of copper in prion diseases: deleterious or beneficial? Curr Pharm Des 12, 2587–2595 Sigurdsson EM, Brown DR, Alim MA, Scholtzova H, Carp RI, Meeker HC, Prelli F, Frangione B & Wisniewski T (2003) Copper chelation delays the onset of prion disease J Biol Chem 278, 46199–46202 Wong BS, Venien-Bryan C, Williamson RA, Burton DR, Gambetti P, Sy MS, Brown DR & Jones IM (2000) Copper refolding of prion protein Biochem Biophys Res Commun 276, 1217–1224 Wong B-S, Li R, Sasson J, Liu T, Pan T, Kang SC, Wisniewski T, Brown DR & Sy MS (2003) Mapping the antigenicity of copper-treated cellular prion protein in the scrapie form Cell Mol Life Sci 60, 1224–1234 McKenzie D, Bartz J, Mirwald J, Olander D, Marsh R & Aiken J (1998) Reversibility of scrapie inactivation is enhanced by copper J Biol Chem 273, 25545–25547 Wong BS, Brown DR, Pan T, Whiteman M, Liu T, Bu X, Li R, Gambetti P, Olesik J, Rubenstein R et al (2001) Oxidative impairment in scrapie-infected mice is associated with brain metals perturbations and altered antioxidant activities J Neurochem 79, 689–698 Wong E, Thackray AM & Bujdoso R (2004) Copper induces increased beta-sheet content in the scrapie-susceptible ovine prion protein PrPVRQ compared with the resistant allelic variant PrPARR Biochem J 380, 273–282 Nishina K & Jenks S & Supattapone S (2004) Ionic strength and transition metals control PrPSc protease resistance and conversion-inducing activity J Biol Chem 279, 40788–40794 Bocharova OV, Breydo L, Salnikov VV & Baskakov IV (2005) Copper(II) inhibits in vitro conversion of prion protein into amyloid fibrils Biochemistry 44, 6776–6787 Kuczius T, Buschmann A, Zhang W, Karch H, Becker K, Peters G & Groschup MH (2004) Cellular prion protein acquires resistance to proteolytic degradation following copper ion binding Biol Chem 385, 739–747 Jobling MF, Huang X, Stewart LR, Barnham KJ, Curtain C, Volitakis I, Perugini M, White AR, Cherny RA, Masters CL et al (2001) Copper and zinc binding modulates the aggregation and neurotoxic properties of the prion peptide PrP106–126 Biochemistry 40, 8073– 8084 FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS 3797 Therapy for prion disease and AD T Wisniewski and E M Sigurdsson 160 Fukuuchi T, Doh-ura K, Yoshihara S & Ohta S (2006) Metal complexes with superoxide dismutase-like activity as candidates for anti-prion drug Bioorg Med Chem Lett 16 5982–5987 161 Orem NR, Geoghegan JC, Deleault NR, Kascsak R & Supattapone S (2006) Copper (II) ions potently inhibit purified PrPres amplification J Neurochem 96, 1409– 1415 3798 162 Hijazi N, Shaked Y, Rosenmann H, Ben-Hur T & Gabizon R (2003) Copper binding to PrPC may inhibit prion disease propagation Brain Res 993, 192–200 163 Haigh CL, Edwards K & Brown DR (2005) Copper binding is the governing determinant of prion protein turnover Mol Cell Neurosci 30, 186–196 164 Percival SS (1998) Copper and immunity Am J Clin Nutr 67, 1064S–1068S FEBS Journal 274 (2007) 3784–3798 ª 2007 The Authors Journal compilation ª 2007 FEBS ... of the prion Therapy for prion disease and AD agent are high PrPSc has been detected in both muscle and saliva of CWD infected deer [117,118] Vaccination as a therapeutic approach for prionoses... Similar approaches are just emerging for prion diseases However, a greater understanding of the role of copper and other metals in the PrPC to PrPSc conversion is needed before this therapeutic. .. Therapy for prion disease and AD greater understanding of the role of metal binding in prion infection presents a therapeutic opportunity Conclusions Immunization appears to be an effective therapeutic