Current Alzheimer Research - Volume 11, Issue 7, 2014

Epidemiologic studies suggest that we are on the precipice of a worldwide epidemic of Alzheimer’s disease (AD), yet current treatment options are limited to short term symptomatic relief. Recent advances in our knowledge of the neurobiology of AD have resulted in the development of several potential disease-modifying approaches based on immunotherapy. The present special ‘Hot Topic’ (HT) issue of “Current Alzheimer Research” deals primarily with the mechanisms of passive vaccination with Intravenous Immunoglobulin (IVIG), particularly within the context of neuroprotection in preclinical models of AD. This HT issue is not meant to report exhaustively on the many other research efforts in the broader immunotherapy arena. Indeed, this journal has recently covered various other aspects of immunotherapy relevant to AD and related disorders. However, we will briefly overview current immunotherapeutic strategies for AD prior to discussing the main topic of IVIG neuroprotection. One of the most significant approaches involves the removal of brain amyloid-β peptide (Aβ) using anti-Aβ antibodies. Aβ immunotherapy emerged as a promising treatment strategy based on human neuropathology and preclinical studies. The hallmark accumulation of parenchymal and vascular Aβ pathology observed in the brains of AD subjects suggested a logical target, and naturally occurring anti-Aβ antibodies were found to be reduced in the cerebrospinal fluid and blood of AD patients [1, 2]. In addition, both active and passive amyloid immunization of AD transgenic mouse models resulted in increased clearance of amyloid plaquelike deposits and improved cognitive performance [3, 4], whereas brain imaging and neuropathological studies suggested the ability of both active and passive anti-Aβ immunotherapies to clear Aβ deposits from the AD brain. AN1792 was the first active immunotherapy strategy for AD using full length Aβ42 as the immunogen; however, a Phase II trial of this anti-amyloid vaccine was halted when meningo-encephalitis appeared in a small subset of patients [5]. Despite this setback, long-term follow-up of patients immunized with AN1792 showed reduced functional decline in antibody responders [6], supporting the hypothesis that Aβ immunotherapy may have long-term functional benefits. In this regard, novel Aβ immunogens with shorter peptide sequences are in development which may avoid the autoimmune responses to full length Aβ42 [7]. The first passive anti-Aβ immunotherapy for AD focused on bapineuzumab. Bapineuzumab, which is composed of humanized anti-Aβ monoclonal antibodies, reduced Aβ burden in the brains of AD patients in two Phase II trials. However, bapineuzumab did not improve clinical outcomes in patients with AD, despite treatment differences in biomarkers observed in APOE ε4 carriers [8, 9]. Other recent approaches, such as systemic co-administration of clioquinol and Aβ42 vaccines, significantly reduce Aβ deposits in the brains of transgenic AD mice [10]. In non-rodent models, a rapid improvement of canine cognitive dysfunction with amyloid immunotherapy suggests the important use of the canine model in testing vaccines for AD [11]. So far, the limitations of Aβ-based immunotherapy include the development of encephalitis, the lack of clinical improvement, and the lack of effect on neurofibrillary tangles (NFTs), another major neuropathological feature of AD. Other critical points relate to the study design and several variables in imunotherapy trials, which are essential for optimizing trial designs and improving conditions for participants [12]. Due to the central role of NFTs in dementia, immunotherapy targeting these tau proteinous aggregates is an important area of research [13, 14]. Notably, an active immunotherapy targeting the tau pathological epitope phospho- Ser422 was found to be efficient, resulting in tau clearance and improved cognitive deficits promoted by tau pathology in a well-defined tau transgenic model [15]. Like Aβ oligomers, the putative role of tau oligomers in AD pathophysiology has prompted an investigation into tau oligomers as potential immunotherapeutic targets for AD and tauopathies [16]. Taken together, these results suggest that immunotherapies targeting Aβ alone may be insufficient for disease modification. To this end, researchers also began testing whether IVIG might serve as an alternative immunotherapeutic strategy. IVIG is a mixture of naturally occurring human IgG antibodies derived from the plasma of healthy young volunteers. Notably, IVIG has been used for nearly half a century for primary humoral immune deficiencies and autoimmune syndromes and, more recently, a number of neurologic disorders such as chronic inflammatory demyelinating polyradiculoneuropathy and Guillain-Barré syndrome [17, 18]. The rationale for using IVIG for the treatment of AD gained traction for a number of reasons. IVIG was found to contain elevated levels of antibodies against multiple conformations of Aβ monomers and aggregates [19, 20], yet its repertoire of naturally occurring antibodies might also be predicted to normalize the inflammatory component of AD. The safety profile of IVIG for other diseases also mitigated concerns for AD clinical trials. Furthermore, if IVIG was found to be beneficial in AD, the potential existed for identifying treatment-specific antibodies to elucidate pathogenic mechanisms and allow for more targeted therapeutic designs. However, despite the initial promise of Phase I and II clinical trials conducted in Germany and the US, a recent multicenter double-blinded Phase III study of 390 subjects, called the Gammaglobulin Alzheimer’s Partnership (GAP), did not meet primary endpoints of slowing cognitive and functional decline [21]. Then again, the GAP study results continued to support IVIG’s positive safety profile and showed potentially beneficial effects for pre-specified moderate AD and apoE4 carrier subgroups. Concurrent with these clinical trials, several preclinical studies demonstrated that IVIG was neuroprotective against Aβ toxicity in vitro and enhanced microglia- mediated Aβ clearance ex vivo, whereas in vivo IVIG delivery reduced inflammation in AD transgenic mice [22, 23]. Hence, the mechanism of action for IVIG is still of considerable interest in the field and there remains the opportunity for testing the extent to which optimized doses of IVIG delivered early enough in the AD trajectory might yet prove beneficial for modifying disease progression. In the present HT issue, we summarize the state of the field with respect to IVIG as a potential therapy for AD and explore further the potential mechanisms of IVIG neuroprotection in preclinical models of AD. Puli and colleagues review our current understanding of the biologic and therapeutic properties of IVIG relevant to AD therapy and highlight their in vitro and in vivo studies on IVIG biological activities, including the suppression of neuroinflammatory microglial activation and concomitant increase in neurogenesis in APP/PS1 mice [24]. Gong and colleagues expound upon IVIG immunomodulatory mechanisms by showing that IVIG regulates complement-derived anaphylatoxins, such as C5a and C3, which in turn upregulates AMPA receptor-PKACREB signaling pathways and improves synaptic function and cognition in the Tg2576 mouse model of AD [25]. Lahiri and Ray add to the diverse repertoire of IVIG neuroprotection by reporting that treatment with IVIG protects neuronal viability and synaptic proteins in primary rat hippocampal neurons as well as in primary human brain cultures challenged with oxidative stress, suggesting a potent neuropreservatory effect of IVIG against oxidative insults [26]. In addition, although IVIG has been reported to reduce amyloid burden in some AD transgenic models, its potential effects on tau NFT-like pathology in rodent models of disease are unclear. Counts and colleagues show that IVIG reduces hippocampal tau pathology in the 3xTg mouse model of AD that exhibits NFT as well as plaque-like deposits. In addition, this study reveals that IVIG preserves plasma levels of mRNAs regulating neuronal cytoskeletal plasticity function and calcium-mediated signaling compared to placebo [27]. It is important to note that not all IVIG preclinical studies have produced consistently positive results [28]. In this issue, Joly-Amado and colleagues describe how four weeks of IVIG infusion in Tg2576 mice led to widespread distribution of human IgG in the forebrain, but had no effect on amyloid burden or cognition [29]. However, the authors conclude by agreeing that the beneficial effects of IVIG in mouse models of AD are not likely due to its anti-Aβ antibody components alone, but must also involve its wide range of antiinflammatory, anti-oxidant, and other prosurvival and neuroprotective properties. Hence, despite the negative topline results from the GAP trial, these unique properties of IVIG suggest that this polyclonal IgG mixture can potentially be a safe and highly effective “top down” therapy for a complex multifactorial disease like AD. Moreover, the data derived from preclinical study designs may help guide current and future IVIG clinical trials targeting early stage patients with more optimized treatment regimens to prevent or delay the onset of AD symptomology [30]. Finally, since efforts to immunize against tau [31] and other AD-related targets have been encouraging, these studies would potentially be excellent subject matters for a future HT issue of the journal.

Alzheimer’s disease (AD) is a chronic neurodegenerative disease associated with intracerebral accumulation of aggregated amyloid-beta (Aβ) and tau proteins, as well as neuroinflammation. Human intravenous immunoglobulin (IVIG) is a mixture of polyclonal IgG antibodies isolated and pooled from thousands of healthy human donors. The scientific rationale for testing IVIG as a potential AD treatment include its natural anti-Aβ antibody activity, its favorable safety profile and inherent anti-inflammatory/immunomodulatory properties. Over the past decade, several clinical and pre-clinical experimental findings, advanced our knowledge about biological and therapeutic properties of IVIG that are relevant to AD therapy. Anti-amyloid antibodies in IVIG show significantly higher binding avidity for amyloid oligomers and fibrils than for Aβ monomers. In a double transgenic murine model of AD, intracerebral injection of IVIG causes suppression of Aβ fibril pathology whereas long term peripheral IVIG treatments causes elevation of total brain Aβ levels with no measurable impact on Aβ deposits or tendency for inducing cerebral microhemmorhage. Furthermore, chronic IVIG treatment suppressed neuroinflammation and fostered adult hippocampal neurogenesis. In clinical studies with AD patients, IVIG showed an acceptable safety profile and has not been reported to increase the incidence of amyloid related imaging abnormalities. Preliminary studies on small number of patients reported clinical benefits in mild to moderate stage AD patients. However, double blind, placebo controlled studies later did not replicate those initial findings. Interestingly though, in APOE4 carriers and in moderate disease stage subgroups, positive cognitive signals were reported. Nevertheless, both clinical and experimental (mouse) studies show that antibodies in IVIG can accumulate in CNS and its biological activities include neutralization of Aβ oligomers, suppression of neuroinflammation and immunomodulation. Identifying mediators of IVIG’s effects at the cellular and molecular level is warranted. In light of its favourable safety profile and aforementioned biological properties, IVIG is still an enigmatic experimental candidate with enormous potential for being an AD therapeutic.

Human intravenous immunoglobulin (IVIG) has been indicated as a potential therapy for autoimmune neurological disorders, as well as in many neurodegenerative diseases, with various underlying therapeutic mechanisms such as regulation of T-cell trafficking, cytokines, Fc receptor blocking, and interruption of complement activation cascade. In Alzheimer’s disease (AD), IVIG presents naturally occurring antibodies against amyloid-beta (Aβ) aggregation, thus IVIG immunotherapy may increase the clearance of Aβ and protect brain function. Recently, we and others reported that besides Aβ clearance, IVIG specifically regulates the levels of complement-derived anaphylatoxins, such as C5a and C3, which play an important role in the regulation of AMPA and NMDA receptor expression in the brain and further upregulate the AMPA-PKA-CREB signaling pathway and synaptic function in AD mouse models. Since down-regulation of complement components has been linked with deficits of cognitive function in age-related dementia following the decline of innate immunity during aging, the IVIG immunotherapy could be an attractive novel AD therapeutic through its local regulation of C3, C5a component levels in brain.

Alzheimer’s disease (AD) is characterized by deleterious accumulation of amyloid-β (Aβ) peptide into senile plaque, neurofibrillary tangles formed from hyperphosphorylated tau protein, and loss of cholinergic synapses in the cerebral cortex. The deposition of Aβ-loaded plaques results in microglial activation and subsequent production of reactive oxygen species (ROS), including free radicals. Neurons in aging and AD brains are particularly vulnerable to ROS and other toxic stimuli. Therefore, agents that decrease the vulnerability of neurons against ROS may provide therapeutic values for the treatment or prevention of AD. In the present study, our goal was to test whether intravenous immunoglobulin (IVIG) treatment could preserve as well as protect neurons from oxidative damage. We report that treatment with IVIG protects neuronal viability and synaptic proteins in primary rat hippocampal neurons. Further, we demonstrate the tolerability of IVIG treatment in the primary human fetal mixed brain cultures. Indeed, a high dose (20mg/ml) of IVIG treatment was well-tolerated by primary human brain cultures that exhibit a normal neuronal phenotype. We also observed a potent neuropreservatory effect of IVIG against ROS-mediated oxidative insults in these human fetal brain cultures. These results indicate that IVIG treatment has great potential to preserve and protect primary human neuronal-enriched cultures and to potentially rescue dying neurons from oxidative insults. Therefore, our findings suggest that IVIG treatment may represent an important therapeutic agent for clinical trials designed to prevent and delay the onset of neurodegeneration as well as AD pathology.

Despite recent negative results of the Gammaglobulin Alzheimer's Partnership (GAP) trial, the good tolerability to intravenous immunoglobulin (IVIG) and its potential benefit for patient subpopulations have highlighted the importance of understanding IVIG’s mechanism of action. IVIG contains antibodies to amyloid suggesting an amyloid clearance mechanism. However, the suboptimal results of the amyloid immunotherapy trials suggest an additional mechanism. Therefore, we tested whether IVIG alters the expression of tau neurofibrillary tangle (NFT)-like deposits within hippocampal CA1 neurons of the 3xTg mouse model of AD. Three-month-old mice were treated intravenously with IVIG (10%, 400 mg/kg) or placebo (10% BSA/saline) every two weeks for either three or six months. At sacrifice, plasma was isolated for gene expression profiling and brains were processed for immunohistochemistry using the AT-180 antibody, which recognizes hyperphosphorylated tau in NFTs. Stereologic analysis of CA1 neurons following three months of treatment revealed no difference in AT-180+ neuron number but a significant 15-20% decrease in AT-180 intraneuronal optical density with IVIG compared to placebo. By contrast, the number of AT-180+ CA1 neurons was reduced by 25- 30% following six months of IVIG treatment compared to placebo. Expression profiling studies showed that IVIG treatment resulted in a significant 40-50% increase in plasma levels of genes regulating neuronal cytoskeletal plasticity function and calcium-mediated signaling compared to placebo. Moreover, several transcripts encoding protein phosphatase subunits were 40-50% higher in IVIG-treated mice. Hence, IVIG reduces hippocampal NFT pathology in the 3xTg mouse through a mechanism that may involve preservation of neuronal plasticity and tau phosphorylation homeostasis.

Intravenous immunoglobulin infusions into Alzheimer patients have been found to provide cognitive benefit over a period of 6 mo in open label studies. One suggestion has been that these preparations contain small amounts of antibodies directed against monomeric and oligomeric Aβ which underlie their effectiveness in patients. To test this hypothesis, we infused Gammagard®, a version of intravenous immunoglobulin (IVIG), into the lateral ventricle of amyloid precursor protein (APP) transgenic mice with pre-existing amyloid deposits. Mice were infused over 4 weeks, and tested behaviorally for the last 2 weeks of treatment. Brains were analyzed for histopathology. We found widespread distribution of human–immunoglobulin G (h-IgG) staining in the mouse forebrain, including cerebral cortices and hippocampus. Some cortical neurons appeared to concentrate the h-IgG, but we did not detect evidence of amyloid plaque labeling by h-IgG. The IVIG-treated mice had no change in phenotype compared to saline-infused animals with respect to activity, learning and memory, or amyloid deposition. APP mice infused with an anti-Aβ monoclonal antibody did show some reduction in amyloid deposits. These data do not support the argument that anti-Aβ antibodies in IVIG preparations are responsible for cognitive benefits seen with these preparations.

Alzheimer’s disease (AD) is the most common neurodegenerative disorder of the central nervous system. Current approaches for AD treatment only ameliorate symptoms. Therapeutic strategies that target the pathological processes of the disease remain elusive. Fluoxetine (FLX) is one of the most widely used antidepressants for the treatment of depression and anxiety associated with AD, however, it is unknown if the drug affects the pathogenesis of the disease. We showed that FLX improved spatial memory, learning and emotional behaviors of APP/PS1 mice, a well characterized model of AD. In the same mice, FLX effectively prevented the protein loss of synaptophysin (SYP) and microtubuleassociated protein 2 (MAP2). FLX was unable to prevent plaque formation, but significantly lowered high levels of soluble β-amyloid (Aβ) in brain tissue, cerebrospinal fluid (CSF) and blood sera. FLX also effectively inhibited the phosphorylation of amyloid precursor protein (APP) at T668, which may be a possible mechanism of the reduced Aβ production in APP/PS1 mouse after treatment.

Objective: To examine the association of mid-life exposure to several psychiatric disorders with the development of late-life dementia. Methods: A matched case-control study using Western Australian state-wide hospital inpatient, outpatient mental health and emergency records linked to death records. Incident dementia cases (2000-2009) aged 65 to 84 years were sex- and age-matched to an electoral roll control. Records as far back as 1970 were used to assess exposure to medical risk factors before age 65 years. Candidate psychiatric risk factors were required to be present at least 10 years before dementia onset to ensure direction of potential causality. Odds ratios were estimated using conditional logistic regression. Results: 13, 568 dementia cases (median age 78.7 years, 43.4 % male) were matched to a control. Depression, bipolar disorder, schizophrenia, anxiety disorder and alcohol dependence were found to be significant and independent risk factors for late-life dementia after adjusting for diabetes, heart disease, cerebrovascular disease and smoking risk factors. The effect of a history of depression, schizophrenia and alcohol dependency on dementia risk varied with age, being strongest for earlier onset late-life dementia and waning at older ages. Conclusion: Severe depression, anxiety disorder, bipolar disorder, schizophrenia and alcoholic dependency disorder treated by specialists in psychiatric facilities in mid-life are important risk factors for late-life dementia. These psychiatric conditions need to be considered in future studies of the risk and prevention of late-life dementia.

Metabotropic glutamate receptor 5 (mGluR5) is highly expressed throughout the forebrain and hippocampus. Several lines of evidence support the role of this receptor in brain development and developmental disorders, as well as in neurodegenerative disorders like Alzheimer’s disease (AD). In the present study, the expression pattern of mGluR5 was investigated by immunocytochemistry in the developing hippocampus from patients with Down's syndrome (DS) and in adults with DS and AD. mGluR5 was expressed in developing human hippocampus from the earliest stages tested (9 gestational weeks), with strong expression in the ventricular/subventricular zones. We observed a consistent similar temporal and spatial neuronal pattern of expression in DS hippocampus. However, in DS we detected increased prenatal mGluR5 expression in white matter astrocytes, which persisted postnatally. In addition, in adult DS patients with widespread ADassociated neurodegeneration (DS-AD) increased mGluR5 expression was detected in astrocytes around amyloid plaque. In vitro data confirm the existence of a modulatory crosstalk between amyloid-β and mGluR5 in human astrocytes. These findings demonstrate a developmental regulation of mGluR5 in human hippocampus and suggest a role for this receptor in astrocytes during early development in DS hippocampus, as well as a potential contribution to the pathogenesis of ADassociated pathology.

Objective: The aim of this study was to analyze the relationship between low bone mineral density (BMD) and conversion from mild cognitive impairment (MCI) to Alzheimer’s disease (AD) dementia in a Chinese cohort. Methods: Men and women (n=946) aged 60–75 underwent a dual X-ray absorptiometry (DXA) study of the lumbar spine and hip and were followed annually for 5 years. Their cognitive and functional status were assessed using the Chinese version of the Mini-Mental State Examination (MMSE) and an assessment of the instrumental activities of daily living (ADL). Results: There was a positive relationship between osteoporosis and a decline in cognition and function (P<0.001) based on MMSE and ADL scores. The subjects with BMD values in the lowest quartile had a 2-fold increased risk of AD conversion compared with the controls. These results suggest that severe BMD loss is associated with an increased risk of AD conversion in both women and men. Conclusions: Osteoporosis was associated with an increased risk of incident AD dementia. Additionally, low BMD at baseline was associated with an increased risk of AD in both women and men.

Alzheimer’s disease (AD) is contributed by multiple pathogenic causes. The anomalous protein amyloid-β (Aβ) is regarded as a pivotal factor in AD, and originates from enzymatic cleavage of a precursor protein by the secretase family. 1-(3’,4’-Dichloro-2-fluoro[1,1’-biphenyl]-4-yl)-cyclopropanecarboxylic acid (CHF5074) is a non-steroidal antiinflammatory derivative able to inhibit Aβ deposition in the brain of transgenic mouse models of AD. The proapoptotic cytokine TRAIL has been reported to mediate Aβ-dependent neurotoxicity. Here, the effects of CHF5074 on Aβ25-35- triggered TRAIL toxicity were evaluated in the differentiated human neuroblastoma cell line SH-SY5Y in vitro. Cells were pre-treated 1h with CHF5074 at graded concentrations (range: 1 nM-1uM) and then challenged for 72 h with either Aβ25-35 or TRAIL. Results show that CHF5074 treatment prevented apoptotic death in SH-SY5Y cell line in a concentration- dependent fashion. Its maximally active concentration was 10 nM. Then, investigation of related molecular mechanisms underlying such protective effect of CHF5074 suggested that the levels of caspases, as well as of various kinases, including stress and MAP kinases, are modulated by CHF5074. Finally, treatment of injured human neuroblastoma cell line SH-SY5Y with CHF5074 resulted in prominent protection from apoptotic death. The bulk of these data suggest that CHF5074 represents a potential candidate for pharmacological neuroprotective treatment in neurodegenerative disorders.