Immunotherapy of Alzheimer's disease (AD): From murine models to anti-amyloid beta (Aβ) human monoclonal antibodies

Controversial Past, Splendid Present, Unpredictable Future: A Brief Review of Alzheimer Disease History

Background: The concept of Alzheimer disease (AD)-since its histological discovery by Alzheimer to the present day-has undergone substantial modifications. Methods: We conducted a classical narrative review of this field with a bibliography selection (giving preference to Medline best match). Results: The following subjects are reviewed and discussed: Alzheimer's discovery, Kraepelin's creation of a new disease that was a rare condition until the 1970's, the growing interest and investment in AD as a major killer in a society with a large elderly population in the second half of the 20th century, the consolidation of the AD clinicopathological model, and the modern AD nosology based on the dominant amyloid hypothesis among many others. In the 21st century, the development of AD biomarkers has supported a novel biological definition of AD, although the proposed therapies have failed to cure this disease. The incidence of dementia/AD has shown a decrease in affluent countries (possibly due to control of risk factors), and mixed dementia has been established as the most frequent etiology in the oldest old. Conclusions: The current concept of AD lacks unanimity. Many hypotheses attempt to explain its complex physiopathology entwined with aging, and the dominant amyloid cascade has yielded poor therapeutic results. The reduction in the incidence of dementia/AD appears promising but it should be confirmed in the future. A reevaluation of the AD concept is also necessary.

Cholinergic Transporters Serve as Potential Targets in Alzheimer's Disease

Alzheimer's disease (AD) is a specific brain disease that gradually worsens due to dementia over a long period. AD accounts for almost 60% to 80% of cases of dementia. Any damage to neurons affects their ability to communicate, leading to alteration in thinking, behaviour and feelings. Besides mental, motor abilities of an individual may also be affected due to AD. Therefore, it is cardinal to understand the key mechanisms by which either AD progression can be ceased or, after the onset of the disease it could be reverted. Both of these steps need the identification of a particular receptor or a molecular marker through which a drug can enter the neurons. Cholinergic transporters are such potential targets of AD, which regulate the movement of acetylcholine and thus regulate the nerve impulse conduction in the brain. The current article entails information regarding a variety of cholinergic transporters, which will provide a research gap to the global scientific community.

Advances in Alzheimer's disease's pharmacological treatment

Alzheimer's disease (AD) is the most common type of dementia in the elderly. Several hypotheses emerged from AD pathophysiological mechanisms. However, no neuronal protective or regenerative drug is available nowadays. Researchers still work in drug development and are finding new molecular targets to treat AD. Therefore, this study aimed to summarize main advances in AD pharmacological therapy. Clinical trials registered in the National Library of Medicine database were selected and analyzed accordingly to molecular targets, therapeutic effects, and safety profile. The most common outcome was the lack of efficacy. Only seven trials concluded that tested drugs were safe and induced any kind of therapeutic improvement. Three works showed therapeutic effects followed by toxicity. In addition to aducanumab recent FDA approval, antibodies against amyloid-β (Aβ) showed no noteworthy results. 5-HT6 antagonists, tau inhibitors and nicotinic agonists' data were discouraging. However, anti-Aβ vaccine, BACE inhibitor and anti-neuroinflammation drugs showed promising results.

Case report: MOG-IgG-associated encephalitis with Epstein-Barr virus infection and Alzheimer's pathologic change in cerebrospinal fluid

Immunoglobulin G antibodies to myelin oligodendrocyte glycoprotein (MOG-IgG) associated disease is a rare, demyelinated disease in the central nerve system (CNS) predominately involving optic nerve, spinal cord, and brain leading to optic neuritis (ON), transverse myelitis (TM), encephalitis. The phenotype of MOG-IgG-associated encephalitis is similar to acute disseminated encephalomyelitis (ADEM) presenting with seizures, abnormal behavioral and psychological symptoms, and cognitive impairment. A few brain biopsies show multiple sclerosis (MS) pattern histopathology with T cells, macrophages, and complement activation. To date, how MOG-IgG is produced is unknown. Herein, we report a case of a 32-year-old male with MOG-IgG-associated encephalitis presenting MOG-IgG in cerebrospinal fluid (CSF) but seronegative, as well as Epstein-Barr virus (EBV) infection and Alzheimer's pathologic change in CSF (Aβ42 = 317 pg/ml, T-Tau = 538 pg/ml, p-Tau =10.09 pg/ml). With a combination treatment of administering intravenous immunoglobulin (0.4 mg/kg/d, 5 days) with a low dose of methylprednisolone (80 mg/d, 5 days) and rituximab (100 mg/week, 3 weeks), the patient recovered significantly after 3 months follow-up. This case provides us with new thoughts into the production of MOG-IgG and the possible pathologic mechanism of MOG-IgG-associated disease (MOG-AD) and simultaneously further confirms the interaction between EBV and changes of CSF biomarkers of Alzheimer's disease (AD).

Formaldehyde-Crosslinked Nontoxic Aβ Monomers to Form Toxic Aβ Dimers and Aggregates: Pathogenicity and Therapeutic Perspectives

Alzheimer's disease (AD) is characterized by the presence of senile plaques in the brain. However, medicines targeting amyloid-beta (Aβ) have not achieved the expected clinical effects. This review focuses on the formation mechanism of the Aβ dimer (the basic unit of oligomers and fibrils) and its tremendous potential as a drug target. Recently, age-associated formaldehyde and Aβ-derived formaldehyde have been found to crosslink the nontoxic Aβ monomer to form the toxic dimers, oligomers and fibrils. Particularly, Aβ-induced formaldehyde accumulation and formaldehyde-promoted Aβ aggregation form a vicious cycle. Subsequently, formaldehyde initiates Aβ toxicity in both the early-and late-onset AD. These facts also explain why AD drugs targeting only Aβ do not have the desired therapeutic effects. Development of the nanoparticle-based medicines targeting both formaldehyde and Aβ dimer is a promising strategy for improving the drug efficacy by penetrating blood-brain barrier and extracellular space into the cortical neurons in AD patients.

Alzheimer's disease neuropathology is exacerbated following traumatic brain injury. Neuroprotection by co-administration of nanowired mesenchymal stem cells and cerebrolysin with monoclonal antibodies to amyloid beta peptide

Military personnel are prone to traumatic brain injury (TBI) that is one of the risk factors in developing Alzheimer's disease (AD) at a later stage. TBI induces breakdown of the blood-brain barrier (BBB) to serum proteins into the brain and leads to extravasation of plasma amyloid beta peptide (ΑβP) into the brain fluid compartments causing AD brain pathology. Thus, there is a need to expand our knowledge on the role of TBI in AD. In addition, exploration of the novel roles of nanomedicine in AD and TBI for neuroprotection is the need of the hour. Since stem cells and neurotrophic factors play important roles in TBI and in AD, it is likely that nanodelivery of these agents exert superior neuroprotection in TBI induced exacerbation of AD brain pathology. In this review, these aspects are examined in details based on our own investigations in the light of current scientific literature in the field. Our observations show that TBI exacerbates AD brain pathology and TiO₂ nanowired delivery of mesenchymal stem cells together with cerebrolysin-a balanced composition of several neurotrophic factors and active peptide fragments, and monoclonal antibodies to amyloid beta protein thwarted the development of neuropathology following TBI in AD, not reported earlier.

Maternal antibodies facilitate Amyloid-β clearance by activating Fc-receptor-Syk-mediated phagocytosis

Maternal antibodies (MAbs) protect against infections in immunologically-immature neonates. Maternally transferred immunity may also be harnessed to target diseases associated with endogenous protein misfolding and aggregation, such as Alzheimer's disease (AD) and AD-pathology in Down syndrome (DS). While familial early-onset AD (fEOAD) is associated with autosomal dominant mutations in the APP, PSEN1,2 genes, promoting cerebral Amyloid-β (Aβ) deposition, DS features a life-long overexpression of the APP and DYRK1A genes, leading to a cognitive decline mediated by Aβ overproduction and tau hyperphosphorylation. Although no prenatal screening for fEOAD-related mutations is in clinical practice, DS can be diagnosed in utero. We hypothesized that anti-Aβ MAbs might promote the removal of early Aβ accumulation in the central nervous system of human APP-expressing mice. To this end, a DNA-vaccine expressing Aβ1-11 was delivered to wild-type female mice, followed by mating with 5xFAD males, which exhibit early Aβ plaque formation. MAbs reduce the offspring's cortical Aβ levels 4 months after antibodies were undetectable, along with alleviating short-term memory deficits. MAbs elicit a long-term shift in microglial phenotype in a mechanism involving activation of the FcγR1/Syk/Cofilin pathway. These data suggest that maternal immunization can alleviate cognitive decline mediated by early Aβ deposition, as occurs in EOAD and DS.

Alzheimer's disease; a review of the pathophysiological basis and therapeutic interventions

Alzheimer's disease (AD) is a neurodegenerative disorder and is identified as the most common cause for dementia. Despite huge global economic burden and the impact on the close family of the patients, there is no definitive cure and thus, improved treatment methods are of need. While memory and cognition are severely affected in AD, exact etiology is yet unknown. The β-Amyloid plaque formation and aggregation hypothesis is among the well-known hypotheses used to explain disease pathogenesis. Currently there are five Food and Drug Administration (FDA) approved drugs as treatment options. All these drugs are used for symptomatic treatment of AD. Thus, disease modifying therapies which can directly address the pathological changes in AD, are needed. Such therapies could be designed based on inhibiting key steps of pathogenesis. Currently there are novel AD drug candidates with various therapeutic mechanisms, undergoing different stages of drug development. Extensive research is being done globally to broaden understanding of the exact mechanisms involved in AD and to develop therapeutic agents that can successfully hinder the occurrence and progression of the disease. In this review, a comprehensive approach to understanding AD and suggestions to be considered in the development of therapeutics for it are presented.

Mechanisms of action of amyloid-beta and its precursor protein in neuronal cell death

Extracellular senile plaques and intracellular neurofibrillary tangles are the neuropathological findings of the Alzheimer's disease (AD). Based on the amyloid cascade hypothesis, the main component of senile plaques, the amyloid-beta (Aβ) peptide, and its derivative called amyloid precursor protein (APP) both have been found to place their central roles in AD development for years. However, the recent therapeutics have yet to reverse or halt this disease. Previous evidence demonstrates that the accumulation of Aβ peptides and APP can exert neurotoxicity and ultimately neuronal cell death. Hence, we discuss the mechanisms of excessive production of Aβ peptides and APP serving as pathophysiologic stimuli for the initiation of various cell signalling pathways including apoptosis, necrosis, necroptosis and autophagy which lead to neuronal cell death. Conversely, the activation of such pathways could also result in the abnormal generation of APP and Aβ peptides. An elucidation of actions of APP and its metabolite, Aβ, could be vital in suggesting novel therapeutic opportunities.

Moringa Oleifera Alleviates Homocysteine-Induced Alzheimer's Disease-Like Pathology and Cognitive Impairments

Alzheimer’s disease (AD) is multifactorial with unclear etiopathology. Due to the complexity of AD, many attempted single therapy treatments, like Aβ immunization, have generally failed. Therefore, there is a need for drugs with multiple benefits. Naturally occurring phytochemicals with neuroprotective, anti-amyloidogenic, antioxidative, and anti-inflammatory properties could be a possible way out. In this study, the effect of Moringa oleifera (MO), a naturally occurring plant with high antioxidative, anti-inflammatory, and neuroprotective effects, was evaluated on hyperhomocysteinemia (HHcy) induced AD-like pathology in rats. Homocysteine (Hcy) injection for 14 days was used to induce AD-like pathology. Simultaneous MO extract gavage followed the injection as a preventive treatment or, after injection completion, MO gavage was performed for another 14 days as a curative treatment. MO was found to not only prevent but also rescue the oxidative stress and cognitive impairments induced by Hcy treatment. Moreover, MO recovered the decreased synaptic proteins PSD93, PSD95, Synapsin 1 and Synaptophysin, and improved neurodegeneration. Interestingly, MO decreased the Hyc-induced tau hyperphosphorylation at different sites including S-199, T-231, S-396, and S-404, and at the same time decreased Aβ production through downregulation of BACE1. These effects in HHcy rats were accompanied by a decrease in calpain activity under MO treatment, supporting that calpain activation might be involved in AD pathogenesis in HHcy rats. Taken together, our data, for the first time, provided evidence that MO alleviates tau hyperphosphorylation and Aβ pathology in a HHcy AD rat model. This and previous other studies support MO as a good candidate for, and could provide new insights into, the treatment of AD and other tauopathies.

Alzheimer's disease: Targeting the Cholinergic System

Acetylcholine (ACh) has a crucial role in the peripheral and central nervous systems. The enzyme choline acetyltransferase (ChAT) is responsible for synthesizing ACh from acetyl-CoA and choline in the cytoplasm and the vesicular acetylcholine transporter (VAChT) uptakes the neurotransmitter into synaptic vesicles. Following depolarization, ACh undergoes exocytosis reaching the synaptic cleft, where it can bind its receptors, including muscarinic and nicotinic receptors. ACh present at the synaptic cleft is promptly hydrolyzed by the enzyme acetylcholinesterase (AChE), forming acetate and choline, which is recycled into the presynaptic nerve terminal by the high-affinity choline transporter (CHT1). Cholinergic neurons located in the basal forebrain, including the neurons that form the nucleus basalis of Meynert, are severely lost in Alzheimer’s disease (AD). AD is the most ordinary cause of dementia affecting 25 million people worldwide. The hallmarks of the disease are the accumulation of neurofibrillary tangles and amyloid plaques. However, there is no real correlation between levels of cortical plaques and AD-related cognitive impairment. Nevertheless, synaptic loss is the principal correlate of disease progression and loss of cholinergic neurons contributes to memory and attention deficits. Thus, drugs that act on the cholinergic system represent a promising option to treat AD patients.

The Differential Profiling of Ubiquitin-Proteasome and Autophagy Systems in Different Tissues before the Onset of Huntington's Disease Models

Huntington's disease (HD) is a genetic and neurodegenerative disease, leading to motor and cognitive dysfunction in HD patients. At cellular level, this disease is caused by the accumulation of mutant huntingtin (HTT) in different cells, and finally results in the dysfunction of different cells. To clean these mutant proteins, ubiquitin-proteasome system (UPS) and autophagy system are two critical pathways in the brain; however, little is known in other peripheral tissues. As mutant HTT affects different tissues progressively and might influence the UPS and autophagy pathways at early stages, we attempted to examine two clearance systems in HD models before the onset. Here, in vitro results showed that the accumulation of UPS signals with time was observed obviously in neuroblastoma and kidney cells, not in other cells. In HD transgenic mice, we observed the impairment of UPS, but not autophagy, over time in the cortex and striatum. In heart and muscle tissues, disturbance of autophagy was observed, whereas dysfunction of UPS was displayed in liver and lung. These results suggest that two protein clearance pathways are disturbed differentially in different tissues before the onset of HD, and enhancement of protein clearance at early stages might provide a potential stratagem to alleviate the progression of HD.

An improved Bacillus subtilis cell factory for producing scyllo-inositol, a promising therapeutic agent for Alzheimer's disease

Background

Bacillus subtilis 168 possesses an efficient pathway to metabolize some of the stereoisomers of inositol, including myo-inositol (MI) and scyllo-inositol (SI). Previously we reported a prototype of a B. subtilis cell factory with modified inositol metabolism that converts MI into SI in the culture medium. However, it wasted half of initial 1.0% (w/v) MI, and the conversion was limited to produce only 0.4% (w/v) SI. To achieve a more efficient SI production, we attempted additional modifications.

Results

All “useless” genes involved in MI and SI metabolism were deleted. Although no elevation in SI production was observed in the deletion strain, it did result in no wastage of MI anymore. Thus additionally, overexpression of the key enzymes, IolG and IolW, was appended to demonstrate that simultaneous overexpression of them enabled complete conversion of all MI into SI.

Conclusions

The B. subtilis cell factory was improved to yield an SI production rate of 10 g/L/48 h at least. The improved conversion was achieved only in the presence of enriched nutrition in the form of 2% (w/v) Bacto soytone in the medium, which may be due to the increasing demand for regeneration of cofactors.

In vitro immunization of Epstein-Barr virus-immortalized B cells augments antigen-specific antibody production

The current method for in vitro immunization (IVI) uses several antigens including toxins, food allergens, pathogenic bacteria, and self-antigen-derived peptides that induce an antigen-specific immune response in peripheral blood mononuclear cells (PBMCs). This protocol, however, requires donor blood collection and preparation of PBMCs before every IVI. In the present study, we aimed to design a more efficient system utilizing B cells immortalized with Epstein-Barr virus (EBV-B) as host cells for IVI to make antigen-specific antibodies. Results showed that previously antigen-sensitized, EBV-B cells exposed to the antigen along with IL-6, CpG oligonucleotides, and CD40 ligand signal produced antigen-specific antibodies. These results provide evidence for a novel and easy method to expand memory-type B cells and produce antigen-specific antibodies.

Dnr1 mutations cause neurodegeneration in Drosophila by activating the innate immune response in the brain

A growing body of evidence in humans implicates chronic activation of the innate immune response in the brain as a major cause of neuropathology in various neurodegenerative conditions, although the mechanisms remain unclear. In an unbiased genetic screen for mutants exhibiting neurodegeneration in Drosophila, we have recovered a mutation of dnr1 (defense repressor 1), a negative regulator of the Imd (immune deficiency) innate immune-response pathway. dnr1 mutants exhibit shortened lifespan and progressive, age-dependent neuropathology associated with activation of the Imd pathway and elevated expression of AMP (antimicrobial peptide) genes. To test the hypothesis that overactivation of innate immune-response pathways in the brain is responsible for neurodegeneration, we demonstrated that direct bacterial infection in the brain of wild-type flies also triggers neurodegeneration. In both cases, neurodegeneration is dependent on the NF-κB transcription factor, Relish. Moreover, we found that neural overexpression of individual AMP genes is sufficient to cause neurodegeneration. These results provide a mechanistic link between innate immune responses and neurodegeneration and may have important implications for the role of neuroinflammation in human neurodegenerative diseases as well.

Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease with well-defined pathophysiological mechanisms, mostly affecting medial temporal lobe and associative neocortical structures. Neuritic plaques and neurofibrillary tangles represent the pathological hallmarks of AD, and are respectively related to the accumulation of the amyloid-beta peptide (Aβ) in brain tissues, and to cytoskeletal changes that arise from the hyperphosphorylation of microtubule-associated Tau protein in neurons. According to the amyloid hypothesis of AD, the overproduction of Aβ is a consequence of the disruption of homeostatic processes that regulate the proteolytic cleavage of the amyloid precursor protein (APP). Genetic, age-related and environmental factors contribute to a metabolic shift favoring the amyloidogenic processing of APP in detriment of the physiological, secretory pathway. Aβ peptides are generated by the successive cleavage of APP by beta-secretase (BACE-1) and gamma-secretase, which has been recently characterized as part of the presenilin complex. Among several beta-amyloid isoforms that bear subtle differences depending on the number of C-terminal amino acids, Aβ (1-42) plays a pivotal role in the pathogenesis of AD. The neurotoxic potential of the Aβ peptide results from its biochemical properties that favor aggregation into insoluble oligomers and protofibrils. These further originate fibrillary Aβ species that accumulate into senile and neuritic plaques. These processes, along with a reduction of Aβ clearance from the brain, leads to the extracellular accumulation of Aβ, and the subsequent activation of neurotoxic cascades that ultimately lead to cytoskeletal changes, neuronal dysfunction and cellular death. Intracerebral amyloidosis develops in AD patients in an age-dependent manner, but recent evidence indicate that it may be observed in some subjects as early as in the third or fourth decades of life, with increasing magnitude in late middle age, and highest estimates in old age. According to recent propositions, three clinical phases of Alzheimer's disease may be defined: (i) pre-symptomatic (or pre-clinical) AD, which may last for several years or decades until the overproduction and accumulation of Aβ in the brain reaches a critical level that triggers the amyloid cascade; (ii) pre-dementia phase of AD (compatible with the definition of progressive, amnestic mild cognitive impairment), in which early-stage pathology is present, ranging from mild neuronal dystrophy to early-stage Braak pathology, and may last for several years according to individual resilience and brain reserve; (iii) clinically defined dementia phase of AD, in which cognitive and functional impairment is severe enough to surmount the dementia threshold; at this stage there is significant accumulation of neuritic plaques and neurofibrillary tangles in affected brain areas, bearing relationship with the magnitude of global impairment. New technologies based on structural and functional neuroimaging, and on the biochemical analysis of cerebrospinal fluid may depict correlates of intracerebral amyloidosis in individuals with mild, pre-dementia symptoms. These methods are commonly referred to as AD-related biomarkers, and the combination of clinical and biological information yields good diagnostic accuracy to identify individuals at high risk of AD. In other words, the characterization of pathogenic Aβ by means of biochemical analysis of biological fluids or by molecular neuroimaging are presented as diagnostic tools to help identify AD cases at the earliest stages of the disease process. The relevance of this early diagnosis of AD relies on the hypothesis that pharmacological interventions with disease-modifying compounds are more likely to produce clinically relevant benefits if started early enough in the continuum towards dementia. Therapies targeting the modification of amyloid-related cascades may be viewed as promising strategies to attenuate or even to prevent dementia. Therefore, the cumulative knowledge on the pathogenesis of AD derived from basic science models will hopefully be translated into clinical practice in the forthcoming years.

A cell factory of Bacillus subtilis engineered for the simple bioconversion of myo-inositol to scyllo-inositol, a potential therapeutic agent for Alzheimer's disease

BACKGROUND

A stereoisomer of inositol, scyllo-inositol, is known as a promising therapeutic agent for Alzheimer's disease, since it prevents the accumulation of beta-amyloid deposits, a hallmark of the disease. However, this compound is relatively rare in nature, whereas another stereoisomer of inositol, myo-inositol, is abundantly available.

RESULTS

Bacillus subtilis possesses a unique inositol metabolism involving both stereoisomers. We manipulated the inositol metabolism in B. subtilis to permit the possible bioconversion from myo-inositol to scyllo-inositol. Within 48 h of cultivation, the engineered strain was able to convert almost half of 10 g/L myo-inositol to scyllo-inositol that accumulated in the culture medium.

CONCLUSIONS

The engineered B. subtilis serves as a prototype of cell factory enabling a novel and inexpensive supply of scyllo-inositol.

Chronic delivery of antibody fragments using immunoisolated cell implants as a passive vaccination tool

Background

Monoclonal antibodies and antibody fragments are powerful biotherapeutics for various debilitating diseases. However, high production costs, functional limitations such as inadequate pharmacokinetics and tissue accessibility are the current principal disadvantages for broadening their use in clinic.

Methodology and Principal Findings

We report a novel method for the long-term delivery of antibody fragments. We designed an allogenous immunoisolated implant consisting of polymer encapsulated myoblasts engineered to chronically release scFv antibodies targeted against the N-terminus of the Aβ peptide. Following a 6-month intracerebral therapy we observed a significant reduction of the production and aggregation of the Aβ peptide in the APP23 transgenic mouse model of Alzheimer's disease. In addition, functional assessment showed prevention of behavioral deficits related to anxiety and memory traits.

Conclusions and Significance

The chronic local release of antibodies using immunoisolated polymer cell implants represents an alternative passive vaccination strategy in Alzheimer's disease. This novel technique could potentially benefit other diseases presently treated by local and systemic antibody administration.

Autoantibodies in patients with Alzheimer's disease: pathogenetic role and potential use as biomarkers of disease progression

Growing evidence suggests that autoantibodies specific to distinct molecular antigens are present in sera or cerebrospinal fluids from patients with Alzheimer's disease (AD). They could have a protective (i.e., anti-β-amyloid) or a pathogenetic role (i.e., anti-GM1 or anti-ATP synthase) but, in any case, they might be considered as useful diagnostic or prognostic markers of the disease. In this review, we briefly summarize the autoantibodies known to be detectable in patients with AD and we discuss their potential role in the pathogenesis of the disease, as well as their potential use as peripheral blood biomarkers.

Novel therapeutic approach for Alzheimer's disease by removing amyloid beta protein from the brain with an extracorporeal removal system

The accumulation of amyloid beta (Abeta) protein in the brain reflects the cognitive impairment noted in Alzheimer's disease. Recent studies have shown that brain Abeta disappeared and cognitive improvement occurred as a result of passive or active Abeta immunization. Peripheral administration of nonimmunization substances, such as GM1 ganglioside, also reduced brain Abeta. Therefore, we hypothesized that the rapid removal of Abeta from the blood by an extracorporeal system may act as a peripheral Abeta sink from the brain. In the present study, we investigated the Abeta removal activity of medical materials as a first step toward the design of an Abeta removal system. First, the removal activities of six materials were studied for Abeta(1-40) and Abeta(1-42) by batch analysis in albumin solution or in human plasma for 1-16 h. Two of the six materials reduced the Abeta concentrations by 90-99% within 1 h. Next, the two effective materials, hexadecyl-alkylated cellulose particles (HDC) and charcoal, were analyzed in a continuous single-pass system with minicolumns. Both materials showed around 81-90% removal activity for more than 2 h, which corresponded to over 4 l of plasma treatment in humans. In a human extracorporeal system, HDC also removed both Abeta(1-40) and Abeta(1-42) from whole blood circulation. In conclusion, biomedical materials were found that could remove Abeta(1-40) and Abeta(1-42) effectively in an extracorporeal system. It is now conceivable that further studies can be undertaken to reduce Abeta concentrations in the brain to improve cognitive function.

Is passive immunization for Alzheimer's disease 'alive and well' or 'dead and buried'?

BACKGROUND

Passive immunization strategies are under investigation as potential disease-modifying therapies for Alzheimer's disease (AD). Current approaches, based on data demonstrating behavioral improvement and reduced pathology in transgenic animal models, have focused exclusively on immune targeting of beta-amyloid.

OBJECTIVE

To examine immunization strategies for AD.

METHODS

A review of relevant publications.

RESULTS/CONCLUSIONS

Preliminary results from three Phase II trials suggest both the promise and the need to exercise caution with this method of immunotherapy. The strategies used were distinct, using monoclonal N-terminal, central epitope, and polyclonal antibodies to maximize the efficacy and safety of each approach. The tested compounds are moving into Phase III trials for mild to moderate AD. We await the discoveries that from these studies that may yield the first disease-modifying therapy for AD.

Developing injectable immunoglobulins to treat cognitive impairment in Alzheimer's disease

BACKGROUND

Alzheimer's disease is a devastating disorder, clinically characterized by a comprehensive cognitive decline. The novel strategy of anti-amyloid-beta immunotherapy has been suggested following encouraging results obtained in murine models of Alzheimer's disease, in non-human primates, and in small-scale clinical trials.

OBJECTIVE

To examine the choice between active or passive anti-amyloid-beta immunization and the choice of the molecule to which the immune machinery should be targeted, which are central issues in future immune therapy of Alzheimer's disease.

METHODS

Research into the new area of Alzheimer's disease immune therapy is primarily based on in vivo and in vitro studies of murine models of Alzheimer's disease. The studies are hence limited to defined genetic deficiencies.

RESULTS/CONCLUSIONS

In humans, infusion of anti-amyloid-beta antibodies is considered a safer approach than active anti-amyloid-beta vaccination. Alzheimer's-disease-protective anti-amyloid-beta monoclonal antibodies should target specific epitopes within the amyloid beta(1 42) peptide, avoiding possibly harmful binding to the ubiquitous normal amyloid precursor protein. Since Alzheimer's disease immunotherapy requires repeated infusion of antibodies over a prolonged period of time, Alzheimer's disease patients will tolerate such antibodies provided the latter are exclusively of human origin. Human monoclonal antibodies that correspond to ubiquitous anti-amyloid-beta, present in all healthy humans, might bear important protective characteristics.

Biomarkers for early diagnosis of Alzheimer disease: 'ALZheimer ASsociated gene'--a new blood biomarker?

Simple, non-invasive tests for an early detection of degenerative dementia by use of biomarkers are urgently required. However, up to the present, no validated extracerebral diagnostic markers (plasma/serum, platelets, urine, connective tissue) for the early diagnosis of Alzheimer disease (AD) are available. In disease stages with evident cognitive disturbances, the clinical diagnosis of probable AD is made with around 90% accuracy using modern clinical, neuropsychological and imaging methods. Diagnostic sensitivity and specificity even in early disease stages are improved by CSF markers, in particular combined tau and amyloid beta peptides (Abeta) and plasma markers (eg, Abeta-42/Abeta-40 ratio). Recently, a novel gene/protein--ALZAS (Alzheimer Associated Protein)--with a 79 amino acid sequence, containing the amyloid beta-42 fragment (Abeta-42), the amyloid precursor protein (APP) transmembrane signal and a 12 amino acid C-terminal, not present in any other known APP alleles, has been discovered on chromosome 21 within the APP region. Reverse transcriptase-PCR revealed the expression of the transcript of this protein in the cortex and hippocampal regions as well as in lymphocytes of human AD patients. The expression of ALZAS is mirrored by a specific autoimmune response in AD patients, directed against the ct-12 end of the ALZAS-peptide but not against the Abeta-sequence. ELISA studies of plasma detected highest titers of ALZAS in patients with mild cognitive impairment (presymptomatic AD), but only moderately increased titers in autopsy-confirmed AD, whereas low or undetectable ct-12 titers were found in cognitively intact age-matched subjects and young controls. The antigen, ALZAS protein, was detected in plasma in later clinical stages of AD. It is suggested that ALZAS represents an indicator in a dynamic equilibrium between both peripheral and brain degenerative changes in AD and may become a useful "non-invasive" diagnostic marker via a simple blood test.

Autoantibody-catalyzed hydrolysis of amyloid beta peptide

We describe IgM class human autoantibodies that hydrolyze amyloid beta peptide 1-40 (Abeta40). A monoclonal IgM from a patient with Waldenström's macroglobulinemia hydrolyzed Abeta40 at the Lys-28-Gly-29 bond and Lys-16-Ala-17 bonds. The catalytic activity was inhibited stoichiometrically by an electrophilic serine protease inhibitor. Treatment with the catalytic IgM blocked the aggregation and toxicity of Abeta40 in neuronal cell cultures. IgMs purified from the sera of patients with Alzheimer disease (AD) hydrolyzed Abeta40 at rates superior to IgMs from age-matched humans without dementia. IgMs from non-elderly humans expressed the least catalytic activity. The reaction rate was sufficient to afford appreciable degradation at physiological Abeta and IgM concentrations found in peripheral circulation. Increased Abeta concentrations in the AD brain are thought to induce neurodegenerative effects. Peripheral administration of Abeta binding antibodies has been suggested as a potential treatment of AD. Our results suggest that catalytic IgM autoantibodies can help clear Abeta, and they open the possibility of using catalytic Abs for AD immunotherapy.

The underestimated potential of the immune system in prevention of Alzheimer's disease pathology

Genetic and environmental factors leading to Alzheimer's disease (AD) converge in a pathogenic pathway that leads to the accumulation of mis-folded amyloid peptide (Abeta) in the brain. Removal of Abeta from the brain has thus been the focus of academic and industrial research in the last decade. The concept of immunization therapy could be proven in animal models mimicking amyloid pathology but a multicenter clinical trial in which AD patients were vaccinated with aggregated Abeta has resulted in somewhat unanticipated and partially conflicting results. The occurrence of meningoencephalitis in 6% of vaccinated individuals forced the discontinuation of the clinical study, preventing the generation of sufficient data for an unequivocal statement about the effectiveness of such a therapy approach. This study, however, clearly showed that vaccination induced the production of antibodies against Abeta in some immunized patients. Moreover, circulating anti-Abeta antibodies are found in healthy humans suggesting a protective role of such physiological antibodies. Nonetheless, the physiological role of the immune system in preventing AD is not fully understood. This article summarizes crucial animal and clinical data underscoring the potential of the immune system for AD treatment.

A Metalloantibody That Irreversibly Binds a Protein Antigen

Antibody affinity is critically important in therapeutic applications, as well as steady state diagnostic assays. Picomolar affinity antibodies, approaching the association limit of protein-protein interactions, have been discovered for highly potent antigens, but even such high-affinity binders have off-rates sufficient to negate therapeutic efficacy. To cross this affinity threshold, antibodies that tether their targets in a manner other than reversible non-covalent interaction will be required. Here we report the design and construction of an antibody that forms an irreversible complex with a protein antigen in a metal-dependent reaction. The complex resists thermal and chemical denaturation, as well as attempts to remove the coordinating metal ion. Such irreversibly binding antibodies could facilitate the development of next generation "reactive antibody" therapeutics and diagnostics.

A Two Decade Contribution of Molecular Cell Biology to the Centennial of Alzheimer's Disease: Are We Progressing Toward Therapy?

Alzheimer's disease (AD), described for the first time 100 years ago, is a neurodegenerative disease characterized by two neuropathological hallmarks: neurofibrillary tangles containing hyperphosphorylated tau and senile plaques. These lesions are likely initiated by an imbalance between production and clearance of amyloid beta, leading to increased oligomerization of these peptides, formation of amyloid plaques in the brain of the patient, and final dementia. Amyloid beta is generated from amyloid precursor protein (APP) by subsequent beta- and gamma-secretase cleavage, the latter being a multiprotein complex consisting of presenilin-1 or -2, nicastrin, APH-1, and PEN-2. Alternatively, APP can be cleaved by alpha- and gamma-secretase, precluding the production of Abeta. In this review, we discuss the major breakthroughs during the past two decades of molecular cell biology and the current genetic and cell biological state of the art on APP proteolysis, including structure-function relationships and subcellular localization. Finally, potential directions for cell biological research toward the development of AD therapies are briefly discussed.