Beta-Amyloid (1-11)

Gantenerumab: a novel human anti-Aβ antibody demonstrates sustained cerebral amyloid-β binding and elicits cell-mediated removal of human amyloid-β

The amyloid-β lowering capacity of anti-Aβ antibodies has been demonstrated in transgenic models of Alzheimer's disease (AD) and in AD patients. While the mechanism of immunotherapeutic amyloid-β removal is controversial, antibody-mediated sequestration of peripheral Aβ versus microglial phagocytic activity and disassembly of cerebral amyloid (or a combination thereof) has been proposed. For successful Aβ immunotherapy, we hypothesized that high affinity antibody binding to amyloid-β plaques and recruitment of brain effector cells is required for most efficient amyloid clearance. Here we report the generation of a novel fully human anti-Aβ antibody, gantenerumab, optimized in vitro for binding with sub-nanomolar affinity to a conformational epitope expressed on amyloid-β fibrils using HuCAL(?) phage display technologies. In peptide maps, both N-terminal and central portions of Aβ were recognized by gantenerumab. Remarkably, a novel orientation of N-terminal Aβ bound to the complementarity determining regions was identified by x-ray analysis of a gantenerumab Fab-Aβ(1-11) complex. In functional assays gantenerumab induced cellular phagocytosis of human amyloid-β deposits in AD brain slices when co-cultured with primary human macrophages and neutralized oligomeric Aβ42-mediated inhibitory effects on long-term potentiation in rat brain. In APP751(swedish)xPS2(N141I) transgenic mice, gantenerumab showed sustained binding to cerebral amyloid-β and, upon chronic treatment, significantly reduced small amyloid-β plaques by recruiting microglia and prevented new plaque formation. Unlike other Aβ antibodies, gantenerumab did not alter plasma Aβ suggesting undisturbed systemic clearance of soluble Aβ. These studies demonstrated that gantenerumab preferentially interacts with aggregated Aβ in the brain and lowers amyloid-β by eliciting effector cell-mediated clearance.

Vaccination with (1-11)E2 in alum efficiently induces an antibody response to β-amyloid without affecting brain β-amyloid load and microglia activation in 3xTg mice

Immunization against β-amyloid (Aβ) is pursued as a possible strategy for the prevention of Alzheimer's disease (AD). In clinical trials, Aβ 1-42 proved poorly immunogenic and caused severe adverse effects; therefore, safer and more immunogenic candidate vaccines are needed. Multimeric protein (1-11)E2 is able to induce an antibody response to Aβ, immunological memory, and IL-4 production, with no concomitant anti-Aβ T cell response. Antisera recognize Aβ oligomers, protofibrils, and fibrils. In this study, we evaluated the effect of prophylactic immunization with three doses of (1-11)E2 in alum in the 3xTg mouse model of AD. Immunization with (1-11)E2 efficiently induced anti-Aβ antibodies, but afforded no protection against Aβ accumulation and neuroinflammation. The identification of the features of the anti-Aβ immune response that correlate with the ability to prevent Aβ accumulation remains an open problem that deserves further investigation.

1-[11C]Arachidonic acid

Arachidonic acid (AA), also known as all-cis-5,8,11,14-eicosatetraenoic acid (20:4n-6, a ω-6 fatty acid), is an essential fatty acid that is found primarily at the sn-2 position of most membrane phospholipids (PLs). Through the AA cascade it is a precursor for the synthesis of prostaglandins and leukotrienes, which have been implicated in the development of a variety of neurological disorders in mammals (1). The AA is released from the PLs by phospholipase A₂ (PLA₂) enzymes (both cytosolic and secretory forms) that are calcium dependent, and they are usually receptor activated. The released AA and its metabolites are believed to modulate a variety of processes in mammals including aging, ion channel functioning, neuropsychiatric disorders, inflammation, and diseases such as Alzheimer’s disease (AD) and Parkinson’s disease (2-7). Because cytokines, nitric oxide, and glutamate influence calcium mobilization in the tissue, they are known to affect PLA₂ activation, the release of AA from PLs, and neuroinflammation observed with different neurological diseases (8-13).

The AD brain has been shown to have higher than normal PLA₂ enzyme activity and increased levels of cytokines, β-amyloid proteins and peptides, glutamatergic markers, and AA metabolites (14-18). Esposito et al. envisioned that elevated AA metabolism in the AD brain could perhaps be used to image the neuroinflammation during the course and therapy of the disease because this fatty acid is either synthesized de novo or from linoleic acid (18:2n-6), which can be considered as its precursor in mammals (19). Using AA labeled with radioactive carbon (1-¹¹C-AA), investigators have determined the regional brain AA incorporation coefficient (K*), which is the ratio of radioactivity in the brain and the integral of AA in plasma, developed using quantitative autoradiography in rodents with ¹⁴C-labeled AA (20) and positron emission tomography (PET) in non-human primates (21) and humans with ¹¹C-labeled AA (19, 22). In addition, labeled AA has been shown to be an ideal brain imaging agent, and K* was not influenced by regional cerebral blood flow (CBF) changes measured with water containing radioactive oxygen (¹⁵O-water) (19).

National Institute on Aging-Alzheimer's Association guidelines for the neuropathologic assessment of Alzheimer's disease: a practical approach

We present a practical guide for the implementation of recently revised National Institute on Aging-Alzheimer's Association guidelines for the neuropathologic assessment of Alzheimer's disease (AD). Major revisions from previous consensus criteria are: (1) recognition that AD neuropathologic changes may occur in the apparent absence of cognitive impairment, (2) an "ABC" score for AD neuropathologic change that incorporates histopathologic assessments of amyloid β deposits (A), staging of neurofibrillary tangles (B), and scoring of neuritic plaques (C), and (3) more detailed approaches for assessing commonly co-morbid conditions such as Lewy body disease, vascular brain injury, hippocampal sclerosis, and TAR DNA binding protein (TDP)-43 immunoreactive inclusions. Recommendations also are made for the minimum sampling of brain, preferred staining methods with acceptable alternatives, reporting of results, and clinico-pathologic correlations.

1-11C-Methyl-4-piperidinyl n-butyrate

Cholinesterase (ChE) is an enzyme that hydrolyzes the neurotransmitter acetylcholine into choline and acetic acid, and thus shuts off neural transmission (1, 2). There are two types of ChE: acetylcholinesterase (AChE, also known as erythrocyte cholinesterase or acetylcholine acetylhydrolase) and butyrylcholinesterase (BChE or BuChE, also known as plasma cholinesterase, pseudocholinesterase, or acylcholine acylhydrolase). Both enzymes are present in cholinergic and noncholinergic tissues as well as in plasma and other body fluids. They differ in substrate specificity, behavior in excess substrate, and susceptibility to inhibitors (1, 2).

BChE is encoded by the BCHE gene, which is located in humans on chromosome 3q26.1-q26.2 (3). Mutations of the BCHE gene result in various genotypes and phenotypes (4), and some BCHE gene variants, such as atypical, K, J, and H variants, cause reduced activity of BChE. The silent variants lead to total loss of the enzyme activity (0–2% of normal activity). On the other hand, some variants result in increased activity, such as the C5+ variant (combination of BChE with an unidentified protein), the Cynthiana variant (increased amount of BChE than normal level), and the Johannesburg variant (increased BChE activity with normal enzyme level). In the absence of muscle relaxants, there is no known disadvantage for individuals with these variants.

BChE is synthesized in many tissues, including the liver, lungs, heart, and brain. Similar to AChE, a single BCHE gene gives rise to different protein products by alternative splicing in the coding region of the original transcript. This provides a series of diverse but related molecular forms of BChE (G1, G2, and G4). G4 is the predominant isoform in the mature brain. These forms have similar catalytic properties, but they exhibit different cellular and extracellular distributions and non-catalytic activities.

BChE possesses three different enzymatic activities: esterase, aryl acylamidase, and peptidase (1). The esterase activity of BChE plays an important role in scavenging anti-AChE compounds such as cocaine, heroin, and organophosphate before they reach AChE at physiologically important sites. In the absence of AChE, BChE is believed to serve as a backup to AChE in supporting and regulating cholinergic transmission (5). BChE also inactivates some drugs, e.g., aspirin, amitriptyline, and bambuterol (1, 6). The aryl acylamidase activity of BChE may be involved in the crosstalk between serotonergic and cholinergic neurotransmission systems, but it is still poorly understood. The peptidase activity of BChE is related to the development and progress of Alzheimer’s disease (AD) (7, 8), which is characterized by a loss of cholinergic neurons. In the brains of patients with AD, the level of the membrane-bound G4 form of AChE is selectively reduced by 90% or more in certain regions, while the level of the G1 form is largely unchanged. On the contrary, the G1 form of BChE shows a 30–60% increase, while the G4 form decreases or remains the same as in the normal brain. It has been indicated that BChE, which is found in the neuritic plaques and tangles, cleaves the amyloid precursor protein to the β-amyloid protein and helps β-amyloid diffusion to β-amyloid plaques (6). Abnormal expressions of BChE and AChE have also been observed in human tumors such as meningioma, glioma, acoustic neurinomas, and lung, colon, and ovarian cancers (9, 10). However, the relationship between altered BChE and AChE expressions and tumorigenesis is not clear, nor is the efficacy of specific inhibitors as chemotherapeutic agents.

Because of the potential diagnostic and therapeutic values, investigators have synthesized various radiolabeled acetylcholine and butyrylcholine analogs as positron emission tomography (PET) tracers (11-16). These tracers have been used to measure ChE activity, detect diseases with cholinergic deficits, and study the efficacy of ChE inhibitors. N-methylpiperidinyl esters are a group of synthetic AChE substrates; of them, 1-¹¹C-methyl-4-piperidinyl acetate (¹¹C-MP4A) and 1-¹¹C-methyl-4-piperidinyl propionate (¹¹C-MP4P) have already been used in the clinic as PET tracers for in vivo assessment of AChE activity associated with AD. 1-¹¹C-Methyl-4-piperidinyl n-butyrate (¹¹C-MP4B or [¹¹C]BMP), a specific radiolabeled substrate of BChE, was developed for in vivo assessment of BChE activity with PET (15-18).