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

In-vivo visualization of key molecular processes involved in Alzheimer's disease pathogenesis: Insights from neuroimaging research in humans and rodent models

Diverse age-associated neurodegenerative disorders are featured at a molecular level by depositions of self-aggregating molecules, as represented by amyloid beta peptides (Abeta) and tau proteins in Alzheimer's disease, and cascade-type chain reactions are supposedly commenced with biochemical aberrancies of these amyloidogenic components. Mutagenesis and multiplication of the genes encoding Abeta, tau and other pathogenic initiators may accelerate the incipient process at the cascade top, rationalizing generations of transgenic and knock-in animal models of these illnesses. Meanwhile, these genetic manipulations do not necessarily compress the timelines of crucial intermediate events linking amyloidogenesis and neuronal lethality, resulting in an incomplete recapitulation of the diseases. Requirements for modeling the entire cascade can be illustrated by a side-by-side comparison of humans and animal models with the aid of imaging-based biomarkers commonly applicable to different species. Notably, key components in a highly reactive state are assayable by probe-assisted neuroimaging techniques exemplified by positron emission tomography (PET), providing critical information on the in-vivo accessibility of these target molecules. In fact, multispecies PET studies in conjunction with biochemical, electrophysiological and neuropathological tests have revealed putative neurotoxic subspecies of Abeta assemblies, translocator proteins accumulating in aggressive but not neuroprotective microglia, and functionally active neuroreceptors available to endogenous neurotransmitters and exogenous agonistic ligands. Bidirectional translational studies between human cases and model strains based on this experimental paradigm are presently aimed at clarifying the tau pathogenesis, and would be expanded to analyses of disrupted calcium homeostasis and mitochondrial impairments. Since reciprocal causalities among the key processes have indicated an architectural interchangeability between cascade and network connections as an etiological representation, longitudinal imaging assays with manifold probes covering the cascade from top to bottom virtually delineate the network dynamics continuously altering in the course of the disease and its treatment, and therefore expedite the evaluation and optimization of therapeutic strategies intended for suppressing the neurodegenerative pathway over its full length.

Inflammation and microglia actions in Alzheimer's disease

A variety of studies have documented increased presence of reactive microglia in the brains of not only Alzheimer's disease (AD) patients but its transgenic mouse models. Since these cells are often characterized in association with fibrillar Abeta peptide-containing plaques, it has been assumed that plaque interaction provides one stimulus for the phenotype observed. The growing appreciation that microglia phenotype changes with age and that resident immune cells are commingled with blood-derived macrophage has complicated understanding of the behavior of these cells in AD. In addition, comparison of microglia within AD brains and the many rodent models suggests that there are population phenotype differences among these cells within any given brain during disease. Recent immunomodulatory strategies that have been employed, although effective at improving behavioral performance, decreasing Abeta plaque load, and altering immune molecule levels, have not yet resolved the details and dynamics of the microglial and macrophage responses. The heterogeneity of microglial presentation in AD brains and its transgenic mouse models and the outcomes of immunoregulatory efforts will be reviewed below along with the remaining question of how much understanding of microglial behavior is actually required in order to propose a microglia-related therapy for AD.

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.