Inherent Anti-amyloidogenic Activity of Human Immunoglobulin γ Heavy Chains

Abstract

We have previously shown that a subpopulation of naturally occurring human IgGs were cross-reactive against conformational epitopes on pathologic aggregates of A␤, a peptide that forms amyloid fibrils in the brains of patients with Alzheimer disease, inhibited amyloid fibril growth, and dissociated amyloid in vivo. Here, we describe similar anti-amyloidogenic activity that is a general property of free human Ig ␥ heavy chains. A ␥ 1 heavy chain, F1, had nanomolar binding to an amyloid fibril-related conformational epitope on synthetic oligomers and fibrils as well as on amyloidladen tissue sections. F1 did not bind to native A␤ monomers, further indicating the conformational nature of its binding site. The inherent anti-amyloidogenic activity of Ig ␥ heavy chains was demonstrated by nanomolar amyloid fibril and oligomer binding by polyclonal and monoclonal human heavy chains that were isolated from inert or weakly reactive antibodies. Most importantly, the F1 heavy chain prevented in vitro fibril growth and reduced in vivo soluble A␤ oligomer-induced impairment of rodent hippocampal long term potentiation, a cellular mechanism of learning and memory. These findings demonstrate that free human Ig ␥ heavy chains comprise a novel class of molecules for developing potential therapeutics for Alzheimer disease and other amyloid disorders. Moreover, establishing the molecular basis for heavy chain-amyloidogenic conformer interactions should advance understanding on the types of interactions that these pathologic assemblies have with biological molecules. Alzheimer disease (AD)3 is approaching global epidemic proportions and is the most common of over 25 incurable protein misfolding diseases that are termed the amyloidoses (1, 2). A hallmark of the disease is deposition of amyloid fibril-containing neuritic plaques that are formed by abnormal processing of ␤-amyloid protein (A␤), a proteolyzed transmembrane 39 -43 fragment of amyloid precursor protein (3). Diverse experimental studies support a central pathogenic role for aggregated A␤, which in the brain initiates a cascade of events that ultimately lead to neuronal dysfunction and death (4 -6). The most neurotoxic A␤ species are low molecular weight oligomers (5), which include noncovalently linked species (7-9) and dityrosine cross-linked ␤-amyloid protein species (CAPS) (10).Active vaccination with A␤ or passive administration of anti-A␤ antibodies has shown promise in transgenic AD animal models and in some AD patients by inducing neuritic plaque clearance, neutralizing neurotoxic soluble A␤ oligomers, and/or improving cognitive functioning (6,8,(11)(12)(13). Immunotherapy has generally targeted linear sequence epitopes on A␤ (13). However, antibodies that do not distinguish between pathologic A␤ conformers and the monomeric peptide may have adverse effects because the native peptide has been implicated in normal lipid and cholesterol homeostasis (14). Of potentially greater use are antibodies that cross-react with conformational epitopes on pathogenic aggregated A...

Rational design of potent domain antibody inhibitors of amyloid fibril assembly

“…Nevertheless, some antibodies that are either sequence-and/or conformation-specific have been reported to inhibit amyloid formation at low substoichiometric antibody concentrations (≤1:10 antibody:monomer molar ratios) (34)(35)(36)(37)(38). Interestingly, these antibodies seem to use distinct mechanisms to inhibit amyloid formation relative to those used by gammabodies.…”

“…For example, a conformation-specific antibody fragment that recognizes Aβ40 fibrillar intermediates (protofibrils) inhibits amyloid formation by preventing protofibrils from converting into fibrils (1:10 antibody:monomer molar ratio) (34). Moreover, some IgG heavy chains inhibit Aβ fibrillization by promoting formation of off-pathway aggregates at even lower substoichiometric concentrations (∼1:20-1:40 antibody:monomer molar ratios) (35). Importantly, these inhibitory antibodies render Aβ in aggregated conformations that are distinct from Aβ monomers.…”

Kinetic analysis of IgG antibodies to beta-amyloid oligomers with surface plasmon resonance

“…SDS treatment did not significantly alter the antigenic neo-epitope formed when nOAb assembled from monomeric precursors. It has been proposed that the increased binding propensity of natural IgG to OAb versus MAb is mediated through b-sheet pairing between OAb and Fc domains [34]. Although this is an intriguing possibility, this model would need to account for the biphasic dissociation found in both mAb (Fig.…”

Hippocampus in health and disease: An overview

“…Exposure to A beta can cause impairment of LTP in animals[57] and is resolved by using anti-A beta immunotherapy. [58] Infusion A beta in rats can induce impairment of LTP,[59] and this is exacerbated by mild chronic stress. Oxidative Stress [60] Increase formation of oxygen-derived free radicals leading to lipid peroxidation in brain is seen in AD patients. Abeta[57–58] and stress[56] both can increase production of free radicals in brains of experimental animals.…”