Natural Anti-Amyloid-beta Antibodies in Intravenous Immunoglobulin (IVIG) Preparation Attenuate Amyloid beta-Induced Neurotoxicity in vitro

Abstract

Rationale: Natural antibodies against neurotoxic amyloid beta 1-42 (Aß42) were detected in IVIG. Accumulation of Aß42 in the brain is a key pathogenic event in Alzheimer's disease (AD). The purpose of this study was to investigate if IVIG preparations can prevent in vitro neurotoxicity induced by Aß42. Methods: Gammagard Liquid, a highly purified IVIG, contains natural antibodies binding to different conformers of Aß. To examine the potential of IVIG to prevent Aß42- induced neurotoxicity we developed and validated an in vitro assay using pheochromocytoma PC-12 cells, and synthetic Aß42. We assessed the fibrillization state of Aß42 preparation by fluorimetric Thioflavine T binding assay, SDS-PAGE and Western Blot. The analysis of cytotoxicity was done by photometric measurement of Lactate Dehydrogenase released into cell supernatants. Results: We found that Aß42 was predominantly oligomeric and induced concentration-dependently cytotoxicity in PC-12 cells. The cytotoxic effect of Aß42 was cell-specific with neuronal cells being most susceptible. Preincubation of Aß42 with monoclonal anti-Aß42 antibodies decreased the Aß42 induced cytotoxicity in PC-12 cells. 6E10, a monoclonal antibody that shows therapeutic effects in murine models of AD, was most effective. A control murine IgG was not effective. Preincubation of Aß42 with IVIG decreased the cytotoxicity by up to 60%. The potency of different lots was comparable. A control human IgG1 antibody had no effect. Conclusions: Our data indicate that natural anti-Aß42 antibodies contained in IVIG are neuroprotective in vitro. Furthermore, different lots of IVIG should contain comparable levels of neuroprotective antibodies which is an important finding for the clinical application of IVIG.