The biochemical and ultrastructural examinations in central cholinergic damage of the rat induced by the intraperitoneal administration of AF64A

Effectiveness of Combinational Treatments for Alzheimer's Disease with Human Neural Stem Cells and Microglial Cells Over-Expressing Functional Genes

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. In AD patients, amyloid-β (Aβ) peptide-mediated degeneration of the cholinergic system utilizing acetylcholine (ACh) for memory acquisition is observed. Since AD therapy using acetylcholinesterase (AChE) inhibitors are only palliative for memory deficits without reversing disease progress, there is a need for effective therapies, and cell-based therapeutic approaches should fulfil this requirement. We established F3.ChAT human neural stem cells (NSCs) encoding the choline acetyltransferase (ChAT) gene, an ACh-synthesizing enzyme, HMO6.NEP human microglial cells encoding the neprilysin (NEP) gene, an Aβ-degrading enzyme, and HMO6.SRA cells encoding the scavenger receptor A (SRA) gene, an Aβ-uptaking receptor. For the efficacy evaluation of the cells, first, we established an appropriate animal model based on Aβ accumulation and cognitive dysfunction. Among various AD models, intracerebroventricular (ICV) injection of ethylcholine mustard azirinium ion (AF64A) induced the most severe Aβ accumulation and memory dysfunction. Established NSCs and HMO6 cells were transplanted ICV to mice showing memory loss induced by AF64A challenge, and brain Aβ accumulation, ACh concentration and cognitive function were analyzed. All the transplanted F3.ChAT, HMO6.NEP and HMO6.SRA cells were found to survive up to 4 weeks in the mouse brain and expressed their functional genes. Combinational treatment with the NSCs (F3.ChAT) and microglial cells encoding each functional gene (HMO6.NEP or HMO6.SRA) synergistically restored the learning and memory function of AF64A-challenged mice by eliminating Aβ deposits and recovering ACh level. The cells also attenuated inflammatory astrocytic (glial fibrillary acidic protein) response by reducing Aβ accumulation. Taken together, it is expected that NSCs and microglial cells over-expressing ChAT, NEP or SRA genes could be strategies for replacement cell therapy of AD.

The AF64A model of cholinergic hypofunction: an update

Based on numerous reports in the literature since 1980, one can now conclude that ethylcholine aziridinium (AF64A) is selective for the cholinergic system in vivo, and that the effect is both dose- and site-dependent. Thus, AF64A treatment, under the correct conditions of dose and time will result in selective reductions in levels of ACh, AChE, ChAT, HAChT, and K(+)- and ouabain-stimulated release of ACh. While other neurotransmitters may also be affected in brains of AF64A treated rats, the effect is only transient and is most probably secondary to the initial cholinergic deficit-induced by AF64A, reflecting an adaptive reaction of these neurotransmitter systems, which are normally integrated with cholinergic interconnections, to the cholinergic deficiency induced by AF64A. This paper provides a historical perspective for the development of AF64A as a selective cholinotoxin, and surveys its potential mechanisms of action at the neurochemical and molecular levels. Moreover, the availability of an animal model such as the AF64A-treated rat, in which the cholinergic system has been compromised selectively for an extended period of time, has allowed investigators to study a wide variety of questions that relate to factors controlling cholinergic function in vivo. Several key illustrations are presented at the end of this paper.