Structural basis of C-terminal ß-amyloid peptide binding by the antibody ponezumab for the treatment of Alzheimer's disease.

Alzheimer's disease, the most common cause of dementia in the elderly and characterized by the deposition and accumulation of plaques, is composed in part of ß-amyloid (Aß) peptides, loss of neurons, and the accumulation of neurofibrillary tangles. Here, we describe ponezumab, a humanized monoclonal antibody, and show how it binds specifically to the carboxyl (C)-terminus of Aß40. Ponezumab can label Aß that is deposited in brain parenchyma found in sections from Alzheimer's disease casualties and in transgenic mouse models that overexpress Aß. Importantly, ponezumab does not label full-length, non-cleaved amyloid precursor protein on the cell surface. The C-terminal epitope of the soluble Aß present in the circulation appears to be available for ponezumab binding because systemic administration of ponezumab greatly elevates plasma Aß40 levels in a dose-dependent fashion after administration to a mouse model that overexpress human Aß. Administration of ponezumab to transgenic mice also led to a dose-dependent reduction in hippocampal amyloid load. To further explore the nature of ponezumab binding to Aß40, we determined the X-ray crystal structure of ponezumab in complex with Aß40 and found that the Aß40 carboxyl moiety makes extensive contacts with ponezumab. Furthermore, the structure-function analysis supported this critical requirement for carboxy group of AßV40 in the Aß-ponezumab interaction. These findings provide novel structural insights into the in vivo conformation of the C-terminus of Aß40 and the brain Aß-lowering efficacy that we observed following administration of ponezumab in transgenic mouse models.

Poloxamer 188 copolymer membrane sealant rescues toxicity of amyloid oligomers in vitro.

Amyloid oligomers and protofibrils increase cell membrane permeability, eventually leading to cell death. Here, we demonstrate that amyloid oligomer toxicity and membrane permeabilization can be reversed using the membrane sealant copolymer poloxamer 188. The data indicate that amyloid oligomer toxicity is caused by defects in the lipid bilayer of the type that are sealed by poloxamer 188. Our results also suggest the possibility of using polymer-based membrane sealants to prevent or reverse amyloid oligomer toxicity in vivo. Because the ability to permeabilize membranes is a generic property of amyloid oligomers, this therapeutic approach may be effective for the treatment of many degenerative diseases caused in part by the interaction of misfolded proteins with cell membranes, as in Alzheimer's disease, type II diabetes, and a host of others.

Mossy fiber plasticity and enhanced hippocampal excitability, without hippocampal cell loss or altered neurogenesis, in an animal model of prolonged febrile seizures.

Seizures induced by fever (febrile seizures) are the most frequent seizures affecting infants and children; however, their impact on the developing hippocampal formation is not completely understood. Such understanding is highly important because of the potential relationship of prolonged febrile seizures to temporal lobe epilepsy. Using an immature rat model, we have previously demonstrated that prolonged experimental febrile seizures render the hippocampus hyperexcitable throughout life. Here we examined whether (1) neuronal loss, (2) altered neurogenesis, or (3) mossy fiber sprouting, all implicated in epileptogenesis in both animal models and humans, were involved in the generation of a pro-epileptic, hyperexcitable hippocampus by these seizures. The results demonstrated that prolonged experimental febrile seizures did not result in appreciable loss of any vulnerable hippocampal cell population, though causing strikingly enhanced sensitivity to hippocampal excitants later in life. In addition, experimental febrile seizures on postnatal day 10 did not enhance proliferation of granule cells, whereas seizures generated by kainic acid during the same developmental age increased neurogenesis in the immature hippocampus. However, prolonged febrile seizures resulted in long-term axonal reorganization in the immature hippocampal formation: Mossy fiber densities in granule cell- and molecular layers were significantly increased by 3 months (but not 10 days) after the seizures. Thus, the data indicate that prolonged febrile seizures influence connectivity of the immature hippocampus long-term, and this process requires neither significant neuronal loss nor altered neurogenesis. In addition, the temporal course of the augmented mossy fiber invasion of the granule cell and molecular layers suggests that it is a consequence, rather than the cause, of the hyperexcitable hippocampal network resulting from these seizures.