Faculty Bibliography

The outbreak of new variant Creutzfeldt-Jakob disease has raised the specter of a potentially large population being at risk to develop this prionosis. None of the prionoses currently have an effective treatment. Recently, vaccination has been shown to be effective in mouse models of another neurodegenerative condition, namely Alzheimer's disease. Here we report that vaccination with recombinant mouse prion protein delays the onset of prion disease in mice. Vaccination was performed both before peripheral prion exposure and after exposure. A delay in disease onset was seen in both groups, but was more prolonged in animals immunized before exposure. The increase in the incubation period closely correlated with the anti-prion protein antibody titer. This promising finding suggests that a similar approach may work in humans or other mammalian species at risk for prion disease

The recent termination of a Phase II clinical trial in which volunteers with Alzheimer's disease (AD) were vaccinated with Amyloid-beta (AP)1-42, has cast doubt on the feasibility of this therapeutic approach. While the exact reasons for the cerebral inflammation in these patients is being determined, it is difficult to evaluate the cause of these adverse effects. The most likely reasons are Abeta1-42 toxicity and/or autoimmunity. Abeta vaccination approaches are based on the hypothesis that Abeta deposition and toxicity are central to the pathogenesis of AD. Therefore, it is counterintuitive to use the whole Abeta peptide for human vaccination. Abeta1-40/42 is a major plaque component that forms inflammatory/toxic fibrils as observed in many in vitro and in vivo studies. Furthermore, numerous studies have shown that Abeta1-40/42 bidirectionally crosses the blood-brain barrier (BBB) in experimental animals. Additionally, in vitro and in vivo studies indicate that minute amounts of Abeta1-42 may seed fibril/amyloid formation. The elderly, a target population for AD therapy, often have a poor immune response to vaccines, which enhances the gravity of these safety concerns. In these patients with an attenuated immune reaction, injected Abeta1-42 may initiate and/or enhance congophilic angiopathy, which eventually may result in reduced cerebral blood flow and/or intracerebral bleeding. Abeta1-42 may also cross the BBB and once within the brain parenchyma it may contribute to plaque formation and/or co-deposit on plaques. Together, these effects within blood vessels and/or brain parenchyma may actually enhance the progression of AD. Given the potential serious side effects of Abeta1-42 vaccination, it is safer to use immunogenic Abeta derivatives, which are less likely to be toxic. The main immunogenic epitopes of Abeta1-42 are contained within the first 30 amino acids of the peptide. Taking this into account, we have developed soluble antigenic Abeta derivatives, which are nonfibrillogenic and nontoxic in human cell culture. Our prototype peptide, K6Abeta1-30-NHz, diminishes amyloid burden to a similar extent as reported for Abeta1-42. Additionally, ramified IL-1beta-positive microglia as well as phagocytes, associated with the Abeta plaques, were absent in the immunized mice, indicating reduced inflammation in these animals at the time point examined. Autoimmunity may be the culprit if follow-up studies reveal that the brain inflammation is related to antibody interactions with AD and/or amyloid precursor protein (APP). In such a scenario, any vaccination approach targeting A(3 can have similar consequences, although preventive treatment initiated prior to amyloid deposition may not result in these adverse reactions. T-cell-related autoimmunity may also be involved and can be expected to be less with Abeta derivatives not containing certain T-cell epitopes. An alternative to the active vaccination approach is passive immunization, which is associated with a lower risk of irreversible autoimmunity. This approach may also be used in patients with a muted immune response to the vaccine. However, in a chronic disease such as AD repeated antibody injections may lead to an anti-idiotype response and the resulting serum immune complexes can cause vasculitis and/or glomerulonephritis. Reduction of soluble Abeta within the peripheral system may be a critical part of the pathway that reduces cerebral plaque burden in Tg mice and ultimately in AD patients. Overall, the use of nontoxic A(3 derivatives and/or antibodies with very limited access into the CNS, such as IgM, may prove to have reduced si Any therapeutic approach will be more effective when used prophylactically because of neuronal loss and increased amyloid burden in the later stages of AD. Reversal of clinical symptoms cannot be expected and early diagnosis of AD may be needed for effective therapy. (C) 2002 Wiley-Liss, Inc

Alzheimer's disease (AD) brains display A beta (Abeta) plaques, inflammatory changes and neurofibrillary tangles (NFTs). Converging evidence suggests a neuronal origin of Abeta. We performed a temporal study of intraneuronal Abeta accumulation in Down syndrome (DS) brains. Sections from temporal cortex of 70 DS cases aged 3 to 73 years were examined immunohistochemicallyf or immunoreactivity (IR) for the Abeta N-terminal, the Abeta40 C-terminus and the Abeta42 C-terminus. N-terminal antibodies did not detect intracellular Abeta. Abeta40 antibodies did not detect significant intracellular Abeta, but older cases showed Abeta40 IR in mature plaques. In contrast, Abeta42 antibodies revealed clear-cut intraneuronal IR. All Abeta42 antibodies tested showed strong intraneuronal Abeta42 IR in very young DS patients, especially in theyoungest cases studied (e.g., 3 or 4yr. old), but this IR declined as extracellular Abeta plaques gradually accumulated and matured. No inflammatory changes were associated with intraneuronal Abeta. We also studied the temporal development of gliosis and NFT formation, revealing that in DS temporal cortex, inflammation and NFT follow Abeta deposition. We conclude that Abeta42 accumulates intracellularly prior to extracellular Abeta deposition in Down syndrome, and that subsequent maturation of extracellular Abeta deposits elicits inflammatory responses andprecedes NFTs

1. We studied cerebrovascular sequestration and blood-brain barrier (BBB) permeability to [125I]- or [123I]-labeled amyloid-beta peptides (A beta) in aged rhesus and aged squirrel monkey, the nonhuman primate models of cerebral beta-amyloidosis and cerebrovascular amyloid angiopathy (CAA), respectively. 2. In aged rhesus, the half-time of elimination of [125I]A beta 1-40, t1/2e, was faster by 1.34 h, the systemic clearance, Clss, increased by 4.21 ml/min/kg and the mean residence time of intact peptide in the circulation shortened by 2 h. 3. Cerebrovascular sequestration of [125I]A beta 1-40 was significant in aged squirrel monkey (20.8 ml/g x 10(2)), but undetectable in the rhesus. 4. The permeability surface area product, PS, for [14C]inulin was low in both species (0.11-0.18 ml/g/s x 10(6)) indicating an intact barrier. 5. The BBB permeability to A beta 1-40 was 34.8- and 13.7-fold higher than for [14C]inulin in aged squirrel and rhesus, respectively, suggesting a specialized A beta transport across the BBB. 6. The single photon computed emission tomography studies confirmed a saturable [123I]A beta 1-40 transport at the BBB in primates (Km = 40 nM). 7. Brain autoradiographic analysis of [125I]A beta 1-42 or [125I]A beta 1-40 after intracarotid infusions of radiotracers confirmed co-localization of the signal with A beta-immunoreactive plaques in rhesus monkeys. 8. Metabolism of [125I]A beta 1-40 in brain and plasma was slower in aged squirrel compared to aged rhesus, by 2.9- and 2.6-fold, respectively. 9. Thus, transport of circulating A beta across the BBB contributes to brain parenchymal accumulation of amyloid in aged nonhuman primates. Negligible capillary binding, rapid systemic and brain degradation, and accelerated body elimination of blood-borne A beta, may prevent the development of CAA in rhesus in contrast to squirrel monkeys