Faculty Bibliography

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

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

Squirrel monkey is a valuable model to study pathogenesis of cerebrovascular amyloid angiopathy (CAA). Previous studies suggested that circulating amyloid-beta40 peptide (Abeta40) crosses the blood-brain barrier (BBB) and may therefore enhance cerebrovascular amyloidosis in aged squirrel monkeys. In the present study, we used single photon emission computed tomography (SPECT) to determine elimination of 123I-Abeta40 and 99mTc-DTPA, an extracellular marker, from the brain in squirrel monkeys at different age. Following intracerebral microinfusions, the time-activity brain clearance curves indicated bi-exponential removal of 123I-Abeta40 with an initial rapid washout (1.1 < or = t 1/2 < or = 2.7 h). This, plus the observed appearance of 123I-radioactivity in plasma suggest significant brain-to-blood transport. In contrast, 99mTc-DTPA was removed slowly by brain interstitial fluid bulk flow (monoexponential decay with 6.8 < or = t 1/2 < or = 16.8 h). A comparison of three middle aged (11-16 years old) vs. two old (22 yrs old) monkeys was consistent with an age-related decline in the BBB capacity to remove 123I-Abeta from the brain. This correlated with an age-dependent increase in A1beta40/42 cerebrovascular immunoreactivity and amyloid deposition. Thus, vascular clearance plays an important role in reducing Abeta levels in the squirrel monkey brain and impaired Abeta40 elimination across the BBB may contribute to the development of CAA

A point mutation of G to C at codon 693 of the amyloid-beta (Abeta) precursor protein gene results in Glu to Gln substitution at position 22 of the Abeta (AbetaQ22) associated with hereditary cerebrovascular amyloidosis with hemorrhage Dutch type. Factors that regulate AbetaQ22 levels in the central nervous system (CNS) are largely unknown. By using ventriculo-cisternal perfusion technique in guinea pigs, we demonstrated that clearance from the cerebrospinal fluid and transport from the CNS to blood of [(125)I]-AbetaQ22 (1 nM) were reduced by 36% and 52%, respectively, in comparison to the wild type Abeta(1-40) peptide. In contrast to significant uptake and transport of Abeta(1-40) across the brain capillaries and leptomeningeal vessels, AbetaQ22 was not taken up at these CNS vascular transport sites, which was associated with its 53% greater accumulation in the brain. The CNS clearance of Abeta(1-40) was half-saturated at 23.6 nM; AbetaQ22 had about 6.8-fold less affinity for the CNS efflux transporters and its elimination relied mainly on transport across the choroid plexus. Thus, the Dutch mutation impairs elimination of Abeta from brain by reducing its rapid transport across the blood-brain barrier and the vascular drainage pathways, which in turn may result in accumulation of the peptide around the blood vessels and in brain

Familial Danish dementia (FDD) is pathologically characterized by widespread cerebral amyloid angiopathy (CAA), parenchymal protein deposits, and neurofibrillary degeneration. FDD is associated with a mutation of the BRI2 gene located on chromosome 13. In FDD there is a decamer duplication, which abolishes the normal stop codon, resulting in an extended precursor protein and the release of an amyloidogenic fragment, ADan. The aim of this study was to describe the major neuropathological changes in FDD and to assess the distribution of ADan lesions, neurofibrillary pathology, glial, and microglial response using conventional techniques, immunohistochemistry, confocal microscopy, and immunoelectron microscopy. We showed that ADan is widely distributed in the central nervous system (CNS) in the leptomeninges, blood vessels, and parenchyma. A predominance of parenchymal pre-amyloid (non-fibrillary) lesions was found. Abeta was also present in a proportion of both vascular and parenchymal lesions. There was severe neurofibrillary pathology, and tau immunoblotting revealed a triplet electrophoretic migration pattern comparable with PHF-tau. FDD is a novel form of CNS amyloidosis with extensive neurofibrillary degeneration occurring with parenchymal, predominantly pre-amyloid rather than amyloid, deposition. These findings support the notion that parenchymal amyloid fibril formation is not a prerequisite for the development of neurofibrillary tangles. The significance of concurrent ADan and Abeta deposition in FDD is under further investigation

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 shown therapeutic potential in mouse models of another neurodegenerative condition, namely Alzheimers disease. Here we report that immunization with recombinant mouse prion protein delays the onset of prion disease in mice (Am. J. Pathol., in press). Vaccination was performed both prior to and after peripheral exposure to the mouse-adapted scrapie strain 139A. A delay in disease onset was seen in both groups, but was more prolonged in animals immunized prior to exposure (p = 0.040-0.002). The increase in the incubation period closely correlated with the anti-prion antibody titer (p = 0.017-0.0001). Histological and Western blot evaluations of the brains of the treated-and control groups did not reveal any apparent differences in the degree of spongiform change or levels of scrapie prion. This was expected because the mice were killed when they scored positive for three consecutive weeks for behavioral signs of prion infection. Overall, the vaccination-mediated delay in prion disease onset is highly reproducible, correlates well with antibody titer and indicates that a similar approach may work in humans or other mammalian species at risk for prion disease

The prion diseases are a rapidly fatal group of neurodegenerative disorders, which currently have no effective therapy. Recently we have shown that active immunization with recombinant PrP protein increases the incubation period in mice exposed peripherally to the 139A strain of scrapie agent (Am.J.Pathol., in press). The antibody titers correlated with the increased incubation. We have extended these observations by using 6 different monoclonal anti-mouse PrP antibodies for passive immunization, with epitopes that span the murine PrP protein. Intraperitoneal antibody injections were performed weekly, starting immediately after and 1 month following peripheral exposure to scrapie strain 139A at two different dilutions. We found a statistically significant prolongation of the incubation period from scrapie exposure to the onset of clinical symptoms. These initial findings suggest that passive immunization can be used to prolong the incubation period among individuals with a known exposure to the prion agent