William R. Paljug

Post-mortem correlates of in vivo PiB-PET amyloid imaging in a typical case of Alzheimer's disease

The positron emission tomography (PET) radiotracer Pittsburgh Compound-B (PiB) binds with high affinity to β-pleated sheet aggregates of the amyloid-β (Aβ) peptide in vitro. The in vivo retention of PiB in brains of people with Alzheimers disease shows a regional distribution that is very similar to distribution of Aβ deposits observed post-mortem. However, the basis for regional variations in PiB binding in vivo, and the extent to which it binds to different types of Aβ-containing plaques and tau-containing neurofibrillary tangles (NFT), has not been thoroughly investigated. The present study examined 28 clinically diagnosed and autopsy-confirmed Alzheimers disease subjects, including one Alzheimers disease subject who had undergone PiB-PET imaging 10 months prior to death, to evaluate region- and substrate-specific binding of the highly fluorescent PiB derivative 6-CN-PiB. These data were then correlated with region-matched Aβ plaque load and peptide levels, [3H]PiB binding in vitro, and in vivo PET retention levels. We found that in Alzheimers disease brain tissue sections, the preponderance of 6-CN-PiB binding is in plaques immunoreactive to either Aβ42 or Aβ40, and to vascular Aβ deposits. 6-CN-PiB labelling was most robust in compact/cored plaques in the prefrontal and temporal cortices. While diffuse plaques, including those in caudate nucleus and presubiculum, were less prominently labelled, amorphous Aβ plaques in the cerebellum were not detectable with 6-CN-PiB. Only a small subset of NFT were 6-CN-PiB positive; these resembled extracellular ‘ghost’ NFT. In Alzheimers disease brain tissue homogenates, there was a direct correlation between [3H]PiB binding and insoluble Aβ peptide levels. In the Alzheimers disease subject who underwent PiB-PET prior to death, in vivo PiB retention levels correlated directly with region-matched post-mortem measures of [3H]PiB binding, insoluble Aβ peptide levels, 6-CN-PiB- and Aβ plaque load, but not with measures of NFT. These results demonstrate, in a typical Alzheimers disease brain, that PiB binding is highly selective for insoluble (fibrillar) Aβ deposits, and not for neurofibrillary pathology. The strong direct correlation of in vivo PiB retention with region-matched quantitative analyses of Aβ plaques in the same subject supports the validity of PiB-PET imaging as a method for in vivo evaluation of Aβ plaque burden.

Caspase inhibition therapy abolishes brain trauma-induced increases in Aβ peptide : Implications for clinical outcome

The detrimental effects of traumatic brain injury (TBI) on brain tissue integrity involve progressive axonal damage, necrotic cell loss, and both acute and delayed apoptotic neuronal death due to activation of caspases. Post-injury accumulation of amyloid precursor protein (APP) and its toxic metabolite amyloid-beta peptide (Abeta) has been implicated in apoptosis as well as in increasing the risk for developing Alzheimers disease (AD) after TBI. Activated caspases proteolyze APP and are associated with increased Abeta production after neuronal injury. Conversely, Abeta and related APP/Abeta fragments stimulate caspase activation, creating a potential vicious cycle of secondary injury after TBI. Blockade of caspase activation after brain injury suppresses apoptosis and improves neurological outcome, but it is not known whether such intervention also prevents increases in Abeta levels in vivo. The present study examined the effect of caspase inhibition on post-injury levels of soluble Abeta, APP, activated caspase-3, and caspase-cleaved APP in the hippocampus of nontransgenic mice expressing human Abeta, subjected to controlled cortical injury (CCI). CCI produced brain tissue damage with cell loss and elevated levels of activated caspase-3, Abeta(1-42) and Abeta(1-40), APP, and caspase-cleaved APP fragments in hippocampal neurons and axons. Post-CCI intervention with intracerebroventricular injection of 100 nM Boc-Asp(OMe)-CH(2)F (BAF, a pan-caspase inhibitor) significantly reduced caspase-3 activation and improved histological outcome, suppressed increases in Abeta and caspase-cleaved APP, but showed no significant effect on overall APP levels in the hippocampus after CCI. These data demonstrate that after TBI, caspase inhibition can suppress elevations in Abeta. The extent to which Abeta suppression contributes to improved outcome following inhibition of caspases after TBI is unclear, but such intervention may be a valuable therapeutic strategy for preventing the long-term evolution of Abeta-mediated pathology in TBI patients who are at risk for developing AD later in life.

Changes in expression of amyloid precursor protein and interleukin-1β after experimental traumatic brain injury in rats

There is increasing evidence linking neurodegenerative mechanisms in Alzheimers disease (AD) and traumatic brain injury (TBI), including increased production of amyloid precursor protein (APP), and amyloid-beta (Abeta) peptide. In vitro data indicate that expression of APP may be regulated in part by the inflammatory cytokine IL-1beta. To further investigate the mechanisms involved, we measured APP and IL-1beta protein levels and examined immunohistochemical localization of APP in brain tissue from rats subjected to controlled cortical impact (CCI) injury. Animals were examined at time intervals ranging from 3 h to 4 weeks after TBI. The 24-h time point revealed a dramatic increase in APP immunoreactivity, detected with both N- and C-terminal antibodies, in the hippocampus and cortex ipsilateral to injury. This finding was sustained up to 3 days post-injury. At these early time points, APP increase was particularly robust in the white matter axonal tracts. By 14 days after injury, APP immunoreactivity was not significantly different from sham controls in cortex, but remained slightly elevated in hippocampus. Western blot data corroborated early increases in hippocampal and cortical APP in injured versus control animals. Despite profound APP changes, no Abeta deposits were observed at any time after injury. Hippocampal and cortical IL-1beta increases were even more robust, with IL-1beta levels peaking by 6 h post-injury and returning to baseline by 24-72 h. Our results demonstrate that both APP and IL-1beta are rapidly elevated after injury. Because of the rapidity in the IL-1beta peak increase, it may serve a role in regulation of APP expression after TBI.

β-Amyloid 42/40 ratio and kalirin expression in Alzheimer disease with psychosis

Psychosis in Alzheimer disease differentiates a subgroup with more rapid decline, is heritable, and aggregates within families, suggesting a distinct neurobiology. Evidence indicates that greater impairments of cerebral cortical synapses, particularly in dorsolateral prefrontal cortex, may contribute to the pathogenesis of psychosis in Alzheimer disease (AD) phenotype. Soluble β-amyloid induces loss of dendritic spine synapses through impairment of long-term potentiation. In contrast, the Rho guanine nucleotide exchange factor (GEF) kalirin is an essential mediator of spine maintenance and growth in cerebral cortex. We therefore hypothesized that psychosis in AD would be associated with increased soluble β-amyloid and reduced expression of kalirin in the cortex. We tested this hypothesis in postmortem cortical gray matter extracts from 52 AD subjects with and without psychosis. In subjects with psychosis, the β-amyloid(1-42)/β-amyloid(1-40) ratio was increased, due primarily to reduced soluble β-amyloid(1-40), and kalirin-7, -9, and -12 were reduced. These findings suggest that increased cortical β-amyloid(1-42)/β-amyloid(1-40) ratio and decreased kalirin expression may both contribute to the pathogenesis of psychosis in AD.

PYROGLUTAMATE AND FULL-LENGTH AMYLOID-B CONCENTRATIONS IN THE SUPERIOR FRONTAL CORTEX ACROSS CLINICAL STAGES OF ALZHEIMER’S DISEASE

and hippocampal subfields (AChE, Nissl, Myelin). Results: In 4/5 AD specimens, focal hypointensities were present predominantly in the subiculum. These hypointensities were best explained statistically by the combination of iron and microglia, not by tau or amyloid. Visual examination suggested that these iron-containing microglia were activated. The controls did not demonstrate these findings. Conclusions:Specimen MR is sensitive to iron-containing microglia in AD, which has potential as a biomarker for inflammation.

Characterization of flutemetamol binding in autopsy brains from [C-11]PiB-imaged subjects

imager with the parameters including: 60 Hz motion, FOV 1⁄4 25.6 cm, 60x60 imaging matrix reconstructed to 64x64, 3x ASSET acceleration, 2.5 mm thick slices (skip 1.5 mm) and 4 phase offsets requiring 3.5 minute acquisition time (figure 1). The first harmonic data were inverted with a 3D direct inversion algorithm. The median stiffness for each individual was calculated from a global region of interest excluding SNR 30%CSF content.Results: The median stiffness of the 14 CN subjects was 2.37 kPa (range: 2.17-2.62 kPa) compared to 2.32 kPa (range: 2.18-67 kPa) within the CN + group and 2.20 kPa (range: 1.96-2.29 kPa) within the AD group. A significant difference was found between the three groups with both CN groups significantly different from the AD group (table 1). Conclusions: The results demonstrate that AD pathology alters the mechanical properties of the brain which can be measured in vivo by MRE. Brain MRE is a new imaging modality that provides a unique class of information which heretofore has not been applied to AD. Measures of brain elasticity may provide unique insights into the fundamental ultrastructural alterations in the brain that occur with AD, as well as how these change with time, correlate with other disease biomarkers and with clinical expression of the disease.

P2-369: Correlation analysis of the histofluorescence of an analogue of Pittsburgh Compound-B and Aβ peptide levels in Alzheimer’s disease

uniformity [1], linearly registered into stereotaxic space [2] and tissue classified [3]. Subsequently, the inner and outer cortical surfaces were extracted [4], cortical thickness between these surfaces was measured in native-space mm and blurred with a 20mm diffusion-smoothing kernel [5]. All 40,962 vertices across the entire cortex underwent mixed-model analysis testing for thickness differences by diagnosis and interactions between follow-up scan interval and diagnosis. Multiple comparisons were accounted for using a 5% False Discovery Rate threshold [6]. Results: Cortical thickness was significantly different between AD and HC subjects in the medial frontal lobes, the posterior superior temporal gyri, the anterior cingulates, and, most significantly, the medial temporal lobes. The AD cohort had significantly greater decline than the HCs in the inferior temporal gyrus, the anterior cingulate, the orbitofrontal cortices, and the superior temporal gyri. Conclusion: The results, especially in the medial temporal lobes, show a progression from medial to lateral with follow-up (see figure). There is a large base-line difference in cortical thickness in the entorhinal cortex (0.7mm), the decline with follow-up in the AD group is 0.2mm/year. Moving laterally to the inferior temporal gyrus, there is little group difference initially, but a 0.45mm/year decline in thickness in the AD group. This suggests that the areas involved earliest in the disease, such as the entorhinal cortex, will have already undergone the most significant thinning, whereas areas involved later will exhibit greater thinning at follow-up.