Assessment of dementia risk in aging adults using both FDG-PET and FDDNP-PET imaging

BACKGROUND

In a previous study, positron emission tomography (PET) with 2-(1-{6-[(2-[F-18]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile (FDDNP), a molecule that binds to plaques and tangles in vitro, identified three subgroups of non-demented subjects according to FDDNP binding patterns: low global (LG) binding; high frontal, parietal, medial temporal binding (HF/PA); and high medial and lateral temporal and posterior cingulate (HT/PC) binding. In this follow-up investigation, we compared 2-deoxy-2-[F-18]fluoro- d-glucose (FDG)-PET cerebral metabolic patterns in the three FDDNP-PET binding subgroups.

METHODS

Fifty-four subjects with normal aging (N = 28) or amnestic forms of mild cognitive impairment (N = 26) underwent FDDNP-PET and FDG-PET scanning. Subjects in the LG, HF/PA, and HT/PC FDDNP subgroups were compared according to visual ratings, statistical parametric mapping, and automated region of interest analyses of their FDG-PET data.

RESULTS

The FDDNP-PET subgroups demonstrated different glucose metabolic patterns according to visual ratings, region of interest, and statistical parametric mapping analyses of FDG-PET data. The LG FDDNP subgroup showed no areas of significant hypometabolism relative to the other subgroups and had low Alzheimer's disease risk by FDG-PET standards. The HF/PA FDDNP subgroup demonstrated hypometabolism in bilateral inferior parietal/parietotemporal, bilateral posterior cingulate, perisylvian, mid-temporal gyrus, and dorsolateral prefrontal regions, which is a pattern suggestive of high Alzheimer's disease risk. The HT/PC FDDNP subgroup demonstrated heterogeneous FDG-PET patterns with predominant anterior frontal and anterior temporal hypometabolism, suggestive of mixed etiologies, including fronto-temporal dementia risk.

CONCLUSIONS

The FDG-PET data provided independent validation that different patterns of FDDNP-PET binding in non-demented individuals may be associated with differential dementia risk.

FDDNP binding using MR derived cortical surface maps

OBJECTIVES

To assess quantitatively the cortical pattern profile of regional FDDNP binding to beta-amyloid and neurofibrillary tangles on MR derived cortical maps, FDDNP PET images were corrected for movement and partial volume (PV), and optimized for kernel size.

METHODS

FDDNP DVR PET images from 23 subjects (7 with Alzheimer's disease (AD), 6 with mild cognitive impairment and 10 controls) were obtained from Logan analysis using cerebellum as reference. A hemispheric cortical surface model for each subject was extracted from the MRI. The same transformations were applied to the FDDNP DVR PET images to map them into the same space. The cortical map with PV correction was calculated as the ratio of the DVR cortical surface and that of the simulated map, created from the mask derived from MRI and smoothed to the PET resolution. Discriminant analysis was used to order the FDDNP DVR cortical surfaces based on subjects' disease state. Linear regression was used to assess the rate of change of DVR vs. MMSE for each hemispheric cortical surface point.

RESULTS

The FDDNP DVR cortical surface corrected for movement and PV had less hemispheric asymmetry. Optimal kernel size was determined to be 9 mm. The corrected cortical surface map of FDDNP DVR showed clear spatial pattern that was consistent with the known pathological progression of AD.

CONCLUSION

Correcting for movement, PV as well as optimizing kernel size provide sensitive statistical analysis of FDDNP distribution which confirms in the living brain known pathology patterns earlier observed with cognitive decline with brain specimens.

Amyloid and tau imaging, neuronal losses and function in mild cognitive impairment

OBJECTIVES

Establish new approaches for early diagnosis of dementia, based on imaging amyloid and tau pathology, cell losses and neuronal function, in subjects with mild cognitive impairment (MCI),. The overall aim is to develop effective tools for monitoring disease progression in the living patient to facilitate discovery of early therapeutic interventions to modify the course of the disease.

DESIGN

Use 2-(1-{6-[(2-[F- 18]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile ([F-18]FDDNP) in combination with positron emission tomography (PET) to produce dynamic images for quantification of regional cortical brain deposition in MCI patients and compare them with controls subjects and patients with Alzheimer's disease (AD). Comparison with other molecular imaging probes for neuronal losses and function were also made.

SETTING

Patients are positioned supine in the tomograph bed with his/her head in the detector ring field. Upon injection of the molecular imaging probe (e.g., [F-18]FDDNP) images are obtained at very short time intervals for up to two hours. This results in dynamic sequences of brain distribution of the probe.

PARTICIPANTS

Patients with clinical diagnosis of AD, MCI and control subjects.

MEASUREMENTS

Subjects in the categories established above were scanned with [F-18]FDDNP-PET and quantification performed using Logan parametric graphical analysis to measure relative quantitative amyloid loads throughout the brain within patient groups. These results were compared in the same patients with cell losses in hippocampus using 4-[F-18]fluoro-N-{2-[4-(2-methoxyphenyl)- 1-piperazinyl]ethyl}-N-(2-pyridinyl)benzamide,([F-18]MPPF) and regional cerebral glucose metabolic rates using 2-deoxy-2-[F-18]fluoro-2-deoxy-D-glucose (2-[F-18]FDG).

RESULTS

[F-18]FDDNP reliably follows neuropathological progression (amyloid plaques [SP]; neurofibrillary tangles [NFT]) in the living brain of AD patients and those with MCI. The distribution of [F-18]FDDNP brain cortical accumulation correlates well with behavioral measures (e.g., MMSE scores) and follows known patterns of pathological distribution observed at autopsy. We have also established conversion of controls to MCI and MCI to AD with precision and sensitivity in patients and control subjects in follow-up studies. Moreover, we have established that hemispheric cortical surface mapping of [F-18]FDDNP binding is a powerful tool for assessment and visualization of the rate of brain pathology deposition. A strong correlation of [F-18]FDDNP binding, cell losses in hippocampus and decreased glucose utilization ([F-18]FDG PET) in several neocortical regions was found in the same AD and MCI subjects.

CONCLUSIONS

The combined evaluation of [F-18]FDDNP PET (targeting NFT and_SP) with neuronal losses in the hippocampus and with [F-18]FDG PET (targeting neuronal function) offers the opportunity for reliable, noninvasive detection of MCI patients at risk for AD. The approach offers a glimpse to the molecular and cellular mechanisms associated with dementia and provides a means for their assessment in the living patient. Monitoring disease progression in MCI patients demonstrates the usefulness of this imaging approach for early diagnosis and provides a means for evaluation of neuroprotective agents and drugs aimed at prevention and modification of disease progression.

Amyloid imaging in distinguishing atypical prion disease from Alzheimer disease

OBJECTIVE

To compare the in vivo uptake of two amyloid-binding PET agents, PIB and FDDNP, in human subjects with a prion protein (PrP) gene (PRNP) mutation that produces a clinical syndrome similar to Alzheimer disease (AD).

BACKGROUND

Amyloid imaging with specific PET ligands offers great promise for early detection and differential diagnosis of AD. Genetic forms of prion disease can present with clinical features that resemble AD, and at autopsy may show deposition of mutant PrP-amyloid. FDDNP binds to PrP-amyloid in postmortem human specimens, but has not been reported in vivo in prion disease. The ability of PIB to bind PrP-amyloid is not known.

METHODS

Two brothers with a 6 octapeptide repeat insertion mutation (6-OPRI) in the PRNP gene underwent clinical, structural MRI, and FDG-PET evaluations. One brother received a PIB-PET evaluation, while the other received an FDDNP-PET scan. PET results were compared with five normal subjects and five individuals with AD scanned with either agent.

RESULTS

PIB uptake was similar to controls in one brother, while FDDNP uptake was intermediate between AD and controls in the other brother.

CONCLUSIONS

Different amyloid-binding agents may have differential sensitivity to prion-related brain pathology. A combination of amyloid imaging agents may be useful in the diagnosis of early-onset dementia.

In vitro detection of (S)-naproxen and ibuprofen binding to plaques in the Alzheimer's brain using the positron emission tomography molecular imaging probe 2-(1-[6-[(2-[(18)F]fluoroethyl)(methyl)amino]-2-naphthyl]ethylidene)malononitrile

Epidemiological studies have suggested that the chronic use of non-steroidal anti-inflammatory drugs (NSAIDs) reduces the relative risk of Alzheimer's disease (AD). The possible neuroprotection by NSAIDs in AD is generally attributed to anti-inflammatory activity. An additional mode of drug action may involve anti-aggregation of beta-amyloid (Abeta) peptides by commonly used NSAIDs. We utilized in vitro competition assays, autoradiography, and fluorescence microscopy with AD brain specimens to demonstrate concentration-dependent decreases in the binding of the in vivo molecular imaging probe, 2-(1-[6-[(2-[(18)F]fluoroethyl)(methyl)amino]-2-naphthyl]ethylidene)malononitrile ([(18)F]FDDNP), against (S)-naproxen and (R)- and (S)-ibuprofen (but not diclofenac) to Abeta fibrils and ex vivo Abeta senile plaques. Conversely, in vitro amyloid dyes Congo Red and Thioflavine T were demonstrated in the same experiments not to bind to the FDDNP binding site. FDDNP and the NSAIDs that share the same binding site also exhibit anti-aggregation effects on Abeta peptides, suggesting that the shared binding site on Abeta fibrils and plaques may be a site of anti-aggregation drug action. Our results indicate for the first time the binding of select NSAIDs to plaques, specifically to the binding site of the molecular imaging probe [(18)F]FDDNP. Our understanding of the molecular requirements of FDDNP binding may help in the optimization of the Abeta anti-aggregation potency of experimental drugs. [(18)F]FDDNP has been used to image plaques in vivo with positron emission tomography (PET), and investigations into the influence of Abeta anti-aggregation on the risk-reduction effects of NSAIDs on AD could utilize [(18)F]FDDNP and PET in determining the occupancy rate of NSAIDs and experimental drugs in plaques in the living brain of AD patients.

Binding characteristics of radiofluorinated 6-dialkylamino-2-naphthylethylidene derivatives as positron emission tomography imaging probes for beta-amyloid plaques in Alzheimer's disease

Senile plaques (SPs) and neurofibrillary tangles (NFTs) are hallmark pathologies accompanying the neurodegeneration involved in Alzheimer's disease (AD), for which beta-amyloid (Abeta) peptide is a major constituent of SPs. Our laboratories previously developed the hydrophobic, fluorescent molecular-imaging probe 2-(1-(6-[(2-[(18)F]fluoroethyl)(methyl)amino]-2-naphthyl)ethylidene)malononitrile ([(18)F]FDDNP), which crosses the blood-brain barrier and determines the localization and load of SPs and NFTs in vivo in AD patients. In this report, we used fluorimetric and radioactive binding assays to determine the binding affinities of FDDNP and its analog, 1-(6-[(2-[(18)F]fluoroethyl)(methyl)amino]naphthalen-2-yl)ethanone ([(18)F]FENE), to synthetic fibrils of Abeta(1-40). FDDNP and FENE both appeared to bind to two kinetically distinguishable binding sites on Abeta(1-40) fibrils. Fluorescence titrations yielded apparent K(d) values of 0.12 and 0.16 nm for high-affinity binding sites for FDDNP and FENE, respectively, and apparent K(d) values of 1.86 and 71.2 nm for the low-affinity binding sites. The traditional radioactive binding assays also produced apparent K(d) values in the low nanomolar range. The presence of two kinetically distinguishable binding sites for FDDNP and FENE suggests multiple binding sites for SPs and identifies the parameters that allow for the structural optimization of this family of probes for in vivo use. The high-affinity binding of the probes to multiple binding sites on fibrils are consistent with results obtained with digital autoradiography, immunohistochemistry, and confocal fluorescence microscopy using human brain specimens of AD patients.