William T. Hu

Novel CSF biomarkers for Alzheimer’s disease and mild cognitive impairment

Altered levels of cerebrospinal fluid (CSF) peptides related to Alzheimer’s disease (AD) are associated with pathologic AD diagnosis, although cognitively normal subjects can also have abnormal levels of these AD biomarkers. To identify novel CSF biomarkers that distinguish pathologically confirmed AD from cognitively normal subjects and patients with other neurodegenerative disorders, we collected antemortem CSF samples from 66 AD patients and 25 patients with other neurodegenerative dementias followed longitudinally to neuropathologic confirmation, plus CSF from 33 cognitively normal subjects. We measured levels of 151 novel analytes via a targeted multiplex panel enriched in cytokines, chemokines and growth factors, as well as established AD CSF biomarkers (levels of Aβ42, tau and p-tau181). Two categories of biomarkers were identified: (1) analytes that specifically distinguished AD (especially CSF Aβ42 levels) from cognitively normal subjects and other disorders; and (2) analytes altered in multiple diseases (NrCAM, PDGF, C3, IL-1α), but not in cognitively normal subjects. A multi-prong analytical approach showed AD patients were best distinguished from non-AD cases (including cognitively normal subjects and patients with other neurodegenerative disorders) by a combination of traditional AD biomarkers and novel multiplex biomarkers. Six novel biomarkers (C3, CgA, IL-1α, I-309, NrCAM and VEGF) were correlated with the severity of cognitive impairment at CSF collection, and altered levels of IL-1α and TECK associated with subsequent cognitive decline in 38 longitudinally followed subjects with mild cognitive impairment. In summary, our targeted proteomic screen revealed novel CSF biomarkers that can improve the distinction between AD and non-AD cases by established biomarkers alone.

Distinct cerebral perfusion patterns in FTLD and AD

Objective: We examined the utility of distinguishing between patients with frontotemporal lobar degeneration (FTLD) and Alzheimer disease (AD) using quantitative cerebral blood flow (CBF) imaging with arterial spin labeled (ASL) perfusion MRI. Methods: Forty-two patients with FTLD and 18 patients with AD, defined by autopsy or CSF-derived biomarkers for AD, and 23 matched controls were imaged with a continuous ASL method to quantify CBF maps covering the entire brain. Results: Patients with FTLD and AD showed distinct patterns of hypoperfusion and hyperperfusion. Compared with controls, patients with FTLD showed significant hypoperfusion in regions of the frontal lobe bilaterally, and hyperperfusion in posterior cingulate and medial parietal/precuneus regions. Compared with controls, patients with AD showed significant hypoperfusion in the medial parietal/precuneus and lateral parietal cortex, and hyperperfusion in regions of the frontal lobe. Direct comparison of patient groups showed significant inferior, medial, and dorsolateral frontal hypoperfusion in FTLD, and significant hypoperfusion in bilateral lateral temporal-parietal and medial parietal/precuneus regions in AD. Conclusions: Doubly dissociated areas of hypoperfusion in FTLD and AD are consistent with areas of significant histopathologic burden in these groups. ASL is a potentially useful biomarker for distinguishing patients with these neurodegenerative diseases.

Progressive aphasia secondary to Alzheimer disease vs FTLD pathology.

Background: The pathology causing progressive aphasia is typically a variant of frontotemporal lobar degeneration, especially with ubiquitin-positive inclusions (FTLD-U). Less commonly the underlying pathology is Alzheimer disease (AD). Objective: To compare clinicopathologic and MRI features of subjects with progressive aphasia and AD pathology to subjects with aphasia and FTLD-U pathology and subjects with typical AD. Methods: We identified 5 subjects with aphasia and AD pathology and 5 with aphasia and FTLD-U pathology with an MRI from a total of 216 aphasia subjects. Ten subjects with typical AD clinical features and AD pathology were also identified. All subjects with AD pathology underwent pathologic reanalysis with TDP-43 immunohistochemistry. Voxel-based morphometry (VBM) was used to assess patterns of gray matter atrophy in the aphasia cases with AD pathology, aphasia cases with FTLD-U, and typical AD cases with AD pathology, compared with a normal control group. Results: All aphasic subjects had fluent speech output. However, those with AD pathology had better processing speed than those with FTLD-U pathology. Immunohistochemistry with TDP-43 antibodies was negative. VBM revealed gray matter atrophy predominantly in the temporoparietal cortices, with notable sparing of the hippocampus in the aphasia with AD subjects. In comparison, the aphasic subjects with FTLD-U showed sparing of the parietal lobe. Typical AD subjects showed temporoparietal and hippocampal atrophy. Conclusions: A temporoparietal pattern of atrophy on MRI in patients with progressive fluent aphasia and relatively preserved processing speed is suggestive of underlying Alzheimer disease pathology rather than frontotemporal lobar degeneration with ubiquitin-only immunoreactive changes. GLOSSARY: AD = Alzheimer disease; ADPR = Alzheimers Disease Patient Registry; ADRC = Alzheimers Disease Research Center; aphasia–AD = subjects with progressive aphasia and Alzheimer disease pathology; aphasia–FTLD-U = subjects with progressive aphasia and frontotemporal lobar degeneration with ubiquitin-only immunoreactive changes pathology; CDR = Clinical Dementia Rating; DCT = discrete cosine transformation; FTLD = frontotemporal lobar degeneration; FTLD-U = frontotemporal lobar degeneration with ubiquitin-only immunoreactive changes; FWHM = full-width at half-maximum; GM = gray matter; MMSE = Mini-Mental State Examination; MNI = Montreal Neurological Institute; NA = not applicable; NIA = National Institute on Aging; NR = not reported; NS = not significant; PPA = primary progressive aphasia; typical AD = subjects with a clinical and pathologic diagnosis of Alzheimer disease; VBM = voxel-based morphometry; WAIS-R = Wechsler Adult Intelligence Scale–Revised; WM = white matter; WMS-R = Wechsler Memory Scale–Revised.

Plasma epidermal growth factor levels predict cognitive decline in Parkinson disease.

Most people with Parkinson disease (PD) eventually develop cognitive impairment (CI). However, neither the timing of onset nor the severity of cognitive symptoms can be accurately predicted. We sought plasma‐based biomarkers for CI in PD.

Temporal lobar predominance of TDP-43 neuronal cytoplasmic inclusions in Alzheimer disease

TAR DNA binding protein-43 (TDP-43) immunoreactive neuronal inclusions are detected in 20–30% of Alzheimer disease (AD) brains, but the distribution of this pathology has not been rigorously studied. In this report, we describe region-specific distribution and density of TDP-43 positive neuronal cytoplasmic inclusions (NCIs) in clinically demented individuals with high probability AD pathology, all with Braak neurofibrillary tangle stages of V or VI. Sections of hippocampus, amygdala, as well as temporal, frontal, and parietal neocortex, were analyzed with TDP-43 immunohistochemistry, and the density of NCIs was assessed using a semiquantitative scoring method. Of the 29 cases, six had TDP-43 positive NCIs in the amygdala only and seven had TDP-43 inclusions restricted to amygdala and hippocampus. In 16 cases, TDP-43 immunoreactivity was more widespread, affecting temporal, frontal or parietal neocortex. These findings indicate that medial temporal lobe limbic structures are vulnerable to TDP-43 pathology in advanced AD, and that the amygdala appears to be the most susceptible region. The distribution of the lesions in this cross-sectional analysis may suggest a progression of TDP-43 pathology in AD, with limbic structures in the medial temporal lobe affected first, followed by higher order association cortices.

Multimodal predictors for Alzheimer disease in nonfluent primary progressive aphasia

Objective: Alzheimer disease (AD) and frontotemporal lobar degeneration (FTLD) are hypothesized to cause clinically distinct forms of primary progressive aphasia (PPA) that predominantly affect expressive speech. AD is thought to cause logopenic progressive aphasia (LPA), and FTLD may cause progressive nonfluent aphasia (PNFA). We sought to determine the value of clinical characterization, neuropsychological analysis, and MRI atrophy in predicting pathology of LPA and PNFA. Methods: Patients with LPA (n = 19) and patients with PNFA (n = 19) were evaluated with neuropsychological assessments, structural MRI, CSF analysis, and neuropathologic examination. Results: Twelve of 19 patients with LPA (63%) and 6 of 19 patients with PNFA (32%) had neuropathologic findings or CSF biomarkers consistent with AD. Neuropsychological testing showed that naming was more impaired in patients with AD, and letter-guided fluency was more affected in patients with a non-AD disorder. Voxel-based morphometry analysis revealed that in patients with AD, patients with LPA and PNFA had significant posterior-superior temporal atrophy; in patients with non-AD, patients with LPA had peri-Sylvian atrophy and patients with PNFA had dorsolateral prefrontal and insular atrophy. Receiver operator characteristic curve analysis showed that combining neuropsychological testing with MRI atrophy pattern had 90% specificity for pathology or CSF biomarkers consistent with AD, and combining clinical features with neuropsychological analysis had 100% sensitivity for pathology or CSF biomarkers consistent with AD. Conclusions: Neither PPA phenotyping nor imaging alone is a reliable predictor of pathology. Multimodal predictors, such as combining neuropsychological testing with MRI analysis, can improve noninvasive prediction of underlying pathology in nonfluent forms of PPA.

Biomarker discovery for Alzheimer’s disease, frontotemporal lobar degeneration, and Parkinson’s disease

Ante-mortem diagnosis of neurodegenerative disorders based on clinical features alone is associated with variable sensitivity and specificity, and biomarkers can potentially improve the accuracy of clinical diagnosis. In patients suspected of having Alzheimer’s disease (AD), alterations in cerebrospinal fluid (CSF) biomarkers that reflect the neuropathologic changes of AD strongly support the diagnosis, although there is a trade-off between sensitivity and specificity due to similar changes in cognitively healthy subjects. Here, we review the current approaches in using CSF AD biomarkers (total tau, p-tau181, and Aβ42) to predict the presence of AD pathology, and our recent work using multi-analyte profiling to derive novel biomarkers for biofluid-based AD diagnosis. We also review our use of the multi-analyte profiling strategy to identify novel biomarkers that can distinguish between subtypes of frontotemporal lobar degeneration, and those at risk of developing cognitive impairment in Parkinson’s disease. Multi-analyte profiling is a powerful tool for biomarker discovery in complex neurodegenerative disorders, and analytes associated with one or more diseases may shed light on relevant biological pathways and potential targets for intervention.

Survival profiles of patients with frontotemporal dementia and motor neuron disease

BACKGROUND Frontotemporal dementia and amyotrophic lateral sclerosis are neurodegenerative diseases associated with TAR DNA-binding protein 43- and ubiquitin-immunoreactive pathologic lesions. OBJECTIVE To determine whether survival is influenced by symptom of onset in patients with frontotemporal dementia and amyotrophic lateral sclerosis. DESIGN, SETTING, AND PATIENTS Retrospective review of patients with both cognitive impairment and motor neuron disease consecutively evaluated at 4 academic medical centers in 2 countries. MAIN OUTCOME MEASURES Clinical phenotypes and survival patterns of patients. RESULTS A total of 87 patients were identified, including 60 who developed cognitive symptoms first, 19 who developed motor symptoms first, and 8 who had simultaneous onset of cognitive and motor symptoms. Among the 59 deceased patients, we identified 2 distinct subgroups of patients according to survival. Long-term survivors had cognitive onset and delayed emergence of motor symptoms after a long monosymptomatic phase and had significantly longer survival than the typical survivors (mean, 67.5 months vs 28.2 months, respectively; P < .001). Typical survivors can have simultaneous or discrete onset of cognitive and motor symptoms, and the simultaneous-onset patients had shorter survival (mean, 19.2 months) than those with distinct cognitive or motor onset (mean, 28.6 months) (P = .005). CONCLUSIONS Distinct patterns of survival profiles exist in patients with frontotemporal dementia and motor neuron disease, and overall survival may depend on the relative timing of the emergence of secondary symptoms.

Amyloid‐beta increases acetylcholinesterase expression in neuroblastoma cells by reducing enzyme degradation

Amyloid‐beta (Aβ) is the principal protein constituent of ‘senile plaques’ and is a suspected mediator in Alzheimers disease (AD). Senile plaques also contain acetylcholinesterase (AChE; EC 3.1.1.7), which may have a role in promoting Αβ‐toxicity. We have found that Αβ can affect AChE expression in a neuron‐like line, the N1E.115 neuroblastoma cell. When 1 µmΑβ 1–42 or 25–35 was added for 24 h to differentiating N1E.115 in culture, AChE activity increased 30–40% in adherent cells, and 100% or more in nonadherent cells. The changes in both tetrameric (G4) and monomeric (G1) AChE forms were comparable. Turnover studies indicated that the elevation of AChE activity reflected slowed AChE degradation rather than accelerated synthesis. With a similar time course, Αβ also increased the quantity of muscarinic receptors on the plasma membrane. Immunocytochemistry for a lysosomal membrane protein (LAMP‐1) indicated no change in abundance or localization of lysosomes in treated cells. But decreased labeling by pH‐sensitive fluorescent dye pointed to an impairment of lysosomal acidification. We consider that the alteration of AChE expression after Αβ‐exposure could reflect lysosomal dysfunction, and might itself enhance Αβ‐toxicity.

Low Plasma Leptin in Cognitively Impaired ADNI Subjects: Gender Differences and Diagnostic and Therapeutic Potential

Analysis of data derived from the Alzheimers Disease Neuroimaging Initiative (ADNI) program showed plasma leptin levels in individuals with Mild Cognitive Impairment (MCI) or Alzheimers disease (AD) to be lower than those of subjects with normal cognition (NC). Approximately 70% of both men and women with MCI have plasma leptin levels lower than the median values of NC. Additionally, half of these subjects carry at least one apolipoprotein-E4 (APOE-ε4) allele. A subgroup of participants also had cerebrospinal fluid (CSF) leptin measured. Plasma leptin typically reflected the levels of leptin in CSF in all groups (Control/MCI/AD) in both genders. The data suggest that plasma leptin deficiency provides an indication of potential CNS leptin deficiency, further supporting the exploration of plasma leptin as a diagnostic marker for MCI or AD. The important question is whether leptin deficiency plays a role in the causation of AD and/or its progression. If this is the case, individuals with early AD or MCI with low plasma leptin may benefit from leptin replacement therapy. Thus, these data indicate that trials of leptin in low leptin MCI/early-stage AD patients should be conducted to test the hypothesis.