Detailed comparison of amyloid PET and CSF biomarkers for identifying early Alzheimer disease

Objective: To compare the diagnostic accuracy of CSF biomarkers and amyloid PET for diagnosing early-stage Alzheimer disease (AD).

Methods: From the prospective, longitudinal BioFINDER study, we included 122 healthy elderly and 34 patients with mild cognitive impairment who developed AD dementia within 3 years (MCI-AD). β-Amyloid (Aβ) deposition in 9 brain regions was examined with [¹⁸F]-flutemetamol PET. CSF was analyzed with INNOTEST and EUROIMMUN ELISAs. The results were replicated in 146 controls and 64 patients with MCI-AD from the Alzheimer's Disease Neuroimaging Initiative study.

Results: The best CSF measures for identifying MCI-AD were Aβ42/total tau (t-tau) and Aβ42/hyperphosphorylated tau (p-tau) (area under the curve [AUC] 0.93–0.94). The best PET measures performed similarly (AUC 0.92–0.93; anterior cingulate, posterior cingulate/precuneus, and global neocortical uptake). CSF Aβ42/t-tau and Aβ42/p-tau performed better than CSF Aβ42 and Aβ42/40 (AUC difference 0.03–0.12, p < 0.05). Using nonoptimized cutoffs, CSF Aβ42/t-tau had the highest accuracy of all CSF/PET biomarkers (sensitivity 97%, specificity 83%). The combination of CSF and PET was not better than using either biomarker separately.

Conclusions: Amyloid PET and CSF biomarkers can identify early AD with high accuracy. There were no differences between the best CSF and PET measures and no improvement when combining them. Regional PET measures were not better than assessing the global Aβ deposition. The results were replicated in an independent cohort using another CSF assay and PET tracer. The choice between CSF and amyloid PET biomarkers for identifying early AD can be based on availability, costs, and doctor/patient preferences since both have equally high diagnostic accuracy.

Classification of evidence: This study provides Class III evidence that amyloid PET and CSF biomarkers identify early-stage AD equally accurately.

Reference: Neurology 10.1212/WNL.0000000000001991 Full text

Nonlinear Association Between Cerebrospinal Fluid and Florbetapir F-18 β-Amyloid Measures Across the Spectrum of Alzheimer Disease

Cerebrospinal fluid (CSF) and positron emission tomographic (PET) amyloid biomarkers have been proposed for the detection of Alzheimer disease (AD) pathology in living patients and for the tracking of longitudinal changes, but the relation between biomarkers needs further study. Indeed a study aimed at determining the association between CSF and PET amyloid biomarkers (cross-sectional and longitudinal measures) and compare the cutoffs for these measures has just been published:

Design, Setting, and Participants Longitudinal clinical cohort study from 2005 to 2014 including 820 participants with at least 1 florbetapir F-18 (hereafter referred to as simply florbetapir)–PET scan and at least 1 CSF β-amyloid 1-42 (Aβ1-42) sample obtained within 30 days of each other (501 participants had a second PET scan after 2 years, including 150 participants with CSF Aβ1-42 measurements). Data were obtained from the Alzheimer’s Disease Neuroimaging Initiative database.

Main Outcomes and Measures Four different PET scans processing pipelines from 2 different laboratories were compared. The PET cutoff values were established using a mixture-modeling approach, and different mathematical models were applied to define the association between CSF and PET amyloid measures.

Results The values of the CSF Aβ1-42 samples and florbetapir-PET scans showed a nonlinear association (R2 = 0.48-0.66), with the strongest association for values in the middle range. The presence of a larger dynamic range of florbetapir-PET scan values in the higher range compared with the CSF Aβ1-42 plateau explained the differences in correlation with cognition (R2 = 0.36 and R2 = 0.25, respectively). The APOEgenotype significantly modified the association between both biomarkers. The PET cutoff values derived from an unsupervised classifier converged with previous PET cutoff values and the established CSF Aβ1-42 cutoff levels. There was no association between longitudinal Aβ1-42 levels and standardized uptake value ratios during follow-up.

Conclusions and Relevance The association between both biomarkers is limited to a middle range of values, is modified by the APOE genotype, and is absent for longitudinal changes; 4 different approaches in 2 different platforms converge on similar pathological Aβ cutoff levels; and different pipelines to process PET scans showed correlated but not identical results. Our findings suggest that both biomarkers measure different aspects of AD Aβ pathology.

Reference JAMA Neurol. Published online March 30, 2015. doi:10.1001/jamaneurol.2014.4829

Increased CSF APPs-α levels in patients with Alzheimer disease treated with acitretin

Objective: Authors investigated induction of α-secretase A disintegrin and metalloprotease 10 (ADAM10) by the synthetic retinoid acitretin (Neotigason; Actavis, München-Riem, Germany) in patients with mild to moderate Alzheimer disease (AD) via measurement of CSF content of α-secretase–derived amyloid precursor protein (APPs-α).

Methods: Twenty-one patients clinically diagnosed with mild to moderate AD received acitretin (30 mg per day) or placebo in a 4-week double-blind study. Primary endpoint was the difference of CSF APPs-α ratios calculated from the APPs-α levels after treatment and at baseline. We monitored safety and tolerability of the treatment. In addition, we assessed biomarkers such as β-amyloid 42 (Aβ₄₂) under treatment conditions.

Results: The acitretin group showed a significant increase in CSF APPs-α levels compared with the placebo group (difference 0.38, 95% confidence interval 0.03–0.72, p = 0.035) within this rather short treatment period. The synthetic retinoid acitretin was overall safe and well tolerated.

Conclusions: Our pilot study highlights that acitretin is able to enhance the nonamyloidogenic APP processing in human patients. Clinical consequences of this regulation should be investigated in larger and longer trials in patients with AD to evaluate acitretin's potential to serve as a novel therapeutic drug.

Classification of evidence: This study provides Class III evidence that in patients with AD, oral acitretin increases CSF APPs-α levels.

Reference: Neurology 10.1212/WNL.0000000000001017

The use of biomarkers for the etiologic diagnosis of MCI in Europe: An EADC survey

The most frequently used biomarker is visually rated MTA (75% of the 37 responders reported using it “always/frequently”) followed by CSF markers (22%), FDG-PET (16%), and amyloid-PET (3%). Only 45% of responders perceive MTA as contributing to diagnostic confidence, where the contribution was rated as “moderate”. Seventy-nine percent of responders felt “very/extremely” comfortable delivering a diagnosis of MCI due to AD when both amyloid and neuronal injury biomarkers were abnormal (P < .02 versus any individual biomarker). Responders largely agreed that a combination of amyloidosis and neuronal injury biomarkers was a strongly indicative AD signature.

DOI: http://dx.doi.org/10.1016/j.jalz.2014.06.006

Diagnostic impact of CSF biomarkers for Alzheimer's disease in a tertiary memory clinic

Background

We aimed to assess the impact of cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease on decision making and patient management in a tertiary memory clinic.

Methods

We included all patients, for 1 year, visiting the VUmc Alzheimer Center for cognitive screening. Neurologists completed questionnaires before and after CSF disclosure. We assessed the change of diagnosis, diagnostic confidence, and impact on patient management.

Results

A total of 438 patients (age 63 ± 8 years, 39% women) were included, of whom 351 (80%) underwent lumbar puncture. After the disclosure of CSF 23/351 diagnoses (7%) were changed. Diagnostic confidence increased from 84% to 89% (P < .001). There were consequences for management in 44/351 patients (13%) with CSF, and 13/87 patients (15%) because of unavailable CSF. There was no effect of age on these results.

Conclusions

CSF biomarkers aid clinicians with decision making during diagnostic work-up of cognitive disorders. This study may be useful for developing guidelines for the implementation of CSF biomarkers in daily practice.

DOI: http://dx.doi.org/10.1016/j.jalz.2014.05.1753

Association of plasma and cortical amyloid beta is modulated by APOE ε4 status

Background

Apolipoprotein E (APOE) ε4 allele's role as a modulator of the relationship between soluble plasma amyloid beta (Aβ) and fibrillar brain Aβ measured by Pittsburgh compound B positron emission tomography ([¹¹C]PiB PET) has not been assessed.

Methods

Ninety-six Alzheimer's Disease Neuroimaging Initiative participants with [¹¹C]PiB scans and plasma Aβ_1–40 and Aβ_1–42 measurements at the time of PET scanning were included. Regional and voxelwise analyses of [¹¹C]PiB data were used to determine the influence of APOE ε4 allele on association of plasma Aβ_1–40, Aβ_1–42, and Aβ_1–40/Aβ_1–42 with [¹¹C]PiB uptake.

Results

In APOE ε4− but not ε4+ participants, positive relationships between plasma Aβ_1–40/Aβ_1–42 and [¹¹C]PiB uptake were observed. Modeling the interaction of APOE and plasma Aβ_1–40/Aβ_1–42 improved the explained variance in [¹¹C]PiB binding compared with using APOE and plasma Aβ_1–40/Aβ_1–42 as separate terms.

Conclusions

The results suggest that plasma Aβ is a potential Alzheimer's disease biomarker and highlight the importance of genetic variation in interpretation of plasma Aβ levels.

Fig. 1. (A–D) Scatterplots of plasma Aβ_1–40/Aβ_1–42 vs average regional [¹¹C]PiB uptake from the (Average regional [¹¹C]PiB uptake = Plasma Aβ_1–40/Aβ_1–42 + APOE ε4 status + [Plasma Aβ_1–40/Aβ_1–42 × APOE ε4 status]) model (A and B), and plasma Aβ_1–40/Aβ_1–42 vs mean [¹¹C]PiB uptake from the cluster identified in the (Voxel [¹¹C]PiB uptake = Plasma Aβ_1–40/Aβ_1–42 + APOE ε4 status + [Plasma Aβ_1–40/Aβ_1–42 × APOE ε4 status]) model (C and D). Aβ, amyloid beta; PiB, Pittsburgh compound B; APOE, apolipoprotein E.

Figure options

Fig. 2. Brain regions (R, right; L, left) identified in the (Voxel [¹¹C]PiB uptake = Plasma Aβ_1–40/Aβ_1–42 + APOE ε4 status + [Plasma Aβ_1–40/Aβ_1–42 × APOE ε4 status]) model (voxel-level threshold of P < .005 [uncorrected], cluster size ≥ 200 voxels). The red-to-yellow scale indicates increasing statistical significance of association. PiB, Pittsburgh compound B; Aβ, amyloid beta; APOE, apolipoprotein E.

Enrichment and Stratification for Predementia Alzheimer Disease Clinical Trials

The tau and amyloid pathobiological processes underlying Alzheimer disease (AD) progresses slowly over periods of decades before clinical manifestation as mild cognitive impairment (MCI), then more rapidly to dementia, and eventually to end-stage organ failure. The failure of clinical trials of candidate disease modifying therapies to slow disease progression in patients already diagnosed with early AD has led to increased interest in exploring the possibility of early intervention and prevention trials, targeting MCI and cognitively healthy (HC) populations. Here, we stratify MCI individuals based on cerebrospinal fluid (CSF) biomarkers and structural atrophy risk factors for the disease. We also stratify HC individuals into risk groups on the basis of CSF biomarkers for the two hallmark AD pathologies. Results show that the broad category of MCI can be decomposed into subsets of individuals with significantly different average regional atrophy rates. By thus selectively identifying individuals, combinations of these biomarkers and risk factors could enable significant reductions in sample size requirements for clinical trials of investigational AD-modifying therapies, and provide stratification mechanisms to more finely assess response to therapy. Power is sufficiently high that detecting efficacy in MCI cohorts should not be a limiting factor in AD therapeutics research. In contrast, we show that sample size estimates for clinical trials aimed at the preclinical stage of the disorder (HCs with evidence of AD pathology) are prohibitively large. Longer natural history studies are needed to inform design of trials aimed at the presymptomatic stage.

Citation: Holland D, McEvoy LK, Desikan RS, Dale AM, for the Alzheimer’s Disease Neuroimaging Initiative (2012) Enrichment and Stratification for Predementia Alzheimer Disease Clinical Trials. PLoS ONE 7(10): e47739. doi:10.1371/journal.pone.0047739

Full text

CSF Markers: Goodbye, Research Use Only; Hello, Clinical

This is Part 1 of a two-part series. See also Part 2.
What a difference a year can make. At the 2011 Alzheimer’s Association International Conference in Paris, France, leading scientists in the CSF Alzheimer’s biomarker field met to tackle the vexing problem of measurement variability with the available commercial assays. Alas, back then a listener could be forgiven for thinking of the Tower of Babel, as groups presented their own stance and talked past each other as much as finding common ground.

Revised Criteria for Mild Cognitive Impairment May Compromise the Diagnosis of Alzheimer Disease Dementia.

OBJECTIVE:

To evaluate the potential impact of revised criteria for mild cognitive impairment (MCI), developed by a work group sponsored by the National Institute on Aging and the Alzheimer's Association, on the diagnosis of very mild and mild Alzheimer disease (AD) dementia.

DESIGN:

Retrospective review of ratings of functional impairment across diagnostic categories.

SETTING:

Alzheimer's Disease Centers and the National Alzheimer's Coordinating Center.

PARTICIPANTS:

Individuals (N = 17 535) with normal cognition, MCI, or AD dementia.

MAIN OUTCOME MEASURES:

The functional ratings of individuals with normal cognition, MCI, or AD dementia who were evaluated at Alzheimer's Disease Centers and submitted to the National Alzheimer's Coordinating Center were assessed in accordance with the definition of "functional independence" allowed by the revised criteria. Pairwise demographic differences between the 3 diagnostic groups were tested using t tests for continuous variables and χ(2) for categorical variables.

RESULTS:

Almost all (99.8%) individuals currently diagnosed with very mild AD dementia and the large majority (92.7%) of those diagnosed with mild AD dementia could be reclassified as having MCI with the revised criteria, based on their level of impairment in the Clinical Dementia Rating domains for performance of instrumental activities of daily living in the community and at home. Large percentages of these individuals with AD dementia also meet the revised "functional independence" criterion for MCI as measured by the Functional Assessment Questionnaire.

CONCLUSIONS:

The categorical distinction between MCI and milder stages of AD dementia has been compromised by the revised criteria. The resulting diagnostic overlap supports the premise that "MCI due to AD" represents the earliest symptomatic stage of AD.

Arch Neurol. 2012 Feb 6. [Epub ahead of print]

Wanted: Better Brain-Process Biomarkers for Drug Trials

Eight years ago, Peter Lansbury decided to become a drug developer. He was a neurology professor at Harvard Medical School with a background in chemistry, and had been doing well-regarded research on the origins of neurodegenerative diseases. Now he had an idea for a blockbuster treatment: a drug that would boost the brain’s ability to dispose of the harmful protein aggregates that seem to cause many of these diseases.
Lansbury and two investors founded a company, Link Medicine, and began screening libraries of chemical compounds for those that would increase autophagy, a natural process that clears away unwanted protein aggregates. Eventually they had a lead autophagy-boosting compound, LNK-754, that worked well in mouse models and appeared safe in human volunteers. In principle, LNK-754 could be useful in treating a number of illnesses including Parkinson’s, Alzheimer’s, and Huntington’s diseases. All that remained, it seemed, was for a large pharmaceutical company to buy the marketing rights and fund the large-scale clinical trials needed to prove LNK-754’s efficacy in humans.
But that hasn’t happened. “It used to be that if you had a drug whose mechanism makes sense, a drug that works in animals and is safe in people, you could immediately go and do a large clinical trial. But for drugs against neurodegenerative diseases, those days are gone,” says Lansbury.
The problem is that for these diseases, the standard measures needed in a conclusive clinical trial—such as cognitive test scores, for Alzheimer’s patients—are expected to show clear evidence of a treatment effect only very gradually, and only in a population of at least hundreds of patients, even for a drug that works. For a would-be disease-modifying drug, that typically means a trial of at least 18 months, costing on the order of $100 million. At the same time, pharmaceutical companies are all too aware that potential neurodegenerative disease treatments have almost always failed in clinical trials, in recent years. “The big pharma companies have become very risk averse,” Lansbury says. “The big issue now is not really the lack of drug strategies, it’s the inability to assess those strategies in short, economical trials.”