Association of Cerebrospinal Fluid Neurofilament Light Concentration With Alzheimer Disease Progression

Serum neurofilament light in familial Alzheimer disease: A marker of early neurodegeneration

Objectives:

To investigate whether serum neurofilament light (NfL) concentration is increased in familial Alzheimer disease (FAD), both pre and post symptom onset, and whether it is associated with markers of disease stage and severity.

Methods:

We recruited 48 individuals from families with PSEN1 or APP mutations to a cross-sectional study: 18 had symptomatic Alzheimer disease (AD) and 30 were asymptomatic but at 50% risk of carrying a mutation. Serum NfL was measured using an ultrasensitive immunoassay on the single molecule array (Simoa) platform. Cognitive testing and MRI were performed; 33 participants had serial MRI, allowing calculation of atrophy rates. Genetic testing established mutation status. A generalized least squares regression model was used to compare serum NfL among symptomatic mutation carriers, presymptomatic carriers, and noncarriers, adjusting for age and sex. Spearman coefficients assessed associations between serum NfL and (1) estimated years to/from symptom onset (EYO), (2) cognitive measures, and (3) MRI measures of atrophy.

Results:

Nineteen of the asymptomatic participants were mutation carriers (mean EYO −9.6); 11 were noncarriers. Compared with noncarriers, serum NfL concentration was higher in both symptomatic (p < 0.0001) and presymptomatic mutation carriers (p = 0.007). Across all mutation carriers, serum NfL correlated with EYO (ρ = 0.81, p < 0.0001) and multiple cognitive and imaging measures, including Mini-Mental State Examination (ρ = −0.62, p = 0.0001), Clinical Dementia Rating Scale sum of boxes (ρ = 0.79, p < 0.0001), baseline brain volume (ρ = −0.62, p = 0.0002), and whole-brain atrophy rate (ρ = 0.53, p = 0.01).

Conclusions:

Serum NfL concentration is increased in FAD prior to symptom onset and correlates with measures of disease stage and severity. Serum NfL may thus be a feasible biomarker of early AD-related neurodegeneration.

HIV/neuroAIDS biomarkers

HIV infection often causes neurological symptoms including cognitive and motor dysfunction, which have been collectively termed HIV/neuroAIDS. Neuropsychological assessment and clinical symptoms have been the primary diagnostic criteria for HIV/neuroAIDS, even for the mild cognitive and motor disorder, the most prevalent form of HIV/neuroAIDS in the era of combination antiretroviral therapy. Those performance-based assessments and symptoms are generally descriptive and do not have the sensitivity and specificity to monitor the diagnosis, progression, and treatment response of the disease when compared to objective and quantitative laboratory-based biological markers, or biomarkers. In addition, effects of demographics and comorbidities such as substance abuse, psychiatric disease, nutritional deficiencies, and co-infection on HIV/neuroAIDS could be more readily determined using biomarkers than using neuropsychological assessment and clinical symptoms. Thus, there have been great efforts in identification of HIV/neuroAIDS biomarkers over the past two decades. The need for reliable biomarkers of HIV/neuroAIDS is expected to increase as the HIV-infected population ages and their vulnerability to neurodegenerative diseases, particularly Alzheimer's disease increases. Currently, three classes of HIV/neuroAIDS biomarkers are being pursued to establish objective laboratory-based definitions of HIV-associated neurologic injury: cerebrospinal fluid biomarkers, blood biomarkers, and neuroimaging biomarkers. In this review, we will focus on the current knowledge in the field of HIV/neuroAIDS biomarker discovery.

Proteomic studies in the discovery of cerebrospinal fluid biomarkers for amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a progressive degenerative motor neuron disease, which usually leads to death within a few years. The diagnosis is mainly based on clinical symptoms and there is a need for ALS-specific biomarkers to make an early and precise diagnosis, for development of disease-modifying drugs and to gain new insights into pathophysiology. Areas covered: In the present review, we summarize studies using mass spectrometric (MS) approaches to identify protein alterations in the cerebrospinal fluid (CSF) of ALS patients. In total, we identified 11 studies fulfilling our criteria by searching in the PubMed database using the keywords 'ALS' and 'CSF' combined with 'proteome', 'proteomic', 'mass spectrometry' or 'protein biomarker'. Ten proteins were differently regulated in ALS CSF compared to controls in at least 2 studies. We will discuss the relevance of the identified proteins regarding the frequency of identification, extent of alteration and brain-specificity. Expert commentary: Most of the identified CSF biomarker candidates are irreproducible or mainly blood-derived. We assign the missing success of CSF proteomic studies in biomarker discovery to a lack of sensitivity, unsuitable normalization, low quality assurance and variations originating from sample preparation. These issues must be improved in future proteomic studies in CSF.

Association of Plasma Neurofilament Light With Neurodegeneration in Patients With Alzheimer Disease

Question

What is the importance of plasma neurofilament light in Alzheimer disease?

Findings

In this case-control study of 193 cognitively healthy controls, 197 patients with mild cognitive impairment, and 180 patients with Alzheimer disease dementia, plasma neurofilament light was associated with Alzheimer disease and correlated with future progression of cognitive decline, brain atrophy, and brain hypometabolism.

Meaning

Plasma neurofilament light may be a promising noninvasive biomarker for Alzheimer disease.

Importance

Existing cerebrospinal fluid (CSF) or imaging (tau positron emission tomography) biomarkers for Alzheimer disease (AD) are invasive or expensive. Biomarkers based on standard blood test results would be useful in research, drug development, and clinical practice. Plasma neurofilament light (NFL) has recently been proposed as a blood-based biomarker for neurodegeneration in dementias.

Objective

To test whether plasma NFL concentrations are increased in AD and associated with cognitive decline, other AD biomarkers, and imaging evidence of neurodegeneration.

Design, Setting, and Participants

In this prospective case-control study, an ultrasensitive assay was used to measure plasma NFL concentration in 193 cognitively healthy controls, 197 patients with mild cognitive impairment (MCI), and 180 patients with AD dementia from the Alzheimer’s Disease Neuroimaging Initiative. The study dates were September 7, 2005, to February 13, 2012. The plasma NFL analysis was performed in September 2016.

Main Outcomes and Measures

Associations were tested between plasma NFL and diagnosis, Aβ pathologic features, CSF biomarkers of neuronal injury, cognition, brain structure, and metabolism.

Results

Among 193 cognitively healthy controls, 197 patients with mild cognitive impairment, and 180 patients with AD with dementia, plasma NFL correlated with CSF NFL (Spearman ρ = 0.59, P < .001). Plasma NFL was increased in patients with MCI (mean, 42.8 ng/L) and patients with AD dementia (mean, 51.0 ng/L) compared with controls (mean, 34.7 ng/L) (P < .001) and had high diagnostic accuracy for patients with AD with dementia vs controls (area under the receiver operating characteristic curve, 0.87, which is comparable to established CSF biomarkers). Plasma NFL was particularly high in patients with MCI and patients with AD dementia with Aβ pathologic features. High plasma NFL correlated with poor cognition and AD-related atrophy (at baseline and longitudinally) and with brain hypometabolism (longitudinally).

Conclusions and Relevance

Plasma NFL is associated with AD diagnosis and with cognitive, biochemical, and imaging hallmarks of the disease. This finding implies a potential usefulness for plasma NFL as a noninvasive biomarker in AD.

Plasma neurofilament light chain levels in patients with MS switching from injectable therapies to fingolimod

Background:

Neurofilament light chain (NFL) is a cerebrospinal fluid (CSF) marker of neuroaxonal damage in multiple sclerosis (MS).

Objective:

To determine the correlation of NFL in CSF and serum/plasma, and in plasma after switching from injectable MS therapies to fingolimod.

Methods:

A first cohort consisted of MS patients ( n = 39) and neurological disease controls ( n = 27) where CSF and plasma/serum had been collected for diagnostic purposes. A second cohort ( n = 243) consisted of patients from a post-marketing study of fingolimod. NFL was determined with Single Molecule Array (Simoa™) technology (detection threshold 1.95 pg/mL).

Results:

Mean NFL pg/mL (standard deviation ( SD)) was 341 (267) and 1475 (2358) in CSF and 8.2 (3.58) and 17.0 (16.94) in serum from controls and MS, respectively. CSF/serum and plasma/serum levels were highly correlated ( n  = 66, rho  = 0.672, p  < 0.0001 and n  = 16, rho  = 0.684, p  = 0.009, respectively). In patients starting fingolimod ( n = 243), mean NFL pg/mL ( SD) in plasma was reduced between baseline (20.4 (10.7)) and at 12 months (13.5 (7.3), p < 3 × 10−6), and levels remained stable at 24 months (13.2 (6.2)).

Conclusion:

NFL in serum and CSF are highly correlated and plasma NFL levels decrease after switching to highly effective MS therapy. Blood NFL measurement can be considered as a biomarker for MS therapy response.

Association between cerebrospinal fluid and plasma neurodegeneration biomarkers with brain atrophy in Alzheimer's disease

The aggregation and deposition of amyloid-β (Aβ) peptides into plaques is an early event in Alzheimer's disease (AD), which is followed by different aspects of neurodegeneration that can be measured in the cerebrospinal fluid (CSF) or plasma using neurofilament light (NFL), neurogranin (Ng), total Tau (T-Tau), and phosphorylated tau (P-Tau) levels. The relationship between these biomarkers and regional brain atrophy across the different stages of AD remains largely unexplored. In this study, we assessed whether NFL, Ng, T-Tau, and P-Tau levels in CSF and NFL in plasma are associated with cortical thinning and subcortical volume loss in cognitively normal, mild cognitive impairment, and AD subjects with and without Aβ pathology. Our main findings showed that CSF NFL levels were associated with brain atrophy in all groups, but plasma NFL only correlated with atrophy in symptomatic cases. In contrast, Ng was associated with regional brain atrophy only in individuals with Aβ pathology. Altogether, our main findings suggest that Ng is strongly associated with Aβ pathology, whereas NFL is more unspecific.

Prolonged Cerebrospinal Fluid Neurofilament Light Chain Increase in Patients with Post-Traumatic Disorders of Consciousness

The mechanisms involved in secondary brain injury after the acute phase of severe traumatic brain injury (TBI) are largely unknown. Ongoing axonal degeneration, consequent to the initial trauma, may lead to secondary brain injury. To test this hypothesis, we evaluated the cerebrospinal fluid (CSF) level of neurofilament light chain (NF-L), a proposed marker of axonal degeneration, in 10 patients who developed a severe disorder of consciousness after a TBI, including 7 in a minimally conscious state and 3 with unresponsive wakefulness syndrome (time since brain injury, 309 ± 169 days). CSF NF-L level was measured with a commercially available NF-L enzyme-linked immunosorbent assay. CSF NF-L level was very high in all 10 patients, ranging from 2.4- to 60.5-fold the upper normal limit (median value, 4458 pg/mL; range, 695-23,000). Moreover, NF-L level was significantly higher after a severe TBI than in a reference group of 9 patients with probable Alzheimer's disease, a population with elevated levels of CSF NF-L attributed to neuronal degeneration (median value, 1173 pg/mL; range, 670-3643; p < 0.01). CSF NF-L level was correlated with time post-TBI (p = 0.04). These results demonstrate prolonged secondary brain injury, suggesting that patients exhibit ongoing axonal degeneration up to 19 months after a severe TBI.

TDP-43 and Cytoskeletal Proteins in ALS

Amyotrophic lateral sclerosis (ALS) represents a rapidly progressing neurodegenerative disease and is characterized by a degeneration of motor neurons. Motor neurons are particularly susceptible to selective and early degeneration because of their extended axon length and their dependency on the cytoskeleton for its stability, signaling, and axonal transport. The motor neuron cytoskeleton comprises actin filaments, neurofilaments like peripherin, and microtubules. The Transactivating Response Region (TAR) DNA Binding Protein (TDP-43) forms characteristic cytoplasmic aggregates in motor neurons of ALS patients, and at least in part, the pathogenesis of ALS seems to be driven by toxic pTDP-43 aggregates in cytoplasm, which lead to a diminished axon formation and reduced axon length. Diminished axon formation and reduced axon length suggest an interaction of TDP-43 with the cytoskeleton of motor neurons. TDP-43 interacts with several cytoskeletal components, e.g., the microtubule-associated protein 1B (MAP1B) or the neurofilament light chain (NFL) through direct binding to its RNA. From a clinical perspective, cytoskeletal biomarkers like phosphorylated neurofilament heavy chain (pNFH) and NFL are already clinically used in ALS patients to predict survival, disease progression, and duration. Thus, in this review, we focus on the interaction of TDP-43 with the different cytoskeleton components such as actin filaments, neurofilaments, and microtubules as well as their associated proteins as one aspect in the complex pathogenesis of ALS.

Applying fluid biomarkers to Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease that starts with a clinically silent phase of a decade or more during which brain pathologies accumulate predominantly in the medial temporal lobe but also elsewhere in the brain. Network dysfunction and clinical symptoms typically appear when senile plaque (amyloid-β) and neurofibrillary tangle (tau) pathologies meet in the brain parenchyma, producing synapse and neuronal loss. For plaque and tangle pathologies, reliable fluid biomarkers have been developed. These require sampling of cerebrospinal fluid. Reliable blood tests for plaque and tangle pathologies are currently lacking, but blood tests for general neurodegeneration have recently been developed. In AD, plaques and tangles often coexist with other pathologies, including Lewy bodies, and to what extent these contribute to symptoms is currently unknown. There are also important differential diagnoses that may be possible to distinguish from AD with the aid of biomarkers. The scope of this review is fluid biomarkers for AD and related pathologies. The purpose is to provide the reader with an updated account of currently available fluid biomarkers for AD and clinically relevant differential diagnoses.

Effect of physical exercise on markers of neuronal dysfunction in cerebrospinal fluid in patients with Alzheimer's disease

INTRODUCTION

Physical exercise has gained increasing focus as a potential mean to maintain cognitive function in patients with Alzheimer's disease (AD). Alongside the markers of specific AD pathology (amyloid β and tau), other pathologies such as neuronal damage and synaptic loss have been proposed as markers of the disease. Here, we study the effect of physical exercise on biomarkers of neuronal and synaptic integrity.

METHODS

Cerebrospinal fluid (CSF) from 51 AD subjects who participated in the randomized controlled trial Preserving Cognition, Quality of Life, Physical Health and Functional Ability in Alzheimer's Disease: The Effect of Physical Exercise (ADEX) was analyzed for the concentration of neurofilament light (NFL), neurogranin (Ng), visinin-like protein-1 (VILIP-1), and chitinase-3-like protein 1 (YKL-40). Participants were subjected to either 16 weeks of moderate- to high-intensity exercise (n = 25) or treatment as usual (control group, n = 26), and CSF was collected before and after intervention.

RESULTS

No significant differences in CSF concentrations of VILIP-1, YKL-40, NFL, and Ng were observed when comparing mean change from baseline between the exercise and control groups. Similarly, when classifying subjects based on their exercise levels, no significant changes were observed for the biomarkers in the control group compared with the high-exercise group (attending 80% of the exercise sessions with an intensity of 70% of maximum heart rate or above).

DISCUSSION

These results are not supportive of a modulatory effect of physical exercise on the selected biomarkers of neuronal and synaptic integrity in patients with AD.

NF-L in cerebrospinal fluid and serum is a biomarker of neuronal damage in an inducible mouse model of neurodegeneration

Accumulation of neurofilaments (NFs), the major constituents of the neuronal cytoskeleton, is a distinctive feature of neurological diseases and several studies have shown that soluble NFs can be detected in the cerebrospinal fluid (CSF) of patients with neurological diseases, such as multiple sclerosis and frontotemporal dementia. Here we have used an inducible transgenic mouse model of neurodegeneration, CamKII-TetOp25 mice, to evaluate whether NF-L levels in CSF or blood can be used as a biochemical biomarker of neurodegeneration. Induction of p25 transgene brain expression led to increase in CSF and serum NF-L levels that correlated with ongoing neurodegeneration. Switching off p25 prevented further increases in both CSF and serum NF-L levels and concomitantly stopped the progression of neurodegeneration. The levels of CSF NF-L detected in p25 mice are about 4-fold higher than the CSF levels detected in patients with chronic neurodegenerative diseases, such as symptomatic FTD (bvFTD). In addition, our data indicate that the NF-L detected in CSF is most likely a cleaved form of NF-L. These results suggest that CSF and serum NF-L are of interest to be further explored as potential translational dynamic biomarkers of neurodegeneration or as pharmacodynamics biomarkers at least in preclinical animal studies.

Neurofilaments and Neurofilament Proteins in Health and Disease

SUMMARYNeurofilaments (NFs) are unique among tissue-specific classes of intermediate filaments (IFs) in being heteropolymers composed of four subunits (NF-L [neurofilament light]; NF-M [neurofilament middle]; NF-H [neurofilament heavy]; and α-internexin or peripherin), each having different domain structures and functions. Here, we review how NFs provide structural support for the highly asymmetric geometries of neurons and, especially, for the marked radial expansion of myelinated axons crucial for effective nerve conduction velocity. NFs in axons extensively cross-bridge and interconnect with other non-IF components of the cytoskeleton, including microtubules, actin filaments, and other fibrous cytoskeletal elements, to establish a regionally specialized network that undergoes exceptionally slow local turnover and serves as a docking platform to organize other organelles and proteins. We also discuss how a small pool of oligomeric and short filamentous precursors in the slow phase of axonal transport maintains this network. A complex pattern of phosphorylation and dephosphorylation events on each subunit modulates filament assembly, turnover, and organization within the axonal cytoskeleton. Multiple factors, and especially turnover rate, determine the size of the network, which can vary substantially along the axon. NF gene mutations cause several neuroaxonal disorders characterized by disrupted subunit assembly and NF aggregation. Additional NF alterations are associated with varied neuropsychiatric disorders. New evidence that subunits of NFs exist within postsynaptic terminal boutons and influence neurotransmission suggests how NF proteins might contribute to normal synaptic function and neuropsychiatric disease states.

Recent publications from the Alzheimer's Disease Neuroimaging Initiative: Reviewing progress toward improved AD clinical trials

INTRODUCTION

The Alzheimer's Disease Neuroimaging Initiative (ADNI) has continued development and standardization of methodologies for biomarkers and has provided an increased depth and breadth of data available to qualified researchers. This review summarizes the over 400 publications using ADNI data during 2014 and 2015.

METHODS

We used standard searches to find publications using ADNI data.

RESULTS

(1) Structural and functional changes, including subtle changes to hippocampal shape and texture, atrophy in areas outside of hippocampus, and disruption to functional networks, are detectable in presymptomatic subjects before hippocampal atrophy; (2) In subjects with abnormal β-amyloid deposition (Aβ+), biomarkers become abnormal in the order predicted by the amyloid cascade hypothesis; (3) Cognitive decline is more closely linked to tau than Aβ deposition; (4) Cerebrovascular risk factors may interact with Aβ to increase white-matter (WM) abnormalities which may accelerate Alzheimer's disease (AD) progression in conjunction with tau abnormalities; (5) Different patterns of atrophy are associated with impairment of memory and executive function and may underlie psychiatric symptoms; (6) Structural, functional, and metabolic network connectivities are disrupted as AD progresses. Models of prion-like spreading of Aβ pathology along WM tracts predict known patterns of cortical Aβ deposition and declines in glucose metabolism; (7) New AD risk and protective gene loci have been identified using biologically informed approaches; (8) Cognitively normal and mild cognitive impairment (MCI) subjects are heterogeneous and include groups typified not only by "classic" AD pathology but also by normal biomarkers, accelerated decline, and suspected non-Alzheimer's pathology; (9) Selection of subjects at risk of imminent decline on the basis of one or more pathologies improves the power of clinical trials; (10) Sensitivity of cognitive outcome measures to early changes in cognition has been improved and surrogate outcome measures using longitudinal structural magnetic resonance imaging may further reduce clinical trial cost and duration; (11) Advances in machine learning techniques such as neural networks have improved diagnostic and prognostic accuracy especially in challenges involving MCI subjects; and (12) Network connectivity measures and genetic variants show promise in multimodal classification and some classifiers using single modalities are rivaling multimodal classifiers.

DISCUSSION

Taken together, these studies fundamentally deepen our understanding of AD progression and its underlying genetic basis, which in turn informs and improves clinical trial design.

Linking deregulation of non-coding RNA to the core pathophysiology of Alzheimer's disease: An integrative review

The human genome encodes a vast repertoire of protein non-coding RNAs (ncRNA), some specific to the brain. MicroRNAs, which interfere with the translation of target mRNAs, are of particular interest since their deregulation has been implicated in neurodegenerative disorders like Alzheimer's disease (AD). However, it remains challenging to link the complex body of observations on miRNAs and AD into a coherent framework. Using extensive graphical support, this article discusses how a diverse panoply of miRNAs convergently and divergently impact (and are impacted by) core pathophysiological processes underlying AD: neuroinflammation and oxidative stress; aberrant generation of β-amyloid-42 (Aβ42); anomalies in the production, cleavage and post-translational marking of Tau; impaired clearance of Aβ42 and Tau; perturbation of axonal organisation; disruption of synaptic plasticity; endoplasmic reticulum stress and the unfolded protein response; mitochondrial dysfunction; aberrant induction of cell cycle re-entry; and apoptotic loss of neurons. Intriguingly, some classes of miRNA provoke these cellular anomalies, whereas others act in a counter-regulatory, protective mode. Moreover, changes in levels of certain species of miRNA are a consequence of the above-mentioned anomalies. In addition to miRNAs, circular RNAs, piRNAs, long non-coding RNAs and other types of ncRNA are being increasingly implicated in AD. Overall, a complex mesh of deregulated and multi-tasking ncRNAs reciprocally interacts with core pathophysiological mechanisms underlying AD. Alterations in ncRNAs can be detected in CSF and the circulation as well as the brain and are showing promise as biomarkers, with the ultimate goal clinical exploitation as targets for novel modes of symptomatic and course-altering therapy.

Metabolomic-guided discovery of Alzheimer's disease biomarkers from body fluid

The rapid increase in the older population has made age-related diseases like Alzheimer's disease (AD) a global concern. Given that there is still no cure for this neurodegenerative disease, the drastic growth in the number of susceptible individuals represents a major emerging threat to public health. The poor understanding of the mechanisms underlying AD is deemed the greatest stumbling block against progress in definitive diagnosis and management of this disease. There is a dire need for biomarkers that can facilitate early diagnosis, classification, prognosis, and treatment response. Efforts have been directed toward discovery of reliable and distinctive AD biomarkers but with very little success. With the recent emergence of high-throughput technology that is able to collect and catalogue vast datasets of small metabolites, metabolomics offers hope for a better understanding of AD and subsequent identification of biomarkers. This review article highlights the potential of using multiple metabolomics platforms as useful means in uncovering AD biomarkers from body fluids. © 2017 Wiley Periodicals, Inc.

Microstructural white matter alterations in preclinical Alzheimer's disease detected using free water elimination diffusion tensor imaging

Brain changes associated with Alzheimer's disease (AD) begin decades before disease diagnosis. While β-amyloid plaques and neurofibrillary tangles are defining features of AD, neuronal loss and synaptic pathology are closely related to the cognitive dysfunction. Brain imaging methods that are tuned to assess degeneration of myelinated nerve fibers in the brain (collectively called white matter) include diffusion tensor imaging (DTI) and related techniques, and are expected to shed light on disease-related loss of structural connectivity. Participants (N = 70, ages 47-76 years) from the Wisconsin Registry for Alzheimer's Prevention study underwent DTI and hybrid diffusion imaging to determine a free-water elimination (FWE-DTI) model. The study assessed the extent to which preclinical AD pathology affects brain white matter. Preclinical AD pathology was determined using cerebrospinal fluid (CSF) biomarkers. The sample was enriched for AD risk (APOE ε4 and parental history of AD). AD pathology assessed by CSF analyses was significantly associated with altered microstructure on both DTI and FWE-DTI. Affected regions included frontal, parietal, and especially temporal white matter. The f-value derived from the FWE-DTI model appeared to be the most sensitive to the relationship between the CSF AD biomarkers and microstructural alterations in white matter. These findings suggest that white matter degeneration is an early pathological feature of AD that may have utility both for early disease detection and as outcome measures for clinical trials. More complex models of microstructural diffusion properties including FWE-DTI may provide increased sensitivity to early brain changes associated with AD over standard DTI.

Biomarkers for the Early Detection and Progression of Alzheimer's Disease

The recent failures of potential disease-modifying drugs for Alzheimer's disease (AD) may reflect the fact that the enrolled participants in clinical trials are already too advanced to derive a clinical benefit. Thus, well-validated biomarkers for the early detection and accurate diagnosis of the preclinical stages of AD will be crucial for therapeutic advancement. The combinatorial use of biomarkers derived from biological fluids, such as cerebrospinal fluid (CSF), with advanced molecular imaging and neuropsychological testing may eventually achieve the diagnostic sensitivity and specificity necessary to identify people in the earliest stages of the disease when drug modification is most likely possible. In this regard, positive amyloid or tau tracer retention on positron emission tomography imaging, low CSF concentrations of the amyloid-β 1-42 peptide, high CSF concentrations in total tau and phospho-tau, mesial temporal lobe atrophy on magnetic resonance imaging, and temporoparietal/precuneus hypometabolism or hypoperfusion on 18F-fluorodeoxyglucose positron emission tomography have all emerged as biomarkers for the progression to AD. However, the ultimate AD biomarker panel will likely involve the inclusion of novel CSF and blood biomarkers more precisely associated with confirmed pathophysiologic mechanisms to improve its reliability for detecting preclinical AD. This review highlights advancements in biological fluid and imaging biomarkers that are moving the field towards achieving the goal of a preclinical detection of AD.

Alpha band disruption in the AD-continuum starts in the Subjective Cognitive Decline stage: a MEG study

The consideration of Subjective Cognitive Decline (SCD) as a preclinical stage of AD remains still a matter of debate. Alpha band alterations represent one of the most significant changes in the electrophysiological profile of AD. In particular, AD patients exhibit reduced alpha relative power and frequency. We used alpha band activity measured with MEG to study whether SCD and MCI elders present these electrophysiological changes characteristic of AD, and to determine the evolution of the observed alterations across AD spectrum. The total sample consisted of 131 participants: 39 elders without SCD, 41 elders with SCD and 51 MCI patients. All of them underwent MEG and MRI scans and neuropsychological assessment. SCD and MCI patients exhibited a similar reduction in alpha band activity compared with the no SCD group. However, only MCI patients showed a slowing in their alpha peak frequency compared with both SCD and no SCD. These changes in alpha band were related to worse cognition. Our results suggest that AD-related alterations may start in the SCD stage, with a reduction in alpha relative power. It is later, in the MCI stage, where the slowing of the spectral profile takes place, giving rise to objective deficits in cognitive functioning.

Serum neurofilament light protein predicts clinical outcome in traumatic brain injury

Axonal white matter injury is believed to be a major determinant of adverse outcomes following traumatic brain injury (TBI). We hypothesized that measurement of neurofilament light protein (NF-L), a protein found in long white-matter axons, in blood samples, may serve as a suitable biomarker for neuronal damage in TBI patients. To test our hypotheses, we designed a study in two parts: i) we developed an immunoassay based on Single molecule array technology for quantification of NF-L in blood, and ii) in a proof-of-concept study, we tested our newly developed method on serial serum samples from severe TBI (sTBI) patients (n = 72) and controls (n = 35). We also compared the diagnostic and prognostic utility of NF-L with the established blood biomarker S100B. NF-L levels were markedly increased in sTBI patients compared with controls. NF-L at admission yielded an AUC of 0.99 to detect TBI versus controls (AUC 0.96 for S100B), and increased to 1.00 at day 12 (0.65 for S100B). Importantly, initial NF-L levels predicted poor 12-month clinical outcome. In contrast, S100B was not related to outcome. Taken together, our data suggests that measurement of serum NF-L may be useful to assess the severity of neuronal injury following sTBI.

Cerebrospinal fluid tau, neurogranin, and neurofilament light in Alzheimer's disease

Cerebrospinal fluid (CSF) tau (total tau, T‐tau), neurofilament light (NFL), and neurogranin (Ng) are potential biomarkers for neurodegeneration in Alzheimer's disease (AD). It is unknown whether these biomarkers provide similar or complementary information in AD. We examined 93 patients with AD, 187 patients with mild cognitive impairment, and 109 controls. T‐tau, Ng, and NFL were all predictors of AD diagnosis. Combinations improved the diagnostic accuracy (AUC 85.5% for T‐tau, Ng, and NFL) compared to individual biomarkers (T‐tau 80.8%; Ng 71.4%; NFL 77.7%). T‐tau and Ng were highly correlated (ρ = 0.79, P < 0.001) and strongly associated with β‐amyloid (Aβ) pathology, and with longitudinal deterioration in cognition and brain structure, primarily in people with Aβ pathology. NFL on the other hand was not associated with Aβ pathology and was associated with cognitive decline and brain atrophy independent of Aβ. T‐tau, Ng, and NFL provide partly independent information about neuronal injury and may be combined to improve the diagnostic accuracy for AD. T‐tau and Ng reflect Aβ‐dependent neurodegeneration, while NFL reflects neurodegeneration independently of Aβ pathology.

Multicenter immunoassay validation of cerebrospinal fluid neurofilament light: a biomarker for neurodegeneration

AIM

Neurofilament light (NfL) chain, a putative cerebrospinal fluid biomarker, can support neurodegenerative disease diagnosis and indicate disease severity and prognosis. Universal validation protocols when used to measure biomarkers can reduce pre and analytical laboratory variation, thus increasing end-user confidence in the consistency of validation data across sites.

METHODOLOGY

Here, a commercially available NfL ELISA (UmanDiagnostics, Umeå, Sweden) was validated in a multicentered setting using comprehensive newly developed standard operating procedures.

RESULTS

The data showed good assay sensitivity and intra and interassay precision. Interlaboratory precision was, however, suboptimal.

CONCLUSION

The UmanDiagnostics assay is suitable for the quantification of NfL in human cerebrospinal fluid. However, sources of interlaboratory variation in the data require further investigation.

CSF neurofilament light levels predict hippocampal atrophy in cognitively healthy older adults

Cerebrospinal fluid (CSF) neurofilament light (NFL) is a marker of axonal degeneration. We tested whether CSF NFL levels predict hippocampal atrophy rate in cognitively healthy older adults independently of the established CSF Alzheimer's disease (AD) biomarkers, β-amyloid 1-42, and phosphorylated tau (P-tau). We included 144 participants in a 2-year longitudinal study with baseline CSF measures and 2 magnetic resonance images. Eighty-eight participants had full data available. A subgroup of 36 participants with very low AD risk was also studied. NFL predicted hippocampal atrophy rate independently of age, β-amyloid 1-42, and P-tau. Including NFL, P-tau, and age in the same model, higher NFL and lower P-tau predicted higher hippocampal atrophy (R² = 0.20, NFL: β = -0.34; p = 0.003; P-tau: β = 0.27; p = 0.009). The results were upheld in the participants with very low AD risk. NFL predicted neurodegeneration in older adults with very low AD probability. We suggest that factors previously shown to be important for brain degeneration in mild cognitive impairment may also impact changes in normal aging, demonstrating that NFL is likely to indicate AD-independent, age-expected neurodegeneration.

Specialized roles of neurofilament proteins in synapses: Relevance to neuropsychiatric disorders

Neurofilaments are uniquely complex among classes of intermediate filaments in being composed of four subunits (NFL, NFM, NFH and alpha-internexin in the CNS) that differ in structure, regulation, and function. Although neurofilaments have been traditionally viewed as axonal structural components, recent evidence has revealed that distinctive assemblies of neurofilament subunits are integral components of synapses, especially at postsynaptic sites. Within the synaptic compartment, the individual subunits differentially modulate neurotransmission and behavior through interactions with specific neurotransmitter receptors. These newly uncovered functions suggest that alterations of neurofilament proteins not only underlie axonopathy in various neurological disorders but also may play vital roles in cognition and neuropsychiatric diseases. Here, we review evidence that synaptic neurofilament proteins are a sizable population in the CNS and we advance the concept that changes in the levels or post-translational modification of individual NF subunits contribute to synaptic and behavioral dysfunction in certain neuropsychiatric conditions.

Cerebrospinal fluid interferon alpha levels correlate with neurocognitive impairment in ambulatory HIV-Infected individuals

HIV-associated neurocognitive disorders (HANDs) continue to be common and are associated with increased morbidity and mortality. However, the underlying mechanisms in the combination antiretroviral therapy (cART) era are not fully understood. Interferon alpha (IFNα) is an antiviral cytokine found to be elevated in the cerebrospinal fluid (CSF) of individuals with advanced HIV-associated dementia in the pre-cART era. In this cross-sectional study, we investigated the association between IFNα and neurocognitive performance in ambulatory HIV-infected individuals with milder impairment. An eight-test neuropsychological battery representing six cognitive domains was administered. Individual scores were adjusted for demographic characteristics, and a composite neuropsychological score (NPT-8) was calculated. IFNα and CSF neurofilament light chain (NFL) levels were measured using enzyme-linked immunosorbent assay (ELISA). There were 15 chronically infected participants with a history of significant immunocompromise (median nadir CD4+ of 49 cells/μl). Most participants were neurocognitively impaired (mean global deficit score of 0.86). CSF IFNα negatively correlated with three individual tests (Trailmaking A, Trailmaking B, and Stroop Color-Word) as well as the composite NPT-8 score (r = -0.67, p = 0.006). These negative correlations persisted in multivariable analyses adjusting for chronic hepatitis B and C. Additionally, CSF IFNα correlated strongly with CSF NFL, a marker of neuronal damage (rho = 0.748, p = 0.0013). These results extend findings from individuals with severe HIV-associated dementia in the pre-cART era and suggest that IFNα may continue to play a role in HAND pathogenesis during the cART era. Further investigation into the role of IFNα is indicated.

Neurofilament light chain: a biomarker for genetic frontotemporal dementia

Objective

To evaluate cerebrospinal fluid (CSF) and serum neurofilament light chain (NfL) levels in genetic frontotemporal dementia (FTD) as a potential biomarker in the presymptomatic stage and during the conversion into the symptomatic stage. Additionally, to correlate NfL levels to clinical and neuroimaging parameters.

Methods

In this multicenter case–control study, we investigated CSF NfL in 174 subjects (48 controls, 40 presymptomatic carriers and 86 patients with microtubule‐associated protein tau (MAPT), progranulin (GRN), and chromosome 9 open reading frame 72 (C9orf72) mutations), and serum NfL in 118 subjects (39 controls, 44 presymptomatic carriers, 35 patients). In 55 subjects both CSF and serum was determined. In two subjects CSF was available before and after symptom onset (converters). Additionally, NfL levels were correlated with clinical parameters, survival, and regional brain atrophy.

Results

CSF NfL levels in patients (median 6762 pg/mL, interquartile range 3186–9309 pg/mL) were strongly elevated compared with presymptomatic carriers (804 pg/mL, 627–1173 pg/mL, P < 0.001), resulting in a good diagnostic performance to discriminate both groups. Serum NfL correlated highly with CSF NfL (r_s= 0.87, P < 0.001) and was similarly elevated in patients. Longitudinal samples in the converters showed a three‐ to fourfold increase in CSF NfL after disease onset. Additionally, NfL levels in patients correlated with disease severity, brain atrophy, annualized brain atrophy rate and survival.

Interpretation

NfL in both serum and CSF has the potential to serve as a biomarker for clinical disease onset and has a prognostic value in genetic FTD.