Neurogranin and Neurofilament Light Chain as Preclinical Biomarkers in Scrapie.

Prion diseases are diagnosed in the symptomatic stage, when the neuronal damage is spread throughout the central nervous system (CNS). The assessment of biological features that allow the detection of asymptomatic cases is needed, and, in this context, scrapie, where pre-symptomatic infected animals can be detected through rectal biopsy, becomes a good study model. Neurogranin (Ng) and neurofilament light chain (NfL) are proteins that reflect synaptic and axonal damage and have been studied as cerebrospinal fluid (CSF) biomarkers in different neurodegenerative disorders. In this study, we evaluated Ng and NfL both at the protein and transcript levels in the CNS of preclinical and clinical scrapie-affected sheep compared with healthy controls and assessed their levels in ovine CSF. The correlation between these proteins and the main neuropathological events in prion diseases, PrPSc deposition and spongiosis, was also assessed. The results show a decrease in Ng and NfL at the protein and gene expression levels as the disease progresses, and significant changes between the control and preclinical animals. On the contrary, the CSF levels of NfL increased throughout the progression of the disease. Negative correlations between neuropathological markers of prion disease and the concentration of the studied proteins were also found. Although further research is needed, these results suggest that Ng and NfL could act as biomarkers for neurodegeneration onset and intensity in preclinical cases of scrapie.

P-tau subgroups in AD relate to distinct amyloid production and synaptic integrity profiles.

BACKGROUND: We previously identified four Alzheimer's disease (AD) subgroups with increasingly higher cerebrospinal fluid (CSF) levels of tau phosphorylated at threonine 181 (p-tau). These subgroups included individuals across the cognitive spectrum, suggesting p-tau subgroups could reflect distinct biological changes in AD, rather than disease severity. Therefore, in the current study, we further investigated which potential processes may be related with p-tau subgroups, by comparing individuals on CSF markers for presynaptic structure [vesicle-associated membrane protein 2 (VAMP2)], postsynaptic structure [neurogranin (NRGN)], axonal damage [neurofilament light (NfL)], and amyloid production [beta-secretase 1 (BACE1) and amyloid-beta 1-40 (Aß40)]. METHODS: We selected 348 amyloid-positive (A+) individuals (53 preclinical, 102 prodromal, 193 AD dementia) and 112 amyloid-negative (A-) cognitively normal (CN) individuals from the Amsterdam Dementia Cohort (ADC). Individuals were labeled according to their p-tau subgroup (subgroup 1: p-tau ≤ 56 pg/ml; subgroup 2: 57-96 pg/ml; subgroup 3: 97-159 pg/ml; subgroup 4: > 159 pg/ml). CSF protein levels were measured with ELISA (NRGN, BACE1, Aß40, NfL) or single-molecule array (Simoa) (VAMP2). We tested whether protein levels differed between the p-tau subgroups within A+ individuals with linear models corrected for age and sex and whether disease stage influenced these relationships. RESULTS: Among A+ individuals, higher p-tau subgroups showed a higher percentage of AD dementia [subgroup 1: n = 41/94 (44%); subgroup 2: n = 81/147 (55%); subgroup 3: n = 59/89 (66%); subgroup 4: n = 7/11 (64%)]. Relative to controls, subgroup 1 showed reduced CSF levels of BACE1, Aß40, and VAMP2 and higher levels of NfL. Subgroups 2 to 4 showed gradually increased CSF levels of all measured proteins, either across the first three (NfL and Aß40) or across all subgroups (VAMP2, NRGN, BACE1). The associations did not depend on the clinical stage (interaction p-values ranging between 0.19 and 0.87). CONCLUSIONS: The results suggest that biological heterogeneity in p-tau levels in AD is related to amyloid metabolism and synaptic integrity independent of clinical stage. Biomarkers reflecting amyloid metabolism and synaptic integrity may be useful outcome measures in clinical trials targeting tau pathology.

Cerebrospinal Fluid Concentration of Neurogranin in Hip Fracture Patients with Delirium.

BACKGROUND: Delirium is associated with an increased risk of incident dementia and accelerated progression of existing cognitive symptoms. Reciprocally, dementia increases the risk of delirium. Cerebrospinal fluid (CSF) concentration of the dendritic protein neurogranin has been shown to increase in early Alzheimer's disease (AD), likely reflecting synaptic dysfunction and/or degeneration. OBJECTIVE: To elucidate the involvement of synaptic dysfunction in delirium pathophysiology, we tested the association between CSF neurogranin concentration and delirium in hip fracture patients with different AD-biomarker profiles, while comparing them to cognitively unimpaired older adults (CUA) and AD patients. METHODS: The cohort included hip fracture patients with (n = 70) and without delirium (n = 58), CUA undergoing elective surgery (n = 127), and AD patients (n = 46). CSF was collected preoperatively and diagnostically in surgery and AD patients respectively. CSF neurogranin concentrations were analyzed in all samples with an in-house ELISA. Delirium was assessed pre-and postoperatively in hip fracture patients by trained investigators using the Confusion Assessment Method. Hip fracture patients were further stratified based on pre-fracture dementia status, delirium subtype, and AD fluid biomarkers. RESULTS: No association was found between delirium and CSF neurogranin concentration (main analysis: delirium versus no delirium, p = 0.68). Hip fracture patients had lower CSF neurogranin concentration than AD patients (p = 0.001) and CUA (p = 0.035) in age-adjusted sensitivity analyses. CONCLUSION: The findings suggest that delirium is not associated with increased CSF neurogranin concentration in hip fracture patients, possibly due to advanced neurodegenerative disease and age and/or because synaptic degeneration is not an important pathophysiological process in delirium.

Prospective Quantification of CSF Biomarkers in Antibody-Mediated Encephalitis.

OBJECTIVE: To determine whether neuronal and neuroaxonal injury, neuroinflammation, and synaptic dysfunction associate with clinical course and outcomes in antibody-mediated encephalitis (AME), we measured biomarkers of these processes in CSF from patients presenting with AME and cognitively normal individuals. METHODS: Biomarkers of neuronal (total tau, VILIP-1) and neuroaxonal damage (neurofilament light chain [NfL]), inflammation (YKL-40), and synaptic function (neurogranin, SNAP-25) were measured in CSF obtained from 45 patients at the time of diagnosis of NMDA receptor (n = 34) or LGI1/CASPR2 (n = 11) AME and 39 age- and sex-similar cognitively normal individuals. The association between biomarkers and modified Rankin Scale (mRS) scores were evaluated in a subset (n = 20) of longitudinally followed patients. RESULTS: Biomarkers of neuroaxonal injury (NfL) and neuroinflammation (YKL-40) were elevated in AME cases at presentation, whereas markers of neuronal injury and synaptic function were stable (total tau) or decreased (VILIP-1, SNAP-25, neurogranin). The log-transformed ratio of YKL-40/SNAP-25 optimally discriminated patients from cognitively normal individuals (area under the receiver operating characteristic curve 0.99; 95% confidence interval 0.97, >0.99). Younger age (ρ = -0.56; p = 0.01), lower VILIP-1 (ρ = -0.60; p < 0.01) and SNAP-25 (ρ = -0.54; p = 0.01), and higher log10(YKL-40/SNAP-25) (ρ = 0.48; p = 0.04) associated with greater disease severity (higher mRS score) in prospectively followed patients. Higher YKL-40 (ρ = 0.60; p = 0.02) and neurogranin (ρ = 0.55; p = 0.03) at presentation were associated with higher mRS scores 12 months following hospital discharge. CONCLUSIONS: CSF biomarkers suggest that neuronal integrity is acutely maintained in AME, despite neuroaxonal compromise. Low levels of biomarkers of synaptic function may reflect antibody-mediated internalization of cell surface receptors and may represent an acute correlate of antibody-mediated synaptic dysfunction, with the potential to inform disease severity and outcomes.

Comparison of variables associated with cerebrospinal fluid neurofilament, total-tau, and neurogranin.

INTRODUCTION: Three cerebrospinal fluid (CSF) markers of neurodegeneration (N) (neurofilament light [NfL], total-tau [T-tau], and neurogranin [Ng]) have been proposed under the AT(N) scheme of the National Institute on Aging-Alzheimer's Association Research Framework. METHODS: We examined, in a community-based population (N = 777, aged 50-95) (1) what variables were associated with each of the CSF (N) markers, and (2) whether the variables associated with each marker differed by increased brain amyloid. CSF T-tau was measured with an automated electrochemiluminescence Elecsys immunoassay; NfL and Ng were measured with in-house enzyme-linked immunosorbent assays. RESULTS: Multiple variables were differentially associated with CSF NfL and T-tau levels, but not Ng. Most associations were attenuated after adjustment for age and sex. T-tau had the strongest association with cognition in the presence of amyloidosis, followed by Ng. Variables associations with NfL did not differ by amyloid status. DISCUSSION: Understanding factors that influence CSF (N) markers will assist in the interpretation and utility of these markers in clinical practice.

Cerebrospinal fluid biomarkers for understanding multiple aspects of Alzheimer's disease pathogenesis.

Alzheimer's disease (AD) is a multifactorial age-related brain disease. Numerous pathological events run forth in the brain leading to AD. There is an initial long, dormant phase before the clinical symptoms become evident. There is a need to diagnose the disease at the preclinical stage since therapeutic interventions are most likely to be effective if initiated early. Undoubtedly, the core cerebrospinal fluid (CSF) biomarkers have a good diagnostic accuracy and have been used in clinical trials as end point measures. However, looking into the multifactorial nature of AD and the overlapping pathology with other forms of dementia, it is important to integrate the core CSF biomarkers with a broader panel of other biomarkers reflecting different aspects of pathology. The review is focused upon a panel of biomarkers that relate to different aspects of AD pathology, as well as various studies that have evaluated their diagnostic potential. The panel includes markers of neurodegeneration: neurofilament light chain and visinin-like protein (VILIP-1); markers of amyloidogenesis and brain amyloidosis: apolipoproteins; markers of inflammation: YKL-40 and monocyte chemoattractant protein 1; marker of synaptic dysfunction: neurogranin. These markers can highlight on the state and stage-associated changes that occur in AD brain with disease progression. A combination of these biomarkers would not only aid in preclinical diagnosis, but would also help in identifying early brain changes during the onset of disease. Successful treatment strategies can be devised by understanding the contribution of these markers in different aspects of disease pathogenesis.

Association of CSF CD40 levels and synaptic degeneration across the Alzheimer's disease spectrum.

The CD40 pathway has been implicated in microglial activation, which is considered as a key factor in the pathogenesis of Alzheimer's disease (AD). However, the association of CSF CD40 and synaptic degeneration in living human is not clear. A total of 294 subjects with different severities of cognitive impairments were included in this study: 84 participants with normal cognition, 143 patients with mild cognitive impairment (MCI) and 67 patients with mild AD. Levels of CD40 in CSF were compared among the three groups. Further, several linear regression models were conducted to explore the associations of CSF CD40 and neurogranin levels (reflecting synaptic degeneration) when controlling for age, gender, educational attainment, APOE4 genotype, clinical diagnosis, CSF Aß42 and tau proteins. We found that CSF CD40 levels were significantly decreased in patients with mild AD compared with healthy controls and MCI patients (control vs. AD, p = 0.0026; MCI vs. AD, p = 0.0268). However, there were no significant differences in CSF CD40 levels between controls and patients with MCI (p = 0.37). In addition, CSF CD40 levels were associated with neurogranin in the pooled sample when controlling for age, gender, educational attainment, APOE4 genotype and diagnosis. In summary, our findings support the notion that the CD40 pathway may contribute to an important mechanism underlying synaptic degeneration in AD.

Neurogranin and tau in cerebrospinal fluid and plasma of patients with acute ischemic stroke.

BACKGROUND: While neurogranin has no value as plasma biomarker for Alzheimer's disease, it may be a potential blood biomarker for traumatic brain injury. This evokes the question whether there are changes in neurogranin levels in blood in other conditions of brain injury, such as acute ischemic stroke (AIS). METHODS: We therefore explored neurogranin in paired cerebrospinal fluid (CSF)/plasma samples of AIS patients (n = 50) from a well-described prospective study. In parallel, we investigated another neuronal protein, i.e. tau, which has already been suggested as potential AIS biomarker in CSF and blood. ELISA as well as Single Molecule Array (Simoa) technology were used for the biochemical analyses. Statistical analyses included Shapiro-Wilk testing, Mann-Whitney analyses and Pearson's correlation analysis. RESULTS: In contrast to tau, of which high levels in both CSF and plasma were related to stroke characteristics like severity and long-term outcome, plasma neurogranin levels were only correlated with infarct volume. Likewise, CSF neurogranin levels were significantly higher in patients with an infarct volume > 5 mL than in patients with smaller infarct volumes. Finally, neurogranin and tau were significantly correlated in CSF, whereas a weaker relationship was observed in plasma. CONCLUSIONS: These findings indicate that although plasma and CSF neurogranin may reflect the volume of acute cerebral ischemia, this synaptic protein is less likely to be a potential AIS biomarker. Levels of tau correlated with severity and outcome of stroke in both plasma and CSF, in the present study as well as previous reports, confirming the potential of tau as an AIS biomarker.

Preclinical amyloid pathology biomarker positivity: effects on tau pathology and neurodegeneration.

Brain autopsy and biomarker studies indicate that the pathology of Alzheimer's disease (AD) is initiated at least 10-20 years before clinical symptoms. This provides a window of opportunity to initiate preventive treatment. However, this emphasizes the necessity for biomarkers that identify individuals at risk for developing AD later in life. In this cross-sectional study, originating from three epidemiologic studies in Sweden (n=1428), the objective was to examine whether amyloid pathology, as determined by low cerebrospinal fluid (CSF) concentration of the 42 amino acid form of ß-amyloid (Aß42), is associated with biomarker evidence of other pathological changes in cognitively healthy elderly. A total of 129 patients were included and CSF levels of Aß42, total tau, tau phosphorylated at threonine 181 (p-tau), neurogranin, VILIP-1, VEGF, FABP3, Aß40, neurofilament light, MBP, orexin A, BDNF and YKL-40 were measured. Among these healthy elderly, 35.6% (N=46) had CSF Aß42 levels below 530 pg ml-1. These individuals displayed significantly higher CSF concentrations of t-tau (P<0.001), p-tau (181) (P<0.001), neurogranin (P=0.009) and FABP3 (P=0.044) compared with amyloid-negative individuals. Our study indicates that there is a subpopulation among healthy older individuals who have amyloid pathology along with signs of ongoing neuronal and synaptic degeneration, as well as tangle pathology. Previous studies have demonstrated that increase in CSF tau and p-tau is a specific sign of AD progression that occurs downstream of the deposition of Aß. On the basis of this, our data suggest that these subjects are at risk for developing AD. We also confirm the association between APOE ɛ4 and amyloid pathology in healthy older individuals.