Comparing the Clinical Utility and Diagnostic Performance of CSF P-Tau181, P-Tau217, and P-Tau231 Assays.

BACKGROUND AND OBJECTIVES: Phosphorylated tau (p-tau) in CSF is considered an important biomarker in Alzheimer disease (AD) and has been incorporated in recent diagnostic criteria. Several variants exist, including p-tau at threonines 181 (p-tau181), 217 (p-tau217), and 231 (p-tau231). However, no studies have compared their diagnostic performance or association to ß-amyloid (Aß) and tau-PET. Understanding which p-tau variant to use remains an important yet answered question. We aimed to compare the diagnostic accuracy of p-tau181, p-tau217, and p-tau231 in CSF for AD and their association with Aß and tau-PET. METHODS: A total of 629 participants in the Swedish BioFINDER-2 study were included (cognitively unimpaired, n = 334; Aß-positive mild cognitive impairment, n = 84; AD dementia, n = 119; and non-AD disorders, n = 92). In addition to p-tau181 and p-tau217 measured using assays with the same detector antibodies from Eli Lilly (p-tau181Lilly, p-tau217Lilly) and p-tau231, we also included p-tau181 measurements from 2 commonly used assays (Innotest and Elecsys). RESULTS: Although all p-tau variants increased across the AD continuum, p-tau217Lilly showed the greatest dynamic range (13-fold increase vs 1.9-5.4-fold increase for other p-tau variants for AD dementia vs non-AD). P-Tau217Lilly showed stronger correlations with Aß- and tau-PET (p < 0.0001). P-Tau217Lilly exhibited higher accuracy than other p-tau variants for separating AD dementia from non-AD (area under the curve [AUC], 0.98 vs 0.88 [p < 0.0001] - 0.96 [p < 0.05]) and for identifying Aß-PET (AUC, 0.86 vs 0.74 [p < 0.0001] and 0.83 [p < 0.001]) and tau-PET positivity (AUC, 0.94 vs 0.80-0.92, p < 0.0001). Finally, p-Tau181Lilly generally performed better than the other p-tau181 assays (e.g., AD dementia vs non-AD, AUC, 0.96 vs 0.88 [p-tau181Innotest] and 0.89 [p-tau181Elecsys]; p < 0.0001). DISCUSSION: CSF p-tau217Lilly seems to be more useful than other included p-tau assays in the workup of AD. Varied results across p-tau181 assays highlights the importance of anti-tau antibodies for biomarker performance. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that p-tau217 provides higher diagnostic accuracy for diagnosis of AD dementia than p-tau181 or p-tau231.

TREM2 ectodomain and its soluble form in Alzheimer's disease.

Triggering receptor expressed on myeloid cells 2 (TREM2) is a receptor mainly expressed on the surface of microglia. It mediates multiple pathophysiological processes in various diseases. Recently, TREM2 has been found to play a role in the development of Alzheimer's disease (AD). TREM2 is a transmembrane protein that is specifically expressed on microglia in the brain. It contains a long ectodomain that directly interacts with the extracellular environment to regulate microglial function. The ectodomain of TREM2 is processed by a disintegrin and metalloprotease, resulting in the release of a soluble form of TREM2 (sTREM2). Recent studies have demonstrated that sTREM2 is a bioactive molecule capable of binding ligands, activating microglia, and regulating immune responses during the AD continuum. Clinical studies revealed that sTREM2 level is elevated in cerebrospinal fluid (CSF) of AD patients, and the sTREM2 level is positively correlated with the levels of classical CSF biomarkers, namely t-tau and p-tau, indicating that it is a reliable predictor of the early stages of AD. Herein, we summarize the key results on the generation, structure, and function of sTREM2 to provide new insights into TREM2-related mechanisms underlying AD pathogenesis and to promote the development of TREM2-based therapeutic strategy.

Quantification of total apolipoprotein E and its isoforms in cerebrospinal fluid from patients with neurodegenerative diseases.

BACKGROUND: The human APOE gene, which codes for apolipoprotein E (apoE), has three major polymorphic alleles: ε2, ε3, and ε4 that give rise to amino acid substitutions. APOE-ε4 is a strong risk factor of sporadic Alzheimer's disease (AD) but the reason why is still unknown despite intense research for more than 20 years. The aim of the study was to investigate if the concentrations of total apoE and the specific apoE isoforms in cerebrospinal fluid (CSF) differ between various neurodegenerative diseases and control individuals, as well as among the APOE genotypes. METHODS: Quantification of total apoE and specific apoE isoforms (E2, E3, and E4) in CSF was performed using high-resolution parallel reaction monitoring mass spectrometry. In total, 1820 individuals were involved in the study including clinically diagnosed AD patients (n = 228), cognitively unimpaired (CU) patients (n = 896), and patients with other neurodegenerative disorders (n = 696). Follow-up data was available for 100 individuals, assessed at two time points. Subjects were dichotomized based on an Aß42/40 CSF concentration ratio cut-off into Aß positive (Aß+, < 0.091) and Aß negative (Aß-, > 0.091) groups. RESULTS: Even though there was a significant increase of total apoE in the amyloid ß-positive (Aß+) group compared with amyloid ß-negative (Aß-) individuals (p < 0.001), the magnitude of the effect was very small (AUC = 0.55). Moreover, CSF total apoE concentrations did not differ between Aß- CU controls and clinically diagnosed AD patients. There was a difference in concentration between isoforms in heterozygous individuals in an isoform-dependent manner (E2 < E3 < E4) (p < 0.001, AUC = 0.64-0.69), and these associations remained when dichotomizing the samples into Aß+ and Aß- groups (p < 0.01, AUC = 0.63-0.74). In the cohort with follow-up samples, neither total apoE nor isoform-specific apoE concentrations differed between the two time points (p > 0.05). CONCLUSIONS: The results indicate that neither the concentrations of total apoE nor the different apoE isoforms in CSF are associated with APOE-ε4 carrier status, Aß status, or clinical dementia diagnoses.

4-Repeat tau seeds and templating subtypes as brain and CSF biomarkers of frontotemporal lobar degeneration.

To address the need for more meaningful biomarkers of tauopathies, we have developed an ultrasensitive tau seed amplification assay (4R RT-QuIC) for the 4-repeat (4R) tau aggregates of progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and other diseases with 4R tauopathy. The assay detected seeds in 106-109-fold dilutions of 4R tauopathy brain tissue but was orders of magnitude less responsive to brain with other types of tauopathy, such as from Alzheimer's disease cases. The analytical sensitivity for synthetic 4R tau fibrils was ~ 50 fM or 2 fg/sample. A novel dimension of this tau RT-QuIC testing was the identification of three disease-associated classes of 4R tau seeds; these classes were revealed by conformational variations in the in vitro amplified tau fibrils as detected by thioflavin T fluorescence amplitudes and FTIR spectroscopy. Tau seeds were detected in postmortem cerebrospinal fluid (CSF) from all neuropathologically confirmed PSP and CBD cases but not in controls. CSF from living subjects had weaker seeding activities; however, mean assay responses for cases clinically diagnosed as PSP and CBD/corticobasal syndrome were significantly higher than those from control cases. Altogether, 4R RT-QuIC provides a practical cell-free method of detecting and subtyping pathologic 4R tau aggregates as biomarkers.

Characterization of Cerebrospinal Fluid BACE1 Species.

The ß-site amyloid precursor protein cleaving enzyme 1 (BACE1) is the main brain ß-secretase responsible for the amyloidogenic processing of the amyloid precursor protein (APP). Previous studies have suggested that cerebrospinal fluid (CSF) ß-secretase activity may be a candidate diagnostic biomarker for Alzheimer's disease (AD), but biochemical characterization of BACE1 protein in CSF is needed. CSF samples from 19 AD patients and 19 age-matched non-AD controls (n = 19) were classified according to their Aß42, total tau, and P-tau CSF biomarker levels. We found that ß-secretase activity was higher in the CSF of AD subjects than in that of the controls. We found that the majority of the ß-secretase activity in the CSF, measured using a peptide substrate homologous to the BACE1 cleavage site, was not inhibited by specific BACE1 inhibitors. We defined enzymatic activity attributable specifically to BACE1 as the activity that was blocked by the specific inhibitors, which is still higher in AD subjects. BACE1 protein levels were characterized by lectin binding, immunoprecipitation, blue native-PAGE, and western blotting using antibodies against specific protein domains. BACE1 was found to be present in human CSF as a mature form of ~ 70 kDa that probably comprised truncated and full-length species, and also as an immature form of ~ 50 kDa that retains the prodomain. CSF-BACE1 was found to assemble into hetero-complexes containing distinct species. Immunoblotting with an antibody against the C-terminus of BACE1 revealed significantly higher levels of the 70-kDa full-length BACE1, while the 50 kDa immature form remained unaltered. When the 70-kDa species was probed with an antibody against the N-terminus of BACE1 (which does not discriminate between truncated and full-length forms), no increase in immunoreactivity was observed, suggesting that truncated forms of BACE1 do not increase in AD. In conclusion, the complexity of BACE1 species in CSF has to be taken into consideration when determining BACE1 activity and protein levels in CSF as biomarkers of AD.

Diagnosis of Alzheimer's disease utilizing amyloid and tau as fluid biomarkers.

Current technological advancements in clinical and research settings have permitted a more intensive and comprehensive understanding of Alzheimer's disease (AD). This development in knowledge regarding AD pathogenesis has been implemented to produce disease-modifying drugs. The potential for accessible and effective therapeutic methods has generated a need for detecting this neurodegenerative disorder during early stages of progression because such remedial effects are more profound when implemented during the initial, prolonged prodromal stages of pathogenesis. The aggregation of amyloid-ß (Aß) and tau isoforms are characteristic of AD; thus, they are considered core candidate biomarkers. However, research attempting to establish the reliability of Aß and tau as biomarkers has culminated in an amalgamation of contradictory results and theories regarding the biomarker concentrations necessary for an accurate diagnosis. In this review, we consider the capabilities and limitations of fluid biomarkers collected from cerebrospinal fluid, blood, and oral, ocular, and olfactory secretions as diagnostic tools for AD, along with the impact of the integration of these biomarkers in clinical settings. Furthermore, the evolution of diagnostic criteria and novel research findings are discussed. This review is a summary and reflection of the ongoing concerted efforts to establish fluid biomarkers as a diagnostic tool and implement them in diagnostic procedures.

Transferrin isoforms in cerebrospinal fluid and their relation to neurological diseases.

Iron plays many important roles in the brain, including involvement in myelination, neurotransmission and electron transfer in the respiratory chain. Transferrin (Tf), an iron transporter, is mainly biosynthesized in the liver, but can also be biosynthesized in the brain; i.e., by oligodendrocytes and the choroid plexus, a cerebrospinal fluid (CSF) producing tissue. The CSF contains two Tf isoforms, brain-type Tf and serum-type Tf, which differ in their glycan structures. Brain-type Tf is uniquely glycolsylated with biantennary asialo- and agalacto-complex type N-glycans that carry bisecting ß1,4-GlcNAc and core α1,6-Fuc. The glycans of serum-type Tf in the CSF are similar to those of Tf in serum. Biochemical analyses reveal that the apparent molecular size of brain-type Tf is smaller than that of serum-type Tf, and that hydrophobic patches are exposed on brain-type Tf as demonstrated by hydrophobic probe binding studies. We found that brain-type Tf levels were decreased in idiopathic normal pressure hydrocephalus, in which CSF production is suspected to decrease, while brain-type Tf increased in spontaneous intracranial hypotension, in which CSF production is suspected to increase. These results suggest that brain-type Tf could be a biomarker of altered CSF production.

Do fragments and glycosylated isoforms of alpha-1-antitrypsin in CSF mirror spinal pathophysiological mechanisms in chronic peripheral neuropathic pain? An exploratory, discovery phase study.

BACKGROUND: Post-translational modifications (PTMs) generate a tremendous protein diversity from the ~ 20,000 protein-coding genes of the human genome. In chronic pain conditions, exposure to pathological processes in the central nervous system could lead to disease-specific PTMs detectable in the cerebrospinal fluid (CSF). In a previous hypothesis-generating study, we reported that seven out of 260 CSF proteins highly discriminated between neuropathic pain patients and healthy controls: one isoform of angiotensinogen (AG), two isoforms of alpha-1-antitrypsin (AT), three isoforms of haptoglobin (HG), and one isoform of pigment epithelium-derived factor (PEDF). The present study had three aims: (1) To examine the multivariate inter-correlations between all identified isoforms of these seven proteins; (2) Based on the results of the first aim, to characterize PTMs in a subset of interesting proteins; (3) To regress clinical pain data using the 260 proteins as predictors, thereby testing the hypothesis that the above-mentioned seven discriminating proteins and/or the characterized isoforms/fragments of aim (2) would be among the proteins having the highest predictive power for clinical pain data. METHODS: CSF samples from 11 neuropathic pain patients and 11 healthy controls were used for biochemical analysis of protein isoforms. PTM characterization was performed using enzymatic reaction assay and mass spectrometry. Multivariate data analysis (principal component analysis and orthogonal partial least square regression) was applied on the quantified protein isoforms. RESULTS: We identified 5 isoforms of AG, 18 isoforms of AT, 5 isoforms of HG, and 5 isoforms of PEDF. Fragments and glycosylated isoforms of AT were studied in depth. When regressing the pain intensity data of patients, three isoforms of AT, two isoforms of PEDF, and one isoform of angiotensinogen "reappeared" as major results, i.e., they were major findings both when comparing patients with healthy controls and when regressing pain intensity in patients. CONCLUSIONS: Altered levels of fragments and/or glycosylated isoforms of alpha-1-antitrypsin might mirror pathophysiological processes in the spinal cord of neuropathic pain patients. In particular, we suggest that a putative disease-specific combination of the levels of two different N-truncated fragments of alpha-1-antitrypsin might be interesting for future CSF and/or plasma biomarker investigations in chronic neuropathic pain.

Sulfatide isoform pattern in cerebrospinal fluid discriminates progressive MS from relapsing-remitting MS.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). Several biomarkers including proteins and lipids have been reported in MS cerebrospinal fluid (CSF), reflecting different aspects of the pathophysiology particularly of relapsing-remitting MS (RRMS). Sulfatide, abundant in the myelin sheath and a proposed target for autoimmune attack in MS, has been reported altered in MS CSF. Here, we investigated the potential of CSF sulfatide and its isoforms as biomarkers in MS. A highly sensitive and quantitative mass spectrometry method was employed to determine levels of sulfatide isoforms in CSF from RRMS and progressive MS (PMS) patients, and healthy donors (HD). We demonstrate that levels of total CSF sulfatide and C24:1, C26:1, and C26:1-OH isoforms were significantly increased in PMS compared with RRMS patients and HD, while C23:0-OH was significantly decreased in CSF from PMS patients compared to the other two groups. Multivariate discriminant analysis showed that CSF sulfatide isoform pattern in PMS patients was distinct and non-overlapping with that of RRMS patients and HD. Sulfatide levels did not correlate with tested biomarkers or clinical parameters. The results suggest that CSF sulfatide isoform levels may be used to discriminate the phenotype of MS and might play a role in the progression of the disease.

A unique glycan-isoform of transferrin in cerebrospinal fluid: A potential diagnostic marker for neurological diseases.

BACKGROUND: Cerebrospinal fluid (CSF) is sequestered from blood by the blood-brain barrier and directly communicates with brain parenchymal interstitial fluid, leading to contain specific biomarkers of neurological diseases. SCOPE OF REVIEW: CSF contains glycan isoforms of transferrin (Tf): one appears to be derived from the brain and the other from blood. MAJOR CONCLUSIONS: CSF contains two glycan-isoforms; brain-type Tf and serum-type Tf. Glycan analysis and immunohistochemistry suggest that serum-type Tf having α2, 6sialylated glycans is derived from blood whereas brain-type Tf having GlcNAc-terminated glycans is derived from the choroid plexus, CSF producing tissue. The ratio of serum-type/brain-type Tf differentiates Alzheimer's disease from idiopathic normal pressure hydrocephalus, which is an elderly dementia caused by abnormal metabolism of CSF. The ratios in Parkinson's disease (PD) patients were higher than those of controls and did not appear to be normally distributed. Indeed, detrended normal Quantile-Quantile plot analysis reveals the presence of an independent subgroup showing higher ratios in PD patients. The subgroup of PD shows higher levels of CSF α-synuclein than the rest, indicating that PD includes two subgroups, which differ in levels of brain-type Tf and α-synuclein. GENERAL SIGNIFICANCE: Glycosylation in central nervous system appears to be unique. The unique glycan may be a tag for glycoprotein, which is biosynthesized in the central nervous system. This article is part of a Special Issue entitled Neuro-glycoscience, edited by Kenji Kadomatsu and Hiroshi Kitagawa.

Ultrasensitive and selective detection of 3-repeat tau seeding activity in Pick disease brain and cerebrospinal fluid.

The diagnosis and treatment of diseases involving tau-based pathology such as Alzheimer disease and certain frontotemporal dementias is hampered by the inability to detect pathological forms of tau with sufficient sensitivity, specificity and practicality. In these neurodegenerative diseases, tau accumulates in self-seeding filaments. For example, Pick disease (PiD) is associated with frontotemporal degeneration and accumulation of 3-repeat (3R) tau isoforms in filaments constituting Pick bodies. Exploiting the self-seeding activity of tau deposits, and using a 3R tau fragment as a substrate, we have developed an assay (tau RT-QuIC) that can detect tau seeds in 2 µl aliquots of PiD brain dilutions down to 10-7-10-9. PiD seeding activities were 100-fold higher in frontal and temporal lobes compared to cerebellar cortex. Strikingly, this test was 103- to 105-fold less responsive when seeded with brain containing predominant 4-repeat (4R) tau aggregates from cases of corticobasal degeneration, argyrophilic grain disease, and progressive supranuclear palsy. Alzheimer disease brain, with 3R + 4R tau deposits, also gave much weaker responses than PiD brain. When applied to cerebrospinal fluid samples (5 µl), tau RT-QuIC analyses discriminated PiD from non-PiD cases. These findings demonstrate that abnormal tau aggregates can be detected with high sensitivity and disease-specificity in crude tissue and fluid samples. Accordingly, this tau RT-QuIC assay exemplifies a new approach to diagnosing tauopathies and monitoring therapeutic trials using aggregated tau itself as a biomarker.

Quantitation of Human Metallothionein Isoforms in Cells, Tissues, and Cerebrospinal Fluid by Mass Spectrometry.

Metallothioneins (MTs) are a family of small, highly conserved, cysteine-rich metal-binding proteins that are important for zinc and copper homeostasis, protection against oxidative stress, and buffering against toxic heavy metals. Individual human MT isoforms are candidate biomarkers for heavy metal toxicity, and selected cancers and neurodegenerative diseases. The similar antigenicity of human MT-1 and MT-2 isoforms precludes development of antibody-based assays for their individual quantitation. Metal-based MT quantitation methods do not directly measure MT isoforms. A bottom-up mass spectrometry-based approach solves these problems by exploiting the unique masses and chromatographic properties of the acetylated N-terminal tryptic peptides of MT isoforms. These unusually hydrophilic 20- to 21-residue peptides contain five invariant cysteines. Strong cation exchange chromatography separates them from bulk internal tryptic peptides. Reversed-phase chromatography further separates them from more hydrophobic peptides of similar mass. Absolute quantitation is obtained by adding MT peptide standards alkylated with 15N-iodoacetamide to biological samples alkylated with 14N-iodoacetamide. Accurate quantitation is enhanced by dimethyl sulfide treatment to reverse oxidation of the N-terminal methionine. Originally optimized for measuring MT isoforms in cell lines, the method has been adapted to quantify MT isoforms in brain tissue and cerebrospinal fluid. The method can also be adapted for relative quantitation of MT isoforms between matched biological samples. It cannot be used to measure human MT-4 because of an arginine at position 4. Except for this type of limitation, the method is applicable to MT quantitation in many other species.

Selecting Aß isoforms for an Alzheimer's disease cerebrospinal fluid biomarker panel.

Although the core cerebrospinal fluid Alzheimer's disease (AD) biomarkers amyloid-ß (Aß1-42) and tau show a high diagnostic accuracy, there are still limitations due to overlap in the biomarker levels with other neurodegenerative and dementia disorders. During Aß1-42 production and clearance in the brain, several other Aß peptides and amyloid precursor protein fragments are formed that could potentially serve as biomarkers for this ongoing disease process. Therefore, this review will present the current status of the findings for amyloid precursor protein and Aß peptide isoforms in AD and clinically related disorders. In conclusion, adding new Aß isoforms to the AD biomarker panel may improve early differential diagnostic accuracy and increase the cerebrospinal fluid biomarker concordance with AD neuropathological findings in the brain.

Optimized Standard Operating Procedures for the Analysis of Cerebrospinal Fluid Aß42 and the Ratios of Aß Isoforms Using Low Protein Binding Tubes.

BACKGROUND: Reduced cerebrospinal fluid (CSF) concentration of amyloid-ß1-42 (Aß1-42) reflects the presence of amyloidopathy in brains of subjects with Alzheimer's disease (AD). OBJECTIVE: To qualify the use of Aß1-42/Aß1-40 for improvement of standard operating procedures (SOP) for measurement of CSF Aß with a focus on CSF collection, storage, and analysis. METHODS: Euroimmun ELISAs for CSF Aß isoforms were used to set up a SOP with respect to recipient properties (low binding, polypropylene), volume of tubes, freeze/thaw cycles, addition of detergents (Triton X-100, Tween-20) in collection or storage tubes or during CSF analysis. Data were analyzed with linear repeated measures and mixed effects models. RESULTS: Optimization of CSF analysis included a pre-wash of recipients (e.g., tubes, 96-well plates) before sample analysis. Using the Aß1-42/Aß1-40 ratio, in contrast to Aß1-42, eliminated effects of tube type, additional freeze/thaw cycles, or effect of CSF volumes for polypropylene storage tubes. 'Low binding' tubes reduced the loss of Aß when aliquoting CSF or in function of additional freeze/thaw cycles. Addition of detergent in CSF collection tubes resulted in an almost complete absence of variation in function of collection procedures, but affected the concentration of Aß isoforms in the immunoassay. CONCLUSION: The ratio of Aß1-42/Aß1-40 is a more robust biomarker than Aß1-42 toward (pre-) analytical interfering factors. Further, 'low binding' recipients and addition of detergent in collection tubes are able to remove effects of SOP-related confounding factors. Integration of the Aß1-42/Aß1-40 ratio and 'low-binding tubes' into guidance criteria may speed up worldwide standardization of CSF biomarker analysis.

GDF15/MIC1 and MMP9 Cerebrospinal Fluid Levels in Parkinson's Disease and Lewy Body Dementia.

Based on animal and ex-vivo experiments, Growth/Differentiation Factor-15 (GDF15, also called Macrophage Inhibitory Cytokine-1, MIC1), a member of the transforming growth factor-beta family, and Matrix Metalloproteinase-9 (MMP9), a member of the matrix metalloprotease family may be potential markers for Lewy body disorders, i.e. Parkinson's disease with (PDD) and without dementia (PDND) and Lewy body dementia (DLB). GDF15 has a prominent role in development, cell proliferation, differentiation, and repair, whereas MMP9 degrades, as a proteolytic enzyme, components of the extracellular matrix. In this study, cerebrospinal fluid GDF15 and MMP9 levels of 59 PDND, 17 PDD and 23 DLB patients, as well as of 95 controls were determined, and associated with demographic, clinical and biochemical parameters. Our analysis confirmed the already described association of GDF15 levels with age and gender. Corrected GDF15 levels were significantly higher in PDD than in PDND patients, and intermediate in DLB patients. Within Lewy body disorders, GDF15 levels correlated positively with age at onset of Parkinsonism and dementia, Hoehn & Yahr stage and cerebrospinal fluid t-Tau and p-Tau levels, and negatively with the Mini Mental State Examination. Remarkably, it does not relevantly correlate with disease duration. MMP9 was not relevantly associated with any of these parameters. Cerebrospinal GDF15, but not MMP9, may be a potential marker of and in Lewy body disorders.

Subgroup differences in 'brain-type' transferrin and α-synuclein in Parkinson's disease and multiple system atrophy.

Two transferrin (Tf) glycan-isoforms were previously found in cerebrospinal fluid (CSF); one appears to be derived from serum (Tf-2) and the other from choroid plexus, a CSF-producing tissue (Tf-1). To analyse metabolic differences associated with the two isoforms, their ratio (Tf-2/Tf-1) was defined as the Tf index. Here we report that Tf indices of patients with tauopathies including Alzheimer's disease (2.29 + 0.64) were similar to those of neurological controls (2.07 + 0.87) (P = 0.147). In contrast, Tf indices with Parkinson's disease (PD, 3.38 ± 1.87) and multiple system atrophy (MSA, 3.15 ± 1.72) were higher than those of the controls (2.07 ± 0.87), the P-values being < 0.001 and 0.024, respectively. Tf indices of PD and MSA did not appear to be normally distributed. Indeed, detrended normal Quantile-Quantile plot analysis revealed the presence of an independent subgroup showing higher Tf indices in PD and MSA. The subgroup of PD showed higher levels of CSF α-synuclein (38.3 ± 17.8 ng/ml) than the rest (25.3 ± 11.3 ng/ml, P = 0.012). These results suggest that PD (and MSA) includes two subgroups, which show different metabolism of CSF transferrin and α-synuclein.

Cerebral white matter lesions - associations with Aß isoforms and amyloid PET.

Small vessel disease (SVD) and amyloid deposition may promote each other, with a potential association between SVD and altered production or clearance of ß-amyloid (Aß) affecting its cleavage products. We investigated the relationship between SVD, multiple isoforms of Aß in cerebrospinal fluid (CSF) and cortical Aß in 831 subjects with cognitive performance ranging from normal to Alzheimer's disease (AD) (the Swedish BioFINDER study). SVD was estimated as white matter lesions (WML) and lacunes. 18F-flutemetamol PET was performed in 321 subjects. Lower CSF levels of Aß38 and Aß40 were consistently associated with increased WML in all subgroups, while lower levels of CSF Aß42 were associated with WML mainly in AD. CSF Aß38 and Aß40 were associated with regional WML in all regions, while CSF Aß42 was associated with temporal WML only. A composite measure of 18F-flutemetamol uptake was not associated with WML, and regional 18F-flutemetamol uptake only with temporal WML. Lacunes were not associated with Aß isoforms nor 18F-flutemetamol uptake. Our results suggest that WML may be associated with alterations in the production or clearance of Aß species, particularly of Aß38 and Aß40. However, in AD cases, Aß42 pathology might be associated with WML, especially in the temporal lobe.

The Levels of Tau Isoforms Containing Exon-2 and Exon-10 Segments Increased in the Cerebrospinal Fluids of the Patients with Sporadic Creutzfeldt-Jakob Disease.

The alteration of protein tau in the cerebrospinal fluid (CSF) of Creutzfeldt-Jakob disease (CJD) has been widely evaluated, possessing a significant diagnostic value for CJD. With the biotin-labeled tau-exon-specific mAbs, direct ELISA methods were established and the levels of tau isoforms containing exon-2 and exon-10 segments in CSF of the patients with various human prion diseases and in brain tissues of scrapie-infected animals were evaluated. The results showed that the levels of tau, especially containing four repeats in microtubule binding domain, were increased in the CSF samples of the patients with sporadic CJD (sCJD). Using the unlabeled (cold) mixed exon-specific mAbs, a competitive tau ELISA was conducted based on a commercial tau kit. It revealed that the majority of the increased tau in the CSF of sCJD cases was derived from the tau isoforms with exon-2 and exon-10 segments. Increases of CSF tau isoforms with exon-2 and exon-10 segments were also observed in the patients of E200K and T188K genetic CJD (gCJD), but not in the cases of fatal familiar insomnia (FFI). The increasing levels of tau isoforms with exon-2 and exon-10 segments in the group of sCJD correlated well with the positive 14-3-3 in CSF. Additionally, the similar alterative profiles of tau isoforms with exon-2 and exon-10 segments were also observed in the brain tissues of scrapie-infected rodents and a sCJD patient. Our data here propose the tau isoforms with exon-2 and exon-10 segments increase in CSF of sCJD and some types of gCJD, which may help to understand the physiological metabolism and pathological significance of various tau isoforms in the pathogenesis of prion diseases.

Vitamin D Binding Protein Isoforms and Apolipoprotein E in Cerebrospinal Fluid as Prognostic Biomarkers of Multiple Sclerosis.

BACKGROUND: Multiple sclerosis (MS) is a multifactorial autoimmune disease of the central nervous system with a heterogeneous and unpredictable course. To date there are no prognostic biomarkers even if they would be extremely useful for early patient intervention with personalized therapies. In this context, the analysis of inter-individual differences in cerebrospinal fluid (CSF) proteome may lead to the discovery of biological markers that are able to distinguish the various clinical forms at diagnosis. METHODS: To this aim, a two dimensional electrophoresis (2-DE) study was carried out on individual CSF samples from 24 untreated women who underwent lumbar puncture (LP) for suspected MS. The patients were clinically monitored for 5 years and then classified according to the degree of disease aggressiveness and the disease-modifying therapies prescribed during follow up. RESULTS: The hierarchical cluster analysis of 2-DE dataset revealed three protein spots which were identified by means of mass spectrometry as Apolipoprotein E (ApoE) and two isoforms of vitamin D binding protein (DBP). These three protein spots enabled us to subdivide the patients into subgroups correlated with clinical classification (MS aggressive forms identification: 80%). In particular, we observed an opposite trend of values for the two protein spots corresponding to different DBP isoforms suggesting a role of a post-translational modification rather than the total protein content in patient categorization. CONCLUSIONS: These findings proved to be very interesting and innovative and may be developed as new candidate prognostic biomarkers of MS aggressiveness, if confirmed.

Diagnostic Accuracy of Cerebrospinal Fluid Amyloid-ß Isoforms for Early and Differential Dementia Diagnosis.

BACKGROUND: Overlapping cerebrospinal fluid biomarkers (CSF) levels between Alzheimer's disease (AD) and non-AD patients decrease differential diagnostic accuracy of the AD core CSF biomarkers. Amyloid-ß (Aß) isoforms might improve the AD versus non-AD differential diagnosis. OBJECTIVE: To determine the added diagnostic value of Aß isoforms, Aß(1-37), Aß(1-38), and Aß(1-40), as compared to the AD CSF biomarkers Aß(1-42), T-tau, and P-tau(181P). METHODS: CSF from patients with dementia due to AD (n = 50), non-AD dementias (n = 50), mild cognitive impairment due to AD (n = 50) and non-demented controls (n = 50) was analyzed with a prototype multiplex assay using MSD detection technology. The non-AD group consisted of frontotemporal dementia (FTD; n = 17), dementia with Lewy bodies (DLB; n = 17), and vascular dementia (n = 16). RESULTS: Aß(1-37) and Aß(1-38) increased accuracy to differentiate AD from FTD or DLB. Aß(1-37), Aß(1-38), and Aß(1-40) levels correlated with Mini-Mental State Examination scores and disease duration in dementia due to AD. The Aß(1-42)/Aß(1-40) ratio improved diagnostic performance of Aß(1-42) in most differential diagnostic situations. Aß(1-42) levels were lower in APOE ε4 carriers compared to non-carriers. CONCLUSIONS: Aß isoforms help to differentiate AD from FTD and DLB. Aß isoforms increase diagnostic performance of Aß(1-42). In contrast to Aß1-42, Aß isoforms seem to be correlated with disease severity in AD. Adding the Aß isoforms to the current biomarker panel could enhance diagnostic accuracy.