Brain-specific proteins in cerebrospinal fluid for the diagnosis of neurodegenerative diseases

Problems associated with biological markers of Alzheimer's disease

The etiopathogenesis of Alzheimer's disease (AD) is still unclear, although clinical diagnostic criteria exist and the neuropathology of AD has been studied in great detail during the last 20 years. The present study addresses certain problems in the search for biological markers for the diagnosis, as well as in the follow-up of the course of AD and its differential diagnosis and reports some of our own observations in comparison with other studies. These include protein, genetic and neuroimaging markers. The definitions of biological markers and search strategies are also discussed.

Effects of hemolysis and storage condition on neuron-specific enolase (NSE) in cerebrospinal fluid and serum: implications in clinical practice

The concentration of neuron-specific enolase (NSE) in serum and cerebrospinal fluid (CSF) has been used as a biomarker in some cancers and, more recently, in neurodegenerative diseases. Pre-analytical conditions are very important for the quality of returned results. In this study, we evaluated the effects of storage conditions (temperature and duration of storage) and hemolysis on the concentration of NSE in serum and CSF. Our results demonstrate that samples for NSE measurement may be stored at -80 degrees C for no more than 6 months in the case of CSF and 9 months in the case of serum samples. Even invisible hemolysis may increase NSE levels in samples. Consequently, an index of hemolysis should be determined before deciding whether or not to perform NSE measurement.

Neuropsychological and behavioural correlates of CSF biomarkers in dementia

To improve clinical, neuropsychological and behavioural characterisation of the cerebrospinal fluid (CSF) biomarkers beta-amyloid((1-42)) protein (Abeta42), protein tau (tau) and tau phosphorylated at threonine 181 (P-tau181) across diagnostic dementia categories, a prospective study was set up. Patients with probable Alzheimer's disease (AD) (n=201), AD with cerebrovascular disease (CVD) (AD+CVD) (n=33), frontotemporal dementia (FTD) (n=27), dementia with Lewy bodies (DLB) (n=22) and healthy controls (n=148) were included. All patients underwent neuropsychological examination and behavioural assessment by means of a battery of behavioural assessment scales. CSF was obtained by lumbar puncture and levels of Abeta42, tau and P-tau181 were determined with commercially available ELISA kits. Negative correlations between CSF Abeta42 levels and aggressiveness (Spearman: r=-0.223; p=0.002) and positive correlations with age at inclusion (r=0.195; p=0.006), age at onset (r=0.205; p=0.003) and MMSE scores (r=0.198; p=0.005) were found in AD. In AD+CVD, CSF Abeta42 levels were correlated with MMSE (r=0.482; p=0.006), Hierarchic Dementia Scale (r=0.503; p=0.017) and Boston Naming Test (r=0.516; p=0.012) scores. In controls, age was positively correlated with CSF tau (r=0.465; p<0.001) and P-tau181 levels (r=0.312; p<0.001). CSF tau and P-tau181 levels correlated significantly in all groups, whereas CSF Abeta42 correlated with tau and P-tau181 levels in healthy controls only. Negative correlations between CSF Abeta42 levels and aggressiveness were found in AD patients. CSF Abeta42 seems to be a stage marker for AD (+/-CVD) given the positive correlations with neuropsychological test results suggesting that CSF Abeta42 might be of help for monitoring disease progression. Different correlations between age and CSF biomarker levels were obtained in healthy controls compared to AD patients, indicating that AD-induced pathophysiological processes change age-dependent regulation of CSF biomarker levels.

Identification of nitrated proteins in Alzheimer's disease brain using a redox proteomics approach

Nitric oxide (NO) has been implicated in the pathophysiology of a number of neurodegenerative diseases including Alzheimer's disease (AD). In the present study, using a proteomics approach, we identified enolase, glyceraldehyde-3-phosphate dehydrogenase, ATP synthase alpha chain, carbonic anhydrase-II, and voltage-dependent anion channel-protein as the targets of nitration in AD hippocampus, a region that shows a extensive deposition of amyloid beta-peptide, compared with the age-matched control brains. Immunoprecipitation and Western blotting techniques were used to validate the correct identification of these proteins. Our results are discussed in context of the role of oxidative stress as one of the important mechanisms of neurodegeneration in AD.

Follow-up investigations of tau protein and S-100B levels in cerebrospinal fluid of patients with Creutzfeldt-Jakob disease

BACKGROUND

S-100B and tau protein have a high differential diagnostic potential for the diagnosis of Creutzfeldt-Jakob disease (CJD). So far there has been only limited information available about the dynamics of these parameters in the cerebrospinal fluid (CSF). However, there is a special interest in finding biochemical markers to monitor disease progression for differential diagnosis and treatment.

PATIENTS AND METHODS

We analyzed CSF of 45 patients with CJD and of 45 patients with other neurological diseases for tau protein and S-100B in a follow-up setting. All diagnoses of CJD were later neuropathologically verified. A ratio between tau protein differences and the time between lumbar puncture was calculated. The same was done for S-100B.

RESULTS

Tau protein levels of 34 cases were above the cut-off level for CJD (>1,300 pg/ml) in the first CSF sample. In 7 of 11 patients with lower tau levels in the first CSF sample, tau levels rose. The above-mentioned ratio was significantly higher in the CJD group than in the group with other neurological diseases. Similar results were obtained for S-100B.

CONCLUSION

We conclude that follow-up investigations and calculation of ratios is a useful tool in the differential diagnosis of CJD. Variations in this pattern were observed in single cases.

Biomarkers: potential uses and limitations

Biomarkers provide a dynamic and powerful approach to understanding the spectrum of neurological disease with applications in observational and analytic epidemiology, randomized clinical trials, screening and diagnosis and prognosis. Defined as alterations in the constituents of tissues or body fluids, these markers offer the means for homogeneous classification of a disease and risk factors, and the can extend our base information about the underlying pathogenesis of disease. Biomarkers can also reflect the entire spectrum of disease from the earliest manifestations to the terminal stages. This brief review describes the major uses of biomarkers in clinical investigation. Careful assessment of the validity of biomarkers is required with respect to the stage of disease. Causes of variability in the measurement of biomarkers range from the individual to the laboratory. Issues that affect the analysis of biomarkers are discussed along with recommendations on how to deal with bias and confounding.

Rapid analysis of fatty acid-binding proteins with immunosensors and immunotests for early monitoring of tissue injury

Fatty acid-binding protein (FABP) holds promise for early detection of tissue injury. This small protein (15kD) appears earlier in the blood than large proteins after cell damage. Combined its characteristics of high concentration tissue contents and low normal plasma values provide the possibility of a rapid rise above the respective reference values, and thus an early indication of the appearance of tissue injury. A general review was presented on the current status of different types of FABP for the detection of tissue injury in patients with myocardial injury, brain injury and also in athletes or horses with skeletal muscle injury. To take full advantage of the characteristics of the early marker FABP, rapid analysis is a crucial parameter. In this review, an overview of the development of immunoassay for the quantification of FABP in buffer, plasma or whole blood was outlined. The characteristics of different FABP immunosensors and immunotests were described. The feasibility of these immunoassays to be used in routine clinical practice and in emergency case was also discussed. Nowadays, the improved automated immunoassays (e.g. a microparticle-enhanced turbidimetric immunoassay), less time-consuming bedside immunosensors and immunotests (e.g. a one-step FABP lateral flow immunotest), are the main advance technology in point-of-care testing. With these point-of-care tests, the application of FABP as an early tissue injury marker has a great potential for many clinical purposes.

Quantitative proteomic analysis of age-related changes in human cerebrospinal fluid

Identification of cerebrospinal fluid (CSF) biomarkers of the common age-related neurodegenerative diseases would be of great value to clinicians because of the difficulties in differential diagnoses of these diseases in clinical practice. Proteins are one class of potential biomarkers currently under investigation in the hope that different ensembles of proteins will aid in the diagnosis of these diseases, as well as in the assessment of progression and response to therapy. However, before undertaking a rational approach to CSF protein biomarkers of age-related neurodegeneration, we must first systematically identify CSF proteins and determine whether their levels change with normal aging. In this study, we used a powerful shotgun proteomic method, two-dimensional microcapillary liquid chromatography electrospray ionization tandem mass spectrometry, to identify proteins in human CSF. Additionally, using pooled CSF samples, we quantitatively compared the CSF proteome of younger adults with that of older adults using isotope-coded affinity tags (ICAT). From these studies we identified more than 300 proteins in CSF and found that there were 30 proteins with >20% change in concentrations between older and younger individuals. Finally, we validated changes in concentration for two of these proteins using Western blots in CSF from a separate set of individuals. These data not only expand substantially our current knowledge regarding human CSF proteins, but also supply the necessary information to appropriately interpret protein biomarkers of age-related neurodegenerative diseases.

Cerebrospinal fluid analysis differentiates multiple system atrophy from Parkinson's disease

We investigated whether cerebrospinal fluid (CSF) analysis discriminates between idiopathic Parkinson's disease (PD; n = 35) and multiple system atrophy (MSA; n = 30). The median CSF concentration of the neurotransmitter metabolites 5-hydroxyindolacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) was reduced significantly (49-70%) in MSA compared to PD. In contrast, several brain-specific proteins (tau, neuron-specific enolase, myelin basic protein) were elevated (130-230%) in MSA compared with those in PD. A combination of CSF tau and MHPG discriminated PD from MSA (adjusted odds ratios: tau, 27.2; MHPG, 0.14). Our data suggest that the more progressive and widespread neurodegenerative nature of MSA, as compared with PD, is reflected in the composition of CSF. We propose that CSF analysis may become part of the diagnostic work-up of patients with parkinsonian syndromes.

Brain- and Heart-Type Fatty Acid-Binding Proteins in the Brain: Tissue Distribution and Clinical Utility

Background: Detection of brain injury by serum markers is not a standard procedure in clinical practice, although several proteins, such as S100B, neuron-specific enolase (NSE), myelin basic protein, and glial fibrillary acidic protein, show promising results. We investigated the tissue distribution of brain- and heart-type fatty acid-binding proteins (B-FABP and H-FABP) in segments of the human brain and the potential of either protein to serve as plasma marker for diagnosis of brain injury.

Methods: B-FABP and H-FABP were measured immunochemically in autopsy samples of the brain (n = 6) and in serum samples from (a) patients with mild traumatic brain injury (MTBI; n = 130) and (b) depressed patients undergoing bilateral electroconvulsive therapy (ECT; n = 14). The protein markers S100B and NSE were measured for comparison. Reference values of B-FABP and H-FABP were established in healthy individuals (n = 92).

Results: The frontal, temporal, and occipital lobes, the striatum, the pons, and the cerebellum had different tissue concentrations of B-FABP and of H-FABP. B-FABP ranged from 0.8 μg/g wet weight in striatum tissue to 3.1 μg/g in frontal lobe. H-FABP was markedly higher, ranging from 16.2 μg/g wet weight in cerebellum tissue to 39.5 μg/g in pons. No B-FABP was detected in serum from healthy donors. H-FABP serum reference value was 6 μg/L. In the MTBI study, serum B-FABP was increased in 68% and H-FABP in 70% of patients compared with S100B (increased in 45%) and NSE (increased in 51% of patients). In ECT, serum B-FABP was increased in 6% of all samples (2 of 14 patients), whereas H-FABP was above its upper reference limit (6 μg/L) in 17% of all samples (8 of 14 patients), and S100B was above its upper reference limit (0.3 μg/L) in 0.4% of all samples.

Conclusions: B-FABP and H-FABP patterns differ among brain tissues, with the highest concentrations in the frontal lobe and pons, respectively. However, in each part of the brain, the H-FABP concentration was at least 10 times higher than that of B-FABP. Patient studies indicate that B-FABP and H-FABP are more sensitive markers for minor brain injury than the currently used markers S100B and NSE.

Interrupting apoptosis in neurodegenerative disease: potential for effective therapy?

Current treatment options for neurodegenerative diseases are limited and mainly affect only the symptoms of disease. Because of the unknown and probably multiple causes of these diseases, they cannot be readily targeted. However, it has been established that apoptosis contributes to neuronal loss in most neurodegenerative diseases. A possible treatment option is to interrupt the signaling networks that link neuronal damage to apoptotic degradation in neurodegeneration. The viability of this option depends upon the extent to which apoptosis accounts for neuron loss, whether or not interruption of apoptosis signaling results in recovery of neurological function and whether or not there are significant downsides to targeting apoptosis. Several compounds acting at different sites in known apoptotic signaling networks are currently in development and a few are in clinical trial. If an apoptosis-targeted compound succeeds in slowing or halting neurological dysfunction in one or more neurodegenerative diseases, a new era in the treatment of neurodegenerative diseases will begin.

Proteomic Analysis of Human Ventricular Cerebrospinal Fluid from Neurologically Normal, Elderly Subjects Using Two-Dimensional LC−MS/MS

A two-dimensional liquid chromatography separation scheme coupled to tandem mass spectrometry (2-D LC-MS/MS) was utilized to profile the proteome of human CSF. Ventricular CSF samples acquired post-mortem from 10 cognitively normal elderly subjects (mean +/- SEM Braak stage = 1.7 +/- 0.2) were analyzed to determine their protein composition. Raw CSF samples were subjected to an immunobased processing method to remove highly abundant albumin and immunoglobulin (Ig), allowing better detection of lower-abundance proteins. Samples were subjected to trypsin proteolysis followed by C18 solid-phase extraction. Tryptic CSF peptides were separated using a 2-D LC column, in which both strong cation exchange (SCX) and C18 phases were packed into a single capillary. MS/MS spectra of CSF peptides were searched against a human sub-database of the NBCI nonredundant database using the SEQUEST algorithm. Search results were further filtered using DTAselect, and individual samples were compared to one another using Contrast. Using this method, we were able to unambiguously identify 249 CSF proteins from 10 subjects. Of these proteins, 38% were unique to individual subjects, whereas only 6% were common to all 10 subjects. These results suggest considerable subject-to-subject variability in the CSF proteome.