Comparison of Different Matrices as Potential Quality Control Samples for Neurochemical Dementia Diagnostics

BACKGROUND

Assay-vendor independent quality control (QC) samples for neurochemical dementia diagnostics (NDD) biomarkers are so far commercially unavailable. This requires that NDD laboratories prepare their own QC samples, for example by pooling leftover cerebrospinal fluid (CSF) samples.

OBJECTIVE

To prepare and test alternative matrices for QC samples that could facilitate intra- and inter-laboratory QC of the NDD biomarkers.

METHODS

Three matrices were validated in this study: (A) human pooled CSF, (B) Aβ peptides spiked into human prediluted plasma, and (C) Aβ peptides spiked into solution of bovine serum albumin in phosphate-buffered saline. All matrices were tested also after supplementation with an antibacterial agent (sodium azide). We analyzed short- and long-term stability of the biomarkers with ELISA and chemiluminescence (Fujirebio Europe, MSD, IBL International), and performed an inter-laboratory variability study.

RESULTS

NDD biomarkers turned out to be stable in almost all samples stored at the tested conditions for up to 14 days as well as in samples stored deep-frozen (at - 80°C) for up to one year. Sodium azide did not influence biomarker stability. Inter-center variability of the samples sent at room temperature (pooled CSF, freeze-dried CSF, and four artificial matrices) was comparable to the results obtained on deep-frozen samples in other large-scale projects.

CONCLUSION

Our results suggest that it is possible to replace self-made, CSF-based QC samples with large-scale volumes of QC materials prepared with artificial peptides and matrices. This would greatly facilitate intra- and inter-laboratory QC schedules for NDD measurements.

Simultaneous quantification of isoniazid, rifampicin, ethambutol and pyrazinamide by liquid chromatography/tandem mass spectrometry

A remediable cause of poor treatment response in drug-susceptible tuberculosis (TB) patients may be low plasma levels of one or more of the first-line anti-TB drugs. The aim of this work was to develop an accurate and precise LC-MS/MS method for simultaneous quantification of all four first-line anti-TB drugs in plasma suitable for therapeutic drug monitoring (TDM). To adjust for degradation and losses during sample preparation, isotopically labeled compounds were used as internal standards. Plasma samples spiked with internal standards were extracted using protein precipitation with methanol and acetonitrile. Simultaneous separation of all four drugs was accomplished with a Chromolith Reversed-Phase column and mobile phases consisting of water, methanol, ammonium acetate and formic acid with subsequent mass spectrometric quantification. The linear range of the calibration curve for isoniazid was 0.5-10 mg/L, for rifampicin 0.75-30 mg/L, for ethambutol 0.25-10 mg/L and for pyrazinamide 4-80 mg/L. The lower limit of quantification was 0.5 mg/L, 0.75 mg/L, 0.25 mg/L and 4.0 mg/L, respectively. Precision estimated by the coefficient of variation was <15% for all four drugs. The LC-MS/MS method can readily be used for simultaneous quantification of first-line anti-TB drugs in plasma and is well suited for TDM.

Use of amyloid-PET to determine cutpoints for CSF markers: A multicenter study

OBJECTIVES

To define CSF β-amyloid 1-42 (Aβ42) cutpoints to detect cortical amyloid deposition as assessed by 11C-Pittsburgh compound B ([11C]PiB)-PET and to compare these calculated cutpoints with cutpoints currently used in clinical practice.

METHODS

We included 433 participants (57 controls, 99 with mild cognitive impairment, 195 with Alzheimer disease [AD] dementia, and 82 with non-AD dementia) from 5 European centers. We calculated for each center and for the pooled cohort CSF Aβ42 and Aβ42/tau ratio cutpoints for cortical amyloid deposition based on visual interpretation of [11C]PiB-PET images.

RESULTS

Amyloid-PET-based calculated CSF Aβ42 cutpoints ranged from 521 to 616 pg/mL, whereas existing clinical-based cutpoints ranged from 400 to 550 pg/mL. Using the calculated cutpoint from the pooled sample (557 pg/mL), concordance between CSF Aβ42 and amyloid-PET was 84%. Similar concordance was found when using a dichotomized Aβ42/tau ratio. Exploratory analysis showed that participants with a positive amyloid-PET and normal CSF Aβ42 levels had higher CSF tau and phosphorylated tau levels and more often had mild cognitive impairment or AD dementia compared with participants who had negative amyloid-PET and abnormal CSF Aβ42 levels.

CONCLUSIONS

Amyloid-PET-based CSF Aβ42 cutpoints were higher and tended to reduce intercenter variability compared with clinical-based cutpoints. Discordant participants with normal CSF Aβ42 and a positive amyloid-PET may be more likely to have AD-related amyloid pathology than participants with abnormal CSF Aβ42 and a negative amyloid-PET.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that an amyloid-PET-based CSF Aβ42 cutpoint identifies individuals with amyloid deposition with a sensitivity of 87% and specificity of 80%.

Validation of a quantitative cerebrospinal fluid alpha-synuclein assay in a European-wide interlaboratory study

Decreased levels of alpha-synuclein (aSyn) in cerebrospinal fluid (CSF) in Parkinson's disease and related synucleinopathies have been reported, however, not consistently in all cross-sectional studies. To test the performance of one recently released human-specific enzyme-linked immunosorbent assay (ELISA) for the quantification of aSyn in CSF, we carried out a round robin trial with 18 participating laboratories trained in CSF ELISA analyses within the BIOMARKAPD project in the EU Joint Program - Neurodegenerative Disease Research. CSF samples (homogeneous aliquots from pools) and ELISA kits (one lot) were provided centrally and data reported back to one laboratory for data analysis. Our study showed that although factors such as preanalytical sample handling and lot-to-lot variability were minimized by our study design, we identified high variation in absolute values of CSF aSyn even when the same samples and same lots of assays were applied. We further demonstrate that although absolute concentrations differ between laboratories the quantitative results are comparable. With further standardization this assay may become an attractive tool for comparing aSyn measurements in diverse settings. Recommendations for further validation experiments and improvement of the interlaboratory results obtained are given.

Important options available--from start to finish--for translating proteomics results to clinical chemistry

In the realm of clinical chemistry, the field of clinical proteomics, that is, the application of proteomic methods for understanding mechanisms and enabling diagnosis, prediction, measurement of activity, and treatment response in disease, is first and foremost a discovery and research tool that feeds assay development downstream. Putative new assay candidates generated by proteomics discovery projects compete with well-established assays with known indications, well-described performance, and of known value in specific clinical settings. Careful attention to the many options available in the design, execution, and interpretation of clinical proteomics studies is thus necessary for translation into clinical practice. We here review and discuss important options associated with clinical proteomics endeavors stretching from the planning phases to the final use in clinical chemistry.

Pre-analytical factors influencing the stability of cerebrospinal fluid proteins

Cerebrospinal fluid (CSF) is a potential source for new biomarkers due to its proximity to the brain. This study aimed to clarify the stability of the CSF proteome when undergoing pre-analytical factors. We investigated the effects of repeated freeze/thaw cycles, protease inhibitors and delayed storage for 4h, 24h or 14 days at -20°C, 4°C and room temperature (RT) after centrifugation compared with our standard practice of two hours at RT before placing the samples in an -80°C environment. The results were obtained using immunoassays for amyloid-beta 1-42 (Aβ42), tau, phosphorylated tau (P-tau) and cystatin C and using surface-enhanced laser desorption/ionisation time-of-flight (SELDI-TOF) mass spectrometry for proteomic profiling. Tau and P-tau were susceptible to repeated freeze/thaw cycles while SELDI-TOF analysis produced eight significant peaks and additional artefact peaks from samples with added protease inhibitors. Delayed storage for different durations and in different temperatures produced six significant SELDI-TOF peaks. Aβ42 and tau were susceptible to increased temperatures and the duration before storage, whereas P-tau and cystatin C were not. Transthyretin and several of its isoforms were found using SELDI-TOF and were susceptible to freeze/thaw cycles and to increased temperature and length of time prior to storage. We recommend that CSF should be collected and centrifuged immediately after sampling and prior to storage at -80°C without the addition of protease inhibitors. Freeze/thawing should be avoided because of the instability of tau, P-tau and transthyretin. Standardised CSF sampling, handling and storage for biomarker research are essential for accurately comparing the results obtained by different studies and institutions.

Chronic administration of the selective P2X3, P2X2/3 receptor antagonist, A-317491, transiently attenuates cancer-induced bone pain in mice

The purinergic P2X3 and P2X2/3 receptors are in the peripheral nervous system almost exclusively confined to afferent sensory neurons, where they are found both at peripheral and central synapses. The P2X3 receptor is implicated in both neuropathic and inflammatory pain. However, the role of the P2X3 receptor in chronic cancer-induced bone pain is less known. Here we investigated the effect of systemic acute and chronic administration of the selective P2X3, P2X2/3 receptor antagonist (5-[[[(3-Phenoxyphenyl)methyl][(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]carbonyl]-1,2,4-benzenetricarboxylic acid sodium salt hydrate) (A-317491) in a murine model of cancer-induced bone pain. Chronic administration of A-317491 (30 μmol/kgs.c., b.i.d.) resulted in a transient attenuation of pain related behaviours in the early stage of the bone cancer model, but had no effect in the late and more progressed stage of bone cancer. Also, acute administration of A-317491 (100 μmol/kgs.c.) had no effect in the progressed stage of the bone cancer pain model. Thus, systemically administered A-317491 did not demonstrate a robust effect in the present mouse model of cancer-induced bone pain.

Characterization and stability of transthyretin isoforms in cerebrospinal fluid examined by immunoprecipitation and high-resolution mass spectrometry of intact protein

Post-translational modifications (PTMs) contribute significantly to the complexity of proteins. PTMs may vary in certain patterns according to diseases and microenviroments making them potential markers for pathological processes. Human transthyretin (TTR) is a transporter of thyroxine and retinol in blood and cerebrospinal fluid (CSF). A single free cysteine thiol group in TTR possesses the ability to form mixed disulfides potentially related to diseases such as TTR amyloidosis and Alzheimer's disease (AD). Additionally, TTR-Cys10 S-thiolations might mirror the oxidative stress and redox balance of CSF. Here we describe a quick and gentle method for immunoprecipitating (IP) TTR from CSF with minimal introduction of sample-handling artifacts. A high-resolution mass spectrometer (LTQ-Orbitrap XL) was used in a simple setup with direct infusion that generates data suitable for confident assignment of TTR isoforms and validation of the protocol. Moreover, we demonstrate how simple storage of CSF at 4°C induces major oxidative modifications of TTR. Using the optimized method, we show data from a limited number of mild cognitive impairment (MCI) and AD patients. The protocol controls and minimizes the introduction of sample-handling artifacts during purification of TTR isoforms for high-resolution MS analysis.

Tau protein: a possible prognostic factor in optic neuritis and multiple sclerosis

Background: Tau protein has been proposed as biomarker of axonal damage leading to irreversible neurological impairment in MS. CSF concentrations may be useful when determining risk of progression from ON to MS.

Objective: To investigate the association between tau protein concentration and 14-3-3 protein in the cerebrospinal fluid (CSF) of patients with monosymptomatic optic neuritis (ON) versus patients with monosymptomatic onset who progressed to multiple sclerosis (MS). To evaluate results against data found in a complete literature review.

Methods: A total of 66 patients with MS and/or ON from the Department of Neurology of Glostrup Hospital, University of Copenhagen, Denmark, were included. CSF samples were analysed for tau protein and 14-3-3 protein, and clinical and paraclinical information was obtained from medical records.

Results: The study shows a significantly increased concentration of tau protein in CSF from patients with relapsing–remitting MS and patients monosymptomatic at onset who progressed to MS, but interestingly no increased tau protein concentration in monosymptomatic ON. The concentration of tau protein was significantly correlated to Expanded Disability Status Scale score. No 14-3-3 protein was detected in any CSF sample.

Conclusions: The results of this study invite further exploration of the possible role of tau protein as a prognostic factor to predict progression from ON to MS in future studies.

A novel presenilin 2 mutation (V393M) in early-onset dementia with profound language impairment

BACKGROUND

Mutations in the Presenilin 2 gene (PSEN2) are rare causes of Alzheimer's disease (AD). Pathogenic mutations in the genes associated with autosomal dominant inherited AD have been shown to alter processing of the amyloid precursor protein (APP) resulting in a relative increase of the amount of Abeta42 peptide.

METHODS AND RESULTS

We present a patient with neuropathologically confirmed early-onset AD characterized by profound language impairment. The patient was heterozygous for a novel missense mutation in exon 11 of the PSEN2 gene leading to a predicted amino acid substitution from valine to methionine in position 393, a conserved residue. However, in vitro expression of PSEN2 V393M cDNA did not result in detectable increase of the secreted Abeta42/40 peptide ratio. The mutation was not found in 384 control individuals tested.

CONCLUSIONS

The possible pathogenic nature of the mutation is not clarified. We discuss the limitations of functional PSEN2 studies and the challenges associated with genetic counselling of family members at risk.