Biobanking of Cerebrospinal Fluid for Biomarker Analysis in Neurological Diseases

Selenoprotein P concentrations and risk of progression from mild cognitive impairment to dementia

There is a growing literature investigating the effects of selenium on the central nervous system and cognitive function. However, little is known about the role of selenoprotein P, the main selenium transporter, which can also have adverse biological effects. We conducted a prospective cohort study of individuals aged 42-81 years who received a clinical diagnosis of mild cognitive impairment. Using sandwich ELISA methods, we measured full-length selenoprotein P concentrations in serum and cerebrospinal fluid to assess the relation with dementia incidence during a median follow-up of 47.3 months. We used Cox proportional hazards regression and restricted cubic splines to model such relation. Of the 54 participants, 35 developed dementia during follow-up (including 26 cases of Alzheimer's dementia). Selenoprotein P concentrations in serum and cerebrospinal fluid were highly correlated, and in spline regression analyses they each showed a positive non-linear association with dementia risk, particularly after excluding dementia cases diagnosed within 24 months of follow-up. We also observed differences in association according to the dementia subtypes considered. Risk ratios of dementia peaked at 2-6 at the highest levels of selenoprotein P, when compared to its median level, also depending on matrix, analytical methodology and dementia subtype. Findings of this study, the first to assess selenoprotein P levels in the central nervous system in vivo and the first to use a prospective study design to evaluate associations with dementia, suggest that higher circulating concentrations of selenoprotein P, both in serum and cerebrospinal fluid, predict progression of MCI to dementia. However, further confirmation of these findings is required, given the limited statistical precision of the associations and the potential for residual confounding.

Particulate matter exposure from motorized traffic and risk of conversion from mild cognitive impairment to dementia: An Italian prospective cohort study

BACKGROUND

Based on epidemiologic and laboratory studies, exposure to air pollutants has been linked to many adverse health effects including a higher risk of dementia. In this study, we aimed to evaluate the effect of long-term exposure to outdoor air pollution on risk of conversion to dementia in a cohort of subjects with mild cognitive impairment (MCI).

METHODS

We recruited 53 Italian subjects newly-diagnosed with MCI. Within a geographical information system, we assessed recent outdoor air pollutant exposure, by modeling air levels of particulate matter with equivalent aerodynamic diameter ≤10 μm (PM₁₀) from motorized traffic at participants' residence. We investigated the relation of PM₁₀ concentrations to subsequent conversion from MCI to any type of dementia. Using a Cox-proportional hazards model combined with a restricted cubic spline model, we computed the hazard ratio (HR) of dementia with its 95% confidence interval (CI) according to increasing PM₁₀ exposure, adjusting for sex, age, and educational attainment.

RESULTS

During a median follow up of 47.3 months, 34 participants developed dementia, in 26 cases diagnosed as Alzheimer's dementia. In non-linear restricted spline regression analysis, mean and maximum annual PM₁₀ levels positively correlated with cerebrospinal fluid total and phosphorylated tau proteins concentrations, while they were inversely associated with β-amyloid. Concerning the risk of dementia, we found a positive association starting from above 10 μg/m³ for mean PM₁₀ levels and above 35 μg/m³ for maximum PM₁₀ levels. Specific estimates for Alzheimer's dementia were substantially similar. Adding other potential confounders to the multivariable model or removing early cases of dementia onset during the follow-up had little effect on the estimates.

CONCLUSIONS

Our findings suggest that exposure to outdoor air pollutants, PM₁₀ in particular, may non-linearly increase conversion from MCI to dementia above a certain ambient air concentration.

CSF Heavy Neurofilament May Discriminate and Predict Motor Neuron Diseases with Upper Motor Neuron Involvement

Objective: To assess whether phosphorylated neurofilament heavy chain (pNfH) can discriminate different upper motor neuron (UMN) syndromes, namely, ALS, UMN-predominant ALS, primary lateral sclerosis (PLS) and hereditary spastic paraparesis (hSP) and to test the prognostic value of pNfH in UMN diseases. Methods: CSF and serum pNfH were measured in 143 patients presenting with signs of UMN and later diagnosed with classic/bulbar ALS, UMNp-ALS, hSP, and PLS. Between-group comparisons were drawn by ANOVA and receiver operating characteristic (ROC) analysis was performed. The prognostic value of pNfH was tested by the Cox regression model. Results: ALS and UMNp-ALS patients had higher CSF pNfH compared to PLS and hSP (p < 0.001). ROC analysis showed that CSF pNfH could differentiate ALS, UMNp-ALS included, from PLS and hSP (AUC = 0.75 and 0.95, respectively), while serum did not perform as well. In multivariable survival analysis among the totality of UMN patients and classic/bulbar ALS, CSF pNfH independently predicted survival. Among UMNp-ALS patients, only the progression rate (HR4.71, p = 0.01) and presence of multifocal fasciculations (HR 15.69, p = 0.02) were independent prognostic factors. Conclusions: CSF pNfH is significantly higher in classic and UMNp-ALS compared to UMN diseases with a better prognosis such as PLS and hSP. Its prognostic role is confirmed in classic and bulbar ALS, but not among UMNp, where clinical signs remained the only independent prognostic factors.

A Cystatin C Cleavage ELISA Assay as a Quality Control Tool for Determining Sub-Optimal Storage Conditions of Cerebrospinal Fluid Samples in Alzheimer's Disease Research

Background:

An N-terminal octapeptide cleavage of the cystatin C protein was discovered by mass spectrometry when cerebrospinal fluid (CSF) was stored at –20°C for 3 months, which did not occur when CSF was stored at –80°C.

Objective:

The aim was to develop an immunoassay as quality assessment tool to detect this –20°C cleavage of cystatin C in CSF and support Alzheimer’s disease research.

Methods:

A specific monoclonal antibody and a double indirect sandwich ELISA were developed: one assay quantifies the octapeptide uncleaved protein specifically and the other quantifies the total cystatin C present in the biological fluid (both cleaved and uncleaved forms). The ratio of these concentrations was calculated to assess the extent of cleavage of cystatin C. The novel ELISA was validated and applied in a short-term (up to 4 weeks) and mid-term (up to one year) stability study of CSF stored at 4°C, –20°C, –80°C, and liquid nitrogen. Impact of freeze-thaw cycles, adsorption, and protease inhibitors were tested.

Results:

The ratio of truncated protein was modified following –20°C storage and seemed to reach a plateau after 6 months. The ratio was impacted neither by freeze-thaw cycles nor adsorption. The –20°C specific cleavage was found to be protease related.

Conclusion:

Using this novel double indirect sandwich ELISA, absolute levels of the total and uncleaved cystatin C and the ratio of truncated cystatin C can be measured. This assay is an easily applicable tool which can be used to confirm that CSF biospecimen are fit-for-purpose for Alzheimer’s disease research.

β-Amyloid in Cerebrospinal Fluid: How to Keep It Floating (Not Sticking) by Standardization of Preanalytic Processes and Collection Tubes

BACKGROUND

Phosphorylated tau (pTau), total tau (tTau), and β-amyloid (Aβ) are established cerebrospinal fluid (CSF) biomarkers used to help diagnose Alzheimer disease. Preanalytic workups of CSF samples lack harmonization, making interlaboratory comparison of these biomarkers challenging. The Aβ adsorbs to sample tubes, yielding underestimated concentrations, and may result in false Alzheimer disease diagnosis. Our primary aim was to compare Aβ recovery across multiple polypropylene tubes and to test the stability of tTau, pTau, and Aβ in the best performing tube.

METHODS

Eight polypropylene tubes were tested using 3 CSF pools with Aβ concentrations <500, 500-1000, and >1000 ng/L. All samples were analyzed in duplicate. Tubes were cut open to assess their different infrared adsorption spectra. Freshly drawn CSF from 14 patients was distributed into 4 Sarstedt 5-mL (no. 63.504.027; Sar5CSF) tubes, left at room temperature for up to 7 days, and analyzed for pTau, tTau, and Aβ by ELISA.

RESULTS

Two Sarstedt 5-mL tubes and a Sarstedt 10-mL (Sar10CSF) tube showed significantly higher Aβ recovery at all 3 concentrations compared with the 5 other tubes. The infrared adsorption spectra of Sar10CSF and Sar5CSF tubes were practically identical, unlike the other tubes. No significant loss of pTau, tTau, and Aβ was observed in CSF left at room temperature for up to 7 days (P > 0.05).

CONCLUSIONS

Recovery of Aβ from Sar5CSF tubes is equivalent to Aβ recovery from Sar10CSF tubes. Levels of pTau, tTau, and Aβ were stable for at least 7 days at room temperature but not at 37 °C.

Effects of ex vivo ischemia time and delayed processing on quality of specimens in tissue biobank

The RNA quality of tissue biobank is crucial for translational research; however, the effects of the ex vivo ischemia time on RNA integrity and expression of genes related to hypoxia, stress, apoptosis and autophagy remains elusive. A total of 18 carcinoma tissues were stored at room temperature for 15 min, 30 min, 1, 2, 4, 8 and 24 h. The integrity and purity of isolated RNA were analyzed. Furthermore, the gene expression of mTOR, hypoxia-inducible factor 1α, phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit β isoform (PI3KCB), threonine kinase 1 (AKT1), NF-κB, protein kinase AMP-activated catalytic subunit α1 (AMPKα1), caspase 8 (CASP8), unc-51 like autophagy activating kinase 1 and Fas cell surface death receptor were analyzed using reverse transcription-quantitative PCR. The results demonstrated that RNA integrity numbers (RINs) remained stable in carcinoma tissues following ex vivo ischemia for 2 h at room temperature and that degradation began at 4 h (P<0.001). Additionally, the expression of PI3KCB, AKT1, AMPKα1 and CASP8 decreased at time points 8–24 h following ex vivo ischemia and delayed processing (P<0.001). In conclusion, >2 h of ex vivo ischemia and delayed processing induced RNA degradation and a decrease in RIN, and the gene expressions of PI3KCB, AKT1, AMPKα1 and CASP8 may be considered as markers to evaluate tissue quality at the gene expression level, providing a method for the standard processing and assessment of tissue specimen.

Intraventricular Hemorrhage Clearance in Human Neonatal Cerebrospinal Fluid: Associations With Hydrocephalus

Background and Purpose- Preterm neonates with intraventricular hemorrhage (IVH) are at risk for posthemorrhagic hydrocephalus and poor neurological outcomes. Iron has been implicated in ventriculomegaly, hippocampal injury, and poor outcomes following IVH. We hypothesized that levels of cerebrospinal fluid blood breakdown products and endogenous iron clearance proteins in neonates with IVH differ from those of neonates with IVH who subsequently develop posthemorrhagic hydrocephalus. Methods- Premature neonates with an estimated gestational age at birth <30 weeks who underwent lumbar puncture for clinical evaluation an average of 2 weeks after birth were evaluated. Groups consisted of controls (n=16), low-grade IVH (grades I-II; n=4), high-grade IVH (grades III-IV; n=6), and posthemorrhagic hydrocephalus (n=9). Control subjects were preterm neonates born at <30 weeks' gestation without brain abnormality or hemorrhage on cranial ultrasound, who underwent lumbar puncture for clinical purposes. Cerebrospinal fluid hemoglobin, total bilirubin, total iron, ferritin, ceruloplasmin, transferrin, haptoglobin, and hemopexin were quantified. Results- Cerebrospinal fluid hemoglobin levels were increased in posthemorrhagic hydrocephalus compared with high-grade IVH (9.45 versus 6.06 µg/mL, P<0.05) and cerebrospinal fluid ferritin levels were increased in posthemorrhagic hydrocephalus compared with controls (511.33 versus 67.08, P<0.01). No significant group differences existed for the other cerebrospinal fluid blood breakdown and iron-handling proteins tested. We observed positive correlations between ventricular enlargement (frontal occipital horn ratio) and ferritin (Pearson r=0.67), hemoglobin (Pearson r=0.68), and total bilirubin (Pearson r=0.69). Conclusions- Neonates with posthemorrhagic hydrocephalus had significantly higher levels of hemoglobin than those with high-grade IVH. Levels of blood breakdown products, hemoglobin, ferritin, and bilirubin correlated with ventricular size. There was no elevation of several iron-scavenging proteins in cerebrospinal fluid in neonates with posthemorrhagic hydrocpehalus, indicative of posthemorrhagic hydrocephalus as a disease state occurring when endogenous iron clearance mechanisms are overwhelmed.

Critical Steps to be Taken into Consideration Before Quantification of β-Amyloid and Tau Isoforms in Blood can be Implemented in a Clinical Environment

This review aims to document difficulties, limitations, and pitfalls when considering protein analysis in blood samples. It proposes an improved workflow for design, development, and validation of (immuno)assays for blood proteins, without providing reflections on a potential hypothesis of the origin of protein mismetabolism and deposition. There is a special focus on assay development for quantification of β-amyloid (Aβ) and tau in blood for diagnostic use or for integration in clinical trials in the field of Alzheimer's disease (AD).

Biobanking of Cerebrospinal Fluid

Cerebrospinal fluid (CSF) is a physiologically essential fluid produced by the brain that is involved in protecting the brain and in the exchange of nutrients and waste products. CSF has long been utilized to confirm clinical suspicion of various infectious and inflammatory disorders, such as meningitis and multiple sclerosis. However, there has been increasing interest in collecting CSF in order to study the clinical significance of additional biomarkers. This chapter outlines the procedures necessary to collect, process, store, and utilize CSF obtained for the purposes of biobanking from both living and deceased patients.

Guidelines for CSF Processing and Biobanking: Impact on the Identification and Development of Optimal CSF Protein Biomarkers

The field of neurological diseases strongly needs biomarkers for early diagnosis and optimal stratification of patients in clinical trials or to monitor disease progression. Cerebrospinal fluid (CSF) is one of the main sources for the identification of novel protein biomarkers for neurological diseases. Despite the enormous efforts employed to identify novel CSF biomarkers, the high variability observed across different studies has hampered their validation and implementation in clinical practice. Such variability is partly caused by the effect of different pre-analytical confounding factors on protein stability, highlighting the importance to develop and comply with standardized operating procedures. In this chapter, we describe the international consensus pre-analytical guidelines for CSF processing and biobanking that have been established during the last decade, with a special focus on the influence of pre-analytical confounders on the global CSF proteome. In addition, we provide novel results on the influence of different delayed storage and freeze/thaw conditions on the CSF proteome using two novel large multiplex protein arrays (SOMAscan and Olink). Compliance to consensus guidelines will likely facilitate the successful development and implementation of CSF protein biomarkers in both research and clinical settings, ultimately facilitating the successful development of disease-modifying therapies.

Cerebrospinal Fluid Neurofilaments May Discriminate Upper Motor Neuron Syndromes: A Pilot Study

BACKGROUND

Patients presenting with upper motor neuron (UMN) signs may widely diverge in prognosis, ranging from amyotrophic lateral sclerosis (ALS) to primary lateral sclerosis (PLS) and hereditary spastic paraplegia (hSP). Neurofilaments are emerging as potential diagnostic and prognostic biomarkers for ALS, but the diagnosis of UMN syndromes still relies mostly on clinical long-term observation and on familiarity or genetic confirmation.

OBJECTIVES

To test whether phosphorylated neurofilament heavy chain (pNfH) may discriminate different UMN syndromes at diagnosis and to test their prognostic role among these diseases.

METHODS

We measured the cerebrospinal fluid (CSF) and serum pNfH of 30 patients presenting with UMN signs and diagnosed with ALS, hSP, and PLS, plus 9 healthy controls (HC).

RESULTS

ALS patients had higher levels of pNfH in CSF and serum compared to HC (p < 0.001 and p < 0.001 in CSF and serum, respectively) and PLS (p = 0.015 and p = 0.038) and hSP (p = 0.003 and p = 0.001) patients. PLS and hSP patients had similar CSF and serum pNfH concentrations, but a higher CSF pNfH concentration, compared to HC (p = 0.002 and p = 0.003 for PLS and hSP, respectively). Receiver operating characteristic curves for discriminating ALS from PLS and hSP showed an area under the curve of 0.79 for CSF and 0.81 for serum. In multivariable survival analysis including relevant clinical factors CSF pNfH represented the strongest variable predicting survival (HR 40.43; 95% CI 3.49-467.79, p = 0.003) independently of clinical group.

CONCLUSIONS

Despite some statistical instability of the results due to limitations in sample size, our study supports the role of CSF pNfH as a prognostic biomarker for motor neuron diseases presenting with UMN signs. A potential power to discriminate between ALS and other UMN syndromes at presentation, and between all of the examined MND and HC, has been detected for both CSF and serum pNfH.