Human organotypic brain slice cultures: a detailed and improved protocol for preparation and long-term maintenance

The investigation of the human brain at cellular and microcircuit level remains challenging due to the fragile viability of neuronal tissue, inter- and intra-variability of the samples and limited availability of human brain material. Especially brain slices have proven to be an excellent source to investigate brain physiology and disease at cellular and small network level, overcoming the temporal limits of acute slices. Here we provide a revised, detailed protocol of the production and in-depth knowledge on long-term culturing of such human organotypic brain slice cultures for research purposes. We highlight the critical pitfalls of the culturing process of the human brain tissue and present exemplary results on viral expression, single-cell Patch-Clamp recordings, as well as multi-electrode array recordings as readouts for culture viability, enabling the use of organotypic brain slice cultures of these valuable tissue samples for basic neuroscience and disease modeling (Fig. 1).

Automated and fast online method for simultaneously determining a broad spectrum of per- and polyfluoroalkyl substances in a small volume of cerebrospinal fluid

Per- and polyfluoroalkyl substances (PFASs) are potentially neurotoxic compounds. Levels of PFASs in cerebrospinal fluid (CSF) could directly reflect their potential harm to the central nervous system. Because of the variety of PFASs and the rarity of CSF, there is an urgent need to establish a rapid online method to detect a broad spectrum of PFASs accurately and simultaneously by consuming a small amount of CSF. In this study, we developed a fast and automated method to analyze 52 PFASs in human CSF samples using online TurboFlow ultra-high-performance liquid chromatography-tandem mass spectrometry. Our method offered excellent matrix-matched standard curve linearity (correlation coefficient > 0.99), good limits of quantitation (MLOQs) (0.01 to 0.08 ng mL^-1), satisfactory accuracy (recoveries of 74.6%-119.1%) and precision (relative standard deviations of 1.4%-13.2%), small sample amount consumption (50 μL), and fast analysis time (18 min per sample) without complex sample pretreatment procedures. These are advantageous for the high throughput screening of PFASs in environmental epidemiology studies. Repeated freeze-thaw experiments showed that it was better to perform the analytical process soon as possible after sample collection. The established method was used to analyze PFASs in 60 people. Short-chain PFASs, perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), and novel PFASs [sodium 2-(N-ethylperfluorooctane-1-sulfonamido)ethyl phosphate (SAmPAP), perfluoroethylcyclohexanesulfonate (PFECHS), and perfluoro-3, 7-dimethyloctanoic acid (P37DMOA)] were reported in CSF for the first time. PFBA and PFPeA were detected in all samples with mean concentrations of 0.24 and 0.22 ng mL^-1, respectively. We also calculated the blood-brain barrier transmission efficiency of PFASs (R_PFAS), and the mean R_PFBA value was above 1, which indicated that PFBA might transfer from serum to CSF.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) crossing the blood-cerebrospinal fluid barrier: Their occurrence in human cerebrospinal fluid

Data remain scarce regarding the occurrence of per- and polyfluoroalkyl substances (PFASs) in the human brain for better understanding the cerebral disorders. In this study, we measured the concentrations and profiles of 26 traditional and emerging PFASs in cerebrospinal fluid (CSF), which is a preferred matrix to monitor pollutants in the human brain. Our results indicated perfluorooctanesulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorohexanesulfonate (PFHxS) and n-methylperfluorooctanesulfonamidoacetic acid were the most frequently detected congeners (detection frequency >90%). As the predominant congeners, PFOA and PFOS contributed 27.7% and 14.5% of the total amount of PFASs (ΣPFASs), with respective mean concentration of 221 and 115 pg mL^-1. In addition, the concentrations of ΣPFASs in CSF of males were generally higher than those of females, which may be related to the different half-lives of PFASs in different sexes. Interestingly, the concentrations of ΣPFASs and several individual congeners (e.g., perfluorohexanoic acid, perfluorodecanoic acid, perfluorononanoic acid, PFHxS and PFOS) increased with age. The highest concentration of ΣPFASs was found in the elderly compared with other age groups, which may be due to the decreased CSF output as age increased. Our data are valuable for further studies regarding the toxic effects of PFASs on the human brain.

Small and long RNA transcriptome of whole human cerebrospinal fluid and serum as compared to their extracellular vesicle fractions reveal profound differences in expression patterns and impacts on biological processes

BACKGROUND

Next generation sequencing (NGS) of human specimen is expected to improve prognosis and diagnosis of human diseases, but its sensitivity urges for well-defined sampling and standardized protocols in order to avoid error-prone conclusions.

METHODS

In this study, large volumes of pooled human cerebrospinal fluid (CSF) were used to prepare RNA from human CSF-derived extracellular vesicles (EV) and from whole CSF, as well as from whole human serum and serum-derived EV. In all four fractions small and long coding and non-coding RNA expression was analyzed with NGS and transcriptome analyses.

RESULTS

We show, that the source of sampling has a large impact on the acquired NGS pattern, and differences between small RNA fractions are more distinct than differences between long RNA fractions. The highest percentual discrepancy between small RNA fractions and the second highest difference between long RNA fractions is seen in the comparison of CSF-derived EV and whole CSF. Differences between miR (microRNA) and mRNA fractions of EV and the respective whole body fluid have the potential to affect different cellular and biological processes. I.e. a comparison of miR in both CSF fractions reveals that miR from EV target four transcripts sets involved in neurobiological processes, whereas eight others, also involved in neurobiological processes are targeted by miR found in whole CSF only. Likewise, three mRNAs sets derived from CSF-derived EV are associated with neurobiological and six sets with mitochondrial metabolism, whereas no such mRNA transcript sets are found in the whole CSF fraction. We show that trace amounts of blood-derived contaminations of CSF can bias RNA-based CSF diagnostics.

CONCLUSIONS

This study shows that the composition of small and long RNA differ significantly between whole body fluid and its respective EV fraction and thus can affect different cellular and molecular functions. Trace amounts of blood-derived contaminations of CSF can bias CSF analysis. This has to be considered for a meaningful RNA-based diagnostics. Our data imply a transport of EV from serum to CSF across the blood-brain barrier.

Development of immunoprecipitation - two-dimensional liquid chromatography - mass spectrometry methodology as biomarker read-out to quantify phosphorylated tau in cerebrospinal fluid from Alzheimer disease patients

In Alzheimer's disease (AD) brain, one of the histopathological hallmarks is the neurofibrillary tangles consisting of aggregated and hyperphosphorylated tau. Currently many tau binding antibodies are under development to target the extracellular species responsible for the spreading of the disease in the brain. As such, an in-house developed antibody JNJ-63733657 with picomolar affinity towards tau phosphorylated at both T212 and T217 (further named p217+tau) was recently tested in phase I clinical trial NCT03375697. Following multiple dose administration in healthy subjects and subjects with AD, there were dose dependant reductions in free p217+tau fragments in cerebrospinal fluid (CSF) following antibody administration, as measured with a novel single molecule ELISA assay (Simoa PT3 x PT82 assay), demonstrating epitope engagement of the therapeutic antibody [Galpern, Haeverans, Janssens, Triana-Baltzer, Kolb, Li, Nandy, Mercken, Van Kolen, Sun, Van Nueten, 2020]. Total p217+tau levels also were reduced in CSF as measured with the Simoa PT3 x PT82 assay. In this study we developed an orthogonal immunoprecipitation - liquid chromatography - triple quadrupole mass spectrometry (IP-LC-TQMS) assay to verify the observed reductions in total p217+ tau levels. In this assay, an excess of JNJ-63733657 is added to the clinical CSF to ensure all p217+tau is bound by the antibody instead of having a pool of bound and unbound antigen and to immunoprecipitate all p217+tau, which is followed by on-bead digestion with trypsin to release surrogate peptides. Tryptic peptides with missed cleavages were monitored when phosphorylation occurred close to the cleavage site as this induced miscleavages. Compared with acidified mobile phases typically used for peptide analysis, reversed phase LC with mobile phase at basic pH resulted in sharper peaks and improved selectivity and sensitivity for the target peptides. With this setup a diphospho-tau tryptic peptide SRTPSLPTPPTREPK*2 could be measured with pT217 accounting for at least one of the phospho-sites. This is the first time that the presence of a diphopsho-tau peptide is reported to be present in human CSF. A two-dimensional LC-TQMS method was developed to remove matrix interferences. Selective trapping of diphospho-peptides via a metal oxide chromatography mechanism was achieved in a first dimension with a conventional reversed phase stationary phase and acidified mobile phase. Subsequent elution at basic pH enabled detection of low picomolar p217+tau levels in human CSF (lower limit of quantification: 2 pM), resulting in an approximate 5-fold increase in sensitivity. This enabled the quantification of total p217+tau in CSF leading to the confirmation that in addition to reductions in free p217+tau levels total p217+tau levels were also reduced following administration of the tau mAb JNJ-63733657, correlating with the previous measurement with the PT3 x PT82 Simoa assay. An orthogonal sample clean-up using offline TiO₂/ZrO₂ combined with 1DLC-TQMS was developed to confirm the presence of mono-ptau (pT217) tryptic peptides in CSF.

High-sensitivity quantification of acetylcholine and choline in human cerebrospinal fluid with a validated LC-MS/MS method

Acetylcholine is the neurotransmitter of the parasympathetic nervous system, synthesized from choline and involved in several neurodegenerative diseases. Exploration of cholinergic neurotransmission in the human central nervous system is limited by the lack of a sensitive and specific method for the determination of acetylcholine and choline expression. We developed an hydrophilic interaction liquid chromatography - mass spectrometry method for the quantification of both molecules in human cerebrospinal fluid samples. An extensive selectivity study towards endogenous interfering compounds, in particular γ-butyrobetain, was performed and the method was validated according to the European Medicine Agency and Food and Drug Administration guidelines for the validation of bioanalytical methods. The performance of the method was excellent with a lower limit of quantification at 5 ng/L (34.2 pmol/L) for acetylcholine and 5 μg/L for choline, a precision in the range 1.3-11.9% and an accuracy between 85.2 and 113.1%. This suitability of the method for the quantification of acetylcholine and choline in clinical samples was demonstrated with the analysis of patient cerebrospinal fluid samples. Altogether, this validated method allows the simultaneous quantitative analysis of acetylcholine and choline in human cerebrospinal fluid with high sensitivity and selectivity. It will allow to better characterize the cholinergic neurotransmission in human pathologies and to study the effects of drugs acting on this system.

Determination of neurosteroids in human cerebrospinal fluid in the 21st century: A review

Determination of steroid hormones synthesized by the human body plays an important role in various fields of endocrinology. Neurosteroids (NS) are steroids that are synthesized in the central (CNS) or peripheral nervous system (PNS), which is not only a source but also a target for neurosteroids. They are discussed as possible biomarkers in various cognitive disorders and research interest in this topic raises continuously. Nevertheless, knowledge on functions and metabolism is still limited, although the concept of neurosteroids was already introduced in the 1980s. Until today, the analysis of neurosteroids is truly challenging. The only accessible matrix for investigations of brain metabolism in living human beings is cerebrospinal fluid (CSF), which therefore becomes a very interesting specimen for analysis. However, neurosteroid concentrations are expected to be very low and the available amount of cerebrospinal fluid is limited. Further, high structural similarities of endogenous neurosteroids challenges analysis. Therefore, comprehensive methods, highly selective and sensitive for a large range of concentrations for different steroids in one aliquot are required and under continuous development. Although research has been increasingly intensified, still only few data are available on reference levels of neurosteroids in human cerebrospinal fluid. In this review, published literature of the last twenty years, as a period with relatively contemporary analytical methods, was systematically investigated. Considerations on human cerebrospinal fluid, different analytical approaches, and available data on levels of in analogy to periphery conceivable occurring neurosteroids, including (pro-) gestagens, androgens, corticoids, estrogens, and steroid conjugates, and their interpretation are intensively discussed.

Lower cerebrospinal fluid CRH concentration in chronic schizophrenia with negative symptoms

Some patients with schizophrenia have impaired hypothalamic-pituitary-adrenal axis function. However, there is a dearth of studies focusing on corticotropin-releasing hormone (CRH) levels in the brains of schizophrenia patients, which motivated us to examine whether cerebrospinal fluid (CSF) CRH concentrations are altered in these patients. We also examined the possible correlation of CSF CRH level with clinical variables such as schizophrenia symptoms and antipsychotic medication. The study population comprised 20 patients with a diagnosis of schizophrenia according to DSM-5 criteria and 25 healthy controls, who underwent lumbar puncture. Most of the patients were treated with antipsychotic drugs and their doses were converted to chlorpromazine (CP) equivalent values. CSF CRH concentrations were measured by an enzyme immunoassay. Symptom severity was assessed using the Positive and Negative Syndrome Scale (PANSS). There was a significantly lower CSF CRH concentration in the patients than in the controls (Mann-Whitney U test: p = 0.014). A significantly negative correlation of CSF CRH levels with PANSS negative scores was found in the patients (Spearman's: ρ = -0.58, p = 0.007). However, CSF CRH concentrations were not significantly correlated with the PANSS total (ρ = -0.035, p = 0.89), positive (ρ = 0.25, p = 0.30), or general psychopathology (ρ = 0.13, p = 0.59) scores. No significant correlation was found with CP equivalent values (ρ = 0.00, p = 1.00). In conclusion, we found that the patients with schizophrenia had lower CSF CRH concentrations compared to the controls and that the lower CSF CRH was associated with negative symptoms of the illness. Further studies in a larger sample and in drug-free patients are warranted.

Pneumococcal serotype determines growth and capsule size in human cerebrospinal fluid

Background

The polysaccharide capsule is a major virulence factor of S. pneumoniae in diseases such as meningitis. While some capsular serotypes are more often found in invasive disease, high case fatality rates are associated with those serotypes more commonly found in asymptomatic colonization. We tested whether growth patterns and capsule size in human cerebrospinal fluid depends on serotype using a clinical isolate of S. pneumoniae and its capsule switch mutants.

Results

We found that the growth pattern differed markedly from that in culture medium by lacking the exponential and lysis phases. Growth in human cerebrospinal fluid was reduced when strains lost their capsules. When a capsule was present, growth was serotype-specific: high carriage serotypes (6B, 9 V, 19F and 23F) grew better than low carriage serotypes (7F, 14, 15B/C and 18C). Growth correlated with the case-fatality rates of serotypes reported in the literature. Capsule size in human cerebrospinal fluid also depended on serotype.

Conclusions

We propose that serotype-specific differences in disease severity observed in meningitis patients may, at least in part, be explained by differences in growth and capsule size in human cerebrospinal fluid. This information could be useful to guide future vaccine design.

Pre-analytical stability of novel cerebrospinal fluid biomarkers

Stability of the cerebrospinal fluid (CSF) composition under different pre-analytical conditions is relevant for the diagnostic potential of biomarkers. Our aim was to examine the pre-analytical stability of promising CSF biomarkers that are currently evaluated for their discriminative use in various neurological diseases. Pooled CSF was aliquoted and experimentally exposed to delayed storage: 0, 1, 2, 4, 24, 72, or 168 h at 4 °C or room temperature (RT), or 1-4 months at -20 °C; or up to 7 freeze/thaw (f/t) cycles, before final storage at -80 °C. Eleven CSF biomarkers were screened using immunoassays, liquid chromatography, or enzymatic methods. Levels of neurogranin (truncP75), chitinase-3-like protein (YKL-40), beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), acetylcholinesterase (AChE) enzymatic activity, theobromine, secreted protein acidic and rich in cysteine-like 1 (SPARCL-1) and homovanillic acid (HVA) levels were not affected by the applied storage conditions. 3-Methoxy-4-hydroxyphenylglycol (MHPG) levels linearly and strongly decreased after 4 h at RT (-10%) or 24 h at 4 °C (-27%), and with 6% after every f/t cycle. 5-Methyltetrahydrofolate (5-MTHF) (-29% after 1 week at RT) and 5-hydroxyindoleacetic acid levels (5-HIAA) (-16% after 1 week at RT) were reduced and 3,4-dihydroxyphenylacetic acid (DOPAC) levels (+22% after 1 week at RT) increased, but only after >24 h at RT. Ten out of eleven potential CSF novel biomarkers showed very limited change under common storage and f/t conditions, suggesting that these CSF biomarkers can be trustfully tested under the pre-analytical conditions present across different cohorts.

Cerebrospinal fluid BDNF pro-peptide levels in major depressive disorder and schizophrenia

The role of brain-derived neurotrophic factor (BDNF) and its related molecules has been extensively studied in the context of psychiatric disorders. In the present study, we focused on the newly identified BDNF pro-peptide, which is generated together with mature BDNF by proteolytic processing of their precursor, proBDNF. Here, we report, for the first time, that BDNF pro-peptide is present in human cerebrospinal fluid (CSF) and quantifiable by western blotting. We measured CSF BDNF pro-peptide levels in 27 patients with schizophrenia, 18 patients with major depressive disorder (MDD), and 27 healthy controls matched for age, sex, and ethnicity (Japanese). The ratio of the BDNF pro-peptide level to the total protein level in MDD patients was significantly lower than that in controls (Kruskal-Wallis with Dunn's multiple comparisons test; p = 0.046). When men and women were examined separately, males with MDD had a significantly lower BDNF pro-peptide/protein ratio than male controls (p = 0.047); this difference was not found in female subjects. The ratio tended to be lower in male schizophrenia patients (p = 0.10). Although we tried to measure the levels of mature BDNF in CSF, they were below the limit of detection of the ELISA and multiple analyte profiling technology. Taken together, the results suggest that reduced CSF BDNF pro-peptide levels are associated with MDD, particularly in males. Further studies involving a larger sample size are warranted.

An UHPLC-MS/MS method for simultaneous quantification of human amyloid beta peptides Aβ1-38, Aβ1-40 and Aβ1-42 in cerebrospinal fluid using micro-elution solid phase extraction

Amyloid beta (Aβ) peptides in cerebrospinal fluid are extensively estimated for identification of Alzheimer's disease (AD) as diagnostic biomarkers. Unfortunately, their pervasive application is hampered by interference from Aβ propensity of self-aggregation, nonspecifically bind to surfaces and matrix proteins, and by lack of quantitive standardization. Here we report on an alternative Ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for simultaneous measurement of human amyloid beta peptides Aβ1-38, Aβ1-40 and Aβ1-42 in cerebrospinal fluid (CSF) using micro-elution solid phase extraction (SPE). Samples were pre-processing by the mixed-mode micro-elution solid phase extraction and quantification was performed in the positive ion multiple reaction monitoring (MRM) mode using electrospray ionization. The stable-isotope labeled Aβ peptides ¹⁵N₅₁- Aβ1-38, ¹⁵N₅₃- Aβ1-40 and ¹⁵N₅₅- Aβ1-42 peptides were used as internal standards. And the artificial cerebrospinal fluid (ACSF) containing 5% rat plasma was used as a surrogate matrix for calibration curves. The quality control (QC) samples at 0.25, 2 and 15ng/mL were prepared. A "linear" regression (1/x² weighting): y=ax+b was used to fit the calibration curves over the concentration range of 0.1-20ng/mL for all three peptides. Coefficient of variation (CV) of intra-batch and inter-batch assays were all less than 6.44% for Aβ1-38, 6.75% for Aβ1-40 and 10.74% for Aβ1-42. The precision values for all QC samples of three analytes met the acceptance criteria. Extract recoveries of Aβ1-38, Aβ1-40 and Aβ1-42 were all greater than 70.78%, both in low and high QC samples. The stability assessments showed that QC samples at both low and high levels could be stable for at least 24h at 4°C, 4h at room temperature and through three freeze-thaw cycles without sacrificing accuracy or precision. And no significant carryover effect was observed. This validated UHPLC/MS/MS method was successfully applied to the quantitation of Aβ peptides in real human CSF samples. Our work may provide a reference method for simultaneous quantitation of human Aβ1-38, Aβ1-40 and Aβ1-42 from CSF.

High-performance liquid chromatography with time-programmed fluorescence detection for the quantification of Levofloxacin in human plasma and cerebrospinal fluid in adults with tuberculous meningitis

An accurate and reliable high-performance liquid chromatography with time-programmed fluorescence detection was developed and validated to measure levofloxacin in human plasma and cerebrospinal fluid (CSF). After solid phase extraction process using Evolute^® ABN 96 fixed well plate; levofloxacin and internal standard-enoxacin were separated using a mobile phase consisting of phosphate buffer 10mM with 0.025% triethylamine pH 3.0 - acetonitrile (88:12, v/v) on a Purosphere RP-8e column (5μm, 125×4.0mm) at a flow rate of 1.2mL/min at 35°C. The excitation/emission wavelengths were set to 269/400nm and 294/500nm, for enoxacin and levofloxacin, respectively. The method was linear over the concentration range of 0.02 to 20.0μg/mL with a limit of detection of 0.01μg/mL. The relative standard deviation of intra-assay and inter-assay precision for levofloxacin at four quality controls concentrations (0.02, 0.06, 3.0 and 15.0μg/mL) were less than 7% and the accuracies ranged from 96.75% to 101.9% in plasma, and from 93.00% to 98.67% in CSF. The validated method was successfully applied to quantify levofloxacin in a considerable quantity of plasma (826) and CSF (477) samples collected from 232 tuberculous meningitis patients, and the preliminary intensive pharmacokinetics analysis from 14 tuberculous meningitis patients in Vietnam is described in this paper.