Biochemical markers of time since death in cerebrospinal fluid: A first step towards "Forensomics"

The polychromatism of postmortem cerebrospinal fluid

Based on the assumption that postmortem cerebrospinal fluid (CSF) is contaminated depending on the chosen sampling technique in the forensic setting resulting in bloody or at least hemolytic CSF samples, we systematically documented a total of 183 postmortem CSF samples. These samples were all assessed for their quality and color, regardless of the cause of death or the postmortem interval. The investigations were carried out through subjective assessment of color and turbidity, as well as objective measurements of the optical density (OD) of the CSF supernatants after centrifugation of each sample, with standardized photographic documentation. The observations revealed that in 28 cases the CSF was absolutely (crystal-) clear and transparent. Most of our samples showed color changes ranging from xanthrochromic to rose. Intensive staining of the supernatants was only found in a small proportion of the examined collective. We found that postmortem CSF has no uniform appearance but rather a diverse range of color spectra, and the color, as well as the OD of the CSF, correlates significantly with the postmortem interval (p < 0.001) when sampled using the proposed standard procedure.

Postmortem metabolomics: influence of time since death on the level of endogenous compounds in human femoral blood. Necessary to be considered in metabolome study planning?

INTRODUCTION

The (un)targeted analysis of endogenous compounds has gained interest in the field of forensic postmortem investigations. The blood metabolome is influenced by many factors, and postmortem specimens are considered particularly challenging due to unpredictable decomposition processes.

OBJECTIVES

This study aimed to systematically investigate the influence of the time since death on endogenous compounds and its relevance in designing postmortem metabolome studies.

METHODS

Femoral blood samples of 427 authentic postmortem cases, were collected at two time points after death (854 samples in total; t1: admission to the institute, 1.3-290 h; t2: autopsy, 11-478 h; median ∆t = 71 h). All samples were analyzed using an untargeted metabolome approach, and peak areas were determined for 38 compounds (acylcarnitines, amino acids, phospholipids, and others). Differences between t2 and t1 were assessed by Wilcoxon signed-ranked test (p < 0.05). Moreover, all samples (n = 854) were binned into time groups (6 h, 12 h, or 24 h intervals) and compared by Kruskal-Wallis/Dunn's multiple comparison tests (p < 0.05 each) to investigate the effect of the estimated time since death.

RESULTS

Except for serine, threonine, and PC 34:1, all tested analytes revealed statistically significant changes between t1 and t2 (highest median increase 166%). Unpaired analysis of all 854 blood samples in-between groups indicated similar results. Significant differences were typically observed between blood samples collected within the first and later than 48 h after death, respectively.

CONCLUSIONS

To improve the consistency of comprehensive data evaluation in postmortem metabolome studies, it seems advisable to only include specimens collected within the first 2 days after death.

A novel method for determining postmortem interval based on the metabolomics of multiple organs combined with ensemble learning techniques

Determining postmortem interval (PMI) is one of the most challenging and essential endeavors in forensic science. Developments in PMI estimation can take advantage of machine learning techniques. Currently, applying an algorithm to obtain information on multiple organs and conducting joint analysis to accurately estimate PMI are still in the early stages. This study aimed to establish a multi-organ stacking model that estimates PMI by analyzing differential compounds of four organs in rats. In a total of 140 rats, skeletal muscle, liver, lung, and kidney tissue samples were collected at each time point after death. Ultra-performance liquid chromatography coupled with high-resolution mass spectrometry was used to determine the compound profiles of the samples. The original data were preprocessed using multivariate statistical analysis to determine discriminant compounds. In addition, three interrelated and increasingly complex patterns (single organ optimal model, single organ stacking model, multi-organ stacking model) were established to estimate PMI. The accuracy and generalized area under the receiver operating characteristic curve of the multi-organ stacking model were the highest at 93% and 0.96, respectively. Only 1 of the 14 external validation samples was misclassified by the multi-organ stacking model. The results demonstrate that the application of the multi-organ combination to the stacking algorithm is a potential forensic tool for the accurate estimation of PMI.

Cerebrospinal fluid in forensic toxicology: Current status and future perspectives

In forensic toxicology, alternative biological materials are very useful and important, e.g. in the case of lack of basic body fluids. One alternative biological material is cerebrospinal fluid (CSF). The procedures of the collection of biological material during the autopsy are performed in accordance with local, usually national recommendations, which most often require updating. It is very difficult to assess the possibility of using CSF as an alternative biological material for toxicological studies for the presence of drugs, intoxicants, including new psychoactive substances (commonly known as designer drugs), psychotropic substances, and ethyl alcohol, based on current data. Previous research suggests that CSF may be useful in toxicological studies, but these aspects need to be investigated more carefully because studies have collected CSF from different sites and often the results of different authors are not comparable. It would be necessary to prepare guidelines, e.g. the site of CSF collection that may influence the results of quantitative analysis. It would also be necessary to replicate some studies with a different collection site or a more recent analytical technique, e.g. for comparative testing of blood ethanol and cerebrospinal fluid. Cerebrospinal fluid can be a valuable information carrier in the absence of classic biological material from an autopsy. Investigating these aspects in more detail could allow the future use of this alternative material for routine toxicology analyzes in a forensic laboratory.

Screening for Fatal Traumatic Brain Injuries in Cerebrospinal Fluid Using Blood-Validated CK and CK-MB Immunoassays

A single, specific, sensitive biochemical biomarker that can reliably diagnose a traumatic brain injury (TBI) has not yet been found, but combining different biomarkers would be the most promising approach in clinical and postmortem settings. In addition, identifying new biomarkers and developing laboratory tests can be time-consuming and economically challenging. As such, it would be efficient to use established clinical diagnostic assays for postmortem biochemistry. In this study, postmortem cerebrospinal fluid samples from 45 lethal TBI cases and 47 controls were analyzed using commercially available blood-validated assays for creatine kinase (CK) activity and its heart-type isoenzyme (CK-MB). TBI cases with a survival time of up to two hours showed an increase in both CK and CK-MB with moderate (CK-MB: AUC = 0.788, p < 0.001) to high (CK: AUC = 0.811, p < 0.001) diagnostic accuracy. This reflected the excessive increase of the brain-type CK isoenzyme (CK-BB) following a TBI. The results provide evidence that CK immunoassays can be used as an adjunct quantitative test aid in diagnosing acute TBI-related fatalities.

Tau protein in cerebrospinal fluid: a novel biomarker of the time of death?

BACKGROUND

Tau proteins are recognized biomarkers of neurodegeneration and neuronal damage in the cerebrospinal fluid (CSF). It has also been suggested that these CSF proteins could increase post-mortem due to neuronal death. The aim of this study was to investigate the changes in CSF total and phosphorylated tau (p-tau) levels in the early post-mortem interval (PMI), to determine whether these proteins could be relevant biomarkers of time since death.

METHODS

Tau and p-tau levels were measured by ELISA in lumbar and cisternal CSF samples from 82 corpses (46 men, 36 women, mean age: 72.4 ± 15.2 years) with a PMI < 12 h. Forty-eight of them were considered neurologically healthy at the time of death. Rectal and tympanic temperatures were also measured in 37 individuals, and two validated temperature-based methods of PMI estimation were applied (Henssge's nomogram and Baccino's method).

RESULTS

CSF tau and p-tau levels were significantly increased, with respective median values of 3315 pg/mL and 68.5 pg/mL in the whole cohort, while lower but still increased levels were observed in neurologically healthy patients. Sub-occipital punctures systematically provided higher tau and p-tau values (p < 0.0001). Despite a great inter-individual variability, the concentrations of both biomarkers were positively correlated with the early PMI, with the highest correlation for cisternal p-tau (r = 0.50, p < 0.0001 in the whole cohort; r = 0.58, p = 0.0003 in the neurologically healthy patients). Higher levels of CSF biomarkers were observed for PMI > 6 h versus PMI ≤ 6 h, the discriminatory power of the biomarkers being higher in the subgroup of neurologically healthy patients. Based on cut-off values obtained by ROC curve analysis, the CSF biomarkers could rectify or adjust the time interval provided by the temperature-based methods in a significant number of cases. A predictive model combining tympanic temperature and cisternal tau values was found to be particularly accurate to assign individuals according to their PMI (≤ or > 6 h), with a Se of 83% and a Sp of 100% (AUC = 0.95).

CONCLUSION

Our findings suggest that CSF tau and p-tau proteins could serve as potential biomarkers of time since death, in association with tympanic temperature. The practical applicability of such an integrated approach has to be assessed by further studies.

Bank vole prion protein extends the use of RT-QuIC assays to detect prions in a range of inherited prion diseases

The cerebrospinal fluid (CSF) real-time quaking-induced conversion assay (RT-QuIC) is an ultrasensitive prion amyloid seeding assay for diagnosis of sporadic Creutzfeldt-Jakob disease (CJD) but several prion strains remain unexplored or resistant to conversion with commonly used recombinant prion protein (rPrP) substrates. Here, bank vole (BV) rPrP was used to study seeding by a wide range of archived post-mortem human CSF samples from cases of sporadic, acquired and various inherited prion diseases in high throughput 384-well format. BV rPrP substrate yielded positive reactions in 70/79 cases of sporadic CJD [Sensitivity 88.6% (95% CI 79.5-94.7%)], 1/2 variant CJD samples, and 9/20 samples from various inherited prion diseases; 5/57 non-prion disease control CSFs had positive reactions, yielding an overall specificity of 91.2% (95% CI 80.1-97.1%). Despite limitations of using post-mortem samples and our results' discrepancy with other studies, we demonstrated for the first time that BV rPrP is susceptible to conversion by human CSF samples containing certain prion strains not previously responsive in conventional rPrPs, thus justifying further optimisation for wider diagnostic and prognostic use.

Metabolomics in postmortem cerebrospinal fluid diagnostics: a state-of-the-art method to interpret central nervous system-related pathological processes

In the last few years, quantitative analysis of metabolites in body fluids using LC/MS has become an established method in laboratory medicine and toxicology. By preparing metabolite profiles in biological specimens, we are able to understand pathophysiological mechanisms at the biochemical and thus the functional level. An innovative investigative method, which has not yet been used widely in the forensic context, is to use the clinical application of metabolomics. In a metabolomic analysis of 41 samples of postmortem cerebrospinal fluid (CSF) samples divided into cohorts of four different causes of death, namely, cardiovascular fatalities, isoIated torso trauma, traumatic brain injury, and multi-organ failure, we were able to identify relevant differences in the metabolite profile between these individual groups. According to this preliminary assessment, we assume that information on biochemical processes is not gained by differences in the concentration of individual metabolites in CSF, but by a combination of differently distributed metabolites forming the perspective of a new generation of biomarkers for diagnosing (fatal) TBI and associated neuropathological changes in the CNS using CSF samples.

Comparative use of aqueous humour 1H NMR metabolomics and potassium concentration for PMI estimation in an animal model

Estimation of the post-mortem interval (PMI) remains a matter of concern in the forensic scenario. Traditional and novel approaches are not yet able to fully address this issue, which relies on complex biological phenomena triggered by death. For this purpose, eye compartments may be chosen for experimental studies because they are more resistant to post-mortem modifications. Vitreous humour, in particular, has been extensively investigated, with potassium concentration ([K⁺]) being the marker that is better correlated with PMI estimation. Recently, a ¹H nuclear magnetic resonance (NMR) metabolomic approach based on aqueous humour (AH) from an animal model was proposed for PMI estimation, resulting in a robust and validated regression model. Here we studied the variation in [K⁺] in the same experimental setup. [K⁺] was determined through capillary ion analysis (CIA) and a regression analysis was performed. Moreover, it was investigated whether the PMI information related to potassium could improve the metabolome predictive power in estimating the PMI. Interestingly, we found that a part of the metabolomic profile is able to explain most of the information carried by potassium, suggesting that the rise in both potassium and metabolite concentrations relies on a similar biological mechanism. In the first 24-h PMI window, the AH metabolomic profile shows greater predictive power than [K⁺] behaviour, suggesting its potential use as an additional tool for estimating the time since death.