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.

Estimating the time of human decomposition based on skeletal muscle biopsy samples utilizing an untargeted LC-MS/MS-based proteomics approach.

Accurate estimation of the postmortem interval (PMI) is crucial in forensic medico-legal investigations to understand case circumstances (e.g. narrowing down list of missing persons or include/exclude suspects). Due to the complex decomposition chemistry, estimation of PMI remains challenging and currently often relies on the subjective visual assessment of gross morphological/taphonomic changes of a body during decomposition or entomological data. The aim of the current study was to investigate the human decomposition process up to 3 months after death and propose novel time-dependent biomarkers (peptide ratios) for the estimation of decomposition time. An untargeted liquid chromatography tandem mass spectrometry-based bottom-up proteomics workflow (ion mobility separated) was utilized to analyse skeletal muscle, collected repeatedly from nine body donors decomposing in an open eucalypt woodland environment in Australia. Additionally, general analytical considerations for large-scale proteomics studies for PMI determination are raised and discussed. Multiple peptide ratios (human origin) were successfully proposed (subgroups < 200 accumulated degree days (ADD), < 655 ADD and < 1535 ADD) as a first step towards generalised, objective biochemical estimation of decomposition time. Furthermore, peptide ratios for donor-specific intrinsic factors (sex and body mass) were found. Search of peptide data against a bacterial database did not yield any results most likely due to the low abundance of bacterial proteins within the collected human biopsy samples. For comprehensive time-dependent modelling, increased donor number would be necessary along with targeted confirmation of proposed peptides. Overall, the presented results provide valuable information that aid in the understanding and estimation of the human decomposition processes.

Do dried blood spots have the potential to support result management processes in routine sports drug testing?-Part 3: LC-MS/MS-based peptide analysis for dried blood spot sampling time point estimation.

Along with the recent acknowledgement of the World Anti-Doping Agency to use dried blood spot (DBS) samples for routine doping control purposes, there have been propositions to use DBS as a matrix that allows regular proactive remotely supervised self-sampling, providing potential longitudinal monitoring of an athlete's exposure to doping agents. However, several organizational aspects have to be considered before implementation, such as the verification of the sample collections time point. Based on a previous untargeted proteomics workflow utilizing liquid chromatography-high-resolution mass spectrometry (LC-HRMS) to identify protein/peptide markers to define the time since deposition of a bloodstain, the aim of the current study was to develop a targeted LC-HRMS/MS analytical method for promising peptidic target analytes. A long-term DBS storage experiment was carried out over a 3-month period (sample collection time points: 0, 2, 4, 7, 14, 21, 28, 42, 56, 70, 84 and 91 days) with DBS samples of 10 volunteers for longitudinal investigation of signal abundance changes of targeted peptide sequences at different storage temperatures (room temperature [RT], 4°C and -20°C). Prior to experimental analysis, LC-HRMS/MS method characteristics were successfully assessed, including intraday precision, carryover and sample extract stability. For estimation of DBS sample collection time points, ratios of two peptides that originate from the same protein prior to tryptic digestion were created. Two targeted peptide area ratios were found to significantly increase after being stored at RT for 28 days, representing potential markers for future use in routine doping controls that contribute to advancing complementary avenues in anti-doping.

Postmortem Metabolomics: Strategies to Assess Time-Dependent Postmortem Changes of Diazepam, Nordiazepam, Morphine, Codeine, Mirtazapine and Citalopram.

Postmortem redistribution (PMR) can result in artificial drug concentration changes following death and complicate forensic case interpretation. Currently, no accurate methods for PMR prediction exist. Hence, alternative strategies were developed investigating the time-dependent postmortem behavior of diazepam, nordiazepam, morphine, codeine, mirtazapine and citalopram. For 477 authentic postmortem cases, femoral blood samples were collected at two postmortem time-points. All samples were quantified for drugs of abuse (targeted; liquid chromatography-tandem mass spectrometry LC-MS/MS) and characterized for small endogenous molecules (untargeted; gas chromatography-high resolution MS (GC-HRMS). Trends for significant time-dependent concentration decreases (diazepam (n = 137), nordiazepam (n = 126)), increases (mirtazapine (n = 55), citalopram (n = 50)) or minimal median postmortem changes (morphine (n = 122), codeine (n = 92)) could be observed. Robust mathematical mixed effect models were created for the generalized postmortem behavior of diazepam and nordiazepam, which could be used to back-calculate drug concentrations towards a time-point closer to the estimated time of death (caution: inter-individual variability). Significant correlations between time-dependent concentration changes of morphine, mirtazapine and citalopram with individual endogenous molecules could be determined; no correlation was deemed strong enough for successful a posteriori estimation on the occurrence of PMR for specific cases. The current dataset did successfully lead to a significant knowledge gain in further understanding the time-dependent postmortem behavior of the studied drugs (of abuse).

Time- and Site-Dependent Postmortem Redistribution of Antidepressants and Neuroleptics in Blood and Alternative Matrices.

Postmortem redistribution (PMR) leads to challenges in postmortem case interpretation. Particularly antidepressants and neuroleptics are expected to undergo PMR based on their physico-chemical properties. For the current study, time- and site-dependent PMR of 20 antidepressants and neuroleptics were investigated in humans (authentic cases); five of which are discussed in detail (citalopram, mirtazapine, quetiapine, risperidone and venlafaxine) along with two metabolites (9-OH-risperidone and O-desmethylvenlafaxine). Blood [femoral (pB) and heart blood (HB)] and tissue biopsy samples (lung, kidney, liver, spleen, thigh muscle and adipose tissue) were collected upon admission to the institute utilizing a computed tomography-guided sample collection workflow (t1). Approximately 24 h later (t2; mean 23 ± 9.3 h), samples from the same body regions were collected manually. Liquid chromatography-tandem mass spectrometry was used for quantification. Most antidepressants and neuroleptics showed significant time-dependent concentration changes indicating the occurrence of PMR. For the first time, two phases of redistribution in pB for quetiapine were proposed (concentration decreases in the early postmortem phase, followed by concentration increases) and contrasting existing literature, both concentration increases and decreases in pB overtime were observed for risperidone and 9-OH-risperidone. Venlafaxine and its metabolite only showed minimal concentration changes, while citalopram exhibited a trend for concentration increases and mirtazapine for concentration decreases in pB overtime. Based on time-dependent tissue data, passive diffusion processes along the muscle-to-pB, liver-to-HB and lung-to-HB concentration gradients could be proposed along with bacterial degradation. Overall, no case interpretation had to be adjusted, which suggests that PMR changes of antidepressants and neuroleptics do not seem to be relevant for forensic case interpretation within the 24 h period that was investigated. However, limitations of the current study (e.g., temperature-controlled storage of the bodies) could have led to an underestimation of occurring postmortem changes, hence, interpretation of postmortem results should always be conducted with care, considering PMR phenomena and inter-individual variability.

Postmortem metabolomics: Correlating time-dependent concentration changes of xenobiotic and endogenous compounds.

Postmortem redistribution (PMR) describes the artificial postmortem concentration changes of xenobiotics that may pose major challenges in forensic toxicology. Only a few studies have systematically investigated time-dependent postmortem drug concentration changes so far and the a posteriori estimation of the occurrence of PMR is not yet possible. In this context, the general concept that postmortem biochemical changes in blood might parallel drug redistribution mechanisms seems promising. Thus, the current study investigated the possible correlations between time-dependent postmortem concentration changes of xenobiotic and endogenous compounds; exemplified for authentic morphine (n = 19) and methadone (n = 11) cases. Peripheral blood samples at two time-points postmortem were analyzed for morphine and methadone concentrations and an (un)targeted postmortem metabolomics approach was utilized to combine targeted quantitative analysis of 56 endogenous analytes and untargeted screening for endogenous compounds (characterizing 1174 features); liquid and gas chromatography-mass spectrometry was used respectively. Individual statistically significant correlations between morphine/methadone and endogenous compounds/features could be determined. Hence, the general applicability of the proposed concept could successfully be confirmed. To verify the reproducibility and robustness of the correlating behavior, a larger dataset must be analyzed next. Once a marker/set of markers is found (e.g. robust correlation with specific xenobiotic or xenobiotic class), these could be used as surrogates to further study the time-dependent PMR in a broader variety of cases (e.g. independent of a xenobiotic drug present). A crucial next step will also be the attempt to create a statistical model that allows a posteriori estimation of PMR occurrence of xenobiotics to assist forensic toxicologists in postmortem case interpretation.

Analytical considerations for postmortem metabolomics using GC-high-resolution MS.

Metabolomics studies that aim to qualitatively and quantitatively characterize the entirety of small endogenous biomolecules in an organism are widely conducted in the clinical setting. They also become more and more popular in the field of forensics (toxicology), e.g., to assist in postmortem investigations by objective postmortem interval estimation. However, other issues in postmortem toxicology, such as the phenomenon of (time-dependent) postmortem redistribution, have not yet been tackled by metabolomics studies. Hence, the aim of the current study was to develop an (un)targeted gas chromatography-high-resolution mass spectrometry-based method for endogenous metabolites as a tool for large-scale (un)targeted human postmortem metabolomics investigations (e.g., to objectively assess PMR) with thorough analytical evaluation of this method to ensure fitness-to-purpose in terms of reliability and robustness. This was achieved by using a targeted metabolite subset (n = 56) and a targeted processing workflow. Evaluation experiments have shown that using an artificial matrix (revised simulated body fluid (rSBF) + 5% bovine serum albumin (BSA)) for calibration purposes, all parameters lay within the scope of the method (sensitivity, selectivity, calibration model, accuracy, precision, processed sample stability, and extraction efficiency). When applying this method to large-scale studies, samples should be run in randomized order if analysis time is expected to exceed 18-24 h and potential biomarkers that are found with this method should be verified by a specialized, targeted method (e.g., by using standard addition in authentic matrix for quantification purposes). Overall, the current method can be successfully used for conduction of time-dependent postmortem metabolomics investigations. Graphical abstract.

Metabolomic Strategies in Biomarker Research-New Approach for Indirect Identification of Drug Consumption and Sample Manipulation in Clinical and Forensic Toxicology?

Drug of abuse (DOA) consumption is a growing problem worldwide, particularly with increasing numbers of new psychoactive substances (NPS) entering the drug market. Generally, little information on their adverse effects and toxicity are available. The direct detection and identification of NPS is an analytical challenge due to their ephemerality on the drug scene. An approach that does not directly focus on the structural detection of an analyte or its metabolites, would be beneficial for this complex analytical scenario and the development of alternative screening methods could help to provide fast response on suspected NPS consumption. A metabolomics approach might represent such an alternative strategy for the identification of biomarkers for different questions in DOA testing. Metabolomics is the monitoring of changes in small (endogenous) molecules (<1,000 Da) in response to a certain stimulus, e.g., DOA consumption. For this review, a literature search targeting "metabolomics" and different DOAs or NPS was conducted. Thereby, different applications of metabolomic strategies in biomarker research for DOA identification were identified: (a) as an additional tool for metabolism studies bearing the major advantage that particularly a priori unknown or unexpected metabolites can be identified; and (b) for identification of endogenous biomarker or metabolite patterns, e.g., for synthetic cannabinoids or also to indirectly detect urine manipulation attempts by chemical adulteration or replacement with artificial urine samples. The majority of the currently available literature in that field, however, deals with metabolomic studies for DOAs to better assess their acute or chronic effects or to find biomarkers for drug addiction and tolerance. Certain changes in endogenous compounds are detected for all studied DOAs, but often similar compounds/pathways are influenced. When evaluating these studies with regard to possible biomarkers for drug consumption, the observed changes appear, albeit statistically significant, too small to reliably work as biomarker for drug consumption. Further, different drugs were shown to affect the same pathways. In conclusion, metabolomic approaches possess potential for detection of biomarkers indicating drug consumption. More studies, including more sensitive targeted analyses, multi-variant statistical models or deep-learning approaches are needed to fully explore the potential of omics science in DOA testing.

Fatal poisoning involving cyclopropylfentanyl - Investigation of time-dependent postmortem redistribution.

A growing number of fatal overdoses involving opioid drugs, in particular involving fentanyl and its analogues, pose an immense threat to public health. Postmortem casework of forensic toxicologists in such cases is challenging, as data on pharmacodynamic and pharmacokinetic properties as well as reference values for acute toxicities and data on potential postmortem redistribution (PMR) mechanisms often do not exist. A fatal case involving cyclopropylfentanyl was investigated at the Zurich Institute of Forensic Medicine and the Zurich Forensic Science Institute; an unknown powder found at the scene was reliably identified as cyclopropylfentanyl by gas chromatography-infrared spectroscopy (GC-IR). Femoral blood samples were collected at two time points after death; 11h postmortem (t1) and during the medico-legal autopsy 29h after death (t2). At the autopsy, additional samples from the heart blood, urine and gastric content were collected. Cyclopropylfentanyl was quantified using a validated liquid chromatography-tandem mass spectrometric (LC-MS/MS) method. Femoral blood concentration of cyclopropylfentanyl at autopsy was 19.8ng/mL (t1=15.7ng/mL; heart blood concentration at autopsy=52.4ng/mL). In the light of the current literature and under the exclusion that no other morphological findings could explain the cause of death, contribution of cyclopropylfentanyl to death was proposed (polydrug use). Significant postmortem concentration increases of cyclopropylfentanyl in femoral blood during 18h after the first sampling were observed, thus indicating a relevant potential to undergo PMR. A central-to-peripheral blood concentration ratio of 2.6 supports this. Consequently, the current case suggests that postmortem cyclopropylfentanyl concentration should always be interpreted with care.

Untargeted metabolomics-like screening approach for chemical characterization and differentiation of canopic jar and mummy samples from Ancient Egypt using GC-high resolution MS.

In Ancient Egypt it was common practice to embalm corpses and specific internal organs to ensure eternal life. The exact nature of the employed embalming fluids, particularly for organ preservation within the canopic jars, is debated. Therefore, the aim of the current study, was to chemically characterize and differentiate canopic jars (n = 28) and mummies (n = 6) using gas chromatography - high resolution mass spectrometry (GC-HR MS) with a new untargeted metabolomics-like screening approach; as part of a larger minimal-invasive transdisciplinary study on Ancient Egyptian human tissues. Post-analytical data processing included deconvolution, screening against the NIST 14 spectral database as well as a high resolution metabolomics library, and positive peak evaluation. In the majority of samples the presence of a coniferous resin was indicated by the detection of longiborneol in combination with abietadiene acid derivatives and guajacol. Beeswax, proposedly used for symbolic reasons and/or as a binding agent, was detected in 10 samples. Previously not mentioned in the literature, but identified in the current sample set, were medical-related substances like aniseed constituents, salicylic acid, chamazulene and jacobine. By applying an untargeted metabolomics-like approach to archaeological samples for the first time, extensive statistical analysis was made possible (using both identified and non-identified features; adding up to 4381 features), which showed significant differences in the overall chemical composition of canopic jar and mummy samples using principle component analysis (PCA) and partial least square-discriminant analysis (PLS-DA). This emphasizes the necessity for more extensive canopic jar studies in the future in order to interpret findings correctly.

Time-Dependent Postmortem Redistribution of Opioids in Blood and Alternative Matrices.

Forensic postmortem case interpretation can be challenging, in particular due to postmortem redistribution (PMR) phenomena. Recent studies have shown that computed tomography (CT)-guided collection of biopsy samples using a robotic arm (virtobot) provides a valuable tool for systematic studies on time-dependent PMR. Utilizing this strategy, several cases involving opioid use such as methadone, fentanyl, tramadol, codeine, oxycodone and hydrocodone were evaluated for time-dependent concentration changes and potential redistribution mechanisms. Upon admission to the institute (t1), blood (femoral and right ventricle heart blood) and tissue biopsy samples (lung, kidney, liver, spleen, thigh muscle and adipose tissue) were collected utilizing CT-guided biopsy. Approximately 24 h later (t2; mean 28 ± 15 h), during the autopsy, samples from the same body regions were collected manually and in addition brain tissue, gastric content, urine and left ventricle heart blood. Analysis was conducted with liquid chromatography tandem mass spectrometry. Significant time-dependent methadone concentration increases in femoral blood (pB) indicate the occurrence of PMR, however, ultimately not relevant for forensic interpretation. The main metabolite of methadone, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), showed a less significant trend for PMR. Redistribution by passive diffusion along the muscle-to-pB concentration gradient seems likely for methadone, but not for EDDP. Results for fentanyl suggest extensive PMR. Other opioids such as tramadol, codeine, hydrocodone and oxycodone showed no consistent trend for significant PMR. Overall, CT-guided biopsy sampling proved to be a valuable tool for the investigation of PMR mechanisms.