Postmortem muscle protein degradation in humans as a tool for PMI delimitation

The micro CT evaluation of crown and root pulp volume versus dentin thickness in teeth in postmortem interval (PMI)

Determining the postmortem interval (PMI) is one of the main study subjects of forensic sciences. The main purpose of this prospective in vitro study that was the Micro-CT evaluation of teeth crown and root pulp volume versus dentin thickness in terms of PMI determination. The study involved 60 female Wistar rats, with weights ranging from 270 to 320 g. These rats were grouped into six different post-mortem period categories. Following the animals' sacrifice, they were subjected to a natural putrefaction period, with a control group, in the grounds of a sheltered garden. Hemi-mandible samples were then extracted and placed in glass tubes for Micro-CT evaluations, following the progression of putrefaction processes. The pulp volume and dentin thickness were assessed using Micro-CT, and the gathered data underwent statistical analysis. Micro-CT was employed to analyze sixty right mandibular second molar teeth in the hemi-mandible. The crown pulp volume exhibited a reduction in group 6, with a value of 0.239 mm3 after a three-month period of natural putrefaction (p < 0.001). There is statistically differences among groups in case of pairwise comparison (p < 0.05). However, the root pulp volume and dentin thickness variables did not display any statistically significant changes. Despite certain limitations associated with this study, the Micro-CT findings concerning teeth pulp volume can serve as an objective parameter, especially for late postmortem investigations and the estimation of time of death.

Handheld hyperspectral imaging as a tool for the post-mortem interval estimation of human skeletal remains

In forensic medicine, estimating human skeletal remains' post-mortem interval (PMI) can be challenging. Following death, bones undergo a series of chemical and physical transformations due to their interactions with the surrounding environment. Post-mortem changes have been assessed using various methods, but estimating the PMI of skeletal remains could still be improved. We propose a new methodology with handheld hyperspectral imaging (HSI) system based on the first results from 104 human skeletal remains with PMIs ranging between 1 day and 2000 years. To differentiate between forensic and archaeological bone material, the Convolutional Neural Network analyzed 65.000 distinct diagnostic spectra: the classification accuracy was 0.58, 0.62, 0.73, 0.81, and 0.98 for PMIs of 0 week-2 weeks, 2 weeks-6 months, 6 months-1 year, 1 year-10 years, and >100 years, respectively. In conclusion, HSI can be used in forensic medicine to distinguish bone materials >100 years old from those <10 years old with an accuracy of 98%. The model has adequate predictive performance, and handheld HSI could serve as a novel approach to objectively and accurately determine the PMI of human skeletal remains.

Effect of temporary freezing on postmortem protein degradation patterns

BACKGROUND

A precise determination of time since death plays a major role in forensic routine. Currently available techniques for estimating the postmortem interval (PMI) are restricted to specific time periods or cannot be applied for individual case-specific reasons. During recent years, it has been repeatedly demonstrated that Western blot analysis of postmortem muscle protein degradation can substantially contribute to overcome these limitations in cases with different background. Enabling to delimit time points at which certain marker proteins undergo distinct degradation events, the method has become a reasonable new tool for PMI delimitation under various forensic scenarios. However, additional research is yet required to improve our understanding of protein decomposition and how it is affected by intrinsic and extrinsic factors. Since there are temperature limits for proteolysis, and investigators are confronted with frozen corpses, investigation of the effects of freezing and thawing on postmortem protein decomposition in the muscle tissue is an important objective to firmly establish the new method. It is also important because freezing is often the only practical means to intermittently preserve tissue samples from both true cases and animal model research.

METHODS

Sets of dismembered pig hind limbs, either freshly detached non-frozen, or thawed after 4 months of freeze-storage (n = 6 each), were left to decompose under controlled conditions at 30 °C for 7 days and 10 days, respectively. Samples of the M. biceps femoris were regularly collected at predefined time points. All samples were processed via SDS-PAGE and Western blotting to identify the degradation patterns of previously characterized muscle proteins.

RESULTS

Western blots show that the proteins degrade predictably over time in precise patterns that are largely unaffected by the freeze-and-thaw process. Investigated proteins showed complete degradation of the native protein band, partly giving rise to degradation products present in distinct time phases of the decomposition process.

CONCLUSION

This study provides substantial new information from a porcine model to assess the degree of bias that freezing and thawing induces on postmortem degradation of skeletal muscle proteins. Results support that a freeze-thaw cycle with prolonged storage in frozen state has no significant impact on the decomposition behavior. This will help to equip the protein degradation-based method for PMI determination with a robust applicability in the normal forensic setting.

Estimation of Late Postmortem Interval: Where Do We Stand? A Literature Review

Estimating time since death can be challenging for forensic experts, and is one of the most challenging activities concerning the forensic world. Various methods have been assessed to calculate the postmortem interval on dead bodies in different stages of decomposition and are currently widely used. Nowadays, the only well-recognized dating technique is carbon-14 radioisotope measurement, whereas other methods have been tested throughout the years involving different disciplines with different and sometimes not univocal results. Today, there is no precise and secure method to precisely determine time since death, and late postmortem interval estimation remains one of the most debated topics in forensic pathology. Many proposed methods have shown promising results, and it is desirable that with further studies some of them might become acknowledged techniques to resolve such a difficult and important challenge. The present review aims at presenting studies about the different techniques that have been tested in order to find a valuable method for estimating time since death for skeletal remains. By providing a comprehensive overview, the purpose of this work is to offer readers new perspectives on postmortem interval estimation and to improve current practice in the management of skeletal remains and decomposed bodies.

Morphological changes and protein degradation during the decomposition process of pig cadavers placed outdoors or in tents-a pilot study

The delimitation of the postmortem interval (PMI) is of utmost importance in forensic science. It is especially difficult to determine the PMI in advanced decomposition stages and/or when dead bodies are found under uncommon circumstances, such as tents, or other (semi-) enclosed environments. In such cases, especially when insect access is restricted, morphological assessment of body decomposition is one of the remaining approaches for delimitation of the PMI. However, as this method allows only vague statements/indications about the PMI, it is required to develop new and more reliable methods. One of the most important candidates is the biochemical analysis of protein degradation. In this regard, it has been demonstrated that specific skeletal muscle protein degradation patterns characterize certain time points postmortem and thus can be used as markers for PMI estimation. In order to test this method in different micro-environments, a pilot study using ten pig carcasses was conducted in summer in Northern Germany. The cadavers were openly placed outside (freely accessible for insects), as well as enclosed in tents nearby, and left to decompose to investigate decomposition processes over a time course of 10 days. Muscle samples of the M. biceps femoris were collected on a regular basis and processed via SDS-PAGE and degradation patterns of selected proteins identified by Western blotting. In addition, morphological changes of the cadavers during decomposition were assessed using the total body score (TBS). Results showed that postmortem protein degradation patterns are largely consistent between treatment groups (open field versus tents) despite major morphological differences in the decomposition rate. This field study provides evidence that muscle protein degradation is mostly unaffected by different levels of exposure, making it a sufficient candidate for PMI delimitation under various circumstances.

Evaluation of Muscle Proteins for Estimating the Post-Mortem Interval in Veterinary Forensic Pathology

Postmortem cadaveric changes are commonly used to estimate the postmortem interval (PMI) in humans and animals. However, these modifications have been poorly investigated in animals of interest to veterinary forensic pathology. The aim of this study was to investigate the potential use of muscle proteins (desmin and dystrophin) as biomarkers for estimating the PMI in dogs. For this study, 10 dead adult dogs were evaluated for 4 days in a temperature-controlled room at 19 ± 1 °C. For each animal, at 3, 24, 48, 72, and 96 h after death, a 1 × 1 × 1 cm cube of muscle tissue was removed from the vastus lateralis and triceps brachii. Protein expression levels were analyzed by immunohistochemical examination and immunoblot analysis. The obtained results showed rapid dystrophin degradation, with complete disappearance at 72 h after death. In contrast, desmin-positive fibers and desmin protein bands detected by immunoblot were observed on all 4 days of observation. Our findings suggest the potential use of muscle proteins as biomarkers for estimating the PMI in dogs.

Inositol pyrophosphate profiling reveals regulatory roles of IP6K2-dependent enhanced IP7 metabolism in the enteric nervous system

Inositol pyrophosphates regulate diverse physiological processes; to better understand their functional roles, assessing their tissue-specific distribution is important. Here, we profiled inositol pyrophosphate levels in mammalian organs using an originally designed liquid chromatography-mass spectrometry (LC-MS) protocol and discovered that the gastrointestinal tract (GIT) contained the highest levels of diphosphoinositol pentakisphosphate (IP₇) and its precursor inositol hexakisphosphate (IP₆). Although their absolute levels in the GIT are diet dependent, elevated IP₇ metabolism still exists under dietary regimens devoid of exogenous IP₇. Of the major GIT cells, enteric neurons selectively express the IP₇-synthesizing enzyme IP6K2. We found that IP6K2-knockout mice exhibited significantly impaired IP₇ metabolism in the various organs including the proximal GIT. In addition, our LC-MS analysis displayed that genetic ablation of IP6K2 significantly impaired IP₇ metabolism in the gut and duodenal muscularis externa containing myenteric plexus. Whole transcriptome analysis of duodenal muscularis externa further suggested that IP6K2 inhibition significantly altered expression levels of the gene sets associated with mature neurons, neural progenitor/stem cells, and glial cells, as well as of certain genes modulating neuronal differentiation and functioning, implying critical roles of the IP6K2-IP₇ axis in developmental and functional regulation of the enteric nervous system. These results collectively reveal an unexpected role of mammalian IP₇-a highly active IP6K2-IP₇ pathway is conducive to the enteric nervous system.

Combining with lab-on-chip technology and multi-organ fusion strategy to estimate post-mortem interval of rat

Background

The estimation of post-mortem interval (PMI) is one of the most important problems in forensic pathology all the time. Although many classical methods can be used to estimate time since death, accurate and rapid estimation of PMI is still a difficult task in forensic practice, so the estimation of PMI requires a faster, more accurate, and more convenient method.

Materials and methods

In this study, an experimental method, lab-on-chip, is used to analyze the characterizations of polypeptide fragments of the lung, liver, kidney, and skeletal muscle of rats at defined time points after death (0, 1, 2, 3, 5, 7, 9, 12, 15, 18, 21, 24, 27, and 30 days). Then, machine learning algorithms (base model: LR, SVM, RF, GBDT, and MLPC; ensemble model: stacking, soft voting, and soft-weighted voting) are applied to predict PMI with single organ. Multi-organ fusion strategy is designed to predict PMI based on multiple organs. Then, the ensemble pruning algorithm determines the best combination of multi-organ.

Results

The kidney is the best single organ for predicting the time of death, and its internal and external accuracy is 0.808 and 0.714, respectively. Multi-organ fusion strategy dramatically improves the performance of PMI estimation, and its internal and external accuracy is 0.962 and 0.893, respectively. Finally, the best organ combination determined by the ensemble pruning algorithm is all organs, such as lung, liver, kidney, and skeletal muscle.

Conclusion

Lab-on-chip is feasible to detect polypeptide fragments and multi-organ fusion is more accurate than single organ for PMI estimation.

Post-Mortem Interval and Microbiome Analysis through 16S rRNA Analysis: A Systematic Review

The determination of the Post-Mortem Interval (PMI) is an issue that has always represented a challenge in the field of forensic science. Different innovative approaches, compared to the more traditional ones, have been tried over the years, without succeeding in being validated as successful methods for PMI estimation. In the last two decades, innovations in sequencing technologies have made it possible to generate large volumes of data, allowing all members of a bacterial community to be sequenced. The aim of this manuscript is to provide a review regarding new advances in PMI estimation through cadaveric microbiota identification using 16S rRNA sequencing, in order to correlate specific microbiome profiles obtained from different body sites to PMI. The systematic review was performed according to PRISMA guidelines. For this purpose, 800 studies were identified through database searching (Pubmed). Articles that dealt with PMI estimation in correlation with microbiome composition and contained data about species, body site of sampling, monitoring time and sequencing method were selected and ultimately a total of 25 studies were considered. The selected studies evaluated the contribution of the various body sites to determine PMI, based on microbiome sequencing, in human and animal models. The results of this systematic review highlighted that studies conducted on both animals and humans yielded results that were promising. In order to fully exploit the potential of the microbiome in the estimation of PMI, it would be desirable to identify standardized body sampling sites and specific sampling methods in order to align data obtained by different research groups.

New Trends in Immunohistochemical Methods to Estimate the Time since Death: A Review

The identification of a reliable and accurate post-mortem interval (PMI) is a major challenge in the field of forensic sciences and criminal investigation. Several laboratory techniques have recently been developed that offer a better contribution to the estimation of PMI, in addition to the traditional physical or physico-chemical (body cooling, lividity, radiocarbon dating, rigor mortis), chemical (autolysis), microbiological (putrefaction), entomological, as well as botanical parameters. Molecular biology (degradation pattern of macromolecules such as proteins, DNA, RNA), biochemical analysis of biological fluids (such as blood, cerebrospinal fluid, and vitreous humor), and immunohistochemistry are some of the most recent technological innovations. A systematic review of the literature was performed with the aim of presenting an up-to-date overview on the correlation between the immunohistochemical (IHC) expression of specific antigenic markers at different PMIs. The systematic review was performed according to PRISMA guidelines. Scopus and PubMed were used as search engines from January 1, 1998 to March 1, 2022 to evaluate the effectiveness of immunohistochemistry in estimating PMI. The following keywords were used: (immunohistochemical) OR (immunohistochemistry) AND (time since death) OR (post-mortem interval) OR (PMI). A total of 6571 articles were collected. Ultimately, 16 studies were included in this review. The results of this systematic review highlighted that IHC techniques, in association with traditional methods, add, in Bayesian terms, additional information to define a more accurate time of death and PMI. However, current IHC results are numerically limited and more data and studies are desirable in the near future.

Antigenicity Preservation Is Related to Tissue Characteristics and the Post-Mortem Interval: Immunohistochemical Study and Literature Review

The main aim of this study was to investigate the post-mortem proteolytic degradation process of selected tissue antigens and correlate it to the post-mortem interval. During the autopsy of 12 cadavers (time interval ranging 1 day–2 years after death) samples of skin, liver, kidney, and spleen were collected. All samples were formalin-fixed and paraffin-embedded. Four µm paraffin sections were used for hematoxylin–eosin staining and immunohistochemical analysis (Ki67, Vimentin, Pan cytokeratin, and CD20). Data reported here show that immunohistochemical reactivity preservation was related to the characteristics of the tissues. In particular, the most resistant tissue was the skin, where the autolysis phenomena were not appreciable before 5 days. On the contrary, the liver and the spleen underwent early autolysis, while the kidney displayed an early autolysis of the tubules and a late one of the glomeruli. As concerns specific antigens, immunoreactivity was lost earliest for nuclear antigens as compared to cytoplasmic ones. In conclusion, our results demonstrate that immunohistochemical detection of specific antigens may be useful in estimating the post-mortem interval, especially when we need to know whether the post-mortem interval is a few days or more than 7–10 days.

Application of Micro-Computed Tomography for the Estimation of the Post-Mortem Interval of Human Skeletal Remains

It is challenging to estimate the post-mortem interval (PMI) of skeletal remains within a forensic context. As a result of their interactions with the environment, bones undergo several chemical and physical changes after death. So far, multiple methods have been used to follow up on post-mortem changes. There is, however, no definitive way to estimate the PMI of skeletal remains. This research aimed to propose a methodology capable of estimating the PMI using micro-computed tomography measurements of 104 human skeletal remains with PMIs between one day and 2000 years. The present study indicates that micro-computed tomography could be considered an objective and precise method of PMI evaluation in forensic medicine. The measured parameters show a significant difference regarding the PMI for Cort Porosity p < 0.001, BV/TV p > 0.001, Mean1 p > 0.001 and Mean2 p > 0.005. Using a machine learning approach, the neural network showed an accuracy of 99% for distinguishing between samples with a PMI of less than 100 years and archaeological samples.

Systematic Review on Post-Mortem Protein Alterations: Analysis of Experimental Models and Evaluation of Potential Biomarkers of Time of Death

Estimating the post-mortem interval (PMI) is a very complex issue due to numerous variables that may affect the calculation. Several authors have investigated the quantitative and qualitative variations of protein expression on post-mortem biological samples in certain time intervals, both in animals and in humans. However, the literature data are very numerous and often inhomogeneous, with different models, tissues and proteins evaluated, such that the practical application of these methods is limited to date. The aim of this paper was to offer an organic view of the state of the art about post-mortem protein alterations for the calculation of PMI through the analysis of the various experimental models proposed. The purpose was to investigate the validity of some proteins as “molecular clocks” candidates, focusing on the evidence obtained in the early, intermediate and late post-mortem interval. This study demonstrates how the study of post-mortem protein alterations may be useful for estimating the PMI, although there are still technical limits, especially in the experimental models performed on humans. We suggest a protocol to homogenize the study of future experimental models, with a view to the next concrete application of these methods also at the crime scene.

Insights into the Differential Preservation of Bone Proteomes in Inhumed and Entombed Cadavers from Italian Forensic Caseworks

Bone is a hard biological tissue and a precious reservoir of information in forensic investigations as it retains key biomolecules commonly used for identification purposes. Bone proteins have recently attracted significant interest for their potential in estimating post-mortem interval (PMI) and age at death (AAD). However, the preservation of such proteins is highly dependent on intrinsic and extrinsic factors that can hinder the potential application of molecular techniques to forensic sciences. The present study aims at investigating the effects that two commonly used types of burial practices (entombment and inhumation) have on bone protein survival. The sample consists of 14 exhumed individuals from cemeteries in Southern Italy with different AADs (29-85 years) and PMIs (1-37 years). LC-MS/MS analyses show that 16 proteins are better preserved under the entombed conditions and 4 proteins are better preserved under the inhumed conditions, whereas no clear differences are detected for post-translational protein modifications. Furthermore, several potential "stable" protein markers (i.e., proteins not affected by the burial environment) are identified for PMI and AAD estimation. Overall, these results show that the two burial environments play a role in the differential preservation of noncollagenous proteins, confirming the potential of LC-MS/MS-based proteomics in forensic sciences.

Post mortem computed tomography meets radiomics: a case series on fractal analysis of post mortem changes in the brain

Estimating the post-mortem interval is a fundamental, albeit challenging task in forensic sciences. To this aim, forensic practitioners need to assess post-mortem changes through a plethora of different methods, most of which are inherently qualitative, thus providing broad time intervals rather than precise determinations. This challenging problem is further complicated by the influence of environmental factors, which modify the temporal dynamics of post-mortem changes, sometimes in a rather unpredictable fashion. In this context, the search for quantitative and objective descriptors of post-mortem changes is highly demanded. In this study, we used computed tomography (CT) to assess the post-mortem anatomical modifications occurring in the time interval 0-4 days after death in the brain of four corpses. Our results show that fractal analysis of CT brain slices provides a set of quantitative descriptors able to map post-mortem changes over time throughout the whole brain. Although incapable of producing a direct estimation of the PMI, these descriptors could be used in combination with other more established methods to improve the accuracy and reliability of PMI determination.

Estimation of the time of death by measuring the variation of lateral cerebral ventricle volume and cerebrospinal fluid radiodensity using postmortem computed tomography

Using postmortem CT (PMCT), changes in the volume of the lateral cerebral ventricles (LCVs) and modifications of the radiodensity of cerebrospinal fluid (CSF) have been examined to identify a possible relationship between these changes and the time of death. Subsequent periodical CT scans termed "sequential scans" for ten corpses at known time of death were obtained, and a 3D segmentation of the entire LCV was carried out to measure its volume and radiodensity over time from ~ 5.5- h up to 273-h postmortem. A linear decrease of the LCV volume for all the cases was observed in the investigated time range, together with an overall logarithmic increase of radiodensity. Although a larger sampling should be performed to improve the result reliability, our finding suggests that the postmortem variation of CSF radiodensity can be a potentially useful tool in determining postmortem interval, a finding that is worthy of further investigation.

Role of molecular techniques in PMI estimation: An update

The time frames between death and reporting of the cadaver, known as post Mortem interval (PMI), is essential in investigation of homicide deaths, suspicious deaths, or other untimely deaths as well as natural deaths. Such information helps to connect the missing links in homicide or other relevant cases. Over the time several methods are developed which depends upon factors as several methods physiological, biochemical, entomological, and archaeological for the estimation of degradation of body with time. These methods lack precision, require expertise to achieve worthy results or authentic estimate. Although these methods are currently in use but, these evaluations are still unreliable and imprecise. Hence, we still need new methods for better estimation of PMI. Initially, the predictable morphological and chemical changes in cadaver are used as PMI indicators but, as the time since death increases, the above methods become less useful for as they can't pin point the time of death rather give a ballpark idea. With the advent of the field of molecular biology, the estimation of PMI is proposed to be executed by evaluating the degradation pattern of the biological markers (DNA, RNA, and Proteins). It is now proved that the DNA is fairly unwavering over long post-mortem phases, RNA is much more labile in nature, and sensitive to degradation in a tissue-specific manner. Thus, the main purpose (aim, agenda) of this document is to provide review that mainly focuses on potential use of RNA markers in estimation of PMI. For this Critical Review, the systematic evaluation of 47 studies is executed according to the chosen inclusion and exclusion criteria.

Dismembered porcine limbs as a proxy for postmortem muscle protein degradation

The estimation of the postmortem interval (PMI) is of critical importance in forensic routine. The most frequently applied methods, however, are all restricted to specific time periods or must be excluded under certain circumstances. In the last years it has been shown that the analysis of muscle protein degradation has the potential to contribute to according delimitations in practice. In particular, upon biochemical analysis, the specific time points of degradation events provide reasonable markers for PMI delimitation. Nevertheless, considerable research is yet required to increase the understanding of protein decomposition and how it is affected by individual and environmental influencing factors. This is best investigated under standardized conditions, however, a considerate selection of proxies, regarding costs, effort, and expected outcome is required. Here, we use pigs to compare muscle protein decomposition in whole bodies and dismembered body parts (amputated hind limbs). Not only do experiments on body parts reduce the costs and allow easier handling in basic research, but also they aid to investigate the practical application of PMI estimation in dismembered body parts, or other extensive injuries, which are not unusual scenarios in crime investigation. Specifically, we investigated whether there are differences in the degradation rates of selected muscle proteins, sampled from dismembered legs and from hind limbs attached to whole pig bodies. Our results show distinct time-dependent degradation patterns of muscle proteins in a predictable manner regardless of sample origin. We are able to demonstrate that amputated hind limbs are suitable proxies for the analysis of muscle protein degradation, especially to investigate certain influencing factors and establish according standardized models.

Influencing Factors on Postmortem Protein Degradation for PMI Estimation: A Systematic Review

The present review provides an overview of the current research status on the effects of influencing factors on postmortem protein degradation used to estimate the PMI (postmortem interval). Focus was set on characteristics of internal and external influencing factors and the respective susceptibility and/or robustness of protein degradation. A systematic literature search up to December 2020 was conducted on the effect of influencing factors investigated in the context of postmortem protein degradation in the tissues of animals and humans using the scientific databases PubMed and Google Scholar, as well as the reference lists of eligible articles. We identified ten studies investigating a total of seven different influencing factors in degrading tissues/organs (n = 7) of humans and animals using six different methodological approaches. Although comparison of study outcomes was impeded by the high variety of investigated factors, and by high risk of bias appraisals, it was evident that the majority of the influencing factors concerned affected protein degradation, thus being able to modulate the precision of protein degradation-based PMI estimation. The results clearly highlight the need for a thorough screening for corresponding factors to enable the introduction of appropriate correction factors and exclusion criteria. This seems especially relevant for the protein degradation-based study of human PMI to increase the reliability and precision of the method and to facilitate a broader applicability in routine forensic casework.

Evaluation of the detectability of early mandible fracture healing findings in terms of vitality aspect by using micro-CT technology in postmortem interval

The purpose of the present study was to investigate the vitality aspect of mandibular fractures using micro-CT in the analysis of bone mineral density and other bone microstructure trabecular parameters in the postmortem interval. This study included 72 female Wistar rats. In the study groups, the rats' mandibles were first fractured and after three days of living, the rats were sacrificed. In the control groups, the rats were sacrificed first and then the mandibles were fractured. All rats were left for a natural putrefaction period according to their group's time as week-0, week-1, week-2, week-4, week-8, and week-12. All fractured hemi-mandibles were scanned by micro-CT and analyzed in terms of BMD and other bone trabecular microstructures. BMD and the other bone trabecular microstructures, such as bone volume, percent bone volume, trabecular separation, and trabecular pattern factor, showed statistically significant differences in both the study and control groups (p ≤ 0.05). There were statistically significant differences between the study and control groups in comparisons of BMD in groups 1, 2, 3, 4 and 5, bone volume and percent bone volume in groups 1 and 3, bone surface and bone surface density in group 6, trabecular separation in group 1, and trabecular number, trabecular pattern factor, and structural model index in group 6. Micro-CT scanning and analysis of BMD and other bone trabecular microstructure parameters for evaluation of vitality aspects of mandible fractures in the PMI has various valuable results that should provide guidance for possible studies in the future.

Bone Diagenesis in Short Timescales: Insights from an Exploratory Proteomic Analysis

The evaluation of bone diagenetic phenomena in archaeological timescales has a long history; however, little is known about the origins of the microbes driving bone diagenesis, nor about the extent of bone diagenesis in short timeframes-such as in forensic contexts. Previously, the analysis of non-collagenous proteins (NCPs) through bottom-up proteomics revealed the presence of potential biomarkers useful in estimating the post-mortem interval (PMI). However, there is still a great need for enhancing the understanding of the diagenetic processes taking place in forensic timeframes, and to clarify whether proteomic analyses can help to develop better models for estimating PMI reliably. To address these knowledge gaps, we designed an experiment based on whole rat carcasses, defleshed long rat bones, and excised but still-fleshed rat limbs, which were either buried in soil or exposed on a clean plastic surface, left to decompose for 28 weeks, and retrieved at different time intervals. This study aimed to assess differences in bone protein relative abundances for the various deposition modalities and intervals. We further evaluated the effects that extrinsic factors, autolysis, and gut and soil bacteria had on bone diagenesis via bottom-up proteomics. Results showed six proteins whose abundance was significantly different between samples subjected to either microbial decomposition (gut or soil bacteria) or to environmental factors. In particular, muscle- and calcium-binding proteins were found to be more prone to degradation by bacterial attack, whereas plasma and bone marrow proteins were more susceptible to exposure to extrinsic agents. Our results suggest that both gut and soil bacteria play key roles in bone diagenesis and protein decay in relatively short timescales, and that bone proteomics is a proficient resource with which to identify microbially-driven versus extrinsically-driven diagenesis.

PP2A-C may be a promising candidate for postmortem interval estimation

Determining the postmortem interval (PMI) is an important task in forensic pathology. However, a reliable means of determining the PMI between 24 h and approximately 7 days after death has not yet been established. A previous study demonstrated that subunit A of protein phosphatase 2A (PP2A-A) is a promising candidate to estimate the PMI during the first 96 h. However, more detailed work is still needed to investigate PP2A's function in PMI estimation. PP2A is a serine/threonine phosphatase consisting of three subunits (PP2A-A, PP2A-B, and PP2A-C), and its activation is reflected by Tyr-307 phosphorylation of the catalytic subunit (P-PP2A-C). In this study, we speculated that the other two subunits of PP2A and the activation of PP2A may play different roles in estimating the PMI. For this purpose, mice were euthanized and stored at different temperatures (4, 15, and 25 °C). At each temperature, the musculus vastus lateralis was collected at different time points (0, 24, 48, and 96 h) to investigate the degradation of PP2A-B, PP2A-C, and P-PP2A-C (Tyr-307). Homocysteine (Hcy) was used to establish a hyperhomocysteinemia animal model to explore the effects of plasma Hcy on PMI estimation. The data showed not only that PP2A-C was more stable than PP2A-B, but also that it was not affected by homocysteine (Hcy). These characteristics make PP2A-C a promising candidate for short-term (24 h to 48 h) PMI estimation.

The applicability of forensic time since death estimation methods for buried bodies in advanced decomposition stages

Estimation of the postmortem interval in advanced postmortem stages is a challenging task. Although there are several approaches available for addressing postmortem changes of a (human) body or its environment (ecologically and/or biochemically), most are restricted to specific timeframes and/or individual and environmental conditions. It is well known, for instance, that buried bodies decompose in a remarkably different manner than on the ground surface. However, data on how established methods for PMI estimation perform under these conditions are scarce. It is important to understand whether and how postmortem changes are affected under burial conditions, if corrective factors could be conceived, or if methods have to be excluded for respective cases. We present the first multi-methodological assessment of human postmortem decomposition carried out on buried body donors in Europe, at the Amsterdam Research Initiative for Sub-surface Taphonomy and Anthropology (ARISTA) in the Netherlands. We used a multidisciplinary approach to investigate postmortem changes of morphology, skeletal muscle protein decomposition, presence of insects and other necrophilous animals as well as microbial communities (i.e., microbiomes) from August to November 2018 associated with two complete body exhumations and eight partial exhumations. Our results clearly display the current possibilities and limitations of methods for PMI estimation in buried remains and provide a baseline for future research and application.

Postmortem Protein Degradation as a Tool to Estimate the PMI: A Systematic Review

Objectives: We provide a systematic review of the literature to evaluate the current research status of protein degradation-based postmortem interval (PMI) estimation. Special attention is paid to the applicability of the proposed approaches/methods in forensic routine practice. Method: A systematic review of the literature on protein degradation in tissues and organs of animals and humans was conducted. Therefore, we searched the scientific databases Pubmed and Ovid for publications until December 2019. Additional searches were performed in Google Scholar and the reference lists of eligible articles. Results: A total of 36 studies were included. This enabled us to consider the degradation pattern of over 130 proteins from 11 different tissues, studied with different methods including well-established and modern approaches. Although comparison between studies is complicated by the heterogeneity of study designs, tissue types, methods, proteins and outcome measurement, there is clear evidence for a high explanatory power of protein degradation analysis in forensic PMI analysis. Conclusions: Although only few approaches have yet exceeded a basic research level, the current research status provides strong evidence in favor of the applicability of a protein degradation-based PMI estimation method in routine forensic practice. Further targeted research effort towards specific aims (also addressing influencing factors and exclusion criteria), especially in human tissue will be required to obtain a robust, reliable laboratory protocol, and collect sufficient data to develop accurate multifactorial mathematical decomposition models.

Intra- and intermuscular variations of postmortem protein degradation for PMI estimation

In recent years, protein decomposition has become of increasing interest for the use in forensic estimation of the postmortem interval (PMI). Especially skeletal muscle tissue has proven to be a prime target tissue, among other reasons, due to its large abundance in the human body. In this regard, it is important to know whether there are any intra- and intermuscular differences in the behavior of protein degradation. Thus, samples from different locations within several skeletal muscles as well as from cardiac and smooth muscle tissue samples were collected from three autopsy cases with varying degree of decomposition. Samples were analyzed by SDS-PAGE and Western blotting and compared for protein degradation patterns. Intramuscular variations turned out to be minimal and without major influence for the use of the method. Observed intermuscular differences provide possibilities for future improvement of the precision and temporal application range. The results of this study show the strengths and current limitations of protein degradation-based PMI estimation and provide a deeper understanding of intraindividual postmortem protein degradation processes.

Omics era in forensic medicine: towards a new age

Background/aim

Forensic medicine and sciences is a multidisciplinary branch of science, which frequently benefit from novel technologies. State of the art omics technologies have begun to be performed in forensic medicine and sciences, particularly in postmortem interval, intoxication, drugs of abuse, diagnosis of diseases and cause of death. This review aims to discuss the role and use of great omics (metabolomics, proteomics, genomics and transcriptomics) in forensic sciences, in detail.

Materials and methods

A detailed review of related literature was performed, and studies were subdivided as per the type of omics.

Results and conclusion

Omics seems as a revolutionary step in forensic science and sure carries it towards a new age. The number of forensic studies utilizing omics steadily increases in last years. Omics strategies should be used together in order to gather more accurate and certain data. Additional studies need to be performed to incorporate omics into routine forensic methodology.

A field study to evaluate PMI estimation methods for advanced decomposition stages

Estimating the postmortem interval (PMI) is one of the major tasks and a continuous challenge in forensic pathology. It is often an exclusion process of available methods, which ultimately can lead to an unsatisfactory outcome due to poor reliability. This problem is most acute in the late PMI, when decomposition proceeds and some methods (such as rigor, livor, and algor mortis) are no longer applicable. Several methods, such as forensic entomology, skeletal muscle protein degradation, and the study of body decomposition by application of a morphological scoring, are expected to provide further information; however, all have certain limitations and weaknesses. Availability of a tool-box of methods allows a case-specific selection of the most appropriate one(s), or eventually provides improvements in the overall accuracy and precision of the PMI estimation by merging and combining methods. To investigate practical (field) application, eventual interferences, and/or synergetic effects, as well as the robustness of these methods towards specific influencing factors, a field study was conducted, using eight pig cadavers of different body weights and physical coverage, left to decompose under natural conditions for 16 days. Morphological changes during decomposition were assessed using the total body score (TBS), muscle samples were collected to analyze protein degradation, and insect colonization was evaluated. The results reveal strengths and current limitations of all tested methods, as well as promising synergistic effects, and thus, provide a baseline for targeted future research.

Post-mortem changes in metabolomic profiles of human serum, aqueous humor and vitreous humor

INTRODUCTION

Application of metabolomic methods to forensic studies may expand the limits of the post-mortem interval (PMI) estimation, and improve the accuracy of the estimation. To this end, it is important to determine which tissue is the most suitable for analysis, and which compounds are the most promising candidates for PMI estimation.

OBJECTIVES

This work is aimed at the comparison of human serum, aqueous humor (AH), and vitreous humor (VH) as perspective tissues for metabolomic-based PMI estimation, at the determination of most promising PMI biomarkers, and at the development of method of PMI estimation based on the measurement of concentrations of PMI biomarkers.

METHODS

Quantitative metabolomic profiling of samples of the human serum, AH, and VH taken at different PMIs has been performed with the use of NMR spectroscopy.

RESULTS

It is found that the metabolomic changes in anatomically isolated ocular fluids are slower and smoother than that in blood. A good positive time correlation (Pearson coefficient r > 0.5) was observed for several metabolites, including hypoxanthine, choline, creatine, betaine, glutamate, and glycine. A model for PMI estimation based on concentrations of several metabolites in AH and VH is proposed.

CONCLUSIONS

The obtained results demonstrate that the metabolomic analysis of AH and VH is more suitable for the PMI estimation than that of serum. The compounds with good positive time correlation can be considered as potential PMI biomarkers.

Peptide analysis of mammalian decomposition fluid in relation to the post-mortem interval

We report the results of a semi-quantitative peptide analysis of decomposition fluid under field-based conditions in the absence of a soil matrix. Sixteen domestic pig (Sus scrofa domesticus) cadavers were used to model human decomposition in trials conducted in the summer and winter months in Western Australia. Physical characteristics were recorded and targeted peptide components of decomposition fluid were analysed using high performance liquid chromatography-triple quadrupole mass spectrometry. Principal component analysis identified 29 peptides, originating from haemoglobin subunits alpha and beta, creatine kinase, beta-enolase and lactate dehydrogenase, that contributed to differences in the mean peak areas of samples collected during the early period of decomposition (days 6-12 and day 2 in winter and summer, respectively) and during the later period (days 24-34 and days 8-10 in winter and summer, respectively). Fold changes for 8 peptides between these periods were significantly different. Three peptides derived from haemoglobin subunit beta, one from beta-enolase and two from lactate dehydrogenase displayed consistent trends, in that a notable increase in mean peak area was followed by a marked decrease in both the summer and winter samples. When temperature was accounted for, these trends occurred at different time points in summer and winter, indicating that factors other than temperature had impacted the rate of degradation of the proteins involved. The single peptides derived from haemoglobin subunit alpha and creatine kinase displayed consistent increases in mean peak area for the summer samples, suggesting that temperature played the most significant role in their degradation. Further analyses revealed that 7 peptides (one originating from haemoglobin subunit alpha, three from haemoglobin subunit beta and three from lactate dehydrogenase) displayed consistent trends that could be correlated with total body score and with the early stages of decomposition. The consistent trends (mean peak area versus time) for peptides derived from several proteins during decomposition trials conducted under different temperature regimes further emphasised the potential of peptide analysis in time since death estimation.

Feasibility Study of MRI Muscles Molecular Imaging in Evaluation of Early Post-Mortem Interval

Estimating early postmortem interval (EPI) is a difficult task in daily forensic activity due to limitations of accurate and reliable methods. The aim of the present work is to describe a novel approach in the estimation of EPI based on quantitative magnetic resonance molecular imaging (qMRMI) using a pig phantom since post-mortem degradation of pig meat is similar to that of human muscles. On a pig phantom maintained at 20° degree, using a 1.5 T MRI scanner we performed 10 scans (every 4 hours) monitoring apparent diffusion coefficient (ADC), fractional anisotropy (FA) magnetization transfer ration (MTR), tractography and susceptibility weighted changes in muscles until 36 hours after death. Cooling of the phantom during the experiment was recorded. Histology was also obtained. Pearson’s Test was carried out for time correlation between post-mortem interval and MRI data. We found a significative inverse correlation between ADC, FA, MT values and PMI. Our preliminary data shows that post-mortem qMRMI is a potential powerful tool in accurately determining EPI and is worth of further investigation.

The impact of environmental factors on the production of peptides in mammalian decomposition fluid in relation to the estimation of post-mortem interval: A summer/winter comparison in Western Australia

We report the peptide content of decomposition fluid produced under field-based conditions and in the absence of a soil matrix. Sixteen domestic pig (Sus scrofa domesticus) cadavers were used to model human decomposition in trials conducted in the summer and winter months in Western Australia. Physical characteristics were recorded and the peptide components of decomposition fluid were analysed using high performance liquid chromatography-time of flight mass spectrometry. A range of peptides was consistently detected in both summer and winter. Thirty seven peptides were common to both trials; 22 originating from haemoglobin subunit beta, 1 from haemoglobin subunit alpha, 4 from beta-enolase, and 2 from creatine kinase. In agreement with our previous findings, 13 peptides occurred consistently, regardless of trial conditions. Degradation patterns for haemoglobin subunits alpha and beta in summer and winter were similar when expressed in ADD and when adjusted for differences in temperature. The consistent identification of several protein-specific peptides generated during decomposition trials conducted under different temperature and rainfall regimes suggests that quantitative peptide analysis may be useful in estimating time since death.

An investigation on annular cartilage samples for post-mortem interval estimation using Fourier transform infrared spectroscopy

Many attempts have been made to estimate the post-mortem interval (PMI) using bioanalytical methods based on multiple biological samples. Cartilage tissues could be used as an alternative for this purpose because their rate of degradation is slower than that of other soft tissue or biofluid samples. In this study, we applied Fourier transform infrared (FTIR) spectroscopy to acquire bioinformation from human annular cartilages within 30 days post-mortem. Principal component analysis (PCA) showed that sex and causes of death have almost no impact on the overall spectral variations caused by post-mortem changes. With pre-processing approaches, several predicted models were established using a conventional machine learning method, known as the partial least square (PLS) regression. The best model achieved a satisfactory prediction with a low error of 1.49 days using the second derivative transform of 3-point smoothing and extended multiplicative scatter correction (EMSC), and the spectral regions from proteins and carbohydrates contributed greatly to the PMI prediction. This study demonstrates the feasibility of cartilage-based FTIR analysis for PMI estimation. Further work will introduce advanced algorithms for more accurate and precise PMI prediction.

A 1H NMR metabolomic approach for the estimation of the time since death using aqueous humour: an animal model

INTRODUCTION

The estimation of the time since death, or post-mortem interval (PMI), still remains a main conundrum in forensic science. Several approaches have been so far proposed from either a qualitative or a quantitative point of view, but they still lack reliability and robustness. Recently, metabolomics has shown to be a potential tool to investigate the time-related post-mortem metabolite modifications in animal models.

OBJECTIVES

Here we propose, for the first time, the use of a ¹H NMR metabolomic approach for the estimation of PMI from aqueous humour (AH) in an ovine model.

METHODS

AH samples were collected at different times after death (from 118 to 1429 min). ¹H NMR experiments were performed and spectral data analysed by multivariate statistical tools.

RESULTS

A multivariate calibration model was built to estimate PMI on the basis of the metabolite content of the samples. The model was validated with an independent test set, obtaining a prediction error of 59 min for PMI < 500 min, 104 min for PMI from 500 to 1000 min, and 118 min for PMI > 1000 min. Moreover, the metabolomic approach suggested a picture of the mechanisms underlying the post-mortem biological modifications, highlighting the role played by taurine, choline, and succinate.

CONCLUSION

The time-related modifications of the ¹H NMR AH metabolomic profile seem to be encouraging in addressing the issue of a reproducible and robust model to be employed for the estimation of the time since death.

Determining the time of death by morphological and immunohistochemical evaluation of collagen fibers in postmortem gingival tissues

The estimation of the post mortem interval (PMI) is still one of the most challenging variables to determine and the different approaches currently used in its estimation generally yield to large post mortem windows. In the present study we combined morphological and immunohistochemical analysis in order to reach a more detailed knowledge on tissue organization and degradation after death. Ultrastructural cellular changes and the extracellular matrix of gingival tissues, collected at different post mortem intervals, were observed by a Transmission Electron Microscopy (TEM), in combination with the immunohistochemical detection of extracellular matrix proteins (i.e. collagen type I and collagen type III) as potential post mortem biochemical markers. The final goal was to find a correlation between morphological modifications, biomarkers expression and the time of death. Samples of gingival tissues obtained from 10 cadavers at different post mortem intervals (short post mortem interval, 1-3 days; mid post mortem interval, 4-6 days; long post mortem interval, 7-9 days) were processed for light microscopy and TEM and they were also immunostained with anti-collagen type I and type III antibodies. Results showed gradual degradation of extracellular matrix in the suboral connective tissue in relation to the different time of death. Moreover PMI was related to an increase of nuclear chromatin condensation and cytoplasmic vacuolization both in epithelial and connective tissues. In conclusion, in addition to traditional forensic approaches to estimate PMI, the combined analyses of cellular morphology, ultrastructure and immunohistochemical expression of collagen proteins allow to better infer the PMI.

Postmortem proteomics to discover biomarkers for forensic PMI estimation

The assessment of postmortem degradation of skeletal muscle proteins has emerged as a novel approach to estimate the time since death in the early to mid-postmortem phase (approximately 24 h postmortem (hpm) to 120 hpm). Current protein-based methods are limited to a small number of skeletal muscle proteins, shown to undergo proteolysis after death. In this study, we investigated the usability of a target-based and unbiased system-wide protein analysis to gain further insights into systemic postmortem protein alterations and to identify additional markers for postmortem interval (PMI) delimitation. We performed proteomic profiling to globally analyze postmortem alterations of the rat and mouse skeletal muscle proteome at defined time points (0, 24, 48, 72, and 96 hpm), harnessing a mass spectrometry-based quantitative proteomics approach. Hierarchical clustering analysis for a total of 579 (rat) and 896 (mouse) quantified proteins revealed differentially expressed proteins during the investigated postmortem period. We further focused on two selected proteins (eEF1A2 and GAPDH), which were shown to consistently degrade postmortem in both rat and mouse, suggesting conserved intra- and interspecies degradation behavior, and thus preserved association with the PMI and possible transferability to humans. In turn, we validated the usefulness of these new markers by classical Western blot experiments in a rat model and in human autopsy cases. Our results demonstrate the feasibility of mass spectrometry-based analysis to discover novel protein markers for PMI estimation and show that the proteins eEF1A2 and GAPDH appear to be valuable markers for PMI estimation in humans.

Examination of the temporal variation of peptide content in decomposition fluid under controlled conditions using pigs as human substitutes

We report the preliminary observations of the peptide content of decomposition fluid produced under controlled laboratory conditions and in the absence of a soil matrix. Four domestic pig (Sus scrofa domesticus) cadavers were used to model human decomposition over a four-week trial period; physical characteristics were recorded and the peptide components of decomposition fluid was analysed using high performance liquid chromatography-time of flight mass spectrometry. Preliminary data analysis indicated that a range of peptides were consistently detected across the course of the trial period and 27 of these were common to all four cadavers; 22 originating from haemoglobin. The peptides associated with haemoglobin subunit alpha and beta displayed a breakdown pattern that remained consistent for all cadavers for the duration of the trial. Though identification of peptides during decomposition has potential for estimating the time since death, quantification of selected peptides is likely to be essential to identify time-dependent trends.

Postmortem protein stability investigations of the human hepatic drug-metabolizing cytochrome P450 enzymes CYP1A2 and CYP3A4 using mass spectrometry

Variability in expression and activity of hepatic drug-metabolizing cytochrome P450 (CYP) enzymes can play a causal role in fatal intoxication cases and is thus of forensic interest. We investigated the feasibility of LC-MS/MS based quantification and in vitro enzyme activity measurements of two major drug-metabolizing enzymes CYP1A2 and CYP3A4 in postmortem human liver microsomes (HLM). In autopsy cases (postmortem interval 24-36 h) we found CYP1A2 and CYP3A4 protein levels similar to that measured in a non-decayed reference HLM pool, whereas CYP1A2 and CYP3A4 enzyme activities were absent or severely decreased. Stability studies showed that CYP1A2 and CYP3A4 protein abundances were relatively stable in tissue stored in vitro for up to seven days at 4 °C. When tissue was stored for more than one day at 21 °C variable and case-specific decay patterns were observed, and CYP abundances declined especially after 3-4 days storage. Investigations of 50 autopsy cases revealed mean CYP1A2 and CYP3A4 levels of 49 and 47 pmol per mg HLM protein and inter-individual variabilities similar to those reported in other studies. This study supports postmortem quantification of CYP proteins in autopsy hepatic tissue by mass spectrometry. SIGNIFICANCE: This study indicates that MS-based detection of drug-metabolizing cytochrome P450 (CYP) proteins is achievable in postmortem hepatic tissue and that acceptable quantification data are obtainable but dependent on the storage conditions and postmortem sampling time. CYP abundance data could contribute to a conceivable way of assessing individual CYP activity phenotypes in a postmortem context.

Na+/K+-ATPase, acetylcholinesterase and glutathione S-transferase activities as new markers of postmortem interval in Swiss mice

Determining precisely the postmortem interval (PMI) is a key parameter for forensic researches, given that various physical, biochemical and metabolic changes begin to occur in the body after death. In the present study, the Na⁺/K⁺-ATPase, glutathione S-transferase (GST) and acetylcholinesterase (AChE) activities were evaluated. For this, male adult Swiss mice were killed by isoflurane inhalation anesthesia and divided into four groups according to time of death (0, 6, 24 and 48 h). The brain, liver, kidney and skeletal muscle tissues were removed. Our results revealed that at the time of 6 h, there was a decrease on Na⁺/K⁺-ATPase and GST activities in the brain and liver tissues, respectively. In addition, at this time point, an increase on renal GST activity was verified. At the time of 24 h, an increase on the cerebral AChE and renal GST activities was observed, while the cerebral Na⁺/K⁺-ATPase activity was decreased. Forty-eight hours after death, cerebral Na⁺/K⁺-ATPase and renal GST activities remained decreased and increased, respectively. In addition, no alteration was observed on the GST activity in the skeletal muscle and brain (in PMIs evaluated). The present study revealed that the brain and kidney (at the times of 24 and 48 h) were the tissues that suffered the most changes in almost all the enzymes evaluated. Our results demonstrated that enzyme activity assessments are reliable, easy-to-perform and low-cost determinations, and could be promising postmortem markers.

Association between protein profile and postmortem interval in human bone remains

Proteomic techniques in bones forensic samples are increasingly, being applied. The main aim of forensic sciences is the estimation of postmortem interval. Most current techniques are useful for the first post-mortem stages. However, in the case of osseous remains, these techniques may be difficult to use due to the high level of decomposition of the sample. Our objective was to attempt to know whether there is a protein profile in human bone remains that would enable a late postmortem. interval ranging from 5 to 20 years postmortem to be estimated. A total of 40 femur bones from 40 different cadavers (data range 5-20 years) were use. Of the 275 total proteins, we excluded the circulating ones (n = 227), leaving a total of 48 proteins (29 structural and 19 functional) were found. A multiple correspondence analysis was applied on the 48 proteins. Finally selecting 32 proteins that allowed us to discriminate between the. two groups of postmortem interval. Analysis of the protein profile present in bone permits an approximation of the date of death within the studied interval, and could be used to complement other tests for estimating the postmortem interval.

Application of Fourier transform infrared spectroscopy with chemometrics on postmortem interval estimation based on pericardial fluids

Postmortem interval (PMI) evaluation remains a challenge in the forensic community due to the lack of efficient methods. Studies have focused on chemical analysis of biofluids for PMI estimation; however, no reports using spectroscopic methods in pericardial fluid (PF) are available. In this study, Fourier transform infrared (FTIR) spectroscopy with attenuated total reflectance (ATR) accessory was applied to collect comprehensive biochemical information from rabbit PF at different PMIs. The PMI-dependent spectral signature was determined by two-dimensional (2D) correlation analysis. The partial least square (PLS) and nu-support vector machine (nu-SVM) models were then established based on the acquired spectral dataset. Spectral variables associated with amide I, amide II, COO-, C-H bending, and C-O or C-OH vibrations arising from proteins, polypeptides, amino acids and carbohydrates, respectively, were susceptible to PMI in 2D correlation analysis. Moreover, the nu-SVM model appeared to achieve a more satisfactory prediction than the PLS model in calibration; the reliability of both models was determined in an external validation set. The study shows the possibility of application of ATR-FTIR methods in postmortem interval estimation using PF samples.

Successive bacterial colonisation of pork and its implications for forensic investigations

AIMS

Bacteria are considered one of the major driving forces of the mammalian decomposition process and have only recently been recognised as forensic tools. At this point, little is known about their potential use as 'post-mortem clocks'. This study aimed to establish the proof of concept for using bacterial identification as post-mortem interval (PMI) indicators, using a multi-omics approach.

METHODS AND RESULTS

Pieces of pork were placed in the University's outdoor facility and surface swabs were taken at regular intervals up to 60 days. Terminal restriction fragment length polymorphism (T-RFLP) of the 16S rDNA was used to identify bacterial taxa. It succeeded in detecting two out of three key contributors involved in decomposition and represents the first study to reveal Vibrionaceae as abundant on decomposing pork. However, a high fraction of present bacterial taxa could not be identified by T-RFLP. Proteomic analyses were also performed at selected time points, and they partially succeeded in the identification of precise strains, subspecies and species of bacteria that colonized the body after different PMIs.

CONCLUSION

T-RFLP is incapable of reliably and fully identifying bacterial taxa, whereas proteomics could help in the identification of specific strains of bacteria. Nevertheless, microbial identification by next generation sequencing might be used as PMI clock in future investigations and in conjunction with information provided by forensic entomologists.

SIGNIFICANCE AND IMPACT OF THE STUDY

To the best of our knowledge, this work represents the first attempt to find a cheaper and easily accessible, culture-independent alternative to high-throughput techniques to establish a 'microbial clock', in combination with proteomic strategies to address this issue.