A metabolomic approach to animal vitreous humor topographical composition: a pilot study

PMI estimation through metabolomics and potassium analysis on animal vitreous humour

INTRODUCTION

The estimation of post-mortem interval (PMI) remains a major challenge in forensic science. Most of the proposed approaches lack the reliability required to meet the rigorous forensic standards.

OBJECTIVES

We applied ¹H NMR metabolomics to estimate PMI on ovine vitreous humour comparing the results with the actual scientific gold standard, namely vitreous potassium concentrations.

METHODS

Vitreous humour samples were collected in a time frame ranging from 6 to 86 h after death. Experiments were performed by using ¹H NMR metabolomics and ion capillary analysis. Data were submitted to multivariate statistical data analysis.

RESULTS

A multivariate calibration model was built to estimate PMI based on 47 vitreous humour samples. The model was validated with an independent test set of 24 samples, obtaining a prediction error on the entire range of 6.9 h for PMI < 24 h, 7.4 h for PMI between 24 and 48 h, and 10.3 h for PMI > 48 h. Time-related modifications of the ¹H NMR vitreous metabolomic profile could predict PMI better than potassium up to 48 h after death, whilst a combination of the two is better than the single approach for higher PMI estimation.

CONCLUSION

The present study, although in a proof-of-concept animal model, shows that vitreous metabolomics can be a powerful tool to predict PMI providing a more accurate estimation compared to the widely studied approach based on vitreous potassium concentrations.

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.

The Eye in Forensic Medicine: A Narrative Review

ABSTRACT

The eye, with its distinctive anatomy, not only reflects a wide variety of diseases in life but also undergoes a myriad of post-mortem changes. Consequently, the eye has long been an area of interest in forensic science, primarily for the estimation of post-mortem interval and therefore the time of death and also for assistance in ascertaining the cause of death. There has been significant progress in the knowledge of ophthalmic forensic science using new technologies which have allowed further possibilities to arise where understanding of this field can assist the forensic pathologist. This review aims to highlight the current knowledge which exists in this field and also to identify important avenues for further investigation. Post-mortem changes of the eye along with its current applications and challenges will be discussed. These include the important areas of post-mortem iris biometrics, pupil size correlation with post-mortem interval, use of point-of-care technology on vitreous humor, and the use of ophthalmic imaging in pediatric abusive head trauma.

The Vital Role of Thanatochemistry in the Postmortem Diagnostic of Diabetic Ketoacidosis-Case Report

Diabetic ketoacidosis (DKA) is a lethal acute hyperglycemic complication of diabetes mellitus (DM) and it represents the initial manifestation of DM in about 15-20% of cases in adults and about 30-40% of cases in children. Postmortem diagnosis of DKA can only be made by applying thanatochemistry. Biochemistry applied postmortem is viewed with skepticism by many practitioners in the forensic field, completely lacking in many forensic services around the world, and especially in the national ones. This article aims to underline the importance of the postmortem application of biochemistry by reviewing the case of a person in the third decade of life who died suddenly at home due to diabetic ketoacidosis (DKA), whose autopsy was performed at an early PMI of approximately 24 h. Routine postmortem examinations (macroscopic, anatomopathological, and toxicological) could not establish a clear cause of death. When attention was turned to biochemical determinations (i.e., determination of glycated hemoglobin, glucose and ketone bodies (acetone, beta-hydroxybutyrate) in the blood, vitreous humor, and cerebrospinal fluid), the identified values clarified the thanatogenic mechanisms by establishing the diagnosis of DKA.

Postmortem Ocular Findings in the Optical Coherence Tomography Era: A Proof of Concept Study Based on Six Forensic Cases

Postmortem analysis of the ocular globe is an important topic for forensic pathology and transplantology. Although crucial elements may be gathered from examining cadaveric eyes, the latter do not routinely undergo in-depth analysis. The paucity of quantitative and objective data that are obtainable using current, invasive necroscopic techniques is the main reason for the limited interest in this highly specialized procedure. The aim of the current study is to describe and to object for the first time the postmortem ocular changes by mean of portable optical coherence tomography for evaluating ocular tissues postmortem. The design involved the postmortem analysis (in situ, and without enucleation) of 12 eyes by portable spectral-domain Optical Coherence Tomography. The scans were performed, in corneal, retinal and angle modality at different intervals: <6 h, 6th, 12th, and 24th hour and after autopsy (25th-72nd hour). The morphological changes in the cornea, sclera, vitreous humor and aqueous humor were easy to explore and objectify in these tissues in first 72 h postmortem. On the other hand, the "in situ" observation of the retina was difficult due to the opacification of the lenses in the first 24 h after death.

Post-mortem ocular changes and time since death: Scoping review and future perspective

The forensics literature on the relationship between ocular changes and the postmortem interval (PMI) has traditionally focused on time-related variations in concentrations of metabolites and elements within the eye. However, structural changes within the eye over time deserve the same attention because there is significant evidence of their importance in determining the time since death. Therefore, we reviewed publications that provided substantial evidence on this issue. In light of our inclusion and exclusion criteria, 26 papers were eligible for review. On the basis of the ocular parameters considered, we grouped the reviewed evidence into eight thematic areas: corneal opacities, corneal thickness, drug-induced pupil diameter variations, retinal changes, segmentation of retinal vessels, intraocular pressure reduction, globe temperature and crystalline alterations. The most important and common limitations of the reviewed studies were small study populations (many were monocentric studies), absence of robust statistical methodology, use of mathematical models valid only in ideal conditions and validation only for short PMIs. Although many phenomena cannot be used to reliably estimate PMI, there is rigorous evidence suggesting that promising factors, including corneal thickness, require methodological innovations for application to forensics practice but could be used in the near future to reliably estimate the time since death.

Forensic NMR metabolomics: one more arrow in the quiver

INTRODUCTION

NMR metabolomics is increasingly used in forensics, due to the possibility of investigating both endogenous metabolic profiles and exogenous molecules that may help to describe metabolic patterns and their modifications associated to specific conditions of forensic interest.

OBJECTIVES

The aim of this work was to review the recent literature and depict the information provided by NMR metabolomics. Attention has been devoted to the identification of peculiar metabolic signatures and specific ante-mortem and post-mortem profiles or biomarkers related to different conditions of forensic concern, such as the identification of biological traces, the estimation of the time since death, and the exposure to drugs of abuse.

RESULTS AND CONCLUSION

The results of the described studies highlight how forensics can benefit from NMR metabolomics by gaining additional information that may help to shed light in several forensic issues that still deserve to be further elucidated.

Glutathione Improves the Antioxidant Activity of Vitamin C in Human Lens and Retinal Epithelial Cells: Implications for Vitreous Substitutes

PURPOSE

Tissues in the eye are particularly susceptible to oxidative damage due to light exposure. While vitamin C (ascorbic acid) has been noted as a vital antioxidant in the vitreous humor, its physiological concentration (1-2 mM) has been shown to be toxic to retinal and lens epithelial cells in in vitro cell culture. We have explored adding vitamin C to hydrogel vitreous substitutes as a potential therapeutic to prevent oxidative damage to intraocular tissues after vitrectomy. However, vitamin C degrades rapidly even when loaded at high concentrations, limiting its long-term effectiveness. Glutathione, another antioxidant found abundantly in the lens at concentrations of 2-10 mM, was proposed to be used in conjunction with vitamin C.

METHODS

Cell viability and reactive oxygen species activity of human retinal and lens epithelial cells treated with various combinations of vitamin C, glutathione, hydrogen peroxide, and a hydrogel vitreous substitute were determined using CellTiter-Glo luminescent cell viability assay and dichlorofluorescein assay, respectively. The vitamin C remaining in hydrogel vitreous substitute or glutathione-vitamin C solutions was determined using a microplate reader at 265 nm wavelength, compared against standard solutions with known concentrations.

RESULTS

Glutathione protected the lens and retinal cells from the negative effect of vitamin C on cell viability and prolonged the antioxidant effect of vitamin C in vitro. While the detected reading of pure vitamin C solution decreased rapidly from 100% to 10% by 3 days, glutathione provided a significant extension to vitamin C stability, with 70% remaining after 14 days when the glutathione was used at physiological concentrations found in the lens (2-10 mM).

CONCLUSIONS

These results indicate glutathione might be an effective addition to vitamin C in intraocular implants, including potential vitreous substitutes, and warrants additional studies on the effectiveness of the vitamin C - glutathione combination in preventing oxidative stress post-vitrectomy.

Gender differences in albumin and ascorbic acid in the vitreous antioxidant system

Ascorbic acid is present at high concentrations in the vitreous and plays a central role in vitreous redox chemistry. Albumin is the main protein in the vitreous with antioxidant properties and occurs in different oxidation states, which can be used as redox indicators, but have not been studied in the vitreous. This study, therefore, addressed the vitreous redox state of cysteine-34 of albumin in relation to the ascorbic acid content, which has been suggested to exert a main function in detoxifying reactive oxygen in the vitreous. A total of 58 vitreous samples obtained from patients undergoing vitrectomy were analyzed for (i) human mercaptalbumin (HMA), the reduced thiol form; (ii) human non-mercaptalbumin1 (HNA1), a reversible oxidative modification with a disulfide at cysteine-34; and (iii) human non-mercaptalbumin2 (HNA2), a non-reversibly (highly) oxidized form of albumin; as well as (iv) ascorbic acid concentrations, to study possible relations. In addition, blood samples were taken to compare albumin redox state between plasma and the vitreous. Vitreous albumin showed greater variability in the redox state of cysteine-34 and a shift to the oxidized fractions compared to plasma albumin (P < 0.001). A strong positive relation was observed between the vitreous ascorbic acid concentrations and the reversibly oxidized form, HNA1 (P < 0.001), and a negative relation with the reduced form, HMA. Positive relations between ascorbic acid and HNA1 in the vitreous were stronger in men than in women. In contrast to HMA and HNA1, there was a distinct gender difference noted for the irreversibly oxidized form, HNA2. While males showed a positive relation between the vitreous ascorbic acid concentrations and HNA2, there was no correlation found with HNA2 in females. Our results support the view that ascorbic acid, by decreasing either directly or indirectly the concentrations of molecular oxygen, generates hydrogen peroxide, and that thiols, including HMA, are acting as antioxidants. This study for the first time provides evidence that vitreous albumin can be used as a marker molecule for the appearance of reactive oxygen species in the vitreous of patients undergoing vitrectomy. Moreover, it can be shown that there are gender differences in vitreous ascorbic acid and albumin concentrations as well as in oxidation state of vitreous albumin.

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.

The Bull's Eye Pattern of the Tear Film in Humans during Visual Fixation on En-Face Optical Coherence Tomography

The aim of the study was to define and characterize the optical behavior of the tear film during visual fixation in humans on en-face optical coherence tomography (OCT). We included 20 healthy participants, 60% female, aged from 25 to 42 years (33.05 ± 4.97 [mean ± SD]) and ten patients with severe dry eye, 50% female, aged from 26 to 42 years (33.7 ± 5.31). To perform high-resolution tear film imaging, participants were asked to gaze at the internal fixation point in the spectral-domain anterior segment OCT device, and meanwhile scanning session was executed at the following time-points after blinking: at the 2nd, 3rd, 4th, 5th, and 6th second. After one hour, OCT imaging was repeated (second session) by a different operator masked to the study to verify the reliability of results. During each measuring session, a pulse oximetry was used for continuously measuring the heart rate and oxygen saturation (SpO2%). A preliminary experiment was also performed to test the absence of geometric patterns from the anterior surface of a motionless artificial eye. OCT imaging showed a motionless, stable anterior surface of the artificial eye and in dry eye patients. Conversely, in the healthy participants of the study, a bull's eye pattern of the tear film was detected by OCT at the 2nd, 3rd, 4th, 5th, and 6th second after blinking, respectively, in 45%, 60%, 45%, 60%, and 40% of OCT scans during the first session, and in 35%, 65%, 65%, 60%, and 35% of cases in the second session. Overall, a total of 200 OCT scans were performed in normal human population. A significant correlation was found between the novel tear film pattern and heart rate during the first and the second session (p < 0.01) in healthy eyes. Conversely, no correlation was revealed with SpO2%. Intraclass correlation (ICC) analysis for OCT imaging of the tear film revealed a statistically significant reproducibility of the results (ICC = 0.838; p < 0.01), indicating the high level of reliability of the method, independently of heart rate and SpO2% variables. There exists a novel, geometric pattern of the tear film during visual fixation detectable by en-face OCT, which is mainly evident as heart rate increases. Its discovery implies in turn the presence of a specific vibration (or imperceptible motion) of the tear film that, at present, is not recognized and corrected by the OCT software (in image postprocessing) unlike other eyeball movements.

Metabolomics in the study of retinal health and disease

Metabolomics is the qualitative and quantitative assessment of the metabolites (small molecules < 1.5 kDa) in body fluids. The metabolites are the downstream of the genetic transcription and translation processes and also downstream of the interactions with environmental exposures; thus, they are thought to closely relate to the phenotype, especially for multifactorial diseases. In the last decade, metabolomics has been increasingly used to identify biomarkers in disease, and it is currently recognized as a very powerful tool with great potential for clinical translation. The metabolome and the associated pathways also help improve our understanding of the pathophysiology and mechanisms of disease. While there has been increasing interest and research in metabolomics of the eye, the application of metabolomics to retinal diseases has been limited, even though these are leading causes of blindness. In this manuscript, we perform a comprehensive summary of the tools and knowledge required to perform a metabolomics study, and we highlight essential statistical methods for rigorous study design and data analysis. We review available protocols, summarize the best approaches, and address the current unmet need for information on collection and processing of tissues and biofluids that can be used for metabolomics of retinal diseases. Additionally, we critically analyze recent work in this field, both in animal models and in human clinical disease, including diabetic retinopathy and age-related macular degeneration. Finally, we identify opportunities for future research applying metabolomics to improve our current assessment and understanding of mechanisms of vitreoretinal diseases, and to hence improve patient assessment and care.

Characterisation of the metabolome of ocular tissues and post-mortem changes in the rat retina

Time-dependent post-mortem biochemical changes have been demonstrated in donor cornea and vitreous, but there have been no published studies to date that objectively measure post-mortem changes in the retinal metabolome over time. The aim of the study was firstly, to investigate post-mortem, time-dependent changes in the rat retinal metabolome and secondly, to compare the metabolite composition of healthy rat ocular tissues. To study post-mortem changes in the rat retinal metabolome, globes were enucleated and stored at 4 °C and sampled at 0, 2, 4, 8, 24 and 48 h post-mortem. To study the metabolite composition of rat ocular tissues, eyes were dissected immediately after culling to isolate the cornea, lens, vitreous and retina, prior to storing at -80 °C. Tissue extracts were subjected to Gas Chromatograph Mass Spectrometry (GC-MS) and Ultra High Performance Liquid Chromatography Mass Spectrometry (UHPLC-MS). Generally, the metabolic composition of the retina was stable for 8 h post-mortem when eyes were stored at 4 °C, but showed increasing changes thereafter. However, some more rapid changes were observed such as increases in TCA cycle metabolites after 2 h post-mortem, whereas some metabolites such as fatty acids only showed decreases in concentration from 24 h. A total of 42 metabolites were identified across the ocular tissues by GC-MS (MSI level 1) and 2782 metabolites were annotated by UHPLC-MS (MSI level 2) according to MSI reporting standards. Many of the metabolites detected were common to all of the tissues but some metabolites showed partitioning between different ocular structures with 655, 297, 93 and 13 metabolites being uniquely detected in the retina, lens, cornea and vitreous respectively. Only a small percentage (1.6%) of metabolites found in the vitreous were only detected in the retina and not other tissues. In conclusion, mass spectrometry-based techniques have been used for the first time to compare the metabolic composition of different ocular tissues. The metabolite composition of the retina stored at 4 °C post-mortem is mostly stable for at least 8 h.

Introduction to metabolomics and its applications in ophthalmology

Metabolomics is the study of endogenous and exogenous metabolites in biological systems, which aims to provide comparative semi-quantitative information about all metabolites in the system. Metabolomics is an emerging and potentially powerful tool in ophthalmology research. It is therefore important for health professionals and researchers involved in the speciality to understand the basic principles of metabolomics experiments. This article provides an overview of the experimental workflow and examples of its use in ophthalmology research from the study of disease metabolism and pathogenesis to identification of biomarkers.

Spatial Variations in Vitreous Oxygen Consumption

We investigated the spatial variation of vitreous oxygen consumption in enucleated porcine eyes. A custom made oxygen source was fabricated that could be localized to either the mid or posterior vitreous cavity and steady state vitreous oxygen tension was measured as a function of distance from the source using a commercially available probe. The reaction rate constant of ascorbate oxidation was estimated ex vivo by measuring the change in oxygen tension over time using vitreous harvested from porcine eyes. Vitreous ascorbate from mid and posterior vitreous was measured spectrophotometrically. When the oxygen source was placed in either the mid-vitreous (N = 6) or the posterior vitreous (N = 6), we measured a statistically significant decrease in vitreous oxygen tension as a function of distance from the oxygen source when compared to control experiments without an oxygen source; (p<0.005 for mid-vitreous and p<0.018 for posterior vitreous at all distances). The mid-vitreous oxygen tension change was significantly different from the posterior vitreous oxygen tension change at 2 and 3mm distances from the respective oxygen source (p<0.001). We also found a statistically significant lower concentration of ascorbate in the mid-vitreous as compared to posterior vitreous (p = 0.02). We determined the reaction rate constant, k = 1.61 M^-1s^-1 ± 0.708 M^-1s^-1 (SE), of the oxidation of ascorbate which was modeled following a second order rate equation. Our data demonstrates that vitreous oxygen consumption is higher in the posterior vitreous compared to the mid-vitreous. We also show spatial variations in vitreous ascorbate concentration.

The "Other" Inositols and Their Phosphates: Synthesis, Biology, and Medicine (with Recent Advances in myo-Inositol Chemistry)

Cell signaling via inositol phosphates, in particular via the second messenger myo-inositol 1,4,5-trisphosphate, and phosphoinositides comprises a huge field of biology. Of the nine 1,2,3,4,5,6-cyclohexanehexol isomers, myo-inositol is pre-eminent, with "other" inositols (cis-, epi-, allo-, muco-, neo-, L-chiro-, D-chiro-, and scyllo-) and derivatives rarer or thought not to exist in nature. However, neo- and d-chiro-inositol hexakisphosphates were recently revealed in both terrestrial and aquatic ecosystems, thus highlighting the paucity of knowledge of the origins and potential biological functions of such stereoisomers, a prevalent group of environmental organic phosphates, and their parent inositols. Some "other" inositols are medically relevant, for example, scyllo-inositol (neurodegenerative diseases) and d-chiro-inositol (diabetes). It is timely to consider exploration of the roles and applications of the "other" isomers and their derivatives, likely by exploiting techniques now well developed for the myo series.

1H NMR Metabolomics Study of Spleen from C57BL/6 Mice Exposed to Gamma Radiation

Due to the potential risk of accidental exposure to gamma radiation, it’s critical to identify the biomarkers of radiation exposed creatures. In the present study, NMR based metabolomics combined with multivariate data analysis to evaluate the metabolites changed in the C57BL/6 mouse spleen after 4 days whole body exposure to 3.0 Gy and 7.8 Gy gamma radiations. Principal component analysis (PCA) and orthogonal projection to latent structures analysis (OPLS) are employed for classification and identification potential biomarkers associated with gamma irradiation. Two different strategies for NMR spectral data reduction (i.e., spectral binning and spectral deconvolution) are combined with normalize to constant sum and unit weight before multivariate data analysis, respectively. The combination of spectral deconvolution and normalization to unit weight is the best way for identifying discriminatory metabolites between the irradiation and control groups. Normalized to the constant sum may achieve some pseudo biomarkers. PCA and OPLS results shown that the exposed groups can be well separated from the control group. Leucine, 2-aminobutyrate, valine, lactate, arginine, glutathione, 2-oxoglutarate, creatine, tyrosine, phenylalanine, π-methylhistidine, taurine, myoinositol, glycerol and uracil are significantly elevated while ADP is decreased significantly. These significantly changed metabolites are associated with multiple metabolic pathways and may be potential biomarkers in the spleen exposed to gamma irradiation.

Monitoring the modifications of the vitreous humor metabolite profile after death: an animal model

We applied a metabolomic approach to monitor the modifications occurring in goat vitreous humor (VH) metabolite composition at different times (0, 6, 12, 18, and 24 hours) after death. The (1)H-NMR analysis of the VH samples was performed for the simultaneous determination of several metabolites (i.e., the metabolite profile) representative of the VH status at different times. Spectral data were analyzed by Principal Component Analysis (PCA) and by Orthogonal Projection to Latent Structures (OPLS) regression technique. PCA and OPLS suggested that different spectral regions were involved in time-related changes. The major time-related compositional changes, here detected, were the increase of lactate, hypoxanthine, alanine, total glutathione, choline/phosphocholine, creatine, and myo-inositol and the decrease of glucose and 3-hydroxybutyrate. We attempted a speculative interpretation of the biological mechanisms underlying these changes. These results show that multivariate statistical approach, based on (1)H NMR metabolite profiling, is a powerful tool for detecting ongoing differences in VH composition and may be applied to investigate several physiological and pathological conditions.