Plasma succinate is a predictor of mortality in critically injured patients

Multiomics Signatures of Coagulopathy in a Polytrauma Swine Model Contrasted with Severe Multisystem Injured Patients

Trauma-induced coagulopathy (TIC) is a leading contributor to preventable mortality in severely injured patients. Understanding the molecular drivers of TIC is an essential step in identifying novel therapeutics to reduce morbidity and mortality. This study investigated multiomics and viscoelastic responses to polytrauma using our novel swine model and compared these findings with severely injured patients. Molecular signatures of TIC were significantly associated with perturbed coagulation and inflammation systems as well as extensive hemolysis. These results were consistent with patterns observed in trauma patients who had multisystem injuries. Here, intervention using resuscitative endovascular balloon occlusion of the aorta following polytrauma in our swine model revealed distinct multiomics alterations as a function of placement location. Aortic balloon placement in zone-1 worsened ischemic damage and mitochondrial dysfunction, patterns that continued throughout the monitored time course. While placement in zone-III showed a beneficial effect on TIC, it showed an improvement in effective coagulation. Taken together, this study highlights the translational relevance of our polytrauma swine model for investigating therapeutic interventions to correct TIC in patients.

When Our Best Friend Becomes Our Worst Enemy: The Mitochondrion in Trauma, Surgery, and Critical Illness

Common for major surgery, multitrauma, sepsis, and critical illness, is a whole-body inflammation. Tissue injury is able to trigger a generalized inflammatory reaction. Cell death causes release of endogenous structures termed damage associated molecular patterns (DAMPs) that initiate a sterile inflammation. Mitochondria are evolutionary endosymbionts originating from bacteria, containing molecular patterns similar to bacteria. These molecular patterns are termed mitochondrial DAMPs (mDAMPs). Mitochondrial debris released into the extracellular space or into the circulation is immunogenic and damaging secondary to activation of the innate immune system. In the circulation, released mDAMPS are either free or exist in extracellular vesicles, being able to act on every organ and cell in the body. However, the role of mDAMPs in trauma and critical care is not fully clarified. There is a complete lack of knowledge how they may be counteracted in patients. Among mDAMPs are mitochondrial DNA, cardiolipin, N-formyl peptides, cytochrome C, adenosine triphosphate, reactive oxygen species, succinate, and mitochondrial transcription factor A. In this overview, we present the different mDAMPs, their function, release, targets, and inflammatory potential. In light of present knowledge, the role of mDAMPs in the pathophysiology of major surgery and trauma as well as sepsis, and critical care is discussed.

Dimethyl malonate protects the lung in a murine model of acute respiratory distress syndrome

BACKGROUND

Succinate is a proinflammatory citric acid cycle metabolite that accumulates in tissues during pathophysiological states. Oxidation of succinate after ischemia-reperfusion leads to reversal of the electron transport chain and generation of reactive oxygen species. Dimethyl malonate (DMM) is a competitive inhibitor of succinate dehydrogenase, which has been shown to reduce succinate accumulation. We hypothesized that DMM would protect against inflammation in a murine model of ARDS.

METHODS

C57BL/6 mice were given ARDS via 67.7 μg of intratracheally administered lipopolysaccharide. Dimethyl malonate (50 mg/kg) was administered via tail vein injection 30 minutes after injury, then daily for 3 days. The animals were sacrificed on day 4 after bronchoalveolar lavage (BAL). Bronchoalveolar lavage cell counts were performed to examine cellular influx. Supernatant protein was quantified via Bradford protein assay. Animals receiving DMM (n = 8) were compared with those receiving sham injection (n = 8). Cells were fixed and stained with FITC-labeled wheat germ agglutinin to quantify the endothelial glycocalyx (EGX).

RESULTS

Total cell counts in BAL was less for animals receiving DMM (6.93 × 10 6 vs. 2.46 × 10 6 , p = 0.04). The DMM group had less BAL macrophages (168.6 vs. 85.1, p = 0.04) and lymphocytes (527.7 vs. 248.3; p = 0.04). Dimethyl malonate-treated animals had less protein leak in BAL than sham treated (1.48 vs. 1.15 μg/μl, p = 0.03). Treatment with DMM resulted in greater staining intensity of the EGX in the lung when compared with sham (12,016 vs. 15,186 arbitrary units, p = 0.03). Untreated animals had a greater degree of weight loss than treated animals (3.7% vs. 1.1%, p = 0.04). Dimethyl malonate prevented the upregulation of monocyte chemoattractant protein-1 (1.66 vs. 0.92 RE, p = 0.02) and ICAM-1 (1.40 vs. 1.01 RE, p = 0.05).

CONCLUSION

Dimethyl malonate reduces lung inflammation and capillary leak in ARDS. This may be mediated by protection of the EGX and inhibition of monocyte chemoattractant protein-1 and ICAM-1. Dimethyl malonate may be a novel therapeutic for ARDS.

Omics Signatures of Tissue Injury and Hemorrhagic Shock in Swine

OBJECTIVE

Advanced mass spectrometry methods were leveraged to analyze both proteomics and metabolomics signatures in plasma upon controlled tissue injury (TI) and hemorrhagic shock (HS)-isolated or combined-in a swine model, followed by correlation to viscoelastic measurements of coagulopathy via thrombelastography.

BACKGROUND

TI and HS cause distinct molecular changes in plasma in both animal models and trauma patients. However, the contribution to coagulopathy of trauma, the leading cause of preventable mortality in this patient population remains unclear. The recent development of a swine model for isolated or combined TI+HS facilitated the current study.

METHODS

Male swine (n=17) were randomized to either isolated or combined TI and HS. Coagulation status was analyzed by thrombelastography during the monitored time course. The plasma fractions of the blood draws (at baseline; end of shock; and at 30 minutes, 1, 2, and 4 hours after shock) were analyzed by mass spectrometry-based proteomics and metabolomics workflows.

RESULTS

HS-isolated or combined with TI-caused the most severe omic alterations during the monitored time course. While isolated TI delayed the activation of coagulation cascades. Correlation to thrombelastography parameters of clot strength (maximum amplitude) and breakdown (LY30) revealed signatures of coagulopathy which were supported by analysis of gene ontology-enriched biological pathways.

CONCLUSION

The current study provides a comprehensive characterization of proteomic and metabolomic alterations to combined or isolated TI and HS in a swine model and identifies early and late omics correlates to viscoelastic measurements in this system.

Untargeted metabolomics in the aqueous humor reveals the involvement of TAAR pathway in glaucoma

Understanding the metabolic dysfunctions and underlying complex pathological mechanisms of neurodegeneration in glaucoma could help discover disease pathways, identify novel biomarkers, and rationalize newer therapeutics. Therefore, we aimed to investigate the local metabolomic alterations in the aqueous humor and plasma of primary glaucomatous patients. This study cohort comprised primary open-angle glaucoma (POAG), primary angle-closure glaucoma (PACG), and cataract control groups. Aqueous humor and plasma samples were collected from patients undergoing trabeculectomy or cataract surgery and subjected to high-resolution mass spectrometry (HRMS) analysis. Spectral information was processed, and the acquired data were subjected to uni-variate as well as multi-variate statistical analyses using MetaboAnalyst ver5.0. To further understand the localized metabolic abnormalities in glaucoma, metabolites affected in aqueous humor were distinguished from metabolites altered in plasma in this study. Nine and twelve metabolites were found to be significantly altered (p < 0.05, variable importance of projection >1 and log2 fold change ≥0.58/≤ -0.58) in the aqueous humor of PACG and POAG patients, respectively. The galactose and amino acid metabolic pathways were locally affected in the PACG and POAG groups, respectively. Based on the observation of the previous findings, gene expression profiles of trace amine-associated receptor-1 (TAAR-1) were studied in rat ocular tissues. The pharmacodynamics of TAAR-1 were explored in rabbits using topical administration of its agonist, β-phenyl-ethylamine (β-PEA). TAAR-1 was expressed in the rat's iris-ciliary body, optic nerve, lens, and cornea. β-PEA elicited a mydriatic response in rabbit eyes, without altering intraocular pressure. Targeted analysis of β-PEA levels in the aqueous humor of POAG patients showed an insignificant elevation. This study provides new insights regarding alterations in both localized and systemic metabolites in primary glaucomatous patients. This study also demonstrated the propensity of β-PEA to cause an adrenergic response through the TAAR-1 pathway.

Omics markers of platelet transfusion in trauma patients

BACKGROUND

Even in the era of the COVID-19 pandemic, trauma remains the global leading cause of mortality under the age of 49. Trauma-induced coagulopathy is a leading driver of early mortality in critically ill patients, and transfusion of platelet products is a life-saving intervention to restore hemostasis in the bleeding patient. However, despite extensive functional studies based on viscoelastic assays, limited information is available about the impact of platelet transfusion on the circulating molecular signatures in trauma patients receiving platelet transfusion.

MATERIALS AND METHODS

To bridge this gap, we leveraged metabolomics and proteomics approaches to characterize longitudinal plasma samples (n = 118; up to 11 time points; total samples: 759) from trauma patients enrolled in the Control Of Major Bleeding After Trauma (COMBAT) study. Samples were collected in the field, in the emergency department (ED), and at intervals up to 168 h (7 days) post-hospitalization. Transfusion of platelet (PLT) products was performed (n = 30; total samples: 250) in the ED through 24 h post-hospitalization. Longitudinal plasma samples were subjected to mass spectrometry-based metabolomics and proteomics workflows. Multivariate analyses were performed to determine omics markers of transfusion of one, two, three, or more PLT transfusions.

RESULTS

Higher levels of tranexamic acid (TXA), inflammatory proteins, carnitines, and polyamines were detected in patients requiring PLT transfusion. Correlation of PLT units with omics data suggested sicker patients required more units and partially overlap with the population requiring transfusion of packed red blood cell products. Furthermore, platelet activation was likely increased in the most severely injured patients. Fatty acid levels were significantly lower in PLT transfusion recipients (at time of maximal transfusion: Hour 4) compared with non-recipients, while carnitine levels were significantly higher. Fatty acid levels restore later in the time course (e.g., post-PLT transfusion).

DISCUSSION

The present study provides the first multi-omics characterization of platelet transfusion efficacy in a clinically relevant cohort of trauma patients. Physiological alterations following transfusion were detected, highlighting the efficacy of mass spectrometry-based omics techniques to improve personalized transfusion medicine. More specialized clinical research studies focused on PLT transfusion, including organized pre and post transfusion sample collection and limitation to PLT products only, are required to fully understand subsequent metabolomic and proteomic alterations.

Metabolic Signatures of Performance in Elite World Tour Professional Male Cyclists

BACKGROUND AND OBJECTIVE

Metabolomics studies of recreational and elite athletes have been so far limited to venipuncture-dependent blood sample collection in the setting of controlled training and medical facilities. However, limited to no information is currently available to determine if findings in laboratory settings are translatable to a real-world scenario in elite competitions. The goal of this study was to define molecular signatures of exertion under controlled exercise conditions and use these signatures as a framework for assessing cycling performance in a World Tour competition.

METHODS

To characterize molecular profiles of exertion in elite athletes during cycling, we performed metabolomics analyses on blood isolated from 28 international-level, elite, World Tour professional male athletes from a Union Cycliste Internationale World Team taken before and after a graded exercise test to volitional exhaustion and before and after a long aerobic training session. Moreover, established signatures were then used to characterize the metabolic physiology of five of these cyclists who were selected to represent the same Union Cycliste Internationale World Team during a seven-stage elite World Tour race.

RESULTS

Using dried blood spot collection to circumvent logistical hurdles associated with field sampling, these studies defined metabolite signatures and fold change ranges of anaerobic or aerobic exertion in elite cyclists, respectively. Blood profiles of lactate, carboxylic acids, fatty acids, and acylcarnitines differed between exercise modes. The graded exercise test elicited significant two- to three-fold accumulations in lactate and succinate, in addition to significant elevations in free fatty acids and acylcarnitines. Conversely, the long aerobic training session elicited a larger magnitude of increase in fatty acids and acylcarnitines without appreciable increases in lactate or succinate. Comparable signatures were revealed after sprinting and climbing stages, respectively, in a World Tour race. In addition, signatures of elevated fatty acid oxidation capacity correlated with competitive performance.

CONCLUSIONS

Collectively, these studies provide a unique view of alterations in the blood metabolome of elite athletes during competition and at the peak of their performance capabilities. Furthermore, they demonstrate the utility of dried blood sampling for omics analysis, thereby enabling molecular monitoring of athletic performance in the field during training and competition.

The Intersection of Pulmonary Vascular Disease and Hypoxia-Inducible Factors

Hypoxia-inducible factors (HIFs) are a family of nuclear transcription factors that serve as the master regulator of the adaptive response to hypoxia. In the lung, HIFs orchestrate multiple inflammatory pathways and signaling. They have been reported to have a major role in the initiation and progression of acute lung injury, chronic obstructive pulmonary disease, pulmonary fibrosis, and pulmonary hypertension. Although there seems to be a clear mechanistic role for both HIF 1α and 2α in pulmonary vascular diseases including PH, a successful translation into a definitive therapeutic modality has not been accomplished to date.

Succinate metabolism and membrane reorganization drives the endotheliopathy and coagulopathy of traumatic hemorrhage

Acute hemorrhage commonly leads to coagulopathy and organ dysfunction or failure. Recent evidence suggests that damage to the endothelial glycocalyx contributes to these adverse outcomes. The physiological events mediating acute glycocalyx shedding are undefined, however. Here, we show that succinate accumulation within endothelial cells drives glycocalyx degradation through a membrane reorganization-mediated mechanism. We investigated this mechanism in a cultured endothelial cell hypoxia-reoxygenation model, in a rat model of hemorrhage, and in trauma patient plasma samples. We found that succinate metabolism by succinate dehydrogenase mediates glycocalyx damage through lipid oxidation and phospholipase A2-mediated membrane reorganization, promoting the interaction of matrix metalloproteinase 24 (MMP24) and MMP25 with glycocalyx constituents. In a rat hemorrhage model, inhibiting succinate metabolism or membrane reorganization prevented glycocalyx damage and coagulopathy. In patients with trauma, succinate levels were associated with glycocalyx damage and the development of coagulopathy, and the interaction of MMP24 and syndecan-1 was elevated compared to healthy controls.

Spontaneous reperfusion enhances succinate concentration in peripheral blood from stemi patients but its levels does not correlate with myocardial infarct size or area at risk

Succinate is enhanced during initial reperfusion in blood from the coronary sinus in ST-segment elevation myocardial infarction (STEMI) patients and in pigs submitted to transient coronary occlusion. Succinate levels might have a prognostic value, as they may correlate with edema volume or myocardial infarct size. However, blood from the coronary sinus is not routinely obtained in the CathLab. As succinate might be also increased in peripheral blood, we aimed to investigate whether peripheral plasma concentrations of succinate and other metabolites obtained during coronary revascularization correlate with edema volume or infarct size in STEMI patients. Plasma samples were obtained from peripheral blood within the first 10 min of revascularization in 102 STEMI patients included in the COMBAT-MI trial (initial TIMI 1) and from 9 additional patients with restituted coronary blood flow (TIMI 2). Metabolite concentrations were analyzed by ¹H-NMR. Succinate concentration averaged 0.069 ± 0.0073 mmol/L in patients with TIMI flow ≤ 1 and was significantly increased in those with TIMI 2 at admission (0.141 ± 0.058 mmol/L, p < 0.05). However, regression analysis did not detect any significant correlation between most metabolite concentrations and infarct size, extent of edema or other cardiac magnetic resonance (CMR) variables. In conclusion, spontaneous reperfusion in TIMI 2 patients associates with enhanced succinate levels in peripheral blood, suggesting that succinate release increases overtime following reperfusion. However, early plasma levels of succinate and other metabolites obtained from peripheral blood does not correlate with the degree of irreversible injury or area at risk in STEMI patients, and cannot be considered as predictors of CMR variables.Trial registration: Registered at www.clinicaltrials.gov (NCT02404376) on 31/03/2015. EudraCT number: 2015-001000-58.

Hypoxia-Inducible Factor 1α and Its Role in Lung Injury: Adaptive or Maladaptive

Hypoxia-inducible factors (HIFs) are transcription factors critical for the adaptive response to hypoxia. There is also an essential link between hypoxia and inflammation, and HIFs have been implicated in the dysregulated immune response to various insults. Despite the prevalence of hypoxia in tissue trauma, especially involving the lungs, there remains a dearth of studies investigating the role of HIFs in clinically relevant injury models. Here, we summarize the effects of HIF-1α on the vasculature, metabolism, inflammation, and apoptosis in the lungs and review the role of HIFs in direct lung injuries, including lung contusion, acid aspiration, pneumonia, and COVID-19. We present data that implicates HIF-1α in the context of arguments both in favor and against its role as adaptive or injurious in the propagation of the acute inflammatory response in lung injuries. Finally, we discuss the potential for pharmacological modulation of HIFs as a new class of therapeutics in the modern intensive care unit.

Metabolic correlates to critical speed in murine models of sickle cell disease

Introduction: Exercise intolerance is a common clinical manifestation in patients with sickle cell disease (SCD), though the mechanisms are incompletely understood. Methods: Here we leverage a murine mouse model of sickle cell disease, the Berkeley mouse, to characterize response to exercise via determination of critical speed (CS), a functional measurement of mouse running speed upon exerting to exhaustion. Results: Upon observing a wide distribution in critical speed phenotypes, we systematically determined metabolic aberrations in plasma and organs-including heart, kidney, liver, lung, and spleen-from mice ranked based on critical speed performances (top vs. bottom 25%). Results indicated clear signatures of systemic and organ-specific alterations in carboxylic acids, sphingosine 1-phosphate and acylcarnitine metabolism. Metabolites in these pathways showed significant correlations with critical speed across all matrices. Findings from murine models were thus further validated in 433 sickle cell disease patients (SS genotype). Metabolomics analyses of plasma from 281 subjects in this cohort (with HbA < 10% to decrease confounding effects of recent transfusion events) were used to identify metabolic correlates to sub-maximal exercise test performances, as measure by 6 min walking test in this clinical cohort. Results confirmed strong correlation between test performances and dysregulated levels of circulating carboxylic acids (especially succinate) and sphingosine 1-phosphate. Discussion: We identified novel circulating metabolic markers of exercise intolerance in mouse models of sickle cell disease and sickle cell patients.

Inhibition of Succinate Dehydrogenase by Pesticides (SDHIs) and Energy Metabolism

Succinate dehydrogenase (SDH) is one of the enzymes of the tricarboxylic acid cycle (Krebs cycle) and complex II of the mitochondrial respiratory chain. A class of fungicides (SDHIs) targets the complex II reaction in the SDH. A large number of those in use have been shown to inhibit SDH in other phyla, including humans. This raises questions about possible effects on human health and non-target organisms in the environment. The present document will address metabolic consequences in mammals; it is neither a review on SDH nor is it about the toxicology of SDHIs. Most clinically relevant observations are linked to a severe decrease in SDH activity. Here we shall examine the mechanisms for compensating a loss of SDH activity and their possible weaknesses or adverse consequences. It can be expected that a mild inhibition of SDH will be compensated by the kinetic properties of this enzyme, but this implies a proportionate increase in succinate concentration. This would be relevant for succinate signaling and epigenetics (not reviewed here). With regard to metabolism, exposure of the liver to SDHIs would increase the risk for non-alcoholic fatty liver disease (NAFLD). Higher levels of inhibition may be compensated by modification of metabolic fluxes with net production of succinate. SDHIs are much more soluble in lipids than in water; consequently, a different diet composition between laboratory animals and humans is expected to influence their absorption.

Endothelial Cell Phenotypes Demonstrate Different Metabolic Patterns and Predict Mortality in Trauma Patients

In trauma patients, shock-induced endotheliopathy (SHINE) is associated with a poor prognosis. We have previously identified four metabolic phenotypes in a small cohort of trauma patients (N = 20) and displayed the intracellular metabolic profile of the endothelial cell by integrating quantified plasma metabolomic profiles into a genome-scale metabolic model (iEC-GEM). A retrospective observational study of 99 trauma patients admitted to a Level 1 Trauma Center. Mass spectrometry was conducted on admission samples of plasma metabolites. Quantified metabolites were analyzed by computational network analysis of the iEC-GEM. Four plasma metabolic phenotypes (A-D) were identified, of which phenotype D was associated with an increased injury severity score (p < 0.001); 90% (91.6%) of the patients who died within 72 h possessed this phenotype. The inferred EC metabolic patterns were found to be different between phenotype A and D. Phenotype D was unable to maintain adequate redox homeostasis. We confirm that trauma patients presented four metabolic phenotypes at admission. Phenotype D was associated with increased mortality. Different EC metabolic patterns were identified between phenotypes A and D, and the inability to maintain adequate redox balance may be linked to the high mortality.

Succinate Activation of SUCNR1 Predisposes Severely Injured Patients to Neutrophil-mediated ARDS

OBJECTIVES

Identify the metabolites that are increased in the plasma of severely injured patients that developed ARDS versus severely injured patients that did not, and assay if these increased metabolites prime pulmonary sequestration of neutrophils (PMNs) and induce pulmonary sequestration in an animal model of ARDS. We hypothesize that metabolic derangement due to advanced shock in critically injured patients leads to the PMNs, which serves as the first event in the ARDS. Summary of Background Data: Intracellular metabolites accumulate in the plasma of severely injured patients.

METHODS

Untargeted metabolomics profiling of 67 critically injured patients was completed to establish a metabolic signature associated with ARDS development. Metabolites that significantly increased were assayed for PMN priming activity in vitro. The metabolites that primed PMNs were tested in a 2-event animal model of ARDS to identify a molecular link between circulating metabolites and clinical risk for ARDS.

RESULTS

After controlling for confounders, 4 metabolites significantly increased: creatine, dehydroascorbate, fumarate, and succinate in trauma patients who developed ARDS ( P < 0.05). Succinate alone primed the PMN oxidase in vitro at physiologically relevant levels. Intravenous succinate-induced PMN sequestration in the lung, a first event, and followed by intravenous lipopolysaccharide, a second event, resulted in ARDS in vivo requiring PMNs. SUCNR1 inhibition abrogated PMN priming, PMN sequestration, and ARDS. Conclusion: Significant increases in plasma succinate post-injury may serve as the first event in ARDS. Targeted inhibition of the SUCNR1 may decrease ARDS development from other disease states to prevent ARDS globally.

Apolipoprotein A-I, elevated in trauma patients, inhibits platelet activation and decreases clot strength

Apolipoprotein A-I (ApoA-I) is elevated in the plasma of a subgroup of trauma patients with systemic hyperfibrinolysis. We hypothesize that apoA-I inhibits platelet activation and clot formation. The effects of apoA-I on human platelet activation and clot formation were assessed by whole blood thrombelastography (TEG), platelet aggregometry, P-selectin surface expression, microfluidic adhesion, and Akt phosphorylation. Mouse models of carotid artery thrombosis and pulmonary embolism were used to assess the effects of apoA-I in vivo. The ApoA-1 receptor was investigated with transgenic mice knockouts (KO) for the scavenger receptor class B member 1 (SR-BI). Compared to controls, exogenous human apoA-I inhibited arachidonic acid and collagen-mediated human and mouse platelet aggregation, decreased P-selectin surface expression and Akt activation, resulting in diminished clot strength and increased clot lysis by TEG. ApoA-I also decreased platelet aggregate size formed on a collagen surface under flow. In vivo, apoA-I delayed vessel occlusion in an arterial thrombosis model and conferred a survival advantage in a pulmonary embolism model. SR-BI KO mice significantly reduced apoA-I inhibition of platelet aggregation versus wild-type platelets. Exogenous human apoA-I inhibits platelet activation, decreases clot strength and stability, and protects mice from arterial and venous thrombosis via the SR-BI receptor.

Omics Markers of Red Blood Cell Transfusion in Trauma

Red blood cell (RBC) transfusion is a life-saving intervention for millions of trauma patients every year worldwide. While hemoglobin thresholds are clinically driving the need for RBC transfusion, limited information is available with respect to transfusion efficacy at the molecular level in clinically relevant cohorts. Here, we combined plasma metabolomic and proteomic measurements in longitudinal samples (n = 118; up to 13 time points; total samples: 690) from trauma patients enrolled in the control of major bleeding after trauma (COMBAT) study. Samples were collected in the emergency department and at continuous intervals up to 168 h (seven days) post-hospitalization. Statistical analyses were performed to determine omics correlate to transfusions of one, two, three, five, or more packed RBC units. While confounded by the concomitant transfusion of other blood components and other iatrogenic interventions (e.g., surgery), here we report that transfusion of one or more packed RBCs—mostly occurring within the first 4 h from hospitalization in this cohort—results in the increase in circulating levels of additive solution components (e.g., mannitol, phosphate) and decreases in the levels of circulating markers of hypoxia, such as lactate, carboxylic acids (e.g., succinate), sphingosine 1-phosphate, polyamines (especially spermidine), and hypoxanthine metabolites with potential roles in thromboinflammatory modulation after trauma. These correlations were the strongest in patients with the highest new injury severity scores (NISS > 25) and lowest base excess (BE < −10), and the effect observed was proportional to the number of units transfused. We thus show that transfusion of packed RBCs transiently increases the circulating levels of plasticizers—likely leaching from the blood units during refrigerated storage in the blood bank. Changes in the levels of arginine metabolites (especially citrulline to ornithine ratios) are indicative of an effect of transfusion on nitric oxide metabolism, which could potentially contribute to endothelial regulation. RBC transfusion was associated with changes in the circulating levels of coagulation factors, fibrinogen chains, and RBC-proteins. Changes in lysophospholipids and acyl-carnitines were observed upon transfusion, suggestive of an effect on the circulating lipidome—though cell-extrinsic/intrinsic effects and/or the contribution of other blood components cannot be disentangled. By showing a significant decrease in circulating markers of hypoxia, this study provides the first multi-omics characterization of RBC transfusion efficacy in a clinically relevant cohort of trauma patients.

Metabolic systems analysis identifies a novel mechanism contributing to shock in patients with endotheliopathy of trauma (EoT) involving thromboxane A2 and LTC4

Purpose

Endotheliopathy of trauma (EoT), as defined by circulating levels of syndecan-1 ≥ 40 ng/mL, has been reported to be associated with significantly increased transfusion requirements and a doubled 30-day mortality. Increased shedding of the glycocalyx points toward the endothelial cell membrane composition as important for the clinical outcome being the rationale for this study.

Results

The plasma metabolome of 95 severely injured trauma patients was investigated by mass spectrometry, and patients with EoT vs. non-EoT were compared by partial least square-discriminant analysis, identifying succinic acid as the top metabolite to differentiate EoT and non-EoT patients (VIP score = 3). EoT and non-EoT patients' metabolic flux profile was inferred by integrating the corresponding plasma metabolome data into a genome-scale metabolic network reconstruction analysis and performing a functional study of the metabolic capabilities of each group. Model predictions showed a decrease in cholesterol metabolism secondary to impaired mevalonate synthesis in EoT compared to non-EoT patients. Intracellular task analysis indicated decreased synthesis of thromboxanA2 and leukotrienes, as well as a lower carnitine palmitoyltransferase I activity in EoT compared to non-EoT patients. Sensitivity analysis also showed a significantly high dependence of eicosanoid-associated metabolic tasks on alpha-linolenic acid as unique to EoT patients.

Conclusions

Model-driven analysis of the endothelial cells' metabolism identified potential novel targets as impaired thromboxane A2 and leukotriene synthesis in EoT patients when compared to non-EoT patients. Reduced thromboxane A2 and leukotriene availability in the microvasculature impairs vasoconstriction ability and may thus contribute to shock in EoT patients. These findings are supported by extensive scientific literature; however, further investigations are required on these findings.

Retention of functional mitochondria in mature red blood cells from patients with sickle cell disease

Sickle cell disease (SCD) is an inherited blood disorder characterized by sickled red blood cells (RBCs), which are more sensitive to haemolysis and can contribute to disease pathophysiology. Although treatment of SCD can include RBC transfusion, patients with SCD have high rates of alloimmunization. We hypothesized that RBCs from patients with SCD have functionally active mitochondria and can elicit a type 1 interferon response. We evaluated blood samples from more than 100 patients with SCD and found elevated frequencies of mitochondria in reticulocytes and mature RBCs, as compared to healthy blood donors. The presence of mitochondria in mature RBCs was confirmed by flow cytometry, electron microscopy, and proteomic analysis. The mitochondria in mature RBCs were metabolically competent, as determined by enzymatic activities and elevated levels of mitochondria-derived metabolites. Metabolically-active mitochondria in RBCs may increase oxidative stress, which could facilitate and/or exacerbate SCD complications. Coculture of mitochondria-positive RBCs with neutrophils induced production of type 1 interferons, which are known to increase RBC alloimmunization rates. These data demonstrate that mitochondria retained in mature RBCs are functional and can elicit immune responses, suggesting that inappropriate retention of mitochondria in RBCs may play an underappreciated role in SCD complications and be an RBC alloimmunization risk factor.

Plasma Levels of Acyl-Carnitines and Carboxylic Acids Correlate With Cardiovascular and Kidney Function in Subjects With Sickle Cell Trait

Subjects with sickle cell trait (SCT) carry one copy of mutated β-globin gene at position E6V at the origin of the production of sickle hemoglobin (HbS). Indeed, individuals with SCT have both normal hemoglobin and HbS, in contrast to patients with sickle cell disease who inherited of two copies of the mutated gene. Although SCT is generally benign/asymptomatic, carriers may develop certain adverse outcomes such as renal complications, venous thromboembolism, exercise-induced rhabdomyolysis … However, little is known about whether similar metabolic pathways are affected in individuals with SCT and whether these metabolic derangements, if present, correlate to clinically relevant parameters. In this study, we performed metabolomics analysis of plasma from individuals with sickle cell trait (n = 34) compared to healthy controls (n = 30). Results indicated a significant increase in basal circulating levels of hemolysis markers, mono- (pyruvate, lactate), di- and tri-carboxylates (including all Krebs cycle intermediates), suggestive of systems-wide mitochondrial dysfunction in individuals with SCT. Elevated levels of kynurenines and indoles were observed in SCT samples, along with increases in the levels of oxidative stress markers (advanced glycation and protein-oxidation end-products, malondialdehyde, oxylipins, eicosanoids). Increases in circulating levels of acyl-carnitines and fatty acids were observed, consistent with increased membrane lipid damage in individuals with sickle cell trait. Finally, correlation analyses to clinical co-variates showed that alterations in the aforementioned pathways strongly correlated with clinical measurements of blood viscosity, renal (glomerular filtration rate, microalbuminuria, uremia) and cardiovascular function (carotid-femoral pulse wave velocity, blood pressure).

The Succinate Receptor SUCNR1 Resides at the Endoplasmic Reticulum and Relocates to the Plasma Membrane in Hypoxic Conditions

The GPCR SUCNR1/GPR91 exerts proangiogenesis upon stimulation with the Krebs cycle metabolite succinate. GPCR signaling depends on the surrounding environment and intracellular localization through location bias. Here, we show by microscopy and by cell fractionation that in neurons, SUCNR1 resides at the endoplasmic reticulum (ER), while being fully functional, as shown by calcium release and the induction of the expression of the proangiogenic gene for VEGFA. ER localization was found to depend upon N-glycosylation, particularly at position N8; the nonglycosylated mutant receptor localizes at the plasma membrane shuttled by RAB11. This SUCNR1 glycosylation is physiologically regulated, so that during hypoxic conditions, SUCNR1 is deglycosylated and relocates to the plasma membrane. Downstream signal transduction of SUCNR1 was found to activate the prostaglandin synthesis pathway through direct interaction with COX-2 at the ER; pharmacologic antagonism of the PGE₂ EP₄ receptor (localized at the nucleus) was found to prevent VEGFA expression. Concordantly, restoring the expression of SUCNR1 in the retina of SUCNR1-null mice renormalized vascularization; this effect is markedly diminished after transfection of the plasma membrane-localized SUCNR1 N8A mutant, emphasizing that ER localization of the succinate receptor is necessary for proper vascularization. These findings uncover an unprecedented physiologic process where GPCR resides at the ER for signaling function.

Dimethyl malonate slows succinate accumulation and preserves cardiac function in a swine model of hemorrhagic shock

BACKGROUND

Succinate (SI) is a citric acid cycle metabolite that accumulates in tissues during hemorrhagic shock (HS) due to electron transport chain uncoupling. Dimethyl malonate (DMM) is a competitive inhibitor of SI dehydrogenase, which has been shown to reduce SI accumulation and protect against reperfusion injury. Whether DMM can be therapeutic after severe HS is unknown. We hypothesized that DMM would prevent SI buildup during resuscitation (RES) in a swine model of HS, leading to better physiological recovery after RES.

METHODS

The carotid arteries of Yorkshire pigs were cannulated with a 5-Fr catheter. After placement of a Swan-Ganz catheter and femoral arterial line, the carotid catheters were opened and the animals were exsanguinated to a mean arterial pressure (MAP) of 45 mm. After 30 minutes in the shock state, the animals were resuscitated to a MAP of 60 mm using lactated ringers. A MAP above 60 mm was maintained throughout RES. One group received 10 mg/kg of DMM (n = 6), while the control received sham injections (n = 6). The primary end-point was SI levels. Secondary end-points included cardiac function and lactate.

RESULTS

Succinate levels increased from baseline to the 20-minute RES point in control, while the DMM cohort remained unchanged. The DMM group required less intravenous fluid to maintain a MAP above 60 (450.0 vs. 229.0 mL; p = 0.01). The DMM group had higher pulmonary capillary wedge pressure at the 20-minute and 40-minute RES points. The DMM group had better recovery of cardiac output and index during RES, while the control had no improvement. While lactate levels were similar, DMM may lead to increased ionized calcium levels.

DISCUSSION

Dimethyl malonate slows SI accumulation during HS and helps preserve cardiac filling pressures and function during RES. In addition, DMM may protect against depletion of ionized calcium. Dimethyl malonate may have therapeutic potential during HS.

Intestinal Dopamine Receptor D2 is Required for Neuroprotection Against 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Dopaminergic Neurodegeneration

A wealth of evidence has suggested that gastrointestinal dysfunction is associated with the onset and progression of Parkinson's disease (PD). However, the mechanisms underlying these links remain to be defined. Here, we investigated the impact of deregulation of intestinal dopamine D2 receptor (DRD2) signaling in response to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration. Dopamine/dopamine signaling in the mouse colon decreased with ageing. Selective ablation of Drd2, but not Drd4, in the intestinal epithelium, caused a more severe loss of dopaminergic neurons in the substantia nigra following MPTP challenge, and this was accompanied by a reduced abundance of succinate-producing Alleoprevotella in the gut microbiota. Administration of succinate markedly attenuated dopaminergic neuronal loss in MPTP-treated mice by elevating the mitochondrial membrane potential. This study suggests that intestinal epithelial DRD2 activity and succinate from the gut microbiome contribute to the maintenance of nigral DA neuron survival. These findings provide a potential strategy targeting neuroinflammation-related neurological disorders such as PD.

The Role of Mitochondria in the Immune Response in Critical Illness

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2022. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2022 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from https://link.springer.com/bookseries/8901 .

Integration of Metabolomic and Clinical Data Improves the Prediction of Intensive Care Unit Length of Stay Following Major Traumatic Injury

Recent advances in emergency medicine and the co-ordinated delivery of trauma care mean more critically-injured patients now reach the hospital alive and survive life-saving operations. Indeed, between 2008 and 2017, the odds of surviving a major traumatic injury in the UK increased by nineteen percent. However, the improved survival rates of severely-injured patients have placed an increased burden on the healthcare system, with major trauma a common cause of intensive care unit (ICU) admissions that last ≥10 days. Improved understanding of the factors influencing patient outcomes is now urgently needed. We investigated the serum metabolomic profile of fifty-five major trauma patients across three post-injury phases: acute (days 0–4), intermediate (days 5–14) and late (days 15–112). Using ICU length of stay (LOS) as a clinical outcome, we aimed to determine whether the serum metabolome measured at days 0–4 post-injury for patients with an extended (≥10 days) ICU LOS differed from that of patients with a short (<10 days) ICU LOS. In addition, we investigated whether combining metabolomic profiles with clinical scoring systems would generate a variable that would identify patients with an extended ICU LOS with a greater degree of accuracy than models built on either variable alone. The number of metabolites unique to and shared across each time segment varied across acute, intermediate and late segments. A one-way ANOVA revealed the most variation in metabolite levels across the different time-points was for the metabolites lactate, glucose, anserine and 3-hydroxybutyrate. A total of eleven features were selected to differentiate between <10 days ICU LOS vs. >10 days ICU LOS. New Injury Severity Score (NISS), testosterone, and the metabolites cadaverine, urea, isoleucine, acetoacetate, dimethyl sulfone, syringate, creatinine, xylitol, and acetone form the integrated biomarker set. Using metabolic enrichment analysis, we found valine, leucine and isoleucine biosynthesis, glutathione metabolism, and glycine, serine and threonine metabolism were the top three pathways differentiating ICU LOS with a p < 0.05. A combined model of NISS and testosterone and all nine selected metabolites achieved an AUROC of 0.824. Differences exist in the serum metabolome of major trauma patients who subsequently experience a short or prolonged ICU LOS in the acute post-injury setting. Combining metabolomic data with anatomical scoring systems allowed us to discriminate between these two groups with a greater degree of accuracy than that of either variable alone.

Red Blood Cell Metabolism in Pyruvate Kinase Deficient Patients

Background: Pyruvate kinase deficiency (PKD) is the most frequent congenital enzymatic defect of glycolysis, and one of the most common causes of hereditary non spherocytic hemolytic anemia. Therapeutic interventions are limited, in part because of the incomplete understanding of the molecular mechanisms that compensate for the metabolic defect.

Methods: Mass spectrometry-based metabolomics analyses were performed on red blood cells (RBCs) from healthy controls (n=10) and PKD patients (n=5).

Results: In PKD patients, decreases in late glycolysis were accompanied by accumulation of pentose phosphate pathway (PPP) metabolites, as a function of oxidant stress to purines (increased breakdown and deamination). Markers of oxidant stress included increased levels of sulfur-containing compounds (methionine and taurine), polyamines (spermidine and spermine). Markers of hypoxia such as succinate, sphingosine 1-phosphate (S1P), and hypoxanthine were all elevated in PKD subjects. Membrane lipid oxidation and remodeling was observed in RBCs from PKD patients, as determined by increases in the levels of free (poly-/highly-unsaturated) fatty acids and acyl-carnitines.

Conclusion: In conclusion, in the present study, we provide the first overview of RBC metabolism in patients with PKD. Though limited in scope, the study addresses the need for basic science to investigate pathologies targeting underrepresented minorities (Amish population in this study), with the ultimate goal to target treatments to health disparities.

Identification of disease- and headache-specific mediators and pathways in migraine using blood transcriptomic and metabolomic analysis

BACKGROUND

Recent data suggest that gene expression profiles of peripheral white blood cells can reflect changes in the brain. We aimed to analyze the transcriptome of peripheral blood mononuclear cells (PBMC) and changes of plasma metabolite levels of migraineurs in a self-controlled manner during and between attacks.

METHODS

Twenty-four patients with migraine were recruited and blood samples were collected in a headache-free (interictal) period and during headache (ictal) to investigate disease- and headache-specific alterations. Control samples were collected from 13 age- and sex-matched healthy volunteers. RNA was isolated from PBMCs and single-end 75 bp RNA sequencing was performed using Illumina NextSeq 550 instrument followed by gene-level differential expression analysis. Functional analysis was carried out on information related to the role of genes, such as signaling pathways and biological processes. Plasma metabolomic measurement was performed with the Biocrates MxP Quant 500 Kit.

RESULTS

We identified 144 differentially-expressed genes in PBMCs between headache and headache-free samples and 163 between symptom-free patients and controls. Network analysis revealed that enriched pathways included inflammation, cytokine activity and mitochondrial dysfunction in both headache and headache-free samples compared to controls. Plasma lactate, succinate and methionine sulfoxide levels were higher in migraineurs while spermine, spermidine and aconitate were decreased during attacks.

CONCLUSIONS

It is concluded that enhanced inflammatory and immune cell activity, and oxidative stress can play a role in migraine susceptibility and headache generation.

Biological and Clinical Factors Contributing to the Metabolic Heterogeneity of Hospitalized Patients with and without COVID-19

The Corona Virus Disease 2019 (COVID-19) pandemic represents an ongoing worldwide challenge. The present large study sought to understand independent and overlapping metabolic features of samples from acutely ill patients (n = 831) that tested positive (n = 543) or negative (n = 288) for COVID-19. High-throughput metabolomics analyses were complemented with antigen and enzymatic activity assays on plasma from acutely ill patients collected while in the emergency department, at admission, or during hospitalization. Lipidomics analyses were also performed on COVID-19-positive or -negative subjects with the lowest and highest body mass index (n = 60/group). Significant changes in amino acid and fatty acid/acylcarnitine metabolism emerged as highly relevant markers of disease severity, progression, and prognosis as a function of biological and clinical variables in these patients. Further, machine learning models were trained by entering all metabolomics and clinical data from half of the COVID-19 patient cohort and then tested on the other half, yielding ~78% prediction accuracy. Finally, the extensive amount of information accumulated in this large, prospective, observational study provides a foundation for mechanistic follow-up studies and data sharing opportunities, which will advance our understanding of the characteristics of the plasma metabolism in COVID-19 and other acute critical illnesses.

Rethinking succinate: an unexpected hormone-like metabolite in energy homeostasis

There has been an explosion of interest in the signaling capacity of energy metabolites. A prime example is the Krebs cycle substrate succinate, an archetypal respiratory substrate with functions beyond energy production as an intracellular and extracellular signaling molecule. Long associated with inflammation, emerging evidence supports a key role for succinate in metabolic processes relating to energy management. As the natural ligand for SUCNR1, a G protein-coupled receptor, succinate is akin to hormones and likely functions as a reporter of metabolism and stress. In this review, we reconcile new and old observations to outline a regulatory role for succinate in metabolic homeostasis. We highlight the importance of the succinate-SUCNR1 axis in metabolic diseases as an integrator of macrophage immune response, and we discuss new metabolic functions recently ascribed to succinate in specific tissues. Because circulating succinate has emerged as a promising biomarker in chronic metabolic diseases, a better understanding of the physiopathological role of the succinate-SUCNR1 axis in metabolism might open new avenues for clinical use in patients with obesity or diabetes.

Viscoelastic testing in oncology patients (including for the diagnosis of fibrinolysis): Review of existing evidence, technology comparison, and clinical utility

The quantification of the coagulopathic state associated with oncologic and hematologic diseases is imperfectly assessed by common coagulation tests such as prothrombin time, activated partial thromboplastin time, fibrinogen levels, and platelet count. These tests provide a static representation of a component of hemostatic integrity, presenting an incomplete picture of coagulation in these patients. Viscoelastic tests (VETs), such as rotational thromboelastometry (ROTEM) and thromboelastography (TEG), as whole blood analyses, provide data related to the cumulative effects of blood components and all stages of the coagulation and fibrinolytic processes. The utility of VETs has been demonstrated since the late 1960s in guiding blood component therapy for patients undergoing liver transplantation. Since then, the scope of viscoelastic testing has expanded to become routinely used for cardiac surgery, obstetrics, and trauma. In the past decade, VETs' expanded usage has been most significant in trauma resuscitation. However, use of VETs for patients with malignancy-associated coagulopathy (MAC) and hematologic malignancies is increasing. For the purposes of this narrative review, we discuss the similarities between trauma-induced coagulopathy (TIC) and MAC. These similarities center on the thrombomodulin-thrombin complex as it switches between the thrombin-activatable fibrinolysis inhibitor coagulation pathway and activating the protein C anticoagulation pathway. This produces a spectrum of coagulopathy and fibrinolytic alterations ranging from shutdown to hyperfibrinolysis that are common to TIC, MAC, and hematologic malignancies. There is expanding literature regarding the utility of TEG and ROTEM to describe the hemostatic integrity of patients with oncologic and hematologic conditions, which we review here.

Transfusion of Anaerobically or Conventionally Stored Blood After Hemorrhagic Shock

Background:

Resuscitation from hemorrhagic shock (HS) by blood transfusion restores oxygen (O₂) delivery and provides hemodynamic stability. Current regulations allow red blood cells (RBCs) to be stored and used for up to 42 days. During storage, RBCs undergo many structural and functional changes. These storage lesions have been associated with adverse events and increased mortality after transfusion, increasing the need for improved RBC storage protocols. This study evaluates the efficacy of anaerobically stored RBCs to resuscitate rats from severe HS compared with conventionally stored RBCs.

Methods and results:

Rat RBCs were stored under anaerobic, anaerobic/hypercapnic, or conventional conditions for a period of 3 weeks. Hemorrhage was induced by controlled bleeding, shock was maintained for 30 min, and RBCs were transfused to restore and maintain blood pressure near the prhemorrhage level. All storage conditions met current regulatory 24-h posttransfusion recovery requirements. Transfusion of anaerobically stored RBCs required significantly less RBC volume to restore and maintain hemodynamics. Anaerobic or anaerobic/hypercapnic RBCs restored hemodynamics better than conventionally stored RBCs. Resuscitation with conventionally stored RBCs impaired indices of left ventricular cardiac function, increased hypoxic tissue staining and inflammatory markers, and affected organ function compared with anaerobically stored RBCs.

Conclusions:

Resuscitation from HS via transfusion of anaerobically stored RBCs recovered cardiac function, restored hemodynamic stability, and improved outcomes.

Biological and Clinical Factors contributing to the Metabolic Heterogeneity of Hospitalized Patients with and without COVID-19

The Corona Virus Disease 2019 (COVID-19) pandemic represents an ongoing worldwide challenge. Exploratory studies evaluating the impact of COVID-19 infection on the plasma metabolome have been performed, often with small numbers of patients, and with or without relevant control data; however, determining the impact of biological and clinical variables remains critical to understanding potential markers of disease severity and progression. The present large study, including relevant controls, sought to understand independent and overlapping metabolic features of samples from acutely ill patients (n = 831), testing positive (n = 543) or negative (n = 288) for COVID-19. High-throughput metabolomics analyses were complemented with antigen and enzymatic activity assays on 831 plasma samples from acutely ill patients while in the emergency department, at admission, and during hospitalization. We then performed additional lipidomics analyses of the 60 subjects with the lowest and highest body mass index, either COVID-19 positive or negative. Omics data were correlated to detailed data on patient characteristics and clinical laboratory assays measuring coagulation, hematology and chemistry analytes. Significant changes in arginine/proline/citrulline, tryptophan/indole/kynurenine, fatty acid and acyl-carnitine metabolism emerged as highly relevant markers of disease severity, progression and prognosis as a function of biological and clinical variables in these patients. Further, machine learning models were trained by entering all metabolomics and clinical data from half of the COVID-19 patient cohort and then tested on the other half yielding ~ 78% prediction accuracy. Finally, the extensive amount of information accumulated in this large, prospective, observational study provides a foundation for follow-up mechanistic studies and data sharing opportunities, which will advance our understanding of the characteristics of the plasma metabolism in COVID-19 and other acute critical illnesses.

Analysis of the Plasma Metabolome after Trauma, Novel Circulating Sphingolipid Signatures, and In-Hospital Outcomes

BACKGROUND

Trauma is the leading cause of death and disability for individuals under age 55. Many severely injured trauma patients experience complicated clinical courses despite appropriate initial therapy. We sought to identify novel circulating metabolomic signatures associated with clinical outcomes following trauma.

STUDY DESIGN

Untargeted metabolomics and circulating plasma immune mediator analysis was performed on plasma collected during 3 post-injury time periods (<6 hours [h], 6 h-24h, day 2-day 5) in critically ill trauma patients enrolled between April 2004 and May 2013 at UPMC Presbyterian Hospital in Pittsburgh, PA. Inclusion criteria were age ≥ 18 years, blunt mechanism, ICU admission, and expected survival ≥ 24 h. Exclusion criteria were isolated head injury, spinal cord injury, and pregnancy. Exploratory endpoints included length of stay (overall and ICU), ventilator requirements, nosocomial infection, and Marshall organ dysfunction (MOD) score. The top 50 metabolites were isolated using repeated measures ANOVA and multivariate empirical Bayesian analysis for further study.

RESULTS

Eighty-six patients were included for analysis. Sphingolipids were enriched significantly (chi-square, p < 10^-6) among the top 50 metabolites. Clustering of sphingolipid patterns identified 3 patient subclasses: nonresponders (no time-dependent change in sphingolipids, n = 41), sphingosine/sphinganine-enhanced (n = 24), and glycosphingolipid-enhanced (n = 21). Compared with the sphingolipid-enhanced subclasses, nonresponders had longer mean length of stay, more ventilator days, higher MOD scores, and higher circulating levels of proinflammatory immune mediators IL-6, IL-8, IL-10, MCP1/CCL2, IP10/CXCL10, and MIG/CXCL9 (all p < 0.05), despite similar Injury Severity Scores (p = 0.12).

CONCLUSIONS

Metabolomic analysis identified broad alterations in circulating plasma sphingolipids after blunt trauma. Circulating sphingolipid signatures and their association with both clinical outcomes and circulating inflammatory mediators suggest a possible link between sphingolipid metabolism and the immune response to trauma.

Benford's law and metabolomics: A tale of numbers and blood

The Newcomb-Benford law - also known as the "law of anomalous numbers" or, more commonly, Benford's law - predicts that the distribution of the first significant digit of random numbers obtained from mixed probability distributions follows a predictable pattern and reveals some universal behavior. Specifically, given a dataset of empirical measures, the likelihood of the first digit of any number being 1 is ∼30 %, ∼18 % for 2, 12.5 % for 3 and so on, with a decreasing probability all the way to number 9. If the digits were distributed uniformly, all the numbers 1 through 9 would have the same probability to appear as the first digit in any given empirical random measurement. However, this is not the case, as this law defies common sense and seems to apply seamlessly to large data. The use of omics technologies and, in particular, metabolomics has generated a wealth of big data in the field of transfusion medicine. In the present meta-analysis, we focused on previous big data from metabolomics studies of relevance to transfusion medicine: one on the quality of stored red blood cells, one on the phenotypes of transfusion recipients, i.e. trauma patients suffering from trauma and hemorrhage, and one of relevance to the 2020 SARS-COV-2 global pandemic. We show that metabolomics data follow a Benford's law distribution, an observation that could be relevant for future application of the "law of anomalous numbers" in the field of quality control processes in transfusion medicine.

Impaired Succinate Response to a Mixed Meal in Obesity and Type 2 Diabetes Is Normalized After Metabolic Surgery

OBJECTIVE

To explore the meal response of circulating succinate in patients with obesity and type 2 diabetes undergoing bariatric surgery and to examine the role of gastrointestinal glucose sensing in succinate dynamics in healthy subjects.

RESEARCH DESIGN AND METHODS

Cohort I comprised 45 patients with morbid obesity and type 2 diabetes (BMI 39.4 ± 1.9 kg/m²) undergoing metabolic surgery. Cohort II was a confirmatory cohort of 13 patients (BMI 39.3 ± 1.4 kg/m²) undergoing gastric bypass surgery. Cohort III comprised 15 healthy subjects (BMI 26.4 ± 0.5 kg/m²). Cohorts I and II completed a 2-h mixed-meal tolerance test (MTT) before the intervention and at 1 year of follow-up, and cohort II also completed a 3-h lipid test (LT). Cohort III underwent a 3-h oral glucose tolerance test (OGTT) and an isoglycemic intravenous glucose infusion (IIGI) study.

RESULTS

In cohort I, succinate response to MTT at follow-up was greater than before the intervention (P < 0.0001). This response was confirmed in cohort II with a greater increase after 1 year of surgery (P = 0.009). By contrast, LT did not elicit a succinate response. Changes in succinate response were associated with changes in the area under the curve of glucose (r = 0.417, P < 0.0001) and insulin (r = 0.204, P = 0.002). In cohort III, glycemia, per se, stimulated a plasma succinate response (P = 0.0004), but its response was greater in the OGTT (P = 0.02; OGTT versus IIGI).

CONCLUSIONS

The meal-related response of circulating succinate in patients with obesity and type 2 diabetes is recovered after metabolic surgery.

Characterization of Acidosis in Trauma Patient

Background

Recent data suggest that acidosis alone is not a good predictor of mortality in trauma patients. Little data are currently available regarding factors associated with survival in trauma patients presenting with acidosis.

Aims

The aims were to characterize the outcomes of trauma patients presenting with acidosis and to identify modifiable risk factors associated with mortality in these patients.

Settings and Design

This is a retrospective observational study of University of Arkansas for Medical Sciences (UAMS) trauma patients between November 23, 2013, and May 21, 2017.

Methods

Data were collected from the UAMS trauma registry. The primary outcome was hospital mortality. Analyses were performed using t-test and Pearson's Chi-squared test. Simple and multiple logistic regressions were performed to determine crude and adjusted odds ratios.

Results

There were 532 patients identified and 64.7% were acidotic (pH < 7.35) on presentation: 75.9% pH 7.2-7.35; 18.5% pH 7.0-7.2; and 5.6% pH ≤ 7.0. The total hospital mortality was 23.7%. Nonsurvivors were older and more acidotic, with a base deficit >-8, Glasgow Coma Scale (GCS) ≤ 8, systolic blood pressure ≤ 90, International Normalized Ratio (INR) >1.6, and Injury Severity Score (ISS) >15. Mortality was significantly higher with a pH ≤ 7.2 but mortality with a pH 7.2-7.35 was comparable to pH > 7.35. In the adjusted model, pH ≤ 7.0, pH 7.0-7.2, INR > 1.6, GCS ≤ 8, and ISS > 15 were associated with increased mortality. For patients with a pH ≤ 7.2, only INR was associated with increase in mortality.

Conclusions

A pH ≤ 7.2 is associated with increased mortality. For patients in this range, only the presence of coagulopathy is associated with increased mortality. A pH > 7.2 may be an appropriate treatment goal for acidosis. Further work is needed to identify and target potentially modifiable factors in patients with acidosis such as coagulopathy.

Metabolic Profiling of a Porcine Combat Trauma-Injury Model Using NMR and Multi-Mode LC-MS Metabolomics-A Preliminary Study

Profiles of combat injuries worldwide have shown that penetrating trauma is one of the most common injuries sustained during battle. This is usually accompanied by severe bleeding or hemorrhage. If the soldier does not bleed to death, he may eventually succumb to complications arising from trauma hemorrhagic shock (THS). THS occurs when there is a deficiency of oxygen reaching the organs due to excessive blood loss. It can trigger massive metabolic derangements and an overwhelming inflammatory response, which can subsequently lead to the failure of organs and possibly death. A better understanding of the acute metabolic changes occurring after THS can help in the development of interventional strategies, as well as lead to the identification of potential biomarkers for rapid diagnosis of hemorrhagic shock and organ failure. In this preliminary study, a metabolomic approach using the complementary platforms of nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography coupled with mass spectrometry (LC-MS) was used to determine the metabolic changes occurring in a porcine model of combat trauma injury comprising of penetrating trauma to a limb with hemorrhagic shock. Several metabolites associated with the acute-phase reaction, inflammation, energy depletion, oxidative stress, and possible renal dysfunction were identified to be significantly changed after a thirty-minute shock period.

COVID-19 infection alters kynurenine and fatty acid metabolism, correlating with IL-6 levels and renal status

BACKGROUNDReprogramming of host metabolism supports viral pathogenesis by fueling viral proliferation, by providing, for example, free amino acids and fatty acids as building blocks.METHODSTo investigate metabolic effects of SARS-CoV-2 infection, we evaluated serum metabolites of patients with COVID-19 (n = 33; diagnosed by nucleic acid testing), as compared with COVID-19-negative controls (n = 16).RESULTSTargeted and untargeted metabolomics analyses identified altered tryptophan metabolism into the kynurenine pathway, which regulates inflammation and immunity. Indeed, these changes in tryptophan metabolism correlated with interleukin-6 (IL-6) levels. Widespread dysregulation of nitrogen metabolism was also seen in infected patients, with altered levels of most amino acids, along with increased markers of oxidant stress (e.g., methionine sulfoxide, cystine), proteolysis, and renal dysfunction (e.g., creatine, creatinine, polyamines). Increased circulating levels of glucose and free fatty acids were also observed, consistent with altered carbon homeostasis. Interestingly, metabolite levels in these pathways correlated with clinical laboratory markers of inflammation (i.e., IL-6 and C-reactive protein) and renal function (i.e., blood urea nitrogen).CONCLUSIONIn conclusion, this initial observational study identified amino acid and fatty acid metabolism as correlates of COVID-19, providing mechanistic insights, potential markers of clinical severity, and potential therapeutic targets.FUNDINGBoettcher Foundation Webb-Waring Biomedical Research Award; National Institute of General and Medical Sciences, NIH; and National Heart, Lung, and Blood Institute, NIH.

Trisomy 21 activates the kynurenine pathway via increased dosage of interferon receptors

Trisomy 21 (T21) causes Down syndrome (DS), affecting immune and neurological function by ill-defined mechanisms. Here we report a large metabolomics study of plasma and cerebrospinal fluid, showing in independent cohorts that people with DS produce elevated levels of kynurenine and quinolinic acid, two tryptophan catabolites with potent immunosuppressive and neurotoxic properties, respectively. Immune cells of people with DS overexpress IDO1, the rate-limiting enzyme in the kynurenine pathway (KP) and a known interferon (IFN)-stimulated gene. Furthermore, the levels of IFN-inducible cytokines positively correlate with KP dysregulation. Using metabolic tracing assays, we show that overexpression of IFN receptors encoded on chromosome 21 contribute to enhanced IFN stimulation, thereby causing IDO1 overexpression and kynurenine overproduction in cells with T21. Finally, a mouse model of DS carrying triplication of IFN receptors exhibits KP dysregulation. Together, our results reveal a mechanism by which T21 could drive immunosuppression and neurotoxicity in DS.

Preoperative Circulating Succinate Levels as a Biomarker for Diabetes Remission After Bariatric Surgery

OBJECTIVE

To determine the potential use of baseline circulating succinate to predict type 2 diabetes remission after bariatric surgery.

RESEARCH DESIGN AND METHODS

Forty-five obese patients with diabetes were randomly assigned to Roux-en-Y gastric bypass (RYGB), sleeve gastrectomy (SG), or laparoscopic greater curvature plication. Anthropometric parameters were evaluated, and a complete biochemical analysis including circulating serum succinate concentrations was performed at baseline and 1 year after surgery. The results were externally validated in a second cohort including 88 obese patients with diabetes assigned to RYGB or SG based on clinical criteria.

RESULTS

Succinate baseline concentrations were an independent predictor of diabetes remission after bariatric surgery. Patients achieving remission after 1 year had lower levels of baseline succinate (47.8 [37.6-64.6] µmol/L vs. 64.1 [52.5-82.9] µmol/L; P = 0.018). Moreover, succinate concentrations were significantly decreased 1 year after surgery (58.9 [46.4-82.4] µmol/L vs. 46.0 [35.8-65.3] µmol/L, P = 0.005). In multivariate analysis, the best logistic regression model showed that baseline succinate (odds ratio [OR] 11.3, P = 0.031) and the type of surgery (OR 26.4, P = 0.010) were independently associated with remission. The C-statistic for this model was 0.899 (95% CI 0.809-0.989) in the derivation cohort, which significantly improved the prediction of remission compared with current available scores, and 0.729 (95% CI 0.612-0.846) in the validation cohort. Interestingly, patients had a different response to the type of surgery according to baseline succinate, with significant differences in remission rates.

CONCLUSIONS

Circulating succinate is reduced after bariatric surgery. Baseline succinate levels have predictive value for diabetes remission independently of previously described presurgical factors and improve upon the current available scores to predict remission.

Serum Levels of Mitochondrial and Microbial Metabolites Reflect Mitochondrial Dysfunction in Different Stages of Sepsis

Mechanisms of mitochondrial dysfunction in sepsis are being extensively studied in recent years. During our study, concentrations of microbial phenolic acids and mitochondrial metabolites (succinic, α-ketoglutaric, fumaric, itaconic acids) as indicators of sepsis and mitochondrial dysfunction, respectively, are measured by gas chromatography–mass spectrometry (GC–MS) in the blood of critically ill patients at the early and late stages of documented sepsis. The increase in levels of some phenylcarboxylic (phenyllactic (PhLA), p-hydroxyphenylacetic (p-HPhAA), p-hydroxyphenyllactic (p-HPhAA)) acids (PhCAs), simultaneously with a rise in levels of mitochondrial dicarboxylic acids, are mainly detected during the late stage of sepsis, especially succinic acid (up to 100–1000 µM). Itaconic acid is found in low concentrations (0.5–2.3 µM) only at early-stage sepsis. PhCAs in vitro inhibits succinate dehydrogenase (SDH) in isolated mitochondria but, unlike itaconic acid which acts as a competitive inhibitor of SDH, microbial metabolites most likely act on the ubiquinone binding site of the respiratory chain. A close correlation of the level of succinic acid in serum and sepsis-induced organ dysfunction is revealed, moreover the most significant correlation is observed at high concentrations of phenolic microbial metabolites (PhCAs) in late-stage sepsis. These data indicate the promise of such an approach for early detection, monitoring the progression of organ dysfunction and predicting the risk of non-survival in sepsis.

Selective organ ischaemia/reperfusion identifies liver as the key driver of the post-injury plasma metabolome derangements

BACKGROUND

Understanding the molecular mechanisms in perturbation of the metabolome following ischaemia and reperfusion is critical in developing novel therapeutic strategies to prevent the sequelae of post-injury shock. While the metabolic substrates fueling these alterations have been defined, the relative contribution of specific organs to the systemic metabolic reprogramming secondary to ischaemic or haemorrhagic hypoxia remains unclear.

MATERIALS AND METHODS

A porcine model of selected organ ischaemia was employed to investigate the relative contribution of liver, kidney, spleen and small bowel ischaemia/reperfusion to the plasma metabolic phenotype, as gleaned through ultra-high performance liquid chromatography-mass spectrometry-based metabolomics.

RESULTS

Liver ischaemia/reperfusion promotes glycaemia, with increases in circulating carboxylic acid anions and purine oxidation metabolites, suggesting that this organ is the dominant contributor to the accumulation of these metabolites in response to ischaemic hypoxia. Succinate, in particular, accumulates selectively in response to the hepatic ischemia, with levels 6.5 times spleen, 8.2 times small bowel, and 6 times renal levels. Similar trends, but lower fold-change increase in comparison to baseline values, were observed upon ischaemia/reperfusion of kidney, spleen and small bowel.

DISCUSSION

These observations suggest that the liver may play a critical role in mediating the accumulation of the same metabolites in response to haemorrhagic hypoxia, especially with respect to succinate, a metabolite that has been increasingly implicated in the coagulopathy and pro-inflammatory sequelae of ischaemic and haemorrhagic shock.

Metabolomics in the Diagnosis of Pheochromocytoma and Paraganglioma

Metabolomics refers to the detection and measurement of small molecules (metabolites) within biological systems, and is therefore a powerful tool for identifying dysfunctional cellular physiologies. For pheochromocytomas and paragangliomas (PPGLs), metabolomics has the potential to become a routine addition to histology and genomics for precise diagnostic evaluation. Initial metabolomic studies of ex vivo tumors confirmed, as expected, succinate accumulation in PPGLs associated with pathogenic variants in genes encoding succinate dehydrogenase subunits or their assembly factors (SDHx). Metabolomics has now shown utility in clarifying SDHx variants of uncertain significance, as well as the accurate diagnosis of PPGLs associated with fumarate hydratase (FH), isocitrate dehydrogenase (IDH), malate dehydrogenase (MDH2) and aspartate transaminase (GOT2). The emergence of metabolomics resembles the advent of genetic testing in this field, which began with single-gene discoveries in research laboratories but is now done by standardized massively parallel sequencing (targeted panel/exome/genome testing) in pathology laboratories governed by strict credentialing and governance requirements. In this setting, metabolomics is poised for rapid translation as it can utilize existing infrastructure, namely liquid chromatography-tandem mass spectrometry (LC-MS/MS), for the measurement of catecholamine metabolites. Metabolomics has also proven tractable to in vivo diagnosis of SDH-deficient PPGLs using magnetic resonance spectroscopy (MRS). The future of metabolomics - embedded as a diagnostic tool - will require adoption by pathologists to shepherd development of standardized assays and sample preparation, reference ranges, gold standards, and credentialing.

Parabiosis Incompletely Reverses Aging-Induced Metabolic Changes and Oxidant Stress in Mouse Red Blood Cells

Mature red blood cells (RBCs) not only account for ~83% of the total host cells in the human body, but they are also exposed to all body tissues during their circulation in the bloodstream. In addition, RBCs are devoid of de novo protein synthesis capacity and, as such, they represent a perfect model to investigate system-wide alterations of cellular metabolism in the context of aging and age-related oxidant stress without the confounding factor of gene expression. In the present study, we employed ultra-high-pressure liquid chromatography coupled with mass spectrometry (UHPLC–MS)-based metabolomics and proteomics to investigate RBC metabolism across age in male mice (6, 15, and 25 months old). We report that RBCs from aging mice face a progressive decline in the capacity to cope with oxidant stress through the glutathione/NADPH-dependent antioxidant systems. Oxidant stress to tryptophan and purines was accompanied by declines in late glycolysis and methyl-group donors, a potential compensatory mechanism to repair oxidatively damaged proteins. Moreover, heterochronic parabiosis experiments demonstrated that the young environment only partially rescued the alterations in one-carbon metabolism in old mice, although it had minimal to no impact on glutathione homeostasis, the pentose phosphate pathway, and oxidation of purines and tryptophan, which were instead aggravated in old heterochronic parabionts.

A prospective pilot study using metabolomics discloses specific fatty acid, catecholamine and tryptophan metabolic pathways as possible predictors for a negative outcome after severe trauma

Background

We wanted to define metabolomic patterns in plasma to predict a negative outcome in severe trauma patients.

Methods

A prospective pilot study was designed to evaluate plasma metabolomic patterns, established by liquid chromatography coupled to mass spectrometry, in patients allocated to an intensive care unit (in the University Hospital Arnau de Vilanova, Lleida, Spain) in the first hours after a severe trauma (n = 48). Univariate and multivariate statistics were employed to establish potential predictors of mortality.

Results

Plasma of patients non surviving to trauma (n = 5) exhibited a discriminating metabolomic pattern, involving basically metabolites belonging to fatty acid and catecholamine synthesis as well as tryptophan degradation pathways. Thus, concentration of several metabolites exhibited an area under the receiver operating curve (ROC) higher than 0.84, including 3-indolelactic acid, hydroxyisovaleric acid, phenylethanolamine, cortisol, epinephrine and myristic acid. Multivariate binary regression logistic revealed that patients with higher myristic acid concentrations had a non-survival odds ratio of 2.1 (CI 95% 1.1–3.9).

Conclusions

Specific fatty acids, catecholamine synthesis and tryptophan degradation pathways could be implicated in a negative outcome after trauma. The metabolomic study of severe trauma patients could be helpful for biomarker proposal.

Electronic supplementary material

The online version of this article (10.1186/s13049-019-0631-5) contains supplementary material, which is available to authorized users.

From omics technologies to personalized transfusion medicine

INTRODUCTION

Blood transfusion is the single most frequent in-hospital medical procedure, a life-saving intervention for millions of recipients worldwide every year. Storage in the blood bank is an enabling strategy for this critical procedure, as it logistically solves the issue of making ~110 million units available for transfusion every year. Unfortunately, storage in the blood bank promotes a series of biochemical and morphological changes to the red blood cell that compromise the integrity and functionality of the erythrocyte in vitro and in animal models, and could negatively impact transfusion outcomes in the recipient. Areas covered: While commenting on the clinical relevance of the storage lesion is beyond the scope of this manuscript, here we will review recent advancements in our understanding of the storage lesion as gleaned through omics technologies. We will focus on how the omics-scale appreciation of the biological variability at the donor and recipient level is impacting our understanding of red blood cell storage biology. Expert commentary: Omics technologies are paving the way for personalized transfusion medicine, a discipline that promises to revolutionize a critical field in medical practice. The era of recipient-tailored additives, processing, and storage strategies may not be too far distant in the future.

All animals are equal but some animals are more equal than others: Plasma lactate and succinate in hemorrhagic shock-A comparison in rodents, swine, nonhuman primates, and injured patients

BACKGROUND

Plasma levels of lactate and succinate are predictors of mortality in critically injured patients in military and civilian settings. In relative terms, these metabolic derangements have been recapitulated in rodent, swine, and nonhuman primate models of severe hemorrhage. However, no direct absolute quantitative comparison has been evaluated across these species.

METHODS

Ultra-high pressure liquid chromatography-mass spectrometry with stable isotope standards was used to determine absolute concentrations of baseline and postshock levels of lactate and succinate in rats, pigs, macaques, and injured patients.

RESULTS

Baseline levels of lactate and succinate were most comparable to humans in macaques, followed by pigs and rats. Baseline levels of lactate in pigs and baseline and postshock levels of lactate and succinate in rats were significantly higher than those measured in macaques and humans. Postshock levels of lactate and succinate in pigs and macaques, respectively, were directly comparable to measurements in critically injured patients.

CONCLUSION

Acknowledging the caveats associated with the variable degrees of shock in the clinical cohort, our data indicate that larger mammals represent a better model than rodents when investigating metabolic derangements secondary to severe hemorrhage.

Red Blood Cell Metabolic Responses to Torpor and Arousal in the Hibernator Arctic Ground Squirrel

Arctic ground squirrels provide a unique model to investigate metabolic responses to hibernation in mammals. During winter months these rodents are exposed to severe hypothermia, prolonged fasting, and hypoxemia. In the light of their role in oxygen transport/off-loading and owing to the absence of nuclei and organelles (and thus de novo protein synthesis capacity), mature red blood cells have evolved metabolic programs to counteract physiological or pathological hypoxemia. However, red blood cell metabolism in hibernation has not yet been investigated. Here we employed targeted and untargeted metabolomics approaches to investigate erythrocyte metabolism during entrance to torpor to arousal, with a high resolution of the intermediate time points. We report that torpor and arousal promote metabolism through glycolysis and pentose phosphate pathway, respectively, consistent with previous models of oxygen-dependent metabolic modulation in mature erythrocytes. Erythrocytes from hibernating squirrels showed up to 100-fold lower levels of biomarkers of reperfusion injury, such as the pro-inflammatory dicarboxylate succinate. Altered tryptophan metabolism during torpor was here correlated to the accumulation of potentially neurotoxic catabolites kynurenine, quinolinate, and picolinate. Arousal was accompanied by alterations of sulfur metabolism, including sudden spikes in a metabolite putatively identified as thiorphan (level 1 confidence)-a potent inhibitor of several metalloproteases that play a crucial role in nociception and inflammatory complication to reperfusion secondary to ischemia or hemorrhage. Preliminary studies in rats showed that intravenous injection of thiorphan prior to resuscitation mitigates metabolic and cytokine markers of reperfusion injury, etiological contributors to inflammatory complications after shock.