Platelet mitochondrial dysfunction in critically ill patients: comparison between sepsis and cardiogenic shock

Platelet Bioenergetics and Associations With Delirium and Coma in Patients With Sepsis: A Prospective Cohort Study

BACKGROUND

Acute brain dysfunction during sepsis, which manifests as delirium or coma, is common and is associated with multiple adverse outcomes, including longer periods of mechanical ventilation, prolonged hospital stays, and increased mortality. Delirium and coma during sepsis may be manifestations of alteration in systemic metabolism. Because access to brain mitochondria is a limiting factor, measurement of peripheral platelet bioenergetics offers a potential opportunity to understand metabolic changes associated with acute brain dysfunction during sepsis.

RESEARCH QUESTION

Are altered platelet mitochondrial bioenergetics associated with acute brain dysfunction during sepsis?

STUDY DESIGN AND METHODS

We assessed participants with critical illness in the ICU for the presence of delirium or coma via validated assessment measures. Blood samples were collected and processed to isolate and measure platelet mitochondrial oxygen consumption. We used Seahorse extracellular flux to measure directly baseline, proton leak, maximal oxygen consumption rate, and extracellular acidification rate. We calculated adenosine triphosphate-linked, spare respiratory capacity, and nonmitochondrial oxygen consumption rate from the measured values.

RESULTS

Maximum oxygen consumption was highest in patients with coma, as was spare respiratory capacity and extracellular acidification rate in unadjusted analysis. After adjusting for age, sedation, modified Sequential Organ Failure Assessment score without the neurologic component, and preexisting cognitive function, increased spare respiratory capacity remained associated with coma. Delirium was not associated with any platelet mitochondrial bioenergetics.

INTERPRETATION

In this single-center exploratory prospective cohort study, we found that increased platelet mitochondrial spare respiratory capacity was associated with coma in patients with sepsis. Future studies powered to determine any relationship between delirium and mitochondrial respiration bioenergetics are needed.

Circulating N-lactoyl-amino acids and N-formyl-methionine reflect mitochondrial dysfunction and predict mortality in septic shock

INTRODUCTION

Sepsis is a highly morbid condition characterized by multi-organ dysfunction resulting from dysregulated inflammation in response to acute infection. Mitochondrial dysfunction may contribute to sepsis pathogenesis, but quantifying mitochondrial dysfunction remains challenging.

OBJECTIVE

To assess the extent to which circulating markers of mitochondrial dysfunction are increased in septic shock, and their relationship to severity and mortality.

METHODS

We performed both full-scan and targeted (known markers of genetic mitochondrial disease) metabolomics on plasma to determine markers of mitochondrial dysfunction which distinguish subjects with septic shock (n = 42) from cardiogenic shock without infection (n = 19), bacteremia without sepsis (n = 18), and ambulatory controls (n = 19) - the latter three being conditions in which mitochondrial function, proxied by peripheral oxygen consumption, is presumed intact.

RESULTS

Nine metabolites were significantly increased in septic shock compared to all three comparator groups. This list includes N-formyl-L-methionine (f-Met), a marker of dysregulated mitochondrial protein translation, and N-lactoyl-phenylalanine (lac-Phe), representative of the N-lactoyl-amino acids (lac-AAs), which are elevated in plasma of patients with monogenic mitochondrial disease. Compared to lactate, the clinical biomarker used to define septic shock, there was greater separation between survivors and non-survivors of septic shock for both f-Met and the lac-AAs measured within 24 h of ICU admission. Additionally, tryptophan was the one metabolite significantly decreased in septic shock compared to all other groups, while its breakdown product kynurenate was one of the 9 significantly increased.

CONCLUSION

Future studies which validate the measurement of lac-AAs and f-Met in conjunction with lactate could define a sepsis subtype characterized by mitochondrial dysfunction.

Modulatory effects of dietary saturated fatty acids on platelet mitochondrial function following short-term exposure to ambient Particulate Matter (PM2.5)

Exposure to ambient fine particulate matter (PM2.5) was found to produce vascular injury, possibly by activating platelets within days after exposure. The aim of this study was to investigate the modulatory effects of dietary saturated fatty acids on platelet mitochondrial respiratory parameters following short-term inhalational exposure to PM2.5. A total of 22 healthy male volunteers were recruited from the Research Triangle area of North Carolina. Platelets were isolated from fresh whole blood samples and mitochondrial respiratory parameters were measured using an extracellular flux analyzer. Intake of saturated fat was averaged from multiple 24-hr dietary recalls. Daily ambient PM2.5 concentrations were obtained from ambient air quality monitoring stations. Correlation and ANOVA were used in data analyses, along with the pick-a-point method and the Johnson-Neyman technique for probing moderation. After controlling for age and omega-3 index, the intake of dietary saturated fatty acids after reaching 9.3% or higher of the total caloric intake significantly moderated the associations between PM2.5 exposure and several platelet mitochondrial respiratory parameters. In conclusion, dietary saturated fatty acids above 9.3% of total caloric intake influenced the relationship between short-term PM2.5 exposure and platelet mitochondrial respiration. Further research is needed to understand these associations and their implications for cardiovascular health.

Mitofusin-2 Regulates Platelet Mitochondria and Function

BACKGROUND

Single-nucleotide polymorphisms linked with the rs1474868 T allele (MFN2 [mitofusin-2] T/T) in the human mitochondrial fusion protein MFN2 gene are associated with reduced platelet MFN2 RNA expression and platelet counts. This study investigates the impact of MFN2 on megakaryocyte and platelet biology.

METHODS

Mice with megakaryocyte/platelet deletion of Mfn2 (Mfn2-/- [Mfn2 conditional knockout]) were generated using Pf4-Cre crossed with floxed Mfn2 mice. Human megakaryocytes were generated from cord blood and platelets isolated from healthy subjects genotyped for rs1474868. Ex vivo approaches assessed mitochondrial morphology, function, and platelet activation responses. In vivo measurements included endogenous/transfused platelet life span, tail bleed time, transient middle cerebral artery occlusion, and pulmonary vascular permeability/hemorrhage following lipopolysaccharide-induced acute lung injury.

RESULTS

Mitochondria was more fragmented in megakaryocytes derived from Mfn2-/- mice and from human cord blood with MFN2 T/T genotype compared with control megakaryocytes. Human resting platelets of MFN2 T/T genotype had reduced MFN2 protein, diminished mitochondrial membrane potential, and an increased rate of phosphatidylserine exposure during ex vivo culture. Platelet counts and platelet life span were reduced in Mfn2-/- mice accompanied by an increased rate of phosphatidylserine exposure in resting platelets, especially aged platelets, during ex vivo culture. Mfn2-/- also decreased platelet mitochondrial membrane potential (basal) and activated mitochondrial oxygen consumption rate, reactive oxygen species generation, calcium flux, platelet-neutrophil aggregate formation, and phosphatidylserine exposure following dual agonist activation. Ultimately, Mfn2-/- mice showed prolonged tail bleed times, decreased ischemic stroke infarct size after cerebral ischemia-reperfusion, and exacerbated pulmonary inflammatory hemorrhage following lipopolysaccharide-induced acute lung injury. Analysis of MFN2 SNPs in the iSPAAR study (Identification of SNPs Predisposing to Altered ALI Risk) identified a significant association between MFN2 and 28-day mortality in patients with acute respiratory distress syndrome.

CONCLUSIONS

Mfn2 preserves mitochondrial phenotypes in megakaryocytes and platelets and influences platelet life span, function, and outcomes of stroke and lung injury.

Blood-based bioenergetics: a liquid biopsy of mitochondrial dysfunction in disease

Mitochondria operate as hubs of cellular metabolism that execute important regulatory functions. Damaged/dysfunctional mitochondria are recognized as major pathogenic contributors to many common human diseases. Assessment of mitochondrial function relies upon invasive tissue biopsies; peripheral blood cells, specifically platelets, have emerged as an ideal candidate for mitochondrial function assessment. Accessibility and documented pathology-related dysfunction have prompted investigation into the role of platelets in disease, the contribution of platelet mitochondria to pathophysiology, and the capacity of platelets to reflect systemic mitochondrial health. Platelet mitochondrial bioenergetics are being investigated in neurodegenerative and cardiopulmonary diseases, infection, diabetes, and other (patho)physiological states such as aging and pregnancy. Early findings support the use of platelets as a biomarker for mitochondrial functional health.

MTH1 protects platelet mitochondria from oxidative damage and regulates platelet function and thrombosis

Human MutT Homolog 1 (MTH1) is a nucleotide pool sanitization enzyme that hydrolyzes oxidized nucleotides to prevent their mis-incorporation into DNA under oxidative stress. Expression and functional roles of MTH1 in platelets are not known. Here, we show MTH1 expression in platelets and its deficiency impairs hemostasis and arterial/venous thrombosis in vivo. MTH1 deficiency reduced platelet aggregation, phosphatidylserine exposure and calcium mobilization induced by thrombin but not by collagen-related peptide (CRP) along with decreased mitochondrial ATP production. Thrombin but not CRP induced Ca2+-dependent mitochondria reactive oxygen species generation. Mechanistically, MTH1 deficiency caused mitochondrial DNA oxidative damage and reduced the expression of cytochrome c oxidase 1. Furthermore, MTH1 exerts a similar role in human platelet function. Our study suggests that MTH1 exerts a protective function against oxidative stress in platelets and indicates that MTH1 could be a potential therapeutic target for the prevention of thrombotic diseases.

Critical care: A concept analysis

Objective

The terms critical care and the Intensive Care Unit (ICU) are often used interchangeably to describe a place of care. Defining critical care becomes challenging because of the colloquial use of the term. Using concept analysis allows for the development of definition and meaning. The aim of this concept analysis is to distinguish the use of the term critical care to develop an operational definition which describes what constitutes critical care.

Method

Walker and Avant's eight-step approach to concept analysis guided this study. Five databases (CINAHL, Scopus, PubMed, ProQuest Dissertation Abstracts and Medline in EBSCO) were searched for studies related to critical care. The search included both qualitative and quantitative studies written in English and published between 1990 and 2022.

Results

Of the 439 papers retrieved, 47 met the inclusion criteria. The defining attributes of critical care included 1) a maladaptive response to illness/injury, 2) admission modelling criteria, 3) advanced medical technologies, and 4) specialised health professionals. Antecedents were associated with illness/injury that progressed to a level of criticality with a significant decline in both physical and psychological functioning. Consequences were identified as either death or survival with/without experiencing post-ICU syndrome.

Conclusion

Describing critical care is often challenging because of the highly technical nature of the environment. This conceptual understanding and operational definition will inform future research as to the scope of critical care and allow for the design of robust evaluative instruments to better understand the nature of care in the intensive care environment.

Platelet polyphosphate and energy metabolism in professional male athletes (soccer players): A cross-sectional pilot study

Human platelet polyphosphate (polyP) is a multifunctional molecule; however, its functions are not yet fully understood. A recent study demonstrated that similar to skeletal muscle, polyP is involved in energy metabolism in platelets, which suggests that well-trained athletes may exhibit elevated platelet polyP levels for energy storage. To test this hypothesis, we quantified platelet polyP along with NADH, a component involved in ATP production in non-trained and well-trained male Japanese participants of the same generation. Washed platelets were prepared from the venous blood of young, healthy, non-athletes, and professional soccer players (pro-athletes). NADH and polyP levels were spectrophotometrically determined using tetrazolium reduction and fluorometrically determined using 4',6-diamidino-2-phenylindole at the excitation/emission wavelengths of 425/525 nm. Body weight and impedances were measured simultaneously. Statistical analyses were performed using the Mann-Whitney U test and Spearman correlation coefficient. Although basal metabolic rate levels were significantly higher, platelet polyP levels were significantly lower in pro-athletes than in that in non-athletes. No significant differences were detected in other body compositions or platelet indices between the two groups. The pro-athlete group showed a moderate, nearly significant correlation (R = 0.439; p = 0.0512) between platelet polyP and NADH levels. Taken together with the weak correlation data between polyP and body mass index, it is suggested that platelet polyP levels may be influenced by platelet and body energy metabolic activity. Further biochemical studies are needed to elucidate this mechanism.

Intestinal IL-33 promotes platelet activity for neutrophil recruitment during acute inflammation

Peripheral serotonin (5-HT) is mainly generated from the gastrointestinal tract and taken up and stored by platelets in the circulation. Although the gut is recognized as a major immune organ, how intestinal local immune responses control whole-body physiology via 5-HT remains unclear. Here, we show that intestinal inflammation enhances systemic platelet activation and blood coagulation. Intestinal epithelium damage induces elevated levels of the alarm cytokine interleukin-33 (IL-33), leading to platelet activation via promotion of gut-derived 5-HT release. More importantly, we found that loss of intestinal epithelial-derived IL-33 lowers peripheral 5-HT levels, resulting in compromised platelet activation and hemostasis. Functionally, intestinal IL-33 contributes to the recruitment of neutrophils to sites of acute inflammation by enhancing platelet activities. Genetic deletion of intestinal IL-33 or neutralization of peripheral IL-33 protects animals from lipopolysaccharide endotoxic shock through attenuated neutrophil extravasation. Therefore, our data establish a distinct role of intestinal IL-33 in activating platelets by promoting 5-HT release for systemic physiology and inflammation.

Effects of SARS‑CoV‑2 mRNA vaccines on platelet polyphosphate levels and inflammation: A pilot study

Platelets function as immune cells in conjunction with white blood cells, targeting invading pathogens and inducing immune reactions. Intercellular communications among these immune cells are partly mediated by platelet polyphosphate (polyP), which was originally recognized as a thrombotic and hemostatic biomolecule. To determine the involvement of polyP in SARS-CoV-2-mRNA vaccine-induced immune responses, specifically in inflammatory responses, the effects of mRNA vaccines on platelet polyP levels were examined. Before and after vaccination with the COVID-19 vaccine (BNT162b2), blood samples were obtained from healthy, non-smoking individuals who did not have any systemic diseases. Test group demographics skewed somewhat towards either older males (first vaccination, n=6; second vaccination, n=8) or younger females (first vaccination, n=14; second vaccination, n=23). polyP levels in washed platelets from the blood samples were determined using the fluorometric method with DAPI. The side-effects of vaccination were recorded as scores. In the female group, platelet polyP levels decreased after the first vaccination, and the side-effect score increased after the second vaccination. Moderate correlation coefficients were observed between the reduction in polyP levels and the side-effect scores and pre-vaccination polyP levels. Despite the small sample size, this pilot study suggests that platelet polyP may suppress the side effects induced by the mRNA vaccines after the first vaccination, but not the second vaccination in younger female subjects, who generally have higher immune responsiveness than their male counterparts.

Mitochondrial Respiration of Platelets: Comparison of Isolation Methods

Multiple non-aggregatory functions of human platelets (PLT) are widely acknowledged, yet their functional examination is limited mainly due to a lack of standardized isolation and analytic methods. Platelet apheresis (PA) is an established clinical method for PLT isolation aiming at the treatment of bleeding diathesis in severe thrombocytopenia. On the other hand, density gradient centrifugation (DC) is an isolation method applied in research for the analysis of the mitochondrial metabolic profile of oxidative phosphorylation (OXPHOS) in PLT obtained from small samples of human blood. We studied PLT obtained from 29 healthy donors by high-resolution respirometry for comparison of PA and DC isolates. ROUTINE respiration and electron transfer capacity of living PLT isolated by PA were significantly higher than in the DC group, whereas plasma membrane permeabilization resulted in a 57% decrease of succinate oxidation in PA compared to DC. These differences were eliminated after washing the PA platelets with phosphate buffer containing 10 mmol·L⁻¹ ethylene glycol-bis (2-aminoethyl ether)-N,N,N′,N′-tetra-acetic acid, suggesting that several components, particularly Ca²⁺ and fuel substrates, were carried over into the respiratory assay from the serum in PA. A simple washing step was sufficient to enable functional mitochondrial analysis in subsamples obtained from PA. The combination of the standard clinical PA isolation procedure with PLT quality control and routine mitochondrial OXPHOS diagnostics meets an acute clinical demand in biomedical research of patients suffering from thrombocytopenia and metabolic diseases.

Platelet Phenotype Analysis of COVID-19 Patients Reveals Progressive Changes in the Activation of Integrin αIIbβ3, F13A1, the SARS-CoV-2 Target EIF4A1 and Annexin A5

Background: The fatal consequences of an infection with severe acute respiratory syndrome coronavirus 2 are not only caused by severe pneumonia, but also by thrombosis. Platelets are important regulators of thrombosis, but their involvement in the pathogenesis of COVID-19 is largely unknown. The aim of this study was to determine their functional and biochemical profile in patients with COVID-19 in dependence of mortality within 5-days after hospitalization. Methods: The COVID-19-related platelet phenotype was examined by analyzing their basal activation state via integrin αIIbβ3 activation using flow cytometry and the proteome by unbiased two-dimensional differential in-gel fluorescence electrophoresis. In total we monitored 98 surviving and 12 non-surviving COVID-19 patients over 5 days of hospital stay and compared them to healthy controls (n = 12). Results: Over the observation period the level of basal αIIbβ3 activation on platelets from non-surviving COVID-19 patients decreased compared to survivors. In line with this finding, proteomic analysis revealed a decrease in the total amount of integrin αIIb (ITGA2B), a subunit of αIIbβ3, in COVID-19 patients compared to healthy controls; the decline was even more pronounced for the non-survivors. Consumption of the fibrin-stabilizing factor coagulation factor XIIIA (F13A1) was higher in platelets from COVID-19 patients and tended to be higher in non-survivors; plasma concentrations of the latter also differed significantly. Depending on COVID-19 disease status and mortality, increased amounts of annexin A5 (ANXA5), eukaryotic initiation factor 4A-I (EIF4A1), and transaldolase (TALDO1) were found in the platelet proteome and also correlated with the nasopharyngeal viral load. Dysregulation of these proteins may play a role for virus replication. ANXA5 has also been identified as an autoantigen of the antiphospholipid syndrome, which is common in COVID-19 patients. Finally, the levels of two different protein disulfide isomerases, P4HB and PDIA6, which support thrombosis, were increased in the platelets of COVID-19 patients. Conclusion: Platelets from COVID-19 patients showed significant changes in the activation phenotype, in the processing of the final coagulation factor F13A1 and the phospholipid-binding protein ANXA5 compared to healthy subjects. Additionally, these results demonstrate specific alterations in platelets during COVID-19, which are significantly linked to fatal outcome.

Sample Preparation as a Critical Aspect of Blood Platelet Mitochondrial Respiration Measurements-The Impact of Platelet Activation on Mitochondrial Respiration

Blood platelets are considered as promising candidates as easily-accessible biomarkers of mitochondrial functioning. However, their high sensitivity to various stimulus types may potentially affect mitochondrial respiration and lead to artefactual outcomes. Therefore, it is crucial to identify the factors associated with platelet preparation that may lead to changes in mitochondrial respiration. A combination of flow cytometry and advanced respirometry was used to examine the effect of blood anticoagulants, the media used to suspend isolated platelets, respiration buffers, storage time and ADP stimulation on platelet activation and platelet mitochondria respiration. Our results clearly show that all the mentioned factors can affect platelet mitochondrial respiration. Briefly, (i) the use of EDTA as anticoagulant led to a significant increase in the dissipative component of respiration (LEAK), (ii) the use of plasma for the suspension of isolated platelets with MiR05 as a respiration buffer allows high electron transfer capacity and low platelet activation, and (iii) ADP stimulation increases physiological coupling respiration (ROUTINE). Significant associations were observed between platelet activation markers and mitochondrial respiration at different preparation steps; however, the fact that these relationships were not always apparent suggests that the method of platelet preparation may have a greater impact on mitochondrial respiration than the platelet activation itself.

The Value of Serum Uncoupling Protein-2 Level for the Patients With Sepsis

BACKGROUND

To investigate the potential utility of serum uncoupling protein-2 (UCP2) level as a biomarker in septic patients.

METHODS

Critically ill patients with diagnoses of sepsis-sepsis non-shock group (n = 20) and septic shock group (n = 53), and a control group (n = 15) were enrolled within 24 h of entry into the ICU. Serum levels of UCP2 were measured by enzyme-linked immunosorbent assay (ELISA) at ICU admission for all the groups and at ICU discharge for septic shock group. Clinical parameters and laboratorial tests (APACHE II, SOFA, lactate, etc.) were also collected.

RESULTS

Serum UCP2 concentrations on ICU admission were significantly increased in septic shock group and sepsis non-shock group, compared with control subjects (263.21 ± 29.99 vs. 115.96 ± 32.99 vs. 60.56 ± 10.05 pg/mL, P < 0.001). Concentrations of UCP2 performed better than other parameters (APACHE II score, SOFA score, procalcitonin, and WBC) in predicting the incidence of sepsis or septic shock on the day of ICU admission, as reflected by AUC. On the day of ICU admission, the AUC for UCP2 level associated with 28-day mortality was 0.704, higher than the AUC for SOFA and APACHE II scores. Patients with higher admission levels of UCP2 (>246.52 pg/mL) had significantly increased 28-day mortality compared with those with lower UCP2 levels (<246.52 pg/mL).

CONCLUSION

Serum UCP2 levels at admission were markedly increased in patients with sepsis, which is useful for early diagnose and prognostic prediction. UCP2 is a potential biomarker for sepsis, or even a subtype of sepsis.

Prognostic Significance of the Fission1/Parkin Ratio for Sepsis: A Prospective Cohort Study

Introduction: Fission1 (Fis1) and parkin are key proteins related to mitochondrial fission and mitophagy, respectively. This study aimed to assess the prognostic value of the Fis1/parkin ratio as a biomarker in patients with sepsis.

Methods: Consecutive patients with sepsis (n = 133) or simple infection (n = 24) were enrolled within 24 h of arrival at the intensive care unit (ICU). Serum levels of Fis1, parkin, mitofusin2 (Mfn2), and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) were measured by enzyme-linked immunosorbent assay (ELISA) upon ICU admission. Clinical parameters and standard laboratory test data were also collected. All patients received follow-up for at least 28 days.

Results: Patients with sepsis presented with significantly decreased serum levels of parkin, Mfn2, and PGC-1α, but an increased serum Fis1 level and Fis1/parkin, Fis1/Mfn2, and Fis1/PGC-1α ratios at ICU admission. Relative to patients with simple infections, the ratios were remarkably elevated in septic patients—particularly septic shock patients. The area under the receiver operating characteristic (ROC) curve of the Fis1/parkin ratio was greater than that of Fis1, parkin, Mfn2, and PGC-1α levels as well as that of the Fis1/Mfn2 and Fis1/PGC-1α ratios for prediction of 28-day mortality due to sepsis. All of the ratios were significantly higher in non-survivors than survivors at the 28-day follow-up examination. Fis1/parkin ratio was found to be an independent predictor of 28-day mortality in patients with sepsis.

Conclusions: The Fis1/parkin ratio is valuable for risk stratification in patients with sepsis and is associated with poor clinical outcomes for sepsis in the ICU.

Using l-Carnitine as a Pharmacologic Probe of the Interpatient and Metabolic Variability of Sepsis

OBJECTIVE

The objective of this review is to discuss the therapeutic use and differential treatment response to Levo-carnitine (l-carnitine) treatment in septic shock, and to demonstrate common lessons learned that are important to the advancement of precision medicine approaches to sepsis. We propose that significant interpatient variability in the metabolic response to l-carnitine and clinical outcomes can be used to elucidate the mechanistic underpinnings that contribute to sepsis heterogeneity.

METHODS

A narrative review was conducted that focused on explaining interpatient variability in l-carnitine treatment response. Relevant biological and patient-level characteristics considered include genetic, metabolic, and morphomic phenotypes; potential drug interactions; and pharmacokinetics (PKs).

MAIN RESULTS

Despite promising results in a phase I study, a recent phase II clinical trial of l-carnitine treatment in septic shock showed a nonsignificant reduction in mortality. However, l-carnitine treatment induces significant interpatient variability in l-carnitine and acylcarnitine concentrations over time. In particular, administration of l-carnitine induces a broad, dynamic range of serum concentrations and measured peak concentrations are associated with mortality. Applied systems pharmacology may explain variability in drug responsiveness by using patient characteristics to identify pretreatment phenotypes most likely to derive benefit from l-carnitine. Moreover, provocation of sepsis metabolism with l-carnitine offers a unique opportunity to identify metabolic response signatures associated with patient outcomes. These approaches can unmask latent metabolic pathways deranged in the sepsis syndrome and offer insight into the pathophysiology, progression, and heterogeneity of the disease.

CONCLUSIONS

The compiled evidence suggests there are several potential explanations for the variability in carnitine concentrations and clinical response to l-carnitine in septic shock. These serve as important confounders that should be considered in interpretation of l-carnitine clinical studies and broadly holds lessons for future clinical trial design in sepsis. Consideration of these factors is needed if precision medicine in sepsis is to be achieved.

Mitochondrial Dysregulation in Sepsis: A Literature Review

BACKGROUND

Until 2016, the condition Sepsis was widely understood to be the systemic immune response syndrome in the presence or suspicion of an infectious source. Systemic immune response syndrome, an adaptive response, has been repeatedly demonstrated to lack specificity for sepsis. The current definition of sepsis describes a dysregulated host response to infection, yet the dysregulated nature of the response has yet to be defined. Successful recognition and management of sepsis are critically dependent on understanding and operationalizing the definition of sepsis.

OBJECTIVE

The authors sought to review the current literature on sepsis and its relationship to oxygen downregulation within the mitochondria along the electron transport chain.

METHODS

Articles retrieved from databases PubMed and CINAHL, pertaining to human cells, post 2001, in English, original experimental, quasi-experimental, or cohort design. Articles were selected and retrieved by the first author and synthesized by both authors.

RESULTS

The 10 articles included in the review were all bench science cellular studies. They demonstrated consistent, statistically significant differences when investigating mitochondrial oxygen downregulation in sepsis versus control, offering strong, statistically significant support for the hypothesis of mitochondrial dysregulation in the septic host.

CONCLUSIONS

The evidence makes a compelling case for mitochondrial dysregulation to inform the current definition of sepsis as a dysregulated host response. As the evidence points to a linear, progressive time/exposure-dependent disruption in oxygen downregulation in sepsis at the cellular level, it lends credence to the recommendations for early intervention and its relationship with survivability. Time is not on the side of the individual with sepsis.

A neuroglobin-based high-affinity ligand trap reverses carbon monoxide-induced mitochondrial poisoning

Carbon monoxide (CO) remains the most common cause of human poisoning. The consequences of CO poisoning include cardiac dysfunction, brain injury, and death. CO causes toxicity by binding to hemoglobin and by inhibiting mitochondrial cytochrome c oxidase (CcO), thereby decreasing oxygen delivery and inhibiting oxidative phosphorylation. We have recently developed a CO antidote based on human neuroglobin (Ngb-H64Q-CCC). This molecule enhances clearance of CO from red blood cells in vitro and in vivo Herein, we tested whether Ngb-H64Q-CCC can also scavenge CO from CcO and attenuate CO-induced inhibition of mitochondrial respiration. Heart tissue from mice exposed to 3% CO exhibited a 42 ± 19% reduction in tissue respiration rate and a 33 ± 38% reduction in CcO activity compared with unexposed mice. Intravenous infusion of Ngb-H64Q-CCC restored respiration rates to that of control mice correlating with higher electron transport chain CcO activity in Ngb-H64Q-CCC-treated compared with PBS-treated, CO-poisoned mice. Further, using a Clark-type oxygen electrode, we measured isolated rat liver mitochondrial respiration in the presence and absence of saturating solutions of CO (160 μm) and nitric oxide (100 μm). Both CO and NO inhibited respiration, and treatment with Ngb-H64Q-CCC (100 and 50 μm, respectively) significantly reversed this inhibition. These results suggest that Ngb-H64Q-CCC mitigates CO toxicity by scavenging CO from carboxyhemoglobin, improving systemic oxygen delivery and reversing the inhibitory effects of CO on mitochondria. We conclude that Ngb-H64Q-CCC or other CO scavengers demonstrate potential as antidotes that reverse the clinical and molecular effects of CO poisoning.

High central venous oxygen saturation is associated with mitochondrial dysfunction in septic shock: A prospective observational study

To test the hypothesis that an impaired mitochondrial function is associated with altered central venous oxygen saturation (ScvO₂), venous‐to‐arterial carbon dioxide tension difference (delta PCO₂) or serum lactate in sepsis patients. This prospective cohort study was conducted in a single tertiary emergency department between April 2017 and March 2019. Patients with suspected sepsis were included in the study. Serum lactate was obtained in sepsis, ScvO₂ and delta PCO₂ were evaluated in septic shock patients. Mitochondrial function was determined from the peripheral blood mononuclear cells. Forty‐six patients with suspected sepsis were included. Of these, twenty patients were septic shock. Mitochondrial oxidative stress levels were increased in the high ScvO₂ group (ScvO₂ > 80%, n = 6), compared with the normal (70%‐80%, n = 9) and low ScvO₂ (<70%, n = 5) groups. A strong linear relationship was observed between the mitochondrial oxidative stress and ScvO₂ (r = .75; P = .01). However, mitochondrial respiration was increased in the low ScvO₂ group. In addition, mitochondrial complex II protein levels were significantly decreased in the high ScvO₂ group (P < .05). Additionally, there was no correlation between serum lactate, delta PCO₂, and mitochondria oxidative stress or mitochondria function. ScvO₂ can be potentially useful for developing new therapeutics to reduce mitochondrial dysfunction in septic shock patient.

A Multivariate Metabolomics Method for Estimating Platelet Mitochondrial Oxygen Consumption Rates in Patients with Sepsis

BACKGROUND

Sepsis-induced alterations in mitochondrial function contribute to organ dysfunction and mortality. Measuring mitochondrial function in vital organs is neither feasible nor practical, highlighting the need for non-invasive approaches. Mitochondrial function may be reflected in the concentrations of metabolites found in platelets and whole blood (WB) samples. We proposed to use these as alternates to indirectly estimate platelet mitochondrial oxygen consumption rate (mOCR) in sepsis patients.

METHODS

We determined the relationships between platelet mOCR and metabolites in both platelets and WB, as measured by quantitative 1H-NMR metabolomics. The associations were identified by building multiple linear regression models with stepwise forward-backward variable selection. We considered the models to be significant with an ANOVA test (p-value ≤ 0.05) and a positive predicted-R2.

RESULTS

The differences in adjusted-R2 and ANOVA p-values (platelet adj-R2: 0.836 (0.0003), 0.711 (0.0004) vs. WB adj-R2: 0.428 (0.0079)) from the significant models indicate the platelet models were more associated with platelet mOCR.

CONCLUSIONS

Our data suggest there are groups of metabolites in WB (leucine, acetylcarnitine) and platelets (creatine, ADP, glucose, taurine) that are associated with platelet mOCR. Thus, WB and platelet metabolites could be used to estimate platelet mOCR.

Platelet Mitochondrial Respiration, Endogenous Coenzyme Q10 and Oxidative Stress in Patients with Chronic Kidney Disease

Chronic kidney disease (CKD) is characterized by a progressive loss of renal function and a decrease of glomerular filtration rate. Reduced mitochondrial function, coenzyme Q₁₀ (CoQ₁₀), and increased oxidative stress in patients with CKD contribute to the disease progression. We tested whether CoQ₁₀ levels, oxidative stress and platelet mitochondrial bioenergetic function differ between groups of CKD patients.

METHODS

Twenty-seven CKD patients were enrolled in this trial, 17 patients had arterial hypertension (AH) and 10 patients had arterial hypertension and diabetes mellitus (AH and DM). The control group consisted of 12 volunteers. A high-resolution respirometry (HRR) method was used for the analysis of mitochondrial bioenergetics in platelets, and an HPLC method with UV detection was used for CoQ₁₀ determination in platelets, blood, and plasma. Oxidative stress was determined as thiobarbituric acid reactive substances (TBARS).

RESULTS

Platelets mitochondrial respiration showed slight, not significant differences between the groups of CKD patients and control subjects. The oxygen consumption by intact platelets positively correlated with the concentration of CoQ₁₀ in the platelets of CKD patients.

CONCLUSION

A decreased concentration of CoQ₁₀ and oxidative stress could contribute to the progression of renal dysfunction in CKD patients. The parameters of platelet respiration assessed by high-resolution respirometry can be used only as a weak biological marker for mitochondrial diagnosis and therapy monitoring in CKD patients.

Peripheral Blood Mononuclear Cells and Platelets Mitochondrial Dysfunction, Oxidative Stress, and Circulating mtDNA in Cardiovascular Diseases

Cardiovascular diseases (CVDs) are devastating disorders and the leading cause of mortality worldwide. The pathophysiology of cardiovascular diseases is complex and multifactorial and, in the past years, mitochondrial dysfunction and excessive production of reactive oxygen species (ROS) have gained growing attention. Indeed, CVDs can be considered as a systemic alteration, and understanding the eventual implication of circulating blood cells peripheral blood mononuclear cells (PBMCs) and or platelets, and particularly their mitochondrial function, ROS production, and mitochondrial DNA (mtDNA) releases in patients with cardiac impairments, appears worthwhile. Interestingly, reports consistently demonstrate a reduced mitochondrial respiratory chain oxidative capacity related to the degree of CVD severity and to an increased ROS production by PBMCs. Further, circulating mtDNA level was generally modified in such patients. These data are critical steps in term of cardiac disease comprehension and further studies are warranted to challenge the possible adjunct of PBMCs’ and platelets’ mitochondrial dysfunction, oxidative stress, and circulating mtDNA as biomarkers of CVD diagnosis and prognosis. This new approach might also allow further interesting therapeutic developments.

The Pathogenesis of Sepsis and Potential Therapeutic Targets

Sepsis is defined as “a life-threatening organ dysfunction caused by a host’s dysfunctional response to infection”. Although the treatment of sepsis has developed rapidly in the past few years, sepsis incidence and mortality in clinical treatment is still climbing. Moreover, because of the diverse manifestations of sepsis, clinicians continue to face severe challenges in the diagnosis, treatment, and management of patients with sepsis. Here, we review the recent development in our understanding regarding the cellular pathogenesis and the target of clinical diagnosis of sepsis, with the goal of enhancing the current understanding of sepsis. The present state of research on targeted therapeutic drugs is also elaborated upon to provide information for the treatment of sepsis.

Regulation of mitochondrial function as a promising target in platelet activation-related diseases

Platelets are anucleated cell elements produced by fragmentation of the cytoplasm of megakaryocytes and have a unique metabolic phenotype compared with circulating leukocytes, exhibiting a high coupling efficiency to mitochondrial adenosine triphosphate production with reduced respiratory reserve capacity. Platelet mitochondria are well suited for ex vivo analysis of different diseases. Even some diseases induce mitochondrial changes in platelets without reflecting them in other organs. During platelet activation, an integrated participation of glycolysis and oxidative phosphorylation is mediated by oxidative stress production-dependent signaling. The platelet activation-dependent procoagulant activity mediated by collagen, thrombin and hyperglycemia induce mitochondrial dysfunction to promote thrombosis in oxidative stress-associated pathological conditions. Interestingly, some compounds exhibit a protective action on platelet mitochondrial dysfunction through control of mitochondrial oxidative stress production or inhibition of respiratory complexes. They can be grouped in a) Natural source-derived compounds (e.g. Xanthohumol, Salvianoloc acid A and Sila-amide derivatives of NAC), b) TPP⁺-linked small molecules (e.g. mitoTEMPO and mitoQuinone) and c) FDA-approved drugs (e.g. metformin and statins), illustrating the wide range of molecular structures capable of effectively interacting with platelet mitochondria. The present review article aims to discuss the mechanisms of mitochondrial dysfunction and their association with platelet activation-related diseases.

Assessment of platelet respiration as emerging biomarker of disease

Mitochondrial dysfunction is currently acknowledged as a central pathomechanism of most common diseases of the 21(st) century. Recently, the assessment of the bioenergetic profile of human peripheral blood cells has emerged as a novel research field with potential applications in the development of disease biomarkers. In particular, platelets have been successfully used for the ex vivo analysis of mitochondrial respiratory function in several acute and chronic pathologies. An increasing number of studies support the idea that evaluation of the bioenergetic function in circulating platelets may represent the peripheral signature of mitochondrial dysfunction in metabolically active tissues (brain, heart, liver, skeletal muscle). Accordingly, impairment of mitochondrial respiration in peripheral platelets might have potential clinical applicability as a diagnostic and prognostic tool as well as a biomarker in treatment monitoring. The aim of this minireview is to summarize current information in the field of platelet mitochondrial dysfunction in both acute and chronic diseases.

Platelet aggregation after blunt trauma is associated with the acute respiratory distress syndrome and altered by cigarette smoke exposure

BACKGROUND

The risk of the acute respiratory distress syndrome (ARDS) is increased in passive and active smokers after blunt trauma. However, the mechanisms responsible, including the role of platelet aggregation, for this association are unknown.

METHODS

We analyzed 215 patients with severe blunt trauma from a prospective observational cohort at a Level I trauma center between 2010 and 2015. Subjects underwent impedance-based platelet aggregometry in response to platelet agonists arachidonic acid, adenosine diphosphate, collagen, and thrombin receptor activating peptide-6. Acute respiratory distress syndrome within the first 8 days of admission was adjudicated using Berlin criteria. Plasma cotinine was measured to assess cigarette smoke exposure. Regression analyses were used to assess the relationship between (1) platelet aggregation and ARDS and (2) cigarette smoke exposure and platelet aggregation.

RESULTS

At both 0 hour and 24 hours, impaired platelet aggregation was associated with increased odds of developing ARDS. Cigarette smoke exposure was associated with increased platelet aggregation upon arrival to the emergency department. However, at 24 hours, cigarette smoke exposure was associated with increased impairment in platelet aggregation, reflecting a statistically significant decline in platelet aggregation over the initial 24 hours after trauma. The relationship between this decline in platelet aggregation and ARDS differed by cigarette smoke exposure status, suggesting that impaired platelet activation differentially affects the risk of ARDS in those with cigarette smoke exposure (arachidonic acid, p for interaction: 0.005, collagen p for interaction: 0.02, adenosine diphosphate, p for interaction: 0.05).

CONCLUSION

Impaired platelet aggregation at 0 hour and 24 hours is associated with an increased risk of developing ARDS after severe blunt trauma. Cigarette smoke-exposed patients are more likely to develop impaired platelet aggregation over the first 24 hours of admission, which may contribute to their increased risk of ARDS.

LEVEL OF EVIDENCE

Prognostic/Epidemiological, level III.

Potential therapy strategy: targeting mitochondrial dysfunction in sepsis

Recently, the definition of sepsis was concluded to be a life-threatening organ dysfunction caused by a dysregulated host response to infection. Severe patients always present with uncorrectable hypotension or hyperlactacidemia, which is defined as septic shock. The new definition emphasizes dysregulation of the host response and multiple organ dysfunction, which is partially attributed to metabolic disorders induced by energy crisis and oxidative stress. Mitochondria are a cellular organelle that are well known as the center of energy production, and mitochondrial damage or dysfunction is commonly induced in septic settings and is a predominant factor leading to a worse prognosis. In the present review, we determine the major mitochondrial disorders from morphology to functions in sepsis. In the following, several clinical or pre-clinical assays for monitoring mitochondrial function are demonstrated according to accumulated evidence, which is the first step of specific therapy targeting to modulate mitochondrial function. Accordingly, various reagents used for regulating mitochondrial enzyme activities and promoting biogenesis have been documented, among which mitochondria-targeted cation, TPP-conjugated antioxidants are the most valuable for future trials and clinical treatment to improve mitochondrial function as they may take advantage of the prognosis associated with septic complications.

Platelet biomechanics, platelet bioenergetics, and applications to clinical practice and translational research

The purpose of this review is to explore the relationship between platelet bioenergetics and biomechanics and how this relationship affects the clinical interpretation of platelet function devices. Recent experimental and technological advances highlight platelet bioenergetics and biomechanics as alternative avenues for collecting clinically relevant data. Platelet bioenergetics drive energy production for key biomechanical processes like adhesion, spreading, aggregation, and contraction. Platelet function devices like thromboelastography, thromboelastometry, and aggregometry measure these biomechanical processes. Platelet storage, stroke, sepsis, trauma, or the activity of antiplatelet drugs alters measures of platelet function. However, the specific mechanisms governing these alterations in platelet function and how they relate to platelet bioenergetics are still under investigation.

Platelets release pathogenic serotonin and return to circulation after immune complex-mediated sequestration

There is a growing appreciation for the contribution of platelets to immunity; however, our knowledge mostly relies on platelet functions associated with vascular injury and the prevention of bleeding. Circulating immune complexes (ICs) contribute to both chronic and acute inflammation in a multitude of clinical conditions. Herein, we scrutinized platelet responses to systemic ICs in the absence of tissue and endothelial wall injury. Platelet activation by circulating ICs through a mechanism requiring expression of platelet Fcγ receptor IIA resulted in the induction of systemic shock. IC-driven shock was dependent on release of serotonin from platelet-dense granules secondary to platelet outside-in signaling by αIIbβ3 and its ligand fibrinogen. While activated platelets sequestered in the lungs and leaky vasculature of the blood-brain barrier, platelets also sequestered in the absence of shock in mice lacking peripheral serotonin. Unexpectedly, platelets returned to the blood circulation with emptied granules and were thereby ineffective at promoting subsequent systemic shock, although they still underwent sequestration. We propose that in response to circulating ICs, platelets are a crucial mediator of the inflammatory response highly relevant to sepsis, viremia, and anaphylaxis. In addition, platelets recirculate after degranulation and sequestration, demonstrating that in adaptive immunity implicating antibody responses, activated platelets are longer lived than anticipated and may explain platelet count fluctuations in IC-driven diseases.

Differential responses to larger volume intra-aortic balloon counterpulsation: Hemodynamic and clinical outcomes

Objectives

Examine hemodynamic and clinical correlates of use of an intra‐aortic balloon pump catheter in a single center.

Background

The intra‐aortic balloon pump catheter (IABC) has been used for 50 years but the clinical benefit is still debated. We reviewed 76 patients with right heart catheter measurements prior to IABC to assess response and outcomes.

Methods

All patients who received IABC with a 50cc balloon for at least 1 hour were included in this retrospective chart review study. Demographics, comorbidities, lab values, and hemodynamic parameters were recorded at baseline and 15 h postinsertion.

Results

Seventy‐six patients had paired measurements of cardiac output. 60 patients had a higher cardiac output with IABC treatment (responder group) and 16 did not (nonresponders). In the 60 patients in the responder group, cardiac output and index significantly increased from baseline 3.6 ± 1.3 L/min to 5.2 ± 1.8 L/min, and 1.8 ± 0.5 L/min/m² to 2.6 ± 0.8 L/min/m² respectively following IABC placement (P < 0.0001 for both comparisons). Various hemodynamic variables were examined and the best predictor of response to IABC was a cardiac power index of 0.3 or less. Regardless of response, in hospital survival was similar between groups.

Conclusions

The majority of patients improve their cardiac output with IABC but survival was unchanged. Further work into the pathophysiology of cardiogenic shock is needed.

Lower mitochondrial dysfunction in survivor septic patients with mitochondrial DNA haplogroup JT

OBJECTIVE

The comparison on mitochondrial function between severe septic patients and healthy control subjects according to mitochondrial deoxyribonucleic acid (mtDNA) haplogroup has not been previously reported; and this was the objective of the current study.

METHODS

Prospective, multicenter, observational study. We obtained blood samples from 198 severe septic patients at days 1, 4 and 8 of severe sepsis diagnosis and from 96 sex- and age-matched healthy controls to determine mtDNA haplogroup and platelet respiratory complex IV (CIV) specific activity. The endpoint of the study was 30-day mortality.

RESULTS

We included 198 severe septic patients (38 with mtDNA haplogroup JT and 160 with mtDNA haplogroup non-JT) and 96 healthy control subjects (16 with mtDNA haplogroup JT and 80 with mtDNA haplogroup non-JT). We have no found statistically significant differences in platelet CIV specific activity between healthy controls and survivor severe septic patients with mtDNA haplogroup JT at days 1, 4 and 8 of severe sepsis diagnosis; and the remaining severe septic patients showed lower platelet CIV specific activity than healthy controls with the same mtDNA haplogroup.

CONCLUSIONS

The new finding of our study was that survivor severe septic patients and healthy controls with mtDNA haplogroup JT showed no different platelet Civ specific activity.

Septic patients with mitochondrial DNA haplogroup JT have higher respiratory complex IV activity and survival rate

OBJECTIVE

The influence of mitochondrial deoxyribonucleic acid (mtDNA) haplogroup or oxidative phosphorylation system (OXPHOS) function on survival of septic patients has been scarcely studied. However, the association between mtDNA haplogroup, OXPHOS capacity at diagnosis of severe sepsis, and survival has been not previously reported, and that was the objective of the present study.

METHODS

This was a prospective, multicenter, observational study. Blood samples from 198 patients at diagnosis of severe sepsis were analyzed to determine mtDNA haplogroup and platelet respiratory complex IV (CIV) specific activity. The end point of the study was 30-day survival.

RESULTS

Septic patients with mtDNA haplogroup JT showed higher 30-day survival than those with mtDNA haplogroup non-JT (31/38 [81.6%] vs 99/160 [61.9%]; P= .02). Septic patients with mtDNA haplogroup JT showed higher platelet CIV specific activity than those with mtDNA haplogroup non-JT (P= .002).

CONCLUSIONS

The main novel finding of our study, including the largest series providing data on platelet CIV specific activity according to mtDNA haplogroup in severe septic patients, was that those with mtDNA haplogroup JT showed higher survival and higher platelet CIV specific activity at diagnosis of severe sepsis than patients with mtDNA haplogroup non-JT.

Decrease of oxidative phosphorylation system function in severe septic patients

OBJECTIVE

The comparison of oxidative phosphorylation system capacities between septic patients and control subjects has been scarcely analyzed and only in studies with small sample size (fewer than 40 septic patients and 40 controls). Thus, the objective of this study was to compare platelet respiratory complex IV (CIV) activity between severe septic patients and healthy individuals in a larger series (including 198 severe septic patients and 96 healthy controls).

METHODS

A prospective, multicenter, observational study was carried out in 6 Spanish intensive care units. We obtained blood samples from 198 severe septic patients at day 1, 4, and 8 of the severe sepsis diagnosis and 96 sex- and age-matched healthy control individuals and determined platelet CIV-specific activity. The end point of the study was 30-day mortality.

RESULTS

Control individuals showed higher platelet CIV-specific activity (P < .001) than surviving (n = 130) or nonsurviving (n = 68) severe septic patients at day 1, 4, and 8 of severe sepsis diagnosis.

CONCLUSIONS

The major finding of our work, involving the largest series to date of severe septic patients with data on oxidative phosphorylation system capacity, was that surviving and nonsurviving septic patients showed lower platelet CIV-specific activity during the first week of sepsis than healthy controls.