Mitochondrial function in sepsis: acute phase versus multiple organ failure

LLL 44-4 : Micronutrients in acute disease and critical illness

Micronutrients (MN), i.e. trace elements and vitamins, are essential components of the diet in relatively small amounts in any form of nutrition, with special needs in critically ill patients. Critical illness is characterised by the presence of inflammation and oxidative stress. MNs are tightly involved in antioxidant and immune defences. In addition, some conditions, and treatments result in large losses of biological fluids containing MNs: therefore, acute renal injury requiring renal replacement therapy, acute intestinal failure, and major burns and trauma are at high risk of acute depletion of body stores, and of deficiency. MN requirements are increased above standard DRI. Blood level interpretation is complicated by inflammation: some biomarkers assist the status determination. Due to the acute challenges of critical illness, it of utmost importance to cover the needs to maintain the organism's endogenous immune and antioxidant defences, and capacity to repair tissues. Practical strategies are proposed.

Advances and Challenges in Sepsis Management: Modern Tools and Future Directions

Sepsis, a critical condition marked by systemic inflammation, profoundly impacts both innate and adaptive immunity, often resulting in lymphopenia. This immune alteration can spare regulatory T cells (Tregs) but significantly affects other lymphocyte subsets, leading to diminished effector functions, altered cytokine profiles, and metabolic changes. The complexity of sepsis stems not only from its pathophysiology but also from the heterogeneity of patient responses, posing significant challenges in developing universally effective therapies. This review emphasizes the importance of phenotyping in sepsis to enhance patient-specific diagnostic and therapeutic strategies. Phenotyping immune cells, which categorizes patients based on clinical and immunological characteristics, is pivotal for tailoring treatment approaches. Flow cytometry emerges as a crucial tool in this endeavor, offering rapid, low cost and detailed analysis of immune cell populations and their functional states. Indeed, this technology facilitates the understanding of immune dysfunctions in sepsis and contributes to the identification of novel biomarkers. Our review underscores the potential of integrating flow cytometry with omics data, machine learning and clinical observations to refine sepsis management, highlighting the shift towards personalized medicine in critical care. This approach could lead to more precise interventions, improving outcomes in this heterogeneously affected patient population.

Construction and validation of a mitochondria-associated genes prognostic signature and immune microenvironment characteristic of sepsis

BACKGROUND

Sepsis is a common critical condition seen in clinical settings, with mitochondrial dysfunction playing an important role in the progression of sepsis. However, a mitochondrial prognosis model related to sepsis has not been established yet, and the relationship between the sepsis immune microenvironment and mitochondria remains unclear.

METHODS

Sepsis prognostic mitochondria-associated genes (MiAGs) were screened by univariate Cox, multivariate Cox, and LASSO analysis from the GEO dataset. Consensus Cluster was used to analyze MiAGs-based molecular subtypes for sepsis. The ESTIMATE and ssGSEA algorithms were used to analyze the situation of sepsis immune cell infiltration and its relation to MiAGs. Further, MiAGs score was calculated to construct a sepsis prognosis risk model to predict the prognosis of sepsis patients. Clinical blood samples were used to investigate the expression level of selected MiAGs in sepsis. Single-cell sequencing analysis, mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and ATP detection were used to verify the influence of MiAGs on mitochondrial dysfunction in sepsis.

RESULTS

A total of 5 MiAGs of sepsis were screened. Based on MiAGs, sepsis MiAGs subtypes were analyzed, where Cluster A had a better prognosis than Cluster B, and there were significant differences in immune infiltration between the two clusters. The sepsis mitochondrial prognosis model suggested that the high MiAG score group had a shorter survival time compared to the low MiAG score group. Significant differences were also observed in the immune microenvironment between the high and low MiAG score groups. Prognostic analysis and the Nomogram indicated that the MiAG score is an independent prognostic factor in sepsis. Single-cell sequencing analysis exhibited the possible influence of MiAGs on the mitochondrial function of monocytes. Finally, the downregulation of the COX7B could effectively improve mitochondrial function in the LPS-stimulated sepsis model.

CONCLUSION

Our findings suggest that MiAGs can be used to predict the prognosis of sepsis and that regulating the mitochondrial prognostic gene COX7B can effectively improve the mitochondrial function of immune cells in sepsis.

Transcription Factor NRF2 in Shaping Myeloid Cell Differentiation and Function

NFE2-related factor 2 (NRF2) is a master transcription factor (TF) that coordinates key cellular homeostatic processes including antioxidative responses, autophagy, proteostasis, and metabolism. The emerging evidence underscores its significant role in modulating inflammatory and immune processes. This chapter delves into the role of NRF2 in myeloid cell differentiation and function and its implication in myeloid cell-driven diseases. In macrophages, NRF2 modulates cytokine production, phagocytosis, pathogen clearance, and metabolic adaptations. In dendritic cells (DCs), it affects maturation, cytokine production, and antigen presentation capabilities, while in neutrophils, NRF2 is involved in activation, migration, cytokine production, and NETosis. The discussion extends to how NRF2's regulatory actions pertain to a wide array of diseases, such as sepsis, various infectious diseases, cancer, wound healing, atherosclerosis, hemolytic conditions, pulmonary disorders, hemorrhagic events, and autoimmune diseases. The activation of NRF2 typically reduces inflammation, thereby modifying disease outcomes. This highlights the therapeutic potential of NRF2 modulation in treating myeloid cell-driven pathologies.

Lactate: The Fallacy of Oversimplification

Almost a quarter of a millennium after the discovery of an acidic substance in sour milk by Swedish chemist Carl Wilhelm Scheele and more than 100 years after the demonstration of a tight connection between this lactic acid and tissue hypoxia in shock, we are still surrounded by false beliefs and misunderstandings regarding this fascinating molecule. Common perceptions of lactate, the conjugate base of lactic acid, as a plain waste product of anaerobic metabolism and a marker of cellular distress could not be further from the truth. Lactate is formed and utilized continuously by our cells, even under fully aerobic conditions, in large quantities, and although marked hyperlactatemia is always a red flag in our patients, not all these conditions are life-threatening and vice versa-not all critically ill patients have hyperlactatemia. Lactate also does not promote acidosis by itself; it is not toxic, nor is it a metabolic renegade. On the contrary, it has many beneficial properties, and an interpretation of hyperlactatemia might be trickier than we tend to think. The aim of this article is to debunk some of the deeply rooted myths regarding this fascinating molecule.

OXYGEN CONSUMPTION AS AN EARLY WARNING SYSTEM IN THE CRITICALLY ILL

ABSTRACT

Introduction: In this study, we assessed whether changes in oxygen consumption (VO 2 ) and other metabolic parameters could be used as an early warning system for detecting clinical deterioration in mechanically ventilated patients. Methods: This was a prospective cohort study of adult patients requiring mechanical ventilation between February 2016 and March 2019. We looked for changes in VO 2 , carbon dioxide production (VCO 2 ), respiratory quotient (RQ), and end-tidal carbon dioxide (EtCO 2 ), occurring prior to clinical deterioration. Clinical deterioration was predefined as a requirement of vasopressor, an increase in serum lactate by 20% where at least one value was above 3 mmol/L, or a decrease in hemoglobin by 20% in the 4 hours prior to clinical deterioration. Results A total of 141 patients were included. There were no detectable changes in VO 2 , VCO 2 , and EtCO 2 within the 4 hours prior to any clinical deterioration. RQ increased significantly within the 4 hours prior to an increase in lactate as compared with no increase in lactate, but there were no detectable changes prior to other clinical deteriorations. Conclusions RQ has the potential to be an early marker of tissue hypoperfusion or mitochondrial dysfunction. However, future studies are necessary to evaluate the use of RQ as a bedside monitor in critical care settings.

Butyrate Supplementation Exacerbates Myocardial and Immune Cell Mitochondrial Dysfunction in a Rat Model of Faecal Peritonitis

Mitochondrial dysfunction and immune cell dysfunction are commonplace in sepsis and are associated with increased mortality risk. The short chain fatty acid, butyrate, is known to have anti-inflammatory effects and promote mitochondrial biogenesis. We therefore explored the immunometabolic effects of butyrate in an animal model of sepsis. Isolated healthy human volunteer peripheral mononuclear cells were stimulated with LPS in the presence of absence of butyrate, and released cytokines measured. Male Wistar rats housed in metabolic cages received either intravenous butyrate infusion or placebo commencing 6 h following faecal peritonitis induction. At 24 h, splenocytes were isolated for high-resolution respirometry, and measurement of mitochondrial membrane potential (MMP), reactive oxygen species (mtROS), and intracellular cytokines (TNF alpha, IL-10) using flow cytometry. Isolated splenocytes from septic and septic butyrate treated rats were stimulated with LPS for 18 h and the effects of butyrate on cytokine release assessed. Ex vivo, butyrate (1.8 mM) reduced LPS-induced TNF alpha (p = 0.019) and IL-10 (p = 0.001) release by human PBMCs. In septic animals butyrate infusion reduced the respiratory exchange ratio (p < 0.001), consistent with increased fat metabolism. This was associated with a reduction in cardiac output (p = 0.001), and increased lactate (p = 0.031) compared to placebo-treated septic animals (p < 0.05). Butyrate treatment was associated with a reduction in splenocyte basal respiration (p = 0.077), proton leak (p = 0.022), and non-mitochondrial respiration (p = 0.055), and an increase in MMP (p = 0.007) and mtROS (p = 0.027) compared to untreated septic animals. Splenocyte intracellular cytokines were unaffected by butyrate, although LPS-induced IL-10 release was impaired (p = 0.039). In summary, butyrate supplementation exacerbates myocardial and immune cell mitochondrial dysfunction in a rat model of faecal peritonitis.

Sepsis, pyruvate, and mitochondria energy supply chain shortage

Balancing high energy-consuming danger resistance and low energy supply of disease tolerance is a universal survival principle that often fails during sepsis. Our research supports the concept that sepsis phosphorylates and deactivates mitochondrial pyruvate dehydrogenase complex control over the tricarboxylic cycle and the electron transport chain. StimulatIng mitochondrial energetics in septic mice and human sepsis cell models can be achieved by inhibiting pyruvate dehydrogenase kinases with the pyruvate structural analog dichloroacetate. Stimulating the pyruvate dehydrogenase complex by dichloroacetate reverses a disruption in the tricarboxylic cycle that induces itaconate, a key mediator of the disease tolerance pathway. Dichloroacetate treatment increases mitochondrial respiration and ATP synthesis, decreases oxidant stress, overcomes metabolic paralysis, regenerates tissue, organ, and innate and adaptive immune cells, and doubles the survival rate in a murine model of sepsis.

Nicotinamide Mononucleotide Administration Triggers Macrophages Reprogramming and Alleviates Inflammation During Sepsis Induced by Experimental Peritonitis

Peritonitis and subsequent sepsis lead to high morbidity and mortality in response to uncontrolled systemic inflammation primarily mediated by macrophages. Nicotinamide adenine dinucleotide (NAD+) is an important regulator of oxidative stress and immunoinflammatory responses. However, the effects of NAD+ replenishment during inflammatory activation are still poorly defined. Hence, we investigated whether the administration of β-nicotinamide mononucleotide (β-NMN), a natural biosynthetic precursor of NAD+, could modulate the macrophage phenotype and thereby ameliorate the dysregulated inflammatory response during sepsis. For this purpose, C57BL6 mice were subjected to the cecal ligation and puncture (CLP) model to provoke sepsis or were injected with thioglycolate to induce sterile peritonitis with recruitment and differentiation of macrophages into the inflamed peritoneal cavity. β-NMN was administered for 4 days after CLP and for 3 days post thioglycolate treatment where peritoneal macrophages were subsequently analyzed. In the CLP model, administration of β-NMN decreased bacterial load in blood and reduced clinical signs of distress and mortality during sepsis. These results were supported by transcriptomic analysis of hearts and lungs 24 h post CLP-induction, which revealed that β-NMN downregulated genes controlling the immuno-inflammatory response and upregulated genes involved in bioenergetic metabolism, mitochondria, and autophagy. In the thioglycolate model, a significant increase in the proportion of CD206 macrophages, marker of anti-inflammatory M2 phenotype, was detected on peritoneal exudate macrophages from β-NMN-administered mice. Transcriptomic signature of these macrophages after bacterial stimulation confirmed that β-NMN administration limited the pro-inflammatory M1 phenotype and induced the expression of specific markers of M2 type macrophages. Furthermore, our data show that β-NMN treatment significantly impacts NAD + metabolism. This shift in the macrophage phenotype and metabolism was accompanied by a reduction in phagolysosome acidification and secretion of inflammatory mediators in macrophages from β-NMN-treated mice suggesting a reduced pro-inflammatory activation. In conclusion, administration of β-NMN prevented clinical deterioration and improved survival during sepsis. These effects relied on shifts in the metabolism of organs that face up an increased energy requirement caused by bacterial infection and in innate immunity response, including reprogramming of macrophages from a highly inflammatory phenotype to an anti-inflammatory/pro-resolving profile.

Association of mitochondrial respiratory chain enzymes with the risk and mortality of sepsis among Chinese children

BACKGROUND

Sepsis is a leading cause of pediatric morbidity and mortality worldwide. The aim of this study was to explore the association of decreased mitochondrial respiratory chain enzyme activities with the risk for pediatric sepsis, and explore their association with mortality among affected children.

METHODS

A total of 50 incident cases with sepsis and 49 healthy controls participated in this study. The level of serum coenzyme Q10 was measured by high-performance liquid chromatography, and selected mitochondrial respiratory chain enzymes in WBC were measured using spectrophotometric. Logistic regression models were used to estimate odds ratio (OR) and 95% confidence interval (CI).

RESULTS

The levels of CoQ10, complex II, complex I + III and FoF1-ATPase were significantly higher in healthy controls than in children with sepsis (p < 0.001, = 0.004, < 0.001 and < 0.001, respectively). In children with sepsis, levels of CoQ10 and complex I + III were significantly higher in survived cases than in deceased cases (p < 0.001). Per 0.05 μmol/L, 50 nmol/min.mg and 100 nmol/min.mg increment in CoQ10, complex I + III and FoF1-ATPase were associated with significantly lowered risk of having sepsis, even after adjusting for confounding factors (OR = 0.85, 0.68 and 0.04, p = 0.001, < 0.001 and < 0.001, respectively). Per 0.05 μmol/L and 50 nmol/min.mg increment in CoQ10 and complex I + III was associated with significantly lowered risk of dying from sepsis during hospitalization, and significance retained after adjustment (OR = 0.73 and 0.76, 95% CI: 0.59 to 0.90 and 0.64 to 0.89, p = 0.004 and 0.001, respectively) in children with sepsis.

CONCLUSIONS

Our findings indicate the promising predictive contribution of low serum CoQ10 and complex I + III to the risk of pediatric sepsis and its associated mortality during hospitalization among Chinese children. Trial registration The trial was registered with www.chictr.org.cn , number ChiCTR-IOR-15006446 on May 05, 2015. Retrospectively registered.

Refining the Pediatric Multiple Organ Dysfunction Syndrome

Since its introduction into the medical literature in the 1970s, the term multiple organ dysfunction syndrome (or some variant) has been applied broadly to any patient with >1 concurrent organ dysfunction. However, the epidemiology, mechanisms, time course, and outcomes among children with multiple organ dysfunction vary substantially. We posit that the term pediatric multiple organ dysfunction syndrome (or MODS) should be reserved for patients with a systemic pathologic state resulting from a common mechanism (or mechanisms) that affects numerous organ systems simultaneously. In contrast, children in whom organ injuries are attributable to distinct mechanisms should be considered to have additive organ system dysfunctions but not the syndrome of MODS. Although such differentiation may not always be possible with current scientific knowledge, we make the case for how attempts to differentiate multiple organ dysfunction from other states of additive organ dysfunctions can help to evolve clinical and research priorities in diagnosis, monitoring, and therapy from largely organ-specific to more holistic strategies.

miR-221-5p-Mediated Downregulation of JNK2 Aggravates Acute Lung Injury

Sepsis and acute lung injury (ALI) are linked to mitochondrial dysfunction; however, the underlying mechanism remains elusive. We previously reported that c-Jun N-terminal protein kinase 2 (JNK2) promotes stress-induced mitophagy by targeting small mitochondrial alternative reading frame (smARF) for ubiquitin-mediated proteasomal degradation, thereby preventing mitochondrial dysfunction and restraining inflammasome activation. Here we report that loss of JNK2 exacerbates lung inflammation and injury during sepsis and ALI in mice. JNK2 is downregulated in mice with endotoxic shock or ALI, concomitantly correlated inversely with disease severity. Small RNA sequencing revealed that miR-221-5p, which contains seed sequence matching to JNK2 mRNA 3’ untranslated region (3’UTR), is upregulated in response to lipopolysaccharide, with dynamically inverse correlation with JNK2 mRNA levels. miR-221-5p targets the 3’UTR of JNK2 mRNA leading to its downregulation. Accordingly, miR-221-5p exacerbates lung inflammation and injury during sepsis in mice by targeting JNK2. Importantly, in patients with pneumonia in medical intensive care unit, JNK2 mRNA levels in alveolar macrophages flow sorted from non-bronchoscopic broncholaveolar lavage (BAL) fluid were inversely correlated strongly and significantly with the percentage of neutrophils, neutrophil and white blood cell counts in BAL fluid. Our data suggest that miR-221-5p targets JNK2 and thereby aggravates lung inflammation and injury during sepsis.

What Is the Utility of Measuring Lactate Levels in Patients with Sepsis and Septic Shock?

Elevations in blood lactate concentrations have been studied in sepsis and other disease states for decades and are well known to be associated with increased mortality. Many studies have also demonstrated the prognostic accuracy of serial lactate levels, and some have suggested that lactate clearance may be a useful therapeutic target for resuscitation. Lactate measurements have therefore gained an increasingly prominent role in sepsis definitions, screening protocols, management guidelines, and quality measures over the past two decades. The heavy emphasis on lactate monitoring, however, has also generated controversy and concerns. Lactate is not specific to infection and its frequent use for sepsis screening and diagnosis may therefore trigger unnecessary broad-spectrum antibiotic use in some patients. Because hyperlactatemia does not always reflect fluid-responsive hypoperfusion, titrating resuscitation to lactate clearance can also lead to unnecessary fluid and volume overload. More broadly, there is a lack of high-quality evidence demonstrating that initial and serial lactate monitoring leads to better patient-centered outcomes. Indeed, a recent randomized controlled trial comparing resuscitation strategies based on lactate clearance versus normalizing capillary refill time showed no benefit and potential harm with lactate-guided therapy. In this article, we review the basic pathobiology of lactate metabolism and delineate why the traditional paradigm that hyperlactatemia reflects tissue hypoxia is overly simplistic and incomplete. We then review the evidence behind the diagnostic, prognostic, and therapeutic uses of lactate monitoring and place this in the context of evolving sepsis diagnosis and management guidelines.

Selenocompounds and Sepsis: Redox Bypass Hypothesis for Early Diagnosis and Treatment: Part A-Early Acute Phase of Sepsis: An Extraordinary Redox Situation (Leukocyte/Endothelium Interaction Leading to Endothelial Damage)

Significance: Sepsis is a health disaster. In sepsis, an initial, beneficial local immune response against infection evolves rapidly into a generalized, dysregulated response or a state of chaos, leading to multiple organ failure. Use of life-sustaining supportive therapies creates an unnatural condition, enabling the complex cascades of the sepsis response to develop in patients who would otherwise die. Multiple attempts to control sepsis at an early stage have been unsuccessful. Recent Advances: Major events in early sepsis include activation and binding of leukocytes and endothelial cells in the microcirculation, damage of the endothelial surface layer (ESL), and a decrease in the plasma concentration of the antioxidant enzyme, selenoprotein-P. These events induce an increase in intracellular redox potential and lymphocyte apoptosis, whereas apoptosis is delayed in monocytes and neutrophils. They also induce endothelial mitochondrial and cell damage. Critical Issues: Neutrophil production increases dramatically, and aggressive immature forms are released. Leukocyte cross talk with other leukocytes and with damaged endothelial cells amplifies the inflammatory response. The release of large quantities of reactive oxygen, halogen, and nitrogen species as a result of the leukocyte respiratory burst, endothelial mitochondrial damage, and ischemia/reperfusion processes, along with the marked decrease in selenoprotein-P concentrations, leads to peroxynitrite damage of the ESL, reducing flow and damaging the endothelial barrier. Future Directions: Endothelial barrier damage by activated leukocytes is a time-sensitive event in sepsis, occurring within hours and representing the first step toward organ failure and death. Reducing or stopping this event is necessary before irreversible damage occurs.

Evaluation of thiamine as adjunctive therapy in COVID-19 critically ill patients: a two-center propensity score matched study

Background

Thiamine is a precursor of the essential coenzyme thiamine pyrophosphate required for glucose metabolism; it improves the immune system function and has shown to reduce the risk of several diseases. The role of thiamine in critically ill septic patient has been addressed in multiple studies; however, it’s role in COVID-19 patients is still unclear. The aim of this study was to evaluate the use of thiamine as an adjunctive therapy on mortality in COVID-19 critically ill patients.

Methods

This is a two-center, non-interventional, retrospective cohort study for critically ill patients admitted to intensive care units (ICUs) with a confirmed diagnosis of COVID19. All patients aged 18 years or older admitted to ICUs between March 1, 2020, and December 31, 2020, with positive PCR COVID-19 were eligible for inclusion. We investigated thiamine use as an adjunctive therapy on the clinical outcomes in critically ill COVID-19 patients after propensity score matching.

Results

A total of 738 critically ill patients with COVID-19 who had been admitted to ICUs were included in the study. Among 166 patients matched using the propensity score method, 83 had received thiamine as adjunctive therapy. There was significant association between thiamine use with in-hospital mortality (OR = 0.39; 95% CI 0.19–0.78; P value = 0.008) as well as the 30-day mortality (OR = 0.37; 95% CI 0.18–0.78; P value = 0.009). Moreover, patients who received thiamine as an adjunctive therapy were less likely to have thrombosis during ICU stay [OR (95% CI) 0.19 (0.04–0.88), P value = 0.03].

Conclusion

Thiamine use as adjunctive therapy may have potential survival benefits in critically ill patients with COVID-19. Additionally, it was associated with a lower incidence of thrombosis. Further interventional studies are required to confirm these findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03648-9.

Mechanism of Mitophagy and Its Role in Sepsis Induced Organ Dysfunction: A Review

Autophagy, an evolutionarily conserved process, plays an important role in maintaining cellular homeostasis under physiological and pathophysiological conditions. It is widely believed that mitochondria influence the development of disease by regulating cellular metabolism. When challenged by different stimuli, mitochondria may experience morphological disorders and functional abnormalities, leading to a selective form of autophagy-mitophagy, which can clear damaged mitochondria to promote mitochondrial quality control. Sepsis is a complex global problem with multiple organ dysfunction, often accompanied by manifold mitochondrial damage. Recent studies have shown that autophagy can regulate both innate and acquired immune processes to protect against organ dysfunction in sepsis. Sepsis-induced mitochondrial dysfunction may play a pathophysiological role in the initiation and progression of sepsis-induced organ failure. Mitophagy is reported to be beneficial for sepsis by eliminating disabled mitochondria and maintaining homeostasis to protect against organ failure. In this review, we summarize the recent findings and mechanisms of mitophagy and its involvement in septic organ dysfunction as a potential therapeutic target.

Metabolic Alterations in Sepsis

Sepsis is defined as “life-threatening organ dysfunction caused by a dysregulated host response to infection”. Contrary to the older definitions, the current one not only focuses on inflammation, but points to systemic disturbances in homeostasis, including metabolism. Sepsis leads to sepsis-induced dysfunction and mitochondrial damage, which is suggested as a major cause of cell metabolism disorders in these patients. The changes affect the metabolism of all macronutrients. The metabolism of all macronutrients is altered. A characteristic change in carbohydrate metabolism is the intensification of glycolysis, which in combination with the failure of entering pyruvate to the tricarboxylic acid cycle increases the formation of lactate. Sepsis also affects lipid metabolism—lipolysis in adipose tissue is upregulated, which leads to an increase in the level of fatty acids and triglycerides in the blood. At the same time, their use is disturbed, which may result in the accumulation of lipids and their toxic metabolites. Changes in the metabolism of ketone bodies and amino acids have also been described. Metabolic disorders in sepsis are an important area of research, both for their potential role as a target for future therapies (metabolic resuscitation) and for optimizing the current treatment, such as clinical nutrition.

Endogenous Glucose Production in Critical Illness

Regulation of endogenous glucose production (EGP) by hormonal, neuronal, and metabolic signaling pathways contributes to the maintenance of euglycemia under normal physiologic conditions. EGP is defined by the generation of glucose from substrates through glycogenolysis and gluconeogenesis, usually in fasted states, for local and systemic use. Abnormal increases in EGP are noted in patients with diabetes mellitus type 2, and elevated EGP may also impact the pathogenesis of nonalcoholic fatty liver disease and congestive heart failure. In this narrative review, we performed a literature search in PubMed to identify recently published English language articles characterizing EGP in critical illness. Evidence from preclinical and clinical studies demonstrates that critical illness can disrupt EGP through multiple mechanisms including increased systemic inflammation, counterregulatory hormone and catecholamine release, alterations in the hypothalamic-pituitary axis, insulin resistance, lactic acidosis, and iatrogenic insults such as vasopressors and glucocorticoids administered as part of clinical care. EGP contributes to hyperglycemia in critical illness when abnormally elevated and to hypoglycemia when abnormally depressed, each of which has been independently associated with increased mortality. Increased EGP may also promote protein catabolism that could worsen critical illness myopathy and impede recovery. Better understanding of the mechanisms and factors contributing to dysregulated EGP in critical illness may help in the development of therapeutic strategies that promote euglycemia, reduce intensive care unit-associated catabolism, and improve patient outcomes.

Serum Mitochondrial Quality Control Related Biomarker Levels are Associated with Organ Dysfunction in Septic Patients

BACKGROUND

To investigate the feasibility and the value of using mitochondrial quality control (MQC)-related proteins as biomarkers in septic patients.

METHODS

The enrolled subjects were divided into four groups: healthy control group (n = 30), intensive care unit (ICU) control group (n = 62), septic nonshock group (n = 40), and septic shock group (n = 94). Serum levels of peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), fission protein 1 (Fis1), mitofusin2 (Mfn2), and Parkin were measured by enzyme-linked immunosorbent assay at the time of enrollment for all groups. Clinical parameters and laboratory test results were also collected.

RESULTS

The levels of MQC-related biomarkers between any two of the four groups were significantly different (P < 0.001 for all). The serum levels of PGC-1α, Mfn2, and Parkin were lowest in healthy individuals; the levels were dramatically higher in the ICU control group compared with the others, and they decreased progressively from the septic nonshock group to the septic shock group. However, the pattern for Fis1 was inverse; the more severe the condition was, the higher the level of Fis1. Moreover, there was moderate correlation between MQC-related biomarkers and the SOFA score (PGC-1α, r = -0.662; Fis1, r = 0.609; Mfn2, r = -0.677; Parkin, r = 0.-0.674, P < 0.001 for all).

CONCLUSIONS

The serum levels of PGC-1α, Fis1, Mfn2, and Parkin were significantly correlated with organ dysfunction and reflected the disease progression and severity. The dynamic surveillance of these four biomarkers could be beneficial to predict outcome and guide treatment.

Anti-inflammatory activity of 3-cinnamoyltribuloside and its metabolomic analysis in LPS-activated RAW 264.7 cells

BACKGROUND

Inflammation is a response to tissue injuries, which is indispensable and important for human health, but excessive inflammation can potentially cause damage to the host organisms. Camellia nitidissima Chi, one traditional medicinal and edible plant in China, was reported to exhibit anti-inflammation capability. Hence, this study was conducted to isolate the bioactive compounds from the flowers of C. nitidissima Chi and evaluate their anti-inflammatory activity.

METHODS

The phytochemicals from the flowers of C. nitidissima Chi were isolated and purified by silica gel, Sephadex LH-20 gel, C18 reversed silica gel, semi-preparative HPLC, and identified by the spectrum technologies. The anti-inflammatory activity of isolated compounds was evaluated using cultured macrophage RAW 264.7 cells. Whereafter the potential metabolic mechanism of the anti-inflammatory activity of the bioactive compound was investigated by a 1H-NMR based metabolomics approach. The metabolites in 1H-NMR spectra were identified by querying the Human Metabolome Database and Madison Metabolomics Consortium Database online. And the multivariate statistical analysis was performed to evaluate the variability of metabolites among samples and between sample classes.

RESULTS

The compound isolated from the flowers of C. nitidissima Chi was identified as 3-cinnamoyltribuloside (3-CT). 3-CT could inhibit the NO production and the mRNA expression of iNOS involved in lipopolysaccharide (LPS)-activated RAW 264.7 cells. Moreover, 3-CT could inhibit the expression of a series of inflammatory cytokines, including TNF-α, IL-1β, and IL-6, both at the mRNA level and protein level. The 1H-NMR based metabolomics approach was applied to investigate the potential metabolic mechanism of the anti-inflammatory activity of 3-CT. Thirty-five metabolites were identified and assigned. Orthogonal signal correction partial least-squares discriminant analysis (OSC-PLS-DA) of the 1H-NMR data showed 3-CT could balance the significant changes in many endogenous metabolites (e.g., choline, glucose, phenylalanine) induced by LPS in RAW 264.7 cells, which related to cholinergic anti-inflammatory pathway, oxidative stress, energy metabolism, and amino acids metabolism.

CONCLUSION

3-CT, isolated from the flowers of C. nitidissima Chi, had potent anti-inflammatory activity in LPS-activated RAW 264.7 cells. Furthermore, our results indicated that 3-CT had effects on the cholinergic anti-inflammatory pathway, oxidative stress, energy metabolism, and amino acids metabolism in LPS-activated RAW 264.7 cells.

CaMKIV regulates mitochondrial dynamics during sepsis

Sepsis and shock states impose mitochondrial stress, and in response, adaptive mechanisms such as fission, fusion and mitophagy are induced to eliminate damaged portions of or entire dysfunctional mitochondria. The mechanisms underlying these events are being elucidated; yet a direct link between loss of mitochondrial membrane potential ΔΨm and the initiation of fission, fusion and mitophagy remains to be well characterized. The direct association between the magnitude of the ΔΨm and the capacity for mitochondria to buffer Ca²⁺ renders Ca²⁺ uniquely suited as the signal engaging these mechanisms in circumstances of mitochondrial stress that lower the ΔΨm. Herein, we show that the calcium/calmodulin-dependent protein kinase (CaMK) IV mediates an adaptive slowing in oxidative respiration that minimizes oxidative stress in the kidneys of mice subjected to either cecal ligation and puncture (CLP) sepsis or endotoxemia. CaMKIV shifts the balance towards mitochondrial fission and away from fusion by 1) directly phosphorylating an activating Serine616 on the fission protein DRP1 and 2) reducing the expression of the fusion proteins Mfn1/2 and OPA-1. CaMKIV, through its function as a direct PINK1 kinase and regulator of Parkin expression, also enables mitophagy. These data support that CaMKIV serves as a keystone linking mitochondrial stress with the adaptive mechanisms of mitochondrial fission, fusion and mitophagy that mitigate oxidative stress in the kidneys of mice responding to sepsis.

Immunosuppression is Inappropriately Qualifying the Immune Status of Septic and SIRS Patients

Immunosuppression is the most commonly used concept to qualify the immune status of patients with either sterile systemic inflammatory response syndrome (SIRS) or sepsis. In this review we attempt to demonstrate that the concept of immunosuppression is an oversimplification of the complex anti-inflammatory response that occurs in patients dealing with a severe sterile or infectious insult. Particularly, the immune status of leukocytes varies greatly depending on the compartment from where they are derived from. Furthermore, although certain functions of immune cells present in the blood stream or in the hematopoietic organs can be significantly diminished, other functions are either unchanged or even enhanced. This juxtaposition illustrates that there is no global defect. The mechanisms called reprogramming or trained innate immunity are probably aimed at preventing a generalized deleterious inflammatory reaction, and work to maintain the defense mechanisms at their due levels.

Mitochondrial Complex I Is an Essential Player in LPS-Induced Preconditioning in Differentiated PC12 Cells

Preconditioning (PC) as a protective strategy against noxious insults can decline cell death and apoptosis. It has been approved that mitochondria play a key role in PC mechanism. The critical role of complex I (CI) in oxidative phosphorylation machinery and intracellular ROS production, particularly in the brain, accentuates its possible role in PC-induced neuroprotection. Here, differentiated PC12 cells were preconditioned with ultra-low dose LPS (ULD, 3 μg/mL) prior to exposure to high concentration of LPS (HD, 750 μg/mL). Our results showed that HD LPS treatment reduces cell viability and CI activity, and intensifies expression of cleaved caspase 3 compared to the control group. Intriguingly, PC induction resulted in enhancement of cell viability and CI activity and reduction of caspase3 cleavage compared to HD LPS group. In order to explore the role of CI in PC, we combined the ULD LPS with rotenone, a CI inhibitor. Following rotenone administration, cell viability significantly reduced while caspase3 cleavage increased compared to PC induction group. Taken together, cell survival and reduction of apoptosis followed by PC can be at least partially attributed to the preservation of mitochondrial CI function.

Alterations in Mitochondrial Function in Blood Cells Obtained From Patients With Sepsis Presenting to an Emergency Department

OBJECTIVE

Mitochondrial dysfunction has been implicated as a key cellular event leading to organ dysfunction in sepsis. Our objective is to measure changes in mitochondrial bioenergetics in subjects with early presentation of sepsis to provide insight into the incompletely understood pathophysiology of the dysregulated host response in sepsis.

DESIGN

Prospective observational study.

SETTING

Single site tertiary academic emergency department.

SUBJECTS

We enrolled a total of 48 subjects in the study, 10 with sepsis or septic shock, 10 with infection without sepsis, 14 older and 14 younger healthy controls.

INTERVENTIONS

Peripheral blood mononuclear cells were measured with high-resolution respirometry (OROBOROS O2K).

MEASUREMENTS AND MAIN RESULTS

The median age in patients with sepsis, infection only, older control and younger controls were 63, 34, 61, and 29 years old, respectively. In the Sepsis group, the median 1st 24-h SOFA score was 8, and the initial median lactate was 4.2 mmol/dL, compared with 1.1 in the Infection Group. The 30-day mortality of the sepsis/septic shock group was 50%, with a median length of stay of 7-days. The Sepsis Group had significantly lower routine and Max respiration when compared with the other groups as well as uncoupled Complex I respiration. There was also a significant decrease in ATP-linked respiration along with the Spare Reserve Capacity in the Sepsis Group when compared with the other group. There were no age-related differences in respiration between the Older and Younger control group.

CONCLUSIONS

Bedside measurement of mitochondrial respiration can be minimally invasive and performed in a timely manner. Mitochondrial dysfunction, detected by decreased oxygen consumption utilized for energy production and depleted cellular bioenergetics reserve.

Mitochondrial DNA, oxidants, and innate immunity

Mitochondrial oxidant damage, including damage to mitochondrial DNA (mtDNA) is a feature of both severe microbial infections and inflammation arising from sterile (non-infectious) sources such as tissue trauma. Damaged mitochondria release intact or oxidized fragments of mtDNA into the cytoplasm, which represent oxidant injury, and the fragments promote a spontaneous innate immune response, exemplifying a modern frontier of immunological research. MtDNA and mitochondrial-derived oxidants are central factors in activating at least three innate immune pathways involving the TLR9 (Toll-like receptor 9), the NLRP3 (NACHT, LRR and PYD domains-containing protein-3) inflammasome, and the cGAS (cyclic AMP-GMP synthase) pathway. The events that allow mtDNA to escape from damaged mitochondria and from damaged cells are incompletely known, but the presence of cytoplasmic mtDNA and cell-free mtDNA as immune regulators are important for understanding the cell's capacity for protecting mitochondrial quality control (MQC) and cell viability during inflammatory states.

Mitochondrial disease disrupts hepatic allostasis and lowers the threshold for immune-mediated liver toxicity

Objective

In individuals with mitochondrial disease, respiratory viral infection can result in metabolic decompensation with mitochondrial hepatopathy. Here, we used a mouse model of liver-specific Complex IV deficiency to study hepatic allostasis during respiratory viral infection.

Methods

Mice with hepatic cytochrome c oxidase deficiency (LivCox10^−/−) were infected with aerosolized influenza, A/PR/8 (PR8), and euthanized on day five after infection following three days of symptoms. This time course is marked by a peak in inflammatory cytokines and mimics the timing of a common clinical scenario in which caregivers may first attempt to manage the illness at home before seeking medical attention. Metabolic decompensation and mitochondrial hepatopathy in mice were characterized by serum hepatic testing, histology, electron microscopy, biochemistry, metabolomics, and bioenergetic profiling.

Results

Following influenza infection, LivCox10^−/− mice displayed marked liver disease including hepatitis, enlarged mitochondria with cristae loss, and hepatic steatosis. This pathophysiology was associated with viremia. Primary hepatocytes from LivCox10^−/− mice cocultured with WT Kupffer cells in the presence of PR8 showed enhanced lipid accumulation. Treatment of hepatocytes with recombinant TNFα implicated Kupffer cell-derived TNFα as a precipitant of steatosis in LivCox10^−/− mice. Eliminating Kupffer cells or blocking TNFα in vivo during influenza infection mitigated the steatosis and mitochondrial morphologic changes.

Conclusions

Taken together, our data shift the narrative of metabolic decompensation in mitochondrial hepatopathy beyond the bioenergetic costs of infection to include an underlying susceptibility to immune-mediated damage. Moreover, our work suggests that immune modulation during metabolic decompensation in mitochondrial disease represents a future viable treatment strategy needing further exploration.

•

Influenza infection leads to worsening mitochondrial function and steatohepatitis in a model of mitochondrial hepatopathy.

•

Kupffer cells may mediate this damage by the uptake of influenza virus and the secretion of TNFa.

•

Hepatocytes affected by mitochondrial disease have a lower threshold for immune mediated toxicity by TNFa.

•

Modulating the immune response leads to an improvement in the phenotype.

Do micronutrient deficiencies contribute to mitochondrial failure in critical illness?

PURPOSE OF REVIEW

Mitochondrial dysfunction seems to be the common denominator of several critical care conditions and particularly of sepsis. Faced with relative failure, and limited progress of sepsis therapies aiming at blocking some oxidative and/or inflammatory pathways, the question of antioxidants micronutrient therapy, particularly of selenium, ascorbic acid and thiamine remains open.

RECENT FINDINGS

The rationale for the essentiality of numerous micronutrients within the mitochondria is well established. Many studies have tested single micronutrients in animal and in-vitro models and provide positive evidences in favor of reduction of organ failure (cardiac and renal mainly). In clinical settings, high-dose selenium administration in sepsis has been disappointing. The most recent high dose, short-term ascorbic acid trial in sepsis is promising though, with an associated reduction of mortality, but analysis of the impact of this intervention on the various organs remains to be conducted.

SUMMARY

Results from animal and human studies indicate that there are indeed intervention options at the level of the mitochondria, but neither the optimal dose nor the optimal combination of micronutrients is yet identified.

Mitochondria and Critical Illness

Classically, mitochondria have largely been believed to influence the development of illness by modulating cell metabolism and determining the rate of production of high-energy phosphate compounds (eg, adenosine triphosphate). It is now recognized that this view is simplistic and that mitochondria play key roles in many other processes, including cell signaling, regulating gene expression, modulating cellular calcium levels, and influencing the activation of cell death pathways (eg, caspase activation). Moreover, these multiple mitochondrial functional characteristics are now known to influence the evolution of cellular and organ function in many disease states, including sepsis, ICU-acquired skeletal muscle dysfunction, acute lung injury, acute renal failure, and critical illness-related immune function dysregulation. In addition, diseased mitochondria generate toxic compounds, most notably released mitochondrial DNA, which can act as danger-associated molecular patterns to induce systemic toxicity and damage multiple organs throughout the body. This article reviews these evolving concepts relating mitochondrial function and acute illness. The discussion is organized into four sections: (1) basics of mitochondrial physiology; (2) cellular mechanisms of mitochondrial pathophysiology; (3) critical care disease processes whose initiation and evolution are shaped by mitochondrial pathophysiology; and (4) emerging treatments for mitochondrial dysfunction in critical illness.

Impairment of Fatty Acid Oxidation in Alveolar Epithelial Cells Mediates Acute Lung Injury

Profound impairment in cellular oxygen consumption, referred to as cytopathic dysoxia, is one of the pathological hallmarks in the lungs of patients with pathogen-induced acute lung injury (ALI). However, the underlying mechanism for this functional defect remains largely unexplored. In this study, we found that primary mouse alveolar epithelial cells (AECs) conducted robust fatty acid oxidation (FAO). More importantly, FAO was strikingly impaired in AECs of mice with LPS-induced ALI. The metabolic deficiency in these cells was likely due to decreased expression of key mediators involved in FAO and mitochondrial bioenergenesis, such as peroxisome proliferator-activated receptor γ coactivator (PGC)-1α, carnitine palmitoyltransferase 1A, and medium-chain acyl-CoA dehydrogenase (CAD). We found that treatment of alveolar epithelial line MLE-12 cells with BAL fluids from mice with ALI decreased FAO, and this effect was largely replicated in MLE-12 cells treated with the proinflammatory cytokine TNF-α, which was consistent with downregulations of PGC-1α, carnitine palmitoyltransferase 1A, long-chain CAD, and medium-chain CAD in the same treated cells. Furthermore, we found that the BAL fluids from ALI mice and TNF-α inhibited MLE-12 bioenergenesis and promoted cell apoptosis. In delineation of the role of FAO in ALI in vivo, we found that conditional ablation of AEC PGC-1α aggravated LPS-induced ALI. In contrast, fenofibrate, an activator of the PPAR-α/PGC-1α cascade, protected mice from this pathology. In summary, these data suggest that FAO is essential to AEC bioenergenesis and functional homeostasis. This study also indicates that FAO impairment-induced AEC dysfunction is an important contributing factor to the pathogenesis of ALI.

Mitochondrial Dysfunction in Cardiac Surgery

Mitochondria are key to the cellular response to energetic demand, but are also vital to reactive oxygen species signaling, calcium hemostasis, and regulation of cell death. Cardiac surgical patients with diabetes, heart failure, advanced age, or cardiomyopathies may have underlying mitochondrial dysfunction or be more sensitive to perioperative mitochondrial injury. Mitochondrial dysfunction, due to ischemia/reperfusion injury and an increased systemic inflammatory response due to exposure to cardiopulmonary bypass and surgical tissue trauma, impacts myocardial contractility and predisposes to arrhythmias. Strategies for perioperative mitochondrial protection and recovery include both well-established cardioprotective protocols and targeted therapies that remain under investigation.

Caspase-1 inhibitor exerts brain-protective effects against sepsis-associated encephalopathy and cognitive impairments in a mouse model of sepsis

Sepsis-associated encephalopathy (SAE) manifested clinically in acute and long-term cognitive impairments and associated with increased morbidity and mortality worldwide. The potential pathological changes of SAE are complex and remain to be elucidated. Pyroptosis, a novel programmed cell death, is executed by caspase-1-cleaved GSDMD N-terminal (GSDMD-NT) and we investigated it in peripheral blood immunocytes of septic patients previously. Here, a caspase-1 inhibitor VX765 was treated with CLP-induced septic mice. Novel object recognition test indicated that VX765 treatment reversed cognitive dysfunction in septic mice. Elevated plus maze, tail suspension test and open field test revealed that depressive-like behaviors of septic mice were relieved. Inhibited caspase-1 suppressed the expressions of GSDMD and its cleavage form GSDMD-NT, and reduced pyroptosis in brain at day 1 and day 7 after sepsis. Meantime, inhibited caspase-1 mitigated the expressions of IL-1β, MCP-1 and TNF-α in serum and brain, diminished microglia activation in septic mice, and reduced sepsis-induced brain-blood barrier disruption and ultrastructure damages in brain as well. Inhibited caspase-1 protected the synapse plasticity and preserved long-term potential, which may be the possible mechanism of cognitive functions protective effects of septic mice. In conclusion, caspase-1 inhibition exerts brain-protective effects against SAE and cognitive impairments in a mouse model of sepsis.

Effect of sepsis on the action potential and cardiac serotonin response in rats

The current study aimed to investigate the effect of sepsis on rat serotonin (5-HT) responses and cardiac action potentials. A total of 20 rats were randomly divided into a sepsis and control group (each, n=10). Rat hearts were harvested and perfused using the Langendorff method 18-h after the induction of sepsis, which was assessed using cecal puncture. Cardiac action potential was subsequently measured using a multichannel electrophysiology instrument. Immunohistochemistry and quantitative analysis were performed to identify the effect of sepsis on myocardial 5-HT expression. The results revealed that mitochondrial changes were present in septic rat hearts. Heart rate (361.10±12.29 bpm vs. 348.60±12.38 bpm; P<0.05) was significantly higher, atrial action potential duration (106.40±2.95 ms vs. 86.60±4.12 ms; P<0.01) was significantly longer and the area (0.62±0.06 µm² vs. 0.39±0.05 µm²; P<0.05) and number (0.92±0.02/field vs. 0.46±0.01/field; P<0.01) of myocardial cells were significantly higher in the septic compared with the control group. These results demonstrated that 5-HT prolongs the atrial action potential, increases heart rate and aggravates myocardial injury, indicating that it may therefore be one of the factors that leads to cardiac dysfunction in sepsis.

Epigenetic and metabolic programming of innate immunity in sepsis

Sepsis, the 10th leading cause of death, is the most expensive condition in the United States. The immune response in sepsis transitions from hyperinflammatory to a hypoinflammatory and immunosuppressive phase; individual variations regarding timing and overlap between hyper- and hypoinflammation exist in a number of patients. While one third of the sepsis-related deaths occur during hyperinflammation, majority of the sepsis-mortality occurs during the hypoinflammatory phase. Currently, no phase-specific molecular-based therapies exist to treat sepsis. Coordinated epigenetic and metabolic perturbations orchestrate this shift from hyper- to hypoinflammation in innate immune cells during sepsis. These epigenetic and metabolic changes during sepsis progression and therapeutic opportunities they pose are described in this review.

Myalgic encephalomyelitis or chronic fatigue syndrome: how could the illness develop?

A model of the development and progression of chronic fatigue syndrome (myalgic encephalomyelitis), the aetiology of which is currently unknown, is put forward, starting with a consideration of the post-infection role of damage-associated molecular patterns and the development of chronic inflammatory, oxidative and nitrosative stress in genetically predisposed individuals. The consequences are detailed, including the role of increased intestinal permeability and the translocation of commensal antigens into the circulation, and the development of dysautonomia, neuroinflammation, and neurocognitive and neuroimaging abnormalities. Increasing levels of such stress and the switch to immune and metabolic downregulation are detailed next in relation to the advent of hypernitrosylation, impaired mitochondrial performance, immune suppression, cellular hibernation, endotoxin tolerance and sirtuin 1 activation. The role of chronic stress and the development of endotoxin tolerance via indoleamine 2,3-dioxygenase upregulation and the characteristics of neutrophils, monocytes, macrophages and T cells, including regulatory T cells, in endotoxin tolerance are detailed next. Finally, it is shown how the immune and metabolic abnormalities of chronic fatigue syndrome can be explained by endotoxin tolerance, thus completing the model.

Association between circulating mononuclear cell mitochondrial DNA copy number and in-hospital mortality in septic patients: A prospective observational study based on the Sepsis-3 definition

Purpose

To explore the association between circulating mononuclear cell mitochondrial DNA copy number and the prognosis of sepsis patients based on the Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3 definition).

Methods

A total of 200 adult patients who had recently devoloped sepsis were prospectively recruited as the study cohort. Demographic and clinical data were recorded along with a 28-day outcome. Mononuclear cell mtDNA copy number was assessed by quantitative PCR.

Results

The 28-day outcome of sepsis patients was significantly associated with circulating mononuclear cell mtDNA copy number. The median mononuclear cell relative mtDNA copy number of survivors was significantly higher than that of nonsurvivors (406.68, range 196.65–625.35 vs. 320.57, range 175.98–437.33, p = 0.001). The Cox proportional hazard survival model analysis indicated that mononuclear cell relative mtDNA copy number was significantly negative associated with the 28-day outcome. For every additional unit of mononuclear cell mtDNA relative copy number, the risk of death falls by 0.1% (HR = 0.999, 95% CI = 0.998 to 1.000, p = 0.017).

Conclusions

Our data indicate first that circulating mononuclear cellular mtDNA copy number might be helpful for outcome predictions in sepsis patients, and second that lower mtDNA copy number implied poor prognosis.

Variability of mitochondrial respiration in relation to sepsis-induced multiple organ dysfunction

Ample experimental evidence suggests that sepsis could interfere with any mitochondrial function; however, the true role of mitochondrial dysfunction in the pathogenesis of sepsis-induced multiple organ dysfunction is still a matter of controversy. This review is primarily focused on mitochondrial oxygen consumption in various animal models of sepsis in relation to human disease and potential sources of variability in experimental results documenting decrease, increase or no change in mitochondrial respiration in various organs and species. To date, at least three possible explanations of sepsis-associated dysfunction of the mitochondrial respiratory system and consequently impaired energy production have been suggested: 1. Mitochondrial dysfunction is secondary to tissue hypoxia. 2. Mitochondria are challenged by various toxins or mediators of inflammation that impair oxygen utilization (cytopathic hypoxia). 3. Compromised mitochondrial respiration could be an active measure of survival strategy resembling stunning or hibernation. To reveal the true role of mitochondria in sepsis, sources of variability of experimental results based on animal species, models of sepsis, organs studied, or analytical approaches should be identified and minimized by the use of appropriate experimental models resembling human sepsis, wider use of larger animal species in preclinical studies, more detailed mapping of interspecies differences and organ-specific features of oxygen utilization in addition to use of complex and standardized protocols evaluating mitochondrial respiration.

Progress of Research in Neonatal Sepsis

Neonatal sepsis remains a significant global problem with little progress made despite major efforts. At present, there is a lack of an accepted international consensus on the definition, diagnosis, and treatment of neonatal sepsis; the unclear understanding of the pathogenesis of neonatal sepsis leads to blindness in treatment, which will result in an unsatisfactory therapeutic outcome. In addition, some serious diseases caused by noninfectious factors, such as trauma, stress, asphyxia, and so on, have very similar pathophysiological results with neonatal sepsis. In this review we synthesize the recent advances in definition, incidence, causative agents, risk factors, pathophysiology, clinical manifestations, and diagnosis and treatment of neonatal sepsis. Of course, there are still many challenges to neonatal sepsis in many ways.

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.

Role of Damage-Associated Molecular Patterns and Uncontrolled Inflammation in Pediatric Sepsis-Induced Multiple Organ Dysfunction Syndrome

The incidence of multiple organ dysfunction syndrome (MODS) in sepsis varies from 17 to 73% and furthermore, increases the risk of death by 60% when controlled for the number of dysfunctional organs. Several MODS phenotypes exist, each unique in presentation and pathophysiology. Common to the phenotypes is the stimulation of the immune response by pathogen-associated molecular patterns (PAMPs), or danger-associated molecular patterns (DAMPs) causing an unremitting inflammation. Two of the MODS phenotypes are discussed in detail, thrombocytopenia-associated multiple organ failure (TAMOF) and the hyperinflammatory phenotype-macrophage activating syndrome (MAS) and hemophagocytic lymphohistiocytosis (HLH). In the end, we will briefly review the role of mitochondrial dysfunction as a significant contributor to the pathogenesis of MODS.

Exposure of Monocytic Cells to Lipopolysaccharide Induces Coordinated Endotoxin Tolerance, Mitochondrial Biogenesis, Mitophagy, and Antioxidant Defenses

In order to limit the adverse effects of excessive inflammation, anti-inflammatory responses are stimulated at an early stage of an infection, but during sepsis these can lead to deactivation of immune cells including monocytes. In addition, there is emerging evidence that the up-regulation of mitochondrial quality control mechanisms, including mitochondrial biogenesis and mitophagy, is important during the recovery from sepsis and inflammation. We aimed to describe the relationship between the compensatory immune and mitochondrial responses that are triggered following exposure to an inflammatory stimulus in human monocytic cells. Incubation with lipopolysaccharide resulted in a change in the immune phenotype of THP-1 cells consistent with the induction of endotoxin tolerance, similar to that seen in deactivated septic monocytes. After exposure to LPS there was also early evidence of oxidative stress, which resolved in association with the induction of antioxidant defenses and the stimulation of mitochondrial degradation through mitophagy. This was compensated by a parallel up-regulation of mitochondrial biogenesis that resulted in an overall increase in mitochondrial respiratory activity. These observations improve our understanding of the normal homeostatic responses that limit the adverse cellular effects of unregulated inflammation, and which may become ineffective when an infection causes sepsis.

Sirtuins and Immuno-Metabolism of Sepsis

Sepsis and septic shock are the leading causes of death in non-coronary intensive care units worldwide. During sepsis-associated immune dysfunction, the early/hyper-inflammatory phase transitions to a late/hypo-inflammatory phase as sepsis progresses. The majority of sepsis-related deaths occur during the hypo-inflammatory phase. There are no phase-specific therapies currently available for clinical use in sepsis. Metabolic rewiring directs the transition from hyper-inflammatory to hypo-inflammatory immune responses to protect homeostasis during sepsis inflammation, but the mechanisms underlying this immuno-metabolic network are unclear. Here, we review the roles of NAD+ sensing Sirtuin (SIRT) family members in controlling immunometabolic rewiring during the acute systemic inflammatory response associated with sepsis. We discuss individual contributions among family members SIRT 1, 2, 3, 4 and 6 in regulating the metabolic switch between carbohydrate-fueled hyper-inflammation to lipid-fueled hypo-inflammation. We further highlight the role of SIRT1 and SIRT2 as potential "druggable" targets for promoting immunometabolic homeostasis and increasing sepsis survival.

Time course of liver mitochondrial function and intrinsic changes in oxidative phosphorylation in a rat model of sepsis

Background

Tissue ATP depletion and oxidative stress have been associated with the severe outcomes of septic shock. One of the compensatory mechanisms to alleviate the sepsis-induced mitochondrial dysfunction could be the increase in oxidative phosphorylation efficiency (ATP/O). We propose to study liver mitochondrial function and oxidative stress and the regulatory mechanism of mitochondrial oxidative phosphorylation efficiency in an animal model of sepsis.

Methods

We induced sepsis in rats by cecal ligation and perforation (CLP). Six, 24, or 36 h following CLP, we measured liver mitochondrial respiration, cytochrome c oxidase activity, and membrane permeability. We determine oxidative phosphorylation efficiency, by measuring ATP synthesis related to oxygen consumption at various exogenous ADP concentrations. Finally, we measured radical oxygen species (ROS) generation by liver mitochondria and mRNA concentrations of UCP2, biogenesis factors, and cytokines at the same end points.

Results

CLP rats presented hypotension, lactic acidosis, liver cytolysis, and upregulation of proinflammatory cytokines mRNA as compared to controls. Liver mitochondria showed a decrease in ATP synthesis and oxygen consumption at 24 h following CLP. A marked uncoupling of oxidative phosphorylation appeared 36 h following CLP and was associated with a decrease in cytochrome c oxidase activity and content and ATP synthase subunit β content (slip mechanism) and an increase in mitochondrial oligomycin-insensitive respiration, but no change in mitochondrial inner membrane permeability (no leak). Upregulation of UCP2 mRNA resulted in a decrease in mitochondrial ROS generation 24 h after the onset of CLP, whereas ROS over-generation associated with slip at cytochrome c oxidase observed at 36 h was concomitant with a decrease in UCP2 mRNA expression.

Conclusions

Despite a compensatory increase in mitochondrial biogenesis factors, liver mitochondrial functions remain altered after CLP. This suggests that the functional compensatory mechanisms reported in the present study (slip at cytochrome c oxidase and biogenesis factors) were not strong enough to increase oxidative phosphorylation efficiency and failed to limit liver mitochondrial ROS over-generation. These data suggest that treatments based on cytochrome c infusion could have a role in mitochondrial dysfunction and/or ROS generation associated with sepsis.

Electronic supplementary material

The online version of this article (10.1186/s40635-018-0197-y) contains supplementary material, which is available to authorized users.

Patterns of Death in Patients with Sepsis and the Use of Hydrocortisone, Ascorbic Acid, and Thiamine to Prevent These Deaths

Background: In general, patients with sepsis die from the host response to the infecting pathogen rather than from the infecting pathogen itself. Four patterns of death have been identified in sepsis, namely vasoplegic shock, single-organ respiratory failure (acute respiratory distress syndrome [ARDS]), multi-system organ failure (MSOF), and persistent MSOF with ongoing inflammation and immunosuppression with recurrent infections (persistent inflammation-immunosuppression and catabolism syndrome [PICS]). To improve the outcome of sepsis adjunctive therapies that modulate the immune system have been tested; these therapies that have targeted specific molecules or pathways have universally failed. Conclusion: We propose that the combination of hydrocortisone, intravenous ascorbic acid, and thiamine (HAT therapy), which synergistically targets multiple pathways, restores the dysregulated immune system and organ injury, and reduces the risk of death and organ failure following sepsis.

Similar Metabolic, Innate Immunity, and Adipokine Profiles in Adult and Pediatric Sepsis Versus Systemic Inflammatory Response Syndrome-A Pilot Study

OBJECTIVES

To examine whether the septic profiles of heat shock protein 72, heat shock protein 90α, resistin, adiponectin, oxygen consumption, CO2 production, energy expenditure, and metabolic pattern, along with illness severity, nutritional, and inflammatory indices, differ between adult and pediatric patients compared with systemic inflammatory response syndrome and healthy controls. To evaluate whether these biomolecules may discriminate sepsis from systemic inflammatory response syndrome in adult and pediatric patients.

DESIGN

Prospective cohort study.

SETTING

University ICU and PICU.

PATIENTS

Seventy-eight adults (sepsis/23; systemic inflammatory response syndrome/23; healthy controls/33), 67 children (sepsis/18; systemic inflammatory response syndrome/23; controls/27), mechanically ventilated.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Flow cytometry determined mean fluorescence intensity for monocyte or neutrophil heat shock protein expression. Resistin, adiponectin, and extracellular heat shock proteins were measured using enzyme-linked immunosorbent assay; energy expenditure by E-COVX (GE Healthcare). Genomic DNA was extracted with PureLink Genomic DNA kit (Invitrogen, Carlsbad, CA) to detect heat shock protein 72 single nucleotide polymorphisms. Similarly, in adult and pediatric patients, Acute Physiology and Chronic Evaluation-II/Acute Physiology and Pediatric Risk of Mortality-III, Simplified Acute Physiology Score-III, C-reactive protein, lactate, and resistin were higher and myocardial contractility, monocyte heat shock protein 72, oxygen consumption, CO2 production, energy expenditure, metabolic pattern, glucose, and albumin lower in sepsis compared with systemic inflammatory response syndrome or controls (p < 0.05). For discriminating sepsis from systemic inflammatory response syndrome, resistin, extracellular heat shock protein 90α, and lactate achieved a receiver operating characteristic curve greater than 0.80 in children and greater than 0.75 in adults (p < 0.05). In both, adults and children, genotype heat shock protein 72 analysis did not disclose any diagnosis or mortality group differences regarding either rs6457452 or rs1061581 haplotypes.

CONCLUSIONS

Sepsis presents with similar profiles in adult and pediatric patients, characterized by enhanced inflammatory hormonal response and by repressed innate immunity, metabolism, and myocardial contractility. These features early distinguish sepsis from systemic inflammatory response syndrome across all age groups.

Transcriptomic data from two primary cell models stimulating human monocytes suggest inhibition of oxidative phosphorylation and mitochondrial function by N. meningitidis which is partially up-regulated by IL-10

Background

Biological interpretation of DNA microarray data may differ depending on underlying assumptions and statistical tests of bioinformatics tools used. We used Gene Set Enrichment Analysis (GSEA) and Ingenuity Pathway Analysis (IPA) to analyze previously generated DNA microarray data from human monocytes stimulated with N. meningitidis and IL-10 (“the model system”), and with meningococcal sepsis plasma before and after immunodepletion of IL-10 (“the patient plasma system”). The objectives were to compare if the two bioinformatics methods resulted in similar biological interpretation of the datasets, and to identify whether GSEA provided additional insight compared with IPA about the monocyte host response to meningococcal activation.

Results

In both experimental models, GSEA and IPA identified genes associated with pro-inflammatory innate immune activation, including TNF-signaling, Toll-like receptor signaling, JAK-STAT-signaling, and type I and type II interferon signaling. GSEA identified genes regulated by the presence of IL-10 with similar gene sets in both the model system and the patient plasma system. In the model system, GSEA and IPA in sum identified 170 genes associated with oxidative phosphorylation/mitochondrial function to be down-regulated in monocytes stimulated with meningococci. In the patient plasma system, GSEA and IPA in sum identified 122 genes associated with oxidative phosphorylation/mitochondrial dysfunction to be down-regulated by meningococcal sepsis plasma depleted for IL-10. Using IPA, we identified IL-10 to up-regulate 18 genes associated with oxidative phosphorylation/mitochondrial function that were down-regulated by N. meningitidis.

Conclusions

Biological processes associated with the gene expression changes in the model system of meningococcal sepsis were comparable with the results found in the patient plasma system. By combining GSEA with IPA, we discovered an inhibitory effect of N. meningitidis on genes associated with mitochondrial function and oxidative phosphorylation, and that IL-10 partially reverses this strong inhibitory effect, thereby identifying, to our knowledge, yet another group of genes where IL-10 regulates the effect of LPS. We suggest that relying on a single bioinformatics tool together with an arbitrarily chosen filtering criteria for data analysis may result in overlooking relevant biological processes and signaling pathways associated with genes differentially expressed between compared experimental conditions.

Electronic supplementary material

The online version of this article (10.1186/s12865-017-0229-5) contains supplementary material, which is available to authorized users.

Adjunctive Steroid Therapy for Treatment of Pediatric Septic Shock

Septic shock remains the major cause of childhood morbidity and mortality worldwide. Although early sepsis recognition, fluid resuscitation, timely administration of antimicrobials, and vasoactive-inotropic drug infusions are all key to achieving good sepsis outcomes, therapy using various steroid drug classes remains an attractive adjunctive intervention to minimize the duration of septic shock and transition to multiple organ dysfunction syndrome. All steroid drug classes possess biological plausibility to affect a beneficial clinical effect among children with septic shock, but none has undergone rigorous, prospective assessment in a large, high-quality pediatric interventional trial.

Calcium/calmodulin-dependent protein kinase regulates the PINK1/Parkin and DJ-1 pathways of mitophagy during sepsis

During sepsis and shock states, mitochondrial dysfunction occurs. Consequently, adaptive mechanisms, such as fission, fusion, and mitophagy, are induced to eliminate damaged portions or entire dysfunctional mitochondria. The regulatory PINK1/Parkin and DJ-1 pathways are strongly induced by mitochondrial depolarization, although a direct link between loss of mitochondrial membrane potential (Δ_Ψ) and mitophagy has not been identified. Mitochondria also buffer Ca²⁺, and their buffering capacity is dependent on Δ_Ψ Here, we characterize a role for calcium/calmodulin-dependent protein kinase (CaMK) I in the regulation of these mechanisms. Loss of Δ_Ψ with either pharmacologic depolarization or LPS leads to Ca²⁺-dependent mitochondrial recruitment and activation of CaMKI that precedes the colocalization of PINK1/Parkin and DJ-1. CaMKI is required and serves as both a PINK1 and Parkin kinase. The mechanisms operate in both immune and nonimmune cells and are induced in in vivo models of endotoxemia, sepsis, and hemorrhagic shock. These data support the idea that CaMKI links mitochondrial stress with the PINK1/Parkin and DJ-1 mechanisms of mitophagy.-Zhang, X., Yuan, D., Sun, Q., Xu, L., Lee, E., Lewis, A. J., Zuckerbraun, B. S., Rosengart, M. R. Calcium/calmodulin-dependent protein kinase regulates the PINK1/Parkin and DJ-1 pathways of mitophagy during sepsis.