DIAGNOSTIC VALUE OF MITOCHONDRIAL DNA AND PERIPHERAL BLOOD MONONUCLEAR CELL RESPIROMETRY FOR BURN-RELATED SEPSIS

Assessment of mitochondrial function and its prognostic role in sepsis: a literature review

Sepsis is characterized by a dysregulated and excessive systemic inflammatory response to infection, associated with vascular and metabolic abnormalities that ultimately lead to organ dysfunction. In immune cells, both non-oxidative and oxidative metabolic rates are closely linked to inflammatory responses. Mitochondria play a central role in supporting these cellular processes by utilizing metabolic substrates and synthesizing ATP through oxygen consumption. To meet fluctuating cellular demands, mitochondria must exhibit adaptive plasticity underlying bioenergetic capacity, biogenesis, fusion, and fission. Given their role as a hub for various cellular functions, mitochondrial alterations induced by sepsis may hold significant pathophysiological implications and impact on clinical outcomes. In patients, mitochondrial DNA concentration, protein expression levels, and bioenergetic profiles can be accessed via tissue biopsies or isolated peripheral blood cells. Clinically, monocytes and lymphocytes serve as promising matrices for evaluating mitochondrial function. These mononuclear cells are highly oxidative, mitochondria-rich, routinely monitored in blood, easy to collect and process, and show a clinical association with immune status. Hence, mitochondrial assessments in immune cells could serve as biomarkers for clinical recovery, immunometabolic status, and responsiveness to oxygen and vasopressor therapies in sepsis. These characteristics underscore mitochondrial parameters in both tissues and immune cells as practical tools for exploring underlying mechanisms and monitoring septic patients in intensive care settings. In this article, we examine pathophysiological aspects, key methods for measuring mitochondrial function, and prominent studies in this field.

Molecular basis of sepsis: A New insight into the role of mitochondrial DNA as a damage-associated molecular pattern

Sepsis remains a critical challenge in the field of medicine, claiming countless lives each year. Despite significant advances in medical science, the molecular mechanisms underlying sepsis pathogenesis remain elusive. Understanding molecular sequelae is gaining deeper insights into the roles played by various damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs) in disease pathogenesis. Among the known DAMPs, circulating cell-free mitochondrial DNA (mtDNA) garners increasing attention as a key player in the immune response during sepsis and other diseases. Mounting evidence highlights numerous connections between circulating cell-free mtDNA and inflammation, a pivotal state of sepsis, characterized by heightened inflammatory activity. In this review, we aim to provide an overview of the molecular basis of sepsis, particularly emphasizing the role of circulating cell-free mtDNA as a DAMP. We discuss the mechanisms of mtDNA release, its interaction with pattern recognition receptors (PRRs), and the subsequent immunological responses that contribute to sepsis progression. Furthermore, we discuss the forms of cell-free mtDNA; detection techniques of circulating cell-free mtDNA in various biological fluids; and the diagnostic, prognostic, and therapeutic implications offering insights into the potential for innovative interventions in sepsis management.

SIRTUIN 5 ALLEVIATES EXCESSIVE MITOCHONDRIAL FISSION VIA DESUCCINYLATION OF ATPASE INHIBITORY FACTOR 1 IN SEPSIS-INDUCED ACUTE KIDNEY INJURY

ABSTRACT

Sepsis-induced acute kidney injury (SAKI) poses a significant clinical challenge with high morbidity and mortality. Excessive mitochondrial fission has been identified as the central pathogenesis of sepsis-associated organ damage, which is also implicated in the early stages of SAKI. Sirtuin 5 (SIRT5) has emerged as a central regulator of cellular mitochondrial function; however, its role in the regulation of sepsis-induced excessive mitochondrial fission in kidney and the underlying mechanism remains unclear. In this study, SAKI was modeled in mice through cecal ligation and puncture, and in human renal tubular epithelial (HK-2) cells stimulated with lipopolysaccharide (LPS), to mimic the cell SAKI model. Our findings revealed that septic mice with a SIRT5 knockout exhibited shortened survival times and elevated levels of renal injury compared to wild-type mice, suggesting the significant involvement of SIRT5 in SAKI pathophysiology. Additionally, we observed that SIRT5 depletion led to increased renal mitochondrial fission, while the use of a mitochondrial fission inhibitor (Mdivi-1) reversed the detrimental effects caused by SIRT5 depletion, emphasizing the pivotal role of SIRT5 in preventing excessive mitochondrial fission. In vitro experiments demonstrated that the overexpression of SIRT5 effectively mitigated the adverse effects of LPS on HK-2 cells viability and mitochondrial fission. Conversely, downregulation of SIRT5 decreased HK-2 cells viability and exacerbated LPS-induced mitochondrial fission. Mechanistically, the protective function of SIRT5 may be in part, ascribed to its desuccinylating action on ATPase inhibitory factor 1. In conclusion, this study provides novel insights into the underlying mechanisms of SAKI, suggesting the possibility of identifying future drug targets in terms of improved mitochondrial dynamics by SIRT5.

Protocol for immunophenotyping out-of-hospital cardiac arrest patients

Immunophenotyping of out-of-hospital cardiac arrest (OHCA) patients is of increasing interest but has challenges. Here, we describe steps for the design of the clinical cohort, planning patient enrollment and sample collection, and ethical review of the study protocol. We detail procedures for blood sample collection and cryopreservation of peripheral blood mononuclear cells (PBMCs). We detail steps to modulate immune checkpoints in OHCA PBMC ex vivo. This protocol also has relevance for immunophenotyping other types of critical illness. For complete details on the use and execution of this protocol, please refer to Tamura et al. (2023).1.

ALTERED PROFILES OF EXTRACELLULAR MITOCHONDRIAL DNA IN IMMUNOPARALYZED PEDIATRIC PATIENTS AFTER THERMAL INJURY

ABSTRACT

Background: Thermal injury is a major cause of morbidity and mortality in the pediatric population worldwide with secondary infection being the most common acute complication. Suppression of innate and adaptive immune function is predictive of infection in pediatric burn patients, but little is known about the mechanisms causing these effects. Circulating mitochondrial DNA (mtDNA), which induces a proinflammatory signal, has been described in multiple disease states but has not been studied in pediatric burn injuries. This study examined the quantity of circulating mtDNA and mtDNA mutations in immunocompetent (IC) and immunoparalyzed (IP) pediatric burn patients. Methods: Circulating DNA was isolated from plasma of pediatric burn patients treated at Nationwide Children's Hospital Burn Center at early (1-3 days) and late (4-7 days) time points postinjury. These patients were categorized as IP or IC based on previously established immune function testing and secondary infection. Three mitochondrial genes, D loop, ND1, and ND4, were quantified by multiplexed qPCR to assess both mtDNA quantity and mutation load. Results: At the early time point, there were no differences in plasma mtDNA quantity; however, IC patients had a progressive increase in mtDNA over time when compared with IP patients (change in ND1 copy number over time 3,880 vs. 87 copies/day, P = 0.0004). Conversely, the IP group had an increase in mtDNA mutation burden over time. Conclusion: IC patients experienced a significant increase in circulating mtDNA quantity over time, demonstrating an association between increased mtDNA release and proinflammatory phenotype in the burn patients. IP patients had significant increases in mtDNA mutation load likely representative of degree of oxidative damage. Together, these data provide further insight into the inflammatory and immunological mechanisms after pediatric thermal injury.

METABOLOMIC AND PROTEOMIC CHANGES IN TRAUMA-INDUCED HYPOCALCEMIA

ABSTRACT

Background: Trauma-induced hypocalcemia is common and associated with adverse outcomes, but the mechanisms remain unclear. Thus, we aimed to characterize the metabolomic and proteomic differences between normocalcemic and hypocalcemic trauma patients to illuminate biochemical pathways that may underlie a distinct pathology linked with this clinical phenomenon. Methods: Plasma was obtained on arrival from injured patients at a Level 1 Trauma Center. Samples obtained after transfusion were excluded. Multiple regression was used to adjust the omics data for injury severity and arrival base excess before metabolome- and proteome-wide comparisons between normocalcemic (ionized Ca 2+ > 1.0 mmol/L) and hypocalcemic (ionized Ca 2+ ≤ 1.0 mmol/L) patients using partial least squares-discriminant analysis. OmicsNet and Gene Ontology were used for network and pathway analyses, respectively. Results: Excluding isolated traumatic brain injury and penetrating injury, the main analysis included 36 patients (n = 14 hypocalcemic, n = 22 normocalcemic). Adjusted analyses demonstrated distinct metabolomic and proteomic signatures for normocalcemic and hypocalcemic patients. Hypocalcemic patients had evidence of mitochondrial dysfunction (tricarboxylic acid cycle disruption, dysfunctional fatty acid oxidation), inflammatory dysregulation (elevated damage-associated molecular patterns, activated endothelial cells), aberrant coagulation pathways, and proteolytic imbalance with increased tissue destruction. Conclusions: Independent of injury severity, hemorrhagic shock, and transfusion, trauma-induced hypocalcemia is associated with early metabolomic and proteomic changes that may reflect unique pathology in hypocalcemic trauma patients. This study paves the way for future experiments to investigate mechanisms, identify intervenable pathways, and refine our management of hypocalcemia in severely injured patients.