Skeletal Muscle Mitochondrial Function is Determined by Burn Severity, Sex, and Sepsis, and is Associated With Glucose Metabolism and Functional Capacity in Burned Children

Effects of exercise training on muscle wasting, muscle strength and quality of life in adults with acute burn injury

OBJECTIVES

Exercise training during the acute phase of burns is difficult to implement but offers potential benefits. This multicenter trial explored the effects of an exercise program on muscular changes and quality of life during burn center stay.

METHODS

Fifty-seven adults with burns ranging between 10% and 70% TBSA were allocated to receive either standard of care (n = 29), or additionally exercise (n = 28), consisting of resistance and aerobic training, commenced as early as possible according to safety criteria. Muscle wasting (primary outcome), quantified by ultrasound-derived quadriceps muscle layer thickness (QMLT) and rectus femoris cross-sectional area (RF-CSA), muscle strength and quality of life (Burn Specific Health Scale-Brief (BSHS-B) and EQ-5D-5L) were assessed at baseline, four and eight weeks later, or hospital discharge. Mixed models were used to analyze between-group changes over time with covariates of interest added in stepwise forward modeling.

RESULTS

The addition of exercise training to standard of care induced significant improvements in QMLT, RF-CSA, muscle strength and the BSHS-B subscale hand function (ß-coefficient. 0.055 cm/week of QMLT, p = 0.005). No added benefit was observed for other quality-of-life measures.

CONCLUSIONS

Exercise training, administered during the acute phase of burns, reduced muscle wasting, and improved muscle strength throughout burn center stay.

Mitochondrial dysfunction and mitophagy: crucial players in burn trauma and wound healing

Burn injuries are a significant cause of death worldwide, leading to systemic inflammation, multiple organ failure and sepsis. The progression of burn injury is explicitly correlated with mitochondrial homeostasis, which is disrupted by the hyperinflammation induced by burn injury, leading to mitochondrial dysfunction and cell death. Mitophagy plays a crucial role in maintaining cellular homeostasis by selectively removing damaged mitochondria. A growing body of evidence from various disease models suggest that pharmacological interventions targeting mitophagy could be a promising therapeutic strategy. Recent studies have shown that mitophagy plays a crucial role in wound healing and burn injury. Furthermore, chemicals targeting mitophagy have also been shown to improve wound recovery, highlighting the potential for novel therapeutic strategies based on an in-depth exploration of the molecular mechanisms regulating mitophagy and its association with skin wound healing.

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

ABSTRACT

Background: Sepsis is the leading cause of mortality among burn patients that survive acute resuscitation. Clinical criteria have poor diagnostic value for burn-induced sepsis, making it difficult to diagnose. Protein biomarkers (e.g., procalcitonin) have been examined with limited success. We aimed to explore other biomarkers related to mitochondria (mitochondrial DNA [mtDNA]) and mitochondrial function of peripheral blood mononuclear cells (PBMCs) for sepsis diagnosis in burn patients. Methods: We conducted a follow-up analysis of a single center, prospective observational study of subjects (n = 10 healthy volunteers, n = 24 burn patients) to examine the diagnostic value of mtDNA and PBMC respirometry. Patients were enrolled regardless of sepsis status and followed longitudinally. Patient samples were classified as septic or not based on empiric clinical criteria. Isolated PBMCs were loaded into a high-resolution respirometer, and circulating mtDNA was measured with a PCR-based assay. Sequential Organ Failure Assessment (SOFA) criteria were also compared. Results: The SOFA criteria comparing septic versus before/nonseptic patients revealed significantly higher heart rate ( P = 0.012) and lower mean arterial pressure ( P = 0.039) in burn sepsis. MtDNA was significantly elevated in septic burn patients compared with healthy volunteers ( P < 0.0001) and nonseptic patients ( P < 0.0001), with no significant difference between healthy volunteers and nonseptic burn patients ( P = 0.187). The area under the ROC curve (AUC) for mtDNA was 0.685 (95% confidence interval = 0.50-0.86). For PBMC respirometry, burn patients exhibited increased routine and maximal respiration potential compared with healthy volunteers. However, no difference was found between nonseptic and septic patient samples. A subanalysis revealed a significant mortality difference in PBMC respirometry after sepsis diagnosis, wherein survivors had higher routine respiration ( P = 0.003) and maximal respiration ( P = 0.011) compared with nonsurvivors. Conclusion: Our findings reveal that mtDNA may have diagnostic value for burn sepsis, whereas PBMC respirometry is nonspecifically elevated in burns, but may have value in mortality prognosis. A larger, multisite study is warranted for further validity of the diagnostic value of mtDNA and PBMC respirometry as biomarkers for prognosis of sepsis and outcomes in burn patients.

Repurposing of Clinically Approved Poly-(ADP-Ribose) Polymerase Inhibitors for the Therapy of Sepsis

ABSTRACT

Sepsis' pathogenesis involves multiple mechanisms that lead to a dysregulation of the host's response. Significant efforts have been made in search of interventions that can reverse this situation and increase patient survival. Poly (ADP-polymerase) (PARP) is a constitutive nuclear and mitochondrial enzyme, which functions as a co-activator and co-repressor of gene transcription, thus regulating the production of inflammatory mediators. Several studies have already demonstrated an overactivation of PARP1 in various human pathophysiological conditions and that its inhibition has benefits in regulating intracellular processes. The PARP inhibitor olaparib, originally developed for cancer therapy, paved the way for the expansion of its clinical use for nononcological indications. In this review we discuss sepsis as one of the possible indications for the use of olaparib and other clinically approved PARP inhibitors as modulators of the inflammatory response and cellular dysfunction. The benefit of olaparib and other clinically approved PARP inhibitors has already been demonstrated in several experimental models of human diseases, such as neurodegeneration and neuroinflammation, acute hepatitis, skeletal muscle disorders, aging and acute ischemic stroke, protecting, for example, from the deterioration of the blood-brain barrier, restoring the cellular levels of NAD+, improving mitochondrial function and biogenesis and, among other effects, reducing oxidative stress and pro-inflammatory mediators, such as TNF-α, IL1-β, IL-6, and VCAM1. These data demonstrated that repositioning of clinically approved PARP inhibitors may be effective in protecting against hemodynamic dysfunction, metabolic dysfunction, and multiple organ failure in patients with sepsis. Age and gender affect the response to PARP inhibitors, the mechanisms underlying the lack of many protective effects in females and aged animals should be further investigated and be cautiously considered in designing clinical trials.

Rehabilitative Exercise Training for Burn Injury

Due to improvements in acute burn care over the last few decades, most patients with severe burns (up to 90% of the total body surface) survive. However, the metabolic and cardiovascular complications that accompany a severe burn can persist for up to 3 years post injury. Accordingly, there is now a greater appreciation of the need for strategies that can hasten recovery and reduce long-term morbidity post burn. Rehabilitation exercise training (RET) is a proven effective treatment to restore lean body mass, glucose and protein metabolism, cardiorespiratory fitness, and muscle strength in burn survivors. Despite this, very few hospitals incorporate RET in programs to aid the rehabilitation of patients with severe burns. Given that RET is a safe and efficacious treatment that restores function and reduces post-burn morbidity, we propose that a long-term exercise prescription plan should be considered for all patients with severe burns. In this literature review, we discuss the current understanding of burn trauma on major organ systems, and the positive benefits of incorporating RET as a part of the long-term rehabilitation of severely burned individuals. We also provide burn-specific exercise prescription guidelines for clinical exercise physiologists.

In Vitro, In Vivo, and In Silico Methods for Assessment of Muscle Size and Muscle Growth Regulation

Trauma, burn injury, sepsis, and ischemia lead to acute and chronic loss of skeletal muscle mass and function. Healthy muscle is essential for eating, posture, respiration, reproduction, and mobility, as well as for appropriate function of the senses including taste, vision, and hearing. Beyond providing support and contraction, skeletal muscle also exerts essential roles in temperature regulation, metabolism, and overall health. As the primary reservoir for amino acids, skeletal muscle regulates whole-body protein and glucose metabolism by providing substrate for protein synthesis and supporting hepatic gluconeogenesis during illness and starvation. Overall, greater muscle mass is linked to greater insulin sensitivity and glucose disposal, strength, power, and longevity. In contrast, low muscle mass correlates with dysmetabolism, dysmobility, and poor survival. Muscle mass is highly plastic, appropriate to its role as reservoir, and subject to striking genetic control. Defining mechanisms of muscle growth regulation holds significant promise to find interventions that promote health and diminish morbidity and mortality after trauma, sepsis, inflammation, and other systemic insults. In this invited review, we summarize techniques and methods to assess and manipulate muscle size and muscle mass in experimental systems, including cell culture and rodent models. These approaches have utility for studies of myopenia, sarcopenia, cachexia, and acute muscle growth or atrophy in the setting of health or injury.

Insulin Modulates Myogenesis and Muscle Atrophy Resulting From Skin Scald Burn in Young Male Rats

BACKGROUND

Burn injuries (BIs) due to scalding are one of the most common accidents among children. BIs greater than 40% of total body surface area are considered extensive and result in local and systemic response. We sought to assess morphological and myogenic mechanisms through both short- and long-term intensive insulin therapies that affect the skeletal muscle after extensive skin BI in young rats.

MATERIALS AND METHODS

Wistar rats aged 21 d were distributed into four groups: control (C), control with insulin (C + I), scald burn injury (SI), and SI with insulin (SI + I). The SI groups were submitted to a 45% total body surface area burn, and the C + I and SI + I groups received insulin (5 UI/Kg/d) for 4 or 14 d. Glucose tolerance and the homeostatic model assessment of insulin resistance index were determined. Gastrocnemius muscles were analyzed for histopathological, morphometric, and immunohistochemical myogenic parameters (Pax7, MyoD, and MyoG); in addition, the expression of genes related to muscle atrophy (MuRF1 and MAFbx) and its regulation (IGF-1) were also assessed.

RESULTS

Short-term treatment with insulin favored muscle regeneration by primary myogenesis and decreased muscle atrophy in animals with BIs, whereas the long-term treatment modulated myogenesis by increasing the MyoD protein. Both treatments improved histopathological parameters and secondary myogenesis by increasing the MyoG protein.

CONCLUSIONS

Treatment with insulin benefits myogenic parameters during regeneration and modulates MuRF1, an important mediator of muscle atrophy.

Review: Insulin resistance and mitochondrial dysfunction following severe burn injury

The insulin signaling pathway plays a pivotal role in glucose metabolism and metabolic homeostasis. Disruption of this pathway is commonly seen in critical illness such as following severe burn injuries where homeostatic control is lost, leading to "insulin resistance" with poor blood glucose control. The aberrant signaling pathways involved in insulin resistance following burn injury include increases in hyperglycemic stress hormones, pro-inflammatory cytokines and free radical production. Leakage of mitochondrial sequestered self-antigens and signaling between mitochondria and endoplasmic reticulum also contribute to insulin resistance. Greater understanding of molecular processes involved in burn-related insulin resistance could potentially lead to the development of novel therapeutic approaches to improve patient management.

Systemic bioinformatics analysis of skeletal muscle gene expression profiles of sepsis

Sepsis is a type of systemic inflammatory response syndrome with high morbidity and mortality. Skeletal muscle dysfunction is one of the major complications of sepsis that may also influence the outcome of sepsis. The aim of the present study was to explore and identify potential mechanisms and therapeutic targets of sepsis. Systemic bioinformatics analysis of skeletal muscle gene expression profiles from the Gene Expression Omnibus was performed. Differentially expressed genes (DEGs) in samples from patients with sepsis and control samples were screened out using the limma package. Differential co-expression and coregulation (DCE and DCR, respectively) analysis was performed based on the Differential Co-expression Analysis package to identify differences in gene co-expression and coregulation patterns between the control and sepsis groups. Gene Ontology terms and Kyoto Encyclopedia of Genes and Genomes pathways of DEGs were identified using the Database for Annotation, Visualization and Integrated Discovery, and inflammatory, cancer and skeletal muscle development-associated biological processes and pathways were identified. DCE and DCR analysis revealed several potential therapeutic targets for sepsis, including genes and transcription factors. The results of the present study may provide a basis for the development of novel therapeutic targets and treatment methods for sepsis.