Inflammatory and protein metabolism signaling responses in human skeletal muscle after burn injury

Skeletal muscle wasting after burn is regulated by a decrease in anabolic signaling in the early flow phase

Following burns a sustained catabolic stress response is activated, resulting in skeletal muscle wasting. A better understanding of the underlying mechanisms of postburn skeletal muscle wasting is essential for the development of preventive and/or therapeutic strategies. Six weeks old female rats underwent a sham, 10% or 40% total body surface area scald burn. Ten days post-injury, severely burned animals gained significantly less weight compared to sham treated and minor burned animals, reflected in a significantly lower ratio of muscle to total body weight for Soleus (SOL) and Extensor Digitorum Longus (EDL) in the severely burned group. Postburn, total fiber number was significantly lower in EDL, while in SOL the amount of type1 fibers significantly increased and type2 fibers significantly decreased. No signs of mitochondrial dysfunction (COX/SDH) or apoptosis (caspase-3) were found. In SOL and EDL, eEF2 and pAKT expression was significantly lower after severe burn. MURF1,2,3 and Atrogin-1 was significantly higher in SOL, whilst in EDL MURF1,2,3 was significantly lower postburn. In both muscles, FOXO3A was significantly lower postburn. This study identified postburn changes in muscle anthropomorphology and proteins involved in pathways regulating protein synthesis and breakdown, with more pronounced catabolic effects in SOL.

Acute muscle mass loss was alleviated with HMGB1 neutralizing antibody treatment in severe burned rats

Burn injury is associated with muscle wasting, though the involved signaling mechanisms are not well understood. In this study, we aimed to examine the role of high mobility group box 1 (HMGB1) in signaling hyper-inflammation and consequent skeletal muscle impairment after burn. Sprague Dawley rats were randomly assigned into three groups: (1) sham burn, (2) burn, (3) burn/treatment. Animals in group 2 and group 3 received scald burn on 30% of total body surface area (TBSA) and immediately treated with chicken IgY and anti-HMGB1 antibody, respectively. Muscle tissues and other samples were collected at 3-days after burn. Body mass and wet/dry weights of the hind limb muscles (total and individually) were substantially decreased in burn rats. Acute burn provoked the mitochondrial stress and cell death and enhanced the protein ubiquitination and LC3A/B levels that are involved in protein degradation in muscle tissues. Further, an increase in muscle inflammatory infiltrate associated with increased differentiation, maturation and proinflammatory activation of bone marrow myeloid cells and αβ CD4+ T and γδ T lymphocytes was noted in in circulation and spleen of burn rats. Treatment with one dose of HMGB1 neutralizing antibody reduced the burn wound size and preserved the wet/dry weights of the hind limb muscles associated with a control in the markers of cell death and autophagy pathways in burn rats. Further, anti-HMGB1 antibody inhibited the myeloid and T cells inflammatory activation and subsequent dysregulated inflammatory infiltrate in the muscle tissues of burn rats. We conclude that neutralization of HMGB1-dependent proteolytic and inflammatory responses has potential beneficial effects in preventing the muscle loss after severe burn injury.

Molecular mechanisms of post-burn muscle wasting and the therapeutic potential of physical exercise

After a severe burn injury, a systemic stress response activates metabolic and inflammatory derangements that, among other, leads to muscle mass loss (muscle wasting). These negative effects on skeletal muscle continue for several months or years and are aggravated by short-term and long-term disuse. The dynamic balance between muscle protein synthesis and muscle protein breakdown (proteolysis) is regulated by complex signalling pathways that leads to an overall negative protein balance in skeletal muscle after a burn injury. Research concerning these molecular mechanisms is still scarce and inconclusive, understanding of which, if any, molecular mechanisms contribute to muscle wasting is of fundamental importance in designing of therapeutic interventions for burn patients as well. This review not only summarizes our present knowledge of the molecular mechanisms that underpin muscle protein balance but also summarizes the effects of exercise on muscle wasting post-burn as promising strategy to counteract the detrimental effects on skeletal muscle. Future research focusing on the pathways causing post-burn muscle wasting and the different effects of exercise on them is needed to confirm this hypothesis and to lay the foundation of therapeutic strategies.

Reliability and feasibility of skeletal muscle ultrasound in the acute burn setting

OBJECTIVES

Despite the impact of muscle wasting after burn, tools to quantify muscle wasting are lacking. This multi-centre study examined the utility of ultrasound to measure muscle mass in acute burn patients comparing different methodologies.

METHODS

B-mode ultrasound was used by two raters to determine feasibility and inter-rater reliability in twenty burned adults following admission. Quadriceps muscle layer thickness (QMLT) and rectus femoris cross-sectional area (RF-CSA) were measured, comparing the use of i) a single versus average measurements, ii) a proximal versus distal location for QMLT, and iii) a maximum- versus no-compression technique for QMLT.

RESULTS

Analysis of twenty burned adults (50 years [95%CI 42-57], 32%TBSA [95%CI 23-40]) yielded ICCs of> 0.97 for QMLT (for either location and compression technique) and> 0.95 for RF-CSA, using average measurements. Relative minimal detectable changes were smaller using no-compression than maximum-compression (6.5% vs. 15%). Using no-compression to measure QMLT was deemed feasible for both proximal and distal locations (94% and 96% of attempted measurements). In 9.5% of cases maximum-compression was not feasible. 95% of RF-CSA measurements were successfully completed.

CONCLUSION

Ultrasound provides feasible and reliable values of quadriceps muscle architecture that can be adapted to clinical scenarios commonly encountered in acute burn settings.

Current understanding of the chronic stress response to burn injury from human studies

There is a marked inflammatory and hypermetabolic response following a burn injury. The interlinked responses are more pronounced than for other forms of trauma and can persist for ≥3 years post-injury in burned patients. After a burn, patients have an increased risk of diseases of ageing including cancer, diabetes and cardiovascular disease, highlighting the need for effective long-term strategies to ameliorate the stress response post-burn. Current therapeutic strategies for post-burn recovery include removal of damaged tissue with surgical excision and wound repair, nutritional supplementation and rehabilitative exercise. These strategies aim to minimize the hypermetabolic and inflammatory responses, as well as reducing the loss of lean body mass. This review briefly summarises the inflammatory and hypermetabolic responses and provides an update on the current therapeutic strategies for burned patients. The review examines the persistent nutritional challenge of ensuring sufficient energy intake of each macronutrient to fuel the hypermetabolic and counteract the catabolic response of burn injury, whilst reducing periods of hyperglycaemia and hypertriglyceridemia. Patients require individualized treatment options tailored to unique systemic responses following a burn, facilitated by a precision medicine approach to improve clinical and physiological outcomes in burned patients. Thus, this review discusses the utility of metabolic flexibility assessment to aid clinical decision making and prescription relating to nutritional supplementation and rehabilitative exercise in the burned patient.

C188-9, a specific inhibitor of STAT3 signaling, prevents thermal burn-induced skeletal muscle wasting in mice

Burn injury is the leading cause of death and disability worldwide and places a tremendous economic burden on society. Systemic inflammatory responses induced by thermal burn injury can cause muscle wasting, a severe involuntary loss of skeletal muscle that adversely affects the survival and functional outcomes of these patients. Currently, no pharmacological interventions are available for the treatment of thermal burn-induced skeletal muscle wasting. Elevated levels of inflammatory cytokines, such as interleukin-6 (IL-6), are important hallmarks of severe burn injury. The levels of signal transducer and activator of transcription 3 (STAT3)-a downstream component of IL-6 inflammatory signaling-are elevated with muscle wasting in various pro-catabolic conditions, and STAT3 has been implicated in the regulation of skeletal muscle atrophy. Here, we tested the effects of the STAT3-specific signaling inhibitor C188-9 on thermal burn injury-induced skeletal muscle wasting in vivo and on C2C12 myotube atrophy in vitro after the administration of plasma from burn model mice. In mice, thermal burn injury severity dependently increased IL-6 in the plasma and tibialis anterior muscles and activated the STAT3 (increased ratio of phospho-STAT3/STAT3) and ubiquitin-proteasome proteolytic pathways (increased Atrogin-1/MAFbx and MuRF1). These effects resulted in skeletal muscle atrophy and reduced grip strength. In murine C2C12 myotubes, plasma from burn mice activated the same inflammatory and proteolytic pathways, leading to myotube atrophy. In mice with burn injury, the intraperitoneal injection of C188-9 (50 mg/kg) reduced activation of the STAT3 and ubiquitin-proteasome proteolytic pathways, reversed skeletal muscle atrophy, and increased grip strength. Similarly, pretreatment of murine C2C12 myotubes with C188-9 (10 µM) reduced activation of the same inflammatory and proteolytic pathways, and ameliorated myotube atrophy induced by plasma taken from burn model mice. Collectively, these results indicate that pharmacological inhibition of STAT3 signaling may be a novel therapeutic strategy for thermal burn-induced skeletal muscle wasting.

Perioperative assessment of muscle inflammation susceptibility in patients with end-stage osteoarthritis

Many individuals with end-stage osteoarthritis (OA) undergo elective total hip/knee arthroplasty (THA/TKA) to relieve pain, improve mobility and quality of life. However, ∼30% suffer long-term mobility impairment following surgery. This may be in part due to muscle inflammation susceptibility (MuIS+), an overt proinflammatory pathology localized to skeletal muscle surrounding the diseased joint, present in some patients with TKA/THA. We interrogated the hypothesis that MuIS+ status results in a perturbed perioperative gene expression profile and decreases skeletal muscle integrity in patients with end-stage OA. Samples were leveraged from the two-site, randomized, controlled trial R01HD084124, NCT02628795. Participants were dichotomized based on surgical (SX) muscle gene expression of TNFRSF1A (TNF-αR). MuIS+/- samples were probed for gene expression and fibrosis. Paired and independent two-tailed t tests were used to determine differences between contralateral (CTRL) and surgical (SX) limbs and between-subject comparisons, respectively. Significance was declared at P < 0.05. Seventy participants (26M/44F; mean age 62.41 ± 8.86 yr; mean body mass index 31.10 ± 4.91 kg/m2) undergoing THA/TKA were clustered as MuIS+ (n = 24) or MuIS- (n = 46). Lower skeletal muscle integrity (greater fibrosis) exists on the SX versus CTRL limb (P < 0.001). Furthermore, MuIS+ versus MuIS- muscle exhibited higher proinflammatory (IL-6R and TNF-α) and catabolic (TRIM63) gene expression (P < 0.001, P = 0.004, and 0.024 respectively), with a trend for greater fibrosis (P = 0.087). Patients with MuIS+ exhibit more inflammation and catabolic gene expression in skeletal muscle of the SX limb, accompanied by decreased skeletal muscle integrity (Trend). This highlights the impact of MuIS+ status emphasizing the potential value of perioperative MuIS assessment to inform optimal postsurgical care.NEW & NOTEWORTHY This study assessed the skeletal muscle molecular characteristics associated with end-stage osteoarthritis and refined an important phenotype, in some patients, termed muscle inflammation susceptibility (MuIS+) that may be an important consideration following surgery. Furthermore, we provide evidence of differential inflammatory and catabolic gene expression between the contralateral and surgical limbs along with differences between the skeletal muscle surrounding the diseased hip versus knee joints.

Nutrients against Glucocorticoid-Induced Muscle Atrophy

Glucocorticoid excess is a critical factor contributing to muscle atrophy. Both endogenous and exogenous glucocorticoids negatively affect the preservation of muscle mass and function. To date, the most effective intervention to prevent muscle atrophy is to apply a mechanical load in the form of resistance exercise. However, glucocorticoid-induced skeletal muscle atrophy easily causes fatigue in daily physical activities, such as climbing stairs and walking at a brisk pace, and reduces body movements to cause a decreased ability to perform physical activity. Therefore, providing adequate nutrients in these circumstances is a key factor in limiting muscle wasting and improving muscle mass recovery. The present review will provide an up-to-date review of the effects of various nutrients, including amino acids such as branched-chain amino acids (BCAAs) and β–hydroxy β–methylbutyrate (HMB), fatty acids such as omega-3, and vitamins and their derivates on the prevention and improvement of glucocorticoid-induced muscle atrophy.

Skeletal muscle wasting after a severe burn is a consequence of cachexia and sarcopenia

Muscle wasting is common and persistent in severely burned patients, worsened by immobilization during treatment. In this review, we posit two major phenotypes of muscle wasting after severe burn, cachexia and sarcopenia, each with distinguishing characteristics to result in muscle atrophy; these characteristics are also likely present in other critically ill populations. An online search was conducted from the PubMed database and other available online resources and we manually extracted published articles in a systematic mini review. We describe the current definitions and characteristics of cachexia and sarcopenia and relate these to muscle wasting after severe burn. We then discuss these putative mechanisms of muscle atrophy in this condition. Severe burn and immobilization have distinctive patterns in mediating muscle wasting and muscle atrophy. In considering these two pathological phenotypes (cachexia and sarcopenia), we propose two independent principal causes and mechanisms of muscle mass loss after burns: (1) inflammation-induced cachexia, leading to proteolysis and protein degradation, and (2) sarcopenia/immobility that signals inhibition of expected increases in protein synthesis in response to protein loss. Because both are present following severe burn, these should be considered independently in devising treatments. Discussing cachexia and sarcopenia as independent mechanisms of severe burn-initiated muscle wasting is explored. Recognition of these associated mechanisms will likely improve outcomes.

Mechanisms of exercise as a preventative measure to muscle wasting

Skeletal muscle is the most abundant tissue in healthy individuals and it has important roles in health beyond voluntary movement. The overall mass and energy requirements of skeletal muscle require it to be metabolically active and flexible to multiple energy substrates. The tissue has evolved to be largely load dependent and it readily adapts in a number of positive ways to repetitive overload, such as various forms of exercise training. However, unloading from extended bed rest and/or metabolic derangements in response to trauma, acute illness, or severe pathology, commonly results in rapid muscle wasting. Decline in muscle mass contributes to multimorbidity, reduces function, and exerts a substantial, negative impact on the quality of life. The principal mechanisms controlling muscle mass have been well described and these cellular processes are intricately regulated by exercise. Accordingly, exercise has shown great promise and efficacy in preventing or slowing muscle wasting through changes in molecular physiology, organelle function, cell signaling pathways, and epigenetic regulation. In this review, we focus on the role of exercise in altering the molecular landscape of skeletal muscle in a manner that improves or maintains its health and function in the presence of unloading or disease.epigenetics; exercise; muscle wasting; resistance training; skeletal muscle.

Tissue-specific effect of colitis on protein synthesis in mice: impact of the dietary protein content

PURPOSE

Inflammatory bowel diseases are associated with an increase in the whole-body protein turnover, thus possibly requiring an additional supply of dietary proteins. Our aim was to evaluate whether increasing dietary protein content could alleviate protein metabolism alterations in the injured splanchnic and peripheral tissues during colitis and spontaneous mucosal healing.

METHODS

Mice with acute chemically induced colitis received either a normal protein (P14, 14% as energy), a moderately (P30, 30%) and a very high-protein (P53, 55%) diets. At different times after the challenge, protein synthesis rate was determined in tissues using a flooding dose of ¹³C valine.

RESULTS

Colon, liver and spleen protein synthesis rates were significantly increased after colitis induction, while being decreased in the caecum, kidneys and muscle. Contrastingly to the two other diets, P30 diet consumption allowed faster recovery of the animals, and this coincided with a rapid resaturation of the initial protein synthesis in the colon. In the other tissues studied, the high-protein diets show different effects depending on the dietary protein content consumed and on the examined tissues, with a general trend of P53 in lowering anabolism rates.

CONCLUSION

This study highlights the severe impact of acute colonic inflammation on protein metabolism in different organs. In addition, dietary protein content modulated the recovery of the initial protein synthesis rate in the various tissues following colitis induction. P30 diet consumption notably showed a better ability to alleviate protein metabolism perturbations induced by colitis, that may explain its documented beneficial effect on colon mucosal healing.

Bone Muscle Crosstalk in Spinal Cord Injuries: Pathophysiology and Implications for Patients' Quality of Life

PURPOSE OF REVIEW

The goal of this review is to provide a comprehensive overview of (i) bone and muscle tissue modifications pathophysiology in spinal cord injury (SCI), (ii) experimental data on the physiopathological mechanisms underpinning these modifications and their similarities with the aging process, and (iii) potential clinical implications in the management of the disabling sequelae of SCI.

RECENT FINDINGS

Several studies attempted to describe the biology underpinning the links between bone and muscle tissues in the setting of highly disabling conditions, such as osteoporosis, sarcopenia, and neurodegenerative disorders, although these bidirectional connections remain still unclear. SCI could be considered an in vivo paradigmatic model of the bone muscle interactions in unloading conditions that might be expanded in the field of neurodegenerative disorders or cancer studies. Future studies should take into consideration the newer insights into bone muscle crosstalk in order to develop multitargeted and therapeutic interventions.

Metformin alleviates muscle wasting post-thermal injury by increasing Pax7-positive muscle progenitor cells

BACKGROUND

Profound skeletal muscle wasting and weakness is common after severe burn and persists for years after injury contributing to morbidity and mortality of burn patients. Currently, no ideal treatment exists to inhibit muscle catabolism. Metformin is an anti-diabetic agent that manages hyperglycemia but has also been shown to have a beneficial effect on stem cells after injury. We hypothesize that metformin administration will increase protein synthesis in the skeletal muscle by increasing the proliferation of muscle progenitor cells, thus mitigating muscle atrophy post-burn injury.

METHODS

To determine whether metformin can attenuate muscle catabolism following burn injury, we utilized a 30% total burn surface area (TBSA) full-thickness scald burn in mice and compared burn injuries with and without metformin treatment. We examined the gastrocnemius muscle at 7 and 14 days post-burn injury.

RESULTS

At 7 days, burn injury significantly reduced myofiber cross-sectional area (CSA) compared to sham, p < 0.05. Metformin treatment significantly attenuated muscle catabolism and preserved muscle CSA at the sham size. To investigate metformin's effect on satellite cells (muscle progenitors), we examined changes in Pax7, a transcription factor regulating the proliferation of muscle progenitors. Burned animals treated with metformin had a significant increase in Pax7 protein level and the number of Pax7-positive cells at 7 days post-burn, p < 0.05. Moreover, through BrdU proliferation assay, we show that metformin treatment increased the proliferation of satellite cells at 7 days post-burn injury, p < 0.05.

CONCLUSION

In summary, metformin's various metabolic effects and its modulation of stem cells make it an attractive alternative to mitigate burn-induced muscle wasting while also managing hyperglycemia.

Erythropoietin Alleviates Burn-induced Muscle Wasting

Background: Burn injury induces long-term skeletal muscle pathology. We hypothesized EPO could attenuate burn-induced muscle fiber atrophy. Methods: Rats were allocated into four groups: a sham burn group, an untreated burn group subjected to third degree hind paw burn, and two burn groups treated with weekly or daily EPO for four weeks. Gastrocnemius muscle was analyzed at four weeks post-burn. Results: EPO attenuated the reduction of mean myofiber cross-sectional area post-burn and the level of the protective effect was no significant difference between two EPO-treated groups (p=0.784). Furthermore, EPO decreased the expression of atrophy-related ubiquitin ligase, atrogin-1, which was up-regulated in response to burn. Compared to untreated burn rats, those receiving weekly or daily EPO groups had less cell apoptosis by TUNEL assay. EPO decreased the expression of cleaved caspase 3 (key factor in the caspase-dependent pathway) and apoptosis-inducing factor (implicated in the caspase-independent pathway) after burn. Furthermore, EPO alleviated connective tissue overproduction following burn via transforming growth factor beta 1-Smad2/3 pathway. Daily EPO group caused significant erythrocytosis compared with untreated burn group but not weekly EPO group. Conclusion: EPO therapy attenuated skeletal muscle apoptosis and fibrosis at four weeks post-burn. Weekly EPO may be a safe and effective option in muscle wasting post-burn.

Molecular Mechanisms Responsible for the Rescue Effects of Pamidronate on Muscle Atrophy in Pediatric Burn Patients

Not only has pamidronate been shown to prevent inflammation associated bone resorption following burn injury, it also reduces protein breakdown in muscle. The aim of this study was to identify the molecular mechanisms responsible for muscle mass rescue in pamidronate treated compared to placebo/standard of care-treated burn patients. Mature myotubes, generated by differentiating murine C2C12 myoblasts, were exposed for 48 h to 1 or 5% serum obtained from 3 groups of children: normal unburned, burned receiving standard of care, and burned receiving standard of care with pamidronate. Exposure to serum from burned patients caused dose-dependent myotube atrophy compared to normal serum as expected based on previous observations of muscle atrophy induced by burn injury in humans and animals. The size of C2C12 myotubes was partially protected upon exposure to the serum from patients treated with pamidronate correlating with the rescue of muscle size previously observed in these patients. At the molecular signaling level, serum from both pamidronate and non-pamidronate-treated burn patients increased pSTAT3/STAT3 and pERK1/2/ERK1/2 compared to normal serum with no significant differences between the two groups of burn patients indicating elevated production of inflammatory cytokines. However, serum from pamidronate-treated patients restored the phosphorylation of AKT and mTOR and reduced protein ubiquitination when compared to burn serum alone, suggesting a prevention of muscle catabolism and a restoration of muscle anabolism. Myotube atrophy induced by burn serum was partially rescued after exposure to a pan anti-TGFβ-1/2/3 antibody, suggesting that this signaling pathway is partially responsible for the atrophy and that bisphosphonate protection of bones from resorption during burn injury prevents the release of muscle pro-catabolic factors such as TGFβ into the circulation.

Calpain inhibition ameliorates scald burn-induced acute lung injury in rats

Background

The molecular pattern of severe burn-induced acute lung injury, characterized by cell structure damage and leukocyte infiltration, remains unknown. This study aimed to determine whether calpain, a protease involved in both processes, mediates severe burn-induced acute lung injury.

Methods

Rats received full-thickness scald burns covering 30% of the total body surface area, followed by instant fluid resuscitation. MDL28170 (Tocris Bioscience), an inhibitor of calpain, was given intravenously 1 h before or after the scald burn. The histological score, wet/dry weight ratio, and caspase-3 activity were examined to evaluate the degree of lung damage. Calpain activity and its source were detected by an assay kit and immunofluorescence staining. The proteolysis of membrane skeleton proteins α-fodrin and ankyrin-B, which are substrates of calpain, was measured by Western blot.

Results

Time-course studies showed that tissue damage reached a peak between 1 and 6 h post-scald burn and gradually diminished at 24 h. More importantly, calpain activity reached peak levels at 1 h and was maintained until 24 h, paralleled by lung damage to some extent. Western blot showed that the levels of the proteolyzed forms of α-fodrin and ankyrin-B correlated well with the degree of damage. MDL28170 at a dose of 3 mg/kg b. w. given 1 h before burn injury not only antagonized the increase in calpain activity but also ameliorated scald burn-induced lung injury, including the degradation of α-fodrin and ankyrin-B. Immunofluorescence images revealed calpain 1 and CD45 double-positive cells in the lung tissue of rats exposed to scald burn injury, suggesting that leukocytes were a dominant source of calpain. Furthermore, this change was blocked by MDL28170. Finally, MDL28170 given at 1 h post-scald burn injury significantly ameliorated the wet/dry weight ratio compared with burn injury alone.

Conclusions

Calpain, a product of infiltrating leukocytes, is a mediator of scald burn-induced acute lung injury that involves enhancement of inflammation and proteolysis of membrane skeleton proteins. Its late effects warrant further study.

Muscle Fn14 gene expression is associated with fat-free mass retention during energy deficit at high altitude

Intramuscular factors that modulate fat-free mass (FFM) loss in lowlanders exposed to energy deficit during high-altitude (HA) sojourns remain unclear. Muscle inflammation may contribute to FFM loss at HA by inducing atrophy and inhibiting myogenesis via the tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible protein 14 (Fn14). To explore whether muscle inflammation modulates FFM loss reportedly developing during HA sojourns, muscle inflammation, myogenesis, and proteolysis were assessed in 16 men at sea level (SL) and following 21 days of energy deficit (-1862 ± 525 kcal/days) at high altitude (HA, 4300 m). Total body mass (TBM), FFM, and fat mass (FM) were assessed using DEXA. Gene expression and proteolytic enzymatic activities were assessed in muscle samples collected at rest at SL and HA. Participants lost 7.2 ± 1.8 kg TBM (P < 0.05); 43 ± 30% and 57 ± 30% of the TBM lost was FFM and FM, respectively. Fn14, TWEAK, TNF alpha-receptor (TNFα-R), TNFα, MYOGENIN, and paired box protein-7 (PAX7) were upregulated (P < 0.05) at HA compared to SL. Stepwise linear regression identified that Fn14 explained the highest percentage of variance in FFM loss (r2  = 0.511, P < 0.05). Dichotomization of volunteers into HIGH and LOW Fn14 gene expression indicated HIGH lost less FFM and more FM (28 ± 28% and 72 ± 28%, respectively) as a proportion of TBM loss than LOW (58 ± 26% and 42 ± 26%; P < 0.05) at HA. MYOGENIN gene expression was also greater for HIGH versus LOW (P < 0.05). These data suggest that heightened Fn14 gene expression is not catabolic and may protect FFM during HA sojourns.

Exercise Altered the Skeletal Muscle MicroRNAs and Gene Expression Profiles in Burn Rats With Hindlimb Unloading

This study investigated microRNA and target gene profiles under different conditions of burn, bed rest, and exercise training. Male Sprague-Dawley rats (n = 48) were assigned to sham ambulatory, sham hindlimb unloading, burn ambulatory, or burn plus hindlimb unloading groups. Rats received a 40% TBSA scald burn or sham treatments and were ambulatory or hindlimb unloaded. Rats were further assigned to exercise or no exercise. Plantaris tissues were harvested on day 14 and pooled to analyze for microRNA and gene expression profiles. Compared with the sham ambulatory-no exercise group, 73, 79, and 80 microRNAs were altered 2-fold in the burn ambulatory, sham hindlimb unloading, and burn hindlimb unloading groups, all with no exercise, respectively. More than 70% of microRNAs were upregulated in response to burn and hindlimb unloading, whereas 60% microRNA of the profile decreased in hindlimb unloaded burn rats with exercise training. MiR-182 was the most affected in rat muscle. Gene ontology biological process and pathway analysis showed that the oxidative stress pathway was most stimulated in the hindlimb unloaded burn rats; while in response to exercise training, all genes in related pathways such as hypermetabolic, inflammation, and blood coagulation were alleviated. MicroRNAs and transcript gene profiles were altered in burn and hindlimb unloading groups, with additive effects on hindlimb unloaded burn rats. The altered genes' signal pathways were associated with muscle mass loss and function impairment. Muscle improvement with exercise training was observed in gene levels with microRNA alterations as well.

Erythropoietin attenuates motor neuron programmed cell death in a burn animal model

Burn-induced neuromuscular dysfunction may contribute to long-term morbidity; therefore, it is imperative to develop novel treatments. The present study investigated whether erythropoietin (EPO) administration attenuates burn-induced motor neuron apoptosis and neuroinflammatory response. To validate our hypothesis, a third-degree hind paw burn rat model was developed by bringing the paw into contact with a metal surface at 75°C for 10 s. A total of 24 male Sprague–Dawley rats were randomly assigned to four groups: Group A, sham-control; Group B, burn-induced; Group C, burn + single EPO dose (5000 IU/kg i.p. at D0); and Group D, burn + daily EPO dosage (3000 IU/kg/day i.p. at D0–D6). Two treatment regimens were used to evaluate single versus multiple doses treatment effects. Before sacrifice, blood samples were collected for hematological parameter examination. The histological analyses of microglia activation, iNOS, and COX-2 in the spinal cord ventral horn were performed at week 1 post-burn. In addition, we examined autophagy changes by biomarkers of LC3B and ATG5. The expression of BCL-2, BAX, cleaved caspase-3, phospho-AKT, and mTOR was assessed simultaneously through Western blotting. EPO administration after burn injury attenuated neuroinflammation through various mechanisms, including the reduction of microglia activity as well as iNOS and COX-2 expression in the spinal cord ventral horn. In addition, the expression of phospho-AKT, mTOR and apoptotic indicators, such as BAX, BCL-2, and cleaved caspase-3, was modulated. Furthermore, the activity of burn-induced autophagy in the spinal cord ventral horn characterized by the expression of autophagic biomarkers, LC3B and ATG5, was reduced after EPO administration. The present results indicate that EPO inhibits the AKT-mTOR pathway to attenuate burn-induced motor neuron programmed cell death and microglia activation. EPO can modulate neuroinflammation and programmed cell death and may be a therapeutic candidate for neuroprotection.

The response of muscle progenitor cells to cutaneous thermal injury

BACKGROUND

Severe burn results in a systemic response that leads to significant muscle wasting. It is believed that this rapid loss in muscle mass occurs due to increased protein degradation combined with reduced protein synthesis. Alterations in the microenvironment of muscle progenitor cells may partially account for this pathology. The aim of this study was to ascertain the response of muscle progenitor cells following thermal injury in mice and to enlighten the cellular cascades that contribute to the muscle wasting.

METHODS

C57BL/6 mice received a 20% total body surface area (TBSA) thermal injury. Gastrocnemius muscle was harvested at days 2, 7, and 14 following injury for protein and histological analysis.

RESULTS

We observed a decrease in myofiber cross-sectional area at 2 days post-burn. This muscle atrophy was compensated for by an increase in myofiber cross-sectional area at 7 and 14 days post-burn. Myeloperoxidase (MPO)-positive cells (neutrophils) increased significantly at 2 days. Moreover, through Western blot analysis of two key mediators of the proteolytic pathway, we show there is an increase in Murf1 and NF-κB 2 days post-burn. MPO-positive cells were also positive for NF-κB, suggesting that neutrophils attain NF-κB activity in the muscle. Unlike inflammatory and proteolytic pathways, the number of Pax7-positive muscle progenitor cells decreased significantly 2 days post-burn. This was followed by a recovery in the number of Pax7-positive cells at 7 and 14 days, suggesting proliferation of muscle progenitors that accompanied regrowth.

CONCLUSION

Our data show a biphasic response in the muscles of mice exposed to burn injury, with phenotypic characteristics of muscle atrophy at 2 days while compensation was observed later with a change in Pax7-positive muscle progenitor cells. Targeting muscle progenitors may be of therapeutic benefit in muscle wasting observed after burn injury.

ER stress and subsequent activated calpain play a pivotal role in skeletal muscle wasting after severe burn injury

Severe burns are typically followed by hypermetabolism characterized by significant muscle wasting, which causes considerable morbidity and mortality. The aim of the present study was to explore the underlying mechanisms of skeletal muscle damage/wasting post-burn. Rats were randomized to the sham, sham+4-phenylbutyrate (4-PBA, a pharmacological chaperone promoting endoplasmic reticulum (ER) folding/trafficking, commonly considered as an inhibitor of ER), burn (30% total body surface area), and burn+4-PBA groups; and sacrificed at 1, 4, 7, 14 days after the burn injury. Tibial anterior muscle was harvested for transmission electron microscopy, calcium imaging, gene expression and protein analysis of ER stress / ubiquitin-proteasome system / autophagy, and calpain activity measurement. The results showed that ER stress markers were increased in the burn group compared with the sham group, especially at post-burn days 4 and 7, which might consequently elevate cytoplasmic calcium concentration, promote calpain production as well as activation, and cause skeletal muscle damage/wasting of TA muscle after severe burn injury. Interestingly, treatment with 4-PBA prevented burn-induced ER swelling and altered protein expression of ER stress markers and calcium release, attenuating calpain activation and skeletal muscle damage/wasting after severe burn injury. Atrogin-1 and LC3-II/LC3-I ratio were also increased in the burn group compared with the sham group, while MuRF-1 remained unchanged; 4-PBA decreased atrogin-1 in the burn group. Taken together, these findings suggested that severe burn injury induces ER stress, which in turns causes calpain activation. ER stress and subsequent activated calpain play a critical role in skeletal muscle damage/wasting in burned rats.

Muscle-bone interactions: movement in the field of mechano-humoral coupling of muscle and bone

Cyclical, mechanical loading of bone by skeletal muscle is widely recognized as a critical determinant of bone structure and mass. A growing body of evidence indicates that substances released from skeletal muscle into the bloodstream also regulate bone mass and metabolism. In this commentary, we discuss the status of research in the area of humoral regulation of bone mass by the skeletal muscle secretome, with an emphasis on the roles of myostatin, irisin, interleukin-6, and exosomes. The interplay between muscle, bone, and other modulators of bone mass, including circadian rhythm and sympathetic tone, is also discussed.

The role of complement in the acute phase response after burns

Severe burns induce a complex systemic inflammatory response characterized by a typical prolonged acute phase response (APR) that starts approximately 4-8h after-burn and persists for months up to a year after the initial burn trauma. During this APR, acute phase proteins (APPs), including C-reactive protein (CRP) and complement (e.g. C3, C4 and C5) are released in the blood, resulting amongst others, in the recruitment and migration of inflammatory cells. Although the APR is necessary for proper wound healing, a prolonged APR can induce local tissue damage, hamper the healing process and cause negative systemic effects in several organs, including the heart, lungs, kidney and the central nervous system. In this review, we will discuss the role of the APR in burns with a specific focus on complement.

Satellite cell activation and apoptosis in skeletal muscle from severely burned children

KEY POINTS

Severe burns result in profound skeletal muscle atrophy that hampers recovery. The activity of skeletal muscle stem cells, satellite cells, acutely following a severe burn is unknown and may contribute to the recovery of lean muscle. Severe burn injury induces skeletal muscle regeneration and myonuclear apoptosis. Satellite cells undergo concurrent apoptosis and activation acutely following a burn, with a net reduction in satellite cell content compared to healthy controls. The activation and apoptosis of satellite cells probably impacts the recovery of lean tissue following a severe burn, contributing to prolonged frailty in burn survivors.

ABSTRACT

Severe burns result in profound skeletal muscle atrophy; persistent muscle loss and weakness are major complications that hamper recovery from burn injury. Many factors contribute to the erosion of muscle mass following burn trauma and we propose that an impaired muscle satellite cell response is key in the aetiology of burn-induced cachexia. Muscle biopsies from the m. vastus lateralis were obtained from 12 male pediatric burn patients (>30% total body surface area burn) and 12 young, healthy male subjects. Satellite cell content, activation and apoptosis were determined via immunohistochemistry, as were muscle fibre regeneration and myonuclear apoptosis. Embryonic myosin heavy chain expression and central nucleation, indices of skeletal muscle regeneration, were elevated in burn patients (P < 0.05). Myonuclear apoptosis, quantified by TUNEL positive myonuclei and cleaved caspase-3 positive myonuclei, was also elevated in burn patients (P < 0.05). Satellite cell content was reduced in burn patients, with approximately 20% of satellite cells positive for TUNEL staining, indicating DNA damage associated with apoptosis (P < 0.05). Additionally, a significant percentage of satellite cells in burn patients expressed Ki67, a marker for cellular proliferation (P < 0.05). Satellite cell activation was also observed in burn patients with increased expression of MyoD compared to healthy controls (P < 0.05). Robust skeletal muscle atrophy occurs after burn injury, even in muscles located distally to the site of injury. The activation and apoptosis of satellite cells probably impacts the recovery of lean tissue following a severe burn, contributing to prolonged frailty in burn survivors.

The blister fluid proteome of paediatric burns

Burn injury is highly traumatic for paediatric patients, with the severity of the burn often dictating the extent of scar formation. The diagnosis of burn wound severity is largely determined by the attending clinician's experience. Thus, a greater understanding of the biochemistry at burn wound site environment and the biology of burns of different severities at an earlier stage may reduce the reliance on subjective diagnoses. In this study, blister fluid was collected from superficial thickness, deep-partial thickness, and full-thickness paediatric burn wounds. Samples were combined together based on burn depth classification and then subjected to four different fractionation methods followed by trypsin digestion. Peptides were analysed by liquid chromatography tandem mass spectrometry in order to measure the proteome of each fraction. In total, 811 individual proteins were identified, including 107, 84, and 146 proteins unique to superficial, deep-partial thickness and full-thickness burn wounds, respectively. The differences in the protein inventory and the associated gene ontologies represented within each burn depth category demonstrated that there are subtle, yet significant, variations in the biochemistry of burn wounds according to severity. Importantly, this study has produced the most comprehensive catalogue of proteins from the paediatric burn wound microenvironment to date.

SIGNIFICANCE

To our knowledge, this study has been the first to comprehensively measure the paediatric burn blister fluid proteome and has provided insight into the proteomic response to burn injury. The study contributes to the knowledge of blister fluid biochemistry of burn injury and provides clinically relevant knowledge through the qualitative evaluation of biochemical differences between burns of different depths. A better understanding of the burn wound environment will ultimately assist with more accurate clinical decision making and improved wound healing and scar reduction procedures.

STAT3 in the systemic inflammation of cancer cachexia

Weight loss is diagnostic of cachexia, a debilitating syndrome contributing mightily to morbidity and mortality in cancer. Most research has probed mechanisms leading to muscle atrophy and adipose wasting in cachexia; however cachexia is a truly systemic phenomenon. Presence of the tumor elicits an inflammatory response and profound metabolic derangements involving not only muscle and fat, but also the hypothalamus, liver, heart, blood, spleen and likely other organs. This global response is orchestrated in part through circulating cytokines that rise in conditions of cachexia. Exogenous Interleukin-6 (IL6) and related cytokines can induce most cachexia symptomatology, including muscle and fat wasting, the acute phase response and anemia, while IL-6 inhibition reduces muscle loss in cancer. Although mechanistic studies are ongoing, certain of these cachexia phenotypes have been causally linked to the cytokine-activated transcription factor, STAT3, including skeletal muscle wasting, cardiac dysfunction and hypothalamic inflammation. Correlative studies implicate STAT3 in fat wasting and the acute phase response in cancer cachexia. Parallel data in non-cancer models and disease states suggest both pathological and protective functions for STAT3 in other organs during cachexia. STAT3 also contributes to cancer cachexia through enhancing tumorigenesis, metastasis and immune suppression, particularly in tumors associated with high prevalence of cachexia. This review examines the evidence linking STAT3 to multi-organ manifestations of cachexia and the potential and perils for targeting STAT3 to reduce cachexia and prolong survival in cancer patients.

The Systemic Effect of Burn Injury and Trauma on Muscle and Bone Mass and Composition

BACKGROUND

By understanding the global inflammatory effects on distant myopathies, surgeons can better guide the rehabilitative process for burn patients. The authors tested the systemic effect of burn injury on distant injured muscle and native bone using immunohistochemistry and validated a new morphometric analytic modality to reproducibly quantify muscle atrophy using computed tomographic imaging.

METHODS

In vivo studies were performed on C57/BL6 mice using an Achilles tenotomy with concurrent burn injury model. Total muscle and bone (tibia and fibula) volume/density were quantified near the site of Achilles tenotomy using micro-computed tomography at 5, 7, and 9 to 12 weeks after surgery. The impact of burn injury on the inflammatory cascade [nuclear factor (NF)-κB, p-NF-κB] and the interconnected protein catabolism signaling pathway (Atrogin-1) was assessed by immunohistochemistry.

RESULTS

Muscle volume and density at the site of Achilles tenotomy in burned mice were significantly diminished compared with nonburned mice at 5 weeks and 9 to 12 weeks. Similar decreases in muscle volume and density were observed when comparing tenotomy to no tenotomy. Cortical bone health remained stable in burn/tenotomy mice compared with tenotomy. Muscle atrophy was associated with up-regulation of p-NF-κB, NF-κB, and Atrogin-1 assessed by immunohistochemistry.

CONCLUSIONS

Burn injury significantly decreases muscle volume and density. Increased muscle atrophy using our computed tomographic morphometric analysis correlated with a significant increase in intramuscular inflammatory markers and proteolysis enzymes. This study demonstrates a unique characterization of how burn injuries may worsen local myopathy. Moreover, it provides a novel approach for quantifying muscle atrophy over an expanded period.

Autologous adipose-derived stem cells attenuate muscular atrophy and protect spinal cord ventral horn motor neurons in an animal model of burn injury

BACKGROUND AIMS

Burn injuries might increase muscle mass loss, but the mechanisms are still unclear. In this study, we demonstrated that burn injury induced spinal cord ventral horn motor neuron (VHMN) apoptosis and subsequently caused muscle atrophy and revealed the potential protection of autologous adipose-derived stem cells (ASCs) transplantation on spinal cord VHMNs and muscle against burn injury.

METHODS

Third-degree hind-paw burns were established by contact with a 75°C metal surface for 10 seconds. Adipose tissues were harvested from the groin fat pad, expanded in culture and labeled with chloromethyl-benzamido/1,1'-dioctadecyl-3,3,3',3'- tetramethyl indocarbocyanine perchlorate. The ASCs were transplanted into the injured hind paw at 4 weeks after burn injury. The lumbar spinal cord, sciatic nerve, gastrocnemius muscle and hind-paw skin were processed for immunofluorescent staining at 4 weeks after transplantation, including terminal deoxynucleotidyl transferase (TUNEL) assay, caspase-3, caspase-9, CD 90 and S100, and the gastrocnemius muscle was evaluated through the use of hematoxylin and eosin staining.

RESULTS

Caspase-3-positive, caspase-9-positive and TUNEL-positive cells were significantly increased in the corresponding dermatome spinal cord VHMNs after burn injury. Moreover, the decrease of Schwann cells in sciatic nerve and the increase of denervation atrophy in gastrocnemius muscle were observed. Furthermore, ASCs transplantation significantly attenuated apoptotic death of VHMNs and the area of muscle denervation atrophy in the gastrocnemius muscle fibers.

CONCLUSIONS

The animal model of third-degree burns in the hind paw showed significant apoptosis in the corresponding spinal cord VHMNs, which suggests that neuroprotection might be the potentially therapeutic target in burn-induced muscle atrophy. ASCs have potential neuroprotection against burn injuries through its anti-apoptotic effects.

The comparison of C-proteasome activity in the plasma of children after burn injury, mild head injury and blunt abdominal trauma

PURPOSE

We aimed to evaluate and compare the changes in circulating 20S proteasome activity in the plasma of children suffering from blunt abdominal trauma, thermal injury and mild head injury.

PATIENTS AND METHODS

The study population comprised 40 patients with burns, 35 children admitted due to mild head injury, and 30 children suffering from blunt abdominal trauma, who were admitted to Pediatric Surgery Department of Medical University of Bialystok Poland, between 2010 and 2014, and their parents gave informed consent, were included into the study. Patients were aged 9 months to 17 years (median=5.73±1.91y). The girls to boys ratio was nearly 1:2 (34 girls and 106 boys). Plasma proteasome activity was assessed using Suc-Leu-Leu-Val-Tyr-AMC peptide substrate, 2-6h, 12-16h, and 48h after the injury. 20 healthy children admitted for planned inguinal hernia repair served as controls.

RESULTS

In our series of patients, the C-proteasome activity was much higher 12-16h after burns, than after mild head injuries, or blunt abdominal injuries, and the difference was statistically significant (p<0.05).

CONCLUSIONS

Circulating 20S proteasome is probably released from damaged tissues in response to the injury and is a biomarker of tissue damage - more severe in the group of burnt patients in comparison to the patients with mild head injury and blunt abdominal trauma. Therefore detection of 20S proteasome may represent a novel marker of immunological activity and cellular degradation in trauma patients.

Serum from human burn victims impairs myogenesis and protein synthesis in primary myoblasts

The pathophysiological response to a severe burn injury involves a robust increase in circulating inflammatory/endocrine factors and a hypermetabolic state, both of which contribute to prolonged skeletal muscle atrophy. In order to characterize the role of circulating factors in muscle atrophy following a burn injury, human skeletal muscle satellite cells were grown in culture and differentiated to myoblasts/myotubes in media containing serum from burn patients or healthy, age, and sex-matched controls. While incubation in burn serum did not affect NFκB signaling, cells incubated in burn serum displayed a transient increase in STAT3 phosphorlyation (Tyr705) after 48 h of treatment with burn serum (≈ + 70%; P < 0.01), with these levels returning to normal by 96 h. Muscle cells differentiated in burn serum displayed reduced myogenic fusion signaling (phospho-STAT6 (Tyr641), ≈−75%; ADAM12, ≈-20%; both P < 0.01), and reduced levels of myogenin (≈−75%; P < 0.05). Concomitantly, myotubes differentiated in burn serum demonstrated impaired myogenesis (assessed by number of nuclei/myotube). Incubation in burn serum for 96 h did not increase proteolytic signaling (assessed via caspase-3 and ubiquitin levels), but reduced anabolic signaling [p-p70S6k (Ser421/Thr424), −30%; p-rpS6 (Ser240/244), ≈-50%] and impaired protein synthesis (−24%) (P < 0.05). This resulted in a loss of total protein content (−18%) and reduced cell size (−33%) (P < 0.05). Overall, incubation of human muscle cells in serum from burn patients results in impaired myogenesis and reduced myotube size, indicating that circulating factors may play a significant role in muscle loss and impaired muscle recovery following burn injury.

Muscle inflammation susceptibility: a prognostic index of recovery potential after hip arthroplasty?

While elective total hip arthroplasty (THA) for end-stage osteoarthritis (OA) improves pain, mobility function, and quality of life in most cases, a large proportion of patients suffer persistent muscle atrophy, pain, and mobility impairment. Extensive skeletal muscle damage is unavoidable in these surgical procedures, and it stands to reason that poor recovery and long-term mobility impairment among some individuals after THA is linked to failed muscle regeneration and regrowth following surgery and that local muscle inflammation susceptibility (MuIS) is a major contributing factor. Here we present results of two integrated studies. In study 1, we compared muscle inflammation and protein metabolism signaling in elective THA (n=15) vs. hip fracture/trauma (HFX; n=11) vs. nonsurgical controls (CON; n=19). In study 2, we compared two subgroups of THA patients dichotomized into MuIS⁺ (n=7) or MuIS⁻ (n=7) based on muscle expression of TNF-like weak inducer of apoptosis (TWEAK) receptor (Fn14). As expected, HFX demonstrated overt systemic and local muscle inflammation and hypermetabolism. By contrast, no systemic inflammation was detected in elective THA patients; however, local muscle inflammation in the perioperative limb was profound in MuIS⁺ and was accompanied by suppressed muscle protein synthesis compared with MuIS⁻. Muscle from the contralateral limb of MuIS⁺ was unaffected, providing evidence of a true inflammation susceptibility localized to the muscle surrounding the hip with end-stage OA. We suggest MuIS status assessed at the time of surgery may be a useful prognostic index for muscle recovery potential and could therefore provide the basis for a personalized approach to postsurgery rehabilitation.

Third-degree hindpaw burn injury induced apoptosis of lumbar spinal cord ventral horn motor neurons and sciatic nerve and muscle atrophy in rats

Background. Severe burns result in hypercatabolic state and concomitant muscle atrophy that persists for several months, thereby limiting patient recovery. However, the effects of burns on the corresponding spinal dermatome remain unknown. This study aimed to investigate whether burns induce apoptosis of spinal cord ventral horn motor neurons (VHMNs) and consequently cause skeletal muscle wasting. Methods. Third-degree hindpaw burn injury with 1% total body surface area (TBSA) rats were euthanized 4 and 8 weeks after burn injury. The apoptosis profiles in the ventral horns of the lumbar spinal cords, sciatic nerves, and gastrocnemius muscles were examined. The Schwann cells in the sciatic nerve were marked with S100. The gastrocnemius muscles were harvested to measure the denervation atrophy. Result. The VHMNs apoptosis in the spinal cord was observed after inducing third-degree burns in the hindpaw. The S100 and TUNEL double-positive cells in the sciatic nerve increased significantly after the burn injury. Gastrocnemius muscle apoptosis and denervation atrophy area increased significantly after the burn injury. Conclusion. Local hindpaw burn induces apoptosis in VHMNs and Schwann cells in sciatic nerve, which causes corresponding gastrocnemius muscle denervation atrophy. Our results provided an animal model to evaluate burn-induced muscle wasting, and elucidate the underlying mechanisms.

Temporal study following burn injury in young rats is associated with skeletal muscle atrophy, inflammation and altered myogenic regulatory factors

INTRODUCTION

Burn injury (BI) greater than 40% has been associated with protein catabolism and it is characterized by a hypermetabolic response followed for muscle loss.

OBJECTIVE

The purpose of this study was to investigate the temporal effects of extensive experimental BI in the skeletal muscle distant from lesion, through morphological analysis, expression of genes related to muscle atrophy, inflammation and the myogenic regulatory factors.

MATERIALS AND METHODS

A total of 60 young male wistar rats were distributed into two groups, control (C) and subjected to scald burn injury (SBI). The animals were euthanized 1, 4 and 14 days post-sham or 45% of the total body surface BI. The medial head of gastrocnemii muscles were submitted to histopathological, morphometric (muscle fibers area and density), MyoD and myogenin immunoexpression, and gene expression for TNF-α, iNOS and E3 ubiquitin ligases (MuRF1 and MAFbx).

RESULTS

Histopathological findings were consistent with increased amount of connective tissue and inflammatory process. Muscle fiber area of SBI groups was smaller than C and no differences were found in fiber muscle density. TNF-α was higher in SBI groups, one and 14 days post-injury; iNOS expression was higher on the first and fourth day post-injury. MuRF-1 was higher on the day four and MAFbx on the day 14.

CONCLUSION

In conclusion, BI causes inflammation, atrophy and myogenesis stimulation in muscle as a result of systemic host response.

Low dose of glucocorticoid decreases the incidence of complications in severely burned patients by attenuating systemic inflammation

BACKGROUND

Excessive systemic inflammatory response remains as a major problem underlying severe burns. This study aimed to assess the effect of low-dose glucocorticoid treatment in downregulating systemic inflammation in severely burned patients.

METHODS

A prospective study from 2001 to 2014 at our hospital was conducted to compare the patients who received low-dose glucocorticoid during the acute phase with those who did not. Patients with burns 70% or greater of their total body surface area were included, and their plasma levels of inflammatory cytokines and clinical outcomes were compared.

RESULTS

A total of 69 patients were included in this study, with 31 patients receiving glucocorticoid treatment and the others not. Patient demographics including age, burn size, and incidence of inhalation injury were similar in both groups. The incidence of pulmonary infection and stress ulcer (and/or hemorrhage) was 24.2% and 3.0% in the treatment group, respectively, significantly lower than 47.8% and 19.6% of the control group (P < .05). Length of hospital stay was almost 13 days shorter in the treatment group (P < .05), whereas there was no significant difference in the overall mortality, duration of mechanical ventilation, and incidence of sepsis between the 2 groups. The enzyme-linked immunosorbent assay results confirmed that the plasma levels of C-reactive protein, tumor necrosis factor-α, interleukin-6, and interleukin-8 were significantly lower in the treatment group (P < .05).

CONCLUSION

Low dose of glucocorticoid treatment during the acute phase could reduce the levels of proinflammatory cytokines in severely burned patients and subsequently decrease the incidence of pulmonary infection and stress ulcer, as well as the length of hospital stay.

The importance of dietary protein for muscle health in inactive, hospitalized older adults

Dietary protein and amino acids are necessary for overall human health. Insufficient protein intake induces a negative protein balance with adverse outcomes such as muscle atrophy and functional decline--outcomes that are worsened in older adults. Furthermore, during inactivity, such as bed rest/hospitalization, skeletal muscle protein synthesis is reduced, protein balance is negative, and older adults lose significant amounts of muscle. Dietary protein and amino acid supplementation (∼ 30 g protein and ∼ 3 g leucine) stimulate skeletal muscle protein anabolism in healthy, community-dwelling older adults and may be considered as possible nutritional interventions to improve the muscle protein balance and potentially support skeletal muscle maintenance in hospitalized older adults. The following is a timely review of metabolic and dietary challenges faced by hospitalized older adults and potential dietary protein and amino acids solutions for maintaining skeletal muscle health during hospitalization-induced inactivity in this population.

Increased expression of atrogenes and TWEAK family members after severe burn injury in nonburned human skeletal muscle

Severe burn induces rapid skeletal muscle proteolysis after the injury, which persists for up to 1 year and results in skeletal muscle atrophy despite dietary and rehabilitative interventions. The purpose of this research was to determine acute changes in gene expression of skeletal muscle mass regulators postburn injury. Specimens were obtained for biopsy from the vastus lateralis of a nonburned leg of eight burned subjects (6M, 2F: 34.8 ± 2.7 years: 29.9 ± 3.1% TBSA burn) at 5.1 ± 1.1 days postburn injury and from matched controls. mRNA expression of cytokines and receptors in the tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) families, and the ubiquitin proteasome E3 ligases, atrogin-1 and MuRF-1, was determined. TNF receptor 1A was over 3.5-fold higher in burn. Expression of TNF-like weak inducer of apoptosis and its receptor were over 1.6 and 6.0-fold higher in burn. IL-6, IL-6 receptor, and glycoprotein 130 were elevated in burned subjects with IL-6 receptor over 13-fold higher. The level of suppressor of cytokine signaling-3 was also increased nearly 6-fold in burn. Atrogin-1 and MuRF-1 were more than 4- and 3-fold higher in burn. These results demonstrate for the first time that severe burn in humans has a remarkable impact on gene expression in skeletal muscle of a nonburned limb of genes that promote inflammation and proteolysis. Because these changes likely contribute to the acute skeletal muscle atrophy in areas not directly affected by the burn, in the future it will be important to determine the responsible systemic cues.

Correlation between circulating proteasome activity, total protein and c-reactive protein levels following burn in children

AIM OF THE STUDY

To characterize burn-induced changes following burn in children by analyzing circulating proteasome (c-proteasome) activity in the plasma in correlation with total protein and c-reactive protein levels in the plasma, and the severity of the burn.

METHODS

Fifty consecutive children scalded by hot water who were managed at the Department of Pediatric Surgery after primarily presenting with burns in 4-20% TBSA were included into the study. The children were aged 9 months up to 14 years (mean age 2.5±1 years). Patients were divided into groups according to the pediatric injury severity score used by American Burns Association. Plasma proteasome activity was assessed using Suc-Leu-Leu-Val-Tyr-AMC peptide substrate, 2-6 h, 12-16 h, 3 days, 5 days, and 7 days after injury. 20 healthy children consecutively admitted for planned inguinal hernia repair served as controls.

RESULTS

Statistically significant elevation of plasma c-proteasome activity was noted in all groups of burned children 12-16 h after the injury. We found a strong negative correlation of c-proteasome activity with total protein levels, and positive correlation with CRP levels 12-16 h after burn. We also found stronger correlation between c-proteasome activity and severity of burn, than CRP level and severity of burn 12-16 h, and 3 days after the burn. Correlations were statistically significant.

CONCLUSIONS

This study characterized circulating 20S proteasome activity levels after burn. C-proteasome activity elevate after burn and correlate negatively with plasma total protein level, thus plasma 20S proteasome activity could be additional biomarker of tissue damage in burn in pediatric population.

ICU-acquired weakness: mechanisms of disability

PURPOSE OF REVIEW

ICU-acquired weakness (ICUAW) is now recognized as a major complication of critical illness. There is no doubt that ICUAW is prevalent - some might argue ubiquitous - after critical illness, but its true role, the interaction with preexisting nerve and muscle lesions as well as its contribution to long-term functional disability, remains to be elucidated.

RECENT FINDINGS

In this article, we review the current state-of-the-art of the basic pathophysiology of nerve and muscle weakness after critical illness and explore the current literature on ICUAW with a special emphasis on the most important mechanisms of weakness.

SUMMARY

Variable contributions of structural and functional changes likely contribute to both early and late myopathy and neuropathy, although the specifics of the temporality of both processes, and the influence patient comorbidities, age, and nature of the ICU insult have on them, remain to be determined.

Targeting anabolic impairment in response to resistance exercise in older adults with mobility impairments: potential mechanisms and rehabilitation approaches

Muscle atrophy is associated with healthy aging (i.e., sarcopenia) and may be compounded by comorbidities, injury, surgery, illness, and physical inactivity. While a bout of resistance exercise increases protein synthesis rates in healthy young skeletal muscle, the effectiveness of resistance exercise to mount a protein synthetic response is less pronounced in older adults. Improving anabolic sensitivity to resistance exercise, thereby enhancing physical function, is most critical in needy older adults with clinical conditions that render them “low responders”. In this paper, we discuss potential mechanisms contributing to anabolic impairment to resistance exercise and highlight the need to improve anabolic responsiveness in low responders. This is followed with evidence suggesting that the recovery period of resistance exercise provides an opportunity to amplify the exercise-induced anabolic response using protein/essential amino acid ingestion. This anabolic strategy, if repeated chronically, may improve lean muscle gains, decrease time to recovery of function during periods of rehabilitation, and overall, maintain/improve physical independence and reduce mortality rates in older adults.