Muscle regeneration after sepsis

Sepsis-Induced Myopathy and Gut Microbiome Dysbiosis: Mechanistic Links and Therapeutic Targets

ABSTRACT

Sepsis is currently defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. The skeletal muscle system is among the host organ systems compromised by sepsis. The resulting neuromuscular dysfunction and impaired regenerative capacity defines sepsis-induced myopathy and manifests as atrophy, loss of strength, and hindered regeneration after injury. These outcomes delay recovery from critical illness and confer increased vulnerability to morbidity and mortality. The mechanisms underlying sepsis-induced myopathy, including the potential contribution of peripheral organs, remain largely unexplored. The gut microbiome is an immunological and homeostatic entity that interacts with and controls end-organ function, including the skeletal muscle system. Sepsis induces alterations in the gut microbiota composition, which is globally termed a state of "dysbiosis" for the host compared to baseline microbiota composition. In this review, we critically evaluate existing evidence and potential mechanisms linking sepsis-induced myopathy with gut microbiota dysbiosis.

Impact of Muscle Mass on Survival in Patients with Sepsis: A Systematic Review and Meta-Analysis

INTRODUCTION

The aim of this study is to investigate the association between loss of muscle mass and prognosis of sepsis.

METHODS

Six databases, including PubMed, Embase, Cochrane Library, Web of Science, Scopus, and Ovid, were searched by the deadline of August 18, 2020. A meta-analysis was conducted on the collected data by means of a random-effects model. The quality of each included article was assessed according to the Newcastle-Ottawa Scale.

RESULTS

Out of 1,819 references, 6 articles and 1 conference abstract were included. Sepsis patients with a loss of muscle mass or sarcopenia had higher mortality (risk ratio [RR]: 1.94, 95% confidence intervals [CI]: 1.59-2.37; I-squared = 18.7%, p < 0.001). The RR of mortality within 30 days (RR: 2.31, 95% CI: 1.78-2.99, p < 0.001) was higher than that of mortality over 30 days. Loss of psoas muscle mass, as evaluated by CT, showed the highest RR of sepsis mortality. In addition, based on data on overall survival retrieved from 4 trials, the pooled hazard ratio (HR) for patients with a loss of muscle mass or sarcopenia was 3.04. Subgroup analysis showed that survival time was the main source of heterogeneity for the overall HR. Furthermore, the scanning areas of muscle mass in survival patients were 0.33 cm2/m2 higher than those measured in deceased patients.

CONCLUSION

A loss of muscle mass, as evaluated by CT scan, was associated with a poor outcome in sepsis.

Sepsis and the muscle tissue. A narrative review

Sepsis and septic shock are considered major factors in the development of myopathy in critically ill patients, which is correlated with increased morbidity rates and ICU length of stay. The underlying pathophysiology is complex, involving mitochondrial dysfunction, increased protein breakdown and muscle inexcitability. Sepsis induced myopathy is characterized by several electrophysiological and histopathological abnormalities of the muscle, also has clinical consequences such as flaccid weakness and failure to wean from ventilator. In order to reach definite diagnosis, clinical assessment, electrophysiological studies and muscle biopsy must be performed, which can be challenging in daily practice. Ultrasonography as a screening tool can be a promising alternative, especially in the ICU setting. Sepsis and mechanical ventilation have additive effects leading to diaphragm dysfunction thus complicating the patient's clinical course and recovery. Here, we summarize the effects of the septic syndrome on the muscle tissue based on the existing literature.

The Surviving Sepsis Campaign: Basic/Translational Science Research Priorities

Objectives:

Expound upon priorities for basic/translational science identified in a recent paper by a group of experts assigned by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine.

Data Sources:

Original paper, search of the literature.

Study Selection:

By several members of the original task force with specific expertise in basic/translational science.

Data Extraction:

None.

Data Synthesis:

None.

Conclusions:

In the first of a series of follow-up reports to the original paper, several members of the original task force with specific expertise provided a more in-depth analysis of the five identified priorities directly related to basic/translational science. This analysis expounds on what is known about the question and what was identified as priorities for ongoing research. It is hoped that this analysis will aid the development of future research initiatives.

The surviving sepsis campaign: basic/translational science research priorities

Objectives

Expound upon priorities for basic/translational science identified in a recent paper by a group of experts assigned by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine.

Data sources

Original paper, search of the literature.

Study selection

This study is selected by several members of the original task force with specific expertise in basic/translational science. Data extraction and data synthesis are not available.

Conclusions

In the first of a series of follow-up reports to the original paper, several members of the original task force with specific expertise provided a more in-depth analysis of the five identified priorities directly related to basic/translational science. This analysis expounds on what is known about the question and what was identified as priorities for ongoing research. It is hoped that this analysis will aid the development of future research initiatives.

Chronic muscle weakness and mitochondrial dysfunction in the absence of sustained atrophy in a preclinical sepsis model

Chronic critical illness is a global clinical issue affecting millions of sepsis survivors annually. Survivors report chronic skeletal muscle weakness and development of new functional limitations that persist for years. To delineate mechanisms of sepsis-induced chronic weakness, we first surpassed a critical barrier by establishing a murine model of sepsis with ICU-like interventions that allows for the study of survivors. We show that sepsis survivors have profound weakness for at least 1 month, even after recovery of muscle mass. Abnormal mitochondrial ultrastructure, impaired respiration and electron transport chain activities, and persistent protein oxidative damage were evident in the muscle of survivors. Our data suggest that sustained mitochondrial dysfunction, rather than atrophy alone, underlies chronic sepsis-induced muscle weakness. This study emphasizes that conventional efforts that aim to recover muscle quantity will likely remain ineffective for regaining strength and improving quality of life after sepsis until deficiencies in muscle quality are addressed.

Prognostic value of NT-proBNP levels in the acute phase of sepsis on lower long-term physical function and muscle strength in sepsis survivors

Background

Sepsis survivors often develop chronic critical illness (CCI) and demonstrate the persistent inflammation, immunosuppression, and catabolism syndrome predisposing them to long-term functional limitations and higher mortality. There is a need to identify biomarkers that can predict long-term worsening of physical function to be able to act early and prevent mobility loss. N-terminal pro-brain natriuretic peptide (NT-proBNP) is a well-accepted biomarker of cardiac overload, but it has also been shown to be associated with long-term physical function decline. We explored whether NT-proBNP blood levels in the acute phase of sepsis are associated with physical function and muscle strength impairment at 6 and 12 months after sepsis onset.

Methods

This is a retrospective analysis conducted in 196 sepsis patients (aged 18–86 years old) as part of the University of Florida (UF) Sepsis and Critical Illness Research Center (SCIRC) who consented to participate in the 12-month follow-up study. NT-proBNP was measured at 24 h after sepsis onset. Patients were followed to determine physical function by short physical performance battery (SPPB) test score (scale 0 to12—higher score corresponds with better physical function) and upper limb muscle strength by hand grip strength test (kilograms) at 6 and 12 months. We used a multivariate linear regression model to test an association between NT-proBNP levels, SPPB, and hand grip strength scores. Missing follow-up data or absence due to death was accounted for by using inverse probability weighting based on concurrent health performance status scores. Statistical significance was set at p ≤ 0.05.

Results

After adjusting for covariates (age, gender, race, Charlson comorbidity index, APACHE II score, and presence of CCI condition), higher levels of NT-proBNP at 24 h after sepsis onset were associated with lower SPPB scores at 12 months (p < 0.05) and lower hand grip strength at 6-month (p < 0.001) and 12-month follow-up (p < 0.05).

Conclusions

NT-proBNP levels during the acute phase of sepsis may be a useful indicator of higher risk of long-term impairments in physical function and muscle strength in sepsis survivors.

Muscle weakness: Understanding the principles of myopathy and neuropathy in the critically ill patient and the management options

Myo-neuropathy of the critically ill patient is a difficult nosological entity to understand and manage. It appears soon after injury, and it is estimated that 20-30% of patients admitted to Intensive Care Units will develop it in some degree. Although muscular and nervous involvement are related, the former has a better prognosis. Myo-neuropathy associates to more morbidity, longer stay in Intensive Care Unit and in hospital, and also to higher costs and mortality. It is considered part of the main determinants of the new entities: the Chronic Critical Patient and the Post Intensive Care Syndrome. This update focuses on aetiology, pathophysiology, diagnosis and strategies that can prevent, alleviate and/or improve muscle (or muscle-nerve) weakness.

The Roles of Continuous Renal Replacement Therapy in Septic Acute Kidney Injury

Despite hundreds of clinical and basic studies that have led to a better mechanistic understanding of sepsis, the number of cases with sepsis in the United States is still rising. Sepsis is a common cause of acute kidney injury (AKI) and may explain long-term complications and mortality. In the current article, a new therapeutic concept using continuous renal replacement therapy to prevent and manage long-term sequelae in septic AKI is described.

A novel paradigm links mitochondrial dysfunction with muscle stem cell impairment in sepsis

Sepsis is an acute systemic inflammatory response of the body to microbial infection and a life threatening condition associated with multiple organ failure. Survivors may display long-term disability with muscle weakness that remains poorly understood. Recent data suggest that long-term myopathy in sepsis survivors is due to failure of skeletal muscle stem cells (satellite cells) to regenerate the muscle. Satellite cells impairment in the acute phase of sepsis is linked to unusual mitochondrial dysfunctions, characterized by a dramatic reduction of the mitochondrial mass and hyperactivity of residual organelles. Survivors maintain the impairment of satellite cells, including alterations of the mitochondrial DNA (mtDNA), in the long-term. This condition can be rescued by treatment with mesenchymal stem cells (MSCs) that restore mtDNA alterations and mitochondrial function in satellite cells, and in fine their regenerative potential. Injection of MSCs in turn increases the force of isolated muscle fibers and of the whole animal, and improves the survival rate. These effects occur in the context of reduced inflammation markers that also raised during sepsis. Targeting muscle stem cells mitochondria, in a context of reduced inflammation, may represent a valuable strategy to reduce morbidity and long-term impairment of the muscle upon sepsis.