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

Predicting early diagnosis of intensive care unit-acquired weakness in septic patients using critical ultrasound and biological markers

OBJECTIVE

Early diagnosis of intensive care unit-acquired weakness (ICUAW) is crucial for improving the outcomes of critically ill patients. Hence, this study was designed to identify predisposing factors for ICUAW and establish a predictive model for the early diagnosis of ICUAW.

METHODS

This prospective observational multicenter study included septic patients from the comprehensive ICUs of West China Hospital of Sichuan University and 10 other hospitals between September and November 2023. Inclusion criteria were as follows: age over 18 years; expected ICU stay longer than 3 days; and voluntary informed consent. Patients were classified into ICUAW (MRC score < 48) and non-ICUAW (MRC score ≥ 48) groups based on muscle strength assessments. The analyzed key predictive factors encompassed demographic data, SOFA and APACHE II scores, inflammatory markers (PCT, IL-6, and CRP), and ultrasound measurements of muscle thickness and cross-sectional area. Logistic regression analysis was conducted for variable selection and nomogram model construction.

RESULTS

A total of 116 septic patients were included, comprising 77 males and 39 females (mean age: 56.94 ± 19.90 years). A nomogram model predicting ICUAW probability was developed, which involved vastus intermedius diameter, rectus femoris cross-sectional area, IL-6, and CRP. The AUC of the composite diagnostic ROC curve was 0.966 (95%CI: 0.936 - 0.996), with a sensitivity of 88% and a specificity of 95.8%.

CONCLUSIONS

Conclusively, a nomogram model is constructed for diagnosing ICUAW in septic patients, which is simple and rapid and allows for visual representation, with excellent diagnostic capability.

Role of mesenchymal stem cells in sepsis and their therapeutic potential in sepsis‑associated myopathy (Review)

Sepsis‑induced myopathy (SIM) is one of the leading causes of death in critically ill patients. SIM mainly involves the respiratory and skeletal muscles of patients, resulting in an increased risk of lung infection, aggravated respiratory failure, and prolonged mechanical ventilation and hospital stay. SIM is also an independent risk factor associated with increased mortality in critically ill patients. At present, no effective treatment for SIM has yet been established. However, mesenchymal stem cells (MSCs) have emerged as a promising therapeutic approach and have been utilized in the treatment of various clinical conditions. A significant body of basic and clinical research supports the efficacy of MSCs in managing sepsis and muscle‑related diseases. This literature review aims to explore the relationship between MSCs and sepsis, as well as their impact on skeletal muscle‑associated diseases. Additionally, the present review discusses the potential mechanisms and therapeutic benefits of MSCs in the context of SIM.

Gut microbiota-derived acetic acids promoted sepsis-induced acute respiratory distress syndrome by delaying neutrophil apoptosis through FABP4

In patients with sepsis, neutrophil apoptosis tends to be inversely proportional to the severity of sepsis, but its mechanism is not yet clear. This study aimed to explore the mechanism of fatty acid binding protein 4 (FABP4) regulating neutrophil apoptosis through combined analysis of gut microbiota and short-chain fatty acids (SCFAs) metabolism. First, neutrophils from bronchoalveolar lavage fluid (BALF) of patients with sepsis-induced acute respiratory distress syndrome (ARDS) were purified and isolated RNA was applied for sequencing. Then, the cecal ligation and puncture (CLP) method was applied to induce the mouse sepsis model. After intervention with differential SCFAs sodium acetate, neutrophil apoptosis and FABP4 expression were further analyzed. Then, FABP4 inhibitor BMS309403 was used to treat neutrophils. We found CLP group had increased lung injury score, lung tissue wet/dry ratio, lung vascular permeability, and inflammatory factors IL-1β, TNF-α, IL-6, IFN-γ, and CCL3 levels in both bronchoalveolar lavage fluid and lung tissue. Additionally, FABP4 was lower in neutrophils of ARDS patients and mice. Meanwhile, CLP-induced dysbiosis of gut microbiota and changes in SCFAs levels were observed. Further verification showed that acetic acids reduced neutrophil apoptosis and FABP4 expression via FFAR2. Besides, FABP4 affected neutrophil apoptosis through endoplasmic reticulum (ER) stress, and neutrophil depletion alleviated the promotion of ARDS development by BMS309403. Moreover, FABP4 in neutrophils regulated the injury of RLE-6TN through inflammatory factors. In conclusion, FABP4 affected by gut microbiota-derived SCFAs delayed neutrophil apoptosis through ER stress, leading to increased inflammatory factors mediating lung epithelial cell damage.

DECIPHERING GUT MICROBIOTA IN PATIENTS WITH SEVERE SEPSIS AND SEPTIC SHOCK

ABSTRACT

Introduction: Gut microbiota dysbiosis is associated with susceptibility to sepsis and poor outcomes. However, changes to the intestinal microbiota during sepsis and their value as biomarkers are unclear. In this study, we compared the intestinal microbiota of patients with sepsis and healthy controls. Methods: Stool was collected from patients with sepsis (subdivided according to mortality) and controls. Microbiome diversity and composition were analyzed by 16S rRNA gene pyrosequencing. The α-diversity of the intestinal microbiome was determined using operational taxonomic unit counts and the Chao1, Shannon, and ACE indices. Adjusted Cox regression analyses assessed 6-month mortality risk factors. Results: Fifty-nine patients (14 in-hospital deaths) and 29 healthy controls were enrolled. Operational taxonomic unit counts and Chao1 and ACE indices were lower in the nonsurvivor than in the other groups. The controls showed a higher Shannon and lower Simpson index than did the sepsis group. The genus Blautia was more abundant in controls than in the sepsis group, and Faecalibacterium less abundant in the nonsurvivor than in the other groups. Regression analysis associated low Shannon index with 6-month mortality. Conclusions: Survivors of sepsis, nonsurvivors, and healthy controls have different gut microbiomes, and a low Shannon index is a risk factor for 6-month mortality.

Intensive care unit-acquired weakness: Recent insights

Intensive care unit-acquired weakness (ICU-AW) is a common complication in critically ill patients and is associated with a variety of adverse outcomes. These include the need for prolonged mechanical ventilation and ICU stay; higher ICU, in-hospital, and 1-year mortality; and increased in-hospital costs. ICU-AW is associated with multiple risk factors including age, underlying disease, severity of illness, organ failure, sepsis, immobilization, receipt of mechanical ventilation, and other factors related to critical care. The pathological mechanism of ICU-AW remains unclear and may be considerably varied. This review aimed to evaluate recent insights into ICU-AW from several aspects including risk factors, pathophysiology, diagnosis, and treatment strategies; this provides new perspectives for future research.

Understanding Post-Sepsis Syndrome: How Can Clinicians Help?

Sepsis is a global health challenge, with over 49 million cases annually. Recent medical advancements have increased in-hospital survival rates to approximately 80%, but the escalating incidence of sepsis, owing to an ageing population, rise in chronic diseases, and antibiotic resistance, have also increased the number of sepsis survivors. Subsequently, there is a growing prevalence of "post-sepsis syndrome" (PSS). This syndrome includes long-term physical, medical, cognitive, and psychological issues after recovering from sepsis. PSS puts survivors at risk for hospital readmission and is associated with a reduction in health- and life span, both at short and long term, after hospital discharge. Comprehensive understanding of PSS symptoms and causative factors is vital for developing optimal care for sepsis survivors, a task of prime importance for clinicians. This review aims to elucidate our current knowledge of PSS and its relevance in enhancing post-sepsis care provided by clinicians.

Gut-muscle axis and sepsis-induced myopathy: The potential role of gut microbiota

Sepsis is described as an immune response disorder of the host to infection in which microorganisms play a non-negligible role. Most survivors of sepsis experience ICU-acquired weakness, also known as septic myopathy, characterized by skeletal muscle atrophy, weakness, and irreparable damage/regenerated or dysfunctional. The mechanism of sepsis-induced myopathy is currently unclear. It has been believed that this state is triggered by circulating pathogens and their related harmful factors, leading to impaired muscle metabolism. Sepsis and its resulting alterations in the intestinal microbiota are associated with sepsis-related organ dysfunction, including skeletal muscle wasting. There are also some studies on interventions targeting the flora, including fecal microbiota transplants, the addition of dietary fiber and probiotics in enteral feeding products, etc., aiming to improve sepsis-related myopathy. In this review, we critically assess the potential mechanisms and therapeutic prospects of intestinal flora in the development of septic myopathy.

CELLULAR SENESCENCE IMPLICATED IN SEPSIS-INDUCED MUSCLE WEAKNESS AND AMELIORATED WITH METFORMIN

ABSTRACT

Background: Sepsis is a life-threatening medical emergency, frequently complicated with intensive care unit-acquired weakness syndrome (ICU-AW). ICU-AW patients display flaccid weakness of the limbs, especially in the proximal limb muscles. However, little is known regarding its pathogenesis. Here, we aimed to identify the potential signaling pathway involved in ICU-AW regulation and identify a potential therapeutic drug for intervention. Methods: Both in vivo and in vitro septic mice were used. For the in vivo septic mice, either cecum ligation and puncture or intraperitoneal injection of LPS was conducted in mice. The body weight and muscle mass were then measured and recorded. Muscle strength was evaluated by limb grip strength test. The expression of proteins extracted from cells and muscles was checked through Western blot analysis. Quantitative reverse transcription-polymerase chain reaction was carried out to test the transcriptional level of genes. Senescence-associated β-galactosidase (SA-β-gal) staining and Sirius red for collagen staining were conducted. Metformin, as an antiaging agent, was then tested for any attenuation of sepsis-related symptoms. For in vitro sepsis modeling, myoblasts were treated with LPS, analyzed for senescence-related protein expression, and subsequently retested upon metformin treatment. Results: We found that both the weight and strength of muscle were dramatically reduced in cecum ligation and puncture- or LPS-induced septic mice. RNA-seq analysis revealed that various cellular senescent genes were involved in sepsis. In line with this, expression of senescence-related genes, p53 and p21 were both upregulated. Both SA-β-gal and Sirius red for collagen staining were enhanced in tibialis anterior muscles. Notably, inhibition of p53 expression by siRNA prominently reduced the number of SA-β-gal-positive myoblasts upon LPS treatment. This indicated sepsis-induced cellular senescence to be dependent on p53. Consistent with the function of metformin in antiaging, metformin attenuated cellular senescence in both murine myoblasts and skeletal muscles during sepsis. Muscle strength of septic mice was improved upon metformin treatment. Metformin intervention is therefore proposed as a potential therapeutic strategy for ICU-AW. Conclusion: Taken together, we revealed a previously unappreciated linkage between cellular senescence and sepsis-induced muscle weakness and propose metformin as a potential therapeutic drug for the treatment of ICU-AW.

IMPORTANCE OF THE INNATE IMMUNE RESPONSE IN SKELETAL MUSCLE TO SEPSIS-INDUCED ALTERATIONS IN PROTEIN BALANCE

ABSTRACT

There is growing appreciation that skeletal muscle is a fully functional component of the body's innate immune system with the potential to actively participate in the host response to invading bacteria as opposed to being a passive target. In this regard, skeletal muscle in general and myocytes specifically possess an afferent limb that recognizes a wide variety of host pathogens via their interaction with multiple classes of cell membrane-bound and intracellular receptors, including toll-like receptors, cytokine receptors, NOD-like receptors, and the NLRP inflammasome. The efferent limb of the innate immune system in muscle is equally robust and with an increased synthesis and secretion of a variety of myocyte-derived cytokines (i.e., myokines), including TNF-α, IL-1, IL-6, and NO as well as multiple chemokines in response to appropriate stimulation. Herein, the current narrative review focuses primarily on the immune response of myocytes per se as opposed to other cell types within whole muscle. Moreover, because there are important differences, this review focuses specifically on systemic infection and inflammation as opposed to the response of muscle to direct injury and various types of muscular dystrophies. To date, however, there are few definitive muscle-specific studies that are necessary to directly address the relative importance of muscle-derived immune activation as a contributor to either the systemic immune response or the local immune microenvironment within muscle during sepsis and the resultant downstream metabolic disturbances.

Impaired muscle stem cell function and abnormal myogenesis in acquired myopathies

Skeletal muscle possesses a high plasticity and a remarkable regenerative capacity that relies mainly on muscle stem cells (MuSCs). Molecular and cellular components of the MuSC niche, such as immune cells, play key roles to coordinate MuSC function and to orchestrate muscle regeneration. An abnormal infiltration of immune cells and/or imbalance of pro- and anti-inflammatory cytokines could lead to MuSC dysfunctions that could have long lasting effects on muscle function. Different genetic variants were shown to cause muscular dystrophies that intrinsically compromise MuSC function and/or disturb their microenvironment leading to impaired muscle regeneration that contributes to disease progression. Alternatively, many acquired myopathies caused by comorbidities (e.g., cardiopulmonary or kidney diseases), chronic inflammation/infection, or side effects of different drugs can also perturb MuSC function and their microenvironment. The goal of this review is to comprehensively summarize the current knowledge on acquired myopathies and their impact on MuSC function. We further describe potential therapeutic strategies to restore MuSC regenerative capacity.