Dynamics of myosin degradation in intensive care unit-acquired weakness during severe critical illness

Effect of High Protein Normocaloric Nutrition on Skeletal Muscle Wasting in Critically Ill Mechanically Ventilated Patients: A Randomized Double-blind Study

Background and aims

Muscle wasting in critically ill patients is associated with poor outcomes. During intensive care unit (ICU) stay, delivering appropriate nutritional support helps minimize muscle loss. We sought to evaluate the impact of high-dose protein on muscle thickness and cross-sectional area (CSA), as well as to track changes in muscle echogenicity and pennation angle (PA) using bedside ultrasound in this population.

Patients and methods

We conducted a randomized, prospective, double-blind trial in which 30 patients mechanically ventilated for more than 48 hours and receiving enteral feed were enrolled. Patients were divided into two groups, and all patients received enteral feeds with total calories of about 25 kcal/kg/day. In the high-protein feed (HPF) group, patients were targeted to receive 1.5 gm/kg/day of protein, whereas in the standard feed (SF) group, patients received 1 gm/kg/day of protein. After ICU admission, muscle thickness, CSA, echogenicity, and PA were measured in all mechanically ventilated patients on days 1, 3, 5, and 7 using bedside ultrasound. The right lower limb vastus lateralis (VL) and the medial head of the gastrocnemius were investigated.

Results

We found a progressive decrease in muscle mass from day 1 to day 7 in all patients. Our study showed that muscle thickness and CSA were significantly higher in the HPF group than the SF group over 7 days, whereas muscle echogenicity and PA changes were not statistically significant.

Conclusion

High-protein feeds prevent muscle wasting in critically ill patients compared to patients receiving SFs during the first week of ICU stay. The qualitative muscle parameters, like muscle echogenicity and PA changes, were not significant.

How to cite this article

Parasuraman V, Anand RK, Khanna P, Shanmugam R, Ray BK. Effect of High Protein Normocaloric Nutrition on Skeletal Muscle Wasting in Critically Ill Mechanically Ventilated Patients: A Randomized Double-blind Study. Indian J Crit Care Med 2025;29(5):431-440.

Muscle Dysfunction and Physical Recovery After Critical Illness

During critical illness, patients experience significant and rapid onsets of muscle wasting and dysfunction with loss of strength, mass, and power. These deficits often persist long after the ICU, leading to impairments in physical function including reduced exercise capacity and increased frailty and disability. While there are numerous studies describing the epidemiology of impaired muscle and physical function in the ICU, there are significantly fewer data investigating mechanisms of prolonged and persistent impairments in ICU survivors. Additionally, while several potential clinical risk factors associated with poor physical recovery have been identified, there remains a dearth of interventions that have effectively improved outcomes long-term among survivors. In this article, we aim to provide a thorough, evidence-based review of the current state of knowledge regarding muscle dysfunction and physical function after critical illness with a focus on post-ICU and post-hospitalization phase of recovery.

Association between phase angle and daily creatinine excretion changes in critically ill patients: an approach to muscle mass

Assessing muscle mass in critically ill patients remains challenging. This retrospective cohort study explores the potential of phase angle (PA°) derived from bioelectrical impedance analysis (BIA) as a surrogate marker for muscle mass monitoring by associating it with daily creatinine excretion (DCE), a structural and metabolic muscle mass marker. In 20 ICU patients, we observed a linear relationship between PA° and DCE at initial (S1) and follow-up (S2) points, with Rho values of 0.78 and 0.65, respectively, as well as between their percentage changes (Rho = 0.80). Multivariate analysis confirmed a strong association between changes in PA° and DCE (adjusted R2 of 0.73), while changes in the extracellular water to total body water (ECW/TBW) ratio showed no significant association. This study establishes a relationship between a BIA-derived independent-weight parameter and DCE, highlighting the potential of PA° for muscle mass monitoring during acute changes, such as those seen in ICU settings. Integrating PA° into clinical practice could provide a non-invasive and reliable tool to enhance muscle assessment and support targeted interventions in critically ill patients.

Functional Magnetic Neuromuscular Stimulation vs. Routine Physiotherapy in the Critically Ill for Prevention of ICU Acquired Muscle Loss: A Randomised Controlled Trial

Background and Objectives: Muscle loss is a known complication of ICU admission. The aim of the study was to investigate the effect of neuromuscular functional magnetic stimulation (FMS) on quadriceps muscle thickness in critically ill patients. Materials and Methods: Among ICU patients one quadriceps was randomized to FMS (Tesla Stym, Iskra Medical, Ljubljana, Slovenia) stimulation and the other to control care. Quadriceps thickness was measured by ultrasound (US) in transversal and longitudinal planes at enrolment, Days 3-5, and Days 9-12. The trial stopped early following an interim analysis comparing muscle thickness differences between groups using repeated measures ANOVA. Results: Of 18 patients randomized, 2 died before completing the trial. The final analysis reported included 16 patients (female 38%, age 68 ± 10 years, SOFA 10.8 ± 2.7). Three mild skin thermal injuries were noted initially, which were later avoided with proper positioning of FMS probe. Primary outcome comparison showed that quadriceps thickness in transversal and longitudinal planes decreased in the non-stimulated legs and, but it did not change in FMS legs (-4.1 mm (95%CI: -9.4 to -0.6) vs. -0.7 mm (95%CI: -4.1 to -0.7) (p = 0.03) and -4.4 mm (95%CI: -8.9 to -1.1) vs. -1.5 mm (95%CI: -2.6 to -2.2) (p = 0.02), respectively) (ANOVA difference between groups p = 0.036 and 0.01, respectively). Conclusions: In the critically ill, neuromuscular FMS is feasible and safe with precautions applied to avoid possible skin thermal injury. FMS decreases the loss of quadriceps muscle thickness.

Guideline on positioning and early mobilisation in the critically ill by an expert panel

A scientific panel was created consisting of 23 interdisciplinary and interprofessional experts in intensive care medicine, physiotherapy, nursing care, surgery, rehabilitative medicine, and pneumology delegated from scientific societies together with a patient representative and a delegate from the Association of the Scientific Medical Societies who advised methodological implementation. The guideline was created according to the German Association of the Scientific Medical Societies (AWMF), based on The Appraisal of Guidelines for Research and Evaluation (AGREE) II. The topics of (early) mobilisation, neuromuscular electrical stimulation, assist devices for mobilisation, and positioning, including prone positioning, were identified as areas to be addressed and assigned to specialist expert groups, taking conflicts of interest into account. The panel formulated PICO questions (addressing the population, intervention, comparison or control group as well as the resulting outcomes), conducted a systematic literature review with abstract screening and full-text analysis and created summary tables. This was followed by grading the evidence according to the Oxford Centre for Evidence-Based Medicine 2011 Levels of Evidence and a risk of bias assessment. The recommendations were finalized according to GRADE and voted using an online Delphi process followed by a final hybrid consensus conference. The German long version of the guideline was approved by the professional associations. For this English version an update of the systematic review was conducted until April 2024 and recommendation adapted based on new evidence in systematic reviews and randomized controlled trials. In total, 46 recommendations were developed and research gaps addressed.

Anabolic Strategies for ICU-Acquired Weakness. What Can We Learn from Bodybuilders?

The study aimed to show the potential clinical application of supplements used among sportsmen for patients suffering from Intensive Care Unit-acquired Weakness (ICUAW) treatment. ICUAW is a common complication affecting approximately 40% of critically ill patients, often leading to long-term functional disability. ICUAW comprises critical illness polyneuropathy, critical illness myopathy, or a combination of both, such as critical illness polyneuromyopathy. Muscle degeneration begins shortly after the initiation of mechanical ventilation and persists post-ICU discharge until proteolysis and autophagy processes normalize. Several factors, including prolonged bedrest and muscle electrical silencing, contribute to muscle weakness, resulting from an imbalance between protein degradation and synthesis. ICUAW is associated with tissue hypoxia, oxidative stress, insulin resistance, reduced glucose uptake, lower adenosine triphosphate (ATP) formation, mitochondrial dysfunction, and increased free-radical production. Several well-studied dietary supplements and pharmaceuticals commonly used by athletes are proven to prevent the aforementioned mechanisms or aid in muscle building, regeneration, and maintenance. While there is no standardized treatment to prevent the occurrence of ICUAW, nutritional interventions have demonstrated the potential for its mitigation. The use of ergogenic substances, popular among muscle-building sociates, may offer potential benefits in preventing muscle loss and aiding recovery based on their work mechanisms.

Myostatin gene invalidation does not prevent skeletal muscle mass loss during experimental sepsis in mice

Loss of muscle mass and function induced by sepsis contributes to physical inactivity and disability in intensive care unit patients. Limiting skeletal muscle deconditioning may thus be helpful in reducing the long-term effect of muscle wasting in patients. We tested the hypothesis that invalidation of the myostatin gene, which encodes a powerful negative regulator of skeletal muscle mass, could prevent or attenuate skeletal muscle wasting and improve survival of septic mice. Sepsis was induced by caecal ligature and puncture (CLP) in 13-week-old C57BL/6J wild-type and myostatin knock-out male mice. Survival rates were similar in wild-type and myostatin knock-out mice seven days after CLP. Loss in muscle mass was also similar in wild-type and myostatin knock-out mice 4 and 7 days after CLP. The loss in muscle mass was molecularly supported by an increase in the transcript level of E3-ubiquitin ligases and autophagy-lysosome markers. This transcriptional response was blunted in myostatin knock-out mice. No change was observed in the protein level of markers of the anabolic insulin/IGF1-Akt-mTOR pathway. Muscle strength was similarly decreased in wild-type and myostatin knock-out mice 4 and 7 days after CLP. This was associated with a modified expression of genes involved in ion homeostasis and excitation-contraction coupling, suggesting that a long-term functional recovery following experimental sepsis may be impaired by a dysregulated expression of molecular determinants of ion homeostasis and excitation-contraction coupling. In conclusion, myostatin gene invalidation does not provide any benefit in preventing skeletal muscle mass loss and strength in response to experimental sepsis. KEY POINTS: Survival rates are similar in wild-type and myostatin knock-out mice seven days after the induction of sepsis. Loss in muscle mass and muscle strength are similar in wild-type and myostatin knock-out mice 4 and 7 days after the induction of an experimental sepsis. Despite evidence of a transcriptional regulation, the protein level of markers of the anabolic insulin/IGF1-Akt-mTOR pathway remained unchanged. RT-qPCR analysis of autophagy-lysosome pathway markers indicates that activity of the pathway may be altered by experimental sepsis in wild-type and myostatin knock-out mice. Experimental sepsis induces greater variations in the mRNA levels of wild-type mice than those of myostatin knock-out mice, without providing any significant catabolic resistance or functional benefits.

Vitamin K1 ameliorates lipopolysaccharide-triggered skeletal muscle damage revealed by faecal bacteria transplantation

BACKGROUND

Sepsis-associated muscle weakness is common in patients of intensive care units (ICUs), and it is closely associated with poor outcomes. The mechanism of sepsis-induced muscle weakness is unclear. Recent studies have found that gut microbiota and metabolites are involved in the regulation of skeletal muscle mass and metabolism. This study aimed to investigate the effects of gut microbiota and metabolites on sepsis-associated muscle weakness.

METHODS

In a lipopolysaccharide (LPS)-induced inflammation mouse model, mice with different sensitivities to LPS-induced inflammation were considered as donor mice for the faecal microbiota transplantation (FMT) assay, and recipient mice were divided into sensitive (Sen) and resistant (Res) groups. Skeletal muscle mass and function, as well as colonic barrier integrity were tested and gut microbiota and metabolite composition were analysed in both groups of mice. The effect of intestinal differential metabolite vitamin K1 on LPS-triggered muscle damage was investigated, and the underlying mechanism was explored.

RESULTS

Recipients exhibited varying LPS-triggered muscle damage and intestinal barrier disruption. Tibialis anterior (TA) muscle of Sen exhibited upregulated expression levels of MuRF-1 (0.825 ± 0.063 vs. 0.304 ± 0.293, P = 0.0141) and MAFbx (1.055 ± 0.079 vs. 0.456 ± 0.3, P = 0.0092). Colonic tight junction proteins ZO-1 (0.550 ± 0.087 vs. 0.842 ± 0.094, P = 0.0492) and occludin (0.284 ± 0.057 vs. 0.664 ± 0.191, P = 0.0487) were significantly downregulated in the Sen group. Metabolomic analysis showed significantly higher vitamin K1 in the faeces (P = 0.0195) and serum of the Res group (P = 0.0079) than those of the Sen group. After vitamin K1 intervention, muscle atrophy-related protein expression downregulated (P < 0.05). Meanwhile SIRT1 protein expression were upregulated (0.320 ± 0.035 vs. 0.685 ± 0.081, P = 0.0281) and pNF-κB protein expression were downregulated (0.815 ± 0.295 vs. 0.258 ± 0.130, P = 0.0308). PI3K (0.365 ± 0.142 vs. 0.763 ± 0.013, P = 0.0475), pAKT (0.493 ± 0.159 vs. 1.183 ± 0.344, P = 0.0254) and pmTOR (0.509 ± 0.088 vs. 1.110 ± 0.190, P = 0.0368) protein expression levels were upregulated in TA muscle. Meanwhile, vitamin K1 attenuated serum inflammatory factor levels.

CONCLUSIONS

Vitamin K1 might ameliorate LPS-triggered skeletal muscle damage by antagonizing NF-κB-mediated inflammation through upregulation of SIRT1 and regulating the balance between protein synthesis and catabolism.

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.

A critical discussion on the relationship between E3 ubiquitin ligases, protein degradation, and skeletal muscle wasting: it's not that simple

Ubiquitination is an important post-translational modification (PTM) for protein substrates, whereby ubiquitin is added to proteins through the coordinated activity of activating (E1), ubiquitin-conjugating (E2), and ubiquitin ligase (E3) enzymes. The E3s provide key functions in the recognition of specific protein substrates to be ubiquitinated and aid in determining their proteolytic or nonproteolytic fates, which has led to their study as indicators of altered cellular processes. MuRF1 and MAFbx/Atrogin-1 were two of the first E3 ubiquitin ligases identified as being upregulated in a range of different skeletal muscle atrophy models. Since their discovery, the expression of these E3 ubiquitin ligases has often been studied as a surrogate measure of changes to bulk protein degradation rates. However, emerging evidence has highlighted the dynamic and complex regulation of the ubiquitin proteasome system (UPS) in skeletal muscle and demonstrated that protein ubiquitination is not necessarily equivalent to protein degradation. These observations highlight the potential challenges of quantifying E3 ubiquitin ligases as markers of protein degradation rates or ubiquitin proteasome system (UPS) activation. This perspective examines the usefulness of monitoring E3 ubiquitin ligases for determining specific or bulk protein degradation rates in the settings of skeletal muscle atrophy. Specific questions that remain unanswered within the skeletal muscle atrophy field are also identified, to encourage the pursuit of new research that will be critical in moving forward our understanding of the molecular mechanisms that govern protein function and degradation in muscle.

Dual lumen cannulation and mobilization of patients with venovenous extracorporeal membrane oxygenation

BACKGROUND

Mobilization is important in longer courses in intensive care unit (ICU), typical for patients requiring venovenous extracorporeal membrane oxygenation (V-V ECMO). For patients supported with ECMO, especially out-of-bed mobilizations improve outcome. We hypothesized that utilization of a dual lumen cannula (DLC) for V-V ECMO would facilitate out-of-bed mobilization compared to single lumen cannulas (SLC).

METHODS

Retrospective single center registry study including all V-V ECMO patients cannulated between 10/2010 and 05/2021 for respiratory failure.

RESULTS

The registry included 355 V-V ECMO patients (median age 55.6 years, 31.8% female, 27.3% with preexisting pulmonary disease), 289/355 (81.4%) primary cannulated with DLC, and 66/355 (18.6%) using SLC. Both groups had similar pre-ECMO characteristics. The runtime of the first ECMO cannula was significantly longer in DLC compared to SLC (169 vs. 115 h, p = 0.015). The frequency of prone positioning during V-V ECMO was similar in both groups (38.4 vs. 34.8%, p = 0.673). There was no difference in in-bed mobilization (41.2 vs. 36.4%, for DLC and SLC, respectively, p = 0.491). Patients with DLC were more often mobilized out-of-bed (25.6 vs. 12.1%, OR 2.495 [95% CI 1.150 to 5.268], for DLC and SLC, respectively, p = 0.023). Hospital survival was similar in both groups (46.4 vs. 39.4%, for DLC and SLC, respectively, p = 0.339).

CONCLUSION

Patients cannulated with a dual lumen cannula for V-V ECMO support were significantly more often mobilized out-of-bed. Since mobilization is important in prolonged ICU courses typical for ECMO patients, this might be an important benefit. Other benefits of DLC were the longer runtime of the initial cannula set and fewer suction events.

The role of the microcirculation and integrative cardiovascular physiology in the pathogenesis of ICU-acquired weakness

Skeletal muscle dysfunction after critical illness, defined as ICU-acquired weakness (ICU-AW), is a complex and multifactorial syndrome that contributes significantly to long-term morbidity and reduced quality of life for ICU survivors and caregivers. Historically, research in this field has focused on pathological changes within the muscle itself, without much consideration for their in vivo physiological environment. Skeletal muscle has the widest range of oxygen metabolism of any organ, and regulation of oxygen supply with tissue demand is a fundamental requirement for locomotion and muscle function. During exercise, this process is exquisitely controlled and coordinated by the cardiovascular, respiratory, and autonomic systems, and also within the skeletal muscle microcirculation and mitochondria as the terminal site of oxygen exchange and utilization. This review highlights the potential contribution of the microcirculation and integrative cardiovascular physiology to the pathogenesis of ICU-AW. An overview of skeletal muscle microvascular structure and function is provided, as well as our understanding of microvascular dysfunction during the acute phase of critical illness; whether microvascular dysfunction persists after ICU discharge is currently not known. Molecular mechanisms that regulate crosstalk between endothelial cells and myocytes are discussed, including the role of the microcirculation in skeletal muscle atrophy, oxidative stress, and satellite cell biology. The concept of integrated control of oxygen delivery and utilization during exercise is introduced, with evidence of physiological dysfunction throughout the oxygen delivery pathway - from mouth to mitochondria - causing reduced exercise capacity in patients with chronic disease (e.g., heart failure, COPD). We suggest that objective and perceived weakness after critical illness represents a physiological failure of oxygen supply-demand matching - both globally throughout the body and locally within skeletal muscle. Lastly, we highlight the value of standardized cardiopulmonary exercise testing protocols for evaluating fitness in ICU survivors, and the application of near-infrared spectroscopy for directly measuring skeletal muscle oxygenation, representing potential advancements in ICU-AW research and rehabilitation.

The Effects of Early Mobilization on Acquired Weakness in Intensive Care Units: A Literature Review

BACKGROUND

Intensive care unit (ICU)-acquired weakness (ICUAW) is defined as a clinical syndrome of neuromuscular weakness, and a consequence of critical illness, unrelated to any other etiology. It is associated with difficult weaning from the ventilator, prolonged ICU stay, increased mortality, and other important long-term outcomes. Early mobilization is defined as any active exercise in which patients use their muscle strength actively or passively within the first 2 to 5 days of critical illness. Early mobilization can be safely initiated from the first day of admission to the ICU during mechanical ventilation.

OBJECTIVES

The purpose of this review is to describe the effects of early mobilization on complications from ICUAW.

METHOD

This was a literature review. Inclusion criteria were as follows: observational studies and randomized controlled trials conducted with adult patients (aged ≥18 years) admitted to the ICU were included. Studies selected were published in the last 11 years (2010-2021).

RESULTS

Ten articles were included. Early mobilization reduces muscle atrophy, ventilation, length of hospital stay, and ventilator-associated pneumonia and improves patients' responses to inflammation and hyperglycemia.

DISCUSSION

Early mobilization appears to have a significant impact on the prevention of ICUAW and appears to be safe and feasible. The results of this review could be useful for improving the provision of efficient and effective tailored care for ICU patients.

Insulin signaling in skeletal muscle during inflammation and/or immobilisation

BACKGROUND

The decline in the downstream signal transduction pathway of anabolic hormone, insulin, could play a key role in the muscle atrophy and insulin resistance observed in patients with intensive care unit acquired weakness (ICUAW). This study investigated the impact of immobilisation via surgical knee and ankle fixation and inflammation via Corynebacterium parvum injection, alone and in combination, as risk factors for altering insulin transduction and, therefore, their role in ICUAW.

RESULTS

Muscle weight was significantly decreased due to immobilisation [estimated effect size (95% CI) - 0.10 g (- 0.12 to - 0.08); p < 0.001] or inflammation [estimated effect size (95% CI) - 0.11 g (- 0.13 to - 0.09); p < 0.001] with an additive effect of both combined (p = 0.024). pAkt was only detectable after insulin stimulation [estimated effect size (95% CI) 85.1-fold (76.2 to 94.0); p < 0.001] irrespective of the group and phosphorylation was not impaired by the different perturbations. Nevertheless, the phosphorylation of GSK3 observed in the control group after insulin stimulation was decreased in the immobilisation [estimated effect size (95% CI) - 40.2 (- 45.6 to - 34.8)] and inflammation [estimated effect size (95% CI) - 55.0 (- 60.4 to - 49.5)] groups. The expression of phosphorylated GS (pGS) was decreased after insulin stimulation in the control group and significantly increased in the immobilisation [estimated effect size (95% CI) 70.6-fold (58.8 to 82.4)] and inflammation [estimated effect size (95% CI) 96.7 (85.0 to 108.5)] groups.

CONCLUSIONS

Both immobilisation and inflammation significantly induce insulin resistance, i.e., impair the insulin signaling pathway downstream of Akt causing insufficient GSK phosphorylation and, therefore, its activation which caused increased glycogen synthase phosphorylation, which could contribute to muscle atrophy of immobilisation and inflammation.

Disintegration of the NuRD Complex in Primary Human Muscle Stem Cells in Critical Illness Myopathy

Critical illness myopathy (CIM) is an acquired, devastating, multifactorial muscle-wasting disease with incomplete recovery. The impact on hospital costs and permanent loss of quality of life is enormous. Incomplete recovery might imply that the function of muscle stem cells (MuSC) is impaired. We tested whether epigenetic alterations could be in part responsible. We characterized human muscle stem cells (MuSC) isolated from early CIM and analyzed epigenetic alterations (CIM n = 15, controls n = 21) by RNA-Seq, immunofluorescence, analysis of DNA repair, and ATAC-Seq. CIM-MuSC were transplanted into immunodeficient NOG mice to assess their regenerative potential. CIM-MuSC exhibited significant growth deficits, reduced ability to differentiate into myotubes, and impaired DNA repair. The chromatin structure was damaged, as characterized by alterations in mRNA of histone 1, depletion or dislocation of core proteins of nucleosome remodeling and deacetylase complex, and loosening of multiple nucleosome-spanning sites. Functionally, CIM-MuSC had a defect in building new muscle fibers. Further, MuSC obtained from the electrically stimulated muscle of CIM patients was very similar to control MuSC, indicating the impact of muscle contraction in the onset of CIM. CIM not only affects working skeletal muscle but has a lasting and severe epigenetic impact on MuSC.

Tenotomy-induced muscle atrophy is sex-specific and independent of NFκB

The nuclear factor-κB (NFκB) pathway is a major thoroughfare for skeletal muscle atrophy and is driven by diverse stimuli. Targeted inhibition of NFκB through its canonical mediator IKKβ effectively mitigates loss of muscle mass across many conditions, from denervation to unloading to cancer. In this study, we used gain- and loss-of-function mouse models to examine the role of NFκB in muscle atrophy following rotator cuff tenotomy - a model of chronic rotator cuff tear. IKKβ was knocked down or constitutively activated in muscle-specific inducible transgenic mice to elicit a twofold gain or loss of NFκB signaling. Surprisingly, neither knockdown of IKKβ nor overexpression of caIKKβ significantly altered the loss of muscle mass following tenotomy. This finding was consistent across measures of morphological adaptation (fiber cross-sectional area, fiber length, fiber number), tissue pathology (fibrosis and fatty infiltration), and intracellular signaling (ubiquitin-proteasome, autophagy). Intriguingly, late-stage tenotomy-induced atrophy was exacerbated in male mice compared with female mice. This sex specificity was driven by ongoing decreases in fiber cross-sectional area, which paralleled the accumulation of large autophagic vesicles in male, but not female muscle. These findings suggest that tenotomy-induced atrophy is not dependent on NFκB and instead may be regulated by autophagy in a sex-specific manner.

Muscular myostatin gene expression and plasma concentrations are decreased in critically ill patients

Background

The objective was to investigate the role of gene expression and plasma levels of the muscular protein myostatin in intensive care unit-acquired weakness (ICUAW). This was performed to evaluate a potential clinical and/or pathophysiological rationale of therapeutic myostatin inhibition.

Methods

A retrospective analysis from pooled data of two prospective studies to assess the dynamics of myostatin plasma concentrations (day 4, 8 and 14) and myostatin gene (MSTN) expression levels in skeletal muscle (day 15) was performed. Associations of myostatin to clinical and electrophysiological outcomes, muscular metabolism and muscular atrophy pathways were investigated.

Results

MSTN gene expression (median [IQR] fold change: 1.00 [0.68–1.54] vs. 0.26 [0.11–0.80]; p = 0.004) and myostatin plasma concentrations were significantly reduced in all critically ill patients when compared to healthy controls. In critically ill patients, myostatin plasma concentrations increased over time (median [IQR] fold change: day 4: 0.13 [0.08/0.21] vs. day 8: 0.23 [0.10/0.43] vs. day 14: 0.40 [0.26/0.61]; p < 0.001). Patients with ICUAW versus without ICUAW showed significantly lower MSTN gene expression levels (median [IQR] fold change: 0.17 [0.10/0.33] and 0.51 [0.20/0.86]; p = 0.047). Myostatin levels were directly correlated with muscle strength (correlation coefficient 0.339; p = 0.020) and insulin sensitivity index (correlation coefficient 0.357; p = 0.015). No association was observed between myostatin plasma concentrations as well as MSTN expression levels and levels of mobilization, electrophysiological variables, or markers of atrophy pathways.

Conclusion

Muscular gene expression and systemic protein levels of myostatin are downregulated during critical illness. The previously proposed therapeutic inhibition of myostatin does therefore not seem to have a pathophysiological rationale to improve muscle quality in critically ill patients.

Trial registration: ISRCTN77569430—13th of February 2008 and ISRCTN19392591 17th of February 2011.

Graphical abstract

Diagnostic Utility of Temporal Muscle Thickness as a Monitoring Tool for Muscle Wasting in Neurocritical Care

Temporalis muscle (TM) atrophy has emerged as a potential biomarker for muscle wasting. However, its diagnostic utility as a monitoring tool in intensive care remains uncertain. Hence, the objective of this study was to evaluate the diagnostic value of sequential ultrasound- and computed tomography (CT)-based measurements of TM thickness (TMT). With a prospective observational design, we included 40 patients without preexisting sarcopenia admitted to a neurointensive care unit. TMT measurements, performed upon admission and serially every 3−4 days, were correlated with rectus femoris muscle thickness (RFT) ultrasound measurements. Interrater reliability was assessed by Bland Altmann plots and intraclass correlation coefficient (ICC). Analysis of variance was performed in subgroups to evaluate differences in the standard error of measurement (SEM). RFT decline was paralleled by ultrasound- as well as CT-based TMT measurements (TMT to RFT: r = 0.746, p < 0.001; CT-based TMT to ultrasound-based RFT: r = 0.609, p < 0.001). ICC was 0.80 [95% CI 0.74, 0.84] for ultrasound-based assessment and 0.90 [95% CI 0.88, 0.92] for CT-based TMT measurements. Analysis of variance for BMI, Heckmatt score, fluid balance, and agitation showed no evidence of measurement errors in these subgroups. This study demonstrates the clinical feasibility and utility of ultrasound- and CT-based TMT measurements for the assessment of muscle wasting.

BNIP3 Is Involved in Muscle Fiber Atrophy in Late-Onset Pompe Disease Patients

Late-onset Pompe disease (LOPD) is a rare genetic disorder produced by mutations in the GAA gene and is characterized by progressive muscle weakness. LOPD muscle biopsies show accumulation of glycogen along with the autophagic vacuoles associated with atrophic muscle fibers. The expression of molecules related to muscle fiber atrophy in muscle biopsies of LOPD patients was studied using immunofluorescence and real-time PCR. BCL2 and adenovirus E1B 19-kDa interacting protein 3 (BNIP3), a well-known atrogene, was identified as a potential mediator of muscle fiber atrophy in LOPD muscle biopsies. Vacuolated fibers in LOPD patient muscle biopsies were smaller than nonvacuolated fibers and expressed BNIP3. The current data suggested that BNIP3 expression is regulated by inhibition of the AKT-mammalian target of rapamycin pathway, leading to phosphorylation of Unc-51 like autophagy activating kinase 1 (ULK1) at Ser317 by AMP-activated protein kinase. Myoblasts and myotubes obtained from LOPD patients and age-matched controls were studied to confirm these results using different molecular techniques. Myotubes derived from LOPD patients were likewise smaller and expressed BNIP3. Conclusively, transfection of BNIP3 into control myotubes led to myotube atrophy. These findings suggest a cascade that starts with the inhibition of the AKT-mammalian target of rapamycin pathway and activation of BNIP3 expression, leading to progressive muscle fiber atrophy. These results open the door to potential new treatments targeting BNIP3 to reduce its deleterious effects on muscle fiber atrophy in Pompe disease.

Skeletal Muscles of Patients Infected with SARS-CoV-2 Develop Severe Myofiber Damage upon One Week of Admission on the Intensive Care Unit

Many critically ill patients infected with SARS-CoV-2 have been submitted to an intensive care unit (ICU). Patients with a SARS-CoV-2 infection that survive critical illness are confronted with months of physical impairments. To maximize recovery, it is important to understand the musculoskeletal involvement in critically ill patients infected with SARS-CoV-2. The aim of the present study was to assess the myocellular changes in SARS-CoV-2 patients that occur throughout the first week of ICU admission. In n = 22 critically ill patients infected with SARS-CoV-2, a biopsy sample from the vastus lateralis muscle was obtained at day 1–3 and day 5–8 following ICU admission. Fluorescence microscopy was used to assess type I and type II muscle fiber size and distribution, myonuclear content, and muscle tissue capillarization. Transmission electron microscopy was used to support quantitative data at an ultrastructural level. Changes in type I and type II muscle fiber size showed large inter-individual variation. The average change in type I fiber size was +309 ± 1834 µm2, ranging from −2129 µm2 (−31%) to +3375 µm2 (+73%). The average change in type II fiber size was −224 ± 1256 µm2, ranging from −1410 µm2 (−36%) to +2592 µm2 (+48%). Ultrastructural observations showed myofibrillar and hydropic degeneration, and fiber necrosis. This study shows that ICU patients admitted with SARS-CoV-2 suffer from substantial muscle fiber damage during ICU admission. These results are a call for action towards more specialized rehabilitation programs for patients admitted to the ICU with SARS-CoV-2 infection.

Safety and Feasibility Assessment of Repetitive Vascular Occlusion Stimulus (RVOS) Application to Multi-Organ Failure Critically Ill Patients: A Pilot Randomised Controlled Trial

Muscle wasting is implicated in the pathogenesis of intensive care unit acquired weakness (ICU-AW), affecting 40% of patients and causing long-term physical disability. A repetitive vascular occlusion stimulus (RVOS) limits muscle atrophy in healthy and orthopaedic subjects, thus, we explored its application to ICU patients. Adult multi-organ failure patients received standard care +/- twice daily RVOS {4 cycles of 5 min tourniquet inflation to 50 mmHg supra-systolic blood pressure, and 5 min complete deflation} for 10 days. Serious adverse events (SAEs), tolerability, feasibility, acceptability, and exploratory outcomes of the rectus femoris cross-sectional area (RFCSA), echogenicity, clinical outcomes, and blood biomarkers were assessed. Only 12 of the intended 32 participants were recruited. RVOS sessions (76.1%) were delivered to five participants and two could not tolerate it. No SAEs occurred; 75% of participants and 82% of clinical staff strongly agreed or agreed that RVOS is an acceptable treatment. RFCSA fell significantly and echogenicity increased in controls (n = 5) and intervention subjects (n = 4). The intervention group was associated with less frequent acute kidney injury (AKI), a greater decrease in the total sequential organ failure assessment score (SOFA) score, and increased insulin-like growth factor-1 (IGF-1), and reduced syndecan-1, interleukin-4 (IL-4) and Tumor necrosis factor receptor type II (TNF-RII) levels. RVOS application appears safe and acceptable, but protocol modifications are required to improve tolerability and recruitment. There were signals of possible clinical benefit relating to RVOS application.

Therapeutic Potential of Electromyostimulation (EMS) in Critically Ill Patients—A Systematic Review

Ample evidence exists that intensive care unit (ICU) treatment and invasive ventilation induce a transient or permanent decline in muscle mass and function. The functional deficit is often called ICU-acquired weakness with critical illness polyneuropathy (CIP) and/or myopathy (CIM) being the major underlying causes. Histopathological studies in ICU patients indicate loss of myosin filaments, muscle fiber necrosis, atrophy of both muscle fiber types as well as axonal degeneration. Besides medical prevention of risk factors such as sepsis, hyperglycemia and pneumonia, treatment is limited to early passive and active mobilization and one third of CIP/CIM patients discharged from ICU never regain their pre-hospitalization constitution. Electromyostimulation [EMS, also termed neuromuscular electrical stimulation (NMES)] is known to improve strength and function of healthy and already atrophied muscle, and may increase muscle blood flow and induce angiogenesis as well as beneficial systemic vascular adaptations. This systematic review aimed to investigate evidence from randomized controlled trails (RCTs) on the efficacy of EMS to improve the condition of critically ill patients treated on ICU. A systematic search of the literature was conducted using PubMed (Medline), CENTRAL (including Embase and CINAHL), and Google Scholar. Out of 1,917 identified records, 26 articles (1,312 patients) fulfilled the eligibility criteria of investigating at least one functional measure including muscle function, functional independence, or weaning outcomes using a RCT design in critically ill ICU patients. A qualitative approach was used, and results were structured by 1) stimulated muscles/muscle area (quadriceps muscle only; two to four leg muscle groups; legs and arms; chest and abdomen) and 2) treatment duration (≤10 days, >10 days). Stimulation parameters (impulse frequency, pulse width, intensity, duty cycle) were also collected and the net EMS treatment time was calculated. A high grade of heterogeneity between studies was detected with major cofactors being the analyzed patient group and selected outcome variable. The overall efficacy of EMS was inconclusive and neither treatment duration, stimulation site or net EMS treatment time had clear effects on study outcomes. Based on our findings, we provide practical recommendations and suggestions for future studies investigating the therapeutic efficacy of EMS in critically ill patients.

Systematic Review Registration: [https://www.crd.york.ac.uk/prospero/], identifier [CRD42021262287].

Hidden Agenda - The Involvement of Endoplasmic Reticulum Stress and Unfolded Protein Response in Inflammation-Induced Muscle Wasting

Critically ill patients at the intensive care unit (ICU) often develop a generalized weakness, called ICU-acquired weakness (ICUAW). A major contributor to ICUAW is muscle atrophy, a loss of skeletal muscle mass and function. Skeletal muscle assures almost all of the vital functions of our body. It adapts rapidly in response to physiological as well as pathological stress, such as inactivity, immobilization, and inflammation. In response to a reduced workload or inflammation muscle atrophy develops. Recent work suggests that adaptive or maladaptive processes in the endoplasmic reticulum (ER), also known as sarcoplasmic reticulum, contributes to this process. In muscle cells, the ER is a highly specialized cellular organelle that assures calcium homeostasis and therefore muscle contraction. The ER also assures correct folding of proteins that are secreted or localized to the cell membrane. Protein folding is a highly error prone process and accumulation of misfolded or unfolded proteins can cause ER stress, which is counteracted by the activation of a signaling network known as the unfolded protein response (UPR). Three ER membrane residing molecules, protein kinase R-like endoplasmic reticulum kinase (PERK), inositol requiring protein 1a (IRE1a), and activating transcription factor 6 (ATF6) initiate the UPR. The UPR aims to restore ER homeostasis by reducing overall protein synthesis and increasing gene expression of various ER chaperone proteins. If ER stress persists or cannot be resolved cell death pathways are activated. Although, ER stress-induced UPR pathways are known to be important for regulation of skeletal muscle mass and function as well as for inflammation and immune response its function in ICUAW is still elusive. Given recent advances in the development of ER stress modifying molecules for neurodegenerative diseases and cancer, it is important to know whether or not therapeutic interventions in ER stress pathways have favorable effects and these compounds can be used to prevent or treat ICUAW. In this review, we focus on the role of ER stress-induced UPR in skeletal muscle during critical illness and in response to predisposing risk factors such as immobilization, starvation and inflammation as well as ICUAW treatment to foster research for this devastating clinical problem.

Impact of protocol-based physiotherapy on insulin sensitivity and peripheral glucose metabolism in critically ill patients

BACKGROUND

The impact of physiotherapy on insulin sensitivity and peripheral glucose metabolism in critically ill patients is not well understood.

METHODS

This pooled analysis investigates the impact of different physiotherapeutic strategies on insulin sensitivity in critically ill patients. We pooled data from two previous trials in adult patients with sequential organ failure assessment score (SOFA)≥ 9 within 72 h of intensive care unit (ICU) admission, who received hyperinsulinaemic euglycaemic (HE) clamps. Patients were divided into three groups: standard physiotherapy (sPT, n = 22), protocol-based physiotherapy (pPT, n = 8), and pPT with added muscle activating measures (pPT+, n = 20). Insulin sensitivity index (ISI) was determined by HE clamp. Muscle metabolites lactate, pyruvate, and glycerol were measured in the M. vastus lateralis via microdialysis during the HE clamp. Histochemical visualization of glucose transporter-4 (GLUT4) translocation was performed in surgically extracted muscle biopsies. All data are reported as median (25th/75th percentile) (trial registry: ISRCTN77569430 and ISRCTN19392591/ethics approval: Charité-EA2/061/06 and Charité-EA2/041/10).

RESULTS

Fifty critically ill patients (admission SOFA 13) showed markedly decreased ISIs on Day 17 (interquartile range) 0.029 (0.022/0.048) (mg/min/kg)/(mU/L) compared with healthy controls 0.103 (0.087/0.111), P < 0.001. ISI correlated with muscle strength measured by medical research council (MRC) score at first awakening (r = 0.383, P = 0.026) and at ICU discharge (r = 0.503, P = 0.002). Different physiotherapeutic strategies showed no effect on the ISI [sPT 0.029 (0.019/0.053) (mg/min/kg)/(mU/L) vs. pPT 0.026 (0.023/0.041) (mg/min/kg)/(mU/L) vs. pPT+ 0.029 (0.023/0.042) (mg/min/kg)/(mU/L); P = 0.919]. Regardless of the physiotherapeutic strategy metabolic flexibility was reduced. Relative change of lactate/pyruvate ratio during HE clamp is as follows: sPT 0.09 (-0.13/0.27) vs. pPT 0.07 (-0.16/0.31) vs. pPT+ -0.06 (-0.19/0.16), P = 0.729, and relative change of glycerol concentration: sPT -0.39 (-0.8/-0.12) vs. pPT -0.21 (-0.33/0.07) vs. pPT+ -0.21 (-0.44/-0.03), P = 0.257. The majority of ICU patients showed abnormal localization of GLUT4 with membranous GLUT4 distribution in 37.5% (3 of 8) of ICU patients receiving sPT, in 42.9% (3 of 7) of ICU patients receiving pPT, and in 53.8% (7 of 13) of ICU patients receiving pPT+ (no statistical testing possible).

CONCLUSIONS

Our data suggest that a higher duration of muscle activating measures had no impact on insulin sensitivity or metabolic flexibility in critically ill patients with sepsis-related multiple organ failure.

Critical Illness Myopathy: Diagnostic Approach and Resulting Therapeutic Implications

Purpose of review

Critical illness myopathy (CIM) is a common neuro-muscular complication of intensive care treatment associated with increased morbidity and mortality. The current guidelines for diagnosis include clinical and electrophysiological criteria as well as a muscle biopsy, and allow diagnosis only at an advanced stage of the disease. To date, there is no treatment for CIM available, apart from symptomatic and rehabilitative interventions. In this review, we discuss different diagnostic approaches and describe new treatment possibilities for CIM.

Recent findings

Of the diagnostic approaches evaluated, a new electrophysiological technique for measuring muscle excitability has the greatest potential to allow earlier diagnosis of CIM than the current guidelines do and thereby may facilitate the conduction of future pathophysiological and therapeutic studies. Although clinical trials are still lacking, in animal models, BGP-15, vamorolone, and ruxolitinib have been shown to have anti-inflammatory effects, to reduce muscle wasting and to improve muscle function and survival.

Summary

In recent years, promising methods for early and confirmatory diagnosis of CIM have been developed, but still need validation. Experimental studies on novel pharmacological interventions show promising results in terms of preventive CIM treatments, but future clinical studies will be needed to study the effectiveness and safety of these drugs.

Sex-Specific Aspects of Skeletal Muscle Metabolism in the Clinical Context of Intensive Care Unit-Acquired Weakness

(1) Background: Female sex is considered a risk factor for Intensive Care Unit-Acquired Weakness (ICUAW). The aim is to investigate sex-specific aspects of skeletal muscle metabolism in the context of ICUAW. (2) Methods: This is a sex-specific sub-analysis from two prospectively conducted trials examining skeletal muscle metabolism and advanced muscle activating measures in critical illness. Muscle strength was assessed by Medical Research Council Score. The insulin sensitivity index was analyzed by hyperinsulinemic-euglycemic (HE) clamp. Muscular metabolites were studied by microdialysis. M. vastus lateralis biopsies were taken. The molecular analysis included protein degradation pathways. Morphology was assessed by myocyte cross-sectional area (MCSA). Multivariable linear regression models for the effect of sex on outcome parameters were performed. (3) Results: n = 83 (♂n = 57, 68.7%; ♀n = 26, 31.3%) ICU patients were included. ICUAW was present in 81.1%♂ and in 82.4%♀ at first awakening (p = 0.911) and in 59.5%♂ and in 70.6%♀ at ICU discharge (p = 0.432). Insulin sensitivity index was reduced more in women than in men (p = 0.026). Sex was significantly associated with insulin sensitivity index and MCSA of Type IIa fibers in the adjusted regression models. (4) Conclusion: This hypothesis-generating analysis suggests that more pronounced impairments in insulin sensitivity and lower MCSA of Type IIa fibers in critically ill women may be relevant for sex differences in ICUAW.

Skeletal muscle alterations in patients with acute Covid-19 and post-acute sequelae of Covid-19

Skeletal muscle-related symptoms are common in both acute coronavirus disease (Covid)-19 and post-acute sequelae of Covid-19 (PASC). In this narrative review, we discuss cellular and molecular pathways that are affected and consider these in regard to skeletal muscle involvement in other conditions, such as acute respiratory distress syndrome, critical illness myopathy, and post-viral fatigue syndrome. Patients with severe Covid-19 and PASC suffer from skeletal muscle weakness and exercise intolerance. Histological sections present muscle fibre atrophy, metabolic alterations, and immune cell infiltration. Contributing factors to weakness and fatigue in patients with severe Covid-19 include systemic inflammation, disuse, hypoxaemia, and malnutrition. These factors also contribute to post-intensive care unit (ICU) syndrome and ICU-acquired weakness and likely explain a substantial part of Covid-19-acquired weakness. The skeletal muscle weakness and exercise intolerance associated with PASC are more obscure. Direct severe acute respiratory syndrome coronavirus (SARS-CoV)-2 viral infiltration into skeletal muscle or an aberrant immune system likely contribute. Similarities between skeletal muscle alterations in PASC and chronic fatigue syndrome deserve further study. Both SARS-CoV-2-specific factors and generic consequences of acute disease likely underlie the observed skeletal muscle alterations in both acute Covid-19 and PASC.

Sepsis induces interleukin 6, gp130/JAK2/STAT3, and muscle wasting

BACKGROUND

Sepsis and inflammation can cause intensive care unit-acquired weakness (ICUAW). Increased interleukin-6 (IL-6) plasma levels are a risk factor for ICUAW. IL-6 signalling involves the glycoprotein 130 (gp130) receptor and the JAK/STAT-pathway, but its role in sepsis-induced muscle wasting is uncertain. In a clinical observational study, we found that the IL-6 target gene, SOCS3, was increased in skeletal muscle of ICUAW patients indicative for JAK/STAT-pathway activation. We tested the hypothesis that the IL-6/gp130-pathway mediates ICUAW muscle atrophy.

METHODS

We sequenced RNA (RNAseq) from tibialis anterior (TA) muscle of cecal ligation and puncture-operated (CLP) and sham-operated wildtype (WT) mice. The effects of the IL-6/gp130/JAK2/STAT3-pathway were investigated by analysing the atrophy phenotype, gene expression, and protein contents of C2C12 myotubes. Mice lacking Il6st, encoding gp130, in myocytes (cKO) and WT controls, as well as mice treated with the JAK2 inhibitor AG490 or vehicle were exposed to CLP or sham surgery for 24 or 96 h.

RESULTS

Analyses of differentially expressed genes in RNAseq (≥2-log2-fold change, P < 0.01) revealed an activation of IL-6-signalling and JAK/STAT-signalling pathways in muscle of septic mice, which occurred after 24 h and lasted at least for 96 h during sepsis. IL-6 treatment of C2C12 myotubes induced STAT3 phosphorylation (three-fold, P < 0.01) and Socs3 mRNA expression (3.1-fold, P < 0.01) and caused myotube atrophy. Knockdown of Il6st diminished IL-6-induced STAT3 phosphorylation (-30.0%; P < 0.01), Socs3 mRNA expression, and myotube atrophy. JAK2 (- 29.0%; P < 0.01) or STAT3 inhibition (-38.7%; P < 0.05) decreased IL-6-induced Socs3 mRNA expression. Treatment with either inhibitor attenuated myotube atrophy in response to IL-6. CLP-operated septic mice showed an increased STAT3 phosphorylation and Socs3 mRNA expression in TA muscle, which was reduced in septic Il6st-cKO mice by 67.8% (P < 0.05) and 85.6% (P < 0.001), respectively. CLP caused a loss of TA muscle weight, which was attenuated in Il6st-cKO mice (WT: -22.3%, P < 0.001, cKO: -13.5%, P < 0.001; WT vs. cKO P < 0.001). While loss of Il6st resulted in a reduction of MuRF1 protein contents, Atrogin-1 remained unchanged between septic WT and cKO mice. mRNA expression of Trim63/MuRF1 and Fbxo32/Atrogin-1 were unaltered between CLP-treated WT and cKO mice. AG490 treatment reduced STAT3 phosphorylation (-22.2%, P < 0.05) and attenuated TA muscle atrophy in septic mice (29.6% relative reduction of muscle weight loss, P < 0.05). The reduction in muscle atrophy was accompanied by a reduction in Fbxo32/Atrogin-1-mRNA (-81.3%, P < 0.05) and Trim63/MuRF1-mRNA expression (-77.6%, P < 0.05) and protein content.

CONCLUSIONS

IL-6 via the gp130/JAK2/STAT3-pathway mediates sepsis-induced muscle atrophy possibly contributing to ICUAW.

Novel protocol combining physical and nutrition therapies, Intensive Goal-directed REhabilitation with Electrical muscle stimulation and Nutrition (IGREEN) care bundle

Background

Although the combination of rehabilitation and nutrition may be important for the prevention of intensive care unit (ICU)-acquired weakness, a protocolized intervention of this combination has not yet been reported. We herein developed an original combined protocol and evaluated its efficacy.

Methods

In this single-center historical control study, we enrolled adult patients admitted to the ICU. Patients in the control group received standard care, while those in the intervention group received the protocol-based intervention. The ICU mobility scale was used to set goals for early mobilization and a neuromuscular electrical stimulation was employed when patients were unable to stand. The nutritional status was assessed for nutritional therapy, and target calorie delivery was set at 20 or 30 kcal/kg/day and target protein delivery at 1.8 g/kg/day in the intervention group. The primary endpoint was a decrease in femoral muscle volume in 10 days assessed by computed tomography.

Results

Forty-five patients in the control group and 56 in the intervention group were included in the analysis. Femoral muscle volume loss was significantly lower in the intervention group (11.6 vs 14.5%, p = 0.03). The absolute risk difference was 2.9% (95% CI 0.1–5.6%). Early mobilization to a sitting position by day 10 was achieved earlier (p = 0.03), and mean calorie delivery (20.1 vs. 16.8 kcal/kg/day, p = 0.01) and mean protein delivery (1.4 vs. 0.8 g/kg/day, p < 0.01) were higher in the intervention group.

Conclusion

The protocolized intervention, combining early mobilization and high-protein nutrition, contributed to the achievement of treatment goals and prevention of femoral muscle volume loss.

Trial registration number

The present study is registered at the University Hospital Medical Information Network-clinical trials registry (UMIN000040290, Registration date: May 7, 2020).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03827-8.

Inhibition of the NLRP3/IL-1β axis protects against sepsis-induced cardiomyopathy

BACKGROUND

Septic cardiomyopathy worsens the prognosis of critically ill patients. Clinical data suggest that interleukin-1β (IL-1β), activated by the NLRP3 inflammasome, compromises cardiac function. Whether or not deleting Nlrp3 would prevent cardiac atrophy and improve diastolic cardiac function in sepsis was unclear. Here, we investigated the role of NLRP3/IL-1β in sepsis-induced cardiomyopathy and cardiac atrophy.

METHODS

Male Nlrp3 knockout (KO) and wild-type (WT) mice were exposed to polymicrobial sepsis by caecal ligation and puncture (CLP) surgery (KO, n = 27; WT, n = 33) to induce septic cardiomyopathy. Sham-treated mice served as controls (KO, n = 11; WT, n = 16). Heart weights and morphology, echocardiography and analyses of gene and protein expression were used to evaluate septic cardiomyopathy and cardiac atrophy. IL-1β effects on primary and immortalized cardiomyocytes were investigated by morphological and molecular analyses. IonOptix and real-time deformability cytometry (RT-DC) analysis were used to investigate functional and mechanical effects of IL-1β on cardiomyocytes.

RESULTS

Heart morphology and echocardiography revealed preserved systolic (stroke volume: WT sham vs. WT CLP: 33.1 ± 7.2 μL vs. 24.6 ± 8.7 μL, P < 0.05; KO sham vs. KO CLP: 28.3 ± 8.1 μL vs. 29.9 ± 9.9 μL, n.s.; P < 0.05 vs. WT CLP) and diastolic (peak E wave velocity: WT sham vs. WT CLP: 750 ± 132 vs. 522 ± 200 mm/s, P < 0.001; KO sham vs. KO CLP: 709 ± 152 vs. 639 ± 165 mm/s, n.s.; P < 0.05 vs. WT CLP) cardiac function and attenuated cardiac (heart weight-tibia length ratio: WT CLP vs. WT sham: -26.6%, P < 0.05; KO CLP vs. KO sham: -3.3%, n.s.; P < 0.05 vs. WT CLP) and cardiomyocyte atrophy in KO mice during sepsis. IonOptix measurements showed that IL-1β decreased contractility (cell shortening: IL-1β: -15.4 ± 2.3%, P < 0.001 vs. vehicle, IL-1RA: -6.1 ± 3.3%, P < 0.05 vs. IL-1β) and relaxation of adult rat ventricular cardiomyocytes (time-to-50% relengthening: IL-1β: 2071 ± 225 ms, P < 0.001 vs. vehicle, IL-1RA: 564 ± 247 ms, P < 0.001 vs. IL-1β), which was attenuated by an IL-1 receptor antagonist (IL-1RA). RT-DC analysis indicated that IL-1β reduced cardiomyocyte size (P < 0.001) and deformation (P < 0.05). RNA sequencing showed that genes involved in NF-κB signalling, autophagy and lysosomal protein degradation were enriched in hearts of septic WT but not in septic KO mice. Western blotting and qPCR disclosed that IL-1β activated NF-κB and its target genes, caused atrophy and decreased myosin protein in myocytes, which was accompanied by an increased autophagy gene expression. These effects were attenuated by IL-1RA.

CONCLUSIONS

IL-1β causes atrophy, impairs contractility and relaxation and decreases deformation of cardiomyocytes. Because NLRP3/IL-1β pathway inhibition attenuates cardiac atrophy and cardiomyopathy in sepsis, it could be useful to prevent septic cardiomyopathy.

Walking down Skeletal Muscle Lane: From Inflammasome to Disease

Over the last decade, innate immune system receptors and sensors called inflammasomes have been identified to play key pathological roles in the development and progression of numerous diseases. Among them, the nucleotide-binding oligomerization domain (NOD-), leucine-rich repeat (LRR-) and pyrin domain-containing protein 3 (NLRP3) inflammasome is probably the best characterized. To date, NLRP3 has been extensively studied in the heart, where its effects and actions have been broadly documented in numerous cardiovascular diseases. However, little is still known about NLRP3 implications in muscle disorders affecting non-cardiac muscles. In this review, we summarize and present the current knowledge regarding the function of NLRP3 in diseased skeletal muscle, and discuss the potential therapeutic options targeting the NLRP3 inflammasome in muscle disorders.

Out of Control: The Role of the Ubiquitin Proteasome System in Skeletal Muscle during Inflammation

The majority of critically ill intensive care unit (ICU) patients with severe sepsis develop ICU-acquired weakness (ICUAW) characterized by loss of muscle mass, reduction in myofiber size and decreased muscle strength leading to persisting physical impairment. This phenotype results from a dysregulated protein homeostasis with increased protein degradation and decreased protein synthesis, eventually causing a decrease in muscle structural proteins. The ubiquitin proteasome system (UPS) is the predominant protein-degrading system in muscle that is activated during diverse muscle atrophy conditions, e.g., inflammation. The specificity of UPS-mediated protein degradation is assured by E3 ubiquitin ligases, such as atrogin-1 and MuRF1, which target structural and contractile proteins, proteins involved in energy metabolism and transcription factors for UPS-dependent degradation. Although the regulation of activity and function of E3 ubiquitin ligases in inflammation-induced muscle atrophy is well perceived, the contribution of the proteasome to muscle atrophy during inflammation is still elusive. During inflammation, a shift from standard- to immunoproteasome was described; however, to which extent this contributes to muscle wasting and whether this changes targeting of specific muscular proteins is not well described. This review summarizes the function of the main proinflammatory cytokines and acute phase response proteins and their signaling pathways in inflammation-induced muscle atrophy with a focus on UPS-mediated protein degradation in muscle during sepsis. The regulation and target-specificity of the main E3 ubiquitin ligases in muscle atrophy and their mode of action on myofibrillar proteins will be reported. The function of the standard- and immunoproteasome in inflammation-induced muscle atrophy will be described and the effects of proteasome-inhibitors as treatment strategies will be discussed.

The impact of hindlimb disuse on sepsis-induced myopathy in mice

Sepsis induces a myopathy characterized by loss of muscle mass and weakness. Septic patients undergo prolonged periods of limb muscle disuse due to bed rest. The contribution of limb muscle disuse to the myopathy phenotype remains poorly described. To characterize sepsis-induced myopathy with hindlimb disuse, we combined the classic sepsis model via cecal ligation and puncture (CLP) with the disuse model of hindlimb suspension (HLS) in mice. Male C57bl/6j mice underwent CLP or SHAM surgeries. Four days after surgeries, mice underwent HLS or normal ambulation (NA) for 7 days. Soleus (SOL) and extensor digitorum longus (EDL) were dissected for in vitro muscle mechanics, morphological, and histological assessments. In SOL muscles, both CLP+NA and SHAM+HLS conditions elicited ~20% reduction in specific force (p < 0.05). When combined, CLP+HLS elicited ~35% decrease in specific force (p < 0.05). Loss of maximal specific force (~8%) was evident in EDL muscles only in CLP+HLS mice (p < 0.05). CLP+HLS reduced muscle fiber cross-sectional area (CSA) and mass in SOL (p < 0.05). In EDL muscles, CLP+HLS decreased absolute mass to a smaller extent (p < 0.05) with no changes in CSA. Immunohistochemistry revealed substantial myeloid cell infiltration (CD68+) in SOL, but not in EDL muscles, of CLP+HLS mice (p < 0.05). Combining CLP with HLS is a feasible model to study sepsis-induced myopathy in mice. Hindlimb disuse combined with sepsis induced muscle dysfunction and immune cell infiltration in a muscle dependent manner. These findings highlight the importance of rehabilitative interventions in septic hosts to prevent muscle disuse and help attenuate the myopathy.

Could Exogenous Insulin Ameliorate the Metabolic Dysfunction Induced by Glucocorticoids and COVID-19?

The finding that high-dose dexamethasone improves survival in those requiring critical care due to COVID-19 will mean much greater usage of glucocorticoids in the subsequent waves of coronavirus infection. Furthermore, the consistent finding of adverse outcomes from COVID-19 in individuals with obesity, hypertension and diabetes has focussed attention on the metabolic dysfunction that may arise with critical illness. The SARS coronavirus itself may promote relative insulin deficiency, ketogenesis and hyperglycaemia in susceptible individuals. In conjunction with prolonged critical care, these components will promote a catabolic state. Insulin infusion is the mainstay of therapy for treatment of hyperglycaemia in acute illness but what is the effect of insulin on the admixture of glucocorticoids and COVID-19? This article reviews the evidence for the effect of insulin on clinical outcomes and intermediary metabolism in critical illness.

Impact of prolonged sepsis on neural and muscular components of muscle contractions in a mouse model

BACKGROUND

Prolonged critically ill patients frequently develop debilitating muscle weakness that can affect both peripheral nerves and skeletal muscle. In-depth knowledge on the temporal contribution of neural and muscular components to muscle weakness is currently incomplete.

METHODS

We used a fluid-resuscitated, antibiotic-treated, parenterally fed murine model of prolonged (5 days) sepsis-induced muscle weakness (caecal ligation and puncture; n = 148). Electromyography (EMG) measurements were performed in two nerve-muscle complexes, combined with histological analysis of neuromuscular junction denervation, axonal degeneration, and demyelination. In situ muscle force measurements distinguished neural from muscular contribution to reduced muscle force generation. In myofibres, imaging and biomechanics were combined to evaluate myofibrillar contractile calcium sensitivity, sarcomere organization, and fibre structural properties. Myosin and actin protein content and titin gene expression were measured on the whole muscle.

RESULTS

Five days of sepsis resulted in increased EMG latency (P = 0.006) and decreased EMG amplitude (P < 0.0001) in the dorsal caudal tail nerve-tail complex, whereas only EMG amplitude was affected in the sciatic nerve-gastrocnemius muscle complex (P < 0.0001). Myelin sheath abnormalities (P = 0.2), axonal degeneration (number of axons; P = 0.4), and neuromuscular junction denervation (P = 0.09) were largely absent in response to sepsis, but signs of axonal swelling [higher axon area (P < 0.0001) and g-ratio (P = 0.03)] were observed. A reduction in maximal muscle force was present after indirect nerve stimulation (P = 0.007) and after direct muscle stimulation (P = 0.03). The degree of force reduction was similar with both stimulations (P = 0.2), identifying skeletal muscle, but not peripheral nerves, as the main contributor to muscle weakness. Myofibrillar calcium sensitivity of the contractile apparatus was unaffected by sepsis (P ≥ 0.6), whereas septic myofibres displayed disorganized sarcomeres (P < 0.0001) and altered myofibre axial elasticity (P < 0.0001). Septic myofibres suffered from increased rupturing in a passive stretching protocol (25% more than control myofibres; P = 0.04), which was associated with impaired myofibre active force generation (P = 0.04), linking altered myofibre integrity to function. Sepsis also caused a reduction in muscle titin gene expression (P = 0.04) and myosin and actin protein content (P = 0.05), but not the myosin-to-actin ratio (P = 0.7).

CONCLUSIONS

Prolonged sepsis-induced muscle weakness may predominantly be related to a disruption in myofibrillar cytoarchitectural structure, rather than to neural abnormalities.

Activation of Tripartite Motif Containing 63 Expression by Transcription Factor EB and Transcription Factor Binding to Immunoglobulin Heavy Chain Enhancer 3 Is Regulated by Protein Kinase D and Class IIa Histone Deacetylases

Rationale

The ubiquitin–proteasome system (UPS) is responsible for skeletal muscle atrophy. We showed earlier that the transcription factor EB (TFEB) plays a role by increasing E3 ubiquitin ligase muscle really interesting new gene-finger 1(MuRF1)/tripartite motif-containing 63 (TRIM63) expression. MuRF 1 ubiquitinates structural proteins and mediates their UPS-dependent degradation. We now investigated how TFEB-mediated TRIM63 expression is regulated.

Objective

Because protein kinase D1 (PKD1), histone deacetylase 5 (HDAC5), and TFEB belong to respective families with close structural, regulatory, and functional properties, we hypothesized that these families comprise a network regulating TRIM63 expression.

Methods and Results

We found that TFEB and transcription factor for immunoglobulin heavy-chain enhancer 3 (TFE3) activate TRIM63 expression. The class IIa HDACs HDAC4, HDAC5, and HDAC7 inhibited this activity. Furthermore, we could map the HDAC5 and TFE3 physical interaction. PKD1, PKD2, and PKD3 reversed the inhibitory effect of all tested class IIa HDACs toward TFEB and TFE3. PKD1 mediated nuclear export of all HDACs and lifted TFEB and TFE3 repression. We also mapped the PKD2 and HDAC5 interaction. We found that the inhibitory effect of PKD1 and PKD2 toward HDAC4, HDAC5, and HDAC7 was mediated by their phosphorylation and 14-3-3 mediated nuclear export.

Conclusion

TFEB and TFE3 activate TRIM63 expression. Both transcription factors are controlled by HDAC4, HDAC5, HDAC7, and all PKD-family members. We propose that the multilevel PKD/HDAC/TFEB/TFE3 network tightly controls TRIM63 expression.

Critical illness myopathy precedes hyperglycaemia and high glucose variability

BACKGROUND

Critical Illness Myopathy (CIM) is a serious ICU complication, and dysglycaemia is widely regarded as a risk factor. Although glucose variability (GV) has been independently linked to ICU mortality, an association with CIM has not been investigated. This study examines the relationship between CIM and GV.

METHODS

Retrospective investigation including ICU patients with SOFA ≥8, mechanical ventilation, and CIM diagnostics. Glucose readings were collected every 6 h throughout the first week of treatment, when CIM is thought to develop. GV was measured using standard deviation (SD), coefficient of variability (CV), mean absolute glucose (MAG), mean amplitude of glycaemic excursions (MAGE), and mean of daily difference (MODD).

RESULTS

74 patients were included, and 50 (67.6%) developed CIM. Time on glycaemic target (70-179 mg/dL), caloric and insulin intakes, mean, maximum and minimum blood glucose values were similar for all patients until the 5th day, after which CIM patients exhibited higher mean and maximum glucose levels. Significantly higher GV in CIM patients were observed on day 5 (SD, CV, MAG, MAGE), day 6 (MODD), and day 7 (SD, CV, MAG).

CONCLUSIONS

CIM patients developed transient increases in GV and hyperglycaemia only late in the first week, suggesting that myopathy precedes dysglycaemia.

Acute skeletal muscle wasting and dysfunction predict physical disability at hospital discharge in patients with critical illness

BACKGROUND

Patients surviving critical illness develop muscle weakness and impairments in physical function; however, the relationship between early skeletal muscle alterations and physical function at hospital discharge remains unclear. The primary purpose of this study was to determine whether changes in muscle size, strength and power assessed in the intensive care unit (ICU) predict physical function at hospital discharge.

METHODS

Study design is a single-center, prospective, observational study in patients admitted to the medicine or cardiothoracic ICU with diagnosis of sepsis or acute respiratory failure. Rectus femoris (RF) and tibialis anterior (TA) muscle ultrasound images were obtained day one of ICU admission, repeated serially and assessed for muscle cross-sectional area (CSA), layer thickness (mT) and echointensity (EI). Muscle strength, as measured by Medical Research Council-sum score, and muscle power (lower-extremity leg press) were assessed prior to ICU discharge. Physical function was assessed with performance on 5-times sit-to-stand (5STS) at hospital discharge.

RESULTS

Forty-one patients with median age of 61 years (IQR 55-68), 56% male and sequential organ failure assessment score of 8.1 ± 4.8 were enrolled. RF muscle CSA decreased significantly a median percent change of 18.5% from day 1 to 7 (F = 26.6, p = 0.0253). RF EI increased at a mean percent change of 10.5 ± 21% in the first 7 days (F = 3.28, p = 0.081). At hospital discharge 25.7% of patients (9/35) met criteria for ICU-acquired weakness. Change in RF EI in first 7 days of ICU admission and muscle power measured prior to ICU were strong predictors of ICU-AW at hospital discharge (AUC = 0.912). Muscle power at ICU discharge, age and ICU length of stay were predictive of performance on 5STS at hospital discharge.

CONCLUSION

ICU-assessed muscle alterations, specifically RF EI and muscle power, are predictors of diagnosis of ICU-AW and physical function assessed by 5x-STS at hospital discharge in patients surviving critical illness.

Intensive Care Unit-Acquired Weakness: Not just Another Muscle Atrophying Condition

Intensive care unit-acquired weakness (ICUAW) occurs in critically ill patients stemming from the critical illness itself, and results in sustained disability long after the ICU stay. Weakness can be attributed to muscle wasting, impaired contractility, neuropathy, and major pathways associated with muscle protein degradation such as the ubiquitin proteasome system and dysregulated autophagy. Furthermore, it is characterized by the preferential loss of myosin, a distinct feature of the condition. While many risk factors for ICUAW have been identified, effective interventions to offset these changes remain elusive. In addition, our understanding of the mechanisms underlying the long-term, sustained weakness observed in a subset of patients after discharge is minimal. Herein, we discuss the various proposed pathways involved in the pathophysiology of ICUAW, with a focus on the mechanisms underpinning skeletal muscle wasting and impaired contractility, and the animal models used to study them. Furthermore, we will explore the contributions of inflammation, steroid use, and paralysis to the development of ICUAW and how it pertains to those with the corona virus disease of 2019 (COVID-19). We then elaborate on interventions tested as a means to offset these decrements in muscle function that occur as a result of critical illness, and we propose new strategies to explore the molecular mechanisms of ICUAW, including serum-related biomarkers and 3D human skeletal muscle culture models.

Approach to critical illness myopathy and polyneuropathy in the older SARS-CoV-2 patients

One of the major concerns of the health care community and the public surrounding the SARS-CoV-2 pandemic is the availability and use of ventilators. Unprecedented surges of patients presented to intensive care units across the country, with older adults making up a large proportion of the patient population. This paper illustrates contemporary approaches to critical illness myopathy (CIM), critical illness polyneuropathy (CIP), and critical illness polyneuromyopathy (CIPNM) in older patients, including incidence, risk factors, mechanisms for pathology, diagnosis, contemporary treatment approaches, and outcomes. We hope that the following analysis may help educate clinicians and ultimately decrease the duration of the mechanical ventilation required by these patients, resulting in improved clinical outcomes and an increase in ventilator availability for other patients in need.

Hydrocortisone mitigates ICU-AW by fine-tuning of muscle atrophic and hypertrophic signaling pathways in a sepsis model with limb immobilization

AIMS

Intensive care unit-acquired weakness (ICU-AW) is a complex spectrum of disability that delays recovery of critically ill-immobilized patients with sepsis. Much discrepancy remain on the use of corticosteroids and their impact on muscle regeneration in critical illness management. Therefore, the aim of this study is to investigate whether hydrocortisone (HCT) modulates muscle mass turnover in ICU-AW induced by sepsis with limb immobilization (SI).

MAIN METHODS

Sepsis by cecal ligation puncture (CLP) with forelimb-immobilization were performed in rats. The study consisted of four groups: Sham (left forelimb-immobilization), Sham HCT (left forelimb-immobilization + HCT), SI (CLP + left forelimb-immobilization) and SI HCT (CLP + left forelimb-immobilization + HCT). Motor force, blood and muscle sampling were assessed.

KEY FINDINGS

HCT prevented body weight loss associated with SI and attenuated systemic and muscular inflammation. Besides, myosin was restituted in SI HCT group in conjunction to muscle mass and strength restoration. Pro-hypertrophic calcineurin (PP2B-Aβ) and nuclear factor of activated T-cells C3 (NFATc3) but not protein kinase B (Akt) were re-activated by HCT. Finally, pro-atrophic extracellular signal-regulated kinases (ERK1/2) and p38 mitogen-activated protein kinases (p38) but not nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) were inhibited in SI HCT group.

SIGNIFICANCE

This study unravels new molecular events thought to control muscle protein synthesis in ICU-AW induced by sepsis and limb immobilization. HCT has a potential to fine-tune muscle-signaling pathways and to reduce the negative outcomes of ICU-AW.

Perioperatively Acquired Weakness

BACKGROUND

Skeletal muscle failure in critical illness (intensive care unit-acquired weakness) is a well-known complication developing early during intensive care unit stay. However, muscle weakness during the perioperative setting has not yet been investigated.

METHODS

We performed a subgroup investigation of a prospective observational trial to investigate perioperative muscle weakness. Eighty-nine patients aged 65 years or older were assessed for handgrip strength preoperatively, on the first postoperative day, at intensive care unit discharge, at hospital discharge, and at 3-month follow-up. Functional status was evaluated perioperatively via Barthel index, instrumental activities of daily living, Timed Up and Go test, and functional independence measure. After exclusion of patients with intensive care unit-acquired weakness or intensive care unit stay of ≥72 hours, 59 patients were included into our analyses. Of these, 14 patients had additional pulmonary function tests preoperatively and on postoperative day 1. Blood glucose was measured intraoperatively every 20 minutes.

RESULTS

Handgrip strength significantly decreased after surgery on postoperative day 1 by 16.4% (P < .001). Postoperative pulmonary function significantly decreased by 13.1% for vital capacity (P = .022) and 12.6% for forced expiratory volume in 1 second (P = .001) on postoperative day 1. Handgrip strength remained significantly reduced at hospital discharge (P = .016) and at the 3-month follow-up (P = .012). Perioperative glucose levels showed no statistically significant impact on muscle weakness. Instrumental activities of daily living (P < .001) and functional independence measure (P < .001) were decreased at hospital discharge, while instrumental activities of daily living remained decreased at the 3-month follow-up (P = .026) compared to preoperative assessments.

CONCLUSIONS

Perioperatively acquired weakness occurred, indicated by a postoperatively decreased handgrip strength, decreased respiratory muscle function, and impaired functional status, which partly remained up to 3 months.

Sepsis therapies: learning from 30 years of failure of translational research to propose new leads

Sepsis has been identified by the World Health Organization (WHO) as a global health priority. There has been a tremendous effort to decipher underlying mechanisms responsible for organ failure and death, and to develop new treatments. Despite saving thousands of animals over the last three decades in multiple preclinical studies, no new effective drug has emerged that has clearly improved patient outcomes. In the present review, we analyze the reasons for this failure, focusing on the inclusion of inappropriate patients and the use of irrelevant animal models. We advocate against repeating the same mistakes and propose changes to the research paradigm. We discuss the long-term consequences of surviving sepsis and, finally, list some putative approaches-both old and new-that could help save lives and improve survivorship.

Serum amyloid A1 mediates myotube atrophy via Toll-like receptors

BACKGROUND

Critically ill patients frequently develop muscle atrophy and weakness in the intensive-care-unit setting [intensive care unit-acquired weakness (ICUAW)]. Sepsis, systemic inflammation, and acute-phase response are major risk factors. We reported earlier that the acute-phase protein serum amyloid A1 (SAA1) is increased and accumulates in muscle of ICUAW patients, but its relevance was unknown. Our objectives were to identify SAA1 receptors and their downstream signalling pathways in myocytes and skeletal muscle and to investigate the role of SAA1 in inflammation-induced muscle atrophy.

METHODS

We performed cell-based in vitro and animal in vivo experiments. The atrophic effect of SAA1 on differentiated C2C12 myotubes was investigated by analysing gene expression, protein content, and the atrophy phenotype. We used the cecal ligation and puncture model to induce polymicrobial sepsis in wild type mice, which were treated with the IкB kinase inhibitor Bristol-Myers Squibb (BMS)-345541 or vehicle. Morphological and molecular analyses were used to investigate the phenotype of inflammation-induced muscle atrophy and the effects of BMS-345541 treatment.

RESULTS

The SAA1 receptors Tlr2, Tlr4, Cd36, P2rx7, Vimp, and Scarb1 were all expressed in myocytes and skeletal muscle. Treatment of differentiated C2C12 myotubes with recombinant SAA1 caused myotube atrophy and increased interleukin 6 (Il6) gene expression. These effects were mediated by Toll-like receptors (TLR) 2 and 4. SAA1 increased the phosphorylation and activity of the transcription factor nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NF-κB) p65 via TLR2 and TLR4 leading to an increased binding of NF-κB to NF-κB response elements in the promoter region of its target genes resulting in an increased expression of NF-κB target genes. In polymicrobial sepsis, skeletal muscle mass, tissue morphology, gene expression, and protein content were associated with the atrophy response. Inhibition of NF-κB signalling by BMS-345541 increased survival (28.6% vs. 91.7%, P < 0.01). BMS-345541 diminished inflammation-induced atrophy as shown by a reduced weight loss of the gastrocnemius/plantaris (vehicle: -21.2% and BMS-345541: -10.4%; P < 0.05), tibialis anterior (vehicle: -22.7% and BMS-345541: -17.1%; P < 0.05) and soleus (vehicle: -21.1% and BMS-345541: -11.3%; P < 0.05) in septic mice. Analysis of the fiber type specific myocyte cross-sectional area showed that BMS-345541 reduced inflammation-induced atrophy of slow/type I and fast/type II myofibers compared with vehicle-treated septic mice. BMS-345541 reversed the inflammation-induced atrophy program as indicated by a reduced expression of the atrogenes Trim63/MuRF1, Fbxo32/Atrogin1, and Fbxo30/MuSA1.

CONCLUSIONS

SAA1 activates the TLR2/TLR4//NF-κB p65 signalling pathway to cause myocyte atrophy. Systemic inhibition of the NF-κB pathway reduced muscle atrophy and increased survival of septic mice. The SAA1/TLR2/TLR4//NF-κB p65 atrophy pathway could have utility in combatting ICUAW.

Muscle degradation, vitamin D and systemic inflammation in hospitalized septic patients

PURPOSE

To date, the relationship between systemic inflammation and muscle changes observed by ultrasonography in septic patients in clinical studies is not known. Furthermore, the role of vitamin D on muscle changes in these patients needs to be investigated.

MATERIALS AND METHODS

Forty-five patients admitted to the ICU due to severe sepsis or septic shock. Blood samples were collected to evaluate systemic inflammation (interleukin (IL)-10, IL-1β, IL-1α, IL-6, IL-8 and tumor necrosis factor-α(TNF-α)) and vitamin D. Muscle mass was evaluated by ultrasound during hospitalization. Clinical tests of muscle strength (Medical Research Council (MRC) scale and handgrip) were performed after the awakening of patients.

RESULTS

There was a reduction in day 2 values to hospital discharge on TNF-alpha, IL-8, IL-6 and IL-10 (p < .05). The muscle mass showed a significant decline from day 6 of the ICU. After awakening, the patients had a significant increase in muscle strength (p < .05). There was a positive association between muscle mass variation (day 2 - ICU) with absolute values of IL-8 (r = 0.38 p = .05). For muscle strength, there was a negative association between handgrip strength with IL-8 (r = -0.36 p < .05) on ICU discharge. The vitamin D showed a positive association with the handgrip strength of the day 1 of the awakening (r = 0.51 p < .05).

CONCLUSIONS

In septic patients, there is an association between inflammation and changes in muscle mass and strength during ICU stay, which is similar to those observed in experimental studies. In addition, there was an association of vitamin D with recovery of muscle strength during hospitalization.

Differential contractile response of critically ill patients to neuromuscular electrical stimulation

Background

Neuromuscular electrical stimulation (NMES) has been investigated as a preventative measure for intensive care unit-acquired weakness. Trial results remain contradictory and therefore inconclusive. As it has been shown that NMES does not necessarily lead to a contractile response, our aim was to characterise the response of critically ill patients to NMES and investigate potential outcome benefits of an adequate contractile response.

Methods

This is a sub-analysis of a randomised controlled trial investigating early muscle activating measures together with protocol-based physiotherapy in patients with a SOFA score ≥ 9 within the first 72 h after admission. Included patients received protocol-based physiotherapy twice daily for 20 min and NMES once daily for 20 min, bilaterally on eight muscle groups. Electrical current was increased up to 70 mA or until a contraction was detected visually or on palpation. Muscle strength was measured by a blinded assessor at the first adequate awakening and ICU discharge.

Results

One thousand eight hundred twenty-four neuromuscular electrical stimulations in 21 patients starting on day 3.0 (2.0/6.0) after ICU admission were included in this sub-analysis. Contractile response decreased from 64.4% on day 1 to 25.0% on day 7 with a significantly lower response rate in the lower extremities and proximal muscle groups. The electrical current required to elicit a contraction did not change over time (day 1, 50.2 [31.3/58.8] mA; day 7, 45.3 [38.0/57.5] mA). The electrical current necessary for a contractile response was higher in the lower extremities. At the first awakening, patients presented with significant weakness (3.2 [2.5/3.8] MRC score). When dividing the cohort into responders and non-responders (> 50% vs. ≤ 50% contractile response), we observed a significantly higher SOFA score in non-responders. The electrical current necessary for a muscle contraction in responders was significantly lower (38.0 [32.8/42.9] vs. 54.7 [51.3/56.0] mA, p < 0.001). Muscle strength showed higher values in the upper extremities of responders at ICU discharge (4.4 [4.1/4.6] vs. 3.3 [2.8/3.8] MRC score, p = 0.036).

Conclusion

Patients show a differential contractile response to NMES, which appears to be dependent on the severity of illness and also relevant for potential outcome benefits.

Trial registration

ISRCTN ISRCTN19392591, registered 17 February 2011

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2540-4) contains supplementary material, which is available to authorized users.