Loss of muscle strength during sepsis is in part regulated by glucocorticoids and is associated with reduced muscle fiber stiffness

Butyrate improves handgrip strength and physical performance by reducing intestinal leak in post-menopausal women, a randomized controlled trial

PURPOSE

Menopause is associated with muscle detriment and physical compromise. However, relevant mechanisms and effective interventions remain elusive. We investigated the therapeutic effects of exogenous butyrate administration on skeletal muscle and physical capacity with relevance to intestinal leak as a potential mechanism in post-menopausal women.

METHODS

We recruited post-menopausal women as placebo (age = 55.4 ± 3.3 years, n = 76) and butyrate (age = 54 ± 2.8 years, n = 70) groups, along with pre-menopausal women (age = 42.3 ± 3 years, n = 75) as controls. The butyrate group received sodium butyrate (570 mg capsules) daily for 12 weeks. We measured plasma biomarkers of intestinal leak (zonulin) and sepsis (lipopolysaccharide-binding protein, LBP) along with handgrip strength (HGS), gait speed, and physical performance (short physical performance battery, SPPB).

RESULTS

Post-menopausal women had higher zonulin and LBP and lower HGS, gait speed, and SPPB scores than pre-menopausal women (all p < 0.05). Butyrate reduced plasma zonulin and LBP levels and improved HGS and SPPB scores in post-menopausal women (all p < 0.05). We found significant correlations of reduction in plasma zonulin and LBP with improvement in HGS and SPPB in the butyrate group (all p < 0.05). Butyrate also modestly improved respiratory muscle strength and reduced systemic inflammation and oxidative stress in post-menopausal women (all p < 0.05).

CONCLUSION

Collectively, our findings demonstrate the muscle-protective effects of butyrate through intestinal mucosal repair. Future research is warranted to elucidate the underlying mechanisms of butyrate in post-menopausal women.

A scoping review of preclinical intensive care unit-acquired weakness models

Background

Animal models focusing on neuromuscular outcomes are crucial for understanding the mechanisms of intensive care unit-acquired weakness (ICU-AW) and exploring potential innovative prevention and treatment strategies.

Aim

To analyse and evaluate preclinical ICU-AW models.

Methods

We manually searched five English and four Chinese databases from 1 January 2002, to 1 February 2024, and reviewed related study references. Full-text publications describing animal models of muscle weakness and atrophy in critical illness were included. Detailed information about model types, animal species, sex, age, induction methods, outcome measures, drawbacks and strengths was extracted from each included study.

Results

A total of 3,451 citations were initially retrieved, with 84 studies included in the final analysis. The most frequently studied animal model included rodents (86.9%), 64.3% of which were male animals. ICU-AW animal models were mostly induced by comprehensive intensive care unit (ICU) interventions (38.1%) and sepsis (51.2%). Most studies focused on limb muscles (66.7%), diaphragm muscles (21.4%) or both (9.5%). Reported outcomes primarily included muscular pathological changes (83.3%), electrophysiological examinations of muscles (57.1%) and animal grip strength (16.6%). However, details such as animal age, mortality data, experimental design, randomisation, blinding, sample size and interventions for the experimental group and/or control group were inadequately reported.

Conclusion

Many preclinical models are used to study ICU-AW, but the reporting of methodological details is often incomplete. Although current ICU animal models can mimic the characteristics of human ICU-AW, there is no standard model. Future preclinical studies should develop a standard ICU-AW animal model to enhance reproducibility and improve scientific rigor in exploring the mechanisms and potential treatment of ICU-AW.

The Association of Intestinal Leak with Sarcopenia and Physical Disability in Patients with Various Stages of Chronic Kidney Disease

Sarcopenia is related to disease severity in chronic kidney disease (CKD) patients; however, its pathophysiology remains poorly known. We investigated the associations of biomarkers of intestinal leak with sarcopenia in various stages of CKD. We recruited 61-76-year-old male controls and patients with various stages of CKD (n = 36-57/group) for measuring plasma lipopolysaccharide-binding protein (LBP) and zonulin (markers of intestinal leak), handgrip strength (HGS), skeletal mass index (SMI), and gait speed (markers of sarcopenia), and short physical performance battery (SPPB; marker of physical capacity). CKD stages 4 and 5 were associated with lower HGS, SMI, gait speed, and cumulative SPPB scores and a higher sarcopenia prevalence than controls and patients with CKD stages 1 and 2 (all p < 0.05). CKD patients (stages 1 and 2) had elevated plasma zonulin and LBP when compared with CKD stages 4 and 5. Plasma zonulin and LBP exhibited significant correlations with renal function, HGS, gait speed, SPPB scores, and oxidative stress markers in CKD stages 4 and 5 (all p < 0.05). However, similar relations were not found in early CKD. Collectively, intestinal leak may be contributing to sarcopenia and physical disability in the advanced stages of CKD.

Is the myonuclear domain ceiling hypothesis dead?

Muscle fibres are multinuclear cells, and the cytoplasmic territory where a single myonucleus controls transcriptional activity is called the myonuclear domain (MND). MND size shows flexibility during muscle hypertrophy. The MND ceiling hypothesis states that hypertrophy results in the expansion of MND size to an upper limit or MND ceiling, beyond which additional myonuclei via activation of satellite cells are required to support further growth. However, the debate about the MND ceiling hypothesis is far from settled, and various studies show conflicting results about the existence or otherwise of MND ceiling in hypertrophy. The aim of this review is to summarise the literature about the MND ceiling in various settings of hypertrophy and discuss the possible factors contributing to a discrepancy in the literature. We conclude by describing the physiological and clinical significance of the MND ceiling limit in the muscle adaptation process in various physiological and pathological conditions.

Redox Balance Differentially Affects Biomechanics in Permeabilized Single Muscle Fibres-Active and Passive Force Assessments with the Myorobot

An oxidizing redox state imposes unique effects on the contractile properties of muscle. Permeabilized fibres show reduced active force generation in the presence of H₂O₂. However, our knowledge about the muscle fibre's elasticity or flexibility is limited due to shortcomings in assessing the passive stress-strain properties, mostly due to technically limited experimental setups. The MyoRobot is an automated biomechatronics platform that is well-capable of not only investigating calcium responsiveness of active contraction but also features precise stretch actuation to examine the passive stress-strain behaviour. Both were carried out in a consecutive recording sequence on the same fibre for 10 single fibres in total. We denote a significantly diminished maximum calcium-saturated force for fibres exposed to ≥500 µM H₂O₂, with no marked alteration of the pCa50 value. In contrast to active contraction (e.g., maximum isometric force activation), passive restoration stress (force per area) significantly increases for fibres exposed to an oxidizing environment, as they showed a non-linear stress-strain relationship. Our data support the idea that a highly oxidizing environment promotes non-linear fibre stiffening and confirms that our MyoRobot platform is a suitable tool for investigating redox-related changes in muscle biomechanics.

Circulating MicroRNAs as Biomarkers of Accelerated Sarcopenia in Chronic Heart Failure

Background:

Sarcopenia is a critical finding in patients with chronic heart failure (CHF). However, the search for a definitive biomarker to predict muscle and functional decline in CHF remains elusive.

Objectives:

We aimed to correlate the circulating levels of selected miRs with the indexes of sarcopenia during healthy aging and in patients with CHF.

Methods:

We analyzed the association of circulating microRNAs (miRs) levels including miR-21, miR-434-3p, miR424-5p, miR-133a, miR-455-3p and miR-181a with sarcopenia indexes in male, 61–73 years old healthy controls and patients with CHF (N = 89–92/group).

Results:

Patients with CHF had lower hand-grip strength (HGS), appendicular skeletal mass index (ASMI) and physical capacity than healthy controls. Circulating miR-21 levels were higher and miR-181a, miR-133a, miR-434-3p and miR-455-3p levels were lower in patients with CHF than healthy controls. Among the sarcopenia indexes, HGS showed the strongest correlation with miR-133a while ASMI showed the strongest correlations with miR-133a, miR-434-3p and miR-455-3p. Among the miRs, miR-434-3p showed the highest area under the curve in testing for sensitivity and specificity for CHF. These changes were associated with higher expressions of the markers of inflammation, oxidative stress and muscle damage in CHF patients.

Conclusion:

Taken together, our data show that circulating miRs can be useful markers of muscle health and physical capacity in the sarcopenic elderly with CHF.

Sarcopenia in pulmonary diseases is associated with elevated sarcoplasmic reticulum stress and myonuclear disorganization

Chronic obstructive pulmonary disease (COPD) is frequently associated with age-related muscle loss or sarcopenia. However, the exact molecular mechanism of muscle loss in COPD remains elusive. We investigated the association of chronic dysregulation of sarcoplasmic reticulum (SR) protein homeostasis (a condition called SR stress) and myonuclear disorganization with sarcopenia in patients with COPD. Markers of SR stress and their downstream consequences, including apoptosis and inflammation, were upregulated in patients with COPD. The maximal SR Ca²⁺ ATPase (SERCA) activity was significantly reduced in advanced COPD as compared to healthy controls. Single muscle fiber diameter and cytoplasmic domain per myonucleus were significantly smaller in patients with advanced COPD than in healthy controls. Increased disruption of myonuclear organization was found in the COPD patients as compared to healthy controls. These changes in SR dysfunction were accompanied by elevated global levels of oxidative stress, including lipid peroxidation and mitochondrial reactive oxygen species (ROS) production. Altogether, our data suggest that muscle weakness in advanced COPD is in part associated with the disruption of SR protein and calcium homeostasis and their pathological consequences.

Prediction of sarcopenia using a battery of circulating biomarkers

Loss of muscle mass and strength with aging, termed sarcopenia is accelerated in several comorbidities including chronic heart failure (CHF) and chronic obstructive pulmonary diseases (COPD). However, the effective circulating biomarkers to accurately diagnose and assess sarcopenia are not known. We recruited male healthy controls and patients with CHF and COPD (n = 81–87/group), aged 55–74 years. Sarcopenia was clinically identified based on hand-grip strength, appendicular skeletal muscle index and physical capacity as recommended by the European working group for sarcopenia. The serum levels of amino-terminal pro-peptide of type-III procollagen, c-terminal agrin fragment-22, osteonectin, irisin, fatty acid-binding protein-3 and macrophage migration inhibitory factor were significantly different between healthy controls and patients with CHF and COPD. Risk scores for individual biomarkers were calculated by logistic regressions and combined into a cumulative risk score. The median cutoff value of 3.86 was used to divide subjects into high- and low-risk groups for sarcopenia with the area under the curve of 0.793 (95% CI = 0.738–0.845, p < 0.001). A significantly higher incidence of clinical sarcopenia was found in high-risk group. Taken together, the battery of biomarkers can be an effective tool in the early diagnosis and assessment of sarcopenia.

Signature molecular changes in the skeletal muscle of hindlimb unloaded mice

Hind-limb unloaded (HU) mouse is a well-recognized model of muscle atrophy; however, the molecular changes in the skeletal muscle during unloading are poorly characterized. We have used Raman spectroscopy to evaluate the structure and behavior of signature molecules involved in regulating muscle structural and functional health. The Raman spectroscopic analysis of gastrocnemius muscles was compared between 16-18 weeks old HU c57Bl/6J mice and ground-based controls. The spectra showed that the signals for asparagine and glutamine were reduced in HU mice, possibly indicating increased catabolism. The peaks for hydroxyproline and proline were split, pointing towards molecular breakdown and reduced tendon repair. We also report a consistently increased intensity in> 1300 cm-1 range in the Raman spectra along with a shift towards higher frequencies in the HU mice, indicating activation of sarcoplasmic reticulum (SR) stress during HU.

A clinically relevant decrease in contractile force differentially regulates control of glucocorticoid receptor translocation in mouse skeletal muscle

Muscle atrophy decreases physical function and overall health. Increased glucocorticoid production and/or use of prescription glucocorticoids can significantly induce muscle atrophy by activating the glucocorticoid receptor, thereby transcribing genes that shift protein balance in favor of net protein degradation. Although mechanical overload can blunt glucocorticoid-induced atrophy in young muscle, those affected by glucocorticoids generally have impaired force generation. It is unknown whether contractile force alters the ability of resistance exercise to mitigate glucocorticoid receptor translocation and induce a desirable shift in protein balance when glucocorticoids are elevated. In the present study, mice were subjected to a single bout of unilateral, electrically induced muscle contractions by stimulating the sciatic nerve at 100 Hz or 50 Hz frequencies to elicit high or moderate force contractions of the tibialis anterior, respectively. Dexamethasone was used to activate the glucocorticoid receptor. Dexamethasone increased glucocorticoid signaling, including nuclear translocation of the receptor, but this was mitigated only by high force contractions. The ability of high force contractions to mitigate glucocorticoid receptor translocation coincided with a contraction-mediated increase in muscle protein synthesis, which did not occur in the dexamethasone-treated mice subjected to moderate force contractions. Though moderate force contractions failed to increase protein synthesis following dexamethasone treatment, both high and moderate force contractions blunted the glucocorticoid-mediated increase in LC3 II:I marker of autophagy. Thus, these data show that force generation is important for the ability of resistance exercise to mitigate glucocorticoid receptor translocation and promote a desirable shift in protein balance when glucocorticoids are elevated.NEW & NOTEWORTHY Glucocorticoids induce significant skeletal muscle atrophy by activating the glucocorticoid receptor. Our work shows that muscle contractile force dictates glucocorticoid receptor nuclear translocation. We also show that blunting nuclear translocation by high force contractions coincides with the ability of muscle to mount an anabolic response characterized by increased muscle protein synthesis. This work further defines the therapeutic parameters of skeletal muscle contractions to blunt glucocorticoid-induced atrophy.

Pneumothorax due to a non-traumatic thoracic wall rupture due to steroid induced muscle wasting

Spontaneous pneumothorax can be classified in primary and secondary variants. We present a 58-year-old patient presented with a 7-week history of severe coughing, chest pain and he noticed progressive swelling of the face and upper part of the body. His medical history revealed osteoporosis and severe rheumatoid arthritis treated with steroids and DMARDs (disease modifying antirheumatic drugs). Computed Tomography (CT) of the thorax revealed complete rupture of the thoracic wall through costa 9-10 with lung herniation. The defect was closed using dual mesh and pneumothorax was treated. Two weeks after surgery subcutaneous emphysema resolved and patient was discharged from hospital.

A Chalcone from Ashitaba (Angelica keiskei) Stimulates Myoblast Differentiation and Inhibits Dexamethasone-Induced Muscle Atrophy

Ashitaba, Angelica keiskei Koidzumi (AK), as a traditional medicine in Korea, Japan, and China, has been known as an elixir of life having therapeutic potential. However, there is no scientific evidence to support that Ashitaba can enhance or maintain muscle strength. To find a new therapeutic agent from the medicinal plant, we evaluated the anti-myopathy effect of chalcones from ethanol extract of AK (EAK) in cellular and animal models of muscle atrophy. To examine anti-myopathy activity, EAK was treated into dexamethasone injected rats and muscle thickness and histopathological images were analyzed. Oral administration of EAK (250 or 500 mg/kg) alleviated muscle atrophic damages and down-regulated the mRNA levels of muscle-specific ubiquitin-E3 ligases. Among ten compounds isolated from EAK, 4-hydroxyderricin was the most effective principle in stimulating myogenesis of C2C12 myoblasts via activation of p38 mitogen-activated protein kinase (MAPK). In three cellular muscle atrophy models with C2C12 myoblasts damaged by dexamethasone or cancer cell-conditioned medium, 4-hydroxyderricin protected the myosin heavy chain (MHC) degradation through suppressing expressions of MAFbx, MuRF-1 and myostatin. These results suggest that the ethanol extract and its active principle, 4-hydroxyderricin from AK, can overcome the muscle atrophy through double mechanisms of decreasing muscle protein degradation and activating myoblast differentiation.

Myofibrillar function differs markedly between denervated and dexamethasone-treated rat skeletal muscles: Role of mechanical load

Although there is good evidence to indicate a major role of intrinsic impairment of the contractile apparatus in muscle weakness seen in several pathophysiological conditions, the factors responsible for control of myofibrillar function are not fully understood. To investigate the role of mechanical load in myofibrillar function, we compared the skinned fiber force between denervated (DEN) and dexamethasone-treated (DEX) rat skeletal muscles with or without neuromuscular electrical stimulation (ES) training. DEN and DEX were induced by cutting the sciatic nerve and daily injection of dexamethasone (5 mg/kg/day) for 7 days, respectively. For ES training, plantarflexor muscles were electrically stimulated to produce four sets of five isometric contractions each day. In situ maximum torque was markedly depressed in the DEN muscles compared to the DEX muscles (-74% vs. -10%), whereas there was not much difference in the degree of atrophy in gastrocnemius muscles between DEN and DEX groups (-24% vs. -17%). Similar results were obtained in the skinned fiber preparation, with a greater reduction in maximum Ca²⁺-activated force in the DEN than in the DEX group (-53% vs. -16%). Moreover, there was a parallel decline in myosin heavy chain (MyHC) and actin content per muscle volume in DEN muscles, but not in DEX muscles, which was associated with upregulation of NADPH oxidase (NOX) 2, neuronal nitric oxide synthase (nNOS), and endothelial NOS expression, translocation of nNOS from the membrane to the cytosol, and augmentation of mRNA levels of muscle RING finger protein 1 (MuRF-1) and atrogin-1. Importantly, mechanical load evoked by ES protects against DEN- and DEX-induced myofibrillar dysfunction and these molecular alterations. Our findings provide novel insights regarding the difference in intrinsic contractile properties between DEN and DEX and suggest an important role of mechanical load in preserving myofibrillar function in skeletal muscle.

Pyropia yezoensis Protein Prevents Dexamethasone-Induced Myotube Atrophy in C2C12 Myotubes

Glucocorticoids (GCs), which are endocrine hormones released under stress conditions, can cause skeletal muscle atrophy. This study investigated whether Pyropia yezoensis crude protein (PYCP) inhibits synthetic GCs dexamethasone (DEX)-induced myotube atrophy associated with proteolytic systems. Mouse skeletal muscle C2C12 myotubes were treated with DEX in the presence or absence of PYCP. DEX exposure (100 μM) for 24 h significantly decreased myotube diameter and myogenin expression, which were all increased by treatment with 20 and 40 μg/mL PYCP. Additionally, PYCP significantly reduced the nuclear expression of the forkhead box transcription factors, FoxO1 and FoxO3a, and ubiquitin-proteasome pathway activation. Further mechanistic research revealed that PYCP inhibited the autophagy-lysosome pathway in DEX-induced C2C12 myotubes. These findings indicate that PYCP prevents DEX-induced myotube atrophy through the regulation of FoxO transcription factors, followed by the inhibition of the ubiquitin-proteasome and autophagy-lysosome pathways. Therefore, we suggest that inhibiting these two proteolytic processes with FoxO transcription factors is a promising strategy for preventing DEX-related myotube atrophy.

Coexisting Systemic Infections in Patients Who Present With a Fall

BACKGROUND

Although the causes of falls are legion, infectious disease-related factors are not commonly reported in the published literature. We investigated the characteristics of patients presenting to the hospital because of a fall and who were subsequently found to have a coexisting systemic infection (CSI).

MATERIALS AND METHODS

This was a retrospective study performed at Massachusetts General Hospital, using the electronic database of adult patients receiving care during the period January 1, 2000 through December 31, 2014. Cases were initially screened by using billing codes for "fall," "sepsis," "bacteremia" and "systemic inflammatory response syndrome" (SIRS). Evaluable patients had documented CSI in the setting of a fall.

RESULTS

Of 161 evaluable patients, 84 (52.2%) were female. The mean age was 75. 2 years (range: 35-102 years, median = 78 years). Fall was considered "mechanical" (e.g., tripped by a rug) in 106 (65.8%) cases, with 126 (78.3%) patients living at home. SIRS criteria were met on initial healthcare encounters of 66 (40.1%) patients. Urinary and lower respiratory tract infections were the most common infectious disease conditions (71 [44.1%] and 37 [23.0%] cases, respectively). Bacteremia was seen in 64 (39.8%) cases. Staphylococcus aureus was the most common cause of bacteremia (21 cases, 31.3% of bloodstream isolates). CSI was not initially suspected by providing clinicians in 64 (39.8%) patients.

CONCLUSIONS

Falls associated with CSIs are often considered "mechanical" in nature, and they frequently fail to meet the SIRS criteria on initial presentation. Aside from its commonly recognized causes, falls may be an atypical manifestation of a systemic infection.

The diaphragm is better protected from oxidative stress than hindlimb skeletal muscle during CLP-induced sepsis

OBJECTIVES

The aim of this study was to determine whether non-lethal sepsis induced by cecal ligation and puncture (CLP) modulates oxidative damage and enzymatic antioxidant defenses in diaphragm and hindlimb skeletal muscles (soleus and Extensor Digitorus Longus (EDL)).

METHODS

Female Wistar rats were divided into four experimental groups: (1) control animals, (2) animals sacrificed 2 hours or (3) 7 days after CLP, and (4) sham-operated animals. At the end of the experimental procedure, EDL, soleus, and diaphragm muscles were harvested and 4-hydroxynonenal (HNE)-protein adducts and protein carbonyl contents were examined in relation to superoxide dismutase and catalase expression and activities.

RESULTS

We observed that both non-respiratory oxidative (i.e. soleus) and glycolytic skeletal muscles (i.e. EDL) are more susceptible to sepsis-induced oxidative stress than diaphragm, as attested by an increase in 4-HNE protein adducts and carbonylated proteins after 2 hours of CLP only in soleus and EDL.

DISCUSSION

These differences could be explained by higher basal enzymatic antioxidant activities in diaphragm compared to hindlimb skeletal muscles. Together, these results demonstrate that diaphragm is better protected from oxidative stress than hindlimb skeletal muscles during CLP-induced sepsis.

Disruption of REDD1 gene ameliorates sepsis-induced decrease in mTORC1 signaling but has divergent effects on proteolytic signaling in skeletal muscle

Sepsis-induced skeletal muscle atrophy and weakness are due in part to decreased mTORC1-mediated protein synthesis and increased proteolysis via the autophagy-lysosomal system and ubiquitin-proteasome pathway. The REDD1 (regulated in development and DNA damage-1) protein is increased in sepsis and can negatively regulate mTORC1 activity. However, the contribution of REDD1 to the sepsis-induced change in muscle protein synthesis and degradation has not been determined. Sepsis was produced by cecal ligation and puncture in female REDD1(-/-) or wild-type (WT) mice, and end points were assessed 24 h later in gastrocnemius; time-matched, pair-fed controls of each genotype were included. Sepsis increased REDD1 protein 300% in WT mice, whereas REDD1 was absent in REDD1(-/-) muscle. Sepsis decreased protein synthesis and phosphorylation of downstream targets of mTORC1 (S6K1 Thr(389), rpS6 Ser(240/244), 4E-BP1 Ser(65)) in WT but not REDD1(-/-) mice. However, Akt and PRAS40 phosphorylation was suppressed in both sham and septic muscle from REDD1(-/-) mice despite unaltered PDK1, PP2A, or TSC2 expression. Sepsis increased autophagy as indicated by decreased ULK1 Ser(757) phosphorylation and p62 abundance and increased LC3B-II/I in WT mice, whereas these changes were absent in septic REDD1(-/-) mice. Conversely, REDD1 deletion did not prevent the sepsis-induced decrease in IGF-I mRNA or the concomitant increase in IL-6, TNFα, MuRF1, and atrogin1 mRNA expression. Lastly, 5-day survival in a separate set of septic mice did not differ between WT and REDD1(-/-) mice. These data highlight the central role of REDD1 in regulating both protein synthesis and autophagy in skeletal muscle during sepsis.

Glucocorticoids and Skeletal Muscle

Glucocorticoids are known to regulate protein metabolism in skeletal muscle, producing a catabolic effect that is opposite that of insulin. In many catabolic diseases, such as sepsis, starvation, and cancer cachexia, endogenous glucocorticoids are elevated contributing to the loss of muscle mass and function. Further, exogenous glucocorticoids are often given acutely and chronically to treat inflammatory conditions such as asthma, chronic obstructive pulmonary disease, and rheumatoid arthritis, resulting in muscle atrophy. This chapter will detail the nature of glucocorticoid-induced muscle atrophy and discuss the mechanisms thought to be responsible for the catabolic effects of glucocorticoids on muscle.