Quantitative and qualitative adaptations of muscle fibers to glucocorticoids

Glucocorticoid-Induced Myopathy: Typology, Pathogenesis, Diagnosis, and Treatment

Glucocorticoid-induced myopathy is a non-inflammatory toxic myopathy typified by proximal muscle weakness, muscle atrophy, fatigue, and easy fatigability. These vague symptoms coupled with underlying disorders may mask the signs of glucocorticoid-induced myopathy, leading to an underestimation of the disease's impact. This review briefly summarizes the classification, pathogenesis, and treatment options for glucocorticoid-induced muscle wasting. Additionally, we discuss current diagnostic measures in clinical research and routine care used for diagnosing and monitoring glucocorticoid-induced myopathy, which includes gait speed tests, muscle strength tests, hematologic tests, bioelectrical impedance analysis (BIA), dual-energy X-ray absorptiometry (DXA), computed tomography (CT), magnetic resonance imaging (MRI), electromyography, quantitative muscle ultrasound, histological examination, and genetic analysis. Continuous monitoring of patients receiving glucocorticoid therapy plays an important role in enabling early detection of glucocorticoid-induced myopathy, allowing physicians to modify treatment plans before significant clinical weakness arises.

Musculoskeletal crosstalk in chronic obstructive pulmonary disease and comorbidities: Emerging roles and therapeutic potentials

Chronic Obstructive Pulmonary Disease (COPD) is a multifaceted respiratory disorder characterized by progressive airflow limitation and systemic implications. It has become increasingly apparent that COPD exerts its influence far beyond the respiratory system, extending its impact to various organ systems. Among these, the musculoskeletal system emerges as a central player in both the pathogenesis and management of COPD and its associated comorbidities. Muscle dysfunction and osteoporosis are prevalent musculoskeletal disorders in COPD patients, leading to a substantial decline in exercise capacity and overall health. These manifestations are influenced by systemic inflammation, oxidative stress, and hormonal imbalances, all hallmarks of COPD. Recent research has uncovered an intricate interplay between COPD and musculoskeletal comorbidities, suggesting that muscle and bone tissues may cross-communicate through the release of signalling molecules, known as "myokines" and "osteokines". We explored this dynamic relationship, with a particular focus on the role of the immune system in mediating the cross-communication between muscle and bone in COPD. Moreover, we delved into existing and emerging therapeutic strategies for managing musculoskeletal disorders in COPD. It underscores the development of personalized treatment approaches that target both the respiratory and musculoskeletal aspects of COPD, offering the promise of improved well-being and quality of life for individuals grappling with this complex condition. This comprehensive review underscores the significance of recognizing the profound impact of COPD on the musculoskeletal system and its comorbidities. By unravelling the intricate connections between these systems and exploring innovative treatment avenues, we can aspire to enhance the overall care and outcomes for COPD patients, ultimately offering hope for improved health and well-being.

Steroid myopathy and rehabilitation in patients with cancer

Steroids are broadly used in oncology, despite known adverse events such as glucocorticosteroid-induced myopathy (SM). To date there are no accepted guidelines on the diagnosis and treatment of SM. The purpose of this review is to provide up-to-date information regarding SM with emphasis on neuro-oncology and hematopoietic stem cell transplant patients, given they are at high risk of experiencing SM following routine treatment with steroids. Our work is a combination of a comprehensive narrative review regarding etiology, pathogenesis, incidence, clinical presentation and treatment options for SM and a scoping review on the exercise therapy for SM. We have identified 24 in vivo studies of different exercise modalities in the settings of glucocorticosteroid treatment. Twenty of 24 studies demonstrated decreased muscle catabolism with exercise training. Both endurance and resistance exercises at mild to moderate intensity were beneficial. The value of high-intensity activities remains questionable as it may worsen muscle atrophy. Rehabilitation interventions, along with pharmacologic and dietary considerations, may be beneficial in preventing or reversing SM. Potential adverse events of some of these interventions and expected caveats in translating findings in preclinical models to human settings warrant caution and demand controlled clinical studies.

Higher cumulative dose of topical corticosteroids is associated with osteoporosis and major osteoporotic fracture: A nationwide case-control study

BACKGROUND

Connections between long-term use of topical corticosteroids (TCSs) of varying potency and osteoporosis and major osteoporotic fracture (MOF) are unclear. Susceptibility to adverse bone effects of TCSs in different sex, age and ethnic groups is unknown too.

OBJECTIVES

To demonstrate the association between cumulative dose of TCSs of varying potency and osteoporosis and MOF in Taiwanese population, with stratified analysis of sex and age.

METHODS

We conducted a nationwide case-control study and obtained data from Taiwan National Health Insurance Research Database. Cumulative TCS doses in different exposure periods were calculated, and the potency of TCSs was converted to prednisolone equivalent. Adjusted odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for osteoporosis and MOF associated with TCS use.

RESULTS

From 2017 to 2020, 129,682 osteoporosis cases and 34,999 MOF cases were selected and randomly matched with 518,728 and 139,996 controls by sex and age. We found clear dose-response relationships between long-term TCS exposure and osteoporosis and MOF. For example, compared to no TCS use, adjusted ORs of osteoporosis were 1.216 (95% CI 1.189-1.243), 1.260 (95% CI, 1.241-1.280) and 1.341 (95% CI, 1.314-1.369) for exposure to low, medium and high cumulative TCS doses, respectively, over 5 years. Adjusted ORs of MOF were 1.118 (95% CI 1.069-1.170), 1.191 (95% CI, 1.156-1.227) and 1.288 (95% CI, 1.238-1.340) for exposure to low, medium and high cumulative TCS doses, respectively, over 5 years. Stratified analysis showed women had higher ORs of osteoporosis and MOF compared to men. Younger people (<50 years) had highest OR of osteoporosis compared to other age groups.

CONCLUSIONS

Higher cumulative TCS dose was associated with increased risk of osteoporosis and MOF. Long-term use of TCSs should be cautious, especially in susceptible populations such as women and young people.

Neurologic Complications of Endocrine Disorders

OBJECTIVE

This article provides an overview of the neurologic complications of the most prevalent endocrine disorders in adults with an emphasis on relevant neurologic symptoms, signs, and laboratory and neuroimaging findings.

LATEST DEVELOPMENTS

Although the mechanisms of many of the neurologic complications discussed here remain unclear, our understanding of the impacts of diabetes and hypothyroidism on the nervous system and muscle, including complications of rapid correction of chronic hyperglycemia, has advanced in recent years. Recent large studies have not demonstrated a convincing association between subclinical or overt hypothyroidism and cognitive decline.

ESSENTIAL POINTS

Neurologists must become familiar with the neurologic complications of endocrine disorders not only because they are common and treatable (and often reversible) but also because they may be iatrogenic, as is the case with adrenal insufficiency in the setting of long-term corticosteroid therapy.

Dexamethasone leads to Zn2+ accumulation and increased unbound Zn2+ in C2C12 muscle and 3T3-L1 adipose cells

Skeletal muscle atrophy is associated with increases in circulating glucocorticoid levels and insulin resistance. Zinc accumulates in atrophic muscle, but the relationship between atrophy, insulin resistance, and Zn²⁺ homeostasis remains unclear. In this study, the effect of the glucocorticoid dexamethasone (DEX) on insulin and Zn²⁺ homeostasis was explored. Treatment of differentiated C2C12 skeletal myotubes and 3T3-L1 adipocytes with DEX significantly increased mRNA expression of the metal-binding proteins Mt1 and 2 and altered energy storage as shown by the increased size of lipid droplets in 3T3-L1 cells. In C2C12 cells the total cellular Zn²⁺ was higher after DEX treatment, and in both C2C12 and 3T3-L1 adipocytes, free unbound Zn²⁺ was increased. Insulin treatment led to a gradual increase in free Zn²⁺ in C2C12 cells, and no significant change in DEX-treated cells such that concentrations were similar 10 min after insulin treatment. These data demonstrate that DEX disturbs Zn²⁺ homeostasis in muscle and fat cells. Further study of the molecular pathways involved to identify novel therapeutic targets for treatment of skeletal muscle atrophy is warranted.

Effects of structured exercise programmes on physiological and psychological outcomes in adults with inflammatory bowel disease (IBD): A systematic review and meta-analysis

BACKGROUND

Exercise has been suggested to counteract specific complications of inflammatory bowel disease (IBD). However, its role as a therapeutic option remains poorly understood. Therefore, we conducted a systematic review and meta-analysis on the effects of exercise in IBD.

METHODS

Five databases (MEDLINE, Embase, CINAHL, CENTRAL and SPORTDiscus) and three registers (Clinicaltrials.gov, WHO ICTRP and ISRCTN) were searched from inception to September 2022, for studies assessing the effects of structured exercise of at least 4 weeks duration on physiological and/or psychological outcomes in adults with IBD. Two independent reviewers screened records, assessed risk of bias using the Cochrane Risk of Bias (RoB 2.0) and ROBINS-I tools, and evaluated the certainty of evidence using the GRADE method. Data were meta-analysed using a random-effects model.

RESULTS

From 4,123 citations, 15 studies (9 RCTs) were included, comprising of 637 participants (36% male). Pooled evidence from six RCTs indicated that exercise improved disease activity (SMD = -0.44; 95% CI [-0.82 to -0.07]; p = 0.02), but not disease-specific quality of life (QOL) (IBDQ total score; MD = 3.52; -2.00 to 9.04; p = 0.21) when compared to controls. Although meta-analysis could not be performed for other outcomes, benefits were identified in fatigue, muscular function, body composition, cardiorespiratory fitness, bone mineral density and psychological well-being. Fourteen exercise-related non-serious adverse events occurred. The overall certainty of evidence was low for disease activity and very low for HRQOL as a result of downgrading for risk of bias and imprecision.

CONCLUSIONS

Structured exercise programmes improve disease activity, but not disease-specific QOL. Defining an optimal exercise prescription and synthesis of evidence in other outcomes, was limited by insufficient well-designed studies to ascertain the true effect of exercise training. This warrants further large-scale randomised trials employing standard exercise prescription to verify this effect to enable the implementation into clinical practice.

REGISTRATION

This systematic review was prospectively registered in an international database of systematic reviews in health-related research (CRD42017077992; https://www.crd.york.ac.uk/prospero/).

Nanomedicine for Treating Muscle Dystrophies: Opportunities, Challenges, and Future Perspectives

Muscular dystrophies are a group of genetic muscular diseases characterized by impaired muscle regeneration, which leads to pathological inflammation that drives muscle wasting and eventually results in weakness, functional dependency, and premature death. The most known causes of death include respiratory muscle failure due to diaphragm muscle decay. There is no definitive treatment for muscular dystrophies, and conventional therapies aim to ameliorate muscle wasting by promoting physiological muscle regeneration and growth. However, their effects on muscle function remain limited, illustrating the requirement for major advancements in novel approaches to treatments, such as nanomedicine. Nanomedicine is a rapidly evolving field that seeks to optimize drug delivery to target tissues by merging pharmaceutical and biomedical sciences. However, the therapeutic potential of nanomedicine in muscular dystrophies is poorly understood. This review highlights recent work in the application of nanomedicine in treating muscular dystrophies. First, we discuss the history and applications of nanomedicine from a broader perspective. Second, we address the use of nanoparticles for drug delivery, gene regulation, and editing to target Duchenne muscular dystrophy and myotonic dystrophy. Next, we highlight the potential hindrances and limitations of using nanomedicine in the context of cell culture and animal models. Finally, the future perspectives for using nanomedicine in clinics are summarized with relevance to muscular dystrophies.

Dexamethasone-Induced Adipose Tissue Redistribution and Metabolic Changes: Is Gene Expression the Main Factor? An Animal Model of Chronic Hypercortisolism

Chronic hypercortisolism has been associated with the development of several metabolic alterations, mostly caused by the effects of chronic glucocorticoid (GC) exposure over gene expression. The metabolic changes can be partially explained by the GC actions on different adipose tissues (ATs), leading to central obesity. In this regard, we aimed to characterize an experimental model of iatrogenic hypercortisolism in rats with significant AT redistribution. Male Wistar rats were distributed into control (CT) and GC-treated, which received dexamethasone sodium phosphate (0.5 mg/kg/day) by an osmotic minipump, for 4 weeks. GC-treated rats reproduced several characteristics observed in human hypercortisolism/Cushing’s syndrome, such as HPA axis inhibition, glucose intolerance, insulin resistance, dyslipidemia, hepatic lipid accumulation, and AT redistribution. There was an increase in the mesenteric (meWAT), perirenal (prWAT), and interscapular brown (BAT) ATs mass, but a reduction of the retroperitoneal (rpWAT) mass compared to CT rats. Overexpressed lipolytic and lipogenic gene profiles were observed in white adipose tissue (WAT) of GC rats as BAT dysfunction and whitening. The AT remodeling in response to GC excess showed more importance than the increase of AT mass per se, and it cannot be explained just by GC regulation of gene transcription.

Nutritional recommendations for patients undergoing prolonged glucocorticoid therapy

Glucocorticoid (GC) therapy is a common treatment used in rheumatic and autoimmune diseases, owing to its anti-inflammatory and immunosuppressive effects. However, GC therapy can also induce a number of adverse effects, including muscle and bone loss, hypertension, metabolic perturbations and increased visceral adiposity. We review available evidence in this area and provide nutritional recommendations that might ameliorate these adverse effects. Briefly, optimizing calcium, vitamin D, sodium and protein intake and increasing consumption of unprocessed and minimally processed foods, while decreasing the consumption of ultra-processed foods, might counteract some of the specific challenges faced by these patients. Importantly, we identify a dearth of empirical data on how nutritional intervention might impact health-related outcomes in this population. Further research is required to investigate the clinical and therapeutic efficacy of these theory-based recommendations.

Rehabilitation Needs for Patients Undergoing CAR T-Cell Therapy

PURPOSE OF REVIEW

Chimeric antigen receptor (CAR) T-cell therapy is a relatively new, innovative treatment strategy to manage refractory hematological cancers, including some types of leukemia, lymphoma, and multiple myeloma. This article outlines the CAR T-cell therapy process, toxicity, and complications, along with an overview of the currently known short- and long-term physical and functional sequelae that will be helpful for general or oncology rehabilitation specialists caring for these patients.

RECENT FINDINGS

There is a dearth of literature on the topic of rehabilitation of patients receiving CAR T-cell therapy. Rehabilitation practices can be extrapolated from the limited functional information on patients who have completed treatment for lymphoma and multiple myeloma. Patients present with cognitive impairment, muscle weakness, reduced exercise capacity, neuropathy, and cancer-related fatigue. Physical activity and rehabilitation programs may be beneficial to address fatigue, psychological symptoms, and quality of life. There is limited rehabilitation research in patients receiving CAR T-cell therapy. These patients may present with general deconditioning and neurological complications which translate to neuromuscular and cognitive impairment that benefit from multidisciplinary rehabilitation intervention prior to, during, and after treatment. Studies measuring the impairments at baseline and evaluation of the impact of rehabilitation practices are much needed to support this.

Methodological considerations in measuring specific force in human single skinned muscle fibres

Chemically skinned fibres allow the study of human muscle contractile function in vitro. A particularly important parameter is specific force (SF), that is, maximal isometric force divided by cross-sectional area, representing contractile quality. Although SF varies substantially between studies, the magnitude and cause of this variability remains puzzling. Here, we aimed to summarize and explore the cause of variability in SF between studies. A systematic search was conducted in Medline, Embase and Web of Science databases in June 2020, yielding 137 data sets from 61 publications which studied healthy, young adults. Five-fold differences in mean SF data were observed. Adjustments to the reported data for key methodological differences allowed between-study comparisons to be made. However, adjustment for fibre shape, swelling and sarcomere length failed to significantly reduce SF variance (I² = 96%). Interestingly, grouping papers based on shared authorship did reveal consistency within research groups. In addition, lower SF was found to be associated with higher phosphocreatine concentrations in the fibre activating solution and with Triton X-100 being used as a skinning agent. Although the analysis showed variance across the literature, the ratio of SF in single fibres containing myosin heavy chain isoforms IIA or I was found to be consistent across research groups. In conclusion, whilst the skinned fibre technique is reliable for studying in vitro force generation of single fibres, the composition of the solution used to activate fibres, which differs between research groups, is likely to heavily influence SF values.

Cushing Syndrome Associated Myopathy: It Is Time for a Change

Cushing syndrome is the result of excessive levels of glucocorticoids. Endogenous Cushing syndrome is rare with an incidence of two to three cases per million per year. Clinically, the presentation consists of a characteristic phenotype including skin symptoms and metabolic manifestations. A frequent co-morbidity with high impact on quality of life is Cushing syndrome associated myopathy. It characteristically affects the proximal myopathy, impairing stair climbing and straightening up. The pathophysiology is complex and involves protein degradation via the forkhead box O3 (FOXO3) pathway, intramuscular fat accumulation, and inactivity-associated muscle atrophy. Surgical remission of Cushing syndrome is the most important step for recovery of muscle function. Restoration depends on age, co-morbidities and postoperative insulin-like growth factor concentrations. At average, functionality remains impaired during the long-term compared to age and sex matched control persons. Growth hormone therapy in individuals with impaired growth hormone secretion could be an option but has not been proved in a randomized trial.

Towards Personalized Management of Sarcopenia in COPD

The awareness of the presence and consequences of sarcopenia has significantly increased over the past decade. Sarcopenia is defined as gradual loss of muscle mass and strength and ultimately loss of physical performance associated with aging and chronic disease. The prevalence of sarcopenia is higher in chronic obstructive pulmonary disease (COPD) compared to age-matched controls. Current literature suggests that next to physical inactivity, COPD-specific alterations in physiological processes contribute to accelerated development of sarcopenia. Sarcopenia in COPD can be assessed according to current guidelines, but during physical performance testing, ventilatory limitation should be considered. Treatment of muscle impairment can halt or even reverse sarcopenia, despite respiratory impairment. Exercise training and protein supplementation are currently at the basis of sarcopenia treatment. Furthermore, effective current and new interventions targeting the pulmonary system (eg, smoking cessation, bronchodilators and lung volume reduction surgery) may also facilitate muscle maintenance. Better understanding of disease-specific pathophysiological mechanisms involved in the accelerated development of sarcopenia in COPD will provide new leads to refine nutritional, exercise and physical activity interventions and develop pharmacological co-interventions.

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.

Ultrasound-based detection of glucocorticoid-induced impairments of muscle mass and structure in Cushing's disease

PURPOSE

To investigate the glucocorticoid-induced impairments of muscle mass and structure in patients presenting different stages of steroid myopathy progression.

METHODS

Thirty-three patients (28 women) affected by active (N = 20) and remitted (N = 13) Cushing's disease were recruited and the following variables were assessed: walking speed, handgrip strength, total body and appendicular muscle mass by bioelectrical impedance analysis (BIA), thickness and echo intensity of lower limb muscles by ultrasonography.

RESULTS

The two groups of patients showed comparable values of both handgrip strength [median (interquartile range) values: active disease: 27.4 (7.5) kg vs. remitted disease: 26.4 (9.4) kg; P = 0.58] and walking speed [active disease: 1.0 (0.2) m/s vs. remitted disease: 1.1 (0.3) m/s; P = 0.43]. Also, the thickness of the four muscles and all BIA-derived sarcopenic indices were comparable (P > 0.05 for all comparisons) between the two groups. On the contrary, the echo intensity of vastus lateralis, tibialis anterior (lower portion), and medial gastrocnemius was significantly (P < 0.05 for all comparisons) higher in patients with active disease compared to patients with remitted disease. Finally, significant negative correlations were found in the whole group of patients between muscle echo intensity and muscle function assessments.

CONCLUSIONS

We provided preliminary evidence that the ultrasound-derived measurements of muscle thickness and echo intensity can be useful to detect and track the changes of muscle mass and structure in patients with steroid myopathy and we suggest that the combined assessment of muscle mass, strength, and performance should be systematically applied in the routine examination of steroid myopathy patients.

MECHANISMS OF ENDOCRINE DISEASE: Sarcopenia in endocrine and non-endocrine disorders

Objective This paper reviews the main mechanisms, diagnostic criteria, treatment options and available data on sarcopenia in endocrine and non-endocrine disorders. The literature notes the presence of sarcopenia as a comorbid condition or a complication of another clinical situation and not a disease that only affects elderly patients. Method We performed a literature review, focusing on the following: mechanisms related to sarcopenia in elderly patients, and sarcopenia as it presents in the context of chronic and endocrine diseases; diagnostic tools and methods; aspects of sarcopenia and treatment options specific to chronic diseases and endocrine disorders respectively. Results Sarcopenia in chronic and endocrine disorders shares many mechanisms with sarcopenia affecting elderly patients, but certain diseases can have a predominant aspect that leads to sarcopenia. The prevalence of sarcopenia varies, depending on different diagnostic criteria, from around 12 to 60% in chronic illnesses and 15 to 90% in endocrine disorders. The interplay between sarcopenia, chronic diseases and elderly patients requires further study, to clarify the impact of each, in terms of prognosis and mortality. Conclusion Awareness of the presentation of sarcopenia in the context of other diseases and ages (and not just the elderly) is fundamental to ensure that preventive measures can be deployed.

Electrical Stimulation Prevents Preferential Skeletal Muscle Myosin Loss in Steroid-Denervation Rats

Severe muscle weakness concomitant with preferential depletion of myosin has been observed in several pathological conditions. Here, we used the steroid-denervation (S-D) rat model, which shows dramatic decrease in myosin content and force production, to test whether electrical stimulation (ES) treatment can prevent these deleterious changes. S-D was induced by cutting the sciatic nerve and subsequent daily injection of dexamethasone for 7 days. For ES treatment, plantarflexor muscles were electrically stimulated to produce four sets of five isometric contractions each day. Plantarflexor in situ isometric torque, muscle weight, skinned muscle fiber force, and protein and mRNA expression were measured after the intervention period. ES treatment partly prevented the S-D-induced decreases in plantarflexor in situ isometric torque and muscle weight. ES treatment fully prevented S-D-induced decreases in skinned fiber force and ratio of myosin heavy chain (MyHC) to actin, as well as increases in the reactive oxygen/nitrogen species-generating enzymes NADPH oxidase (NOX) 2 and 4, phosphorylation of p38 MAPK, mRNA expression of the muscle-specific ubiquitin ligases muscle ring finger-1 (MuRF-1) and atrogin-1, and autolyzed active calpain-1. Thus, ES treatment is an effective way to prevent muscle impairments associated with loss of myosin.

Diagnostic work-up in steroid myopathy

INTRODUCTION

Steroid myopathy is a well-known sign of endogenous Cushing's syndrome as well as a side effect of glucocorticoid administration. The clinical finding of muscle weakness and the clinical inspection of the muscle size are the most commonly used diagnostic tools, sometimes in combination with needle electromyography, but there are no means to detect the myopathy before the appearance of clinical or electrodiagnostic signs. Until now, no guidelines have been produced for a disease-specific evaluation of muscle impairment in patients with Cushing's syndrome.

REVIEW

We reviewed the measurement properties and limitations of the following tools that are currently adopted in clinical research and routine care for diagnosis and monitoring of steroid myopathy: muscle strength assessment; needle biopsy; intramuscular and surface electromyography; laboratory assays; muscle mass assessments (through bioelectrical impedance analysis, dual-energy X-ray absorptiometry, and computed tomography).

CONCLUSIONS

We suggest that the management of steroid myopathy patients in clinical research and practice would benefit from a multidisciplinary approach based on the combined assessment of muscle mass, strength, and performance. However, further studies are required to establish an operational definition of steroid myopathy and to identify population-specific criteria for diagnosis of the myopathic process.

GLUCOCORTICOID EXCESS IN BONE AND MUSCLE

Glucocorticoids (GC), produced and released by the adrenal glands, regulate numerous physiological processes in a wide range of tissues. Because of their profound immunosuppressive and anti-inflammatory actions, GC are extensively used for the treatment of immune and inflammatory conditions, the management of organ transplantation, and as a component of chemotherapy regimens for cancers. However, both pathologic endogenous elevation and long-term use of exogenous GC are associated with severe adverse effects. In particular, excess GC has devastating effects on the musculoskeletal system. GC increase bone resorption and decrease formation leading to bone loss, microarchitectural deterioration and fracture. GC also induce loss of muscle mass and strength leading to an increased incidence of falls. The combined effects on bone and muscle account for the increased fracture risk with GC. This review summarizes the advance in knowledge in the last two decades about the mechanisms of action of GC in bone and muscle and the attempts to interfere with the damaging actions of GC in these tissues with the goal of developing more effective therapeutic strategies.

Persistence of myopathy in Cushing's syndrome: evaluation of the German Cushing's Registry

BACKGROUND

Cushing's syndrome (CS) is characterized by an excessive secretion of glucocorticoids that results in a characteristic clinical phenotype. One feature of clinical hypercortisolism is breakdown of protein metabolism translating into clinical consequences including glucocorticoid-induced myopathy. While surgery is effective in control of cortisol excess, the effect of biochemical remission on muscular function is yet unclear.

METHODS

In a cross-sectional study we analyzed 47 patients with CS during the florid phase (ActiveCS). 149 additional patients were studied 2-53 years (mean: 13 years) after surgery in biochemical long-term remission (RemissionCS). Also, 93 rule-out CS patients were used as controls (CON). All subjects were assessed for grip strength using a hand grip dynamometer and underwent the chair rising test (CRT).

RESULTS

Hand grip strength (85% vs 97% of norm, P = 0.002) and the CRT performance (9.5 s vs 7.1 s, P = 0.001) were significantly lower in ActiveCS compared to the CON group. Six months after treatment grip strength further decreased in CS (P = 0.002) and CRT performance remained impaired. The RemissionCS group (mean follow-up 13 years) had reduced hand grip strength (92% compared to normal reference values for dominant hand, P < 0.001). The chair rising test performance was at 9.0 s and not significantly different from the ActiveCS group (P = 0.45).

CONCLUSION

CS affects muscle strength in the acute phase, but functional impairment remains detectable also during long-term follow-up despite biochemical remission.

Glucocorticoids Induce Bone and Muscle Atrophy by Tissue-Specific Mechanisms Upstream of E3 Ubiquitin Ligases

Glucocorticoid excess, either endogenous with diseases of the adrenal gland, stress, or aging or when administered for immunosuppression, induces bone and muscle loss, leading to osteopenia and sarcopenia. Muscle weakness increases the propensity for falling, which, combined with the lower bone mass, increases the fracture risk. The mechanisms underlying glucocorticoid-induced bone and muscle atrophy are not completely understood. We have demonstrated that the loss of bone and muscle mass, decreased bone formation, and reduced muscle strength, hallmarks of glucocorticoid excess, are accompanied by upregulation in both tissues in vivo of the atrophy-related genes atrogin1, MuRF1, and MUSA1. These are E3 ubiquitin ligases traditionally considered muscle-specific. Glucocorticoids also upregulated atrophy genes in cultured osteoblastic/osteocytic cells, in ex vivo bone organ cultures, and in muscle organ cultures and C2C12 myoblasts/myotubes. Furthermore, glucocorticoids markedly increased the expression of components of the Notch signaling pathway in muscle in vivo, ex vivo, and in vitro. In contrast, glucocorticoids did not increase Notch signaling in bone or bone cells. Moreover, the increased expression of atrophy-related genes in muscle, but not in bone, and the decreased myotube diameter induced by glucocorticoids were prevented by inhibiting Notch signaling. Thus, glucocorticoids activate different mechanisms in bone and muscle that upregulate atrophy-related genes. However, the role of these genes in the effects of glucocorticoids in bone is unknown. Nevertheless, these findings advance our knowledge of the mechanism of action of glucocorticoids in the musculoskeletal system and provide the basis for novel therapies to prevent glucocorticoid-induced atrophy of bone and muscle.

Dexamethasone-induced muscular atrophy is mediated by functional expression of connexin-based hemichannels

Long-term treatment with high glucocorticoid doses induces skeletal muscle atrophy. However, the molecular mechanism of such atrophy remains unclear. We evaluated the possible involvement of connexin-based hemichannels (Cx HCs) in muscle atrophy induced by dexamethasone (DEX), a synthetic glucocorticoid, on control (Cx43(fl/fl)Cx45(fl/fl)) and Cx43/Cx45 expression-deficient (Cx43(fl/fl)Cx45(fl/fl):Myo-Cre) skeletal myofibers. Myofibers of Cx43(fl/fl)Cx45(fl/fl) mice treated with DEX (5h) expressed several proteins that form non-selective membrane channels (Cx39, Cx43, Cx45, Panx1, P2X7 receptor and TRPV2). After 5h DEX treatment in vivo, myofibers of Cx43(fl/fl)Cx45(fl/fl) mice showed Evans blue uptake, which was absent in myofibers of Cx43(fl/fl)Cx45(fl/fl):Myo-Cre mice. Similar results were obtained in vitro using ethidium as an HC permeability probe, and DEX-induced dye uptake in control myofibers was blocked by P2X7 receptor inhibitors. DEX also induced a significant increase in basal intracellular Ca(2+) signal and a reduction in resting membrane potential in Cx43(fl/fl)Cx45(fl/fl) myofibers, changes that were not elicited by myofibers deficient in Cx43/Cx45 expression. Moreover, treatment with DEX induced NFκB activation and increased mRNA levels of TNF-α in control but not in Cx43/Cx45 expression-deficient myofibers. Finally, a prolonged DEX treatment (7days) increased atrogin-1 and Murf-1 and reduced the cross sectional area of Cx43(fl/fl)Cx45(fl/fl) myofibers, but these parameters remained unaffected in Cx43(fl/fl)Cx45(fl/fl):Myo-Cre myofibers. Therefore, DEX-induced expression of Cx43 and Cx45 plays a critical role in early sarcolemma changes that lead to atrophy. Consequently, this side effect of chronic glucocorticoid treatment might be avoided by co-administration with a Cx HC blocker.

Metabolic comorbidities in Cushing's syndrome

Cushing's syndrome (CS) patients have increased mortality primarily due to cardiovascular events induced by glucocorticoid (GC) excess-related severe metabolic changes. Glucose metabolism abnormalities are common in CS due to increased gluconeogenesis, disruption of insulin signalling with reduced glucose uptake and disposal of glucose and altered insulin secretion, consequent to the combination of GCs effects on liver, muscle, adipose tissue and pancreas. Dyslipidaemia is a frequent feature in CS as a result of GC-induced increased lipolysis, lipid mobilisation, liponeogenesis and adipogenesis. Protein metabolism is severely affected by GC excess via complex direct and indirect stimulation of protein breakdown and inhibition of protein synthesis, which can lead to muscle loss. CS patients show changes in body composition, with fat redistribution resulting in accumulation of central adipose tissue. Metabolic changes, altered adipokine release, GC-induced heart and vasculature abnormalities, hypertension and atherosclerosis contribute to the increased cardiovascular morbidity and mortality. In paediatric CS patients, the interplay between GC and the GH/IGF1 axis affects growth and body composition, while in adults it further contributes to the metabolic derangement. GC excess has a myriad of deleterious effects and here we attempt to summarise the metabolic comorbidities related to CS and their management in the perspective of reducing the cardiovascular risk and mortality overall.