Metformin ameliorates skeletal muscle atrophy in Grx1 KO mice by regulating intramuscular lipid accumulation and glucose utilization

Current research trends on the effect of diabetes mellitus on rotator cuff tendon healing/tendinopathy

Rotator cuff tendon tears are a leading cause of shoulder pain. They are challenging to treat, and tendon-bone healing has a high failure rate despite successful surgery. Tendons connect the muscles and bones, which make them important for the body's overall mobility and stability. Metabolic diseases, including diabetes or high blood pressure, can affect the healing process after repair of a damaged tendon. With a global incidence of 9.3%, diabetes is considered as a significant risk factor for rotator cuff tendon healing because it causes structural, inflammatory, and vascular changes in the tendon. However, the mechanisms of how diabetes affects tendon healing remain unknown. Several factors have been suggested, including glycation product accumulation, adipokine dysregulation, increased levels of reactive oxygen species, apoptosis, inflammatory cytokines, imbalanced matrix-metalloproteinase-to-tissue-inhibitor ratio, and impaired angiogenesis and differentiation of the tendon sheath. Despite the effects of diabetes on tendon function and healing, few treatments are available to improve recovery in these patients. This review summarizes the current literature on the pathophysiological changes of the tendon in diabetes and hyperlipidemia. Preclinical and clinical evidence regarding the association between diabetes and tendon healing is presented. Moreover, current approaches to improve tendon healing in patients with diabetes are reviewed.

Combination therapy of metformin and morin attenuates insulin resistance, inflammation, and oxidative stress in skeletal muscle of high-fat diet-fed mice

Lipid accumulation, inflammation, and oxidative stress are the most important causes of muscle insulin resistance. The aim of this study was to investigate the single and combined treatment effects of metformin (MET) and morin (MOR) on lipid accumulation, inflammation, and oxidative stress in the skeletal muscle of mice fed a high-fat diet. The mice were supplemented with MET (230 mg/kg diet), MOR (100 mg/kg diet), and MET + MOR for 9 weeks. Our results revealed that single treatment with MET or MOR, and with a stronger effect of MET + MOR combined treatment, reduced body weight gain, improved glucose intolerance and enhanced Akt phosphorylation in the muscle tissue. In addition, plasma and muscle triglyceride levels were decreased after treatment with MET and MOR. The expression of genes involved in macrophage infiltration and polarization and pro-inflammatory cytokines showed that MET + MOR combined treatment, significantly reduced inflammation in the muscle. Furthermore, combined treatment of MET + MOR with greater efficacy than the single treatment improved several oxidative stress markers in the muscle. Importantly, combined treatment of MET and MOR could increase the expression of nuclear factor erythroid 2-related factor 2, the master regulator of the antioxidant response. These findings suggest that combination of MET with MOR might ameliorate insulin resistance, inflammation, and oxidative stress in the skeletal muscle of mice fed high-fat diet.

Sarcopenia and Diabetes: A Detrimental Liaison of Advancing Age

Sarcopenia is an age-related clinical complaint characterized by the progressive deterioration of skeletal muscle mass and strength over time. Type 2 diabetes (T2D) is associated with faster and more relevant skeletal muscle impairment. Both conditions influence each other, leading to negative consequences on glycemic control, cardiovascular risk, general health status, risk of falls, frailty, overall quality of life, and mortality. PubMed/Medline, Scopus, Web of Science, and Google Scholar were searched for research articles, scientific reports, observational studies, clinical trials, narrative and systematic reviews, and meta-analyses to review the evidence on the pathophysiology of di-abetes-induced sarcopenia, its relevance in terms of glucose control and diabetes-related outcomes, and diagnostic and therapeutic challenges. The review comprehensively addresses key elements for the clinical definition and diagnostic criteria of sarcopenia, the pathophysiological correlation be-tween T2D, sarcopenia, and related outcomes, a critical review of the role of antihyperglycemic treatment on skeletal muscle health, and perspectives on the role of specific treatment targeting myokine signaling pathways involved in glucose control and the regulation of skeletal muscle metabolism and trophism. Prompt diagnosis and adequate management, including lifestyle inter-vention, health diet programs, micronutrient supplementation, physical exercise, and pharmaco-logical treatment, are needed to prevent or delay skeletal muscle deterioration in T2D.

Skeletal and cardiac muscle have different protein turnover responses in a model of right heart failure

Right heart failure (RHF) is a common and deadly disease in aged populations. Extra-cardiac outcomes of RHF such as skeletal muscle atrophy contribute to morbidity and mortality. Despite the significance of maintaining right ventricular (RV) and muscle function, the mechanisms of RHF and muscle atrophy are unclear. Metformin (MET) improves cardiac and muscle function through the regulation of metabolism and the cellular stress response. However, whether MET is a viable therapeutic for RHF and muscle atrophy is not yet known. We used deuterium oxide labeling to measure individual protein turnover in the RV as well as subcellular skeletal muscle proteostasis in aged male mice subjected to 4 weeks of hypobaric hypoxia (HH)-induced RHF. Mice exposed to HH had elevated RV mass and impaired RV systolic function, neither of which was prevented by MET. HH resulted in a higher content of glycolytic, cardiac, and antioxidant proteins in the RV, most of which were inhibited by MET. The synthesis of these key RV proteins was generally unchanged by MET, suggesting MET accelerated protein breakdown. HH resulted in a loss of skeletal muscle mass due to inhibited protein synthesis alongside myofibrillar protein breakdown. MET did not impact HH-induced muscle protein turnover and did not prevent muscle wasting. Together, we show tissue-dependent responses to HH-induced RHF where the RV undergoes hypertrophic remodeling with higher expression of metabolic and stress response proteins. Skeletal muscle undergoes loss of protein mass and atrophy, primarily due to myofibrillar protein breakdown. MET did not prevent HH-induced RV dysfunction or muscle wasting, suggesting that the identification of other therapies to attenuate RHF and concomitant muscle atrophy is warranted.

Metformin protects fibroblasts from patients with GNE myopathy by restoring autophagic flux via an AMPK/mTOR-independent pathway

UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) myopathy is an autosomal recessive disease characterized by rimmed vacuoles (RVs). Previous studies have shown that metformin protects against several neuromuscular disorders. In the present study, we summarize the clinical features of three GNE patients with the p.D207V mutation. The pathogenesis of GNE myopathy is described, and the significance of metformin in this disease is observed. Skin biopsy-derived fibroblasts from patients with GNE myopathy, carrying a D207V mutation in GNE, were cultured. GNE fibroblasts and control fibroblasts were treated under normal culture conditions, serum starvation conditions, or serum starvation + metformin conditions. Histopathological and immunohistochemical analyses of muscle samples showed that autophagy was involved in the formation of RVs in the muscle of patients. Starved GNE fibroblasts showed decreased autophagy-related proteins and impaired autophagic flow (p < 0.05). The mRFP-GFP-LC3 assay showed that the fusion of autophagosomes with lysosomes was partially blocked in GNE cells. Notably, metformin treatment upregulated the expression of autophagy proteins, increased the number of autolysosomes (p < 0.001), and influenced the viability of GNE cells (p < 0.001). Furthermore, adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) and phosphorylated (p)-AMPK expression levels were upregulated in serum-starved GNE fibroblasts, while the mammalian target of rapamycin (mTOR) and p-mTOR expression levels were downregulated in both groups. Metformin treatment inhibited the AMPK-mTOR signaling pathway. Our results suggest that metformin plays a protective role in the GNE fibroblast by restoring autophagic flux and through the AMPK/mTOR-independent pathway.

Effect of oral cannabis administration on the fat depots of obese and streptozotocin-induced diabetic rats

The prevalence of obesity and insulin-resistance is on the rise, globally. Cannabis have been shown to have anti-diabetic/obesity properties, however, the effect mediated at various fat depots remains to be clarified. The aim of this study was to (1) investigate the anti-diabetic property of an oral cannabis administration in an obese and streptozotocin-induced diabetic rat model and (2) to determine and compare the effect mediated at the peritoneal and intramuscular fat level. Cannabis concentration of 1.25 mg/kg body weight (relative to THC content) was effective in reversing insulin-resistance in the rat model, unlike the other higher cannabinoid concentrations. At the peritoneal fat level, gene expression of fat beigeing markers, namely Cidea and UCP1, were significantly increased compared to the untreated control. At the intramuscular fat level, on the other hand, CE1.25 treatment did not promote fat beigeing but instead significantly increased mitochondrial activity, relative to the untreated control. Therefore, these findings indicate that the mechanism of action of oral cannabis administration, where glucose and lipid homeostasis is restored, is not only dependent on the dosage but also on the type of fat depot investigated.

Effects of luseogliflozin treatment on hyperglycemia-induced muscle atrophy in rats

Diabetes mellitus is recognized as a risk factor for sarcopenia. Luseogliflozin, a selective sodium-glucose cotransporter 2 (SGLT2) inhibitor, reduces inflammation and oxidative stress by improving hyperglycemia, subsequently improving hepatosteatosis or kidney dysfunction. However, the effects of SGLT2 inhibitor on the regulation of skeletal muscle mass or function in hyperglycemia are still unknown. In this study, we investigated the effects of luseogliflozin-mediated attenuation of hyperglycemia on the prevention of muscle atrophy. Twenty-four male Sprague-Dawley rats were randomly divided into four groups: control, control with SGLT2 inhibitor treatment, hyperglycemia, and hyperglycemia with SGLT2 inhibitor treatment. The hyperglycemic rodent model was established using a single injection of streptozotocin, a compound with preferential toxicity toward pancreatic beta cells. Muscle atrophy in streptozotocin-induced hyperglycemic model rats was inhibited by the suppression of hyperglycemia using luseogliflozin, which consequently suppressed hyperglycemia-mediated increase in the levels of advanced glycation end products (AGEs) and activated the protein degradation pathway in muscle cells. Treatment with luseogliflozin can restore the hyperglycemia-induced loss in the muscle mass to some degree partly through the inhibition of AGEs-induced or homeostatic disruption of mitochondria-induced activation of muscle degradation.

Metformin Pre-Treatment as a Means of Mitigating Disuse-Induced Rat Soleus Muscle Wasting

Currently, no ideal treatment exists to combat skeletal muscle disuse-induced atrophy and loss of strength. Because the activity of AMP-activated protein kinase (AMPK) in rat soleus muscle is suppressed at the early stages of disuse, we hypothesized that pre-treatment of rats with metformin (an AMPK activator) would exert beneficial effects on skeletal muscle during disuse. Muscle disuse was performed via hindlimb suspension (HS). Wistar rats were divided into four groups: (1) control (C), (2) control + metformin for 10 days (C+Met), (3) HS for 7 days (HS), (4) metformin treatment for 7 days before HS and during the first 3 days of 1-week HS (HS+Met). Anabolic and catabolic markers were assessed using WB and RT-PCR. Treatment with metformin partly prevented an HS-induced decrease in rat soleus weight and size of slow-twitch fibers. Metformin prevented HS-related slow-to-fast fiber transformation. Absolute soleus muscle force in the HS+Met group was increased vs. the HS group. GSK-3β (Ser9) phosphorylation was significantly increased in the HS+Met group vs. the HS group. Metformin pre-treatment partly prevented HS-induced decrease in 18S+28S rRNA content and attenuated upregulation of calpain-1 and ubiquitin. Thus, pre-treatment of rats with metformin can ameliorate disuse-induced reductions in soleus muscle weight, the diameter of slow-type fibers, and absolute muscle strength.

Insights into Pathogenesis, Nutritional and Drug Approach in Sarcopenia: A Systematic Review

Sarcopenia is a multifactorial condition related to the loss of muscle mass and strength due to aging, eating habits, physical inactivity, or even caused by another disease. Affected individuals have a higher risk of falls and may be associated with heart disease, respiratory diseases, cognitive impairment, and consequently an increased risk of hospitalization, in addition to causing an economic impact due to the high cost of care during the stay in hospitals. The standardization of appropriate treatment for patients with sarcopenia that could help reduce pathology-related morbidity is necessary. For these reasons, this study aimed to perform a systematic review of the role of nutrition and drugs that could ameliorate the health and quality of life of sarcopenic patients and PRISMA guidelines were followed. Lifestyle interventions have shown a profound impact on sarcopenia treatment but using supplements and different drugs can also impact skeletal muscle maintenance. Creatine, leucine, branched-chain amino acids, omega 3, and vitamin D can show benefits. Although with controversial results, medications such as Metformin, GLP-1, losartan, statin, growth hormone, and dipeptidyl peptidase 4 inhibitors have also been considered and can alter the sarcopenic's metabolic parameters, protect against cardiovascular diseases and outcomes, while protecting muscles.

Metformin reduces myogenic contracture and myofibrosis induced by rat knee joint immobilization via AMPK-mediated inhibition of TGF-β1/Smad signaling pathway

PURPOSE

The two structural components contributing to joint contracture formation are myogenic and arthrogenic contracture, and myofibrosis is an important part of myogenic contracture. Myofibrosis is a response to long-time immobilization and is described as a condition with excessive deposition of endomysial and perimysial connective tissue components in skeletal muscle. The purpose of this study was to confirm whether metformin can attenuate the formation of myogenic contracture and myofibrosis through the phosphorylation level of adenosine monophosphate-activated protein kinase (AMPK) and inhabitation of subsequent transforming growth factor beta (TGF-β) 1/Smad signaling pathway.

MATERIALS AND METHODS

An immobilized rat model was used to determine whether metformin could inhibit myogenic contracture and myofibrosis. The contents of myogenic contracture of knee joint was calculated by measuring instrument of range of motion (ROM), and myofibrosis of rectus femoris were determined by ultrasound shear wave elastography and Masson staining. Protein expression of AMPK and subsequent TGF-β1/Smad signaling pathway were determined by western blot. Subsequently, Compound C, a specific AMPK inhibitor, was used to further clarify the role of the AMPK-mediated inhibition of TGF-β1/Smad signaling pathway.

RESULTS

We revealed that the levels of myogenic contracture and myofibrosis were gradually increased during immobilization, and overexpression of TGF-β1-induced formation of myofibrosis by activating Smad2/3 phosphorylation. Activation of AMPK by metformin suppressed overexpression of TGF-β1 and TGF-β1-induced Smad2/3 phosphorylation, further reducing myogenic contracture and myofibrosis during immobilization. In contrast, inhibition of AMPK by Compound C partially counteracted the inhibitory effect of TGF-β1/Smad signaling pathway by metformin.

CONCLUSION

Notably, we first illustrated the therapeutic effect of metformin through AMPK-mediated inhibition of TGF-β1/Smad signaling pathway in myofibrosis, which may provide a new therapeutic strategy for myogenic contracture.

Potential Therapeutic Strategies for Skeletal Muscle Atrophy

The maintenance of muscle homeostasis is vital for life and health. Skeletal muscle atrophy not only seriously reduces people's quality of life and increases morbidity and mortality, but also causes a huge socioeconomic burden. To date, no effective treatment has been developed for skeletal muscle atrophy owing to an incomplete understanding of its molecular mechanisms. Exercise therapy is the most effective treatment for skeletal muscle atrophy. Unfortunately, it is not suitable for all patients, such as fractured patients and bedridden patients with nerve damage. Therefore, understanding the molecular mechanism of skeletal muscle atrophy is crucial for developing new therapies for skeletal muscle atrophy. In this review, PubMed was systematically screened for articles that appeared in the past 5 years about potential therapeutic strategies for skeletal muscle atrophy. Herein, we summarize the roles of inflammation, oxidative stress, ubiquitin-proteasome system, autophagic-lysosomal pathway, caspases, and calpains in skeletal muscle atrophy and systematically expound the potential drug targets and therapeutic progress against skeletal muscle atrophy. This review focuses on current treatments and strategies for skeletal muscle atrophy, including drug treatment (active substances of traditional Chinese medicine, chemical drugs, antioxidants, enzyme and enzyme inhibitors, hormone drugs, etc.), gene therapy, stem cell and exosome therapy (muscle-derived stem cells, non-myogenic stem cells, and exosomes), cytokine therapy, physical therapy (electroacupuncture, electrical stimulation, optogenetic technology, heat therapy, and low-level laser therapy), nutrition support (protein, essential amino acids, creatine, β-hydroxy-β-methylbutyrate, and vitamin D), and other therapies (biomaterial adjuvant therapy, intestinal microbial regulation, and oxygen supplementation). Considering many treatments have been developed for skeletal muscle atrophy, we propose a combination of proper treatments for individual needs, which may yield better treatment outcomes.

Exposure to High Altitude Promotes Loss of Muscle Mass That Is Not Rescued by Metformin

Fullerton, Zackery S., Benjamin D. McNair, Nicholas A. Marcello, Emily E. Schmitt, and Danielle R. Bruns. Exposure to high altitude promotes loss of muscle mass that is not rescued by metformin. High Alt Med Biol. 23:215-222, 2022. Background: Exposure to high altitude (HA) causes muscle atrophy. Few therapeutic interventions attenuate muscle atrophy; however, the diabetic drug, metformin (Met), has been suggested as a potential therapeutic to preserve muscle mass with aging and obesity-related atrophy. The purpose of the present study was to test the hypothesis that HA would induce muscle atrophy that could be attenuated by Met. Methods: C57Bl6 male and female mice were exposed to simulated HA (∼5,200 m) for 4 weeks, while control (Con) mice remained at resident altitude (∼2,180 m). Met was administered in drinking water at 200 mg/(kg·day). We assessed muscle mass, myocyte cell size, muscle and body composition, and expression of molecular mediators of atrophy. Results: Mice exposed to HA were leaner and had a smaller hind limb complex (HLC) mass than Con mice. Loss of HLC mass and myocyte size were not attenuated by Met. Molecular markers for muscle atrophy were activated at HA in a sex-dependent manner. While the atrophic regulator, atrogin, was unchanged at HA or with Met, myostatin expression was upregulated at HA. In female mice, Met further stimulated myostatin expression. Conclusions: Although HA exposure resulted in loss of muscle mass, particularly in male mice, Met did not attenuate muscle atrophy. Identification of other interventions to preserve muscle mass during ascent to HA is warranted.

Metformin use is associated with a lower risk of rotator cuff disease in patients with type 2 diabetes mellitus

AIMS

- Metformin has been mentioned to be protective against inflammation, degeneration, and oxidative stress, conditions that are associated with rotator cuff disease. To access the association between metformin use and risk of rotator cuff disease in patients with type 2 diabetes mellitus (DM).

METHODS

- This was a retrospective cohort study utilizing Taiwan National Health Insurance Research Database between January 1, 2000, and December 31, 2012 to retrieved participants. Metformin and propensity score matched never metformin users were determined at baseline (between the date of onset of DM and the index date), and followed to December 31, 2013. Propensity scores were adopted to address measurable confounders (including demographic variables, Diabetes Complications Severity Index, and relevant comorbidities and co-medication). A multivariable Cox proportional hazards regression model was applied to estimate the adjusted hazard ratios (HRs) for the risk of the first diagnosis of rotator cuff disease on the full cohort and on the propensity score matched cohort.

RESULTS

- In the propensity score matched cohort, a total of 34,964 individuals (19,416 [55.5%] men), 17,482 individuals were taking metformin, 559 [3.2%] of whom developed rotator cuff disease. Incidence of rotator cuff disease was 4.51 per 10,000 person-months in the metformin users and 5.11 in the controls. Among metformin group, the aHR (95% CI) was 0.879 (0.784-0.984) after full adjustment. The potential beneficial effect on the risk of rotator cuff disease was consistently observed across all subgroups, including sex, age, concomitant other glucose lowering drugs, and level of Diabetes Complications Severity Index (all P for interaction > 0.050).

CONCLUSION

- Metformin use was associated with a lower risk of rotator cuff disease in patients with type 2 DM.

Sarcopenia, frailty and type 2 diabetes mellitus (Review)

Skeletal muscle is the largest and most energy‑consuming organ in the human body, which plays an important role in energy metabolism and glucose uptake. There is a notable decrease in glucose uptake in the skeletal muscle of patients with type 2 diabetes mellitus (DM). Endurance exercise can reduce hyperglycemia and improve insulin resistance in patients with type 2 DM. Insulin exerts a variety of effects, many of which are mediated by Akt, including increasing glucose uptake, promoting glycogen synthesis and inhibiting glycogen degradation, increasing free fatty acid uptake, increasing protein synthesis, promoting muscle hypertrophy and inhibiting protein degradation. Skeletal muscle mass progressively declines with aging, resulting in loss of muscle strength and physical function. Sarcopenia is a syndrome characterized by loss of skeletal muscle mass and muscle weakness or loss of physical function, and frailty is another syndrome that has received great interest in recent years. Decreased organ function results in vulnerability to external stress. Frailty is associated with falls, fractures and hospitalization; however, there is the reversibility of returning to a healthy state with appropriate interventions. Frailty is classified into three subgroups: Physical frailty, social frailty and cognitive frailty, whereby sarcopenia is the main component of physical frailty. The present review discusses the associations between sarcopenia, frailty and type 2 DM based on current evidence.

Chronic intermittent hypoxia aggravates skeletal muscle aging by down-regulating Klc1/grx1 expression via Wnt/β-catenin pathway

OBJECTIVE

Sleep breathing disorder may affect skeletal muscle decline in the elderly, but the mechanism is not clear. Therefore, this study explores the mechanism of skeletal muscle aging in chronic intermittent hypoxia (CIH) rats.

METHODS

In vitro and in vivo CIH models were constructed in L6 cells and SD rats by treating chronic intermittent hypoxia. Pathological changes of skeletal muscle in vivo were measured by hematoxylin-eosin (HE) staining. Cell proliferation and apoptosis were detected by CCK-8 and Flow cytometer, respectively. The expression of KLC1/GRX1 and the proteins related to the Wnt/β-catenin pathway were measured by qRT-PCR and western blot.

RESULTS

CIH model was successfully established induced by chronic intermittent hypoxia with lower skeletal muscle index (SMI), increased inward migration of muscle fiber cell nucleus, and muscle cells' distance. The results showed that Wnt/β-catenin signalling was activatedin both L6 cells and CIH rats' model. KLC1 and GRX1 were significantly downregulated in the CIH model. Loss of function showed that downregulation of KLC1 promoted L6 cell and skeletal muscle aging in vitro and in vivo, respectively.

CONCLUSION

Our results demonstrated that CIH aggravated skeletal muscle aging by down-regulating KLC1/GRX1 expression via the Wnt/β-catenin pathway.