β-Hydroxy β-methylbutyrate improves dexamethasone-induced muscle atrophy by modulating the muscle degradation pathway in SD rat

β-hydroxy-β-methylbutyrate Attenuates Age-Dependent Loss of Flight Ability and Extends Lifespan in Drosophila

β-hydroxy-β-methylbutyrate (HMB) has been shown to enhance muscle function and strength in older humans and rodents after periods of consumption extending for several weeks. We investigated the feasibility of utilizing Drosophila as a model organism to study the biological effects of HMB on aging muscle when consumed throughout adult life. Using flight ability as an index of flight muscle function, we found that HMB attenuates the age-dependent decline in flight ability. Male and female flies fed a diet supplemented with 10 mg/mL HMB had significantly higher flight scores from median age until the onset of flight senescence than control flies fed a standard diet. HMB supplementation also resulted in improved flight scores in males before median age and delayed the onset of flight senescence in females. Notably, the consumption of HMB throughout adult life increased the rate of survival and extended lifespan. The effect on lifespan did not result from changes in food consumption or body weight. Old flies on the HMB-supplemented diet retained a higher proportion of flight muscle mitochondria whose morphology resembled that of young flies than the control diet group. Together, these results suggest that HMB attenuates the age-dependent decline in flight ability and prolongs lifespan by enhancing muscle health.

Does β-Hydroxy-β-Methylbutyrate Have Any Potential to Support the Treatment of Duchenne Muscular Dystrophy in Humans and Animals?

Skeletal muscle is the protein reservoir of our body and an important regulator of glucose and lipid homeostasis. The dystrophin gene is the largest gene and has a key role in skeletal muscle construction and function. Mutations in the dystrophin gene cause Duchenne and Becker muscular dystrophy in humans, mice, dogs, and cats. Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular condition causing progressive muscle weakness and premature death. β-hydroxy β-methylbutyrate (HMB) prevents deleterious muscle responses under pathological conditions, including tumor and chronic steroid therapy-related muscle losses. The use of HMB as a dietary supplement allows for increasing lean weight gain; has a positive immunostimulatory effect; is associated with decreased mortality; and attenuates sarcopenia in elderly animals and individuals. This study aimed to identify some genes, metabolic pathways, and biological processes which are common for DMD and HMB based on existing literature and then discuss the consequences of that interaction.

Mechanism for exercise-mediated prevention against muscle wasting on extensor digitorum longus muscle in Spontaneously Diabetic Torii fatty rats

We previously reported the significant increase in limb muscle strength and cross-sectional area of the type IIb muscle fibers in the extensor digitorum longus (EDL) muscle in a type 2 diabetic animal model, with Spontaneously Diabetic Torii (SDT) fatty rats (n = 6) undergoing regular treadmill exercise from 8 to 16 weeks of age compared with sedentary SDT fatty rats (n = 6). This study investigated the mechanism by which exercise training prevented skeletal muscle wasting in the EDL muscle of the SDT fatty rats. The endurance exercise for 8 weeks downregulated the expression of muscle RING-finger protein-1 (an E3 ubiquitin ligase) and upregulated the expression of CD31, insulin receptor substrate-2, and phosphorylated endothelial nitric oxide synthase in the EDL muscle of 16-week-old SDT fatty rats.Endurance exercise training might reduce muscle wasting by preventing muscle degradation and increasing the angiogenic response in the EDL muscle in type 2 diabetes.

The Preventive Effect of Specific Collagen Peptides against Dexamethasone-Induced Muscle Atrophy in Mice

Muscle atrophy, also known as muscle wasting, is the thinning of muscle mass due to muscle disuse, aging, or diseases such as cancer or neurological problems. Muscle atrophy is closely related to the quality of life and has high morbidity and mortality. However, therapeutic options for muscle atrophy are limited, so studies to develop therapeutic agents for muscle loss are always required. For this study, we investigated how orally administered specific collagen peptides (CP) affect muscle atrophy and elucidated its molecular mechanism using an in vivo model. We treated mice with dexamethasone (DEX) to induce a muscular atrophy phenotype and then administered CP (0.25 and 0.5 g/kg) for four weeks. In a microcomputed tomography analysis, CP (0.5 g/kg) intake significantly increased the volume of calf muscles in mice with DEX-induced muscle atrophy. In addition, the administration of CP (0.25 and 0.5 g/kg) restored the weight of the gluteus maximus and the fiber cross-sectional area (CSA) of the pectoralis major and calf muscles, which were reduced by DEX. CP significantly inhibited the mRNA expression of myostatin and the phosphorylation of Smad2, but it did not affect TGF-β, BDNF, or FNDC5 gene expression. In addition, AKT/mTOR, a central pathway for muscle protein synthesis and related to myostatin signaling, was enhanced in the groups that were administered CP. Finally, CP decreased serum albumin levels and increased TNF-α gene expression. Collectively, our in vivo results demonstrate that CP can alleviate muscle wasting through a multitude of mechanisms. Therefore, we propose CP as a supplement or treatment to prevent muscle atrophy.

Perioperative Oral β-Hydroxy-β-Methylbutyrate Supplementation Ameliorates Sarcopenia in Rats Undergoing Major Hepatectomy

β-Hydroxy-β-methylbutyrate (HMB), a metabolite of leucine, is known to increase muscle mass and strength. However, the effect of perioperative HMB supplementation in liver surgery is unclear. Moreover, the impact of HMB on the skeletal muscle fiber type also remains unclear. We investigated the impact of HMB on the body composition and skeletal muscle fiber type in sarcopenic rats undergoing major hepatectomy. Nine-week-old male F344/NSlc rats were maintained in hindlimb suspension (HLS) and were forcedly supplemented with HMB calcium salt (HMB-Ca, 0.58 g/kg×2 times) or distilled water in addition to free feeding. After 2 wk of HLS, the rats underwent 70% hepatectomy and were sacrificed 3 d after surgery. Body composition factors and the proportion of slow-twitch fibers in hindlimb muscles were evaluated. HMB maintained the body composition and hindlimb force and acted against their deterioration in sarcopenic rats, exerting a particular effect on lean mass weight, which was significant. In the histological study, HMB significantly increased the proportion of slow-twitch fibers in the soleus (p=0.044) and plantaris (p=0.001) of sarcopenic rats. HMB ameliorated deterioration of the body composition and increased the proportion of slow-twitch fibers in sarcopenic rats undergoing major hepatectomy.

Targeting Hydrogen Sulfide Modulates Dexamethasone-Induced Muscle Atrophy and Microvascular Rarefaction, through Inhibition of NOX4 and Induction of MGF, M2 Macrophages and Endothelial Progenitors

Long-term use of Glucocorticoids produces skeletal muscle atrophy and microvascular rarefaction. Hydrogen sulfide (H2S) has a potential role in skeletal muscle regeneration. However, the mechanisms still need to be elucidated. This is the first study to explore the effect of Sodium hydrosulfide (NaHS) H2S donor, against Dexamethasone (Dex)-induced soleus muscle atrophy and microvascular rarefaction and on muscle endothelial progenitors and M2 macrophages. Rats received either; saline, Dex (0.6 mg/Kg/day), Dex + NaHS (5 mg/Kg/day), or Dex + Aminooxyacetic acid (AOAA), a blocker of H2S (10 mg/Kg/day) for two weeks. The soleus muscle was examined for contractile properties. mRNA expression for Myostatin, Mechano-growth factor (MGF) and NADPH oxidase (NOX4), HE staining, and immunohistochemical staining for caspase-3, CD34 (Endothelial progenitor marker), vascular endothelial growth factor (VEGF), CD31 (endothelial marker), and CD163 (M2 macrophage marker) was performed. NaHS could improve the contractile properties and decrease oxidative stress, muscle atrophy, and the expression of NOX4, caspase-3, Myostatin, VEGF, and CD31 and could increase the capillary density and expression of MGF with a significant increase in expression of CD34 and CD163 as compared to Dex group. However, AOAA worsened the studied parameters. Therefore, H2S can be a promising target to attenuate muscle atrophy and microvascular rarefaction.

Nutrients against Glucocorticoid-Induced Muscle Atrophy

Glucocorticoid excess is a critical factor contributing to muscle atrophy. Both endogenous and exogenous glucocorticoids negatively affect the preservation of muscle mass and function. To date, the most effective intervention to prevent muscle atrophy is to apply a mechanical load in the form of resistance exercise. However, glucocorticoid-induced skeletal muscle atrophy easily causes fatigue in daily physical activities, such as climbing stairs and walking at a brisk pace, and reduces body movements to cause a decreased ability to perform physical activity. Therefore, providing adequate nutrients in these circumstances is a key factor in limiting muscle wasting and improving muscle mass recovery. The present review will provide an up-to-date review of the effects of various nutrients, including amino acids such as branched-chain amino acids (BCAAs) and β–hydroxy β–methylbutyrate (HMB), fatty acids such as omega-3, and vitamins and their derivates on the prevention and improvement of glucocorticoid-induced muscle atrophy.

The Effect of Long-Lasting Swimming on Rats Skeletal Muscles Energy Metabolism after Nine Days of Dexamethasone Treatment

This study investigates the effect of Dexamethasone (Dex) treatment on blood and skeletal muscle metabolites level and skeletal muscle activity of enzymes related to energy metabolism after long-duration swimming. To evaluate whether Dex treatment, swimming, and combining these factors act on analyzed data, rats were randomly divided into four groups: saline treatment non-exercise and exercise and Dex treatment non-exercised and exercised. Animals in both exercised groups underwent long-lasting swimming. The concentration of lipids metabolites, glucose, and lactate were measured in skeletal muscles and blood according to standard colorimetric and fluorimetric methods. Also, activities of enzymes related to aerobic and anaerobic metabolism were measured in skeletal muscles. The results indicated that Dex treatment induced body mass loss and increased lipid metabolites in the rats' blood but did not alter these changes in skeletal muscles. Interestingly, prolonged swimming applied after 9 days of Dex treatment significantly intensified changes induced by Dex; however, there was no difference in skeletal muscle enzymatic activities. This study shows for the first time the cumulative effect of exercise and Dex on selected elements of lipid metabolism, which seems to be essential for the patient's health due to the common use of glucocorticoids like Dex.

Organ-differential Roles of Akt/FoxOs Axis as a Key Metabolic Modulator during Aging

FoxOs and their post-translational modification by phosphorylation, acetylation, and methylation can affect epigenetic modifications and promote the expression of downstream target genes. Therefore, they ultimately affect cellular and biological functions during aging or occurrence of age-related diseases including cancer, diabetes, and kidney diseases. As known for its key role in aging, FoxOs play various biological roles in the aging process by regulating reactive oxygen species, lipid accumulation, and inflammation. FoxOs regulated by PI3K/Akt pathway modulate the expression of various target genes encoding MnSOD, catalases, PPARγ, and IL-1β during aging, which are associated with age-related diseases. This review highlights the age-dependent differential regulatory mechanism of Akt/FoxOs axis in metabolic and non-metabolic organs. We demonstrated that age-dependent suppression of Akt increases the activity of FoxOs (Akt/FoxOs axis upregulation) in metabolic organs such as liver and muscle. This Akt/FoxOs axis could be modulated and reversed by antiaging paradigm calorie restriction (CR). In contrast, hyperinsulinemia-mediated PI3K/Akt activation inhibited FoxOs activity (Akt/FoxOs axis downregulation) leading to decrease of antioxidant genes expression in non-metabolic organs such as kidneys and lungs during aging. These phenomena are reversed by CR. The results of studies on the process of aging and CR indicate that the Akt/FoxOs axis plays a critical role in regulating metabolic homeostasis, redox stress, and inflammation in various organs during aging process. The benefical actions of CR on the Akt/FoxOs axis in metabolic and non-metabolic organs provide further insights into the molecular mechanisms of organ-differential roles of Akt/FoxOs axis during aging.

Curcuma longa L. Water Extract Improves Dexamethasone-Induced Sarcopenia by Modulating the Muscle-Related Gene and Oxidative Stress in Mice

Dexamethasone (DEX) promotes proteolysis, which causes muscle atrophy. Muscle atrophy is connected to sarcopenia. We evaluated the effect of Curcuma longa L. water extract (CLW) on DEX-induced muscle atrophy. ICR mice were divided into three groups (eight mice per group) to investigate the capability of CLW in inhibiting muscle atrophy. The control group (Ex-CON) was administered distilled water (DW) by gavage and subjected to exercise; the muscle atrophy group (Ex-DEX) was administered DW by gavage, an injection of DEX (1 mg/kg body weight/day) intraperitoneally (IP), and subjected to exercise; and the treatment group (Ex-CLW) was administered CLW (1 g/kg body weight/day) by gavage, DEX IP injection, and subjected to exercise. Following the injection of DEX, the expression levels of myostatin, MuRF-1, and Atrogin-1 were increased. However, these expression levels were decreased in the Ex-CLW group, thereby leading to the conclusion that CLW inhibits muscle atrophy. ROS (that was overproduced by DEX) decreased antioxidant enzyme activity and increased malondialdehyde (MDA) levels, which led to muscle atrophy. When CLW was ingested, the antioxidant enzyme activities increased while the MDA levels decreased. These findings suggest that CLW could serve as a natural product for the prevention of muscle atrophy by modulating muscle atrophy-related genes and increasing antioxidant potential.

Integrated analysis of long non-coding RNAs (lncRNAs) and mRNA expression profiles identifies lncRNA PRKG1-AS1 playing important roles in skeletal muscle aging

This study aimed to identify long non-coding RNAs (lncRNAs) involving in the skeletal muscle aging process. Skeletal muscle samples from old and young subjects were collected for lncRNA-sequencing. Differentially expressed genes (DEGs) and DElncRNAs between young and old groups were identified and a co-expression network was built. Further, a dexamethasone-induced muscle atrophy cell model was established to characterize the function of a critical lncRNA. A total of 424 DEGs, including 271 upregulated genes and 153 downregulated genes as well as 152 DElncRNAs including 76 up-regulated and 76 down-regulated lncRNAs were obtained. Functional analysis demonstrated that the DEGs were significantly related to immune response. Coexpression network demonstrated lncRNA AC004797.1, PRKG1-AS1 and GRPC5D-AS1 were crucial lncRNAs. Their expressions were further validated by qRT-PCR in human skeletal muscle and the muscle atrophy cell model. Further in vitro analysis suggested that knock-down of PRKG1-AS1 could significantly increase cell viability and decrease cell apoptosis. qRT-PCR and western blot analyses demonstrated that knock-down of PRKG1-AS1 could increase the expression of MyoD, MyoG and Mef2c. This study demonstrated that lncRNAs of GPRC5D-AS1, AC004797.1 and PRKG1-AS1 might involve the aging-associated disease processes.

Dose-dependent and time-dependent metabolic, hemodynamic, and redox disturbances in dexamethasone-treated Wistar rats

OBJECTIVES

Dexamethasone is used experimentally to induce insulin resistance and type 2 diabetes. However, data concerning the dose, the duration of treatment, and the associated comorbidities are inconsistent. The aim of this study was to compare the effects of different doses of dexamethasone and the duration of treatment necessary for the development of a model of insulin resistance that mimics the clinical condition with the associated comorbidities.

METHODS

Dexamethasone was administered intramuscularly to male Wistar rats, at doses of 500 and 1,000 µg/kg/day for the subchronic treatment (eight consecutive days) and at doses of 5, 25, 50, and 100 µg/kg/day in chronic treatment (28 consecutive days). Effects on body weight, metabolism, hemodynamics, renal function, and redox status were evaluated.

RESULTS

Both treatments induced a progressive body weight loss that was drastic in subchronic treatment, improved glucose tolerance without affecting fasting glycemia. Doses of 1,000 and 100 µg/kg were associated with hypertriglyceridemia, hypertension, and increased heart rate, cardiac and renal hypertrophy. Increased creatinemia associated with reduced creatinuria were observed in sub-chronic treatment while increased proteinuria and reduced creatinuria were noticed in chronic treatment. 1,000 µg/kg dexamethasone caused an increase in hepatic, and renal malondialdehyde (MDA) and glutathione (GSH) coupled with a reduction in catalase activity. The dose of 100 µg/kg induced a rise in GSH and catalase activity but reduced MDA levels in the kidney.

CONCLUSIONS

Doses of 1,000 µg/kg for subchronic and 100 µg/kg for chronic treatment exhibited similar effects and are the best doses to respective time frames to induce the model.

Ubiquitin Ligases at the Heart of Skeletal Muscle Atrophy Control

Skeletal muscle loss is a detrimental side-effect of numerous chronic diseases that dramatically increases mortality and morbidity. The alteration of protein homeostasis is generally due to increased protein breakdown while, protein synthesis may also be down-regulated. The ubiquitin proteasome system (UPS) is a master regulator of skeletal muscle that impacts muscle contractile properties and metabolism through multiple levers like signaling pathways, contractile apparatus degradation, etc. Among the different actors of the UPS, the E3 ubiquitin ligases specifically target key proteins for either degradation or activity modulation, thus controlling both pro-anabolic or pro-catabolic factors. The atrogenes MuRF1/TRIM63 and MAFbx/Atrogin-1 encode for key E3 ligases that target contractile proteins and key actors of protein synthesis respectively. However, several other E3 ligases are involved upstream in the atrophy program, from signal transduction control to modulation of energy balance. Controlling E3 ligases activity is thus a tempting approach for preserving muscle mass. While indirect modulation of E3 ligases may prove beneficial in some situations of muscle atrophy, some drugs directly inhibiting their activity have started to appear. This review summarizes the main signaling pathways involved in muscle atrophy and the E3 ligases implicated, but also the molecules potentially usable for future therapies.

Enriched environment ameliorates dexamethasone effects on emotional reactivity and metabolic parameters in mice

Convincing evidence shows that stress is associated with the development and course of psychiatric and metabolic disorders. The hypothalamic-pituitary-adrenal (HPA) axis mediates the stress response, a cascade of events that culminate in the release of glucocorticoids from the adrenal cortex. Chronic hypercortisolism typically characterizes stress-related illnesses, such as depression, anxiety, and metabolic syndrome. Considering previous studies pointing that environmental enrichment (EE) mitigates the deleterious effects of stress on neurobiological systems, we hypothesized that EE can confer resiliency against prolonged glucocorticoid administration-induced behavioral and metabolic alterations in mice. In this regard, three-month-old male Swiss mice were exposed to a four-week period of standard environment (SE) or EE. After this period, still in the respective environments, dexamethasone was administered intraperitoneally (i.p.) at a dose of 4 mg/kg, for 21 consecutive days, in order to generate the emotional-related behavioral outcomes, as previously described. It is demonstrated herein that EE prevents the dexamethasone-induced anxiety-like and passive stress-coping behaviors, as observed in the open field and tail suspension tests. Moreover, EE mitigated the hyperproteinemia and body weight loss induced by excess dexamethasone and decreased basal glucose levels. Taken together, these results support the hypothesis that EE attenuates the effects of chronic administration of synthetic glucocorticoids in mice, a strategy that may be translated to the clinical perspective.

Emerging Strategies Targeting Catabolic Muscle Stress Relief

Skeletal muscle wasting represents a common trait in many conditions, including aging, cancer, heart failure, immobilization, and critical illness. Loss of muscle mass leads to impaired functional mobility and severely impedes the quality of life. At present, exercise training remains the only proven treatment for muscle atrophy, yet many patients are too ill, frail, bedridden, or neurologically impaired to perform physical exertion. The development of novel therapeutic strategies that can be applied to an in vivo context and attenuate secondary myopathies represents an unmet medical need. This review discusses recent progress in understanding the molecular pathways involved in regulating skeletal muscle wasting with a focus on pro-catabolic factors, in particular, the ubiquitin-proteasome system and its activating muscle-specific E3 ligase RING-finger protein 1 (MuRF1). Mechanistic progress has provided the opportunity to design experimental therapeutic concepts that may affect the ubiquitin-proteasome system and prevent subsequent muscle wasting, with novel advances made in regards to nutritional supplements, nuclear factor kappa-light-chain-enhancer of activated B cells (NFB) inhibitors, myostatin antibodies, β2 adrenergic agonists, and small-molecules interfering with MuRF1, which all emerge as a novel in vivo treatment strategies for muscle wasting.

Regulation of Skeletal Muscle Function by Amino Acids

Amino acids are components of proteins that also exist free-form in the body; their functions can be divided into (1) nutritional, (2) sensory, and (3) biological regulatory roles. The skeletal muscle, which is the largest organ in the human body, representing ~40% of the total body weight, plays important roles in exercise, energy expenditure, and glucose/amino acid usage—processes that are modulated by various amino acids and their metabolites. In this review, we address the metabolism and function of amino acids in the skeletal muscle. The expression of PGC1α, a transcriptional coactivator, is increased in the skeletal muscle during exercise. PGC1α activates branched-chain amino acid (BCAA) metabolism and is used for energy in the tricarboxylic acid (TCA) cycle. Leucine, a BCAA, and its metabolite, β-hydroxy-β-methylbutyrate (HMB), both activate mammalian target of rapamycin complex 1 (mTORC1) and increase protein synthesis, but the mechanisms of activation appear to be different. The metabolite of valine (another BCAA), β-aminoisobutyric acid (BAIBA), is increased by exercise, is secreted by the skeletal muscle, and acts on other tissues, such as white adipose tissue, to increase energy expenditure. In addition, several amino acid-related molecules reportedly activate skeletal muscle function. Oral 5-aminolevulinic acid (ALA) supplementation can protect against mild hyperglycemia and help prevent type 2 diabetes. β-alanine levels are decreased in the skeletal muscles of aged mice. β-alanine supplementation increased the physical performance and improved the executive function induced by endurance exercise in middle-aged individuals. Further studies focusing on the effects of amino acids and their metabolites on skeletal muscle function will provide data essential for the production of food supplements for older adults, athletes, and individuals with metabolic diseases.

Suppression of protein degradation by leucine requires its conversion to β-hydroxy-β-methyl butyrate in C2C12 myotubes

The aims of this study were to investigate whether the inhibitory effect of Leucine (Leu) on starvation-induced protein degradation was mediated by its metabolite β-hydroxy-β-methyl butyrate (HMB), and to explore the mechanisms involved. The results showed that the beneficial effects of Leu on protein degradation and the oxygen consumption rate (OCR) of cells were observed at low levels (0.5 mM) rather than at high levels (10 mM). However, these effects were inferior to those of HMB. Moreover, HMB was able to increase/decrease the proportion of MyHC I/MyHC IIb protein expression, respectively. In these KICD-transfected cells, Leu was approximately as effective as HMB in inhibiting protein degradation and increasing the OCR as well as MyHC I protein expression of cells, and these effects of Leu were reverted to a normal state by mesotrione, a specific suppressor of KICD. In conclusion, HMB seems to be an active metabolite of Leu to suppress muscle protein degradation in a starvation model, and the mechanisms may be associated with improved mitochondrial oxidative capacity in muscle cells.

Small-molecule-mediated chemical knock-down of MuRF1/MuRF2 and attenuation of diaphragm dysfunction in chronic heart failure

BACKGROUND

Chronic heart failure (CHF) leads to diaphragm myopathy that significantly impairs quality of life and worsens prognosis. In this study, we aimed to assess the efficacy of a recently discovered small-molecule inhibitor of MuRF1 in treating CHF-induced diaphragm myopathy and loss of contractile function.

METHODS

Myocardial infarction was induced in mice by ligation of the left anterior descending coronary artery. Sham-operated animals (sham) served as controls. One week post-left anterior descending coronary artery ligation animals were randomized into two groups-one group was fed control rodent chow, whereas the other group was fed a diet containing 0.1% of the compound ID#704946-a recently described MuRF1-interfering small molecule. Echocardiography confirmed development of CHF after 10 weeks. Functional and molecular analysis of the diaphragm was subsequently performed.

RESULTS

Chronic heart failure induced diaphragm fibre atrophy and contractile dysfunction by ~20%, as well as decreased activity of enzymes involved in mitochondrial energy production (P < 0.05). Treatment with compound ID#704946 in CHF mice had beneficial effects on the diaphragm: contractile function was protected, while mitochondrial enzyme activity and up-regulation of the MuRF1 and MuRF2 was attenuated after infarct.

CONCLUSIONS

Our murine CHF model presented with diaphragm fibre atrophy, impaired contractile function, and reduced mitochondrial enzyme activities. Compound ID#704946 rescued from this partially, possibly by targeting MuRF1/MuRF2. However, at this stage of our study, we refrain to claim specific mechanism(s) and targets of compound ID#704946, because the nature of changes after 12 weeks of feeding is likely to be complex and is not necessarily caused by direct mechanistic effects.

Beta-hydroxy beta-methyl butyrate decreases muscle protein degradation via increased Akt/FoxO3a signaling and mitochondrial biogenesis in weanling piglets after lipopolysaccharide challenge

The aim of this study was to investigate the effects of dietary β-hydroxy-β-methylbutyrate (HMB) on lipopolysaccharide (LPS)-induced muscle atrophy and to investigate the mechanisms involved. Sixty pigs (21 ± 2 days old, 5.86 ± 0.18 kg body weight) were used in a 2 × 3 factorial design and the main factors included diet (0, 0.60%, or 1.20% HMB) and immunological challenge (LPS or saline). After 15 d of treatment with LPS and/or HMB, growth performance, blood parameters, and muscle protein degradation rate were measured. The results showed that in LPS-injected pigs, 0.60% HMB supplementation increased the average daily gain and average daily feed intake and decreased the feed : gain ratio (P < 0.05), with a concurrent increase of lean percentage. Moreover, 0.60% HMB supplementation decreased the serum concentrations of blood urea nitrogen, IL-1β, and TNF-α and the rate of protein degradation as well as cell apoptosis in selected muscles (P < 0.05). In addition, dietary HMB supplementation (0.60%) regulated the expression of genes involved in mitochondrial biogenesis and increased the phosphorylation of Akt and Forkhead Box O3a (FoxO3a) in selected muscles, accompanied by decreased protein expression of muscle RING finger 1 and muscle atrophy F-box. These results indicate that HMB may exert protective effects against LPS-induced muscle atrophy by normalizing the Akt/FoxO3a axis that regulates ubiquitin proteolysis and by improving mitochondrial biogenesis.

Alpha lipoic acid protects against dexamethasone-induced metabolic abnormalities via APPL1 and PGC-1 α up regulation

BACKGROUND

Glucocorticoids (GCs) have various uses in the medicine in different specialties. However, GCs administration is usually accompanying with multiple side effects such as hyperglycemia and hyperlipidemia. Alpha lipoic acid (ALA) has been documented to posse anti-diabetic properties.

AIM OF THE STUDY

this study highlights the role of ALA in avoiding dexamethasone induced metabolic disturbance.

MATERIALS & METHODS

30 rats were randomly divided into 5 groups: Group (1): Control group; Groups 3, 4, and 5: rats received dexamethasone 1 mg/kg/day for 10 days; Groups 2, 4, and 5: Rats received ALA 100 mg/kg/day all the duration of the study, 2 weeks before dexamethasone, or concomitant with dexamethasone respectively. For each rat, we collected blood samples for measurement of glucose, lipid profiles, adiponectin, irisin, and Phosphoinositide 3-kinase (PI3K). We also isolated gastrocnemius muscles for measurement of insulin receptor substrate-1(IRS-1), peroxisome proliferator-activated receptor γ coactivator 1 α(PGC1-α), and adaptor protein, phosphotyrosine interacting with PH domain and leucine zipper 1(APPL) gene expression.

RESULTS

Dexamethasone administration caused hyperglycemia, hyperlipemia, decrease the level of adiponectin, irisin, and PI3K besides decreasing the gene expression of IRS-1, PGC-1 α, and APPL1. ALA administration pre or concomitant to dexamethasone avoided these results.

CONCLUSION

ALA can prevent metabolic abnormalities induced by dexamethasone via PGC1α and APPL1 upregulation.

Effect of β-hydroxy-β-methylbutyrate on miRNA expression in differentiating equine satellite cells exposed to hydrogen peroxide

Background

Skeletal muscle injury activates satellite cells to initiate processes of proliferation, differentiation, and hypertrophy in order to regenerate muscle fibers. The number of microRNAs and their target genes are engaged in satellite cell activation. β-Hydroxy-β-methylbutyrate (HMB) is known to prevent exercise-induced muscle damage. The purpose of this study was to evaluate the effect of HMB on miRNA and relevant target gene expression in differentiating equine satellite cells exposed to H₂O₂. We hypothesized that HMB may regulate satellite cell activity, proliferation, and differentiation, hence attenuate the pathological processes induced during an in vitro model of H₂O₂-related injury by changing the expression of miRNAs.

Methods

Equine satellite cells (ESC) were isolated from the samples of skeletal muscle collected from young horses. ESC were treated with HMB (24 h) and then exposed to H₂O₂ (1 h). For the microRNA and gene expression assessment microarrays, technique was used. Identified miRNAs and genes were validated using real-time qPCR. Cell viability, oxidative stress, and cell damage were measured using colorimetric method and flow cytometry.

Results

Analysis of miRNA and gene profile in differentiating ESC pre-incubated with HMB and then exposed to H₂O₂ revealed difference in the expression of 27 miRNAs and 4740 genes, of which 344 were potential target genes for identified miRNAs. Special attention was focused on differentially expressed miRNAs and their target genes involved in processes related to skeletal muscle injury. Western blot analysis showed protein protection in HMB-pre-treated group compared to control. The viability test confirmed that HMB enhanced cell survival after the hydrogen peroxide exposition.

Conclusions

Our results suggest that ESC pre-incubated with HMB and exposed to H₂O₂ could affect expression on miRNA levels responsible for skeletal muscle development, cell proliferation and differentiation, and activation of tissue repair after injury. Enrichment analyses for targeted genes revealed that a large group of genes was associated with the regulation of signaling pathways crucial for muscle tissue development, protein metabolism, muscle injury, and regeneration, as well as with oxidative stress response.

Effects of beta-hydroxy-beta-methylbutyrate (HMB) on the expression of ubiquitin ligases, protein synthesis pathways and contractile function in extensor digitorum longus (EDL) of fed and fasting rats

Beta-hydroxy-beta-methylbutyrate (HMB), a leucine metabolite, enhances the gain of skeletal muscle mass by increasing protein synthesis or attenuating protein degradation or both. The aims of this study were to investigate the effect of HMB on molecular factors controlling skeletal muscle protein synthesis and degradation, as well as muscle contractile function, in fed and fasted conditions. Wistar rats were supplied daily with HMB (320 mg/kg body weight diluted in NaCl-0.9%) or vehicle only (control) by gavage for 28 days. After this period, some of the animals were subjected to a 24-h fasting, while others remained in the fed condition. The EDL muscle was then removed, weighed and used to evaluate the genes and proteins involved in protein synthesis (AKT/4E-BP1/S6) and degradation (Fbxo32 and Trim63). A sub-set of rats were used to measure in vivo muscle contractile function. HMB supplementation increased AKT phosphorylation during fasting (three-fold). In the fed condition, no differences were detected in atrogenes expression between control and HMB supplemented group; however, HMB supplementation did attenuate the fasting-induced increase in their expression levels. Fasting animals receiving HMB showed improved sustained tetanic contraction times (one-fold) and an increased muscle to tibia length ratio (1.3-fold), without any cross-sectional area changes. These results suggest that HMB supplementation under fasting conditions increases AKT phosphorylation and attenuates the increased of atrogenes expression, followed by a functional improvement and gain of skeletal muscle weight, suggesting that HMB protects skeletal muscle against the deleterious effects of fasting.

Inhibition of interleukin-6 decreases atrogene expression and ameliorates tail suspension-induced skeletal muscle atrophy

BACKGROUND

Interleukin-6 (IL-6) is an inflammatory cytokine. Whether systemic IL-6 affects atrogene expression and disuse-induced skeletal muscle atrophy is unclear.

METHODS

Tail-suspended mice were used as a disuse-induced muscle atrophy model. We administered anti-mouse IL-6 receptor antibody, beta-hydroxy-beta-methylbutyrate (HMB) and vitamin D to the mice and examined the effects on atrogene expression and muscle atrophy.

RESULTS

Serum IL-6 levels were elevated in the mice. Inhibition of IL-6 receptor suppressed muscle RING finger 1 (MuRF1) expression and prevented muscle atrophy. HMB and vitamin D inhibited the serum IL-6 surge, downregulated the expression of MuRF1 and atrogin-1 in the soleus muscle, and ameliorated atrophy in the mice.

CONCLUSION

Systemic IL-6 affects MuRF1 expression and disuse-induced muscle atrophy.

Beta-hydroxy-beta-methylbutyrate supplementation and skeletal muscle in healthy and muscle-wasting conditions

Beta-hydroxy-beta-methylbutyrate (HMB) is a metabolite of the essential amino acid leucine that has been reported to have anabolic effects on protein metabolism. The aims of this article were to summarize the results of studies of the effects of HMB on skeletal muscle and to examine the evidence for the rationale to use HMB as a nutritional supplement to exert beneficial effects on muscle mass and function in various conditions of health and disease. The data presented here indicate that the beneficial effects of HMB have been well characterized in strength-power and endurance exercise. HMB attenuates exercise-induced muscle damage and enhances muscle hypertrophy and strength, aerobic performance, resistance to fatigue, and regenerative capacity. HMB is particularly effective in untrained individuals who are exposed to strenuous exercise and in trained individuals who are exposed to periods of high physical stress. The low effectiveness of HMB in strength-trained athletes could be due to the suppression of the proteolysis that is induced by the adaptation to training, which may blunt the effects of HMB. Studies performed with older people have demonstrated that HMB can attenuate the development of sarcopenia in elderly subjects and that the optimal effects of HMB on muscle growth and strength occur when it is combined with exercise. Studies performed under in vitro conditions and in various animal models suggest that HMB may be effective in treatment of muscle wasting in various forms of cachexia. However, there are few clinical reports of the effects of HMB on muscle wasting in cachexia; in addition, most of these studies evaluated the therapeutic potential of combinations of various agents. Therefore, it has not been possible to determine whether HMB was effective or if there was a synergistic effect. Although most of the endogenous HMB is produced in the liver, there are no reports regarding the levels and the effects of HMB supplementation in subjects with liver disease. Several studies have suggested that anabolic effects of HMB supplementation on skeletal muscle do not occur in healthy, non-exercising subjects. It is concluded that (i) HMB may be applied to enhance increases in the mass and strength of skeletal muscles in subjects who exercise and in the elderly and (ii) studies examining the effects of HMB administered alone are needed to obtain conclusions regarding the specific effectiveness in attenuating muscle wasting in various muscle-wasting disorders.

Leucine Metabolism in T Cell Activation: mTOR Signaling and Beyond

In connection with the increasing interest in metabolic regulation of the immune response, this review discusses current advances in understanding the role of leucine and leucine metabolism in T lymphocyte (T cell) activation. T cell activation during the development of an immune response depends on metabolic reprogramming to ensure that sufficient nutrients and energy are taken up by the highly proliferating T cells. Leucine has been described as an important essential amino acid and a nutrient signal that activates complex 1 of the mammalian target of rapamycin (mTORC1), which is a critical regulator of T cell proliferation, differentiation, and function. The role of leucine in these processes is further discussed in relation to amino acid transporters, leucine-degrading enzymes, and other metabolites of leucine metabolism. A new model of T cell regulation by leucine is proposed and outlines a chain of events that leads to the activation of mTORC1 in T cells.

Muscle wasting and aging: Experimental models, fatty infiltrations, and prevention

Identification of cost-effective interventions to maintain muscle mass, muscle strength, and physical performance during muscle wasting and aging is an important public health challenge. It requires understanding of the cellular and molecular mechanisms involved. Muscle-deconditioning processes have been deciphered by means of several experimental models, bringing together the opportunities to devise comprehensive analysis of muscle wasting. Studies have increasingly recognized the importance of fatty infiltrations or intermuscular adipose tissue for the age-mediated loss of skeletal-muscle function and emphasized that this new important factor is closely linked to inactivity. The present review aims to address three main points. We first mainly focus on available experimental models involving cell, animal, or human experiments on muscle wasting. We next point out the role of intermuscular adipose tissue in muscle wasting and aging and try to highlight new findings concerning aging and muscle-resident mesenchymal stem cells called fibro/adipogenic progenitors by linking some cellular players implicated in both FAP fate modulation and advancing age. In the last part, we review the main data on the efficiency and molecular and cellular mechanisms by which exercise, replacement hormone therapies, and β-hydroxy-β-methylbutyrate prevent muscle wasting and sarcopenia. Finally, we will discuss a potential therapeutic target of sarcopenia: glucose 6-phosphate dehydrogenase.

β-Hydroxy-β-methylbutyrate, mitochondrial biogenesis, and skeletal muscle health

The metabolic roles of mitochondria go far beyond serving exclusively as the major producer of ATP in tissues and cells. Evidence has shown that mitochondria may function as a key regulator of skeletal muscle fiber types and overall well-being. Maintaining skeletal muscle mitochondrial content and function is important for sustaining health throughout the lifespan. Of great importance, β-hydroxy-β-methylbutyrate (HMB, a metabolite of L-leucine) has been proposed to enhance the protein deposition and efficiency of mitochondrial biogenesis in skeletal muscle, as well as muscle strength in both exercise and clinical settings. Specifically, dietary supplementation with HMB increases the gene expression of peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α), which represents an upstream inducer of genes of mitochondrial metabolism, coordinates the expression of both nuclear- and mitochondrion-encoded genes in mitochondrial biogenesis. Additionally, PGC-1α plays a key role in the transformation of skeletal muscle fiber type, leading to a shift toward type I muscle fibers that are rich in mitochondria and have a high capacity for oxidative metabolism. As a nitrogen-free metabolite, HMB holds great promise to improve skeletal muscle mass and function, as well as whole-body health and well-being of animals and humans.

A novel in vitro model of sarcopenia using BubR1 hypomorphic C2C12 myoblasts

Sarcopenia is the age-related loss of skeletal muscle mass and function with adverse outcomes that include physical disability, poor quality of life, and death. The detailed molecular mechanisms remain unknown. An in vitro muscle atrophy model is needed to enable mechanistic studies. To create such a model, we employed BubR1 insufficiency which causes premature ageing in mice. Using C2C12 cells, a recognized in vitro model of the skeletal muscle cell, we obtained the BubR1 hypomorphic C2C12 (C2C12BKD) cells by using shRNA. The resulting C2C12BKD cells displayed several characteristics of the sarcopenic muscle cell. In C2C12BKD cells, formation of myotubes, assessed by analysis of fusion index, was markedly reduced as was the expression of myogenin and MyoD, two marker genes for myogenesis. Moreover, the cells showed increased expression of the muscle-specific ubiquitin ligases Atrogin-1 and MuRF-1, indicating increased protein degradation through the ubiquitin-proteasome dependent proteolytic pathway. These results suggest that C2C12BKD cells are potentially useful as a novel in vitro model of sarcopenia.