An electrical stimulation intervention protocol to prevent disuse atrophy and muscle strength decline: an experimental study in rat.

BACKGROUND: Skeletal muscle is negatively impacted by conditions such as spaceflight or prolonged bed rest, resulting in a dramatic decline in muscle mass, maximum contractile force, and muscular endurance. Electrical stimulation (ES) is an essential tool in neurophysiotherapy and an effective means of preventing skeletal muscle atrophy and dysfunction. Historically, ES treatment protocols have used either low or high frequency electrical stimulation (LFES/HFES). However, our study tests the use of a combination of different frequencies in a single electrical stimulation intervention in order to determine a more effective protocol for improving both skeletal muscle strength and endurance. METHODS: An adult male SD rat model of muscle atrophy was established through 4 weeks of tail suspension (TS). To investigate the effects of different frequency combinations, the experimental animals were treated with low (20 Hz) or high (100 Hz) frequency before TS for 6 weeks, and during TS for 4weeks. The maximum contraction force and fatigue resistance of skeletal muscle were then assessed before the animals were sacrificed. The muscle mass, fiber cross-sectional area (CSA), fiber type and related protein expression were examined and analyzed to gain insights into the mechanisms by which the ES intervention protocol used in this study regulates muscle strength and endurance. RESULTS: After 4 weeks of unloading, the soleus muscle mass and fiber CSA decreased by 39% and 58% respectively, while the number of glycolytic muscle fibers increased by 21%. The gastrocnemius muscle fibers showed a 51% decrease in CSA, with a 44% decrease in single contractility and a 39% decrease in fatigue resistance. The number of glycolytic muscle fibers in the gastrocnemius also increased by 29%. However, the application of HFES either prior to or during unloading showed an improvement in muscle mass, fiber CSA, and oxidative muscle fibers. In the pre-unloading group, the soleus muscle mass increased by 62%, while the number of oxidative muscle fibers increased by 18%. In the during unloading group, the soleus muscle mass increased by 29% and the number of oxidative muscle fibers increased by 15%. In the gastrocnemius, the pre-unloading group showed a 38% increase in single contractile force and a 19% increase in fatigue resistance, while in the during unloading group, a 21% increase in single contractile force and a 29% increase in fatigue resistance was observed, along with a 37% and 26% increase in the number of oxidative muscle fibers, respectively. The combination of HFES before unloading and LFES during unloading resulted in a significant elevation of the soleus mass by 49% and CSA by 90%, with a 40% increase in the number of oxidative muscle fibers in the gastrocnemius. This combination also resulted in a 66% increase in single contractility and a 38% increase in fatigue resistance. CONCLUSION: Our results indicated that using HFES before unloading can reduce the harmful effects of muscle unloading on the soleus and gastrocnemius muscles. Furthermore, we found that combining HFES before unloading with LFES during unloading was more effective in preventing muscle atrophy in the soleus and preserving the contractile function of the gastrocnemius muscle.

Angiotensin 1-7 protects against ventilator-induced diaphragm dysfunction.

Mechanical ventilation (MV) is a life-saving instrument used to provide ventilatory support for critically ill patients and patients undergoing surgery. Unfortunately, an unintended consequence of prolonged MV is the development of inspiratory weakness due to both diaphragmatic atrophy and contractile dysfunction; this syndrome is labeled ventilator-induced diaphragm dysfunction (VIDD). VIDD is clinically important because diaphragmatic weakness is an important contributor to problems in weaning patients from MV. Investigations into the pathogenesis of VIDD reveal that oxidative stress is essential for the rapid development of VIDD as redox disturbances in diaphragm fibers promote accelerated proteolysis. Currently, no standard treatment exists to prevent VIDD and, therefore, developing a strategy to avert VIDD is vital. Guided by evidence indicating that activation of the classical axis of the renin-angiotensin system (RAS) in diaphragm fibers promotes oxidative stress and VIDD, we hypothesized that activation of the nonclassical RAS signaling pathway via angiotensin 1-7 (Ang1-7) will protect against VIDD. Using an established animal model of prolonged MV, our results disclose that infusion of Ang1-7 protects the diaphragm against MV-induced contractile dysfunction and fiber atrophy in both fast and slow muscle fibers. Further, Ang1-7 shielded diaphragm fibers against MV-induced mitochondrial damage, oxidative stress, and protease activation. Collectively, these results reveal that treatment with Ang1-7 protects against VIDD, in part, due to diminishing oxidative stress and protease activation. These important findings provide robust evidence that Ang1-7 has the therapeutic potential to protect against VIDD by preventing MV-induced contractile dysfunction and atrophy of both slow and fast muscle fibers.

Blood Flow Restriction Combined with Electrical Stimulation Attenuates Thigh Muscle Disuse Atrophy.

PURPOSE: This study aimed to investigate the effects of blood flow restriction (BFR) combined with electrical muscle stimulation (EMS) on skeletal muscle mass and strength during a period of limb disuse. METHODS: Thirty healthy participants (22 ± 3 yr; 23 ± 3 kg·m-2) were randomly assigned to control (CON; n = 10), BFR alone (BFR; n = 10), or BFR combined with EMS (BFR + EMS; n = 10). All participants completed unloading of a single leg for 14 d, with no treatment (CON), or while treated with either BFR or BFR + EMS (twice daily, 5 d·wk-1). BFR treatment involved arterial three cycles of 5-min occlusion using suprasystolic pressure, each separated by 5 min of reperfusion. EMS (6 s on, 15 s off; 200 µs; 60 Hz; 15% maximal voluntary contraction [MVC]) was applied continuously throughout the three BFR cycles. Quadriceps muscle mass (whole-thigh lean mass via dual-energy x-ray absorptiometry and vastus lateralis [VL] muscle thickness via ultrasound) and strength (via knee extension MVC) were assessed before and after the 14-d unloading period. RESULTS: After limb unloading, whole-thigh lean mass decreased in the control group (-4% ± 1%, P < 0.001) and BFR group (-3% ± 2%, P = 0.001), but not in the BFR + EMS group (-0.3% ± 3%, P = 0.8). VL muscle thickness decreased in the control group (-4% ± 4%, P = 0.005) and was trending toward a decrease in the BFR group (-8% ± 11%, P = 0.07) and increase in the BFR + EMS group (+5% ± 10%, P = 0.07). Knee extension MVC decreased over time (P < 0.005) in the control group (-18% ± 15%), BFR group (-10% ± 13%), and BFR + EMS group (-18% ± 15%), with no difference between groups (P > 0.5). CONCLUSION: Unlike BFR performed in isolation, BFR + EMS represents an effective interventional strategy to attenuate the loss of muscle mass during limb disuse, but it does not demonstrate preservation of strength.

Nutritional Strategies to Offset Disuse-Induced Skeletal Muscle Atrophy and Anabolic Resistance in Older Adults: From Whole-Foods to Isolated Ingredients.

Preserving skeletal muscle mass and functional capacity is essential for healthy ageing. Transient periods of disuse and/or inactivity in combination with sub-optimal dietary intake have been shown to accelerate the age-related loss of muscle mass and strength, predisposing to disability and metabolic disease. Mechanisms underlying disuse and/or inactivity-related muscle deterioration in the older adults, whilst multifaceted, ultimately manifest in an imbalance between rates of muscle protein synthesis and breakdown, resulting in net muscle loss. To date, the most potent intervention to mitigate disuse-induced muscle deterioration is mechanical loading in the form of resistance exercise. However, the feasibility of older individuals performing resistance exercise during disuse and inactivity has been questioned, particularly as illness and injury may affect adherence and safety, as well as accessibility to appropriate equipment and physical therapists. Therefore, optimising nutritional intake during disuse events, through the introduction of protein-rich whole-foods, isolated proteins and nutrient compounds with purported pro-anabolic and anti-catabolic properties could offset impairments in muscle protein turnover and, ultimately, the degree of muscle atrophy and recovery upon re-ambulation. The current review therefore aims to provide an overview of nutritional countermeasures to disuse atrophy and anabolic resistance in older individuals.

Increasing myosin light chain 3f (MLC3f) protects against a decline in contractile velocity.

Disuse induces adaptations in skeletal muscle, which lead to muscle deterioration. Hindlimb-unloading (HU) is a well-established model to investigate cellular mechanisms responsible for disuse-induced skeletal muscle dysfunction. In myosin heavy chain (MHC) type IIB fibers HU induces a reduction in contraction speed (Vo) and a reduction in the relative myosin light chain 3f (MLC3f) protein content compared with myosin light chain 1f (MLC1f) protein. This study tested the hypothesis that increasing the relative MLC3f protein content via rAd-MLC3f vector delivery would attenuate the HU-induced decline in Vo in single MHC type IIB fibers. Fischer-344 rats were randomly assigned to one of three groups: control, HU for 7 days, and HU for 7 days plus rAd-MLC3f. The semimembranosus muscles were injected with rAd-MLC3f (3.75 x 1011-5 x 1011 ifu/ml) at four days after the initiation of HU. In single MHC type IIB fibers the relative MLC3f content decreased by 25% (12.00±0.60% to 9.06±0.66%) and Vo was reduced by 29% (3.22±0.14fl/s vs. 2.27±0.08fl/s) with HU compared to the control group. The rAd-MLC3f injection resulted in an increase in the relative MLC3f content (12.26±1.19%) and a concomitant increase in Vo (2.90±0.15fl/s) of MHC type IIB fibers. A positive relationship was observed between the percent of MLC3f content and Vo. Maximal isometric force and specific tension were reduced with HU by 49% (741.45±44.24µN to 379.09±23.77µN) and 33% (97.58±4.25kN/m2 to 65.05±2.71kN/m2), respectively compared to the control group. The rAd-MLC3f injection did not change the HU-induced decline in force or specific tension. Collectively, these results indicate that rAd-MLC3f injection rescues hindlimb unloading-induced decline in Vo in MHC type IIB single muscle fibers.

Physical strategies to prevent disuse-induced functional decline in the elderly.

Disuse situations can have serious adverse health consequences in the elderly, including mainly functional impairment with subsequent increase in the risk of falls or morbimortality. The present review provides clinicians and care givers with detailed and practical information on the feasibility and effectiveness of physical strategies that are currently available to prevent or attenuate the functional decline that occurs secondarily to disuse situations in the elderly, notably in the hospital setting. In this context, active approaches such as resistance exercises and maximal voluntary contractions, which can be performed both isometrically and dynamically, are feasible during most immobilization situations including in hospitalized old people and represent powerful tools for the prevention of muscle atrophy. Aerobic exercise should also be prescribed whenever possible to reduce the loss of cardiovascular capacity associated with disuse periods. Other feasible strategies for patients who are unwilling or unable to perform volitional exercise comprise neuromuscular electrical stimulation, vibration, and blood flow restriction. However, they should ideally be applied synchronously with voluntary exercise to obtain synergistic benefits.

Contralateral effects of unilateral training: sparing of muscle strength and size after immobilization.

The contralateral effects of unilateral strength training, known as cross-education of strength, date back well over a century. In the last decade, a limited number of studies have emerged demonstrating the preservation or "sparing" effects of cross-education during immobilization. Recently published evidence reveals that the sparing effects of cross-education show muscle site specificity and involve preservation of muscle cross-sectional area. The new research also demonstrates utility of training with eccentric contractions as a potent stimulus to preserve immobilized limb strength across multiple modes of contraction. The cumulative data in nonclinical settings suggest that cross-education can completely abolish expected declines in strength and muscle size in the range of ∼13% and ∼4%, respectively, after 3-4 weeks of immobilization of a healthy arm. The evidence hints towards the possibility that unique mechanisms may be involved in preservation effects of cross-education, as compared with those that lead to functional improvements under normal conditions. Cross-education effects after strength training appear to be larger in clinical settings, but there is still only 1 randomized clinical trial demonstrating the potential utility of cross-education in addition to standard treatment. More work is necessary in both controlled and clinical settings to understand the potential interaction of neural and muscle adaptations involved in the observed sparing effects, but there is growing evidence to advocate for the clinical utility of cross-education.

Resveratrol Improves Muscle Atrophy by Modulating Mitochondrial Quality Control in STZ-Induced Diabetic Mice.

SCOPE: In this study, we aim to determine the effects of resveratrol (RSV) on muscle atrophy in streptozocin-induced diabetic mice and to explore mitochondrial quality control (MQC) as a possible mechanism. METHODS AND RESULTS: The experimental mice were fed either a control diet or an identical diet containing 0.04% RSV for 8 weeks. Examinations were subsequently carried out, including the effects of RSV on muscle atrophy and muscle function, as well as on the signaling pathways related to protein degradation and MQC processes. The results show that RSV supplementation improves muscle atrophy and muscle function, attenuates the increase in ubiquitin and muscle RING-finger protein-1 (MuRF-1), and simultaneously attenuates LC3-II and cleaved caspase-3 in the skeletal muscle of diabetic mice. Moreover, RSV treatment of diabetic mice results in an increase in mitochondrial biogenesis and inhibition of the activation of mitophagy in skeletal muscle. RSV also protects skeletal muscle against excess mitochondrial fusion and fission in the diabetic mice. CONCLUSION: The results suggest that RSV ameliorates diabetes-induced skeletal muscle atrophy by modulating MQC.

Therapeutic effects of diclofenac, pregabalin, and duloxetine on disuse-induced chronic musculoskeletal pain in rats.

The aim of this study was to clarify the mechanism of disuse-induced muscle hyperalgesia through the evaluation of the pharmacological behaviour of muscle hyperalgesia profiles in chronic post-cast pain (CPCP) rats with acute and chronic-phase mirror-image muscle hyperalgesia treated with diclofenac (NSAID), pregabalin (an inhibitor of Ca2+ channel α2δ), and duloxetine (SNRI). After 2 weeks of cast immobilization, the peak cross-sectional area and muscle wet weight of the ipsilateral soleus and gastrocnemius muscles decreased more significantly in CPCP rats than in untreated rats. Histological findings revealed disuse-induced muscle atrophy in CPCP rats. The blood biochemical parameters of CPCP rats in acute and chronic phases did not differ significantly from those of untreated rats. The diclofenac and pregabalin-treated groups exhibited no improvement in acute or chronic muscle hyperalgesia. In contrast, the duloxetine-treated group exhibited an improvement in acute muscle hyperalgesia, but showed no apparent effect on chronic muscle hyperalgesia on ipsilateral or contralateral sides. However, the chronic muscle hyperalgesia was reversed by intrathecal administration of DAMGO (a µ-opioid receptor agonist). The results suggest that chronic muscle hyperalgesia in CPCP rats did not result from an inflammatory mechanism, and there is only a low probability that it's caused by a neuropathic mechanism.

Interventional strategies to combat muscle disuse atrophy in humans: focus on neuromuscular electrical stimulation and dietary protein.

Numerous situations, such as the recovery from illness or rehabilitation after injury, necessitate a period of muscle disuse in otherwise healthy individuals. Even a few days of immobilization or bed rest can lead to substantial loss of skeletal muscle tissue and compromise metabolic health. The decline in muscle mass is attributed largely to a decline in postabsorptive and postprandial muscle protein synthesis rates. Reintroduction of some level of muscle contraction by the application of neuromuscular electrical stimulation (NMES) can augment both postabsorptive and postprandial muscle protein synthesis rates and, as such, prevent or attenuate muscle loss during short-term disuse in various clinical populations. Whereas maintenance of habitual dietary protein consumption is a prerequisite for muscle mass maintenance, supplementing dietary protein above habitual intake levels does not prevent muscle loss during disuse in otherwise healthy humans. Combining the anabolic properties of physical activity (or surrogates) with appropriate nutritional support likely further increases the capacity to preserve skeletal muscle mass during a period of disuse. Therefore, effective interventional strategies to prevent or alleviate muscle disuse atrophy should include both exercise (mimetics) and appropriate nutritional support.

The influence of aging on the effectiveness of heat stress in preventing disuse muscle atrophy.

This study examined the aging effect on disuse muscle atrophy prevention using heat stress. Wistar rats aged 7 and 60 weeks were divided into three groups as follows: control, immobilized (Im), and immobilized and heat stressed (ImH). Heat stress was given by immersing the hindlimbs in hot water (42 °C) for 60 min, once in every 3 days and the gastrocnemius (GAS) and soleus (SOL) muscles were extracted after 14 days. Muscle-fiber types were classified using ATPase staining. Heat shock protein 70 (HSP70) was assessed through Western blotting. In GAS muscle of both groups and SOL muscle of 7-week-old rats, the fiber diameter of each muscle type in the ImH group significantly increased compared with that in the Im group. However, this could not be observed in the SOL muscle of the 60-week-old rats. The increased percentage of type-I fibers and variability of types I and II muscle-fiber diameter were evident in the SOL muscle of the 60-week rats. HSP70 was significantly elevated in the ImH group compared with in the Im group in both muscle types of both age groups. Thus, effectiveness of heat stress in the prevention of disuse muscle atrophy appears unsatisfactory in aging muscle fibers.

The complex of PAMAM-OH dendrimer with Angiotensin (1-7) prevented the disuse-induced skeletal muscle atrophy in mice.

Angiotensin (1-7) (Ang-(1-7)) is a bioactive heptapeptide with a short half-life and has beneficial effects in several tissues - among them, skeletal muscle - by preventing muscle atrophy. Dendrimers are promising vehicles for the protection and transport of numerous bioactive molecules. This work explored the use of a neutral, non-cytotoxic hydroxyl-terminated poly(amidoamine) (PAMAM-OH) dendrimer as an Ang-(1-7) carrier. Bioinformatics analysis showed that the Ang-(1-7)-binding capacity of the dendrimer presented a 2:1 molar ratio. Molecular dynamics simulation analysis revealed the capacity of neutral PAMAM-OH to protect Ang-(1-7) and form stable complexes. The peptide coverage ability of the dendrimer was between ~50% and 65%. Furthermore, an electrophoretic mobility shift assay demonstrated that neutral PAMAM-OH effectively bonded peptides. Experimental results showed that the Ang-(1-7)/PAMAM-OH complex, but not Ang-(1-7) alone, had an anti-atrophic effect when administered intraperitoneally, as evaluated by muscle strength, fiber diameter, myofibrillar protein levels, and atrogin-1 and MuRF-1 expressions. The results of the Ang-(1-7)/PAMAM-OH complex being intraperitoneally injected were similar to the results obtained when Ang-(1-7) was systemically administered through mini-osmotic pumps. Together, the results suggest that Ang-(1-7) can be protected for PAMAM-OH when this complex is intraperitoneally injected. Therefore, the Ang-(1-7)/PAMAM-OH complex is an efficient delivery method for Ang-(1-7), since it improves the anti-atrophic activity of this peptide in skeletal muscle.

Skeletal muscle PGC-1ß signaling is sufficient to drive an endurance exercise phenotype and to counteract components of detraining in mice.

Peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α and -1ß serve as master transcriptional regulators of muscle mitochondrial functional capacity and are capable of enhancing muscle endurance when overexpressed in mice. We sought to determine whether muscle-specific transgenic overexpression of PGC-1ß affects the detraining response following endurance training. First, we established and validated a mouse exercise-training-detraining protocol. Second, using multiple physiological and gene expression end points, we found that PGC-1ß overexpression in skeletal muscle of sedentary mice fully recapitulated the training response. Lastly, PGC-1ß overexpression during the detraining period resulted in partial prevention of the detraining response. Specifically, an increase in the plateau at which O2 uptake (V̇o2) did not change from baseline with increasing treadmill speed [peak V̇o2 (ΔV̇o2max)] was maintained in trained mice with PGC-1ß overexpression in muscle 6 wk after cessation of training. However, other detraining responses, including changes in running performance and in situ half relaxation time (a measure of contractility), were not affected by PGC-1ß overexpression. We conclude that while activation of muscle PGC-1ß is sufficient to drive the complete endurance phenotype in sedentary mice, it only partially prevents the detraining response following exercise training, suggesting that the process of endurance detraining involves mechanisms beyond the reversal of muscle autonomous mechanisms involved in endurance fitness. In addition, the protocol described here should be useful for assessing early-stage proof-of-concept interventions in preclinical models of muscle disuse atrophy.

Tetramethylpyrazine ameliorated disuse-induced gastrocnemius muscle atrophy in hindlimb unloading rats through suppression of Ca2+/ROS-mediated apoptosis.

The purpose of this study was to examine the possible mechanism underlying the protective effect of tetramethylpyrazine (TMP) against disuse-induced muscle atrophy. Sprague-Dawley rats were randomly assigned to receive 14 days of hindlimb unloading (HLU, a model of disuse atrophy) or cage controls. The rats were given TMP (60 mg/kg body mass) or vehicle (water) by gavage. Compared with vehicle treatment, TMP significantly attenuated the loss of gastrocnemius muscle mass (-33.56%, P < 0.01), the decrease of cross-sectional area of slow fiber (-10.99%, P < 0.05) and fast fiber (-15.78%, P < 0.01) during HLU. Although TMP failed to further improve recovery of muscle function or fatigability compared with vehicle treatment, it can suppress the higher level of lactate (-22.71%, P < 0.01) induced by HLU. Besides, TMP could effectually reduce the increased protein expression of muscle RING-finger protein 1 induced by HLU (-14.52%, P < 0.01). Furthermore, TMP can ameliorate the calcium overload (-54.39%, P < 0.05), the increase of malondialdehyde content (-19.82%, P < 0.05), the decrease of superoxide dismutase activity (21.34%, P < 0.05), and myonuclear apoptosis (-78.22%, P < 0.01) induced by HLU. Moreover, TMP significantly reduced HLU-induced increase of Bax to B-cell lymphoma 2 (-36.36%, P < 0.01) and cytochrome c release (-36.16%, P < 0.05). In conclusion, TMP attenuated HLU-induced gastrocnemius muscle atrophy through suppression of Ca2+/reactive oxygen species increase and consequent proteolysis and apoptosis. Therefore, TMP might exhibit therapeutic effect against oxidative stress, cytosolic calcium overload, and mitochondrial damage in disuse-induced muscle atrophy.

l-Carnitine supplement reduces skeletal muscle atrophy induced by prolonged hindlimb suspension in rats.

l-Carnitine was recently found to downregulate the ubiquitin proteasome pathway (UPP) and increase insulin-like growth factor 1 concentrations in animal models. However, the effect of l-carnitine administration on disuse muscle atrophy induced by hindlimb suspension has not yet been studied. Thus, we hypothesized that l-carnitine may have a protective effect on muscle atrophy induced by hindlimb suspension via the Akt1/mTOR and/or UPP. Male Wistar rats were assigned to 3 groups: hindlimb suspension group, hindlimb suspension with l-carnitine administration (1250 mg·kg-1·day-1) group, and pair-fed group adjusted hindlimb suspension. l-Carnitine administration for 2 weeks of hindlimb suspension alleviated the decrease in weight and fiber size in the soleus muscle. In addition, l-carnitine suppressed atrogin-1 mRNA expression, which has been reported to play a pivotal role in muscle atrophy. The present study shows that l-carnitine has a protective effect against soleus muscle atrophy caused by hindlimb suspension and decreased E3 ligase messenger RNA expression, suggesting the possibility that l-carnitine protects against muscle atrophy, at least in part, through the inhibition of the UPP. These observations suggest that l-carnitine could serve as an effective supplement in the decrease of muscle atrophy caused by weightlessness in the fields of clinical and rehabilitative research.

Additive effect of PTH (1-34) and zoledronate in the prevention of disuse osteopenia in rats.

Immobilization is known to cause a rapid bone loss due to increased osteoclastic bone resorption and decreased osteoblastic bone formation. Zoledronate (Zln) is a potent anti-resorptive pharmaceutical, while intermittent PTH is a potent bone anabolic agent. The aim of the present study was to investigate whether PTH or Zln alone or in combination could prevent immobilization-induced osteopenia. Immobilization was achieved by injecting 4IU Botox (BTX) into the right hind limb musculature. Seventy-two 16-week-old female Wistar rats were randomized into 6 groups; baseline (Base), control (Ctrl), BTX, BTX+PTH, BTX+Zln, and BTX+PTH+Zln. PTH (1-34) (80µg/kg) was given 5days/week and Zln (100µg/kg) was given once at study start. The animals were killed after 4weeks of treatment. The bone properties were evaluated using DEXA, µCT, dynamic bone histomorphometry, and mechanical testing. BTX resulted in lower femoral trabecular bone volume fraction (BV/TV) (-25%, p<0.05), lower tibial trabecular bone formation rate (BFR/BS) (-29%, p<0.05), and lower bone strength (Fmax) at the distal femur (-19%, p<0.001) compared with Ctrl. BTX+PTH resulted in higher femoral BV/TV (+31%, p<0.05), higher tibial trabecular BFR/BS (+297%, p<0.05), and higher Fmax at the distal femur (+11%, p<0.05) compared with BTX. BTX+Zln resulted in higher femoral BV/TV (+36%, p<0.05), lower tibial trabecular BFR/BS (-93%, p<0.05), and higher Fmax at the distal femur (+10%, p<0.05) compared with BTX. BTX+PTH+Zln resulted in higher femoral BV/TV (+70%, p<0.001), higher tibial trabecular BFR/BS (+59%, p<0.05), and higher Fmax at the distal femur (+32%, p<0.001) compared with BTX. In conclusion, BTX-induced immobilization led to lower BV/TV, BFR/BS, and Fmax. In general, PTH or Zln alone prevented the BTX-induced osteopenia, whereas PTH and Zln given in combination not only prevented, but also increased BV/TV and BFR/BS, and maintained Fmax at the distal femoral metaphysis compared with Ctrl.

The non-thermal effects of pulsed ultrasound irradiation on the development of disuse muscle atrophy in rat gastrocnemius muscle.

This study examined the effects of therapeutic pulsed ultrasound (US) on the development of disuse muscle atrophy in rat gastrocnemius muscle. Male Wistar rats were randomly distributed into control, immobilization (Im), sham US, and US groups. In the Im, sham US and US groups, the bilateral ankle joints of each rat were immobilized in full plantar flexion with a plaster cast for a 4-wk period. The pulsed US (frequency, 1 MHz; intensity, 1.0 W/cm(2); pulsed mode 1:4; 15 min) was irradiated to the gastrocnemius muscle in the US group over a 4-wk immobilization period. The pulsed US irradiation delivered only non-thermal effects to the muscle. In conjunction with US irradiation, 5-bromo-2'-deoxyuridine (BrdU) was injected subcutaneously to label the nuclei of proliferating satellite cells 1 h before each pulsed US irradiation. Immobilization resulted in significant decreases in the mean diameters of type I, IIA and IIB muscle fibers of the gastrocnemius muscle in the Im, sham US and US groups compared with the control group. However, the degrees of muscle fiber atrophy for all types were significantly lower in the US group compared with the Im and sham US groups. Although the number of capillaries and the concentrations of insulin-like growth factor and basic fibroblast growth factor did not change in the muscle, the number of BrdU-positive nuclei in the muscle was significantly increased by pulsed US irradiation in the US group. The results of this study suggest that pulsed US irradiation inhibits the development of disuse muscle atrophy partly via activation of satellite cells.

Nutritional strategies to attenuate muscle disuse atrophy.

Situations such as recovery from injury or illness require otherwise healthy humans to undergo periods of disuse, which lead to considerable losses of skeletal muscle mass and, subsequently, numerous negative health consequences. It has been established that prolonged disuse (>10 days) leads to a decline in basal and postprandial rates of muscle protein synthesis, without an apparent change in muscle protein breakdown. It also seems, however, that an early and transient (1-5 days) increase in basal muscle protein breakdown may also contribute to disuse atrophy. A period of disuse reduces energy requirements and appetite. Consequently, food intake generally declines, resulting in an inadequate dietary protein consumption to allow proper muscle mass maintenance. Evidence suggests that maintaining protein intake during a period of disuse attenuates disuse atrophy. Furthermore, supplementation with dietary protein and/or essential amino acids can be applied to further aid in muscle mass preservation during disuse. Such strategies are of particular relevance to the older patient at risk of developing sarcopenia. More work is required to elucidate the impact of disuse on basal and postprandial rates of muscle protein synthesis and breakdown. Such information will provide novel targets for nutritional interventions to further attenuate muscle disuse atrophy and, as such, support healthy aging.

Prevention of disuse muscle atrophy by dietary ingestion of 8-prenylnaringenin in denervated mice.

Flavonoids have attracted considerable attention in relation to their effects upon health. 8-Prenylnaringenin (8-PN) is found in the common hop (Humulus lupulus) and assumed to be responsible for the health impact of beer consumption. We wanted to clarify the effects of prenylation on the physiological functions of dietary flavonoids by comparing the effects of 8-PN with that of intact naringenin in the prevention of disuse muscle atrophy using a model of denervation in mice. Consumption of 8-PN (but not naringenin) prevented loss of weight in the gastrocnemius muscle further supported by the lack of induction of the protein content of a key ubiquitin ligase involved in muscle atrophy, atrogin-1, and by the activation of Akt phosphorylation. 8-PN content in the gastrocnemius muscle was tenfold higher than that of naringenin. These results suggested that, compared with naringenin, 8-PN was effectively concentrated into skeletal muscle to exert its preventive effects upon disuse muscle atrophy. It is likely that prenylation generates novel functions for 8-PN by enhancing its accumulation into muscle tissue through dietary intake.

Branched-chain amino acids reduce hindlimb suspension-induced muscle atrophy and protein levels of atrogin-1 and MuRF1 in rats.

Atrogin-1 and MuRF1, muscle-specific ubiquitin ligases, and autophagy play a role in protein degradation in muscles. We hypothesized that branched-chain amino acids (BCAAs) may decrease atrogin-1, MuRF1, and autophagy, and may have a protective effect on disuse muscle atrophy. To test this hypothesis, we selected hindlimb suspension (HS)-induced muscle atrophy as a model of disuse muscle atrophy because it is an established model to investigate the effects of decreased muscle activity. Sprague-Dawley male rats were assigned to 4 groups: control, HS (14 days), oral BCAA administration (600 mg/[kg day], 22.9% L-isoleucine, 45.8% L-leucine, and 27.6% L-valine), and HS and BCAA administration. After 14 days of the treatment, muscle weights and protein concentrations, cross-sectional area (CSA) of the muscle fibers, atrogin-1 and MuRF1 proteins, and microtubule-associated protein 1 light chain 3 II/I (ratio of LC3 II/I) were measured. Hindlimb suspension significantly reduced soleus muscle weight and CSA of the muscle fibers. Branched-chain amino acid administration partly but significantly reversed the HS-induced decrease in CSA. Hindlimb suspension increased atrogin-1 and MuRF1 proteins, which play a pivotal role in various muscle atrophies. Branched-chain amino acid attenuated the increase in atrogin-1 and MuRF1 in soleus muscles. Hindlimb suspension significantly increased the ratio of LC3 II/I, an indicator of autophagy, whereas BCAA did not attenuate the increase in the ratio of LC3 II/I. These results indicate the possibility that BCAA inhibits HS-induced muscle atrophy, at least in part, via the inhibition of the ubiquitin-proteasome pathway. Oral BCAA administration appears to have the potential to prevent disuse muscle atrophy.