Potential benefits of taurine in the prevention of skeletal muscle impairment induced by disuse in the hindlimb-unloaded rat

Attenuation of skeletal muscle atrophy via acupuncture, electro-acupuncture, and electrical stimulation

Background

Accelerated skeletal muscle wasting is a shared trait among many pathologies and aging. Acupuncture has been used as a therapeutic intervention to control pain; however, little is known about its effects on skeletal muscle atrophy and function. The study's purpose was to compare the effects of acupuncture, electro-acupuncture, and electrical stimulation on cast-induced skeletal muscle atrophy.

Methods

Forty female Sprague Dawley rats were randomly divided into groups: Control, casted (CAST), CAST+Acupuncture (CAST-A), 4) CAST+Electro-acupuncture (CAST-EA), and CAST+Electrical stimulation (CAST-ES) (n = 8). Plaster casting material was wrapped around the left hind limb. Acupuncture and electro-acupuncture (10 Hz, 6.4 mA) treatments were applied by needling acupoints (stomach-36 and gallbladder-34). Electrical stimulation (10 Hz, 6.4 mA) was conducted by needling the lateral and medial gastrocnemius muscles. Treatments were conducted for 15 min, three times/week for 14 days. Muscle atrophy F-box (MAFbx), muscle RING finger 1 (MuRF1), and contractile properties were assessed.

Results

Fourteen days of cast-immobilization decreased muscle fiber CSA by 56% in the CAST group (p = 0.00); whereas, all treatment groups demonstrated greater muscle fiber CSA than the CAST group (p = 0.00). Cast-immobilization increased MAFbx and MuRF1 protein expression in the CAST group (p<0.01) while the CAST-A, CAST-EA, and CAST-ES groups demonstrated lower levels of MAFbx and MuRF1 protein expression (p<0.02) compared to the CAST group. Following fourteen days of cast-immobilization, peak twitch tension did not differ between the CAST-A and CON groups (p = 0.12).

Conclusion

Skeletal muscle atrophy, induced by 14 days of cast-immobilization, was significantly attenuated by acupuncture, electro-acupuncture, or electrical stimulation.

Effects of dietary β-alanine supplementation on growth performance, meat quality, carnosine content, amino acid composition and muscular antioxidant capacity in Chinese indigenous Ningxiang pig

β-alanine has been demonstrated to improve carcass traits and meat quality of animals. However, no research has been found on the effects of dietary β-alanine in the meat quality control of finishing pigs, which are among the research focus. Therefore, this study aimed to evaluate the effects of dietary β-alanine supplementation on growth performance, meat quality, carnosine content, amino acid composition and muscular antioxidant capacity of Chinese indigenous Ningxiang pigs. The treatments contained a basal diet (control, CON) and a basal diet supplemented with 600 mg/kg β-alanine. Each treatment group consisted of five pens, with five pigs per pen. Results showed that compared with CON, supplemental β-alanine did not affect the final body weight, average daily gain, average daily feed intake and the feed-to-gain ratio of pigs. Dietary β-alanine supplementation tended to increase the pH_45 min (p = 0.071) while decreasing the shear force (p = 0.085) and the drip loss (p = 0.091). Moreover, it improved (p < 0.05) the activities of glutathione peroxidase and catalase and lessened (p < 0.05) malondialdehyde concentration. Added β-alanine in diets of finishing pigs could enhance the concentrations of arginine, alanine, and glutamate (p < 0.05) in the longissimus dorsi muscle and tended to raise the levels of cysteine, glycine and anserine (p = 0.060, p = 0.098 and p = 0.091 respectively). Taken together, our results showed that dietary β-alanine supplementation contributed to the improvement of the carcass traits, meat quality and anserine content, the amelioration of muscle antioxidant capacity and the regulation of amino acid composition in Chinese indigenous Ningxiang pigs.

Metabolic Pathways and Ion Channels Involved in Skeletal Muscle Atrophy: A Starting Point for Potential Therapeutic Strategies

Skeletal muscle tissue has the important function of supporting and defending the organism. It is the largest apparatus in the human body, and its function is important for contraction and movements. In addition, it is involved in the regulation of protein synthesis and degradation. In fact, inhibition of protein synthesis and/or activation of catabolism determines a pathological condition called muscle atrophy. Muscle atrophy is a reduction in muscle mass resulting in a partial or complete loss of function. It has been established that many physiopathological conditions can cause a reduction in muscle mass. Nevertheless, it is not well known that the molecular mechanisms and signaling processes caused this dramatic event. There are multiple concomitant processes involved in muscle atrophy. In fact, the gene transcription of some factors, oxidative stress mechanisms, and the alteration of ion transport through specific ion channels may contribute to muscle function impairment. In this review, we focused on the molecular mechanisms responsible for muscle damage and potential drugs to be used to alleviate this disabling condition.

Taurine alleviates endoplasmic reticulum stress, inflammatory cytokine expression and mitochondrial oxidative stress induced by high glucose in the muscle cells of olive flounder (Paralichthysolivaceus)

The aim of the present study was to evaluate the effects of taurine on endoplasmic reticulum stress, inflammatory cytokine expression and mitochondrial oxidative stress induced by high glucose in primary cultured muscle cells of olive flounder (Paralichthys olivaceus). Three experimental groups were designed as follows: muscle cells of olive flounder incubated with three kinds of medium containing 5 mM glucose (control), 33 mM glucose (HG) or 33 mM glucose + 10 mM taurine (HG + T), respectively. Results showed that taurine addition significantly alleviated the decreased activity of superoxide dismutase (SOD) and the ratio of reduced to oxidized glutathione (GSH/GSSG) induced by high glucose. The increase of cellular reactive oxygen species (ROS), malondialdehyde content and cell apoptosis induced by high glucose were alleviated by taurine. Besides, gene expression of glucose-regulated protein 78, PKR-like ER kinase, tumor necrosis factor-α, interleukin-6, interleukin-1β, interleukin-8, muscle atrophy F-box protein and muscle RING-finger protein 1 were significantly up-regulated in the HG group, and taurine addition decreased the expression of these genes. High glucose led to the swelling of the endoplasmic reticulum (ER). Meanwhile, the nuclear translocation of nuclear factor κB (NF-κB) and the release of cytochrome C from mitochondria induced by high glucose were suppressed by taurine addition. These results demonstrated that taurine alleviated ERS, inflammation and mitochondrial oxidative stress induced by high glucose in olive flounder muscle cells. The ROS production, NF-κB signaling pathway and mitochondria function were the main targets of the biological effects of taurine under high glucose condition.

Protective role of taurine against oxidative stress (Review)

Taurine is a fundamental mediator of homeostasis that exerts multiple roles to confer protection against oxidant stress. The development of hypertension, muscle/neuro‑​associated disorders, hepatic cirrhosis, cardiac dysfunction and ischemia/reperfusion are examples of some injuries that are linked with oxidative stress. The present review gives a comprehensive description of all the underlying mechanisms of taurine, with the aim to explain its anti‑oxidant actions. Taurine is regarded as a cytoprotective molecule due to its ability to sustain normal electron transport chain, maintain glutathione stores, upregulate anti‑oxidant responses, increase membrane stability, eliminate inflammation and prevent calcium accumulation. In parallel, the synergistic effect of taurine with other potential therapeutic modalities in multiple disorders are highlighted. Apart from the results derived from research findings, the current review bridges the gap between bench and bedside, providing mechanistic insights into the biological activity of taurine that supports its potential therapeutic efficacy in clinic. In the future, further clinical studies are required to support the ameliorative effect of taurine against oxidative stress.

The Effects of Calcium-β-Hydroxy-β-Methylbutyrate on Aging-Associated Apoptotic Signaling and Muscle Mass and Function in Unloaded but Nonatrophied Extensor Digitorum Longus Muscles of Aged Rats

Beta-hydroxy-beta-methylbutyrate (HMB), a naturally occurring leucine metabolite, has been shown to attenuate plantar flexor muscle loss and increase myogenic stem cell activation during reloading after a period of significant muscle wasting by disuse in old rodents. However, it was less clear if HMB would alter dorsiflexor muscle response to unloading or reloading when there was no significant atrophy that was induced by unloading. In this study, we tested if calcium HMB (Ca-HMB) would improve muscle function and alter apoptotic signaling in the extensor digitorum longus (EDL) of aged animals that were unloaded but did not undergo atrophy. The EDL muscle was unloaded for 14 days by hindlimb suspension (HS) in aged (34-36 mo.) male Fisher 344 × Brown Norway rats. The rats were removed from HS and allowed normal cage ambulation for 14 days of reloading (R). Throughout the study, the rats were gavaged daily with 170 mg of Ca-HMB or water 7 days prior to HS, then throughout 14 days of HS and 14 days of recovery after removing HS. The animals' body weights were significantly reduced by ~18% after 14 days of HS and continued to decline by ~22% during R as compared to control conditions; however, despite unloading, EDL did not atrophy by HS, nor did it increase in mass after R. No changes were observed in EDL twitch contraction time, force production, fatigue resistance, fiber cross-sectional area, or markers of nuclear apoptosis (myonuclei + satellite cells) after HS or R. While HS and R increased the proapoptotic Bax protein abundance, BCL-2 abundance was also increased as was the frequency of TUNEL-positive myonuclei and satellite cells, yet muscle mass and fiber cross-sectional area did not change and Ca-HMB treatment had no effect reducing apoptotic signaling. These data indicate that (i) increased apoptotic signaling preceded muscle atrophy or occurred without significant EDL atrophy and (ii) that Ca-HMB treatment did not improve EDL signaling, muscle mass, or muscle function in aged rats, when HS and R did not impact mass or function.

Protein and amino acids for skeletal muscle health in aging

Proteins and its building blocks, amino acids, have many physiological roles in the body. While some amino acids can be synthesized endogenously, exogenous protein and amino acids are necessary to maintain homeostasis. Because skeletal muscle contains a large portion of endogenous protein and plays important roles in movement, regulation, and metabolism, imbalanced protein and amino acid availability may result in clinical conditions including skeletal muscle atrophy, impaired muscle growth or regrowth, and functional decline. Aging is associated with changes in protein metabolism and multiple physiological and functional alterations in the skeletal muscle that are accentuated by decreased dietary protein intake and impaired anabolic responses to stimuli. Inactivity and chronically elevated inflammation of the skeletal muscle can initiate and/or augment pathological remodeling of the tissue (i.e., increase of fat and fibrotic tissues and atrophy of the muscle). Defining an adequate amount of dietary protein that is appropriate to maintain the availability of amino acids for biological needs is necessary but is still widely debated for older adults. This chapter will provide (i) an overview of dietary protein and amino acids and their role in skeletal muscle health; (ii) an overview of skeletal muscle structure and function and the deterioration of muscle that occurs with advancing age; (iii) a discussion of the relationship between protein/amino acid metabolism and skeletal muscle decline with aging; and (iv) a brief discussion of optimal protein intakes for older adults to maintain skeletal muscle health in aging.

Taurine administration ablates sepsis induced diaphragm weakness

Infection induced diaphragm weakness is a major contributor to death and prolonged mechanical ventilation in critically ill patients. Infection induced muscle dysfunction is associated with activation of muscle proteolytic enzymes, and taurine is known to suppress proteolysis. We therefore postulated that taurine administration may prevent infection induced diaphragm dysfunction. The purpose of this study was to test this hypothesis using a clinically relevant animal model of infection, i.e. cecal ligation puncture induced sepsis (CLP). Studies were performed on (n = 5-7 mice/group): (a) sham operated controls, (b) animals with sepsis induced by CLP, (c) sham operated animals given taurine (75 mg/kg/d, intraperitoneally), and (d) CLP animals given taurine. At intervals after surgery animals were euthanized, diaphragm force generation measured in vitro, and diaphragm calpain, caspase and proteasomal activity determined. CLP elicited a large reduction in diaphragm specific force generation at 24 h (1-150 Hz, p < 0.001) and taurine significantly attenuated CLP induced diaphragm weakness at all stimulation frequencies (p < 0.001). CLP induced significant increases in diaphragm calpain, caspase and proteasomal activity; taurine administration prevented increases in the activity of all three pathways. In additional time course experiments, diaphragm force generation remained at control levels over 72 h in CLP animals treated with daily taurine administration, while CLP animals demonstrated severe, sustained reductions in diaphragm strength (p < 0.01 for all time points). Our results indicate that taurine administration prevents infection induced diaphragm weakness and reduces activation of three major proteolytic pathways. Because this agent is has been shown to be safe, non-toxic when administered to humans, taurine may have a role in treating infection induced diaphragm weakness. Future clinical studies will be needed to assess this possibility.

Overnight Steady-State Infusions of Parenteral Nutrition on Myosin Heavy Chain Transcripts in Rectus Abdominis Muscle Related to Amino Acid Transporters, Insulin-like Growth Factor 1, and Blood Amino Acids in Patients Aimed at Major Surgery

BACKGROUND

Evaluation of improvements by nutrition support to severely ill patients requires sensitive methods to demonstrate activation of protein synthesis in various tissues from groups with a limited number of patients to be statistically efficient. This study examines effects of standard parenteral nutrition (PN) on abdominal muscle transcripts of amino acid (AA) transporters, myosin heavy chains (MHCs), and the insulin-like growth factor 1 and its receptor (IGF-1/IGF-1R) in patients aimed at major surgery.

METHODS

Twenty-two randomized patients received steady-state PN (0.16 gN/kg/d, 30 kcal/kg/d) or saline infusions for 12 hours before operation. Blood samples and muscle biopsies were obtained at operation start. Muscle messenger RNA (mRNA) levels of AA transporters (solute carrier family members SNAT2, LAT1, LAT3, LAT4, TAUT, PAT1, CD98), IGF-1, IGF-1R, MHC isoforms (MHC1, MHC2A, MHC2X), and LAT3 protein were quantified and related to concentrations of AA, IGF-1, insulin, and metabolic substrates in blood.

RESULTS

Muscle mRNA LAT3, LAT4, IGF-1R, and MHC2A increased by PN infusion, with correlations to specific AA transporters and MHC isoforms (P < .01-.05). TAUT and LAT3 correlated to slow (MHC1) and fast (MHC2A, MHC2X) isoforms (P < .001-.02). Muscle IGF-1 mRNA correlated to plasma essential AAs, whereas IGF-1R mRNA was related to LAT3, MHC2A, and serum IGF-1 (P < .001-.03).

CONCLUSIONS

The results confirm that short-term preoperative PN activates transcription of AA transporters and myosin isoforms. Thus, combinations of methods on gene transcription and translation of muscle proteins can be applied to define efficient combinations of nutrition and hormones to catabolic patients in preoperative and postoperative settings.

Effect of dietary β-alanine supplementation on growth performance, meat quality, carnosine content, and gene expression of carnosine-related enzymes in broilers

The objective of the current study was to investigate the effect of dietary β-alanine supplementation on growth performance, meat quality, antioxidant ability, carnosine content, and gene expression of carnosine-related enzymes in broiler chicks. We randomly assigned 540 1-day-old Arbor Acres broilers to 5 dietary treatments supplemented with 0 (control group), 250, 500, 1,000, or 2,000 mg/kg of β-alanine (mg β-alanine per kg feed). Each treatment included 6 replicates of 18 birds. The feeding trial lasted for 42 d. Dietary β-alanine supplementation linearly and quadratically increased the average daily gain (ADG) during the starting period (d 1 to 21, P = 0.02 and P = 0.002). The feed conversion ratio (FCR) decreased quadratically in response to dietary β-alanine supplementation during the starting and entire periods (P < 0.001 and P = 0.003, respectively). For the entire period, the predicted best FCR would be achieved when β-alanine was fed at a level of 1,100 mg/kg from quadratic regression. The concentrations of carnosine and β-alanine in breast muscle increased quadratically with dietary β-alanine supplementation (d 42, P < 0.001 and P = 0.001, respectively). The predicted dietary β-alanine level for highest breast carnosine content was 1,196 mg/kg. Dietary supplementation with β-alanine reduced the taurine concentrations in plasma (d 42, linear and quadratic, P < 0.001). Breast muscle yield increased linearly and quadratically in response to dietary β-alanine addition (d 21, P = 0.017 and P = 0.007). Dietary supplementation with β-alanine quadratically reduced the shear force (P = 0.003), whereas a*45 min and a*24 h values increased quadratically in response to dietary β-alanine supplementation (d 42, P = 0.020 and P = 0.021, respectively). Dietary β-alanine addition quadratically enhanced the expression of carnosine synthase and taurine transporter mRNAs (P < 0.05). Overall, dietary β-alanine supplementation improved growth performance and carnosine content, ameliorated antioxidant capacity and meat quality, and upregulated the gene expression of carnosine synthesis-related enzymes in broiler chicks.

ISSN exercise & sports nutrition review update: research & recommendations

Background

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. In the year 2017 alone, 2082 articles were published under the key words ‘sport nutrition’. Consequently, staying current with the relevant literature is often difficult.

Methods

This paper is an ongoing update of the sports nutrition review article originally published as the lead paper to launch the Journal of the International Society of Sports Nutrition in 2004 and updated in 2010. It presents a well-referenced overview of the current state of the science related to optimization of training and performance enhancement through exercise training and nutrition. Notably, due to the accelerated pace and size at which the literature base in this research area grows, the topics discussed will focus on muscle hypertrophy and performance enhancement. As such, this paper provides an overview of: 1.) How ergogenic aids and dietary supplements are defined in terms of governmental regulation and oversight; 2.) How dietary supplements are legally regulated in the United States; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of nutritional approaches to augment skeletal muscle hypertrophy and the potential ergogenic value of various dietary and supplemental approaches.

Conclusions

This updated review is to provide ISSN members and individuals interested in sports nutrition with information that can be implemented in educational, research or practical settings and serve as a foundational basis for determining the efficacy and safety of many common sport nutrition products and their ingredients.

Resveratrol Enhances Exercise-Induced Cellular and Functional Adaptations of Skeletal Muscle in Older Men and Women

Older men (n = 12) and women (n = 18) 65-80 years of age completed 12 weeks of exercise and took either a placebo or resveratrol (RSV) (500 mg/d) to test the hypothesis that RSV treatment combined with exercise would increase mitochondrial density, muscle fatigue resistance, and cardiovascular function more than exercise alone. Contrary to our hypothesis, aerobic and resistance exercise coupled with RSV treatment did not reduce cardiovascular risk further than exercise alone. However, exercise added to RSV treatment improved the indices of mitochondrial density, and muscle fatigue resistance more than placebo and exercise treatments. In addition, subjects that were treated with RSV had an increase in knee extensor muscle peak torque (8%), average peak torque (14%), and power (14%) after training, whereas exercise did not increase these parameters in the placebo-treated older subjects. Furthermore, exercise combined with RSV significantly improved mean fiber area and total myonuclei by 45.3% and 20%, respectively, in muscle fibers from the vastus lateralis of older subjects. Together, these data indicate a novel anabolic role of RSV in exercise-induced adaptations of older persons and this suggests that RSV combined with exercise might provide a better approach for reversing sarcopenia than exercise alone.

Taurine: A Potential Ergogenic Aid for Preventing Muscle Damage and Protein Catabolism and Decreasing Oxidative Stress Produced by Endurance Exercise

The aim of this study was to evaluate the effects of taurine and chocolate milk supplementation on oxidative stress and protein metabolism markers, and aerobic parameters in triathletes.

Methods: A double-blind, crossover study was conducted with 10 male triathletes, aged 30.9 ± 1.3 year, height 1.79 ± 0.01 m and body weight 77.45 ± 2.4 kg. Three grams of taurine and 400 ml of chocolate milk (TAUchoc), or a placebo (chocolate milk) (CHOC) was ingested post exercise for 8 weeks. Oxidative stress marker levels, and 24 h urinary nitrogen, creatinine, and urea excretion were measured before and after 8 weeks of training and supplementation with TAUchoc or CHOC. A maximal incremental running test on a treadmill was performed in order to evaluate aerobic parameters: V_max, heart rate (HR) and rate of perceived exertion (RPE).

Results: TAUchoc treatment during the 8 weeks resulted in increased taurine plasma levels (PRE 201.32 ± 29.03 μmol/L and POST 234.36 ± 35.51 μmol/L, p = 0.01), decreased malondialdehyde levels (19.4%, p = 0.03) and urinary nitrogen excretion (−33%, p = 0.03), and promoted positive nitrogen balance (p = 0.01). There were no changes in reduced glutathione (TAUchoc PRE 0.72 ± 0.08 mmol/L and POST 0.83 ± 0.08 mmol/L; CHOC PRE 0.69 ± 0.08 mmol/L and POST 0.81 ± 0.06 mmol/L), vitamin E plasma levels (TAUchoc PRE 33.99 ± 2.52 μmol/L and 35.95 ± 2.80 μmol/L and CHOC PRE 31.48 ± 2.12 μmol/L and POST 33.77 ± 3.64 μmol/L), or aerobic parameters, which were obtained in the last phase of the maximal incremental running test (V_max TAUchoc PRE 13 ± 1.4 km/h and POST 13.22 ± 1.34 km/h; CHOC PRE 13.11 ± 2.34 km/h and POST 13.11 ± 2.72 km/h), the heart rate values were TAUchoc PRE 181.89 ± 24.18 bpm and POST 168.89 ± 46.56 bpm; CHOC PRE 181.56 ± 2.14 bpm and POST 179.78 ± 3.4 bpm, and the RPE were TAUchoc PRE 8.33 ± 2.4 AU and POST 9.1 ± 2.1 AU; CHOC PRE 8.11 ± 4.94 AU and POST 8.78 ± 2.78 AU).

Conclusion: Taurine supplementation did not improve aerobic parameters, but was effective in increasing taurine plasma levels and decreasing oxidative stress markers, which suggests that taurine may prevent oxidative stress in triathletes.

Risk of Myopathy in Patients in Therapy with Statins: Identification of Biological Markers in a Pilot Study

Statin therapy may induce skeletal muscle damage ranging from myalgia to severe rhabdomyolysis. Our previous preclinical studies showed that statin treatment in rats involves the reduction of skeletal muscle ClC-1 chloride channel expression and related chloride conductance (gCl). An increase of the activity of protein kinase C theta (PKC theta) isoform, able to inactivate ClC-1, may contribute to destabilize sarcolemma excitability. These effects can be detrimental for muscle function leading to drug-induced myopathy. Our goal is to study the causes of statin-induced muscle side effects in patients at the aim to identify biological markers useful to prevent and counteract statin-induced muscle damage. We examined 10 patients, who experienced myalgia and hyper-CK-emia after starting statin therapy compared to 9 non-myopathic subjects not using lipid-lowering drugs. Western Blot (WB) analysis showed a 40% reduction of ClC-1 protein and increased expression of phosphorylated PKC in muscle biopsies of statin-treated patients with respect to untreated subjects, independently from their age and statin type. Real-time PCR analysis showed that despite reduction of the protein, the ClC-1 mRNA was not significantly changed, suggesting post-transcriptional modification. The mRNA expression of a series of genes was also evaluated. MuRF-1 was increased in accord with muscle atrophy, MEF-2, calcineurin (CN) and GLUT-4 transporter were reduced, suggesting altered transcription, alteration of glucose homeostasis and energy deficit. Accordingly, the phosphorylated form of AMPK, measured by WB, was increased, suggesting cytoprotective process activation. In parallel, mRNA expression of Notch-1, involved in muscle cell proliferation, was highly expressed in statin-treated patients, indicating active regeneration. Also, PGC-1-alpha and isocitrate-dehydrogenase increased expression together with increased activity of mitochondrial citrate-synthase, measured by spectrophotometric assay, suggests mitochondrial biogenesis. Thus, the reduction of ClC-1 protein and consequent sarcolemma hyperexcitability together with energy deficiency appear to be among the most important alterations to be associated with statin-related risk of myopathy in humans. Thus, it may be important to avoid statin treatment in pathologies characterized by energy deficit and chloride channel malfunction. This study validates the measure of ClC-1 expression as a reliable clinical test for assessing statin-dependent risk of myopathy.

Potential Benefits of Ameliorating Metabolic and Nutritional Abnormalities in People With Profound Developmental Disabilities

Background:

People with profound developmental disabilities have some of the most severe neurological impairments seen in society, have accelerated mortality due to huge medical challenges, and yet are often excluded from scientific studies. They actually have at least 2 layers of conditions: (1) the original disability and (2) multiple under-recognized and underexplored metabolic and nutritional imbalances involving minerals (calcium, zinc, and selenium), amino acids (taurine, tryptophan), fatty acids (linoleic acid, docosahexaenoic acid, arachidonic acid, adrenic acid, Mead acid, plasmalogens), carnitine, hormones (insulinlike growth factor 1), measures of oxidative stress, and likely other substances and systems.

Summary:

This review provides the first list of metabolic and nutritional abnormalities commonly found in people with profound developmental disabilities and, based on the quality of life effects of similar abnormalities in neurotypical people, indicates the potential effects of these abnormalities in this population which often cannot communicate symptoms.

Key messages:

We propose that improved understanding and management of these disturbed mechanisms would enhance the quality of life of people with profound developmental disabilities. Such insights may also apply to people with other conditions associated with disability, including some diseases requiring stem cell implantation and living in microgravity.

Growth hormone secretagogues prevent dysregulation of skeletal muscle calcium homeostasis in a rat model of cisplatin-induced cachexia

BACKGROUND

Cachexia is a wasting condition associated with cancer types and, at the same time, is a serious and dose-limiting side effect of cancer chemotherapy. Skeletal muscle loss is one of the main characteristics of cachexia that significantly contributes to the functional muscle impairment. Calcium-dependent signaling pathways are believed to play an important role in skeletal muscle decline observed in cachexia, but whether intracellular calcium homeostasis is affected in this situation remains uncertain. Growth hormone secretagogues (GHS), a family of synthetic agonists of ghrelin receptor (GHS-R1a), are being developed as a therapeutic option for cancer cachexia syndrome; however, the exact mechanism by which GHS interfere with skeletal muscle is not fully understood.

METHODS

By a multidisciplinary approach ranging from cytofluorometry and electrophysiology to gene expression and histology, we characterized the calcium homeostasis in fast-twitch extensor digitorum longus (EDL) muscle of adult rats with cisplatin-induced cachexia and established the potential beneficial effects of two GHS (hexarelin and JMV2894) at this level. Additionally, in vivo measures of grip strength and of ultrasonography recordings allowed us to evaluate the functional impact of GHS therapeutic intervention.

RESULTS

Cisplatin-treated EDL muscle fibres were characterized by a ~18% significant reduction of the muscle weight and fibre diameter together with an up-regulation of atrogin1/Murf-1 genes and a down-regulation of Pgc1-a gene, all indexes of muscle atrophy, and by a two-fold increase in resting intracellular calcium, [Ca2+ ]i , compared with control rats. Moreover, the amplitude of the calcium transient induced by caffeine or depolarizing high potassium solution as well as the store-operated calcium entry were ~50% significantly reduced in cisplatin-treated rats. Calcium homeostasis dysregulation parallels with changes of functional ex vivo (excitability and resting macroscopic conductance) and in vivo (forelimb force and muscle volume) outcomes in cachectic animals. Administration of hexarelin or JMV2894 markedly reduced the cisplatin-induced alteration of calcium homeostasis by both common as well as drug-specific mechanisms of action. This effect correlated with muscle function preservation as well as amelioration of various atrophic indexes, thus supporting the functional impact of GHS activity on calcium homeostasis.

CONCLUSIONS

Our findings provide a direct evidence that a dysregulation of calcium homeostasis plays a key role in cisplatin-induced model of cachexia gaining insight into the etiopathogenesis of this form of muscle wasting. Furthermore, our demonstration that GHS administration efficaciously prevents cisplatin-induced calcium homeostasis alteration contributes to elucidate the mechanism of action through which GHS could potentially ameliorate chemotherapy-associated cachexia.

The effect of acute taurine ingestion on 4-km time trial performance in trained cyclists

Taurine (TAU) has been shown to improve exercise time to exhaustion and 3-km running performance; however, no studies have considered the effect of acute TAU ingestion on short duration cycling time trial (TT) performance. The aim of this study was to determine the effects of a single oral acute dose of 1000 mg of TAU on a laboratory simulated 4-km cycling TT. Eleven trained male cyclists performed three, 4-km TTs. The first of the trials was a familiarisation, followed by two subsequent trials which were performed two hours after the consumption of either 1000 mg of TAU or placebo (P), using a double-blind randomised crossover design. Capillary blood samples were obtained prior to the start and immediately after each TT for the measurement of lactate, pH and HCO3-. There was no effect of TAU (p = 0.731, d = 0.151) on performance (390 ± 27 and 388 ± 21 s for TAU and P, respectively), nor were there any condition main effects for VO2, lactate, pH, or HCO3- (p > 0.05) despite post TT changes in lactate (7.3 ± 2.5 mmol l-1, p < 0.001, d = 2.86, 7.6 ± 2.0 mmol l-1 p < 0.001, d = 3.75); pH (-0.255 ± 0.1, p < 0.001, d = 2.62, -0.258 ± 0.09, p < 0.001, d = 2.87); HCO3- (-13.58 ± 2.7 mmol l-1, p < 0.001, d = 5.04 vs. -13.36 ± 2.3, p < 0.001, d = 5.72 for TAU and P, respectively). The findings of this study suggest that a pre-exercise dose of 1000 mg TAU offers no performance advantage during 4-km TT nor does it alter the blood buffering responses in trained cyclists.

The role of E3 ubiquitin-ligases MuRF-1 and MAFbx in loss of skeletal muscle mass

The ubiquitin-proteasome system (UPS) is the main regulatory mechanism of protein degradation in skeletal muscle. The ubiquitin-ligase enzymes (E3s) have a central role in determining the selectivity and specificity of the UPS. Since their identification in 2001, the muscle specific E3s, muscle RING finger-1 (MuRF-1) and muscle atrophy F-box (MAFbx), have been shown to be implicated in the regulation of skeletal muscle atrophy in various pathological and physiological conditions. This review aims to explore the involvement of MuRF-1 and MAFbx in catabolism of skeletal muscle during various pathologies, such as cancer cachexia, sarcopenia of aging, chronic kidney disease (CKD), diabetes, and chronic obstructive pulmonary disease (COPD). In addition, the effects of various lifestyle and modifiable factors (e.g. nutrition, exercise, cigarette smoking, and alcohol) on MuRF-1 and MAFbx regulation will be discussed. Finally, evidence of potential strategies to protect against skeletal muscle wasting through inhibition of MuRF-1 and MAFbx expression will be explored.

Taurine: the appeal of a safe amino acid for skeletal muscle disorders

Taurine is a natural amino acid present as free form in many mammalian tissues and in particular in skeletal muscle. Taurine exerts many physiological functions, including membrane stabilization, osmoregulation and cytoprotective effects, antioxidant and anti-inflammatory actions as well as modulation of intracellular calcium concentration and ion channel function. In addition taurine may control muscle metabolism and gene expression, through yet unclear mechanisms. This review summarizes the effects of taurine on specific muscle targets and pathways as well as its therapeutic potential to restore skeletal muscle function and performance in various pathological conditions. Evidences support the link between alteration of intracellular taurine level in skeletal muscle and different pathophysiological conditions, such as disuse-induced muscle atrophy, muscular dystrophy and/or senescence, reinforcing the interest towards its exogenous supplementation. In addition, taurine treatment can be beneficial to reduce sarcolemmal hyper-excitability in myotonia-related syndromes. Although further studies are necessary to fill the gaps between animals and humans, the benefit of the amino acid appears to be due to its multiple actions on cellular functions while toxicity seems relatively low. Human clinical trials using taurine in various pathologies such as diabetes, cardiovascular and neurological disorders have been performed and may represent a guide-line for designing specific studies in patients of neuromuscular diseases.

Effects of Nandrolone in the Counteraction of Skeletal Muscle Atrophy in a Mouse Model of Muscle Disuse: Molecular Biology and Functional Evaluation

Muscle disuse produces severe atrophy and a slow-to-fast phenotype transition in the postural Soleus (Sol) muscle of rodents. Antioxidants, amino-acids and growth factors were ineffective to ameliorate muscle atrophy. Here we evaluate the effects of nandrolone (ND), an anabolic steroid, on mouse skeletal muscle atrophy induced by hindlimb unloading (HU). Mice were pre-treated for 2-weeks before HU and during the 2-weeks of HU. Muscle weight and total protein content were reduced in HU mice and a restoration of these parameters was found in ND-treated HU mice. The analysis of gene expression by real-time PCR demonstrates an increase of MuRF-1 during HU but minor involvement of other catabolic pathways. However, ND did not affect MuRF-1 expression. The evaluation of anabolic pathways showed no change in mTOR and eIF2-kinase mRNA expression, but the protein expression of the eukaryotic initiation factor eIF2 was reduced during HU and restored by ND. Moreover we found an involvement of regenerative pathways, since the increase of MyoD observed after HU suggests the promotion of myogenic stem cell differentiation in response to atrophy. At the same time, Notch-1 expression was down-regulated. Interestingly, the ND treatment prevented changes in MyoD and Notch-1 expression. On the contrary, there was no evidence for an effect of ND on the change of muscle phenotype induced by HU, since no effect of treatment was observed on the resting gCl, restCa and contractile properties in Sol muscle. Accordingly, PGC1α and myosin heavy chain expression, indexes of the phenotype transition, were not restored in ND-treated HU mice. We hypothesize that ND is unable to directly affect the phenotype transition when the specialized motor unit firing pattern of stimulation is lacking. Nevertheless, through stimulation of protein synthesis, ND preserves protein content and muscle weight, which may result advantageous to the affected skeletal muscle for functional recovery.

Acute effects of taurine on sarcoplasmic reticulum Ca2+ accumulation and contractility in human type I and type II skeletal muscle fibers

Taurine occurs in high concentrations in muscle and is implicated in numerous physiological processes, yet its effects on many aspects of contractility remain unclear. Using mechanically skinned segments of human vastus lateralis muscle fibers, we characterized the effects of taurine on sarcoplasmic reticulum (SR) Ca2+ accumulation and contractile apparatus properties in type I and type II fibers. Prolonged myoplasmic exposure (>10 min) to taurine substantially increased the rate of accumulation of Ca2+ by the SR in both fiber types, with no change in the maximum amount accumulated; no such effect was found with carnosine. SR Ca2+ accumulation was similar with 10 or 20 mM taurine, but was significantly slower at 5 mM taurine. Cytoplasmic taurine (20 mM) had no detectable effects on the responsiveness of the Ca2+ release channels in either fiber type. Taurine caused a small increase in Ca2+ sensitivity of the contractile apparatus in type I fibers, but type II fibers were unaffected; maximum Ca2+-activated force was unchanged in both cases. The effects of taurine on SR Ca2+ accumulation 1) only became apparent after prolonged cytoplasmic exposure, and 2) persisted for some minutes after complete removal of taurine from the cytoplasm, consistent with the hypothesis that the effects were due to an action of taurine from inside the SR. In summary, taurine potentiates the rate of SR Ca2+ uptake in both type I and type II human fibers, possibly via an action from within the SR lumen, with the degree of potentiation being significantly reduced at low physiological taurine levels.

Effects of resveratrol on the recovery of muscle mass following disuse in the plantaris muscle of aged rats

Aging is associated with poor skeletal muscle regenerative ability following extended periods of hospitalization and other forms of muscular disuse. Resveratrol (3,5,4’-trihydroxystilbene) is a natural phytoalexin which has been shown in skeletal muscle to improve oxidative stress levels in muscles of aged rats. As muscle disuse and reloading after disuse increases oxidative stress, we hypothesized that resveratrol supplementation would improve muscle regeneration after disuse. A total of thirty-six male Fisher 344 × Brown Norway rats (32 mo.) were treated with either a water vehicle or resveratrol via oral gavage. The animals received hindlimb suspension for 14 days. Thereafter, they were either sacrificed or allowed an additional 14 day period of cage ambulation during reloading. A total of six rats from the vehicle and the resveratrol treated groups were used for the hindlimb suspension and recovery protocols. Furthermore, two groups of 6 vehicle treated animals maintained normal ambulation throughout the experiment, and were used as control animals for the hindlimb suspension and reloading groups. The data show that resveratrol supplementation was unable to attenuate the decreases in plantaris muscle wet weight during hindlimb suspension but it improved muscle mass during reloading after hindlimb suspension. Although resveratrol did not prevent fiber atrophy during the period of disuse, it increased the fiber cross sectional area of type IIA and IIB fibers in response to reloading after hindlimb suspension. There was a modest enhancement of myogenic precursor cell proliferation in resveratrol-treated muscles after reloading, but this failed to reach statistical significance. The resveratrol-associated improvement in type II fiber size and muscle mass recovery after disuse may have been due to decreases in the abundance of pro-apoptotic proteins Bax, cleaved caspase 3 and cleaved caspase 9 in reloaded muscles. Resveratrol appears to have modest therapeutic benefits for improving muscle mass after disuse in aging.

Nutritional strategies to counteract muscle atrophy caused by disuse and to improve recovery

Periods of immobilisation are often associated with pathologies and/or ageing. These periods of muscle disuse induce muscle atrophy which could worsen the pathology or elderly frailty. If muscle mass loss has positive effects in the short term, a sustained/uncontrolled muscle mass loss is deleterious for health. Muscle mass recovery following immobilisation-induced atrophy could be critical, particularly when it is uncompleted as observed during ageing. Exercise, the best way to recover muscle mass, is not always applicable. So, other approaches such as nutritional strategies are needed to limit muscle wasting and to improve muscle mass recovery in such situations. The present review discusses mechanisms involved in muscle atrophy following disuse and during recovery and emphasises the effect of age in these mechanisms. In addition, the efficiency of nutritional strategies proposed to limit muscle mass loss during disuse and to improve protein gain during recovery (leucine supplementation, whey proteins, antioxidants and anti-inflammatory compounds, energy intake) is also discussed.

Paracrine effects of IGF-1 overexpression on the functional decline due to skeletal muscle disuse: molecular and functional evaluation in hindlimb unloaded MLC/mIgf-1 transgenic mice

Slow-twitch muscles, devoted to postural maintenance, experience atrophy and weakness during muscle disuse due to bed-rest, aging or spaceflight. These conditions impair motion activities and can have survival implications. Human and animal studies demonstrate the anabolic role of IGF-1 on skeletal muscle suggesting its interest as a muscle disuse countermeasure. Thus, we tested the role of IGF-1 overexpression on skeletal muscle alteration due to hindlimb unloading (HU) by using MLC/mIgf-1 transgenic mice expressing IGF-1 under the transcriptional control of MLC promoter, selectively activated in skeletal muscle. HU produced atrophy in soleus muscle, in terms of muscle weight and fiber cross-sectional area (CSA) reduction, and up-regulation of atrophy gene MuRF1. In parallel, the disuse-induced slow-to-fast fiber transition was confirmed by an increase of the fast-type of the Myosin Heavy Chain (MHC), a decrease of PGC-1α expression and an increase of histone deacetylase-5 (HDAC5). Consistently, functional parameters such as the resting chloride conductance (gCl) together with ClC-1 chloride channel expression were increased and the contractile parameters were modified in soleus muscle of HU mice. Surprisingly, IGF-1 overexpression in HU mice was unable to counteract the loss of muscle weight and the decrease of fiber CSA. However, the expression of MuRF1 was recovered, suggesting early effects on muscle atrophy. Although the expression of PGC-1α and MHC were not improved in IGF-1-HU mice, the expression of HDAC5 was recovered. Importantly, the HU-induced increase of gCl was fully contrasted in IGF-1 transgenic mice, as well as the changes in contractile parameters. These results indicate that, even if local expression does not seem to attenuate HU-induced atrophy and slow-to-fast phenotype transition, it exerts early molecular effects on gene expression which can counteract the HU-induced modification of electrical and contractile properties. MuRF1 and HDAC5 can be attractive therapeutic targets for pharmacological countermeasures and then deserve further investigations.

Automated methods for the analysis of skeletal muscle fiber size and metabolic type

It is of interest to quantify the size, shape, and metabolic subtype of skeletal muscle fibers in many areas of biomedical research. To do so, skeletal muscle samples are sectioned transversely to the length of the muscle and labeled for extracellular or membrane proteins to delineate the fiber boundaries and additionally for biomarkers related to function or metabolism. The samples are digitally photographed and the fibers "outlined" for quantification of fiber cross-sectional area (CSA) using pointing devices interfaced to a computer, which is tedious, prone to error, and can be nonobjective. Here, we review methods for characterizing skeletal muscle fibers and describe new automated techniques, which rapidly quantify CSA and biomarkers. We discuss the applications of these methods to the characterization of mitochondrial dysfunctions, which underlie a variety of human afflictions, and we present a novel approach, utilizing images from the online Human Protein Atlas to predict relationships between fiber-specific protein expression, function, and metabolism.