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Many cancer patients undergoing treatment experience cancer-related fatigue (CRF). Inflammatory markers are correlated with CRF but are not routinely targeted for treatment. We previously demonstrated in an NIH-funded placebo-controlled, double-blind, randomized clinical trial (NCT00878995, closed to follow-up) that seven weekly injections of 100 mg adjunct testosterone preserved lean body mass in cancer patients undergoing standard-of-care treatment in a hospital setting. Because testosterone therapy can reduce circulating proinflammatory cytokines, we conducted an ancillary analysis to determine if this testosterone treatment reduced inflammatory burden and improved CRF symptoms and health-related quality of life. Randomization was computer-generated and managed by the pharmacy, which dispensed testosterone and placebo in opaque syringes to the administering study personnel. A total of 24 patients were randomized (14 placebo, 10 testosterone), and 21 were included in the primary analysis (11 placebo, 10 testosterone). Testosterone therapy did not ameliorate CRF symptoms (placebo to testosterone difference in predicted mean multidimensional fatigue symptom inventory scores: -5.6, 95% CI: -24.6 to 13.3), improve inflammatory markers, or preserve health-related quality of life and functional measures of performance in late-stage cancer patients.

Patients with chronic traumatic brain injury (TBI) requiring long-term, permanent care suffer a myriad of clinical symptoms (i.e., impaired cognition, fatigue, and other conditions) that persist for years beyond the acute brain injury. In addition to these comorbid clinical symptoms, chronic TBI patients exhibit altered amino acid and hormonal profiles with distinct cytokine patterns suggesting chronic inflammation. This metabolic link suggests a role of the gut-brain axis in chronic TBI. Thus, we utilized a two-site trial to investigate the role of the gut-brain axis in comorbidities of chronic TBI. The fecal microbiome profile of 22 moderate/severe TBI patients residing in permanent care facilities in Texas and California was compared to 18 healthy age-matched control subjects working within the participating facilities. Each fecal microbiome was characterized by 16S(V4) ribosomal RNA (rRNA) gene sequencing and metagenomic genome sequencing approaches followed by confirmatory full 16S rRNA gene sequencing or focused tuf gene speciation and specific quantitative polymerase chain reaction evaluation of selected genera or species. The average chronic TBI patient fecal microbiome structure was significantly different compared to the control cohort, and these differences persisted after group stratification analysis to identify any unexpected confounders. Notably, the fecal microbiome of the chronic TBI cohort had absent or reduced Prevotella spp. and Bacteroidies spp. Conversely, bacteria in the Ruminococcaceae family were higher in abundance in TBI compared to control profiles. Previously reported hypoaminoacidemia, including significantly reduced levels of l-tryptophan, l-sarcosine, ß-alanine, and alanine, positively correlated with the reduced levels of Prevotella spp. in the TBI cohort samples compared to controls. Although the sequelae of gut-brain axis disruption after TBI is not fully understood, characterizing TBI-related alterations in the fecal microbiome may provide biomarkers and therapeutic targets to address patient morbidity.

Introduction: Long-term head-down bed rest (HDBR) results in musculoskeletal losses similar to those observed during long-term space flight. Agents such as testosterone, in addition to regular exercise, are effective countermeasures for reducing loss of skeletal muscle mass and function., Objective: We investigated the skeletal muscle proteome of healthy men in response to long term HDBR alone (CON) and to HDBR with exercise (PEX) or exercise plus testosterone (TEX) countermeasures., Method: Biopsies were performed on the vastus lateralis before (pre) HDBR and on HDBR days 32 (mid) and 64 (post). Extracted proteins from these skeletal muscle biopsies were subjected to 2-dimensional gel electrophoresis (2DE), stained for phosphoproteins (Pro-Q Diamond dye) and total proteins (Sypro Ruby dye). Proteins showing significant fold differences (t-test p ≤ 0.05) in abundance or phosphorylation state at mid or post were identified by mass spectroscopy (MS)., Results: From a total of 932 protein spots, 130 spots were identified as potentially altered in terms of total protein or phosphoprotein levels due to HDBR and/or countermeasures, and 59 unique molecules emerged from MS analysis. Top canonical pathways identified through IPA included calcium signaling, actin cytoskeleton signaling, integrin linked kinase (ILK) signaling, and epithelial adherens junction signaling. Data from the pre-HDBR proteome supported the potential for predicting physiological post-HDBR responses such as the individual's potential for loss vs. maintenance of muscle mass and strength., Conclusions: HDBR resulted in alterations to skeletal muscle abundances and phosphorylation of several structural and metabolic proteins. Inclusion of exercise alone or in combination with testosterone treatment modulated the proteomic responses towards cellular reorganization and hypertrophy, respectively. Finally, the baseline proteome may aid in the development of personalized countermeasures to mitigate health risks in astronauts as related to loss of muscle mass and function., Competing Interests: The authors have declared that no competing interests exist.

Intramyocellular triglyceride (imTG) in skeletal muscle plays a significant role in metabolic health, and an infusion of [ 13 C 16 ]palmitate can be used to quantitate the in vivo fractional synthesis rate (FSR) and absolute synthesis rate (ASR) of imTGs. However, the extramyocellular TG (emTG) pool, unless precisely excised, contaminates the imTG pool, diluting the imTG-bound tracer enrichment and leading to underestimation of FSR. Because of the difficulty of excising the emTGs precisely, it would be advantageous to be able to calculate the imTG synthesis rate without dissecting the emTGs from each sample. Here, we tested the hypothesis that the ASR of total TGs (tTGs), a combination of imTGs and emTGs, calculated as "FSR × tTG pool," reasonably represents the imTG synthesis. Muscle lipid parameters were measured in nine healthy women at 90 and 170 min after the start of [ 13 C 16 ]palmitate infusion. While the measurements of tTG content, enrichment, and FSR did not correlate ( P > 0.05), those of the tTG ASR were significantly correlated ( r = 0.947, P < 0.05). These results demonstrate that when imTGs and emTGs are pooled, the resulting underestimation of imTG FSR is balanced by the overestimation of the imTG content. We conclude that imTG metabolism is reflected by the measurement of the tTG ASR., (Copyright © 2018 by the American Society for Biochemistry and Molecular Biology, Inc.)

Introduction: Prolonged confinement to head-down bed rest (HDBR) results in musculoskeletal losses similar to those observed during long-duration space flight. Exercise countermeasures by themselves have not completely prevented the deleterious losses in muscle mass or function in HDBR or space flight., Purpose: The objective was to investigate the safety and efficacy of intermittent, low-dose testosterone treatment in conjunction with NASA exercise (SPRINT) countermeasures during 70 d of 6° HDBR., Methods: Healthy men (35 ± 8 yr) were randomized into one of three groups that remained inactive (CON) or performed exercise 6 d·wk in addition to receiving either placebo (PEX) or testosterone treatment (TEX, 100 mg·wk). Testosterone/placebo injections were administered once a week for 2 wk, followed by 2 wk off and so on, during HDBR., Results: Total, leg, and trunk lean body mass (LBM) consistently decreased in CON, increased in TEX, and had little or no changes in PEX. Total, leg, and trunk fat mass consistently increased in CON and PEX and decreased in TEX. Leg strength decreased in CON, whereas PEX and TEX were protected against loss in strength. Changes in leg LBM correlated positively with changes in leg muscle strength., Conclusions: Addition of a testosterone countermeasure enhanced the preventative actions of exercise against body composition changes during long-term HDBR in healthy eugonadal men. This is the first report to demonstrate that cycled, low-dose testosterone treatment increases LBM under conditions of strict exercise control. These results are clinically relevant to the development of safe and effective therapies against muscle atrophy during long-term bed rest, aging, and disease where loss of muscle mass and strength is a risk. The potential space flight applications of such countermeasure combinations deserve further investigations.

Due to immunosenescence, older adults are particularly susceptible to lung-based viral infections, with increased severity of symptoms in those with underlying chronic lung disease. Repeated respiratory viral infections produce lung maladaptations, accelerating pulmonary dysfunction. Toll like 3 receptor (TLR3) is a membrane protein that senses exogenous double-stranded RNA to activate the innate immune response to a viral infection. Polyinosinic-polycytidylic acid [poly(I:C)] mimics double stranded RNA and has been shown to activate TLR3. Utilizing an established mouse viral exacerbation model produced by repetitive intranasal poly(I:C) administration, we sought to determine whether repetitive poly(I:C) treatment induced negative muscle adaptations (i.e. atrophy, weakness, and loss of function). We determined skeletal muscle morphological properties (e.g. fiber-type, fiber cross-sectional area, muscle wet mass, etc.) from a treated group ((poly(I:C), n = 9) and a sham-treated control group (PBS, n = 9); age approximately 5 months. In a subset (n = 4 for both groups), we determined in vivo physical function (using grip test for strength, rotarod for overall motor function, and treadmill for endurance) and muscle contractile properties with in vitro physiology (in the EDL, soleus and diaphragm). Our findings demonstrate that poly(I:C)-treated mice exhibit both muscle morphological and functional deficits. Changes of note when comparing poly(I:C)-treated mice to PBS-treated controls include reductions in fiber cross-sectional area (-27% gastrocnemius, -25% soleus, -16% diaphragm), contractile dysfunction (soleus peak tetanic force, -26%), muscle mass (gastrocnemius -19%, soleus -23%), physical function (grip test -34%), body mass (-20%), and altered oxidative capacity (140% increase in succinate dehydrogenase activity in the diaphragm, but 66% lower in the gastrocnemius). Our data is supportive of a new model of cachexia/sarcopenia that has potential for future research into the mechanisms underlying muscle wasting., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: Cancer cachexia negatively impacts cancer-related treatment options, quality of life, morbidity, and mortality, yet no established therapies exist. We investigated the anabolic properties of testosterone to limit the loss of body mass in late stage cancer patients undergoing standard of care cancer treatment., Methods: A randomized, double-blind, placebo-controlled phase II clinical trial was undertaken to assess the potential therapeutic role of adjunct testosterone to limit loss of body mass in patients with squamous cell carcinoma of the cervix or head and neck undergoing standard of care treatment including chemotherapy and chemoradiation. Patients were randomly assigned in blocks to receive weekly injections of either 100 mg testosterone enanthate or placebo for 7 weeks. The primary outcome was per cent change in lean body mass, and secondary outcomes included assessment of quality of life, tests of physical performance, muscle strength, daily activity levels, resting energy expenditure, nutritional intake, and overall survival., Results: A total of 28 patients were enrolled, 22 patients were studied to completion, and 21 patients were included in the final analysis (12 placebo, nine testosterone). Adjunct testosterone increased lean body mass by 3.2% (95% confidence interval [CI], 0-7%) whereas those receiving placebo lost 3.3% (95% CI, -7% to 1%, P = 0.015). Although testosterone patients maintained more favourable body condition, sustained daily activity levels, and showed meaningful improvements in quality of life and physical performance, overall survival was similar in both treatment groups., Conclusions: In patients with advanced cancer undergoing the early phase of standard of care therapy, adjunct testosterone improved lean body mass and was also associated with increased quality of life, and physical activity compared with placebo., (© 2018 The Authors. Journal of Cachexia, Sarcopenia and Muscle published by John Wiley & Sons Ltd on behalf of the Society on Sarcopenia, Cachexia and Wasting Disorders.)

Background: Impaired adipose tissue function and lower levels of high density lipoprotein cholesterol (HDL-C) have been implicated in the development of vascular dementia, and metabolic diseases such as hypertension, atherosclerosis, type 2 diabetes (T2D) and metabolic syndrome. Interestingly, both the substrate fluxes in adipose tissue and HDL-C concentration differ between men and women. Moreover, adipose tissue cholesterol efflux has been implicated in modulation of HDL-C levels. Thus, we aimed to determine if the association between serum estradiol levels and adipose tissue cholesterol efflux is sex-dependent., Method: We evaluated the serum estradiol levels and adipose tissue cholesterol efflux in young healthy men (n=5) and women (n=3). Adipose tissue cholesterol efflux was determined using subcutaneous microdialysis probes. Linear regression analyses were used to determine the relationship between the parameters, p<0.05 was considered as statistically significant., Results: Our data demonstrated that serum estradiol levels directly associated with adipose tissue cholesterol efflux; however, the relationships may be sex-dependent. We discussed our results in the context of currently available data regarding sex-dependent variability in adipose tissue function and HDL-C metabolism as a potential contributor to higher rates of vascular dementia in men. Further research is required to understand the sex-dependent and -independent variabilities in adipose tissue metabolism to determine novel targets for interventions to prevent the development of vascular dementia., (Copyright © 2017 ISDN. Published by Elsevier Ltd. All rights reserved.)

Background: Circulating acyl-carnitines (acyl-CNTs) are associated with insulin resistance (IR) and type 2 diabetes (T2D) in both rodents and humans. However, the mechanisms whereby circulating acyl-CNTs are increased in these conditions and their role in whole-body metabolism remains unknown. The purpose of this study was to determine if, in humans, blood cells contribute in production of circulating acyl-CNTs and associate with whole-body fat metabolism., Methods and Results: Eight non-diabetic healthy women (age: 47 ± 19 y; BMI: 26 ± 1 kg·m -2 ) underwent stable isotope tracer infusion and hyperinsulinemic-euglycemic clamp study to determine in vivo whole-body fatty acid flux and insulin sensitivity. Blood samples collected at baseline (0 min) and after 3 h of clamp were used to determine the synthesis rate of palmitoyl-carnitine (palmitoyl-CNT) in vitro. The fractional synthesis rate of palmitoyl-CNT was significantly higher during hyperinsulinemia (0.788 ± 0.084 vs. 0.318 ± 0.012%·hr -1 , p = 0.001); however, the absolute synthesis rate (ASR) did not differ between the periods (p = 0.809) due to ∼30% decrease in blood palmitoyl-CNT concentration (p = 0.189) during hyperinsulinemia. The ASR of palmitoyl-CNT significantly correlated with the concentration of acyl-CNTs in basal (r = 0.992, p < 0.001) and insulin (r = 0.919, p = 0.001) periods; and the basal ASR significantly correlated with plasma palmitate oxidation (r = 0.764, p = 0.027)., Conclusion: In women, blood cells contribute to plasma acyl-CNT levels and the acyl-CNT production is linked to plasma palmitate oxidation, a marker of whole-body fat metabolism. Future studies are needed to confirm the role of blood cells in acyl-CNT and lipid metabolism under different physiological (i.e., in response to meal) and pathological (i.e., hyperlipidemia, IR and T2D) conditions., (Copyright © 2016 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.)

We explored the effects of recombinant human growth hormone (rhGH) replacement on physical and cognitive functioning in subjects with a moderate-to-severe traumatic brain injury (TBI) with abnormal growth hormone (GH) secretion. Fifteen individuals who sustained a TBI at least 12 months prior to study enrollment were identified as having abnormal GH secretion by glucagon stimulation testing (maximum GH response less than 8 ng/mL). Peak cardiorespiratory capacity, body composition, and muscle force testing were assessed at baseline and one year after rhGH replacement. Additionally, standardized neuropsychological tests that assess memory, processing speed, and cognitive flexibility, as well as self-report inventories related to depression and fatigue, were administered at baseline and 1 year after rhGH replacement. Comparison tests were performed with proper post hoc analyses. All analyses were carried out at α < 0.05. Peak O 2 consumption, peak oxygen pulse (estimate of cardiac stroke volume), and peak ventilation all significantly increased (p < 0.05). Maximal isometric and isokinetic force production were not altered. Skeletal muscle fatigue did not change but the perceptual rating of fatigue was reduced by ∼25% (p = 0.06). Cognitive performance did not change significantly over time, whereas self-reported symptoms related to depression and fatigue significantly improved. The observed changes suggest that rhGH replacement has a positive impact on cardiorespiratory fitness and a positive impact on perceptual fatigue in survivors of TBI with altered GH secretion.

Individuals with a history of traumatic brain injury (TBI) are at increased risk for a number of disorders, including Alzheimer's disease, Parkinson's disease, and chronic traumatic encephalopathy. However, mediators of the long-term morbidity are uncertain. We conducted a multi-site, prospective trial in chronic TBI patients (∼18 years post-TBI) living in long-term 24-h care environments and local controls without a history of head injury. Inability to give informed consent was exclusionary for participation. A total of 41 individuals (17 moderate-severe TBI, 24 controls) were studied before and after consumption of a standardized breakfast to determine if concentrations of amino acids, cytokines, C-reactive protein, and insulin are potential mediators of long-term TBI morbidity. Analyte concentrations were measured in serum drawn before (fasting) and 1 h after meal consumption. Mean ages were 44 ± 15 and 49 ± 11 years for controls and chronic TBI patients, respectively. Chronic TBI patients had significantly lower circulating concentrations of numerous individual amino acids, as well as essential amino acids (p = 0.03) and large neutral amino acids (p = 0.003) considered as groups, and displayed fundamentally altered cytokine-amino acid relationships. Many years after injury, TBI patients exhibit abnormal metabolic responses and altered relationships between circulating amino acids, cytokines, and hormones. This pattern is consistent with TBI, inducing a chronic disease state in patients. Understanding the mechanisms causing the chronic disease state could lead to new treatments for its prevention.

Mitochondrial health is critical to physiological function, particularly in tissues with high ATP turnover, such as striated muscle. It has been postulated that derangements in skeletal muscle mitochondrial function contribute to impaired physical function in older adults. Here, we determined mitochondrial respiratory capacity and coupling control in skeletal muscle biopsies obtained from young and older adults. Twenty-four young (28 ± 7 yr) and thirty-one older (62 ± 8 yr) adults were studied. Mitochondrial respiration was determined in permeabilized myofibers from the vastus lateralis after the addition of substrates oligomycin and CCCP. Thereafter, mitochondrial coupling control was calculated. Maximal coupled respiration (respiration linked to ATP production) was lower in muscle from older vs. young subjects (P < 0.01), as was maximal uncoupled respiration (P = 0.06). Coupling control in response to the ATP synthase inhibitor oligomycin was lower in older adults (P < 0.05), as was the mitochondria flux control ratio, coupled respiration normalized to maximal uncoupled respiration (P < 0.05). Calculation of respiratory function revealed lower respiration linked to ATP production (P < 0.001) and greater reserve respiration (P < 0.01); i.e., respiratory capacity not used for phosphorylation in muscle from older adults. We conclude that skeletal muscle mitochondrial respiratory capacity and coupling control decline with age. Lower respiratory capacity and coupling efficiency result in a reduced capacity for ATP production in skeletal muscle of older adults., (Copyright © 2015 the American Physiological Society.)

Context: In older adults, loss of mobility due to sarcopenia is exacerbated in men with low serum T. T replacement therapy is known to increase muscle mass and strength, but the effect of weekly (WK) vs monthly (MO) administration on specific fiber types is unknown., Objective: To determine the efficacy of WK vs MO T replacement on the size and functional capacity of individual fast and slow skeletal muscle fiber types., Design, Setting, and Patients: Subjects were randomized into a 5-month, double-blind, placebo-controlled trial. All subjects (ages, 61-71 y) were community-dwelling men who had T levels < 500 ng/dL., Intervention: Subjects were dosed weekly for 5 months, receiving continuous T (WK, n = 5; 100 mg T enanthate, im injection), monthly cycled T (MO, n = 7; alternating months of T and placebo), or placebo (n = 7). Muscle biopsies of the vastus lateralis were obtained before and after treatment., Main Outcome Measures: Main outcomes for individual slow and fast fibers included fiber diameter, peak force (P0), rate of tension development, maximal shortening velocity, peak power, and Ca(2+) sensitivity., Results: Both treatments increased fiber diameter and peak power, with WK treatment 5-fold more effective than MO in increasing type I fiber P0. WK effects on fiber diameter and force were 1.5-fold higher in slow fibers compared to fast fibers. In fast type II fibers, diameter and P0 increased similarly between treatments. The increased power was entirely due to increased fiber size and force., Conclusions: In conclusion, T replacement effects were fiber-type dependent, restricted to increases in cell size, P0, and peak power, and dependent on the paradigm selected (WK vs MO).

Rapamycin at high doses (2-10 mg/kg body weight) inhibits mammalian target of rapamycin complex 1 (mTORC1) and protein synthesis in mice. In contrast, low doses of rapamycin (10 μg/kg) increase mTORC1 activity and protein synthesis in skeletal muscle. Similar changes are found with SLF (synthetic ligand for FKBP12, which does not inhibit mTORC1) and in mice with a skeletal muscle-specific FKBP12 deficiency. These interventions also increase Ca(2+) influx to enhance refilling of sarcoplasmic reticulum Ca(2+) stores, slow muscle fatigue, and increase running endurance without negatively impacting cardiac function. FKBP12 deficiency or longer treatments with low dose rapamycin or SLF increase the percentage of type I fibers, further adding to fatigue resistance. We demonstrate that FKBP12 and its ligands impact multiple aspects of muscle function., (© 2014 by The American Society for Biochemistry and Molecular Biology, Inc.)

Background: Fatigue is a common and debilitating phenomenon experienced by individuals with traumatic brain injury (TBI) that can negatively influence rate and extent of functional recovery by reducing participation in brain injury rehabilitation services and increasing maladaptive lifestyle practices. The underlying mechanisms of TBI-related fatigue are not entirely understood and focused research on symptom reduction or prevention is limited., Review: The current review of the literature suggests that the aetiology of TBI-related fatigue can be viewed as a multifactorial and complex model impacting physiological systems (i.e. endocrine, skeletal muscle and cardiorespiratory) that can be directly or indirectly influenced by neuropsychological correlates including cognitive and psychological impairment. Distinguishing central from peripheral fatigue is helpful in this regard. Potential therapeutic strategies and pharmacological agents to help alleviate fatigue in this patient population are discussed.

Reductions in skeletal muscle function occur during the course of healthy aging as well as with bed rest or diverse diseases such as cancer, muscular dystrophy, and heart failure. However, there are no accepted pharmacologic therapies to improve impaired skeletal muscle function. Nitric oxide may influence skeletal muscle function through effects on excitation-contraction coupling, myofibrillar function, perfusion, and metabolism. Here we show that augmentation of nitric oxide-cyclic guanosine monophosphate signaling by short-term daily administration of the phosphodiesterase 5 inhibitor sildenafil increases protein synthesis, alters protein expression and nitrosylation, and reduces fatigue in human skeletal muscle. These findings suggest that phosphodiesterase 5 inhibitors represent viable pharmacologic interventions to improve muscle function., (© 2013 Wiley Periodicals, Inc.)

Background: Standard-of-care (SOC) cancer treatments are primarily aimed at reducing size and progression of a tumor. There is a need for successful supplemental anabolic therapies to combat cancer cachexia in addition to these SOC treatment modalities. Anabolic interventions, including testosterone and amino acid supplements, may be beneficial in reducing and/or reversing muscle wasting in these patient populations., Methods: A 48-year-old Caucasian female with recurrent cervical cancer was scheduled to receive three 21-day cycles of cisplatin and topetecan chemotherapy. She qualified, consented, and enrolled into a blinded interventional pilot study where she received daily whey protein (10 g, three times per day with meals) and a weekly injection of testosterone enanthate (100 mg intramuscular) before and during the SOC chemotherapy treatment period. Body composition, serum inflammatory markers, mixed muscle protein synthesis and breakdown rates, physical function, fatigue, and quality of life were assessed before and after the intervention period., Results: Body composition, as assessed by an increase in body weight and lean body mass and reduction in fat mass; physical function; fatigue; and quality of life each improved across the entire intervention period despite general increases in inflammatory markers and no improvements in muscle protein turnover towards the end of the intervention., Conclusions: Concomitant treatment of oral amino acids and testosterone may be a viable therapeutic option for fighting cachexia and improving body composition and quality of life during chemotherapeutic treatment of recurrent cervical cancer. These positive outcomes may be attainable over time despite overall poor inflammatory status.

The combination of increasing blood flow and amino acid (AA) availability provides an anabolic stimulus to the skeletal muscle of healthy young adults by optimizing both AA delivery and utilization. However, aging is associated with a blunted response to anabolic stimuli and may involve impairments in endothelial function. We investigated whether age-related differences exist in the muscle protein anabolic response to AAs between younger (30 ± 2 yr) and older (67 ± 2 yr) adults when macrovascular and microvascular leg blood flow were similarly increased with the nitric oxide (NO) donor, sodium nitroprusside (SNP). Regardless of age, SNP+AA induced similar increases above baseline (P ≤ 0.05) in macrovascular flow (4.3 vs. 4.4 ml·min(-1)·100 ml leg(-1) measured using indocyanine green dye dilution), microvascular flow (1.4 vs. 0.8 video intensity/s measured using contrast-enhanced ultrasound), phenylalanine net balance (59 vs. 68 nmol·min(-1)·100 ml·leg(-1)), fractional synthetic rate (0.02 vs. 0.02%/h), and model-derived muscle protein synthesis (62 vs. 49 nmol·min(-1)·100 ml·leg(-1)) in both younger vs. older individuals, respectively. Provision of AAs during NO-induced local skeletal muscle hyperemia stimulates skeletal muscle protein metabolism in older adults to a similar extent as in younger adults. Our results suggest that the aging vasculature is responsive to exogenous NO and that there is no age-related difference per se in AA-induced anabolism under such hyperemic conditions.

Context: Cycling androgens has been reported by athletes to improve physical performance by enhancing muscle mass and strength, a paradigm that has not been studied, and may have clinical value in older men being treated with testosterone., Objective: We investigated the efficacy of a monthly cycled testosterone regimen that uses half the testosterone dose as the current standard of care continuous therapy on body composition and muscle strength in older men., Design, Setting, and Patients: Twenty-four community-dwelling older men 70 ± 2 yr of age with total testosterone levels below 500 ng/dl were randomized at the Institute for Translational Sciences-Clinical Research Center into a 5-month double-blind placebo-controlled trial., Intervention: Subjects were dosed weekly for 5 months, receiving continuous testosterone (TE, n = 8; 100 mg testosterone enanthate, im injection), monthly cycled testosterone (MO, n = 8; alternating months of testosterone and placebo), or placebo (PL, n = 8)., Main Outcome Measures: Main outcomes included body composition by dual-energy x-ray absorptiometry and upper and lower body muscle strength. Secondary outcomes included body weight, serum hormones, and mixed-muscle protein fractional synthesis rate (FSR)., Results: Total lean body mass was increased and percent fat was reduced after 5 months in TE and MO (P < 0.05). Upper body muscle strength increased in TE, and lower body muscle strength increased in TE and MO (P < 0.05). FSR increased in TE and MO (P < 0.05) but not in PL., Conclusions: Cycled testosterone improved body composition and increased muscle strength compared with placebo and increased FSR similarly to continuous testosterone.

Aging is associated with a gradual decline in circulating testosterone concentrations and decreased musculature in men. While testosterone administration is often considered when symptoms of hypogonadism are presented, the long-term effects of androgen use on muscle physiology are not yet fully understood. The definition of hypogonadism in men remains obscure but is generally indicated by total testosterone concentrations less than a threshold value of 300-500 ng/dL. Androgen replacement therapy is generally safe in men and women with low endogenous testosterone concentrations. The development of selective androgen receptor modulators (SARMs) may provide additional options in treatment of hypogonadism while lowering the potential of side effects often associated with long-term androgen use. Androgen administration, either alone or in combination with other treatments, can be successful in improving muscle mass by increasing protein anabolism and reducing protein catabolism in men and women. Further research is necessary to optimize the anabolic and anticatabolic properties of androgens for treatment and prevention of muscle loss in men and women., (Copyright © 2010 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.)

Age-related skeletal muscle loss is thought to stem from suboptimal nutrition and resistance to anabolic stimuli. Impaired microcirculatory (nutritive) blood flow may contribute to anabolic resistance by reducing delivery of amino acids to skeletal muscle. In this study, we employed contrast-enhanced ultrasound, microdialysis sampling of skeletal muscle interstitium, and stable isotope methodology, to assess hemodynamic and metabolic responses of older individuals to endurance type (walking) exercise during controlled amino acid provision. We hypothesized that older individuals would exhibit reduced microcirculatory blood flow, interstitial amino acid concentrations, and amino acid transport when compared with younger controls. We report for the first time that aging induces anabolic resistance following endurance exercise, manifested as reduced (by ∼40%) efficiency of muscle protein synthesis. Despite lower (by ∼40-45%) microcirculatory flow in the older than in the younger participants, circulating and interstitial amino acid concentrations and phenylalanine transport into skeletal muscle were all equal or higher in older individuals than in the young, comprehensively refuting our hypothesis that amino acid availability limits postexercise anabolism in older individuals. Our data point to alternative mediators of age-related anabolic resistance and importantly suggest correction of these impairments may reduce requirements for, and increase the efficacy of, dietary protein in older individuals.

Purpose of Review: Cancer cachexia is associated with marked alterations in skeletal muscle protein metabolism that lead to muscle wasting and, in some cases, death. The inflammatory response elicited by cancer is a likely, if not primary, mediator of these alterations. This review focuses on the possible relationship between inflammatory signaling and altered amino acid metabolism in cancer., Recent Findings: Loss of skeletal muscle in cancer patients can potentially be due to anorexia and early satiety, reduced muscle protein synthesis, and/or increased muscle protein breakdown. Inflammation has been associated with each of these mechanisms. Effects on appetite appear to be mediated by the melanocortin system in the hypothalamus. Studies in animal models of cachexia suggest that modulation of orexigenic and anorexigenic pathways in this system may improve nutrient consumption. Inflammatory cytokines such as IL-6 and TNF-alpha are likely to contribute to the effects of inflammation on muscle protein metabolism through several pathways., Summary: Limited studies in humans suggest that targeted anti-inflammatory and nutritional interventions may ameliorate the net catabolic effect on skeletal muscle protein metabolism. Future studies of the precise mechanism of muscle protein loss, as well as novel or combination therapies to inhibit inflammation and promote anabolism, are warranted.

Mice with a malignant hyperthermia mutation (Y522S) in the ryanodine receptor (RyR1) display muscle contractures, rhabdomyolysis, and death in response to elevated environmental temperatures. We demonstrate that this mutation in RyR1 causes Ca(2+) leak, which drives increased generation of reactive nitrogen species (RNS). Subsequent S-nitrosylation of the mutant RyR1 increases its temperature sensitivity for activation, producing muscle contractures upon exposure to elevated temperatures. The Y522S mutation in humans is associated with central core disease. Many mitochondria in the muscle of heterozygous Y522S mice are swollen and misshapen. The mutant muscle displays decreased force production and increased mitochondrial lipid peroxidation with aging. Chronic treatment with N-acetylcysteine protects against mitochondrial oxidative damage and the decline in force generation. We propose a feed-forward cyclic mechanism that increases the temperature sensitivity of RyR1 activation and underlies heat stroke and sudden death. The cycle eventually produces a myopathy with damaged mitochondria.

Skeletal muscle of patients with Duchenne-type muscular dystrophy and mdx mice exhibits elevated activity of the transcription factor NF-kappaB (nuclear factor-kappaB), which may play a role in muscle catabolism. We measured skeletal muscle NF-kappaB activity in mdx mice at three ages (10 days, 4 weeks, and 8 weeks) to test the hypothesis that NF-kappaB activity is elevated in an age-dependent manner in these mice. In addition, we tested the hypothesis that NF-kappaB activity could be reduced in mdx skeletal muscle by dietary supplementation with curcumin (1% w/v) or by fatiguing muscle contractions. We found that NF-kappaB activity was elevated at 4 and 8 weeks of age but not at 10 days, and was resistant to inhibition by either fatiguing contractions or dietary curcumin. We conclude that NF-kappaB activity is elevated in dystrophic skeletal muscle in an age-related manner and is resistant to inhibition by physiological and pharmacological means. These findings are consistent with a role for NF-kappaB activation in dystrophic muscle wasting but suggest that predicted interventions such as exercise or inhibitors of the early steps in the NF-kappa activation pathway may not be effective and that targeted research is needed to identify novel therapeutic strategies.

Malignant hyperthermia (MH) is a life-threatening disorder characterized by skeletal muscle rigidity and elevated body temperature in response to halogenated anesthetics such as isoflurane or halothane. Mutation of tyrosine 522 of RyR1 (the predominant skeletal muscle calcium release channel) to serine has been associated with human malignant hyperthermia. In the present study, mice created harboring this mutation were found to represent the first murine model of human malignant hyperthermia. Mice homozygous for the Y522S mutation exhibit skeletal defects and die during embryonic development or soon after birth. Heterozygous mice, which correspond to the human occurrence of this mutation, are MH susceptible, experiencing whole body contractions and elevated core temperatures in response to isoflurane exposure or heat stress. Skeletal muscles from heterozygous mice exhibit increased susceptibility to caffeine- and heat-induced contractures in vitro. In addition, the heterozygous expression of the mutation results in enhanced RyR1 sensitivity to activation by temperature, caffeine, and voltage but not uncompensated sarcoplasmic reticulum calcium leak or store depletion. We conclude that the heterozygous expression of the Y522S mutation confers susceptibility to both heat- and anesthetic-induced MH responses.

Background: Unloading of skeletal muscle causes atrophy and loss of contractile function. In part, this response is believed to be mediated by the transcription factor nuclear factor-kappa B (NF-kappaB). Both curcumin, a component of the spice turmeric, and N-acetylcysteine (NAC), an antioxidant, inhibit activation of NF-kappaB by inflammatory stimuli, albeit by different mechanisms. In the present study, we tested the hypothesis that dietary curcumin or NAC supplementation would inhibit unloading-induced NF-kappaB activity in skeletal muscle and thereby protect muscles against loss of mass and function caused by prolonged unloading., Methods: We used hindlimb suspension to unload the hindlimb muscles of adult mice. Animals had free access to drinking water or drinking water supplemented with 1% NAC and to standard laboratory diet or diet supplemented with 1% curcumin. For 11 days, half the animals in each dietary group were suspended by the tail (unloaded) and half were allowed to ambulate freely., Results: Unloading caused a 51-53% loss of soleus muscle weight and cross-sectional area relative to freely-ambulating controls. Unloading also decreased total force and force per cross-sectional area developed by soleus. Curcumin supplementation decreased NF-kappaB activity measured in peripheral tissues of ambulatory mice by gel shift analysis. In unloaded animals, curcumin supplementation did not inhibit NF-kappaB activity or blunt the loss of muscle mass in soleus. In contrast, NAC prevented the increase in NF-kappaB activity induced by unloading but did not prevent losses of muscle mass or function., Conclusion: In conclusion, neither dietary curcumin nor dietary NAC prevents unloading-induced skeletal muscle dysfunction and atrophy, although dietary NAC does prevent unloading induced NF-kappaB activation.

This study tested the hypothesis that skeletal muscle contraction activates nuclear factor-kappaB (NF-kappaB), a putative regulator of muscle protein breakdown. Muscle biopsies were obtained from the vastus lateralis of healthy humans before, immediately after, and 1 h after fatiguing resistance exercise of the lower limbs. Biopsies were analyzed for nuclear NF-kappaB DNA binding activity by using electrophoretic mobility shift assay. NF-kappaB activity, measured immediately after exercise, was less than preexercise activity; after 1-h recovery, activity returned to preexercise levels. In follow-up studies in adult mice, basal NF-kappaB activity varied among individual muscles. NF-kappaB activity in diaphragm fiber bundles was decreased after a 10-min bout of fatiguing tetanic contractions in vitro. NF-kappaB activity in soleus was increased by 12 days of unloading by hindlimb suspension; this increase was reversed by 10 min of fatiguing exercise. These data provide no support for our original hypothesis. Instead, acute fatiguing exercise appears to decrease NF-kappaB activity in muscle under a variety of conditions.

The immunophilin FKBP12 binds the skeletal muscle Ca2+ release channel or ryanodine receptor (RyR1), but the functional consequences of this interaction are not known. In this study, we have generated skeletal muscle specific FKBP12-deficient mice to investigate the role of FKBP12 in skeletal muscle. Primary myotubes from these mice show no obvious change in either Ca2+ stores or resting Ca2+ levels but display decreased voltage-gated intracellular Ca2+ release and increased L-type Ca2+ currents. Consistent with the decreased voltage-gated Ca2+ release, maximal tetanic force production is decreased and the force frequency curves are shifted to the right in extensor digitorum longus (EDL) muscles of the mutant mice. In contrast, there is no decrease in maximal tetanic force production in the mutant diaphragm or soleus muscle. The force frequency curve is shifted to the left in the FKBP12-deficient diaphragm muscle compared with controls. No changes in myosin heavy chain (MHC) phenotype are observed in EDL or soleus muscle of the FKBP12-deficient mice, but diaphragm muscle displays an increased ratio of slow to fast MHC isoforms. Also, calcineurin levels are increased in the diaphragm of the mutant mice but not in the soleus or EDL. In summary, FKBP12 deficiency alters both orthograde and retrograde coupling between the L-type Ca2+ channel and RyR1 and the consequences of these changes depend on muscle type and activity. In highly used muscles such as the diaphragm, adaptation to the loss of FKBP12 occurs, possibly due to the increased Ca2+ influx.

The present study investigated the responses of leg glucose and protein metabolism during an acute bout of resistance exercise. Seven subjects (5 men, 2 women) were studied at rest and during a strenuous lower body resistance exercise regimen consisting of approximately 8 sets of 10 repetitions of leg press at approximately 75% 1 repetition maximum and 8 sets of 8 repetitions of knee extensions at approximately 80% 1 repetition maximum. L-[ring-2H5]phenylalanine was infused throughout the study for measurement of phenylalanine rates of appearance, disappearance, protein synthesis, and protein breakdown across the leg. Femoral arterial and venous blood samples were collected at rest and during exercise for determination of leg blood flow, concentrations of glucose, lactate, alanine, glutamine, glutamate, leucine, and phenylalanine, and phenylalanine enrichments. Muscle biopsies were obtained at rest and immediately after exercise. Leg blood flow was nearly three times (P <0.009) higher and glucose uptake more than five times higher (P=0.009) during exercise than at rest. Leg lactate release was 86 times higher than rest during the exercise bout. Although whole body phenylalanine rate of appearance, an indicator of whole body protein breakdown, was reduced during exercise; leg phenylalanine rate of appearance, rate of disappearance, protein synthesis, and protein breakdown did not change. Arterial and venous alanine concentrations and glutamate uptake were significantly higher during exercise than at rest. We conclude that lower body resistance exercise potently stimulates leg glucose uptake and lactate release. In addition, muscle protein synthesis is not elevated during a bout of resistance exercise.

This study addressed the role of blood flow and nitric oxide in leg glucose uptake. Seven subjects (5 men, 2 women) were studied during conditions of resting blood flow and increased blood flow, achieved by infusion of the nitric oxide (NO) donor sodium nitroprusside (SNP) into the femoral artery. Femoral arterial and venous blood samples were obtained and blood flow was determined by infusion of indocyanine green dye. SNP infusion significantly increased leg blood flow (769 +/- 103 v 450 +/- 65 mL. min(-1). leg(-1), P <.001), but did not affect arterial (4.68 +/- 0.13 mmol/L control, 4.63 +/- 0.09 mmol/L SNP) or venous (4.60 +/- 0.14 mmol/L control, 4.54 +/- 0.10 mmol/L SNP) glucose concentrations. Glucose uptake was significantly (P <.01) higher during SNP infusion (65 +/- 6 micromol. min(-1). leg(-1)) than during the basal period (34 +/- 6 micromol. min(-1). leg(-1)), whereas lactate release was unaffected (rest, 45 +/- 11 micromol. min(-1). leg(-1); SNP, 42 +/- 14 micromol. min(-1). leg(-1)). We conclude that blood flow and/or NO increase basal leg glucose uptake.

Since the early 1980s biologists have recognized that skeletal muscle generates free radicals. Of particular interest are two closely related redox cascades--reactive oxygen species (ROS) and nitric oxide (NO) derivatives. The ROS cascade is initiated by superoxide anion radicals derived from the mitochondrial electron transport chain, the membrane-associated NAD(P)H oxidase complex, or other sources. NO is produced by two NO synthase isoforms constitutively expressed by muscle fibers. ROS and NO derivatives are produced continually and are detectable in both the cytosolic and extracellular compartments. Production increases during strenuous exercise. Both ROS and NO modulate contractile function. Under basal conditions, low levels of ROS enhance force production. Excessive ROS accumulation inhibits force, for example, during fatiguing exercise. NO inhibits skeletal muscle contraction, an effect that is partially mediated by cyclic GMP as a second messenger. With aging, redox modulation of muscle contraction may be altered by changes in the rates of ROS and NO production, the levels of endogenous antioxidants that buffer ROS and NO, and the sensitivities of regulatory proteins to ROS and NO action. The impact of aging on contractile regulation depends on the relative magnitude of these changes and their net effects on ROS and NO activities at the cellular level.