Prevalence of fatigue and cognitive impairment after traumatic brain injury

BACKGROUND

Following traumatic brain injury (TBI) some patients develop lingering comorbid symptoms of fatigue and cognitive impairment. The mild cognitive impairment self-reported by patients is often not detected with neurocognitive tests making it difficult to determine how common and severe these symptoms are in individuals with a history of TBI. This study was conducted to determine the relative prevalence of fatigue and cognitive impairment in individuals with a history of TBI.

METHODS

The Fatigue and Altered Cognition Scale (FACs) digital questionnaire was used to assess self-reported fatigue and cognitive impairment. Adults aged 18-70 were digitally recruited for the online anonymous study. Eligible participants provided online consent, demographic data, information about lifetime TBI history, and completed the 20 item FACs questionnaire.

RESULTS

A total of 519 qualifying participants completed the online digital study which included 204 participants with a history of TBI of varied cause and severity and 315 with no history of TBI. FACs Total Score was significantly higher in the TBI group (57.7 ± 22.2) compared to non-TBI (39.5 ± 23.9; p<0.0001) indicating more fatigue and cognitive impairment. When stratified by TBI severity, FACs score was significantly higher for all severity including mild (53.9 ± 21.9, p<0.0001), moderate (54.8 ± 24.4, p<0.0001), and severe (59.7 ± 20.9, p<0.0001) TBI. Correlation analysis indicated that more severe TBI was associated with greater symptom severity (p<0.0001, r = 0.3165). Ancillary analysis also suggested that FACs scores may be elevated in participants with prior COVID-19 infection but no history of TBI.

CONCLUSIONS

Adults with a history of even mild TBI report significantly greater fatigue and cognitive impairment than those with no history of TBI, and symptoms are more profound with greater TBI severity.

Low growth hormone secretion associated with post-acute sequelae SARS-CoV-2 infection (PASC) neurologic symptoms: A case-control pilot study

OBJECTIVE

To determine if patients that develop lingering neurologic symptoms of fatigue and "brain fog" after initial recovery from coronavirus disease 2019 (COVID-19) have persistent low growth hormone (GH) secretion as seen in other conditions with similar symptom etiology.

DESIGN

In this case-control observational pilot study, patients reporting lingering neurologic post-acute sequelae of SARS-CoV-2 (PASC, n = 10) symptoms at least 6 months after initial infection were compared to patients that recovered from COVID-19 without lingering symptoms (non-PASC, n = 13). We compared basic blood chemistry and select metabolites, lipids, hormones, inflammatory markers, and vitamins between groups. PASC and non-PASC subjects were tested for neurocognition and GH secretion, and given questionnaires to assess symptom severity. PASC subjects were also tested for glucose tolerance and adrenal function.

RESULTS

PASC subjects reported significantly worse fatigue, sleep quality, depression, quality of life, and gastrointestinal discomfort compared to non-PASC. Although PASC subjects self-reported poor mental resilience, cognitive testing did not reveal significant differences between groups. Neurologic PASC symptoms were not linked to inflammatory markers or adrenal insufficiency, but were associated with reduced growth hormone secretion.

CONCLUSIONS

Neurologic PASC symptoms are associated with gastrointestinal discomfort and persistent disruption of GH secretion following recovery from acute COVID-19. (www.

CLINICALTRIALS

gov; NCT04860869).

Efficient assessment of brain fog and fatigue: Development of the Fatigue and Altered Cognition Scale (FACs)

Debilitating symptoms of fatigue and accompanying "brain fog" are observed among patients with various chronic health conditions. Unfortunately, an efficient and psychometrically sound instrument to assess these co-occurring symptoms is unavailable. Here, we report the development and initial psychometric properties of the Fatigue and Altered Cognition Scale (the FACs), a measure of self-reported central fatigue and brain fog. Traumatic brain injury (TBI) was chosen to model and develop the FACs due to research team expertise and established links between TBI and the symptom complex. Potential items were generated by researchers and clinicians with experience treating these symptoms, drawing from relevant literature and review of patient responses to measures from past and current TBI studies. The 20 candidate items for the FACs-ten each to assess altered cognition (i.e., brain fog) and central fatigue-were formatted on an electronic visual analogue response scale (eVAS) via an online survey. Demographic information and history of TBI were obtained. A total of 519 participants consented and provided usable data (average age = 40.23 years; 73% female), 204 of whom self-reported a history of TBI (75% reported mild TBI). Internal consistency and reliability values were calculated. Confirmatory factor analysis (CFA) examined the presumed two-factor structure of the FACs and a one-factor solution for comparison. A measurement invariance test of the two latent constructs (altered cognition, fatigue) among participants with and without TBI was conducted. All items demonstrated normal distribution. Cronbach's alpha coefficients indicated good internal consistency for both factors (α's = .95). Omega reliability values were favorable (α's = .95). CFA supported the presumed two-factor model and item loadings which outperformed the one-factor model. Measurement invariance found the two-factor structure was consistent between the two groups. Implications of these findings, study limitations, and potential use of the FACs in clinical research and practice are discussed.

Is there a role for growth hormone replacement in adults to control acute and post-acute COVID-19?

The SARS-CoV-2 pandemic created a multitude of medical crossroads requiring real time adaptations of best practice covering preventative and interventional aspects of care. Among the many discoveries borne from efforts to address the myriad clinical presentations across multiple organ systems was a common impact on tissues with cells that express the ACE-2 receptor. The vast majority of acute infections began and often ended in the respiratory tract, but more recent evaluations have confirmed significant extrapulmonary manifestations including symptom clusters that extend beyond the acute phase of infection collectively referred to as "post-acute sequelae SARS-CoV-2 infection" (PASC) or more commonly as "long (-haul) COVID". Both acute SARS-CoV-2 infection and PASC are associated with gut microbiome dysbiosis and alterations in the gut-brain and HPA-axis in a subset of the infected. Mounting evidence suggests these extrapulmonary manifestations may ultimately lead to reduced growth hormone (GH) secretion as demonstrated following stimulation tests. Disrupted GH secretion could cause or exacerbate long lasting neuropsychological symptoms as seen in other similar manifesting conditions. Ongoing clinical research has shown promising improvement in PASC patients with fatigue and cognition complaints can be achieved via GH replacement therapy. GH stimulation testing should be considered in PASC workups and future research should delve deeper into the mechanistic effects of GH on acute COVID and PASC.

Traumatic brain injury, abnormal growth hormone secretion, and gut dysbiosis

The gut microbiome has been implicated in a variety of neuropathologies with recent data suggesting direct effects of the microbiome on host metabolism, hormonal regulation, and pathophysiology. Studies have shown that gut bacteria impact host growth, partially mediated through the growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis. However, no study to date has examined the specific role of GH on the fecal microbiome (FMB) or the changes in this relationship following a traumatic brain injury (TBI). Current literature has demonstrated that TBI can lead to either temporary or sustained abnormal GH secretion (aGHS). More recent literature has suggested that gut dysbiosis may contribute to aGHS leading to long-term sequelae now known as brain injury associated fatigue and cognition (BIAFAC). The aGHS observed in some TBI patients presents with a symptom complex including profound fatigue and cognitive dysfunction that improves significantly with exogenous recombinant human GH treatment. Notably, GH treatment is not curative as fatigue and cognitive decline typically recur upon treatment cessation, indicating the need for additional studies to address the underlying mechanistic cause.

Impact of Adjunct Testosterone on Cancer-Related Fatigue: An Ancillary Analysis from a Controlled Randomized Trial

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.

Virtual Reality “exergames”: A promising countermeasure to improve motivation and restorative effects during long duration spaceflight missions

Long duration spaceflight missions will require novel exercise systems to protect astronaut crew from the detrimental effects of microgravity exposure. The SPRINT protocol is a novel and promising exercise prescription that combines aerobic and resistive training using a flywheel device, and it was successfully employed in a 70-day bed-rest study as well as onboard the International Space Station. Our team created a VR simulation to further augment the SPRINT protocol when using a flywheel ergometer training device (the Multi-Mode Exercise Device or M-MED). The simulation aspired to maximal realism in a virtual river setting while providing real-time biometric feedback on heart rate performance to subjects. In this pilot study, five healthy, male, physically-active subjects aged 35 ± 9.0 years old underwent 2 weeks of SPRINT protocol, either with or without the VR simulation. After a 1-month washout period, subjects returned for a subsequent 2 weeks in the opposite VR condition. We measured physiological and cognitive variables of stress, performance, and well-being. While physiological effects did not suggest much difference with the VR condition over 2 weeks, metrics of motivation, affect, and mood restoration showed detectable differences, or trended toward more positive outcomes than exercise without VR. These results provide evidence that a well-designed VR “exergaming” simulation with biometric feedback could be a beneficial addition to exercise prescriptions, especially if users are exposed to isolation and confinement.

The physiologic responses to a fluid bolus administration in old and young healthy adults

BACKGROUND

Organ function is known to decline with age. Optimizing cardiac, pulmonary and renal function in older adults has led to significant improvements in perioperative care. However, when substantial blood loss and fluid shifts occur, perioperative outcomes still remains poor, especially in older adults. We suspect that this could be due to age-related changes in endothelial function-an organ controlling the transport of fluid and solutes. The capillary filtration coefficient (CFC) is an important determinant of fluid transport. The CFC can be measured in vivo, which provides a tool to estimate endothelial barrier function. We have previously shown that the CFC increases when giving a fluid bolus resulting in increased vascular and extravascular volume expansion, in young adults. This study aimed to compare the physiologic determinants of fluid distribution in young versus older adults so that clinicians can best optimize perioperative fluid therapy.

METHODS

Ten healthy young volunteers (ages 21-35) and nine healthy older volunteers (ages 60-75) received a 10 mL/kg fluid bolus over the course of twenty minutes. Hemodynamics, systolic and diastolic heart function, fluid volumetrics and microcirculatory determinants were measured before, during, and after the fluid bolus.

RESULTS

Diastolic function was reduced in older versus younger adults before and after fluid bolus (P < 0.01). Basal CFC and plasma oncotic pressure were lower in the older versus younger adults. Further, CFC did not increase in older adults following the fluid bolus, whereas it did in younger adults (p < 0.05). Cumulative urinary output, while lower in older adults, was not significantly different (p = 0.059). Mean arterial pressure and systemic vascular resistance were elevated in the older versus younger adults (p < 0.05).

CONCLUSION

Older adults show a less reactive CFC to a fluid bolus, which could reduce blood to tissue transport of fluid. Diastolic dysfunction likely contributes to fluid maldistribution in older adults.

Skeletal muscle thermogenesis enables aquatic life in the smallest marine mammal

Basal metabolic rate generally scales with body mass in mammals, and variation from predicted levels indicates adaptive metabolic remodeling. As a thermogenic adaptation for living in cool water, sea otters have a basal metabolic rate approximately three times that of the predicted rate; however, the tissue-level source of this hypermetabolism is unknown. Because skeletal muscle is a major determinant of whole-body metabolism, we characterized respiratory capacity and thermogenic leak in sea otter muscle. Compared with that of previously sampled mammals, thermogenic muscle leak capacity was elevated and could account for sea otter hypermetabolism. Muscle respiratory capacity was modestly elevated and reached adult levels in neonates. Premature metabolic development and high leak rate indicate that sea otter muscle metabolism is regulated by thermogenic demand and is the source of basal hypermetabolism.

Changes in Northern Elephant Seal Skeletal Muscle Following Thirty Days of Fasting and Reduced Activity

Northern elephant seals (NES, Mirounga angustirostris) undergo an annual molt during which they spend ∼40 days fasting on land with reduced activity and lose approximately one-quarter of their body mass. Reduced activity and muscle load in stereotypic terrestrial mammalian models results in decreased muscle mass and capacity for force production and aerobic metabolism. However, the majority of lost mass in fasting female NES is from fat while muscle mass is largely preserved. Although muscle mass is preserved, potential changes to the metabolic and contractile capacity are unknown. To assess potential changes in NES skeletal muscle during molt, we collected muscle biopsies from 6 adult female NES before the molt and after ∼30 days at the end of the molt. Skeletal muscle was assessed for respiratory capacity using high resolution respirometry, and RNA was extracted to assess changes in gene expression. Despite a month of reduced activity, fasting, and weight loss, skeletal muscle respiratory capacity was preserved with no change in OXPHOS respiratory capacity. Molt was associated with 162 upregulated genes including those favoring lipid metabolism. We identified 172 downregulated genes including those coding for ribosomal proteins and genes associated with skeletal muscle force transduction and glucose metabolism. Following ∼30 days of molt, NES skeletal muscle metabolic capacity is preserved although mechanotransduction may be compromised. In the absence of exercise stimulus, fasting-induced shifts in muscle metabolism may stimulate pathways associated with preserving the mass and metabolic capacity of slow oxidative muscle.

Alterations of the GH/IGF-I Axis and Gut Microbiome after Traumatic Brain Injury: A New Clinical Syndrome?

CONTEXT

Pituitary dysfunction with abnormal growth hormone (GH) secretion and neurocognitive deficits are common consequences of traumatic brain injury (TBI). Recognizing the comorbidity of these symptoms is of clinical importance; however, efficacious treatment is currently lacking.

EVIDENCE ACQUISITION

A review of studies in PubMed published between January 1980 to March 2020 and ongoing clinical trials was conducted using the search terms "growth hormone," "traumatic brain injury," and "gut microbiome."

EVIDENCE SYNTHESIS

Increasing evidence has implicated the effects of TBI in promoting an interplay of ischemia, cytotoxicity, and inflammation that renders a subset of patients to develop postinjury hypopituitarism, severe fatigue, and impaired cognition and behavioral processes. Recent data have suggested an association between abnormal GH secretion and altered gut microbiome in TBI patients, thus prompting the description of a hypothesized new clinical syndrome called "brain injury associated fatigue and altered cognition." Notably, these patients demonstrate distinct characteristics from those with GH deficiency from other non-TBI causes in that their symptom complex improves significantly with recombinant human GH treatment, but does not reverse the underlying mechanistic cause as symptoms typically recur upon treatment cessation.

CONCLUSION

The reviewed data describe the importance of alterations of the GH/insulin-like growth factor I axis and gut microbiome after brain injury and its influence in promoting neurocognitive and behavioral deficits in a bidirectional relationship, and highlight a new clinical syndrome that may exist in a subset of TBI patients in whom recombinant human GH therapy could significantly improve symptomatology. More studies are needed to further characterize this clinical syndrome.

Exercise and Testosterone Countermeasures to Mitigate Metabolic Changes during Bed Rest

BACKGROUND/OBJECTIVES

Exercise is a front-line countermeasure used to maintain astronaut health during long-duration spaceflight; however, reductions in metabolic health still occur. Accordingly, we evaluated serial changes in metabolic parameters in a spaceflight analog and evaluated the efficacy of exercise with or without the addition of low-dose testosterone treatment on mitigating adverse metabolic changes.

SUBJECTS/METHODS

Healthy young (<55 years) men were randomly assigned to one of three groups during 70-days of strict, diet controlled, 6° head-down bed rest: Control (CON, n=9), exercise plus testosterone countermeasure (TEX, n=8), or exercise countermeasure plus placebo (PEX, n=9). Basal metabolic rate (BMR), glucose tolerance, and insulin sensitivity were measured before, during, and after bed rest. Exercise energy expenditure and excess post-exercise oxygen consumption were measured in TEX and PEX subjects during bed rest.

RESULTS

Leptin decreased during bed rest (Pre to BR+0 changed from 6.9 ± 5.1, 5.8 ± 4.2, and 4.7 ± 4.1 to 7.9 ±3.6, 6.5 ± 4.6, and 4.1 ±3.0 ug• L^-1 for CON, PEX, and TEX respectively). Bed rest induced a decrease in BMR (Pre to BR57 changed from 1655 ± 212, 1629 ± 108, and 1706 ± 146 to 1476 ± 166, 1668 ± 142, and 1603 ± 132 kcal • day^-1 ± 95%CI for CON, PEX, and TEX respectively). Similarly, bed rest negatively affected glucose metabolism assessed by 2hr OGTT glucose (Pre to BR66 changed from 6.29 ± 0.72, 5.13 ± 0.72, and 5.87 ± 0.73 to 6.62 ± 0.72, 5.83 ± 0.72, and 7.08 ± 0.72 mmol • L^-1 ± 95%CI). Reambulation following bed rest positively affected glucose tolerance in CON (2hr OGTT glucose at BR+12: 5.3 ± 0.72, 6.42 ± 0.73, and 6.04 ± 0.73 mmol • L^-1 ± 95%CI). Testosterone protected against bed rest induced insulin resistance (HOMA-IR from Pre to BR+66 changed from 1.74 ± 0.54, 1.18 ± 0.55, and 1.45 ± 0.56 to 2.24 ± 0.56, 1.47 ± 0.54, and 1.07 ± 0.54).

CONCLUSION

This study confirmed that inactivity during 70 days of head-down bed rest adversely affects metabolic health. The daily exercise countermeasures were beneficial but not completely protective of bed rest induced decrements in metabolic health. Supplementary countermeasures such as testosterone may provide additional benefits not provided by exercise alone.

Growth Hormone Alters Brain Morphometry, Connectivity, and Behavior in Subjects with Fatigue after Mild Traumatic Brain Injury

Pituitary dysfunction with reduced growth hormone (GH) secretion is common in patients following traumatic brain injury (TBI), and these patients often develop chronic symptoms including fatigue and altered cognition. We examined 18 subjects with a history of mild TBI, fatigue, and insufficient GH secretion. Subjects received GH replacement in a year-long, double-blind, placebo-controlled, crossover study, and were assessed for changes in physical performance, body composition, resting energy expenditure, fatigue, sleep, mood, and neuropsychological status. Additionally, magnetic resonance imaging (MRI) was used to assess changes in brain structure and resting state functional connectivity. GH replacement resulted in decreased fatigue, sleep disturbance, and anxiety, as well as increased resting energy expenditure, improved body composition, and altered perception of submaximal effort when performing exercise testing. Associated brain changes included increased frontal cortical thickness and gray matter volume and resting state connectivity changes in regions associated with somatosensory networks. GH replacement altered brain morphology and connectivity and reduced fatigue and related symptoms in mild TBI patients. Additional studies are needed to understand the mechanisms causing TBI-related fatigue and symptom relief with GH replacement.

MicroRNA sequencing of rat hippocampus and human biofluids identifies acute, chronic, focal and diffuse traumatic brain injuries

High-throughput sequencing technologies could improve diagnosis and classification of TBI subgroups. Because recent studies showed that circulating microRNAs (miRNAs) may serve as noninvasive markers of TBI, we performed miRNA-seq to study TBI-induced changes in rat hippocampal miRNAs up to one year post-injury. We used miRNA PCR arrays to interrogate differences in serum miRNAs using two rat models of TBI (controlled cortical impact [CCI] and fluid percussion injury [FPI]). The translational potential of our results was evaluated by miRNA-seq analysis of human control and TBI (acute and chronic) serum samples. Bioinformatic analyses were performed using Ingenuity Pathway Analysis, miRDB, and Qlucore Omics Explorer. Rat miRNA profiles identified TBI across all acute and chronic intervals. Rat CCI and FPI displayed distinct serum miRNA profiles. Human miRNA profiles identified TBI across all acute and chronic time points and, at 24 hours, discriminated between focal and diffuse injuries. In both species, predicted gene targets of differentially expressed miRNAs are involved in neuroplasticity, immune function and neurorestoration. Chronically dysregulated miRNAs (miR-451a, miR-30d-5p, miR-145-5p, miR-204-5p) are linked to psychiatric and neurodegenerative disorders. These data suggest that circulating miRNAs in biofluids can be used as "molecular fingerprints" to identify acute, chronic, focal or diffuse TBI and potentially, presence of neurodegenerative sequelae.

Effects of adjunct testosterone on cardiac morphology and function in advanced cancers: an ancillary analysis of a randomized controlled trial

BACKGROUND

Adjunct testosterone therapy improves lean body mass, quality of life, and physical activity in patients with advanced cancers; however, the effects of testosterone on cardiac morphology and function are unknown. Accordingly, as an ancillary analysis of a randomized, placebo-controlled trial investigating the efficacy of testosterone supplementation on body composition in men and women with advanced cancers, we explored whether testosterone supplementation could prevent or reverse left ventricular (LV) atrophy and dysfunction.

METHODS

Men and women recently diagnosed with late stage (≥IIB) or recurrent head and neck or cervical cancer who were scheduled to receive standard of care chemotherapy or concurrent chemoradiation were administered an adjunct 7 week treatment of weekly intramuscular injections of either 100 mg testosterone (T, n = 1 M/5F) or placebo (P, n = 6 M/4F) in a double-blinded randomized fashion. LV morphology (wall thickness), systolic function (ejection fraction, EF), diastolic function (E/A; E'/E), arterial elastance (Ea), end-systolic elastance (Ees), and ventricular-arterial coupling (Ea/Ees) were assessed.

RESULTS

No significant differences were observed in LV posterior wall thickness in placebo (pre: 1.10 ± 0.1 cm; post: 1.16 ± 0.2 cm; p = 0.11) or testosterone groups (pre: 0.99 ± 0.1 cm; post: 1.14 ± 0.20 cm; p = 0.22). Compared with placebo, testosterone significantly improved LVEF (placebo: - 1.8 ± 4.3%; testosterone: + 6.2 ± 4.3%; p < 0.05), Ea (placebo: 0.0 ± 0.2 mmHg/mL; testosterone: - 0.3 ± 0.2 mmHg/mL; p < 0.05), and Ea/Ees (placebo: 0.0 ± 0.1; testosterone: - 0.2 ± 0.1; p < 0.05).

CONCLUSIONS

In patients with advanced cancers, testosterone was associated with favorable changes in left ventricular systolic function, arterial elastance, and ventricular-arterial coupling. Given the small sample size, the promising multisystem benefits of testosterone warrants further evaluation in a definitive randomized trial.

TRIAL REGISTRATION

This study was prospectively registered on ClinicalTrials.gov (NCT00878995; date of registration: April 9, 2009).

Proteomic investigation of human skeletal muscle before and after 70 days of head down bed rest with or without exercise and testosterone countermeasures

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.

Efficacy of Testosterone plus NASA Exercise Countermeasures during Head-Down Bed Rest

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.

Efficacy of Exercise and Testosterone to Mitigate Atrophic Cardiovascular Remodeling

PURPOSE

Early and consistent evaluation of cardiac morphology and function throughout an atrophic stimulus is critically important for the design and optimization of interventions. This randomized controlled trial was designed 1) to characterize the time course of unloading-induced morphofunctional remodeling and 2) to examine the effects of exercise with and without low-dose testosterone supplementation on cardiac biomarker, structural, and functional parameters during unloading.

METHODS

Twenty-six subjects completed 70 d of head-down tilt bed rest (BR): 9 were randomized to exercise training (Ex), 8 to EX and low-dose testosterone (ExT), and 9 remained sedentary (CONT). Exercise consisted of high-intensity, continuous, and resistance exercise. Cardiac morphology (left ventricular mass [LVM]) and mechanics (longitudinal, radial, and circumferential strain and twist), cardiovascular biomarkers, and cardiorespiratory fitness (V˙O2peak) were assessed before, during, and after BR.

RESULTS

Sedentary BR resulted in a progressive decline in LVM, longitudinal, radial, and circumferential strain in CONT, whereas Ex and ExT mitigated decreases in LVM and function. Twist was increased throughout BR in sedentary BR, whereas after an initial increase at BR7, there were no further changes in twist in Ex and ExT. HDL cholesterol was significantly decreased in all groups compared with pre-BR (P < 0.007). There were no significant changes in other cardiovascular biomarkers. Change in twist was significantly related to change in V˙O2max (R = 0.68, P < 0.01).

CONCLUSION

An integrated approach with evaluation of cardiac morphology, mechanics, V˙O2peak, and biomarkers provides extensive phenotyping of cardiovascular atrophic remodeling. Exercise training and exercise training with low-dose testosterone supplementation abrogates atrophic remodeling.

Exercise Training Mitigates Multisystem Deconditioning during Bed Rest

INTRODUCTION

This study investigated the safety and effectiveness of a new integrated aerobic and resistance exercise training prescription (SPRINT) using two different sets of exercise equipment: a suite of large International Space Station-like exercise equipment similar to what is found on the International Space Station and a single device with aerobic and resistance exercise capability in the spaceflight analog of bed rest (BR).

METHODS

Subjects (n = 34) completed 70 d of 6° head down tilt BR: 9 were randomized to remain sedentary (CONT), 9 to exercise training using traditional equipment (EX), 8 to exercise using traditional equipment and low-dose testosterone supplementation (ExT), and 8 to exercise using a combined resistance and aerobic flywheel device. Peak aerobic capacity, ventilatory threshold, cardiac morphology and function (echocardiography), muscle mass (magnetic resonance imaging) and strength/power (isokinetic, leg press, and vertical jump), and bone health (bone mineral density, blood and urine bone markers) were assessed before and after BR.

RESULTS

The SPRINT protocol mitigated BR-induced muscle and cardiac deconditioning regardless of the exercise device used. Molecular markers of bone did not change in the CONT or EX groups. Peak aerobic capacity was maintained from pre- to post-BR in all exercise groups similarly, whereas significant declines were observed in the CONT group (~10%). Significant interaction effects between the CONT group and all EX groups were observed for muscle performance including leg press total work, isokinetic upper and lower leg strength, vertical jump power, and maximal jump height as well as muscle size.

CONCLUSIONS

This is the first trial to evaluate multisystem deconditioning and the role of an integrated exercise countermeasure. These findings have important implications for the design and implementation of exercise-based countermeasures on future long-duration spaceflight missions.

Testosterone replacement therapy and hospitalization rates in men with COPD

Testosterone deficiency is common in men with chronic obstructive pulmonary disease (COPD) and may exacerbate their condition. Research suggests that testosterone replacement therapy (TRT) may have a beneficial effect on respiratory outcomes in men with COPD. To date, however, no large-scale nationally representative studies have examined this association. The objective of the study was to assess whether TRT reduced the risk of respiratory hospitalizations in middle-aged and older men with COPD. We conducted two retrospective cohort studies. First, using the Clinformatics Data Mart—a database of one of the largest commercially insured populations in the United States—we examined 450 men, aged 40–63 years, with COPD who initiated TRT between 2005 and 2014. Second, using the national 5% Medicare database, we examined 253 men, aged ≥66 years, with COPD who initiated TRT between 2008 and 2013. We used difference-in-differences (DID) statistical modeling to compare pre- versus post-respiratory hospitalization rates in TRT users versus matched TRT nonusers over a parallel time period. DID analyses showed that TRT users had a greater relative decrease in respiratory hospitalizations compared with nonusers. Specifically, middle-aged TRT users had a 4.2% greater decrease in respiratory hospitalizations compared with nonusers (−2.4 decrease vs. 1.8 increase; p = 0.03); and older TRT users had a 9.1% greater decrease in respiratory hospitalizations compared with nonusers (−0.8 decrease vs. 8.3 increase; p = 0.04). These findings suggest that TRT may slow disease progression in patients with COPD. Future studies should examine this association in larger cohorts of patients, with particular attention to specific biological pathways.

Quantification of muscle triglyceride synthesis rate requires an adjustment for total triglyceride content

Intramyocellular triglyceride (imTG) in skeletal muscle plays a significant role in metabolic health, and an infusion of [¹³C₁₆]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 [¹³C₁₆]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.

Skeletal muscle protein accretion rates and hindlimb growth are reduced in late gestation intrauterine growth-restricted fetal sheep

KEY POINTS

Adults who were affected by intrauterine growth restriction (IUGR) suffer from reductions in muscle mass, which may contribute to insulin resistance and the development of diabetes. We demonstrate slower hindlimb linear growth and muscle protein synthesis rates that match the reduced hindlimb blood flow and oxygen consumption rates in IUGR fetal sheep. These adaptations resulted in hindlimb blood flow rates in IUGR that were similar to control fetuses on a weight-specific basis. Net hindlimb glucose uptake and lactate output rates were similar between groups, whereas amino acid uptake was significantly lower in IUGR fetal sheep. Among all fetuses, blood O₂ saturation and plasma glucose, insulin and insulin-like growth factor-1 were positively associated and norepinephrine was negatively associated with hindlimb weight. These results further our understanding of the metabolic and hormonal adaptations to reduced oxygen and nutrient supply with placental insufficiency that develop to slow hindlimb growth and muscle protein accretion.

ABSTRACT

Reduced skeletal muscle mass in the fetus with intrauterine growth restriction (IUGR) persists into adulthood and may contribute to increased metabolic disease risk. To determine how placental insufficiency with reduced oxygen and nutrient supply to the fetus affects hindlimb blood flow, substrate uptake and protein accretion rates in skeletal muscle, late gestation control (CON) (n = 8) and IUGR (n = 13) fetal sheep were catheterized with aortic and femoral catheters and a flow transducer around the external iliac artery. Muscle protein kinetic rates were measured using isotopic tracers. Hindlimb weight, linear growth rate, muscle protein accretion rate and fractional synthetic rate were lower in IUGR compared to CON (P < 0.05). Absolute hindlimb blood flow was reduced in IUGR (IUGR: 32.9 ± 5.6 ml min^-1 ; CON: 60.9 ± 6.5 ml min^-1 ; P < 0.005), although flow normalized to hindlimb weight was similar between groups. Hindlimb oxygen consumption rate was lower in IUGR (IUGR: 10.4 ± 1.4 μmol min^-1  100 g^-1 ; CON: 14.7 ± 1.3 μmol min^-1  100 g^-1 ; P < 0.05). Hindlimb glucose uptake and lactate output rates were similar between groups, whereas amino acid uptake was lower in IUGR (IUGR: 1.3 ± 0.5 μmol min^-1  100 g^-1 ; CON: 2.9 ± 0.2 μmol min^-1  100 g^-1 ; P < 0.05). Blood O₂ saturation (r²  = 0.80, P < 0.0001) and plasma glucose (r²  = 0.68, P < 0.0001), insulin (r²  = 0.40, P < 0.005) and insulin-like growth factor (IGF)-1 (r²  = 0.80, P < 0.0001) were positively associated and norepinephrine (r²  = 0.59, P < 0.0001) was negatively associated with hindlimb weight. Slower hindlimb linear growth and muscle protein synthesis rates match reduced hindlimb blood flow and oxygen consumption rates in the IUGR fetus. Metabolic adaptations to slow hindlimb growth are probably hormonally-mediated by mechanisms that include increased fetal norepinephrine and reduced IGF-1 and insulin.

Sex-dependent difference in the relationship between adipose-tissue cholesterol efflux and estradiol concentrations in young healthy humans

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.

Glucocorticoids increase skeletal muscle NF-κB inducing kinase (NIK): links to muscle atrophy

Glucocorticoids (GC) are a frontline therapy for numerous acute and chronic diseases because of their demonstrated efficacy at reducing systemic inflammation. An unintended side effect of GC therapy is the stimulation of skeletal muscle atrophy. Pathophysiological mechanisms responsible for GC-induced skeletal muscle atrophy have been extensively investigated, and the ability to treat patients with GC without unintended muscle atrophy has yet to be realized. We have reported that a single, standard-of-care dose of Methylprednisolone increases in vivo expression of NF-κB-inducing kinase (NIK), an important upstream regulatory kinase controlling NF-κB activation, along with other key muscle catabolic regulators such as Atrogin-1 and MuRF1 that induce skeletal muscle proteolysis. Here, we provide experimental evidence that overexpressing NIK by intramuscular injection of recombinant human NIK via adenoviral vector in mouse tibialis anterior muscle induces a 30% decrease in the average fiber cross-sectional area that is associated with increases in mRNA expression of skeletal muscle atrophy biomarkers MuRF1, Atrogin-1, myostatin and Gadd45. A single injection of GC induced NIK mRNA and protein within 2 h, with the increased NIK localized to nuclear and sarcolemmal locations within muscle fibers. Daily GC injections induced skeletal muscle fore limb weakness as early as 3 days with similar atrophy of muscle fibers as observed with NIK overexpression. NIK overexpression in primary human skeletal muscle myotubes increased skeletal muscle atrophy biomarkers, while NIK knockdown significantly attenuated GC-induced increases in NIK and Atrogin-1. These results suggest that NIK may be a novel, previously unrecognized mediator of GC-induced skeletal muscle atrophy.

Functional Changes after Recombinant Human Growth Hormone Replacement in Patients with Chronic Traumatic Brain Injury and Abnormal Growth Hormone Secretion

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 O₂ 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.

Palmitoyl-carnitine production by blood cells associates with the concentration of circulating acyl-carnitines in healthy overweight women

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.

Hypogonadism and the risk of rheumatic autoimmune disease

Testosterone deficiency has been linked with autoimmune disease and an increase in inflammatory markers, such as C-reactive protein (CRP), tumor necrosis factor, and interleukin-6 (IL-6). However, no large-scale longitudinal studies have examined this association. We examined whether untreated hypogonadism was associated with an increased risk of rheumatic autoimmune disease in a large nationally representative cohort. Using one of the nation's largest commercial insurance databases, we conducted a retrospective cohort study in which we identified 123,460 men diagnosed with hypogonadism between January 1, 2002 and December 31, 2014 and with no prior history of rheumatic autoimmune disease. We matched this cohort to 370,380 men without hypogonadism, at a 1 to 3 ratio, on age and index/diagnosis date. All patients were followed until December 31, 2014 or until they lost insurance coverage or were diagnosed with a rheumatic autoimmune disease. Cox proportional hazards regression was used to calculate adjusted hazard ratios (aHRs). Untreated hypogonadism was associated with an increased risk of developing any rheumatic autoimmune disease (HR = 1.33, 95 % CI = 1.28, 1.38), rheumatoid arthritis (HR = 1.31, 95 % CI = 1.22, 1.44), and lupus (HR = 1.58, 95 % CI = 1.28, 1.94). These findings persisted using latency periods of 1 and 2 years. Hypogonadism was not associated with the control outcome, epilepsy (HR = 1.04, 95 % CI = 0.96, 1.15). Patients diagnosed with hypogonadism who were not treated with testosterone had an increased risk of developing any rheumatic autoimmune disease, rheumatoid arthritis, and lupus. Future research should further examine this association, with particular attention to underlying mechanisms.

Hypoaminoacidemia Characterizes Chronic Traumatic Brain Injury

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.

Leucine partially protects muscle mass and function during bed rest in middle-aged adults

BACKGROUND

Physical inactivity triggers a rapid loss of muscle mass and function in older adults. Middle-aged adults show few phenotypic signs of aging yet may be more susceptible to inactivity than younger adults.

OBJECTIVE

The aim was to determine whether leucine, a stimulator of translation initiation and skeletal muscle protein synthesis (MPS), can protect skeletal muscle health during bed rest.

DESIGN

We used a randomized, double-blind, placebo-controlled trial to assess changes in skeletal MPS, cellular signaling, body composition, and skeletal muscle function in middle-aged adults (n = 19; age ± SEM: 52 ± 1 y) in response to leucine supplementation (LEU group: 0.06 g ∙ kg(-1) ∙ meal(-1)) or an alanine control (CON group) during 14 d of bed rest.

RESULTS

Bed rest decreased postabsorptive MPS by 30% ± 9% (CON group) and by 10% ± 10% (LEU group) (main effect for time, P < 0.05), but no differences between groups with respect to pre-post changes (group × time interactions) were detected for MPS or cell signaling. Leucine protected knee extensor peak torque (CON compared with LEU group: -15% ± 2% and -7% ± 3%; group × time interaction, P < 0.05) and endurance (CON compared with LEU: -14% ± 3% and -2% ± 4%; group × time interaction, P < 0.05), prevented an increase in body fat percentage (group × time interaction, P < 0.05), and reduced whole-body lean mass loss after 7 d (CON compared with LEU: -1.5 ± 0.3 and -0.8 ± 0.3 kg; group × time interaction, P < 0.05) but not 14 d (CON compared with LEU: -1.5 ± 0.3 and -1.0 ± 0.3 kg) of bed rest. Leucine also maintained muscle quality (peak torque/kg leg lean mass) after 14 d of bed-rest inactivity (CON compared with LEU: -9% ± 2% and +1% ± 3%; group × time interaction, P < 0.05).

CONCLUSIONS

Bed rest has a profoundly negative effect on muscle metabolism, mass, and function in middle-aged adults. Leucine supplementation may partially protect muscle health during relatively brief periods of physical inactivity. This trial was registered at clinicaltrials.gov as NCT00968344.

Mitochondrial respiratory capacity and coupling control decline with age in human skeletal muscle

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.

Effect of age on basal muscle protein synthesis and mTORC1 signaling in a large cohort of young and older men and women

The rate of muscle loss with aging is higher in men than women. However, women have smaller muscles throughout the adult life. Protein content is a major determinant of skeletal muscle size. This study was designed to determine if age and sex differentially impact basal muscle protein synthesis and mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling. We performed a secondary data analysis on a cohort of 215 healthy, non-obese (BMI<30kg·m(-2)) young (18-40y; 74 men, 52 women) and older (60-87y; 57 men, 32 women) adults. The database contained information on physical characteristics, basal muscle protein fractional synthetic rate (FSR; n=215; stable isotope methodology) and mTORC1 signaling (n=125, Western blotting). FSR and mTORC1 signaling were measured at rest and after an overnight fast. mTORC1 and S6K1 phosphorylation were higher (p<0.05) in older subjects with no sex differences. However, there were no age or sex differences or interaction for muscle FSR (p>0.05). Body mass index, fat free mass, or body fat was not a significant covariate and did not influence the results. We conclude that age and sex do not influence basal muscle protein synthesis. However, basal mTORC1 hyperphosphorylation in the elderly may contribute to insulin resistance and the age-related anabolic resistance of skeletal muscle protein metabolism to nutrition and exercise.

Weekly versus monthly testosterone administration on fast and slow skeletal muscle fibers in older adult males

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).

Nutritional/metabolic response in older cancer patients

The combination of age-related muscle loss (sarcopenia) and the diagnosis of cancer (and the onset of cachexia) is likely a metabolic challenge that skeletal muscle of older cancer patients is not prepared to handle. Albeit to a smaller extent than healthy older controls, the skeletal muscle of older cancer patients is still acutely anabolic to the provision of amino acids. To provide an anabolic stimulus to skeletal muscle during a time when it is susceptible to an advanced rate of breakdown due to cancer- and tumor-related factors, enhanced intake of protein and amino acid sources might be necessary and should likely be higher than the current US recommended daily intake of 0.8 g protein/kg body weight/day. Future studies should investigate whether the acute effects of amino acids on muscle protein anabolism can be sustained over a longer period of time in the presence of cancer cachexia in older patients.

Elevation of serum fortilin levels is specific for apoptosis and signifies cell death in vivo

Background

Billions of cells undergo apoptosis each day in the average normal adult. The ability to readily assess the degree of apoptosis in human diseases is hampered by the lack of sensitive and specific serum biomarkers of apoptosis. Fortilin is a novel prosurvival molecule that protects cells against various noxious stimuli. While fortilin is secreted into the extracellular space under certain conditions, the relationship between the serum concentration of fortilin and the presence and extent of apoptosis in vivo remains unknown.

Methods & results

Using a newly developed fortilin ELISA system, we show here that fortilin exists in the normal human and mouse circulation. We further demonstrate that fortilin serum levels are significantly elevated in patients with solid cancer, in response to anti-cancer chemo- or radiation therapy. The elevation of fortilin serum levels is more robust and sensitive than that of such previously-reported serum biomarkers of apoptosis as fragmented cytokeratin-18, cytochrome c, and nucleosomal DNA. In addition, targeted apoptotic liver damage induced by Jo2 anti-Fas (CD95) antibody consistently and significantly increased serum fortilin levels in C57BL/6J mice. Finally, when challenged by anti-human-Fas IgM antibody, Jurkat leukemic T cells apoptosed and released fortilin into the medium before plasma membrane integrity was compromised.

Conclusions

Taken together, these data suggest that serum fortilin levels reflect the degree and extent of apoptosis occurring in vivo.

General significance

Fortilin is a viable serum biomarker of in vivo apoptosis and can be utilized to noninvasively assess the status of in vivo apoptosis in humans.

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Ultra-sensitive fortilin ELISA has been developed. Fortilin circulates in blood.

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Fortilin serum levels become highly elevated after apoptosis-inducing therapy.

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Fortilin is more robust and sensitive than other serum apoptosis markers.

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Fortilin is actively secreted before plasma membrane becomes disrupted.

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Fortilin is an excellent serum biomarker of in vivo apoptosis.

Comparison of bolus injection and constant infusion methods for measuring muscle protein fractional synthesis rate in humans

BACKGROUND

The use of stable isotope tracer techniques to measure muscle protein fractional synthesis rate (FSR) has been well established and widely used. The most common method that has been utilized so far is a primed constant infusion (CI) method, which requires 3-4 h of tracer infusion. However, recently our group has developed a bolus injection (BI) method, which requires an injection of bolus of tracer and can be completed within 1 h. In this study, we compared calf (gastrocnemius) muscle protein FSR measured using these two different methods--CI and BI.

METHOD

FSRs were measured in eight people (5 men and 3 women; age: 62.3±6.9 years (mean±SD); body weight: 75.4±21.5 kg) at basal, postabsorptive state using L-[ring-2H5]-phenylalanine. In the CI protocol, a primed continuous infusion was given for 4 h, and muscle biopsies were taken at 120 and 240 min; in the BI, a bolus injection of the tracer was given at 0 min and biopsies were taken at 5 and 60 min. Tracer enrichments in blood and muscle tissue were determined by gas chromatography-mass spectrometry. Data are expressed as mean±SE; t-test, linear regression and Levene Median equal variance test analyses were performed.

RESULTS

CI FSR was 0.066±0.006%/h, whereas BI FSR was 0.058±0.008%/h, p=NS. The linear regression analysis showed a significant relationship between BI and CI, p=0.038. The intra-class correlation coefficient was 0.83. The standard deviation of the differences in the measurements was 0.015%/h. The Levene Median equal variance test demonstrated no difference in variance between the CI and BI measurements (p=0.722).

CONCLUSION

No difference could be detected in calf muscle protein FSR measured by CI and BI methods; the BI method can be used for the measurement of muscle protein FSR in humans.

Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults

The RDA for protein describes the quantity that should be consumed daily to meet population needs and to prevent deficiency. Protein consumption in many countries exceeds the RDA; however, intake is often skewed toward the evening meal, whereas breakfast is typically carbohydrate rich and low in protein. We examined the effects of protein distribution on 24-h skeletal muscle protein synthesis in healthy adult men and women (n = 8; age: 36.9 ± 3.1 y; BMI: 25.7 ± 0.8 kg/m2). By using a 7-d crossover feeding design with a 30-d washout period, we measured changes in muscle protein synthesis in response to isoenergetic and isonitrogenous diets with protein at breakfast, lunch, and dinner distributed evenly (EVEN; 31.5 ± 1.3, 29.9 ± 1.6, and 32.7 ± 1.6 g protein, respectively) or skewed (SKEW; 10.7 ± 0.8, 16.0 ± 0.5, and 63.4 ± 3.7 g protein, respectively). Over 24-h periods on days 1 and 7, venous blood samples and vastus lateralis muscle biopsy samples were obtained during primed (2.0 μmol/kg) constant infusion [0.06 μmol/(kg⋅min)] of l-[ring-(13)C6]phenylalanine. The 24-h mixed muscle protein fractional synthesis rate was 25% higher in the EVEN (0.075 ± 0.006%/h) vs. the SKEW (0.056 ± 0.006%/h) protein distribution groups (P = 0.003). This pattern was maintained after 7 d of habituation to each diet (EVEN vs. SKEW: 0.077 ± 0.006 vs. 0.056 ± 0.006%/h; P = 0.001). The consumption of a moderate amount of protein at each meal stimulated 24-h muscle protein synthesis more effectively than skewing protein intake toward the evening meal.

Isotopic decay of urinary or plasma 3-methylhistidine as a potential biomarker of pathologic skeletal muscle loss

BACKGROUND

Skeletal muscle loss accompanying aging or cancer is associated with reduced physical function and predicts morbidity and mortality. 3-Methylhistidine (3MH) has been proposed as a biomarker of myofibrillar proteolysis, which may contribute to skeletal muscle loss.

METHODS

We hypothesized that the terminal portion of the isotope decay curve following an oral dose of isotopically labeled 3MH can be measured non-invasively from timed spot urine samples. We investigated the feasibility of this approach by determining isotope enrichment in spot urine samples and corresponding plasma samples and whether meat intake up to the time of dosing influences the isotope decay.

RESULTS

Isotope decay constants (k) were similar in plasma and urine, regardless of diet. Post hoc comparison of hourly sampling over 10 h with three samples distributed over 10 or fewer hours suggests that three distributed samples over 5-6 h of plasma or urine sampling yield decay constants similar to those obtained over 10 h of hourly sampling.

CONCLUSION

The findings from this study suggest that an index of 3MH production can be obtained from an easily administered test involving oral administration of a stable isotope tracer of 3MH followed by three plasma or urine samples collected over 5-6 h the next day.

Neuropsychological and physiological correlates of fatigue following traumatic brain injury

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.

Translational studies in older men using testosterone to treat sarcopenia

Sarcopenia is the loss of skeletal muscle mass and strength that occurs with aging. Our research group has found an efficacious administration paradigm using testosterone to combat sarcopenia in humans. In addition, our research has uncovered an important regulatory enzyme of inflammation, nuclear factor-κB-inducing kinase that may regulate human skeletal muscle catabolism, and that appears to be counter-regulated by administration of standard doses of testosterone. This is important because a number of age-related clinical circumstances trigger acute and chronic muscle loss including cancer, chronic obstructive pulmonary disease, hospitalization, acute and chronic illness, and diseases in which systemic inflammation occurs. Moreover, it is often the treatment itself that can induce muscle loss. For example, glucocorticoids are tremendously effective at reducing inflammation and are a frontline therapy for many inflammatory-based diseases, yet paradoxically trigger muscle loss. We will discuss our research findings and the clinical significance of our human clinical translational research with testosterone.

Sildenafil increases muscle protein synthesis and reduces muscle fatigue

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.

Cancer cachexia and anabolic interventions: a case report

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 safety, pharmacokinetics, and effects of LGD-4033, a novel nonsteroidal oral, selective androgen receptor modulator, in healthy young men

BACKGROUND

Concerns about potential adverse effects of testosterone on prostate have motivated the development of selective androgen receptor modulators that display tissue-selective activation of androgenic signaling. LGD-4033, a novel nonsteroidal, oral selective androgen receptor modulator, binds androgen receptor with high affinity and selectivity. Objectives. To evaluate the safety, tolerability, pharmacokinetics, and effects of ascending doses of LGD-4033 administered daily for 21 days on lean body mass, muscle strength, stair-climbing power, and sex hormones.

METHODS

In this placebo-controlled study, 76 healthy men (21-50 years) were randomized to placebo or 0.1, 0.3, or 1.0 mg LGD-4033 daily for 21 days. Blood counts, chemistries, lipids, prostate-specific antigen, electrocardiogram, hormones, lean and fat mass, and muscle strength were measured during and for 5 weeks after intervention.

RESULTS

LGD-4033 was well tolerated. There were no drug-related serious adverse events. Frequency of adverse events was similar between active and placebo groups. Hemoglobin, prostate-specific antigen, aspartate aminotransferase, alanine aminotransferase, or QT intervals did not change significantly at any dose. LGD-4033 had a long elimination half-life and dose-proportional accumulation upon multiple dosing. LGD-4033 administration was associated with dose-dependent suppression of total testosterone, sex hormone-binding globulin, high density lipoprotein cholesterol, and triglyceride levels. follicle-stimulating hormone and free testosterone showed significant suppression at 1.0-mg dose only. Lean body mass increased dose dependently, but fat mass did not change significantly. Hormone levels and lipids returned to baseline after treatment discontinuation.

CONCLUSIONS

LGD-4033 was safe, had favorable pharmacokinetic profile, and increased lean body mass even during this short period without change in prostate-specific antigen. Longer randomized trials should evaluate its efficacy in improving physical function and health outcomes in select populations.

The role of androgens and estrogens on healthy aging and longevity

Aging is associated with a loss of sex hormone in both men (andropause) and women (menopause). In men, reductions in testosterone can trigger declines in muscle mass, bone mass, and in physical function. In women, the impact of the loss of sex hormones, such as estradiol, on bone is well elucidated, but evidence is limited on whether the loss of estradiol negatively affects muscle mass and physical function. However, deficiencies in multiple anabolic hormones have been shown to predict health status and longevity in older persons. Thus, consideration should be given as to whether targeted hormone replacement therapies may prove effective at treating clinical conditions, such as age-related sarcopenia, cancer cachexia, and/or acute or chronic illnesses. If initiated carefully in the appropriate clinical population, hormone replacement therapies in men and women may prevent and reverse muscle and bone loss and functional declines and perhaps promote healthy aging and longevity.

Leucine supplementation chronically improves muscle protein synthesis in older adults consuming the RDA for protein

BACKGROUND & AIM

Protein-energy supplementation is routinely employed to combat muscle loss. However, success is often compromised by increased satiety, poor palatability, high costs and low compliance.

METHODS

For 2-weeks we supplemented meals of older individuals with leucine (4 g/meal; 3 meals/day; days 2-14). Metabolic studies were performed prior to (Day 1) and following (Day 15) supplementation. Leucine was not provided on metabolic study days. Venous blood and vastus lateralis muscle biopsies were obtained during a primed constant infusion of L-[ring-(13)C(6)] phenylalanine. Mixed muscle fractional synthesis rate (FSR), body composition and markers of nutrient signaling (mTOR, 4E-BP1 and p70S6K1 phosphorylation) were measured before and after a low protein/carbohydrate simulated meal.

RESULTS

The meal modestly increased FSR on Day 1 (postabsorptive: 0.063 ± 0.004 vs. postprandial: 0.075 ± 0.006%/h; p = 0.03), however, two weeks of leucine supplementation increased postabsorptive FSR (p = 0.004) and the response to the meal (p = 0.01) (postabsorptive: 0.074 ± 0.007 vs. postprandial: 0.10 ± 0.007%/h). Changes in FSR were mirrored by increased phosphorylation of mTOR, 4E-BP1 and p70S6K1 (p ≤ 0.1). No change in fat free mass was observed (p > 0.05).

CONCLUSIONS

In older adults, leucine supplementation may improve muscle protein synthesis in response to lower protein meals.

A randomized pilot study of monthly cycled testosterone replacement or continuous testosterone replacement versus placebo in older men

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.