Effects of inactivity on human muscle glutathione synthesis by a double-tracer and single-biopsy approach

Initial Glutathione Depletion During Short-Term Bed Rest: Pinpointing Synthesis and Degradation Checkpoints in the γ-Glutamyl Cycle

Hypokinesia triggers oxidative stress and accelerates the turnover of the glutathione system via the γ-glutamyl cycle. Our study aimed to identify the regulatory checkpoints controlling intracellular glutathione levels. We measured the intermediate substrates of the γ-glutamyl cycle in erythrocytes from 19 healthy young male volunteers before and during a 10-day experimental bed rest. Additionally, we tracked changes in glutathione levels and specific metabolite ratios up to 21 days of bed rest. Using gas chromatography-mass spectrometry and the internal standard technique, we observed a 9 ± 9% decrease in glutathione levels during the first 5 days of bed rest, followed by an 11 ± 9% increase from the 5th to the 10th day, nearly returning to baseline ambulatory levels. The cysteinyl-glycine-to-glutathione ratio, reflecting γ-glutamyl cyclotransferase activity (a key enzyme in glutathione breakdown), rose by 14 ± 22% in the first 5 days and then fell by 10 ± 14% over the subsequent 5 days, again approaching baseline levels. Additionally, the γ-glutamyl cysteine-to-cysteine ratio, indicative of γ-glutamyl cysteine synthetase activity (crucial for glutathione synthesis), increased by 12 ± 30% on day 5 and by 29 ± 41% on day 10 of bed rest. The results observed on day 21 of bed rest confirm those seen on day 10. By calculating the ratio of product concentration to precursor concentration, we assessed the efficiency of these key enzymes in glutathione turnover. These results were corroborated by directly measuring glutathione synthesis and degradation rates in vivo using stable isotope techniques. Our findings reveal significant changes in glutathione kinetics during the initial days of bed rest and identify potential therapeutic targets for maintaining glutathione levels.

Development of a cell-free strategy to recover aged skeletal muscle after disuse

Extended periods of bed rest and limb immobilization are required for healing post-injury or disease, yet disuse can result in significant muscle atrophy and decreased quality of life in older adults. Physical rehabilitation is commonly prescribed to recover these deficits, yet accumulation of reactive oxygen species and sustained rates of protein degradation persist during the rehabilitation period that can significantly delay or prevent recovery. Pericytes, considered the primary mesenchymal and vascular stromal cell in skeletal muscle, secrete beneficial factors that maintain baseline muscle mass, yet minimal information exists regarding the pericyte response to disuse and recovery. In the current study, single-cell RNA sequencing and functional assays were performed to demonstrate that pericytes in mouse skeletal muscle lose the capacity to synthesize antioxidants during disuse and recovery. This information was used to guide the design of a strategy in which healthy donor pericytes were stimulated with hydrogen peroxide (H2 O2 ) to produce small extracellular vesicles (sEVs) that effectively restored myofibre size in adult and aged muscle after disuse. Proteomic assessment detected 11 differentially regulated proteins in primed sEVs that may account for recovery of muscle, including proteins associated with extracellular matrix composition and anti-inflammatory and antioxidant processes. This study demonstrates that healthy H2 O2 -primed pericyte-derived sEVs effectively improve skeletal muscle recovery after immobilization, presenting a novel acellular approach to rebuild muscle mass in older adults after a period of disuse. KEY POINTS: Previous studies suggest that prolonged oxidative stress is a barrier to skeletal muscle recovery after a period of immobilization. In this study we demonstrate that muscle-resident perivascular stromal cells (pericytes) become dysfunctional and lack the capacity to mount an antioxidant defence after disuse in mice. Hydrogen peroxide treatment of healthy pericytes in vitro simulates the release of small extracellular vesicles (sEVs) that effectively recover skeletal muscle fibre size and extracellular matrix remodelling in young adult and aged mice after disuse. Pericyte-derived sEVs present a novel acellular strategy to recover skeletal muscle after disuse.

Mapping glycine uptake and its metabolic conversion to glutathione in mouse mammary tumors using functional mass spectrometry imaging

Although glutathione plays a key role in cancer cell viability and therapy response there is no clear trend in relating the level of this antioxidant to clinical stage, histological grade, or therapy response in patient tumors. The likely reason is that static levels of glutathione are not a good indicator of how a tissue deals with oxidative stress. A better indicator is the functional capacity of the tissue to maintain glutathione levels in response to this stress. However, there are few methods to assess glutathione metabolic function in tissue. We have developed a novel functional mass spectrometry imaging (fMSI) method that can map the variations in the conversion of glycine to glutathione metabolic activity across tumor tissue sections by tracking the fate of three glycine isotopologues administered in a timed sequence to tumor-bearing anesthetized mice. This fMSI method generates multiple time point kinetic data for substrate uptake and glutathione production from each spatial location in the tissue. As expected, the fMSI data shows glutathione metabolic activity varies across the murine 4T1 mammary tumor. Although glutathione levels are highest at the tumor periphery there are regions of high content but low metabolic activity. The timed infusion method also detects variations in delivery of the glycine isotopologues thereby providing a measure of tissue perfusion, including evidence of intermittent perfusion, that contributes to the observed differences in metabolic activity. We believe this new approach will be an asset to linking molecular content to tissue function.

Highlighting Functional Mass Spectrometry Imaging Methods in Bioanalysis

Most mass spectrometry imaging (MSI) methods provide a molecular map of tissue content but little information on tissue function. Mapping tissue function is possible using several well-known examples of "functional imaging" such as positron emission tomography and functional magnetic resonance imaging that can provide the spatial distribution of time-dependent biological processes. These functional imaging methods represent the net output of molecular networks influenced by local tissue environments that are difficult to predict from molecular/cellular content alone. However, for decades, MSI methods have also been demonstrated to provide functional imaging data on a variety of biological processes. In fact, MSI exceeds some of the classic functional imaging methods, demonstrating the ability to provide functional data from the nanoscale (subcellular) to whole tissue or organ level. This Perspective highlights several examples of how different MSI ionization and detection technologies can provide unprecedented detailed spatial maps of time-dependent biological processes, namely, nucleic acid synthesis, lipid metabolism, bioenergetics, and protein metabolism. By classifying various MSI methods under the umbrella of "functional MSI", we hope to draw attention to both the unique capabilities and accessibility with the aim of expanding this underappreciated field to include new approaches and applications.

Multiple Infusion Start Time Mass Spectrometry Imaging of Dynamic SIL-Glutathione Biosynthesis Using Infrared Matrix-Assisted Laser Desorption Electrospray Ionization

Due to the high association of glutathione metabolism perturbation with a variety of disease states, there is a dire need for analytical techniques to study glutathione kinetics. Additionally, the elucidation of microenvironmental effects on changes in glutathione metabolism would significantly improve our understanding of the role of glutathione in disease. We therefore present a study combining a multiple infusion start time protocol, stable isotope labeling technology, infrared matrix-assisted laser desorption electrospray ionization, and high-resolution accurate mass-mass spectrometry imaging to study spatial changes in glutathione kinetics across in sectioned mouse liver tissues. After injecting a mouse with the isotopologues [2-¹³C,¹⁵N]-glycine, [1,2-¹³C₂]-glycine, and [1,2-¹³C₂,¹⁵N]-glycine at three different time points, we were able to fully resolve and spatially map their metabolism into three isotopologues of glutathione and calculate their isotopic enrichment in glutathione. We created a tool in the open-source mass spectrometry imaging software MSiReader to accurately compute the percent isotope enrichment (PIE) of these labels in glutathione and visualize them in heat-maps of the tissue sections. In areas of high flux, we found that each label enriched an approximate median of 1.6%, 1.8%, and 1.5%, respectively, of the glutathione product pool measured in each voxel. This method may be adapted to study the heterogeneity of glutathione flux in diseased versus healthy tissues.

The Role of Nrf2 in Skeletal Muscle on Exercise Capacity

Nuclear factor erythroid 2-related factor 2 Nfe2l2 (Nrf2) is believed to play a crucial role in protecting cells against oxidative stress. In addition to its primary function of maintaining redox homeostasis, there is emerging evidence that Nrf2 is also involved in energy metabolism. In this review, we briefly discuss the role of Nrf2 in skeletal muscle metabolism from the perspective of exercise physiology. This article is part of a special issue “Mitochondrial Function, Reactive Oxygen/Nitrogen Species and Skeletal Muscle” edited by Håkan Westerblad and Takashi Yamada.

Quantitative Redox Biology of Exercise

Biology is rich in claims that reactive oxygen and nitrogen species are involved in every biological process and disease. However, many quantitative aspects of redox biology remain elusive. The important quantitative parameters you need to address the feasibility of redox reactions in vivo are: rate of formation and consumption of a reactive oxygen and nitrogen species, half-life, diffusibility and membrane permeability. In the first part, we explain the basic chemical kinetics concepts and algebraic equations required to perform "street fighting" quantitative analysis. In the second part, we provide key numbers to help thinking about sizes, concentrations, rates and other important quantities that describe the major oxidants (superoxide, hydrogen peroxide, nitric oxide) and antioxidants (vitamin C, vitamin E, glutathione). In the third part, we present the quantitative effect of exercise on superoxide, hydrogen peroxide and nitric oxide concentration in mitochondria and whole muscle and calculate how much hydrogen peroxide concentration needs to increase to transduce signalling. By taking into consideration the quantitative aspects of redox biology we can: i) refine the broad understanding of this research area, ii) design better future studies and facilitate comparisons among studies, and iii) define more efficiently the "borders" between cellular signaling and stress.

Oxidative Stress, Frailty and Cardiovascular Diseases: Current Evidence

The aim of this chapter is to review the results of recent studies analyzing the role of oxidative stress and systemic inflammation as potential contributors to frailty and CVD, and to explain a possible pathogenic relationship between the latter two conditions. Available evidence suggests that frail patients have elevated levels of oxidative stress biomarkers and proinflammatory cytokines, as well as with reduced concentrations of endogenous antioxidants. This implies that oxidative stress and systemic inflammation might play a role in the pathogenesis of frailty, but an underlying mechanism of this relationship is still mostly hypothetical. Oxidative stress and systemic inflammation are also involved in the pathogenesis of CVD. Cardiovascular conditions are established risk factor for frailty and in turn, presence of frailty constitutes an unfavorable prognostic factor in cardiac patients. Finally, some cardiovascular risk factors, such as lack of physical activity, smoking, obesity and inappropriate diet, are also involved in the etiology of oxidative stress, chronic inflammation and frailty. This complex interplay between intrinsic and extrinsic elements should be considered during holistic management of older persons with frailty and/or cardiovascular conditions.

Glutathione and Nitric Oxide: Key Team Players in Use and Disuse of Skeletal Muscle

Glutathione (GSH) is the main non-enzymatic antioxidant playing an important role in detoxification, signal transduction by modulation of protein thiols redox status and direct scavenging of radicals. The latter function is not only performed against reactive oxygen species (ROS) but GSH also has a fundamental role in buffering nitric oxide (NO), a physiologically-produced molecule having-multifaceted functions. The efficient rate of GSH synthesis and high levels of GSH-dependent enzymes are characteristic features of healthy skeletal muscle where, besides the canonical functions, it is also involved in muscle contraction regulation. Moreover, NO production in skeletal muscle is a direct consequence of contractile activity and influences several metabolic myocyte pathways under both physiological and pathological conditions. In this review, we will consider the homeostasis and intersection of GSH with NO and then we will restrict the discussion on their role in processes related to skeletal muscle function and degeneration.

Sarcolemmal loss of active nNOS (Nos1) is an oxidative stress-dependent, early event driving disuse atrophy

Skeletal muscle atrophy following unloading or immobilization represents a major invalidating event in bedridden patients. Among mechanisms involved in atrophy development, a controversial role is played by neuronal NOS (nNOS; NOS1), whose dysregulation at the protein level and/or subcellular distribution also characterizes other neuromuscular disorders. This study aimed to investigate unloading-induced changes in nNOS before any evidence of myofiber atrophy, using vastus lateralis biopsies obtained from young healthy subjects after a short bed-rest and rat soleus muscles after exposure to short unloading periods. Our results showed that (1) changes in nNOS subcellular distribution using NADPH-diaphorase histochemistry to detect enzyme activity were observed earlier than using immunofluorescence to visualize the protein; (2) loss of active nNOS from the physiological subsarcolemmal localization occurred before myofiber atrophy, i.e. in 8-day bed-rest biopsies and in 6 h-unloaded rat soleus, and was accompanied by increased nNOS activity in the sarcoplasm; (3) nNOS (Nos1) transcript and protein levels decreased significantly in the rat soleus after 6 h and 1 day unloading, respectively, to return to ambulatory levels after 4 and 7 days of unloading, respectively; (4) unloading-induced nNOS redistribution appeared dependent on mitochondrial-derived oxidant species, indirectly measured by tropomyosin disulfide bonds which had increased significantly in the rat soleus already after a 6 h-unloading bout; (5) activity of displaced nNOS molecules is required for translocation of the FoxO3 transcription factor to myofiber nuclei. FoxO3 nuclear localization in rat soleus increased after 6 h unloading (about four-fold the ambulatory level), whereas it did not when nNOS expression and activity were inhibited in vivo before and during 6 h unloading. In conclusion, this study demonstrates that the redistribution of active nNOS molecules from sarcolemma to sarcoplasm not only is ahead of the atrophy of unloaded myofibers, and is induced by increased production of mitochondrial superoxide anion, but also drives FoxO3 activation to initiate muscle atrophy. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Effects of Iron Overload and Oxidative Damage on the Musculoskeletal System in the Space Environment: Data from Spaceflights and Ground-Based Simulation Models

The space environment chiefly includes microgravity and radiation, which seriously threatens the health of astronauts. Bone loss and muscle atrophy are the two most significant changes in mammals after long-term residency in space. In this review, we summarized current understanding of the effects of microgravity and radiation on the musculoskeletal system and discussed the corresponding mechanisms that are related to iron overload and oxidative damage. Furthermore, we enumerated some countermeasures that have a therapeutic potential for bone loss and muscle atrophy through using iron chelators and antioxidants. Future studies for better understanding the mechanism of iron and redox homeostasis imbalance induced by the space environment and developing the countermeasures against iron overload and oxidative damage consequently may facilitate human to travel more safely in space.

Effects of Hypoxia and Bed Rest on Markers of Cardiometabolic Risk: Compensatory Changes in Circulating TRAIL and Glutathione Redox Capacity

In chronic diseases, hypoxia and physical inactivity are associated with atherosclerosis progression. In contrast, a lower mortality from coronary artery disease and stroke is observed in healthy humans residing at high altitude in hypoxic environments. Eleven young, male volunteers completed the following 10-day campaigns in a randomized order: hypoxic ambulatory, hypoxic bed rest and normoxic bed rest. Before intervention, subjects were evaluated in normoxic ambulatory condition. Normobaric hypoxia was achieved in a hypoxic facility simulating 4000 m of altitude. Following hypoxia, either in bed rest or ambulatory condition, markers of cardiometabolic risk shifted toward a more atherogenic pattern consisting of: (a) lower levels of total HDL cholesterol and HDL2 sub-fraction and decreased hepatic lipase; (b) activation of systemic inflammation, as determined by C-reactive protein and serum amyloid A; (c) increased plasma homocysteine; (d) decreased delta-5 desaturase index in cell membrane fatty acids, a marker of insulin sensitivity. Bed rest and hypoxia additively decreased total HDL and delta-5 desaturase index. In parallel to the pro-atherogenic effects, hypoxia activated selected anti-atherogenic pathways, consisting of increased circulating TNF-related apoptosis-inducing ligand (TRAIL), a protective factor against atherosclerosis, membrane omega-3 index and erythrocyte glutathione availability. Hypoxia mediated changes in TRAIL concentrations and redox glutathione capacity (i.e., GSH/GSSG ratio) were greater in ambulatory conditions (+34 ± 6% and +87 ± 31%, respectively) than in bed rest (+17 ± 7% and +2 ± 27% respectively). Hypoxia-induced cardiometabolic risk is blunted by moderate level of physical activity as compared to bed rest. TRAIL and glutathione redox capacity may contribute to the positive interaction between physical activity and hypoxia. Highlights: - Hypoxia and bed rest activate metabolic and inflammatory markers of atherogenesis. - Hypoxia and physical activity activate selected anti-atherogenic pathways. - Hypoxia and physical activity positive interaction involves TRAIL and glutathione.

Alkalinization with potassium bicarbonate improves glutathione status and protein kinetics in young volunteers during 21-day bed rest

BACKGROUND & AIMS

Physical inactivity is associated with lean body mass wasting, oxidative stress and pro-inflammatory changes of cell membrane lipids. Alkalinization may potentially counteract these alterations. We evaluated the effects of potassium bicarbonate supplementation on protein kinetics, glutathione status and pro- and anti-inflammatory polyunsaturated fatty acids (PUFA) in erythrocyte membranes in humans, during experimental bed rest.

METHODS

Healthy, young, male volunteers were investigated at the end of two 21-day bed rest periods, one with, and the other without, daily potassium bicarbonate supplementation (90 mmol × d^-1), according to a cross-over design. Oxidative stress in erythrocytes was evaluated by determining the ratio between reduced (GSH) and oxidized glutathione (GSSG). Glutathione turnover and phenylalanine kinetics, a marker of whole body protein metabolism, were determined by stable isotope infusions. Erythrocyte membranes PUFA composition was analyzed by gas-chromatography.

RESULTS

At the end of the two study periods, urinary pH was 10 ± 3% greater in subjects receiving potassium bicarbonate supplementation (7.23 ± 0.15 vs. 6.68 ± 0.11, p < 0.001). Alkalinization increased total glutathione concentrations by 5 ± 2% (p < 0.05) and decreased its rate of clearance by 38 ± 13% (p < 0.05), without significantly changing GSH-to-GSSG ratio. After alkalinization, net protein balance in the postabsorptive state improved significantly by 17 ± 5% (p < 0.05) as well as the sum of n-3 PUFA and the n-3-to-n-6 PUFA ratio in erythrocyte membranes (p < 0.05).

CONCLUSIONS

Alkalinization during long-term inactivity is associated with improved glutathione status, anti-inflammatory lipid pattern in cell membranes and reduction in protein catabolism at whole body level. This study suggests that, in clinical conditions characterized by inactivity, oxidative stress and inflammation, alkalinization could be a useful adjuvant therapeutic strategy.

Effects of β-hydroxy-β-methylbutyrate on skeletal muscle mitochondrial content and dynamics, and lipids after 10 days of bed rest in older adults

Loss of muscle mass during periods of disuse likely has negative health consequences for older adults. We have previously shown that β-hydroxy-β-methylbutyrate (HMB) supplementation during 10 days of strict bed rest (BR) attenuates the loss of lean mass in older adults. To elucidate potential molecular mechanisms of HMB effects on muscle during BR and resistance training rehabilitation (RT), we examined mediators of skeletal muscle mitochondrial dynamics, autophagy and atrophy, and intramyocellular lipids. Nineteen older adults (60-76 yr) completed 10 days BR followed by 8-wk RT rehabilitation. Subjects were randomized to either HMB (3 g/day HMB; n = 11) or control (CON; n = 8) groups. Skeletal muscle cross-sectional area (CSA) was determined by histology from percutaneous vastus lateralis biopsies. We measured protein markers of mitochondrial content [oxidative phosphorylation (OXPHOS)], fusion and fission (MFN2, OPA1, FIS1, and DRP1), autophagy (Beclin1, LC3B, and BNIP3), and atrophy [poly-ubiquinated proteins (poly-ub)] by Western blot. Fatty acid composition of several lipid classes in skeletal muscle was measured by infusion-MS analysis. Poly-ub proteins and OXPHOS complex I increased in both groups following BR (P < 0.05, main effect for time), and muscle triglyceride content tended to increase following BR in the HMB group (P = 0.055). RT rehabilitation increased OXPHOS complex II protein (P < 0.05), and total OXPHOS content tended (P = 0.0504) to be higher in HMB group. In addition, higher levels of DRP1 and MFN2 were maintained in the HMB group after RT (P < 0.05). BNIP3 and poly-ub proteins were significantly reduced following rehabilitation in both groups (P < 0.05). Collectively, these data suggest that HMB influences mitochondrial dynamics and lipid metabolism during disuse atrophy and rehabilitation.NEW & NOTEWORTHY Mitochondrial content and dynamics remained unchanged over 10 days of BR in older adults. HMB stimulated intramuscular lipid storage as triacylglycerol following 10 days of bed rest (BR) and maintained higher mitochondrial OXPHOS content and dynamics during the 8-wk resistance exercise rehabilitation program.

Hypoxia-Induced Oxidative Stress Modulation with Physical Activity

Increased oxidative stress, defined as an imbalance between prooxidants and antioxidants, resulting in molecular damage and disruption of redox signaling, is associated with numerous pathophysiological processes and known to exacerbate chronic diseases. Prolonged systemic hypoxia, induced either by exposure to terrestrial altitude or a reduction in ambient O2 availability is known to elicit oxidative stress and thereby alter redox balance in healthy humans. The redox balance modulation is also highly dependent on the level of physical activity. For example, both high-intensity exercise and inactivity, representing the two ends of the physical activity spectrum, are known to promote oxidative stress. Numerous to-date studies indicate that hypoxia and exercise can exert additive influence upon redox balance alterations. However, recent evidence suggests that moderate physical activity can attenuate altitude/hypoxia-induced oxidative stress during long-term hypoxic exposure. The purpose of this review is to summarize recent findings on hypoxia-related oxidative stress modulation by different activity levels during prolonged hypoxic exposures and examine the potential mechanisms underlying the observed redox balance changes. The paper also explores the applicability of moderate activity as a strategy for attenuating hypoxia-related oxidative stress. Moreover, the potential of such moderate intensity activities used to counteract inactivity-related oxidative stress, often encountered in pathological, elderly and obese populations is also discussed. Finally, future research directions for investigating interactive effects of altitude/hypoxia and exercise on oxidative stress are proposed.

Oxidative stress and frailty: A systematic review and synthesis of the best evidence

OBJECTIVE

Oxidative stress (OS) is associated with accelerated aging. Previous studies have suggested a possible relationship between OS and frailty but this association remains unclear. We conducted a systematic review to investigate potential interactions between OS and frailty.

METHODS

A systematic literature search of original reports providing data on 'OS and antioxidant' parameters and frailty was carried out across major electronic databases from inception until May 2016. Cross-sectional/case control and longitudinal studies reporting data on the association between frailty and anti-oxidants-OS biomarkers were considered for inclusion. Results were summarized with a synthesis based on the best evidence.

RESULTS

From 1856 hits, 8 studies (cross-sectional/case control) were included (N=6349; mean age of 75±12years; 56.4% females). Overall, there were 588 (=9.3%) frail, 3036 pre-frail (=47.8%), 40 (=0.6%) pre-frail/robust, and 2685 (=42.3%) robust subjects. Six cross-sectional/case control studies demonstrated that frailty was associated with an increase in peripheral OS biomarkers, including lipoprotein phospholipase A2 (1 study), isoprostanes (2 studies), malonaldehyde (2 studies), 8-hydroxy-20-deoxyguanosine (2 studies), derivate of reactive oxygen metabolites (2 studies), oxidized glutathione/glutathione (1 study), 4-hydroxy-2,3-nonenal (1 study), and protein carbonylation levels (1 study). In addition, preliminary evidence points to lower anti-oxidant parameters (vitamin C, E, α-tocopherol, biological anti-oxidant potential, total thiol levels) in frailty.

CONCLUSION

Frailty and pre-frailty appear to be associated with higher OS and possibly lower anti-oxidant parameters. However, due to the cross-sectional design, it is not possible to disentangle the directionality of the relationships observed. Thus, future high-quality and in particular longitudinal research is required to confirm or refute these relationships and to further elucidate pathophysiological mechanisms.

One Week of Bed Rest Leads to Substantial Muscle Atrophy and Induces Whole-Body Insulin Resistance in the Absence of Skeletal Muscle Lipid Accumulation

Short (<10 days) periods of muscle disuse, often necessary for recovery from illness or injury, lead to various negative health consequences. The current study investigated mechanisms underlying disuse-induced insulin resistance, taking into account muscle atrophy. Ten healthy, young males (age: 23 ± 1 years; BMI: 23.0 ± 0.9 kg · m(-2)) were subjected to 1 week of strict bed rest. Prior to and after bed rest, lean body mass (dual-energy X-ray absorptiometry) and quadriceps cross-sectional area (CSA; computed tomography) were assessed, and peak oxygen uptake (VO2peak) and leg strength were determined. Whole-body insulin sensitivity was measured using a hyperinsulinemic-euglycemic clamp. Additionally, muscle biopsies were collected to assess muscle lipid (fraction) content and various markers of mitochondrial and vascular content. Bed rest resulted in 1.4 ± 0.2 kg lean tissue loss and a 3.2 ± 0.9% decline in quadriceps CSA (both P < 0.01). VO2peak and one-repetition maximum declined by 6.4 ± 2.3 (P < 0.05) and 6.9 ± 1.4% (P < 0.01), respectively. Bed rest induced a 29 ± 5% decrease in whole-body insulin sensitivity (P < 0.01). This was accompanied by a decline in muscle oxidative capacity, without alterations in skeletal muscle lipid content or saturation level, markers of oxidative stress, or capillary density. In conclusion, 1 week of bed rest substantially reduces skeletal muscle mass and lowers whole-body insulin sensitivity, without affecting mechanisms implicated in high-fat diet-induced insulin resistance.

FemHab: The effects of bed rest and hypoxia on oxidative stress in healthy women

Independently, both inactivity and hypoxia augment oxidative stress. This study, part of the FemHab project, investigated the combined effects of bed rest-induced unloading and hypoxic exposure on oxidative stress and antioxidant status. Healthy, eumenorrheic women were randomly assigned to the following three 10-day experimental interventions: normoxic bed rest (NBR;n= 11; PiO2 = 133 mmHg), normobaric hypoxic bed rest (HBR;n= 12; PiO2 = 90 mmHg), and ambulatory hypoxic confinement (HAMB;n= 8: PiO2 = 90 mmHg). Plasma samples, obtained before (Pre), during (D2, D6), immediately after (Post) and 24 h after (Post+1) each intervention, were analyzed for oxidative stress markers [advanced oxidation protein products (AOPP), malondialdehyde (MDA), and nitrotyrosine], antioxidant status [superoxide dismutase (SOD), catalase, ferric-reducing antioxidant power (FRAP), glutathione peroxidase (GPX), and uric acid (UA)], NO metabolism end-products (NOx), and nitrites. Compared with baseline, AOPP increased in NBR and HBR on D2 (+14%; +12%;P< 0.05), D6 (+19%; +15%;P< 0.05), and Post (+22%; +21%;P< 0.05), respectively. MDA increased at Post+1 in NBR (+116%;P< 0.01) and D2 in HBR (+114%;P< 0.01) and HAMB (+95%;P< 0.05). Nitrotyrosine decreased (-45%;P< 0.05) and nitrites increased (+46%;P< 0.05) at Post+1 in HAMB only. Whereas SOD was higher at D6 (+82%) and Post+1 (+67%) in HAMB only, the catalase activity increased on D6 (128%) and Post (146%) in HBR and HAMB, respectively (P< 0.05). GPX was only reduced on D6 (-20%;P< 0.01) and Post (-18%;P< 0.05) in HBR. No differences were observed in FRAP and NOx. UA was higher at Post in HBR compared with HAMB (P< 0.05). These data indicate that exposure to combined inactivity and hypoxia impairs prooxidant/antioxidant balance in healthy women. Moreover, habitual activity levels, as opposed to inactivity, seem to blunt hypoxia-related oxidative stress via antioxidant system upregulation.

Sarcopenia and the Common Mental Disorders: a Potential Regulatory Role of Skeletal Muscle on Brain Function?

While it is understood that body composition impacts on physical conditions, such as diabetes and cardiovascular disease, it is only now apparent that body composition might play a role in the genesis of common mental disorders, depression and anxiety. Sarcopenia occurs in ageing and comprises a progressive decline in muscle mass, strength and function, leading to frailty, decreased independence and poorer quality of life. This review presents an emerging body of evidence to support the hypothesis that shared pathophysiological pathways for sarcopenia and the common mental disorders constitute links between skeletal muscle and brain function. Contracting skeletal muscle secretes neurotrophic factors that are known to play a role in mood and anxiety, and have the dual role of nourishing neuronal growth and differentiation, while protecting the size and number of motor units in skeletal muscle. Furthermore, skeletal muscle activity has important immune and redox effects that impact behaviour and reduce muscle catabolism.

Expression changes in human skeletal muscle miRNAs following 10 days of bed rest in young healthy males

AIM

Studies in humans show global changes in mRNA and protein expression occur in human skeletal muscle during bed rest. As microRNAs are important regulators of expression, we analysed the global microRNA expression changes in human muscle following 10 days of sustained bed rest, with the rationale that miRNAs play key roles in atrophy of skeletal muscle.

METHODS

We analysed expression of miRNA and selected target proteins before and after 10 days of bed rest in biopsies obtained from the vastus lateralis muscle of 6 healthy males.

RESULTS

Fifteen of 152 miRNAs detected in human muscle tissue were differentially expressed, and all of them with exception of two were downregulated. The downregulated miRNAs include the following: miR-206, a myomir involved in function and maintenance of skeletal muscle; miR-23a, involved in insulin response and atrophy defence; and several members of the let-7 family involved in cell cycle, cell differentiation and glucose homeostasis. Predicted gene targets of these miRNAs are members of the MAPK, TNF receptor, ALK1, TGF-beta receptor and SMAD signalling pathways. All of these pathways were previously indicated to be involved in skeletal muscle response to physical inactivity. We also measured protein expression of selected miRNA targets and observed a decrease in HDAC4.

CONCLUSION

Our data demonstrate that miRNAs in postural muscles are affected by sustained inactivity and unloading, as induced by prolonged bed rest, and hence are potentially involved in regulation of skeletal muscle adjustments to inactivity. We also propose new miRNAs involved in regulation of biological processes in adult human muscle.

Nitrosative stress in human skeletal muscle attenuated by exercise countermeasure after chronic disuse

Activity-induced nitric oxide (NO) imbalance and "nitrosative stress" are proposed mechanisms of disrupted Ca(2+) homeostasis in atrophic skeletal muscle. We thus mapped S-nitrosylated (SNO) functional muscle proteins in healthy male subjects in a long-term bed rest study (BBR2-2 Study) without and with exercise as countermeasure in order to assess (i) the negative effects of chronic muscle disuse by nitrosative stress, (ii) to test for possible attenuation by exercise countermeasure in bed rest and (iii) to identify new NO target proteins. Muscle biopsies from calf soleus and hip vastus lateralis were harvested at start (Pre) and at end (End) from a bed rest disuse control group (CTR, n=9) and two bed rest resistive exercise groups either without (RE, n=7) or with superimposed vibration stimuli (RVE, n=7). At subcellular compartments, strong anti-SNO-Cys immunofluorescence patterns in control muscle fibers after bed rest returned to baseline following vibration exercise. Total SNO-protein levels, Nrf-2 gene expression and nucleocytoplasmic shuttling were changed to varying degrees in all groups. Excess SNO-protein levels of specific calcium release/uptake proteins (SNO-RyR1, -SERCA1 and -PMCA) and of contractile myosin heavy chains seen in biopsy samples of chronically disused skeletal muscle were largely reduced by vibration exercise. We also identified NOS1 as a novel NO target in human skeletal muscle controlled by activity driven auto-nitrosylation mechanisms. Our findings suggest that aberrant levels of functional SNO-proteins represent signatures of uncontrolled nitrosative stress management in disused human skeletal muscle that can be offset by exercise as countermeasure.

Proteomic and carbonylation profile analysis of rat skeletal muscles following acute swimming exercise

Previous studies by us and other groups characterized protein expression variation following long-term moderate training, whereas the effects of single bursts of exercise are less known. Making use of a proteomic approach, we investigated the effects of acute swimming exercise (ASE) on protein expression and carbonylation patterns in two hind limb muscles: the Extensor Digitorum Longus (EDL) and the Soleus, mostly composed of fast-twitch and slow-twitch fibres, respectively. Carbonylation is one of the most common oxidative modifications of proteins and a marker of oxidative stress. In fact, several studies suggest that physical activity and the consequent increase in oxygen consumption can lead to increase in reactive oxygen and nitrogen species (RONS) production, hence the interest in examining the impact of RONS on skeletal muscle proteins following ASE. Results indicate that protein expression is unaffected by ASE in both muscle types. Unexpectedly, the protein carbonylation level was reduced following ASE. In particular, the analysis found 31 and 5 spots, in Soleus and EDL muscles respectively, whose carbonylation is reduced after ASE. Lipid peroxidation levels in Soleus were markedly reduced as well. Most of the decarbonylated proteins are involved either in the regulation of muscle contractions or in the regulation of energy metabolism. A number of hypotheses may be advanced to account for such results, which will be addressed in future studies.

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

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

Proteomic analysis and protein carbonylation profile in trained and untrained rat muscles

Understanding the relationship between physical exercise, reactive oxygen species and skeletal muscle modification is important in order to better identify the benefits or the damages that appropriate or inappropriate exercise can induce. Unbalanced ROS levels can lead to oxidation of cellular macromolecules and a major class of protein oxidative modification is carbonylation. The aim of this investigation was to study muscle protein expression and carbonylation patterns in trained and untrained animal models. We analyzed two muscles characterized by different metabolisms: tibialis anterior and soleus. Whilst tibialis anterior is mostly composed of fast-twitch fibers, the soleus muscle is mostly composed of slow-twitch fibers. By a proteomic approach we identified 15 protein spots whose expression is influenced by training. Among them in tibialis anterior we observed a down-regulation of several glycolitic enzymes. Concerning carbonylation, we observed the existence of a high basal level of protein carbonylation. Although this level shows some variation among individual animals, several proteins (mostly involved in energy metabolism, muscle contraction, and stress response) appear carbonylated in all animals and in both types of skeletal muscle. Moreover we identified 13 spots whose carbonylation increases after training.

Blood vessel remodeling and physical inactivity in humans

Physical inactivity is associated with an increase in cardiovascular risk that cannot be fully explained by traditional or novel risk factors. Inactivity is also associated with changes in hemodynamic stimuli, which exert direct effects on the vasculature leading to remodeling and a proatherogenic phenotype. In this review, we synthesize and summarize in vivo evidence relating to the impact of local and systemic models of physical inactivity on conduit arteries, resistance vessels, and the microcirculation in humans. Taken together, the literature suggests that a rapid inward structural remodeling of vessels occurs in response to physical inactivity. The magnitude of this response is dependent on the "dose" of inactivity. Moreover, changes in vascular function are found at resistance and microvessel levels in humans. In conduit arteries, a strong interaction between vascular function and structure is present, which results in conflicting data regarding the impact of inactivity on conduit artery function. While much of the cardioprotective effect of exercise is related to the nitric oxide pathway, deconditioning may primarily be associated with activation of vasoconstrictor pathways. The effects of deconditioning on the vasculature are therefore not simply the opposite of those in response to exercise training. Given the importance of sedentary behavior, future studies should provide further insight into the impact of inactivity on the vasculature and other (novel) markers of vascular health. Moreover, studies should examine the role of (hemodynamic) stimuli that underlie the characteristic vascular adaptations during deconditioning. Our review concludes with some suggestions for future research directions.