Maximal Oxidative Capacity Research Articles

Effect of the Phosphodiesterase 5 Inhibitor Sildenafil on Ischemia-Reperfusion-Induced Muscle Mitochondrial Dysfunction and Oxidative Stress.

Lower-limb ischemia-reperfusion (IR) is frequent and associated with significant morbidity and mortality. Phosphodiesterase 5 inhibitors demonstrated antioxidant and beneficial effects in several organs submitted to IR, but their effects on muscle mitochondrial functions after lower-limb IR are unknown. Unilateral hindlimb IR (2 h tourniquet followed by 2 h reperfusion) without or with sildenafil (1mg/kg ip 30 minutes before ischemia) was performed in 18 mice. Maximal oxidative capacity (VMax), relative contribution of the mitochondrial respiratory chain complexes, calcium retention capacity (CRC)—a marker of apoptosis—and reactive oxygen species (ROS) production were determined using high-resolution respirometry, spectrofluorometry, and electron paramagnetic resonance in gastrocnemius muscles from both hindlimbs. IR significantly reduced mitochondrial VMax (from 11.79 ± 1.74 to 4.65 ± 1.11 pmol/s*mg wet weight (ww), p < 0.05, −50.2 ± 16.3%) and CRC (from 2.33 ± 0.41 to 0.84 ± 0.18 µmol/mg dry weight (dw), p < 0.05; −61.1 ± 6.8%). ROS tended to increase in the ischemic limb (+64.3 ± 31.9%, p = 0.08). Although tending to reduce IR-related ROS production (−42.4%), sildenafil failed to reduce muscle mitochondrial dysfunctions (−63.3 ± 9.2%, p < 0.001 and −55.2 ± 7.6% p < 0.01 for VMax, and CRC, respectively). In conclusion, lower limb IR impaired skeletal muscle mitochondrial function, but, despite tending to reduce ROS production, pharmacological preconditioning with sildenafil did not show protective effects.

Abstract P284: The Chemotherapeutic Agent Docetaxel Disrupts Mitochondrial Energetics in 3D Human Bioengineered Myobundles

Taxanes (i.e. docetaxel, (TAX)) comprise the first line-treatment for breast cancer (BC), mostly in combination with anthracyclines like doxorubicin (DOX). The efficacy of these drugs as antineoplastic agents has helped to boost 10-year survival rates to &gt; 90%, leading to a fast-growing population of over 3 million BC survivors in the US. However, epidemiological evidence shows that the highly abrasive nature of these therapies can give rise to a vicious cycle of metabolic decline and physical inactivity that compromises quality of life and increases risk of numerous musculoskeletal and cardio-metabolic disorders including arthritis, sarcopenic obesity, cardiovascular disease and type 2 diabetes. Major side effects of TAX include peripheral neuropathy, arthralgia, myalgia and muscle weakness. Taxanes act primarily by stabilizing microtubules (MTs), which causes cell cycle arrest. Importantly, MT dynamics can also impact mitochondrial function. For example, the MT protein unit, tubulin, can bind to the outer mitochondrial protein channel, VDAC, and thereby affect ATP transport to the cytosol. Herein, we sought to test the hypothesis that TAX exacerbates DOX-induced mitochondrial dysfunction, which is thought to underlie anthracyclines’ cardiotoxicity. To this end, we leveraged a newly developed 3-D bioengineered model of human muscle organoids (myobundles), derived from primary human skeletal muscle progenitor cells (HSkM), to study mechanisms of TAX-induced myotoxicity and its interactions with DOX. Preliminary findings in primary HSkM cells exposed to 3 daily x 3 h treatments with TAX (1 - 100 nM) +/- 10 nM DOX caused a robust ~10-fold acetylation of a-tubulin at lysine 40 (AcK40), reflecting marked stabilization of MTs. TAX treatment decreased basal and ATP-linked respiration (JO 2 ) up to 30 % (p&lt;0.05), in a dose-dependent manner. However, maximal uncoupled JO 2 (+FCCP) remained unchanged, suggesting TAX disrupts mitochondrial thermodynamics and energy transfer, rather than maximal oxidative phosphorylation capacity. Exposure of 3D myobundles to a TAX+/-DOX regimen that mimicked human pharmacokinetics post-infusion led to a 30-fold increase (p&lt;0.005) in AcK40 a-tubulin. TAX alone induced a biphasic JO 2 response to ADP (KM ADP 2- and 4-fold higher, p&lt;0.05), but when combined with DOX there was a 50 % loss in maximal JO 2 (p&lt;0.005) with no changes in KM ADP . We hypothesize that the TAX-driven stabilization of MTs leads to detrimental MT-mitochondria interactions that disrupt ATP/ADP transfer between cellular compartments, exacerbating DOX toxicity and ultimately impairing muscle function. The present findings provide novel insights into the mechanisms of TAX-induced myotoxicities, which is of paramount importance for developing therapeutic strategies to improve cardiovascular health and quality of life of long-term breast cancer survivors.

Impaired fat oxidation during exercise in multiple acyl-CoA dehydrogenase deficiency.

We investigated the in vivo skeletal muscle metabolism in patients with multiple acyl‐CoA dehydrogenase deficiency (MADD) during exercise, and the effect of a glucose infusion. Two adults with MADD on riboflavin and l‐carnitine treatment and 10 healthy controls performed an incremental exercise test measuring maximal oxidative capacity (VO2max) and a submaximal exercise test (≤1 hour) on a cycle ergometer. During submaximal exercise, we studied fat and carbohydrate oxidation, using stable isotope tracer methodology and indirect calorimetry. On another day, the patients repeated the submaximal exercise receiving a 10% glucose infusion. The patients had a lower VO2max than controls and stopped the submaximal exercise test at 51 and 58 minutes due to muscle pain and exhaustion. The exercise‐induced increase in total fatty acid oxidation was blunted in the patients (7.1 and 1.1 vs 12 ± 4 μmol × kg−1 × min−1 in the healthy controls), but total carbohydrate oxidation was higher (67 and 63 vs 25 ± 11 μmol × kg−1 × min−1 in controls). With glucose infusion, muscle pain decreased and average heart rate during exercise dropped in both patients from 124 to 119 bpm and 138 to 119 bpm. We demonstrate that exercise intolerance in MADD‐patients relates to an inability to increase fat oxidation appropriately during exercise, which is compensated partially by an increase in carbohydrate metabolism.

Treatment of landfill gas with low methane content by biocover systems

Landfills are significant sources of anthropogenic atmospheric methane (CH4), which contributes to climate change. Large amounts of CH4 are emitted from landfills in dilute form due to mixing with air in leachate collection systems, or during lateral migration away from landfills. The objective of this study was to investigate the CH4 oxidation efficiency of a compost material subject to LFG diluted with atmospheric air resulting in CH4 concentrations of 5–10% v/v. CH4 oxidation rates and carbon dioxide (CO2) production were measured through batch and dynamic column experiments where two laboratory scale biofilters were constructed. The columns were run at increasing flow rates. Column gas concentration profiles for each of five flow campaigns were compared to each other. This showed that oxygen (O2) was present through the entire column and elevated CO2 concentrations throughout the biofilters were found. Moreover, the oxidation process tended to be centred in the lower parts of both columns. It was observed that the biofilters performed better once they had adapted to the increasing loads of CH4. In both columns, the maximum removal rate of CH4 was found to be 98–100%. Using CH4 mass balances the maximum oxidation rate was 238 g CH4 m−2 d−1 in Column 1 and 483 g CH4 m−2 d−1 in Column 2 (equal to the load). None of the biofilters reached their maximum CH4 oxidation capacity, hence they could have been exposed to a larger CH4 load. It was found that the retention time in the columns was not a factor limiting the oxidation process. High O2 consumption and carbon mass balances underlined the strong microbial activity in the biofilters and it was not suspected that the methane oxidising bacteria were O2 limited. The results of this study suggest that biofilters have great potential for reducing CH4 in diluted LFG.

Lipocalin 2 regulates retinoic acid-induced activation of beige adipocytes

Lipocalin-2 (LCN2) has been previously characterized as an adipokine regulating thermogenic activation of brown adipose tissue and retinoic acid (RA)-induced thermogenesis in mice. The objective of this study was to explore the role and mechanism for LCN2 in the recruitment and retinoic acid-induced activation of brown-like or ‘beige’ adipocytes. We found LCN2 deficiency reduces key markers of thermogenesis including uncoupling protein-1 (UCP1) and peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α) in inguinal white adipose tissue (iWAT) and inguinal adipocytes derived from Lcn2 −/− mice. Lcn2 −/− inguinal adipocytes have attenuated insulin-induced upregulation of thermogenic gene expression and p38 mitogen-activated protein kinase (p38MAPK) signaling pathway activation. This is accompanied by a lower basal and maximal oxidative capacity in Lcn2 −/− inguinal adipocytes, indicating mitochondrial dysfunction. Recombinant Lcn2 was able to restore insulin-induced p38MAPK phosphorylation in both WT and Lcn2 −/− inguinal adipocytes. Rosiglitazone treatment during differentiation of Lcn2 −/− adipocytes is able to recruit beige adipocytes at a normal level, however, further activation of beige adipocytes by insulin and RA is impaired in the absence of LCN2. Further, the synergistic effect of insulin and RA on UCP1 and PGC-1α expression is markedly reduced in Lcn2 −/− inguinal adipocytes. Most intriguingly, LCN2 and the retinoic acid receptor-alpha (RAR-α) are concurrently translocated to the plasma membrane of adipocytes in response to insulin, and this insulin-induced RAR-α translocation is absent in adipocytes deficient in LCN2. Our data suggest a novel LCN2-mediated pathway by which RA and insulin synergistically regulates activation of beige adipocytes via a non-genomic pathway of RA action.

Breaking-up sedentary time can regulate maximal fat oxidation capacity during exercise

Breaking-up sedentary time can regulate maximal fat oxidation capacity during exercise

Role of Angptl4/Fiaf in exercise-induced skeletal muscle AMPK activation.

Angiopoietin-like protein 4 (Angptl4)/fasting-induced adipose factor (Fiaf) expression levels are increased by exercise in skeletal muscle. We have previously shown that Angptl4 regulates food intake and energy expenditure via modulation of hypothalamic AMP-activated protein kinase (AMPK) activity. AMPK is an important signaling molecule that integrates skeletal muscle metabolism during exercise. Therefore, we investigated the involvement of Angptl4 in exercise-induced AMPK activation in skeletal muscle. Angptl4 protein and mRNA expression levels were significantly increased in the gastrocnemius and soleus muscles of mice following a 50-min running bout. Treatment of C2C12 myotubes with Angptl4 increased phosphorylation of AMPK and acetyl-CoA carboxylase (ACC), which were markers of AMPK activation, and the mitochondrial maximum respiratory capacity. Treadmill exercise increased AMPK and ACC phosphorylation in the gastrocnemius of normal mice; this phosphorylation increase was attenuated in mice lacking Angptl4. Endurance to swimming and hanging was also reduced in Angptl4 knockout mice. Taken together, our current data demonstrate that exercise-induced upregulation of skeletal muscle Angptl4 is critical for AMPK activation and exercise tolerance. These findings unveil a new role for skeletal muscle Angptl4 in exercise physiology. NEW & NOTEWORTHY 1) Angiopoietin-like protein 4 (Angptl4) treatment activates AMP-activated protein kinase (AMPK) signaling in skeletal muscle cells. 2) Angptl4 increases the maximum mitochondrial oxidative capacity through AMPK activation in skeletal muscle cells. 3) Lack of Angptl4 mitigates exercise-induced skeletal muscle AMPK activation. 4) Angptl4-deficient mice show a lower endurance to exercise.

Unraveling the Athlete’s Paradox—Higher Insulin Sensitivity and Lower PKC? Activation Despite Higher Bioactive Lipids in Endurance-Trained Athletes

High intramyocellular lipid (IMCL) content associates negatively with insulin sensitivity (IS) in insulin resistant, but not in endurance-trained humans. It has been hypothesized that different cellular distribution of bioactive lipids such as diacylglycerols (DAG) and ceramides (CER) could interfere with insulin action and underlie this “athlete’s paradox.” We examined endurance-trained athletes (ATH; n=9) and sedentary individuals (SED; n=12) with comparable total IMCL, as measured by 1H-magnetic resonance spectroscopy, who underwent spiroergometry and hyperinsulinemic-euglycemic clamps to assess maximal oxidative capacity and IS, respectively. In skeletal muscle biopsies, translocation of protein kinase C (PKC) θ and ε were determined by Western blotting and concentrations of DAG and CER were measured using targeted LC-tandem mass spectrometry upon separating fractions of cellular membranes, lipid droplets and cytosol by ultracentrifugation. Maximal oxidative capacity and IS were 46% and 47% higher in ATH than in SED (both p&amp;lt;0.01), respectively. The membrane:cytosol ratio of PKCθ, which reflects PKCθ activity, was 62% lower in ATH consistent with their increased IS (p&amp;lt;0.01), while there was no group difference for PKCε. Total and membrane DAG (40% and 48%, both p&amp;lt;0.01) as well as membrane CER (15%, p&amp;lt;0.05) were higher in ATH while the respective concentrations in lipid droplets and cytosol did not differ. In SED, IS correlated inversely with all stereoselective subspecies of lipid-droplet DAG. On the other hand, cytosolic sn-1,2 (C16:0-C18:2) and sn-1,3 (C18:1-C18:0) DAG correlated positively with IS in ATH. In conclusion, higher IS in endurance-trained ATH can be explained by lower muscle PKCθ activation, which may be due to differences in the stereoselectivity and/or subcompartmentation of cellular DAG between ATH and insulin resistant SED. Disclosure D. Pesta: None. E. Anadol-Schmitz: None. S. Gancheva: None. D.F. Markgraf: None. O.P. Zaharia: None. H. Katsuyama: None. Y. Kupriyanova: None. J. Hwang: None. D. Zhang: None. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research &amp; Development, Merck &amp; Co., Inc., Novo Nordisk Inc.. Research Support; Self; Gilead Sciences, Inc. M. Roden: Speaker's Bureau; Self; Boehringer Ingelheim GmbH. Research Support; Self; Boehringer Ingelheim GmbH. Consultant; Self; Poxel SA. Research Support; Self; Danone Nutricia Early Life Nutrition, GlaxoSmithKline plc., Nutricia Advanced Medical Nutrition, Sanofi.

Differences in Muscle Metabolism Between Triathletes and Normally Active Volunteers Investigated Using Multinuclear Magnetic Resonance Spectroscopy at 7T.

Purpose: The influence of endurance training on skeletal muscle metabolism can currently be studied only by invasive sampling or through a few related parameters that are investigated by either proton (1H) or phosphorus (31P) magnetic resonance spectroscopy (MRS). The aim of this study was to compare the metabolic differences between endurance-trained triathletes and healthy volunteers using multi-parametric data acquired by both, 31P- and 1H-MRS, at ultra-high field (7T) in a single experimental protocol. This study also aimed to determine the interrelations between these MRS-derived metabolic parameters.Methods: Thirteen male triathletes and ten active male volunteers participated in the study. Proton MRS data from the vastus lateralis yielded concentrations of acetylcarnitine, carnosine, and intramyocellular lipids (IMCL). For the measurement of phosphodiesters (PDEs), inorganic phosphate (Pi), phosphocreatine (PCr), and maximal oxidative capacity (Qmax) phosphorus MRS data were acquired at rest, during 6 min of submaximal exercise and following immediate recovery.Results: The triathletes exhibited significantly higher IMCL levels, higher initial rate of PCr resynthesis (VPCr) during the recovery period, a shorter PCr recovery time constant (τPCr), and higher Qmax. Multivariate stepwise regression analysis identified PDE as the strongest independent predictor of whole-body maximal oxygen uptake (VO2max).Conclusion: In conclusion, we cannot suggest a single MRS-based parameter as an exclusive biomarker of muscular fitness and training status. There is, rather, a combination of different parameters, assessable during a single multi-nuclear MRS session that could be useful for further cross-sectional and/or focused interventional studies on skeletal muscle fitness and training effects.

Aerobic-Strength Exercise Improves Metabolism and Clinical State in Parkinson's Disease Patients.

www.ClinicalTrials.gov, identifier NCT02253732.

Greater Oxidative Capacity in Primary Myotubes from Endurance-trained Women.

Exercise training promotes skeletal muscle mitochondrial biogenesis and an increase in maximal oxygen consumption. Primary myotubes retain some metabolic properties observed in vivo but it is unknown whether this includes exercise-induced mitochondrial adaptations. The goal of this study was to test if primary myotubes from exercise-trained women have higher mitochondrial content and maximal oxygen consumption compared with untrained women. Six trained and nine untrained white women participated in this study. Muscle biopsies from the vastus lateralis muscle of the right leg were obtained and primary muscle cells were isolated. Maximal respiration rates, mitochondrial mRNA and protein content, and succinate dehydrogenase activity were measured in skeletal muscle and primary myotubes from trained and untrained women. Trained women, compared with untrained women, had higher maximal whole-body oxygen consumption (+18%, P = 0.03), in vivo maximal skeletal muscle oxidative capacity measured with near infrared spectroscopy (+48%, P < 0.01), and maximal oxygen consumption in permeabilized muscle fibers (+38%, P = 0.02), which coincided with higher protein levels of muscle mitochondrial enzymes. Primary myotubes from trained women had higher maximal oxygen consumption (+38%, P = 0.03), suggesting that some elements of exercise-induced metabolic programming persists ex vivo. Consistent with this idea, myotubes from trained women had higher mRNA levels of transcriptional regulators of mitochondrial biogenesis in addition to higher protein levels of mitochondrial enzymes. These data suggest the existence of an "exercise metabolic program," where primary myotubes isolated from exercise-trained individuals exhibit greater mitochondrial content and oxidative capacity compared with untrained individuals. These myotubes may be a useful model to study molecular mechanisms relevant to exercise adaptations in human skeletal muscle.

Cardiorespiratory Fitness and Cardiac Autonomic Function in Diabetes.

This review summarizes the current knowledge on the relationship of physical activity, exercise, and cardiorespiratory fitness (CRF) with cardiovascular autonomic neuropathy (CAN) based on epidemiological, clinical, and interventional studies. The prevalence of CAN increases with age and duration of diabetes. Further risk factors for CAN comprise poor glycemic control, dyslipidemia, abdominal obesity, hypertension, and the presence of diabetic complications. CAN has been also linked to reduced CRF. We recently showed that CRF parameters (e.g., maximal oxidative capacity or oxidative capacity at the anaerobic threshold) are associated with cardiac autonomic function in patients recently diagnosed with type 1 or type 2 diabetes. Exercise interventions have shown that physical activity can increase cardiovagal activity and reduce sympathetic overactivity. In particular, long-term and regularly, but also supervised, performed endurance and high-intense and high-volume exercise improves cardiac autonomic function in patients with type 2 diabetes. By contrast, the evidence in those with type 1 diabetes and also in individuals with prediabetes or metabolic syndrome is weaker. Overall, the studies reviewed herein addressing the question whether favorably modulating the autonomic nervous system may improve CRF during exercise programs support the therapeutic concept to promote physical activity and to achieve physical fitness. However, high-quality exercise interventions, especially in type 1 diabetes and metabolic syndrome including prediabetes, are further required to better understand the relationship between physical activity, fitness, and cardiac autonomic function.

Androgen receptor gene polymorphisms and maximal fat oxidation in healthy men. A longitudinal study.

Androgens play a major role in fat oxidation; however, the effects of androgens depend, among other factors, on the intrinsic characteristics of the androgen receptor (AR). Lower repetitions of CAG and GGN polymorphism appear to have a protective effect on fat accumulation in the transition from adolescent to mid-twenties. Whether a similar protective effect is present later in life remains unknown. The aims of this study were: a) to evaluate if extreme CAG and GGN repeat polymorphisms of the androgen receptors influence body fat mass, its regional distribution, resting metabolic rate (RMR), maximal fat oxidation capacity (MFO) and serum leptin, free testosterone and osteocalcin in healthy adult men; and b) to determine the longitudinal effects on fat tissue accumulation after 6.4 years of follow-up. CAG and GGN repeats length were measured in 319 healthy men (mean ± standard deviation [SD]: 28.3 ± 7.6 years). From these, we selected the subjects with extreme short (CAGS < or equal 19; n = 7) and long (CAGL > or equal 24; n = 10) CAG repeats, and the subjects with short (GGNS < or equal to 22; n = 9) and long (GGNL > or equal to 25; n = 10) GGN repeats. Body composition was assessed by DXA and serum levels of leptin, free testosterone and osteocalcin by ELISA. After 6.4 years of follow-up, DXA was repeated, and resting metabolic rate (RMR), MFO and VO2max determined by indirect calorimetry. CAGS and CAGL subjects had similar RMR and accumulated comparable amounts of fat tissue over 6.4 ± 1.0 years of follow-up. However, CAGL had higher MFO and total lean mass than CAGS(p < 0.05). Men with GGNSaccumulated greater amount of total fat mass than men with GGNL, particularly in the trunk region seven years later. This concurred with a greater MFO in the GGNLgroup (p < 0.05), who accumulated less fat mass. Free testosterone was associated with MFO in absolute values (r = 0.45; p < 0.05) and MFO per kg of lower extremity lean mass per height squared (r = 0.35; p < 0.05). CAG and GGN repeat polymorphisms may influence muscle fat oxidation capacity and may have a role in the accumulation of fat over the years.

Modifications in Retinal Mitochondrial Respiration Precede Type 2 Diabetes and Protracted Microvascular Retinopathy.

To characterize retinal mitochondrial respiration associated with type 2 diabetes (T2D) progression in a cone-rich diurnal rodent, the Nile rat (genus Arvicanthis, species niloticus). Nile rats were fed a standard rodent diet that resulted in rising glucose levels from 6 months. Age-matched control animals were fed a high-fiber diet that prevented diabetes up to 18 months. The functional status of specific retinal mitochondrial components and mitochondrial outer membrane integrity were studied by using high-resolution respirometry. Ocular complications were documented with funduscopy, electroretinography (ERG), and trypsin digestion of retinal vasculature. Mitochondrial functional changes were detected during hyperinsulinemia with maintained normoglycemia (2 months), corresponding to stage 1 of human T2D. Our data showed increased contribution of mitochondrial respiration through the NADH pathway relative to maximal oxidative phosphorylation capacity, with simultaneous electron entry into NADH (Complex I and related dehydrogenases) and succinate (Complex II) pathways. These compensatory events coincided with compromised mitochondrial outer membrane integrity. The first clinical sign of retinopathy (pericyte loss) was only detected at 12 months (after 6 months of sustained hyperglycemia) alongside a common ocular complication of diabetes, cataractogenesis. Further prolongation of hyperglycemia (from 12 to 18 months) led to capillary degeneration and delayed photopic ERG oscillatory potentials. Oxidative phosphorylation compensatory changes in the retina can be detected as early as 2 months, before development of hyperglycemia, and are associated with reduced mitochondrial outer membrane integrity.

Fatigability, Exercise Intolerance, and Abnormal Skeletal Muscle Energetics in Heart Failure.

Among central and peripheral factors contributing to exercise intolerance (EI) in heart failure (HF), the extent to which skeletal muscle (SM) energy metabolic abnormalities occur and contribute to EI and increased fatigability in HF patients with reduced or preserved ejection fraction (HFrEF and HFpEF, respectively) are not known. An energetic plantar flexion exercise fatigability test and magnetic resonance spectroscopy were used to probe the mechanistic in vivo relationships among SM high-energy phosphate concentrations, mitochondrial function, and EI in HFrEF and HFpEF patients and in healthy controls. Resting SM high-energy phosphate concentrations and ATP flux rates were normal in HFrEF and HFpEF patients. Fatigue occurred at similar SM energetic levels in all subjects, consistent with a common SM energetic limit. Importantly, HFrEF New York Heart Association class II-III patients with EI and high fatigability exhibited significantly faster rates of exercise-induced high-energy phosphate decline than did HFrEF patients with low fatigability (New York Heart Association class I), despite similar left ventricular ejection fractions. HFpEF patients exhibited severe EI, the most rapid rates of high-energy phosphate depletion during exercise, and impaired maximal oxidative capacity. Symptomatic fatigue during plantar flexion exercise occurs at a common energetic limit in all subjects. HFrEF and HFpEF patients with EI and increased fatigability manifest early, rapid exercise-induced declines in SM high-energy phosphates and reduced oxidative capacity compared with healthy and low-fatigability HF patients, suggesting that SM metabolism is a potentially important target for future HF treatment strategies.

Uncoupling effect of palmitate is exacerbated in skeletal muscle mitochondria of sea-acclimatized king penguins (Aptenodytes patagonicus)

In king penguin juveniles, the environmental transition from a terrestrial to a marine habitat, occurring at fledging, drastically stimulates lipid catabolism and the remodelling of muscle mitochondria to sustain extensive swimming activity and thermoregulation in the cold circumpolar oceans. However, the exact nature of these mechanisms remains only partially resolved. Here we investigated, in vitro, the uncoupling effect of increasing doses of fatty acids in pectoralis muscle intermyofibrillar mitochondria isolated, either from terrestrial never-immersed or experimentally cold water immersed pre-fledging king penguins or from sea-acclimatized fledged penguins. Mitochondria exhibited much greater palmitate-induced uncoupling respiration and higher maximal oxidative capacity after acclimatization to marine life. Such effects were not reproduced experimentally after repeated immersions in cold water, suggesting that the plasticity of mitochondrial characteristics may not be primarily driven by cold exposure per se but by other aspects of sea acclimatization.

Temperature-related differences in mitochondrial function among clones of the cladoceran Daphnia pulex

This study assessed the thermal sensitivity of mitochondrial respiration in the small crustacean Daphnia pulex. More specifically, we wanted to determine if clones that inhabit different latitudes and habitats showed differences in the thermal sensitivity of their mitochondrial function. The experimental design included two clones from temperate environments (Fence from Ontario and Hawrelak from Alberta) and two clones from subarctic environments (A24 from Manitoba and K154 from Quebec). The integrated mitochondrial function was measured with high-resolution respirometry following whole-animal permeabilization. Mitochondrial respiration was performed under six different temperatures (10, 15, 20, 25, 30, and 35°C) in the clone Hawrelak and at two temperatures (10 and 20°C) in the three other clones. In the clone Hawrelak, complexes I and II respiration showed higher sensitivity to temperature variation compared to complex IV respiration. Interestingly, the threshold plot showed no excess capacity of complex IV at 20°C in this clone. The clones showed significant divergence in the ability to oxidize the complex I and complex IV substrates relative to the maximal oxidative phoshorylation capacity of mitochondria. More importantly, some of the clonal divergences were only detected under low assay temperatures, pointing toward the importance of this parameter in comparative studies. Future and more complex studies on clones from wider environmental gradients will help to resolve the link between mitochondrial function and adaptations of organisms to particular conditions, principally temperature.

Effects of Cycling Exercise on Mitochondrial Function and Efficacy of Peripheral Blood Mononuclear Cells Under Hypoxic Condition in Sedentary Men

Dysfunction of peripheral blood mononuclear cells (PBMCs) has been found in hypoxemic patients suffering from cardiopulmonary disorders or those exposed to hypoxic environments such as high altitudes. The mitochondrial bioenergetics of PBMCs serves a critical role in PBMC‐related immune function. The purpose of this study is to elucidate whether cycling exercise affect mitochondrial function and efficacy in PBMCs under hypoxic stress. Twelve sedentary males engaged in moderate exercise (60% VO2max) for 40 min while exposed to 12%O2 (HE) in a normobaric hypoxia chamber. Before and immediately after HE, Substrate‐Uncoupler‐Inhibitor Titrations (SUIT) protocols and TMRE, a mitochondrial membrane potential fluorescent dye, were applied on PBMCs and analyzed by a high resolution respirometer (OROBOROS Oxygraph‐2k). This study can be summarized as follows: (1) although no differences in routine or maximal mitochondrial O2 consumption rate, the HE heightened mitochondrial membrane potential in intact PBMCs and (2) the HE depressed pyruvate‐/glutamate‐dependent complex I (NADH‐related) O2 consumption rate in mitochondria of permeabilized PBMCs. Hence, we conclude that the HE is insufficient to influence maximal oxidative phosphorylation and electron transport capacity of mitochondria despite of depressing the NADH‐related mitochondrial efficacy in PBMCs.

Analyzing Short Term Protein Oxidation Provides Evidence about Its Role in Whole Body Protein Metabolism

INTRODUCTIONProtein intake has been suggested to play an important role in development of obesity; on one hand in newborn, where excess protein intake might stimulate development of obesity in later life (Kirchberg et al. 2014). On the other hand, protein consumption is promoted for weight management (Martens et al. 2014). At present, no formal recommendations for the upper limit of protein intake have been presented. Information about rate‐limiting steps in protein catabolism is scarce. We therefore studied the role of protein oxidation in this process.OBJECTIVESTo monitor protein oxidation we have developed a non‐invasive natural enriched 13C‐protein breath test using naturally enriched 13C‐milk protein (fractions). We used this technique to analyze the kinetics of protein oxidation and its interfering factors.METHOD/DESIGNThe breath test was preceded by an overnight fast. After consuming the substrate, dissolved in 500 ml water, breath samples were collected up to 330 minutes and analyzed by Isotope Ratio Mass Spectrometry for the 13CO2:12CO2 ratio.RESULTSWhey was oxidized for 28.6% ± 6.8% (mean ± SD) after 240 minutes, compared to 22.9% ± 6.2% for glucose in the same period. Postprandial oxidation kinetics of glucose and whey started to diverge after 70 min after which whey was being oxidized faster than glucose.Different doses of milk protein (10, 30, 50, 60, 70 g) were oxidized for 15.3, 24.2, 22.3, 21.5 and 14.5% respectively. Maximal milk protein oxidation was measured during the 60 g dose at a rate of 0.062 g/min, leading to a maximal oxidation capacity of 1.3 g/kg bodyweight/day.Combining protein (30 g 13C‐whey) with carbohydrates (30 g non‐labeled glucose) resulted in two‐fold increase in oxidation of 13C‐whey compared to oxidation of 13C‐whey alone. A three‐fold increase in oxidation of 13C‐glucose was measured when non‐labeled whey was added compared to oxidation of 13C‐glucose alone.CONCLUSIONSWhey is oxidized faster than glucose from 70 min onwards, which seem to suggest that stomach emptying was not the cause of the difference in oxidation. The interaction of whey and glucose suggest that the oxidation of whey is not driven by energy demand. The stimulating effect of glucose might hint to the involvement of insulin. Oxidation of whey protein is quantitatively of high importance and not down regulated by concomitant administration of other substrates. Analyzing biological variations in acute protein oxidation in defining the upper limit of intake, seem to be relevant.Support or Funding InformationThe 13C‐milk substrates were provided by Hanze Nutrition BV.

Acute exhaustive aerobic exercise training impair cardiomyocyte function and calcium handling in Sprague-Dawley rats.

IntroductionRecent data from long-distance endurance participants suggest that cardiac function is impaired after completion. Existing data further indicate that right ventricular function is more affected than left ventricular function. The cellular mechanisms underpinning cardiac deterioration are limited and therefore the aim of this study was to examine cardiomyocyte and molecular responses of the right and left ventricle to an acute bout of exhaustive endurance exercise.Materials and methodsMale Sprague-Dawley rats were assigned to sedentary controls or acute exhaustive endurance exercise consisting of a 120 minutes long forced treadmill run. The contractile function and Ca2+ handling properties in isolated cardiomyocytes, protein expression levels of sarcoplasmic reticulum Ca2+-ATPase and phospholamban including two of its phosphorylated states (serine 16 and threonine 17), and the mitochondrial respiration in permeabilized cardiac muscle fibers were analyzed.ResultsThe exercise group showed a significant reduction in cardiomyocyte fractional shortening (right ventricle 1 Hz and 3 Hz p<0.001; left ventricle 1 Hz p<0.05), intracellular Ca2+ amplitude (right ventricle 1 and 3 Hz p<0.001; left ventricle 1 Hz p<0.01 and 3 Hz p<0.05) and rate of diastolic Ca2+ decay (right ventricle 1 Hz p<0.001 and 3 Hz p<0.01; left ventricle 1 and 3 Hz p<0.01). Cardiomyocyte relaxation during diastole was only significantly prolonged at 3 Hz in the right ventricle (p<0.05) compared to sedentary controls. We found an increase in phosphorylation of phospholamban at serine 16 and threonine 17 in the left (p<0.05), but not the right, ventricle from exhaustively exercised animals. The protein expression levels of sarcoplasmic reticulum Ca2+-ATPase and phospholamban was not changed. Furthermore, we found a reduction in maximal oxidative phosphorylation and electron transport system capacities of mitochondrial respiration in the right (p<0.01 and p<0.05, respectively), but not the left ventricle from rats subjected to acute exhaustive treadmill exercise.ConclusionAcute exhaustive treadmill exercise is associated with impairment of cardiomyocyte Ca2+ handling and mitochondrial respiration that causes depression in both contraction and diastolic relaxation of cardiomyocytes.