Mitochondrial Oxidative Capacity Research Articles

Reduced methionine synthase expression results in uracil accumulation in mitochondrial DNA and impaired oxidative capacity.

Adequate thymidylate [deoxythymidine monophosphate (dTMP) or the "T" base in DNA] levels are essential for stability of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). Folate and vitamin B12 (B12) are essential cofactors in folate-mediated one-carbon metabolism (FOCM), a metabolic network which supports synthesis of nucleotides (including dTMP) and methionine. Perturbations in FOCM impair dTMP synthesis, causing misincorporation of uracil (or a "U" base) into DNA. During B12 deficiency, cellular folate accumulates as 5-methyltetrahdryfolate (5-methyl-THF), limiting nucleotide synthesis. The purpose of this study was to determine how reduced levels of the B12-dpendent enzyme methionine synthase (MTR) and dietary folate interact to affect mtDNA integrity and mitochondrial function in mouse liver. Folate accumulation, uracil levels, mtDNA content, and oxidative phosphorylation capacity were measured in male Mtr+/+ and Mtr+/- mice weaned onto either a folate-sufficient control (C) diet (2 mg/kg folic acid) or a folate-deficient (FD) diet (lacking folic acid) for 7 weeks. Mtr heterozygosity led to increased liver 5-methyl-THF levels. Mtr+/- mice consuming the C diet also exhibited a 40-fold increase in uracil in liver mtDNA. Mtr+/- mice consuming the FD diet exhibited less uracil accumulation in liver mtDNA as compared to Mtr+/+ mice consuming the FD diet. Furthermore, Mtr+/- mice exhibited 25% lower liver mtDNA content and a 20% lower maximal oxygen consumption rates. Impairments in mitochondrial FOCM are known to lead to increased uracil in mtDNA. This study demonstrates that impaired cytosolic dTMP synthesis, induced by decreased Mtr expression, also leads to increased uracil in mtDNA.

Microbiota Mediate Enhanced Exercise Capacity Induced by Exercise Training.

We investigated the effects of gut microbes, and the mechanisms mediating the enhanced exercise performance induced by exercise training, i.e., skeletal muscle blood flow, and mitochondrial biogenesis and oxidative function in male mice. All mice received a graded exercise test before (PRE) and after exercise training via forced treadmill running at 60% to 70% of maximal running capacity 5 d·wk -1 for 5 wk (POST). To examine the role of the gut microbes, the graded exercise was repeated after 7 d of access to antibiotic (ABX)-treated water, used to eliminate gut microbes. Peripheral blood flow, mitochondrial oxidative capacity, and markers of mitochondrial biogenesis were collected at each time point. Exercise training led to increases of 60% ± 13% in maximal running distance and 63% ± 11% work to exhaustion ( P < 0.001). These increases were abolished after ABX ( P < 0.001). Exercise training increased hindlimb blood flow and markers of mitochondrial biogenesis and oxidative function, including AMP-activated protein kinase, sirtuin-1, PGC-1α citrate synthase, complex IV, and nitric oxide, all of which were also abolished by ABX treatment. Our results support the concept that gut microbiota mediate enhanced exercise capacity after exercise training and the mechanisms responsible, i.e., hindlimb blood flow, mitochondrial biogenesis, and metabolic profile. Finally, results of this study emphasize the need to fully examine the impact of prescribing ABX to athletes during their training regimens and how this may affect their performance.

Pulmonary rehabilitation restores limb muscle mitochondria and improves the intramuscular metabolic profile.

Exercise, as the cornerstone of pulmonary rehabilitation, is recommended to chronic obstructive pulmonary disease (COPD) patients. The underlying molecular basis and metabolic process were not fully elucidated. Sprague-Dawley rats were classified into five groups: non-COPD/rest (n = 8), non-COPD/exercise (n = 7), COPD/rest (n = 7), COPD/medium exercise (n = 10), and COPD/intensive exercise (n = 10). COPD animals were exposed to cigarette smoke and lipopolysaccharide instillation for 90 days, while the non-COPD control animals were exposed to room air. Non-COPD/exercise and COPD/medium exercise animals were trained on a treadmill at a decline of 5° and a speed of 15 m/min while animals in the COPD/intensive exercise group were trained at a decline of 5° and a speed of 18 m/min. After eight weeks of exercise/rest, we used ultrasonography, immunohistochemistry, transmission electron microscopy, oxidative capacity of mitochondria, airflow-assisted desorption electrospray ionization-mass spectrometry imaging (AFADESI-MSI), and transcriptomics analyses to assess rectal femoris (RF). At the end of 90 days, COPD rats' weight gain was smaller than control by 59.48 ± 15.33 g (P = 0.0005). The oxidative muscle fibers proportion was lower (P < 0.0001). At the end of additional eight weeks of exercise/rest, compared to COPD/rest, COPD/medium exercise group showed advantages in weight gain, femoral artery peak flow velocity (Δ58.22 mm/s, 95% CI: 13.85-102.60 mm/s, P = 0.0104), RF diameters (Δ0.16 mm, 95% CI: 0.04-0.28 mm, P = 0.0093), myofibrils diameter (Δ0.06 μm, 95% CI: 0.02-0.10 μm, P = 0.006), oxidative muscle fiber percentage (Δ4.84%, 95% CI: 0.15-9.53%, P = 0.0434), mitochondria oxidative phosphorylate capacity (P < 0.0001). Biomolecules spatial distribution in situ and bioinformatic analyses of transcriptomics suggested COPD-related alteration in metabolites and gene expression, which can be impacted by exercise. COPD rat model had multi-level structure and function impairment, which can be mitigated by exercise.

Crosstalk between Adipose Tissue and Hepatic Mitochondria in the Development of the Inflammation and Liver Injury during Ageing in High-Fat Diet Fed Rats.

Obesity is considered an epidemic disorder, due to an imbalance between energy consumption and metabolizable energy intake. This balance is increasingly disrupted during normal aging processes due to the progressive impairment of mechanisms that normally control energy homeostasis. Obesity is triggered by an excessive lipid depots but reflects systemic inflammation along with large adipocytes secreting proinflammatory adipokines, an increase of the free fatty acids levels in the bloodstream, and ectopic lipid accumulation. Hepatic fat accumulation is the most common cause of chronic liver disease, characterized by mitochondrial dysfunction with a consequent impaired fat metabolism and increased oxidative stress. Therefore, mitochondrial dysfunction is associated to hepatic lipid accumulation and related complications. In this study, we assessed the crosstalk between adipose tissue and liver, analyzing the time-course of changes in hepatic mitochondrial fatty acid oxidation capacity versus fatty acid storage, focusing on the contribution of adipose tissue inflammation to hepatic lipid accumulation, using a rodent model of high fat diet-induced obesity. Our results demonstrate that both high-fat diet-induced obesity and aging induce dysregulation of adipose tissue function and similar metabolic alterations mediated by mitochondrial function impairment and altered inflammatory profile. The high fat diet-induced obesity anticipates and exacerbates liver mitochondrial dysfunction that occurs with aging processes.

Adult skeletal muscle peroxisome proliferator-activated receptor γ -related coactivator 1 is involved in maintaining mitochondrial content.

The peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1) family of transcriptional coactivators are regulators of mitochondrial oxidative capacity and content in skeletal muscle. Many of these conclusions are based primarily on gain-of-function studies using muscle-specific overexpression of PGC1s. We have previously reported that genetic deletion of both PGC-1α and PGC-1β in adult skeletal muscle resulted in a significant reduction in oxidative capacity with no effect on mitochondrial content. However, the contribution of PGC-1-related coactivator (PRC), the third PGC-1 family member, in regulating skeletal muscle mitochondria is unknown. Therefore, we generated an inducible skeletal muscle-specific PRC knockout mouse (iMS-PRC-KO) to assess the contribution of PRC in skeletal muscle mitochondrial function. We measured mRNA expression of electron transport chain (ETC) subunits as well as markers of mitochondrial content in the iMS-PRC-KO animals and observed an increase in ETC gene expression and mitochondrial content. Furthermore, the increase in ETC gene expression and mitochondrial content was associated with increased expression of PGC-1α and PGC-1β. We therefore generated an adult-inducible PGC-1 knockout mouse in which all PGC-1 family members are deleted (iMS-PGC-1TKO). The iMS-PGC-1TKO animals exhibited a reduction in ETC mRNA expression and mitochondrial content. These data suggest that in the absence of PRC alone, compensation occurs by increasing PGC-1α and PGC-1β to maintain mitochondrial content. Moreover, the removal of all three PGC-1s in skeletal muscle results in a reduction in both ETC mRNA expression and mitochondrial content. Taken together, these results suggest that PRC plays a role in maintaining baseline mitochondrial content in skeletal muscle.

Fine particulate matter induces adipose tissue expansion and weight gain: Pathophysiology.

Dysregulations in energy balance represent a major driver of obesity. Recent evidence suggests that environmental factors also play a pivotal role in inducing weight gain. Chronic exposure to fine particulate matter (PM2.5 ) is associated with white adipose tissue (WAT) expansion in animals and higher rates of obesity in humans. This review discusses metabolic adaptions in central and peripheral tissues that promote energy storage and WAT accumulation in PM2.5 -exposed animals and humans. Chronic PM2.5 exposure produces inflammation and leptin resistance in the hypothalamus, decreasing energy expenditure and increasing food intake. PM2.5 promotes the conversion of brown adipocytes toward the white phenotype, resulting in decreased energy expenditure. The development of inflammation in WAT can stimulate adipogenesis and hampers catecholamine-induced lipolysis. PM2.5 exposure affects the thyroid, reducing the release of thyroxine and tetraiodothyronine. In addition, PM2.5 exposure compromises skeletal muscle fitness by inhibiting Nitric oxide (NO)-dependent microvessel dilation and impairing mitochondrial oxidative capacity, with negative effects on energy expenditure. This evidence suggests that pathological alterations in the hypothalamus, brown adipose tissue, WAT, thyroid, and skeletal muscle can alter energy homeostasis, increasing lipid storage and weight gain in PM2.5 -exposed animals and humans. Further studies will enrich this pathophysiological model.

Inhaled formoterol impairs aerobic exercise capacity in endurance-trained individuals: a randomised controlled trial.

The 2022 Global Initiative for Asthma guidelines emphasise the inhaled long-acting β2-agonist formoterol as part of the first treatment step, and therefore formoterol use among athletes will probably increase. However, prolonged supratherapeutic use of inhaled β2-agonists impairs training outcomes in moderately trained men. We investigated whether inhaled formoterol, at therapeutic doses, imposes detrimental effects in endurance-trained individuals of both sexes. 51 endurance-trained participants (31 male, 20 female; mean±sd maximal oxygen consumption (V̇ O2 max) 62±6 mL·min-1·kg bw-1 and 52±5 mL·min-1·kg bw-1, respectively) inhaled formoterol (24 µg; n=26) or placebo (n=25) twice daily for 6 weeks. At baseline and follow-up, we assessed V̇ O2 max and incremental exercise performance during a bike-ergometer ramp-test; body composition by dual-energy X-ray absorptiometry; muscle oxidative capacity by high-resolution mitochondrial respirometry, enzymatic activity assays and immunoblotting; intravascular volumes by carbon monoxide rebreathing; and cardiac left ventricle mass and function by echocardiography. Compared to placebo, formoterol increased lean body mass by 0.7 kg (95% CI 0.2-1.2 kg; treatment×trial p=0.022), but decreased V̇ O2 max by 5% (treatment×trial p=0.013) and incremental exercise performance by 3% (treatment×trial p<0.001). In addition, formoterol lowered muscle citrate synthase activity by 15% (treatment×trial p=0.063), mitochondrial complex II and III content (treatment×trial p=0.028 and p=0.007, respectively), and maximal mitochondrial respiration through complexes I and I+II by 14% and 16% (treatment×trial p=0.044 and p=0.017, respectively). No apparent changes were observed in cardiac parameters and intravascular blood volumes. All effects were sex-independent. Our findings demonstrate that inhaled therapeutic doses of formoterol impair aerobic exercise capacity in endurance-trained individuals, which is in part related to impaired muscle mitochondrial oxidative capacity. Thus, if low-dose formoterol fails to control respiratory symptoms in asthmatic athletes, physicians may consider alternative treatment options.

Methane Admixture Protects Liver Mitochondria and Improves Graft Function after Static Cold Storage and Reperfusion

Mitochondria are targets of cold ischemia-reperfusion (IR), the major cause of cell damage during static cold preservation of liver allografts. The bioactivity of methane (CH4) has recently been recognized in various hypoxic and IR conditions as having influence on many aspects of mitochondrial biology. We therefore hypothesized that cold storage of liver grafts in CH4-enriched preservation solution can provide an increased defence against organ dysfunction in a preclinical rat model of liver transplantation. Livers were preserved for 24 h in cold histidine-tryptophan-ketoglutarate (HTK) or CH4-enriched HTK solution (HTK-CH4) (n = 24 each); then, viability parameters were monitored for 60 min during normothermic isolated reperfusion and perfusate and liver tissue were collected. The oxidative phosphorylation capacity and extramitochondrial Ca2+ movement were measured by high resolution respirometry. Oxygen and glucose consumption increased significantly while hepatocellular damage was decreased in the HTK-CH4 grafts compared to the HTK group. Mitochondrial oxidative phosphorylation capacity was more preserved (128.8 ± 31.5 pmol/s/mL vs 201.3 ± 54.8 pmol/s/mL) and a significantly higher Ca2+ flux was detected in HTK-CH4 storage (2.9 ± 0.1 mV/s) compared to HTK (2.3 ± 0.09 mV/s). These results demonstrate the direct effect of CH4 on hepatic mitochondrial function and extramitochondrial Ca2+ fluxes, which may have contributed to improved graft functions and a preserved histomorphology after cold IR.

Metabolic response during high-intensity interval exercise and resting vascular and mitochondrial function in CrossFit participants

High-intensity functional training (HIFT) can play a major role in preventing cardiometabolic disease. The majority of HIFT interventions incorporate CrossFit (CF) training. We measured aerobic capacity, metabolic response during high-intensity interval exercise (HIIE), resting mitochondrial oxidative capacity, and resting vascular function in adults who participated in CF training (&amp;gt; one year) vs. a sedentary group completing &amp;lt;2 h·wk-1 of structure exercise for &amp;gt; one year (SED). Twenty-one participants were recruited (CF n = 13 vs. SED n = 8). CF participants had a 33.0% greater relative VO2 peak (p&amp;lt;.001) and lower body fat percentage (CF = 18.6 [3.8] vs. SED = 30.3 [8.4]; p&amp;lt;.001). CF participants had higher exercising substrate oxidation when expressed as absolute and body weight relative values (p&amp;lt;.013), but not when expressed relative to lean mass (p&amp;gt;.200). CF participants had greater mitochondrial oxidative capacity (p=.014). There were no differences in large artery function, but CF participants had greater baseline arterial diameter (p=.004) and faster reperfusion following arterial occlusion (p&amp;lt;.05). These data support HIFT programs’ effectiveness in improving fitness, weight status, and metabolic, mitochondrial, and vascular function.

Effects of the sodium-glucose cotransporter 2 inhibitor dapagliflozin on substrate metabolism in prediabetic insulin resistant individuals: A randomized, double-blind crossover trial

Aims/hypothesisSodium-glucose cotransporter 2 inhibitor (SGLT2i) treatment in type 2 diabetes mellitus patients results in glucosuria, causing an energy loss, and triggers beneficial metabolic adaptations. It is so far unknown if SGLT2i exerts beneficial metabolic effects in prediabetic insulin resistant individuals, yet this is of interest since SGLT2is also reduce the risk for progression of heart failure and chronic kidney disease in patients without diabetes. MethodsFourteen prediabetic insulin resistant individuals (BMI: 30.3 ± 2.1 kg/m2; age: 66.3 ± 6.2 years) underwent 2-weeks of treatment with dapagliflozin (10 mg/day) or placebo in a randomized, placebo-controlled, cross-over design. Outcome parameters include 24-hour and nocturnal substrate oxidation, and twenty-four-hour blood substrate and insulin levels. Hepatic glycogen and lipid content/composition were measured by MRS. Muscle biopsies were taken to measure mitochondrial oxidative capacity and glycogen and lipid content. ResultsDapagliflozin treatment resulted in a urinary glucose excretion of 36 g/24-h, leading to a negative energy and fat balance. Dapagliflozin treatment resulted in a higher 24-hour and nocturnal fat oxidation (p = 0.043 and p = 0.039, respectively), and a lower 24-hour carbohydrate oxidation (p = 0.048). Twenty-four-hour plasma glucose levels were lower (AUC; p = 0.016), while 24-hour free fatty acids and nocturnal β-hydroxybutyrate levels were higher (AUC; p = 0.002 and p = 0.012, respectively) after dapagliflozin compared to placebo. Maximal mitochondrial oxidative capacity was higher after dapagliflozin treatment (dapagliflozin: 87.6 ± 5.4, placebo: 78.1 ± 5.5 pmol/mg/s, p = 0.007). Hepatic glycogen and lipid content were not significantly changed by dapagliflozin compared to placebo. However, muscle glycogen levels were numerically higher in the afternoon in individuals on placebo (morning: 332.9 ± 27.9, afternoon: 368.8 ± 13.1 nmol/mg), while numerically lower in the afternoon on dapagliflozin treatment (morning: 371.7 ± 22.8, afternoon: 340.5 ± 24.3 nmol/mg). Conclusions/interpretationDapagliflozin treatment of prediabetic insulin resistant individuals for 14 days resulted in significant metabolic adaptations in whole-body and skeletal muscle substrate metabolism despite being weight neutral. Dapagliflozin improved fat oxidation and ex vivo skeletal muscle mitochondrial oxidative capacity, mimicking the effects of calorie restriction. Trial registrationClinicalTrials.gov NCT03721874.

Cigarette smoking and mitochondrial dysfunction in peripheral artery disease.

This study evaluated the association of smoking with mitochondrial function in gastrocnemius muscle of people with peripheral artery disease (PAD). Participants were enrolled from Chicago, Illinois and consented to gastrocnemius biopsy. Mitochondrial oxidative capacity was measured in muscle with respirometry. Abundance of voltage-dependent anion channel (VDAC) (mitochondrial membrane abundance), peroxisome proliferator-activated receptor-γ coactivator (PGC-1α) (mitochondrial biogenesis), and electron transport chain complexes I-V were measured with Western blot. Fourteen of 31 people with PAD (age 72.1 years, ABI 0.64) smoked cigarettes currently. Overall, there were no significant differences in mitochondrial oxidative capacity between PAD participants who currently smoked and those not currently smoking (complex I+II-mediated oxidative phosphorylation: 86.6 vs 78.3 pmolO2/s/mg, respectively [p = 0.39]). Among participants with PAD, those who currently smoked had a higher abundance of PGC-1α (p < 0.01), VDAC (p = 0.022), complex I (p = 0.021), and complex III (p = 0.021) proteins compared to those not currently smoking. People with PAD who currently smoked had lower oxidative capacity per VDAC unit (complex I+II-mediated oxidative phosphorylation [137.4 vs 231.8 arbitrary units, p = 0.030]) compared to people with PAD not currently smoking. Among people without PAD, there were no significant differences in any mitochondrial measures between currently smoking (n = 5) and those not currently smoking (n = 63). Among people with PAD, cigarette smoking may stimulate mitochondrial biogenesis to compensate for reduced oxidative capacity per unit of mitochondrial membrane, resulting in no difference in overall mitochondrial oxidative capacity according to current smoking status among people with PAD. However, these results were cross-sectional and a longitudinal study is needed.

Muscle PGC-1α modulates hepatic mitophagy regulation during aging

Aging has been suggested to be associated with changes in oxidative capacity, autophagy, and mitophagy in the liver, but a simultaneous evaluation of these key cellular processes is lacking. Moreover, skeletal muscle transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α has been reported to mediate inter-organ signaling through myokines with regulatory effects in the liver, but the potential role of muscle PGC-1α on hepatic changes with age remains to be resolved. The aim of the present study was therefore to investigate 1) the effect of aging on mitochondrial autophagy and mitophagy capacity in mouse liver and 2) whether muscle PGC-1α is required for maintaining autophagy and mitophagy capacity in the liver during aging. The liver was obtained from young (Young) and aged (Aged) inducible muscle-specific PGC-1α knockout (iMKO) and floxed littermate control mice (Lox). Aging increased liver p62, Parkin and BCL2/adenovirus E1B 19 kDa protein-interacting protein (BNIP)3 protein with no effect of muscle specific PGC-1α knockout, while liver Microtubule-associated protein 1A/1B-light chain 3(LC3) II/I was unchanged with age, but tended to be lower in iMKO mice than in controls. Markers of liver mitochondrial oxidative capacity and oxidative stress were unchanged with age and iMKO. However, Parkin protein levels in isolated liver mitochondria were 2-fold higher in Aged iMKO mice than in Aged controls. In conclusion, aging had no effect on oxidative capacity and lipid peroxidation in the liver. However, aging was associated with increased levels of autophagy and mitophagy markers. Moreover, muscle PGC-1α appears to regulate hepatic mitochondrial translocation of Parkin in aged mice, suggesting that the metabolic capacity of skeletal muscle can modulate mitophagy regulation in the liver during aging.

Peroxisome proliferator-activated receptor γ coactivator 1-α overexpression improves angiogenic signalling potential of skeletal muscle-derived extracellular vesicles.

What is the central question of this study? Skeletal muscle extracellular vesicles likely act as pro-angiogenic signalling factors: does overexpression of peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) alter skeletal muscle myotube extracellular vesicle release, contents and angiogenic potential? What is the main finding and its importance? Overexpression of PGC-1α results in secretion of extracellular vesicles that elevate measures of angiogenesis and protect against acute oxidative stress in vitro. Skeletal muscle with high levels of PGC-1α expression, commonly associated with exercise induced angiogenesis and high basal capillarization, may secrete extracellular vesicles that support capillary growth and maintenance. Skeletal muscle capillarization is proportional to muscle fibre mitochondrial content and oxidative capacity. Skeletal muscle cells secrete many factors that regulate neighbouring capillary endothelial cells (ECs), including extracellular vesicles (SkM-EVs). Peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) regulates mitochondrial biogenesis and the oxidative phenotype in skeletal muscle. Skeletal muscle PGC-1α also regulates secretion of multiple angiogenic factors, but it is unknown whether PGC-1α regulates SkM-EV release, contents and angiogenic signalling potential. PGC-1α was overexpressed via adenovirus in primary human myotubes. EVs were collected from PGC-1α-overexpressing myotubes (PGC-EVs) as well as from green fluorescent protein-overexpressing myotubes (GFP-EVs), and from untreated myotubes. EV release and select mRNA contents were measured from EVs. Additionally, ECs were treated with EVs to measure angiogenic potential of EVs in normal conditions and following an oxidative stress challenge. PGC-1α overexpression did not impact EV release but did elevate EV content of mRNAs for several antioxidant proteins (nuclear factor erythroid 2-related factor 2, superoxide dismutase 2, glutathione peroxidase). PGC-EV treatment of cultured human umbilical vein endothelial cells (HUVECs) increased their proliferation (+36.6%), tube formation (length: +28.1%; number: +25.7%) and cellular viability (+52.9%), and reduced reactive oxygen species levels (-41%) compared to GFP-EVs. Additionally, PGC-EV treatment protected against tube formation impairments and induction of cellular senescence following acute oxidative stress. Overexpression of PGC-1α in human myotubes increases the angiogenic potential of SkM-EVs. These angiogenic benefits coincided with increased anti-oxidative capacity of recipient HUVECs. High PGC-1α expression in skeletal muscle may prompt the release of SkM-EVs that support vascular redox homeostasis and angiogenesis.

Repeatability assessment for simultaneous measurement of arterial blood flow, venous oxygen saturation, and muscle perfusion following dynamic exercise.

The purpose of the present study was to demonstrate a new sequence and determine the repeatability of simultaneous dynamic measurements of blood flow, venous oxygen saturation (SvO2 ), and relative perfusion (change from resting perfusion) in calf muscle during recovery from plantar flexion exercise. The feasibility of near simultaneous measurement of bio-energetic parameters was also demonstrated. A sequence was developed to simultaneously measure arterial blood flow using flow-encoded projection, SvO2 using susceptibility-based oximetry, and relative perfusion using arterial spin labeling in combination with dynamic plantar flexion exercise. The parameters were determined at rest and during recovery from single leg plantar flexion exercise. Test-retest repeatability was analyzed using Bland-Altman analysis and intraclass correlation coefficients (ICC). The mitochondrial capacity of skeletal muscle was also measured immediately afterwards with dynamic phosphorus magnetic resonance spectroscopy. Eight healthy subjects participated in the study for test-retest repeatability. Popliteal artery blood flow at rest was 1.79 ± 0.58 ml/s and increased to 11.18 ± 3.02 ml/s immediately after exercise. Popliteal vein SvO2 decreased to 45.93% ± 6.5% from a resting value of 70.46% ± 4.76% following exercise. Relative perfusion (change from rest value) was 51.83 ± 15.00 ml/100 g/min at the cessation of exercise. The recovery of blood flow and SvO2 was modeled as a single exponential with time constants of 38.03 ± 6.91 and 71.19 ± 14.53 s, respectively. All the measured parameters exhibited good repeatability with ICC ranging from 0.8 to 0.95. Bioenergetics measurements were within normal range, demonstrating the feasibility of near simultaneous measurement of hemodynamic and energetic parameters. Clinical feasibility was assessed with Barth syndrome patients, demonstrating reduced oxygen extraction from the blood and reduced mitochondrial oxidative capacity compared with healthy controls. The proposed protocol allows rapid imaging of multiple parameters in skeletal muscle that might be affected in disease.

Abstract 10883: Cigarette Smoking and Mitochondrial Function in Peripheral Artery Disease

Introduction: In humans without peripheral artery disease (PAD) and animal models, exposure to cigarette smoke is associated with reduced mitochondrial respiratory function. Many people with PAD smoke cigarettes, but the association of smoking with mitochondrial function in lower extremity skeletal muscle of people with PAD is unknown. Methods: From the Chicago, IL area, 31 people with PAD (ankle brachial index (ABI) &lt; 0.90) were enrolled and consented to gastrocnemius muscle biopsy. Mitochondrial oxidative capacity in gastrocnemius muscle was measured with respirometry. Western blots were performed to quantify mitochondrial membrane abundance via voltage-dependent anion channel (VDAC), mitochondrial biogenesis via peroxisome proliferator-activated receptor-γ coactivator (PGC-1α) , and electron transport chain complexes I-V. Results: Among 31 people with PAD (mean 72.1 years, mean ABI 0.64), 14 (45.2%) smoked cigarettes currently. Participants who currently smoked had higher abundance of PGC-1α (0.75 vs. 0.45 arbitrary units (AU), P&lt;0.01), VDAC (0.62 vs. 0.37 AU, P=0.022), electron transport chain complex I (0.46 vs. 0.21 AU, P=0.031), and complex III (0.76 vs. 0.42 AU, P=0.031), compared to those who did not currently smoke. After normalizing to VDAC, participants who currently smoked had lower mitochondrial oxidative capacity per unit of mitochondrial membrane compared to those who did not currently smoke (complex I+II-mediated oxidative phosphorylation (156.3 vs. 287.0 AU, P=0.017), complex I+II-mediated electron transport chain capacity (184.8 vs. 343.1 AU, P=0.019), complex I-mediated fatty acid oxidative phosphorylation (45.9 vs. 82.1 AU, P=0.034)). After statistical adjustment for age, sex, race, ABI, and body mass index (BMI), most associations were attenuated but remained statistically significant for the higher abundance of VDAC (0.65 vs. 0.35 AU, P=0.037) and complex I (0.50 vs. 0.18 AU, P=0.038) in participants who currently smoked compared to those who did not currently smoke. Conclusions: Results suggest that among people with PAD, current cigarette smoking may stimulate a compensatory increase in mitochondrial biogenesis that may counteract effects of reduced oxidative capacity per unit mitochondrial membrane.

Robust arm and leg muscle adaptation to training despite ACE inhibition: a randomized placebo-controlled trial.

Angiotensin-converting enzyme (ACE) inhibitor treatment is widely applied, but the fact that plasma ACE activity is a potential determinant of training-induced local muscular adaptability is often neglected. Thus, we investigated the hypothesis that ACE inhibition modulates the response to systematic aerobic exercise training on leg and arm muscular adaptations. Healthy, untrained, middle-aged participants (40 ± 7 yrs) completed a randomized, double-blinded, placebo-controlled trial. Participants were randomized to placebo (PLA: CaCO3) or ACE inhibitor (ACEi: enalapril) for 8weeks and completed a supervised, high-intensity exercise training program. Muscular characteristics in the leg and arm were extensively evaluated pre and post-intervention. Forty-eight participants (nACEi = 23, nPLA = 25) completed the trial. Exercise training compliance was above 99%. After training, citrate synthase, 3-hydroxyacyl-CoA dehydrogenase and phosphofructokinase maximal activity were increased in m. vastus lateralis in both groups (all P < 0.05) without statistical differences between them (all time × treatment P > 0.05). In m. deltoideus, citrate synthase maximal activity was upregulated to a greater extent (time × treatment P < 0.05) in PLA (51 [33;69] %) than in ACEi (28 [13;43] %), but the change in 3-hydroxyacyl-CoA dehydrogenase and phosphofructokinase maximal activity was similar between groups. Finally, the training-induced changes in the platelet endothelial cell adhesion molecule-1 protein abundance, a marker of capillary density, were similar in both groups in m. vastus lateralis and m. deltoideus. Eight weeks of high-intensity whole-body exercise training improves markers of skeletal muscle mitochondrial oxidative capacity, glycolytic capacity and angiogenesis, with no overall effect of pharmacological ACE inhibition in healthy adults.

The Effects of Exercise Training on Mitochondrial Function in Cardiovascular Diseases: A Systematic Review and Meta-Analysis.

Mitochondria dysfunction is implicated in the pathogenesis of cardiovascular diseases (CVD). Exercise training is potentially an effective non-pharmacological strategy to restore mitochondrial health in CVD. However, how exercise modifies mitochondrial functionality is inconclusive. We conducted a systematic review using the PubMed; Scopus and Web of Science databases to investigate the effect of exercise training on mitochondrial function in CVD patients. Search terms included “mitochondria”, “exercise”, “aerobic capacity”, and “cardiovascular disease” in varied combination. The search yielded 821 records for abstract screening, of which 20 articles met the inclusion criteria. We summarized the effect of exercise training on mitochondrial morphology, biogenesis, dynamics, oxidative capacity, antioxidant capacity, and quality. Amongst these parameters, only oxidative capacity was suitable for a meta-analysis, which demonstrated a significant effect size of exercise in improving mitochondrial oxidative capacity in CVD patients (SMD = 4.78; CI = 2.99 to 6.57; p < 0.01), but with high heterogeneity among the studies (I2 = 75%, p = 0.003). Notably, aerobic exercise enhanced succinate-involved oxidative phosphorylation. The majority of the results suggested that exercise improves morphology and biogenesis, whereas findings on dynamic, antioxidant capacity, and quality, were inadequate or inconclusive. A further randomized controlled trial is clearly required to explain how exercise modifies the pathway of mitochondrial quantity and quality in CVD patients.

Social isolation induces succinate dehydrogenase dysfunction in anxious mice

We have previously reported social isolation induces anxiety-like behavior, cognitive decline, and reduction in brain ATP levels in mice. These changes were ameliorated by treatment with dihydromyricetin (DHM), a compound that positively modulates γ-aminobutyric A (GABAA) receptor. To gain further insight into the subcellular mechanisms underlying these changes, we utilized a social isolation-induced anxiety mouse model and investigated changes in mitochondrial oxidative capacity via the electron transport chain. We found that 4 weeks of social isolation decreased ATP levels by 43% and succinate dehydrogenase capacity by 52% of the control, while daily DHM (2 mg/kg oral) administration restored succinate dehydrogenase capacity. These results suggest that social isolation decreased mitochondrial capacity to generate ATP. DHM can be developed to be a therapeutic against anxiety and mitochondrial stress.

Associations of GPCR autoantibodies with clinical, histological, metabolic and hemodynamic features in non-ischemic heart failure patients

Abstract Background Roughly one third of cases of chronic heart failure (HF) are caused by genetic predisposition, metabolic stress and cardiac inflammation. Animal studies suggest that heart-reactive autoantibodies, most notably those directed against G-protein-coupled receptors (GPCR), could also play a pathogenetic role in the disease. However, so far, a causal link between humoral GPCR-autoimmunity and human non-ischemic heart failure other than Chagas' cardiomyopathy remains unclear. Purpose Here, we investigated possible associations of GPCR autoantibodies with inflammatory, hemodynamic, metabolic and functional parameters in patients with chronic non-ischemic HF unrelated to Chagas' disease. Methods We prospectively included 95 patients with newly diagnosed non-ischemic heart failure of unknown origin. Basic cardiac characterization comprised transthoracic echocardiography, cardiac magnetic resonance imaging, coronary angiography and right heart catheterization with endomyocardial biopsy. Mitochondrial oxidative phosphorylation capacity and coupling was measured using high-resolution respirometry in permeabilized myocardial fibers. A panel of candidate GPCR-autoantibodies was determined by validated and certified immune-assays in peripheral venous blood of the HF-patients and 60 matched healthy individuals. Results were normalized to total IgG. Results Among 10 candidate GPCR-autoantibodies determined, only autoantibodies for α1-adrenergic receptor (α1AR), β1-adrenergic receptor (β1AR), muscarinic receptor M5 (M5AR), angiotensin II receptor type 1 (AT1R) and type 2 (AT2R) exhibited HF-associated alterations: Autoantibodies against β1AR, M5R and AT2R were increased. Autoantibodies against α1AR and AT1R were decreased (Figure). These alterations were significant (p&amp;lt;0.01), but not, or only weakly, correlated with markers of cardiac inflammation, cardiac damage, hemodynamics, endomyocardial histology or left ventricular inflammation judged by T2-mapping. However, in HF-patients, increased AT2R autoantibodies were associated with improved myocardial mitochondrial coupling (r=−0.27, p=0.021), and decreased AT2R autoantibodies were associated with insulin resistance (r=−0.24 p=0.027). Conclusion(s) Some previously postulated alterations of GPCR autoantibodies were confirmed in thoroughly characterized HF-patients. However, association of these alterations with cardiac function was not traceable, which argues against a specific pathogenic role. Our data are compatible with multifaceted interactions of GPCR-autoantibodies with the myocardium and potentially with glucose metabolism, possibly indicating a disease-modifying or compensatory role. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): Research comission of the Heinrich-Heine University Duesseldorf

Prediabetes relates to impaired mitochondrial function in human ventricular myocardium

Abstract Background/Introduction With the growing prevalence of prediabetes in developed countries, complications of this predecessor of diabetes mellitus type 2 become increasingly important for medical research and practice. Prediabetes is defined as impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) and may also incorporate elevated hemoglobin A1. While overt type 2 diabetes is a well-established risk factor and can even be the cause of cardiac failure, this is not yet proven for prediabetes. Mitochondrial impairment is a key pathomechanism in heart failure, but it remains uncertain, whether prediabetes impairs myocardial energy metabolism in humans just as type 2 diabetes does. Purpose We aimed to scrutinize the impact of prediabetes on myocardial mitochondrial metabolism and cardiac function. Methods We included 50 heart transplant recipients with normal glucose tolerance (GT, n=25), prediabetes (n=8, 3 IFG and 5 IGT) or type 2 diabetes mellitus (T2DM, n=17), who had received a healthy donor heart from a non-diabetic donor. In this cohort, the impact of the recipients' metabolism should be displayed in the donor heart after transplantation. We performed oral glucose tolerance tests to assess the diabetes status, and cardiac magnetic resonance imaging to assess cardiac systolic and diastolic function, circulating biomarkers of oxidative stress in serum samples (thiobarbituric acid reactive substances (TBARS) and redox potential), as well as global T2 relaxation times as a marker of myocardial inflammation. In transcatheter endomyocardial biopsies, we assessed myocardial mitochondrial oxidative capacity using high-resolution respirometry and myocardial mRNA expression of nuclear factor kappa B p105 subunit (NFKB1). Results GT and IFG/IGT patients exhibited comparable demographic and clinical characteristics, whereas T2DM had higher BMI, glycemia, triglycerides and creatine kinase (all p&amp;lt;0.05). None of systolic (p=0.99), diastolic cardiac function (p=0.81), myocardial NFKB1 expression (p=0.74), circulating oxidative stress markers (p=0.94 and 0.95) or cardiac T2 relaxation times (p=0.99) were altered in IFG/IGT compared to GT, but diastolic strainrate was impaired (p=0.03) and circulating oxidative stress (TBARS: p=0.03, redox potential: p=0.04) were higher in T2DM than in GT. However, myocardial mitochondrial function stood out to be already impaired in IFG/IGT to a similar extend as in T2DM. This particularly applied to substrates of mitochondrial complex I (GT vs. IFG/IGT vs. T2DM: 126±7 vs. 89±12 vs. 93±6 pmol s–1 mg–1. p=0.02) and II (188±13 vs. 123±17 vs. 138±11 pmol s–1 mg–1. p=0.02). Intrinsic uncoupling was not altered in IFG/IGT but tended to be higher in T2DM (leak control ratio: 0.49±0.02 vs. 0.46±0.06 vs. 0.57±0.04 [arbirary units]). Conclusion Our findings point towards mitochondrial impairment as a predecessor of overt heart failure in prediabetes and may represent an early footprint of prediabetic cardiomyopathy. Funding Acknowledgement Type of funding sources: None.