NADPH supply and the contribution of NAD(P)+ transhydrogenase (NNT) to H2O2 balance in skeletal muscle mitochondria.

H2O2 is endogenously generated and its removal in the matrix of skeletal muscle mitochondria (SMM) is dependent on NADPH likely provided by NAD(P)+ transhydrogenase (NNT) and isocitrate dehydrogenase (IDH2). Importantly, NNT activity is linked to mitochondrial protonmotive force. Here, we demonstrate the presence of NNT function in detergent-solubilized and intact functional SMM isolated from rats and wild type (Nnt+/+) mice, but not in SMM from congenic mice carrying a mutated NNT gene (Nnt-/-). Further comparisons between SMM from both Nnt mouse genotypes revealed that the NADPH supplied by NNT supports up to 600 pmol/mg/min of H2O2 removal under selected conditions. Surprisingly, SMM from Nnt-/- mice removed exogenous H2O2 at wild-type levels and exhibited a maintained or even decreased net emission of endogenous H2O2 when substrates that support Krebs cycle reactions were present (e.g., pyruvate plus malate or palmitoylcarnitine plus malate). These results may be explained by a compensation for the lack of NNT, since the total activities of concurrent NADP+-reducing enzymes (IDH2, malic enzymes and glutamate dehydrogenase) were ~70% elevated in Nnt-/- mice. Importantly, respiratory rates were similar between SMM from both Nnt genotypes despite differing NNT contributions to H2O2 removal and their implications for an evolving concept in the literature are discussed. We concluded that NNT is capable of meaningfully sustaining NADPH-dependent H2O2 removal in intact SMM. Nonetheless, if the available substrates favor non-NNT sources of NADPH, the H2O2 removal by SMM is maintained in Nnt-/- mice SMM.

Nicotinamide nucleotide transhydrogenase is required for brain mitochondrial redox balance under hampered energy substrate metabolism and high-fat diet.

Among mitochondrial NADP-reducing enzymes, nicotinamide nucleotide transhydrogenase (NNT) establishes an elevated matrix NADPH/NADP+ by catalyzing the reduction of NADP+ at the expense of NADH oxidation coupled to inward proton translocation across the inner mitochondrial membrane. Here, we characterize NNT activity and mitochondrial redox balance in the brain using a congenic mouse model carrying the mutated Nnt gene from the C57BL/6J strain. The absence of NNT activity resulted in lower total NADPH sources activity in the brain mitochondria of young mice, an effect that was partially compensated in aged mice. Nonsynaptic mitochondria showed higher NNT activity than synaptic mitochondria. In the absence of NNT, an increased release of H2 O2 from mitochondria was observed when the metabolism of respiratory substrates occurred with restricted flux through relevant mitochondrial NADPH sources or when respiratory complex I was inhibited. In accordance, mitochondria from Nnt-/- brains were unable to sustain NADP in its reduced state when energized in the absence of carbon substrates, an effect aggravated after H2 O2 bolus metabolism. These data indicate that the lack of NNT in brain mitochondria impairs peroxide detoxification, but peroxide detoxification can be partially counterbalanced by concurrent NADPH sources depending on substrate availability. Notably, only brain mitochondria from Nnt-/- mice chronically fed a high-fat diet exhibited lower activity of the redox-sensitive aconitase, suggesting that brain mitochondrial redox balance requires NNT under the metabolic stress of a high-fat diet. Overall, the role of NNT in the brain mitochondria redox balance especially comes into play under mitochondrial respiratory defects or high-fat diet.

Facilitation of Ca2+ -induced opening of the mitochondrial permeability transition pore either by nicotinamide nucleotide transhydrogenase deficiency or statins treatment.

Mitochondrial redox imbalance and high Ca2+ uptake induce the opening of the permeability transition pore (PTP) that leads to disruption of energy-linked mitochondrial functions and triggers cell death in many disease states. In this review, we discuss the major results from our studies investigating the consequences of NAD(P)-transhydrogenase (NNT) deficiency, and of statins treatment for mitochondrial functions and susceptibility to Ca2+ -induced PTP. We highlight the aggravation of high fat diet-induced fatty liver disease in the context of NNT deficiency and the role of antioxidants in the prevention of statins toxicity to mitochondria.

Evaluation of mitochondrial respiratory function in highly glycolytic glioma cells reveals low ADP phosphorylation in relation to oxidative capacity.

High-grade gliomas are aggressive and intensely glycolytic tumors. In the present study, we evaluated the mitochondrial respiratory function of glioma cells (T98G and U-87MG) and fresh human glioblastoma (GBM) tissue. To this end, measurements of oxygen consumption rate (OCR) were performed under various experimental conditions. The OCR of T98G and U-87MG cells was well coupled to ADP phosphorylation based on the ratio of ATP produced per oxygen consumed of ~2.5. In agreement, the basal OCR of GBM tissue was also partially associated with ADP phosphorylation. The basal respiration of intact T98G and U-87MG cells was not limited by the supply of endogenous substrates, as indicated by the increased OCR in response to a protonophore. These cells also displayed a high affinity for oxygen, as evidenced by the values of the partial pressure of oxygen when respiration is half maximal (p 50). In permeabilized glioma cells, ADP-stimulated OCR was only approximately 50% of that obtained in the presence of protonophore, revealing a significant limitation in oxidative phosphorylation (OXPHOS) relative to the activity of the electron transport system (ETS). This characteristic was maintained when the cells were grown under low glucose conditions. Flux control coefficient analyses demonstrated that the impaired OXPHOS was associated with the function of both mitochondrial ATP synthase and the adenine nucleotide translocator, but not the phosphate carrier. Altogether, these data indicate that the availability and metabolism of respiratory substrates and mitochondrial ETS are preserved in T98G and U-87MG glioma cells even though these cells possess a relatively restrained OXPHOS capability.

Tissue and sex specificities in Ca2+ handling by isolated mitochondria in conditions avoiding the permeability transition.

NEW FINDINGS: What is the central question of this study? The assessment of Ca(2+) handling by isolated mitochondria can be biased by dysfunctions secondary to Ca(2+) -induced mitochondrial permeability transition (MPT). As a result of this uncertainty and the differing experimental conditions between studies, the tissue and sex diversities in mitochondrial Ca(2+) transport are still unsettled questions. What is the main finding and its importance? If MPT is not prevented during Ca(2+) transport assays, some measured variables are biased. Accounting for the implied importance of preventing MPT, we observed substantial tissue specificities in the mitochondrial Ca(2+) handling, particularly in the Ca(2+) efflux pathways. The characteristics of mitochondria, including their Ca(2+) transport functions, may exhibit tissue specificity and sexual dimorphism. Given that measurements of Ca(2+) handling by isolated mitochondria may be biased by dysfunction secondary to Ca(2+) -induced mitochondrial permeability transition (MPT) pore opening, this study evaluated the extent to which MPT inhibition by ciclosporin affected the measurement of Ca(2+) transport in isolated rat liver mitochondria. The results indicate that the steady-state levels of external Ca(2+) and the rates of mitochondrial Ca(2+) efflux through the selective pathways can be overestimated by up to fourfold if MPT pore opening is not prevented. We analysed Ca(2+) transport in isolated mitochondria from the liver, skeletal muscle, heart and brain of male and female rats in incubation conditions containing MPT inhibitors, NAD-linked substrates and relevant levels of free Ca(2+), Mg(2+) and Na(+). The Ca(2+) influx rates were similar among the samples, except that the liver mitochondria displayed values fourfold higher. In contrast, the Ca(2+) efflux rates exhibited more tissue diversity, especially in the presence of Na(+). Interestingly, the Na(+)-independent Ca(2+) efflux was highest in the heart mitochondria (∼ 4 nmol mg(-1) min(-1)), thus challenging the view that cardiac mitochondrial Ca(2+) efflux relies almost exclusively on a Na(+)-dependent pathway. Sex specificity was observed in only two kinetic indexes of heart mitochondrial Ca(2+) homeostasis and in the ADP-stimulated respiration of liver mitochondria (∼ 20% higher in females). The present study shows the methodological importance of preventing MPT when measuring the properties and the physiological variability of the Ca(2+) handling by isolated mitochondria.

Aging-dependent mitochondrial bioenergetic impairment in the skeletal muscle of NNT-deficient mice.

Overall health relies on features of skeletal muscle that generally decline with age, partly due to mechanisms associated with mitochondrial redox imbalance and bioenergetic dysfunction. Previously, aged mice genetically devoid of the mitochondrial NAD(P)+ transhydrogenase (NNT, encoded by the nicotinamide nucleotide transhydrogenase gene), an enzyme involved in mitochondrial NADPH supply, were shown to exhibit deficits in locomotor behavior. Here, by using young, middle-aged, and older NNT-deficient (Nnt-/-) mice and age-matched controls (Nnt+/+), we aimed to investigate how muscle bioenergetic function and motor performance are affected by NNT expression and aging. Mice were subjected to the wire-hang test to assess locomotor performance, while mitochondrial bioenergetics was evaluated in fiber bundles from the soleus, vastus lateralis and plantaris muscles. An age-related decrease in the average wire-hang score was observed in middle-aged and older Nnt-/- mice compared to age-matched controls. Although respiratory rates in the soleus, vastus lateralis and plantaris muscles did not significantly differ between the genotypes in young mice, the rates of oxygen consumption did decrease in the soleus and vastus lateralis muscles of middle-aged and older Nnt-/- mice. Notably, the soleus, which exhibited the highest NNT expression level, was the muscle most affected by aging, and NNT loss. Additionally, histology of the soleus fibers revealed increased numbers of centralized nuclei in older Nnt-/- mice, indicating abnormal morphology. In summary, our findings suggest that NNT expression deficiency causes locomotor impairments and muscle dysfunction during aging in mice.

Enhanced insulin secretion and glucose tolerance in rats exhibiting low plasma free fatty acid levels and hypertriglyceridaemia due to congenital albumin deficiency.

Congenitally analbuminaemic individuals and rats (NARs) exhibit several metabolic abnormalities, including hypertriglyceridaemia and plasma free fatty acid deficiency. Our aim was to study glucose homeostasis and insulin secretion in NARs. Plasma concentrations of lipids, glucose and insulin and secretion of insulin from the pancreatic islets were measured in female NARs and control animals (Sprague-Dawley rats; SDRs). Glucose homeostasis tests were also performed. Plasma glucose levels were similar between NARs and SDRs, irrespective of feeding status. However, fed insulinaemia was ∼37% higher (P 0.05) in NARs than in SDRs. The NARs displayed a markedly increased glucose tolerance, i.e. the integrated glycaemic response was one-third that of the control animals. Enhanced glucose tolerance was associated with threefold higher insulinaemia at peak glycaemia after a glucose load than in the control animals. Similar peripheral insulin sensitivity was observed between groups. Isolated pancreatic islets from NARs secreted significantly more insulin than islets from SDRs in response to a wide range of glucose concentrations (2.8-33.3 mm). Despite having similar liver glycogen contents in the fully fed state, NARs had ∼40% (P 0.05) lower glycogen contents than SDRs after 6 h fasting. The injection of a gluconeogenic substrate, pyruvate, elicited a faster rise in glycaemia in NARs compared with SDRs. Overall, NARs displayed enhanced glucose tolerance, insulin secretion and gluconeogenic flux. The higher glucose tolerance in NARs compared with SDRs is attributed to enhanced islet responsiveness to secretagogues, while peripheral insulin sensitivity seems not to be involved in this alteration. We propose that the enhanced glucose metabolism is a chronic compensatory adaptation to decreased free fatty acid availability in NARs.

Dichloroacetate reactivates pyruvate-supported peroxide removal by liver mitochondria and prevents NAFLD aggravation in NAD(P)+ transhydrogenase-null mice consuming a high-fat diet.

The mechanisms by which a high-fat diet (HFD) promotes non-alcoholic fatty liver disease (NAFLD) appear to involve liver mitochondrial dysfunction and redox imbalance. The functional loss of the enzyme NAD(P)+ transhydrogenase, a main source of mitochondrial NADPH, results in impaired mitochondrial peroxide removal, pyruvate dehydrogenase inhibition by phosphorylation, and progression of NAFLD in HFD-fed mice. The present study aimed to investigate whether pharmacological reactivation of pyruvate dehydrogenase by dichloroacetate attenuates the mitochondrial redox dysfunction and the development of NAFLD in NAD(P)+ transhydrogenase-null (Nnt-/-) mice fed an HFD (60% of total calories from fat). For this purpose, Nnt-/- mice and their congenic controls (Nnt+/+) were fed chow or an HFD for 20 weeks and received sodium dichloroacetate or NaCl in the final 12 weeks via drinking water. The results showed that HFD reduced the ability of isolated liver mitochondria from Nnt-/- mice to remove peroxide, which was prevented by the dichloroacetate treatment. HFD-fed mice of both Nnt genotypes exhibited increased body and liver mass, as well as a higher content of hepatic triglycerides, but dichloroacetate treatment attenuated these abnormalities only in Nnt-/- mice. Notably, dichloroacetate treatment decreased liver pyruvate dehydrogenase phosphorylation levels and prevented the aggravation of NAFLD in HFD-fed Nnt-/- mice. Conversely, dichloroacetate treatment elicited moderate hepatocyte ballooning in chow-fed mice, suggesting potentially toxic effects. We conclude that the protection against HFD-induced NAFLD by dichloroacetate is associated with its role in reactivating pyruvate dehydrogenase and reestablishing the pyruvate-supported liver mitochondrial capacity to handle peroxide in Nnt-/- mice.

The higher susceptibility of congenital analbuminemic rats to Ca2+-induced mitochondrial permeability transition is associated with the increased expression of cyclophilin D and nitrosothiol depletion.

Congenital analbuminemia is a rare autosomal recessive disorder characterized by a trace level of albumin in blood plasma and mild clinical symptoms. Analbuminemic patients generally present associated abnormalities, among which dyslipidemia is a hallmark. In this study, we show that mitochondria isolated from different tissues (liver, heart and brain) from 3-month-old analbuminemic rats (NAR) present a higher susceptibility to Ca(2+)-induced mitochondrial permeability transition (MPT), as assessed by either Ca(2+)-induced mitochondrial swelling, dissipation of membrane potential or mitochondrial Ca(2+) release. The Ca(2+) retention capacity of the liver mitochondria isolated from 3-month-old NAR was about 50% that of the control. Interestingly, the assessment of this variable in 21-day-old NAR indicated that the mitochondrial Ca(2+) retention capacity was preserved at this age, as compared to age-matched controls, which indicates that a reduced capacity for mitochondrial Ca(2+) retention is not a constitutive feature. The search for putative mediators of MPT sensitization in NAR revealed a 20% decrease in mitochondrial nitrosothiol content and a 30% increase in cyclophilin D expression. However, the evaluation of other variables related to mitochondrial redox status showed similar results between the controls and NAR, i.e., namely the contents of reduced mitochondrial membrane protein thiol groups and total glutathione, H(2)O(2) release rate, and NAD(P)H reduced state. We conclude that the higher expression of cyclophilin D, a major component of the MPT pore, and decreased nitrosothiol content in NAR mitochondria may underlie MPT sensitization in these animals.

Improvements in metabolic and neuromuscular fitness after 12-week bodypump® training.

Greco, CC, Oliveira, AS, Pereira, MP, Figueira, TR, Ruas, VD, Gonçalves, M, and Denadai, BS. Improvements in metabolic and neuromuscular fitness after 12-week Bodypump® training. J Strength Cond Res 25(12): 3422-3431, 2011-The purpose of this study was to evaluate the effects of a 12-week group fitness training program (Bodypump®) on anthropometry, muscle strength, and aerobic fitness. Nineteen women (21.4 ± 2.0 years old) were randomly assigned to a training group (n = 9) and to a control group (n = 10). We show that this training program improved the 1 repetition maximum squats by 33.1% (p < 0.001) and the maximal isometric voluntary contraction (MVC) by 13.6% (p < 0.05). Additionally, decreases in knee extensor electromyographic activity during the MVC (30%, p < 0.01) and during the squats (15%, p < 0.05) and lunges of a simulated Bodypump® session were observed after the training. Concomitantly, blood lactate and heart rate after squats of a simulated Bodypump® session were decreased by 33 and 7% (p < 0.05), respectively. Body mass, body fat, and the running velocity at the onset of blood lactate accumulation did not change significantly in response to this training program. We conclude that Bodypump® training improves muscular strength and decreases metabolic stress during lower limb exercises. However, no significant improvements in running aerobic fitness nor in body mass and body fat were observed. Practitioners of Bodypump® training may benefit from the increased muscular strength and the decreased muscular fatigability during exercise tasks whose motor patterns are related to those involved in this training program. However, these functional gains do not seem to be transferable into running aerobic fitness.

Lack of plasma albumin impairs intravascular lipolysis and explains the associated free fatty acids deficiency and hypertriglyceridemia.

BACKGROUND: Abnormalities in lipid metabolism and transport are hallmarks in analbuminemic Nagase rats (NAR) and humans. Triglyceridemia is nearly 3- to 5-fold higher in female NAR than in control Sprague-Dawley rats (SDR). Also, NAR present with a severe plasma free fatty acid (FFA) deficit. There are conflicting results regarding the mechanisms underlying NAR hypertriglyceridemia. OBJECTIVE: We aimed at investigating whether liver lipogenesis and triglyceride secretion rates into the plasma contribute to the hypertriglyceridemia in NAR. We also studied whether heparin or albumin administration would release the hypothesized lipolysis inhibition in NAR. METHODS: The incorporation of tritiated water into lipids and the linear accumulation rate of plasma triglycerides after Triton WR1339 injection were the measures of liver lipogenesis and triglyceride secretion rates. RESULTS: Lipogenesis (596 ± 40 vs. 929 ± 124 µmol 3H2O/g/h) and triglyceride (4.25 ± 1.00 vs. 7.04 ± 1.68 mg/dL/min) secretion rates were slower (P ≤ 0.05) in fasted NAR than in control SDR. The injection of either heparin or albumin elicited an increase in NAR plasma FFA levels over time. FFA levels reached control levels 90 min after the albumin administration, increasing from 0.36 ± 0.05 to 1.34 ± 0.16 mEq/L (P ≤ 0.05). These results indicate that the lack of plasma albumin inhibits intravascular lipolysis and causes the FFA deficit observed in NAR. CONCLUSION: NAR hepatic triglyceride synthesis and output do not contribute to NAR hypertriglyceridemia. We propose that the lack of albumin diminishes intravascular lipolysis which reduces the plasma triglyceride removal rate and explain both NAR hypertriglyceridemia and FFA deficiency.

Mitochondrial NAD(P)+ Transhydrogenase is Unevenly Distributed in Different Brain Regions, and its Loss Causes Depressive-like Behavior and Motor Dysfunction in Mice.

NAD(P)+ transhydrogenase (NNT) links redox states of the mitochondrial NAD(H) and NADP(H) via a reaction coupled to proton-motive force across the inner mitochondrial membrane. NNT is believed to be ubiquitously present in mammalian cells, but its expression may vary substantially in different tissues. The present study investigated the tissue distribution and possible roles of NNT in the mouse brain. The pons exhibited high NNT expression/activity, and immunohistochemistry revealed intense NNT labeling in neurons from brainstem nuclei. In some of these regions, neuronal NNT labeling was strongly colocalized with enzymes involved in the biosynthesis of 5-hydroxytryptamine (5-HT) and nitric oxide (NO), which directly or indirectly require NADPH. Behavioral tests were performed in mice lacking NNT activity (Nnt-/-, mice carrying the mutated NntC57BL/6J allele from the C57BL/6J strain) and the Nnt+/+ controls. Our data demonstrated that aged Nnt-/- mice (18-20 months old), but not adult mice (3-4 months old), showed an increased immobility time in the tail suspension test that was reversed by fluoxetine treatment, providing evidence of depressive-like behavior in these mice. Aged Nnt-/- mice also exhibited behavioral changes and impaired locomotor activity in the open field and rotarod tests. Despite the colocalization between NNT and NO synthase, the S-nitrosation and cGMP levels were independent of the Nnt genotype. Taken together, our results indicated that NNT is unevenly distributed throughout the brain and associated with 5-THergic and NOergic neurons. The lack of NNT led to alterations in brain functions related to mood and motor behavior/performance in aged mice.

Influence of exercise mode and maximal lactate-steady-state concentration on the validity of OBLA to predict maximal lactate-steady-state in active individuals.

The aim of this study was to analyze the effects of exercise mode on the validity of onset of blood lactate accumulation (OBLA-3.5-mM fixed blood lactate concentration) to predict the work-rate at maximal lactate steady state (MLSS(work-rate)). Eleven recreationally active males (21.3+/-2.9 years, 72.8+/-6.7kg, 1.78+/-0.1m) performed randomly incremental tests to determine OBLA (stage duration of 3min), and 2 to 4 constants work-rate exercise tests to directly determine maximal lactate steady state parameters on a cycle-ergometer and treadmill. For both exercise modes, the OBLA was significantly correlated to MLSS(work-rate), (cycling: r=0.81 p=0.002; running: r=0.94, p<0.001). OBLA (156.2+/-41.3W) was lower than MLSS(work-rate) (179.6+/-26.4W) during cycling exercise (p=0.007). However, for running exercise, there was no difference between OBLA (3.2+/-0.6ms(-1)) and MLSS(work-rate) (3.1+/-0.4ms(-1)). The difference between OBLA and MLSS(work-rate) on the cycle-ergometer (r=0.86; p<0.001) and treadmill (r=0.64; p=0.048) was significantly related to the specific MLSS. We can conclude that the validity of OBLA on predicting MLSS(work-rate) is dependent on exercise mode and that its disagreement is related to individual variations in MLSS.

Aerobic Fitness Level Typical of Elite Athletes is not Associated With Even Faster VO2 Kinetics During Cycling Exercise.

The aim of this study was to address the question if the VO2 kinetics is further improved as the aerobic training status increases from trained to elite level athletes. Maximal oxygen uptake (VO2max), work-rate associated to VO2max (IVO2max) and VO2 kinetics of moderate (Mod) and maximal exercise (Max) were determined in fifty- five subjects. Then, they were assigned into three groups: low (LF), intermediate (IF) and high (HF) aerobic fitness level. In average, the VO2max of LF, IF and HF groups were, respectively, 36.0 ± 3.1, 51.1 ± 4.5 and 68.1 ± 3.9 ml·kg·min(-1) (p ≤ 0.05 among each other). VO2 kinetics mean response time of both exercise intensities were significantly faster (p ≤ 0.05) in HF (Mod, 27.5 ± 5.5 s; Max, 32.6 ± 8.3 s) and IF (Mod, 25.0 ± 3.1 s; Max, 42.6 ± 10.4 s) when compared to LF (Mod, 35.7 ± 7.9 s; Max: 57.8 ± 17.8 s). We can conclude that VO2 kinetics is improved as the fitness level is increased from low to intermediate but not further improved as the aerobic fitness level increases from intermediate to high. Key pointsCurrently, it is reasonable to believe that the rate-limiting step of VO2 kinetics depends on exercise intensity.The well known physiological adaptations induced by endurance training are likely the most extreme means to overcome rate-limiting steps determining VO2 kinetics across exercise intensities.However, exercise adaptation leading individuals to the high-end of aerobic fitness level range (VO2max > 65 ml.kg.min-1) is not able to further improve VO2 kinetics during both, moderate and maximal intensity exercise.

Mitochondrial calcium transport and the redox nature of the calcium-induced membrane permeability transition.

Mitochondria possess a Ca2+ transport system composed of separate Ca2+ influx and efflux pathways. Intramitochondrial Ca2+ concentrations regulate oxidative phosphorylation, required for cell function and survival, and mitochondrial redox balance, that participates in a myriad of signaling and damaging pathways. The interaction between Ca2+ accumulation and redox imbalance regulates opening and closing of a highly regulated inner membrane pore, the membrane permeability transition pore (PTP). In this review, we discuss the regulation of the PTP by mitochondrial oxidants, reactive nitrogen species, and the interactions between these species and other PTP inducers. In addition, we discuss the involvement of mitochondrial redox imbalance and PTP in metabolic conditions such as atherogenesis, diabetes, obesity and in mtDNA stability.

Effects of gender on stroke rates, critical speed and velocity of a 30-min swim in young swimmers.

Our objective was to analyze the effect of gender on the relationship between stroke rates corresponding to critical speed (SRCS) and maximal speed of 30 min (SRS30) in young swimmers. Twenty two males (GM1) (Age = 15.4 ± 2.1 yr., Body mass = 63.7 ± 12.9 kg, Stature = 1.73 ± 0.09 m) and fourteen female (GF) swimmers (Age = 15.1 ± 1.6 yr., Body mass = 58.3 ± 8.8 kg, Stature = 1.65 ± 0.06 m) were studied. A subset of males (GM2) was matched to the GF by their velocity for a 30 min swim (S30). The critical speed (CS) was determined through the slope of the linear regression line between the distances (200 and 400 m) and participant's respective times. CS was significantly higher than S30 in males (GM1 - 1.25 and 1.16 and GM2 - 1.21 and 1.12 m·s(-1)) and females (GF - 1.15 and 1.11 m·s(-1)). There was no significant difference between SRCS and SRS30 in males (GM1 - 34.16 and 32.32 and GM2 - 34.67 and 32.46 cycle·s(-1), respectively) and females (GF - 34.18 and 33.67 cycle·s(-1), respectively). There was a significant correlation between CS and S30 (GM1 - r = 0.89, GF - r = 0.94 and GM2 - r = 0.90) and between SRCS and SRS30 (GM1 - r = 0.89, GF - r = 0.80 and GM2 - r = 0.88). Thus, the relationship between SRCS and SRS30 is not influenced by gender, in swimmers with similar and different aerobic capacity levels. Key pointsThe main finding of this study was that the relationship between SRCS and SRS30, which is not dependent on gender, in swimmers with similar and different aerobic capacity levels.In swimmers who had different S30 values, CS was higher than S30 in boys and girls, and CS and S30 were higher in boys than girls, but SRCS and SRS30 were similar between genders.In swimmers who had similar S30 values, CS was higher than S30 in boys and girls. However, boys still presented higher values of CS than girls. SRCS was higher than SRS30 in boys, but these variables were similar in girls. SRCS and SRS30 were similar between genders.Girls presented lower submaximal blood lactate levels than boys.

Redox imbalance due to the loss of mitochondrial NAD(P)-transhydrogenase markedly aggravates high fat diet-induced fatty liver disease in mice.

The mechanisms by which a high fat diet (HFD) promotes non-alcoholic fatty liver disease (NAFLD) appear to involve liver mitochondrial dysfunctions and redox imbalance. We hypothesized that a HFD would increase mitochondrial reliance on NAD(P)-transhydrogenase (NNT) as the source of NADPH for antioxidant systems that counteract NAFLD development. Therefore, we studied HFD-induced liver mitochondrial dysfunctions and NAFLD in C57Unib.B6 congenic mice with (Nnt+/+) or without (Nnt-/-) NNT activity; the spontaneously mutated allele (Nnt-/-) was inherited from the C57BL/6J mouse substrain. After 20 weeks on a HFD, Nnt-/- mice exhibited a higher prevalence of steatohepatitis and content of liver triglycerides compared to Nnt+/+ mice on an identical diet. Under a HFD, the aggravated NAFLD phenotype in the Nnt-/- mice was accompanied by an increased H2O2 release rate from mitochondria, decreased aconitase activity (a redox-sensitive mitochondrial enzyme) and higher susceptibility to Ca2+-induced mitochondrial permeability transition. In addition, HFD led to the phosphorylation (inhibition) of pyruvate dehydrogenase (PDH) and markedly reduced the ability of liver mitochondria to remove peroxide in Nnt-/- mice. Bypass or pharmacological reactivation of PDH by dichloroacetate restored the peroxide removal capability of mitochondria from Nnt-/- mice on a HFD. Noteworthy, compared to mice that were chow-fed, the HFD did not impair peroxide removal nor elicit redox imbalance in mitochondria from Nnt+/+ mice. Therefore, HFD interacted with Nnt mutation to generate PDH inhibition and further suppression of peroxide removal. We conclude that NNT plays a critical role in counteracting mitochondrial redox imbalance, PDH inhibition and advancement of NAFLD in mice fed a HFD. The present study provide seminal experimental evidence that redox imbalance in liver mitochondria potentiates the progression from simple steatosis to steatohepatitis following a HFD.