Mitochondrial uncoupling reduces exercise capacity despite several skeletal muscle metabolic adaptations

Protective effects of 2,4-dinitrophenol in okadaic acid-induced cellular model of Alzheimer's disease

Alzheimer's disease (AD) research started several decades ago and despite the many efforts employed to develop new treatments or approaches to slow and/or revert disease progression, AD treatment remains an unsolved issue. Knowing that mitochondria loss of function is a central hub for many AD-associated pathophysiological processes, there has been renewed interest in exploring mitochondria as targets for intervention. In this perspective, the present study was aimed to investigate the possible beneficial effects of 2,4 dinitrophenol (DNP), a mitochondrial uncoupler agent, in an in vitro model of AD. Retinoic acid-induced differentiated SH-SY5Y cells were incubated with okadaic acid (OA), a neurotoxin often used as an AD experimental model, and/or with DNP. OA caused a decrease in neuronal cells viability, induced multiple mitochondrial anomalies including increased levels of reactive oxygen species, decreased bioenergetics and mitochondria content markers, and an altered mitochondria morphology. OA-treated cells also presented increased lipid peroxidation levels, and overactivation of tau related kinases (GSK3β, ERK1/2 and AMPK) alongside with a significant augment in tau protein phosphorylation levels. Interestingly, DNP co-treatment ameliorated and rescued OA-induced detrimental effects not only on mitochondria but also but also reinstated signaling pathways homeostasis and ameliorated tau pathology. Overall, our results show for the first time that DNP has the potential to preserve mitochondria homeostasis under a toxic insult, like OA exposure, as well as to reestablish cellular signaling homeostasis. These observations foster the idea that DNP, as a mitochondrial modulator, might represent a new avenue for treatment of AD.

Quantifying energy expenditure in Göttingen Minipigs with the 13C-bicarbonate method under basal and drug-treated conditions

Effective treatments of obesity focusing on energy expenditure (EE) are needed. To evaluate future EE-modulating drug candidates, appropriate animal models and methods to assess EE are needed. This study aimed to evaluate the stable isotope 13C-bicarbonate method (13C-BM) for estimating EE in Göttingen minipigs under basal and drug-treated conditions. Four experiments (Expt.1-4) were conducted to assess: 1) the 13C-BM reproducibility using breath sample collection (n = 8), on two consecutive days, 2) the effect of two dose levels (5 and 10 mg/kg body weight (BW)) of the mitochondrial uncoupler dinitrophenol (DNP) in a crossover design (n = 8), 3) sampling method agreement; blood vs. exhaled air (n = 6) and 4) 13C-BM using constant isotope infusion compared with indirect calorimetry (IC) (n = 3). Results correlated significantly (p < 0.001) between days (Expt.1), with an average coefficient of variance of 5.4 ± 2.3%. Administration of 10 mg DNP/kg BW increased (p < 0.01) EE by 33.2 ± 6.4% (Expt.2). Results based on different sampling methods correlated significantly (p < 0.001) and EE increased after 10 mg DNP/kg BW (p < 0.05) in Expt.3. However, results based on blood sampling were significantly higher (p < 0.01) than those of exhaled air. No effect of DNP and significantly different EE results (p < 0.05) was observed in a limited number of animals, when constant isotope infusion and blood sampling was compared with IC (Expt.4). In conclusion, the 13C-BM is useful for investigating treatment effects on EE in minipigs. However, further validation under standardized conditions is needed to provide accurate estimates of the 13C recovery factor and respiratory quotient, both of decisive importance when using the 13C-BM.

Postictal hypoxia involves reactive oxygen species and is ameliorated by chronic mitochondrial uncoupling

Prolonged severe hypoxia follows brief seizures and represents a mechanism underlying several negative postictal manifestations without interventions. Approximately 50% of the postictal hypoxia phenomenon can be accounted for by arteriole vasoconstriction. What accounts for the rest of the drop in unbound oxygen is unclear. Here, we determined the effect of pharmacological modulation of mitochondrial function on tissue oxygenation in the hippocampus of rats after repeatedly evoked seizures. Rats were treated with mitochondrial uncoupler 2,4 dinitrophenol (DNP) or antioxidants. Oxygen profiles were recorded using a chronically implanted oxygen-sensing probe, before, during, and after seizure induction. Mitochondrial function and redox tone were measured using in vitro mitochondrial assays and immunohistochemistry. Postictal cognitive impairment was assessed using the novel object recognition task. Mild mitochondrial uncoupling by DNP raised hippocampal oxygen tension and ameliorated postictal hypoxia. Chronic DNP also lowered mitochondrial oxygen-derived reactive species and oxidative stress in the hippocampus during postictal hypoxia. Uncoupling the mitochondria exerts therapeutic benefits on postictal cognitive dysfunction. Finally, antioxidants do not affect postictal hypoxia, but protect the brain from associated cognitive deficits. We provided evidence for a metabolic component of the prolonged oxygen deprivation that follow seizures and its pathological sequelae. Furthermore, we identified a molecular underpinning of this metabolic component, which involves excessive oxygen conversion into reactive species. Mild mitochondrial uncoupling may be a potential therapeutic strategy to treat the postictal state where seizure control is absent or poor.

Synergistic survival-related effects of larval exposure to an aquatic pollutant and food stress get stronger during and especially after metamorphosis and shape fitness of terrestrial adults

To improve the ecological risk assessment of aquatic pollutants it is needed to study their effects not only in the aquatic larval stage, but also in the terrestrial adult stage of the many animals with a complex life cycle. This remains understudied, especially with regard to interactive effects between aquatic pollutants and natural abiotic stressors. We studied effects of exposure to the pesticide DNP (2,4-Dinitrophenol) and how these were modulated by limited food availability in the aquatic larvae, and the possible delayed effects in the terrestrial adults of the damselfly Lestes viridis. Our results revealed that DNP and low food each had large negative effects on the life history, behaviour and to a lesser extent on the physiology of not only the larvae, but also the adults. Food limitation magnified the negative effects of DNP as seen by a strong decline in larval survival, metamorphosis success and adult lifespan. Notably, the synergism between the aquatic pollutant and food limitation for survival-related traits was stronger in the non-exposed adults than in the exposed larvae, likely because metamorphosis is stressful itself. Our results highlight that identifying effects of aquatic pollutants and synergisms with natural abiotic stressors, not only in the aquatic larval but also in the terrestrial adult stage, is crucial to fully assess the ecological impact of aquatic pollutants and to reveal the impact on the receiving terrestrial ecosystem through a changed aquatic-terrestrial subsidy.

Variations in cost of transport and their ecological consequences: a review

Movement is essential in the ecology of most animals, and it typically consumes a large proportion of individual energy budgets. Environmental conditions modulate the energetic cost of movement (cost of transport, COT), and there are pronounced differences in COT between individuals within species and across species. Differences in morphology affect COT, but the physiological mechanisms underlying variation in COT remain unresolved. Candidates include mitochondrial efficiency and the efficiency of muscle contraction-relaxation dynamics. Animals can offset increased COT behaviourally by adjusting movement rate and habitat selection. Here, we review the theory underlying COT and the impact of environmental changes on COT. Increasing temperatures, in particular, increase COT and its variability between individuals. Thermal acclimation and exercise can affect COT, but this is not consistent across taxa. Anthropogenic pollutants can increase COT, although few chemical pollutants have been investigated. Ecologically, COT may modify the allocation of energy to different fitness-related functions, and thereby influence fitness of individuals, and the dynamics of animal groups and communities. Future research should consider the effects of multiple stressors on COT, including a broader range of pollutants, the underlying mechanisms of COT and experimental quantifications of potential COT-induced allocation trade-offs.

Fifty Years of Research on Protonophores: Mitochondrial Uncoupling As a Basis for Therapeutic Action

Protonophores are compounds capable of electrogenic transport of protons across membranes. Protonophores have been intensively studied over the past 50 years owing to their ability to uncouple oxidation and phosphorylation in mitochondria and chloroplasts. The action mechanism of classical uncouplers, such as DNP and CCCP, in mitochondria is believed to be related to their protonophoric activity; i.e., their ability to transfer protons across the lipid part of the mitochondrial membrane. Given the recently revealed deviations in the correlation between the protonophoric activity of some uncouplers and their ability to stimulate mitochondrial respiration, this review addresses the involvement of some proteins of the inner mitochondrial membrane, such as the ATP/ADP antiporter, dicarboxylate carrier, and ATPase, in the uncoupling process. However, these deviations do not contradict the Mitchell theory but point to a more complex nature of the interaction of DNP, CCCP, and other uncouplers with mitochondrial membranes. Therefore, a detailed investigation of the action mechanism of uncouplers is required for a more successful pharmacological use, including their antibacterial, antiviral, anticancer, as well as cardio-, neuro-, and nephroprotective effects.

Neuroprotective Potential of Mild Uncoupling in Mitochondria. Pros and Cons

There has been an explosion of interest in the use of uncouplers of oxidative phosphorylation in mitochondria in the treatment of several pathologies, including neurological ones. In this review, we analyzed all the mechanisms associated with mitochondrial uncoupling and the metabolic and signaling cascades triggered by uncouplers. We provide a full set of positive and negative effects that should be taken into account when using uncouplers in experiments and clinical practice.

Down syndrome is an oxidative phosphorylation disorder

Down syndrome is the most common genomic disorder of intellectual disability and is caused by trisomy of chromosome 21. Several genes in this chromosome repress mitochondrial biogenesis. The goal of this study was to evaluate whether early overexpression of these genes may cause a prenatal impairment of oxidative phosphorylation negatively affecting neurogenesis. Reduction in the mitochondrial energy production and a lower mitochondrial function have been reported in diverse tissues or cell types, and also at any age, including early fetuses, suggesting that a defect in oxidative phosphorylation is an early and general event in Down syndrome individuals. Moreover, many of the medical conditions associated with Down syndrome are also frequently found in patients with oxidative phosphorylation disease. Several drugs that enhance mitochondrial biogenesis are nowadays available and some of them have been already tested in mouse models of Down syndrome restoring neurogenesis and cognitive defects. Because neurogenesis relies on a correct mitochondrial function and critical periods of brain development occur mainly in the prenatal and early neonatal stages, therapeutic approaches intended to improve oxidative phosphorylation should be provided in these periods.

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Several chromosome 21-encoded proteins repress mitochondrial biogenesis.

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These proteins are overexpressed in fetal brains of Down syndrome (DS) individuals.

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Oxidative phosphorylation function is essential for neurogenesis.

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Upregulation of these proteins adversely impact on neurogenesis.

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Prenatal therapy with drugs inhibiting these proteins would increase DS neurogenesis.

Intraoperative Perfusion Assessment in Enhanced Reality Using Quantitative Optical Imaging: An Experimental Study in a Pancreatic Partial Ischemia Model

To reduce the risk of pancreatic fistula after pancreatectomy, a satisfactory blood flow at the pancreatic stump is considered crucial. Our group has developed and validated a real-time computational imaging analysis of tissue perfusion, using fluorescence imaging, the fluorescence-based enhanced reality (FLER). Hyperspectral imaging (HSI) is another emerging technology, which provides tissue-specific spectral signatures, allowing for perfusion quantification. Both imaging modalities were employed to estimate perfusion in a porcine model of partial pancreatic ischemia. Perfusion quantification was assessed using the metrics of both imaging modalities (slope of the time to reach maximum fluorescence intensity and tissue oxygen saturation (StO2), for FLER and HSI, respectively). We found that the HSI-StO2 and the FLER slope were statistically correlated using the Spearman analysis (R = 0.697; p = 0.013). Local capillary lactate values were statistically correlated to the HSI-StO2 and to the FLER slope (R = −0.88; p < 0.001 and R = −0.608; p = 0.0074). HSI-based and FLER-based lactate prediction models had statistically similar predictive abilities (p = 0.112). Both modalities are promising to assess real-time pancreatic perfusion. Clinical translation in human pancreatic surgery is currently underway.

Computer-assisted quantification and visualization of bowel perfusion using fluorescence-based enhanced reality in left-sided colonic resections

BACKGROUND

Fluorescence-based enhanced reality (FLER) is a computer-based quantification method of fluorescence angiographies to evaluate bowel perfusion. The aim of this prospective trial was to assess the clinical feasibility and to correlate FLER with metabolic markers of perfusion, during colorectal resections.

METHODS

FLER analysis and visualization was performed in 22 patients (diverticulitis n = 17; colorectal cancer n = 5) intra- and extra-abdominally during distal and proximal resection, respectively. The fluorescence signal of indocyanine green (0.2 mg/kg) was captured using a near-infrared camera and computed to create a virtual color-coded cartography. This was overlaid onto the bowel (enhanced reality). It helped to identify regions of interest (ROIs) where samples were subsequently obtained. Resections were performed strictly guided according to clinical decision. On the surgical specimen, samplings were made at different ROIs to measure intestinal lactates (mmol/L) and mitochondria efficiency as acceptor control ratio (ACR).

RESULTS

The native (unquantified) fluorescent signal diffused to obvious ischemic areas during the distal appreciation. Proximally, a lower diffusion of ICG was observed. Five anastomotic complications occurred. The expected values of local capillary lactates were correlated with the measured values both proximally (3.62 ± 2.48 expected vs. 3.17 ± 2.8 actual; rho 0.89; p = 0.0006) and distally (4.5 ± 3 expected vs. 4 ± 2.5 actual; rho 0.73; p = 0.0021). FLER values correlated with ACR at the proximal site (rho 0.76; p = 0.04) and at the ischemic zone (rho 0.71; p = 0.01). In complicated cases, lactates at the proximal resection site were higher (5.8 ± 4.5) as opposed to uncomplicated cases (2.45 ± 1.5; p = 0.008). ACR was reduced proximally in complicated (1.3 ± 0.18) vs. uncomplicated cases (1.68 ± 0.3; p = 0.023).

CONCLUSIONS

FLER allows to image the quantified fluorescence signal in augmented reality and provides a reproducible estimation of bowel perfusion (NCT02626091).

Mitochondrial Uncoupling: A Key Controller of Biological Processes in Physiology and Diseases

Mitochondrial uncoupling can be defined as a dissociation between mitochondrial membrane potential generation and its use for mitochondria-dependent ATP synthesis. Although this process was originally considered a mitochondrial dysfunction, the identification of UCP-1 as an endogenous physiological uncoupling protein suggests that the process could be involved in many other biological processes. In this review, we first compare the mitochondrial uncoupling agents available in term of mechanistic and non-specific effects. Proteins regulating mitochondrial uncoupling, as well as chemical compounds with uncoupling properties are discussed. Second, we summarize the most recent findings linking mitochondrial uncoupling and other cellular or biological processes, such as bulk and specific autophagy, reactive oxygen species production, protein secretion, cell death, physical exercise, metabolic adaptations in adipose tissue, and cell signaling. Finally, we show how mitochondrial uncoupling could be used to treat several human diseases, such as obesity, cardiovascular diseases, or neurological disorders.

Cost of transport is a repeatable trait but is not determined by mitochondrial efficiency in zebrafish (Danio rerio)

The energy used to move a given distance (cost of transport; CoT) varies significantly between individuals of the same species. A lower CoT allows animals to allocate more of their energy budget to growth and reproduction. A higher CoT may cause animals to adjust their movement across different environmental gradients to reduce energy allocated to movement. The aim of this project was to determine whether CoT is a repeatable trait within individuals, and to determine its physiological causes and ecological consequences. We found that CoT is a repeatable trait in zebrafish (Danio rerio). We rejected the hypothesis that mitochondrial efficiency (P/O ratios) predicted CoT. We also rejected the hypothesis that CoT is modulated by temperature acclimation, exercise training or their interaction, although CoT increased with increasing acute test temperature. There was a weak but significant negative correlation between CoT and dispersal, measured as the number of exploration decisions made by fish, and the distance travelled against the current in an artificial stream. However, CoT was not correlated with the voluntary speed of fish moving against the current. The implication of these results is that CoT reflects a fixed physiological phenotype of an individual, which is not plastic in response to persistent environmental changes. Consequently, individuals may have fundamentally different energy budgets as they move across environments, and may adjust movement patterns as a result of allocation trade-offs. It was surprising that mitochondrial efficiency did not explain differences in CoT, and our working hypothesis is that the energetics of muscle contraction and relaxation may determine CoT. The increase in CoT with increasing acute environmental temperature means that warming environments will increase the proportion of the energy budget allocated to locomotion unless individuals adjust their movement patterns.

2,4 Dinitrophenol Attenuates Mitochondrial Dysfunction and Improves Neurobehavioral Outcomes Postanoxia in Neonatal Rats

Following anoxia, a rapid and marked mitochondrial-linked cell death occurs in the cerebral cortex of newborn rats which leads to insult advancement within a couple of days and causes lifelong neurobehavioral abnormalities. The present study investigated the role of 2,4 dinitrophenol (2,4 DNP) in three doses, i.e.,1, 2.5, and 5 mg/kg on anoxia-induced time-dependent mitochondrial dysfunction and associated neurobehavioral outcome using a well-established global model of anoxia. Briefly, rat pups of 30-h age (P2) were subjected to two episodes of anoxia (10 min each) at 24 h of the time interval in an enclosed chamber supplied with 100% N₂ and immersed in a water bath (35-37 °C) to avoid hypothermia. Results demonstrated that the uncoupler 2,4 DNP, in the dose 2.5 and 5 mg/kg injected i.p. within 5 min after second anoxic episode significantly (P < 0.05) preserved mitochondrial function on day 7 preferentially by maintaining mitochondrial membrane potential (MMP) and inhibiting mitochondrial permeability transition (MPT) pore. Further, 2,4 DNP preserved mitochondrial function by improving different states of mitochondrial respiration (s2, s3, s4, s5), respiratory control ratio (RCR), antioxidant enzyme system like superoxide dismutase (SOD) and catalase (CAT), and mitochondrial complex enzymes (I, II, IV, V) after anoxia. Furthermore, a marked decrease in the levels of expression of cytochrome C (cyt C) and pro-apoptotic (Bcl-2 family) and apoptotic (caspase-9/3) proteins was observed on day 7 indicating that the treatment with 2,4 DNP prevented mitochondrial dysfunction and further insult progression (day 1 to day 7). Moreover, 2,4 DNP decreased the apoptotic cell death on day 7 and overall improved the neurobehavioral outcomes like reflex latency and hanging latency which suggests its role in treating neonatal anoxia.

Protective role of Parkin in skeletal muscle contractile and mitochondrial function

KEY POINTS

Parkin, an E3 ubiquitin ligase encoded by the Park2 gene, has been implicated in the regulation of mitophagy, a quality control process in which defective mitochondria are degraded. The exact physiological significance of Parkin in regulating mitochondrial function and contractility in skeletal muscle remains largely unexplored. Using Park2^-/- mice, we show that Parkin ablation causes a decrease in muscle specific force, a severe decrease in mitochondrial respiration, mitochondrial uncoupling and an increased susceptibility to opening of the permeability transition pore. These results demonstrate that Parkin plays a protective role in the maintenance of normal mitochondrial and contractile functions in skeletal muscles.

ABSTRACT

Parkin is an E3 ubiquitin ligase encoded by the Park2 gene. Parkin has been implicated in the regulation of mitophagy, a quality control process in which defective mitochondria are sequestered in autophagosomes and delivered to lysosomes for degradation. Although Parkin has been mainly studied for its implication in neuronal degeneration in Parkinson disease, its role in other tissues remains largely unknown. In the present study, we investigated the skeletal muscles of Park2 knockout (Park2^-/- ) mice to test the hypothesis that Parkin plays a physiological role in mitochondrial quality control in normal skeletal muscle, a tissue highly reliant on mitochondrial content and function. We first show that the tibialis anterior (TA) of Park2^-/- mice display a slight but significant decrease in its specific force. Park2^-/- muscles also show a trend for type IIB fibre hypertrophy without alteration in muscle fibre type proportion. Compared to Park2^+/+ muscles, the mitochondrial function of Park2^-/- skeletal muscles was significantly impaired, as indicated by the significant decrease in ADP-stimulated mitochondrial respiratory rates, uncoupling, reduced activities of respiratory chain complexes containing mitochondrial DNA (mtDNA)-encoded subunits and increased susceptibility to opening of the permeability transition pore. Muscles of Park2^-/- mice also displayed a decrease in the content of the mitochondrial pro-fusion protein Mfn2 and an increase in the pro-fission protein Drp1 suggesting an increase in mitochondrial fragmentation. Finally, Park2 ablation resulted in an increase in basal autophagic flux in skeletal muscles. Overall, the results of the present study demonstrate that Parkin plays a protective role in the maintenance of normal mitochondrial and contractile functions in normal skeletal muscles.

Exercise Training Reveals Inflexibility of the Diaphragm in an Animal Model of Patients With Obesity-Driven Heart Failure With a Preserved Ejection Fraction

BACKGROUND

Respiratory muscle weakness contributes to exercise intolerance in patients with heart failure with a preserved ejection fraction (HFpEF)-a condition characterized by multiple comorbidities with few proven treatments. We aimed, therefore, to provide novel insight into the underlying diaphragmatic alterations that occur in HFpEF by using an obese cardiometabolic rat model and further assessed whether exercise training performed only after the development of overt HFpEF could reverse impairments.

METHODS AND RESULTS

Obese ZSF1 rats (n=12) were compared with their lean controls (n=8) at 20 weeks, with 3 additional groups of obese ZSF1 rats compared at 28 weeks following 8 weeks of either sedentary behavior (n=13), high-intensity interval training (n=11), or moderate-continuous training (n=11). Obese rats developed an obvious HFpEF phenotype at 20 and 28 weeks. In the diaphragm at 20 weeks, HFpEF induced a shift towards an oxidative phenotype and a fiber hypertrophy paralleled by a lower protein expression in MuRF1 and MuRF2, yet mitochondrial and contractile functional impairments were observed. At 28 weeks, neither the exercise training regimen of high-intensity interval training or moderate-continuous training reversed any of the diaphragm alterations induced by HFpEF.

CONCLUSIONS

This study, using a well-characterized rat model of HFpEF underpinned by multiple comorbidities and exercise intolerance (ie, one that closely resembles the patient phenotype), provides evidence that diaphragm alterations and dysfunction induced in overt HFpEF are not reversed following 8 weeks of aerobic exercise training. As such, whether alternative therapeutic interventions are required to treat respiratory muscle weakness in HFpEF warrants further investigation.

Mitochondrial respiration in highly aerobic canines in the non-raced state and after a 1600-km sled dog race

At the annual Iditarod Race, Alaskan Huskies repeatedly run for up to 8 hours at 16 km/h to complete 1600 km. We previously demonstrated high rates of mitochondrial protein synthesis in Alaskan Huskies, which we suspected allowed rapid remodeling of mitochondrial proteins in response to energetic stress. The purpose of this study was to examine mitochondrial respiration in permeabilized skeletal muscle fibers of Alaskan Huskies in the offseason (Non-raced) and following the 1600 km Iditarod Sled Dog Race (Raced). We hypothesized that compared to Non-raced Huskies, raced Huskies that completed a 1600 km race would have greater mitochondrial respiratory capacities, and improvements in capacities of oxidative phosphorylation (OXPHOS) based on NADH-generating substrates as compared to fatty acids. Using high-resolution respirometry (HRR) we investigated the respiration of permeabilized muscle fibers from Alaskan Huskies. Maximum capacities were 254±26 pmol^.s^-1.mg^-1 for OXPHOS (coupled, P) and 254±37 pmol^.s^-1.mg^-1 for the electron transfer system (ETS; non-coupled, E). After racing respiratory capacities from NADH-linked substrates, but not fat-derived substrates increased. Finally, the OXPHOS to ETS capacity ratio (P/E) increased after racing from 0.90±0.03 to 0.97±0.02. From our previous studies and the current study, we conclude that Alaskan Huskies maintain high mitochondrial protein turnover to facilitate rapid adaptation to environmental extremes and energetic challenges.

Obesity and neuroinflammatory phenotype in mice lacking endothelial megalin

BACKGROUND

The multiligand receptor megalin controls the brain uptake of a number of ligands, including insulin and leptin. Despite the role of megalin in the transport of these metabolically relevant hormones, the role of megalin at the blood-brain-barrier (BBB) has not yet been explored in the context of metabolic regulation.

METHODS

Here we investigate the role of brain endothelial megalin in energy metabolism and leptin signaling using an endothelial cell-specific megalin deficient (EMD) mouse model.

RESULTS

We found megalin is important to protect mice from developing obesity and metabolic syndrome when mice are fed a normal chow diet. EMD mice developed neuroinflammation, by triggering several pro-inflammatory cytokines, displayed reduced neurogenesis and mitochondrial deregulation.

CONCLUSIONS

These results implicate brain endothelial megalin expression in obesity-related metabolic changes through the leptin signaling pathway proposing a potential link between obesity and neurodegeneration.

Mitochondria-targeted dodecyltriphenylphosphonium (C12TPP) combats high-fat-diet-induced obesity in mice

Background:

A membrane-penetrating cation, dodecyltriphenylphosphonium (C₁₂TPP), facilitates the recycling of fatty acids in the artificial lipid membrane and mitochondria. C₁₂TPP can dissipate mitochondrial membrane potential and may affect total energy expenditure and body weight in animals and humans.

Methods:

We investigated the metabolic effects of C₁₂TPP in isolated brown-fat mitochondria, brown adipocyte cultures and mice in vivo. Experimental approaches included the measurement of oxygen consumption, carbon dioxide production, western blotting, magnetic resonance imaging and bomb calorimetry.

Results:

In mice, C₁₂TPP (50 μmol per (day•kg body weight)) in the drinking water significantly reduced body weight (12%, P<0.001) and body fat mass (24%, P<0.001) during the first 7 days of treatment. C₁₂TPP did not affect water palatability and intake or the energy and lipid content in feces. The addition of C₁₂TPP to isolated brown-fat mitochondria resulted in increased oxygen consumption. Three hours of pretreatment with C₁₂TPP also increased oligomycin-insensitive oxygen consumption in brown adipocyte cultures (P<0.01). The effects of C₁₂TPP on mitochondria, cells and mice were independent of uncoupling protein 1 (UCP1). However, C₁₂TPP treatment increased the mitochondrial protein levels in the brown adipose tissue of both wild-type and UCP1-knockout mice. Pair-feeding revealed that one-third of the body weight loss in C₁₂TPP-treated mice was due to reduced food intake. C₁₂TPP treatment elevated the resting metabolic rate (RMR) by up to 18% (P<0.05) compared with pair-fed animals. C₁₂TPP reduced the respiratory exchange ratio, indicating enhanced fatty acid oxidation in mice.

Conclusions:

C₁₂TPP combats diet-induced obesity by reducing food intake, increasing the RMR and enhancing fatty acid oxidation.

Novel Mitochondrial Cationic Uncoupler C4R1 Is an Effective Treatment for Combating Obesity in Mice

Obesity is associated with premature mortality, impaired quality of life, and large healthcare costs. However, treatment options remain quite limited. Here we studied potential anti-obesity effects of a novel cationic mitochondrial uncoupler, C4R1 (derivative of rhodamine 19) in C57Bl/6 mice. Obesity was induced by long-term (eight weeks) high fat diet feeding at thermoneutrality. The treated group of mice received consecutively two doses of C4R1 in drinking water (30 and 12-14 µmol/kg daily) during 30 days. Effects of C4R1 were dose-dependent. After six days of C4R1 treatment at dose 30 µmol/kg daily, food intake was reduced by 68%, body weight by 19%, and fat mass by 21%. Body weight decrease was explained partly by reduced food intake and partly by increased metabolism, likely resulting from uncoupling. Body fat reduction upon C4R1 treatment was associated with improved lipid utilization estimated from decrease in respiratory quotient to the minimal level (0.7). Interestingly, the classical uncoupler 2,4-dinitrophenol at similar dose (27 µmol/kg daily) did not have any effect. Our results are relevant to the search for substances causing mild uncoupling of mitochondria that could be a promising therapeutic strategy to treat obesity.

UCP2- and non-UCP2-mediated electric current in eukaryotic cells exhibits different properties

Using live eukaryotic cells, including cancer cells, MCF-7 and HCT-116, normal hepatocytes and red blood cells in anode and potassium ferricyanide in cathode of MFC could generate bio-based electric current. Electrons and protons generated from the metabolic reaction in both cytosol and mitochondria contributing to the leaking would mediate the generation of electric current. Both resveratrol (RVT) and 2,4-dinitrophenol (DNP) used to induce proton leak in mitochondria were found to promote electric current production in all cells except red blood cells without mitochondria. Proton leak might be important for electric current production by bringing the charge balance in cells to enhance the further electron leak. The induced electric current by RVT can be blocked by Genipin, an inhibitor of UCP2-mediated proton leak, while that induced by DNP cannot. RVT could reduce reactive oxygen species (ROS) level in cells better than that of DNP. In addition, RVT increased mitochondrial membrane potential (MMP), while DNP decreased it. Results highly suggested the existence of at least two types of electric current that showed different properties. They included UCP2-mediated and non-UCP2-mediated electric current. UCP2-mediated electric current exhibited higher reactive oxygen species (ROS) reduction effect per unit electric current production than that of non-UCP2-mediated electric current. Higher UCP2-mediated electric current observed in cancer cells might contribute to the mechanism of drug resistence. Correlation could not be established between electric current production with either ROS and MMP without distinguishing the types of electric current.

Echinochrome A Improves Exercise Capacity during Short-Term Endurance Training in Rats

Echinochrome A (Echi A) improves mitochondrial function in the heart; however, its effects on skeletal muscle are still unclear. We hypothesized that Echi A administration during short-term exercise may improve exercise capacity. Twenty-four male Sprague-Dawley rats were randomly divided into the following groups: control group (CG), Echi A-treated group (EG), aerobic exercise group (AG), and aerobic exercise treated with Echi A group (AEG) (n = 6 per group). Echi A was administered intra-peritoneally (0.1 mg/kg of Echi A in 300 µL phosphate-buffered saline) daily 30 min before each exercise training. The AG and AEG groups performed treadmill running (20 m/min, 60 min/day) five days/week for two weeks. The exercise capacity was significantly higher in the AG and AEG groups compared to other groups. Interestingly, the exercise capacity increased more effectively in the AEG group. The body weight in the EG tended to be slightly lower than that in the other groups. There were no significant changes in the plasma lipids among the groups. However, the gastrocnemius muscle mitochondria content was greater in the EG and AEG groups. These findings show that Echi A administration after short-term endurance training enhances exercise capacity, which was associated with an increase in skeletal muscle mitochondrial content.

Metabolism-Guided Bowel Resection

Background. Strip-based handheld devices can measure lactatemia on capillary blood obtained by needle puncturing. We aimed to assess the kinetic of bowel capillary lactates, metabolomics profiling, and mitochondria respiratory rate in a prolonged model of bowel hypoperfusion. Materials and Methods. In 6 pigs, a 3- to 4-cm ischemic segment was created in 6 small bowel loops (total = 36 loops) by clamping the vascular supply, for a duration of 1 to 6 hours. Hourly, 5 blood samples were obtained by puncturing the serosa, and lactates were measured using a handheld analyzer. Samples were made at the following regions of interest (ROIs): center of the ischemic area (1), proximal and distal clinical margins of resection (2a-2b), and vascularized zones (3a-3b). Every hour, surgical biopsies of ROIs were sampled. Activity of bowel mitochondria complexes was measured after 1, 3, and 5 hours of ischemia. Quantification of metabolites was performed on all samples (total N = 180). Results. Capillary lactates were significantly higher at ROI 1 versus ROI 3ab at all time points. After 1 hour lactates at the margins were significantly higher than those at vascularized areas ( P = .0095), showing a mismatch between visual assessment and actual perfusion status. From 2 to 6 hours, there was no difference in lactates between ROIs 2a-2b and 3a-3b. Maximal tissue respiration decreased significantly after 1 hour (ROI 1 vs ROI 3ab). Seven metabolites (lactate, glucose, aspartate, choline, creatine, taurine, and tyrosine) expressed significantly different evolutions between ROIs. Conclusions. Capillary lactates could help precisely estimate local bowel perfusion status.

Regular postexercise cooling enhances mitochondrial biogenesis through AMPK and p38 MAPK in human skeletal muscle

This study investigated the effect of regular postexercise cold water immersion (CWI) on muscle aerobic adaptations to endurance training. Eight males performed 3 sessions/wk of endurance training for 4 wk. Following each session, subjects immersed one leg in a cold water bath (10°C; COLD) for 15 min, while the contralateral leg served as a control (CON). Muscle biopsies were obtained from vastus lateralis of both CON and COLD legs prior to training and 48 h following the last training session. Samples were analyzed for signaling kinases: p38 MAPK and AMPK, peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), enzyme activities indicative of mitochondrial biogenesis, and protein subunits representative of respiratory chain complexes I-V. Following training, subjects' peak oxygen uptake and running velocity were improved by 5.9% and 6.2%, respectively (P < 0.05). Repeated CWI resulted in higher total AMPK, phosphorylated AMPK, phosphorylated acetyl-CoA carboxylase, β-3-hydroxyacyl-CoA-dehydrogenase and the protein subunits representative of complex I and III (P < 0.05). Moreover, large effect sizes (Cohen's d > 0.8) were noted with changes in protein content of p38 (d = 1.02, P = 0.064), PGC-1α (d = 0.99, P = 0.079), and peroxisome proliferator-activated receptor α (d = 0.93, P = 0.10) in COLD compared with CON. No differences between conditions were observed in the representative protein subunits of respiratory complexes II, IV, and V and in the activities of several mitochondrial enzymes (P > 0.05). These findings indicate that regular CWI enhances p38, AMPK, and possibly mitochondrial biogenesis.

Mitochondrial uncoupling as a regulator of life-history trajectories in birds: an experimental study in the zebra finch

Mitochondria have a fundamental role in the transduction of energy from food into ATP. The coupling between food oxidation and ATP production is never perfect, but may nevertheless be of evolutionary significance. The 'uncoupling to survive' hypothesis suggests that 'mild' mitochondrial uncoupling evolved as a protective mechanism against the excessive production of damaging reactive oxygen species (ROS). Because resource allocation and ROS production are thought to shape animal life histories, alternative life-history trajectories might be driven by individual variation in the degree of mitochondrial uncoupling. We tested this hypothesis in a small bird species, the zebra finch (Taeniopygia guttata), by treating adults with the artificial mitochondrial uncoupler 2,4-dinitrophenol (DNP) over a 32-month period. In agreement with our expectations, the uncoupling treatment increased metabolic rate. However, we found no evidence that treated birds enjoyed lower oxidative stress levels or greater survival rates, in contrast to previous results in other taxa. In vitro experiments revealed lower sensitivity of ROS production to DNP in mitochondria isolated from skeletal muscles of zebra finch than mouse. In addition, we found significant reductions in the number of eggs laid and in the inflammatory immune response in treated birds. Altogether, our data suggest that the 'uncoupling to survive' hypothesis may not be applicable for zebra finches, presumably because of lower effects of mitochondrial uncoupling on mitochondrial ROS production in birds than in mammals. Nevertheless, mitochondrial uncoupling appeared to be a potential life-history regulator of traits such as fecundity and immunity at adulthood, even with food supplied ad libitum.