Dietary long-chain, but not medium-chain, triglycerides impair exercise performance and uncouple cardiac mitochondria in rats

A High-Fat Diet Disrupts Nerve Lipids and Mitochondrial Function in Murine Models of Neuropathy

As the prevalence of prediabetes and type 2 diabetes (T2D) continues to increase worldwide, accompanying complications are also on the rise. The most prevalent complication, peripheral neuropathy (PN), is a complex process which remains incompletely understood. Dyslipidemia is an emerging risk factor for PN in both prediabetes and T2D, suggesting that excess lipids damage peripheral nerves; however, the precise lipid changes that contribute to PN are unknown. To identify specific lipid changes associated with PN, we conducted an untargeted lipidomics analysis comparing the effect of high-fat diet (HFD) feeding on lipids in the plasma, liver, and peripheral nerve from three strains of mice (BL6, BTBR, and BKS). HFD feeding triggered distinct strain- and tissue-specific lipid changes, which correlated with PN in BL6 mice versus less robust murine models of metabolic dysfunction and PN (BTBR and BKS mice). The BL6 mice showed significant changes in neutral lipids, phospholipids, lysophospholipids, and plasmalogens within the nerve. Sphingomyelin (SM) and lysophosphatidylethanolamine (LPE) were two lipid species that were unique to HFD BL6 sciatic nerve compared to other strains (BTBR and BKS). Plasma and liver lipids were significantly altered in all murine strains fed a HFD independent of PN status, suggesting that nerve-specific lipid changes contribute to PN pathogenesis. Many of the identified lipids affect mitochondrial function and mitochondrial bioenergetics, which were significantly impaired in ex vivo sural nerve and dorsal root ganglion sensory neurons. Collectively, our data show that consuming a HFD dysregulates the nerve lipidome and mitochondrial function, which may contribute to PN in prediabetes.

Potential Role of Leptin in Cardiac Steatosis Induced by Highly Saturated Fat Intake during Adolescence

SCOPE

To identify the age-dependent effect of diets containing elevated amounts of either saturated or unsaturated fatty acids on cardiac steatosis in mice.

METHODS AND RESULTS

Five- and eight-week-old C57BL/6J mice cohorts are given free access to either a saturated or an unsaturated fatty-acid-enriched diet during 8 weeks. Body weight (BW) and food intake are monitored during this period. Cardiac lipid content, carnitine palmitoyltransferase-I (CPT-I) activity, and the amount of uncoupling proteins 2 and 3 (UCP2 and UCP3) are analyzed and correlated with blood leptin concentration. Leptin and PPARγ gene expression is quantified in white adipose tissue (WAT). Both diets have a similar effect on food intake, BW, and adiposity, independently of the age. Nevertheless, cardiac steatosis is specifically identified in adolescent mice consuming the saturated diet. These animals also display lower activity of cardiac CPT-I, a down-regulation of cardiac UCP2, together with lower concentration of plasma leptin. Accordingly, leptin gene expression is reduced in the visceral WAT.

CONCLUSION

Consumption of diets containing elevated amounts of saturated fat during adolescence and early adult life promotes cardiac steatosis in mice. An insufficient endocrine activity of WAT, in terms of leptin production, may account for such an effect.

Interval running training improves age-related skeletal muscle wasting and bone loss: Experiments with ovariectomized rats

NEW FINDINGS

What is the central question of this study? What is the effect and mechanism of interval running training on age-related muscle wasting and bone loss in an ovariectomized rat model? What is the main finding and its importance? Interval running training improved muscle growth and osteogenic differentiation by enhancing the expression of bone morphogenic proteins and sirtuins in ageing-induced ovariectomized rats. Therefore, the repetition of low and high intensities within a single exercise bout, such as interval running training, may be recommended as a practical intervention to prevent skeletal muscle wasting and bone loss in the elderly.

ABSTRACT

Effective prophylactic strategies are needed for the suppression of age-related muscle wasting and bone loss after menopause. Exercise training is attractive due to its potential for improving energy metabolism, as well as age-related muscle wasting and bone loss. In particular, interval running (IR) training involves a repetition of low and high intensities within a single exercise bout. Therefore, this study elucidated the effect of interval training on muscle and bone health, as well as anti-ageing, in ovariectomized (OVX) rats. The anti-ageing effect of IR on muscle and bone was tested using western blotting and micro-computed tomography analysis, tartrate-resistant acid phosphatase and immunohistochemical staining. IR significantly inhibited the expression of inflammatory molecules, and improved antioxidant activity via down-regulation of mitogen-activated protein kinases (MAPKs) in the ageing-induced OVX rats skeletal muscle. IR compared with continuous running (CR) improved muscle mass and growth in OVX rats by the promotion of muscle growth-related factors including MyoD, myogenin, phospho-mechanistic target of rapamycin (p-mTOR), sirtuins (SIRTs), and bone morphogenic proteins (BMPs). IR also effectively recovered OVX-induced bone loss via the down-regulation of bone resorption and osteoclast formation in receptor activator of nuclear factor κB ligand (RANKL)-treated bone marrowmacrophages (BMMs). In particular, IR led to high expression of SIRT1 and 6, which promoted osteogenic differentiation and bone formation via modulating the BMP signalling pathway compared with CR training. The in vivo effect of IR was confirmed by immunohistochemical staining with the improvement of bone formation molecules such as BMPs and SIRTs. These results suggested that IR training affected myogenic and osteogenic formation. So, IR training may be considered for prevention of muscle wasting and bone loss for the elderly.

Low-fat diet, and medium-fat diets containing coconut oil and soybean oil exert different metabolic effects in untrained and treadmill-trained mice

BACKGROUND

Diets containing fats of different proportions and types have been demonstrated to influence metabolism. These fats differ in long chain fatty acids (LCFAs) or medium chain fatty acids (MCFAs) content. In our laboratory using swimming as the training modality, MCFAs increased endurance attributed to increased activities of oxidative enzymes. How it affects whole-body metabolism remains unexplored. The present study investigated the metabolic, biochemical and genetic adaptations with treadmill running as the training modality.

METHODS

C57BL/6N mice were divided into untrained and trained groups and provided with low-fat (10% kcal from soybean oil), coconut oil (10% kcal from soybean oil, 20% kcal from coconut oil) or soybean oil (30% kcal from soybean oil) diet. Training was performed on a treadmill for 30 days. After recovery, whole-body metabolism at rest and during exercise, endurance, substrate metabolism, mitochondrial enzyme activities, and gene expression of training-adaptive genes in the muscle and liver were measured.

RESULTS

At rest, medium-fat diets decreased respiratory exchange ratio (RER) (p < 0.05). Training increased RER in all diet groups without affecting oxygen consumption (p < 0.05). During exercise, diets had no overt effects on metabolism while training decreased oxygen consumption indicating decreased energy expenditure (p < 0.05). Coconut oil without training improved endurance based on work (p < 0.05). Training improved all endurance parameters without overt effects of diet (p < 0.05). Moreover, training increased the activities of mitochondrial enzymes likely related to the increased expression of estrogen related receptor (ERR) α and ERRβ (p < 0.05). Coconut oil inhibited peroxisome proliferator-activated receptor (PPAR) β/δ activation and glycogen accumulation in the muscle but activated PPARα in the liver in the trained state (p < 0.05). Substrate utilization data suggested that coconut oil and/or resulting ketone bodies spared glycogen utilization in the trained muscle during exercise thereby preserving endurance.

CONCLUSION

Our data demonstrated the various roles of diet and fat types in training adaptation. Diets exerted different roles in PPAR activation and substrate handling in the context of endurance exercise training. However, the role of fat types in training adaptations is limited as training overwhelms and normalizes the effects of diet in the untrained state particularly on endurance performance, mitochondrial biogenesis, and ERR expression.

Coconut Oil Aggravates Pressure Overload-Induced Cardiomyopathy without Inducing Obesity, Systemic Insulin Resistance, or Cardiac Steatosis

Studies evaluating the effects of high-saturated fat diets on cardiac function are most often confounded by diet-induced obesity and by systemic insulin resistance. We evaluated whether coconut oil, containing C12:0 and C14:0 as main fatty acids, aggravates pressure overload-induced cardiomyopathy induced by transverse aortic constriction (TAC) in C57BL/6 mice. Mortality rate after TAC was higher (p < 0.05) in 0.2% cholesterol 10% coconut oil diet-fed mice than in standard chow-fed mice (hazard ratio 2.32, 95% confidence interval 1.16 to 4.64) during eight weeks of follow-up. The effects of coconut oil on cardiac remodeling occurred in the absence of weight gain and of systemic insulin resistance. Wet lung weight was 1.76-fold (p < 0.01) higher in coconut oil mice than in standard chow mice. Myocardial capillary density (p < 0.001) was decreased, interstitial fibrosis was 1.88-fold (p < 0.001) higher, and systolic and diastolic function was worse in coconut oil mice than in standard chow mice. Myocardial glucose uptake was 1.86-fold (p < 0.001) higher in coconut oil mice and was accompanied by higher myocardial pyruvate dehydrogenase levels and higher acetyl-CoA carboxylase levels. The coconut oil diet increased oxidative stress. Myocardial triglycerides and free fatty acids were lower (p < 0.05) in coconut oil mice. In conclusion, coconut oil aggravates pressure overload-induced cardiomyopathy.

Novel ketone diet enhances physical and cognitive performance

Ketone bodies are the most energy-efficient fuel and yield more ATP per mole of substrate than pyruvate and increase the free energy released from ATP hydrolysis. Elevation of circulating ketones via high-fat, low-carbohydrate diets has been used for the treatment of drug-refractory epilepsy and for neurodegenerative diseases, such as Parkinson's disease. Ketones may also be beneficial for muscle and brain in times of stress, such as endurance exercise. The challenge has been to raise circulating ketone levels by using a palatable diet without altering lipid levels. We found that blood ketone levels can be increased and cholesterol and triglycerides decreased by feeding rats a novel ketone ester diet: chow that is supplemented with (R)-3-hydroxybutyl (R)-3-hydroxybutyrate as 30% of calories. For 5 d, rats on the ketone diet ran 32% further on a treadmill than did control rats that ate an isocaloric diet that was supplemented with either corn starch or palm oil (P < 0.05). Ketone-fed rats completed an 8-arm radial maze test 38% faster than did those on the other diets, making more correct decisions before making a mistake (P < 0.05). Isolated, perfused hearts from rats that were fed the ketone diet had greater free energy available from ATP hydrolysis during increased work than did hearts from rats on the other diets as shown by using [31P]-NMR spectroscopy. The novel ketone diet, therefore, improved physical performance and cognitive function in rats, and its energy-sparing properties suggest that it may help to treat a range of human conditions with metabolic abnormalities.-Murray, A. J., Knight, N. S., Cole, M. A., Cochlin, L. E., Carter, E., Tchabanenko, K., Pichulik, T., Gulston, M. K., Atherton, H. J., Schroeder, M. A., Deacon, R. M. J., Kashiwaya, Y., King, M. T., Pawlosky, R., Rawlins, J. N. P., Tyler, D. J., Griffin, J. L., Robertson, J., Veech, R. L., Clarke, K. Novel ketone diet enhances physical and cognitive performance.

Gradual downhill running improves age-related skeletal muscle and bone weakness: implication of autophagy and bone morphogenetic proteins

NEW FINDINGS

What is the central question of this study? Exercise training by running has an effect on age-related muscle and bone wasting that improves physical activity and quality of life in the elderly. However, the effect of downhill running on age-related muscle and bone wasting, and its mechanisms, are unclear. What is the main finding and its importance? Gradual downhill running can improve skeletal muscle growth and bone formation by enhancing autophagy and bone morphogenetic protein signalling in aged rats. Therefore, downhill running exercise might be a practical intervention to improve skeletal muscle and bone protection in the elderly. Recent evidence suggests that autophagy and the bone morphogenetic protein (BMP) signalling pathway regulate skeletal muscle growth and bone formation in aged rats. However, the effect of downhill running on muscle growth and bone formation is not well understood. Thus, we investigated the effect of downhill and uphill running on age-related muscle and bone weakness. Young and late middle-aged rats were randomly assigned to control groups (young, YC; and late middle-aged, LMC) and two types of running training groups (late middle-aged downhill, LMD; and late middle-aged uphill, LMU). Training was progressively carried out on a treadmill at a speed of 21 m min^-1 with a slope of +10 deg for uphill training versus 16 m min^-1 with a slope of -16 deg for downhill training, both for 60 min day^-1 , 5 days week^-1 for 8 weeks. Downhill and uphill training increased autophagy-related protein 5, microtubule-associated protein light chain, Beclin-1 and p62 proteins in aged rats. In addition, superoxide dismutase, haem oxygenase-1 and the BMP signalling pathway were elevated. Phosphorylation of mammalian target of rapamycin and myogenic differentiation were increased significantly in the LMD and LMU groups. Consequently, in the femur, BMP-2, BMP-7 and autophagy molecules were highly expressed in the LMD and LMU groups. These results suggest that both downhill and uphill training appear to have a positive effect on expression of autophagy molecules and BMPs. In particular, these physiological adaptations from gradual downhill exercise have an effect on bone morphological changes and muscle quality similar to gradual uphill training interventions in ageing.

A Ketogenic Diet in Rodents Elicits Improved Mitochondrial Adaptations in Response to Resistance Exercise Training Compared to an Isocaloric Western Diet

Purpose: Ketogenic diets (KD) can facilitate weight loss, but their effects on skeletal muscle remain equivocal. In this experiment we investigated the effects of two diets on skeletal muscle mitochondrial coupling, mitochondrial complex activity, markers of oxidative stress, and gene expression in sedentary and resistance exercised rats. Methods: Male Sprague-Dawley rats (9-10 weeks of age, 300-325 g) were fed isocaloric amounts of either a KD (17 g/day, 5.2 kcal/g, 20.2% protein, 10.3% CHO, 69.5% fat, n = 16) or a Western diet (WD) (20 g/day, 4.5 kcal/g, 15.2% protein, 42.7% CHO, 42.0% fat, n = 16) for 6 weeks. During these 6 weeks animals were either sedentary (SED, n = 8 per diet group) or voluntarily exercised using resistance-loaded running wheels (EXE, n = 8 per diet group). Gastrocnemius was excised and used for mitochondrial isolation and biochemical analyses. Results: In the presence of a complex II substrate, the respiratory control ratio (RCR) of isolated gastrocnemius mitochondria was higher (p < 0.05) in animals fed the KD compared to animals fed the WD. Complex I and IV enzyme activity was higher (p < 0.05) in EXE animals regardless of diet. SOD2 protein levels and GLUT4 and PGC1α mRNA expression were higher (p < 0.05) in EXE animals regardless of diet. Conclusion: Our data indicate that skeletal muscle mitochondrial coupling of complex II substrates is more efficient in chronically resistance trained rodents fed a KD. These findings may provide merit for further investigation, perhaps on humans.

Short- and medium-chain fatty acids in energy metabolism: the cellular perspective

Short- and medium-chain fatty acids (SCFAs and MCFAs), independently of their cellular signaling functions, are important substrates of the energy metabolism and anabolic processes in mammals. SCFAs are mostly generated by colonic bacteria and are predominantly metabolized by enterocytes and liver, whereas MCFAs arise mostly from dietary triglycerides, among them milk and dairy products. A common feature of SCFAs and MCFAs is their carnitine-independent uptake and intramitochondrial activation to acyl-CoA thioesters. Contrary to long-chain fatty acids, the cellular metabolism of SCFAs and MCFAs depends to a lesser extent on fatty acid-binding proteins. SCFAs and MCFAs modulate tissue metabolism of carbohydrates and lipids, as manifested by a mostly inhibitory effect on glycolysis and stimulation of lipogenesis or gluconeogenesis. SCFAs and MCFAs exert no or only weak protonophoric and lytic activities in mitochondria and do not significantly impair the electron transport in the respiratory chain. SCFAs and MCFAs modulate mitochondrial energy production by two mechanisms: they provide reducing equivalents to the respiratory chain and partly decrease efficacy of oxidative ATP synthesis.

Oral Coenzyme Q10 supplementation does not prevent cardiac alterations during a high altitude trek to everest base cAMP

Exposure to high altitude is associated with sustained, but reversible, changes in cardiac mass, diastolic function, and high-energy phosphate metabolism. Whilst the underlying mechanisms remain elusive, tissue hypoxia increases generation of reactive oxygen species (ROS), which can stabilize hypoxia-inducible factor (HIF) transcription factors, bringing about transcriptional changes that suppress oxidative phosphorylation and activate autophagy. We therefore investigated whether oral supplementation with an antioxidant, Coenzyme Q10, prevented the cardiac perturbations associated with altitude exposure. Twenty-three volunteers (10 male, 13 female, 46±3 years) were recruited from the 2009 Caudwell Xtreme Everest Research Treks and studied before, and within 48 h of return from, a 17-day trek to Everest Base Camp, with subjects receiving either no intervention (controls) or 300 mg Coenzyme Q10 per day throughout altitude exposure. Cardiac magnetic resonance imaging and echocardiography were used to assess cardiac morphology and function. Following altitude exposure, body mass fell by 3 kg in all subjects (p<0.001), associated with a loss of body fat and a fall in BMI. Post-trek, left ventricular mass had decreased by 11% in controls (p<0.05) and by 16% in Coenzyme Q10-treated subjects (p<0.001), whereas mitral inflow E/A had decreased by 18% in controls (p<0.05) and by 21% in Coenzyme Q10-treated subjects (p<0.05). Coenzyme Q10 supplementation did not, therefore, prevent the loss of left ventricular mass or change in diastolic function that occurred following a trek to Everest Base Camp.

How exercise may amend metabolic disturbances in diabetic cardiomyopathy

SIGNIFICANCE

Over-nutrition and sedentary lifestyle has led to a worldwide increase in obesity, insulin resistance, and type 2 diabetes (T2D) associated with an increased risk of development of cardiovascular disorders. Diabetic cardiomyopathy, independent of hypertension or coronary disease, is induced by a range of systemic changes and may through multiple processes result in functional and structural cardiac derangements. The pathogenesis of this cardiomyopathy is complex and multifactorial, and it will eventually lead to reduced cardiac working capacity and increased susceptibility to ischemic injury.

RECENT ADVANCES

Metabolic disturbances such as altered lipid handling and substrate utilization, decreased mechanical efficiency, mitochondrial dysfunction, disturbances in nonoxidative glucose pathways, and increased oxidative stress are hallmarks of diabetic cardiomyopathy. Interestingly, several of these disturbances are found to precede the development of cardiac dysfunction.

CRITICAL ISSUES

Exercise training is effective in the prevention and treatment of obesity and T2D. In addition to its beneficial influence on diabetes/obesity-related systemic changes, it may also amend many of the metabolic disturbances characterizing the diabetic myocardium. These changes are due to both indirect effects, exercise-mediated systemic changes, and direct effects originating from the high contractile activity of the heart during physical training.

FUTURE DIRECTIONS

Revealing the molecular mechanisms behind the beneficial effects of exercise training is of considerable scientific value to generate evidence-based therapy and in the development of new treatment strategies.