Improvement In Oxidative Capacity Research Articles

Triheptanoin, an odd-medium-chain triglyceride, impacts brain cognitive function in young and aged mice

ABSTRACT The brain aging process triggers cognitive function impairment, such as memory loss and compromised quality of life. Cognitive impairment is based on bioenergetic status, with reduced glucose uptake and metabolism in aged brains. Anaplerotic substrates are reported to promote mitochondrial ATP generation, having been tested in clinical trials for the treatment of neurological disorders and metabolic diseases. Objectives and Methods: To assess whether the improvement in oxidative capacity ameliorates cognitive function in adults (12 weeks), and aged (22-month-old) C57/6BJ mice, they received (1) a ketogenic diet, (2) a ketogenic diet supplemented with the anaplerotic substance, triheptanoin, or (3) a control diet for 12 weeks. Spontaneous alternation and time spent in a previously closed arm in the Y-maze test and time interacting with an unknown object in the novel object recognition test (NORT) were used to evaluate working memory. Acetylcholinesterase (AChE) activity in the prefrontal lobe, brain left hemisphere, and cerebellum was also evaluated. Glucose transporter 3 (GLUT3) expression in the prefrontal lobe was analyzed by western blotting. Results: The ketogenic diet (KD) reduced spontaneous alternation in aged mice, leading to lower AChE activity in the aged prefrontal lobe and cerebellum, and in the parieto-temporal-occipital lobe of adult mice. Furthermore, KD decreased GLUT3 protein expression in the frontal lobe of the adults. Discussion: Supplementation of KD with triheptanoin prevented memory impairment and showed similar values of AChE activity and GLUT3 expression compared to the controls. Our data suggest that triheptanoin has a potential role in the bioenergetic capacity of the brain, improving cognitive function.

373-OR: Paternal SGLT2 Inhibition Upregulates Hepatic Expression of Oxidative Phosphorylation Genes in Both Fetal and Adult Offspring

Paternal obesity has a detrimental impact on metabolic health of his offspring, suggesting an opportunity for preventive strategies prior to conception. Indeed, treatment of male mice with the SGLT2 inhibitor canagliflozin (CANA, 25mg/kg/d) for 4 weeks prior to breeding reduces obesity, hepatic steatosis, and glycemia in offspring. To identify molecular mediators, we analyzed mRNA-seq in fetal and adult liver from male offspring of fathers treated with chow (pCHOW), 60% high-fat diet (pHFD), or HFD+CANA (pCANA). Differentially expressed genes were identified using Limma (R). In adult offspring, paternal SGLT2 inhibition altered the expression of 213 genes (FDR<0.05, 137 upregulated, 67 downregulated with FC ≥|1.5|, vs. paternal HFD, n=5/group). Pathway analysis revealed enrichment of oxidative phosphorylation and ribosome in upregulated genes, including 11 subunits of complex IV (Cox6b2), complex III (Uqcrq, Uqcr10), complexI(Ndufs7, Ndufa1, Ndufa2/3/7/11) and complex V(Atp5mpl, Atp5e), with similar trend for complex II Sdhb (FC=1.32, FDR=0.07). Mitochondrial DNA (quantitated by NADH dehydrogenase 1 relative to β-globin DNA) did not differ between pCANA and pHFD. To determine whether this pattern was present early in life, before emergence of offspring metabolic phenotypes, we analyzed E16.5 fetal liver. 95 genes were differentially expressed in pCANA vs. pHFD (p<0.05, 55 upregulated, 40 downregulated with FC ≥|1.5|, n=5 vs. n=3); of these, 99% were also inversely regulated by pHFD vs. pChow. 16 OXPHOS genes were downregulated by pHFD but upregulated by pCANA (FC≥|1.2|). ETFB was downregulated by pHFD (FC -1.6), but upregulated by pCANA in both fetal (FC 1.3) and adult (FC 1.5) liver. In summary, paternal CANA modulates liver mitochondrial gene expression in his offspring during both embryonic and adult life, suggesting that improvements in oxidative capacity may mediate the protective effects of paternal SGLT2 inhibition. Disclosure L. Su: None. S. Osataphan: None. C. Macchi: None. J.I. Chimene-Weiss: None. J. Dreyfuss: None. H. Pan: None. M. Patti: Consultant; Self; Fractyl Laboratories, Inc. Research Support; Self; Dexcom, Inc., Xeris Pharmaceuticals, Inc. Other Relationship; Self; Academy of Nutrition and Dietetics, American Diabetes Association, American Society of Metabolic and Bariatric Surgery, Endocrine Society, Insulet Corporation, King Abdullah International Medical Research Center, SUNY Downstate. Funding National Institutes of Health (R01DK106193, P30DK046200)

2536

OBJECTIVES/SPECIFIC AIMS: Obesity is a rapidly growing epidemic and long-term interventions aimed to reduce body weight are largely unsuccessful due to an increased drive to eat and a reduced metabolic rate established during weight loss. Previously, our lab demonstrated that exercise has beneficial effects on weight loss maintenance by increasing total energy expenditure above and beyond the cost of an exercise bout and reducing the drive to eat when allowed to eat ad libitum (relapse). We hypothesized that exercise’s ability to counter these obesogenic-impetuses are mediated via improvements in skeletal muscle oxidative capacity, and tested this using a mouse model with augmented oxidative capacity in skeletal muscle. METHODS/STUDY POPULATION: We recapitulated the exercise-induced improvements in oxidative capacity using FVB mice that overexpress lipoprotein lipase in skeletal muscle (mLPL). mLPL and wild type (WT) mice were put through a weight-loss-weight-regain paradigm consisting of a high fat diet challenge for 13 weeks, with a subsequent 1-week calorie-restricted medium fat diet to induce a ~15% weight loss. This newly established weight was maintained for 2 weeks and followed with a 24-hour relapse. Metabolic phenotype was characterized by indirect calorimetry during each phase. At the conclusion of the relapse day, mice were sacrificed and tissues were harvested for molecular analysis. RESULTS/ANTICIPATED RESULTS: During weight loss maintenance, mLPL mice had a higher metabolic rate (p=0.0256) that was predominantly evident in the dark cycle (p=0.0015). Furthermore, this increased metabolic rate was not due to differences in activity (p=0.2877) or resting metabolic rate (p=0.4881). During relapse, mLPL mice ingested less calories and were protected from rapid weight regain (p=0.0235), despite WT mice exhibiting higher metabolic rates during the light cycle (p=0.0421). DISCUSSION/SIGNIFICANCE OF IMPACT: These results highlight the importance of muscular oxidative capacity in preventing a depression in total energy expenditure during weight loss maintenance, and in curbing overfeeding and weight regain during a relapse. Moreover, our data suggest that the thermic effect of food is responsible for the differences in metabolic rate, because no differences were found in activity or resting metabolic rate. Additional studies are warranted to determine the molecular mechanisms driving the ability of oxidative capacity to assist with weight loss maintenance.

Reduced skeletal muscle oxidative capacity and impaired training adaptations in heart failure.

Systolic heart failure (HF) is associated with exercise intolerance that has been attributed, in part, to skeletal muscle dysfunction. The purpose of this study was to compare skeletal muscle oxidative capacity and training-induced changes in oxidative capacity in participants with and without HF. Participants with HF (n = 16, 65 ± 6.6 years) were compared with control participants without HF (n = 23, 61 ± 5.0 years). A subset of participants (HF: n = 7, controls: n = 5) performed 4 weeks of wrist-flexor exercise training. Skeletal muscle oxidative capacity was determined from the recovery kinetics of muscle oxygen consumption measured by near-infrared spectroscopy (NIRS) following a brief bout of wrist-flexor exercise. Oxidative capacity, prior to exercise training, was significantly lower in the HF participants in both the dominant (1.31 ± 0.30 min−1 vs. 1.59 ± 0.25 min−1, P = 0.002; HF and control groups, respectively) and nondominant arms (1.29 ± 0.24 min−1 vs. 1.46 ± 0.23 min−1, P = 0.04; HF and control groups, respectively). Following 4 weeks of endurance training, there was a significant difference in the training response between HF and controls, as the difference in oxidative training adaptations was 0.69 ± 0.12 min−1 (P < 0.001, 95% CI 0.43, 0.96). The wrist-flexor training induced a ∼50% improvement in oxidative capacity in participants without HF (mean difference from baseline = 0.66 ± 0.09 min−1, P < 0.001, 95% CI 0.33, 0.98), whereas participants with HF showed no improvement in oxidative capacity (mean difference from baseline = −0.04 ± 0.08 min−1, P = 0.66, 95% CI −0.24, 0.31), suggesting impairments in mitochondrial biogenesis. In conclusion, participants with HF had reduced oxidative capacity and impaired oxidative adaptations to endurance exercise compared to controls.

Role of PGC-1α in exercise and fasting-induced adaptations in mouse liver

The transcriptional coactivator peroxisome proliferator-activated receptor (PPAR)-γ coactivator (PGC)-1α plays a role in regulation of several metabolic pathways. By use of whole body PGC-1α knockout (KO) mice, we investigated the role of PGC-1α in fasting, acute exercise and exercise training-induced regulation of key proteins in gluconeogenesis and metabolism in the liver. In both wild-type (WT) and PGC-1α KO mice liver, the mRNA content of the gluconeogenic proteins glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) was upregulated during fasting. Pyruvate carboxylase (PC) remained unchanged after fasting in WT mice, but it was upregulated in PGC-1α KO mice. In response to a single exercise bout, G6Pase mRNA was upregulated in both genotypes, whereas no significant changes were detected in PEPCK or PC mRNA. While G6Pase and PC protein remained unchanged, liver PEPCK protein content was higher in trained than untrained mice of both genotypes. The mRNA content of the mitochondrial proteins cytochrome c (Cyt c) and cytochrome oxidase (COX) subunit I was unchanged in response to fasting. The mRNA and protein content of Cyt c and COXI increased in the liver in response to a single exercise bout and prolonged exercise training, respectively, in WT mice, but not in PGC-1α KO mice. Neither fasting nor exercise affected the mRNA expression of antioxidant enzymes in the liver, and knockout of PGC-1α had no effect. In conclusion, these results suggest that PGC-1α plays a pivotal role in regulation of Cyt c and COXI expression in the liver in response to a single exercise bout and prolonged exercise training, which implies that exercise training-induced improvements in oxidative capacity of the liver is regulated by PGC-1α.

Training of late middle aged rats increases oxidative capacity without increasing mitochondrial content

There is some evidence that aged muscle does not increase mitochondrial protein content after exercise training, suggesting an improvement in mitochondrial quality rather than quantity. The purpose of this study was to determine if an improvement in oxidative capacity without an increase in mitochondrial content also occurs in a rat model, and to investigate one of the markers involved in mitochondrial biogenesis. Late middle aged (28 mo; 70% survival rate) Fisher 344-BN male rats performed treadmill running exercise 5 times/wk for 7 wk and were compared to an age-matched sedentary group. Muscle aerobic performance was assessed using a pump-perfused hindlimb model. Contralateral gastrocnemius and plantaris muscles were harvested for biochemical and molecular measurements. Endurance training increased muscle VO2 max (15%) and citrate synthase and complex IV activity (~25%) compared to the control group. CS protein content was not significantly different between training and sedentary groups, suggesting that mitochondrial content did not increase with training. PGC-1α protein but not mRNA was increased only in the plantaris muscle with training. These results show that endurance training of late middle aged rats increases oxidative enzyme activity without an increase in protein content. The training-induced improvement in mitochondrial function but not content may occur secondary to increased mitochondrial turnover. Supported by CIHR and the Alberta Provincial CIHR Training Program in Bone and Joint Health

Post-Exercise Insulin Sensitivity and Glucose Disposal are Unaffected by Intramuscular Triglyceride (IMTG) Levels

PURPOSE The relationships between exercise, IMTGs and insulin sensitivity are still not fully understood. The aim of this study was, therefore, to determine the effects of acute (5 hr) vs. chronic (6 days of 1 hr/day) swimming exercise on whole-body insulin sensitivity and glucose disposal in male Wistar rats following 6 wk of high-fat (60% fat) feeding. METHODS 9-week old male Wistar rats were assigned to one of four treatment groups (high-fat fed chronic exercise, high-fat fed acute exercise, high-fat fed control, chow-fed control). Post-exercise, all animals fed ad libitum for 6–7 hr, before an overnight fast. Approximately 24 hr post-exercise, half of the animals from each group were randomly assigned to a euglycemic/hyperinsulinemic clamp to assess insulin sensitivity and 2- deoxyglucose uptake. IMTG levels and glycogen levels were also assessed. RESULTS Chronic exercise improved insulin sensitivity when compared to acute exercise (p= 0.03), while glycogen levels paralleled this improvement in insulin sensitivity. IMTG levels were not altered significantly, but there was a trend towards an increase in both exercise groups when compared to the high-fat fed control group (p = 0.06). IMTG values were identical between exercise groups and did not, therefore, parallel the changes in insulin sensitivity. CONCLUSIONS These data suggest that post-exercise, mechanisms other than IMTGs are the major factor in insulin sensitivity improvement. Improvements in oxidative capacity and mitochondrial function, which occur following chronic training, are likely to be involved in these changes.

Post-Exercise Insulin Sensitivity and Glucose Disposal are Unaffected by Intramuscular Triglyceride (IMTG) Levels

PURPOSE The relationships between exercise, IMTGs and insulin sensitivity are still not fully understood. The aim of this study was, therefore, to determine the effects of acute (5 hr) vs. chronic (6 days of 1 hr/day) swimming exercise on whole-body insulin sensitivity and glucose disposal in male Wistar rats following 6 wk of high-fat (60% fat) feeding. METHODS 9-week old male Wistar rats were assigned to one of four treatment groups (high-fat fed chronic exercise, high-fat fed acute exercise, high-fat fed control, chow-fed control). Post-exercise, all animals fed ad libitum for 6–7 hr, before an overnight fast. Approximately 24 hr post-exercise, half of the animals from each group were randomly assigned to a euglycemic/hyperinsulinemic clamp to assess insulin sensitivity and 2- deoxyglucose uptake. IMTG levels and glycogen levels were also assessed. RESULTS Chronic exercise improved insulin sensitivity when compared to acute exercise (p= 0.03), while glycogen levels paralleled this improvement in insulin sensitivity. IMTG levels were not altered significantly, but there was a trend towards an increase in both exercise groups when compared to the high-fat fed control group (p = 0.06). IMTG values were identical between exercise groups and did not, therefore, parallel the changes in insulin sensitivity. CONCLUSIONS These data suggest that post-exercise, mechanisms other than IMTGs are the major factor in insulin sensitivity improvement. Improvements in oxidative capacity and mitochondrial function, which occur following chronic training, are likely to be involved in these changes.

Regulation of mitochondrial biogenesis in muscle by endurance exercise.

Behavioural and hereditary conditions are known to decrease mitochondrial volume and function within skeletal muscle. This reduces endurance performance, and is manifest both at high- and low-intensity levels of exertion. A programme of regular endurance exercise, undertaken over a number of weeks, produces significant adaptations within skeletal muscle such that noticeable improvements in oxidative capacity are evident, and the related decline in endurance performance can be attenuated. Notwithstanding the important implications that this has for the highly trained endurance athlete, an improvement in mitochondrial volume and function through regular physical activity also endows the previously sedentary and/or aging population with an improved quality of life, and a greater functional independence. An understanding of the molecular and cellular mechanisms that govern the increases in mitochondrial volume with repeated bouts of exercise can provide insights into possible therapeutic interventions to care for those with mitochondrially-based diseases, and those unable to withstand regular physical activity. This review focuses on the recent developments in the molecular aspects of mitochondrial biogenesis in chronically exercising muscle. Specifically, we discuss the initial signalling events triggered by muscle contraction, the activation of transcription factors involved in both nuclear and mitochondrial DNA transcription, as well as the post-translational import mechanisms required for mitochondrial biogenesis. We consider the importance and relevance of chronic physical activity in the induction of mitochondrial biogenesis, with particular emphasis on how an endurance training programme could positively affect the age-related decline in mitochondrial content and delay the progression of age- and physical inactivity-related diseases.

Adaptive strategies of respiratory muscles in response to endurance exercise.

The purpose of this review is to discuss the adaptive strategies of mammalian respiratory muscles in response to whole-body endurance exercise training. It is now clear that endurance training results in small (i.e., 20-30%) but significant increases in mitochondrial enzyme activity and the activities of key antioxidant enzymes (i.e., superoxide dismutase and glutathione peroxidase) within the rodent diaphragm. Interestingly, the magnitude of this training-induced increase in costal diaphragmatic oxidative and antioxidant enzyme activity is relatively independent of the exercise duration and intensity. Although the crural diaphragm of rodents is also capable of increasing its oxidative and antioxidant capacity in response to endurance training, high-to moderate-intensity exercise of long duration is required to promote these changes. Endurance training also increases the oxidative capacity of other key rodent inspiratory muscles, such as the parasternal intercostals and external intercostals. Furthermore, endurance training results in small (approximately 10%) increased in the oxidative capacity of key abdominal (expiratory) muscles. Whether the improvement in oxidative capacity of respiratory muscles is of significant magnitude to result in improvement in respiratory muscle performance remains an unanswered question.

Low intensity exercise training in patients with chronic heart failure

The present study was designed to evaluate whether a specific program of low intensity exercise training may be sufficient to improve the exercise tolerance of patients with chronic heart failure. Recent studies have shown that exercise training can improve exercise tolerance in patients with stable chronic heart failure, mainly through peripheral adaptations. These changes have been observed with exercise regimens at intensities of 70% to 80% of peak oxygen uptake and > 8 weeks. We studied 27 patients (23 men, 4 women; mean [+/- SD] age 57 +/- 6 years) with mild chronic heart failure. We classified patients into two groups: trained group and untrained group. The trained group underwent a low intensity (40% of peak oxygen uptake) training program three times/week for 8 weeks. The untrained group performed no exercise. An increase in peak oxygen uptake (17%, p < 0.0001), lactic acidosis threshold (20%, p < 0.0002) and peak work load (21%, p < 0.0002) were obtained in the trained group only. Cardiac output and stroke volume were unchanged. A high correlation was found between the increases in peak oxygen uptake and volume density of mitochondria of vastus lateralis muscle (r = 0.77, p < 0.0002). Patients with stable chronic heart failure can achieve significant improvement in functional capacity from a low intensity exercise training regimen. The mechanism responsible for this favorable effect involves an increase in mitochondrial density, which reflects an improvement in oxidative capacity of trained skeletal muscles.

Adaptive changes in work capacity, skeletal muscle capillarization and enzyme levels during training and detraining.

Six male subjects exercised on a bicycle ergometer 30 min with left leg and 30 min with right leg 3 times a week for 8 weeks. This training resulted in a 14.6% increase in VO2 max with two-leg exercise and a 23.1% increase with one-leg exercise. A significant decrease towards pretraining VO2 max was seen during the following 8 weeks of detraining. Muscle biopsy samples were obtained at rest from m. vastus lateralis before and after training and 4 and 8 weeks after training. During training the number of capillaries per mm2 and the number of capillaries per fiber increased about 20%. The number of capillaries around each fiber type (CA) increased 20--30%. The average area of each fibre type increased only about 5%. The fibre area per CA decreased by about 10%. During 8 weeks of detraining decreases were seen in the number of capillaries per fibre, CA and in fibre area, while fibre area per CA and number of capillaries per mm2 were almost unchanged at the end of the detraining period. Pronounced increases in activities of oxidative enzymes were observed after training, while only minor increases were seen in glycolytic enzyme activities. All enzyme activities decreased towards pre-training levels during detraining. The results indicate that the training-induced improvement in oxidative capacity and in muscle capillarization expressed as capillaries per fibre and CA disappears within 8 weeks after cessation of training. However, the fibre area per CA and number of capillaries per mm2 point at a favourable long term effect on the average diffusion distance between capillaries and muscle fibres.