Effects of endurance exercise on carnitine palmitoyltransferase I from rat heart, skeletal muscle and liver mitochondria

Mildronate protects heart mtDNA from oxidative stress toxicity induced by exhaustive physical exercise

Exhaustive physical exercises are potentially dangerous for human's physical health and may lead to chronic heart disease. Therefore, individuals involved in such activity require effective and safe cardioprotectors. The goal of this research was to study Mildronate (a cardioprotective drug) effect on the level of oxidative stress markers in hearts of mice under conditions of exhausting physical exercise, such as forced swimming for 1 h per day for 7 days. Forced swimming lead to mtDNA damage accumulation, increase in diene conjugates level and loss of reduced glutathione despite an increase in antioxidant genes expression and activation of mitochondrial biogenesis. Mildronate treatment reduced oxidative stress, probably due to the inhibition of fatty acids transport to mitochondria and an increase in the intensity of glucose oxidation, which in part confirms by increase in glucose transporter expression. Thus, we can assume that Mildronate is an effective cardioprotector in exhaustive physical exercises.

Identification of a novel malonyl-CoA IC(50) for CPT-I: implications for predicting in vivo fatty acid oxidation rates

Published values regarding the sensitivity (IC(50)) of CPT-I (carnitine palmitoyltransferase I) to M-CoA (malonyl-CoA) inhibition in isolated mitochondria are inconsistent with predicted in vivo rates of fatty acid oxidation. Therefore we have re-examined M-CoA inhibition kinetics under various P-CoA (palmitoyl-CoA) concentrations in both isolated mitochondria and PMFs (permeabilized muscle fibres). PMFs have an 18-fold higher IC(50) (0.61 compared with 0.034 μM) in the presence of 25 μM P-CoA and a 13-fold higher IC(50) (6.3 compared with 0.49 μM) in the presence of 150 μM P-CoA compared with isolated mitochondria. M-CoA inhibition kinetics determined in PMFs predicts that CPT-I activity is inhibited by 33% in resting muscle compared with >95% in isolated mitochondria. Additionally, the ability of M-CoA to inhibit CPT-I appears to be dependent on P-CoA concentration, as the relative inhibitory capacity of M-CoA is decreased with increasing P-CoA concentrations. Altogether, the use of PMFs appears to provide an M-CoA IC(50) that better reflects the predicted in vivo rates of fatty acid oxidation. These findings also demonstrate that the ratio of [P-CoA]/[M-CoA] is critical for regulating CPT-I activity and may partially rectify the in vivo disconnect between M-CoA content and CPT-I flux within the context of exercise and Type 2 diabetes.

High-intensity interval aerobic training reduces hepatic very low-density lipoprotein-triglyceride secretion rate in men

A single bout of strenuous endurance exercise reduces fasting plasma triglyceride (TG) concentrations the next day (12-24 h later) by augmenting the efficiency of very low-density lipoprotein (VLDL)-TG removal from the circulation. Although much of the hypotriglyceridemia associated with training is attributed to the last bout of exercise, the relevant changes in VLDL-TG metabolism have never been investigated. We therefore examined basal VLDL-TG kinetics in a group of sedentary young men (n=7) who underwent 2 mo of supervised high-intensity interval training (3 sessions/wk; running at 60 and 90% of peak oxygen consumption in 4-min intervals for a total of 32 min; gross energy expenditure: 446+/-29 kcal) and a nonexercising control group (n=8). Each subject completed two stable isotope-labeled tracer infusion studies in the postabsorptive state, once before and again after the intervention (approximately 48 h after the last exercise bout in the training group). Peak oxygen consumption increased by approximately 18% after training (P <or= 0.05), whereas body weight and body composition were not altered. Fasting plasma VLDL-TG concentration was reduced after training by approximately 28% (P <or= 0.05), and this was due to reduced hepatic VLDL-TG secretion rate (by approximately 35%, P <or= 0.05) with no changes (<5%, P>0.7) in VLDL-TG plasma clearance rate and the mean residence time of VLDL-TG in the circulation. No significant changes in VLDL-TG concentration and kinetics were observed in the nonexercising control group (all P >or= 0.3). We conclude that a short period of high-intensity interval aerobic training lowers the rate of VLDL-TG secretion by the liver in previously sedentary men. This is different from the mechanism underlying the hypotriglyceridemia of acute exercise; however, it remains to be established whether our finding reflects an effect of the longer time lapse from the last exercise bout, an effect specific to the type of exercise performed, or an effect of aerobic training itself.

Optimizing fat oxidation through exercise and diet

Interventions aimed at increasing fat metabolism could potentially reduce the symptoms of metabolic diseases such as obesity and type 2 diabetes and may have tremendous clinical relevance. Hence, an understanding of the factors that increase or decrease fat oxidation is important. Exercise intensity and duration are important determinants of fat oxidation. Fat oxidation rates increase from low to moderate intensities and then decrease when the intensity becomes high. Maximal rates of fat oxidation have been shown to be reached at intensities between 59% and 64% of maximum oxygen consumption in trained individuals and between 47% and 52% of maximum oxygen consumption in a large sample of the general population. The mode of exercise can also affect fat oxidation, with fat oxidation being higher during running than cycling. Endurance training induces a multitude of adaptations that result in increased fat oxidation. The duration and intensity of exercise training required to induce changes in fat oxidation is currently unknown. Ingestion of carbohydrate in the hours before or on commencement of exercise reduces the rate of fat oxidation significantly compared with fasted conditions, whereas fasting longer than 6 h optimizes fat oxidation. Fat oxidation rates have been shown to decrease after ingestion of high-fat diets, partly as a result of decreased glycogen stores and partly because of adaptations at the muscle level.

Subsarcolemmal and intermyofibrillar mitochondria play distinct roles in regulating skeletal muscle fatty acid metabolism

Skeletal muscle contains two populations of mitochondria that appear to be differentially affected by disease and exercise training. It remains unclear how these mitochondrial subpopulations contribute to fiber type-related and/or training-induced changes in fatty acid oxidation and regulation of carnitine palmitoyltransferase-1beta (CPT1beta), the enzyme that controls mitochondrial fatty acid uptake in skeletal muscle. To this end, we found that fatty acid oxidation rates were 8.9-fold higher in subsarcolemmal mitochondria (SS) and 5.3-fold higher in intermyofibrillar mitochondria (IMF) that were isolated from red gastrocnemius (RG) compared with white gastrocnemius (WG) muscle, respectively. Malonyl-CoA (10 muM), a potent inhibitor of CPT1beta, completely abolished fatty acid oxidation in SS and IMF mitochondria from WG, whereas oxidation rates in the corresponding fractions from RG were inhibited only 89% and 60%, respectively. Endurance training also elicited mitochondrial adaptations that resulted in enhanced fatty acid oxidation capacity. Ten weeks of treadmill running differentially increased palmitate oxidation rates 100% and 46% in SS and IMF mitochondria, respectively. In SS mitochondria, elevated fatty acid oxidation rates were accompanied by a 48% increase in citrate synthase activity but no change in CPT1 activity. Nonlinear regression analyses of mitochondrial fatty acid oxidation rates in the presence of 0-100 muM malonyl-CoA indicated that IC(50) values were neither dependent on mitochondrial subpopulation nor affected by exercise training. However, in IMF mitochondria, training reduced the Hill coefficient (P < 0.05), suggesting altered CPT1beta kinetics. These results demonstrate that endurance exercise provokes subpopulation-specific changes in mitochondrial function that are characterized by enhanced fatty acid oxidation and modified CPT1beta-malonyl-CoA dynamics.

Regular exercise is associated with a protective metabolic phenotype in the rat heart

Adaptation of myocardial energy substrate utilization may contribute to the cardioprotective effects of regular exercise, a possibility supported by evidence showing that pharmacological metabolic modulation is beneficial to ischemic hearts during reperfusion. Thus we tested the hypothesis that the beneficial effect of regular physical exercise on recovery from ischemia-reperfusion is associated with a protective metabolic phenotype. Function, glycolysis, and oxidation of glucose, lactate, and palmitate were measured in isolated working hearts from sedentary control (C) and treadmill-trained (T: 10 wk, 4 days/wk) female Sprague-Dawley rats submitted to 20 min ischemia and 40 min reperfusion. Training resulted in myocardial hypertrophy (1.65 +/- 0.05 vs. 1.30 +/- 0.03 g heart wet wt, P < 0.001) and improved recovery of function after ischemia by nearly 50% (P < 0.05). Glycolysis was 25-30% lower in T hearts before and after ischemia (P < 0.05), whereas rates of glucose oxidation were 45% higher before ischemia (P < 0.01). As a result, the fraction of glucose oxidized before and after ischemia was, respectively, twofold and 25% greater in T hearts (P < 0.05). Palmitate oxidation was 50-65% greater in T than in C before and after ischemia (P < 0.05), whereas lactate oxidation did not differ between groups. Alteration in content of selected enzymes and proteins, as assessed by immunoblot analysis, could not account for the reduction in glycolysis or increase in glucose and palmitate oxidation observed. Combined with the studies on the beneficial effect of pharmacological modulation of energy metabolism, the present results provide support for a role of metabolic adaptations in protecting the trained heart against ischemia-reperfusion injury.

Lipid-Induced Insulin Resistance in the Liver

Hepatic lipid accumulation may be a result of one or several of the following factors: increased delivery of adipose tissue or dietary fatty acids to the liver, increased de novo synthesis of fatty acids in the liver, decreased rate of hepatic fatty-acid oxidation, or decreased rate in the exit of fatty acids from the liver in the form of triglycerides. Delivery of fatty acids to the liver appears to be the most potent mechanism for hepatic lipid accumulation. Hepatic lipid accumulation is linked to the development of hepatic insulin resistance, which is demonstrated by the impaired suppression of hepatic glucose output by insulin. Current evidence suggests that defects associated with the molecular mechanisms responsible for the propagation of the insulin signal in the liver cells are responsible for the impaired insulin effect and that these defects can develop secondary to lipid accumulation in the liver. Hepatic lipid accumulation appears to affect the activity of phosphatidylinositol 3-kinase, which has a central role in mediating the insulin action in hepatocytes. Generally, exercise has been shown to enhance the insulin action in the liver. Although an exercise-related mechanistic link between attenuation in hepatic lipid accumulation and enhancement in insulin action in the liver has not been described yet, the benefits of exercise on hepatic insulin action may relate to the potential effects of exercise on regulating/preventing hepatic lipid accumulation. However, direct effects of exercise on insulin action in the liver, independent of any effects on hepatic lipid metabolism, cannot currently be excluded. Further research is needed to evaluate the relative importance of exercise in the treatment of hepatic insulin resistance, specifically as it relates to lipid accumulation in the liver.

The effects of endurance training and exhaustive exercise on mitochondrial enzymes in tissues of the rat (Rattus norvegicus)

The aim of the present study was to ascertain the effects of training and exhaustive exercise on mitochondrial capacities to oxidize pyruvate, 2-oxoglutarate, palmitoylcarnitine, succinate and ferrocytochrome c in various tissues of the rat. Endurance capacity was significantly increased (P<0.01) by an endurance training program over a period of 5-6 weeks. The average run time to exhaustion was 214.2+/-23.8 min for trained rats in comparison with 54.5+/-11.7 min for their untrained counterparts. Oxidative capacities were reduced in liver (P<0.05) and brown adipose tissue (P<0.05) as a result of endurance training. On the contrary, the oxidative capacity of skeletal muscle was slightly increased and that of heart almost unaffected except for the oxidation of palmitoylcarnitine, which was significantly reduced (P<0.05) as a result of training.

Sensitivity of CPT I to malonyl-CoA in trained and untrained human skeletal muscle

The present study examined the sensitivity of carnitine palmitoyltransferase I (CPT I) activity to its inhibitor malonyl-CoA (M-CoA), and simulated metabolic conditions of rest and exercise, in aerobically trained and untrained humans. Maximal CPT I activity was measured in mitochondria isolated from resting human skeletal muscle. Mean CPT I activity was 492.8 +/- 72.8 and 260.8 +/- 33.6 micromol. min(-1). kg wet muscle(-1) in trained and untrained subjects, respectively (pH 7.0, 37 degrees C). The sensitivity to M-CoA was greater in trained muscle; the IC(50) for M-CoA was 0.17 +/- 0.04 and 0.49 +/- 0.17 microM in trained and untrained muscle, respectively. The presence of acetyl-CoA, free coenzyme A (CoASH), and acetylcarnitine, in concentrations simulating rest and exercise conditions did not release the M-CoA-induced inhibition of CPT I activity. However, CPT I activity was reduced at pH 6.8 vs. pH 7.0 in both trained and untrained muscle in the presence of physiological concentrations of M-CoA. The results of this study indicate that aerobic training is associated with an increase in the sensitivity of CPT I to M-CoA. Accumulations of acetyl-CoA, CoASH, and acetylcarnitine do not counteract the M-CoA-induced inhibition of CPT I activity. However, small decreases in pH produce large reductions in the activity of CPT I and may contribute to the decrease in fat metabolism that occurs during moderate and intense aerobic exercise intensities.

Dietary fatty acids influence the activity and metabolic control of mitochondrial carnitine palmitoyltransferase I in rat heart and skeletal muscle

The fatty acid composition of the diet has been found to influence the activity and sensitivity of mitochondrial carnitine palmitoyltransferase I (CPT I; EC 2.3.1.21) to inhibition by malonyl CoA in rat heart and skeletal muscle. The nutritional state of rats has been shown to have less influence on the activity and metabolic control of mitochondrial CPT I in heart and skeletal muscle tissue than in the liver, a tissue in which CPT I activity and sensitivity to inhibition by malonyl CoA can be shown to be regulated acutely under different nutritional conditions. However, because manipulation of the nutritional state in these previous studies was restricted mainly to examining the effect of starvation, this study was undertaken to determine whether, as in liver, the fatty acid content and composition of the diet can regulate the activity and metabolic control of CPT I in heart and skeletal muscle. Rats were fed for up to 10 wk either a nonpurified low fat diet (30 g fat/kg) or a high fat diet (200 g fat/kg) containing one of the following five oil types: hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or menhaden (fish) oil (MO). Feeding a diet enriched in MO had the most pronounced effect. Rats fed MO had a significantly greater skeletal muscle CPT I specific activity and tissue capacity, and a lower sensitivity of CPT I to malonyl CoA inhibition compared with rats fed a low fat diet, but the duration of feeding required to modulate this sensitivity was longer than that observed previously for the liver enzyme. Progressively greater sensitivity of heart CPT I to malonyl CoA occurred with feeding duration in all groups. These studies indicate that the fatty acid composition of the diet is involved in the regulation of mitochondrial CPT I activity in heart and skeletal muscle.

Effects of L-carnitine on the pyruvate dehydrogenase complex and carnitine palmitoyl transferase activities in muscle of endurance athletes

The effects of L-carnitine on the pyruvate dehydrogenase (PDH) complex and carnitine palmitoyl transferase (CPT) were studied in muscle of 16 long-distance runners (LDR). These subjects received placebo or L-carnitine (2 g orally) during a 4-week period of training. Athletes receiving L-carnitine showed a dramatic increase (P < 0.001) in the PDH complex activities. By contrast, the levels of CPT, both 1 and 2, were unchanged. No significant changes were observed after placebo administration. We previously reported [Huertas R. et al., Biochem. Biophys. Res. Commun. 188 (1992) 102-107] that L-carnitine induces an increase in the activities of complexes I, III and IV of the respiratory chain in muscle of LDR. Taken together, our data suggest that the improvement in (maximal oxygen consumption) VO2max observed in LDR after L-carnitine administration is based on these biochemical findings.

Modulation of fatty-acid-binding protein content of rat heart and skeletal muscle by endurance training and testosterone treatment

The effects of training and/or testosterone treatment and its aromatization to oestradiol on fatty-acid-binding protein (FABP) content and cytochrome c oxidase activity in heart, soleus and extensor digitorum longus (EDL) muscles were studied in intact adult female rats. One group of rats remained sedentary, whereas the others were trained for 7 weeks. Thereafter the trained rats were divided into control and testosterone-treated groups, with or without an aromatase inhibitor. Testosterone was administered by a silastic implant. Training was continued for 2 weeks. In untreated sedentary rats the immunochemically assayed FABP contents were 497 +/- 28, 255 +/- 49 and 58 +/- 17 micrograms/g wet weight for the heart, soleus, and EDL respectively. In the heart the FABP content was increased after training (29%), testosterone treatment (33%) or both manipulations (53%). In soleus muscle FABP increased only after testosterone treatment (16%), whereas in EDL no changes were found. Inhibiting the aromatase enzyme complex abolished the testosterone-induced effect on FABP content in soleus (suggesting an oestradiol effect) but not in heart muscle. Among the three muscles studied the FABP content was found to be related to the cytochrome c oxidase activity in a non-linear way. In conclusion, it is shown that the FABP contents and mitochondrial activities of heart and skeletal muscle are affected by training and sex hormones and that these effects are different for heart and skeletal muscles.

Treatment with anabolic steroids increases the activity of the mitochondrial outer carnitine palmitoyltransferase in rat liver and fast-twitch muscle

Treatment of male rats with the anabolic steroids fluoxymesterone or methylandrostanolone increased the activity of the outer carnitine palmitoyltransferase in liver and fast-twitch muscle mitochondria. This effect was not potentiated by physical exercise and was not observed in heart and slow-twitch muscle mitochondria. Anabolic steroids did not affect the sensitivity of the liver enzyme to inhibition by malonyl-CoA. The data presented herein suggest that androgens may have an important physiological role in the regulation of fatty acid oxidation in liver and fast-twitch muscle mitochondria. In addition, our results are at odds with the notion that (most of) the metabolic effects of anabolic steroids on muscle are only evident when physical training is parallely performed.

The metabolic syndrome and signal transduction of gene expression

Epidemiological studies have clearly shown that the so-called metabolic syndrome which is linked to insulin resistance and a reduced glucose utilization of muscle represents an important risk factor for cardiovascular disease. However, only little is known of the intracellular consequences of insulin resistance. An important feature of an altered substrate utilization is related to signal transduction of gene expression. For the example of myosin heavy chain expression, it is shown that metabolic signals exist which reflect the fuel flux and substrate utilization of the heart muscle cell. The signals were characterized in functional states of the heart associated with altered metabolic influences (fasting, diabetes, sucrose feeding, increased calorie intake, carnitine palmitoyltransferase inhibition). In the pressure-overloaded heart, metabolic interventions which are expected to increase glucose utilization (sucrose feeding, captopril treatment) have a pronounced effect. Although a link with gene expression remains to be established, it should be noted that the sarcoplasmic reticulum Ca(2+)-pump activity seems to be affected in a functionally comparable manner. It is concluded that metabolic signals alter the protein phenotype of heart muscle and it is expected that a deranged signal transduction affects, not only the heart, but also vascular muscle.

Cardiac carnitine acyltransferase activities in exercised normal and dystrophic hamsters

Carnitine acyltransferase activities in the hearts of normal and dystrophic, sedentary and swim exercised hamsters were studied, in order to analyze the relationship between carnitine metabolism and exercise in cardiomyopathy. After 12 weeks, the mean specific activities of cardiac carnitine acetyltransferase (CAT), carnitine octanoyltransferase (COT) and carnitine palmitoyltransferase (CPT) were significantly higher in the dystrophic sedentary group, relative to the normal sedentary group (p less than 0.05). There was no significant effect of exercise on the mean specific activity of the carnitine acyltransferases, compared to the dystrophic or normal sedentary controls. Thus, the improvements in cardiac histopathology due to exercise noted previously are not associated with altered carnitine acyltransferase activity.