Mitochondrial function adaptations to changed metabolic conditions

The skeletal muscle mitochondria play a decisive role for the metabolic capacity of the body. A capability to adapt to changed metabolic conditions and energy demands is crucial for weight control and physical exercise. The aim of this thesis was to describe how the mitochondria adapt its function to different environmental conditions and changed metabolic demands. In study I, the aim was to evaluate mitochondrial adaptations to hypoxic exercise. The effect of one-legged cycle training at hypoxia was compared to equivalent normoxic training, performed at the same relative intensity. Eight untrained volunteers performed one-legged cycle training during 4 weeks. Muscle biopsies were taken before and after the exercise period. The leg trained during normoxia increased its mitochondrial population (+20.8%, P<0.05) and there was a trend towards increased respiratory capacity (+31.2%, P<0.08), while adaptations were absent in the hypoxically trained leg. Altitude training might thus be disadvantageous for mitochondrial adaptations and muscle oxidative function. In study II, the aim was to investigate the effect of ultra endurance exercise on mitochondrial function. Elite ultra endurance athletes performed running, kayaking, and cycling at 60% of their maximal oxygen consumption for 24 h. Muscle biopsies were taken preexercise, postexercise, and after 28 h of recovery. We found that mitochondrial efficiency was reduced, while the mitochondrial capacity to utilize fat was up regulated (+40%, P<0.05) after exercise. This increase in fat oxidation was reflected at whole body level substrate utilization, thus it might benefit performance during prolonged exercise. In study III and IV, the aims were to study mitochondrial function in obesity and effects of weight loss, respectively. Weight gain varies among individuals despite equal calorie overconsumption. Furthermore, weight loss resulting from low calorie diets is often less than expected and long-term success is low. This suggests differences and changes in metabolic efficiency and basal metabolism. Since mitochondrial uncoupling accounts for a substantial portion of the basal metabolic rate, we compared mitochondrial respiration in obese subjects to normal weight reference groups (study III). In study IV, we studied how mitochondrial capacity was affected by calorie restriction. Muscle biopsies were taken from 11 obese women, with an average BMI of 39 kg/m2, in conjunction with their gastric bypass surgery and at 6-months of follow-up. We found that obese subjects had a decreased oxidative capacity (-47%, P<0.01) per mitochondrial volume, compared to the to normal weight reference groups. A low capacity for fuel oxidation could play a role in the predisposition for obesity. Six months after the gastric bypass surgery, the subjects had lost on average 25.5 kg of their body weight. Coupled, ADP generating respiration, had increased significantly (+69%, P≤0.01), while the uncoupled respiration was not significantly altered. Mitochondrial efficiency increased significantly. An increased mitochondrial efficiency could partly explain the reduced basal metabolism and thus the reduced inclination for weight loss at calorie restriction. The reduced capacity among the obese is thus suggested to rather be an effect of the obesity than a casual factor

An Interactive Internet-Based Plate for Assessing Lunchtime Food Intake : A Validation Study on Male Employees

Background: Misreporting food intake is common because most health screenings rely on self-reports. The more accurate methods (eg, weighing food) are costly, time consuming, and impractical. Objectives: We developed a new instrument for reporting food intake—an Internet-based interactive virtual food plate. The objective of this study was to validate this instrument’s ability to assess lunch intake. Methods: Participants were asked to compose an ordinary lunch meal using both a virtual and a real lunch plate (with real food on a real plate). The participants ate their real lunch meals on-site. Before and after pictures of the composed lunch meals were taken. Both meals included identical food items. Participants were randomized to start with either instrument. The 2 instruments were compared using correlation and concordance measures (total energy intake, nutritional components, quantity of food, and participant characteristics). Results: A total of 55 men (median age: 45 years, median body mass index [BMI]: 25.8 kg/m2) participated. We found an overall overestimation of reported median energy intake using the computer plate (3044 kJ, interquartile range [IQR] 1202 kJ) compared with the real lunch plate (2734 kJ, IQR 1051 kJ, P&lt;.001). Spearman rank correlations and concordance correlations for energy intake and nutritional components ranged between 0.58 to 0.79 and 0.65 to 0.81, respectively. Conclusion: Although it slightly overestimated, our computer plate provides promising results in assessing lunch intake. © Filippo Castiglione.Funding: The Swedish Transport Administration and the Erik and Edith Fernström’s foundation, Sweden.</p

Unexpected cardiovascular response during ultra-endurance exercise.

During prolonged exercise at fixed work rate heart rate (HR) increases slowly with concomitant decrease in stroke volume (SV) in order to maintain cardiac output. Simultaneously, an increased oxygen uptake (VO2) occurs. In this paper we report an unexpected and previously not observed cardiovascular response to ultra-endurance exercise. Nine well-trained male athletes performed 24-h exercise in a controlled laboratory setting, with altering blocks of kayaking, running and cycling. Each block consisted of 110 min of exercise and 10 min of rest. Measurements (HR, VO2 and blood samples) were conducted during cycling at fixed work rate every 6th hour. The average work intensity was approximately 55 % of respective VO2peak. HR was increased at 6 h with 15 beats/min (13 %) compared to pre-exercise (Pre-Ex), but thereafter unexpectedly returned towards initial values. VO2 on the other hand was increased with 0.22 l/min (10 %) at 6 h and 0.37 l/min (17 %) at 12 h compared to Pre-Ex, and thereafter remained stable. This implies an increased oxygen pulse (VO2/HR) with approximately 10 % compared to Pre-Ex at the later half of the exercise. The cardiovascular drift did not progress continuously, but instead changed drastically when duration exceeded 6 hours. The changes in HR and VO2 might have different and complex explanations. HR drift might be explained mainly by central circulatory adaptation (e.g. desensitisation of cardiac adrenergic receptors) whereas drift in VO2 may depend upon peripheral changes (e.g. decreased mitochondrial efficiency). Consequently, using solely HR for determining exercise intensity and energy expenditure becomes invalid during ultra-endurance exercise, if the cardiovascular drift is not measured and taken into account.  Physiology of Adenture Racin

Reduced efficiency, but increased fat oxidation, in mitochondria from human skeletal muscle after 24-h ultraendurance exercise.

The hypothesis that ultraendurance exercise influences muscle mitochondrial function has been investigated. Athletes in ultraendurance performance performed running, kayaking, and cycling at 60% of their peak O(2) consumption for 24 h. Muscle biopsies were taken preexercise (Pre-Ex), postexercise (Post-Ex), and after 28 h of recovery (Rec). Respiration was analyzed in isolated mitochondria during state 3 (coupled to ATP synthesis) and state 4 (noncoupled respiration), with fatty acids alone [palmitoyl carnitine (PC)] or together with pyruvate (Pyr). Electron transport chain activity was measured with NADH in permeabilized mitochondria. State 3 respiration with PC increased Post-Ex by 39 and 41% (P &lt; 0.05) when related to mitochondrial protein and to electron transport chain activity, respectively. State 3 respiration with Pyr was not changed (P &gt; 0.05). State 4 respiration with PC increased Post-Ex but was lower than Pre-Ex at Rec (P &lt; 0.05 vs. Pre-Ex). Mitochondrial efficiency [amount of added ADP divided by oxygen consumed during state 3 (P/O ratio)] decreased Post-Ex by 9 and 6% (P &lt; 0.05) with PC and PC + Pyr, respectively. P/O ratio remained reduced at Rec. Muscle uncoupling protein 3, measured with Western blotting, was not changed Post-Ex but tended to decrease at Rec (P = 0.07 vs. Pre-Ex). In conclusion, extreme endurance exercise decreases mitochondrial efficiency. This will increase oxygen demand and may partly explain the observed elevation in whole body oxygen consumption during standardized exercise (+13%). The increased mitochondrial capacity for PC oxidation indicates plasticity in substrate oxidation at the mitochondrial level, which may be of advantage during prolonged exercise.At the time of Maria Fernström's disputation the article was in manuscript.Physiology of Adventure Racin

On-Line Monitoring of Apoptosis in Insulin-Secreting Cells

Apoptosis was monitored in intact insulin-producing cells both with microfluorometry and with two-photon laser scanning microscopy (TPLSM), using a fluorescent protein based on fluorescence resonance energy transfer (FRET). TPLSM offers three-dimensional spatial information that can be obtained relatively deep in tissues. This provides a potential for future in vivo studies of apoptosis. The cells expressed a fluorescent protein (C-DEVD-Y) consisting of two fluorophores, enhanced cyan fluorescent protein (ECFP) and enhanced yellow fluorescent protein (EYFP), linked by the amino acid sequence DEVD selectively cleaved by caspase-3–like proteases. FRET between ECFP and EYFP in C-DEVD-Y could therefore be monitored on-line as a sensor of caspase-3 activation. The relevance of using caspase-3 activation to indicate β-cell apoptosis was demonstrated by inhibiting caspase-3–like proteases with Z-DEVD-fmk and thereby showing that caspase-3 activation was needed for high-glucose–and cytokine-induced apoptosis in the β-cell and for staurosporine-induced apoptosis in RINm5F cells. In intact RINm5F cells expressing C-DEVD-Y and in MIN6 cells expressing the variant C-DEVD-Y2, FRET was lost at 155 ± 23 min (n = 9) and 257 ± 59 min (n = 4; mean ± SE) after activation of apoptosis with staurosporine (6 μmol/l), showing that this method worked in insulin-producing cells

Ultraendurance exercise increases the production of reactive oxygen species in isolated mitochondria from human skeletal muscle

Exercise-induced oxidative stress is important for the muscular adaptation to training but may also cause muscle damage. We hypothesized that prolonged exercise would increase mitochondrial production of reactive oxygen species (ROS) measured in vitro and that this correlates with oxidative damage. Eight male athletes (24–32 yr) performed ultraendurance exercise (kayaking/running/cycling) with an average work intensity of 55% V̇o2peak for 24 h. Muscle biopsies were taken from vastus lateralis before exercise, immediately after exercise, and after 28 h of recovery. The production of H2O2 was measured fluorometrically in isolated mitochondria with the Amplex red and peroxidase system. Succinate-supported mitochondrial H2O2 production was significantly increased after exercise (73% higher, P = 0.025) but restored to the initial level at recovery. Plasma level of free fatty acids (FFA) increased fourfold and exceeded 1.2 mmol/l during the last 6 h of exercise. Plasma FFA at the end of exercise was significantly correlated to mitochondrial ROS production (r = 0.74, P < 0.05). Mitochondrial content of 4-hydroxy-nonenal-adducts (a marker of oxidative damage) was increased only after recovery and was not correlated with mitochondrial ROS production. Total thiol group level and glutathione peroxidase activity were elevated after recovery. In conclusion, ultraendurance exercise increases ROS production in isolated mitochondria, but this is reversed after 28 h recovery. Mitochondrial ROS production was not correlated with oxidative damage of mitochondrial proteins, which was increased at recovery but not immediately after exercise

Effects of supplementing with an 18% carbohydrate-hydrogel drink versus a placebo during whole-body exercise in -5 °C with elite cross-country ski athletes: a crossover study

BACKGROUND: Whilst the ergogenic effects of carbohydrate intake during prolonged exercise are well-documented, few investigations have studied the effects of carbohydrate ingestion during cross-country skiing, a mode of exercise that presents unique metabolic demands on athletes due to the combined use of large upper- and lower-body muscle masses. Moreover, no previous studies have investigated exogenous carbohydrate oxidation rates during cross-country skiing. The current study investigated the effects of a 13C-enriched 18% multiple-transportable carbohydrate solution (1:0.8 maltodextrin:fructose) with additional gelling polysaccharides (CHO-HG) on substrate utilization and gastrointestinal symptoms during prolonged cross-country skiing exercise in the cold, and subsequent double-poling time-trial performance in ~ 20 °C. METHODS: Twelve elite cross-country ski athletes (6 females, 6 males) performed 120-min of submaximal roller-skiing (69.3 ± 2.9% of [Formula: see text]O2peak) in -5 °C while receiving either 2.2 g CHO-HG·min- 1 or a non-caloric placebo administered in a double-blind, randomized manner. Whole-body substrate utilization and exogenous carbohydrate oxidation was calculated for the last 60 min of the submaximal exercise. The maximal time-trial (2000 m for females, 2400 m for males) immediately followed the 120-min submaximal bout. Repeated-measures ANOVAs with univariate follow-ups were conducted, as well as independent and paired t-tests, and significance was set at P &lt; 0.05. Data are presented as mean ± SD. RESULTS: Exogenous carbohydrate oxidation contributed 27.6 ± 6.6% to the total energy yield with CHO-HG and the peak exogenous carbohydrate oxidation rate reached 1.33 ± 0.27 g·min- 1. Compared to placebo, fat oxidation decreased by 9.5 ± 4.8% with CHO-HG, total carbohydrate oxidation increased by 9.5 ± 4.8% and endogenous carbohydrate utilization decreased by 18.1 ± 6.4% (all P &lt; 0.05). No severe gastrointestinal symptoms were reported in either trial and euhydration was maintained in both trials. Time-trial performance (8.4 ± 0.4 min) was not improved following CHO-HG compared to placebo (- 0.8 ± 3.5 s; 95% confidence interval - 3.0 to 1.5 s; P = 0.46). No sex differences were identified in substrate utilization or relative performance. CONCLUSIONS: Ingestion of an 18% multiple-transportable carbohydrate solution with gelling polysaccharides was found to be well-tolerated during 120 min of submaximal whole-body exercise, but did not improve subsequent maximal double-poling performance