Effects of exercise on VLDL-triglyceride oxidation and turnover

American Journal of Physiology-Endocrinology and Metabolism

Søndergaard

Jensen

et al. 2014

Self Cite

Nielsen S. Kinetics and utilization of lipid sources during acute exercise and acipimox. Am J Physiol Endocrinol Metab 307: E199 -E208, 2014. First published June 3, 2014 doi:10.1152/ajpendo.00043.2014.-Overweight is associated with abnormalities of lipid metabolism, many of which are reversed by exercise. We investigated the impact of experimental antilipolysis and acute exercise on lipid kinetics and oxidation from VLDL-TG, plasma FFA, and "residual lipids" in overweight men (n ϭ 8) using VLDL-TG and palmitate tracers in combination with muscle biopsies in a randomized, placebo-controlled design. Participants received placebo or acipimox on each study day (4 h of rest, 90 min of exercise at 50% V O2 max). Exercise suppressed VLDL-TG secretion significantly during placebo but not acipimox (placebo-rest: 64.2 Ϯ 9.4; placebo-exercise: 48.3 Ϯ 8.0; acipimox-rest: 55.2 Ϯ 13.4; acipimoxexercise: 52.0 Ϯ 10.9). Resting oxidation of VLDL-TG FA and FFA was significantly reduced during acipimox compared with placebo, whereas "residual lipid oxidation" increased significantly [VLDL-TG oxidation (placebo: 18 Ϯ 3 kcal/h; acipimox: 11 Ϯ 2 kcal/h), FFA oxidation (placebo: 14 Ϯ 2 kcal/h; acipimox: 4 Ϯ 0.5 kcal/h), and residual lipid oxidation (placebo: 3 Ϯ 5 kcal/h; acipimox: 14 Ϯ 5 kcal/h)]. Additionally, during exercise on both placebo and acipimox, oxidation of VLDL-TG and FFA increased, but the relative contribution to total lipid oxidation diminished, except for FFA, which remained unchanged during acipimox. Residual lipid oxidation increased significantly during exercise in both absolute and relative terms. Changes in selected cellular enzymes and proteins provided no explanations for kinetic changes. In conclusion, suppressed FFA availability blunts the effect of exercise on VLDL-TG secretion and modifies the contribution of lipid sources for oxidation. very low-density lipoprotein; exercise; antilipolysis; lipid oxidation OVERWEIGHT IS ASSOCIATED with proatherogenic abnormalities of lipid metabolism. The alterations reflect reduced insulin suppression of both hepatic very low-density lipoprotein triglyceride (VLDL-TG) secretion and adipose tissue lipolysis, leading to greater plasma triglycerides (TG) and free fatty acid (FFA) concentrations (30). Many of these abnormalities are reversed by physical exercise (21). During low-to moderateintensity exercise, fasting lipid oxidation accounts for ϳ50% of energy expenditure (EE) (25,33,46), and the major sources are plasma FFA, intramyocellular lipids (IML), and VLDL-TG fatty acids (FA). Plasma FFA oxidation (19), measured isotopically (15), increases rapidly during exercise. Conversely, measurements of VLDL-TG oxidation are methodologically challenging (24) and have been calculated mostly from regional A-V concentration differences (19); however, these differences cannot differentiate between tissue oxidation and storage, and IML oxidation has usually been calculated indirectly by subtracting plasma FFA oxidation from total lipid oxidation measured by indirect calorimetry (...

mentioning

confidence: 99%

Kinetics and utilization of lipid sources during acute exercise and acipimox

American Journal of Physiology-Endocrinology and Metabolism

Søndergaard

Jensen

et al. 2014

Self Cite

“…However, in this study we used a novel and validated method that allows direct measurements of VLDL-TG FA oxidation (21). VLDL-TG contributes significantly to energy expenditure (EE) at rest (10-15%) (23,24), but the effective amount oxidized remains unaltered during acute aerobic exercise in healthy lean subjects (22). In this study, we extend these findings to include an unchanged VLDL-TG FA oxidation following long-term training in healthy men.…”

Section: European Journal Of Endocrinologymentioning

confidence: 92%

“…This is the first study to perform combined direct measurements of whole-body VLDL-TG and palmitate kinetics and oxidation before and after long-term supervised endurance training in healthy sedentary men. Most previous studies have examined VLDL-TG kinetics in relation to a single bout of exercise and reported increased VLDL-TG clearance of short duration (1 day) (9,10,12,22). In order to investigate the long-term effects of training while at the same time avoiding interference of any residual effects induced by acute exercise, this study was designed so that the metabolic study day was placed 60-72 h after the last exercise bout.…”

Section: European Journal Of Endocrinologymentioning

confidence: 99%

“…The previously mentioned acute kinetic changes during exercise and in the early recovery period (22) could indicate that a redistribution of TG and VLDL-TG takes place during that period, replenishing TG depots in, for example, muscle and liver during the recovery period, thereby potentially improving the ability to meet energy needs. The data from this study lends indirect support to the theory of a temporary acute TG FA redistribution, as the hepatic secretion rate was unchanged 60-72 h after the last exercise bout, despite improved physical performance and insulin sensitivity.…”

Section: European Journal Of Endocrinologymentioning

confidence: 99%

“…Importantly, however, the methods used do not allow direct measurements of VLDL-TG FA oxidation, which is central to understanding the mechanisms underlying prolonged effects of training on systemic VLDL-TG metabolism. Previous studies have reported (21,22,23) that postabsorptive VLDL-TG FA accounts for 10-15% of whole-body resting energy expenditure (REE) in healthy sedentary humans (22,23,24). Moreover, VLDL-TG secretion and clearance rates were significantly decreased during acute exercise as well as during the immediate recovery of the exercise bout of 90 min at 50% of maximal oxygen uptake (VO 2 max), whereas VLDL-TG FA oxidation rate was largely unchanged compared with resting levels (22).…”

Section: Introductionmentioning

confidence: 99%

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Ten weeks of aerobic training does not result in persistent changes in VLDL triglyceride turnover or oxidation in healthy men

European Journal of Endocrinology

Christensen

Vissing

et al. 2014

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Objective: Very low density lipoprotein triglyceride (VLDL-TG) and free fatty acids (FFA) constitute a substantial proportion of human energy supply both at rest and during exercise. Exercise acutely decreases VLDL-TG concentration, and VLDL-TG clearance is increased after an exercise bout. However, the effects of long-term training are not clear. Design: The aim was to investigate long-term effects of training by direct assessments of VLDL-TG and palmitate kinetics and oxidation in healthy lean men (nZ9) at rest, before and after a 10-week training program, compared with a non-training control group (nZ9). Methods: VLDL-TG kinetics were assessed by a primed constant infusion of [1-14 C]VLDL-TG, and VLDL-TG oxidation by specific activity ( 14 CO 2 ) in expired air. The metabolic study days were placed 60-72 h after the last exercise bout.Results: Palmitate kinetics and oxidation were assessed by a 2 h constant infusion of [9,10-3 H]palmitate. In the training group (nZ9), maximal oxygen uptake increased significantly by z20% (P!0.05), and the insulin sensitivity (assessed by the hyperinsulinemic-euglycemic clamp) improved significantly (P!0.05). Despite these metabolic improvements, no changes were observed in VLDL-TG secretion, clearance, or oxidation or in palmitate kinetics. Conclusion:We conclude that 10 weeks of exercise training did not induce changes in VLDL-TG and palmitate kinetics in healthy lean men.

Lean body mass, not FFA, predicts VLDL-TG secretion rate in healthy men

Søndergaard

Sørensen

et al. 2015

Obesity

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Objective: Triglyceride is a risk factor for cardiovascular disease. However, the impact of body composition and free fatty acid (FFA) levels on very-low-density-lipoprotein triglyceride (VLDL-TG) secretion remains controversial. The aim was to identify predictors of VLDL-TG secretion in a data set compiled from seven previously published studies. Methods: VLDL-TG kinetics was studied in 96 healthy men covering a wide span in body composition. A primed-constant infusion of ex vivo labeled [1-14 C]-triolein VLDL-TG was used. Body composition was determined by dual X-ray absorptiometry and computed tomography scanning. Energy expenditure was measured by indirect calorimetry. Palmitate flux was measured by a [9, H]-palmitate infusion. Results: VLDL-TG secretion rate correlated significantly with body mass index (BMI), lean body mass (LBM), total fat mass, resting energy expenditure (REE), and insulin. A trend toward an inverse relationship between VLDL-TG secretion rate and FFA concentration was observed. In mixed model linear regression analysis, VLDL-TG secretion rate was positively associated with LBM (P 5 0.03), and VLDL-TG clearance rate was inversely related to total fat mass (P < 0.01). Conclusions: LBM is a predictor of VLDL-TG secretion in healthy men, whereas FFA availability is not associated with VLDL-TG secretion. The work suggests reporting VLDL-TG secretion rates normalized for LBM when comparing subjects with differences in body composition.