Training and fatty acid metabolism

FT-IR spectrometry analysis of plasma fatty acyl moieties selective mobilization during endurance exercise

This study was designed to describe changes in plasma fatty acyl moieties during a 2-h endurance exercise. Sixteen endurance-trained subjects cycled 2 h at 55% of maximal power output and capillary blood was sampled every 15 min. Fourier-transform infrared (FT-IR) spectrometry was used to determine correlated changes between plasma fatty acyl moieties (FAM) structural characteristics and metabolic parameters (oxygen consumption, respiratory exchange ratio, glucose, lactate, TG, glycerol, and albumin). Opposite changes were found between carbohydrate and fatty acid metabolism during the second hour of exercise, i.e., a decrease of glucose and lactate concentrations while albumin, FAM, and TG increased. For fatty acid metabolism, FAM and TG did not showed the same pattern of changes at the end of exercise, i.e., TG remained constant after 90 min while FAM continued to increase. This late FAM concentration increase was correlated to the changes in albumin concentration and the nu C=C-H/nu(as) CH3 and nu(as) CH2/nu(as) CH3 ratios. These ratios clearly showed that FAM unsaturation increased while chain length decreased. It was hypothesized that PUFA from TG adipose lipolysis ketone bodies (beta-hydroxybutyric acid) from liver may have been released in higher amounts as glycogen stores became depleted after 90 min of exercise.

Lipotoxicity: the obese and endurance-trained paradox

The potential lipotoxic effect of intramyocellular triglyceride (IMTG) accumulation has been suggested to be a major component in the development of insulin resistance. Increased levels of IMTGs correlate with insulin resistance in both obese and diabetic patients, but this relationship does not exist in endurance trained (ETr) subjects. This may be, in part, related to differences in the gene expression and activities of key enzymes involved in fatty acid transport and oxidation as well as in the perodixation status of the IMTGs in obese/diabetic patients as compared with ETr subjects. Disruptions in fat and lipid homeostasis in skeletal muscle have been shown to activate protein kinase C (PKC), which acts on several downstream signalling pathways, including the insulin and the IkappaB kinase (IKK)/NFkappaB signalling pathways. Additionally, an increased peroxidation of IMTGs may reduce insulin sensitivity by increasing TNFalpha, which is known to increase the expression of suppressor of cytokine signalling proteins (SOCS). A common characteristic observed when activating both PKC and TNFalpha/SOCS3 is the inhibition of tyrosine phosphorylation of IRS-1 and subsequently an inhibition of its activation of downstream signalling molecules. These may be important players in the development of insulin resistance and understanding their activation and expression in both obese and ETr humans should assist in understanding how and why IMTGs become lipotoxic.

The distribution of white blood cell fat oxidation in health and disease

Fat oxidation is important for maintaining health and for supplying energy for exercise. We have proposed that the predisposition for individual rates of fat oxidation is determined genetically but may be modulated by acute exercise or exercise training. The purpose of this study was to examine cellular fat oxidation in white blood cells (WBC) using [9,10-3H]palmitic acid. Sedentary controls free of symptoms (SED-C, n=32), were compared with known carnitine palmitoyltransferase (CPT) II-deficient patients (n =2), patients with fatiguing diseases (chronic fatigue syndrome, CFS, n=6; multiple sclerosis, MS, n=31), obesity (OB, n=5), eating disorders (ED, n=16), sedentary individuals prior to and after exercise (SED-Ex, n=12), exercise-trained sedentary individuals (SED-Tr, n=12), and elite runners (ER, n=5). Fat oxidation in WBC for all subjects was normally distributed (mean=0.270 +/- 0.090 nmol/h per 10(9) WBC) and ranged from 0.09 nmol/h per 10(9) WBC in CPT II-deficient patients to 0.59 nmol/h per 10(9) WBC in ER. There were no significant sex or acute exercise effects on WBC fat oxidation. Patients with MS, OB or ED were not different from SED-C; however, in CPT II-deficient patients, fat oxidation was low, while that of CFS patients was high. Exercise training in SED-C resulted in a 16% increase in fat oxidation but in ER it was still 97% higher than in SED-C. We propose that while WBC fat oxidation is not significantly affected by sex or acute exercise, and only by 15-20% with training, genetic factors play a role in determining both high and low fat oxidation in certain groups of individuals. The genetic predisposition for individual rates of fat oxidation may be easily measured using WBC fat oxidation, as has been shown for CPT II-deficient patients and for elite runners. Ranges of WBC fat oxidation that are abnormally low (<20 nmol/h per 10(9) WBC, normal 20-35) or high (>35 nmol/h per 10(9) WBC) are proposed based on genetic factors evaluated in this study.

Utilization of long-chain fatty acids in human skeletal muscle during exercise

Long-chain fatty acids (LCFA) are important sources of energy in contracting skeletal muscle: during the course of endurance exercise the contribution of LCFA in energy metabolism increases whereas when the intensity of exercise increases, the energy need is covered more and more by carbohydrates. Although this has been known for nearly 100 years, the mechanisms controlling fatty acid uptake and oxidation during various exercise modes are still not completely elucidated. Besides passive diffusion, data suggest that both membrane-associated and cytosolic fatty acid binding proteins are involved in the uptake of LCFA into skeletal muscle. However, data from human studies suggest that the regulation of fatty acid utilization in skeletal muscle during exercise lies mainly within the entrance into the mitochondria or metabolism within the mitochondria. Although possible compartmentalization within the cell makes definitive conclusions difficult, available evidence suggests that changes in malonyl CoA concentration in muscle do not play a major regulatory role in controlling LCFA oxidation during exercise in man. In contrast, it is suggested that the availability of free carnitine may play a major regulatory role in oxidation of LCFA during exercise.

Biochemical aspects of overtraining in endurance sports : the metabolism alteration process syndrome

Recent studies have shown that endurance overtraining could result from successive and cumulative alterations in metabolism, which become chronic during training. The onset of this process is a biochemical alteration in carbohydrate (saccharide) metabolism. During endurance exercises, the amount of saccharide chains from two blood glycoproteins (alpha(2)-macroglobulin and alpha(1)-acid glycoprotein) was found to have decreased, i.e. concentrations of these proteins remained unchanged but their quality changed. These saccharide chains were probably used for burning liver glycogen stores during exercise. This step was followed by alterations in lipid metabolism. The most relevant aspect of this step was that the mean chain length of blood fatty acids decreased, i.e. the same amount of fatty acids were found within the blood, but overtrained individuals presented shorter fatty acids than well-trained individuals. This suggests that alterations appeared in the liver synthesis of long-chain fatty acids or that higher peroxidation of blood lipoparticles occurred. For the final step of this overtraining process, it was found that these dysfunctions in carbohydrate/lipid metabolism led to the higher use of amino acids, which probably resulted from protein catabolism. The evolution of three protein concentrations (alpha(1)-acid glycoprotein, alpha(2)-macroglobulin and IgG(3)) correlated with this amino acid concentration increase, suggesting a specific catabolism of these proteins. At this time only, overtraining was clinically diagnosed through conventional symptoms. Therefore, this process described successive alterations in exercise metabolism that shifted from the main energetic stores of exercise (carbohydrates and lipids) towards molecular pools (proteins) normally not substantially used for the energetic supply of skeletal muscles. Now, a general biochemical model of the overtraining process may be proposed which includes most of the previously identified metabolic hypotheses.

Non-esterified fatty acid levels and physical inactivity: the relative importance of low habitual energy expenditure and cardio-respiratory fitness

The fasting concentration of non-esterified fatty acids (NEFA) and the degree to which it declines during an oral glucose tolerance test are closely associated with insulin resistance and glucose intolerance. However, relatively few studies have described possible environmental determinants of NEFA concentrations. Physical activity is likely to be related to NEFA levels, but habitual activity level is difficult to quantify in epidemiological studies. In particular, it is unclear whether NEFA is more closely related to cardio-respiratory fitness or to habitual energy expenditure. In order to quantify these relationships, we analysed data from the Ely prospective population-based study in which 931 subjects underwent a glucose tolerance test with measurements of cardio-respiratory fitness and 4 d energy expenditure by heart-rate monitoring, a technique previously validated against whole-body calorimetry and doubly-labelled water. In order to estimate the latent variables of usual fitness and energy expenditure, a subset of 190 subjects underwent repeat testing on three further occasions over 1 year. In analyses adjusting only for age and sex, energy expenditure and cardio-respiratory fitness were both negatively correlated with the total area under the NEFA curve following the oral glucose load (standardised beta coefficients -0.030 and -0.039 respectively; both P<0.001) However, further adjustment for degree of obesity and bivariate measurement error suggested that the effect of energy expenditure was significantly greater than that for fitness (-0.047 and -0.005 respectively). These results suggest that the area under the NEFA curve in the oral glucose tolerance test, a measure of insulin sensitivity, is strongly associated with the habitual level of physical activity.

Discriminant serum biochemical parameters in top class marathon performances

Blood chemical parameters were analyzed by Fourier-transform infrared spectrometry (notably for determining the concentrations of glucose, lactate, urea, glycerol, triglycerides, and proteins) in 14 top-class marathon runners (133.7+/-4.1 min at marathon, 10.1% difference between extremes) who performed a 10-km run at their individual marathon velocity. Marathon performance level was correlated to glycemia increase during exercise (9% difference between extremes; r=0.93; p<0.005). The best marathon runners presented longer and/or less unsaturated blood fatty acids during exercise (17% difference between extremes; r=0.89; p<0.01), suggesting an improved fatty acid selectivity for muscular metabolism. The marathon performance level was also found correlated to a decrease of blood triglycerides during exercise (r=20.95; p<0.003) and to a proportional glycerol concentration increase (11% difference between extremes; r=0.94; p<0.005). The best marathon runners presented higher amino acid blood delivery (r=0.88; p<0.01), which was correlated to an apparent protein catabolism. These results show that the best runners have enhanced both carbohydrate, lipid, and amino acid metabolisms to improve energetic supply to skeletal muscle during exercise.

Endurance training and GH administration in elderly women: effects on abdominal adipose tissue lipolysis

In the present study, the effect of endurance training alone and endurance training combined with recombinant human growth hormone (rhGH) administration on subcutaneous abdominal adipose tissue lipolysis was investigated. Sixteen healthy women [age 75 +/- 2 yr (mean +/- SE)] underwent a 12-wk endurance training program on a cycle ergometer. rhGH was administered in a randomized, double-blinded, placebo-controlled design in addition to the training program. Subcutaneous abdominal adipose tissue lipolysis was estimated by means of microdialysis combined with measurements of subcutaneous abdominal adipose tissue blood flow (ATBF; (133)Xe washout). Whole body fat oxidation was estimated simultaneously by indirect calorimetry. Before and after completion of the training program, measurements were performed both at rest and during 60 min of continuous cycling at a workload corresponding to 60% of pretraining peak oxygen uptake. Endurance training alone did not affect subcutaneous abdominal adipose tissue lipolysis either at rest or during exercise, as reflected by identical levels of interstitial adipose tissue glycerol, subcutaneous abdominal ATBF, and plasma nonesterified fatty acids before and after completion of the training program. Similarly, no effect on subcutaneous abdominal adipose tissue lipolysis was observed when combining endurance training with rhGH administration. However, in both the placebo and the GH groups, fat oxidation was significantly increased during exercise performed at the same absolute workload after completion of the training program. We conclude that the changed lipid metabolism during exercise observed after endurance training alone or after endurance training combined with rhGH administration is not due to alterations in subcutaneous abdominal adipose tissue metabolism in elderly women.