Anders Dyhr Toft

Prolonged exercise, lymphocyte apoptosis and F2-isoprostanes

Abstract. Exercise induces a post-exercise decline in the number of circulating lymphocytes. The aim of the present study was to investigate whether strenuous exercise induces lymphocyte apoptosis and generation of reactive oxygen species. Eleven healthy male subjects exercised for 2.5xa0h on a treadmill. Apoptotic lymphocytes were defined by being annexin positive and 7-aminoactinomycin-D negative. Measurement of F2-isoprostanes was used as a marker of oxidant stress in vivo. An increase (60%, P<0.05) in the percentage of apoptotic circulating lymphocytes was found 2xa0h post-exercise, whereas the total number of apoptotic cells did not change in relation to exercise. The concentration of plasma F2-isoprostanes increased approximately 1.6-fold in response to exercise, but declined towards pre-exercise values within the 1stxa0h of recovery. The plasma concentrations of adrenaline, noradrenaline and cortisol increased during exercise. In conclusion, the results of the present study demonstrate that even in a study design in which high levels of apoptosis-inducing factors are generated, such as cortisol and isoprostanes, lymphocyte apoptosis does not contribute to post-exercise lymphocytopenia.

Exercise and the immune system - influence of nutrition and ageing

In essence, the immune system is enhanced during moderate and severe exercise, and only intense long-duration exercise is followed by impairment of the immune system. The latter includes suppressed concentration of lymphocytes, suppressed natural killer cell activity, lymphocyte proliferation and secretory IgA in saliva. During the time of immune impairment, referred to as the open window, microbial agents, especially viruses may invade the host and infections may be established. One reason for the overtraining effect seen in elite athletes could be that this window of opportunism for pathogens is longer and the degree of immunosuppression more pronounced. Alterations in metabolism and metabolic factors may contribute to exercise-associated changes in immune function. Reductions in plasma-glutamine concentrations, altered plasma-glucose level, free oxygen radicals and prostaglandins (PG) released by the elevated number of neutrophils and monocytes may influence the function of lymphocytes and contribute to the impaired function of the later cells. Thus, nutritional supplementation with glutamine, carbohydrate, anti-oxidants or PG-inhibitors may, in principle, influence exercise-associated immune function. Although several intervention studies have been performed, it is premature to make recommendations regarding nutritional supplementation to avoid post-exercise impairment of the immune system.

Bactericidal effect of colistin on planktonic Pseudomonas aeruginosa is independent of hydroxyl radical formation

The bactericidal effect of several major types of antibiotics has recently been demonstrated to be dependent on the formation of toxic amounts of hydroxyl radicals (OH·) resulting from oxidative stress in metabolically active cells. Since killing by the antimicrobial peptide colistin does not require bacterial metabolic activity, we tested whether the bactericidal effect of colistin depends on the formation of OH·. In Pseudomonas aeruginosa cultures, OH-mediated killing by ciprofloxacin was demonstrated by decreased bacterial survival and induction of 3-(p-hydroxyphenyl) fluorescein (HPF) fluorescence. OH·-mediated killing by ciprofloxacin was further confirmed by rescue of cells and reduction of HPF fluorescence due to prevention of OH· accumulation by scavenging with thiourea, by chelating with dipyridyl, by decreasing metabolism as well as by anoxic growth. In contrast, no formation of OH· was seen in P. aeruginosa during killing by colistin, and prevention of OH· accumulation could not rescue P. aeruginosa from killing by colistin. These results therefore demonstrate that the bactericidal activity of colistin on P. aeruginosa is not dependent on oxidative stress. In conclusion, antimicrobial peptides that do not rely on OH· formation should be considered for treatment of Gram-negative bacteria growing at low oxygen tension such as in endobronchial mucus and paranasal sinuses in cystic fibrosis patients, in abscesses and in infectious biofilm.

Source and kinetics of interleukin-6 in humans during exercise demonstrated by a minimally invasive model

The objective of this study was to use a novel and non-invasive model to explore whether: (1) exercise-induced increases in systemic levels of interleukin-6 (IL-6) and other cytokines can be ascribed to local production in working muscle; and (2) how acute release of retained blood from an exercised limb impacts on metabolites in the systemic circulation. On two experimental days, at least 3xa0weeks apart, six healthy moderately trained male subjects performed one-legged knee-extensor exercise for 2xa0h at 60% of their maximal workload. On one occasion venous outflow from the exercised leg was inhibited for 18xa0min by inflating a cuff around the thigh as proximally as possible immediately following exercise. On the control occasion venous outflow was not inhibited. Venous blood samples were collected from an arm vein at 2-min intervals after exercise. During inhibition of venous outflow from the exercised leg systemic plasma levels of IL-6 decreased within minutes to near pre-exercise levels, whereas plasma glucose levels increased to higher levels than without the cuff. After release of the cuff, systemic levels of IL-6 increased rapidly to match levels on the control occasion. On release of the cuff, plasma levels of free fatty acids (FFAs) declined more than without the cuff. In conclusion, the observed increase in systemic IL-6 plasma concentrations during exercise can be attributed to release from the working limb. Other potential sources of IL-6 outside the working limb do not contribute significantly to the increase in plasma IL-6 levels during exercise.

Effects of eccentric cycling exercise on IGF-I splice variant expression in the muscles of young and elderly people.

Recovery from micro damage resulting from intensive exercise has been shown to take longer in older muscles. To investigate the factors that may contribute to muscle repair, we have studied the expression of two splice variants of the insulin‐like growth factor‐I (IGF‐I) gene. IGF‐IEa and mechano growth factor (MGF) were studied in response to 1u2003h of eccentric cycling exercise in young and old individuals. Subjects (nine young, aged 20–27 years and eight elderly, aged 67–75 years) completed an eccentric exercise protocol that consisted of 60u2003min of reverse pedal cycling. Workloads were chosen to give the same relative increases in oxygen uptake (VO2max) and heart rate in young and old subjects. Muscle biopsy samples were obtained from the quadriceps muscle before and 2¼u2003h after completion of the exercise bout and were analyzed for IGF‐IEa and MGF mRNA levels using real‐time quantitative PCR. No difference was observed between the baseline levels of the two splice variants between the two subject groups. Eccentric cycling exercise resulted in a significant increase in the mean MGF mRNA in both young and old subjects but did not alter IGF‐IEa mRNA levels in either age group. As reported previously ( Toft et al., 2002 ), the levels of serum creatine kinase and myoglobin, markers of muscle damage, were increased significantly from baseline and to 5 days after exercise in both young and old subjects. This supports previous research in suggesting that the MGF splice variant is sensitive to muscle damage‐inducing exercise and is differentially regulated compared with IGF‐IEa.