Effects of a 6-Week Sprint Interval Training Protocol at Different Altitudes on Circulating Extracellular Vesicles.

PURPOSE: To investigate the modulation of circulating exosome-like extracellular vesicles (ELVs) after 6 weeks of sprint interval training (SIT) at sea-level, 2,000 m, 3,000 m and 4,000 m. METHODS: Thirty trained endurance male athletes (18-35y) participated in a six-week SIT program (30 s all-out sprint, 4 min 30 s recovery; 4-9 repetitions, 2 sessions/week) at sea-level (SL, n = 8), 2,000 m (FiO2 0.167, n = 8), 3,000 m (FiO2 0.145, n = 7) or 4,000 m (FiO2 0.13, n = 7). Venous blood samples were taken before and after the training period. Plasma ELVs were isolated by size exclusion chromatography, counted by nanoparticle tracking analysis (NTA), and characterized according to international standards. Candidate ELVs miRNAs were quantified by real-time PCR. RESULTS: When the 3 hypoxic groups were analyzed separately, only very minor differences could be detected in the levels of circulating particles, ELVs markers or miRNA. However, the levels of circulating particles increased (+262%) after training when the 3 hypoxic groups were pooled, and tended to increase at sea-level (+65%), with no difference between these two groups. A trend to an increase was observed for the two ELVs markers, TSG101 (+65%) and HSP60 (+441%), at sea-level, but not in hypoxia. Training also seemed to decrease the abundance of miR-23a-3p and to increase the abundance of miR-21-5p in hypoxia but not at sea-level. CONCLUSIONS: A 6-week SIT program tended to increase the basal levels of circulating ELVs when performed at sea-level, but not in hypoxia. In contrast, ELVs miRNA cargo seemed to be modulated in hypoxic conditions only. Further research should explore the potential differences in the origin of ELVs between normoxic and local and systemic hypoxic conditions.