Endothelial progenitor cells are thought to have the capacity to repair damaged endothelium and improve endothelial function and perfusion. Animal studies have shown endothelial progenitor cells are incorporated into the damaged endothelial layer of the hindlimb, thereby increasing perfusion (Circ Res 1999;85:221-228).
Two recent studies examining the effect of intensive exercise (marathon running and rowing) on young participants by Maria Bonsignore and colleagues yielded conflicting results. One showed down-regulation of progenitor cells the morning after the race (J Appl Physiol 2002;93:1691-1697), while the other showed significant increases in progenitor cells shortly after “all-out rowing” (Am J Physiol 2005;289:R1496-R1503).
As part of a wider study initiated by the Marathon Study Group looking at risk stratification in marathon runners, Adams and his team analysed blood samples from 78 older, healthy, marathon runners (age 63+-3 years), both before and immediately after they had completed a marathon race. Cells were fluorescently labelled with specific antibodies for cell surface markers such as CD34, CD133 or KDR, and then the circulating progenitor cells were measured using Fluorescent Activated Cell Sorting (FACS).
Measurements before and after the race showed a significant decrease in progenitor cells that reacted positively to CD34, CD117 and CD133. In addition, a significant increase in white blood cells was detected, demonstrating that an inflammatory response had been triggered.
Adams said further studies were underway to see how long it takes to normalise circulating progenitor cell levels, and whether the temporary decrease has any impact on heart and endothelial function.
“This is pure speculation, but if circulating progenitor cells continue to be depressed it may be that the arteries do not recover so quickly from the extreme inflammatory state produced by marathons,” said Adams, adding he did not believe less intensive exercise had this adverse effect.
“What’s still under debate is the signal responsible for the training-induced liberalisation of cells from the bone marrow. We speculate that under intensive exercise the inflammatory situation may suppress liberalisation of progenitor cells from the bone marrow.”