Abstract 1749: Endothelial Progenitor Cells and Vascular Endothelial Function Follow a Parallel Circadian Pattern
Background: Endothelial Progenitor Cells (EPCs) are mobilized in response to endothelial injury and their counts correlate with endothelial function and cardiovascular risk burden. This rare cell population can be characterized by either flow cytometric analysis or mononuclear cell culture and colony counting, however, the 24-hour circadian variation and inter-relation of EPC measures with endothelial function remain unknown. We hypothesized that EPC levels and endothelial function will have a similar circadian variation.
Methods: In 12 healthy subjects (8 men, 42 ± 18 yrs), we investigated the circadian variation of: 1-circulating cells positive for:
the number of colonies formed by culturing mononuclear cells utilizing a 7-day assay and
flow-mediated vasodilation utilizing brachial artery reactivity at 8am, noon, 4pm, 8pm, midnight, 4am and 8am.
Results: ANOVA for repeated measures over 24 hours indicated significant changes in the number of colony counts (p < .001, highest at midnight). Similarly, flow-mediated vasodilation was highest at midnight (p < .001). In contrast, CD34+ and dual positive CD34+ /CD133+ cell counts peaked a little earlier at 8 pm (8 pm vs.8 am p = .07 and .01 for paired t-tests, respectively). (Figure⇓)
Conclusion: Endothelial function and EPCs estimated as colony forming units peak at midnight and are lower at other times of the day. The highest counts of circulating progenitors are seen at 8pm. There is a parallel change in circulating EPCs and vascular endothelial function during a 24-hour period, with lower levels in the morning hours.