Ischemia-related changes in circulating stem and progenitor cells and associated clinical characteristics in peripheral artery disease

Abstract

The extent and clinical significance of stem and progenitor cell (SPC) increases in response to lower-extremity ischemia in people with peripheral artery disease (PAD) are unclear. We compared changes in SPC levels immediately following a treadmill exercise test between individuals with and without PAD. Among participants with PAD, we determined whether more severe PAD was associated with greater increases in SPCs following treadmill exercise-induced lower-extremity ischemia. We measured SPC levels in 25 participants with PAD and 20 without PAD before and immediately after a treadmill exercise test. Participants with PAD, compared to participants without PAD, had greater increases in CD34(+)CD45(dim) (+0.08±0.03 vs -0.06±0.04, p=0.008), CD34(+)CD45(dim)CD133(+) (+0.08±0.05 vs -0.08±0.04, p=0.014), CD34(+)CD45(dim)CD31(+) (+0.10±0.03 vs -0.07±0.04, p=0.002), and CD34(+)CD45(dim)ALDH(+) SPCs (+0.18±0.07 vs -0.05±0.08, p=0.054) measured as a percentage of all white blood cells. Among participants with PAD, those with any increases in the percent of SPCs immediately after the treadmill exercise test compared to those with no change or a decrease in SPCs had lower baseline ankle-brachial index values (0.65±0.17 vs 0.90±0.19, p=0.004) and shorter treadmill times to onset of ischemic leg symptoms (2.17±1.54 vs 5.25±3.72 minutes, p=0.012). In conclusion, treadmill exercise-induced lower-extremity ischemia is associated with acute increases in circulating SPCs among people with PAD. More severe PAD is associated with a higher prevalence of SPC increases in response to lower-extremity ischemia. Further prospective study is needed to establish the prognostic significance of ischemia-related increases in SPCs among patients with PAD.

Keywords: ischemia; peripheral artery disease; stem and progenitor cells; treadmill exercise.

Figure 1. Gating strategy and test/retest reliability of stem and progenitor cell measurements by FACS analysis

A) CD45⁺ cells were analyzed after doublet, debris, dead cell and red blood cell exclusion. The CD34⁺ cell fraction was then identified and further purified by removing any cells that express high levels of CD45 and low forward scatter properties. Expression of ALDH, CD133, and CD31 were then analyzed. This strategy is a modification of the previously published, widely used International Society for Hematotherapy and Graft Engineering gating strategy . B) Coefficient of variation and correlation coefficients of the test/retest analysis of CD34⁺CD45^dimALDH⁺, CD34⁺CD45^dim, CD34⁺CD45^dimCD133⁺, and CD34⁺CD45^dimCD31⁺ SPC populations are listed.

Figure 2. Association of percent change of stem and progenitor cells 15 minutes and 24 hours post treadmill exercise test with ankle brachial index scores among participants with and without peripheral artery disease

Scatter plot depicting the correlation between ABI and SPC changes. Correlation coefficients of the relationship between ABI and SPC changes for 24 PAD and 19 non-PAD participants at 15 minutes post treadmill exercise test and 11 PAD and 10 non-PAD participants at 24 hours post treadmill exercise test are listed on the scatter plots. Data values listed are correlation coefficients between PAD and non-PAD as determined by regression analysis.