1. Endothelial Progenitor Cells (EPCs)
The following section examines endothelial progenitor cells and their role in cardiovascular regenerative medicine.

2. Endothelial dysfunction
EPCs in CV diseases
EPCs
Pathophysiology
Therapeutics
CV risk factors
Endothelial dysfunction
Collaterals
Restenosis
CV disease
Atherosclerosis
Heart disease
Peripheral vascular disease
EPCs in CV diseases
CV risk factors contribute to atherogenesis by inducing endothelial cell injury and dysfunction.
Many studies have been investigating EPCs for their potential role in angiogenesis, and due to their relatively high frequency in the circulation and the limited degree of neovascularization that occurs in healthy adults, EPCs may well have an important role beyond angiogenesis.
Courtesy of Arshed A. Quyyumi, MD.

3. Circulating EPCs aid in cardiac repair
CD34+, CD133+, and VEGF2R+
Circulate in blood stream
Contribute to repair of vascular or myocardial injury and collateral formation
Circulating EPCs aid in cardiac repair
Neovascularization is considered to result from the proliferation, migration, and remodeling of fully differentiated EPCs derived from pre-existing blood vessels.
Circulating EPCs are mobilized endogenously in response to tissue ischemia or exogenously by cytokine therapy and thereby contribute to neovascularization of ischemic tissues.
As seen in the photo, EPC colonies are characterized by a central cluster of rounded cells surrounded by radiating thin, flat cells.
Asahara T et al. Science. 1997;275:964-7.
Takahashi T et al. Nature Med. 1999;5:434-8.

4. EPC physiology Originate in bone marrow Circulate in blood stream
Number and function (proliferation, migration, homing) modulated by age, CV risk factors, and disease
Release stimulated by organ and vascular injury
Participate in vascular repair (collateralization) and re-endothelialization, partly by paracrine effects
Circulating numbers by exercise and drugs (statins and ACE inhibitors)
Independent predictors of endothelial dysfunction and long-term prognosis in patients with CAD
EPC physiology
In one study, the levels of circulating EPCs were found to be a better predictor of vascular reactivity than the presence or absence of conventional risk factors. Also, EPCs from subjects with a high CV disease risk had higher rates of in vitro senescence than cells from subjects at low risk.
Levels of EPCs may be a surrogate biologic marker for vascular function and cumulative cardiovascular risk.
These findings suggest that endothelial injury in the absence of sufficient circulating progenitor cells may increase the risk of CV disease.
Hill JM et al. N Engl J Med. 2003;348:

5. EPC number has prognostic importance
N = 519 males with CAD, mean age 66 y
1.00
Group 3 (high EPC level)
0.98
0.96
Group 2 (medium EPC level)
Event-free
survival
0.94
Group 1 (low EPC level)
0.92
EPC number has prognostic importance
In a recent analysis of death from CV causes, higher levels of CD34+KDR+ EPCs were associated with a decreased risk of death from CV causes.
Cumulative event-free survival increased dramatically with increasing levels of baseline EPCs.
The risk of death from CV causes was increased more than 3 times among males with low EPCs levels, as compared with males having high levels.
0.90
100
200
300
365
Days
Werner N et al. N Engl J Med. 2005;353:

6. Association between CV risk factors and EPC colony counts
N = 45 males without CAD, > 21 years (mean age 50.3) 70 60
r = –47.0
P = 0.001 50 40
EPC colony-forming units 30 20
Association between CV risk factors and EPC colony counts 10
A strong association was found between CV risk factors and EPC colony counts.
The number of colony-forming units was strongly correlated with the subjects’ Framingham risk score, with a significant inverse correlation between the score and EPC counts.
Framingham risk score
Hill JM et al. N Engl J Med. 2003;348:

7. Mobilization of EPCs after myocardial infarction
N = 16 patients with AMI, 8 controls
P < P < 0.001
P < P < 0.05
300
200
MNCCD34+ (/106WBCs)
100
Mobilization of EPCs after myocardial infarction
EPCs circulate in adult peripheral blood (PB) and contribute to neovascularization. However, little is known whether EPCs and their putative precursor, CD34+ mononuclear cells (MNCCD34+), are mobilized into PB in acute ischemic events. Flow cytometry revealed that circulating MNCCD34+ counts significantly increased in patients with acute MI, peaking on day 7 after onset.
During culture, PB-MNCs formed multiple cell clusters, and EPC-like attaching cells with endothelial cell lineage markers sprouted from the clusters. In patients with acute MI, more cell clusters and EPCs developed from cultured PB-MNCs obtained on day 7 than those on day 1.
Plasma levels of vascular endothelial growth factor (VEGF) significantly increased, peaking on day 7, positively correlating with circulating MNCCD34+ counts, the first clinical demonstration showing that EPCs and MNCCD34+ are indeed mobilized during an acute ischemic event in humans.
Day
Time after onset
Shintani S et al. Circulation. 2001;103:

8. VEGF levels correlate with increase in EPCs
450
r = 0.35
P = 0.01
400
350
300
250
MNCCD34+ (cells/106 WBCs)
200
150
VEGF levels correlate with increase in EPCs
100 50
The potential relationship between MNCCD34+ counts and plasma cytokine levels in acute MI were examined.
A simple regression analysis revealed that the number of circulating MNCCD34+ positively correlated with the plasma levels of VEGF.
In addition, a recent report has shown that VEGF functions as a mobilizer for EPCs in patients with CAD receiving therapeutic VEGF gene transfer. 50
100
150
200
250
300
350
400
450
Plasma VEGF (pg/mL)
Shintani S et al. Circulation. 2001;103:

9. EPC activity and coronary collaterals
30 patients with isolated left anterior descending disease
Divided into groups with (0.33) and without (0.09) adequate Collateral Flow Index (CFI)
CD34/CD133 Dual Positive Cells (% of total lymphocytes) A
0.4
0.3
0.2
0.1
Coll n=13
Coll n=10
P = 0.017 B
R = 0.75 P <
0.8
0.6
CD34/CD133 Dual Positive Cells (% of total lymphocytes)
0.4
EPC activity and coronary collaterals
0.2
The mechanisms underlying the variation in collateral formation between patients, even with similar patterns of CAD, remain unclear. This study sought to determine whether circulating humoral or cellular factors could provide additional information.
There was an inverse correlation between serum mitogenicity and CFI (r = –0.61, P < 0.01). No significant differences were detected between the 2 groups in plasma levels of total VEGF, VEGF165, or placental growth factor.
There was a strong positive correlation between numbers of CD34/CD133+ circulating hemopoietic precursor cells and CFI (r = 0.75, P < 0.001).
In patients with inadequate CFI, the numbers of differentiated EPCs appearing in the circulation and in culture were significantly reduced by 75% (P < 0.05) and 70% (P < 0.05), respectively.
Angiogram provided by Carl J. Pepine, MD.
CFI
Inadequate coronary collateral development associated with ¯ numbers of circulating EPCs and impaired chemotactic and pro-angiogenic activity
Lambiase PD et al. Circulation. 2004;109:

10. Decrease in EPCs associated with CV disease
Endothelial Progenitor Cells
Vasculoprotective agents
CV risk factors
Atherosclerosis
Disease Regression?
Disease Progression
Decrease in EPCs associated with CV disease
Improvement of endothelial function
Enhanced re-endothelialization
Reduced plaque size
Improved angiogenesis
Myocardial infarction
Ischemic stroke
Erectile dysfunction
Renal insufficiency
Peripheral artery disease
Vasculoprotective agents increase the number and function of EPCs, improving endothelial function and preventing the progression of atherosclerosis.
CV risk factors and several CV diseases have been associated with impaired number and function of circulating EPCs.
For example, all conditions of discernable atherosclerotic disease are accompanied by reduced EPC counts and migratory capacity.
Werner N, Nickenig G. Arterioscler Thromb Vasc Biol. 2006;26: