Statins, EPCs, and Capillary Density Figure 7. Statins Differentially Affect Angiogenesis of LOEPCs in Vitro. Panel A: Representative photomicrographs of porcine LOEPCs plated on polymerized Matrigel for 24 hours with no drug treatment (Control), or Pravastatin, Simvastatin or Atorvastatin (100 nM each). Images are representative of three independent experiments. Scale bar = 500 microns. Panel B: Mean vessel length was measured from photomicrographs. Means +/2 SEM are shown for three independent experiments. Significant differences from untreated cells (Control) are indicated by * (p,0.05). Panel C: Branch Point Determination-the number of branch points within LOEPCs plated on Matrigel was determined from each photomicrograph. The means +/2 SEM are shown for three experiments. Significant differences from untreated cells (Control) are indicated by * (p,0.05). doi:10.1371/journal.pone.0024868.g007 The Relationship Between Early and Late Outgrowth EPCs The identification and measurement of EPCs has evolved considerably since their original description by Ashahara et al. [18]. However, LOEPCs lack specific markers to identify the cells de novo and quantification of EPCs relies on culture-based assays. Differences in adherence to either fibronectin or type I collagen coated dishes distinguish early and late outgrowth EPCs growth, respectively. Early outgrowth EPCs are functionally distinct from LOEPCs in that they are unable to proliferate under clonogenic conditions, express cell surface markers consistent with monocytes, and fail to form functional vessels when transplanted in vivo [5,6]. While the relationship between early outgrowth EPCs and cardiovascular disease risk factors has been PLoS ONE | www.plosone.org 8 September 2011 | Volume 6 | Issue 9 | e24868