Outgrowing Endothelial Cells That Are Derived from Human Umbilical Cord Blood Improve Neovascularization in Hind-Limb Ischemia.

Backgroud: Human umbilical cord blood (UCB) contains a high number of endothelial progenitor cells (EPCs) and may be useful for the treatment of ischemic disease. Recently, we have isolated EPCs from UCB having different biologic properties for angiogenic capabilities in vitro. In this present study, the aim is to examine the usefulness of OECs in hind-limb ischemia.

Methods: Mononuclear cells from UCB cultured using EGM-2 medium with VEGF, IGF-1 and FGF for 21 days. Early spindle-shaped cells (early OECs), which were grown during the first week of culture and late cobblestone shaped cells (late OECs), which were in peak growth during the third week of culture were found. The hind-limb ischemia was established as follows: Athymic nude mice (BALB/C-nu) 18–22 g in weight were anesthetized with pentobarbital (60 mg/kg) and their left femoral arteries and main extension arteries were operatively resected. To examine the effect of the vasculogenesis of the two types of OECs, the mice were divided into three groups (PBS, early and late OECs). Twenty-four hours after operative excision 5 × 10⁵ OECs in 200 μl and an equal volume of PBS were administered by intramuscular injection into the mice on hind-limb ischemia. To compare the effect of OECs on neovascularization in vivo, the analysis of blood flow of ischemic and healthy hind limbs was performed on days 1 and 21 after surgery using near-infrared (NIR) imaging with incocyanne Green (ICG).

Results: Late OECs expressed a high level of mRNA on endothelial marker genes and formed capillary tubes in Matrigel plates. The early spindle cells excreted more angiogenic cytokines and had more migratory ability. We divided the mice into two groups according to the degree of perfusion; good (22.5–50%/min) and poor (0–22.5%) perfusion. OECs improved the blood flow of the ischemic hind-limb in the ’good’ perfusion group but not in the ’poor’ perfusion group. Early OECs led to a more significant improvement in blood flow than that of the late OECs.

Conclusion: The different types of OECs from UCB have different biologic properties in vitro and different vasculogenic potential in vivo as well. The results might have potential application for the treatment of hind-limb ischemia.