Optimization of cryopreservation procedures for porcine endothelial progenitor cells

The Effect of Cryopreservation on the Bone Healing Capacity of Endothelial Progenitor Cells in a Bone Defect Model

Endothelial progenitor cells (EPCs) have proven to be a highly effective cell therapy for critical-sized bone defects. Cryopreservation can enable long-term storage of EPCs, allowing their immediate availability on demand. This study compares the therapeutic potential of EPCs before and after cryopreservation in a small animal critical-sized bone defect model. Five-millimeter segmental defects were created in the right femora of Fischer 344 rats, followed by stabilization with a miniplate and screws. The animals received 2 × 106 fresh EPCs (n = 7) or 2 × 106 cryopreserved EPCs (n = 9) delivered on a gelatin scaffold. Cryopreserved EPCs were stored for 7 days at -80°C prior to thawing and loading onto the gelatin scaffold. Biweekly radiographs were taken until the animals were euthanized 10 weeks after surgery. The operated femora were then evaluated using microscopic-computed tomography (micro-CT) and biomechanical testing. All animals treated with fresh (n = 7/7) or cryopreserved (n = 9/9) EPCs achieved radiographic union at 10 weeks. Animals treated with fresh EPCs had statistically significant higher radiographic scores at 2 weeks (p < 0.05) but showed no statistically significant differences thereafter (p > 0.05). Micro-CT analysis showed no statistically significant differences between the groups in bone volume (BV) or BV normalized to total volume (p > 0.05), with excellent bone formation in both groups. Finally, there were no differences in biomechanical outcomes between the groups (p > 0.05). These results demonstrate that cryopreserved EPCs are highly effective and equivalent to fresh EPCs for healing critical-sized bone defects in a rat model of nonunion.

Potential Role of Caveolin-1 in Regulating the Function of Endothelial Progenitor Cells from Experimental MODS Model

Multiple organ dysfunction syndrome (MODS) remains a great challenge in critical care because of its common occurrence, high cost of care, and high mortality. Vascular endothelial injury is the initiation step in the development of MODS, and EPCs are essential for the process of organ repair. It is unclear whether and how caveolin-1 (Cav-1) in EPCs contributes to the pathogenesis of MODS. The present study is aimed at investigating the potential role of Cav-1 in EPCs during MODS. We established a MODS model in pigs, isolated and characterized EPCs from the MODS model, and tracked Cav-1 expression and various in vitro behaviors of EPCs from the MODS model. Then, we knockdown Cav-1 expression with siRNA or induce Cav-1 expression with proinflammatory factors to evaluate potential effects on EPCs. Our results suggest that Cav-1 expression correlated with EPC functions during MODS and Cav-1 regulates the function of endothelial progenitor cells via PI3K/Akt/eNOS signaling during MODS. Thus, Cav-1 in EPCs could be an attractive target for the treatment of MODS.

Bone marrow derived endothelial progenitor cells retain their phenotype and functions after a limited number of culture passages and cryopreservation

A critical limitation for tissue engineering and autologous therapeutic applications of bone marrow derived EPCs is their low frequency, which is even lower in number and activity level in patients with cardiovascular risk factors and other diseases. New strategies for obtaining and reserving sufficient ready-to-use EPCs for clinical use have hit major obstacles, because effects of serial passage and cryopreservation on EPC phenotype and functions are still needed to be explored. The present study aims at investigating effects of a limited number of culture passages as well as cryopreservation on EPC phenotype and functions. We isolated EPCs from rat bone marrow and cultured them up to passage 12 (totaling achievements of 40 population doublings). The phenotype and functions of fresh cultured and post-cryopreserved EPCs at passages 7 and 12, respectively, were evaluated. EPCs at passage 12 maintained the morphological characteristics, marker phenotype, Dil-ac-LDL uptake and FITC-UEA-1 binding functions, enhanced EPCs proliferation, tube formation and migration, but decreased CD133 expression compared with EPCs at passage 7. Cryopreservation caused limited impairment in EPC phenotype and functions. In brief, our results demonstrated that a limited number of culture passages and cryopreservation did not change EPC phenotype and functions, and can be used for the development of robust strategies and quality control criterion for obtaining sufficient and high-quality ready-to-use EPCs for tissue engineering and therapeutic applications.

Effects of cryopreservation on excretory function, cellular adhesion molecules and vessel lumen formation in human umbilical vein endothelial cells

Cryopreservation is widely used in regenerative medicine for tissue preservation. In the present study, the effects of cryopreservation on excretory function, cellular adhesion molecules and vessel lumen formation in human umbilical vein endothelial cells (HUVECs) were investigated. After 0, 4, 8, 12 or 24 weeks of cryopreservation in liquid nitrogen, the HUVECs were thawed. The excretory functions markers (endothelin-1, prostaglandin E1, von Willebrand factor and nitric oxide) of HUVECs were measured by ELISA assay. The expression of intercellular adhesion molecule-1 (ICAM-1) in HUVECs was analyzed using flow cytometry. An angiogenesis assay was used to determine the angiogeneic capabilities of the thawed HUVECs. The results demonstrated that cryopreserved/thawed and recultivated HUVECs were unsuitable for tissue-engineered microvascular construction. Specifically, the excretory function of the cells was significantly decreased in the post-cryopreserved HUVECs at 24 weeks. In addition, the level of ICAM-1 in HUVECs was significantly upregulated from the fourth week of cryopreservation. Furthermore, the tube-like structure-forming potential was weakened with increasing cryopreservation duration, and the numbers of lumen and the length of the pipeline were decreased in the thawed HUVECs, in a time-dependent manner. In conclusion, the results of the present study revealed that prolonged cryopreservation may lead to HUVEC dysfunction and did not create stable cell lines for tissue-engineered microvascular construction.

Cryopreservation and Enumeration of Human Endothelial Progenitor and Endothelial Cells for Clinical Trials

BACKGROUND

Endothelial progenitor cells (EPC) are markers of endothelial injury and may serve as a surrogate marker for vascular repair in interventional clinical trials. Objectives of this study were to modify a method of isolation of peripheral blood mononuclear cells (PBMC) and enumeration of EPC and mature endothelial cells (EC) from peripheral blood and to evaluate influence of cryopreservation on viability of PBMC and on numbers of EPC and EC.

PATIENTS/METHODS

EPC and EC were analyzed in healthy volunteers in freshly isolated PBMC collected in CPT (cell preparation tubes) and in PBMC cryopreserved with: 1) Gibco Recovery™ Cell Culture Freezing Medium, 2) custom freezing medium. Viability of PBMC was tested using DAPI. EPC were gated for CD45- CD34+CD133+/-VEGFR2+/- and EC were gated for CD45-CD146+CD34+/-VEGFR2+/-.

RESULTS

Cryopreservation for 7 days at -80°C decreased viable PBMC from 94 ± 0.5% (fresh) to 84 ± 4% (the custom medium) and to 69 ± 8% (Gibco medium), while cryopreservation at -65°C decreased viability to 60 ± 6% (p<0.001, the custom medium) and 49 ± 5% (p<0.001, Gibco medium). In fresh samples early EPC (CD45- CD34+CD133+VEGFR2+) were enumerated as 0.2 ± 0.06%, late EPC(CD45-CD146+CD34+VEGFR2+) as 0.6 ± 0.1% and mature EC (CD45-CD146+CD34-VEGFR2+) as 0.8 ± 0.3%of live PBMC. Cryopreservation with Gibco and the custom freezing medium at -80°C for 7 days decreased numbers EPC and EC, however, this decrease was not statistically significant.

CONCLUSIONS

Our data indicate that cryopreservation at -80°C for 7 days decreases, although not significantly, viability of PBMC and numbers of subsets of EC and EPC. This method may provide an optimized approach to isolation and short-term cryopreservation of subsets of EPC and of mature EC suitable for multicenter trials.