Safety of Hypoxia-Primed Mesenchymal Stem Cells Derived from Umbilical Cord and Adipose Tissuesin Animals

Background: Mesenchymal stem cells (MSCs) have been applied to treat various diseases. Research has shown that hypoxic conditions (2-9% oxygen) that closely reflect the physiological milieu of numerous human tissues, can enhance the biological activities of MSCs in vitro. While many studies highlight the advantages of hypoxic MSCs in vitro , less is known about their effects in vivo . This study assessed the safety of hypoxia-primed MSCs derived from adipose tissues and umbilical cords (AD-MSCs and UC-MSCs, respectively) in healthy animals. Methods: MSCs were isolated from human adipose tissues and umbilical cords, designated as AD-MSCs and UC-MSCs, respectively. These cells were cultured under hypoxic conditions with 5% oxygen to induce priming. For safety evaluation, the primed cells were administered to healthy animal models, including rabbits, Swiss mice, and rats. The safety assessments included analyses of vascular and muscular stimulation, systemic hypersensitivity, acute toxicity, and subchronic toxicity. Results: Our data indicated that UC-MSCs induced vascular stimulation but not muscular stimulation, whereas AD-MSCs caused neither. Additionally, neither AD-MSCs nor UC-MSCs affected hematopoietic parameters (white blood cell, red blood cell, platelet, or hemoglobin levels), altered the levels of proinflammatory cytokines (IL-6, IL-1β, IFN-γ, and TNF-α), or induced allergenic responses in rabbits. Furthermore, intravenous injection of either UC-MSCs or AD-MSCs at a dose of 50 × 10 ⁶ cells/kg did not cause acute toxicity in mice. However, injections of higher doses of these cells led to intravenous thrombosis and embolism in various organs of experimental animals, ultimately resulting in animal death. Finally, according to the subchronic toxicity assay, the administration of MSCs generally did not impact liver, kidney, or spleen function in rats. Conclusions: Hypoxic MSCs are safe for therapeutic use with consideration of thrombogenic risk and could be alternatives to normoxic MSCs for disease treatment.