Prolonged oxygen exposure causes the mobilization and functional damage of stem or progenitor cells and exacerbates cardiac ischemia or reperfusion injury in healthy mice.

Oxygen is often administered to patients and occasionally to healthy individuals as well; however, the cellular toxicity of oxygen, especially following prolonged exposure, is widely known. To evaluate the potential effect of oxygen exposure on circulating stem/progenitor cells and cardiac ischemia/reperfusion (I/R) injury, we exposed healthy adult mice to 100% oxygen for 20 or 60 min. We then examined the c-kit-positive stem/progenitor cells and colony-forming cells and measured the cytokine/chemokine levels in peripheral blood. We also induced cardiac I/R injury in mice at 3 h after 60 min of oxygen exposure and examined the recruitment of inflammatory cells and the fibrotic area in the heart. The proportion of c-kit-positive stem/progenitor cells significantly increased in peripheral blood at 3 and 24 h after oxygen exposure for either 20 or 60 min (p < .01 vs. control). However, the abundance of colony-forming cells in peripheral blood conversely decreased at 3 and 24 h after oxygen exposure for only 60 min (p < .05 vs. control). Oxygen exposure for either 20 or 60 min resulted in significantly decreased plasma vascular endothelial growth factor levels at 3 h, whereas oxygen exposure for only 60 min reduced plasma insulin-like growth factor 1 levels at 24 h (p < .05 vs. control). Protein array indicated the increase in the levels of some cytokines/chemokines, such as CXCL6 (GCP-2) at 24 h after 60 min of oxygen exposure. Moreover, oxygen exposure for 60 min enhanced the recruitment of Ly6g- and CD11c-positive inflammatory cells at 3 days (p < .05 vs. control) and increased the fibrotic area at 14 days in the heart after I/R injury (p < .05 vs. control). Prolonged oxygen exposure induced the mobilization and functional impairment of stem/progenitor cells and likely enhanced inflammatory responses to exacerbate cardiac I/R injury in healthy mice.