Conditioned Medium from Mesenchymal Stem Cells Reduced Ischemia/Reperfusion Injury-Induced Endothelial Dysfunction in Rats’ Vascular Grafts

Objectives: During the harvesting and implantation of bypass arteries/veins in coronary artery bypass grafting (CABG), ischemia/reperfusion (IR) injury can induce vascular endothelial dysfunction and long-term graft patency. Previous studies have demonstrated the protective effects of conditioned medium (CM) from bone marrow-derived mesenchymal stem cells (MSCs) against IR injury. We hypothesized that physiological saline-supplemented CM would protect rats’ vascular grafts from IR injury.

Methods: CM from rat MSCs indicates the presence of 23 factors involved in apoptosis, inflammation, and oxidative stress. Thoracic aortic rings from male Lewis rats were harvested and immediately mounted in organ bath chambers (control group, n = 7) or preserved for 24 hours in 4°C saline-supplemented either with a vehicle (IR group, n = 8) or CM (IR + CM group, n = 7), before mounting. To simulate free radical burst and endothelial dysfunction, which usually occurs during reperfusion in vivo, hypochlorite was added to the baths (200 μM, 30 min). The assessment of maximal endothelium-dependent relaxation (Rmax) to acetylcholine and immunohistochemical analysis for nitrotyrosine (as a nitroxidative stress marker), 4-hydroxynonenal (HNE, an indicator of oxidative stress), and apoptosis-related caspase proteins was performed.

Results: IR injury was associated with significantly impaired endothelium-dependent vasorelaxation to acetylcholine (Rmax to acetylcholine: control 91 ± 1% vs. IR 59 ± 3%, p < 0.05), higher myeloperoxidase (MPO) immunoreactivity, nitrotyrosine, HNE, caspase-3, -8, -9, and -12 compared to control rats. However, the preservation of aortic rings from IR group with CM significantly improved endothelium-dependent vasorelaxation (Rmax to acetylcholine: IR 59 ± 3% vs. IR + CM 70 ± 2%, p < 0.05) and lowered HNE, caspase-3, -8, and -9 immunoreactivity compared with the IR group.

Conclusion: The preservation of rats’ vascular grafts with CM alleviates endothelial dysfunction following IR injury. This protective effect may be associated with lower level of oxidative stress and the inhibition of caspase-3, -8 and -9-mediated damage. Although data of preclinical animal studies should not be extrapolated to humans, CM may be a therapeutic option to store vascular grafts of patients undergoing CABG.