Determination of optimized oxygen partial pressure to maximize the liver regenerative potential of the secretome obtained from adipose-derived stem cells

A hypoxic-preconditioned secretome from stem cells reportedly promotes the functional and regenerative capacity of the liver more effectively than a control secretome. However, the optimum oxygen partial pressure (pO ) in the cell culture system that maximizes the therapeutic potential of the secretome has not yet been determined. We first determined the cellular alterations in adipose tissue-derived stem cells (ASCs) cultured under different pO (21%, 10%, 5%, and 1%). Subsequently, partially hepatectomized mice were injected with the secretome of ASCs cultured under different pO , and then sera and liver specimens were obtained for analyses. Of all AML12 cells cultured under different pO , the AML12 cells cultured under 1% pO showed the highest mRNA expression of proliferation-associated markers (IL-6, HGF, and VEGF). In the cell proliferation assay, the AML12 cells cultured with the secretome of 1% pO showed the highest cell proliferation, followed by the cells cultured with the secretome of 21%, 10%, and 5% pO , in that order. When injected into the partially hepatectomized mice, the 1% pO secretome most significantly increased the number of Ki67-positive cells, reduced serum levels of proinflammatory mediators (IL-6 and TNF-α), and reduced serum levels of liver transaminases. In addition, analysis of the liver specimens indicated that injection with the 1% pO secretome maximized the expression of the intermediate molecules of the PIP3/Akt and IL-6/STAT3 signaling pathways, all of which are known to promote liver regeneration. The data of this study suggest that the secretome of ASCs cultured under 1% pO has the highest liver reparative and regenerative potential of all the secretomes tested here.