Determination of Optimized Oxygen Partial Pressure to Maximize the Liver Regenerative Potential of the Secretome Obtained from Adipose-derived Stem Cells

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.