The secretome of mesenchymal stem cells and oxidative stress: challenges and opportunities in cell-free regenerative medicine

Over the last decade, mesenchymal stem cells (MSCs) have been considered a suitable source for cell-based therapy, especially in regenerative medicine. First, the efficacy and functions of MSCs in clinical applications have been attributed to their differentiation ability, called homing and differentiation. However, it has recently been confirmed that MSCs mostly exert their therapeutic effects through soluble paracrine bioactive factors and extracellular vesicles, especially secretome. These secreted components play critical roles in modulating immune responses, improving the survival, and increasing the regeneration of damaged tissues. The secretome content of MSCs is variable under different conditions. Oxidative stress (OS) is one of these conditions that is highly important in MSC therapy and regenerative medicine. High levels of reactive oxygen species (ROS) are produced during isolation, cell culture, and transplantation lead to OS, which induces cell death and apoptosis and limits the efficacy of their regeneration capability. In turn, the preconditioning of MSCs in OS conditions contributes to the secretion of several proteins, cytokines, growth factors, and exosomes, which can improve the antioxidant potential of MSCs against OS. This potential of MSC secretome has turned it into a new promising cell-free tissue regeneration strategy. This review provides a view of MSC secretome under OS conditions, focusing on different secretome contents of MSCs and thier possible therapeutic potential against cell therapy.