Natural compounds as a strategy to optimize “in vitro” expansion of stem cells

The efficient use of stem cells for transplantation is often limited by the relatively low numbers of stem cells collected. The ex vivo expansion of human stem cells for clinical use is a potentially valuable approach to increase stem cell number. Currently, most of the procedures used to expand stem cells are carried out using a 21% oxygen concentration, that is about 4- to 10-fold greater than the concentration characteristic of their natural niches. Hyperoxia might cause oxidative stress with a deleterious effect on the physiology of cultured stem cells. In this review, we investigate and critically examine the available information on the ability of natural compounds to counteract hyperoxia-induced damage in different type of stem cells ex vivo. In particular, we focused on proliferation and stemness maintenance in an attempt to draw up useful indications to define new culture media with a promoting activity on cell expansion in vitro.