Analysis of the Regenerative Benefit of Pretreatment of Adipose-Derived Stromal Cells with Hypoxia

Peripheral arterial disease (PAD) is a serious and prevalent condition in which blockages of blood vessels of the peripheral circulation, which has effects ranging from resting pain to ulceration and tissue loss. It has been reported as recently as 2007 that 27 million North Americans and Europeans suffer from PAD, and that number is likely to rise. Several groups have shown that human adipose-derived stromal cells (hASCs), when delivered intravascularly or intramuscularly, have the ability to increase blood flow and rescue limbs from autoamputation in rodent ischemic hindlimb models. The mechanisms by which those benefits came about have not been investigated directly; therefore, it was a goal of these studies to determine the mechanisms by which hindlimb rescue may have been realized in ischemic hindlimb models. In light of evidence that hypoxia increases certain aspects of hASCs' regenerative profiles, it was an expressed goal of this work to determine whether intravascular homing and angiogenic induction of hASCs can be increased by pretreatment with hypoxic culture.;It was found that hASCs are able to adhere in vitro to endothelial cells via VLA-4/VCAM-1, and possibly Mac-1/ICAM-1, interactions and that this ability is increased by hypoxic culture. In vivo experimentation illustrated that despite possessing a capacity for intravascular homing, hASCs are too adhesive inside the vasculature to be considered for therapeutic use. hASCs were also shown to secrete angiogenic proteins and migrate toward gradients of PDGF-BB in vitro. Secretion of angiogenic proteins was increased after culture in hypoxic conditions. In vivo experiments showed that hASCs increased vascular density in inflamed/remodeling rat mesenteries. It was determined that these increases were a result of hASC assumption of pericyte phenotypes. Hypoxic culture of hASCs did not alter final mesenteric vascularity, but it promoted paracrine activity at early time points as the mechanism responsible for increased vascular density.;Therapeutic strategies involving intravascular delivery are too dangerous, owing to high baseline adhesion of hASCs. Complementary mechanisms of indirect paracrine support and direct perivascular investment may mean that hASCs represent a therapeutic agent with the ability to utilize two distinct mechanisms of action based on oxygen concentration.