Using adult human stem cells, UC Davis researchers successfully induced the formation of new blood vessels in mice with reduced blood flow (ischemia) to their limbs.

The breakthrough treatment resulted in fully functioning limbs that showed both increased blood flow to previously damaged areas and an increase in the number of blood vessels.

The study, "Revascularization of Ischemic Limbs After Transplantation of Human Bone Marrow Cells With High Aldehyde Dehydrogenase Activity," published in the May 21 edition of the journal Blood, paves the way for the stem cell-based treatment of peripheral arterial disease in humans. Peripheral arterial disease, or PAD, is painful condition common in diabetic patients —and can lead to amputation.

“We have shown that you can introduce adult stem cells to the blood that will go directly to the areas of low oxygen and initiate the formation of new blood vessels,” said Jan Nolta, professor of internal medicine and director of the UC Davis Stem Cell Program.

The “homing” behavior of the cells to find damaged vessels was particularly remarkable with ALDH bright cells, a particular population of stem cells used for the study, added Nolta. Images of mouse limbs show how the cells target the area of low oxygen and result in revascularization of the injured limb.

“We don’t even have to know what area needs repair. A unique characteristic of these adult stem cells is that when they are injected, they go to areas of damage to start the repair. That’s why we like to call them the ‘paramedics of the body,’” she said.

PAD is characterized by reduced blood flow to the legs and feet caused by blockage of the arteries. In severe cases, it causes persistent pain and tissue damage. There are no drugs currently approved to treat the condition in its worst form, critical limb ischemia (CLI), and when surgical interventions and other standards of care fail, amputation can be the only option.

The new findings also have important implications for treating other kinds of ischemic damage, said senior author David Hess, an assistant professor of physiology and pharmacology at the University of Western Ontario’s Robarts Research Institute.

“These principles could be applied not only to ischemic limbs, but also to aid in the formation of new blood vessels in ischemic tissue anywhere in the body, for example after a stroke or heart attack,” said Hess, who began the work while a postdoctoral fellow in Nolta’s laboratory when she was at Washington University in St. Louis.

Nolta, who arrived at UC Davis in 2006, said the key to the findings was the isolation of the ALDH bright cells, which highly express the enzyme aldehyde dehydrogenase. This population contains the most primitive subsets of three types of cells from the bone marrow. The first type, hematopoietic stem cells (HSCs), give rise to all blood cell types in the body. The other two are mesenchymal stem cells (MSC) and endothelial progenitor cells (EPCs). Blood vessels contain mixtures of the latter two cell types, and HSCs and MSCs can both have significant healing effects on damaged tissue.

Using human bone marrow, the researchers simultaneously isolated the three different types of stem cells in the ALDH bright population. These stem cells, called proangiogenic stem cells, were purified to remove any inflammatory or contaminating mature cells. The cells were labeled with glowing iron nanoparticles for imaging purposes, which allowed them to be tracked by the team, and then injected into the circulation of mice that had one of their leg arteries removed.

Imaging studies showed that the stem cells went directly to the site of low blood flow in the limbs. Laser doppler imaging showed an increase in blood flow for the treated limbs. Using standard cytology techniques, the research team counted the number of blood vessels and confirmed new blood vessel formation.

“We have shown that this population of stem cells can successfully revascularize a limb, restoring it to its full function,” Nolta said.

The findings, Hess said, are immediately clinically applicable because these human stem cells were used in immune-deficient mouse models, which cannot reject the cells. In fact, Aldagen, a North Carolina-based biopharmaceutical company, used preclinical data from the research as part of the data package submitted to the Food and Drug Administration for clearance to begin a multicenter trial using the same cells used to treat the mice.

Aldagen, the company that first brought ALDH bright cells into the clinic, completed a Phase I-II trial and found the treatment safe and well-tolerated, and that these cells could improve the clinical status of patients with severe CLI and improve blood flow in affected legs. In this trial, patients with late-stage critical limb ischemia were injected with ALDH bright cells prepared from the patients’ own bone marrow.

Nolta and a team at the UC Davis Vascular Center hope to begin clinical trials for the treatment of peripheral arterial disease in the coming year, as well as to continue basic and clinical research on the potential use of stem cells to treat heart attack and stroke. They are working to understand the mechanism behind the homing behavior observed in the stem cells.

“We have found that the key is a class of molecules called chemokines,” Nolta explained, who, along with her colleagues, is preparing to publish additional work showing how stem cells are able to find their way to areas of low oxygen in the body. “We know that if we eliminate specific molecules, the stem cells lose their homing abilities,” she said.

UC Davis is playing a leading role in stem cell research, with more than 125 scientists and physicians working on a variety of investigations on the Davis and Sacramento campuses. The university recently broke ground in Sacramento for the state-supported, 92,000-square-foot Institute for Regenerative Cures, with laboratories and cell manufacturing and testing rooms.

That project, along with the Translational Human Embryonic Stem Cell Shared Research Facility in Davis, will complement the university's National Institutes of Health-supported Clinical and Translational Science Center and help turn stem cells into cures.

More information.

Charles Casey is a senior public information officer for the UC Davis Health System.