Scientists have found in a mice study that human adult stem cells injected around the damage caused by a heart attack survive in the heart and improve its pumping efficiency for a year.
The study, by researchers at The University of Texas MD Anderson Cancer Center, used innovative imaging techniques developed by researchers at MD Anderson to track the stem cells' location and performance over time.
Injection of a patient's own adult stem cells into the heart has shown some efficacy in assisting recovery after a heart attack in early human clinical trials, said study senior author Dr. Edward T. H. Yeh.
"But nobody knows how they work, or how long the stem cells last and function in the heart. This study shows how one type of adult stem cell works," said Yeh.
The team's research focused on adult stem cells - those that can differentiate into a limited variety of tissues - that circulate in the blood and are distinguished by the presence of the CD34 protein on the cell surface.
These CD34-positive cells usually differentiate into blood vessel cells, also known as endothelial cells.
Earlier research by Yeh and colleagues showed CD34+ cells are capable of becoming heart muscle cells, called cardiomyocytes, blood vessel cells and smooth muscle cells.
A series of experiments showed that the CD34+ cells survived in the left ventricle of the heart for 12 months or longer.
Left ventricular ejection fraction - a measure of how much blood is pumped from the heart to other organs at each contraction - improved in treated mice compared with controls for 52 weeks. LVEF went from 50 percent at baseline to 37 percent after heart attack and treatment, compared with 51 percent and 28 percent in untreated mice.
This improvement was the result of increased blood vessel formation in and around the injured area, or paracrine signaling by the stem cells to other nearby cells, rather than formation of new heart muscle.
Using an antibody technique developed by Yeh and colleagues, the team found that antibodies that blocked formation of new blood vessels completely negated the treatment benefit while antibodies that blocked heart muscle cell formation had no effect.
The study has been published in Circulation Research.