ANN ARBOR --- University of Michigan scientists have identified a sequence of amino acids found in fibronectin, a common blood protein, that has a remarkable ability to accelerate healing of hard-to-treat skin wounds in obese, diabetic mice.
One drop of the substance completely healed skin puncture wounds in obese diabetic mice in just eight days, according to a study published in the June 2000 issue of the Journal of Clinical Investigation. The same skin wounds in untreated diabetic mice took 20 days to 42 days to heal.
Skin ulcers that will not heal are a common complication in diabetes, a chronic disease that affects 6 percent of the population. People with diabetes cannot produce insulin. Lack of insulin causes blood vessels and tissue membranes to degenerate, interfering with normal healing by preventing the body's tissue-repair cells from getting into the damaged area.
"Fibronectin is the key to the wound healing process," says Donna L. Livant, Ph.D., an assistant professor of cellular biology in the U-M Medical School, who directed the study. "It circulates freely through the body in blood plasma, lymph, serum and interstitial fluid around cells. When tissue is damaged, fibronectin at the injury site is broken into fragments and binds to receptors on surrounding cells, stimulating them to invade the wound and repair the injury."
In her research, Livant isolated one specific peptide in fibronectin called PHSRN, which triggered the invasion process. Livant then modified PHSRN to make it 100 times more active and chemically stable than the original. Initial laboratory tests confirmed the peptide's ability to stimulate the movement of wound-healing cells and increase the growth of new blood vessels to areas of tissue damage.
To see whether the peptide could heal wounds in living animals, Livant and her research team used a well-known strain of mice with a genetic mutation that---when inherited from both parents---produces obese, diabetic offspring. Littermates inheriting just one copy of the mutated gene do not develop diabetes.
In the U-M experiment, anesthetized diabetic mice and normal littermate controls received small biopsy wounds in the skin of their upper back. Age-matched sets of wounded diabetic and control mice were divided into three groups. Wounds in the first group were treated with a single tiny drop (five microliters) of Livant's activated peptide. Wounds in the second group received an equal amount of a randomized control peptide. The third group of mice remained untreated---receiving nothing but ordinary saline solution.
After eight days, skin wounds treated with the activated peptide in both diabetic and non-diabetic mice were completely closed and healed, according to Livant. Wounds in untreated non-diabetic mice healed in nine days, but skin closure time in untreated diabetic mice ranged from 20 days to 42 days. There was no significant difference in wound closure time between mice treated with the randomized control peptide and saline solution.
"When we examined sections of wounded tissue under a microscope, we found that wound areas treated with PHSRN were invaded right away by cells involved in the healing process," Livant says. "This resulted in a rapid decrease in wound size, suggesting that the peptide attracts cells or activates a pathway which functions in wound contraction.
"PHSRN appears to be an effective way to speed up cell migration and wound closure," Livant adds. "Since delayed cell migration is the reason wounds heal slowly in people with diabetes, it could prove to be efficacious in the diabetic patient. However, we haven't tested the peptide's effectiveness at repairing non-healing or chronic wounds, which can occur in diabetes. More data will be needed before we can say for sure."
Co-authors on the Journal of Clinical Investigation paper, all from the U-M Medical School, include R. Kaye Brabec, research associate; Kotoku Kurachi, Ph.D., professor of human genetics; David L. Allen, Ph.D., postdoctoral research associate; Yanling Wu, Ph.D., research associate; Ronald Haaseth, Ph.D., research associate; Philip Andrews, Ph.D., professor of biological chemistry; Stephen P. Ethier, Ph.D., professor of radiation oncology, and Sonja Markwart, research associate.
The U-M holds issued patents and patent applications on use of the PHSRN peptide in wound healing. The study was funded by the National Institutes of Health, the March of Dimes and the U-M Office of the Vice President for Research.
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