Millions of older people every year develop wounds, such as diabetic ulcers and bedsores, that just don't heal. These wounds are not only painful but costly to treat. A protein found in several bodily fluids, however, may eventually provide some relief. According to a report in the October issue of the journal Nature Medicine, research conducted on mice demonstrates that a protein called secretory leukocyte protease inhibitor (SLPI, or "slippy") is critical in healing normal wounds. Furthermore, topical application of SLPI to nonhealing wounds reversed tissue destruction and promoted healing.

Previous investigations had suggested that SLPI plays a role in mending wounds, revealing that the protein has antibacterial, antiviral, anti-inflammatory and antifungal properties. The new study sought to identify SLPI's role more specifically. To that end, researchers at the National Institute of Dental and Craniofacial Research genetically engineered a line of mice that lack the SLPI gene. These knockout mice, they observed, exhibited greatly compromised wound healing, increased inflammation and increased activity of an enzme known as elastase, which destroys tissue. "SLPI appears to be a component of innate or natural host defense that maintains a balance between protective inflammatory responses and overzealous or uncontrolled inflammation that can lead to tissue destruction and failure to heal," reports principal investigator Sharon Wahl.

Given that SLPI is found in saliva, among other fluids, the researchers suggest that the wound-licking behavior of many animals may be nature's way of administering SLPI. And research conducted in recent years showed that SLPI in saliva can inhibit HIV-1 infection. Whether topical application of SLPI can help chronic human skin wounds should become apparent in a clinical trial, which is currently being planned.