Mesenchymal stromal cells (MSCs) harvested from the mouth of one donor horse led to improved healing of other horses’ open body and leg wounds. The researchers’ findings suggest MSCs originating in the mouth might spur cellular changes that improve the way equine skin heals, said Olivier Lepage, DVM, PhD, of the Group for Medical and Rehabilitation Research in Sport Horses (GREMERES), part of the Centre for Equine Health at the National Veterinary School at Lyon – VetAgro Sup, in Marcy l’Etoile, France.
Skin wounds in horses—especially on the lower legs—are notoriously difficult and time-consuming to heal, Lepage said. They can create stubborn biofilms that further delay healing, and can close with tough layers of exuberant granulation tissue—also known as proud flesh—that is not only unsightly but also less stretchy than normal skin.
Mesenchymal stromal cells have shown promise helping other “difficult” soft tissues—such as tendons—heal in horses, and they’ve been associated with limited improved healing in skin wounds, said Lepage. In laboratory studies MSCs have shown immunomodulatory, anti-inflammatory, reparative, and regenerative properties. They also emit the highly beneficial secretome of lipids, nucleic acid, and proteins—mainly growth factors, chemokines, cytokines, adhesion molecules, and proteases—that appear to promote good healing.
The mouth, in particular, seems like a part of the body with critical healing potential, said Lepage. “You know how whenever you cut the inside of your mouth, it almost always seems to end up healing perfectly, with practically no scarring?” he said. “That’s kind of what we were trying to harness here in this study.”
And, conveniently, the mouth’s mucosa is full of MSCs.
Using Stem Cells From a Donor Horse’s Mouth to Treat Other Horses’ Wounds
Lepage and his fellow researchers used local anesthesia and a sedative on the study horses and created eight identical 1-inch-square full-thickness skin wounds: four on the left and right cannon bones and four on the left and right sides over the ribs (about a foot behind the elbow) of eight healthy adult horses. The four geldings and four mares, of mixed breeds and ranging in age from 9 to 15 years, had no scars, skin disease, or lameness, Lepage said.
“Wounds were not covered after surgery to mimic spontaneous trauma in the field,” his team reported.
Meanwhile, the scientists took a small section of tissue—less than one square inch—from oral mucosa of a ninth horse and extracted MSCs from it. From those MSCs, the researchers also extracted MSC secretome samples.
The scientists designated each of the eight wounds on each horse to either be left alone to heal by itself or to be treated with one of three ointments: hyaluronic acid (HA) gel, HA gel mixed with whole MSCs from the donor horse’s mouth, or HA mixed with secretome from those harvested MSCs.
The eight horses were divided into two groups of four. One group received the treatments twice within a 48-hour interval, he said. The other group received the treatments four times over four consecutive days.
In all cases the scientists bandaged the wounds after treatment and changed the dressing every 24 hours for the first four days, then every four days until the 16th day. After Day 16, the horses were left unbandaged,
Early Oral MSC Treatment Associated With Better Skin Healing
As seen in previous studies, the researchers found that the wounds on the horses’ sides healed dramatically faster than those on the horses’ cannon bones, Lepage said. In this study body skin wounds healed three times as fast as leg skin wounds.
The researchers found a notable improvement in wound healing, especially in the body skin wounds, when using the MSC-HA treatments, he said.
Using laser technology for accurate wound size measurement, the team noted significant decreases in both the circumference and the surface area of the side wounds only if they had been treated with either whole MSCs or secretome, he added.
In the leg wounds the oral MSCs in HA gel appeared to have “a stimulating effect” on wound contraction and epithelization—but only in the first two weeks of wound healing. In fact, all the leg wounds, regardless of treatment, expanded for about the first three weeks before shrinking and healing completely within 60 days. The leg wounds that healed the fastest were those treated with HA gel alone.
Greater stimulating effects were seen when the horses received the treatment twice rather than four times, he added.
“We can conclude from these observations that using horse cells harvested from oral mucosa is a feasible technique to produce OM (oral mucosa)-MSC or its secretome and that a beneficial effect can be obtained with these regenerative medicine treatments when used at an early stage of the wound healing process,” Lepage and his colleagues reported.
Lepage: Early Treatment Is Key
The findings seem to point toward a “probable therapeutic window” for best results, said Lepage.
“We assume that, in the first phase of healing, the presence of OM-MSC or its secretome leads to amplification of the wound-healing process,” he and his colleagues reported.
Most likely, that improvement results from what scientists refer to as paracrine interactions—a sort of pro-healing cell signaling spurred by the presence of MSCs and/or their secretome.
“Through these paracrine interactions, MSCs can regulate collagen production, enhance skin regeneration, promote angiogenesis (blood vessel development), and increase wound closure rates,” the team stated.
Proud Flesh: an Ongoing Issue
Regardless of the treatment, however, the skin wounds in the cannon bones had similar rates of proud flesh development, said Lepage. This might be a consequence of constant bandaging for the first 16 days, he explained.
Ideally, scientists will be able to detect biomarkers that would indicate at what point in the healing process the treatment plan should be modified to avoid proud flesh growth, he said.
“Effect of Allogeneic Oral Mucosa Mesenchymal Stromal Cells on Equine Wound Repair,” was published in December 2021 in Veterinary Medicine International.