Innovative treatments Stem cell therapies may improve healing for horses
“Stem cell applications are something that bring up a bit of controversy,” explained Peter Morresey, equine veterinarian at Rood and Riddle Equine Hospital in Lexington, Ky.
Stem cell therapies provide a number of challenges and opportunities, and Morresey recently provided a perspective on contemporary applications for use of stem cell therapies.
“In practice, stem cells have gotten way ahead of what we know,” Morresey continued. “They’ve been promoted in the media and have captured people’s imagination, but sometimes, the practice isn’t going along at the same speed as science.”
Stem cell therapies are used today in a variety of conditions as a form of regenerative medicine.
“With regenerative medicine, we’re trying to restore structure and function to something that is compromised by either trauma, age or wear-and-tear,” Morresey explained.
Looking at horses, Morresey cited there are numerous places where stem-capable cells can be found.
In addition to the zygote and the blastocyst, he said, “In an adult horse, there are lots of places we can find cells that have the quality of a stem cell.”
Morresey listed corneal epithelium, peripheral blood, muscle, bone marrow, tendon, adipose, skin fibroblast, cartilage and the periosteum as places where stem cells can be found, in addition to placental tissue, including umbilical cord blood, umbilical cord matrix, amniotic fluid and amniotic membrane.
“Not all of the placental tissues are going to be very practical for us to use commercially,” he said.
Stem cells can be harvested from the horse through two main methods – bone marrow aspiration or through adipose tissue.
“Bone marrow aspirate is one of the most widely used types of stem cells,” Morresey explained, noting four major products can be harvested from these methods, including bone marrow mesenchymal stem cells (MSCs) and adipose tissue MSCs. “What’s so special about the MSCs? They’re closely associated with the vascular supply. These cells alter the wound environment to make it more favorable for the wound to heal.”
He continued MSCs provide a scaffold that allows new tissue to replace the tissue, and they are involved in creating blood vessels to supply necessary nutrients to new tissue.
“They’re also able to replace cells that are lost,” he added. “We think about these cells as sitting and waiting for a signal to go into action, and by their actions, they modify the environment to make it more favorable to healing and become part of the tissue itself.”
Today, there are a number of theories about how stem cells provide a therapeutic utility.
The first theory looks at how stems cells introduced to an environment are able to provide a scaffold for tissue repair and differentiate into the surrounding tissue.
“There’s a lot of research into this model, and researchers don’t actually find that the stem cells are recoverable from an area where they are introduced,” Morresey said. “They don’t stay there necessarily. They may move on, or as they divide, the marker may dilute to the point where they can’t be located.”
The second concept for utilizing stem cells is in immune modulation, which is the idea that stem cells create a better environment for healing to occur.
“Inflammation is associated with healing,” he explained, “and the good thing about stem cells is, when introduced, they seem to damp down inflammation, turn down inflammatory cells and cause autoinflammatory mediators to be produced in greater quantity.”
“Stem cells also produce various growth factors and other things that stimulate other cells, allowing the tissue to grow and divide,” Morresey said.
The “hit-and-run” theory of stem cell use suggests that stem cells don’t stay in the area where they are introduced. Rather they influence healing, then migrate elsewhere or disappear.
“This is the theory that the stem cells are introduced, do favorable things, direct the resident cells to enable healing and are lost from the system,” Morresey explained. “The other concept is ‘homing,’ which is where they get into an environment, then cause a beneficial set-up of signals that cause other things to happen. Then, those cells become attracted to the environment and cause other cells to come in.”
Clinically, stem cells are used in several major areas.
“One of the major things in equine practice is going to be osteoarthritis, which is a cause of decreased mobility or loss of athletic function,” Morresey said. “There are resident stem cells in joints surrounding the cartilage, and the thought is, putting MSCs into the environment will recruit cells into the area that will have a favorable effect on healing.”
Often, stem cells are used in tendon and ligament injuries. The best route to use stem cells in these situations has been the subject of research, as well.
“Direct injection into the area is commonly used, but there’s also been some work looking at the arterial injection of the stem cells or also intravenous injection and which is superior,” he said. “When we directly inject stem cells, we run the risk of doing damage when we put the needle in.”
Stem cells are commonly used to treat horses with laminitis, as well, to provide a scaffold for tissue regrowth. Often cells are injected arterially, but Morresey said there isn’t much research that supports use of stem cells for treating laminitis.
Spinal cord injuries, such as chronic compression injuries, may be helpful , but Morresey said, “The jury is still out on whether stem cells are helpful for spinal injuries.”
Questions about type of stem cells used, dose and delivery mechanism are common when looking at stem cell therapies.
“There’s no one set theory on how cells are going to be the best delivered or which cell will be best at doing the job,” Morresey explained. “There are also some situations where what we put in with the stem cells actually harm healing.”
Because stem cell therapies are widely considered “state of the art” treatment, there is a lack of standardization for the therapy.
“There’s also a huge diversity of understanding amongst researchers about what these cells can do, how they’re best used and how they’re best sourced,” Morresey said.
He also noted ethical issues surround stem cell use, particularly as it relates to the destruction of embryos to harvest embryonic stem cells.
Morresey concluded that there are emerging regulatory issues from the Food and Drug Administration.
“There’s a lot more here going on than we realize,” Morresey emphasized. “It’s not just as simple as putting stem cells in and having a response that will be repeatable.”
Morresey shared his insights on regenerative medicine during a mid-March 2018 webinar at thehorse.com.
Saige Albert is managing editor of the Wyoming Livestock Roundup. Send comments on this article to firstname.lastname@example.org.