Sorting Out IRAP, PRP, and Stem Cells

Today's wealth of scientific advancements can make it difficult to keep track of all the different treatment options available for injured horses. A flexor tendon injury, for example, that once had a relatively standard treatment protocol can now be aided by traditional methods as well as relatively new therapies such as stem cell, platelet-rich plasma (PRP), or IRAP (interleukin-1 receptor antagonist protein). During a presentation at the 2011 North American Veterinary Regenerative Medicine Conference held June 2-4 in Lexington, Ky., Jamie Textor, DVM, Dipl. ACVS, an equine surgeon and PhD candidate at the University of California, Davis, explained the different treatment options in the regenerative medicine field.

The Basics

First, Textor explained that regenerative medicine's goal is to aid in healing tissue (such as tendon, ligament, and bone) in an organized manner--specifically, to preserve all function (such as elasticity and range of motion), approximate what the original tissue was like in strength and resilience, and to help the tissue heal with no scar.

She explained that when tissue heals in an unorganized way, the cells that make up the matter have little to no stretching ability. This means the new tissue is not as strong or resilient as the original tissue, leaving the door open for reinjury.

So what do veterinarians need to aid the tissue healing process? According to Textor, several things:

  • "Seeds," or cells, that are specific to repairing the tissue that's been damaged. The body's first responders (fibroblasts) are generic cells that try to fix everything rather than a certain type of tissue;
  • The ability to rebuild the scaffold, or the architecture that's been damaged. Veterinarians must see that the fiber network in the affected area heals properly to ensure the tissue has its original strength and range of motion;
  • Inflammation reduction (Textor explained that inflammation is beneficial when a wound or injury is open and contaminated because it leads to bacteria killing, and it also helps the body clean out the damaged tissue; however, since most sports injuries [i.e., tendons and ligaments] are closed contaminated wounds, inflammation needs to be minimized because in the long run it actually delays the healing process.); and
  • A good rehabilitation program ("If you don't use it, you lose it," Textor said, indicating the need for continued controlled movement to maintain the tissue's ability to function properly).

Stem cells, PRP, and IRAP therapy each use slightly different methods, but all can aid in proper tissue healing, Textor noted.

Stem Cells

Textor explained that some stem cells can transform into any type of cell, which is why they're so sought after to aid in tissue healing. These cells can be found in both bone marrow and fat and "are being used currently to treat pretty much everything, whether we have enough information to support that treatment or not," she said.

Once the aspirates (bone marrow or fat collection) have been gathered, there are two ways they can be prepared for administration:

  • They can be spun in a centrifuge (which is quicker, but tends to yield a lower number of usable stem cells as no proliferation has taken place), or
  • They can be sent to a laboratory for proliferation (which takes longer, but yields a more concentrated and larger stem cell population).

The veterinarian then injects the stem cells using a minimally invasive procedure either directly into the lesion (the most common method) or via an intravenous (IV) catheter. Textor explained that because stem cells have the ability to "home" to the damaged area, the cells are able to travel through the horse's veins to the lesion.

Textor noted that stem cells have been observed to aid in inflammation reduction and also help fill in the lesion with more proper fiber alignment (as seen under a microscope) than lesions that heal without the aid of stem cells. Additionally, stem cells have been observed in a clinical setting to aid severely laminitic horses with tissue healing and proper hoof growth; however, no studies have been completed that examine their efficacy in this area.

Of the three treatment options she discussed, Textor added that stem cells tend to be the most expensive option for owners. She added that while there currently is no set number of treatments that a horse should receive, many horses receive multiple stem cell treatments.

Platelet-Rich Plasma

The smallest of all blood cells, platelets are found in blood and are responsible for the clotting mechanism. Platelets are the first responders to any injury, Textor noted.

Essentially, PRP therapy delivers a high concentration of platelets in the form of blood plasma to a lesion, increasing the amount of growth factors at the site, to help the injury heal. The plasma is created by spinning whole blood down in a centrifuge, eliminating the red and white blood cells and leaving behind a high concentration of platelets. A stall-side filtration system that separates the red and white cells from the plasma in a relatively short amount of time is also commercially available, Textor added.

The veterinarian injects the plasma directly into the lesion or to multiple areas immediately surrounding the lesion to aid in healing.

Textor explained that some research has proven PRP therapy a useful addition to treating tendon injuries, suspensory desmitis, and experimental lesions to the superficial digital flexor tendon.

Platelet-rich plasma therapy is generally less expensive than stem cell therapy, Textor noted. As with stem cells, science has not yet dictated the exact number of treatments that should be used throughout a course of PRP, but most horses receive multiple doses.

IRAP

Finally, Textor discussed the use of IRAP therapy. She explained that while IRAP technically isn't a regenerative therapy, it's commonly grouped together with stem cells and PRP and referred to as one.

She explained that IRAP is an anti-inflammatory therapy that blocks interleukin-1--one of the major inflammatory substances the body releases in the event of injury--from causing inflammation. Without inflammation, tissue reinjury can be avoided. Textor explained that the process of IRAP production occurs naturally in the horse; however, amplifying the amount of IRAP around the injured area has a more dramatic and quicker affect than the naturally-occurring process.

The substance used in IRAP is made from white cells in the horse's bloodstream. Veterinarians collect blood from the horse and incubate it in the presence of specially designed glass beads, which amplify IRAP production. When the IRAP has reached the desired level, veterinarians can administer the substance to the injured horse.

Textor noted that IRAP is most commonly used as a joint therapy, although veterinarians are starting to experiment with using it for soft tissue injuries as well.

"A lot of people like this as an alternative for steroid joint injections," she explained. "For instance, some vets like it for fat little ponies who like to founder because you can avoid the risk of steroid treatment in a joint, which could trigger an episode of laminitis."

There is some published research regarding IRAP therapy, Textor said. She described a study in which researchers examined the effect of using IRAP therapy in horses with knee chips that remained in ongoing exercise. The results showed that the horses that received IRAP had decreased lameness as compared to the controls.

IRAP is generally administered weekly for four weeks, Textor noted.

Which therapy owners choose is generally based on cost and convenience, Textor said, as there are not yet any comparative studies examining which treatment is most effective for a given injury.

"Science is evolving, so stick with us and understand that things might change," she concluded. "We're learning more all the time."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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