Interleukin-1 Receptor Antagonist Protein (IRAP) continues to gain traction in the realm of joint disease treatments. This regenerative therapy, also called autologous conditioned serum (ACS, autologous means self-derived), can be produced using samples from the horse’s own body.
Veterinarians collect a small volume of blood from the patient and allow it to clot. Then, they mix the serum—the liquid portion of blood that separates from red blood cells—with special borosilicate glass beads included in commercial ACS kits. This produces anti-inflammatory molecules called interleukin-1 receptor protein agonists, which block the action of interleukin-1, a very potent pro-inflammatory molecule.
Veterinarians inject the “conditioned” serum directly into the affected joint(s) to exert this anti-inflammatory effect. Additional growth factors produced during the incubation process that can help with healing include interleukin-10, fibroblast growth factor, vascular endothelial growth factor, and platelet-derived growth factor, among others.
The conditioned serum takes about 24 hours to produce. One recent review confirmed that horses with experimentally induced osteoarthritis treated with IRAP had a significant improvement in lameness and healing.
Treatment protocols vary, but injecting 2-10 mL of conditioned serum (depending on the size/volume of the joint) into the affected joint every three to 10 days, for a total of three treatments, appears effective. For long-term maintenance of chronic joint disease, a single injection of IRAP administered on an as-needed basis appears effective.
IRAP/ACS injections can, like any joint injection, cause a “joint flare,” associated with heat, pain, and lameness. Some practitioners use IRAP to treat soft-tissue injuries; however, no scientific studies have been conducted supporting this application.
Talking about the Platelet Rich Plasma (PRP) therapy, you must know that platelets are specific types of blood cells that naturally contain a rich array of growth factors. Veterinarians can generate PRP using a commercial system that separates the platelets from other blood components, such as red and white blood cells, and concentrates them into an easily injectable product.
Like IRAP, collecting a patient’s blood and using it to produce PRP makes this an autologous process, where the body’s tissues heal itself.
Despite minimal research in this field, many sport horse practitioners report positive results after injecting PRP directly into injured joints. Based on the available data, between 2 and 6 mL of prepared PRP can be injected per joint. As with IRAP/ACS, post-injection flares can occur.
The more widely accepted—and studied—use is in managing soft-tissue injuries. PRP appears to promote tissue healing (rather than laying down scar tissue), resulting in tendons and ligaments with improved strength and elasticity compared to untreated horses. In turn, horses have a reduced risk of reinjury.
Once a veterinarian diagnoses a tendon or ligament lesion, PRP produced using a stallside kit can be injected directly into the defect using an ultrasound-guided or needle arthroscope approach. The “fresher” the lesion, the better, and injections can be repeated every three to four weeks.
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