Osteoarthritis (OA) is a major cause of wastage in the equine industry, especially considering that an estimated 81% of the 9.3 million horses in America are involved in equitation and performance. A mainstay treatment for OA is the use of intra-articular (IA) injection of hyaluronic acid and corticosteroids. The 2009 American Association of Equine Practitioners (AAEP) convention, held Dec. 5-9 in Las Vegas, Nev., included a presentation by Elysia Schaefer, DVM, a surgery resident at the University of Illinois College of Veterinary Medicine, on the in vitro (outside the live animal's body) effects of hyaluronic acid and corticosteroids on cartilage cells subjected to inflammatory conditions.
Molecules called glycosaminoglycans (GAGs) in cartilage help it resist compressive forces in the joint as a horse bears weight and, thus, help protect against osteoarthritis. When GAGs bind to proteins, they're called proteoglycans. She began by reviewing that corticosteroids exert anti-inflammatory effects, while hyaluronic acid (HA) plays a role in joint lubrication and is a key component of articular cartilage as the backbone of proteoglycans (GAGs) within the joint.
The study proceeded with the hypothesis that administering HA (Hylartin-V) alone or in combination with the steroid betamethasone could mitigate osteoarthritis. Investigators collected normal cartilage cells from fetlock joints, grew them in culture, and on Day 7 they added interleukin-1 (a deleterious protein) to induce inflammation, along with treatment medications.
Investigators analyzed inflamed cartilage cells 24 hours later, determining that high molecular weight HA at a high dose is beneficial for GAG synthesis and retention of proteoglycans in the extracellular matrix to maintain hydrostatic pressure. This resistance to compression forces mitigates the progression of osteoarthritis.
Betamethasone also demonstrated anti-inflammatory and chondroprotective effects, but only at the lower dose of 0.06 mg/mL; the high dose (0.6 mgl/mL) of betamethasone was detrimental to articular cartilage cells. Interestingly, HA combined with betamethasone did not demonstrate synergistic effects, whereas previous studies indicated that HA combined with another corticosteroid, triamcinolone, does.
Schaefer noted researchres are unable to assess physiologic joint clearance of drugs or inflammatory agents in such an in vitro study, nor are they able to assess resolution of clinical lameness or pain. Therefore, she recommends further studies be conducted in live horses.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.