“Equine pain management is one of the most challenging issues veterinarians face on a daily basis,” said Melissa King, DVM, PhD, Dipl. ACVS, ACVSMR.
Not only can it be difficult to suppress the pain associated with conditions such as osteoarthritis (OA), but the extended use of conventional therapies (non-steroidal anti-inflammatories, corticosteroids, and opioids) can have negative systemic side effects.
King, an assistant professor of equine sports medicine at Colorado State University’s Veterinary Teaching Hospital, in Fort Collins, has been studying a new tool to manage joint pain in horses: anti-nerve growth factor (anti-NGF mAb), which has been shown to have significant analgesic effects in other species. She presented her findings at the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida.
In the presence of tissue injury, the body produces neurotrophins, or nerve grow factors (NFG). When a damaged joint, for instance, releases NGF, a cascade of events occur that enhance the sensation of noxious stimuli. The result? Pain. Researchers have developed antibodies against NGF—the aforementioned anti-NGF mAb—to try to stem this pain response.
King said studies have shown anti-NGF mAb to be an effective pain modulator in rats with OA; dogs and cats with degenerative joint disease; and humans with knee OA. So she sought to determine anti-NGF mAb’s analgesic effect in live horses.
In their study, King and her colleagues induced synovitis (a type of joint inflammation) in the hock joint of 24 horses. They injected a sterile saline solution into each horse’s opposite hock, which served as its control. They then split the horses into four treatment groups of six that received intra-articular anti-NGF mAb doses of either 0.1 mg, 1 mg, or 10 mg or a placebo.
The team performed a lameness examination and collected synovial fluid and ground-reaction forces from all horses at three time points: prior to synovitis induction, four hours after synovitis induction (but still prior to anti-NGF administration), and 10 hours post-anti-NGF mAb administration. At 10 hours they also performed standing arthroscopy to collect tissue biopsies from the affected hocks.
In the joints treated with the higher doses (1 mg and 10 mg) the researchers found:
- Less pain in response to joint flexion and symmetrical limb loading;
- Significantly less glycosaminoglycan and PGE2 (inflammatory markers) in the synovial fluid;
- Significantly less inflammatory cell infiltrate on histopathology (microscopic exam); and
- No significant changes or effects on articular cartilage viability.
“Anti-NGF mAb has multiple therapeutic and disease-modifying effects, short-term safety, and is efficacious,” said King. “It’s the first new pain treatment in several years.”
While this treatment is not currently available for use in horses, King said she hopes it will be an option in the near future.