The use of an IL1‐receptor antagonist to reverse the changes associated with established tendinopathy in a rat model.

Interleukin‐1 (IL1) is a cytokine that plays a role in inflammation and is a potential contributor to the inflammation present in tendinopathy. Its inhibition may be of use in the treatment of tendinopathy and has been a target for treatment. To evaluate how an IL1‐receptor antagonist (IL1‐RA) reverses pathologic changes associated with established patellar tendinopathy, we randomized 48 Sprague‐Dawley retired breeder rats into three groups having weekly bilateral patellar tendon injections for 6 weeks. The control group received 0.1 mL saline for 6 weeks. The intervention groups were treated with 0.1 mL 2% carrageenan for 4 weeks. Beginning at week three, the IL1‐RA group received 0.94 mg of the IL1‐RA (2.5 mg/kg) added to the 0.1 mL 2% carrageenan and 0.94 mg of the IL1‐RA alone for the final 2 weeks, while the CAR received 0.1 mL saline for the final 2 weeks. Animals were euthanized 6 weeks after initial injection. The CAR group demonstrated significantly (P < 0.05) shorter tendon lengths (7.81 ± 0.44 mm) than the control (8.25 ± 0.58 mm) and IL1‐RA (8.34 ± 0.52 mm) group (P < 0.05). Macroscopically, plaque‐like formations were reduced and margins of the tendon were more evident in the IL1‐RA group compared to the CAR group. CAR group demonstrated significantly greater histopathologic changes (inflammatory cell density, disorganization of collagen, nuclear rounding, and angiogenesis) than the control and IL1‐RA group. No significant difference in mechanical properties of the tendon was noted. These findings demonstrate IL1‐RA can reduce pathologic changes in the patellar tendon in an established tendonitis model although did not demonstrate a difference in mechanical properties. [ABSTRACT FROM AUTHOR]