Reduction in the structural changes of experimental osteoarthritis by a nitric oxide inhibitor

Objective: To evaluate the in-vivo therapeutic efficacy of N-iminoethyl-L-L ysine (L-NIL), a selective inhibitor of inducible nitric oxide synthase (iN OS) in a dose response study, on the progression of lesions in the experime ntal osteoarthritic (OA) dog model. Design: The sectioning of the anterior cruciate ligament of the right stifl e joint of mongrel dogs was done by a stab wound. Dogs were separated into experimental groups: Group 1 received no treatment, Groups 2, 3, and 4 rece ived oral L-NIL (0.3, 1 or 10 mg/kg/day, respectively) starting immediately after surgery. The OA dogs were killed at 12 weeks after surgery. Results: Macroscopically, L-NIL decreased the size of the cartilage lesions on condyles and plateaus. The histologic severity of the cartilage lesions was decreased in the L-NIL-treated dogs. This effect was more pronounced a t the highest dosage tested (3 and 10 mg/kg/day). Conclusions: This study confirms the effectiveness of L-NIL, a selective in hibitor of iNOS, in attenuating the progression of experimental OA. It also clearly shows that the effect is dose-dependent.