Selective inhibition of inducible nitric oxide synthase reduces progression of experimental osteoarthritis in vivo - Possible link with the reductionin chondrocyte apoptosis and caspase 3 level

Objective. To evaluate the in vivo therapeutic efficacy of,N-iminorthyl-L-l ysine (L-NIL), a selective inhibitor;or of inducible nitric oxide synthase, on the progression of structural lesions in the experimental canine model of osteoarthritis (OA), and to explore the effect of L-NIL on the level of chondrocyte apoptosis and of important proteins invoiced in the apoptotic p henomenon, i.e., caspase 3 (inducer) and Bcl-2 (inhibitor). Methods. The OA model was created by sectioning the anterior cruciate ligam ent. Dogs were placed into 4 experimental groups: unoperated dogs that rece ived no treatment (controls), operated (OA) dogs that received placebo trea tment, OA dogs that received oral L-NIL at 10 mg/kg/day and OA dogs that re ceived oral GNU, at 1.0 mg/kg/day In both L-NIL groups, treatment started i mmediately after surgery. The OA dogs were killed at 12 weeks after surgery . Results. OA dogs treated with L-NIL showed a reduction in the size of osteo phytes and a significant decrease in the severity of macroscopic and histol ogic cartilage lesions on both condyles and plateaus, compared with untreat ed OA dogs, L-NIL treatment also significantly decreased metalloprotease ac tivity in cartilage. Immunohistochemical analysis revealed that the levels of chondrocyte apoptosis, caspase 3, and Bcl-2 were markedly increased in O A cartilage (P < 0.0001), A positive correlation between the levels of chon drocyte apoptosis and levels of caspase 3 was found (r = 0.54, P < 0.001). OA dogs treated with the higher dosage L-NIL showed significantly reduced l evels of chondrocyte apoptosis (P < 0.003) and caspase 3 (P < 0.04), but no effect on the increased level of Bcl-2 mas demonstrated, Conclusion. This study shows that L-NIL reduces the progression of experime ntal OA. This effect could be related to a reduced level of chondrocyte apo ptosis and is likely mediated by a decrease in the level of caspase 3 activ ity. A sparing effect of L-NIL on the increased level of Bcl-2 may also be a contributing factor.