Hiperalgesia articular no modelo de osteoartrite por transecção do ligamento cruzado anterior em ratos : efeito de inibidores da síntese de óxido nítrico e de polissacarídeos de elevado peso molecular

Abstract

Animal models have been employed for the study of osteoarthritis (OA), but the articular hyperalgesia has received little attention. In this study, we standardized a method to study hyperalgesia in an OA model in rats, through the anterior cruciate ligament transection (ACLT), as well as the role of Nitric Oxide (NO). High molecular weight (MW) polysaccharides, such as Hylan G-F 20, as a gel preparation, have been used to relive pain in OA patients. Whether their activity is due to the high MW or to the gel state (viscossuplementation) is a matter of debate. We used the ACLT model to evaluate the effect of a polysaccharide from gum guar (GG) in the hyperalgesia. Wistar rats were subjected to ACLT (OA group). The hyperalgesia was measured using the test for articular incapacitation (AI) in rats (Tonussi & Ferreira, 1992), until 28 days. The joint lavage was used for determining cell influx (CI) and NO levels. The activity of the inducible NO synthase enzyme (iNOS) was evaluated by immunohistochemistry of the synovia. The articular cartilage was evaluated by quantifying the glycosaminoglycans (GAG) content of the cartilage of the femoral condyles. The animals of the OA group were compared to a sham group and to naive animals. Animals of the OA group received indomethacin (2mg/kg/d s.c.), L-NAME (30mg/kg i.p.) or 1400W (0,5mg/kg/d s.c.), NOS inhibitors, 30 min before the surgery and until sacrifice, at 7 days (prophylactic intervention). Animals of the OA group were compared to sham and naive groups. Other animals of the OA group received L-NAME or 1400W 3 days after the surgery, until sacrifice, at 7 days (therapeutic intervention). Still other animals of the OA group received GG (100μg i. art.), as a gel or as solution, from 4 through 7 days of OA and were compared to both a sham group and to a group that received Hylan G-F 20 (100microg i. art.), as a gel. Control groups received the vehicles. The OA group displayed significantly increased AI during the first 7 days (P<0.001). There was no difference in CI among all groups. NO release, at 7 days, was increased in the OA group (P<0.05), that was associated with an increased activity of the iNOS in the synovia. The GAG content was significantly increased in the OA group, measured at 14 days (P<0.05). Indomethacin significantly reduced the AI, as compared to the OA group (P<0.05). L-NAME and 1400W reduced the AI, only when given prophylactically (P<0.01), that was reversed by the co-administration of L-NAME and L-arginine. GG, either as a gel or as a solution, as well as the Hylan G-F20, significantly reduced the AI (P<0.05), as compared to the OA group. This is the first demonstration of a model to study hyperalgesia, quantitatively, in OA experimental models. There is increased release of NO in the ACLT model, probably via iNOS activation. The administration of NOS inhibitors inhibits the AI only if given prophylactically. This is also the first demonstration that GG promotes analgesia in the ACLT model in rats. Moreover, the anti-nociceptive effect of polysaccharides, at least in this model, is independent of their colloidal state.