The Effects of Intra-articular Monosodium Iodoacetate Injection on Joint Pain and both Tibiofemoral and Patellofemoral Joints in Rat Knee

Abstract

Purpose: Several experimental animal models have been developed for human osteoarthritis (OA) and used to study the preclinical efficacy of disease and symptom modifying OA drug candidates in various species. One of these models is induced chemically by an intra-articular injection of monosodium iodoacetate (MIA) into rat knee. Intra-articular MIA disrupts chondrocyte glycolysis through the inhibition of glyceraldehyde-3-phosphate dehydrogenase, results in chondrocyte death and damage in the entire joint space, and leads to OA symptoms. Hitherto, most data of MIA-induced damage in rat knee has been obtained from tibiofemoral joint and not much information is available from patellofemoral junction. In order to improve this rat MIA model as the animal model of OA in preclinical efficacy studies, the effects of intra-articular MIA injection were characterized on the entire rat knee including both tibiofemoral and patellofemoral joints. Methods: The study was conducted using male Lewis rats. Unilateral OA was induced in their knee joints at the age of 3 months by the intra-articular injection of MIA at the dose of 1 mg. The effects of MIA injection on body weight and OA symptoms were followed during the study. Knee joint discomfort and pain were used as OA symptoms. The knee joint discomfort was determined as static weight bearing and measured as hind paw weight distribution using Incapacitance Tester. The knee joint pain was determined as static mechanical secondary allodynia and measured as paw withdrawal threshold using von Frey monofilaments. Rats were terminated at 4 weeks after the MIA injection and their hind limbs were harvested for analyses. Digital radiographs were obtained and both tibiofemoral and patellofemoral joints were analyzed in radiographs using Carimas software. Knee joints were fixed and representative images were obtained by micro-computed tomography. Then, knee joints were decalcified, embedded in paraffin, and sectioned in a coronal plane. The histological OA assessment of tibiofemoral joint was performed according to the recommendations of Osteoarthritis Research Society International (OARSI) histopathology initiative followed by the analysis of epiphyseal bone structure. Knee joints were also embedded in plastic without decalcification and sectioned in a sagittal plane. Both tibiofemoral and patellofemoral joints were analyzed by bone histomorphometry. For the determination of dynamic histomorphometry parameters, bone labelling was performed with oxytetracycline at 8 days and with calcein green at one day before sacrifice. This experimental protocol was approved by National Animal Experiment Board, Regional State Administrative Agency for Southern Finland, Hämeenlinna, Finland. Results: Intra-articular MIA injection into rat knee decreased paw withdrawal threshold, starting at 3 days after the injection and continuing up to the end of the study. This demonstrated the presence of mechanical hypersensitivity and neuropathic pain in MIA-injected hind limb. In tibiofemoral joint, the neuropathic pain was associated with mild to moderate degenerative changes demonstrated by increased total joint and tibial scores and increased cartilage degeneration width and volume. The cartilage degeneration included the loss of chondrocytes, proteoglycans and collagen matrix down to intermediate layer. These degenerative changes were observed together with a reduction in the amount of epiphyseal bone including decreased epiphyseal bone area fraction, decreased trabecular bone area fraction and decreased subchondral bone plate area. In MIA-injected patellofemoral joint, the neuropathic pain was associated with apparent damage including the degradation of articular surface both in femoral condyle and patella and a reduction in the density of subchondral bone in patella. Dynamic bone histomorphometry revealed impaired and ceased endochondral ossification in the articular cartilage of MIA-injected tibiofemoral and patellofemoral joints, respectively, in association with increased subchondral bone turnover. Conclusions: This study characterized the effects of intra-articular MIA injection on the entire rat knee including both tibiofemoral and patellofemoral joints together with OA symptoms in the rat MIA model used widely in the preclinical efficacy studies of OA. The injection of MIA induced a neuropathic pain in association with a significant damage both in tibiofemoral and patellofemoral joints. Therefore, treatment effects on the patellofemoral joint could be studied as well when testing the preclinical efficacy of OA drug candidates in the rat MIA model.