Initiation and progression of ochronotic osteoarthropathy in alkaptonuric mice

Abstract

models: 1) intra-articular injection of monoiodoacetate (MIA) at the dose of 1 mg/kg, 2) medial meniscal tear (MMT) combined with medial collateral ligament transection (MCLT), 3) anterior cruciate ligament transection (ACLT) combined with partial medial meniscectomy (pMMx), 4) ACLT. Body weight, static weight bearing determined as hind paw weight distribution, and static mechanical allodynia determined as paw withdrawal threshold were followed in each model during the study. Knee joints were harvested and digital radiographs were obtained from them at two different time points in each model as follows: in the MIA model at 2 and 4 weeks, in the MMT + MCLT model at 3 and 6 weeks, in the ACLT + pMMx model at 4 and 8 weeks, and in the ACLT model at 5 and 10 weeks. Microscopic assessment of degenerative changes was performed in knee joints as recommended by the OARSI histopathology initiative. Results: Static weight bearing was decreased in operated knee joints during the first week of the study, demonstrating an operation-related joint discomfort. Paw withdrawal threshold was decreased in operated and MIA-injected knee joints during the first week and at the end of the study, indicating operation and OA-related joint pain. Microscopic assessment of OA demonstrated progressive degenerative changes in knee joints in all animal models. Mild to moderate changes were observed in the MIA and ACLT models. In the MIA model, mild degenerative changes included the loss of chondrocytes, proteoglycans (PG) and collagen matrix in superficial layer of articular cartilage in medial tibial plateau at 2 weeks, and the chondrocyte and PG loss exacerbated down to intermediate layer at 4 weeks. In the ACLT model, chondrocytes, PG and collagen matrix were lost mainly in superficial layer at 5 weeks, their loss exacerbated down to tidemark at 10 weeks, and these changes were associated with the presence of moderate to large osteophytes and minimal synovial inflammation. The MMT + MCLT and ACLT + pMMx models exhibited moderate to severe degenerative changes. In the articular cartilage of medial tibial plateau, chondrocytes, PG and collagen matrix were lost from superficial layer down to tidemark in the MMT + MCLT model at 3 and 6 weeks, and in the ACLT + pMMx model at 4 and 8 weeks. These changes were associated with the presence of large osteophytes and mild synovial inflammation in both models. Conclusions: This study characterized progressive degenerative changes as recommended by the OARSI histopathology initiative in knee joints of four rat OA models used frequently in the preclinical in vivo efficacy studies of DMOADs. Mild to moderate degenerative changes were observed in the MIA and ACLT models and moderate to severe changes in the MMT + MCLT and ACLT + pMMx models. In all OA models, the development of degenerative changes was associated with decreased paw withdrawal threshold, indicating OA-related joint pain.