Effective technical protocol for producing a mono-iodoacetate-induced temporomandibular joint osteoarthritis in a rat model.

Abstract

An animal model of osteoarthritis (OA) induced by monosodium iodoacetate (MIA) can be effectively adjusted based on the concentration of MIA to control the onset, progression, and severity of OA as required. The rat temporomandibular joint osteoarthritis (TMJOA) model using MIA is a useful tool for studying the effectiveness of disease-modifying OA drugs in TMJOA research. However, the intricate and complex anatomy of the rat TMJ often poses challenges in achieving consistent TMJOA induction during experiments. In the previous paper, a reference point was established by drawing parallel lines based on the line connecting the external ear and the zygomatic arch. However, this is not suitable for the anatomical characteristics of the rat. We used the zygomatic arch as a reference, which is a technical protocol that considers it. In our protocol, we designated a point approximately 1 mm away from the point where the zygomatic arch bends towards the ear as the injection site. To ensure precise injection of MIA and increase the likelihood of inducing OA, it is recommended to insert the needle at a 45° angle so that the needle tip contacts the joint projection. To confirm TMJOA induction, we identified changes in the condyle using in vivo micro-computed tomography (CT) in a rat model of MIA-induced OA and measured the degree of pain-related inflammation using head withdrawal threshold (HWT) measurements. Micro-CT scanning revealed typical OA-like lesions, including degenerative changes and subchondral bone remodeling induced by MIA in the TMJ. Pain, a major clinical feature of OA, showed an appropriate response corresponding to the structural changes shown in micro-CT scanning. In addition, the MIA concentration suitable for long-term observation of lesions was determined through ex vivo micro-CT imaging and HWT measurements. The 8 mg concentration exhibited a significant difference compared to others, confirming the sustained presence of lesions, particularly through changes in subchondral bone over an extended period. Consequently, we have successfully established a reliable rat TMJOA induction model and identified the MIA concentration suitable for long-term observation of subchondral bone research, which will greatly contribute to the study of TMJOA-an incurable disease lacking specific treatment options.