Bone response to mechanical loading in adult rats with collagen-induced arthritis

To elucidate the effects of inflammation on the response of bone to mechanical stress, we performed experiments using a rat with collagen-induced arthritis (CIA) model. Six-month-old female Wistar rats were used in the experiment. Bovine type II collagen sensitization and additional sensitization after 1 week were preformed in all CIA groups. Loads were applied using a four-point bending device. The right tibia was loaded in both CIA and control (CONT) groups at 35 N (low groups), 40 N (medium groups), or 47 N (high groups) for 36 cycles at 2 Hz three times per week for 3 weeks. Histomorphometrical data were collected from the periosteal and endosteal surfaces of the tibia in all rats. The tibia periosteal surface was subdivided into lateral and medial surfaces. Formation surface (FS), mineral apposition rate (MAR) and bone formation rate (BFR) were calculated. At lateral surface of periosteal surface, all three parameters showed significant differences between the loaded and nonloaded tibiae. All these parameters were significantly lower in CIA groups than in CONT groups, and interaction was seen between applied loading and CIA. There was a significant correlation between peak strain and the right-left difference of FS in the CONT groups. At medial surface of periosteal surface, there were force-related increase in FS, MAR, and BFR on the loaded side in both CIA and CONT groups, except MAR in the CONT group. All three parameters showed significant differences between the loaded and nonloaded tibiae. At endocortical surface, force-related increase was observed only in FS on the loaded side in CONT groups, and FS was significantly higher on the loaded side than the nonloaded side. CIA lowered all three parameters significantly. We examined the response to mechanical loading on the tibia in untreated CONT rats and rats with CIA by bone histomorphometry, and found that arthritis suppressed bone formation induced by mechanical loading.