Bone mass changes of tibial and vertebral bones in young and adult rats with collagen-induced arthritis

To study the effect of arthritis on bone mass, bone mineral density (BMD) o f cancellous and cortical bone in the tibial metaphysis and diaphysis in 2- and 7-month-old rats with collagen-induced arthritis (CIA) was serially me asured using peripheral quantitative computed tomography (pQCT), BMD in the fourth lumbar vertebra in 7-month-old CIA rats was also measured by pQCT, The fourth lumbar vertebral body, distal femur, and proximal tibia in 7-mon th-old CIA rats were analyzed histomorphometrically. Changes in BMD differe d between 2-month-old (young) and 7-month-old (adult) CIA rats. Although th e BMD for the proximal tibia (2 mm and 5 mm distal from the growth cartilag e) in young CIA rats decreased compared with that in control rats, the valu es exceeded the initial value during the arthritis course. On the other han d, bone loss in adult CIA rats occurred predominantly in the cancellous bon e of the periarticular region of the tibia (2 mm distal from the growth car tilage), in which the enhancement of bone resorption and reduced bone forma tion were observed histomorphometrically. No remarkable changes were demons trated in BMD or histomorphometric al analysis for the lumbar vertebra duri ng the experimental course. These results suggest that bone loss in adult C IA rats resembles the osteoporosis that develops during the early stage of human rheumatoid arthritis. We conclude that adult CIA rats are more approp riate than young CIA rats as an experimental model of secondary osteoporosi s due to rheumatoid arthritis. (C) 2001 by Elsevier Science Inc. All rights reserved.