Dose-related histopathology and bone remodeling characteristics of the knee articular cartilage and subchondral bone induced by glucocorticoids in rats

Abstract

The aim of the current study was to investigate histopathological changes and bone remodeling in the knee articular cartilage and subchondral bone in rats following treatment with glucocorticoids. A total of 30 3-month-old female Sprague-Dawley rats were randomly divided into either a vehicle control group or one of three experimental groups wherein dexamethasone (Dex) was administered at a dose of 1.0, 2.5 or 5.0 mg/kg (Dex1.0, Dex2.5 and Dex5.0, respectively), for 8 weeks. Articular cartilage and the epiphyseal subchondral bone of the proximal tibias were evaluated by histopathology or for bone remodeling using histomorphometry. No histological changes were identified in the knee articular cartilage but the bone formation rate of the subchondral bone was lower in the Dex1.0 group compared with that of the control group. Compared with the control and the Dex1.0 group, the width of the articular cartilage and the subchondral plate were larger, with abnormal morphology and increased apoptosis of chondrocytes, decreased cell/matrix volume ratio in the cartilage and fewer blood vessels in the subchondral plate in the Dex2.5 and Dex5.0 groups. A higher Dex dose resulted in more severe inhibition of bone formation, a greater number of apoptotic osteocytes and constrained bone resorption. All microstructure parameters indicated no significant changes in the Dex2.5 group but exhibited deterioration in the Dex5.0 group compared with the normal and Dex1.0 group. There were no significant differences in morphological changes, or in static and dynamic bone indices between the Dex2.5 and Dex5.0 groups. In conclusion, long-term glucocorticoid use induced dose-related histopathological changes in the knee articular cartilage, along with unbalanced bone remodeling and osteopenia in the subchondral bone. The degree of damage to the articular cartilage was milder and transformed from compensation to degeneration at higher doses.

Keywords: articular cartilage; glucocorticoid; knee; rat; subchondral bone.

Figure 1.

Morphology of the AC and subchondral zone from rats treated with vehicle or three doses of Dex. Staining was performed using the Masson-Goldner trichrome bone stain technique. (A) Image of the proximal tibial epiphyseal area with an intact lateral plateau of AC. Magnification, ×4. The black frame and corner arrow in indicate the observed and measured site of AC and subchondral zone, which is magnified and shown separately in panel C. (B) Enlarged section indicating the AC layers and subchondral zone shown in panel C. Original magnification, ×40. (C) AC and subchondral zone in each group. Black columns indicate the width of either AC or subchondral zone. Black arrows point to chondrocytes in the AC. Chondrocytes are normal in the Cont and Dex1.0 mg groups but are triangular or spindle-like with large vacuoles in the Dex2.5 and Dex5.0 groups. Yellow arrows point to blood vessels within the subchondral cortical plate. Magnification, ×20. Dex, dexamethasone; Cont, control group, Dex1.0, Dex 1.0 mg/kg group; Dex2.5, Dex 2.5 mg/kg group; Dex5.0, Dex 5.0 mg/kg group; AC, articular cartilage.

Figure 2.

Parameters of the AC and subchondral zone from rats treated with vehicle or three doses of Dex. (A) Comparison of the AC width in each group. (B) Cell/matrix volume ratio of the AC zones in each group. (C) Calcified and subchondral cortical plate width changes in the subchondral zone in each group. (D) Number of blood vessels within the subchondral cortical plate in each group. ^aP<0.05 vs. Cont; ^bP<0.05 vs. Dex1.0. Dex, dexamethasone; Cont, control group; Dex1.0, Dex 1.0 mg/kg group; Dex2.5, Dex 2.5 mg/kg group; Dex5.0, Dex 5.0 mg/kg group; Super, superficial zone, Trans, transitional zone; Radia, radial zone; Total, total AC width; AC, articular cartilage.

Figure 3.

Microphotographs of fluorescence and autofluorescence of subchondral trabecular bone from rats treated with three doses of Dex. (A) Fluorescence images of subchondral trabecular bone. Fluorescent labeling surrounds the trabecular bone. White arrows point to double labels for tetracycline (yellow label) and calcein (green label). Pink arrows point to single calcein labels. Magnification, ×10. (B) Autofluorescence image of trabecular bone. Green arrows point to osteocyte lacunae. Magnification, ×20. Dex, dexamethasone; Cont, control group; Dex1.0, Dex 1.0 mg/kg group; Dex2.5, Dex 2.5 mg/kg group; Dex5.0, Dex 5.0 mg/kg group.

Figure 4.

Osteoblast and osteoclast morphology changes in subchondral trabecular bone from rats treated with three doses of Dex. Tissues were stained with Masson Goldner trichrome bone stain. Magnification, ×40. (A) Black arrows point to osteoblasts. (B) Black arrows point to osteoclasts. Dex, dexamethasone; Cont, control group; Dex1.0, Dex 1.0 mg/kg group; Dex2.5, Dex 2.5 mg/kg group; Dex5.0, Dex 5.0 mg/kg group.