Quantification of bone changes in a collagen-induced arthritis mouse model by reconstructed three dimensional micro-CT

Abstract

Background: Inflammatory arthritis is a chronic disease, resulting in synovitis and subchondral and bone area destruction, which can severely affect a patient's quality of life. The most common form of inflammatory arthritis is rheumatoid arthritis (RA) in which many of the disease mechanisms are not well understood. The collagen-induced arthritis (CIA) mouse model is similar to RA as it exhibits joint space narrowing and bone erosion as well as involves inflammatory factors and cellular players that have been implicated in RA pathogenesis. Quantitative data for disease progression in RA models is difficult to obtain as serum blood markers may not always reflect disease state and physical disease indexes are subjective. Thus, it is important to develop tools to objectively assess disease progression in CIA.

Results: Micro-CT (Computed Tomography) is a relatively mature technology that has been used to track a variety of anatomical changes in small animals. In this study, micro-CT scans of several joints of control and CIA mice were acquired at 0, 4, 7, and 9 weeks after the immunization with collagen type II. Each micro-CT scan was analyzed by applying a segmentation algorithm to individual slices in each image set to provide 3-dimensional representations of specific bones including the humerus, femur, and tibia. From these representations, the volume and mean density of these bones were measured and compared. This analysis showed that both the volume and the density of each measured bone of the CIA mice were significantly smaller than those of the controls at week 7.

Conclusions: This study demonstrates that micro-CT can be used to quantify bone changes in the CIA mouse model as an alternative to disease index assessments. In conclusion, micro-CT could be useful as a non-invasive method to monitor the efficacy of new treatments for RA tested in small animals.

Keywords: Bone density; Bone volume; Collagen induced arthritis; Computed tomography; Disease index; Imaging; Micro-CT; Rheumatoid arthritis.

Figure 1

Visualization of the left femur bone by micro CT. Whole-body micro-CT images of a representative control (A) and CIA mouse at (B) week 0. Transverse, coronal, and sagittal planes are shown.

Figure 2

Measurement of bone density by micro-CT. Segmented slices of femur bones from control (A) and CIA mice (B) at the first time scan. The arrows indicate regions of interest (ROIs) with the red edges detecting the margins marking the boundaries of the bone.

Figure 3

Mean bone density in the bones of control and CIA mice. Shown are the mean densities and standard errors over time for (A) femur, (B) humerus, and (C) tibia from control and CIA mouse groups. P values were calculated by comparing each pair of control and CIA densities for each scan time (week 0, week 4, week 7, and week 9), and statistical significance was considered significant (*) if P < 0.05.

Figure 4

Measurement of bone density by micro-CT. Shown are representative longitudinal isosurface volume renderings of the femur from a (A) control mouse and a (B) CIA mouse from week 0 after initiation of collagen immunization. All rendering thresholds were set to 800 Hounsfield units.

Figure 5

Mean bone volume in the bones of control and CIA mice. Shown are the mean volumes and standard errors over time for (A) femur, (B) humerus, and (C) tibia bones from control and CIA mouse groups. P values were calculated by comparing each pair of control and CIA volumes for each scan time (week 0, week 4, week 7, and week 9), and statistical significance was considered significant (*) if P < 0.05.

Figure 6

Comparison of histology in synovial membranes of control and CIA mice. Shown are representative H&E stained sagittal sections of the humerus and radius-ulna joint examined by light microscopy from (A) control and (B) CIA mice.

Figure 7

Comparison of histology in cartilage and bone of control and CIA mice. Shown are representative H&E stained sagittal sections of the humerus and radius-ulna joint examined by light microscopy from (A) control and (B) CIA mice.