Visualization of collagenase-induced cartilage degradation using NMR microscopy

Near Infrared Spectroscopy Enables Differentiation of Mechanically and Enzymatically Induced Cartilage Injuries

This study evaluates the feasibility of near infrared (NIR) spectroscopy to distinguish between different cartilage injury types associated with post-traumatic osteoarthritis and idiopathic osteoarthritis (OA) induced by mechanical and enzymatic damages. Bovine osteochondral samples (n = 72) were subjected to mechanical (n = 24) and enzymatic (n = 36) damage; NIR spectral measurements were acquired from each sample before and after damage, and from a separate control group (n = 12). Biomechanical measurements were then conducted to determine the functional integrity of the samples. NIR spectral variations resulting from different damage types were investigated and the samples classified using partial least squares discriminant analysis (PLS-DA). Partial least squares regression (PLSR) was then employed to investigate the relationship between the NIR spectra and biomechanical properties of the samples. Results of the study demonstrate that substantial spectral changes occur in the region of 1700–2200 nm due to tissue damages, while differences between enzymatically and mechanically induced damages can be observed mainly in the region of 1780–1810 nm. We conclude that NIR spectroscopy, combined with multivariate analysis, is capable of discriminating between cartilage injuries that mimic idiopathic OA and traumatic injuries based on specific spectral features. This information could be useful in determining the optimal treatment strategy during cartilage repair in arthroscopy.

An in vitro model for the pathological degradation of articular cartilage in osteoarthritis

The objective of this study was to develop an in vitro cartilage degradation model that emulates the damage seen in early-stage osteoarthritis. To this end, cartilage explants were collagenase-treated to induce enzymatic degradation of collagen fibers and proteoglycans at the articular surface. To assess changes in mechanical properties, intact and degraded cartilage explants were subjected to a series of confined compression creep tests. Changes in extracellular matrix structure and composition were determined using biochemical and histological approaches. Our results show that collagenase-induced degradation increased the amount of deformation experienced by the cartilage explants under compression. An increase in apparent permeability as well as a decrease in instantaneous and aggregate moduli was measured following collagenase treatment. Histological analysis of degraded explants revealed the presence of surface fibrillation, proteoglycan depletion in the superficial and intermediate zones and loss of the lamina splendens. Collagen cleavage was confirmed by the Col II-3/4Cshort antibody. Degraded specimens experienced a significant decrease in proteoglycan content but maintained total collagen content. Repetitive testing of degraded samples resulted in the gradual collapse of the articular surface and the compaction of the superficial zone. Taken together, our data demonstrates that enzymatic degradation with collagenase can be used to emulate changes seen in early-stage osteoarthritis. Further, our in vitro model provides information on cartilage mechanics and insights on how matrix changes can affect cartilage's functional properties. More importantly, our model can be applied to develop and test treatment options for tissue repair.

The evolution of articular cartilage imaging and its impact on clinical practice

Over the past four decades, articular cartilage imaging has developed rapidly. Imaging now plays a critical role not only in clinical practice and therapeutic decisions but also in the basic research probing our understanding of cartilage physiology and biomechanics.

Premature osteoarthritis in the Disproportionate micromelia (Dmm) mouse

OBJECTIVE

Degeneration of articular cartilage leads to the development of osteoarthritis (OA), but the molecular pathology of the disease is poorly understood. The Disproportionate micromelia (Dmm) mouse has a deletion mutation in the C-propeptide encoding region of Col2a1, which leads to a defective cartilage matrix. The objective of this study was to determine whether heterozygous (Dmm/+) mice develop premature OA, and could therefore serve as an animal model for studying the molecular pathways leading to OA.

DESIGN

Histological analysis was utilized to determine the state of articular cartilage degeneration in Dmm/+ mice at 3, 6, 9, 12, 15, and 22 months of age. Severity of OA was quantified with a modified Mankin scoring system. In addition, articular cartilage thickness, cell density, and the extracellular matrix (ECM) fraction of articular cartilage were quantified.

RESULTS

Articular cartilage erosion was significantly more severe in Dmm/+ than in wild-type (+/+) mice beginning at 9 months, and modified Mankin scoring revealed Dmm/+ articular cartilage to be in a more severe osteoarthritic state as early as 3 months. In addition, Dmm/+ articular cartilage was thinner than +/+ cartilage and showed increased cell density and decreased matrix fraction compared with +/+ from the earliest time points measured.

CONCLUSIONS

The present study demonstrates that Dmm/+ mice develop premature OA. The observed degenerative changes of Dmm/+ articular cartilage closely resemble those of human OA patients, with or without Col2a1 mutations, suggesting that Dmm/+ mice are a useful model for investigating mechanisms involved in OA.

MRI of articular cartilage: revisiting current status and future directions

OBJECTIVE

The purpose of this article is to review the current understanding of the MRI appearance of articular cartilage and its relationship to the microscopic and macroscopic structure of articular cartilage, the optimal pulse sequences to be used in imaging, the appearance of both degenerative and traumatic chondral lesions, the appearance of the most common cartilage repair procedures, and future directions and developments in cartilage imaging.

CONCLUSION

Articular cartilage plays an essential role in the function of the diarthrodial joints of the body but is frequently the target of degeneration or traumatic injury. The recent development of several surgical procedures that hold the promise of forming repair tissue that is hyaline or hyalinelike cartilage has increased the need for accurate, noninvasive assessment of both native articular cartilage and postoperative repair tissue. MRI is the optimal noninvasive method for assessment of articular cartilage.

High-resolution diffusivity imaging at 3.0 T for the detection of degenerative changes: a trypsin-based arthritis model

RATIONALE AND OBJECTIVES

To establish whether it is possible to quantitatively characterize the degenerative changes in cartilage that typify arthritis on a sub-150-microm resolution scale using a 3.0 T whole body MR-scanner with a reasonable measurement time.

MATERIALS AND METHODS

This problem is addressed through diffusion-microimaging investigations on an arthritis model based on the enzymatic destruction of the proteoglycans in cartilage specimen. A 35-mm birdcage resonator made high spatial resolution possible, and diffusion-micro-imaging was achieved with the use of a strong gradient system.

RESULTS

Diffusion-weighted and quantitative parameter maps were acquired with 117 x 234 microm2 pixel resolution in less than 9 minutes. Diffusivity profiles and parameter images exhibit an increase in diffusivity in degenerated tissue.

CONCLUSION

In a trypsin-based arthritis model, the spatial localization and quantification of damaged areas have been shown to be possible on a whole body 3.0 T MR system. Measurement times achieved for these high spatial resolution studies make in vivo investigations feasible.

MRI techniques in early stages of cartilage disease

Cartilage degenerative diseases affect millions of people. Our understanding of these diseases and our ability to establish efficacious treatment strategies have been confounded by the difficulty of nondestructively evaluating the state of cartilage. Imaging strategies that allow visualization of cartilage integrity would revolutionize the field by allowing us to visualize early stages of degeneration and thus to evaluate predisposing factors for cartilage disease and changes resulting from interventions (eg, therapies) in culture studies, tissue-engineered systems, animal models, and in vivo in humans. Here we briefly review current state-of-the-art MRI strategies relevant to understanding and following treatment in early cartilage degeneration. We review MRI as applied to the assessment of the whole joint, of cartilage as a whole (as an organ), of cartilage tissue, and of cartilage molecular composition and structure. Each of these levels is amenable to assessment by MRI and offers different information that, in the long run, will serve as an important element of cartilage imaging.