Subchondral bone and ligament changes precede cartilage degradation in guinea pig osteoarthritis.

There is increasing recognition that osteoarthritis (OA) is a complex disease involving the whole synovial joint, rather than the articular cartilage alone, however its aetiology and pathogenesis is not understood. Our initial studies revealed elevated turnover of bone and ligament collagen in human and mouse OA, respectively. To investigate the relative appearance of pathology in cartilage, bone and ligament, we studied the progression of spontaneous OA in the Dunkin-Hartley (DH) guinea pig knee, and compared with age-matched control Bristol Strain 2 (BS2) knees. The classical radiographic OA score of the DH knees compared to BS2 knees was 2-fold higher at 24 weeks of age. The patella perimeter and subchondral bone density was significantly greater in the DHs at 24 and 36 weeks compared to BS2. The femoral intercondylar notch width was found to be significantly lower in the DHs at 24 and 36 weeks, compared to BS2, indicating bone remodelling at the cruciate ligament (CL) insertion site. We found significantly greater laxity of the DH anterior CL at 12, 16 and 20 weeks compared to BS2. This elevated laxity was associated with increased remodelling of the CLs, based on markers of collagen turnover, and occurred prior to bone and cartilage pathology. We propose that the laxity of the CL leads to remodelling of the subchondral bone, and intercondylar notch, due to a change in load through the joint. Remodelling of the CLs and bone occurs prior to and concomitant with histopathological changes in the articular cartilage respectively, demonstrating the fundamental role of the ligament and subchondral bone in the aetiology of knee OA.

Fundamental subchondral bone changes in spontaneous knee osteoarthritis.

Osteoarthritis has an unknown aetiology, and tissue samples from early stage human osteoarthritis tissue cannot be reliably obtained. Therefore understanding the development of OA relies on using animal models: such as the spontaneous changes seen in the Dunkin-Hartley guinea pig strain, which are biochemically, histologically and radiologically similar to human OA. We investigated the role of bone change in early OA development using the non-OA developing Bristol strain-2 as control from 3 to 36 weeks by standard microfocal X-ray imaging and histological techniques. The patella, tibia and femur epiphyseal region and immediate subchondral area were analysed for bone density at all ages. We found that both radiological and histological osteoarthritis scores increased progressively for the Dunkin-Hartley, but not for the BS2 demonstrating its value as a control. The Dunkin-Hartley had a higher bone density and greater subchondral bone thickness from 24 weeks of age. We conclude that prior to any gross osteoarthritis pathology the Dunkin-Hartley are undergoing subchondral bone remodelling, thus demonstrating the fundamental role of early bone remodelling in the development of osteoarthritis.

Development of an assay for the quantification of type I collagen synthesis in the guinea pig.

There is a need for a reliable assay for the quantification of collagen type I synthesis in the guinea pig, an important model for many connective tissue diseases. Procollagen type I C-terminal propeptide (PICP) is the established marker of type I collagen synthesis but, to date, no assay has been developed to measure PICP in guinea pig tissue extracts. A monoclonal antibody, known to cross-react with intact guinea pig procollagen type I (anti-PICP), was tested for its ability to bind soluble guinea pig PICP in crude skin extracts using a biosensor. Anti-PICP was immobilised to the surface of a sensor chip and antibody-antigen binding was detected using the phenomenon of surface plasmon resonance (SPR). The binding component in the SPR-immunoassay was identified as PICP by purification and N-terminal sequencing. Guinea pig PICP was purified from skin by gel filtration, ion exchange chromatography and lectin affinity chromatography. Purified PICP was then biotinylated and used with anti-PICP to develop a competition ELISA that was able to selectively and sensitively measure PICP in extracts of guinea pig connective tissue.

Cruciate ligament laxity and femoral intercondylar notch narrowing in early-stage knee osteoarthritis.

OBJECTIVE: The influence of the cruciate ligaments in spontaneous osteoarthritis (OA) is not understood, although ligament rupture is known to cause secondary OA. Additionally, femoral notch narrowing at the anterior cruciate ligament (ACL) insertion site is associated with disease severity, but it is unknown whether ligament deterioration precedes or follows osteophyte formation. We examined cruciate ligament mechanics and metabolism and the intercondylar notch width in OA-prone Dunkin-Hartley (DH) guinea pigs at ages up to and including the age at OA onset (24 weeks), and compared the data with those in age-matched controls (Bristol strain 2 [BS2] guinea pigs). METHODS: Guinea pigs were assessed at 3, 6, 9, 12, 16, 20, 24, and 36 weeks of age. ACLs were mechanically tested, and the intercondylar notch width index (NWI) was determined. Cruciate ligament metabolism was determined by measuring the following markers of collagen turnover: matrix metalloproteinase 2 (MMP-2), tissue inhibitor of metalloproteinases 2, C-terminal type I procollagen propeptide (PICP), and the immature collagen-derived crosslink dihydroxylysinonorleucine (DHLNL). RESULTS: DH guinea pigs had significantly laxer ACLs than did BS2 guinea pigs, at 12, 16, and 24 weeks. We observed elevated levels of pro and active MMP-2, PICP, and DHLNL in the cruciate ligaments of DH animals at most ages, compared with BS2 guinea pigs. The NWI in DH animals was significantly lower than that in BS2 guinea pigs at 24 and 36 weeks. CONCLUSION: In DH guinea pigs, laxer ACLs, which are associated with increased collagen turnover, may cause joint instability and predispose these animals to the early onset of OA. Decreased intercondylar notch width in the DH animals indicates that bone remodeling at the ACL insertion site is a response to elevated ACL laxity.