Osteoarthritic cartilage lesions in the bovine patellar groove: a macroscopic, histological and immunohistological analysis.

A high percentage of osteoarthritis (OA)-like patellar groove lesions in the stifle joint in calcium-deficient bulls has been recently reported. The prevalence of these lesions in bulls deficient in or supplemented with calcium was compared to findings in culled and healthy bulls to determine whether they represent normal anatomical variations, developmental anomalies or OA. It was hypothesized that the patellar groove lesions may represent OA. Distal cartilage samples from 160 femurs were analysed using a macroscopic Société Française d'Arthroscopie (SFA) OA grading system. Samples representing different SFA grades were subjected to Osteoarthritis Research Society International (OARSI) histological and high-mobility group box 1 (HMGB1) immunohistological OA grading. For a qualitative analysis three OA samples were immunostained for interleukin (IL)-1ß, matrix metalloproteinase (MMP)-13 and collagenase-produced COL2-3/4M neoepitopes. Patellar groove lesions were found in 48% of the femurs and were highest in calcium-deficient animals (71%, P<0.001). All three different grading systems disclosed OA in culled bulls, but no focal areas of cartilage necrosis. OARSI and HMGB1 grades were fairly concordant (Spearman's ρ=0.95, P<0.001; Cohen's κ=0.23, P<0.005), both with a slight disparity with the SFA grade (ρ=0.80 and 0.87, P<0.01; κ=0.36 and 0.46, P<0.001). IL-1ß, MMP-13 and COL2-3/4M staining patterns were compatible with OA. The study showed that patellar groove lesions are common in bulls. In all SFA, OARSI and HMGB1 graded samples the lesions clearly demonstrated OA and showed OA-typical pathophysiology. Arthroscopic SFA grading showed similar changes in calcium-deficient and calcium-supplemented bulls, but in the absence of a time course study and histological data the primary nature of these lesions could not be established with certainty.

Bovine chronic osteoarthritis causes minimal change in synovial fluid.

Chronic osteoarthritis (OA) is a degenerative disease of the articular cartilage. DNA-binding high mobility group protein B1 (HMGB1) is released on cellular death/activation and acts as an endogenous danger signal and a proinflammatory cytokine. Matrix metalloproteinase (MMP)-2 and in MMP-9 are induced to mediate proteolytic degradation/remodelling of joint tissues. Collagen degradation in the bone and synovium leads to release of type I collagen-derived cross-linked carboxy-terminal telopeptide (ICTP). These molecules have been linked to the pathogenesis of OA and could have potential as synovial fluid (SF) biomarkers in OA. Cartilage and SF were obtained from 27 dairy bulls (30-61 months old) and control cartilage from six young healthy dairy bulls. OA lesions were evaluated grossly (five grades), histologically (seven Osteoarthritis Research Society International [ORSI] grades) and immunohistochemically (four HMGB1 grades). The OARSI lesion score was calculated as the product of the OARSI grade and the OARSI score (the total area of the lesions). SF concentrations of HMGB1, MMP-2 and -9 and ICTP were measured by enzyme-linked immunosorbent assay, gelatin zymography and radioimmunoassay, respectively. Seventy-two percent (39/54) of stifle joints and 85% (23/27) of the dairy bulls had at least one gross OA lesion and 94% of the lesions were localized to the distal end of the femur, with the patellar groove and the lateral trochlear ridge being predilection sites. Gross and histological grades correlated with the HMGB1 grade, but SF total cell count, percent neutrophils or the measured biomarkers did not correlate with the tissue lesions, with the exception of ICTP concentration, which correlated with the total joint score. The switch of HMGB1 from DNA-binding nuclear protein to an extracellular alarmin/cytokine correlates with the gross and histological grades of OA tissue lesions. However, the activity and extent of the tissue lesions did not correlate with other SF biomarkers, perhaps because the histological grades represent outcome measures, while SF reflects process parameters. The only exception was ICTP concentration, which reflects enhanced destruction/remodelling.

High mobility group box-1 (HMGB-1) in osteoarthritic cartilage.

OBJECTIVES: Nucleosomal high mobility group box-1 (HMGB-1) is translocated and released from necrotic and activated cells as an endogenous danger signal (alarmin) and cytokine. It was hypothesised that it plays a role in osteoarthritis (OA). characterised by cellular activation, inflammation and enchondral bone formation. METHODS: Bovine knee joint samples, collected from culled animals, were scored using histologic/histochemical grading to intact looking, mild, moderate or severe and immunohistochemically stained for HMGB-1. Chondrocyte pellets, produced from human bone marrow-derived mesenchymal stem cells and stimulated with tumour necrosis factor-a (TNF-alpha), were similarly stained. RESULTS: In healthy looking OA cartilage chondrocyte nuclei were usually HMGB-1 negative and in mild OA staining was restricted to nuclei. In moderate OA lesions HMGB-1 was also seen in the cytoplasm and occasionally pericellular matrix and in severe OA lesions often also in intra- and inter-territorial matrix. The tidemark in healthy cartilage did not contain HMGB-1, which however was seen at this interface as linear deposits even in intact-looking and mild OA lesions, as multiple wave-like deposits in moderate and as heavy granular deposits in severe lesions. TNF-alpha stimulation of chondrocytes caused translocation of HMGB-1 from the nucleus to the cytoplasm. CONCLUSIONS: In resting chondrocytes tight nucleosomal HMGB-1 binding might cause steric hindrance of immunostaining. TNF-alpha- or OA-mediated activation leads to nuclear staining and cytoplasmic translocation. Advancing OA leads to increasingly intense extra-/pericellular deposition of HMGB-1 alarmin, indicating local chondrocyte activation and/or necrosis. In particular, HMGB-1 at the tidemark might play a role in the pathological thickening of subchondral bone plate/osteophyte formation.