Peptides of type II collagen can induce the cleavage of type II collagen and aggrecan in articular cartilage.

The objective of this study was to determine whether a fragment(s) of type II collagen can induce cartilage degradation. Fragments generated by cyanogen bromide (CB) cleavage of purified bovine type II collagen were separated by HPLC. These fragments together with selected overlapping synthetic peptides were first analysed for their capacity to induce cleavage of type II collagen by collagenases in chondrocyte and explant cultures of healthy adult bovine articular cartilage. Collagen cleavage was measured by immunoassay and degradation of proteoglycan (mainly aggrecan) was determined by analysis of cleavage products of core protein by Western blotting. Gene expression of matrix metalloproteinases MMP-13 and MMP-1 was measured using Real-time PCR. Induction of denaturation of type II collagen in situ in cartilage matrix with exposure of the CB domain was identified with a polyclonal and monoclonal antibodies that only react with this domain in denatured but not native type II collagen. As well as the mixture of CB fragments and peptide CB12, a single synthetic peptide CB12-II (residues 195-218), but not synthetic peptide CB12-IV (residues 231-254), potently and consistently induced in explant cultures at 10 microM and 25 microM, in a time, cell and dose dependent manner, collagenase-induced cleavage of type II collagen accompanied by upregulation of MMP-13 expression but not MMP-1. In isolated chondrocyte cultures CB12-II induced very limited upregulation of MMP-13 as well as MMP-1 expression. Although this was accompanied by concomitant induction of cleavage of type II collagen by collagenases, this was not associated by aggrecan cleavage. Peptide CB12-IV, which had no effect on collagen cleavage, clearly induced aggrecanase specific cleavage of the core protein of this proteoglycan. Thus these events involving matrix molecule cleavage can importantly occur independently of each other, contrary to popular belief. Denaturation of type II collagen with exposure of the CB12-II domain was also shown to be much increased in osteoarthritic human cartilage compared to non-arthritic cartilage. These observations reveal that peptides of type II collagen, to which there is increased exposure in osteoarthritic cartilage, can when present in sufficient concentration induce cleavage of type II collagen (CB12-II) and aggrecan (CB12-IV) accompanied by increased expression of collagenases. Such increased concentrations of denatured collagen are present in adult and osteoarthritic cartilages and the exposure of chondrocytes to the sequences they encode, either in soluble or more likely insoluble form, may therefore play a role in the excessive resorption of matrix molecules that is seen in arthritis and development.

In vivo absorption of porous apatite- and wollastonite-containing glass-ceramic.

The behavior of porous apatite- and wollastonite-containing glass-ceramic (AW) in the bone marrow cavity was investigated. Cylinders of porous AW (4 mm in diameter and 20 mm long, mean porosity of 70% and mean pore diameter of 200 microm) were implanted into the bone marrow cavity of rabbit femurs, and analyzed by chronological radiograms and by scanning electron microscopy one, three, six, and 12 months later. The pores of porous AW are interconnected and homogeneously distributed, and its compressive strength is nearly equal to that of human cancellous bone. Bone formed in the pores at the center of the material by one month and bonded to the material directly. The volume of newly formed bone in the material pores reached a peak at three months, and decreased gradually after six months. The trabecular structures of AW were gradually remodeled by newly formed bone, while AW-bone bonding was maintained during bone remodeling and material absorption. AW was absorbed continuously, and at six and 12 months the residual material corresponded to about 64 and 30% of the starting material, respectively. Porous AW may therefore be useful as an absorbable bone substitute.

Lectin-like oxidized low-density lipoprotein receptor 1 mediates leukocyte infiltration and articular cartilage destruction in rat zymosan-induced arthritis.

OBJECTIVE: The relationship between rheumatoid arthritis and atherosclerosis has been recognized for >20 years. This study aimed to elucidate the roles of oxidized low-density lipoprotein (ox-LDL; one of the main pathogenic factors of atherosclerosis) and its endothelial receptor, lectin-like ox-LDL receptor 1 (LOX-1), in arthritic joints using a rat zymosan-induced arthritis (ZIA) model. METHODS: LOX-1 expression and ox-LDL accumulation in arthritic joints were detected by immunohistochemistry using specific mouse anti-LOX-1 and anti-ox-LDL monoclonal antibodies, respectively. To elucidate the effects of the expressed LOX-1 on arthritis, ZIA rats were treated with anti-LOX-1 antibody or normal mouse IgG. The severity of arthritis was analyzed by joint swelling. Cell infiltration, synovial hyperplasia, and proteoglycan losses were also determined by histologic scoring. Proinflammatory cytokine and nitrite levels in serum and joint fluid were also measured. RESULTS: Immunohistochemical study of ZIA demonstrated LOX-1 expression on synovial endothelium and postcapillary venules at 6 hours after the induction of inflammation, with maximum expression detected at 24 hours. LOX-1 was also expressed weakly on both joint cartilage and synovium. Ox-LDL, a ligand of LOX-1, was also detected in articular chondrocytes. Administration of anti-LOX-1 antibody, which blocks LOX-1 activity, suppressed joint swelling (by 33.5%), leukocyte infiltration, and joint nitrite accumulation at 24 hours, as well as cartilage destruction at 7 days, compared with control rats. CONCLUSION: LOX-1 induction in arthritic joints might play a role in promoting joint inflammation and cartilage destruction by mediating leukocyte infiltration into the arthritic joints of ZIA rats.