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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 zymosaninduced 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 antiox-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.

We cloned a cDNA encoding a novel lysyl oxidaserelated protein, named LOXC, by suppression subtractive hybridization between differentiated and calcified ATDC5 cells, a clonal mouse chondrogenic EC cell line. The deduced amino acid sequence of mouse LOXC consists of 757 amino acids and shows 50% identity with that of mouse lysyl oxidase. Northern blot analysis showed a distinct hybridization band of 5.4 kilobases, and Western blot analysis showed an immunoreactive band at 82 kilodaltons. Expression of LOXC mRNA was detected in osteoblastic MC3T3-E1 cells and embryonic fibroblast C3H10T1/2 cells, whereas none of NIH3T3 fibroblasts and myoblastic C2C12 cells expressed LOXC mRNA in vitro. Moreover, the LOXC mRNA and protein levels dramatically increased throughout a process of chondrogenic differentiation in ATDC5 cells. In vivo, LOXC gene expression was localized in hypertrophic and calcified chondrocytes of growth plates in adult mice. The conditioned media of COS-7 cells transfected with the fulllength LOXC cDNA showed the lysyl oxidase activity in both type I and type II collagens derived from chick embryos, and these activities of LOXC were inhibited by ␤-aminopropionitrile, a specific inhibitor of lysyl oxidase. Our data indicate that LOXC is expressed in cartilage in vivo and modulates the formation of a collagenous extracellular matrix.Endochondral bone formation is a multistep programmed event in skeletal development. Undifferentiated mesenchymal chondroprogenitor cells differentiate into chondrocytes through a cellular condensation process. Such chondrocytes surround themselves with an abundant layer of extracellular matrix, including type II, IX, and XI collagens, that is characteristic of cartilage (1, 2). These cells go through sequential processes of proliferation and maturation and then change their genetic program to be converted into hypertrophic and calcified chondrocytes, expressing type X collagen. These events are under the regulatory control of a variety of growth and differentiation modulating factors, including bone morphogenetic proteins (3, 4), fibroblast growth factors (5, 6), parathyroid hormone-related peptide (7-9), and Indian hedgehog (10). It is also clear that the components of extracellular matrix in cartilage play important roles in modulating and maintaining the phenotype of chondrocytes. During a process of hypertrophic conversion and calcification of chondrocytes, mineralization of extracellular matrix occurs before these chondrocytes are replaced by bone tissues. However, the molecular mechanisms underlying these sequential events remain largely unknown.We previously reported that the clonal mouse cell line, ATDC5, enables the monitoring of the multistep chondrogenic differentiation in a single culture (11)(12)(13)(14). When cultured in the presence of insulin, ATDC5 cells form cartilaginous nodules through cellular condensation. When the formation of cartilage nodules is completed, the cells are then converted to type X collagen-expressing hypertrophic chondrocytes, following...

Abstract:We took three types of bioactive bone cement (designated AWC, HAC, and TCPC), each with a different bioactive filler, and evaluated the influence of each filler on the mechanical properties and osteoconductivity of the cement. The cements consisted of bisphenol-a-glycidyl methacrylate-based (Bis-GMA based) monomers as an organic matrix, with a bioactive filler of apatite/wollastonite containing glass-ceramic (AW-GC) or sintered hydroxyapatite (HA) or ␤-tricalcium phosphate (␤-TCP) powder. Each filler was mixed with the monomers in proportions of 50, 70, and 80% (w/w), giving a total of nine cement subgroups. The nine subgroups were designated AWC50, AWC70, AWC80, HAC50, HAC70, HAC80, TCPC50, TCPC70, and TCPC80. The compressive and bending strengths of AWC were found to be higher than those of HAC and TCPC for all bioactive filler contents. We also evaluated the cements in vivo by packing them into the intramedullary canals of rat tibiae. To compare the osteoconductivity of the cements, an affinity index was calculated for each cement; it equaled the length of bone in direct apposition to the cement, expressed as a percentage of the total length of the cement surface. Microradiographic examination up to 26 weeks after implantation revealed that AWC showed a higher affinity index than HAC and TCPC for each filler content although the affinity indices of all nine subgroups (especially the AWC and HAC subgroups) increased with time. New bone had formed along the AWC surface within 4 weeks, even in the cement containing AW-GC filler at only 50% (w/w); observation of the cement-bone interfaces using a scanning electron microscope showed that all the cements had directly contacted the bone. At 4 weeks the AWC had bonded to the bone via a 10 m-thick reactive layer; the width of the layer, in which partly degraded AW-GC particles were seen, became slightly thicker with time. On the other hand, in the HACand TCPC-implanted tibiae, some particles on the cement surface were surrounded by new bone and partly absorbed or degraded. The results suggest that the stronger bonding between the inorganic filler and the organic matrix in the AWC cements gave them better mechanical properties. The results also indicate that the higher osteoconductivity of AWC was caused by the higher reactivity of the AW-GC powder on the cement surface.