Lubricin was isolated from bovine ankle, metacarpophalangeal and knee and human knee synovial fluids. The lubricins isolated from the bovine joint fluids had the same amino acid and carbohydrate compositions, but differences were observed in the relative molecular masses. The Mr values of bovine metacarpophalangeal and ankle lubricin determined by light-scattering measurements were about 200 000, whereas values of 132 000 and 143 000 were obtained for the bovine knee lubricin. The human knee lubricin had a similar carbohydrate composition to bovine knee lubricin except for the higher glucosamine content, and the amino acid composition differed slightly. The human sample had a lower glutamic acid content and a leucine/isoleucine ratio of 2:1 compared with 1:1 in the bovine. The Mr value of the human knee lubricin (166 000) was also lower than that of the bovine metacarpophalangeal and ankle samples. The Mr value of the bovine knee lubricin determined by sedimentation-equilibrium measurements was 171 000. The length measurements determined by electron microscopy and also the sedimentation measurements showed considerable polydispersity and indicate that the degree of extension of lubricin molecules can vary. Friction measurements showed that the human knee synovial-fluid lubricin had equivalent lubricating ability in a test system in vitro to that observed for lubricin isolated from normal bovine synovial fluids. The lubricating ability of lubricin was concentration-dependent, and each lubricin sample was able to act as a lubricant in vitro in an equivalent manner to whole synovial fluid at concentrations that are thought to occur in vivo.
Hyaluronic acid (HA) is a linear polysaccharide with repeating disaccharide units of glucuronic acid and N-acetylglucosamine and is found in the extracellular matrix of connective tissues. Reaction of high molecular weight sodium hyaluronate (NaHA, MW approximately 2 x 10(6] with EDC at pH 4.75, either in the presence or absence of a primary diamine, gave the N-acylurea and O-acylisourea as NaHA-carbodiimide adducts. None of the expected intermolecular coupling with the amine component was observed. On the basis of this new observation, this method for chemical modification of HA was used in conjunction with new synthetic carbodiimides to prepare HA derivatives bearing lipophilic, aromatic, cross-linked, and tethered functional groups. The degree of conversion to NaHA-acylurea products appears to depend upon both the characteristics of various carbodiimides and the conformational structure of NaHA.
Friction measurements were performed on fractions prepared from bovine synovial fluid by using a cartilage on glass apparatus. A fraction containing lubricating glycoprotein-I (LGP-I) as the only detectable component at concentrations of 30-50 p g / d was able to lubricate in an identical manner to whole synovial fluid. These data indicate that LGP-I is the molecule responsible for the lubricating ability of synovial fluid. '2510dine-labeled LGP-I also lubricated in a manner similar to synovial fluid, whereas when this sample was reduced and alkylated or treated with neuraminidase, the lubricating activity was greatly decreased. In tests to measure binding of ' "I LGP-I to cartilage, an initial linear increase in binding was observed, followed by a decrease in binding at higher concentrations. In contrast, both the reduced and alkylated and the neuraminidase treated samples did not show the same concentrationdependent binding to the cartilage. It is suggested, therefore, that at least part of the lubricating ability of LGP-I is dependent upon its ability to bind to articular cartilage.
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