title: The effect of phospholipase digestion upon the boundary lubricating ability of synovial fluid.
abstract: OBJECTIVE
  To identify the boundary lubricant in synovial fluid (SF). Is synovial lubrication mediated by surface active phospholipid as opposed to mucinous glycoprotein?
  
  
  METHODS
  A sonicated preparation of phosphatidylcholine and bovine SF were tested in vitro in a bearing of latex oscillating against polished glass under a load of 0.35 x 10(6) N/m2. The friction apparatus isolates conditions of boundary lubrication and has been validated against a cartilaginous bearing. Coefficient of friction (mu) was measured and compared against mu from physiologic saline, which served as a control. Separate digestions were carried out upon the SF with trypsin, phospholipase C, and phospholipase A2 in the presence and absence of proteolytic inhibitors.
  
  
  RESULTS
  Digestions of bovine SF by phospholipase C in the presence of protease inhibitors did not remove boundary lubricating ability compared to an undigested control (p = 0.89). Digestion of bovine SF with trypsin removed all lubricating ability and raised friction (p = 0.004). Commercial purified phospholipase C contained trypsin-like activity when activity was tested with N alpha-benzoyl-L-arginine ethyl ester as substrate. Similar results were observed for phospholipase A2, which possesses a lower amount of trypsin activity.
  
  
  CONCLUSIONS
  The results indicate that phospholipid does not play a prominent role in synovial fluid's ability to lubricate an artificial bearing. Rather, the boundary lubricating ability of SF is attributable to lubricin, a mucinous glycoprotein.
authors.affiliation: Department of Medicine, Brown University School of Medicine, Providence, Rhode Island, USA. gregory_jay_MD@brown.edu
authors.forename: G D
authors.initials: GD
authors.lastname: Jay
authors.forename: C J
authors.initials: CJ
authors.lastname: Cha
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D006023:Glycoproteins / Q000737:chemistry; D066298:In Vitro Techniques; D008153:Lubrication; D010713:Phosphatidylcholines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism*; D013582:Synovial Fluid / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism / Q000494:pharmacology*; D000099158:Proteoglycan 4
chemical_list: D006023:Glycoproteins; D010713:Phosphatidylcholines; D010743:Phospholipids; D010738:Type C Phospholipases; D000099158:Proteoglycan 4