Phospholipid composition of articular cartilage boundary lubricant

The mechanism of lubrication in normal human joints depends on loading and velocity conditions. Boundary lubrication, a mechanism in which layers of m olecules separate opposing surfaces, occurs under severe loading. This stud y was aimed at characterizing the phospholipid composition of the adsorbed molecular layer on the surface of normal cartilage that performs as a bound ary lubricant. The different types of phospholipid adsorbed onto the surfac e of cartilage were isolated by extraction and identified by chromatography on silica gel paper and mass spectroscopy. The main phospholipid classes i dentified were quantified by a phosphate assay. Gas chromatography and elec trospray ionization mass spectrometry were used to further characterize the fatty acyl chains in each major phospholipid component and to identify the molecular species present. Phosphatidylcholine (41%), phosphatidylethanola mine (27%) and sphingomyelin (32%) were the major components of the lipid l ayer on the normal cartilage surface. For each lipid type, a mixture of fat ty acids was detected, with a higher percentage of unsaturated species comp ared to saturated species. The most abundant fatty acid observed with all t hree lipid types was oleic acid (C18:1). Additional work to further quantif y the molecular species using electrospray ionization mass spectrometry is recommended. (C) 2001 Orthopaedic Research Society. Published by Elsevier S cience Ltd. All rights reserved.