Synovial fluid lipoproteins: review of current concepts and new directions

Recent developments in plasma lipoprotein and apolipoprotein research have been striking, but few studies have focused on the analysis of lipoproteins in synovial fluid (SF). SF contains small amounts of lipoproteins and apolipoproteins. The lipid concentration of normal human SF is extremely low and is in sharp contrast to the concentrations found in plasma. Little is known about the lipids in pathological SF, but studies have noted increased cholesterol and lipoprotein content in rheumatoid arthritis (RA) SF ranging from 40% to 60% of the total plasma lipoproteins. Recently apolipoproteins AI, B and E have also been found to be in increased amounts in RA SF. Several theories have been proposed to account for the increased presence of SF lipids in RA. Animal and human studies indicate the SF cholesterol, lipoproteins, and apolipoproteins may aggravate the inflammatory reaction within the synovial space. Research suggests an immunologic role for plasma lipoproteins on lymphocyte and monocytes in the blood and lymph. SF lipoproteins and apolipoproteins should be studied to define their actions within the synovial space.