Glycolipid Composition of Human Cataractous Lenses: Characterization of Lewis^x Glycolipids

We have studied the glycolipid composition of human cataractous lenses. Neutral and acidic lipid fractions were isolated by column chromatographies on DEAE-Sephadex and Iatrobeads. The neutral glycolipid fraction and acidic glycolipid fraction contained 0.6-0.9 μg of lipid-bound glucose (Glc) per mg of protein and 0.8-1.3 μg of lipid-bound sialic acid (NeuAc) per mg of protein, respectively. The neutral glycolipid fraction was found to contain LacCer (39.0% of total neutral glycolipids), Gb₃ (16.2%), Gb₄ (1.1%), nLc₄ (5.0%), X (29.0%), and Y (9.2%). The acidic lipid fraction was found to contain mainly GM3 (33.1% of the total ganglioside fraction), GM1 (8.3%), LM1 (7.3%), GD1a (16.0%), and G (30.1%). The structures of neutral glycolipids X and Y and ganglioside G were elucidated by high performance thin-layer chromatography overlay method of glycolipids, gas-liquid chromatography, proton NMR spectrometry, and liquid secondary ion mass spectrometry as follows: 1) X, Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glcβ1-1′Cer, III³FucnLc₄ (Le^x); 2) Y, Galβ1-4(Fucα1-3)GlcNAcßl-3Galßl-4(Fucal-3)GlcNAcβ1- 3Galβ1-4Glcβ1-1′Cer, V³FucIII³FucnLc₆; and 3) G, NeuAcα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Gal-β1- 4Glcβ1-1′Cer, IV³NeuAcIII³FucnLc₄ (sialosyl-Le^x). A minor neutral glycolipid Z was isolated and tentatively characterized as GlcNAcβ1-3?Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1- 4Glcβ1-1′Cer (GlcNAc-Le^x), suggesting that it may be the precursor of glycolipid Y. The major long-chain base of these human cataract glycolipids was C18:0 sphingosine (sphinganine). The major fatty acids were C16:0, C24:1 and C24:0, and monounsaturated fatty acids accounted for 40-55% of the total fatty acids.