Characterization of human apolipoprotein B100 oligosaccharides in LDL subfractions derived from normal and hyperlipidemic plasa: deficiency of alpha-N-acetylneuraminyllactosyl-ceramide in light and small dense LDL particles

The carbohydrate composition of apolipoprotein (apo) B100, particularly its degree of sialylation, may contribute to the atherogenic properties of low -density lipoprotein (LDL). We analyzed LDL apoB100 glycans derived from no rmolipidemic, hypercholesterolemic, and hypertriglyceridemic diabetic subje cts. Using exoglycosidase carbohydrate sequencing and matrix-assisted laser desorption/ionization mass spectrometry to analyze fluorescently labeled o ligosaccharides, we report evidence for several carbohydrates not previousl y identified on apoB100, including truncated complex biantennary N-glycans and hybrid N-glycans. The distribution and diversity of the apoB100 glycans isolated from all individuals was highly conserved. The N-glycan compositi on of apoB100 derived from five LDL subpopulations (LDL1, d = 1.018-1.023; LDL2, d = 1.023-1.030; LDL3, d = 1.030-1.040; LDL4, d = 1.040-1.051; LDL5, d = 1.051-1.065 g/ml) did not vary in normolipidemic or hypercholesterolemi c subjects. Furthermore, we found no evidence for "desialylated" apoB100 gl ycans in any of the samples analyzed. Analysis of the most abundant LDL gan glioside, alpha-N-acetylneuraminyllactosyl-ceramide, revealed a deficiency in small dense LDL and in the most buoyant subpopulation. These data provid e a novel explanation for the apparent deficiency of sialic acid in small d ense LDL and indicate that the global apoB100 N-glycan composition is invar iable in the patient groups studied.