Abstract 323: Dietary Saturated Fat Increases the Susceptibility of Low-Density Lipoprotein to Aggregation by Sphingomyelinase

Early steps in the development of atherosclerosis are characterized by accumulation of extracellular aggregated low density lipoprotein (LDL) particles in the arterial intima. Sphingomyelinase (SMase), an intimal enzyme that hydrolyses sphingomyelin on the surface monolayer of LDL particles, is particularly effective in inducing LDL aggregation. In this study, we analyzed individual differences in SMase-induced LDL aggregation with the aim of identifying specific lipid components of LDL that can be linked with their susceptibility for aggregation. For this purpose we isolated plasma LDL from 100 randomly selected subjects participating in the Finnish Health 2000 Health Examination Survey. LDL aggregation was analyzed by measuring the size of LDL aggregates with dynamic light scattering during their modification by human recombinant sphingomyelinase. Large variations were observed in the aggregation lag phase between the different LDL donors. In particular, LDL from some donors expressed rapid aggregation potential, whereas LDL from other donors was very resistant to aggregation. Large aggregates (>1000 nm) were observed in 13 of the LDL samples after incubation for 2 h in the presence of SMase and the size of the aggregates plateaued at about 4500 nm, the first samples reaching this size after incubation for 3 h. In four out of the 100 samples only very small aggregation was observed and LDL particles had an average size <350 nm after incubation for 6 h. The intake of saturated fat was found to correlate positively with increased susceptibility for LDL aggregation ( p ≤0.005 ) . Thus, LDL isolated from butter-using donors aggregated faster than LDL derived from vegetable oil -using donors. Lipidomic analysis demonstrated that LDL particles with the highest susceptibility for aggregation had a larger number of saturated fatty acids in their surface phospholipids when compared with that of the aggregation-resistant LDL particles. This study provides novel insights of the influence of dietary fats on LDL atherogenicity.