(489aa) Effect of Sphingomyelinase-Mediated Generation of Ceramide On Aggregation of Low Density Lipoprotein

Cardiovascular disease is the leading cause of death in the US. Despite decades of intensive research, the formation of atherosclerotic lesions is not fully understood. The initiation of atherosclerosis is believed to be enhanced by the aggregation of low density lipoprotein (LDL). In our present study we focus on neutral, Mg²⁺-dependent Sphingomyelinase (Smase)-induced aggregation of LDL. The kinetics of Smase-mediated ceramide formation from LDL-sphingomyelin was measured using a fluorescence assay for various enzyme concentrations (0-0.22 units Smase/mL) with a fixed substrate concentration (0.33 mg LDL/mL). The kinetics of LDL aggregate formation was measured by dynamic light scattering (DLS, method of cumulants) for the above enzyme concentrations. These data were used to address the relationships between the Smase-catalyzed hydrolysis of LDL-sphingomyelin and the resulting LDL aggregation (due to hydrophobic domain formation by ceramide) kinetics. Our results show a linear correlation between ceramide concentration and resulting LDL aggregate sizes. The latter appears to be independent of Smase concentration, illustrating the major role of ceramide (and the hydrophobic effect) in LDL aggregation. This work demonstrates the role that colloidal science can play in better understanding human disease.