**1. Introduction**

This chapter starts by discussing the main compositional and structural properties of lipoproteins, which are water-soluble, heterogeneous nanoparticles responsible for carrying lipids, cholesterol and triglycerides in the body. The differences in their composition and structure are strictly related to how the different lipoproteins are produced and what their roles are in the body. We then move on to discuss the relationship between how lipoprotein type and lipoprotein subclass relate with the risk to develop atherosclerosis. We review recent evidence that suggests differences in low-density lipoprotein (LDL) overall size, shape and protein layer thicknesses within small dense LDL subfractions of normolipidemic and hyper triglyceridemic

individuals. This is of importance since structural differences across a certain lipoprotein class or subclass are not taken into account in clinical studies and this might explain controversies in the role of, for example, small dense LDL in the development of atherosclerosis. We then move on to discuss how lipoprotein capacity for lipid transfer and lipid exchange has been studied along the years and focus on recent results that quantify these abilities using simplistic model membranes lacking specific receptors. Despite the simplicity of these model systems, the results mirror those obtained for cholesterol efflux and in clinicals studies. Finally, we discuss advances in plaque remodelling therapies based on the engineering of nanoparticles mimicking nascent high-density lipoprotein (HDL) particles with focus on the challenges for the formulation of therapies that are effective in the clinics.
