HDL particle concentration and size

HDL particle concentration and size (HDL-P_ima) were quantified by calibrated ion mobility analysis (IMA) (29). Briefly, HDL isolated by ultracentrifugation from EDTA plasma was introduced into the gas-phase ions by ESI. The resulting highly charged ions were largely neutralized by α particles, yielding a small proportion of singly charged cations, which were introduced into the mobility analyzer. As the particles moved through a strong electromagnetic field, they were separated according to their electrophoretic mobility and then enumerated by a particle counter. HDL peak areas were converted into aqueous particle concentrations using glucose oxidase calibration curves.

Because electrophoretic mobility depends chiefly on size, IMA data are expressed in terms of particle diameter (nanometers), which corresponds to the calculated diameter of a singly charged spherical particle with the same electrophoretic mobility (29). The method yields a stoichiometry of APOA1 and the sizes and relative abundance of HDL subspecies in excellent agreement with those determined by nondenaturing gradient gel electrophoresis and analytical ultracentrifugation (29, 30). Because calibrated IMA accurately quantifies the size and concentration of gold nanoparticles and reconstituted HDL (29), we term the concentration and size of HDL determined by this method, HDL-P_ima.