Characterization of cholesterol-rich nanoemulsions (LDE) from different lipid mixtures: A USAXS and DLS study on...

Lipid Nanoparticles (LDE) have been used as a drug delivery vehicle to treat various diseases. LDEs resemble the structure of human low-density lipoprotein (LDL), but lack apoliprotein B (apo-B). The aim of this study was to determine whether changes in the proportion of unesterified cholesterol (UC) or triacylglycerols (TG) affect the physical stability of LDE in aqueous solutions over a six-month observation period, as analysed by Ultra Small-angle X-ray Scattering (USAXS), Dynamic Light Scattering (DLS) and zeta potential measurements. It was shown that variations in UC or TG content in the initial lipid mixture did not alter the size of the resulting LDE nanoparticles, which remained within the 30-35 nm range. This particle size was maintained for up to three months in formulations with varying TG content and up to four months in those with varying UC content. Thereafter, a progressive increase in nanoparticle size was observed, which suggests enhanced aggregate formation and reduced of LDE stability between 3 and 6 months of storage. This loss of stability did not appear to be directly related to changes in UC or TG composition. Notably, USAXS and DLS measurements yielded comparable results, which reinforces the reliability of the data. In addition, the zeta potential remained close to zero for all seven nanoparticle compositions throughout the six months, indicating that all LDE formulations had electrostatic neutral potential and remain so when they progressively aggregate with time. Complementary analyses also showed that LDE particles are, on average, spherical in shape. Overall, these findings provide relevant insights for the rational design of lipid mixtures in the preparation of nanoemulsions for drug delivery applications.