Effect of Alkyl Chain Length and Unsaturation of the Phospholipid on the Physicochemical Properties of Lipid Nanoparticles.

Previously, we developed lipid nanoparticles (LNs) containing poorly water-soluble drugs using two types of phospholipids, a neutral phospholipid (hydrogenated soybean phosphatidylcholine) and a negatively-charged phospholipid (dipalmitoylphosphatidylglycerol), with mean particle sizes of less than 100 nm. Here, we studied the effects of alkyl chain length and unsaturation of neutral and negatively-charged phospholipids on the physicochemical properties of LNs. Three neutral phospholipids, dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine, having different alkyl chain lengths, were compared. The mean particle size of the LNs increased with the alkyl chain length, while the concentration of the drug entrapped in the LNs decreased. The particle size of all of the LNs could be maintained at less than 100 nm for 1 month in cool and dark conditions, with the LNs with longer alkyl chain lipids showing greater stability. In the unsaturated phospholipids, the double bond in the alkyl chain of dioleoylphosphatidylcholine and dierucoylphosphatidylcholine did not affect the physicochemical properties of the LNs. The negatively-charged phospholipids dipalmitoylphosphatidylglycerol and distearoylphosphatidylglycerol were also compared; LNs with longer alkyl chain lipids had larger particle sizes and lower drug concentrations, similar to the results for neutral phospholipids. We concluded that although some changes in physicochemical properties were observed among LNs with different phospholipid alkyl chain lengths, this methodology was general. LNs with suitable physicochemical properties could be prepared irrespective of the type of phospholipids used.