LIPID-COMPOSITION AND STRUCTURE OF COMMERCIAL PARENTERAL EMULSIONS

In order to study the influence of the phospholipid/triacyiglycerol (P L/TG) ratio of parenteral emulsions on the distribution and the physic o-chemical properties of their fat particles, commercial 10, 20 or 30% fat formulas were fractionated by centrifugation into an upper lipid cake (resuspended in aqueous glycerol) and a subnatant or mesophase, f rom which a PL-rich subfraction (d = 1.010-1.030 g/l) was purified by density gradient ultracentrifugation. Chemical and P-31-NMR analyses o f these fractions indicated that at least two types of fat particles c oexist in parenteral emulsions: (i) TG-rich particles (mean diameter: 330, 400, 470 nm in the 10, 20, 30% emulsion) which contain practicall y all the TG and esterified phytosterols of native emulsions, but only a fraction of their FL, unesterified cholesterol and phytosterols, an d other minor lipids; (ii) PL-bilayer particles or liposomes (mean dia meter: 80-100 nm) which are constituted with the remaining PL and rela tively very small amounts of TG and other lipids. The higher the oil c ontent of the emulsion, the lower the amount of these PL-rich particle s, which represent the major particle population of the mesophase. Ind eed, minute amounts of TG-rich particles (probably the smallest ones) are also present in the mesophase, even in the PL-rich subfraction whi ch contains the bulk of liposomal FL. Since the PL-rich particles of t he infused emulsion generate lipoprotein X-like particles, only the la rge TG-rich particles can be considered as true chylomicron counterpar ts.