Protein Adsorption Patterns and Analysis on IV Nanoemulsions—The Key Factor Determining the Organ Distribution

Intravenous nanoemulsions have been on the market for parenteral nutrition since the 1950s; meanwhile, they have also been used successfully for IV drug delivery. To be well tolerable, the emulsions should avoid uptake by the MPS cells of the body; for drug delivery, they should be target-specific. The organ distribution is determined by the proteins adsorbing them after injection from the blood (protein adsorption pattern), typically analyzed by two-dimensional polyacrylamide gel electrophoresis, 2-D PAGE. The article reviews the 2-D PAGE method, the analytical problems to be faced and the knowledge available on how the composition of emulsions affects the protein adsorption patterns, e.g., the composition of the oil phase, stabilizer layer and drug incorporation into the interface or oil core. Data were re-evaluated and compared, and the implications for the in vivo distribution are discussed. Major results are that the interfacial composition of the stabilizer layer is the main determining factor and that this composition can be modulated by simple processes. Drug incorporation affects the pattern depending on the localization of the drug (oil core versus interface). The data situation regarding in vivo effects is very limited; mainly, it has to be referred to in the in vivo data of polymeric nanoparticles. As a conclusion, determination of the protein adsorption patterns can accelerate IV nanoemulsion formulation development regarding optimized organ distribution and related pharmacokinetics.

. Overview of the topics discussed, e.g., composition and size of the emulsions discussed.

Section Study and characteristic parameters of the emulsions investigated 2.2.1
Adsorption patterns of 20% emulsions stabilized with lecithin from different manufactures Lipofundin MCT 20% (B. Braun Melsungen AG, Germany), Intralipid 20% (Pharmacia AB, Sweden), Abbolipid 20% (Abbott, Germany) and Schwalipid 20% were compared to each other. For all investigated fat emulsions the amount of stabilizer (lecithin) was about 1.2% and the particle size distribution of all these emulsions differed just slightly (mean diameter about 250 nm Effect of type of oil phase on protein adsorption So called "structured lipids" (SLs) as alternative to LCT in emulsions for parenteral nutrition were investigated and compared to an LCT emulsion (Intralipid N 10%). The emulsions investigated were composed of Short-Long-Short (SLS) fatty acids at the glycerol back bone, the respective exchange with medium chain fatty acids (MLM SLs) and long fatty acids (LLL) (e.g., pure soy bean oil). The overall composition of the emulsions was: 10% lipid phase, 1.2% Lipoid E80 as emulsifier and 2.1% glycerol. The average particle size was: 265 nm (Intralipid), 349 nm (LLL), 407 nm (MLM) and 306 nm (SLS).

2.2.5
Effect of stabilizer composition on adsorption patterns. The effect on fatty acids with different chain lengths and a non-ionic PEG containing stabilizer (Solutol) and mixtures of these stabilizers in comparison to a solely lecithin stabilized emulsion were investigated. The detailed formulations investigated in this study are shown in Table 4.

2.2.6
Surface modification of Lipofundin emulsions for drug targeting Lipofundin MCT 10% without modification and Lipofundin MCT 10% upon admixing of 2% Poloxamer 407 solution were analysed and compared to each other.

2.2.7
Influence of surface charge Four different formulations (two anionic and two cationic emulsions) and the commercially available anionic emulsion Lipofundin MCT 10% were investigated. The standard composition consisted of MCT (8.5% w/w), Lipoid E-80 (1.2% w/w), α-tocopherol (0.02% w/w), Poloxamer 188 (2.0% w/w), glycerol (2.25% w/w) and bi-distilled water (to 100% w/w) with additional stearylamine (0.3% w/w) or oleylamine (0.3% w/w) for the two cationic formulations and oleic acid (2.83% w/w) or deoxycholic acid (0.5% w/w) for the two anionic formulations. The physical characterization of these nanoemulsions is given in Table 6.  Table 9 gives an overview of the investigated emulsions, they were all in the size range of about 200-259 nm.

2.2.9
Effect of age Lipofundin N 10%, Lipofundin MCT 10%, and Lipofundin MCT 20% and Lipofundin N 20% emulsions of different age were investigated (i.e., freshly prepared, 16 and 28 months of age) regarding size, physical stability and protein adsorption pattern. Furthermore, a study was performed with propofol-loaded emulsions. The storage times were 4 and 26 months, respectively.