Objective： To investigate the effects of sub-micro emulsion composition on cellular uptake and disposition of incorporated lipophilic drug.
Methods： Sub-micro emulsions containing 10% oil, 1.2% lecithin and 2.25% glycerol were prepared, and the fluorescent agent coumarin 6 was used as a model drug. The effects of oil types, co-surfactants and cationic lipid on uptake and elimination kinetics of 6-coumarin in HeLa cells were studied. The uptake mechanism of sub-micro emulsions was further investigated.
Results： Oil type and Tweens had no influence on the cellular uptake. Modifications of surfactants with Span series increased the cellular influx, among which Span 20 with hydrophilic-lipophilic balance (HLB) value of 8.6 was the best enhancer. The intracellular drug level reached up to (46.09±1.98)ng/μg protein which had significant difference with control group \[(38.54±0.34)ng/μg protein\]. The positively charged emulsions significantly increased the uptake rate constant and elimination rate constant which were 4 times and 1.5 times of those in anionic groups, respectively. The uptake enhancement was also observed in cationic emulsions, cellular concentrations at plateau were (42.73±0.84)ng/μg protein, which was about 3 times of that in anionic emulsions \[(15.71±0.74)ng/μg protein\], when extracellular drug concentration kept at 100 ng/ml. Cationic emulsions delivered the payload mainly by direct drug transfer to contacted cells, while the negative ones depended on both drug passive diffusion and clathrin-mediated endocytosis of drug containing oil droplets which accounted for 20% of the intracellular drug.
Conclusion： Interfacial characteristic of sub-micro emulsions such as co-surfactants HLB as well as zeta potentials can influence lipophilic drug both in cellular uptake and elimination.