Controlling lipolysis through steric surfactants: new insights on the controlled degradation of submicron emulsions after oral and intravenous administration.

In this work we have investigated how steric surfactants influence the metabolic degradation of emulsions (lipolysis). To do so, we have prepared submicron emulsions stabilized with Pluronic F68, Pluronic F127, Myrj 52 or Myrj 59, four non-ionic surfactants with key differences on their structure. Submicron emulsions have been prepared also with mixtures of these surfactants with different proportions between them. Then, in vitro methods have been applied to analyze the lipolysis of these emulsions, both under duodenal and intravenous conditions, to simulate lipolysis after oral and intravenous administration. Our results show that the properties of the surfactant influence dramatically the lipolysis rates observed both under duodenal and intravenous conditions, e.g., intravenous lipolysis was completely blocked when Pluronic F127 was used, while it was almost complete within 6h when using Myrj 52. The reason for this seems to be the steric hindrance that the surfactant produces around the droplet and at the interface. As a result, we can modify the lipolysis patterns by changing some characteristics of the surfactant, or by varying the proportion between two surfactants in a mixture. These findings may be applied in the development of novel strategies to rationally design submicron emulsions as lipophilic drug carriers.