In Vitro Assessment of a Doubly Adjuvanted Self-Emulsified Nanoemulsion as a Delivery Vehicle for Antigenic Proteins

Background/Objectives: Leishmaniasis is a prevailing infectious disease transmitted via infected phlebotomine sandflies. The lack of an efficient vaccine with respect to immunogenic antigens and adjuvanted delivery systems impedes its control. Following the induction of immune responses in mice vaccinated with multi-epitope Leishmania peptides (LeishPts) encapsulated in doubly adjuvanted self-nanoemulsifying drug delivery systems (ST-SNEDDSs), this study aims to assess ST-SNEDDS-based nanoemulsions as vehicles for the delivery of antigenic proteins. Methods: Model antigens (e.g., BSA-FITC, OVA) were encapsulated in ST-SNEDDS after being complexed with the cationic phospholipid dimyristoyl phosphatidylglycerol (DMPG) via hydrophobic ion pairing. The nanoemulsions were characterized with respect to droplet diameter, zeta potential, stability, protein loading, protein release from the nanodroplets in different release media and cell uptake. Results: Both model antigens exhibited high encapsulation efficiency (>95%) and their release from the nanodroplets was shown to be strongly affected by the type of release medium (e.g., PBS, FBS 10% v/v) and the ratio of its volume to that of the oily phase, in agreement with predictions of protein release. Protein-loaded nanoemulsion droplets labeled with Cy-5 were found to be efficiently taken up by macrophages (J774A.1) in vitro. However, no colocalization of the labeled nanodroplets and BSA-FITC could be observed. Conclusions: It was revealed that in contrast with LeishPts, whole protein molecules may not be appropriate antigenic cargo for ST-SNEDDS formulations due to the rapid protein release from the nanodroplets in release media simulating in vitro culture and in vivo conditions such as FBS 10% v/v.