Characterization and side effect analysis of a newly designed nanoemulsion targeting human serum albumin for drug delivery

Human serum albumin (HSA), the most abundant protein in plasma, plays an important role in the transportation of metabolic and exogenous compounds, particularly drugs. However, it takes a carrier to bring the metabolite or compound to the plasma for subsequent transportation in blood using HSA. A nanoemulsion which constitutes a mixture of two immiscible liquid phases can act as an effective drug carrier due to its unique properties. In this study, we report the characterization results of a newly designed nanoemulsion via dynamic light scattering (DLS) and scanning electron microscopy (SEM), followed by results on the alterations in the structure of HSA upon interaction with the nanoemulsion using circular dichroism (CD) as well as intrinsic and extrinsic fluorescence spectroscopy methods at ambient and physiological temperatures. Results of SEM and DLS show that particles making up the nanoemulsion have a nearly monodisperse size distribution and spherical morphology. Results of intrinsic fluorescence spectroscopy show decreasing emission intensity with increasing nanoemulsion concentration. Results from this study using 1-anilino-8-naphthalene sulfonic acid (ANS) confirm the intrinsic fluorescence data and reveal that adding the nanoemulsion to HSA leads to an increase in fluorescence intensity. These results imply that the interaction between the nanoemulsion and HSA cause a structural transformation in which native HSA turns "inside out" to expose its hydrophobic core to the surrounding environment. Far-UV-CD results indicate that the nanoemulsion induces a loss in α-helical structure of the HSA protein. In summary, the exposure of the blood carrier protein HSA to a newly designed nanoemulsion resulted in significant alterations of protein structure and conformation depicted by a red shift in maximum fluorescence intensity, decreased α-helical structure, and increased exposure of nonpolar or accessible hydrophobic surface of HSA to the solvent.