Mechanistic investigation of transcutaneous protein delivery using solid-in-oil nanodispersion: A case study with phycocyanin

Phycocyanin (PC), a water-soluble protein-chromophore complex composed of hexameric (αβ)₆ subunits, has important biological functions in blue-green algae as well as pharmacological activities in biomedicine. We have previously developed a solid-in-oil (S/O) nanodispersion method to deliver biomacromolecules through the skin, although the transcutaneous mechanism has not yet been fully elucidated. To study the mechanism of transcutaneous protein delivery, we therefore enabled S/O nanodispersion by coating PC with hydrophobic surfactants and evaluated how the proteinaceous macromolecules formulated in an oil phase might permeate the skin. The extent of S/O nanodispersion of PC was dependent on the type of surfactant, suggesting that the selection of a suitable surfactant is crucial for encapsulating a large protein having a subunit structure. By measuring the intrinsic fluorescence of PC, we found that S/O nanodispersion facilitated the accumulation of PC in the stratum corneum (SC) of Yucatan micropig skin. Furthermore, after crossing the SC layer, the fluorescent recovery of PC was evident, indicating the release of the biologically active form of PC from the SC into the deeper skin layer.