Reduction-Responsive Release of Solid Lipid Nanoparticle Composed of Stearic Acid and Cystamine

A reduction-responsive solid lipid nanoparticles (SLNs) were prepared by an emulsification evaporation and solidification method using stearic acid (SA) and cystamine as constituting materials. The mean hydrodynamic diameter of the SLN decreased from 510.6 nm to 117.0 nm, as the molar ratio of SA to cystamine increased from 1:0 to 1:1. On the TEM photo, negatively stained SLNs were found as black circles and the diameter was tens to hundreds of nanometer. According to the EDS analysis, the sulfur content of SLN was found to be 1.19% (w/w) to 3.62% (w/w), depending on the molar ratio of SA to cystamine (1:0.125 to 1:1) employed in the preparation. According to the differential scanning calorimetric analysis, the melting point decreased gradually from about 52 °C to 50 °C as the molar ratio of SA to cystamine increased from 1:0 to 1:1. Even if cystamine (a disulfide compound) was contained in SLN, the release degree at 25 °C was not significantly affected by dithiothreitol (DTT, a reducing agent). Whereas, the release degree at 37 °C and 52 °C was significantly suppressed by DTT when cystamine was contained in SLN, possibly because cystamine would be more readily reduced to aminoethanethiols in the SLN matrix at the higher temperatures.