Podophyllotoxin-loaded solid lipid nanoparticles for epidermal targeting.

The purpose of this study was to evaluate solid lipid nanoparticles as the topical carrier for epidermal targeting of podophyllotoxin (POD). The high pressure homogenization was employed to prepare drug-loaded solid lipid nanoparticles. The POD-loaded SLN stabilized by 0.5% poloxamer 188 and 1.5% soybean lecithin (P-SLN) and 2% polysorbate 80 (T-SLN) was characterized by photon correlation spectroscopy (PCS). P-SLN showed an average diameter of 73.4 nm and a zeta potential of -48.36 mV. The imaging of AFM indicated that the P-SLN had a spherical shape. DSC and X-ray diffraction analysis showed that POD was dispersed in SLN in an amorphous state. The in vitro permeation study showed that P-SLN increased the accumulative amount of POD in porcine skin 3.48 times over 0.15% tincture. But T-SLN with a diameter of 123.1 nm and a zeta potential of -17.4 mV did not show a high accumulative amount of POD when compared with P-SLN, though both P-SLN and T-SLN could avoid the systemic uptake of POD. Because of the fluorescence property of POD, fluorescence microscopy imaging was employed to visualize the penetration of POD into skin from SLN. The penetration of POD from P-SLN seemed to follow two pathways along the stratum corneum and hair follicle route. The imaging revealed that P-SLN had a strong localization of POD within epidermis. The penetration of P-SLN with low particle size into stratum corneum along the skin surface 'furrow' and the consequent controlled release of POD might lead to the epidermal targeting. P-SLN provides a good epidermal targeting effect and may be a promising carrier for topical delivery of POD.