Nanostructured lipid carriers as nitroxide depot system measured by electron paramagnetic resonance spectroscopy

Various nanometer scaled transport systems are used in pharmaceutics and cosmetics to increase penetration or storage of actives. Nanostructured lipid carriers (NLCs) are efficient drug delivery systems for dermatological applications. Electron paramagnetic resonance (EPR) spectroscopy was used for the determination of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) distribution within the carrier and to investigate the dynamics of skin penetration. Results of ex vivo penetration of porcine skin and in vivo data - forearm of human volunteers - are compared and discussed to previously obtained results with invasomes under comparable conditions. W-band measurements show 35% of TEMPO associated with the lipid compartments of the NLC. Application of TEMPO loaded NLC to skin ex vivo increases the observation time by 12min showing a stabilisation of the nitroxide radical. Moreover, stabilisation is also seen with data generated in vivo. Thus, same as invasomes NLCs are a suitable slow release depot system.