Intracellular Delivery of Poorly Soluble Polyphenols: Elucidating the Interplay of Self-Assembling Nanocarriers and Human Chondrocytes

Increased molecular understanding of multifactorial diseases paves the way for novel therapeutic approaches requiring sophisticated carriers for intracellular delivery of actives. We designed and characterized self-assembling lipid-core nanocapsules for coencapsulation of two poorly soluble natural polyphenols curcumin and resveratrol. The polyphenols were identified as high potential therapeutic candidates intervening in the intracellular inflammation cascade of chondrocytes during the progress of osteoarthritis. To elucidate the interplay between chondrocytes and nanocapsules and their therapeutic effect, we pursued a complementary analytical approach combining label-free visualization with biological assays. Primary human chondrocytes did not show any adverse effects upon nanocapsule application and coherent anti-Stokes Raman scattering images visualized their intracellular uptake. Further, by systematically blocking different uptake mechanisms, an energy independent uptake into the cells could be identified. Additionally, we tested the therapeutic effect of the polyphenol-loaded carriers on inflamed chondrocytes. Treatment with nanocapsules resulted in a major reduction of nitric oxide levels, a well-known apoptosis trigger during the course of osteoarthritis. For a more profound examination of this protective effect on joint cells, we pursued studies with atomic force microscopy investigations. Significant changes in the cell cytoskeleton as well as prominent dents in the cell membrane upon induced apoptosis were revealed. Interestingly, these effects could not be detected for chondrocytes which were pretreated with the nanocapsules. Overall, besides presenting a sophisticated carrier system for joint application, these results highlight the necessity of establishing combinatorial analytical approaches to elucidate cellular uptake, the interplay of codelivered drugs and their therapeutic effect on the subcellular level.