Chapter 22 - Investigating the Intracellular Dynamics of Hypericin-Loaded Nanoparticles and Polyvinylpyrrolidone-Hypericin by Image Correlation Spectroscopy

Abstract

Investigation of the temporal and spatial behavior of nanoparticles (NPs) within the intracellular environment provides insight in NP delivery routes, biointeractions, and subcellular targeting. Here, we investigate the delivery of the naturally occurring hydrophobic photosensitizer hypericin in human cervical epithelial HeLa cells and human primary dendritic cells (DCs) by using biocompatible and biodegradable poly l-lactic acid (PLLA) NPs. Temporal and spatiotemporal image correlation spectroscopy (TICS and STICS) is used for the assessment of the intracellular diffusion and/or flow velocity of hydrophobic hypericin (delivered by encapsulation within PLLA NPs). As the physicochemical nature of hypericin is crucial for cellular studies, for comparison, the hydrophilic form of hypericin [polyvinylpyrrolidone-hypericin (PVP-Hyp)] is also studied. By using spatiotemporal image cross-correlation spectroscopy (STICCS) and specific fluorescent labeling of early endosomes, late endosomes, lysosomes, and mitochondria, the directed motion of the NPs and PVP-Hyp in association with the organelles is investigated. The NPs and PVP-Hyp associate with a small fraction of the whole organelle population. STICCS suggests that the directed motion of the organelles is influenced by their interaction with the NPs and photosensitizer.