Accumulation and Interaction of Hypericin in Low-density Lipoprotein- A Photophysical Study

The accumulation and interaction of hypericin with the biologically important macromolecule, low‐density lipoprotein (LDL), is investigated using various steady‐state and time‐resolved fluorescence measurements. It is concluded that multiple hypericins can penetrate considerably deeply into the LDL molecule. Up to ∼20 nonaggregated hypericin molecules can enter LDL; but upon increasing the hypericin concentration, the fluorescence lifetime of hypericin decreases drastically, suggesting most likely the self‐quenching of aggregated hypericin. There is also evidence of energy transfer from tryptophans of the constituent protein, apoB‐100, to hypericin in LDL. The results demonstrate the ability of LDL to solubilize hypericin (a known photosensitizer) in nonaggregated form, which has implications for the construction of drug delivery systems.