Protoporphyrin-IX nanostructures modulate their protein aggregation ability via differential oxidation and protein binding

Abstract

Porphyrias are caused by genetic defects in the heme biosynthetic pathway and are associated with accumulation of high levels of porphyrins that become cytotoxic. Porphyrins, due to their amphipathic nature, spontaneously associate into different nanostructures but very little is known about the effect of porphyrin speciation on the cytotoxic effects of porphyrins. Previously we demonstrated the unique ability of fluorescent biological porphyrins, including protoporphyrin IX (PP-IX), to cause organelle selective protein aggregation, which we posit to be a major mechanism by which porphyrins exerts their cytotoxic effect. Herein, we tested the hypothesis that PP-IX-mediated protein aggregation is modulated by different PP-IX nanostructures via a mechanism that depends on their oxidizing potential and protein binding ability. We demonstrate that PP-IX nanostructure formation is reversible in nature, and that nanostructure size modulates consequent protein oxidation and aggregation potential. We also show that albumin, the most abundant serum protein, preferentially binds PP-IX dimers and enhances their oxidizing ability. Additionally, extracellular albumin protects from intracellular porphyrinogenic stress and protein aggregation by acting as a PP-IX sponge. This work highlights the importance of PP-IX speciation in the context of the porphyrias, and offers insights into potential novel therapeutic approaches.