Phthalocyanine Tetrasulfonates Affect the Amyloid Formation and Cytotoxicity of α-Synuclein

α-Synuclein is a pathological component of Parkinson's disease by constituting the filamentous component of Lewy bodies. Phthalocyanine (Pc) effects on the amyloidosis of α-synuclein have been examined. The copper complex of phthalocyanine tetrasulfonate (PcTS-Cu²⁺) caused the self-oligomerization of α-synuclein while Pc-Cu²⁺ did not affect the protein, indicating that introduction of the sulfonate groups was critical for the selective protein interaction. The PcTS-Cu²⁺ interaction with α-synuclein has occurred predominantly at the N-terminal region of the protein with a K_d of 0.83 μM apart from the hydrophobic NAC (non-Aβ component of Alzheimer's disease amyloid) segment. Phthalocyanine tetrasulfonate (PcTS) lacking the intercalated copper ion also showed a considerable affinity toward α-synuclein with a K_d of 3.12 μM, and its binding site, on the other hand, was located at the acidic C-terminus. These mutually exclusive interactions between PcTS and PcTS-Cu ²⁺ toward α-synuclein resulted in distinctive features on the kinetics of protein aggregation, morphologies of the final aggregates, and their in vitro cytotoxicities. The PcTS actually suppressed the fibrous amyloid formation of α-synuclein, but it produced the chopped-wood-looking protein aggregates. The aggregates showed rather low toxicity (9.5%) on human neuroblastoma cells (SH-SY5Y). In fact, the PcTS was shown to effectively rescue the cell death of α-synuclein overexpressing cells caused by the lactacystin treatment as a proteasome inhibitor. The anti-aggregative and anti-amyloidogenic properties of PcTS were also demonstrated with alcohol dehydrogenase, glutathione S-transferase, and amyloid β/A4 protein under their aggregative conditions. The PcTS-Cu²⁺, on the other hand, promoted the protein aggregation of α-synuclein, which gave rise to the fibrillar protein aggregates whose cytotoxicity became significant to 35.8%. Taken together, the data provided in this study indicate that PcTS/PcTS-Cu ²⁺ could be considered as possible candidates for the development of therapeutic or prophylactic strategies against the α-synuclein-related neurodegenerative disorders.