alpha-synuclein and phthalocyanine

The fibrillation of amyloidogenic proteins is a critical step in the etiology of neurodegenerative disorders such as Alzheimer and Parkinson diseases. There is major interest in the therapeutic intervention on such aberrant aggregation phenomena, and the utilization of polyaromatic scaffolds has lately received considerable attention. In this regard, the molecular and structural basis of the anti-amyloidogenicity of polyaromatic compounds, required to evolve this molecular scaffold toward therapeutic drugs, is not known in detail. We present here biophysical and biochemical studies that have enabled us to characterize the interaction of metal-substituted, tetrasulfonated phthalocyanines (PcTS) with α-synuclein (AS), the major protein component of amyloid-like deposits in Parkinson disease. The inhibitory activity of the assayed compounds on AS amyloid fibril formation decreases in the order PcTS[Ni(II)] ~ PcTS > PcTS[Zn(II)] >> PcTS[Al(III)] ≈ 0. Using NMR and electronic absorption spectroscopies we demonstrated conclusively that the differences in binding capacity and anti-amyloid activity of phthalocyanines on AS are attributed to their relative ability to self-stack through π-π interactions, modulated by the nature of the metal ion bound at the molecule. Low order stacked aggregates of phthalocyanines were identified as the active amyloid inhibitory species, whose effects are mediated by residue specific interactions. Such sequence-specific anti-amyloid behavior of self-stacked phthalocyanines contrasts strongly with promiscuous amyloid inhibitors with self-association capabilities that act via nonspecific sequestration of AS molecules. The new findings reported here constitute an important contribution for future drug discovery efforts targeting amyloid formation.

Topics: alpha-Synuclein; Alzheimer Disease; Amyloid; Drug Discovery; Humans; Indoles; Isoindoles; Nuclear Magnetic Resonance, Biomolecular; Parkinson Disease

Alpha-synuclein is a pathological component of Parkinson's disease by constituting the filamentous component of Lewy bodies. Phthalocyanine (Pc) effects on the amyloidosis of alpha-synuclein have been examined. The copper complex of phthalocyanine tetrasulfonate (PcTS-Cu(2+)) caused the self-oligomerization of alpha-synuclein while Pc-Cu(2+) did not affect the protein, indicating that introduction of the sulfonate groups was critical for the selective protein interaction. The PcTS-Cu(2+) interaction with alpha-synuclein has occurred predominantly at the N-terminal region of the protein with a K(d) of 0.83 microM apart from the hydrophobic NAC (non-Abeta component of Alzheimer's disease amyloid) segment. Phthalocyanine tetrasulfonate (PcTS) lacking the intercalated copper ion also showed a considerable affinity toward alpha-synuclein with a K(d) of 3.12 microM, 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 alpha-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 alpha-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 alpha-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 beta/A4 protein under their aggregative conditions. The PcTS-Cu(2+), on the other hand, promoted the protein aggregation of alpha-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 alpha-synuclein-related neurodegenerative disorders.

Topics: alpha-Synuclein; Amyloid; Cell Death; Cell Line, Tumor; Copper; Ferric Compounds; Genetic Vectors; Growth Inhibitors; Humans; Indoles; Isoindoles; Nerve Tissue Proteins; Synucleins; Tetrapyrroles