Electrochemical Detection of Interaction Between α-Synuclein and Clioquinol

Understanding the Inhibitory and Antioxidant Effects of Pyrroloquinoline Quinone (PQQ) on Copper(II)-Induced α-Synuclein-119 Aggregation

Parkinson's disease (PD) is associated with the aggregation and misfolding of a-synuclein (a-syn) protein in dopaminergic neurons. The misfolding process is heavily linked to copper dysregulation in PD. Experimental evidence supports the hypothesis that the co-presence of Cu(II) and α-syn facilitates the aggregation of α-syn, affecting the pathological development of PD. Recent literature has shown that pyrroloquinoline quinone (PQQ) contains strong neuroprotective activity by reducing the reactive oxygen species (ROS) production by α-syn. Despite these known facts, minimal studies have been done on the antioxidant effect of PQQ against ROS formation in the presence of Cu(II) and α-syn-119. Thus, it is of great significance to study the interaction between all three components, PQQ, Cu(II), and α-syn-119. In this proof-of-concept study, a variety of chemical techniques were employed to examine the antioxidant effect of PQQ on ROS that α-syn-119 produced in the presence of Cu(II). Our results showed that PQQ effectively prevented ROS formation in SH-SY5Y human differentiated neuronal cells. Thioflavin T (ThT) fluorescence assay, circular dichroism (CD) spectroscopy, and transmission electron microscopy (TEM) were applied, where PQQ was able to actively prevent fibrillation of α-syn-119 in the presence of Cu(II). This finding was further confirmed using electrochemical impedance spectroscopy (EIS), where the binding of PQQ to the α-syn-119 suppressed the aggregation process on the electrode surface. With these encouraging results, we envisage that PQQ and its derivatives can be a promising candidate for further studies as a multitarget therapeutic agent toward PD therapy.

Electrochemical biosensors for the detection and study of α-synuclein related to Parkinson's disease - A review

Parkinson's disease (PD) is a long-term degenerative disorder that affects predominately dopaminergic neurons in the substantia nigra, which mainly control movement. Alpha-synuclein (α-syn) is a major constituent of Lewy bodies that are reported to be the most important toxic species in the brain of PD patients. In this critical review, we highlight novel electrochemical biosensors that have been recently developed utilizing aptamers and antibodies in connection with various nanomaterials to study biomarkers related to PD such as α-syn. We also review several research articles that have utilized electrochemical biosensors to study the interaction of α-syn with biometals as well as small molecules such as clioquinol, (-)-epigallocatechin-3-gallate (EGCG) and baicalein. Due to the significant advances in nanomaterials in the past decade, electrochemical biosensors capable of detecting multiple biomarkers in clinically relevant samples in real-time have been achieved. This may facilitate the path towards commercialization of electrochemical biosensors for clinical applications and high-throughput screening of small molecules for structure-activity relationship (SAR) studies.

Metal Chelation Therapy and Parkinson's Disease: A Critical Review on the Thermodynamics of Complex Formation between Relevant Metal Ions and Promising or Established Drugs

The present review reports a list of approximately 800 compounds which have been used, tested or proposed for Parkinson's disease (PD) therapy in the year range 2014-2019 (April): name(s), chemical structure and references are given. Among these compounds, approximately 250 have possible or established metal-chelating properties towards Cu(II), Cu(I), Fe(III), Fe(II), Mn(II), and Zn(II), which are considered to be involved in metal dyshomeostasis during PD. Speciation information regarding the complexes formed by these ions and the 250 compounds has been collected or, if not experimentally available, has been estimated from similar molecules. Stoichiometries and stability constants of the complexes have been reported; values of the cologarithm of the concentration of free metal ion at equilibrium (pM), and of the dissociation constant Kd (both computed at pH = 7.4 and at total metal and ligand concentrations of 10-6 and 10-5 mol/L, respectively), charge and stoichiometry of the most abundant metal-ligand complexes existing at physiological conditions, have been obtained. A rigorous definition of the reported amounts is given, the possible usefulness of this data is described, and the need to characterize the metal-ligand speciation of PD drugs is underlined.