The Chemistry of Neurodegeneration: Kinetic Data and Their Implications

Matic Pavlin, Matej Repič, Robert Vianello, Janez Mavri

We collected experimental kinetic rate constants for chemical processes responsible for the development and progress of neurodegeneration, focused on the enzymatic and non-enzymatic degradation of amine neurotransmitters and their reactive and neurotoxic metabolites. A gross scheme of neurodegeneration on the molecular level is based on two pathways. Firstly, reactive species oxidise heavy atom ions, which enhances the interaction with alpha-synuclein, thus promoting its folding to the beta form and giving rise to insoluble amyloid plaques. The latter prevents the function of vesicular transport leading to gradual neuronal death. In the second pathway, radical species, OH(·) in particular, react with the methylene groups of the apolar part of the lipid bilayer of either the cell or mitochondrial wall, resulting in membrane leakage followed by dyshomeostasis, loss of resting potential and neuron death. Unlike all other central neural system (CNS)-relevant biogenic amines, dopamine and noradrenaline are capable of a non-enzymatic auto-oxidative reaction, which produces hydrogen peroxide. This reaction is not limited to the mitochondrial membrane where scavenging enzymes, such as catalase, are located. On the other hand, dopamine and its metabolites, such as dopamine-o-quinone, dopaminechrome, 5,6-dihydroxyindole and indo-5,6-quinone, also interact directly with alpha-synuclein and reversibly inhibit plaque formation. We consider the role of the heavy metal ions, selected scavengers and scavenging enzymes, and discuss the relevance of certain foods and food supplements, including curcumin, garlic, N-acetyl cysteine, caffeine and red wine, as well as the long-term administration of non-steroid anti-inflammatory drugs and occasional tobacco smoking, that could all act toward preventing neurodegeneration. The current analysis can be employed in developing strategies for the prevention and treatment of neurodegeneration, and, hopefully, aid in the building of an overall kinetic molecular model of neurodegeneration itself.