Tissue distribution and neuroprotective effects of citrus flavonoid tangeretin in a rat model of Parkinson's disease

The flavonoid baicalein inhibits fibrillation of alpha-synuclein and disaggregates existing fibrils

The aggregation of alpha-synuclein has been implicated as a critical step in the development of Parkinson's disease. Parkinson's disease is a progressive neurodegenerative disorder caused by the loss of dopaminergic neurons from the substantia nigra; currently, no cure exists. Baicalein is a flavonoid with antioxidant properties; upon oxidation, it forms several products including quinones. We show here that low micromolar concentrations of baicalein, and especially its oxidized forms, inhibit the formation of alpha-synuclein fibrils. In addition, existing fibrils of alpha-synuclein are disaggregated by baicalein. The product of the inhibition reaction is predominantly a soluble oligomer of alpha-synuclein, in which the protein molecules have been covalently modified by baicalein quinone to form a Schiff base with a lysine side chain in alpha-synuclein. The binding of baicalein was abolished by conversion of the Tyr residues into Phe, demonstrating that Tyr is involved in the interaction of alpha-synuclein with baicalein. In disaggregation baicalein causes fragmentation throughout the length of the fibril. These observations suggest that baicalein and similar compounds may have potential as therapeutic leads in combating Parkinson's disease and that diets rich in flavonoids may be effective in preventing the disorder.

Cellular uptake and metabolism of flavonoids and their metabolites: implications for their bioactivity

Flavonoids have been proposed to act as beneficial agents in a multitude of disease states, including cancer, cardiovascular disease, and neurodegenerative disorders. The biological effect of these polyphenols and their in vivo circulating metabolites will ultimately depend on the extent to which they associate with cells, either by interactions at the membrane or more importantly their uptake. This review summarises the current knowledge on the cellular uptake of flavonoids and their metabolites with particular relevance to further intracellular metabolism and the generation of potential new bioactive forms. Uptake and metabolism of the circulating forms of flavanols, flavonols, and flavanones into cells of the skin, the brain, and cancer cells is reviewed and potential biological relevance to intracellular formed metabolites is discussed.

Potential therapeutic properties of green tea polyphenols in Parkinson's disease

Tea is one of the most frequently consumed beverages in the world. It is rich in polyphenols, a group of compounds that exhibit numerous biochemical activities. Green tea is not fermented and contains more catechins than black tea or oolong tea. Although clinical evidence is still limited, the circumstantial data from several recent studies suggest that green tea polyphenols may promote health and reduce disease occurrence, and possibly protect against Parkinson's disease and other neurodegenerative diseases. Green tea polyphenols have demonstrated neuroprotectant activity in cell cultures and animal models, such as the prevention of neurotoxin-induced cell injury. The biological properties of green tea polyphenols reported in the literature include antioxidant actions, free radical scavenging, iron-chelating properties, (3)H-dopamine and (3)H-methyl-4-phenylpyridine uptake inhibition, catechol-O-methyltransferase activity reduction, protein kinase C or extracellular signal-regulated kinases signal pathway activation, and cell survival/cell cycle gene modulation. All of these biological effects may benefit patients with Parkinson's disease. Despite numerous studies in recent years, the understanding of the biological activities and health benefits of green tea polyphenols is still very limited. Further in-depth studies are needed to investigate the safety and efficacy of green tea in humans and to determine the different mechanisms of green tea in neuroprotection.

Synthesis of Deuterium-Labeled Flavanones

Deuterium incorporation at the C-3 position of flavanones was achieved by treatment of flavanones and 2'-hydroxychalcones with D3PO4 and AcOD. We propose that the deuteration reaction mechanism for 2'-hydroxychalcones substrates is as follows. In the first step, 2'-hydroxychalcones cyclize to the corresponding flavanones by an intramolecular Michael-type reaction. Then deuteriums are incorporated into the flavanones via enolization.

Antioxidants as treatment for neurodegenerative disorders

Oxidative stress is a ubiquitously observed hallmark of neurodegenerative disorders. Neuronal cell dysfunction and cell death due to oxidative stress may causally contribute to the pathogenesis of progressive neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease, as well as acute syndromes of neurodegeneration, such as ischaemic and haemorrhagic stroke. Neuroprotective antioxidants are considered a promising approach to slowing the progression and limiting the extent of neuronal cell loss in these disorders. The clinical evidence demonstrating that antioxidant compounds can act as protective drugs in neurodegenerative disease, however, is still relatively scarce. In the following review, the available data from clinical, animal and cell biological studies regarding the role of antioxidant neuroprotection in progressive neurodegenerative disease will be summarised, focussing particularly on Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. The general complications in developing potent neuroprotective antioxidant drugs directed against these long-term degenerative conditions will also be discussed. The major challenges for drug development are the slow kinetics of disease progression, the unsolved mechanistic questions concerning the final causalities of cell death, the necessity to attain an effective permeation of the blood-brain barrier and the need to reduce the high concentrations currently required to evoke protective effects in cellular and animal model systems. Finally, an outlook as to which direction antioxidant drug development and clinical practice may be leading to in the near future will be provided.