Inhibition of the formation of the neurotoxin 5-S-cysteinyl-dopamine by polyphenols David Vauzour, Katerina Vafeiadou, Jeremy P.E. Spencer * Molecular Nutrition Group, School of Chemistry, Food and Pharmacy, The University of Reading, Whiteknights Campus, Reading RG6 6AP, UK Received 26 July 2007 Available online 7 August 2007 Abstract The death of nigral neurons in Parkinson’s disease is thought to involve the formation of the endogenous neurotoxin, 5-S-cysteinyl- dopamine. In the present study, we show that the polyphenols, (+)-catechin and caffeic acid, which contain a catechol moiety, inhibit tyrosinase-induced formation of 5-S-cysteinyl-dopamine via their capacity to undergo tyrosinase-induced oxidation to yield cysteinyl- polyphenol adducts. In contrast, the inhibition afforded by the flavanone, hesperetin, was not accompanied by the formation of cys- teinyl-hesperetin adducts, indicating that it may inhibit via direct interaction with tyrosinase. Whilst the stilbene resveratrol also inhibited 5-S-cysteinyl-dopamine formation, this was accompanied by the formation of dihydrobenzothiazine, a strong neurotoxin. Our data indi- cate that the inhibitory effects of polyphenols against 5-S-cysteinyl-dopamine formation are structure-dependent and shed further light on the mechanisms by which polyphenols exert protection against neuronal injury relevant to neurodegenerative diseases. Ó 2007 Elsevier Inc. All rights reserved. Keywords: 5-S-Cysteinyl-dopamine; Tyrosinase; Neurodegeneration; Parkinson disease; Catechin; Hesperetin; Caffeic acid; Resveratrol A hallmark of Parkinson’s disease (PD) is the selective loss of dopaminergic neurons in the substantia nigra pars compacta. Although the precise mechanism of neurodegen- eration is unclear, evidence suggests that endogenous dopa- mine may act as a neurotoxin following its oxidation to an o-quinone and reaction with cellular thiols to form 5-S- glutathionyl- and 5-S-cysteinyl-dopamine. The latter has been shown to be neurotoxic [1,2] and both have been reported to be elevated in the brains of patients who died from Parkinson disease [3]. The initial oxidation of dopa- mine to dopamine–o-quinone may occur spontaneously [4] or via reaction with xanthine oxidase [5], tyrosinase [6] or prostaglandin H synthase [7]. Tyrosinase, is a bifunc- tional enzyme that catalyses both the hydroxylation of tyrosine to L-DOPA and the consequent oxidation of the resulting catechol-containing species to an o-quinone [8]. The presence of tyrosinase promoter activity and tyrosi- nase-like activity in the central nervous system, in particu- lar in the substantia nigra [9,10], implicates it in neuromelanin formation and in neurodegenerative disorders like Parkinson 0 s disease. For example, whilst tyrosinase may reduce the neurotoxicity of dopamine– o-quinones by rapidly oxidizing the o-quinone form to neuromelanin [11], it may also contribute to the formation of neurotoxic 5-S-cysteinyl-dopamine in the substantia nigra [12]. Polyphenols constitute a diverse range of compounds which possess at least one aromatic ring with one or more hydroxyl groups [13]. They are ubiquitous in fruits and vegetables and have been reported to possess radical scav- enging and iron chelating properties. There has been much interest in the potential neuroprotective effects of polyphe- nols [14,15]. For example, the consumption of flavonoid- rich foods reverses age-related cognitive deficits in rats [16] and prevents the loss of neurons in the CA1 and CA2 regions of the ischemic rat hippocampus [17]. In addi- tion, the flavanol epigallocatechin gallate has been observed to prevent the loss of dopaminergic neurons in a mouse model of PD [18] and the citrus flavonoid 0006-291X/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2007.07.153 * Corresponding author. E-mail address: j.p.e.spencer@reading.ac.uk (J.P.E. Spencer). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 362 (2007) 340–346