Elsevier

Neuroscience

Volume 121, Issue 2, 6 October 2003, Pages 287-296
Neuroscience

The mitochondrial complex i inhibitor annonacin is toxic to mesencephalic dopaminergic neurons by impairment of energy metabolism

https://doi.org/10.1016/S0306-4522(03)00441-XGet rights and content

Abstract

The death of dopaminergic neurons induced by systemic administration of mitochondrial respiratory chain complex I inhibitors such as 1-methyl-4-phenylpyridinium (MPP+; given as the prodrug 1-methyl-1,2,3,6-tetrahydropyridine) or the pesticide rotenone have raised the question as to whether this family of compounds are the cause of some forms of Parkinsonism. We have examined the neurotoxic potential of another complex I inhibitor, annonacin, the major acetogenin of Annona muricata (soursop), a tropical plant suspected to be the cause of an atypical form of Parkinson disease in the French West Indies (Guadeloupe). When added to mesencephalic cultures for 24 h, annonacin was much more potent than MPP+ (effective concentration [EC50]=0.018 versus 1.9 μM) and as effective as rotenone (EC50=0.034 μM) in killing dopaminergic neurons. The uptake of [3H]-dopamine used as an index of dopaminergic cell function was similarly reduced. Toxic effects were seen at lower concentrations when the incubation time was extended by several days whereas withdrawal of the toxin after a short-term exposure (<6 h) arrested cell demise. Unlike MPP+ but similar to rotenone, the acetogenin also reduced the survival of non-dopaminergic neurons. Neuronal cell death was not excitotoxic and occurred independently of free radical production. Raising the concentrations of either glucose or mannose in the presence of annonacin restored to a large extent intracellular ATP synthesis and prevented neuronal cell demise. Deoxyglucose reversed the effects of both glucose and mannose. Other hexoses such as galactose and fructose were not protective. Attempts to restore oxidative phosphorylation with lactate or pyruvate failed to provide protection to dopaminergic neurons whereas idoacetate, an inhibitor of glycolysis, inhibited the survival promoting effects of glucose and mannose indicating that these two hexoses acted independently of mitochondria by stimulating glycolysis. In conclusion, our study demonstrates that annonacin promotes dopaminergic neuronal death by impairment of energy production. It also underlines the need to address its possible role in the etiology of some atypical forms of Parkinsonism in Guadeloupe.

Section snippets

Mesencephalic cell cultures

Animals were treated in accordance with the Guide for the Care and Use of Laboratory Animals (National Research Council 1996), the European Communities Council Directive 86/609/EEC, and the guidelines of the local institutional committee. All efforts were made to minimize the number of animals used and their suffering. The embryos were removed at embryonic day 15.5 from pregnant Wistar rats (Elevage Janvier, Le Genest St Isle, France) that had been anesthetized then decapitated. The ventral

Annonacin specifically inhibits complex i activity

We first verified that annonacin acted as a specific inhibitor of the complex I of the mitochondrial respiratory chain using homogenates of adult rat brain cortex. The residual complex I activity in the presence of 100 nM annonacin was 21% of control values while even concentrations up to 1000 nM had no significant effect on complex IV activity (Fig. 1B). The concentration causing a 50% reduction of complex I activity was estimated to be 30 nM.

Annonacin is toxic to dopaminergic neurons

When mesencephalic cultures were treated with

Discussion

Our study demonstrates that low concentrations of the mitochondrial complex I inhibitor annonacin promote the death of dopaminergic neurons in mesencephalic cultures. Annonacin was approximately as effective as rotenone but 50-fold more potent than the prototypical dopaminergic neurotoxin MPP+. Unlike MPP+, but similar to rotenone, the effects of annonacin were not restricted to the dopaminergic neurons. Restoring glycolysis by treatment with glucose or mannose prevented neurodegeneration

Acknowledgements

This work was supported by Institut National de la Santé et de la Recherche Médicale (INSERM), Contrat de Recherche et d'Etude Stratégique (CeRS 4CR07F) to A.L., Secrétariat d'Etat à l'Outre-Mer (SEOM) and Délégation à la Recherche Clinique, University Hospital Antilles-Guyane (Pointe-à-Pitre, Guadeloupe, France). P.P.M. was supported by Centre de Recherche Pierre Fabre (Castres, France) and G.H. by the Deutsche Forschungsgemeinschaft (DFG).

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