A neurodegenerative tauopathy endemic to the Caribbean island of Guadeloupe has been associated with the consumption of anonaceous plants that contain acetogenins, potent lipophilic inhibitors of complex I of the mitochondrial respiratory chain. To test the hypothesis that annonacin, a prototypical acetogenin, contributes to the etiology of the disease, we investigated whether annonacin affects the cellular distribution of the protein tau. In primary cultures of rat striatal neurons treated for 48 h with annonacin, there was a concentration-dependent decrease in ATP levels, a redistribution of tau from the axons to the cell body, and cell death. Annonacin induced the retrograde transport of mitochondria, some of which had tau attached to their outer membrane. Taxol, a drug that displaces tau from microtubules, prevented the somatic redistribution of both mitochondria and tau but not cell death. Antioxidants, which scavenged the reactive oxygen species produced by complex I inhibition, did not affect either the redistribution of tau or cell death. Both were prevented, however, by forced expression of the NDI1 nicotinamide adenine dinucleotide (NADH)-quinone-oxidoreductase of Saccharomyces cerevisiae, which can restore NADH oxidation in complex I-deficient mammalian cells and stimulation of energy production via anaerobic glycolysis. Consistently, other ATP-depleting neurotoxins (1-methyl-4-phenylpyridinium, 3-nitropropionic, and carbonyl cyanide m-chlorophenylhydrazone) reproduced the somatic redistribution of tau, whereas toxins that did not decrease ATP levels did not cause the redistribution of tau. Therefore, the annonacin-induced ATP depletion causes the retrograde transport of mitochondria to the cell soma and induces changes in the intracellular distribution of tau in a way that shares characteristics with some neurodegenerative diseases.

In Guadeloupe, there is an abnormally high frequency of atypical parkinsonism. Only one-third of the patients that develop parkinsonian symptoms were reported to present the classical features of idiopathic Parkinson disease and one-third a syndrome resembling progressive supranuclear palsy (PSP). The others were unclassifiable, according to established criteria. We carried out a cross-sectional study of 160 parkinsonian patients to: (i) define more precisely the clinical phenotypes of the PSP-like syndrome and the parkinsonism that was considered unclassifiable in comparison with previously known disorders; (ii) define the neuropsychological and brain imaging features of these patients; (iii) evaluate to what extent a candidate aetiological factor, the mitochondrial complex I inhibitor annonacin contained in the fruit and leaves of the tropical plant Annona muricata (soursop) plays a role in the neurological syndrome. Neuropsychological tests and MRI were used to classify the patients into those with Parkinson's disease (31%), Guadeloupean PSP-like syndrome (32%), Guadeloupean parkinsonism-dementia complex (PDC, 31%) and other parkinsonism-related disorders (6%). Patients with a PSP-like syndrome developed levodopa-resistant parkinsonism, associated with early postural instability and supranuclear oculomotor dysfunction. They differed, however, from classical PSP patients by the frequency of tremor (>50%), dysautonomia (50%) and the occurrence of hallucinations (59%). PDC patients had levodopa-resistant parkinsonism associated with frontosubcortical dementia, 52% of these patients had hallucinations, but, importantly, none had oculomotor dysfunction. The pattern of neuropsychological deficits was similar in both subgroups. Cerebral atrophy was seen in the majority of the PSP-like and PDC patients, with enlargement of the third ventricle and marked T2-hypointensity in the basal ganglia, particularly the substantia nigra. Consumption of soursop was significantly greater in both PSP-like and PDC patients than in controls and Parkinson's disease patients. In conclusion, atypical Guadeloupean parkinsonism comprises two forms of parkinsonism and dementia that differ clinically by the presence of oculomotor signs, but have similar cognitive profiles and neuroimaging features, suggesting that they may constitute a single disease entity, and both were similarly exposed to annonaceous neurotoxins, notably annonacin.

Guadeloupean Parkinsonism has been linked epidemiologically to the consumption of Annonaceae fruits. These were proposed to be etiological agents for sporadic atypical Parkinsonism worldwide, because of their content of neurotoxins such as isoquinolinic alkaloids and Annonaceous acetogenins. The pulp of Annona cherimolia Mill. from Spain was screened for these toxic molecules using Matrix-Assisted Laser Desorption Ionisation - Time of Flight mass spectrometry (MALDI-TOF MS) and it was found not to be a source of exposure. However, kaurenoic acid, a diterpene considered to be cytotoxic, was detected in high amounts (66 mg/fresh fruit). Treatment of rat embryonic striatal primary cultures, up to a high concentration (50 µM), did not cause neuronal death nor astrogliosis, suggesting that this molecule is not at risk of implication in human neurodegenerative diseases.