Pages 1-12 | Published online: 09 Mar 2017
Recent investigations have focused on the potential role of gastrointestinal (GI) abnormalities in the pathogenesis of Parkinson's disease (PD). The ‘dual-hit’ hypothesis of PD speculates that a putative pathogen enters the brain via two routes: the olfactory system and the GI system. Here, we investigated (1) whether local exposures of the neurotoxin rotenone in the gut or the brain of mice could induce PD-like neurological and GI phenotypes as well as a characteristic neuropathology in accordance with this ‘dual-hit hypothesis’ and (2) the effects of a diet containing uridine and fish oil providing docosahexaenoic acid (DHA), in both models. Mice were given rotenone either orally or by an injection in the striatum. Dietary interventions were started 1 week before rotenone exposures. We found that (1) both oral and intrastriatal administration of rotenone induced similar PD-like motor deficits, dopaminergic cell loss, delayed intestinal transit, inflammation, and alpha-synuclein accumulation in the colon; (2) the uridine and DHA containing diet prevented rotenone-induced motor and GI dysfunctions in both models. The models suggest possible bidirectional communication between the gut and the brain for the genesis of PD-like phenotype and pathology. The dietary intervention may provide benefits in the prevention of motor and non-motor symptoms in PD.
IntroductionPatients suffering from Parkinson's disease (PD) often develop non-motor symptoms such as hyposmia1 Ross GW, Abbott RD, Petrovitch H, Tanner CM, Davis DG, Nelson J, et al. Association of olfactory dysfunction with incidental Lewy bodies. Mov Disord 2006 Dec;21(12):2062–7. doi: 10.1002/mds.21076,2 Ponsen MM, Stoffers D, Booij J, van Eck-Smit BLF, Wolters EC, Berendse HW. Idiopathic hyposmia as a preclinical sign of Parkinson's disease. Ann Neurol 2004 Aug;56(2):173–81. doi: 10.1002/ana.20160 and gastrointestinal (GI) dysfunctions.3 Pfeiffer RF. Gastrointestinal dysfunction in Parkinson's disease. Lancet Neurol 2003 Feb;2(2):107–16. doi: 10.1016/S1474-4422(03)00307-7,4 Fasano A, Visanji NP, Liu LWC, Lang AE, Pfeiffer RF. Gastrointestinal dysfunction in Parkinson's disease. Lancet Neurol 2015 Jun;14(6):625–39. doi: 10.1016/S1474-4422(15)00007-1 These symptoms may precede the classical motor symptoms by many years,5 Abbott RD, Petrovitch H, White LR, Masaki KH, Tanner CM, Curb JD, et al. Frequency of bowel movements and the future risk of Parkinson's disease. Neurology 2001 Aug 14;57(3):456–62. doi: 10.1212/WNL.57.3.456–7 Chen H, Zhao EJ, Zhang W, Lu Y, Liu R, Huang X, et al. Meta-analyses on prevalence of selected Parkinson's nonmotor symptoms before and after diagnosis. Transl Neurodegener 2015;4(1):1. doi: 10.1186/2047-9158-4-1 and their occurrence in otherwise healthy people is associated with an increased risk of developing PD.5 Abbott RD, Petrovitch H, White LR, Masaki KH, Tanner CM, Curb JD, et al. Frequency of bowel movements and the future risk of Parkinson's disease. Neurology 2001 Aug 14;57(3):456–62. doi: 10.1212/WNL.57.3.456,8 Ponsen MM, Stoffers D, Twisk JWR, Wolters EC, Berendse HW. Hyposmia and executive dysfunction as predictors of future Parkinson's disease: a prospective study. Mov Disord 2009 May 15;24(7):1060–5. doi: 10.1002/mds.22534 Therefore, a better understanding of these non-motor impairments may provide important insights into the etiology and progression of PD. In recent years, special focus has been placed upon the GI tract and the associated enteric nervous system (ENS) in the development of PD.9 Pan-Montojo F, Schwarz M, Winkler C, Arnhold M, O'Sullivan GA, Pal A, et al. Environmental toxins trigger PD-like progression via increased alpha-synuclein release from enteric neurons in mice. Sci Rep 2012;2:898. doi: 10.1038/srep00898–12 Felice VD, Quigley EM, Sullivan AM, O'Keeffe GW, O'Mahony SM. Microbiota-gut-brain signalling in Parkinson's disease: implications for non-motor symptoms. Parkinsonism Relat Disord 2016 Jun;27:1–8. doi: 10.1016/j.parkreldis.2016.03.012 The ENS is a major player in the gut–brain axis which is a bidirectional communication system between the central nervous system (CNS) and the GI tract.13 Cryan JF, Dinan TG. Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nat Rev Neurosci 2012 Oct;13(10):701–12. doi: 10.1038/nrn3346
Animal models are invaluable tools to investigate the underlying mechanisms of the pathogenesis of PD and to test potential symptomatic, neuroprotective, and neurorestorative therapies. To date, many studies have used different compounds and routes of administration in order to reproduce a PD phenotype in animals. Most of these studies focused on the motor symptoms, and only few explored the role of the gut–brain or brain–gut axis in the development of the disease.14 Miwa H, Kubo T, Suzuki A, Kondo T. Intragastric proteasome inhibition induces alpha-synuclein-immunopositive aggregations in neurons in the dorsal motor nucleus of the vagus in rats. Neurosci Lett 2006 Jun 19;401(1–2):146–9. doi: 10.1016/j.neulet.2006.03.003–17 Pan-Montojo F, Anichtchik O, Dening Y, Knels L, Pursche S, Jung R, et al. Progression of Parkinson's disease pathology is reproduced by intragastric administration of rotenone in mice. PloS One 2010;5(1):e8762. doi: 10.1371/journal.pone.0008762
The pesticide rotenone is a potent mitochondrial complex I inhibitor that promotes reactive oxygen species formation. Mitochondrial respiratory chain has shown to be vulnerable during PD pathophysiology. Although there are many different rotenone models of PD, all of which may differ in the resulting phenotype depending on the procedural details, many hallmarks of PD have been replicated in these models, including loss of dopaminergic cell bodies in the substantia nigra (SN),18 Betarbet R, Canet-Aviles RM, Sherer TB, Mastroberardino PG, McLendon C, Kim J-H, et al. Intersecting pathways to neurodegeneration in Parkinson's disease: effects of the pesticide rotenone on DJ-1, alpha-synuclein, and the ubiquitin-proteasome system. Neurobiol Dis 2006 May;22(2):404–20. doi: 10.1016/j.nbd.2005.12.003 alpha-synuclein aggregation,19 Sherer TB, Kim JH, Betarbet R, Greenamyre JT. Subcutaneous rotenone exposure causes highly selective dopaminergic degeneration and alpha-synuclein aggregation. Exp Neurol 2003 Jan;179(1):9–16. doi: 10.1006/exnr.2002.8072,20 Johnson ME, Bobrovskaya L. An update on the rotenone models of Parkinson's disease: their ability to reproduce the features of clinical disease and model gene-environment interactions. Neurotoxicology 2015 Jan;46:101–16. doi: 10.1016/j.neuro.2014.12.002 and GI dysfunction.15 Drolet RE, Cannon JR, Montero L, Greenamyre JT. Chronic rotenone exposure reproduces Parkinson's disease gastrointestinal neuropathology. Neurobiol Dis 2009 Oct;36(1):96–102. doi: 10.1016/j.nbd.2009.06.017,16 Murakami S, Miyazaki I, Sogawa N, Miyoshi K, Asanuma M. Neuroprotective effects of metallothionein against rotenone-induced myenteric neurodegeneration in parkinsonian mice. Neurotox Res 2014 Oct;26(3):285–98. doi: 10.1007/s12640-014-9480-1,21 Greene JG, Noorian AR, Srinivasan S. Delayed gastric emptying and enteric nervous system dysfunction in the rotenone model of Parkinson's disease. Exp Neurol 2009 Jul;218(1):154–61. doi: 10.1016/j.expneurol.2009.04.023 Rotenone exposure is known to be associated with an increased risk of developing PD in humans.22 Tanner CM, Kamel F, Ross GW, Hoppin JA, Goldman SM, Korell M, et al. Rotenone, paraquat, and Parkinson's disease. Environ Health Perspect 2011 Jun;119(6):866–72. doi: 10.1289/ehp.1002839 Therefore, rotenone might be a good candidate to mimic the human PD-like characteristics in animal models.
In early untreated PD patients and in subjects with PD-related brain pathology but still without motor symptoms, neurons of the ENS and the olfactory bulbs were found to contain alpha-synuclein aggregates.23 Braak H, de Vos RAI, Bohl J, Del Tredici K. Gastric alpha-synuclein immunoreactive inclusions in Meissner's and Auerbach's plexuses in cases staged for Parkinson's disease-related brain pathology. Neurosci Lett 2006 Mar 20;396(1):67–72. doi: 10.1016/j.neulet.2005.11.012,24 Shannon KM, Keshavarzian A, Mutlu E, Dodiya HB, Daian D, Jaglin JA, et al. Alpha-synuclein in colonic submucosa in early untreated Parkinson's disease. Mov Disord 2012 May;27(6):709–15. doi: 10.1002/mds.23838 Braak and coworkers proposed in their ‘dual-hit hypothesis’ that alpha-synuclein pathology primes in the ENS and spreads to the brain, thereby suggesting an active retrograde transport via the vagal nerve (gut to brain).25 Hawkes CH, Del Tredici K, Braak H. Parkinson's disease: a dual-hit hypothesis. Neuropathol Appl Neurobiol 2007 Dec;33(6):599–614. doi: 10.1111/j.1365-2990.2007.00874.x,26 Hawkes CH, Del Tredici K, Braak H. A timeline for Parkinson's disease. Parkinsonism Relat Disord 2010 Feb;16(2):79–84. doi: 10.1016/j.parkreldis.2009.08.007 Environmental factors might also start the pathology in the olfactory bulbs, affecting the brain more directly and then spreading to the ENS (brain to gut).25 Hawkes CH, Del Tredici K, Braak H. Parkinson's disease: a dual-hit hypothesis. Neuropathol Appl Neurobiol 2007 Dec;33(6):599–614. doi: 10.1111/j.1365-2990.2007.00874.x This study aimed to investigate whether rotenone exposures in the gut or the brain would either induce pathology and symptoms restricted to the gut or the brain, respectively, or could induce PD-like pathology in accordance with Braak's hypothesis25 Hawkes CH, Del Tredici K, Braak H. Parkinson's disease: a dual-hit hypothesis. Neuropathol Appl Neurobiol 2007 Dec;33(6):599–614. doi: 10.1111/j.1365-2990.2007.00874.x and thereby develop a similar PD-like phenotype including both motor problems and GI dysfunction.
In addition, we investigated the effects of a specific dietary intervention combining uridine and docosahexaenoic acid (DHA) on motor and non-motor symptoms, in both rotenone mouse models. Uridine and DHA are dietary precursors for membrane phospholipid synthesis, and their administration may synergistically support synaptic membrane formation, relevant to PD.27 Cansev M, Ulus IH, Wang L, Maher TJ, Wurtman RJ. Restorative effects of uridine plus docosahexaenoic acid in a rat model of Parkinson's disease. Neurosci Res 2008 Nov;62(3):206–9. doi: 10.1016/j.neures.2008.07.005,28 Holguin S, Huang Y, Liu J, Wurtman R. Chronic administration of DHA and UMP improves the impaired memory of environmentally impoverished rats. Behav Brain Res 2008 Aug 5;191(1):11–6. doi: 10.1016/j.bbr.2008.02.042 This dietary intervention was shown to partially restore dopaminergic neurotransmission in the 6-OHDA model of PD in rats.27 Cansev M, Ulus IH, Wang L, Maher TJ, Wurtman RJ. Restorative effects of uridine plus docosahexaenoic acid in a rat model of Parkinson's disease. Neurosci Res 2008 Nov;62(3):206–9. doi: 10.1016/j.neures.2008.07.005 A recent study demonstrated that dietary fat intake may modify PD risk directly or by altering the response to environmental neurotoxins including pesticides; high levels of polyunsaturated fatty acids (PUFAs), like DHA decreased the association of PD with pesticide exposure.29 Kamel F, Goldman SM, Umbach DM, Chen H, Richardson G, Barber MR, et al. Dietary fat intake, pesticide use, and Parkinson's disease. Parkinsonism Relat Disord 2014 Jan;20(1):82–7. doi: 10.1016/j.parkreldis.2013.09.023 Individually, both DHA and uridine have been shown to induce favorable effects with preventive intake in various animal models of PD, albeit by different modes of action. In the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model, both DHA30 Bousquet M, Saint-Pierre M, Julien C, Salem N, Cicchetti F, Calon F. Beneficial effects of dietary omega-3 polyunsaturated fatty acid on toxin-induced neuronal degeneration in an animal model of Parkinson's disease. FASEB J 2008 Apr;22(4):1213–25. doi: 10.1096/fj.07-9677com and uridine31 Klivenyi P, Gardian G, Calingasan NY, Yang L, von Borstel R, Saydoff J, et al. Neuroprotective effects of oral administration of triacetyluridine against MPTP neurotoxicity. Neuromolecular Med 2005;6(2–3):87–92. doi: 10.1385/NMM:6:2-3:087 prevented neurodegeneration. Similarly, in the 6-OHDA rat model, both DHA32 Delattre AM, Kiss A, Szawka RE, Anselmo-Franci JA, Bagatini PB, Xavier LL, et al. Evaluation of chronic omega-3 fatty acids supplementation on behavioral and neurochemical alterations in 6-hydroxydopamine-lesion model of Parkinson's disease. Neurosci Res 2010 Mar;66(3):256–64. doi: 10.1016/j.neures.2009.11.006 and uridine33 Myers CS, Fisher H, Wagner GC. Uridine reduces rotation induced by L-dopa and methamphetamine in 6-OHDA-treated rats. Pharmacol Biochem Behav 1995 Dec;52(4):749–53. doi: 10.1016/0091-3057(95)00169-W reduced drug-induced rotational behavior, possibly by enhancing dopamine turnover in remaining neurons. To date, there have been no studies exploring the beneficial effects of this active diet on the GI dysfunction associated with PD. Now, we test the combined administration of DHA and uridine on non-motor and motor symptoms of PD using two different rotenone mouse models of PD.
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