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Review Article

Exp Neurobiol 2014; 23(2): 124-129

Published online June 30, 2014

https://doi.org/10.5607/en.2014.23.2.124

© The Korean Society for Brain and Neural Sciences

Naringin: A Protector of the Nigrostriatal Dopaminergic Projection

Un Ju Jung1, Eunju Leem2,3 and Sang Ryong Kim2,3,4,5*

1Center for Food and Nutritional Genomics Research, 2School of Life Sciences, 3BK21 Plus KNU Creative BioResearch Group, 4Institute of Life Science & Biotechnology, Kyungpook National University, Daegu 702-701, 5Brain Science and Engineering Institute, Kyungpook National University, Daegu 700-842, Korea

Correspondence to: *To whom correspondence should be addressed.
TEL: 82-53-950-7362, FAX: 82-53-943-2762
e-mail: srk75@knu.ac.kr

Received: April 22, 2014; Revised: May 14, 2014; Accepted: May 14, 2014

Parkinson's disease is the second most common neurodegenerative disorder characterized by the progressive degeneration of dopaminergic neurons and a biochemical reduction of striatal dopamine levels. Despite the lack of fully understanding of the etiology of Parkinson's disease, accumulating evidences suggest that Parkinson's disease may be caused by the insufficient support of neurotrophic factors, and by microglial activation, resident immune cells in the brain. Naringin, a major flavonone glycoside in grapefruits and citrus fruits, is considered as a protective agent against neurodegenerative diseases because it can induce not only anti-oxidant effects but also neuroprotective effects by the activation of anti-apoptotic pathways and the induction of neurotrophic factors such as brain-derived neurotrophic factor and vascular endothelial growth factor. We have recently reported that naringin has neuroprotective effects in a neurotoxin model of Parkinson's disease. Our observations show that intraperitoneal injection of naringin induces increases in glial cell line-derived neurotrophic factor expression and mammalian target of rapamycin complex 1 activity in dopaminergic neurons of rat brains with anti-inflammatory effects. Moreover, the production of glial cell line-derived neurotrophic factor by naringin treatment contributes to the protection of the nigrostriatal dopaminergic projection in a neurotoxin model of Parkinson's disease. Although the effects of naringin on the nigrostriatal dopaminergic system in human brains are largely unknown, these results suggest that naringin may be a beneficial natural product for the prevention of dopaminergic degeneration in the adult brain.

Keywords: Parkinson’s disease, naringin, mTORC1, GDNF, neuroprotection

Parkinson's disease is the second common neurodegenerative disorder and is characterized by the progressive degeneration of dopaminergic (DA) neurons and biochemical reduction in striatal dopamine levels, associated with major clinical symptoms including tremor at rest, rigidity, bradykinesia and postural instability [1, 2]. Although the developments of knowledge-based therapeutics have been extensively studied, fully understanding of the etiology of Parkinson's disease still remains lack. However, one treatment area that has gained significant momentum is the use of various growth factors such as glial cell line-derived neurotrophic factor (GDNF) [3, 4, 5, 6]. GDNF induces trophic effects by the activation the Akt/mammalian target of rapamycin (mTOR) signaling pathway in neurons [7]; in DA neurons of Parkinson's disease brains, GDNF levels are reduced more than any neurotrophic factor [8].

Although the etiology of Parkinson's disease is unknown as described above, another accumulating evidence suggests that Parkinson's disease is partly caused by activation of microglia, resident immune cells in the brain. Under neuropathological conditions, microglia are activated in response to DA neuronal damages, and activated microglia could produce various potentially neurotoxic molecules, including inducible nitric oxide synthase (iNOS) and proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β) [9, 10, 11, 12, 13]. iNOS and proinflammatory cytokines may be involved in nigrostriatal DA neuronal death [12, 13]. Moreover, increasing evidence suggests that activated microglia generate reactive oxygen species, resulting in oxidative stress to DA neurons in the substantia nigra of Parkinson's disease patients and animal models of Parkinson's disease generated by administration of 1-methyl-4-phenylpyridinium (MPP+) [9]. These results suggest that the control of microglial activation can be useful to prevent the degeneration of the nigrostriatal DA projection.

GDNF is a member of the transforming growth factor-β family of trophic factors, and has been identified in many types of neurons including DA neurons [14]. Treatment with GDNF has consistently demonstrated neurotrophic and protective effects in animal models of Parkinson's disease [3, 4, 5, 6], and conditional ablation of GDNF in adult mice results in a delayed and progressive loss of DA neurons [15]. These results suggest that GDNF is an indispensable neurotrophic factor for the survival and protection of DA neurons. However, GDNF has a critical problem to treat Parkinson's disease patients. GDNF must be directly treated in the brain to apply to Parkinson's disease patients because it does not cross the blood-brain barrier which is the brain's protective membrane. To treat Parkinson's disease patients, the first clinical trial utilizing the direct delivery of GDNF into the brain was actually initiated in 1996. However, clinical trial by intracerebroventricular injection and intraputaminal infusion of GDNF failed to treat Parkinson's disease patients [16, 17], probably because of the limited penetration and distribution to the target brain areas. These clinical results suggest that the therapeutic potential of GDNF for Parkinson's disease is likely to depend on sustained delivery of the appropriate amount to the target areas.

An alternative to delivering neurotrophic protein molecules within brain extracellular space is to directly activate the intracellular signaling pathways responsible for their effects. This activation is possible by viral vector approaches to transduction of neurons [18]. Many of the cellular effects of GDNF are initiated by binding to GNDF family receptor alpha-1 (GFRα1) [19], and the stimulation of the receptors by treatment with GDNF activates the Akt/mTOR signaling pathway, resulting in the downstream activation of prosurvival pathway in neurons [7]. In addition, many research groups have reported that the activation of Akt/mTOR signaling pathway enhances the activity of intracellular cell survival pathways under a variety of conditions, such as ischemic shock, oxidative stress and the withdrawal of trophic factors [20, 21, 22]. Consistent with these results, we have recently reported that the activation of mammalian target of rapamycin complex 1 (mTORC1) by adeno-associated virus 1 transduction with a gene encoding the constitutively active form of Akt or ras homolog enriched in brain (Rheb) with a mutation of the serine to histidine at the 16 position [Rheb(S16H)] in the substantia nigra induces neurotrophic effects, resulting in the protection and restoration of the nigrostriatal DA projection in a neurotoxin model of Parkinson's disease [23, 24, 25]. Moreover, MPP+ treatment as a neurotoxin model of Parkinson's disease decreases Akt phosphorylation resulting in loss of mTORC1 activation, and the decreased level of Akt phosphorylation is also observed in the substantia nigra of Parkinson's disease patients [26]. These results indicate that the neurotrophic effects by mTORC1 activation are necessary for the survival of DA neurons and functional maintenance of DA system in the adult brain.

As described above, however, brain surgery is necessarily needed to apply the delivery of GDNF and viral vectors inducing its effects such as mTORC1 activation to Parkinson's disease patients. Although gene therapy by viral vectors is still ongoing to treat Parkinson's disease patients, the issues for brain surgery suggest that another of alternatives such as natural compounds or chemical drugs to the induction of neurotrophic effects through internal medication could be beneficial to prevent the degeneration of the nigrostriatal DA projection in the adult brain. However, although Parkinson's disease-induced motor manifestations can be treated successfully for a limited period by treatment with chemical drugs, which restore dopaminergic function, there is still no treatment that forestalls deterioration attributable to progressive neurodegeneration [18].

Naringin is a major flavonone glycoside in grapefruits and citrus fruits [27], and it is considered as a protective agent against neurodegenerative diseases because it can induce not only anti-oxidant effects [27, 28] but also neuroprotective effects by the induction of neurotrophic factors such as brain-derived neurotrophic factor and vascular endothelial growth factor, and by the activation of anti-apoptotic pathways [29, 30, 31]. However, it is still unknown whether naringin has neuroprotective effects against the degeneration of the nigrostriatal DA projection in the adult brain, which is associated with Parkinson's disease. To investigate the possibility of naringin-mediated neuroprotection on the nigrostriatal DA projection, we have recently examined whether daily intraperitoneal injection of naringin can induce neuroprotective effects in the MPP+-treated rat model of Parkinson's disease [32]. Our observations showed that intraperitoneal injection of naringin could significantly increases the level of GDNF with activation of mTORC1 in nigral DA neurons, and naringin-induced the production of GDNF contributed to the neuroprotection of the nigrostriatal DA projection in a neurotoxin model of Parkinson's disease [32]. In addition to the neurotrophic and protective effects, we found that naringin could attenuate the level of TNF-α in microglia increased by MPP+-induced neurotoxicity, indicating the anti-inflammatory activity of naringin against inflammation in the substantia nigra [32].

It is largely unknown whether activated mTORC1 can activate production of neurotrophic factors, contributing to the protection of the nigrostriatal DA projection, by intracellular signaling pathways in neurons of the adult brain. The answer for this question describes the relations between GDNF reproduction and mTORC1 activation. We have recently found that Rheb (S16H) expression by a viral vector induces a robust ability to induce GDNF in adult DA neurons in vivo, which is dependent on mTORC1 activity and contributed to the protection of the nigrostriatal DA projection [33]. To ascertain whether mTORC1 activated by treatment with naringin mediates the induction of GDNF, we further examined the effects of rapamycin, a specific inhibitor of mTORC1 [34], on the level of GDNF (Fig. 1). Rats received daily intraperitoneal injection of rapamycin (5 mg/kg) or naringin (80 mg/kg), or co-injection of rapamycin and naringin for 4 days. Similar to the previous results [32, 33], GDNF expression was increased in the substantia nigra of rat brain by treatment with naringin, and the naringin-increased levels were obvious in DA neurons as demonstrated by immunofluorescence double-labeling for tyrosine hydroxylase, indicating DA neurons, and GDNF (Fig. 1A). Although rapamycin treatment did not alter the basic level of GDNF in the substantia nigra, indicating a modest inhibitory effect, it attenuated the expression of GDNF induced by naringin as demonstrated by Western blot analysis (Fig. 1B). Similar to Rheb(S16H)-induced effects, these results show that naringin-activated mTORC1 stimulates the production of GDNF in DA neurons of the adult brain.

Naringin is a major flavonone glycoside in grapefruits and citrus fruits [27], which is expectable to be harmless to health. Our present observations on the effects of naringin in a neurotoxin model of Parkinson's disease show that treatment with naringin can impart to adult DA neurons the important ability to reproduce GDNF as a therapeutic agent against Parkinson's disease with additional anti-inflammatory effects on brain inflammation (Fig. 2). These results suggest that naringin may be a beneficial natural product offering promise for the prevention of neurodegeneration involved in Parkinson's disease. However, it is still unclear whether naringin can induce the activation of another prosurvival pathway except GDNF-mediated pathway, and post-treatment with naringin can restore the function of DA neurons in adult brains. Therefore, to make the possibility to treat Parkinson's disease patients clear, further study is needed to determine the effects of post-treatment with naringin such as the induction of dopamine and the regeneration of axons after damage in DA system of adult brain as well as the study on the mechanisms of naringin-induced effects in the adult brain.

  1. Savitt JM, Dawson VL, Dawson TM. Diagnosis and treatment of Parkinson disease: molecules to medicine. J Clin Invest 2006;116:1744-1754.
    Pubmed
  2. Burke RE, O'Malley K. Axon degeneration in Parkinson's disease. Exp Neurol 2013;246:72-83.
    Pubmed
  3. Lin LF, Doherty DH, Lile JD, Bektesh S, Collins F. GDNF: a glial cell line-derived neurotrophic factor for midbrain dopaminergic neurons. Science 1993;260:1130-1132.
    Pubmed
  4. Siegel GJ, Chauhan NB. Neurotrophic factors in Alzheimer's and Parkinson's disease brain. Brain Res Brain Res Rev 2000;33:199-227.
    Pubmed
  5. Manfredsson FP, Okun MS, Mandel RJ. Gene therapy for neurological disorders: challenges and future prospects for the use of growth factors for the treatment of Parkinson's disease. Curr Gene Ther 2009;9:375-388.
    Pubmed
  6. Allen SJ, Watson JJ, Shoemark DK, Barua NU, Patel NK. GDNF, NGF and BDNF as therapeutic options for neurodegeneration. Pharmacol Ther 2013;138:155-175.
    Pubmed
  7. Creedon DJ, Tansey MG, Baloh RH, Osborne PA, Lampe PA, Fahrner TJ, Heuckeroth RO, Milbrandt J, Johnson EM. Neurturin shares receptors and signal transduction pathways with glial cell line-derived neurotrophic factor in sympathetic neurons. Proc Natl Acad Sci U S A 1997;94:7018-7023.
    Pubmed
  8. Chauhan NB, Siegel GJ, Lee JM. Depletion of glial cell line-derived neurotrophic factor in substantia nigra neurons of Parkinson's disease brain. J Chem Neuroanat 2001;21:277-288.
    Pubmed
  9. Block ML, Hong JS. Microglia and inflammation-mediated neurodegeneration: multiple triggers with a common mechanism. Prog Neurobiol 2005;76:77-98.
    Pubmed
  10. Colton CA, Mott RT, Sharpe H, Xu Q, Van Nostrand WE, Vitek MP. Expression profiles for macrophage alternative activation genes in AD and in mouse models of AD. J Neuroinflammation 2006;3:27.
    Pubmed
  11. Yu HH, Wu FL, Lin SE, Shen LJ. Recombinant arginine deiminase reduces inducible nitric oxide synthase iNOS-mediated neurotoxicity in a coculture of neurons and microglia. J Neurosci Res 2008;86:2963-2972.
    Pubmed
  12. Kim SR, Chung ES, Bok E, Baik HH, Chung YC, Won SY, Joe E, Kim TH, Kim SS, Jin MY, Choi SH, Jin BK. Prothrombin kringle-2 induces death of mesencephalic dopaminergic neurons in vivo and in vitro via microglial activation. J Neurosci Res 2010;88:1537-1548.
    Pubmed
  13. Nam JH, Leem E, Jeon MT, Kim YJ, Jung UJ, Choi MS, Maeng S, Jin BK, Kim SR. Inhibition of prothrombin kringle-2-induced inflammation by minocycline protects dopaminergic neurons in the substantia nigra in vivo. Neuroreport 2014;25:489-495.
    Pubmed
  14. Pochon NA, Menoud A, Tseng JL, Zurn AD, Aebischer P. Neuronal GDNF expression in the adult rat nervous system identified by in situ hybridization. Eur J Neurosci 1997;9:463-471.
    Pubmed
  15. Pascual A, Hidalgo-Figueroa M, Piruat JI, Pintado CO, Gomez-Diaz R, Lopez-Barneo J. Absolute requirement of GDNF for adult catecholaminergic neuron survival. Nat Neurosci 2008;11:755-761.
    Pubmed
  16. Nutt JG, Burchiel KJ, Comella CL, Jankovic J, Lang AE, Laws ER, Lozano AM, Penn RD, Simpson RK, Stacy M, Wooten GF. Randomized, double-blind trial of glial cell line-derived neurotrophic factor (GDNF) in PD. Neurology 2003;60:69-73.
    Pubmed
  17. Peterson AL, Nutt JG. Treatment of Parkinson's disease with trophic factors. Neurotherapeutics 2008;5:270-280.
    Pubmed
  18. Ries V, Henchcliffe C, Kareva T, Rzhetskaya M, Bland R, During MJ, Kholodilov N, Burke RE. Oncoprotein Akt/PKB induces trophic effects in murine models of Parkinson's disease. Proc Natl Acad Sci U S A 2006;103:18757-18762.
    Pubmed
  19. Kholodilov N, Kim SR, Yarygina O, Kareva T, Cho JW, Baohan A, Burke RE. Glial cell line-derived neurotrophic factor receptor-alpha1 expressed in striatum in trans regulates development and injury response of dopamine neurons of the substantia nigra. J Neurochem 2011;116:486-498.
    Pubmed
  20. Datta SR, Brunet A, Greenberg ME. Cellular survival: a play in three Akts. Genes Dev 1999;13:2905-2927.
    Pubmed
  21. Brunet A, Datta SR, Greenberg ME. Transcription-dependent and -independent control of neuronal survival by the PI3K-Akt signaling pathway. Curr Opin Neurobiol 2001;11:297-305.
    Pubmed
  22. Chang N, El-Hayek YH, Gomez E, Wan Q. Phosphatase PTEN in neuronal injury and brain disorders. Trends Neurosci 2007;30:581-586.
    Pubmed
  23. Cheng HC, Kim SR, Oo TF, Kareva T, Yarygina O, Rzhetskaya M, Wang C, During M, Talloczy Z, Tanaka K, Komatsu M, Kobayashi K, Okano H, Kholodilov N, Burke RE. Akt suppresses retrograde degeneration of dopaminergic axons by inhibition of macroautophagy. J Neurosci 2011;31:2125-2135.
    Pubmed
  24. Kim SR, Chen X, Oo TF, Kareva T, Yarygina O, Wang C, During M, Kholodilov N, Burke RE. Dopaminergic pathway reconstruction by Akt/Rheb-induced axon regeneration. Ann Neurol 2011;70:110-120.
    Pubmed
  25. Kim SR, Kareva T, Yarygina O, Kholodilov N, Burke RE. AAV transduction of dopamine neurons with constitutively active Rheb protects from neurodegeneration and mediates axon regrowth. Mol Ther 2012;20:275-286.
    Pubmed
  26. Selvaraj S, Sun Y, Watt JA, Wang S, Lei S, Birnbaumer L, Singh BB. Neurotoxin-induced ER stress in mouse dopaminergic neurons involves downregulation of TRPC1 and inhibition of AKT/mTOR signaling. J Clin Invest 2012;122:1354-1367.
    Pubmed
  27. Jagetia GC, Reddy TK. The grapefruit flavanone naringin protects against the radiation-induced genomic instability in the mice bone marrow: a micronucleus study. Mutat Res 2002;519:37-48.
    Pubmed
  28. Golechha M, Chaudhry U, Bhatia J, Saluja D, Arya DS. Naringin protects against kainic acid-induced status epilepticus in rats: evidence for an antioxidant, anti-inflammatory and neuroprotective intervention. Biol Pharm Bull 2011;34:360-365.
    Pubmed
  29. Kim HJ, Song JY, Park HJ, Park HK, Yun DH, Chung JH. Naringin Protects against Rotenone-induced Apoptosis in Human Neuroblastoma SH-SY5Y Cells. Korean J Physiol Pharmacol 2009;13:281-285.
    Pubmed
  30. Choi BS, Sapkota K, Kim S, Lee HJ, Choi HS, Kim SJ. Antioxidant activity and protective effects of Tripterygium regelii extract on hydrogen peroxide-induced injury in human dopaminergic cells, SH-SY5Y. Neurochem Res 2010;35:1269-1280.
    Pubmed
  31. Rong W, Wang J, Liu X, Jiang L, Wei F, Hu X, Han X, Liu Z. Naringin treatment improves functional recovery by increasing BDNF and VEGF expression, inhibiting neuronal apoptosis after spinal cord injury. Neurochem Res 2012;37:1615-1623.
    Pubmed
  32. Leem E, Nam JH, Jeon MT, Shin WH, Won SY, Park SJ, Choi MS, Jin BK, Jung UJ, Kim SR. Naringin protects the nigrostriatal dopaminergic projection through induction of GDNF in a neurotoxin model of Parkinson's disease. J Nutr Biochem 2014
  33. Nam JH, Leem E, Joen MT, Jeong KH, Park JW, Jung UJ, Kholodilov N, Burke RE, Jin BK, Kim SR. Induction of GDNF and BDNF by hRheb(S16H) transduction of SNpc neurons: Neuroprotective mechanisms of hRheb(S16H) in a model of Parkinson' s disease. Mol Neurobiol 2014
  34. Zhou J, Blundell J, Ogawa S, Kwon CH, Zhang W, Sinton C, Powell CM, Parada LF. Pharmacological inhibition of mTORC1 suppresses anatomical, cellular, and behavioral abnormalities in neural-specific Pten knock-out mice. J Neurosci 2009;29:1773-1783.
    Pubmed