Minocycline prevents nigrostriatal dopaminergic neurodegeneration in the MPTP model of Parkinson's disease

Parkinson's disease is a chronic neurodegenerative disorder characterized by the loss of dopamine neurons in the substantia nigra, decreased striatal dopamine levels, and consequent extrapyramidal motor dysfunction. We now report that minocycline, a semisynthetic tetracycline, recently shown to have neuroprotective effects in animal models of stroke/ischemic injury and Huntington's disease, prevents nigrostriatal dopaminergic neurodegeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. Minocycline treatment also blocked dopamine depletion in the striatum as well as in the nucleus accumbens after MPTP administration. The neuroprotective effect of minocycline is associated with marked reductions in inducible NO synthase (iNOS) and caspase 1 expression. In vitro studies using primary cultures of mesencephalic and cerebellar granule neurons (CGN) and/or glia demonstrate that minocycline inhibits both 1-methyl-4-phenylpyridinium (MPP(+))-mediated iNOS expression and NO-induced neurotoxicity, but MPP(+)-induced neurotoxicity is inhibited only in the presence of glia. Further, minocycline also inhibits NO-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) in CGN and the p38 MAPK inhibitor, SB203580, blocks NO toxicity of CGN. Our results suggest that minocycline blocks MPTP neurotoxicity in vivo by indirectly inhibiting MPTP/MPP(+)-induced glial iNOS expression and/or directly inhibiting NO-induced neurotoxicity, most likely by inhibiting the phosphorylation of p38 MAPK. Thus, NO appears to play an important role in MPTP neurotoxicity. Neuroprotective tetracyclines may be effective in preventing or slowing the progression of Parkinson's and other neurodegenerative diseases.

Protection by pioglitazone in the MPTP model of Parkinson's disease correlates with I kappa B alpha induction and block of NF kappa B and iNOS activation

Inflammation has been implicated in the pathogenesis of Parkinson's disease (PD). In the chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD, inducible NO synthase (iNOS) derived nitric oxide (NO) is an important mediator of dopaminergic cell death. Ligands of the peroxisome proliferator-activated receptor (PPAR) exert anti-inflammatory effects. We here investigated whether pioglitazone, a PPARgamma agonist, protected mice from MPTP-induced dopaminergic cell loss, glial activation, and loss of catecholamines in the striatum. As shown by western blot, PPARgamma was expressed in the striatum and the substantia nigra of vehicle- and MPTP-treated mice. Oral administration of 20 mg/(kg day) of pioglitazone protected tyrosine hydroxylase (TH)-positive substantia nigra neurons from death induced by 5 x 30 mg/kg MPTP. However, the decrease of dopamine in the striatum was only partially prevented. In mice treated with pioglitazone, there were a reduced activation of microglia, reduced induction of iNOS-positive cells and less glial fibrillary acidic protein positive cells in both striatum and substantia nigra pars compacta. In addition, treatment with pioglitazone almost completely blocked staining of TH-positive neurons for nitrotyrosine, a marker of NO-mediated cell damage. Because an increase in inhibitory protein-kappa-Balpha (IkappaBalpha) expression and inhibition of translocation of the nuclear factor kappaB (NFkappaB) subunit p65 to the nucleus in dopaminergic neurons, glial cells and astrocytes correlated with the protective effects of pioglitazone, our results suggest that pioglitazone sequentially acts through PPARgamma activation, IkappaBalpha induction, block of NFkappaB activation, iNOS induction and NO-mediated toxicity. In conclusion, treatment with pioglitazone may offer a treatment opportunity in PD to slow the progression of disease that is mediated by inflammation.

Deficiency of inducible nitric oxide synthase protects against MPTP toxicity in vivo

MPTP produces clinical, biochemical, and neuropathologic changes reminiscent of those that occur in idiopathic Parkinson's disease (PD). In the present study we show that MPTP treatment led to activation of microglia in the substantia nigra pars compacta (SNpc), which was associated and colocalized with an increase in inducible nitric oxide synthase (iNOS) expression. In iNOS-deficient mice the increase of iNOS expression but not the activation of microglia was blocked. Dopaminergic SNpc neurons of iNOS-deficient mice were almost completely protected from MPTP toxicity in a chronic paradigm of MPTP toxicity. Because the MPTP-induced decrease in striatal concentrations of dopamine and its metabolites did not differ between iNOS-deficient mice and their wild-type littermates, this protection was not associated with a preservation of nigrostriatal terminals. Our results suggest that iNOS-derived nitric oxide produced in microglia plays an important role in the death of dopaminergic neurons but that other mechanisms contribute to the loss of dopaminergic terminals in MPTP neurotoxicity. We conclude that inhibition of iNOS may be a promising target for the treatment of PD.

Exercise-induced behavioral recovery and neuroplasticity in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned mouse basal ganglia

Physical activity has been shown to be neuroprotective in lesions affecting the basal ganglia. Using a treadmill exercise paradigm, we investigated the effect of exercise on neurorestoration. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned mouse model provides a means to investigate the effect of exercise on neurorestoration because 30-40% of nigrostriatal dopaminergic neurons survive MPTP lesioning and may provide a template for neurorestoration to occur. MPTP-lesioned C57 BL/6J mice were administered MPTP (four injections of 20 mg/kg free-base, 2 hr apart) or saline and divided into the following groups: (1). saline; (2). saline + exercise; (3). MPTP; and (4) MPTP + exercise. Mice in exercise groups were run on a motorized treadmill for 30 days starting 4 days after MPTP lesioning (a period after which MPTP-induced cell death is complete). Initially, MPTP-lesioned + exercise mice ran at slower speeds for a shorter amount of time compared to saline + exercise mice. Both velocity and endurance improved in the MPTP + exercise group to near normal levels over the 30-day exercise period. The expression of proteins and genes involved in basal ganglia function including the dopamine transporter (DAT), tyrosine hydroxylase (TH), and the dopamine D1 and D2 receptors, as well as alterations on glutamate immunolabeling were determined. Exercise resulted in a significant downregulation of striatal DAT in the MPTP + exercise compared to MPTP nonexercised mice and to a lesser extent in the saline + exercised mice compared to their no-exercise counterparts. There was no significant difference in TH protein levels between MPTP and MPTP + exercise groups at the end of the study. The expression of striatal dopamine D1 and D2 receptor mRNA transcript was suppressed in the saline + exercise group; however, dopamine D2 transcript expression was increased in the MPTP + exercise mice. Immunoelectron microscopy indicated that treadmill exercise reversed the lesioned-induced increase in nerve terminal glutamate immunolabeling seen after MPTP administration. Our data demonstrates that exercise promotes behavioral recovery in the injured brain by modulating genes and proteins important to basal ganglia function.

WIN55,212-2, a cannabinoid receptor agonist, protects against nigrostriatal cell loss in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by the progressive loss of nigrostriatal dopamine neurons leading to motor disturbances and cognitive impairment. Current pharmacotherapies relieve PD symptoms temporarily but fail to prevent or slow down the disease progression. In this study, we investigated the molecular mechanisms by which the non-selective cannabinoid receptor agonist WIN55,212-2 (WIN) protects mouse nigrostriatal neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity and neuroinflammation. Stereological analyses showed that chronic treatment with WIN (4 mg/kg, intraperitoneal), initiated 24 h after MPTP administration, protected against MPTP-induced loss of tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta independently of CB1 cannabinoid receptor activation. The neuroprotective effect of WIN was accompanied by increased dopamine and 3,4-dihydroxyphenylacetic acid levels in the substantia nigra pars compacta and dorsal striatum of MPTP-treated mice. At 3 days post-MPTP, we found significant microglial activation and up-regulation of CB2 cannabinoid receptors in the ventral midbrain. Treatment with WIN or the CB2 receptor agonist JWH015 (4 mg/kg, intraperitoneal) reduced MPTP-induced microglial activation, whereas genetic ablation of CB2 receptors exacerbated MPTP systemic toxicity. Furthermore, chronic WIN reversed MPTP-associated motor deficits, as revealed by the analysis of forepaw step width and percentage of faults using the inverted grid test. In conclusion, our data indicate that agonism at CB2 cannabinoid receptors protects against MPTP-induced nigrostriatal degeneration by inhibiting microglial activation/infiltration and suggest that CB2 receptors represent a new therapeutic target to slow the degenerative process occurring in PD.

Astaxanthin protects against MPTP/MPP+-induced mitochondrial dysfunction and ROS production in vivo and in vitro

Astaxanthin (AST) is a powerful antioxidant that occurs naturally in a wide variety of living organisms. We have investigated the role of AST in preventing 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced apoptosis of the substantia nigra (SN) neurons in the mouse model of Parkinson's disease (PD) and 1-methyl-4-phenylpyridinium (MPP+)-induced cytotoxicity of SH-SY5Y human neuroblastoma cells. In in vitro study, AST inhibits MPP+-induced production of intracellular reactive oxygen species (ROS) and cytotoxicity in SH-SY5Y human neuroblastoma cells. Preincubation of AST (50 μM) significantly attenuates MPP+-induced oxidative damage. Furthermore, AST is able to enhance the expression of Bcl-2 protein but reduce the expression of α-synuclein and Bax, and suppress the cleavage of caspase-3. Our results suggest that the protective effects of AST on MPP+-induced apoptosis may be due to its anti-oxidative properties and anti-apoptotic activity via induction of expression of superoxide dismutase (SOD) and catalase and regulating the expression of Bcl-2 and Bax. Pretreatment with AST (30 mg/kg) markedly increases tyrosine hydroxylase (TH)-positive neurons and decreases the argyrophilic neurons compared with the MPTP model group. In summary, AST shows protection from MPP+/MPTP-induced apoptosis in the SH-SY5Y cells and PD model mouse SN neurons, and this effect may be attributable to upregulation of the expression of Bcl-2 protein, downregulation of the expression of Bax and α-synuclein, and inhibition of the activation of caspase-3. These data indicate that AST may provide a valuable therapeutic strategy for the treatment of progressive neurodegenerative disease such as Parkinson's disease.

Safinamide: From molecular targets to a new anti-Parkinson drug

Ideal treatment in Parkinson's disease (PD) aims at relieving symptoms and slowing disease progression. Of all remedies, levodopa remains the most effective for symptomatic relief, but the medical need for neuroprotectant drugs is still unfulfilled. Safinamide, currently in phase III clinical trials for the treatment of PD, is a unique molecule with multiple mechanisms of action and a very high therapeutic index. It combines potent, selective, and reversible inhibition of MAO-B with blockade of voltage-dependent Na+ and Ca2+ channels and inhibition of glutamate release. Safinamide has neuroprotective and neurorescuing effects in MPTP-treated mice, in the rat kainic acid, and in the gerbil ischemia model. Safinamide potentiates levodopa-mediated increase of DA levels in DA-depleted mice and reverses the waning motor response after prolonged levodopa treatment in 6-OHDA-lesioned rats. Safinamide has excellent bioavailability, linear kinetics, and is suitable for once-a-day administration. Therefore, safinamide may be used in PD to reduce l-dopa dosage and also represents a valuable therapeutic drug to test disease-modifying potential.

Celastrol protects against MPTP- and 3-nitropropionic acid-induced neurotoxicity

Oxidative stress and inflammation are implicated in neurodegenerative diseases including Parkinson's disease (PD) and Huntington's disease (HD). Celastrol is a potent anti-inflammatory and antioxidant compound extracted from a perennial creeping plant belonging to the Celastraceae family. Celastrol is known to prevent the production of proinflammatory cytokines, inducible nitric oxide synthase and lipid peroxidation. Mice were treated with celastrol before and after injections of MPTP, a dopaminergic neurotoxin, which produces a model of PD. A 48% loss of dopaminergic neurons induced by MPTP in the substantia nigra pars compacta was significantly attenuated by celastrol treatment. Moreover, celastrol treatment significantly reduced the depletion in dopamine concentration induced by MPTP. Similarly, celastrol significantly decreased the striatal lesion volume induced by 3-nitropropionic acid, a neurotoxin used to model HD in rats. Celastrol induced heat shock protein 70 within dopaminergic neurons and decreased tumor necrosis factor-alpha and nuclear factor kappa B immunostainings as well as astrogliosis. Celastrol is therefore a promising neuroprotective agent for the treatment of PD and HD.

Neuroprotection of MPTP-induced toxicity in zebrafish dopaminergic neurons

Parkinson's disease is characterized by a severe loss of dopaminergic neurons resulting in a range of motor deficits. The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is known to cause a similar loss of dopaminergic neurons in the human midbrain with corresponding Parkinsonian symptoms. Several animal species have also shown sensitivity to MPTP, including primates, mice, goldfish, and, most recently, zebrafish. This study demonstrates that the effect of MPTP on dopaminergic neurons in zebrafish larvae is mediated by the same pathways that have been demonstrated in mammalian species. MPTP-induced neurodegeneration was prevented by co-incubation with either the monoamine oxidase-B (MAO-B) inhibitor l-deprenyl or the dopamine transporter (DAT) inhibitor nomifensine. Furthermore, targeted inactivation of the DAT gene by antisense morpholinos also protected neurons from MPTP damage. Thus, the mechanism for MPTP-induced dopaminergic neuron toxicity in mammals is conserved in zebrafish larvae. Effects on swimming behavior and touch response that result from MPTP damage are partially ameliorated by both l-deprenyl and DAT knockdown.

Neuroprotective effect of vasoactive intestinal peptide (VIP) in a mouse model of Parkinson's disease by blocking microglial activation

Parkinson's disease (PD) is a common neurodegenerative disorder with no effective protective treatment, characterized by a massive degeneration of dopaminergic neurons in the substantia nigra (SNpc) and the subsequent loss of their projecting nerve fibers in the striatum. To elucidate PD pathogenic factors, and thus to develop therapeutic strategies, a murine PD model based on the administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been used extensively. It has been demonstrated that activated microglia cells actively participate in the pathogenesis of MPTP-induced PD through the release of cytotoxic factors. Because current treatments for PD are not effective, considerable research focused lately on a number of regulatory molecules termed microglia-deactivating factors. Vasoactive intestinal peptide (VIP), a neuropeptide with a potent anti-inflammatory effect, has been found to be protective in several inflammatory disorders. This study investigates the putative protective effect of VIP in the MPTP model for PD. VIP treatment significantly decreases MPTP-induced dopaminergic neuronal loss in SNpc and nigrostriatal nerve-fiber loss. VIP prevents MPTP-induced activation of microglia in SNpc and striatum and the expression of the cytotoxic mediators, iNOS, interleukin 1beta, and numor necrosis factor alpha. VIP emerges as a potential valuable neuroprotective agent for the treatment of pathologic conditions in the central nervous system, such as PD, where inflammation-induced neurodegeneration occurs.

Developmental loss and resistance to MPTP toxicity of dopaminergic neurones in substantia nigra pars compacta of gamma-synuclein, alpha-synuclein and double alpha/gamma-synuclein null mutant mice

The growing body of evidence suggests that intermediate products of alpha-synuclein aggregation cause death of sensitive populations of neurones, particularly dopaminergic neurones, which is a critical event in the development of Parkinson's disease and other synucleinopathies. The role of two other members of the family, beta-synuclein and gamma-synuclein, in neurodegeneration is less understood. We studied the effect of inactivation of gamma-synuclein gene on mouse midbrain dopaminergic neurones. Reduced number of dopaminergic neurones was found in substantia nigra pars compacta (SNpc) but not in ventral tegmental area (VTA) of early post-natal and adult gamma-synuclein null mutant mice. Similar reductions were revealed in alpha-synuclein and double alpha-synuclein/gamma-synuclein null mutant animals. However, in none of these mutants did this lead to significant changes of striatal dopamine or dopamine metabolite levels and motor dysfunction. In all three studied types of null mutants, dopaminergic neurones of SNpc were resistant to methyl-phenyl-tetrahydropyridine (MPTP) toxicity. We propose that both synucleins are important for effective survival of SNpc neurones during critical period of development but, in the absence of these proteins, permanent activation of compensatory mechanisms allow many neurones to survive and become resistant to certain toxic insults.

Reduction of L-DOPA-induced dyskinesia by the selective metabotropic glutamate receptor 5 antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned macaque model of Parkinson's disease

Long-term motor complications of dopamine replacement, such as L-DOPA-induced dyskinesia (LID) and reduced quality of L-DOPA action, remain obstacles in the treatment of Parkinson's disease. Dysfunctional glutamatergic neurotransmitter systems have been observed in both the untreated parkinsonian and dyskinetic states and represent novel targets for treatment. Here, we assess the pharmacokinetic profile and corresponding pharmacodynamic effects on behavior of the orally active, selective metabotropic glutamate receptor type 5 (mGlu5) antagonist, 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) (as the hydrochloride salt) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned macaque. Six parkinsonian, MPTP-lesioned cynomolgus monkeys, with established LID, were administered acute challenges with MTEP (4.5-36 mg/kg p.o.) or vehicle, either alone or in combination with L-DOPA (33 +/- 1 mg/kg p.o.). Motor activity, parkinsonian disability, and dyskinesia were assessed for a 6-h period. Plasma drug levels were assessed by liquid chromatography-tandem mass spectrometry. MTEP had no antiparkinsonian action as monotherapy. However, administration of L-DOPA in combination with MTEP (36 mg/kg) reduced peak dose LID by 96%. Moreover, although total on-time (duration for which L-DOPA exerted an antiparkinsonian effect) was not significantly reduced, MTEP (36 mg/kg) reduced the duration of on-time with disabling LID by 70% compared with that for L-DOPA alone. These effects were associated with a peak plasma concentration of 20.9 microM and an area under the curve from 0 to 24 h of 136.1 h x microM (36 mg/kg). Although total on-time was not reduced, the peak antiparkinsonian benefit of l-DOPA/MTEP (36 mg/kg) was less than that with L-DOPA alone. Selective mGlu5 inhibitors may have significant potential to ameliorate dyskinesia, but care should be taken to ensure that such effects do not come at the expense of the peak antiparkinsonian benefit of L-DOPA.

Ovarian steroids and raloxifene prevent MPTP-induced dopamine depletion in mice

The activity of steroids was studied in 1-methyl-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesioned retired breeder C57BL/6 male mice as a model of Parkinson's disease. Steroids were injected daily for 5 days before MPTP (4 injections, 15 mg/kg i.p., at 2 h intervals) and hormonal treatment continued for 5 more days. Mice that received 17beta-estradiol or progesterone or raloxifene (a selective estrogen receptor modulator) and MPTP had striatal concentrations of dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) similar to those in control animals, whereas mice that received MPTP alone or with 17alpha-estradiol (the isomer with weak estrogenic activity) had an extensive decrease of DA and its metabolites. These results suggest stereospecific prevention of MPTP-induced dopamine loss by 17beta-estradiol, which is also observed with progesterone and raloxifene.

GOSPEL: a neuroprotective protein that binds to GAPDH upon S-nitrosylation

We recently reported a cell death cascade whereby cellular stressors activate nitric oxide formation leading to S-nitrosylation of GAPDH that binds to Siah and translocates to the nucleus. The nuclear GAPDH/Siah complex augments p300/CBP-associated acetylation of nuclear proteins, including p53, which mediate cell death. We report a 52 kDa cytosolic protein, GOSPEL, which physiologically binds GAPDH, in competition with Siah, retaining GAPDH in the cytosol and preventing its nuclear translocation. GOSPEL is neuroprotective, as its overexpression prevents NMDA-glutamate excitotoxicity while its depletion enhances death in primary neuron cultures. S-nitrosylation of GOSPEL at cysteine 47 enhances GAPDH-GOSPEL binding and the neuroprotective actions of GOSPEL. In intact mice, virally delivered GOSPEL selectively diminishes NMDA neurotoxicity. Thus, GOSPEL may physiologically regulate the viability of neurons and other cells.

Pro-inflammatory cytokines modulate iron regulatory protein 1 expression and iron transportation through reactive oxygen/nitrogen species production in ventral mesencephalic neurons

Both inflammatory processes associated with microglia activation and abnormal iron deposit in dopaminergic neurons are involved in the pathogenesis of Parkinson's disease (PD). However, the relationship between neuroinflammation and iron accumulation was not fully elucidated. In the present study, we aimed to investigate whether the pro-inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) released by microglia, could affect cellular iron transportation in primary cultured ventral mesencephalic (VM) neurons. The results showed that IL-1β or TNF-α treatment led to increased ferrous iron influx and decreased iron efflux in these cells, due to the upregulation of divalent metal transporter 1 with the iron response element (DMT1+IRE) and downregulation of ferroportin1 (FPN1). Increased levels of iron regulatory protein 1 (IRP1), transferrin receptor 1 (TfR1) and hepcidin were also observed in IL-1β or TNF-α treated VM neurons. IRP1 upregulation could be fully abolished by co-administration of radical scavenger N-acetyl-l-cysteine and inducible NO synthetase inhibitor Nω-nitro-l-arginine methyl ester hydrochloride. Further experiments demonstrated that IL-1β and TNF-α release was remarkably enhanced by iron load in activated microglia triggered by lipopolysaccharide or 1-methyl-4-phenylpyridinium (MPP(+)). In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice, salicylate application could not block DMT1+IRE upregulation in dopaminergic neurons of substantia nigra. These results suggested that IL-1β and TNF-α released by microglia, especially under the condition of iron load, might contribute to iron accumulation in VM neurons by upregulating IRP1 and hepcidin levels through reactive oxygen/nitrogen species production. This might provide a new insight into unraveling that microglia might aggravate this iron mediated neuropathologies in PD.

KEAP1-modifying small molecule reveals muted NRF2 signaling responses in neural stem cells from Huntington's disease patients

The activity of the transcription factor nuclear factor-erythroid 2 p45-derived factor 2 (NRF2) is orchestrated and amplified through enhanced transcription of antioxidant and antiinflammatory target genes. The present study has characterized a triazole-containing inducer of NRF2 and elucidated the mechanism by which this molecule activates NRF2 signaling. In a highly selective manner, the compound covalently modifies a critical stress-sensor cysteine (C151) of the E3 ligase substrate adaptor protein Kelch-like ECH-associated protein 1 (KEAP1), the primary negative regulator of NRF2. We further used this inducer to probe the functional consequences of selective activation of NRF2 signaling in Huntington's disease (HD) mouse and human model systems. Surprisingly, we discovered a muted NRF2 activation response in human HD neural stem cells, which was restored by genetic correction of the disease-causing mutation. In contrast, selective activation of NRF2 signaling potently repressed the release of the proinflammatory cytokine IL-6 in primary mouse HD and WT microglia and astrocytes. Moreover, in primary monocytes from HD patients and healthy subjects, NRF2 induction repressed expression of the proinflammatory cytokines IL-1, IL-6, IL-8, and TNFα. Together, our results demonstrate a multifaceted protective potential of NRF2 signaling in key cell types relevant to HD pathology.

Endogenous activation of mGlu5 metabotropic glutamate receptors contributes to the development of nigro-striatal damage induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice

We combined the use of knock-out mice and subtype-selective antagonists [2-methyl-6-(phenylethynyl)pyridine (MPEP) and (E)-2-methyl-6-(2-phenylethenyl)-pyridine (SIB1893)] to examine whether endogenous activation of mGlu5 metabotropic glutamate receptors contributes to the pathophysiology of nigro-striatal damage in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of parkinsonism. High doses of MPTP (four injections of 20 mg/kg, i.p., every 2 hr) induced a high mortality rate and a nearly total degeneration of the nigro-striatal pathway in wild-type mice. mGlu5 knock-out mice were less sensitive to MPTP toxicity, as shown by a higher survival and a milder nigro-striatal damage. Protection against MPTP (80 mg/kg) toxicity was also observed after MPEP injections (four injections of 5 mg/kg, i.p., 30 min before each MPTP injection). MPEP treatment did not further increase neuroprotection against 80 mg/kg of MPTP in mGlu5 knock-out mice, indicating that the drug acted by inhibiting mGlu5 receptors. In wild-type mice, MPEP was also neuroprotective when challenged against lower doses of MPTP (either 30 mg/kg, single injection, or four of 10 mg/kg injections). The action of MPEP was mimicked by SIB1893 but not by the mGlu1 receptor antagonist 7-hydroxyiminocyclopropan[b]chromen-1a-carboxylic acid ethyl ester. MPEP did not change the kinetics of 1-methyl-4-phenylpyridinium ion formation in the striatum of mice injected with MPTP. We conclude that mGlu5 receptors act as amplifiers of MPTP toxicity and that mGlu5 receptor antagonists may limit the extent of nigro-striatal damage in experimental models of parkinsonism.

Multiple small doses of levodopa plus entacapone produce continuous dopaminergic stimulation and reduce dyskinesia induction in MPTP-treated drug-naïve primates

Long-acting dopamine agonist drugs induce a lower incidence of dyskinesia in MPTP-treated primates and patients with Parkinson's disease compared to pulsatile treatment with levodopa, supporting the concept of continuous dopaminergic stimulation as a means of dyskinesia avoidance. We examined the effects of L-dopa administered with or without the COMT inhibitor entacapone on dyskinesia induction in previously untreated MPTP-treated common marmosets. Administration of L-dopa (12.5 mg/kg p.o.) plus carbidopa twice daily produced fluctuating improvement in motor behavior coupled with dyskinesia. Coadministration with entacapone produced similar patterns of motor improvement and dyskinesia that were not different from that produced by L-dopa alone. Treatment with L-dopa (6.25 mg/kg p.o.) plus carbidopa four times daily reversed motor disability and induced dyskinesia in a manner that was not different from the twice-daily treatment regimens. However, coadministration with entacapone produced more continuous improvement in locomotor activity with less dyskinesia than animals treated with L-dopa four times daily alone. These data support the notion that pulsatile stimulation contributes to the development of dyskinesia and suggests that more frequent dosing of L-dopa plus entacapone may be a useful treatment strategy for patients in the early stages of Parkinson's disease.

Prevention of MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) dopaminergic neurotoxicity in mice by chronic lithium: involvements of Bcl-2 and Bax

Lithium has been reported to exert neuroprotective activity in several neuronal cell cultures and in vivo models against glutamate toxicity. Since this action was reported to be associated with alterations in the antiapoptotic Bcl-2 family proteins, the effect of chronic lithium diet on the ability of the parkinsonism neurotoxin, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to deplete striatal dopamine in mice was determined. Mice were fed for with a diet containing 1.1, 2.2, 3.3, and 4.4 g/kg lithium chloride (LiCl) for 4 weeks, during which time serum levels of lithium were monitored. The 3.3 g/kg lithium diet gave serum level value very similar to what is observed in lithium therapy in man and the 4.4 g/kg well above this. At the end of this period the mice received 24 mg/kg MPTP i.p. once daily for 3 days. A direct relation was established with the increase in serum lithium and its ability to prevent MPTP induced depletion of striatal dopamine (DA) and its metabolites DPOAC and HVA. With the diet containing the highest lithium concentration there was an almost complete prevention of striatal dopamine depletion and the reduction in tyrosine hydroxylase activity and protein and it prevented the increase in dopamine turnover (DOPAC + HVA/DA) normally observed in MPTP treatment. Lithium did not interfere with the metabolism of MPTP, or with its brain uptake, since, the level of its monoamine oxidase (MAO) B derived metabolite, MPP+, in the striata of lithium and non-lithium treated mice were almost identical. Striatal Bcl-2 was significantly decreased, while Bax was increased in MPTP treated mice. Lithium treatment not only increased striatal Bcl-2 in control mice, but also prevented its reduction as induced by MPTP, and an opposing effect was seen with Bax. The neuroprotective action of lithium in this model of Parkinson's disease has been attributed to its antiapoptotic activity which among other factors includes induction of Bcl-2 and reduction of Bax.

Pharmacological inhibition of neuronal NADPH oxidase protects against 1-methyl-4-phenylpyridinium (MPP+)-induced oxidative stress and apoptosis in mesencephalic dopaminergic neuronal cells

Oxidative stress is widely recognized as a key mediator of degenerative processes in Parkinson's disease (PD). Recently, we demonstrated that the dopaminergic toxin MPP+ initiates oxidative stress to cause caspase-3-dependent apoptotic cell death in mesencephalic dopaminergic neuronal (N27) cells. In this study, we determined the source of reactive oxygen species (ROS) produced during MPP+-induced apoptotic cell death. In addition to mitochondria, plasma membrane NADPH oxidase is considered a major producer of ROS inside the cell. Here, we show that N27 neuronal cells express key NADPH oxidase subunits gp91phox and p67phox. We used structurally diverse NADPH oxidase inhibitors, aminoethyl-benzenesulfonylfluoride (AEBSF, 100-1000microM), apocynin (100-1000microM), and diphenylene iodonium (DPI, 3-30microM), to inhibit intrinsic NADPH oxidase activity in N27 cells. Flow cytometric analysis using the ROS-sensitive dye hydroethidine revealed that AEBSF blocked 300microM MPP+-induced ROS production for over 45min in N27 cells, in a dose-dependent manner. Further treatment with DPI, apocynin, and SOD also blocked MPP+-induced ROS production. In Sytox cell death assays, co-treatment with AEBSF, apocynin, or DPI for 24h significantly suppressed MPP+-induced cytotoxic cell death. Similarly, co-treatment with these inhibitors also significantly attenuated MPP+-induced increases in caspase-3 enzymatic activity. Furthermore, quantitative DNA fragmentation ELISA assays revealed that AEBSF, DPI, and apocynin rescue N27 cells from MPP+-induced apoptotic cell death. Together, these results indicate for the first time that intracellular ROS generated by NAPDH oxidase are present within the mesencephalic neuronal cells, and are a key determinant of MPP+-mediated dopaminergic degeneration in in vitro models of dopaminergic degeneration. This study supports a critical role of NADPH oxidase in the oxidative damage in PD; targeting this enzyme may lead to novel therapies for PD.

Stereospecific prevention by 17beta-estradiol of MPTP-induced dopamine depletion in mice

Neuroprotective activity of estrogens is reported in Alzheimer disease and recently has also been suggested for Parkinson disease, a disease affecting more men than women. To characterize this estrogenic activity, we studied the effects of 17beta- and 17alpha-estradiol treatment (1 microg twice daily 5 days before, during the day of four MPTP (15 mg/kg) injections, and for the following 5 days) on dopamine striatal toxicity induced by the neurotoxin MPTP in retired breeder male C57BL/6 mice. Striatal dopamine concentrations and its metabolites dihydroxyphenylacetic acid and homovanillic acid measured by HPLC in MPTP mice that received 17beta-estradiol were comparable to control animals, whereas MPTP mice treated with saline or 17alpha-estradiol showed important decreases of dopamine and its metabolites. Striatal serotonin and its metabolite 5-hydroxyindoleacetic acid concentrations remained unchanged after MPTP and treatments with steroids. Striatal [(3)H]GBR 12935 binding autoradiography to the dopamine transporter was as extensively decreased and correlated with dopamine depletion in MPTP mice, whereas this transporter mRNA decrease in the substantia nigra pars compacta was less pronounced. Treatment with steroids did not significantly change [(3)H]GBR 12935 binding, whereas dopamine transporter mRNA levels were not significantly different from controls. Under the present paradigm in retired breeder male mice, our results show dopaminergic and stereospecificity of estradiol to augment dopamine levels in MPTP-lesioned mice without protecting against the extensive loss of dopamine terminals and moderate cell body loss.

Obligatory Role for Complex I Inhibition in the Dopaminergic Neurotoxicity of 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to mice and nonhuman primates causes a parkinsonian disorder characterized by a loss of dopamine-producing neurons in the substantia nigra and corresponding motor deficits. MPTP has been proposed to exert its neurotoxic effects through a variety of mechanisms, including inhibition of complex I of the mitochondrial respiratory chain, displacement of dopamine from vesicular stores, and formation of reactive oxygen species from mitochondrial or cytosolic sources. However, the mechanism of MPTP-induced neurotoxicity is still a matter of debate. Recently, we reported that the yeast single-subunit nicotinamide adenine dinucleotide (reduced) dehydrogenase (NDI1) is resistant to rotenone, a complex I inhibitor that produces a parkinsonian syndrome in rats, and that overexpression of NDI1 in SK-N-MC cells prevents the toxicity of rotenone. In this study, we used viral-mediated overexpression of NDI1 in SK-N-MC cells and animals to determine the relative contribution of complex I inhibition in the toxicity of MPTP. In cell culture, NDI1 overexpression abolished the toxicity of 1-methyl-4-phenylpyridinium, the active metabolite of MPTP. Overexpression of NDI1 through stereotactic administration of a viral vector harboring the NDI1 gene into the substantia nigra protected mice from both the neurochemical and behavioral deficits elicited by MPTP. These data identify inhibition of complex I as a requirement for dopaminergic neurodegeneration and subsequent behavioral deficits produced by MPTP. Furthermore, combined with reports of a complex I defect in Parkinson's disease (PD) patients, the present study affirms the utility of MPTP in understanding the molecular mechanisms underlying dopaminergic neurodegeneration in PD.

Metallothionein-mediated neuroprotection in genetically engineered mouse models of Parkinson's disease

Parkinson's disease is characterized by a progressive loss of dopaminergic neurons in the substantia nigra zona compacta, and in other sub-cortical nuclei associated with a widespread occurrence of Lewy bodies. The cause of cell death in Parkinson's disease is still poorly understood, but a defect in mitochondrial oxidative phosphorylation and enhanced oxidative and nitrative stresses have been proposed. We have studied control(wt) (C57B1/6), metallothionein transgenic (MTtrans), metallothionein double gene knock (MTdko), alpha-synuclein knock out (alpha-syn(ko)), alpha-synuclein-metallothionein triple knock out (alpha-syn-MTtko), weaver mutant (wv/wv) mice, and Ames dwarf mice to examine the role of peroxynitrite in the etiopathogenesis of Parkinson's disease and aging. Although MTdko mice were genetically susceptible to 1, methyl, 4-phenyl, 1,2,3,6-tetrahydropyridine (MPTP) Parkinsonism, they did not exhibit any overt clinical symptoms of neurodegeneration and gross neuropathological changes as observed in wv/wv mice. Progressive neurodegenerative changes were associated with typical Parkinsonism in wv/wv mice. Neurodegenerative changes in wv/wv mice were observed primarily in the striatum, hippocampus and cerebellum. Various hallmarks of apoptosis including caspase-3, TNFalpha, NFkappaB, metallothioneins (MT-1, 2) and complex-1 nitration were increased; whereas glutathione, complex-1, ATP, and Ser(40)-phosphorylation of tyrosine hydroxylase, and striatal 18F-DOPA uptake were reduced in wv/wv mice as compared to other experimental genotypes. Striatal neurons of wv/wv mice exhibited age-dependent increase in dense cored intra-neuronal inclusions, cellular aggregation, proto-oncogenes (c-fos, c-jun, caspase-3, and GAPDH) induction, inter-nucleosomal DNA fragmentation, and neuro-apoptosis. MTtrans and alpha-Syn(ko) mice were genetically resistant to MPTP-Parkinsonism and Ames dwarf mice possessed significantly higher concentrations of striatal coenzyme Q10 and metallothioneins (MT 1, 2) and lived almost 2.5 times longer as compared to control(wt) mice. A potent peroxynitrite ion generator, 3-morpholinosydnonimine (SIN-1)-induced apoptosis was significantly attenuated in MTtrans fetal stem cells. These data are interpreted to suggest that peroxynitrite ions are involved in the etiopathogenesis of Parkinson's disease, and metallothionein-mediated coenzyme Q10 synthesis may provide neuroprotection.

Bee venom and its component apamin as neuroprotective agents in a Parkinson disease mouse model

Bee venom has recently been suggested to possess beneficial effects in the treatment of Parkinson disease (PD). For instance, it has been observed that bilateral acupoint stimulation of lower hind limbs with bee venom was protective in the acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. In particular, a specific component of bee venom, apamin, has previously been shown to have protective effects on dopaminergic neurons in vitro. However, no information regarding a potential protective action of apamin in animal models of PD is available to date. The specific goals of the present study were to (i) establish that the protective effect of bee venom for dopaminergic neurons is not restricted to acupoint stimulation, but can also be observed using a more conventional mode of administration and to (ii) demonstrate that apamin can mimic the protective effects of a bee venom treatment on dopaminergic neurons. Using the chronic mouse model of MPTP/probenecid, we show that bee venom provides sustained protection in an animal model that mimics the chronic degenerative process of PD. Apamin, however, reproduced these protective effects only partially, suggesting that other components of bee venom enhance the protective action of the peptide.

KW-6002 protects from MPTP induced dopaminergic toxicity in the mouse

The risk of Parkinson's disease (PD) is associated with a lower intake of caffeine, a non-selective adenosine A2A antagonist. In agreement, genetic or pharmacological inactivation of adenosine A2A receptors in animal models of PD has demonstrated both symptomatic and neuroprotective effects. These findings and the lack of disease modifying therapies have led to intense research on adenosine A2A antagonists as a novel treatment for PD. In the present study the neuroprotective effect of the A2A receptor antagonist KW-6002 was investigated using different models of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice, which induced dopaminergic terminal and or dopaminergic cell loss and inflammation. Treatment with KW-6002 prevented the loss of dopaminergic striatal terminals and nigral cell bodies and inhibited the nigral microglia activation. Our results confirm previous findings that pharmacological inactivation of A2A receptors inhibits MPTP-induced dopaminergic damage at the level of striatum. In addition, we demonstrate for the first time that, after MPTP treatment in mice, an A2A antagonist is neuroprotective, and has anti-inflammatory effects, at the level of the substantia nigra. Thus, our data further support the use of A2A receptor antagonists as a novel neuroprotective therapy for PD.