Biochemical, behavioral and immunohistochemical alterations in MPTP-treated mouse model of Parkinson's disease

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one), a radical scavenger, prevents 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity in the substantia nigra but not the striatum

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic neurotoxicity and behavioral impairment in rodents, and previous studies suggest that nitric oxide and reactive oxygen species are involved in MPTP-induced neurotoxicity. The present study examines the effect of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one), a radical scavenger, on MPTP-induced neurotoxicity in the striatum and substantia nigra pars compacta (SNc) of C57BL/6J mice. MPTP treatment (10 mg/kg s.c. x 4 with 2-h intervals) decreased dopamine levels and tyrosine hydroxylase immunostaining in the striatum and SNc. Pretreatment with edaravone (1 and 3 mg/kg i.p.) significantly reduced the neurotoxicity in the SNc but not striatum. An immunohistochemical study showed that MPTP caused microglial activation both in the striatum and SNc, whereas it increased 3-nitrotyrosine immunoreactivity, an in vivo biomarker of peroxynitrite production, in the SNc but not the striatum. Furthermore, MPTP increased lipid peroxidation product thiobarbituric acid reactive substance in the midbrain, but not the striatum. Edaravone inhibited activation of the microglia and the increased 3-nitrotyrosine immunoreactivity in the SNc but not the striatum, and it also inhibited thiobarbituric acid reactive substance levels in the midbrain. Behavioral analyses showed that edaravone improved MPTP-induced impairment of locomotion and Rotorod performance. These results suggest that edaravone protects against MPTP-induced neurotoxicity in the SNc by blocking the production of reactive oxygen species or peroxynitrite and imply that dopaminergic degeneration in the SNc may play an important role in MPTP-induced motor dysfunction of mice.

1alpha,25-Dihydroxyvitamin D(3) Protects Dopaminergic Neurons in Rodent Models of Parkinson's Disease through Inhibition of Microglial Activation

Background

Recent studies have demonstrated the molecular basis of the immunomodulatory and anti-inflammatory activities of 1,25-dihydroxyvitamin D₃(1,25-(OH)₂D₃). This hormone improves behavioral deficits and normalizes the nigral dopamine levels in animal models of Parkinson's disease (PD).

Methods

We studied whether the administration of 1,25-(OH)₂D₃ would protect against 6-hydroxydopa (6-OHDA)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neuronal injury, and its potential regulatory effect on microglia activation.

Results

We found that 1,25-(OH)₂D₃ pretreatment significantly decreased 6-OHDA- and MPTP-induced dopaminergic neuronal loss in the substantia nigra pars compacta by preventing the activation of microglia. This observed neuroprotective effect in MPTP-treated mice that were given 1,25-(OH)₂D₃ may be attributable to inhibition of proinflammatory cytokine expression.

Conclusion

These results suggest that 1,25-(OH)₂D₃ is a potentially valuable neuroprotective agent; it may therefore be considered for the treatment of pathologic conditions of the central nervous system, such as PD, where inflammation-induced neurodegeneration occurs.

Paeoniflorin attenuates neuroinflammation and dopaminergic neurodegeneration in the MPTP model of Parkinson's disease by activation of adenosine A1 receptor

1. This study examined whether Paeoniflorin (PF), the major active components of Chinese herb Paeoniae alba Radix, has neuroprotective effect in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD). 2. Subcutaneous administration of PF (2.5 and 5 mg kg(-1)) for 11 days could protect tyrosine hydroxylase (TH)-positive substantia nigra neurons and striatal nerve fibers from death and bradykinesia induced by four-dose injection of MPTP (20 mg kg(-1)) on day 8. 3. When given at 1 h after the last dose of MPTP, and then administered once a day for the following 3 days, PF (2.5 and 5 mg kg(-1)) also significantly attenuated the dopaminergic neurodegeneration in a dose-dependent manner. Post-treatment with PF (5 mg kg(-1)) significantly attenuated MPTP-induced proinflammatory gene upregulation and microglial and astrocytic activation. 4. Pretreatment with 0.3 mg kg(-1) 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A1 receptor (A1AR) antagonist, 15 min before each dose of PF, reversed the neuroprotective and antineuroinflammatory effects of PF. 5. In conclusion, this study demonstrated that PF could reduce the MPTP-induced toxicity by inhibition of neuroinflammation by activation of the A1AR, and suggested that PF might be a valuable neuroprotective agent for the treatment of PD.

In vivo modulation of the Parkinsonian phenotype by Nrf2

Oxidative stress has been implicated in the etiology of Parkinson's disease (PD) and in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of PD. In this report we show that Nrf2, a transcription factor that regulates the expression of phase 2 and antioxidative enzymes, modulates MPTP neurotoxicity in rodents. Nrf2 knockout and wild-type mice were administered MPTP doses ranging from 20 to 60mg/kg. Seven days after MPTP administration dopamine transporter (DAT) levels were measured using [(125)I]-RTI-121 quantitative autoradiography as an index of dopamine terminal integrity in the striatum. The results indicate that MPTP administration resulted in a greater loss of DAT levels in the striatum of Nrf2 knockout mice than in wild-type at all MPTP doses tested. Activation of the Nrf2 pathway by oral administration of the Nrf2 inducer 3H-1,2-dithiole-3-thione (D3T) to wild-type mice produced partial protection against MPTP-induced neurotoxicity. The protective effect of D3T was not due to a change in MPTP metabolism since the level of the MPTP metabolite MPP+ was not significantly different in the D3T treated striatum relative to vehicle control. Administration of D3T to Nrf2 knockout mice did not protect against MPTP neurotoxicity suggesting that the Nrf2 pathway is necessary for the D3T-mediated attenuation of MPTP neurotoxicity. This study demonstrates the significance of activating intrinsic antioxidative mechanisms in an in vivo model of neurodegeneration. The in vivo activation of the Nrf2 pathway in the brain may be an important strategy to mitigate the effects of oxidative stress in neurodegenerative disorders and neurological disease.

Neuroprotective effects of modafinil in a marmoset Parkinson model: behavioral and neurochemical aspects

The vigilance-enhancing agent modafinil has neuroprotective properties: it prevents striatal ischemic injury, nigrostriatal pathway deterioration after partial transsection and intoxication with 1-methyl-1,2,3,6-tetrahydropyridine. The present study determines the protective effects of modafinil in the marmoset 1-methyl-1,2,3,6-tetrahydropyridine Parkinson model on behavior and on monoamine levels. Twelve marmoset monkeys were treated with a total dose of 6 mg/kg 1-methyl-1,2,3,6-tetrahydropyridine. Simultaneously, six animals received a daily oral dose of modafinil (100 mg/kg) and six animals received vehicle for 27 days. Behavior was observed daily and the locomotor activity, hand-eye coordination, small fast movements, anxiety-related behavior and startle response of the animals were tested twice a week for 3 weeks. Modafinil largely prevented the 1-methyl-1,2,3,6-tetrahydropyridine-induced change in observed behavior, locomotor activity, hand-eye coordination and small fast movements, whereas the vehicle could not prevent the devastating effects of 1-methyl-1,2,3,6-tetrahydropyridine. Dopamine levels in the striatum of the vehicle+1-methyl-1,2,3,6-tetrahydropyridine-treated animals were reduced to 5% of control levels, whereas the dopamine levels of the modafinil+1-methyl-1,2,3,6-tetrahydropyridine-treated animals were reduced to 41% of control levels. The present data suggest that modafinil prevents decrease of movement-related behavior and dopamine levels after 1-methyl-1,2,3,6-tetrahydropyridine intoxication and can be an efficaceous pharmacological intervention in the treatment of Parkinson's disease.

Differential protection against MPTP or methamphetamine toxicity in dopamine neurons by deletion of ppN/OFQ expression

Nociceptin (N/OFQ) is an endogenous neuropeptide that plays a role in the behavioral deficits associated with Parkinson's disease (PD). The purpose of the present study was to characterize the protective effects of prepro (pp)N/OFQ gene deletion against two dopamine toxins, MPTP and methamphetamine (METH). Results demonstrate that ppN/OFQ gene deletion attenuates the loss of both the number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNpc) and loss of TH and vesicular monoamine transporter-2 (VMAT) immunoreactivity in the caudate putamen (CPu) of MPTP-treated mice. This protection was unaffected by age or gender, although, when loss of TH exceeded 90% in 5-6 month-old mice, the protective effect was greatly diminished. In contrast, METH administration preferentially damaged dopaminergic terminals in the CPu with little effect on dopamine neurons in the SNpc, an effect not reversed by ppN/OFQ gene deletion. To determine if N/OFQ and MPP+ act directly and synergistically on dopamine neurons, differentiated SH-SY5Y cells were incubated with N/OFQ and/or MPP+. N/OFQ did not increase MPP+-mediated cell loss, suggesting an indirect action of N/OFQ. These studies demonstrate that inhibition of the endogenous N/OFQ system may represent a new therapeutic target for prevention of neuronal loss associated with PD.

Potential neuroprotective effect of low dose whole-body γ-irradiation against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic toxicity in C57 mice

Low dose whole-body gamma-irradiation is recently reported to confer neuroprotection against optic nerve crush and contusive spinal cord injury. Here, we extended the study and investigated whether the pretreatment of a single low dose whole-body gamma-irradiation may have a preventive effect in MPTP-induced model of PD. One week after the last MPTP treatment, HPLC determination of striatal dopamine and immunostaining for tyrosine hydroxylase (TH), CD11b and GFAP to detect dopamine neurons and associated glial reaction in the substantia nigra pars compacta (SNpc) were performed. MPTP treatment reduced striatal DA levels significantly; nigral TH immunoreactivity was reduced to a lower extent; robust gliosis was also observed in SNpc. We found that 3.5 Gy irradiation but not 5.5 Gy restores the level of DA and its metabolites decreased by MPTP. However, there was no difference in the number of TH positive neurons between 3.5 Gy irradiated and saline treated mice after MPTP treatment. Irradiation also did not have obvious influence on microgliosis and astroglial reaction induced by MPTP treatment. In conclusion, the results presented here demonstrated that low dose whole-body gamma-irradiation renders neuroprotection against MPTP-mediated damage of striatal dopaminergic nerve fibers, though it does not seem to influence the MPTP-induced reduction of SNpc dopaminergic neurons and associated glial responses.

Neuroprotective effect of arundic acid, an astrocyte-modulating agent, in mouse brain against MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes the damage of dopaminergic neurons as seen in Parkinson's disease. Oxidative stress has been as one of several pathogenic hypotheses for Parkinson's disease. Here we investigated whether arundic acid, an astrocyte-modulating agent, can protect against alterations of nitric oxide synthase (NOS) and superoxide dismutase (SOD) expression on MPTP neurotoxicity in mice, utilizing an immunohistochemistry. For this purpose, anti-tyrosine hydroxylase (TH) antibody, anti-dopamine transporter (DAT) antibody, anti-Cu/Zn-SOD antibody, anti-Mn-SOD antibody, anti-nNOS antibody, anti-eNOS antibody and anti-iNOS antibody were used. The present study showed that the arundic acid had a protective effect against MPTP-induced neuronal damage in the striatum and substantia nigra of mice. The protective effect may be, at least in part, caused by the reductions of the levels of reactive nitrogen (RNS) and oxygen species (ROS) against MPTP neurotoxicity. These results suggest that the pharmacological modulation of astrocyte may offer a novel therapeutic strategy for the treatment of Parkinson's disease. Furthermore, our results provide further evidence that a combination of nNOS inhibitors, iNOS inhibitors and free radical scavengers may be effective in the treatment of neurodegenerative diseases. Thus our present results provide valuable information for the pathogenesis of degeneration of the nigrostriatal dopaminergic neuronal pathway.