Dopaminergic neuron loss and exacerbated neuroinflammation are events tightly involved in PD pathology that may result from an inadequate response to toxic, oxidant or inflammatory agents in the basal ganglia. In recent years a protein termed Nrf2 has been characterized as critical regulator of the cell response to these agents, the so-called phase II response. There are compelling evidences from basic and clinical studies indicating that the phase II response is impaired in PD. In this project we will determine if pharmacological intervention on Nrf2 may provide a neuroprotective therapy for PD.
We have reported that sulforaphane, a compound obtained from broccoli sprouts, induces a phase II response in midbrain and striatum though activation of Nrf2. In this project we will analyze the sensitivity of wild type and Nrf2-deficient mice submitted to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We will monitor motor deficits, alterations in phase II gene expression, possible protection of dopaminergic neurons and reduction of inflammation parameters. Based on preliminary work from our and other groups we expect to find a more pronounced parkinsonian lesion in the Nrf2-null mice. Then, we will determine the therapeutic possibilities of sulforaphane in the same experimental setting. Dose and dosing of sulforaphane will be carefully determined to elicit a consistent phase II response in the basal ganglia that could be correlated with neuroprotective and anti-inflammatory activity against MPTP.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
The current pharmacological approach to PD is based on the relief of symptoms, but does not stop the disease progression. In this project, we explore a new approach to neuroprotection based on targeting the transcription factor Nrf2 pharmacologically with sulforaphane. Our project attempts to identify Nrf2 as a new target to endorse a neuroprotective therapy alone or in combination with levodopa.
This study will provide important information on the relevance of phase II reactions in PD pathology. We expect that induction of phase II response in brain will prevent key pathogenic processes that lead to dopaminergic neuron loss in PD, including oxidative and inflammatory stress. If these studies are positive they will have identified Nrf2 as a new target to stop disease progression in PD and will have identified sulforaphane as a starting drug to endorse a Nrf2-based therapy to clinic.
Dopaminergic neuron loss and exacerbated neuroinflammation are events tightly involved in PD pathology that may result from an inadequate response to toxic, oxidant or inflammatory agents in the basal ganglia. The current pharmacological approach to PD is based on the relief of symptoms, but does not stop the disease progression. In recent years a protein termed Nrf2 has been characterized as critical regulator of the cell response to oxidative stress. It induces expression of a group of antioxidant, antixenobiotic and cytoprotective genes that include limiting enzymes of glutathione synthesis (GCL-C), NADPH quinone oxidoreductase (NQO1) and heme oxygenase-1 (HO-1), the so-called phase II response. There are compelling evidences from basic and clinical studies indicating that the phase II response is impaired in PD. Interestingly, this impairment might be restored with SFN, a natural compound obtained from broccoli sprouts, that, as found in this study, induces a phase II response in ventral midbrain and STR though activation of Nrf2.
In this project we studied if pharmacological intervention on Nrf2 might provide a brain protective therapy for PD. The effects of SFN were analyzed in mice exposed for five consecutive days to MPTP (methyl-4-phenyl-1,2,5,6-tetrahydropyridine), a toxin that causes a form of Parkinson's disease in humans, primates and mice. Indeed, already 3 days after the first MPTP injection we observed a significant decrease in the number of dopaminergic neurons in the mouse SN and dopaminergic denervation of STR. Importantly, these changes were more severe in MPTP-only treated mice than in animals treated with MPTP and SFN. Moreover, these effects were associated with the reduced numbers of microglial cells and astrocytes in VMB and STR, what suggests a smaller glial scar and a smaller damage in the animals exposed to MPTP and SFN injections. Additional analysis of the on-going inflammatory reactions allowed us to find out that sulphoraphane efficiently reduced the mRNA levels of pro-inflammatory cytokines, IL-6 and TNF-alpha, in STR. These protective effects of SFN were parallel to the induction of phase II response. We noted increased levels of HO-1, NQO1 and GCL-C proteins. At least for HO-1 this increase was more evident in astrocytes, further supporting role of this glial cell type in nurturing and protecting neurons against oxidative stress.
In summary, pharmacological targeting of Nrf2 with SFN reduced dopaminergic neuron death, gliosis and neuroinflammation following MPTP treatment and it might be effective in the therapy of PD in humans.