Aromatic-Turmerone Analogs Protect Dopaminergic Neurons in Midbrain Slice Cultures through Their Neuroprotective Activities.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra. The inflammatory activation of microglia participates in dopaminergic neurodegeneration in PD. Therefore, chemicals that inhibit microglial activation are considered to have therapeutic potential for PD. Aromatic (ar)-turmerone is a main component of turmeric oil extracted from Curcuma longa and has anti-inflammatory activity in cultured microglia. The aims of the present study are (1) to investigate whether naturally occurring S-enantiomer of ar-turmerone (S-Tur) protects dopaminergic neurons in midbrain slice cultures and (2) to examine ar-turmerone analogs that have higher activities than S-Tur in inhibiting microglial activation and protecting dopaminergic neurons. R-enantiomer (R-Tur) and two analogs showed slightly higher anti-inflammatory effects in microglial BV2 cells. S- and R-Tur and these two analogs reversed dopaminergic neurodegeneration triggered by microglial activation in midbrain slice cultures. Unexpectedly, this neuroprotection was independent of the inhibition of microglial activation. Additionally, two analogs more potently inhibited dopaminergic neurodegeneration triggered by a neurotoxin, 1-methyl-4-phenylpyridinium, than S-Tur. Taken together, we identified two ar-turmerone analogs that directly and potently protected dopaminergic neurons. An investigation using dopaminergic neuronal precursor cells suggested the possible involvement of nuclear factor erythroid 2-related factor 2 in this neuroprotection.

Involvement of exosomes in dopaminergic neurodegeneration by microglial activation in midbrain slice cultures.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive degeneration of dopamine neurons in the substantia nigra. Microglial activation is frequently observed in the brains of patients with PD and animal models. Interferon-γ (IFN-γ)/lipopolysaccharide (LPS) treatment triggers microglial activation and the reduction of dopamine neurons in midbrain slice cultures. We have previously reported that nitric oxide (NO) is mainly involved in this dopaminergic degeneration. However, this degeneration was not completely suppressed by the inhibition of NO synthesis, suggesting that factors other than NO also contribute to dopaminergic neurodegeneration. Exosomes are extracellular vesicles with diameters of 40-200 nm that contain various proteins and micro RNAs and are regarded as a novel factor that mediates cell-to-cell interactions. Previous studies have demonstrated that exosome release is enhanced by microglial stimulation and that microglia-derived exosomes increases neuronal apoptosis. In the present study, we investigated whether exosomes are involved in dopaminergic neurodegeneration triggered by microglial activation in midbrain slice cultures. IFN-γ/LPS treatment to the midbrain slice cultures activated microglia, increased exosomal release, and decreased dopamine neurons. GW4869, an inhibitor of a neutral sphingomyelinase 2, decreased exosomal release and significantly prevented dopaminergic neurodegeneration by IFN-γ/LPS without affecting NO production. In contrast, D609, an inhibitor of sphingomyelin synthase and NO synthase, did not affect dopaminergic neurodegeneration, although it strongly inhibited NO production. The protective effect mediated by inhibition of NO synthase would be counteracted by enhanced exosomal release caused by D609 treatment. In addition, dopaminergic neurodegeneration is triggered by the treatment of exosomes isolated from culture media of IFN-γ/LPS-treated slices. These results suggest that exosomes are involved in dopaminergic neurodegeneration by microglial activation.