Monoamine oxidase–B (MAO-B) has recently emerged as a potential therapeutic target for Alzheimer’s disease (AD) because of its association with aberrant γ-aminobutyric acid (GABA) production in reactive astrocytes. Although short-term treatment with irreversible MAO-B inhibitors, such as selegiline, improves cognitive deficits in AD patients, long-term treatments have shown disappointing results. We show that prolonged treatment with selegiline fails to reduce aberrant astrocytic GABA levels and rescue memory impairment in APP/PS1 mice, an animal model of AD, because of increased activity in compensatory genes for a GABA-synthesizing enzyme, diamine oxidase (DAO). We have developed a potent, highly selective, and reversible MAO-B inhibitor, KDS2010 (IC50 = 7.6 nM; 12,500-fold selectivity over MAO-A), which overcomes the disadvantages of the irreversible MAO-B inhibitor. Long-term treatment with KDS2010 does not induce compensatory mechanisms, thereby significantly attenuating increased astrocytic GABA levels and astrogliosis, enhancing synaptic transmission, and rescuing learning and memory impairments in APP/PS1 mice.

Although the etiology of Parkinson's disease (PD) remains elusive, recent studies suggest that oxidative stress contributes to the cascade leading to dopaminergic (DAergic) neurodegeneration. The Nrf2 signaling is the main pathway responsible for cellular defense system against oxidative stress. Nrf2 is a transcription factor that regulates environmental stress response by inducing expression of antioxidant enzyme genes. We have synthesized novel vinyl sulfone derivatives. They exhibited a broad range of activities in inducing HO-1, whose gene expression is under the control of Nrf2. Among them, compound 12g was confirmed to activate Nrf2 and induce expression of the Nrf2-dependent antioxidant enzymes NQO1, GCLC, GLCM, and HO-1, at both mRNA and protein levels in DAergic neuronal cells. This was accompanied by protection of DAergic neurons in both in vitro and MPTP-induced in vivo models of PD. In addition, compound 12g effectively resulted in attenuation of the PD-associated behavioral deficits in the mouse model.

Highlights d Reactive astrocytes in SNpc produce excessive GABA via MAO-B in animal models of PD d Aberrant tonic inhibition causes reduced DA production in neurons and motor deficits d Dormant neurons are rescued by MAO-B inhibition or optogenetic neuronal activation

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BACKGROUND AND PURPOSENeuroinflammation through microglial activation is involved in the pathogenesis of neurodegenerative diseases including Parkinson's disease (PD), a major neurodegenerative disorder characterized by dopaminergic neuronal death in the substantia nigra. We examined our novel synthetic compound VSC2 for its anti-inflammatory properties towards development of a PD therapy. EXPERIMENTAL APPROACHWe tested the effects of VSC2 on production of various NF-κB-dependent proinflammatory molecules and Nrf2-dependent antioxidant enzymes in BV-2 microglia and in vivo. KEY RESULTSThe vinyl sulfone compound, VSC2, most effectively suppressed the production of NO in LPS-activated microglia. It also down-regulated expression of inducible NOS (iNOS), COX-2, IL-1β and TNF-α and inhibited nuclear translocalization and transcriptional activity of NF-κB. VSC2 increased total and nuclear Nrf2 levels, induced Nrf2 transcriptional activity and was bound to Keap1 with high affinity. Expression of the Nrf2-regulated antioxidant enzyme genes NAD(P)H quinone oxidoreducase-1 (NQO-1), haem oxygenase-1 (HO-1) and glutamylcysteine ligase (GCL) were up-regulated by VSC2. In the MPTP mouse model of PD, oral administration of VSC2 decreased the number of activated microglia in the substantia nigra, lowered the levels of iNOS, COX-2 and IL-1β, and protected the dopaminergic neurons. VSC2 also elevated the levels of NQO1, HO-1, GCL and Nrf2 in the nigrostriatal area. CONCLUSIONS AND IMPLICATIONSVSC2 has both anti-inflammatory and antioxidant properties and prevented neuroinflammation in microglia and in an animal model of PD. This suggests VSC2 as a potential candidate for PD therapy. Abbreviations

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