The etiology of Parkinson disease (PD) is unclear but may involve environmental toxins such as pesticides leading to dysfunction of the ubiquitin proteasome system (UPS). Here, we measured the relative toxicity of ziram (a UPS inhibitor) and analogs to dopaminergic neurons and examined the mechanism of cell death. UPS (26 S) activity was measured in cell lines after exposure to ziram and related compounds. Dimethyl-and diethyldithiocarbamates including ziram were potent UPS inhibitors. Primary ventral mesencephalic cultures were exposed to ziram, and cell toxicity was assessed by staining for tyrosine hydroxylase (TH) and NeuN antigen. Ziram caused a preferential damage to TH؉ neurons and elevated ␣-synuclein levels but did not increase aggregate formation. Mechanistically, ziram altered UPS function through interfering with the targeting of substrates by inhibiting ubiquitin E1 ligase. Sodium dimethyldithiocarbamate administered to mice for 2 weeks resulted in persistent motor deficits and a mild reduction in striatal TH staining but no nigral cell loss. These results demonstrate that ziram causes selective dopaminergic cell damage in vitro by inhibiting an important degradative pathway implicated in the etiology of PD. Chronic exposure to widely used dithiocarbamate fungicides may contribute to the development of PD, and elucidation of its mechanism would identify a new potential therapeutic target. Parkinson disease (PD)2 is a common neurodegenerative disease characterized by relatively selective degeneration of dopaminergic (DA) neurons in the substantia nigra (nigrostriatal neurons). The etiology probably involves both environmental and genetic factors including pesticide exposure (1-3). Hundreds of pesticides are used alone or in combinations making it difficult to separate individual effects. Because no individual pesticide has been established by epidemiologic studies, we chose to perform an unbiased screen of potential toxicants for their ability to interfere with the ubiquitin-proteasome system (UPS), a biological pathway implicated in the etiology of PD. Impaired UPS activity has been reported in the brains of patients with PD, and mutations in two UPS genes, Parkin and UCHL-1, cause rare genetic forms of PD (4). Although these results are not universally reproduced (5-7), in some studies administration of UPS inhibitors to rodents recapitulates many of the clinical and pathological aspects of PD (8 -10). We hypothesized that chronic pesticide exposure may increase the risk of developing PD by inhibiting the UPS. We screened several pesticides for their ability to inhibit the UPS and found a number of toxicants that can lower activity at relevant concentrations (11). We then focused on dithiocarbamate fungicides because they were found to be one of the most potent UPS inhibitors and are widely used in crop protection.In the present study, zinc dimethyldithiocarbamate (ziram) was one of several dimethyl-and diethyldithiocarbamates found to inhibit the UPS at 0.15-1 M. Furthermore, ziram increased ␣-syn...

Background: ␥-Secretase modulators (GSMs) hold potential as disease modifiers in Alzheimer disease; however, their mechanism of action is not completely understood. Results: Second generation in vivo active GSMs were described and shown to modulate A␤ production via a non-APP targeting mechanism, different from the NSAIDs class of GSMs. Conclusion: A growing class of second generation GSMs appears to target ␥-secretase and displays a different mechanism of action compared with first generation GSMs. Significance: The identification of in vivo active non-APP targeting second generation GSMs may facilitate the development of novel therapeutics against AD.

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Background:The ␥-secretase complex is a drug target in the treatment of Alzheimer disease (AD). Results: Two novel second generation ␥-secretase modulators (GSMs) modulate both N␤ and A␤ but not Notch intracellular domain (NICD) production. Conclusion: Second generation and NSAID-based GSMs have different modes of action regarding Notch processing. Significance: GSMs that do not affect NICD signaling are essential for the development of tolerable AD therapeutics.

␥-Secretase inhibition represents a major therapeutic strategy for lowering amyloid ␤ (A␤) peptide production in Alzheimer's disease (AD).Progress toward clinical use of ␥-secretase inhibitors has, however, been hampered due to mechanism-based adverse events, primarily related to impairment of Notch signaling. The ␥-secretase inhibitor MRK-560 represents an exception as it is largely tolerable in vivo despite displaying only a small selectivity between A␤ production and Notch signaling in vitro. In exploring the molecular basis for the observed tolerability, we show that MRK-560 displays a strong preference for the presenilin 1 (PS1) over PS2 subclass of ␥-secretases and is tolerable in wild-type mice but causes dose-dependent Notch-related side effect in PS2-deficient mice at drug exposure levels resulting in a substantial decrease in brain A␤ levels. This demonstrates that PS2 plays an important role in mediating essential Notch signaling in several peripheral organs during pharmacological inhibition of PS1 and provide preclinical in vivo proof of concept for PS2-sparing inhibition as a novel, tolerable and efficacious ␥-secretase targeting strategy for AD.