Paroxetine prevents loss of nigrostriatal dopaminergic neurons by inhibiting brain inflammation and oxidative stress in an experimental model of Parkinson's disease

The present study examined whether the antidepressant paroxetine promotes the survival of nigrostriatal dopaminergic (DA) neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. MPTP induced degeneration of nigrostriatal DA neurons and glial activation as visualized by tyrosine hydroxylase, macrophage Ag complex-1, and/or glial fibrillary acidic protein immunoreactivity. Real-time PCR, Western blotting, and immunohistochemistry showed upregulation of proinflammatory cytokines, activation of microglial NADPH oxidase and astroglial myeloperoxidase, and subsequent reactive oxygen species production and oxidative DNA damage in the MPTP-treated substantia nigra. Treatment with paroxetine prevented degeneration of nigrostriatal DA neurons, increased striatal dopamine levels, and improved motor function. This neuroprotection afforded by paroxetine was associated with the suppression of astroglial myeloperoxidase expression and/or NADPH oxidase-derived reactive oxygen species production and reduced expression of proinflammatory cytokines, including IL-1beta, TNF-alpha, and inducible NO synthase, by activated microglia. The present findings show that paroxetine may possess anti-inflammatory properties and inhibit glial activation-mediated oxidative stress, suggesting that paroxetine and its analogues may have therapeutic value in the treatment of aspects of Parkinson's disease related to neuroinflammation.

Fluoxetine protects against amyloid-beta toxicity, in part via daf-16 mediated cell signaling pathway, in Caenorhabditis elegans

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and is the most common form of dementia in elderly people. The accumulation of amyloid beta (Abeta) is one of the histopathological hallmarks of AD. Abeta is aggregated to form oligomers which are toxic to neurons and are critical to the onset and progression of AD. In a Caenorhabditis elegans (C. elegans) model of AD, human Abeta is expressed intracellularly in the body wall muscle. The expression and subsequent aggregation of Abeta in the muscle lead to progressive paralysis. Although the mechanism of action is unknown, antidepressants have been used with FDA approved drugs for dementia in AD and have been shown to enhance cognitive function in human and in animal models of AD. We found that the antidepressant fluoxetine, a selective serotonin reuptake inhibitor, significantly delayed Abeta-induced paralysis in the C. elegans model of Abeta toxicity by reducing Abeta oligomers. Our results showed that insulin signaling and DAF-16/FOXO transcription factors were required for fluoxetine-mediated delayed paralysis. We also found that fluoxetine increased thermal stress resistance and extended life span. These findings suggests that fluoxetine may have benefit for the treatment of AD by the reduction of proteotoxicity.

Reduction of beta-amyloid pathology by celastrol in a transgenic mouse model of Alzheimer's disease

Background

Aβ deposits represent a neuropathological hallmark of Alzheimer's disease (AD). Both soluble and insoluble Aβ species are considered to be responsible for initiating the pathological cascade that eventually leads to AD. Therefore, the identification of therapeutic approaches that can lower Aβ production or accumulation remains a priority. NFκB has been shown to regulate BACE-1 expression level, the rate limiting enzyme responsible for the production of Aβ. We therefore explored whether the known NFκB inhibitor celastrol could represent a suitable compound for decreasing Aβ production and accumulation in vivo.

Methods

The effect of celastrol on amyloid precursor protein (APP) processing, Aβ production and NFκB activation was investigated by western blotting and ELISAs using a cell line overexpressing APP. The impact of celastrol on brain Aβ accumulation was tested in a transgenic mouse model of AD overexpressing the human APP695sw mutation and the presenilin-1 mutation M146L (Tg PS1/APPsw) by immunostaining and ELISAs. An acute treatment with celastrol was investigated by administering celastrol intraperitoneally at a dosage of 1 mg/Kg in 35 week-old Tg PS1/APPsw for 4 consecutive days. In addition, a chronic treatment (32 days) with celastrol was tested using a matrix-driven delivery pellet system implanted subcutaneously in 5 month-old Tg PS1/APPsw to ensure a continuous daily release of 2.5 mg/Kg of celastrol.

Results

In vitro, celastrol dose dependently prevented NFκB activation and inhibited BACE-1 expression. Celastrol potently inhibited Aβ_1-40 and Aβ_1-42 production by reducing the β-cleavage of APP, leading to decreased levels of APP-CTFβ and APPsβ. In vivo, celastrol appeared to reduce the levels of both soluble and insoluble Aβ_1-38, Aβ_1-40 and Aβ_1-42. In addition, a reduction in Aβ plaque burden and microglial activation was observed in the brains of Tg PS1/APPsw following a chronic administration of celastrol.

Conclusions

Overall our data suggest that celastrol is a potent Aβ lowering compound that acts as an indirect BACE-1 inhibitor possibly by regulating BACE-1 expression level via an NFκB dependent mechanism. Additional work is required to determine whether chronic administration of celastrol can be safely achieved with cognitive benefits in a transgenic mouse model of AD.