Neuroprotective effects of tetrahydroxystilbene glucoside against rotenone-induced toxicity in PC12 cells

Ultrastructural Changes of Neuroendocrine Pheochromocytoma Cell Line PC-12 Exposed In Vitro to Rotenone

Rotenone is a pesticide used in research for its ability to induce changes similar, in vivo and in vitro, to those observed in Parkinson's disease (PD). This includes a selective death of dopaminergic neurons in the substantia nigra. Nonetheless, the precise mechanism through which rotenone modifies structure and function of neurons remains unclear. The PC12 cells closely resemble dopamine terminal neurons. This makes it a preferred model for studying the morphology of central dopamine neurons and predicting neurotoxicity. In this paper, we investigated the effects of 0.5 µM rotenone for 24-48 h on PC12 cell viability and ultrastructure (TEM), trying to identify primary and more evident alterations that can be related to neuronal damages similar to that seen in animal PD models. Cell viability decreased after 24 h rotenone treatment, with a further decrease after 48 h. Ultrastructural changes included vacuolar degeneration, mitochondrial mild swelling, decrease in the number of neuropeptide granules, and the loss of cell-to-cell adhesion. These findings are in agreement with previous research suggesting that rotenone, by inhibiting energy production and increasing ROS generation, is responsible for significant alterations of the ultrastructure and cell death of PC12 cells. Our data confirm the link between rotenone exposure, neuronal damage, and changes in dopamine metabolism, suggesting its role in the pathogenesis of PD.

Lipid Carrier Nanostructured Astilbin Ameliorates Rotenone-Induced Neurodegeneration in Mice Brain via Modulation of GSK3β-Nrf2 Signaling Pathways

Astilbin is a flavanonol, found in St John's wort (Hypericum perforatum) and many other plants. It has been demonstrated that astilbin contains anti-inflammatory, antioxidant, and immune-suppressive properties. However, the bioavailability of astilbin remains a question for which drug delivery-based nanoparticles can be utilized. We formulated a nanostructured lipid carrier loaded with astilbin (NLC-AS) and tested its effects on the rotenone exposed PC12 cells and in a neurodegenerative mice model of Parkinson's disease (PD) induced by rotenone. Results show that rotenone caused dose-dependent inhibition of PC12 cell growth with about 50% cell death at 2 µM rotenone. Rotenone caused apoptosis in PC12 cells which was reduced to a notable level by NLC-AS through suppression of oxidative stress, especially via elevation of GSH and total antioxidant capacity, and inhibition of monoamine oxidase. Rotenone significantly augmented neurodegeneration in mouse brains by triggering apoptosis and oxidative damage, while NLC-AS treatment halted these processes. Rotenone-exposed mice showed neuronal deficits and impaired neurocognitive functions like loss of memory and learning restrictions which were restored to a remarkable level by NLC-AS administration. The protective effect of NLC-AS was mediated through the inhibition of GSK3β and induction of Nrf2 genes in the brain tissues. These findings suggest that NLC-AS administration may efficiently regulate the signs of PD in mice and prevent neurodegeneration and neurocognitive dysfunctions.

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.