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Docosahexaenoic acid (DHA) is an omega‑3 polyunsaturated fatty acid, derived mainly from fish oil. It is well known that DHA is present in high concentrations in nervous tissue and plays an important role in brain development and neuroprotection. However, the molecular mechanisms underlying its role remain to be fully elucidated. In this study, to enhance our understanding of the pathophysiological role of DHA, we investigated the possible neuroprotective mechanisms of action of DHA against hydrogen peroxide (H2O2)‑induced oxidative damage in a rat pheochromocytoma cell line (PC12). Specifically, we evaluated the viability, oxidation potential, and the expression and production of antioxidant/cytoprotective enzymes, and eventual apoptosis. We found that pre‑treatment with DHA (24 h) protected the cells from H2O2‑induced oxidative damage. In particular, pre‑treatment with DHA: i) Antagonized the consistent decrease in viability observed following exposure to H2O2 for 24 h; ii) reduced the high levels of intracellular reactive oxygen species (ROS) associated with H2O2‑induced oxidative stress; iii) increased the intracellular levels of enzymatic antioxidants [superoxide dismutase (SOD) and glutathione peroxidase (GSH‑Px)] both under basal conditions and following H2O2 exposure; iv) augmented the intracellular levels of reduced glutathione (GSH) and ascorbic acid, while it reduced the malondialdehyde (MDA) levels under conditions of oxidative stress; v) upregulated the expression of nuclear factor (erythroid‑derived 2)‑like 2 (NFE2L2) and its downstream target protein, heme‑oxygenase‑1 (HO‑1); and vi) induced an anti‑apoptotic effect by decreasing Bax and increasing Bcl2 expression. These findings provide evidence suggesting that DHA is able to prevent H2O2‑induced oxidative damage to PC12 cells, which is attributed to its antioxidant and anti‑apoptotic effects via the regulation NFE2L2/HO‑1 signaling. Therefore, DHA may play protective role in neurodegenerative diseases associated with oxidative stress.

Amyloid beta (1-42) peptide is considered responsible for the formation of senile plaques that accumulate in the brains of patients with Alzheimer's disease (AD). In the last years considerable attention has been focused on identifying natural food products, such as phytochemicals that prevent or almost retard the appearance of amyloid beta (1-42)-related neurotoxic effects. In this study, human neuroblastoma cells (IMR-32) was used as system model to evaluate the protective role of rhaponticin (3,3',5-trihydroxy-4'-methoxystilbene 3-O-d-glucoside) a stilbene glucoside extracted from rhubarb roots (Rhei rhizoma) and rhapontigenin, its aglycone metabolite, against amyloid beta (1-42)-dependent toxicity. The obtained results show that rhapontigenin maintains significant cell viability in a dose-dependent manner and it exerts a protective effect on mitochondrial functionality, as evidenced by mitochondrial oxygen consumption experiments. A similar behaviour, but to a lesser extent, has been shown by rhaponticin. The protective mechanism mediated by the two stilbenes could be related to their effect on bcl-2 gene family expression. Bax, a pro-apoptotic gene, resulted down-regulated by the treatment with rhaponticin and rhapontigenin compared with the results obtained in the presence of amyloid beta (1-42) peptide. Conversely, bcl-2, an anti-apoptotic gene, highly down-regulated by amyloid beta (1-42) treatment, resulted expressed in the presence of stilbenes similarly to that shown by control cells. The obtained results support the hypothesis that amyloid beta (1-42)-induced neurotoxicity occurs via bax over-expression, bcl-2 down-regulation, firstly indicating that rhaponticin and its aglycone moiety may alter this cell death pathway. Based on these studies, we suggest that rhaponticin and its main metabolite could be developed as agents for the management of AD.