Neuroprotective Effects of Di-O-demethylcurcumin in Aβ25-35 Induced Neurotoxicity in SK-N-SH Cell Line

Abstract

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder. The hallmark of pathological AD is amyloid plaque which is the accumulation of amyloid β (Aβ) in extracellular neuronal cells, which leads to neurotoxicity via reactive oxygen species (ROS) generation related apoptosis. Neuronal cell death is the main cause of brain dysfunction and cognitive impairment. Aβ activates neuronal death via endoplasmic reticulum (ER) stress, mitochondria apoptosis and neuroinflammatory pathway. This study investigated the underlying mechanisms and effects of di-O-demethylcurcumin in preventing Aβ-induced apoptosis. Pretreatment with di-O-demethylcurcumin for 2 h, which was followed by Aβ25-35 (10 μM) in human neuroblastoma SK-N-SH cells improved cell viability and decreased neuronal cell apoptosis. Di-O-demethylcurcumin also increased the ratio of Bcl-XL/Bax protein, and reduced intracellular ROS level, cytochrome c protein expression, cleaved caspase-9 protein expression, and cleaved caspase-3 protein expression in mitochondria apoptosis pathway. Additionally, di-O-demethylcurcumin treatment also reduced the expression of ER stress protein markers, including protein kinase RNA like endoplasmic reticulum kinase (PERK) phosphorylation, eukaryotic translation initiation factor 2alpha (eIF2α) phosphorylation, inositol-requiring enzyme 1 (IRE1) phosphorylation, X-box-binding protein-1 (XBP-1), activating transcription factor (ATF6), C/EBP homologous protein (CHOP), and cleaved caspase-12 protein. CHOP and cleaved caspase-12 protein are the key mediators of apoptosis. Moreover, di-O-demethylcurcumin activated the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway and the suppression nuclear of factor-κB (NF-κB) signaling pathway and their downstream targets. The results showed that treatment with di-O-demethylcurcumin promoted the translocation of Nrf2 protein from the cytoplasm to the nucleus, increased the expression of Nrf2-ARE pathway-related downstream proteins including hemeoxygenase (HO-1), NAD(P)H:quinone oxidoreductase 1 (NQO-1) and glutamate-cystein ligase catalytic subunit (γ-GCLC), and increased superoxide dismutase (SOD) enzymes activity. On the other hand, di-O-demethylcurcumin suppressed the degradation of IKBα, translocation of the p65 subunit of NF-κB from cytoplasm to nucleus and thereby, attenuated the expression of inducible nitric oxide synthase (iNOS) protein and nitric oxide (NO) production. Taken together, these results suggest that di-O-demethylcurcumin might involve a candidate potential protectant for regulating of endoplasmic reticulum (ER) stress, mitochondria apoptosis and neuroinflammatory pathway induced by Aβ25-35.