Retraction notice to "Curcumin restores Nrf2 levels and prevents quinolinic acid-induced neurotoxicity " [JNB 24 (2013) 14-24].

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief as it contains inappropriately manipulated images in Figure 7B. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter, and apologies are offered to the readers of the journal that this problem was not detected during the submission process.

Receptor for AGEs (RAGE) as mediator of NF-kB pathway activation in neuroinflammation and oxidative stress.

Recently, it has been proposed that the receptor for advanced glycation end-products (RAGE) plays a crucial role in damaging cellular processes, such as neuroinflammation, neurodegeneration, excitotoxicity and oxidative stress. RAGE is a multiligand receptor belonging to the immunoglobulin superfamily of cell surface molecules acting as a counter-receptor for diverse molecules. Engagement of RAGE converts a brief pulse of cellular activation into sustained cellular dysfunction and tissue damage. Indeed, the involvement of RAGE in physiopathological processes has been demonstrated for several neurodegenerative diseases. It is the full-length form of RAGE the one constituting the cellular receptor which is able to activate intracellular signals. After the binding of ligands to RAGE, oxidative stress is increased; then, over-expression of RAGE produces vicious cycles that perpetuate oxidative stress and contribute to neuroinflammation by nuclear factor-kB (NF-kB) up-regulation. The NF-kB activation promotes the expression of proinflammatory cytokines, including RAGE expression, to induce a prolonged activation and promotion of signaling mechanisms for cell damage. Because inflammatory and oxidative events have been demonstrated to concertedly interact during neurodegenerative events, this review is aimed to discuss the role of RAGE as mediator of an interaction between inflammation and oxidative stress through NF-kB signaling pathway.

RETRACTED: 6-OHDA-induced apoptosis and mitochondrial dysfunction are mediated by early modulation of intracellular signals and interaction of Nrf2 and NF-κB factors.

6-Hydroxydopamine (6-OHDA) is a neurotoxin that generates an experimental model of Parkinson's disease in rodents and is commonly employed to induce a lesion in dopaminergic pathways. The characterization of those molecular mechanisms linked to 6-OHDA-induced early toxicity is needed to better understand the cellular events further leading to neurodegeneration. The present work explored how 6-OHDA triggers early downstream signaling pathways that activate neurotoxicity in the rat striatum. Mitochondrial function, caspases-dependent apoptosis, kinases signaling (Akt, ERK 1/2, SAP/JNK and p38) and crosstalk between nuclear factor kappa B (NF-κB) and nuclear factor-erythroid-2-related factor 2 (Nrf2) were evaluated at early times post-lesion. We found that 6-OHDA initiates cell damage via mitochondrial complex I inhibition, cytochrome c and apoptosis-inducing factor (AIF) release, as well as activation of caspases 9 and 3 to induce apoptosis, kinase signaling modulation and NF-κB-mediated inflammatory responses, accompanied by inhibition of antioxidant systems regulated by the Nrf2 pathway. Our results suggest that kinases SAP/JNK and p38 up-regulation may play a role in the early stages of 6-OHDA toxicity to trigger intrinsic pathways for apoptosis and enhanced NF-κB activation. In turn, these cellular events inhibit the activation of cytoprotective mechanisms, thereby leading to a condition of general damage.

RETRACTED: Curcumin restores Nrf2 levels and prevents quinolinic acid-induced neurotoxicity.

Neurological diseases comprise a group of heterogeneous disorders characterized by progressive brain dysfunction and cell death. In the next years, these diseases are expected to constitute a world-wide health problem. Because excitotoxicity and oxidative stress are involved in neurodegenerative diseases, it becomes relevant to describe pharmacological therapies designed to activate endogenous cytoprotective systems. Activation of transcription factor Nrf2 stimulates cytoprotective vitagenes involved in antioxidant defense. In this work, we investigated the ability of the antioxidant curcumin to induce transcription factor Nrf2 in a neurodegenerative model induced by quinolinic acid in rats. Animals were administered with curcumin (400 mg/kg, p.o.) for 10 days, and then intrastriatally infused with quinolinic acid (240 nmol) on day 10 of treatment. Curcumin prevented rotation behavior (6 days post-lesion), striatal morphological alterations (7 days post-lesion) and neurodegeneration (1 and 3 days post-lesion) induced by quinolinic acid. Curcumin also reduced quinolinic acid-induced oxidative stress (measured as protein carbonyl content) at 6 h post-lesion. The protective effects of curcumin were associated to its ability to prevent the quinolinic acid-induced decrease of striatal intra-nuclear Nrf2 levels (30 and 120 min post-lesion), and total superoxide dismutase and glutathione peroxidase activities (1 day post-lesion). Therefore, results of this study support the concept that neuroprotection induced by curcumin is associated with its ability to activate the Nrf2 cytoprotective pathway and to increase the total superoxide dismutase and glutathione peroxidase activities.

Structural and functional characterization of Nrf2 degradation by the glycogen synthase kinase 3/ß-TrCP axis.

The transcription factor NF-E2-related factor 2 (Nrf2) is a master regulator of a genetic program, termed the phase 2 response, that controls redox homeostasis and participates in multiple aspects of physiology and pathology. Nrf2 protein stability is regulated by two E3 ubiquitin ligase adaptors, Keap1 and ß-TrCP, the latter of which was only recently reported. Here, two-dimensional (2D) gel electrophoresis and site-directed mutagenesis allowed us to identify two serines of Nrf2 that are phosphorylated by glycogen synthase kinase 3ß (GSK-3ß) in the sequence DSGISL. Nuclear magnetic resonance studies defined key residues of this phosphosequence involved in docking to the WD40 propeller of ß-TrCP, through electrostatic and hydrophobic interactions. We also identified three arginine residues of ß-TrCP that participate in Nrf2 docking. Intraperitoneal injection of the GSK-3 inhibitor SB216763 led to increased Nrf2 and heme oxygenase-1 levels in liver and hippocampus. Moreover, mice with hippocampal absence of GSK-3ß exhibited increased levels of Nrf2 and phase 2 gene products, reduced glutathione, and decreased levels of carbonylated proteins and malondialdehyde. This study establishes the structural parameters of the interaction of Nrf2 with the GSK-3/ß-TrCP axis and its functional relevance in the regulation of Nrf2 by the signaling pathways that impinge on GSK-3.