Discovery of the first dual GSK3β inhibitor/Nrf2 inducer. A new multitarget therapeutic strategy for Alzheimer's disease

A neuroprotective role of kaempferol against chlorpyrifos-induced oxidative stress and memory deficits in rats via GSK3β-Nrf2 signaling pathway

Chlorpyrifos (CPF) is an agricultural pesticide and a potential food contaminant, which causes neurotoxicity. Here, we aimed at exploring the link between the repeated exposure to CPF and memory dysfunction in rats and the possible protective effect of kaempferol, a flavonoid with appreciable antioxidant and anti-inflammatory activities. Rats were divided into: Control group (received drug vehicles for 14 days); CPF-treated group (received subcutaneous 18 mg/kg BW of CPF daily for 14 days and CPF + Kaempferol treated group (received the same CPF dose +21 mg/kg BW of Kaempferol intraperitoneally for 14 days. On the 14^th day, Y-maze and novel target recognition behavioral tests were employed to evaluate memory deficits. 24 h after the last dose of CPF, animals were sacrificed, and brain tissues were used for the determination of oxidative stress biomarkers and gene expression levels of GSK3β and Nrf2. The results revealed that CPF-treated rats suffered from severe deterioration of spatial and non-spatial memory functions with low activities of antioxidant enzymes and acetylcholinesterase (AChE). The administration of kaempferol significantly protected against CPF-induced neuronal damage, increased the activities of antioxidant enzymes and AChE and induced a better performance in the behavioral tests. The protective effect of kaempferol was mediated through the inhibition of GSK3β gene expression and the induction of Nrf2 expression in the brain tissues. In conclusion, the repeated exposure to CPF is associated with oxidative stress and memory deficits in rats. However, kaempferol administration effectively alleviated CPF- induced brain toxicity, possibly through the modulation of GSK3β-Nrf2 signaling pathway.

Novel Protein Kinase Inhibitors Related to Tau Pathology Modulate Tau Protein-Self Interaction Using a Luciferase Complementation Assay

The current number of drugs available for the treatment of Alzheimer’s disease (AD) is strongly limited and their benefit for therapy is given only in the early state of the disease. An effective therapy should affect those processes which mainly contribute to the neuronal decay. There have been many approaches for a reduction of toxic Aβ peptides which mostly failed to halt cognitive deterioration in patients. The formation of neurofibrillary tangles (NFT) and its precursor tau oligomers have been suggested as main cause of neuronal degeneration because of a direct correlation of their density to the degree of dementia. Reducing of tau aggregation may be a viable approach for the treatment of AD. NFT consist of hyperphosphorylated tau protein and tau hyperphosphorylation reduces microtubule binding. Several protein kinases are discussed to be involved in tau hyperphosphorylation. We developed novel inhibitors of three protein kinases (gsk-3β, cdk5, and cdk1) and discussed their activity in relation to tau phosphorylation and on tau–tau interaction as a nucleation stage of a tau aggregation in cells. Strongest effects were observed for those inhibitors with effects on all the three kinases with emphasis on gsk-3β in nanomolar ranges.

Development of bioresources in Okinawa: understanding the multiple targeted actions of antioxidant phytochemicals

In research to develop healthy foods or preventive medicines from edible and medicinal herbs in Okinawa, we focused on the antioxidant activities of those bioresources. We first confirmed that the herbal antioxidant activities of such herbs increased upon ultraviolet irradiation treatment. This observation explains the high antioxidant activity of Okinawan vegetables, which grow under exposure to stronger ultraviolet light compared with those in other prefectures in Japan. Antidiabetic, hepatoprotective, cancer preventive, and cardioprotective actions were clarified using herbal extracts, and quercetin, chlorogenic acid, and gallic acid derivatives were isolated as antioxidant components from the herbs. Dimerumic acid was also isolated from the mold Monascus anka. All these antioxidants showed strong radical scavenging activities in vitro and beneficial effects in animal models. However, the concentrations of these compounds used in vivo seemed to be too low to have a physiologically important antioxidant effect based on their radical scavenging activities in vitro. Therefore, I performed a literature survey of antioxidant activities in vivo. Accumulating evidence has emerged that antioxidant phytochemicals show not only radical scavenging activities in vitro but also pleiotropic actions in vivo. The multitargeted, beneficial effects of antioxidant phytochemicals can be rationally explained using the xenohormesis concept, in which phytochemicals are the products of plant evolutionary adaptation to stress in plants, and their ability to induce a stress-adaptive response has been evolutionarily conserved in animals.

NRF2 and the Hallmarks of Cancer

The transcription factor NRF2 is the master regulator of the cellular antioxidant response. Though recognized originally as a target of chemopreventive compounds that help prevent cancer and other maladies, accumulating evidence has established the NRF2 pathway as a driver of cancer progression, metastasis, and resistance to therapy. Recent studies have identified new functions for NRF2 in the regulation of metabolism and other essential cellular functions, establishing NRF2 as a truly pleiotropic transcription factor. In this review, we explore the roles of NRF2 in the hallmarks of cancer, indicating both tumor suppressive and tumor-promoting effects.

Current progress on antioxidants incorporating the pyrazole core

The search of new antioxidants, as drugs candidates, is an active field of medicinal chemistry. The synthesis of compounds with antioxidant potential has increased in recent years and a high number of structurally diverse compounds have been published. This review aims to show the current state-of-the-art on the development of antioxidant compounds incorporating the pyrazole pharmacophore. It is a well-timed review driven by the increasing number of papers, on this issue, that have been published since the beginning of the 21st century (from 2000 to 2017). The aim is to look deeper into the structures already published in the literature containing the pyrazole core as the unique pharmacophore or combined with other pharmacophores and see the relationship between the presence of this five-membered nitrogen heterocycle and the behaviour of the compounds as potential antioxidant agents. An attempt was made to whenever possible establish structure-activity relationships that could help the design of new and more potent antioxidant agents containing this important pharmacophore.

Procyanidin B2 mitigates behavioral impairment and protects myelin integrity in cuprizone-induced schizophrenia in mice

Numerous studies have suggested that neuropathological changes in schizophrenia may be related to damage to white matter or demyelination. Procyanidin B2, which is a constituent of many fruits such as grapes and strawberries, has various biological activities such as anti-inflammatory and anti-tumor activity, as has been reported. This study aimed to estimate the effects of procyanidin B2 on behavioral impairment and the protection of myelin integrity in a cuprizone-induced schizophrenia model. Mice were exposed to cuprizone (0.2% w/w in chow) for five weeks to induce schizophrenia-like behavioral changes and demyelination. Procyanidin B2 (20 or 100 mg kg⁻¹ day⁻¹) or vehicle was administered orally to mice after withdrawal from cuprizone. Behavioral impairment was detected with an open-field test, a rotarod test and a Morris water maze. Myelin integrity was assessed using LFB staining and MBP expression, including immunofluorescence and western blotting. In addition, enhancements in the expression of HO-1 and NQO1 suggested that procyanidin B2 may regulate oxidative homeostasis via promoting the translation of Nrf2 to the nucleus. Data indicated that procyanidin B2 could mitigate behavioral impairment and protect myelin integrity in the cuprizone-induced model via regulating oxidative stress by activating Nrf2 signaling.

Numerous studies have suggested that neuropathological changes in schizophrenia may be related to damage to white matter or demyelination.

Neuroprotective effect of a new variant of Epo nonhematopoietic against oxidative stress

Human erythropoietin is mainly recognized for its hematopoietic function; however, by binding to its receptor (EpoR), it can activate different signaling pathways as STAT, PI3K, MAPK and RAS to increase cellular differentiation or provide neuroprotective effects, among others. A recombinant human erythropoietin variant with low glycosylation and without hematopoietic effect (EpoL) was purified from skimmed goat milk. Recombinant human erythropoietin (Epo) was obtained from CHO cell line and used as control to compare EpoL effects. Neuroprotection studies were performed in PC12 cells and rat hippocampal slices. Cells were pretreated during 1h with EpoL or Epo and exposed to oxidative agents (H2O2 or FCCP); cell viability was assayed at the end of the experiment by the MTT method. Hippocampal slices were exposed to 15min of oxygen and glucose deprivation (OGD) and the neuroprotective drugs EpoL or Epo were incubated for 2h post-OGD in re-oxygenated medium. Cell cultures stressed with oxidative agents, and pretreated with EpoL, showed neuroprotective effects of 30% at a concentration 10 times lower than that of Epo. Moreover, similar differences were observed in OGD ex vivo assays. Neuroprotection elicited by EpoL was lost when an antibody against EpoR was present, indicating that its effect is EpoR-dependent. In conclusion, our results suggest that EpoL has a more potent neuroprotective profile than Epo against oxidative stress, mediated by activation of EpoR, thus EpoL represents an important target to develop a potential biopharmaceutical to treat different central nervous system pathologies related to oxidative stress such as stroke or neurodegenerative diseases.

Kelch-like ECH-associated protein 1 (KEAP1) differentially regulates nuclear factor erythroid-2-related factors 1 and 2 (NRF1 and NRF2)

Nuclear factor erythroid-2-related factor 1 (NRF1) and NRF2 are essential for maintaining redox homeostasis and coordinating cellular stress responses. They are highly homologous transcription factors that regulate the expression of genes bearing antioxidant-response elements (AREs). Genetic ablation of NRF1 or NRF2 results in vastly different phenotypic outcomes, implying that they play different roles and may be differentially regulated. Kelch-like ECH-associated protein 1 (KEAP1) is the main negative regulator of NRF2 and mediates ubiquitylation and degradation of NRF2 through its NRF2-ECH homology-like domain 2 (Neh2). Here, we report that KEAP1 binds to the Neh2-like (Neh2L) domain of NRF1 and stabilizes it. Consistently, NRF1 is more stable in KEAP1^+/+ than in KEAP1^-/- isogenic cell lines, whereas NRF2 is dramatically stabilized in KEAP1^-/- cells. Replacing NRF1's Neh2L domain with NRF2's Neh2 domain renders NRF1 sensitive to KEAP1-mediated degradation, indicating that the amino acids between the DLG and ETGE motifs, not just the motifs themselves, are essential for KEAP1-mediated degradation. Systematic site-directed mutagenesis identified the core amino acid residues required for KEAP1-mediated degradation and further indicated that the DLG and ETGE motifs with correct spacing are insufficient as a KEAP1 degron. Our results offer critical insights into our understanding of the differential regulation of NRF1 and NRF2 by KEAP1 and their different physiological roles.

Dietary Total Prenylflavonoids from the Fruits of Psoralea corylifolia L. Prevents Age-Related Cognitive Deficits and Down-Regulates Alzheimer's Markers in SAMP8 Mice

Alzheimer's disease (AD) is a serious threat for the aging society. In this study, we examined the preventive effect of the total prenylflavonoids (TPFB) prepared from the dried fruits of Psoralea corylifolia L., using an age-related AD mouse model SAMP8. We found that long-term dietary TPFB at 50 mg/kg·day significantly improved cognitive performance of the SAMP8 mice in Morris water maze tests, similar to 150 mg/kg·day of resveratrol, a popular neuro-protective compound. Furthermore, TPFB treatment showed significant improvements in various AD markers in SAMP8 brains, which were restored to near control levels of the normal mice, SAMR1. TPFB significantly reduced the level of amyloid β-peptide 42 (Aβ42), inhibited hyperphosphorylation of the microtubule-associated protein Tau, induced phosphorylation of Ser9 of the glycogen synthase kinase 3β (GSK-3β), and decreased the expression of the proinflammatory cytokines TNFα, IL-6, and IL-1β. Finally, TPFB also markedly reduced the level of serum derivatives of reactive oxygen metabolites (d-ROMs), a biomarker of oxidative stress in vivo. These results showed that dietary TPFB could effectively prevent age-related cognitive deficits and AD-like neurobiochemical changes, and may have a potential role in the prevention of Alzheimer's disease.

GSK-3β, a double-edged sword in Nrf2 regulation: Implications for neurological dysfunction and disease

In the past decade, it has become evident that glycogen synthase kinase 3β (GSK-3β) modulates the nuclear factor erythroid 2-related factor 2 (Nrf2) oxidative stress response. GSK-3β functions as an inhibitor, both directly in the activation and indirectly in the post-induction of Nrf2. The incidence of oxidative stress in neurological dysfunction and disease has made this signaling pathway an attractive therapeutic target. There is minimal evidence, however, to support a distinctive function for GSK-3β mediated Nrf2 inhibition in nervous system decline, apart from the typical oxidative stress response. In both Alzheimer's disease and brain ischemia, this pathway has been explored for potential benefits on disease etiology and advancement. Presently, it is unclear whether GSK-3β mediated Nrf2 inhibition markedly influences these disease states. Furthermore, the potential that each has unique function in neurodegenerative decline is unsubstantiated.

Are Astrocytes the Predominant Cell Type for Activation of Nrf2 in Aging and Neurodegeneration?

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that regulates hundreds of antioxidant genes, and is activated in response to oxidative stress. Given that many neurodegenerative diseases including Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, Huntington’s disease and multiple sclerosis are characterised by oxidative stress, Nrf2 is commonly activated in these diseases. Evidence demonstrates that Nrf2 activity is repressed in neurons in vitro, and only cultured astrocytes respond strongly to Nrf2 inducers, leading to the interpretation that Nrf2 signalling is largely restricted to astrocytes. However, Nrf2 activity can be observed in neurons in post-mortem brain tissue and animal models of disease. Thus this interpretation may be false, and a detailed analysis of the cell type expression of Nrf2 in neurodegenerative diseases is required. This review describes the evidence for Nrf2 activation in each cell type in prominent neurodegenerative diseases and normal aging in human brain and animal models of neurodegeneration, the response to pharmacological and genetic modulation of Nrf2, and clinical trials involving Nrf2-modifying drugs.