Hesperidin attenuates learning and memory deficits in APP/PS1 mice through activation of Akt/Nrf2 signaling and inhibition of RAGE/NF-κB signaling

The neuroprotective effect of deep brain stimulation at nucleus basalis of Meynert in transgenic mice with Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the most common type of dementia and mainly treated by drugs, while the therapeutic outcomes are very limited. This study aimed to determine the optimized parameters of deep brain stimulation (DBS) which was applied to the treatment of AD and propose the involved mechanisms.

METHODS

Amyloid-β precursor protein/Presenilin1 (APP/PS1) transgenic mice were used and received DBS at nucleus basalis of Meynert (NBM). The optimized parameters of DBS were determined by using different stimulation frequencies, durations and ages of mice under Morris water maze test. The involved mechanisms and the possible signal pathways were also investigated.

RESULTS

The optimized parameters for DBS were high frequency (100 Hz) for 21 days starting from early age (4 months old). Under the above parameters, the soluble Aβ40 and Aβ42 in the hippocampus and cortex were down-regulated significantly. DBS increased survival neurons and reduced apoptotic cells in the hippocampus and cortex. Meanwhile, the apoptosis-related proteins caspase-3, caspase-8 and Bid were down-regulated. Moreover, DBS caused a significant increase of superoxide dismutase, glutathione peroxidase and choline acetyltransferase activity as well as a decrease of methane dicarboxylic aldehyde content and acetylcholine esterase activity. Phosphorylation of Akt (p-Akt)/total Akt (t-Akt) was up-regulated while p-extracellular signal-regulated kinase 1/2 (ERK1/2)/t-ERK1/2 was down-regulated. The neuroprotective effect of DBS was attenuated by their inhibitors.

CONCLUSIONS

NBM-DBS starting from 4 months of age for 21 days at a high frequency (100 Hz) has therapeutic effects on AD through activating phosphatidylinositol 3'-kinase (PI3K)/Akt pathway and inhibiting ERK1/2 pathway.

Hesperidin protects against IL-1β-induced inflammation in human osteoarthritis chondrocytes

Hesperidin is a vitamin P flavonoid compound primarily present in citrus fruits, which possesses an anti-inflammatory effect. The functional role of hesperidin in interleukin (IL)-1β-stimulated human osteoarthritis (OA) chondrocytes is still unknown. In the present study, anti-inflammatory effects of hesperidin in IL-1β-stimulated chondrocytes were investigated. The results demonstrated that hesperidin treatment markedly decreased nitric oxide and prostaglandin E2 production and markedly downregulated inducible nitric oxide synthase and cyclooxygenase-2 expression in IL-1β-stimulated OA chondrocytes. In addition, hesperidin markedly reduced IL-1β-induced matrix metalloproteinase (MMP)-3 and MMP-13 expression in human OA chondrocytes. Furthermore, hesperidin markedly decreased the activation of nuclear factor (NF)-κB in human OA chondrocytes. In conclusion, it was revealed for the first time that hesperidin inhibited inflammatory responses in IL-1β-stimulated human chondrocytes, potentially through inhibiting the activation of the NF-κB signaling pathway. These data suggest that hesperidin may be a potential agent for the treatment of OA.

The effect of Bacopa monnieri on gene expression levels in SH-SY5Y human neuroblastoma cells

Bacopa monnieri is a plant used as a nootropic in Ayurveda, a 5000-year-old system of traditional Indian medicine. Although both animal and clinical studies supported its role as a memory enhancer, the molecular and cellular mechanism underlying Bacopa's nootropic action are not understood. In this study, we used deep sequencing (RNA-Seq) to identify the transcriptome changes upon Bacopa treatment on SH-SY5Y human neuroblastoma cells. We identified several genes whose expression levels were regulated by Bacopa. Biostatistical analysis of the RNA-Seq data identified biological pathways and molecular functions that were regulated by Bacopa, including regulation of mRNA translation and transmembrane transport, responses to oxidative stress and protein misfolding. Pathway analysis using the Ingenuity platform suggested that Bacopa may protect against brain damage and improve brain development. These newly identified molecular and cellular determinants may contribute to the nootropic action of Bacopa and open up a new direction of investigation into its mechanism of action.

Flavonoid Hesperidin Induces Synapse Formation and Improves Memory Performance through the Astrocytic TGF-β1

Synapse formation and function are critical events for the brain function and cognition. Astrocytes are active participants in the control of synapses during development and adulthood, but the mechanisms underlying astrocyte synaptogenic potential only began to be better understood recently. Currently, new drugs and molecules, including the flavonoids, have been studied as therapeutic alternatives for modulation of cognitive processes in physiological and pathological conditions. However, the cellular targets and mechanisms of actions of flavonoids remain poorly elucidated. In the present study, we investigated the effects of hesperidin on memory and its cellular and molecular targets in vivo and in vitro, by using a short-term protocol of treatment. The novel object recognition test (NOR) was used to evaluate memory performance of mice intraperitoneally treated with hesperidin 30 min before the training and again before the test phase. The direct effects of hesperidin on synapses and astrocytes were also investigated using in vitro approaches. Here, we described hesperidin as a new drug able to improve memory in healthy adult mice by two main mechanisms: directly, by inducing synapse formation and function between hippocampal and cortical neurons; and indirectly, by enhancing the synaptogenic ability of cortical astrocytes mainly due to increased secretion of transforming growth factor beta-1 (TGF-β1) by these cells. Our data reinforces the known neuroprotective effect of hesperidin and, by the first time, characterizes its synaptogenic action on the central nervous system (CNS), pointing astrocytes and TGF-β1 signaling as new cellular and molecular targets of hesperidin. Our work provides not only new data regarding flavonoid’s actions on the CNS but also shed light on possible new therapeutic alternative based on astrocyte biology.

Thymol improves high-fat diet-induced cognitive deficits in mice via ameliorating brain insulin resistance and upregulating NRF2/HO-1 pathway

The impaired insulin signaling has been recognized as a common pathogenetic mechanism between diabetes and Alzheimer's disease (AD). In the progression of AD, brain is characterized by defective insulin receptor substrate-1 (IRS-1) and increased oxidative stress. Thymol, a monoterpene phenol isolated from medicinal herbs, has exhibited robust neuroprotective effects. The present study was designed to investigate the protective effect of thymol on HFD-induced cognitive deficits, and explore the possible mechanisms. C57BL/6 J mice were fed for 12 weeks with either HFD or normal diet. The mice fed with HFD were dosed with metformin (200 mg/kg) or thymol (20, 40 mg/kg) daily. It was observed that thymol treatment significantly reversed the gain of body weight and peripheral insulin resistance induced by HFD. Meanwhile, thymol improved the cognitive impairments in the Morris Water Maze (MWM) test and decreased HFD-induced Aβ deposition and tau hyperphosphorylation in the hippocampus, which may be correlated with the inhibition of hippocampal oxidative stress and inflammation. In addition, thymol down-regulated the level of P-Ser307 IRS-1, and hence enhancing the expression of P-Ser473 AKT and P-Ser9 GSK3β. We further found that the protective effects of thymol on cognitive impairments were associated with the up-regulation of nuclear respiratory factor (Nrf2)/heme oxygenase-1(HO-1) pathway. In conclusion, thymol exhibited beneficial effects on HFD-induced cognitive deficits through improving hippocampal insulin resistance, and activating Nrf2/HO-1 signaling.

Genetic ablation of the p66Shc adaptor protein reverses cognitive deficits and improves mitochondrial function in an APP transgenic mouse model of Alzheimer's disease

The mammalian ShcA adaptor protein p66^Shc is a key regulator of mitochondrial reactive oxygen species (ROS) production and has previously been shown to mediate amyloid β (Aβ)-peptide-induced cytotoxicity in vitro. Moreover, p66^Shc is involved in mammalian longevity and lifespan determination as revealed in the p66^Shc knockout mice, which are characterized by a 30% prolonged lifespan, lower ROS levels and protection from age-related impairment of physical and cognitive performance. In this study, we hypothesized a role for p66^Shc in Aβ-induced toxicity in vivo and investigated the effects of genetic p66^Shc deletion in the PSAPP transgenic mice, an established Alzheimer's disease mouse model of β-amyloidosis. p66^Shc-ablated PSAPP mice were characterized by an improved survival and a complete rescue of Aβ-induced cognitive deficits at the age of 15 months. Importantly, these beneficial effects on survival and cognitive performance were independent of Aβ levels and amyloid plaque deposition, but were associated with improved brain mitochondrial respiration, a reversal of mitochondrial complex I dysfunction, restored adenosine triphosphate production and reduced ROS levels. The results of this study support a role for p66^Shc in Aβ-related mitochondrial dysfunction and oxidative damage in vivo, and suggest that p66^Shc ablation may be a promising novel therapeutic strategy against Aβ-induced toxicity and cognitive impairment.

Therapeutic role of sirtuins in neurodegenerative disease and their modulation by polyphenols

Searching for effective therapeutic agents‏‎ to ‎‏prevent‏ ‏neurodegeneration ‎is a challenging task due ‎to ‎the growing list of neurodegenerative disorders associated with a multitude of inter-related pathways.‎ The induction and inhibition of several different signaling pathways has been shown to slow down and/or attenuate ‎neurodegeneration and decline in cognition and locomotor function. Among these signaling pathways, a new class of enzymes known as sirtuins or silent information regulators of gene transcription has been shown to play important regulatory roles in the ageing process. SIRT1, a nuclear sirtuin, has received ‎particular interest due to its role as a deacetylase for several metabolic and signaling proteins involved in stress response, apoptosis, mitochondrial function, self-renewal, and ‎neuroprotection. ‎A new strategy to treat ‎neurodegenerative diseases is targeted therapy. In ‎this ‎paper, we‎ ‎ reviewed up-to-date findings regarding the targeting of ‎SIRT1 by polyphenolic ‎compounds,‎ ‎as a ‎new ‎‏approach in the search for novel, safe and effective treatments for ‎ ‎neurodegenerative ‎diseases. ‎.

RAGE Expression and ROS Generation in Neurons: Differentiation versus Damage

RAGE is a multiligand receptor able to bind advanced glycation end-products (AGEs), amphoterin, calgranulins, and amyloid-beta peptides, identified in many tissues and cells, including neurons. RAGE stimulation induces the generation of reactive oxygen species (ROS) mainly through the activity of NADPH oxidases. In neuronal cells, RAGE-induced ROS generation is able to favor cell survival and differentiation or to induce death through the imbalance of redox state. The dual nature of RAGE signaling in neurons depends not only on the intensity of RAGE activation but also on the ability of RAGE-bearing cells to adapt to ROS generation. In this review we highlight these aspects of RAGE signaling regulation in neuronal cells.