Neuroprotective Effect of Alpha-Linolenic Acid against Aβ-Mediated

Apr 18, 2018 - Glial cells support and protect neurons from oxidative damage via modulation of synaptic plasticity and secretion of growth factors. ...
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Bioactive Constituents, Metabolites, and Functions

Neuroprotective effect of alpha-linolenic acid against A#-mediated inflammatory responses in C6 glial cell Ah Young Lee, Myoung Hee Lee, Sanghyun Lee, and Eun Ju Cho J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b00836 • Publication Date (Web): 18 Apr 2018 Downloaded from http://pubs.acs.org on April 18, 2018

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Journal of Agricultural and Food Chemistry

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Neuroprotective effect of alpha-linolenic acid against Aβ-mediated

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inflammatory responses in C6 glial cell

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Ah Young Leea, Myoung Hee Leeb, Sanghyun Leec, Eun Ju Choa,*

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a

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University, Busan 46241, Republic of Korea.

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b

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Development Administration, Gyeongnam 50424, Republic of Korea.

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c

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of Korea.

Department of Food Science and Nutrition & Kimchi Research Institute, Pusan National

Department of Southern Area Crop Science, National Institute of Crop Science, Rural

Department of Integrative Plant Science, Chung-Ang University, Gyeonggi 17546, Republic

10 11 12 13 14 15 16 17 18 19 20

Corresponding author: Eun Ju Cho, Department of Food Science and Nutrition, Pusan

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National University, Busan 46241, Republic of Korea. Tel: +82-51-510-2837, Fax: +82-51-

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583-3648. E-mail address: [email protected] (E. J. Cho).

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ABSTRACT

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Therapeutic approaches for neurodegeneration, such as Alzheimer’s disease (AD), have been

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widely studied. One of the critical hallmarks of AD is accumulation of amyloid beta (Aβ). Aβ

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induces neurotoxicity and releases inflammatory mediators or cytokines through activation of

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glial cell, and these pathological features are observed in AD patient’s brain. The purpose of

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this study is to investigate the protective effect of alpha-linolenic acid (ALA) on Aβ25-35-

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induced neurotoxicity in C6 glial cells. Exposure of C6 glial cells to 50 µM Aβ25-35 caused

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cell death, over-production of nitric oxide (NO), and pro-inflammatory cytokines release

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[interleukin (IL)-6 and tumor necrosis factor-α], while treatment of ALA increased cell

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viability and markedly attenuated Aβ25-35-induced excessive production of NO and those

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inflammatory cytokines. Inhibitory effect of ALA on generation of NO and cytokines was

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mediated by down-regulation of inducible nitric oxide synthase and cyclooxygenase-2 protein

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and mRNA expressions. In addition, ALA treatment inhibited reactive oxygen species

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generation induced by Aβ25-35 through the enhancement of the nuclear factor-erythroid 2-

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related factor-2 (Nrf-2) protein levels and subsequent induction of heme-oxygenase-1 (HO-1)

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expression in C6 glial cells dose- and time-dependently. Furthermore, the levels of neprilysin

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and insulin-degrading enzyme protein expressions, which contribute to degradation of Aβ,

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were also increased by treatment of ALA compared to Aβ25-35–treated control group. In

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conclusion, effects of ALA on Aβ degradation were shown to be mediated trough inhibition

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of inflammatory responses and activation of antioxidative system, Nrf-2/HO-1 signaling

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pathway, in C6 glial cells. Our findings suggest that ALA might have the potential for

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therapeutics of AD.

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KEY WORDS: alpha-linolenic acid, neuroinflammation, glial cell, amyloid beta, amyloid 2

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beta degradation

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INTRODUCTION

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Alzheimer’s disease (AD) is the most common and multifactorial neurodegenerative

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diseases. One of the pathological features of AD is the deposition of amyloid beta (Aβ), a

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protein involved in oxidative stress, neuronal apoptosis and inflammatory responses. Many

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previous studies have shown that the accumulation of Aβ is accompanied by high levels of

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pro-inflammatory cytokines produced by both glial cells and neurons.1-4 Excessive

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production of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor

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necrosis factor-α (TNF-α) contributes to amyloidogenic processing of the amyloid precursor

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protein (APP). In addition, increased expression of these cytokines was found to impair Aβ

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clearance and degradation in glial cells.5,6

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Glial cells support and protect neurons from oxidative damage via modulation of synaptic

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plasticity and secretion of growth factors.7-8 Several enzymatic systems have been described

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to mediate the process of Aβ degradation in glial cells. Both neprilysin (NEP) and insulin

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degrading enzyme (IDE) are critical Aβ-degrading enzymes that reduce Aβ accumulation in

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AD brains.9-12 Moreover, glial cell dysfunction was shown to induce inhibition of Aβ

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clearance, subsequent neurotoxicity, and Aβ accumulation.13 In addition, exogenous Aβ could

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activate glial cell to generate reactive oxygen species (ROS) as well as reactive nitrogen

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species (RNS), which promote secretion of inflammatory cytokines and inflammatory

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process, thus contributing to AD progression.14-16 Therefore, suppression of inflammatory

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process in glial cells has been proposed as a therapeutic strategy for neurodegenerative

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disease.

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A number of studies demonstrated the role of omega-3 polyunsaturated fatty acids in brain

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development and function.17,18 However, most of these focused on neuroprotective effects of 4

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eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA). Recently, plant-derived

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omega-3 fatty acid, rather than fish-derived products containing EPA and DHA, has attracted

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interest due to its benefits for human health.19 Alpha-linolenic acid (ALA), enriched in

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vegetable oils such as perilla oil (containing 60-70% ALA) or linseed oil (containing 30-50%

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ALA), has been shown to enhance neurological function including neurogenesis and synaptic

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function in the rodent brain.20 We previously suggested that administration of perilla oil and

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ALA improved cognitive impairment induced by Aβ25-35 in a mouse model of AD.21,22 Perilla

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oil, which has the largest proportion of ALA, suppressed the expression of inflammatory

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mediators, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), in Aβ25-35-

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injected brain tissues. Furthermore, ALA supplementation significantly enhanced the

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expression of Aβ degrading enzyme, IDE. Other reports also supported that dietary ALA

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modulates oxidative or inflammatory response in vitro and in vivo.23-25 However, no studies

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have reported the neuroprotective potential of ALA in modulating glial cell function against

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Aβ. In the present study, we assessed the anti-inflammatory properties of ALA in Aβ25-35-

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treated C6 glial cell, and investigated the molecular mechanisms underlying regulation of

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inflammatory response and Aβ degradation.

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MATERIALS AND METHODS

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Sample preparation

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Perilla frutescens oil was provided by Southern Area Crop Science, Rural Development

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Administration (Miryang, Republic of Korea). ALA was obtained from perilla oil after

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treatment with urea and cooling by high-yield methods as described in a previous study.26

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ALA was freshly prepared as a stock solution in dimethyl sulfoxide (DMSO), and stored at

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4˚C with nitrogen gas for stability before use. DMSO is used for dissolving hydrophobic

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compounds including omega-3 fatty acids in vitro or cellular system.27,28 Nitrogen gas is the

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generally used to protect oil or fatty acid from air contact, and is able to avoid the

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contaminant. At low temperatures under nitrogen atmosphere, progression of lipid

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peroxidation is relatively low. 29-31

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Instruments and reagents Fetal bovine serum (FBS), Dulbecco’s modified eagle’s medium (DMEM), and

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penicillin/streptomycin

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dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), dichlorofluorescin diacetate

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(DCF-DA) and DMSO were supplied by Sigma Chemical Co. (St Louis, MO, USA).

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Radioimmunoprecipitation assay (RIPA) buffer, 30% acrylamide bis solution and pre-stained

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protein size marker were obtained from Elpis Biotech (Daejeon, Korea). Polyvinylidene

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fluoride (PVDF) membrane was from Millipore (Billerica, MA, USA). Primary antibodies

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and secondary antibodies were purchased from Cell Signaling (Beverly, MA, USA).

were

supplied

by Welgene

(Daegu, Korea).

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Cell culture 6

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C6 glial cells were obtained from KCLB (Korean Cell Line Bank, Seoul, Korea). The cells

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were maintained in DMEM containing 1% penicillin/streptomycin and 10% FBS at 37°C in a

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5% CO2 incubator with. Cells were sub-cultured with 0.05% trypsin-EDTA in phosphate

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buffered saline (PBS).

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Cell viability

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After becoming confluent, the cells were harvested and plated at a density of 5 × 104 cells/mL

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into 96-well palate overnight. The cells were then treated with ALA (1, 2.5, 5, and 25 µg/mL)

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for 2 h, and followed by Aβ25-35 (50 µM) for 24 h. After incubation, cell viability was

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determined using the MTT assay. MTT solution was added to each 96-well plate, the plate

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was incubated for 4 h at 37°C, and the medium containing MTT was removed. The

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incorporated formazan crystals incorporated in viable cells were solubilized with DMSO and

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the absorbance of each well was read at 540 nm.

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Measurement of nitric oxide (NO) production

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NO production was investigated by quantifying nitrite accumulation in the medium treated

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with Griess reagent. To measure nitrites, cell supernatants were mixed with Griess reagent at

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1:1 volume ratio. Nitrite concentration was measured using microplate spectrophotometer at a

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wave length of 540 nm.

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Measurement of ROS production 7

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The ROS scavenging activity of ALA was measured using DCFH-DA.32 C6 glial cells were

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plated at a density of 5 × 104 cells/mL into 96-well plate overnight. The treatment with ALA

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(5 and 25 µg/mL) was performed for 2 h, after which Aβ25-35 (50 µM) was added, and the

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cells were further incubated for 24 h. The cells were then incubated with 80 µM DCFH-DA at

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37°C for 30 min. The fluorescence was read for 60 min, at 480 nm excitation and 535 nm

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emission, using a fluorescence plate reader (BMG LABTECH, Ortenberg, Germany).

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Measurement of pro-inflammatory cytokines production

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The supernatants of C6 glial cells treated with Aβ25-35 (50 µM) and ALA (5 and 25 µg/mL)

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were transferred to a separate plate. The production of TNF-α and IL-6 were was measured

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using ELISA kits (R&D system, Minneapolis, USA) according to manufacturer’s instructions.

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Reverse transcription polymerase chain reaction (RT-PCR)

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Total RNA was isolated using Trizol reagent (Invitrogen, Carlsbad, CA) according to

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manufacturer’s instructions. Cells were lysed and transferred to microfuge tubes. RNA was

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reverse-transcribed into cDNA and used as a template for RT-PCR amplification. The primers

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and amplification conditions are listed in Table 1. PCR products were analyzed on 1%

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agarose gels, and bands were visualized using LED slider imager (Maestrogen, Las Vegas,

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NV, USA).

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Western blotting 8

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C6 glial cell extracts were prepared according to the manufacturer’s instructions using RIPA

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buffer supplemented with 1× protease inhibitor cocktail. Proteins were separated by

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electrophoresis in a precast 10-13% SDS-PAGE and blotted onto PVDF membranes. The

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membrane was blocked with 5% skim milk solution for 1 h at room temperature, and

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incubated overnight at 4°C with primary antibody [iNOS (1:200, Santa Cruz, CA, USA);

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COX-2 (1:200, Santa Cruz); IL-6 (1:1000, Santa Cruz); TNF-α (1:000, Cell Signaling);

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nuclear factor-erythroid 2-related factor-2 (Nrf-2, 1:1000, Cell Signaling, MA, USA); heme-

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oxygenase-1 (HO-1, 1:2000, Cell Signaling); IDE (1:200, Santa Cruz, CA, USA); NEP

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(1:1000, Millipore); and β-actin (1:200, Santa Cruz)]. The membrane was washed and

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incubated with the appropriate HRP-conjugated secondary antibodies. Western bands were

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visualized using a chemiluminescent imaging system (Davinci Chemi, Seoul, Korea).

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Statistical analysis

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The results are expressed as mean ± SD. Statistical significance was determined by one way

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ANOVA followed by post-hoc analysis with Tukey’s test using IBM SPSS 23 program. The

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significance was set at #P < 0.05,

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from the normal group; *significantly different from the Aβ25-35-treated control group.

##

P < 0.01, *P < 0.05, **P < 0.01. #Significantly different

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RESULTS

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Effect of ALA on cell viability in Aβ25-35-treated C6 glial cells

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The treatment with ALA at concentrations between 1 and 25 µg/mL did not show cytotoxicity

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in C6 glial cells (data not shown). C6 glial cells were treated with ALA, and the effect on

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Aβ25-35–induced cytotoxicity was determined. Compared to the normal group (100%), the 9

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exposure of cells to Aβ25-35 for 24 h induced toxicity in C6 glial cells, reducing the cell

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viability to 39.46% (Fig. 1). However, in the presence of ALA (1, 2.5, 5, and 25 µg/mL), cell

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viability was significantly increased as compared to the cells treated with Aβ25-35 alone. These

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results suggest that ALA protects C6 glial cell against Aβ25-35-induced cellular damage.

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Effect of ALA on NO production in Aβ25-35-treated C6 glial cell

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To investigate the effect of ALA on Aβ25-35-induced NO production in C6 glial cells, the cells

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were treated with various concentrations of ALA (1, 2.5, 5, and 25 µg/mL), after which Aβ

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was added for 24 h. Fig. 2 indicates significantly increased NO production by Aβ25-35

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compared to normal group. By contrast, the treatment with ALA, especially at 25 µg/mL,

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effectively attenuated Aβ25-35-induced NO production.

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Effect of ALA on protein and mRNA expression of iNOS and COX-2 in Aβ25-35-treated C6

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glial cells

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To clarify the potential effects of ALA on inflammatory mediators, iNOS and COX-2, we

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examined their protein and mRNA levels using Western blot and RT-PCR, respectively. As

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shown in Fig. 3A, the protein levels of iNOS and COX-2 were markedly increased after Aβ25-

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35 treatment.

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COX-2 protein levels, as compared to control group.

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In parallel with the inhibitory effect of ALA on iNOS and COX-2 protein over-expression, we

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further analyzed the mRNA expression. We observed that iNOS and COX-2 mRNA levels

However, the treatment with ALA leads to a significant suppression of iNOS and

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were also up-regulated following Aβ25-35 treatment, while the treatment with ALA leads to

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inhibition of iNOS and COX-2 mRNA expression (Fig. 3B). These results demonstrate the

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inhibitory effect of ALA on Aβ25-35 treatment-induced NO production associated with the

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down-regulation of iNOS and COX-2 protein and mRNA expression in C6 glial cells.

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Effect of ALA on pro-inflammatory cytokines production in Aβ25-35-treated C6 glial cells

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Fig. 4 illustrates the effect of ALA on production of TNF-α and IL-6 pro-inflammatory

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cytokines induced by Aβ25-35. The treatment with Aβ25-35 induced over-production of TNF-α

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and IL-6 in C6 glial cells, as compared to non-treated group (Fig. 4A). However, ALA

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treatment significantly decreased the over-production of both TNF-α and IL-6. In addition,

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Aβ25-35 induced up-regulation of TNF-α and IL-6 protein expression, which was markedly

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down-regulated by the treatment with ALA (Fig. 4B). These results demonstrate that

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increased production of pro-inflammatory such as TNF-α and IL-6 in C6 glial cells induced

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by Aβ25-35 was related to the inhibition of iNOS and COX-2 protein/gene expression, and that

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ALA inhibited these inflammatory responses by regulating the expression of pro-

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inflammatory cytokines and mediators.

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Effect of ALA on ROS production in Aβ25-35-treated C6 glial cells

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We examined whether ALA attenuates ROS production induced by Aβ25-35 in C6 glial cells.

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Fig. 5A shows that the treatment of C6 glial cells with Aβ25-35 significantly increased ROS

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levels in a time-dependent manner, as compared to un-treated group. Compared with Aβ25-3511

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treated control group (100%), the treatment with ALA (5 and 25 µg/mL) significantly

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inhibited the excess in ROS production, by decreasing it to 86.12% and 85.22%, respectively

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(Fig. 5B).

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Effect of ALA on Nrf-2/HO-1 signaling pathway in C6 glial cell

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Given the inhibitory effect of ALA treatment on inflammatory reaction and ROS production,

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we evaluated whether ALA regulates Nrf-2/HO-1 signaling in C6 glial cells by Western blot

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analysis. Our results indicate that ALA promotes the up-regulation of Nrf2 protein expression,

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and consequently, the increase in the expression of HO-1 protein a downstream target of Nrf-

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2, in a dose- (Fig. 6A) and time-dependent manner (Fig. 6B). These results reveal that ALA-

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dependent activation of Nrf-2/HO-1 signaling activation contributes to down-regulation of

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neuroinflammation and ROS generation.

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Effect of ALA on Aβ degradation in Aβ25-35-treated C6 glial cells

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The effect of ALA on NEP and IDE expression in C6 glial cells was also investigated.

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Western blot analysis showed that the treatment of cells with ALA significantly increased

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NEP and IDE expression dose-dependently (Fig. 7). The treatment with Aβ25-35 significantly

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reduced the levels of NEP and IDE. However, the protein levels of Aβ-degrading enzymes

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NEP and IDE were significantly increased following the treatment with ALA. Thus our

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results suggest that ALA may inhibit the accumulation of Aβ in the brain.

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DISCUSSION

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Neuroinflammation is one of the critical characteristics in the brain of AD patients.33 It has

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been reported that the initial defense against Aβ accumulation is involved in inflammatory

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responses including enzymatic degradation. Activated glial cells produce pro-inflammatory

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mediators and cytokines, resulting in promote the synthesis and APP processing. Increased

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Aβ production and deposition lead to further glial cell activation, which maintains the vicious

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cycle.34,35 The cytokines induced by Aβ in turn reduce the expression of Aβ-degrading

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enzymes, which drive the progression of AD.36,37 Since inflammatory responses have been

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implicated in neuropathological changes and the development of AD, it is conceivable that

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stimulating anti-inflammatory activity in glial cells may represent a therapeutic strategy for

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AD.

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Our study showed that the treatment of C6 glial cells with Aβ25-35 induced toxicity,

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resulting into cell death. However, ALA significantly reversed the decrease in cell viability as

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confirmed by MTT assays. Although RNS and ROS play a critical role in neurotransmission

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and synaptic function in the brain, the over-production of those are associated with

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neuroinflammation, which result in neurodegeneration.38 High levels of NO and pro-

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inflammatory cytokines in activated glial cells can be considered as a pathophysiological

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feature of AD.39 Our data revealed that Aβ25-35 elevated the levels of NO production and pro-

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inflammatory cytokines such as TNF-α and IL-6. These findings are consistent with previous

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studies showing activation of inflammatory mediators and cytokines expression by Aβ in

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glial cell lines.40,41 However, ALA prominently inhibited the production of NO, TNF-α, and

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IL-6 cytokines as well as decreased protein levels of TNF-α and IL-6 in Aβ25-35-stimulated C6

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glial cells as shown by western blotting. It has been reported that neuroprotection against Aβ 13

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can result from the inhibition of pro-inflammatory mediators through down-regulation of

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iNOS or COX-2 protein.42,43 In this study, the exposure to Aβ25-35 stimuli up-regulated iNOS

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and COX-2 protein and mRNA expression, while the ALA reduced both protein and mRNA

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levels of iNOS and COX-2. These findings suggest that the inhibition of NO and pro-

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inflammatory cytokines production by ALA was mediated by the effect on iNOS and COX-2

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expression. Based on our results, we suggest that ALA attenuates Aβ25-35-induced glial

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activation and down-regulates inflammatory neurotoxicity.

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ROS accumulation is strongly associated with glial inflammatory responses in

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neurodegenerative disease. Increased ROS production plays an important role in the

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activation of iNOS and COX-2 by inflammatory stimuli such as Aβ.44 The inhibition of ROS

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may be an effective way to protect the cells from Aβ-induced neuroinflammation. We

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examined the intracellular ROS formation induced by Aβ25-35 in C6 glial cells. Our findings

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reveal that ALA significantly suppresses the over-production of ROS induced by Aβ25-35. A

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potential mechanism underlying the inhibition of pro-inflammatory cytokines was previously

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reported that oxidative stress and inflammation were attenuated by ALA-enriched diet

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through inactivation of nuclear factor-kappa B signaling pathway.45 Ambrozova et al. (2010)

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also demonstrated that omega-3 fatty acids such as ALA inhibited ROS and RNS generation

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in macrophage cells.46

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The up-regulation of Nrf-2 and HO-1 expression is an effective strategy to resist the

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oxidative stress. Nrf-2 has been considered as a regulator of inflammation and

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neuroprotection.47,48 The expression of Nrf-2 can decrease Aβ-induced degeneration by

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limiting cellular oxidative response and inflammatory damage.49 Activated Nrf-2 can induce

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the expression of HO-1, its downstream antioxidant target. Substantial evidence also suggests 14

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that up-regulation of HO-1 expression contributes to protection against cellular oxidative

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damage and inflammation by inhibiting iNOS activity.50,51 To investigate the molecular

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mechanism underlying the effect of ALA on inhibition of ROS generation and inflammation,

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we examined the protein levels of Nrf-2 and HO-1 in C6 glial cells. Our data shows that the

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treatment with ALA increased Nrf-2 activation and induced HO-1 protein expression in a

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concentration- and time-dependent manner. Similar to our results, DHA treatment attenuated

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neuronal injury by activating Nrf-2 and up-regulating HO-1 expression, demonstrating

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neuroprotective effect.52 Pal and Ghosh (2012) demonstrated that ALA exerts antioxidant

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effects by reducing lipid peroxidation and modulating antioxidant enzymes such as

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superoxide dismutase, glutathione peroxidase and catalase.53 These results suggest that ALA

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protects against Aβ-induced oxidative stress and neuroinflammation through induction of

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Nrf-2/HO-1 signaling.

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We previously showed that ALA has anti-oxidant activity as a scavenger of hydroxyl

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radical, demonstrating that ALA is capable of inhibiting ROS production and lipid

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peroxidation.54 Several reports have also shown that dietary omega-3 fatty acids are able to

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modify the oxidative status by attenuating oxidative stress in vitro and in vivo.55-57

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Polyunsaturated fatty acid (PUFA) containing two or more double bonds can react with

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oxygen, resulting in formation of hydroperoxides. This oxidation is progressed by free radical

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chain reaction through initiation, propagation, and termination at the bis-allylic positions.

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However, lipids are complex, multi-component, and heterogeneous system. Miyashita (2014)

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demonstrated that omega-3 fatty acids including ALA in micelles and liposomes can form

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tight and unique conformation, and reduce hydroxyl compounds derived from oxidation

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products, thus omega-3 fatty acids may protect against oxidative attack.58 In addition, the 15

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omage-3 fatty acids can be incorporated into membrane phospholipids or bound to membrane

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receptors, acting as inhibitor of ROS production and regulator of biological processes.59

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Although further studies are needed to investigate the detailed physiological effects and

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molecular mechanisms, these evidences support the antioxidant role of ALA in biological

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system.

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Glial-mediated oxidative stress and neuroinflammation are closely associated with the

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degradation of Aβ in AD progression.60,61 The mechanisms underlying degradation of Aβ

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have attracted attention given their potential therapeutic application in the treatments of AD.

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This particularly applies to the roles of IDE and NEP, major Aβ-degrading enzymes in glial

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cells.62-64 Since oxidative stress and neuroinflammation were attenuated in ALA-treated glial

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cells, we investigated whether the activities of Aβ degrading enzymes are modified by the

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treatment with ALA. In the present study, we found that treatment with Aβ25-35 resulted in a

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significant decrease in the expression of IDE and NEP. However, ALA treatment significantly

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increased protein expression levels of IDE and NEP, which are capable of degrading Aβ.

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These effects of ALA on Aβ degradation may be affected by the inhibition of oxidative stress,

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with a subsequent reduction of neuroinflammation induced by Aβ.

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A number of studies demonstrated that omega-3 fatty acid consumption is associated with

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lower risk of AD and slower rate of cognitive decline.65 The protective effects of omega-3

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fatty acids, especially EPA or DHA, on AD have been well established in vitro, in vivo, and

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by several clinical studies.66,67 EPA attenuated glial-produced pro-inflammatory cytokines,

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thus subsequently inhibiting neuroinflammation.68 ALA deficiency induces abnormality of

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nervous system, including neurons, astrocytes, oligodendrocytes, and endoplasmic

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reticulum.69 Considering to protective effect of ALA on neurons, previous studies 16

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demonstrated that injection or administration of ALA prevented neuronal cell death with

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down-regulation of Bax protein expression in stroke animal models.70,71 Moreover, ALA

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attenuated glutamate-induced neurotoxicity and promoted neuronal survival in vitro.20,72,73

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We also confirmed that treatment of ALA reduced neuronal cell death against hydrogen

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peroxide and Aβ by down-regulation of apoptotic signaling pathway.74,75 These results

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suggest that ALA directly protects neuron as well as glial cells from oxidative stress. Because

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of limited rate of conversion from ALA to EPA/DHA, the protective effect of ALA on glial

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cells most likely does not involve bioconversion of ALA to EPA/DHA.

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Our findings show that ALA increased cell viability and decreased ROS production in

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Aβ25-35-treated glial cells. ALA also up-regulated the expression of Nrf-2 and HO-1,

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demonstrated as protective against oxidative stress. The mechanisms underlying anti-

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inflammatory effect of ALA involve interference with NO production and protein/mRNA

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expressions of iNOS, COX-2, TNF-α, and IL-6. The induction of antioxidant activity and

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inhibition of inflammatory cytokine release by the treatment with ALA has a potential to

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induce degradation of Aβ as shown by promotion of IDE and NEP protein expressions. This

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study suggests that intake of ALA should be considered as an attractive alternative to that of

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fish oil in the treatment/prevention of neurodegenerative disorders such as AD.

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347

ABBREVIATIONS USED

348

AD, Alzheimer’s disease; ALA, alpha-linolenic acid; APP, amyloid precursor protein; COX-2,

349

cyclooxygenase-2; DCF-DA, dichlorofluorescin diacetate; DHA, docosahexaenoic acid;

350

DMEM, Dulbecco’s modified eagle’s medium; DMSO, dimethyl sulfoxide; EPA, 17

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eicosapentaenoic acid; FBS, fetal bovine serum; HO-1, heme-oxygenase-1; IDE, insulin

352

degrading enzyme; IL, interleukin; iNOS, inducible nitric oxide synthase; MTT, 3-(4,5-

353

dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide; Nrf-2, nuclear factor-erythroid 2-

354

related factor-2; NEP, neprilysin; NO, nitric oxide; RIPA, radioimmunoprecipitation assay;

355

RNS, reactive nitrogen species; ROS, reactive oxygen species; PBS, phosphate buffered

356

saline; PUFA, polyunsaturated fatty acid; PVDF, polyvinylidene fluoride; TNF-alpha, tumor

357

necrosis factor-alpha

358

359

ACKNOWLEDGMENTS

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This work was carried out with the support of the “Cooperative Research Program for

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Agriculture Science & Technology Development (PJ01015603),” Rural Development

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Administration, Republic of Korea.

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FIGURE CAPTIONS

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Figure 1. Effect of ALA on cell viability in Aβ25-35-treated C6 glial cells. Values are mean

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± SD (n = 6).

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ALA; Alpha-linolenic acid.

##

P < 0.01 compared to normal group; **P < 0.01 compared to control group.

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Figure 2. Effect of ALA on NO production in Aβ25-35-treated C6 glial cells. Values are

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mean ± SD (n = 6). ##P < 0.01 compared to normal group;

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group. ALA; Alpha-linolenic acid.

**

P < 0.01 compared to control

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Figure 3. Effect of the levels of ALA on iNOS and COX-2 protein (A) and mRNA (B)

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expressions in Aβ25-35-treated C6 glial cells. ALA; Alpha-linolenic acid. Images of band are

584

from a representative experiment and bars represent the mean ± SD (n = 3). #P < 0.05, ##P