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01.12.2016 | Research | Ausgabe 1/2016 Open Access

Journal of Neuroinflammation 1/2016

Rice bran derivatives alleviate microglia activation: possible involvement of MAPK pathway

Zeitschrift:
Journal of Neuroinflammation > Ausgabe 1/2016
Autoren:
Harsharan S. Bhatia, Julian Baron, Stephanie Hagl, Gunter P. Eckert, Bernd L. Fiebich
Wichtige Hinweise

Electronic supplementary material

The online version of this article (doi:10.​1186/​s12974-016-0615-6) contains supplementary material, which is available to authorized users.

Abstract

Background

Hyperactivation of microglia is considered to be a key hallmark of brain inflammation and plays a critical role in regulating neuroinflammatory events. Neuroinflammatory responses in microglia represent one of the major risk factors for various neurodegenerative diseases. One of the strategies to protect the brain and slow down the progression of these neurodegenerative diseases is by consuming diet enriched in anti-oxidants and polyphenols. Therefore, the present study aimed to evaluate the anti-inflammatory effects of rice bran extract (RBE), one of the rich sources of vitamin E forms (tocopherols and tocotrienols) and gamma-oryzanols, in primary rat microglia.

Methods

The vitamin E profile of the RBE was quantified by high-performance liquid chromatography (HPLC). Microglia were stimulated with lipopolysaccharide (LPS) in the presence or absence of RBE. Release of prostaglandins (prostaglandin (PG) E2, 8-iso-prostaglandin F (8-iso-PGF)) were determined with enzyme immunoassay (EIA). Protein levels and genes related to PGE2 synthesis (Cyclooxygenase-2 (COX-2), microsomal prostaglandin E synthase-1 (mPGES-1)) and various pro- and anti-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-10), were assessed by western blot, ELISA, and quantitative real-time PCR. Furthermore, to elucidate the molecular targets of RBE, the phosphorylated state of various mitogen-activated protein kinase (MAPK) signaling molecules (p38 MAPK, ERK 1/2, and JNK) and activation of NF-kB pathway was studied.

Results

RBE significantly inhibited the release of PGE2 and free radical formation (8-iso-PGF) in LPS-activated primary microglia. Inhibition of PGE2 by RBE was dependent on reduced COX-2 and mPGES-1 immunoreactivity in microglia. Interestingly, treatment of activated microglia with RBE further enhanced the gene expression of the microglial M2 marker IL-10 and reduced the expression of pro-inflammatory M1 markers (TNF-α, IL-1β). Further mechanistic studies showed that RBE inhibits microglial activation by interfering with important steps of MAPK signaling pathway. Additionally, microglia activation with LPS leads to IkB-α degradation which was not affected by the pre-treatment of RBE.

Conclusions

Taken together, our data demonstrate that RBE is able to affect microglial activation by interfering in important inflammatory pathway. These in vitro findings further demonstrate the potential value of RBE as a nutraceutical for the prevention of microglial dysfunction related to neuroinflammatory diseases, including Alzheimer’s disease.
Zusatzmaterial
Additional file 1: Figure S1. (A-K). Possible effects of rice bran extract (RBE) on the proliferation of microglia. Microglia were treated with either RBE (300 μg/ml) alone or RBE (50–300 μg/ml) in combination with LPS (10 ng/ml) for a total of 48 h. Thereafter, samples were stained with propidium iodide and processed for proliferation assay (for detailed protocol, see the “Methods” section) by using flow cytometer. Samples were acquired with the FL-2 fluorescence channel set to a linear scale, in order to amplify the diploid DNA peak. Graph A) represents the dot plot of cells acquired on the basis of side scattered light (SSC) and forward scattered light (FSC) and B) represents the pulse processing by using pulse area vs. pulse width. Graphs C-I) are representative histograms after each treatment. Markers represent the percentage of cells in the G0/G1, S, and G2/M phases from left to right, respectively. J) Represents histogram after 48 h treatment of M-CSF (50 ng/ml) used as positive control for proliferation. K) Showing quantification of microglial cells in each phase of cell cycle after respective treatments. Data are presented in percentage of cells in each phase. Results are expressed as means ± SEM of three independent experiments. Statistical analyses were carried out by using one-way ANOVA with post hoc Student-Newman-Keuls test (multiple comparisons). * p < 0.05; compared with percentage of control cells in each phase. (TIF 536 kb)
Literatur
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