Research ArticleHydroxytyrosol Inhibits LPS-Induced Neuroinflammatory Responses via Suppression of TLR-4-Mediated NF-κB P65 Activation and ERK Signaling Pathway
Introduction
Neuroinflammation is a characteristic feature of various neurological disorders including Alzheimer’s disease (AD), Parkinson’s disease (PD), multiple sclerosis and acute traumatic brain injury as well as infectious neuropathology (Grigoriadis et al., 2015, Latta et al., 2015, Rocha et al., 2015, Bergold, 2016). Microglia are the major resident immune cells in the brain that contribute to immune surveillance and regulate the homeostasis of the central nervous system (CNS) (Nimmerjahn et al., 2005). However, over-activated microglia secrete proinflammatory cytokines and oxygen free radicals, often resulting in cerebral injury under various pathologic conditions. Therefore, inhibition of microglia activation has been regarded as one of prime targets for treatment of diverse neuropathological conditions (Glass et al., 2010).
Hydroxytyrosol (3,4-dihydroxyphenil-ethanol, HT), which is a small phenolic molecule derived from olive-oil, has shown strong anti-oxidant, anti-inflammatory and antithrombotic activities. For example, Fuccelli et al. recently found that HT demonstrated anti-inflammatory and anti-oxidant abilities in a mouse model of systemic inflammation induced by LPS (Fuccelli et al., 2018). HT also reduced liver inflammation and oxidative stress by reducing the production of oxygen species and lipid peroxidation (Pirozzi et al., 2016). In vitro, HT inhibited the production of inflammatory mediators such as COX-2 and PGE2 in human isolated peripheral blood monocytes (Rosignoli et al., 2013). In addition, some evidence showed that HT prevented the inflammatory progress of atherosclerosis by decreasing the concentration of proinflammatory cytokines, inhibiting the endothelial activation and expression of chemotactic and adhesion molecules (Souza et al., 2017). Recently, several clinical trials and population studies indicated that the main polyphenols such as HT, oleuropein, and tyrosol, are mainly responsible for the neuroprotection effect in neurodegenerative disease such as AD and PD, as well as improvement of cognitive performance (Alcalay et al., 2012, Casamenti et al., 2015, Peyrol et al., 2017, Robles-Almazan et al., 2018). However, the effects of HT on neuroinflammation in microglial cells have not been reported yet.
In the present study, we investigated the anti-neuroinflammatory effects of HT on LPS-stimulated microglial cells, along with underlying signaling mechanisms. Our results showed that HT potently inhibited proinflammatory cytokine production associated with the downregulation of TLR-4 mediated NF-κB activation and ERK signaling pathway. In addition, we found that HT modulated the polarization of microglia by down-regulating the expression of M1 marker CD86 and up-regulating that of M2 marker CD206. In vivo administration of HT significantly suppressed microglia and astrocyte activation induced by LPS and decreased levels of proinflammatory mediators. Those findings strongly indicate that HT is a potential therapeutic candidate for inflammation related neurodegenerative diseases or acute brain injury.
Section snippets
Materials
LPS (Escherichia coli 0111: B4), DAPI, IL-4, and MTT were obtained from Sigma-Aldrich (St Louis, MO, USA). HT were purchased from Aladdin (Shanghai, China). Enzyme-linked immunosorbent assay (ELISA) kit for TNF-α and IL-6 were purchased from Multi Sciences (Hangzhou, China). NO assay kit was from Beyotime (Shanghai, China). The antibodies against NF-κB p65, phospho-NF-κB p65, nitric oxide synthase (iNOS), COX-2, p38 mitogen-activated protein kinase (MAPK), phospho-p38 MAPK, ERK1/2,
Effects of HT and LPS on BV2 cell viability
To determine the cytotoxic effects of HT and LPS on BV2 cells, the cells were treated with HT in the presence or absence of LPS for 24 h. As shown in Fig. 1, HT did not show significant cytotoxic effects at the concentrations up to 200 μM, and LPS at concentration of 0.5 μg/mL also had no significant adversary effect on cell viability. Therefore, HT at the concentrations of 25, 50 and 100 μM were selected in the subsequent experiments.
Effects of HT on the LPS-induced proinflammatory cytokines and COX-2 production
To determine whether HT exerts anti-inflammatory action, we
Discussion
In the present study, we investigated potential inhibitory effects of HT on LPS-induced neuroinflammation using both in vitro and in vivo models. Our results demonstrated that HT potently inhibits LPS-induced proinflammatory responses in microglia by suppressing TLR-4 mediated NF-κB activation and ERK signaling pathway. To our knowledge, this is the first report of such effects of HT on LPS-induced neuroinflammation in microglia cells and the molecular mechanism underlying these effects.
HT is
Acknowledgements
This work was supported by the National Natural Science Foundation of China (81470263), Tianjin Science and Technology Project, China (13RCGFSY19300), and by the Clinical Medicine Research Centre for ITCWM Acute Abdomen Diseases of Tianjin Municipal Science and Technology Commission (15ZXLCSY00030).
References (46)
Treatment of traumatic brain injury with anti-inflammatory drugs
Exp Neurol
(2016)- et al.
Nutritionally relevant concentrations of resveratrol and hydroxytyrosol mitigate oxidative burst of human granulocytes and monocytes and the production of pro-inflammatory mediators in LPS-stimulated RAW 264.7 macrophages
Int Immunopharmacol
(2017) - et al.
Mechanisms underlying inflammation in neurodegeneration
Cell
(2010) - et al.
Bisabolangelone isolated from Ostericum koreanum inhibits the production of inflammatory mediators by down-regulation of NF-kappaB and ERK MAP kinase activity in LPS-stimulated RAW264.7 cells
Int Immunopharmacol
(2010) - et al.
Neuroinflammation in Alzheimer's disease; a source of heterogeneity and target for personalized therapy
Neuroscience
(2015) - et al.
Toll-like receptors in antiviral innate immunity
J Mol Biol
(2014) - et al.
The influence of microglia on the pathogenesis of Parkinson's disease
Progr Neurobiol
(2009) - et al.
Microglial activation and chronic neurodegeneration
Neurotherapeutics
(2010) - et al.
Transport mechanism and metabolism of olive oil hydroxytyrosol in Caco-2 cells
FEBS Lett
(2000) - et al.
Hydroxytyrosol prevents metabolic impairment reducing hepatic inflammation and restoring duodenal integrity in a rat model of NAFLD
J Nutr Biochem
(2016)
Hydroxytyrosol: bioavailability, toxicity, and clinical applications
Food Res Int
Effect of olive oil phenols on the production of inflammatory mediators in freshly isolated human monocytes
J Nutr Biochem
Major phenolic compounds in olive oil: metabolism and health effects
J Nutr Biochem
Anti-inflammatory effects of anisalcohol on lipopolysaccharide-stimulated BV2 microglia via selective modulation of microglia polarization and down-regulation of NF-kappaB p65 and JNK activation
Mol Immunol
Phlorofucofuroeckol B suppresses inflammatory responses by down-regulating nuclear factor kappaB activation via Akt, ERK, and JNK in LPS-stimulated microglial cells
Int Immunopharmacol
The association between Mediterranean diet adherence and Parkinson’s disease
Mov Disord
Inflammation in the nervous system: the human perspective
Glia
Oleuropein aglycone: a possible drug against degenerative conditions. In vivo evidence of its effectiveness against Alzheimer's disease
J Alzheimers Dis
Arginase 1+ microglia reduce Abeta plaque deposition during IL-1beta-dependent neuroinflammation
J Neuroinflamm
Hydroxytyrosol exerts anti-inflammatory and anti-oxidant activities in a mouse model of systemic inflammation
Molecules
The interplay between cyclic AMP, MAPK, and NF-kappaB pathways in response to proinflammatory signals in microglia
BioMed Res Int
Characterization of ameboid microglia isolated from developing mammalian brain
J Neurosci
A basic overview of multiple sclerosis immunopathology
Eur J Neurol
Cited by (33)
Oils as a source of bioactive lipids (olive oil, palm oil, fish oil)
2022, Bioactive LipidsOlive oil
2022, Functional Foods and their Implications for Health PromotionScutellarin alleviates depression-like behaviors induced by LPS in mice partially through inhibition of astrocyte-mediated neuroinflammation
2021, Neuroscience LettersCitation Excerpt :In this study, SCU treatment reversed the decline of BDNF mRNA in cultured astrocytes exposure to LPS. It has been reported that different from mature BDNF, pro-BDNF positively modulates depression [26,27], suggesting that the imbalance of these two factors may play key role in depression. It is very meaningful to distinguish pro-BDNF and mature BDNF in future research.
Inhibition of the pesticide rotenone-induced Ca<sup>2+</sup> signaling, cytotoxicity and oxidative stress in HCN-2 neuronal cells by the phenolic compound hydroxytyrosol
2021, Pesticide Biochemistry and PhysiologyCitation Excerpt :This study established the effect of rotenone on Ca2+ homeostasis and oxidative stress balance in HCN-2 neuronal cell lines. Hydroxytyrosol, a natural phenolic compound, was shown to be protective potential in brain models treated with α-synuclein (Hornedo-Ortega et al., 2018), LPS (Zhang et al., 2020), arsenic (Soni et al., 2018), or amyloid-beta (Nardiello et al., 2018). However, to the best of our knowledge, the effect of hydroxytyrosol on viability, Ca2+ signaling and oxidative stress is still unknown in rotenone-treated HCN-2 cells.