Elsevier

International Immunopharmacology

Volume 66, January 2019, Pages 309-316
International Immunopharmacology

Luteoloside attenuates neuroinflammation in focal cerebral ischemia in rats via regulation of the PPARγ/Nrf2/NF-κB signaling pathway

https://doi.org/10.1016/j.intimp.2018.11.044Get rights and content

Highlights

  • Luteoloside exerted a protective effect on cerebral ischemic injury induced by MCAO in rats

  • Luteoloside played an anti-inflammatory role in cerebral ischemic process by suppressing NF-κB signaling pathways.

  • Luteoloside could up-regulated the PPARγ expression and activited the Nrf2 signaling to attenuate cerebral ischemic injury.

Abstract

Luteoloside, a flavonoid compound, has been reported to have anti-inflammatory, anti-oxidative, antibacterial, antiviral, anticancer, and cardioprotective effects, among others, but its neuroprotective effects have rarely been studied. The purpose of this study was to investigate the protective effect of luteoloside on cerebral ischemia and explore its potential mechanism. Middle cerebral artery occlusion (MCAO) was performed to investigate the effects of luteoloside on cerebral ischemia-reperfusion (I/R). Male Sprague-Dawley rats were randomly divided into six groups: sham, MCAO, luteoloside (20 mg/kg, 40 mg/kg, 80 mg/kg) and nimodipine (4 mg/kg). The results showed that luteoloside alleviated neurologic deficits and cerebral edema as well as improved cerebral infarction and histopathological changes in MCAO rats. Luteoloside significantly inhibited I/R-induced neuroinflammation, as demonstrated by reduced levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in the brain tissues of MCAO rats. Furthermore, our results demonstrated that luteoloside significantly suppressed the activation of nuclear factor-kappa B (NF-κB) signaling, upregulated the protein expression of peroxisome proliferator activated receptor gamma (PPARγ) and increased NF-E2-related factor (Nrf2) nuclear accumulation in MCAO rats. Collectively, our findings suggested that luteoloside played a crucial neuroprotective role by inhibiting NF-κB signaling in focal cerebral ischemia in rats. Furthermore, PPARγ and Nrf2 were also important for the anti-inflammatory effect of luteoloside. In addition, our data suggested that luteoloside might be an effective treatment for cerebral ischemia and other neurological disorders.

Introduction

Ischemic stroke is one of the main causes of death and disability in developed countries [1]. Ischemic stroke occurs when blood supply to the brain becomes interrupted. Although cerebral ischemia causes high morbidity in the clinic, therapeutic options for acute ischemic stroke remain very limited, and few neuroprotective treatments have been successfully developed to prevent ischemic stroke.

Cerebral ischemia-reperfusion (I/R) injury after thrombolysis in stroke leads to the rapid death or apoptosis of neurons in ischemic penumbra. The process of neuronal injury after cerebral ischemia is very complicated, but an increasing number of studies has demonstrated that the inflammatory response plays an important role in the above process [2]. The increased production of inflammatory cytokines and proinflammatory mediators aggravates neurological injury and promotes apoptosis of neural cells following ischemia [3]. Therefore, preventing inflammation and apoptosis is a feasible strategy for ischemic stroke intervention.

Nuclear factor-kappa B (NF-κB) is a critical transcription factor that regulates inflammation and various autoimmune diseases [4]. Expression of a large number of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-α), interleukin-lβ (IL-1β), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), can be regulated by the activation of NF-κB [5,6]. Studies suggest that NF-κB is activated in cerebral vascular endothelial cells, glial cells and neurons after cerebral ischemia, which triggers a dramatic increase in the expression of inflammatory cytokines, leading to an inflammatory cascade reaction and aggravating brain damage [7].

Peroxisome proliferator activated receptor gamma (PPARγ) is a ligand-activated nuclear transcription factor. PPARγ agonists have been reported to show anti-inflammatory and anti-oxidant effects in several models of central nervous system disorders, such as ischemic stroke, Alzheimer's disease and Parkinson's disease [8,9]. Several in vitro and in vivo studies demonstrate that PPARγ reduces proinflammatory cytokine release by inhibiting the nuclear transcription factor NF-κB [10,11].

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that plays an important role in the response to oxidative stress. In recent years, increasing evidence has shown that activation of the Nrf2 pathway significantly inhibits NF-κB and plays a protective role in the inflammatory response [12,13]. In brief, the interaction of Nrf2 and the NF-κB pathway plays an important role in the development of cerebral ischemia pathology and has become an important neuropathologic mechanism and therapeutic target.

Luteoloside (also called cynaroside or luteolin‑7‑O‑glucoside) is a flavonoid compound found in many plants and herbs. It has been reported that luteoloside has anti-oxidative, anti-inflammatory, antibacterial, antiviral, anticancer and other functions [[14], [15], [16], [17]]. For example, recent studies showed that luteoloside exerted cardioprotective effects in vitro [[18], [19], [20]]. However, there are few reports on the neuroprotective effects of luteoloside.

Therefore, this study was designed to evaluate the protective effects of luteoloside on cerebral I/R injury induced by middle cerebral artery embolism (MCAO) and to investigate whether the inflammatory response mediated by PPARγ/Nrf2/NF-kB signaling is implicated in this process.

Section snippets

Compounds and reagents

Luteoloside (purity > 98%) was obtained from Herbpurify Co., Ltd. (Chengdu, China). ToxinSensor™ Single Test Kit, GenScript Biotech Co., Ltd. (Nanjing, China). 2,3,5‑Triphenyltetrazolium chloride (TTC) was obtained from Solarbio Science & Technology Co., Ltd., (Beijing, China). TNF-α and IL-1β Enzyme-Linked Immunosorbent Assay (ELISA) kits were provided by Nanjing Jiancheng Bioengineering Institute (Nanjing, China). Anti-IκBα, anti-p-IκBα, anti-p65, anti-p-p65, anti-PPARγ, anti-Nrf2 and lamin B

Luteoloside improved neural function and decreased damage and cerebral edema induced by MCAO in the rat brain

First, the effects of luteoloside on neural function in rats were evaluated by neurologic scores. There was no difference in the scores of the rats in the luteoloside group compared with those in the sham group (P > 0.05), and the scores of the MCAO rats were significantly increased (P ˂ 0.01). However, treatment with either luteoloside or nimodipine significantly decreased the scores compared with the MCAO-treatment group (Fig. 2A).

Next, the results showed that the administration of

Discussion

Cerebral ischemia remains the leading cause of morbidity and mortality worldwide, and no available drugs have been shown to be effective in clinical trials of ischemic stroke [1]. Therefore, the search for promising and safe neuroprotective agents is particularly urgent and important. Recently, many natural herbal extracts have attracted increasing attention because of their outstanding biological activities in many diseases. Luteoloside is a flavonoid compound that is widely found in plants

Acknowledgements

This research received specific grant from National Natural Science Foundation of China (31872311, 81273652, 81541072).

Conflict of interest

The authors declare that they have no competing interests.

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    The first two authors equally contributed to this work.

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