Beta-naphthoflavone inhibits LPS-induced inflammation in BV-2 cells via AKT/Nrf-2/HO-1-NF-κB signaling axis

Abstract

Numerous studies have shown that over-activation of microglia could cause neuroinflammation and release pro-inflammatory mediators, which could result in neurodegenerative diseases, like Parkinson’s disease, Alzheimer’s disease etc. Beta-naphthoflavone (BNF) has anti-oxidant and anti-inflammatory effects in borderline tissues, but BNF has not been reported the effect associated with neuroinflammation. Therefore, the purpose of this experiment is to inquiry the impact and mechanism of BNF on neuroinflammation. The results indicated that BNF significantly inhibited the production of pro-inflammatory mediators (inducible nitric-oxide synthase (iNOS), Cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α) andinterleukin-6 (IL-6)) in LPS-exposed BV-2 cells. Analysis of western blot results found that BNF accelerated the activation of AKT/Nrf-2/HO-1 signaling pathway and suppressed NF-κB pathway activation. Further study showed that BNF inhibited activation of NF-κB pathway via promoting HO-1, and SnPP IX (a HO-1 inhibitor) could inhibit anti-inflammatory function of BNF. We also found that BNF reduced the apoptosis rate of Human neuroblastoma cells (SHSY5Y) and mouse hippocampal neuron cell line (HT22) by inhibiting release of inflammatory mediators in LPS-exposed BV2 cells. In a word, our results suggested that BNF could inhibit inflammatory response via AKT/Nrf-2/HO-1-NF-κB signaling axis in BV-2 cells and exerts neuroprotective impact via inhibiting the activation of BV2 cells.

Introduction

Neurodegenerative disease, which was caused by loss of a specific neuron or its myelin, is a complex central nervous system disease (Kang et al., 2017; Csencsits-Smith et al., 2016). Such diseases can cause great damage to the physical and mental health of patients, seriously reduce the quality of life of patients, and bring huge economic losses to the family. Accumulating evidence has suggested that the pathogenic mechanism of neurodegenerative disease is associated with several elements, including genetic and environmental factors, physiological aging and oxidative stress (Gitler et al., 2017; He et al., 2018; Manoharan et al., 2016). The specific cause is still unclear. However, evidences have confirmed that mediated inflammation by activated microglia may be integral to the neurodegenerative progression. Activated microglia can produce and release a large number of different neurotoxic factors, including interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), inducible nitric-oxide synthase (iNOS) and cyclooxygenase-2 (COX-2)), which may damage neurons and lead to neurodegenerative disease (Block et al., 2007; Kim et al., 2014; Kim and Joh, 2006; Huang et al., 2018). Thus, suppression of microglia-mediated neuroinflammation could be a useful treatment in neurodegenerative disease.

Beta-naphthoflavone (BNF), derivatived of natural flavonoids has anti-oxidant and anti-inflammatory effects. As the ligands for aromatic hydrocarbon receptors, BNF was widely used in the pharmaceutical industry. Recently, BNF has been reported to protect from peritonitis via decreasing TNF-α-induced endothelial cell activation (Ghanem et al., 2009; Hayashi et al., 2012; Hsu et al., 2015). Moreover, numerous studies have shown that BNF treatment attenuated neonatal hyperoxic lung injury and acute liver injury by inhibiting inflammation of peripheral tissues (Lingappan et al., 2018; Maturu et al., 2017). However, no researches have revealed impacts of BNF on neuroinflammation. Therefore, in this study, our purpose is to investigate whether BNF has an anti-inflammatory impact on neuroinflammation and reveal its anti-neuroinflammatory mechanism.