Frutescone O from Baeckea frutescens Blocked TLR4-Mediated Myd88/NF-κB and MAPK Signaling Pathways in LPS Induced RAW264.7 Macrophages.

Jiqin Hou,Xiaobing Lin,Lin Zhu,Ming Yan,Junhan Zhang,Xiaofei An,Hao Wang,Ruina Tian,Decai Fan

doi:10.3389/fphar.2021.643188

Abstract

Frutescone O was isolated from the aerial parts of Baeckea frutescens L., which was commonly used as a folk medicinal material for treating anti-inflammatory disease in South East Asia. This study aimed to investigate the anti-inflammatory activity and related signaling cascade of Frutescone O (Fru) in LPS induced RAW264.7 cells. The anti-inflammation activity of Frutescone O was determined according to the inhibitory effects on the secretion of nitric oxide (NO), expression of inducible NO synthase, and pro-inflammatory cytokines. The regulation of Myeloid differentiation factor 88 (Myd88), inhibition of NF-κB, and MAPK pathways were further investigated for molecular mechanisms. Fru significantly decreased the expression of iNOS and the production of NO in LPS-stimulated RAW264.7 cells. It also dose-dependently suppressed LPS induced expression of IL-1β, IL-6, and TNF-α. Furthermore, Fru remarkably inhibited the upregulation of NF-κB (p50) expression in the nucleus and the phosphorylation ratio of p38, JNK, ERK, and Myd88 signaling protein. The molecular docking and cellular thermal shift assay (CETSA) results indicated that Fru participated in a robust and stable interaction with the active site of TLR4-MD2. Thus, Fru suppressed the LPS induced inflammation in RAW264.7 cells by blocking the TLR4 mediated signal transduction through the NF-κB and MAPK signaling pathways and inhibiting the Myd88 and iNOS expression.

Highlights

Baeckea frutescens L. is a small tree found in mountainous regions
The purity of compound Frutescone O (Fru) was determined to be over 98% by normalization of the peak area detected by HPLC-UV (Figure 1A)
The purity of Fru was determined to be over 98% by normalization of the peak area detected by HPLC-UV (Figure 1A)

Summary

Introduction

Baeckea frutescens L. is a small tree found in mountainous regions. It is a medicinal plant of the family Myrtaceae and subfamily Myrtoideae. As a traditional folk medicine in South East Asia, it is often used to treat inflammatory diseases, including rheumatism, snake bites, dermatitis, and the common cold (Hou et al, 2017). Fru is a meroterpenoid isolated from Baeckea frutescens and has various medical functions (Razmavar et al, 2014). Fru was supposed to be related to the NF-κB signaling pathway regulation via the suppression of p65 nuclear translocation in LPS-induced macrophages (Hou et al, 2017). The anti-inflammatory mechanism of Fru is further studied in LPS-stimulated RAW264.7 cells

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Conclusion