Longifolioside A inhibits TLR4-mediated inflammatory responses by blocking PKCδ activation in LPS-stimulated THP-1 macrophages

• Published in: Cytokine (Philadelphia, Pa.) Vol. 131; p. 155116
• Main Authors: Lee, Su Ui, Oh, Eun Sol, Ryu, Hyung Won, Kim, Mun-Ock, Kang, Myung-Ji, Song, Yu Na, Lee, Ro Woon, Kim, Doo-Young, Ro, Hyunju, Jung, Sunin, Hong, Sung-Tae, Oh, Sei-Ryang
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.07.2020
• Subjects: Inflammation; Lipopolysaccharides; Longifolioside A; Toll-like receptor 4; Toll/interleukin-1 receptor domain-containing adapter protein; Toll/interleukin-1 receptor domain-containing adapter protein; eNOS; JNK; Toll-like receptor 4; Inflammation; TIRAP; Lipopolysaccharides; IRAK; NF-κB; nNOS; ERK 1/2; iNOS; TLR4; MYD88; Longifolioside A; e.g; ELISA
• ISSN: 1043-4666; 1096-0023
• DOI: 10.1016/j.cyto.2020.155116

Longifolioside A is an iridoid glucoside compound isolated from Pseudolysimachion rotundum var. subintegrum, which has been used in traditional herbal medicines to treat respiratory inflammatory diseases. Logifolioside A is a potent antioxidant; however, its underlying pharmacological mechanisms of action in inflammatory diseases are unknown. Here, we investigated the inhibitory effects of longifolioside A in lipopolysaccharide (LPS)-stimulated toll-like receptor 4 (TLR4) signal transduction systems using human THP-1 macrophages and HEK293 cells stably expressing human TLR4 protein (293/HA-hTLR4). Longifolioside A significantly reduced the release of inflammatory cytokines such as interleukin (IL)-6, -8, and tumor necrosis factor (TNF)-α in LPS-stimulated THP-1 macrophages. Furthermore, longifolioside A inhibited the expression of inflammatory mediator genes such as inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 that produce nitric oxide (NO) and prostaglandin E2 (PGE2), respectively. Longifolioside A suppressed the phosphorylation of PKCδ, IRAK4, IKKα/β, IκBα, and mitogen-activated protein (MAP) kinases (ERK 1/2 and JNK, but not p38), thereby inactivating the nuclear localization of NF-κB and AP-1, and thus decreasing the expression of inflammatory response genes. Notably, longifolioside A disrupted the interaction between human TLR4 and the TIR domain-containing adaptor protein (TIRAP), an early step during TLR4 activation, thereby reducing IL-8 secretion in 293/HA-hTLR4 cells. This inhibitory effect was comparable to that of TAK-242 (a TLR4 inhibitor, or resatorvid). Our results indicate that longifolioside A prevents inflammatory response by suppressing TLR4 activation required for NF-κB and AP-1 activation.