Urolithin A attenuates pro-inflammatory mediator production by suppressing PI3-K/Akt/NF-kappa B and JNK/AP-1 signaling pathways in lipopolysaccharide-stimulated RAW264 macrophages: Possible involvement of NADPH oxidase-derived reactive oxygen species

摘要

Urolithin A, a gut microbial metabolite of ellagic acid, is reported to exert anti-inflammatory effects in vitro and in vivo. However, complete mechanisms underlying the regulation of inflammatory responses by urolithin A remain unclear. This study aimed to evaluate the anti-inflammatory potential of urolithin A and its underlying mechanisms in lipopolysaccharide (LPS)-stimulated RAW264 macrophages. Urolithin A significantly attenuated the pro-inflammatory mediator production in LPS-stimulated RAW264 and mouse peritoneal macrophages. This compound significantly suppressed the LPS-elicited nuclear factor-kappa B (NF-kappa B) and activator protein-1 (AP-1) activation. The phosphorylation of Akt and c-Jun N-terminal kinase (JNK) was also inhibited by the treatment with urolithin A. Through experiments using kinase inhibitors, urolithin A abolished the LPS-induced phosphatidylinositol 3-kinase (PI3-K)/Akt/NF-kappa B and JNK/AP-1 signaling pathways, resulting in suppression of proinflammatory mediator production. Furthermore, treatment with this compound significantly reduced the intracellular accumulation of reactive oxygen species, which are known to act as secondary messengers in the activation of redox-sensitive transcription factors NF-kappa B and AP-1. Urolithin A treatment also diminished the LPS-evoked activation of NADPH oxidase (NOX), which is the main source of reactive oxygen species in activated macrophages. The inhibition of this activity by urolithin A led to the prevention of LPS-elicited NF-kappa B and AP-1 activation as well as Akt and JNK phosphorylation, resulting in the reduction of pro-inflammatory mediator production. Collectively, these results indicate that urolithin A treatment attenuates pro-inflammatory mediator production by suppressing NOX-derived reactive oxygen species-mediated PI3-K/Akt/NF-kappa B and JNK/AP-1 signaling pathways in LPS-stimulated macrophages.