Anti-inflammatory effect of the six compounds isolated from Nauclea officinalis Pierre ex Pitard, and molecular mechanism of strictosamide via suppressing the NF-κB and MAPK signaling pathway in LPS-induced RAW 264.7 macrophages

Ethnopharmacological relevance: Nauclea officinalis Pierre ex Pitard. is a Chinese medicinal herb that contains high level of alkaloids which is the most abundant and active constituent. Strictosamide isolated from Nauclea officinalis Pierrc ex Pitard. showed significant effects on inflammatory response, compared with pumiloside, 3-epi-pumiloside, vincosamide, 3 alpha,5 alpha-tetrahydrodeoxycordifoline lactam and naucleamide A-10-O-beta-D-glucopyranoside of this plant. Aim of study: we investigated the biological activities of the six compounds mentioned-above, and the underlying molecular mechanism exerted by the most potent one, strictosamide. Materials and methods: The effects of strictosamide and other five compounds on the inhibitory activity of nitric oxide (NO) were screened by Griess test. The contents of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) in media were detected by using Enzyme-linked immunosorbent (ELISA) kits. The effects on the mRNA expression of nitric oxide synthase (iNOS), TNT-alpha and IL-1 beta of strictosamide were further investigated by RT-qPCR. Western blot assay was conducted to illustrate the effects of strictosamide on iNOS and phosphorylation of p65, inhibitor of NF-kappa B (I kappa B)-alpha, I kappa B-kinase (IKK)-alpha as well as p-extracellular signal regulated kinase (ERK), p-c-jun N-terminal kinase (JNK) and p-p38 in the protein levels. Results: Strictosamide potently suppressed the productions of NO, TNF-alpha and IL-1 beta in LPS-induced RAW 264.7 macrophages, and it dose-dependently alleviated the LPS-simulated protein level of iNOS as well as the mRNA expressions of iNOS, TNF-alpha and IL-1 beta. In addition, molecular data revealed that strictosamide markedly decreased the expressions of p-p65, p-I kappa B alpha and p-IKK alpha. Furthermore, strictosamide significantly attenuated LPS-induced the phosphorylation of p38, ERIK and JNK. Conclusions: At present study, the results indicated that the anti-inflammatory activity of strictosamide was associated with the restraint of NO, TNF-alpha and IL-1 beta via negative regulation of both NF-kappa B and mitogen-activated protein kinases (MAPKs) in LPS-induced RAW 264.7 cells.