Spilanthol Inhibits Inflammatory Transcription Factors and iNOS Expression in Macrophages and Exerts Anti-inflammatory Effects in Dermatitis and Pancreatitis.

Edina Bakondi,Csaba Hegedűs,Sándor Kéki,Salam Bhopen Singh,Máté Á Demény,Katalin Kovács,Éva Szabó,Péter Hegyi,László Virág,Tamara Madácsy,Tibor Nagy,József Maléth,Zsolt Regdon,Máté Nagy-Pénzes,Zoltán Hajnády

doi:10.3390/ijms20174308

Abstract

Activated macrophages upregulate inducible nitric oxide synthase (iNOS) leading to the profuse production of nitric oxide (NO) and, eventually, tissue damage. Using macrophage NO production as a biochemical marker of inflammation, we tested different parts (flower, leaf, and stem) of the medicinal plant, Spilanthes acmella. We found that extracts prepared from all three parts, especially the flowers, suppressed NO production in RAW macrophages in response to interferon-γ and lipopolysaccharide. Follow up experiments with selected bioactive molecules from the plant (α-amyrin, β-caryophylline, scopoletin, vanillic acid, trans-ferulic acid, and spilanthol) indicated that the N-alkamide, spilanthol, is responsible for the NO-suppressive effects and provides protection from NO-dependent cell death. Spilanthol reduced the expression of iNOS mRNA and protein and, as a possible underlying mechanism, inhibited the activation of several transcription factors (NFκB, ATF4, FOXO1, IRF1, ETS, and AP1) and sensitized cells to downregulation of Smad (TF array experiments). The iNOS inhibitory effect translated into an anti-inflammatory effect, as demonstrated in a phorbol 12-myristate 13-acetate-induced dermatitis and, to a smaller extent, in cerulein-induced pancreatitis. In summary, we demonstrate that spilanthol inhibits iNOS expression, NO production and suppresses inflammatory TFs. These events likely contribute to the observed anti-inflammatory actions of spilanthol in dermatitis and pancreatitis.

Highlights

Inflammation is the protective response of the innate immune system to an injury or pathogen invasion
Overall our study identified spilanthol as a potent bioactive molecule that reduces nitric oxide (NO) production in activated macrophages
Spilanthol interferes with activation of several TFs known to switch on the inducible nitric oxide synthase (iNOS) promoter

Summary

Introduction

Inflammation is the protective response of the innate immune system to an injury or pathogen invasion. Inflammatory macrophages release large amounts of proinflammatory cytokines, chemokines, and reactive oxygen and nitrogen species (ROS/RNS) locally, which kills and phagocytoses pathogens, activates the vascular endothelium, recruits and activates leukocytes [1]. Activated inflammatory macrophages play a central role in the orchestration of the inflammatory response. In addition to producing a wide variety of proinflammatory cytokines and chemokines, they are important sources of reactive oxygen and nitrogen species (ROS/RNS). There is a correlation between the activity of the disease and iNOS expression in inflamed tissues or circulating monocytes [7]. Recent research findings identified novel targets such as various secreted mediators or their receptors, intracellular signaling molecules, and transcription factors (NFκB/IκB, MAP kinases, and AP-1), enzymes (PLA2, iNOS) and the release of ROS/RNS [15]. The surging popularity of herbal medicines and a multi-target treatment approach to reduce doses and improve efficacy and safety, lend legitimacy to the search for naturally occurring complementary anti-inflammatory agents (e.g., curcumins, ginger, resveratrol, various plant polyphenols, cannabinoids, epigallocatechin, capsaicin, and berberin)

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Conclusion