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.