Given the central role of macrophages in tissue repair and regeneration, we formulated the hypothesis that one of the cellular targets of Arnica m. an action is the macrophage and accordingly decided to evaluate this plant’s effects in vitro on the THP-1 human cell line, a widely used model for immune modulation. This cell line is widely used in laboratories for the study of macrophage biochemistry and molecular biology.
The advantage of a cell line resides essentially in the easier reproducibility of experiments in the same conditions, avoiding the variations due to individual sensitivity of different donors. Since we used very low doses of drugs—even with the highest Arnica m. 2c dilution, in the assay medium the sesquiterpene lactones are in the 10−8 Mol/L dose—we expected small effect sizes and so preferred to use a highly reproducible model. THP-1 cells resemble primary monocytes, but when treated with low doses of phorbol esters (PMA) they differentiate to cells with the morphological and functional features of tissue macrophages. On the basis of environmental cues and molecular mediators, macrophages differentiate to either a proinflammatory type (M1) or to an anti-inflammatory or pro-reparatory type (M2).
Accordingly, we used THP-1 macrophages polarized by interleukin-4 (IL-4) treatment to a phenotype that takes on characteristic properties functional to immune regulation, wound healing, and tissue remodeling. The results of this work indicate that Arnica m. acts on macrophages by modulating a number of genes and by increasing cell motility. RNA-Seq analysis allowed the identification of several genes which are particularly sensitive to ultra-low doses and high dilutions of this plant extract.
Molecular analysis of gene expression suggests that a primary action of this medicinal plant is the stimulation of tissue matrix synthesis. These findings provide new insights into wound-associated molecular events and specifically point to macrophage fibronectin production as a potential therapeutic target of Arnica m. for the treatment of wound repair.