Achillea millefolium L. s.l. – is the antiphlogistic activity mediated by protease inhibition?

Achillea millefolium L. s.l. is traditionally used not only in the treatment of gastro-intestinal and hepato-biliary disorders, but also as an antiphlogistic drug.

As various proteases, for instance human neutrophil elastase (HNE) and matrix metalloproteinases (MMP-2 and -9), are associated with the inflammatory process, the aim of this study was to test a crude plant extract in different protease inhibition assays for understanding the mechanisms of antiinflammatory action. Furthermore, two fractions enriched in phenolic compounds – flavonoids and dicaffeoylquinic acids (DCCAs), respectively – were also tested in order to evaluate the contribution of those substances to the antiphlogistic activity of the drug.

Briefly, various concentrations of the extract and the two fractions were incubated with the respective proteases and a chromogenous substrate. After measuring the absorbance against a blank sample, the percentage of protease inhibition was determined and allowed calculation of the IC₅₀ values.

The extract and the flavonoid fraction inhibited HNE showing IC₅₀ values of 20µg/mL, whereas the DCCA fraction was less active (IC₅₀=65µg/mL). The inhibitory activity on MMP-2 and -9 was observed at IC₅₀ values from 600 to 800µg/mL, whereas the DCCA fraction showed stronger effects than the flavonoid fraction and the crude extract.

In conclusion, the antiphlogistic activity of Achillea millefolium L. s.l. is at least partly mediated by inhibition of human neutrophil elastase and matrix metalloproteinase-2 and -9, whereas the extract was equally or even stronger effective than the two fractions which is consistent with the holistic approach of phytotherapy.