Comparison of Aqueous and Lactobacterial-Fermented <i>Mercurialis perennis</i> L. (Dog’s Mercury) Extracts with Respect to Their Immunostimulating Activity

Lactic acid (LA) fermentation of dog’s mercury (<i>M. perennis</i> L.) herbal parts was investigated in samples inoculated with either Lactobacteria (<i>Lactobacillus plantarum</i> and <i>Pediococcus pentosaceus</i>, LBF) or whey (WF). Depending on fermentation time, LA concentrations were monitored in a range of 3.4–15.6 g/L with a concomitant pH decline from 6.5 to 3.9. A broad spectrum of cinnamic acids depsides containing glucaric, malic and 2-hydroxyglutaric acids along with quercetin and kaempferol glycosides were detected by LC-DAD-ESI-MSⁿ. Moreover, in this study novel constituents were also found both in unfermented and fermented extracts. Furthermore, amino acids and particular Lactobacteria metabolites such as biogenic amines (e.g., putrescine, 4-aminobutyric acid, cadaverine) and 5-oxoproline were assigned in WF extracts by GC-MS analysis after silylation. Enhanced NFκB and cytokine expression (IL-6, TNFα, IL-8 and IL-1β) was induced by all extracts, both non-fermented and fermented, in NFκB-THP-1 reporter cells, showing a concentration-dependent immunostimulatory effect. The WF extracts were tested for micronuclei formation in THP-1 cells and toxicity in luminescent bacteria (<i>V. fischeri</i>), whereby no mutagenic or toxic effects could be detected, which corroborates their safe use in pharmaceutical remedies.