Synanthropic Plants as an Underestimated Source of Bioactive Phytochemicals: A Case of Galeopsis bifida (Lamiaceae)

Hemp nettle (Galeopsis bifida Boenn.) is a synanthropic species of the Lamiaceae family that is widely distributed across Europe, Asia, and Siberia. Galeopsis bifida is deeply embedded in the ethnomedical tradition of Asian healers; however, this plant is still poorly characterized, both chemically and pharmacologically. To study Siberian populations of G. bifida, we used high-performance liquid chromatography with photodiode array and electrospray triple quadrupole mass detection for metabolic profiling. Ninety compounds were identified, including iridoid glycosides, phenylethanoid glycosides, hydroxycinnamates, and flavone glycosides, most of which were identified in G. bifida for the first time, while some phenolics were found to have potential chemotaxonomic significance in the Lamiaceae family and Galeopsis genus. An unequal quantitative distribution of the selected metabolites was observed within separate organs of the G. bifida plant, characterized by high accumulation of most compounds within the aerial part of the plant (leaves, flowers). Analysis of the content of specific chosen compounds within the leaves of different populations of G. bifida from Eastern Siberia revealed the existence of two chemical types based on metabolic specifics: the southern type accumulates flavone glucuronides, while the northern type tends to accumulate high levels of phenylpropanoids and acylated flavone glucosides. The first study of the bioactivity of G. bifida extract demonstrated that the herb has low toxicity in acute experiments and expresses antioxidant potential against free radicals in the form of DPPH˙, ABTS˙+, and superoxide radical, as well as high ferric reducing antioxidant power, oxygen radical absorbance capacity, and protective action in the carotene bleaching assay. In general, our results suggest the herb of G. bifida as a new, prospective synanthropic plant for medical application.