Phytochemical Characterization of Water Avens (Geum rivale L.) Extracts: Structure Assignment and Biological Activity of the Major Phenolic Constituents

Abstract

Water avens (Geum rivale L.) is a common Rosaceae plant widely spread in Europe and North America. It is rich in biologically active natural products, some of which are promising as prospective pharmaceuticals. The extracts of water avens are well known for their triterpenoid metabolites and associated anti-inflammatory, antimicrobial and antioxidant activities. However, the polyphenolic profiles of G. rivale L. are still awaiting complete characterization. Accordingly, the contribution of its individual components to the antioxidant, antibacterial and neuroprotective activity of the extracts is still unknown. As this plant can be available on an industrial scale, a better knowledge of its properly-relevant constituents might give access to new highly-efficient pharmaceutical substances and functional products. Therefore, herein we comprehensively characterize the secondary metabolome of G. rivale by ESI-HR-MS, ESI-HR-MSn and NMR spectroscopy with a special emphasis on the polyphenolic composition of its aerial parts. Furthermore, a multilateral evaluation of the antioxidant, neuroprotective and antibacterial properties of the aqueous and ethyl acetate fractions of the total aqueous alcoholic extract as well as individual isolated polyphenols was accomplished. Altogether four phenolic acid derivatives (trigalloyl hexose, caffeoyl-hexoside malate, ellagic acid and ellagic acid pentoside), six flavonoids (three quercetin derivatives, kaempferol and three its derivatives and two isorhamnetin derivatives) and four tannins (HHDP-hexoside, proantocyanidin dimer, pedunculagin I and galloyl-bis-HHDP-hexose) were identified in this plant for the first time. The obtained aqueous and ethyl acetate fractions of the total extract as well as the isolated individual compounds showed pronounced antioxidant activity. In addition, a pronounced antibacterial activity against several strains was proved for the studied fractions (for ethyl acetate fraction the highest activity against E. coli АТСС 25922 and S. aureus strains ATCC 27853 and SG-511 (MIC 15.6 μg/mL) was observed; for aqueous fraction—against Staphylococcus aureus SG-511 (MIC 31.2 μg/mL)). However, the anti-neurodegenerative (neuroprotective) properties could not be found with the employed methods. However, the antibacterial activity of the fractions could not be associated with any of the isolated individual major phenolics (excepting 3-O-methylellagic acid). Thus, the aerial parts of water avens represent a promising source of polyphenolic compounds with antioxidant activity and therefrom derived human health benefits, although the single constituents isolated so far lack a dominant selectively bioactive constituent in the bioassays performed.

First Insight into the Neuroprotective and Antibacterial Effects of Phlorotannins Isolated from the Cell Walls of Brown Algae Fucus vesiculosus and Pelvetia canaliculata

“…However, fortunately, the diluted extracts were absolutely non-colored, and no interference with the well-established and routinely used spectrophotometric assay could be expected. Therefore, here we relied on the standard spectrophotometric test well-established in our lab [ 32 ]. Similar to the polyphenols of terrestrial plants, the phlorotannins represent reducing compounds and are readily involved in electron donation reactions.…”

“…The analysis of the antimicrobial activity was accomplished as described by Orlova et al [ 32 ] with changes. Thereby, the minimum inhibitory concentrations (MIC) of the intracellular and CW-bound phlorotannin extracts were determined by the broth microdilution method, as recommended by the Clinical Laboratory Standards Institute, USA [ 33 ].…”

Ellagitannins from Eucalyptus camaldulensis and their potential use in the food industry

“…In phenolic compounds, antibacterial activity is one of the most sought-after due to its great capacity to inhibit pathogenic bacteria and the bactericidal effect that some of them have [62]. In antibacterial activity, pedunculagin has shown an anti-hemolytic effect on S. aureus [63] as well as in fractions of pedunculaginrich extracts [64,65], which is a bacterium commonly found in some foods causing food poisoning, being the main cause of food poisoning worldwide [51]. Anti-hemolytic effect is important due to the hemolysis produced by the alpha toxin of S. aureus.…”

“…This hemolytic toxin causes the rupture of the red blood cell membrane. The α-hemolysin binds to the cell surface and facilitates the transport of molecules such as potassium ion (K + ) and Ca 2+ ions, which causes necrotic death of the host cell [66], On the other hand, fractions obtained from Clidemia hirta, rich in pedunculagin have been effective to inhibit E. coli at concentrations greater than 100 μg/mL [64], as well as extracts of Geum rivale L. rich in pedunculagin were able to inhibit E. coli and L. monocytogenes at lower concentrations [65].…”

Suspension Cell Culture of Polyscias fruticosa (L.) Harms in Bubble-Type Bioreactors—Growth Characteristics, Triterpene Glycosides Accumulation and Biological Activity

“…The antibacterial activity analysis was modified from Orlova et al [72]. Bacterial strains used were Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Staphylococcus aureus ATCC 25923, MRSA ATCC 33591.…”