Hieracium waldsteinii (Asteraceae) and Onosma stellulata (Boraginaceae) as a Source of Antioxidant and Antimicrobial Agents

Abstract

The current study aimed to phytochemically characterize (including a detailed phenolic profile) two endemic Balkan's species (Hieracium waldsteinii and Onosma stellulata) and determine their possible application as a source of natural antioxidant and antimicrobial agents. The main phenolic compound in both species (in all examined parts) was chlorogenic acid. Eriodictyol, genistein and naringenin were quantified only in H. waldsteinii while isorhamnetin‐3‐O‐rutinoside and sinapic acid were characteristic for O. stellulata. The highest antioxidant activity (98 mg AAE/g dry weight for TAC assay) was ascribed to the flower extract of H. waldsteinii while the lowest results (∼4.3 mg AAE/g dry weight for FRP assay) were exhibited by the extracts obtained from the plant's stem. Antimicrobial assays showed moderate antibacterial, i. e., moderate/strong activity against several tested fungi (in particular Trichoderma viride). Correlation analysis revealed strong positive connection between phenolic compounds and reducing power of extracts as well as between total phenolic and flavonoid content and the obtained minimal inhibitory concentration recorded in antibacterial assays.

Antimicrobial and Cytotoxic Activities of Selected Hieracium L. s. str. (Asteraceae) Extracts and Isolated Sesquiterpene Lactones

“…As for other previously investigated Hieracium species, it can be observed that the activity of dry 80 % MeOH extracts of leaves, stems and flowers of H. waldsteinii against bacteria S. aureus , B. cereus , L. monocytogenes , S. Typhimurium , E. coli , E. cloacae and P. aeruginosa , and fungi A. fumigatus , A. versicolor , A. ochraceus , T. viride , P. funiculosum and P. verrucosum var. cyclopium , determined in the same microdilution test, was in many cases comparable to the activity of Hieracium extracts investigated in this work; regarding activity of H. waldsteinii extracts against Micrococcus luteus , it was better than the activity of our Hieracium extracts against other tested species of this genus, M. flavus [11] . As for hexane extracts of H. umbellatum roots, leaves and stems, their antimicrobial activity against E. coli was assessed by modified microdilution method, based on measurement of optical density; roots and stems extracts showed weak activity and leaves extract was not active [9]…”

“…Previously investigated polar extracts of H. waldsteinii leaves, stems and flowers (on HT29 – human colon adenocarcinoma) and H. umbellatum flowering aerial parts (on HeLa, MCF7 – human breast adenocarcinoma and A431 – human skin epidermoid carcinoma) showed weak activity or were not active at maximal tested concentrations of 10 μg/mL ( H. umbellatum ) and 500 μg/mL ( H. waldsteinii ) [10,11] …”

“…cyclopium, determined in the same microdilution test, was in many cases comparable to the activity of Hieracium extracts investigated in this work; regarding activity of H. waldsteinii extracts against Micrococcus luteus, it was better than the activity of our Hieracium extracts against other tested species of this genus, M. flavus. [11] As for hexane extracts of H. umbellatum roots, leaves and stems, their antimicrobial activity against E. coli was assessed by modified microdilution method, based on measurement of optical density; roots and stems extracts showed weak activity and leaves extract was not active. [9] Established antimicrobial effect of H. scheppigianum dried CH 2 Cl 2 extract could be at least partly linked to its previously identified triterpenes of ursane and oleane type.…”

“…Non‐polar extracts of H. umbellatum roots, leaves and stems were tested against one bacteria and polar extracts of its flowering aerial parts on three cancer cell lines [9,10] . Polar extracts of H. waldsteinii leaves, stems and flowers were tested against eight bacteria and six fungi, as well as one cancer cell lines [11] …”

“…[9,10] Polar extracts of H. waldsteinii leaves, stems and flowers were tested against eight bacteria and six fungi, as well as one cancer cell lines. [11] The subjects of this research were isolates of six more Hieracium species: dried methanol (MeOH) extracts of H. calophyllum R. UECHTR., H. coloriscapum ROHLENA & ZAHN, H. pseudoschenkii (ROHLENA & ZAHN) NIKETIĆ, H. glabratum WILLD.…”