Chemical and biological screening of stinging nettle leaves extracts obtained by modern extraction techniques

Biologically active compounds were isolated from stinging nettle (Urtica dioica L.) leaves using non-conventional extraction techniques such as ultrasound-assisted (UAE), microwave-assisted (MAE) and subcritical water extraction (SCW). Based on the extraction efficiency of six various solvents determined preliminary, water was selected as appropriate solvent for further extraction. The highest total phenolics (463.59 mg CAE/g SN) and flavonoids (11.00 mg CE/g SN) contents, and antioxidant activity (DPPH radical scavenging (IC50 = 16.93 μg/mL), reducing power (EC50 = 30.07 μg/mL) and polarographic assays (HPMC = 243.2%/mL) were ascribed to SCW extract. Cytotoxic and antimicrobial assays also confirmed domination of SCW technique. Superior cytotoxic activity against Hep2c, RD and L2OB cell lines (13.42 μg/mL, 9.69 μg/mL and 7.52 μg/mL, respectively) and potent antimicrobial activity extract against Staphylococcus aureus (MIC = 9.76 μg/mL) were also observed. The highest number of individual phenolic compounds were found in MAE extract. Rutin was identified as the most dominant compound in UAE, MAE and SCW extracts (578.36 μg/g, 722.83 μg/g and 215.49 μg/g, respectively), while sinapic acid as the most dominant phenolic acid (50.49 μg/g, 63.12 μg/g and 18.08 μg/g, respectively).