Effect of high hydrostatic pressure extraction on biological activities of stinging nettle extracts

Stinging nettle is traditionally used as a therapeutic herb. In the present work, the biological properties and toxicity of novel nettle leaf extracts obtained by high pressure assisted extraction (HPE) were studied and compared with similar extracts obtained with the same solvent under atmospheric pressure conditions. The studied extracts were obtained at pressure levels of 200 and 500 MPa, ≈10 min, 0 to 70% ethanol : water (v/v). Each extract was characterized for its individual compound profile and different biological properties, such as antioxidant activity, pro-oxidant activity (DNA degradation capacity) and antihypertensive activity, as well as cytotoxicity against Caco-2 and HaCat cell cultures. The main results indicate that in addition to the antioxidant and antihypertensive activities observed for the control extracts, a clear improvement of all the biological activities of the extracts obtained by HPE was observed. The extracts obtained at 200 MPa, 10 min, 35 and 70% ethanol were the ones presenting higher concentrations of phenolic acids and flavonoids, such as chlorogenic acid, isoferulic acid, and rutin; besides, they showed better results concerning all the studied biological activities. Those extracts also showed potential for DNA protection, since they were able not only to cause less damage in the DNA molecule than the controls, but also showed no pro-oxidant activity. Concerning cytotoxicity, it was observed that HPE extracts, at a concentration up to 1.0 mg mL-1, presented a metabolism inhibition below 10 and 15% for Caco-2 and HaCat cell lines, respectively.