Sambucus nigra L. leaves inhibit TNF-α secretion by LPS-stimulated human neutrophils and strongly scavenge reactive oxygen species

Sambucus nigra (elderberry) leaves were used in folk medicine to treat skin inflammations, ulcers, burns or boils, as well as to treat wounds, including infected and chronic ones. For centuries, elderberry leaves have been used mainly in eastern and southern Europe, as well as in western Asia.The study aimed to investigate the anti-inflammatory and antioxidant activity of four different extracts, such as aqueous and ethanolic prepared at room temperature and the solvent's boiling point, from the leaves of elderberry.The effect of extracts both on the secretion of cytokines (TNF-α, IL-1β, and IL-8) and reactive oxygen species (ROS) by neutrophils stimulated with bacteria-derived products was investigated. The cytotoxicity of extracts was analyzed by staining with propidium iodide measured by flow cytometry. The anti-inflammatory activity of extracts was also investigated through their influence on lipoxygenase activity. The antioxidant properties, including scavenging superoxide anion, hydrogen peroxide, nitric oxide, and 2,2-diphenyl-1-picrylhydrazyl radical were investigated in cell-free systems. The total content of phenolic compounds was tested using the Folin-Ciocalteu reagent. The qualitative and quantitative determination of the content of individual phenolic acids and flavonoids was performed by HPLC-DAD-MSn and HPLC-DAD method, respectively.Elderberry leaves extracts turned out to affect the inflammatory response of neutrophils by inhibiting the secretion of TNF-α and ROS. The ethanolic and aqueous extracts at a concentration of 50 μg × mL-1 reduce the secretion of TNF-α by approximately 40% and 10%, respectively. ROS secretion was decreased by around 50% for all extracts at concentration of 5 μg × mL-1. All the extracts were able to inhibit the activity of lipoxygenase. The ethanolic extracts were characterized by a higher content of phenolic compounds and a higher antioxidant activity, especially against nitric oxide, compared to the aqueous extracts.Our research has confirmed that elderberry leaves are a plant material with anti-inflammatory activity, especially against reactive oxygen species, and a potentially rich source of antioxidants. Preliminary analyses performed in this study could be the first step in confirming the traditional use of elderberry leaves in relieving inflammation.