Inhibitory effects of Willow bark extracts on proinflammatory processes in LPS activated human monocytes

Willow bark (Salix daphnoides, purpurea, and fragilis) is successfully applied in the treatment of painful and pro-inflammatory diseases. Aim of the present study was to study the effects of five fractions (A-E) of a standardized willow bark extract, differing in polyphenol and salicylate content, on the regulation of inflammatory processes in activated human monocytes.

Monocytes from buffy coats of healthy subjects were isolated by Histopaque-density gradient centrifugation and adhesion. The monocytes were pre-incubated for 90min with 5–30µg/mL willow bark extract and their fractions A-E, 30µg/mL diclofenac or aspirin. Thereafter they were incubated in serum-free RPMI 1640 medium with interferon-gamma (INF-γ; 50 U/mL; 45min) and lipopolysaccharide (LPS; 1µg/mL) for 5 to 48 hours. Apoptosis of monocytes (YO-PRO-1®-staining), intracellular NO-concentration (DAF-FM-diacetate), gene (real-time PCR) and protein (Cell Elisa) expressions of caspase-3, cyclooxygenase-2 (COX-2) and tumor necrosis factor-alpha, and nitrite concentration in the supernatant (Griess–reagens) were analyzed.

The willow bark extract and all fractions (A-E) inhibited the pro-inflammatory increase of survival rate of monocytes by IFN-gamma/LPS significantly. The increased gene and protein expressions of COX-2 and tumor necrosis factor-alpha, and the inhibitory effects on nitrite relase and NO-concentration of LPS activated monocytes were significantly reduced by willow bark extract and to varying extents by its fractions. The anti-inflammatory effects of the plant extracts were compared to the NSAID diclofenac and to aspirin, which were used as reference.

Fractions of a standardized willow bark extract differ in their inhibitory effects on inflammatory processes suggest a predominant role of the polyphenol content.