The flavonoid baicalin exhibits anti-inflammatory activity by binding to chemokines

Baicalin (BA) is a flavonoid compound purified from the medicinal plant Scu tellaria baicalensis Georgi acid has been reported to possess anti-inflamma tory and anti-viral activities. In order to elucidate the mechanism(s) of a ction of BA, we tested whether BA could interfere with chemokines or chemok ine receptors, which are critical mediators of inflammation and infection. We observed that BA inhibited the binding of a number of chemokines to huma n leukocytes or cells transfected to express specific chemokine receptors. This was associated with a reduced capacity of the chemokines to induce cel l migration. Go-injection of BA with CXC chemokine interleukin-8 (IL-8) int o rat skin significantly inhibited IL-8 elicited neutrophil infiltration. B A did not directly compete with chemokines for binding to receptors, but ra ther acted through its selective binding to chemokine ligands. This conclus ion was supported by the fact that BA cross-linked to oxime resin bound che mokines of the CXC (stromal cell-derived factor (SDF)-1 alpha, IL-8), CC (m acrophage inflammatory protein (MIP)-1 beta, monocyte chemotactic protein ( MCP)-2), and C (lymphotactin (Ltn)) subfamilies, BA did not interact with C X3C chemokine fractalkine/neurotactin or other cytokines, such as TNF-alpha and IFN-gamma, indicating that its action is selective. These results sugg est that one possible anti-inflammatory mechanism of BA is to bind a variet y of chemokines and limit their biological function. (C) 2000 Elsevier Scie nce B.V. All rights reserved.