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

Baicalin (BA) is a flavonoid compound purified from the medicinal plant Scutellaria baicalensis Georgi and has been reported to possess anti-inflammatory and anti-viral activities. In order to elucidate the mechanism(s) of action of BA, we tested whether BA could interfere with chemokines or chemokine receptors, which are critical mediators of inflammation and infection. We observed that BA inhibited the binding of a number of chemokines to human leukocytes or cells transfected to express specific chemokine receptors. This was associated with a reduced capacity of the chemokines to induce cell migration. Co-injection of BA with CXC chemokine interleukin-8 (IL-8) into rat skin significantly inhibited IL-8 elicited neutrophil infiltration. BA did not directly compete with chemokines for binding to receptors, but rather acted through its selective binding to chemokine ligands. This conclusion was supported by the fact that BA cross-linked to oxime resin bound chemokines of the CXC (stromal cell-derived factor (SDF)-1α, IL-8), CC (macrophage inflammatory protein (MIP)-1β, monocyte chemotactic protein (MCP)-2), and C (lymphotactin (Ltn)) subfamilies. BA did not interact with CX3C chemokine fractalkine/neurotactin or other cytokines, such as TNF-α and IFN-γ, indicating that its action is selective. These results suggest that one possible anti-inflammatory mechanism of BA is to bind a variety of chemokines and limit their biological function.