Shikonin inhibits myeloid differentiation protein-2 to prevent lipopolysaccharide-induced acute lung injury. - GreenMedInfo Summary

BACKGROUND AND PURPOSE: Acute lung injury (ALI) is a challenging clinical syndrome which manifests as an acute inflammatory response. Myeloid differentiation protein 2 (MD2) has an important role in mediating lipopolysaccharide (LPS)-induced inflammation. Currently, there are no effective molecular-based therapies for ALI or viable biomarkers for predicting the severity of disease. Recent preclinical studies have shown that shikonin (SHI), a natural naphthoquinone, prevents LPS-inflammation. However, little is known about the underlying mechanisms.

EXPERIMENTAL APPROACH: The binding affinity of SHI to MD2 was analyzed using computer docking, surface plasmon resonance analysis and ELISA. In vitro, the anti-inflammatory effect and mechanism of SHI were investigated through ELISA, RT-qPCR, Western blotting and immunoprecipitation assay. In vivo, lung injury was induced by intratracheal administration of LPS and assessed by the change of histopathological and inflammatory markers. The underlying mechanisms were investigated by immunoprecipitation in lung tissue.

KEY RESULTS: We discovered that SHI directly binds to MD2 and interferes with the activation of toll-like receptor 4 (TLR4) by LPS. In cultured macrophages, SHI inhibited TLR4 signaling and proinflammatory cytokine production. These effects were produced through suppression of key signaling proteins including the nuclear factor-κB and the mitogen activated protein kinase pathway. We also show that SHI inhibits MD2-TLR4 complex formation, and reduces LPS-induced inflammatory responses in a mouse model of ALI.

CONCLUSIONS AND IMPLICATIONS: Our studies have uncovered the mechanism underlying the biological activity of SHI in ALI and suggest that targeting of MD2 may prove to be beneficial as a treatment option.