Ethanol extract of Prunella vulgaris var. lilacina inhibits HMGB1 release by induction of heme oxygenase-1 in LPS-activated RAW 264.7 cells and CLP-induced septic mice.

The ethanol extract of the flower of P. vulgaris var. lilacina (EEPV) has been used traditionally as an antiinflammatory agent in many countries. Inducers of heme oxygenase-1 (HO-1) reduce high mobility group box 1 (HMGB1), a late phase cytokine, in sepsis. Although EEPV has been used as an antiinflammatory agent, no report is available as to whether it modifies HMGB1 in sepsis due to HO-1 induction. It was found that EEPV increased HO-1 protein expression in RAW 264.7 cells, which was significantly inhibited by LY294002, but not PD98059, SB203580 or SP600125. In addition, EEPV activated NF-E2-related factor (Nrf2) to move from the cytosol to the nucleus, and EEPV-induced HO-1 and activation of ARE-luciferase activity were significantly reduced by siNrf2 transfection and LY294002 but not SB203508. EEPV also significantly inhibited NF-κB luciferase activity, and decreased both iNOS/NO and COX-2/PGE(2) production in lipopolysaccharide (LPS)-stimulated macrophages which was reversed by siHO-1 RNA transfection. Importantly, EEPV inhibited HMGB1 release in LPS-activated macrophages in a PI3K-sensitive manner and reduced serum HMGB1 level and lung HMGB1 expression in cecal ligation and puncture (CLP)-induced septic mice. It is concluded that EEPV induces HO-1 expression through PI3K/Nrf2 signal pathways, which may be beneficial for the treatment of sepsis due to a reduction of HMGB1 release.