Anti-inflammatory lindenane sesquiterpeniods and dimers from Sarcandra glabra and its upregulating AKT/Nrf2/HO-1 signaling mechanism

Sarcandra glabra (Thunb.) Nakai (Chloranthaceae), grown and cultivated evergreen shrub in south of China, has been used in traditional Chinese medicines (TCMs) to treat bruises, bone fractures and arthritis which were partly due to inflammation. Previous phytochemical and pharmacological researches indicated that flavonoids, coumarins, phenolic acids as its main anti-inflammatory ingredients related to its traditional efficacy. Our present research aimed to elucidate whether the fascinating and abundant lindenane-type sesquiterpeniods are also its anti-inflammatory components and uncover its anti-inflammatory mechanism. On the guidance of results of phytochemical fraction and anti-inflammatory activity evaluation, ten anti-inflammatory lindenane sesquiterpenes with half maximal inhibitory concentration (IC50) values from 8.13 ± 0.37 to 24.06 ± 0.60 μM, including seven dimmers (1-7) and three monomers (8-10) were discovered and characterized from the anti-inflammatory fraction of roots of title plant. Considering the activity and quantity, shizukaol D was selected as the target for further mechanism study. Firstly, shizukaol D could downregulate the expression of inducible nitric oxide synthase (iNOS) and suppress the protein level of nuclear factor kappa B (NF-κB) p65 as well as the nuclear translocation of NF-κB p65. Meanwhile, shizukaol D also decreased the level of reactive oxygen species (ROS) and enhanced the activities of phase II defense enzymes superoxide dismutase (SOD), glutathione (GSH) and glutathione peroxidase (GSH-px) by elevating the expression of heme oxygenase-1 (HO-1) and NAD(P)H: quinone oxidoreductase 1 (NQO1) via promoting nuclear factor E2-related factor 2 (Nrf2) activation as well as its nuclear translocation, and regulating the pathway of phosphoinositide 3-kinases (PI3K)/ protein kinase B (AKT) rather than mitogen-activated protein kinase (MAPK) to the activation of Nrf2/HO-1 signaling. Taken together, our research provided the phytochemical and pharmacological evidences for that the major sesquiterpenoid dimers can be defined as the anti-inflammatory ingredients of S.glabra and this kind of sesquiterpenoids, such as shizukaol D, can be as an attractive therapeutic candidate for inflammatory diseases.