Protection Of Natural Nrf2 Activators Against Oxidative Insults In Human Bronchial Epithelial Cells

Many environmental pollutions,such as heavy metals,industrial gas,and cigarette smoke surround humans.Lung is directly exposed to the environment,and is apt to be damaged.Therefore,the incidence and mortality of lung diseases,such as lung cancer and chronic obstructive pulmonary disease,remain high.Oxidative stress is the important factor for the pathogenesis of lung diseases.Activation of nuclear factor erythroid 2-related factor 2(Nrf2)signaling pathway is an effective strategy to prevent and treat human lung diseases caused by oxidative injury.Natural product is an important source to find Nrf2 inducers with the capability of preventing and treating lung diseases.The present study test the Nrf2 inducing effect of many natural molecules,discover potential Nrf2 activators,and illustrate their mechanism of Nrf2 activation and protectionagainst oxidative insults in human bronchial epithelial cells.Part I:Discovery of Nrf2 inducers from cinnamon and their protection against oxidative insults in human bronchial epithelial Beas-2B cellsCinnamon,used as spice and Chinese traditional medicine,is able to induce Nrf2 signaling pathway and has the potential of preventing oxidative stress-induced diseases.Cinnamon contains diverse chemical components,including sesquiterpenoids,phenolic acids,lignans,flavonoids,phenylpropanoids,coumarins,and steroids.Cinnamaldehyde derivatives and phenolic compounds are considered to be the main antioxidants in cinnamon.Our research group found that cinnamaldehyde was a weak Nrf2 inducer.Cinnamon may contain some novel and potent Nrf2 activators.In this study,the constituents isolated from cinnamon were tested for their potential inhibitory effects against oxidative stress using an NAD(P)H:quinone reductase(QR)assay.A lignan pinoresinol(PRO)and a flavonol(-)-(2R,3R)-5,7-dimethoxy-3',4'-methylenedioxy-flavan-3-ol(MFO)were found to be potent inhibitors of oxidative stress.The two compounds were identified to be Nrf2 activators by dual luciferase reporter gene assay and immunoblot analysis.The results showed that MFO and PRO induced Nrf2 to translocate into the nucleus,enhanced the protein and mRNA levels of NQO1 and y-GCS,and prolonged the half life of Nrf2 protein.Furthermore,PRO and MFO upregulated the GSH production,inhibited the ROS accumulation,and prevented sodium arsenite[As(III)]-induced oxidative insults in human bronchial epithelial Beas-2B cells.Part II:Nrf2 inducing effects of isopimarane diterpenoids and their protection against oxidative insults in human bronchial epithelial Beas-2B cellsIn this research,66 diterpenoids were evaluated for their antioxidant potential using the quinone reductase(QR)assay to give three potent active diterpenoids,BD,SA,and SC.Further studies indicated that three isoprenamidine diterpenes induced Nrf2 signaling pathway in human bronchial epithelial Beas-2B cells.They promoted the expression of Nrf2 related genes and proteins in Beas-2B cells.The ubiquitination assay and protein half-life measurement displayed that isobornane diterpene inhibited the ubiquitination and prolonged the half-life of the Nrf2 protein.In addition,we have found that the induction of Nrf2 by SA was related to PI3K,PKC,and PERK pathway.Isopimarane diterpenes protected Beas-2B cells against oxidative damage induced by sodium arsenite[As(?)]and cigarette smoke extract(CES).Taken together,our results demonstrate that lignan PRO,flavonol MFO,and isobornane diterpenoids(BD,SA and SC)are novel Nrf2 inducers that are capable of inhibiting oxidative stress,and protecting human bronchial epithelial Beas-2B cells against oxidative insults.