Genetic or pharmacologic amplification of nrf2 signaling inhibits acute inflammatory liver injury in mice.
Oxidative stress-mediated destruction of normal parenchymal cells during hepatic inflammatory responses contributes to the pathogenesis of immune-mediated hepatitis and is implicated in the progression of acute inflammatory liver injury to chronic inflammatory liver disease. The transcription factor NF-E2-related factor 2 (Nrf2) regulates the expression of a battery of antioxidative enzymes and Nrf2 signaling can be activated by small-molecule drugs that disrupt Keap1-mediated repression of Nrf2 signaling. Therefore, genetic and pharmacologic approaches were used to activate Nrf2 signaling to assess protection against inflammatory liver injury. Profound increases in indicators of cell death were observed in both Nrf2 wild-type (Nrf2-WT) mice and Nrf2-disrupted (Nrf2-KO) mice 24 h following intravenous injection of concanavalin A (12.5 mg/kg, ConA), a model for T cell-mediated acute inflammatory liver injury. However, hepatocyte-specific conditional Keap1 null (Alb-Cre:Keap1(flox/-), cKeap1-KO) mice with constitutively enhanced expression of Nrf2-regulated antioxidative genes as well as Nrf2-WT mice but not Nrf2-KO mice pretreated with three daily doses of a triterpenoid that potently activates Nrf2 (30 mumol/kg, cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl-imidazolide [CDDO-Im]) were highly resistant to ConA-mediated inflammatory liver injury. CDDO-Im pretreatment of both Nrf2-WT and Nrf2-KO mice resulted in equivalent suppression of serum proinflammatory soluble proteins suggesting that the hepatoprotection afforded by CDDO-Im pretreatment of Nrf2-WT mice but not Nrf2-KO mice was not due to suppression of systemic proinflammatory signaling, but instead was due to activation of Nrf2 signaling in the liver. Enhanced hepatic expression of Nrf2-regulated antioxidative genes inhibited inflammation-mediated oxidative stress, thereby preventing hepatocyte necrosis. Attenuation of hepatocyte death in cKeap1-KO mice and CDDO-Im pretreated Nrf2-WT mice resulted in decreased late-phase proinflammatory gene expression in the liver thereby diminishing the sustained influx of inflammatory cells initially stimulated by the ConA challenge. Taken together, these results clearly illustrate that targeted cytoprotection of hepatocytes through Nrf2 signaling during inflammation prevents the amplification of inflammatory responses in the liver.
Osburn
William O
WO
Department of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA.
Yates
Melinda S
MS
Dolan
Patrick D
PD
Chen
Sining
S
Liby
Karen T
KT
Sporn
Michael B
MB
Taguchi
Keiko
K
Yamamoto
Masayuki
M
Kensler
Thomas W
TW
D000154:Aconitate Hydratase / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000410:Alanine Transaminase / Q000097:blood; D000818:Animals; D056486:Chemical and Drug Induced Liver Injury / Q000235:genetics* / Q000378:metabolism; D003208:Concanavalin A; D016207:Cytokines / Q000097:blood / Q000235:genetics; D003598:Cytoskeletal Proteins / Q000235:genetics*; D005260:Female; D020869:Gene Expression Profiling; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology*; D000072019:Kelch-Like ECH-Associated Protein 1; D015227:Lipid Peroxidation; D008099:Liver / Q000201:enzymology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D051267:NF-E2-Related Factor 2 / Q000235:genetics*; D009828:Oleanolic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D015398:Signal Transduction
C472829:1-(2-cyano-3,12-dioxooleana-1,9-dien-28-oyl) imidazole; D048868:Adaptor Proteins, Signal Transducing; D016207:Cytokines; D003598:Cytoskeletal Proteins; D007093:Imidazoles; C117301:Keap1 protein, mouse; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D003208:Concanavalin A; D009828:Oleanolic Acid; D000410:Alanine Transaminase; D000154:Aconitate Hydratase