ToxSci Advance Access originally published online on April 15, 2008
Toxicological Sciences 2008 104(1):218-227; doi:10.1093/toxsci/kfn079
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Genetic or Pharmacologic Amplification of Nrf2 Signaling Inhibits Acute Inflammatory Liver Injury in Mice
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* Department of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland
Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
Dartmouth Medical School, Department of Pharmacology and Toxicology, Hanover, New Hampshire 03755
Tohoku University Graduate School of Medicine and ERATO Environmental Response Project, 2-1 Seiryo-cho, Aoba-ku, Sendai 980-8575, Japan
1 To whom correspondence should be addressed at 615 North Wolfe Street, Baltimore, MD 21205. Fax: (410) 955-0116. E-mail: tkensler{at}jhsph.edu.
Received January 17, 2008; accepted April 9, 2008
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Abstract |
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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:Keap1flox/–, 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 µmol/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.
Key Words: liver inflammation; Nrf2; Keap1; antioxidative enzymes; cytoprotection; triterpenoid.