Possible involvement of reactive oxygen species in D‐galactosamine–induced sensitization against tumor necrosis factor‐α–induced hepatocyte apoptosis

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Abstract
Intravenous administration of tumor necrosis factor‐α (TNF‐α) (0.5 μg/mouse) caused hepatocyte apoptosis in BALB/c mice when they were sensitized with D‐galactosamine (GalN, 20 mg/mouse). Activation of nuclear factor κB (NF‐κB) and expression of apoptotic Bcl‐2 family members were not significantly different between livers of mice treated with TNF‐α alone and GalN + TNF‐α, indicating that neither activation of NF‐κB nor expression of Bcl‐2 family is involved in the sensitization by GalN against TNF‐α‐induced hepatocyte apoptosis. To identify differentially expressed genes implicated in GalN‐induced hepatocyte sensitization, we adopted mRNA fingerprinting using an arbitrarily primed polymerase chain reaction. The present analysis revealed that mRNA expression of extracellular antioxidant, selenoprotein P, was up‐regulated in the livers after GalN administration. GalN‐induced increase in its protein level was confirmed by Western blotting. Increased expression of this gene was also observed in the liver of mice treated with concanavalin A, but not anti‐Fas antibody. mRNA of another antioxidant, glutathione peroxidase‐1, was also up‐regulated, and lipid peroxides were produced in the liver after GalN administration. Selenoprotein P mRNA level also increased in Huh‐7 human hepatoma cells incubated with GalN (5 or 10 mM). Accordingly, formation of reactive oxygen species (ROS) was observed in GalN‐treated Huh‐7 cells. H2O2 induced up‐regulation of selenoprotein P mRNA and sensitized Huh‐7 cells to TNF‐α‐induced apoptosis. These results suggest that ROS produced by GalN may play a pivotal role in hepatocyte sensitization toward TNF‐α‐induced apoptosis.

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