Antisense Oligonucleotide Inhibition of Tumor Necrosis Factor Receptor 1 Protects the Liver from Radiation-Induced Apoptosis

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Abstract
Purpose: Liver damage by radiation limits its efficacy in cancer treatment. As radiation can generate apoptotic signals, we wished to examine the potential to protect the liver by inhibiting apoptosis through two key mediators, FAS and tumor necrosis factor receptor 1 (TNFR1). Experimental Design: Radiation-induced liver damage was assessed by serum aspartate aminotransferase and alanine aminotransferase, hepatocyte micronucleus formation, and apoptosis assays (terminal nucleotidyl transferase–mediated nick end labeling and caspase-3 cleavage) in mice. Protection was evaluated by pretreating mice with antisense oligonucleotides (ASO) for FAS or TNFR1 prior to radiation. TNF-α production in liver and in Kupffer cells were determined by ELISA. Results: Radiation increased liver FAS and TNFR1 transcription in a dose- and time-dependent manner (maximized at 25 Gy and 8 hours postirradiation). Pretreatment with ASOs for FAS and TNFR1 resulted in the inhibition of liver FAS and TNFR1 by 78% and 59%, respectively. Inductions of serum aspartate aminotransferase and alanine aminotransferase were observed at 2 hours after radiation and could be reduced by pretreating mice with ASO for TNFR1 but not FAS or control oligonucleotide. Radiation-induced liver apoptosis (terminal nucleotidyl transferase–mediated nick end labeling staining and caspase-3 activation on Western blot) and hepatocyte micronucleus formation were reduced by pretreatment with ASO for TNFR1. In addition, radiation stimulated TNF-α production both in irradiated liver and in cultured Kupffer cells by >50% and 100%, respectively. Conclusion: This study suggests that ionizing radiation activates apoptotic signaling through TNFR1 in the liver, and thus provides a rationale for anti-TNFR1 apoptotic treatment to prevent radiation-induced liver injury.