Caspase Inhibition Prevents Tumor Necrosis Factor-α-Induced Apoptosis and Promotes Necrotic Cell Death in Mouse Hepatocytes in Vivo and in Vitro

How different cell death modes and cell survival pathways cross talk remains elusive. We determined the interrelation of apoptosis, necrosis, and autophagy in tumor necrosis factor (TNF)-alpha a/actinomycin D (ActD) and lipopolysaccharide/D-galactosamine (GalN)-induced hepatotoxicity in vitro and in vivo. We found that TNF-alpha/ActD-induced apoptosis was completely blocked by a general caspase inhibitor ZVAD-fmk at 24 hours but hepatocytes still died by necrosis at 48 hours. Inhibition of caspases also protected mice against lipopolysaccharide/GalN-induced apoptosis and liver injury at the early time point, but this protection was diminished after prolonged treatment by switching apoptosis to necrosis. Inhibition of receptor-interacting protein kinase (RIP)1 by necrostatin 1 partially inhibited TNF-alpha/ZVAD-induced necrosis in primary hepatocytes. Pharmacologic inhibition of autophagy or genetic deletion of Atg5 in hepatocytes did not protect against TNF-alpha/ActD/ZVAD-induced necrosis. Moreover, pharmacologic inhibition of RIP1 or genetic deletion of RIP3 failed to protect and even exacerbated liver injury after mice were treated with lipopolysaccharide/GalN and a pan-caspase inhibitor. In conclusion, our results suggest that different cell death mode and cell survival pathways are closely integrated during TNF-alpha-induced liver injury when both caspases and NF-kappa B are blocked. Moreover, results from our study also raised concerns about the safety of currently ongoing clinical trials that use caspase inhibitors.