Inhibition of P53 Protects Liver Tissue Against Endotoxin-induced Apoptotic and Necrotic Cell Death

There is increasing evidence that apoptotic and necrotic hepatocyte death following endotoxin-induced liver injury act as signals for leukocyte sequestration in the liver vasculature. p53 has been implicated to promote apoptosis through trans-activation and down-regulation of specific pro- and anti-apoptotic genes. Here, we report that inhibition of p53 decreases apoptotic and necrotic tissue injury as well as inflammatory cell response. Sprague-Dawley rats were injected intraperitoneally with 2.2 mg/kg pifithrin-alpha (PFT), a p53-inactivating agent, or the vehicle DMSO 30 min before intravenous exposure to lipopolysaccharide (LPS). In vehicle-pretreated animals, LPS induced significant apoptosis and necrosis of hepatocytes, which was associated with intrahepatic leukocyte recruitment, microvascular dysfunction, and enzyme release. Inhibition of p53 effectively attenuated (P<0.05) hepatocellular apoptosis and necrosis, but also reduced leukocyte recruitment and microvascular dysfunction. Western blot analysis revealed that PFT lowered the nuclear-to-cytoplasmic p53 ratio and reduced both activation of NF-kappaB and cleavage of procaspase 3 (P<0.05). In parallel, immunohistochemistry of PFT-pretreated, but not vehicle-pretreated, endotoxic animals exhibited nuclear p53 exclusion and reduced NF-kappaB p65 staining. This indicates that p53 mediates, at least in part, LPS-associated apoptosis and contributes to inflammatory endotoxic tissue injury through leukocyte activation and intraorgan sequestration.