Stravitz, R. Todd

Listing and transplanting patients with acute liver failure (ALF) is challenging, requiring rapid assessment of the likelihood of recovery. The availability of a large number of ALF liver explants, along with their clinical data, afforded an opportunity to retrospectively evaluate liver transplantation (LT) decision-making. We hypothesized that, with the benefit of hindsight, a small number of patients might have recovered without LT. Three hundred liver explants from ALF patients of varying etiologies who had undergone LT over 22 years in the Acute Liver Failure Study Group registry were reviewed for histopathological features and degree of necrosis by a committee of 8 hepatopathologists. A second committee of 8 experienced transplant hepatologists independently reviewed clinical data on these same 300 patients and retrospectively scored the likelihood that each patient required transplantation. Only 3 (1%) of those reviewed by the Clinical Committee were considered to “Definitely” not require liver grafting, while an additional 10 (3.3%) were deemed to “Possibly” not require transplantation (Not Likely Group, N=13). There was no difference in the degree of necrosis in explants in these groups, when compared to the remaining Likely Group, N=287 (95.6%), except in acetaminophen (APAP)-associated ALF, where the degree of necrosis was more uniformly graded as severe, correlating with the need for transplantation. Virtually every patient undergoing LT for ALF retrospectively appeared to need their transplant, based on expert clinical consensus review. Overall, there was poor correlation between clinical severity and apparent degree of necrosis seen in the 300 liver explants, except perhaps for APAP subjects.

Toxic bile salts induce hepatocyte apoptosis, a model relevant to liver injury during cholestasis. However, the signaling mechanisms culminating in bile salt-induced apoptosis remain unclear. Because protein kinase C (PKC) is activated by bile salts in hepatocytes and causes apoptosis in other cells, we tested the hypothesis that bile salt-induced hepatocyte apoptosis is mediated by PKC. The PKC inhibitors chelerythrine and Go-6976 reduced, whereas a PKC agonist, phorbol 12-myristate 13-acetate (PMA), increased glycochenodeoxycholate (GCDC)-induced hepatocyte apoptosis. Membrane-associated total PKC activity was increased in GCDC-treated hepatocytes. Quantitative immunoblot analysis demonstrated membrane translocation of PKC-alpha, PKC-delta, and PKC-epsilon to hepatocyte membranes after administration of GCDC. Direct activation of PKC-alpha and PKC-delta by GCDC was also demonstrated using recombinant, baculovirus-expressed PKC isoforms in a medium of defined lipid composition. Chelerythrine and Go-6976 reduced, whereas PMA enhanced, cathepsin B activity during treatment of hepatocytes with GCDC, demonstrating coupling of PKC activity to the protease effector mechanisms of apoptosis. In conclusion, our data suggest for the first time that PKC-dependent signaling pathways play a critical role in bile salt-induced hepatocyte apoptosis.