Glycochenodeoxycholic acid (GCDC) induced hepatocyte apoptosis is associated with early modulation of intracellular PKC activity

The effect of GCDC-induced Apoptosis on PKC activity and PKC's role in GCDC-induced hepatocyte Apoptosis is unclear. The specific aims of this study were to determine if GCDC-induced Apoptosis changed intracellular PKC activity and if modulation of PKC activity affected GCDC-induced hepatocyte Apoptosis. Apoptosis was induced in isolated hepatocytes using GCDC. PKC activity was measured and specific PKC and calpain inhibitors were used to study the effects of PKC and calpain modulation on GCDC-induced Apoptosis. After 4 h exposure, 50 microM GCDC induced Apoptosis in 42% of hepatocytes. Intracellular PKC activity decreased to 44% of controls 2 h after exposure of hepatocytes to GCDC (p < 0.001). Pre-incubation of hepatocytes with the calpain protease inhibitor restored PKC activity in GCDC exposed hepatocytes to 91 +/- 5% of control cells. Pre-incubation of hepatocytes with a calpain inhibitor decreased GCDC-induced Apoptosis as did pre-incubation with the PKC activating phorbol ester, PMA. The combination of calpain inhibition and PMA further reduced GCDC-induced Apoptosis but caused low level hepatic Apoptosis. Inhibition of PKC with chelerythrine also substantially reduced GCDC-induced hepatocyte Apoptosis. GCDC-induced Apoptosis is associated with decreases in total cellular PKC activity, which appear to be dependent on intracellular calpain-like protease activity. The combination of protease inhibition and phorbol ester pretreatment preserved total cellular PKC activity and decreased GCDC-induced Apoptosis but induced low level Apoptosis in the absence of GCDC exposure. PKC inhibition also decreased GCDC-induced hepatocyte Apoptosis highlighting the complex interactions of PKC and proteases during GCDC-induced Apoptosis.