Mechanism of early carbon tetrachloride toxicity in cultured rat hepatocytes

CCl4 causes liver necrosis in a dose-dependent manner in vivo. However, we found that primary rat hepatocytes in culture were killed after a 2 hr incubation with carbon tetrachloride gas at CCl4 partial pressures above a threshold between 45 and 54 mmHg. Below this threshold concentration no increase in hepatocyte death was observed. We sought to explain the very abrupt CCl4 concentration threshold for hepatocyte death. Two inhibitors of cytochrome P450 2E1, cimetidine and diallyl sulfide, inhibited lipid peroxidation as measured by production of isoprostanes, but did not reduce hepatocyte death from CCl4. At 37 degrees, CCl4 accelerated the mitochondrial permeability transition in vitro, at a threshold CCl4 concentration similar to that which caused hepatocyte death. Phospholipase A(2) inhibitors, mepacrine and 4-bromophhenacyl bromide, inhibited the increase in mitochondrial permeability, but did not inhibit hepatocyte death caused by CCl4. Rat liver microsomal lipids were used to make liposomes loaded with Ponceau Red (FW 760.6). No leakage of Ponceau red was found at CCl4 concentrations greater than the threshold for cell death. However. CCl4 caused acceleration of liposome fusion, over the CCl4 concentration range spanning the threshold for hepatocyte death. Early hepatocyte death in cell culture is independent of metabolism of CCl4, and may be related to direct effects of CCl4 on intracellular membranes.