TY - JOUR
T1 - Ethanol metabolism by a transplantable hepatocellular carcinoma. Role of microsomes and mitochondria
AU - Cederbaum, A. I.
AU - Becker, F. F.
AU - Rubin, E.
PY - 1976
Y1 - 1976
N2 - Ethanol metabolism in slices or homogenates of transplantable hepatocellular carcinoma HC 252 (HC 252) was 50 to 60% of the rate found in host liver slices or homogenates when they were expressed per gram of tissue wet weight and 70 to 80% of the liver when the rates were expressed per milligram of tissue protein. At 10 mM ethanol, the activities of alcohol dehydrogenase in tumor and liver supernatants were comparable. Tumor microsomes did not oxidize ethanol in the presence of a NADPH generating system, indicating the absence of the microsomal ethanol oxidizing system and catalase mediated peroxidation of ethanol. The HC 252 microsomes were contaminated with catalase, and acetaldehyde production occurred in the presence of a H2O2 generating system (xanthine oxidase). The virtual absence of ethanol oxidation and drug metabolism (aminopyrine demethylase and aniline hydroxylase) in HC 252 microsomes may be due to the low activities of NADPH cytochrome c reductase, NADPH oxidase, and NADPH dependent oxygen uptake. Microsomal oxidation of ethanol was present in Morris hepatoma 5123C, a well differentiated tumor of intermediate growth rate, while activity was negligible in microsomes from Morris hepatoma 7288CTC, a less differentiated tumor. Microsomal NADPH oxidase was present in the well differentiated tumor 5123C but was lacking in the less differentiated tumor 7288CTC. Several microsomal, mitochondrial, and cytosolic properties of HC 252 are similar to those of Morris hepatoma 7288CTC but differ from those of the more differentiated 5123C tumor and normal liver. The content of mitochondrial protein in HC 252 was only 25% that of liver, and oxygen consumption per gram of tumor was only 28% that of the liver. When corrected for the mitochondrial protein content, oxygen uptake in tumor HC 252 and liver homogenates was comparable. Isolated tumor and liver mitochondria displayed comparable State 4 and 3 rates of oxygen consumption with succinate and glutamate as substrates. The activities of the reconstituted malate aspartate and α glycerophosphate shuttles were only slightly lower in isolated HC 252 mitochondria compared to liver mitochondria, when shuttles were reconstituted with purified enzymes. Antimycin inhibited alcohol metabolism, and pyruvate stimulated alcohol metabolism, much less in tumor slices than in liver slices, suggesting the presence of an augmented mitochondria independent, cytosolic mechanism for oxidizing reducing equivalents in the tumor. These factors suggest that oxidation of NADH is the limiting factor in ethanol metabolism. Whereas, in the liver mitochondrial reoxidation is predominant, in HC 252, cytosolic reoxidation of NADH also plays a major role.
AB - Ethanol metabolism in slices or homogenates of transplantable hepatocellular carcinoma HC 252 (HC 252) was 50 to 60% of the rate found in host liver slices or homogenates when they were expressed per gram of tissue wet weight and 70 to 80% of the liver when the rates were expressed per milligram of tissue protein. At 10 mM ethanol, the activities of alcohol dehydrogenase in tumor and liver supernatants were comparable. Tumor microsomes did not oxidize ethanol in the presence of a NADPH generating system, indicating the absence of the microsomal ethanol oxidizing system and catalase mediated peroxidation of ethanol. The HC 252 microsomes were contaminated with catalase, and acetaldehyde production occurred in the presence of a H2O2 generating system (xanthine oxidase). The virtual absence of ethanol oxidation and drug metabolism (aminopyrine demethylase and aniline hydroxylase) in HC 252 microsomes may be due to the low activities of NADPH cytochrome c reductase, NADPH oxidase, and NADPH dependent oxygen uptake. Microsomal oxidation of ethanol was present in Morris hepatoma 5123C, a well differentiated tumor of intermediate growth rate, while activity was negligible in microsomes from Morris hepatoma 7288CTC, a less differentiated tumor. Microsomal NADPH oxidase was present in the well differentiated tumor 5123C but was lacking in the less differentiated tumor 7288CTC. Several microsomal, mitochondrial, and cytosolic properties of HC 252 are similar to those of Morris hepatoma 7288CTC but differ from those of the more differentiated 5123C tumor and normal liver. The content of mitochondrial protein in HC 252 was only 25% that of liver, and oxygen consumption per gram of tumor was only 28% that of the liver. When corrected for the mitochondrial protein content, oxygen uptake in tumor HC 252 and liver homogenates was comparable. Isolated tumor and liver mitochondria displayed comparable State 4 and 3 rates of oxygen consumption with succinate and glutamate as substrates. The activities of the reconstituted malate aspartate and α glycerophosphate shuttles were only slightly lower in isolated HC 252 mitochondria compared to liver mitochondria, when shuttles were reconstituted with purified enzymes. Antimycin inhibited alcohol metabolism, and pyruvate stimulated alcohol metabolism, much less in tumor slices than in liver slices, suggesting the presence of an augmented mitochondria independent, cytosolic mechanism for oxidizing reducing equivalents in the tumor. These factors suggest that oxidation of NADH is the limiting factor in ethanol metabolism. Whereas, in the liver mitochondrial reoxidation is predominant, in HC 252, cytosolic reoxidation of NADH also plays a major role.
UR - http://www.scopus.com/inward/record.url?scp=0017093175&partnerID=8YFLogxK
M3 - Article
C2 - 134037
AN - SCOPUS:0017093175
SN - 0021-9258
VL - 251
SP - 5366
EP - 5374
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 17
ER -