Polyisoprenoid, cholesterol and ubiquinone levels in human hepatocellular carcinomas.

The lipid composition of human hepatocellular carcinomas was examined. The level of dolichol in the tumours was decreased compared to control tissue, whereas the concentration of dolichyl phosphate did not exhibit any major change. A decrease in the amount of dolichyl ester was also observed. The pattern of individual polyisoprenoids in the free dolichol pool was changed in several carcinomas with a relative increase in the shorter dolichols. The isoprenol composition in the dolichyl ester and phosphate fractions of tumours were basically similar to those of controls. alpha-Unsaturated polyisoprenols are present in control livers at a level of 3% of the total free polyisoprenoid fraction, while this value was increased in the tumours. Similar to dolichol, the amount of ubiquinone was also decreased. The content of cholesterol was increased, while the fatty acid pattern of the dolichyl esters showed minor alterations. These modifications in lipid content indicate different mechanisms for the regulation of dolichol and dolichyl phosphate concentrations. The high levels of sterols in contrast to the low polyisoprenol content suggests interference with the regulation of the mevalonate pathway, which is the common biosynthetic route for cholesterol, ubiquinone and dolichol.