Metabolism of octadecenoic acid in the Morris hepatoma 7288C and 7288CTC and in host liver

Abstract

Host Liver. The effect of the growth of the Morris hepatoma 7288CTC (CTC) upon the host liver stearoyl-CoA desaturase was examined. Host liver stearoyl-CoA desaturase activity showed a significant decrease very early during tumor growth (2-4 days after implantation of tumor tissue). There was a rise in activity to normal levels by day 8 of tumor growth followed by a final decrease in activity, at day 12-15, to near zero levels. The latter decrease was preceded by a loss of host body weight and decreased food intake (anorexia) and is probably not due to any direct action by the tumor. The early decrease in activity was not associated with any physiological changes known to affect this system. This early decrease may be a result of a direct action by the tumor, through the release of some metabolically active factor. Morris Hepatoma 7288C and 7288CTC. The method by which the Morris hepatoma 7288C and 7288CTC maintains high levels of octadecenoic acid (18:1) was investigated by examination of the biosynthesis, incorporation, and turnover of this fatty acid. In vitro analysis of the stearoyl-CoA desaturase system shows this system to be low in this cell line, however, labeling studies, and use of sterculic acid, an inhibitor of this desaturase system, indicates that 18:1 synthesis in these cells through the stearoyl-CoA desaturase system accounts for 40-50% of the cellular mass of 18:1. These cells are dependent upon incorporation of exogenous 18:1 for the remainder. Double labeling experiments show 18:1 to be incorporated from the medium at twice the rate of stearic acid (18:0) while both are turned over as a unit in the cell. Fatty acid analysis of total medium lipid show no enrichment of 18:1 over other fatty acids but individual lipid classes (such as free fatty acids) have been shown to be enriched in 18:1. Enrichment of 18:1 is, therefore, possibly a result of either preferential incorporation of 18:1 or selective incorporation of a particular lipid class (such as free fatty acids) from the medium which fortuitously contains high levels of 18:1. The high levels of 18:1 are not required for cell viability in culture since lowering of 18:1 levels, using sterculic acid, did not affect culture growth rate.