The importance of free fatty acid in tumor nutrition.

Summary Free fatty acid was found in the ascites fluid of the Ehrlich ascites tumor, about 3% of the total fatty acid contained in the fluid being in unesterified form. The major components of the ascites free fatty acid fraction—palmitate, stearate, oleate, and linoleate—also were the main species of fatty acid contained in the tumor cells. Tracer experiments with palmitate and oleate indicated that from 40 to 50% of the free fatty acid flux in the ascites fluid resulted from uptake by the tumor cells. Most of the free fatty acid taken up by the cells was incorporated into lipid esters. In contrast, less than 1% of the glucose radioactivity administered intraperitoneally was recovered from tumor cell lipid, and 94% of that incorporated into lipid was in watersoluble material following saponification. A small fraction of the radioactive free fatty acid taken up was converted to watersoluble components of the cells. Estimates of the rate of utilization of the free fatty acid contained in the ascites fluid were made using palmitate as the isotopic tracer. Although large variations were noted, the values calculated for the free fatty acid turnover rate indicate that this substrate can provide a large fraction of the fatty acid required by these tumor cells in vivo. It is suggested that much of the fatty acid required by the Ehrlich ascites tumor cell is supplied preformed by the host and that most of this is circulated to the tumor as free fatty acid.