The effect of fatty acid structure on utilization by Ehrlich ascites tumor cells.

The effect of fatty acid structure on utilization by Ehrlich ascites tumor cells was studied in vitro. Unesterified palmitate, stéarate, oleate, and linoleate were metabolized in a qualitatively similar fashion and at roughly comparable rates. Each of these fatty acids was rapidly taken up by the cells in unesterified form. The amount of free fatty acid taken up during the first few minutes was determined by the molar ratio of fatty acid to al bumin in the incubation medium and differed for each fatty acid: stéarate> palmitate > oleate > linoleate. This concentration of cell-iree fatty acid was then maintained with little or no further change during continued exposure for 1 hr to the same medium. On the other hand, the amounts of free fatty acid oxidized to C02 and incorporated into lipid esters increased progressively. The rates of oxidation and esterification were re lated to the fatty acid-albumin molar ratio in the medium and, thus, to the steady-state concentration of free fatty acid associ ated with the cells. Radioactive linoleate was oxidized at a somewhat greater rate than the other long-chain free fatty acids. Acetate, ß-hydroxybutyrate, octanoate, and laurate were metab olized at considerably lower rates than the long-chain free fatty acids. Pyruvate was oxidized as rapidly as palmitate but was poorly incorporated into cell lipid. Attempts to demonstrate net utilization of lipid esters contained in Ehrlich ascites tumor fluid by the cells in vitro were negative. Radioactive palmitate contained in biologically labeled rat chylomicrons was utilized very slowly relative to unesterified palmitate. These observations support the hypothesis that exogenously supplied free fatty acid is a major source of fat for this tumor cell.