Extent of 14C incorporation into cholesterol of infant skin fibroblasts incubated with carboxyl-labeled oleic, -linoleic or -arachidonic acid.

In order to determine the incorporation of C1-14C derived from mono- and poly-unsaturated fatty acids into cholesterol of human cells cultured in exponential phase, infant skin fibroblasts (SF) were used at the 5th passage. On Day 6, the SF were preincubated 36 h in a medium containing 5 per cent lipoprotein-deficient serum, and thereafter [1-14C] oleic, -linoleic or -arachidonic acid-without (OL1, LI1 and AR1 group SF), or with the addition of 0.25 mM cold fatty acids (OL2), LI2 and AR2 group SF). Cholesterol specific radioactivity (SRA) peaked 1 h after, and leveled off afterwards in the OL1, LI1 and AR1 groups. Cholesterol-SRA was relatively low in the other groups, but increased progressively, giving a biphasic response: C1-14C derived from from linoleic and arachidonic acids was actively incorporated into cholesterol during the first hours, as compared to C1-14C derived from oleic acid, but stabilized between 6 and 12 h for the LI2 and AR2 group SF incubation. This result appears to be due to the stimulation of pyruvate decarboxylation, observed elsewhere, and consequently to the dilution of the radioactive units in a large pool of non-labeled acetyl-CoA units derived from glucose, when these SF were incubated with 0.25 mM polyunsaturated fatty acids.