Ketone bodies, glucose and glutamine as lipogenic precursors in human diploid fibroblasts

Incorporation of [14C] from acetoacetate, D(‐)‐ and L(+)‐3‐hydroxybutyrate, glucose, glutamine, acetate and palmitate in cellular lipids were studied in cultures in human diploid fibroblasts (HDF). The results showed that acetoacetate was 2–10 times more effective as a lipogenic precursor than was either D‐ or L‐3‐hydroxybutyrate. Its extent of incorporation into lipids was 2‐ to 8‐fold more than the other precursors examined under conditions when the overall rates of nonsaponifiable and saponi‐fiable lipogenesis as measured by3H2O incorporation were essentially unchanged. Acetoacetate supported both saponifiable and nonsaponifiable lipid syntheses with half‐saturation values (Km app.) of 185 μM and 30 μM, respectively. Glucose stimulated acetoacetate incorporation into lipids whereas, conversely, acetoacetate inhibited [14C] glucose incorporation into lipids. The presence of low density lipoproteins (LDL) cholesterol (@40 μg cholesterol/mL) inhibited the incorporation of [14C] from acetoacetate 56% into nonsaponifiable lipids; the inhibition was consistently higher (75%) when [14C] glucose or glutamine were the precrusors. The loss of 3‐hydroxy‐3‐methyl‐glutaryl CoA (HMG CoA) reductase activity upon addition of LDL‐cholesterol was greater than the suppression of [14C] incorporation from acetoacetate or glucose into nonsaponifiable lipids. In the presence of glucose, [14C] acetoacetate was incorporated into 3‐βOH sterols (digitonin precipitable). 7.7±1.1 times more effectively than was [14C] glucose. The results suggest that HDF would be a suitable model to investigate the effects of various precrusors of HMG CoA on the rate of cholesterol biosynthesis.