QUANTITATIVE-ANALYSIS OF ACETOACETATE METABOLISM IN AS-30D HEPATOMA-CELLS WITH C-13 AND C-14 ISOTOPIC TECHNIQUES

Experimental hepatoma cells utilize acetoacetate as an oxidative energ y source and as a precursor for lipid synthesis. The significance of k etone body metabolism in tumors lies in the study of tumor-host metabo lism and the ketonemic condition that is often present in cancer patie nts. The quantitative importance of acetoacetate and glucose was inves tigated in AS-30D cells with use of C-13 and C-14 isotopic methods. In addition, the effects of acetoacetate were compared with those of dic hloroacetic acid (DCA), an activator of pyruvate dehydrogenase (PDH). The (CO2)-C-14 ratio method evaluated the entry of pyruvate into the t ricarboxylic acid (TCA) cycle and revealed that acetoacetate diverted pyruvate from PDH to pyruvate carboxylation. In contrast, DCA increase d the oxidation of glucose largely through PDH, indicating that PDH is not maximally active in the absence of DCA. Isotopomer spectral analy sis of lipid synthesis demonstrated that, in the absence of acetoaceta te, glucose supplied 65% of the acetyl-CoA used for de novo lipogenesi s. When 5 mM acetoacetate was included in the incubation, glucose was displaced as a lipogenic precursor and acetoacetate supplied 85% of th e acetyl-CoA for lipogenesis vs. only 2% for glucose. Thus AS-30D cell s have a large capacity for acetoacetate utilization for de novo lipog enesis.