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 energy source and as a precursor for lipid synthesis. The significance of ketone body metabolism in tumors lies in the study of tumor-host metabolism and the ketonemic condition that is often present in cancer patients. The quantitative importance of acetoacetate and glucose was investigated 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 dichloroacetic acid (DCA), an activator of pyruvate dehydrogenase (PDH). The (CO2)-C-14 ratio method evaluated the entry of pyruvate into the tricarboxylic acid (TCA) cycle and revealed that acetoacetate diverted pyruvate from PDH to pyruvate carboxylation. In contrast, DCA increased the oxidation of glucose largely through PDH, indicating that PDH is not maximally active in the absence of DCA. Isotopomer spectral analysis of lipid synthesis demonstrated that, in the absence of acetoacetate, glucose supplied 65% of the acetyl-CoA used for de novo lipogenesis. When 5 mM acetoacetate was included in the incubation, glucose was displaced as a lipogenic precursor and acetoacetate supplied 85% of the acetyl-CoA for lipogenesis vs. only 2% for glucose. Thus AS-30D cells have a large capacity for acetoacetate utilization for de novo lipogenesis.