AJP - Endocrinology and Metabolism, Vol 272, Issue 6 E945-E951, Copyright © 1997 by American Physiological Society
Quantitative analysis of acetoacetate metabolism in AS-30D hepatoma cells with 13C and 14C isotopic techniques
A. L. Holleran, G. Fiskum and J. K. Kelleher
Department of Physiology, George Washington University School of Medicine and Health Sciences, Washington, District of Columbia 20037, USA.
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 13C and 14C isotopic methods. In addition, the
effects of acetoacetate were compared with those of dichloroacetic acid
(DCA), an activator of pyruvate dehydrogenase (PDH). The 14CO2 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.
