The metabolism of butyrate, glucose and glutamine in colonic epithelial cell lines

Abstract

In order to delay the onset and advancement of cancer, this research focused on inspecting the utilization, interaction, and fate of metabolic substrates normally obtained either from colonic bacteria, i.e. short chain fatty acids such as butyrate, or from metabolic substrates derived from the blood circulation to the colonic mucosa, i.e. glucose and glutamine. These experiments determined if butyrate, being growth inhibitory in colon cancer cells, also interferes with the metabolism of other metabolic substrates, such as glucose and glutamine. The cell line FRC/TEX/CLD, CL4D, provided by Dr. Summerhayes (Harvard University), derived from fetal rat colon, and two tumorigenic daughter cell lines, RAS and SRC, are used to examine the effects of butyrate (0, 0. 1, 1, 3 mM) on the rates of oxidation and lipogenesis from [1-14 C] butyrate, [6-14C] glucose, and [14C] glutamine. In addition, the rate of ketogenesis from butyrate, the rate of lactate formation from glucose, and the rate of macromolecular synthesis from [14C] glutamine and [3H] leucine are measured. Butyrate suppresses growth, proliferation, DNA and protein synthesis in transformed colonic cells; however, these effects are not observed in normal colonic cells. Butyrate and glutamine are the major respiratory fuels for all three colonic cell lines. The rate of butyrate oxidation occurs in a dose dependent manner, while chronically inhibiting the rate of glutamine oxidation. Glycolysis is the major pathway accounting for glucose disappearance, with the addition of butyrate increasing glucose oxidation and lactate production. Both acutely and chronically, butyrate proceeds through the TCA cycle at very high rates, producing a reduced NAD/NADH redox environment. Acutely, increased rates of glutamine proceeds through the TCA cycle to provide TCA cycle intermediates. However, chronically, due to the reduced NAD/NADH environment, the rate that glutamine proceeds through the TCA cycle is significantly suppressed. Given that glutamine no longer provides the anaeploric effect, there are increased rates of glucose oxidation for more TCA cycle intermediates. The high rate of lactate production could perhaps compensate for the chronic inhibition of glutamine, and lack of ATP production.