Tumor cells have a high tolerance for acidic and hypoxic microenvironments, also producing abundant
lactic acid through accelerated glycolysis in the presence or absence of O(2). While the accumulation of
lactate is thought to be a major contributor to the reduction of pH-circumscribing aggressive
tumors, it is not known if other endogenous metabolic products contribute this acidity. Furthermore, anaerobic metabolism in
cancer cells bears similarity to homo-fermentative lactic acid bacteria, however very little is known about an alternative pathway that may drive
adenosine triphosphate (
ATP) production independent of glycolysis. In this study, we quantify over 40 end-products (
amines,
acids,
alcohols,
aldehydes, or
ketones) produced by malignant
neuroblastoma under accelerated glycolysis (+
glucose (GLU) supply 1-10 mM) +/- mitochondrial toxin;
1-methyl-4-phenylpyridinium (MPP(+)) to abate aerobic respiration to delineate differences between anaerobic vs. aerobic cell required metabolic pathways. The data show that an acceleration of anaerobic glycolysis prompts an expected reduction in extracellular pH (pH(ex)) from neutral to 6.7 +/- 0.006. Diverse metabolic
acids associated with this drop in acidity were quantified by ionic exchange liquid chromatography (LC), showing concomitant rise in
lactate (Ctrls 7.5 +/- 0.5 mM; +GLU 12.35 +/- 1.3 mM; +GLU + MPP 18.1 +/- 1.8 mM),
acetate (Ctrl 0.84 +/- 0.13 mM: +GLU 1.3 +/- 0.15 mM; +GLU + MPP 2.7 +/- 0.4 mM),
fumarate, and a-ketoglutarate (<10 microM) while a range of other metabolic organic
acids remained undetected.
Amino acids quantified by
o-phthalaldehyde precolumn derivatization/electrochemical detection-LC show accumulation of
L: -alanine (1.6 +/- .052 mM),
L: -glutamate (285 +/- 9.7 microM),
L: -asparagine (202 +/- 2.1 microM), and
L: -aspartate (84.2 +/- 4.9 microM) produced during routine metabolism, while other
amino acids remain undetected. In contrast, the data show no evidence for accumulation of
acetaldehyde,
aldehydes, or
ketones (
Purpald/2,4-
dinitrophenylhydrazine-Brady's
reagent),
acetoin (Voges-Proskauer test), or
alcohols (
NAD(+)-linked
alcohol dehydrogenase). In conclusion, these results provide preliminary evidence to suggest the existence of an active
pyruvate-
alanine transaminase or
phosphotransacetylase/
acetyl-CoA synthetase pathway to be involved with anaerobic energy metabolism of
cancer cells.