Circumventing the crabtree effect: Replacing media glucose with galactose increases susceptibility of HepG2 cells to mitochondrial toxicants

Many highly proliferative cells generate almost all ATP via glycolysis despite abundant O-2 and a normal complement of fully functional mitochondria, a circumstance known as the Crabtree effect. Such anacrobically poised cells are resistant to xenobiotics that impair mitochondrial function, such as the inhibitors rotenone, antimycin, oligomycin, and compounds like carbonyl cyanide 4(trifluoromethoxy)phenylhydrazone (FCCP), that uncouple the respiratory electron transfer system from phosphorylation. These cells are also resistant to the toxicity of many drugs whose deleterious side effect profiles are either caused, or exacerbated, by impairment of mitochondrial function. Drug-induced mitochondrial toxicity is shown by members of important drug classes, including the thiazolidinediones, statins, fibrates, antivirals, antibiotics, and anticancer agents. To increase detection of druginduced mitochondrial effects in a preclinical cell-based assay, HepG2 cells were forced to rely on mitochondrial oxidative phosphorylation rather than glycolysis by substituting galactose for glucose in the growth media. Oxygen consumption doubles in galactose-grown HepG2 cells and their susceptibility to canonical mitochondrial toxicants correspondingly increases. Similarly, toxicity of several drugs with known mitochondrial liabilities is more readily apparent in aerobically poised HepG2 cells compared to glucose-grown cells. Some drugs were equally toxic to both glucoseand galactose-grown cells, suggesting that mitochondrial impairment is likely secondary to other cytotoxic mechanisms.