“…Most previous studies demonstrated that these adverse effects of nucleoside analogs are directly associated with mitochondrial injury, on the basis of the abnormal morphology of mitochondria, depletion of mitochondrion-encoded enzyme subunits, and decreased mitochondrial gene number (2,3,5,6,10,11,14,15,29). Clinical toxicities due to the mitochondrial dysfunction induced by nucleoside analogs may limit the use of certain treatment regimens and may even produce fatal complications, as documented for some cases of severe lactic acidosis (2,12,13,26,27). Therefore, it is important to evaluate new drugs from the nucleoside analogs for their potential to cause mitochondrial toxicity by measuring specific markers of toxicity, such as the level of mitochondrial DNA (mtDNA) synthesis or production of lactic acid in drug-treated cell cultures (1,2,5,6,12,20,29).…”