Abstract
Drug-induced mitochondrial toxicity can occur as a result of inhibition of mitochondrial DNA (mtDNA) replication as with certain nucleoside reverse transcriptase inhibitors or inhibition of mtDNA-encoded protein synthesis as with certain antibacterials. Both types of dysfunction have the overall effect of reducing the level of proteins encoded by mtDNA. A lateral-flow immunoassay which measures the levels of both a mtDNA-encoded protein and a nuclear DNA-encoded protein allows simple and rapid determination of the ratio of these 2 proteins and, hence, identifies changes in mtDNA-encoded protein levels. Here, we describe an assay that compares the level of Complex IV (cytochrome c oxidase), a mitochondrial protein which has 3 subunits encoded by mtDNA and made by mitochondrial ribosomes, with that of frataxin, a protein encoded by nuclear DNA and made by cytosolic ribosomes. We tested a selection of antibacterials and antiretrovirals in cells and show that the ratio of Complex IV: frataxin decreases when a drug inhibits either mtDNA replication or mtDNA-encoded protein synthesis. The results obtained with the assay were confirmed by Western blotting and immunocytochemical analysis. The assay has high reproducibility, requires small amounts of sample, is quantitative, and is able to identify drugs which ultimately lead to a decrease in mtDNA-encoded proteins.