ZIDOVUDINE CAUSES EARLY INCREASES IN MITOCHONDRIAL RIBONUCLEIC-ACID ABUNDANCE AND INDUCES ULTRASTRUCTURAL-CHANGES IN CULTURED MOUSE MUSCLE-CELLS

BACKGROUND: Zidovudine (azidothymidine, AZT) causes a toxic mitochondr ial myopathy in AIDS patients with changes in mitochondrial (mt) DNA a nd mitochondrial structure. To determine early subcellular events in A ZT myopathy in vitro we examined C2C12 myotubes treated with AZT (0.2, 2, 10 mu g/ml) for up to 4 weeks. We identified AZT-induced effects o n muscle intracellular compartments by determining the comparative abu ndance of selected myotube cytoplasmic and mtRNAs and mtDNA. EXPERIMEN TAL DESIGN: RNA and DNA were extracted from cultured C2C12 myotubes, b lotted and probed with cDNAs specific for the mitochondrial gene produ cts cytochrome b and cytochrome c oxidase I, nuclear-encoded sarcomeri c troponin C, and cytoplasmic glyceraldehyde-3-phosphate dehydrogenase , Transmission electron microscopy was performed on parallel samples. RESULTS: After 4 weeks of AZT, cytochrome b and cytochrome c oxidase I mtRNA abundance increased to 64% and to 31% above respective control levels. No change occurred in mtDNA abundance or nuclear encoded glyce raldehyde-3-phosphate dehydrogenase mRNA compared with the nuclear enc oded sarcomeric troponin C control. Transmission electron microscopy s howed focal, disruption of mitochondrial cristae with intramyocytic li pid droplets after 14 days of AZT treatment. CONCLUSIONS: Increased mt RNA abundance in absence of changes in mtDNA abundance suggests that e arly AZT toxicity to mitochondria may relate to defects in mtDNA repli cation or mtRNA transcription.