Early effects of AZT on mitochondrial functions in the absence of mitochondrial DNA depletion in rat myotubes

Zidovudine (AZT) is a potent inhibitor of human immunodeficiency virus (HIV ) replication. In humans, as well as in animal models, lon-term. treatment with AZT induces a severe myopathy characterised by structural and function al alterations of mitochondria associated with depletion of mitochondrial D NA (mtDNA). In the present work, we compared the effects induced by AZT on mitochondria upon short-or long-term treatments of cultured rat myotubes. M orphological alterations were investigated by electron microscopy, and mtDN A depletion and deletions were analysed by Southern blot. Mitochondrial mem brane potential was determined after JC-1 staining by laser-scanning confoc al microscopy in whole cells, and by flow cytometry in isolated muscle mito chondria. We found that the early effects of AZT on mitochondrial functions were a marked, yet reversible reduction in mitochondrial membrane potentia l, in the absence of any effect on mtDNA. The long-term treatment, in addit ion to mitochondrial membrane potential alterations, induced morphological changes in mitochondria, and a remarkable reduction in the amount of mtDNA, without any significant evidence of mtDNA deletions. In both treatments, a block of the spontaneous contraction of myotubes was observed. To study in more detail the early effects induced by AZT, the ability of the drug to i nteract with cardiolipin, an important component of internal mitochondrial membrane, was investigated by atomic force microscopy (AFM) in an artificia l membrane model system. The results suggest that the primary effects of AZ T may be related to a physical interference with the membrane structure lea ding to a consequent modification of its physical characteristics. (C) 2001 Elsevier Science Inc. All rights reserved.