MITOCHONDRIAL AND CELLULAR TOXICITY INDUCED BY FIALURIDINE IN HUMAN MUSCLE IN-VITRO

Fialuridine (FIAU), when used experimentally in the treatment of patie nts with chronic hepatitis B, caused irreversible acute hepatic failur e, myopathy, myoglobinuria, severe lactic acidosis, neuropathy, and de ath. To investigate the primary cellular elements involved in the neur omuscular toxicity of FIAU, we examined its effects on human myotubes in cultures and searched for signs of recovery. From a total of 75 fla sks of normal myotubes prepared from human muscle biopsies, 63 were ex posed to various concentrations of FIAU (0.01 mu M, 0.1 mu M, 1 mu M, 10 mu M, 50 mu M, and 100 mu M) for 1 to 3 weeks, whereas 12 served as controls. After 3 weeks of FIAU treatment, 27 flasks were observed fo r 3 additional weeks to assess spontaneous recovery. All cultures were evaluated with: (a) light microscopy; (b) quantitative immunocytochem istry examining the number of myotubes immunostained for neural-cell a dhesion molecule (N-CAM); (c) Oil-Red-O stain, to assess the lipid dro plet accumulation; and (d) electron microscopy with morphometric measu rements of the volumetric density of each organelle per unit volume of tissue (magnification, x24,000). After 3 weeks of FIAU treatment, we found a severe reduction in the number of N-CAM-positive myotubes that varied according to the concentration of FIAU and the duration of tre atment. Electron microscopy demonstrated a varying degree of destructi on of the myotubes with significant increase in lipid droplets, lysoso mes, and the rough endoplasmic reticulum. Major changes in mitochondri a were noted even early in the treatment and consisted of concentric l amellar structures, paracrystalline inclusions, and vacuolization. The se abnormalities remained unchanged without signs of recovery for up t o 3 weeks after withdrawal of FIAU. We conclude that FIAU induces mito chondrial changes and intracellular lipid accumulations similar, but m ore severe, to those described with the other nucleoside analogues, su ch as zidovudine. In contrast to zidovudine, however, the FIAU-induced abnormalities do not improve or reverse after withdrawal of the drug. The observations are consistent with the irreversible mitochondrial c hanges noted in the FIAU-treated patients due to defective mitochondri al DNA replication.