Cellular and molecular events leading to mitochondrial toxicity of 1-(2-deoxy-2-fluoro-1-beta-D-arabinofuranosyl)-5-iodouracil in human liver cells.

Abstract

We have explored the mechanism(s) related to FIAU-induced liver toxicity, particularly focusing on its effect on mitochondrial function in a human hepatoma cell lineHepG2. The potential role of FMAU and FAU, metabolites detected in FIAU-treated patients were also ascertained. FIAU and FMAU inhibited cell growth and were effectively phosphorylated. A substantial increase in lactic acid production in medium of cells incubated with 1-10 ,uM FIAU or FMAU was consistent with mitochondrial dysfunction. Slot blot analysis demonstrated that a two week exposure to 10 ,uM FIAU or FMAU was not associated with a decrease in total mitochondrial (mt) DNA content. However, FIAU and FMAU were incorporated into nuclear and mtDNA and relative values suggest that both compounds incorporate at a much higher rate into mtDNA. Electron micrographs of cells incubated with 10 ,IM FIAU or FMAU revealed the presence of enlarged mitochondria with higher cristae density and lipid vesicles. In conclusion, these data suggest that despite the lack of inhibition of mtDNA content, incorporation of FIAU and FMAU into mtDNA of HepG2 cells leads to marked mitochondrial dysfunction as evidenced by disturbance in cellular energy metabolism and detection of

Antiviral activity and toxicity of fialuridine in the woodchuck model of hepatitis B virus infection

“…10,[29][30][31][32][33][34][35] In vitro, FIAU also causes disturbances in mitochondrial function. In some, 33,35,36 but not all reports, 37 lactic acid production was increased by FIAU. In contrast to findings with ddC, which consistently produced significant decrements in steady-state abundance of mtDNA, variable results have been reported with FIAU from decrements that were slight 36 or moderate 38 to no effect on mtDNA abundance.…”

“…[38][39][40][41] Because ddC lacks the 3Ј-OH group necessary for DNA chain extension, incorporation of ddC into DNA results in obligatory chain termination and inhibition of mtDNA synthesis. Unlike dideoxynucleosides, FIAU has a functional 3Ј-OH group that allows chain extension and incorporation of FIAU into mitochondrial 35,38 and nuclear 36,37,39 DNA. It may follow that alterations of mitochondrial function and structure, at least in short-term in vitro studies, are the result of altering the genetic cascade within mitochondria.…”

Mitochondrial DNA Depletion, Oxidative Stress, and Mutation: Mechanisms 0f Dysfunction from Nucleoside Reverse Transcriptase Inhibitors

“…Ultrastructural defects are found in mitochondria (Cui et al, 1995). mtDNA decrease in abundance in HepG2 cells after 14 days' exposure to FIAU and FMAU (Lewis et al, 1996); FIAU and FMAU, but not FAU, cause mitochondrial structural defects in vitro after at least 2 weeks' treatment.…”

“…The abundance of defective mtDNA may increase to a point at which a threshold of energy depletion may be reached and symptoms become manifested. This threshold effect on energetics in NRTI toxicity is analogous to that seen with heritable mitochondrial illnesses, including those that include mtDNA depletion Wallace, 1992a, Cooley et al, 1990Lambert et al, 1990 Distorted cristae and decreased mtDNA in CEM cells Cui et al, 1997Martin et al, 1994Medina et al, 1994Youssef and Badr, 1992 D4T Peripheral nerve Painful peripheral neuropathy in 55% of patients Browne et al, 1993Cohen et al, 1994 Distorted cristae and decreased mtDNA in CEM cells Cui et al, 1997Martin et al, 1994Medina et al, 1994 Cui et al, 1995Klecker et al, 1994Lewis et al, 1994aLewis and Tankersley, 1995Richardson et al, 1994Tennant et al, 1998 NRTIs, nucleoside reverse transcriptase inhibitors; AZT, zidovudine; DDC, zalcitabine; 3TC, lamivudine; DDI, didanosine; D4T, stavudine.…”

Severe hepatic dysfunction after adenovirus-mediated transfer of the herpes simplex virus thymidine kinase gene and ganciclovir administration

“…Phosphorylated nucleoside analogs appear to be transported into the mitochondria and to exert their inhibitory effect on mtDNA synthesis. [30][31][32] Mitochondria are selective in their membrane permeability, however, it has been shown 33,34 that other antiviral nucleotide anologues can be efficiently incorporated into mitochondrial DNA and inhibit mtDNA polymerase. 31,35 In humans multi-system toxicity due to nucleoside analogues, affecting slowly proliferating but metabolically active tissues (liver, pancreas, muscle, neuronal tissue), has been described for zidovudine, didanosine and zalcitabine, fialuridine, stavudine and lamivudine.…”