title: Uridine supplementation antagonizes zalcitabine-induced microvesicular steatohepatitis in mice.
abstract: Zalcitabine is an antiretroviral nucleoside analogue that exhibits long-term toxicity to hepatocytes by interfering with the replication of mitochondrial DNA (mtDNA). Uridine antagonizes this effect in vitro. In the present study we investigate the mechanisms of zalcitabine-induced hepatotoxicity in mice and explore therapeutic outcomes with oral uridine supplementation. BalbC mice (7 weeks of age, 9 mice in each group) were fed 0.36 mg/kg/d of zalcitabine (corresponding to human dosing adapted for body surface), or 13 mg/kg/d of zalcitabine. Both zalcitabine groups were treated with or without Mitocnol (0.34 g/kg/d), a dietary supplement with high bioavailability of uridine. Liver histology and mitochondrial functions were assessed after 15 weeks. One mouse exposed to high dose zalcitabine died at 19 weeks of age. Zalcitabine induced a dose dependent microvesicular steatohepatitis with abundant mitochondria. The organelles were enlarged and contained disrupted cristae. Terminal transferase dUTP nick end labeling (TUNEL) assays showed frequent hepatocyte apoptosis. mtDNA was depleted in liver tissue, cytochrome c-oxidase but not succinate dehydrogenase activities were decreased, superoxide and malondialdehyde were elevated. The expression of COX I, an mtDNA-encoded respiratory chain subunit was reduced, whereas COX IV, a nucleus-encoded subunit was preserved. Uridine supplementation normalized or attenuated all toxic abnormalities in both zalcitabine groups, but had no effects when given without zalcitabine. Uridine supplementation was without apparent side effects.
  
  
  CONCLUSIONS
  Zalcitabine induces mtDNA-depletion in murine liver with consequent respiratory chain dysfunction, up-regulated synthesis of reactive oxygen species and microvesicular steatohepatitis. Uridine supplementation attenuates this mitochondrial hepatotoxicity without apparent intrinsic effects.
authors.affiliation: Department of Rheumatology and Clinical Immunology, Medizinische Universitätsklinik, Freiburg, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Lebrecht
authors.forename: Yetlanezi A
authors.initials: YA
authors.lastname: Vargas-Infante
authors.forename: Bernhard
authors.initials: B
authors.lastname: Setzer
authors.forename: Janbernd
authors.initials: J
authors.lastname: Kirschner
authors.forename: Ulrich A
authors.initials: UA
authors.lastname: Walker
mesh_terms: D000818:Animals; D056486:Chemical and Drug Induced Liver Injury / Q000188:drug therapy* / Q000473:pathology*; D004261:DNA Replication / Q000187:drug effects; D004272:DNA, Mitochondrial / Q000235:genetics; D019587:Dietary Supplements; D005234:Fatty Liver / Q000139:chemically induced* / Q000188:drug therapy* / Q000473:pathology; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D050356:Lipid Metabolism / Q000187:drug effects; D015227:Lipid Peroxidation / Q000187:drug effects; D051379:Mice; D008807:Mice, Inbred BALB C; D008930:Mitochondria, Liver / Q000187:drug effects; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D018894:Reverse Transcriptase Inhibitors / Q000009:adverse effects*; D013385:Succinate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D014529:Uridine / Q000008:administration & dosage / Q000494:pharmacology*; D016047:Zalcitabine / Q000009:adverse effects*
chemical_list: D004272:DNA, Mitochondrial; D017382:Reactive Oxygen Species; D018894:Reverse Transcriptase Inhibitors; D016047:Zalcitabine; D011451:Prostaglandin-Endoperoxide Synthases; D013385:Succinate Dehydrogenase; D014529:Uridine