title: Uridine abrogates mitochondrial toxicity related to nucleoside analogue reverse transcriptase inhibitors in HepG2 cells.
abstract: OBJECTIVE
  To assess in vitro if uridine may be suitable to prevent or treat mitochondrial toxicity related to nucleoside analogue reverse transcriptase inhibitors (NRTIs).
  
  
  METHODS
  Human HepG2-hepatocytes were exposed to NRTIs with or without uridine for 25 days. Cell growth, lactate production, intracellular lipids, mitochondrial DNA (mtDNA) and the ratio between the respiratory chain components COX II (mtDNA-encoded) and COX IV (nuclear-encoded) were measured.
  
  
  RESULTS
  HepG2 cells exposed to zalcitabine (177 nM) without uridine developed a severe depletion of mtDNA (to 8% of wild-type mtDNA levels), resulting in a decline of cell proliferation and COX II levels, with increased lactate and lipid accumulation. Uridine fully abrogated the adverse effects of zalcitabine on hepatocyte proliferation and normalized lactate synthesis, intracellular lipids and COX II levels by adjusting mtDNA levels to about 65% of NRTI-unexposed control cells. This effect was dose-dependent, with a maximum at 200 microM of uridine. Uridine also rapidly and fully restored cell function when added to cells with established mitochondrial dysfunction (zalcitabine for 15 days) despite continued zalcitabine exposure. Uridine also normalized cell proliferation in HepG2 cells exposed to 36 microM of stavudine and protected HepG2-cells exposed to 7 microM of zidovudine + 8 microM of lamivudine (pyrimidine analogues), but failed to improve cell function or mtDNA in cells exposed to 11.8 or 118 microM of didanosine (a purine analogue).
  
  
  CONCLUSIONS
  The pyrimidine precursor uridine may attenuate the mitochondrial toxicity of antiretroviral pyrimidine NRTIs in vitro, and its supplementation may represent a promising strategy in the prevention or treatment of mitochondrial toxicities in HIV-infected patients.
authors.affiliation: Department of Rheumatology and Clinical Immunology, Medizinische Universitätsklinik, Freiburg, Germany. ulrich.walker@klinikum.uni-freiburg.de
authors.forename: Ulrich A
authors.initials: UA
authors.lastname: Walker
authors.forename: Nils
authors.initials: N
authors.lastname: Venhoff
authors.forename: Eva C
authors.initials: EC
authors.lastname: Koch
authors.forename: Manfred
authors.initials: M
authors.lastname: Olschewski
authors.forename: Josef
authors.initials: J
authors.lastname: Schneider
authors.forename: Bernhard
authors.initials: B
authors.lastname: Setzer
mesh_terms: D019380:Anti-HIV Agents / Q000633:toxicity*; D051546:Cyclooxygenase 2; D004272:DNA, Mitochondrial / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007773:Lactates / Q000378:metabolism; D050356:Lipid Metabolism; D008565:Membrane Proteins; D008928:Mitochondria / Q000187:drug effects*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D018894:Reverse Transcriptase Inhibitors / Q000633:toxicity*; D014407:Tumor Cells, Cultured; D014529:Uridine / Q000494:pharmacology*; D016047:Zalcitabine / Q000633:toxicity*
chemical_list: D019380:Anti-HIV Agents; D004272:DNA, Mitochondrial; D007527:Isoenzymes; D007773:Lactates; D008565:Membrane Proteins; D018894:Reverse Transcriptase Inhibitors; D016047:Zalcitabine; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D003576:Electron Transport Complex IV; D014529:Uridine