title: Vitamin C in cultured human (HeLa) cells: lack of effect on DNA protection and repair.
abstract: OBJECTIVE
  Dietary antioxidants, including vitamin C, may be in part responsible for the cancer-preventive effects of fruits and vegetables. Human intervention trials with clinical endpoints have failed to confirm their protective effects, and mechanistic studies have given inconsistent results. Our aim was to investigate antioxidant/ pro-oxidant effects of vitamin C at the cellular level.
  
  
  METHODS
  We have used the comet assay to investigate effects of vitamin C on DNA damage, antioxidant status, and DNA repair, in HeLa (human tumor) cells, and HPLC to measure uptake of vitamin C into cells.
  
  
  RESULTS
  Even at concentrations in the medium as high as 200 μM, vitamin C did not increase the background level of strand breaks or of oxidized purines in nuclear DNA. Vitamin C is taken up by HeLa cells and accumulates to mM levels. Preincubation of cells with vitamin C did not render them resistant to strand breakage induced by H2O2 or to purine oxidation by photosensitizer plus light. Vitamin C had no effect on the rate of repair of strand breaks or oxidized bases by HeLa cells. However, vitamin C at a concentration of less than 1 μM, or extract from cells preincubated for 6 h with vitamin C, was able to induce damage (strand breaks) in lysed, histone-depleted nuclei (nucleoids).
  
  
  CONCLUSIONS
  In these cultured human cells, vitamin C displays neither antioxidant nor pro-oxidant properties; nor does it affect DNA strand break or base excision repair.
authors.affiliation: Department of Pharmacology and Toxicology, University of Navarra, C/Irunlarrea 1, 31008 Pamplona, Spain. amazqueta@unav.es
authors.forename: Amaya
authors.initials: A
authors.lastname: Azqueta
authors.forename: Solange
authors.initials: S
authors.lastname: Costa
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Lorenzo
authors.forename: Nasser E
authors.initials: NE
authors.lastname: Bastani
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Collins
mesh_terms: D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D001205:Ascorbic Acid / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D002851:Chromatography, High Pressure Liquid; D020552:Comet Assay; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006367:HeLa Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000633:toxicity; D016877:Oxidants / Q000633:toxicity; D018384:Oxidative Stress / Q000187:drug effects; D017319:Photosensitizing Agents / Q000633:toxicity; D013997:Time Factors
chemical_list: D000975:Antioxidants; D016877:Oxidants; D017319:Photosensitizing Agents; D006861:Hydrogen Peroxide; D001205:Ascorbic Acid