title: Antioxidant and prooxidant properties of caffeine, theobromine and xanthine.
abstract: BACKGROUND
  Caffeine, along with its catabolic products theobromine and xanthine, is a key component of tea and coffee. These compounds are structurally similar to uric acid, a known antioxidant which is present in blood at relatively high concentrations, but also shows prooxidant activity. In view of the structural similarity between uric acid and caffeine and its metabolites, we studied the antioxidant and prooxidant properties of these compounds.
  
  
  METHODS
  Antioxidant activity was determined by measuring the quenching effect of the compounds on oxidative DNA degradation by a hydroxyl radical generating system. Prooxidant activity was studied by measuring the ability of the compounds to oxidatively degrade DNA in the presence of copper ions.
  
  
  RESULTS
  Caffeine, theobromine and xanthine have a quenching effect on the production of hydroxyl radicals, as well as on oxidative DNA breakage by hydroxyl radicals. Consistent with previous observations that many known antioxidants of plant origin are also capable of prooxidant action, the purine alkaloids also show oxidative DNA breakage in the presence of transition metal ions.
  
  
  CONCLUSIONS
  The alkaloid caffeine and its catabolic products theobromine and xanthine exhibit both antioxidant and prooxidant properties. The results lead to the observation that caffeine and its metabolites may also contribute to the overall antioxidant and chemopreventive properties of caffeine-bearing beverages, such as tea.
authors.affiliation: Department of Biochemistry, Faculty of Life Sciences, AMU, Aligarh, India. smhadi@del6.vsnl.net.in
authors.forename: Sonish
authors.initials: S
authors.lastname: Azam
authors.forename: Naghma
authors.initials: N
authors.lastname: Hadi
authors.forename: Nizam Uddin
authors.initials: NU
authors.lastname: Khan
authors.forename: Sheikh Mumtaz
authors.initials: SM
authors.lastname: Hadi
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D002110:Caffeine / Q000737:chemistry / Q000494:pharmacology*; D002417:Cattle; D003300:Copper / Q000737:chemistry / Q000378:metabolism; D004247:DNA / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D004249:DNA Damage; D017665:Hydroxyl Radical / Q000737:chemistry / Q000378:metabolism; D016877:Oxidants / Q000737:chemistry / Q000494:pharmacology*; D010957:Plasmids / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D013805:Theobromine / Q000737:chemistry / Q000494:pharmacology*; D014527:Uric Acid / Q000737:chemistry / Q000494:pharmacology; D019820:Xanthine / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D016877:Oxidants; D019820:Xanthine; D014527:Uric Acid; D017665:Hydroxyl Radical; D002110:Caffeine; D003300:Copper; D004247:DNA; C427203:calf thymus DNA; D013805:Theobromine