8-Chloroadenine: a novel product formed from hypochlorous acid-induced damage to calf thymus DNA

Hypochlorous acid (HOCl) is formed by the action of the enzyme myeloperoxidase on hydrogen peroxide and chloride ions. It has been shown to be highly bactericidal and cytotoxic by a variety of mechanisms, one of which, may be the modification of DNA. Previously we have demonstrated by GC-MS analysis that exposure of calf thymus DNA to HOCl causes extensive pyrimidine modification, including 5-chlorocytosine formation. Using GC-MS analysis, we now demonstrate the formation of an additional chlorinated base product, 8-Cl adenine. The addition of 50 μM HOCl was sufficient to produce a significant increase in this product. The reaction of HOCl with adenine in calf thymus DNA was shown to be rapid with the reaction complete after 1 min. pH-dependence studies suggest HOCl rather than its conjugate base (OCl-) to be responsible for 8-Cl adenine formation. Other commercially available chlorinated base products, 6-Cl guanine or 2-Cl adenine were not detected. Therefore, 8-Cl adenine might prove a useful biomarker for studying the role of reactive chlorine species (RCS) during inflammatory processes.