Formation of spiroiminodihydantoin nucleoside by reaction of 8-oxo-7,8-dihydro-2 '-deoxyguanosine with hypochlorous acid or a myeloperoxidase-H2O2-Cl- system

Hypochlorous acid (HOCl), generated by myeloperoxidase from H2O2 and Cl-, i s a strong chlorinating and oxidizing agent, playing an important role in h ost defense and inflammatory tissue injury. As several recent studies have shown that various oxidizing agents including peroxynitrite and singlet oxy gen react readily with 8-oxo-7,8-dihydro-2 ' -deoxyguanosine (8-oxodGuo) to yield further oxidized products, we have studied the reaction of 8-oxodGuo with reagent HOCl and with a myeloperoxidase-H2O2-Cl- system. When I mM 8- oxodGuo was reacted with 0.5 mM HOCl at pH 7.4 and 37 degreesC, two major p roducts were formed. They were identified as the diastereomers of spiroimin odihydantoin deoxyribonucleoside (dSph) on the basis of their identical ESI -MS and UV spectra and HPLC retention times with those of the major reactio n products which were reported to be formed in other oxidation systems incl uding potassium monopersulfate plus cobalt (II) chloride, peroxynitrite plu s thiol, and type II photosensitization. Under the above reaction condition s, the yield of the diastereomers of dSph was 0.38 mM, with 0.57 mM 8-oxodG uo remaining unreacted. Since the presence of 50% D2O, 10 mM sodium azide, or 2% ethanol did not affect the yield of the products, involvement of sing let oxygen and hydroxyl radical in the formation of dSph from 8-oxodGuo wit h HOCl was ruled out. A 1000-fold excess of dGuo did not inhibit the reacti on of 8-oxodGuo with HOCl, indicating that 8-oxodGuo reacts more readily th an dGuo with HOCL dSph was also formed by reaction of 8-oxodGuo with myelop eroxidase in the presence of H2O2 and Cl-. Our results suggest that formati on of dSph from 8-oxodGuo is mediated, possibly via an addition of Cl- to, or two-electron oxidation of 8-oxodGuo, with HOCl or the myeloperoxidase-H2 O2-Cl- system.