Hypochlorite Reacts with an Organic Hydroperoxide Forming Free Radicals, But not Singlet Oxygen, and Thus Initiates Lipid Peroxidation

O. M. Panasenko,^1,2 J. Arnhold,³ and J. Schiller³

¹Institute of Physico-Chemical Medicine, ul. M. Pirogovskaya 1a, Moscow, 119828 Russia; E-mail: panasenko@glas.apc.org

²To whom correspondence should be addressed.

³Institute of Medical Physics and Biophysics, Leipzig University, Liebigstr. 27, 04103 Leipzig, Germany; fax: (0341) 971-5709.

Submitted April 22, 1997; revision submitted June 11, 1997.

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The mechanism of the reaction of hypochlorite with t-butyl hydroperoxide as a model organic hydroperoxide was studied. The reaction produces chemiluminescence with rate constant 13 ± 2 mM^-1·sec^-1. The chemiluminescence of this reaction was compared with that of the hypochlorite reaction with H₂O₂ where singlet oxygen (¹O₂) is formed. In the hypochlorite reaction with H₂O₂, the effect of hypochlorite concentration on the integrated chemiluminescence intensity is quadratic; a red filter with transmission >600 nm did not significantly decrease the chemiluminescence intensity; substitution of D₂O for H₂O increased the luminescence intensity 10-fold; infrared monomol emission was observed at 1270 nm. These results confirm the formation of ¹O₂ during the hypochlorite reaction with H₂O₂. However, when t-butyl hydroperoxide was used instead of H₂O₂, the concentration effect significantly differed from quadratic, and the red filter decreased the luminescence intensity by ~99%; D₂O slightly decreased the luminescence intensity. Finally, addition of t-butyl hydroperoxide to hypochlorite was not associated with monomol emission of ¹O₂ in the infrared region. The data exclude the possibility of singlet oxygen formation in the hypochlorite reaction with the organic hydroperoxide. According to ¹H-NMR spectroscopy, di-t-butyl peroxide is the main product of the hypochlorite reaction with t-butyl hydroperoxide; its production can be explained by radical formation, i.e., by generation of t-butyloxy radical. t-Butyl hydroperoxide and cumene hydroperoxide promoted hypochlorite-induced lipid peroxidation of phospholipid liposomes. The free radical scavenger butylated hydroxytoluene completely inhibited this effect. The data suggest that organic hydroperoxides, always present in certain amounts in vivo, may be the intermediates that interact with hypochlorite-forming free radicals which are initiators of lipid peroxidation.

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KEY WORDS: hypochlorite, lipid peroxidation, singlet oxygen, free radicals, hydroperoxide.

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