Peroxyl Radical Is Produced upon the Interaction of Hypochlorite with tert-Butyl Hydroperoxide

As we reported previously, hypochlorite interacting with organic hydroperoxides causes their decomposition ((1995) Biochemistry (Moscow), 60, 1079-1086). This interaction was supposed to be a free-radical process and serve as a source of free radicals initiating lipid peroxidation (LP). The present study is the first attempt to detect and identify free radicals produced in the reaction of hypochlorite with tert-butyl hydroperoxide, (CH3)3COOH, which we have used as an example of organic hydroperoxides. We have used a direct method for free radical detection, EPR of spin trapping, and the following spin traps: N-tert-butyl-α-phenylnitrone (PBN) and α-(4-pyridyl-1-oxyl)-N-tert-butylnitrone (4-POBN). When hypochlorite was added to (CH3)3COOH in the presence of a spin trap, an EPR spectrum appeared representing a superposition of two signals. One of them belonged to a spin adduct formed as a result of direct interaction of hypochlorite with the spin trap (hyperfine splitting constants were: αβH H = 0.148 mT; aN = 1.537 mT; and ΔHPP = 0.042 mT for 4-POBN and αβH = 0.190 mT; aN = 1.558 mT; and ΔHPP = 0.074 mT for PBN). The other signal was produced by hypochlorite interactions with (CH3)3COOH itself (hyperfine splitting constants were: αβH = 0.233 mT; aN = 1.484 mT; ΔHPP = 0.063 mT and αβH = 0.360 mT; aN = 1.547 mT; ΔHPP = 0.063 mT for 4-POBN and PBN, respectively). Comparison of spectral characteristics of this spin adduct with those of tert-butoxyl or tert-butyl peroxyl radicals produced in known reactions of (CH3)3COOH with Fe2+ and Ce4+, respectively, showed that the radical (CH3)3COO. is produced from the interaction of hypochlorite with (CH3)3COOH. Like Ce4+ but not Fe2+, hypochlorite addition to (CH3)3COOH was accompanied by a bright flash of chemiluminescence characteristic of the reactions in which peroxyl radicals are produced. Thus, all these results suggest peroxyl radical production in the reaction of hypochlorite with hydroperoxide. This reaction is one of the most possible ways for the initiation of free-radical LP that occurs in vivo, when hypochlorite interacts with unsaturated lipids comprising natural protein–lipid complexes, such as lipoproteins and biological membranes.