Inhibition of radiation-induced lipid peroxidation by tetrahydrocurcumin: possible mechanisms by pulse radiolysis.

The antioxidant property of tetrahydrocurcumin (THC), a reduced derivative of curcumin, was examined by its ability to inhibit radiation-induced lipid peroxidation in rat liver microsomes and compared with curcumin. The lipid peroxidation caused by irradiation of N2O-purged and aerated buffered aqueous solutions was found to be inhibited by THC in a dose- and concentration-dependent manner. In order to understand the actual reaction mechanisms involved in the inhibition process, pulse radiolysis investigation of THC with radiolytically produced radicals like hydroxyl, model peroxyl radicals, and azide radicals were done and the transients were detected by kinetic spectrophotometry. The reaction of THC with hydroxyl and azide radicals gave rise to transient absorption in the region 200-400 nm with two peaks at 310 nm and 390 nm. From the spectral properties and kinetics of these radicals, a suitable mechanism is discussed to explain the antioxidant actions of THC.

Physico-chemical properties and antioxidant activities of methoxy phenols.

A few structurally related phenols, dehydrozingerone (DZ), bromopentenone (BP), eugenol (EG) and isoeugenol (IEG), derived from plant products show antioxidant properties by inhibiting lipid peroxidation in membrane models. The phenoxyl radicals produced by the scavenging of free radicals during the inhibition of lipid peroxidation, were also generated by specific one-electron oxidants using pulse radiolysis. The radical lifetimes (second order rate constants for radical-radical reactions), reactivities with hydroxyl and model peroxyl radicals and the one-electron reduction potentials with respect to the standard couples were quantified. These results along with their lipophilicity data were correlated with their antioxidant activity (IC50 values).

Free radical reductive degradation of vic-dibromoalkanes and reaction of bromine atoms with polyunsaturated fatty acids: possible involvement of Br(.) in the 1,2-dibromoethane-induced lipid peroxidation.

Bromine atoms generated upon reductive degradation of 1,2-dibromoethane and various other vic-dibromoalkanes have been shown to react with polyunsaturated fatty acids via both abstraction of bisallylic hydrogen and addition to the double bonds. The abstraction process occurs with 53, 68, and 77% efficiency from linoleic (18:2), linolenic (18:3), and arachidonic acid (20:4), respectively. The corresponding absolute rate constants have been evaluated to be 1.2 x 10(9), 1.8 x 10(9), and 5.1 x 10(9) M-1 s-1 for these three polyunsaturated fatty acids (PUFAs). The rate constants for the bromine atom addition reaction appear to be very similar for all PUFAs and have been determined to (1.2 +/- 0.3) x 10(9) M-1 s-1. Absolute rate constants in the order of 10(5)-10(6) s-1 have also been measured for the bromine atom elimination from various beta-bromoalkyl radicals. The results render bromine atoms a potential initiator for lipid peroxidation, and their reactions may well provide an important chemical basis for the overall toxic action of 1,2-dibromoethane and related substrates.