ANTIOXIDANT PROPERTIES OF THE TRIPHENYLETHYLENE ANTIESTROGEN DRUG TOREMIFENE

The aim of the present study was to investigate antioxidativity of the triphenylethylene antiestrogen toremifene. Toremifene and its structu ral analogues were studied for their ability to inhibit chain reaction s of lipid peroxidation and to act as scavengers of free radicals in v itro, and the effects of toremifene were compared to those of the estr ogens, tamoxifen and known antioxidants. Moreover, the in vivo antioxi dativity of toremifene was tested in a long-term experiment with rats. The ability of toremifene to prevent lipid peroxidation was assayed i n two different test systems. In the first assay (initiated with ascor bate/ADP-FeCl3, detection by the formation of TBA-reactive material) t oremifene was found to act as an efficient membrane antioxidant with a n IC50-value (18 mu M) comparable to that of tamoxifen (26 mu M) and a lpha-tocopherol (43 mu M). Toremifene derivatives 4-hydroxytoremifene (IC50 = 8 mu M) and Fc 1159 (IC50 = 31 mu M), as well as diethylstilbe strol (IC50 = 17 mu M) were also active while estradiol showed only we ak antioxidativity (IC50 = 300 mu M) in this test system. In the other assay (peroxidation initiated with t-butylhydroperoxide, detection by luminol-enhanced chemiluminescence) toremifene prevented lipid peroxi dation only at high concentrations (IC50 = 450 mu M) but the metabolit e 4-hydroxytoremifene (IC50 0.18 mu M), estradiol (IC50 = 4.6 mu M) an d diethylstilbestrol (IC50 = 1.7 mu M) showed potent antioxidant activ ity. The potency of 4-hydroxytoremifene even exeeded that of alpha-toc opherol (IC50 = 2.0 mu M) and butylated hydroxyanisole (IC50 = 1.1 mu M). Toremifene was found to have some superoxide anion but no peroxyl radical scavenging activity. Interestingly, diethylstilbestrol turned out to be a potent scavenger of peroxyl radicals. Treatment of female Sprague-Dawley rats with toremifene (12 or 48 mg/kg) was found to decr ease serum levels of lipid peroxides. This was seen at various time po ints (2 days, 5 weeks, 6 and 12 months) during long-term administratio n of toremifene to rats, and results obtained with two different metho ds (diene conjugation, TBA-reactive material) gave similar results. Th e present study thus showed that (i) like steroidal estrogens and tamo xifen toremifene is a potent membrane antioxidant in vitro, (ii) the a ntioxidant action of toremifene is not due to scavenging of free radic als and, importantly, (iii) toremifene acts antioxidatively also in li ving organisms in vivo.