The synthetic oestrogens diethylstilboestrol, hexoestrol and 17 α-ethynyloestradiol are known to be carcinogenic, yet they all exert antioxidant properties in vitro in that they are good inhibitors of iron ion-dependent lipid peroxidation. In rat liver microsomes incubated with Fe(III)-ascorbate or Fe(III)-ADP/NADPH and also in ox-brain phospholipid liposomes incubated with Fe(III)-ascorbate; the overall order of effectiveness of the compounds tested as inhibitors of lipid peroxidation was diethylstilboestrol ⪢ hexoestrol ⪢ 17 α-ethynyloestradiol ⪢ 4-hydroxytamoxifen ⪢ 17 β-oestradiol ⪢ tamoxifen. Compounds acting as antioxidants towards lipids may also exert pro-oxidant effects towards other molecules such as DNA and thus must never be assumed to be safe for human use.
