Carcinogenic antioxidants

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.