Estradiol-17β as an antioxidant: Some distinct features when compared with common fat-soluble antioxidants

• Published in: The Journal of laboratory and clinical medicine 1996-10, Vol.128 (4), p.367-375
• Main Authors: Ayres, Stacey, Tang, Maoyun, Ravi Subbiah, M.T.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Hormones. Endocrine system; Medical sciences; Pharmacology. Drug treatments
• ISSN: 0022-2143; 1532-6543
• DOI: 10.1016/S0022-2143(96)80008-4

Estrogens are potent antioxidants both in vitro and in vivo. In this study the antioxidant affect of estradiol-17β (estradiol) was compared with those of fat-soluble antioxidants (α-tocopherol and β-carotene) in terms of both fatty acid (thiobarbituric acid-reactive substances and diene conjugation) and cholesterol oxidation (oxysterols). The addition of α-tocopherol (54 μmol/L) inhibited low-density lipoprotein (LDL) oxidation by 92.6% and high-density lipoprotein (HDL) oxidation by 76.5%. In similar experiments, estradiol (54 μmol/L) inhibited LDL oxidation by 77.5% but inhibited HDL oxidation by only 55.4%. Beta-carotene had no antioxidant effect. Lag times (diene conjugation method) for α-tocopherol and β-carotene increased by 175% and 125%, respectively. Estradiol markedly reduced the maximum formation of diene conjugates as compared with results with α-tocopherol and β-carotene, and it exhibited a linear curve (no change in lag time). In terms of cholesterol oxidation, estradiol was far more effective than α-tocopherol or β-carotene in inhibiting oxysterol formation (μg/ml plasma) (control = 24.56 ± 2.31, β-carotene = 20.59 ± 3.32, α-tocopherol = 20.19 ± 1.58, estradiol = 14.38 ± 0.70). This study shows that estradiol is as effective an antioxidant as α-tocopherol in terms of fatty acid peroxidation but is far more effective than α-tocopherol in terms of cholesterol peroxidation.