Abstract

Background: Estradiol (E2) has a potent antioxidant effect on low density lipoproteins (LDL) in vitro and in vivo, which could be important in explaining the cardioprotective effect of hormone replacement therapy (HRT) in post menopausal women. Estriol (E3), on the other hand, is a weak estrogen with low metabolic effects on different tissues, and at present no cardioprotective effect has been attributed to this steroid. Aim: To study the antioxidant effect of E3 on LDL and to compare it with the potent antioxidant action exhibited by E2. Subjects and methods: After LDL was isolated by ultra centrifugation from plasma of 12 healthy untreated post menopausal women, it was divided into aliquots containing 0.5 mg of LDL protein. Estriol and E2 in doses of 0, 1, 5, 15 and 50 microM were incubated with different aliquots of LDL. CuSO4 15 microM was added to each aliquot to induce an oxidative stress. The aliquots were then incubated during 4 hours at 37 degrees C. Malonaldehyde (MDA) was measured as a marker of LDL oxidation, and expressed as nM/mg protein. Results: (mean +/- SD): Estriol induced a dose-dependent decrease in MDA concentration (baseline 62.8 +/- 21.7; 1 microM: 61.5 +/- 23.0; 5 microM: 52.9 +/- 20.3; 15 microM 43.5 +/- 20.1 and 50 microM: 31.0 +/- 17.6 nM/mg protein; F = 92.4; p < 0.0001), reaching a mean decrease of 50.7% at the highest dose tested. Estradiol has a similar dose-dependent decrease in MDA concentration (F = 60.2; p < 0.0001), revealing a more potent effect than E3 (p < 0.05), with a mean decrease of 67.4% at the highest dose tested. Conclusions: Our results demonstrate that estriol shows an important antioxidant action of LDL in vitro, although its effect is less potent than estradiol. These results raise the possibility that estriol could have a cardioprotective effect in post menopausal women, possibility that has not been yet demonstrated.