Effect of menopause on low-density lipoprotein oxidation: is oestrogen an important determinant?

Objectives: Significantly increased risk for developing cardiovascular disease in post-menopausal women is linked with the Fall of oestrogen. Although supraphysiological levels of oestrogen may inhibit oxygen free radical mediated low-density lipoprotein (LDL) oxidation, the effect of physiological level of oestrogen on LDL oxidation is unknown. Methods: The present study compared oxidizability of LDL in healthy pre- and post-menopausal women by using a commonly employed copper ion-dependent method. Results: Pre-menopausal women (n = 20. mean age 27) had significantly higher serum oestradiol level (576 +/- 109 pmol/l) in comparison to post-menopausal women (n = 23. mean age 51, oestradiol 64 +/- 18 pmol/l, P < 0.001). The oxidation of LDL in two groups was not different by measuring either the lag phase of conjugated dienes formation (54 +/- 12 vs. 55 +/- 14 min, P >0.05) or the generation of thiobarbituric acid reactive substances over 4 h of oxidation. The major lipid soluble antioxidant in LDL, vitamin E (determined as alpha-tocopherol) is similar in two groups (2.34+/-0.48 vs. 2.40+/-0.56 nmol/mg LDL, pre- and post-menopausal subjects, respectively, P > 0.05). Linear regression analysis found a weak but significant correlation between LDL vitamin E level and oxidizability of LDL in both groups but did not show effect of serum oestradiol levels. Conclusion: The results suggest that physiological levels of oestrogen may not be able to affect in vitro LDL oxidation. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.