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

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.

The present study compared oxidizability of LDL in healthy pre- and post-menopausal women by using a commonly employed copper ion-dependent method.

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, P0.05) 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, P0. 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.

The results suggest that physiological levels of oestrogen may not be able to affect in vitro LDL oxidation.