Combined oestrogen–progestogen replacement therapy does not inhibit low‐density lipoprotein oxidation in postmenopausal women

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Abstract
The use of oestrogen containing hormone replacement therapy (HRT) is related to a significantly reduced atherosclerotic cardiovascular risk in postmenopausal women. Oestrogen is thought to be antioxidant and may inhibit low-density lipoprotein (LDL) oxidation in vitro. We investigated the effect of combined oestrogen and progestogen HRT on LDL oxidation in postmenopausal women. Eighteen healthy women were given oestrogen/progestogen, and the susceptibility of LDL to oxidation was measured as the level of autoantibody to oxidative modified LDL and the production of conjugated dienes during copper-dependent oxidation after 3 and 6 months HRT. The levels of vitamin E, the major antioxidant in LDL, were also measured. After HRT, the anti-oxidatively modified LDL antibody level remained unchanged [1.58+/-0.16, 0.10 (-0.10, 0.26), and 0.08 (-0.09, 0.19), mean+/-s.d. at baseline, and mean change with 95% confidence intervals for differences at 3 and 6 months, respectively, P>0.05] as did the production of conjugated dienes when determined as lag phase [51.2+/-7.5, -0.3 (-3.9, 3.3), and 1.5 (-3.4, 6.4) min, P>0.05]. The LDL vitamin E content, measured as alpha-tocopherol, was also not altered [2.34+/-0.54, -0.07 (-0.27, 0.13), and -0.07 (-0.33, 0.16) nmol mg(-1) LDL, P>0.05] by treatment. Combined oestrogen and progestogen therapy for 6 months in postmenopausal women does not protect LDL against oxidation.