Low concentrations of 17 beta-estradiol reduce oxidative modification of low-denity lipoproteins in the presence of vitamin C and vitamin E

Micromolar concentrations of estradiol are required to inhibit the oxidatio n of low-density lipoproteins (LDL) in vitro. Recent evidence suggests that estradiol must be modified before it can become an effective antioxidant a t physiological levels. Our aim was to determine other possible conditions under which low concentrations of 17 beta-estradiol can reduce LDL oxidatio n. LDL susceptibility to oxidation was monitored by measurements of conjuga ted diene formation. High levels of 17 beta-estradiol reduced oxidative mod ification of LDL. Vitamin C and vitamin E also increased LDL resistance to Cu2+- mediated oxidation. More importantly, 10 nM 17 beta-estradiol, which on its own had no effect, exhibited significant antioxidant actions in the presence of either vitamins C or E. In conclusion, supraphysiological conce ntrations of 17 beta-estradiol are required to exert antioxidant effects di rectly in vitro. However, in the presence of vitamins C and E, concentratio ns of 17 beta-estradiol close to physiological levels can also protect LDL from oxidation. (C) 1999 Elsevier Science Inc.