Estrogens and atherosclerosis

Area of Science:

• Cardiovascular Science
• Endocrinology
• Immunology

Background:

• Epidemiological and experimental studies suggested estradiol (E2) prevents atherosclerosis.
• However, hormone replacement therapy (HRT) studies in women showed conflicting results.
• Mouse models were used to investigate the discrepancy in E2's effect on atherosclerosis.

Purpose of the Study:

• To elucidate the mechanisms behind estradiol's (E2) role in atherosclerosis development.
• To understand why HRT did not confirm E2's atheroprotective effects.
• To identify potential reasons for increased cardiovascular events in women using HRT.

Main Methods:

• Utilized mouse models of atherosclerosis.
• Assessed changes in lipid metabolism and serum cholesterol.
• Analyzed inflammatory-immune responses, including T helper cell (Th1) profiles and interferon-gamma production.
• Investigated nitric oxide (NO) bioavailability at the endothelial level.

Main Results:

• Estradiol (E2) showed negligible influence on lipid metabolism, despite decreasing serum cholesterol.
• E2 induced a pro-inflammatory immune response, favoring a T helper cell (Th1) profile and increasing interferon-gamma.
• This inflammatory response could destabilize atheromatous plaques and increase cardiovascular events.
• E2 increased endothelial nitric oxide (NO) bioavailability, but this did not affect fatty streak development.

Conclusions:

• Estradiol's (E2) atheroprotective effect may be counteracted by its induction of an inflammatory-immune response.
• The Th1-biased immune response and increased interferon-gamma may explain cardiovascular risks associated with HRT.
• Endothelial mechanisms for atheroprotection by E2 require further molecular characterization.
• Findings support developing strategies to mitigate detrimental effects while preserving beneficial ones of E2.