The phytoestrogens Genistein and Daidzein, and 17 beta-estradiol inhibit development of neointima in aortas from male and female rabbits in vitro after injury.

BACKGROUND

17 beta-Estradiol and phytoestrogens are known to have beneficial effects on the cardiovascular systems of women. The exact mechanisms for how estrogens and phytoestrogens influence the cardiovascular system are not yet understood in detail.

OBJECTIVE

The objective of this study was to investigate whether 17 beta-estradiol and the phytoestrogens Genistein and Daidzein have an effect on post-injury processes in vessel walls.

METHODS

In this in-vitro experiment, the sex-specific effects of 50 micrograms/ml 17 beta-estradiol (equivalent to 180 mumol/l), and of the isoflavones Genistein (5 and 50 micrograms/ml, equivalent to 18.5 and 185 mumol/l), and Daidzein (5 and 50 micrograms/ml, equivalent to 19.7 and 197 mumol/l) on endothelium-denuded aortas from female and male rabbits after vascular injury were studied. Morphometry and immunohistochemistry were performed for quantitative and qualitative analysis.

RESULTS

Neointimal cells were in part positive for alpha-actin staining of smooth muscle cells. Staining with 5'-bromo-2'deoxyuridine plus 2'-deoxycytidine showed that proliferative activity in the neointima had significantly decreased after 28 days for groups that had been treated with 50 micrograms/ml Genistein. Immunofluorescence staining for the expression of nuclear estrogen receptor protein in the arterial wall for aortic rings from female and male rabbits was positive. 17 beta-Estradiol, Genistein, and its analog Daidzein (with no protein tyrosine kinase activity) inhibited formation of neointima sex-independently at equivalent concentrations of 50 micrograms/ml. However, a concentration of 5 micrograms/ml Genistein decreased formation of neointima significantly for aortic rings from male rabbits only, whereas 5 micrograms/ml Genistein increased formation of neointima in rings from female rabbits, which corresponded to the increase in proliferative activity detected after 28 days.

CONCLUSIONS

Genistein and Daidzein both inhibited proliferation at certain concentrations, so this effect is supposed to be independent from Genistein's protein tyrosine kinase activity. The antiproliferative properties of all three estrogens were observed in the absence of endothelium and therefore are independent from endothelium-mediated effects.