We investigated the hypothesis that the antiatherosclerotic effect of 17 be
ta -estradiol (E-2) is due to a shift in the nitric oxide (NO)/superoxide (
O-2(-)) balance in the vessel wall, thereby increasing the bioavailability
of NO. In human umbilical vein cultured endothelial cells, E-2 (1-100 nmol/
l), but not 17 alpha -estradiol, caused a time- and concentration-dependent
decrease in expression of the NADPH oxidase subunit gp91phox (up to 60% in
hibition at both the mRNA and protein level). This effect was prevented by
coincubation with the estrogen receptor antagonists tamoxifen and ICI 182,7
80 (1 mu mol/l each). Within the same concentration range, E-2 also up-regu
lated endothelial nitric oxide synthase expression (similar to twofold). Mo
reover, preincubation of the cells with E-2 or a gp91phox antisense oligonu
cleotide significantly decreased their capacity to generate O-2(-) on phorb
ol ester stimulation (i.e., assembly of the active NADPH oxidase complex).
Blockade of NO synthase activity, on the other hand, had no effect on phorb
ol ester-stimulated O-2(-) formation. In addition, E-2 (100 nmol/l) inhibit
ed the increase in adhesion molecule and chemokine expression in cells expo
sed to cyclic strain. Cyclic strain enhanced endothelial O-2(-) formation,
thereby offsetting the inhibitory effect of NO on the expression of these g
ene products. E-2 thus seems to act as an antioxidant at the genomic level
which by improving the NO/O-2(-) balance normalizes expression of proathero
sclerotic gene products in endothelial cells.