Estrogens, selective estrogen receptor modulators, and a selective estrogen receptor down-regulator inhibit endothelial production of tissue factor pathway inhibitor 1.
BACKGROUND
Hormone therapy, oral contraceptives, and tamoxifen increase the risk of thrombotic disease. These compounds also reduce plasma content of tissue factor pathway inhibitor-1 (TFPI), which is the physiological inhibitor of the tissue factor pathway of coagulation. The current aim was to study if estrogens and estrogen receptor (ER) modulators may inhibit TFPI production in cultured endothelial cells and, if so, identify possible mechanisms involved.


METHODS
Human endothelial cell cultures were treated with 17beta-estradiol (E2), 17alpha-ethinylestradiol (EE2), tamoxifen, raloxifene, or fulvestrant. Protein levels of TFPI in cell media and cell lysates were measured by an enzyme-linked immunosorbent assay, and TFPI mRNA levels were assessed by quantitative PCR. Expression of ERalpha was analysed by immunostaining.


RESULTS
All compounds (each in a concentration of 10 nM) reduced TFPI in cell medium, by 34% (E2), 21% (EE2), 16% (tamoxifen), and 28% (raloxifene), respectively, with identical inhibitory effects on cellular TFPI levels. Expression of TFPI mRNA was principally unchanged. Treatment with fulvestrant, which was also associated with down-regulation of secreted TFPI (9% with 10 nM and 26% with 1000 nM), abolished the TFPI-inhibiting effect of raloxifene, but not of the other compounds. Notably, the combination of 1000 nM fulvestrant and 10 nM raloxifene increased TFPI secretion, and, conversely, 10 nM of either tamoxifen or raloxifene seemed to partly (tamoxifen) or fully (raloxifene) counteract the inhibitory effect of 1000 nM fulvestrant. The cells did not express the regular nuclear 66 kDa ERalpha, but instead a 45 kDa ERalpha, which was not regulated by estrogens or ER modulators.


CONCLUSIONS
E2, EE2, tamoxifen, raloxifene, and fulvestrant inhibited endothelial production of TFPI by a mechanism apparently independent of TFPI transcription.
Dahm
Anders E A
AE
Department of Haematology, Ullevål University Hospital, 0407 Oslo, Norway. a.e.a.dahm@medisin.uio.no
Iversen
Nina
N
Birkenes
Baard
B
Ree
Anne Hansen
AH
Sandset
Per Morten
PM
D002478:Cells, Cultured; D015536:Down-Regulation; D042783:Endothelial Cells / Q000378:metabolism*; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000032:analysis; D004997:Ethinyl Estradiol / Q000494:pharmacology; D000077267:Fulvestrant; D006801:Humans; D008074:Lipoproteins / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D020849:Raloxifene Hydrochloride / Q000037:antagonists & inhibitors; D020845:Selective Estrogen Receptor Modulators / Q000494:pharmacology*
D047628:Estrogen Receptor alpha; D008074:Lipoproteins; D012333:RNA, Messenger; D020845:Selective Estrogen Receptor Modulators; C051928:lipoprotein-associated coagulation inhibitor; D000077267:Fulvestrant; D004997:Ethinyl Estradiol; D020849:Raloxifene Hydrochloride; D004958:Estradiol