title: Differential impact of conventional and low-dose oral hormone therapy (HT), tibolone and raloxifene on functionality of the activated protein C system.
abstract: Recent studies have shown that hormone therapy (HT) is associated with an acquired resistance to activated protein C (APC). The aims of the present study were to evaluate a possible dose-response relationship and differential effects of different HT regimens on functionality of the APC system. Two hundred two healthy women were randomly assigned to receive treatment for 12 weeks with tablets containing either low-dose HT containing 1 mg 17ss-oestradiol + 0.5 mg norethisterone acetate (NETA) (n = 50), conventional-dose HT containing 2 mg 17ss-oestradiol and 1 mg NETA (n = 50), 2.5 mg tibolone (n = 51), or 60 mg raloxifene (n = 51). Normalized APC system sensitivity ratios (nAPCsr) were determined in plasma collected at baseline and after 12 weeks using a thrombin generation-based APC resistance test probed with either recombinant APC (rAPC) or thrombomodulin (rTM). NAPCsr increased in both the conventional- and low-dose HT groups, consistent with reduced sensitivity to APC. The increase was slightly more pronounced in the conventional-dose group, but the difference between the two HT groups was not statistically significant. The sensitivity to APC was only marginally altered in those allocated to tibolone. Consequently, tibolone showed a different phenotype as compared with the low-dose HT group. A small increase in nAPCsr with both rAPC and rTM was seen in the raloxifene-group, but the increase was less than in the low-dose HT group. Our findings indicate that oestrogen-progestin therapy induces an APC resistant phenotype, which may be related to dose, whereas tibolone and raloxifene only marginally alter the sensitivity to APC.
authors.affiliation: Department of Haematology Ullevål University Hospital Trust, Oslo, Norway. a.l.eilertsen@medisin.uio.no
authors.forename: Anette L
authors.initials: AL
authors.lastname: Eilertsen
authors.forename: Sigurd
authors.initials: S
authors.lastname: Liestøl
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Mowinckel
authors.forename: H C
authors.initials: HC
authors.lastname: Hemker
authors.forename: Per-Morten
authors.initials: PM
authors.lastname: Sandset
mesh_terms: D020016:Activated Protein C Resistance / Q000097:blood / Q000139:chemically induced* / Q000150:complications / Q000378:metabolism; D000284:Administration, Oral; D001777:Blood Coagulation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004958:Estradiol / Q000009:adverse effects; D020847:Estrogen Receptor Modulators / Q000008:administration & dosage / Q000009:adverse effects*; D015914:Estrogen Replacement Therapy / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008875:Middle Aged; D009640:Norethindrone / Q000009:adverse effects / Q000031:analogs & derivatives; D000077563:Norethindrone Acetate; D009652:Norpregnenes / Q000008:administration & dosage / Q000009:adverse effects*; D017698:Postmenopause / Q000378:metabolism; D011486:Protein C / Q000378:metabolism*; D020849:Raloxifene Hydrochloride / Q000008:administration & dosage / Q000009:adverse effects*; D020845:Selective Estrogen Receptor Modulators / Q000008:administration & dosage / Q000009:adverse effects*; D013607:Tablets; D013923:Thromboembolism / Q000209:etiology / Q000378:metabolism; D016896:Treatment Outcome; D020246:Venous Thrombosis / Q000209:etiology / Q000378:metabolism
chemical_list: D004338:Drug Combinations; D020847:Estrogen Receptor Modulators; D009652:Norpregnenes; D011486:Protein C; D020845:Selective Estrogen Receptor Modulators; D013607:Tablets; D020849:Raloxifene Hydrochloride; D004958:Estradiol; D000077563:Norethindrone Acetate; C027385:tibolone; D009640:Norethindrone