DOAC-Remove abolishes the effect of direct oral anticoagulants on activated protein C resistance testing in real-life venous thromboembolism patients.

Background Direct oral anticoagulants (DOACs) may cause false results of activated protein C resistance (APC-R) ratio. DOAC-Remove, a new reagent based on activated carbon, has been designed to eliminate the interference of DOACs on coagulation assays. The aim of the study was to investigate whether the use of DOAC-Remove enables to determine APC-R in patients treated with DOACs. Methods We assessed 74 venous thromboembolism (VTE) patients, including 25 on rivaroxaban, 25 on apixaban and 24 taking dabigatran. APC-R was determined using the Russell Viper Venom Time (RVVT)-based clotting test. APC-R and DOAC concentrations were tested at baseline and following DOAC-Remove. Thrombophilia, including factor V Leiden (FVL) mutation was tested. Results FVL mutation was found in 20 (27%) patients. The APC-R ratio at baseline was measurable in 43 patients (58.1%), including 20 (80%) on rivaroxaban, 19 (76%) on apixaban and four (16.7%) on dabigatran. In patients with measurable APC-R at baseline, the ratio >2.9 was found in 23 patients (53.5%). In 16 (37.2%) subjects APC-R ratio <1.8 suggested FVL mutation which was genetically confirmed. Four (9.3%) FVL carriers on dabigatran showed negative/equivocal APC-R results. In 11 (14.9%) patients taking rivaroxaban or apixaban, in whom blood was collected 2-5 h since the last dose, we observed unmeasurable APC-R. DOAC-Remove almost completely eliminated all plasma DOACs. After addition of DOAC-Remove all APC-R ratios were measurable. In four FVL carriers on dabigatran with false negative APC-R, DOAC-Remove resulted in APC-R ratios <1.8. Conclusions DOAC-Remove effectively reduces DOACs concentration in plasma, which enables FVL testing using APC-R.

Elevated Plasma Factor IXa Activity in Premenopausal Women on Hormonal Contraception.

OBJECTIVE: Combined oral contraceptives induce a reversible hypercoagulable state with an enhanced risk of venous thromboembolism, but the underlying mechanism(s) remain unclear. Subjects on combined oral contraceptives also demonstrate a characteristic resistance to APC (activated protein C) in the thrombin generation assay. Here, we report the potential role of plasma factor IXa (FIXa) as a mechanism for hormone-induced systemic hypercoagulability. APPROACH AND RESULTS: A novel assay was used to determine FIXa activity in plasma samples from volunteer blood donors. Plasma from 36 premenopausal females on hormonal contraception and 35 not on hormonal contraception, 35 postmenopausal females, and 10 males were analyzed for FIXa activity, total PS (protein S), total tissue factor pathway inhibitor (TFPI), and TFPI-α antigen. Premenopausal females on hormonal contraception demonstrated significantly increased FIXa activity and decreased TFPI-α compared with the other groups. Remarkably, FIXa values were not normally distributed in the hormonal contraception group, but skewed toward the high end. Plasma FIXa activity inversely correlated with both TFPI-α and total PS antigen. Ex vivo determination of TF-dependent FIX activation in FV-deficient plasma demonstrated that inhibitory anti-TFPI antibodies enhanced FIXa generation by 2- to 3-fold, whereas addition of 75 nmol/L PS reduced FIXa generation by ≈2-fold. Further, increasing FIXa concentration enhanced APC resistance during TF-triggered plasma thrombin generation. CONCLUSIONS: Elevation of plasma FIXa activity in association with reductions in TFPI-α and PS is a potential mechanism for systemic hypercoagulability and resistance to APC in premenopausal females on hormonal contraception.

Mechanisms Contributing to Acquired Activated Protein C Resistance in Patients Treated with Thalidomide: A Molecular Dynamics Study.

INTRODUCTION: There is a high incidence of venous thromboembolism (VTE) in patients with Multiple Myeloma (MM), however; until now, the exact mechanisms behind VTE in MM are unknown, and some of the elements that may play a significant role are the treatment with an immunomodulator (IMiD) and acquired resistance to activated protein C (APC). OBJECTIVE: The study aims to reveal the possible mechanisms linked to the reduced antithrombotic activity of APC associated with thalidomide. METHODS: The molecular docking approach was used to ascertain the in silico inhibitory potential of thalidomide on the APC protease domain in the architecture of the catalytic triad and its interaction with major substrate binding sites. RESULTS: The coupling showed that the inhibitory activity of thalidomide depends on the induction of structural changes in the protease domain of APC, at the level of the Ser/His/Asp catalytic triad, as a result of a significant increase between the distances of CαAsp102 and Cα Ser195 (11.175 angstroms, increase 14.83%) and between CαSer195 and CαHis57 (9.478 angstroms, increase 13.78 %). This can result in an inefficient transfer of the proton between these residues, the other possible mechanism of inhibition, is a potential reduced binding of the substrate as a result of a direct interaction through a carbon-hydrogen bond on His57, an H-bond on Arg306, and a carbon hydrogen bond on Arg506. CONCLUSION: We demonstrate the in silico inhibitory potential of thalidomide on APC, through two possible inhibition mechanisms, a pathophysiologically relevant finding to understand the factors that can affect the stability and functions of APC in vivo.

[Oral contraceptive pill and thrombotic risk: epidemiological studies]. / Pillola e rischio trombotico: gli studi wpidemiogici.

The venous thromboembolism (VTE) is a rare event during childbearing age and during the assumption of combined oral contraceptive. The absolute risk of VTE in users of combined oral contraceptives is 20-30 per 100000 women years. A number of case-control studies published in recent years have shown an apparent increase in the risk of VTE among users of oral contraceptives (OCs) containing desogestrel, gestodene, drospirenone and cyproterone, relative to the use of levonorgestrel. The data derived from these recent studies is of borderline statistical significance because any important factors are not considered to evaluate the real correlation between the assumption of OCs and risk of venous thromboembolism. Among the factors that should be considered, there are: EE dose, duration of use, coexistance of other risk factors of venous thromboembolism (age, BMI, familiarity, surgical interventions) and other prescription bias. The lack of these factors is likely to contribute to the increased risk of venous thromboembolism observed in users of third-generation OCs when compared to that in users of second-generation OCs. To date, because of the inadequacy of epidemiological studies, the data about the correlation between OCs and TVE, are not conclusive and it will be necessary to carry out other studies to clarify this debating point, definitively.

Evaluation of the effect of a new oral contraceptive containing estetrol and drospirenone on hemostasis parameters.

OBJECTIVE: To assess the effect on hemostasis parameters of a new combined oral contraceptive (COC). STUDY DESIGN: In this randomized, single centre, open-label, exploratory study, healthy women received either 15 mg estetrol/3 mg drospirenone (E4/DRSP) (n = 39), 30 mcg ethinylestradiol/150 mcg levonorgestrel (EE/LNG) (n = 30), or 20 mcg ethinylestradiol/3 mg drospirenone (EE/DRSP) (n = 32) for six 28-day cycles. Blood was collected at baseline, cycle 3, and cycle 6. Median change from baseline was evaluated for procoagulant, anticoagulant, and fibrinolytic parameters, and for sex hormone-binding globulin (SHBG). RESULTS: Median change of endogenous thrombin potential (ETP) based activated protein C sensitivity resistance (APCr) at cycle 6 was +30% for E4/DRSP, +165% for EE/LNG (p-value <0.05 vs E4/DRSP), and +219% for EE/DRSP (p-value <0.05 vs E4/DRSP). Changes to prothrombin fragment 1 + 2 and SHBG for E4/DRSP, EE/LNG, and EE/DRSP were +23%, +71%, and +64% (p-value <0.05 vs E4/DRSP); and +55%, +74% and +251% (p-value <0.05 vs E4/DRSP), respectively. At cycle 6, changes to other hemostasis parameters for E4/DRSP were similar or smaller than for EE/LNG or EE/DRSP. CONCLUSIONS: In this study, changes in hemostasis parameters after treatment with 6 cycles of E4/DRSP were smaller or similar to those observed for EE/LNG. Similar, but more pronounced changes were also observed versus EE/DRSP, which supports the hypothesis that the effect of COCs on hemostasis parameters is mainly mediated by the estrogenic component. Further studies are needed to provide more insight into the venous thromboembolic risk of E4/DRSP. IMPLICATIONS STATEMENT: This study reports that the effects on hemostasis parameters of a COC containing 15 mg E4/3 mg DRSP are less or similar to those for EE/LNG or EE/DRSP. It also demonstrates that the choice of estrogen modulates the effects of COCs on hemostasis parameters.

Effect of oral contraceptives on thrombin generation measured via calibrated automated thrombography.

In a study population consisting of healthy men (n = 8), women not using oral contraceptives (OC) (n = 28) and women using different kinds of OC (n = 187) we used calibrated automated thrombography (CAT) in the absence and presence of added activated protein C (APC) to compare parameters that can be obtained from thrombin generation curves, i.e. lag time, time to peak, peak height and endogenous thrombin potential (ETP). Both with and without APC, plasmas of OC users exhibited the shortest lag time and time to peak, and the highest peak height and ETP. In the absence of APC none of these parameters differed between users of OC containing different progestogens. In contrast, in the presence of APC shorter lag times and time to peak, and higher peak height and ETP were observed in plasma of users of gestodene-, desogestrel-, drospirenone- and cyproterone acetate-containing OC than in plasma of users of levonorgestrel- containing OC. The ETP determined in the absence of APC (ETP(-APC)) had no predictive value for the APCsr (r = 0.11; slope 0.9 x 10(-3); 95% CI: -0.1 x 10(-3) to 2.0 x 10(-3)) whereas the ETP measured in the presence of APC (ETP+APC) showed an excellent correlation with the APCsr (r = 0.95; slope 6.6 x 10(-3); 95% CI: 6.3 x 10(-3) to 6.9 x 10(-3)) indicating that the APCsr is entirely determined by the ETP+APC. In conclusion, OC use increases thrombin generation, but differential effects of second and third generation OCs on the protein C system likely determine the differences in the risk of venous thrombosis between these kinds of OC.

Differential impact of conventional and low-dose oral hormone therapy (HT), tibolone and raloxifene on functionality of the activated protein C system.

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.

Decreased plasma sensitivity to activated protein C by oral contraceptives is associated with decreases in plasma glucosylceramide.

Oral contraceptive (OC) use increases venous thrombosis (VTE) risk and causes activated protein C (APC) resistance. Plasma glucosylceramide (GlcCer) deficiency is associated with VTE and GlcCer functions as an APC anticoagulant cofactor. Because estradiol decreases GlcCer in cultured cells, we hypothesized OC use would decrease plasma GlcCer and contribute to APC resistance. In a pilot study, seven female adults alternatively took second and third generation OCs and plasma samples were analyzed for GlcCer using high performance liquid chromatography and for APC sensitivity using modified prothrombin time assays. Second and third generation OC usage decreased the APC sensitivity ratio by 8.1% +/- 4.7% (P = 0.004) and 11.7% +/- 8.2% (P = 0.013) and plasma GlcCer levels by 10.1% +/- 6.8% (P = 0.008) and 11.0% +/- 5.1% (P = 0.002), respectively. The plasma GlcCer level correlated with the sensitivity of plasma to APC (P = 0.017, r = 0.51, n = 21 plasma samples). Thus, both second and third generation OC usage decreased plasma GlcCer which could cause a reduction in the plasma sensitivity to APC/protein S, thereby potentially increasing VTE risk.

Effect of oral and transdermal estrogen replacement therapy on hemostatic variables associated with venous thrombosis: a randomized, placebo-controlled study in postmenopausal women.

OBJECTIVE: The purpose of this study was to investigate whether the effect of transdermal estrogen therapy in postmenopausal women differs from that of oral therapy with regard to resistance to activated protein C (APC), an important risk factor for venous thrombosis, and levels of related proteins, such as protein S, protein C, and prothrombin. METHODS AND RESULTS: In a randomized, double-blind, placebo-controlled study, 152 healthy hysterectomized postmenopausal women received daily either placebo (n=49), transdermal 17beta-estradiol (E2) 50 microg (tE2 group, n=33), oral E2 1 mg (oE2 group, n=37), or oral E2 1 mg combined with gestodene 25 microg (oE2+G group, n=33) for 13 28-day treatment cycles, followed by 4 cycles of placebo for each group. Plasma samples were collected at baseline and in cycles 4, 13, and 17. In cycle 13, significant increases versus baseline and placebo were found in normalized APC sensitivity ratios (nAPCsr) in all treated groups (tE2, +26.9%; oE2, +102.7%; oE2+G, +69.9%). Increases in nAPCsr were significantly higher in the oral treatment groups than in the tE2 group. In addition, compared with baseline and placebo, after 13 cycles, decreases were observed in total protein S (tE2, -4.1%; oE2, -7.9%; oE2+G, -5.8%), free protein S (tE2, -7.1%; oE2, -8.4%; oE2+G, -5.2%), and protein C in the oE2+G group (-6.4%), but these changes did not explain the increase in nAPCsr. Changes in prothrombin were small and also did not affect the nAPCsr. CONCLUSIONS: Increases were observed in resistance to APC, which were more pronounced in the oral treatment groups than in the transdermal group. The increase in resistance to APC was not explained by changes in protein S, protein C, or prothrombin and may contribute to the increased incidence of venous thrombosis in users of hormone replacement therapy.

Impact of progestagens on activated protein C (APC) resistance among users of oral contraceptives.

Oral contraceptive (OC) use is associated with an increased risk of venous thromboembolism. Previous data reported higher thrombotic risk in women using third-generation combined OC than in those using second generation OC. The difference could be explained by differential effects of progestagens on plasma sensitivity to activated protein C (APC). The main purpose of this cross-sectional study was to assess the influence of a progestagen-only OC (chlormadinone acetate) as well as the effect of several combined OC with different progestagen components on APC resistance. The effect of APC on endogenous thrombin potential (ETP) was investigated in the plasma of healthy women using either combined OC (n=82) or progestagen-only OC (n=28), and in non-users (n=64). Carriers of factor V Leiden were excluded. Compared with non-users, there was no significant change in APC resistance in women using progestagen-only OC. Women who used combined OC were less sensitive to APC than non-users (P < 0.001) and the difference was significantly more pronounced in women using third-generation OC (n=41) than in those who used second-generation OC containing levonorgestrel (n=22) (P < 0.05). Compared with OC containing levonorgestrel, use of norethisterone-containing OC (n = 9) was associated with an increased resistance to APC (P < 0.05). Women who used cyproterone-containing OC (n = 10) were less sensitive to APC than those using third-generation OC (P < 0.05) or second-generation OC containing levonorgestrel (P < 0.05). Protein S, factor II and FVIII levels explained in part the OC-related changes in APC sensitivity variations. ETP-based APC resistance may contribute to explain why different brands of OC can be associated with different levels of thrombogenicity.

Thrombotic variables and risk of idiopathic venous thromboembolism in women aged 45-64 years. Relationships to hormone replacement therapy.

Hormone replacement therapy (HRT) has been shown to increase the relative risk of idiopathic venous thromboembolism (VTE) about threefold in several observational studies and one randomised controlled trial. Whether or not this relative risk is higher in women with underlying thrombophilia phenotypes, such as activated protein C (APC) resistance, is unknown. We therefore restudied the participants in a case-control study of the relationship between the use of HRT and the occurrence of idiopathic VTE in women aged 45-64 years. After protocol exclusions, 66 of the cases in the original study and 163 of the controls were studied. Twenty haematological variables relevant to risk of VTE were analysed, including thrombotic states defined from the literature. The relative risk of VTE showed significant associations with APC resistance (OR 4.06; 95% CI 1.62, 10.21); low antithrombin (3.33; 1.15, 9.65) or protein C (2.93; 1.06, 8.14); and high coagulation factor IX (2.34; 1.26, 4.35), or fibrin D-dimer (3.84; 1.99, 7.42). HRT use increased the risk of VTE in women without any of these thrombotic states (OR 4.09; 95% CI 1.26, 13.30). A similar effect of HRT use on the relative risk of VTE was also found in women with prothrombotic states. Thus for example, the combination of HRT use and APC resistance increased the risk of VTE about 13-fold compared with women of similar age without either APC resistance or HRT use (OR 13.27; 95% CI 4.30, 40.97). We conclude that the combination of HRT use and thrombophilias (especially if multiple) increases the relative risk of VTE substantially; hence women known to have thrombophilias (especially if multiple) should be counselled about this increased risk prior to prescription of HRT. However, HRT increases the risk of VTE about fourfold even in women without any thrombotic abnormalities: possible causes are discussed.

A randomized cross-over study on the effects of levonorgestrel- and desogestrel-containing oral contraceptives on the anticoagulant pathways.

The use of oral contraceptives (OC) causes disturbances of the procoagulant, anticoagulant and fibrinolytic pathways of blood coagulation which may contribute to the increased risk of venous thrombosis associated with OC therapy. Here we report the results of a cycle-controlled randomized cross-over study, in which we determined the effects of so-called second and third generation OC's on a number of anticoagulant parameters. In this study, 28 non-OC using women were randomly prescribed either a second generation (150 microg levonorgestrel/30 microg ethinylestradiol) or a third generation OC (150 microg desogestrel/30 microg ethinylestradiol) and who switched to the other OC after a two month wash out period. The anticoagulant parameters determined were: antithrombin (AT), alpha2-macroglobulin (alpha2-M), alpha1-antitrypsin, protein C inhibitor (PCI), protein C, total and free protein S and activated protein C sensitivity ratios (APC-sr) measured with two functional APC resistance tests which quantify the effect of APC on either the activated partial thromboplastin time (aPTT) or on the endogenous thrombin potential (ETP). During the use of desogestrel-containing OC the plasma levels of alpha2-M, alpha1-antitrypsin, PCI and protein C significantly increased, whereas AT and protein S significantly decreased. Similar trends were observed with levonorgestrel-containing OC, although on this kind of OC the changes in AT, PCI and protein S (which was even slightly increased) did not reach significance. Compared with levonorgestrel, desogestrel-containing OC caused a significant decrease of total (p <0.005) as well as free protein S (p <0.0001) and more pronounced APC resistance in both the aPTT (p = 0.02) and ETP-based (p <0.0001) APC resistance tests. These observations indicate that the activity of the anticoagulant pathways in plasma from users of desogestrel-containing OC is more extensively impaired than in plasma from users of levonorgestrel-containing OC.

Different effects of oral and transdermal hormone replacement therapies on factor IX, APC resistance, t-PA, PAI and C-reactive protein--a cross-sectional population survey.

The effects of hormone replacement therapy (HRT) on thrombosis risk, thrombotic variables, and the inflammatory marker C-reactive protein (CRP) may vary by route of administration (oral versus transdermal). We studied the relationships of 14 thrombotic variables (previously related to cardiovascular risk) and CRP to menopausal status and to use of HRT subtypes in a cross-sectional study of 975 women aged 40-59 years. Our study confirmed previously-reported associations between thrombotic variables and menopausal status. Oral HRT use was associated with increased plasma levels of Factor IX, activated protein C (APC) resistance, and CRP; and with decreased levels of tissue plasminogen activator (t-PA) antigen and plasminogen activator inhibitor (PAI) activity. Factor VII levels were higher in women taking unopposed oral oestrogen HRT. The foregoing associations were not observed in users of transdermal HRT; hence they may be consequences of the "first-pass" effect of oral oestrogens on hepatic protein synthesis. We conclude that different effects of oral and transdermal HRT on thrombotic and inflammatory variables may be relevant to their relative thrombotic risk; and suggest that this hypothesis should be tested in prospective, randomised studies.

Effect of raloxifene on activated protein C (APC) resistance in postmenopausal women and on APC resistance and homocysteine levels in elderly men: two randomized placebo-controlled studies.

Raloxifene, a selective estrogen receptor modulator, like hormonal replacement therapy increases the risk of venous thromboembolism in postmenopausal women. A possible explanation for the increased thrombotic risk could be an increase in acquired resistance to activated protein C (APC). In two randomized, placebo-controlled, double-blind studies we determined the effect of raloxifene on the normalized APC sensitivity ratios (nAPCsr). The nAPCsr were determined with the thrombin generation-based APC resistance test. In the first study 83 postmenopausal women (age, 51.1 +/- 2.7 years) randomly received daily 0.625 mg conjugated equine estrogen and 2.5 mg medroxyprogesterone acetate (n=17), 60 mg raloxifene (n=23), 150 mg raloxifene (n=20) or placebo (n=23) for 24 months. At baseline and after 6, 12 and 24 months the nAPCsr were measured. In the second study 30 elderly men (age, 64.4 +/- 2.4 years) randomly received 120 mg raloxifene (n=15) or placebo (n=15) for 3 months. At baseline and after 3 months the nAPCsr and fasting homocysteine levels were measured. In postmenopausal women conjugated equine estrogen/medroxyprogesterone acetate significantly increased the nAPCsr from 1.26 +/- 0.82 to 2.87 +/- 0.86 at 24 months (P <0.0005 compared with placebo). Raloxifene had no significant effect on nAPCsr compared with placebo in both women and men. The results did not change after excluding carriers of factor V Leiden. Also fasting homocysteine levels were not affected by raloxifene in the aging men. It is concluded that raloxifene, in contrast to combined hormonal replacement therapy, does not increase APC resistance.

Impact of oral contraceptive use on APC-resistance: a prospective, randomized clinical trial with three low-dose preparations.

The evaluation of the study was of the impact of oral contraceptive (OC) use on activated protein C (APC-resistance). Eight hundred eighteen young fertile women were screened for a study designed to compare three different marketed OC preparations. The women could have used either other oral contraceptive preparations before switching to the study medications (switchers) or were not using hormonal contraceptives (new starters) before the study began. Prior to study drug intake and during treatment, APC-resistance was determined with three different tests. Forty-one of 809 women evaluated (5.07%) carried the Factor V Leiden mutation. Twenty-two further participants (2.72%) had a positive screening test, but did not provide samples for the confirmatory mutation test. Two women with homozygous Factor V Leiden mutations and 39 women with heterozygous mutations were identified. The homozygous carriers were identified in all three of the screening tests employed, whereas none of the tests detected all 39 heterozygotes. In the pretreatment screening tests, previous OC users (switchers) had slightly lower APC ratios than the women using non-hormonal birth control methods (starters). During treatment the difference between starters and switchers was no longer apparent, but the APC ratio values of the screening tests slightly increased for both. The homozygous carriers were not treated. Differences in APC-resistance between users of the three different oral contraceptive preparations were not found. In conclusion, laboratory screening for APC-resistance using Coatest APC, ProC Global, or ProC APC-FV-Leiden clearly identifies homozygous mutant carriers. However, with regard to heterozygous mutant carriers, the sensitivity and specificity of the tests, especially during OC intake, is limited. The results of APC screening tests should have, at present, no impact on contraceptive counseling because the predictive value for thromboembolic risk of the test results and even the mutant status is low.

Oral contraceptives, thrombosis and haemostasis.

The use of oral contraceptives is a well-established acquired risk factor for venous thrombosis. In 1995, a number of epidemiological studies were published which suggested that women who use third generation oral contraceptives that contain desogestrel or gestodene as progestagen are exposed to a two- to threefold higher risk for venous thrombosis than women using second generation oral contraceptives which contain levonorgestrel. In this paper, the effects of oral contraceptives on the haemostatic system are discussed. It appears that plasma from oral contraceptive users is resistant to the anticoagulant action of activated protein C (APC). This phenomenon, called acquired APC resistance, is more pronounced in users of desogestrel or gestodene-containing oral contraceptives than in women who use oral contraceptive pills with levonorgestrel. On the basis of these observations, it was proposed that acquired APC resistance may be the mechanistic basis of the increased risk for venous thrombosis during oral contraceptive use and for the further increased thrombotic risk of third generation oral contraceptive users. Furthermore, the results of a recent cross-over study are discussed. This study indicated that a large number of other haemostatic parameters were changed during oral contraceptive use. Some of these changes were more pronounced on desogestrel-containing oral contraceptives. The cross-over study also showed that the increased fibrinolytic activity during OC use is counterbalanced by an enhanced activity of thrombin-activatable fibrinolysis inhibitor (TAFI), a protein that participates in the inhibition of fibrinolysis.

Effects on hemostasis after two-year use of low dose combined oral contraceptives with gestodene or levonorgestrel.

We studied 67 healthy women who were randomly allocated to receive third generation gestodene (Gynera) or second generation levonorgestrel (Microgynon 30) combination of low-dose estrogen oral contraceptives (OCs) for their hemostatic effects over 2 years. Hemostatic changes were apparent within 3 months of OC use. Hematocrit (Hct) was not affected, but hemoglobin (Hb) concentration decreased by 18 months. Shortened prothrombin time (PT) and activated plasma thromboplastin time (APTT) were associated with elevated fibrinogen within the 12-month use of both OCs. Factor VII was reduced only in Micro 30 during the 18 months of use. Enhanced thrombin-antithrombin (TAT)-complex level was seen at 18 months of Gynera use. Prothrombin fragment1+2 (F1+2) rise was seen at 3 months with Micro 30. Reduced antithrombin III (ATIII) activity was seen at 18 months with Gynera and at 24 months with Micro 30. Increased protein C activity was seen at 3 months and reduced protein S occurred at 18 months of Gynera use. Tissue plasminogen activator (t-PA) activity was enhanced for 6 months in both OCs with raised D-dimer levels for 12 months with Gynera and 6 months with Micro 30. Decreased t-PA antigen was seen at 18 months and decreased urokinaselike plasminogen activator (u-PA) antigen occurred throughout the 24 months of both OCs use. Enhanced u-PA activity was only seen in Gynera users. Elevated plasminogen levels were apparent throughout both OCs use. PAI-1 levels were significantly decreased with Micro 30. With Gynera, the decreased PAI-1 activity was seen only at 18 months and PAI-1 antigen at 12 months. No change in platelets and von Willebrand factor (vWF) were seen in long-term OC use except that beta-thromboglobulin (beta-TG) showed decreased trends reaching statistical significance by 18 and 24 months of Micro 30 use and by 24 months of Gynera use. A further significant decrease in beta-TG, u-PA antigen, ATIII, and protein S levels were seen 3 months after pill stoppage compared with pretreatment levels. Activated protein C resistance (APCR) was negative in all subjects before and during OC use. The study indicated dynamic balance between coagulation and fibrinolysis with no endothelial activation. However, because some hemostatic markers showed wide fluctuations during OC use, a longer term study is warranted to investigate any adverse hemostatic changes that might enhance the risks of venous thromboembolism in Asian subjects known to be less prone to thrombosis.

[Thrombophilic syndrome associated to phenotypic resistance to activated protein C in postmenopausal women]. / Sindrome trombofilica associata a resistenza fenotipica alla proteina C attivata in donne in postmenopausa.

AIM: Hormone replacement therapy (HRT) may reduce the risk of cardiovascular events in healthy postmenopausal women. However recent studies suggest a 2-4 fold increased risk of idiopathic venous thromboembolism (VTE) among users of HRT. Our aim was to evaluate the overall effect of HRT on hemostatic variables probably related to increased VTE risk reported in epidemiological studies. METHODS: Therefore, 100 healthy postmenopausal women aged 45-60 years divided into 50 HRT non-users and 50 HRT users were examined. The authors assayed on the automated coagulometer ACL7000 (Instrumentation Laboratory, Milan) the procoagulant proteins: factor VIII (VIII:C) and factor VII (VII:C); the natural anticoagulant proteins: antithrombin (ATIII), protein C (PC), protein S (PS) and the resistance to anticoagulant action of activated protein C (APC-Resistance). The free tissue factor pathway inhibitor (TFPI) was measured with an ELISA method (Diagnostica Stagò; France, Roche). The in vivo coagulation and fibrinolysis activation was evaluated by the assays of prothrombin fragment 1+2 (F1+2) and plasmin- antiplasmin complexes (PAP) using ELISA techniques. RESULTS: Increased levels of FVIII:C and FVII:C were observed in HRT users and HRT non-users women compared to controls (FVIII:C= 126+/-58%, 120+/-59% vs 85+/-15% p=0.0001; FVII: C 113+/-23%, 103+/-19% vs 90+/-16% p=0.0001). The activation peptides were significantly different compared to those found in control subjects; higher values were observed in HRT users compared to HRT non-users (F1+2=1.11+/-0.44 nM, 077+/-0.31 nM vs 0.45+/-0.35 p=0.00001; P-AP= 606+/-406 ng/ml, 514+/-205 ng/ml vs 235+/-59 p=0.0001). The ATIII and the PC were similar among the 3 different groups of subjects, but reduced levels of PS were observed in HRT users (PS 93+/-23%, 105+/-22% vs 109+/-12 p=0.0001). The mean normalized APC sensitivity ratio (APC-SR) was lower in the two populations of women as compared with that of controls (nAPC-SR 1.02+/-0.7, 1.02+/-0.8 vs 1.1+/-25 p=0.02). The values of free TFPI were reduced in HRT users compared to HRT non-users (9.1+/-1.9 ng/ml, 10.1+/-2.3 ng/ml vs 4.6+/-1.5 ng/ml p<0.0001). CONCLUSION: HRT appears to be associated to a shift in the procoagulant-anticoagulant balance towards a procoagulant state. The changes in hemostatic system could explain the increased risk of VTE in healthy postmenopausal women during HRT, nevertheless this risk could be higher in women known to have a congenital or acquired thrombophilic state.

Impact of hormone-associated resistance to activated protein C on the thrombotic potential of oral contraceptives: a prospective observational study.

INTRODUCTION: The increased thrombotic risk of oral contraceptives (OC) has been attributed to various alterations of the hemostatic system, including acquired resistance to activated protein C (APC). To evaluate to what extent OC-associated APC resistance induces a prothrombotic state we monitored plasma levels of thrombin and molecular markers specific for thrombin formation in women starting OC use. Elevated plasma levels of thrombin have been reported to characterize situations of high thrombotic risk such as trauma-induced hypercoagulability, but have not yet been studied during OC use. PATIENTS AND METHODS: Blood samples were collected prospectively from healthy women (n = 21) before and during three menstruation cycles after start of OC. APC resistance was evaluated using a thrombin generation-based assay. Plasma levels of thrombin and APC were directly measured using highly sensitive oligonucleotide-based enzyme capture assay (OECA) technology. Thrombin generation markers and other hemostasis parameters were measured additionally. RESULTS: All women developed APC resistance as indicated by an increased APC sensitivity ratio compared with baseline after start of OC (p = 0.0003). Simultaneously, plasma levels of thrombin, prothrombin fragment 1+2, and of thrombin-antithrombin complexes did not change, ruling out increased thrombin formation. APC plasma levels were also not influenced by OC use, giving further evidence that increased thrombin formation did not occur. CONCLUSIONS: In the majority of OC users no enhanced thrombin formation occurs despite the development of APC resistance. It cannot be ruled out, however, that thrombin formation might occur to a greater extent in the presence of additional risk factors. If this were the case, endogenous thrombin levels might be a potential biomarker candidate to identify women at high thrombotic risk during OC treatment. Large-scale studies are required to assess the value of plasma levels of thrombin as predictors of OC-associated thrombotic risk.

Tamoxifen induces resistance to activated protein C.

INTRODUCTION: The estrogen antagonist tamoxifen (TAM) increases the thrombotic risk similar to estrogen containing oral contraceptives (OC). In OC users this risk is attributed to alterations of hemostasis resulting in acquired resistance to activated protein C (APC). TAM-induced APC resistance has not been reported yet. MATERIALS AND METHODS: Blood samples were collected prospectively from women with breast cancer before (n=25) and monthly after start of adjuvant TAM treatment (n=75). APC resistance was evaluated on basis of the effect of APC on the endogenous thrombin generation potential. To detect increased in vivo APC generation APC plasma levels were measured using a highly sensitive oligonucleotide-based enzyme capture assay. Routine hemostasis parameters were measured additionally. RESULTS: APC sensitivity decreased by 41% (p=0.001) compared to baseline after one month of TAM application and remained significantly decreased during the study period. Free protein S increased (p=0.008) while other analyzed procoagulant factors, inhibitors, and activation markers of coagulation decreased or did not change significantly. In five patients the APC concentration increased to non-physiological levels but an overall significant increase of APC was not observed. CONCLUSIONS: This is the first study showing acquired APC resistance under TAM therapy. Acquired APC resistance might explain the increased thrombotic risk during TAM treatment. Observed changes of hemostasis parameters suggest different determinants of TAM-induced APC resistance than in OC-induced APC resistance. The presence of acquired APC resistance in TAM patients warrants further evaluation if these patients may benefit from antithrombotic prophylaxis in the presence of additional thrombotic risk factors.