Acquired activated protein-C resistance

The Predictability of Factor V Leiden (FV:Q506) Gene Mutation via Clotting-Based Diagnosis of Activated Protein C Resistance

After the discovery of activated protein C resistance (APCR) due to factor V Leiden mutation and the causal relationship of the phenomenon with clinical thromboembolism, a wide variety of functional clotting-based assays were developed for testing of APCR in relation to the specific DNA-based analysis of FV:Q506 Leiden. The aim of this study is to assess a clotting-based APCR assay using procoagulant crotalidae snake venom with respect to the sensitivity, specificity, and predictability for the presence of the factor V Leiden mutation. APCR testing and factor V DNA analyses have been performed concurrently on 319 patient specimens. APCR values of the patients with homozygous factor V Leiden mutation (70.4±13.5 s) were significantly lower (p<0.001) in comparison to the subjects with the heterozygous mutation (87.6±13.4 s). The assay is highly sensitive (98.7%) and specific (91.9%) for the screening of factor V Leiden mutation. The sensitivity and specificity of the APCR testing reached to 100% below the cut-off value of 120 s among the patients with homozygous factor V Leiden mutation. Therefore, this method could help the desired effective optimal screening strategy for the laboratory search of hereditary thrombophilia focusing on the diagnosis of APCR due to FV:Q506.

Effects of non-oral postmenopausal hormone therapy on markers of cardiovascular risk: a systematic review

OBJECTIVE

To review the effects of non-oral administration of postmenopausal hormone therapy (HT) on risk markers for atherosclerotic and venous thromboembolic disease.Non-oral postmenopausal HT appears not to increase venous thromboembolic risk, whereas the effect on coronary heart disease risk is less clear.

DESIGN

Systematic review of literature obtained from MEDLINE, EMBASE, and CENTRAL databases from 1980 until and including April 2006. Terms for "postmenopausal hormone therapy" and for "non-oral administration" were combined in the search.

SETTING

Randomized clinical trials.

PATIENT(S)

Postmenopausal women, both healthy and with established cardiovascular disease or specified cardiovascular risk factors

INTERVENTION(S)

Non-oral HT (e.g., transdermal or intranasal) compared with oral HT or no treatment/placebo.

MAIN OUTCOME MEASURE(S)

Lipoprotein(a), homocysteine, C-reactive protein (CRP), cell adhesion molecules, markers of endothelial dysfunction, coagulation, and fibrinolysis.

RESULT(S)

Seventy-two studies investigating either transdermal or intranasal administration were included. For non-oral HT, decreases in lipoprotein(a), cell adhesion molecules, and factor VII generally were significant, resistance to activated protein C (APCr) was slightly increased, and other markers including CRP and homocysteine did not change. Compared with oral HT, changes in CRP and APCr were smaller, changes in cell adhesion molecules and some fibrinolytic parameters tended to be smaller, whereas changes in other factors including lipoprotein(a) and homocysteine did not differ.

CONCLUSION(S)

Potentially unfavorable changes seen with oral HT on two important markers, CRP and APCr, are substantially smaller with non-oral HT. Non-oral HT has minor effects on the other cardiovascular risk markers studied. Therefore, compared with oral HT, non-oral HT appears be safer with respect to atherosclerotic and venous thromboembolic disease risk.

Endogenous or exogenous coagulation factor level and the response to activated protein C

BACKGROUND

The abnormal response to activated protein C could be the mechanism to explain the prothrombotic role of elevated coagulation factor levels.

OBJECTIVE

We evaluated the effect of factor VIII, II, or X (FVIII, FII, or FX) levels on activated protein C resistance technique and its association with the resistant phenotype.

MATERIALS AND METHODS

The correlation between APCR and FVIII was assessed in 36 samples, after Desmopressin infusion and the correlation between FII or FX and APCR in 15 patients with plasma levels between 100-125 U/dl. Also, the effect of the addition of purified human factors (FII, FX) to a normal plasma pool (final concentration: 100, 120, 140, 180, 220 U/dl) was estimated on the APCR technique.

RESULTS

APCR values correlated with FVIII increase (r(Spearman) = 0.839; p < 0.001); APCR was abnormal (<2.4) in 9/36 samples, showing higher FVIII values in the abnormal group (VIII(abnormalAPCR) = 176.7 +/- 14.2; VIII(normalAPCR) = 103.5 +/- 8.0). APCR did not correlate with endogenous FII (r(Spearman) = 0.423) or FX (r(Spearman) = -0.169). However, the addition of human FII or FX to the normal plasma pool caused a decrease in APCR (r(SpearmanFII) = -0.843; r(SpearmanFX) = -0.958) without reaching abnormal (<2.4) results. FVIII levels may be associated with a resistant phenotype at values >153.0 U/dl, according to the linear regression analysis. Exogenous FII or FX levels greater than 120 U/dl would affect the APCR, without obtaining abnormal results.

CONCLUSIONS

The data do not allow the direct association of the FII or FX increase with a defect in the protein C system in the current conditions.

Sex hormone–binding globulin—A surrogate marker for the prothrombotic effects of combined oral contraceptives

OBJECTIVE

The purpose of this study was to investigate the plausibility of serum sex hormone-binding globulin (SHBG) concentration as a risk marker for venous thromboembolism (VTE) during use of combined oral contraceptives (COC). Study design This was a prospective, randomized cross-over study. Thirty-five women were treated with COCs containing the same amount of ethinyl estradiol and either levonorgestrel (LNG/EE) or desogestrel (DG/EE). Serum SHBG and markers of hemostasis were determined before and after 2 months on each treatment.

RESULTS

SHBG increased significantly with both preparations. Treatment with DG/EE caused more pronounced prothrombotic changes in hemostatic parameters than LNG/EE. With both treatment regimens, there was a significant correlation between changes in resistance to activated protein C (APCr) and changes in plasma SHBG.

CONCLUSION

The correlation between SHBG and the well-established risk factor APCr might indicate the usefulness of SHBG as a risk marker for VTE during COC treatment.

Haemostasis in normal and abnormal pregnancy

Haemostasis is a complex and dynamic equilibrium involving pro-coagulants, the natural anticoagulation system and fibrinolysis. Normal human pregnancy is associated with profound alterations to the process of haemostasis such that the pro-coagulant effect becomes dominant. There are very few studies which have attempted to elucidate the adaptations that take place in the uteroplacental circulation where the haemostatic system faces the conflicting tasks of maintaining blood fluidity during pregnancy while preparing for the haemostatic challenge of delivery. It is hypothesised that excessive thrombosis within the uteroplacental circulation provides the mechanistic basis for the reported associations between the inherited thrombophilias and major pregnancy complications. The evidence underpinning this widely quoted hypothesis is weak.

The association between extrinsic activated protein C resistance and venous thromboembolism in women

Recently, discussions have focused on the question of whether acquired APC resistance (APCsr) is a clue to the observed association between risk of venous thromboembolism (VTE) and OC use especially with the so-called third-generation OCs. It seems plausible that abnormalities in an extrinsic-based APCsr reflect an increased risk of VTE in women, but this has not yet been properly studied. The objective of our study was to determine whether there was an association of extrinsic APC resistance with VTE risk in a case-control study. Sixty-seven women with confirmed VTE diagnosis were consecutively recruited in primary health care settings, interviewed and blood samples were taken at least 6 months after VTE. Cases were age-matched to 290 population controls. Extrinsic APC resistance was measured as normalized APC ratio (APCsr). The effect of APC on tissue factor-initiated thrombin generation was measured in plasma using alpha2-macroglobulin attached thrombin activity as an endpoint. The extrinsic APCsr was significantly associated with factor V Leiden (FVL) mutation, both in the cases and in the controls. Also, in the women using OC, significantly higher values of APCsr were observed, which confirms the results of other studies. We did not identify a significant association between the extrinsic APCsr and VTE in women not using OC who are non-carriers of factor V Leiden using different approaches: comparison of medians, analyses with unconditional logistic regression using various cut-points of the APCsr distribution, and the comparison between the highest and the lowest quartile of APCsr. With all attempts, the risk estimates were close to unity. In conclusion, we were not able to find evidence for any association of extrinsic APCsr with VTE in women who were not using OCs and non-carriers of FVL.

Elevated prothrombin and activated protein C resistance in patients with thoracic aortic atheroma

Patients with protruding aortic atheroma containing mobile emboli are at risk for peripheral emboli and stroke. This risk may possibly be reduced by anticoagulation, but whether or not such patients have an increased prevalence of thrombotic risk factors has not been previously determined. Twenty-two patients were studied (11 with protruding thoracic aortic atheromas and superimposed mobile thrombi on transesophageal echocardiography were compared to 11 age-matched controls). The authors evaluated activated protein C resistance (APC-R) by measuring the prolongation of the partial thromboplastin time (PTT) in response to activated protein C (APC). Concentrations of fibrinogen, antithrombin III (AT III), factor II, factor V, and D-dimer were also determined in all patients. There was significant resistance to APC (a smaller prolongation in PTT) in patients with atheromas and thrombi. They also had significantly higher concentrations of factor II. Factor V and fibrinogen were higher, and AT III lower, in patients than in controls; however, these latter differences did not reach statistical significance. Patients with aortic atheroma and mobile thrombi may have an increased prevalence of thrombotic risk factors. There is significantly increased resistance to activated protein C in patients with protruding atheroma and mobile thrombi in their thoracic aorta. There was also a trend toward elevated fibrinogen, homocysteine, and apo (a) concentrations as well as lower antithrombin III concentrations in these patients.