In vitro evidence of gender-related heparin resistance

Thromboelastography-Based Evaluation of Gender-Associated Hypercoagulability

BACKGROUND

Age, race, and gender differences in coagulation status of healthy volunteers have been reported in previous case series; however, rigorous multivariate analysis adjusting for these factors is lacking. We aimed to investigate the effects of age, race, and gender on baseline coagulation status in healthy volunteers.

METHODS

Thirty healthy volunteer controls with no history of bleeding or thrombotic events and no previous anticoagulant or antiplatelet use were recruited. Citrated and heparinized blood samples were drawn, and kaolin and platelet-mapping thromboelastography (TEG) assays performed.

RESULTS

Thirty participants had a mean age of 37, mean body mass index of 29 kg/m², and were 47% African-American and 70% female. Women were significantly older than men (40 ± 11 y vs 28 ± 7 y, P = .002); there were no significant differences in demographics by race. Multivariate analysis of variance for the effect of age, race, and gender across TEG parameters yielded evidence for gender differences in hypercoagulability (Pillai's trace P = .02), which appear to be driven by differences in K-time, alpha angle, maximal amplitude, and G parameter. Women were hypercoagulable compared to men, as manifested by shorter K-time, steeper alpha angle, higher maximal amplitude, and larger G parameter.

DISCUSSION

Women at baseline have relatively hypercoagulable fibrin deposition kinetics, platelet contributions to clot formation, and overall clot strength compared to men, even when adjusted for age and race. Additional research is needed to specifically detail the key patient-level factors, clinical implications, and opportunities for tailored therapy related to gender-associated hypercoagulability.

Heparin Resistance Is Common in Patients Undergoing Extracorporeal Membrane Oxygenation but Is Not Associated with Worse Clinical Outcomes

Extracorporeal membrane oxygenation (ECMO) protocols generally require systemic anticoagulation with heparin to prevent circuit thrombosis. The prevalence, risk factors, and outcomes of heparin resistance in this setting are ill-defined. To better understand the prevalence and clinical consequences of heparin resistance in this population, we conducted a retrospective analysis of all patients treated with ECMO at a single academic medical center between 2016 and 2019. Univariate and multivariate analyses were used to evaluate predictors and outcomes of heparin resistance. Of 67 patients in our study, 50.7% met the threshold for heparin resistance for at least 1 day, which was managed in all cases with increases in heparin dose. Patients with heparin resistance were more likely to be male (82.4% vs. 48.5%, p = 0.005) and to have a higher mean platelet count (132 vs. 104 × 103/mL, p = 0.027) compared with those without heparin resistance. Multivariate logistic regression found no significant association between the development of heparin resistance and rates of thrombosis, hemorrhage, or overall survival. Additional prospective studies are required to clarify the clinical implications of heparin resistance in this population.

Factors other than body weight predicting heparin loading to acquire optimal activated clotting time in endovascular neurointerventions

OBJECTIVES

The aim of this study was to investigate the relationship between the activated clotting time (ACT) and heparin loading based on body weight (BW), and factors other than BW that may contribute to the ACT after heparin loading to establish a more accurate regimen for achieving ACT targets during endovascular neurointerventions.

PATIENTS AND METHODS

Japanese patients who underwent endovascular coiling of unruptured intracranial aneurysms or carotid artery stenting in our institution between January 2014 and November 2017 were enrolled. The ACT was measured before (pre-ACT) and 3 min after heparinization (post-ACT). The correlation between ACT and heparin loading based on BW and factors that may contribute to the ACT after heparin loading were analyzed retrospectively.

RESULTS

A total of 199 cases (109 males, age: 66 ± 12 years) were analyzed. There were positive correlations between the heparin loading per kg of BW and post-ACT, post-ACT - pre-ACT (ΔACT) (Spearman's r = 0.2946, 0.2633, P: <0.0001, 0.0002, respectively). Heparin loading per kg of BW, gender, hematocrit (Ht), estimate glomerular filtration rate (eGFR) were significant confounding factors to ΔACT. The calculated predicted ΔACT based on these significant factors was found to be highly correlated with ΔACT compared with the heparin loading per kg of BW. (Spearman's r = 0.5820, P = <0.0001).

CONCLUSION

Initial BW-based heparin loading is a simple way in endovascular neurointerventions. ACT after heparin loading based on BW has individual differences greatly, it is possible to estimate more accurately the heparin loading for acquiring the optimal ACT considering not only BW but also gender, Ht and eGFR.

Coagulation phenotype of wild-type mice on different genetic backgrounds

Genetically engineered mouse models are used to investigate beneficial treatment in haemophilia by comparison with wild-type mice. It has been recognized that wild-type and haemophilic mice of different genetic backgrounds show different bleeding phenotypes. We assessed ex-vivo coagulation parameters in nine wild-type substrains of 129S1/Sv, BALB/c and C57BL/6 mice applying thromboelastography (TEG), activated partial thromboplastin time (aPTT), prothrombin time (PT) and fibrinogen levels. The comprehensive ex-vivo data are discussed in view of results from a tail-tip bleeding assay. Time to first clot formation (R-time) showed higher within-substrain (CV range: 28–54%) and higher between-substrain (median range: 25.53–42.60 min) variation for BALB/c than for C57BL/6 mice (CV range: 14–31%; median range: 22.45–24.93 min). Median R-time for 129S1/Sv mice was 30.42 min (CV: 33%). No distinct strain differences were observed for maximum amplitude (MA), aPTT, or PT, but males generally showed higher MA and shorter aPTT than females. Males of all substrains had higher fibrinogen levels than females. The heightened in-vivo variability (CV range: 81–171%; median range: 36.00–469.50 mg) in the tail-tip bleeding assay and increased blood loss in wild-type C57BL/6 male mice was not reflected in ex-vivo coagulation parameters. In general, ex-vivo coagulation results appeared consistent within substrains, but showed substrain and sex differences of variable magnitudes. We conclude that alignment of the mouse substrain genetic background to the experimental model is critical to reduce data variability and animal numbers.

Anticoagulant properties of enoxaparin 400 IU/mL-40 % ethanol catheter lock solution

Unfractionated heparin (UFH) is the most widely used interdialytic lock solution but has no anti-infectious properties. Ethanol at a content ≥40 %v/v eradicates experimental biofilm but has no anticoagulant properties. In contrast to UFH, enoxaparin (Enox) can be combined with 40 % ethanol without precipitation. Enoxaparin 400 UI/mL–40 % ethanol (Enox/Eth) has antibiofilm properties and therefore has promise as an alternative lock solution. This study assessed the anticoagulant properties of Enox/Eth. Enox and Enox/Eth were diluted in whole blood at a final Enox concentration of 0.5, 1 (N = 6 samples), 1.5 (N = 4) and 2 (N = 6) IU/mL. Anti-Xa activity was determined by chromogenic assay and the inhibition of endogenous thrombin potential (ETP) by thrombinography. Quantitative data were compared by the Mann-Withney U test. For Enox concentrations of 0.5, 1, 1.5 and 2 UI/mL in whole blood samples, the mean ± SD values of the anti-Xa activity were 0.68 ± 0.09, 1.26 ± 0.14, 1.73 ± 0.30, 2.35 ± 0.32 UI/mL for Enox/Eth and 0.94 ± 0.15, 1.80 ± 0.22, 2.74 ± 0.23, 3.54 ± 0.44 UI/mL for Enox (P = 0.03, P = 0.03, P = 0.13, P = 0.03); and of the percentage of ETP inhibition was 17.36 ± 9.65, 30.27 ± 17.06, 36.5 ± 17.06, 57.82 ± 15.42 for Enox/Eth, and 42.96 ± 15.68, 68.93 ± 10.01, 83.5 ± 8.81, 91.19 ± 4.67 for Enox (P = 0.03, P = 0.03, P = 0.13, P = 0.03), respectively. The median and IQR values of Enox concentration inhibiting 50 % of ETP (IC50 ETP) were 1.8 [1.1–2.4] IU/mL for Enox/Eth and 0.7 [0.3–0.9] IU/mL for Enox, P = 0.03. Enox/Eth has strong anticoagulant activity, albeit lower than that of Enox, but with an extremely low IC50 ETP compared to the Enox concentration of non-diluted Enox/Eth.

[Resistance to curative treatment by unfractionned heparin]

Unfractionated heparin has been used as antithrombotic therapy for many years. Its main effect is attributed to the activation of antithrombin (AT), the heparin/AT complex inactivating both factor IIa (thrombin) and factor Xa. Resistance to unfractionated heparin with clinical or biological expression is uncommon. The occurrence of venous or arterial thrombosis or the extension of thrombosis in a patient receiving unfractionated heparin, should always raise suspicion of either AT deficiency or type 2 heparin-induced thrombocytopenia (HIT type 2). HIT type 2 is not a true heparin resistance but an immune complication that requires heparin discontinuation and the use of alternative anticoagulants. Biological heparin resistance is suspected in the presence of a normal or not prolonged activated partial thromboplastin time despite the administration of increasing dose of heparin. Measurement of anti-Xa activity is useful to adjust heparin treatment. Isolated biological heparin resistance is encountered in several physiological and pathological situations including inflammatory and infectious disorders, pregnancy and thrombocytosis. It also occurs in acquired antithrombin deficiency of nephrotic syndrome, l-asparaginase treatment or cardiopulmonary bypass. Biological heparin resistance is relatively common, but clinically significant resistance to heparin is rare and should always raise suspicion of either AT deficiency or type 2 heparin-induced thrombocytopenia.

Gender-specific and menstrual cycle dependent differences in circulating microparticles

In comparison to age-matched men, young women are at increased risk to suffer from venous thromboembolism (VTE). Some risk factors of inherited and acquired thrombophilia are known, but approximately 30% of the overall risk remains unexplained. Recently, a role for microparticles (MP) in coagulation has been suggested. We investigated, if gender- and menstrual cycle-specific differences in circulating MP exist. Platelet- and endothelial cell-derived microparticles (PMP, EMP) and subpopulations thereof were evaluated flow-cytometrically in healthy women (n = 27) in different phases of their menstrual cycles (follicular phase: n = 14, luteal phase: n = 13) and in healthy men (n = 18). Additionally, D-dimer levels were determined. Compared to men, women had elevated numbers of annexin V-binding MP (p = 0.007), PMP (CD61; p = 0.013), P-selectin-exposing PMP (p = 0.002) and E-selectin-exposing EMP (p = 0.009). During the luteal phase, women had strongly elevated concentrations of MP, PMP, P-selectin- and CD63-exposing PMP as well as E-selectin-exposing EMP (p = 0.001, p < 0.001, p = 0.004, p = 0.003, and p < 0.001, respectively), and the ratio of P-selectin-exposing PMP/platelet increased more than three-fold as compared to men (p = 0.01). When different phases of the menstrual cycle were analysed, MP (annexin V; p = 0.025), PMP (CD61: p < 0.001; CD63: p = 0.015) and E-Selectin-positive EMP (p = 0.006) were all increased in the luteal phase. Although D-dimer concentrations in women were increased compared to men (p = 0 = 0.006), no menstrual cycle-specific differences were observed. In summary, circulating MP and subpopulations thereof are increased in women when compared to men, and this increase seems to be modulated by the menstrual cycle. Therefore, circulating MP may be an additional risk factor contributing to the hitherto unexplained procoagulatory state of young women.

Ionic liquid-derived blood-compatible composite membranes for kidney dialysis

A novel heparin- and cellulose-based biocomposite is fabricated by exploiting the enhanced dissolution of polysaccharides in room temperature ionic liquids (RTILs). This represents the first reported example of using a new class of solvents, RTILs, to fabricate blood-compatible biomaterials. Using this approach, it is possible to fabricate the biomaterials in any form, such as films or membranes, fibers (nanometer- or micron-sized), spheres (nanometer- or micron-sized), or any shape using templates. In this work, we have evaluated a membrane film of this composite. Surface morphological studies on this biocomposite film showed the uniformly distributed presence of heparin throughout the cellulose matrix. Activated partial thromboplastin time and thromboelastography demonstrate that this composite is superior to other existing heparinized biomaterials in preventing clot formation in human blood plasma and in human whole blood. Membranes made of these composites allow the passage of urea while retaining albumin, representing a promising blood-compatible biomaterial for renal dialysis, with a possibility of eliminating the systemic administration of heparin to the patients undergoing renal dialysis.

Gender and inter-species influence on coagulation tests of rats and mice

INTRODUCTION

Rats and mice have been used to evaluate effects of natural and synthetic oestrogens. However, data about oestrogen's effects on haemostasis in rodents is very limited. The aim of this work was to standardize blood coagulation screening tests in adult male, female, and ovariectomized (Ovx) Wistar rats and CD1 mice in an effort to evaluate the influence of gender and species differences on haemostasis.

MATERIALS AND METHODS

Values were obtained for the following haemostatic parameters: prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin clotting time (TT), and fibrinogen (FIB), through modifications of the conventional techniques used for human blood coagulation analysis.

RESULTS

Both rats and mice showed gender intra-species and inter-species differences of high significance in PT, aPTT, TT, and FIB values. Intra-species differences were found in TT (+10% p<0.01) and FIB concentration (-21% p<0.001) between male and Ovx rats. Male vs. Ovx mice showed a TT difference of -20% (p<0.001). The main inter-species differences found were PT values of male rats vs. male mice (-39%) and female rats vs. female mice (-35%, both p<0.001). Female rats and mice aPTT values vs. those corresponding to Ovx animals showed differences of +15% and +32% (p<0.001), respectively.

CONCLUSIONS

These data reveal the great importance of gender intra- and inter-species differences on the values of haemostatic screening tests, which should be taken into consideration when evaluating the effects of oestrogens and other drugs on the coagulation system.