Armin Schultz

Effect of oral contraceptives and ovarian cycle on platelet function

In past decades, numerous epidemiological and clinical studies in women taking oral contraceptives revealed the impact of sex steroids on coagulation factors and the incidence of venous thrombosis. To date, only scarce data regarding the impact of oral contraceptives on platelet function are available. The aim of this study was to further elucidate the impact of sex steroids on platelet function. We conducted an observational study in young women using different types and dosages of monophasic oral contraceptives (OCs) compared to women not taking OCs. During the follicular phase, the mean closure time (CT) in Col/Epi was 168.0 ± 64.9 s compared to 131.5 ± 28.9 s during the luteal phase (p = 0.012). In Col/Epi cartridges, no difference was detected between women taking second/third generation OCs and low-dose OCs (145.2 ± 44.3 vs. 169.4 ± 63.5, p = 0.34). In contrast, mean Col/Epi values of women using anti-androgen-containing OCs were less (110.3 ± 15.6 s) than in both other OC groups (p = 0.03 for both comparisons). The same holds for Col/Epi values from women during the follicular- and luteal phases compared to women using anti-androgen-containing OCs (p = 0.0002, p = 0.013). Significant correlations between progesterone and platelet function in women not using OCs (p = 0.02) could be found. In conclusion, the results of the study show that platelet function might be modulated by OCs and the female cycle. As for OCs, the main factor seems to be the progestagen. During the female cycle, the main impact on platelet function might be mediated by progesterone.

A quick glance at rapid aldosterone action.

Not all of the actions of aldosterone are mediated by the classic genomic pathway involving transcription and translation. Non-genomic or non-classical rapid responses that do not require these steps have been known for some time, but have only attracted significant interest in the last decade. At the cellular level, second messengers and kinase cascades are commonly involved. Most of these non-classical effects are insensitive to inhibitors of the classical cytosolic mineralocorticoid receptor. Non-genomic aldosterone action has been observed in clinical studies particularly in the cardiovascular system, and further research may improve the understanding of their participation in the pathogenesis of aldosterone related diseases and eventually enhance the options for therapy.

Rapid effects of aldosterone on vascular cells: clinical implications

Aldosterone has attracted considerable interest as an independent cardiovascular risk marker, which has been demonstrated in a number of studies. Furthermore, recent studies revealed the prevalence of hyperaldosteronism to be about tenfold higher than previously assumed, which underlines its clinical importance. Aldosterone affects virtually any part of the cardiovascular system, namely cardiac fibroblasts and myocytes, and vascular endothelial and smooth muscle cells. In the latter cells, our laboratory has demonstrated a variety of rapid effects of the steroid, e.g. on intracellular calcium, inositol trisphosphate, and cAMP. There is also evidence for a modulation of genomic events by rapid aldosterone effects that occur via phosphorylation of transcription factors such as CREB. Furthermore, rapid tyrosine phosphorylation has been observed in vascular cells. The majority of rapid responses reported to date are insensitive towards the classic mineralocorticoid receptor (MR) antagonist, spironolactone. The in vitro experiments are complemented by a series of clinical studies in healthy volunteers, which could demonstrate rapid modulation of cardiovascular parameters after aldosterone administration, e.g. of systemic vascular resistance. In addition, an interaction of aldosterone with the adrenergic system has been observed. Most recently, rapid aldosterone induced contraction of resistance arteries has been reported. In general, the rapid in vivo effects of aldosterone are likely to participate in the pathogenesis of cardiovascular disorders. As many rapid and thus nonclassic aldosterone responses cannot be blocked by spironolactone, further research is required in order to provide adequate inhibitors to interfere with these pathways.

Delayed genomic and acute nongenomic action of glucocorticosteroids in seasonal allergic rhinitis

Background  Glucocorticosteroids are effective in the treatment of allergic rhinitis, a disease characterized by a variety of symptoms, e.g. rhinorrhea and itching. The time course of symptomatic relief for allergic rhinitis by steroids has not been examined in detail to date, although the onset of steroid action is one of the main discriminations between genomic and nongenomic actions of steroids. We therefore investigated the time course of subjective and objective measures of nasal affection after steroid administration in patients with allergic rhinitis following specific allergen challenge.

The Effects of Modifying In Vivo Cytochrome P450 3A (CYP3A) Activity on Etoricoxib Pharmacokinetics and of Etoricoxib Administration on CYP3A Activity

To investigate the influence of modifying in vivo cytochrome P450 3A (CYP3A) activity on the pharmacokinetics of etoricoxib, a selective inhibitor of cyclooxygenase‐2, and of etoricoxib administration on CYP3A activity, a 3‐part, randomized, crossover study was conducted in 3 panels of healthy volunteers. In part I, 8 subjects were administered a single dose of 60 mg etoricoxib alone and following daily doses of 400 mg ketoconazole, a known strong inhibitor of CYP3A. In part II, 8 different subjects were administered a single dose of 60 mg etoricoxib alone and following daily doses of 600 mg rifampin, a known strong inducer of CYP3A. In parts I and II, plasma samples were collected following each etoricoxib dose and analyzed for etoricoxib. In part III, 8 different subjects were administered 120 mg etoricoxib or placebo once daily for 11 days, and the erythromycin breath test was administered on day 11 of each period. Coadministration of etoricoxib with daily doses of ketoconazole resulted in an average 43% increase in etoricoxib AUC; based on previous studies, this increase would not be expected to have any clinically meaningful effect. In contrast, coadministration of etoricoxib with daily doses of rifampin had a potentially clinically important effect on etoricoxib pharmacokinetics (average 65% decrease in etoricoxib AUC). Etoricoxib had no effect on hepatic CYP3A activity, as assessed by the erythromycin breath test.

Circadian variation of platelet function measured with the PFA-100.

The circadian rhythm plays an important role in the physiology and pathophysiology of the human being. Previous investigations revealed a circadian rhythm also in platelet function but these investigations have been limited to optical aggregometry with platelet-rich plasma and low shear stress. The aim of the present study was to further elucidate the impact of the circadian rhythm on platelet function using whole blood at high shear rates. Platelet function determined with the platelet function analyzer PFA-100® and concentration of fibrinogen and factor VIII activity were measured in healthy volunteers during day and night time, and even at shorter intervals (8:00, 12:00, 16:00, 20:00, 22:00, 0:00, 2:00, 4:00, 6:00 h). The mean peak closure time of the collagen/epinephrine cartridge of the PFA-100® was maximal at 2:00 h (192.0 ± 57.4 s) and declined to the trough value at 8:00 h (140.1 ± 33.4 s) (p = 0.004). This was paralleled by data from the collagen/ADP cartridge (22:00 h: 99.1 ± 38.5 s/2:00 h: 81.3 ± 16.7 s; p = 0.049). Concentration of fibrinogen and factor VIII activity were lowest during night time (22:00–4:00 h). These findings demonstrate a circadian rhythm in platelet function as measured with the PFA-100®. The PFA-100® seems to be an appropriate tool to describe circadian alterations and is easier to use than optical aggregometry in analogous studies.

To be or not to be (a receptor)

In addition to cellular responses that are elicited by steroids involving the modulation of transcription in the nucleus, it is now generally accepted that additional phenomena occur that do not depend on the genome. However, there is a puzzling variety of candidate receptors described in the literature.

Dalteparin dose-dependently increases ROTEM® thrombelastography parameters only at supratherapeutic anti-factor Xa levels: An in vitro study

1. The low molecular weight heparin (LMWH) dalteparin is used, for example, to prevent primary venous thromboembolism in patients undergoing surgery or in medically ill patients. The anticoagulant activity of dalteparin can be monitored by measuring anti‐factor Xa levels and activated partial thromboplastin time (aPTT); however, aPTT is an unreliable parameter in this case. The aim of the present in vitro study was to evaluate the thrombelastograph ROTEM® (Tem International, Munich, Germany) with respect to determining the anticoagulant activity of dalteparin at therapeutic and supratherapeutic plasma concentrations.

Coagulation status in coronary artery disease patients with type II diabetes mellitus compared with non-diabetic coronary artery disease patients using the PFA-100 and ROTEM

Previous investigations in patients with coronary artery disease (CAD) revealed differences in thromboelastographic parameters indicating different states of coagulability. The aim of the present study was to investigate the coagulation status of patients with documented CAD and type II diabetes mellitus (DM) and non-diabetic patients with coronary artery disease with the PFA-100® and the ROTEM®. No differences were found in platelet function as measured with collagen/epinephrine (263.6 ± 70.6 s vs. 254.6 ± 65.3 s) and collagen/ADP cartridges (105.3 ± 63.2 s vs. 90.6 ± 47.3 s) in CAD patients with DM and CAD patients without DM. Measured with the EXTEM reagent of the ROTEM®, mean maximum clot elasticity (MCE) in patients with CAD and DM (233.6 ± 86.9) was significantly longer than in CAD patients without DM (186.7 ± 54.5), (p = 0.03). A similar result was seen using the INTEM reagent; patients with CAD and DM (234.4 ± 83.9) showed a higher value for MCE than CAD patients without DM (190.8 ± 57.8) which was of borderline significance (p = 0.053). Moreover, a weak trend for higher maximum clot firmness (MCF) was seen in CAD patients with DM compared with CAD patients without DM with the EXTEM reagent (68.1 ± 7.5 vs. 63.6 ± 8.6, p = 0.08) and the INTEM reagent (68.4 ± 7.2 vs. 64.1 ± 8.2, p = 0.09). The ROTEM® analysis indicates increased coagulability in patients with coronary artery disease and diabetes mellitus compared to non-diabetic CAD patients. Moreover, the ROTEM® device seems to be an appropriate and easy-to-use tool to describe the coagulation status in these patients groups.

The PFA-100® cannot detect blood group-dependent inhibition of platelet function by eptifibatide or abciximab at therapeutic plasma concentrations

Previous investigations revealed that AB0 blood groups are associated with divergent concentrations of several coagulation factors. Concentrations of von Willebrand factor (vWF) and factor VIII are lower in individuals with blood group 0 compared to subjects with blood group A, B or AB, which might in turn result in a reduced inhibition of platelet aggregation in individuals with blood group 0. The aim of the present in vitro investigation was to elucidate the impact of AB0 blood group-dependent vWF concentrations on eptifibatide and abciximab mediated inhibition of GPIIb/IIIa function. Platelet function was measured with the platelet function analyzer PFA-100® at baseline and at increasing concentrations of eptifibatide and abciximab. It was stratified for blood group 0 vs A. If measured with the collagen/ADP cartridge, blood group 0 was associated with a prolonged mean baseline closure time in comparison with blood group A (94.3 ± 14.6 s vs. 74.6 ± 9.9 s, p = 0.007) which was paralleled by reduced concentrations of vWF and factor VIII. In contrast, no statistically significant differences in closure times (167.4 ± 83.9 s vs. 140.1 ± 99.0 s, p = 0.562) could be found in the presence of eptifibatide (0.1 µg/ml). Higher concentrations of abciximab (1 µg/ml) than those of eptifibatide were needed to increase the closure times in both cartridges of the PFA-100, but at this concentration of abciximab differences in closure times could not be detected most probably due to higher variability at these drug concentrations. The PFA-100® is not suitable for monitoring abciximab or eptifibatide within the therapeutic concentration range because the highest concentrations where the PFA-100® had measurable closure times of below 300 s is much too low to lead to the necessary platelet inhibition and, consequently, does not resemble the in vivo situation.