Martin Feuring

Rapid, nongenomic steroid actions: A new age?

In the traditional theory of steroid action, steroids bind to intracellular receptors and modulate nuclear transcription after translocation of steroid-receptor complexes into the nucleus. Due to similarities of molecular structure, specific receptors for steroids, vitamin D(3) derivatives, and thyroid hormone are considered to represent a superfamily of steroid receptors. While genomic steroid effects characterized by their delayed onset of action and their sensitivity to blockers of transcription and protein synthesis have been known for several decades, rapid actions of steroids have been more widely recognized and characterized in detail only recently. Rapid effects of steroids, thyroid hormones, and the steroid hormone metabolite of vitamin D(3), 1alpha, 25-dihydroxyvitamin D(3), on cellular signaling and function may be transmitted by specific membrane receptors. Binding sites in membranes have been characterized, exposing binding features compatible with an involvement in rapid steroid signaling. Characteristics of putative membrane receptors are completely distinct from intracellular steroid receptors, a fact which is further supported by the inability of classic steroid receptor antagonists to block nongenomic steroid actions. A putative progesterone membrane receptor has been cloned and functionally expressed with regard to progesterone binding. Development of drugs that specifically affect nongenomic action alone or even both modes of action may find applications in various, areas such as in the cardiovascular and central nervous systems and treatment of preterm labor, infertility, and electrolyte abnormalities.

Nongenomic effects of aldosterone: cellular aspects and clinical implications.

Nongenomic action of aldosterone has been observed in many cell types which often are different from the classic target tissues for mineralocorticoid action, such as vascular cells. As judged from their time scale and insensitivity toward inhibitors of protein synthesis, effects are not mediated by the classic mineralocorticoid receptor pathway. Here we summarize studies on rapid in vitro aldosterone effects, e.g. ion fluxes, and second messengers involved therein. Furthermore, several clinical studies on in vivo aldosterone action have shown rapid effects on cardiovascular parameters, among them baroreflex and vascular resistance. Taken together with the beneficial effect of aldosterone antagonism in heart failure patients that was demonstrated in the Randomized Aldactone Evaluation Study (RALES), aldosterone may be an equally important factor of the renin-angiotensin-aldosterone system in cardiovascular pathogenesis.

Acute effects of aldosterone on intracardiac monophasic action potentials

BACKGROUND Elevated plasma aldosterone levels represent an independent risk factor for increased mortality in congestive heart failure. Sudden cardiac deaths contribute substantially to the excessive mortality in congestive heart failure and so does atrial fibrillation as one of the major causes of stroke in elderly persons. So far, the electrophysiological properties of aldosterone have not been thoroughly characterized. In the present study, the effects of aldosterone on intracardiac monophasic action potentials were investigated in humans. METHODS AND RESULTS Monophasic action potentials were recorded in six patients with supraventricular arrhythmias. Eleven ml of 0.9% NaCl (placebo) were injected intravenously, and monophasic action potentials recorded for 10 min. Thereafter, aldosterone (0.5 mg in 0.9% NaCl) was injected and recording of monophasic action potentials continued as previously. The mean action potential duration at 90% repolarization was calculated for the entire 10-min period of each treatment. All patients were in sinus rhythm and had normal electrolyte status. In the placebo period, mean MAPd90 was 287+/-22 ms (mean+/-S.D.), and 299+/-25 ms following aldosterone (P<0.02). After adjustment for heart rate, the difference remained statistically significant (P<0.01). The maximal effect of aldosterone was seen 4-6 min after injection. CONCLUSION Aldosterone increases monophasic action potential duration within minutes after intravenous application. Therefore, this effect is likely to be mediated nongenomically. It may be hypothesized that aldosterone exerts its unfavorable effects partly via altering myocardial repolarization.

Non-genomic aldosterone action: from the cell membrane to human physiology☆

According to the traditional model, steroid hormones bind to intracellular receptors and subsequently modulate transcription and protein synthesis, thus triggering genomic events finally responsible for delayed effects. In addition, very rapid effects of steroids mainly affecting intracellular signaling have been widely recognized which are clearly incompatible with the genomic model. These rapid, non-genomic steroid actions are likely to be transmitted via specific membrane receptors. Evidences for non-genomic steroid effects and distinct receptors involved are now presented for all steroid groups including vitamin D(3) and thyroid hormones. Mechanisms of action are being studied with regard to signal perception and transduction involved, and for various steroids including aldosterone a patchy sketch of a membrane receptor/second messenger cascade shows up being not essentially dissimilar to cascades involved in catecholamine or peptide hormone action. Aside non-classical membrane receptors with a high affinity for aldosterone, these effects involve phospholipase C, phosphoinositide turnover, intracellular pH and calcium, protein kinase C and tyrosine kinases. Increasing evidence is being accumulated for rapid physiological responses in humans, e.g. at the level of circulatory or metabolic effects, rendering clinical significance to these rapid actions.

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.

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.

Lack of Effect of Aprepitant on Digoxin Pharmacokinetics in Healthy Subjects

Aprepitant is a highly selective neurokinin‐1 receptor antagonist that, in combination with a corticosteroid and a 5‐hydroxytryptamine3 (5HT3) receptor antagonist, has been shown to be efficacious in the prevention of highly emetogenic chemotherapy‐induced nausea and vomiting. In vitro data suggest that aprepitant is a substrate and a weak inhibitor of P‐glycoprotein. Thus, the effect of aprepitant on the pharmacokinetics of digoxin, a P‐glycoprotein substrate, was examined in a double‐blind, placebo‐controlled, randomized, two‐period crossover study in 12 healthy subjects. Each subject received daily oral doses of digoxin 0.25 mg on Days 1 through 13 during both treatment periods. Aprepitant 125 mg (or matching placebo) was coadministered orally with digoxin on Day 7, and aprepitant 80 mg (or matching placebo) was coadministered orally with digoxin on Days 8 to 11. Aprepitant did not affect the pharmacokinetics of digoxin. The geometric mean ratios (90% confidence interval [CI]) for plasma AUC0–24 h of digoxin (with/without aprepitant) were 0.99 (0.91, 1.09) and 0.93 (0.83, 1.05) on Days 7 and 11, respectively, and the geometric mean ratios (90% CI) for the 24‐hour urinary excretion of immunoreactive digoxin (with/without aprepitant) were 0.91 (0.80, 1.04) and 1.00 (0.91, 1.09) on Days 7 and 11, respectively. Thus, aprepitant, when dosed as a 5‐day regimen, did not interact with a known substrate of the P‐glycoprotein transporter.

Improved laboratory confirmation of heparin-induced thrombocytopenia type II. Time course of antibodies and combination of antigen and biologic assays.

We studied whether laboratory confirmation of heparin-induced thrombocytopenia (HIT) can be improved after antigen clearance by determining free antibody and combining the results of an antigenic and a biologic assay. Blood samples taken over 40 days in 14 patients with HIT with thromboembolism underwent fluorescence-linked immunofiltration and the carbon 14-serotonin release assays. Of the 14 patients, 11 showed positive results in both assays at day 1 after stopping heparin. The 3 patients with negative results seroconverted in one or both assays during the subsequent 7 days. Combining the positive results of the assays increased the sensitivity from 85% at day 1 to 100% at day 7. Assay results became negative in all patients within 40 days. The platelet count normalized between days 2 and 9 after withdrawal of heparin. It is assumed that the free antibody can be detected after withdrawal of heparin and after clearance of the platelet factor 4-heparin complex in patients with HIT.

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.

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.